（1） Overview of automatic voltage control
In the photovoltaic power station, automatic voltage control (AVC) can receive the load setting of bus voltage and total reactive power from the dispatching and the setting of bus voltage and reactive power in the power station, adjust the reactive power of grid connected inverter, the input of reactive power compensation equipment (SVG / SVC) or the transformation ratio of substation step-up transformer through certain strategies, and adjust the reactive power and electric day of the power station, so as to make the voltage of parallel node within the normal operation range.
- Voltage control measures
(1) Change the voltage regulation of generator terminal.
(2) Change the transformer ratio and adjust the voltage.
(3) Voltage regulation of compensation equipment.
- Overview of common AVC control strategies
(1) In the steady state of the power grid, the AVC host has the ability to make full use of the reactive power regulation capacity of the inverter to regulate the voltage. When the reactive power regulation capacity of the inverter is insufficient, the reactive power regulation of svcsvg device shall be considered. On the basis of qualified voltage, reasonable dynamic reactive power reserve shall be reserved for svcsvg device.
(2) In case of power grid failure, AVC host can quickly adjust the reactive power of SVC / SVG device to restore the voltage to the normal level.
(3) When the power grid recovers from the fault, the AVC host can replace the reactive power that has been put into SVC / SVG device by adjusting the reactive power output of the inverter, so as to reserve a reasonable dynamic reactive power reserve.
(4) When there are multiple groups of SVC / SVG devices in the booster station, the AVC host can coordinate and control each group of SVC / SVG devices to avoid unreasonable flow of reactive power between each group of devices.
(5) When all reactive power regulation capabilities are exhausted and the voltage is still unqualified, the AVC host can give the recommended strategy of regulating the tap or automatically adjust the tap.
（2） Operation and maintenance specification of AVC system
- Operation and exit rules of AVC system
(1) The AVC device of the unit shall be put into operation normally, and the AVC function shall be put into and out normally. Under the stable working condition of the unit, the shift chief operator can order the operation personnel on duty to operate after obtaining the consent of the provincial dispatching dispatcher on duty.
(2) When the shutdown and maintenance of the equipment affect the normal operation of the AVC function of the unit, an application shall be submitted to the provincial dispatching and can be carried out only after approval.
(3) In case of the following emergencies around the AVC system, the AVC system can be shut down and reported to the provincial dispatching dispatcher at the same time. After the abnormal conditions are handled, contact the provincial dispatching to resume operation.
1) System accidents endanger the safety of the unit.
2) AVC system fails and cannot operate normally.
3) Generator unit maintenance, startup and shutdown, or AVC device system is abnormal, and the automatic regulator fails to operate in the normal automatic mode.
4) When starting up, after the unit is connected to the grid, check that there is no abnormality in the AVC device, and the shift supervisor can report to the provincial dispatching and apply for AVC input.
5) During shutdown, after switching the auxiliary power of the unit and before the electrical operation of generator disconnection, the shift supervisor contacted the provincial dispatching to exit AVC.
- On / off steps of AVC system
(1) Input steps of AVC function.
1) After receiving the shift supervisor’s order, check that there is no alarm in the monitoring screen of AVC background machine. “AVC upper computer running status” is “exit”.
2) Check that “AVC device operation mode” is “remote” and “AVC control status” is “exit” in the monitoring screen of AVC background machine.
3) In the monitoring screen of AVC background machine, check that “AVC fault” is “normal”, and check that “DCS is allowed to be put into operation” is “exit”.
4) Check that the green light of “general locking of magnetization increase” is on in the monitoring screen of AVC background machine.
5) In the “AVC system screen” of DCS system, click the “AVC control” button to open the window, click the “unit DCS allows AVC regulation” button, and click the “OK” button. At this time, the “unit DCS allows AVC regulation” signal is on.
6) Check that “AVC upper computer operation status” is “input” in the AVC background computer monitoring screen.
7) Check that “AVC control status” is “on” in the AVC background monitor screen.
8) Check that “DCS allowed input” is “input” in the AVC background machine monitoring screen.
9) Comprehensively check the AVC function in AVC system and DCS system, and report to the shift supervisor after normal operation.
(2) Exit steps of AVC function.
1) After receiving the shift supervisor’s order, in the “AVC system screen” of DCS system, click the “AVC control” button to open the window, click the “unit DCS allows AVC regulation” reset button, and click the “OK” button. At this time, the “unit DCS allows AVC regulation” signal is off. Click the “Cancel” button to check that the signal has been reset.
2) Check that “AVC upper computer operation status” is “exit” in the AVC background computer monitoring screen.
3) Check that “AVC device operation mode” is “remote” in the monitoring screen of AVC background machine.
4) Check that the “AVC control status” is “exit” in the AVC background monitor screen.
5) Check that “AVC control fault” is “normal” in the AVC background monitor screen.
5) Check that “DCS allowed input” is “exit” in the AVC background machine monitoring screen.
7) Check that the green light of “general locking of magnetization increase of unit 1” is on in the monitoring screen of AVC background machine.
8) In the AVC background machine monitoring screen, check that the green light of “11 unit total reduction locking” is on.
9) Report to the shift supervisor after comprehensively checking the normal and resetting the signal.
- Precautions for AVC operation
(1) Pay close attention to the power factor and the temperature of each point of the generator when the generator is in phase, and the temperature is not allowed to exceed the rated value.
(2) When the leading phase of the generator is deep, pay attention to the vibration at the end of the generator.
(3) Pay attention to the operation of the generator brush when the generator has a deep phase leading degree.
(4) During the operation of the unit, if it is necessary to start the large-capacity 6kV equipment, pay attention to stagger the starting time and the recording time of the voltage assessment point as far as possible (the voltage assessment point shall be recorded every 15min), so as to prevent the voltage drop caused by the instantaneous start of the large-capacity auxiliary machine from causing the voltage unqualified point.
(5) In case of system abnormality or accident, contact the dispatcher in time to exit AVC
(6) When AVC is automatically switched from remote to local, check whether AGC and primary frequency modulation functions are normal, because the remote communication of AVC, AGC and primary frequency modulation is one channel, and the channel between master station and RTU is abnormal or interrupted, resulting in that AVC device has not received the control command issued by the dispatcher for 15min. At this time, AVC control mode is automatically switched to “local” to exit remote control operation and turn to local planned curve operation, Perform AVC adjustment according to the preset voltage plan curve. At this time, contact the communication professional for inspection and processing. When the dispatching command returns to normal, contact the dispatching to switch the AVC to remote control.
(7) When the AVC function automatically exits, the alarm in the AVC system shall be checked, as if there is an invalid regulation signal alarm. Check what conditions cause the locking. When the locking reason is confirmed and there are no other abnormalities, the AVC function can be put into operation after resetting the signal.
Read more: What is a voltage transformer?