A method and system for regulating photovoltaic distribution network voltage in a substation under limited information conditions

Abstract

The present invention relates to the technical field of distribution network voltage regulation. Disclosed are a method and system for regulating voltage in a substation photovoltaic distribution network under limited information conditions. This method can regulate voltage using only limited information, such as nameplate parameters and real-time output voltage, current, and power, when the detailed operating status and parameters of a distributed photovoltaic power generation system are unavailable. Simultaneously, the method prioritizes the use of idle capacity in photovoltaic inverters for voltage regulation, ensuring maximum utilization of renewable energy. Active power is only utilized when the reactive capacity is fully utilized and the voltage remains high, ensuring system voltage stability.

Description

Technical Field

[0001] The present invention relates to the technical field of distribution network voltage regulation, and in particular to a method and system for regulating the voltage of a photovoltaic distribution network in a substation under limited information conditions. Background Art

[0002] In recent years, the installed capacity of distributed photovoltaic power generation has grown rapidly. However, the output of photovoltaic power generation is significantly affected by environmental factors, exhibits significant randomness, and its peak-to-valley characteristics differ significantly from the load curve. When photovoltaic power generation exceeds local demand, a reverse current can occur, causing voltage limits at the access point, degrading power quality indicators, and even impacting the safe and stable operation of the distribution network. Current distributed photovoltaic power generation systems, especially household photovoltaic systems, are generally connected to the grid in a free-flowing manner, neither subject to the unified dispatching control of the upper power grid nor lacking any coordinated control strategies among themselves. To improve the power quality of the active distribution network under high photovoltaic penetration, enhance the photovoltaic power generation absorption capacity, and achieve friendly grid connection, effective management and control of distributed photovoltaic clusters is necessary.

[0003] Distributed photovoltaic power generation systems are typically mature commercial products purchased independently by users, lacking unified planning and deployment. Consequently, they exhibit varying capacities, diverse product models and brands, and random installation times and grid connection locations. These characteristics present new challenges for effectively managing the vast number of distributed photovoltaic power generation systems involved in active distribution network voltage regulation. Furthermore, because distributed photovoltaic power generation systems come from different manufacturers and brands, they vary in communication protocols and the openness of control interfaces. Parameters such as the operating status of distributed photovoltaic power generation systems are difficult to obtain directly and can only be estimated indirectly through limited information such as output voltage and current.

[0004] Under the urgent need for voltage regulation of active distribution networks and the limited information available on distributed photovoltaic power generation system clusters, it is urgent to study a method and system for voltage regulation of photovoltaic distribution networks in substations under limited information conditions, to coordinate and control massive distributed photovoltaic power generation systems, and to utilize the remaining capacity to implement voltage regulation in an orderly manner while giving priority to active output. Summary of the Invention

[0005] The present invention provides a method and system for regulating the voltage of a photovoltaic distribution network in an area under limited information conditions, so as to solve the problems existing in the prior art.

[0006] In order to achieve the above object, the present invention is implemented through the following technical solutions:

[0007] In a first aspect, the present invention provides a method for regulating the voltage of a photovoltaic distribution network in a substation under limited information conditions, which is applied to a distributed photovoltaic power generation system. The method comprises:

[0008] Step 1: Initialize the distributed photovoltaic power generation system, set the distributed photovoltaic power generation system active power instruction P to 1.1, the reactive power instruction Q to 0, and set a status flag Flag, initialized to 0;

[0009] Step 2: In each control cycle, the maximum power point PMPPT of the photovoltaic power generation system is first estimated. The estimation steps are as follows:

[0010] Determine the value of Flag. If it is 0, the sampled value of the inverter output active power Pout in the distributed photovoltaic power generation system is normalized according to the rated capacity on the inverter nameplate to obtain the per-unit value of the output active power Ppu, and use it as the estimated value of the maximum power point of the distributed photovoltaic power generation system. If Flag = 1, the estimation of the maximum power point of the distributed photovoltaic power generation system is blocked, and PMPPT always uses the estimated value before blocking.

[0011] Step 3: In each control cycle, when the average voltage V is in different partitions, the photovoltaic control terminal generates active power instructions P and reactive power instructions Q of the distributed photovoltaic power generation system according to different control modes to achieve control.

