Active Power Grid Harmonic Resonance Suppression Method Based on Harmonic Virtual Resistance Technology

Abstract

The present invention provides an active power grid harmonic resonance suppression method based on harmonic virtual resistance technology, the method comprising the following steps: step 1, first adding an active harmonic control device based on power electronic power devices at the common connection point of the power grid; step 2, then determining the harmonic equivalent impedance value required for harmonic resonance suppression according to the equivalent connection impedance parameter of the power system and the equivalent parameter analysis of the parallel capacitor branch; step 3, finally, according to the harmonic virtual resistance control method and the voltage source power electronic converter control method, the effective control of the harmonic equivalent impedance of the active power grid harmonic resonance suppression device based on power electronic power devices is achieved. By applying the harmonic virtual resistance control technology, the effective control of the equivalent harmonic impedance of the active power grid harmonic resonance suppression device based on power electronic power devices is achieved, thereby achieving the purpose of suppressing power grid harmonic resonance.

Description

Technical Field

[0001] The present invention relates to the technical field of active power grid harmonic resonance suppression devices and methods, and in particular to an active power grid harmonic resonance suppression method based on harmonic virtual resistance technology. Background Art

[0002] With the continuous development and progress of wind power generation technology, there are more and more offshore wind power generation projects and they are constantly developing towards larger capacity and offshore, resulting in a large number of high-voltage submarine cable transmission lines in the power system. Compared with traditional transmission lines, high-voltage submarine cable transmission lines show obvious capacitance characteristics, resulting in obvious parallel capacitance branches in the equivalent circuit of the regional power grid. Fixed capacitor-type reactive compensation devices in the power system or cable-type transmission lines in the urban power grid also show obvious capacitance characteristics, and can also be equivalent to parallel capacitance branches in the equivalent circuit of the power system. Conventional high-voltage transmission lines and transformers and other power transmission and distribution equipment in the power grid show obvious inductance characteristics. When there is an obvious parallel capacitance branch in the regional power grid, the inductance branch and the capacitance branch can easily form a resonant circuit. If there is harmonic excitation at the resonant frequency in the power grid, the system is prone to harmonic resonance amplification, causing a significant increase in the harmonic content of the power grid voltage, which ultimately causes sensitive power loads to fail to work properly, relay protection devices to operate, and even damage to power transmission and distribution and power equipment in the power system, seriously endangering the stability of the power system and the safety of power transmission and distribution and power equipment.

[0003] In order to solve the above resonance problem, the currently commonly used technical solution is to add high-voltage passive filtering devices to the power system to suppress the harmonic resonance in the power system through high-voltage passive filters. However, the high-voltage passive filter solution has a series of disadvantages such as large footprint, large fundamental reactive power consumption, the need to add additional reactive power compensation devices, and poor frequency adaptability. It has obvious limitations in practical engineering applications, especially when the power system parameters change significantly and cause the resonant frequency to change. The high-voltage passive filter will not only lose its resonance suppression effect, but will even aggravate the harmonic resonance amplification phenomenon of the system at the new resonant frequency.

[0004] The active power grid harmonic resonance suppression device based on harmonic virtual resistance technology perfectly combines the active harmonic control device based on power electronic power devices and the harmonic virtual resistance control technology. By controlling the equivalent harmonic impedance of the active harmonic control device based on power electronic power devices, it can effectively suppress the harmonic resonance of the power grid and ensure that the voltage harmonics of the power grid meet the relevant standards of the power system. At the same time, the active power grid harmonic resonance suppression device based on harmonic virtual resistance technology presents high impedance characteristics to the fundamental frequency of the power grid, does not consume fundamental reactive power, and does not require the addition of other compensation devices. The equipment occupies a small area and has strong frequency adaptability, which can effectively solve the harmonic resonance problem of the power system. Summary of the Invention

[0005] To solve the problems described in the background art, the present invention provides an active power grid harmonic resonance suppression method based on harmonic virtual resistance technology. By applying harmonic virtual resistance control technology, effective control of the equivalent harmonic impedance of the active power grid harmonic resonance suppression device based on power electronic power devices is achieved, thereby achieving the purpose of suppressing power grid harmonic resonance.

[0006] To achieve the above object, the present invention is implemented by the following technical solutions:

[0007] An active power grid harmonic resonance suppression method based on harmonic virtual resistance technology, the method comprising the following steps:

[0008] Step 1: First, an active power grid harmonic resonance suppression device based on power electronic power devices is added at the point of common coupling of the power grid;

[0009] Step 2: Then, according to the equivalent connection impedance parameters of the power system and the equivalent parameters of the shunt capacitor branch, analyze and determine the harmonic equivalent impedance value required for harmonic resonance suppression;

[0010] Step 3: Finally, through the harmonic virtual resistance control method and the voltage source type power electronic converter control method, effective control of the harmonic equivalent impedance of the active power grid harmonic resonance suppression device based on power electronic power devices is achieved.

