Multi-network converter current coordinated distribution and voltage optimization control method considering nonlinearity and negative sequence load

Abstract

The invention discloses a current coordinated distribution and voltage optimization control method of a multi-network converter considering nonlinearity and negative sequence load. The method comprises the following steps: carrying out harmonic separation on three-phase load side current and three-phase capacitor voltage through feedforward compensation to obtain a fundamental wave positive sequence component, a fundamental wave negative sequence component and an h-order harmonic component; fundamental wave positive sequence active and reactive power are solved, and angular frequency and output voltage are respectively obtained through an active frequency regulator and a reactive voltage regulator; virtual impedance of a fundamental wave positive sequence, a fundamental wave negative sequence and a harmonic component is set, a multi-frequency-point virtual impedance voltage drop instruction is calculated, and a voltage reference instruction value is obtained by subtracting the multi-frequency-point virtual impedance voltage drop instruction value from the output voltage of the constructed network type converter; calculating a three-phase modulation wave signal based on the voltage reference instruction value, the capacitor voltage, the load side current, the inductor current and the DC voltage; and calculating a pulse signal of the switching device based on the three-phase modulated wave signal. The virtual impedance of the networking converter is set to be a negative value, the harmonic voltage drop on a common coupling point can be reduced, the sum of the virtual impedance and the actual impedance is adjusted to be a certain proportion, and the harmonic current of each order of the multi-networking converter can be distributed according to the proportion.

Description

Technical Field

[0001] The present invention belongs to the field of converter control technology, and specifically relates to a method for current coordinated distribution and voltage optimization control of a multi-grid converter taking into account nonlinear and negative-sequence loads. A series of control strategies such as harmonic separation, multi-frequency point virtual impedance reshaping, grid control algorithm and multi-parallel vector proportional integral voltage control are adopted to complete the coordinated distribution of currents between multiple parallel converters and improve the voltage quality of the common connection point. The present invention is suitable for a multi-grid converter parallel system connected to multiple nonlinear and negative-sequence loads, and can be used for off-grid or grid-connected systems. Background Art

[0002] In the early stage of new energy development, the scale of the station was not large, and most grid-connected converters adopted grid-following control based on phase-locked synchronization. The grid-following converter is essentially a current source, and its inertia and damping support capabilities for the power grid are weak. As the proportion of new energy access increases, the system inertia and damping are lacking. In the event of a fault, the grid-following converter has poor anti-interference and weak support capabilities, which reduces the safety and stability of the power grid. The grid-building converter simulates the traditional synchronous machine, controls the output power to track the set value, obtains the frequency and voltage reference values, and realizes tracking through the subsequent voltage control link, so that the converter outputs a voltage with constant amplitude and frequency, presenting characteristics similar to those of the traditional synchronous machine, and has inertia and damping support for the power grid. In summary, the grid-building converter is the first choice for power electronic grid-connected converters in future new power systems.

[0003] The negative sequence and nonlinear loads connected to the power system cause asymmetry and harmonic distortion of the grid voltage. Grid harmonics have a great impact on power equipment and power-consuming equipment, which will lead to problems such as increased power loss, shortened equipment life, and reduced power quality. Therefore, the power system needs to effectively manage and control grid harmonics. At present, there are many literatures on the coordinated control of fundamental positive sequence loads by multi-grid parallel converter systems, such as droop control. However, there is less research on the coordinated sharing of negative sequence loads and nonlinear harmonic loads and the management of grid distortion voltage. Summary of the invention

[0004] In view of the problems existing in the prior art, the present invention provides a current coordinated distribution and voltage optimization control strategy for a multi-grid converter taking into account nonlinear and negative sequence loads.

[0005] The converter proposed in the present invention reshapes each frequency point into a negative virtual impedance, which can compensate for 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 in the harmonic frequency band is adjusted to a certain proportion, and the harmonic current can be distributed proportionally, thereby improving the accuracy of the coordinated distribution of harmonic currents and having good adaptability in the scenario of multi-grid converter parallel system.

