Method for controlling active power of optical storage dynamic voltage restorer

Abstract

The invention relates to the technical field of dynamic voltage restorers, in particular to a method for controlling the active power of a light storage dynamic voltage restorer, which comprises the following steps of: performing vector control on the size of a phase angle alpha between a power grid voltage US and a load voltage UL through a dynamic voltage restorer in normal operation according to power provided by a photovoltaic energy storage end; power values provided by a power grid and photovoltaic energy storage are dynamically adjusted. According to the invention, the load voltage can be kept constant, and the alpha angle can be dynamically adjusted according to the illumination intensity of the photovoltaic side, so that the output power of the photovoltaic side is adjusted, the photovoltaic utilization rate is effectively improved, the normal operation function of the dynamic voltage restorer is realized, and a power grid can be dynamically adjusted and effectively supported.

Description

Technical Field

[0001] The invention relates to the technical field of dynamic voltage restorers, and in particular to a method for controlling active power of a photovoltaic storage dynamic voltage restorer. Background Art

[0002] In recent years, the renewable energy power generation system has attracted the attention of various countries for its environmentally friendly, efficient, decentralized and flexible power generation methods. With the continuous penetration of renewable energy and the increased complexity and uncertainty of the access of a large number of power electronic equipment, the power quality problem of microgrids has become increasingly prominent. Among them, the most common power quality problems, such as voltage sag and surge, directly affect the normal operation of critical loads, causing significant economic losses and even casualties. For this reason, the dynamic voltage restorer (DVR) that can effectively solve the power quality problem has been widely used.

[0003] The DC side of a traditional dynamic voltage restorer usually uses energy storage batteries to provide energy, which is insufficient in compensation depth and time, and has extremely high requirements for battery performance. With the rapid development of renewable energy, some studies have connected renewable energy as energy to the DC side, and derived a dynamic voltage restorer combined with renewable energy. Its typical application is photovoltaic DVR. However, photovoltaic power generation is affected by environmental conditions such as light intensity and external temperature, resulting in the output of the photovoltaic system having the characteristics of random fluctuations. At present, there is a lack of research on how to overcome the characteristics of random fluctuations in photovoltaics, improve the energy utilization efficiency of photovoltaic systems, and achieve the normal operation of dynamic voltage restorers. Summary of the invention

[0004] In order to improve the utilization efficiency of photovoltaic energy, the present invention proposes a control method for the active power of a photovoltaic dynamic voltage restorer, which effectively improves the photovoltaic utilization rate, realizes the normal operation function of the dynamic voltage restorer, and realizes dynamic regulation and effective support of the power grid.

[0005] In order to achieve the above object, the technical solution specifically adopted by the present invention is as follows:

[0006] A control method for the active power of a photovoltaic energy storage dynamic voltage restorer, the control method controls the grid voltage U according to the power that can be provided by the photovoltaic energy storage end through a normally operating dynamic voltage restorer S With load voltage U L The vector control of the phase angle α between the two can dynamically adjust the power values ​​provided by the power grid and the photovoltaic energy storage. It can not only maximize the use of the photovoltaic energy storage side power, but also ensure the stability of the load side and reduce the demand for power grid power. Specifically, the control includes the following steps: First, the active power P on the load side is LAnd the power P that the dynamic voltage restorer DVR can provide DVR Combined, the grid voltage U S With load voltage U L The phase difference α between them; on this basis, the voltage amplitude U Lref With grid voltage U S With load voltage U L The phase difference α between them is integrated to obtain the load voltage reference value; the actual grid voltage value is obtained through voltage acquisition, and compared with the load reference voltage reference value to obtain the reference value of the compensation voltage that the dynamic voltage restorer DVR needs to output; finally, the voltage loop is used to compare the compensation voltage reference value with the actual output dynamic voltage restorer DVR voltage value to obtain the error, and the error is controlled by PI and modulated by SPWM to obtain the driving signal of the switch tube.

