Thyristor Starter Control for Speed-Responsive Intermittent Commutation
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Solution Overview
Problem
In thyristor starters for synchronous machines, the low induced voltage during startup or low-speed operation can lead to failed commutation of the inverter, necessitating intermittent commutation. This results in decreased responsiveness for controlling the direct current flowing through the DC reactor as the rotation speed increases.
Innovation Solution
A thyristor starter with a converter, DC reactor, inverter, and controller that sequentially adopts two modes: intermittent commutation and load commutation. The controller includes a current controller, corrector, and control angle calculator, where the correction value increases with the rotation speed in the intermittent commutation mode to improve responsiveness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If intermittent commutation is adopted to enable inverter commutation at low speeds, then commutation reliability is improved, but responsiveness for controlling direct current deteriorates as rotation speed increases
Solution Approach 1:
The patent applies dynamics by making the phase control angle adjustable based on operating conditions. The control angle calculator dynamically adjusts the phase control angle of the converter thyristor depending on the rotation speed of the synchronous machine. At low speeds, a larger phase control angle is used to ensure reliable commutation, while at higher speeds, the phase control angle is reduced to improve current control responsiveness, thus adapting the system behavior to different operational states.
Solution Approach 2:
The patent changes the parameter of phase control angle based on rotation speed. The control angle calculator computes an appropriate phase control angle according to the detected rotation speed. This parameter change allows the system to maintain optimal performance across different speed ranges, resolving the contradiction between commutation reliability at low speeds and control responsiveness at high speeds.
2Reliability
If phase control angle is narrowed to set direct current to zero during commutation, then inverter commutation is enabled, but control precision for direct current deteriorates
Solution Approach 1:
The system dynamically adjusts the phase control angle based on rotation speed and commutation requirements. During commutation events at low speeds, the phase control angle is temporarily increased to enable reliable inverter commutation by forcing direct current to zero. Once commutation is complete and rotation speed increases, the phase control angle is reduced to restore precise direct current control, thus dynamically balancing commutation reliability with control precision.
Solution Approach 2:
The patent employs periodic narrowing of the phase control angle specifically during commutation events. The control angle calculator periodically adjusts the phase control angle to enable commutation when needed, then restores the normal control angle for precise current control. This periodic action allows the system to achieve both reliable commutation and precise current control at different times in the operation cycle.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The proposed solution enhances the responsiveness of controlling the direct current through the DC reactor during intermittent commutation, effectively addressing the challenges of low-speed operation and increasing rotation speeds.
Implementation Method 1
a converter that converts alternating-current (AC) power into direct-current (DC) power
Implementation Method 2
a DC reactor that smooths the DC power
Implementation Method 3
an inverter that converts DC power supplied from the converter through the DC reactor into AC power of a variable frequency
Implementation Method 4
the induced voltage generated in the synchronous machine is relatively low when the synchronous machine is started or operates at a low speed
Data Source
AI summary
A converter controller of a thyristor starter includes: a current controller that generates a voltage command value of an output voltage of a converter by performing a control operation using an integral element of a deviation of a direct current with respect to a current command value; a corrector that adds a correction value to the voltage command value; and a control angle calculator that calculates a phase control angle of a thyristor in the converter based on the voltage command value to which the correction value is added. In an intermittent commutation mode, the correction value is set to increase as a rotation speed of a synchronous machine increases.