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A new DC/AC inverter with ability of supplying two AC loads, independently, based on flying‐capacitor topology is proposed. Flying capacitor enables the converter to have three‐level output voltages which results in high‐quality output waveforms. Comparing to conventional flying capacitor inverter (FCI) for supplying two loads, the new inverter has...
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Citations
... It filled the limitation gap of two-level inverters in high-voltage and high-power applications. In [6], NPC-15SDI is proposed, which clamps the midpoint through six bidirectional switches based on NSC. The larger number of switches makes the volume and complexity of the inverter increase rapidly, and most of the switches must withstand the full DC voltage. ...
This article presents a photovoltaic micro-grid system structure with multiport three-level converter(MP-TLC). In this structure, two AC power supplies/loads with different operating amplitudes and frequencies can be directly connected through MP-TLC without multiple power conversion units. Compared with the traditional configuration, the structure of the multi-port converter photovoltaic microgrid system operates under a multi-level voltage, which reduces the number of power conversion stages, reduces the number of power switches, and reduces the overall volume and cost of the system. In addition, a carrier-based time-sharing space vector modulation strategy is proposed to solve the problem of two output couplings of MP-TLC under SPWM modulation, so that the two output ports can work relatively independently. Compared with the traditional SVPWM modulation strategy, the carrier-based time-sharing space vector modulation strategy omits many trigonometric function calculation processes, which effectively improves the calculation speed of the algorithm. This article also presents a voltage-pumping DC-DC converter for the DC boost link in a photovoltaic micro-grid system. The converter can obtain a high voltage gain at a very low duty cycle and is suitable for a wider range of photovoltaic cell voltage input. The experimental results verify the effectiveness of the wide voltage input photovoltaic microgrid system based on MP-TLC.
... Thus, making the above-mentioned converter topologies an infeasible choice for microgrid applications, where a fully independent operation of the ac systems is required. In [38], a flying capacitor dual-output (FCDO) converter was proposed. Compared to other dual-output topologies, the FCDO converter provides independent multilevel voltages across its dual-output ports; thereby becoming a suitable candidate to interface multiple ac sources and loads operating at different amplitude and frequency to the hybrid microgrid. ...
This paper presents a hybrid microgrid configuration with a flying capacitor dual-output (FCDO) converter. The output ports of the FCDO converter can directly interface ac sources/loads operating at different amplitudes and frequencies without additional ac/dc/ac converter units. Compared to the conventional configuration, the hybrid microgrid with the FCDO converter operates at multilevel voltages, reduced power conversion stages, less power switch count, and fewer control loops. The paper also presents a cascaded model predictive control (CMPC) algorithm for such configuration to control the variables, namely three-phase dual-output currents, ac/dc bus and FC voltages, and active/reactive power. The proposed CMPC sequentially executes multiple single-objective MPC units with adaptive dynamic reference (ADR) models to control the multivariable. The controller first obtains the optimum voltage vector for each output port by minimizing the output current errors, where the ADR model generates the appropriate references. Finally, the controller identifies the optimum state from the determined voltage vector pair by minimizing the FC voltage errors. Unlike conventional MPC, the CMPC algorithm reduces the computational burden of the controller and attains multivariable control without additional control loops and weighting factors. Furthermore, the converter's performance with CMPC algorithm is validated experimentally on a low-power hybrid microgrid.
... This paper provides a review and detailed comparative study for three five-level topologies, including state-of-the-art 978-1-6654-5233-5/23/$31.00 ©2023 IEEE five-level modified MMC (5L-M-MMC) [16], five-level flying capacitor using two three-level flying capacitor converters connected in parallel (2x3L-FC) [22], [23], and five-level flying capacitor (5L-FC) [18], [24], where these topologies are depicted in Fig. 1. This comparison is conducted using simulation results in PLECS utilizing a 10 kW system. ...
The rapid growth of the penetration level of renewable energy sources in low-voltage (LV) networks increases the research interest in more efficient, compact, reliable, and easily expandable energy conversion devices. Thus, multilevel converters, a promising concept for dc-ac conversion, are gaining increased interest due to their smaller size relative to the conventional two-level structure. However, several issues related to the number of components and the added complexity cannot be ignored. To enrich the literature review concerning this topic, this work reviews and provides a comparative assessment of three state-of-the-art multilevel topologies for LV applications. This review considered three structures: state-of-the-art five-level modified MMC (5L-M-MMC), five-level flying capacitor using two three-level flying capacitor converters connected in parallel (2x3L-FC), and five-level flying capacitor (5L-FC). This comparative study is supported by simulation results based on a 10 kW system.
... Furthermore, 7-level FCMC are applied to single-phase inverters in [13] and as a power factor correction front end boost converter in [14]. Also, in [15] a single-phase N-level FC multilevel rectifier is used in a solid-state transformer, and a compact dual-output inverter is presented in [16]. Finally, in [17] a 9-level FCMC for electric aircraft applications is proposed and a 13-level inverter is presented in [18]. ...
