Power coordination control strategy of photo-thermal and photovoltaic combined power generation system

Abstract

The invention discloses a power coordination control strategy of a photo-thermal and photovoltaic combined power generation system. The power coordination control strategy is specifically implemented according to the following steps of 1, building a photovoltaic subsystem model, a photo-thermal subsystem model and a control framework; step 2, when the photovoltaic subsystem has unbalanced power; judging whether the unbalanced power exceeds a power set value or not, and entering step 3 when the unbalanced power exceeds the power set value; 3, adjusting the unbalanced power of the photovoltaic subsystem according to the DC voltage of the photovoltaic subsystem; and the operation state of the photo-thermal subsystem is set according to the size of the direct current voltage of the photovoltaic subsystem, so that coordination control is completed. According to the power coordination control strategy of the photo-thermal and photovoltaic combined power generation system, the energy transmission efficiency is accurately calculated by establishing the mathematical model of the photo-thermal and photovoltaic combined power generation system and the power coordination control strategy of the system.

Description

Technical Field

[0001] The present invention belongs to the technical field of renewable energy power generation, and in particular relates to a power coordination control strategy for a solar-thermal-photovoltaic combined power generation system. Background Art

[0002] As an innovative model, the photovoltaic-solar thermal combined power generation (PV-CSP) system cleverly combines high-efficiency photovoltaic power generation technology with solar thermal power generation technology with large-scale energy storage and low-loss time adjustment capabilities. This system not only takes advantage of the low cost and mature technology of photovoltaic power generation, but also gives full play to the expertise of solar thermal power generation in efficient energy storage and on-demand release, effectively alleviating the challenges of renewable energy to grid stability due to time-varying and random fluctuations.

[0003] The photovoltaic-solar thermal combined power generation system consists of a photovoltaic subsystem and a solar thermal subsystem. The distribution of light and heat in the solar thermal subsystem is complex, the energy exchange process is highly nonlinear, the system has many variables and complex multi-energy coupling relationships, resulting in a high model order, many parameters and difficulty in accurate identification. How to reasonably approximate and equate the multi-energy conversion process and establish a dynamic model of the combined power generation system that can be embedded in a variety of power grid models for simulation needs to be studied urgently.

[0004] According to the power command of the power grid and the light intensity, the photovoltaic-solar thermal combined power generation system can operate in different control modes, and the state of the heat storage link directly affects the adjustable margin of the system. Therefore, how to consider the impact of the system energy storage state on its power regulation ability and coordinate the photovoltaic and solar thermal subsystems to effectively track the power command of the power grid is one of the key issues for the combined power generation system to participate in the operation and control of the power grid. Making full use of the flexible adjustment ability of the solar thermal power generation system, complementing with photovoltaic power generation, and jointly supporting the stability of the grid frequency and voltage is the current mainstream grid-connected operation mode of the photovoltaic-solar thermal combined power generation system. Summary of the invention

[0005] The purpose of the present invention is to provide a power coordination control strategy for a solar-thermal-photovoltaic combined power generation system, and to accurately calculate the energy transfer efficiency by establishing a mathematical model of the solar-thermal-photovoltaic combined power generation system and the power coordination control strategy of the system.

[0006] The technical solution adopted by the present invention is a power coordination control strategy for a solar-thermal-photovoltaic combined power generation system, which is specifically implemented according to the following steps:

[0007] Step 1: Build the photovoltaic subsystem model, solar thermal subsystem model and control architecture;

[0008] Step 2: When unbalanced power occurs in the photovoltaic subsystem, determine whether the unbalanced power exceeds the power setting value, and if so, proceed to step 3;

[0009] Step 3: Adjust the unbalanced power of the photovoltaic subsystem according to the size of the DC voltage of the photovoltaic subsystem; and set the operating state of the solar thermal subsystem according to the size of the DC voltage of the photovoltaic subsystem to complete the coordinated control.

[0010] The present invention is also characterized in that:

[0011] The specific formula for building the photovoltaic subsystem model in step 1 is:

[0012] According to circuit theory and Shockloy diffusion theory, we can get:

[0013]

[0014] In the formula, I ph is the photocurrent, R s is the series internal resistance, R sh is the parallel bypass resistor, I pv is the output current of the photovoltaic cell, k is the Boltzmann constant, I o is the diode reverse saturation current, A is the diode factor, q is the unit charge constant, V is the photovoltaic cell operating voltage, and T is the photovoltaic cell operating temperature.

[0015] The specific steps of building the photothermal model in step 1 are as follows:

[0016] In the construction of the solar thermal subsystem, the heliostats in the field focus the sunlight onto the collector surface through the concentrating and collecting link of the collector field. Assuming that the heliostat control system can accurately track the altitude and azimuth of the sun, the solar radiation energy Q reflected by the field is inc (unit is J) as follows:

[0017] Q inc =η hf A hf I bn (2);

[0018] Where: A hf is the area of ​​the heliostat in the field, in m 2 ;I bn is the average radiation intensity incident on the heliostat, in W / m 2 ; η hf is the mirror field efficiency;

[0019] Secondly, the construction of the solar thermal subsystem model also includes the construction of the collector model, the heat exchanger model and the calculation of the energy storage capacity of the solar thermal subsystem.

[0020] The specific steps of building the collector model are as follows:

[0021] In the construction of the solar thermal subsystem, the core component of the solar thermal subsystem is the collector, which is composed of multiple tube bundle plates. Multiple heat absorbing tubes are connected in parallel in each tube bundle plate. The heat transfer medium flows through each tube bundle plate once according to the designed path, absorbing the heat reflected by the mirror field to the collector surface; the heat absorbing tube is divided into multiple pipe micro-elements of equal length, and the following assumptions are made: the heat transfer medium only flows along the radial direction of the heat absorbing tube; the heat absorbing surface of the heat absorbing tube is a semi-cylindrical surface and is heated evenly; the wall surface temperature of a single pipe micro-element is consistent and the medium temperature in the tube is consistent, and the medium flow rate in each heat absorbing tube in the tube bundle plate is the same; according to the energy, mass and thermodynamic equations, the pipe micro-element model of the heat absorbing tube is constructed as follows:

[0022]

[0023] Q tra =hA m (T m -T s ) (4);

[0024]

[0025] Where: M m is the pipe element mass, in kg; C m is the specific heat capacity of the heat absorbing tube wall, C s is the average specific heat capacity, C si and C so are the specific heat capacities of the heat transfer medium flowing into and out of the microelement of the pipe, both in J / (kg·K); T m is the tube wall temperature, T s is the average temperature of the medium in the pipeline microelement, T in and T out are the temperatures of the heat transfer medium flowing into and out of the pipe microelement, both in K; Q a is the heat absorbed by the tube wall, Q loss is the heat loss, which is mainly composed of convection, radiation and reflection heat loss of the collector, Q tra is the heat absorbed by the heat transfer medium, the unit is J; h is the heat transfer coefficient; A m is the heat exchange area, in m 2 ;m sin and m sout are the medium flow rates flowing into and out of the micro-element of the pipe, in m 3 / s; is the average density of the heat transfer medium, in kg / m 3 ; V s is the volume of the pipe element, in m 3 ;

[0026] Formulas (3) to (6) are linearized, and the surface temperature of the pipeline microelement, the medium temperature at the outlet of the pipeline microelement, and the medium flow rate at the outlet of the pipeline microelement are obtained through iterative calculation to complete the construction of the collector model.

