Frequency tracking-based control method and system for spare power automatic switching of substation containing new energy

Abstract

The invention discloses a frequency tracking-based control method and system for spare power automatic switching of a substation containing new energy, and the method comprises the steps: monitoring a tripping signal of a circuit breaker of a main line, and obtaining a bus voltage U when the tripping signal appears; if the bus voltage is Ult; and if the voltage is 0.3 UN, a non-voltage state is determined, and conventional spare power automatic switching non-voltage switching-on logic is executed. If the bus voltage U is larger than or equal to 0.3 UN, it is judged that the device is in a voltage state, and quasi-synchronization closing condition judgment is carried out. And after the conditions are met, fast quasi-synchronization closing is executed immediately. And if the quasi-synchronous switching-on condition is not met, performing synchronous switching-on after power approximate matching is realized. According to the method, the frequency of the island system is calculated by adopting the extended Kalman filtering algorithm, high estimation precision can be kept, and meanwhile, the method has rapid tracking performance. And the accuracy of quasi-synchronous closing is improved.

Description

Technical Field

[0001] The present invention relates to the field of substation automatic control, and in particular to a method and system for quickly launching a backup power supply of a substation under the condition of extensive access of new energy. Background Art

[0002] With the widespread access to distributed renewable energy, the power system has shown characteristics such as low inertia level and weak anti-interference ability. In particular, new energy generators are prone to disconnection from the grid due to frequency and voltage disturbances. The reliable and stable operation of the power system faces many new problems and challenges.

[0003] In order to improve the power supply stability of the power system, the backup automatic switching device is widely used in the power system. The action logic of the traditional backup automatic switching strategy needs to meet the busbar no-voltage condition to act, but with the access of a large number of new energy sources, the power supply mode of the power system has changed to a multi-terminal power supply mode where inverter power sources and rotating power sources coexist, and the structure has become more complex. After the main circuit breaker trips due to a system fault, the new energy power source and the load form an island, and the traditional backup automatic switching busbar no-voltage action condition is not met and cannot act correctly.

[0004] With the continuous increase in the proportion of new energy access, in order to deal with the problem that the backup power supply cannot be timely and correctly operated, the traditional solution generally considers first decoupling all new energy to meet the busbar no-voltage operation conditions, and then put in the backup power supply, and then reconnect the new energy after the system restores power supply. Although the traditional solution can ensure the correct operation of the backup power supply, it will cause the load to be without power supply for a period of time, and at the same time affect the utilization rate of new energy. The document "The fast switching method and setting method of the backup power supply of the power grid containing wind farms, Jiang Huilan, High Voltage Technology" proposes a backup protection scheme with the fast switching method as the main protection and the capture synchronous switching method as the backup protection. This method uses the beat voltage between the backup power supply voltage and the residual voltage to set the switching conditions, which not only has more sufficient time to operate, but also has a smaller impact after closing. However, the above method may not be able to achieve fast closing and grid connection when the power gap between the source and load of the isolated island system is large and the frequency of the isolated island changes rapidly. For this reason, the document "A new automatic backup scheme for large photovoltaic power stations, Cai Qian, Power Engineering Technology" proposed a new automatic backup scheme based on energy-consuming resistors. Energy-consuming resistors are put into use according to the power imbalance, and the impact current can still be effectively suppressed when the power gap between the source and the load is large. However, the use of parallel resistors will greatly limit the transmission capacity of the tie line.

[0005] From the above analysis, it can be seen that for substations with high penetration of new energy, their backup automatic investment still has problems such as long grid-connected time, low correct action rate, and limited closing scenarios. Summary of the invention

[0006] The technical problem to be solved by the present invention is how to achieve fast and effective switching while taking into account the access of a large number of new energy sources.

[0007] The present invention solves the above technical problems through the following technical means:

[0008] The control method of the automatic switching of a substation containing new energy based on frequency tracking includes the following steps:

[0009] When the main line trips, the bus voltage U is obtained; when U is less than the set value, the bus is determined to be in a no-voltage state, and the backup automatic no-voltage closing logic is executed. When U is greater than or equal to the set value, the voltage difference, frequency difference, and phase difference between the island side and the grid side are calculated. When the voltage difference, frequency difference, and phase difference all meet the conditions, fast quasi-synchronous closing is performed. If the conditions are not met, the power matching synchronous closing stage is entered; an approximate match between the power supply and demand relationship is achieved, and then the closing and grid-connected operation is performed.

