A method for current coordinated distribution and voltage optimization control of multi-configuration network type converter considering nonlinear and negative sequence load

Abstract

The method for current coordination distribution and voltage optimization control of multi-configuration grid-connected converter considering nonlinearity and negative sequence load includes: three-phase load-side current, three-phase capacitor voltage, fundamental positive sequence component, fundamental negative sequence component and hth harmonic component obtained by harmonic separation of the three-phase capacitor voltage with feedforward compensation; fundamental positive sequence active and reactive power is obtained, and then angle frequency and output voltage are obtained through active frequency regulator and reactive voltage regulator respectively; virtual impedance of fundamental positive sequence, fundamental negative sequence and harmonic component is set, multi-frequency point virtual impedance voltage drop instruction is calculated, grid-connected converter output voltage minus multi-frequency point virtual impedance voltage drop instruction value to obtain voltage reference instruction value; based on the voltage reference instruction value, capacitor voltage, load-side current, inductance current and DC voltage, three-phase modulation wave signal is calculated; based on the three-phase modulation wave signal, pulse signal of switching device is calculated. By setting the virtual impedance of the grid-connected converter as a negative value, the harmonic voltage drop on the point of common coupling can be reduced, and by adjusting the sum of the virtual impedance and the actual impedance to a certain proportion, the harmonic currents of the multi-configuration grid-connected converter can be distributed in proportion.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of converter control, and particularly relates to a current coordination distribution and voltage optimization control method of multi-structure network type converter considering nonlinear and negative sequence load. BACKGROUND

[0002] In the early stage of new energy development, the scale of the station is not large, and the grid-connected converter mostly adopts the follow-grid type control based on phase-locked synchronization. The follow-grid type converter is essentially a current source, and has weak inertia and damping support capability for the power grid. With the increase of the proportion of new energy access, the system inertia and damping are lacking. In the case of fault, the follow-grid type converter has poor disturbance resistance and weak support capability, which reduces the safety and stability of the power grid. The grid-forming type converter simulates the traditional synchronous machine, controls the output power to track the set value, obtains the frequency and voltage reference value, and realizes tracking through the subsequent voltage control link, so that the converter outputs a voltage with constant amplitude and frequency, which has similar characteristics to the traditional synchronous machine, and has inertia and damping support for the power grid. In summary, the grid-forming type converter is the preferred choice for future new-type power system power electronic grid-connected converters.

[0003] The negative sequence and nonlinear load connected in the power system causes the asymmetry of the grid voltage and the harmonic distortion. The grid harmonic has a great influence on power equipment and electrical equipment, which can cause problems such as increased power loss, shortened equipment life, and decreased power quality. Therefore, the power system needs to effectively manage and control the grid harmonic. At present, the coordination control of the multi-structure network type converter parallel system for the fundamental positive sequence load has been studied in many literatures such as droop control. However, there are few studies on the coordinated sharing of negative sequence load and nonlinear harmonic load and the treatment of grid distorted voltage. SUMMARY

[0004] In view of the problems existing in the prior art, the application provides a current coordination distribution and voltage optimization control strategy of multi-structure network type converter considering nonlinear and negative sequence load.

[0005] The converter proposed in the application adopts the remodeling of each frequency point into negative virtual impedance, which can compensate the harmonic voltage drop on the line impedance and reduce the voltage distortion at the common coupling point. Then the sum of the virtual impedance and the actual impedance of each converter at the harmonic frequency band is adjusted to a certain proportion, and the harmonic current can be distributed in proportion, improving the accuracy of harmonic current coordination distribution and having good adaptability in the multi-structure network type converter parallel system scene.

[0006] The first aspect of the present application provides a multi-structure grid type converter current coordination distribution and voltage optimization control method considering nonlinearity and negative sequence load, and the specific implementation includes the following steps:

[0007] S1. Based on the three-phase load side current i abc of the grid type converter, subtract the feedforward compensation under different frequencies, multiply the transfer function under the corresponding frequency, and the fundamental positive sequence component of the load side current can be obtained respectively Fundamental negative sequence component hth harmonic component Similarly, the three-phase capacitor voltage u abc of the grid type converter is obtained Fundamental positive sequence component of capacitor voltage Fundamental negative sequence component of capacitor voltage

[0008] S2. According to the fundamental positive sequence component of the load side current and the fundamental positive sequence component of the capacitor voltage , the angular frequency ω and the output voltage of the grid type converter are calculated by the active power regulator and the reactive voltage regulator

[0009] S3. According to the output voltage of the grid type converter and in S1, the virtual impedance of the fundamental positive sequence, the fundamental negative sequence and the harmonic component are set as and respectively, and multiplied by , and the output voltage of the grid type converter is subtracted from the product after the above multiplication to obtain the voltage reference instruction value

