Control methods and equipment for parallel LC-type energy storage converters in weak power grids

Abstract

This application provides a control method and device for parallel LC-type energy storage converters in weak power grids, applicable to the field of power technology. The method includes: constructing a PCS topology for the LCL-type energy storage converter based on multiple parallel LC-type energy storage converters and the line impedance and transformer short-circuit impedance on the grid side; constructing a third-order mathematical model based on the PCS topology; wherein the third-order mathematical model includes the differential model of the filter inductance and the differential model of the filter capacitor of the LC-type energy storage converter, as well as the differential model of the equivalent inductance of the line impedance and transformer short-circuit impedance; identifying parameters of the differential model of the equivalent inductance based on a sliding mode observer to obtain the observed values ​​of unknown parameters in the third-order mathematical model; wherein the unknown parameters include the equivalent impedance of the line impedance and transformer short-circuit impedance, and the grid-side voltage on the grid side; and obtaining the output control voltage based on the observed values ​​of the unknown parameters and the third-order mathematical model. This application improves the stability of the energy storage converter control.

Description

Technical Field

[0001] This application relates to the field of power technology, and in particular to a control method and equipment for a parallel LC-type energy storage converter in a weak power grid. Background Technology

[0002] LC filter-based energy storage converters (PCS) are widely used in large-scale energy storage power stations and industrial and commercial energy storage applications due to their advantages such as high power factor, low current harmonic distortion, and low device voltage stress (only half that of the output voltage).

[0003] Energy storage power stations are connected to the grid by a large number of PCS in parallel. The LC type PCS, which is more commonly used in practice, is usually composed of several units connected in parallel and then connected to the large power grid through transmission lines and step-up transformers. Due to the existence of transmission line impedance and transformer short-circuit impedance, the power grid exhibits weak grid characteristics at this time. The parallel LC type PCS, after being connected in series with the line impedance and transformer short-circuit impedance, form a pseudo-LCL type PCS structure.

[0004] Currently, this type of energy storage converter still uses the LC-type PCS control strategy, but this control strategy is prone to system instability in weak power grids. Summary of the Invention

[0005] This application provides a control method and equipment for a parallel LC-type energy storage converter in a weak power grid, in order to solve the technical problem of unstable control of the parallel LC-type energy storage converter in a weak power grid.

[0006] According to the first aspect disclosed in this application, this application provides a control method for a parallel LC-type energy storage converter in a weak power grid, the method comprising:

[0007] Based on multiple parallel LC-type energy storage converters and the line impedance and transformer short-circuit impedance on the grid side, a PCS topology for the LCL-type energy storage converter is constructed.

[0008] Based on the PCS topology, a third-order mathematical model is constructed; wherein, the third-order mathematical model includes the differential model of the filter inductor and the differential model of the filter capacitor of the LC energy storage converter in the dq coordinate system, as well as the differential model of the equivalent inductance of the line impedance and the transformer short-circuit impedance in the dq coordinate system.

[0009] The parameters of the equivalent inductance differential model are identified based on the sliding mode observer to obtain the observed values ​​of the unknown parameters in the third-order mathematical model; wherein, the unknown parameters include the equivalent impedance of the line impedance and the transformer short-circuit impedance, as well as the grid-side voltage on the grid side.

[0010] The output control voltage is obtained based on the observed values ​​of the unknown parameters and the third-order mathematical model.

[0011] In one feasible implementation, parameter identification is performed on the equivalent inductance differential model based on a sliding mode observer to obtain observed values ​​of unknown parameters in the third-order mathematical model, including:

[0012] Based on the equivalent inductance differential model, a grid-side inductance model is constructed;

[0013] Based on the grid-side inductance model and the equivalent inductance differential model, an observation error model is constructed.

[0014] Based on the observation error model and the sliding mode observer, the model control voltage of the grid-side inductance model is obtained;

[0015] Based on the model control voltage of the grid-side inductance model, the observed values ​​of the unknown parameters are obtained.

[0016] In one feasible implementation, the model control voltage of the grid-side inductance model is obtained based on the observation error model and the sliding mode observer, including:

[0017] The first Lyapunov function is constructed based on the current error of the observation error model.

[0018] Construct a second Lyapunov function based on the unknown parameters;

[0019] By combining the first Lyapunov function and the second Lyapunov function, a third Lyapunov function is obtained;

[0020] Based on the third Lyapunov function and the sliding mode observer, the model control voltage of the grid-side inductance model is obtained.

[0021] In one feasible implementation, obtaining the observed values ​​of the unknown parameters based on the model control voltage of the grid-side inductor model includes:

[0022] The model control voltage based on the grid-side inductance model is used to converge the third Lyapunov function, thereby obtaining the observed values ​​of the unknown parameters.

[0023] In one feasible implementation, the output control voltage is obtained based on the observed values ​​of the unknown parameters and the third-order mathematical model, including:

[0024] Based on the observed values ​​of the unknown parameters, the current error on the grid side, and the equivalent inductance differential model, the expected voltage of the LC-type energy storage converter at the common coupling point is obtained.

[0025] Based on the desired voltage and the differential model of the filter capacitor, the set current is obtained;

[0026] The output control voltage is obtained based on the set current and the differential model of the filter inductor.

[0027] In one feasible implementation, based on the observed values ​​of the unknown parameters, the current error on the grid side, and the equivalent inductance differential model, the expected voltage of the LC-type energy storage converter at the point of common coupling is obtained, including:

[0028] Based on the observed values ​​of the unknown parameters and the equivalent inductance differential model, the virtual control voltage is determined;

[0029] A fourth Lyapunov function is constructed based on the virtual control voltage and the current error on the grid side;

[0030] The fourth Lyapunov function is brought to converge, and the desired voltage is obtained.

[0031] In one feasible implementation, the set current includes a d-axis current set value and a q-axis current set value in the dq coordinate system. The set current is obtained based on the desired voltage and the differential model of the filter capacitor, including:

[0032] Based on the d-axis voltage error of the desired voltage in the dq coordinate system, a fifth Lyapunov function is constructed.

[0033] Based on the q-axis voltage error of the desired voltage in the dq coordinate system, a sixth Lyapunov function is constructed.

[0034] Based on the fifth Lyapunov function and the differential model of the filter capacitor, the d-axis current setting value of the set current in the dq coordinate system is obtained.

[0035] Based on the sixth Lyapunov function and the differential model of the filter capacitor, the q-axis current setting value of the set current in the dq coordinate system is obtained.

[0036] In one feasible implementation, the output control voltage is obtained based on the set current and the differential model of the filter inductor, including:

[0037] Based on the set current, a seventh Lyapunov function is constructed;

[0038] Based on the fifth, sixth, and seventh Lyapunov functions, an eighth Lyapunov function is constructed.

[0039] The output control voltage is obtained based on the eighth Lyapunov function and the differential model of the filter inductor.

[0040] According to a second aspect disclosed in this application, this application provides a control device for a parallel LC-type energy storage converter in a weak power grid, the device comprising:

[0041] The topology building module is used to construct the PCS topology of LCL energy storage converters based on multiple parallel LC energy storage converters and the line impedance and transformer short-circuit impedance on the grid side.

