A coordinated control method for compensating water hammer effect of water turbine in large-scale photovoltaic power station

Abstract

The present application relates to a kind of scale photovoltaic power station compensation water turbine water hammer effect synergic control method.First, the frequency variation Δf is calculated, whether the power grid frequency fluctuation exceeds the judgment of hydroelectric frequency modulation dead zone;Judgment whether water hammer effect appears to water turbine, the power reference value of compensation water turbine water hammer effect caused by appearing water hammer effect is calculated;Then detect whether photovoltaic-energy storage system exports active power, controller opens when water hammer effect appears to water turbine, and photovoltaic-energy storage system compensates water hammer effect of water turbine;Again, the operating mode of photovoltaic power generation system is detected, and the output power of photovoltaic-energy storage system is adjusted according to the operating state of photovoltaic power generation system.The present application can improve the negative damping effect of hydroelectric generating set, effectively inhibit the system ultra-low frequency oscillation caused by water hammer effect of hydroelectric generating set, and according to the power counter-adjustment caused by water hammer effect, the load reduction rate of photovoltaic power generation system is dynamically adjusted, the number of times of charging and discharging of energy storage battery is reduced, and the battery life is improved.

Description

Technical Field

[0001] This invention relates to the field of power system stability control technology, and in particular to a collaborative control method for compensating for the water hammer effect of turbines in large-scale photovoltaic power plants. Background Technology

[0002] In Southwest my country's power grid, due to the small operating capacity of thermal power plants, frequency regulation is mainly based on hydropower. However, during frequency regulation, the water hammer effect from the turbines often causes frequency oscillations, exhibiting a reverse regulation effect in the initial stage of regulation, posing a safety hazard to the power grid. The parameter settings of the turbine governor and water inertia are the main reasons for the water hammer effect, with water inertia causing changes in turbine flow rate to lag behind changes in turbine gate opening. Based on these reasons, the participation of renewable energy power plants in frequency regulation is considered to mitigate the impact of the water hammer effect during hydropower participation. With the increasing penetration rate of photovoltaics, centralized photovoltaic power plants are becoming increasingly large-scale. However, conventional photovoltaic systems mostly use maximum power point tracking (MPPT) for control. Grid-connected inverters have fast response speeds and almost no rotational inertia, making it difficult for them to participate in grid regulation. They cannot provide the necessary voltage and frequency for active distribution networks containing large-scale photovoltaic power plants, nor can they provide the necessary damping for grids with relatively poor stability. To solve these problems and provide the necessary rotational inertia for the system, virtual synchronous machine technology has emerged. Through virtual inertia control, the virtual synchronous machine can simultaneously provide virtual inertia and virtual damping for the system. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide a collaborative control method for compensating for the water hammer effect of water turbines in large-scale photovoltaic power plants, so as to solve the problem of ultra-low frequency oscillation of the system caused by the water hammer effect of water turbines.

[0004] The technical solution of this invention is: a collaborative control method for compensating for water hammer effect in turbines in large-scale photovoltaic power plants, the specific steps of which are as follows:

[0005] Step 1: Calculate the change in grid frequency Δf, and determine whether the change in grid frequency Δf exceeds the dead zone of hydropower frequency regulation; determine whether the turbine is experiencing water hammer effect, and calculate the reference value for power reversal caused by water hammer effect when water hammer effect occurs;

[0006] Step 2: Detect whether the photovoltaic-energy storage system outputs active power. The controller turns on when the water turbine experiences water hammer effect, and the photovoltaic-energy storage system compensates for the water turbine's water hammer effect.

[0007] Step 3: Detect the operating mode of the photovoltaic power generation system and adjust the output power of the photovoltaic-energy storage system according to the operating status of the photovoltaic power generation system.

