Dynamic frequency coordination control method combining frequency synchronous control in VSC-HVDC with bilateral frequency limit control in LCC-HVDC

A dynamic frequency coordination control method combining frequency synchronous control in voltage source converter based high voltage direct current (VSC-HVDC) with bilateral frequency limit control in line commutated converter based high voltage direct current (LCC-HVDC), comprising the following steps:

• Step 1:
• during system disturbances, prioritizing the frequency synchronous control in the VSC-HVDC to stabilize a grid frequency, and using a power adjustment output by the frequency synchronous control as an activation criterion for the bilateral frequency limit control in the LCC-HVDC;
• Step 2:
• when the power adjustment exceeds a preset limit range and a system frequency deviation exceeds a control dead zone of the bilateral frequency limit control in the LCC-HVDC, utilizing the bilateral frequency limit control to determine and output a conventional direct current (DC) power adjustment;
• Step 3:
• based on the conventional DC power adjustment, employing additional reactive power control of the VSC-HVDC to provide additional reactive power to the LCC-HVDC to regulate a voltage stability of a grid;
• Step 4:
• using a VSC-HVDC power adjustment as an input signal for a judgment logic;
• Step 5:
• converting the input signal into additional reactive power for the VSC-HVDC;
• Step 6:
• superimposing the additional reactive power on an original reactive power command of the VSC-HVDC to generate a new reactive power command for the VSC-HVDC;
• and
• Step 7:
• adjusting an actual operating reactive power of the VSC-HVDC based on the new reactive power command;
• wherein Step 4 comprises:
• Step 4.1:
• when the VSC-HVDC power adjustment is greater than a maximum power adjustment threshold of a frequency synchronous controller, or when the VSC-HVDC power adjustment is less than a minimum power adjustment threshold of the frequency synchronous controller, allowing the bilateral frequency limit control in the LCC-HVDC to output the conventional DC power adjustment;
• and
• Step 4.2:
• when the VSC-HVDC power adjustment is greater than or equal to the minimum power adjustment threshold of the frequency synchronous controller and less than or equal to the maximum power adjustment threshold of the frequency synchronous controller, allowing the bilateral frequency limit control in the LCC-HVDC to output 0;
• wherein in Step 3, the additional reactive power mentioned is the additional reactive power for the VSC-HVDC, and a method to calculate the additional reactive power for the VSC-HVDC is as follows:
• a product of the conventional DC power adjustment and tan φ is calculated, wherein φ represents a power factor of a valve side of the conventional DC connected to the VSC-HVDC.