A method and system for suppressing overvoltage in distributed photovoltaic power station

Abstract

The present invention relates to a method and system for suppressing overvoltage in a distributed photovoltaic power station. The method suppresses overvoltage in a distributed photovoltaic power station by implementing a multi-mode coordinated control method of a maximum power mode, a reactive power control mode, and a maximum power factor control mode based on the regulation of overvoltage, without requiring the access of voltage regulating devices such as capacitor banks and transformers.

Description

Technical Field

[0001] The present invention relates to the technical field of photovoltaic power generation, and in particular to an overvoltage suppression method and system for a distributed photovoltaic power station. Background Art

[0002] Distributed photovoltaic grid connection will cause many adverse effects on low-voltage distribution networks, such as increasing the probability of voltage over-limit in distribution networks and increasing the difficulty of controlling relay protection. When the photovoltaic power generation capacity is relatively small relative to the power grid, the disturbance of distributed photovoltaic output power has little impact on the power grid. However, as the scale of distributed photovoltaic grid connection gradually expands, low-voltage distribution networks are prone to reverse power flow and voltage over-limit at the end of the line. Among them, the problem that cannot be ignored is that the reactive power support capacity of photovoltaic power sources is weak, which greatly increases the risk of voltage over-limit at the grid connection point.

[0003] Traditional voltage regulating devices (such as parallel capacitor banks and transformer on-load voltage regulation) operate frequently, which affects the life of the equipment and makes the voltage control of the distribution network more complicated. Summary of the invention

[0004] In view of this, the present invention provides an overvoltage suppression method and system for a distributed photovoltaic power station, which suppresses the overvoltage of the distributed photovoltaic power station by adopting a multi-mode coordinated control method without the need for the connection of voltage regulating devices such as capacitor banks and transformers.

[0005] To achieve the above object, the present invention provides the following solutions:

[0006] A method for suppressing overvoltage in a distributed photovoltaic power station, the method comprising the following steps:

[0007] In the maximum power mode, it is determined whether the low-voltage side bus voltage of the distributed photovoltaic power station exceeds the bus voltage upper limit value to obtain a first determination result; the maximum power mode is to control the operation of each photovoltaic power generation unit in the distributed photovoltaic power station by using the maximum power control method;

[0008] If the first judgment result indicates yes, then switch to the reactive power control mode, when the upper limit of the reactive power control mode is reached, judge whether the low-voltage side bus voltage still exceeds the upper limit of the bus voltage, and obtain a second judgment result; the switching to the reactive power control mode is to reduce the low-voltage side bus voltage by adjusting the reactive power of each photovoltaic power generation unit; the upper limit of the reactive power control mode is that the total reactive power of the distributed photovoltaic power station reaches the upper limit of the total reactive power that can be generated by the distributed photovoltaic power station;

[0009] If the second judgment result indicates yes, switch to the maximum power factor control mode; the maximum power factor control mode is to reduce the low-voltage side bus voltage by adjusting the maximum power factor of the distributed photovoltaic power station so that the low-voltage side bus voltage does not exceed the bus voltage upper limit;

[0010] In reactive power control mode or maximum power factor control mode, when a maximum power mode instruction is received, switch to maximum power mode and return to step "In maximum power mode, determine whether the low-voltage side bus voltage of the distributed photovoltaic power station exceeds the bus voltage upper limit value to obtain a first judgment result".

[0011] Optionally, the method of adjusting the reactive power of each photovoltaic power generation unit to reduce the low-voltage side bus voltage specifically includes:

[0012] According to the difference between the low-voltage bus voltage and the bus voltage upper limit, the PI control algorithm is used to generate the total reactive power command of the distributed photovoltaic power station;

[0013] According to the total reactive power instruction of the distributed photovoltaic power station, the reactive power instruction of each photovoltaic power generation unit is calculated;

[0014] While maximizing the active power of each photovoltaic power generation unit, adjusting the reactive power of each photovoltaic power generation unit according to the reactive power instruction of each photovoltaic power generation unit;

[0015] Determine whether the low-voltage side bus voltage of the distributed photovoltaic power station after reactive power regulation exceeds the bus voltage upper limit value, and obtain a third determination result;

[0016] If the third judgment result indicates yes, then return to the step of "generating a total reactive power instruction of the distributed photovoltaic power station by using a PI control algorithm according to the difference between the low-voltage side bus voltage and the upper limit value of the bus voltage";

[0017] If the third judgment result indicates no, then return to the step of "adjusting the reactive power of each photovoltaic power generation unit according to the reactive power instruction of each photovoltaic power generation unit while maximizing the active power of each photovoltaic power generation unit".

