Low-voltage ride-through control method for network-constructed converter, network-constructed converter controller, network-constructed converter and computer readable storage medium

Abstract

The invention belongs to the technical field of low voltage ride through, and particularly relates to a low voltage ride through control method for a network-constructed converter, a network-constructed converter controller, a network-constructed converter and a computer readable storage medium. During the low-voltage fault ride-through period, virtual synchronous machine control is carried out according to the internal potential reference value to obtain a control instruction of the network construction type converter, and the network construction type converter is controlled according to the control instruction; wherein when the amplitude of the power grid voltage is smaller than a set voltage threshold value, the output of the reactive loop and the output of the power grid voltage feed-forward link are added to serve as an internal potential reference value; the reactive loop is used for performing reactive voltage droop control according to the power grid voltage amplitude and the actual reactive power value, and the power grid voltage feed-forward link is that the d-axis component of the power grid voltage is superposed with the voltage drop of the virtual inductance under the alternating current amplitude limiting value. The power grid voltage feed-forward link can quickly adjust the internal potential reference value without delay, so that the converter can quickly adapt to new power grid conditions, and the reactive response speed can be improved.

Description

Technical Field

[0001] This invention belongs to the field of low voltage ride-through technology, specifically relating to a low voltage ride-through control method for a grid-type converter, a grid-type converter controller, a grid-type converter, and a computer-readable storage medium. Background Technology

[0002] Grid-connected converters typically employ virtual synchronous machine (VSM) control. The principle of VSM control is to simulate the electromagnetic characteristics, frequency regulation, and excitation control of a synchronous machine on the grid-connected converter. Grid-connected converters use a reactive power control loop to simulate the reactive power and voltage regulation characteristics of a synchronous machine. The main control methods employed in the reactive power control loop are reactive power-voltage droop control and reactive power-voltage droop control with integrators. Because many regional power grids require grid-connected converters to meet a given droop coefficient for reactive power and voltage, and converters using proportional reactive power-voltage droop control cannot accurately track the droop coefficient, the commonly used reactive power control method is reactive power-voltage droop control with integrators.

[0003] In response to low voltage ride-through faults, the authors Sun Pengfei, Tian Zhen, et al. published a review of transient synchronous stability research on grid-connected systems using power synchronous grid converters in the January 25, 2025 issue of "Automation of Electric Power Systems". This strategy discloses a fault ride-through strategy for grid-connected converters, which provides reactive power support to the grid through a reactive power-voltage control link. However, it has a problem, especially when the grid voltage is not so high. This results in a long reactive power response time, which may cause grid voltage fluctuations and even lead to harmonics affecting the normal operation of some precision equipment. Summary of the Invention

[0004] The purpose of this invention is to provide a low-voltage ride-through control method for a grid-type converter, a grid-type converter controller, a grid-type converter, and a computer-readable storage medium, in order to solve the problem of long reactive power response time caused by using only a reactive-voltage control loop for reactive power support in the prior art.

[0005] To address the aforementioned technical problems, this invention provides a technical solution for a low-voltage ride-through control method for grid-connected converters, specifically including:

[0006] A low-voltage ride-through control method for a grid-connected converter, the method comprising:

[0007] During low-voltage fault ride-through, the control command for the grid-type converter is obtained by virtual synchronous machine control based on the internal potential reference value, and the grid-type converter is controlled according to the control command. Among them, when the grid voltage amplitude is less than the set voltage threshold, the output of the reactive power loop and the output of the grid voltage feedforward link are added as the internal potential reference value. The reactive power loop is used to perform reactive voltage droop control based on the grid voltage amplitude and the actual reactive power value. The grid voltage feedforward link is the voltage drop of the virtual inductor under the AC current limit value, which is the d-axis component of the grid voltage superimposed on the voltage drop of the virtual inductor.

[0008] The beneficial effects of the above technical solution are as follows: The low voltage ride-through control method of the present invention adds a grid voltage feedforward link to calculate the internal potential reference value on the basis of reactive voltage droop control. The idea of ​​setting grid voltage feedforward is not only to regard grid voltage as a disturbance that needs to be canceled, but also to predict and compensate for the voltage drop caused by virtual impedance under the worst operating conditions (current reaches the AC current limit value). In particular, under the case of a sudden drop in grid voltage, the grid voltage feedforward link can quickly adjust the internal potential reference value without delay, so that the converter can quickly adapt to the new grid conditions and improve the reactive power response speed.