[0042] The model building module is used to build a third-order mathematical model based on the PCS topology; wherein, the third-order mathematical model includes the differential model of the filter inductor and the differential model of the filter capacitor of the LC energy storage converter in the dq coordinate system, as well as the differential model of the equivalent inductance of the line impedance and the transformer short-circuit impedance in the dq coordinate system.

[0043] The sliding mode observation module is used to identify parameters of the equivalent inductance differential model based on the sliding mode observer and obtain the observed values ​​of unknown parameters in the third-order mathematical model; wherein, the unknown parameters include the equivalent impedance of the line impedance and the transformer short-circuit impedance, as well as the grid-side voltage on the grid side;

[0044] The control output module is used to obtain the output control voltage based on the observed values ​​of the unknown parameters and the third-order mathematical model.

[0045] According to a third aspect disclosed in this application, this application provides an electronic device, including a processor and a memory communicatively connected to the processor;

[0046] The memory stores computer-executed instructions;

[0047] The processor executes computer execution instructions stored in the memory to implement the method described in any one of the first aspects.

[0048] According to the fourth aspect disclosed in this application, this application provides a computer-readable storage medium storing computer-executable instructions, which, when executed, are used to implement the method described in any one of the first aspects.

[0049] According to the fifth aspect disclosed in this application, this application provides a computer program product, including a computer program, which, when executed, is used to implement the method described in any one of the first aspects.

[0050] Compared with existing technologies, the control method and equipment for parallel LC-type energy storage converters in weak power grids provided in this application have the following advantages:

[0051] 1. By using current sharing control without tie lines, parallel LC type PCS can be regarded as a single LC type PCS. Combining the transformer short-circuit impedance and line impedance, an LCL type PCS is formed without increasing costs.

[0052] 2. The grid-side current control adopts a proportional + inertial element, which realizes that the voltage setpoints calculated by the parallel PCS are equal, providing a basis for current sharing without tie lines.

[0053] 3. The controller design adopts an LCL-type third-order model, which solves the problem of poor system stability caused by model approximation.

[0054] 4. A compensation item for grid-side current has been added to the inductor current setting, which can correct current deviations more quickly. Attached Figure Description

[0055] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0056] Figure 1 A main circuit diagram of two LC-type energy storage converters connected in parallel is provided for an embodiment of this application;

[0057] Figure 2 A control block diagram of a single energy storage converter provided in an embodiment of this application;

[0058] Figure 3 A flowchart illustrating a control method for a parallel LC-type energy storage converter in a weak power grid, provided in an embodiment of this application;

[0059] Figure 4 for Figure 1 A schematic diagram of the PCS topology of converting the main circuit structure of two parallel LC-type energy storage converters into an LCL-type energy storage converter.

[0060] Figure 5 A flowchart illustrating a method for obtaining observed values ​​of unknown parameters in a third-order mathematical model, provided in an embodiment of this application;

[0061] Figure 6 A schematic diagram illustrating the observation results of an unknown parameter provided in an embodiment of this application;

[0062] Figure 7 A flowchart illustrating a method for obtaining an output control voltage according to an embodiment of this application;

[0063] Figure 8 for Figure 1 A schematic diagram of voltage and current waveform monitoring after the start-up of an energy storage converter;

[0064] Figure 9 for Figure 1 A schematic diagram of voltage and current waveform monitoring after another energy storage converter is started.

[0065] Figure 10 When the d-axis current is set to 1000A, Figure 1 A schematic diagram of voltage and current waveform monitoring after the two parallel energy storage converters in the middle are started;

[0066] Figure 11 When the d-axis current is set to 1500A, Figure 1 A schematic diagram of voltage and current waveform monitoring after the two parallel energy storage converters in the middle are started;

[0067] Figure 12 A schematic diagram of the structure of a control device for a parallel LC-type energy storage converter in a weak power grid provided in this application embodiment;

[0068] Figure 13 This is a schematic diagram of the structure of an electronic device provided in an embodiment of this application.

[0069] The accompanying drawings illustrate specific embodiments of this application, which will be described in more detail below. These drawings and descriptions are not intended to limit the scope of the concept in any way, but rather to illustrate the concept of this application to those skilled in the art through reference to particular embodiments. Detailed Implementation

[0070] Exemplary embodiments will now be described in detail, examples of which are illustrated in the accompanying drawings. When the following description relates to the drawings, unless otherwise indicated, the same numbers in different drawings denote the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with this application. Rather, they are merely examples of apparatuses and methods consistent with some aspects of this application as detailed in the appended claims.

[0071] Before providing a further detailed description of the embodiments of this application, the nouns and terms used in the embodiments of this application will be explained first. The nouns and terms used in the embodiments of this application shall be interpreted as follows:

[0072] PCS refers to a power storage converter, which is a bidirectional power conversion device that connects the battery system and the power grid. It consists of components such as a DC / AC bidirectional converter and a control unit. Its main functions include controlling the battery charging and discharging process, regulating the power grid, and obtaining battery system status information in real time through a communication interface.

[0073] LC refers to a second-order filter structure consisting of a single inductor (L) and a capacitor (C) connected in series or in parallel.

[0074] LCL refers to a third-order filter structure consisting of two inductors (L1, L2) and one capacitor (C).

[0075] PCC stands for Point of Common Coupling, which is the physical connection point between the user system (such as distributed power sources, energy storage, or electrical equipment) and the public power grid in a power system.

[0076] As the capacity of energy storage power stations continues to expand, these stations typically consist of multiple high-power energy storage converters (PCSs) connected in parallel and then stepped up by a transformer before being connected to the high-voltage grid. Due to the short-circuit impedance and line impedance of the step-up transformer, the parallel-connected LC-type PCSs form a pseudo-LCL-type structure with these impedances. This structure results in a weak grid characteristic, where load fluctuations cause fluctuations in the point of common coupling (PCC) voltage, further affecting the current control of the PCS, causing fluctuations in the PCS inductor current, and even causing oscillations in the entire system. Conventional LC-type PCS uses inductor current as the control target, which does not correspond to the grid-side current corresponding to the dispatch command. LCL-type PCS, on the other hand, uses grid-side current as the control object and is a typical cascaded third-order system. Designing it as a third-order system can improve system stability, but it increases control complexity.

[0077] The pseudo-LCL structure formed by parallel LC-type PCS is not exactly the same as the conventional LCL structure. If the parallel PCS is regarded as a large-capacity PCS, it can be regarded as an LCL structure and can be designed according to the LCL structure. However, the parallel PCS needs to implement current sharing control.

[0078] Figure 1 The present application provides a main circuit structure diagram of two LC-type energy storage converters connected in parallel. The circuit uses multiple insulated gate bipolar transistors (IGBTs), and each IGBT is connected in anti-parallel to a diode. These switching devices form the core part of the LC-type energy storage converter. By controlling their conduction and turn-off, DC to AC power conversion can be achieved.

[0079] Filter inductor ( Connected between the output of the energy storage converter and the power grid, the inductor is used to filter out high-frequency harmonics in the output current, making the output current closer to a sine wave; Connected to a three-phase AC power grid to achieve grid-connected power transmission; current sensor ( ) is used to measure the current of each phase output to the power grid; filter capacitor ( It is connected in parallel with the AC output terminal, along with the filter inductor. Together they form an LC filter, further improving the output power quality; current sensor ( () represents the phase current output by the energy storage converter to the three-phase AC power grid.

