Power distribution network overcurrent protection and distributed photovoltaic real-time cooperative control method and system

Abstract

The invention discloses a real-time cooperative control method and system for overcurrent protection and distributed photovoltaic of a power distribution network, which is applied to three-section overcurrent protection of a 10kV line, acquires data in real time by using hardware and a data acquisition system of an existing 10kV transformer substation, and determines whether to perform overcurrent protection or not by using voltage measured by a voltage transformer on a 10kV bus as a reference direction. Calculating the size of a phase angle between the fault current and the bus voltage, detecting whether a fault occurs or not according to the starting state of the third section of line overcurrent protection, and judging whether an external fault occurs or not in real time based on the phase angle between the fault current and the bus voltage; if an external fault occurs, the feed-in of the fault current is reduced by adjusting the output power of the distributed photovoltaic system in real time, so that the overcurrent protection maloperation of the line is prevented, and the load power loss of the line is avoided. And after the external fault is removed, the maximum power tracking control mode of the photovoltaic station is automatically recovered, and the normal operation of the photovoltaic station is recovered. On the basis of not increasing extra hardware cost, the control method provided by the invention can be realized only by adding a real-time control software module.

Description

Technical Field

[0001] The present invention belongs to the technical field of distributed photovoltaic access to a distribution network, and specifically relates to a real-time coordinated control method and system for overcurrent protection of a distribution network and distributed photovoltaics. Background Art

[0002] With the rapid development of new energy power generation, the distribution network has shown a new "multi-point and multi-source" power distribution mode after a large number of distributed photovoltaics have been connected to the distribution network. The access of distributed photovoltaics has changed the fault level and fault current direction of the distribution network. When an out-of-area fault occurs in an adjacent line, the input of the distributed photovoltaic fault current may cause the overcurrent protection of the line to malfunction and trip the line, causing the load of the line to lose power, affecting the reliability of the distribution network power supply.

[0003] For 10kV distribution network lines connected to distributed photovoltaics, the overcurrent protection at the exit of the 10kV line generally adopts three-stage overcurrent protection: the first stage is instantaneous overcurrent protection without delay, and the current setting value is very high; the second stage is overcurrent protection with delay, and the current setting value is also high; the third stage is also overcurrent protection with delay, and the current setting value only needs to avoid the maximum load current. When an adjacent line fails, due to the high current setting values ​​of the first and second stages, the fault current fed by the distributed photovoltaics will not cause the first and second stages of overcurrent protection to malfunction, but it may cause the third stage of protection protecting the line to malfunction. Summary of the invention

[0004] In order to solve the deficiencies of the prior art and prevent the line overcurrent protection from malfunctioning and the line load from losing power, the present invention adopts the following technical solution:

[0005] The real-time coordinated control method of distribution network overcurrent protection and distributed photovoltaic is applied to the three-stage overcurrent protection of 10kV line, including the following steps:

[0006] Step 1: parameter acquisition and calculation; obtain the instantaneous value of the bus phase voltage to calculate the amplitude and phase angle of the bus line voltage; obtain the instantaneous value of the line current to calculate the amplitude and phase angle of the line current; calculate the phase angle between the line current and the bus line voltage through the phase angle of the bus line voltage and the phase angle of the line current;

[0007] Step 2: Detection of fault occurrence and judgment of out-of-zone fault; judge whether the third stage of line overcurrent protection is activated. If it is activated, it means that a fault has occurred. Then, judge whether the fault is an out-of-zone fault based on the phase angle between the line current and the bus voltage. If the amplitude of the line current is greater than the set value of the third stage of the line overcurrent protection, further judge whether the phase angle between the current and the bus voltage is less than the minimum phase angle threshold and greater than the maximum phase angle threshold. If so, judge that the fault is an out-of-zone fault. If no out-of-zone fault occurs in any of the three phases of the line, return to step 1 to obtain parameters, continue to detect whether a fault occurs and judge whether the fault is an out-of-zone fault.

