A hydro-photovoltaic microgrid control method based on off-grid photovoltaic load reduction operation

Abstract

The present invention discloses a hydropower microgrid control method based on photovoltaic load reduction operation under off-grid conditions, comprising the following steps: 1. Before the microgrid system is off-grid, a maximum power tracking test is performed on the photovoltaic power generation system in the microgrid under different lighting conditions, the maximum power point voltage and power values under different lighting conditions are recorded, and a power-voltage curve of the system is established; 2. The light intensity under the current working environment of the photovoltaic power generation system is measured, and the photovoltaic power generation system is set to voltage load reduction operation according to the current light intensity; the microgrid controller sets the small hydropower station to constant power generation according to the currently measured local load and the output power of the photovoltaic power generation system; 3. The current microgrid system frequency and frequency change rate are determined, and the power generation of the photovoltaic power generation system and the small hydropower station is adjusted; 4. The voltage U output by the photovoltaic power generation system is measured. pv With power P pv , judge (dP pv / dU pv ), update the maximum power point voltage and power values in step 1 according to real-time data.

Description

Technical Field

[0001] The present invention belongs to the field of water-photovoltaic microgrid regulation, and in particular relates to a water-photovoltaic microgrid regulation method based on off-grid photovoltaic load reduction operation. Background Art

[0002] my country's southeastern and southwestern mountainous areas are rich in hydropower resources, offering promising prospects for the development of small hydropower. Driven by the dual carbon goals, distributed photovoltaics are rapidly developing, with an increasing number of distributed power sources, such as photovoltaics and hydropower, being connected to the grid via long-distance transmission lines. However, due to their remote locations and complex terrain, power grids in mountainous areas often suffer from relatively poor power supply reliability due to long power lines and large power supply radiuses. In the event of a power outage in the upper grid, microgrid systems relying on abundant local photovoltaic and hydropower resources are an effective way to ensure reliable power supply for mountain residents.

[0003] When operating off-grid, small hydropower stations have poor frequency regulation capabilities, making it difficult to maintain the microgrid system frequency within a normal range by relying solely on small hydropower. To address this frequency stability issue, existing researchers have primarily sought to increase energy storage to ensure microgrid system frequency stability.

[0004] During grid-connected operation, with the large-capacity grid connection of photovoltaics, some scholars have proposed to reduce the load of photovoltaics and reserve some active power for frequency regulation to achieve active support for system frequency changes.

[0005] In existing technologies, due to the poor frequency regulation capabilities of small hydropower stations during off-grid operation, it is difficult to maintain microgrid system frequency fluctuations within a normal range by relying solely on small hydropower. To address this frequency stability issue, existing researchers have primarily sought to increase energy storage to ensure microgrid system frequency stability. However, in engineering applications, energy storage stations are typically configured with large capacities. During grid-connected operation, the energy storage is often idle, increasing investment while also resulting in a certain amount of resource waste.

[0006] With the large-scale integration of photovoltaic power generation in grid-connected operation, some researchers have proposed using photovoltaic power generation to reduce load, reserving some active power for system frequency regulation to provide active support for system frequency fluctuations. Han Ping et al. proposed using a master-slave photovoltaic array configuration to determine the current maximum power operating point and subsequently implement load reduction control (a method for active frequency response of photovoltaic power plants based on load reduction control). However, their research focused on grid-connected conditions and did not consider coordination with other distributed power sources in off-grid environments. Li Huayi et al. designed a photovoltaic load reduction tracking method based on offline fitting (a study on virtual synchronous generator control for photovoltaic load reduction in standalone microgrids). They selected data points where the slope of the photovoltaic load reduction curve under different irradiance levels was abruptly determined as segmentation points. Using measured data, they performed a linear fit to obtain fitting parameters and establish a four-segment linear function for photovoltaic load reduction power. This method can effectively approximate the photovoltaic power-voltage curve, but the four-segment linear function requires a large amount of data, requiring a large number of data points to re-fit the data under different light intensities, which is time-consuming and unsuitable for off-grid operation where frequency regulation relies solely on photovoltaic power generation. Summary of the Invention

[0007] To address the above issues, the present invention proposes a hydro-photovoltaic microgrid control method based on photovoltaic load reduction operation in an off-grid environment. The photovoltaic power-voltage curve is established through offline fitting + online parameter update method, and a fast frequency response is achieved based on the power-voltage curve. The photovoltaic spare capacity is used to replace the regulation function of energy storage, ensuring the frequency stability of the microgrid system while reducing the investment in the microgrid system.

