Power Converter Grid Synchronization via PMU Feedback
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Solution Overview
Problem
Renewable energy power generation systems face challenges in maintaining synchronization with the electrical grid during low or zero-voltage fault events, leading to potential out-of-step operation and large transient currents due to weak grid connections and lack of sufficient residual grid voltage for reference.
Innovation Solution
A power delivery system that incorporates a phasor measurement unit (PMU) to obtain phasor data and generate signals used by a controller to synchronize power converters with the grid, allowing for adaptive control and impedance determination, even during fault events, by combining local and remote measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a traditional current controlled generator is used in a weak grid connection (SCR below 1.5), then the generator cannot operate stably, but switching to a voltage controlled generator requires slow tuning and additional hardware investment
Solution Approach 1:
The system continuously monitors grid voltage and phase angle through PMU measurements and uses this feedback to dynamically adjust the power converter control strategy. During normal operation, the system operates in voltage-controlled mode, and during LVRT events, it automatically transitions to a control mode that maintains synchronization using the pre-captured phase angle reference, eliminating the need for additional hardware while ensuring stable operation across varying grid conditions
Solution Approach 2:
The control system dynamically adapts its operating mode based on real-time grid conditions. The controller switches between different control strategies: normal voltage-controlled operation, LVRT mode with phase angle maintenance using stored reference, and post-fault resynchronization mode. This dynamic adaptation allows stable operation without requiring the system to be designed for the worst-case scenario with additional hardware
2Reliability
If high power rating generators are included to ride through fault events, then the farm can avoid load shedding, but during low-voltage or zero-voltage faults, keeping synchronized with the grid becomes difficult due to insufficient residual grid voltage
Solution Approach 1:
Before entering an LVRT event, the system captures and stores the phase angle reference from PMU measurements. This preliminary action ensures that when the grid voltage drops during a fault, the controller already has the necessary reference information to maintain synchronization, eliminating the need to rely on insufficient residual grid voltage during the fault event
Solution Approach 2:
The PMU serves as an intermediary that provides accurate phase angle and frequency measurements during grid faults. When residual grid voltage is insufficient for reliable synchronization, the PMU's phase angle measurement acts as a mediator reference, allowing the controller to maintain proper synchronization without directly relying on the degraded grid voltage signal
3Reliability
If the generator controller independently determines frequency during severe fault events, then the generator can continue operating, but the output may be out of step with the grid causing large transient currents during recovery
Solution Approach 1:
The controller continuously receives feedback from the PMU regarding actual grid phase angle and frequency. During fault recovery, this feedback enables the controller to adjust the generator output frequency and phase to match the recovering grid, preventing the large transient currents that would occur from phase angle differences between independently controlled generators and the grid
Solution Approach 2:
The system replaces the traditional mechanical synchronization method (relying on residual grid voltage and automatic frequency locking) with an electronic control system that uses PMU phase angle measurements. This substitution allows precise control of the generator output phase and frequency, enabling smooth resynchronization with the grid during fault recovery without the harmful transient currents associated with mechanical synchronization methods
Data Source
AI summary
A power delivery system includes at least one conductor having a first end and a second end and a phasor measurement unit (PMU) coupled to the first end of the conductor. The PMU is configured to obtain phasor data at the first end and generate a phasor signal that includes the phasor data. The power delivery system also includes a power generation system coupled to the second end of the conductor and configured to provide power to the conductor. The power generation system includes a power source, a power converter, and a controller. The controller is communicatively coupled to the PMU and is configured to receive the phasor signal and control the power converter based at least partially on the phasor data.