Virtual inertia frequency modulation method for doubly-fed pumped storage unit and renewable energy power generation system

Abstract

The invention discloses a virtual inertia frequency modulation method and system for a doubly-fed pumped storage unit and a renewable energy power generation system. The method comprises the following steps: obtaining structure information of a first power generation unit, a second power generation unit and a third power generation unit; establishing inertia models of the three power generation units; according to the frequency control method based on the inertia model, the power supply unit supports the frequency of the power system in a cooperative mode. Renewable power generation units such as photovoltaic power generation units and wind power generation units can be cooperatively controlled, so that the power generation loss of the distributed power generation system is provided by the photovoltaic power generation units and the wind power generation units under the condition that the pumping time is selected.

Description

Technical Field

[0001] The present invention relates to the technical field of virtual inertia frequency regulation, and in particular to a virtual inertia frequency regulation method for a double-fed pumped storage unit and a renewable energy power generation system. Background Art

[0002] The gradual replacement of synchronous generators by non-rotating power electronic devices such as wind power and photovoltaics has posed a major challenge to the stability of the power grid, especially the frequency response characteristics of the power grid. The power grid load generally has peak and valley characteristics, and the "anti-peak" attribute of wind power makes the traditional synchronous generators with frequency regulation tasks offline at night, further reducing the total inertia of the power system. In order to improve the flexibility and reliability of the power system, a feasible method is to deploy pumped storage. Pumped storage technology is one of the more mature main flexible and adjustable power sources. Due to its high flexibility, large energy and simple operation, pumped storage has been widely used in various fields of the power system, including variable load, phase modulation, frequency modulation, energy storage, system standby and black start.

[0003] Among all pumped storage configurations, doubly-fed pumped storage is one of the common types using doubly-fed induction generators. It has the advantages of faster response, more flexible power control range, and simpler physical structure. In addition, compared with ordinary pumped storage configurations that require compromises between the operating states of the pump and the turbine, doubly-fed pumped storage is able to maintain the turbine speed at the optimal operating point while taking into account the water speed and current load conditions, thereby improving overall efficiency and widening the range of energy storage and power generation. In addition, the variable speed operation of doubly-fed pumped storage allows it to achieve rapid power output regulation by absorbing or releasing the kinetic energy hidden in the rotor, creating an equivalent inertia larger than its natural inertia, enhancing its frequency regulation performance.

[0004] However, in most of the current studies on the participation of doubly-fed pumped storage in frequency regulation, the frequency support service provided by doubly-fed pumped storage cannot be sustained for a long time, otherwise the rotor speed will exceed the allowable range. In addition, most of the existing methods mainly consider the dynamic characteristics under the power generation mode, and do not consider the frequency response strategy when the doubly-fed pumped storage is in the pumping mode. In fact, when the doubly-fed pumped storage absorbs energy from the grid for energy storage, when the total power demand increases to a higher level, the grid may face a greater risk of frequency drop. Therefore, in order to reduce the risk of frequency drop, it is necessary to coordinate the control of distributed generation systems with other power generation units, especially renewable power generation units such as photovoltaic and wind power, so that the power generation loss of the distributed generation system is provided by photovoltaic and wind turbines when the pumping time is selected. Summary of the invention

[0005] In view of the above-mentioned problems, the present invention is proposed.

[0006] In order to solve the above technical problems, the present invention provides the following technical solutions: a virtual inertia frequency regulation method for a double-fed pumped storage unit and a renewable energy power generation system, comprising:

[0007] Acquire structural information of the first power generation unit, the second power generation unit, and the third power generation unit;

[0008] Establish inertia models of three power generation units;

[0009] The frequency control method based on the inertia model shown supports the power system frequency in a coordinated manner for the power supply units.

[0010] As a preferred solution of the virtual inertia frequency regulation method of the doubly-fed pumped storage unit and renewable energy power generation system described in the present invention, the structural information includes identifying whether the power generation unit has a power electronic device that directly responds to changes in grid frequency.

[0011] As a preferred solution of the virtual inertia frequency regulation method of the doubly-fed pumped storage unit and renewable energy power generation system of the present invention, wherein: the inertia model includes, if the power generation unit is powered by a power electronic device that can directly respond to the change of the grid frequency, then the equivalent virtual inertia of the power generation unit frequency regulation is derived by using mechanical characteristics;

[0012] If the generating unit is powered by power electronic devices that cannot directly respond to grid frequency changes, the virtual inertia available in the frequency response mode of the generating unit is estimated.

[0013] As a preferred scheme of the virtual inertia frequency regulation method of the doubly-fed pumped storage unit and renewable energy power generation system described in the present invention, wherein: the power supply unit supports the power system frequency in a collaborative manner, including determining the participation degree of three different power supply units by the virtual inertia of each power generation unit.

[0014] As a preferred solution of the virtual inertia frequency regulation method of the doubly-fed pumped storage unit and renewable energy power generation system of the present invention, wherein: the inertia levels of the power generation units are different, and different participation factors need to be designed at different stages of frequency support according to the unique dynamic behavior and different safety operation constraints;

[0015] The participation factor obtains different values ​​in the frequency drop scenario and the frequency increase scenario.

