Design of a Novel Hybrid Control Strategy for ES Grid-Connected Inverter for Smooth Microgrid Transition Operation

Abstract

A novel hybrid control strategy for energy storage (ES) is applied in accordance to the recommendations by the IEEE Std. 1676. The strategy mainly consists of the model predictive controller (MPC), two-degree of freedom algorithm and modified droop control. In inverter control layer, MPC and two-degree of freedom algorithm are adopted to construct a generalized controller to enable ES operate in microgrid grid-connected and islanded operation modes with a single control structure, motivating the smooth transition between microgrid operating modes. And MPC and two-degree of freedom algorithm are used in the control layer's current inner loop and voltage outer loop, respectively. Comparing with the traditional double loop control from the perspective of structure, with the novel strategy the control layer's current inner loop is without pulse width modulation (PWM) and only a single proportional-integral (PI) controller is applied in its voltage outer loop, so that ES's robust performance can be enhanced. And because of the high frequency inverter's equivalent transfer function with the smaller time constant, MPC's transfer function approximated as being unitary. Therefore, when the two-degree of freedom algorithm construct the inverse model for the controlled object in control layer's voltage outer loop, from the application layer perspective, the control layer can be recognized as unity gain. Thus, the control layer's harmful disturbances associated with the operation mode transitions can be removed. In the application layer, through adding decoupling inductance and introducing microgrid's voltage and angular frequency feedforward compensations to carry out PQ and modified droop controls, the grid-connected and island control targets of ES application layer can be realized. In particular, when microgrid operation mode is switched to island, with the help of modified droop control, microgrid's voltage and frequency can be quickly restored to standard values. Through the theoretical derivation and simulation results, it can be proved that under microgrid's plan or non-plan operation mode switching, the proposed method can not only can not only implement the microgrid smooth switching, but also strengthen its transient performance. INDEX TERMS Model predictive controllers, two-degree of freedom, smooth transition, decoupling inductance, feedforward compensation.

A Review of Microgrid Energy Management and Control Strategies

“…This section reviews methods used in literature to maintain the stability of MG parameters during transition events. Zheng et al [147] present a smooth transition control scheme for ESS to operate in grid-connected and islanded modes. A combination of MPC and a two-degree of the freedom control algorithm is implemented as a single control structure to promote smooth transition between modes, which can alleviate control disturbances by adopting a control structure that appears as unity power gain.…”

Autonomous Multi-Factor Energy Flows Controller (AmEFC): Enhancing Renewable Energy Management with Intelligent Control Systems Integration

“…Scaling up, city-scale grids interlink multiple micro-grids within urban settings, supporting sophisticated energy sharing and management, in alignment with sustainable energy initiatives like the Paris Agreement [58] [62]. These interconnected systems rely on advanced controls and communication for real-time monitoring and predictive analytics, enhancing decision-making for energy allocation, and supporting the integration of electric vehicles as energy storage solutions [63] [64].…”

A smooth grid connection strategy for compressed air energy storage based on adaptive PI control

“…For smooth switching, reference adopts the methods of V/f control and PQ control switching, and introduces current compensation to reduce the transient impact before and after switching the control strategy. References (Wang et al, 2016;Zheng F et al, 2019) use a virtual synchronous generator to switch to PQ control, and controls the current loop instructions to ensure that the inner loop parameters are consistent when the control mode is switched to achieve smooth switching. Reference proposes a smooth grid connection strategy for optical storage virtual synchronous machines based on adaptive model predictive control.…”