Converter networking control method and device, electronic equipment and storage medium

Abstract

The invention provides a converter networking control method and device, electronic equipment and a storage medium, and relates to the technical field of converter control, and the method comprises the steps: determining an internal potential phase angle reference value of a converter and an internal potential amplitude reference value of the converter; determining a voltage reference value of the converter based on the internal potential amplitude reference value, the first inner loop control formula and the second inner loop control formula; converting the voltage reference value into a three-phase modulation wave based on the internal potential phase angle reference value; and based on a modulation mode, modulating a difference value between the voltage waveform output by the converter and the three-phase modulation wave to be in a target interval. According to the method, the voltage source characteristics of network construction control are reserved, stable operation under the capacitive load is ensured, all-working-condition operation of network construction control is met, and the current limiting effect of network construction control is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of converter control, and in particular, to a network-forming control method, device, electronic device and storage medium for a converter. Background Art

[0002] In recent years, with the continuous increase in the penetration rate of new energy and the large-scale application of power electronic devices, the system inertia and voltage support ability have been continuously declining. The network-forming control can support the stable operation of the power grid by simulating the control of a synchronous generator to establish its own frequency and voltage.

[0003] Currently, the main method for network-forming control current limiting is that after the network-forming outer loop control generates the phase angle and internal potential, the network-forming inner loop control calculates the current reference value through a virtual circuit, and then generates the voltage reference value through the current inner loop control. However, this inner loop control is unstable in the capacitive load scenario, affecting the full-condition operation of the network-forming control. Summary of the Invention

[0004] The present invention provides a network-forming control method, device, electronic device and storage medium for a converter, to solve the defect in the prior art that the inner loop control is unstable in the capacitive load scenario, affecting the full-condition operation of the network-forming control, and to achieve retaining the voltage source characteristic of the network-forming control, ensuring stable operation under capacitive loads, meeting the full-condition operation of the network-forming control, and improving the current limiting effect of the network-forming control.

[0005] The present invention provides a network-forming control method for a converter, including: Determining a reference value for the phase angle of the internal potential of the converter and a reference value for the amplitude of the internal potential of the converter; Based on the reference value of the internal potential amplitude, a first inner loop control formula and a second inner loop control formula, determining a voltage reference value for the converter; the first inner loop control formula is used to generate a current reference value for the converter, and the second inner loop control formula is used to generate a voltage reference value for the converter; the second inner loop control formula can cancel the current reference value generated by the first inner loop control formula; Based on the reference value of the phase angle of the internal potential, converting the voltage reference value into a three-phase modulation wave; Based on the modulation method, modulating the difference between the voltage waveform output by the converter and the three-phase modulation wave to be within a target range.

[0006] A grid-forming control method for a converter provided by the present invention, determining the voltage reference value of the converter based on the internal potential amplitude reference value, the first inner-loop control formula, and the second inner-loop control formula includes: determining the current reference value of the converter based on the internal potential amplitude reference value and the first inner-loop control formula; determining the voltage reference value of the converter based on the current reference value and the second inner-loop control formula.

[0007] A grid-forming control device for a converter provided by the present invention, determining the current reference value of the converter based on the internal potential amplitude reference value and the first inner-loop control formula includes: when the converter is in steady-state operation, determining the first inner-loop control formula as an equivalent inner-loop control formula, and the equivalent inner-loop control formula is:

[0008] Where is d the first current reference value on the axis, q is the second current reference value on the axis, s is the complex frequency of Laplace transform, is the proportionality coefficient, is d is q the first internal potential amplitude reference value on the axis, is d the second internal potential amplitude reference value on the axis, is q the first grid-side voltage value on the axis, d is the second grid-side voltage value on the axis, q is the equivalent reactance of the converter,

[0009]

[0010] Where is d the first current reference value on the coordinate axis, is q the second current reference value on the coordinate axis, s is the complex frequency of the Laplace transform, is the proportionality coefficient, is the integral coefficient, is d the first internal potential amplitude reference value on the coordinate axis, is q the second internal potential amplitude reference value on the coordinate axis, is d the first grid-side voltage value on the coordinate axis, is q the second grid-side voltage value on the coordinate axis, is d the first converter current value on the coordinate axis, is q the second converter current value on the coordinate axis, is the virtual reactance of the converter, is the virtual resistance of the converter; Based on the internal potential amplitude reference value and the virtual inner loop control formula, determine the current reference value of the converter.

[0011] According to a grid-forming control method of a converter provided by the present invention, the second inner loop control formula is:

[0012] wherein, is the first voltage reference value on the d coordinate axis, is the second voltage reference value on the q coordinate axis.

[0013] According to a grid-forming control method of a converter provided by the present invention, generating the current reference value of the converter based on the internal potential amplitude reference value and the first inner loop control formula includes: when the converter is in a fault period, generating an initial current reference value based on the internal potential amplitude reference value and the first inner loop control formula; limiting the initial current reference value based on a third inner loop control formula to obtain the current reference value; the third inner loop control formula is used to keep the phase angle of the initial current reference value unchanged.

[0014] A grid-forming control method for a converter provided by the present invention, the determining of the internal potential phase angle reference value of the converter and the internal potential amplitude reference value of the converter includes: performing dq decomposition on the three-phase current of the power grid and the three-phase voltage of the power grid respectively to obtain a first grid-side current value on the d coordinate axis, a second grid-side current value on the q coordinate axis, the first grid-side voltage value and the second grid-side voltage value; determining the active power measurement value of the converter based on a first product of the first grid-side current value and the first grid-side voltage value and a second product of the second grid-side current value and the second grid-side voltage value; determining the reactive power measurement value of the converter based on a third product of the first grid-side current value and the second grid-side voltage value and a fourth product of the first grid-side voltage value and the second grid-side current value; determining the internal potential phase angle reference value based on the active power measurement value and the active power reference value of the converter; determining the internal potential amplitude reference value based on the reactive power measurement value, the reactive power reference value of the converter, the voltage amplitude of the grid connection point and the voltage reference amplitude of the grid connection point, where the grid connection point is the connection point between the power grid and the converter.