[0007] The photovoltaic system of the present invention is composed of a power grid, a load, a transformer, a dynamic voltage restorer, a filter unit, a photovoltaic array, an energy storage module, etc. According to the power balance of the system, the active power relationship between the dynamic voltage restorer, the power grid and the load is as follows:

[0008]

[0009] Among them, P L is the power required by the load, P S is the power value provided by the grid, P DVR is the output power value of the dynamic voltage restorer, α is the grid voltage U S With load voltage U L The phase angle between It represents the load voltage U L and load current I L Phase difference. It can be seen that when the load power P L When the grid is operating normally, the α angle is changed according to the power generated by the light intensity received by the photovoltaic panel, and the grid output power P is adjusted. S , thereby realizing the output power P of the dynamic voltage restorer DVR The purpose of dynamic regulation is to provide power to the DC end of the dynamic voltage restorer, which means that the photovoltaic output power can be dynamically adjusted. Therefore, according to the power that the photovoltaic panel can provide under different light intensities, by controlling the α angle, the goal of fully utilizing the power on the photovoltaic energy storage side of the dynamic voltage restorer can be achieved.

[0010] Regarding the angle control of α, the following situations are given when the power grid is operating normally:

[0011] When the light intensity is zero or weak, the power output of the grid and the photovoltaic side of the dynamic voltage restorer is as follows:

[0012] Case 1: When 0<α<α1, the grid voltage operates normally, U S =U L , Then P DVR <0, that is, the grid is responsible for bearing all the load power, and a small amount of active power flows to the dynamic voltage restorer side for DC side energy storage;

[0013] Situation 2: When When , according to the formula we can get P L =P S ,The power required by the load is fully provided by the grid, and the DVR side neither outputs nor absorbs active power, and does not exchange power with the grid;

[0014] When the light intensity gradually increases to a relatively strong level, the power output of the grid and the photovoltaic side of the dynamic voltage restorer is as follows:

[0015] Situation 3: When have to but Right now P DVR >0; the dynamic voltage restorer starts to output power, and the power required by the load is jointly provided by the grid and the dynamic voltage restorer. As α gradually increases, the photovoltaic output power on the dynamic voltage restorer side will gradually increase.

[0016] Case 4: As the angle α continues to increase, when α=α3, and it just satisfies When , according to the formula: The power required by the load is all provided by the photovoltaic side of the dynamic voltage restorer, and no power transmission is required on the grid side;

[0017] Case 5: As the angle α continues to increase, it exceeds the critical state of the power grid and DVR, that is, α3<α<π, According to the formula, we can get:

[0018] Furthermore, when a grid voltage sag occurs, the dynamic voltage restorer uses vector control α to make the power on the photovoltaic side flow from the DC end to the load to support the grid, which can be divided into the following situations:

[0019] When the grid voltage drops temporarily and the light intensity is zero or weak, the power output of the grid and the photovoltaic side of the dynamic voltage restorer is as follows:

[0020] Case 1: First, we discuss under what circumstances the output power of the dynamic voltage restorer is 0, and further determine the dividing line. From the formula, we can get: P L =P S , Based on this, we can get: When , the output of the dynamic voltage restorer is 0, and the power required by the load is provided by the grid side;

[0021] Situation 2: When When , according to the formula:

[0022]

[0023] When the grid voltage drops temporarily and the light intensity gradually increases to a strong level, the power output of the grid and the photovoltaic side of the dynamic voltage restorer is as follows:

[0024] Situation 3: When When, according to but And U' S <U L ,Right now

[0025] Case 4: As the angle α continues to increase, when α=α3, and it just satisfies When , according to the formula:

[0026] Case 5: As the angle α continues to increase, it exceeds the critical value between the power grid and the dynamic voltage restorer, that is, α3<α<π, According to the formula, we can get:

[0027] Furthermore, when a sudden rise in grid voltage occurs, the dynamic voltage restorer uses vector control α to make the power on the photovoltaic side flow from the DC end to the load to support the grid, which can be divided into the following situations:

[0028] When the grid voltage suddenly rises and the light intensity is zero or weak, the power output of the grid and the photovoltaic side of the dynamic voltage restorer is as follows:

[0029] Scenario 1: When When , according to the formula we can get

[0030] Case 2: When discussing the change of α, the output power of the dynamic voltage restorer is 0. According to the formula: Assume P L =P S , then Get when When , the output power of the dynamic voltage restorer is 0, and the power required by the load is provided by the grid side.

