A water-solar-storage complementary power generation system based on pumped storage units and a control method

Abstract

The present invention discloses a model and control method of a water-photovoltaic-storage complementary power generation system based on a pumped-storage unit. The photovoltaic power generation system converts light energy into electrical energy, the electrochemical energy storage system is used to stabilize voltage and smooth photovoltaic fluctuations, and the pumped-storage system converts water potential energy into electrical energy. The total electrical energy is finally delivered to the AC bus. The control system monitors the power transmission on the AC bus and the original planned power generation demand, and uses a bidirectional AC-DC-AC controller to control the pumped-storage system. This application reduces the impact of photovoltaic power generation on the distribution network system, improves power supply reliability and improves power quality by controlling the pumped-storage system and the electrochemical energy storage system, thereby improving the relative stability of the frequency of the water-photovoltaic-storage complementary power generation system.

Description

Technical Field

[0001] The present invention belongs to the technical field of multi-energy complementary power generation, and specifically relates to a water-photovoltaic-storage complementary power generation system based on a pumped storage unit and a control method. Background Art

[0002] As social production gradually transforms and upgrades, the proportion of electricity consumption in the tertiary industry has increased year by year. In addition to the contradiction of electricity consumption, the contradiction of electricity consumption has also become a top priority to ensure the safety and stability of the power system. The establishment of a large-capacity energy storage system can provide sufficient active support and certain peak-shaving and frequency regulation capabilities for the power grid. Currently, commonly used energy storage methods include battery (capacitor) energy storage, mechanical energy storage, and gravitational potential energy storage. Among them, the hydropower station using gravitational potential energy storage is more mature and widely used in the power system. However, conventional pumped storage units will operate at a constant speed with the highest overall efficiency, and cannot participate in the automatic adjustment of the system frequency, and there is no way to actively adapt to changes in power demand.

[0003] Solar energy itself has certain limitations. Uncontrollable weather changes, temperature fluctuations, and cloud cover cause photovoltaic power generation and output power to fluctuate greatly. The actual operation is a nonlinear random fluctuation output process, resulting in a considerable portion of its output electricity being wasted. The combined energy storage system can effectively overcome the negative impact of the randomness and volatility of photovoltaic power generation. Summary of the invention

[0004] The purpose of the present invention is to provide a water-solar-storage complementary power generation system and control method based on a pumped-storage unit, which converts excess solar energy into water potential energy for storage, and then converts the potential energy into electrical energy to supply the power system when the load of the power system reaches a peak, thereby making full use of solar energy resources, changing the energy structure, alleviating the contradiction between power generation and production and domestic water use to a certain extent, and improving the quality of electricity, ensuring stable, safe and reliable operation of the power grid.

[0005] To achieve the above object, the present invention adopts the following technical solution:

[0006] The present invention first provides a water-solar-storage complementary power generation system based on a pumped storage unit, the system comprising:

[0007] The DC bus is used to gather DC power and output it to the grid-connected output system;

[0008] A photovoltaic power generation system, connected to the DC bus, for converting light energy into first electrical energy and transmitting the first electrical energy to the DC bus;

[0009] An electrochemical energy storage system is connected to the DC bus and adjusts the DC output size of the entire system by controlling the size of the second electrical energy output or input;

[0010] The grid-connected output system is used to convert DC input into AC output, and is connected to the AC bus together with the AC input to output electrical energy to the outside;

[0011] A pumped storage power station is connected to the grid-connected output system and is used to convert the potential energy of water into a third electric energy, and transmit the third electric energy to the grid-connected output system; at the same time, the pumped storage power station can also obtain electric energy from the grid-connected output system and convert it into the potential energy of water for storage;

[0012] The control device A has a PQ control mode and a grid-connected / island switch control mode, is connected to the photovoltaic power generation system, the electrochemical energy storage system and the grid-connected output system, and is used to detect the DC output size on the DC bus and issue instructions to control the working status of the photovoltaic power generation system and the electrochemical energy storage system.

