A voltage ride-through control method and device of a network-constructed converter and the converter

Abstract

This invention discloses a voltage ride-through control method, device, and converter for a grid-connected converter, relating to the field of power electronics technology. The method includes: obtaining the target output current in a preset two-phase coordinate system corresponding to the three-phase output current of the converter; wherein the target output current is related to the reactive current of the converter, and the output terminal of the converter is connected to the power grid; obtaining a virtual impedance voltage drop value based on the target output current and a preset maximum reactive current limit value; determining the voltage condition of the power grid based on the virtual impedance voltage drop value; if a voltage fault has occurred, reducing the active power setpoint of the converter to a preset power value. This invention can utilize virtual impedance control technology to detect grid voltage faults, improving the accuracy and timeliness of grid voltage fault detection; thus, in the event of a grid voltage fault, by limiting the active power and reducing the output current of the converter, power angle instability is avoided, achieving stable voltage ride-through of the grid voltage fault.

Description

Technical Field

[0001] This invention relates to the field of power electronics technology, and in particular to a voltage ride-through control method, device, and converter 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 power grid. After the converter is connected to the grid, when a fault occurs at a remote end causing a voltage drop in the grid, it is usually disconnected from the grid to avoid overcurrent and for protection devices. However, disconnecting the converter from the grid can exacerbate the grid fault. Therefore, in order to protect the grid, the converter needs to have low voltage ride-through (LVRT) capability, providing some reactive power support to the grid while maintaining stable operation.

[0003] However, converters with voltage source characteristics such as VSG (Virtual Synchronous Generator) control lack low voltage ride-through capability because they cannot provide controllable reactive power. When a fault occurs at a remote end and causes a voltage drop, their voltage source characteristics can easily lead to problems such as overcurrent. That is, after the grid voltage drops instantaneously, the voltage output of the voltage source cannot adjust in time. The potential difference between the voltage source output voltage and the grid voltage generates current in the grid impedance. Since the grid impedance is usually very small, even if the grid voltage drop is shallow, the output current will be very large, which can easily cause a large current surge, leading to the burnout of the power electronic components of the converter or even grid disconnection.

[0004] Therefore, how to limit the output current of the grid-connected converter in the event of a grid voltage fault, so as to achieve grid voltage fault ride-through, is an urgent problem to be solved. Summary of the Invention

[0005] The purpose of this invention is to provide a voltage ride-through control method, device, and converter for a grid-connected converter, which can limit the output current of the grid-connected converter in the event of a grid voltage fault, so as to achieve grid voltage fault ride-through.

[0006] To solve the above-mentioned technical problems, the present invention provides a voltage ride-through control method for a grid-type converter, comprising:

[0007] Obtain the target output current in a preset two-phase coordinate system corresponding to the three-phase output current of the converter; wherein, the target output current is the first axis output current or the second axis output current in the preset two-phase coordinate system, the target output current is related to the reactive current of the converter, and the output terminal of the converter is connected to the power grid;

[0008] The virtual impedance voltage drop value is obtained based on the target output current and the preset maximum reactive current limit value;

[0009] The voltage condition of the power grid is determined based on the virtual impedance voltage drop value;

[0010] If a voltage fault occurs, the active power setpoint of the converter is reduced to a preset power value.

[0011] On the other hand, obtaining the virtual impedance voltage drop value based on the target output current and the preset maximum reactive current limit includes:

[0012] The virtual impedance voltage drop value is determined by a proportional-integral control circuit based on the target output current and the preset maximum reactive current limit.

[0013] On the other hand, the preset two-phase coordinate system is a dq rotating coordinate system, and the determination of the virtual impedance voltage drop value through a proportional-integral control loop based on the target output current and the preset maximum reactive current limit includes:

[0014] pass Calculate the virtual impedance voltage drop value; where, u vd Let i be the virtual impedance voltage drop value. qLim i is the preset maximum reactive current limit value. q For the target 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;

[0015] If i q If the virtual impedance voltage drop is greater than 0, then when the virtual impedance voltage drop is greater than the current limiting threshold, the virtual impedance voltage drop will be adjusted to the current limiting threshold; if i q If the value is less than 0, then when the virtual impedance voltage drop is less than the current limiting threshold, the virtual impedance voltage drop will be adjusted to the current limiting threshold.

