Alternating current line relay protection method cooperating with converter control strategy

Abstract

The invention provides an AC line relay protection method cooperating with a converter control strategy. The method comprises the following steps: monitoring the state of a converter; when the current converter is in a normal state, executing a relay protection strategy according to the first electrical quantity collected by the grid connection point; under the condition that the converter is in the fault ride-through state, correcting a first electrical quantity collected by the grid-connected point, eliminating the influence of the fault ride-through state on the electrical quantity, and obtaining a second electrical quantity; and executing a relay protection strategy according to the second electrical quantity. According to the invention, the reliability and sensitivity of the relay protection strategy of the AC line are ensured, and the safety of the new energy system is improved.

Description

Technical Field

[0001] The present invention relates to the field of new energy technology, and in particular to an AC line relay protection method in coordination with a converter control strategy. Background Art

[0002] In related technologies, the fault protection strategy of new energy (wind energy, solar energy or tidal energy, etc.) systems usually has a current limiting link, which leads to the weak fault characteristics of the new energy system during a fault, and further leads to the low reliability and sensitivity of the current-based fault protection strategy of the AC line. Summary of the invention

[0003] The present invention aims to at least solve or improve the technical problem of low reliability of the current-based fault protection strategy of AC lines in new energy systems in the prior art.

[0004] To this end, a first aspect of the present invention proposes an AC line relay protection method in coordination with a converter control strategy.

[0005] A second aspect of the present invention provides an AC line relay protection device in coordination with a converter control strategy.

[0006] In view of this, according to the first aspect of the present invention, the present invention proposes an AC line relay protection method of a coordinated converter control strategy, including: monitoring the state of the converter; when the converter is in a normal state, executing a relay protection strategy based on a first electrical quantity collected at the grid connection point; when the converter is in a fault-crossing state, correcting the first electrical quantity collected at the grid connection point to eliminate the impact of the fault-crossing state on the electrical quantity and obtain a second electrical quantity; executing the relay protection strategy based on the second electrical quantity.

[0007] The AC line relay protection method of the coordinated converter control strategy proposed in the present invention includes: monitoring the state of the converter, the working state of the converter is divided into a normal state and a fault ride-through state, etc. When the working state of the converter is divided into a normal state and a fault ride-through state, a relay protection strategy is executed according to a first electrical quantity collected by the grid connection point. When the converter is in a fault ride-through state, the voltage at the grid connection point drops and the current changes. In this case, the first electrical quantity collected by the grid connection point is corrected to eliminate the influence of the fault ride-through state, and a second electrical quantity is obtained. Then, the relay protection strategy is executed according to the second electrical quantity, thereby ensuring the reliability and sensitivity of the relay protection strategy for the AC line and improving the safety of the new energy system.

[0008] In addition, the AC line relay protection method of the coordinated converter control strategy in the above technical solution provided by the present invention may also have the following additional technical features:

[0009] In some embodiments, optionally, when the converter is in a fault ride-through state, the collected first electrical quantity of the grid-connected point is corrected to eliminate the impact of the fault ride-through state on the electrical quantity, and obtain the second electrical quantity, including: when the converter is in a fault ride-through state, according to the voltage drop coefficient of the grid-connected point, correcting the amplitude of the first current; according to the d-axis current reference value and the q-axis current reference value of the converter in the fault ride-through state, correcting the phase of the first current; obtaining the second current.

[0010] Specifically, when the converter is in a fault ride-through state, the first electrical quantity of the grid-connected point collected is corrected to eliminate the influence of the fault ride-through state on the electrical quantity and obtain the second electrical quantity, including: when the converter is in a fault ride-through state, the voltage drop coefficient of the grid-connected point is obtained, and the amplitude of the first current is corrected according to the voltage drop coefficient of the grid-connected point, and the phase of the first current is corrected according to the d-axis current reference value and the q-axis current reference value of the converter in the fault ride-through state, and the second current is obtained by correcting the first current, that is, the amplitude of the first current is corrected by the voltage drop coefficient so that the amplitude of the current conforms to the situation in the normal state, and the phase of the first current is corrected by the d-axis current reference value and the q-axis current reference value of the converter in the fault ride-through state so that the phase of the current conforms to the situation in the normal state, thereby eliminating the influence of the fault ride-through state on the second current.

[0011] In some embodiments, optionally, the amplitude of the first current is corrected according to the voltage drop coefficient of the grid connection point, including: when the converter is in a fault ride-through state, determining the voltage drop coefficient of the grid connection point; when the voltage of the grid connection point drops by n times, amplifying the amplitude of the first current by n times.

[0012] In this embodiment, the amplitude of the first current is corrected according to the voltage drop coefficient, including: if the voltage at the grid-connected point drops by n times, then the voltage drop coefficient is determined to be n, and the amplitude of the first current is amplified by n times to correct the amplitude of the first current, thereby achieving the effect of amplifying the amplitude of the first current, and the amplification of the amplitude of the first current is related to the voltage drop coefficient, which can ensure the accuracy of the amplitude correction of the first current.

