Research On LCC Inverter And Its Control For Electrified Transportation Auxiliary Inverter

The development and transformation of electrified transportation requires higher efficiency and reliability for power electronic equipment.As the core device of the auxiliary power supply system of electrified transportation,the auxiliary inverter is responsible for transforming various types of electric energy into three-phase AC to supply the load.Its working reliability is the key to the normal operation of electrical equipment.The topology and control of part of the traditional three-phase four-wire inverter are complex,and large volume can be caused by power frequency transformer.Therefore,it is essential to study the topology and high reliability of inverter.In order to ensure good power quality output while taking into account the three-phase imbalance of output voltage,a three-phase four-wire inverter topology based on LCC network is adopted in this paper.This topology makes full use of the unique advantages of LCC network,which means the output voltage of each phase is independent of load current and has the function of output voltage self-balancing when supplying power to a variety of unbalanced loads.This topology does not need power frequency transformer,which reduces the volume and cost of the system.And higher DC bus voltage utilization can be achieved through the inherent gain of LCC network.Firstly,the mathematical model of LCC inverter is established according to its topology structure.Based on the topology evolution process and construction principle of LCC network,the basic characteristics of LCC inverter are analyzed in detail.Combined with the working characteristics of LCC network and the design criteria of traditional filter,the parameter design method of LCC network is proposed.Taking the suppression effect of the transfer function H₂₂（s）from input voltage to output current of LCC network on each low-order harmonic as a reference to meet the good voltage quality of output under nonlinear loads.The parameters of LCC network are optimized from the perspective of inductor current ripple and inductor volume.At the same time,the influence of different power levels on parameter design is summarized.Based on the parameter design method of LCC network in this paper,the influence of parameter deviation of LCC network and ESR of passive components on the output voltage of LCC inverter is analyzed.The influence of dead time and nonlinear loads on the output voltage of LCC inverter is also researched.Based on the influencing factors of the LCC inverter output waveform quality and the limitations of traditional dq decoupling control strategy based on symmetrical component method applied to the LCC inverter,a three-phase independent control strategy,which can be explained as each phase adopts an independent controller,is proposed in this paper.For unbalanced loads,the voltage loop for extracting output voltage amplitude plays a role.For nonlinear loads,the current loop based on the direct compensation of output harmonic current plays a role.The control strategy does not need dq axis decoupling,and the mathematical model of the single-phase LCC inverter is required only.The structure of the control system is simple and easy to implement and modularize.Also,it ensures high reliability.Simulation and experimental results illustrate that the topology and the proposed control strategy can effectively improve the waveform quality of the output voltage under unbalanced and nonlinear loads.