[0008] The present invention is achieved through at least one of the following technical solutions.

[0009] A method for regulating a hydro-photovoltaic microgrid based on photovoltaic load shedding operation in an off-grid environment comprises the following steps:

[0010] Step 1: Before the microgrid system is put into off-grid operation, a maximum power tracking test is performed on the photovoltaic power generation system in the microgrid under different light intensities, the maximum power point voltage-power values under different light intensities are recorded, and a linear function is established to describe the power-voltage curve of the photovoltaic power generation system;

[0011] Step 2: Measure the light intensity under the current working environment of the photovoltaic power generation system. Based on the data from step 1, the photovoltaic controller sets the photovoltaic power generation unit to load reduction operation; the microgrid controller sets the small hydropower station to constant power generation based on the currently measured local load and the output power of the photovoltaic power generation system;

[0012] Step 3: Measure the frequency of the microgrid system, determine the current frequency and frequency change rate of the microgrid system, and adjust the power generation of the photovoltaic power generation system and the small hydropower station;

[0013] Step 4: Measure the output voltage U of the photovoltaic power generation system pv With power Ppv , for (dP pv / dU pv ) to make a judgment to adjust the power generation of the photovoltaic power generation system and the small hydropower station, and update the maximum power point voltage and power value in step 1 according to real-time data.

[0014] Furthermore, in step 1, the test is based on the factory technical parameters of the photovoltaic modules and simulates various light intensities. During the test, the maximum power point voltage and power values under different light intensities are recorded and stored in detail to form a data table. The table is stored in the photovoltaic controller so that the control program can read and write.

[0015] Furthermore, in step 1, when the voltage is [0-U mi ] range, the power-voltage curve is fitted as a straight line passing through the origin with a slope of I i , the power-voltage curve is expressed as:

[0016] P pvi =I i ·U pvi

[0017]

[0018] Among them, P pvi is the photovoltaic output power fitting value under light intensity i; U pvi is the photovoltaic output voltage fitting value under light intensity i; U mi is the actual value of the photovoltaic output maximum power point voltage under light intensity i; P mi is the actual maximum power output of the photovoltaic under the light intensity i; K rel is the slope correction coefficient;

[0019] When the voltage exceeds U mi After that, the power-voltage curve shows a downward trend, and the decline is large. A small voltage change will lead to a large power fluctuation, which will control the output voltage of the photovoltaic power generation system to be less than the maximum power point voltage value U mi .

[0020] Furthermore, in step 2, the microgrid controller sets the photovoltaic power generation system to 0.45U under the current light intensity. mi Voltage load reduction operation, U mi It is the actual value of the photovoltaic output maximum power point voltage under light intensity i.

[0021] Furthermore, the reference value of power generation of small hydropower station P hdref for:

[0022] P hdref =P load -P pvi

[0023] Among them, P load is the currently measured local load, P pvi is the fitted value of photovoltaic output power under light intensity i.

[0024] Furthermore, in step 3, the current microgrid system frequency f and the frequency change rate df / dt are judged, and the power generation of the photovoltaic power generation system and the small hydropower station power generation system is adjusted, specifically including:

[0025] When 49.8≤f≤50.2, maintain the current operating status of the photovoltaic power generation system and the small hydropower station power generation system;

[0026] When f>50.2, judge df / dt:

[0027] When df / dt≥0, the photovoltaic power generation system is adjusted to operate with reduced load according to the calculated maximum voltage difference ΔU1, that is, the reference voltage U pvref =U pv -ΔU1; U calculated after load reduction pvref When <0, adjust the power generation system of small hydropower stations to reduce power generation;

