Networking-direct current voltage stabilization fusion control method and system

Abstract

The invention belongs to the technical field of power electronic control, and particularly relates to a networking-direct current voltage stabilization fusion control method and system. The converter is enabled to respond to both the alternating current side and the direct current side through an alternating current and direct current double droop strategy, and the converter is enabled to quickly respond to a direct current droop power instruction by introducing direct current power-angle prediction feed-forward and direct current power-current prediction feed-forward so as to ensure that the voltage of a direct current bus is stable. After the control method is used, the modes of all the converters of the flexible DC system are not distinguished, frequency modulation and voltage regulation response is made on alternating voltage at all ports, and the maintenance effect on a power grid is enhanced. The full-port maintenance DC bus voltage is stable, and the stability is enhanced.

Description

Technical Field

[0001] The present invention belongs to the technical field of power electronic control, and in particular relates to a grid-building-DC voltage stabilization fusion control method and system. Background Art

[0002] As an advanced power transmission technology, the flexible direct current transmission system connects multiple AC power grids through converters, realizing efficient and flexible energy exchange between power grids. When the converter adopts a grid-forming control strategy, it can automatically adjust the frequency and voltage to provide stable support for the power grid.

[0003] However, referring to Figure 1 In a traditional multi-port meshed flexible DC transmission system, in order to establish a stable DC bus voltage, at least one port needs to operate in a stable DC voltage mode. This means that at least one port cannot simultaneously achieve meshing operation to automatically support the AC grid it is connected to. This limitation leads to a reduction in the system's fault tolerance, because if the port supporting the DC bus fails, the entire system may collapse.

[0004] In addition, since traditional systems need to switch between different modes, they require more complex coordination control strategies. This not only increases the complexity and cost of the system, but may also affect the stability and response speed of the system. More specifically, when power fluctuations occur at the networking port, all power changes need to be borne by the port running in the steady direct voltage mode. This unbalanced power distribution method further reduces the stability of the system and may lead to a decline in system performance.

[0005] In summary, the traditional multi-port grid-type flexible DC transmission system has obvious deficiencies in grid operation and DC bus support. In order to improve the fault tolerance, stability and flexibility of the system, a new control method is needed to optimize the operation of the system. Summary of the invention

[0006] In order to overcome the problems in the prior art, the present invention proposes a grid-building-DC voltage stabilization fusion control method and system.

[0007] The technical solution of the present invention to solve the above technical problems is as follows:

[0008] In a first aspect, the present invention provides a grid-building-DC voltage stabilization fusion control method, wherein a converter is connected between an AC grid and a DC power transmission system, and the grid-building-DC voltage stabilization fusion in the transformer comprises the following steps:

[0009] According to the AC droop characteristics and the DC droop characteristics, the AC droop power and the DC droop power are calculated respectively; the AC droop power, the DC droop power and the active power setting value are superimposed to obtain a final power reference value, i.e., a DC active power instruction;

[0010] Based on the DC active power command, predict the angle change required by the DC active power command, i.e., the feedforward angle, and superimpose the feedforward angle on the converter output angle to obtain a reference voltage angle; and calculate the reference voltage amplitude through the VSG reactive loop;

[0011] The difference between the reference voltage and the actual voltage is calculated, and the analog voltage of the virtual impedance is superimposed thereon, and the reference current of the current inner loop is obtained through PI modulation; based on the DC active power instruction, the current change required for the DC active power instruction, i.e., the feedforward current, is predicted; the feedforward current is superimposed on the reference current of the current inner loop to obtain an adjusted reference current, and after modulation by the PI controller, a modulation voltage for PWM modulation is obtained, and the modulation voltage is applied to the PWM modulator to generate a final output voltage for driving the converter, thereby realizing the control of the power flow between the AC power grid and the DC power transmission system.

