Research On Control Technology Of Single Phase And Three Phase UPS Inverter And Its Parallel System

As the user's demand for higher power quality,multi-module UPS redundant parallel system has gradually become the primary choice of the electrical equipment in various industries.The inverter is an important part of the UPS system,and its stability directly affects the reliability of the entire UPS system.Therefore,it is of great significance to study the redundant parallel control technology of PWM inverter,improve the reliability of the parallel system,and promote the application of UPS in all kinds of important occasions.In this paper,the PWM inverter topology is a bridge topological structure with the industrial frequency transformer in the the output side to isolate.And the LC filter is composed of transformer's leakage and output capacitance.The mathematical models of single-phase and three-phase PWM inverter are respectively established in the paper and their control strategies are studied.For the single-phase PWM inverter,a double-loop control strategy based on proportional resonant(PR)control in the voltage loop and the proportional(P)control in the current loop is adopted.The design method for controller parameter is proposed in the paper when the DC bus voltage varies widely.The method of extracting the DC component from the PWM pulse of the transformer and introducing it to the closed-loop control is proposed to suppress the transformer bias effectively.For the three-phase PWM inverter,a double-loop control strategy of double-PIR control in voltage loop and current loop is adopted.The current loop resonance part can suppress the voltage distortion under the nonlinear load and the voltage loop resonance part can suppress the negative sequence voltage component under the unbalanced load.The simulation results show the effectiveness of the proposed control strategy.The mathematical model of inverter parallel system is established to analyze the causes of parallel system circulation.And the relationship between power difference and voltage amplitude and phase is deduced.Beside,an improved period synchronization control strategy based on output impedance model compensation is proposed.And this paper adopts the reactive power modulation current sharing control strategy based on CAN bus.In order to adapt to the application under the condition of UPS,a two-stage lock-in synchronization control scheme is adopted.In addition,this paper analyzes the causes of thermal plugging current of the module and puts forward a method to control the thermal interpolation buffer based on load current feedback.In the last,the effectiveness of the buffer control strategy is verified by simulation.Finally,prototypes of 15 kVA single-phase and three-phase UPS parallel system are designed and constructed.The experimental results verify the effectiveness of the proposed control strategy and method.