[0008] Furthermore, Step 1 specifically includes:

[0009] Step 1.1 Monitor the power grid frequency f in real time and determine whether the change in power grid frequency Δf exceeds the hydropower frequency regulation dead zone of 0.05Hz;

[0010] Step 1.2 Calculate the turbine angular velocity offset and mechanical power offset ,according to and Identifying phase hysteresis caused by water hammer effect: and When the signs are the same, the response of a typical hydraulic unit is opposite to the desired control, and water hammer effect exists; and When the signs are opposite, the water hammer effect does not exist;

[0011] Step 1.3 When water hammer effect occurs, the reference value for power reversal caused by water hammer effect in the turbine. The calculation formula is:

[0012]

[0013] in, The active power output of the turbine before the disturbance occurs. This represents the change in load power demand. This refers to the output power of the water turbine.

[0014] Furthermore, Step 2 specifically includes:

[0015] Step 2.1 The photovoltaic-energy storage system is connected in a power complementary manner. On the AC side, the control method of virtual synchronous machine is used to make the grid-connected inverter simulate the inertia and damping characteristics of synchronous generator in order to suppress the frequency fluctuation of the system.

[0016] Step 2.2 Detect whether the photovoltaic-energy storage system outputs active power. The controller turns on when the water turbine experiences water hammer effect, and the photovoltaic-energy storage system compensates for the water hammer effect of the water turbine. It turns off when the water hammer effect ends. When there is no water hammer effect in the water turbine, the controller remains off.

[0017] Furthermore, Step 3 specifically includes:

[0018] Step 3.1 The photovoltaic power generation system operates in rated load shedding mode. When the turbine experiences water hammer, the power adjustment reference value is adjusted based on the water hammer effect. Dynamically adjust the photovoltaic load reduction coefficient;

[0019] The formula for calculating the photovoltaic load reduction factor is:

[0020]

[0021] The formula for calculating the photovoltaic offload rate is:

[0022]

[0023] The formula for calculating photovoltaic load shedding power is:

[0024]

[0025] In the formula, For photovoltaic load reduction factor, This is the rated load reduction factor for photovoltaic systems. For photovoltaic load reduction rate, This represents the maximum power output of the photovoltaic system. Reduce the load on photovoltaic power;

[0026] Step 3.2 When the turbine does not experience water hammer, check the SOC of the energy storage battery: If the battery is not fully charged, increase the photovoltaic load reduction factor. When the photovoltaic power generation system operates in MPPT mode, the energy storage battery is charged; when the energy storage battery is fully charged, the photovoltaic power generation system operates in rated load shedding rate DPPT mode.

[0027] Beneficial effects:

[0028] The method provided by this invention can improve the negative damping effect of hydropower units, effectively suppress the ultra-low frequency oscillation of the system caused by water hammer effect, and dynamically adjust the load reduction rate of photovoltaic power generation system according to the power reversal caused by water hammer effect, reduce the number of charge and discharge cycles of energy storage battery, and effectively improve battery life. Attached Figure Description

[0029] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0030] Figure 1 This is a flowchart of a collaborative control method for compensating for water hammer effect in turbines in a large-scale photovoltaic power plant, according to the present invention.

[0031] Figure 2 This is a schematic diagram of the hydropower unit-photovoltaic-energy storage system of the present invention;

[0032] Figure 3 This is a schematic diagram of the frequency response principle of a hydroelectric generator unit;

[0033] Figure 4 This is a schematic diagram of the photovoltaic MPPT / DPPT control principle;

[0034] Figure 5 This is a schematic diagram of the water hammer effect detection and controller conduction status of a water turbine;

[0035] Figure 6 This is a schematic diagram of the water hammer effect compensation method and system operation principle of the present invention;

[0036] Figure 7 This invention provides power compensation for the water hammer effect.

[0037] Figure 8 This invention provides frequency compensation for the water hammer effect. Detailed Implementation

[0038] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0039] The purpose of this invention is to provide a collaborative control method for compensating for the water hammer effect of hydroelectric turbines in large-scale photovoltaic power plants. This method aims to improve the negative damping effect of hydroelectric generators, effectively suppress the ultra-low frequency oscillations of the system caused by the water hammer effect, and reduce the number of charge-discharge cycles of energy storage batteries. This invention first builds a hydroelectric generator-photovoltaic-energy storage model in MATLAB / SIMULINK, setting scenarios where the photovoltaic-energy storage system does not participate in the frequency regulation of the hydroelectric generator and when it does.