[0080] The #2 ANPC three-level inverter is a three-level inverter that employs Active Neutral Point Clamping (ANPC) technology. Compared to two-level inverters, three-level inverters offer lower switching losses, higher efficiency, and better output waveform quality. The DC side of the three-level inverter also features parallel capacitors to provide a stable DC input. The AC side structure is similar to the AC side of the energy storage converter above, including a filter inductor. Current measurement point ( and filter capacitors It is used to filter the electrical energy output from the inverter before feeding it into the power grid.

[0081] Figure 2 This application provides a control block diagram for a single energy storage converter, mainly comprising four parts: a PCS circuit, a filter circuit, a grid side, and a control circuit module. The control circuit module monitors various electrical parameters in real time and generates pulse width modulation (PWM) signals using a specific control algorithm, thereby controlling the switching of power devices in the PCS circuit to achieve stable operation and power conversion of the energy storage converter. The specific control process includes:

[0082] The grid-side voltage in the three-phase stationary coordinate system is transformed using the Clake transform. and current Energy storage converter output voltage and current Transform to a two-phase stationary coordinate system ( (coordinate system), to obtain and This transformation simplifies the complexity of the control algorithm.

[0083] By inputting grid-side voltage Components in coordinate system A dual proportional-integral phase-locked loop (DPLL) can accurately detect the phase and frequency of the grid-side voltage, providing a synchronization signal for subsequent control. Its output typically includes information such as the phase angle synchronized with the grid, used for coordinate transformation and current control.

[0084] Using the phase angle provided by DPLL, Current in coordinate system and voltage Transform to a two-phase rotating coordinate system (dq coordinate system) to obtain In the dq coordinate system, the steady-state value of the control variable is DC, which facilitates the implementation of zero steady-state error control.

[0085] The input to the outer current loop is the current reference value in the dq coordinate system. and actual current feedback value Through a proportional-integral (PI) regulator, the outer current loop generates a voltage reference value in the dq coordinate system based on the deviation between the reference value and the feedback value. This allows for precise control of the output current.

[0086] The input to the nonlinear voltage outer loop is the DC-side voltage. and its reference value It adjusts the reference value of the inner current loop through specific control algorithms (such as nonlinear control strategies) to ensure the stability of the DC side voltage.

[0087] Nonlinear current inner loop receives DC side voltage and current and its reference value Switching signals are generated through a nonlinear control algorithm. It is used to control the on / off state of power switching devices in the PCS.

[0088] The Space Vector Pulse Width Modulation (SVPWM) module outputs based on the nonlinear current inner loop. Generate specific PWM signals The IGBTs in the power switching circuit are switched on and off to realize the power conversion function of the energy storage converter.

[0089] In the aforementioned control process, traditional current sharing control methods for multi-machine grid-connected current sharing mainly include droop control, master-slave control, and distributed collaborative control. However, when facing a weak grid, high grid impedance leads to severe P / Q (active power / reactive power) coupling, reducing the accuracy of traditional droop control. The common approach is to introduce virtual impedance or adaptive droop coefficients to improve performance. In master-slave control, a failure of the master inverter can cause system collapse and low reliability; master-slave synchronization in weak grids may be affected by voltage distortion. In distributed collaborative control, communication delays or interruptions may cause system instability, requiring optimization of the communication topology to improve robustness. Secondly, filter design directly affects current sharing performance and system stability. In LCL filters, the resonant frequency may fall into the control bandwidth, leading to harmonic amplification. The solution requires additional passive and active damping control, increasing control complexity. Furthermore, in parallel LCL-type energy storage PCS, they may couple with each other, causing high-frequency oscillations.

[0090] Therefore, current energy storage converters still employ the LC-type PCS control strategy, but this approximate modeling is prone to system instability in weak power grids. On the other hand, if the LCL-type PCS control strategy is adopted, there are difficulties in accurately calculating line impedance and transformer short-circuit impedance, and the voltage connected to the grid cannot be measured.

[0091] To address the aforementioned technical issues, this application proposes a control method and device for parallel LC-type energy storage converters in weak power grids. By using parallel LC-type PCSs as a single LC-type PCS, and employing an LCL-type third-order model for controller design, the problem of poor system stability caused by model approximation is solved.

[0092] The following detailed description, through specific embodiments, illustrates the technical solution of the control method and equipment for parallel LC-type energy storage converters under weak power grids provided in this application. It should be noted that the following embodiments may exist independently or in combination; for identical or similar content, descriptions may not be repeated in different embodiments.

[0093] Figure 3 A flowchart illustrating a control method for a parallel LC-type energy storage converter in a weak power grid, as provided in this application embodiment, is shown below. Figure 3 In some embodiments, the control method for the parallel LC-type energy storage converter under the weak power grid includes the following steps:

[0094] S100 is based on multiple parallel LC-type energy storage converters and the line impedance and transformer short-circuit impedance on the grid side to construct the PCS topology of the LCL-type energy storage converter.

[0095] In this case, multiple LC-type PCS units connected in parallel are regarded as one LC-type PCS. At this time, they can be connected in series with the line impedance and the transformer short-circuit impedance to form an LCL-type PCS, and thus construct the PCS topology of the LCL-type energy storage converter.

[0096] Specifically, will Figure 1 The two parallel LC energy storage converters in the main circuit diagram, along with the line impedance and transformer short-circuit impedance on the grid side, are converted into... Figure 4 The PCS topology of the LCL type energy storage converter.

[0097] Among them, Figure 4 In the middle, the voltage output of devices such as energy storage converters The inductor (L) provides the energy source for the entire circuit; the inductor (L) and capacitor (C) in each sub-circuit together form a filter. The main function of the inductor (L) is to suppress high-frequency changes in the current. The capacitor (C) works in conjunction with the inductor (L) to filter out high-frequency harmonic components in the voltage, making the output voltage smoother and more stable; connecting the inductor... Located between the filter sub-circuit and the power grid, it serves to connect and is equivalent to the line impedance and transformer short-circuit impedance; grid-side voltage source This indicates the receiving end of electrical energy. Current. They are from two voltage sources. The outflowing current, after passing through its respective filter inductor L, will have a portion charging or discharging the filter capacitor C (forming capacitive current), while the other portion will continue to flow forward; after the action of the filter inductor L and capacitor C, the output voltage is relatively smooth. and Flow to the connected inductor current These two currents converge at the junction, forming the total current flowing into the power grid. .

[0098] S200, based on PCS topology, constructs a third-order mathematical model; the third-order mathematical model includes the differential model of the filter inductor and the differential model of the filter capacitor of the LC type energy storage converter in the dq coordinate system, as well as the differential model of the equivalent inductance of the line impedance and the transformer short-circuit impedance in the dq coordinate system.

[0099] Among them, the LCL-type PCS takes the grid-side current as the control object and is a typical cascaded third-order system, which is used to construct a third-order mathematical model.

[0100] Specifically, in combination Figure 4 The PCS topology is constructed using a third-order mathematical model, which includes the differential model of the filter inductor and the differential model of the filter capacitor in the dq coordinate system for the LC-type energy storage converter, as well as the differential model of the equivalent inductance of the line impedance and the transformer short-circuit impedance in the dq coordinate system.

