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Common-Mode Voltage Mitigation of Dual T-type Inverter Drives using Fast MPC Approach
Abstract
This paper proposes an intensive study for common-mode voltage (CMV) elimination/reduction in a five-level dual T-type multilevel converter (5LDT-MLC) drive. An advanced and fast model predictive control (MPC) approach is developed for CMV reduction (CMVR) and CMV elimination (CMVE) based on preselection of the switching states (SS). In addition, the proposed approach considers the torque control and the capacitor balancing of the proposed drive as essential aspects of MLC drives. A detailed study for the impact of the converter SS on the CMV is presented. The main features of the proposed MPC approach are reducing the complexity of the cost-function, the tuning burden of the weighting factors, and the computation time by more than 80% compared to conventional MPC techniques. A hardware implementation based on Silicon Carbide (SiC) T-type MLC is built. The experimental results demonstrate the effectiveness of the proposed MPC approach to mitigate/eliminate the CMV along with achieving the torque command and balancing the DC link capacitors. Unlike conventional CMVR techniques, the proposed approach reduces the CMV by 75% of its normal values without jeopardizing the harmonic contents, drive efficiency, and flux as well as torque ripples.
... However, too many unique possibilities still exist and must be examined continuously. A fast MPC (FMPC) for multi-level T-type converter was proposed in [23] based on the predefined selection of the switching states. This method succeeded to reduce the computation load about 80% without affecting the response of the controlled converter. ...
... Case Study 3: Experimental-Based Computational Load Comparison: To show the advantages of the proposed IMPC in terms of computational load, the classical MPC, FMPS [23], and IMPC (proposed) are implemented on STM32H745 microcontroller to capture the required com- putational time for controlling the most common multi-level topologies. ...
... As this experiment aims solely to compute the processing time for classical MPC, FMPS [23], and IMPC, only the control loops were implemented with constant states measurements without using physical multi-level converters. ...
In this paper, a new control technique called inverse model predictive control (IMPC) is proposed for power electronic converters. The proposed IMPC technique is primarily based on the inverse of the conventional finite set model predictive control. The key advantage of this design is that it avoids predicting the controlled states for all possible switching-state vectors, while maintaining the advantage of adhering to multiple constraints and achieving multiple objectives. IMPC predicts the optimal control signal that minimizes the cost function and converts it into a switching vector. Unlike classical MPC, the computational time required for IMPC is significantly reduced which makes it easily applicable to all types and levels of power electronics converters. The proposed method does not depend on the number of possible switching vectors and is compatible with low-cost microcontrollers commonly used for industrial applications. Additionally, the proposed control inherits the benefits of MPC, such as the ability to achieve its objectives while adhering to various constraints, minimal parameters tuning requirements, and reduced computational time. To demonstrate the effectiveness of the proposed technique, experimental results are presented for a five-level active neutral point clamped flying capacitor inverter (ANPC-FC) as a case study.
... Furthermore, no switch current is injected to or extracted from the midpoint of the DC-link capacitors, thereby significantly reducing the DC-link voltage ripple. NPL.H has a great merit for dual-motor applications as the required capacitance and overall volume of the DC-link capacitors can be greatly reduced, compared to existing inverters for dualmotor applications [5]- [9], [11]. ...
... Considering that the switch currents may have a positive or negative polarity with a non-unity power factor, the absolute function is applied to the AC currents in (5), (6), (10), (11), and (12). The switch RMS currents in NPL.H can be obtained by simply integrating the square of above equations in one fundamental AC period and taking the square root. ...
This paper introduces a neutral-point-less, H-type 3-level dual inverter (NPL.H) topology for motor drive applications. This multi-level topology craftily eliminates the neutral clamp and neutral point current altogether, resulting in a drastically lower minimum DC-link capacitance, compared to conventional 3-level inverter topologies, while retaining the multi-level benefits. NPL.H has additional merits, including lower output harmonics, lower current stress, lower capacitor current ripple, etc. The topology is optimal for balanced 6-phase, dual 3-phase, or 3-phase open-end winding motors. This paper proposes a low-order frequency form (LoF) for fast and accurate calculations of the important circuit variables (e.g., RMS currents of switching devices, inverter bridge input, and DC-link capacitor and the voltage ripple of the DC-link capacitor), and demonstrates an example in detail with the Sinusoidal Pulse Width Modulation (SPWM). Many practical design parameters (e.g., dead-time) are reflected in our method to enhance the accuracy of the analytical model. The theoretical RMS current expressions of NPL.H are successfully derived via LoF. Through simulation and experiment, we validate the precision and effectiveness of LoF as well as the strengths of the NPL.H topology. Our NPL.H can eliminate at least 75% of the DC-link capacitance of the conventional T-type 3-level topology while maintaining the same voltage ripple performance under otherwise same operating conditions, and up to 73% compared to the traditional 2-level inverter. Our new NPL.H topology unlocks a significantly higher power density for electric transportation and other high-power applications, where the size of a DC-link capacitor bank has traditionally been a major blockade for a high power density.
... MPC is a kind of lead control method that uses a dynamic model of the system to predict its future response and has the advantages of fast dynamic response and simple design. It has been used widely in the fields of motor control [20][21][22], aircraft [23] and power converters [24][25][26][27][28][29][30][31][32][33][34][35]. In [26], a control method of a five-level grid-connected photovoltaic inverter based on the model predictive control is applied for controlling active and reactive powers injected into the grid. ...