[0010] S4. Based on the above voltage reference instruction value , the capacitor voltage u αβ is subtracted to obtain the voltage error value, and the current reference value of the voltage loop output is obtained through the multi-parallel vector proportional integral voltage controller , and the load side current i αβ in the αβ coordinate system is added Lαβ , and the inductance current i αβ is subtracted to obtain the current error value, and the current loop output value is obtained through the proportional regulator, and the capacitor voltage u Lαβ and the current mutual feedback decoupling quantity jωi dc are superimposed, and then divided by 0.5 times the DC voltage V abc , and then converted to the abc coordinate system to obtain the three-phase modulation wave signal m abc ;

[0011] S5 pulse generation, based on three-phase modulation wave signal m abc , the switch device pulse signal is obtained through the modulation generation module;

[0012] The fundamental positive sequence component, the fundamental negative sequence component and the h harmonic component of the current and voltage in step S1 are specifically:

[0013] Input three-phase component x abc , which is converted into αβ coordinate system component x αβ through Clark transformation αβ , x The fundamental positive sequence component is obtained through the fundamental positive sequence feedforward compensation quantity and the fundamental positive sequence extraction function G1(s) αβ The fundamental negative sequence component is obtained through the fundamental negative sequence feedforward compensation quantity and the fundamental negative sequence extraction function G2(s) x αβ The h harmonic component is obtained through the h harmonic feedforward compensation quantity and the h harmonic extraction function G i (s) The output value will participate in the next iteration operation as the feedforward compensation quantity; if the above each time domain variable is written as an s domain expression, the specific calculation formula is:

[0014]

[0015] Among them, G1(s), G2(s), G i (s) are the extraction transfer functions in the αβ coordinate system of each sequence, ω is the actual angular frequency, ω c is the cutoff frequency of the extraction algorithm;

[0016] The active frequency regulator in step S2 is as follows:

[0017]

[0018] Among them, P ref and P + are the fundamental positive sequence active reference power and the fundamental positive sequence active power, ω0 is the angular frequency reference value, ω is the actual angular frequency, J is the moment of inertia, and D is the damping coefficient;

[0019] The reactive voltage regulator adds a voltage static compensation term ΔE to eliminate the influence of the virtual impedance and the actual impedance voltage drop of the converter on the voltage droop relationship, so that the grid-connected converter has a droop relationship with the reactive droop coefficient K q The reactive voltage regulator is specifically as follows:

[0020]

[0021] wherein, is the output voltage of the grid-forming converter in the αβ coordinate system, V * is the peak value of the output voltage of the grid-forming converter, V is the reference value of the output voltage of the grid-forming converter, ΔE is a static voltage compensation term, R t is the virtual resistance of the fundamental positive sequence is the total resistance value of the line resistance R r L t is the virtual inductance of the fundamental positive sequence is the total inductance value of the line inductance L r Q ref and Q + are the reference power and the power of the fundamental positive sequence reactive power, respectively, LPF(x) represents a first-order low-pass filtering of x, and |x| represents the modulus value of x;

[0022] The voltage reference instruction value in step S3 is specifically:

[0023] The virtual impedance voltage drop instruction value of the fundamental positive sequence the fundamental negative sequence and the hth harmonic frequency point is calculated The specific calculation formula is:

[0024]

[0025] The specific calculation formula of the voltage reference instruction value output by the multi-frequency point virtual impedance reshaping algorithm is:

[0026]

[0027] The three-phase modulation wave signal m abc in step S4 is specifically calculated as:

[0028]

[0029] wherein, k up and k ui are the parameter values of the multi-parallel vector proportional integral voltage controller; K is the constant of the proportional regulator, is the voltage reference value for PWM modulation; T αβ→abc represents the conversion from the αβ coordinate system to the abc coordinate system;

[0030] By adjusting each virtual impedance, the sum of the virtual impedance and the actual impedance of each converter at the hth harmonic frequency is adjusted to a certain proportion, and the hth harmonic current can be distributed in proportion. The specific calculation formula is: ​​

[0031]

[0032] wherein, and is the output current vector of the i-th converter at the h-th harmonic frequency, the line impedance and the virtual impedance, wherein R ri and L ri are the actual resistance and the actual inductance of the output feeder of the i-th converter;

[0033] By adjusting the damping coefficient D and the droop coefficient K in the active and reactive power regulator q , when each converter takes P refi / D i is equal and K qi Q refi is equal, the fundamental positive sequence active power of each converter is proportional to the damping coefficient of each converter, and the reactive power is proportional to the inverse of the reactive droop coefficient of each converter, and the specific calculation formula is:

[0034]

[0035] wherein, P i + , D i , and K qi are the fundamental positive sequence active power, the damping coefficient, the reactive power and the reactive droop coefficient of the i-th converter;

[0036] The over-regulated h-th harmonic virtual impedance of the multi-structure network type converter parallel system is The h-th harmonic of the point of common coupling voltage can be attenuated by k times (0≤k<1), and the specific calculation formula is:

[0037]

[0038] In the second aspect, the application provides a main circuit of a multi-structure network type converter current coordination distribution and voltage optimization control method considering nonlinear and negative sequence load, which comprises a plurality of parallel connected multi-structure network type converters, nonlinear and negative sequence load and a power grid, each multi-structure network type converter is composed of a direct current power supply, a converter and an inductance-capacitance filter, the direct current power supply in a single multi-structure network type converter is connected to the inductance-capacitance filter through the converter to output three-phase power, a plurality of multi-structure network type converters are connected in parallel through different line impedances and connected to a point of common coupling, the point of common coupling is connected to nonlinear and negative sequence load, the point of common coupling can be connected to the power grid to become a grid-connected system, or the point of common coupling can not be connected to the power grid to become an off-grid system.