[0008] Step 3: Switching the control mode of the photovoltaic station; once it is determined that an out-of-area fault has occurred, the substation control system will issue control commands to photovoltaic stations 1 to n connected to the line in sequence, so that the control mode of the photovoltaic station is converted from MPPT (maximum power point tracking) control to P / Q (active power and reactive power) control mode, and the active power target value Pref (active power target value under P, Q control mode) is set to 0, thereby reducing the fault current output of the photovoltaic and avoiding malfunction of the protection at the 10kV line outlet;

[0009] Step 4: Restore the normal control mode; after the PV station is converted from MPPT (maximum power point tracking) control to P / Q (active power and reactive power) control mode, after the delay waiting period for the fault outside the area to be removed, the control mode of PV station 1 to PV station n is converted from P / Q active power and reactive power control mode to MPPT maximum power point tracking control mode;

[0010] Step 5: Loop execution; repeat steps 1 to 4 to perform the next cycle detection and system control.

[0011] Furthermore, in step 1, the instantaneous value of the bus line voltage is calculated by obtaining the instantaneous value of the three-phase bus phase voltage of lines A, B, and C, and the amplitude V of the three-phase bus line voltage is calculated using the discrete Fourier transform formula. ab 、V bc 、V ca and phase angle α ab , α bc , α ca ; Obtain the instantaneous value of the three-phase current of lines A, B, and C, and use the discrete Fourier transform formula to calculate the amplitude of the three-phase line current I a ,I b ,I c and phase angle β a , β b , β c ; Phase angle between line current and bus voltage:

[0012]

[0013] When the current leads the voltage, the phase angle is positive; when the current lags the voltage, the phase angle is negative.

[0014] Furthermore, in step 2, if the line A phase current I a Greater than the setting value I of the third stage of overcurrent protection of this line 3d , then further judge Is it less than the minimum phase angle threshold, that is, the current I a Hysteresis V bc The absolute value of the current I exceeds the preset minimum phase angle threshold and is greater than the maximum phase angle threshold. a Advanced V bc If the absolute value of the phase angle exceeds the preset maximum phase angle threshold, the fault is judged to be an out-of-zone fault;

[0015] Otherwise, it is judged that it is not an out-of-zone fault, and further judge the B phase current I b Is it greater than the setting value I of the third stage of overcurrent protection of this line? 3d , if I b Greater than I 3d , then further judge Is it less than the minimum phase angle threshold, that is, the current I b Hysteresis V ca The absolute value of the current I exceeds the preset phase angle threshold and is greater than the maximum phase angle threshold. b Advanced V ca If the absolute value of the phase angle exceeds the preset threshold, the fault is judged to be an out-of-zone fault.

[0016] Otherwise, it is judged that it is not an out-of-zone fault, and further judge the C phase current I c Is it greater than the setting value I of the third stage of overcurrent protection of this line? 3d , if greater than I 3d , then judge Is it less than the minimum phase angle threshold, that is, the current I c Hysteresis V ab The absolute value of the current I exceeds the preset phase angle threshold and is greater than the maximum phase angle threshold. c Advanced V ab If the absolute value of the phase angle exceeds the preset threshold, the fault is judged to be an out-of-zone fault;

[0017] If the above judgment shows that the three phases A, B, and C are not out-of-zone faults, then return to step 1 to obtain parameters, and repeat the above steps to continue to detect whether a fault has occurred and determine whether the fault is an out-of-zone fault.

[0018] Furthermore, in step 2, the minimum phase angle threshold is -60°, and the maximum phase angle threshold is 120°.

[0019] Furthermore, the instantaneous value formula of the bus line voltage is as follows:

[0020] v ab =v a -v b

[0021] v bc =v b -v c

[0022] v ca =v c -v a

[0023] Among them, v a 、v b 、v c Represent the instantaneous values ​​of the bus phase voltages of lines A, B, and C respectively.

[0024] Furthermore, in step 1, the distribution network is a 10kV distribution network. Since the third stage of the 10kV line outlet protection has an action delay of 0.8 seconds and the photovoltaic inverter power electronic components have a fast response characteristic, when a line fault occurs, there is enough time for the substation control system to issue a control command to regulate the fault current of the photovoltaic output to avoid misoperation of the protection.

