Current-limiting control method and device of network-constructing converter, converter and storage medium

Abstract

This invention discloses a current limiting control method, device, converter, and storage medium for a grid-type converter, relating to the field of power electronics technology. The method includes: acquiring the three-phase output reference voltage of the converter; converting the three-phase output reference voltage to obtain a first-axis output reference voltage and a second-axis output reference voltage in a preset two-phase coordinate system; using a preset maximum output current limit value of the converter, performing virtual impedance current limiting adjustment on the first-axis output reference voltage and / or the second-axis output reference voltage to obtain a first-axis target output reference voltage and a second-axis target output reference voltage in a preset two-phase coordinate system, thereby obtaining the three-phase target output voltage of the converter. This invention, by utilizing virtual impedance control technology to limit the output current of the grid-type converter, enables the converter to maintain voltage source characteristics after current limiting, thus improving the stability of the converter while ensuring its safe operation.

Description

Technical Field

[0001] This invention relates to the field of power electronics technology, and in particular to a current limiting control method, device, converter, and storage medium for a grid-type converter. Background Technology

[0002] With the increasing penetration rate of distributed renewable energy, more and more converters (such as inverters) are being connected to the grid, resulting in a significant reduction in the total damping and inertia provided by traditional generators in the grid. This causes the grid to experience faster frequency changes and decreased anti-interference capability when facing disturbances. To address this issue, the concept of Virtual Synchronous Generator (VSG) control technology has been proposed. This control technology can mimic the operating mechanism of a synchronous generator, enabling grid-connected inverters to have grid support, providing grid inertia performance, frequency, and voltage support, thereby improving grid stability. However, grid-connected control strategies for converters with voltage source characteristics, such as VSG control, face difficulties in voltage source current limiting, making it challenging to effectively limit current output without altering the voltage source characteristics.

[0003] In existing technologies, controllers typically incorporate a current limiting element for the converter's output current between its voltage and current dual closed-loop control. When the voltage loop's output reference current exceeds a certain threshold, the limiting element activates, altering the current loop's reference input current to limit the current. Under normal circumstances, current limiting control is inactive. However, when the converter experiences significant disturbances or operates under unstable conditions, current limiting control kicks in to prevent excessive current generation and the resulting complex transient response. This approach, once current limiting is triggered, transforms the voltage source into a current source, losing its voltage source characteristics and becoming prone to instability in weak grid conditions. Furthermore, its current limiting transient response is complex, resulting in poor power angle stability. Therefore, how to limit the converter's output current while maintaining its voltage source characteristics, thereby ensuring safe operation and improving converter stability, is a pressing issue that needs to be addressed. Summary of the Invention

[0004] The purpose of this invention is to provide a current limiting control method, device, converter, and computer-readable storage medium for a grid-type converter, so as to limit the output current of the converter while maintaining the voltage source characteristics of the converter, thereby improving the stability of the converter while ensuring its safe operation.

[0005] To solve the above-mentioned technical problems, the present invention provides a current limiting control method for a grid-type converter, comprising:

[0006] Obtain the three-phase output reference voltage of the converter; wherein, the output terminal of the converter is connected to the power grid;

[0007] The first-axis output reference voltage and the second-axis output reference voltage in a preset two-phase coordinate system corresponding to the three-phase output reference voltage are obtained by conversion.

[0008] Using the preset maximum output current limit value of the converter, virtual impedance current limiting adjustment is performed on the first axis output reference voltage and / or the second axis output reference voltage to obtain the first axis target output reference voltage and the second axis target output reference voltage in the preset two-phase coordinate system; wherein, the preset maximum output current limit value includes the second axis output current limit value corresponding to the first axis output reference voltage and / or the first axis output current limit value corresponding to the second axis output reference voltage;

[0009] The three-phase target output voltage of the converter is obtained based on the first axis target output reference voltage and the second axis target output reference voltage.

[0010] On the other hand, the converter is an inverter, and the three-phase output reference voltage is the three-phase reference voltage of the virtual synchronous generator (VSG).

[0011] On the other hand, the preset two-phase coordinate system is a dq rotating coordinate system.

[0012] On the other hand, obtaining the three-phase target output voltage of the converter based on the first axis target output reference voltage and the second axis target output reference voltage includes:

[0013] Based on the first axis target output reference voltage and the second axis target output reference voltage, the first axis target output voltage and the second axis target output voltage are obtained under a preset two-phase coordinate system through dual closed-loop control of the voltage outer loop and the current inner loop.

[0014] The first axis target output voltage and the second axis target output voltage are converted into the three-phase target output voltage.

[0015] On the other hand, the step of using the preset maximum output current limit value of the converter to perform virtual impedance current limiting adjustment on the first axis output reference voltage and / or the second axis output reference voltage to obtain the first axis target output reference voltage and the second axis target output reference voltage in the preset two-phase coordinate system includes:

[0016] Based on the second axis output current limit and the second axis output current, a proportional-integral control loop determines the first axis voltage adjustment value; using the first axis voltage adjustment value, the first axis output reference voltage is adjusted to obtain the first axis target output reference voltage; and / or

[0017] Based on the first axis output current limit and the first axis output current, the second axis voltage adjustment value is determined through a proportional-integral control loop; using the second axis voltage adjustment value, the second axis output reference voltage is adjusted to obtain the second axis target output reference voltage; wherein, the second axis output current and the first axis output current are obtained by transforming the three-phase output current of the converter through the preset two-phase coordinate system.