[0039] The top layer central controller calculates and issues the virtual impedance value and droop coefficient of each group of network type converter according to the current coordinated distribution proportion and the voltage optimization demand of the point of common coupling, so as to ensure the coordinated distribution of the current and the voltage optimization of the point of common coupling.

[0040] In a third aspect, the application provides a multi-virtual synchronous generator current coordinated distribution and voltage optimization control device considering nonlinearity and negative sequence load, comprising a detection module, a harmonic separation module with feedforward compensation, a network type control module, a multi-frequency point virtual impedance remodeling module, a multi-parallel vector proportional integral voltage controller module and a modulation module; the detection module feeds the load side current and the capacitor voltage to the harmonic separation module with feedforward compensation, and feeds the capacitor voltage, the inductance current and the load side current to the multi-parallel vector proportional integral voltage controller module; the harmonic separation module with feedforward compensation outputs the fundamental positive sequence, the fundamental negative sequence and the harmonic current to the virtual multi-frequency point virtual impedance remodeling module, and feeds the fundamental positive sequence voltage and current to the network type control module; the network type control module feeds the network type converter output voltage and angular frequency to the multi-frequency point virtual impedance remodeling module, feeds the angular frequency to the multi-parallel vector proportional integral voltage controller module, and feeds the angular frequency to the harmonic separation module with feedforward compensation; the multi-frequency point virtual impedance remodeling module feeds the voltage reference value to the multi-parallel vector proportional integral voltage controller module; the multi-parallel vector proportional integral voltage controller module feeds the three-phase modulation wave signal to the modulation module.

[0041] The detection module is configured to determine the capacitor voltage u abc , the load side current i abc and the inductance current i Labc .

[0042] The harmonic separation module with feedforward compensation is configured to separate the fundamental positive sequence component abc , the fundamental negative sequence component abc and the hth harmonic current component from the load side current i abc and the capacitor voltage u abc .

[0043] The network type control module is configured to calculate the positive sequence active power P and the reactive power Q based on the load side current i αβ and the capacitor voltage u αβ , and then obtain the network type converter output voltage and the angular frequency ω.

[0044] The multi-frequency point virtual impedance remodeling module is configured to calculate the virtual impedance value based on the network type converter output voltage And the fundamental positive sequence, fundamental negative sequence, h harmonic component and corresponding virtual impedance, the voltage reference instruction value of the multi-frequency point virtual impedance remodeling algorithm output is calculated A multi-parallel vector proportional integral voltage controller module is used for the voltage reference instruction value of the multi-frequency point virtual impedance remodeling algorithm output Subtract the capacitor voltage u αβ The output voltage error value is obtained through the multi-parallel vector proportional integral voltage controller to obtain the current reference value of the voltage loop output Add the load side current i in the alpha beta coordinate system αβ And subtract the inductance current i Lαβ The current error value is obtained, and the current loop output value is obtained through the proportional regulator, and then the capacitor voltage u αβ And the current mutual inductance decoupling amount jωi Lαβ , divided by 0.5 times the DC voltage V dc , and then the three-phase modulation wave signal m abc is obtained.

[0045] A modulation module is used to obtain the switching device pulse signal through the modulation generation module based on the three-phase modulation wave signal m abc , so as to realize the control of the converter.

[0046] In a fourth aspect, the application provides a computer readable storage medium, the storage medium stores a computer program, and the computer program is executed by a computer to realize the current coordinated distribution and voltage optimization control method of the multi-structure network type converter considering nonlinear and negative sequence load.

[0047] The application provides a current coordinated distribution and voltage optimization control method of a multi-structure network type converter considering nonlinear and negative sequence load, which is suitable for a grid-connected or off-grid main circuit system composed of a multi-parallel structure network type converter, a power grid, nonlinear and negative sequence load. The application remolds the output impedance of each harmonic of each converter, so that the output impedance of each harmonic of each converter is inversely proportional to the capacity of the converter, thereby realizing the distribution of harmonic currents among the converters according to the capacity ratio. At the same time, by setting a negative virtual impedance, the harmonic voltage drop on the output line can be compensated, and the voltage distortion at the point of common coupling can be reduced.

[0048] The converter proposed in the application remolds each frequency point into a negative virtual impedance, which can compensate the harmonic voltage drop on the line impedance and ensure the voltage stability at the point of common coupling. Then, the sum of the virtual impedance and the actual impedance of each converter at the harmonic frequency band is adjusted to a certain proportion, and the harmonic current can be distributed in proportion, thereby improving the accuracy of harmonic current coordinated distribution.