[0031] When the grid voltage suddenly rises and the light intensity gradually increases to a strong level, the power output of the grid and the photovoltaic side of the dynamic voltage restorer is as follows:

[0032] Case 3: Discussing when α changes to the point where the DVR starts to output power, starting from the formula: Assuming P DVR >0, then Right now When , the power required by the load is provided by the grid and DVR together, and as the angle α gradually increases, the output power of the photovoltaic side of the dynamic voltage restorer will gradually increase.

[0033] Case 4: As the angle α continues to increase, when α=α3, and satisfies When , according to the formula we can get: All the power required by the load is provided by the photovoltaic side of the dynamic voltage restorer, and no power needs to be transmitted on the grid side.

[0034] Case 5: As the angle α continues to increase, it exceeds the critical value between the power grid and the dynamic voltage restorer, that is, α3<α<π, According to the formula, we can get: This means that the photovoltaic output power is relatively large at this time. In addition to providing the required power for the load, the dynamic voltage restorer can also transmit excess active power to the grid, which plays a great supporting role for the grid.

[0035] The present invention has the following characteristics and beneficial effects:

[0036] The present invention can not only keep the load voltage constant, but also dynamically adjust the angle α according to the light intensity on the photovoltaic side, thereby adjusting the output power on the photovoltaic side. While effectively improving the photovoltaic utilization rate, it realizes the normal operation function of the dynamic voltage restorer and can realize dynamic adjustment and effective support of the power grid. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Other features, objects and advantages of the present invention will become more apparent from the detailed description of non-limiting embodiments made with reference to the following drawings:

[0038] Figure 1 is a block diagram of a photovoltaic power grid system in an embodiment of the present invention;

[0039] Figure 2 This is the α variation diagram under normal grid voltage conditions;

[0040] Figure 3 It is the variation diagram of α in case of grid voltage sag;

[0041] Figure 4 This is the α variation diagram when the grid voltage suddenly rises;

[0042] Figure 5 It is the control block diagram of the dynamic voltage restorer DVR algorithm;

[0043] Figure 6 This is the load simulation result diagram of the dynamic voltage restorer DVR when the power grid has power quality problems;

[0044] Figure 7 The simulation diagram of load, dynamic voltage restorer DVR and power flow in the grid when the light intensity is weak and accompanied by power quality problems, and the α angle is small;

[0045] Figure 8 The simulation diagram of load, dynamic voltage restorer DVR, and power flow in the power grid when the light intensity is moderate and accompanied by power quality problems and the α angle is moderate. DETAILED DESCRIPTION

[0046] The present invention is described in detail below in conjunction with specific embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but are not intended to limit the present invention in any form. It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments can be combined with each other.

[0047] In order to improve the efficiency of photovoltaic energy utilization, the present invention provides a control method for the active power of a photovoltaic dynamic voltage restorer. The control method is implemented by dynamically adjusting the power values ​​provided by the power grid and photovoltaic energy storage by vector control of the load side voltage phase angle according to the power that the photovoltaic energy storage terminal can provide when the dynamic voltage restorer is operating normally. This method can maximize the use of the photovoltaic energy storage side power while ensuring the stability of the load side, reduce the demand for grid power, and embody the role of supporting and regulating the grid. The specific control block diagram is shown in the figure. Figure 5 As shown, firstly, the load side active power P L And the power P that the dynamic voltage restorer DVR can provide DVR Combined, the grid voltage U S With load voltage U L The phase angle α between them; on this basis, the voltage amplitude U Lref With grid voltage U S With load voltage U LThe phase angle α between them is integrated to obtain the load voltage reference value; the actual grid voltage value is obtained through voltage acquisition, and compared with the load reference voltage reference value to obtain the reference value of the compensation voltage that the dynamic voltage restorer DVR needs to output; finally, the voltage loop is used to compare the compensation voltage reference value with the actual output dynamic voltage restorer DVR voltage value to obtain the error, and the error is controlled by PI and modulated by SPWM to obtain the driving signal of the switch tube.