[0011] Further, the active power grid harmonic resonance suppression device in Step 1 includes a power supply circuit breaker S connected in series in sequence at the point of common coupling of the power grid APF , a soft start resistor R APF , a connecting reactor L APF , a power valve group G APF ; it also includes a bypass contactor or circuit breaker K connected in parallel across the soft start resistor R APF at both ends APF .

[0012] Further, Step 2 specifically includes:

[0013] In the harmonic equivalent circuit of the power grid system with an active power grid harmonic resonance suppression device based on harmonic virtual resistance technology, is the grid background harmonic voltage, Z s is the harmonic equivalent impedance of the power grid system, C F is the harmonic equivalent capacitance value of the system capacitive branch, Z Load is the harmonic equivalent impedance value of the load in the system, R V is the harmonic equivalent resistance value of the active power grid harmonic resonance suppression device based on harmonic virtual resistance technology;

[0014] After the capacitive branch is connected to the grid connection point, the harmonic voltage value of the grid system at the connection point is shown in Equation 1. The harmonic equivalent impedance of the grid system and the load harmonic equivalent impedance are generally inductive, while the harmonic impedance of the capacitive branch is capacitive. Then, the harmonic equivalent impedance of each branch of the grid system can be expressed by Equation 2;

[0015]

[0016]

[0017] Since the value of the load harmonic equivalent impedance X Load is much higher than the harmonic equivalent impedance value of the grid system and the harmonic equivalent impedance value of the capacitive branch, the influence of the load branch harmonic equivalent impedance on harmonic resonance can be ignored. Then, after adding the active grid harmonic resonance suppression device based on the harmonic virtual resistance technology, the harmonic voltage value at the grid connection point is shown in Equation 3. Considering that the equivalent harmonic impedance of the grid system is inductive and the harmonic equivalent impedance of the capacitive branch is capacitive, substituting Equation 2 into Equation 3 can be further expanded to obtain the expression shown in Equation 4.

[0018]

[0019]

[0020] To effectively suppress the harmonic resonance at the grid connection point, the harmonic equivalent resistance value of the active grid harmonic resonance suppression device based on the harmonic virtual resistance technology should meet the design requirements shown in Equation 5. For further analysis of the expression shown in Equation 5, the definition shown in Equation 6 is made. Substituting Equation 6 into Equation 5 can obtain the relationship shown in Equation 7;

[0021]

[0022]

[0023]

[0024] It can be seen from Equation 7 that if the value of K is greater than or equal to 2, then regardless of the value of Q designed, the harmonic voltage value at the grid connection point is less than the grid background harmonic voltage value, that is, there is no harmonic resonance amplification in the grid; if the value of K is greater than 0 and less than 2, then there may be harmonic resonance amplification at the grid connection point; to ensure that the active grid harmonic resonance suppression device based on the harmonic virtual resistance technology can effectively suppress the grid harmonic resonance, the harmonic equivalent resistance R V of the active grid harmonic resonance suppression device based on the harmonic virtual resistance technology should meet the requirements shown in Equation 8;

[0025]

[0026] Further, in the third step, the harmonic equivalent impedance control of the active power grid harmonic resonance suppression device based on power electronic power devices is performed through a harmonic control algorithm to ensure that the harmonic equivalent impedance of the active power grid harmonic resonance suppression device based on power electronic power devices is always a pure resistance and the equivalent resistance value is always equal to the harmonic equivalent resistance value designed for resonance suppression. Then, the active power grid harmonic resonance suppression device based on power electronic power devices is externally identical to the R in the equivalent circuit. V Since it is realized by an active device based on power electronic power devices, the harmonic equivalent impedance control is called the harmonic virtual resistance control method.

