Research On Modularized UPS Parallel Operation And Its Control Technology

With the users'increasing demand of high power quality and rapid growth of distributed power supply, modularized UPS paralleling system finds more and more wide use. Depending on the circuit topology, modularized UPS is divided into rectifier module and inverter module. By the paralleling control on Boost-PFC circuit, modularized rectifier can be realized; based on instantaneous voltage PID control method, a kind of instantaneous current sharing strategy is introduced to realize inverters'parallel operation.The principle of APFC is introduced and the working process of the double Boost-PFC circuit topology with single switching tube is analyzed. Based on the structure of the control strategy, the voltage loop and current loop of the control system are analyzed. The current reference command plays a leading role for the current of the inductance, and the affection of the voltage difference is a lesser factor. The output voltage is mainly affected by the voltage reference command, the soft starting command and the output current. According to the expression of the inductance current and the output voltage, the method of the parallel operation is brought forward. Through the simulation and experiment on the system, the theory analysis and the method are certified.On the basis of the pole-assignment method of PID controller design of inverters, it is easy to get the parameters of the PID controller. Then convert the controller's parameters to the discrete domain, the digital PID controller for inverters is explained clearly. The simulation and the experiments give evidence that the digital PID controller work well at dynamic response and the steady-state response. This kind of digital PID controller can be used in the control of inverters.The mathematical model of the multiple inverter parallel system is established. Through the analysis of the model, it reached that the output voltage of the parallel system is mainly affected by the average reference voltage and the higher-order harmonics of the current. The circulating current is affected by the difference between the reference voltage and the system's average reference voltage. Based on the reason of the circulating current, a kind of instantaneous current sharing strategy is brought forward, which reduce the gain of the circulating current to reference voltage difference and make the instantaneous current sharing come true. Through the simulation and experiment on a two-inverter parallel system, the theory analysis and the instantaneous current sharing strategy are certified.