Parallel PCS Phase Synchronization for Seamless On/Off-Grid Switching
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
In energy storage systems, during on/off-grid switching, the lack of communication between power conversion systems (PCSs) leads to varying output voltage angles, causing large cross currents and instability in power supply to local loads due to asynchronous phase differences.
Innovation Solution
Implementing a method where each PCS independently detects the power grid voltage and adjusts its output voltage angle to a reference angle based on the angular frequency of the power grid voltage, ensuring synchronized angles across all PCSs, thereby preventing large cross currents during on/off-grid switching.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If each PCS independently performs on/off-grid switching without communication, then the switching operation is simple and fast, but the output voltage angles of different PCSs vary greatly causing large cross currents
Solution Approach 1:
The patent applies preliminary action by having each PCS pre-calculate and store the reference angle during the on-grid state before switching occurs. When islanding is detected, each PCS immediately switches to this pre-calculated reference angle without needing to communicate with other PCSs, thus avoiding large cross currents while maintaining independent operation.
Solution Approach 2:
The patent uses copying by having each PCS independently calculate the same reference angle based on the grid voltage angle during on-grid operation. Each PCS creates a copy of the reference angle information locally, enabling synchronized switching across all PCSs without requiring real-time communication during the critical switching moment.
2Device complexity
If PCSs operate independently without communication, then the system complexity is reduced, but the phase synchronization between PCSs cannot be ensured
Solution Approach 1:
The patent applies self-service by enabling each PCS to independently calculate its own reference angle during on-grid operation and autonomously switch to this angle during islanding. Each PCS serves itself by maintaining the necessary synchronization information locally, eliminating the need for complex inter-PCS communication systems while ensuring phase synchronization.
Solution Approach 2:
The patent uses parameter changes by transitioning the control mode from grid-following (during on-grid operation) to grid-forming (during islanding). The reference angle, which is derived from grid voltage during normal operation, becomes the fixed control parameter during islanding, enabling each PCS to maintain synchronized operation without communication by changing how this critical parameter is utilized.
3Measurement precision
If the reference angle is calculated during on-grid state, then the angle information is accurate and synchronized, but additional calculation resources are required during normal operation
Solution Approach 1:
The patent applies preliminary action by performing the reference angle calculation during the on-grid state when grid voltage information is already available and accurate. This pre-calculation stores the synchronized angle information for immediate use during islanding, avoiding the need for complex real-time calculations during the critical switching moment and reducing overall system energy consumption.
Data Source
AI summary
An energy storage system includes at least two power conversion systems PCSs, output terminals of the at least two PCSs are connected in parallel to connect to an alternating current power grid, and input terminals of the at least two PCSs are connected to an energy storage power supply. The first PCS is any one of the at least two PCSs. The voltage detection circuit detects a power grid voltage at a parallel connection point of the output terminals of the at least two PCSs. When determining, based on the power grid voltage at the parallel connection point, that islanding occurs in the alternating current power grid, the controller adjusts an angle of an output voltage of the first PCS to a reference angle, so that angles of output voltages of the at least two PCSs are the same.