[0025] Furthermore, in step 4, the delay is T 3d +ε, T3d represents the third delay setting of the overcurrent protection of this line, which means the millisecond time value where ε is greater than 0.

[0026] Furthermore, the cyclic detection in step 5 is performed once every 5 ms.

[0027] A real-time collaborative control system for distribution network overcurrent protection and distributed photovoltaics, comprising a line control and protection device, a substation control system, a photovoltaic field station control system and an interconnected communication network. The line control and protection device adopts the real-time collaborative control method for distribution network overcurrent protection and distributed photovoltaics to obtain and calculate parameters, detect the occurrence of faults and judge out-of-area faults. Based on the occurrence of out-of-area faults, the substation control system sequentially issues control commands to photovoltaic fields connected to the line, and the photovoltaic field station control mode is switched and restored through the photovoltaic field station control system.

[0028] The advantages and beneficial effects of the present invention are:

[0029] The present invention is aimed at 10kV distribution network lines with distributed photovoltaic access, fully utilizes the fast and controllable response characteristics (millisecond level) of photovoltaic inverter power electronic components, and proposes that during the period of out-of-area fault of the 10kV distribution network line, by judging whether the line overcurrent protection is activated and the direction of the fault current, it is judged in real time whether it is an out-of-area fault. If it is, the output power of the distributed photovoltaic is adjusted in real time, thereby reducing the feed-in of the fault current, preventing the overcurrent protection of the line from malfunctioning, and avoiding power loss of the load of the line, so as to achieve the purpose of improving the reliability of the distribution network power supply. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is a schematic diagram of the prior art in which the distributed photovoltaic system causes the line protection to malfunction when an adjacent line fails.

[0031] Figure 2 In the embodiment of the present invention, the photovoltaic power is converted from the maximum power tracking control mode to the active and reactive power control mode.

[0032] Figure 3a It is one of the flow charts of the coordinated control method of line overcurrent protection and distributed photovoltaic in an embodiment of the present invention.

[0033] Figure 3b This is the second flow chart of the coordinated control method of line overcurrent protection and distributed photovoltaics in an embodiment of the present invention.

[0034] Figure 4 It is a schematic diagram of the judgment criteria of out-of-zone faults in an embodiment of the present invention.

[0035] Figure 5 It is a schematic diagram of a coordinated control system of line overcurrent protection and distributed photovoltaics in an embodiment of the present invention.

[0036] Figure 6 It is a schematic diagram of a 10kV line connected to four photovoltaic stations simulated in an embodiment of the present invention.

[0037] Figure 7 Schematic diagram of the structure of a photovoltaic system simulated in an embodiment of the present invention.

[0038] Figure 8a It is a schematic diagram of current (kA) and voltage (kV) at protection 1 in an embodiment of the present invention without using the present invention.

[0039] Figure 8b It is a schematic diagram of the effective value (kA) of the current at the protection 1 in an embodiment of the present invention without adopting the present invention.

[0040] Figure 8c It is a schematic diagram of the starting state and tripping state of the third stage of protection 1 in an embodiment of the present invention that does not adopt the present invention.

[0041] Figure 9a It is a schematic diagram of current (kA) and voltage (kV) at protection 1 of the present invention in an embodiment of the present invention.

[0042] Figure 9b It is a schematic diagram of the effective value (kA) of the current at the protection 1 of the present invention in an embodiment of the present invention.

[0043] Fig.9c It is a schematic diagram of the starting state and tripping state of the third stage of protection 1 of the present invention in an embodiment of the present invention. DETAILED DESCRIPTION

[0044] The specific implementation of the present invention is described in detail below in conjunction with the accompanying drawings. It should be understood that the specific implementation described here is only used to illustrate and explain the present invention, and is not used to limit the present invention.