[0012] Furthermore, the AC droop power and the DC droop power are calculated according to the AC droop characteristics and the DC droop characteristics respectively; the AC droop power, the DC droop power and the active power setting value are superimposed to obtain a final power reference value, that is, a DC active power instruction, and the calculation formula is as follows:

[0013]

[0014] In the formula, K wf is the AC droop coefficient, f n is the rated frequency, f is the actual frequency; K wdc is the DC droop coefficient, U dc is the actual DC voltage, U dcn is the rated DC voltage; P setf is the AC droop power, P setdc is the DC droop power; P set The power command issued by the coordination controller is the active power setting value; P ref is the final active power reference value, that is, the DC active power instruction.

[0015] Furthermore, the calculation formula of the feedforward angle is:

[0016]

[0017] In the formula, θ k is the predicted feedforward angle, P setdc is the DC droop power, Lgrid is the equivalent impedance of the power grid, L virtual is the virtual impedance in the voltage loop, U d is the d-axis component of the grid-side voltage.

[0018] Furthermore, the calculation formula of the feedforward current is:

[0019]

[0020] In the formula, i dk is the predicted feedforward current, P setdc is the DC droop power, U d is the d-axis component of the grid-side voltage.

[0021] In a second aspect, the present invention further provides a grid-building-DC voltage stabilization fusion control system, comprising a converter, an AC grid and a DC power transmission system, wherein the converter is connected between the AC grid and the DC power transmission system;

[0022] All converters include a grid-building-DC voltage stabilization fusion control unit, which includes: an AC-DC dual droop calculation module, a DC active power command-angle prediction feedforward calculation module, a VSG active power-angle calculation module, a VSG reactive power-voltage calculation module, a DC active power command-current prediction feedforward calculation module and a voltage-current inner loop control module;

[0023] The AC / DC dual droop calculation module is used to calculate the AC droop power and the DC droop power according to the AC droop characteristics and the DC droop characteristics respectively; superimpose the AC droop power, the DC droop power and the active power setting value to obtain a final power reference value, i.e., a DC active power instruction;

[0024] The DC active power instruction-angle prediction feedforward calculation module predicts the angle change required for the DC active power instruction, i.e., the feedforward angle, based on the DC active power instruction;

[0025] A VSG active power-angle calculation module, used to obtain the converter output angle, superimpose the feedforward angle on the converter output angle, and obtain a reference voltage angle;

[0026] The VSG reactive power-voltage calculation module is used to calculate the reference voltage amplitude through the VSG reactive power loop;

[0027] The DC active power instruction-current prediction feedforward calculation module is used to predict the current change required for the DC active power instruction, that is, the feedforward current, based on the DC active power instruction;

[0028] The voltage-current inner loop control module is used to calculate the difference between the reference voltage and the actual voltage, and superimpose the analog voltage of the virtual impedance thereon, and obtain the reference current of the current inner loop through PI modulation; the feedforward current is superimposed on the reference current of the current inner loop to obtain an adjusted reference current, and after modulation by the PI controller, a modulation voltage for PWM modulation is obtained, and the modulation voltage is applied to the PWM modulator to generate a final output voltage for driving the converter, thereby realizing the control of the power flow between the AC power grid and the DC power transmission system.

[0029] Furthermore, in the AC / DC dual droop calculation module, the DC active power command calculation formula is as follows:

[0030]

[0031] In the formula, K wf is the AC droop coefficient, f n is the rated frequency, f is the actual frequency; K wdc is the DC droop coefficient, U dc is the actual DC voltage, U dcn is the rated DC voltage; P setf is the AC droop power, P setdc is the DC droop power; P set The power command issued by the coordination controller is the active power setting value; P ref is the final active power reference value, that is, the DC active power instruction.

[0032] Furthermore, in the DC active power command-angle prediction feedforward calculation module, the feedforward angle is calculated as follows:

[0033]

[0034] In the formula, θ k is the predicted feedforward angle, P setdc is the DC droop power, L grid is the equivalent impedance of the power grid, L virtual is the virtual impedance in the voltage loop, U d is the d-axis component of the grid-side voltage.

