Pulse Width Modulation And Model Predictive Control Of Three Phase Converters

With the wide use of converters in a variety of industrial applications, such as High Voltage Direct Current Transmission (HVDC), Uninterruptible Power Supply (UPS), wind energy system, photovoltaics, its modulation and control strategy have become hot topics in power electronics. This paper takes the three phase inverter and rectifier as research subject, focusing on the Pulse Width Modulation (PWM) algorithms of the two level and three level inverters and Model Predictive Direct Power Control (MPDPC) of the rectifier.Based on analyzing the two level Space Vector PWM (SVPWM) principle,8 different SVPWM strategies are realized:symmetrical seven segment SVPWM, asymmetrical seven segment SVPWM and six discontinuous SVPWM algorithms. The relationship between SVPWM and Carrier-Based PWM (CBPWM) is analyzed comprehensively, which involves the relationship between space vector sectors and CBPWM fundamental modulation signals; the relationship between vector operating time and zero sequence signal; the relationship between vector operating time and fundamental modulation signals. On the basis of that, the CBPWM strategies respectively equal to the 8 SVPWM algorithms are derived according to the regular sampling principle and the volt-second balance principle.In the over-modulation range, the principle of SVPWM algorithm is introduced in detail, and in order to reduce the complexity of that, two simple CBPWM algorithms which are equal to the complex SVPWM algorithm in over-modulation region ? and ? are deduced, respectively. The equivalence of SVPWM and CBPWM is validated by both simulation and experimental results.For the modulation of three level inverters, based on analyzing the two popular PWM schemes-SVPWM and CBPWM, this paper derives how to realize the SVPWM algorithms through CBPWM according to the volt-second balance principle. The zero sequence injected to sinusoidal modulation signal is deducted. Furthermore, in order to analyze the relationship between SVPWM modulation index and CBPWM modulation signals, the concrete expressions of modulation signals with the modulation index as independent variable are derived. Simulation and experiment are performed to verify the correctness of theoretical analysis.In the three level SVPWM over-modulation range, the superposition principle is adopted to analyze the reconstruction process of reference voltage vector. For simplicity, a CBPWM algorithm which is equal to the complicated SVPWM is proposed. In this CBPWM algorithm, the modulation signal of each phase is the sum of two simple modulation signals (most of them are constant). The equivalence of the two PWM strategies is validated by both simulation and experimental results.For the control of a rectifier, the conventional MPDPC and the recently reported Duty Optimal MPDPC (DO-MPDPC) are introduced, based on which, the limitations of the two schemes are analyzed and summarized. Then a new Ripple Reduced MPDPC (RR-MPDPC) scheme using extended switching vectors and time-optimized control is proposed. The transient and steady state performance comparisons, including the comparison of robustness to parameter variations, among the conventional MPDPC, DO-MPDPC and the proposed RR-MPDPC are carried out through both simulation and experiment. The transient performance comparison involves the responses to a step change in active power reference, a step change in reactive power reference, a step change in load. The results confirm that the proposed RR-MPDPC scheme can achieve better steady performance without degrading the dynamic performance.In order to extend the equivalent actuating vector range further, a Performance-Enhanced MPDPC (PE-MPDPC) strategy is proposed. In PE-MPDPC, two active vectors and a zero vector are adopted in a sampling period, whose equivalent actuating vector is optimized with an optimal'length'and an optimal'phase'(direction). The effectiveness of PE-MPDPC is validated by simulation and experimental results.