Power Converter Phase Tracking for Zero-Voltage Ride-Through
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Solution Overview
Problem
Smaller power sources, such as wind and solar systems, typically go offline during voltage faults, which can exacerbate system-wide instabilities and disrupt power to large regions, as they are not designed to maintain input during low-voltage or zero-voltage conditions, contrary to the new requirements from utility operators.
Innovation Solution
A method and apparatus for controlling the AC output of a power converter to estimate the phase angle of the voltage during recovery from a fault and adjust the current output accordingly, with a response time inversely proportional to the network voltage amplitude, allowing the power converter to continue supplying power during voltage faults and supporting network stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If smaller power sources go offline during voltage faults, then device complexity and operational simplicity are maintained, but system stability and power network reliability deteriorate
Solution Approach 1:
The control system pre-estimates the phase angle of the voltage that will be present when the network voltage recovers from the fault. This preliminary estimation allows the power converter to be ready with the correct current phase angle when voltage recovery occurs, enabling seamless ride-through without requiring complex real-time adjustments during the fault condition.
Solution Approach 2:
The response time of the phase tracking is dynamically adjusted based on the network voltage amplitude. When voltage amplitude is high, the response time is shorter; when voltage amplitude is low (during faults), the response time is extended. This dynamic adaptation allows the system to maintain stability during faults while remaining responsive during normal operation, resolving the contradiction between reliability and complexity.
2Reliability
If power sources remain online during voltage faults, then power network reliability improves, but the difficulty of detecting and measuring voltage conditions increases
Solution Approach 1:
The system performs phase angle estimation in advance, during the fault condition when voltage is present but reduced. By estimating the phase angle of the anticipated recovered voltage while the fault is ongoing, the system prepares the current output phase before voltage recovery occurs, maintaining power availability without requiring complex real-time measurement during the critical recovery moment.
Solution Approach 2:
The control system continuously monitors network voltage conditions and uses this feedback to adjust the phase angle estimation and current output. The feedback mechanism allows the system to adapt to changing voltage conditions during faults, maintaining accurate phase angle estimation and power source availability even under difficult measurement conditions.
3Productivity
If response time is shortened to maintain power during faults, then productivity is improved, but measurement precision of voltage conditions deteriorates
Solution Approach 1:
The phase tracking response time is made dynamic rather than fixed. During normal high-voltage conditions, the response time is short, enabling fast tracking and continuous power delivery. During low-voltage fault conditions, the response time is automatically extended to allow for more accurate phase angle estimation under challenging measurement conditions. This dynamic adjustment resolves the contradiction between productivity and measurement precision.
Solution Approach 2:
The system changes the response time parameter based on the network voltage amplitude. When voltage amplitude drops during a fault, the response time parameter is increased (slowed down) to improve measurement accuracy. When voltage returns to normal levels, the response time parameter is decreased (speeded up) to maintain high productivity. This parameter adaptation allows the system to optimize both measurement precision and power delivery continuity under different operating conditions.
Data Source
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AI summary
A power converter control system (324) having a phase tracker (404) that is designed and configured to estimate the phase of the voltage on the power network (208) that will be on the network when network recovers from a fault on the network. Such a power converter control system (324) allows a power-network- connected power source to ride-through a fault event and continue supplying power thereto at the designed phase and frequency. In one embodiment, the phase tracker (404) provides this estimate by having a response time slow enough that the voltage drop or sag caused by the fault substantially does not affect the control system. In another embodiment, the phase detector is designed and configured to freeze the frequency of its output upon detection of a fault event on the power network.