[0027] The calculation of the energy storage capacity of the solar thermal subsystem is as follows:

[0028] In the construction of the CSP subsystem, by configuring the heat storage link, the output power of the CSP subsystem is not limited by the current solar radiation intensity and can be adjusted according to the grid demand. The energy storage state of the CSP subsystem directly affects the active power adjustment range and adjustable margin of the system. The energy storage state variable S of the CSP subsystem is defined as SOE Describe the energy stored in the photothermal subsystem at the current moment:

[0029] S SOE (t)=[M0+∫0 t (m in -m out )dt] / M ref (7);

[0030] Where: m in and m out are the heat transfer medium flow rates flowing into and out of the heat storage link, in kg / s; M0 is the initial heat transfer medium mass, in kg; M ref is the tank capacity in kg, when m in >m out When the heat storage link is in the heat storage state, the mass of the high-temperature medium in the heat storage link decreases, S SOE Decrease; when m in <m out When the heat storage link is in the heat release state, the mass of the high-temperature medium in the heat storage link increases, S SOE Increase.

[0031] The specific steps of building a heat exchanger model are:

[0032] The solar thermal subsystem realizes heat-to-electricity energy conversion through the power generation link, and the heat exchanger is modeled. The solar thermal subsystem is usually equipped with a tubular heat exchanger, which consists of a preheating section, an evaporation section, and a superheating section. The high-temperature medium flows into the heat exchanger to exchange heat with water, generating high-temperature, high-pressure steam, which drives the steam turbine and generator to rotate and converts thermal energy into electrical energy. To ensure the safe and stable operation of the system, the steam generation system of the solar thermal subsystem usually operates near the rated operating point. The lumped parameter method is used to establish the heat exchanger model as follows:

[0033]

[0034] Where: s1 and s2 are lumped parameter variables; ρ m is the density of the steam-water mixture in the heat exchanger, in kg / m3 ;h s and h fw are the enthalpy values ​​of steam and water respectively; v t is the water flow rate, in m / s; c a is the specific heat capacity of the heat exchanger tube wall, in J / (kg·K); M is the mass of the heat exchanger, in kg; T is the temperature of the heat exchanger tube wall, in K; h m is the enthalpy of the steam-water mixture before the steam-water separator; D s and D fw are the flow rates of steam and water respectively, in m 3 / s; Q is the heat absorbed by water during the heat exchange process, the unit is J.

[0035] The specific steps to build the control architecture in step 1 are:

[0036] By constructing photovoltaic subsystem and solar thermal subsystem models and adopting a control architecture for coordinated control, when the solar thermal subsystem model changes through the power grid power command or the solar radiation intensity, the control state of converter 3 determines whether the operating mode is power tracking mode or fluctuation smoothing mode, and converter 3, converter 2 and converter 1 transmit signals to the central controller, which coordinates the solar thermal subsystem and photovoltaic subsystem models to jointly respond to the change of the power grid power command through the central controller.

[0037] Step 2 The specific steps are:

[0038] When the photovoltaic output fluctuation in the photovoltaic subsystem causes unbalanced power in the system, the central controller obtains the current system operation status, and the central controller determines whether the photovoltaic subsystem power fluctuation exceeds the upper and lower limits of the power of the grid-side converter station 3 for a continuous period of time based on the photovoltaic subsystem power prediction value. If it does not exceed the set power limit, it is a normal fluctuation. In the constant DC voltage control mode of the converter station 3, the system DC voltage remains stable, the solar thermal energy storage side converter station 2 maintains constant power operation, and the unbalanced power is output from the converter station 3 to the grid side. If it exceeds the set power limit, it goes to step 3.

[0039] The specific steps of step 3 are as follows: if the unbalanced power of the photovoltaic subsystem exceeds the power limit set by the grid-side converter station 3, the converter station 3 switches from the fixed DC voltage control power tracking mode to the fluctuation smoothing mode, and the central controller adjusts the output power of the photovoltaic subsystem according to the power fluctuation of the photovoltaic subsystem every minute. Its DC bus voltage varies with the size of the unbalanced power according to the preset fluctuation smoothing coefficient. When the DC voltage change exceeds the DC voltage margin range set by the converter station 2 on the solar thermal subsystem side, the converter station 2 switches from the power tracking control mode to the fluctuation smoothing mode. At this time, the system distributes the unbalanced power according to the unbalanced power distribution strategy and the fluctuation smoothing coefficients of the converter station 2 and the converter station 3. The solar thermal energy storage power station adjusts the output according to the unbalanced power distributed by the system. If the system DC voltage increases, the output is reduced; otherwise, the output is increased.

[0040] When the solar thermal output adjustment in the solar thermal subsystem reaches the upper or lower limit, its operation mode is switched from the fluctuation smoothing mode to the current limiting mode. The solar thermal subsystem makes current limiting adjustments based on the degree of fluctuation and the reference values ​​of the heat exchanger medium valve opening and the turbine valve opening. When the system DC voltage increases, the solar thermal subsystem operates at maximum power. When the system DC voltage decreases, the solar thermal subsystem operates at minimum power, completing coordinated control.

[0041] Compared with the prior art, the present invention has the following beneficial effects:

[0042] The power coordination control strategy of the solar-thermal-photovoltaic combined power generation system provided by the present invention uses energy flow as a clue to segmentally model the multivariable coupling and heat transfer dynamic process of the system, and proposes a power coordination control strategy that takes the energy storage state into consideration, accurately calculates the energy transfer efficiency, and realizes the coordination between the photovoltaic subsystem and the solar-thermal subsystem under different working conditions and control modes, thereby improving the system regulation capability and response performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 A schematic diagram of the model structure of the power coordination control strategy of the solar-thermal-photovoltaic combined power generation system of the present invention;

[0044] Figure 2 is an equivalent circuit diagram of the photovoltaic cell in the present invention;

[0045] Figure 3 Schematic diagram of the architecture of the power coordination control strategy of the solar-thermal-photovoltaic combined power generation system of the present invention. DETAILED DESCRIPTION

[0046] The present invention will be further explained below in conjunction with the accompanying drawings and specific embodiments.