[0013] As a preferred embodiment of the present invention, the photovoltaic power generation system specifically comprises: a photovoltaic array, a DC combiner box and a DC distribution cabinet;

[0014] As a preferred embodiment of the present invention, the photovoltaic array converts solar energy into direct current and conducts multi-level convergence through the direct current combiner box and direct current distribution cabinet, and finally all direct current energy is collected into the direct current bus.

[0015] As a preferred embodiment of the present invention, the electrochemical energy storage system specifically comprises:

[0016] Batteries, used to store or release part of the DC power;

[0017] Supercapacitors, used to store or release some DC power;

[0018] The DC-DC converter is used to control the charging and discharging of the DC bus to achieve the bidirectional flow of electric energy and is of non-isolated type.

[0019] As a preferred embodiment of the present invention, the electrochemical energy storage system is configured as a hybrid energy storage system of supercapacitors and batteries, which is used to solve the problems of voltage sag and voltage drop in microgrids and improve the power quality of microgrids. The hybrid energy storage system of supercapacitors and batteries organically combines the two energy storage devices, integrates the advantages of the two energy storage methods, makes up for the shortcomings of the two energy storage technologies, and improves the performance of the energy storage system.

[0020] As a preferred embodiment of the present invention, the second electric energy transmitted in the battery and supercapacitor is adjusted to the charging and discharging state and the amount of electric energy under the action of the control device A, so as to stabilize or smooth the output power of photovoltaic power generation, store and output energy for a short time, and achieve the purpose of "peak shaving and valley filling" in a small range of the DC output part.

[0021] As a preferred embodiment of the present invention, the pumped storage system specifically comprises:

[0022] The upper and lower pools are connected by water pipes and are used to store water;

[0023] A reversible water pump turbine is arranged on the water delivery pipeline to provide power for water delivery;

[0024] A generator motor connected to the reversible pump turbine can be used as both a generator and a motor;

[0025] An AC-DC-AC converter connected to the generator motor for bidirectional transmission of electrical energy;

[0026] The control device B is connected to the above-mentioned reversible pump-turbine and AC-DC-AC converter, and is used to adjust the operating conditions of the generator motor and the reversible pump-turbine according to the instructions of the external central control host and the working state of the AC-DC-AC converter.

[0027] As a preferred embodiment of the present invention, the control strategy of the pumped storage power station adopts a variable frequency AC excitation speed regulation system.

[0028] As a preferred embodiment of the present invention, the generator motor adopts a variable speed pumped storage unit, and the generator motor passes through a three-phase excitation current. By controlling the speed and water flow, the output power of the pumped storage power station is accurately controlled; the generator motor adopts a full-power bidirectional variable-current type continuous speed control method to ensure that the input and output power of the pumped storage power station are continuously adjustable. When the stator winding in the generator motor 14 passes through a three-phase excitation current, a rotating magnetic field can be generated even if the rotor is mechanically stationary. This means that the mechanical speed plus the AC frequency is equal to the synchronous speed of the power grid. The mechanical speed is independent of the excitation current frequency and is the result of the energy balance of the entire generator motor and the reversible pump turbine output. When the turbine output is greater than the generator output, the speed will increase, and the generator output can be controlled by the excitation system. The excitation system can continuously control the excitation current frequency to balance the difference between the stator voltage frequency and the mechanical speed. The control device B can not only control the active and reactive power, but also control the speed of the unit. Under each working condition, the optimal value is obtained by the control device B to control it.

[0029] As a preferred embodiment of the present invention, the reversible pump turbine adopts a mixed flow turbine, which mainly includes: a volute, a seat ring, a guide vane, a runner, and a tailwater pipe; the guide vane can change its position to adjust the water flow rate of pumping or releasing water.

[0030] As a preferred embodiment of the present invention, the control device B has a power smoothing mode, which smoothes the output fluctuation of the photovoltaic power generation system by controlling the output power of the pumped storage power station, and mainly adopts a power smoothing strategy based on a first-order low-pass filter algorithm. As a preferred embodiment of the present invention, the grid-connected output system includes:

[0031] AC bus, used to collect, distribute and transmit electrical energy;

[0032] A transformer substation, connected to the AC bus, and used to convert part of the AC power of the AC bus into different voltage levels for external transmission;

[0033] The AC load is connected to the AC bus and is an electrical load having a voltage level equivalent to that of the AC bus.

