Abstract
This paper suggests an enhanced control scheme for a four-leg battery energy storage systems (BESS) under unbalanced and nonlinear load conditions operating in the isolated microgrid. Simplicity, tiny steady-state error, fast transient response, and low total harmonic distortion (THD) are the main advantages of the method. Firstly, a new decoupled per-phase model for the three-phase four-leg inverter is presented. It can eliminate the effect of power stage coupling on control design; thus, the three-phase four-leg power inverter can be viewed as three single input single output (SISO) control systems. Then, using an improved orthogonal signal generation method, the per-phase model of the four-leg inverter in the stationary and synchronous frame is derived. As the second step, a per-phase multi-loop control scheme for the four-leg inverter under unbalanced load conditions is suggested. The proposed control strategy has the ability to provide balanced output voltages under unbalanced load conditions by avoiding the need to deal with the symmetrical components. Finally, a multi-resonant harmonic compensator is used to actively prevent low-order harmonic currents to distort the output voltages of the three-phase four-leg grid-forming power converter. Simulations results are also presented to verify the performance of the suggested control strategy.
Highlights
The isolated microgrids can be defined as a group of dispersed generators, communication systems, protection devices, sensitive loads, distributed energy storage systems (DESSs) and power electronic interfaces connected through a relatively small grid and isolated from the main grid [1,2,3,4]
The part focuses on microgrid under unbalanced load conditions. This control strategy is proposed using the per-phase proposing a multi-loop control scheme for grid-forming battery energy storage systems (BESS) operating in an isolated microgrid under modeling ofload the conditions
Thethe results of this partpart show thatthat the compensation, and the Overall, results of this show compensation, and the total harmonic distortion (THD) is reduced from 5.9 to 2.68%. The results of this part show that the per-phase per-phase multi-loop multi-loop control control strategy strategy that that consists consists of of the the cascaded cascaded voltage-current voltage-current controller, controller, the per-phase multi-loop control strategy that consists of the cascaded voltage-current controller, and the multi-resonant harmonic compensator, has the ability to keep the output voltages of the distributed generations (DGs) balanced with low THD under the situation of unbalanced and nonlinear load
Summary
The isolated microgrids can be defined as a group of dispersed generators, communication systems, protection devices, sensitive loads, distributed energy storage systems (DESSs) and power electronic interfaces connected through a relatively small grid and isolated from the main grid [1,2,3,4]. It is important to propose an improved control scheme for a grid-forming power converter operating in an isolated microgrids to provide balanced output control scheme for a grid-forming power converter operating in an isolated microgrids to provide voltages under unbalanced load conditions with a fast transient response, of zero steady-state error without any sensitivity to frequency variations and low THD under nonlinear load conditions. The part focuses on microgrid under unbalanced load conditions This control strategy is proposed using the per-phase proposing a multi-loop control scheme for grid-forming BESS operating in an isolated microgrid under modeling ofload the conditions. This strategy and is proposed the per-phase of the harmonic controller is used to actively prevent low-order harmonic currents distort the four-leg VSC in the stationary and rotating reference frames.
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