[0015] The present invention also provides a grid-forming control device for a converter, including: A first determination module, configured to determine the internal potential phase angle reference value of the converter and the internal potential amplitude reference value of the converter; A second determination module, configured to determine the voltage reference value of the converter based on the internal potential amplitude reference value, a first inner-loop control formula and a second inner-loop control formula; the first inner-loop control formula is used to generate the current reference value of the converter, and the second inner-loop control formula is used to generate the voltage reference value of the converter; the second inner-loop control formula can cancel the current reference value generated by the first inner-loop control formula; A conversion module, configured to convert the voltage reference value into three-phase modulation waves based on the internal potential phase angle reference value; A modulation module, based on a modulation method, modulates the difference between the voltage waveform output by the converter and the three-phase modulation waves to be within a target range.

[0016] The present invention also provides an electronic device, including a memory, a processor, and a computer program stored on the memory and executable on the processor, where when the processor executes the computer program, the grid-forming control method as described in any one of the above is implemented.

[0017] The present invention also provides a non-transitory computer-readable storage medium, on which a computer program is stored, and when the computer program is executed by a processor, the grid-forming control method as described in any one of the above is implemented.

[0018] The present invention also provides a computer program product, including a computer program which, when executed by a processor, implements the converter grid-forming control method as described in any one of the above.

[0019] A converter grid-forming control method, device, electronic device and storage medium provided by the present invention obtain converter grid-forming control by connecting a grid-forming outer loop control, a grid-forming inner loop control and a modulation module in sequence. Among them, the second inner loop control formula in the grid-forming inner loop control can cancel the current reference value generated by the first inner loop control formula, so that the voltage reference value of the converter can approach the internal potential amplitude reference value, completely retaining the voltage source characteristics of the grid-forming control, ensuring stable operation under capacitive loads, meeting the full operating conditions of the grid-forming control, and improving the current limiting effect of the grid-forming control. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0021] Figure 1 It is a schematic circuit structure diagram of the connection between a voltage source converter and a power grid provided by the present invention.

[0022] Figure 2 It is a schematic flow diagram of the converter grid-forming control method provided by the present invention.

[0023] Figure 3 It is a schematic structure diagram of the voltage inner loop control module provided by the present invention.

[0024] Figure 4 It is a schematic structure diagram of the current inner loop control module provided by the present invention.

[0025] Figure 5 It is a schematic diagram of the voltage result of the fault current limiting test provided by the present invention.

[0026] Figure 6 It is a schematic diagram of the current result of the fault current limiting test provided by the present invention.

[0027] Figure 7 It is a schematic diagram of the voltage result of the connection capacitive load test provided by the present invention.

[0028] Figure 8 It is a schematic diagram of the capacitance result of the connection capacitive load test provided by the present invention.

[0029] Figure 9 It is a schematic structure diagram of the converter grid-forming control device provided by the present invention.

[0030] Figure 10 It is a schematic structural diagram of the electronic device provided by the present invention. Specific embodiments

[0031] To make the objectives, technical solutions and advantages of the present invention clearer, the technical solutions in the present invention will be clearly and completely described below with reference to the accompanying drawings in the present invention. Apparently, the described embodiments are some but not all of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art without creative efforts based on the embodiments in the present invention belong to the scope of protection of the present invention.

[0032] Grid-forming control is applied in different scenarios, such as new energy transmission, offshore wind power transmission, weak grid and island grid operation, etc. However, different application scenarios pose different requirements on grid-forming devices such as energy storage, Static Var Generator (SVG), flexible DC, etc., including but not limited to overcurrent capacity, instantaneous voltage support capacity, inertia level, frequency adaptability, etc. Although a large number of grid-forming control strategies have been proposed by academia and industrial manufacturers, most of them focus on the outer-loop control of grid-forming in specific application scenarios, that is, the generation of phase angle and internal potential, to meet the support requirements in different application scenarios.

[0033] After the grid-forming outer-loop control generates the phase angle and internal potential, one method is to calculate the current reference value through virtual circuit calculation and then generate the voltage reference value through current inner-loop control. This inner-loop control is unstable in capacitive load scenarios, affecting the full-condition operation of grid-forming control and resulting in limited current limiting effect. Another method is to calculate the virtual voltage drop through virtual impedance and reduce the amplitude of the voltage reference value. Although this method reduces the control complexity, the current limiting effect is limited and it is easy to cause repeated switching of the virtual impedance.

[0034] Based on the above existing problems, the converter grid-forming control method proposed by the present invention obtains the converter grid-forming control by connecting the grid-forming outer-loop control, grid-forming inner-loop control and modulation wave generation module in sequence. Among them, the second inner-loop control formula in the grid-forming inner-loop control can cancel the current reference value generated by the first inner-loop control formula, so that the voltage reference value of the converter can be close to the internal potential amplitude reference value, completely retaining the voltage source characteristics of grid-forming control, ensuring stable operation under capacitive load, meeting the full-condition operation of grid-forming control, and improving the current limiting effect of grid-forming control.

[0035] The following combines Figures 1-8 Describe the converter grid-forming control method of the present invention.