[0028] When df / dt<0, the photovoltaic power generation system operates with a constant voltage difference ΔU2, that is, the reference voltage U pvref =U pv -ΔU2;

[0029] When f<49.8, judge df / dt:

[0030] When df / dt≤0, the photovoltaic power generation system operates with the calculated maximum voltage difference ΔU1, that is, the reference voltage U pvref =U pv -ΔU1;

[0031] When (dP pv / dU pv )=0, the measured P pv is the maximum power of the photovoltaic power generation unit under the current working conditions, and the measured U pv The maximum power point voltage value of the photovoltaic power generation unit is used to update the data in the data table with the maximum power point voltage value and power value of the current light intensity. At the same time, in order to make the photovoltaic power generation unit always operate on the left side of the maximum power point, the power generation system of the small hydropower station is adjusted to increase the power generation;

[0032] When df / dt>0, the photovoltaic power generation system operates with a constant voltage difference ΔU2, that is, the reference voltage U pvref =U pv -ΔU2;

[0033] Among them, P pv is the actual output power value of the photovoltaic power generation system measured under the current working conditions, U pv It is the actual value of the photovoltaic power generation system output voltage measured under the current working conditions.

[0034] Furthermore, the maximum voltage difference ΔU1 is:

[0035]

[0036] Where, P hd is the currently measured power generation of the small hydropower station, I i is the slope of the power-voltage curve, P load The current measured local load.

[0037] Furthermore, the constant voltage difference ΔU2 is:

[0038]

[0039] Where K j Is a positive integer.

[0040] Furthermore, the adjustment of the power generation of the small hydropower station increases the power generation or decreases the power generation P hdref for:

[0041] P hdref =P load -0.45*P mi

[0042] Where, P load is the current measured local load; P mi is the actual maximum power output of the photovoltaic under light intensity i;

[0043] Synchronously set the reference voltage of the photovoltaic power generation system to: U pvref =0.45*U mi , U mi It is the actual value of the photovoltaic output maximum power point voltage under light intensity i.

[0044] 1Furthermore, when (dP pv / dU pv )=0, update the maximum power point voltage and power value under the current working condition;

[0045] According to the power voltage curve of photovoltaic power generation unit, when (dP pv / dU pv )=0, the measured P pv is the maximum power of the photovoltaic power generation unit under the current working conditions, and the measured U pvThe maximum power point voltage value of the photovoltaic power generation unit is used to update the data in the data table with the maximum power point voltage value and power value of the current light intensity.

[0046] Compared with the prior art, the present invention has the following beneficial effects:

[0047] 1. The present invention establishes a photovoltaic power-voltage curve through an offline fitting + online parameter update method, and achieves rapid frequency response based on the power-voltage curve. It can reduce the investment in energy storage of mountain microgrid systems and utilize the adjustable capacity of photovoltaics to participate in system frequency stability control.

[0048] 2. Below the maximum power point, photovoltaics have a certain adjustable capacity; at the same time, compared with traditional generator sets, photovoltaics have a fast adjustment capability. The present invention makes full use of these two characteristics of photovoltaics to achieve effective adjustment of the microgrid without energy storage. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 A structural diagram of a microgrid system in a transformer substation according to an embodiment of the present invention;

[0050] Figure 2 Microgrid system control flow chart according to an embodiment of the present invention;

[0051] Figure 3 Power-voltage waveforms of photovoltaic engineering models at different temperatures;

[0052] Figure 4 Power-voltage waveforms of the photovoltaic engineering model under different light intensities;

[0053] Figure 5 Control block diagram of a photovoltaic power generation system according to an embodiment of the present invention. DETAILED DESCRIPTION

[0054] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely for explaining the present invention and are not intended to limit the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative work are within the scope of protection of the present invention.

[0055] like Figure 1 As shown, the microgrid system of the off-grid hydro-photovoltaic microgrid in mountainous area based on photovoltaic load reduction operation in this embodiment includes a small hydropower station, a photovoltaic power generation system, a local load, a substation microgrid controller, etc.

