Inverter control method and device based on virtual impedance and excitation device

Abstract

The application is suitable for the field of vector detection technology, and provides an inverter control method and device based on virtual impedance and an excitation device.The inverter control method based on virtual impedance comprises the following steps: when it is detected that the output current of the inverter is less than a preset current value, a first modulation voltage is determined based on the output current and the output voltage, the inverter is pulse width modulated so that the output voltage of the inverter reaches a constant; when it is detected that the output current is greater than or equal to the preset current value, a second modulation voltage is determined based on a filtered current, a filtered voltage, the output current and a preset virtual impedance, the inverter is pulse width modulated so that the inverter is equivalent to a virtual inductor and generates series resonance with a capacitor; wherein the filtered current and the filtered voltage are obtained by band-pass filtering the output current and the output voltage. The inverter is controlled by introducing virtual impedance, a virtual inductor is formed, and thus the size of the vector detection equipment is reduced.

Description

Technical Field

[0001] This invention belongs to the field of vector detection technology, and particularly relates to an inverter control method, device and excitation device based on virtual impedance. Background Technology

[0002] Vector detection is a crucial aspect of relay protection. Errors in the vector and logic of relay protection in distribution networks can lead to maloperation or failure to operate under both normal and fault conditions. Relevant regulations explicitly stipulate that newly installed equipment or devices with significant circuit modifications must be tested and judged using primary current and operating voltage before being put into operation to ensure the safe operation of secondary equipment in the distribution network. In the practical application of vector detection systems, a high-amplitude sinusoidal current is required as excitation for the device being detected. Taking sinusoidal current excitation as an example, to meet the amplitude and phase requirements of the current, a large excitation source and passive devices are often needed.

[0003] Current vector detection experiments typically employ an AC power supply, a power capacitor, and a power inductor to generate an excitation quantity with the required amplitude. The principle is to achieve resonance using a large-capacity capacitor and inductor, thereby increasing the current in the circuit to the desired amplitude. However, large-capacity inductors contain components such as iron cores and windings, resulting in significant size and weight. Furthermore, the size and weight of the inductor increase with its inductance and flux, thus requiring substantial manpower and resources for testing, making the process inconvenient and inefficient.

[0004] Furthermore, due to the complex and varied structures and parameters of various systems under test, capacitors must also be adjustable when performing vector detection. Currently, there are two main methods for adjusting the inductance of mainstream adjustable inductors: one is to use taps for inductance adjustment, which results in poor continuity of inductance adjustment and a still bulky size; the other is to use transformer-type impedance adjustment, which controls the equivalent input of the secondary side to change the equivalent impedance of the primary side port connected to the circuit. This method can only achieve continuous inductance adjustment within a limited range, and because this type of adjustable inductor has primary and secondary side structures, it also results in wasted capacity and still cannot escape the constraints of size and weight. Summary of the Invention

[0005] This invention provides an inverter control method, apparatus, and excitation device based on virtual impedance to solve the problems of inflexible inductance adjustment and excessive size of inductors used in vector detection, which affect detection efficiency.

[0006] This invention is achieved through the following technical solution:

[0007] In a first aspect, embodiments of the present invention provide an inverter control method based on virtual impedance, applied to an excitation device of a vector detection system, wherein the excitation device includes a power supply, an inverter, and a capacitor connected in series; the method includes:

[0008] When the output current of the inverter is detected to be less than the preset current value, a first modulation voltage is determined based on the output current and output voltage of the inverter, and pulse width modulation is performed on the inverter based on the first modulation voltage so that the output voltage of the inverter reaches a constant value.

[0009] When the output current is detected to be greater than or equal to the preset current value, a second modulation voltage is determined based on the filter current, filter voltage, output current, and preset virtual impedance. The inverter is then pulse-width modulated based on the second modulation voltage to make the inverter equivalent to a virtual inductor and generate series resonance with the capacitor. The filter current and filter voltage are obtained by bandpass filtering the output current and output voltage, and the preset virtual impedance is set based on the capacitance value of the capacitor and the preset series resonant frequency.

[0010] In conjunction with the first aspect, in some embodiments, the preset virtual impedance includes virtual reactance, and determining the second modulation voltage based on the filter current, filter voltage, output current, and preset virtual impedance includes:

[0011] Based on the filtered current and the filtered voltage, the first active power and the first reactive power of the inverter are determined.

[0012] Based on the first active power and the first reactive power, the first reference voltage is determined by the droop control equation;

[0013] The feedback voltage drop is determined based on the virtual reactance and the filtered current;

[0014] The feedback voltage drop is added to the first reference voltage to obtain the second reference voltage;

[0015] The second modulation voltage is determined based on the second reference voltage, the output current, the filter current, and the filter voltage.