[0018] Optionally, the step of calculating the reactive power instruction of each photovoltaic power generation unit according to the total reactive power instruction of the distributed photovoltaic power station specifically includes:

[0019] According to the total reactive power instruction of the distributed photovoltaic power station, the formula Q i_ref =k i Q T_ref , calculate the reactive power command of each photovoltaic power generation unit;

[0020] Among them, Qi_ref represents the reactive power command of the i-th photovoltaic power generation unit, k i represents the reactive power coefficient of the i-th photovoltaic power generation unit, Q T_ref Indicates the total reactive power command of the distributed photovoltaic power station.

[0021] Optionally, the reactive power instruction of each photovoltaic power generation unit is calculated according to the total reactive power instruction of the distributed photovoltaic power station, and ...

[0022] Using the formula Calculate the upper limit of reactive power that can be generated by each photovoltaic power generation unit;

[0023] According to the reactive power upper limit of each photovoltaic power generation unit, calculate the total reactive power upper limit of the distributed photovoltaic power station;

[0024] According to the reactive power upper limit of each photovoltaic power generation unit and the total reactive power upper limit of the distributed photovoltaic power station, the formula Calculate the reactive power coefficient of each photovoltaic power generation unit;

[0025] Among them, Q i_lim represents the reactive power upper limit of the ith photovoltaic power generation unit, Pi and Se_i represent the active power and rated apparent capacity of the grid-connected converter of the ith photovoltaic power generation unit, respectively, Q T_lim It represents the upper limit of the total reactive power that can be generated by the distributed photovoltaic power station, and n represents the number of photovoltaic power generation units included in the distributed photovoltaic power station.

[0026] Optionally, the method of adjusting the maximum power factor of the distributed photovoltaic power station to reduce the low-voltage side bus voltage so that the low-voltage side bus voltage does not exceed the bus voltage upper limit value specifically includes:

[0027] Reduce the maximum power factor of distributed photovoltaic power stations;

[0028] Adjusting the active power of the grid-connected converter of each photovoltaic power generation unit according to the maximum power factor;

[0029] Determine whether the bus voltage on the low-voltage side of the distributed photovoltaic power station after the maximum power factor adjustment exceeds the bus voltage upper limit value, and obtain a fourth determination result;

[0030] If the fourth judgment result indicates yes, then return to step “reducing the maximum power factor of the distributed photovoltaic power station”;

[0031] If the fourth judgment result indicates no, then return to the step of "adjusting the active power of the grid-connected converter of each photovoltaic power generation unit according to the maximum power factor".

[0032] Optionally, adjusting the active power of the grid-connected converter of each photovoltaic power generation unit according to the maximum power factor specifically includes:

[0033] For each of the photovoltaic power generation units, the judgment formula Whether it is established, obtaining a fifth judgment result;

[0034] If the fifth judgment result indicates no, reducing the active power of the grid-connected converter of the photovoltaic power generation unit while keeping the apparent power of the grid-connected converter of the photovoltaic power generation unit unchanged;

[0035] If the fifth judgment result indicates yes, the apparent power and the active power of the grid-connected converter of the photovoltaic power generation unit are kept unchanged.

[0036] An overvoltage suppression system for a distributed photovoltaic power station, the system comprising:

[0037] A first judgment module is used to judge whether the low-voltage side bus voltage of the distributed photovoltaic power station exceeds the bus voltage upper limit value, and obtain a first judgment result;

[0038] A reactive power control module, configured to control the operation of each photovoltaic power generation unit in the distributed photovoltaic power station by using a maximum power control method if the first judgment result indicates no;

[0039] A reactive power control module is used to, if the first judgment result indicates yes, adjust the reactive power of each photovoltaic power generation unit to reduce the low-voltage side bus voltage, and when the total reactive power of the distributed photovoltaic power station reaches the upper limit of the total reactive power that can be generated by the distributed photovoltaic power station, determine whether the low-voltage side bus voltage still exceeds the bus voltage upper limit value to obtain a second judgment result;

[0040] The maximum power factor control module is used to adjust the maximum power factor of the distributed photovoltaic power station to reduce the low-voltage side bus voltage if the second judgment result indicates yes, so that the low-voltage side bus voltage does not exceed the bus voltage upper limit.