[0047] Example 1

[0048] The present invention provides a power coordination control strategy for a solar-thermal-photovoltaic combined power generation system, such as Figure 1-3 As shown, the specific implementation steps are as follows:

[0049] Step 1: Build the photovoltaic subsystem model, solar thermal subsystem model and control architecture;

[0050] Firstly, using energy conversion as a clue, based on the basic operating principles of each sub-link in the solar-thermal-photovoltaic combined power generation system, the energy conversion mechanism of the photovoltaic subsystem and the solar-thermal subsystem were modeled respectively.

[0051] The photovoltaic subsystem model consists of a photovoltaic array, an inverter, and a grid-connected link. The photovoltaic array is composed of photovoltaic cells as the basic component unit, which are connected in series and parallel to achieve AC / DC conversion through an inverter. The core of the photovoltaic energy conversion in the photovoltaic subsystem is the photovoltaic cell. The equivalent circuit of the photovoltaic cell is as follows: Figure 2 As shown, I ph I is the photocurrent, which is related to semiconductor materials and is closely related to light intensity and temperature. s is the diode junction current. When the external radiation is 0, a unidirectional current is formed in the PN junction under the action of the external voltage; I sh is the bypass leakage current; R s It is the series internal resistance, which is mainly composed of the battery body resistance and the electrode surface conductor resistance; R sh It is a parallel bypass resistor, which is mainly caused by silicon wafer structural defects or surface pollution; I pv is the output current of the photovoltaic cell; U is the output voltage of the photovoltaic cell.

[0052] According to circuit theory and Shockloy diffusion theory:

[0053]

[0054] In the formula, I ph is the photocurrent, R s is the series internal resistance, R sh is the parallel bypass resistor, I pv is the output current of the photovoltaic cell, k is the Boltzmann constant, I o is the diode reverse saturation current, A is the diode factor, q is the unit charge constant, V is the photovoltaic cell operating voltage, and T is the photovoltaic cell operating temperature.

[0055] In the solar thermal subsystem, the energy conversion from light to heat is carried out through the concentrating and collecting device. That is, in the concentrating and collecting link of the collector field, the heliostats in the mirror field focus the sunlight onto the collector surface, heat the heat transfer medium therein, and realize the energy conversion from light to heat. Assuming that the heliostat control system can accurately track the altitude and azimuth of the sun, the solar radiation energy Q reflected by the mirror field inc(unit is J) as follows:

[0056] Q inc =η hf A hf I bn (2);

[0057] Where: A hf is the area of ​​the heliostat in the field, in m 2 ;I bn is the average radiation intensity incident on the heliostat, in W / m 2 ; η hf is the mirror field efficiency.

[0058] The core component of the solar thermal subsystem is the collector, which is composed of multiple tube bundle plates, and multiple heat absorbing tubes are connected in parallel in each tube bundle plate. The heat transfer medium flows through each tube bundle plate once according to the designed path, absorbing the heat reflected to the collector surface by the mirror field. The heat absorbing tube is divided into multiple pipe micro-elements of equal length, and the following assumptions are made: the heat transfer medium only flows along the radial direction of the heat absorbing tube; the heat absorbing surface of the heat absorbing tube is a semi-cylindrical surface and is heated evenly; the wall surface temperature of a single pipe micro-element is consistent and the medium temperature in the tube is consistent, and the medium flow rate in each heat absorbing tube in the tube bundle plate is the same. According to the energy, mass and thermodynamic equations, the pipe micro-element model of the heat absorbing tube is constructed as follows:

[0059]

[0060] Q tra =hA m (T m -T s ) (4);

[0061]

[0062] Where: M m is the pipe element mass, in kg; C m is the specific heat capacity of the heat absorbing tube wall, C s is the average specific heat capacity, C si and C so are the specific heat capacities of the heat transfer medium flowing into and out of the microelement of the pipe, both in J / (kg·K); T m is the tube wall temperature, T s is the average temperature of the medium in the pipeline microelement, T in and T out are the temperatures of the heat transfer medium flowing into and out of the pipe microelement, both in K; Q a is the heat absorbed by the tube wall, Q loss is the heat loss, which is mainly composed of convection, radiation and reflection heat loss of the collector, Q trais the heat absorbed by the heat transfer medium, the unit is J; h is the heat transfer coefficient; A m is the heat exchange area, in m 2 ;m sin and m sout are the medium flow rates flowing into and out of the micro-element of the pipe, in m 3 / s; is the average density of the heat transfer medium, in kg / m 3 ; Vs is the volume of the pipeline element, in m 3 Equations (3)-(6) are linearized, and the surface temperature of the pipe microelement, the medium temperature at the outlet of the pipe microelement, and the medium flow rate at the outlet of the pipe microelement are obtained through iterative calculation.

[0063] The heat storage link decouples the photothermal and thermal-mechanical energy conversion processes of the CSP subsystem and alleviates the impact of sudden changes in solar radiation intensity on the output of the CSP subsystem. By configuring the heat storage link, the output power of the CSP subsystem is not limited by the current solar radiation intensity and can be adjusted according to the needs of the power grid. The energy storage state of the CSP subsystem directly affects the active power adjustment range and adjustable margin of the system. The energy storage state variable S of the CSP subsystem is SOE Describe the energy stored in the CSP system at the current moment:

[0064] S SOE (t)=[M0+∫0 t (m in -m out )dt] / M ref (7);

[0065] Where: m in and m out are the heat transfer medium flow rates flowing into and out of the heat storage link, in kg / s; M0 is the initial heat transfer medium mass, in kg; M ref is the tank capacity in kg. in >m out When the heat storage link is in the heat storage state, the mass of the high-temperature medium in the heat storage link decreases, S SOE Decrease; when m in <m out When the heat storage link is in the heat release state, the mass of the high-temperature medium in the heat storage link increases, S SOE Increase.