[0016] In conjunction with the first aspect, in some embodiments, determining the second modulation voltage based on the second reference voltage, the output current, the filter current, and the filter voltage includes:

[0017] The output current, the filtered current, and the filtered voltage are each subjected to Park transformation. The output current, the filtered current, and the filtered voltage after Park transformation, along with the second reference voltage, are input to a voltage-current dual closed-loop control system to obtain the second modulation voltage. The voltage-current dual closed-loop control system includes an outer voltage loop and an inner current loop. The outer voltage loop uses a PI controller, and the inner current loop uses a P controller. The outer voltage loop is used to control the filtered voltage, and the inner current loop is used to control the output current.

[0018] In conjunction with the first aspect, in some embodiments, the characteristic equation of the voltage-current dual closed-loop control system is:

[0019] D s =s 3 L n C n +s 2 (C n r+C n k pc k pwm )+s(1+k p k pc k pwm )+k i k pc k pwm =0

[0020] Among them, L n Here, r is the filter inductance, and C is the equivalent resistance of the line. n For the filter capacitor, k pwm k represents the voltage gain of the inverter. pc For the parameters of the P controller, k p k i s are the parameters of the PI controller.

[0021] In conjunction with the first aspect, in some embodiments, determining the first modulation voltage based on the output current and output voltage of the inverter includes:

[0022] Based on the output current and the output voltage, determine the second active power and the second reactive power;

[0023] The second reference voltage is determined by the droop control equation based on the second active power and the second reactive power.

[0024] The output current and the output voltage are subjected to Park transformation, and the second reference voltage, as well as the Park-transformed output current and output voltage, are input to the voltage-current dual closed-loop control system to obtain the first modulation voltage.

[0025] In conjunction with the first aspect, in some embodiments, the droop control equation includes:

[0026] ω=ω n -m(P ref -P)

[0027] U ref =U n -n(Q ref -Q)

[0028] Where ω is a reference value for angular frequency; ω n U is the rated value of the angular frequency; m is the active frequency droop factor, and n is the reactive voltage droop factor; n P represents the rated voltage. ref This is a reference value for active power; Q ref The reactive power reference value is P; active power is Q, reactive power is U. ref This is the reference voltage.

[0029] In conjunction with the first aspect, in some embodiments, the pulse width modulation of the inverter using the second modulation voltage includes:

[0030] Perform an inverse Park transform on the second modulation voltage to obtain the modulation signal;

[0031] The modulation signal is input into the inverter to control the pulse drive switch.

[0032] In conjunction with the first aspect, in some embodiments, the inverter is a three-phase bridge inverter.

[0033] Secondly, embodiments of the present invention provide a virtual impedance inverter control device applied to an excitation device of a vector detection system. The excitation device includes a power supply, an inverter, and a capacitor connected in series. The device includes:

[0034] The constant voltage control module is used to determine a first modulation voltage based on the output current and output voltage of the inverter when the output current of the inverter is detected to be less than a preset current value, and to perform pulse width modulation on the inverter based on the first modulation voltage so that the output voltage of the inverter reaches a constant value.

[0035] A virtual impedance control module is used to determine a second modulation voltage based on the filter current, filter voltage, output current, and preset virtual impedance when the output current is detected to be greater than or equal to the preset current value. The module then applies pulse width modulation to the inverter based on the second modulation voltage, so that the inverter is equivalent to a virtual inductor and resonates in series with the capacitor. The filter current and filter voltage are obtained by bandpass filtering the output current and output voltage, and the preset virtual impedance is set based on the capacitance value of the capacitor and a preset series resonant frequency.

[0036] Thirdly, embodiments of the present invention provide an excitation device for a vector detection system, comprising a power supply, an inverter, and a capacitor connected in series; wherein the inverter is controlled by an inverter control method based on virtual impedance as described in any of the first aspects above, the output terminal of the capacitor is used to connect to the device under test, and the output terminal is the end not connected to the inverter.

[0037] This invention provides an inverter control method, apparatus, and excitation device based on virtual impedance. When the inverter's output current is detected to be less than a preset current value, a first modulation voltage is determined using the inverter's output current and output voltage. The inverter is then controlled based on this first modulation voltage to achieve a constant voltage. When the inverter's output current is detected to be greater than or equal to the preset current value, a second modulation voltage is determined using the filtered current, filtered voltage, output current, and a preset virtual impedance. The inverter is then controlled based on this second modulation voltage to achieve series resonance between the inverter and the capacitor. In other words, after the inverter voltage stabilizes, virtual impedance is introduced to control the inverter, making its output impedance inductive and achieving series resonance with the capacitor. This converts the power supply current into an excitation quantity that satisfies the vector detection conditions. Furthermore, in this embodiment, the preset value of the virtual impedance is based on the capacitor's capacitance value, so the controlled inverter can be equivalent to an adjustable virtual inductor. Therefore, this solution is suitable for providing excitation quantities for vector detection of various devices under test. Simultaneously, this solution can reduce the size of the vector detection equipment, thereby helping to improve the testing efficiency of vector detection. Attached Figure Description

[0038] To more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings used in the description of the embodiments or related technologies will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0039] Figure 1This is a schematic diagram illustrating an application scenario of an inverter control method based on virtual impedance provided in an embodiment of the present invention.