[0041] Optionally, the reactive power control module specifically includes:

[0042] The total reactive power command generation submodule is used to generate the total reactive power command of the distributed photovoltaic power station using the PI control algorithm according to the difference between the low-voltage side bus voltage and the upper limit of the bus voltage;

[0043] The reactive power instruction calculation submodule is used to calculate the reactive power instruction of each photovoltaic power generation unit according to the total reactive power instruction of the distributed photovoltaic power station;

[0044] A reactive power regulation submodule, used to regulate the reactive power of each photovoltaic power generation unit according to the reactive power instruction of each photovoltaic power generation unit while maximizing the active power of each photovoltaic power generation unit;

[0045] The third judgment submodule is used to judge whether the low-voltage side bus voltage of the distributed photovoltaic power station after reactive power adjustment exceeds the bus voltage upper limit value, and obtain a third judgment result;

[0046] A first return submodule, configured to return to the total reactive power instruction generation submodule if the third judgment result indicates yes;

[0047] The second return submodule is used to return to the reactive power regulation submodule if the third judgment result indicates no.

[0048] Optionally, the reactive power instruction calculation submodule specifically includes:

[0049] The reactive power instruction calculation unit is used to calculate the total reactive power instruction of the distributed photovoltaic power station using the formula Q i_ref =k i Q T_ref , calculate the reactive power command of each photovoltaic power generation unit;

[0050] Among them, Q i_ref represents the reactive power command of the i-th photovoltaic power generation unit, k i represents the reactive power coefficient of the i-th photovoltaic power generation unit, Q T_ref Indicates the total reactive power command of the distributed photovoltaic power station.

[0051] Optionally, the reactive power control module further includes:

[0052] The reactive power upper limit calculation submodule is used to calculate the reactive power upper limit using the formula Calculate the upper limit of reactive power that can be generated by each photovoltaic power generation unit;

[0053] The total reactive power upper limit calculation submodule is used to calculate the total reactive power upper limit of the distributed photovoltaic power station according to the reactive power upper limit of each photovoltaic power generation unit;

[0054] The reactive power coefficient calculation submodule is used to calculate the reactive power coefficient based on the reactive power upper limit of each photovoltaic power generation unit and the total reactive power upper limit of the distributed photovoltaic power station using the formula Calculate the reactive power factor of each photovoltaic power generation unit;

[0055] Among them, Q i_limrepresents the reactive power upper limit of the ith photovoltaic power generation unit, Pi and Se_i represent the active power and rated apparent capacity of the grid-connected converter of the ith photovoltaic power generation unit, respectively, Q T_lim It represents the upper limit of the total reactive power that can be generated by the distributed photovoltaic power station, and n represents the number of photovoltaic power generation units included in the distributed photovoltaic power station.

[0056] According to the specific embodiments provided by the present invention, the present invention discloses the following technical effects:

[0057] The present invention provides an overvoltage suppression method and system for a distributed photovoltaic power station, the method comprising the following steps: in a maximum power mode, judging whether the bus voltage on the low-voltage side of the distributed photovoltaic power station exceeds the upper limit of the bus voltage, and obtaining a first judgment result; the maximum power mode is to use a maximum power control method to control the operation of each photovoltaic power generation unit in the distributed photovoltaic power station; if the first judgment result indicates yes, switching to a reactive power control mode, when the upper limit of the reactive power control mode is reached, judging whether the bus voltage on the low-voltage side still exceeds the upper limit of the bus voltage, and obtaining a second judgment result; the switching to the reactive power control mode is to reduce the bus voltage on the low-voltage side by adjusting the reactive power of each photovoltaic power generation unit. line voltage; the upper limit of the reactive power control mode is when the total reactive power of the distributed photovoltaic power station reaches the upper limit of the total reactive power that can be generated by the distributed photovoltaic power station; if the second judgment result indicates yes, switch to the maximum power factor control mode; the maximum power factor control mode is to reduce the low-voltage side bus voltage by adjusting the maximum power factor of the distributed photovoltaic power station, so that the low-voltage side bus voltage does not exceed the upper limit of the bus voltage; in the reactive power control mode or the maximum power factor control mode, when the maximum power mode instruction is received, switch to the maximum power mode, and return to the step "in the maximum power mode, determine whether the low-voltage side bus voltage of the distributed photovoltaic power station exceeds the upper limit of the bus voltage, and obtain the first judgment result". The present invention realizes the multi-mode coordinated control of the maximum power mode, the reactive power control mode and the maximum power factor control mode based on the regulation of overvoltage to achieve the suppression of overvoltage in the distributed photovoltaic power station, without the need to connect voltage regulating devices such as capacitor banks and transformers. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0059] Figure 1 A schematic diagram of the structure of a distributed photovoltaic power station provided by an embodiment of the present invention;

[0060] Figure 2 A schematic diagram of an overvoltage suppression method for a distributed photovoltaic power station provided by an embodiment of the present invention;

[0061] Figure 3 A flow chart of an overvoltage suppression method for a distributed photovoltaic power station provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0062] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0063] The purpose of the present invention is to provide a method and system for suppressing overvoltage in a distributed photovoltaic power station, which can suppress overvoltage in a distributed photovoltaic power station by adopting a multi-mode coordinated control method without the need for access to voltage regulating devices such as capacitor banks and transformers.