[0018] On the other hand, determining the first axis voltage adjustment value through a proportional-integral control circuit based on the second axis output current limit value and the second axis output current includes:

[0019] pass Calculate the first axis voltage adjustment value; where, u vd i is the first axis voltage adjustment value. qLim i is the output current limit value for the second axis. q k is the output current of the second axis. i k is the integral coefficient. p Let be the scaling factor, and s be the operator variable of the Laplace transform; if i q >0 then i qLim If i is a positive number, then q <0 then i qLim It is a negative number;

[0020] If i q If i > 0, then when the first axis voltage adjustment value is greater than the first threshold, the first axis voltage adjustment value is adjusted to the first threshold; if i q If <0, then when the first axis voltage adjustment value is less than the second threshold, the first axis voltage adjustment value will be adjusted to the second threshold.

[0021] The step of determining the second axis voltage adjustment value through a proportional-integral control loop based on the first axis output current limit and the first axis output current includes:

[0022] pass Calculate the second axis voltage adjustment value; where, u vq i is the second axis voltage adjustment value. dLim i is the output current limit value for the first axis. d The first axis output current; if i d >0 then i dLim If i is a positive number, then d <0 then i dLim It is a negative number;

[0023] If i d If the value is greater than 0, then when the second axis voltage adjustment value is greater than the third threshold, the second axis voltage adjustment value will be adjusted to the third threshold; if id If the value is less than 0, then when the second axis voltage adjustment value is less than the fourth threshold, the second axis voltage adjustment value will be adjusted to the fourth threshold.

[0024] On the other hand, the first threshold, the second threshold, the third threshold, and the fourth threshold are all 0.

[0025] The present invention also provides a current limiting control device for a grid-type converter, comprising:

[0026] A reference acquisition module is used to acquire the three-phase output reference voltage of the converter; wherein, the output terminal of the converter is connected to the power grid;

[0027] The coordinate transformation module is used to transform the three-phase output reference voltage to obtain the first-axis output reference voltage and the second-axis output reference voltage in a preset two-phase coordinate system.

[0028] The current limiting adjustment module is used to perform virtual impedance current limiting adjustment on the first axis output reference voltage and / or the second axis output reference voltage using the preset maximum output current limit value of the converter, so as to obtain the first axis target output reference voltage and the second axis target output reference voltage in the preset two-phase coordinate system; wherein, the preset maximum output current limit value includes the second axis output current limit value corresponding to the first axis output reference voltage and / or the first axis output current limit value corresponding to the second axis output reference voltage;

[0029] The reference control module is used to obtain the three-phase target output voltage of the converter based on the first axis target output reference voltage and the second axis target output reference voltage.

[0030] The present invention also provides a converter, comprising:

[0031] Memory, used to store computer programs;

[0032] A processor is used to execute the computer program to implement the steps of the current limiting control method for a grid-type converter as described above.

[0033] In addition, the present invention provides a computer-readable storage medium storing a computer program, which, when executed by a processor, implements the steps of the current limiting control method for a grid-type converter as described above.

[0034] The present invention provides a current limiting control method for a grid-connected converter, comprising: acquiring the three-phase output reference voltage of the converter; wherein the output terminal of the converter is connected to the power grid; converting the three-phase output reference voltage to obtain a first-axis output reference voltage and a second-axis output reference voltage in a preset two-phase coordinate system; using a preset maximum output current limit value of the converter, performing virtual impedance current limiting adjustment on the first-axis output reference voltage and / or the second-axis output reference voltage to obtain a first-axis target output reference voltage and a second-axis target output reference voltage in a preset two-phase coordinate system; wherein the preset maximum output current limit value includes a second-axis output current limit value corresponding to the first-axis output reference voltage and / or a first-axis output current limit value corresponding to the second-axis output reference voltage; and acquiring the three-phase target output voltage of the converter based on the first-axis target output reference voltage and the second-axis target output reference voltage.

[0035] As can be seen, this invention utilizes the preset maximum output current limit of the converter to perform virtual impedance current limiting adjustment on the first axis output reference voltage and / or the second axis output reference voltage, obtaining the first axis target output reference voltage and the second axis target output reference voltage in a preset two-phase coordinate system. This allows the virtual impedance control technology to limit the output current of the grid-type converter, enabling the converter to maintain its voltage source characteristics even after current limiting. This ensures the safe operation of the converter while improving its stability. Furthermore, this invention also provides a current limiting control device for a grid-type converter, a converter, and a computer-readable storage medium, which also possess the aforementioned beneficial effects. Attached Figure Description

[0036] 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 embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0037] Figure 1 A flowchart of a current limiting control method for a grid-type converter provided in an embodiment of the present invention;

[0038] Figure 2 This is a control block diagram of VSG control for inverter output provided in an embodiment of the present invention;

[0039] Figure 3 This is a schematic diagram of the topology of a virtual impedance circuit provided in an embodiment of the present invention;

[0040] Figure 4 This is a structural block diagram of a current limiting control device for a grid-type converter provided in an embodiment of the present invention;

[0041] Figure 5 This is a schematic diagram of the structure of a converter provided in an embodiment of the present invention;

[0042] Figure 6 This is a schematic diagram of the specific structure of a converter provided in an embodiment of the present invention. Detailed Implementation

[0043] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0044] Please refer to Figure 1 , Figure 1 A flowchart illustrating a current-limiting control method for a grid-type converter provided in an embodiment of the present invention. The method may include:

[0045] Step 101: Obtain the three-phase output reference voltage of the converter; wherein, the output terminal of the converter is connected to the power grid.