[0013] In some embodiments, optionally, when the converter is in a fault ride-through state, determining the voltage drop coefficient of the grid connection point includes: when the converter is in a fault ride-through state, using a dq transformation method based on instantaneous reactive power theory to determine the voltage drop coefficient of the grid connection point.

[0014] In this embodiment, when the converter is in a fault ride-through state, the voltage drop coefficient of the grid connection point is determined, including: when the converter is in a fault ride-through state, the voltage drop coefficient of the grid connection point is determined by using a dq transformation method based on instantaneous reactive power theory, thereby ensuring the accuracy of the determination of the voltage drop coefficient.

[0015] In some embodiments, optionally, according to the d-axis current reference value and the q-axis current reference value of the converter in the fault ride-through state, correcting the phase of the first current includes: bringing the d-axis current reference value and the q-axis current reference value into: The current phase change is obtained, where Δθ represents the current phase change, represents the q-axis current reference value, represents the d-axis current reference value, Indicates the voltage phase change; the phase of the first current is corrected according to the current phase change.

[0016] In this embodiment, the phase of the first current is corrected according to the d-axis current reference value and the q-axis current reference value of the converter in the fault ride-through state, including: calculating the current phase change amount using the d-axis current reference value and the q-axis current reference value formula, and then correcting the phase of the first current according to the current phase change amount.

[0017] The formula is: Δθ represents the current phase change, represents the q-axis current reference value, represents the d-axis current reference value, Indicates the voltage phase change.

[0018] In some embodiments, optionally, it also includes: the converter detects the voltage drop through the dq transformation method based on the instantaneous reactive power theory; and determines whether to enter the fault ride-through state according to the voltage drop.

[0019] In this embodiment, it also includes: the converter detects the voltage drop through the dq transformation method based on the instantaneous reactive power theory, and determines whether to enter the fault ride-through state according to the voltage drop, so as to ensure that the converter can accurately switch to the fault ride-through state.

[0020] In some embodiments, optionally, the converter adopts a PQ (constant power) control strategy, and the control strategy when the converter is in a fault ride-through state is determined according to the national standard GB / T19964-2012.

[0021] In this embodiment, the converter adopts a PQ control strategy. The control strategy when the converter is in a fault ride-through state is determined according to the national standard GB / T19964-2012, thereby ensuring the safety of the new energy system.

[0022] In some embodiments, optionally, the relay protection strategy includes at least one of the following: a current protection strategy, a gas protection strategy, a differential protection strategy, a high-frequency protection strategy, a distance protection strategy, a balance protection strategy, a negative-sequence and zero-sequence protection strategy, and a directional protection strategy.

[0023] In this embodiment, the relay protection strategy includes at least one of the following: current protection strategy, gas protection strategy, differential protection strategy, high frequency protection strategy, distance protection strategy, balance protection strategy, negative sequence and zero sequence protection strategy and directional protection strategy.

[0024] In some embodiments, optionally, the first electrical quantity is a positive sequence value.

[0025] In this embodiment, the first electrical quantity is a positive sequence value, thereby improving the accuracy of calculation and control.

[0026] According to the second aspect of the present invention, the present invention proposes an AC line relay protection device with a coordinated converter control strategy, wherein a communication link is provided between the AC line relay protection device with a coordinated converter control strategy and the converter, and the AC line relay protection device with a coordinated converter control strategy is used to execute the steps of the AC line relay protection method with a coordinated converter control strategy provided in the first aspect embodiment.

[0027] The AC line relay protection device of the cooperative converter control strategy provided by the present invention is used to execute the steps of the AC line relay protection method of the cooperative converter control strategy provided by the first aspect embodiment. Therefore, it has all the beneficial effects of the steps of the AC line relay protection method of the cooperative converter control strategy provided by the first aspect embodiment, which are no longer stated one by one here.

[0028] Additional aspects and advantages of the present invention will become apparent from the following description or may be learned by practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The above and / or additional aspects and advantages of the present invention will become apparent and easily understood from the description of the embodiments in conjunction with the following drawings, in which:

[0030] Figure 1 One of the flow charts of an AC line relay protection method in coordination with a converter control strategy provided by an embodiment of the present invention is shown;

[0031] Figure 2 A second flowchart of an AC line relay protection method in a coordinated converter control strategy provided by an embodiment of the present invention is shown;

[0032] Figure 3A schematic diagram of a scenario of a new energy system to which an AC line relay protection method of a coordinated converter control strategy provided by an embodiment of the present invention is applied;

[0033] Figure 4 A configuration diagram of an AC line relay protection method in coordination with a converter control strategy provided by an embodiment of the present invention is shown;

[0034] Figure 5 A schematic diagram of the phase angles of current and voltage in a normal state in an AC line relay protection method of a coordinated converter control strategy provided by an embodiment of the present invention is shown;

[0035] Figure 6 A schematic diagram of the phase angles of current and voltage in a fault ride-through state in an AC line relay protection method of a coordinated converter control strategy provided by an embodiment of the present invention is shown. DETAILED DESCRIPTION

[0036] In order to more clearly understand the above-mentioned purpose, features and advantages of the present invention, the present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be noted that the embodiments of the present invention and the features in the embodiments can be combined with each other without conflict.