[0010] The present invention optimizes the automatic backup strategy of substations under high penetration of new energy access, and proposes a combination of fast quasi-synchronous closing and closing after the source and load power are approximately matched. The method matches the corresponding automatic backup control strategy according to different situations, which is fast and effective, and ensures the reliability of power supply.

[0011] Furthermore, the phase angle difference Δδ is calculated as follows:

[0012]

[0013] Where Δδ t is the phase angle difference at the current moment, Δf t is the frequency difference at the current moment, is the frequency change rate, T dz It is the closing action time.

[0014] Furthermore, the frequency fast tracking algorithm of the extended Kalman filter is used to calculate the frequency of the isolated island system. When used to calculate the frequency difference and the phase angle difference, the specific calculation steps of the frequency of the isolated island system are as follows:

[0015] Step 1: Prediction model establishment

[0016] The sampling values ​​of the voltage and current fundamental wave signals in the island system can be expressed as:

[0017]

[0018] Among them, y k is the true value of the signal at time k, A is the amplitude; T s is the sampling interval; is the phase; ω k is the frequency at time k; z k is the signal measurement value at time k, v kis the current measurement noise, which obeys Gaussian distribution, with mean 0 and variance σ v 2 ;

[0019] The sampling value of the fundamental signal of the island system satisfies the following relationship:

[0020] y k =2cos(ω k T s )y k-1 -y k-2

[0021] That is, according to the sampling values ​​of the signals at the previous two moments, the sampling value at the current moment can be calculated;

[0022] The state equation of the island system can be expressed as:

[0023]

[0024] Among them, x k-1 represents the state vector at time k-1, x k represents the state vector at time k, f(·) represents the state equation of the island system, η k is the process noise that follows Gaussian distribution, with mean 0 and variance σ η 2 ;

[0025] The measurement equation of the island system can be expressed as:

[0026]

[0027] Among them, x k represents the state vector at time k, z k is the signal measurement value at time k, h(·) represents the measurement equation of the island system;

[0028] Step 2: State value prediction

[0029] The prediction equation of the system can be expressed as:

[0030]

[0031] Among them, x k - is the state prediction value obtained from the state equation at time k;

[0032] Step 3: Covariance matrix calculation

[0033] The covariance matrix of the predicted state can be expressed as:

[0034]

[0035] Among them, P k - is the covariance matrix of the predicted value at time k, P k-1 is the covariance matrix of the state vector at time k-1, F k is the state transfer matrix, obtained by taking partial derivatives of the system state equation, F k T is the transpose of the state transfer matrix, Q is the process noise covariance matrix;

[0036] Step 4: Kalman gain calculation

[0037] The Kalman gain can be expressed as:

[0038]

[0039] Among them, K k is the Kalman gain at time k, H k is the measurement matrix, obtained by taking partial derivatives of the system measurement equation, and R is the measurement noise covariance matrix;

[0040] Step 5: Status value correction

[0041] The state value correction can be expressed as:

[0042]

[0043] Among them, x k Update the state value at time k;

[0044] Step 6: Covariance matrix correction

[0045] The corrected covariance matrix can be expressed as:

[0046]

[0047] Among them, P k is the covariance matrix correction value at time k, and I is the unit matrix;

[0048] Just repeat the prediction and correction steps from Step 2 to Step 6.

[0049] Furthermore, when the pressure difference ΔU M ≤20%U N When the frequency difference Δf≤0.5Hz and the phase angle difference Δδ≤20°, fast quasi-synchronous closing is performed immediately.

[0050] Furthermore, the power matching is calculated according to the following formula:

[0051]

[0052] Among them, ΔP is the power transmitted from the island to the grid side, u N is the rated voltage during normal operation; R m is the power matching resistor value.

[0053] Corresponding to the above method, the present invention also provides a control system for a new energy substation backup automatic switching based on frequency tracking, comprising:

[0054] Bus voltage acquisition module: when the main line trips, the bus voltage U is acquired;

[0055] Control module: When U is less than the set value, the bus is determined to be in a no-voltage state and the backup automatic no-voltage closing logic is executed. When U is greater than or equal to the set value, the voltage difference, frequency difference and phase difference between the island side and the grid side are calculated. When the voltage difference, frequency difference and phase difference meet the conditions, fast quasi-synchronous closing is performed. If the conditions are not met, the power matching synchronous closing stage is entered to achieve an approximate match between the power supply and demand relationship, and then the closing and grid-connected operation is performed.

