Research On Dc-voltage Control Of Quasi-Z-source Inverter For PMSM Drives

The dc-link voltage is unadjustable in permanent magnet synchronous motor(PMSM) drive system composing by dc-source voltage and voltage-source inverter(VSI). When motor works in the complicate condition, the dc-link voltage will be fluctuant and the whole system will be unstable. To solve this problem, the DC-DC converter is series connected between the dc-source and inverter, controlling the dc-link voltage. Quasi-Z-source inverter(q-ZSI) can control the dc-link voltage and ac phase voltage at the same time, which is a new approach to the above problem. This paper researchs on the modeling and control of q-ZSI for PMSM drive system.Because q-ZSI is nonlinear time-varying circuit, the method of state space averaging is used to build the small-signal model and steady mode of q-ZSI under Modified SVPWM modulation. By comparing the small signal model and circuit simulation model, the correctness of the small signal linear model is verified. Based on the small-signal model, the effect of main paraments in quasi-Z-source network to System dynamic is studied.To improve the dynamics, close-loop feedback control system is designed on the base of the math model of q-ZSI. Dc-link voltage and input current double close-loop structure is used in the control system, in which current loop reduces the response time and voltage loop fouce the dc-link voltage tracks on the reference closely. The power feedforward control is added to feed-back control system formming compound control. The experiments show that double close-loop feedback control enhances the dynamics and stability of control system and feedforward control compensates the disturbance of power change.The PMSM revolving speed is limited by dc-source voltage in VSI driving system. the flux-weakening control solves the above problem, but it reduces the maximum electromagnetic torque and system efficiency. When PMSM works in regeneration mode,the regeneration energy will raise the dc-link voltage in VSI. The brake resistor is added to consume the regeneration energy, which is waste of energy. Considering the dc-link Voltage of q-ZSI is adjustable, q-ZSI is applied to sovle those two problems. Raising dc-link Voltage broadens revolving speed limit. In regeneration mode, dc-link voltage is kept constant and regeneration energy is stored in voltage source at the same time. The simulations and experiments prove the availability of control methods.