Inverter controller, inverter grid-connected structure and grid low-frequency oscillation suppression method

Abstract

The present invention discloses an inverter controller, an inverter grid-connected structure and a method for suppressing low-frequency oscillation of a power grid. The inverter controller includes a power terminal voltage calculation module, a reactive link modulation voltage amplitude calculation module, an active link modulation voltage phase calculation module and a PWM modulation module. An active power regulation module is also attached to the active link. The proposed controller can analyze the interaction between the components of VSG transient energy through the attached active power regulation module, and thus adjust the reference power of the VSG active link based on this to reduce the interaction of internal energy, so as to improve the low-frequency oscillation suppression capability of the inverter grid-connected system.

Description

Technical Field

[0001] The present invention relates to the field of power electronic inverter grid-connected control, and in particular to an inverter controller, an inverter grid-connected structure and a method for suppressing low-frequency oscillation of a power grid. Background Art

[0002] Regional grid interconnection has become a development trend of the power system. Grid interconnection is conducive to the delivery of new energy power generation (photovoltaic power generation, wind power generation, etc.) and is also conducive to improving energy utilization efficiency. With the improvement of the degree of grid interconnection, the penetration rate of distributed energy, electric vehicles and other energy storage devices will also leap to a new level. Generally, the power generation devices of distributed power sources and the charging and discharging devices of electric vehicles are mainly connected to the grid through power electronic devices. The advantages are flexible control methods and fast response speed, but the power electronic devices in the traditional power control mode lack inertia and damping. When a large number of power electronic devices are connected to the grid, low-frequency oscillation will occur in the grid, threatening the safe and stable operation of the grid.

[0003] In view of this, this application is hereby filed. Summary of the invention

[0004] The technical problem to be solved by the present invention is: how to suppress the low-frequency oscillation of the power grid when a large number of power electronic devices are connected to the power grid. The purpose is to provide an inverter controller, an inverter grid-connected structure and a method for suppressing low-frequency oscillation of the power grid. On the basis of the VSG control strategy, by reducing the interaction between the components of VSG transient energy, the power system can absorb more transient energy, thereby suppressing the low-frequency oscillation of the power grid and ensuring the safe and stable operation of the power system.

[0005] The present invention is achieved through the following technical solutions:

[0006] First, the present invention proposes an inverter controller, including: a power and terminal voltage calculation module, a reactive link modulation voltage amplitude calculation module, an active link modulation voltage phase calculation module, an active power regulation module and a PWM modulation module; the input end of the power and terminal voltage calculation module is connected to the measured values ​​of three voltages and three-phase currents at the output end of the inverter, and the output end is connected to the input ends of the reactive link modulation voltage amplitude calculation module and the active link modulation voltage phase calculation module; the input end of the active power regulation module obtains the VSG active power increment, and the output end is connected to the input end of the active link modulation voltage phase calculation module; the output ends of the reactive link modulation voltage amplitude calculation module and the active link modulation voltage phase calculation module are connected to the input end of the PWM regulation module, and the output end of the PWM regulation module outputs a PWM control signal for driving the inverter to suppress low-frequency oscillation of the power grid.

[0007] The present invention is based on the VSG control strategy. According to the definition of transient energy flow, the transient energy flow of VSG and its various components (potential energy component, damping component and kinetic energy component of transient energy) are first calculated, and the interaction between the components is analyzed, and it is concluded that the interaction of the components in the transient energy flow is mainly concentrated between the potential energy component and the damping component. If the interaction between the potential energy component and the damping component can be reduced, the stability of the VSG grid-connected system can be improved from the perspective of energy, thereby better suppressing the low-frequency oscillation of the power system. Therefore, an inverter controller proposed by the present invention is added with an active power regulation module to optimize the damping component, and the main factor affecting the change rate of the damping component (the increment of active power relative to the steady-state value of active power) is used as input, determined by logical judgment and active power regulation reference value, and combined with the active power output by the power and terminal voltage calculation module, the inverter modulation wave phase is calculated in the active link modulation voltage phase calculation module. At the same time, the reactive power output by the power and terminal voltage calculation module and the output terminal voltage amplitude are used to calculate the modulation voltage amplitude in the reactive link modulation voltage amplitude calculation module to obtain the modulation voltage amplitude. Finally, the PWM modulation module is used to generate a PWM control signal according to the modulation voltage amplitude and the inverter modulation wave phase to drive the inverter, thereby improving the low-frequency oscillation suppression capability of the inverter grid-connected system and ensuring the safe and stable operation of the power system.

