Converter fault ride-through comprehensive control method based on direct control

Abstract

The invention discloses a converter fault ride-through comprehensive control method based on direct control, and relates to the technical field of converter control. According to the method, the voltage amplitude and the voltage phase angle of the converter during the fault ride-through period are directly controlled, and certain virtual impedance is increased, so that the current limiting processing capability of the converter during the fault ride-through period is ensured, the accuracy of the control of the converter is ensured by a plurality of control dimensions, and the stability of the converter during the fault ride-through period is improved. And through reactive power regulation and control, the recovery capability of the corresponding grid-connected point voltage of the converter is improved, and the stability of the converter during the fault ride-through period is further improved. By directly regulating and controlling the voltage amplitude, the voltage phase angle, the virtual impedance and the reactive power, an additional current inner ring is prevented from being added, so that an additional voltage and current sensor is not needed, and the control simplicity in the fault ride-through period of the converter is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of converter control, and in particular relates to a converter fault ride-through comprehensive control method based on direct control. Background Art

[0002] With the continuous development and application of new energy technologies, distributed new energy is widely used in new distribution systems due to its high flexibility and strong controllability. As an interface device connecting distributed new energy and distribution systems, converters play a vital role in power systems. When a power grid fails, the distributed energy system is protected by cutting off the connection between the distributed energy system and the power grid. However, as the proportion of distributed new energy in the distribution system increases, this behavior of cutting off the power grid will seriously deteriorate the stability of the power grid. Therefore, in the current power system, converters are required to actively participate in grid regulation during grid failures.

[0003] The existing technologies mostly analyze and study the parameter design and optimization, control strategy and other aspects of grid-connected converters. For example, an additional current inner loop is added to the converter to take into account the current limiting control and stability performance during fault ride-through. However, correspondingly, the additional current loop adds more voltage and current sensors, which makes the control of the converter during fault ride-through more complicated and lacks simplicity. The existing technologies also solve the stability problem of the converter by controlling the output voltage of the converter during fault ride-through, but this technology only focuses on voltage regulation and ignores the current limiting processing during fault ride-through, resulting in poor stability of the converter during fault ride-through. Therefore, there is an urgent need for a comprehensive control method for converter fault ride-through based on direct control to solve the defects of the existing technologies. Summary of the invention

[0004] The present invention aims to provide a comprehensive control method for converter fault ride-through based on direct control to solve the above-mentioned technical problems, construct a control model of the converter, and realize the control of the converter fault ride-through by regulating the voltage amplitude, voltage phase angle, virtual impedance and reactive power, so as to improve the stability and control simplicity of the converter during fault ride-through.

[0005] In order to solve the above technical problems, an embodiment of the present invention provides a direct control-based converter fault ride-through integrated control method, comprising:

[0006] Acquiring rated operation information of the converter, and determining a power outer loop function, an output power function, and an output current function of the converter according to the rated operation information, so as to construct a converter control model;

[0007] When a fault occurs in the power grid, the fault voltage information of the power grid and the output current information of the converter are collected;

[0008] Determine a voltage amplitude control value and a voltage phase angle control value of the converter according to the fault voltage information and a converter control model;

[0009] Determine a virtual impedance control value of the converter according to the rated operation information and the output current information;

[0010] Determine the reactive power control value of the converter according to the fault voltage information and the rated operation information in combination with the converter control model;

[0011] The converter is controlled according to the voltage amplitude control value, the voltage phase angle control value, the virtual impedance control value and the reactive power control value.

[0012] It can be understood that, compared with the prior art, the present invention constructs the power outer loop function, output power function and output current function of the converter through the rated operation information of the converter, and then constructs the converter control model. Based on the converter control model, the voltage amplitude, voltage phase angle, virtual impedance and reactive power regulation of the converter are realized, and the regulation of the converter during fault crossing is realized. By directly controlling the voltage amplitude and voltage phase angle of the converter during fault crossing, and adding a certain virtual impedance, the current limiting processing capability of the converter during fault crossing is guaranteed, and the accurate control of the converter is guaranteed with multiple control dimensions, thereby improving the stability of the converter during fault crossing. Through reactive power regulation, the recovery ability of the converter corresponding to the grid connection point voltage is improved, and the stability of the converter during fault crossing is further improved. By directly regulating the voltage amplitude, voltage phase angle, virtual impedance and reactive power, the addition of an additional current inner loop is avoided, so that no additional voltage and current sensors are required, and the control simplicity of the converter during fault crossing is improved.

[0013] As a preferred solution, the step of obtaining rated operation information of the converter and determining the power outer loop function, output power function and output current function of the converter according to the rated operation information to construct a converter control model specifically includes:

[0014] Acquire rated operation information of the converter, wherein the rated operation information includes: rated active power, rated reactive power, reference angular velocity, filter inductance and three-phase current information;

[0015] Determining a power outer loop function of the converter according to the rated active power, the rated reactive power and the reference angular velocity;

[0016] Determining an output power function of the converter according to the power outer loop function and in combination with the filter inductance;

[0017] Determining the output current function of the converter according to the power outer loop function in combination with the three-phase current information and the filter inductance;

[0018] A converter control model is constructed according to the power outer loop function, the output power function and the output current function.

