Power Balance Control Schemes For Cascaded Multilevel Inverters

With the development of power electronic technology,higher voltage grade is demanded in industrial application,cascaded multilevel inverter is widely used in the field of high voltage and high power.The independent dc power supply is needed by each power unit of cascaded multilevel inverter.So there is an important significance to reasonably and effectively use each independent dc power supply,make each unit power balance and improve the inverter performance.Power balance control schemes for cascaded multilevel inverters are used as the research object in this paper.The main research contents and innovation points are as follows:The output active power of cascaded multilevel inverter is theoretically analyzed.The principle of power balance control scheme is concretely explained.Those experiments have laid a solid foundation for the raise and research of power balance control schemes for cascaded multilevel inverters in this paper.A power balance control scheme for the selective harmonic elimination PWM strategies of cascaded multilevel inverter with traditional H-bridge units is proposed.The scheme achieves the output power balance in one output cycle through splitting the fundamental voltage amplitude equation expression of harmonic elimination equations equivalently,which ensures the fundamental voltage generated by each traditional H-Bridge unit in one phase is equal and the voltage waveform is quarter cycle symmetry.Two different power balance control schemes for the sinusoidal PWM strategies of cascaded multilevel inverter with traditional H-bridge units is proposed.The two new schemes achieve the output power balance in one output cycle through interchanging the different carriers up and down according to quarter cycle and according to adjacent interval,which ensures the fundamental voltage generated by each traditional H-Bridge unit in one phase is equal without affecting the quality of the output voltage waveform.A power balance control scheme for the selective harmonic elimination PWM strategies of cascaded multilevel inverter with hybrid H-bridge units is proposed.The scheme achieves the output power balance in one output cycle through splitting the fundamental voltage amplitude equation expression of harmonic elimination equations equivalently,which ensures the fundamental voltage generated by each hybrid H-Bridge unit in one phase is proportional to the corresponding input voltage and the voltage waveform is quarter cycle symmetry.A power balance control scheme for the hybrid modulation strategies by staircase and carrier of cascaded multilevel inverter with hybrid H-bridge units is proposed.The schemeachieves the output power balance in one output cycle through adjusting the conduction angle of the H-bridge unit with high voltage under the different amplitude modulation,which ensures the fundamental voltage generated by each hybrid H-Bridge unit in one phase is proportional to the corresponding input voltage and the voltage waveform is quarter cycle symmetry.A power balance control scheme for the sinusoidal PWM strategies of cascaded multilevel inverter with five switches for each H-bridge unit is proposed.The scheme achieves the output power balance in one output cycle through using the phase-shifted staggered saw-tooth carrier phase disposition,which ensures the fundamental voltage generated by each unit in one phase is equal with good harmonic characteristics.A power balance control scheme for the sinusoidal PWM strategies of cascaded multilevel inverter with capacitor-clamped H-bridge units is proposed.The scheme achieves the output power balance in one output cycle through using the phase-shifted saw-tooth carrier phase disposition,which ensures the fundamental voltage generated by each unit in one phase is equal without affecting the quality of the output voltage waveform.The new schemes are simulated and researched by using MATLAB/Simulink software and the experiment platform.