A power grid terminal voltage control system and method

Abstract

The present invention provides a power grid end voltage control system and method, the system includes: a passive power spring and a power spring control module; the passive power spring is connected in parallel at both ends of a key load in the power grid; the power spring control module is used to control the passive power spring to release or absorb reactive power according to the comparison results of the collected voltages at both ends of the load with the low voltage control threshold and the high voltage control threshold; the power spring control module is also used to calculate the gradient value of the reactive power released by the passive power spring and the voltage at both ends of the key load changing with time when the passive power spring releases reactive power; based on the comparison result of the gradient value and the preset gradient threshold, the electric vehicle is controlled to release active power. The present invention does not need to install an additional current sensor, and only needs to add a power spring near the charging station to control the power of the power spring and / or the electric vehicle, so that it can better adapt to the rural weak power grid environment and improve the voltage stability of various loads.

Description

Technical Field

[0001] The present invention relates to the technical field of power system stability control, and in particular to a power grid terminal voltage control system and method. Background Art

[0002] Due to the long power supply radius and large radiation area of ​​the power grid, the power supply capacity at the end of the distribution network is insufficient and the power supply quality is poor. This is particularly evident in weak power grids in counties and rural areas. As electric vehicles become more and more popular in rural areas, the addition of such impact loads further exacerbates the power supply quality problems of weak power grids, and innovative technical means are urgently needed. Summary of the invention

[0003] The present invention provides a power grid terminal voltage control system and method to solve the problem of poor power supply quality in county and rural power systems.

[0004] According to one aspect of the present invention, there is provided a power grid terminal voltage control system, comprising:

[0005] Passive power spring and power spring control module;

[0006] The passive power spring is connected in parallel at both ends of a key load in the power grid;

[0007] The power spring control module is used to control the passive power spring to release reactive power or absorb reactive power according to the comparison results of the collected voltages at both ends of the load with the low voltage management threshold and the high voltage management threshold;

[0008] The electric spring control module is also used to calculate the gradient value of the reactive power released by the passive electric spring and the voltage across the critical load that changes over time when the passive electric spring releases reactive power; based on the comparison result of the gradient value with a preset gradient threshold, send a control instruction to the charging pile control module to control the electric vehicle to release active power.

[0009] Optionally, the passive power spring includes an LCL filter, and the power spring controller includes an active damping feedback regulator;

[0010] The active damping feedback regulator is used to suppress the resonance of the power grid system when the LCL filter resonates.

[0011] Optionally, the transfer function of the active damping feedback regulator is:

[0012]

[0013] In the formula, k ad is the negative high-pass filter gain, is the low frequency cutoff frequency, is the high frequency cutoff frequency;

[0014] The transfer function of the LCL filter is:

[0015]

[0016] Where, L i1 is the first inductor in the LCL filter, L i2 is the second inductor in the LCL filter, C i is the capacitance in the LCL filter;

[0017] When the LCL filter resonates, a first-order high-pass filter is used to extract the high-order harmonic components near the resonant frequency for negative feedback control, that is, a feedback link G(s) is added to make the resonance The real part of the open-loop transfer function is negative, which eliminates the resonant peak.

[0018] Optionally, a voltage sensor is also included to monitor the voltage across the critical load and feed back the voltage data to the power spring control module in real time.

[0019] According to another aspect of the present invention, there is provided a method for controlling voltage at the end of a power grid, comprising:

[0020] obtaining a first voltage across the critical load;

[0021] Comparing the first voltage with a low voltage management threshold and a high voltage management threshold respectively;

[0022] Based on the comparison result, a passive power spring is controlled to release reactive power or absorb reactive power; the passive power spring is connected in parallel to both ends of the critical load;

[0023] When the passive power spring releases reactive power, calculating the gradient value of the reactive power released by the passive power spring and the voltage across the critical load that changes with time;

[0024] Based on the comparison result between the gradient value and the preset gradient threshold, a control instruction is sent to the charging pile control module to control the electric vehicle to release active power.