[0027] Further, the third step specifically includes the following:

[0028] 1) The sampled value V_grid of the grid voltage is phase-locked by a phase-locked loop to obtain the grid voltage phase value θ; the DC voltage values V dc_A1 to V dc_CN of each unit of the three-phase power valve group are averaged to obtain the average DC voltage of the unit and the given value V dc * of the unit DC voltage are subjected to PI closed-loop control to obtain the fundamental active current command value I d * ;

[0029] 2) The grid voltage V_grid and the grid voltage phase value θ output by the phase-locked loop are Park-transformed to obtain the grid voltage feedforward component V d grid ;

[0030] 3) The sampled value I_APF of the output current of the resonance suppression device is Park-transformed according to the grid voltage phase value θ to obtain the D-axis component I d APF and the Q-axis component I q APF of the resonance suppression device in the DQ synchronous rotating coordinate system. The D-axis given value I d * and I q * of the fundamental current are subjected to PI closed-loop control operation, and combined with the grid voltage feedforward component V d grid to obtain the output control signals V d APF* and V q APF* of the resonance suppression device, where the D-axis given value I d *is obtained from the DC voltage control output of the valve group unit, while the fundamental current Q-axis given value I q * is calculated by the fundamental reactive power control algorithm at the top layer of the system. For the pure resonance suppression device I q * is 0;

[0031] 4) The output control signals V d APF* and V q APF* are combined with the grid voltage phase value θ and the three-phase fundamental output control signals V of the resonance suppression device are obtained through the inverse Park transformation Af APF* , V Bf APF* and V Cf APF* ;

[0032] 5) By performing harmonic PARK transformation on the grid voltage signal V_grid and the output current I_APF of the resonance suppression device in combination with the grid voltage phase value θ, the grid voltage harmonic components V hd grid and V hq grid in the harmonic synchronous rotating coordinate system can be obtained, as well as the harmonic components I hd APF and I hq APF of the output current of the resonance suppression device. From V hd grid and V hq grid and the harmonic virtual resistance value R of the resonance suppression device V the harmonic current command values I hd * and I hd * can be obtained. By performing closed-loop PI control with the harmonic components I hd APF and I hq APF of the output current of the resonance suppression device, the harmonic control signals V hd APF* and V hq APF* of the device output can be obtained. After harmonic inverse PARK transformation, the three-phase harmonic output control signals V Ah APF* , V Bh APF* and V Ch APF* of the device are obtained.

[0033] Articles 1)-4) of the invention relate to the control method of voltage source power electronic converter, and article 5) relates to the control method of harmonic virtual resistance.

[0034] An active power grid harmonic resonance suppression device using the active power grid harmonic resonance suppression method based on harmonic virtual resistance technology comprises power supply circuit breakers S connected in series in sequence at a common connection point of the power grid. APF , soft start resistor R APF , connect the reactor L APF , Power valve group G APF ; Also includes the soft start resistor R APF Bypass contactor or circuit breaker K at both ends APF ; The power valve group G is controlled by the harmonic virtual resistance control method and the voltage source power electronic converter control method. APF Control is performed to achieve effective control of the harmonic equivalent impedance of the active power grid harmonic resonance suppression device.

[0035] Furthermore, it also includes a compensating transformer connected to the power supply circuit breaker S APF Between the public connection point to the grid.

[0036] Compared with the prior art, the present invention has the following beneficial effects:

[0037] The active power grid harmonic resonance suppression method and device based on harmonic virtual resistance technology of the present invention perfectly combine the latest active harmonic control device based on power electronic power devices with harmonic virtual resistance control technology. Through control technology, the electrical characteristics of the active harmonic control device based on power electronic power devices are made completely identical to the pure resistance characteristics, thereby achieving effective suppression of harmonic resonance at the common connection point of the power grid, and has the following advantages.

[0038] 1) Strong frequency adaptability

[0039] The active power grid harmonic resonance suppression method and device based on harmonic virtual resistance technology make the active harmonic control device based on power electronic power devices exhibit pure resistance characteristics through virtual resistance control technology. The control system can control the harmonics of the corresponding resonance frequency according to the change of the resonance frequency characteristics of the power system. Therefore, the device has stronger frequency adaptability. After the traditional passive harmonic resonance suppression device is installed and put into operation, if the resonance frequency changes due to major changes in the grid parameters of the power system, the passive harmonic resonance suppression device will not only lose its original resonance suppression effect, but may also exacerbate the system resonance at the latest frequency. It is necessary to carry out major renovations on the primary equipment of the device or replace it with a new device. However, for the active power grid harmonic resonance suppression device based on harmonic virtual resistance technology, only by changing the harmonic control frequency in the control can it effectively suppress the system resonance at the latest frequency, without any renovation of the primary equipment of the device, and the device has stronger frequency adaptability.