[0037] In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention may also be implemented in other ways different from those described herein. Therefore, the protection scope of the present invention is not limited to the specific embodiments disclosed below.

[0038] Refer to the following Figures 1 to 6 An AC line relay protection method in coordination with a converter control strategy provided according to some embodiments of the present invention is described.

[0039] According to a first aspect of the present invention, the present invention provides an AC line relay protection method in coordination with a converter control strategy. Figure 1 FIG. 1 shows one of the flow charts of an AC line relay protection method in a coordinated converter control strategy provided by an embodiment of the present invention. Figure 1 As shown, the process of the AC line relay protection method of the coordinated converter control strategy provided by one embodiment of the present invention is as follows:

[0040] Step 102: Monitor the status of the converter.

[0041] Specifically, the state of the converter is monitored. The converter has a normal state and a fault ride-through state. When the converter is in the normal state, the current and voltage at the grid connection point are normal. When the converter is in the fault ride-through state, the current and voltage at the grid connection point will change.

[0042] Step 104: When the converter is in a normal state, a relay protection strategy is executed according to the first electrical quantity collected by the grid connection point.

[0043] Specifically, when it is monitored that the converter is in a normal state, the relay protection strategy is executed according to the first electrical quantity collected at the grid connection point. That is, when the new energy system is operating normally, the relay protection strategy is implemented through the first electrical quantity collected at the grid connection point.

[0044] Step 106: When the converter is in a fault ride-through state, the first electrical quantity collected at the grid connection point is corrected to eliminate the influence of the fault ride-through state on the electrical quantity, thereby obtaining a second electrical quantity.

[0045] Specifically, when it is monitored that the converter is in a fault ride-through state, the first electrical quantity collected at the grid connection point is corrected to eliminate the impact of the fault ride-through state on the electrical quantity and obtain the second electrical quantity. That is, when the new energy system is operating faultily, the first electrical quantity collected at the grid connection point is corrected to obtain the second electrical quantity to eliminate the impact of the fault ride-through state.

[0046] Step 108: Execute a relay protection strategy according to the second electrical quantity.

[0047] Specifically, the relay protection strategy is executed according to the second electrical quantity, that is, in the case of faulty operation of the new energy system, the first electrical quantity collected at the grid connection point is corrected and the relay protection strategy is performed using the modified second electrical quantity.

[0048] The AC line relay protection method of the coordinated converter control strategy proposed in the present invention includes: monitoring the state of the converter, the working state of the converter is divided into a normal state and a fault ride-through state, etc. When the working state of the converter is divided into a normal state and a fault ride-through state, a relay protection strategy is executed according to a first electrical quantity collected at a grid connection point. When the converter is in a fault ride-through state, the voltage at the grid connection point drops and the current changes. In this case, the first electrical quantity collected at the grid connection point is corrected to eliminate the influence of the fault ride-through state, and a second electrical quantity is obtained. The relay protection strategy is executed according to the second electrical quantity, thereby ensuring the reliability and sensitivity of the relay protection strategy for the AC line and improving the safety of the new energy system.

[0049] The converter may be an inverter or a rectifier.

[0050] In some embodiments, optionally, when the converter is in a fault ride-through state, the collected first electrical quantity of the grid-connected point is corrected to eliminate the impact of the fault ride-through state on the electrical quantity, and obtain the second electrical quantity, including: when the converter is in a fault ride-through state, according to the voltage drop coefficient of the grid-connected point, correcting the amplitude of the first current; according to the d-axis current reference value and the q-axis current reference value of the converter in the fault ride-through state, correcting the phase of the first current; obtaining the second current.

[0051] Specifically, when the converter is in a fault ride-through state, the first electrical quantity of the grid-connected point collected is corrected to eliminate the influence of the fault ride-through state on the electrical quantity and obtain the second electrical quantity, including: when the converter is in a fault ride-through state, the voltage drop coefficient of the grid-connected point is obtained, and the amplitude of the first current is corrected according to the voltage drop coefficient of the grid-connected point, and the phase of the first current is corrected according to the d-axis current reference value and the q-axis current reference value of the converter in the fault ride-through state, and the second current is obtained by correcting the first current, that is, the amplitude of the first current is corrected by the voltage drop coefficient so that the amplitude of the current conforms to the situation in the normal state, and the phase of the first current is corrected by the d-axis current reference value and the q-axis current reference value of the converter in the fault ride-through state so that the phase of the current conforms to the situation in the normal state, thereby eliminating the influence of the fault ride-through state on the second current.

