(1) New energy multi-time scale high-precision power prediction technology
New energy power prediction is divided into wind power prediction, photovoltaic power generation power prediction, new energy station basic information, power, meteorological information (wind speed, solar irradiance) and other data, to establish the mapping relationship between meteorological forecast data and power data (i.e. power prediction model); According to the input data such as weather forecast or measured power, the new energy power can be predicted in advance within a period of time (seven days, days, days, ultra-short term, etc.).
New energy power prediction can reduce the uncertainty of new energy power by turning random fluctuation of wind power and photovoltaic power into basic known parameters; In the planning market, it is helpful for power grid enterprises to adjust the combination of units, optimize the power generation plan of conventional power units, adjust the daily power generation plan according to the ultra-short-term prediction results, optimize the rotation reserve, and achieve the best economy under the constraints of system security. In the power market, the dispatcher can determine the reserve capacity needed to purchase in the standby market according to the forecast results, and buy or sell the difference reserve electricity in the real-time market according to the ultra-short-term forecast results, and the power generation enterprise can participate in the market bidding according to the forecast results. Therefore, the prediction accuracy of new energy power directly affects the economic benefits of market participants.
China Meteorological Administration, China Electric Power Research Institute Co., LTD., Tsinghua University, North China Electric Power University and other institutions have carried out a lot of research, according to the characteristics of China's new energy, in the ultra-short, short, medium and long term and other time scales to establish a relatively complete new energy power prediction system; The prediction models include statistical methods based on multiple data sources, physical methods based on microscale meteorology and computational fluid mechanics, and adaptive configuration coupled wind power prediction methods. At present, the new energy power prediction system with independent intellectual property rights has covered the provincial power companies and new energy stations of the network, and the prediction accuracy has reached the international advanced level. In the future, numerical weather forecasting, data mining, artificial intelligence and other technologies can be integrated to continuously improve the accuracy of new energy power prediction.
(2) New energy active support control technology
The existing grid-connected equipment of new energy power generation lacks the ability of quick response and active support to the system frequency and voltage. With the continuous increase of the proportion of new energy in the power system, the problem of system frequency and voltage stability is prominent. Grid-friendly new energy power generation control technology with active support capability should be developed, which mainly includes two aspects: active frequency dynamic support technology, which can realize active frequency support capability through reserve capacity, rotor kinetic energy control, and energy storage configuration; Inertia support technology provides rapid inertia support by attaching virtual inertia control, using the kinetic energy stored in the rotating mass to respond to changes in system frequency.
China has carried out theoretical research on the active support control technology of new energy generator sets and stations connected to the power grid, covering reactive voltage, active frequency and inertia support, and carried out engineering applications in several new energy stations. In terms of frequency active support, the grid-related standards of new energy sites have been revised, such as "Technical Regulations for Wind farm Access to the power system Part 1: Onshore wind power" (GB/T 19963.1-2021) proposed that wind farms should have the ability to participate in primary frequency modulation of the power system under certain conditions. Inertia support for new energy generation is mainly divided into two types: inertia support technology based on rotary grid-connected equipment and power electronic equipment. The former refers to the direct coupling between synchronous rotary grid-connected equipment and the power grid. When power disturbance occurs in the system, the rotating equipment releases the stored kinetic energy of the rotor to resist the frequency offset of the system and provide the moment of inertia support to the power grid. The latter refers to the flexible regulation of power electronic devices to simulate the electromechanical swing process of synchronous generators, resist the frequency change of the power grid and realize the virtual inertial support of new energy generation.
The inertia control of wind turbines is mainly aimed at variable speed wind turbines, and the flexible converter control strategy is used to achieve inertia response and suppress the deep drop of the grid frequency. The standby power of photovoltaic power generation and the energy stored by the direct current capacitance on the inverter side can also provide inertia support for the system during the dynamic process. In the future, we can focus on the development of key technologies of new energy active support for large-scale new energy clusters through the DC transmission system, and the coordinated control technology of temporary active support for new energy stations.
(3) New energy power generation technology for grid construction
The current new energy generation mainly adopts the current source control mode, relies on phase-locked loop synchronization, follows the frequency and voltage of the grid operation, and has almost no moment of inertia. Even with a certain frequency support and fault voltage support capability through additional control links, the stable operation of current-source new energy will still be challenged when the proportion of new energy continues to increase in the long term and the power grid cannot provide a stable reference voltage. New energy needs to break through the current source control mode that relies on phase-locked synchronization, realize the transformation from the "grid following type" to the "grid construction type" task role as soon as possible, and become the main carrier to maintain the frequency and voltage of the grid.
Grid construction new energy generation technology adopts appropriate control algorithm to generate grid-connected potential, so that the new energy generation using power electronic conversion device has the characteristics of inertia, damping, primary frequency modulation, reactive voltage regulation and so on, and then has the ability to independently establish the frequency and voltage of the grid. At present, the domestic research on the new energy power generation technology of grid construction is mainly divided into voltage source virtual synchro technology and self-synchronization voltage source new energy power generation technology. Although the relevant technology originated from abroad, it is still in the stage of theoretical research and prototype development, and has not been applied in engineering.
Chinese enterprises have carried out the engineering application of new energy power generation technology for grid construction, such as the development of 50 kW virtual synchronous generator in 2013, and the new centralized virtual synchronous machine with a capacity of 1.4×105 kW in 2016. In the future, we can focus on the broad band stability characteristics and oscillation suppression of the new energy cluster of power grid construction, fault crossing of the new energy cluster of power grid construction.