[0101] Specifically, the differential model of the filter inductor satisfies the following formula (1):

[0102]

[0103] Specifically, the differential model of the filter capacitor satisfies the following formula (2):

[0104]

[0105] Specifically, the differential model of the equivalent inductance satisfies the following formula (3):

[0106]

[0107] Where L represents the filter inductance of the PCS, C represents the filter capacitance of the PCS, d represents the differential operator, t represents time, and R represents the equivalent series resistance of the filter inductance. Indicates the grid-side inductance, and through This represents the equivalent value of the line impedance and the transformer short-circuit impedance. Represents the angular frequency of the power grid signal. Let represent the voltages at the common coupling points on the d-axis and q-axis in the dq coordinate system, respectively. These represent the grid-side voltages on the d-axis and q-axis in the dq coordinate system, respectively. These represent the filter inductor currents on the d-axis and q-axis in the dq coordinate system, respectively. These represent the grid-side currents on the d-axis and q-axis in the dq coordinate system, respectively.

[0108] Specifically, the dq coordinate system is a two-phase rotating coordinate system used to transform complex three-phase AC systems into a two-dimensional model that is easier to analyze and control. The d-axis (direct axis) is aligned with the rotor magnetic field direction and represents the excitation component (such as the N-pole centerline of a permanent magnet); the q-axis (quadrature axis) leads the d-axis by 90 electrical degrees and represents the torque component (related to the armature magnetic field or torque generation direction); rotational characteristics: the dq coordinate system rotates synchronously with the rotor's mechanical speed, causing stator current, voltage, and other electrical quantities to appear as direct currents (or slow variables) in this coordinate system, thus simplifying the control equations.

[0109] S300 uses a sliding mode observer to identify parameters of the equivalent inductance differential model and obtain the observed values ​​of unknown parameters in the third-order mathematical model. The unknown parameters include the equivalent impedance of the line impedance and the transformer short-circuit impedance, as well as the grid-side voltage on the grid side.

[0110] In this approach, multiple LC-type PCS units connected in parallel are considered as a single LC-type PCS. In this case, they can be connected in series with the line impedance and transformer short-circuit impedance to form an LCL-type PCS. However, since the line impedance and transformer short-circuit impedance are difficult to calculate accurately, the grid-side voltage cannot be measured for LC-type PCS. Therefore, an observer is used to obtain the measured values ​​of these unknown parameters.

[0111] Figure 5 This application provides a flowchart illustrating a method for obtaining observed values ​​of unknown parameters in a third-order mathematical model, as illustrated in the embodiments of this application. Figure 5 In some embodiments, the method for obtaining observations of unknown parameters in a third-order mathematical model includes the following steps:

[0112] S310, based on the equivalent inductance differential model, constructs the grid-side inductance model.

[0113] Among them, PCS cannot collect , Because the line length varies, its value cannot be determined precisely, therefore... and An observer is used for estimation.

[0114] set up The observed value is , The observed value is ,but The observation error is ,and , The observation error is ,and To facilitate the design of the observer, the formula (3) of the equivalent inductance differential model is converted into the following formula (4):

[0115]

[0116] Then the grid-side inductance model in the dq coordinate system satisfies the following formula (5):

[0117]

[0118] in, These represent the model control voltages on the d-axis and q-axis in the dq coordinate system, respectively.

[0119] The grid-side inductance model serves to ensure that the model current is equal to the actual grid-side current.

[0120] S320, based on the grid-side inductance model and the equivalent inductance differential model, constructs an observation error model.

[0121] Wherein, the current error of the grid-side inductor model is assumed to be... Defined as Subtracting equation (4) from equation (5) and ignoring higher-order insignificants, the observation error model satisfies the following formula (6):

[0122]

[0123] For the observation error model, if the error can be zero, it means that the corresponding terms of the two equations are equal, because in reality... It is unknown, but It is calculated and considered known, thus it can be used as a substitute. .

[0124] S330, based on the observation error model and sliding mode observer, obtains the model control voltage of the grid-side inductance model.

[0125] Optionally, based on the observation error model and the sliding mode observer, the model control voltage of the grid-side inductance model is obtained, including:

[0126] Step S331: Construct the first Lyapunov function based on the current error of the observation error model.

[0127] Let the first Lyapunov function be... Satisfy the following formula (7):

[0128]

[0129] The derivative of the first Lyapunov function satisfies the following formula (8):

[0130]

[0131] Step S332: Construct the second Lyapunov function based on the unknown parameters.

[0132] To control the identification error, a second Lyapunov function is defined. Satisfy the following formula (9):

[0133]

[0134] in, This indicates the control parameters.

[0135] The derivative of the second Lyapunov function then satisfies the following formula (10):

[0136]

[0137] Step S333: Combine the first Lyapunov function and the second Lyapunov function to obtain the third Lyapunov function.

[0138] The third Lyapunov function is obtained by combining the first and second Lyapunov functions. .

[0139] The derivative of the third Lyapunov function then satisfies the following formula (11):

[0140]

[0141] Step S334: Based on the third Lyapunov function and the sliding mode observer, obtain the model control voltage of the grid-side inductance model.

[0142] In equation (11), , , Since it is an unknown quantity, therefore let , , The coefficient on the left is 0, which eliminates the influence of these three unknowns. Let its coefficient be a known quantity. For quantities with opposite signs, the last two terms can be negative, thus yielding formula (12):

[0143]

[0144] in, Represents a symbolic function. This represents the sliding mode control coefficient.

[0145] Among them, when using a sliding mode observer, it should be ensured that the current in the grid-side inductance model converges to the actual grid-side current, and the model control voltage should satisfy the following formula (13):

[0146]

[0147] S340 is a model control voltage based on the grid-side inductance model, used to obtain observed values ​​of unknown parameters.

[0148] Optionally, the model control voltage based on the grid-side inductance model is used to obtain the observed values ​​of the unknown parameters, including: the model control voltage based on the grid-side inductance model is used to make the third Lyapunov function converge and obtain the observed values ​​of the unknown parameters.

[0149] Among them, the model control voltage based on the grid-side inductance model is obtained. Thus making The convergence is achieved, and the control rate of the observed variables is obtained as formula (14):

[0150]

[0151] in, This indicates the control parameters.

[0152] From the control rate in the above formula, the unknown parameters can be obtained. , , The observed values.

[0153] For details, please refer to Figure 6 The observation results of the unknown parameters are as follows Figure 6 As shown:

[0154] Figure 6 (a) shows the observed grid-side current value Igd_smo and the actual grid-side current value Igd on the d-axis in the dq coordinate system. Figure 6 Figure (b) shows the observed grid-side current Igq_smo and the actual grid-side current Igq on the q-axis in the dq coordinate system. Figure 6 (c) shows the observed value of grid-side inductance Lg_smo and the actual value of grid-side inductance Lg; Figure 6 The figure (d) shows the observed grid-side current value ugd_smo and the actual grid-side current value ugd on the d-axis in the dq coordinate system. Figure 6 (e) shows the observed grid-side current ugq_smo and the actual grid-side current ugq on the q-axis in the dq coordinate system; Figure 6 In the diagram (f), the model control voltage Udm on the d-axis and the model control voltage Uqm on the q-axis are shown in the dq coordinate system. Figure 6In the diagram (g), the grid-side control voltage Ud on the d-axis and the grid-side control voltage Uq on the q-axis are shown in the dq coordinate system.

