Minimized DC-link Capacitor PMSM Inverter Control Strategy

Permanent magnet synchroonous motor(PMSM)has been widely used in transportation,domestic appliances,aerospace and industry due to the bendfits of high efficiency and power density.Some PMSM drive system requires high reliability and low electromagnetic noise.DC-link capacitors of inverter used in electrics and other fields tend to be minimized.Using small DC-link capacitors will influence the estimation precision of sensorless control algorithm and influenc e over-current protection.This paper tries to use periodic carrier frequency modulation(PCFM)to spread frequency spectrum of phase currents harmonics with fixed frequency pulse width modulation(FFPWM).And proposes a new method applicable for harmonic analysis of phase currents with PCFM.Influence of phase currents harmonic,which triggered by the phase relationships between PCFM waveform and phase current waveform can be analyzed using the method.This paper gets the conclusion that using sawtooth PCFM can reduce current harmonic amplitude effectively from the effect for reducing harmonic components of the three-phase current with different types of PCFM.The influence on the accuracy of sensorless control strategy based on the virtual coordinate caused by PCFM is discussed.Using periodic carrier continuous frequency modulation can reduce the bad affect.Then,build the model of motor control sysytem and calculate the pump voltage of small-value bus capacitor after the control system over-current.This paper proposes a new strategy used for over current protection of small-value bus capacitor motor control system.The new strategy is analysed in detail,build the simplified circuit model based on circuit topology when over-current protection occurs in motor control sysytem.The expression is gaven to calculate the minimum value of bus capacitor to ensure the safety of control system.The influence on the accuracy of sensorless control strategy based on the virtual coordinate caused by small-value bus capacitor is discussed and modify the sensorless control strategy to improve the accuracy.The simulation result demonstates that the improved sensorless control strategy apply to small-value bus capacitor control sysytem.At last,a PMSM sensorless control system is established.To verify the influence on the accuracy of sensorless control strategy which is caused by different PCFM.And using periodic carrier continuous frequency modulation can reduce the bad affect for sensorless control system is correct.