[0034] The DC-AC converter is connected to the control device A, the DC bus, the AC bus and the control device B, and is used to convert the DC power input by the DC bus into AC power, and at the same time feed back the real-time total output of the DC power during the conversion process to the control device A; and feed back the real-time total output of the AC power during the conversion process to the control device B.

[0035] As a preferred embodiment of the invention, the frequency of the AC bus is 50 Hz and the voltage level is 10 kV.

[0036] As a preferred embodiment of the invention, the water-photovoltaic-storage complementary power generation system based on the pumped storage unit controls the entire water-photovoltaic-storage complementary power generation system through the control device A and the control device B;

[0037] The present invention also provides a control method for the water-photovoltaic-storage complementary power generation system based on the pumped storage unit, the control method is:

[0038] The control device A has a PQ control mode and a grid-connected / islanded switch control mode. Since the photovoltaic system adopts PQ control in both grid-connected operation and islanded operation, only the grid-connected / islanded switch control of the electrochemical energy storage system is considered; the three-phase voltage deviation value allowed for a power grid of 10kV and below is 7% of the rated voltage, and the allowable frequency deviation is 0.2Hz. When it is detected that the line frequency or voltage exceeds the allowable range, the system switches to the island mode; when the line frequency or voltage returns to the normal range, the photovoltaic power generation system and the electrochemical energy storage system are reconnected to the grid;

[0039] When the first electric energy output is less than the expected output value of the central control host or the first electric energy fluctuates for a short time due to instability, the control device A controls the electrochemical energy storage system to release the second electric energy so that the entire DC output reaches a predetermined value and smoothes the voltage fluctuation and frequency fluctuation;

[0040] The control device B collects the power output on the AC bus and the demand issued by the external central control host, and then adjusts the state of the generator motor and the reversible pump turbine according to the collected power on the AC bus and the demand issued by the external central control host:

[0041] When the power output on the AC bus is less than the demand, the control device B issues a power generation command to transport the water in the upper water tank to the lower water tank through the reversible pump turbine, converting the potential energy of the water into electrical energy to increase the AC output of the AC bus;

[0042] When the power output on the AC bus is greater than the demand, the control device B issues an energy storage instruction to transport the water in the lower water tank to the upper water tank through the reversible pump turbine, converting the excess power into the potential energy of the water.

[0043] The beneficial effects of the present invention are:

[0044] (1) The present invention connects a storage system with fast response speed, high reliability and large storage capacity to the photovoltaic power generation system. The energy storage device is connected to the power grid in conjunction with the new energy system, breaking through the bottleneck limitation of long-distance power transmission and realizing local energy consumption. In conjunction with the system load forecast and photovoltaic output forecast, the photovoltaic power generation power is controllably intervened. Pumped storage is performed at the peak of photovoltaic power generation output. When the load of the power system is at its peak, the power station releases water to generate electricity, effectively reducing the impact of the joint operation system on the power grid.

[0045] (2) The pumped storage power station part of the complementary power generation system proposed in the present invention uses a variable speed AC excitation pumped storage unit, which can better adapt to the two operating conditions of power generation and pumping by changing the speed, so that the operating efficiency of the turbine and the water pump is improved, and it can also adapt to a wider range of water head amplitude and power. At the same time, it can also adjust the phase and frequency of the rotor AC excitation current to achieve high-speed (tens of milliseconds) regulation of active power.

[0046] (3) In view of the fact that photovoltaic power generation is easily affected by factors such as light intensity, ambient temperature, and cloud cover, the present invention proposes a solution for connecting energy storage batteries to the DC bus side of a photovoltaic power station. By utilizing the fast charge and discharge response of electrochemical energy storage, the photovoltaic power generation output can be stabilized and smoothed. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] The drawings in the specification, which constitute a part of the present application, are used to provide further understanding of the present application. The illustrative embodiments of the present application and their descriptions are used to explain the present application and do not constitute improper limitations on the present application.