[0016] On the other hand, determining the voltage condition of the power grid based on the virtual impedance voltage drop includes:

[0017] If the virtual impedance voltage drop value is not equal to the current limiting threshold, then the voltage condition of the power grid is determined to be faulty.

[0018] On the other hand, after obtaining the virtual impedance voltage drop value based on the target output current and the preset maximum reactive current limit, the method further includes:

[0019] The target output reference voltage is adjusted using the virtual impedance voltage drop value to obtain the adjusted target output reference voltage; wherein, the target output reference voltage is the first axis output reference voltage or the second axis output reference voltage in the preset two-phase coordinate system obtained by converting the three-phase output reference voltage of the converter, and the target output reference voltage is related to the reactive power of the converter;

[0020] The three-phase target output voltage of the converter is obtained based on the non-target output reference voltage and the adjusted target output reference voltage; wherein, the non-target output reference voltage is the output reference voltage of another axis other than the target output reference voltage in the preset two-phase coordinate system obtained by converting the three-phase output reference voltage.

[0021] On the other hand, the preset two-phase coordinate system is a dq rotating coordinate system, the target output current is the q-axis output current, and the target output reference voltage is the d-axis output reference voltage.

[0022] On the other hand, obtaining the three-phase target output voltage of the converter based on the non-target output reference voltage and the adjusted target output reference voltage includes:

[0023] Based on the non-target output reference voltage and the adjusted target output reference voltage, the first axis target output voltage and the second axis target output voltage in the preset two-phase coordinate system are obtained through dual closed-loop control of the voltage outer loop and the current inner loop.

[0024] The first axis target output voltage and the second axis target output voltage are converted into the three-phase target output voltage.

[0025] 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).

[0026] The present invention also provides a voltage ride-through control device for a grid-type converter, comprising:

[0027] A current conversion module is used to obtain the target output current in a preset two-phase coordinate system corresponding to the three-phase output current of the converter; wherein, the target output current is the first axis output current or the second axis output current in the preset two-phase coordinate system, the target output current is related to the reactive current of the converter, and the output terminal of the converter is connected to the power grid;

[0028] The voltage drop acquisition module is used to acquire the virtual impedance voltage drop value based on the target output current and the preset maximum reactive current limit value;

[0029] The fault determination module is used to determine the voltage status of the power grid based on the virtual impedance voltage drop value;

[0030] The fault ride-through module is used to reduce the active power setpoint of the converter to a preset power value if a voltage fault occurs.

[0031] Furthermore, the present invention also provides a converter, comprising:

[0032] Memory, used to store computer programs;

[0033] A processor is used to execute the computer program to implement the steps of the voltage ride-through control method for a grid-type converter as described above.

[0034] The present invention provides a voltage ride-through control method for a grid-connected converter, comprising: obtaining a target output current in a preset two-phase coordinate system corresponding to the three-phase output current of the converter; wherein the target output current is the first-axis output current or the second-axis output current in the preset two-phase coordinate system, the target output current is related to the reactive current of the converter, and the output terminal of the converter is connected to the power grid; obtaining a virtual impedance voltage drop value based on the target output current and a preset maximum reactive current limit value; determining the voltage condition of the power grid based on the virtual impedance voltage drop value; if the voltage condition indicates a fault, reducing the active power setpoint of the converter to a preset power value;

[0035] As can be seen, this invention obtains the virtual impedance voltage drop value based on the target output current and the preset maximum reactive current limit, enabling the detection of grid voltage faults using virtual impedance control technology, thus improving the accuracy and timeliness of grid voltage fault detection. Furthermore, in the event of a grid voltage fault, by limiting active power to reduce the converter's output current, power angle instability is avoided, achieving stable voltage ride-through. In addition, this invention also provides a voltage ride-through control device and converter for a grid-connected converter, which also possesses 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 voltage ride-through control method for a grid 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 voltage ride-through 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 voltage ride-through control method for a grid-type converter provided in an embodiment of the present invention. The method includes:

[0045] Step 101: Obtain the target output current in the preset two-phase coordinate system corresponding to the three-phase output current of the converter.