[0040] Figure 2 This is a schematic diagram of the line impedance of an inverter and a capacitor connected in series according to an embodiment of the present invention;

[0041] Figure 3 This is a schematic diagram of the structure of an inverter provided in an embodiment of the present invention;

[0042] Figure 4 This is a flowchart illustrating an inverter control method based on virtual impedance provided in an embodiment of the present invention.

[0043] Figure 5 This is a block diagram of a voltage and current dual closed-loop control system provided in an embodiment of the present invention when the inverter output current is less than a preset current value.

[0044] Figure 6 This is a schematic diagram of the control principle based on virtual impedance provided in an embodiment of the present invention;

[0045] Figure 7 This is a block diagram of a voltage and current dual closed-loop control system based on virtual impedance provided in an embodiment of the present invention;

[0046] Figure 8 This is a schematic diagram of the equivalent structure of parallel micro-source inverters in a microgrid provided in an embodiment of the present invention;

[0047] Figure 9 This is a schematic diagram of inverter power coupling provided in an embodiment of the present invention;

[0048] Figure 10 This is a schematic diagram of the structure of an inverter control device based on virtual impedance provided in an embodiment of the present invention. Detailed Implementation

[0049] In the following description, specific details such as particular system architectures and techniques are set forth for illustrative purposes and not for limitation, in order to provide a thorough understanding of the embodiments of the invention. However, those skilled in the art will understand that the invention can be implemented in other embodiments without these specific details. In other instances, detailed descriptions of well-known systems, apparatuses, circuits, and methods are omitted so as not to obscure the description of the invention with unnecessary detail.

[0050] It should be understood that, when used in this specification and the appended claims, the term "comprising" indicates the presence of the described features, integrals, steps, operations, elements and / or components, but does not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components and / or collections thereof.

[0051] In the description of this invention and the appended claims, the terms "first," "second," "third," etc., are used only to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0052] References to "one embodiment" or "some embodiments" as described in this specification mean that one or more embodiments of the invention include a particular feature, structure, or characteristic described in connection with that embodiment. Therefore, phrases such as "in one embodiment," "in some embodiments," "in other embodiments," "in still other embodiments," etc., appearing in different parts of this specification do not necessarily refer to the same embodiment, but rather mean "one or more, but not all, embodiments," unless otherwise specifically emphasized.

[0053] Addressing the issues of inflexible inductance adjustment and excessive size affecting detection efficiency of the inductors used in the aforementioned vector detection, the inverter control method based on virtual impedance in this embodiment of the invention determines a first modulation voltage based on the inverter's output current and output voltage when the detected output current of the inverter is less than a preset current value, and controls the inverter based on the first modulation voltage to achieve constant voltage; when the detected output current of the inverter is greater than or equal to the preset current value, determines a second modulation voltage based on the filter current, filter voltage, output current, and preset virtual impedance, and controls the inverter based on the second modulation voltage, thereby causing the inverter and capacitor to resonate in series. Once the inverter voltage stabilizes, a virtual impedance is introduced to control the inverter, making its output impedance inductive and resonating in series with a capacitor. This converts the power supply current into an excitation quantity that satisfies the vector detection conditions. Furthermore, in this embodiment, the preset value of the virtual impedance is based on the capacitance value of the capacitor, so the controlled inverter can be equivalent to an adjustable virtual inductor. Therefore, the method provided by this embodiment is suitable for providing excitation quantities for vector detection of various devices under test, and can reduce the size of the vector detection device and improve detection efficiency.

[0054] For example, embodiments of the present invention can be applied to, for example... Figure 1The exemplary scenario shown illustrates an example where the excitation device 10 in a vector detection system injects an excitation quantity into the device under test (DUT) 13. The excitation device 10 includes a power supply 11, an inverter 12, and a capacitor C. In this scenario, the power supply 11, inverter 12, capacitor C, and DUT 13 are connected in series, with a sampling point 14 between the inverter 12 and capacitor C. The power supply 11 is a DC test power supply, and the DUT 13 is a newly installed relay protection device or a relay protection device with significant circuit changes. When the power supply is started, based on the output current collected from sampling point 14, the inverter 12 is first subjected to voltage droop control to maintain a constant voltage. When the collected output current reaches a preset current value, a virtual impedance is introduced to control the inverter 12, making it equivalent to a virtual inductor and achieving a series resonance state with capacitor C. This series resonance converts the output of the power supply 11 into an excitation quantity that meets the vector detection conditions. Inputting this excitation quantity into the DUT 13 helps complete the vector detection.