[0049] The advantages of the application are that a series of control strategies such as harmonic separation, multi-frequency point virtual impedance remodeling, network configuration control algorithm and multi-parallel vector proportional integral voltage control are proposed, the resistive and inductive output impedance of each harmonic frequency point can be independently adjusted, and the effects of reducing the voltage distortion of the point of common coupling and optimizing the harmonic current coordinated distribution are achieved. BRIEF DESCRIPTION OF DRAWINGS

[0050] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or prior art description will be briefly introduced. Obviously, the drawings in the following description are only embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor on the basis of the provided drawings.

[0051] Figure 1 A step flow chart of a multi-network type converter current coordinated distribution and voltage optimization control method considering nonlinear and negative sequence load provided by the embodiment of the present application;

[0052] Figure 2 A main circuit diagram of a multi-network type converter current coordinated distribution and voltage optimization control method considering nonlinear and negative sequence load provided by the embodiment of the present application;

[0053] Figure 3 A control block diagram of a harmonic separation algorithm with feedforward compensation;

[0054] Figure 4 A control block diagram of a network configuration type control algorithm;

[0055] Figure 5 A control block diagram of a multi-frequency point virtual impedance remodeling algorithm;

[0056] Figure 6 A control block diagram of a multi-parallel vector proportional integral voltage controller algorithm;

[0057] Figure 7 A harmonic current distribution model schematic diagram of a multi-converter parallel system;

[0058] Figure 8 A point of common coupling voltage simulation waveform diagram of the embodiment of the present application.

[0059] Figures 9a-9b A double-machine load current simulation waveform diagram of the embodiment of the present application, wherein, Figure 9a is a load current simulation waveform diagram of a converter, Figure 9b is a load current simulation waveform diagram of another converter. DETAILED DESCRIPTION

[0060] With reference to the drawings of the embodiments of the present application, the technical solutions in the embodiments of the present application will be clearly and completely described. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all the other embodiments obtained by those skilled in the art without creative work fall within the scope of the present application.

[0061] Embodiment 1

[0062] With reference to Figure 1 , the embodiment provides a multi-structure grid type converter current coordination distribution and voltage optimization control method considering nonlinearity and negative sequence load, and the embodiment is characterized in that the specific implementation includes the following steps.

[0063] S1. Based on the three-phase load side current i abc of the grid type converter, subtract the feedforward compensation under different frequencies, and multiply the transfer function under the corresponding frequency to obtain the fundamental positive sequence component of the load side current, the fundamental negative sequence component , and the hth harmonic component. Similarly, the three-phase capacitor voltage u abc of the grid type converter is obtained. The fundamental positive sequence component of the capacitor voltage is obtained through the above-mentioned manner. The fundamental negative sequence component , and the hth harmonic component.

[0064] S2. According to the load side current fundamental positive sequence component and the capacitor voltage fundamental positive sequence component , the angular frequency ω and the grid type converter output voltage are calculated through the active power regulator and the reactive voltage regulator.

[0065] S3. According to the grid type converter output voltage and in S1, the virtual impedance of the fundamental positive sequence, the fundamental negative sequence and the harmonic component are respectively set as and , which are respectively multiplied by , and the grid type converter output voltage is subtracted from the product after the multiplication to obtain the voltage reference instruction value

[0066] S4. Based on the voltage reference instruction value , the capacitor voltage u αβ is subtracted to obtain the voltage error value, and the current reference value of the voltage loop output is obtained through the multi-parallel vector proportional integral voltage controller. The load side current i αβ in the αβ coordinate system is added.And subtract the inductive current i Lαβ Get the current error value, through the proportional regulator to get the current loop output value, and superimposed capacitor voltage u αβ And current mutual inductance decoupling amount jωi Lαβ , divided by 0.5 times the DC voltage V dc , and converted into abc coordinate system to get three-phase modulation wave signal m abc , calculated to get three-phase modulation wave signal m abc ;

[0067] S5 pulse generation, based on three-phase modulation wave signal m abc , through the modulation generation module to get the switch device pulse signal;

[0068] The fundamental positive sequence component, fundamental negative sequence component, h harmonic component of the current and voltage in step S1, the control block diagram is shown in Figure 3 , specifically:

[0069] Input three-phase component x abc , through Clark transformation into αβ coordinate system under the component x αβ , x αβ Through the fundamental positive sequence feedforward compensation amount And fundamental positive sequence extraction function G1(s) to get the fundamental positive sequence component x αβ Through the fundamental negative sequence feedforward compensation amount And fundamental negative sequence extraction function G2(s) to get the fundamental negative sequence component x αβ Through the h harmonic feedforward compensation amount And h harmonic extraction function G i (s) to get the h harmonic component Output value As feedforward compensation amount involved in the next iteration operation; if the above each time domain variable is written as s domain expression, its specific calculation formula is:

[0070]

[0071] Among them, G1(s), G2(s), G i (s) are the extraction transfer functions in each sequence αβ coordinate system, ω is the actual angular frequency, ω c Is the cut-off frequency of the extraction algorithm;

[0072] The active frequency regulator in step S2 is as follows, the control block diagram is shown in Figure 4 :

[0073]

[0074] Among them, Pref and P + are the fundamental positive-sequence active reference power and the fundamental positive-sequence active power respectively, ω0 is the angular frequency reference value, ω is the actual angular frequency, J is the moment of inertia, and D is the damping coefficient;

[0075] The reactive voltage regulator adds a voltage static compensation term ΔE to eliminate the influence of the virtual impedance and the actual impedance voltage drop of the converter on the voltage droop relationship, so that the grid-connected converter has a droop relationship with the reactive droop coefficient K q The reactive voltage regulator is specifically as follows:

[0076]

[0077] wherein, is the output voltage of the grid-connected converter in the αβ coordinate system, V * is the peak value of the output voltage of the grid-connected converter, V is the reference value of the output voltage of the grid-connected converter, ΔE is the voltage static compensation term, R t is the total resistance value of the fundamental positive-sequence virtual resistance and the line resistance R r , L t is the total inductance value of the fundamental positive-sequence virtual inductance and the line inductance L r , Q ref and Q + are the fundamental positive-sequence reactive reference power and the fundamental positive-sequence reactive power respectively, and LPF(x) represents first-order low-pass filtering of x, and |x| represents the modulus value of x;

[0078] The voltage reference instruction value specifically is:

[0079]

[0080] The specific calculation formula of the voltage reference instruction value output by the multi-frequency point virtual impedance reshaping algorithm is:

[0081]

[0082] The three-phase modulation wave signal m abc specifically has the calculation formula:

[0083]

[0084] wherein, k up and k ui are the parameter values of the multi-parallel vector proportional-integral voltage controller; K is a constant of a proportional regulator, is the voltage reference value for PWM modulation; T​αβ→abc Indicates from αβ Coordinate system conversion to abc Coordinate system;

[0085] By adjusting each virtual impedance, the sum of the virtual impedance and actual impedance of each converter at the hth harmonic frequency is adjusted to a certain ratio, and the hth harmonic current can be distributed proportionally. The model diagram is shown in Figure 7 As shown, the specific calculation formula is:

[0086]

[0087] Where, and is the output current vector, line impedance and virtual impedance of the hth harmonic frequency of the i-th converter, where R ri and L ri is the actual resistance and actual inductance of the output feeder of the i-th converter;

[0088] By adjusting the damping coefficient D and droop coefficient K in the active and reactive power regulator q , when each converter takes P refi / D i When equal and K qi Q refi When the fundamental positive sequence active power of each converter is equal, it is proportional to the damping coefficient of each converter, and the reactive power is proportional to the inverse of the reactive droop coefficient of each converter. The specific calculation formula is:

[0089]

[0090] Where, P i + 、D i 、 and K qi is the fundamental positive sequence active power, damping coefficient, reactive power and reactive droop coefficient of the i-th converter;

[0091] The multi-grid parallel converter system is configured to adjust the virtual impedance of the hth harmonic to The hth harmonic of the common coupling point voltage can be attenuated by k times (0≤k<1). The specific calculation formula is:

[0092]

[0093] Example 2

[0094] refer to Figure 2The embodiment provides a main circuit of a multi-constructive-network-type converter current coordination distribution and voltage optimization control method considering nonlinear and negative sequence loads, which is composed of multiple parallel multi-parallel constructive-network-type converters, nonlinear and negative sequence loads and a power grid, each of the constructive-network-type converters is composed of a direct current power supply, a converter and an inductance-capacitance filter, the direct current power supply in a single constructive-network-type converter is connected to the inductance-capacitance filter through the converter to output three-phase power, multiple constructive-network-type converters are connected in parallel to a common coupling point through different line impedances, the common coupling point is connected to the nonlinear and negative sequence loads, and the common coupling point can be connected to the power grid to become a grid-connected system or the common coupling point can not be connected to the power grid to become an off-grid system;

[0095] The top-level central controller calculates and issues virtual impedance values and droop coefficients of each group of constructive-network-type converters according to current coordination distribution proportions of the constructive-network-type converters and voltage optimization requirements of the common coupling point, so that the current coordination distribution and the voltage optimization of the common coupling point are ensured.

