A grid-forming flexible interconnection control method for transient voltage support and harmonic mitigation and related devices

Abstract

The application provides a network-configuration type flexible interconnection control method for transient voltage support and harmonic suppression and a related device, and belongs to the field of distribution network control. The steps of the method comprise: obtaining parameter data of a double-end flexible interconnection device and a distribution network; based on the obtained data, using a direct current bus voltage control strategy and a transient voltage support and harmonic suppression strategy to control two three-phase voltage source type converters of the double-end flexible interconnection device. The transient voltage support and harmonic suppression strategy is to introduce a low-pass filter link into a reactive power control link of traditional droop control, so as to slow down the output change rate of the reactive power controller. The application slows down the output change rate by introducing a low-pass filter link into a reactive power control link of traditional pure proportional droop control, smoothes the reactive power fluctuation, avoids voltage impact, suppresses transient voltage oscillation and instability, and improves the safe and stable operation ability of the distribution network during a fault.

Description

Technical Field

[0001] This invention belongs to the field of control technology for power distribution networks in power systems, specifically relating to a flexible interconnection control method and related devices for transient voltage support and harmonic suppression. Background Technology

[0002] Current power distribution networks are characterized by a high proportion of renewable energy integration, bidirectional power flow, intelligence, high reliability, user-side participation, power electronics, and integrated energy systems. These changes place demands on the transformation of the power distribution network itself, requiring it to possess greater flexibility and intelligence to cope with future energy crises.

[0003] The high proportion of distributed generation (DG) connected to the distribution network has altered the traditional single-phase power flow pattern. Because DG output fluctuates over time, large-scale DG integration makes it difficult for the power system to achieve high-precision real-time operation optimization during frequent load fluctuations, leading to problems such as distribution network overload, bidirectional power flow, and voltage exceeding limits. Simultaneously, traditional distribution networks expose a series of issues, including weak grid structure, low levels of distribution automation, and insufficient control capabilities, affecting power supply reliability. To address these problems, flexible interconnected devices (FIDs), as a new type of power electronic device, are widely used in distribution networks. A typical double-ended flexible interconnected device is the back-to-back converter (BTBC), which enables bidirectional energy transfer and flexible power control between AC systems. In practical applications, one end often uses constant DC bus voltage control, while the other end controls AC parameters.

[0004] Currently, using existing control strategies on back-to-back converters can easily lead to transient voltage faults when the distribution network faces a fault. Specifically, a distribution network fault causes a sudden change in the converter's instantaneous power absorption. Existing control strategies cannot effectively mitigate this drastic change, leading to output oscillations and ultimately transient voltage instability. In severe cases, this can even cause equipment shutdown, seriously damaging the safe and stable operation of the distribution network and resulting in substantial economic losses and adverse social impacts. Summary of the Invention

[0005] In view of this, the present invention provides a grid-type flexible interconnection control method and related device for transient voltage support and harmonic suppression, which aims to solve the problem of voltage transient faults that occur during distribution network faults and improve the safe and stable operation capability of the distribution network under fault conditions.

[0006] To achieve the above objectives, the technical solution provided by the present invention is as follows: In a first aspect, the present invention provides a grid-type flexible interconnection control method for transient voltage support and harmonic suppression, comprising the following steps: Acquire parameter data of the two-end flexible interconnection equipment and the power distribution network; Based on the parameter data, the first three-phase voltage source converter of the double-ended flexible interconnection equipment is controlled by a constant DC bus voltage control strategy, and the second three-phase voltage source converter of the double-ended flexible interconnection equipment is controlled by a transient voltage support and harmonic suppression strategy. Among them, the transient voltage support and harmonic suppression strategy introduces a low-pass filter into the reactive power control stage of the traditional droop control, so as to slow down the output change rate of the reactive power controller through the low-pass filter; the reactive power control stage of the traditional droop control adopts pure proportional control.

[0007] Furthermore, the transfer function of the reactive power control link in the transient voltage support and harmonic suppression strategy is as follows:

[0008] In the formula, The transfer function for the reactive power control loop. This is the reactive power-voltage droop factor. This is the cutoff frequency of the low-pass filter stage. For the Laplace operator; The corresponding dynamic control equations are:

[0009] In the formula, This refers to the actual terminal voltage of the second-phase three-phase voltage source converter. This is the reference value for the terminal voltage of the second-phase three-phase voltage source converter. This is the reference value for reactive power absorption of the second-phase three-phase voltage source converter. This refers to the grid voltage amplitude of distribution network G2, which is the distribution network connected to the second three-phase voltage source converter. The phase angle difference between the distribution network G2 voltage and the terminal voltage of the second three-phase voltage source converter. This refers to the line reactance of distribution network G2.

[0010] Furthermore, when a voltage dip fault occurs in distribution network G2, the second- and third-phase voltage source converters slow down the output change rate of the reactive power controller through the transfer function of the reactive power control loop; they also adjust the range of the converter terminal voltage to the terminal voltage reference value in real time through the dynamic control equation; and they attenuate the high-frequency harmonic signals during the fault process through the low-pass filter loop.

[0011] Furthermore, the cutoff frequency satisfies the following constraint:

[0012] In the formula, The sampling frequency.

[0013] Furthermore, the specific implementation process of the transient voltage support and harmonic suppression strategy is as follows: The reference and actual values ​​of active power and reactive power of the second-phase three-phase voltage source converter are obtained, and the terminal voltage reference value is obtained through the power control loop. The reference value of the terminal voltage and the actual terminal voltage are processed through a voltage control circuit to obtain the reference value of the current. The difference between the current reference value and the actual current is sent to the current control loop, and then combined with the compensation signal of the decoupling loop to obtain the d-axis reference value and q-axis reference value of the converter arm voltage. The d-axis and q-axis reference values ​​are transformed by dq-abc coordinates and then PWM modulated to generate trigger pulses to drive the converter switching transistors.

[0014] Furthermore, the specific implementation process of the constant DC bus voltage control strategy is as follows: The reference and actual values ​​of the DC bus voltage are obtained, and the reference value of the d-axis current of the first three-phase voltage source converter is obtained through the first PI control loop. The reference and actual values ​​of reactive power of the first three-phase voltage source converter are obtained, and the q-axis current reference value is obtained through the second PI control loop. The difference between the d-axis current reference value and the actual d-axis current, and the difference between the q-axis current reference value and the actual q-axis current, are sent to the current control loop respectively. Then, combined with the compensation signal from the decoupling loop and the grid voltage signal, the d-axis reference value and q-axis reference value of the converter arm voltage are obtained. The d-axis and q-axis reference values ​​are transformed by dq-abc coordinates and then PWM modulated to generate trigger pulses to drive the converter switching transistors.

[0015] Furthermore, the parameter data includes topology parameters and electrical operating parameters; The topology parameters are the connection relationships of the two-terminal flexible interconnection devices. The connection relationship is that the first three-phase voltage source converter and the second three-phase voltage source converter are directly coupled through the DC bus and are respectively connected to the AC terminals of distribution network G1 and distribution network G2. Distribution network G1 and distribution network G2 are the two distribution networks that the two three-phase voltage source converters of the two-terminal flexible interconnection devices are respectively connected to. Electrical operating parameters include line reactance, grid frequency, control gain, sampling frequency, voltage amplitude, phase angle difference, and measured values ​​of voltage and current.

[0016] In a second aspect, the present invention provides a grid-type flexible interconnection control device for transient voltage support and harmonic suppression, comprising: The data acquisition module is used to acquire parameter data of the two-end flexible interconnection equipment and the power distribution network; The interconnection control module is used to control the first three-phase voltage source converter of the double-ended flexible interconnection equipment based on parameter data, using a constant DC bus voltage control strategy, and to control the second three-phase voltage source converter of the double-ended flexible interconnection equipment using a transient voltage support and harmonic suppression strategy. Among them, the transient voltage support and harmonic suppression strategy introduces a low-pass filter into the reactive power control stage of the traditional droop control, so as to slow down the output change rate of the reactive power controller through the low-pass filter; the reactive power control stage of the traditional droop control adopts pure proportional control.