[0055] Figure 2 A schematic diagram of the line impedance for the inverter and capacitor connected in series in the above application scenario is shown. See also Figure 2 After introducing a preset virtual impedance to control the inverter 12, the equivalent output impedance 21 of the inverter 12 includes the virtual resistance R. v and virtual reactance X v That is, the equivalent output impedance is Z. v =R v +jX v , where X v Much larger than R v The equivalent output impedance 21 is inductive. Here, the virtual resistance R... v Its function is to appropriately increase the resistive component of the line impedance to prevent deviations in the line inductive reactance due to factors such as sampling errors and sampling interference.

[0056] It should be noted that the impedance of inverter 12 can be equivalent to the aforementioned equivalent output impedance 21 because a virtual reactance X is introduced when controlling it. v And a virtual resistance R is preset. v When performing vector detection, the capacitor parameters can be known in advance, and the series resonant frequency can be set in advance. Therefore, the virtual reactance X can be calculated using the series resonance formula. v The corresponding inductance value, combined with the preset virtual resistance R v The virtual impedance settings constitute the aforementioned values.

[0057] The series resonance formula is as follows:

[0058]

[0059] Where, ω s X is the series resonant frequency (angular frequency), C is the capacitance of the capacitor, and L is the virtual reactance. v The corresponding inductance value.

[0060] In one embodiment, see Figure 3 Inverter 12 can be a three-phase bridge inverter.

[0061] Figure 4 This is a flowchart illustrating an inverter control method based on virtual impedance according to an embodiment of the present invention. (Refer to...) Figure 4 The detailed description of this inverter control method based on virtual impedance is as follows:

[0062] S101, when the output current of the inverter is detected to be less than the preset current value, a first modulation voltage is determined based on the output current and the output voltage, and pulse width modulation is performed on the inverter based on the first modulation voltage so that the output voltage of the inverter reaches a constant value.

[0063] In this embodiment of the invention, the preset current value is a relatively small current value. For example, the preset current value is 10% of the maximum current that the inverter can generate.

[0064] In some embodiments, the process of determining the first modulation voltage based on the output current and output voltage in step S101 may include: determining the second active power and the second reactive power based on the output current and output voltage; determining the second reference voltage based on the second active power and the second reactive power through a droop control equation; performing Park transformation on the output current and output voltage, and inputting the second reference voltage and the Park-transformed output current and output voltage to a voltage-current dual closed-loop control system to obtain the first modulation voltage.

[0065] In some embodiments, step S101, which involves pulse width modulation of the inverter based on the first modulation voltage, may include: performing a Park inverse transformation on the first modulation voltage and inputting the signal obtained after the Park inverse transformation into the inverter to control the pulse drive switch.

[0066] See Figure 5 The voltage and current dual closed-loop control system in the above embodiment includes an outer voltage loop and an inner current loop; wherein, the outer voltage loop adopts a PI controller with parameters k. p +k i / s ensures good tracking performance and stability of the control system; the inner current loop uses a P controller with parameters k pc This can improve the dynamic response capability of the control system. Figure 5 In the middle, k pwm L represents the voltage gain of the inverter.n Here, r is the filter inductance, and C is the equivalent resistance of the line. n This is a filter capacitor.

[0067] In this embodiment of the invention, the series resonant device consisting of an inverter and a capacitor requires a startup process. Therefore, constant voltage control is used during the low current phase. That is, the control voltage gradually increases from low to a stable value, thereby enabling better introduction of virtual reactance to control the inverter.

[0068] S102, when the output current is detected to be greater than or equal to the preset current value, a second modulation voltage is determined based on the filter current, filter voltage, output current and preset virtual impedance, and the inverter is pulse width modulated based on the second modulation voltage so that the inverter is equivalent to a virtual inductor and generates series resonance with the capacitor; wherein, the filter current and filter voltage are obtained by bandpass filtering the output current and output voltage, and the preset virtual impedance is set based on the capacitance value of the capacitor and the preset series resonant frequency.

[0069] In some embodiments, a virtual reactance is introduced at the end of the droop control to correct the synthesized reference voltage; the control principle is described in [reference needed]. Figure 6 The process of determining the second modulation voltage based on the filter current, filter voltage, output current, and preset virtual impedance in step S102 may include:

[0070] S201, based on filter current i nabc and filter voltage u nabc Determine the first active power P and the first reactive power Q of the inverter.

[0071] S202, based on the first active power P and the first reactive power Q, the first reference voltage U is determined through the droop control equation. ref .

[0072] S203, based on virtual reactance X v and filter current i nabc Determine the feedback voltage drop ΔU v .