... In order to eliminate the differential term of state variables in (25), the estimation value of the equivalent load currentî o is defined as follows: ...
This article introduces a new control strategy for a bidirectional DC/DC converter used in photovoltaic energy storage systems (PV-ESSs), aimed to address the DC bus voltage deviation problem. The purpose of this paper is to design and practically implement a robust continuous control set predictive current control (CCS-PCC) method based on a nonlinear disturbance observer (NDO) to tightly regulate the common DC bus voltage in islanded DC microgrids. The CCS-PCC controller is used to replace the current loop PI controller, which effectively overcomes the shortcomings of the traditional linear lag control and improves the dynamic performance of the system. At the same time, the CCS-PCC method solves the inherent defect of finite control set predictive current control (FCS-PCC), where the switching frequency is not fixed. It effectively reduces the current ripple and realizes constant frequency control. In order to effectively suppress the DC bus voltage fluctuation during transients, the nonlinear disturbance observer is designed and combined with CCS-PCC. The feedforward method based on the NDO was utilized to enhance the disturbance rejection capability of the system. The simulation and experimental results show the feasibility and effectiveness of the proposed CCS-PCC+NDO approach, both during transient and steady-state operating conditions.
... In [6][7][8], to attenuate the CMV, a cost function optimization method was used by including the CMV term with a weighting factor. However, in [9][10][11], the voltage vector preselection method was applied by appropriately choosing the voltage vector that would reduce the CMV. For the second software approaches, several CMV reduction algorithms based on PWM have already been suggested, such as the Remote state PWM (RPWM), the Active Zero-State (AZSPWM) and the Near-State PWM (NSPWM) [10,12,13]. ...
Thanks to their various advantages in terms of reliability in addition to their low size and low cost, transformer-less PV inverters are widely used in several applications. Nevertheless, not using a transformer leads to an undesirable leakage current that can be generated by the high-frequency variation of the Common Mode Voltage (CMV). In this paper, a novel Direct Power Control (DPC) strategy is developed to reduce the CMV in a transformer-less two-level grid-connected VSI. The Proposed DPC (P-DPC) algorithm is based on the application of virtual vectors instead of original vectors in order to control the active and reactive powers and commonly to reduce the CMV variations. Consequently, the amplitude and variations of the produced CMV are effectively reduced, resulting in enhanced overall performance of the grid-connected conversion system. Numerical simulation and hardware implementation in an FPGA board prove the effectiveness of the P-DPC in terms of CMV and leakage current reduction as compared to conventional DPC strategies.
... The proposed topology in [29] aims to develop an MPC approach considering both common mode volage reduction and common mode voltage elimination in addition to capacitor balancing of the five-level dual T-type multilevel converter (5LDT-MLC) induction drives. The main features of the developed approach are multi-objective optimization problem, reducing the computation time and weighting factors to be tuned. ...
Cascaded multilevel inverters render higher output voltage, allowing for grid power injection without the use of booster transformers. Large leakage current is produced by voltage across parasitic capacitance in transformerless cascaded multilevel inverters (CMLIs) used mostly for solar photovoltaic sources. This voltage depends on the control law, modulation and inverter topology. To resolve leakage currents, numerous alternatives have emerged, which would include new converter topology, modulation methods, and control techniques. The AC signal of the requisite voltage for power injection into the grid is generated by CMLIs without the use of an additional boost stage. With lower total harmonic distortion and smaller filters, this additional benefit enhances the overall performance of PV systems. Various redesigned circuit architecture is recommended for transformerless operation because traditional CMLIs need additional switches. This work describes a new generalized circuit design named as X10 inverter for removing leakage current in an asymmetric lowered switch count cascaded multilevel inverter. The proposed approach employs two switches, one on each side of the DC sources. This insertion automatically disconnects the sources from the load, resulting in a lower common mode voltage transition and the elimination of leakage current. Inverters with any number of output voltage levels and sources can use the proposed technique. The proposed topology's efficacy in lowering leakage current and improving topology efficiency is evaluated using simulation and experimental setup.
... These MLC have the advantage of lower harmonic contents than two-level converters, as the former generates a high number of different voltage steps compared to the two-level converter that can generate only three different step voltage levels in the coupling voltage. Moreover, MLC results in reduced common mode voltage compared to 2L-VSI [5]. Multilevel converter can be classified into three main categories, which are diode clamped converters (DCCs), flying capacitor converters (FCCs), and cascaded H-bridge converters (CHBs). ...
Model predictive controller has been widely implemented for different power electronic converters motivated by their well-known merits. However, the computation burden increases tremendously if the converter’s voltage levels and/or phases are increased. This results in longer sample time and deteriorated performance. In this work, predictive current control (PCC) of a six-phase induction motor (IM) fed from a three-level voltage source (3L-VSI) is explored. First, the available 729 voltage vectors (VVs) are examined and classified according to their magnitudes into 24 groups. Then, based on the controller objectives, one group consisting only of 13 VVs is nominated. This group not only satisfies torque and flux tracking requirements but also greatly reduces the effect of the unwanted circulating xy currents. The effectiveness of the proposed method is validated using an experimental test bench.