[0064] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0065] Typical distributed photovoltaic power station structure Figure 1 As shown in Figure 1, multiple photovoltaic power generation units are connected in parallel to a common low-voltage bus, and then connected to the system after being stepped up by a transformer.

[0066] The present invention proposes a multi-mode coordinated control method for the overvoltage problem of distributed photovoltaic power stations. Figure 2 As shown. The coordinated control method mainly consists of two parts: the coordinated control strategy of the power station and the switching of multiple operating modes of distributed photovoltaic power generation units. Among them, the coordinated control strategy of the power station is responsible for real-time monitoring of the low-voltage bus voltage and controlling the operating mode of each distributed photovoltaic power generation unit; each distributed photovoltaic power generation unit switches between the three operating modes of maximum power mode (MPP mode), reactive power control mode, and maximum power factor control mode according to the coordinated control strategy of the power station, thereby effectively suppressing the overvoltage of the power station.

[0067] Specifically, Figure 3 As shown, an embodiment of the present invention provides an overvoltage suppression method for a distributed photovoltaic power station, the method comprising the following steps:

[0068] Step 101, in the maximum power mode, determine whether the low-voltage side bus voltage of the distributed photovoltaic power station exceeds the bus voltage upper limit value, and obtain a first judgment result; the maximum power mode is to use the maximum power control method to control the operation of each photovoltaic power generation unit in the distributed photovoltaic power station.

[0069] Bus voltage monitoring strategy Real-time monitoring of low voltage bus voltage U T . If U T Does not exceed the bus voltage upper limit U T_lim , that is U T ≤U T_lim When the bus voltage monitoring strategy controls each photovoltaic power generation unit to operate in MPP (Maximum Power) mode; if the bus overvoltage occurs, that is, U T >U T_lim , then the reactive power coordinated control strategy is entered and the reactive power control mode is switched to, that is, step 102 is executed.

[0070] Step 102, if the first judgment result indicates yes, then switch to the reactive power control mode, when the upper limit of the reactive power control mode is reached, judge whether the low-voltage side bus voltage still exceeds the upper limit of the bus voltage, and obtain a second judgment result; the switching to the reactive power control mode is to adjust the reactive power of each photovoltaic power generation unit to reduce the low-voltage side bus voltage; the upper limit of the reactive power control mode is that the total reactive power of the distributed photovoltaic power station reaches the upper limit of the total reactive power that can be generated by the distributed photovoltaic power station;

[0071] The purpose of the coordinated reactive power control strategy of the power station is to T >U T_lim When the active power of the photovoltaic power generation unit is ensured to operate in the MPP mode, the apparent power capacity of the grid-connected converter is fully utilized, and the grid-connected converter is used to generate reactive power to control the voltage (because the grid-connected converter can reduce the power station voltage when absorbing reactive power, the embodiment of the present invention regards the photovoltaic power generation unit absorbing reactive power as positive).

[0072] The reactive power coordination control strategy of the power station, i.e., the specific steps of step 102 include:

[0073] (1) Calculate the upper limit value Q of reactive power that can be generated by each photovoltaic power generation unit i_lim :

[0074]

[0075] Where i = 1, 2, ... n. n means that there are n distributed photovoltaic power generation units in the power station; P i and S e_iThey respectively represent the active power and rated apparent capacity of the grid-connected converter of the i-th photovoltaic power generation unit.

[0076] (2) Calculate the upper limit of the total reactive power that can be generated by the power station Q T_lim :

[0077]

[0078] (3) Calculate the reactive power coefficient k of each distributed photovoltaic power generation unit i :

[0079]

[0080] (4) Calculate the low voltage bus voltage U T and bus voltage upper limit U T_lim The difference ΔU T :

[0081] ΔU T =U T -U T_lim

[0082] (5) When ΔU T >0, PI control (proportional / integral control) is adopted, and ΔU T Generate the total reactive power command Q of the power station T_ref .

[0083] (6) Calculate the reactive power command value Q of each distributed photovoltaic power generation unit i_ref :

[0084] Q i_ref =k i Q T_ref

[0085] Among them, Q i_ref is the reactive power instruction of the i-th photovoltaic power generation unit.