[0019] As a preferred solution, the step of determining the power outer loop function of the converter according to the rated active power, the rated reactive power and the reference angular velocity specifically includes:

[0020] Determining a frequency control function and a voltage control function of the converter according to the rated active power, the rated reactive power and the reference angular velocity;

[0021] A power outer loop function of the converter is determined according to the frequency control function and the voltage control function.

[0022] As a preferred solution, the step of determining the frequency control function and the voltage control function of the converter according to the rated active power, the rated reactive power and the reference angular velocity specifically includes:

[0023] Determining a frequency control function and a voltage control function of the converter according to the rated active power, the rated reactive power and the reference angular velocity;

[0024] Wherein, the frequency control function is specifically:

[0025]

[0026] Among them, P0 is the rated active power of the converter, P out is the output active power of the converter, D p is the damping coefficient of the frequency control function, ω0 is the reference angular velocity of the frequency control function, ω0 is the output angular velocity of the frequency control function, M J is the moment of inertia of the frequency control function; θ out is the equivalent output phase angle of the frequency control function;

[0027] The voltage control function is specifically:

[0028] V eq =D q (Q0-Q out )+V eq0 ,

[0029] Among them, V eq is the converter equivalent output voltage, D q is the damping coefficient of the voltage control function, Q0 is the rated reactive power of the converter, Q out is the output reactive power of the converter, V eq0 is the equivalent reference voltage of the converter.

[0030] As a preferred solution, the output power function of the converter is determined according to the power outer loop function in combination with the filter inductance, specifically including:

[0031] According to the power outer loop function, the output power function of the converter is determined in combination with the filter inductance; wherein the output power function is specifically:

[0032]

[0033] Among them, P out is the output active power of the converter, V eq is the converter equivalent output voltage, L f is the filter inductance on the output side of the converter, L g is the equivalent reactance of the line connecting the converter and the grid, θ out is the equivalent output phase angle of the frequency control function, ω0 is the reference angular velocity of the frequency control function, Q out is the output reactive power of the converter.

[0034] As a preferred solution, the output current function of the converter is determined according to the power outer loop function in combination with the three-phase current information and the filter inductance, specifically including:

[0035] According to the power outer loop function, the output current function of the converter is determined in combination with the three-phase current information and the filter inductance, wherein the output current function is specifically:

[0036]

[0037] Among them, L f is the filter inductance on the output side of the converter, L g is the equivalent reactance of the line connecting the converter and the grid, i abc is the three-phase current of the converter, R g is the equivalent resistance of the line connecting the converter and the grid, V eq is the converter equivalent output voltage, v g is the rated voltage amplitude of the power grid.

[0038] This preferred scheme constructs a converter control model by constructing the power outer loop function, output power function and output current function of the converter, so that the output power of the converter can be controlled, thereby realizing flexible control of the output voltage amplitude and voltage phase angle of the converter, ensuring the control accuracy of the converter during fault ride-through, and thus improving the stability of the converter during fault ride-through.

[0039] As a preferred solution, determining the voltage amplitude control value and the voltage phase angle control value of the converter according to the fault voltage information in combination with the converter control model specifically includes:

[0040] Determine a voltage amplitude control value and a voltage phase angle control value of the converter according to the fault voltage information and a converter control model;

[0041] The expression of the voltage amplitude control value is:

[0042]

[0043] Among them, V e ′ q is the voltage phase angle control value of the equivalent output during the converter fault ride-through period, D q is the damping coefficient of the voltage control function, Q0 is the rated reactive power of the converter, Q out is the output reactive power of the converter, V eq0 is the equivalent reference voltage of the converter, v g ′ is the fault voltage after the power grid fault, v g Rated voltage amplitude of the power grid;

[0044] The expression of the voltage phase angle control value is:

[0045]

[0046] Among them, θ o ′ ut is the voltage amplitude control value of the equivalent output during the converter fault ride-through period; θ out is the equivalent output phase angle of the frequency control function, v g ′ is the fault voltage after the power grid fault, v g Rated voltage amplitude of the power grid.

[0047] This preferred scheme determines the voltage amplitude control value and voltage phase angle control value of the converter through the converter control model, so that the output voltage of the converter can be regulated, the potential difference between the converter and the power grid can be reduced, and the overcurrent impact during the converter fault ride-through can be controlled, thereby improving the stability of the converter during the fault ride-through.

[0048] As a preferred solution, determining the virtual impedance control value of the converter according to the rated operation information and the output current information specifically includes:

[0049] The output current information includes: the coordinate axis current value of the three-phase current output by the converter in a preset coordinate system; the rated operation information includes: the maximum current value allowed to pass during the converter fault;

[0050] Determine the transient peak current of the converter according to the coordinate axis current values ​​of the three-phase current output by the converter in a preset coordinate system;

[0051] The virtual impedance control value of the converter is determined according to the transient peak current and the maximum current value allowed to pass during the converter fault; wherein the expression of the virtual impedance control value is:

[0052]

[0053] Among them, R vir is a virtual resistor, X vir is the virtual reactance, k1 and k2 are the virtual impedance coefficients, i mag is the transient peak current, I limit It is the maximum current value allowed to pass through the converter during a fault.