[0036] Figure 1 It is a schematic circuit structure diagram of the connection between the voltage source converter and the power grid, such asFigure 1 As shown in the figure, it includes: a DC power supply U dc 101, a converter 102, a converter equivalent impedance 103, a connection point 104 between the power grid and the converter, a power grid equivalent impedance 105, and a power grid power supply U g 106, is the three-phase voltage of the power grid, is the three-phase current of the power grid, is the three-phase current of the converter.

[0037] Figure 2 is a schematic flow chart of the grid-forming control method for the converter provided by the present invention. As Figure 2 shown in the figure, it includes: S201. Determine the internal potential phase angle reference value of the converter and the internal potential amplitude reference value of the converter.

[0038] It should be noted that both the power grid and the converter output three-phase alternating current. Therefore, before determining the internal potential phase angle reference value and the internal potential amplitude reference value, the electrical quantities (such as voltage and current) in the three-phase stationary coordinate system are decomposed by two-phase rotation (dq Transformation, dq) using the initial internal potential phase angle reference value to obtain dq voltage and dq current, and then the internal potential phase angle reference value and the internal potential amplitude reference value are calculated using the dq voltage and dq current.

[0039] S202. Based on the internal potential amplitude reference value, the first inner-loop control formula, and the second inner-loop control formula, determine the voltage reference value of the converter.

[0040] Among them, the first inner-loop control formula is used to generate the current reference value of the converter, and the second inner-loop control formula is used to generate the voltage reference value of the converter; the second inner-loop control formula can cancel the current reference value generated by the first inner-loop control formula; S203. Based on the internal potential phase angle reference value, convert the voltage reference value into a three-phase modulation wave.

[0041] S204. Based on the modulation method, modulate the difference between the voltage waveform output by the converter and the three-phase modulation wave to be within the target interval.

[0042] Here, the target interval can be an interval close to zero, that is to say, the voltage waveform output by the converter approaches the three-phase modulation wave.

[0043] It should be noted that the converter can be a flexible DC converter. Flexible DC is high-voltage DC power transmission based on a voltage-source converter. In the grid-forming control mode of a flexible DC power transmission system, the grid voltage / frequency stability is autonomously maintained through a fast and accurate inner-loop control strategy.

[0044] Here, the internal potential phase angle reference value is used to describe the angular position of the internal potential (i.e., no-load electromotive force) of a generator or synchronous motor relative to a certain reference phasor during operation.

[0045] Here, the internal potential amplitude reference value and the internal potential phase angle reference value can be obtained based on voltage and current. Among them, any suitable method can be used to determine the internal potential amplitude reference value and the internal potential phase angle reference value. For example, they can be obtained by substituting voltage and current into a calculation formula.

[0046] Exemplarily, the internal potential amplitude reference value can be obtained through reactive voltage control, the internal potential phase angle reference value can be obtained through active control, and the active measurement value and the reactive measurement value can be calculated by a data processing module using the current and voltage after dq decomposition.

[0047] Exemplarily, determining the internal potential phase angle reference value of the converter and the internal potential amplitude reference value of the converter includes: respectively performing dq decomposition on the three-phase current of the power grid and the three-phase voltage of the power grid to obtain the first grid-side current value on the d-axis, the second grid-side current value on the q-axis, the first grid-side voltage value, and the second grid-side voltage value; determining the active measurement value of the converter based on the first product of the first grid-side current value and the first grid-side voltage value and the second product of the second grid-side current value and the second grid-side voltage value; determining the reactive measurement value of the converter based on the third product of the first grid-side current value and the second grid-side voltage value and the fourth product of the first grid-side voltage value and the second grid-side current value; determining the internal potential phase angle reference value based on the active measurement value and the active reference value of the converter; determining the internal potential amplitude reference value based on the reactive measurement value, the reactive reference value of the converter, the voltage amplitude at the connection point, and the reference voltage amplitude at the connection point, where the connection point is the connection point between the power grid and the converter.

[0048] Here, the three-phase voltage of the power grid is Figure 1 in and the three-phase current of the power grid is Figure 1 in and the three-phase current of the converter is Figure 1 in , where the three-phase current of the converter can also be called the valve-side three-phase current.

[0049] Here, the active measurement value can be the sum of the first product and the second product or the weighted sum of the first product and the second product. The reactive measurement value can be the difference between the third product and the fourth product or the weighted difference.

[0050] Exemplarily, the internal potential angle reference value is calculated according to the calculation formula, and the internal potential angle reference value is calculated by the following formula:

[0051] where and are the inertia time constant and the damping coefficient respectively, is the active power reference value after primary frequency modulation and DC voltage control adjustment, is the rated angular velocity, is the active power measurement value.

[0052] Exemplarily, the internal potential amplitude reference value is calculated according to the calculation formula, and the internal potential amplitude reference value is calculated by the following formula:

[0053] where and are the PI control parameters of voltage and reactive power droop, and are the grid connection point voltage and reactive power reference value respectively, is the reactive power measurement value, is the droop coefficient.

[0054] Exemplarily, the process of the data processing module for data processing specifically includes: collecting the three-phase grid voltage , the three-phase grid current , the three-phase valve-side current , and using the internal potential angle reference value to perform dq decomposition on , and respectively to obtain the grid voltage on the d-axis V sd i.e., the first grid-side voltage value, the grid voltage on the q-axis V sq i.e., the second grid-side voltage value, the grid current on the d-axis I sd i.e., the first grid-side current value, the grid current on the q-axis I sq i.e., the second grid-side current value, the first converter current on the d-axis I d and the second converter current on the q-axis I q , and adding the product of V sd and I sd to Vsq The product with I sq obtains the active power measurement value , and subtracts V sq from the product of I sd to obtain the reactive power measurement value V sd by subtracting the product of I sq from .

