Converter control mode switching method and system based on virtual current and voltage calculation

Abstract

The present invention belongs to the technical field of converter control, and specifically relates to a method and system for switching converter control modes based on virtual current and voltage calculation, comprising: obtaining a switching topology structure of a converter control mode; constructing a virtual current equation based on the obtained topology structure, and calculating a port voltage of the converter; calculating a virtual current and a virtual voltage of the converter under a current control mode based on real-time current and voltage according to the obtained virtual current equation, the port voltage and the current control mode of the converter; switching the converter control mode at the same working point according to the obtained virtual current and virtual voltage of the converter, and completing the switching of the converter control mode based on virtual current and voltage calculation.

Description

Technical Field

[0001] The present invention belongs to the technical field of converter control, and in particular relates to a converter control mode switching method and system based on virtual current and voltage calculation. Background Art

[0002] The statements in this section merely provide background information related to the present invention and do not necessarily constitute prior art.

[0003] With the development of society, the proportion of renewable energy power generation in the power system has gradually increased. As a key device for renewable energy grid-connected power generation, the control method of the converter has received extensive attention and research. The existing converter control methods can be divided into grid-following (GFL) control and grid-forming (GFM) control. Most of the existing grid-connected converters use grid-following control, which has the advantages of accurate power output, rapid power regulation, and maximum utilization of renewable energy. However, as the proportion of power electronic equipment in the power system continues to increase, the inertia of the system continues to decrease, the strength of the entire power grid is reduced, and accidents are very likely to occur.

[0004] To solve this problem, grid-building control can be used. Compared with grid-following control, grid-building control has the function of supporting the power grid and enhancing the stability of the system, but the power adjustment speed of grid-building control is slow and the stability is poor under strong power grid. The inventors found that the advantages and disadvantages of grid-building control and grid-following control can complement each other. If the appropriate control strategy can be selected according to the operating conditions of the power system, the complex and changeable operating requirements of the power system can be met.

[0005] When the control mode is switched, it will cause fluctuations in the converter. The fluctuations in the switching process can be reduced by compensation or pre-synchronization, but compensation often cannot completely eliminate the fluctuations. The pre-synchronization method needs to be run in advance and cannot be switched immediately, and many switch controls need to be added. Both need to consider the synchronization problem of the two control modes. Therefore, how to achieve smooth switching between control modes is a difficult problem that needs to be solved urgently. Summary of the invention

[0006] To solve the above problems, the present invention proposes a method and system for switching converter control modes based on virtual current and voltage calculation. When operating in one control mode of following the grid or building the grid, the other control mode can operate at the same working point using virtual current and virtual voltage by adjusting the reference value. When switching the control mode, there is no need to consider the phase angle synchronization problem, and it will not cause converter fluctuations, thereby achieving smooth and fast switching of the converter control mode.

[0007] According to some embodiments, a first solution of the present invention provides a method for switching a converter control mode based on virtual current and voltage calculation, which adopts the following technical solution:

[0008] A method for switching a converter control mode based on virtual current and voltage calculation, comprising:

[0009] Obtaining a switching topology structure of a converter control method;

[0010] Based on the obtained topology, a virtual current equation is constructed to calculate the port voltage of the converter;

[0011] According to the obtained virtual current equation, the port voltage and the current control mode of the converter, the virtual current and virtual voltage of the converter under the current control mode are calculated based on the real-time current and voltage;

[0012] According to the obtained virtual current and virtual voltage of the converter, the converter control mode is switched at the same working point to complete the switching of the converter control mode based on the virtual current and voltage calculation.

[0013] As a further technical limitation, the control mode of the converter includes at least grid-following control and grid-forming control.

[0014] Furthermore, the following-grid type control and the building-grid type control adopt droop control, virtual synchronization control, matching control or virtual oscillator control.

[0015] As a further technical limitation, during the switching of the converter control mode, the converter output voltage reference value is adjusted according to the obtained virtual current and virtual voltage of the converter, and the converter is controlled to operate at the same operating point, so that the converter can quickly and smoothly switch the control mode at the same operating point.