[0012] Optionally, the partitions include 5, namely, zone I, zone II, zone III, zone IV, and zone V5, and the control modes include 5, namely, control mode 1, control mode 2, control mode 3, control mode 4, and control mode 5;

[0013] Control mode 1 is when the voltage V is in zone I, that is, V L0 <V<V U0 , where V L0 Indicates the voltage value corresponding to the boundary between zone I and zone II, V U0 Indicates the voltage value corresponding to the boundary point between zone I and zone IV. The PV control terminal does not need to regulate the voltage. The reactive power command Q remains at 0. The active power command P should not be less than the actual maximum power point. At the same time, the active power command cannot be greater than the allowable capacity limit. Set P = Sn, where Sn is the allowable capacity limit of the inverter and the per-unit value is 1.1.

[0014] Optionally, control mode 2 is when the voltage is in zone II, that is, V L1 <V<V L0 , where V L1 Indicates the voltage value corresponding to the boundary point between zone II and zone III. Set the active power instruction P=Sn. In this interval, voltage regulation is only based on reactive power. The reactive power instruction value is proportional to the voltage deviation value.

[0015] Optionally, control mode 3 is when the voltage is in zone IV, that is, V U0 <V<V U1 , where VU1 Indicates the voltage value corresponding to the boundary point between zone IV and zone V5. Reactive power is used for voltage regulation first. Active power is used for voltage regulation only when reactive power cannot meet the voltage regulation requirements.

[0016] Optionally, control mode 4 is when the voltage is in zone III, that is, V≤V L1 , the distributed photovoltaic power generation system has reached its maximum voltage regulation capability. At this time, the reactive and active power command values ​​generated by the photovoltaic control terminal are: P = Sn, Q = Q max , where Q max It indicates the maximum reactive power that the distributed generation can output, in per-unit form. Its reference value is the same as the reference value of the active power instruction P.

[0017] Optionally, control mode 5 is when the voltage is in the V5 region, that is, V ≥ V U1 , the photovoltaic control terminal sets both active and reactive commands to 0, and the distributed photovoltaic power generation system is equivalent to a locked off-grid state.

[0018] Optionally, in each control cycle, the value of the flag bit Flag is updated according to different rules depending on the control mode. The specific update strategy is: in the BF segment in control mode 4 and control mode 5, the flag bit Flag is set to 1, that is, Flag = 1; in other modes, it is set to 0, that is, Flag = 0.

[0019] In the second aspect, the present application provides a photovoltaic distribution network voltage control system in a substation under limited information conditions, including a memory, a processor, and a computer program stored in the memory and runnable on the processor. When the processor executes the computer program, the steps of the method described in the first aspect are implemented.

[0020] Beneficial effects:

[0021] The present invention provides a method for regulating voltage in a substation photovoltaic distribution network under limited information conditions. Without access to the detailed operating status and parameters of a distributed photovoltaic power generation system, voltage regulation is performed solely based on limited information such as nameplate parameters and real-time output voltage, current, and power. This method also prioritizes the use of idle capacity in photovoltaic inverters for voltage regulation, ensuring maximum utilization of renewable energy. Active power is only utilized when the voltage remains high after reactive power capacity has been fully utilized, ensuring system voltage stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a flow chart of a method for controlling the voltage of a photovoltaic distribution network in a substation under limited information conditions according to a preferred embodiment of the present invention;

[0023] Figure 2This is a structural diagram of an application system of a method for controlling voltage of a photovoltaic distribution network in a substation under limited information conditions according to a preferred embodiment of the present invention;

[0024] Figure 3 Schematic diagram of five partitions according to a preferred embodiment of the present invention;

[0025] Figure 4 Schematic diagram of the static characteristic curve corresponding to the voltage in zone II in a preferred embodiment of the present invention;

[0026] Figure 5 Schematic diagram of the static characteristic curve corresponding to the voltage in the IV region in a preferred embodiment of the present invention. DETAILED DESCRIPTION

[0027] The following is a clear and complete description of the technical solutions of the present invention. It should be understood that the embodiments described are only a portion of the embodiments of the present invention, not all of them. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without inventive effort are intended to fall within the scope of protection of the present invention.