[0035] Furthermore, in the DC active power command-current prediction feedforward calculation module, the feedforward current is calculated as follows:

[0036]

[0037] In the formula, i dk is the predicted feedforward current, P setdc is the DC droop power, U d is the d-axis component of the grid-side voltage.

[0038] Compared with the prior art, the present invention has the following technical effects:

[0039] The present invention proposes a grid-building-DC voltage stabilization fusion control method, which enables the converter to respond to both sides of the AC and DC through the AC and DC dual droop strategy, and enables the converter to respond quickly to the DC droop power command by introducing DC power-angle prediction feedforward and DC power-current prediction feedforward to ensure the stability of the DC bus voltage. After using this control method, all converters in the flexible DC system do not distinguish between modes, and respond to the AC voltage with frequency and voltage modulation at all ports, thereby enhancing the maintenance effect on the power grid. The DC bus voltage is maintained stable at all ports, which enhances stability. The coordinated control strategy does not require mode switching and rapid action, thereby reducing system complexity. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] In order to more clearly illustrate the technical solutions and advantages in the embodiments of the present invention or the prior art, the drawings required for use in the embodiments or the prior art descriptions are briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0041] Figure 1 This is the topological structure diagram of the traditional method;

[0042] Figure 2 It is a topological structure diagram of the present invention;

[0043] Figure 3 is the topology diagram of the three-level converter;

[0044] Figure 4 It is the VSG active power-angle and VSG reactive power-voltage control diagram of the present invention;

[0045] Figure 5 This is the voltage and current inner loop control diagram of the present invention. DETAILED DESCRIPTION

[0046] In order to further explain the technical means and effects taken by the present invention to achieve the predetermined invention purpose, the specific implementation methods, structures, features and effects of the technical solutions proposed by the present invention are described in detail below in conjunction with the accompanying drawings and preferred embodiments. The specific features, structures or characteristics in one or more embodiments may be combined in any suitable form. Unless otherwise defined, all technical and scientific terms used in the present invention have the same meaning as those commonly understood by technicians in the technical field of the present invention.

[0047] In one embodiment of the present invention, referring to Figure 2-Figure 5, a grid-building-DC voltage stabilization fusion control method is provided, in which a converter is connected between an AC grid and a DC transmission system, and the grid-building-DC voltage stabilization fusion control method in the transformer includes the following steps:

[0048] Step 100: Calculate AC droop power and DC droop power according to AC droop characteristics and DC droop characteristics respectively; superimpose the AC droop power, the DC droop power and the active power setting value to obtain a final power reference value, i.e., a DC active power instruction;

[0049] Step 200: Based on the DC active power command, predict the angle change required for the DC active power command, that is, the feedforward angle, and superimpose the feedforward angle on the converter output angle to obtain a reference voltage angle;

[0050] Step 300: Calculate the reference voltage amplitude through the VSG (virtual synchronous generator) reactive loop;

[0051] Step 400: Calculate the difference between the reference voltage and the actual voltage, and superimpose the analog voltage of the virtual impedance thereon, and obtain the reference current of the current inner loop through PI (Proportional-Integral) modulation; Based on the DC active power instruction, predict the current change required by the DC active power instruction, that is, the feedforward current; Superimpose the feedforward current on the reference current of the current inner loop to obtain an adjusted reference current, and after modulation by the PI controller, obtain a modulation voltage for PWM modulation, and apply the modulation voltage to a PWM modulator (pulse width modulator) to generate a final output voltage for driving the converter, thereby realizing the control of power flow between the AC power grid and the DC power transmission system.

[0052] The following is a detailed explanation of each of the above steps:

[0053] In step 100, AC droop power and DC droop power are calculated according to AC droop characteristics and DC droop characteristics respectively; the AC droop power, the DC droop power and the active power setting value are superimposed to obtain a final power reference value, i.e., a DC active power instruction.