[0155] from Figure 6 The results show that there are observation errors in the three unknown parameters mentioned above, but this does not affect the control of the grid-side current. This is because when When the error is 0, we can obtain the result from the 4th and 5th terms of formula (12). Comparing formulas (4) and (5), we can obtain:

[0156]

[0157] Although the above three parameters have steady-state errors, the equations represented by formulas (4) and (5) have no errors, so they have no impact on current control.

[0158] The S400 obtains the output control voltage based on the observed values ​​of unknown parameters and a third-order mathematical model.

[0159] After obtaining the observed values ​​of the unknown parameters, the output control voltage is further obtained by combining the third-order mathematical model, so as to realize the control of the parallel LC type energy storage controller through the output control voltage.

[0160] Figure 7 A flowchart illustrating a method for obtaining an output control voltage according to an embodiment of this application is provided. (See attached diagram.) Figure 7 In some embodiments, the method for obtaining the output control voltage includes the following steps:

[0161] S410, based on the observed values ​​of unknown parameters, the current error on the grid side, and the differential model of the equivalent inductance, obtains the expected voltage of the LC type energy storage converter at the common coupling point.

[0162] Optionally, based on observed values ​​of unknown parameters, grid-side current errors, and an equivalent inductance differential model, the expected voltage of the LC-type energy storage converter at the point of common coupling is obtained, including:

[0163] Step S411: Determine the virtual control voltage based on the observed values ​​of the unknown parameters and the equivalent inductance differential model.

[0164] Among them, after the observer obtains the unknown parameters, the virtual control voltages on the d-axis and q-axis in the dq coordinate system are set. Then, the formula (3) of the equivalent inductance differential model becomes the following formula (15):

[0165]

[0166] By setting a virtual control voltage as an intermediate variable, the equivalent inductance differential model can be easily used for subsequent calculations.

[0167] Step S412: Construct the fourth Lyapunov function based on the virtual control voltage and the current error on the grid side.

[0168] The control objective of the parallel PCS is to make Reaching the set value As can be seen from the virtual control voltage, the control... It is achieved by changing the voltage at the PCC of the PCS. Implementation. Assume... The desired voltage is Since the voltage at PCC is equal in parallel PCS, the voltage calculated for different parallel PCS is... They should be equal, therefore different PCS are calculated. The points system cannot be used.

[0169] Let the network-side current errors along the d-axis and q-axis in the dq coordinate system be respectively... Taking the d-axis as an example, let the Lyapunov function be... For formula (16):

[0170]

[0171] in, This represents the time constant.

[0172] right Differentiating gives .

[0173] set up .

[0174] Right now Then, using formula (15), formula (17) should be satisfied:

[0175]

[0176] Similarly, we can obtain:

[0177]

[0178] in, Let represent the expected values ​​of the virtual control voltage on the d-axis and q-axis in the dq coordinate system, respectively. Let represent the derivatives of the expected values ​​of the virtual control voltage on the d-axis and q-axis in the dq coordinate system, respectively. Indicates control parameters, Let represent the derivatives of the current error on the grid side along the d-axis and q-axis in the dq coordinate system, respectively. express The desired voltage.

[0179] set up Then the derivative of the fourth Lyapunov function Satisfy the following formula (18):

[0180]

[0181] Step S413, converge the fourth Lyapunov function to obtain the desired voltage.

[0182] When solving for the desired control voltage, the error between the sliding mode control coefficient and the output voltage error should satisfy the following condition: ,but Thus ensuring converged to .according to , From the definition of , we can obtain formula (19):

[0183]

[0184] Considering that droop control is required in the unconnected current sharing algorithm, and that droop control will cause voltage control error, the above formula is modified to formula (20):

[0185]

[0186] in, Indicates the current droop factor. , These represent the set values ​​of the grid-side current on the d-axis and q-axis in the dq coordinate system, respectively.

[0187] The S420 obtains the set current based on the differential model of the desired voltage and the filter capacitor.

[0188] Optionally, the set current includes the d-axis current setpoint and the q-axis current setpoint in the dq coordinate system. The set current is obtained based on the desired voltage and the differential model of the filter capacitor, including:

[0189] Step S421: Based on the d-axis voltage error of the desired voltage in the dq coordinate system, construct the fifth Lyapunov function.

[0190] Among them, the parallel PCS can each obtain an equal PCC voltage setpoint. The voltage at the PCC is jointly controlled by the parallel LC type PCS, so it is necessary to realize the current sharing control of the PCS. To realize the current sharing of PCS without interconnection, the conventional approach is to use the droop method. However, the droop method introduces an inner loop current in the voltage loop, which violates the double closed-loop design principle. In order to realize the current sharing of two PCS without interconnection, this application adopts the following control strategy, taking the droop formula as the control target. The control strategy satisfies the following formula (21):

[0191]

[0192] Substituting formula (20) into formula (21) eliminates the current term and reduces the error caused by droop. , When it is not 0, and There is a small error, namely phase droop, but the angular frequency is the same as the grid-side voltage angular frequency.

[0193] Step S422: Based on the q-axis voltage error of the desired voltage in the dq coordinate system, construct the sixth Lyapunov function.

[0194] In steps 1 and 2, let the voltage error along the d-axis in the dq coordinate system be... voltage error along the q-axis The Lyapunov subfunction is defined to satisfy the following formula (22):

[0195]

[0196] in, This represents the integral coefficient of the nonlinear voltage loop.

[0197] Among them, the fifth and sixth Lyapunov functions ensure that the step signal is tracked without steady-state error for the setpoint based on this function.

[0198] Step S423: Based on the fifth Lyapunov function and the differential model of the filter capacitor, obtain the d-axis current setting value of the set current in the dq coordinate system.

[0199] Among them, then for Differentiation yields formula (23):

[0200]

[0201] Can make ,in Representing the proportionality coefficient, we can obtain formula (24):

[0202]

[0203] Then the d-axis current setting value is obtained. Satisfy the following formula (25):

[0204]

[0205] The variables in formula (25) Substituting into formula (23), we get formula (26):

[0206]

[0207] in, These represent the set values ​​of the filter inductor current on the d-axis and the filter inductor current on the q-axis in the dq coordinate system, respectively. They represent The derivative of This represents the proportionality coefficient. This represents the integral coefficient of the nonlinear voltage loop.

[0208] Step S424: Based on the sixth Lyapunov function and the differential model of the filter capacitor, obtain the q-axis current setting value of the set current in the dq coordinate system.

[0209] Similarly, the q-axis current setting value can be obtained. The following formula (26) is satisfied:

[0210]

[0211] The S430 obtains the output control voltage based on the differential model of the set current and the filter inductor.

[0212] Optionally, based on the differential model of the set current and the filter inductor, the output control voltage is obtained, including:

[0213] Step S431: Construct the seventh Lyapunov function based on the set current.

[0214] Among them, constructing Lyapunov subfunctions To achieve inner-loop current control. Let the d-axis current error... q-axis current error And redefine the seventh Lyapunov function , This represents the Lyapunov weighting coefficient.

