The control circuit of the generator thyristor direct excitation system consists of measurement comparison, error signal adjustment, trigger pulse links, and if necessary, power amplification, pulse distribution and other links. The control circuit is also the automatic voltage regulator circuit. The main rectifier circuit is controlled by the control circuit, so the power supply of the main rectifier circuit is also the controlled power supply.
1. Measurement and comparison link
The measurement part in the measurement comparison link is used to measure the terminal voltage of the generator. Generally, a three-phase step-down transformer, rectification, and filtering are used to obtain the generator terminal voltage signal. There are also methods where the terminal voltage signal is obtained directly from the generator terminal voltage through resistor division, rectification, and filtering.
Due to the diversity of electronic circuit forms, some use a double regulator bridge comparison circuit as the comparison part in the measurement and comparison process; some use a
Single Zener bridge comparison circuit; some use operational amplifiers to form comparison circuits, etc.
2. Error signal adjustment link
The function of the error signal adjustment link is to amplify the weak error signal and perform differential and integral operations on it, so that it can meet the requirements of timely and rapid control. The proportional, integral, differential (PID) adjustment method is usually used, and the PID-adjusted signal is used to control the generation time of the trigger pulse to obtain better adjustment characteristics.
3. Trigger pulse formation link
There are various forms of trigger pulse forming links. Some use single-junction transistors to form relaxation oscillators, some use resistance-capacitance phase-shift bridge trigger circuits, some use blocking oscillation circuits, and some use analog integrated flip-flops and other forms.
One issue that needs to be noted for the thyristor rectifier circuit is that the trigger circuit must be synchronized with the main circuit voltage. The trigger circuit must ensure that the trigger pulse is sent out at the same phase angle in each cycle of the main circuit voltage. The forms of trigger signal voltage include sine wave, sharp pulse, square pulse, strong trigger pulse and pulse train, etc.
4. Pressure regulation principle
When the generator terminal voltage deviates from the rated value due to external disturbances (such as changes in load, speed and temperature, etc.), that is, when the controlled quantity deviates, the control circuit responds immediately to increase or decrease the conduction angle of the thyristor. Then the excitation current is increased or decreased accordingly to keep the generator terminal voltage unchanged, thereby achieving the purpose of adjusting the generator terminal voltage according to the deviation.
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