Blocking Voltage Distribution Balance, Digital Control And PWM Method Of Five-Level Inverter Based On Hybrid Clamping Technology

Multilevel converters have become a research hotspot in high-voltage and high-power applications because of their many advantages, such as their low voltage stress on power switches, low harmonic and EMI output. Its corresponding PWM control methods also have become a research hotspot.How stray inductance and forward conduction of diode result in unequal blocking voltage distribution during every commutation between different switching states in five-level inverter based on hybrid clamping technology is analyzed in detail. To deal with this problem, a novel method with advantage of simplicity and low cost is proposed, which can also be applied to improved diode clamping multilevel inverter . The waveforms are given to confirm the validity of this novel method.Considering the large number of power switches in the inverter based on hybrid clamping technology, DSP+FPGA controlling structure is adopted to control a three-phase five-level inverter based on hybrid clamping technology. TO make use of its agility of software programming, DSP takes charge of calculating pulse width. TO make use of its configuration agility and large number of I/O ports, FPGA takes charge of putting out PWM controlling signals with dead-time . TO make use of hardware parallel running, FPGA takes charge of controlling brake unit and fault protection. The validity of the controlling method is confirmed by experiments based on a five-level inverter.Considering the principle of different acute angle's direction of carrier wil result in different turning on and off mode of switch, a new PWM method called acute angle's direction optimized combination PWM is proposed after improving switching state combination PWM method. In the new PWM method, carrier in the higher area has upward acute angle while carrier in the lower area has downward acute angle, which leads to lower switching loss. Especially in low modulation situation, switching loss of some power switches become less in evidence in the case of keeping switching frequency unchanged, while the switching frequency can be 1.5 times more , ensuring that switching loss is not exceed maximum switching loss . The waveform and harmonic of phase voltage and line voltage in switching state combination PWM method and new PWM method are compared and analyzed through simulation. Corresponding program and experiment waveforms are given at last.In the end, the research work is summarized and future research tasks aregiven.