[0040] 2) No additional fundamental reactive power compensation device is required

[0041] The active power grid harmonic resonance suppression method and device based on harmonic virtual resistance technology exhibit pure resistance characteristics for the harmonics of the resonance frequency, while presenting high impedance or open circuit states for the fundamental frequency or other harmonic frequencies. Therefore, during the operation of the device, only a small harmonic current of the resonance frequency and a very small fundamental active current flow through to maintain the system loss, and no large fundamental current or harmonic current of other frequencies will flow through. Thus, it will not cause fundamental reactive power consumption to the power system. The traditional passive harmonic resonance suppression device exhibits ultra-low impedance characteristics for the harmonics of the resonance frequency, and also has relatively low impedance values for the fundamental and other frequency harmonics. Since the fundamental voltage value of the power grid is very high, the traditional passive harmonic resonance suppression device will emit a large amount of fundamental reactive power to the power system while suppressing the harmonic resonance at the point of common coupling of the power grid. To ensure that the power factor meets the requirements of the power grid, an additional fundamental reactive power compensation device must be installed while applying the passive harmonic resonance suppression device.

[0042] 3) Smaller floor area

[0043] The active power grid harmonic resonance suppression method and device based on harmonic virtual resistance technology are realized through the hardware of the active harmonic control device based on power electronic power devices. Compared with the traditional passive harmonic resonance suppression device, the device has a higher power density and does not require an additional fundamental reactive power compensation device. Therefore, the active power grid harmonic resonance suppression device based on harmonic virtual resistance technology has a smaller floor area and has obvious advantages in floor area in application scenarios with severely limited site areas such as offshore wind power generation.

[0044] 4) Lower active power loss

[0045] The active power grid harmonic resonance suppression method and device based on harmonic virtual resistance technology only flows a small resonant frequency harmonic current and a small fundamental active current to maintain system loss during operation, and does not flow a large fundamental current or other frequency harmonic current. Therefore, the active loss during the operation of the equipment is very low. During the operation of the traditional passive harmonic resonance suppression device, not only the resonant frequency harmonic current will flow, but also a large fundamental reactive current will flow, and an additional fundamental reactive compensation device needs to be added. Therefore, the active loss of the traditional passive harmonic resonance suppression device during operation will be large. The active power grid harmonic resonance suppression device based on harmonic virtual resistance technology has obvious advantages in terms of active loss.

[0046] 5) Harmonic resonance suppression and reactive power compensation functions

[0047] The active power grid harmonic resonance suppression method and device based on harmonic virtual resistance technology adopts harmonic virtual resistance control technology, and realizes the power grid harmonic resonance suppression function by controlling the active harmonic control device based on power electronic power devices. The active harmonic control device based on power electronic power devices has the same hardware configuration as the fundamental reactive power compensation device such as static VAR generator (SVG). Therefore, the harmonic virtual resistance control technology can be combined with the dynamic reactive power compensation control technology, so that the active power grid harmonic resonance suppression device based on harmonic virtual resistance technology can have the function of SVG dynamic reactive power compensation while suppressing the power grid harmonic resonance, which can save users a lot of equipment and operation and maintenance costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 This is an electrical connection diagram of the active power grid harmonic resonance suppression device based on harmonic virtual resistance technology of the present invention;

[0049] Figure 2 This is the system harmonic equivalent circuit diagram when the active power grid harmonic resonance suppression device based on harmonic virtual resistance technology is not added;

[0050] Figure 3 The system harmonic equivalent circuit diagram when an active power grid harmonic resonance suppression device based on harmonic virtual resistance technology is added;

[0051] Figure 4 This is a diagram of the harmonic control algorithm of the present invention. DETAILED DESCRIPTION

[0052] The specific implementation modes provided by the present invention are described in detail below with reference to the accompanying drawings.

[0053] An active power grid harmonic resonance suppression method based on harmonic virtual resistance technology, comprising:

[0054] Step 1: First, add an active power grid harmonic resonance suppression device based on power electronic power devices at the point of common coupling (PCC) of the power grid;

[0055] Step 2: Then, analyze and determine the harmonic equivalent impedance value required for harmonic resonance suppression according to the equivalent connection impedance parameters of the power system and the equivalent parameters of the shunt capacitor branch;

[0056] Step 3: Finally, through the harmonic virtual resistance control method and the voltage source type power electronic converter control method, effectively control the harmonic equivalent impedance of the active power grid harmonic resonance suppression device based on power electronic power devices.

[0057] Ultimately, the active power grid harmonic resonance suppression device based on the harmonic virtual resistance technology can effectively suppress the harmonic resonance condition of the power grid, ensuring that the voltage harmonic content at the PCC of the power grid meets the relevant standards of the power system.