[0016] As a preferred solution of the virtual inertia frequency modulation method of the doubly-fed pumped storage unit and renewable energy power generation system described in the present invention, wherein: the first power generation unit, the second power generation unit, and the third power generation unit include at least three different power supply units: doubly-fed pumped storage, wind power, and photovoltaic power;

[0017] In the frequency drop scenario, three generating units will be in action to support the frequency, and the proposed participating factors include but are not limited to:

[0018]

[0019] Where J represents the moment of inertia of the system, n and m represent the number of wind power and photovoltaic power, respectively; x i,t ={1,0} is a binary indicator indicating the availability of the ith generating unit at time slot t, xi,t = 0, indicating that frequency support will not be available or that the photovoltaic cell has no power output at time slot t; i,t =1, the statement can obtain frequency support; J DFPS represents the equivalent virtual inertia of the double-fed pumped storage; J WT,i , J pv,i represents the equivalent virtual inertia of the i-th power generation unit of wind power and photovoltaic power respectively; PF DFPS PF WT PF PV Respectively represent the participation factors of the doubly-fed pumped storage, wind power and photovoltaic power generation units; i represents any power generation unit among the doubly-fed pumped storage, wind power and photovoltaic;

[0020] Wind power begins to absorb energy during the rotor speed recovery phase, and the participation factor is revised to:

[0021]

[0022] Among them, b t,i is a binary indicator for judging the rotor status of the wind turbine in the i-th power generation unit in time slot t; w WT,i represents the frequency of the i-th wind power unit, w min is the minimum frequency, when w WT,i 3w min and When b t,i =1, otherwise, b t,i = 0; when it comes to the calculation of the participation factor of double-fed pumped storage or photovoltaic, b t,i =1.

[0023] As a preferred solution of the virtual inertia frequency regulation method of the doubly-fed pumped storage unit and renewable energy power generation system described in the present invention, in which: in the frequency rise scenario, the participation factors of the three power generation units are expressed as:

[0024]

[0025] Among them, b t ￠ ,i is the number of generating units in time slot t, except b t,iAnother binary indicator that determines the status of double-fed pumped storage and wind power. For double-fed pumped storage, its value is still 1; for wind power, when w WT,i 3w min and When b t ￠ ,i =1, otherwise, b t ￠ ,i =0.

[0026] A virtual inertia frequency regulation system of a double-fed pumped storage unit and a renewable energy power generation system using the method of the present invention is characterized by:

[0027] An analysis unit, acquiring structural information of the first power generation unit, the second power generation unit, and the third power generation unit;

[0028] A model generation unit, which establishes inertia models of three power generation units;

[0029] The control unit supports the power system frequency in a coordinated manner with the power supply units based on the frequency control method of the inertia model shown.

[0030] A computer device comprises: a memory and a processor; the memory stores a computer program, wherein: the processor implements the steps of any one of the methods of the present invention when executing the computer program.

[0031] A computer-readable storage medium stores a computer program, wherein: when the computer program is executed by a processor, the steps of any one of the methods of the present invention are implemented.

[0032] Beneficial effects of the present invention: The virtual inertia frequency regulation method of the doubly-fed pumped storage unit and renewable energy power generation system provided by the present invention combines the existing power supply capabilities of doubly-fed pumped storage, wind power and photovoltaics to construct their equivalent virtual inertia models. Then, the load support parts of three different power supply units are allocated according to the designed participation factors, which include the total virtual inertia level of each unit. At the same time, an overall frequency support scheme is proposed, which allows the three power supply units to participate in the frequency support in a coordinated manner and combines their respective dynamic characteristics. In addition, an improved virtual inertia control scheme for wind power is proposed to achieve the recovery of its rotor speed in a safe manner. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying creative work.

[0034] Figure 1 An overall flow chart of a virtual inertia frequency regulation method for a double-fed pumped storage unit and a renewable energy power generation system provided in the first embodiment of the present invention;

[0035] Figure 2 A system structure diagram of a double-fed pumped storage unit and a virtual inertia frequency modulation method for a renewable energy power generation system provided by a second embodiment of the present invention;

[0036] Figure 3 A detailed structural diagram of a speed regulator controller in a virtual inertia frequency regulation method for a double-fed pumped storage unit and a renewable energy power generation system provided in a second embodiment of the present invention;

[0037] Figure 4 The overall frequency control structure of three different devices in the virtual inertia frequency regulation method of the double-fed pumped storage unit and renewable energy power generation system provided by the first embodiment of the present invention;

[0038] Figure 5 A rotor-side converter control diagram of a virtual inertia frequency modulation method for a double-fed pumped storage unit and a renewable energy power generation system provided in a third embodiment of the present invention;

[0039] Figure 6 A 9-node power system diagram of a virtual inertia frequency regulation method for a double-fed pumped storage unit and a renewable energy power generation system provided in a fourth embodiment of the present invention;

[0040] Figure 7 A simulation diagram of power output changes of a double-fed pumped storage unit, a photovoltaic power station and a wind turbine unit, as well as a power grid frequency change in a virtual inertia frequency modulation method of a double-fed pumped storage unit and a renewable energy power generation system provided in a fourth embodiment of the present invention;

[0041] Figure 8 This is a comparison diagram of the angular velocities of a wind turbine in the virtual inertia frequency modulation method of a doubly-fed pumped storage unit and a renewable energy power generation system under the SVIC and CVIC schemes provided in the fourth embodiment of the present invention. DETAILED DESCRIPTION

[0042] In order to make the above-mentioned purposes, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are described in detail below in conjunction with the drawings of the specification. Obviously, the described embodiments are part of the embodiments of the present invention, but not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary persons in the art without creative work should fall within the scope of protection of the present invention.

[0043] Example 1, reference Figure 1 , 4, which is an embodiment of the present invention, provides a virtual inertia frequency regulation method for a double-fed pumped storage unit and a renewable energy power generation system, comprising:

[0044] S1: Obtaining structural information of the first power generation unit, the second power generation unit, and the third power generation unit.

[0045] Furthermore, the structural information includes identifying whether the power generation unit has a power electronic device that directly responds to changes in grid frequency.