[0045] The access of distributed photovoltaics changes the fault level and fault current direction of the distribution network, such as Figure 1 As shown in the figure, when a fault occurs in an adjacent line, due to the input of the distributed photovoltaic fault current, the fault current flows from the distributed photovoltaic to the fault point. When the fault current flowing through protection 1 exceeds the set value of the protection, it will cause the overcurrent protection 1 of this line to malfunction and trip this line, causing the load of this line to lose power, affecting the reliability of the distribution network power supply.

[0046] The overcurrent protection 1 at the outlet of the 10kV line generally adopts three-stage overcurrent protection: the first stage is instantaneous overcurrent protection without delay, and the current setting value is very high; the second stage is overcurrent protection with delay, and the current setting value is also high, and the action delay is generally set at 0.3 seconds; the third stage is also overcurrent protection with delay, and the current setting value only needs to avoid the maximum load current, and the action delay is generally set at 0.8 seconds. Since the maximum current of the photovoltaic inverter is generally limited to 1.2-1.5 times the rated current, when the adjacent line fails, the fault current fed by the distributed photovoltaic may cause the third stage protection of the line to malfunction. Since the current setting values ​​of the first and second stages are high, the fault current fed by the distributed photovoltaic will not cause the first and second stages of overcurrent protection to malfunction. In order to ensure the safe and reliable operation of the power grid, the power grid dispatch currently requires that all distributed photovoltaics connected to the power grid have observable, measurable and controllable functions. Therefore, the distributed photovoltaic station and the power grid dispatch will have a communication network to accept the power generation instructions of the power grid dispatch and the control commands in emergency situations. Since the third stage of the 10kV line export protection has an action delay of 0.8 seconds and the power electronic components of the photovoltaic inverter have a fast response characteristic, when a line fault occurs, there is enough time to issue a control command from the substation control system to regulate the fault current of the photovoltaic output to avoid false protection.

[0047] For this line, the direction of the fault current can be used to determine whether the fault is internal or external. A voltage transformer is required to determine the direction of the fault current. Although voltage transformers are generally not installed on 10kV lines, voltage transformers are installed on 10kV busbars. Therefore, the voltage transformers on the busbars can be used to determine the direction of the fault current.

[0048] Under normal conditions, photovoltaic power adopts the maximum power point tracking (MPPT) control mode. When an out-of-area fault occurs in the line, the photovoltaic control mode can be converted from MPPT to active and reactive power (P / Q) control mode (Ctrl changes from 0 to 1). Figure 2 As shown, the active power target value is set to zero to reduce the output fault current, thereby avoiding false operation of the protection at the 10kV line outlet.

[0049] The present invention uses the voltage measured by the voltage transformer installed on the 10kV bus as the reference direction, and judges whether the third stage of the line overcurrent protection is activated and the direction of the fault current in real time to judge whether an out-of-zone fault has occurred. If so, the control mode of the photovoltaic connected to this line is converted from the maximum power point tracking (MPPT) control mode to the active and reactive power (P / Q) control mode, and the active power target value is set to zero, thereby reducing the fault current of the photovoltaic output and avoiding protection malfunction.

[0050] like Figure 3a , Figure 3b As shown, the present invention proposes a real-time coordinated control method for overcurrent protection of a 10kV distribution network and distributed photovoltaics, comprising the following steps:

[0051] Step 1: Parameter acquisition and calculation; obtain the instantaneous value of the three-phase bus phase voltage to calculate the instantaneous value of the bus line voltage, and use the discrete Fourier transform (DFT) formula to calculate the amplitude and phase angle of the bus line voltage; obtain the instantaneous value of the three-phase current of the line, and use the discrete Fourier transform (DFT) formula to calculate the amplitude and phase angle of the line current; calculate the phase angle between the line current and the bus line voltage.

[0052] Specifically, the instantaneous values ​​of the three-phase bus voltages (A, B, C) are obtained from the 10kV line control and protection system (respectively denoted as v a 、v b 、v c ), the instantaneous value of the three-phase current of the line (A, B, C) (respectively denoted as i a 、i b 、i c ).