[0058] I. Active Power Grid Harmonic Resonance Suppression Device

[0059] In Step 1, the electrical connection of the active power grid harmonic resonance suppression device based on the harmonic virtual resistance technology is as Figure 1 shown. There are multiple power consumption or generation loads at the PCC of the power grid, and there are capacitive branches such as long-distance cables in the system, which cause harmonic resonance amplification in the system, resulting in the voltage harmonic content at the PCC of the power grid exceeding the relevant standards of the power system and endangering the stability of the power system and the safety of surrounding electrical equipment. By adding an active power grid harmonic resonance suppression device based on the harmonic virtual resistance technology at the PCC, the effective suppression of harmonic resonance can be achieved, ensuring that the voltage harmonics of the power grid at the PCC meet the standard requirements. The active power grid harmonic resonance suppression device based on the harmonic virtual resistance technology mainly consists of a power supply circuit breaker S APF 、a soft start resistor R APF 、a bypass contactor or circuit breaker K APF 、a connecting reactor K APF 、a power valve group, a control system, a cooling and other auxiliary systems, etc. According to parameters such as the voltage level at the PCC and the capacity of the resonance suppression device, a compensation transformer may also be required.

[0060] Figure 1 is the electrical connection diagram of the active power grid harmonic resonance suppression device based on the harmonic virtual resistance technology. The AC power grid passes through the power supply switch S 0Connected to the system common connection point, the common connection point supplies power to Load Branch 1 through switch S1. Load Branch 1 is an electrical load or a power plant station, but its power supply line includes a long-distance high-voltage cable line, resulting in a capacitive shunt branch in the equivalent model of this branch. The common connection point supplies power to Load Branch 2 through switch S2. Load Branch 2 is a conventional electrical load, and there may be sensitive loads in the load that are vulnerable to the quality of the grid voltage waveform. To suppress grid harmonic resonance, a resonance suppression device can be added at the common connection point through switch S3.

[0061] II. Harmonic equivalent impedance values required for harmonic resonance suppression

[0062] When the active grid harmonic resonance suppression device based on harmonic virtual resistance technology is not added, the system harmonic equivalent circuit is as Figure 2 shown, where is the grid background harmonic voltage, Z s is the grid system harmonic equivalent impedance, C F is the harmonic equivalent capacitance value of the system capacitive branch, and Z Load is the harmonic equivalent impedance value of the load in the system.

[0063] For the common grid, generally values are all small and can meet the requirements of relevant power system standards. However, when the capacitive branch is connected to the grid common connection point, according to circuit theory, the harmonic voltage value at the common connection point of the system is as shown in Equation 1. The grid system harmonic equivalent impedance and the load harmonic equivalent impedance are generally inductive, while the harmonic impedance of the capacitive branch is capacitive. Then, the harmonic equivalent impedances of the system can be expressed by Equation 2. Substituting Equation 2 into Equation 1, it can be obtained that when there is no active grid harmonic resonance suppression device based on harmonic virtual resistance technology connected, the harmonic voltage at the grid common connection point is as shown in Equation 3. Since the load harmonic equivalent impedance value X Load is generally very large, its value is much higher than the grid system harmonic equivalent impedance value and the capacitive branch harmonic equivalent impedance value. Therefore, from Equation 3, it can be seen that when the grid system harmonic equivalent impedance value X s and the capacitive branch harmonic equivalent impedance value X C are equal or close, the harmonic voltage value will be much larger than the grid system background harmonic voltage value The system has a situation of harmonic resonance amplification, and the grid voltage harmonics at the common connection point are very likely to exceed the requirements of relevant grid standards, endangering the safety and stability of the grid and surrounding electrical equipment. And the harmonic frequency that makes the grid system harmonic equivalent impedance value X s and the capacitive branch harmonic equivalent impedance value X C equal or close is called the system harmonic resonance frequency.

[0064]

[0065]

[0066]

[0067] To suppress the power grid harmonic resonance caused by the connection of capacitive branches, an active power grid harmonic resonance suppression device based on harmonic virtual resistance technology can be added at the public connection point of the power grid. After adding, the harmonic equivalent circuit of the power grid system is as follows Figure 3 shown. After adding the resonance suppression device, it is equivalent to adding a parallel compensation branch at the public connection point. Since the resonance suppression device adopts the harmonic virtual resistance control technology, its harmonic equivalent resistance is R V . C F The parallel capacitive branch, the Z Load load branch, and the equivalent virtual resistance R V of the resonance suppression device are connected in parallel to form the harmonic equivalent circuit at the back end of the public connection point.

[0068] As Figure 3 shown, where R V is the harmonic equivalent resistance value of the active power grid harmonic resonance suppression device based on harmonic virtual resistance technology. Then, the harmonic voltage value at the public connection point of the power grid after adding the active power grid harmonic resonance suppression device based on harmonic virtual resistance technology is as shown in Equation 4. From the previous analysis, it can be seen that the harmonic equivalent impedance Z Load of the load branch has a very large value. Therefore, in the subsequent analysis, the influence of the harmonic equivalent impedance of the load branch can be ignored, and Equation 4 can be simplified to Equation 5. Considering that the equivalent harmonic impedance of the power grid system is inductive and the harmonic equivalent impedance of the capacitive branch is capacitive, Equation 5 can be further expanded to obtain the expression shown in Equation 6.

