Conducted Interference Suppression Of Three-phase Inverter

Power electronic equipments especially used as component of independent power systems are widely applied to national economy and national defence constructions.Under the environment of high-voltage,high-current,high-power and high-frequency,power electronic devices generate high voltage change rate and current change rate in the moment of switching on and off.This would form high-frequency interference sources through parasitic parameters and result in serious electromagnetic interference(EMI).The EMI has the adverse effects on the systems such as input and output current distortion,power factor decrease,efficiency reduction,even damage of equipments.The three-phase inverter circuit has widely applied in alternating current interconnection and motor drive.Severe electromagnetic interference could lead more serious impact on the power grid and electrical and electronic equipment within the same network.Further more,EMI has direct impact on the motors such as over-voltage,output reduction,increased high-frequency loss,unit over-heat burning.The focus of this thesis is the conducted interference suppression of three-phase inverters.This study analyzes the differential mode interference spectrum characteristics of three-phase inverter SPWM modulation mode.High current change rate on bridge arm is generated during turn-on transients of power device,which cause differential mode interference by oscillations between parasitic capacitor and parasitic inductor.In order not to affect the load current,a coupled inductance-differential mode filter is introduced between the bridge arm and the load,which reduces the peak current of the bridge arm and suppress the high current change rate.The over-voltage problem is caused by the flux transition to the winding coils of both sides with the coupled inductance during the dynamic circuit.By adding the winding continuous current loop,the over-voltage of the winding coil can be greatly suppressed and the oscillating current can be effectively reduced.The spectrum distribution characteristics of common-mode voltage interference in modulation modes such as SPWM,SVPWM and AZSVPWM1 are analyzed.With the high-frequency on-off response to the power electronic device,the central node of the bridge arm forms a sharp voltage change rate with respect to the reference ground,which generates parasitic oscillation through parasitic capacitor,forming common-mode interference.For the existing parasitic parameters of the main circuit,a new coupled inductor-EMI filter is proposed.The reverse-coupled inductor with a capacitor in the new coupled-inductor EMI filter is equivalent to a negative capacitor after decoupling.It can be utilized to cancel the middle-point-to-ground parasitic capacitor of the bridge arm and block the input and output side loop.At the same time,the decoupled equivalent branches and R_hC_h branches form a common-mode and differential-mode filter respectively.The experimental results indicate that common-mode interference and differential-mode interference for three-phase inverter can be suppressed effectively.To further eliminate the common-mode voltage on the output side of the three-phase and three-bridge inverter,way of introduction and topology structure of compensating power supply should be added.Based on this,the correspondence between the compensation controlled voltage source and the instantaneous values of the midpoint voltages of the three bridge arms is investigated.In the three-phase inverters,the fourth bridge arm is added as the compensating voltage source,which eliminates the common-mode voltage or makes the common-mode voltage constant.With the characteristic extraction and logical analysis of output voltage in dead-time interval,combined with the relationship between the current direction of each phase and the on-off state of power devices,a full-cycle phase-coded state method is created to control the trigger state of the fourth bridge arm.The corresponding relationship between the actual voltage vector and the theoretical reference voltage vector is deduced.The experimental results show that adding compensating bridge arm and optimizing control strategy can effectively suppress common-mode interference on the output side.Considering delay compensation,the time-optimized five-voltage space vector predictive current control is suggested.Under the premise that the??axis current error cost function error is the smallest,the switching combination of effective voltage space vectors is determined and the optimal time of each set of effective voltage space vectors is calculated.The stability of the system is verified based on the Lyapunov principle,and the system still has superior dynamic performance under the condition of parameter mismatch.This method can effectively suppress common-mode voltage,improve steady-state control accuracy and decrease load current harmonics.The simulation results verify the effectiveness of the controlling method.