A coordinated control method for photovoltaic energy storage stations connected to the grid based on voltage and power factor

Abstract

The present invention discloses a photovoltaic energy storage station grid-connected coordinated control method combining voltage and power factor, which belongs to the field of photovoltaic station grid-connected control, including: when the photovoltaic station grid-connected system has a power factor at a junction point exceeding the lower limit, the reactive power output by the energy storage station is used to adjust the power factor, which is the target value of the reactive power of the energy storage station that needs to be compensated for reactive power when the power factor at the junction point exceeds the lower limit, and is the reactive power capacity of the energy storage station; when the system grid-connected point voltage exceeds the limit, the photovoltaic station performs reactive control to achieve coordinated regulation of voltage and power factor, which is the total reactive power target value that the photovoltaic inverter needs to perform reactive compensation for when the grid-connected point voltage exceeds the limit, and is the reactive power of the photovoltaic inverter that compensates for insufficient regulation of the energy storage power factor, or when the power factor at the junction point does not exceed the lower limit. This method improves the ability of the photovoltaic station grid-connected system to resist voltage changes and improves voltage quality.

Description

Technical Field

[0001] The present invention belongs to the field of photovoltaic station grid-connected control, and more specifically, relates to a photovoltaic energy storage station grid-connected coordinated control method combining voltage and power factor. Background Art

[0002] In recent years, photovoltaic power generation has gradually become one of the important power generation methods of the power system due to its renewable, clean and pollution-free advantages. With the continuous increase in the capacity of large-scale photovoltaic power stations, the strength of the power grid dominated by traditional synchronous machines has weakened, and the risk of transient voltage fluctuations or even over-limits due to power imbalance in the system has increased. Therefore, photovoltaic power stations must have active voltage regulation capabilities to maintain the stability of the voltage at the grid connection point by outputting reactive power.

[0003] In existing engineering applications, active voltage regulation is mainly achieved by injecting reactive power. However, the increase in reactive power output from the station will lead to a decrease in the power factor transmitted to the power grid. According to the grid connection requirements, the power factor of the station input to the grid cannot be too low, otherwise it will directly affect the economic benefits of power supply. If necessary, reactive power needs to be adjusted for compensation. In particular, the "new energy + energy storage" model has brought new opportunities to enhance the support capacity of photovoltaic stations. How to tap the reactive support capacity of energy storage to solve the problem of grid connection point voltage and confluence point power factor exceeding the limit is of great research significance. Summary of the invention

[0004] In view of the defects of the prior art and the need for improvement, the present invention provides a photovoltaic energy storage station grid-connected coordinated control method combining voltage and power factor, which aims to solve the problem of grid-connected point voltage and confluence point power factor exceeding the limit during voltage fluctuations.

[0005] To achieve the above object, according to one aspect of the present invention, a photovoltaic energy storage station grid-connected coordinated control method combining voltage and power factor is provided, comprising: when the power factor of the confluence point of the photovoltaic station grid-connected system exceeds the lower limit, the energy storage station in the photovoltaic station grid-connected system outputs The reactive power is used to adjust the power factor, where: The target value of reactive power for energy storage that the energy storage station needs to compensate for when the power factor at the junction point exceeds the lower limit. is the reactive capacity of the energy storage station; when the grid-connected voltage of the photovoltaic station exceeds the limit, the photovoltaic station Reactive power control is performed to achieve coordinated regulation of voltage and power factor, where: The total reactive power target value that the photovoltaic inverter needs to compensate for when the grid-connected point voltage exceeds the limit. To compensate the reactive power of the photovoltaic inverter for insufficient power factor regulation of energy storage, hour , Or when the PV station grid-connected system does not have a power factor exceeding the lower limit at the confluence point .

[0006] Furthermore, for:

[0007] ;

[0008] in, is the actual active power at the junction, is the reference power factor value, is the actual reactive power at the junction.

[0009] Furthermore, for:

[0010] ;

[0011] in, is the capacity of the energy storage station, The active power released by the energy storage station.

[0012] Furthermore, for:

[0013] ;

[0014] in, is the total reactive capacity of the PV inverter, U is the grid voltage, U DB1 is the lower limit of the dead zone voltage, U DB2 is the upper limit of the dead zone voltage, U min is the lower limit of the grid connection point voltage, U max It is the upper limit of the grid connection point voltage.