The conventional Euler-based sequential predictive current control (SPCC) methods for multilevel inverters (MLIs) have aimed to minimize computational complexity, resulting in higher flying capacitor (FC) voltage ripples and poor transient response. These methods typically employ either cost function with weighting factors or offline selection of voltage vectors (VVs) to reduce the common-mode voltage (CMV). However, improper weighting factor selection and the presence of CMV term in ac current models negatively impact MLI harmonic performance. To address these issues, a new SPCC formulation is proposed, enabling direct estimation of the optimal voltage level (OVL) based on reference ac currents. This approach eliminates the need for a cost function in ac currents control and simultaneously reduces both computational complexity and CMV. By removing ac current model's dependency on CMV, the proposed formulation further enhances MLI harmonic performance. The mathematical formulation of the proposed SPCC is presented for a four-level inverter (FLI) with both passive and motor drive loads in this study. During the formulation, Heun's integration method is employed to develop FLI's FC voltage discrete-time models. The performance of the proposed SPCC is demonstrated experimentally on a dSPACE-DS1103 controlled FLI with passive load laboratory prototype. It is further compared with the conventional SPCC methods and their performances are evaluated comprehensively on the laboratory prototype.
This article studies the resilient formation tracking control problem for spacecraft swarm while considering actuation attacks and input saturation. A distributed Lyapunov-based model predictive controller (DLMPC) framework is designed for spacecraft swarm to track the target trajectory in a preset formation shape and achieve attitude consensus. To ensure formation safety, a collision avoidance term is introduced into the DLMPC framework. To guarantee the feasibility and stability of the DLMPC, we first construct the Lyapunov-based adaptive auxiliary controller and then use its stability to construct the stability constraint. The DLMPC inherits the characteristic of the Lyapunov-based adaptive auxiliary controller and employs online optimization to guarantee better formation tracking performance. As a novel framework for spacecraft formation control, the proposed DLMPC has the advantage of improving the formation tracking performance through persistently online optimization, especially, in adversarial dynamic environments. The simulation results validate the superiority and resilience of the DLMPC, and the proposed DLMPC framework shows improvement in formation tracking performance.
This article presents bibliography of multilevel inverters from 2021-2022. The list of journal papers relating to multilevel inverters is included. The bibliography includes papers from 2021-2022.
To guarantee their locomotion, biped robots need to walk stably. The latter is achieved by a high performance in joint control. This article addresses this issue by proposing a novel human-simulated fuzzy (HF) membrane control system of the joint angles. The proposed control system, human-simulated fuzzy membrane controller (HFMC), contains several key elements. The first is an HF algorithm based on human-simulated intelligent control (HSIC). This HF algorithm incorporates elements of both multi-mode proportional-derivative (PD) and fuzzy control, aiming at solving the chattering problem of multi-mode switching while improving control accuracy. The second is a membrane architecture that makes use of the natural parallelisation potential of membrane computing to improve the real-time performance of the controller. The proposed HFMC is utilised as the joint controller for a biped robot. Numerical tests in a simulation are carried out with the planar and slope walking of a five-link biped robot, and the effectiveness of the HFMC is verified by comparing and evaluating the results of the designed HFMC, HSIC and PD. Experimental results demonstrate that the proposed HFMC not only retains the advantages of traditional PD control but also improves control accuracy, real-time performance and stability.
This paper proposes an output-feedback solution for DC/DC converter applications that considers model-plant mismatches and load variations as constraints in industrial applications. The following two major contributions of this study are particularly advantageous: (a) nonlinear damping terms to inject the critical damping performance into the closed-loop system with the cooperation of the feedback gain structure depending on the damping coefficients, and (b) estimation of the output voltage derivative by the model-independent observer with only one simple closed-loop eigenvalue and current feedback removal. The experimental study highlights the practical merit of the proposed solution by demonstrating the critical damping performance that suppresses the peak current level using a 3-kW bidirectional DC/DC converter.
This paper reviews the classification and application of the model predictive control (MPC) in electrical drive systems. Main attention is drawn to the discrete form of MPC, i.e. finite control set model predictive control (FCS-MPC), which outputs directly the switching states of power converters. To show the diversity and simple realization with various control performances of the strategy, in this paper, several different FCS-MPCs with their working mechanisms are introduced. Comparison of FCS-MPC with conventional control strategies for electric drives is presented. Furthermore, extensive control issues, e.g. encoderless control and disturbance observation are also included in this work. Finally, the trend of research hot topics on MPC is discussed.
This paper proposes a new approach for the capacitor balancing of a dual three-level (3L) T-type converter based on Silicon Carbide (SiC) discrete semiconductors. The study is performed while the converter feeds an open-ends induction motor (OEIM). The model predictive control (MPC) scheme is developed to balance the DC link capacitors and to control the machine torque simultaneously. The proposed technique for MPC reduces the number of redundant switching states used in computations without affecting the operating voltage vectors. This reduces the computational time substantially. In addition, the proposed control strategy mitigates the weighting factors tuning problem of capacitor balancing in addition to the conventional MPC cost function. Matlab simulation results for the proposed drive system under different case studies are presented. Hardware experimental setup for the proposed converter is built, tested, and verified. A comparison between experimental and simulation results is presented. It is observed that the theoretical as well as the experimental results are in full agreement.