[0025] Optionally, comparing the first voltage with a low voltage management threshold and a high voltage management threshold respectively, and controlling the passive power spring to release reactive power or absorb reactive power based on the comparison result, comprises:

[0026] Comparing the first voltage with the low voltage management threshold, and if the first voltage is less than the low voltage management threshold, controlling the passive power spring to release reactive power;

[0027] comparing the first voltage with the high voltage management threshold, and if the first voltage is greater than the high voltage management threshold, controlling the passive power spring to absorb reactive power;

[0028] If the first voltage is greater than or equal to the low voltage management threshold and less than or equal to the high voltage management threshold, the passive power spring is not controlled to release or absorb reactive power.

[0029] Optionally, the calculation of the gradient value of the reactive power released by the passive power spring and the voltage across the critical load varying with time:

[0030]

[0031] In the formula, represents the gradient; Indicates the critical load voltage modulus; Represents the reactive current output by the passive power spring; t represents the time of the current sampling point, and t+1 represents the time of the next sampling point.

[0032] Optionally, based on the comparison result between the gradient value and a preset gradient threshold, sending a control instruction to a charging pile control module to control the electric vehicle to release active power includes:

[0033] When the gradient value is greater than the preset gradient threshold, continuing to control the passive power spring to release reactive power;

[0034] When the gradient value is less than or equal to the preset gradient threshold, the passive power spring is stopped from controlling to increase the release of reactive power, and a control instruction is sent to the charging pile control module to control the electric vehicle to release active power.

[0035] Optionally, based on the comparison result between the gradient value and the preset gradient threshold, a control instruction is sent to the charging pile control module to control the electric vehicle to release active power, and then the method further includes:

[0036] When the electric vehicle is in a state of releasing active power, when it is monitored that the first voltage is greater than the low voltage management threshold, a control instruction is sent to the charging pile control module so that the active power output by the electric vehicle no longer increases.

[0037] The technical solution of the embodiment of the present invention is to connect a passive electric spring in parallel at both ends of the key load in the power grid, and the electric spring control module can control the passive electric spring to release reactive power or absorb reactive power according to the comparison results of the collected voltage at both ends of the load with the low voltage control threshold and the high voltage control threshold, so as to ensure the voltage stability of the key load of the power grid; in addition, the electric spring control module is also used to calculate the gradient value of the reactive power released by the passive electric spring and the voltage at both ends of the key load when the passive electric spring releases reactive power; based on the gradient value, determine whether the reactive power released by the electric spring can effectively increase the load voltage. If the load voltage cannot be effectively increased, send a control instruction to the charging pile control module to control the electric vehicle to release active power. The present invention does not require the installation of an additional current sensor, and only needs to add an electric spring near the charging station to control the power of the electric spring and / or the electric vehicle, so that it can better adapt to the rural weak power grid environment and improve the voltage stability of various loads.

[0038] It should be understood that the contents described in this section are not intended to identify the key or important features of the embodiments of the present invention, nor are they intended to limit the scope of the present invention. Other features of the present invention will become easily understood through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0040] Figure 1 It is an architecture diagram of a power grid terminal voltage control system provided by an embodiment of the present invention;

[0041] Figure 2 A flow chart of a method for controlling voltage at the end of a power grid provided by an embodiment of the present invention;

[0042] Figure 3 It is a single-phase voltage waveform for the passive power spring to absorb reactive current and manage the high voltage of the critical load in the embodiment of the present invention;

[0043] Figure 4 It is a single-phase waveform diagram of low voltage control of key loads when an electric vehicle is used to compensate for active power of a power grid in an embodiment of the present invention;

[0044] Figure 5 is a waveform diagram of the grid-connected current of the power spring when the current feedback active damping controller is not used in the embodiment of the present invention;

[0045] Figure 6This is a waveform diagram of the grid-connected current of the power spring when a current feedback active damping controller is used in an embodiment of the present invention. DETAILED DESCRIPTION

[0046] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0047] It should be noted that the terms "first", "second", etc. in the specification and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchanged where appropriate, so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units that are clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0048] Figure 1 The present invention provides a structure of a power grid terminal voltage control system. Figure 1 As shown, the system includes:

[0049] Passive power spring and power spring control module;

[0050] The passive power spring is connected in parallel at both ends of a key load in the power grid;

[0051] The power spring control module is used to control the passive power spring to release reactive power or absorb reactive power according to the comparison results of the collected voltages at both ends of the load with the low voltage management threshold and the high voltage management threshold;

[0052] The electric spring control module is also used to calculate the gradient value of the reactive power released by the passive electric spring and the voltage across the critical load that changes over time when the passive electric spring releases reactive power; based on the comparison result of the gradient value with a preset gradient threshold, send a control instruction to the charging pile control module to control the electric vehicle to release active power.