[0017] Furthermore, the transfer function of the reactive power control link in the transient voltage support and harmonic suppression strategy is as follows:

[0018] In the formula, The transfer function for the reactive power control loop. This is the reactive power-voltage droop factor. This is the cutoff frequency of the low-pass filter stage. For the Laplace operator; The corresponding dynamic control equations are:

[0019] In the formula, This refers to the actual terminal voltage of the second-phase three-phase voltage source converter. This is the reference value for the terminal voltage of the second-phase three-phase voltage source converter. This is the reference value for reactive power absorption of the second-phase three-phase voltage source converter. This refers to the grid voltage amplitude of distribution network G2, which is the distribution network connected to the second three-phase voltage source converter. The phase angle difference between the distribution network G2 voltage and the terminal voltage of the second three-phase voltage source converter. This refers to the line reactance of distribution network G2.

[0020] Furthermore, when a voltage dip fault occurs in distribution network G2, the second- and third-phase voltage source converters slow down the output change rate of the reactive power controller through the transfer function of the reactive power control loop; they also adjust the range of the converter terminal voltage to the terminal voltage reference value in real time through the dynamic control equation; and they attenuate the high-frequency harmonic signals during the fault process through the low-pass filter loop.

[0021] Furthermore, the cutoff frequency satisfies the following constraint:

[0022] In the formula, The sampling frequency.

[0023] Furthermore, the specific implementation process of the transient voltage support and harmonic suppression strategy is as follows: The reference and actual values ​​of active power and reactive power of the second-phase three-phase voltage source converter are obtained, and the terminal voltage reference value is obtained through the power control loop. The reference value of the terminal voltage and the actual terminal voltage are processed through a voltage control circuit to obtain the reference value of the current. The difference between the current reference value and the actual current is sent to the current control loop, and then combined with the compensation signal of the decoupling loop to obtain the d-axis reference value and q-axis reference value of the converter arm voltage. The d-axis and q-axis reference values ​​are transformed by dq-abc coordinates and then PWM modulated to generate trigger pulses to drive the converter switching transistors.

[0024] Furthermore, the specific implementation process of the constant DC bus voltage control strategy is as follows: The reference and actual values ​​of the DC bus voltage are obtained, and the reference value of the d-axis current of the first three-phase voltage source converter is obtained through the first PI control loop. The reference and actual values ​​of reactive power of the first three-phase voltage source converter are obtained, and the q-axis current reference value is obtained through the second PI control loop. The difference between the d-axis current reference value and the actual d-axis current, and the difference between the q-axis current reference value and the actual q-axis current, are sent to the current control loop respectively. Then, combined with the compensation signal from the decoupling loop and the grid voltage signal, the d-axis reference value and q-axis reference value of the converter arm voltage are obtained. The d-axis and q-axis reference values ​​are transformed by dq-abc coordinates and then PWM modulated to generate trigger pulses to drive the converter switching transistors.

[0025] Furthermore, the parameter data includes topology parameters and electrical operating parameters; The topology parameters are the connection relationships of the two-terminal flexible interconnection devices. The connection relationship is that the first three-phase voltage source converter and the second three-phase voltage source converter are directly coupled through the DC bus and are respectively connected to the AC terminals of distribution network G1 and distribution network G2. Distribution network G1 and distribution network G2 are the two distribution networks that the two three-phase voltage source converters of the two-terminal flexible interconnection devices are respectively connected to. Electrical operating parameters include line reactance, grid frequency, control gain, sampling frequency, voltage amplitude, phase angle difference, and measured values ​​of voltage and current.

[0026] Thirdly, the present invention provides a computer device, the device including a processor and a memory: The memory is used to store computer programs and send the instructions of the computer programs to the processor; The processor executes the following steps according to the instructions of the computer program: Acquire parameter data of the two-end flexible interconnection equipment and the power distribution network; Based on the parameter data, the first three-phase voltage source converter of the double-ended flexible interconnection equipment is controlled by a constant DC bus voltage control strategy, and the second three-phase voltage source converter of the double-ended flexible interconnection equipment is controlled by a transient voltage support and harmonic suppression strategy. Among them, the transient voltage support and harmonic suppression strategy introduces a low-pass filter into the reactive power control stage of the traditional droop control, so as to slow down the output change rate of the reactive power controller through the low-pass filter; the reactive power control stage of the traditional droop control adopts pure proportional control.

[0027] Fourthly, the present invention provides a computer-readable storage medium on which a computer program is stored, and when executed by a processor, the computer program performs the following steps: Acquire parameter data of the two-end flexible interconnection equipment and the power distribution network; Based on the parameter data, the first three-phase voltage source converter of the double-ended flexible interconnection equipment is controlled by a constant DC bus voltage control strategy, and the second three-phase voltage source converter of the double-ended flexible interconnection equipment is controlled by a transient voltage support and harmonic suppression strategy. Among them, the transient voltage support and harmonic suppression strategy introduces a low-pass filter into the reactive power control stage of the traditional droop control, so as to slow down the output change rate of the reactive power controller through the low-pass filter; the reactive power control stage of the traditional droop control adopts pure proportional control.

[0028] In summary, this invention provides a control method and related apparatus for network-type flexible interconnection with transient voltage support and harmonic suppression. The method includes acquiring parameter data of the double-ended flexible interconnection equipment and the distribution network; based on the parameter data, controlling the first three-phase voltage source converter of the double-ended flexible interconnection equipment using a constant DC bus voltage control strategy, and controlling the second three-phase voltage source converter of the double-ended flexible interconnection equipment using a transient voltage support and harmonic suppression strategy; wherein, the transient voltage support and harmonic suppression strategy introduces a low-pass filter into the reactive power control stage of the traditional droop control, so as to delay the output change rate of the reactive power controller through the low-pass filter; the traditional droop control reactive power control stage uses pure proportional control. This invention, by introducing a low-pass filter into the reactive power control stage of the traditional pure proportional droop control to delay the output change rate of the reactive power controller, smooths reactive power fluctuations, avoids voltage surges, thereby suppressing transient voltage oscillations and instability, and improving the safe and stable operation capability of the distribution network under fault conditions. Attached Figure Description

[0029] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0030] Figure 1 A flowchart of a network-type flexible interconnection control method for transient voltage support and harmonic suppression provided in an embodiment of the present invention; Figure 2 This is a topology diagram of a dual-ended flexible interconnection system provided in an embodiment of the present invention; Figure 3 A block diagram of a flexible interconnect control device for transient voltage support and harmonic suppression provided in an embodiment of the present invention; Figure 4 This is a block diagram of a computer device provided in an embodiment of the present invention. Detailed Implementation

[0031] To make the objectives, features, and advantages of this invention more apparent and understandable, the technical solutions of the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the embodiments described below are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0032] The background technology of this invention will be further introduced below.

[0033] In recent years, my country has built a new power system primarily based on new energy sources. Under this new power system, the distribution network exhibits characteristics such as high-proportion renewable energy integration, bidirectional power flow, intelligence, high reliability, user-side participation, power electronics, and integrated energy systems. These changes necessitate the transformation of the distribution network to achieve greater flexibility and intelligence to address future energy crises. The high proportion of distributed generators (DGs) integrated into the distribution network alters the traditional single-phase power flow pattern. Because DG output fluctuates with time, when large-scale DG integration occurs, the power system struggles to achieve high-precision real-time operation optimization when DGs and loads fluctuate frequently. This leads to distribution network overload, bidirectional power flow, and voltage exceeding limits. Traditional distribution networks expose a series of problems, including weak grid structure, low levels of distribution automation, and insufficient control capabilities, all of which affect power supply reliability.