[0048] Example 1

[0049] The photovoltaic power grid system block diagram of the present invention is as follows Figure 1 As shown, it consists of a power grid, a load, a transformer, a dynamic voltage restorer DVR, a filter unit, a photovoltaic array, an energy storage module, etc., wherein the dynamic voltage restorer DVR adopts a mid-point clamped three-level topology inverter, which has the advantages of more output levels, less harmonic content, and higher withstand voltage level of each switch tube.

[0050] According to the power balance of the system, the active power relationship between the dynamic voltage restorer, the grid and the load is as follows:

[0051] P L =P S +P DVR (1)

[0052] Among them, P L is the power required by the load, P S is the power value provided by the grid, P DVR is the output power value of the dynamic voltage restorer. According to the relationship between the phase angles, the above formula can be further deepened:

[0053]

[0054] Where α is the grid voltage U S With load voltage U L The phase difference between It represents the load voltage U L and load current I L By analyzing the above formula, we can know that when the load power P L When the grid is operating normally, the α angle is changed according to the power generated by the light intensity received by the photovoltaic panel, and the grid output power P is adjusted. S , thereby realizing the output power P of the dynamic voltage restorer DVRThe purpose of dynamic regulation is to provide power to the DC end of the dynamic voltage restorer, and the photovoltaic power provides power, which means that the photovoltaic output power is dynamically adjusted. Therefore, according to the power that the photovoltaic panel can provide under different light intensities, by controlling the angle α, the goal of fully utilizing the power on the photovoltaic energy storage side of the dynamic voltage restorer is achieved. When the light conditions are poor, the active power is mainly provided by the grid side to the load side. When the light conditions are moderate or sufficient, the power provided by the grid is reduced and the output power of the photovoltaic side is increased, which, to a certain extent, supports the grid.

[0055] Regarding the angle control of α, the following situations are given when the power grid is operating normally. Figure 2 :α variation diagram under normal grid voltage condition. Cases 1 and 2 describe the power output of the grid and the photovoltaic side of the dynamic voltage restorer when the light intensity is zero or weak.

[0056] Case 1: When 0<α<α1, the grid voltage is operating normally, U S =U L , Then P DVR <0, that is, the grid is responsible for bearing all the load power, and a small amount of active power flows to the dynamic voltage restorer side for DC side energy storage.

[0057] Situation 2: When According to formula (2), we can get: P L =P S The power required by the load is all provided by the power grid. The DVR side neither outputs nor absorbs active power, and does not exchange power with the power grid.

[0058] Situations 3, 4, and 5 describe the power output of the grid and the photovoltaic side of the dynamic voltage restorer when the light intensity gradually increases to a relatively strong level.

[0059] Situation 3: When When but Right now P DVR > 0. At this time, the dynamic voltage restorer starts to output power, and the power required by the load is jointly provided by the power grid and the dynamic voltage restorer. As α gradually increases, the photovoltaic output power on the dynamic voltage restorer side will gradually increase, increasing the utilization of photovoltaics, reducing the power output of the power grid to a certain extent, and achieving the role of partial support for the power grid.

[0060] Case 4: As the angle α continues to increase, when α=α3, and it just satisfies When , according to formula (2), we can get: This means that all the power required by the load is provided by the photovoltaic side of the dynamic voltage restorer, and no power transmission is required on the grid side, which significantly saves the energy of the grid and fully supports the grid.

[0061] Case 5: As the angle α continues to increase, it exceeds the critical state of the power grid and DVR, that is, α3<α<π, According to formula (2), we can get: This means that the active power output of the photovoltaic energy storage at this time is relatively large. In addition to providing the required active power for the load, the dynamic voltage restorer can also transmit the excess active power to the power grid, which greatly supplements the power grid.