[0009] Furthermore, the set voltage threshold value is:

[0010]

[0011] In the formula, U T k is the voltage threshold value. u I is the droop coefficient for reactive voltage droop control. max U is the AC current limiting value. n This is the rated voltage of the power grid.

[0012] Furthermore, when the grid voltage amplitude is greater than or equal to the voltage threshold, the output of the reactive power loop is added to the rated value of the internal potential as the reference value of the internal potential.

[0013] Furthermore, the reactive power loop includes: multiplying the difference between the grid voltage rating and the grid voltage amplitude by the droop coefficient of the reactive power voltage droop control, adding the resulting product to the reactive power command value, subtracting the actual reactive power value, and then outputting the resulting difference after adjustment by the regulator.

[0014] Furthermore, the voltage drop of the virtual inductor under the AC current limiting value is expressed as wLI max w is the angular frequency of the virtual synchronous machine, L is the virtual inductance, and I... max This is the AC current limiting value.

[0015] Furthermore, the regulator is a PI regulator.

[0016] Furthermore, the virtual synchronous machine control includes a power angle calculation stage and a current calculation stage. The power angle calculation stage is used to obtain the reference angle by simulating the primary frequency modulation, inertia, and damping characteristics of the virtual synchronous machine. The current calculation stage is used to obtain the current d-axis and q-axis reference values ​​by using the internal potential reference value and the virtual impedance.

[0017] To address the aforementioned technical problems, this invention also provides a technical solution for a grid-type converter controller, specifically including:

[0018] A grid-type converter controller includes a processor, the processor being configured to execute a computer program to implement the steps of the following method:

[0019] During low-voltage fault ride-through, the control command for the grid-type converter is obtained by virtual synchronous machine control based on the internal potential reference value, and the grid-type converter is controlled according to the control command. Among them, when the grid voltage amplitude is less than the set voltage threshold, the output of the reactive power loop and the output of the grid voltage feedforward link are added as the internal potential reference value. The reactive power loop is used to perform reactive voltage droop control based on the grid voltage amplitude and the actual reactive power value. The grid voltage feedforward link is the voltage drop of the virtual inductor under the AC current limit value, which is the d-axis component of the grid voltage superimposed on the voltage drop of the virtual inductor.

[0020] The beneficial effects of the above technical solution are as follows: This invention improves the control strategy executed by the grid-type converter controller. Specifically, it adds a grid voltage feedforward link to calculate the internal potential reference value on the basis of reactive voltage droop control. The idea of ​​setting up grid voltage feedforward is not only to treat the grid voltage as a disturbance that needs to be canceled, but also to predict and compensate for the voltage drop caused by the virtual impedance under the worst operating conditions (current reaches the AC current limit value). In particular, under the case of a sudden drop in grid voltage, the grid voltage feedforward link can quickly adjust the internal potential reference value without delay, so that the converter can quickly adapt to the new grid conditions and improve the reactive power response speed.

[0021] Furthermore, the set voltage threshold value is:

[0022]

[0023] In the formula, U T k is the voltage threshold value. u I is the droop coefficient for reactive voltage droop control. max U is the AC current limiting value. n This is the rated voltage of the power grid.

[0024] Furthermore, when the grid voltage amplitude is greater than or equal to the voltage threshold, the output of the reactive power loop is added to the rated value of the internal potential as the reference value of the internal potential.

[0025] Furthermore, the reactive power loop includes: multiplying the difference between the grid voltage rating and the grid voltage amplitude by the droop coefficient of the reactive power voltage droop control, adding the resulting product to the reactive power command value, subtracting the actual reactive power value, and then outputting the resulting difference after adjustment by the regulator.

[0026] Furthermore, the voltage drop of the virtual inductor under the AC current limiting value is expressed as wLI max w is the angular frequency of the virtual synchronous machine, L is the virtual inductance, and I... max This is the AC current limiting value.

[0027] Furthermore, the regulator is a PI regulator.

[0028] Furthermore, the virtual synchronous machine control includes a power angle calculation stage and a current calculation stage. The power angle calculation stage is used to obtain the reference angle by simulating the primary frequency modulation, inertia, and damping characteristics of the virtual synchronous machine. The current calculation stage is used to obtain the current d-axis and q-axis reference values ​​by using the internal potential reference value and the virtual impedance.