[0054] The calculation formula of DC active power command is as follows:

[0055]

[0056] In the formula, K wf is the AC droop coefficient, f n is the rated frequency, f is the actual frequency; K wdc is the DC droop coefficient, U dc is the actual DC voltage, U dcn is the rated DC voltage; P setfis the AC droop power, P setdc is the DC droop power; P set The power command issued by the coordination controller is the active power setting value; P ref is the final active power reference value, that is, the DC active power instruction.

[0057] The AC droop coefficient is calculated according to the primary frequency modulation time constant in the same way as in conventional grid construction, and the DC droop coefficient should be selected according to the acceptable DC voltage fluctuation.

[0058] After obtaining the reference power, the active reference value is input into the synchronous generator equation to gradually change the angle to output the corresponding power.

[0059] The most common second-order equivalent equation for a synchronous generator is:

[0060]

[0061] Where P is the actual output power, w n is the rated frequency, w ref is the system output frequency, and the reference voltage angle will be obtained after the subsequent integration of the frequency. w is the actual system frequency calculated by sampling; J is the inertia, and D is the damping, which corresponds to the parameters of the actual generator.

[0062] Step 200: Based on the DC active power command, predict the angle change required for the DC active power command, that is, the feedforward angle, and superimpose the feedforward angle on the converter output angle to obtain a reference voltage angle.

[0063] In order to improve the response speed to the DC side voltage, the angle required to achieve the DC droop power is predicted and fed forward.

[0064] In order to calculate the feedforward angle, it is necessary to identify the grid impedance first. Here is an example of a conventional method, the reactive power injection method. A small disturbance is superimposed on the reference voltage for 0.5s. The actual voltage and q-axis current (corresponding to reactive power) before and after the disturbance injection are compared. When the q-axis voltage U is ignored, q Based on the premise of the line resistance, the impedance is calculated according to the following formula:

[0065]

[0066] Where U d is the d-axis voltage during the disturbance injection period, i q is the q-axis current during the disturbance injection period, U d_1 is the d-axis voltage before disturbance injection, i q_1 is the q-axis current before the disturbance injection, and the grid impedance L is identified grid .

[0067] Perform feedforward angle prediction calculation according to the calculation formula:

[0068]

[0069] In the formula, θ k is the predicted feedforward angle, P setdc is the DC droop power, L grid is the equivalent impedance of the power grid, L virtual is the virtual impedance in the voltage loop, U d is the d-axis component of the grid-side voltage.

[0070] Step 300: Calculate the reference voltage amplitude through the VSG reactive loop;

[0071] The feed-forward angle is superimposed on the output angle of the converter to improve the response speed to the DC bus voltage.

[0072] The reference voltage amplitude of the converter is calculated by the conventional VSG reactive loop, and voltage-reactive droop is performed, and the reactive command value is superimposed to obtain the reference reactive power, which is integrated to obtain the d-axis reference voltage Ud.

[0073] At this point, the outer loop calculation of the network is completed, and the reference voltage angle and reference voltage amplitude are obtained, thereby obtaining the reference voltage.

[0074] Step 300: Calculate the difference between the reference voltage and the actual voltage, and superimpose the analog voltage of the virtual impedance thereon, and obtain the reference current of the current inner loop through PI modulation; predict the current change required by the DC active power instruction based on the DC active power instruction, that is, the feedforward current; superimpose the feedforward current on the reference current of the current inner loop to obtain an adjusted reference current, and after modulation by the PI controller, obtain a modulation voltage for PWM modulation, apply the modulation voltage to the PWM modulator, generate a final output voltage for driving the converter, thereby realizing the control of the power flow between the AC power grid and the DC power transmission system.

[0075] Perform voltage and current inner loop calculation. The d-axis is similar to the q-axis. Subtract the actual voltage from the reference voltage, and superimpose the analog voltage calculation of the virtual impedance on it. The reference current is obtained through PI modulation. In order to speed up the response to the DC voltage, the "DC active power command-current prediction feedforward" calculation is performed to predict the current change required for the power and superimpose it on the d-axis reference current of the current inner loop.