[0096] Embodiment 3

[0097] The embodiment provides a control device of a multi-virtual synchronous generator current coordination distribution and voltage optimization control considering nonlinear and negative sequence loads, which comprises a detection module, a harmonic separation module with feedforward compensation, a constructive-network-type control module, a multi-frequency-point virtual impedance remodeling module, a multi-parallel vector proportional integral voltage controller module and a modulation module; the detection module feeds load-side current and capacitor voltage to the harmonic separation module with feedforward compensation, and feeds capacitor voltage, inductance current and load-side current to the multi-parallel vector proportional integral voltage controller module; the harmonic separation module with feedforward compensation outputs fundamental positive sequence, fundamental negative sequence and harmonic current to the virtual multi-frequency-point virtual impedance remodeling module, and feeds fundamental positive sequence voltage and current to the constructive-network-type control module; the constructive-network-type control module feeds constructive-network-type converter output voltage and angular frequency to the multi-frequency-point virtual impedance remodeling module, feeds angular frequency to the multi-parallel vector proportional integral voltage controller module and feeds angular frequency to the harmonic separation module with feedforward compensation; the multi-frequency-point virtual impedance remodeling module feeds voltage reference value to the multi-parallel vector proportional integral voltage controller module; and the multi-parallel vector proportional integral voltage controller module feeds three-phase modulation wave signals to the modulation module.

[0098] The detection module is used for determining capacitor voltage u abc , load-side current i abc and inductance current i Labc .

[0099] The harmonic separation module with feedforward compensation is used for separating fundamental positive sequence component fundamental negative sequence component and hth harmonic current component from the load-side current i abc and the capacitor voltage u abc . and fundamental positive sequence component

[0100] a grid-forming control module, configured to calculate a load-side current i αβ and a capacitor voltage u αβ to calculate positive sequence active power P and reactive power Q, and then obtain a grid-forming converter output voltage and an angular frequency ω;

[0101] a multi-frequency point virtual impedance reshaping module, configured to calculate a voltage reference instruction value output by a multi-frequency point virtual impedance reshaping algorithm based on the grid-forming converter output voltage and fundamental positive sequence, fundamental negative sequence, hth harmonic components and corresponding set virtual impedance

[0102] a multi-parallel vector proportional-integral voltage controller module, configured to the voltage reference instruction value output by the multi-frequency point virtual impedance reshaping algorithm subtract the capacitor voltage u αβ to obtain a voltage loop output current reference value through the multi-parallel vector proportional-integral voltage controller add the load-side current i in the αβ coordinate system αβ and subtract the inductor current i Lαβ to obtain a current error value, and then obtain a current loop output value through a proportional regulator, and then subtract the capacitor voltage u αβ and current mutual feedback decoupling quantity jωi Lαβ , divided by 0.5 times the DC voltage V dc , and then obtain a three-phase modulation wave signal m abc ;

[0103] a modulation module, configured to obtain a switching device pulse signal through a modulation generation module based on the three-phase modulation wave signal m abc , so as to realize control of the converter.

[0104] Embodiment 4

[0105] The embodiment provides a computer readable storage medium, and the storage medium stores a computer program. When the computer program is executed by a computer, the method for current coordination distribution and voltage optimization control of a multi-grid-forming converter considering nonlinearity and negative sequence load in the embodiment 1 is realized.

[0106] The above embodiments are implemented, and the following effects are achieved:

[0107] The simulation of the grid-forming converter can be based on a simulation tool such as Matlab / Simulink. A simulation model of the converter is built in Matlab / Simulink, so as to verify the control method of the multi-grid-forming converter.

[0108] The related parameter configurations of the control circuit of the grid-forming converter are as follows:

[0109] The algorithm coefficients of the multi-parallel vector proportional integral voltage controller are K up = 0.03 and K ui = 0.3, the proportional regulator K = 30, the moment of inertia J1 = 0.1 in the converter 1, the damping coefficient D1 = 10, the reactive power droop coefficient K q1 = 0.002, the unit of the fundamental positive sequence virtual impedance is Ω, the unit of the fundamental negative sequence virtual impedance is mH, the same below, the virtual impedance of the harmonic component The moment of inertia J2 = 0.05 in the converter 2, the damping coefficient D2 = 5, the reactive power droop coefficient K q2 = 0.002, the unit of the fundamental positive sequence virtual impedance the unit of the fundamental negative sequence virtual impedance is mH, the same below, the virtual impedance of the harmonic component

[0110] Figure 8 is the voltage waveform diagram of the point of common coupling. As shown in the figure, the voltage waveform has no obvious distortion, the THD is 2.55%, and the system can keep stable operation.

[0111] Figures 9a-9b is the waveform diagram of the double-machine load current. As shown in the figure, it can be seen from the simulation diagram that the double-machine load current waveform is distributed in a 2:1 ratio and has no phase shift.

[0112] It should be noted that, in this text, relational terms such as first and second are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "contain" or any other variant thereof are intended to cover non-exclusive inclusion, so that the process, method, article or device including a series of elements is inherent. Without more limitations, the element defined by the statement "including a" does not exclude the presence of another identical element in the process, method, article or device including the element. In addition, the above technical solutions provided by the embodiments of the present application have not been described in detail, which is to avoid excessive repetition. ​

[0113] The foregoing description of the disclosed embodiments enables a person skilled in the art to make or use the application. Modifications of these embodiments will occur to those skilled in the art and are within the scope of the underlying principles taught by the present application. The present application is thus to be limited only by the principles of the present application and the specific embodiments described herein and claimed.

