Active Crowbar Self-Test via Loop Current Detection
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Solution Overview
Problem
Conventional active crowbar circuits in doubly-fed induction generators face challenges in self-testing without causing over-current issues to the rotor-side converter, making it difficult to determine if the IGBT switch is turned on or off normally due to uncertain voltage across the bridge arm and high resistance.
Innovation Solution
A self-test method for the active crowbar circuit that involves maintaining the rotor current at a minimum value, turning off the rotor-side converter, and then testing if the active crowbar circuit can be turned on and off normally by monitoring the loop current, ensuring the rotor-side converter and active crowbar circuit do not turn on simultaneously during the self-test.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the conventional self-test method detects the voltage of the rectifier bridge to determine if the IGBT switch is turned on, then the IGBT switch status can be detected, but the voltage across the bridge arm is uncertain due to parasite capacitors when the IGBT switch is turned off, making the threshold voltage difficult to design and requiring additional voltage sensors
Solution Approach 1:
The patent replaces voltage-based detection (electrical measurement) with current-based detection. Instead of measuring voltage across the rectifier bridge which is affected by parasite capacitors, the system measures the current flowing through the active crowbar circuit. This substitution eliminates the uncertainty caused by voltage fluctuations and removes the need for additional voltage sensors, while still enabling accurate detection of IGBT switch status.
Solution Approach 2:
The patent introduces a current sensor as an intermediary measurement device to detect the status of the IGBT switch indirectly through the current flowing through the active crowbar circuit. This intermediary approach allows detection of switch status without directly measuring the problematic voltage across the bridge arm, avoiding the issues with parasite capacitors and threshold voltage determination.
2Measurement precision
If the self-test method detects the current of the active crowbar circuit to determine if the IGBT switch is turned on, then the IGBT switch status can be detected, but the resistance of the active crowbar circuit is very small (smaller than 1Ω), causing over-current problem when the rotor-side converter and IGBT switch are turned on simultaneously by PWM signal
Solution Approach 1:
The patent implements preliminary action by executing the self-test procedure during the startup phase of the doubly-fed induction generator system, before the rotor-side converter is activated for normal operation. The controller first activates the active crowbar circuit for self-testing, confirms proper operation, and only then proceeds to start the rotor-side converter. This sequential activation prevents simultaneous conduction and eliminates the over-current hazard.
Solution Approach 2:
The patent employs dynamic control of the switching signals to the rotor-side converter and active crowbar circuit. The controller dynamically manages the timing and state of these components, ensuring that during the self-test phase, only the active crowbar circuit is activated while the rotor-side converter remains inactive. This dynamic switching control prevents overlapping operation that would cause over-current conditions.
3Reliability
If the active crowbar circuit is used to protect the rotor-side circuitry during grid voltage sag, then the inrush current is absorbed and rotor-side circuitry is protected, but the active crowbar circuit requires a self-test procedure to ensure normal operation, which complicates the startup procedure
Solution Approach 1:
The patent implements self-service by enabling the active crowbar circuit to perform self-diagnosis and self-testing autonomously during the startup sequence. The controller activates the crowbar circuit, monitors the current response, and automatically determines whether the circuit is functioning correctly without requiring external manual testing or additional diagnostic equipment. This self-testing capability ensures reliability while keeping the procedure integrated into the normal startup process.
Data Source
AI summary
Provided is a doubly-fed induction generator system and a self-test method for the active crowbar circuit of the doubly-fed induction generator system. The invention is featured by using the controller of the doubly-fed induction generator system to carry out a self-test procedure to detect the loop current of the active crowbar circuit for determining if the active crowbar circuit can be turned on and off normally. Also, the rotor-side converter and the active crowbar circuit of the doubly-fed induction generator system are forbidden to turn on simultaneously during the execution of the self-test procedure.