[0028] Unless otherwise defined, the technical or scientific terms used in the present invention shall have the usual meanings understood by persons of ordinary skill in the field to which the present invention belongs. The words "first", "second" and similar terms used in the present invention do not indicate any order, quantity or importance, but are only used to distinguish different components. Similarly, words such as "one" or "a" do not indicate a quantity limitation, but rather indicate the existence of at least one. Words such as "connected" or "connected" are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. "Up", "down", "left", "right" and the like are only used to indicate relative positional relationships. When the absolute position of the object being described changes, the relative positional relationship also changes accordingly.

[0029] See Figure 1 and Figure 2 This application provides a method for controlling the voltage of a photovoltaic distribution network in a substation under limited information conditions, which is applied to a distributed photovoltaic power generation system and includes:

[0030] Step 1: Initialize the distributed photovoltaic power generation system, set the distributed photovoltaic power generation system active power instruction P to 1.1, the reactive power instruction Q to 0, and set a status flag Flag, initialized to 0;

[0031] Step 2: In each control cycle, the maximum power point PMPPT of the photovoltaic power generation system 1 is first estimated. The estimation steps are as follows:

[0032] Determine the value of Flag. If it is 0, the sampled value of the inverter output active power Pout in the distributed photovoltaic power generation system is normalized according to the rated capacity on the inverter nameplate to obtain the per-unit value of the output active power Ppu, and use it as the estimated value of the maximum power point of the distributed photovoltaic power generation system 1. If Flag = 1, the estimation of the maximum power point of the distributed photovoltaic power generation system 1 is blocked, and the PMPPT always uses the estimated value before blocking.

[0033] Step 3: In each control cycle, when the average voltage V is located in different partitions, the photovoltaic control terminal 2 generates active power instructions P and reactive power instructions Q of the distributed photovoltaic power generation system 1 according to different control modes to achieve control.

[0034] It should be understood that the above-described method for controlling the voltage of a photovoltaic distribution network in a substation under limited information conditions can be applied to a voltage control system for a substation in a substation under limited information conditions. The system comprises a substation control terminal 3, a photovoltaic control terminal 2, and a communication system. Given limited information such as the nameplate parameters of the distributed photovoltaic power generation system 1 and the real-time output voltage, current, and power, the system rationally controls the active and reactive power output based on the system average voltage and, in accordance with the principle of prioritizing the use of the idle capacity of the distributed photovoltaic power generation system 1, to achieve voltage regulation and maximize the utilization of distributed photovoltaic energy. The communication system collects the voltage of each node from the photovoltaic control terminal 2, and calculates the average voltage of each node in the substation. The voltage, current, and power data at the local photovoltaic inverter grid connection point are monitored and transmitted to the substation control terminal 3 via the communication system. The substation control terminal 3 receives the system average voltage information, executes the voltage control strategy, generates the active and reactive power command values ​​for the photovoltaic inverter output, and transmits them to the photovoltaic inverter.

[0035] Distributed photovoltaic power generation systems 1, especially distributed photovoltaic power generation systems 1, are usually connected to a low-voltage distribution network. Therefore, taking a low-voltage substation as an example, the implementation method and system of a substation photovoltaic distribution network voltage control method under limited information conditions involved in the present invention are explained. The system is mainly composed of a substation control terminal 3, a photovoltaic control terminal 2 and a communication system. The substation control terminal 3 is located at the transformer 4 and is the control center of the entire substation. It can not only communicate with the upper power grid 5, but also communicate with each photovoltaic control terminal 2 in the substation. The photovoltaic control terminal 2 is a local controller added near the installation point of the distributed photovoltaic power generation system 1. It plays the role of converting communication protocols, receiving instructions from the substation control terminal 3, monitoring the voltage, current and power of the grid-connected point of the distributed photovoltaic power generation system 1, executing voltage control strategies, and generating local voltage control instructions.

