The Research On Interharmonic Source Model For Single Phase Variable Frequency Drivers And Its Characteristics

Because of filter element is not infinite in Variable Frequency Drives(VFD)circuit DC side,ripple wave will be produced in DC side,which will be modulated by rectifier circuit to system side and causes interharmonics.There already have some research about three phase interharmonic source model,because of the variable-frequency technology has advantages of energy saving,low noise and so on,it is widely used in single-phase electric appliance,but at the present,few researches about interharmonics in the single-phase converter have been done.In order to understand and master the characteristics and level of the interharmonic source in single phase converter,it will cause interharmonic resonance when variable frequency drives are widely used in the 0.4kV power distribution system,which will do harm to the power quality of distribution system.This article from the following areas were studied: First,theory model of the voltage source type single-phase VFD is established,through collecting and analyzing the operation data,values and frequency of interharmonic were obtained of single phase VFD.And interharmonic resonance is analyzed between interharmonic source and system parameter including reactive power compensation device.The concrete analysis are as follows:(1)Baesd on the modulation theory,the system parameters and the machine parameters of the physical isolation are equivalent to the DC-side circuit through the switching function.The DC-side equivalent circuit of the single-phase VFD is established,DC ripple component of the interharmonic is analyzed.Ripple wave is extracted and the value of the interharmonic current inject into system is calculated by the rectifier switch function.The theoretical calculation model is verified by simulation and different parameter changes.(2)The voltage and current data of single phase inverter air conditioner and single phase frequency conversion refrigerator were measured experimentally,through data processing to master its various electrical characteristics,Analyze the interharmonics state of the actual single-phase converter equipment,including interharmonic frequency and values.Interharmonic frequency remains constant and interharmonic magnitude fluctuates within a certain range and it can be used as a harmonic current source,when it working in steady state.(3)The system model of the parallel resonance is calculated and simulated when interharmonic source inject into system,resonant frequency and system interharmonic voltage are calculated.Influence of different parameters on the resonant frequency and the amplitude of the interharmonic voltage is analyzed.Based on the measured interharmonic data,it is qualitatively discussed whether interharmonic content of system voltage exceeds the national standard interharmonic limit when a large number of single phase variable frequency drives access power distribution system when matches resonance.