Oscillation suppression method, inverter controller and oscillation suppression system

Abstract

The invention discloses an oscillation suppression method, an inverter controller and an oscillation suppression system, and relates to the technical field of new energy. The oscillation suppression method comprises the following steps: acquiring a first active power value and a first reactive power value of a first inverter; determining an output voltage phase angle and a target induced electromotive force amplitude of the first inverter according to the first active power value and the first reactive power value; determining a d-axis voltage reference value and a q-axis voltage reference value of the first inverter according to the output voltage phase angle and the target induced electromotive force amplitude; and according to the d-axis voltage reference value and the q-axis voltage reference value, performing voltage and current double-loop control to obtain a target pulse width modulation signal. According to the embodiment of the invention, the method can offset the negative damping of the oscillation suppression system and suppress the low-frequency oscillation of the oscillation suppression system on the premise that the network-side impedance and the control parameters of the matched rectifier are not accurately obtained.

Description

Technical Field

[0001] The present application belongs to the field of new energy technology, and specifically relates to an oscillation suppression method, an inverter controller, and an oscillation suppression system. Background Art

[0002] In the new energy power generation technology, when the grid-following controlled inverter is connected to a non-ideal grid, due to the existence of grid-side impedance, the grid-connected current will cause a voltage difference on the grid-side impedance and affect the stability of the voltage at the common connection point (PCC). The phase-locked loop and grid voltage feedforward control will introduce the grid-side impedance into the control positive feedback path. When the number of inverters connected in parallel increases, the equivalent grid-side impedance will increase, the PCC voltage stability will decrease, and the system will have negative damping in the impedance-weak frequency band, which will lead to low-frequency oscillation in the system and cause some inverters to shut down due to overcurrent. Existing oscillation suppression methods mainly include reducing the bandwidth of the phase-locked loop, reducing the voltage feedforward coefficient, increasing the bandwidth of the current loop, adding a pre-filter, and various other impedance reshaping methods.

[0003] However, existing research mainly addresses the scenario where multiple inverters are directly connected in parallel to the grid at the renewable energy power generation site, which is different from the inverter configuration in the aging test plant of the manufacturing enterprise. In the aging test, the inverter and the rectifier form a towing system and are connected in parallel at the common connection point before being connected to the grid. Since the inverter output current is mainly commutated in the rectifier rather than fed into the grid, the short-circuit ratio of the grid has changed in meaning, and stability cannot be simply judged by the grid impedance and the inverter output impedance. The various impedance reshaping methods mentioned above rely on the accurate acquisition of parameters such as the system impedance and the control parameters of the supporting rectifiers. However, due to the complexity of the plant lines and the unknown rectifier control parameters, to solve the oscillation problem in the aging scenarios of different models, the on-site impedance must first be accurately measured and the impedance parameters of the rectifier must be known. Therefore, the above method is not a general method for suppressing the low-frequency oscillation phenomenon of the towing system in the aging experiment, which is not conducive to accelerating the aging of products before leaving the factory. Summary of the invention

[0004] The technical problem to be solved by the present application is to provide an oscillation suppression method, an inverter controller and an oscillation suppression system in view of the above-mentioned deficiencies in the prior art. The method can be used to offset the negative damping of the oscillation suppression system and suppress the low-frequency oscillation of the oscillation suppression system without accurately knowing the grid-side impedance and the control parameters of the matching rectifier.

[0005] In a first aspect, an embodiment of the present application provides an oscillation suppression method, which is applied to a controller in a first inverter with a supporting function in an oscillation suppression system, and the method includes: obtaining a first active power value and a first reactive power value of the first inverter; determining an output voltage phase angle and a target induced electromotive force amplitude of the first inverter according to the first active power value and the first reactive power value; determining a d-axis voltage reference value and a q-axis voltage reference value of the first inverter according to the output voltage phase angle and the target induced electromotive force amplitude; performing voltage and current dual-loop control according to the d-axis voltage reference value and the q-axis voltage reference value to obtain a target pulse width modulation signal, and the target pulse width modulation signal is used to control the on and off of a three-phase converter bridge to offset the negative damping of the oscillation suppression system, thereby suppressing the oscillation of the oscillation system.

[0006] Based on the same inventive concept, in the second aspect, an embodiment of the present application also provides a controller of an inverter, including: an acquisition module, used to acquire a first active power value and a first reactive power value of a first inverter; a first determination module, used to determine the output voltage phase angle and the target induced electromotive force amplitude of the first inverter according to the first active power value and the first reactive power value; a second determination module, used to determine the d-axis voltage reference value and the q-axis voltage reference value of the first inverter according to the output voltage phase angle and the target induced electromotive force amplitude; a control module, used to perform voltage and current dual-loop control according to the d-axis voltage reference value and the q-axis voltage reference value to obtain a target pulse width modulation signal, and the target pulse width modulation signal is used to control the on and off of the three-phase converter bridge to offset the negative damping of the oscillation suppression system, thereby suppressing the oscillation of the oscillation system.

[0007] Based on the same inventive concept, in a third aspect, an embodiment of the present application further provides an oscillation suppression system, the oscillation suppression system comprising an oscillation suppression subsystem and a towing subsystem; the oscillation suppression subsystem comprises M groups of first inverters with supporting functions, M groups of power supply modules and M groups of first transformers, where M is a positive integer; wherein the first inverter corresponds to the power supply module and the first transformer one by one; among the M groups of power supply modules, each group of power supply modules is connected to a corresponding group of first transformers through its corresponding group of first inverters, and each group of power supply modules is connected to a common connection point with its corresponding group of first transformers respectively; the power supply module is used to The corresponding first inverter supplies power; among the M groups of first inverters, each group of first inverters includes a controller as described in any one of the second aspects; the tow system includes N groups of first rectifiers, N groups of second inverters and N groups of second transformers, where N is a positive integer; wherein the first rectifiers correspond one to one with the second inverters and the second transformers respectively; among the N groups of first rectifiers, each group of first rectifiers is connected to a corresponding group of second transformers through a corresponding group of second inverters, and each group of first rectifiers is connected to a common connection point with a corresponding group of second transformers respectively; the first rectifier is used to supply power to its corresponding second inverter.

[0008] According to the oscillation suppression method, inverter controller and oscillation suppression system provided in the embodiments of the present application, the first active power value and the first reactive power value of the first inverter are first obtained, and then the output voltage phase angle of the first inverter is determined according to the first active power value and the first reactive power value, and then the d-axis voltage reference value and the q-axis voltage reference of the first inverter are determined according to the output voltage phase angle and the target induced electromotive force amplitude, and then the voltage and current dual-loop control is performed according to the d-axis voltage reference value and the q-axis voltage reference value to obtain the target pulse width modulation signal to offset the negative damping of the oscillation suppression system, thereby suppressing the oscillation of the oscillation system. Thus, on the one hand, compared with the existing method of reshaping the impedance of the grid-following inverter, the embodiment of the present application can offset the negative damping of the oscillation suppression system and suppress the low-frequency oscillation of the oscillation suppression system under the premise of inaccurate knowledge of the grid-side impedance and the control parameters of the supporting rectifier, thereby avoiding the model inaccuracy problem caused by the inconsistency of manufacturing parameters, and can be used as a general method for suppressing the low-frequency oscillation phenomenon of the towing system in the aging experiment, and can be quickly transplanted to other aging models on site, with strong applicability; on the other hand, compared with some active damping solutions in the prior art, the embodiment of the present application does not need to add additional voltage / current sensors, which can save production costs; on the other hand, compared with the inverter parameter adjustment method in the prior art, it can increase the number of inverters connected in parallel at the same time in the aging test, and can be flexibly expanded, which can speed up the progress of product aging and shipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 A schematic diagram showing a flow chart of an oscillation suppression method provided in an embodiment of the present application;

[0010] Figure 2 A control block diagram of a first inverter virtual synchronous machine provided in an embodiment of the present application is shown;

[0011] Figure 3 A control block diagram of voltage and current dual-loop control provided by an embodiment of the present application is shown;

[0012] Figure 4 A schematic diagram showing a structure of a controller of an inverter provided in an embodiment of the present application is shown;

[0013] Figure 5 A schematic diagram of the structure of an oscillation suppression system provided in an embodiment of the present application is shown.

[0014] Figure 6 A schematic diagram showing the voltage and current of a common connection point in the prior art;

[0015] Figure 7 A schematic diagram showing the voltage and current of the output port of the inverter in the prior art;

[0016] Figure 8A schematic diagram showing active power and reactive power output by a power grid in the prior art;

[0017] Fig. 9 A schematic diagram showing active power and reactive power output by an inverter in the prior art;

[0018] Fig.10 A schematic diagram showing the inverter phase input voltage and bus voltage in the prior art;

[0019] Fig.11 A schematic diagram showing the voltage and current of the common connection point provided by an embodiment of the present application;

[0020] Fig.12 A schematic diagram showing the voltage and current of the inverter output port provided by an embodiment of the present application;

[0021] Fig.13 A schematic diagram showing active power and reactive power output by a power grid provided in an embodiment of the present application;

[0022] Fig.14 A schematic diagram showing active power and reactive power output by an inverter provided in an embodiment of the present application;

[0023] Fig.15 A schematic diagram showing active power and reactive power output by a virtual synchronous machine provided in an embodiment of the present application;

[0024] Fig.16 A schematic diagram showing the inverter phase voltage and bus voltage provided in an embodiment of the present application. DETAILED DESCRIPTION

[0025] In order to enable those skilled in the art to better understand the technical solution of the present application, the present application is further described in detail below with reference to the accompanying drawings and embodiments.