[0046] The target output current is either the first axis output current or the second axis output current in a preset two-phase coordinate system. The target output current is related to the reactive current of the converter, and the output terminal of the converter is connected to the power grid.

[0047] 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 voltage ride-through control method for the grid-connected converter provided in this embodiment can be applied to the control process of grid-connected inverters, such as the virtual synchronous generator (VSG) control process of the inverter. That is, the grid-connected inverter can use the method provided in this embodiment to limit the active power setpoint of the VSG control during a grid voltage fault, correspondingly adjusting the output phase of the VSG control, thereby reducing the output current of the converter and achieving stable ride-through of the grid voltage fault. The voltage ride-through control method for the grid-connected converter provided in this embodiment can also be applied to other control processes of grid-connected inverters or the control process of grid-connected AC converters, such as the inverter control scenario of a UPS (Uninterruptible Power System). As long as virtual impedance control technology can be used to detect grid voltage faults, and in the event of a grid voltage fault, the output current of the converter can be reduced by limiting the active power to achieve stable ride-through of the grid voltage fault, this embodiment does not impose any restrictions on this.

[0048] In this embodiment, the output terminal of the converter can be connected to the power grid; that is, the converter can be a grid-connected converter. In this embodiment, the three-phase output current of the converter can be the current output of a voltage source converter (i.e., the three-phase current), specifically the output current of the current meter at the current sampling moment, such as... Figure 2 The current i output through inverter filter inductor L1 and inverter output filter inductor L2 is g In this embodiment, the target output current can be obtained by rotating and transforming the three-phase output current to obtain the current value on one axis (the first axis and the second axis) of the corresponding current values ​​on two axes (the first axis and the second axis) in a preset two-phase coordinate system (i.e., the output current of the first axis and the output current of the second axis) that is related to the reactive current of the converter.

[0049] Accordingly, 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 dq transformation on the three-phase output reference voltage to obtain 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), and convert the q-axis output current (i.e., the reactive current related to the reactive current) into a d-axis output current (i.e., the second axis output current). Figure 2 i in qThe target output current is determined by the α-axis or β-axis rotational coordinate system. 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 current (i.e., the first axis output current) and the β-axis output current (i.e., the second axis output current), so that the α-axis output current or β-axis output current related to the reactive current is determined as the target output current. This embodiment does not impose any limitations on this.

[0050] Step 102: Obtain the virtual impedance voltage drop value based on the target output current and the preset maximum reactive current limit value.

[0051] In this embodiment, the preset maximum reactive current limit value can be a preset limit value used to limit the maximum amplitude of the reactive current of the inverter; such as the limit value for limiting the maximum amplitude of the target output current. Since the target output current is related to the reactive current, the setting of the preset maximum reactive current limit value can be such that the amplitude of the target output current is less than or equal to the amplitude of the preset maximum reactive current limit value, so as to limit the maximum amplitude of the reactive current.

[0052] In other words, this embodiment utilizes virtual impedance control technology to calculate the voltage drop across the virtual impedance based on the target output current and the preset maximum reactive current limit, in order to detect the voltage status of the power grid. Thus, when the detected voltage status indicates a fault, the active power setpoint of the converter is reduced to a preset power value to achieve stable voltage fault ride-through.

[0053] For example, such as Figure 2 and Figure 3 As shown, the method provided in this embodiment is applied to the VSG control of an inverter, and the control circuit topology changes after adding virtual impedance 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.

[0054] 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:

[0055]

[0056]

[0057]

[0058] 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:

[0059]

[0060]

[0061]

[0062] 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.

[0063] 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 -i q2 ; s is the operator variable of the Laplace transform, C is the capacitance value, u Cd and u Cq The three-phase capacitor voltage (u) Ca u Cb and u Cc It is obtained by dq rotation transformation.

[0064] 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 When performing current limiting control, the virtual impedance voltage drop can be deducted before applying it 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 can be reduced by the corresponding virtual impedance voltage drop to achieve the purpose of current limiting.