[0034] Power electronic devices inherently possess efficient power control and conversion capabilities, enabling interconnection between power grids of different frequencies, operating states, and voltage levels. This facilitates the modularization and regionalization of distribution networks, reduces maintenance costs, improves device scalability, and allows for integration with energy storage technologies to form multi-energy complementarity. This drives the development of distribution networks towards greater efficiency, environmental friendliness, and intelligence, demonstrating promising prospects. To address these challenges, flexible interconnected devices (FIDs) are widely used in distribution networks. As a novel type of power electronic device, FIDs offer broad application scenarios in modern power systems due to their precise control over power flow magnitude and direction, and rapid fault response.

[0035] Currently, whether a new power system can successfully achieve stable operation against interference is a key test of the power grid's operational capabilities. Existing research focuses on the transient stability of distribution networks after experiencing faults (such as voltage sag events). To date, few studies have investigated the factors affecting the transient stability of distribution networks after experiencing faults from the perspective of reactive power absorption limitation by the single-sided converter of back-to-back converters.

[0036] FID (Flexible Interconnection Device) is a new type of power electronic device that replaces traditional interconnection switching equipment in distribution networks. It consists of a voltage source converter (VSC), an automatic switching device, and pulse width modulation (PWM). It can flexibly control the power flow between connected feeders. Compared to traditional switching equipment, it significantly improves feeder load balancing, rapid fault isolation, and timely load transfer. A typical dual-ended flexible interconnection device is the back-to-back converter (BTBC), which enables bidirectional energy transfer and flexible power control between AC systems. In practical applications, one end often uses constant DC bus voltage control, while the other end controls AC parameters.

[0037] However, existing technologies generally suffer from the following defects and shortcomings: when using the aforementioned control strategy on back-to-back converters, voltage transient faults are prone to occur when the distribution network faces a fault. When a distribution network fault occurs, causing a sudden change in the instantaneous power absorption of the converter, the existing converter control strategy is unable to mitigate this drastic change, leading to a surge in the output of the control loop, causing output oscillations, and ultimately resulting in transient voltage instability. In severe cases, this can lead to equipment shutdown, seriously damaging the safe and stable operation of the distribution network, causing substantial economic losses and adverse social impacts.

[0038] Based on this, the present invention provides a grid-type flexible interconnection control method and related device for transient voltage support and harmonic suppression, so as to solve the problem of voltage transient faults that occur during distribution network faults and improve the safe and stable operation capability of distribution network under fault conditions.

[0039] Please see Figure 1 and Figure 2 , Figure 1 The flowchart of a flexible interconnection control method for transient voltage support and harmonic suppression according to the present invention is shown. Figure 2 A topology of a two-terminal flexible interconnection system is shown, comprising two-terminal flexible interconnection devices, including two three-phase voltage source converters (VSC1, VSC2), distribution network G1, and distribution network G2. The following is combined with... Figure 2 This section introduces voltage transient problems.

[0040] There is no DC transmission line between VSC1 and VSC2 that constitute the BTBC. Instead, they are directly coupled through a DC bus. The output of distribution network G1 is connected to the AC end of VSC1, and the output of distribution network G2 is connected to the AC end of VSC2. Through the DC bus connecting VSC1 and VSC2, bidirectional energy transfer and flexible power control between AC systems can be achieved.

[0041] according to Figure 2 The structure shown allows for the analysis of a double-ended flexible interconnect device: The active and reactive power injected into the power grid are obtained by the following formula:

[0042] In the formula, and These represent the active and reactive power injected into the distribution network by the converter, respectively. This represents the d-axis component of the converter output voltage. The d-axis component of the current injected into the grid to the converter. This represents the q-axis component of the converter output voltage. The q-axis component of the current injected into the grid for the converter.

[0043] During low-voltage ride-through, grid-type converters may experience transient voltage instability due to excessive reactive power absorption. V gfd Indicates the converter voltage. X gs and R gs To represent line reactance and inductance, use δ Let represent the phase angle difference between the grid voltage and the converter voltage. The active and reactive power injected into the grid are obtained using the following formula: For X gs >> R gs Then, we can further deduce that:

[0044] Therefore, the relationship between the absorbed reactive power and the converter terminal voltage can be obtained, and it is clear that... q g yes V gfd It is a quadratic function. In practice, it can be approximated as... δ If we consider it as 0 degrees, then according to the following formula, we get... q g The minimum value.

[0045]

[0046] when V gfd Less than q g Take the minimum value corresponding to V gfdAt this time, if the converter wants to absorb more reactive power, it will cause the converter voltage to drop, forming positive feedback, which will lead to voltage collapse. In reality, when the power grid faces a fault (such as a voltage sag fault), during the low voltage ride-through process, the reactive power absorbed by the converter is likely to exceed the limit, causing voltage transient problems.

[0047] The following describes various embodiments of the present invention.

[0048] Please see Figure 1 This embodiment provides a grid-type flexible interconnection control method with transient voltage support and harmonic suppression, including the following steps: S1: Obtain parameter data for the dual-end flexible interconnection equipment and the power distribution network.

[0049] It should be noted that the double-ended flexible interconnection equipment refers to a back-to-back converter device consisting of two three-phase voltage source converters directly coupled through a DC bus, without DC transmission lines, and the two converters are connected to different distribution networks respectively; the parameter data is the basic data for the control strategy parameter tuning and control logic implementation.

[0050] This step can be combined with the topology of the dual-end flexible interconnection system to obtain relevant parameters for control strategy parameter tuning and control logic implementation through sensor acquisition and factory calibration parameters.

[0051] S2: Based on parameter data, the first three-phase voltage source converter of the double-ended flexible interconnection equipment is controlled by a constant DC bus voltage control strategy, and the second three-phase voltage source converter of the double-ended flexible interconnection equipment is controlled by a transient voltage support and harmonic suppression strategy. Among them, the transient voltage support and harmonic suppression strategy introduces a low-pass filter into the reactive power control stage of the traditional droop control, so as to slow down the output change rate of the reactive power controller through the low-pass filter; the reactive power control stage of the traditional droop control adopts pure proportional control.

[0052] It should be noted that the constant DC bus voltage control strategy is the control strategy for the first three-phase voltage source converter. The goal is to maintain the DC bus voltage of the double-ended flexible interconnection equipment and ensure the power transmission balance between the two converters.

[0053] The transient voltage support and harmonic suppression strategy is the control strategy for the second and third phase voltage source converters, which is used to solve the problem of voltage transient instability during distribution network faults.

[0054] Traditional droop control is a power-voltage / frequency control strategy for distributed power sources / converters. In this strategy, the reactive power control stage uses pure proportional control, meaning that the amount of reactive power adjustment is directly proportional to the voltage deviation. This strategy has a fast response speed but weak disturbance rejection capability.

[0055] A low-pass filter is a signal processing stage that allows low-frequency signals to pass through while attenuating high-frequency signals. In this embodiment, it is embedded in the reactive power control stage to adjust the changing characteristics of the controller output.

[0056] In this step, constant DC bus voltage control is implemented for the first three-phase voltage source converter. Closed-loop regulation maintains the DC bus voltage within the set range, ensuring the stability of the power transmission channel of the dual-ended converter. An improved droop control is implemented for the second three-phase voltage source converter. Its core logic is to introduce a low-pass filter into the traditional pure proportional reactive power control loop. When a fault in the distribution network causes a sudden power surge, the low-pass filter slows down the output change rate of the reactive power controller, avoiding the abrupt output change problem under traditional pure proportional control. This smooths the reactive power output of the converter and reduces the impact on the distribution network voltage.

[0057] In existing technologies, reactive power control of back-to-back converters uses pure proportional droop control. During distribution network faults, instantaneous power surges directly trigger a sharp change in the controller output, leading to drastic fluctuations in the converter's reactive power output and causing transient voltage oscillations or even instability in the distribution network. This embodiment introduces a low-pass filter in the reactive power control stage. Through the signal attenuation and rate regulation of this stage, the output change rate of the reactive power controller is slowed down, smoothing power fluctuations under fault conditions from the source of control. This avoids the impact of sharp power changes on the distribution network voltage, ultimately achieving the goal of suppressing transient voltage oscillations and maintaining safe and stable operation of the distribution network under fault conditions. At the same time, the low-pass filter can attenuate high-frequency harmonic components, taking into account the harmonic suppression effect. Compared with traditional control strategies, this represents a breakthrough in transient voltage support and power quality improvement.