[0062] As the angle α gradually increases, the output power of the dynamic voltage restorer also increases, which means that the output voltage of the inverter is more demanding, which poses a challenge to the switch selection of the inverter. If an inappropriate inverter is selected, the working range of the dynamic voltage restorer DVR may be limited, and the power output of the photovoltaic energy storage side may also be limited, causing unnecessary losses to renewable energy. In order to ensure that the dynamic voltage restorer can fully utilize the energy on the photovoltaic side, a midpoint clamped three-level inverter is used to replace the ordinary full-bridge structure. This circuit is an efficient, reliable and suitable topology for high-power occasions. The number of switch tubes is increased to 12, which can not only meet the high voltage stress of the switch, but also enable the inverter to work in a wider phase angle range at the same voltage level. The output voltage of the midpoint clamped three-level inverter is composed of three different levels, so the output waveform is closer to a sine wave, thereby reducing the harmonic content of the output voltage.

[0063] Example 2

[0064] When a grid voltage sag occurs, the grid voltage drops by S is less than the load voltage U L Compared with the analysis when the grid voltage is normal, it is more difficult. For the angle control of α, the following situations are also given respectively, referring to Figure 3 :α variation diagram under grid voltage sag. Cases 1 and 2 describe the power output of the grid and the photovoltaic side of the dynamic voltage restorer when the light intensity is zero or weak.

[0065] Case 1: First, we discuss under what circumstances the output power of the dynamic voltage restorer is 0, and further determine the dividing line. From formula (2), we get: P L =P S , It can be seen that when When , the output of the dynamic voltage restorer is 0. The power required by the load is provided by the grid side.

[0066] Situation 2: When According to formula (2), we can get: This means that the dynamic voltage restorer side starts to output power. To a certain extent, it saves the active power output of the power grid and provides a certain support to the power grid. Compared with the normal operation of the power grid voltage, the DVR enters operation earlier.

[0067] Situations 3, 4, and 5 describe the power output of the grid and the photovoltaic side of the dynamic voltage restorer when the light intensity gradually increases to a relatively strong level.

[0068] Situation 3: When When, according to but And U' S <U L ,Right now The active power required by the load is jointly provided by the power grid and the DVR, and as α gradually increases, the photovoltaic output on the dynamic voltage restorer side will gradually increase, increasing the utilization of photovoltaics and reducing the power output of the power grid to a certain extent, thereby achieving a certain support effect on the power grid.

[0069] Case 4: As the angle α continues to increase, when α=α3, it just satisfies When , according to formula (2), we can get: This means that all the active power required by the load is provided by the photovoltaic side of the dynamic voltage restorer, and there is no need to transmit power on the grid side, which significantly saves the energy of the grid and fully supports the grid.

[0070] Case 5: As the angle α continues to increase, it exceeds the critical value between the power grid and the dynamic voltage restorer, that is, α3<α<π, According to formula (2), we can get: This means that the power output of the photovoltaic energy storage is relatively large at this time. In addition to providing the required active power for the load, the dynamic voltage restorer can also transmit the excess active power to the power grid, which greatly supports the power grid. From the above, it can be seen that when the grid voltage drops temporarily, the dynamic voltage restorer can not only ensure its own normal operation, but also realize the power flow from the photovoltaic side to the load through vector control α, further realizing effective and powerful support for the power grid.

[0071] Example 3

[0072] When a sudden rise in grid voltage occurs, the expanded grid voltage U' S is greater than the load voltage UL Compared with the analysis of grid voltage sag, the difference is not big, only some individual cases are different. For the vector control of α, the following situations are given respectively, referring to Figure 4 : α variation diagram under the condition of grid voltage surge. Cases 1 and 2 describe the power output of the grid and the photovoltaic side of the dynamic voltage restorer when the light intensity is zero or weak.

[0073] Scenario 1: When According to formula (2), we can get: This means that the dynamic voltage restorer side is absorbing active power at this time. It can be seen that while the grid side is responsible for bearing all the load power, the excess active power flows to the dynamic voltage restorer side for DC side energy storage.

[0074] Case 2: When discussing the change of α, the output power of the dynamic voltage restorer is 0. According to formula (2), we can get: Assuming P L =P S , then Get when When , the output power of the dynamic voltage restorer is 0. The power required by the load is provided by the grid side.