[0046] It is understood that the converter in this embodiment can be a grid-connected converter (i.e., a grid-connected converter), meaning that the output of the converter can be connected to the grid. The current limiting control method for the grid-connected converter provided in this embodiment can be applied to the virtual synchronous generator (VSG) control process of a grid-connected inverter. That is, the grid-connected inverter can use the method provided in this embodiment to adjust the three-phase target output voltage controlled by the VSG (e.g., ...). Figure 2 The current limiting control method for grid-connected converters provided in this embodiment can also be applied to other control processes of grid-connected converters, such as other control processes of grid-connected inverters or grid-connected AC converters. For example, in the inverter control scenario of a UPS (Uninterruptible Power System), the UPS can use the phase output of its phase-locked loop to calculate the three-phase voltage (i.e., the three-phase output reference voltage), and convert it into two-phase voltages in a preset two-phase coordinate system (i.e., the first axis output reference voltage and the second axis output reference voltage). By adjusting these two-phase voltages, the target three-phase output voltage can be adjusted to limit the inverter's output current. This embodiment does not impose any limitations on this.

[0047] In this embodiment, the three-phase output reference voltage of the converter can be the three-phase reference voltage required to obtain the target three-phase output voltage of the converter (i.e., the target three-phase output voltage), such as the voltage outer loop setpoint input to the voltage outer loop control; for example, the three-phase reference voltage of the VSG (e.g., the voltage of the VSG). Figure 2 The three-phase capacitor voltage u between the inverter filter inductor L1 and the inverter output filter inductor L2 Cabc The reference voltage or the three-phase voltage corresponding to the phase output of the UPS phase-locked loop.

[0048] Correspondingly, the specific method by which the processor obtains the three-phase output reference voltage of the converter in this step can be set by the designer according to the practical scenario and user requirements. For example, it can be implemented in a way that is the same as or similar to the calculation method of the reference value of the three-phase output voltage of the converter control in the existing technology. For example, when applied to VSG control, such as... Figure 2 As shown, the processor can adjust the collected three-phase capacitor voltage u Cabc and three-phase output current i gabc The active power P is calculated. fdb and reactive power Q fdb According to the active power P fdb Reactive power Q fdb Active power reference value P ref and reactive power reference value Q ref Determine the target output voltage phase θ and electromotive force E m Based on the target output voltage phase θ and electromotive force E m This yields the three-phase output reference voltage, which is used to adjust the three-phase capacitor voltage u. Cabc The reference voltage (such as the voltage given in the outer voltage loop); correspondingly, when applied to UPS control, a process similar to that of the phase-locked loop in a conventional UPS can be used to calculate the three-phase output reference voltage using the phase output of the phase-locked loop. This embodiment does not impose any limitations on this.

[0049] Step 102: Convert to obtain the first axis output reference voltage and the second axis output reference voltage in the preset two-phase coordinate system corresponding to the three-phase output reference voltage.

[0050] In this step, the processor can perform rotational transformation on the three-phase output reference voltage to obtain the corresponding voltage values ​​on two axes (the first axis and the second axis) in a preset two-phase coordinate system, namely the first axis output reference voltage and the second axis output reference voltage.

[0051] Correspondingly, the specific type of the preset two-phase coordinate system in this embodiment, i.e., the rotation transformation method of the three-phase output reference voltage, can be set by the designer according to the practical scenario and user needs. For example, the preset two-phase coordinate system can be a dq rotating coordinate system, that is, the processor can perform a dq transformation on the three-phase output reference voltage to obtain the d-axis output reference voltage (i.e., the first axis output reference voltage) and the q-axis output reference voltage (i.e., the second axis output reference voltage). Figure 2 The initial d-axis reference capacitor voltage U′ c,dref and the initial q-axis reference capacitor voltage U′ c,qref The preset two-phase coordinate system can also be any other rotating coordinate system, such as the αβ rotating coordinate system. For example, if the preset two-phase coordinate system is the αβ rotating coordinate system, the processor can perform an αβ transformation on the three-phase output reference voltage to obtain the α-axis output reference voltage (i.e., the first axis output reference voltage) and the β-axis output reference voltage (i.e., the second axis output reference voltage). This embodiment does not impose any limitations on this.

[0052] Step 103: Using the preset maximum output current limit value of the converter, perform virtual impedance current limiting adjustment on the first axis output reference voltage and / or the second axis output reference voltage to obtain the first axis target output reference voltage and the second axis target output reference voltage in the preset two-phase coordinate system.

[0053] The preset maximum output current limit includes the second axis output current limit corresponding to the first axis output reference voltage and / or the first axis output current limit corresponding to the second axis output reference voltage.

[0054] It is understood that the preset maximum output current limit value in this embodiment can be a pre-set limit value for limiting the output current (i.e., three-phase output current) of the converter. That is, when the preset maximum output current limit value includes the first shaft output current limit value, it can limit the amplitude of the first shaft output current converted from the three-phase output current of the converter to be less than or equal to the amplitude of the first shaft output current limit value; when the preset maximum output current limit value includes the second shaft output current limit value, it can limit the amplitude of the second shaft output current converted from the three-phase output current of the converter to be less than or equal to the amplitude of the second shaft output current limit value; thus, by setting the preset maximum output current limit value, the output current of the subsequent converter can be limited and adjusted.