[0054] This preferred solution achieves overcurrent suppression of the converter by regulating the virtual impedance of the converter, and ensures that the output current of the converter meets the standard, thereby ensuring the current limiting processing capability of the converter during fault ride-through, and further improving the stability of the converter during fault ride-through.

[0055] As a preferred solution, after determining the virtual impedance control value of the converter, the method further includes:

[0056] The current limiting voltage drop value corresponding to the virtual impedance control value is determined according to the virtual impedance control value, wherein the expression of the current limiting voltage drop value is:

[0057]

[0058] Among them, V d1 and V q1 are the d-axis and q-axis current limiting voltage drops caused by the virtual impedance during the converter fault ride-through period, i d and i q are the d-axis current and q-axis current respectively, R vir is the virtual resistance, X vir is the virtual reactance.

[0059] As a preferred solution, determining the reactive power control value of the converter according to the fault voltage information and the rated operation information in combination with the converter control model specifically includes:

[0060] According to the fault voltage information and the rated operation information, the reactive power control value of the converter is determined in combination with the converter control model, wherein the reactive power control value is specifically:

[0061]

[0062] Among them, Q0 is the reactive power control value, is the maximum reactive power that the converter can provide, I n is the rated output current of the converter, v g ′ is the fault voltage after the power grid fault, v g Rated voltage amplitude of the power grid.

[0063] This preferred solution controls the reactive power of the converter so that the converter has dynamic reactive power support capability during fault ride-through, allowing the power grid to return to normal working conditions more quickly, reducing the converter's fault ride-through time, and improving the converter's stability by reducing the fault ride-through time. BRIEF DESCRIPTION OF THE DRAWINGS

[0064] Figure 1 : A flowchart of a method for integrated control of a converter fault ride-through based on direct control provided by an embodiment of the present invention;

[0065] Figure 2 : A schematic diagram of the structure of a converter control model provided by an embodiment of the present invention;

[0066] Figure 3 : A schematic diagram of the vector relationship between the equivalent output voltage of the converter and the grid voltage before and after a voltage drop fault occurs in the grid provided by an embodiment of the present invention;

[0067] Figure 4 : A control flow chart of a virtual impedance provided by an embodiment of the present invention;

[0068] Figure 5 : A flow chart of a converter low voltage fault ride-through comprehensive control method provided by an embodiment of the present invention;

[0069] Figure 6 : Another flow chart of integrated control implementation of converter fault ride-through based on direct control provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0070] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0071] With the continuous development of new energy technology and power systems, new distribution systems with new energy as the main body are becoming more and more popular. Distributed new energy is widely used in new distribution systems due to its high flexibility and strong controllability. As an interface device connecting distributed new energy and distribution systems, the importance of converters is self-evident. When facing a complex and changeable power grid environment, traditional converters exhibit problems such as power fluctuations and poor power quality, which seriously affect the stability and reliability of the system. To this end, by simulating the external characteristics of traditional synchronous generators, the moment of inertia and damping are added to the converter, which can significantly improve the dynamic response capability and grid adaptability of the grid-connected converter, and ensure that there is an effective "synchronization" mechanism between the converter and the distribution network. When a grid failure occurs, the original grid specification allows the distributed energy system to actively cut off the connection with the grid for self-protection. However, as the proportion of distributed new energy in the distribution system increases, this behavior of actively cutting off the grid will seriously deteriorate the stability of the grid. Therefore, the new grid specification imposes more stringent requirements on grid-connected converters, requiring converters to actively participate in grid regulation during grid failures. When a power grid fails, the distributed energy system needs to continue to be connected to the distribution network for a certain period of time and have a certain ability to ride through the fault and support the grid voltage to help the grid voltage recover and further improve the stability of the distribution network during failures and the operational reliability of the system.

[0072] However, most of the current existing technologies focus on the analysis and research of converter parameter design and optimization, or analyze the impact of small disturbances on converter stability through small signal modeling, but there are few studies on converters under large disturbance conditions such as grid voltage sag faults, that is, there are few studies on converter fault ride-through. Some existing technology studies have solved the stability problem of converters during fault ride-through, but ignored the current limiting process during ride-through; some studies have added additional current inner loops to balance current limiting control and stability performance during fault ride-through, but correspondingly, the additional current loops have added more voltage and current sensors to obtain the required voltage and current information. All of these have led to insufficient stability of the converter during fault ride-through and more complex control.

[0073] Embodiment 1

[0074] Please refer to Figure 1 , is a step flow chart of a method for integrated control of converter fault ride-through based on direct control provided by an embodiment of the present invention, including steps S101 to S106.

[0075] Step S101: obtaining rated operation information of the converter, and determining the power outer loop function, output power function and output current function of the converter according to the rated operation information, so as to construct a converter control model.