[0016] Furthermore, in the process of adjusting the converter output voltage reference value according to the obtained virtual current and virtual voltage of the converter, the obtained virtual current and virtual voltage of the converter are input into the grid-following control method and the grid-forming control method to calculate the output active power and reactive power; specifically, the grid-following control obtains the current inner-loop input value by subtracting the calculated output power from the power setting value, and then performs proportional-integral adjustment to obtain the output voltage reference value of the grid-following control by subtracting the obtained current inner-loop input value from the dq-axis virtual voltage value; the grid-forming control inputs the calculated power value into the droop control to generate a phase angle and a target voltage amplitude, and performs proportional-integral adjustment to generate the current inner-loop input value by subtracting the voltage setting value of the dq-axis from the virtual voltage, and then performs proportional-integral adjustment to obtain the output voltage reference value of the grid-forming control by subtracting the obtained current inner-loop input value from the dq-axis virtual voltage value.

[0017] As a further technical limitation, a modulation signal of a transistor in the converter is obtained according to a PWM control signal, and the port voltage of the converter is calculated according to the obtained modulation signal and the voltage amplitude on the DC side of the converter.

[0018] According to some embodiments, a second solution of the present invention provides a converter control mode switching system based on virtual current and voltage calculation, which adopts the following technical solution:

[0019] A converter control mode switching system based on virtual current and voltage calculation, comprising:

[0020] An acquisition module, configured to acquire a switching topology structure of a converter control mode;

[0021] A calculation module, which is configured to construct a virtual current equation based on the obtained topological structure and calculate the port voltage of the converter; and calculate the virtual current and virtual voltage of the converter under the current control mode based on the real-time current and voltage according to the obtained virtual current equation, the port voltage and the current control mode of the converter;

[0022] The switching module is configured to switch the converter control mode at the same working point according to the obtained virtual current and virtual voltage of the converter, thereby completing the switching of the converter control mode based on the virtual current and voltage calculation.

[0023] As a further technical limitation, in the acquisition module, the control method of the converter includes at least grid-following control and grid-forming control; the grid-following control and the grid-forming control adopt droop control, virtual synchronization control, matching control or virtual oscillator control.

[0024] As a further technical limitation, in the switching module, during the switching process of the converter control mode, the converter output voltage reference value is adjusted according to the obtained virtual current and virtual voltage of the converter, and the converter is controlled to operate at the same working point, so that the converter performs fast and smooth switching of the control mode at the same working point; in the process of adjusting the converter output voltage reference value according to the obtained virtual current and virtual voltage of the converter, the obtained converter virtual current and virtual voltage are input into the grid-following control method and the grid-building control method, and the output active power and reactive power are calculated; specifically The grid-following control obtains the current inner-loop input value by making a difference between the calculated output power and the power setting value, and then performs proportional-integral adjustment to obtain the output voltage reference value of the grid-following control; the grid-building control inputs the calculated power value into the droop control to generate a phase angle and a target voltage amplitude, and makes a difference between the voltage setting value of the dq axis and the virtual voltage, and then performs proportional-integral adjustment to obtain the current inner-loop input value, and makes a difference between the voltage setting value of the dq axis and the virtual voltage, and then performs proportional-integral adjustment to obtain the output voltage reference value of the grid-building control.

[0025] As a further technical limitation, in the calculation module, a modulation signal of a transistor in the converter is obtained according to a PWM control signal, and the port voltage of the converter is calculated according to the obtained modulation signal and the voltage amplitude of the DC side of the converter. Compared with the prior art, the beneficial effects of the present invention are as follows:

[0026] When the present invention operates in one of the grid-following type or grid-building type control modes, the other control mode can operate at the same working point by adjusting the reference value using virtual current and virtual voltage. When switching the control mode, there is no need to consider the phase angle synchronization problem, and it will not cause fluctuations in the converter, thereby achieving smooth and fast switching of the converter control mode. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The drawings in the specification that constitute a part of this embodiment are used to provide a further understanding of this embodiment. The schematic embodiments of this embodiment and their descriptions are used to explain this embodiment and do not constitute improper limitations on this embodiment.

[0028] Figure 1 It is a flow chart of a method for switching a converter control mode based on virtual current and voltage calculation in Embodiment 1 of the present invention;

[0029] Figure 2 This is a diagram of a smooth and fast switching architecture between network following control and network building control based on virtual current and voltage calculation in the first embodiment of the present invention;

[0030] Figure 3 Schematic diagram of a network-based control architecture in Embodiment 1 of the present invention;

[0031] Figure 4 This is a schematic diagram of a networked control architecture in Embodiment 1 of the present invention;

[0032] Figure 5 Schematic diagram of the topological structure of a two-level converter in Embodiment 1 of the present invention;

[0033] Figure 6 This is a schematic diagram of the grid-connected topology of a voltage source converter in Embodiment 1 of the present invention;

