Tobias Geyer

ABB | ABB · Corporate Research

p>This paper proposes the computation of three-level optimized pulse patterns (OPPs) that achieve not only load-friendly but also converter-friendly operation. To this end, the conduction and switching losses are modeled as a function of the OPP switching angles and the amplitude and phase of the converter current. By minimizing the current harmoni...

p>This paper proposes the computation of three-level optimized pulse patterns (OPPs) that achieve not only load-friendly but also converter-friendly operation. To this end, the conduction and switching losses are modeled as a function of the OPP switching angles and the amplitude and phase of the converter current. By minimizing the current harmoni...

Finite control set model predictive control (FCS-MPC) is a salient control method for power conversion systems that has recently enjoyed remarkable popularity. Several studies highlight the performance benefits that long prediction horizons achieve in terms of closed-loop stability, harmonic distortions, and switching losses. However, the practical...

This article presents a direct model predictive con-trol (MPC) scheme for drive systems consisting of a three-phase three-level neutral-point-clamped (3L-NPC) inverter and an induction machine (IM). Even though the discussed MPC algorithm is a direct control strategy, it operates the inverter at a fixed switching frequency, while the output harmoni...

This paper presents a control method for three-level neutral point clamped (NPC) inverter medium-voltage (MV) drives that addresses the stator current control problem and balancing of the neutral point (NP) potential in a single control loop. To do so, a model predictive control (MPC) algorithm, designed as a multiple-input multiple-output (MIMO) c...

A newly proposed model predictive pulse pattern controller, which is applicable to higher-order converter systems, is implemented on a low-cost field-programmable gate array. It is shown that how the computations of the underlying quadratic program of the control algorithm can be reduce, thus enabling a resource-efficient implementation. The implem...

A model predictive controller based on optimized pulse patterns is proposed that is suitable for higher-order linear systems, such as converters with $LC$ filters. The controller manipulates the switching times of an optimized pulse pattern. The switching time modifications are approximated by the strengths of impulses, which are based on a small...

In this article, the performance of gradient-based predictive pulse pattern control (GP $^{3}$ C) is evaluated for a medium-voltage variable-speed drive consisting of a three-level neutral-point-clamped (NPC) inverter and a medium-voltage induction machine. To this end, real-time tests are performed in a hardware-in-the-loop (HIL) environment, whi...

This paper proposes a control and modulation strategy for medium-voltage (MV) drives that exhibits excellent steady-state and transient behavior. Specifically, optimized pulse patterns (OPPs) and direct model predictive control (MPC) are employed so that the associated advantages of both, such as minimum stator current total demand distortion (TDD)...

This paper presents the application of Model Predictive Control (MPC) in high-performance drives. A wide variety of machines have been considered: induction machines, synchronous machines, linear motors, switched reluctance motors, and multiphase machines. The control of these machines has been done by introducing minor and easy-to-understand modif...

This paper presents a control scheme that combines the optimal steady-state performance of optimized pulse patterns (OPPs) with the fast dynamics of direct model predictive control (MPC). Due to inherent challenges that relate to the utilization of OPPs in a closed-loop setting, OPPs are traditionally used in slow control loops. As a result, the as...

This paper presents a direct model predictive control (MPC) method for drive systems with superior steady-state and dynamic performance. Specifically, the discussed MPC algorithm achieves a steady-state behavior that is similar or better than that of a linear controller with a dedicated modulator, and fast transient responses that characterize dire...

A finite control set model predictive control (FCS-MPC) strategy consists of a prediction model, a cost function and an optimization algorithm. Consequently, the performance of the FCS-MPC depends on the proper design of these three elements. This paper assesses the influence of the prediction model of an uninterruptible power supply (UPS). Since t...

Recently, an efficient multistep direct model predictive control (MPC) scheme for power converters has been proposed. It relies on the Sphere Decoding Algorithm (SDA) to solve the associated long-horizon optimal control problem. Since the SDA evaluates only a small number of candidate solutions to find the optimal one, a significant reduction in th...

The operation of a three-level (3L) converter with a neutral point (NP) employed in a medium voltage (MV) wind energy conversion system (WECS) is investigated. In particular, the voltage ripple of the upper or the lower half of the dc-link and its dependence on the relative phase of the carriers in a carrier-based pulse width modulation (CB-PWM) sc...

