Abstract
The new voltage and current double loop control strategy is proposed to solve the DC microgrid bus voltage fluctuation caused by loads fluctuation, parameters perturbation and unbalanced three-phase power supply. Firstly, the $dq$ axis mathematical model of three-phase AC-DC bidirectional converter in DC microgrid is analyzed and established, and then the controllers are designed according to the $dq$ axis mathematical model. The outer loop is a voltage loop based on variable gain linear extended state observer (VGLESO) and sliding mode theory. VGLESO can not only effectively overcome the problem of peak output of traditional high-gain LESO in the initial stage of operation, and ensure that the system has good startup characteristics, but also quickly track and compensate the total disturbance of the system without additional current sensors. The inner loop is a current loop based on adaptive PI, which can eliminate the influence of system parameters perturbation on bus voltage and improve the system’s adaptability. Under the action of the inner and outer loops, the system has good dynamic and static characteristics. Finally, the feasibility and correctness of the control strategy are verified by Matlab/Simulink.
Highlights
With the promotion and popularization of distributed energy grid connection and the increasingly strict requirements of users on the power quality of terminal power supply, the traditional AC distribution network gradually shows its deficiencies in the ability to accept new energy and power quality [1]–[3].The circuit topology of a typical DC microgrid is shown in fig.1 Compared with the AC distribution network, the use number and frequency of power electronic devices of the DC microgrid are much smaller than that of the AC distribution network, which reduces the energy conversion link of the distributed power grid connection and the cost of grid connection
SIMULATION AND ANALYSIS In order to test the suppression effect of variable gain linear extended state observer (VGLESO) on the "initial peak" and verify the control effect of the control strategy proposed in this paper, the DC microgrid shown in fig.9 was built in Matlab/Simulink
Aiming at the problem that the traditional PI controller is too sensitive to the system parameter perturbation, the adaptive PI control law based on the fal function is designed
Summary
With the promotion and popularization of distributed energy grid connection and the increasingly strict requirements of users on the power quality of terminal power supply, the traditional AC distribution network gradually shows its deficiencies in the ability to accept new energy and power quality [1]–[3]. Current feedforward control with current signal as input is transformed into current feedforward control with voltage signal as input by VGLESO (The specific structure is shown in fig.3) This method can effectively suppress the initial peak value of LESO, and effectively reduce the use of current sensors and reduce the cost of the device, at the same time, it can reduce the chattering of sliding mode control; In this paper, the gain of the PI controller of the current inner loop is corrected by the nonlinear fal function to improve the system’s adaptability to parameter perturbation(The specific structure is shown in fig.). DESIGN OF VOLTAGE OUTER LOOP BASED ON VGLESO AND SLIDING MODE THEORY As the core of linear active disturbance rejection control, LESO can track the state variables in the system in real time, and approximate the total disturbance of the system.
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