[0026] The features and exemplary embodiments of various aspects of the present application will be described in detail below. In order to make the purpose, technical solutions and advantages of the present application clearer, the present application will be further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only configured to explain the present application and are not configured to limit the present application. For those skilled in the art, the present application can be implemented without the need for some of these specific details. The following description of the embodiments is only to provide a better understanding of the present application by illustrating the examples of the present application.

[0027] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the statement "include..." do not exclude the presence of other identical elements in the process, method, article or device including the elements.

[0028] Example 1

[0029] The oscillation suppression method provided in the embodiment of the present application can be applied to a controller in a first inverter having a supporting function in an oscillation suppression system, that is, the oscillation suppression method can be executed by a controller in a first inverter having a supporting function in an oscillation suppression system. The first inverter can be an inverter having a supporting function in an oscillation suppression system. For example, the first inverter can include a grid-type inverter.

[0030] It should be noted that the first inverter in the embodiment of the present application is controlled by a virtual synchronous machine (VSG), and the inner loop of the virtual synchronous machine uses voltage-current dual-loop control.

[0031] like Figure 1 As shown, the oscillation suppression method provided in the embodiment of the present application may include steps S110 to S140.

[0032] S110. Obtain a first active power value and a first reactive power value of a first inverter.

[0033] S120. Determine an output voltage phase angle and a target induced electromotive force amplitude of the first inverter according to the first active power value and the first reactive power value.

[0034] S130 . Determine a d-axis voltage reference value and a q-axis voltage reference value of the first inverter according to the output voltage phase angle and the target induced electromotive force amplitude.

[0035] S140. Perform voltage and current dual-loop control according to the d-axis voltage reference value and the q-axis voltage reference value to obtain a target pulse width modulation signal. The target pulse width modulation signal is used to control the on and off of the three-phase converter bridge to offset the negative damping of the oscillation suppression system, thereby suppressing the oscillation of the oscillation system.

[0036] According to the oscillation suppression method provided in the embodiment of the present application, the first active power value and the first reactive power value of the first inverter are first obtained, and then the output voltage phase angle of the first inverter is determined according to the first active power value and the first reactive power value, and then the d-axis voltage reference value and the q-axis voltage reference of the first inverter are determined according to the output voltage phase angle and the target induced electromotive force amplitude, and then the voltage and current dual-loop control is performed according to the d-axis voltage reference value and the q-axis voltage reference value to obtain a target pulse width modulation signal to offset the negative damping of the oscillation suppression system, thereby suppressing the oscillation of the oscillation system. Thus, on the one hand, compared with the existing method of reshaping the impedance of the grid-following inverter, the embodiment of the present application can offset the negative damping of the oscillation suppression system and suppress the low-frequency oscillation of the oscillation suppression system under the premise of inaccurate knowledge of the grid-side impedance and the control parameters of the supporting rectifier, thereby avoiding the model inaccuracy problem caused by the inconsistency of manufacturing parameters, and can be used as a general method for suppressing the low-frequency oscillation phenomenon of the towing system in the aging experiment, and can be quickly transplanted to other aging models on site, with strong applicability; on the other hand, compared with some active damping solutions in the prior art, the embodiment of the present application does not need to add additional voltage / current sensors, which can save production costs; on the other hand, compared with the inverter parameter adjustment method in the prior art, it can increase the number of inverters connected in parallel at the same time in the aging test, and can be flexibly expanded, which can speed up the progress of product aging and shipment.

[0037] The specific implementation of the above steps is introduced below.

[0038] In step S110, the first active power value may be an intermediate power value of the first inverter. The first reactive power value may be an intermediate power value of the first inverter.

[0039] In some examples, the adjustment range of the reactive power of the first inverter includes [0, 10% Srated], where Srated represents the rated capacity of the first inverter.

[0040] Specifically, considering the assessment of the power grid on the power consumption factors of enterprises, the reactive power transmitted by the first inverter to the grid cannot be too large. For example, the 330kW first inverter is allowed to send a maximum of 30kVar reactive power. The first inverter appropriately sends reactive power to help maintain the voltage amplitude of the common connection point (PCC) and reduce the pressure of the virtual synchronous machine (VSG) to send reactive power. In other words, the reactive command of the first inverter can be set to a fixed value in the range of [0, 10% Srated].

[0041] For example, the rated capacity of the first inverter can be obtained through a product specification sheet of the first inverter or a manufacturer's website, etc.

[0042] In some implementations, obtaining a first active power value and a first reactive power value of a first inverter includes:

[0043] Obtaining the grid voltage angular frequency, the initial angular frequency of the first inverter AC voltage, the initial induced electromotive force amplitude, the voltage rated amplitude, the active frequency droop coefficient, the reactive voltage droop coefficient, the active power reference value and the reactive power reference value;

[0044] Substituting the initial angular frequency, the grid voltage angular frequency, the active frequency droop coefficient and the active power reference value into formula (1) for calculation, the first active power value of the first inverter is obtained;

[0045] Formula (1) includes:

[0046] P m =(ω 0 -ω 1 )·m ω+ P 0 (1)

[0047] Among them, P m Represents the first active power value; ω 1 represents the initial angular frequency; ω 0 Indicates the grid voltage angular frequency; m ω Indicates the active frequency droop coefficient; P 0 Indicates the active power reference value;

[0048] Substituting the initial induced electromotive force amplitude, the voltage rated amplitude, the reactive voltage droop coefficient, and the reactive power reference value into formula (2) for calculation, the first reactive power value of the first inverter is obtained;

[0049] Formula (2) includes:

[0050] Q m =(U 0 -E 1 )·n v +Q 0 (2)

[0051] Among them, Q m Indicates the first reactive power value; U 0 Indicates the rated voltage amplitude; E 1 Represents the initial induced electromotive force amplitude; n v Indicates the reactive voltage droop coefficient; Q 0 Indicates the reactive power reference value.

[0052] In this embodiment, the first active power value of the first inverter can be quickly and accurately determined by the above formula (1), and the first reactive power value of the first inverter can be quickly and accurately determined by the above formula (2).

[0053] The initial angular frequency may be an initial value of the angular frequency of the AC voltage of the first inverter.

[0054] The initial induced electromotive force amplitude may be an initial value of the induced electromotive force amplitude of the first inverter;

[0055] The voltage rated magnitude may be a rated value of the voltage magnitude of the first inverter.

[0056] The active power droop coefficient may be an active power droop coefficient of the first inverter.

[0057] The reactive voltage droop coefficient may be a reactive voltage droop coefficient of the first inverter.

[0058] The active power reference value may be a reference value of the active power of the first inverter.

[0059] The reactive power reference value may be a reference value of reactive power of the first inverter.

[0060] Exemplarily, the controller of the first inverter may pre-store the grid voltage angular frequency, the initial angular frequency of the first inverter AC voltage, the initial induced electromotive force amplitude, the voltage rated amplitude, the active frequency droop coefficient, the reactive voltage droop coefficient, the active power reference value and the reactive power reference value for subsequent direct call-up.

[0061] As another example, the virtual synchronous machine added in the embodiment of the present application performs a pre-synchronization operation before being connected to the power grid, and can obtain the frequency, phase and amplitude information of the power grid through the phase-locked loop, thereby obtaining the grid voltage angular frequency and voltage rated amplitude in the active and reactive control loops; the active power reference value and the reactive power reference value can be determined according to the actual requirements for the first inverter. For example, when the first inverter is powered by an external power supply, the active power reference value can be set to 0 to save power consumption.

[0062] For example, in the aging experiment, the virtual synchronous generator used for networking absorbs / emits reactive power to support the voltage of the common connection point (PCC), and the lower limit requirement for the hardware capacity of the first inverter mainly depends on the maximum reactive power it needs to output. Therefore, when the first inverter is used as an inverter for networking support and does not participate in the aging experiment as a product to be shipped, the active power reference value and the reactive power reference value can be set to 0; when the first inverter is used as a product to be shipped after aging, the active power reference value can be set to the value required by the experiment, and the reactive power reference value can be set to 0, but the number of inverters controlled by the networking type needs to be increased according to the event situation to share the reactive output and avoid insufficient capacity of a single inverter.

[0063] That is to say, Figure 2As shown in FIG. 1 , in the VSG control strategy adopted by the grid-type control, the active power setting is controlled by the “active power-frequency droop” output, and the reactive power setting is controlled by the “reactive power-voltage droop” output. The output expressions of the droop control are shown in formulas (1) and (2).