[0006] In a first aspect, the present invention provides a method for current coordinated distribution and voltage optimization control of a multi-grid converter considering nonlinear and negative sequence loads, and the specific implementation includes the following steps:

[0007] S1. Three-phase load side current i based on grid-connected converter abc , minus the feedforward compensation at different frequencies, and multiplying by 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 h harmonic component Similarly, the three-phase capacitor voltage u of the grid-type converter abc The fundamental positive sequence component of the capacitor voltage is obtained by the above method: Fundamental negative sequence component h harmonic component

[0008] S2. According to the load side current fundamental positive sequence component and capacitor voltage fundamental positive sequence component 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 grid-type converter output voltage and S1 Set the virtual impedance of the fundamental positive sequence, fundamental negative sequence and harmonic components to and Respectively Multiply by the grid-connected converter output voltage Subtract the product after the above multiplication to get the voltage reference command value

[0010] S4. Based on the above voltage reference command value Subtract the capacitor voltage u αβ The voltage error value is obtained, and the current reference value of the voltage loop output is obtained through a 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 The current error value is obtained, and the current loop output value is obtained through the proportional regulator, and then the capacitor voltage u is superimposed. αβ and the current mutual feedback decoupling jωi Lαβ , divided by 0.5 times the DC voltage V dc , and then converted into the abc coordinate system to obtain the three-phase modulation wave signal m abc , calculate the three-phase modulation wave signal m abc ;

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

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

[0013] Input three-phase component x abc , which is transformed into the component x in the αβ coordinate system through Clark transformation αβ , x αβ After fundamental positive sequence feedforward compensation And the fundamental positive sequence extraction function G1(s) to obtain the fundamental positive sequence component x αβ After fundamental negative sequence feedforward compensation And the fundamental negative sequence extraction function G2(s) to obtain the fundamental negative sequence component x αβ After h harmonic feedforward compensation and hth harmonic extraction function G i (s) to get the hth harmonic component Output value It will be used as the feedforward compensation in the next iteration. If the above time domain variables are written as s domain expressions, the specific calculation formula is:

[0014]

[0015] Among them, G1(s), G2(s), G i (s) are the extracted transfer functions in the αβ coordinate system of each order, 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 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;

[0019] The reactive voltage regulator adds a voltage static compensation term ΔE 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 converter has a reactive droop coefficient K at the common connection point. q The droop relationship of the characteristics of the reactive voltage regulator is as follows:

[0020]

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

[0022] The voltage reference command value described in step S3 Specifically:

[0023] Calculate the fundamental positive sequence Fundamental Negative Sequence The virtual impedance voltage drop command value at the hth harmonic frequency point The specific calculation formula is:

[0024]

[0025] Voltage reference command value output by multi-frequency point virtual impedance reshaping algorithm The specific calculation formula is:

[0026]

[0027] The three-phase modulation wave signal m described in step S4 abc , the specific calculation formula is:

[0028]

[0029] Among them, k up and k ui is the parameter value of the multi-parallel vector proportional integral voltage controller; K is the constant of the proportional regulator, is the voltage reference value used for PWM modulation; T αβ→abc Indicates from αβ Coordinate system conversion to 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 ratio, and the hth harmonic current can be distributed proportionally. The specific calculation formula is:

[0031]

[0032] In the formula, 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;

[0033] 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 they are 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. The specific calculation formula is:

[0034]

[0035] 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;

[0036] The multi-grid type parallel converter system, through adjusting the hth harmonic virtual impedance is The hth harmonic of the common coupling point voltage can be attenuated by k times (0≤k<1), and the specific calculation formula is:

[0037]