[0066] The solar thermal subsystem realizes heat-to-electricity energy conversion through the power generation link, which is mainly composed of three parts: tubular heat exchanger, steam turbine and generator. There are mature models for steam turbines and generators. This application only models the heat exchanger. The solar thermal subsystem is usually equipped with a tubular heat exchanger, which consists of a preheating section, an evaporation section and a superheating section. The high-temperature medium flows into the heat exchanger to exchange heat with water, generating high-temperature and high-pressure steam, which drives the steam turbine and generator to rotate and convert thermal energy into electrical energy. In order to ensure the safe and stable operation of the system, the steam generation system of the solar thermal subsystem usually operates near the rated operating point. The lumped parameter method is used to establish the heat exchanger model as follows:

[0067]

[0068] Where: s1 and s2 are lumped parameter variables; ρ m is the density of the steam-water mixture in the heat exchanger, in kg / m 3 ;h s and h fw are the enthalpy values ​​of steam and water respectively; v t is the water flow rate, in m / s; c a is the specific heat capacity of the heat exchanger tube wall, in J / (kg·K); M is the mass of the heat exchanger, in kg; T is the temperature of the heat exchanger tube wall, in K; h m is the enthalpy of the steam-water mixture before the steam-water separator; D s and D fw are the flow rates of steam and water respectively, in m 3 / s; Q is the heat absorbed by water during the heat exchange process, the unit is J.

[0069] The specific working principle of the solar-thermal-photovoltaic combined power generation system model provided by the present invention is as follows:

[0070] The power generated by the photovoltaic subsystem is gathered by the box transformer and then converted into DC by converter station 1. The power upper and lower limits of converter station 1 are 150-540MW. It is transmitted to converter station 3 via the DC line and then converted into AC by converter station 3 for access to the power grid.

[0071] In the concentrating and collecting link of the solar thermal subsystem, the heliostats in the mirror field focus sunlight onto the collector surface, heating the heat transfer medium therein to achieve light-to-heat energy conversion.

[0072] The heat storage link is formed by connecting the hot tank, cold tank and collector, and the heat storage link stores / releases heat according to the power command of the power grid. In the power generation link, the hot molten salt pump drives the high-temperature medium into the heat exchanger, generating high-temperature and high-pressure steam to drive the steam turbine to do work, realizing heat-electricity energy conversion, and then connected to the DC system through the converter station 2.

[0073] like Figure 3As shown, when the power command of the power grid or the solar radiation intensity changes, the control state of the converter 3 determines whether the operation mode is the power tracking mode or the fluctuation smoothing mode. The converter 3 transmits a signal to the main controller to coordinately adjust the solar thermal subsystem and the photovoltaic subsystem to jointly respond to the change of the power command of the power grid. The photovoltaic subsystem maintains stability by adjusting system variables such as the output voltage, and the solar thermal subsystem ensures the stable regulation of the medium temperature at the collector outlet, the heat exchanger and the main steam pressure of the turbine. The coordinated control of the two ensures the safe and stable operation of the system and accurate response to the power grid command.

[0074] Step 2: When unbalanced power occurs in the photovoltaic subsystem, determine whether the unbalanced power exceeds the power setting value, and if so, proceed to step 3;

[0075] In the CSP-PV combined power generation system, when the predicted output of the PV subsystem is inconsistent with the actual output, the system will generate unbalanced power. Considering the characteristics of the PV and CSP subsystems, as well as the interaction with the power grid, a power regulation control strategy for the CSP-PV combined power generation system is proposed:

[0076] When the photovoltaic output fluctuation in the photovoltaic subsystem causes unbalanced power in the system, the central control system obtains the operating status of the combined power generation system. The central controller determines whether the power fluctuation of the photovoltaic subsystem exceeds the upper and lower power limits of 580-755MW of the grid-side converter station 3 for a continuous period of time based on the photovoltaic subsystem power prediction value. If it does not exceed the set power limit, it is a normal fluctuation. Under the constant DC voltage control mode of converter station 3, the system DC voltage remains stable, the converter station 2 on the solar thermal subsystem side maintains constant power operation, and the unbalanced power is output by converter station 3 to the grid side.

[0077] Step 3: Adjust the unbalanced power of the photovoltaic subsystem according to the size of the DC voltage of the photovoltaic subsystem; and set the operating state of the solar thermal subsystem according to the size of the DC voltage of the photovoltaic subsystem to complete the coordinated control.

[0078] If the unbalanced power of the photovoltaic subsystem exceeds the power limit set by the grid-side converter station 3, the converter station 3 switches from the fixed DC voltage control power tracking mode to the fluctuation smoothing mode. The central controller adjusts the output power of the photovoltaic subsystem according to the power fluctuation of the photovoltaic subsystem every minute. Its DC bus voltage varies with the size of the unbalanced power according to the preset fluctuation smoothing coefficient. When the DC voltage change exceeds the DC voltage margin range set by the converter station 2 on the solar thermal subsystem side, where the power upper and lower limits of the converter station 2 are 0-240MW, the converter station 2 switches from the power tracking control mode to the fluctuation smoothing mode. At this time, the system distributes the unbalanced power according to the unbalanced power allocation strategy and the fluctuation smoothing coefficients of the converter stations 2 and 3. The solar thermal energy storage power station adjusts the output according to the unbalanced power allocated by the system. If the system DC voltage increases, the output is reduced; otherwise, the output is increased.

[0079] When the solar thermal output adjustment in the solar thermal subsystem reaches the upper or lower limit, its operation mode is switched from the fluctuation smoothing mode to the current limiting mode. The solar thermal subsystem makes current limiting adjustments based on the degree of fluctuation and the reference values ​​of the heat exchanger medium valve opening and the turbine valve opening. When the system DC voltage increases, the solar thermal subsystem operates at maximum power. When the system DC voltage decreases, the solar thermal subsystem operates at minimum power, completing coordinated control.

[0080] Example 2

[0081] This embodiment provides a power coordination control strategy for a solar-thermal-photovoltaic combined power generation system. Figure 1-3 As shown, the specific implementation steps are as follows:

[0082] Step 1: Build the photovoltaic subsystem model, solar thermal subsystem model and control architecture;

[0083] The specific formula for building the photovoltaic subsystem model in step 1 is:

[0084] According to circuit theory and Shockloy diffusion theory, we can get:

[0085]

[0086] In the formula, I ph is the photocurrent, R s is the series internal resistance, R sh is the parallel bypass resistor, I pv is the output current of the photovoltaic cell, k is the Boltzmann constant, I o is the diode reverse saturation current, A is the diode factor, q is the unit charge constant, V is the photovoltaic cell operating voltage, and T is the photovoltaic cell operating temperature.

[0087] The specific construction of the solar thermal model in step 1 is as follows: In the construction of the solar thermal subsystem, the heliostats in the mirror field focus the sunlight onto the collector surface. Assuming that the heliostat control system can accurately track the solar altitude and azimuth, the solar radiation energy Q reflected by the mirror field inc (unit is J) as follows:

[0088] Q inc =η hf A hf I bn (2);

[0089] Where: A hf is the area of ​​the heliostat in the field, in m 2 ;I bn is the average radiation intensity incident on the heliostat, in W / m 2 ; η hf is the mirror field efficiency;

[0090] Secondly, the construction of the solar thermal subsystem model also includes the construction of the collector model, the heat exchanger model and the calculation of the energy storage capacity of the solar thermal subsystem.