[0064] In other implementations, the first inverter may be communicatively connected to both the active power acquisition device and the reactive power acquisition device, and thus may acquire the first active power value through the active power acquisition device and acquire the first reactive power value through the reactive power acquisition device.

[0065] In some further implementations, the first active power value and the first reactive power value of the first inverter may be pre-stored in the controller of the first inverter so as to be directly called later.

[0066] In step S120, after obtaining the first active power value and the first reactive power value of the first inverter, the controller in the first inverter can also determine the output voltage phase angle and the target induced electromotive force amplitude of the first inverter according to the first active power value and the first reactive power value.

[0067] The output voltage phase angle may be a phase angle of the output voltage of the first inverter.

[0068] The target induced electromotive force magnitude may be a target value of the induced electromotive force magnitude of the first inverter.

[0069] In some implementations, determining the output voltage phase angle and the target induced electromotive force amplitude of the first inverter according to the first active power value and the first reactive power value includes:

[0070] Determine a target angular frequency value of the AC voltage of the first inverter according to the first active power value, and determine an output voltage phase angle of the first inverter according to the target angular frequency value;

[0071] A target induced electromotive force magnitude of the first inverter is generated according to the first reactive power value.

[0072] In some examples, determining a target angular frequency value of the AC voltage of the first inverter according to the first active power value, and determining an output voltage phase angle of the first inverter according to the target angular frequency value includes:

[0073] Obtaining grid voltage angular frequency, virtual inertia of the first inverter, actual value of active power and active damping coefficient;

[0074] Substitute the virtual inertia, grid voltage angular frequency, actual active power value, active damping coefficient and first active power value into formula (3) to calculate and obtain the target angular frequency value of the AC voltage of the first inverter;

[0075] Formula (3) includes:

[0076]

[0077] Where, J represents the virtual inertia; ω 0 Indicates the grid voltage angular frequency; P m represents the first active power value; P represents the actual value of active power; D represents the active damping coefficient; ω represents the target angular frequency value;

[0078] Substitute the target angular frequency value into formula (4) to calculate and obtain the output voltage phase angle of the first inverter;

[0079] Formula (4) includes:

[0080]

[0081] Where θ is the output voltage phase angle.

[0082] In this embodiment, the target angular frequency value of the AC voltage of the first inverter can be determined quickly and accurately by the above formula (3); the output voltage phase angle of the first inverter can be determined quickly and accurately by the above formula (4).

[0083] The actual value of active power may be an actual value of the active power of the first inverter.

[0084] The active damping coefficient may be an active damping coefficient of the first inverter.

[0085] Exemplarily, the virtual inertia of the first inverter may be set according to the requirements and operating conditions of the oscillation suppression system. For example, the virtual inertia may be 2kgm / s, 3kgm / s, 12kgm / s, etc.

[0086] Exemplarily, the active damping coefficient is less than 1, and the value of the active damping coefficient can be set according to actual conditions and is not limited here. For example, the value of the active damping coefficient can be 0.3, 0.5, etc.

[0087] Exemplarily, the grid voltage angular frequency, the virtual inertia of the first inverter, the actual value of active power and the active damping coefficient may be pre-stored in the controller of the first inverter for subsequent direct calling.

[0088] That is to say, Figure 2 As shown, in the reactive power control link, the rotor motion equation is added to simulate the moment of inertia and damping characteristics. The active power control link expression is shown in formula (3) and formula (4).

[0089] In some other examples, determining a target angular frequency value of the AC voltage of the first inverter according to the first active power value, and determining an output voltage phase angle of the first inverter according to the target angular frequency value includes:

[0090] Obtaining grid voltage angular frequency, actual active power value, operation factor, first proportional coefficient, first time constant and second time constant;

[0091] Substitute the grid voltage angular frequency, the actual value of active power, the operation factor, the first proportional coefficient, the first time constant, the second time constant and the first active power value into formula (10) to calculate and obtain the target angular frequency value of the AC voltage of the first inverter;

[0092] Formula (10) includes:

[0093]

[0094] Among them, ω 0 Indicates the grid voltage angular frequency; P m represents the first active power value; P represents the actual value of active power; ω represents the target angular frequency value; k p represents the first proportionality coefficient; T a represents the first time constant; T b represents the second time constant; s represents the operation factor.

[0095] Exemplarily, the controller in the first inverter pre-stores the grid voltage angular frequency, the actual value of active power, the operation factor, the first proportional coefficient, the first time constant and the second time constant for subsequent direct calling.

[0096] In some examples, generating a target induced electromotive force amplitude of the first inverter according to the first reactive power value includes:

[0097] Obtaining the reactive voltage loop and reactive power actual value of the first inverter;

[0098] Substitute the reactive voltage loop, the actual reactive power value and the first reactive power value into formula (5) to calculate and obtain the target induced electromotive force amplitude of the first inverter;

[0099] Formula (5) includes:

[0100]

[0101] Where E represents the target induced electromotive force amplitude; k iQ Represents the reactive voltage loop; Q m represents the first reactive power value; Q represents the actual value of reactive power.

[0102] In this embodiment, the target induced electromotive force amplitude of the first inverter can be determined quickly and accurately through the above formula (5).

[0103] The reactive voltage loop of the first inverter may be a gain of an integral controller.

[0104] Exemplarily, the reactive voltage loop and the actual reactive power value of the first inverter may be pre-stored in the controller of the first inverter so as to be directly called later.

[0105] That is to say, Figure 2 As shown in FIG. 5 , in the reactive voltage link, an integral term is introduced to eliminate the error of reactive power control and generate the target induced electromotive force amplitude. The specific expression is shown in formula (5).

[0106] In some other examples, generating a target induced electromotive force amplitude of the first inverter according to the first reactive power value includes:

[0107] Obtaining a reactive voltage loop, an operation factor, a second proportional coefficient and an actual value of reactive power;

[0108] Substitute the reactive voltage loop, the operation factor, the second proportional coefficient, the actual reactive power value and the first reactive power value into formula (11) to calculate and obtain the target induced electromotive force amplitude of the first inverter;

[0109] Formula (11) includes:

[0110]

[0111] Where, E(s) represents the target induced electromotive force amplitude; k iQ Represents the reactive voltage loop; Q m represents the first reactive power value; Q represents the actual value of reactive power; k pQ represents the second proportional coefficient; s represents the operation factor.

[0112] It should be noted that Figure 2 The ki / s in the above is the k iQ / s.

[0113] Exemplarily, the controller in the first inverter may pre-store the reactive voltage loop, the operation factor, the second proportional coefficient and the actual value of reactive power for subsequent direct calling.

[0114] In step S130, after determining the output voltage phase angle and target induced electromotive force amplitude of the first inverter according to the first active power value and the first reactive power value, the controller in the first inverter can also determine the d-axis voltage parameter value and q-axis voltage reference value of the first inverter according to the output voltage phase angle and the target induced electromotive force amplitude.

[0115] The d-axis voltage parameter value may be a voltage parameter value of the d-axis of the first inverter in the dq coordinate system.

[0116] The q-axis voltage reference value may be a voltage parameter value of the q-axis of the first inverter in the dq coordinate system.

[0117] In some examples, determining a d-axis voltage reference value and a q-axis voltage reference value of the first inverter according to an output voltage phase angle and a target induced electromotive force amplitude includes:

[0118] Substituting the output voltage phase angle and the target induced electromotive force amplitude into formula (6), the d-axis voltage reference value of the first inverter is obtained;

[0119] Formula (6) includes:

[0120] U dref =Ecosθ(6)

[0121] Among them, U dref represents the d-axis voltage reference value; E represents the target induced electromotive force amplitude; θ represents the output voltage phase angle;

[0122] Substituting the output voltage phase angle and the target induced electromotive force amplitude into formula (7), the q-axis voltage reference value of the first inverter is obtained;

[0123] Formula (7) includes:

[0124] U qref = Esinθ(7)

[0125] Among them, U qref Indicates the q-axis voltage reference value.

[0126] In this embodiment, the d-axis voltage reference value can be determined quickly and accurately through the above formula (6); and the q-axis voltage reference value can be determined quickly and accurately through the above formula (7).

[0127] That is to say, Figure 2 As shown, in the embodiment of the present application, the active power setting is controlled by the "active power-frequency droop" output, and the reactive power setting is controlled by the "reactive power-voltage droop" output. In the active power control link, the rotor motion equation is added to simulate the moment of inertia and damping characteristics, and the AC current angular frequency value (i.e., the target angular frequency value) is output. The output voltage phase angle of the VSG can be obtained by integration; in the reactive power control link, the integral term is used to eliminate the control error and generate the target induced electromotive force amplitude. Based on this, the given AC voltage loop dq component can be obtained, and its specific expression is shown in the above formulas (6) and (7).

[0128] In step S140, after determining the d-axis voltage parameter value and the q-axis voltage reference value of the first inverter according to the output voltage phase angle and the target induced electromotive force amplitude, the controller in the first inverter can also perform voltage-current dual-loop control according to the d-axis voltage reference value and the q-axis voltage reference value to obtain the target pulse width modulation signal.