[0038] In a second aspect, the present invention provides a main circuit of a multi-grid-type converter current coordinated distribution and voltage optimization control method considering nonlinear and negative-sequence loads, comprising multiple parallel grid-type converters, nonlinear and negative-sequence loads and a power grid, each grid-type converter consisting of a DC power supply, a converter, and an inductor and capacitor filter, the DC power supply in a single grid-type converter is connected to the inductor and capacitor filter through the converter to output three-phase electricity, multiple grid-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, the common coupling point can be connected to the power grid to become a grid-connected system, or the common coupling point is not connected to the power grid to become an off-grid system;

[0039] The top-level central controller calculates and issues the virtual impedance value and droop coefficient of each grid-type converter according to the current coordination distribution ratio of each grid-type converter and the voltage optimization requirements of the common coupling point, thereby ensuring the coordinated distribution of current and the voltage optimization of the common coupling point.

[0040] In a third aspect, the present invention provides a multi-virtual synchronous generator current coordinated distribution and voltage optimization control device considering nonlinear and negative sequence loads, including: a detection module, a harmonic separation module with feedforward compensation, a meshed control module, a multi-frequency point virtual impedance reshaping module, a multi-parallel vector proportional integral voltage controller module and a modulation module; the detection module feeds the load side current and capacitor voltage to the harmonic separation module with feedforward compensation, and feeds the capacitor voltage, inductor current and load side current to the multi-parallel vector proportional integral voltage controller module; the harmonic separation module with feedforward compensation feeds the virtual multi-frequency point virtual impedance reshaping module, the multi-parallel vector proportional integral voltage controller module, and the ... The point virtual impedance reshaping module outputs fundamental positive sequence, fundamental negative sequence, and harmonic current, and feeds fundamental positive sequence voltage and current to the meshing control module; the meshing control module feeds the meshing converter output voltage and angular frequency to the multi-frequency point virtual impedance reshaping 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 reshaping module feeds a voltage reference value to the multi-parallel vector proportional integral voltage controller module; the multi-parallel vector proportional integral voltage controller module feeds a three-phase modulation wave signal to the modulation module;

[0041] A detection module is used to determine the capacitor voltage u abc , load side current i abc and the inductor current i Labc ;

[0042] Harmonic separation module with feedforward compensation is used to separate the load side current i abc and capacitor voltage u abc Separate the fundamental positive sequence component Fundamental negative sequence component and hth harmonic current components And the fundamental positive sequence component

[0043] The grid-type control module is used to control the load side current i αβ and capacitor voltage u αβ Calculate the positive sequence active power P and reactive power Q, and then get the grid-connected converter output voltage and angular frequency ω;

[0044] Multi-frequency point virtual impedance reshaping module for grid-based converter output voltage The voltage reference command value output by the multi-frequency point virtual impedance reshaping algorithm is calculated by combining the fundamental positive sequence, fundamental negative sequence, hth harmonic component and the corresponding virtual impedance. Multi-parallel vector proportional integral voltage controller module for voltage reference command value output by multi-frequency point virtual impedance reshaping algorithm Subtract the capacitor voltage u αβ The output voltage error value is passed through a 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 αβ coordinate system αβ and subtract the inductor current i Lαβ The current error value is obtained, and the current loop output value is obtained through the proportional regulator, and then compared with the capacitor voltage u αβ and the current mutual feedback decoupling jωi Lαβ , divided by 0.5 times the DC voltage V dc , and then the three-phase modulation wave signal m is obtained abc ;

[0045] Modulation module, used for three-phase modulation wave signal m abc , the switching device pulse signal is obtained through the modulation generation module, thereby realizing the control of the converter.

[0046] In a fourth aspect, the present application provides a computer-readable storage medium, which stores a computer program. When the computer program is executed by a computer, it implements the multi-grid converter current coordination distribution and voltage optimization control method considering nonlinear and negative-sequence loads as described in the present invention.