[0076] In this embodiment, the step of acquiring rated operation information of the converter and determining the power outer loop function, output power function and output current function of the converter according to the rated operation information to construct a converter control model specifically includes:

[0077] Acquire rated operation information of the converter, wherein the rated operation information includes: rated active power, rated reactive power, reference angular velocity, filter inductance and three-phase current information;

[0078] Determining a power outer loop function of the converter according to the rated active power, the rated reactive power and the reference angular velocity;

[0079] Determining an output power function of the converter according to the power outer loop function and in combination with the filter inductance;

[0080] Determining the output current function of the converter according to the power outer loop function in combination with the three-phase current information and the filter inductance;

[0081] A converter control model is constructed according to the power outer loop function, the output power function and the output current function.

[0082] In this embodiment, determining the power outer loop function of the converter according to the rated active power, the rated reactive power and the reference angular velocity specifically includes:

[0083] Determining a frequency control function and a voltage control function of the converter according to the rated active power, the rated reactive power and the reference angular velocity;

[0084] A power outer loop function of the converter is determined according to the frequency control function and the voltage control function.

[0085] In this embodiment, determining the frequency control function and the voltage control function of the converter according to the rated active power, the rated reactive power and the reference angular velocity specifically includes:

[0086] Determining a frequency control function and a voltage control function of the converter according to the rated active power, the rated reactive power and the reference angular velocity;

[0087] Wherein, the frequency control function is specifically:

[0088]

[0089] Among them, P0 is the rated active power of the converter, P out is the output active power of the converter, D p is the damping coefficient of the frequency control function, ω0 is the reference angular velocity of the frequency control function, ω0 is the output angular velocity of the frequency control function, M J is the moment of inertia of the frequency control function; θout is the equivalent output phase angle of the frequency control function;

[0090] The voltage control function is specifically:

[0091] V eq =D q (Q0-Q out )+V eq0 ,

[0092] Among them, V eq is the converter equivalent output voltage, D q is the damping coefficient of the voltage control function, Q0 is the rated reactive power of the converter, Q out is the output reactive power of the converter, V eq0 is the equivalent reference voltage of the converter.

[0093] In an alternative embodiment, please refer to Figure 2 , is a schematic diagram of a converter control model provided by an embodiment of the present invention, wherein C is the DC side capacitor of the converter, L f and C f are the filter inductance and filter capacitance on the output side of the converter, R g and L g is the equivalent resistance and reactance of the line connecting the converter and the grid, v abc and i abc are the three-phase voltage and three-phase current output by the converter, P0 and Q0 are the rated active power and rated reactive power values ​​of the converter, P out and Q out are the output active power and reactive power values ​​of the converter, ω0 and ω out is the reference angular velocity and output angular velocity of the frequency control function (Pf loop), M J is the moment of inertia of the frequency control function (Pf loop), D p and D q are the damping coefficients of the frequency control function (Pf loop) and the voltage control function (QV loop), θ out is the equivalent output phase angle of the frequency control function (Pf loop), V eq and V eq0 is the converter equivalent output voltage and equivalent reference voltage, V dq and I dq They are the dq axis voltage and current output by the current loop and voltage loop respectively.

[0094] In an alternative embodiment, if Figure 2As shown, the frequency control function (Pf loop) and the voltage control function (QV loop) output the voltage phase angle and the voltage amplitude to the voltage loop respectively, and then output the d-axis and q-axis currents through the voltage loop, and output the d-axis and q-axis voltages through the current loop, and finally output the adjustment signal through the PWM modulation device to realize the regulation of the converter.

[0095] It should be noted that in order to ensure that the converter can have an effective "synchronization" mechanism with the power grid, the converter adopts virtual synchronous generator technology to ensure that the converter can self-synchronize and connect to the grid. Virtual synchronous generator technology simulates the rotational inertia and damping in traditional synchronous machines, so that it has a certain inertia and the ability to damp grid oscillations, which greatly improves the converter's ability to resist grid fluctuations.

[0096] It should be noted that the power outer loop function includes: frequency control function (Pf loop) and voltage control function (QV loop). Through the power outer loop function, the converter can actively control its own output power to achieve flexible control of equivalent output voltage and phase angle, and then achieve self-synchronous grid connection. The frequency control function (Pf loop) is used for frequency control, so that it can simulate the inertia and primary frequency modulation of traditional synchronous machines to help stabilize the grid frequency; the voltage control function (QV loop) is used for voltage control, so that it can simulate the excitation system of traditional synchronous machines, adjust the output voltage by adjusting reactive power, and keep the voltage of the converter grid connection point stable.

[0097] In this embodiment, determining the output power function of the converter according to the power outer loop function in combination with the filter inductor specifically includes:

[0098] According to the power outer loop function, the output power function of the converter is determined in combination with the filter inductance; wherein the output power function is specifically:

[0099]

[0100] Among them, P out is the output active power of the converter, V eq is the converter equivalent output voltage, L f is the filter inductance on the output side of the converter, L g is the equivalent reactance of the line connecting the converter and the grid, θ out is the equivalent output phase angle of the frequency control function, ω0 is the reference angular velocity of the frequency control function, Q out is the output reactive power of the converter.