[0055] In another embodiment, after performing dq decomposition on the three-phase grid-side voltage , the three-phase grid-side current , and the three-phase valve-side current , the decomposed electricity can be filtered through a low-pass filter to obtain V sd , V sq , I sd , I sq , I d and I q .

[0056] In the embodiment of the present invention, the three-phase current and voltage data are collected through the data processing module, the dq decomposition is performed on the three-phase current and voltage data, and the reactive power measurement value and the active power measurement value are calculated to improve the accuracy of the data, thereby improving the precise control of the inner loop control strategy.

[0057] It should be noted that the principle of the second inner loop control formula for canceling the current reference value is that first, substituting the inner potential amplitude reference value into the first inner loop control formula can obtain the current reference value of the converter, and then substituting the current reference value into the second control formula, the voltage reference value approaching the inner potential amplitude reference value can be obtained by canceling the current reference value.

[0058] It should be noted that the grid-forming inner loop control can meet the steady-state operation of the converter and also meet the situation of the converter-side current fault.

[0059] Specifically, after the grid-forming outer loop control generates the inner potential phase angle reference value and the inner potential amplitude reference value of the converter and inputs them to the grid-forming inner loop control, the grid-forming inner loop control substitutes the inner potential amplitude reference value into the first inner loop control formula to generate the current reference value of the converter. The current reference value is substituted into the second inner loop control formula to obtain the voltage reference value of the converter, and the voltage reference value is converted into a three-phase modulation wave. The modulation module is based on the modulation method to make the difference between the voltage waveform output by the converter and the three-phase modulation wave fall within the target interval.

[0060] In an embodiment of the present invention, the grid-forming control of the converter is obtained by connecting the grid-forming outer loop control, the grid-forming inner loop control, and the modulation module in sequence. Among them, the second inner loop control formula in the grid-forming inner loop control can cancel the current reference value generated by the first inner loop control formula, so that the voltage reference value of the converter can approach the amplitude reference value of the internal potential, completely retaining the voltage source characteristic of the grid-forming control, ensuring stable operation under capacitive loads, meeting the full operating conditions of the grid-forming control, and improving the current limiting effect of the grid-forming control.

[0061] Furthermore, determining the voltage reference value of the converter based on the amplitude reference value of the internal potential, the first inner loop control formula, and the second inner loop control formula includes: determining the current reference value of the converter based on the amplitude reference value of the internal potential and the first inner loop control formula; determining the voltage reference value of the converter based on the current reference value and the second inner loop control formula.

[0062] It should be noted that the voltage inner loop control is used to generate the current reference value, and the current inner loop control is used to generate the voltage reference value.

[0063] In an embodiment of the present invention, by combining the voltage inner loop control and the current inner loop control using the first inner loop control formula and the second inner loop control formula, the converter achieves the effect of canceling the inner loop, thereby ensuring stable operation under capacitive loads.

[0064] In one embodiment, determining the current reference value of the converter based on the amplitude reference value of the internal potential and the first inner loop control formula includes: when the converter is in a steady-state operation, determining the first inner loop control formula as the equivalent inner loop control formula, and the equivalent inner loop control formula is:

[0065] Wherein, is d the first current reference value on the axis, q is the second current reference value on the axis, s is the complex frequency of the Laplace transform, is d the first amplitude reference value of the internal potential on the axis, q is axis, d the first grid-side voltage value on the is q the second grid-side voltage value on the isd The first converter current value on the coordinate axis is q the second converter current value on the coordinate axis is the equivalent reactance of the converter is the equivalent resistance of the converter; Based on the internal potential amplitude reference value and the equivalent inner loop control formula, determine the current reference value of the converter.

[0066] It should be noted that the current reference value can be determined by the voltage inner loop control module. Figure 3 is the structural schematic diagram of the voltage inner loop control module provided by the present invention. As Figure 3 shown, perform dq decomposition on the internal potential amplitude reference value to obtain the first internal potential amplitude reference value on the d coordinate axis and the second internal potential amplitude reference value on the q coordinate axis . Here, the current reference value includes the first current reference value on the d coordinate axis and the second current reference value on the q coordinate axis. Taking the d coordinate axis as an example, as Figure 3 in the generating unit 301, subtract from the first grid-side voltage value on the d coordinate axis to obtain the first difference. Multiply the virtual reactance by the negative value of the second converter current value on the q coordinate axis to obtain the first product. Multiply the virtual resistance by the first converter current value on the d coordinate axis to obtain the second product. Subtract the first product and the second product from the first difference to obtain the second difference. Multiply the second difference by the formula to obtain the third product. Add the third product to the first converter current value on the d coordinate axis to obtain the first current reference value on the d coordinate axis . Similarly, the generation principle of the second current reference value on the q coordinate axis is the same as that of the first current reference value . As Figure 3 in the generating unit 302, which will not be elaborated here.

[0067] It should be noted that when the converter is in steady-state operation, replace the virtual reactance Figure 3 and the virtual resistance in with the equivalent reactance and the equivalent resistance .

[0068] In the embodiments of the present invention, in the case of the steady-state operation of the circuit, by combining the voltage inner-loop control and the current inner-loop control using the first inner-loop control formula and the second inner-loop control formula, the converter achieves the effect of canceling the inner loop, thereby ensuring stable operation under capacitive loads.

[0069] In another embodiment, determining the current reference value of the converter based on the inner-potential amplitude reference value and the first inner-loop control formula includes: When the converter is in a fault, determining the first inner-loop control formula as a virtual inner-loop control formula, and the virtual inner-loop control formula is:

[0070] Wherein, is d the first current reference value on the axis, q is s the second current reference value on the is the complex frequency of the Laplace transform, is the proportionality coefficient, is d the first inner-potential amplitude reference value on the axis, q is axis, d the first grid-side voltage value on the is q the second grid-side voltage value on the is d the first converter current value on the is q the second converter current value on the is the virtual reactance of the converter, is the virtual resistance of the converter; Determine the current reference value of the converter based on the inner-potential amplitude reference value and the virtual inner-loop control formula.