[0036] Specifically, when implementing internal voltage control within a substation, each photovoltaic control terminal 2 first collects the voltage value Vi at the grid connection point of the distributed photovoltaic power generation system 1 and transmits it to the substation control terminal 3 at the substation via a communication channel. Based on the voltage values ​​at each monitoring point, the substation control terminal 3 calculates the average voltage V within the substation and transmits it to each photovoltaic control terminal 2. Based on the value of V, the nameplate parameters of the distributed photovoltaic power generation system 1, and the grid connection point voltage, current, and power information, each photovoltaic control terminal 2 generates corresponding active and reactive power adjustments according to its built-in voltage regulation strategy and transmits them to the distributed photovoltaic power generation system 1 for execution.

[0037] The specific scheme of the voltage regulation strategy built into the photovoltaic control terminal 2 is as follows:

[0038] In the present invention, the average voltage V is divided into 5 intervals, such as Figure 3 As shown, the average voltage of the low-voltage distribution network is V≤V L1 In zone III, the average voltage V L1 <V<V L0 In zone II, the average voltage V L0 <V<V U0 In the I region, the average voltage V U0 <V<V U1 IV region and average voltage V≥V U1 In the figure, V5 is the rated voltage. In the five zones, zone I is called the control dead zone, zones II and IV are called the proportional control zones, and zones III and V5 are called the saturation control zones. According to the relevant requirements of the low-voltage distribution network voltage standard, when the voltage is expressed in per-unit value, V U1 Can be set to 1.1, V L1 Can be set to 0.93. V U0 and V L0 The value of can be determined according to a certain quantile based on the distribution law of the voltage history data, such as p(V L0 ≤V≤V U0 )=1-α (α is 0.1) means the average voltage of the low voltage distribution network V is at V L0 <V<V U0 The probability within the interval is 0.9, α represents the significance level, and p represents the probability, which means that approximately 90% of the time, the average voltage of the low-voltage distribution network is always in the regulation dead zone and does not require the distributed photovoltaic power generation system 1 to be regulated.

[0039] After the system is started, it is initialized first. During initialization, the active power instruction P of the distributed photovoltaic power generation system 1 is set to 1.1, and the reactive power instruction Q is set to 0. At the same time, a status flag Flag is set and initialized to 0.

[0040] After initialization, the control strategy first estimates the maximum power point (PMPPT) of the distributed photovoltaic power generation system 1 in each control cycle. The estimation steps are as follows: first determine the value of Flag. If it is 0, the sampled value of the active power Pout output by the inverter in the distributed photovoltaic power generation system 1 is normalized according to the rated capacity on the inverter nameplate to obtain Ppu, and use it as the estimated value of the maximum power point of the distributed photovoltaic power generation system 1, that is, PMPPT = Ppu; if Flag = 1, the estimation of the maximum power point of the distributed photovoltaic power generation system 1 is locked, and PMPPT is always used according to the estimated value before locking.

[0041] In each control cycle, when the average voltage V is in different partitions, the photovoltaic control terminal 2 generates the active power command P and reactive power command Q of the distributed photovoltaic power generation system 1 according to different control modes, which are specifically divided into the following five situations:

[0042] 1) When the voltage V is in region I, that is, V L0 <V<V U0 , the photovoltaic control terminal 2 does not need to regulate the voltage, so the reactive power command Q remains at 0. In order to ensure that the inverter operates reliably at the maximum power point, the active power command P should not be less than the actual maximum power point. At the same time, in order to ensure the safe operation of the inverter, the active power command cannot be greater than the allowable capacity limit. Therefore, P = Sn is set, where Sn is the allowable capacity limit of the inverter, usually 1.1 times the rated power, so the per-unit value is 1.1;

[0043] 2) When the voltage is in zone II, that is, V L1 <V<V L0 , the distributed photovoltaic power generation system 1 needs to adjust the voltage by increasing the output active or reactive power (or reducing the absorbed reactive power). However, the active power is limited by the photovoltaic output capacity and can only reach the maximum PMPPT. At the same time, in order to maximize the use of renewable energy, it is necessary to maintain the maximum power point state, so the active power command P = Sn is still set. In this range, only reactive power is used for voltage regulation. The reactive power command value is proportional to the voltage deviation value, and the specific relationship is:

[0044] Q=-k1(VV L0 ), V L1 <V<V L0 (1)