[0047] The present invention proposes a method for current coordinated distribution and voltage optimization control of a multi-grid-type converter taking into account nonlinearity and negative-sequence loads, which is applicable to a grid-connected or off-grid main circuit system composed of multiple parallel grid-type converters, power grids, nonlinearity and negative-sequence loads. The present invention reshapes the output impedance of each harmonic sub-order of each converter so that the output impedance of each harmonic sub-order of each converter is inversely proportional to the converter capacity, thereby achieving the distribution of harmonic currents among converters according to the capacity ratio. At the same time, by setting a negative virtual impedance to compensate for the harmonic voltage drop on the output line, the voltage distortion at the common coupling point can be reduced.

[0048] The converter proposed in the present invention reshapes each frequency point into a negative virtual impedance, and can compensate for the harmonic voltage drop on the line impedance, thereby ensuring the voltage stability at the common coupling point. Then, the sum of the virtual impedance and the actual impedance of each converter in the harmonic frequency band is adjusted to a certain ratio, and the harmonic current can be distributed proportionally, thereby improving the accuracy of the coordinated distribution of harmonic currents.

[0049] The advantages of the present invention are: a series of control strategies such as harmonic separation, multi-frequency point virtual impedance reshaping, network control algorithm and multi-parallel vector proportional integral voltage control are proposed, and the resistive and inductive output impedances of each harmonic frequency point can be independently adjusted at will, so as to achieve the effect of reducing the voltage distortion at the common coupling point and optimizing the coordinated distribution of harmonic currents. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying any creative work.

[0051] Figure 1 A flowchart of a method for current coordination distribution and voltage optimization control of a multi-grid converter considering nonlinearity and negative sequence loads provided by an embodiment of the present invention;

[0052] Figure 2 A main circuit diagram of a method for current coordinated distribution and voltage optimization control of a multi-grid converter considering nonlinearity and negative sequence loads provided by an embodiment of the present invention;

[0053] Figure 3 This is the control block diagram of the harmonic separation algorithm with feedforward compensation;

[0054] Figure 4 It is the control block diagram of the network control algorithm;

[0055] Figure 5 The control block diagram of the multi-frequency point virtual impedance reshaping algorithm;

[0056] Figure 6 It is the control block diagram of the algorithm of multi-parallel vector proportional integral voltage controller;

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

[0058] Figure 8 4 is a common coupling point voltage simulation waveform diagram of an embodiment of the present invention.

[0059] Figure 9a to Figure 9b This is a simulation waveform diagram of the dual-machine load current in an embodiment of the present invention, wherein: Figure 9a is the load current simulation waveform of the converter. Figure 9b It is the load current simulation waveform of another converter. DETAILED DESCRIPTION

[0060] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0061] Example 1

[0062] Reference Figure 1 This embodiment provides a method for current coordinated distribution and voltage optimization control of a multi-grid type converter considering nonlinear and negative sequence loads, characterized in that the specific implementation includes the following steps:

[0063] S1. Three-phase load side current i based on grid-connected converter abc , minus the feedforward compensation at different frequencies, and multiplying by 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 h harmonic component Similarly, the three-phase capacitor voltage u of the grid-type converter abc The fundamental positive sequence component of the capacitor voltage is obtained by the above method: Fundamental negative sequence component h harmonic component

[0064] S2. According to the load side current fundamental positive sequence component and capacitor voltage fundamental positive sequence component 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.

[0065] S3. According to the grid-type converter output voltage and S1 Set the virtual impedance of the fundamental positive sequence, fundamental negative sequence and harmonic components to and Respectively Multiply by the grid-connected converter output voltage Subtract the product after the above multiplication to get the voltage reference command value

[0066] S4. Based on the above voltage reference command value Subtract the capacitor voltage u αβ The voltage error value is obtained, and the current reference value of the voltage loop output is obtained through a multi-parallel vector proportional integral voltage controller. Add the load side current i in the αβ coordinate system αβAnd subtract the inductor 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 is superimposed. αβ and the current mutual feedback decoupling jωi Lαβ , divided by 0.5 times the DC voltage V dc , and then converted into the abc coordinate system to obtain the three-phase modulation wave signal m abc , calculate the three-phase modulation wave signal m abc ;