[0071] Here, a fault means that the positive-sequence component of the AC voltage is less than 0.85 per-unit value (p.u.) or the zero-sequence component is greater than 0.05 p.u. During a fault, the flexible DC transmission system enters the fault-ride-through control, and a virtual impedance is inserted through the voltage inner-loop control of the converter. After the fault is cleared, the virtual impedance is removed.

[0072] Here, the virtual impedance (i.e., the virtual resistance and the virtual reactance) simulates the electrical characteristics of traditional physical impedances (such as resistors, inductors, or capacitors) through a control algorithm without actually adding physical components.

[0073] It should be noted that the value of the virtual reactance and the value of the virtual resistance can be preset values or calculated in real time. Among them, the values of the virtual resistance and the virtual reactance can be calculated through the total amplitude of the virtual impedance. After the total amplitude of the virtual impedance is calculated, the ratio of the resistance and the reactance can be set as needed to obtain the final virtual resistance and virtual reactance. The total amplitude of the virtual impedance is calculated by the following formula:

[0074] where is the maximum current amplitude, is the phase angle difference between the grid-connected point voltage and the internal electromotive force, is the reference value of the internal electromotive force amplitude, is the grid-connected point voltage amplitude. The grid-connected point is the connection point between the power grid and the converter, is the imaginary part unit.

[0075] Here, the control structure for generating the current reference value by adding the virtual impedance can refer to Figure 3 the control structure.

[0076] In the embodiment of the present invention, after a current fault occurs in the circuit, by increasing the virtual impedance, the current reference value generated by the voltage inner loop control is reduced, so as to achieve the effect of current limiting.

[0077] Furthermore, the second inner loop control formula is:

[0078] where is the first voltage reference value on the d-axis, is the second voltage reference value on the q-axis.

[0079] It should be noted that during the steady-state operation of the circuit, the voltage inner loop control and the current inner loop control are combined using the equivalent inner loop control formula and the second inner loop control formula to achieve the effect of canceling the inner loop. During a circuit fault, a virtual impedance is added to the virtual inner loop control formula to reduce the current reference value. Then, according to the current reference value obtained after increasing the impedance, the voltage reference value is obtained using the second inner loop control formula, and the converter output voltage is controlled to be the voltage reference value, so as to achieve the effect of current limiting.

[0080] It should be noted that the voltage reference value can be determined by the current inner loop control module, Figure 4 is the structural schematic diagram of the current inner loop control module provided by the present invention. As Figure 4 shown, taking the d-axis as an example, as Figure 4 in the generating unit 401 generates the first current reference value on the d-axis Subtract the first converter current value on the d-axis , to obtain a third difference, and multiply the equivalent reactance by the negative value of the second converter current value on the q-axis to obtain a fourth product. Multiply the equivalent resistance by the first converter current value on the d-axis to obtain a fifth product. Multiply the third difference by the formula to obtain a sixth product. Add the fourth product, the fifth product, the sixth product, and the first grid-side voltage value on the d-axis to obtain the first voltage reference value on the d-axis . Similarly, the generation principle of the second voltage reference value on the q-axis is the same as that of the first voltage reference value . For example, in Figure 4 the generation unit 402, which will not be elaborated here.

[0081] In the embodiment of the present invention, for the equivalent inner-loop control formula, the second inner-loop control formula can cancel the effect of the equivalent inner loop and maintain the steady-state operation of the circuit. For the virtual inner-loop control formula, the second inner-loop control formula can reduce the voltage according to the virtual inner-loop control formula, so as to achieve the purpose of current limiting.

[0082] In another embodiment, generating the current reference value of the converter based on the inner potential amplitude reference value and the first inner-loop control formula includes: when the converter is in a fault period, generating an initial current reference value based on the inner potential amplitude reference value and the first inner-loop control formula; limiting the initial current reference value based on a third inner-loop control formula to obtain the current reference value; the third inner-loop control formula is used to keep the phase angle of the initial current reference value unchanged.

[0083] It should be noted that the initial current reference value can be obtained according to the equivalent inner-loop control formula or the virtual inner-loop control formula.

[0084] It should be noted that the third inner-loop control formula can be combined with the equivalent inner-loop control formula to form a first current limiting method; the third inner-loop control formula can be combined with the virtual inner-loop control formula to form a second current limiting method; the virtual inner-loop control formula alone forms a third current limiting method.

[0085] In the embodiment of the present invention, the reference current of the voltage inner-loop control is reduced through current saturation limiting, so that the voltage reference value is reduced by the inner-loop control of the electric current, and the output voltage of the converter is reduced to achieve the purpose of current limiting.

[0086] Furthermore, the third inner-loop control formula is:

[0087] Among them, is the maximum current amplitude, and arctan is the arctangent function.

[0088] It should be noted that the third inner-loop control formula can use the current reference value saturation limiter to lower the initial current reference value, and the current amplitude calculated in the current saturation limiter is the positive-sequence current amplitude.

[0089] It should be noted that when a severe three-phase unbalance fault occurs, if the negative-sequence current control lags, there is a possibility that the current of one or two phases is overcurrent at the initial stage of the fault. When using this current-limiting method alone, a higher requirement for the negative-sequence current suppression function is required. Therefore, the virtual inner-loop control formula and the third inner-loop control method can be combined to achieve the current-limiting effect.