Model predictive control (MPC) has established itself as a promising control methodology in power electronics. This survey paper highlights the most relevant MPC techniques for power electronic systems. These can be classified into two major groups, namely, MPC without modulator, referred to as direct MPC, and MPC with a subsequent modulation stage...

This article proposes two alternatives of a direct model predictive control (MPC) scheme for a three-phase two-level grid-connected converter with an LCL filter. Although both approaches are implemented as direct control methods, i.e., they combine control and modulation in one computational stage, they operate the converter at a constant switching...

Long-horizon finite-control-set model predictive control is implemented on a field-programmable gate array (FPGA). To solve the underlying least-squares integer program, a non-recursive sphere decoding algorithm is developed. By exploiting the problem structure, few multipliers are required, and the algorithm computes the optimal solution in a few...

Direct model predictive control (MPC) with reference tracking, also referred to as finite control set MPC (FCS-MPC), has gained significant attention in recent years, mainly from the academic community. Thanks to its applicability to a wide range of power electronic systems, it is considered a promising control method for such systems. However, to...

Optimized pulse patterns (OPPs) minimize the harmonic distortions of inductive loads. To simplify the analysis and computation, quarter- and half-wave symmetry is typically imposed. Moreover, for three-level converters, the switch positions are required to be non-negative in the positive half-wave of the fundamental period. This paper investigates...

This paper considers a medium-voltage static synchronous compensator (STATCOM) that is based on a delta-connected modular multilevel converter (MMC) and operates at switching frequencies of 150 Hz or less. Offline computed optimal pulse patterns (OPPs) facilitate the shaping of the grid current spectrum at such low switching frequencies. However, S...

This work focuses on a Finite Control Set Model Predictive Control (FCS-MPC) method for controlling the output voltage of a two-level three-phase power converter with an output LC filter. This type of control has been proven to be a suitable strategy for uninterruptible power supply (UPS) systems, capable of achieving a high quality output voltage...

A new model predictive torque and flux controller is proposed, which controls the electromagnetic torque and the rotor (rather than the stator) flux magnitude. Analytical expressions for the weighting factors are derived that ensure that the proposed controller achieves the same closed-loop performance as predictive current control. In particular,...

In this paper we present modifications to the sphere decoder initially introduced in [2] and modified in [3] that significantly reduce the computation times during transients. The relative position of the unconstrained solution of the integer quadratic program underlying model predictive control (MPC) with respect to the convex hull of the (truncat...

For dc/ac modular multilevel converters (MMCs) in double-star configuration, this paper proposes a fast closed-loop control method based on optimized pulse patterns (OPPs). Thanks to the direct manipulation of the OPP switching instants, OPPs with discontinuous switching angles can be used, and the intrinsic cell capacitor voltage ripple is compens...

In power electronics, the $\ell_{1}$ -norm (instead of the squared 2-norm) is often used in the objective function of model predictive controllers (MPCs) with reference tracking. Although the $\ell_{1}$ -norm is preferred for its computational simplicity, it might lead to a performance deterioration and closed-loop instability. This paper analyzes...

A new model predictive torque and flux controller is proposed, which controls the electromagnetic torque and the rotor (rather than the stator) flux magnitude. Analytical expressions for the weighting factors are derived that ensure that the proposed controller achieves the same closed-loop performance as predictive current control. In particular,...

Finite control set model predictive torque and flux control uses a scalar weight in its cost function to determine the trade-off between the torque and flux magnitude tracking error terms. This weight strongly influences the current distortions. It will be shown that an optimal weight can be computed algebraically, which minimizes the current disto...

This paper proposes a trajectory-based controller for a pulse-width modulated high-power converter which connects to the power grid through an LCL filter. The controller is separated into a feed-forward controller, which takes the non-linear behaviour of the pulse-width modulator into account as well as a linear feedback controller. The linear feed...

This paper analyses the limitations of a reduced order model for Modular Multilevel Converters (MMCs) by elucidating the relation between its accuracy, operating frequency and converter parameters. A reduced order simplifies the analysis of the MMC and thereby may provide additional information about the converter behaviour. However, the accuracy o...