[0073] S204 will reduce the feedback voltage by ΔU v Added to the first reference voltage U ref The second reference voltage is obtained.

[0074] S205, based on the second reference voltage Output current i Labc , filter current i nabc and filter voltage u nabc Determine the second modulation voltage.

[0075] Figure 6 L in n For the filter inductor, C n Z is the filter capacitor, r is the line equivalent resistance, and Z is the line equivalent resistance. n This is the equivalent impedance of the line.

[0076] Optionally, step S205 is implemented as follows: the output current i Labc , filter current i nabc and filter voltage u nabc Perform Park transformation separately, that is, convert the parameters in the three-phase stationary coordinate system into the parameters in the two-phase rotating coordinate system. Figure 6 (abc / dq) in the two phases, then the output current i in the two-phase rotating coordinate system. Ldq , filter current i ndq and filter voltage u ndq and the second reference voltage The input is fed into the voltage and current dual closed-loop control system to obtain the second modulation voltage output by the voltage and current dual closed-loop control system.

[0077] See Figure 7 The voltage and current dual closed-loop control system in the above embodiment includes an outer voltage loop and an inner current loop; wherein, the outer voltage loop adopts a PI controller with parameters k. p +k i / s ensures good tracking performance and stability of the control system; the inner current loop uses a P controller with parameters k pc This can improve the dynamic response capability of the control system. Figure 7 In the middle, L n r is the filter inductor, r is the filter resistor, and C is the filter resistor. n X is the filter capacitor. v The reactance is the virtual impedance. Introducing virtual impedance can easily cause harmonic interference. Therefore, in this implementation of the voltage and current dual closed-loop control system, a bandpass filter is also considered to suppress low-frequency or high-frequency signals other than the fundamental frequency.

[0078] In some embodiments, step S102, which involves pulse width modulation of the inverter based on the second modulation voltage, may include: performing a Park inverse transform on the second modulation voltage to obtain a modulation signal; and inputting the modulation signal into the inverter to control the pulse drive switch.

[0079] The above embodiments decouple the inverter's power through virtual impedance, making the line inductive. Different control strategies can be applied under different currents, making the parameters collected by the vector detection system more accurate and improving the system's precision. By applying virtual impedance, the reactance and capacitor form a series resonant circuit, which greatly reduces the size and weight of the equipment compared to the traditional series connection of inductors and capacitors. At the same time, the equivalent impedance of the inverter can be flexibly adjusted, thus enabling universal testing of various types of devices under test.

[0080] Figure 8 This is a schematic diagram of the equivalent structure of parallel micro-power grid micro-inverters provided in an embodiment of the present invention.

[0081] The following combination Figure 8 The droop control equation in the embodiments of the present invention is derived and explained as follows:

[0082] See Figure 8 Each micro-source is equivalent to a voltage source, and LOAD is the load. Wherein, U i These are the amplitudes of the output voltages of each inverter, where i takes values ​​of 1, 2, ..., N; U PCC It is the voltage amplitude of the line at the point of common coupling (PCC), δ i It is the output voltage U i and U PCC The phase angle difference between them, δ0 represents the voltage phase angle at point PCC; Z i It is the line impedance, R i It is the line resistance, L i It is the line inductance, θ i It is the line impedance angle, P i Q is the active power output of the inverter. i It is the reactive power output by the inverter.

[0083] Combination Figure 8 The active power P output by the inverter can be calculated. i and reactive power Q i They are respectively:

[0084]

[0085]

[0086] In this field, the line impedance is generally considered to be inductive, therefore Z i ≈X i θ i ≈90°; where X i It is the line reactance. And δ i It is generally considered to be very small, that is, it has sinδ.i ≈δ i cosδ i ≈1. Therefore, the active power P i and reactive power Q i This can be simplified to:

[0087]

[0088]

[0089] From the above two equations, it can be seen that the active power P output by the inverter is... i Phase difference δ with the inverter output voltage i Related to reactive power Q i The amplitude U of the inverter output voltage i Related to phase difference δ i With angular frequency ω i Satisfy ω i =dδ i / dt, therefore, controls the output voltage angular frequency ω of the inverter. i It can achieve voltage phase difference δ i This control allows for the control of the active power output of the inverter. The amplitude U of the inverter's output voltage is controlled. i It can regulate the reactive power output of the inverter.

[0090] Based on the above derivation, the droop control equation can be determined as follows:

[0091] ω=ω n -m(P ref -P)

[0092] U ref =U n -n(Q ref -Q)

[0093] Where ω is a reference value for angular frequency; ω n U is the rated value of the angular frequency; m is the active frequency droop factor, and n is the reactive voltage droop factor; n P represents the rated voltage. ref This is a reference value for active power; Q ref The reactive power reference value is P; active power is Q, reactive power is U. ref This is the reference voltage.