[0090] In the embodiment of the present invention, the reference current of the voltage inner-loop control is reduced through current saturation limiting, and then the voltage inner-loop control reduces the voltage reference value, and the output voltage of the converter is reduced to achieve the purpose of current limiting.

[0091] Apply the converter grid-forming control device provided by the present invention to two sending-end converter stations, and conduct tests on fault current limiting and connecting capacitive loads respectively: Figure 5 is a schematic diagram of the voltage result of the fault current-limiting test provided by the present invention. As Figure 5 shown, the horizontal axis represents time, and the vertical axis represents voltage. It is set that one of the converter stations has an AC network-side three-phase metallic grounding fault at t = 0.2 s (s), the fault resistance is 0.1 ohm, the fault lasts for 1 s, and the period from 0.2 s to 1.2 s is the fault period, and the three-phase voltage drops to 0 during the fault period.

[0092] Figure 6 is a schematic diagram of the current result of the fault current-limiting test provided by the present invention. As Figure 6 shown, the horizontal axis represents time, and the vertical axis represents current. The three-phase fault current does not exceed the current transient limit (1.3 pu). As Figure 5 and 6 show, the converter grid-forming control device proposed by the present invention is effective.

[0093] Figure 7 is a schematic diagram of the voltage result of the test for connecting a capacitive load provided by the present invention. As Figure 7 shown, the horizontal axis represents time, and the vertical axis represents voltage. The load of one of the converter stations is set to 0, and when t = 6 s, a capacitive load of 0.3 pu is connected and maintained for 2 s. It can be seen that the voltage is stable after 6 s.

[0094] Figure 8It is a schematic diagram of the capacitance result for connecting a capacitive load provided by the present invention. As Figure 8 shown, the horizontal axis represents time, and the vertical axis represents capacitance. It can be seen that when t = 6s, after applying a capacitive load of 0.3 pu, the reactive power is -0.3 pu. From Figure 7 and 8 it is shown that the converter grid-forming control device provided by the present invention is applicable to the operating conditions of capacitive loads.

[0095] Next, the converter grid-forming control device provided by the present invention will be described. The converter grid-forming control device described below can be mutually referred to in correspondence with the converter grid-forming control method described above.

[0096] Figure 9 It is a schematic structural diagram of the converter grid-forming control device provided by the present invention. As Figure 9 shown, the converter grid-forming control device 900 includes: A first determination module 910, configured to determine the internal potential phase angle reference value of the converter and the internal potential amplitude reference value of the converter; A second determination module 920, configured to determine the voltage reference value of the converter based on the internal potential amplitude reference value, a first inner-loop control formula, and a second inner-loop control formula; the first inner-loop control formula is used to generate the current reference value of the converter, and the second inner-loop control formula is used to generate the voltage reference value of the converter; the second inner-loop control formula can cancel the current reference value generated by the first inner-loop control formula; A conversion module 930, configured to convert the voltage reference value into three-phase modulation waves based on the internal potential phase angle reference value; A modulation module 940, configured to modulate the difference between the voltage waveform output by the converter and the three-phase modulation waves to be within a target range based on a modulation method.

[0097] In an embodiment, the second determination module 920 is specifically configured to: determine the current reference value of the converter based on the internal potential amplitude reference value and the first inner-loop control formula; determine the voltage reference value of the converter based on the current reference value and the second inner-loop control formula.

[0098] In an embodiment, the second determination module 920 is further specifically configured to: when the converter is in a steady-state operation, determine the first inner-loop control formula as an equivalent inner-loop control formula, and the equivalent inner-loop control formula is:

[0099] where is d the first current reference value on the coordinate axis, is qThe second current reference value on the coordinate axis, s is the complex frequency of the Laplace transform, is the proportionality coefficient, is the integral coefficient, is d the first internal potential amplitude reference value on the coordinate axis, is q the second internal potential amplitude reference value on the coordinate axis, is d the first grid-side voltage value on the coordinate axis, is q the second grid-side voltage value on the coordinate axis, is d the first converter current value on the coordinate axis, is q the second converter current value on the coordinate axis, is the equivalent reactance of the converter, is the equivalent resistance of the converter; based on the internal potential amplitude reference value and the equivalent inner loop control formula, determine the current reference value of the converter.

[0100] In one embodiment, the second determination module 920 is further specifically configured to: the determining the current reference value of the converter based on the internal potential amplitude reference value and the first inner loop control formula includes: when the converter is in a fault period, determining the first inner loop control formula as a virtual inner loop control formula, and the virtual inner loop control formula is:

[0101] wherein, is d the first current reference value on the coordinate axis, is q the second current reference value on the coordinate axis, s is the complex frequency of the Laplace transform, is the proportionality coefficient, is the integral coefficient, is d the first internal potential amplitude reference value on the coordinate axis, is q the second internal potential amplitude reference value on the coordinate axis, is d the first grid-side voltage value on the coordinate axis, is q the second grid-side voltage value on the coordinate axis, is d the first converter current value on the coordinate axis, is q the second converter current value on the coordinate axis, is the virtual reactance of the converter, is the virtual resistance of the converter; Based on the internal potential amplitude reference value and the virtual inner loop control formula, determine the current reference value of the converter.

[0102] In one embodiment, the second inner loop control formula is:

[0103] wherein, is d the first voltage reference value on the coordinate axis, is q the second voltage reference value on the coordinate axis.

[0104] In one embodiment, the second determination module 920 is further specifically configured to: during a fault of the converter, generate an initial current reference value based on the internal potential amplitude reference value and the first inner loop control formula; limit the initial current reference value based on a third inner loop control formula to obtain the current reference value; the third inner loop control formula is used to keep the phase angle of the initial current reference value unchanged.

