Abstract
Against to the problems of low utilization rate of DC-side voltage of Cascaded H-bridge (CHB) multi-level inverter Carrier Disposition (CD) modulation strategy and unbalanced output power of each cascaded H-bridge units, a power balanced based In-Phase Disposition Trapezoidal Pulse Width Modulation (IPD-TPWM) strategy is proposed in this article. By selecting an appropriate trapezoidal wave triangulation rate $\delta $ , the modulation strategy can greatly increase the amplitude of the CHB inverter output voltage fundamental wave while ensuring the waveform quality of output phase voltage, and realize the power-balance of H-bridge units within a full modulation ratio range by changing the arrangement of triangular carriers in the vertical direction while using the carrier segment in the half carrier period of the IPD-TPWM strategy as the basic unit. Therefore, it has solved the problem of low utilization rate of DC-side voltage and unbalanced output power of each unit. At the same time, the Total Harmonic Distortion (THD) of output line voltage of the modulation strategy is lower than that of IPD-SPWM strategy in the whole modulation degree, which effectively improves the quality waveform of the output line voltage, and can be conveniently used in N-level CHB inverters. Moreover, the working stress of all the unit switching tubes is the same, the heat dissipation distribution is uniform, the switching loss is effectively reduced, and the service life and system reliability are improved. Finally, the Matlab/Simulink simulation model and experimental platform are established to verify the validity and practicality of the modulation strategy.
Highlights
Cascaded H-Bridge (CHB) multi-level inverter is one of the most common multi-level inverter topologies, and has been widely used in medium voltage high-power inverters and AC drive industry
CPS-PWM strategy has the advantage of natural equalization of the output power of each cascaded H-bridge units [6], Total Harmonic Distortion (THD) of output line voltage waveform is minimum under IPD-PWM strategy [7]
On the basis of the IPD-TPWM power, the carrier is reconstructed by changing the arrangement of carriers in the vertical direction, so that the output voltages of the various units are equal in one reconstructed carrier cycle, ensuring that the output power average values of each cascaded unit is equal and the time required for power-balance is one reconstructed carrier period
Summary
Cascaded H-Bridge (CHB) multi-level inverter is one of the most common multi-level inverter topologies, and has been widely used in medium voltage high-power inverters and AC drive industry. The strategy uses multiple trapezoidal modulation waveforms and a single triangular carrier to sample This strategy can improve the output voltage amplitude, its experimental control process is more complicated, and the power-balance problem of each cascaded unit is not resolved. Based on the IPD-SPWM strategy, Literature [15] has proposed a power-balance control method of alternating changing the position for corresponding carrier of two units on the time axis. Literature [16] has proposed a hybrid multi-carrier PWM strategy, which can achieve output power-balance naturally between different units When this strategy is applied to CHB Sevenlevel inverters, the THD of line voltage uAB is higher or equal to CPS-PWM strategy at modulation index M∈[0.35,0.9]. If the phase angle ωt in Formula (6) is lagged behind 2π/3 and 4π/3 respectively, the expressions of voltage ratios of uAC and uBC to DC side can be obtained respectively
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