[0034] Figure 7 Schematic diagram of active power and reactive power during smooth switching from GFL to GFM in Embodiment 1 of the present invention;

[0035] Figure 8 A schematic diagram of the A-phase voltage at the grid connection point when the GFL switches smoothly to the GFM in the first embodiment of the present invention;

[0036] Fig. 9 Schematic diagram of active power and reactive power during smooth switching from GFM to GFL in Embodiment 1 of the present invention;

[0037] Fig.10 A schematic diagram of the A-phase voltage at the grid connection point during smooth switching from GFM to GFL in the first embodiment of the present invention;

[0038] Fig.11 It is a structural block diagram of a converter control mode switching system based on virtual current and voltage calculation in the second embodiment of the present invention. DETAILED DESCRIPTION

[0039] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0040] It should be noted that the following detailed descriptions are exemplary and are intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present application belongs.

[0041] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0042] In the present invention, terms such as "upper", "lower", "left", "right", "front", "back", "vertical", "horizontal", "side", "bottom", etc. indicate directions or positional relationships based on the directions or positional relationships shown in the accompanying drawings. They are relational words determined only for the convenience of describing the structural relationships of the various parts or elements of the present invention, and do not specifically refer to any part or element in the present invention and should not be understood as limitations on the present invention.

[0043] In the present invention, terms such as "fixed connection", "connected", "connection", etc. should be understood in a broad sense, indicating that it can be fixedly connected, integrally connected or detachably connected; it can be directly connected or indirectly connected through an intermediate medium. For relevant scientific research or technical personnel in this field, the specific meanings of the above terms in the present invention can be determined according to specific circumstances, and they cannot be understood as limitations on the present invention.

[0044] In the absence of conflict, the embodiments of the present invention and the features of the embodiments may be combined with each other.

[0045] Embodiment 1

[0046] Embodiment 1 of the present invention introduces a method for switching a converter control mode based on virtual current and voltage calculation.

[0047] like Figure 1 A method for switching a converter control mode based on virtual current and voltage calculation is shown, comprising:

[0048] Obtaining a switching topology structure of a converter control method;

[0049] Based on the obtained topology, a virtual current equation is constructed to calculate the port voltage of the converter;

[0050] According to the obtained virtual current equation, the port voltage and the current control mode of the converter, the virtual current and virtual voltage of the converter under the current control mode are calculated based on the real-time current and voltage;

[0051] According to the obtained virtual current and virtual voltage of the converter, the converter control mode is switched at the same working point to complete the switching of the converter control mode based on the virtual current and voltage calculation.

[0052] In the process of switching the converter control mode in this embodiment, the virtual current is calculated for control. When the converter operates with one control strategy, the other control strategy realizes closed-loop control through the virtual current. By setting the control target value of the virtual current control, the two controls operate at the same operating point, thereby realizing fast and smooth switching of different control modes.

[0053] This embodiment adopts Figure 2The smooth and fast switching architecture diagram of network following control and network building control based on virtual current and voltage calculation is shown in Figure 2 middle, V dc is the DC side voltage, VSC is the voltage source converter, V i is the converter port voltage, L 1 is the inductance on the source side of the filter, L 2 is the inductance of the filter grid side, Z Add impedance to the filter, C f is the filter capacitance, R f is the resistance in series with the filter capacitor in the filter, V g1 is the voltage after filtering, V g2 is the grid voltage, i o is the output current, V g1,gfm is the filtered voltage input to the GFM control loop, i o,gfm is the output current input to the GFM control loop, V g1,gfl is the filtered voltage input to the GFL control loop, i o,gfl is the output current input to the GFL control loop, V ref,gfm is the voltage reference value of the GFM control output, V ref,gfl It is the voltage reference value of GFL control output.

[0054] In this embodiment, a virtual current calculation equation is written based on line parameters and voltage in the line; it should be noted that the virtual current calculation method of GFL and GFM is the same. In this embodiment, GFL is used as an example to write the equation, and the subscripts are gfl and the subscript is gfm , respectively represent the corresponding variables in GFL and GFM control; that is,

[0055] ;

[0056] in, V c is the capacitor voltage in the filter;

[0057] ;

[0058] in, I 1,gfl is the current output from the converter port;

[0059] ;

[0060] .