[0101] In this embodiment, determining the output current function of the converter according to the power outer loop function in combination with the three-phase current information and the filter inductance specifically includes:

[0102] According to the power outer loop function, the output current function of the converter is determined in combination with the three-phase current information and the filter inductance, wherein the output current function is specifically:

[0103]

[0104] Among them, L f is the filter inductance on the output side of the converter, L g is the equivalent reactance of the line connecting the converter and the grid, i abc is the three-phase current of the converter, R g is the equivalent resistance of the line connecting the converter and the grid, V eq is the converter equivalent output voltage, v g is the rated voltage amplitude of the power grid.

[0105] Step S102: When a fault ride-through occurs in the power grid, the fault voltage information of the power grid and the output current information of the converter are collected.

[0106] It should be noted that, considering that the grid voltage has certain voltage fluctuations, according to the standard "GB / T12325-2008 Power Quality Supply Voltage Deviation", the three-phase supply voltage deviation of 20kV and below is ±7% of the nominal voltage. Therefore, it can be judged whether the grid is in a low voltage state and whether the converter is in a fault ride-through state according to this standard.

[0107] In an optional embodiment, when the grid voltage satisfies v g ′ <0.93v g When , it is considered that the grid voltage is out of the normal voltage fluctuation range and is at a low voltage level, that is, the grid has a fault ride-through. At this time, the converter needs to be regulated to improve the stability of the converter during the fault ride-through period.

[0108] In an alternative embodiment, please refer to Figure 3 , is a schematic diagram of the vector relationship between the equivalent output voltage of the converter and the grid voltage before and after a voltage drop fault occurs in the grid provided by an embodiment of the present invention; Figure 3 As shown, v g ′ and i ′ abc are the fault voltage and converter output current after a grid fault.

[0109] like Figure 3As shown in the figure, when the grid voltage drops, the output equivalent voltage of the voltage control function (QV loop) will not immediately follow the grid voltage to undergo a voltage mutation. At this time, a large impact current will be generated on the grid-connected converter line, which can easily burn out power electronic devices such as IGBT in the converter, seriously affecting the stable and reliable operation of the grid-connected system.

[0110] Therefore, when a fault occurs in the distribution system and causes the grid-connected converter system grid-connected point voltage to drop, the converter needs to have a certain low voltage ride-through capability. In order to limit the instantaneous impact current of the grid-side fault and effectively improve the stability of the converter during the low voltage fault ride-through, it is necessary to adjust the equivalent voltage amplitude and voltage phase angle output by the converter. Moreover, appropriately increasing the line impedance during the converter fault ride-through is also conducive to limiting the overcurrent impact during the fault and improving the current limiting processing capability of the converter during the fault ride-through. For specific adjustments, please refer to the description of steps S103 to S106 below.

[0111] Step S103: determining a voltage amplitude control value and a voltage phase angle control value of the converter according to the fault voltage information and a converter control model.

[0112] In this embodiment, determining the voltage amplitude control value and the voltage phase angle control value of the converter according to the fault voltage information in combination with the converter control model specifically includes:

[0113] Determine a voltage amplitude control value and a voltage phase angle control value of the converter according to the fault voltage information and a converter control model;

[0114] The expression of the voltage amplitude control value is:

[0115]

[0116] Among them, V e ′ q is the voltage phase angle control value of the equivalent output during the converter fault ride-through period, D q is the damping coefficient of the voltage control function, Q0 is the rated reactive power of the converter, Q out is the output reactive power of the converter, V eq0 is the equivalent reference voltage of the converter, v g ′ is the fault voltage after the power grid fault, v g Rated voltage amplitude of the power grid;

[0117] The expression of the voltage phase angle control value is:

[0118]

[0119] Among them, θo ′ ut is the voltage amplitude control value of the equivalent output during the converter fault ride-through period; θ out is the equivalent output phase angle of the frequency control function, v g ′ is the fault voltage after the power grid fault, v g Rated voltage amplitude of the power grid.

[0120] It should be noted that at the moment of a grid fault, the large difference between the converter equivalent output voltage and the grid voltage is an important reason for the large overcurrent on the grid-connected line. Therefore, the converter output voltage amplitude and phase angle can be directly controlled. Reducing the converter output phase angle and equivalent voltage amplitude during a grid-side fault can reduce the potential difference between the converter and the grid, thereby controlling the overcurrent impact at the moment of the fault, thereby improving the converter stability during fault ride-through.

[0121] It should be noted that increasing the line impedance can suppress the current during the fault ride-through period, but the addition of the line impedance will cause the output current of the converter to be greatly reduced during normal operation, resulting in the need for additional voltage drop to supplement. Therefore, this embodiment uses virtual impedance to achieve overcurrent suppression. The line impedance voltage drop required for current limiting can be subtracted from the dq axis voltage rating to achieve the effect of line impedance current limiting, and the specific description is shown in step S104 below.

[0122] Step S104: determining a virtual impedance control value of the converter according to the rated operation information and the output current information.