[0040] Example 1

[0041] like Figure 1-6 As shown, the technical solution of the present invention is: a collaborative control method for compensating for the water hammer effect of turbines in large-scale photovoltaic power plants, the specific steps of which are as follows:

[0042] Step 1: Calculate the change in grid frequency Δf, and determine whether the change in grid frequency Δf exceeds the dead zone of hydropower frequency regulation; determine whether the turbine is experiencing water hammer effect, and calculate the reference value for power reversal caused by water hammer effect when water hammer effect occurs;

[0043] Step 2: Detect whether the photovoltaic-energy storage system outputs active power. The controller turns on when the water turbine experiences water hammer effect, and the photovoltaic-energy storage system compensates for the water turbine's water hammer effect.

[0044] Step 3: Detect the operating mode of the photovoltaic power generation system and adjust the output power of the photovoltaic-energy storage system according to the operating status of the photovoltaic power generation system.

[0045] Step 1 specifically includes:

[0046] Step 1.1 Monitor the power grid frequency f in real time and determine whether the change in power grid frequency Δf exceeds the hydropower frequency regulation dead zone of 0.05Hz;

[0047] Step 1.2 Calculate the turbine angular velocity offset and mechanical power offset ,according to and Identifying phase hysteresis caused by water hammer effect: and When the signs are the same, the response of a typical hydraulic unit is opposite to the desired control, and water hammer effect exists; and When the signs are opposite, the water hammer effect does not exist;

[0048] Step 1.3 When water hammer effect occurs, the reference value for power reversal caused by water hammer effect in the turbine. The calculation formula is:

[0049]

[0050] in, The active power output of the turbine before the disturbance occurs. This represents the change in load power demand. This refers to the output power of the water turbine.

[0051] Step 2 specifically includes:

[0052] Step 2.1 The photovoltaic-energy storage system is connected in a power complementary manner. On the AC side, the control method of virtual synchronous machine is used to make the grid-connected inverter simulate the inertia and damping characteristics of synchronous generator in order to suppress the frequency fluctuation of the system.

[0053] Step 2.2 Detect whether the photovoltaic-energy storage system outputs active power. The controller turns on when the water turbine experiences water hammer effect, and the photovoltaic-energy storage system compensates for the water hammer effect of the water turbine. It turns off when the water hammer effect ends. When there is no water hammer effect in the water turbine, the controller remains off.

[0054] Step 3 specifically includes:

[0055] Step 3.1 The photovoltaic power generation system operates in rated load shedding mode. When the turbine experiences water hammer, the power adjustment reference value is adjusted based on the water hammer effect. Dynamically adjust the photovoltaic load reduction coefficient;

[0056] The formula for calculating the photovoltaic load reduction factor is:

[0057]

[0058] The formula for calculating the photovoltaic offload rate is:

[0059]

[0060] The formula for calculating photovoltaic load shedding power is:

[0061]

[0062] In the formula, For photovoltaic load reduction factor, This is the rated load reduction factor for photovoltaic systems. For photovoltaic load reduction rate, This represents the maximum power output of the photovoltaic system. Reduce the load on photovoltaic power;

[0063] Step 3.2 When the turbine does not experience water hammer, check the SOC of the energy storage battery: If the battery is not fully charged, increase the photovoltaic load reduction factor. When the photovoltaic power generation system operates in MPPT mode, the energy storage battery is charged; when the energy storage battery is fully charged, the photovoltaic power generation system operates in rated load shedding rate DPPT mode.

[0064] Implementing the embodiments of the present invention yields the following results: Figure 7-8 As shown, it has the following beneficial effects:

[0065] The method provided by this invention can improve the negative damping effect of hydropower units, effectively suppress the ultra-low frequency oscillation of the system caused by water hammer effect, and dynamically adjust the load reduction rate of photovoltaic power generation system according to the power reversal caused by water hammer effect, reduce the number of charge and discharge cycles of energy storage battery, and effectively improve battery life.