[0129] In some implementations, voltage-current dual-loop control is performed according to a d-axis voltage reference value and a q-axis voltage reference value to obtain a target pulse width modulation signal, including:

[0130] Obtaining a d-axis voltage reference value increment, a q-axis voltage reference value increment, a d-axis voltage measured value, and a q-axis voltage measured value of the first inverter;

[0131] determining a difference between a d-axis voltage reference value and an increment of the d-axis voltage reference value as a first difference, and determining a difference between a q-axis voltage reference value and an increment of the q-axis voltage reference value as a second difference;

[0132] Determining a first control variable and a second control variable of the first inverter according to the first difference, the second difference, the d-axis voltage measured value, and the q-axis voltage measured value;

[0133] Determining a d-axis voltage modulation amount and a q-axis voltage modulation amount of the first inverter according to the first control amount and the second control amount;

[0134] The d-axis voltage modulation amount and the q-axis voltage modulation amount are coordinate-converted to obtain a three-phase modulation amount, which includes an a-phase modulation amount, a b-phase modulation amount and a c-phase modulation amount;

[0135] The three-phase modulation quantity is pulse-width modulated to obtain a target pulse-width modulated signal.

[0136] The d-axis voltage reference value increment may be an increment of the d-axis voltage reference value introduced by the virtual impedance path in the first inverter.

[0137] The q-axis voltage reference value increment may be an increment of the q-axis voltage reference value introduced by the virtual impedance path in the first inverter.

[0138] The d-axis voltage measured value may be an actually measured value of the d-axis voltage in the first inverter.

[0139] The q-axis voltage measured value may be an actually measured value of the q-axis voltage in the first inverter.

[0140] In some examples, obtaining a d-axis voltage reference value increment and a q-axis voltage reference value increment of the first inverter includes:

[0141] Obtaining a measured value of a d-axis current, a measured value of a q-axis current, a resistance component, an inductance component, and a target angular frequency value of a virtual impedance of the first inverter, wherein the resistance component and the inductance component are determined by a per-unit value of the virtual impedance;

[0142] Substitute the measured value of the d-axis current, the measured value of the q-axis current, the resistance component, the inductance component and the target angular frequency value into formula (8) to calculate and obtain the d-axis voltage reference value increment of the first inverter;

[0143] Formula (8) includes:

[0144]

[0145] in, Indicates the d-axis voltage reference value increment; i d Represents the measured value of d-axis current; R v Represents the resistance component; i q Indicates the measured value of q-axis current; L v represents the inductance component; ω represents the target angular frequency value;

[0146] Substitute the measured value of the d-axis current, the measured value of the q-axis current, the resistance component, the inductance component and the target angular frequency value into formula (9) to calculate and obtain the d-axis voltage reference value increment;

[0147] Formula (9) includes:

[0148]

[0149] in, Indicates the q-axis voltage reference value increment.

[0150] In this embodiment, the d-axis voltage reference value increment can be determined quickly and accurately through the above formula (8); and the q-axis voltage reference value increment can be determined quickly and accurately through the above formula (9).

[0151] In the embodiment of the present application, in order to improve or avoid oscillation instability of the first inverter when the grid-side impedance is small, a virtual impedance is added to the output side of the first inverter, and the increase method in the dq coordinate system is as follows: Figure 3 For example, when the rated voltage is 330kW / 800V, the virtual inductance can be set to 0.1-0.2pu. For example, when the virtual inductance is set to 0.163pu, the virtual inductance can be calculated to be The virtual resistance is generally 1 / 3 to 1 / 10 of the virtual inductive reactance, for example, 1 / 3 of the virtual inductive reactance, that is, 0.1Ω.

[0152] In some examples, such as Figure 3 As shown, the d-axis voltage modulation amount m dand q-axis voltage modulation m q Input the conversion module of dq coordinates and abc coordinates, and then the d-axis voltage modulation amount m d and q-axis voltage modulation m q Perform abc coordinate transformation to obtain the three-phase modulation, which includes the a-phase modulation m a , b phase modulation m b and c-phase modulation m c .

[0153] That is to say, Figure 3 As shown, the introduced grid-type inverter (i.e., the first inverter) filter inductor is connected in series with a virtual impedance, and the virtual impedance is realized in the dq coordinate system, that is, the dq component of the inverter side current is multiplied by the corresponding coefficient of the virtual impedance and then added to the dq voltage loop. The specific implementation expressions are shown in formulas (8) and (9).

[0154] In some other examples, the d-axis voltage reference value increment and the q-axis voltage reference value increment of the first inverter may be pre-stored in the controller of the first inverter so as to be directly acquired later.

[0155] In some examples, determining a first control amount and a second control amount of the first inverter according to the first difference, the second difference, the measured d-axis voltage value, and the measured q-axis voltage value includes:

[0156] Obtaining a d-axis current measured value and a q-axis current measured value of the first inverter;

[0157] After performing proportional-integral control on the first difference and a third difference of the actual measured value of the d-axis voltage, a d-axis current reference value of the first inverter is obtained; and after performing proportional-integral control on the second difference and a fourth difference of the actual measured value of the q-axis voltage, a q-axis current reference value of the first inverter is obtained;

[0158] After proportional-integral control is performed on the fifth difference between the d-axis current reference value and the actual d-axis current value, the first control quantity of the first inverter is obtained, and after proportional-integral control is performed on the sixth difference between the q-axis current reference value and the actual q-axis current value, the second control quantity of the first inverter is obtained.

[0159] The d-axis current measured value may be an actually measured value of the d-axis current in the first inverter.

[0160] The q-axis current measured value may be an actually measured value of the q-axis current in the first inverter.

[0161] The first control amount may be a control amount of the d-axis voltage.

[0162] The second controlled variable may be a controlled variable of the q-axis voltage.

[0163] As an example, the controller of the first inverter may pre-store the d-axis current measured value and the q-axis current measured value so as to be directly called later.

[0164] As another example, the controller of the first inverter is in communication connection with the current measuring device, and the current measuring device may be provided to obtain the actual measured value of the d-axis current and the actual measured value of the q-axis current.

[0165] For example, Figure 3 As shown, the third difference can be input into the proportional integral controller PI(s), and the proportional integral controller PI(s) performs proportional integral control on the third difference to obtain the d-axis current reference value of the first inverter; and the fourth difference can be input into the proportional integral controller PI(s), and the proportional integral controller PI(s) performs proportional integral control on the fourth difference to obtain the q-axis current reference value of the first inverter. The fifth difference can be input into the proportional integral controller PI(s), and the proportional integral controller PI(s) performs proportional integral control on the fifth difference to obtain the first control amount of the first inverter, and the sixth difference can be input into the proportional integral controller PI(s), and the proportional integral controller PI(s) performs proportional integral control on the sixth difference to obtain the second control amount of the first inverter.

[0166] In some examples, determining a d-axis voltage modulation amount and a q-axis voltage modulation amount of the first inverter according to the first control amount and the second control amount includes:

[0167] Obtain grid voltage feedforward coefficient;

[0168] The product of the measured value of the d-axis voltage and the grid voltage feedforward coefficient is determined as a first product, and the product of the measured value of the q-axis voltage and the grid voltage feedforward coefficient is determined as a second product;

[0169] The sum of the first product and the first control amount is determined as the d-axis voltage modulation amount of the first inverter, and the sum of the second product and the second control amount is determined as the q-axis voltage modulation amount of the first inverter.

[0170] The grid voltage feed-forward coefficient may be a grid voltage feed-forward coefficient in the current inner loop.

[0171] For example, the controller of the first inverter may pre-store a grid voltage feed-forward coefficient for subsequent direct call. The value of the grid voltage feed-forward coefficient may be set according to actual conditions and is not limited here. For example, it may be -1, 0.5, 1, 1.2, etc.

[0172] like Figure 3 As shown, the grid voltage feedforward coefficient is Kvf, and the measured value of the d-axis voltage is U d The measured value of q-axis voltage is U q , U d×Kvf is determined as the first product, and U q ×Kvf is determined as the second product, and the sum of the first product and the first control amount is determined as the d-axis voltage modulation amount m of the first inverter d , the sum of the second product and the second control amount is determined as the q-axis voltage modulation amount m of the first inverter q .

[0173] In the embodiment of the present application, the oscillation suppression method adopts a network control strategy of virtual synchronous machine + voltage and current dual-loop control.

[0174] In the embodiment of the present application, the VSG enters the operating state after the phase-locking stage, the pre-synchronization stage, the pre-charging stage, and the soft-start loading stage, and then the number of parallel units in the towing system is increased one by one. During the process of increasing the number of units, the VSG continuously and automatically adjusts the reactive output to maintain the stability of the voltage at the common connection point.

[0175] In an embodiment of the present application, the oscillation suppression method can be used for the weaker grid conditions in the aging room of the production workshop. The capacity proportion of the first inverter is positively correlated with the maximum number of first inverters allowed to be stably connected in parallel by the system. Increasing the number of first inverters connected in parallel can further improve the stability of the oscillation suppression system.