[0045] The corresponding static characteristic curve is as follows Figure 4 As shown in formula (1), Q is the reactive power command value, k1 is the proportional coefficient, which means Figure 4 The slope of the curve in zone II is Q maxIt represents the maximum reactive power that the distributed power source can output, which is limited by two factors: a) the maximum available reactive power capacity when considering the capacity of the distributed photovoltaic power generation system 1, which is S n Indicates the capacity limit allowed for the inverter in the distributed photovoltaic power generation system 1, with a per-unit value of 1.1, P MPPT represents the active power corresponding to the maximum power point of the distributed photovoltaic power generation system 1, which is an estimated value, namely PMPPT; b) the maximum available reactive capacity when considering the system's power factor constraint on the distributed photovoltaic power generation system 1 is taken as: Q max =P MPPT tan(arccos(λ1)), where λ1 is the allowable lagging power factor limit (usually 0.8). When the voltage is within this range, since Flag = 0, the estimated value of PMPPT is Ppu, which is the per-unit value of the actual output active power Pout. The final maximum available reactive capacity is:

[0046]

[0047] 3) When the voltage is in the IV region, that is, V U0 <V<V U1 , indicating that the distributed photovoltaic power generation system 1 needs to adjust the voltage by reducing the output active or reactive power (or increasing the absorbed reactive power). However, in order to make full use of renewable energy, reactive power should be used for voltage regulation first, and only when reactive power cannot meet the voltage regulation requirements can active power be used for voltage regulation. The voltage regulation process is as follows Figure 5 As shown, line ABCD is the reactive-voltage static characteristic curve (for Figure 5 , AB and CD segments in ABCD are straight lines, and BC segment is an arc. Line EBF is the active power-voltage static characteristic curve (EB and BF are both straight lines). The slopes of AB and BF are the same. The projection of point B on the P axis is PMPPT, and the projection on the Q axis is Q min for:

[0048]

[0049] Where λ2 is the allowable leading power factor limit (usually 0.8 leading). Point C indicates that the distributed photovoltaic power generation system 1 not only operates within the allowable capacity limit Sn, but also outputs active and reactive power that reaches the allowable leading power factor limit. The corresponding relationship between reactive power Q2 and active power P2 is: The slope of ABF is It should be noted that Figure 5 China believes So point B is above point C. In reality, it is possible at this time Figure 5 Points B and C coincide, and the reactive-voltage static characteristic curve no longer has a BC arc segment.

[0050] In the entire IV zone, the photovoltaic control terminal 2 calculates the active and reactive power instructions according to the principles of equations (4) and (5):

[0051]

[0052]

[0053] In the formula, k2 is the proportional coefficient, that is Figure 5 The slope of the ABF;

[0054] 4) When the voltage is at III, that is, V≤V L1 , the distributed photovoltaic power generation system 1 has reached its maximum voltage regulation capability. At this time, the reactive and active power command values ​​generated by the photovoltaic control terminal 2 are: P = Sn, Q = Q max , Q max is the calculation result of formula (2);

[0055] 5) When the voltage is in the V5 region, that is, V≥V U1 , the photovoltaic control terminal 2 sets both the active and reactive commands to 0, and the distributed photovoltaic power generation system 1 is equivalent to a locked off-grid state.

[0056] In each control cycle, the photovoltaic control terminal 2 also updates the value of the flag according to the different intervals of the average voltage V. The specific update strategy is: when V is in the IV zone BF segment and the V5 zone, it is set to 1, that is, Flag = 1; when V is in other zones, it is set to 0, that is, Flag = 0.

[0057] The present application also provides a system for regulating voltage of a photovoltaic distribution network in a substation under limited information conditions, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor implements the steps of the above-mentioned method when executing the computer program. This system for regulating voltage of a photovoltaic distribution network in a substation under limited information conditions can implement various embodiments of the above-mentioned method for regulating voltage of a photovoltaic distribution network in a substation under limited information conditions, and can achieve the same beneficial effects, which are not described in detail here.