[0029] To address the aforementioned technical problems, the present invention also provides a technical solution for a grid-type converter, specifically comprising:

[0030] A grid-type converter includes an AC / DC converter and a grid-type converter controller for controlling the AC / DC converter. The grid-type converter controller includes a processor for executing a computer program to implement the steps of the following method:

[0031] During low-voltage fault ride-through, the control command for the grid-type converter is obtained by virtual synchronous machine control based on the internal potential reference value, and the grid-type converter is controlled according to the control command. Among them, when the grid voltage amplitude is less than the set voltage threshold, the output of the reactive power loop and the output of the grid voltage feedforward link are added as the internal potential reference value. The reactive power loop is used to perform reactive voltage droop control based on the grid voltage amplitude and the actual reactive power value. The grid voltage feedforward link is the voltage drop of the virtual inductor under the AC current limit value, which is the d-axis component of the grid voltage superimposed on the voltage drop of the virtual inductor.

[0032] The beneficial effects of the above technical solution are as follows: The grid-type converter of the present invention is a grid-type converter that adopts a new low-voltage ride-through control strategy. The new low-voltage ride-through control strategy adds a grid voltage feedforward link to calculate the internal potential reference value on the basis of reactive voltage droop control. The idea of ​​setting grid voltage feedforward is not only to treat grid voltage as a disturbance that needs to be canceled, but also to predict and compensate for the voltage drop caused by virtual impedance under the worst operating conditions (current reaches the AC current limit value). In particular, under the case of a sudden drop in grid voltage, the grid voltage feedforward link can quickly adjust the internal potential reference value without delay, so that the converter can quickly adapt to the new grid conditions and improve the reactive power response speed.

[0033] Furthermore, the set voltage threshold value is:

[0034]

[0035] In the formula, U T k is the voltage threshold value. u I is the droop coefficient for reactive voltage droop control. max U is the AC current limiting value. n This is the rated voltage of the power grid.

[0036] Furthermore, when the grid voltage amplitude is greater than or equal to the voltage threshold, the output of the reactive power loop is added to the rated value of the internal potential as the reference value of the internal potential.

[0037] Furthermore, the reactive power loop includes: multiplying the difference between the grid voltage rating and the grid voltage amplitude by the droop coefficient of the reactive power voltage droop control, adding the resulting product to the reactive power command value, subtracting the actual reactive power value, and then outputting the resulting difference after adjustment by the regulator.

[0038] Furthermore, the voltage drop of the virtual inductor under the AC current limiting value is expressed as wLI max w is the angular frequency of the virtual synchronous machine, L is the virtual inductance, and I... max This is the AC current limiting value.

[0039] Furthermore, the regulator is a PI regulator.

[0040] Furthermore, the virtual synchronous machine control includes a power angle calculation stage and a current calculation stage. The power angle calculation stage is used to obtain the reference angle by simulating the primary frequency modulation, inertia, and damping characteristics of the virtual synchronous machine. The current calculation stage is used to obtain the current d-axis and q-axis reference values ​​by using the internal potential reference value and the virtual impedance.

[0041] To address the aforementioned technical problems, the present invention also provides a technical solution for a computer-readable storage medium, specifically comprising:

[0042] A computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, performs the steps of the following method:

[0043] During low-voltage fault ride-through, the control command for the grid-type converter is obtained by virtual synchronous machine control based on the internal potential reference value, and the grid-type converter is controlled according to the control command. Among them, when the grid voltage amplitude is less than the set voltage threshold, the output of the reactive power loop and the output of the grid voltage feedforward link are added as the internal potential reference value. The reactive power loop is used to perform reactive voltage droop control based on the grid voltage amplitude and the actual reactive power value. The grid voltage feedforward link is the voltage drop of the virtual inductor under the AC current limit value, which is the d-axis component of the grid voltage superimposed on the voltage drop of the virtual inductor.

[0044] The beneficial effects of the above technical solution are as follows: The present invention provides a computer-readable storage medium storing software code implementing a low-voltage ride-through control method for a grid-connected converter, thus providing a hardware foundation for implementing the method. The method of the present invention adds a grid voltage feedforward stage to the reactive voltage droop control to calculate the internal potential reference value. This grid voltage feedforward approach not only treats the grid voltage as a disturbance that needs to be canceled, but also anticipates and compensates for the voltage drop caused by the virtual impedance under the worst operating conditions (current reaching the AC current limit). Especially in the case of a sudden drop in grid voltage, this grid voltage feedforward stage can quickly adjust the internal potential reference value without delay, enabling the converter to quickly adapt to new grid conditions and improving the reactive power response speed.