[0048] Figure 1 It is a schematic diagram of a water-photovoltaic-storage complementary power generation system model and a control method based on a pumped storage unit of the present invention;

[0049] In the figure: 1. Photovoltaic power generation system; 2. Grid-connected output system; 3. Pumped-storage power station; 4. Electrochemical energy storage system; 5. DC bus; 6. Photovoltaic array; 7. DC combiner box; 8. DC distribution cabinet; 9. DC-DC converter; 10. Battery; 11. Supercapacitor; 12. Control device B; 13. AC-DC-AC converter; 14. Generator motor; 15. Upper water tank; 16. Lower water tank; 17. Control device A; 18. DC-AC converter; 19. Substation; 20. AC load; 21. Reversible pump turbine; 22. AC bus. DETAILED DESCRIPTION

[0050] The present invention is described in detail below in conjunction with the accompanying drawings. The following embodiments or drawings are used to illustrate the present invention, but are not used to limit the scope of the present invention.

[0051] The present invention provides a water-solar-storage complementary power generation system model and control method based on a pumped storage unit. Figure 1 The water-photovoltaic-storage complementary power generation system comprises: a photovoltaic power generation system 1, a grid-connected output system 2, a pumped storage power station 3, an electrochemical energy storage system 4, a DC bus 5, and a control device A17.

[0052] The photovoltaic power generation system 1 adopts the maximum power tracking principle to work with the highest light utilization efficiency. First, the photovoltaic array absorbs solar energy and converts it into direct current. Then the direct current is multi-stage converged by the DC combiner box 7 and the DC distribution cabinet 8 to convert the solar energy into the first electrical energy and transmit it to the DC bus 5.

[0053] The electrochemical energy storage system 4 controls the size of the second electrical energy output or input to adjust the DC output size of the entire system.

[0054] The DC bus 5 is used to gather DC power and transmit it to the grid-connected output system.

[0055] The control device A has a PQ control mode and a grid-connected / island switch control mode, is connected to the photovoltaic power generation system, the electrochemical energy storage system and the grid-connected output system, and is used to detect the DC output size on the DC bus and issue instructions to control the working status of the photovoltaic power generation system and the electrochemical energy storage system.

[0056] The electrochemical energy storage system 4 is composed of a battery 10 and a supercapacitor 11 to store and release direct current. The battery can solve the short-term problems of voltage fluctuation and insufficient power supply caused by the volatility and instability of solar energy during photovoltaic power generation, and also uses the battery to assist the supercapacitor 11. However, the charging voltage of the battery cannot be too high, requiring the charger to have voltage stabilization and voltage limiting functions. Its charging current cannot be too large, requiring the charger to have current stabilization and current limiting functions, so its charging circuit is also relatively complex. The charging time is long, and the number of charge and discharge times is only hundreds of times, which limits the service life and high maintenance costs. Supercapacitors refer to porous media made of special materials. Compared with ordinary capacitors, they have higher dielectric constants, greater pressure resistance and energy storage capacity, and have the advantage of fast energy release of capacitors. The hybrid energy storage system of supercapacitors and batteries organically combines the two energy storage devices, integrates the advantages of the two energy storage methods, makes up for the shortcomings of the two energy storage technologies, and improves the performance of the energy storage system. Then, the second electric energy transmitted in the battery and supercapacitor is adjusted to the charging and discharging state and the amount of electric energy under the action of the control device A, so as to stabilize or smooth the output power of photovoltaic power generation, store and output energy in a short time, and achieve "peak shaving and valley filling" in a small range of the DC output part.

[0057] The control device A17 is connected to the grid-connected output system, the photovoltaic power generation system and the electrochemical energy storage system, and controls the transmission direction and size of the second electric energy of the electrochemical energy storage system according to the relationship between the output in the DC bus and the total DC output demand issued by the external central control host.

[0058] The control device A 17 has a PQ control mode and a grid-connected / island switch control mode. Since the photovoltaic system adopts PQ control in both grid-connected operation and island operation, only the grid-connected / island switch control of the battery energy storage system is considered; the three-phase voltage deviation value allowed by the 10kV and below power grid is 7% of the rated voltage, and the allowable frequency deviation is 0.2Hz. When it is detected that the line frequency or voltage exceeds the allowable range, the system switches to the island; when the line frequency or voltage returns to the normal range, the photovoltaic power generation system and the electrochemical energy storage system are re-connected to the grid.