[0056] Furthermore, the phase angle difference Δδ is calculated as follows:

[0057]

[0058] Where Δδ t is the phase angle difference at the current moment, Δf t is the frequency difference at the current moment, is the frequency change rate, T dz It is the closing action time.

[0059] Furthermore, the frequency fast tracking algorithm of the extended Kalman filter is used to calculate the frequency of the isolated island system. When used to calculate the frequency difference and the phase angle difference, the specific calculation steps of the frequency of the isolated island system are as follows:

[0060] Step 1: Prediction model establishment

[0061] The sampling values ​​of the voltage and current fundamental wave signals in the island system can be expressed as:

[0062]

[0063] Among them, y k is the true value of the signal at time k, A is the amplitude; T s is the sampling interval; is the phase; ω k is the frequency at time k; z k is the signal measurement value at time k, v k is the current measurement noise, which obeys Gaussian distribution, with mean 0 and variance σ v 2 ;

[0064] The sampling value of the fundamental signal of the island system satisfies the following relationship:

[0065] y k =2cos(ω k T s )y k-1 -y k-2

[0066] That is, according to the sampling values ​​of the signals at the previous two moments, the sampling value at the current moment can be calculated;

[0067] The state equation of the island system can be expressed as:

[0068]

[0069] Among them, x k-1 represents the state vector at time k-1, x k represents the state vector at time k, f(·) represents the state equation of the island system, η k is the process noise that follows Gaussian distribution, with mean 0 and variance σ η 2 ;

[0070] The measurement equation of the island system can be expressed as:

[0071]

[0072] Among them, x k represents the state vector at time k, z k is the signal measurement value at time k, h(·) represents the measurement equation of the island system;

[0073] Step 2: State value prediction

[0074] The prediction equation of the system can be expressed as:

[0075]

[0076] Among them, x k - is the state prediction value obtained from the state equation at time k;

[0077] Step 3: Covariance matrix calculation

[0078] The covariance matrix of the predicted state can be expressed as:

[0079]

[0080] Among them, P k - is the covariance matrix of the predicted value at time k, P k-1is the covariance matrix of the state vector at time k-1, F k is the state transfer matrix, obtained by taking partial derivatives of the system state equation, F k T is the transpose of the state transfer matrix, Q is the process noise covariance matrix;

[0081] Step 4: Kalman gain calculation

[0082] The Kalman gain can be expressed as:

[0083]

[0084] Among them, K k is the Kalman gain at time k, H k is the measurement matrix, obtained by taking partial derivatives of the system measurement equation, and R is the measurement noise covariance matrix;

[0085] Step 5: Status value correction

[0086] The state value correction can be expressed as:

[0087]

[0088] Among them, x k Update the state value at time k;

[0089] Step 6: Covariance matrix correction

[0090] The corrected covariance matrix can be expressed as:

[0091]

[0092] Among them, P k is the covariance matrix correction value at time k, and I is the unit matrix;

[0093] Just repeat the prediction and correction steps from Step 2 to Step 6.

[0094] Furthermore, when the pressure difference ΔU M ≤20%U N When the frequency difference Δf≤0.5Hz and the phase angle difference Δδ≤20°, fast quasi-synchronous closing is performed immediately.

[0095] Furthermore, the power matching is calculated according to the following formula:

[0096]

[0097] Among them, ΔP is the power transmitted from the island to the grid side, u N is the rated voltage during normal operation; R m is the power matching resistor value.

[0098] The advantages of the present invention are:

[0099] The present invention optimizes the automatic backup strategy of substations under high-penetration renewable energy access, and proposes a automatic backup scheme that combines fast quasi-synchronous closing with closing after approximate matching of source and load power.

[0100] 1) In the early stage of island formation, its frequency and phase angle are not much different from the main grid. When the power difference between the source and load is not large, the system frequency change rate is relatively small, and fast quasi-synchronous closing can be adopted. Extended Kalman filtering is used for fast frequency tracking, and the backup power supply is connected to the grid in the early stage of the isolated grid operation, ensuring the reliability of power supply.