[0055] In other words, this embodiment utilizes virtual impedance control technology to adjust the first-axis output reference voltage and / or the second-axis output reference voltage based on a preset maximum output current limit value. This adjusts the reference values ​​used to generate the three-phase target output voltage, such as... Figure 2 The two-axis voltages that need to be input to the outer voltage loop are the conventional initial d-axis reference capacitor voltage U′. c,dref and the initial q-axis reference capacitor voltage U′c,qref Change to the adjusted d-axis reference capacitor voltage U c,dref (i.e., the first-axis target output reference voltage) and the q-axis reference capacitor voltage U c,qref (i.e., the second axis target output reference voltage); thereby adjusting the three-phase target output voltage ultimately used to control the controllable switches (such as switching transistors or MOSFETs) in the converter, and achieving current limiting of the converter's output current.

[0056] For example, such as Figure 2 and Figure 3 As shown, the method provided in this embodiment is applied to VSG control, and the topology change of the control circuit after adding virtual impedance is as follows: Figure 3 In the form of increasing virtual impedance Z v ,and Among them, R v For virtual resistance impedance, X v This is a virtual inductance reactance.

[0057] According to Kirchhoff's Law (KVL), the grid voltage (e) can be obtained. a e b and e c ) and the output voltage (u) of the converter Ca u Cb and u Cc ) and the converter's output current (i a2 i b2 and i c2 That is, the three-phase output current i g The relationship between ) is as follows:

[0058]

[0059]

[0060]

[0061] In equations (1)-(3), R1 is the bridge arm side resistance, L1 is the converter filter inductance, and i a1 i b1 and i c1 R2 is the current of the three-phase filter inductor, R2 is the output resistance of the converter, and L2 is the output filter inductance of the converter. v For virtual inductance, u a u b and u c This represents the output three-phase voltage. If the two-phase coordinate system is preset to the dq rotating coordinate system, the three-phase coordinate system is converted to the dq rotating coordinate system, and further simplified to obtain:

[0062]

[0063]

[0064]

[0065] In equations (4)-(6), u d and u q It can be made by u a u b and u c i is obtained through dq rotation transformation. d1 and i q1 It can be made by i a1 i b1 and i c1 u is obtained through dq rotation transformation. Cd and u Cq It can be made by u Ca u Cb and u Cc i is obtained through dq rotation transformation. d2 and i q2 It can be made by i a2 i b2 and i c2 E is obtained through dq rotation transformation. d and e q It can be made by e a e b and e c After dq rotation transformation, we get ω = 2*pi*f, where pi represents π and f is the rated frequency of the inductor.

[0066] You will then receive: u q =(sL1+R1+sL) v +R v )i q1 +ωL1i d1 +ωL v i d1 +u Cq u Cd =(sL2+R2)i d2 -ωL2i q2 +e d u Cq =(sL2+R2)i q2 +ωL2i d2 +e q sCu Cd -ωCu Cq =i d1 -i d2 sCu Cq +ωCu Cd =i q1 -iq2 Where s is the operator variable of the Laplace transform, C is the capacitance value, and u Cd and u Cq The three-phase capacitor voltage (u) Ca u Cb and u Cc It is obtained by dq rotation transformation.

[0067] Let u′ Cd =(sL v +R v )i d1 +u Cd ,u′ Cq =(sL v +R v )i q1 +u Cq ; where u′ Cd and u′ Cq The output voltage u in the loop control C The voltage control quantity, and u Cd and u Cq For current-limiting control, after deducting the virtual impedance voltage drop, u in the loop control... C The voltage control quantity can be understood as the controlled voltage u after triggering virtual impedance current limiting. C The voltage needs to be reduced by the virtual impedance voltage drop in order to achieve the purpose of current limiting.

[0068] Let I dLim and I qLim To represent the maximum allowable current limit in the circuit in the dq rotating coordinate system, let:

[0069] u vd =(sL v +R v )i d1 =(sL v +R v )i dLim (7)

[0070] u vq =(sL v +R v )i q1 =(sL v +R v )i qLim (8)

[0071] Among them, u vd and u vq Let be the voltage drop across the virtual impedance in the dq rotating coordinate system.

[0072] Given the following formula:

[0073]

[0074]

[0075] Among them, I d +jI q (i.e. i d2 +ji q2 ) represents the output current value; I dLim +jI qLim This represents the current value after current limiting, where R and X are the actual impedance and inductive reactance parameters, such as u. d with u Cd The impedance and inductive reactance between; j is the symbol for the imaginary unit, i dLim i is the d-axis output current limit value (i.e., the first axis output current limit value). qLim This is the q-axis output current limit value (i.e., the second axis output current limit value).

[0076] From equations (7)-(9) above, we can obtain u vd =R(i d -i dLim )+X(i qLim -i q ) and u vq =R(i q -i qLim )+X(i d -i dLim Since the resistance R in the actual circuit is very small and can be ignored, it can be converted to: u vd =X(i qLim -i q ) and u vq =X(i d -i dLim Because it is difficult to accurately obtain the final i after rate limiting. d i q After improvement, we can obtain:

[0077]

[0078]

[0079] Where, k i k is the integral coefficient. p Let be the scaling factor, s be the operator variable of the Laplace transform, and i be the scaling factor. d and i q For the three-phase output current i g The d-axis output current (i.e., the first axis output current) and the q-axis output current (i.e., the second axis output current) are obtained through dq rotation transformation.