[0086] (7) Control each distributed photovoltaic power generation unit to switch to reactive power control mode. Each distributed photovoltaic power generation unit executes reactive power instruction Q while maintaining active power MPP mode. i =Q i_ref , implement power station voltage control (Qi is the actual reactive power of each photovoltaic power generation unit), at this time, the grid-connected converter apparent power S of each photovoltaic power generation unit i =S e_i .

[0087] (8) After executing the reactive power coordinated control strategy, if Q T_ref ≤Q T_lim And U T ≤U T_lim, it indicates that the reactive power coordinated control strategy can effectively suppress the overvoltage of the power station, so the control strategy and the operation mode of the photovoltaic power generation unit are maintained unchanged; if Q T_ref Reach Q T_lim (i.e. Q i_ref =Q i_lim ) when the power station is still overvoltage (i.e. U T >U T_lim ), then enter the maximum power factor control strategy.

[0088] Step 103: If the second judgment result indicates yes, switch to the maximum power factor control mode; the maximum power factor control mode is the maximum power mode.

[0089] The maximum power factor control strategy maintains the apparent power S of each photovoltaic power generation unit. i =S e_i Under the condition of constant, the low voltage bus voltage U T Does not exceed the bus voltage upper limit U T_lim (U T ≤U T_lim ) as a constraint, with the goal of minimizing the total active power loss of the power station, by reducing the active power P of each photovoltaic power generation unit i To increase the maximum reactive power Q of the grid-connected converter i_lim , thereby achieving effective suppression of power station overvoltage.

[0090] Specifically, calculate the maximum reactive power Q of each distributed photovoltaic power generation unit i_lim For active power P i The first derivative pΔQ i_lim ,Depend on:

[0091]

[0092] available:

[0093]

[0094] Among them, P i_0 represents the current active power of the i-th photovoltaic power generation unit, and p represents the differential operator.

[0095] The above formula shows that P i_0 The larger the pΔQ i_lim The larger the absolute value of , the larger the increment of the reactive power upper limit that can be obtained by reducing the same active power ΔPi. Therefore, when further suppressing the overvoltage of the power station by reducing the active power, the active power P should be reduced first. i_0 High, that is, a photovoltaic power generation unit with a high power factor.

[0096] Control each distributed photovoltaic power generation unit to switch to the maximum power factor control mode and control the maximum power factor value and The value of decreases gradually from 1 but never falls below 0. As the value of decreases from 1, the active power of the photovoltaic power generation unit will gradually decrease, and the absorbed reactive power will gradually increase.

[0097] When each distributed photovoltaic power generation unit switches to the maximum power factor control mode:

[0098] (1) If the power factor of the photovoltaic power generation unit is The running state remains unchanged;

[0099] (2) If the power factor of the photovoltaic power generation unit is Then maintain the apparent power S i =S e_i unchanged, reduce active power P i , and at the same time emits reactive power according to the following formula.

[0100]

[0101] Step 104, in reactive power control mode or maximum power factor control mode, when receiving the maximum power mode instruction, switch to the maximum power mode and return to the step "in maximum power mode, determine whether the low-voltage side bus voltage of the distributed photovoltaic power station exceeds the bus voltage upper limit value, and obtain the first judgment result".

[0102] That is, when each distributed photovoltaic power generation unit receives the MPP operation mode instruction, the active power P i According to the maximum power mode, execute the reactive power command Q i =Q i_ref =0.

[0103] An embodiment of the present invention further provides an overvoltage suppression system for a distributed photovoltaic power station, the system comprising:

[0104] The first judgment module is used to judge whether the low-voltage side bus voltage of the distributed photovoltaic power station exceeds the bus voltage upper limit value in the maximum power mode to obtain a first judgment result; the maximum power mode is to control the operation of each photovoltaic power generation unit in the distributed photovoltaic power station by using the maximum power control method;

[0105] A reactive power control module is used to switch to a reactive power control mode if the first judgment result indicates yes, and when the upper limit of the reactive power control mode is reached, determine whether the low-voltage side bus voltage still exceeds the upper limit of the bus voltage to obtain a second judgment result; the switching to the reactive power control mode is to reduce the low-voltage side bus voltage by adjusting the reactive power of each photovoltaic power generation unit; the upper limit of the reactive power control mode is that the total reactive power of the distributed photovoltaic power station reaches the upper limit of the total reactive power that can be generated by the distributed photovoltaic power station.