[0053] Among them, the power spring maintains the stability of the critical load voltage by transferring the power fluctuation of the power grid to the equipment (non-critical load) that is insensitive to voltage changes. The power spring is connected in series with the non-critical load to form an intelligent load, which can automatically match the power consumption with the power generation. The passive power spring used in this embodiment does not contain active devices, and it controls the absorption and release of reactive power through the power spring controller.

[0054] like Figure 1 As shown, the power spring control module in the figure can be electrically connected to the passive power spring, and control the power spring to absorb and release reactive power by sending a control signal to the switch device of the passive power spring. Specifically, the power spring controller can be a PQ grid-connected controller, which outputs a voltage signal corresponding to the iq instruction by setting an iq instruction, and then drives the switch device of the passive power spring via PWM to control the power spring to absorb and release reactive power; the power spring controller can also be a chip controller, which can directly send a control signal to the switch device of the passive power spring to control the power spring to absorb and release reactive power.

[0055] This embodiment can use a voltage acquisition device to collect the voltage across the critical load in the power system. The power spring control module can obtain the voltage across the critical load and compare the voltage across the critical load with the low voltage control threshold and the high voltage control threshold in the force spring control module. The corresponding control instruction is selected according to the comparison result to control the passive power spring to release reactive power or absorb reactive power.

[0056] In this embodiment, the electric spring control module can also monitor the voltage across the critical load when the passive electric spring is in the state of releasing reactive power, and calculate the gradient value of the reactive power released by the passive electric spring and the voltage across the critical load over time; in one embodiment, the gradient value of the reactive current output by the passive electric spring and the voltage across the critical load over time can also be calculated. The gradient value can be used to reflect the effective value of the ability to increase the voltage of the critical load, that is, when the gradient value is greater than or equal to the preset gradient threshold, it means that the passive electric spring can effectively increase the voltage value of the critical load; and when the gradient value is less than the preset gradient threshold, it means that the passive electric spring cannot effectively increase the voltage value of the critical load, and then it is necessary to control the charging pile control module to control the electric vehicle to release active power to increase the voltage across the critical load.

[0057] like Figure 1 The electric spring control module of the embodiment shown can be communicatively connected with the charging pile control module. For example, the electric spring control module can send control instructions to the charging pile control module through wireless communication or wired communication to control the electric vehicle to release active power.

[0058] It should be noted that the connection method between the power spring and the power grid in this embodiment can be a conventional connection method, that is, the passive power spring can be connected in parallel at both ends of the critical load; the connection method between the electric vehicle charging pile and the power grid can also adopt a conventional connection method, that is, the electric vehicle charging pile can be connected in parallel at both ends of the critical load of the power system.

[0059] The technical solution of the embodiment of the present invention is to connect a passive electric spring in parallel at both ends of the key load in the power grid, and the electric spring control module can control the passive electric spring to release reactive power or absorb reactive power according to the comparison results of the collected voltage at both ends of the load with the low voltage control threshold and the high voltage control threshold, so as to ensure the voltage stability of the key load of the power grid; in addition, the electric spring control module is also used to calculate the gradient value of the reactive power released by the passive electric spring and the voltage at both ends of the key load when the passive electric spring releases reactive power; based on the gradient value, determine whether the reactive power released by the electric spring can effectively increase the load voltage. If the load voltage cannot be effectively increased, send a control instruction to the charging pile control module to control the electric vehicle to release active power. The present invention does not require the installation of an additional current sensor, and only needs to add an electric spring near the charging station to control the power of the electric spring and / or the electric vehicle, so that it can better adapt to the rural weak power grid environment and improve the voltage stability of various loads.

[0060] In one embodiment, the passive power spring includes an LCL filter, and the power spring controller includes an active damping feedback regulator; the active damping feedback regulator is used to suppress resonance of the power grid system when resonance occurs in the LCL filter.