[0065] Let I dLim and I qLim To represent the maximum allowable current limit in the circuit in the dq rotating coordinate system, let:

[0066] u vd =(sL v +R v )i d1 =(sL v +R v )i dLim (7)

[0067] u vq =(sL v +R v )i q1 =(sL v +R v )i qLim (8)

[0068] Among them, u vd and u vq This represents the voltage drop of the virtual impedance in the dq rotating coordinate system, i.e., the virtual impedance voltage drop along the d-axis and the virtual impedance voltage drop along the q-axis.

[0069] Given the following formula:

[0070]

[0071]

[0072] 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. qLim This is the q-axis output current limit value.

[0073] 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 uvq =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:

[0074]

[0075]

[0076] Where, k i k is the integral coefficient. p Let be the proportionality coefficient, s be the operator variable of the Laplace transform, and i be the proportionality coefficient. 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.

[0077] When the voltage at the far end drops, according to the following formula (13), for the same active power, the required power angle is larger. If it is not restricted, it is easy to cause power angle instability, resulting in the tripping of the inverter and disconnection from the grid.

[0078]

[0079] In equation (13), V A V is the terminal voltage. B Q is the remote voltage. A Reactive power is δ, power angle is R e and X e For the grid impedance and inductive reactance, i.e., V A With V B The impedance and inductive reactance between them. To avoid such a situation, this embodiment can use the d-axis virtual impedance voltage drop (virtual impedance voltage drop value) to determine whether a fault has occurred in the grid voltage. If a fault state is triggered, the active power setpoint will be reduced to a preset power value (such as 0) to achieve the purpose of stabilizing the voltage fault ride-through.

[0080] Furthermore, as shown in equation (14), when the voltage at the far end drops, the reactive power will suddenly increase, causing reactive current overcurrent and resulting in instability.

[0081]

[0082] Therefore, in this embodiment, the reactive current i related to the converter can also be calculated according to the above formula (11). q Apply amplitude limiting. For example... Figure 2As shown, by adding a virtual impedance current limiting link to the existing dual closed-loop control of voltage outer loop and current inner loop, the output current of the inverter can be effectively limited 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, equation (11) can be limited. 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 q There are positive and negative directions, set i qLim Positive and negative limits can also be distinguished, which can be done using the following formula (15):

[0083]

[0084] It is evident that, under overcurrent conditions, the reactive current can be limited to i. qLim and -i qLim (Depending on whether it triggers a high-level or low-level penetration) within the amplitude.

[0085] Correspondingly, the process described above for adjusting the active power setpoint based on the d-axis virtual impedance voltage drop (virtual impedance voltage drop value) can be achieved through if(u vd ! = 0):P Min =P Max =0 is achieved; where P Min and P Max The active power setpoint P is respectively ref The lower and upper limits; that is, when the d-axis virtual impedance voltage drop (i.e., the virtual impedance voltage drop value related to reactive power) is not 0 (i.e., the current limiting threshold), it is determined that a grid voltage fault has occurred, and the active power setpoint P is used to determine the fault. ref The lower limit value P Min and upper limit value P Max Setting all values ​​to 0 allows the active power setpoint P to be set to 0. ref Reduce to 0 (i.e., the preset power value) to ensure stable power angle, and restore active power simultaneously after the fault is recovered.

[0086] It is understandable that the specific method by which the processor obtains the virtual impedance voltage drop value based on the target output current and the preset maximum reactive current limit value in this step can be set by the designer according to the usage scenario and user needs. For example, the processor can determine the virtual impedance voltage drop value through a proportional-integral control loop based on the target output current and the preset maximum reactive current limit value; for example, as shown in equation (11) above, the processor can... The virtual impedance voltage drop value is calculated; where u vd i represents the virtual impedance voltage drop. qLim To preset the maximum reactive current limit, i q For the target output current, k i k is the integral coefficient. pLet 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.