[0075] Situations 3, 4, and 5 describe the power output of the grid and the photovoltaic side of the dynamic voltage restorer when the light intensity gradually increases to a relatively strong level.

[0076] Case 3: Discussing the situation when α changes to the point where the DVR starts to output power, starting from formula (2): Assuming P DVR >0, then Right now When the load power is 100W, the power required by the load is jointly provided by the grid and the DVR, and as the angle α gradually increases, the output power of the photovoltaic side of the dynamic voltage restorer will gradually increase, further increasing the utilization of photovoltaic energy storage, saving the power output of the grid to a certain extent, and achieving the role of partial support for the grid.

[0077] Case 4: As the angle α continues to increase, when α=α3, According to formula (2), we can get: This means that all the power required by the load is provided by the photovoltaic side of the dynamic voltage restorer, and there is no need to transmit power on the grid side, which significantly reduces the energy of the grid and fully supports the grid.

[0078] Case 5: As the angle α continues to increase, it exceeds the critical value between the power grid and the dynamic voltage restorer, that is, α3<α<π, According to formula (2), we can get: This means that the photovoltaic output power is relatively large at this time. In addition to providing the required power for the load, the dynamic voltage restorer can also transmit the excess active power to the grid, which greatly supports the grid. As can be seen from the above, when the grid voltage rises suddenly, the dynamic voltage restorer can not only ensure its own normal operation, but also realize the power on the photovoltaic side to flow from the DC end to the load through vector control α, further realizing effective and strong support for the grid.

[0079] Figure 6-Figure 8 What is shown is the simulation result of the dynamic voltage restorer using the Simulink simulation software in Matlab. The simulation time is 0.5s in total. The grid voltage drops temporarily during 0.1s-0.2s, and rises sharply during 0.3s-0.4s. The grid voltage is normal during the rest of the time.

[0080] Through Table 1 Figure 7-Figure 8 The simulation results are summarized in detail, such as light intensity, α angle change, load power required, grid output power, and dynamic voltage restorer output power.

[0081] Table 1 Summary of various situations of simulation result diagram

[0082]

[0083] It can be seen from Table 1 that even if power quality problems occur, the proposed active power control method of the dynamic voltage restorer based on vector control can not only keep the load voltage constant, but also dynamically adjust the angle α according to the light intensity on the photovoltaic side, thereby adjusting the output power on the photovoltaic side.

[0084] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments. The above embodiments and descriptions are only preferred examples of the present invention and are not intended to limit the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, which fall within the scope of the present invention. The scope of protection of the present invention is defined by the attached claims and their equivalents.

Claims

1. A method for controlling active power of a photovoltaic dynamic voltage restorer, characterized in that: The grid voltage U is adjusted according to the power that the photovoltaic energy storage terminal can provide through the normally operating dynamic voltage restorer. S With load voltage U L The phase angle α between them is controlled by vector to dynamically adjust the power values ​​provided by the power grid and photovoltaic energy storage.

2. The method for controlling active power of a photovoltaic dynamic voltage restorer according to claim 1, characterized in that: According to the power balance of the system, the active power relationship between the dynamic voltage restorer, the grid and the load is as follows: Among them, P L is the power required by the load, P S is the power value provided by the grid, P DVR is the output power value of the dynamic voltage restorer, α is the grid voltage U S With load voltage U L The phase angle between It represents the load voltage U L and load current I L The phase difference.

3. The method for controlling active power of a photovoltaic dynamic voltage restorer according to claim 1, characterized in that: The specific steps include: first, the load side active power P L And the power P that the dynamic voltage restorer DVR can provide DVR Combined, the grid voltage U S With load voltage U L The phase angle α between them; on this basis, the voltage amplitude U Lref With grid voltage U S With load voltage U L The phase angle α between them is integrated to obtain the load voltage reference value; Then, the actual grid voltage value is obtained through voltage acquisition, and compared with the load reference voltage reference value to obtain the reference value of the compensation voltage that the dynamic voltage restorer DVR needs to output. Finally, the voltage loop is used to compare the compensation voltage reference value with the actual output dynamic voltage restorer DVR voltage value to obtain the error. The error is controlled by PI and SPWM to obtain the driving signal of the switch tube.