[0176] It should be noted that, compared with the existing low-frequency oscillation suppression methods, the multi-grid inverter parallel oscillation suppression method for the aging system based on the virtual synchronous mechanism network support method in the embodiment of the present application has the advantages mainly reflected in the adaptability to aging scenarios and the versatility of impedance conditions. Compared with the method of reshaping the impedance of the grid-type inverter, the embodiment of the present application does not require accurate measurement of the grid impedance, nor does it require accurate measurement of the true value of the inverter internal filter parameter, avoiding the model inaccuracy problem caused by manufacturing parameter inconsistency, and can be quickly transplanted to other aging models on site, with strong applicability; compared with some active damping solutions, the embodiment of the present application does not need to add additional voltage / current sensors, saving production costs; compared with the inverter parameter adjustment method, the embodiment of the present application can increase the number of stable parallel units, and can be flexibly expanded, and the upper limit of the number of parallel units can be increased by increasing the proportion of grid-type capacity.

[0177] Based on the same inventive concept, an embodiment of the present application further provides a controller of an inverter. The controller of the inverter provided in the embodiment of the present application is described below in conjunction with the accompanying drawings.

[0178] Example 2

[0179] like Figure 4 As shown, the controller 100 of the inverter provided in the embodiment of the present application may include an acquisition module 110 , a first determination module 120 , a second determination module 130 and a control module 140 .

[0180] Wherein, the acquisition module 110 is used to acquire a first active power value and a first reactive power value of the first inverter;

[0181] A first determination module 120, configured to determine an output voltage phase angle and a target induced electromotive force amplitude of the first inverter according to a first active power value and a first reactive power value;

[0182] A second determination module 130 is used to determine a d-axis voltage reference value and a q-axis voltage reference value of the first inverter according to an output voltage phase angle and a target induced electromotive force amplitude;

[0183] The control module 140 is used to perform voltage and current dual-loop control according to the d-axis voltage reference value and the q-axis voltage reference value to obtain a target pulse width modulation signal. The target pulse width modulation signal is used to control the on and off of the three-phase converter bridge to offset the negative damping of the oscillation suppression system, thereby suppressing the oscillation of the oscillation system.

[0184] According to the controller of the inverter provided in the embodiment of the present application, the first active power value and the first reactive power value of the first inverter are first obtained, and then the output voltage phase angle of the first inverter is determined according to the first active power value and the first reactive power value, and then the d-axis voltage reference value and the q-axis voltage reference of the first inverter are determined according to the output voltage phase angle and the target induced electromotive force amplitude, and then the voltage and current dual-loop control is performed according to the d-axis voltage reference value and the q-axis voltage reference value to obtain the target pulse width modulation signal to offset the negative damping of the oscillation suppression system, thereby suppressing the oscillation of the oscillation system. Thus, on the one hand, compared with the existing method of reshaping the impedance of the grid-following inverter, the embodiment of the present application can offset the negative damping of the oscillation suppression system and suppress the low-frequency oscillation of the oscillation suppression system under the premise of inaccurate knowledge of the grid-side impedance and the control parameters of the supporting rectifier, thereby avoiding the model inaccuracy problem caused by the inconsistency of manufacturing parameters, and can be used as a general method for suppressing the low-frequency oscillation phenomenon of the towing system in the aging experiment, and can be quickly transplanted to other aging models on site, with strong applicability; on the other hand, compared with some active damping solutions in the prior art, the embodiment of the present application does not need to add additional voltage / current sensors, which can save production costs; on the other hand, compared with the inverter parameter adjustment method in the prior art, it can increase the number of inverters connected in parallel at the same time in the aging test, and can be flexibly expanded, which can speed up the progress of product aging and shipment.

[0185] In some implementations, the acquisition module 110 is specifically configured to:

[0186] Obtaining the grid voltage angular frequency, the initial angular frequency of the AC voltage of the first inverter, the initial induced electromotive force amplitude, the voltage rated amplitude, the active frequency droop coefficient, the reactive voltage droop coefficient, the active power reference value and the reactive power reference value;

[0187] Substituting the initial angular frequency, the grid voltage angular frequency, the active frequency droop coefficient and the active power reference value into formula (1) for calculation, the first active power value of the first inverter is obtained;

[0188] Formula (1) includes:

[0189] P m =(ω 0 -ω 1 )·m ω +P 0 (1)

[0190] Among them, P m Represents the first active power value; ω 1 represents the initial angular frequency; ω 0 Indicates the grid voltage angular frequency; m ω Indicates the active frequency droop coefficient; P 0 Indicates the active power reference value;

[0191] Substituting the initial induced electromotive force amplitude, the voltage rated amplitude, the reactive voltage droop coefficient, and the reactive power reference value into formula (2) for calculation, the first reactive power value of the first inverter is obtained;

[0192] Formula (2) includes:

[0193] Q m =(U 0 -E 1 )·n v +Q 0 (2)

[0194] Among them, Q m Indicates the first reactive power value; U 0 Indicates the rated voltage amplitude; E 1 Represents the initial induced electromotive force amplitude; n v Indicates the reactive voltage droop coefficient; Q 0 Indicates the reactive power reference value.

[0195] In some implementations, the first determining module 120 is specifically configured to:

[0196] Determine a target angular frequency value of the AC voltage of the first inverter according to the first active power value, and determine an output voltage phase angle of the first inverter according to the target angular frequency value;

[0197] A target induced electromotive force magnitude of the first inverter is generated according to the first reactive power value.

[0198] In some implementations, the first determining module 120 is specifically configured to:

[0199] Obtaining grid voltage angular frequency, virtual inertia of the first inverter, actual value of active power and active damping coefficient;

[0200] Substitute the virtual inertia, grid voltage angular frequency, actual active power value, active damping coefficient and first active power value into formula (3) to calculate and obtain the target angular frequency value of the AC voltage of the first inverter;

[0201] Formula (3) includes:

[0202]

[0203] Where, J represents the virtual inertia; ω 0 Indicates the grid voltage angular frequency; P m represents the first active power value; P represents the actual value of active power; D represents the active damping coefficient; ω represents the target angular frequency value;

[0204] Substitute the target angular frequency value into formula (4) to calculate and obtain the output voltage phase angle of the first inverter;

[0205] Formula (4) includes:

[0206]

[0207] Where θ is the output voltage phase angle.

[0208] In some implementations, the first determining module 120 is specifically configured to:

[0209] Obtaining the reactive voltage loop and reactive power actual value of the first inverter;

[0210] Substitute the reactive voltage loop, the actual reactive power value and the first reactive power value into formula (5) to calculate and obtain the target induced electromotive force amplitude of the first inverter;

[0211] Formula (5) includes:

[0212]

[0213] Where E represents the target induced electromotive force amplitude; k iQ Represents the reactive voltage loop; Q m represents the first reactive power value; Q represents the actual value of reactive power.

[0214] In some implementations, the second determining module 130 is specifically configured to:

[0215] Substituting the output voltage phase angle and the target induced electromotive force amplitude into formula (6), the d-axis voltage reference value of the first inverter is obtained;

[0216] Formula (6) includes:

[0217] U dref =Ecosθ(6)

[0218] Among them, U dref represents the d-axis voltage reference value; E represents the target induced electromotive force amplitude; θ represents the output voltage phase angle;

[0219] Substituting the output voltage phase angle and the target induced electromotive force amplitude into formula (7), the q-axis voltage reference value of the first inverter is obtained;

[0220] Formula (7) includes:

[0221] U qref = Esinθ(7)

[0222] Among them, U qref Indicates the q-axis voltage reference value.

[0223] In some implementations, the control module 140 is specifically configured to:

[0224] Obtaining a d-axis voltage reference value increment, a q-axis voltage reference value increment, a d-axis voltage measured value, and a q-axis voltage measured value of the first inverter;

[0225] determining a difference between a d-axis voltage reference value and an increment of the d-axis voltage reference value as a first difference, and determining a difference between a q-axis voltage reference value and an increment of the q-axis voltage reference value as a second difference;

[0226] Determining a first control variable and a second control variable of the first inverter according to the first difference, the second difference, the d-axis voltage measured value, and the q-axis voltage measured value;

[0227] Determining a d-axis voltage modulation amount and a q-axis voltage modulation amount of the first inverter according to the first control amount and the second control amount;

[0228] The d-axis voltage modulation amount and the q-axis voltage modulation amount are coordinate-converted to obtain a three-phase modulation amount, which includes an a-phase modulation amount, a b-phase modulation amount and a c-phase modulation amount;

[0229] The three-phase modulation quantity is pulse-width modulated to obtain a target pulse-width modulated signal.

[0230] In some implementations, the control module 140 is specifically configured to:

[0231] Obtaining a measured value of a d-axis current, a measured value of a q-axis current, a resistance component, an inductance component, and a target angular frequency value of a virtual impedance of the first inverter, wherein the resistance component and the inductance component are determined by a per-unit value of the virtual impedance;

[0232] Substitute the measured value of the d-axis current, the measured value of the q-axis current, the resistance component, the inductance component and the target angular frequency value into formula (8) to calculate and obtain the d-axis voltage reference value increment of the first inverter;

[0233] Formula (8) includes:

[0234]

[0235] in, Indicates the d-axis voltage reference value increment; i d Represents the measured value of d-axis current; R v Represents the resistance component; i q Indicates the measured value of q-axis current; L v represents the inductance component; ω represents the target angular frequency value;

[0236] Substitute the measured value of the d-axis current, the measured value of the q-axis current, the resistance component, the inductance component and the target angular frequency value into formula (9) to calculate and obtain the d-axis voltage reference value increment;

[0237] Formula (9) includes:

[0238]

[0239] in, Indicates the q-axis voltage reference value increment.