[0015] Furthermore, for:

[0016] ;

[0017] ;

[0018] in, It is the first photovoltaic station i The reactive capacity of each photovoltaic power generation unit, M is the number of photovoltaic power generation units in the photovoltaic station, P N is the rated power of the photovoltaic power generation unit, P iIt is the first photovoltaic station i The active power output of each photovoltaic power generation unit.

[0019] Furthermore, the photovoltaic station is based on Reactive power control is performed to achieve coordinated regulation of voltage and power factor, specifically including: the photovoltaic station adopts equal margin allocation method, according to Calculate the reactive power target value of each photovoltaic power generation unit; the master control station in the photovoltaic field station sends each reactive power target value to the corresponding photovoltaic power generation unit to achieve real-time coordinated reactive power control between photovoltaic power generation units.

[0020] Furthermore, the reactive power target value of each photovoltaic power generation unit is:

[0021] ;

[0022] in, For the i The reactive power target value of each photovoltaic power generation unit, , M is the number of photovoltaic power generation units in the photovoltaic station, For the i The reactive capacity of each photovoltaic power generation unit, is the reactive capacity of the photovoltaic station.

[0023] According to another aspect of the present invention, there is provided a photovoltaic energy storage station grid-connected coordination control system combining voltage and power factor, comprising: a processor; a memory storing a computer executable program, wherein when the program is executed by the processor, the processor executes the photovoltaic energy storage station grid-connected coordination control method combining voltage and power factor as described above.

[0024] According to another aspect of the present invention, a computer-readable storage medium is provided, on which a computer program is stored, and when the program is executed by a processor, the photovoltaic energy storage station grid-connected coordinated control method combining voltage and power factor as described above is implemented.

[0025] In general, the above technical solutions conceived by the present invention can achieve the following beneficial effects:

[0026] (1) A photovoltaic energy storage station grid-connected coordinated control method combining voltage and power factor is provided. When the voltage at the grid-connected point exceeds the limit, the photovoltaic inverter uses reactive power droop control to adjust the voltage; when the power factor at the confluence point exceeds the lower limit, the energy storage outputs reactive power to adjust the power factor; when the reactive capacity of the energy storage cannot complete the power factor adjustment, the remaining reactive power demand is Sent to the photovoltaic inverter, the photovoltaic inverter will Added to the target value of its reactive power control, the coordinated regulation of voltage and power factor is achieved, the ability of the photovoltaic station grid-connected system to resist voltage changes is improved, and the voltage quality is improved; that is, when the voltage changes, the control method can not only adjust the grid-connected point voltage within the prescribed allowable range, but also adjust the confluence point power factor to above 0.98, thereby improving the operating voltage quality and economy of the photovoltaic grid-connected station at the same time;

[0027] (2) The photovoltaic station adopts the equal margin allocation method to calculate the reactive power target value of each photovoltaic power generation unit inverter, and sends the target value to the photovoltaic inverter to achieve real-time coordinated control between inverters; the photovoltaic station adopts centralized control for grid connection point voltage regulation; the energy storage is close to the confluence point, and local reactive power compensation control is adopted to reduce reactive power loss on the line and reduce network loss. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 A flow chart of a photovoltaic energy storage station grid-connected coordinated control method combining voltage and power factor provided in an embodiment of the present invention.

[0029] Figure 2 A schematic diagram of the photovoltaic station grid-connected system structure and AC grid voltage variation provided by an embodiment of the present invention.

[0030] Figure 3 A schematic diagram of voltage over-limit detection at a photovoltaic station grid connection point provided by an embodiment of the present invention.

[0031] Figure 4 A reactive power control block diagram of a photovoltaic station unit inverter provided in an embodiment of the present invention.

[0032] Figure 5 A block diagram of the power factor control of an energy storage station provided in an embodiment of the present invention.

[0033] Figure 6 This is a schematic diagram of the simulation results of the voltage characteristic power factor control effect under this method when the grid load suddenly changes and causes overvoltage at the grid connection point.

[0034] Figure 7 This is a schematic diagram of the simulation results of the output of each photovoltaic power generation unit under this method when the grid load suddenly changes and causes overvoltage at the grid connection point. DETAILED DESCRIPTION

[0035] 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 in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0036] In the present invention, the terms "first", "second", etc. (if any) in the present invention and the drawings are used to distinguish similar objects but not necessarily to describe a specific order or sequence.