[0123] In this embodiment, determining the virtual impedance control value of the converter according to the rated operation information and the output current information specifically includes:

[0124] The output current information includes: the coordinate axis current value of the three-phase current output by the converter in a preset coordinate system; the rated operation information includes: the maximum current value allowed to pass during the converter fault;

[0125] Determine the transient peak current of the converter according to the coordinate axis current values ​​of the three-phase current output by the converter in a preset coordinate system;

[0126] The virtual impedance control value of the converter is determined according to the transient peak current and the maximum current value allowed to pass during the converter fault; wherein the expression of the virtual impedance control value is:

[0127]

[0128] Among them, R vir is the virtual resistance, X viris the virtual reactance, k1 and k2 are the virtual impedance coefficients, i mag is the transient peak current, I limit It is the maximum current value allowed to pass through the converter during a fault.

[0129] In an optional embodiment, the coordinate axis current value of the three-phase current output by the converter in the preset coordinate system refers to the three-phase current i output by the converter. abc After the dq axis transformation, the d-axis current i d and q-axis current i q , the specific conversion formula is as follows:

[0130]

[0131] Among them, i d and i q are d-axis current and q-axis current respectively, i0 is zero-sequence current, θ out is the equivalent output phase angle of the frequency control function, i a 、i b and i c The three-phase current i abc The a-phase current, b-phase current and c-phase current.

[0132] In an optional embodiment, the expression of the transient peak current of the converter is as follows:

[0133]

[0134] Among them, i mag is the transient peak current, i d and i q are the d-axis current and q-axis current respectively.

[0135] In an optional embodiment, after obtaining the virtual impedance control value, the method further includes calculating the dq axis current limiting voltage drop value corresponding to the virtual impedance control value, and the expression of the dq axis current limiting voltage drop is specifically:

[0136]

[0137] Among them, V d1 and V q1 are the d-axis and q-axis current limiting voltage drops caused by the virtual impedance during the converter fault ride-through period, i d and i q are the d-axis current and q-axis current respectively, R vir is the virtual resistance, X vir is the virtual reactance.

[0138] In an alternative embodiment, please refer to Figure 4 , is a control flow chart of a virtual impedance provided by an embodiment of the present invention, such as Figure 4 As shown, the d-axis current i is obtained. d and q-axis current i q Calculate the transient peak current i mag , combined with the maximum current value I allowed to pass during the converter fault limit The virtual resistance and virtual reactance are calculated based on the virtual impedance coefficient, and the dq-axis current limiting voltage drop value is calculated based on the virtual resistance and virtual reactance.

[0139] It should be noted that according to the standard "GB / T 29319-2024 Technical Regulations for Photovoltaic Power Generation System Access to Distribution Network", the photovoltaic power generation system connected to the grid with a voltage level of 380V should not reduce the active current during low-voltage ride-through, but the converter can be made to have a certain dynamic reactive support capability as much as possible on the basis of ensuring the maximum active transmission capacity. Therefore, the embodiment of the present invention is configured so that when the grid-side voltage drops to 85% or more of the rated voltage, the converter maintains normal operation; and when the grid-side voltage drops to less than 85% of the rated voltage, the converter can inject a certain reactive current into the grid for reactive compensation. By providing a certain reference reactive power to the converter, reactive voltage support for the grid is achieved when the grid-side voltage drops to less than 85% of the rated voltage. Please see the description of step S105 for details.

[0140] Step S105: determining the reactive power control value of the converter according to the fault voltage information and the rated operation information in combination with the converter control model.

[0141] In this embodiment, determining the reactive power control value of the converter according to the fault voltage information and the rated operation information in combination with the converter control model specifically includes:

[0142] According to the fault voltage information and the rated operation information, the reactive power control value of the converter is determined in combination with the converter control model, wherein the reactive power control value is specifically:

[0143]

[0144] Among them, Q0 is the reactive power control value, is the maximum reactive power that the converter can provide, I n is the rated output current of the converter, v′ g is the fault voltage after the power grid fault, v g Rated voltage amplitude of the power grid.

[0145] Step S106: Controlling the converter according to the voltage amplitude control value, the voltage phase angle control value, the virtual impedance control value and the reactive power control value.

[0146] In an alternative embodiment, please refer to Figure 5, is a flow chart of a converter low voltage fault ride-through comprehensive control method provided by an embodiment of the present invention, wherein V d2 and V q2 is the input voltage of the voltage loop d-axis and q-axis, and its expression is:

[0147]

[0148] Among them, V d2 and V q2 is the input voltage of the voltage loop d-axis and q-axis, V′ eq is the voltage phase angle control value of the equivalent output during the converter fault ride-through period, V d1 and V q1 They are the d-axis and q-axis current limiting voltage drops caused by the virtual impedance during the converter fault ride-through period.

[0149] like Figure 5 As shown in the figure, under normal grid voltage, the virtual impedance does not work, and the voltage drop it generates is 0. At this time, the converter equivalent output voltage phase angle and voltage amplitude remain at the rated value, and the reactive power value set by the voltage control function (QV loop) is 0. When the three-phase voltage of the grid drops due to a short circuit fault, a large overcurrent shock will be generated at the moment of the fault, that is, overcurrent suppression is required during the converter fault ride-through. Figure 5 The comprehensive control method shown in the figure reduces the equivalent voltage amplitude and voltage phase angle of the converter output in proportion to the voltage drop degree to limit the current impact at the moment of fault. At the same time, the virtual impedance will be activated during the fault ride-through period and limit the impact current to I limit , until the current in the grid-connected line returns to normal. In addition, since the grid voltage is lower than the rated value during the fault, the converter will continue to provide reactive power to the grid, and when the grid voltage drops below 85% of the rated voltage, it will provide 1.5% reactive current (set by reactive power) for every 1% drop. The specific voltage amplitude, voltage phase angle, virtual impedance and reactive power control values ​​can be set according to the above description.