[0046] In one implementation of the present application, the first power generation unit, the second power generation unit, and the third power generation unit include at least three different power supply units, namely, doubly-fed pumped storage, wind power, and photovoltaics. The coordinated virtual inertia control of doubly-fed pumped storage, wind power, and photovoltaics is used to achieve frequency support. In this mode, doubly-fed pumped storage has power electronic devices that directly respond to changes in grid frequency, while wind power and photovoltaics do not. They are usually equipped with advanced power electronic devices, such as doubly-fed induction generator (DFIG) controllers, which can respond quickly to changes in grid frequency. These devices directly adjust the output power by adjusting the current control on the rotor side, thereby quickly providing or absorbing power to stabilize the grid frequency. Traditional wind power and photovoltaic power generation systems rely on natural resources (such as wind speed and light intensity), and their output power is limited by environmental conditions, and they usually do not have the ability to directly respond to changes in grid frequency. However, some modern wind power and photovoltaic systems can indirectly achieve virtual inertia response through power electronic inverters and control algorithms, but this response is not naturally available, but is achieved through special designs and algorithms.

[0047] In an optional embodiment, the first power generation unit, the second power generation unit, and the third power generation unit may include the following combination:

[0048] Energy storage system (battery energy storage), gas turbine, tidal power generation system. Battery energy storage system can be used as a flexible frequency regulation resource, which can respond immediately to changes in grid frequency through its fast response characteristics. Battery energy storage system is usually connected to the grid using a bidirectional inverter, which can directly detect changes in grid frequency through advanced control systems and inject or absorb power according to demand. Gas turbine is a traditional power generation system with the ability to start and stop quickly, and is usually used as peak load or emergency power supply in power systems. Although gas turbines themselves do not have the inertial response like synchronous generators, they can also participate in frequency regulation through modern power electronics and automatic control systems.

[0049] Tidal power generation system is a renewable energy generation unit that relies on the movement of tides to generate electricity. Similar to wind power and photovoltaic power, tidal power generation is greatly affected by natural conditions and has a weak ability to respond to grid frequency fluctuations. However, if the system is connected to the grid through power electronic equipment (such as inverters), it can also provide frequency response under certain conditions.

[0050] Based on the second optional embodiment, the battery energy storage system is usually equipped with a bidirectional power electronic inverter, which can achieve frequency coupling with the power grid. Through these inverters, the energy storage system can detect and respond to changes in the power grid frequency very quickly. Tidal power generation systems are usually connected to the power grid through power electronic inverters. Although the power generation capacity of tidal energy depends on natural phenomena (tidal movement), the inverter can regulate the output power of the system to a certain extent. Gas turbines can respond to changes in grid frequency through modern control systems and power electronic devices, but their response speed is relatively slow and is suitable for medium- and long-term peak load or frequency compensation. Therefore, all three can be identified as having power electronic devices that directly respond to changes in grid frequency.

[0051] S2: Establish the inertia model of the three power generation units.

[0052] Furthermore, if the generating unit is powered by a power electronic device that can directly respond to changes in grid frequency, the equivalent virtual inertia of the frequency modulation of the generating unit is derived using mechanical characteristics; if the generating unit is powered by a power electronic device that cannot directly respond to changes in grid frequency, the virtual inertia that can be provided in the frequency response mode of the generating unit is estimated.

[0053] S3: A frequency control method based on the inertia model shown supports the power system frequency in a coordinated manner for the power supply units.

[0054] In the embodiment of the present application, for a power system integrating double-fed pumped storage, wind power and photovoltaic units, Figure 4The overall frequency control structure of three different devices is given (In the frequency regulation control structure of the doubly fed pumped storage, wind power and photovoltaic devices, the frequency deviation of the power grid is sampled to generate a power increment command, and the three power supply units participate in the control in frequency response mode. It should be noted that in this study, the power increment commands of the three devices are allocated to them through a defined participation factor, which is determined by the total equivalent inertia of each device. For the wind turbine, its reference power command is generated by combining the conventional virtual inertia control module with the power grid model of the frequency deviation; the doubly fed pumped storage generates the power output increment through the main frequency regulation and the unit control module command; for the photovoltaic unit, its power generation command is the product of the frequency deviation, the frequency deviation change rate and its participation factor.). In this scheme, the frequency deviation of the power grid is sampled to generate a power increment command, and the three power supply units perform frequency response mode. It should be noted that in this study, the power increment commands of the three units are allocated to them through a defined participation factor, which is determined by the total equivalent inertia of each unit. For wind power, its reference power command is generated by the traditional virtual inertia control module combined with the grid model of frequency deviation; the double-fed pumped storage generates power output increments through the primary frequency regulation and unit control block; for the photovoltaic power generation unit, its power generation command is the product of the frequency deviation, the frequency deviation change rate and its participation factor. For the entire system, the power regulation change limit of the double-fed pumped storage is set to 30%, and the frequency control dead zone is set to ±0.02Hz.

[0055] The participation of the three different power supply units will be determined by their estimated inertia levels. Considering the three power generation units in the grid as a whole, the grid frequency dynamics can generally be given by the following formula:

[0056]

[0057] Where H is the total inertia coefficient of the system, P ref is the active power reference value of the frequency modulation circuit, P is the measured power of the power grid, and D p is the damping factor, Dω is the frequency deviation, Indicates the rate of change of frequency deviation.

[0058] It should be said that, first of all, the equivalent virtual inertia of the three power supply units is estimated separately. This is done based on their current power supply capacity and internal dynamic characteristics. A participation factor is defined, which allocates load support tasks according to the equivalent virtual inertia of each unit. The participation factor can reflect the relative ability of each unit to regulate the grid frequency. According to the participation factor of each unit, the corresponding frequency support tasks are assigned. This means that in the grid frequency regulation, each unit needs to adjust its own power output in response to the frequency deviation of the grid. In actual operation, according to the real-time frequency deviation of the grid and the operating status of each unit, the participation factor and power output of each unit are adjusted in real time to ensure the stability of the grid frequency.