[0061] Among them, LCL filters are usually used in three-phase grid-connected inverters. For the two parallel current source grid-connected circuits equivalent to the passive power spring and the electric vehicle, since the passive power spring can only output reactive power, the electric vehicle only outputs active power. Through the Thevenin theorem and the superposition theorem, the output current of the i-th inverter in the multi-machine parallel system is:

[0062]

[0063] In the formula, and are the grid-connected current reference values ​​of the i-th and j-th inverters respectively, is the output impedance of each current source in the equivalent circuit, is the line impedance, is the open-loop gain of the output current of each current source. As can be seen from the above formula, the grid-connected current output by each current source in the multi-machine parallel system is not only affected by U L It is also affected by the reference current of other current sources, that is, there is coupling, which leads to the generation of harmonics in parallel resonance.

[0064] In order to suppress parallel resonance, the resonance peak needs to be damped. An active damping feedback regulator can be set in the power spring controller to introduce active damping to eliminate the inherent resonance of the converter LCL filter.

[0065] Specifically, grid-connected current feedback can effectively suppress the inverter resonance spike. According to the transfer function of the system grid-connected current, a new active damping feedback regulator is formed by connecting a low-pass filter in series with a first-order negative high-pass filter, which can effectively suppress the resonance problem of the parallel system.

[0066] In one embodiment, the active damping feedback regulator includes a first-order high-pass filter and a low-pass filter connected in series with the first-order high-pass filter; the first-order high-pass filter is used to extract high-order harmonic components near the vibration frequency for negative feedback control when the LCL filter resonates, so that the resonance peak at the resonance point is eliminated.

[0067] In one embodiment, the transfer function of the active damping feedback regulator is:

[0068]

[0069] In the formula, k ad is the negative high-pass filter gain, is the low frequency cutoff frequency, is the high frequency cutoff frequency;

[0070] The transfer function of the LCL filter is:

[0071]

[0072] Where, L i1 is the first inductor in the LCL filter, L i2 is the second inductor in the LCL filter, C i is the capacitance in the LCL filter;

[0073] When the LCL filter resonates, a first-order high-pass filter is used to extract the high-order harmonic components near the resonant frequency for negative feedback control, that is, a feedback link G(s) is added to make the resonance The real part of the open-loop transfer function is negative, which eliminates the resonant peak.

[0074] The LCL filter is a conventional filter, including three first inductors L i1 , three second inductors L i2 , and three capacitors C i ; Among them, the capacitance values ​​of the three first inductors can be equal, the capacitance values ​​of the three second inductors can be equal, and the capacitance values ​​of the three capacitors can also be equal. For details, please refer to Figure 1 LCL filter shown.

[0075] Figure 2 A method for controlling a voltage at a terminal of a power grid is provided in an embodiment of the present invention, such as Figure 2 As shown, including:

[0076] S101, obtaining a first voltage across two ends of a critical load;

[0077] S102, comparing the first voltage with a low voltage management threshold and a high voltage management threshold respectively;

[0078] S103, based on the comparison result, controlling the passive power spring to release reactive power, or absorbing reactive power; the passive power spring is connected in parallel to both ends of the critical load;

[0079] In this embodiment, the voltage across the critical load in the power system can be collected, the power spring control module can obtain the voltage across the critical load, and compare the voltage across the critical load with the low voltage management threshold and the high voltage management threshold in the force spring control module, and select the corresponding control instruction according to the comparison result to control the passive power spring to release reactive power or absorb reactive power.

[0080] S104, when the passive power spring releases reactive power, calculating the gradient value of the reactive power released by the passive power spring and the voltage across the critical load that changes with time;

[0081] S105. Based on the comparison result between the gradient value and the preset gradient threshold, a control instruction is sent to the charging pile control module to control the electric vehicle to release active power.

[0082] The power spring control module can also monitor the voltage across the critical load when the passive power spring is in the state of releasing reactive power, and calculate the gradient value of the reactive power released by the passive power spring and the voltage across the critical load over time; in one embodiment, the gradient value of the reactive current output by the passive power spring and the voltage across the critical load over time can also be calculated. The gradient value can be used to reflect the effective value of the ability to increase the voltage of the critical load, that is, when the gradient value is greater than or equal to the preset gradient threshold, it means that the passive power spring can effectively increase the voltage value of the critical load; and when the gradient value is less than the preset gradient threshold, it means that the passive power spring cannot effectively increase the voltage value of the critical load, and then it is necessary to control the charging pile control module to control the electric vehicle to release active power to increase the voltage across the critical load.