[0106] The reactive power control module specifically includes: a total reactive power instruction generation submodule, which is used to generate the total reactive power instruction of the distributed photovoltaic power station by using the PI control algorithm according to the difference between the low-voltage side bus voltage and the upper limit value of the bus voltage; a reactive power instruction calculation submodule, which is used to calculate the reactive power instruction of each photovoltaic power generation unit according to the total reactive power instruction of the distributed photovoltaic power station; a reactive power regulation submodule, which is used to adjust the reactive power of each photovoltaic power generation unit according to the reactive power instruction of each photovoltaic power generation unit while performing active power maximization control of each photovoltaic power generation unit; a third judgment submodule, which is used to judge whether the low-voltage side bus voltage of the distributed photovoltaic power station after reactive power adjustment exceeds the upper limit value of the bus voltage, and obtain a third judgment result; a first return submodule, which is used to return to the total reactive power instruction generation submodule if the third judgment result indicates yes; and a second return submodule, which is used to return to the reactive power regulation submodule if the third judgment result indicates no.

[0107] The reactive power instruction calculation submodule specifically includes: a reactive power instruction calculation unit for calculating the total reactive power instruction of the distributed photovoltaic power station using the formula Q i_ref =k i Q T_ref , calculate the reactive power command of each photovoltaic power generation unit; where Q i_ref represents the reactive power command of the i-th photovoltaic power generation unit, k i represents the reactive power coefficient of the i-th photovoltaic power generation unit, Q T_ref Indicates the total reactive power command of the distributed photovoltaic power station.

[0108] The reactive power control module also includes: a reactive power upper limit calculation submodule for calculating the reactive power upper limit using the formula Calculate the reactive power upper limit of each photovoltaic power generation unit; the total reactive power upper limit calculation submodule is used to calculate the total reactive power upper limit of the distributed photovoltaic power station according to the reactive power upper limit of each photovoltaic power generation unit; the reactive power coefficient calculation submodule is used to calculate the reactive power upper limit of each photovoltaic power generation unit and the total reactive power upper limit of the distributed photovoltaic power station using the formula Calculate the reactive power coefficient of each photovoltaic power generation unit; where Q i_lim represents the reactive power upper limit of the ith photovoltaic power generation unit, Pi and Se_i represent the active power and rated apparent capacity of the grid-connected converter of the ith photovoltaic power generation unit, respectively, Q T_lim It represents the upper limit of the total reactive power that can be generated by the distributed photovoltaic power station, and n represents the number of photovoltaic power generation units included in the distributed photovoltaic power station.

[0109] The maximum power factor control module is used to switch to the maximum power factor control mode if the second judgment result indicates yes; the maximum power factor control mode is to reduce the low-voltage side bus voltage by adjusting the maximum power factor of the distributed photovoltaic power station so that the low-voltage side bus voltage does not exceed the bus voltage upper limit value.

[0110] The return module is used to switch to the maximum power mode and return to the first judgment module when receiving the maximum power mode instruction in the reactive power control mode or the maximum power factor control mode.

[0111] According to the specific embodiments provided by the present invention, the present invention discloses the following technical effects:

[0112] 1. Each distributed photovoltaic power generation unit can switch between three operating modes: maximum power mode (MPP mode), reactive power control mode, and maximum power factor control mode according to the coordinated control strategy.

[0113] 2. When an overvoltage occurs in the power station, the reactive power coordination control strategy is first entered to keep the maximum active power of the photovoltaic power generation unit unchanged, and the rated apparent capacity of the grid-connected converter is fully utilized to control the reactive power to suppress the overvoltage.

[0114] 3. When the reactive power coordinated control strategy is not sufficient to suppress overvoltage, the maximum power factor control strategy is used to gradually reduce the maximum power factor of all distributed photovoltaic power generation units starting from the photovoltaic power generation unit with a high power factor, thereby achieving the best overvoltage suppression effect with the minimum active power loss (power generation loss).

[0115] In this specification, each embodiment is described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the embodiments can be referred to each other. For the device disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple, and the relevant parts can be referred to the method part.

[0116] The principles and implementation methods of the present invention are described in this article using specific examples. The description of the above embodiments is only used to help understand the method and core idea of ​​the present invention. At the same time, for those skilled in the art, according to the idea of ​​the present invention, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting the present invention.