[0067] S5 pulse generation, based on the three-phase modulation wave signal m abc , a switching device pulse signal is obtained through a modulation generation module;

[0068] The fundamental positive sequence component, fundamental negative sequence component, and hth harmonic component of the current and voltage described in step S1 are as shown in the control block diagram. Figure 3 As shown, specifically:

[0069] Input three-phase components x abc , which is transformed into the component x in the αβ coordinate system through Clark transformation αβ , x αβ After fundamental positive sequence feedforward compensation And the fundamental positive sequence extraction function G1(s) to obtain the fundamental positive sequence component x αβ After fundamental negative sequence feedforward compensation And the fundamental negative sequence extraction function G2(s) to obtain the fundamental negative sequence component x αβ After h harmonic feedforward compensation and hth harmonic extraction function G i (s) to get the hth harmonic component Output value It will be used as the feedforward compensation in the next iteration. If the above time domain variables are written as s domain expressions, the specific calculation formula is:

[0070]

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

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

[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 actual impedance voltage drop of the converter on the voltage droop relationship, so that the grid converter has a reactive droop coefficient K at the common connection point. q The droop relationship of the characteristics of the reactive voltage regulator is as follows:

[0076]

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

[0078] The voltage reference command value described in step S3 Specifically:

[0079]

[0080] Voltage reference command value output by multi-frequency point virtual impedance reshaping algorithm The specific calculation formula is:

[0081]

[0082] The three-phase modulation wave signal m described in step S4 abc , the specific calculation formula is:

[0083]

[0084] Among them, k up and k ui is the parameter value of the multi-parallel vector proportional integral voltage controller; K is the constant of the proportional regulator, is the voltage reference value used for PWM modulation; Tαβ→abc Indicates from αβ Coordinate system conversion to abc Coordinate system;

[0085] 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 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] In the formula, 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 they are 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. 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 type parallel converter system adjusts 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), and the specific calculation formula is:

[0092]

[0093] Example 2

[0094] refer to Figure 2This embodiment provides a main circuit of a multi-grid-type converter current coordinated distribution and voltage optimization control method considering nonlinear and negative-sequence loads, including multiple parallel grid-type converters, nonlinear and negative-sequence loads and a grid. Each grid-type converter is composed of a DC power supply, a converter, and an inductor and capacitor filter. The DC power supply in a single grid-type converter is connected to the inductor and capacitor filter through the converter to output three-phase electricity. Multiple grid-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. The common coupling point can be connected to the grid to become a grid-connected system, or the common coupling point is not connected to the grid to become an off-grid system.

[0095] The top-level central controller calculates and issues the virtual impedance value and droop coefficient of each grid-type converter according to the current coordination distribution ratio of each grid-type converter and the voltage optimization requirements of the common coupling point, thereby ensuring the coordinated distribution of current and the voltage optimization of the common coupling point;

[0096] Example 3

[0097] The present embodiment provides a control device for current coordinated distribution and voltage optimization control of multiple virtual synchronous generators considering nonlinear and negative sequence loads, including: a detection module, a harmonic separation module with feedforward compensation, a meshed control module, a multi-frequency point virtual impedance reshaping module, a multi-parallel vector proportional integral voltage controller module and a modulation module; the detection module feeds the load side current and capacitor voltage to the harmonic separation module with feedforward compensation, and feeds the capacitor voltage, inductor current and load side current to the multi-parallel vector proportional integral voltage controller module; the harmonic separation module with feedforward compensation feeds the virtual multi-frequency point virtual impedance reshaping module, the multi-parallel vector proportional integral voltage controller module, and the ... The point virtual impedance reshaping module outputs fundamental positive sequence, fundamental negative sequence, and harmonic current, and feeds fundamental positive sequence voltage and current to the meshing control module; the meshing control module feeds the meshing converter output voltage and angular frequency to the multi-frequency point virtual impedance reshaping 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 reshaping module feeds a voltage reference value to the multi-parallel vector proportional integral voltage controller module; the multi-parallel vector proportional integral voltage controller module feeds a three-phase modulation wave signal to the modulation module;