[0094] It is understandable that when the first reference voltage is determined through the droop control equation, P in the above droop control equation represents the first active power, Q represents the first reactive power, and U represents the first reactive power. refThe first reference voltage is used; when the second reference voltage is determined through the droop control equation, P in the above droop control equation is the second active power, Q is the second reactive power, and U is the second reactive power. ref This is the second reference voltage.

[0095] Based on decoupling control theory, by analyzing the degree of control of the input on the output, i.e., the coupling relationship between δ-P, δ-Q, ΔU-P, and ΔU-Q, the power coupling model of the inverter can be obtained, such as... Figure 9 As shown. See also Figure 9 The phase difference δ and the difference between the inverter's output voltage and the voltage at the PCC point ΔU are the input quantities, while the active power P and reactive power Q are the output quantities.

[0096] In this embodiment of the invention, by selecting an appropriate virtual reactance based on series resonance, the problems caused by power coupling during the control process can be reduced, thereby achieving a precise decoupling effect.

[0097] It should also be noted that the virtual reactance introduced in this embodiment of the invention will not affect the stability of the voltage and current dual closed-loop control system. The specific analysis is as follows:

[0098] according to Figure 7 The closed-loop output voltage can be derived as follows:

[0099] u ndq =G u (s)U ref -[G u (s)X v +Z n (s)]i ndq

[0100] Among them, G u (s) is the voltage gain function brought by the inverter, U ref For the reference voltage, i ndq X is the filter current. v Z is the virtual reactance of the equivalent circuit. n (s) represents the output impedance of the inverter when no virtual impedance is introduced.

[0101] After adding the virtual reactance, let the equivalent output impedance of the inverter be Z. s (s)=G u (s)X v +Z n (s), which can be derived from Mason's formula:

[0102]

[0103] Among them, L n r is the filter inductor, r is the filter resistor, and C is the filter resistor. n For the filter capacitor, kpwm k represents the voltage gain of the inverter. pc For the parameters of the P controller, k p k i s are the parameters of the PI controller.

[0104] Therefore, we can conclude Figure 7 The characteristic equation of the voltage-current dual closed-loop control system is:

[0105] D s =s 3 L n C n +s 2 (C n r+C n k pc k pwm )+s(1+k p k pc k pwm )+k i k pc k pwm =0

[0106] It can be seen that the characteristic equation of this voltage-current dual closed-loop control system does not contain the virtual reactance X. v Therefore, the introduction of virtual impedance will not affect the stability of the system.

[0107] Introducing virtual reactance can easily amplify higher harmonics in the current, affecting the phase of the output impedance. Therefore, considering phase and harmonic interference, a bandpass filter is introduced to reduce the impact of virtual impedance. The equivalent output impedance is then:

[0108]

[0109] Where, ω b Let be the center angular frequency (fundamental frequency) of the bandpass filter, and k be a control parameter where k > 0.

[0110] Bandpass filters are used to allow waves of a specific frequency band to pass through while blocking other frequency bands. Adding a virtual reactance containing a bandpass filter to a control system (a system applying inverter control methods based on virtual impedance) can reduce coupling problems caused by the line and achieve separate control of active and reactive power. Furthermore, this bandpass filter can reduce harmonic interference introduced by the virtual reactance without affecting the phase of the output impedance; its harmonic suppression effect is superior to that of a low-pass filter.

[0111] The aforementioned inverter control method based on virtual impedance introduces virtual impedance to control the inverter, making the inverter's output impedance inductive and resonating in series with a capacitor, thereby converting the power supply current into an excitation quantity that satisfies the vector detection conditions. Moreover, in this embodiment, the preset value of the virtual impedance is set based on the capacitance value of the capacitor, so the controlled inverter can be equivalent to an adjustable virtual inductor. Therefore, the method provided by this embodiment is suitable for providing excitation quantities for vector detection of various devices under test, and can reduce the size of the vector detection device and improve detection efficiency.

[0112] It should be understood that the sequence number of each step in the above embodiments does not imply the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present invention.

[0113] Corresponding to the inverter control method based on virtual impedance described in the above embodiments, Figure 10 A schematic diagram of the structure of an inverter control device based on virtual impedance provided in an embodiment of the present invention is shown. For ease of explanation, only the parts related to the embodiment of the present invention are shown.

[0114] See Figure 10 The inverter control device 1000 based on virtual impedance in this embodiment of the invention may include a constant voltage control module 1010 and a virtual impedance control module 1020.

[0115] The constant voltage control module 1010 can be used to determine a first modulation voltage based on the output current and output voltage when the output current of the inverter is detected to be less than the preset current value, and to perform pulse width modulation on the inverter based on the first modulation voltage so that the output voltage of the inverter reaches a constant value.