[0008] As a further description of the present invention, the inverter controller also includes a dq inverse transformation module, which is used to obtain a modulated voltage signal after dq inverse transformation of the reactive link modulation voltage amplitude calculation result and the active link phase calculation result. The input end of the dq inverse transformation module is connected to the output end of the reactive link modulation voltage amplitude calculation module and the active link modulation voltage phase calculation module, and the output end of the dq inverse transformation module is connected to the input end of the PWM regulation module.

[0009] As a further description of the present invention, the power and terminal voltage calculation module includes: a voltage dq conversion unit, a current dq conversion unit, a power calculation unit and a terminal voltage amplitude calculation unit; the input end of the voltage dq conversion unit is connected to the three-phase voltage of the inverter, the input end of the current dq conversion unit is connected to the three-phase current of the inverter, the output end of the voltage dq conversion unit is connected to the input end of the terminal voltage amplitude calculation unit, the output end of the current dq conversion unit is connected to the input end of the power calculation unit, and the dq rotation coordinate system angle position inputs of the voltage dq conversion unit and the current dq conversion unit are both the phase angle of the inverter modulation voltage.

[0010] As a further description of the present invention, the reactive link modulation voltage amplitude calculation module includes: a first subtractor, a third subtractor, a first gain operator and a first integral operator connected in sequence, and a second subtractor and a reactive droop controller connected in sequence; the input end of the first subtractor is connected to the output end of the terminal voltage amplitude calculation unit and receives the inverter terminal voltage setting value; the input end of the second subtractor is connected to the output reactive power output end of the power calculation unit and receives the inverter output reactive power setting value; the output end of the reactive droop controller is connected to the input end of the third subtractor; the first integral operator outputs the reactive link modulation voltage amplitude.

[0011] As a further description of the present invention, the active link modulation voltage phase calculation module includes: a fourth subtractor, an active droop controller, a fifth subtractor, a second gain operator, a second integrator, a multiplier and a third integrator connected in sequence, and a sixth subtractor and a third gain operator connected in sequence; the input end of the fourth subtractor is connected to the active power output end of the power calculation unit and receives the inverter output active power setting value; the input end of the sixth subtractor is connected to the output end of the second integrator and receives the input fixed value; the output end of the third gain operator is connected to the input end of the fifth subtractor; the third integrator outputs the active link modulation voltage phase.

[0012] As a further description of the present invention, the active power regulation module includes: a comparator and an active power regulation reference value generator connected in sequence; the input end of the comparator obtains the VSG active power increment; the output end of the active power regulation reference value generator is connected to the input end of the fourth subtraction operator.

[0013] Then, the present invention proposes an inverter grid-connected structure, including the above-mentioned inverter controller, inverter, LC filter, transmission line and drive circuit. The input end of the inverter controller is connected to the terminal voltage and current measurement output end of the inverter, and the output end of the inverter controller is connected to the modulation signal input end of the inverter. The input end of the LC filter is connected to the output end of the inverter, the output end of the LC filter is connected to the input end of the transmission line, and the output end of the transmission line is connected to the grid side; the input end of the inverter controller is connected between the LC filter and the transmission line; the drive circuit is connected between the output end of the inverter controller and the input end of the inverter.

[0014] The three-phase voltage and three-phase current of the inverter-side LC filter are input to the inverter controller, and after analysis and calculation, a PWM control signal is output to the drive circuit, which drives the inverter to realize the inverter function. The DC voltage output from the DC side is connected to the power grid after passing through the inverter, LC filter and transmission line.