[0058] In one embodiment of the present invention, the transfer function of the reactive power control link of the transient voltage support and harmonic suppression strategy is:

[0059] In the formula: The transfer function for the reactive power control loop. This is the reactive power-voltage droop factor. This is the cutoff frequency of the low-pass filter stage. For the Laplace operator; The corresponding dynamic control equations are:

[0060] In the formula: This refers to the actual terminal voltage of the second-phase three-phase voltage source converter. This is the reference value for the terminal voltage of the second-phase three-phase voltage source converter. This is the reference value for reactive power absorption of the second-phase three-phase voltage source converter. This refers to the grid voltage amplitude of distribution network G2, which is the distribution network connected to the second three-phase voltage source converter. The phase angle difference between the distribution network G2 voltage and the terminal voltage of the second three-phase voltage source converter. This refers to the line reactance of distribution network G2.

[0061] In this embodiment, to address the transient voltage instability problem caused by sudden changes in reactive power of the converter during distribution network faults, an improved reactive power control strategy embedded in a low-pass filter is designed. Its core is to use the aforementioned transfer function within the traditional pure proportional droop control reactive power control stage. G q A first-order low-pass filter is introduced in (s), utilizing the reactive power-voltage droop coefficient. k vdroop2 The relationship between reactive power and voltage regulation is determined by the cutoff frequency of the low-pass filter stage. The output rate of the reactive power controller is slowed down, and the corresponding dynamic control equations also address the converter terminal voltage deviation and the voltage amplitude based on the distribution network G2. V s2 Phase angle difference δ 2. Line reactance X gs2 The calculated reactive power deviation is coupled and adjusted to achieve dynamic response of the converter terminal voltage. This design not only smooths reactive power fluctuations under fault conditions through low-pass filtering and suppresses transient voltage oscillations and instability, but also attenuates high-frequency harmonic components. At the same time, the dynamic control equation ensures the accuracy and responsiveness of voltage regulation, ultimately improving the safe and stable operation capability of the distribution network under fault conditions.

[0062] Based on the improved reactive power control strategy proposed in the above embodiments, in a further embodiment of the present invention, when a voltage sag fault occurs in distribution network G2, the second three-phase voltage source converter slows down the output change rate of the reactive power controller through the transfer function of the reactive power control link; it also adjusts the range of the converter terminal voltage to the terminal voltage reference value in real time through the dynamic control equation; and it also attenuates the high-frequency harmonic signals during the fault process through the low-pass filter link.

[0063] In this embodiment, when a voltage dip in distribution network G2 causes a sudden power surge, the second-phase three-phase voltage source converter first uses the transfer function of the reactive power control loop and relies on the embedded low-pass filter loop to slow down the output change rate of the reactive power controller, avoiding abrupt output changes under traditional pure proportional control, thereby smoothing reactive power fluctuations. At the same time, through dynamic control equations, combined with parameters such as voltage amplitude, phase angle difference, and line reactance of distribution network G2, the reactive power deviation is calculated in real time, and the converter terminal voltage is adjusted to the reference range to quickly support the voltage recovery to a stable level. In addition, the low-pass filter loop can also synchronously attenuate high-frequency harmonic signals generated during the fault process and suppress voltage and current ripple.

[0064] In a further embodiment of the present invention, the cutoff frequency of the low-pass filter satisfies the following constraint:

[0065] In the formula: The sampling frequency.

[0066] In a further embodiment of the present invention, the specific implementation process of the transient voltage support and harmonic suppression strategy is as follows (in conjunction with...). Figure 2 (The structure shown is explained below) Step 1: Obtain the reference and actual values ​​of active power and reactive power of the second three-phase voltage source converter, and obtain the terminal voltage reference value through the power control loop.

[0067] This step involves collecting the active power reference value of the second three-phase voltage source converter (VSC2). p g2_ref / actual value p g2 Reactive power reference value q g2_ref / actual value q g2 The power control circuit outputs reference values ​​for the d-axis and q-axis voltages. The power control circuit includes an active power control sub-circuit and a reactive power control sub-circuit. The transfer function used in the active power control sub-loop is:

[0068] In the formula: This is the active power-frequency droop factor.

[0069] Since the converter terminal voltage is directed from the abc three-phase to the d-axis, this link... G p (s) The output value is zero, and the phase angle can be obtained by integrating the output. θ g .

[0070] The reactive power control sub-loop adopts the improved transfer function proposed in the aforementioned embodiments, using the reactive power deviation as input and relying on a low-pass filter to slow down the output change rate; combined with dynamic control equations, it realizes dynamic adjustment of the terminal voltage, and finally obtains the d-axis terminal voltage reference value. V gfd2_ref .

[0071] Step 2: The reference terminal voltage value and the actual terminal voltage are passed through a voltage control circuit to obtain the current reference value.

[0072] This step will use the reference values ​​for the voltages at the d and q axes (e.g.) V gfd2_ref ) and the actual terminal voltage of the converter V gfd2 The voltage deviation signal is obtained by subtracting the voltage. After the deviation is adjusted by the voltage control circuit (PI controller), the current reference value is output.

[0073] The transfer function of the voltage control loop is:

[0074] In the formula: For proportional gain, To achieve rapid convergence of voltage deviation through PI control, the d-axis current reference value is output. i gid2_ref and q-axis current reference value i giq2_ref .

[0075] Step 3: The difference between the current reference value and the actual current is sent to the current control loop, and then combined with the compensation signal of the decoupling loop to obtain the d-axis reference value and q-axis reference value of the converter arm voltage.

[0076] This step involves subtracting the reference current value from the actual d-axis and q-axis currents of the converter to obtain the current deviation signal. After the deviation is adjusted by the current control loop (PI controller), it is combined with the decoupling compensation signal to obtain the d-axis and q-axis reference values ​​of the bridge arm voltage.

[0077] The transfer function of the current control element is:

[0078] In the formula: For proportional gain, This is the integral gain, used for fast tracking of current deviation.

[0079] The decoupling compensation stage is based on the line inductance of distribution network G2. L Grid frequency ω Construct the compensation equation:

[0080] In the formula: u sd2 , u sq2 These represent the d-axis and q-axis voltages of distribution network G2, respectively. u cd2 , u cq2 These represent the d-axis and q-axis voltages at the output of VSC2, respectively. i d2 , i q2 This represents the d-axis and q-axis currents at the VSC2 side outlet. L The inductor of the G2 line connected to VSC2. ω This refers to the power grid frequency.

[0081] This equation is used to eliminate cross-coupling interference between grid voltage and converter current, ultimately obtaining the d-axis reference value of the converter arm voltage. u cd2 and q-axis reference value u cq2 .

[0082] Step 4: After transforming the d-axis reference value and q-axis reference value into dq-abc coordinates, perform PWM modulation to generate trigger pulses to drive the converter switching transistors.

[0083] This step converts the reference values ​​of the d and q axis bridge arm voltages into voltage signals in a stationary three-phase coordinate system through dq-abc coordinate transformation, and then inputs them into the PWM modulation module for PWM modulation to generate trigger pulses to drive the converter switching transistors.

[0084] In this embodiment, to address the transient voltage instability and harmonic issues during distribution network faults, a low-pass filter is introduced into the reactive power stage of the traditional droop control. Combined with multi-closed-loop control and decoupling compensation mechanisms for power, voltage, and current, this approach can not only delay reactive power surges and support the rapid recovery of transient voltage to a stable range, but also attenuate high-frequency harmonic signals, effectively improving the safe and stable operation capability and power quality of the distribution network under fault conditions.

[0085] In one embodiment of the present invention, a constant DC bus voltage control strategy is used to maintain a constant DC bus voltage during power transmission, ensuring balanced power transmission between the two converters. This enables flexible power adjustment, allowing the back-to-back converters to flexibly allocate and adjust power according to different operating conditions and demands. In the event of a grid-side fault, the converter with constant DC bus voltage control can respond quickly, limiting fluctuations in the DC bus voltage. Simultaneously, it can coordinate the control of the two converters, achieving coordinated control of both converters. This coordinated control method ensures stable system operation of the back-to-back converters under different operating conditions.