[0080] According to equations (11) and (12), as Figure 2The control block diagram for the entire VSG is shown below. Figure 2 As shown, based on the original dual closed-loop control of voltage outer loop and current inner loop, adding a virtual impedance current limiting link can effectively limit the output current of the converter without changing the voltage loop characteristics. In order to reduce the impact of the current limiting link on the normal output current when the current limiting link is not triggered, equations (11) and (12) can be subjected to amplitude limiting. For example, in order to ensure that the current limiting link does not affect the normal output current when the current limiting link is not triggered, since i d i q There are positive and negative directions, set i dLim i qLim It also distinguishes between positive and negative limiting, which can be expressed by the following formula (13):

[0081]

[0082] It is evident that, under overcurrent conditions, the output current amplitude can be limited to i. dLim i qLim -i dLim and -i qLim Within the amplitude (depending on the direction of the current).

[0083] It is understandable that the above process utilizes the first shaft output current limit value i from the preset maximum output current limit value of the converter. dLim Second axis output current limit value i qLim The first axis outputs a reference voltage U′. c,dref Second axis output reference voltage U′ c,qref This demonstration uses virtual impedance current limiting adjustment as an example, specifically the target output reference voltage U of the first axis. c,dref =U′ c,dref -u vd Second axis target output reference voltage U c,qref =U′ c,qref -u vq To enable users to access i dLim and i qLim The settings can be adjusted to flexibly limit the total output current based on actual conditions. Correspondingly, in this step, the processor can also utilize the first axis output current limit value i. dLim Or the second axis output current limit value i qLim Adjust the second axis output reference voltage U′ accordingly. c,qref Or the first axis output reference voltage U′ c,dref The first-axis target output reference voltage U is obtained in the preset two-phase coordinate system. c,dref Second axis target output reference voltage U c,qref This allows users to access i dLim or i qLimThe settings allow for independent limiting of active or reactive current; if the second-axis output reference voltage U is not adjusted... c,qref At that time, the second axis output reference voltage U′ can be used. c,dref The target output reference voltage U for the second axis is determined. c,qref .

[0084] In other words, in this step, the processor can determine the first axis voltage adjustment value based on the second axis output current limit and the second axis output current through a proportional-integral control loop; use the first axis voltage adjustment value to adjust the first axis output reference voltage to obtain the first axis target output reference voltage; and / or determine the second axis voltage adjustment value based on the first axis output current limit and the first axis output current through a proportional-integral control loop; use the second axis voltage adjustment value to adjust the second axis output reference voltage to obtain the second axis target output reference voltage; wherein, the second axis output current and the first axis output current are obtained by transforming the three-phase output current of the converter through a preset two-phase coordinate system.

[0085] Accordingly, the determination of the first axis voltage adjustment value based on the second axis output current limit and the second axis output current through a proportional-integral control loop can include: calculating the first axis voltage adjustment value using the above formula (11) or a formula with weighting parameters added to formula (11); where u vd i is the first axis voltage adjustment value. qLim i is the second axis output current limit value. q For the second axis output current, k i k is the integral coefficient. p Let be the scaling factor, and s be the operator variable of the Laplace transform; if i q >0 then i qLim If i is a positive number, then q <0 then i qLim If i is negative; q If the first axis voltage adjustment value is greater than the first threshold, then the first axis voltage adjustment value is adjusted to the first threshold; if the first axis voltage adjustment value is not greater than the first threshold, the first axis voltage adjustment value is not adjusted. q If the value is less than 0, then when the first axis voltage adjustment value is less than the second threshold, the first axis voltage adjustment value will be adjusted to the second threshold; when the first axis voltage adjustment value is not less than the second threshold, the first axis voltage adjustment value will not be adjusted.

[0086] The above-mentioned determination of the second axis voltage adjustment value based on the first axis output current limit and the first axis output current through a proportional-integral control loop may include: calculating the second axis voltage adjustment value using the above formula (12) or a calculation formula that adds weighting parameters to formula (12); where u vq i is the second axis voltage adjustment value. dLimi is the first axis output current limit value. d This is the output current of the first axis; if i d >0 then i dLim If i is a positive number, then d <0 then i dLim If i is negative; d If the value is greater than 0, then when the second-axis voltage adjustment value is greater than the third threshold, the second-axis voltage adjustment value will be adjusted to the third threshold; if the second-axis voltage adjustment value is not greater than the third threshold, the second-axis voltage adjustment value will not be adjusted. d If the value is less than 0, then when the second axis voltage adjustment value is less than the fourth threshold, the second axis voltage adjustment value will be adjusted to the fourth threshold; when the second axis voltage adjustment value is not less than the fourth threshold, the second axis voltage adjustment value will not be adjusted.

[0087] Correspondingly, the specific values ​​of the first to fourth thresholds, i.e., the impact of the current limiting circuit on the normal output current when the current limiting is not triggered, can be set by the designer or user according to the practical scenario and user needs, as shown in equation (13). The first to fourth thresholds can all be 0; the first to fourth thresholds can also be set to other values. This embodiment does not impose any restrictions on this.

[0088] Step 104: Obtain the three-phase target output voltage of the converter based on the first axis target output reference voltage and the second axis target output reference voltage.

[0089] It is understood that in this embodiment, the processor can determine the three-phase target output voltage of the converter at the next moment based on the first axis target output reference voltage and the second axis target output reference voltage, so as to control the controllable switch in the converter accordingly and adjust the subsequent output three-phase voltage of the converter.