[0069]

[0070]

[0071]

[0072] To effectively suppress the harmonic resonance at the public connection point of the power grid, the harmonic equivalent resistance value of the active power grid harmonic resonance suppression device based on harmonic virtual resistance technology should meet the design requirements shown in Equation 7. To further analyze the expression shown in Equation 7, the definition shown in Equation 8 is made. Substituting Equation 8 into Equation 7 gives the relationship shown in Equation 9.

[0073] As can be seen from Equation 9, if the value of K is greater than or equal to 2, regardless of the value of Q designed, the harmonic voltage value at the point of common coupling of the power grid is less than the background harmonic voltage value of the power grid, that is, there is no harmonic resonance amplification in the power grid. If the value of K is greater than 0 and less than 2, there may be harmonic resonance amplification at the point of common coupling of the power grid. To ensure that the active power grid harmonic resonance suppression device based on the harmonic virtual resistance technology can effectively suppress the power grid harmonic resonance, the harmonic equivalent resistance design of the active power grid harmonic resonance suppression device based on the harmonic virtual resistance technology should meet the requirements shown in Equation 10.

[0074]

[0075]

[0076]

[0077]

[0078] III. Harmonic Virtual Resistance Control Technology

[0079] After selecting an appropriate harmonic equivalent resistance value according to the harmonic resonance suppression requirements at the point of common coupling of the system, the harmonic equivalent impedance at the resonance frequency of the active power grid harmonic resonance suppression device based on power electronic power devices is controlled through the harmonic control algorithm as Figure 4 shown, ensuring that the harmonic equivalent impedance of the active power grid harmonic resonance suppression device based on power electronic power devices is always a pure resistance and the equivalent resistance value is always equal to the harmonic equivalent resistance value designed for resonance suppression. Then, the active power grid harmonic resonance suppression device based on power electronic power devices is externally identical to the R in the equivalent circuit V but is implemented through an active device based on power electronic power devices, so it is called the harmonic virtual resistance control technology. After adopting the above harmonic equivalent resistance parameter design and harmonic virtual resistance control technology, the active power grid harmonic resonance suppression device based on the harmonic virtual resistance technology can effectively suppress the harmonic resonance at the point of common coupling of the power grid, ensure that the grid voltage harmonics at the point of common coupling of the power grid meet the relevant grid standards, and ensure the safe and stable operation of the power system and surrounding electrical equipment.

[0080] The specific control method is as follows:

[0081] 1) The sampled value of the grid voltage V_grid is phase-locked by a phase-locked loop to obtain the grid voltage phase value θ; the DC voltage values V dc_A1 to V dc_CN (Vdc_A1 to Vdc_AN, Vdc_B1 to Vdc_BN, Vdc_C1 to Vdc_CN) of each unit of the three-phase power valve group are averaged to obtain the average DC voltage of the unit With the unit DC voltage set value V dc * Perform PI closed-loop control to obtain the fundamental active current command value I d * ;

[0082] 2) The grid voltage V_grid and the grid voltage phase value θ output by the phase-locked loop are transformed by Park transformation to obtain the grid voltage feedforward component V d grid ;

[0083] 3) The output current sampling value I_APF of the harmonic suppression device is transformed by PARK according to the grid voltage phase value θ to obtain the D-axis component I d APF and Q-axis component I q APF , and the fundamental current D-axis set value I d * and I q * Perform PI closed-loop control operations, and combine with the grid voltage feedforward component V d grid to obtain the output control signals V d APF* and V q APF* , where the fundamental current D-axis set value I d * is obtained from the output control of the valve group unit DC voltage, while the fundamental current Q-axis set value I q * is calculated by the system top-level fundamental reactive power control algorithm. For a pure harmonic suppression device, I q * is 0;

[0084] 4) The output control signals V d APF* and V q APF* are combined with the grid voltage phase value θ and transformed by inverse Park transformation to obtain the three-phase fundamental output control signals V Af APF* , V Bf APF* and V Cf APF* ;

[0085] 5) By performing harmonic PARK transformation on the grid voltage signal V_grid and the output current I_APF of the harmonic suppression device in combination with the grid voltage phase value θ, the grid voltage harmonic component V in the harmonic synchronous rotating coordinate can be obtainedhd grid and V hq grid , the resonance suppression device outputs the current harmonic component I hd APF and I hq APF , by V hd grid and V hq grid And the harmonic virtual resistance value R of the resonance suppression device V The harmonic current command value I can be obtained hd * and I hd * , and the resonance suppression device output current harmonic component I hd APF and I hq APF By performing closed-loop PI control, the device output harmonic control signal V can be obtained. hd APF* and V hq APF* After the harmonic inverse PARK transformation, the three-phase harmonic output control signal V Ah APF* , V Bh APF* and V Ch APF* .