... Finally, the balancing strategy selects the switching state that balances the capacitor voltages and ensures the required voltage level, simultaneously. This strategy uses the capacitor and input voltages estimates to decide if the capacitor voltages must be increased or decreased, according to Equation (16). The capacitor voltage balancing strategy is based on the redundancy of switching states and directly provides the control signals for the FCMC [28]. ...
... Regarding the THD of the output voltage and current, it is 16.52% and 2.46%, respectively, and the output current tracking error is about ±0.15A. Table 2 summarises the obtained results, where we have added an ideal case (first row), where constant voltage sources replace the capacitors; the voltage sources values are given by Equation (16). Also, results with an equivalent series resistance (ESR) of 10 times the nominal value are shown in the last row. ...
Abstract Flying capacitor multi‐level converters use charged capacitors as a critical element. For proper operation, the capacitor voltages must be known and regulated. Direct measurement is straightforward, but when the number of required measurements is high, this is a complicated approach. This paper introduces an estimation method for n capacitor voltages. The scheme is based on a system of (n+1) equations, which is defined in a way that it incorporates information of the actual capacitor voltages and open‐loop estimates of the capacitor voltages. The solution of the system gives the best estimates of the capacitor voltages in the sense of least square errors. The method requires only output voltage and output current sensors and its computational burden is low, saving cost and design efforts, and simplifying the hardware system. The performance of the proposed scheme is evaluated experimentally in a 9‐level flying capacitor chopper, where the estimates are used by the voltage balancing strategy and by the output current controller.
... Common types of multilevel power converter are cascaded Hbridge type (CHT) [5][6][7][8][9][10][11], flying-capacitor type (FCT) [12,13] and diode-clamped type (DCT) [14,15]. A DCT multilevel power converter uses several series capacitors in the DC bus to create different voltage levels and several clamped diodes are connected between the power electronic arm and these voltage levels. ...
... The major problems are the voltage balance for the series capacitors and the voltage rating of the clamped diodes in the DCT multilevel power converter [14]. Several capacitors are inserted into the power electronic arm in an FCT multilevel power converter [12,13]. The states of the power electronic switches determine the capacitors through which the current path flows to provide an output voltage with different levels. ...
... The states of the power electronic switches determine the capacitors through which the current path flows to provide an output voltage with different levels. In [12], two power electronic arms are used to form a dualoutput FCT three-level inverter, and a three-phase FCT three-level inverter and a three-phase full-bridge inverter (FBI) are integrated to output a set of three-phase five-level voltage [13]. However, the voltages in the capacitors for an FCT multilevel power converter should be carefully regulated by redundant switching states of power electronic arms [13]. ...
This study proposes a seven‐level power conversion system for a solar power generation system. This seven‐level power conversion system consists of a DC–DC power converter and a cascade DC–AC inverter. The cascade DC–AC inverter comprises a full‐bridge inverter and a T‐type inverter. The T‐type inverter generates a three‐level quasi‐square‐wave voltage and the full‐bridge inverter provides a three‐level high‐frequency pulse voltage. The amplitude of the three‐level quasi‐square‐wave voltage is double that of the three‐level high‐frequency pulse voltage, so seven levels of AC voltage are synthesized. Only the full‐bridge inverter with lower DC bus voltage uses high‐frequency switching so switching losses are effectively reduced. The novelty of the proposed cascade DC–AC inverter is that the output power of T‐type inverter is controlled by regulating the DC bus voltage, so no real power is supplied from the full‐bridge inverter and an independent power source is not required to provide power to the full‐bridge inverter. The negative terminal voltage for solar cell array keeps almost constant to reduce the leakage current of proposed seven‐level power conversion system. A hardware prototype with a digital signal processor controller is developed to verify the performance of seven‐level power conversion system for a solar power generation system.
Dual-output three-level converters are widely used in multiphase motor drives, and their common-mode voltage (CMV) and neutral point (NP) balance problems can affect the safe and stable operation of systems. Owing to their unique structure, certain disabled switching states exist. Suppressing the CMV to comply with operational constraints is worthy of further investigation. In this paper, an improved time-sharing virtual space vector (ITVSV) modulation strategy is proposed. In addition, the working principle of the converter is analyzed and divided into two effective working modes. The proposed strategy defines two kinds of virtual vector synthesis methods, using virtual vectors instead of the basic small vector of large CMV to reduce the degrees of freedom of voltage fluctuation. The switching loss can be reduced by adjusting the switching sequence in some areas. Furthermore, it is demonstrated that the NP voltage is self-balancing within one primitive period. Finally, the effectiveness of the ITVSV for suppressing CMV and NP voltage balance is verified by experimental results.