[0098] A detection module is used to determine the capacitor voltage u abc , load side current i abc and the inductor current i Labc ;

[0099] Harmonic separation module with feedforward compensation is used to separate the load side current i abc and capacitor voltage u abc Separate the fundamental positive sequence component Fundamental negative sequence component and hth harmonic current components And the fundamental positive sequence component

[0100] The grid-type control module is used to control the load side current i αβ and capacitor voltage u αβ Calculate the positive sequence active power P and reactive power Q, and then get the grid-connected converter output voltage and angular frequency ω;

[0101] Multi-frequency point virtual impedance reshaping module for grid-based converter output voltage The voltage reference command value output by the multi-frequency point virtual impedance reshaping algorithm is calculated by combining the fundamental positive sequence, fundamental negative sequence, hth harmonic component and the corresponding virtual impedance.

[0102] Multi-parallel vector proportional integral voltage controller module for voltage reference command value output by multi-frequency point virtual impedance reshaping algorithm Subtract the capacitor voltage u αβ The output voltage error value is passed through a 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 αβ coordinate system αβ and subtract the inductor current i Lαβ The current error value is obtained, and the current loop output value is obtained through the proportional regulator, and then compared with the capacitor voltage u αβ and the current mutual feedback decoupling jωi Lαβ , divided by 0.5 times the DC voltage V dc , and then the three-phase modulation wave signal m is obtained abc ;

[0103] Modulation module, used for three-phase modulation wave signal m abc , the switching device pulse signal is obtained through the modulation generation module, thereby realizing the control of the converter.

[0104] Example 4

[0105] This embodiment provides a computer-readable storage medium, which stores a computer program. When the computer program is executed by a computer, the current coordinated distribution and voltage optimization control method of a multi-grid converter considering nonlinear and negative-sequence loads described in Example 1 is implemented.

[0106] The implementation of the above embodiments has the following specific effects:

[0107] The simulation of the multi-grid converter can be performed based on simulation tools such as Matlab / Simulink, etc. A converter simulation model is built in Matlab / Simulink to verify the control method of the multi-grid converter involved in the present application.

[0108] The relevant parameters of the control circuit of the grid-type converter are configured 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, proportional regulator K = 30, moment of inertia J1 = 0.1, damping coefficient D1 = 10, reactive droop coefficient K in converter 1 q1 =0.002, fundamental wave positive sequence virtual impedance ( The unit is Ω, The unit is mH, the same below), fundamental negative sequence virtual impedance Virtual impedance of harmonic components Converter 2 rotation inertia J2 = 0.05, damping coefficient D2 = 5, reactive droop coefficient K q2 =0.002, fundamental wave positive sequence virtual impedance Fundamental Negative Sequence Virtual Impedance Virtual impedance of harmonic components

[0110] Figure 8 The voltage waveform at the common connection point is shown in the figure. As shown in the figure, the voltage waveform has no obvious distortion, the THD is 2.55%, and the system can maintain stable operation.

[0111] Figure 9a to Figure 9b The waveform diagram of the dual-machine load current is shown in the figure. As can be seen from the simulation diagram, the dual-machine load current waveform is distributed in a 2:1 ratio and there is no phase shift.

[0112] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply that there is any such actual relationship or order between these entities or operations. Moreover, the term "include", "comprise" or any other variant thereof is intended to cover non-exclusive inclusion, so that the process, method, article or equipment that includes a series of elements are inherent to the elements. In the absence of more restrictions, the elements limited by the sentence "comprise one..." do not exclude the presence of other identical elements in the process, method, article or equipment that includes the elements. In addition, the above-mentioned technical solution provided in the embodiment of the present application is consistent with the corresponding technical solution in the prior art in principle, and the part is not described in detail, so as not to repeat too much.