The dual T-type multilevel converter (MLC) is an advanced topology with a reduced switching device count compared to conventional diode clamped converter. This paper proposes a reduced switching state model predictive control (MPC) of a dual T-type drive system considering the DC link capacitor balancing, the common-mode voltage (CMV) along with torque control of an open-ends induction motor. The proposed study addresses the CMV in two different scenarios; i.e. CMV reduction (CMVR) and CMV elimination (CMVE). A Matlab simulation for the proposed drive system is presented. A dual T-type converter prototype based on Silicon-Carbide discrete MOSFET switch is designed, implemented and tested in laboratory. The proposed MPC scheme achieves the torque command as well as balances the dual DC links in an efficient manner. It is observed that the CMVE has some limitation compared to CMVR particularly at rated speed operation. It is worth mentioning that the proposed reduced switching states technique could reduce the computation time from 5.5 ms to 140 μs for CMVR and 70 μs for CMVE. In addition, the results demonstrate the effectiveness of CMVR scheme in reducing the harmonic contents, the torque and flux ripples, and converter switching loss compared to CMVE scheme.
Renewable energy systems integration prefers DC–AC converters of high efficiency, low harmonic injection and small size. Multilevel converter (MLC) is preferred compared to two-level converter thanks to its low harmonic injection, even at low switching frequency values, and accepting high power as well as voltage levels. Among reduced switching devices count MLCs is the T-type topology. This article introduces a review of the different advanced topologies of T-type MLC in comparison with the conventional neutral point clamped converters. The operation of each topology, the design consideration and the performance in low-voltage applications such as AC drive systems, grid-tie integration of renewable energy and power train drive applications are discussed. In addition, the design considerations using enhanced semiconductor switches are elaborated. Different studies regarding MLCs—like common-mode voltage elimination or reduction, open-switch fault diagnosis, open- as well as short-circuit fault tolerance, and DC link capacitor voltage balancing for T-type topologies—are illustrated. Finally, recommendations for future work research directions are highlighted.
This paper presents a new and very simple strategy for torque and flux control of AC machines. The method is based on Model Predictive Control and uses one cost function for the torque and a separate cost function for the flux. This strategy introduces a drastic simplification, achieving a very fast dynamic behavior in the controlled machines. Experimental results obtained with an induction machine confirm the drive's very good performance.
Model Predictive Control (MPC) is a very attractive solution for controlling power electronic converters. The aim of this paper is to present and discuss the latest developments in MPC for power converters and drives, describing the current state of this control strategy and analyzing the new trends and challenges it presents when applied to power electronic systems. The paper revisits the operating principle of MPC and identifies three key elements in the MPC strategies, namely the prediction model, the cost function and the optimization algorithm. The paper summarizes the most recent research concerning these elements, providing details about the different solutions proposed by the academic and industrial communities.
This paper studies the effect of common-mode voltage elimination (CMVE) on the iron loss of electrical machine core laminations under multilevel converter supply. Three identical magnetic ring cores are excited by either a three-level converter or a five-level voltage source converter to study the behavior of CMVE on a three-phase system. Both multilevel converters are controlled by using a space vector pulse width modulation as it is one of the most often used techniques for CMVE. These experimental results are confirmed numerically with a dynamic iron loss model. In addition, the effect of CMVE, at different switching frequencies, on the core loss of a synchronous machine is numerically studied. The results presented in this paper show that the core loss is considerably increased when the CMVE is implemented. However this iron loss increase in five-level drive systems is lower compared to the three-level ones. Therefore, it is important that the designers of drive systems take such effects into consideration.
This study proposes a generalised approach based on model predictive strategy for the current control, dc-link capacitor voltages balancing, switching frequency reduction and common-mode voltage mitigation in multilevel diode-clamped converters. A generalised discrete-time model of the converters is presented, where all the control objectives are formulated in terms of the switching states. The control goals are expressed as a cost function, and with the help of suitable weighting factors these goals are met simultaneously. The cost function minimisation is used as criteria for choosing the best switching state which would be applied to the converter during next sampling interval. The real-time digital control issues such as computational burden and delay compensation are also discussed. The feasibility of the proposed method is verified by simulations in three- to six-level converters, and by experiments in three- and four-level converters.
The effect of multilevel inverter supply on power losses in magnetic cores and electrical machines is studied. A dynamic numerical model for the hysteresis, eddy-current and excess losses in a core lamination is first developed. By both measurements and simulations for a ring-core inductor, we demonstrate how increasing the number of inverter voltage levels decreases the iron losses when compared to traditional two-level supply. Although the switching frequency has a significant impact on the iron losses in the case of a traditional two-level inverter, using three or five voltage levels makes the losses almost independent of the switching. Finally, finite-element simulations show that similar reductions are also possible for the core losses of 150-kVA and 12.5-MW wound-field synchronous machines, in which rather low switching frequencies are typically used. Calorimetric loss measurements are also presented for the 150-kVA machine in order to confirm the significant effect of switching frequency on the core losses with two-level inverter supply.
Model predictive control (MPC) for power converters and drives is a control technique that has gained attention into the research community. The main reason is that although MPC presents high computational burden it can handle multivariable case and system constrains and nonlinearities easily in a very intuitive way. Taking advantage of that, MPC has been successfully used for different applications such as active front end, power converters connected to RL loads, uninterruptible power supplies and high performance drive for induction machines among others. This paper provides a review of the application of MPC in the power electronics area.