[0076] The feedforward current calculation formula is:

[0077]

[0078] In the formula, i dk is the predicted feedforward current, P setdcis the DC droop power, U d is the d-axis component of the voltage.

[0079] The current is then modulated by PI to obtain a modulated voltage, which is then applied to PWM modulation for final voltage output. At this point, the control process ends.

[0080] Based on the same inventive concept, an embodiment of the present invention also provides a network-DC voltage stabilization fusion control system for implementing the network-DC voltage stabilization fusion control method involved above. The implementation scheme for solving the problem provided by the system is similar to the implementation scheme recorded in the above method, so the specific limitations in one or more system embodiments provided below can refer to the above limitations on a network-DC voltage stabilization fusion control method, which will not be repeated here.

[0081] All converters in the flexible DC system use the grid-building-DC voltage stabilization fusion control algorithm, which responds to voltage changes on both the AC and DC sides at the same time, that is, the same control mode maintains the voltage on both sides at the same time. The algorithm responds much faster to the DC side voltage than the AC side, thus giving priority to ensuring the stability of the DC bus voltage. The coordinated controller does not need to set the mode, but only sets the power for the steady-state power transmission target. The converter automatically responds to the transient process of voltage fluctuations according to the grid-building algorithm.

[0082] In one embodiment, referring to Figure 2 , provides a flexible DC system with full-port networking. The converter is connected between the AC grid and the DC transmission system. All converters include a networking-DC voltage stabilization fusion control unit. Each converter tries to maintain the voltage on both the AC and DC sides at the same time. Therefore, the coordination controller can adjust the power setting according to the load rate of different substations in just a few seconds, and ensure that the sum of the power sent to all converters is 0. The transient response is performed by the converter itself. The converter can use a common three-level inverter, and its topology is as follows Figure 3 shown.

[0083] The network-DC voltage stabilization fusion control unit includes: an AC-DC dual droop calculation module, a DC active power command-angle prediction feedforward calculation module, a VSG active power-angle calculation module, a VSG reactive power-voltage calculation module, a DC active power command-current prediction feedforward calculation module and a voltage-current inner loop control module;

[0084] A grid-building-DC voltage stabilization fusion control system comprises a converter, an AC power grid and a DC power transmission system, wherein the converter is connected between the AC power grid and the DC power transmission system; all converters comprise a grid-building-DC voltage stabilization fusion control unit, wherein the grid-building-DC voltage stabilization fusion control unit comprises: an AC / DC dual droop calculation module, a DC active power command-angle prediction feedforward calculation module, a VSG active power-angle calculation module, a VSG reactive power-voltage calculation module, a DC active power command-current prediction feedforward calculation module and a voltage-current inner loop control module.

[0085] Since the grid control is a voltage source characteristic, the active power is gradually changed by integrating the changing angle, and the response speed is much lower than the traditional voltage stabilization control that directly controls the current. Although DC droop is introduced, the converter's response speed to the DC voltage is too slow, which will inevitably cause bus voltage oscillation. To solve this problem, the "DC active power command-angle prediction feedforward calculation module" and "DC active power command-current prediction feedforward calculation module" are further proposed to improve the response speed.

[0086] In this embodiment, the AC / DC dual droop calculation module is used to calculate the AC droop power and the DC droop power according to the AC droop characteristics and the DC droop characteristics respectively; the AC droop power, the DC droop power and the active power setting value are superimposed to obtain a final power reference value, that is, a DC active power instruction;

[0087] Specifically, AC droop control: a frequency offset is calculated according to the rated frequency and the actual frequency, and the frequency offset is multiplied by the AC droop coefficient to obtain the AC droop power;

[0088] DC droop control: a DC voltage offset is calculated based on the actual DC voltage and the rated DC voltage, and the DC voltage offset is multiplied by the DC droop coefficient to obtain the DC droop power;

[0089] The AC droop power is superimposed on the DC droop power, and then on the active power setting value to obtain the final active power reference value, that is, the DC active power instruction. The final active power reference value is input into the synchronous generator equation to gradually change the angle to output the corresponding power.