[0058] The above describes in detail the preferred embodiments of the present invention. It should be understood that those skilled in the art can make numerous modifications and variations based on the concepts of the present invention without inventive effort. Therefore, any technical solutions that can be derived by those skilled in the art through logical analysis, reasoning, or limited experimentation based on the concepts of the present invention and the prior art should be within the scope of protection defined by the claims.

Claims

1. A method for regulating the voltage of a photovoltaic distribution network in a substation under limited information conditions, applied to a distributed photovoltaic power generation system, characterized in that: The method comprises: Step 1: Initialize the distributed photovoltaic power generation system, set the distributed photovoltaic power generation system active power instruction P to 1.1, the reactive power instruction Q to 0, and set a status flag Flag, initialized to 0; Step 2: In each control cycle, the maximum power point PMPPT of the photovoltaic power generation system is first estimated. The estimation steps are as follows: Determine the value of Flag. If it is 0, the sampled value of the inverter output active power Pout in the distributed photovoltaic power generation system is normalized according to the rated capacity on the inverter nameplate to obtain Ppu, which is used as the estimated value of the maximum power point of the distributed photovoltaic power generation system. If Flag=1, the estimation of the maximum power point of the distributed photovoltaic power generation system is blocked, and PMPPT always uses the estimated value before blocking. Step 3: In each control cycle, when the average voltage V is in different partitions, the photovoltaic control terminal generates active power instructions P and reactive power instructions Q of the distributed photovoltaic power generation system according to different control modes to achieve control; There are five partitions, namely, Zone I, Zone II, Zone III, Zone IV, and Zone V5, and five control modes, namely, Control Mode 1, Control Mode 2, Control Mode 3, Control Mode 4, and Control Mode 5. Control mode 1 is when the voltage V is in zone I, that is, V L0 <V<V U0 , where V L0 Indicates the voltage value corresponding to the boundary between zone I and zone II, V U0 Indicates the voltage value corresponding to the boundary between zone I and zone IV. The PV control terminal does not need to regulate the voltage. The reactive power command Q remains at 0. The active power command P should not be less than the actual maximum power point. At the same time, the active power command cannot be greater than the allowable capacity limit. Set P = Sn, where Sn is the allowable capacity limit of the inverter in the distributed PV power generation system, and the per-unit value is 1.

1. In each control cycle, the flag value is updated according to different rules based on the different control modes. The specific update strategy is: in the BF segment of control mode 4 and control mode 5, the flag is set to 1, that is, Flag=1; in other modes, it is set to 0, that is, Flag=0.

2. The method for controlling the voltage of a photovoltaic distribution network in a substation under limited information conditions according to claim 1, characterized in that: Control mode 2 is when the voltage is in zone II, that is, V L1 <V<V L0 , where V L1 Indicates the voltage value corresponding to the boundary point between zone II and zone III. Set the active power instruction P=Sn. In this interval, voltage regulation is only based on reactive power. The reactive power instruction value is proportional to the voltage deviation value.

3. The method for controlling the voltage of a photovoltaic distribution network in a substation under limited information conditions according to claim 1, characterized in that: Control mode 3 is when the voltage is in the IV zone, that is, V U0 <V<V U1 , where V U1 Indicates the voltage value corresponding to the boundary point between zone IV and zone V5. Reactive power is used for voltage regulation first. Active power is used for voltage regulation only when reactive power cannot meet the voltage regulation requirements.

4. The method for controlling the voltage of a photovoltaic distribution network in a substation under limited information conditions according to claim 1, characterized in that: Control mode 4 is when the voltage is in zone III, that is, V≤V L1 , the distributed photovoltaic power generation system has reached its maximum voltage regulation capability. At this time, the reactive and active power command values ​​generated by the photovoltaic control terminal are: P=Sn, Q=Q max .

5. The method for controlling the voltage of a photovoltaic distribution network in a substation under limited information conditions according to claim 1, characterized in that: Control mode 5 is when the voltage is in the V5 region, that is, V≥V U1 , the photovoltaic control terminal sets both active and reactive commands to 0, and the distributed photovoltaic power generation system is equivalent to a locked off-grid state.

6. A photovoltaic distribution network voltage control system in a substation under limited information conditions, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that: When the processor executes the computer program, the steps of the method according to any one of claims 1 to 5 are implemented.

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