[0015] Finally, the present invention proposes a method for suppressing low-frequency oscillation of a power grid, comprising the following steps:

[0016] Obtain the three-phase voltage and three-phase current of the inverter;

[0017] The power and terminal voltage calculation module calculates the output terminal voltage amplitude of the inverter according to the three-phase voltage, and calculates the output active power and output reactive power of the inverter according to the three-phase current;

[0018] The reactive link modulation voltage amplitude calculation module calculates the modulation voltage amplitude according to the output terminal voltage amplitude and the output reactive power;

[0019] According to the VSG transient energy flow model, the change rate of the damping component in the VSG transient energy flow is analyzed and obtained;

[0020] The active power regulation module regulates the change rate of the damping component and outputs an active power regulation reference value;

[0021] The active link modulation voltage phase calculation module calculates the inverter modulation wave phase according to the output active power and the active power adjustment reference value;

[0022] The PWM modulation module generates a PWM control signal according to the modulation voltage amplitude and the inverter modulation wave phase, which is used to drive the inverter to suppress low-frequency oscillation of the power grid.

[0023] As a further description of the present invention, the method for obtaining the active power regulation reference value includes the following steps:

[0024] Obtaining the increment △P of the output active power P of the inverter relative to the active power steady-state value P0;

[0025] Set the upper threshold value △P of the increment △P up and the lower threshold △P down ;

[0026] When the increment ΔP is greater than the upper threshold ΔP up When the active power adjustment reference value is set to:

[0027] When the increment ΔP is less than the lower threshold ΔP down When the active power adjustment reference value is set to:

[0028] In the formula, is the initial active power reference value; Kp1 and Kp2 are the active power reference value adjustment coefficients.

[0029] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0030] An inverter controller, an inverter grid-connected structure and a method for suppressing low-frequency oscillations of a power grid provided in an embodiment of the present invention can reduce the interaction between the components of VSG transient energy, so that it helps the system absorb more transient energy, thereby improving the ability of the inverter grid-connected VSG to suppress low-frequency oscillations of the power system; a method is proposed to achieve stable operation of the inverter grid-connected power system. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the technical solutions of the exemplary embodiments of the present invention, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without paying creative work.

[0032] Figure 1 A schematic diagram of the structure of an inverter controller provided in Embodiment 1 of the present invention;

[0033] Figure 2 A schematic diagram of an inverter grid-connected structure proxy topology structure provided in Embodiment 2 of the present invention;

[0034] Figure 3 A correction curve diagram of active power reference value in the low-frequency oscillation suppression process provided by Embodiment 3 of the present invention;

[0035] Figure 4 This is a comparison diagram of the low-frequency oscillation of the system before and after the controller provided in Example 3 of the present invention is activated.

[0036] Marks and corresponding parts names in the attached drawings:

[0037] 1-power and terminal voltage calculation module, 2-reactive link modulation voltage amplitude calculation module, 3-active link modulation voltage phase calculation module, 4-active power regulation module, 5-PWM modulation module, 6-dq inverse transformation module, 11-voltage dq transformation unit, 12-current dq transformation unit, 13-power calculation unit, 14-terminal voltage amplitude calculation unit, 21-first subtraction operator, 22-second subtraction operator, 23-third subtraction operator, 24-reactive droop controller, 25 -first gain operator, 26-first integrator, 31-fourth subtraction operation, 32-active power droop controller, 33-fifth subtraction operator, 34-second gain operator, 35-second integrator, 36-multiplier, 37-third integrator, 38-sixth subtraction operator, 39-third gain operator, 41-comparator, 42-active power regulation reference value generator, 51-inverter, 52-LC filter, 53-transmission line, 54-drive circuit. DETAILED DESCRIPTION

[0038] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with embodiments and drawings. The exemplary embodiments of the present invention and their description are only used to explain the present invention and are not intended to limit the present invention.

[0039] In the following description, a large number of specific details are set forth in order to provide a thorough understanding of the present invention. However, it is apparent to one of ordinary skill in the art that these specific details are not necessarily employed to practice the present invention. In other embodiments, in order to avoid obscuring the present invention, well-known structures, circuits, materials, or methods are not specifically described.