[0059] In the grid-connected mode, the control structure of the power outer loop and the current inner loop is adopted. The power outer loop needs to collect the grid voltage U and grid current I in real time, and then calculate the instantaneous power measurement value. Divide the difference between them and the given active power P and reactive power Q by the given voltage U sd, get the given values ​​id and iq of the inner loop, get the current id and iq through the change of dq coordinates, and control the inverter through the PI link and feedforward decoupling link. After the coordinates of voltage and current are inverted and transformed with the SPWM modulation module, the driving signal of the IGBT is obtained, thereby ensuring that the inverter outputs power to the grid at a given power value.

[0060] In island mode, the voltage and frequency of the photovoltaic power generation system and the electrochemical energy storage system are required to be stable. V / f control is mainly adopted, using a double closed-loop structure of voltage outer loop and current inner loop. The PI controller adjusts the difference between the ud and uq values ​​obtained by measuring the load side voltage through coordinate changes to obtain the reference values ​​of the capacitor current in the d-axis and q-axis respectively. Finally, the reference voltage component in the inverter inner axis coordinate system is obtained through the PI controller and the feedforward decoupling link to realize the control of the inverter.

[0061] When the first electric energy output is less than the expected output value of the central control host or the first electric energy fluctuates for a short time due to instability, the control device A will control the electrochemical energy storage system to release the second electric energy so that the entire DC output reaches a predetermined value and smoothes voltage fluctuations and frequency fluctuations.

[0062] The pumped-storage power station 3 comprises an upper water tank and a lower water tank connected by a water pipeline, a reversible pump-turbine arranged on the water pipeline, a generator motor connected to the reversible pump-turbine, an AC-DC-AC converter connected to the generator motor and used for bidirectional transmission of electric energy, and a control device B connected to the reversible pump-turbine and the AC-DC-AC converter; the pumped-storage power station is connected to the grid-connected output system, and is used to convert the potential energy of water into a third electric energy, and transmit the third electric energy to the grid-connected output system; at the same time, the pumped-storage power station can also obtain electric energy from the grid-connected output system and convert it into the potential energy of water for storage.

[0063] The control device B is connected to the AC-DC-AC converter and the reversible pump turbine respectively, and is responsible for the detection and control of the AC output of the entire pumped storage power station.

[0064] The generator motor 14 adopts a variable speed pumped storage unit, which can accurately control the system output power by controlling the speed and water flow. It adopts a full-power bidirectional variable-current type continuous speed control method to ensure that the input and output power of the pumped storage power station are continuously adjustable. The variable speed AC excitation generator motor unit can adjust the speed by changing the excitation frequency, and can automatically perform automatic frequency control, instantaneous active power and reactive power adjustment in power generation conditions. In this way, when the load changes suddenly, the speed of the motor is changed quickly, the kinetic energy of the rotor is fully utilized, the load is released and absorbed, and the disturbance to the power system is much smaller than that of conventional motors.

[0065] The generator motor 14 is connected to the reversible pump turbine 21 to provide power for the reversible pump turbine.

[0066] The reversible pump turbine 21 is arranged on the pipeline connecting the upper water tank 15 and the lower water tank 16. The pump turbine takes into account both the working conditions of the water pump and the water turbine, and has the characteristics of high head and frequent conversion of the unit operating conditions. The reversible pump turbine adopts a mixed flow turbine, which mainly includes: a volute, a seat ring, a guide vane, a runner, and a tailwater pipe. The guide vane can change its position to adjust the water flow of pumping or releasing water.

[0067] The control device B collects the power output on the AC bus and the demand issued by the external central control host, and then adjusts the status of the generator motor and the reversible pump turbine according to the collected power on the AC bus and the demand issued by the external central control host.