[0086] The specific implementation process of this strategy is as follows (in order to) Figure 2 (The structure shown is explained below) Step 1: Obtain the reference value and actual value of the DC bus voltage, and obtain the d-axis current reference value of the first three-phase voltage source converter through the first PI control loop; This step involves acquiring a DC bus voltage reference value. U dc_ref Compared with actual value U dc The difference between the two is used to obtain the voltage deviation signal. After the deviation is adjusted by the first PI control loop, the d-axis current reference value of the first three-phase voltage source converter (VSC1) is output. i d1_ref .

[0087] The transfer function of the first PI control loop is:

[0088] In the formula: For the proportional gain of the DC voltage control loop, This is the integral gain of the DC voltage control circuit.

[0089] Step 2: Obtain the reference value and actual value of reactive power of the first three-phase voltage source converter, and obtain the q-axis current reference value through the second PI control loop; This step involves collecting the reactive power reference value Q of VSC1. 1ref The reactive power deviation signal is obtained by subtracting the actual value Q1 from the actual value. After the deviation is adjusted by the second PI control loop, the q-axis current reference value i of VSC1 is output. q1_ref .

[0090] The transfer function of the second PI control loop is the same as that of the first PI control loop.

[0091] Step 3: The difference between the d-axis current reference value and the actual d-axis current, and the difference between the q-axis current reference value and the actual q-axis current are sent to the current control loop respectively. Then, combined with the compensation signal of the decoupling loop and the grid voltage signal, the d-axis reference value and q-axis reference value of the converter arm voltage are obtained. This step will use the d-axis current reference value. i d1_ref With actual d-axis current i d1 q-axis current reference value i q1_ref With actual q-axis current i q1The current deviation signal is obtained by subtracting the values ​​of the two signals. After the deviation is adjusted by the current control circuit, it is combined with the compensation signal from the decoupling circuit and the d-axis and q-axis grid voltages of the distribution network G1. u sd1 , u sq1 Finally, the d-axis reference value of the converter bridge arm voltage is obtained. u cd1 and q-axis reference value u cq1 .

[0092] The transfer function of the current control element is:

[0093] In the formula: k kp This represents the proportional gain of the control loop. k ki This represents the integral gain of the control loop.

[0094] The decoupling compensation stage employs a cross-coupling compensation equation:

[0095] In the formula: u sd1 , u sq1 These represent the d-axis and q-axis voltages of distribution network G1, respectively. u cd1 , u cq1 These represent the d-axis and q-axis voltages at the output of VSC1, respectively. i d1 , i q1 This represents the d-axis and q-axis currents at the output of VSC1. L The inductor of the G1 line connected to VSC1. ω This refers to the power grid frequency.

[0096] Step 4: After transforming the d-axis reference value and q-axis reference value into dq-abc coordinates, perform PWM modulation to generate trigger pulses to drive the converter switching transistors.

[0097] This step will set the reference values ​​for the d-axis and q-axis bridge arm voltages. u cd1 , u cq1 The voltage signal is converted into a stationary three-phase coordinate system through dq-abc coordinate transformation, and then input into the PWM modulation module for PWM modulation to generate trigger pulses to drive the switching transistor of VSC1.

[0098] In this embodiment, to address the DC bus voltage stability requirement of back-to-back converters, d-axis and q-axis current reference values ​​are generated through a dual-PI closed-loop system of DC bus voltage and reactive power. After current control and decoupling compensation to eliminate cross-coupling interference, the bridge arm voltage reference value is obtained. Then, the converter is driven by dq-abc coordinate transformation and PWM modulation, ultimately achieving constant DC bus voltage and balanced power transmission. It also provides a rapid response to grid faults to limit voltage fluctuations and ensure stable system operation.

[0099] In one embodiment of the present invention, the parameter data includes topology parameters and electrical operating parameters; The topology parameters are the connection relationships of the two-terminal flexible interconnection devices. The connection relationship is that the first three-phase voltage source converter and the second three-phase voltage source converter are directly coupled through the DC bus and are respectively connected to the AC terminals of distribution network G1 and distribution network G2. Distribution network G1 and distribution network G2 are the two distribution networks that the two three-phase voltage source converters of the two-terminal flexible interconnection devices are respectively connected to. Electrical operating parameters include line reactance, grid frequency, control gain, sampling frequency, voltage amplitude, phase angle difference, and measured values ​​of voltage and current.

[0100] Based on the above embodiments, this invention addresses the problem of transient voltage instability caused by reactive power absorption exceeding limits during low-voltage ride-through of grid-connected converters. It employs differentiated control of a dual-terminal flexible interconnection device (BTBC): VSC1 uses constant DC bus voltage control to achieve flexible power adjustment, providing a stable power transmission foundation for the system; VSC2 uses a grid-type flexible interconnection control method combining transient voltage support and harmonic suppression. When a voltage dip fault occurs in the distribution network and the measured power value on the VSC2 side changes rapidly, this method allows the output of the reactive power controller to change smoothly with the measured reactive power value, buffering power surges. Through coordinated adjustment of the voltage control loop and current control loop, transient voltage support for the grid-type flexible interconnection distribution network is successfully achieved, effectively widening the reactive power absorption stability region and improving the safe and stable operation capability of the distribution network under power system transient fault conditions.

[0101] Based on the same inventive concept, this application also provides a flexible interconnection control device for transient voltage support and harmonic suppression, used to implement the aforementioned flexible interconnection control method for transient voltage support and harmonic suppression. The solution provided by this device is similar to the solution described in the above method. Therefore, the specific limitations in the embodiments of the flexible interconnection control device for transient voltage support and harmonic suppression provided below can be found in the limitations of the flexible interconnection control method for transient voltage support and harmonic suppression described above, and will not be repeated here.

[0102] Please see Figure 3 The present invention also provides a network-type flexible interconnection control device for transient voltage support and harmonic suppression, comprising: The data acquisition module is used to acquire parameter data of the two-end flexible interconnection equipment and the power distribution network; The interconnection control module is used to control the first three-phase voltage source converter of the double-ended flexible interconnection equipment based on parameter data, using a constant DC bus voltage control strategy, and to control the second three-phase voltage source converter of the double-ended flexible interconnection equipment using a transient voltage support and harmonic suppression strategy. Among them, the transient voltage support and harmonic suppression strategy introduces a low-pass filter into the reactive power control stage of the traditional droop control, so as to slow down the output change rate of the reactive power controller through the low-pass filter; the reactive power control stage of the traditional droop control adopts pure proportional control.

[0103] In one embodiment of the present invention, the transfer function of the reactive power control link of the transient voltage support and harmonic suppression strategy is:

[0104] In the formula, The transfer function for the reactive power control loop. This is the reactive power-voltage droop factor. This is the cutoff frequency of the low-pass filter stage. For the Laplace operator; The corresponding dynamic control equations are:

[0105] In the formula, This refers to the actual terminal voltage of the second-phase three-phase voltage source converter. This is the reference value for the terminal voltage of the second-phase three-phase voltage source converter. This is the reference value for reactive power absorption of the second-phase three-phase voltage source converter. This refers to the grid voltage amplitude of distribution network G2, which is the distribution network connected to the second three-phase voltage source converter. The phase angle difference between the distribution network G2 voltage and the terminal voltage of the second three-phase voltage source converter. This refers to the line reactance of distribution network G2.

[0106] In one embodiment of the present invention, when a voltage sag fault occurs in distribution network G2, the second three-phase voltage source converter slows down the output change rate of the reactive power controller through the transfer function of the reactive power control link; it also adjusts the range of the converter terminal voltage to the terminal voltage reference value in real time through the dynamic control equation; and it attenuates the high-frequency harmonic signals during the fault process through the low-pass filter link.