[0090] The DC active power command is calculated in the AC and DC dual droop calculation module, and the calculation formula is as follows:

[0091]

[0092] In the formula, K wf is the AC droop coefficient, f n is the rated frequency, f is the actual frequency; K wdc is the DC droop coefficient, U dc is the actual DC voltage, U dcnis the rated DC voltage; P setf is the AC droop power, P setdc is the DC droop power; P set The power command issued by the coordination controller is the active power setting value; P ref is the final active power reference value, that is, the DC active power instruction.

[0093] The AC droop coefficient is calculated according to the primary frequency modulation time constant in the same way as in conventional grid construction, and the DC droop coefficient should be selected according to the acceptable DC voltage fluctuation.

[0094] There are various equivalent ways for synchronous generators, so their equations can be in many forms. The most common second-order equivalent equation is:

[0095]

[0096] Where P is the actual output power, w n is the rated frequency, w ref is the system output frequency, and the reference voltage angle will be obtained after the subsequent integration of this frequency. w is the actual system frequency calculated by sampling. J is the inertia, and D is the damping, which corresponds to the parameters of the actual generator and is selected according to the characteristics of the generator to be simulated.

[0097] In this embodiment, the DC active power instruction-angle prediction feedforward calculation module predicts the angle change required for the DC active power instruction, that is, the feedforward angle, based on the DC active power instruction.

[0098] Specifically, in order to improve the response speed to the DC side voltage, the angle required to achieve the DC droop power is predicted and fed forward.

[0099] In order to calculate the feedforward angle, it is necessary to identify the grid impedance first. Here is an example of a conventional method, the reactive power injection method. A small disturbance is superimposed on the reference voltage for 0.5s. The actual voltage and q-axis current (corresponding to reactive power) before and after the disturbance injection are compared. When the q-axis voltage U is ignored, q Based on the premise of the line resistance, the impedance is calculated according to the following formula:

[0100]

[0101] Where U d 、i q is the d-axis voltage and q-axis current during the disturbance injection period, U d_1 、i q_1 The d-axis voltage and q-axis current before the disturbance injection are identified to obtain the grid impedance L grid .

[0102] Perform feedforward angle prediction calculation according to the calculation formula:

[0103]

[0104] In the formula, θ k is the predicted feedforward angle, P setdc is the DC droop power, L grid is the equivalent impedance of the power grid, L virtual is the virtual impedance in the voltage loop, U d is the d-axis component of the grid-side voltage.

[0105] In this embodiment, the VSG active power-angle calculation module is used to obtain the converter output angle, and superimpose the feedforward angle on the converter output angle to obtain a reference voltage angle.

[0106] In this embodiment, the VSG reactive-voltage calculation module is used to calculate the reference value of reactive power through the VSG reactive loop, perform voltage-reactive droop control, superimpose the reactive command value (optional) issued by the coordination controller on the reactive power reference value to obtain the final reference reactive power, and integrate the final reference reactive power to obtain the reference voltage.

[0107] In this embodiment, the DC active power command-current prediction feedforward calculation module is used to predict the current change required for the DC active power command, that is, the feedforward current, based on the DC active power command.

[0108] Specifically, the feedforward current calculation formula is:

[0109]

[0110] In the formula, i dk is the predicted feedforward current, P setdc is the DC droop power, U d is the d-axis component of the grid-side voltage.