[0083] The technical solution of the embodiment of the present invention is to connect a passive power spring in parallel at both ends of the key load in the power grid, and the power spring control module can control the passive power spring to release reactive power or absorb reactive power according to the comparison results of the collected voltage at both ends of the load with the low voltage control threshold and the high voltage control threshold, so as to ensure the voltage stability of the key load of the power grid; in addition, the power spring control module is also used to calculate the gradient value of the reactive power released by the passive power spring and the voltage at both ends of the key load when the passive power spring releases reactive power; based on the gradient value, determine whether the reactive power released by the power spring can effectively increase the load voltage, if it cannot effectively increase the load voltage, send a control instruction to the charging pile control module to control the electric vehicle to release active power. The present invention does not need to install an additional current sensor, and only needs to add a power spring near the charging station to control the power of the power spring and / or the electric vehicle, so that it can better adapt to the rural weak power grid environment and improve the voltage stability of various loads.

[0084] In one embodiment, the first voltage is compared with a low voltage management threshold and a high voltage management threshold respectively, and based on the comparison result, the passive power spring is controlled to release reactive power or absorb reactive power, including:

[0085] Comparing the first voltage with the low voltage management threshold, and if the first voltage is less than the low voltage management threshold, controlling the passive power spring to release reactive power;

[0086] comparing the first voltage with the high voltage management threshold, and if the first voltage is greater than the high voltage management threshold, controlling the passive power spring to absorb reactive power;

[0087] If the first voltage is greater than or equal to the low voltage management threshold and less than or equal to the high voltage management threshold, the passive power spring is not controlled to release or absorb reactive power.

[0088] Based on Kirchhoff's voltage law, the power system of this embodiment satisfies:

[0089]

[0090] Where U G is the grid voltage, U Z =I G Z is the line voltage drop, U L is the critical load voltage. Z is the equivalent impedance of the power grid, I G Represents the equivalent current of the power grid. Assume that in the initial state, the power spring current I S The phase of the load circuit is 0, and the current I L When the modulus of the critical load voltage is When the power spring is between the low voltage control threshold and the high voltage control threshold, the power spring is in a standby state. The low voltage control threshold and the high voltage control threshold can be an empirical value or a threshold obtained through multiple tests.

[0091] When the first voltage is greater than the low voltage management threshold, , the power spring can be controlled to absorb inductive reactive power; at the same time, the charging power of the electric vehicle remains unchanged, making the key load voltage U L With grid voltage U G The angle of the key load voltage U L Reduce it so that it drops to less than the high pressure management threshold th2.

[0092] When the first voltage is less than the low voltage management threshold, that is, , the power spring can be controlled to output inductive reactive power to the grid; at the same time, the charging power of the electric vehicle remains unchanged, making the key load voltage U L With grid voltage U G The angle increases, which makes the key load voltage U L Increase it so that it increases to be greater than the low voltage control threshold th1.

[0093] In one embodiment, the gradient of the reactive power released by the passive power spring and the voltage across the critical load over time is calculated:

[0094]

[0095] In the formula, represents the gradient; Indicates the critical load voltage modulus; Represents the reactive current output by the passive power spring; t represents the time of the current sampling point, and t+1 represents the time of the next sampling point.

[0096] It should be noted that the gradient can represent the effective value of the ability to increase the voltage of the critical load, that is, when the gradient value is greater than or equal to the preset gradient threshold, it means that the passive power spring can effectively increase the voltage value of the critical load; and when the gradient value is less than the preset gradient threshold, it means that the passive power spring cannot effectively increase the voltage value of the critical load. In this embodiment, the gradient function shown in the above formula can be represented by a function of the reactive current output by the passive power spring and the voltage across the critical load over time.

[0097] In one embodiment, based on the comparison result between the gradient value and the preset gradient threshold, a control instruction is sent to the charging pile control module to control the electric vehicle to release active power, including:

[0098] When the gradient value is greater than the preset gradient threshold, continuing to control the passive power spring to release reactive power;

[0099] When the gradient value is less than or equal to the preset gradient threshold, the passive power spring is stopped from controlling to increase the release of reactive power, and a control instruction is sent to the charging pile control module to control the electric vehicle to release active power.

[0100] When the gradient value is greater than the preset gradient threshold, hour, is the gradient threshold, indicating that the passive power spring can effectively increase the voltage value of the critical load. Therefore, there is no need to control the electric vehicle to release active power to the power grid. It is only necessary to control the passive power spring to continuously release reactive power to the power grid to raise the voltage of the critical load to between the low-voltage management threshold and the high-voltage management threshold.