[0037] Embodiment 1

[0038] A photovoltaic energy storage station grid-connected coordinated control method combining voltage and power factor, see Figure 1 , combined with Figure 2-Figure 7 The photovoltaic energy storage station grid-connected coordination control method combining voltage and power factor in this embodiment is described in detail. The method includes operation S1' and operation S1".

[0039] The photovoltaic power generation unit includes a photovoltaic power generation array, a DC / DC boost circuit and an inverter connected in sequence. Figure 2 The schematic diagram of the photovoltaic station grid-connected system structure and the AC grid load change position is shown in Figure 2 shown.

[0040] Operation S1', when the power factor of the confluence point of the photovoltaic station grid-connected system exceeds the lower limit, the energy storage station in the photovoltaic station grid-connected system outputs The reactive power is used to adjust the power factor, where: The target value of reactive power for energy storage that the energy storage station needs to compensate for when the power factor at the junction point exceeds the lower limit. is the reactive capacity of the energy storage station.

[0041] Energy storage reactive capacity of energy storage station Obtained through the following methods: Real-time detection of the active power released by the energy storage station Based on the ability of the energy storage inverter to generate inductive and capacitive reactive power, its reactive capacity upper limit (i.e. the reactive capacity of the energy storage station) can be obtained. )for:

[0042] ;

[0043] in, is the capacity of the energy storage station, The active power released by the energy storage station.

[0044] The lower limit of the power factor at the junction point indicates that the power factor at this point is , which affects the economic benefits of power supply. In order to better improve the utilization rate of power supply lines, reactive power compensation is required. The principle block diagram of power factor control of energy storage station is as follows: Figure 5 As shown. The target value of reactive power of energy storage for reactive compensation for:

[0045] ;

[0046] in, is the actual active power at the junction; is the reference power factor value, for example, 0.98, leading or lagging is determined by Decide; is the actual reactive power at the junction.

[0047] Operation S1'', when the grid-connected system of the photovoltaic station exceeds the grid-connected point voltage limit, the photovoltaic station Reactive power control is performed to achieve coordinated regulation of voltage and power factor, where: The total reactive power target value that the photovoltaic inverter needs to compensate for when the grid-connected point voltage exceeds the limit. To compensate the reactive power of the photovoltaic inverter for insufficient power factor regulation of energy storage, hour , Or when the PV station grid-connected system does not have a power factor exceeding the lower limit at the confluence point .

[0048] The grid connection point voltage exceeds the limit when the grid connection point overvoltage exceeds the upper limit or the grid connection point undervoltage exceeds the lower limit. The upper limit value is, for example, 1.07 pu and the lower limit value is, for example, 0.97 pu. Figure 3 The control block diagram shown is used to detect voltage over-limit at the grid connection point of the photovoltaic station.

[0049] When the grid-connected voltage of the photovoltaic station exceeds the limit, the photovoltaic station needs to compensate the total reactive power target value for:

[0050] ;

[0051] in, is the total reactive capacity of the PV inverter, U is the grid voltage, U DB1 is the lower limit of the dead zone voltage, U DB2 is the upper limit of the dead zone voltage, U min is the lower limit of the grid connection point voltage, U max It is the upper limit of the grid connection point voltage. U min For example, 0.97 pu; U max For example, 1.07 pu; U DB1 and U DB2Used to avoid unnecessary voltage regulation control, reduce inverter reactive action, and improve control reliability; U DB1 For example, 1.00pu, U DB2 For example, 1.04pu.

[0052] Reactive capacity of photovoltaic stations Obtained by: Real-time detection of the active power output of each photovoltaic power generation unit in the photovoltaic field P i ; Based on the ability of photovoltaic inverters to generate inductive and capacitive reactive power, and generally have an overload capacity of 1.1 times, that is, at 1.1 times the rated power P N Long-term operation under working conditions can obtain reactive power constraints ; Based on the energy industry standard requirements, when the active power output of the photovoltaic inverter is greater than 50% of its rated power, the power factor should be no less than 0.98 (leading or lagging), and the reactive power constraint can be obtained ; Combining the above two reactive constraints, the actual reactive capacity of each photovoltaic power generation unit is ,Right now ; Calculate the total reactive capacity of the photovoltaic inverter in the photovoltaic field from the actual reactive capacity of each photovoltaic power generation unit .