[0068] When the power output on the AC bus is less than the demand, the control device B issues a power generation command, and the control device B12 controls the generator motor 14 through the AC-DC-AC converter 13, so that the generator motor works in the generator mode, and the water in the upper water tank is transported to the lower water tank through the reversible pump turbine, and the potential energy of the water is converted into electrical energy to increase the AC output of the AC bus;

[0069] When the electric energy output on the AC bus is greater than the demand, the control device B issues an energy storage instruction, and the control device B12 controls the generator motor 14 through the AC-DC-AC converter 13, so that the generator motor works in the motor mode, and the water in the lower water tank is transported to the upper water tank through the reversible pump turbine, thereby converting the excess electric energy into the potential energy of the water.

[0070] The control device B has another working mode: power smoothing mode. In this mode, the output power of the pumped storage power station is controlled to smooth the fluctuation of photovoltaic output, so that the bundled output of the combined system can meet the requirements of the active power change rate of the power grid. This embodiment adopts a power smoothing strategy based on a first-order low-pass filtering algorithm.

[0071] When the stator winding in the generator motor 14 is passed through a three-phase excitation current, a rotating magnetic field can be generated even when the rotor is mechanically stationary. If the percentages of the mechanical speed, stator voltage frequency, and excitation current frequency are defined as K m , K1, K2, we can give the equation: K m+K2=K1. This means that the mechanical speed plus the AC frequency equals the grid synchronous speed. The mechanical speed is independent of the excitation current frequency and is the result of the energy balance of the entire generator motor and reversible pump turbine output. When the turbine output is greater than the generator output, the speed will increase, and the generator output can be controlled by the excitation system. The excitation system can continuously control the excitation current frequency to balance K1 and K m The control device B can not only control the active and reactive power, but also control the unit speed. Under each working condition, the optimal value is obtained by the control device B to control it.

[0072] The grid-connected output system 2 includes a DC-AC transformer for converting DC input into AC output, an AC bus for collecting, distributing and transmitting electric energy, a transformer substation for converting the AC power transmitted by the AC bus into different voltage levels for external transmission, and an AC load connected to the AC bus. The frequency of the AC bus is 50Hz and the voltage level is 10kV. The DC-AC transformer is connected to the control device A, the DC bus, the AC bus and the control device B, and is used to convert the DC power input by the DC bus into AC power, and at the same time feed back the total real-time output of the DC power during the conversion process to the control device A; and feed back the total real-time output of the AC power during the conversion process to the control device B.

[0073] The principles and implementation methods of the present invention are described in this article using specific examples. The description of the above embodiments is only used to help understand the method and core idea of ​​the present invention. At the same time, for those skilled in the art, according to the idea of ​​the present invention, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting the present invention.

