1. Research Background
With growing concerns about environmental sustainability and energy efficiency, electric vehicles (EVs) and renewable energy sources have become key focuses in modern power systems. The integration of EV charging, discharging, and energy storage into a single power station represents a significant advancement in smart grid technology. This system combines the functions of traditional charging stations with bidirectional power conversion, enabling efficient two-way energy flow between EVs and the grid. It offers an optimal solution for managing large-scale renewable energy integration and promoting the widespread adoption of electric vehicles. The focus of this paper is on the Parallel Power Regulation System (PCS) used within such integrated power stations. This system consists of multiple bidirectional converter modules operating in parallel, controlled through a centralized architecture. Based on commands from the upper-level Energy Management System (EMS), the PCS can operate in various modes, including standalone, grid-connected, and seamless switching between them. The paper presents a detailed analysis of the control strategies involved in these operations, particularly emphasizing the smooth transition between independent and grid-connected modes.
Structure of the Parallel Power Regulation System in an Integrated Charging and Discharging Power Station
2. Operating Modes and Control Strategies
V2G Mode and Control Strategy
In the Vehicle-to-Grid (V2G) mode, the PCS employs a dual-loop control structure, where the inner loop controls the inductor current on the inverter side, and the outer loop regulates the grid-side inductor current. The EMS provides active and reactive power commands to the system. This control method effectively suppresses grid current resonance, ensures a high power factor, and delivers excellent steady-state and dynamic performance. During charging, the converter operates as a voltage-type high-frequency PWM rectifier, while during discharging, it functions as an inverter. The four-quadrant operation capability of the high-frequency PWM converter enables seamless charge-discharge transitions. In this mode, the PCS can absorb or supply both active and reactive power to the distribution network, helping maintain stable tidal currents at the Point of Common Coupling (PCC), making it a controllable unit relative to the grid.Standalone Mode and Control Strategy
In standalone operation, the PCS uses a dual-loop control scheme, with the inner loop controlling the inductor current and the outer loop regulating the capacitor voltage. This approach ensures high-quality output voltage and improved system dynamics. The converter operates in voltage source mode, and the main challenges are synchronization and current sharing among parallel modules. A digital synchronization control scheme is implemented, where the central controller generates a power frequency square wave signal that is optically converted and sent to each module. To ensure balanced power distribution, a power-sharing control strategy is adopted, which depends on the output power and impedance of each PCS module.Seamless Switching Mode and Control Strategy
The seamless switching control system comprises a voltage control unit and a current control unit. To achieve a smooth transition between grid-connected and standalone modes, the inductor current inner loop is maintained, while the outer loop switches between the grid-side inductor current loop and the filter capacitor voltage loop. When transitioning to grid-connected mode, the bidirectional converter detects the grid voltage amplitude and phase, adjusting its own output accordingly. Once the grid conditions are met, a static switch is triggered, and the system smoothly transitions from standalone to grid-connected mode. Similarly, during grid faults or maintenance, the system can seamlessly switch back to standalone operation. Fast grid state detection and phase-lock control help minimize switching impact and ensure smooth mode transitions.3. Simulation and Experimental Verification
A two-module 500kVA PCS parallel test system was built using the TMS320F2812 microprocessor as the core controller. In V2G mode, the system operated as a current-mode converter, with the centralized controller issuing grid power commands. Experimental results showed good incoming current waveform quality and a high power factor. In standalone mode, the system functioned as a voltage-source converter, demonstrating excellent voltage waveform quality and fast response to load changes. During abrupt load variations, the system achieved instantaneous current balancing and strong dynamic performance. The experimental waveforms confirmed that the proposed double-loop seamless switching strategy ensured stable and smooth voltage transitions, supporting reliable operation of the integrated power station.
Experiment Waveform of V2G to Standalone Mode Transition
Experiment Waveform of Standalone to V2G Mode Transition
4. Conclusion
The power regulation system is a critical component in the integrated charging, discharging, and storage power station. It manages EV charging and discharging, battery energy storage, and load leveling. This paper thoroughly analyzes the control strategies for V2G, standalone, and seamless switching operations. Based on a three-phase converter with LCL filtering, a dual-loop control strategy is proposed, including inverter-side inductor current inner loop, filter capacitor voltage outer loop, and grid-side inductor current outer loop. The research demonstrates that the proposed control strategy ensures economical and reliable operation of the integrated power station, making it a promising solution for future smart grid applications.70W Medical Power Supply,70W Medical Device Power Supply,70W Medical Power Adapter,70W Rade Power Supplies
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