[0101] 2) When the power difference between the source and the load is large, the present invention proposes a solution to close the circuit breaker after the source and load power are approximately matched. In the scenario of "source is greater than load", energy-consuming resistors are put into use, and in the scenario of "source is less than load", part of the load is cut off to achieve approximate source-load matching. Its essence is to absorb the redundant power in the island system, reduce the power exchange generated at the moment of grid connection and closing, and thus suppress the closing impact current.

[0102] Additional aspects and advantages of the present invention will be given in part in the following description and in part will be obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0103] Figure 1 It is a flow chart of a control method for a new energy substation backup automatic switching proposed in one embodiment of the present invention;

[0104] Figure 2 It is a topological structure diagram of a 110kV substation containing new energy sources in one embodiment of the present invention;

[0105] Figure 3 is a flow chart of extended Kalman filter calculation in one embodiment of the present invention;

[0106] Figure 4 is a frequency tracking schematic diagram of an extended Kalman filter algorithm and a discrete Fourier transform algorithm in one embodiment of the present invention;

[0107] Figure 5 Schematic diagram of frequency tracking error of an extended Kalman filter algorithm and a discrete Fourier transform algorithm in one embodiment of the present invention;

[0108] Figure 6 It is a schematic diagram of the change of three-phase current of the standby power supply line before and after closing using a fast quasi-synchronous closing scheme in one embodiment of the present invention;

[0109] Figure 7It is a schematic diagram of the phase difference change between the island system and the backup power supply before and after closing using a fast quasi-synchronous closing scheme in one embodiment of the present invention;

[0110] Figure 8 1 is a schematic diagram comparing the current changes of the backup power supply line when the energy dissipation resistor is put into use and when the energy dissipation resistor is not put into use in the scenario of "the source is greater than the load" in one embodiment of the present invention, wherein (a) is without the energy dissipation resistor, and (b) is with the energy dissipation resistor;

[0111] Fig. 9 1 is a schematic diagram comparing the current changes of the backup power supply line when part of the load is removed and when the load is not removed in the "source is less than the load" scenario in one embodiment of the present invention, where (a) is the load not removed and (b) is the load removed DETAILED DESCRIPTION

[0112] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described in combination with the embodiments of the present invention. Obviously, the described embodiments are 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.

[0113] like Figure 1 As shown, the first embodiment of the present invention proposes a method for controlling automatic switching of a substation containing new energy, and the method comprises the following steps:

[0114] S10, monitoring the tripping signal of the main line circuit breaker, and obtaining the bus voltage U when a tripping signal occurs;

[0115] S20, if bus voltage U<0.3U N , determine that it is in a no-pressure state, and execute the conventional standby automatic no-pressure closing logic;

[0116] S30, if bus voltage U≥0.3U N , determine that it is in a voltage state, and calculate the voltage amplitude difference ΔU, phase angle difference Δδ and frequency difference Δf between the island system and the grid system. Calculate the frequency f of the island system based on the extended Kalman filter algorithm g Considering the inherent closing action time of the circuit breaker, the calculation formula of Δδ is:

[0117]

[0118] Where Δδ t is the phase angle difference at the current moment, Δf t is the frequency difference at the current moment, is the frequency change rate, T dz It is the closing action time.

[0119] The quasi-synchronous closing conditions are judged. The judgment criteria are as follows:

[0120] 1. Pressure difference ΔU M ≤20%U N

[0121] 2. Frequency difference Δf≤0.5Hz

[0122] 3. Phase angle difference Δδ≤20°

[0123] When the conditions are met, fast quasi-synchronous closing is performed immediately.

[0124] S40: If the quasi-synchronous closing conditions are not met, the power matching synchronous closing is performed. In the scenario of "source is less than load", part of the load is cut off. In the scenario of "source is greater than load", energy-consuming resistors are added at the grid connection point to achieve an approximate match between power supply and demand, and then the closing and grid connection operation is performed.

[0125] It should be noted that, in theory, the balance power required for power matching should be set as the difference between the output power of new energy and the load power, that is, the power ΔP transmitted to the grid side. According to the power balance principle, we have:

[0126]

[0127] Among them, u N R is the rated voltage during normal operation. m That is the required power matching resistance value.

