Alan Wilson

Model Predictive Control of Multilevel Cascaded H-Bridge Inverters

This paper presents a model predictive current control algorithm that is suitable for multilevel converters and its application to a three-phase cascaded H-bridge inverter. This control method uses a discrete-time model of the system to predict the future value of the current for all voltage vectors, and selects the vector which minimizes a cost function. Due to the large number of voltage vectors available in a multilevel inverter, a large number of calculations are needed, making difficult the implementation of this control in a standard control platform. A modified control strategy that considerably reduces the amount of calculations without affecting the systems performance is proposed. Experimental results for five- and nine-level inverters validate the proposed control algorithm.

A Comparative Assessment of Model Predictive Current Control and Space Vector Modulation in a Direct Matrix Converter

Matrix converters (MCs) are a very attractive alternative to conventional back-to-back converters with dc links. In this paper, a performance comparison between the well-established space vector modulation (SVM) technique and model predictive control (MPC) is presented for the current regulation in a direct MC. Both methods are analyzed and contrasted through simulation and experimental results. In order to establish their strengths and weaknesses, the assessment is made by measuring and comparing output and input currents and voltages with the same voltage source and load current conditions. Our results show that MPC is simpler than SVM from a conceptual point of view and provides better source current behavior, particularly with a distorted source voltage.

Control of a Matrix Converter With Imposed Sinusoidal Source Currents

A new strategy for matrix converters which allows optimal control of source and load currents is presented in this paper. This method uses the commutation state of the converter in the subsequent sampling time, according to an optimization algorithm given by the discrete system model and a simple cost function. The control goals include regulation of output current using an arbitrary reference and good tracking of the source current to its reference, to achieve a sinusoidal waveform. Experimental results from a 7.5 kW prototype support the theoretical development.

Imposed Sinusoidal Source and Load Currents for an Indirect Matrix Converter

A new strategy for indirect matrix converters which allows an optimal control of source and load currents is presented in this paper. This method uses the commutation state of the converter in the subsequent sampling time according to an optimization algorithm given by a simple cost functional and the discrete system model. The control goals are regulation of output current according to an arbitrary reference and also a good tracking of the source current to its reference which is imposed to have a sinusoidal waveform with low distortion. Experimental results support the theoretical development.

Model predictive control of three-phase four-leg neutral-point-clamped inverters

This paper presents a finite control set model predictive control strategy with a prediction horizon of one sample time to control the three-phase four-leg neutral-point-clamped (NPC) inverter with an output LC filter. The four-leg NPC converter is developed to deliver power to the unbalanced/nonlinear three-phase loads and it can produce three output voltages independently with one additional leg. The proposed predictive method uses the discrete model of the inverter and load to predict the future load and capacitor voltage behavior for each valid switching state of the converter. The control method chooses a state which generates minimum error between the output voltages and their references and as well as between the capacitor voltages. The feasibility of the proposed predictive control scheme is verified by computer simulations, showing a good performance and the capacity to compensate disturbances while maintaining balancing of the dc-link capacitor voltages.

Model predictive control of a Doubly Fed Induction Generator with an Indirect Matrix Converter

A simple and intuitive Doubly Fed Induction Generator (DFIG) predictive rotor current control scheme is presented. Predictive control of an Indirect Matrix Converter (IMC) is combined with predictive rotor current control of a DFIG to achieve a very good dynamic response as the rotor currents smoothly follow the applied reference in a ±30% range of the generator nominal rpm. Simulation results are presented for constant torque and rotational speed, as well as for variable rotational speed corresponding to a 10 kW generator dynamic response. Derivation and conjunction of each model equations are also presented along with a delay error compensation strategy to counter the practical implementation issue implicit in discrete time control computation.

Predictive control of a direct matrix converter operating under an unbalanced AC source

Matrix converters are capable of managing bidirectional power flow while fully controlling the source currents and load voltages. The topology is characterized by its reduced size and weight compared to Voltage Source Inverters because there is no DC link stage. Unfortunately, any source voltage disturbance like unbalances, among others, can be reflected directly on the load. This work uses the advantages of the predictive control algorithms in a direct matrix converter operating under polluted sources to overcome this potential drawback. Particularly, three control schemes based on predictive control algorithms are proposed to compensate for source voltage unbalance. As a result, the topology combined with the proposed control schemes behaves as a buffer for supply voltage unbalances as they do not reach the load.

Predictive current control of three-phase two-level four-leg inverter

Distributed power systems are getting more attention now-a-days due to their high flexibility and reliability. In this paper, predictive current control strategy is proposed for the grid-connected four-leg inverters. This kind of converter is developed to deliver power to the unbalanced/nonlinear three-phase loads and as well to the grid. The discrete-time model of the converter and load is used to predict the future behavior of the load currents for each valid switching state. The control method chooses a switching state that minimizes the error between the output currents and their references. The feasibility of the proposed method is verified by computer simulations, showing a good performance and capacity to compensate the disturbances.

A simple and effective solution for superior performance in two-level four-leg voltage source inverters: Predictive voltage control

In this paper predictive voltage control strategy is proposed to control the output voltage of a three phase four-leg inverter. The four-leg inverter is developed to deliver power to three-phase loads under light, heavy, balanced and unbalanced load and source conditions and it can produce three output voltages independently with one additional leg. To predict the voltage behavior for each valid switching state, discrete model of the converter and load is developed. The control method chooses a state with minimum error between the output voltages and their references. The performance of the proposed predictive voltage control scheme is compared with carrier-based PWM method which is an equivalent to the symmetrically aligned-class I 3-D SVPWM. The feasibility of the proposed method is verified by MATLAB/Simulink. These results show that the proposed method has good performance and the capacity to compensate disturbances compared to classical methods.

Cost-function based predictive voltage control of two-level four-leg inverters using two step prediction horizon for standalone power systems

This paper presents a cost-function based predictive voltage control strategy with a prediction horizon of two samples to effectively control the output voltage of three-phase four-leg inverter used for the standalone power systems. The three-phase inverter with an additional leg is developed to deliver symmetrical sinusoidal three-phase voltages irrespective of the arbitrary consumer load profiles. The proposed controller uses the discrete model of the inverter and RLC filter for two-step prediction of output voltage for each switching state of the inverter. The control method chooses a switching state that minimizes the error between the output voltage and its reference. The proposed controller offers an excellent reference tracking with less voltage harmonic distortion for balanced, unbalanced and nonlinear loading conditions. The feasibility of the proposed control scheme has been verified by MATLAB/Simulink.