Claims

1. A method for suppressing overvoltage in a distributed photovoltaic power station, characterized in that: The method comprises the following steps: In the maximum power mode, it is determined whether the low-voltage side bus voltage of the distributed photovoltaic power station exceeds the bus voltage upper limit value to obtain a first determination result; the maximum power mode is to control the operation of each photovoltaic power generation unit in the distributed photovoltaic power station by using the maximum power control method; If the first judgment result indicates yes, then switch to the reactive power control mode, when the upper limit of the reactive power control mode is reached, judge whether the low-voltage side bus voltage still exceeds the upper limit of the bus voltage, and obtain a second judgment result; the switching to the reactive power control mode is to reduce the low-voltage side bus voltage by adjusting the reactive power of each photovoltaic power generation unit; the upper limit of the reactive power control mode is that the total reactive power of the distributed photovoltaic power station reaches the upper limit of the total reactive power that can be generated by the distributed photovoltaic power station; If the second judgment result indicates yes, switch to the maximum power factor control mode; the maximum power factor control mode is to reduce the low-voltage side bus voltage by adjusting the maximum power factor of the distributed photovoltaic power station so that the low-voltage side bus voltage does not exceed the bus voltage upper limit; In the reactive power control mode or the maximum power factor control mode, when the maximum power mode instruction is received, switch to the maximum power mode, and return to the step "in the maximum power mode, determine whether the low-voltage side bus voltage of the distributed photovoltaic power station exceeds the bus voltage upper limit value, and obtain a first determination result"; The method of adjusting the reactive power of each photovoltaic power generation unit to reduce the low-voltage side bus voltage specifically includes: According to the difference between the low-voltage bus voltage and the bus voltage upper limit, the PI control algorithm is used to generate the total reactive power command of the distributed photovoltaic power station; According to the total reactive power instruction of the distributed photovoltaic power station, the reactive power instruction of each photovoltaic power generation unit is calculated; While maximizing the active power of each photovoltaic power generation unit, adjusting the reactive power of each photovoltaic power generation unit according to the reactive power instruction of each photovoltaic power generation unit; Determine whether the low-voltage side bus voltage of the distributed photovoltaic power station after reactive power regulation exceeds the bus voltage upper limit value, and obtain a third determination result; If the third judgment result indicates yes, then return to step "according to the difference between the low-voltage side bus voltage and the bus voltage upper limit value, use the PI control algorithm to generate a total reactive power instruction for the distributed photovoltaic power station"; If the third judgment result indicates no, then return to the step of "while performing active power maximization control of each photovoltaic power generation unit, adjusting the reactive power of each photovoltaic power generation unit according to the reactive power instruction of each photovoltaic power generation unit"; The step of calculating the reactive power instruction of each photovoltaic power generation unit according to the total reactive power instruction of the distributed photovoltaic power station specifically includes: According to the total reactive power command of the distributed photovoltaic power station, the formula Q i_ref =k i Q T_ref , calculate the reactive power command of each photovoltaic power generation unit; Among them, Q i_ref represents the reactive power command of the i-th photovoltaic power generation unit, k i represents the reactive power coefficient of the i-th photovoltaic power generation unit, Q T_ref Indicates the total reactive power command of the distributed photovoltaic power station; The reactive power instruction of each photovoltaic power generation unit is calculated according to the total reactive power instruction of the distributed photovoltaic power station, and the ... Using the formula Calculate the upper limit of reactive power that can be generated by each photovoltaic power generation unit; According to the reactive power upper limit of each photovoltaic power generation unit, calculate the total reactive power upper limit of the distributed photovoltaic power station; According to the reactive power upper limit of each photovoltaic power generation unit and the total reactive power upper limit of the distributed photovoltaic power station, the formula Calculate the reactive power coefficient of each photovoltaic power generation unit; Among them, Q i_lim represents the reactive power upper limit of the i-th photovoltaic power generation unit, P i and S e_i They represent the active power and rated apparent capacity of the grid-connected converter of the i-th photovoltaic power generation unit, Q T_lim It represents the upper limit of the total reactive power that can be generated by the distributed photovoltaic power station, and n represents the number of photovoltaic power generation units included in the distributed photovoltaic power station.

2. The overvoltage suppression method of a distributed photovoltaic power station according to claim 1, characterized in that: The method of adjusting the maximum power factor of the distributed photovoltaic power station to reduce the low-voltage side bus voltage so that the low-voltage side bus voltage does not exceed the bus voltage upper limit value specifically includes: Reduce the maximum power factor of distributed photovoltaic power stations; Adjusting the active power of the grid-connected converter of each photovoltaic power generation unit according to the maximum power factor; Determine whether the bus voltage on the low-voltage side of the distributed photovoltaic power station after the maximum power factor adjustment exceeds the bus voltage upper limit value, and obtain a fourth determination result; If the fourth judgment result indicates yes, then return to step "reducing the maximum power factor of the distributed photovoltaic power station"; If the fourth judgment result indicates no, then return to step "adjusting the active power of the grid-connected converter of each photovoltaic power generation unit according to the maximum power factor".