[0215] Because the rate of change of voltage is slower than that of change of current, the derivative of voltage in the current loop can be ignored. The derivative of satisfies the following formula (27):

[0216]

[0217] Step S432: Construct the eighth Lyapunov function based on the fifth, sixth, and seventh Lyapunov functions.

[0218] The eighth Lyapunov function is defined as follows: And by taking the derivative, we get the following formula (28):

[0219]

[0220] Step S433: Based on the eighth Lyapunov function and the differential model of the filter inductor, the output control voltage is obtained.

[0221] According to formula (28), if we let:

[0222]

[0223] in, This is the proportional coefficient for the current loop droop control. It equals the following formula (29):

[0224]

[0225] According to formula (28), and substituting formula (1) into formula (28), we can obtain the three-phase PCS control voltage output as formula (29):

[0226]

[0227] in, and These represent the output control voltages along the d-axis and q-axis in the dq coordinate system, respectively.

[0228] Through Lyapunov functions It can be seen that the desired voltage control objective converges, achieving the effect of current sharing. At this time, the output of the inner loop control voltage is not only related to the inner loop current error, but also to the voltage error and some parameters of the control objective function, thus enhancing the stability of the system.

[0229] In this embodiment, multiple parallel LC-type PCSs are treated as a single large-capacity LC-type PCS, connected in series with the line impedance and transformer short-circuit impedance to form an LCL-type PCS. Based on this LCL-type PCS topology, a third-order mathematical model of the parallel system is established. A sliding mode observer is then used to monitor the line impedance, transformer short-circuit impedance, and grid-side voltage, resolving the parameter setting issue in LCL modeling. Simultaneously, treating multiple parallel LC-type PCSs as a single PCS necessitates addressing the current sharing problem among the parallel PCSs, and ensuring that the voltage settings of the filter capacitors in the parallel PCSs are identical.

[0230] Therefore, this application adopts a proportional + inertial control method for grid-side current control. The pseudo-LCL structure formed by paralleling LC-type PCS is designed as an LCL-type PCS, ensuring that the voltage setpoints of the parallel PCS are the same. To achieve current sharing among the parallel PCS, a nonlinear backstepping method is used for control based on conventional droop control, improving the stability of the third-order system and enhancing the stability of tie-line-less current sharing control.

[0231] Specifically, the dispatch current command is directly used as the setpoint for the grid-side inductor current. Parallel LC-type PCSs work together to achieve this goal. Therefore, each parallel PCS needs to jointly collect the grid-side current, not just its output current. Based on the grid-side inductor model, the control quantity for the PCS to adjust the grid-side current is the voltage at PCC. According to the control objective, the desired voltage at PCC can be calculated. The voltage at PCC is controlled jointly by the parallel LC-type PCSs, and it is necessary to ensure that the setpoint voltage at PCC calculated by each parallel LC-type PCS is equal.

[0232] However, in this grid-side inductor model, the grid-side line impedance and transformer short-circuit impedance are difficult to determine accurately, and the grid-side voltage cannot be measured. Therefore, a sliding mode observer is used for parameter identification when designing the control algorithm. When solving for the voltage setpoint at PCC based on the grid-side inductor model, the integral value of the integral element in the conventional PI control strategy varies due to different PCS start-up times, resulting in different voltage setpoints at PCC. Therefore, the integral element is replaced with an inertial element. Since the stable value of the inertial element is only related to the input quantity and the amplification factor of the inertial element, and the amplification factor of the inertial element can be set to the same value, the error in the voltage setpoint at PCC calculated by different PCS due to different integral values ​​is eliminated.

[0233] Simultaneously, calculating the voltage setpoint at the PCC requires the grid feedforward voltage. However, the grid-side voltage is unmeasurable for the PCS. This invention selects the rated value of the grid-side voltage, ensuring that the feedforward voltages of the parallel PCS are equal. However, the actual grid-side voltage will change during operation, inevitably leading to errors in the setpoint voltage at the PCC. These errors will further cause errors in the grid-side current, but these errors can be suppressed through grid-side current error feedback.

[0234] Specifically, based on Figure 1 The system with two LC-type energy storage converters connected in parallel, using the control method described in this embodiment, has its system operation results as shown in the reference. Figure 8-10 As shown:

[0235] See Figure 8 , Figure 8 It means Figure 1 The figure shows the inductor current waveform, grid-side current waveform, and capacitor voltage waveform of the first PCS after it is started up independently. It can be seen from the figure that the current waveform basically remains around 1000A after 0.3s of grid connection.

[0236] See Figure 9 , Figure 9 It means Figure 1The waveforms of the inductor current, grid-side current, and capacitor voltage of the second PCS after it is started up independently are shown in the figure. It can be seen from the figure that the current waveform basically remains around 1000A after 0.3s of grid connection, and the capacitor voltage is relatively stable.

[0237] See Figure 10 , Figure 10 It means Figure 1 After two PCS units operate in parallel for 1 second, their grid-side current setting is 1000A. The parallel connection of the two PCS units achieves current sharing, and the current of each PCS unit stabilizes around 500A. Furthermore, the voltage at the common coupling point on the d-axis of the grid-side dq coordinate system of the two PCS current loops... They are equal.

[0238] See Figure 11 , Figure 11 It means Figure 1 After two PCS units operate in parallel for 1 second, their grid-side current setting is 1500A. The parallel connection of the two PCS units achieves current sharing, and the current of each PCS unit stabilizes around 750A. Furthermore, the voltage at the common coupling point on the d-axis of the grid-side dq coordinate system of the two PCS current loops... They are still equal.

[0239] Figure 12 This is a schematic diagram of the control device for a parallel LC-type energy storage converter under a weak power grid, provided in an embodiment of this application. (See attached diagram.) Figure 12 The control device for the parallel LC-type energy storage converter under the weak power grid includes various functional modules for implementing the aforementioned control method for the parallel LC-type energy storage converter under the weak power grid. Any functional module can be implemented by software and / or hardware.

[0240] In some embodiments, the control device 1200 for the parallel LC-type energy storage converter under a weak power grid includes a topology construction module 1201, a model construction module 1202, a sliding mode observation module 1203, and a control output module 1204. Wherein:

[0241] The topology building module 1201 is used to construct the PCS topology of the LCL energy storage converter based on multiple parallel LC energy storage converters and the line impedance and transformer short-circuit impedance on the grid side.

[0242] The model building module 1202 is used to build a third-order mathematical model based on the PCS topology; the third-order mathematical model includes the differential model of the filter inductor and the differential model of the filter capacitor of the LC type energy storage converter in the dq coordinate system, as well as the differential model of the equivalent inductance of the line impedance and the transformer short-circuit impedance in the dq coordinate system.

[0243] The sliding mode observation module 1203 is used to identify parameters of the equivalent inductance differential model based on the sliding mode observer and obtain the observed values ​​of unknown parameters in the third-order mathematical model. Among them, the unknown parameters include the equivalent impedance of the line impedance and the transformer short-circuit impedance, as well as the grid-side voltage on the grid side.

[0244] The control output module 1204 is used to obtain the output control voltage based on the observed values ​​of unknown parameters and a third-order mathematical model.