[0087] Correspondingly, the processor can also adjust the calculated virtual impedance voltage drop value to reduce the impact of the added virtual impedance current limiting circuit on normal reactive current when current limiting is not triggered; for example, the processor can adjust the virtual impedance current limiting circuit in the i-axis. q When the virtual impedance voltage drop is greater than 0, if the virtual impedance voltage drop is greater than the current limiting threshold, the virtual impedance voltage drop will be adjusted to the current limiting threshold; if the virtual impedance voltage drop is not greater than the current limiting threshold, the virtual impedance voltage drop will not be adjusted. q When the virtual impedance voltage drop is less than 0, the virtual impedance voltage drop is adjusted to the current limiting threshold when the virtual impedance voltage drop is less than the current limiting threshold. When the virtual impedance voltage drop is not less than the current limiting threshold, the virtual impedance voltage drop is not adjusted. The specific value of the current limiting threshold can be set by the designer or user, as shown in equation (15) above. The current limiting threshold can be set to 0 so that the virtual impedance current limiting circuit has no effect on the normal reactive current when the current limiting is not triggered; the current limiting threshold can also be set to other values. This embodiment does not impose any restrictions on this.

[0088] Furthermore, in this embodiment, virtual impedance technology can be used to limit the output current of the converter without changing the characteristics of the voltage source. For example, the processor can use the virtual impedance voltage drop value to adjust the target output reference voltage to obtain the adjusted target output reference voltage; based on the non-target output reference voltage and the adjusted target output reference voltage, the three-phase target output voltage of the converter is obtained; wherein, the target output reference voltage is the first axis output reference voltage or the second axis output reference voltage in a preset two-phase coordinate system obtained by converting the three-phase output reference voltage of the converter, and the target output reference voltage is related to the reactive power of the converter; the non-target output reference voltage is the output reference voltage of another axis other than the target output reference voltage in the preset two-phase coordinate system obtained by converting the three-phase output reference voltage.

[0089] The aforementioned three-phase output reference voltage 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), for example, the three-phase reference voltage of the VSG (such as...). Figure 2 The three-phase capacitor voltage u between the inverter filter inductor L1 and the inverter output filter inductor L2 CabcThe reference voltage is the three-phase voltage corresponding to the phase output of the UPS phase-locked loop. This embodiment does not limit the specific method for obtaining the three-phase output reference voltage. For example, it can be implemented using the same or similar methods as those used in the prior art for calculating the reference value of the three-phase output voltage for converter control, such as when applied to VSG control. Figure 2 As shown, the processor can adjust the collected three-phase capacitor voltage u Cabc and three-phase output current i g (i gabc The active power P was 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 The three-phase output reference voltage is obtained, 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.

[0090] Correspondingly, the processor can perform rotational transformation on the three-phase target output voltage of the converter to obtain two-axis output reference voltages in a preset two-phase coordinate system; determine the one-axis output reference voltage related to the reactive power of the converter as the target output reference voltage, and determine the other-axis output reference voltage as a non-target output reference voltage; adjust the target output reference voltage using the virtual impedance voltage drop value to obtain the adjusted target output reference voltage, such as calculating the difference between the target output reference voltage and the virtual impedance voltage drop value to obtain the adjusted target output reference voltage. Figure 2 As shown, when the preset two-phase coordinate system can be a dq rotating coordinate system, the processor can perform a dq transformation on the three-phase output reference voltage to obtain the d-axis output reference voltage U′ related to the reactive power of the converter. c,dref (i.e., target output reference voltage) and q-axis output reference voltage U c,qref (i.e., non-target output reference voltage); calculate the d-axis output reference voltage U′. c,dref With virtual impedance voltage drop u vd The difference is used to obtain the adjusted target output reference voltage U. c,dref .

[0091] Correspondingly, the specific method for obtaining the three-phase target output voltage of the converter based on the non-target output reference voltage and the adjusted target output reference voltage can be set by the designer according to the practical scenario and user needs. For example, the processor can directly convert the non-target output reference voltage and the adjusted 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, based on the non-target output reference voltage and the adjusted target output reference voltage; 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 adjusted target output reference voltage U c,dref Non-target output reference voltage U c,qref The 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 In the diagram, L1 is the inverter filter inductor, L2 is the inverter output filter inductor, and I... in,d and I in,q byi 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.

[0092] Step 103: Determine the voltage status of the power grid based on the virtual impedance voltage drop value.