[0128] Considering that it is impossible to achieve precise adjustment in actual engineering applications, it is sufficient to achieve approximate matching. For the scenario of "source is greater than load", the rated power P can be adjusted at the grid-connected outlet of the new energy source. N Set the resistance value of the energy dissipation resistor and divide it into n parts during configuration. (Round up) calculation to ensure that the power consumption is greater than the unbalanced amount of the island power. When performing load shedding operation in the "source is less than load" scenario, the corresponding load outgoing line is selected to be tripped through the circuit breaker at the beginning of each outgoing line of the substation according to the power imbalance.

[0129] This embodiment uses the law of voltage and frequency changes in the island system after the circuit breaker is opened to achieve rapid quasi-synchronous closing. After the main power supply is disconnected, rapid quasi-synchronous closing is given priority. In the early stage of the formation of the island, its frequency and phase angle are not much different from the main grid. When the voltage difference, phase angle difference and frequency difference between the backup power supply and the island system are quickly detected and are within the allowable range, a closing pulse signal is immediately issued to complete rapid switching, which can achieve rapid power restoration. The power matching synchronous closing method serves as a backup for the rapid quasi-synchronous closing method. It uses the input of energy-consuming resistors or the removal of part of the load to achieve approximate power matching and effectively suppress the impact current.

[0130] As a further preferred technical solution, Figure 3 As shown, in step S30, the island system frequency f is calculated based on the extended Kalman filter algorithm g ,include:

[0131] Step 1: Prediction model establishment

[0132] The sampling values ​​of voltage and current fundamental wave signals in the power system can be expressed as:

[0133]

[0134] Among them, y k is the true value of the signal at time k, A is the amplitude; T s is the sampling interval; is the phase; ω k is the frequency at time k; z k is the signal measurement value at time k, v k is the current measurement noise, which obeys Gaussian distribution, with mean 0 and variance σ v 2 .

[0135] The sampling value of the fundamental signal of the island system satisfies the following relationship:

[0136] y k =2cos(ω k T s )y k-1 -y k-2

[0137] That is, the sampling value at the current moment can be calculated based on the sampling values ​​of the signal at the previous two moments.

[0138] The state equation of the island system can be expressed as:

[0139]

[0140] Among them, x k-1 represents the state vector at time k-1, x k represents the state vector at time k, f(·) represents the state equation of the island system, η k is the process noise that follows Gaussian distribution, with mean 0 and variance σ η 2 .

[0141] The measurement equation of the island system can be expressed as:

[0142]

[0143] Among them, x krepresents the state vector at time k, z k is the signal measurement value at time k, and h(·) represents the measurement equation of the island system.

[0144] Step 2: State value prediction

[0145] The prediction equation of the system can be expressed as:

[0146]

[0147] Among them, x k - is the state prediction value obtained from the state equation at time k.

[0148] Step 3: Covariance matrix calculation

[0149] The covariance matrix of the predicted state can be expressed as:

[0150]

[0151] Among them, P k - is the covariance matrix of the predicted value at time k, P k-1 is the covariance matrix of the state vector at time k-1, F k is the state transfer matrix, obtained by taking partial derivatives of the system state equation, F k T is the transpose of the state transfer matrix, and Q is the process noise covariance matrix.

[0152] Step 4: Kalman gain calculation

[0153] The Kalman gain can be expressed as:

[0154]

[0155] Among them, K k is the Kalman gain at time k, H k is the measurement matrix, obtained by taking partial derivatives of the system measurement equation, and R is the measurement noise covariance matrix.

[0156] Step 5: Status value correction

[0157] The state value correction can be expressed as:

[0158]

[0159] Among them, x k Update the state value at time k.

[0160] Step 6: Covariance matrix correction

[0161] The corrected covariance matrix can be expressed as:

[0162]

[0163] Among them, P k is the covariance matrix correction value at time k, and I is the unit matrix.

[0164] Step 2-6 is a complete iterative process of the extended Kalman filter. The steps of the prediction stage and the correction stage can be repeated continuously at subsequent moments.

[0165] Extended Kalman filter: the signal state x at the previous moment k-1 As the input quantity, the state prediction value x at this moment is obtained through the state equation k - , and calculate the error covariance matrix P of the predicted value k - At the same time, the signal measurement value z at this moment k As input, the state prediction value x k - Correction is performed and the Kalman gain K is calculated k , get the corrected state update value x k , through iterative solution, accurate and fast tracking of state quantity is achieved. In the initial value setting, the initial value of fundamental frequency ω0 is set to 50Hz, and the initial value change value of frequency Δω0 is set to 0.

