Research On Low Switching Frequency Control Method Of Inverter In Virtual Co-Phase Power Supply System

The virtual co-phase power supply system can ensure that the trains are separated by uninterrupted power and overpower.The system is implemented by high-power electronic devices.In order to reduce the temperature rise and loss of switching devices,the control system often uses a lower switching frequency,and the reduction of the switching frequency will,as a result,increase the coupling degree of the system,which affects the dynamic and steady state effect of the system.Therefore,it is of great significance to study the low switching frequency control technology on the inverter side of the virtual cn-phase power supply.The main work of this paper includes:Firstly,the working principle of the combined virtual co-phase power supply system is introduced,and the control objective of the system is clarified.On this basis,the control principle of the single-phase inverter dq decoupling is established,and the double loop decoupling control system model of the converter is established,and the control block diagram of the system is given.Aiming at the serious problem of cross-coupling between dq axis currents when the control system of high-power,low-switching frequency converter adopts low sampling frequency,the concept of complex vector is introduced,and the complex vector model of single-phase inverter is built.Complex vector decoupling control system for singlephase inverter at low switching frequency is constructed,and effective decoupling of singlephase inverter at low switching frequency is realized.Secondly,according to the characteristic of the dead time of the switching device of the unified bridge arm when the converter is working,its influence on the on and off process of the power device is deeply analyzed,and then the influence of the dead time on the output voltage waveform of the converter is completed.A dead-time compensation scheme based on the average compensation algorithm is designed,which realizes the compensation for the dead-time of the switching device and improves the waveform quality of the inverter output voltage.Then,when a traditional second-order generalized integrator was used to construct a virtual quadrature component for a single-phase system,the β-axis could not suppress the interference of the DC component in the input signal.An improved generalized second-order integrator algorithm was designed to effectively suppress this component.At the same time,an OSG method based on reference quantity calculation is introduced,and a virtual quadrature signal is constructed by using the given dq value of the signal,which has a better dynamic response speed compared with the traditional SOGI method.Finally,a single-phase inverter experimental platform with TMS320F28335 DSP is built,and the effectiveness of the complex vector decoupling control algorithm,dead-time compensation algorithm and OSG method based on reference calculation is verified.