[0053] Calculate the instantaneous value of the bus line voltage: After obtaining the instantaneous value of the three-phase voltage of the bus, calculate the instantaneous value of the bus line voltage according to the following formula:

[0054] v ab =v a -v b

[0055] v bc =v b -v c

[0056] v ca =v c -v a

[0057] Calculate the bus voltage amplitude and phase angle: Use the discrete Fourier transform (DFT) formula to calculate the bus voltage amplitude (V ab 、V bc 、V ca ) and phase angle (α ab , α bc , α ca ).

[0058] Calculate the amplitude and phase angle of the line current: After obtaining the instantaneous value of the three-phase current of the line, the discrete Fourier transform (DFT) formula is used to calculate the amplitude (I a ,I b ,I c ) and phase angle (β a , β b , β c ).

[0059] Calculate the phase angle between the line current and the bus voltage: The phase angle between the current and the bus voltage is an important basis for judging the fault inside and outside the zone. The phase angle between the line current and the bus voltage is calculated using the following formula:

[0060]

[0061] The definition of the phase angle between current and voltage is as shown in the above formula. When the current leads the voltage, the phase angle is positive; when the current lags the voltage, the phase angle is negative.

[0062] Step 2: Out-of-area fault determination;

[0063] The bus voltage phase angle, current amplitude and phase angle calculated in the above steps are used to first determine whether the third stage of the line overcurrent protection is activated. If it is activated, it means that a fault has occurred. Then, based on the phase angle between the line current and the bus voltage, it is further determined whether the fault is an out-of-zone fault. The judgment process is as follows: Figure 3a and Figure 3b As shown in the figure, the criterion for judging whether the fault is an out-of-zone fault is as follows: Figure 4 As shown (to judge I a With V bcTake the phase angle between as an example, the shaded part is the out-of-zone fault).

[0064] If the line A phase current I a Greater than the setting value I of the third stage of overcurrent protection of this line 3d , then further judge Is it less than the minimum phase angle threshold -60° (i.e. the current I a Hysteresis V bc exceeds 60°, the preset minimum phase angle threshold) and is greater than the maximum phase angle threshold of 120° (i.e., the current I a Advanced V bc exceeds 120°, the preset maximum phase angle threshold), if so, the fault is judged to be an out-of-zone fault;

[0065] Otherwise, it is judged that it is not an out-of-zone fault, and further judge the B phase current I b Is it greater than the setting value I of the third stage of overcurrent protection of this line? 3d , if I b Greater than I 3d , then further judge Is it less than the minimum phase angle threshold -60° (i.e. the current I b Hysteresis V ca exceeds 60°, the preset phase angle threshold) and is greater than the maximum phase angle threshold of 120° (i.e., the current I b Advanced V ca exceeds 120°, the preset phase angle threshold), if so, the fault is judged to be an out-of-zone fault;

[0066] Otherwise, it is judged that it is not an out-of-zone fault, and further judge the C phase current I c Is it greater than the setting value I of the third stage of overcurrent protection of this line? 3d , if greater than I 3d , then judge Is it less than the minimum phase angle threshold -60° (i.e. the current I c Hysteresis V ab exceeds 60°, the preset phase angle threshold) and is greater than the maximum phase angle threshold of 120° (i.e., the current I c Advanced V ab If the phase angle exceeds 120°, the preset phase angle threshold, the fault is judged to be an out-of-zone fault.

[0067] If the above judgment is that the three phases A, B, and C are not out-of-zone faults, then return to step 1 to obtain parameters, and repeat the above steps to continue to detect whether a fault has occurred and determine whether the fault is an out-of-zone fault.

[0068] Step 3: Switch the photovoltaic station control mode;

[0069] For this line, once it is determined that an out-of-zone fault has occurred, the substation control system will issue control commands to photovoltaic stations 1 to n connected to this line in sequence, so that the control mode of the photovoltaic station is converted from MPPT (maximum power point tracking) control to P / Q (active power and reactive power) control mode, and the active power target value Pref (active power target value under P, Q control mode) is set to 0, thereby reducing the fault current output of the photovoltaic and avoiding false protection at the 10kV line outlet.