[0090] Correspondingly, the specific method by which the processor obtains the three-phase target output voltage of the converter based on the first-axis target output reference voltage and the second-axis target output reference voltage in this step can be set by the designer according to the practical scenario and user needs. For example, the processor can directly convert the first-axis target output reference voltage and the second-axis target output reference voltage into the three-phase target output voltage. Alternatively, the processor can obtain the first-axis target output voltage and the second-axis target output voltage in a preset two-phase coordinate system through dual closed-loop control of the voltage outer loop and the current inner loop, and then convert the first-axis target output voltage and the second-axis target output voltage into the three-phase target output voltage. Figure 2 As shown, the first axis target output reference voltage U c,dref Second axis target output reference voltage U c,qrefThe three-phase voltage (i.e., the three-phase target output voltage) used for PWM control can be obtained through dual closed-loop control of the voltage outer loop and the current inner loop and dq transformation. Figure 2 middle, I in,d and I in,q by i in I is obtained through dq transformation. g,d and I g,d From the output current i g (i.e. i a1 i b1 and i c1 U is obtained through dq transformation. c,d and U c,q From the three-phase capacitor voltage u Cabc i is obtained through dq transformation. in This refers to the current of the three-phase filter inductor. This embodiment does not impose any limitations on this.

[0091] In this embodiment, the present invention utilizes the preset maximum output current limit value of the converter to perform virtual impedance current limiting adjustment on the first axis output reference voltage and / or the second axis output reference voltage, thereby obtaining the first axis target output reference voltage and the second axis target output reference voltage in a preset two-phase coordinate system. This can limit the output current of the grid-type converter using virtual impedance control technology, so that the converter can still maintain voltage source characteristics after current limiting, thereby improving the stability of the converter while ensuring its safe operation.

[0092] Corresponding to the above method embodiments, this invention also provides a current limiting control device for a grid-type converter. The current limiting control device for a grid-type converter described below and the current limiting control method for a grid-type converter described above can be referred to in correspondence with each other.

[0093] Please refer to Figure 4 , Figure 4 This is a structural block diagram of a current limiting control device for a grid-type converter provided in an embodiment of the present invention. The device may include:

[0094] Reference acquisition module 10 is used to acquire the three-phase output reference voltage of the converter; wherein, the output terminal of the converter is connected to the power grid;

[0095] The coordinate transformation module 20 is used to transform the first-axis output reference voltage and the second-axis output reference voltage in a preset two-phase coordinate system corresponding to the three-phase output reference voltage.

[0096] The current limiting adjustment module 30 is used to perform virtual impedance current limiting adjustment on the first axis output reference voltage and / or the second axis output reference voltage using the preset maximum output current limit value of the converter, so as to obtain the first axis target output reference voltage and the second axis target output reference voltage in a preset two-phase coordinate system; wherein, the preset maximum output current limit value includes the second axis output current limit value corresponding to the first axis output reference voltage and / or the first axis output current limit value corresponding to the second axis output reference voltage;

[0097] The reference control module 40 is used to obtain the three-phase target output voltage of the converter based on the first axis target output reference voltage and the second axis target output reference voltage.

[0098] In some embodiments, the converter is an inverter, and the three-phase output reference voltage is the three-phase reference voltage of the virtual synchronous generator (VSG).

[0099] In some embodiments, the preset two-phase coordinate system is the dq rotating coordinate system.

[0100] In some embodiments, the reference control module 40 may include:

[0101] The dual-loop control submodule is used to obtain the first-axis target output voltage and the second-axis target output voltage in a preset two-phase coordinate system through dual closed-loop control of the voltage outer loop and the current inner loop, based on the first-axis target output reference voltage and the second-axis target output reference voltage.

[0102] The coordinate transformation submodule is used to convert the first-axis target output voltage and the second-axis target output voltage into a three-phase target output voltage.

[0103] In some embodiments, the current limiting adjustment module 30 may include:

[0104] The first axis adjustment submodule is used to determine the first axis voltage adjustment value through a proportional-integral control loop based on the second axis output current limit and the second axis output current; adjust the first axis output reference voltage using the first axis voltage adjustment value to obtain the first axis target output reference voltage; and / or

[0105] The second axis adjustment submodule is used to determine the second axis voltage adjustment value through a proportional-integral control loop based on the first axis output current limit value and the first axis output current; using the second axis voltage adjustment value, the second axis output reference voltage is adjusted to obtain the second axis target output reference voltage; wherein, the second axis output current and the first axis output current are obtained by transforming the three-phase output current of the converter through a preset two-phase coordinate system.

[0106] In some embodiments, the first axis adjustment submodule may include:

[0107] The first computing unit is used to... Calculate the first axis voltage adjustment value; where, u vd i is the first axis voltage adjustment value. qLim i is the second axis output current limit value. q For the second axis output current, k i k is the integral coefficient. p Let be the scaling factor, and s be the operator variable of the Laplace transform; if i q >0 then i qLim If i is a positive number, then q <0 then i qLim It is a negative number;

[0108] The first limiting unit, used if i q If i > 0, then when the first axis voltage adjustment value is greater than the first threshold, the first axis voltage adjustment value will be adjusted to the first threshold; if i q If the value is less than 0, then when the first axis voltage adjustment value is less than the second threshold, the first axis voltage adjustment value will be adjusted to the second threshold.