[0107] In one embodiment of the present invention, the cutoff frequency satisfies the following constraint:

[0108] In the formula, The sampling frequency.

[0109] In one embodiment of the present invention, the specific implementation process of the transient voltage support and harmonic suppression strategy is as follows: The reference and actual values ​​of active power and reactive power of the second-phase three-phase voltage source converter are obtained, and the terminal voltage reference value is obtained through the power control loop. The reference value of the terminal voltage and the actual terminal voltage are processed through a voltage control circuit to obtain the reference value of the current. The difference between the current reference value and the actual current is sent to the current control loop, and then combined with the compensation signal of the decoupling loop to obtain the d-axis reference value and q-axis reference value of the converter arm voltage. The d-axis and q-axis reference values ​​are transformed by dq-abc coordinates and then PWM modulated to generate trigger pulses to drive the converter switching transistors.

[0110] In one embodiment of the present invention, the specific implementation process of the constant DC bus voltage control strategy is as follows: The reference and actual values ​​of the DC bus voltage are obtained, and the reference value of the d-axis current of the first three-phase voltage source converter is obtained through the first PI control loop. The reference and actual values ​​of reactive power of the first three-phase voltage source converter are obtained, and the q-axis current reference value is obtained through the second PI control loop. The difference between the d-axis current reference value and the actual d-axis current, and the difference between the q-axis current reference value and the actual q-axis current, are sent to the current control loop respectively. Then, combined with the compensation signal from the decoupling loop and the grid voltage signal, the d-axis reference value and q-axis reference value of the converter arm voltage are obtained. The d-axis and q-axis reference values ​​are transformed by dq-abc coordinates and then PWM modulated to generate trigger pulses to drive the converter switching transistors.

[0111] In one embodiment of the present invention, the parameter data includes topology parameters and electrical operating parameters; The topology parameters are the connection relationships of the two-terminal flexible interconnection devices. The connection relationship is that the first three-phase voltage source converter and the second three-phase voltage source converter are directly coupled through the DC bus and are respectively connected to the AC terminals of distribution network G1 and distribution network G2. Distribution network G1 and distribution network G2 are the two distribution networks that the two three-phase voltage source converters of the two-terminal flexible interconnection devices are respectively connected to. Electrical operating parameters include line reactance, grid frequency, control gain, sampling frequency, voltage amplitude, phase angle difference, and measured values ​​of voltage and current.

[0112] Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the above-described division of functional units and modules is merely an example. In practical applications, the above functions can be assigned to different functional units and modules as needed, that is, the internal structure of the system can be divided into different functional units or modules to complete all or part of the functions described above. The functional units and modules in the embodiments can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit. Furthermore, the specific names of the functional units and modules are only for easy differentiation and are not intended to limit the scope of protection of this application. The specific working process of the units and modules in the above system can be referred to the corresponding process in the foregoing method embodiments, and will not be repeated here.

[0113] Reference Figure 4 This invention also provides a computer device, including: a memory and a processor, and a computer program stored in the memory. When the computer program is executed on the processor, it performs the following steps: Acquire parameter data of the two-end flexible interconnection equipment and the power distribution network; Based on the parameter data, the first three-phase voltage source converter of the double-ended flexible interconnection equipment is controlled by a constant DC bus voltage control strategy, and the second three-phase voltage source converter of the double-ended flexible interconnection equipment is controlled by a transient voltage support and harmonic suppression strategy. Among them, the transient voltage support and harmonic suppression strategy introduces a low-pass filter into the reactive power control stage of the traditional droop control, so as to slow down the output change rate of the reactive power controller through the low-pass filter; the reactive power control stage of the traditional droop control adopts pure proportional control.

[0114] In one embodiment of the present invention, the transfer function of the reactive power control link of the transient voltage support and harmonic suppression strategy is:

[0115] In the formula, The transfer function for the reactive power control loop. This is the reactive power-voltage droop factor. This is the cutoff frequency of the low-pass filter stage. For the Laplace operator; The corresponding dynamic control equations are:

[0116] In the formula, This refers to the actual terminal voltage of the second-phase three-phase voltage source converter. This is the reference value for the terminal voltage of the second-phase three-phase voltage source converter. This is the reference value for reactive power absorption of the second-phase three-phase voltage source converter. This refers to the grid voltage amplitude of distribution network G2, which is the distribution network connected to the second three-phase voltage source converter. The phase angle difference between the distribution network G2 voltage and the terminal voltage of the second three-phase voltage source converter. This refers to the line reactance of distribution network G2.

[0117] In one embodiment of the present invention, when a voltage sag fault occurs in distribution network G2, the second three-phase voltage source converter slows down the output change rate of the reactive power controller through the transfer function of the reactive power control link; it also adjusts the range of the converter terminal voltage to the terminal voltage reference value in real time through the dynamic control equation; and it attenuates the high-frequency harmonic signals during the fault process through the low-pass filter link.

[0118] In one embodiment of the present invention, the cutoff frequency satisfies the following constraint:

[0119] In the formula, The sampling frequency.

[0120] In one embodiment of the present invention, the specific implementation process of the transient voltage support and harmonic suppression strategy is as follows: The reference and actual values ​​of active power and reactive power of the second-phase three-phase voltage source converter are obtained, and the terminal voltage reference value is obtained through the power control loop. The reference value of the terminal voltage and the actual terminal voltage are processed through a voltage control circuit to obtain the reference value of the current. The difference between the current reference value and the actual current is sent to the current control loop, and then combined with the compensation signal of the decoupling loop to obtain the d-axis reference value and q-axis reference value of the converter arm voltage. The d-axis and q-axis reference values ​​are transformed by dq-abc coordinates and then PWM modulated to generate trigger pulses to drive the converter switching transistors.

[0121] In one embodiment of the present invention, the specific implementation process of the constant DC bus voltage control strategy is as follows: The reference and actual values ​​of the DC bus voltage are obtained, and the reference value of the d-axis current of the first three-phase voltage source converter is obtained through the first PI control loop. The reference and actual values ​​of reactive power of the first three-phase voltage source converter are obtained, and the q-axis current reference value is obtained through the second PI control loop. The difference between the d-axis current reference value and the actual d-axis current, and the difference between the q-axis current reference value and the actual q-axis current, are sent to the current control loop respectively. Then, combined with the compensation signal from the decoupling loop and the grid voltage signal, the d-axis reference value and q-axis reference value of the converter arm voltage are obtained. The d-axis and q-axis reference values ​​are transformed by dq-abc coordinates and then PWM modulated to generate trigger pulses to drive the converter switching transistors.

[0122] In one embodiment of the present invention, the parameter data includes topology parameters and electrical operating parameters; The topology parameters are the connection relationships of the two-terminal flexible interconnection devices. The connection relationship is that the first three-phase voltage source converter and the second three-phase voltage source converter are directly coupled through the DC bus and are respectively connected to the AC terminals of distribution network G1 and distribution network G2. Distribution network G1 and distribution network G2 are the two distribution networks that the two three-phase voltage source converters of the two-terminal flexible interconnection devices are respectively connected to. Electrical operating parameters include line reactance, grid frequency, control gain, sampling frequency, voltage amplitude, phase angle difference, and measured values ​​of voltage and current.

[0123] The computer device may be a desktop computer, laptop, handheld computer, or cloud server, etc. This computer device may include, but is not limited to, a processor and memory. Those skilled in the art will understand that... Figure 4 The examples of computer devices are merely examples and do not constitute a limitation on computer devices. They may include more or fewer components than shown in the illustration, or combinations of certain components, or different components. For example, they may also include input / output devices, network access devices, etc.

[0124] The processor referred to can be a Central Processing Unit (CPU), but it can also be other general-purpose processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. A general-purpose processor can be a microprocessor or any conventional processor.

[0125] In some embodiments, the memory may be an internal storage unit of the computer device, such as a hard drive or RAM. In other embodiments, the memory may be an external storage device of the computer device, such as a plug-in hard drive, Smart Media Card (SMC), Secure Digital (SD) card, or Flash Card. Furthermore, the memory may include both internal and external storage units of the computer device. The memory is used to store the operating system, applications, boot loader, data, and other programs, such as the program code of the computer program. The memory can also be used to temporarily store data that has been output or will be output.