[0086] The active grid harmonic resonance suppression device based on harmonic virtual resistance technology is in the power valve group G APF The harmonic virtual resistance control technology is used in the control of the power valve group G APF The hardware implementation adopts an active harmonic control device based on power electronic power devices, wherein the active harmonic control device based on power electronic power devices includes but is not limited to: a three-phase three-wire star-connected H-bridge cascade type active harmonic control device, a three-phase three-wire delta-connected H-bridge cascade type active harmonic control device, a three-phase four-wire star-connected H-bridge cascade type active harmonic control device, a three-phase three-wire three-level type active harmonic control device, a three-phase four-wire three-level type active harmonic control device, a three-phase three-wire two-level type active harmonic control device, a three-phase MMC type active harmonic control device, a three-phase multiplexed type active harmonic control device, etc.

[0087] The above embodiments are implemented based on the technical solution of the present invention, and detailed implementation methods and specific operation processes are given, but the protection scope of the present invention is not limited to the above embodiments. The methods used in the above embodiments are conventional methods unless otherwise specified.

Claims

1. An active power grid harmonic resonance suppression method based on harmonic virtual resistance technology, characterized in that, the method includes the following: Step 1: First, add an active power grid harmonic resonance suppression device based on power electronic power devices at the point of common coupling (PCC) of the power grid; Step 2: Then, analyze and determine the harmonic equivalent impedance value required for harmonic resonance suppression according to the equivalent connection impedance parameters of the power system and the equivalent parameters of the shunt capacitor branch; Step 3: Finally, through the harmonic virtual resistance control method and the voltage source type power electronic converter control method, effectively control the harmonic equivalent impedance of the active power grid harmonic resonance suppression device based on power electronic power devices; The specific content of Step 2 includes: In the harmonic equivalent circuit of the power grid system with the active power grid harmonic resonance suppression device based on the harmonic virtual resistance technology, is the grid background harmonic voltage, Z s is the harmonic equivalent impedance of the power grid system, C F is the harmonic equivalent capacitance value of the system capacitive branch, Z Load is the harmonic equivalent impedance value of the load in the system, R V is the harmonic equivalent resistance value of the active power grid harmonic resonance suppression device based on the harmonic virtual resistance technology; After the capacitor branch is connected to the PCC of the power grid, the harmonic voltage value at the PCC of the power grid system is shown in Equation 1. The harmonic equivalent impedance of the power grid system and the load harmonic equivalent impedance are generally inductive, while the harmonic impedance of the capacitive branch is capacitive. Then, the harmonic equivalent impedance of each branch of the power grid system is expressed by Equation 2; Due to the load harmonic equivalent impedance value X Load whose value is much higher than the grid system harmonic equivalent impedance value and the capacitor branch harmonic equivalent impedance value. Ignoring the influence of the load branch harmonic equivalent impedance on harmonic resonance, the harmonic voltage value at the point of common coupling of the grid after adding the active grid harmonic resonance suppression device based on the harmonic virtual resistance technology is shown in Equation 3. Considering that the grid system equivalent harmonic impedance is inductive and the capacitive branch harmonic equivalent impedance is capacitive, substituting Equation 2 into Equation 3 and further expanding it gives the expression shown in Equation 4; To effectively suppress the harmonic resonance at the PCC of the power grid, the harmonic equivalent resistance value of the active power grid harmonic resonance suppression device based on harmonic virtual resistance technology should meet the design requirements shown in Equation 5. For further analysis of the expression shown in Equation 5, define Equation 6, and substitute Equation 6 into Equation 5 to obtain the relational expression shown in Equation 7; It can be seen from Equation 7 that if the value of K is greater than or equal to 2, the harmonic voltage value at the point of common coupling of the power grid is less than the background harmonic voltage value of the power grid regardless of the designed value of Q, that is, there is no harmonic resonance amplification in the power grid; if the value of K is greater than 0 and less than 2, harmonic resonance amplification may occur at the point of common coupling of the power grid; to ensure that the active power grid harmonic resonance suppression device based on the harmonic virtual resistance technology can effectively suppress the power grid harmonic resonance, the harmonic equivalent resistance R V shall meet the requirements shown in Equation 8; 2. An active power grid harmonic resonance suppression method based on harmonic virtual resistance technology according to claim 1, characterized in that, The active power grid harmonic resonance suppression device in the first step described includes a power supply circuit breaker S connected in series in sequence at the point of common coupling of the power grid APF , a soft start resistor R APF , a connecting reactor L APF , a power valve group G APF ; it also includes a bypass contactor or circuit breaker K connected in parallel across the soft start resistor R APF at both ends APF .