[0166] Below Figure 2 The example of a 110kV substation containing renewable energy is used for explanation. The renewable energy station transmits power to the grid during normal operation, with a rated output power of 15MW. 1DL, 2DL and 3DL constitute a 110kV standby automatic switch. During normal operation, 1DL and 3DL are in a closed state, and 2DL is in a disconnected state. In the simulation model, the main circuit breaker trips at 0.8s, forming an island.

[0167] The schematic diagram of the frequency tracking simulation results based on the extended Kalman filter algorithm and discrete Fourier transform algorithm is as follows Figure 4 As shown in the figure, the window length selected by the discrete Fourier transform is 10ms. The frequency tracking error diagram of the extended Kalman filter algorithm and the discrete Fourier transform algorithm is shown in the figure. Figure 5 As shown. Figure 4 and Figure 5It can be seen that when the grid frequency changes, the discrete Fourier transform algorithm is insensitive to the frequency change, has poor real-time performance, and cannot accurately track the continuous change of frequency. The extended Kalman filter algorithm can achieve better frequency tracking. From the error percentage curve, it can be seen that about 20ms after the frequency changes, the extended Kalman filter algorithm can stabilize the tracking error below 0.4%, and the discrete Fourier transform algorithm tracking error is maintained at about 1%. The extended Kalman filter algorithm has a small overall tracking error, fast tracking speed, and much higher calculation accuracy than the discrete Fourier transform algorithm. It can achieve fast and accurate tracking of the frequency of the island system.

[0168] An analysis is conducted based on three situations: meeting the quasi-synchronous closing conditions, requiring the use of energy-consuming resistors, and requiring partial load shedding.

[0169] Scenario 1: The penetration rate of new energy is 95%. According to the backup automatic switching scheme, the quasi-synchronous closing condition is first judged. It is assumed that the fast quasi-synchronous closing condition judgment is completed 50ms after the fault occurs. When it is judged that the conditions are met, a closing command is issued. Usually, a fast circuit breaker, such as a vacuum circuit breaker, is used. Assume that the circuit breaker closing time is 50ms. That is, the closing condition judgment is completed 50ms after the new energy island is formed, and the closing is realized in 100ms.

[0170] The schematic diagram of the three-phase current change of the backup power supply line before and after the implementation of the fast quasi-synchronous closing scheme is as follows Figure 6 As shown in the figure, the phase difference between the island system and the backup power supply is shown in the figure Figure 7 As shown. Figure 6 and Figure 7 It can be seen that the peak value of the impact current generated by the direct closing operation 100ms after the island is formed is 1.47pu. This is because the power difference between the output power of the new energy and the load is relatively small, and the frequency deviation rate of the formed island system is relatively low. In the initial stage, the quasi-synchronous closing conditions are met, and the backup power supply should be put into use as soon as possible to ensure the reliability of power supply.

[0171] Scenario 2: New energy penetration rate is 150%.

[0172] It is determined that the quasi-synchronous closing conditions are not met. The source-load relationship is judged. The penetration rate of new energy is 150%, which is a "source is greater than load" scenario. The comparison diagram of the backup power supply line current change when the energy-consuming resistor is put into use and when the energy-consuming resistor is not put into use is shown in the figure below. Figure 8 As shown, (a) is when no energy-dissipating resistor is used, and (b) is when energy-dissipating resistor is used.

[0173] Scenario three: New energy penetration rate is 50%.

[0174] It is determined that the quasi-synchronous closing conditions are not met. The source-load relationship is judged. The penetration rate of new energy is 50%, which is a "source is smaller than load" scenario. The comparison diagram of the current change of the backup power supply line when part of the load is removed and when no load is removed is shown in the figure. Fig. 9 As shown, (a) is the uncut load and (b) is the cut-off part of the load.

[0175] Depend on Figure 8 and Fig. 9 It can be seen that when the power difference is relatively large, if no measures are taken to make the output power of renewable energy and the load power approximately match and the switch is closed directly, an inrush current with a peak value of more than 3.5pu will appear after closing. After taking measures, the peak value of the inrush current can be suppressed to less than 1.5pu.