[0109] The second axis adjustment submodule may include:

[0110] The second computing unit is used to... Calculate the second-axis voltage adjustment value; where, u vq i is the second axis voltage adjustment value. dLim i is the first axis output current limit value. d This is the output current of the first axis; if i d >0 then i dLim If i is a positive number, then d <0 then i dLim It is a negative number;

[0111] The second limiting unit is used if i d If i > 0, then when the second axis voltage adjustment value is greater than the third threshold, the second axis voltage adjustment value will be adjusted to the third threshold; if i d If the value is less than 0, then when the second axis voltage adjustment value is less than the fourth threshold, the second axis voltage adjustment value will be adjusted to the fourth threshold.

[0112] In some embodiments, the first threshold, the second threshold, the third threshold, and the fourth threshold are all 0.

[0113] In this embodiment, the present invention uses the current limiting adjustment module 30 to perform virtual impedance current limiting adjustment on the first axis output reference voltage and / or the second axis output reference voltage using the preset maximum output current limit value of the converter. This results in the first axis target output reference voltage and the second axis target output reference voltage under the preset two-phase coordinate system. The virtual impedance control technology can limit the output current of the grid-type converter, so that the converter can still maintain the voltage source characteristics after current limiting. This improves the stability of the converter while ensuring its safe operation.

[0114] Corresponding to the above method embodiments, this invention also provides a converter. The converter described below and the current limiting control method of the grid-type converter described above can be referred to each other.

[0115] Please refer to Figure 5 , Figure 5 This is a schematic diagram of a converter provided in an embodiment of the present invention. The converter may include:

[0116] Memory D1 is used to store computer programs;

[0117] The processor D2 is used to execute a computer program to implement the steps of the current limiting control method for the grid-type converter provided in the above method embodiments.

[0118] For details, please refer to Figure 6 , Figure 6 This is a schematic diagram of a converter according to an embodiment of the present invention. The converter can vary significantly depending on its configuration or performance, and may include one or more central processing units (CPUs) 322 (e.g., one or more processors) and a memory 332, and one or more storage media 330 (e.g., one or more mass storage devices) for storing application programs 342 or data 344. The memory 332 and storage media 330 can be temporary or persistent storage. The program stored in the storage media 330 may include one or more modules (not shown in the diagram), each module including a series of instruction operations on the device. Furthermore, the central processing unit 322 may be configured to communicate with the storage media 330 and execute the series of instruction operations in the storage media 330 on the converter 301.

[0119] The inverter 301 may also include one or more power supplies 326, one or more wired or wireless network interfaces 350, one or more input / output interfaces 358, and / or one or more operating systems 341. Examples include Windows Server™, Mac OS X™, Unix™, Linux™, FreeBSD™, etc.

[0120] The converter 301 can be specifically an inverter controlled by VSG; or it can be specifically a UPS device.

[0121] The steps in the current limiting control method for grid-type converters described above can be implemented by the structure of the converter.

[0122] Corresponding to the above method embodiments, this invention also provides a computer-readable storage medium. The computer-readable storage medium described below and the current limiting control method for a grid-type converter described above can be referred to in correspondence.

[0123] A computer-readable storage medium storing a computer program, which, when executed by a processor, implements the steps of the current limiting control method for a grid-type converter as described in the above method embodiments.

[0124] The computer-readable storage medium can specifically be a USB flash drive, a portable hard drive, a read-only memory (ROM), a random access memory (RAM), a magnetic disk, or an optical disk, or any other readable storage medium capable of storing program code.

[0125] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the apparatus, converter, and computer-readable storage medium disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the descriptions are relatively simple; relevant parts can be referred to in the method section.

[0126] The present invention provides a detailed description of a current limiting control method, apparatus, converter, and computer-readable storage medium for a grid-type converter. Specific examples have been used to illustrate the principles and implementation methods of the invention. The descriptions of these embodiments are merely illustrative of the method and its core ideas. It should be noted that those skilled in the art can make various improvements and modifications to the invention without departing from its principles, and these improvements and modifications also fall within the scope of protection of the present invention.

Claims

1. A current limiting control method for a grid-type converter, characterized in that, include: Obtain the three-phase output reference voltage of the converter; wherein, the output terminal of the converter is connected to the power grid; The first-axis output reference voltage and the second-axis output reference voltage in a preset two-phase coordinate system corresponding to the three-phase output reference voltage are obtained by conversion. Using the preset maximum output current limit value of the converter, virtual impedance current limiting adjustment is performed on the first axis output reference voltage and / or the second axis output reference voltage to obtain the first axis target output reference voltage and the second axis target output reference voltage in the preset two-phase coordinate system; wherein, the preset maximum output current limit value includes the second axis output current limit value corresponding to the first axis output reference voltage and / or the first axis output current limit value corresponding to the second axis output reference voltage; The three-phase target output voltage of the converter is obtained based on the first axis target output reference voltage and the second axis target output reference voltage. The step of using the output current limiting value of the converter to perform virtual impedance current limiting adjustment on the first axis output reference voltage and / or the second axis output reference voltage to obtain the first axis target output reference voltage and the second axis target output reference voltage in the preset two-phase coordinate system includes: Based on the second axis output current limit and the second axis output current, a proportional-integral control loop determines the first axis voltage adjustment value; using the first axis voltage adjustment value, the first axis output reference voltage is adjusted to obtain the first axis target output reference voltage; and / or Based on the first axis output current limit and the first axis output current, the second axis voltage adjustment value is determined through a proportional-integral control loop; using the second axis voltage adjustment value, the second axis output reference voltage is adjusted to obtain the second axis target output reference voltage; wherein, the second axis output current and the first axis output current are obtained by transforming the three-phase output current of the converter through the preset two-phase coordinate system; The step of determining the first axis voltage adjustment value through a proportional-integral control circuit based on the second axis output current limit and the second axis output current includes: pass Calculate the first shaft voltage adjustment value; where, This is the adjustment value for the first axis voltage. This is the output current limit value for the second axis. This is the output current of the second axis. The integral coefficient is... This is the proportionality coefficient. Let be the operator variable of the Laplace transform; if but If it is a positive number, but It is a negative number; like If the first axis voltage adjustment value is greater than the first threshold, then the first axis voltage adjustment value is adjusted to the first threshold; if If the first axis voltage adjustment value is less than the second threshold, then the first axis voltage adjustment value will be adjusted to the second threshold. The step of determining the second axis voltage adjustment value through a proportional-integral control loop based on the first axis output current limit and the first axis output current includes: pass Calculate the second axis voltage adjustment value; where, This is the second axis voltage adjustment value. This is the output current limit value for the first axis. The output current of the first axis; if but If it is a positive number, but It is a negative number; like If the second axis voltage adjustment value is greater than the third threshold, then the second axis voltage adjustment value is adjusted to the third threshold; if If the second axis voltage adjustment value is less than the fourth threshold, then the second axis voltage adjustment value will be adjusted to the fourth threshold.