[0091] The specific construction of the collector model is as follows: In the construction of the solar thermal subsystem, the core component of the solar thermal subsystem is the collector, which is composed of multiple tube bundle plates. Multiple heat absorbing tubes are connected in parallel in each tube bundle plate. The heat transfer medium flows through each tube bundle plate once according to the designed path, absorbing the heat reflected by the mirror field to the collector surface; the heat absorbing tube is divided into multiple pipe micro-elements of equal length, and the following assumptions are made: the heat transfer medium only flows along the radial direction of the heat absorbing tube; the heat absorbing surface of the heat absorbing tube is a semi-cylindrical surface, and is heated evenly; the wall surface temperature of a single pipe micro-element is consistent and the medium temperature in the tube is consistent, and the medium flow rate in each heat absorbing tube in the tube bundle plate is the same. According to the energy, mass and thermodynamic equations, the pipe micro-element model of the heat absorbing tube is constructed as follows:

[0092]

[0093] Q tra =h Am (T m -T s ) (4);

[0094]

[0095] Where: M m is the pipe element mass, in kg; C m is the specific heat capacity of the heat absorbing tube wall, C s is the average specific heat capacity, C si and C so are the specific heat capacities of the heat transfer medium flowing into and out of the microelement of the pipe, both in J / (kg·K); T mis the tube wall temperature, T s is the average temperature of the medium in the pipeline microelement, T in and T out are the temperatures of the heat transfer medium flowing into and out of the pipe microelement, both in K; Q a is the heat absorbed by the tube wall, Q loss is the heat loss, which is mainly composed of convection, radiation and reflection heat loss of the collector, Q tra is the heat absorbed by the heat transfer medium, the unit is J; h is the heat transfer coefficient; A m is the heat exchange area, in m 2 ;m sin and m sout are the medium flow rates flowing into and out of the micro-element of the pipe, in m 3 / S; is the average density of the heat transfer medium, in kg / m 3 ; V s is the volume of the pipe element, in m 3 .

[0096] Formulas (3) to (6) are linearized, and the surface temperature of the pipeline microelement, the medium temperature at the outlet of the pipeline microelement, and the medium flow rate at the outlet of the pipeline microelement are obtained through iterative calculation to complete the construction of the collector model.

[0097] The calculation of the energy storage capacity of the CSP subsystem is as follows: In the construction of the CSP subsystem, by configuring the heat storage link, the output power of the CSP subsystem is not limited by the current solar radiation intensity and can be adjusted according to the grid demand. The energy storage state of the CSP subsystem directly affects the active power adjustment range and adjustable margin of the system. The energy storage state variable S of the CSP subsystem is defined as SOE , specifically:

[0098] S SOE (t)=[M0+∫0 t (m in -m out )dt] / M ref (7);

[0099] Where: m in and m out are the heat transfer medium flow rates flowing into and out of the heat storage link, in kg / s; M0 is the initial heat transfer medium mass, in kg; M ref is the tank capacity in kg. in >m out When the heat storage link is in the heat storage state, the mass of the high-temperature medium in the heat storage link decreases, S SOE Decrease; when m in <m outWhen the heat storage link is in the heat release state, the mass of the high-temperature medium in the heat storage link increases, S SOE Increase.

[0100] The specific construction of the heat exchanger model is as follows: the solar thermal subsystem realizes heat-electricity energy conversion through the power generation link, and the heat exchanger is modeled. The solar thermal subsystem is usually equipped with a tubular heat exchanger, which consists of a preheating section, an evaporation section, and a superheating section. The high-temperature medium flows into the heat exchanger to exchange heat with water, generating high-temperature, high-pressure steam, which drives the steam turbine and generator to rotate and converts thermal energy into electrical energy. In order to ensure the safe and stable operation of the system, the steam generation system of the solar thermal subsystem usually works near the rated operating point. The lumped parameter method is used to establish the heat exchanger model as follows:

[0101]

[0102]

[0103] Where: s1 and s2 are lumped parameter variables; ρ m is the density of the steam-water mixture in the heat exchanger, in kg / m 3 ;h s and h fw are the enthalpy values ​​of steam and water respectively; v t is the water flow rate, in m / s; c a is the specific heat capacity of the heat exchanger tube wall, in J / (kg·K); M is the mass of the heat exchanger, in kg; T is the temperature of the heat exchanger tube wall, in K; h m is the enthalpy of the steam-water mixture before the steam-water separator; D s and d fw are the flow rates of steam and water respectively, in m 3 / s; Q is the heat absorbed by water during the heat exchange process, the unit is J.

[0104] The specific steps of building the control architecture in step 1 are: by constructing the photovoltaic subsystem and the solar thermal subsystem models, the control architecture is used for coordinated control. When the solar thermal subsystem model changes through the power grid power instruction or the solar radiation intensity, the control state of the converter 3 determines whether the operating mode is the power tracking mode or the fluctuation smoothing mode. The converter 3, the converter 2 and the converter 1 transmit signals to the central controller, and the central controller coordinates and adjusts the solar thermal subsystem and the photovoltaic subsystem models to jointly respond to the changes in the power grid power instruction.

[0105] Step 2: When unbalanced power occurs in the photovoltaic subsystem, determine whether the unbalanced power exceeds the power setting value, and if so, proceed to step 3;

[0106] The specific steps of step 2 are: when the photovoltaic output fluctuation in the photovoltaic subsystem causes unbalanced power in the system, the central controller obtains the current system operation status, and the central controller determines whether the power fluctuation of the photovoltaic subsystem exceeds the power lower limit of 580MW of the grid-side converter station 3 based on the photovoltaic subsystem power prediction value for a continuous period of time. If it does not exceed the set 580MW, it is a normal fluctuation. Under the constant DC voltage control mode of converter station 3, the system DC voltage remains stable, the converter station 2 on the solar thermal energy storage side maintains constant power operation, and the unbalanced power is output from the converter station 3 to the grid side. If it exceeds the set power limit, enter step 3.

[0107] Step 3: Adjust the unbalanced power of the photovoltaic subsystem according to the size of the DC voltage of the photovoltaic subsystem; and set the operating state of the solar thermal subsystem according to the size of the DC voltage of the photovoltaic subsystem to complete the coordinated control.