[0059] In the embodiment of this application, due to the different inertia levels of the three units, their unique dynamic behaviors and different safety operation constraints, different participation factors need to be designed at different stages of frequency support. In the frequency drop scenario, in the first stage, the three generating units will act to support the frequency. The participation factors are proposed below:

[0060]

[0061] Where J represents the moment of inertia of the system, n and m represent the number of wind power and photovoltaic power, respectively; x i,t ={1,0} is a binary indicator indicating the availability of the ith generating unit at time slot t, xi,t = 0, indicating that frequency support will not be available or that the photovoltaic cell has no power output at time slot t; i,t =1, the statement can obtain frequency support; J DFPS represents the equivalent virtual inertia of the double-fed pumped storage; J WT,i , J pv,i represents the equivalent virtual inertia of the i-th power generation unit of wind power and photovoltaic power respectively; PF DFPS PF WT PF PV They represent the participation factors of the doubly-fed pumped storage, wind power and photovoltaic power generation units respectively; i represents any one of the doubly-fed pumped storage, wind power and photovoltaic power generation units.

[0062] Wind power begins to absorb energy during the rotor speed recovery phase, and the participation factor is revised to:

[0063]

[0064] Among them, b t,i is a binary indicator for judging the rotor status of the wind turbine in the i-th power generation unit in time slot t; w WT,i represents the frequency of the i-th wind power unit, w min is the minimum frequency, when w WT,i 3w min and When b t,i =1, otherwise, b t,i = 0; when it comes to the calculation of the participation factor of double-fed pumped storage or photovoltaic, b t,i =1.

[0065] Wind power (i.e. the rotor speed has reached the minimum level and the speed must be restored to prevent tripping) begins to absorb energy during the rotor speed recovery phase, which may cause a power shortage in the grid and cause a secondary frequency drop.

[0066] It should be noted that there are three stages in the frequency drop scenario:

[0067] 1. Initial frequency drop response stage: In this stage, when the grid frequency drops, the three power generation units of double-fed pumped storage, wind power and photovoltaic are activated to provide frequency support.

[0068] 2. Wind turbine rotor speed recovery phase: If the wind turbine rotor speed reaches a minimum level and needs to be restored to a safe level to prevent tripping, the wind turbine begins to absorb energy, which may cause a secondary frequency drop in the grid.

[0069] 3. Frequency rise phase: When the grid frequency starts to rise, it is necessary to consider how to maintain the stability of the grid and ensure that all power generation units operate within safe operating limits.

[0070] In addition, in the second stage, when the rotor speed of the wind turbine drops below the minimum safety threshold, measures must be taken to increase the rotor speed to avoid the wind turbine being disconnected from the grid.

[0071] To restore the rotor speed, the wind turbine needs to absorb energy from the grid. This will increase the total power demand on the grid, which may cause a power shortage and lead to a secondary drop in grid frequency.

[0072] To alleviate this situation, the participation factor of wind turbines needs to be adjusted to reduce their demand for grid power. After the adjustment, the power demand of wind turbines on the grid will be reduced, thus reducing the impact on grid stability.

[0073] At this stage, the participation factor may be adjusted according to the rotor status of the wind turbine. For example, if the wind turbine's rotor speed has reached the minimum level, its participation factor may be set to 0 or a smaller value to indicate that it is temporarily unable to provide frequency support to the grid.

[0074] At the same time, the participation factors of other power generation units (such as double-fed pumped storage DFPS and photovoltaic PV) may increase accordingly to compensate for the reduced power output of wind turbines and ensure the stability of grid frequency.

[0075] When adjusting the participation factor, a balance needs to be found between the safe operation of the wind turbine and the stability of the grid: the wind turbine needs enough energy to restore its rotor speed, while the grid also needs to avoid a frequency drop due to power shortages.

[0076] In an optional embodiment, there may be no coordinated support for multiple steps in the frequency drop scenario, such as biomass power generation, small hydropower generation, and flywheel energy storage system. The power grid has a frequency drop at a certain moment, and the three power generation units start frequency regulation at the same time without dividing the stages. Each unit directly responds to the frequency fluctuations of the power grid through its characteristics to ensure that the frequency returns to normal levels as soon as possible. At this time, all power generation units continue to provide support for the frequency with a fixed strategy until the power grid is restored to stability. Biomass power generation is a relatively stable renewable energy source with a relatively stable power output, which is suitable for long-term power generation support. Because it relies on burning biomass raw materials for power generation, the reaction time is relatively slow, but the power output can be adjusted by fuel supply in a short time. When the frequency drop occurs, the biomass power plant will increase the power output according to the preset control logic. Although the response speed of biomass power generation is not as fast as the energy storage system, it can continue to provide stable power support for the system to ensure the stable recovery of the power grid frequency after the drop.

[0077] Small hydropower stations have good frequency response capabilities and can quickly adjust power output through water flow regulation. Compared with large hydropower, small hydropower is more flexible and suitable for providing fast, short-term response support when the grid frequency fluctuates. When the frequency drops, small hydropower stations can quickly increase power generation by adjusting water flow. This allows it to quickly provide support in the early stages of a grid frequency drop, slow down the frequency drop, and provide stable power output throughout the frequency recovery process.

[0078] The flywheel energy storage system is an energy storage device that can instantly provide high-power output. It has a very short response time and can usually provide frequency support within milliseconds. The flywheel energy storage system stores kinetic energy through a high-speed rotating flywheel and can quickly respond to frequency changes in the power grid. When a frequency drop occurs, the flywheel energy storage system can almost instantly release its stored energy to provide inertial support for the power grid to resist the rapid drop in frequency. Although the energy storage capacity of flywheel energy storage is limited and cannot provide long-term power support, its rapid response characteristics make it a key frequency regulation resource in the short term.