[0176] This embodiment optimizes the backup automatic switching strategy of substations under high penetration of new energy access, and proposes a backup automatic switching scheme that combines fast quasi-synchronous closing and closing after the source and load power are approximately matched. In the early stage of the formation of the island, its frequency and phase angle are not much different from the main grid. When the source and load power difference is not large, the system frequency change rate is also relatively small, and fast quasi-synchronous closing can be adopted. The extended Kalman filter is used for fast frequency tracking, and the backup power supply is connected to the grid in the early stage of the isolated grid operation to ensure the reliability of power supply. When the source and load power difference is large, the present invention proposes a scheme of closing after the source and load power are approximately matched. In the scenario of "source is greater than load", energy-consuming resistors are put into use, and in the scenario of "source is less than load", part of the load is cut off to achieve approximate source and load matching. Its essence is to absorb the redundant power in the island system, reduce the power exchange generated at the moment of grid connection and closing, and thus suppress the closing impact current.

[0177] 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 of the technical features may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A control method for automatic switching of a substation containing new energy based on frequency tracking, characterized in that: The following steps are involved: When the main line trips, the bus voltage U is obtained; when U is less than the set value, the bus is determined to be in a no-voltage state, and the backup automatic no-voltage closing logic is executed; when U is greater than or equal to the set value, the voltage difference, frequency difference, and phase difference between the island side and the grid side are calculated. When the voltage difference, frequency difference, and phase difference all meet the conditions, fast quasi-synchronous closing is performed. If the conditions are not met, the power matching synchronous closing stage is entered to achieve an approximate match of the power supply and demand relationship, and then the closing and grid-connected operation is performed.

2. The control method of the frequency tracking-based automatic switching of a substation containing new energy according to claim 1 is characterized in that: The phase angle difference Δδ calculation process is: Where Δδ t is the phase angle difference at the current moment, Δf t is the frequency difference at the current moment, is the frequency change rate, T dz It is the closing action time.

3. The control method of the frequency tracking-based automatic switching of a substation containing new energy sources according to claim 1 or 2, characterized in that: The frequency fast tracking algorithm of the extended Kalman filter is used to calculate the frequency of the island system. When it is used to calculate the frequency difference and phase angle difference, the specific calculation steps of the frequency of the island system are as follows: Step 1: Prediction model establishment The sampling values ​​of the voltage and current fundamental wave signals in the island system can be expressed as: Among them, y k is the true value of the signal at time k, A is the amplitude; T s is the sampling interval; is the phase; ω k is the frequency at time k; z k is the signal measurement value at time k, v k is the current measurement noise, which obeys Gaussian distribution, with mean 0 and variance σ v 2 ; The sampling value of the fundamental signal of the island system satisfies the following relationship: and k =2cos(ω k T s )and k-1 -and k-2 That is, according to the sampling values ​​of the signals at the previous two moments, the sampling value at the current moment can be calculated; The state equation of the island system can be expressed as: Among them, x k-1 represents the state vector at time k-1, x k represents the state vector at time k, f(·) represents the state equation of the island system, η k is the process noise that follows Gaussian distribution, with mean 0 and variance σ η 2 ; The measurement equation of the island system can be expressed as: Among them, x k represents the state vector at time k, z k is the signal measurement value at time k, h(·) represents the measurement equation of the island system; Step 2: State value prediction The prediction equation of the system can be expressed as: Among them, x k - is the state prediction value obtained from the state equation at time k; Step 3: Covariance matrix calculation The covariance matrix of the predicted state can be expressed as: Among them, P k - is the covariance matrix of the predicted value at time k, P k-1 is the covariance matrix of the state vector at time k-1, F k is the state transfer matrix, obtained by taking partial derivatives of the system state equation, F k T is the transpose of the state transfer matrix, Q is the process noise covariance matrix; Step 4: Kalman gain calculation The Kalman gain can be expressed as: Among them, K k is the Kalman gain at time k, H k is the measurement matrix, obtained by taking partial derivatives of the system measurement equation, and R is the measurement noise covariance matrix; Step 5: Status value correction The state value correction can be expressed as: Among them, x k Update the state value at time k; Step 6: Covariance matrix correction The corrected covariance matrix can be expressed as: Among them, P k is the covariance matrix correction value at time k, and I is the unit matrix; Just repeat the prediction and correction steps from Step 2 to Step 6.

4. The control method for automatic switching of a substation containing new energy based on frequency tracking according to claim 1 or 2 is characterized in that: When the pressure difference ΔU M ≤20%U N When the frequency difference Δf≤0.5Hz and the phase angle difference Δδ≤20°, fast quasi-synchronous closing is performed immediately.