2. The current limiting control method for a grid-type converter according to claim 1, characterized in that, The converter is an inverter, and the three-phase output reference voltage is the three-phase reference voltage of the virtual synchronous generator (VSG).

3. The current limiting control method for a grid-type converter according to claim 1, characterized in that, The preset two-phase coordinate system is a dq rotating coordinate system.

4. The current limiting control method for a grid-type converter according to claim 1, characterized in that, The step of obtaining the three-phase target output voltage of the converter based on the first axis target output reference voltage and the second axis target output reference voltage includes: Based on the first axis target output reference voltage and the second axis target output reference voltage, the first axis target output voltage and the second axis target output voltage are obtained under a preset two-phase coordinate system through dual closed-loop control of the voltage outer loop and the current inner loop. The first axis target output voltage and the second axis target output voltage are converted into the three-phase target output voltage.

5. The current limiting control method for a grid-type converter according to claim 1, characterized in that, The first threshold, the second threshold, the third threshold, and the fourth threshold are all 0.

6. A current limiting control device for a grid-type converter, characterized in that, include: A reference acquisition module is used to acquire the three-phase output reference voltage of the converter; wherein, the output terminal of the converter is connected to the power grid; The coordinate transformation module is used to transform the three-phase output reference voltage to obtain the first-axis output reference voltage and the second-axis output reference voltage in a preset two-phase coordinate system. The current limiting adjustment module is used to perform virtual impedance current limiting adjustment on the first axis output reference voltage and / or the second axis output reference voltage using the preset maximum output current limit value of the converter, so as to obtain the first axis target output reference voltage and the second axis target output reference voltage in the preset two-phase coordinate system; wherein, the preset maximum output current limit value includes the second axis output current limit value corresponding to the first axis output reference voltage and / or the first axis output current limit value corresponding to the second axis output reference voltage; The reference control module is used to obtain the three-phase target output voltage of the converter based on the first axis target output reference voltage and the second axis target output reference voltage; The current limiting adjustment module includes: The first axis adjustment submodule is used to determine the first axis voltage adjustment value through a proportional-integral control loop based on the second axis output current limit value and the second axis output current; adjust the first axis output reference voltage using the first axis voltage adjustment value to obtain the first axis target output reference voltage; and / or The second axis adjustment submodule is used to determine the second axis voltage adjustment value through a proportional-integral control loop based on the first axis output current limit value and the first axis output current; and to adjust the second axis output reference voltage using the second axis voltage adjustment value to obtain the second axis target output reference voltage; wherein the second axis output current and the first axis output current are obtained by transforming the three-phase output current of the converter through the preset two-phase coordinate system; The first axis adjustment submodule includes: The first computing unit is used to... Calculate the first shaft voltage adjustment value; where, This is the adjustment value for the first axis voltage. This is the output current limit value for the second axis. This is the output current of the second axis. The integral coefficient is... This is the proportionality coefficient. Let be the operator variable of the Laplace transform; if but If it is a positive number, but It is a negative number; The first limiting unit is used if If the first axis voltage adjustment value is greater than the first threshold, then the first axis voltage adjustment value is adjusted to the first threshold; if If the first axis voltage adjustment value is less than the second threshold, then the first axis voltage adjustment value will be adjusted to the second threshold. The second axis adjustment submodule includes: The second computing unit is used to... Calculate the second axis voltage adjustment value; where, This is the second axis voltage adjustment value. This is the output current limit value for the first axis. The output current of the first axis; if but If it is a positive number, but It is a negative number; The second limiting unit is used if If the second axis voltage adjustment value is greater than the third threshold, then the second axis voltage adjustment value is adjusted to the third threshold; if If the second axis voltage adjustment value is less than the fourth threshold, then the second axis voltage adjustment value will be adjusted to the fourth threshold.

7. A converter, characterized in that, include: Memory, used to store computer programs; A processor, configured to implement the steps of the current limiting control method for a grid-type converter as described in any one of claims 1 to 5 when executing the computer program.

8. A computer-readable storage medium, characterized in that, The computer-readable storage medium stores a computer program that, when executed by a processor, implements the steps of the current limiting control method for a grid-type converter as described in any one of claims 1 to 5.

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