Abstract
This paper proposes an improved discontinuous pulse-width modulation (DPWM) method based on phase-shifted PWM (PS-PWM) for three-phase cascaded H-bridge (CHB) multilevel inverters. Due to the CHB multilevel inverters employ a large number of power semiconductor switches, they suffer from device failures because the switches are one of the major failure factors in a power electronic system. Therefore, the reliability and life-time of CHB multilevel inverters are mainly determined by the reliability of switches. The most failure of switches is occurred by its accumulated thermal stress which is generated by power losses including the conduction and switching loss. By applying the conventional DPWM, the life-time of switches can be extended because it reduces the switching loss. The conventional DPWM, however, still operates with high speed carrier frequency and it is not enough to reduce the switching loss of the CHB multilevel inverter with a large number of inverter cells. The proposed novel DPWM method provides the improved switching loss reduction through the different switching behaviors for each leg. Additionally, the rotation scheme promises even power distribution and life-time management among inverter cells in a CHB multilevel inverter. The simulation results and experimental results confirm the switching loss reduction and even power distribution abilities of the proposed modulation method.
Highlights
Multilevel topologies are receiving increasing attention in industry due to various advantages such as capability for high voltage system, low harmonic distortion, and easy scalability [1]–[3]
SIMULATION RESULTS The simulation is conducted to verify the effectiveness of the proposed modulation method for cascaded H-bridge (CHB) multilevel inverter
The required DC source each H-bridge cell is 30V and it is small for the original purpose of CHB multilevel inverter
Summary
Multilevel topologies are receiving increasing attention in industry due to various advantages such as capability for high voltage system, low harmonic distortion, and easy scalability [1]–[3]. The CHB multilevel inverter is composed of the series connected single-phase H-bridge cells that require four power semiconductor switches and isolated DC supplies in each of them. The phase-shifted PWM (PS-PWM) is most popular carrier-based modulation technique, it generates great switching loss because all the switches are operated with the carrier frequency for a fundamental period of the output voltage. The reference signal for modulation is formed by mixing the sinusoidal wave and clamping period with rotation scheme It provides even power distribution among switching devices in an inverter cell. The proposed modulation scheme adopts the conventional 60◦ DPWM and clamping state both in a fundamental period of the output voltage. The states of two legs are determined by comparing reference voltage vref with triangular carrier waveform and these operate in a complementary manner. The magnitude between output voltages is small compared with bipolar PWM method and the total harmonic distortion (THD) of output voltage reduces
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