Model Predictive Control of an Indirect Matrix Converter with Active Damping Capability

Abstract

In this paper, a model predictive control (MPC) scheme is proposed to control indirect matrix converter (IMC), which is used for three phase-to-three phase direct power conversion. IMC is composed of back-to-back connected conventional current source rectifier (CSR) and voltage source inverter (VSI) without any intermediate energy storage component between them. The aim in the control of CSR side is generally to have unity power factor with relatively low total harmonic distortion (THD) and the aim in the control of VSI side is to be able to synthesize sinusoidal load currents with desired peak value and frequency. Imposed source current MPC technique in abc frame is used for the rectifier side and cost function evaluation process calculates three-phase supply current errors respect to its reference. Supply currents for next sampling interval are predicted using the discrete form of input filter model. The peak value of sinusoidal supply current reference is generated from the error in load current space vector using a PI compensator. This generated reference is synchronized with supply voltage by the multiplication of Proportional-Integral (PI) compensator output value and instantaneous three-phase supply voltage. An active damping technique, which does not require to select an optimum value for fictitious damping resistor, is also included in the proposed control scheme in order to mitigate the resonance phenomenon of lightly damped input LC filter to suppress the higher order harmonics in supply currents. Load currents with desired peak and frequency are also obtained by imposing sinusoidal currents in abc frame. The cost function for VSI stage evaluates output load current error. Load current predictions are obtained by using the discrete form of load model. These two cost functions are combined into a single cost function without any weighting factor since both error terms are in the same nature. The switching state that minimizes this pre-defined cost function among the 24-valid switching combinations of IMC is selected and applied to converter. The proposed model predictive control with active damping method shows good performance in terms of THD levels in supply currents even at low current demands from supply side. The proposed model predictive control method combined with active damping strategy guarantees unity power factor operation and draws sinusoidal load currents at desired peak and frequency.