[0079] In another optional embodiment, the following three power supply units are selected for analysis in the frequency drop scenario: gas turbine, battery energy storage system, geothermal power generation system. When the grid frequency drops initially, these three power supply units will start to provide support to the grid in a coordinated manner to prevent the frequency from dropping further. Gas turbine is a traditional power generation method that starts quickly and can quickly increase the output power by adjusting the combustion rate within a few seconds. Although its inertial response is weak, its rapid adjustment characteristics make it an effective response resource in the initial stage. GT usually has a high participation factor at this stage and can quickly inject power into the system. The battery energy storage system can respond quickly to grid frequency fluctuations in milliseconds. Its bidirectional inverter can quickly discharge when the frequency drops to provide power support to the grid. BESS plays an important role in the initial stage, has a large participation factor, and is a key frequency regulation resource for rapid response. Geothermal power generation is usually a relatively stable renewable energy source, and its output power is not easily affected by environmental factors, but its inertial response is relatively slow. Geothermal power generation systems can provide stable power support to the grid for a long time by controlling the fine-tuning of power output, but in the initial stage, their response speed is slow, so the participation factor is relatively small.

[0080] During the initial frequency drop phase, battery energy storage systems and gas turbines take on the main response tasks and quickly provide power support, while the geothermal power generation system, as a stable energy source, provides certain basic support.

[0081] Gas turbine combustion adjustment stage:

[0082] In the second phase of the frequency drop, the gas turbine enters the combustion adjustment phase. At this point, the rotor speed and combustion state of the gas turbine must be maintained within a safe operating range to prevent the generator from tripping. At the same time, the energy storage capacity of the battery energy storage system may begin to weaken and cannot continue to maintain high power output. As its combustion adjusts, the participation factor of the gas turbine may need to be reduced to prevent equipment stress caused by excessive load. In this phase, the gas turbine needs to balance power output and equipment safety to ensure that it will not trip due to overload operation. During the gas turbine adjustment phase, the battery energy storage system may continue to provide partial support, but its discharge capacity may decrease, especially if the frequency drop lasts for a long time. Therefore, the participation factor of the BESS may also be reduced to avoid excessive discharge of the battery. Since the geothermal power generation system is relatively stable, although it starts slowly, it will gradually increase its power output in the second phase. At this time, the participation factor of the geothermal power generation system will gradually increase to compensate for the reduction in power output of the gas turbine and battery energy storage system.

[0083] During the gas turbine combustion adjustment stage, the participation factors of the gas turbine and battery energy storage system may decrease, while the participation factor of the geothermal power generation system will gradually increase to ensure the power supply balance of the system and prevent a secondary drop in frequency.

[0084] Frequency increase stage:

[0085] When the frequency starts to rise, the grid frequency gradually returns to normal and the system enters a stable operation phase. At this time, it is necessary to control the output of all power generation units to avoid excessive frequency rise and ensure that each power generation unit is within a safe operating range.

[0086] As the frequency recovers, the gas turbine can gradually reduce its output power and its participation factor decreases. The flexibility of the gas turbine enables it to quickly adjust its output to avoid frequency overshoot due to excessive output. During the frequency recovery phase, the battery energy storage system may enter charging mode to absorb excess power to restore the battery energy storage capacity. If the frequency recovers too quickly, the battery energy storage system can balance the system power by absorbing electrical energy to prevent excessive frequency recovery. The participation factor of the BESS at this stage may need to be dynamically adjusted according to the frequency conditions, and it can both discharge and charge. Since the output power of the geothermal power generation system is relatively stable, it will continue to provide constant power support during the frequency recovery phase. The participation factor of geothermal power generation will remain stable to ensure a smooth transition of the system to normal conditions.

[0087] During the frequency recovery phase, the gas turbine gradually reduces its power output, the battery energy storage system may switch to absorbing excess power, and the geothermal power generation system continues to maintain stable output to ensure smooth operation of the system.

[0088] For the frequency increase scenario, the participation factors of the three generating units will be given by:

[0089]

[0090] Among them, b t ￠ ,i is the number of generating units in time slot t, except b t,i Another binary indicator that determines the status of double-fed pumped storage and wind power. For double-fed pumped storage, its value is still 1; for wind power, when w WT,i 3w min and When b t ￠ ,i =1, otherwise, b t ￠ ,i =0.

[0091] The frequency rise scenario refers to a situation where the actual frequency of the power grid is higher than its rated frequency. This may be due to the fact that the power generation output in the grid exceeds the load demand, or because some regulation mechanisms in the grid (such as the frequency regulation of the generator set) respond excessively. In this case, measures need to be taken to reduce power generation or increase load to return the grid frequency to normal levels.

[0092] The power reduction scenario (often referred to as the frequency reduction scenario) means that the actual frequency of the power grid is lower than the rated frequency. This is usually because the load demand exceeds the generation capacity, causing the grid frequency to decrease. In this case, it is necessary to increase the generation capacity or reduce the load to restore the frequency to normal levels.

[0093] The participation factor of a power generation unit represents the ratio of the output power of the power generation unit to the total output power, which is between 0 and 1. The actual frequency of the power grid is adjusted by adjusting the output power of different power generation units.

