Abstract
The cascaded H-bridge multilevel inverter (CHMI) is a modular structure that consists of many power semiconductor switches. With this increase in the number of power semiconductor switches, it is hard to predict and handle the failure of the devices, and hence reliability of CHMI decreases. The major cause of power semiconductor switch failure is junction temperature that is produced by power losses. The study proposes a multi-carrier pulse-width modulation (PWM) scheme for reduction in switching losses of CHMI. In the proposed modulation scheme, the two legs conduct switching operation at different frequencies for switching reduction. One leg conducts switching operation with high frequency, while the other leg conducts switching operation with fundamental frequency. The switching operations with different frequencies cause unbalanced switching loss to each leg. Therefore, the junction temperature that is based on power losses leads to different life-times for the power semiconductor switch. Additionally, the switching frequency of the two legs is alternated to evenly distribute switching losses and junction temperature. Simulation and experimental results verify the performance of the proposed PWM scheme.
Highlights
Multilevel inverters exhibit various advantages such as decreased blocking voltage of power semiconductor switch, lower total harmonic distortion (THD), and easy maintenance [1]
This paper proposes a modified PS-pulse-width modulation (PWM) scheme that is increased the life-time of power semiconductor switches by decreasing power losses
In the clamped phase-shifted PWM (PS-PWM) scheme for decreased power loss, as shown in Fig. 7(a), the switching frequency of LegB corresponds to the fundamental frequency of output voltage and not the frequency of triangular carrier waveform
Summary
Multilevel inverters exhibit various advantages such as decreased blocking voltage of power semiconductor switch, lower total harmonic distortion (THD), and easy maintenance [1]. This paper proposes a modified PS-PWM scheme that is increased the life-time of power semiconductor switches by decreasing power losses. A. CONVENTIONAL PS-PWM SCHEME The proposed modulation scheme modifies PS-PWM scheme based on unipolar modulation method for decreased power losses, and the reference voltages of cells in same phase require only one waveform. The switching state of LegA in each cell is determined by gating signal that is generated by comparing vxi,clamp,ref with triangular carrier waveform. The switching frequency of LegB corresponds to the frequency of triangular carrier waveform, and the switching loss and operation count is identical to that of the conventional PS-PWM scheme. The reliability and life-time is improved only power semiconductor switches of LegA the reliability of CHMI is identical to that of the conventional PS-PWM scheme.
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