Leakage Current Suppression Of Active Neutral Point Clamed Five-Level Inverter

In high-voltage high-power occasions,compared with the populared three-level inverter,switching loss and current harmonic is reduced in Active-neutral-point-clamed five-level inverter.Therefore,the filter is reduced too.At the same time,the common-mode voltage amplitude is reduced to one half of the former,and the safety performance of the system is improved correspondingly.An output level with multiple commutation paths provides more options,which makes the control of the dc side capacitance voltage and the flying-capacitor voltage more relaxed.In the theoretical analysis and practical engineering application of the five-level inverter,the leakage current problem has always been a hot and difficult.Due to the presence of soil,water and other media,the photovoltaic array composed of solar panels contains parasitic capacitance.When the high frequency common-mode voltage is considered,the dc-side capacitance,filter and network impedance can be regarded as short circuit.Therefore,high frequency leakage current is generated in the unisolated system circuit.Cand LC will greatly reduce the safety of the system,which can cause electric shock or fire,and worse,it may cause the destruction of people.In this paper,the topology and working process of ANPC-5L are described and the mathematical model of ANPC-5L inverter is constructed.Secondly,the generation mechanism of leakage current and common-mode voltage is deduced and analyzed theoretically.According to the mathematical expressions of both,a modulation method which can restrain leakage current is proposed.Then the carrier realization of this method is proposed to simplify the calculation.At last,this method is compared with Sinusoidal Pulse Width Modulation,Space Vector Pulse Width Modulation,Low Common-mode Voltage Pulse Width Modulation in common-mode voltage,leakage current,neutral-point voltage,flying-capacity voltage and current harmonic distortion rate.To verify the correctness of the modulation strategy proposed in this paper.A lOkW three-phase ANPC-5L inverter experiment platform was designed and built.This platform mainly includes:ANPC-5L hardware circuit design and software system design.The hardware system design includes direct current capacitance plate design,main circuit board design,grid-connected interface board design,signal processing board design and control board design.The software control system design includes DSP and CPLD program design on the control board.On the basis of this platform,the grid-off experiment of these four modulation strategies is carried out,and the experimental results show the correctness and feasibility of the scheme.