In this paper, an inverter-fed ac motor drive is analyzed in order to investigate the conducted electromagnetic interferences at both the input and output sides of the inverter. HF lumped equivalent circuits for the inverter and the motor stator windings are proposed. The overall circuit model allows time- and frequency-domain analysis to be performed with standard circuit simulators. The proposed model can also predict common- and differential-mode HF current components. The equivalent circuit is verified by experimental tests carried out on a prototype of ac motor drive.
The paper presents a five-level inverter scheme with reduced power circuit complexity for an induction motor drive. The scheme is realized by cascading conventional two-level and three-level neutral point clamped inverters in conjunction with an open-end winding three-phase induction motor drive. An inverter control scheme with common-mode voltage (CMV) elimination, along with a simple DC link voltage control, is developed by using only switching states with zero CMV for the entire modulation range. Theoretical considerations are experimentally verified for a variety of operating conditions.
An improved two-stage model predictive current control (MPCC) for three-phase three-level converters in the paper, which can simultaneously achieve common-mode voltage (CMV) reduction, effective dc-link capacitor voltage control, and decreased computational burden, is proposed. Compared to the other current control strategies, it has the capability of handling multiple control objectives and possesses a simple structure. Furthermore, it greatly reduces the CMV since the peak CMVs of all the candidate voltage vectors are constrained to be less than one sixth of the dc-link voltage. In addition, an optimal two-stage voltage vector selection mechanism is employed in the proposed method. It helps to significantly reduce the computational complexity. Simulation and experimental results are provided to verify the effectiveness of the proposed method.
In this paper, a computation-efficient model predictive control (MPC) is proposed to eliminate common-mode voltages (CMV) of three-phase five-level active neutral-point-clamped (3P-5L-ANPC) converters. Originated from the CMV analysis of the 3P-5L-ANPC with all possible 125 possible voltage vectors, only 19 voltage vectors that generate zero CMV are adopted as the candidate voltage vectors for the MPC. A best voltage vector from the candidate voltage vectors is selected to track the current references. Then, appropriate switching combinations of the selected best voltage vector are determined to effectively balance flying and dc-link capacitor voltages without any additional hardware components. Furthermore, the proposed MPC only chooses 5 candidate voltage vectors involving in MPC optimization according to the location of the reference voltage vector, which significantly alleviates the computational burden. Finally, the effectiveness of the proposed MPC in terms of the steady state and dynamic performance is validated by simulated and experimental results.
Three-level inverter has an outstanding performance and is more advantageous in the switching vector selection than two-level inverter. In particular, the neutral-point voltage unbalance and common mode voltage (CMV) reduction of three-level inverter should be carefully regulated for the appropriate operation, both of which however are mutually coupled resulting that the conventional space vector modulation (SVM) scheme cannot deal with them properly. To overcome this limitation, this paper proposes an improved space vector modulation (ISVM) technique to reduce the CMV and neutral-point voltage imbalance simultaneously. The generating mechanism of neutral-point voltage oscillation is derived. Based on the analysis, the proposed ISVM method adopts four voltage vectors (large, medium, small and zero vectors) with adjusted dwell times to eliminate the ac unbalance of the neutral-point voltage. Considering the occurrence of neutral-point voltage disturbances, the dc neutral-point unbalance voltage is controlled by selecting the P-type or N-type small vector and adjusting the dwell times of small vectors for neutral-point voltage recovery. In addition, a novel switching sequence arrangement method with the minimal number of switches transition in one switching cycles and between switching cycles is proposed to reduce the total switching loss. Theoretical analysis and verification results show that the proposed ISVM scheme can reduce the magnitude of CMV to half of value using the conventional SVM, and an accurate control of ac and dc unbalanced neutral-point voltage can be obtained.
A low input current total harmonic distortion (THD) rectifier is presented, tailored around an open-end winding permanent magnet synchronous generator. Specifically, a six-level converter topology is obtained by connecting the generator stator winding to a three level T-type unidirectional rectifier on one side, and to an auxiliary two-level inverter on the other side. The T-type rectifier manages the entire active power stream and operates at the line frequency in order to minimize the switching power losses. The auxiliary inverter is instead driven by a standard PWM technique, being tasked to sinusoidally shape the input current and to actively balance the voltage across the dc-bus capacitors of the T-type rectifier. Such an inverter, being rated at a lower power and at a lower voltage than the T-type rectifier, can exploit low-cost power
mosfet
s. The proposed topology, featuring a very low input current THD, could well supplement in aircraft, portable or distributed generation applications, modern high-speed permanent magnet synchronous generators featuring a quite small stator impedance. Simulation and experimental results confirm the effectiveness of the proposed configuration.
The integration of switched-capacitor techniques into multilevel inverters (MLIs) with a dc source string contributes to the boosting of voltage gain, renders it particularly attractive in reducing the number of input dc sources in the series string. However, the recent two-stage MLI topologies suffer from high voltage stress across the backend H-bridge. Addressing this concern, an improved topology, namely the one-switched-capacitor integrated MLI (1SCI-MLI) is proposed in this paper. An extended topology of 1SC-MLI is also established by appropriate incorporation of another switched-capacitor circuit. The two proposed topologies are endowed with voltage boosting capability. They also feature low switch count and low number of dc sources. More importantly, they resolve the high voltage stress problem in the existing counterparts. Their corresponding operational analysis and comparisons with recent MLI topologies are discussed. Simulation and experimental results from a laboratory prototype are presented to validate the effectiveness of the proposed topologies.