Claims

1. A control method for a water-photovoltaic-storage complementary power generation system based on a pumped storage unit, characterized in that: The water-photovoltaic-storage complementary power generation system comprises: The grid-connected output system is used to convert the DC input electric energy into AC output electric energy and output the electric energy together with the AC input electric energy; The DC bus is used to gather DC power and output it to the grid-connected output system; A photovoltaic power generation system, connected to the DC bus, for converting light energy into first electrical energy and transmitting the first electrical energy to the DC bus; An electrochemical energy storage system is connected to the DC bus and adjusts the DC output size of the entire system by controlling the size of the second electrical energy output or input; A pumped storage power station, comprising an upper water tank and a lower water tank connected by a water pipeline, a reversible pump turbine arranged on the water pipeline, a generator motor connected to the reversible pump turbine, an AC-DC-AC converter connected to the generator motor and used for bidirectional transmission of electric energy, and a control device B connected to the reversible pump turbine and the AC-DC-AC converter; the pumped storage power station is connected to the grid-connected output system, and is used to convert the potential energy of water into a third electric energy, and transmit the third electric energy to the grid-connected output system; at the same time, the pumped storage power station can also obtain electric energy from the grid-connected output system and convert it into the potential energy of water for storage; The pumped storage power station adopts variable frequency AC excitation speed regulation; the generator motor adopts a variable speed pumped storage unit; the generator motor passes through a three-phase excitation current, and the output power of the pumped storage power station is accurately controlled by controlling the rotation speed and water flow; the generator motor adopts a full-power bidirectional variable current type continuous speed regulation method to ensure that the input and output power of the pumped storage power station are continuously adjustable; when the stator winding in the generator motor passes through a three-phase excitation current, a rotating magnetic field can be generated even if the rotor is mechanically stationary; A control device A has a PQ control mode and a grid-connected / island switch control mode, is connected to the photovoltaic power generation system, the electrochemical energy storage system and the grid-connected output system, and is used to detect the DC output size on the DC bus and issue instructions to control the working status of the photovoltaic power generation system and the electrochemical energy storage system; The control method comprises: The control device A has a PQ control mode and a grid-connected / islanded switch control mode. Since the photovoltaic system adopts PQ control in both grid-connected and islanded operation, only the grid-connected / islanded switch control of the electrochemical energy storage system is considered; the three-phase voltage deviation value allowed for a power grid of 10kV and below is 7% of the rated voltage, and the allowable frequency deviation is 0.2Hz; when it is detected that the line frequency or voltage exceeds the allowable range, the system switches to the island; when the line frequency or voltage returns to the normal range, the photovoltaic power generation system and the electrochemical energy storage system are reconnected to the grid; When the first electric energy output is less than the expected output value of the central control host or the first electric energy fluctuates for a short time due to instability, the control device A controls the electrochemical energy storage system to release the second electric energy so that the entire DC output reaches a predetermined value and smoothes the voltage fluctuation and frequency fluctuation; The control device B collects the power output on the AC bus and the demand issued by the external central control host, and then adjusts the state of the generator motor and the reversible pump turbine according to the collected power on the AC bus and the demand issued by the external central control host; When the power output on the AC bus is less than the demand, the control device B issues a power generation command to transport the water in the upper water tank to the lower water tank through the reversible pump turbine, converting the potential energy of the water into electrical energy to increase the AC output of the AC bus; When the power output on the AC bus is greater than the demand, the control device B issues an energy storage instruction to transport the water in the lower water tank to the upper water tank through the reversible pump turbine, converting the excess power into the potential energy of the water.

2. The control method according to claim 1, characterized in that: The photovoltaic power generation system comprises a photovoltaic array, a DC combiner box and a DC distribution cabinet; The photovoltaic array is directly connected to the DC combiner box, and the DC combiner box is connected to the DC distribution cabinet; The photovoltaic array converts solar energy into direct current and conducts multi-level convergence through the direct current combiner box and direct current distribution cabinet, and finally all direct current energy is collected into the direct current bus.

3. The control method according to claim 1, characterized in that: The electrochemical energy storage system comprises: Batteries, used to store or release part of the DC power; Supercapacitors, used to store or release some DC power; The DC-DC converter is used to control the charging and discharging of the DC bus to achieve the bidirectional flow of electric energy and is of non-isolated type.

4. The control method according to claim 3, characterized in that The second electric energy transmitted in the battery and supercapacitor is adjusted to the charging and discharging state and the electric energy size under the action of the control device A, so as to stabilize or smooth the photovoltaic power output power, store and output energy in a short time, and achieve the purpose of "peak shaving and valley filling" in a small range of the DC output part.

5. The control method according to claim 1, characterized in that: The control device B is used to adjust the operating conditions of the generator motor and the reversible pump turbine according to the instructions of the external central control host and the working state of the AC-DC-AC converter.

6. The control method according to claim 1, characterized in that: The reversible pump turbine adopts a mixed flow turbine, including: a volute, a seat ring, a guide vane, a runner, and a tailwater pipe; the guide vane can change position to adjust the water flow rate of pumping or releasing water.

7. The control method according to claim 1, characterized in that: The grid-connected output system comprises: AC bus, used to collect, distribute and transmit electrical energy; A transformer substation, connected to the AC bus, and used to convert part of the AC power of the AC bus into different voltage levels for external transmission; AC load, directly connected to the AC bus, is an electrical device with a voltage level equivalent to that of the AC bus; The DC-AC converter is connected to the control device A, the DC bus, the AC bus and the control device B, and is used to convert the DC power input by the DC bus into AC power, and at the same time feed back the real-time total output of the DC power during the conversion process to the control device A; and feed back the real-time total output of the AC power during the conversion process to the control device B.

8. The control method according to claim 7, characterized in that: The frequency of the AC bus is 50 Hz and the voltage level is 10 kV.

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