[0052] In some embodiments, optionally, the amplitude of the first current is corrected according to the voltage drop coefficient of the grid connection point, including: when the converter is in a fault ride-through state, determining the voltage drop coefficient of the grid connection point; when the voltage of the grid connection point drops by n times, amplifying the amplitude of the first current by n times.

[0053] In this embodiment, the amplitude of the first current is corrected according to the voltage drop coefficient, including: if the voltage at the grid-connected point drops by n times, then the voltage drop coefficient is determined to be n, and the amplitude of the first current is amplified by n times to correct the amplitude of the first current, thereby achieving the effect of amplifying the amplitude of the first current, and the amplification of the amplitude of the first current is related to the voltage drop coefficient, which can ensure the accuracy of the amplitude correction of the first current.

[0054] In some embodiments, optionally, when the converter is in a fault ride-through state, determining the voltage drop coefficient of the grid connection point includes: when the converter is in a fault ride-through state, using a dq transformation method based on instantaneous reactive power theory to determine the voltage drop coefficient of the grid connection point.

[0055] In this embodiment, when the converter is in a fault ride-through state, the voltage drop coefficient of the grid connection point is determined, including: when the converter is in a fault ride-through state, the voltage drop coefficient of the grid connection point is determined by using a dq transformation method based on instantaneous reactive power theory, thereby ensuring the accuracy of the determination of the voltage drop coefficient.

[0056] In some embodiments, optionally, according to the d-axis current reference value and the q-axis current reference value of the converter in the fault ride-through state, correcting the phase of the first current includes: bringing the d-axis current reference value and the q-axis current reference value into: The current phase change is obtained, where Δθ represents the current phase change, represents the q-axis current reference value, represents the d-axis current reference value, Indicates the voltage phase change; the phase of the first current is corrected according to the current phase change.

[0057] In this embodiment, the phase of the first current is corrected according to the d-axis current reference value and the q-axis current reference value of the converter in the fault ride-through state, including: calculating the current phase change amount using the d-axis current reference value and the q-axis current reference value formula, and then correcting the phase of the first current according to the current phase change amount.

[0058] The formula is: Δθ represents the current phase change, represents the q-axis current reference value, represents the d-axis current reference value, Indicates the voltage phase change.

[0059] In some embodiments, optionally, it also includes: the converter detects the voltage drop through the dq transformation method based on the instantaneous reactive power theory; and determines whether to enter the fault ride-through state according to the voltage drop.

[0060] In this embodiment, it also includes: the converter detects the voltage drop through the dq transformation method based on the instantaneous reactive power theory, and determines whether to enter the fault ride-through state according to the voltage drop, so as to ensure that the converter can accurately switch to the fault ride-through state.

[0061] In some embodiments, optionally, the converter adopts a PQ (active power and reactive power) control strategy, and the control strategy when the converter is in a fault ride-through state is determined according to the national standard GB / T19964-2012.

[0062] In this embodiment, the converter adopts a PQ control strategy. The control strategy when the converter is in a fault ride-through state is determined according to the national standard GB / T19964-2012, thereby ensuring the safety of the new energy system.

[0063] In some embodiments, optionally, the relay protection strategy includes at least one of the following: a current protection strategy, a gas protection strategy, a differential protection strategy, a high-frequency protection strategy, a distance protection strategy, a balance protection strategy, a negative-sequence and zero-sequence protection strategy, and a directional protection strategy.

[0064] In this embodiment, the relay protection strategy includes at least one of the following: current protection strategy, gas protection strategy, differential protection strategy, high frequency protection strategy, distance protection strategy, balance protection strategy, negative sequence and zero sequence protection strategy and directional protection strategy.

[0065] In some embodiments, optionally, the first electrical quantity is a positive sequence value.

[0066] In this embodiment, the first electrical quantity is a positive sequence value, thereby improving the accuracy of calculation and control.

[0067] Figure 2 FIG2 shows a second flow chart of an AC line relay protection method in a coordinated converter control strategy provided by an embodiment of the present invention. Figure 2 As shown, the process of the AC line relay protection method of the coordinated converter control strategy provided by one embodiment of the present invention is as follows:

[0068] Step 202: Start;

[0069] Step 204: monitor the control signal LVRT_ON;

[0070] Step 206: Determine whether to switch to the fault ride-through strategy; if the determination result is yes, execute step 208; if the determination result is no, execute step 204;

[0071] Step 208: The protection device detects voltage drop using the dq transformation method of instantaneous reactive power theory;

[0072] Step 210: Calculate the first current to be corrected;

[0073] Step 212:

[0074] Step 214: Correcting the amplitude of the first current according to the voltage drop coefficient;

[0075] Step 216: I′=nI N ;

[0076] Step 218: Correcting the phase angle of the first current according to the reactive current value;

[0077] Step 220:

[0078] Step 222: Continue with the relay protection strategy.