[0240] In some implementations, the control module 140 is specifically configured to:

[0241] Obtaining a d-axis current measured value and a q-axis current measured value of the first inverter;

[0242] After performing proportional-integral control on the first difference and a third difference of the actual measured value of the d-axis voltage, a d-axis current reference value of the first inverter is obtained; and after performing proportional-integral control on the second difference and a fourth difference of the actual measured value of the q-axis voltage, a q-axis current reference value of the first inverter is obtained;

[0243] After proportional-integral control is performed on the fifth difference between the d-axis current reference value and the actual d-axis current value, the first control quantity of the first inverter is obtained, and after proportional-integral control is performed on the sixth difference between the q-axis current reference value and the actual q-axis current value, the second control quantity of the first inverter is obtained.

[0244] In some implementations, the control module 140 is specifically configured to:

[0245] Obtain grid voltage feedforward coefficient;

[0246] The product of the measured value of the d-axis voltage and the grid voltage feedforward coefficient is determined as a first product, and the product of the measured value of the q-axis voltage and the grid voltage feedforward coefficient is determined as a second product;

[0247] The sum of the first product and the first control amount is determined as the d-axis voltage modulation amount of the first inverter, and the sum of the second product and the second control amount is determined as the q-axis voltage modulation amount of the first inverter.

[0248] In some embodiments, the adjustment range of the reactive power of the first inverter includes [0, 10% Srated], where Srated represents the rated capacity of the first inverter.

[0249] The controller of the inverter provided in the embodiment of the present application can be used to execute the oscillation suppression method, that is, it has the beneficial effects and implementation methods of the oscillation suppression method provided in Example 1 of the present application. For details, please refer to the specific description of the oscillation suppression method in the above Example 1, which will not be repeated in this embodiment.

[0250] Based on the same inventive concept, an embodiment of the present application further provides an oscillation suppression system. The oscillation suppression system provided by the embodiment of the present application is described below in conjunction with the accompanying drawings.

[0251] Example 3

[0252] The application scenario of the oscillation suppression system provided in the embodiment of the present application may include a microgrid, wherein the microgrid may be a small power distribution grid system composed of a distributed power source, an energy storage device, an energy conversion device, a load, a monitoring and protection device, etc.

[0253] like Figure 5 As shown, the oscillation suppression system provided in the embodiment of the present application may include an oscillation suppression subsystem 1 and a towing subsystem 2;

[0254] The oscillation suppression subsystem 1 includes M groups of first inverters 10 with support functions, M groups of power supply modules 11 and M groups of first transformers 12, where M is a positive integer; wherein the first inverter 10 corresponds to the power supply module 11 and the first transformer 12 one by one;

[0255] Among the M groups of power supply modules 11, each group of power supply modules 11 is connected to a corresponding group of first transformers 12 through a corresponding group of first inverters 10, and each group of power supply modules 11 and a corresponding group of first transformers 12 are respectively connected to a common connection point PCC;

[0256] The power supply module 11 is used to supply power to the corresponding first inverter 10;

[0257] In the M groups of first inverters 10, each group of first inverters 10 includes a controller 100 as described in any one of Embodiment 2;

[0258] The towing system 2 includes N groups of first rectifiers 20, N groups of second inverters 21 and N groups of second transformers 22, where N is a positive integer; wherein the first rectifiers 20 correspond to the second inverters 21 and the second transformers 22 respectively one by one;

[0259] Among the N groups of first rectifiers 20, each group of first rectifiers 20 is connected to a corresponding group of second transformers 22 through a corresponding group of second inverters 21, and each group of first rectifiers 20 and a corresponding group of second transformers 22 are respectively connected to a common connection point PCC;

[0260] The first rectifier 20 is used to supply power to its corresponding second inverter 22 .

[0261] The first inverter 10 can be used to convert the electric energy from a battery such as a solar panel or a DC power source into an AC power source, and can also be used to enhance the stability of the power grid by simulating the inertia and dynamic characteristics of a synchronous generator.

[0262] The second inverter 21 can be used to convert the electric energy from a battery such as a solar panel or a DC power source into an AC power source.

[0263] Exemplarily, both the first transformer 12 and the second transformer 22 may include power frequency transformers. The voltage corresponding to the first transformer 12 may be 800V / 400V, and the voltage corresponding to the second transformer 22 may be 400 / 10kV, or other values, which are not limited here.

[0264] Exemplarily, the second inverter may be a grid-following inverter.

[0265] Exemplarily, the voltage of the common connection point PCC may be 400 V, or other values, which are not limited here.

[0266] Exemplarily, the DC side voltage in the towing system 2 may be 1200 V, or other values, which are not limited here.

[0267] Exemplarily, the DC side voltage in the oscillation suppression subsystem 1 may be 1350 V, or other values, which are not limited here.

[0268] Exemplarily, the voltage of the common connection point PCC may be 400 V, or other values, which are not limited here.

[0269] It should be noted that Figure 5 The leakage inductance of the first transformer and the second transformer are combined with the line impedance for description. Figure 5 Middle: L g Represents the grid-side inductance; R g Indicates the grid side resistance; L il Represents the inverter inductance; R il Indicates the inverter resistance; Lrl Represents the rectifier inductance; R rl represents the rectifier resistance; A, B, and C represent phase A, phase B, and phase C respectively; U represents the voltage of phase A, V represents the voltage of phase B, and W represents the voltage of phase C.

[0270] In some examples, the power supply module includes at least one of an independent DC source, a maximum power point tracking input-side AD / DC module in a string inverter, and an inverter operating in four quadrants;

[0271] And / or, the first inverter includes at least one of a single-stage / two-stage string inverter, a centralized inverter and an energy storage converter.

[0272] Specifically, the first inverter provided in the embodiment of the present application may include a single-stage / two-stage string inverter, a centralized inverter, an energy storage converter, etc. of similar capacity; the DC side power supply scheme of the first inverter in the embodiment of the present application is not limited to the AC / DC module scheme on the MPPT input side of the string inverter, but other four-quadrant inverters can also be used for pairing, and a dedicated DC test power supply can also be used for power supply; the boost part of the first inverter can be enabled, and the single-stage operation of the boost part can also be disabled.

[0273] It should be noted that the embodiment of the present application introduces a grid-forming inverter (i.e., the first inverter) to access a common connection point on the basis of a general multi-grid-type inverter (i.e., the second inverter) parallel-drag system, and the grid-forming control strategy is to use a virtual synchronous machine + voltage and current dual-loop control.

[0274] In the embodiment of the present application, the control parameters and electrical connection structure of the grid-following inverter for the aging experiment do not need to be changed. The introduction of the grid-building inverter can be achieved by modifying the control structure of a group of inverters in the towing system, or by introducing an additional grid-building inverter powered by an external DC power supply.

[0275] The oscillation suppression system provided in the embodiment of the present application includes the controller provided in Example 2 of the present application, that is, it has the beneficial effects and implementation methods of the controller provided in Example 2 of the present application. For details, please refer to the specific description of the controller in the above Example 2, which will not be repeated in this embodiment.

[0276] In the simulation, the power supply module is used as the second rectifier as an example, and the current doubling method is used to simulate the scenario of multiple towing systems in parallel. The grid-side impedance of the system is based on the rated power of 330kW per unit, and the assumed grid-side short-circuit ratio (SCRgrid) is converted and set. The resistance on the line is 10% of the inductive reactance. The specific impedance setting method from the ideal grid to the PCC point uses the following expression:

[0277]

[0278] Among them, Z g Represents the grid-side impedance; V g Indicates the grid voltage; P indicates the actual value of active power; SCR grid Indicates the grid-side short-circuit ratio; ω g Indicates the grid voltage angular frequency; L g Represents the grid-side inductance; R g Indicates the grid side resistance.

[0279] The impedance of each set of second rectifier and first inverter to PCC uses short circuit ratio SCR VSR Indicates that the impedance of each group of the first rectifier and the second inverter to the PCC uses the short-circuit ratio SCR GCI The specific expression is as follows:

[0280]

[0281] Among them, Z GCI Indicates the inverter impedance; Z VSR Represents the rectifier impedance; SCR GCI Indicates the inverter short-circuit ratio; SCR VSR Indicates the rectifier short-circuit ratio; L il Represents the inverter inductance; R il Represents the second inverter resistance; L rl Represents the rectifier inductance; R rl Represents the rectifier resistance.

[0282] In the simulation test for routine verification of the present application, take: SCR grid =3, SCR VSR =SCR GCI =2.75. It should be noted that the above values ​​are only used for examples and are not used to limit the present application. In actual implementation, the above values ​​can be set according to actual conditions.