[0093] It is understandable that conventional methods of detecting grid voltage by voltage amplitude cannot detect grid voltage faults (such as high-low voltage faults) in a timely and accurate manner. For example, since the function of VSG is to output reactive power to support stable voltage amplitude without drop, conventional methods of detecting grid voltage faults by voltage amplitude will be severely delayed or even fail. Therefore, in this step, the processor can determine the voltage status of the grid connected to the converter output terminal based on the obtained virtual impedance voltage drop value, that is, detect whether a grid fault has occurred, ensuring the accuracy and timeliness of grid voltage fault detection.

[0094] Correspondingly, the specific method for determining the grid voltage based on the virtual impedance voltage drop in this step can be set by the designer according to the practical scenario and user needs. For example, the processor can set the target output current i q When the virtual impedance voltage drop is greater than 0, a voltage fault in the power grid can be determined when the virtual impedance voltage drop exceeds the current limiting threshold; in i q When the virtual impedance voltage drop is less than 0, if the virtual impedance voltage drop is less than the current limiting threshold, the voltage condition of the power grid can be determined to be faulty; otherwise, the voltage condition of the power grid is determined to be faultless. Correspondingly, if the added virtual impedance current limiting circuit limits the virtual impedance voltage drop to the current limiting threshold (e.g., 0) when current limiting is not triggered, the processor can also determine that the voltage condition of the power grid is faulty when the virtual impedance voltage drop is not the current limiting threshold; and determine that the voltage condition of the power grid is faultless when the virtual impedance voltage drop is the current limiting threshold. This embodiment does not impose any limitations on this.

[0095] Step 104: If a voltage fault occurs, reduce the active power setpoint of the converter to the preset power value.

[0096] In this step, when the processor determines that the voltage condition of the power grid is faulty (such as voltage drop), it can reduce the active power setpoint of the converter to a preset power value to achieve stable voltage fault ride-through.

[0097] Correspondingly, this embodiment does not limit the specific value of the preset power value. For example, the active power given value can be 0 or other smaller power values. As long as the preset power value is lower than the active power given value of the converter when the grid voltage is normal, so as to achieve grid voltage fault ride-through, this embodiment does not impose any restrictions on this.

[0098] In this embodiment, the present invention obtains the virtual impedance voltage drop value based on the target output current and the preset maximum reactive current limit value. It can use virtual impedance control technology to detect grid voltage faults, thereby improving the accuracy and timeliness of grid voltage fault detection. In the event of a grid voltage fault, the output current of the converter is reduced by limiting the active power, thus avoiding power angle instability and achieving stable ride-through of grid voltage faults.

[0099] Corresponding to the above method embodiments, this invention also provides a voltage ride-through control device for a grid-type converter. The voltage ride-through control device for a grid-type converter described below and the voltage ride-through control method for a grid-type converter described above can be referred to in correspondence with each other.

[0100] Please refer to Figure 4 , Figure 4This is a structural block diagram of a voltage ride-through control device for a grid-type converter provided in an embodiment of the present invention. The device may include:

[0101] The current conversion module 10 is used to obtain the target output current in a preset two-phase coordinate system corresponding to the three-phase output current of the converter; wherein, the target output current is the first axis output current or the second axis output current in the preset two-phase coordinate system, the target output current is related to the reactive current of the converter, and the output terminal of the converter is connected to the power grid.

[0102] The voltage drop acquisition module 20 is used to acquire the virtual impedance voltage drop value based on the target output current and the preset maximum reactive current limit value;

[0103] The fault determination module 30 is used to determine the voltage status of the power grid based on the virtual impedance voltage drop value;

[0104] The fault ride-through module 40 is used to reduce the active power setpoint of the converter to a preset power value if a voltage fault occurs.

[0105] In some embodiments, the voltage drop acquisition module 20 can be specifically used to determine the virtual impedance voltage drop value through a proportional-integral control circuit based on the target output current and the preset maximum reactive current limit value.

[0106] In some embodiments, the preset two-phase coordinate system is a dq rotating coordinate system, and the voltage drop acquisition module 20 may include:

[0107] The calculation submodule is used to... Calculate the virtual impedance voltage drop; where u vd i represents the virtual impedance voltage drop. qLim To preset the maximum reactive current limit, i q For the target 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] Adjust the submodule for if i q If i > 0, then when the virtual impedance voltage drop is greater than the current limiting threshold, the virtual impedance voltage drop will be adjusted to the current limiting threshold; if i q If the value is less than 0, then when the virtual impedance voltage drop is less than the current limiting threshold, the virtual impedance voltage drop will be adjusted to the current limiting threshold.