[0079] Specifically, Figure 3 The new energy system is a 110kV large-scale new energy system, and its power transmission lines are as follows: Figure 3 As shown, the new energy is equipped with 25MW photovoltaic (PV) power generation. The new energy is connected to the grid through the inverter. The inverter adopts PQ control and only outputs active power during normal operation. In the event of a fault, the fault current is limited according to the national standard GB / T19964-2012 to protect the converter. At the same time, in order to deal with asymmetric faults, a negative sequence current suppression control strategy is provided, and the negative sequence current is designated as 0. A communication channel is provided between the converter and the protection device to transmit working status information (set to LVRT_ON signal, 0 represents normal operation, and 1 represents fault ride-through). The protection device is equipped with traditional overcurrent protection and a data processing module.

[0080] like Figure 4 As shown, after the electrical quantity information is collected and input into the protection device, the protection device first determines whether the sampled first current needs to be corrected according to the state of the converter. If the LVRT_ON signal is 1, that is, in the case of a control strategy in a fault crossing state, the collected first current is corrected, and the current voltage drop coefficient can be obtained by using the dq transformation method based on the instantaneous reactive power theory. Assuming that the current line generates a symmetrical fault voltage drop of 33% of the normal operating voltage, the voltage drop coefficient is approximately equal to 3, then the amplitude of the first current is corrected to 3 times, and the phase angle of the first current is corrected by 130°. Using the corrected first current for traditional protection judgment can eliminate the influence of the working state of the converter on the relay protection strategy, and the traditional relay protection strategy can be continued.

[0081] When the converter of the new energy system operates normally, the control target requires the new energy to provide active power to the system as much as possible, and the converter adopts PQ control under normal operation.

[0082] The voltage equations of the converter outlet d-axis and q-axis are as follows:

[0083] Among them, v d Represents the d-axis component of the three voltages of the AC grid, v q represents the q-axis component of the three voltages of the AC grid, u d represents the d-axis component of the converter output voltage, u q represents the q-axis component of the output voltage of the converter, i d represents the d-axis component of the output current of the converter, i qrepresents the q-axis component of the output current of the converter, R represents the line equivalent resistance, L represents the line equivalent inductance, and ω represents the electrical angular velocity.

[0084] Replace the derivative in the expression after dq transformation with the expression of PI (proportional integral, Proportionintegration), and get the following system control transfer function:

[0085] in, represents the d-axis component of the converter output voltage, K ip Represents the proportional adjustment coefficient in current PI control, Indicates the integral adjustment coefficient in current PI control, i d * Indicates the d-axis current reference value, i d represents the d-axis component of the converter output current, v d represents the d-axis component of the three voltages of the AC power grid, L represents the equivalent inductance of the line, ω is the electrical angular velocity, i q Represents the q-axis component of the output current of the converter.

[0086] in, represents the q-axis component of the converter output voltage, K ip Represents the proportional adjustment coefficient in current PI control, Indicates the integral adjustment coefficient in current PI control, i q * Indicates the q-axis current reference value, i q represents the q-axis component of the converter output current, that is, the reactive current value, v q represents the q-axis component of the three voltages of the AC power grid, L represents the equivalent inductance of the line, ω is the electrical angular velocity, i d Represents the d-axis component of the output current of the converter.

[0087] The voltage loop output of the converter load voltage is the target value of the inductance and current, while the current loop output of the inductance and current is the target value of the port voltage. By modulating the port voltage, a switching signal is obtained. Under normal operation, the reference current of the given d-axis is Given q-axis reference current Achieve the goal of outputting active power as much as possible.

[0088] When the converter is in a fault ride-through state, the AC line relay protection method of the coordinated converter control strategy provided by the present invention is used to correct the electrical quantity in order to analyze the impact of the restoration protection strategy. Specifically, the photovoltaic grid-connected (low voltage ride-through, Low Voltage Ride Through, LVRT) technology requires that the photovoltaic system be able to remain connected to the grid for a period of time specified by the national standard, and can input a portion of reactive power to the grid to support the recovery of the grid voltage, thereby achieving low voltage ride-through. According to the requirements of the national standard GB / T19964-2012, the d-axis and q-axis reference current expressions of the converter control are as follows:

[0089] Among them, I q * represents the q-axis current reference value, K represents a constant, U th Indicates standard voltage, U pcc Indicates the output voltage of the converter, I N Indicates the rated current, Indicates the d-axis current reference value, I max 2 Indicates the upper current limit.

[0090] I max 2 According to the current limit of power electronic devices, the maximum current limit value can be 1.2I N , K can be set to 1.5. When the voltage drop is maximized, the upper deformation is as follows:

[0091]

[0092] The specific method of correcting the collected first current according to the fault condition and the inclusion strategy is as follows.