[0113] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present application. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined in the present invention may be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present invention will not be limited to the embodiments shown herein, but will conform to the widest scope consistent with the principles and novel features disclosed in the present invention.

Claims

1. A method for current coordinated distribution and voltage optimization control of multi-grid converters considering nonlinear and negative sequence loads, characterized in that: The following steps are involved: S1. Three-phase load side current i based on grid-connected converter abc , minus the feedforward compensation at different frequencies, and multiplying by 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 h harmonic component Similarly, the three-phase capacitor voltage u of the grid-type converter abc The fundamental positive sequence component of the capacitor voltage is obtained by the above method: Fundamental negative sequence component h harmonic component S2. According to the load side current fundamental positive sequence component and capacitor voltage fundamental positive sequence component 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. S3. According to the grid-type converter output voltage and S1 Set the virtual impedance of the fundamental positive sequence, fundamental negative sequence and harmonic components to and Respectively Multiply by the grid-connected converter output voltage Subtract the product after the above multiplication to get the voltage reference command value S4. Based on the above voltage reference command value Subtract the capacitor voltage u αβ The voltage error value is obtained, and the current reference value of the voltage loop output is obtained through a 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 The current error value is obtained, and the current loop output value is obtained through the proportional regulator, and then the capacitor voltage u is superimposed. αβ and the current mutual feedback decoupling jωi Lαβ , divided by 0.5 times the DC voltage V dc , and then converted into the abc coordinate system to obtain the three-phase modulation wave signal m abc , calculate the three-phase modulation wave signal m abc ; S5 pulse generation, based on the three-phase modulation wave signal m abc , the switching device pulse signal is obtained through the modulation generation module.

2. The method according to claim 1, characterized in that The fundamental positive sequence component, fundamental negative sequence component, and hth harmonic component of the current and voltage described in step S1 are specifically: Input three-phase components x abc , which is transformed into the component x in the αβ coordinate system through Clark transformation αβ , x αβ After fundamental positive sequence feedforward compensation And the fundamental positive sequence extraction function G1(s) to obtain the fundamental positive sequence component x αβ After fundamental negative sequence feedforward compensation And the fundamental negative sequence extraction function G2(s) to obtain the fundamental negative sequence component x αβ After h harmonic feedforward compensation and hth harmonic extraction function G i (s) to get the hth harmonic component Output value It will be used as the feedforward compensation in the next iteration. If the above time domain variables are written as s domain expressions, the specific calculation formula is: Among them, G1(s), G2(s), G i (s) are the extraction functions in the αβ coordinate system of each order, ω is the actual angular frequency, ω c is the cutoff frequency of the extraction algorithm.

3. The method according to claim 1, characterized in that The active frequency regulator described in step S2 is as follows: Among them, P ref 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; The reactive voltage regulator adds a voltage static compensation term ΔE 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 converter has a reactive droop coefficient K at the common connection point. q The droop relationship of the characteristics of the reactive voltage regulator is as follows: in, is the output voltage of the grid-type converter in the αβ coordinate system, V * is the peak value of the grid-type converter output voltage, V is the grid-type converter output reference value, ΔE is the voltage static compensation term, R t is the fundamental positive sequence virtual resistance With line resistance R r The total resistance, L t is the fundamental positive sequence virtual inductance and line inductance L r The total inductance, Q ref and Q + are the fundamental positive-sequence reactive reference power and the fundamental positive-sequence reactive power respectively. LPF(x) means first-order low-pass filtering of x. x| means modulus value of x.

4. The method according to claim 1, characterized in that The voltage reference command value described in step S3 Specifically: Calculate the fundamental positive sequence Fundamental Negative Sequence The virtual impedance voltage drop command value at the hth harmonic frequency point The specific calculation formula is: Voltage reference command value output by multi-frequency point virtual impedance reshaping algorithm The specific calculation formula is:

5. The method according to claim 1, characterized in that The three-phase modulation wave signal m described in step S4 abc , the specific calculation formula is: Among them, g v (s) is the transfer function of the voltage controller, k up and k ui is the parameter value of the multi-parallel vector proportional integral voltage controller; K is the constant of the proportional regulator, is the voltage reference value used for PWM modulation; T αβ→abc Indicates from αβ The coordinate system is transformed into the abc coordinate system.