[0109] In some embodiments, the fault determination module 30 may be specifically used to determine that the voltage condition of the power grid is faulty if the virtual impedance voltage drop value is not equal to the current limiting threshold.

[0110] In some embodiments, the device may further include:

[0111] The reference adjustment module is used to adjust the target output reference voltage using the virtual impedance voltage drop value to obtain the adjusted target output reference voltage. The target output reference voltage is the first axis output reference voltage or the second axis output reference voltage in the preset two-phase coordinate system obtained by converting the three-phase output reference voltage of the converter. The target output reference voltage is related to the reactive power of the converter.

[0112] The target acquisition module is used to acquire the three-phase target output voltage of the converter based on the non-target output reference voltage and the adjusted target output reference voltage; wherein, the non-target output reference voltage is the output reference voltage of another axis other than the target output reference voltage in the preset two-phase coordinate system obtained by converting the three-phase output reference voltage.

[0113] In some embodiments, the preset two-phase coordinate system is a dq rotating coordinate system, the target output current is the q-axis output current, and the target output reference voltage is the d-axis output reference voltage.

[0114] In some embodiments, the target acquisition module may include:

[0115] The dual closed-loop 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 by using dual closed-loop control of the voltage outer loop and the current inner loop, based on the non-target output reference voltage and the adjusted target output reference voltage.

[0116] The conversion 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.

[0117] 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).

[0118] In this embodiment, the present invention obtains the virtual impedance voltage drop value by the voltage drop acquisition module 20 based on the target output current and the preset maximum reactive current limit value. This enables the use of virtual impedance control technology to detect grid voltage faults, thereby improving the accuracy and timeliness of grid voltage fault detection. In the event of a grid voltage fault, the output current of the converter is reduced by limiting the active power, thus avoiding power angle instability and achieving stable grid voltage fault ride-through.

[0119] Corresponding to the above method embodiments, this invention also provides a converter. The converter described below and the voltage ride-through control method of the grid-type converter described above can be referred to each other.

[0120] 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:

[0121] Memory D1 is used to store computer programs;

[0122] Processor D2 is used to execute computer programs to implement the steps of the voltage ride-through control method for grid-type converters provided in the above method embodiments.

[0123] 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.

[0124] 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.

[0125] The converter 301 can be specifically an inverter controlled by VSG; or it can be specifically a UPS device.

[0126] The steps in the voltage ride-through control method for grid-type converters described above can be implemented by the structure of the converter.

[0127] Corresponding to the above method embodiments, this invention also provides a computer-readable storage medium. The computer-readable storage medium described below and the voltage ride-through control method for a grid-type converter described above can be referred to in correspondence.

[0128] A computer-readable storage medium storing a computer program, which, when executed by a processor, implements the steps of the voltage ride-through control method for a grid-type converter as described in the above method embodiments.

[0129] 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.

[0130] 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.

[0131] The voltage ride-through control method, apparatus, and converter for a grid-type converter provided by this invention have been described in detail above. Specific examples have been used to illustrate the principles and implementation methods of this invention. The descriptions of the embodiments above are merely for the purpose of helping to understand the method and core ideas of this invention. It should be noted that those skilled in the art can make various improvements and modifications to this invention without departing from its principles, and these improvements and modifications also fall within the protection scope of this invention.