[0108] The specific steps of step 3 are: if the unbalanced power of the photovoltaic subsystem exceeds 580MW set by the grid-side converter station 3, the converter station 3 switches from the fixed DC voltage control power tracking mode to the fluctuation smoothing mode, and the central controller adjusts the output power of the photovoltaic subsystem according to the power fluctuation of the photovoltaic subsystem every minute. Its DC bus voltage varies with the size of the unbalanced power according to the preset fluctuation smoothing coefficient. When the DC voltage change exceeds the DC voltage margin range set by the converter station 2 on the solar thermal subsystem side, the converter station 2 switches from the power tracking control mode to the fluctuation smoothing mode. At this time, the system distributes the unbalanced power according to the unbalanced power distribution strategy and the fluctuation smoothing coefficients of the converter station 2 and the converter station 3. The solar thermal energy storage power station adjusts the output according to the unbalanced power distributed by the system. If the system DC voltage increases, the output is reduced; otherwise, the output is increased. When the solar thermal output adjustment in the solar thermal subsystem reaches the upper or lower limit, its operation mode is switched from the fluctuation smoothing mode to the current limiting mode. The solar thermal subsystem makes current limiting adjustments based on the degree of fluctuation and the reference values ​​of the heat exchanger medium valve opening and the turbine valve opening. When the system DC voltage increases, the solar thermal subsystem operates at maximum power. When the system DC voltage decreases, the solar thermal subsystem operates at minimum power, completing coordinated control.

[0109] Example 3

[0110] This embodiment provides a power coordination control strategy for a solar-thermal-photovoltaic combined power generation system. Figure 1-3 As shown, the specific implementation steps are as follows:

[0111] Step 1: Build the photovoltaic subsystem model, solar thermal subsystem model and control architecture;

[0112] The specific formula for building the photovoltaic subsystem model in step 1 is:

[0113] According to circuit theory and Shockloy diffusion theory, we can get:

[0114]

[0115] In the formula, I ph is the photocurrent, R s is the series internal resistance, R sh is the parallel bypass resistor, I pv is the output current of the photovoltaic cell, k is the Boltzmann constant, I o is the diode reverse saturation current, A is the diode factor, q is the unit charge constant, V is the photovoltaic cell operating voltage, and T is the photovoltaic cell operating temperature.

[0116] The specific construction of the solar thermal model in step 1 is as follows: In the construction of the solar thermal subsystem, the heliostats in the mirror field are used to focus sunlight onto the collector surface. Assuming that the heliostat control system can accurately track the solar altitude and azimuth, the solar radiation energy Q reflected by the mirror field is inc (unit is J) as follows:

[0117] Q inc =η hf A hf I bn (2);

[0118] Where: A hf is the area of ​​the heliostat in the field, in m 2 ;I bn is the average radiation intensity incident on the heliostat, in W / m 2 ; η hf is the mirror field efficiency;

[0119] Secondly, the construction of the solar thermal subsystem model also includes the construction of the collector model, the heat exchanger model and the calculation of the energy storage capacity of the solar thermal subsystem.

[0120] The specific construction of the collector model is as follows: In the construction of the solar thermal subsystem, the core component of the solar thermal subsystem is the collector, which is composed of multiple tube bundle plates. Multiple heat absorbing tubes are connected in parallel in each tube bundle plate. The heat transfer medium flows through each tube bundle plate once according to the designed path, absorbing the heat reflected by the mirror field to the collector surface; the heat absorbing tube is divided into multiple pipe micro-elements of equal length, and the following assumptions are made: the heat transfer medium only flows along the radial direction of the heat absorbing tube; the heat absorbing surface of the heat absorbing tube is a semi-cylindrical surface, and is heated evenly; the wall surface temperature of a single pipe micro-element is consistent and the medium temperature in the tube is consistent, and the medium flow rate in each heat absorbing tube in the tube bundle plate is the same. According to the energy, mass and thermodynamic equations, the pipe micro-element model of the heat absorbing tube is constructed as follows:

[0121]

[0122] Qtra =hA m (T m -T s ) (4);

[0123]

[0124] Where: M m is the pipe element mass, in kg; C m is the specific heat capacity of the heat absorbing tube wall, C s is the average specific heat capacity, C si and C so are the specific heat capacities of the heat transfer medium flowing into and out of the microelement of the pipe, both in J / (kg·K); T m is the tube wall temperature, T s is the average temperature of the medium in the pipeline microelement, T in and T out are the temperatures of the heat transfer medium flowing into and out of the pipe microelement, both in K; Q a is the heat absorbed by the tube wall, Q loss is the heat loss, which is mainly composed of convection, radiation and reflection heat loss of the collector, Q tra is the heat absorbed by the heat transfer medium, the unit is J; h is the heat transfer coefficient; A m is the heat exchange area, in m 2 ;m sin and m sout are the medium flow rates flowing into and out of the micro-element of the pipe, in m 3 / s; is the average density of the heat transfer medium, in kg / m 3 ; V s is the volume of the pipe element, in m 3 .

[0125] Formulas (3) to (6) are linearized, and the surface temperature of the pipeline microelement, the medium temperature at the outlet of the pipeline microelement, and the medium flow rate at the outlet of the pipeline microelement are obtained through iterative calculation to complete the construction of the collector model.

[0126] The calculation of the energy storage capacity of the CSP subsystem is as follows: In the construction of the CSP subsystem, by configuring the heat storage link, the output power of the CSP subsystem is not limited by the current solar radiation intensity and can be adjusted according to the grid demand. The energy storage state of the CSP subsystem directly affects the active power adjustment range and adjustable margin of the system. The energy storage state variable S of the CSP subsystem is defined as SOE , specifically:

[0127] S SOE (t)=[M0+∫0 t (m in -m out)dt] / M ref (7); (7);

[0128] Where: m in and m out are the heat transfer medium flow rates flowing into and out of the heat storage link, in kg / s; M0 is the initial heat transfer medium mass, in kg; M ref is the tank capacity in kg. in >m out When the heat storage link is in the heat storage state, the mass of the high-temperature medium in the heat storage link decreases, S SOE Decrease; when m in <m out When the heat storage link is in the heat release state, the mass of the high-temperature medium in the heat storage link increases, S SOE Increase.

[0129] The specific construction of the heat exchanger model is as follows: the solar thermal subsystem realizes heat-electricity energy conversion through the power generation link, and the heat exchanger is modeled. The solar thermal subsystem is usually equipped with a tubular heat exchanger, which consists of a preheating section, an evaporation section, and a superheating section. The high-temperature medium flows into the heat exchanger to exchange heat with water, generating high-temperature, high-pressure steam, which drives the steam turbine and generator to rotate and converts thermal energy into electrical energy. In order to ensure the safe and stable operation of the system, the steam generation system of the solar thermal subsystem usually works near the rated operating point. The lumped parameter method is used to establish the heat exchanger model as follows:

[0130]

[0131] Where: s1 and s2 are lumped parameter variables; ρ m is the density of the steam-water mixture in the heat exchanger, in kg / m 3 ;h s and h fw are the enthalpy values ​​of steam and water respectively; v t is the water flow rate, in m / s; c a is the specific heat capacity of the heat exchanger tube wall, in J / (kg·K); M is the mass of the heat exchanger, in kg; T is the temperature of the heat exchanger tube wall, in K; h m is the enthalpy of the steam-water mixture before the steam-water separator; D s and D fw are the flow rates of steam and water respectively, in m 3 / s; Q is the heat absorbed by water during the heat exchange process, the unit is J.