[0101] When the gradient value is less than or equal to the preset gradient threshold, that is, , indicating that the load voltage modulus caused by the increase of reactive current output by the power spring The effect of increasing the reactive power is not obvious. If the reactive current output by the power spring is further increased, it will lead to greater line loss and lower grid power factor. At this time, the power spring stops outputting reactive power and requests the electric vehicle to enter the V2G mode through the communication module to control the electric vehicle to release active power, so as to reduce the critical load voltage to between the low voltage management threshold and the high voltage management threshold.

[0102] In one embodiment, based on the comparison result between the gradient value and the preset gradient threshold, a control instruction is sent to the charging pile control module to control the electric vehicle to release active power, and then the method further includes:

[0103] When the electric vehicle is in a state of releasing active power, when it is monitored that the first voltage is greater than the low voltage management threshold, a control instruction is sent to the charging pile control module so that the active power output by the electric vehicle no longer increases.

[0104] When the electric vehicle is in the state of releasing active power, the electric spring control module can continuously receive the voltage signals at both ends of the critical load collected by the voltage sensor. When it is monitored that the voltage at both ends of the critical load is greater than the low voltage management threshold, it means that the voltage of the critical load has returned to the stable range. A control instruction can be sent to the charging pile control module to prevent the active power output of the electric vehicle from increasing.

[0105] For the weak power grid scenario, the specific calculation example of the method of the present invention is as follows, and the application in this scenario also falls within the protection scope of the present invention.

[0106] The design parameters of the system composed of the shunt passive power spring, electric vehicle charging pile and power grid in the present invention are as follows: the grid voltage is 380V, L1 = L2 = 2mH, the filtering capacitor C = 10uF, the line impedance R = 3Ω, X = Lg = 0.1mH, the critical load is a constant power load, P = 10000W. th1 and tht2 are set to 210V and 230V respectively, and the gradient threshold is set to 0.01.

[0107] 1) When the effective voltage of the critical load is 240V > th2, the passive power spring outputs inductive reactive current. At this time, the effective value of the critical load voltage drops to 221V, and the single-phase voltage waveform of the critical load is as Figure 3 .

[0108] 2) When the effective voltage of the critical load is 185V < th1, the passive power spring outputs capacitive reactive current. According to the gradient formula, the injection of capacitive current can increase the load voltage to a maximum of 201V < th1. At this time, the power spring control module sends a control instruction to the charging pile control module, and then sends a V2G request to the charging pile. The electric vehicle starts to output active power to the power grid, and the effective value of the critical load voltage rises to 220V. The single-phase voltage waveform of the critical load is as Figure 4 .

[0109] 3) Add grid-connected current negative feedback control to the power spring control module, that is, add an active damping feedback regulator to provide active damping to the system. The comparison of the grid-connected current waveforms of the dual-machine parallel connection with and without current feedback active damping control is as Figure 5 and Figure 6 , Figure 5 is the grid-connected current waveform of the dual-machine parallel connection with current feedback active damping control without feedback control, and its total harmonic distortion rate of grid-connected current THD = 7.67%. Figure 6 is the grid-connected current waveform of the dual-machine parallel connection with current feedback active damping control with feedback control, and its total harmonic distortion rate of grid-connected current PHD = 3.99%. It can be seen that this active damping control can effectively suppress the grid-connected current harmonics.

[0110] It should be understood that various forms of processes shown above can be used, reordering, adding or deleting steps. For example, the steps described in the present invention can be executed in parallel, sequentially or in a different order, as long as the desired results of the technical solution of the present invention can be achieved. There is no limitation here.