Claims

1. A voltage ride-through control method for a grid-connected converter, characterized in that, include: Obtain the target output current in a preset two-phase coordinate system corresponding to the three-phase output current of the converter; wherein, the target output current is the first axis output current or the second axis output current in the preset two-phase coordinate system, the target output current is related to the reactive current of the converter, and the output terminal of the converter is connected to the power grid; The virtual impedance voltage drop value is obtained based on the target output current and the preset maximum reactive current limit value; The voltage condition of the power grid is determined based on the virtual impedance voltage drop value; If the voltage condition indicates a fault, the active power setpoint of the converter will be reduced to a preset power value. The step of obtaining the virtual impedance voltage drop value based on the target output current and the preset maximum reactive current limit includes: The virtual impedance voltage drop value is determined by a proportional-integral control circuit based on the target output current and the preset maximum reactive current limit value. The preset two-phase coordinate system is a dq rotating coordinate system. The step of determining the virtual impedance voltage drop value based on the target output current and the preset maximum reactive current limit through a proportional-integral control loop includes: pass Calculate the virtual impedance voltage drop value; wherein, The virtual impedance voltage drop value, The preset maximum reactive current limit value, The target output current, 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 virtual impedance voltage drop is greater than the current limiting threshold, then the virtual impedance voltage drop will be adjusted to the current limiting threshold; if If the virtual impedance voltage drop is less than the current limiting threshold, the virtual impedance voltage drop will be adjusted to the current limiting threshold.

2. The voltage ride-through control method for a grid-type converter according to claim 1, characterized in that, Determining the voltage status of the power grid based on the virtual impedance voltage drop value includes: If the virtual impedance voltage drop value is not equal to the current limiting threshold, then the voltage condition of the power grid is determined to be faulty.

3. The voltage ride-through control method for a grid-type converter according to claim 1 or 2, characterized in that, After obtaining the virtual impedance voltage drop value based on the target output current and the preset maximum reactive current limit, the method further includes: The target output reference voltage is adjusted using the virtual impedance voltage drop value to obtain the adjusted target output reference voltage; wherein, the target output reference voltage is the first axis output reference voltage or the second axis output reference voltage in the preset two-phase coordinate system obtained by converting the three-phase output reference voltage of the converter, and the target output reference voltage is related to the reactive power of the converter; The three-phase target output voltage of the converter is obtained based on the non-target output reference voltage and the adjusted target output reference voltage; wherein, the non-target output reference voltage is the output reference voltage of another axis other than the target output reference voltage in the preset two-phase coordinate system obtained by converting the three-phase output reference voltage.

4. The voltage ride-through control method for a grid-type converter according to claim 3, characterized in that, The preset two-phase coordinate system is a dq rotating coordinate system, the target output current is the q-axis output current, and the target output reference voltage is the d-axis output reference voltage.

5. The voltage ride-through control method for a grid-type converter according to claim 3, characterized in that, The three-phase target output voltage of the converter is obtained based on the non-target output reference voltage and the adjusted target output reference voltage, including: Based on the non-target output reference voltage and the adjusted target output reference voltage, the first axis target output voltage and the second axis target output voltage in the preset two-phase coordinate system are obtained 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.

6. The voltage ride-through control method for a grid-type converter according to claim 3, 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).

7. A voltage ride-through control device for a grid-type converter, characterized in that, include: A current conversion module is used to obtain the target output current in a preset two-phase coordinate system corresponding to the three-phase output current of the converter; wherein, the target output current is the first axis output current or the second axis output current in the preset two-phase coordinate system, the target output current is related to the reactive current of the converter, and the output terminal of the converter is connected to the power grid; The voltage drop acquisition module is used to acquire the virtual impedance voltage drop value based on the target output current and the preset maximum reactive current limit value; The fault determination module is used to determine the voltage status of the power grid based on the virtual impedance voltage drop value; The fault ride-through module is used to reduce the active power setpoint of the converter to a preset power value if the voltage condition indicates a fault. The voltage drop acquisition module is specifically used to determine the virtual impedance voltage drop value based on the target output current and the preset maximum reactive current limit value through a proportional-integral control circuit. The preset two-phase coordinate system is a dq rotating coordinate system, and the voltage drop acquisition module includes: The calculation submodule is used to... Calculate the virtual impedance voltage drop value; wherein, The virtual impedance voltage drop value, The preset maximum reactive current limit value, The target output current, 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; Adjust the submodule for use if If the virtual impedance voltage drop is greater than the current limiting threshold, then the virtual impedance voltage drop will be adjusted to the current limiting threshold; if If the virtual impedance voltage drop is less than the current limiting threshold, the virtual impedance voltage drop will be adjusted to the current limiting threshold.

8. A converter, characterized in that, include: Memory, used to store computer programs; A processor, configured to execute the computer program to implement the steps of the voltage ride-through control method for a grid-type converter as described in any one of claims 1 to 6.

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