Claims

1. A method for current coordinated distribution and voltage optimization control of multi-configuration network type converter considering nonlinearity and negative sequence load, characterized in that, The method comprises the following steps: S1. Three-phase load-side current i of the network-forming converter abc Subtracting the feed-forward compensation at different frequencies, multiplying the transfer function at the corresponding frequency, the fundamental positive sequence component of the load-side current can be obtained respectively Fundamental negative sequence component hth harmonic component Similarly, the three-phase capacitor voltage u of the network-forming converter abc The fundamental positive sequence component of the capacitor voltage is obtained in the above manner Fundamental negative sequence component hth harmonic component S2. The fundamental positive sequence component of the load-side current and the fundamental positive sequence component of the capacitor voltage The angular frequency ω and the network-forming inverter output voltage are calculated by the active power regulator and the reactive voltage regulator S3. According to the grid-type converter output voltage and S1 Set the virtual impedances of the fundamental positive sequence, fundamental negative sequence and harmonic components to be and Respectively Multiply by the grid-type converter output voltage Subtract the product after the above multiplication to obtain the voltage reference command value S4. Based on the above voltage reference instruction value Subtract the capacitor voltage u αβ Get the voltage error value, and get the current reference value of the voltage loop output through the multi-parallel vector proportional integral voltage controller Add the load side current i in the αβ coordinate system αβ And subtract the inductance current i Lαβ Get the current error value, get the current loop output value through the proportional regulator, and superimpose the capacitor voltage u αβ And the current mutual inductance decoupling quantity jωi Lαβ Divided by 0.5 times the DC voltage V dc Convert to abc coordinate system to get three-phase modulation wave signal m abc Calculate to get three-phase modulation wave signal m abc ; S5 pulse generation, based on the three-phase modulated wave signal m abc The switch device pulse signal is obtained through the modulation generation module.

2. The method of claim 1, wherein, The fundamental positive sequence component, the fundamental negative sequence component and the hth harmonic component of the current and voltage in step S1 are specifically: input three-phase component x abc is converted into αβ coordinate system component x αβ by Clark transformation αβ , the fundamental positive sequence feedforward compensation quantity and the fundamental positive sequence transfer function G1(s) to obtain the fundamental positive sequence component x αβ , the fundamental negative sequence feedforward compensation quantity and the fundamental negative sequence transfer function G2(s) to obtain the fundamental negative sequence component x αβ , the hth harmonic feedforward compensation quantity and the hth harmonic transfer function G i (s) to obtain the hth harmonic component output value will participate in the next iteration operation as a feedforward compensation quantity; if the above each time domain variable is written as an s domain expression, the specific calculation formula is: where G1(s), G2(s), G i (s) are the transfer functions in the respective orders αβ coordinate system, ω is the actual angular frequency, ω c is the cut-off frequency of the extraction algorithm.

3. The method of claim 1, wherein, The active power regulator in step S2 is as follows: where P ref and P + are the fundamental positive-sequence active power reference and the fundamental positive-sequence active power, respectively, ω0is the angular frequency reference value, ω is the actual angular frequency, J is the moment of inertia, and D is the damping coefficient. The reactive voltage regulator adds a voltage static compensation term △E to eliminate the influence of the virtual impedance and actual impedance voltage drop of the converter on the voltage droop relationship, so that the grid-connected converter has a reactive droop coefficient K q The reactive voltage regulator has the following specific characteristics: wherein, is the output voltage of the grid-forming converter in the αβ coordinate system, V * is the output voltage peak value of the grid-forming converter, V is the output reference value of the grid-forming converter, ΔE is the voltage static compensation term, R t is the fundamental positive sequence virtual resistance and the total resistance value of the line resistance R r , L t is the fundamental positive sequence virtual inductance and the total inductance value of the line inductance L r , Q ref and Q + are the fundamental positive sequence reactive power reference and the fundamental positive sequence reactive power, respectively, LPF(x) represents a first-order low-pass filtering of x, and |x| represents the modulus value of x.

4. The method of claim 1, wherein, The voltage reference command value described in step S3 Specifically: the fundamental positive sequence the fundamental negative sequence the virtual impedance voltage drop instruction value of the hth harmonic frequency point The specific calculation formula is: Voltage reference command values output by a multi-frequency point virtual impedance reshaping algorithm The specific calculation formula is:

5. The method of claim 1, wherein, The three-phase modulation wave signal m described in step S4 abc The specific calculation formula is: where g v (s) is the transfer function of the voltage controller, k up and k ui are the parameter values of the multiple parallel vector proportional-integral voltage controller; K is the constant of the proportional regulator, is the voltage reference value for PWM modulation; T αβ→abc denotes the transformation from the αβ coordinate system to the abc coordinate system.