[0245] In some embodiments, the sliding mode observation module 1203 is specifically used for:

[0246] Based on the equivalent inductance differential model, a grid-side inductance model is constructed;

[0247] An observation error model is constructed based on the grid-side inductance model and the equivalent inductance differential model.

[0248] Based on the observation error model and sliding mode observer, the model control voltage of the grid-side inductance model is obtained;

[0249] Model control voltage based on grid-side inductance model is used to obtain observed values ​​of unknown parameters.

[0250] In some embodiments, the sliding mode observation module 1203 is further configured to:

[0251] The first Lyapunov function is constructed based on the current error of the observation error model;

[0252] Constructing a second Lyapunov function based on unknown parameters;

[0253] By combining the first and second Lyapunov functions, a third Lyapunov function is obtained.

[0254] Based on the third Lyapunov function and sliding mode observer, the model control voltage of the grid-side inductance model is obtained.

[0255] In some embodiments, the sliding mode observation module 1203 is further configured to:

[0256] The model control voltage based on the grid-side inductance model is used to converge the third Lyapunov function and obtain the observed values ​​of the unknown parameters.

[0257] In some embodiments, the control output module 1204 is specifically used for:

[0258] Based on the observed values ​​of unknown parameters, the current error on the grid side, and the differential model of the equivalent inductance, the expected voltage of the LC energy storage converter at the common coupling point is obtained.

[0259] Based on the differential model of the desired voltage and filter capacitor, the set current is obtained;

[0260] The output control voltage is obtained based on the differential model of the set current and the filter inductor.

[0261] In some embodiments, the control output module 1204 is further configured to:

[0262] The virtual control voltage is determined based on the observed values ​​of unknown parameters and the differential model of the equivalent inductance.

[0263] The fourth Lyapunov function is constructed based on the virtual control voltage and the current error on the grid side;

[0264] To achieve convergence of the fourth Lyapunov function, the desired voltage is obtained.

[0265] In some embodiments, the set current includes a d-axis current set value and a q-axis current set value in the dq coordinate system, and the control output module 1204 is further configured to:

[0266] Based on the d-axis voltage error of the desired voltage in the dq coordinate system, a fifth Lyapunov function is constructed.

[0267] Based on the q-axis voltage error of the desired voltage in the dq coordinate system, a sixth Lyapunov function is constructed.

[0268] Based on the fifth Lyapunov function and the differential model of the filter capacitor, the d-axis current setting value of the set current in the dq coordinate system is obtained.

[0269] Based on the sixth Lyapunov function and the differential model of the filter capacitor, the q-axis current setting value of the set current in the dq coordinate system is obtained.

[0270] In some embodiments, the control output module 1204 is further configured to:

[0271] Based on the given current, construct the seventh Lyapunov function;

[0272] Based on the fifth, sixth, and seventh Lyapunov functions, construct the eighth Lyapunov function;

[0273] The output control voltage is obtained based on the eighth Lyapunov function and the differential model of the filter inductor.

[0274] The control device 1200 for a parallel LC-type energy storage converter under a weak power grid provided in this application embodiment is used to execute the technical solution provided in the aforementioned control method embodiment for a parallel LC-type energy storage converter under a weak power grid. Its implementation principle and technical effects are similar to those in the aforementioned method embodiment, and will not be repeated here.

[0275] It should be noted that the division of the various modules in the above device is merely a logical functional division. In actual implementation, they can be fully or partially integrated into a single physical entity, or they can be physically separated. Furthermore, these modules can be implemented entirely in software via processing element calls, entirely in hardware, or partially in software calls via processing element calls, with some modules implemented in hardware. For example, the topology building module 1210 can be a separate processing element, or it can be integrated into a chip in the above device. Alternatively, it can be stored as program code in the memory of the above device, and its functions can be called and executed by a processing element of the device. The implementation of other modules is similar. Moreover, these modules can be fully or partially integrated together, or they can be implemented independently. The processing element here can be an integrated circuit with signal processing capabilities. In the implementation process, each step of the above method or each of the above modules can be completed through integrated logic circuits in the hardware of the processor element or through software instructions.

[0276] Figure 13 This is a schematic diagram of the structure of an electronic device provided in an embodiment of this application. (See attached diagram.) Figure 13 The electronic device 1300 includes a processor 1301 and a memory 1302 communicatively connected to the processor 1301;

[0277] Memory 1302 stores computer-executed instructions;

[0278] The processor 1301 executes the computer execution instructions stored in the memory 1302 to implement the aforementioned technical solution of the control method for parallel LC-type energy storage converters under weak power grids.

[0279] In the aforementioned electronic device 1300, the memory 1302 and the processor 1301 are electrically connected directly or indirectly to achieve data transmission or interaction. For example, these components can be electrically connected to each other through one or more communication buses or signal lines, such as bus connections. The bus can be an Industry Standard Architecture (ISA) bus, a Peripheral Component Interconnect (PCI) bus, or an Extended Industry Standard Architecture (EISA) bus, etc. Buses can be classified as address buses, data buses, control buses, etc., but this does not mean that there is only one bus or one type of bus. The memory 1302 stores computer execution instructions for implementing the control method of the aforementioned parallel LC-type energy storage converter under weak power grids, including at least one software function module that can be stored in the memory 1302 in the form of software or firmware. The processor 1301 executes various functional applications and data processing by running the software programs and modules stored in the memory 1302.

[0280] The memory 1302 includes at least one type of readable storage medium, not limited to Random Access Memory (RAM), Read Only Memory (ROM), Programmable Read-Only Memory (PROM), Erasable Programmable Read-Only Memory (EPROM), Electrically Erasable Programmable Read-Only Memory (EEPROM), etc. The memory 1302 stores programs, and the processor 1301 executes the programs after receiving execution instructions. Furthermore, the software programs and modules within the memory 1302 may also include an operating system, which may include various software components and / or drivers for managing system tasks (e.g., memory management, storage device control, power management, etc.) and can communicate with various hardware or software components to provide an operating environment for other software components.

[0281] Processor 1301 can be an integrated circuit chip with signal processing capabilities. The aforementioned processor 1301 can be a general-purpose processor, including a Central Processing Unit (CPU), a Network Processor (NP), a Digital Signal Processor (DSP), an Application Specific Integrated Circuit (ASIC), etc. It can implement or execute the methods, steps, and logic block diagrams disclosed in the embodiments of this application. The general-purpose processor can be a microprocessor, or processor 1301 can be any conventional processor.

[0282] The electronic device 1300 is used to execute the technical solution provided in the aforementioned embodiment of the control method for parallel LC-type energy storage converters under weak power grids. Its implementation principle and technical effect are similar to those in the aforementioned method embodiment, and will not be repeated here.

[0283] This application also provides a computer-readable storage medium storing computer-executable instructions. When these computer-executable instructions are executed, they are used to implement the technical solution of the control method for a parallel LC-type energy storage converter under a weak power grid as described above.

[0284] The aforementioned computer-readable storage medium can be implemented by any type of volatile or non-volatile storage device or a combination thereof, such as static random access memory (SRAM), electrically erasable programmable read-only memory (EEPROM), erasable programmable read-only memory (EPROM), programmable read-only memory (PROM), read-only memory (ROM), magnetic storage, flash memory, magnetic disk, or optical disk. The computer-readable storage medium can be any available medium accessible to a general-purpose or special-purpose computer.

