Abstract：With the continuous development of power electronics technology, three-phase voltage source inverters controlled by pulse width modulation (PWM) have been widely used in AC drive systems, electric vehicles, and ships. Such methods have fixed carrier frequency, and the PWM noise peak of line voltage is very high, causing acoustic noises in the motor and electromagnetic noises in the inverter. Scholars have proposed various random PWM methods to suppress PWM noise peaks, such as RPWM method optimization from random algorithms and carrier sequences. The in-phase disposition pulse width modulation (IPD-PWM) has a smaller THD of line voltage than the phase-shifted pulse width modulation (PS-PWM). However, these modulation methods are mainly applied to single H-bridge inverters. Compared with single H-bridge inverters, cascaded H-bridge inverters have a smaller total harmonic distortion (THD) of output voltage. In addition, asymmetric cascaded H-bridge inverters have a larger output power and a smaller output voltage THD than symmetric cascaded H-bridge inverters. Therefore, this paper proposes a power-balanced hybrid RPWM (PB-HRPWM) method for asymmetric cascaded H-bridge three-phase inverters with a voltage ratio of 1:1:1:3. The proposed PB-HRPWM method can be summarized as follows. (1) The driving pulses of the high-voltage H-bridge unit and the modulation wave of the low-voltage H-bridge unit are generated by comparing the modulation wave of the high-voltage H-bridge unit with the reference level. (2) The random pulses are generated by comparing in-phase random level-shifted carriers with the modulation wave of the low-voltage H-bridge unit. (3) The random pulses are circularly distributed according to 1/2 Tah by pulse logic operation method to obtain the driving pulses of the low-voltage H-bridge unit. (4) The driving pulses of high and low-voltage H-bridges control the operation of the three-phase inverter. The proposed PB-HRPWM method effectively reduces the PWM noise peak of line voltage, and the power balance between the low-voltage H-bridge units can be realized. Compared with conventional random and non-random PWM methods, the proposed PB-HRPWM method has a lower PWM noise peak of line voltage and a smaller total harmonic distortion of line voltage. Simulations and experiments verify the effectiveness and feasibility of the proposed PB-HRPWM method. In summary, the proposed PB-HRPWM method integrates IPD-PWM, step wave modulation, random modulation, and power balance through the proposed in-phase disposition random carriers and pulse logic operations. Therefore, utilizing the low waveform distortion of IPD-PWM and the high-frequency spectrum dispersion of random frequency modulation can decrease the THD and PWM noise peak of line voltage. The power balance target is decoupled from the modulation wave or carrier reconstruction through pulse logic operations between random pulses and pulse signals, avoiding complex modulation wave or carrier design in digital processors.
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2024, Vol. 39 