[0150] In an alternative embodiment, please refer to Figure 6 , which is another implementation flow chart of the integrated control of the converter fault ride-through based on direct control provided by the embodiment of the present invention; firstly, a grid-connected converter model is constructed, and a converter fault ride-through control method based on direct control is designed. The grid voltage amplitude is detected to judge the grid state, when v′ g <0.93v g When the fault is detected, the integrated control method of the converter fault ride-through based on direct control is executed to make the converter return to normal working state.

[0151] This embodiment constructs the power outer loop function, output power function and output current function of the converter through the rated operation information of the converter, and then constructs the converter control model. Based on the converter control model, the voltage amplitude, voltage phase angle, virtual impedance and reactive power of the converter are regulated, and the converter is regulated during the fault ride-through period. By directly controlling the voltage amplitude and voltage phase angle of the converter during the fault ride-through period, and adding a certain virtual impedance, the current limiting processing capability of the converter during the fault ride-through period is guaranteed, and the accurate control of the converter is guaranteed with multiple control dimensions, thereby improving the stability of the converter during the fault ride-through period. Through reactive power regulation, the recovery capability of the converter corresponding to the grid connection point voltage is improved, and the stability of the converter during the fault ride-through period is further improved. By directly regulating the voltage amplitude, voltage phase angle, virtual impedance and reactive power, the addition of an additional current inner loop is avoided, so that no additional voltage and current sensors are required, and the control simplicity of the converter during the fault ride-through period is improved.

[0152] In summary, the embodiment of the present invention constructs the power outer loop function, output power function and output current function of the converter through the rated operation information of the converter, and then constructs the converter control model. Based on the converter control model, the voltage amplitude, voltage phase angle, virtual impedance and reactive power of the converter are controlled, and the converter is regulated during the fault ride-through period. By directly controlling the voltage amplitude and voltage phase angle of the converter during the fault ride-through period, and adding a certain virtual impedance, the current limiting processing capability of the converter during the fault ride-through period is guaranteed, and the accurate control of the converter is guaranteed with multiple control dimensions, thereby improving the stability of the converter during the fault ride-through period. Through reactive power control, the recovery ability of the converter corresponding to the grid connection point voltage is improved, and the stability of the converter during the fault ride-through period is further improved. By directly controlling the voltage amplitude, voltage phase angle, virtual impedance and reactive power, the addition of an additional current inner loop is avoided, so that no additional voltage and current sensors are required, and the control simplicity of the converter during the fault ride-through period is improved.

[0153] The specific embodiments described above further illustrate the purpose, technical solutions and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. It is particularly pointed out that for those skilled in the art, any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the scope of protection of the present invention.

Claims

1. A direct control-based integrated control method for converter fault ride-through, characterized in that: include: Acquiring rated operation information of the converter, and determining a power outer loop function, an output power function, and an output current function of the converter according to the rated operation information, so as to construct a converter control model; When a fault occurs in the power grid, the fault voltage information of the power grid and the output current information of the converter are collected; Determine a voltage amplitude control value and a voltage phase angle control value of the converter according to the fault voltage information and a converter control model; Determine a virtual impedance control value of the converter according to the rated operation information and the output current information; Determine the reactive power control value of the converter according to the fault voltage information and the rated operation information in combination with the converter control model; The converter is controlled according to the voltage amplitude control value, the voltage phase angle control value, the virtual impedance control value and the reactive power control value.

2. A direct control-based integrated control method for converter fault ride-through as claimed in claim 1, characterized in that: The step of obtaining rated operation information of the converter, and determining the power outer loop function, output power function and output current function of the converter according to the rated operation information to construct a converter control model specifically includes: Acquire rated operation information of the converter, wherein the rated operation information includes: rated active power, rated reactive power, reference angular velocity, filter inductance and three-phase current information; Determining a power outer loop function of the converter according to the rated active power, the rated reactive power and the reference angular velocity; Determining an output power function of the converter according to the power outer loop function and in combination with the filter inductance; Determining the output current function of the converter according to the power outer loop function in combination with the three-phase current information and the filter inductance; A converter control model is constructed according to the power outer loop function, the output power function and the output current function.

3. A direct control-based converter fault ride-through integrated control method as claimed in claim 2, characterized in that: Determining the power outer loop function of the converter according to the rated active power, the rated reactive power and the reference angular velocity specifically includes: Determining a frequency control function and a voltage control function of the converter according to the rated active power, the rated reactive power and the reference angular velocity; A power outer loop function of the converter is determined according to the frequency control function and the voltage control function.