[0283] In the simulation experiment without adopting the low-frequency oscillation suppression strategy, the rectifier of the grid-following towing system completed phase locking and closed the switch to the grid at 0.5 seconds. The grid-following inverter started from 0.5 seconds, experienced 1 second phase locking time, 0.5 second pre-charging time, closed the switch to the grid and started soft starting. At 3 seconds, the active and reactive power reached the rated values ​​of 330kW and 14.5kVar respectively. From 4 seconds, the coefficient of the current multiplier began to increase uniformly to simulate the number of parallel towing units increasing at a rate of 10 units / second, until the number of parallel towing units increased to 23 at 6.2 seconds; at 11 seconds, the number of parallel towing units was increased to 24.

[0284] The result of multiple units connected in parallel when the low-frequency oscillation suppression strategy is not adopted, that is, the result of multiple units connected in parallel in the prior art is as follows: Figures 6 to 10 shown. Figure 6 and Figure 7 The voltage and current waveforms at the PCC point and the output voltage and current waveforms of a certain inverter are given respectively; Figure 8 and Fig. 9 The active power and reactive power output by the ideal power grid and a certain inverter are given respectively; Fig.10 The phase voltage (PV) input voltage of a certain inverter and the voltage of the intermediate DC bus of the inverter are given. Among them, Figures 6 to 10 The horizontal axis in the table is time, and the unit is s; Figure 6 The vertical axis of the upper middle figure is the voltage of the common connection point PCC, in V. Figure 6 The vertical axis of the lower middle figure is the PCC current, in A; Figure 7 The vertical axis of the upper middle figure is the inverter output port voltage, in V. Figure 7 The vertical axis of the lower figure is the inverter output port current, in A; Figure 8 The vertical axis of the upper middle figure is the active power output of the power grid, in W. Figure 8 The vertical axis of the lower middle figure is the reactive power output by the power grid, in units of Var; Fig. 9 The vertical axis of the upper middle figure is the active power of the inverter, in W. Fig. 9 The vertical axis of the lower middle figure is the reactive power of the inverter, in Var; Fig.10 The vertical axis of the upper figure is the inverter phase input voltage, in V. Fig.10 The vertical axis in the lower middle figure is the bus voltage, in V.

[0285] Depend on Figures 6 to 10 It can be concluded that when low-frequency oscillation suppression measures are not adopted, the system can remain stable when the number of parallel units reaches 23, but the DC bus has a small low-frequency oscillation of 4-5Hz and is difficult to fully converge, indicating that the system is in a critical stable state; when the number of units continues to increase, the DC bus oscillation amplitude becomes larger and begins to diverge, and the three-phase current shows obvious sub / super synchronous oscillation; the bus voltage collapses first and the system becomes unstable.

[0286] In a simulation experiment using a low-frequency oscillation suppression strategy, that is, using the oscillation suppression method provided in an embodiment of the present application, the grid-forming inverter is started first, and after a 1-second phase-locked phase, a 0.5-second soft start phase and pre-synchronization, it is closed and connected to the grid at 1.5 seconds; the starting timing of the grid-following inverter (i.e., the second inverter) remains unchanged, and after the 3rd second, both the single group of grid-following towing system (i.e., the towing subsystem) and the grid-forming inverter (i.e., the first inverter) enter the rated operating state; starting from the 4th second, the number of parallel units of the grid-following towing system is increased at a rate of 10 units / second, and increases to 23 units in 6.2 seconds; it increases to 24 units at the 11th second, and continues to increase to 34 units at a rate of 10 units / second from the 13th second to the 14th second, and finally maintains 34 units in parallel operation.

[0287] The results of multiple parallel connections when using the low-frequency oscillation suppression strategy are as follows: Figures 11 to 16 shown. Fig.11 and Fig.12 The voltage and current waveforms at the PCC point and the output voltage and current waveforms of a certain inverter are given respectively; Figures 13 to 15 The active power and reactive power output of an ideal power grid, a grid-following inverter, and a grid-building inverter are given respectively; Fig.16 The PV input voltage of a certain inverter and the voltage of the DC bus in the middle of the inverter are given. Figures 11 to 16 The horizontal axis in the table is time, and the unit is s; Fig.11 The vertical axis of the upper middle figure is the voltage of the common connection point PCC, in V. Fig.11 The vertical axis of the lower middle figure is the PCC current, in A; Fig.12 The vertical axis of the upper middle figure is the inverter output port voltage, in V. Fig.12 The vertical axis of the lower figure is the inverter output port current, in A; Fig.13 The vertical axis of the upper middle figure is the active power output of the power grid, in W. Fig.13 The vertical axis of the lower middle figure is the reactive power output by the power grid, in units of Var; Fig.14 The vertical axis of the upper middle figure is the active power of the inverter, in W. Fig.14 The vertical axis of the lower middle figure is the reactive power of the inverter, in Var; Fig.15 The vertical axis of the upper middle figure is the active power output by the virtual synchronous machine, in W. Fig.15 The vertical axis of the lower middle figure is the reactive power output by the virtual synchronous machine, in units of Var; Fig.16 The vertical axis of the upper figure is the inverter phase input voltage, in V. Fig.16 The vertical axis in the lower middle figure is the bus voltage, in V.

[0288] Depend on Figures 11 to 16It can be seen that after adding the grid-forming support, there is no sign of oscillation instability when the number of grid-following units increases to more than 24 units. When the number continues to increase to 34 units, there is still no low-frequency oscillation. This shows that the oscillation suppression method proposed in the embodiment of the present application can at least increase the number of grid-following inverter pairs by more than 11 units.

[0289] It is to be understood that the above embodiments are merely exemplary embodiments used to illustrate the principles of the present application, but the present application is not limited thereto. For those skilled in the art, various modifications and improvements can be made without departing from the spirit and substance of the present application, and these modifications and improvements are also considered to be within the scope of protection of the present application.

Claims

1. An oscillation suppression method, characterized in that: A controller in a first inverter having a supporting function in an oscillation suppression system, the method comprising: Obtaining a first active power value and a first reactive power value of the first inverter; Determining an output voltage phase angle and a target induced electromotive force amplitude of the first inverter according to the first active power value and the first reactive power value; Determining a d-axis voltage reference value and a q-axis voltage reference value of the first inverter according to the output voltage phase angle and the target induced electromotive force amplitude; According to the d-axis voltage reference value and the q-axis voltage reference value, voltage and current dual-loop control is performed to obtain a target pulse width modulation signal, and the target pulse width modulation signal is used to control the on and off of the three-phase converter bridge to offset the negative damping of the oscillation suppression system, thereby suppressing the oscillation of the oscillation system.

2. The method according to claim 1, characterized in that The obtaining of a first active power value and a first reactive power value of the first inverter includes: Obtaining the grid voltage angular frequency, the initial angular frequency of the first inverter AC voltage, the initial induced electromotive force amplitude, the voltage rated amplitude, the active frequency droop coefficient, the reactive voltage droop coefficient, the active power reference value and the reactive power reference value; Substituting the initial angular frequency, the grid voltage angular frequency, the active frequency droop coefficient and the active power reference value into formula (1) for calculation, to obtain a first active power value of the first inverter; The formula (1) includes: P m =(ω0-ω1)·m ω +P0 (1) Among them, P m represents the first active power value; ω1 represents the initial angular frequency; ω0 represents the grid voltage angular frequency; m ω Indicates the active frequency droop coefficient; P0 indicates the active power reference value; Substituting the initial induced electromotive force amplitude, the voltage rated amplitude, the reactive voltage droop coefficient and the reactive power reference value into formula (2) for calculation, to obtain a first reactive power value of the first inverter; The formula (2) includes: Q m =(U0-E1)·n v +Q0(2) Among them, Q m represents the first reactive power value; U0 represents the rated voltage amplitude; E1 represents the initial induced electromotive force amplitude; n v It represents the reactive voltage droop coefficient; Q0 represents the reactive power reference value.

3. The method according to claim 1, characterized in that Determining the output voltage phase angle and target induced electromotive force amplitude of the first inverter according to the first active power value and the first reactive power value includes: Determine a target angular frequency value of the AC voltage of the first inverter according to the first active power value, and determine an output voltage phase angle of the first inverter according to the target angular frequency value; A target induced electromotive force amplitude of the first inverter is generated according to the first reactive power value.

4. The method according to claim 3, characterized in that Determining a target angular frequency value of the AC voltage of the first inverter according to the first active power value, and determining a phase angle of the output voltage of the first inverter according to the target angular frequency value, comprises: Obtaining grid voltage angular frequency, virtual inertia of the first inverter, actual value of active power and active damping coefficient; Substituting the virtual inertia, the grid voltage angular frequency, the actual active power value, the active damping coefficient and the first active power value into formula (3) for calculation, the target angular frequency value of the AC voltage of the first inverter is obtained; The formula (3) includes: Where J represents virtual inertia; ω0 represents grid voltage angular frequency; P m represents the first active power value; P represents the actual value of active power; D represents the active damping coefficient; ω represents the target angular frequency value; Substituting the target angular frequency value into formula (4) for calculation, the output voltage phase angle is obtained; The formula (4) includes: Where θ is the output voltage phase angle.