This work proposes and validates model predictive control as an alternative control strategy for H-NPC converters for single-phase grid-tied string photovoltaic systems. The presented control scheme achieves the good quality current waveforms with unity power factor, dc-link voltage control, neutral-point voltage minimization. Furthermore, the pred...

This paper considers a model predictive controller with reference tracking that manipulates the integer switch positions of a power converter. It can be shown that the optimal switch position can be computed in a new coordinate system by solving the closest vector problem in a lattice by iterative slicing. A list of Voronoi relevant vectors definin...

Voltage source inverter (VSI) with output LC filter can be used to generate sinusoidal output voltages with reduced low frequency harmonics content. This application is suitable for uninterruptible power supply (UPS) systems. Finite control set model predictive control (FCS-MPC) has proved to be a good candidate for controlling such kind of devices...

For direct model predictive control with long horizons, the sphere decoding algorithm is reformulated as a non-recursive algorithm. The algorithm is well suited for the use in practical systems using an FPGA to solve the optimization problem. A case study with a three-phase neutral point clamped inverter with an RL load is used to show the effectiv...

In this original book on model predictive control (MPC) for power electronics, the focus is put on high-power applications with multilevel converters operating at switching frequencies well below 1 kHz, such as medium-voltage drives and modular multi-level converters. Consisting of two main parts, the first offers a detailed review of three-phase...

For linear systems with integer inputs, the model predictive control problem with output reference tracking is formulated as an integer least-squares (ILS) problem. The ILS problem is solved using a modified sphere decoding algorithm, which is a particular branch-and-bound method. To reduce the computational complexity of the sphere decoder, a redu...

This paper considers a model predictive controller with reference tracking that manipulates the integer switch positions of a power converter. It is shown that the optimal switch position can be determined with a reduced online computational burden. Instead of solving the optimization problem in each sampling period, the optimization problem can be...

Common approaches for direct model predictive control (MPC) for current reference tracking in power electronics suffer from the high computational complexity encountered when solving integer optimal control problems over long prediction horizons. We propose an efficient alternative method based on approximate dynamic programming, greatly reducing t...

A method to control the output current of a three-phase grid-tied inverter is presented. An LCL-filter is used to reduce the current distortion injected into the grid. The objective is to minimise current distortion and switching frequency to reduce losses. The control approach is based on finite control set model predictive control with sphere dec...

IEEE Industrial Electronics Technology News (ITEN), May 2014, http://ies-iten.com/

In this paper, a new model predictive direct current control (MPDCC) strategy is proposed for a medium-voltage (MV) neutral-point-clamped converter with an LCL-filter-based connection to the grid. The proposed strategy addresses the issues of resonance damping and harmonic attenuation through the virtual resistor (VR) concept, and is thus, termed M...

This paper presents a model predictive direct power control scheme for high-power grid-connected neutral-point-clamped converters. The controller regulates the instantaneous real and reactive powers, as well as the neutral-point potential of the converter, within a set of symmetrical bounds while, at the same time, minimizing the switching frequenc...

In this paper, a recently proposed reduced order model for Modular Multilevel Converters is validated and used to analyze the role of the circulating current in the power transfer inside the converter. This model simplifies the analysis of the converter by removing the discontinuities and reducing the order of the system. Therefore, continuous anal...

In order to fully exploit the benefits of modular converters, dedicated hard- and software integration technologies have been developed to complement modular multi-level circuit topologies. The technologies investigated include a wireless auxiliary power supply, a two-phase cooling, solid insulation, wireless optical communication, redundant EtherC...

Modular multilevel converters (M2LCs) are typically controlled by a hierarchical control scheme, which essentially requires at least two control loops: one to control the load current and another to control circulating currents. This paper presents an M2LC with a single controller, which is based on model predictive direct current control (MPDCC) w...

Power conversion in the medium-voltage range faces the challenge of performing power exchanges between electrical grids and loads that are both becoming ever more complex. The task is further complicated by the presence of electrical oscillations. Advanced control methods are therefore required to enable high-quality power conversion and to provide...