Evaluation of DC-link Voltage Ripple in Seven-Phase PWM Voltage Source Inverters

The analysis of dc-link inverter current and voltage ripple is important for the optimization of the input components, mainly the dc-link capacitor. In this paper reference is made to two-level seven-phase PWM voltage source inverters with balanced load, typically multiphase ac motor. The peak-to-peak amplitude of the dc-link voltage switching ripple within the fundamental period is analytically determined as a function of operating conditions: modulation index, output currents amplitude and phase angle. The maximum of voltage switching ripple is also derived in order to help with choice of the dc-link capacitor. The two most popular inverter modulation techniques are considered: sinusoidal PWM and centered PWM (CPWM, equivalent to space vector modulation, SVM). A comparison between them is made in terms of the dc voltage switching ripple envelope. Numerical simulations are carried out by Matlab/Simulink in order to verify the analytical results.