In this paper, a novel structure of switched capacitor converter (SCC) is proposed. First, the basic unit of the proposed SCC is presented. After that, a generalized structure of the proposed SCC is discussed. The presented SCC uses one dc source, several switches, diodes, and capacitors to produce multistep dc boosted output voltage. The capacitors in the SCC can be charged in trinary asymmetrical pattern. A detailed comparative study between the proposed and other recently developed SCC structures is presented. It is shown that the proposed SCC can produce an output voltage level with lower total standing voltage and lower maximum switch stress voltage as compared to most of the suggested SCC structures. Further, a switched capacitor multilevel inverter (SCMLI) based on cross-switched multilevel inverter has been developed and analyzed for symmetric and asymmetric dc source configurations. For fair comparison with the existing SCMLI structures, the overall cost of the structures is compared based on a cost function (CF). The proposed SCMLI provides lower cost function/output voltage level (CF
/NL
) in comparison with most of the other SCMLI structures for both symmetric and asymmetric dc source configurations. Extensive experimental studies validate the operation and performance of the proposed SCMLI structure.
A very simple sequential model predictive control (SMPC) is recently proposed to achieve high performance control of induction motor (IM) drives. By evaluating two separate cost functions for torque and amplitude of stator flux linkage in a cascaded way, the weighting factor in conventional MPC is eliminated. However, it is shown in this paper that conventional SMPC cannot achieve stable operation over the full speed range, if the cost function for stator flux linkage is firstly evaluated. To solve this problem, this paper proposes a generalized SMPC (GSMPC), which is effective when any one of the two cost functions is firstly evaluated. Compared to conventional SMPC, GSMPC not only eliminates the limitation on execution order of two cost functions, but also presents less stator flux ripples and lower current THDs with even lower average switching frequency. Furthermore, a simple field-weakening strategy is proposed and combined with GSMPC to widen the speed range by adjusting the torque and stator flux linkage reference online. Both simulation and experimental results are presented to confirm the effectiveness of the proposed method.
An optimal current control strategy for Asymmetrical Hybrid Multilevel Inverters is proposed in this paper enabling their use on motor drives, static synchronous compensators, photovoltaic and wind generators, where a fast and precise current regulation is required. A key feature of these highly efficient converters is that an AC machine (motor or transformer) operates according to an open-end winding configuration, connected on one side to a main Multi-Level Inverter and, on the other side, to an auxiliary Two-Level Inverter. The first efficiently controls the main power stream operating at a low switching frequency, while the two-level inverter acts as an active power filter, exploiting a conventional high frequency two-level PWM technique. The proposed control scheme optimally exploits the key features of the two inverters by suitably sharing the control task. In fact, a predictive current control is assigned to the MLI, which can be accomplished by low switching frequency operations, while the high switching frequency of the PWM operated TLI is exploited to accomplish a fast and precise closed loop current control, processing only a part of the power stream flowing through the system, thus producing low power losses. Simulations and experimental results confirm the consistence of the proposed approach.
cascaded multilevel inverter (CMI) is one of the most popular multilevel inverter topologies. This topology is synthesized with some series connected identical H-bridge cells. CMI requires several isolated dc sources which brings about some difficulties when dealing with this type of inverter. This paper addresses the problem by proposing a switched capacitor (SC) based CMI. The proposed topology, which is referred to as switched capacitor single source CMI (SCSS-CMI), makes use of some capacitors instead of the dc sources. Hence it requires only one dc source to charge the employed capacitors. Usually, the capacitor charging process in a SC cell is companied by some current spikes which extremely harm the charging switch and the capacitor. The capacitors in SCSS-CMI are charged through a simple auxiliary circuit which eradicates the mentioned current spikes and provides zero current switching condition for the charging switch. A computer-aid simulated model along with a laboratory-built prototype are adopted to assess the performances of SCSS-CMI, under different conditions.
flying-capacitor modular multilevel converter (FC-MMC) overcomes the zero/low-fundamental-frequency operation issues of conventional MMC without injecting common-mode voltage (CMV). However, FC-MMC suffers from high current stress due to the large amplitude of inner high-frequency current. The square-wave design for the inner high-frequency components could effectively reduce the current stress, but the per-phase LC circuit (formed by arm inductor and flying-capacitor) challenges the square-wave current control. This paper investigates the equivalent LC circuit in FC-MMC, and proposes a control method to improve the performance of inner current control. Accordingly, the desired square wave is achieved for inner high-frequency current. The current stresses on semiconductor switches and flying capacitor are reduced by around 25% and 45% respectively. Simulation and experimental results prove the effectiveness of the proposal.
This paper proposes a high efficiency single-phase T-type BCM microinverter. The conventional full-bridge BCM microinverter has achieved ZVS soft switching and thereby improved the efficiency, but it suffers from high switching losses in light load conditions. The proposed T-type BCM microinverter reserves ZVS soft switching and uses multilevel technique to further decrease the switching losses. The BCM operation with multilevel technique will have too low switching frequency when the grid voltage approaches half of the DC link voltage. To solve this problem, this paper adopts a third operation mode for the T-type switching leg to maintain the switching frequency above a minimum value. The corresponding mode transitions are also detailed to ensure a smooth operation. Because of the turn-off delay of the freewheeling transistor, the actual lower current boundary deviates from the programmed one, which will distort output current. To address this issue, this paper also proposes a boundary compensation method. A prototype has been built for performance verification, which can test both full-bridge and T-type topology. Compared with the full-bridge BCM microinverter, the proposed T-type BCM microinverter has a higher efficiency over the whole load range.