[0116] The virtual impedance control module 1020 can be used to determine a second modulation voltage based on the filter current, filter voltage, output current and preset virtual impedance when the detected output current is greater than or equal to a preset current value. Based on the second modulation voltage, the inverter is pulse-width modulated so that the inverter is equivalent to a virtual inductor and generates series resonance with the capacitor. The filter current and filter voltage are obtained by bandpass filtering the output current and output voltage. The preset virtual impedance is set based on the capacitance value of the capacitor and the preset series resonant frequency.

[0117] Optionally, the constant voltage control module 1010 can be used to: determine the second active power and the second reactive power based on the output current and the output voltage; determine the second reference voltage based on the second active power and the second reactive power through the droop control equation; perform Park transformation on the output current and the output voltage, and input the second reference voltage and the Park-transformed output current and output voltage to the voltage-current dual closed-loop control system to obtain the first modulation voltage.

[0118] Optionally, the virtual impedance control module 1020 can be used to: determine the first active power and the first reactive power of the inverter based on the filter current and the filter voltage; determine the first reference voltage based on the first active power and the first reactive power through the droop control equation; determine the feedback voltage drop based on the virtual impedance and the filter current; add the feedback voltage drop and the first reference voltage to obtain the second reference voltage; and determine the second modulation voltage based on the second reference voltage, the output current, the filter current, and the filter voltage.

[0119] Optionally, the virtual impedance control module 1020 can be used to: perform Park transformation on the second reference voltage, output current, filter current, and filter voltage respectively, and input them to the voltage-current dual closed-loop control system to obtain the second modulation voltage; wherein, the voltage-current dual closed-loop control system includes a voltage outer loop and a current inner loop, the voltage outer loop adopts a PI controller, and the current inner loop adopts a P controller; the voltage outer loop is used to control the filter voltage, and the current inner loop is used to control the output current.

[0120] Optionally, the virtual impedance control module 1020 can be used to: perform Park inverse transformation on the second modulation voltage to obtain a modulation signal; and input the modulation signal into the inverter to control the pulse drive switch.

[0121] In the above embodiments, the descriptions of each embodiment have different focuses. For parts that are not described in detail or recorded in a certain embodiment, please refer to the relevant descriptions of other embodiments.

[0122] Those skilled in the art will recognize that the templates, units, and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementations should not be considered beyond the scope of this invention.

[0123] If the module / unit is implemented as a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, all or part of the processes in the above embodiments of the present invention can also be implemented by a computer program instructing related hardware. The computer program can be stored in a computer-readable storage medium, and when executed by a processor, it can implement the steps of the various embodiments of the inverter control method based on virtual impedance described above. The computer program includes computer program code, which can be in the form of source code, object code, executable files, or certain intermediate forms. The computer-readable medium can include: any entity or device capable of carrying the computer program code, a recording medium, a USB flash drive, a portable hard drive, a magnetic disk, an optical disk, a computer memory, a read-only memory, a random access memory, an electrical carrier signal, a telecommunication signal, and a software distribution medium, etc.

[0124] This application also provides an excitation device for a vector detection system, see [link to relevant documentation]. Figure 1 The excitation device 10 includes a power supply 11, an inverter 12, and a capacitor C connected in series.

[0125] The inverter 12 is controlled by an inverter control method based on virtual impedance as described in any of the above embodiments. The output terminal of the capacitor C is used to connect to the device under test 13. Here, the output terminal refers to the end that is not connected to the inverter 12.

[0126] The excitation device 10 of the aforementioned vector detection system forms a series resonant circuit with a virtual inductor and capacitor C, which is equivalent to the inverter 12. This reduces the capacity requirements of passive devices such as capacitors and inductors in vector detection tests. Moreover, it achieves a series resonant state with the capacitor without using a large-volume inductor, thereby providing the device under test 13 with the required amplitude and phase of resonant current. This invention uses virtual impedance to decouple the inverter's power, making the line parameters inductive. The equivalent output impedance of the inverter can be flexibly adjusted by changing the preset virtual impedance. Therefore, the excitation device of this embodiment is not only small in size but also adaptable to different testing needs, exhibiting good versatility.

[0127] The above-described embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be included within the protection scope of the present invention.

Claims

1. An inverter control method based on virtual impedance, characterized in that, An excitation device for a vector detection system, the excitation device comprising a power supply, an inverter, and a capacitor connected in series; the method includes: When the output current of the inverter is detected to be less than the preset current value, a first modulation voltage is determined based on the output current and output voltage of the inverter, and pulse width modulation is performed on the inverter based on the first modulation voltage so that the output voltage of the inverter reaches a constant value. When the output current is detected to be greater than or equal to the preset current value, a second modulation voltage is determined based on the filter current, filter voltage, output current, and preset virtual impedance. The inverter is then pulse-width modulated based on the second modulation voltage to make the inverter equivalent to a virtual inductor and generate series resonance with the capacitor. The filter current and filter voltage are obtained by bandpass filtering the output current and output voltage, and the preset virtual impedance is set based on the capacitance value of the capacitor and the preset series resonant frequency.