[0126] This invention also provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, performs the following steps: Acquire parameter data of the two-end flexible interconnection equipment and the power distribution network; Based on the parameter data, the first three-phase voltage source converter of the double-ended flexible interconnection equipment is controlled by a constant DC bus voltage control strategy, and the second three-phase voltage source converter of the double-ended flexible interconnection equipment is controlled by a transient voltage support and harmonic suppression strategy. Among them, the transient voltage support and harmonic suppression strategy introduces a low-pass filter into the reactive power control stage of the traditional droop control, so as to slow down the output change rate of the reactive power controller through the low-pass filter; the reactive power control stage of the traditional droop control adopts pure proportional control.

[0127] In one embodiment of the present invention, the transfer function of the reactive power control link of the transient voltage support and harmonic suppression strategy is:

[0128] In the formula, The transfer function for the reactive power control loop. This is the reactive power-voltage droop factor. This is the cutoff frequency of the low-pass filter stage. For the Laplace operator; The corresponding dynamic control equations are:

[0129] In the formula, This refers to the actual terminal voltage of the second-phase three-phase voltage source converter. This is the reference value for the terminal voltage of the second-phase three-phase voltage source converter. This is the reference value for reactive power absorption of the second-phase three-phase voltage source converter. This refers to the grid voltage amplitude of distribution network G2, which is the distribution network connected to the second three-phase voltage source converter. The phase angle difference between the distribution network G2 voltage and the terminal voltage of the second three-phase voltage source converter. This refers to the line reactance of distribution network G2.

[0130] In one embodiment of the present invention, when a voltage sag fault occurs in distribution network G2, the second three-phase voltage source converter slows down the output change rate of the reactive power controller through the transfer function of the reactive power control link; it also adjusts the range of the converter terminal voltage to the terminal voltage reference value in real time through the dynamic control equation; and it attenuates the high-frequency harmonic signals during the fault process through the low-pass filter link.

[0131] In one embodiment of the present invention, the cutoff frequency satisfies the following constraint:

[0132] In the formula, The sampling frequency.

[0133] In one embodiment of the present invention, the specific implementation process of the transient voltage support and harmonic suppression strategy is as follows: The reference and actual values ​​of active power and reactive power of the second-phase three-phase voltage source converter are obtained, and the terminal voltage reference value is obtained through the power control loop. The reference value of the terminal voltage and the actual terminal voltage are processed through a voltage control circuit to obtain the reference value of the current. The difference between the current reference value and the actual current is sent to the current control loop, and then combined with the compensation signal of the decoupling loop to obtain the d-axis reference value and q-axis reference value of the converter arm voltage. The d-axis and q-axis reference values ​​are transformed by dq-abc coordinates and then PWM modulated to generate trigger pulses to drive the converter switching transistors.

[0134] In one embodiment of the present invention, the specific implementation process of the constant DC bus voltage control strategy is as follows: The reference and actual values ​​of the DC bus voltage are obtained, and the reference value of the d-axis current of the first three-phase voltage source converter is obtained through the first PI control loop. The reference and actual values ​​of reactive power of the first three-phase voltage source converter are obtained, and the q-axis current reference value is obtained through the second PI control loop. The difference between the d-axis current reference value and the actual d-axis current, and the difference between the q-axis current reference value and the actual q-axis current, are sent to the current control loop respectively. Then, combined with the compensation signal from the decoupling loop and the grid voltage signal, the d-axis reference value and q-axis reference value of the converter arm voltage are obtained. The d-axis and q-axis reference values ​​are transformed by dq-abc coordinates and then PWM modulated to generate trigger pulses to drive the converter switching transistors.

[0135] In one embodiment of the present invention, the parameter data includes topology parameters and electrical operating parameters; The topology parameters are the connection relationships of the two-terminal flexible interconnection devices. The connection relationship is that the first three-phase voltage source converter and the second three-phase voltage source converter are directly coupled through the DC bus and are respectively connected to the AC terminals of distribution network G1 and distribution network G2. Distribution network G1 and distribution network G2 are the two distribution networks that the two three-phase voltage source converters of the two-terminal flexible interconnection devices are respectively connected to. Electrical operating parameters include line reactance, grid frequency, control gain, sampling frequency, voltage amplitude, phase angle difference, and measured values ​​of voltage and current.

[0136] In this embodiment, if the integrated unit is implemented as a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, all or part of the processes in the methods of the above embodiments can be implemented by a computer program instructing related hardware. The computer program can be stored in a computer-readable storage medium, and when executed by a processor, it can implement the steps of the various method embodiments described above. The computer program includes computer program code, which can be in the form of source code, object code, executable files, or certain intermediate forms. The computer-readable medium can include at least: any entity or device capable of carrying computer program code to a photographing device / terminal device, a recording medium, a computer memory, a read-only memory (ROM), a random access memory (RAM), an electrical carrier signal, a telecommunication signal, and a software distribution medium. Examples include USB flash drives, portable hard drives, magnetic disks, or optical disks. In some jurisdictions, according to legislation and patent practice, computer-readable media cannot be electrical carrier signals or telecommunication signals.

[0137] This invention provides a computer program product, including a computer program that, when executed by a processor, performs the following steps: Acquire parameter data of the two-end flexible interconnection equipment and the power distribution network; Based on the parameter data, the first three-phase voltage source converter of the double-ended flexible interconnection equipment is controlled by a constant DC bus voltage control strategy, and the second three-phase voltage source converter of the double-ended flexible interconnection equipment is controlled by a transient voltage support and harmonic suppression strategy. Among them, the transient voltage support and harmonic suppression strategy introduces a low-pass filter into the reactive power control stage of the traditional droop control, so as to slow down the output change rate of the reactive power controller through the low-pass filter; the reactive power control stage of the traditional droop control adopts pure proportional control.

[0138] In one embodiment of the present invention, the transfer function of the reactive power control link of the transient voltage support and harmonic suppression strategy is:

[0139] In the formula, The transfer function for the reactive power control loop. This is the reactive power-voltage droop factor. This is the cutoff frequency of the low-pass filter stage. For the Laplace operator; The corresponding dynamic control equations are:

[0140] In the formula, This refers to the actual terminal voltage of the second-phase three-phase voltage source converter. This is the reference value for the terminal voltage of the second-phase three-phase voltage source converter. This is the reference value for reactive power absorption of the second-phase three-phase voltage source converter. This refers to the grid voltage amplitude of distribution network G2, which is the distribution network connected to the second three-phase voltage source converter. The phase angle difference between the distribution network G2 voltage and the terminal voltage of the second three-phase voltage source converter. This refers to the line reactance of distribution network G2.

[0141] In one embodiment of the present invention, when a voltage sag fault occurs in distribution network G2, the second three-phase voltage source converter slows down the output change rate of the reactive power controller through the transfer function of the reactive power control link; it also adjusts the range of the converter terminal voltage to the terminal voltage reference value in real time through the dynamic control equation; and it attenuates the high-frequency harmonic signals during the fault process through the low-pass filter link.

[0142] In one embodiment of the present invention, the cutoff frequency satisfies the following constraint:

[0143] In the formula, The sampling frequency.

[0144] In one embodiment of the present invention, the specific implementation process of the transient voltage support and harmonic suppression strategy is as follows: The reference and actual values ​​of active power and reactive power of the second-phase three-phase voltage source converter are obtained, and the terminal voltage reference value is obtained through the power control loop. The reference value of the terminal voltage and the actual terminal voltage are processed through a voltage control circuit to obtain the reference value of the current. The difference between the current reference value and the actual current is sent to the current control loop, and then combined with the compensation signal of the decoupling loop to obtain the d-axis reference value and q-axis reference value of the converter arm voltage. The d-axis and q-axis reference values ​​are transformed by dq-abc coordinates and then PWM modulated to generate trigger pulses to drive the converter switching transistors.