[0061] As one or more implementation methods, obtaining the converter port voltage through the PWM signal includes: the actual port voltage V i , GFL control port voltage V i,gfl , GFM port voltage V i,gfm Specific:

[0062] This embodiment is as follows Figure 5 Taking the two-level converter shown in FIG. as an example, the converter port voltage can be calculated according to the PWM control signal; V ia , V ib , V ic , respectively V i The voltages of the three phases A, B, and C of PWM1, PWM3, and PWM5 are Figure 5 The modulation signals of IGBT1, IGBT3 and IGBT5 are: U dc is the DC side voltage amplitude; V i The calculation formula is:

[0063] ;

[0064] ;

[0065] .

[0066] The control strategy currently used by the converter adopts real current value control, and another control strategy adopts virtual current control, such as Figure 2 As shown in the figure, when the converter adopts grid control, the actual measured voltage and current values ​​( V g1 , i o ) is input into the network control to Vref , gfm As a modulation wave for control, the grid-following control will calculate the virtual current and virtual voltage ( V g1，gfl , i o，gfl ) is input into the grid-following control to generate the grid-following control target voltageV ref,gfl , forming a closed-loop control.

[0067] When the grid-following control adopts power control and the grid-building control adopts droop control, such as Figure 3 and Figure 4 As shown in Figure 2, when the converter is operated in grid-following control, the grid-type control is controlled by virtual current, and its active power and reactive power control targets ( P ref , Q ref ) is set to be the same as the grid-following control. At this time, the two controls operate at the same working point. Since the line parameters are consistent and the grid-connected voltage is consistent, when the output power is consistent, the voltage target value generated by the two controls ( V ref,gfl , V ref,gfm ) are also consistent. When control switching is required, the two are directly switched, and the control switching will not cause fluctuations.

[0068] Case Analysis

[0069] based on Figure 6 The circuit topology shown in the figure is simulated; the DC side voltage is 200V, the AC side power supply effective value is 53V, the frequency is 50Hz, L 1 is 2mH, L 2 is 0.5 mH, Cf is 0.02 mF, Rf is 3 Ω, R is 10 Ω, Ll is 2 mH, and Rl is 1 Ω. The converter adopts the control method proposed in this embodiment.

[0070] Operating condition 1:

[0071] When the power system runs for 1 second, the converter switches from GFL control to GFM control through the method proposed in this embodiment. Figure 7 and Figure 8 It can be seen that, through the method proposed in this embodiment, a fast and fluctuation-free switching from GFL control to GFM control is achieved.

[0072] Operating condition 2:

[0073] When the power system runs for 1 second, the converter switches from GFM control to GFL control through the method proposed in this embodiment. Fig. 9 and Fig.10 It can be seen that, through the method proposed in this embodiment, fast and fluctuation-free switching of the two control strategies is achieved.

[0074] This embodiment is applicable to various GFM and GFL controls. GFL or GFM operation is selected according to system requirements to achieve fast and interference-free switching between the two control modes and adapt to various grid conditions.

[0075] When the present embodiment operates in one of the grid-following type or grid-building type control modes, the other control mode can operate at the same working point by adjusting the reference value and using the virtual current and virtual voltage. When switching the control mode, there is no need to consider the phase angle synchronization problem, which will not cause the fluctuation of the converter, thereby achieving smooth and fast switching of the converter control mode.

[0076] Embodiment 2

[0077] The second embodiment of the present invention introduces a converter control mode switching system based on virtual current and voltage calculation.

[0078] like Fig.11 A converter control mode switching system based on virtual current and voltage calculation is shown, comprising:

[0079] An acquisition module, configured to acquire a switching topology structure of a converter control mode;

[0080] A calculation module, which is configured to construct a virtual current equation based on the obtained topological structure and calculate the port voltage of the converter; and calculate the virtual current and virtual voltage of the converter under the current control mode based on the real-time current and voltage according to the obtained virtual current equation, the port voltage and the current control mode of the converter;

[0081] The switching module is configured to switch the converter control mode at the same working point according to the obtained virtual current and virtual voltage of the converter, thereby completing the switching of the converter control mode based on the virtual current and voltage calculation.

[0082] As one or more implementation modes, in the acquisition module, the control mode of the converter includes at least grid-following control and grid-forming control; the grid-following control and the grid-forming control adopt droop control, virtual synchronization control, matching control or virtual oscillator control.