[0094] Example 2, reference Figure 2 , 3 , which is an embodiment of the present invention, provides a virtual inertia frequency regulation method for a double-fed pumped storage unit and a renewable energy power generation system, wherein establishing the inertia model of three power generation units specifically includes the following methods:

[0095] In this paper, the system structure of double-fed pumped storage is as follows Figure 2 As shown in the figure. In this structure, the rotating shaft of the reversible pump turbine is connected to the doubly fed induction generator through a gearbox, and the rotor winding of the doubly fed induction generator is integrated into the power system through a back-to-back converter. At the same time, the speed governor is responsible for adjusting the power output by adjusting the guide vanes through the power converter according to the deviation between the reference speed and the actual speed. Figure 3 The detailed structure of the speed governor controller is given, which includes an electro-hydraulic servo actuator and a PID controller, which helps to determine the reference of the mechanical guide value. The mathematical model of the speed governor is:

[0096]

[0097] Where: sref is the grid angular velocity reference value, T n and T v is the frequency measurement system constant, R p and R T are the static and transient droop coefficients, the PV array output voltage, T R and T d are all time constants, P ref is the reference power of double-fed pumped storage, k p , k i and k d is the PID controller gain. E is the power reference of the speed controller, ws is the measured value of the grid angular velocity, Y is the output of the actuator, y is the output of the PID controller, and s represents the complex variable in the transfer function.

[0098] At the same time, since the doubly fed pumped storage will participate in the grid frequency regulation, it is necessary to analyze its inertia characteristics. For a synchronous generator, the kinetic energy stored in the rotor is given by

[0099]

[0100] Where: E is the kinetic energy stored in the rotor, J is the moment of inertia, ω e is the synchronous angular velocity. The synchronous generator can adjust its total power output by changing the angular velocity to absorb or release kinetic energy. For double-fed pumped storage, power decoupling control makes it difficult for the angular velocity to respond immediately to changes in the grid frequency. Therefore, by adding a frequency regulation loop to the rotor-side converter, kinetic energy can be used to simulate the frequency response characteristics of the synchronous generator. As the grid frequency changes, the system changes its angular velocity, which causes changes in kinetic energy, i.e.

[0101]

[0102] Among them J D is the actual moment of inertia of the double-fed pumped storage, J DFPS is the virtual moment of inertia of the doubly-fed pumped storage, Dw e is the change of synchronous angular velocity, w r0 and Dw r are the initial angular velocity and the change of the rotor angular velocity, DE D is the changing kinetic energy. Based on formula (4), we can derive the equivalent virtual inertia J of the double-fed pumped storage system with respect to the change of grid frequency: DFPS , as given

[0103]

[0104] Where Df is the frequency deviation. Obviously, the virtual inertia of the double-fed pumped storage depends not only on its own natural inertia, but also on w r0 、Dw r and Df.

[0105] The AC excitation system model of the doubly-fed pumped storage is one of the key system models that can be used for output power regulation. In the dq coordinate system, the state space expression of the induction motor AC excitation system is:

[0106]

[0107] Among them, I SR =Ids ,I qs ,I dr ,I qr ,V SR =V ds ,V qs ,V dr ,V qr ,

[0108]

[0109] In addition, the output active power P of the double-fed pumped storage on the stator winding is given S / Reactive power Q S and electromagnetic torque M em .

[0110]

[0111] Where p is the number of poles; V ds 、V qs Represents the voltage of the stator winding in the dq axis coordinate system; I ds ,I qs represents the current in the stator winding in the dq axis coordinate system; V dr 、V qr Represents the voltage on the rotor winding in the dq axis coordinate system; I dr ,I qr represents the current in the rotor winding in the dq axis coordinate system; y ds ,y qs represents the magnetic flux of the stator dq axis; R S ,R r are the resistances of the stator and rotor windings, L s ,L r are the self-inductance of the stator and rotor, L m is the mutual inductance between the stator and the rotor, ω S is the synchronous speed, σ is the leakage coefficient. Considering that the direction of the stator flux is consistent with the d-axis of the dq coordinate system, we further have:

[0112]

[0113] In addition, when p = 1, we can get

[0114]

[0115] For distributed generation units including photovoltaic and wind power, they are decoupled from the grid frequency because they are powered by power electronic devices that cannot directly respond to changes in grid frequency. Therefore, in order to enable generators based on power electronics technology to cope with changes in grid frequency, the concept of virtual inertia is proposed. It focuses on considering the inertia levels of double-fed pumped storage, photovoltaic and wind power to determine the coordinated frequency response tasks between them. Therefore, it is necessary to estimate the virtual inertia that photovoltaic and wind power can provide in frequency response mode. For wind turbines connected to the grid, their virtual rotation inertia J WT It can be approximately given by the following formula:

[0116]

[0117] where n pg is a pole pair; w e0 is the steady-state angular frequency of the power grid; a0=D d +b, where b is a constant value determined by the frequency deviation, D d a damping factor provided for power converter control; and

[0118]

[0119] where k df and k df are virtual inertia coefficient and droop coefficient respectively; J d is the real moment of inertia of the rotor; P0 is the current power supply level.

[0120] For a photovoltaic unit, its virtual inertia level can be estimated by the frequency-energy characteristics of the photovoltaic

[0121]

[0122] Where Dw(t) represents the frequency deviation, DE(t) represents the voltage deviation, C dc Indicates the DC side capacitance, U dcref represents the reference voltage under the d-axis, h represents the initial phase of the voltage, P L is the load change, R is the speed regulator coefficient, k p is the droop coefficient, I m is the inverter current, A,x,ω n ,ω d and γ are the amplitude of the attenuation term, damping coefficient, natural oscillation frequency, oscillation frequency and initial phase respectively; k1, k2, k3 are constants related to the structure and parameters of the photovoltaic device.

[0123] Considering the frequency trough of photovoltaic response, the photovoltaic equivalent inertia constant is:

[0124]

[0125] Where S N Indicates rated capacity, J pv is the photovoltaic equivalent inertia, t nadir Indicates the time, is the time to reach the lowest frequency point, T RH Represents the time constant of frequency recovery.