6. The method according to claim 4, characterized in that By adjusting the virtual impedances in claim 4, the sum of the virtual impedance and the 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 specific calculation formula is: In the formula, 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.

7. The method according to claim 3, characterized in that 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 they are 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. The specific calculation formula is: In the formula, 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.

8. The method according to claim 6, characterized in that The multi-grid type parallel converter system adjusts 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), and the specific calculation formula is:

9. The main circuit of the current coordinated distribution and voltage optimization control method of multi-grid converter considering nonlinear and negative sequence loads is characterized by: It includes multiple parallel grid-type converters, nonlinear and negative-sequence loads and power grids. Each grid-type converter is composed of a DC power supply, a converter, and an inductor and capacitor filter. The DC power supply in a single grid-type converter is connected to the inductor and capacitor filter through the converter to output three-phase electricity. Multiple grid-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. The common coupling point can be connected to the power grid to become a grid-connected system, or the common 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 droop coefficient of each grid-type converter according to the current coordination distribution ratio of each grid-type converter and the voltage optimization requirements of the common coupling point, thereby ensuring the coordinated distribution of current and the voltage optimization of the common coupling point.

10. A control device for current coordinated distribution and voltage optimization control of multiple virtual synchronous generators considering nonlinear and negative sequence loads, characterized in that: include: Detection module, harmonic separation module with feedforward compensation, mesh control module, multi-frequency point virtual impedance reshaping module, multi-parallel vector proportional integral voltage controller module and modulation module; The detection module feeds the load side current and capacitor voltage to the harmonic separation module with feedforward compensation, and feeds the capacitor voltage, inductor current and 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, fundamental negative sequence and harmonic current to the virtual multi-frequency point virtual impedance reshaping module, and feeds the fundamental positive sequence voltage and current to the meshing control module; the meshing control module feeds the meshing converter output voltage and angular frequency to the multi-frequency point virtual impedance reshaping 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 reshaping module feeds voltage reference values ​​to the multi-parallel vector proportional integral voltage controller module; The multi-parallel vector proportional integral voltage controller module feeds a three-phase modulation wave signal to the modulation module; A detection module is used to determine the capacitor voltage u abc , load side current i abc and the inductor current i Labc ; Harmonic separation module with feedforward compensation is used to separate the load side current i abc and capacitor voltage u abc Separate the fundamental positive sequence component Fundamental negative sequence component and hth harmonic current components And the fundamental positive sequence component The grid-type control module is used to control the load side current i αβ and capacitor voltage u αβ Calculate the positive sequence active power P and reactive power Q, and then get the grid-connected converter output voltage and angular frequency ω; Multi-frequency point virtual impedance reshaping module for grid-based converter output voltage The voltage reference command value output by the multi-frequency point virtual impedance reshaping algorithm is calculated by combining the fundamental positive sequence, fundamental negative sequence, hth harmonic component and the corresponding virtual impedance. Multi-parallel vector proportional integral voltage controller module for voltage reference command value output by multi-frequency point virtual impedance reshaping algorithm Subtract the capacitor voltage u αβ The output voltage error value is passed through a 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 αβ coordinate system αβ and subtract the inductor current i Lαβ The current error value is obtained, and the current loop output value is obtained through the proportional regulator, and then compared with the capacitor voltage u αβ and the current mutual feedback decoupling jωi Lαβ , divided by 0.5 times the DC voltage V dc , and then the three-phase modulation wave signal m is obtained abc ; Modulation module, used for three-phase modulation wave signal m abc , the switching device pulse signal is obtained through the modulation generation module, thereby realizing the control of the converter.

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