6. The method of claim 4, wherein, By adjusting the virtual impedance, the sum of the virtual impedance and the actual impedance of each converter at the hth harmonic frequency is adjusted to a certain proportion, and the hth harmonic current can be distributed in proportion, and the specific calculation formula is: wherein and is the output current vector of the ih harmonic frequency of the ith converter, the line impedance and the virtual impedance, wherein R ri and L ri are the actual resistance and the actual inductance of the output feeder of the ith converter.

7. The method of claim 3, wherein, By adjusting the damping coefficient D and the droop coefficient K in the active and reactive power regulator q When each converter takes P refi / D i and K qi Q refi When each converter takes P When each converter takes P In the formula, P i + , D i , and K qi are the fundamental positive sequence active power, damping coefficient, reactive power and reactive power droop coefficient of the i-th converter.

8. The method of claim 6, wherein, The multi-structure network type converter parallel system adjusts the h times harmonic virtual impedance as The h times harmonic of the point of common coupling voltage can be attenuated by k times, 0≤k<1, and the specific calculation formula is:

9. The main circuit of the method for current coordinated distribution and voltage optimization control of multi-configuration network type converter considering nonlinear and negative sequence load, used for realizing the method for current coordinated distribution and voltage optimization control of multi-configuration network type converter considering nonlinear and negative sequence load according to any one of claims 1-8, characterized in that, The grid-forming converter, the nonlinear and negative sequence load and the power grid are connected in parallel, each grid-forming converter is composed of a DC power supply, a converter and an inductance-capacitance filter, the DC power supply in a single grid-forming converter is connected to the inductance-capacitance filter through the converter to output three-phase power, a plurality of grid-forming converters are connected in parallel through different line impedances and connected to a public coupling point, the public coupling point is connected to the nonlinear and negative sequence load, the public coupling point can be connected to the power grid to become a grid-connected system, or the public coupling point is not connected to the power grid to become an off-grid system; The top-level central controller calculates and issues the virtual impedance value and the droop coefficient of each group of grid-forming converters according to the current coordinated distribution proportion and the voltage optimization demand of the public coupling point, so as to ensure the coordinated distribution of the current and the voltage optimization of the public coupling point.

10. A control device for coordinated distribution of multi-virtual synchronous generator currents and voltage optimization control considering non-linear and negative sequence loads, characterized by, It comprises: The detection module, the harmonic separation module with feedforward compensation, the grid-forming control module, the multi-frequency point virtual impedance remodeling module, the multi-parallel vector proportional integral voltage controller module and the modulation module; The detection module feeds the load-side current and the capacitor voltage to the harmonic separation module with feedforward compensation, and feeds the capacitor voltage, the inductance current and the load-side current to the multi-parallel vector proportional integral voltage controller module; the harmonic separation module with feedforward compensation outputs the fundamental positive sequence, the fundamental negative sequence and the harmonic current to the multi-frequency point virtual impedance remodeling module, and feeds the fundamental positive sequence voltage and current to the grid-forming control module; the grid-forming control module feeds the grid-forming converter output voltage and angular frequency to the multi-frequency point virtual impedance remodeling module, feeds the angular frequency to the multi-parallel vector proportional integral voltage controller module, and feeds the angular frequency to the harmonic separation module with feedforward compensation; The multi-frequency point virtual impedance remodeling module feeds the voltage reference value to the multi-parallel vector proportional integral voltage controller module; The multi-parallel vector proportional integral voltage controller module feeds the three-phase modulation wave signal to the modulation module; a detection module for determining the capacitor voltage u abc , the load-side current i abc and the inductance current i Labc ; Harmonic separation module with feed forward compensation for separating from a load side current i abc and a capacitor voltage u abc a fundamental positive sequence component a fundamental negative sequence component and a h-th harmonic current component and a fundamental positive sequence component A grid-forming control module for calculating a grid voltage αβ and a capacitor voltage u αβ The positive sequence active P and reactive power Q are calculated, from which the grid-forming converter output voltage and the angular frequency ω; A multi-frequency point virtual impedance reshaping module is used to output voltage reference instruction values of a multi-frequency point virtual impedance reshaping algorithm based on network configuration type converter output voltage and the fundamental positive sequence, the fundamental negative sequence, the hth harmonic component and the corresponding set virtual impedance, the voltage reference instruction values of the multi-frequency point virtual impedance reshaping algorithm are calculated A plurality of parallel vector proportional integral voltage controller modules are used for voltage reference instruction values output by a multi-frequency point virtual impedance reshaping algorithm Subtract the capacitor voltage u αβ An output voltage error value is obtained, and a current reference value of a voltage loop output is obtained through a plurality of parallel vector proportional integral voltage controllers Add the load side current i in the αβ coordinate system αβ And subtract the inductor current i Lαβ A current error value is obtained, a current loop output value is obtained through a proportional regulator, and the capacitor voltage u αβ And the current mutual inductance decoupling quantity jωi Lαβ , divided by 0.5 times the DC voltage V dc , and then a three-phase modulation wave signal m abc is obtained; a modulation module for modulating the three-phase modulation wave signal m abc to obtain a switching device pulse signal via the modulation generation module, thereby realizing control of the converter.

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