[0045] Furthermore, the set voltage threshold value is:

[0046]

[0047] In the formula, U T k is the voltage threshold value. u I is the droop coefficient for reactive voltage droop control. max U is the AC current limiting value. n This is the rated voltage of the power grid.

[0048] Furthermore, when the grid voltage amplitude is greater than or equal to the voltage threshold, the output of the reactive power loop is added to the rated value of the internal potential as the reference value of the internal potential.

[0049] Furthermore, the reactive power loop includes: multiplying the difference between the grid voltage rating and the grid voltage amplitude by the droop coefficient of the reactive power voltage droop control, adding the resulting product to the reactive power command value, subtracting the actual reactive power value, and then outputting the resulting difference after adjustment by the regulator.

[0050] Furthermore, the voltage drop of the virtual inductor under the AC current limiting value is expressed as wLI maxw is the angular frequency of the virtual synchronous machine, L is the virtual inductance, and I... max This is the AC current limiting value.

[0051] Furthermore, the regulator is a PI regulator.

[0052] Furthermore, the virtual synchronous machine control includes a power angle calculation stage and a current calculation stage. The power angle calculation stage is used to obtain the reference angle by simulating the primary frequency modulation, inertia, and damping characteristics of the virtual synchronous machine. The current calculation stage is used to obtain the current d-axis and q-axis reference values ​​by using the internal potential reference value and the virtual impedance. Attached Figure Description

[0053] Figure 1 This is the control block diagram of the power angle calculation stage in the virtual synchronous machine control strategy;

[0054] Figure 2 This is a control block diagram of the current calculation stage in the virtual synchronous machine control strategy;

[0055] Figure 3 This is a control block diagram for obtaining the internal potential reference value when the grid voltage amplitude is greater than or equal to the voltage threshold value according to the present invention.

[0056] Figure 4 This is a control block diagram of the present invention for obtaining the internal potential reference value when the grid voltage amplitude is less than the voltage threshold value;

[0057] Figure 5 This is a waveform comparison of reactive current response time according to the present invention. Detailed Implementation

[0058] The core concept of this invention lies in the fact that, in calculating the internal potential reference value, in addition to the output of reactive voltage droop control, there is also the output of the grid voltage feedforward stage. The grid voltage feedforward stage is the voltage drop of the virtual inductor superimposed on the d-axis component of the grid voltage under the AC current limiting value, thereby improving the reactive power response speed. Based on this, a low-voltage ride-through control method for a grid-connected converter, a grid-connected converter controller, a grid-connected converter, and a computer-readable storage medium can be realized according to this invention. To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings.

[0059] An implementation method for low voltage ride-through control of a grid-type converter:

[0060] In this embodiment, the low-voltage ride-through control method for the grid-type converter is mainly the control strategy adopted by the grid-type converter during low-voltage fault ride-through.

[0061] The basic framework of this control strategy is to adopt a virtual synchronous machine control strategy, which includes a power angle calculation stage and a current calculation stage. The control block diagrams for the current calculation stage and the power angle calculation stage are shown below. Figure 1 , 2 As shown in the diagram. Here, R represents the virtual resistance, L represents the virtual inductance, and U... d U represents the d-axis component of the grid voltage. q P represents the q-axis component of the grid voltage. ref This represents the active power command value, ω represents the virtual synchronous machine angular frequency, ω0 represents the reference angular frequency, and k f denoted by , Pe represents the active power feedback value, J represents the inertial time constant, D represents the damping coefficient, and s represents the Laplace operator.

[0062] Figure 1 This is the control block diagram for the current calculation stage, which is used to calculate the current based on the internal potential reference value E. ref And the virtual impedance provides the reference values ​​I for the current d and q axes. d_ref I q_ref .

[0063] Figure 2 This is the control block diagram for the power angle calculation stage. The power angle control stage is used to obtain the reference angle θ by simulating the primary frequency modulation, inertia, and damping characteristics of a virtual synchronous machine. Where T0 = P ref / ω,△T=k f ·(ω0-ω), T m =T0+△T,T e =P e / ω,T d =(T m -T e -T d )·D / Js,ω=(T m -T e -T d ) / Js+ω0,θ=ω / s.