Predictive current control is the use of predictive model for controlling load current tracking reference value, which forecasts future current values based on the selection one of the 27 voltage vectors of T-type NPC inverter. The cost function will minimize tolerance between control and reference current and 2 capacitor voltage values. These distortions depend on system load parameter elements. However, they are not the constant in the real event, which vary with operational conditions causing the distortion in control. In this paper, the new inductance estimation method is applied to predict future inductance values on-line, future current values as well as voltage values of 2 capacitors in order to improve the current quality. The proposed method is introduced and compared with the conventional algorithm to express the advantage of new technique. Simulation results are obtained by PSIM software and experimental results verify the feasibility and effectiveness of the algorithm.
Multilevel converter topologies for open-end stator winding medium-voltage (MV) induction motor drives have been researched from the last two decades. In this paper, a dual n -level modular multilevel converter (MMC) topology has been proposed for open-end stator winding MV induction motor drives. The control requirements of the proposed system are low device switching frequency, minimal harmonic distortion of machine stator currents, elimination of common-mode voltages in machine stator windings, and maintaining floating capacitor voltages around their nominal value. Based on these requirements, an emerging modulation technique for MV induction motor drives known as synchronous optimal pulsewidth modulation has been developed for the proposed dual nL-MMC topology. The laboratory measurements from a dual three-level MMC fed 1.5-kW open-end stator winding induction motor drive demonstrate the performance of proposed technique.
Describes the general principles and current research into Model Predictive Control (MPC); the most up-to-date control method for power converters and drives. The book starts with an introduction to the subject before the first chapter on classical control methods for power converters and drives. This covers classical converter control methods and classical electrical drives control methods. The next chapter on Model predictive control first looks at predictive control methods for power converters and drives and presents the basic principles of MPC. It then looks at MPC for power electronics and drives. The third chapter is on predictive control applied to power converters. It discusses: control of a three-phase inverter; control of a neutral point clamped inverter; control of an active front end rectifier, and; control of a matrix converter. In the middle of the book there is Chapter four - Predictive control applied to motor drives. This section analyses predictive torque control of industrial machines and predictive control of permanent magnet synchronous motors. Design and implementation issues of model predictive control is the subject of the final chapter. The following topics are described in detail: cost function selection; weighting factors design; delay compensation; effect of model errors, and prediction of future references. While there are hundreds of books teaching control of electrical energy using pulse width modulation, this will be the very first book published in this new topic. Unique in presenting a completely new theoretic solution to control electric power in a simple way. Discusses the application of predictive control in motor drives, with several examples and case studies. Matlab is included on a complementary website so the reader can run their own simulations.
This paper proposes a space-vector modulation (SVM) algorithm for a five-phase open-end winding motor drive system, fed by a dual nonsquare matrix converter (MC). The input to each of the MCs (MC-1 and MC-2) is a three-phase utility grid, and the output is a five-phase with variable voltage, variable frequency capability. The major contribution of this paper is the elimination of the detrimental common-mode voltage (CMV) that appears across the motor winding. In addition, the proposed SVM allows for a unity power factor at the input side, while boosting the output phase voltage by up to 150% of input. This paper presents a comprehensive analysis, to obtain the expression for the SVM modulating signals that are used to generate the switching pulses for the MC. To verify the idea, a modular, reconfigurable 5-kW MC prototype, feeding a five-phase induction motor is built. The control algorithm is implemented on a dSPACE-1006 platform. The test shows that the CMV is successfully eliminated from the motor winding. Other results (i.e., current and voltage waveforms) are also found to be in very close agreement with the theoretical prediction and MATLAB simulation.
Exploiting the rich switching redundancies of the dual inverter, new hybrid pulsewidth-modulation (PWM) switching methods are proposed in this paper using the degree of freedom of operating the individual inverters independently, in addition to exercising the degree of freedom of controlling the switching action of the individual legs independently. Two voltage entities, namely, common-mode voltage (CMV) and differential-mode voltage are identified in the dual inverter, and all hybrid PWMs are envisaged aimed at reducing and also eliminating the CMV in it. The effects of such attempts on motor shaft voltage and also the motor bearing currents are presented in detail. Furthermore, bearing current profiles of an open-end winding induction motor are also presented with both conventional and hybrid PWMs proposed in this paper. Electric discharge machining discharge currents are completely eliminated with the use of all hybrid PWM methods proposed in this paper. In addition, implications of completely eliminating the CMV are also presented in this paper. All hybrid PWMs proposed in this paper are first simulated using MATLAB and are experimentally verified on a dual two-level inverter feeding a 1.1-kW 415-V 3-φ open-end winding induction motor drive.
In this paper, the conventional I- and T-type three-level neutral-point-clamped (3L-NPC) inverter for low-voltage renewable energy systems is first investigated. Literature research shows that the T-type inverter improves I-type's insulated-gate bipolar transistor (IGBT) + IGBT current paths. However, the IGBT + diode paths are the same. The calculation in this paper further reveals that the IGBT + diode current paths dominate the conduction losses and even the whole semiconductor losses. Based on the aforementioned recognitions, a novel T-type inverter is presented as an alternative to be applied in the low-voltage renewable energy systems. In the proposed 3L-NPC, four CoolMosfets replace the IGBT + diode middle bidirectional switch. In the proposed topology, there is no diode involved in the current path supposing the unity power factor. In this way, the conduction loss is expected to be reduced compared with that from the conventional T-type 3L-NPC, particularly in the low and medium power ranges.