[0053] In summary, for:

[0054] ;

[0055] ;

[0056] in, It is the first photovoltaic station i The reactive capacity of each photovoltaic power generation unit, M is the number of photovoltaic power generation units in the photovoltaic station, P N is the rated power of the photovoltaic power generation unit, P i It is the first photovoltaic station i The active power output of each photovoltaic power generation unit.

[0057] Since the actual reactive capacity of energy storage is affected by the output active power, there will be a phenomenon of insufficient reactive power. When the reactive capacity of the energy storage cannot complete the power factor adjustment, the remaining reactive power Assigned to the photovoltaic station. When the reactive power capacity of the energy storage can complete the power factor adjustment, there will be no excess reactive power allocated to the photovoltaic inverter. The principle block diagram of the reactive power control of the photovoltaic station unit inverter is as follows: Figure 4 shown.

[0058] According to an embodiment of the present invention, the photovoltaic station Reactive power control is performed to achieve coordinated regulation of voltage and power factor, including: the reactive power distribution of photovoltaic inverters in the photovoltaic field adopts equal margin distribution method, according to Calculate the reactive power target value of each photovoltaic power generation unit; the master control station in the photovoltaic field station sends each reactive power target value to the corresponding photovoltaic power generation unit to achieve real-time coordinated reactive power control between photovoltaic power generation units.

[0059] Preferably, the reactive power target value of each photovoltaic power generation unit is:

[0060] ;

[0061] in, For the i The reactive power target value of each photovoltaic power generation unit, , M is the number of photovoltaic power generation units in the photovoltaic station, For the i The reactive capacity of each photovoltaic power generation unit, is the reactive capacity of the photovoltaic station.

[0062] The photovoltaic station uses the equal margin allocation method to calculate the reactive power target value of each photovoltaic power generation unit. The master control station in the station sends the reactive power target value to the photovoltaic inverter through GOOSE communication to achieve real-time coordinated control between inverters.

[0063] In order to verify the effectiveness of the photovoltaic energy storage station grid-connected coordinated control method combining voltage and power factor in the embodiment of the present invention, a system was built on the Matlab / Simulink platform as follows: Figure 2 The main parameters of the multi-machine photovoltaic station grid-connected system shown are as follows: total photovoltaic station inverter capacity = 5×20MVA; energy storage station capacity = 10 MVA; system rated frequency = 50Hz; grid impedance ratio R g / X g =0.363.

[0064] Simulation settings: During high light periods, the grid load of the photovoltaic grid-connected system changes suddenly at 1 second, resulting in overvoltage at the grid-connected point. The simulation results of the voltage characteristic power factor control effect of the proposed method are shown in Figure 2. Figure 6As shown; under the proposed control method, the simulation results of the output of each photovoltaic power generation unit are as follows Figure 7 shown.

[0065] See also Figure 6 , through this method, the photovoltaic station does not need to perform voltage regulation control during normal voltage operation, thereby reducing the reactive operation frequency of the photovoltaic inverter, maintaining the power factor above 0.98, and improving the economic benefits of power generation. Compared with traditional droop control, this method has obvious advantages during voltage fluctuations. It can not only stabilize the voltage at the photovoltaic station grid connection point between 0.97 and 1.07, but also maintain the power factor at 0.98, thereby significantly improving the voltage quality and power quality during voltage transients. Figure 7 ,This method distributes reactive power according to reactive capacity, which can avoid ,exceeding the output limit of some photovoltaic inverters and evenly exert the reactive ,support capacity of each photovoltaic inverter.

[0066] In summary, the photovoltaic energy storage station grid-connected coordinated control method combining voltage and power factor provided in the embodiment of the present invention can flexibly utilize the reactive capacity of the photovoltaic inverter and the energy storage station when the voltage changes, and adjust the grid connection point voltage and power factor so that they can meet the grid specifications at the same time, thereby improving the operating safety and economy of the photovoltaic energy storage station grid-connected system.

[0067] Embodiment 2

[0068] A photovoltaic energy storage station grid-connected coordination control system combining voltage and power factor includes: a processor; a memory storing a computer executable program, which, when executed by the processor, enables the processor to execute the photovoltaic energy storage station grid-connected coordination control method combining voltage and power factor. The relevant technical solutions are the same as those in the first embodiment, and will not be described in detail here.