[0064] Regarding the internal potential reference value E ref The values ​​are as follows Figure 3 and Figure 4 As shown. U m U represents the grid voltage amplitude. T k is the voltage threshold value. u I is the reactive voltage droop factor. max U is the AC current limiting value. n E0 is the rated value of the mains voltage, and Q is the rated value of the internal electromotive force. ref Q is the reactive power command value. e k represents the reactive power feedback value (i.e., the actual reactive power value). pand k i These are the proportional and integral coefficients of the PI regulator in the reactive power loop.

[0065] Figure 3 For the grid voltage amplitude U m Greater than or equal to the voltage threshold value U T Under these conditions, the internal potential reference value E is obtained. ref Control block diagram. At grid voltage amplitude U m Greater than or equal to the voltage threshold value U T Under these circumstances, the current reference value obtained through the reactive voltage droop factor does not reach the AC current limit value I of the converter. max At this time, the internal potential reference value E ref This is the internal potential rating E0 plus the output of the reactive power loop. Specifically, the reactive power loop converts the grid voltage rating U... n With grid voltage amplitude U m The difference multiplied by the droop coefficient k of reactive voltage droop control u The resulting product is then multiplied by the reactive power command value Q. ref Add them together and then subtract the actual reactive power value Q. e The resulting difference is then adjusted by a regulator before being output. The most commonly used regulator here is the PI regulator, but other regulators available in existing technologies, such as PID and fuzzy PID, can also be selected. When using a PI regulator, Figure 3 The mathematical expression corresponding to the control strategy is:

[0066]

[0067] Figure 4 For the grid voltage amplitude U m Less than the voltage threshold U T Under these conditions, the internal potential reference value E is obtained. ref Control block diagram. At grid voltage amplitude U m Less than the voltage threshold U T Under these conditions, the current reference value obtained through the reactive voltage droop factor reaches the AC current limit value I of the converter. max At this time, the internal potential reference value E ref Add the output of the grid voltage feedforward stage to the output of the reactive power loop. Figure 4 The architecture of the reactive power loop is the same Figure 3 The architecture of the reactive power loop is consistent, and the regulator in the reactive power loop can also be a PI regulator, or other regulators in existing technology. When a PI regulator is used, Figure 4 The mathematical expression corresponding to the control strategy is:

[0068]

[0069] In the two mathematical expressions above, .

[0070] Moreover, regarding the voltage threshold value U... T The value to be selected is The specific reasons and derivation process for this value are as follows:

[0071] From the voltage-reactive power droop relationship, the reactive power can be obtained as: Q = (U n -U T )*k u The reactive power formula in the dq coordinate system is: Q = -1.5 * U d *I q ; Grid-based control will synchronize with the grid phase, therefore U d =U T When the current reaches the limit, I q =I max Solving the three equations in this paragraph together, we get U. T expression .

[0072] Based on the above introduction, the entire implementation process is as follows: 1) During low-voltage fault ride-through, when the grid voltage amplitude is less than the set voltage threshold, the output of the reactive power loop is added to the output of the grid voltage feedforward link as the internal potential reference value; when the grid voltage amplitude is greater than or equal to the voltage threshold, the output of the reactive power loop is added to the rated internal potential value as the internal potential reference value. 2) Based on the internal potential reference value, virtual synchronous machine control is performed to obtain the control command for the grid-type converter, and the grid-type converter is controlled according to the control command. Specific technical details will not be elaborated here.

[0073] Therefore, during a low-voltage ride-through fault, the present invention, when the aforementioned grid voltage amplitude U m Less than the voltage threshold U T At that time, the internal potential reference value of the grid controller is the output of the grid voltage feedforward link plus the reactive power loop. The reactive power loop control ensures that the reactive power and voltage meet the droop coefficient. The grid voltage feedforward can improve the reactive power response speed. Figure 5 The waveforms showing the reactive current response time are as follows: the red dashed line represents the reactive current waveform using the existing technology, and the green solid line represents the reactive current waveform using the present invention. The reactive current response time using the present invention is reduced by 10ms compared to the existing technology, thus improving the reactive current response speed.