[0093] When a symmetrical fault such as a three-phase fault occurs in the transmission line, if the control strategy is not switched, that is, the low voltage ride-through control is not entered, the photovoltaic power generation system continues to work under PQ control. At the same time, considering the difference between the time scale of the fault and the time scale of the operating output adjustment, it is assumed that the control target of the boost circuit MPPT (Maximum Power Point Tracking) control link remains unchanged, that is, in the state without switching of the new control strategy, the d-axis and q-axis reference currents of the inverter control link are still: It can be considered that when the transmission line of the photovoltaic power generation system fails symmetrically, it can be simulated as a constant power source P PV .

[0094] Without considering the switching of the new control strategy, under normal circumstances, there is P PV =U NI N , P PV Indicates constant power value, U N Indicates rated voltage, I N Indicates the rated current. If it is assumed that the outgoing line fails, the grid connection point voltage U pcc Drop to rated voltage U N of Right now U' represents the first voltage, n represents the voltage drop coefficient, where Theoretically, I′=nI N , I′ represents the first current, n represents the voltage drop coefficient, so that the photovoltaic power source is a constant power source as a whole, that is, P PV =U′I′.

[0095] After considering that the system energy source enters the fault ride-through state, due to the change of the control strategy, the voltage drop degree considering the value of n can be expressed by the following formula:

[0096] U th Indicates standard voltage, U pcc represents the output voltage of the converter, n represents the voltage drop coefficient, U N Indicates rated voltage.

[0097] By expressing the voltage drop degree and substituting it into the reference value of the q-axis current in the control strategy, we can know the relationship between the voltage support reactive power and the n value of the current control strategy:

[0098] I q * represents the q-axis current reference value, n represents the voltage drop coefficient, I N Indicates rated current.

[0099] Under normal operation, The phase angle of the renewable energy output current is synchronized with the grid current phase angle, such as Figure 5 As shown, under normal conditions, the phase angles of current and voltage are the same, where I a Indicates the current of the converter in normal state, U a Indicates the voltage when the converter is in normal state, such as Figure 6 As shown in FIG. 1 , in the case of a fault ride-through state, the setting of the q-axis reference current changes the phase angle of the fault current. The fault voltage phase angle change, combined with the q-axis reference current phase angle change, is the fault current phase angle change. In this case, I a Indicates the current of the converter in normal state, U a Indicates the voltage when the converter is in normal state, I af Indicates the current of the converter in the fault ride-through state, Iaf-q The q-axis component of the current when the converter is in the fault ride-through state, I af-d The d-axis component of the current when the converter is in the fault ride-through state, U af represents the voltage of the converter in the fault ride-through state, θ represents the current phase angle change, Indicates the voltage phase angle change.

[0100] The q-axis reference current I can be calculated. q * The function of restoring the fault current phase angle is expressed as follows:

[0101] Among them, Δθ represents the current phase angle change, represents the q-axis current reference value, Indicates the d-axis current reference value, I max 2 Indicates the upper limit of current, which can be 1.2 times the rated current I N , Indicates the voltage phase angle change.

[0102] The aforementioned and Substituting into the above formula, we can get:

[0103]

[0104] Based on the assumption of constant power source, the amplitude correction of the first current can be obtained, which is to multiply the current value equal to the voltage drop amplitude. The phase correction of the first current can be obtained from the reactive support reference value of the control strategy. The q-axis reference current value is calculated from the voltage drop degree to obtain the phase angle change. n represents the voltage drop coefficient.

[0105] When an asymmetric fault such as a two-phase fault occurs in the transmission line, since the current strategy for negative sequence control is still controversial, all collected values ​​of the present invention are first calculated as positive sequence values, and then the phase angle and amplitude of the current are corrected by the above method to participate in the subsequent calculation of the protection strategy.

[0106] Specifically, due to the weak fault characteristics of the crossing state, the accuracy of the relay protection strategy is low. Current research focuses on improving the algorithm of the relay protection strategy. However, current research focuses on improving the protection algorithm under specific scenarios and fixed topologies. In new power systems, due to the randomness of new energy output, frequent topology changes may occur, resulting in the need to frequently modify the corresponding algorithms. The present invention can continue to use the traditional relay protection strategy by correcting the first current without changing the new strategy, thereby reducing development costs.

[0107] The main points of the AC line relay protection method of the coordinated converter control strategy provided by the present invention are: determining the state of the converter or other power electronic equipment of the protected line, and the reference value specified by the state can be calculated from the current working state, the protected line is configured with a communication channel between the power electronic equipment and the protection device, the communication channel transmits the state information of the current control strategy of the equipment, such as the fault crossing state or the normal state, the protected line is configured with a protection device with information data calculation capability, the protection device uses the protection method without limitation, the protection device corrects the currently collected operating electrical quantity according to the control strategy, and uses the corrected data to calculate the traditional protection scheme. Through the technical solution of the present invention, the weak fault characteristics caused by the control strategy of the new energy system under the characteristic scenario are eliminated, so that the traditional relay protection strategy can still meet the reliability requirements in the new energy system. The technical solution of the present invention does not change the relay protection strategy itself, has the characteristics of versatility, and reflects the technical architecture of the integration of control and protection in the new energy system.