The book develops a systematic approach to motor drives. While the emphasis is on practice; extensive modeling, simulation and analysis is developed to assist readers in their understanding of the subject matter from fundamental principles. Also, each motor drive is illustrated with an industrial application in detail at the end of chapters to enable readers to relate theory to practice.
Open-end winding three-phase drive topologies have been extensively investigated in the last two decades. In the majority of cases supply of the inverters at the two sides of the winding is provided from isolated dc sources. Recently, studies related to multiphase open-end winding drives have also been conducted, using isolated dc sources at the two winding sides. This paper investigates for the first time a five-phase open-end winding configuration, which is obtained by connecting a two-level five-phase inverter at each side of the stator winding, with both inverters supplied from a common dc source. In such a configuration it is essential to eliminate the common-mode voltage (CMV) that is inevitably created by usual PWM techniques. Based on the vector space decomposition (VSD), the switching states that create zero CMV are identified and plotted. A space vector pattern with large redundancy of switching states is obtained. Suitable space vectors are then selected to realize the required voltage reference at the machine terminals with zero CMV. The large number of redundant states enables some freedom in the choice of switching states to impress these space vectors. Out of numerous possibilities, two particular switching sequences are chosen for further investigation. Both are implemented in an experimental setup, and the results are presented and discussed.
The development of high-processing-capability microprocessors allows the implementation of new digital control methods for neutral-point-clamped (NPC) multilevel converter in power-electronic applications. This paper presents a new predictive digital control method for multilevel converters, called “fast predictive.” This method computes the optimal vector using the NPC three-phase multilevel dynamic model equations just once in each control cycle, while current predictive methods need 27 calculations. The closest vector to the optimal vector is found by minimizing the distance between each one of the 27 available vectors to the optimal vector. Space vector modulation could be also used. The obtained performance is similar to the predictive optimal control that uses the converter model to find all the 27 responses of the multilevel and then searches for the vector that minimizes control errors. Relative to predictive optimal control, the fast predictive improves digital processing speed by at least 150% in multilevel converters with 27 vectors. This speed improvement would allow multilevel converters with five or higher number of levels (125 instead of 27 vectors) to be controlled using the same sampling frequency of the three-level inverter. The fast-predictive controller is used in a multilevel rectifier with near-unity power factor to enforce the ac currents. Fast predictive control is also used in the rectifier dc voltage to reduce sensitivity of the dc voltage to dc load disturbances. The simulation and experimental results show that the fast-predictive controller is able to control the ac currents of a three-phase multilevel rectifier, achieving nearly 1.5% total harmonic distortion while balancing the capacitors' dc voltages. The use of predictive control to regulate the dc voltage shows an improvement of approximately 7% compared to a proportional-integral controller.
In this paper two of the most extensively used high performance control strategies for electrical drives as Field Oriented Control (FOC) and Direct Torque Control (DTC) are compared to a new Predictive Torque Control method (PTC). Same commutation and sampling frequency are taken into account in order to compare these techniques. Preliminary results verify the excellent performance of the predictive strategy both in transient and steady state.
This paper provides theoretical and experimental discussions on conducted electromagnetic interference (EMI) emissions from an inverter-driven motor rated at 400 V and 15 kW. It focuses on a line EMI filter and its combination with a motor EMI filter, along with their effects on attenuation of conducted emission voltage. When no EMI filter is connected, the motor drive cannot meet the conducted emission limits prescribed by Category 3 in the IEC61800-3 regulations. The reason is that the common-mode voltage generated by a voltage-source pulse width modulation (PWM) inverter causes a common-mode leakage current flowing into the ground wire lead through parasitic capacitors inside the motor. When the line EMI filter is connected, the motor drive can meet Category 3. The motor EMI filter eliminates the common-mode voltage from the motor terminals, thus bringing a drastic reduction to the leakage current. The combination of the two EMI filters can comply with the limits prescribed by Category 2, which are much stricter than those by Category 3.
The phenomenon of dc-capacitor-voltage drift is the main technical drawback of a passive front-end multilevel diode-clamped converter (DCC). This paper formulates and analyzes the dc-capacitor-voltage-drift phenomenon of a passive front-end five-level DCC, which operates based on a sinusoidal pulsewidth-modulation (SPWM) switching strategy. The analysis shows dependence of the voltage drift on the modulation index and the ac-side power factor of the DCC. The analysis concludes that an SPWM strategy, without the use of auxiliary power circuitry, is not able to prevent the voltage-drift phenomenon of a five-level DCC. This paper also proposes a space-vector-modulation (SVM)-based switching strategy that takes advantage of redundant switching vectors of the SVM method to counteract the voltage-drift phenomenon. The limit to the range of operation of a five-level DCC, which is based on the proposed SVM strategy, is also presented. The salient feature of the proposed strategy is that it enables voltage balancing of the dc capacitors with no requirements for additional controls or auxiliary-power circuitry, within the specified range of operation. The performance of a DCC under various operating conditions, based on time-domain simulation studies in the MATLAB/SIMULINK environment, is evaluated. This paper demonstrates capability of the proposed SVM strategy to control and maintain voltage balance of dc capacitors.