[0111] The above specific embodiments do not constitute a limitation to the protection scope of the present invention. Those skilled in the art should understand that various modifications, combinations, sub-combinations and substitutions can be made according to design requirements and other factors. Any modifications, equivalent substitutions and improvements made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A power grid terminal voltage control system, characterized in that: include: Passive power spring and power spring control module; The passive power spring includes an LCL filter, and the power spring control module includes an active damping feedback regulator; The active damping feedback regulator is used to suppress the resonance of the power grid system when the LCL filter resonates; The active damping feedback regulator comprises a first-order high-pass filter and a low-pass filter connected in series with the first-order high-pass filter; The first-order high-pass filter is used to extract the high-order harmonic components near the vibration frequency for negative feedback control when the LCL filter resonates, so that the resonance peak at the resonance point is eliminated; The transfer function of the active damping feedback regulator is: In the formula, k ad is the negative high-pass filter gain, is the low frequency cutoff frequency, is the high frequency cutoff frequency; The transfer function of the LCL filter is: Where, L i1 is the first inductor in the LCL filter, L i2 is the second inductor in the LCL filter, C i is the capacitance in the LCL filter; When the LCL filter resonates, a first-order high-pass filter is used to extract the high-order harmonic components near the resonant frequency for negative feedback control, that is, a feedback link G(s) is added to make the resonance The real part of the open-loop transfer function is negative, so the resonant peak is eliminated; The passive power spring is connected in parallel at both ends of a key load in the power grid; The power spring control module is used to control the passive power spring to release reactive power or absorb reactive power according to the comparison results of the collected voltages at both ends of the load with the low voltage management threshold and the high voltage management threshold; The electric spring control module is also used to calculate the gradient value of the reactive power released by the passive electric spring and the voltage across the critical load that changes over time when the passive electric spring releases reactive power; based on the comparison result of the gradient value with a preset gradient threshold, send a control instruction to the charging pile control module to control the electric vehicle to release active power.

2. The power grid terminal voltage control system according to claim 1, characterized in that: It also includes a voltage sensor for monitoring the voltage across the critical load and feeding back the voltage data to the power spring control module in real time.

3. A method for controlling voltage at the end of a power grid, implemented based on the power grid end voltage control system according to any one of claims 1 to 2, characterized in that: include: obtaining a first voltage across the critical load; Comparing the first voltage with a low voltage management threshold and a high voltage management threshold respectively; Based on the comparison result, the passive power spring is controlled to release reactive power or absorb reactive power; The passive power spring is connected in parallel to both ends of the critical load; When the passive power spring releases reactive power, calculating the gradient value of the reactive power released by the passive power spring and the voltage across the critical load that changes with time; Based on the comparison result between the gradient value and the preset gradient threshold, a control instruction is sent to the charging pile control module to control the electric vehicle to release active power.

4. The method for controlling the voltage at the end of the power grid according to claim 3, characterized in that: The step of comparing the first voltage with a low voltage control threshold and a high voltage control threshold respectively, and controlling the passive power spring to release reactive power or absorb reactive power based on the comparison result, comprises: Comparing the first voltage with the low voltage management threshold, and if the first voltage is less than the low voltage management threshold, controlling the passive power spring to release reactive power; comparing the first voltage with the high voltage management threshold, and if the first voltage is greater than the high voltage management threshold, controlling the passive power spring to absorb reactive power; If the first voltage is greater than or equal to the low voltage management threshold and less than or equal to the high voltage management threshold, the passive power spring is not controlled to release or absorb reactive power.

5. The method for controlling the voltage at the end of the power grid according to claim 3, characterized in that: The calculation of the reactive power released by the passive power spring and the gradient value of the voltage across the critical load that changes with time is: In the formula, represents the gradient; Indicates the critical load voltage modulus; Represents the reactive current output by the passive power spring; t represents the time of the current sampling point, and t+1 represents the time of the next sampling point.

6. The method for controlling the voltage at the end of the power grid according to claim 3, characterized in that: The method of sending a control instruction to a charging pile control module based on a comparison result between the gradient value and a preset gradient threshold value to control the electric vehicle to release active power includes: When the gradient value is greater than the preset gradient threshold, continuing to control the passive power spring to release reactive power; When the gradient value is less than or equal to the preset gradient threshold, the passive power spring is stopped from being controlled to increase the release of reactive power, and a control instruction is sent to the charging pile control module to control the electric vehicle to release active power.

7. The method for controlling the voltage at the end of the power grid according to claim 6, characterized in that: Based on the comparison result between the gradient value and the preset gradient threshold, a control instruction is sent to the charging pile control module to control the electric vehicle to release active power, and then the method further includes: When the electric vehicle is in a state of releasing active power, when it is monitored that the first voltage is greater than the low voltage management threshold, a control instruction is sent to the charging pile control module so that the active power output by the electric vehicle no longer increases.

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