[0074] An implementation method for a grid-type converter controller:

[0075] This invention discloses a grid-type converter controller. This controller is used to output control commands to control the grid-type converter, typically by outputting PWM waves to control the on / off switching of each controllable switch in the grid-type converter. A grid-type converter refers to a converter that employs grid control; this converter is essentially AC / DC or DC / AC, used for DC power transmission. The grid-type converter controller includes a processor and a memory. The processor and memory communicate and exchange data via an internal bus, and the memory stores computer programs / instructions. The processor provides computational, signal processing, and control capabilities, and executes the computer program / instructions to implement the low-voltage ride-through control method for the grid-type converter of this invention. Specifically, the processor can be a general-purpose processor, such as a Digital Signal Processor (DSP). Alternatively, it can be a high-speed random access memory (RAM).

[0076] The main process of this method is as follows:

[0077] 1) During low-voltage fault ride-through, at grid voltage amplitude U m Less than the set voltage threshold value U T At that time, the output of the reactive power loop is added to the output of the grid voltage feedforward link as the internal potential reference value E. ref The detailed control block diagram for obtaining the internal potential reference value in this case is as follows: Figure 4 As shown; at the grid voltage amplitude U m Greater than or equal to the set voltage threshold value U T At that time, the output of the reactive power loop is added to the rated internal potential E0 to obtain the internal potential reference value E. ref The detailed control block diagram for obtaining the internal potential reference value in this case is as follows: Figure 3 As shown.

[0078] Among them, the reactive power loop is used to perform reactive voltage droop control based on the grid voltage amplitude and the actual reactive power value; the grid voltage feedforward link is the d-axis component U of the grid voltage. d The voltage drop ωLI of the superimposed virtual inductance under AC current limiting max The voltage threshold value can be set to... .

[0079] 2) The control command for the grid-type converter is obtained through virtual synchronous machine control based on the internal potential reference value, and the grid-type converter is controlled according to this control command. This virtual synchronous machine control specifically includes, for example: Figure 1 The current calculation steps shown are as follows: Figure 2 The step of calculating the work angle is shown.

[0080] An implementation method for a grid-type converter:

[0081] This invention discloses a grid-type converter, comprising an AC / DC converter and a grid-type converter controller for controlling the AC / DC converter. The grid-type converter controller typically outputs a PWM wave to control the on / off state of each controllable switch in the grid-type converter. The grid-type converter controller includes a processor and a memory. The processor and memory communicate and exchange data via an internal bus, and the memory stores computer programs / instructions. The processor provides computational, signal processing, and control capabilities, and executes the computer program / instructions to implement the low-voltage ride-through control method for the grid-type converter of this invention. Specifically, the processor can be a general-purpose processor, such as a digital signal processor (DSP). Alternatively, it can be a high-speed random access memory (RAM).

[0082] The main process of this method is as follows:

[0083] 1) During low-voltage fault ride-through, at grid voltage amplitude U m Less than the set voltage threshold value U T At that time, the output of the reactive power loop is added to the output of the grid voltage feedforward link as the internal potential reference value E. ref The detailed control block diagram for obtaining the internal potential reference value in this case is as follows: Figure 4 As shown; at the grid voltage amplitude U m Greater than or equal to the set voltage threshold value U T At that time, the output of the reactive power loop is added to the rated internal potential E0 to obtain the internal potential reference value E. ref The detailed control block diagram for obtaining the internal potential reference value in this case is as follows: Figure 3 As shown.

[0084] Among them, the reactive power loop is used to perform reactive voltage droop control based on the grid voltage amplitude and the actual reactive power value, which is essentially reactive voltage droop control; the grid voltage feedforward link is the d-axis component U of the grid voltage. d The voltage drop ωLI of the superimposed virtual inductance under AC current limiting max The voltage threshold value can be set to... .

[0085] 2) The control command for the grid-type converter is obtained through virtual synchronous machine control based on the internal potential reference value, and the grid-type converter is controlled according to this control command. This virtual synchronous machine control specifically includes, for example: Figure 1 The current calculation steps shown are as follows: Figure 2 The step of calculating the work angle is shown.

[0086] One embodiment of a computer-readable storage medium:

[0087] The present invention provides a computer-readable storage medium storing computer-executable instructions / programs, which, when called and executed by a processor, cause the processor to implement a low-voltage ride-through control method for a grid-type converter according to the present invention.