[0111] In this embodiment, the voltage-current inner loop control module is used to calculate the difference between the reference voltage and the actual voltage, and superimpose the analog voltage of the virtual impedance thereon, and obtain the reference current of the current inner loop through PI modulation; the feedforward current is superimposed on the reference current of the current inner loop to obtain an adjusted reference current, and after modulation by the PI controller, a modulation voltage for PWM modulation is obtained, and the modulation voltage is applied to the PWM modulator to generate a final output voltage for driving the converter, thereby realizing the control of the power flow between the AC power grid and the DC power transmission system.

[0112] The d-axis is similar to the q-axis. The actual voltage is subtracted from the reference voltage, and the analog voltage of the virtual impedance is superimposed on it. The reference current is obtained through PI modulation. In order to speed up the response to the DC voltage, the DC active power command-current prediction feedforward calculation module is calculated and the current change required for the power is predicted and superimposed on the d-axis reference current of the current inner loop. The current is then modulated by PI to obtain the modulation voltage, which is applied to PWM modulation for the final voltage output. At this point, the control process ends.

[0113] It is worth noting that the voltage component U q , direct axis voltage component U d , the calculation formula is as follows:

[0114] Clark transformation is performed on the three-phase voltage signal and three-phase current signal output by the inverter to obtain the two-phase voltage U in the αβ coordinate system. α U β , two-phase current I α I β , specifically:

[0115] U α =1 / 3*(2*U a -U b -U c )

[0116]

[0117] I α =1 / 3*(2*I a -I b -I c )

[0118]

[0119] Among them, U a , U b , U c is the three-phase voltage signal output by the three-level inverter, I a ,I b ,I c It is the three-phase current signal output by the three-level inverter;

[0120] Perform Park transformation on the two-phase voltage and two-phase current in the αβ coordinate system to obtain the actual direct-axis voltage component U d , current component I d and the quadrature axis voltage component U q , current component I q , specifically:

[0121] U d =U α*cos(θ)+U β *sin(θ)

[0122] U q =-U α *sin(θ)+U β *cos(θ)

[0123] I d =I α *cos(φ)+I β *sin(φ)

[0124] I q =-I α *sin(φ)+I β *cos(φ)

[0125] Where θ is the current voltage angle, and φ is the current current angle.

[0126] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. Such modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention, and should be included in the protection scope of the present invention.

Claims

1. A network construction-DC voltage stabilization fusion control method, characterized in that: The converter is connected between the AC power grid and the DC power transmission system. The grid-building and DC voltage stabilization fusion in the transformer includes the following steps: According to the AC droop characteristics and the DC droop characteristics, the AC droop power and the DC droop power are calculated respectively; the AC droop power, the DC droop power and the active power setting value are superimposed to obtain a final power reference value, i.e., a DC active power instruction; Based on the DC active power command, predict the angle change required by the DC active power command, i.e., the feedforward angle, and superimpose the feedforward angle on the converter output angle to obtain a reference voltage angle; and calculate the reference voltage amplitude through the VSG reactive loop; The difference between the reference voltage and the actual voltage is calculated, and the analog voltage of the virtual impedance is superimposed thereon, and the reference current of the current inner loop is obtained through PI modulation; based on the DC active power instruction, the current change required for the DC active power instruction, i.e., the feedforward current, is predicted; the feedforward current is superimposed on the reference current of the current inner loop to obtain an adjusted reference current, and after modulation by the PI controller, a modulation voltage for PWM modulation is obtained, and the modulation voltage is applied to the PWM modulator to generate a final output voltage for driving the converter, thereby realizing the control of the power flow between the AC power grid and the DC power transmission system.

2. A network construction-DC voltage stabilization fusion control method according to claim 1, characterized in that: The AC droop power and the DC droop power are calculated according to the AC droop characteristics and the DC droop characteristics respectively; the AC droop power, the DC droop power and the active power setting value are superimposed to obtain a final power reference value, that is, a DC active power instruction, and the calculation formula is as follows: In the formula, K wf is the AC droop coefficient, f n is the rated frequency, f is the actual frequency; K wdc is the DC droop coefficient, U dc is the actual DC voltage, U dcn is the rated DC voltage; P setf is the AC droop power, P setdc is the DC droop power; P set The power command issued by the coordination controller is the active power setting value; P ref is the final active power reference value, that is, the DC active power instruction.