[0105] In one embodiment, the first determination module 910 is specifically configured to: perform dq decomposition on the three-phase current of the power grid and the three-phase voltage of the power grid respectively to obtain the first grid-side current value on the d coordinate axis, the second grid-side current value on the q coordinate axis, the first grid-side voltage value and the second grid-side voltage value; determine the active power measurement value of the converter based on the first product of the first grid-side current value and the first grid-side voltage value, and the second product of the second grid-side current value and the second grid-side voltage value; determine the reactive power measurement value of the converter based on the third product of the first grid-side current value and the second grid-side voltage value, and the fourth product of the first grid-side voltage value and the second grid-side current value; determine the internal potential phase angle reference value based on the active power measurement value and the active power reference value of the converter; determine the internal potential amplitude reference value based on the reactive power measurement value, the reactive power reference value of the converter, the voltage amplitude at the grid connection point and the reference voltage amplitude at the grid connection point, where the grid connection point is the connection point between the power grid and the converter.

[0106] Figure 10 Illustrates a schematic diagram of the physical structure of an electronic device, such as Figure 10As shown in the figure, the electronic device may include: a processor 1010, a communications interface 1020, a memory 1030, and a communication bus 1040. Among them, the processor 1010, the communications interface 1020, and the memory 1030 complete communication with each other through the communication bus 1040. The processor 1010 may call the logical instructions in the memory 1030 to execute the grid-forming control method for the converter. The method includes: determining the internal potential phase angle reference value and the internal potential amplitude reference value of the converter; determining the voltage reference value of the converter based on the internal potential amplitude reference value, the first inner-loop control formula, and the second inner-loop control formula; the first inner-loop control formula is used to generate the current reference value of the converter, and the second inner-loop control formula is used to generate the voltage reference value of the converter; the second inner-loop control formula can cancel the current reference value generated by the first inner-loop control formula; converting the voltage reference value into a three-phase modulation wave based on the internal potential phase angle reference value; based on the modulation method, modulating the difference between the voltage waveform output by the converter and the three-phase modulation wave to be within a target range.

[0107] In addition, when the logical instructions in the above-mentioned memory 1030 are implemented in the form of software functional units and sold or used as an independent product, they can be stored in a computer-readable storage medium. Based on such an understanding, the technical solution of the present invention, in essence, or the part that contributes to the prior art, or a part of this technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions for causing a computer device (which may be a personal computer, a server, or a network device, etc.) to execute all or part of the steps of the methods described in various embodiments of the present invention. The foregoing storage medium includes: various media such as USB flash drives, mobile hard disks, read-only memories (ROM, Read-Only Memory), random access memories (RAM, Random Access Memory), magnetic disks, or optical discs that can store program codes.

[0108] On the other hand, the present invention also provides a computer program product, which includes a computer program that can be stored on a non-transitory computer-readable storage medium. When the computer program is executed by a processor, the computer can execute the converter grid-forming control method provided by the above-mentioned various methods. The method includes: determining a reference value of the internal potential phase angle of the converter and a reference value of the internal potential amplitude of the converter; based on the reference value of the internal potential amplitude, a first inner-loop control formula, and a second inner-loop control formula, determining a voltage reference value of the converter; the first inner-loop control formula is used to generate a current reference value of the converter, and the second inner-loop control formula is used to generate a voltage reference value of the converter; the second inner-loop control formula can cancel out the current reference value generated by the first inner-loop control formula; based on the reference value of the internal potential phase angle, converting the voltage reference value into a three-phase modulation wave; based on the modulation method, modulating the difference between the voltage waveform output by the converter and the three-phase modulation wave to be within a target range.

[0109] In another aspect, the present invention also provides a non-transitory computer-readable storage medium, on which a computer program is stored. When the computer program is executed by a processor, it is implemented to execute the converter grid-forming control method provided by the above-mentioned various methods. The method includes: determining a reference value of the internal potential phase angle of the converter and a reference value of the internal potential amplitude of the converter; based on the reference value of the internal potential amplitude, a first inner-loop control formula, and a second inner-loop control formula, determining a voltage reference value of the converter; the first inner-loop control formula is used to generate a current reference value of the converter, and the second inner-loop control formula is used to generate a voltage reference value of the converter; the second inner-loop control formula can cancel out the current reference value generated by the first inner-loop control formula; based on the reference value of the internal potential phase angle, converting the voltage reference value into a three-phase modulation wave; based on the modulation method, modulating the difference between the voltage waveform output by the converter and the three-phase modulation wave to be within a target range.

[0110] The device embodiments described above are merely illustrative. The units described as separate components may or may not be physically separated, and the components shown as units may or may not be physical units, that is, they may be located in one place or distributed to multiple network units. Some or all of the modules can be selected according to actual needs to achieve the purpose of the solution of this embodiment. A person of ordinary skill in the art can understand and implement it without creative labor.

[0111] Through the description of the above embodiments, those skilled in the art can clearly understand that each embodiment can be implemented by means of software plus a necessary general hardware platform, and of course, it can also be implemented by hardware. Based on such an understanding, the essence of the above technical solution, or the part that contributes to the prior art, can be embodied in the form of a software product. This computer software product can be stored in a computer-readable storage medium, such as ROM / RAM, magnetic disk, optical disk, etc., and includes several instructions to enable a computer device (which can be a personal computer, a server, or a network device, etc.) to execute the methods described in each embodiment or some parts of the embodiments.