[0285] An exemplary readable storage medium is coupled to a processor, enabling the processor to read information from and write information to the readable storage medium. Alternatively, the readable storage medium can be an integral part of the processor. Both the processor and the readable storage medium can reside in an Application Specific Integrated Circuit (ASIC). Alternatively, the processor and the readable storage medium can exist as discrete components in the control unit of a control device for a parallel LC-type energy storage converter in a weak grid.

[0286] This application also provides a computer program product, including a computer program, which, when executed, is used to implement the technical solution of the control method for parallel LC-type energy storage converters under weak power grids as described above.

[0287] In the above embodiments, those skilled in the art will understand that the above method embodiments can be implemented entirely or partially by software, hardware, firmware, or any combination thereof. When implemented in software, it can be implemented entirely or partially in the form of a computer program product. A computer program product includes one or more computer instructions. When the computer program instructions are loaded and executed on a computer, all or part of the flow or function according to the embodiments of this application is generated. The computer can be a general-purpose computer, a special-purpose computer, a computer network, or other programmable device. The computer instructions can be stored in a computer-readable storage medium or transmitted from one computer-readable storage medium to another. For example, computer instructions can be transmitted from one website, computer, server, or data center to another website, computer, server, or data center via wired (e.g., coaxial cable, fiber optic, digital subscriber line (DSL)) or wireless (e.g., infrared, wireless network, microwave, etc.) means. The computer-readable storage medium can be any available medium that a computer can access or a data storage device such as a server or data center that integrates one or more available media. The available media can be magnetic media (e.g., floppy disks, hard disks, magnetic tapes), optical media (e.g., DVDs), or semiconductor media (e.g., solid-state drives (SSDs)).

[0288] In the above embodiments, the descriptions of each embodiment have their own emphasis. For parts not described in detail in a certain embodiment, please refer to the relevant descriptions of other embodiments. The technical features of the above embodiments can be combined arbitrarily. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as the combination of these technical features does not contradict each other, it should be considered within the scope of this specification.

[0289] Other embodiments of this application will readily occur to those skilled in the art upon consideration of the specification and practice of the embodiments disclosed herein. This application is intended to cover any variations, uses, or adaptations of this application that follow the general principles of this application and include common knowledge or customary techniques in the art not disclosed herein. The specification and examples are to be considered exemplary only, and the true scope and spirit of this application are indicated by the appended claims.

[0290] It should be understood that this application is not limited to the precise structure described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The scope of this application is limited only by the appended claims.

Claims

1. A control method for a parallel LC-type energy storage converter in a weak power grid, characterized in that, The method includes: Based on multiple parallel LC-type energy storage converters and the line impedance and transformer short-circuit impedance on the grid side, a PCS topology for the LCL-type energy storage converter is constructed. Based on the PCS topology, a third-order mathematical model is constructed; wherein, the third-order mathematical model includes the differential model of the filter inductor and the differential model of the filter capacitor of the LC energy storage converter in the dq coordinate system, as well as the differential model of the equivalent inductance of the line impedance and the transformer short-circuit impedance in the dq coordinate system. The parameters of the equivalent inductance differential model are identified based on the sliding mode observer to obtain the observed values ​​of the unknown parameters in the third-order mathematical model; wherein, the unknown parameters include the equivalent impedance of the line impedance and the transformer short-circuit impedance, as well as the grid-side voltage on the grid side. The output control voltage is obtained based on the observed values ​​of the unknown parameters and the third-order mathematical model.

2. The method according to claim 1, characterized in that, Based on the sliding mode observer, parameter identification is performed on the equivalent inductance differential model to obtain the observed values ​​of unknown parameters in the third-order mathematical model, including: Based on the equivalent inductance differential model, a grid-side inductance model is constructed; Based on the grid-side inductance model and the equivalent inductance differential model, an observation error model is constructed. Based on the observation error model and the sliding mode observer, the model control voltage of the grid-side inductance model is obtained; Based on the model control voltage of the grid-side inductance model, the observed values ​​of the unknown parameters are obtained.

3. The method according to claim 2, characterized in that, Based on the observation error model and the sliding mode observer, the model control voltage of the grid-side inductance model is obtained, including: The first Lyapunov function is constructed based on the current error of the observation error model. Construct a second Lyapunov function based on the unknown parameters; By combining the first Lyapunov function and the second Lyapunov function, a third Lyapunov function is obtained; Based on the third Lyapunov function and the sliding mode observer, the model control voltage of the grid-side inductance model is obtained.

4. The method according to claim 3, characterized in that, Based on the model control voltage of the grid-side inductor model, the observed values ​​of the unknown parameters are obtained, including: The model control voltage based on the grid-side inductance model is used to converge the third Lyapunov function, thereby obtaining the observed values ​​of the unknown parameters.

5. The method according to any one of claims 1-4, characterized in that, Based on the observed values ​​of the unknown parameters and the third-order mathematical model, the output control voltage is obtained, including: Based on the observed values ​​of the unknown parameters, the current error on the grid side, and the equivalent inductance differential model, the expected voltage of the LC-type energy storage converter at the common coupling point is obtained. Based on the desired voltage and the differential model of the filter capacitor, the set current is obtained; The output control voltage is obtained based on the set current and the differential model of the filter inductor.

6. The method according to claim 5, characterized in that, Based on the observed values ​​of the unknown parameters, the current error on the grid side, and the equivalent inductance differential model, the expected voltage of the LC-type energy storage converter at the point of common coupling is obtained, including: Based on the observed values ​​of the unknown parameters and the equivalent inductance differential model, the virtual control voltage is determined; A fourth Lyapunov function is constructed based on the virtual control voltage and the current error on the grid side; The fourth Lyapunov function is brought to converge, and the desired voltage is obtained.

7. The method according to claim 5, characterized in that, The set current includes d-axis current setpoints and q-axis current setpoints in the dq coordinate system. Based on the desired voltage and the differential model of the filter capacitor, the set current is obtained, including: Based on the d-axis voltage error of the desired voltage in the dq coordinate system, a fifth Lyapunov function is constructed. Based on the q-axis voltage error of the desired voltage in the dq coordinate system, a sixth Lyapunov function is constructed. Based on the fifth Lyapunov function and the differential model of the filter capacitor, the d-axis current setting value of the set current in the dq coordinate system is obtained. Based on the sixth Lyapunov function and the differential model of the filter capacitor, the q-axis current setting value of the set current in the dq coordinate system is obtained.

8. The method according to claim 7, characterized in that, Based on the set current and the differential model of the filter inductor, the output control voltage is obtained, including: Based on the set current, a seventh Lyapunov function is constructed; Based on the fifth, sixth, and seventh Lyapunov functions, an eighth Lyapunov function is constructed. The output control voltage is obtained based on the eighth Lyapunov function and the differential model of the filter inductor.

9. An electronic device, characterized in that, Includes a processor and a memory communicatively connected to the processor; The memory stores computer-executed instructions; The processor executes computer execution instructions stored in the memory to implement the method as described in any one of claims 1 to 8.

10. A computer program product, characterized in that, Includes a computer program, which, when executed, is used to implement the method as described in any one of claims 1 to 8.

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