[0066] The above-described specific implementations can be partially adjusted by those skilled in the art in different ways without departing from the principles and purpose of the present invention. The scope of protection of the present invention is defined by the claims and is not limited to the above-described specific implementations. All implementation schemes within the scope of the claims are bound by the present invention.

Claims

1. A collaborative control method for compensating for water hammer effect in turbines of large-scale photovoltaic power plants, characterized in that, The method includes the following steps: Step 1: Calculate the change in grid frequency Δf, and determine whether the change in grid frequency Δf exceeds the dead zone of hydropower frequency regulation; determine whether the turbine is experiencing water hammer effect, and calculate the reference value for power reversal caused by water hammer effect when water hammer effect occurs; Step 2: Detect whether the photovoltaic-energy storage system outputs active power. If the photovoltaic-energy storage system outputs active power, determine whether the photovoltaic power generation system is operating in DPPT mode. If so, adjust the photovoltaic load shedding rate to compensate for the water hammer effect of the turbine. If the photovoltaic-energy storage system does not output active power, determine whether the state of charge (SOC) of the energy storage battery is between 10% and 90%. If so, the energy storage system compensates for the water hammer effect of the turbine. The controller calculates the turbine angular velocity offset Δω and mechanical power offset Δω based on these parameters. P m Determine whether conduction or deactivation is determined by whether the signs of Δω and Δω are the same: P m When the signs are the same, the controller is turned on; when the signs are opposite, the controller is turned off. Step 3: Detect the operating mode of the photovoltaic power generation system and adjust the output power of the photovoltaic-energy storage system according to the operating status of the photovoltaic power generation system; Step 3 specifically includes: Step 3.1 The photovoltaic power generation system operates in rated load shedding mode. When the turbine experiences water hammer, the power adjustment reference value is adjusted based on the water hammer effect. Dynamically adjust the photovoltaic load reduction coefficient; The formula for calculating the photovoltaic load reduction factor is: ； The formula for calculating the photovoltaic offload rate is: ； The formula for calculating photovoltaic load shedding power is: ； In the formula, For photovoltaic load reduction factor, This is the rated load reduction factor for photovoltaic systems. For photovoltaic load reduction rate, This represents the maximum power output of the photovoltaic system. Reduce the load on photovoltaic power; Step 3.2 When the turbine does not experience water hammer, check the SOC of the energy storage battery; when the battery is not fully charged, make the photovoltaic power generation system work in MPPT mode and charge the energy storage battery; when the energy storage battery is fully charged, make the photovoltaic power generation system work in rated load shedding rate DPPT mode.

2. The collaborative control method for compensating for water hammer effect in turbines in a large-scale photovoltaic power plant according to claim 1, characterized in that, Step 1 specifically includes: Step 1.1 Monitor the power grid frequency f in real time and determine whether the change in power grid frequency Δf exceeds the hydropower frequency regulation dead zone of 0.05Hz; Step 1.2 Calculate the turbine angular velocity offset and mechanical power offset ,according to and Identifying phase hysteresis caused by water hammer effect: and When the signs are the same, the response of the hydraulic unit is opposite to the desired control, and water hammer effect exists; and When the signs are opposite, the water hammer effect does not exist; Step 1.3 When water hammer effect occurs, the reference value for power reversal caused by water hammer effect in the turbine. The calculation formula is: ； in, The active power output of the turbine before the disturbance occurs. This represents the change in load power demand. This refers to the output power of the water turbine.

3. The collaborative control method for compensating for water hammer effect in turbines in a large-scale photovoltaic power plant according to claim 1, characterized in that, Step 2 specifically includes: Step 2.1 The photovoltaic-energy storage system is connected in a power complementary manner. On the AC side, the control method of virtual synchronous machine is used to make the grid-connected inverter simulate the inertia and damping characteristics of synchronous generator in order to suppress the frequency fluctuation of the system. Step 2.2 Detect whether the photovoltaic-energy storage system outputs active power. The controller turns on when the water turbine experiences water hammer effect, and the photovoltaic-energy storage system compensates for the water hammer effect of the water turbine. It turns off when the water hammer effect ends. When there is no water hammer effect in the water turbine, the controller remains off.

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