[0126] Example 3, reference Figure 5 , is an embodiment of the present invention, and provides a virtual inertia frequency modulation method for a double-fed pumped storage unit and a renewable energy power generation system. In order to ensure that the double-fed pumped storage unit operates according to the instructions issued by the frequency modulation control scheme, it is necessary to design an active power control module, which is mainly based on the rotor-side converter control of the induction motor AC excitation system. Therefore, for simplicity, this paper ignores the dynamics of the grid-side converter control. Figure 5 The rotor-side converter control diagram is given, and the state space expressions of the controlled system and control input are given:

[0127]

[0128] where s r =1-w m / w s ; L rr =L r +L m ;k p1 ,k i1 ,k p2 ,k i2 are the gains of the proportional and integral parts of the first and second PI controllers, respectively; are the reference values ​​of the power command from the frequency control loop, which are the active power and reactive power reference values, P s ,Q s They are the measured values ​​of active power and reactive power respectively.

[0129] In formula (21), V dr and V qr are the input signals of the AC excitation system shown in equation (6), which can directly affect the output active and reactive power. It follows the principle of direct power control and uses two independent PI controllers to generate the reference input signal.

[0130] It should be said that the above is about the design of active power control module in double-fed pumped storage (DFPS) system, which is to ensure that DFPS can adjust its power generation output according to the needs of grid frequency regulation. The control strategy is mainly based on the rotor side converter (RSC) control of the AC excitation system of the induction motor.

[0131] In grid frequency regulation, when the grid frequency drops (indicating insufficient power supply), the double-fed pumped storage (DFPS) needs to quickly increase its power output to support the grid. Conversely, when the grid frequency rises (indicating excess power supply), the double-fed pumped storage needs to reduce its power output or increase its pumped storage.

[0132] Direct Power Control: The active and reactive power output of the motor can be directly controlled by controlling the d-axis and q-axis currents of the motor separately.

[0133] PI controller: Two independent PI controllers are used to generate voltage reference signals for the d-axis and q-axis. These voltage signals adjust the power output of the motor by controlling the magnetic field of the motor.

[0134] State-space model: Equations (20) and (21) describe the state-space expression of the control object and the control input, which is a standard method for dynamic modeling and control design of power systems.

[0135] If the above functions are implemented in the form of software functional units and sold or used as independent products, they can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, or the part that contributes to the prior art or the part of the technical solution, can be embodied in the form of a software product. The computer software product is stored in a storage medium, including several instructions for a computer device (which can be a personal computer, a server, or a network device, etc.) to perform all or part of the steps of the method described in each embodiment of the present invention. The aforementioned storage medium includes: U disk, mobile hard disk, read-only memory (ROM, Read-Only Memory), random access memory (RAM, Random Access Memory), disk or optical disk and other media that can store program codes.

[0136] The logic and / or steps represented in the flowchart or otherwise described herein, for example, can be considered as an ordered list of executable instructions for implementing logical functions, and can be embodied in any computer-readable medium for use by an instruction execution system, device or apparatus (such as a computer-based system, a system including a processor, or other system that can fetch instructions from an instruction execution system, device or apparatus and execute instructions), or in conjunction with such instruction execution systems, devices or apparatuses. For the purposes of this specification, "computer-readable medium" can be any device that can contain, store, communicate, propagate or transmit a program for use by an instruction execution system, device or apparatus, or in conjunction with such instruction execution systems, devices or apparatuses.

[0137] More specific examples of computer-readable media (a non-exhaustive list) include the following: an electrical connection with one or more wires (electronic device), a portable computer disk case (magnetic device), a random access memory (RAM), a read-only memory (ROM), an erasable and programmable read-only memory (EPROM or flash memory), an optical fiber device, and a portable compact disk read-only memory (CDROM). In addition, the computer-readable medium may even be a paper or other suitable medium on which the program is printed, since the program may be obtained electronically, for example, by optically scanning the paper or other medium, followed by editing, deciphering or, if necessary, processing in another suitable manner, and then stored in a computer memory.

[0138] It should be understood that the various parts of the present invention can be implemented by hardware, software, firmware or a combination thereof. In the above-mentioned embodiments, a plurality of steps or methods can be implemented by software or firmware stored in a memory and executed by a suitable instruction execution system. For example, if implemented by hardware, as in another embodiment, it can be implemented by any one of the following technologies known in the art or their combination: a discrete logic circuit having a logic gate circuit for implementing a logic function for a data signal, a dedicated integrated circuit having a suitable combination of logic gate circuits, a programmable gate array (PGA), a field programmable gate array (FPGA), etc.

[0139] Example 2, reference Figure 6 , 7 8 is an embodiment of the present invention, which provides a virtual inertia frequency regulation method for a doubly-fed pumped storage unit and a renewable energy power generation system. In order to verify the beneficial effects of the present invention, scientific demonstration is carried out through economic benefit calculation and simulation experiments.

[0140] To evaluate the effectiveness and performance of the proposed scheme, a simulation case study was conducted using MATLAB / Simulink. Figure 6The test system shown is a modified 9-node power system, which contains 5 power generation units, including 2 thermal power units with a capacity of 200MW, a double-fed pumped storage unit with a capacity of 280MW, a wind farm with a total capacity of 450MW and a large photovoltaic power plant with a total capacity of 300MW. In the frequency control scheme, all wind turbines in the wind farm are set to frequency response mode, working together with the double-fed pumped storage and photovoltaic power plants. In order to conduct a comparative study, the conventional virtual inertia control (CVIC), the scheme without any virtual inertia control (Non-VIC) and a novel synergetic virtual inertia control (SVIC) scheme proposed in the present invention are selected for comparative analysis.