3. The overvoltage suppression method of a distributed photovoltaic power station according to claim 2, characterized in that: The step of adjusting the active power of the grid-connected converter of each photovoltaic power generation unit according to the maximum power factor specifically includes: For each of the photovoltaic power generation units, the judgment formula Whether it is established, obtain the fifth judgment result; wherein, Indicates the maximum power factor, represents the power factor of the i-th photovoltaic power generation unit; If the fifth judgment result indicates no, reducing the active power of the grid-connected converter of the photovoltaic power generation unit while keeping the apparent power of the grid-connected converter of the photovoltaic power generation unit unchanged; If the fifth judgment result indicates yes, the apparent power and the active power of the grid-connected converter of the photovoltaic power generation unit are kept unchanged.

4. An overvoltage suppression system for a distributed photovoltaic power station, characterized in that: The system comprises: The first judgment module is used to judge whether the low-voltage side bus voltage of the distributed photovoltaic power station exceeds the bus voltage upper limit value in the maximum power mode to obtain a first judgment result; the maximum power mode is to control the operation of each photovoltaic power generation unit in the distributed photovoltaic power station by using the maximum power control method; A reactive power control module is used to switch to a reactive power control mode if the first judgment result indicates yes, and when the upper limit of the reactive power control mode is reached, determine whether the low-voltage side bus voltage still exceeds the upper limit of the bus voltage to obtain a second judgment result; the switching to the reactive power control mode is to reduce the low-voltage side bus voltage by adjusting the reactive power of each photovoltaic power generation unit; the upper limit of the reactive power control mode is when the total reactive power of the distributed photovoltaic power station reaches the upper limit of the total reactive power that can be generated by the distributed photovoltaic power station; A maximum power factor control module, for switching to a maximum power factor control mode if the second judgment result indicates yes; the maximum power factor control mode is to reduce the low-voltage side bus voltage by adjusting the maximum power factor of the distributed photovoltaic power station so that the low-voltage side bus voltage does not exceed the bus voltage upper limit; A return module, used for switching to the maximum power mode when receiving a maximum power mode instruction in the reactive power control mode or the maximum power factor control mode, and returning to the first judgment module; The reactive power control module specifically comprises: The total reactive power command generation submodule is used to generate the total reactive power command of the distributed photovoltaic power station using the PI control algorithm according to the difference between the low-voltage side bus voltage and the upper limit of the bus voltage; The reactive power instruction calculation submodule is used to calculate the reactive power instruction of each photovoltaic power generation unit according to the total reactive power instruction of the distributed photovoltaic power station; A reactive power regulation submodule, used to regulate the reactive power of each photovoltaic power generation unit according to the reactive power instruction of each photovoltaic power generation unit while maximizing the active power of each photovoltaic power generation unit; The third judgment submodule is used to judge whether the low-voltage side bus voltage of the distributed photovoltaic power station after reactive power adjustment exceeds the bus voltage upper limit value, and obtain a third judgment result; A first return submodule, configured to return to the total reactive power instruction generation submodule if the third judgment result indicates yes; A second return submodule, configured to return to the reactive power regulation submodule if the third judgment result indicates no; The reactive power instruction calculation submodule specifically includes: The reactive power instruction calculation unit is used to calculate the total reactive power instruction of the distributed photovoltaic power station using the formula Q i_ref =k i Q T_ref , calculate the reactive power command of each photovoltaic power generation unit; Among them, Q i_ref represents the reactive power command of the i-th photovoltaic power generation unit, k i represents the reactive power coefficient of the i-th photovoltaic power generation unit, Q T_ref Indicates the total reactive power command of the distributed photovoltaic power station; The reactive power control module also includes: The reactive power upper limit calculation submodule is used to calculate the reactive power upper limit using the formula Calculate the upper limit of reactive power that can be generated by each photovoltaic power generation unit; The total reactive power upper limit calculation submodule is used to calculate the total reactive power upper limit of the distributed photovoltaic power station according to the reactive power upper limit of each photovoltaic power generation unit; The reactive power coefficient calculation submodule is used to calculate the reactive power coefficient based on the reactive power upper limit of each photovoltaic power generation unit and the total reactive power upper limit of the distributed photovoltaic power station using the formula Calculate the reactive power coefficient of each photovoltaic power generation unit; Among them, Q i_lim represents the reactive power upper limit of the ith photovoltaic power generation unit, Pi and Se_i represent the active power and rated apparent capacity of the grid-connected converter of the ith photovoltaic power generation unit, respectively, Q T_lim It represents the upper limit of the total reactive power that can be generated by the distributed photovoltaic power station, and n represents the number of photovoltaic power generation units included in the distributed photovoltaic power station.

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