[0145] In one embodiment of the present invention, the specific implementation process of the constant DC bus voltage control strategy is as follows: The reference and actual values ​​of the DC bus voltage are obtained, and the reference value of the d-axis current of the first three-phase voltage source converter is obtained through the first PI control loop. The reference and actual values ​​of reactive power of the first three-phase voltage source converter are obtained, and the q-axis current reference value is obtained through the second PI control loop. The difference between the d-axis current reference value and the actual d-axis current, and the difference between the q-axis current reference value and the actual q-axis current, are sent to the current control loop respectively. Then, combined with the compensation signal from the decoupling loop and the grid voltage signal, the d-axis reference value and q-axis reference value of the converter arm voltage are obtained. The d-axis and q-axis reference values ​​are transformed by dq-abc coordinates and then PWM modulated to generate trigger pulses to drive the converter switching transistors.

[0146] In one embodiment of the present invention, the parameter data includes topology parameters and electrical operating parameters; The topology parameters are the connection relationships of the two-terminal flexible interconnection devices. The connection relationship is that the first three-phase voltage source converter and the second three-phase voltage source converter are directly coupled through the DC bus and are respectively connected to the AC terminals of distribution network G1 and distribution network G2. Distribution network G1 and distribution network G2 are the two distribution networks that the two three-phase voltage source converters of the two-terminal flexible interconnection devices are respectively connected to. Electrical operating parameters include line reactance, grid frequency, control gain, sampling frequency, voltage amplitude, phase angle difference, and measured values ​​of voltage and current.

[0147] In the above embodiments, the descriptions of each embodiment have different focuses. For parts that are not described in detail or recorded in a certain embodiment, please refer to the relevant descriptions of other embodiments.

[0148] Those skilled in the art will recognize that the units and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of this application.

[0149] In the embodiments disclosed in this application, it should be understood that the disclosed devices / terminal equipment and methods can be implemented in other ways. For example, the device / terminal equipment embodiments described above are merely illustrative. For instance, the division of modules or units is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the displayed or discussed mutual coupling or direct coupling or communication connection may be through some interfaces; the indirect coupling or communication connection between devices or units may be electrical, mechanical, or other forms.

[0150] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A flexible interconnection control method for transient voltage support and harmonic suppression, characterized in that, Includes the following steps: Acquire parameter data of the two-end flexible interconnection equipment and the power distribution network; Based on the parameter data, the first three-phase voltage source converter of the double-ended flexible interconnection equipment is controlled by a constant DC bus voltage control strategy, and the second three-phase voltage source converter of the double-ended flexible interconnection equipment is controlled by a transient voltage support and harmonic suppression strategy. The transient voltage support and harmonic suppression strategy involves introducing a low-pass filter into the reactive power control stage of the traditional droop control, so as to slow down the output change rate of the reactive power controller through the low-pass filter; the reactive power control stage of the traditional droop control adopts pure proportional control.

2. The flexible interconnection control method for transient voltage support and harmonic suppression according to claim 1, characterized in that, The transfer function of the reactive power control element of the transient voltage support and harmonic suppression strategy is as follows: In the formula, The transfer function for the reactive power control loop. This is the reactive power-voltage droop factor. The cutoff frequency of the low-pass filter stage is [the cutoff frequency of the low-pass filter stage]. For the Laplace operator; The corresponding dynamic control equations are: In the formula, This refers to the actual terminal voltage of the second-phase three-phase voltage source converter. This is the reference value for the terminal voltage of the second-phase three-phase voltage source converter. This is the reference value for reactive power absorption of the second-phase three-phase voltage source converter. This refers to the grid voltage amplitude of distribution network G2, which is the distribution network connected to the second three-phase voltage source converter. The phase angle difference between the distribution network G2 voltage and the terminal voltage of the second three-phase voltage source converter. This refers to the line reactance of distribution network G2.

3. The flexible interconnection control method for transient voltage support and harmonic suppression according to claim 2, characterized in that, When a voltage dip fault occurs in distribution network G2, the second and third phase voltage source converters slow down the output change rate of the reactive power controller through the transfer function of the reactive power control link; they also adjust the range of the converter terminal voltage to the terminal voltage reference value in real time through the dynamic control equation; and they attenuate high-frequency harmonic signals during the fault process through the low-pass filter link.

4. The flexible interconnection control method for transient voltage support and harmonic suppression according to claim 2, characterized in that, The cutoff frequency satisfies the following constraint: In the formula, The sampling frequency.

5. The flexible interconnection control method for transient voltage support and harmonic suppression according to claim 1 or 2, characterized in that, The specific implementation process of the transient voltage support and harmonic suppression strategy is as follows: The reference and actual values ​​of active power and reactive power of the second and third phase voltage source converter are obtained, and the terminal voltage reference value is obtained through the power control loop. The reference terminal voltage value and the actual terminal voltage are processed by a voltage control circuit to obtain the current reference value; The difference between the current reference value and the actual current is sent to the current control loop, and then combined with the compensation signal of the decoupling loop to obtain the d-axis reference value and q-axis reference value of the converter arm voltage. The d-axis and q-axis reference values ​​are transformed by dq-abc coordinates and then PWM modulated to generate trigger pulses to drive the converter switching transistors.

6. The flexible interconnection control method for transient voltage support and harmonic suppression according to claim 1, characterized in that, The specific implementation process of the constant DC bus voltage control strategy is as follows: The reference and actual values ​​of the DC bus voltage are obtained, and the reference value of the d-axis current of the first three-phase voltage source converter is obtained through the first PI control loop. The reference value and actual value of reactive power of the first three-phase voltage source converter are obtained, and the q-axis current reference value is obtained through the second PI control loop. The difference between the d-axis current reference value and the actual d-axis current, and the difference between the q-axis current reference value and the actual q-axis current, are respectively sent to the current control loop. Then, combined with the compensation signal of the decoupling loop and the grid voltage signal, the d-axis reference value and q-axis reference value of the converter arm voltage are obtained. The d-axis and q-axis reference values ​​are transformed by dq-abc coordinates and then PWM modulated to generate trigger pulses to drive the converter switching transistors.

7. The flexible interconnection control method for transient voltage support and harmonic suppression according to claim 1, characterized in that, The parameter data includes topology parameters and electrical operating parameters; The topology parameters refer to the connection relationship of the two-terminal flexible interconnection equipment. The connection relationship is that the first three-phase voltage source converter and the second three-phase voltage source converter are directly coupled through the DC bus and are respectively connected to the AC terminals of distribution network G1 and distribution network G2. Distribution network G1 and distribution network G2 are the two distribution networks respectively connected to the two three-phase voltage source converters of the two-terminal flexible interconnection equipment. The electrical operating parameters include line reactance, grid frequency, control gain, sampling frequency, voltage amplitude, phase angle difference, and measured values ​​of voltage and current.

8. A flexible interconnection control device with transient voltage support and harmonic suppression, characterized in that, include: The data acquisition module is used to acquire parameter data of the two-end flexible interconnection equipment and the power distribution network; The interconnection control module is used to control the first three-phase voltage source converter of the double-ended flexible interconnection device based on the parameter data, using a constant DC bus voltage control strategy, and to control the second three-phase voltage source converter of the double-ended flexible interconnection device using a transient voltage support and harmonic suppression strategy. The transient voltage support and harmonic suppression strategy involves introducing a low-pass filter into the reactive power control stage of the traditional droop control, so as to slow down the output change rate of the reactive power controller through the low-pass filter; the reactive power control stage of the traditional droop control adopts pure proportional control.

9. A computer device, characterized in that, The device includes a processor and a memory: The memory is used to store computer programs and send the instructions of the computer programs to the processor; The processor executes, according to the instructions of the computer program, a flexible interconnection control method for transient voltage support and harmonic suppression as described in any one of claims 1-7.

10. A computer-readable storage medium, characterized in that, The computer-readable storage medium stores a computer program that, when executed by a processor, implements a network-type flexible interconnection control method for transient voltage support and harmonic suppression as described in any one of claims 1-7.

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