3. A network construction-DC voltage stabilization fusion control method according to claim 1, characterized in that: The calculation formula of the feedforward angle is: In the formula, θ k is the predicted feedforward angle, P setdc is the DC droop power, L grid is the equivalent impedance of the power grid, L virtual is the virtual impedance in the voltage loop, U d is the d-axis component of the grid-side voltage.

4. A network construction-DC voltage stabilization fusion control method according to claim 1, characterized in that: The calculation formula of the feedforward current is: In the formula, i dk is the predicted feedforward current, P setdc is the DC droop power, U d is the d-axis component of the grid-side voltage.

5. A network-DC voltage stabilization fusion control system, characterized in that: It includes a converter, an AC power grid and a DC power transmission system, wherein the converter is connected between the AC power grid and the DC power transmission system; All converters include a grid-building-DC voltage stabilization fusion control unit, which includes: an AC-DC dual droop calculation module, a DC active power command-angle prediction feedforward calculation module, a VSG active power-angle calculation module, a VSG reactive power-voltage calculation module, a DC active power command-current prediction feedforward calculation module and a voltage-current inner loop control module; The AC / DC dual droop calculation module is used to calculate the AC droop power and the DC droop power according to the AC droop characteristics and the DC droop characteristics respectively; superimpose the AC droop power, the DC droop power and the active power setting value to obtain a final power reference value, i.e., a DC active power instruction; The DC active power instruction-angle prediction feedforward calculation module predicts the angle change required for the DC active power instruction, i.e., the feedforward angle, based on the DC active power instruction; A VSG active power-angle calculation module, used to obtain the converter output angle, and to superimpose the feedforward angle onto the converter output angle to obtain a reference voltage angle; The VSG reactive power-voltage calculation module is used to calculate the reference voltage amplitude through the VSG reactive power loop; The DC active power instruction-current prediction feedforward calculation module is used to predict the current change required for the DC active power instruction, that is, the feedforward current, based on the DC active power instruction; The voltage-current inner loop control module is used to calculate the difference between the reference voltage and the actual voltage, and superimpose the analog voltage of the virtual impedance thereon, and obtain the reference current of the current inner loop through PI modulation; the feedforward current is superimposed on the reference current of the current inner loop to obtain an adjusted reference current, and after modulation by the PI controller, a modulation voltage for PWM modulation is obtained, and the modulation voltage is applied to the PWM modulator to generate a final output voltage for driving the converter, thereby realizing the control of the power flow between the AC power grid and the DC power transmission system.

6. A network-building-DC voltage stabilization fusion control system according to claim 5, characterized in that: In the AC / DC dual droop calculation module, the DC active power instruction calculation formula is as follows: In the formula, K wf is the AC droop coefficient, f n is the rated frequency, f is the actual frequency; K wdc is the DC droop coefficient, U dc is the actual DC voltage, U dcn is the rated DC voltage; P setf is the AC droop power, P setdc is the DC droop power; P set The power command issued by the coordination controller is the active power setting value; P ref is the final active power reference value, that is, the DC active power instruction.

7. A network-building-DC voltage stabilization fusion control system according to claim 5, characterized in that: In the DC active power command-angle prediction feedforward calculation module, the feedforward angle is calculated as follows: In the formula, θ k is the predicted feedforward angle, P setdc is the DC droop power, L grid is the equivalent impedance of the power grid, L virtual is the virtual impedance in the voltage loop, U d is the d-axis component of the grid-side voltage.

8. A network construction-DC voltage stabilization fusion control method according to claim 5, characterized in that: In the DC active power command-current prediction feedforward calculation module, the calculation formula of the feedforward current is: In the formula, i dk is the predicted feedforward current, P setdc is the DC droop power, U d is the d-axis component of the grid-side voltage.

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