5. The control method for automatic switching of a substation containing new energy based on frequency tracking according to claim 1 or 2, characterized in that: The power matching is calculated according to the following formula: Among them, ΔP is the power transmitted from the island to the grid side, u N R is the rated voltage during normal operation; m is the power matching resistor value.

6. A control system for automatic switching of a new energy substation based on frequency tracking, characterized in that: include: Bus voltage acquisition module: when the main line trips, the bus voltage U is acquired; Control module: When U is less than the set value, the bus is determined to be in a no-voltage state and the backup automatic no-voltage closing logic is executed. When U is greater than or equal to the set value, the voltage difference, frequency difference and phase difference between the island side and the grid side are calculated. When the voltage difference, frequency difference and phase difference meet the conditions, fast quasi-synchronous closing is performed. If the conditions are not met, the power matching synchronous closing stage is entered to achieve an approximate match between the power supply and demand relationship, and then the closing and grid-connected operation is performed.

7. The control system for automatic switching of a substation containing new energy based on frequency tracking according to claim 6 is characterized in that: The phase angle difference Δδ calculation process is: Where Δδ t is the phase angle difference at the current moment, Δf t is the frequency difference at the current moment, is the frequency change rate, T dz It is the closing action time.

8. The control system for automatic switching of a substation containing new energy based on frequency tracking according to claim 6 or 7, characterized in that: The frequency fast tracking algorithm of the extended Kalman filter is used to calculate the frequency of the island system. When it is used to calculate the frequency difference and phase angle difference, the specific calculation steps of the frequency of the island system are as follows: Step 1: Prediction model establishment The sampling values ​​of the voltage and current fundamental wave signals in the island system can be expressed as: Among them, y k is the true value of the signal at time k, A is the amplitude; T s is the sampling interval; is the phase; ω k is the frequency at time k; z k is the signal measurement value at time k, v k is the current measurement noise, which obeys Gaussian distribution, with mean 0 and variance σ v 2 ; The sampling value of the fundamental signal of the island system satisfies the following relationship: and k =2cos(ω k T s )and k-1 -and k-2 That is, according to the sampling values ​​of the signals at the previous two moments, the sampling value at the current moment can be calculated; The state equation of the island system can be expressed as: Among them, x k-1 represents the state vector at time k-1, x k represents the state vector at time k, f(·) represents the state equation of the island system, η k is the process noise that follows Gaussian distribution, with mean 0 and variance σ η 2 ; The measurement equation of the island system can be expressed as: Among them, x k represents the state vector at time k, z k is the signal measurement value at time k, h(·) represents the measurement equation of the island system; Step 2: State value prediction The prediction equation of the system can be expressed as: Among them, x k - is the state prediction value obtained from the state equation at time k; Step 3: Covariance matrix calculation The covariance matrix of the predicted state can be expressed as: Among them, P k - is the covariance matrix of the predicted value at time k, P k-1 is the covariance matrix of the state vector at time k-1, F k is the state transfer matrix, obtained by taking partial derivatives of the system state equation, F k T is the transpose of the state transfer matrix, Q is the process noise covariance matrix; Step 4: Kalman gain calculation The Kalman gain can be expressed as: Among them, K k is the Kalman gain at time k, H k is the measurement matrix, obtained by taking partial derivatives of the system measurement equation, and R is the measurement noise covariance matrix; Step 5: Status value correction The state value correction can be expressed as: Among them, x k Update the state value at time k; Step 6: Covariance matrix correction The corrected covariance matrix can be expressed as: Among them, P k is the covariance matrix correction value at time k, and I is the unit matrix; Just repeat the prediction and correction steps from Step 2 to Step 6.

9. The control system for automatic switching of a substation containing new energy based on frequency tracking according to claim 6 or 7, characterized in that: When the pressure difference ΔU M ≤20%U N When the frequency difference Δf≤0.5Hz and the phase angle difference Δδ≤20°, fast quasi-synchronous closing is performed immediately.

10. The control system for automatic switching of a substation containing new energy based on frequency tracking according to claim 6 or 7, characterized in that: The power matching is calculated according to the following formula: Among them, ΔP is the power transmitted from the island to the grid side, u N R is the rated voltage during normal operation; m is the power matching resistor value.

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