Research On Power Electronic Transformer Control Strategy In Microgrid

In the great situation of the overuse of traditional energy and the national new energy strategy,the research of micro grid technology integrated with distributed generation,power electronic converter and modern control technology is becoming more and more in-depth.How to realize the safe and stable operation of micro grid and the friendly interc onnection with the main power grid have been the focus and core of the research.Power electronic transformer is a new type of high-power energy transmission equipment,which itself contains a large number of power electronic devices.With the help of effective control strategy,it can effectively improve the power quality of the distribution syste m.It also contains AC and DC interface,and applies it to the micro grid system,which can facilitate the access of various distributed power sources,and can play the role of isolating microgrid and large grid,reducing the mutual impact between the microgrid and the large grid,and improving the stability of the microgrid system.This paper introduces the composition of the microgrid system,including all kinds o f distributed power supply and energy storage unit,and introduces the control strategy of distributed grid connected inverter,including constant power control,constant voltage and frequency control,and droop control.Then,a hybrid energy storage device consistin g of battery and super capacitor is introduced,and the control strategy of the energy sto rage system is given,and the simulation analysis is carried out.The working principle and structure of AC/AC type and AC/DC/AC type PET are i ntroduced.A type of AC/DC/AC type of three stage structure is selected and its mathem atical model is derived.According to its mathematical model,the control strategy is put forward.The input stage adopts double loop control of voltage and current,isolation leve l opening loop control,and the output level adopt virtual same.Step generator control.T he effectiveness of the control strategy is verified by simulation at all levels.The topology of the micro network system with power electronic transformer is prop osed,and the system network operation and island operation are simulated respectively.The simulation results show that the power electronic transformers can maintain the stabi lity of the voltage and frequency of the microgrid bus under the two running states,and have good dynamic performance,and the output level of the PET is due to the output l evel.The principle of virtual synchronous motor is adopted.The inertia J and damping c oefficient D are introduced in the control system.The output level inverter can also sho w the inertia and damping characteristics of the synchronous generator,and the frequencycan be changed slowly,which is beneficial to the stability of the microgrid system.In the process of switching from the network to the isolated island,the control strategy of t he power electronic transformer output level and the micro source grid connected inverter does not need to be changed,and the impact of the mode switching on the system is r educed.Finally,the droop control strategy is introduced into the parallel operation system of power electronic transformer.By setting the parameters of the output stage control syste-m reasonably,the output impedance of the power transformer is perceptual in the range of power frequency,and it can meet the requirement of droop control.