[0112] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements for some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A grid-forming control method for an inverter, characterized in that, Including: Determine the internal potential phase angle reference value of the converter and the internal potential amplitude reference value of the converter; Based on the internal potential amplitude reference value, the first inner-loop control formula, and the second inner-loop control formula, determine the voltage reference value of the converter; The first inner-loop control formula is used to generate the current reference value of the converter, and the second inner-loop control formula is used to generate the voltage reference value of the converter; the second inner-loop control formula can cancel the current reference value generated by the first inner-loop control formula; Based on the internal potential phase angle reference value, convert the voltage reference value into a three-phase modulation wave; Based on the modulation method, modulate the difference between the voltage waveform output by the converter and the three-phase modulation wave to be within the target range.

2. The grid-forming control method of the converter according to claim 1, characterized in that The determining the voltage reference value of the converter based on the internal potential amplitude reference value, the first inner-loop control formula, and the second inner-loop control formula includes: Based on the internal potential amplitude reference value and the first inner-loop control formula, determine the current reference value of the converter; Based on the current reference value and the second inner-loop control formula, determine the voltage reference value of the converter.

3. The converter network-forming control method according to claim 2, wherein The determining the current reference value of the converter based on the internal potential amplitude reference value and the first inner-loop control formula includes: When the converter is in steady-state operation, determine the first inner-loop control formula as the equivalent inner-loop control formula, and the equivalent inner-loop control formula is: ； Among them, is d the first current reference value on the coordinate axis, is q the second current reference value on the coordinate axis, s is the complex frequency of the Laplace transform, is the proportionality coefficient, is the integral coefficient, is d the first internal potential amplitude reference value on the coordinate axis, is q the second internal potential amplitude reference value on the coordinate axis, is d the first grid-side voltage value on the coordinate axis, is q the second grid-side voltage value on the coordinate axis, is d the first converter current value on the coordinate axis, is q the second converter current value on the coordinate axis, is the equivalent reactance of the converter, is the equivalent resistance of the converter; Based on the internal potential amplitude reference value and the equivalent inner-loop control formula, determine the current reference value of the converter.

4. The grid-forming control method of the converter according to claim 2, characterized in that, The determining the current reference value of the converter based on the internal potential amplitude reference value and the first inner-loop control formula includes: When the converter is in a fault period, determine the first inner-loop control formula as the virtual inner-loop control formula, and the virtual inner-loop control formula is: ； Among them, is d the first current reference value on the coordinate axis, is q the second current reference value on the coordinate axis, s is the complex frequency of the Laplace transform, is the proportionality coefficient, is the integral coefficient, is d the first internal potential amplitude reference value on the coordinate axis, is q the second internal potential amplitude reference value on the coordinate axis, is d the first grid-side voltage value on the coordinate axis, is q the second grid-side voltage value on the coordinate axis, is d the first converter current value on the coordinate axis, is q the second converter current value on the coordinate axis, is the virtual reactance of the converter, is the virtual resistance of the converter; Based on the internal potential amplitude reference value and the virtual inner-loop control formula, determine the current reference value of the converter.

5. The converter network-forming control method according to claim 3 or 4, characterized in that The second inner-loop control formula is: ； Among them, is d the first voltage reference value on the coordinate axis, is q the second voltage reference value on the coordinate axis, is the equivalent reactance of the converter, is the equivalent resistance of the converter.

6. The grid-forming control method of the converter according to claim 2, wherein The generating the current reference value of the converter based on the internal potential amplitude reference value and the first inner-loop control formula includes: When the converter is in a fault period, based on the internal potential amplitude reference value and the first inner-loop control formula, generate an initial current reference value; Based on the third inner-loop control formula, limit the initial current reference value to obtain the current reference value; the third inner-loop control formula is used to keep the phase angle of the initial current reference value unchanged.

7. The grid-forming control method of the converter according to claim 5, wherein The determining the internal potential phase angle reference value of the converter and the internal potential amplitude reference value of the converter includes: Perform dq decomposition on the three-phase current of the power grid and the three-phase voltage of the power grid respectively to obtain the first grid-side current value on the d-axis, the second grid-side current value on the q-axis, the first grid-side voltage value, and the second grid-side voltage value; Based on the first product of the first grid-side current value and the first grid-side voltage value, and the second product of the second grid-side current value and the second grid-side voltage value, determine the active power measurement value of the converter; Determine the reactive power measurement value of the converter based on the third product of the first grid-side current value and the second grid-side voltage value, and the fourth product of the first grid-side voltage value and the second grid-side current value; Determine the internal potential phase angle reference value based on the active power measurement value and the active power reference value of the converter; Determine the internal potential amplitude reference value based on the reactive power measurement value, the reactive power reference value of the converter, the voltage amplitude of the grid connection point, and the voltage reference amplitude of the grid connection point, where the grid connection point is the connection point between the power grid and the converter.

8. A converter grid-forming control device, characterized in that, Comprising: A first determination module for determining the internal potential phase angle reference value of the converter and the internal potential amplitude reference value of the converter; A second determination module for determining the voltage reference value of the converter based on the internal potential amplitude reference value, the first inner-loop control formula, and the second inner-loop control formula; The first inner-loop control formula is used to generate the current reference value of the converter, and the second inner-loop control formula is used to generate the voltage reference value of the converter; The second inner-loop control formula can cancel the current reference value generated by the first inner-loop control formula; A conversion module for converting the voltage reference value into a three-phase modulation wave based on the internal potential phase angle reference value; A modulation module for modulating the difference between the voltage waveform output by the converter and the three-phase modulation wave to be within a target range based on the modulation method.

9. An electronic device, comprising a memory, a processor, and a computer program stored on the memory and running on the processor, characterized in that, When the processor executes the computer program, it implements the converter network-forming control method according to any one of claims 1-7.

10. A non-transitory computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by the processor, it implements the converter network-forming control method according to any one of claims 1 to 7.

Images