[0056] A method for regulating hydro-photovoltaic microgrids in mountainous areas based on photovoltaic load shedding operation, such as Figure 2 As shown, the specific implementation method includes the following steps:

[0057] Step 1: Before the microgrid system is put into operation, a maximum power tracking test is performed on the photovoltaic power generation system in the microgrid under different light intensities. The maximum power point voltage-power values under different light intensities are recorded, and a linear function is established to describe the power-voltage curve of the photovoltaic power generation system.

[0058] The test is based on the factory technical parameters of the photovoltaic modules and simulates various light intensities. During the test, the maximum power point voltage and power values under each light intensity are recorded and stored in detail to form a data table, as shown in Table 1. This table is stored in the photovoltaic controller so that the control program can read and write. Since the influence of temperature on the maximum power is relatively small, such as Figure 3 The photovoltaic output power and voltage curve of the engineering model is shown. When the temperature changes, the photovoltaic output power does not change much. The operating conditions of the photovoltaic power generation system of the present invention only consider different light intensities and ignore the influence of temperature.

[0059] Table 1 Maximum power point voltage and power value of photovoltaic power generation system under different light intensities

[0060]

[0061] (In the table, U m is the maximum power point voltage value under different light intensities; P m is the maximum power value under different light intensities.

[0062] According to the data recorded in Table 1, it is proposed to use a linear function to describe the photovoltaic power generation system in [0-U mi ]Power-voltage curve within voltage, such as Figure 4 As shown, although the photovoltaic power generation system is described by a linear function in [0-U mi The power-voltage curve within the voltage has a certain power error, which in turn affects the deviation of frequency regulation, but the voltage has no error. In addition, a fluctuation range of ±0.2Hz is allowed during normal operation of the power grid, so it can be used for approximate description.

[0063] When the voltage is [0-U mi ] range, the power-voltage curve is fitted as a straight line passing through the origin with a slope of I i , the power-voltage curve is expressed as:

[0064] P pvi =I i ·U pvi

[0065]

[0066] Among them, P pvi is the photovoltaic output power fitting value under light intensity i; U pviis the photovoltaic output voltage fitting value under light intensity i; U mi is the actual value of the photovoltaic output maximum power point voltage under light intensity i; P mi is the actual maximum power output of the photovoltaic under the light intensity i; K rel is the slope correction coefficient, which can be 1.2 to 1.3. As a preferred embodiment, K rel It can be 1.2 to 1.3.

[0067] When the voltage exceeds U mi After that, the power-voltage curve shows a downward trend, and the decline is large. A small voltage change will lead to a large power fluctuation. The present invention will control the output voltage of the photovoltaic power generation system to be less than the maximum power point voltage value U mi .

[0068] According to the test data in the above table and the linear function calculation formula, the mathematical expression of the power-voltage curve under different light intensities can be obtained.

[0069] Step 2: The control strategy of the photovoltaic power generation system is as follows: Figure 5 As shown, the specific implementation is as follows:

[0070] First, measure the light intensity S in the current working environment of the photovoltaic power generation system i , the actual output power value of the photovoltaic power generation system P pv The actual value of the output voltage U pv , the grid connection point voltage U of the photovoltaic power generation system connected to the grid through the DC / AC inverter abc With current I abc Then, based on the grid-connected point voltage and current data, the system frequency data is output through a widely used phase-locked loop algorithm. The system frequency is then determined, and the power-frequency response control method proposed in the embodiment of the present invention is used to output a voltage reference signal for the photovoltaic power generation system. The load and small hydropower power signals required for the power-frequency response are transmitted by the substation microgrid controller. Finally, based on the difference between the actual output voltage and the voltage reference signal, a current reference signal is generated after passing through a voltage loop. The current reference signal is then passed through a current loop to generate a modulation signal. The modulation signal is then output through SPWM to modulate pulses to control the DC / AC inverter for grid-connected control.

[0071] According to the data in Table 1, the photovoltaic power generation system is initialized according to the current light intensity S i 0.45U under mi Voltage load reduction operation, at this time 0.45U mi It is the initialization given voltage reference signal. The microgrid controller is based on the current measured local load P load And the photovoltaic power generation system output power fitting value P pvi Set the constant power generation of small hydropower station, the reference value of power generation of small hydropower station Phdref = P load -P pvi .