[0108] The AC line relay protection method with coordinated converter control strategy provided by the present invention is suitable for typical line scenarios in which new energy systems adopt large-scale new energy transmission lines. The operation of the converter equipment of the protected line and the fault ride-through control strategy are determined, the protected line is configured with a traditional relay protection strategy, and the protection device and the converter equipment are configured with an information path to transmit current control status information. The electrical quantities collected by the protection device are corrected according to the working status of the converter equipment. The protection strategy uses the corrected electrical quantities for calculation and judgment, and continues to use the traditional relay protection strategy to execute analysis and subsequent protection actions.

[0109] The normal operating strategy of the converter on the new energy side is PQ power control, and the control strategy after the fault ride-through state is determined according to the national standard GB / T19964-2012.

[0110] The protected line is equipped with a protection device, which has data processing capability and adopts traditional relay protection algorithms such as overcurrent protection, differential protection or distance protection. In other words, the relay protection strategy includes current protection, differential protection or distance protection.

[0111] When the converter is in a fault ride-through state, the amplitude of the first current is corrected according to the voltage drop degree, and the phase of the first current is corrected according to the d-axis current reference value and the q-axis current reference value.

[0112] In the case of a fault ride-through state, the first current after correcting the amplitude and phase, that is, the first current if there is no converter control, is judged and executed using the traditional protection strategy, and the correction method itself is a restoration of the corresponding control strategy.

[0113] The converter control detects the voltage drop by the dq transformation method based on the instantaneous reactive power theory to determine whether it enters the low voltage ride-through state. The protection device communicates with the converter, and the converter sends status information to the protection device. The protection device determines whether it is in the fault ride-through state based on the converter status information and corrects the collected first current.

[0114] The amplitude of the first current is corrected according to the detected voltage drop degree, and the phase angle of the first current is corrected according to the control strategy reference value calculation method.

[0115] The above methods may be implemented in various ways according to specific features and / or example applications. For example, these methods may be implemented by a combination of hardware, firmware, and / or software. For example, in a hardware implementation, the processor may be implemented in one or more application-specific integrated circuits (ASICs), digital signal processors (DSPs), programmable logic devices (PLDs), field programmable gate arrays (FPGAs), controllers, microcontrollers, microprocessors, electronic devices, other equipment units for performing the above functions, and / or combinations thereof.

[0116] According to the second aspect of the present invention, the present invention proposes an AC line relay protection device with a coordinated converter control strategy, wherein a communication link is provided between the AC line relay protection device with a coordinated converter control strategy and the converter, and the AC line relay protection device with a coordinated converter control strategy is used to execute the steps of the AC line relay protection method with a coordinated converter control strategy provided in the first aspect embodiment.

[0117] The AC line relay protection device of the cooperative converter control strategy provided by the present invention is used to execute the steps of the AC line relay protection method of the cooperative converter control strategy provided by the first aspect embodiment. Therefore, it has all the beneficial effects of the steps of the AC line relay protection method of the cooperative converter control strategy provided by the first aspect embodiment, which are no longer stated one by one here.

[0118] According to the third aspect of the present invention, the present invention proposes an electronic device, including a processor and a memory, the memory storing programs or instructions that can be run on the processor, and when the program or instructions are executed by the processor, the steps of the AC line relay protection method of the coordinated converter control strategy provided in the embodiment of the first aspect are implemented.

[0119] The electronic device proposed in the present invention includes a memory storing a program or instruction that, when executed by a processor, implements the steps of the AC line relay protection method with a coordinated converter control strategy as provided in the first aspect embodiment. Therefore, it has all the beneficial effects of the AC line relay protection method with a coordinated converter control strategy as provided in the first aspect embodiment, which are no longer stated one by one here.

[0120] According to the fourth aspect of the present invention, the present invention proposes a readable storage medium, the non-volatile readable storage medium stores a program or instruction, and when the program or instruction is executed, the steps of the AC line relay protection method of the coordinated converter control strategy provided in the first aspect embodiment are performed.

[0121] The readable storage medium proposed in the present invention stores a program or instruction that implements the steps of the AC line relay protection method with a coordinated converter control strategy as provided in the first aspect embodiment when executed. Therefore, it has all the beneficial effects of the AC line relay protection method with a coordinated converter control strategy as provided in the first aspect embodiment, which are no longer stated one by one here.