[0132] The specific steps of building the control architecture in step 1 are: by constructing the photovoltaic subsystem and the solar thermal subsystem models, the control architecture is used for coordinated control. When the solar thermal subsystem model changes through the power grid power instruction or the solar radiation intensity, the control state of the converter 3 determines whether the operating mode is the power tracking mode or the fluctuation smoothing mode. The converter 3, the converter 2 and the converter 1 transmit signals to the central controller, and the central controller coordinates and adjusts the solar thermal subsystem and the photovoltaic subsystem models to jointly respond to the changes in the power grid power instruction.

[0133] Step 2: When unbalanced power occurs in the photovoltaic subsystem, determine whether the unbalanced power exceeds the power setting value, and if so, proceed to step 3;

[0134] The specific steps of step 2 are: when the photovoltaic output fluctuation in the photovoltaic subsystem causes unbalanced power in the system, the central controller obtains the current system operation status, and the central controller determines whether the power fluctuation of the photovoltaic subsystem exceeds the power upper limit of 755MW of the grid-side converter station 3 based on the photovoltaic subsystem power prediction value for a continuous period of time. If it does not exceed the set 755MW, it is a normal fluctuation. Under the constant DC voltage control mode of converter station 3, the system DC voltage remains stable, the converter station 2 on the solar thermal energy storage side maintains constant power operation, and the unbalanced power is output from the converter station 3 to the grid side. If it exceeds the set power limit, enter step 3.

[0135] Step 3: Adjust the unbalanced power of the photovoltaic subsystem according to the size of the DC voltage of the photovoltaic subsystem; and set the operating state of the solar thermal subsystem according to the size of the DC voltage of the photovoltaic subsystem to complete the coordinated control.

[0136] The specific steps of step 3 are as follows: if the unbalanced power of the photovoltaic subsystem exceeds 755MW set by the grid-side converter station 3, the converter station 3 switches from the fixed DC voltage control power tracking mode to the fluctuation smoothing mode. The central controller adjusts the output power of the photovoltaic subsystem according to the power fluctuation of the photovoltaic subsystem every minute. Its DC bus voltage changes with the size of the unbalanced power according to the preset fluctuation smoothing coefficient. When the DC voltage change exceeds the DC voltage margin range set by the converter station 2 on the solar thermal subsystem side, the converter station 2 switches from the power tracking control mode to the fluctuation smoothing mode. At this time, the system follows the unbalanced power allocation strategy, combining the converter station 2 with the converter station 2. The fluctuation smoothing coefficient of station 3 distributes the unbalanced power. The solar thermal energy storage power station adjusts the output according to the unbalanced power distributed by the system. If the system DC voltage increases, the output is reduced; otherwise, the output is increased. When the solar thermal output adjustment reaches the upper or lower limit in the solar thermal subsystem, its operation mode is switched from the fluctuation smoothing mode to the current limiting mode. The solar thermal subsystem adjusts the current limiting according to the fluctuation degree and the reference value of the heat exchanger medium valve opening and the reference value of the turbine valve opening. When the system DC voltage increases, the solar thermal subsystem operates at the maximum power. When the system DC voltage decreases, the solar thermal subsystem operates at the minimum power to complete the coordinated control.

Claims

1. The power coordination control strategy of the solar-thermal-photovoltaic combined power generation system is characterized by: Follow the steps below to implement it: Step 1: Build the photovoltaic subsystem model, solar thermal subsystem model and control architecture; Step 2: When unbalanced power occurs in the photovoltaic subsystem, determine whether the unbalanced power exceeds the power setting value, and if so, proceed to step 3; Step 3: Adjust the unbalanced power of the photovoltaic subsystem according to the size of the DC voltage of the photovoltaic subsystem; and set the operating state of the solar thermal subsystem according to the size of the DC voltage of the photovoltaic subsystem to complete the coordinated control.

2. The power coordination control strategy of the solar-thermal-photovoltaic combined power generation system according to claim 1 is characterized in that: The specific formula for building the photovoltaic subsystem model in step 1 is: According to circuit theory and Shockloy diffusion theory, we can get: In the formula, I ph is the photocurrent, R s is the series internal resistance, R sh is the parallel bypass resistor, I pv is the output current of the photovoltaic cell, k is the Boltzmann constant, I o is the diode reverse saturation current, A is the diode factor, q is the unit charge constant, V is the photovoltaic cell operating voltage, and T is the photovoltaic cell operating temperature.

3. The power coordination control strategy of the solar-thermal-photovoltaic combined power generation system according to claim 1 is characterized in that: The construction of the photothermal model described in step 1 is specifically as follows: In the construction of the solar thermal subsystem, the heliostats in the field focus the sunlight onto the collector surface through the concentrating and collecting link of the collector field. Assuming that the heliostat control system can accurately track the altitude and azimuth of the sun, the solar radiation energy Q reflected by the field is inc (unit is J) as follows: Q inc =the hf A hf I bn (2); Where: A hf is the area of ​​the heliostat in the field, in m 2 ; I bn is the average radiation intensity incident on the heliostat, in W / m 2 ; η hf is the mirror field efficiency; Secondly, the construction of the solar thermal subsystem model also includes the construction of the collector model, the heat exchanger model and the calculation of the energy storage capacity of the solar thermal subsystem.

