Primary Frequency Response in PV Power Plant

Author: Park

2022-03-16 16:24

With the gradual establishment of a new power system which renewable energy as the main source, profound changes have taken place in the power system in terms of power supply structure. Thermal power stations are still the main frequency regulation resources of the power system and undertake the most important frequency regulation work. With the rapid increase in installed capacity of renewable energy such as photovoltaic and wind power, the proportion of renewable energy is 36.6% by the year of 2020(‘Renewable Capacity Statistics 2021’ from IRENA), but due to the volatility, intermittency and randomness of new energy, the power system is facing an urgent demand for frequency response. The normal frequency power systems is either 50Hz or 60Hz, in general, the allowance of the frequency range is ±0.2~0.5Hz. The transboundary frequency limit will have a great impact on the safe operation of the power system, and even cause the collapse of the power system.

 

The Technical Provisions of The Primary Frequency Regulation

Primary frequency response is mainly for the first-class load short-term rapid fluctuations, the differential control, when the grid frequency over the limit, the value exceeds the dead zone value set by the primary frequency response, automatically provide active support to ensure the frequency stability of the power system.

Primary frequency control is the fastest deployed type of frequency control. It is generally deployed within a few seconds for a duration of up to several minutes.

 

1. Primary frequency regulation response control parameters and strategies

(1) Fast frequency regulation response dead zone: the primary frequency response dead zone of PV power plant should be set within the range of 0.02Hz~0.06Hz, according to the needs of the local power grid to determine the specific value. This value is 0.015Hz in Great Britain.

(2) Primary frequency regulation response amplitude limit: PV power plant in accordance with not less than 10% of the rated load limit (the value can be determined according to the actual situation of each regional power grid), and shall not cause the inverter off-grid or shutdown due to the primary regulation frequency response.

(3) Regulation difference rate: 3% (the value can be determined according to the actual situation of each regional power grid). The speed droop which is the ratio of the relative change in frequency to the relative change in power output of Britain in most cases is set to 4%.

(4) High-frequency disturbance of the grid, the active power of the new energy station down to 10% of the rated load can no longer be adjusted downward.

(5) Low-frequency disturbance of the power grid, new energy power station should according to real-time operating conditions respond quickly to the frequency of the power grid, without reserving active in advance.

(6) The primary frequency response function of new energy power station is coordinated with PPC control, and the control target of the active power of a new energy power station is the algebraic sum of PPC command value and primary frequency response regulation, in which, when the new energy station is under non-load limiting condition, PPC command is calculated according to the real power generated at the moment when the frequency exceeds the dead zone. When the grid frequency exceeds 50±0.1HZ, the priority of new energy primary frequency regulation is higher than that of PPC.

(7) When there are new parameter requirements from the relevant national power management departments and local power management institution, the new parameter requirements will be implemented and the test report will be finally obtained through acceptance.

 

2. A frequency regulation response performance requirements(Base on the Grid Code of the Great Britain)

As shown in Figure 1, primary frequency response is the fastest type of frequency response provided after a loss of generation. It must be released and ramped up to the required level within 10 s and then sustained for at least an additional 20 s. Once primary frequency control has stabilized the frequency, secondary frequency is implemented to start bringing the frequency back to its target value.

Figure 1 Primary and Secondary frequency control in Great-Britain.

Primary frequency response is the automatic response to a decrease in system frequency. PV power plants, on the other side, increase in active power output. From the grid code of National Grid(Great Britain), as shown in figure 2. Response in this category should provide their generation capability within 10 seconds of the frequency deviation. The device is required to maintain the frequency above a 0.8 Hz drop until secondary response becomes available. also, it should be sustainable for 20 seconds following initiation. Devices may supply some or all of the primary response requirement.

Figure 2 Interpretation of Primary and Secondary Response Values

Different countries have different rules for frequency regulation, and even in the same country, there are differences in the rule of frequency regulation for different power grids. And the definition of primary frequency regulation varies from region to region. GoodWe inverters can meet the requirements of grid frequency regulation in China, UK, India, Europe and other countries and regions. 

For more content, please check out the PDF files enclosed.

 

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