[0141] The performance of the three schemes under the condition of a step change in load is tested. Assume that the load level changes stepwise at the time point "t = 10s" from 900MW to 1000MW. At this time, the double-fed pumped storage, wind turbines and photovoltaic power plants begin to support the grid frequency by increasing power output. Using three different frequency regulation methods, the simulation results are as follows: Figure 7 shown. Figure 7 The power output changes of the double-fed pumped storage, photovoltaic power station and wind turbine, as well as the changes in the grid frequency are shown in Figure 1. Figure 7 It can be seen that under the SVIC scheme, the doubly-fed pumped storage, photovoltaic power stations and wind turbines collaboratively contribute to the frequency support task. Figure 7 (d) shows that when the VIC solution is adopted, the grid frequency decreases the least and recovers to normal value at the fastest speed. Figure 8 The angular speed of one of the wind turbines under the SVIC and CVIC schemes is compared. It can be seen that when the SVIC method is used, when the grid frequency returns to normal, the angular speed of the wind turbine will smoothly return to the original level at the time point "t = 17.8s", thereby reducing the risk of secondary frequency drop. When the CVIC scheme is used, the rotor speed may continue to decrease and slowly return to the original level after reaching the minimum level, which may cause the wind turbine to be disconnected from the grid and cause a secondary frequency drop.

[0142] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

Claims

1. A virtual inertia frequency modulation method for a double-fed pumped storage unit and a renewable energy power generation system, characterized in that: include: Acquire structural information of the first power generation unit, the second power generation unit, and the third power generation unit; Establish inertia models of three power generation units; The frequency control method based on the inertia model shown supports the power system frequency in a coordinated manner for the power supply units.

2. The virtual inertia frequency modulation method of the double-fed pumped storage unit and renewable energy power generation system according to claim 1, characterized in that: The structural information includes identifying whether the power generation unit has a power electronic device that directly responds to changes in grid frequency.

3. The virtual inertia frequency modulation method of the double-fed pumped storage unit and renewable energy power generation system according to claim 2, characterized in that: The inertia model includes, if the generating unit is powered by a power electronic device that can directly respond to changes in grid frequency, then the equivalent virtual inertia of the frequency modulation of the generating unit is derived using mechanical characteristics; If the generating unit is powered by power electronic devices that cannot directly respond to grid frequency changes, the virtual inertia available in the frequency response mode of the generating unit is estimated.

4. The virtual inertia frequency modulation method of the double-fed pumped storage unit and renewable energy power generation system according to claim 3, characterized in that: The power supply units support the power system frequency in a coordinated manner, including determining the participation of three different power supply units according to the virtual inertia of each power generation unit.

5. The virtual inertia frequency modulation method of the double-fed pumped storage unit and renewable energy power generation system according to claim 4, characterized in that: The inertia levels of the generating units are different, and different participation factors need to be designed at different stages of frequency support according to the unique dynamic behavior and different safe operation constraints; The participation factor includes, but is not limited to, obtaining different values ​​in a frequency drop scenario and a frequency increase scenario respectively.

6. The virtual inertia frequency modulation method of the double-fed pumped storage unit and renewable energy power generation system according to claim 5, characterized in that: The first power generation unit, the second power generation unit and the third power generation unit at least include three different power supply units: double-fed pumped storage, wind power and photovoltaic; In the frequency drop scenario, three generating units will be in action to support the frequency, and the proposed participating factors include but are not limited to: Where J represents the moment of inertia of the system, n and m represent the number of wind power and photovoltaic power, respectively; x i,t ={1,0} is a binary indicator indicating the availability of the ith generating unit at time slot t, xi,t = 0, indicating that frequency support will not be available or that the photovoltaic cell has no power output at time slot t; i,t =1, the statement can obtain frequency support; J DFPS represents the equivalent virtual inertia of the double-fed pumped storage; J WT,i , J pv,i represents the equivalent virtual inertia of the i-th power generation unit of wind power and photovoltaic power respectively; PF DFPS PF WT PF PV Respectively represent the participation factors of the doubly-fed pumped storage, wind power and photovoltaic power generation units; i represents any power generation unit among the doubly-fed pumped storage, wind power and photovoltaic; Wind power begins to absorb energy during the rotor speed recovery phase, and the participation factor is revised to: Among them, b t,i is a binary indicator for judging the rotor status of the wind turbine in the i-th power generation unit in time slot t; w WT,i represents the frequency of the i-th wind power unit, w min is the minimum frequency, when w WT,i 3w min and When b t,i =1, otherwise, b t,i = 0; when it comes to the calculation of the participation factor of double-fed pumped storage or photovoltaic, b t,i =1.

7. The virtual inertia frequency modulation method of the double-fed pumped storage unit and renewable energy power generation system according to claim 6, characterized in that: In the frequency increase scenario, the participation factors of the three generating units are expressed as: Among them, b t ￠ ,i is the number of generating units in time slot t, except b t,i Another binary indicator that determines the status of double-fed pumped storage and wind power. For double-fed pumped storage, its value is still 1; for wind power, when w WT,i 3w min and When b t ￠ ,i =1, otherwise, b t ￠ ,i =0.

8. A virtual inertia frequency modulation system of a double-fed pumped storage unit and a renewable energy power generation system using the method according to any one of claims 1 to 7, characterized in that: An analysis unit, acquiring structural information of the first power generation unit, the second power generation unit, and the third power generation unit; A model generation unit, which establishes inertia models of three power generation units; The control unit supports the power system frequency in a coordinated manner with the power supply units based on the frequency control method of the inertia model shown.

9. A computer device comprising: A memory and a processor; the memory stores a computer program, wherein the processor implements the steps of any method as claimed in claim 1 when executing the computer program.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the steps of the method according to any one of claims 1 to 7 are implemented.

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