5. The method according to claim 3, characterized in that: The step of generating a target induced electromotive force amplitude of the first inverter according to the first reactive power value comprises: Obtaining the reactive voltage loop and reactive power actual value of the first inverter; Substituting the reactive voltage loop, the actual reactive power value and the first reactive power value into formula (5) for calculation, the target induced electromotive force amplitude of the first inverter is obtained; The formula (5) includes: Where E represents the target induced electromotive force amplitude; k iQ Represents the reactive voltage loop; Q m represents the first reactive power value; Q represents the actual value of reactive power.

6. The method according to claim 1, characterized in that Determining the d-axis voltage reference value and the q-axis voltage reference value of the first inverter according to the output voltage phase angle and the target induced electromotive force amplitude includes: Substituting the output voltage phase angle and the target induced electromotive force amplitude into formula (6) to obtain the d-axis voltage reference value of the first inverter; The formula (6) includes: U dref =Ecosθ(6) Among them, U dref represents the d-axis voltage reference value; E represents the target induced electromotive force amplitude; θ represents the output voltage phase angle; Substituting the output voltage phase angle and the target induced electromotive force amplitude into formula (7) to obtain the q-axis voltage reference value of the first inverter; The formula (7) includes: U qref =Esinθ(7) Among them, U qref Indicates the q-axis voltage reference value.

7. The method according to claim 1, characterized in that The step of performing voltage and current dual-loop control according to the d-axis voltage reference value and the q-axis voltage reference value to obtain a target pulse width modulation signal includes: Obtaining a d-axis voltage reference value increment, a q-axis voltage reference value increment, a d-axis voltage measured value, and a q-axis voltage measured value of the first inverter; determining a difference between the d-axis voltage reference value and the d-axis voltage reference value increment as a first difference, and determining a difference between the q-axis voltage reference value and the q-axis voltage reference value increment as a second difference; Determining a first control variable and a second control variable of the first inverter according to the first difference, the second difference, the d-axis voltage measured value, and the q-axis voltage measured value; Determining a d-axis voltage modulation amount and a q-axis voltage modulation amount of the first inverter according to the first control amount and the second control amount; Performing coordinate transformation on the d-axis voltage modulation amount and the q-axis voltage modulation amount to obtain a three-phase modulation amount, wherein the three-phase modulation amount includes an a-phase modulation amount, a b-phase modulation amount and a c-phase modulation amount; The three-phase modulation amount is pulse-width modulated to obtain a target pulse-width modulation signal.

8. The method according to claim 7, characterized in that The step of obtaining a d-axis voltage reference value increment and a q-axis voltage reference value increment of the first inverter includes: Obtaining a measured d-axis current value, a measured q-axis current value, a resistance component, an inductance component, and a target angular frequency value of a virtual impedance of the first inverter, wherein the resistance component and the inductance component are determined by a per-unit value of the virtual impedance; Substituting the d-axis current measured value, the q-axis current measured value, the resistance component, the inductance component and the target angular frequency value into formula (8) for calculation, to obtain the d-axis voltage reference value increment of the first inverter; The formula (8) includes: in, Indicates the d-axis voltage reference value increment; i d Represents the measured value of d-axis current; R v Represents the resistance component; i q Indicates the measured value of q-axis current; L v represents the inductance component; ω represents the target angular frequency value; Substituting the d-axis current measured value, the q-axis current measured value, the resistance component, the inductance component and the target angular frequency value into formula (9) for calculation, to obtain the d-axis voltage reference value increment; The formula (9) includes: in, Indicates the q-axis voltage reference value increment.

9. The method according to claim 7, characterized in that: Determining a first control amount and a second control amount of the first inverter according to the first difference, the second difference, the d-axis voltage measured value, and the q-axis voltage measured value includes: Obtaining a d-axis current measured value and a q-axis current measured value of the first inverter; After performing proportional-integral control on the first difference and a third difference of the actual measured value of the d-axis voltage, a d-axis current reference value of the first inverter is obtained; and after performing proportional-integral control on the second difference and a fourth difference of the actual measured value of the q-axis voltage, a q-axis current reference value of the first inverter is obtained; After performing proportional-integral control on the fifth difference between the d-axis current reference value and the d-axis current actual value, a first control quantity of the first inverter is obtained, and after performing proportional-integral control on the sixth difference between the q-axis current reference value and the q-axis current actual value, a second control quantity of the first inverter is obtained.

10. The method according to claim 7, characterized in that Determining the d-axis voltage modulation amount and the q-axis voltage modulation amount of the first inverter according to the first control amount and the second control amount includes: Obtain grid voltage feedforward coefficient; Determine the product of the d-axis voltage measured value and the grid voltage feedforward coefficient as a first product, and determine the product of the q-axis voltage measured value and the grid voltage feedforward coefficient as a second product; The sum of the first product and the first control amount is determined as the d-axis voltage modulation amount of the first inverter, and the sum of the second product and the second control amount is determined as the q-axis voltage modulation amount of the first inverter.

11. The method according to claim 1, characterized in that: The adjustment range of the reactive power of the first inverter includes [0, 10% Srated], where Srated represents the rated capacity of the first inverter.

12. A controller for an inverter, characterized in that: include: An acquisition module, used to acquire a first active power value and a first reactive power value of the first inverter; A first determining module, configured to determine an output voltage phase angle and a target induced electromotive force amplitude of a first inverter according to the first active power value and the first reactive power value; A second determination module is used to determine a d-axis voltage reference value and a q-axis voltage reference value of the first inverter according to the output voltage phase angle and the target induced electromotive force amplitude; The control module is used to perform voltage and current dual-loop control according to the d-axis voltage reference value and the q-axis voltage reference value to obtain a target pulse width modulation signal, wherein the target pulse width modulation signal is used to control the on and off of the three-phase converter bridge to offset the negative damping of the oscillation suppression system, thereby suppressing the oscillation of the oscillation system.

13. The inverter controller according to claim 12, characterized in that: The acquisition module is specifically used for: Obtaining the grid voltage angular frequency, the initial angular frequency of the AC voltage of the first inverter, the initial induced electromotive force amplitude, the voltage rated amplitude, the active frequency droop coefficient, the reactive voltage droop coefficient, the active power reference value and the reactive power reference value; Substituting the initial angular frequency, the grid voltage angular frequency, the active frequency droop coefficient and the active power reference value into formula (1) for calculation, to obtain a first active power value of the first inverter; The formula (1) includes: P m =(ω0-ω1)·m ω +P0 (1) Among them, P m represents the first active power value; ω1 represents the initial angular frequency; ω0 represents the grid voltage angular frequency; m ω Indicates the active frequency droop coefficient; P0 indicates the active power reference value; Substituting the initial induced electromotive force amplitude, the voltage rated amplitude, the reactive voltage droop coefficient and the reactive power reference value into formula (2) for calculation, to obtain a first reactive power value of the first inverter; The formula (2) includes: Q m =(U0-E1)·n v +Q0(2) Among them, Q m represents the first reactive power value; U0 represents the rated voltage amplitude; E1 represents the initial induced electromotive force amplitude; n v It represents the reactive voltage droop coefficient; Q0 represents the reactive power reference value.

14. The inverter controller according to claim 12, characterized in that: The first determining module is specifically configured to: Determine a target angular frequency value of the AC voltage of the first inverter according to the first active power value, and determine an output voltage phase angle of the first inverter according to the target angular frequency value; A target induced electromotive force amplitude of the first inverter is generated according to the first reactive power value.

15. An oscillation suppression system, characterized in that: The oscillation suppression system includes an oscillation suppression subsystem and a towing subsystem; The oscillation suppression subsystem includes M groups of first inverters with support functions, M groups of power supply modules and M groups of first transformers, where M is a positive integer; wherein the first inverters correspond one to one with the power supply modules and the first transformers; Among the M groups of power supply modules, each group of power supply modules is connected to a corresponding group of first transformers through a corresponding group of first inverters, and each group of power supply modules is connected to a common connection point with a corresponding group of first transformers; The power supply module is used to supply power to the corresponding first inverter; In the M groups of first inverters, each group of first inverters comprises a controller as claimed in any one of claims 11 to 13; The pair-drag subsystem includes N groups of first rectifiers, N groups of second inverters and N groups of second transformers, where N is a positive integer; wherein the first rectifiers correspond to the second inverters and the second transformers respectively on a one-to-one basis; Among the N groups of first rectifiers, each group of first rectifiers is connected to a corresponding group of second transformers through a corresponding group of second inverters, and each group of first rectifiers and a corresponding group of second transformers are respectively connected to the common connection point; The first rectifier is used to supply power to its corresponding second inverter.

16. The system according to claim 15, characterized in that The power supply module includes at least one of an independent DC source, a maximum power point tracking input side AD / DC module in a string inverter, and an inverter operating in four quadrants; And / or, the first inverter includes at least one of a single-stage / two-stage string inverter, a centralized inverter and an energy storage converter.

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