[0072] Step 3. Measure the microgrid system frequency f, the actual value of small hydropower generation P hd , the local load P load , the actual output power of the photovoltaic power generation system P pv and the actual output voltage U pv .

[0073] Step 4. Judge the current microgrid system frequency f and the frequency change rate df / dt. Given that the allowable value of the normal frequency deviation of the power system in China is ±0.2 Hz, then:

[0074] When 49.8 < f < 50.2, maintain the operating states of the current photovoltaic power generation system and the small hydropower station power generation system;

[0075] When f > 50.2, judge df / dt:

[0076] When df / dt ≥ 0, adjust the photovoltaic power generation system to operate with load reduction by the calculated maximum voltage difference ΔU1, that is, the reference voltage U of the photovoltaic power generation system[[ID=,29]] pvref = U pv - ΔU1; when the calculated U after load reduction pvref < 0, adjust the small hydropower station power generation system to reduce power generation;

[0077] When df / dt < 0, the photovoltaic power generation system operates with load reduction by a constant voltage difference ΔU2, that is, the reference voltage U of the photovoltaic power generation system pvref = U pv ​​​​​​​​​​​​​​​​​​​​​​​​When df / dt>0, the photovoltaic power generation system operates with a constant voltage difference ΔU2, that is, the reference voltage U pvref =U pv -ΔU2.

[0082] Among them, ΔU1 and ΔU2:

[0083]

[0084]

[0085] Where, P hd K is the current measured power generation of the small hydropower station. j is a positive integer. As a preferred embodiment, K j The values can be 1, 2, 3, n, etc.

[0086] Among them, adjusting the power generation of small hydropower to increase or decrease power generation:

[0087] P hdref =P load -0.45*P mi

[0088] Considering that photovoltaic power generation needs to have a certain range of power regulation capabilities, the reference voltage of the photovoltaic power generation system is set to:

[0089] U pvref =0.45*U mi

[0090] Return to step 3.

[0091] The preferred embodiments of the present invention disclosed above are intended only to help illustrate the present invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the present invention to the specific embodiments described. Obviously, many modifications and variations are possible based on the content of this specification. These embodiments are selected and described in detail in this specification to better explain the principles and practical applications of the present invention, thereby enabling those skilled in the art to better understand and utilize the present invention. The present invention is limited only by the claims and their full scope and equivalents.