4. The power coordination control strategy of the solar-thermal-photovoltaic combined power generation system according to claim 3 is characterized in that: The collector model is specifically constructed as follows: In the construction of the solar thermal subsystem, the core component of the solar thermal subsystem is the collector, which is composed of multiple tube bundle plates. Multiple heat absorbing tubes are connected in parallel in each tube bundle plate. The heat transfer medium flows through each tube bundle plate once according to the designed path, absorbing the heat reflected by the mirror field to the collector surface; the heat absorbing tube is divided into multiple pipe micro-elements of equal length, and the following assumptions are made: the heat transfer medium only flows along the radial direction of the heat absorbing tube; the heat absorbing surface of the heat absorbing tube is a semi-cylindrical surface and is heated evenly; the wall surface temperature of a single pipe micro-element is consistent and the medium temperature in the tube is consistent, and the medium flow rate in each heat absorbing tube in the tube bundle plate is the same; according to the energy, mass and thermodynamic equations, the pipe micro-element model of the heat absorbing tube is constructed as follows: Q tra =hA m (T m -T s ) (4); Where: M m is the pipe element mass, in kg; C m is the specific heat capacity of the heat absorbing tube wall, C s is the average specific heat capacity, C si and C so are the specific heat capacities of the heat transfer medium flowing into and out of the microelement of the pipe, both in J / (kg·K); T m is the tube wall temperature, T s is the average temperature of the medium in the pipeline microelement, T in and T out are the temperatures of the heat transfer medium flowing into and out of the pipe microelement, both in K; Q a is the heat absorbed by the tube wall, Q loss is the heat loss, which is mainly composed of convection, radiation and reflection heat loss of the collector, Q tra The heat absorbed by the heat transfer medium, the unit is J; h is the heat transfer coefficient; A m is the heat exchange area, in m 2 ; m sin and m sout are the medium flow rates flowing into and out of the micro-element of the pipe, in m 3 / S; is the average density of the heat transfer medium, in kg / m 3 ; V s is the volume of the pipe element, in m 3 ; Formulas (3) to (6) are linearized, and the surface temperature of the pipeline microelement, the medium temperature at the outlet of the pipeline microelement, and the medium flow rate at the outlet of the pipeline microelement are obtained through iterative calculation to complete the construction of the collector model.

5. The power coordination control strategy of the solar-thermal-photovoltaic combined power generation system according to claim 3 is characterized in that: The calculation of the energy storage capacity of the photothermal subsystem is specifically as follows: In the construction of the CSP subsystem, by configuring the heat storage link, the output power of the CSP subsystem is not limited by the current solar radiation intensity and can be adjusted according to the grid demand. The energy storage state of the CSP subsystem directly affects the active power adjustment range and adjustable margin of the system. The energy storage state variable S of the CSP subsystem is defined as SOE , specifically: Where: m in and m out are the heat transfer medium flow rates flowing into and out of the heat storage link, in kg / s; M0 is the initial heat transfer medium mass, in kg; M ref is the tank capacity in kg, when m in >m out When the heat storage link is in the heat storage state, the mass of the high-temperature medium in the heat storage link decreases, S SOE Decrease; when m in <m out When the heat storage link is in the heat release state, the mass of the high-temperature medium in the heat storage link increases, S SOE Increase.

6. The power coordination control strategy of the solar-thermal-photovoltaic combined power generation system according to claim 3 is characterized in that: The construction of the heat exchanger model is specifically as follows: The solar thermal subsystem realizes heat-to-electricity energy conversion through the power generation link, and the heat exchanger is modeled. The solar thermal subsystem is usually equipped with a tubular heat exchanger, which consists of a preheating section, an evaporation section, and a superheating section. The high-temperature medium flows into the heat exchanger to exchange heat with water, generating high-temperature, high-pressure steam, which drives the steam turbine and generator to rotate and converts thermal energy into electrical energy. To ensure the safe and stable operation of the system, the steam generation system of the solar thermal subsystem usually operates near the rated operating point. The lumped parameter method is used to establish the heat exchanger model as follows: Where: s1 and s2 are lumped parameter variables; ρ m is the density of the steam-water mixture in the heat exchanger, in kg / m 3 ;h s and h fw are the enthalpy values ​​of steam and water respectively; v t is the water flow rate, in m / s; c a is the specific heat capacity of the heat exchanger tube wall, in J / (kg·K); M is the mass of the heat exchanger, in kg; T is the temperature of the heat exchanger tube wall, in K; h m is the enthalpy of the steam-water mixture before the steam-water separator; D s and D fw are the flow rates of steam and water respectively, in m 3 / s; Q is the heat absorbed by water during the heat exchange process, the unit is J.

7. The power coordination control strategy of the solar-thermal-photovoltaic combined power generation system according to claim 1 is characterized in that: The specific steps for building the control architecture described in step 1 are: By constructing photovoltaic subsystem and solar thermal subsystem models and adopting a control architecture for coordinated control, when the solar thermal subsystem model changes through the power grid power command or the solar radiation intensity, the control state of converter 3 determines whether the operating mode is power tracking mode or fluctuation smoothing mode, and converter 3, converter 2 and converter 1 transmit signals to the central controller, which coordinates the solar thermal subsystem and photovoltaic subsystem models to jointly respond to the change of the power grid power command through the central controller.

8. The power coordination control strategy of the solar-thermal-photovoltaic combined power generation system according to claim 1 is characterized in that: The specific steps of step 2 are: When the photovoltaic output fluctuation in the photovoltaic subsystem causes unbalanced power in the system, the central controller obtains the current system operation status, and determines whether the power fluctuation of the photovoltaic subsystem exceeds the upper and lower power limits of the power grid side converter station 3 based on the photovoltaic subsystem power prediction value for a continuous period of time. If it does not exceed the set power limit, it is a normal fluctuation. Under the constant DC voltage control mode of converter station 3, the system DC voltage remains stable, the converter station 2 on the solar thermal energy storage side maintains constant power operation, and the unbalanced power is output from the converter station 3 to the grid side. If it exceeds the set power limit, go to step 3.

9. The power coordination control strategy of the solar-thermal-photovoltaic combined power generation system according to claim 1, characterized in that: The specific steps of step 3 are as follows: if the unbalanced power of the photovoltaic subsystem exceeds the power limit set by the grid-side converter station 3, the converter station 3 switches from the fixed DC voltage control power tracking mode to the fluctuation smoothing mode, and the central controller adjusts the output power of the photovoltaic subsystem according to the power fluctuation of the photovoltaic subsystem every minute, and its DC bus voltage varies with the size of the unbalanced power according to the preset fluctuation smoothing coefficient. When the DC voltage change exceeds the DC voltage margin range set by the converter station 2 on the solar thermal subsystem side, the converter station 2 switches from the power tracking control mode to the fluctuation smoothing mode. At this time, the system distributes the unbalanced power according to the unbalanced power distribution strategy and the fluctuation smoothing coefficients of the converter station 2 and the converter station 3. The solar thermal energy storage power station adjusts the output according to the unbalanced power distributed by the system. If the system DC voltage increases, the output is reduced; On the contrary, the output will be increased; When the solar thermal output adjustment in the solar thermal subsystem reaches the upper or lower limit, its operation mode is switched from the fluctuation smoothing mode to the current limiting mode. The solar thermal subsystem makes current limiting adjustments based on the degree of fluctuation and the reference values ​​of the heat exchanger medium valve opening and the turbine valve opening. When the system DC voltage increases, the solar thermal subsystem operates at maximum power. When the system DC voltage decreases, the solar thermal subsystem operates at minimum power, completing coordinated control.

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