[0070] Step 4: Restore normal control mode;

[0071] After the photovoltaic station switches from MPPT (maximum power point tracking) control to P / Q (active power and reactive power) control mode, the delay T 3d +200 milliseconds (T3d is the third delay setting value of the overcurrent protection of this line) After the fault outside the waiting area is removed, the control mode of photovoltaic station 1 to photovoltaic station n is converted from P / Q control mode to MPPT control again to restore the normal control mode.

[0072] Step 5: Loop execution;

[0073] Repeat steps 1 to 4 to perform the next cycle detection and system control.

[0074] like Figure 5 As shown, the present invention also proposes a real-time collaborative control system for overcurrent protection of a 10kV distribution network and distributed photovoltaics, including a 10kV line control protection device (R1, R2, Rn and other lines), a 10kV substation control system, a photovoltaic station control system (PV1, PV2, PV3, PV4 and other photovoltaic stations) and communication networks connected thereto respectively. The collaborative control system of the present invention obtains the instantaneous value of the three-phase bus phase voltage and the instantaneous value of the three-phase current of the line from the 10kV line control protection device. If a fault occurs in the 10kV line and the fault is determined to be an out-of-zone fault, the collaborative control system will issue a control command to the photovoltaic station connected to the line through the communication network, reduce the output of the fault current of the photovoltaic station, and thus avoid malfunction of the protection.

[0075] In the embodiment of the present invention, firstly, a 10kV line (such as Figure 6 As shown in Figure 2), the simulated photovoltaic system is as follows: Figure 7 The simulated photovoltaic power generation power of each photovoltaic station and the load at that point are shown in the following table.

[0076] Photovoltaic and load access points Photovoltaic power generation capacity (active power, reactive power) Load capacity PV1 P=3.2MW,Q=0.6MVAr 2.0MVA, power factor 0.95 PV2 P=3.2MW,Q=0.6MVAr 2.0MVA, power factor 0.95 PV3 P=3.2MW,Q=0.6MVAr 2.0MVA, power factor 0.95 PV4 P=3.2MW,Q=0.6MVAr 2.0MVA, power factor 0.95

[0077] Simulate an out-of-area 3-phase short-circuit fault at the adjacent line exit (such as Figure 6Assume that the fault occurs at 0.5 seconds, the fault resistance is 0.1 ohms, and the circuit breaker action time is 100ms. Figures 8a to 8c The cooperative control method of the present invention is not used. When an out-of-zone fault occurs, the current flows through protection 1 ( Figure 6 The current at BRK1 in the figure and the starting status and tripping status of the third stage of protection 1 (the setting value of the third stage of protection 1 is 0.7kA and the delay is 0.8s).

[0078] from Figure 8b (The red line is the current setting value of the third section of protection 1) It can be seen that when the out-of-zone fault occurs at 0.5 seconds, the current of this line increases rapidly to about 1.1kA and exceeds the setting value of the third section of protection 1 of 0.7kA, and the third section of protection 1 is activated. Since the coordinated control method of the present invention is not adopted, the fault current continues to remain at about 1.1kA. After a delay of 0.8 seconds in the third section, protection 1 is activated at 1.3 seconds and a trip signal is issued. At 1.4 seconds, the circuit breaker BRK1 malfunctions and trips this line, causing the line to lose power. Figure 8c The blue line in the middle is start, and the red line is trip.

[0079] Under the same fault conditions, Figures 9a to 9c It is shown that after adopting the coordinated control method of the present invention, when an out-of-zone fault occurs, the current flows through protection 1 ( Figure 6 The current at BRK1 in the figure and the starting status and tripping status of the third stage of protection 1 (the setting value of the third stage of protection 1 is 0.7kA and the delay is 0.8s).