4. A method for integrated control of converter fault ride-through based on direct control as claimed in claim 3, characterized in that: Determining the frequency control function and the voltage control function of the converter according to the rated active power, the rated reactive power and the reference angular velocity specifically includes: Determining a frequency control function and a voltage control function of the converter according to the rated active power, the rated reactive power and the reference angular velocity; Wherein, the frequency control function is specifically: Among them, P0 is the rated active power of the converter, P out is the output active power of the converter, D p is the damping coefficient of the frequency control function, ω0 is the reference angular velocity of the frequency control function, ω0 is the output angular velocity of the frequency control function, M J is the moment of inertia of the frequency control function; θ out is the equivalent output phase angle of the frequency control function; The voltage control function is specifically: IN eq =D q (Q0-Q out )+V eq0 , Among them, V eq is the converter equivalent output voltage, D q is the damping coefficient of the voltage control function, Q0 is the rated reactive power of the converter, Q out is the output reactive power of the converter, V eq0 is the equivalent reference voltage of the converter.

5. A method for integrated control of converter fault ride-through based on direct control as claimed in claim 3 or 4, characterized in that: Determining the output power function of the converter according to the power outer loop function and in combination with the filter inductance specifically includes: According to the power outer loop function, the output power function of the converter is determined in combination with the filter inductance; wherein the output power function is specifically: Among them, P out is the output active power of the converter, V eq is the converter equivalent output voltage, L f is the filter inductance on the output side of the converter, L g is the equivalent reactance of the line connecting the converter and the grid, θ out is the equivalent output phase angle of the frequency control function, ω0 is the reference angular velocity of the frequency control function, Q out is the output reactive power of the converter.

6. A method for integrated control of converter fault ride-through based on direct control as claimed in claim 3 or 4, characterized in that: Determining the output current function of the converter according to the power outer loop function in combination with the three-phase current information and the filter inductance specifically includes: According to the power outer loop function, the output current function of the converter is determined in combination with the three-phase current information and the filter inductance, wherein the output current function is specifically: Among them, L f is the filter inductance on the output side of the converter, L g is the equivalent reactance of the line connecting the converter and the grid, i abc is the three-phase current of the converter, R g is the equivalent resistance of the line connecting the converter and the grid, V eq is the converter equivalent output voltage, ν g is the rated voltage amplitude of the power grid.

7. A direct control-based integrated control method for converter fault ride-through as claimed in claim 3, characterized in that: Determining the voltage amplitude control value and the voltage phase angle control value of the converter according to the fault voltage information in combination with the converter control model specifically includes: Determine a voltage amplitude control value and a voltage phase angle control value of the converter according to the fault voltage information and a converter control model; The expression of the voltage amplitude control value is: Among them, V e ′ q is the voltage phase angle control value of the equivalent output during the converter fault ride-through period, D q is the damping coefficient of the voltage control function, Q0 is the rated reactive power of the converter, Q out is the output reactive power of the converter, V eq0 is the equivalent reference voltage of the converter, ν g ′ is the fault voltage after the power grid fault, ν g Rated voltage amplitude of the power grid; The expression of the voltage phase angle control value is: Among them, θ o ′ ut is the voltage amplitude control value of the equivalent output during the converter fault ride-through period; θ out is the equivalent output phase angle of the frequency control function, v g ′ is the fault voltage after the power grid fault, v g Rated voltage amplitude of the power grid.

8. The method for integrated control of converter fault ride-through based on direct control according to claim 1, characterized in that: The step of determining the virtual impedance control value of the converter according to the rated operation information and the output current information specifically includes: The output current information includes: the coordinate axis current value of the three-phase current output by the converter in a preset coordinate system; the rated operation information includes: the maximum current value allowed to pass during the converter fault; Determine the transient peak current of the converter according to the coordinate axis current values ​​of the three-phase current output by the converter in a preset coordinate system; The virtual impedance control value of the converter is determined according to the transient peak current and the maximum current value allowed to pass during the converter fault; wherein the expression of the virtual impedance control value is: Among them, R vir is the virtual resistance, X vir is the virtual reactance, k1 and k2 are the virtual impedance coefficients, i mag is the transient peak current, I limit It is the maximum current value allowed to pass through the converter during a fault.

9. A direct control-based integrated control method for converter fault ride-through as claimed in claim 8, characterized in that: After the virtual impedance control value of the converter is determined, the method further includes: The current limiting voltage drop value corresponding to the virtual impedance control value is determined according to the virtual impedance control value, wherein the expression of the current limiting voltage drop value is: Among them, V d1 and V q1 are the d-axis and q-axis current limiting voltage drops caused by the virtual impedance during the converter fault ride-through period, i d and i q are the d-axis current and q-axis current respectively, R vir is the virtual resistance, X vir is the virtual reactance.

10. The method for integrated control of converter fault ride-through based on direct control according to claim 1, characterized in that: Determining the reactive power control value of the converter according to the fault voltage information and the rated operation information in combination with the converter control model specifically includes: According to the fault voltage information and the rated operation information, the reactive power control value of the converter is determined in combination with the converter control model, wherein the reactive power control value is specifically: Among them, Q0 is the reactive power control value, Q max is the maximum reactive power that the converter can provide, I n is the rated output current of the converter, ν g ′ is the fault voltage after the power grid fault, ν g Rated voltage amplitude of the power grid.

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