[0069] Embodiment 3

[0070] A computer-readable storage medium stores a computer program, which, when executed by a processor, implements the above-mentioned photovoltaic energy storage station grid-connected coordination control method combining voltage and power factor. The relevant technical solution is the same as that of embodiment 1, and will not be described in detail here.

[0071] It will be easily understood by those skilled in the art that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A photovoltaic energy storage station grid-connected coordination control method combining voltage and power factor, characterized in that: include: When the power factor of the confluence point of the photovoltaic station grid-connected system exceeds the lower limit, the energy storage station in the photovoltaic station grid-connected system outputs min{ Q * ESS , Q maxESS } reactive power to adjust the power factor, where: Q * ESS The target value of reactive power for energy storage that the energy storage station needs to compensate for when the power factor at the junction point exceeds the lower limit. Q maxESS is the reactive capacity of energy storage station; When the grid-connected system of a photovoltaic station exceeds the grid voltage limit, the photovoltaic station Q * +△ Q Reactive power control is performed to achieve coordinated regulation of voltage and power factor, where: Q * is the total reactive power target value that the photovoltaic inverter needs to compensate for when the grid-connected point voltage exceeds the limit, △ Q To compensate the reactive power of the photovoltaic inverter for insufficient power factor regulation of energy storage, Q * ESS > Q maxESS Time Q = Q * ESS - Q maxESS , Q * ESS ≤ Q maxESS Or the photovoltaic station grid-connected system does not have a power factor exceeding the lower limit at the confluence point△ Q = 0; The photovoltaic station is based on Q * +△ Q Reactive power control is performed to achieve coordinated regulation of voltage and power factor, including: The photovoltaic station adopts the equal margin allocation method, according to Q * +△ Q Calculate the reactive power target value of each photovoltaic power generation unit; the reactive power target value of each photovoltaic power generation unit is: Q refi = ( Q * +△ Q )( Q * maxi / Q * max );in, Q refi For the i The reactive power target value of each photovoltaic power generation unit, i =1, 2, ..., M , M is the number of photovoltaic power generation units in the photovoltaic station, Q * maxi It is the first photovoltaic station i The reactive capacity of a photovoltaic power generation unit, Q * max is the total reactive capacity of the PV inverter; The master control station in the photovoltaic station sends each reactive power target value to the corresponding photovoltaic power generation unit to achieve real-time coordinated reactive power control between the photovoltaic power generation units.

2. The photovoltaic energy storage station grid-connected coordination control method combining voltage and power factor as claimed in claim 1 is characterized in that: Q * ESS for: Q * ESS = P pcc cos -1 λ ref - Q pcc ; in, P pcc is the actual active power at the junction, λ ref is the reference power factor value, Q pcc is the actual reactive power at the junction.

3. The photovoltaic energy storage station grid-connected coordination control method combining voltage and power factor as claimed in claim 1 is characterized in that: Q maxESS for: Q maxESS = [( S ESS ) 2 -( P ESS ) 2 ] 1 / 2 in, S ESS is the capacity of the energy storage station, P ESS The active power released by the energy storage station.

4. The photovoltaic energy storage station grid-connected coordination control method combining voltage and power factor as claimed in claim 1, characterized in that: Q * for: in, U is the grid voltage, U DB1 is the lower limit of the dead zone voltage, U DB2 is the upper limit of the dead zone voltage, U min is the lower limit of the grid connection point voltage, U max It is the upper limit of the grid connection point voltage.

5. The photovoltaic energy storage station grid-connected coordination control method combining voltage and power factor as claimed in claim 4 is characterized in that: Q * max for: in, P N is the rated power of the photovoltaic power generation unit, P i It is the first photovoltaic station i The active power output of each photovoltaic power generation unit.

6. A photovoltaic energy storage station grid-connected coordination control system combining voltage and power factor, characterized in that: include: processor; A memory storing a computer executable program, wherein when the program is executed by the processor, the processor executes the photovoltaic energy storage station grid-connected coordination control method combining voltage and power factor as described in any one of claims 1-5.

7. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the program is executed by a processor, a photovoltaic energy storage station grid-connected coordination control method combining voltage and power factor as described in any one of claims 1 to 5 is implemented.

Images