[0088] The main process of this method is as follows:

[0089] 1) During low-voltage fault ride-through, at grid voltage amplitude U m Less than the set voltage threshold value U T At that time, the output of the reactive power loop is added to the output of the grid voltage feedforward link as the internal potential reference value E. ref The detailed control block diagram for obtaining the internal potential reference value in this case is as follows: Figure 4 As shown; at the grid voltage amplitude U m Greater than or equal to the set voltage threshold value U T At that time, the output of the reactive power loop is added to the rated internal potential E0 to obtain the internal potential reference value E. ref The detailed control block diagram for obtaining the internal potential reference value in this case is as follows: Figure 3 As shown.

[0090] Among them, the reactive power loop is used to perform reactive voltage droop control based on the grid voltage amplitude and the actual reactive power value, which is essentially reactive voltage droop control; the grid voltage feedforward link is the d-axis component U of the grid voltage. d The voltage drop ωLI of the superimposed virtual inductance under AC current limiting max The voltage threshold value can be set to... .

[0091] 2) The control command for the grid-type converter is obtained through virtual synchronous machine control based on the internal potential reference value, and the grid-type converter is controlled according to this control command. This virtual synchronous machine control specifically includes, for example: Figure 1 The current calculation steps shown are as follows: Figure 2 The step of calculating the work angle is shown.

[0092] In summary, during low-voltage ride-through faults, when the grid voltage amplitude meets the requirements, the internal potential reference value of the grid-connected converter is the output of the grid voltage feedforward link plus the reactive power loop. The reactive power loop control ensures that reactive power and voltage meet the droop factor requirements, and the grid voltage feedforward link improves the reactive power response speed.

Claims

1. A low-voltage ride-through control method for a grid-connected converter, characterized in that, The method includes: During low-voltage fault ride-through, the control command for the grid-type converter is obtained by virtual synchronous machine control based on the internal potential reference value, and the grid-type converter is controlled according to the control command. Specifically, when the grid voltage amplitude is less than the set voltage threshold, the output of the reactive power loop is added to the output of the grid voltage feedforward link as the internal potential reference value; the reactive power loop is used to perform reactive voltage droop control based on the grid voltage amplitude and the actual reactive power value; the grid voltage feedforward link is the voltage drop of the grid voltage d-axis component superimposed with the virtual inductance under the AC current limit value.

2. The low-voltage ride-through control method for a grid-type converter according to claim 1, characterized in that, The set voltage threshold value is: In the formula, U T k is the voltage threshold value. u I is the droop coefficient for reactive voltage droop control. max U is the AC current limiting value. n This is the rated voltage of the power grid.

3. The low-voltage ride-through control method for a grid-type converter according to claim 1, characterized in that, When the grid voltage amplitude is greater than or equal to the voltage threshold, the output of the reactive power loop is added to the rated value of the internal potential as the reference value of the internal potential.

4. The low-voltage ride-through control method for a grid-type converter according to claim 1, characterized in that, The reactive power loop includes: multiplying the difference between the grid voltage rating and the grid voltage amplitude by the droop coefficient of the reactive power voltage droop control, adding the product to the reactive power command value, subtracting the actual reactive power value, and then outputting the difference after adjustment by the regulator.

5. The low-voltage ride-through control method for a grid-type converter according to any one of claims 1 to 4, characterized in that, The voltage drop of the virtual inductor under AC current limiting is expressed as wLI max w is the angular frequency of the virtual synchronous machine, L is the virtual inductance, and I... max This is the AC current limiting value.

6. The low-voltage ride-through control method for a grid-type converter according to claim 4, characterized in that, The regulator is a PI regulator.

7. The low-voltage ride-through control method for a grid-type converter according to any one of claims 1 to 4, characterized in that, The virtual synchronous machine control includes a power angle calculation stage and a current calculation stage. The power angle calculation stage is used to obtain the reference angle by simulating the primary frequency modulation, inertia, and damping characteristics of the virtual synchronous machine. The current calculation stage is used to obtain the current d-axis and q-axis reference values ​​by using the internal potential reference value and the virtual impedance.

8. A grid-type converter controller, comprising a processor, characterized in that, The processor is used to execute a computer program to implement the steps of the method according to any one of claims 1 to 7.

9. A grid-type converter, comprising an AC / DC converter and a grid-type converter controller for controlling the AC / DC converter, wherein the grid-type converter controller includes a processor, characterized in that, The processor is used to execute a computer program to implement the steps of the method according to any one of claims 1 to 7.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by a processor, it implements the steps of the method according to any one of claims 1 to 7.

Images