3. An active power grid harmonic resonance suppression method based on harmonic virtual resistance technology according to claim 1, characterized in that, In the third step described above, the harmonic equivalent impedance control at the resonant frequency of the active power grid harmonic resonance suppression device based on power electronic power devices is carried out through the harmonic control algorithm, ensuring that the harmonic equivalent impedance of the active power grid harmonic resonance suppression device based on power electronic power devices is always a pure resistance and the equivalent resistance value is always equal to the harmonic equivalent resistance value designed for resonance suppression. Then, the active power grid harmonic resonance suppression device based on power electronic power devices is exactly the same as the R in the equivalent circuit in terms of external characteristics. V Since it is realized by an active device based on power electronic power devices, the harmonic equivalent impedance control is called the harmonic virtual resistance control method.

4. An active power grid harmonic resonance suppression method based on harmonic virtual resistance technology according to claim 3, characterized in that, The specific content of Step 3 includes the following: 1) The sampled value V_grid of the grid voltage is phase-locked by a phase-locked loop to obtain the grid voltage phase value θ; the DC voltage values V dc_A1 to V dc_CN of each unit of the three-phase power valve bank are averaged to obtain the average DC voltage of the unit which is subjected to PI closed-loop control with the given DC voltage value V dc * to obtain the fundamental active current command value I d * ; 2) The grid voltage V_grid and the grid voltage phase value θ output by the phase-locked loop are transformed by Park transformation to obtain the grid voltage feedforward component V d grid ; 3) The sampled output current I_APF of the harmonic suppression device is subjected to PARK transformation according to the grid voltage phase value θ to obtain the D-axis component I of the harmonic suppression device in the DQ synchronous rotating coordinate system. d APF and the Q-axis component I q APF , which is subjected to PI closed-loop control operation with the D-axis given value I d * and I q * , and combined with the grid voltage feed-forward component V d grid to obtain the output control signals V d APF* and V q APF* , where the D-axis given value I d * of the fundamental current is obtained by the DC voltage control output of the valve group unit, and the Q-axis given value I q * of the fundamental current is calculated by the fundamental reactive power control algorithm at the top layer of the system. For a pure harmonic suppression device, I q * is 0. 4) The resonant suppression device outputs a control signal V d APF* and V q APF* Combined with the grid voltage phase value θ, the three-phase fundamental output control signals V Af APF* of the resonant suppression device are obtained through the inverse Park transformation Bf APF* ,V Cf APF* ; 5) By performing harmonic PARK transformation on the grid voltage signal V_grid and the output current I_APF of the resonance suppression device in combination with the grid voltage phase value θ, the grid voltage harmonic components V hd grid and V hq grid in the harmonic synchronous rotating coordinate are obtained. The harmonic components I hd APF and I hq APF of the output current of the resonance suppression device, from V hd grid and V hq grid and the harmonic virtual resistance value R V of the resonance suppression device, the harmonic current command values I hd * and I hd * are obtained. By performing closed-loop PI control with the harmonic components I hd APF and I hq APF of the output current of the resonance suppression device, the device output harmonic control signals V hd APF* and V hq APF* are obtained. After performing inverse harmonic PARK transformation, the three-phase harmonic output control signals V Ah APF* , V Bh APF* and V Ch APF* of the device are obtained; Among them, items 1)-4) relate to the voltage source type power electronic converter control method, and item 5) relates to the harmonic virtual resistance control method.

5. An active power grid harmonic resonance suppression device applying the active power grid harmonic resonance suppression method based on harmonic virtual resistance technology according to claim 1, characterized in that, It includes power supply circuit breakers S connected in series at the public connection point of the power grid. APF , soft start resistor R APF , connect the reactor L APF 、Power valve group G APF ; Also includes the soft start resistor R APF Bypass contactor or circuit breaker K at both ends APF ; The power valve group G is controlled by the harmonic virtual resistance control method and the voltage source power electronic converter control method. APF Control is performed to achieve effective control of the harmonic equivalent impedance of the active power grid harmonic resonance suppression device.

6. An active power grid harmonic resonance suppression device according to claim 5, characterized in that, It also includes a compensating transformer, which is connected between the power supply circuit breaker S APF and the point of common connection with the power grid.

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