Claims

1. A method for regulating a hydro-photovoltaic microgrid based on photovoltaic load shedding operation under off-grid conditions, characterized in that: The following steps are involved: Step 1: Before the microgrid system is off-grid, perform a maximum power tracking test on the photovoltaic power generation system in the microgrid under different light intensities, record the maximum power point voltage-power value under different light intensities, and establish a linear function to describe the power-voltage curve of the photovoltaic power generation system. mi ] range, the power-voltage curve is fitted as a straight line passing through the origin with a slope of I i , the power-voltage curve is expressed as: P pvi =I i IN pvi Among them, P pvi is the photovoltaic output power fitting value under light intensity i; U pvi is the photovoltaic output voltage fitting value under light intensity i; U mi is the actual value of the photovoltaic output maximum power point voltage under light intensity i; P mi is the actual maximum power output of the photovoltaic under the light intensity i; K rel is the slope correction coefficient; When the voltage exceeds U mi After that, the power-voltage curve shows a downward trend, and the decline is large. A small voltage change will lead to a large power fluctuation, which will control the output voltage of the photovoltaic power generation system to be less than the maximum power point voltage value U mi ; Step 2: Measure the light intensity under the current working environment of the photovoltaic power generation system. Based on the data from step 1, the photovoltaic controller sets the photovoltaic power generation unit to load reduction operation; the microgrid controller sets the small hydropower station to constant power generation based on the currently measured local load and the output power of the photovoltaic power generation system; Step 3: Measure the microgrid system frequency, determine the current microgrid system frequency and frequency change rate, and adjust the power generation of the photovoltaic power generation system and small hydropower station. Specifically, it includes: When 49.8≤f≤50.2, maintain the current operating status of the photovoltaic power generation system and the small hydropower station power generation system; When f>50.2, judge df / dt: When df / dt≥0, the photovoltaic power generation system is adjusted to operate with reduced load according to the calculated maximum voltage difference ΔU1, that is, the reference voltage U pvref =U pv -ΔU1; U calculated after load reduction pvref When <0, adjust the power generation system of small hydropower stations to reduce power generation; When df / dt<0, the photovoltaic power generation system operates with a constant voltage difference ΔU2, that is, the reference voltage U pvref =U pv -ΔU2; the constant voltage difference ΔU2 is: Where K j is a positive integer; When f<49.8, judge df / dt: When df / dt≤0, the photovoltaic power generation system operates with the calculated maximum voltage difference ΔU1, that is, the reference voltage U pvref =U pv -ΔU1; the maximum voltage difference ΔU1 is: Where, P hd is the currently measured power generation of the small hydropower station, I i is the slope of the power-voltage curve, P load is the currently measured local load; When (dP pv / dU pv )=0, the measured P pv is the maximum power of the photovoltaic power generation unit under the current working conditions, and the measured U pv The maximum power point voltage value of the photovoltaic power generation unit is used to update the data in the data table with the maximum power point voltage value and power value of the current light intensity. At the same time, in order to make the photovoltaic power generation unit always operate on the left side of the maximum power point, the power generation system of the small hydropower station is adjusted to increase the power generation; When df / dt>0, the photovoltaic power generation system operates with a constant voltage difference ΔU2, that is, the reference voltage U pvref =U pv -ΔU2; Among them, P pv is the actual output power value of the photovoltaic power generation system measured under the current working conditions, U pv The actual output voltage value of the photovoltaic power generation system measured under the current working conditions; Step 4: Measure the output voltage U of the photovoltaic power generation system pv With power P pv , for (dP pv / dU pv ) to make a judgment to adjust the power generation of the photovoltaic power generation system and the small hydropower station, and update the maximum power point voltage and power value in step 1 according to real-time data.

2. The off-grid hydro-photovoltaic microgrid control method based on photovoltaic load reduction operation according to claim 1 is characterized in that: In step 1, the test is based on the factory technical parameters of the photovoltaic modules and simulates various light intensities. During the test, the maximum power point voltage and power values under different light intensities are recorded and stored in detail to form a data table. The table is stored in the photovoltaic controller so that the control program can read and write.

3. The off-grid hydro-photovoltaic microgrid control method based on photovoltaic load reduction operation according to claim 1 is characterized in that: In step 2, the microgrid controller sets the photovoltaic power generation system to 0.45U under the current light intensity. mi Voltage load reduction operation, U mi It is the actual value of the photovoltaic output maximum power point voltage under light intensity i.

4. The off-grid hydro-photovoltaic microgrid control method based on photovoltaic load reduction operation according to claim 1 is characterized in that: Reference value of power generation of small hydropower station P hdref for: P hdref =P load -P pvi Among them, P load is the currently measured local load, P pvi is the fitted value of photovoltaic output power under light intensity i.

5. The off-grid hydropower microgrid control method based on photovoltaic load reduction operation according to claim 1 is characterized in that the power generation of the small hydropower station is adjusted to increase or decrease the power generation P hdref for: P hdref =P load -0.45*P mi Where, P load is the current measured local load; P mi is the actual maximum power output of the photovoltaic under light intensity i; Synchronously set the reference voltage of the photovoltaic power generation system to: U pvref =0.45*U mi , U mi It is the actual value of the photovoltaic output maximum power point voltage under light intensity i.

6. The off-grid hydro-photovoltaic microgrid control method based on photovoltaic load shedding operation according to claim 1 is characterized in that when (dP pv / dU pv )=0, update the maximum power point voltage and power value under the current working condition; According to the power voltage curve of photovoltaic power generation unit, when (dP pv / dU pv )=0, the measured P pv is the maximum power of the photovoltaic power generation unit under the current working conditions, and the measured U pv The maximum power point voltage value of the photovoltaic power generation unit is used to update the data in the data table with the maximum power point voltage value and power value of the current light intensity.

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