2. The inverter control method based on virtual impedance as described in claim 1, characterized in that, The preset virtual impedance includes virtual reactance. Determining the second modulation voltage based on the filter current, filter voltage, output current, and preset virtual impedance includes: Based on the filtered current and the filtered voltage, the first active power and the first reactive power of the inverter are determined. Based on the first active power and the first reactive power, the first reference voltage is determined by the droop control equation; The feedback voltage drop is determined based on the virtual reactance and the filtered current; The feedback voltage drop is added to the first reference voltage to obtain the second reference voltage; The second modulation voltage is determined based on the second reference voltage, the output current, the filter current, and the filter voltage.

3. The inverter control method based on virtual impedance as described in claim 2, characterized in that, Determining the second modulation voltage based on the second reference voltage, the output current, the filter current, and the filter voltage includes: The output current, the filtered current, and the filtered voltage are each subjected to Park transformation. The output current, the filtered current, and the filtered voltage after Park transformation, along with the second reference voltage, are input to a voltage-current dual closed-loop control system to obtain the second modulation voltage. The voltage-current dual closed-loop control system includes an outer voltage loop and an inner current loop. The outer voltage loop uses a PI controller, and the inner current loop uses a P controller. The outer voltage loop is used to control the filtered voltage, and the inner current loop is used to control the output current.

4. The inverter control method based on virtual impedance as described in claim 3, characterized in that, The characteristic equation of the voltage-current dual closed-loop control system is: D s =s 3 L n C n +s 2 (C n r+C n k pc k pwm )+s(1+k p k pc k pwm )+k i k pc k pwm =0 Among them, L n Here, r is the filter inductance, and C is the equivalent resistance of the line. n For the filter capacitor, k pwm k represents the voltage gain of the inverter. pc For the parameters of the P controller, k p k i s are the parameters of the PI controller.

5. The inverter control method based on virtual impedance as described in claim 1, characterized in that, Determining the first modulation voltage based on the output current and output voltage of the inverter includes: Based on the output current and the output voltage, determine the second active power and the second reactive power; The second reference voltage is determined by the droop control equation based on the second active power and the second reactive power. The output current and the output voltage are subjected to Park transformation, and the second reference voltage, as well as the Park-transformed output current and output voltage, are input to the voltage-current dual closed-loop control system to obtain the first modulation voltage.

6. The inverter control method based on virtual impedance as described in claim 3 or 5, characterized in that, The droop control equations include: oh = oh n -m(P ref -P) U ref =U n -n(Q ref -Q) Where ω is a reference value for angular frequency; ω n U is the rated value of the angular frequency; m is the active frequency droop factor, and n is the reactive voltage droop factor; n P is the rated voltage. ref This is a reference value for active power; Q ref The reactive power reference value is P; active power is Q, reactive power is U. ref This is the reference voltage.

7. The inverter control method based on virtual impedance as described in claim 1, characterized in that, The pulse width modulation of the inverter based on the second modulation voltage includes: Perform an inverse Park transform on the second modulation voltage to obtain the modulation signal; The modulation signal is input into the inverter to control the pulse drive switch.

8. The inverter control method based on virtual impedance as described in claim 1, characterized in that, The inverter is a three-phase bridge inverter.

9. An inverter control device based on virtual impedance, characterized in that, An excitation device for a vector detection system, the excitation device comprising a power supply, an inverter, and a capacitor connected in series; the device includes: The constant voltage control module is used to determine a first modulation voltage based on the output current and output voltage of the inverter when the output current of the inverter is detected to be less than a preset current value, and to perform pulse width modulation on the inverter based on the first modulation voltage so that the output voltage of the inverter reaches a constant value. A virtual impedance control module is used to determine a second modulation voltage based on the filter current, filter voltage, output current, and preset virtual impedance when the output current is detected to be greater than or equal to the preset current value. The module then applies pulse width modulation to the inverter based on the second modulation voltage, so that the inverter is equivalent to a virtual inductor and resonates in series with the capacitor. The filter current and filter voltage are obtained by bandpass filtering the output current and output voltage, and the preset virtual impedance is set based on the capacitance value of the capacitor and a preset series resonant frequency.

10. An excitation device for a vector detection system, characterized in that, It includes a power supply, an inverter, and a capacitor connected in series; wherein the inverter is controlled by an inverter control method based on virtual impedance as described in any one of claims 1 to 8, the output terminal of the capacitor is used to connect to the device under test, and the output terminal is the end not connected to the inverter.

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