4. The method for controlling active power of a photovoltaic dynamic voltage restorer according to claim 1, characterized in that: When the load power P L When the grid is operating normally, the α angle is changed according to the power generated by the light intensity received by the photovoltaic panel, and the grid output power P is adjusted. S , thereby realizing the output power P of the dynamic voltage restorer DVR For the purpose of dynamic regulation, at the same time, photovoltaics provide power to the DC end of the dynamic voltage restorer to achieve dynamic regulation of photovoltaic output power.

5. A method for controlling active power of a photovoltaic dynamic voltage restorer as claimed in claim 4, characterized in that: When the light intensity is zero or weak, the power output of the grid and the photovoltaic side of the dynamic voltage restorer is as follows: Case 1: When 0<α<α1, the grid voltage operates normally, U S =U L , Then P DVR <0; Situation 2: When hour, P L =P S .

6. A method for controlling active power of a photovoltaic dynamic voltage restorer as claimed in claim 4, characterized in that: When the light intensity gradually increases to a relatively strong level, the power output of the grid and the photovoltaic side of the dynamic voltage restorer is as follows: Situation 3: When hour, but Right now P DVR >0; Case 4: As the angle α continues to increase, when α=α3, and it just satisfies hour, Case 5: As the angle α continues to increase, it exceeds the critical state of the power grid and DVR, that is, α3<α<π, hour, 7. A method for controlling active power of a photovoltaic dynamic voltage restorer as claimed in claim 1, characterized in that: When a grid voltage sag occurs, the dynamic voltage restorer uses vector control α to direct the power on the photovoltaic side from the DC end to the load, thereby supporting the grid.

8. A method for controlling active power of a photovoltaic dynamic voltage restorer as claimed in claim 7, characterized in that: When the grid voltage drops temporarily and the light intensity is zero or weak, the power output of the grid and the photovoltaic side of the dynamic voltage restorer is as follows: Scenario 1: When When , the output of the dynamic voltage restorer is 0, and the power required by the load is provided by the grid side; Situation 2: When hour, U L >U' S , 9. A method for controlling active power of a photovoltaic dynamic voltage restorer as claimed in claim 7, characterized in that: When the grid voltage drops temporarily and the light intensity gradually increases to a strong level, the power output of the grid and the photovoltaic side of the dynamic voltage restorer is as follows: Situation 3: When When, according to but And U' S <U L ,Right now P DVR >0; Case 4: As the angle α continues to increase, when α=α3, and it just satisfies hour, Case 5: As the angle α continues to increase, it exceeds the critical value between the power grid and the dynamic voltage restorer, that is, α3<α<π, hour, 10. The method for controlling active power of a photovoltaic dynamic voltage restorer according to claim 1, characterized in that: When a sudden rise in grid voltage occurs, the dynamic voltage restorer uses vector control α to direct the power on the photovoltaic side from the DC end to the load, thereby supporting the grid.

11. A method for controlling active power of a photovoltaic dynamic voltage restorer as claimed in claim 10, characterized in that: When the grid voltage suddenly rises and the light intensity is zero or weak, the power output of the grid and the photovoltaic side of the dynamic voltage restorer is as follows: Scenario 1: When hour, U' S >U L , Situation 2: When When , the output power of the dynamic voltage restorer is 0, and the power required by the load is provided by the grid side.

12. The method for controlling active power of a photovoltaic dynamic voltage restorer according to claim 10, characterized in that: When the grid voltage suddenly rises and the light intensity gradually increases to a strong level, the power output of the grid and the photovoltaic side of the dynamic voltage restorer is as follows: Case 3: Discuss when α changes to the point where the DVR starts to output power. Assume that P DVR >0, then Case 4: As the angle α continues to increase, when α=α3, and satisfies hour, Case 5: As the angle α continues to increase, it exceeds the critical value between the power grid and the dynamic voltage restorer, that is, α3<α<π, hour,

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