[0122] A storage medium may be a tangible device that can retain and store instructions for use by an instruction execution device. A computer storage medium may be an electronic storage device, a magnetic storage device, an optical storage device, an electromagnetic storage device, a semiconductor storage device, or any suitable combination of the above devices, but is not limited thereto. A non-exhaustive list of more specific examples of computer storage media includes: portable computer floppy disks, hard disks, random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM or flash memory), static random access memory (SRAM), portable compact disc read-only memory (CD-ROM), digital universal disk (DVD), memory card, floppy disk, encoding mechanical device (such as a punch card or a groove with a raised structure with instructions recorded) and any suitable combination of the above devices. The computer storage medium used herein should not be understood as a transmission signal itself, such as radio waves or other freely propagating electromagnetic waves, electromagnetic waves propagating through waveguides or other transmission media, or electrical signals transmitted through wires.

[0123] In the present invention, the terms "first", "second", and "third" are used for descriptive purposes only and should not be understood as indicating or implying relative importance; the term "plurality" refers to two or more, unless otherwise clearly defined. The terms "installed", "connected", "connected", "fixed", etc. should be understood in a broad sense. For example, "connected" can be a fixed connection, a detachable connection, or an integral connection; "connected" can be a direct connection or an indirect connection through an intermediate medium. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0124] In the description of the present invention, it is necessary to understand that the directions or positional relationships indicated by the terms "up", "down", "left", "right", "front", "back", etc. are based on the directions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the components or units referred to must have a specific direction, be constructed and operated in a specific orientation, and therefore, should not be understood as limiting the present invention.

[0125] In the description of this specification, the description of the terms "one embodiment", "some embodiments", "specific embodiments", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0126] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. An AC line relay protection method in coordination with a converter control strategy, characterized in that: include: Monitor the status of the inverter; When the converter is in a normal state, executing a relay protection strategy according to the first electrical quantity collected by the grid connection point; When the converter is in a fault ride-through state, the first electrical quantity collected by the grid connection point is corrected to eliminate the influence of the fault ride-through state on the electrical quantity, thereby obtaining a second electrical quantity; The relay protection strategy is executed according to the second electrical quantity.

2. The AC line relay protection method of the coordinated converter control strategy according to claim 1 is characterized in that: When the converter is in a fault ride-through state, the first electrical quantity collected by the grid connection point is corrected to eliminate the influence of the fault ride-through state on the electrical quantity, and a second electrical quantity is obtained, including: When the converter is in a fault ride-through state, the amplitude of the first current is corrected according to a voltage drop coefficient of the grid connection point; Correcting the phase of the first current according to a d-axis current reference value and a q-axis current reference value of the converter in the fault ride-through state; A second current is obtained.

3. The AC line relay protection method of the coordinated converter control strategy according to claim 2 is characterized in that: According to the voltage drop coefficient of the grid connection point, the amplitude of the first current is corrected, including: When the converter is in a fault ride-through state, determining a voltage drop coefficient of a grid connection point; When the voltage at the grid connection point drops by n times, the amplitude of the first current is amplified by n times.

4. The AC line relay protection method of the coordinated converter control strategy according to claim 3 is characterized in that: When the converter is in a fault ride-through state, determining a voltage drop coefficient of a grid connection point includes: When the converter is in a fault ride-through state, a voltage drop coefficient at a grid connection point is determined by using a dq transformation method based on instantaneous reactive power theory.

5. The AC line relay protection method of the coordinated converter control strategy according to claim 2 is characterized in that: Correcting the phase of the first current according to a d-axis current reference value and a q-axis current reference value of the converter in the fault ride-through state includes: Substitute the d-axis current reference value and the q-axis current reference value into: The current phase change is obtained, where Δθ represents the current phase change, represents the q-axis current reference value, represents the d-axis current reference value, Indicates the voltage phase change; The phase of the first current is corrected according to the current phase change amount.

6. The AC line relay protection method of the coordinated converter control strategy according to any one of claims 1 to 5, characterized in that: Also includes: The converter detects voltage drop by using a dq conversion method based on instantaneous reactive power theory; Whether to enter the fault ride-through state is determined according to the voltage drop condition.

7. The AC line relay protection method of the coordinated converter control strategy according to any one of claims 1 to 5, characterized in that: The converter adopts a PQ control strategy, and the control strategy when the converter is in the fault ride-through state is determined according to the national standard GB / T19964-2012.

8. The AC line relay protection method of the coordinated converter control strategy according to any one of claims 1 to 5, characterized in that: The relay protection strategy includes at least one of the following: Current protection strategy, gas protection strategy, differential protection strategy, high frequency protection strategy, distance protection strategy, balance protection strategy, negative sequence and zero sequence protection strategy and directional protection strategy.

9. The AC line relay protection method in coordinated converter control strategy according to any one of claims 1 to 5, characterized in that: The first electrical quantity is a positive sequence value.

10. An AC line relay protection device in coordination with a converter control strategy, characterized in that: There is a communication link between the AC line relay protection device of the collaborative converter control strategy and the converter, and the AC line relay protection device of the collaborative converter control strategy is used to execute the steps of the AC line relay protection method of the collaborative converter control strategy as described in any one of claims 1 to 9.

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