[0083] As one or more implementation modes, in the switching module, during the process of switching the converter control mode, the converter output voltage reference value is adjusted according to the obtained virtual current and virtual voltage of the converter, and the converter is controlled to operate at the same working point, so that the converter performs fast and smooth switching of the control mode at the same working point; in the process of adjusting the converter output voltage reference value according to the obtained virtual current and virtual voltage of the converter, the obtained converter virtual current and virtual voltage are input into the grid-following control method and the grid-building control method, and the output active power and reactive power are calculated; specifically The grid-following control obtains the current inner-loop input value by making a difference between the calculated output power and the power setting value, and then performs proportional-integral adjustment to obtain the output voltage reference value of the grid-following control; the grid-building control inputs the calculated power value into the droop control to generate a phase angle and a target voltage amplitude, and makes a difference between the voltage setting value of the dq axis and the virtual voltage, and then performs proportional-integral adjustment to obtain the current inner-loop input value, and makes a difference between the voltage setting value of the dq axis and the virtual voltage, and then performs proportional-integral adjustment to obtain the output voltage reference value of the grid-building control.

[0084] As one or more implementation modes, in the calculation module, a modulation signal of a transistor in the converter is obtained according to a PWM control signal, and the port voltage of the converter is calculated according to the obtained modulation signal and the voltage amplitude of the DC side of the converter. The detailed steps are the same as the method for switching the control mode of the converter based on virtual current and voltage calculation provided in Example 1, and will not be repeated here.

[0085] Although the preferred embodiments of the present invention have been described, those skilled in the art may make other changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

[0086] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

[0087] The above description is only a preferred embodiment of the present embodiment and is not intended to limit the present embodiment. For those skilled in the art, the present embodiment may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present embodiment shall be included in the protection scope of the present embodiment.

Claims

1. A method for switching a converter control mode based on virtual current and voltage calculation, characterized in that: include: Obtaining a switching topology structure of a converter control method; Based on the obtained topology, a virtual current equation is constructed to calculate the port voltage of the converter; According to the obtained virtual current equation, the port voltage and the current control mode of the converter, the virtual current and virtual voltage of the converter under the current control mode are calculated based on the real-time current and voltage; According to the obtained virtual current and virtual voltage of the converter, the converter control mode is switched at the same working point, and the switching of the converter control mode based on the virtual current and voltage calculation is completed; During the switching process of the converter control mode, the converter output voltage reference value is adjusted according to the obtained virtual current and virtual voltage of the converter, and the converter is controlled to operate at the same working point, so that the converter can switch the control mode quickly and smoothly at the same working point; In the process of adjusting the converter output voltage reference value according to the obtained virtual current and virtual voltage of the converter, the obtained virtual current and virtual voltage of the converter are input into the grid-following control method and the grid-forming control method to calculate the output active power and reactive power; specifically, the grid-following control obtains the current inner loop input value by making a difference between the calculated output power and the power setting value, and then performs proportional-integral adjustment, and obtains the output voltage reference value of the grid-following control by making a difference between the obtained current inner loop input value and the dq axis virtual voltage value; The grid-forming control inputs the calculated power value into the droop control to generate the phase angle and the target voltage amplitude. The voltage setting value of the dq axis is subtracted from the virtual voltage to perform proportional-integral adjustment to generate the current inner loop input value, which is subtracted from the virtual voltage value of the dq axis to perform proportional-integral adjustment to obtain the output voltage reference value of the grid-forming control.

2. The method for switching the converter control mode based on virtual current and voltage calculation as claimed in claim 1, characterized in that: The control mode of the converter at least includes grid-following control and grid-building control.

3. The method for switching the converter control mode based on virtual current and voltage calculation as claimed in claim 2, characterized in that: The following-grid type control and the building-grid type control adopt droop control, virtual synchronization control, matching control or virtual oscillator control.

4. The method for switching converter control mode based on virtual current and voltage calculation as claimed in claim 1, characterized in that: The modulation signal of the transistor in the converter is obtained according to the PWM control signal, and the port voltage of the converter is calculated according to the obtained modulation signal and the voltage amplitude of the DC side of the converter.

5. A converter control mode switching system based on virtual current and voltage calculation, which adopts a converter control mode switching method based on virtual current and voltage calculation as claimed in any one of claims 1 to 4, characterized in that: include: An acquisition module, configured to acquire a switching topology structure of a converter control mode; A calculation module, which is configured to construct a virtual current equation based on the acquired topology structure and calculate the port voltage of the converter; According to the obtained virtual current equation, the port voltage and the current control mode of the converter, the virtual current and virtual voltage of the converter under the current control mode are calculated based on the real-time current and voltage; The switching module is configured to switch the converter control mode at the same working point according to the obtained virtual current and virtual voltage of the converter, thereby completing the switching of the converter control mode based on the virtual current and voltage calculation.

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