[0080] from Figure 9b(The red line is the current setting value of the third section of protection 1) It can be seen that when the out-of-zone fault occurs at 0.5 seconds, the current of this line increases rapidly to about 1.1kA and exceeds the setting value of the third section of protection 1 of 0.7kA, and the third section of protection 1 is activated. Due to the use of the collaborative control method of the present invention, at 0.55 seconds (assuming that the delay of judging the out-of-zone fault and the communication network is 50ms), the collaborative control system sends the control command to the photovoltaic field station connected to the line through the communication network, converts the control mode of the photovoltaic field station from the maximum power point tracking (MPPT) control mode to the active and reactive power (P / Q) control mode, and sets the active power target value to zero. At about 0.56 seconds, the fault current begins to decrease rapidly, and at about 0.57 seconds, the fault current decreases to the setting value of the third section of 0.7kA, and the third section of protection 1 is reset, avoiding the malfunction of protection 1. At 1.4 seconds, the out-of-zone fault is isolated by the protection of the adjacent line, and the voltage of this line returns to normal. At 1.55 seconds, the coordinated control system switched the control mode of the PV station from the P / Q control mode to the MPPT control mode and resumed normal operation. During the conversion process, there was a brief overcurrent state, which caused the third stage of protection 1 to start briefly, but during the entire coordinated control process, protection 1 did not act or issue any tripping command. The blue line in Figure 9C is the start-up, and the red line is the tripping.

[0081] In summary, after adopting the collaborative control method of the present invention, when an out-of-area fault occurs in an adjacent line, the fault current of the photovoltaic output connected to this line can be effectively reduced, thereby avoiding malfunction of the line protection and improving power supply reliability.

[0082] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some or all of the technical features thereof may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A real-time coordinated control method for distribution network overcurrent protection and distributed photovoltaics, applied to 10kV line three-stage overcurrent protection, characterized by The steps include: Step 1: parameter acquisition and calculation; obtain the instantaneous value of the bus phase voltage to calculate the amplitude and phase angle of the bus line voltage; obtain the instantaneous value of the line current to calculate the amplitude and phase angle of the line current; calculate the phase angle between the line current and the bus line voltage through the phase angle of the bus line voltage and the phase angle of the line current; Step 2: Detection of fault occurrence and judgment of out-of-zone fault; judge whether the third stage of line overcurrent protection is activated. If it is activated, it means that a fault has occurred. Then, judge whether the fault is an out-of-zone fault based on the phase angle between the line current and the bus voltage. If the amplitude of the line current is greater than the set value of the third stage of the line overcurrent protection, further judge whether the phase angle between the current and the bus voltage is less than the minimum phase angle threshold and greater than the maximum phase angle threshold. If so, judge that the fault is an out-of-zone fault. If no out-of-zone fault occurs in any of the three phases of the line, return to step 1 to obtain parameters, continue to detect whether a fault occurs and judge whether the fault is an out-of-zone fault. Step 3: Switching the control mode of the photovoltaic station; once it is determined that an out-of-area fault has occurred, a control command is issued to the photovoltaic station connected to the line, so that the control mode of the photovoltaic station is converted from the maximum power point tracking control to the active power and reactive power control mode, and the active power target value is set to 0; Step 4: Restore the normal control mode; after switching to the active power and reactive power control mode, wait for the fault outside the area to be removed, and then switch the control mode of the photovoltaic station from the active power and reactive power control mode to the maximum power point tracking control mode; Step 5: Loop execution; repeat steps 1 to 4 to perform the next cycle detection and control.

2. The method for real-time coordinated control of distribution network overcurrent protection and distributed photovoltaic according to claim 1 is characterized in that: In step 1, the instantaneous value of the bus line voltage is calculated by obtaining the instantaneous value of the three-phase bus phase voltage of lines A, B, and C, and the amplitude V of the three-phase bus line voltage is calculated using the discrete Fourier transform formula. ab 、V bc 、V ca and phase angle α ab , α bc , α ca ; Obtain the instantaneous value of the three-phase current of lines A, B, and C, and use the discrete Fourier transform formula to calculate the amplitude of the three-phase line current I a ,I b ,I c and phase angle β a , β b , β c ; Phase angle between line current and bus voltage: When the current leads the voltage, the phase angle is positive; when the current lags the voltage, the phase angle is negative.

3. The real-time coordinated control method of distribution network overcurrent protection and distributed photovoltaic according to claim 2 is characterized in that: In step 2, if the line A phase current I a Greater than the setting value I of the third stage of overcurrent protection of this line 3d , then further judge Is it less than the minimum phase angle threshold, that is, the current I a Hysteresis V bc The absolute value of the current I exceeds the preset minimum phase angle threshold and is greater than the maximum phase angle threshold. a Advanced V bc If the absolute value of the phase angle exceeds the preset maximum phase angle threshold, the fault is judged to be an out-of-zone fault; Otherwise, it is judged that it is not an out-of-zone fault, and further judge the B phase current I b Is it greater than the setting value I of the third stage of overcurrent protection of this line? 3d , if I b Greater than I 3d , then further judge Is it less than the minimum phase angle threshold, that is, the current I b Hysteresis V ca The absolute value of the current I exceeds the preset phase angle threshold and is greater than the maximum phase angle threshold. b Advanced V ca If the absolute value of the phase angle exceeds the preset threshold, the fault is judged to be an out-of-zone fault. Otherwise, it is judged that it is not an out-of-zone fault, and further judge the C phase current I c Is it greater than the setting value I of the third stage of overcurrent protection of this line? 3d , if greater than I 3d , then judge Is it less than the minimum phase angle threshold, that is, the current I c Hysteresis V ab The absolute value of the current I exceeds the preset phase angle threshold and is greater than the maximum phase angle threshold. c Advanced V ab If the absolute value of the phase angle exceeds the preset threshold, the fault is judged to be an out-of-zone fault; If the above judgment shows that the three phases A, B, and C are not out-of-zone faults, then return to step 1 to obtain parameters, and repeat the above steps to continue to detect whether a fault has occurred and determine whether the fault is an out-of-zone fault.

4. The real-time coordinated control method of distribution network overcurrent protection and distributed photovoltaic according to claim 3 is characterized in that: In step 2, the minimum phase angle threshold is -60°, and the maximum phase angle threshold is 120°.

5. The real-time coordinated control method of distribution network overcurrent protection and distributed photovoltaic according to claim 2 is characterized in that: The instantaneous value formula of the bus line voltage is as follows: v ab =v a -v b v bc =v b -v c v ca =v c -v a Among them, v a 、v b 、v c Represent the instantaneous values ​​of the bus phase voltages of lines A, B, and C respectively.

6. The real-time coordinated control method of distribution network overcurrent protection and distributed photovoltaic according to claim 1 is characterized in that: In step 1, the distribution network is a 10kV distribution network.

7. The real-time coordinated control method of distribution network overcurrent protection and distributed photovoltaic according to claim 1 is characterized in that: In step 3, once it is determined that an out-of-zone fault has occurred, a control command is issued to the photovoltaic station connected to the line to reduce the active power of the photovoltaic to 0.

8. The real-time coordinated control method of distribution network overcurrent protection and distributed photovoltaic according to claim 1 is characterized by: In step 4, the delay is T 3d +ε, T3d represents the third delay setting of the overcurrent protection of this line, which means the millisecond time value where ε is greater than 0.

9. The real-time coordinated control method of distribution network overcurrent protection and distributed photovoltaic according to claim 1 is characterized by: The cyclic detection in step 5 is performed every 5 ms.

10. A real-time coordinated control system for overcurrent protection of distribution network and distributed photovoltaic, including a line control and protection device, a substation control system, a photovoltaic field station control system and an interconnected communication network, characterized in that: The line control and protection device adopts the real-time coordinated control method of distribution network overcurrent protection and distributed photovoltaic as described in any one of claims 1 to 8 to obtain and calculate parameters, detect the occurrence of faults and judge out-of-area faults, and based on the occurrence of out-of-area faults, the substation control system sequentially issues control commands to the photovoltaic stations connected to this line, and switches the photovoltaic station control mode, reduces the output of active power and restores to normal working state through the photovoltaic station control system.

Images