[0040] Throughout the specification, references to "one embodiment," "an embodiment," "an example," or "an example" mean that a particular feature, structure, or characteristic described in conjunction with the embodiment or example is included in at least one embodiment of the present invention. Therefore, the phrases "one embodiment," "an embodiment," "an example," or "an example" appearing in various places throughout the specification do not necessarily all refer to the same embodiment or example. In addition, particular features, structures, or characteristics may be combined in one or more embodiments or examples in any suitable combination and / or sub-combination. In addition, it will be appreciated by those of ordinary skill in the art that the figures provided herein are for illustrative purposes and that the figures are not necessarily drawn to scale. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0041] In the description of the present invention, the directions or positional relationships indicated by terms such as “front”, “rear”, “left”, “right”, “up”, “down”, “vertical”, “horizontal”, “high”, “low”, “inside” and “outside” are based on the directions or positional relationships shown in the accompanying drawings and are only for the convenience of describing the present invention and simplifying the description. They do not indicate or imply that the device or element referred to must have a specific direction, be constructed and operated in a specific direction. Therefore, they should not be understood as limiting the scope of protection of the present invention.

[0042] Example 1

[0043] In view of the lack of inertia and damping of power electronic equipment in traditional power control mode, when a large number of power electronic equipment are connected to the power grid, low-frequency oscillation will occur in the power grid, threatening the safe and stable operation of the power grid. This embodiment first calculates the transient energy flow of VSG and its various components (potential energy component, damping component and kinetic energy component of transient energy) according to the definition of transient energy flow; then analyzes the interaction between the components, and concludes that the interaction between the components in the transient energy flow is mainly concentrated between the potential energy component and the damping component; finally, the analysis concludes that if the interaction between the potential energy component and the damping component can be reduced, the stability of the VSG grid-connected system can be improved from the perspective of energy, thereby better suppressing the low-frequency oscillation of the power system.

[0044] Based on the above analysis, this embodiment provides Figure 1 An inverter controller shown includes: a power and terminal voltage calculation module 1, a reactive link modulation voltage amplitude calculation module 2, an active link modulation voltage phase calculation module 3, an active power regulation module 4 and a PWM modulation module 5; the input end of the power and terminal voltage calculation module 1 is connected to the measured values ​​of the three voltages and three-phase currents at the output end of the inverter, and the output end is connected to the input ends of the reactive link modulation voltage amplitude calculation module 2 and the active link modulation voltage phase calculation module 3; the input end of the active power regulation module 4 obtains the VSG active power increment, and the output end is connected to the input end of the active link modulation voltage phase calculation module 3; the output ends of the reactive link modulation voltage amplitude calculation module 2 and the active link modulation voltage phase calculation module 3 are connected to the input end of the PWM regulation module, and the output end of the PWM regulation module outputs a PWM control signal for driving the inverter to suppress low-frequency oscillation of the power grid.

[0045] The inverter controller optimizes the damping component by adding an active power adjustment module 4, takes the main factor affecting the change rate of the damping component (the increment of active power relative to the steady-state value of active power) as input, determines the active power adjustment reference value through logical judgment, and calculates the inverter modulation wave phase in the active link modulation voltage phase calculation module 3 in combination with the active power output by the power and terminal voltage calculation module 1. At the same time, the reactive power output by the power and terminal voltage calculation module 1 and the output terminal voltage amplitude are used to obtain the modulation voltage amplitude in the reactive link modulation voltage amplitude calculation module 2. Finally, the PWM modulation module 5 is used to generate a PWM control signal according to the modulation voltage amplitude and the inverter modulation wave phase, which is used to drive the inverter, thereby improving the low-frequency oscillation suppression capability of the inverter grid-connected system and ensuring the safe and stable operation of the power system.

[0046] Furthermore, the inverter controller also includes a dq inverse transformation module 6, which is used to obtain a modulated voltage signal after dq inverse transformation of the reactive link modulation voltage amplitude calculation result and the active link phase calculation result. The input end of the dq inverse transformation module 6 is connected to the output end of the reactive link modulation voltage amplitude calculation module 2 and the active link modulation voltage phase calculation module 3, and the output end of the dq inverse transformation module 6 is connected to the input end of the PWM adjustment module.

[0047] The internal circuit structures of the power and terminal voltage calculation module 1, the reactive link modulation voltage amplitude calculation module 2, the active link modulation voltage phase calculation module 3, the active power regulation module 4 and the dq inverse transformation module 6 in the above-mentioned inverter controller are described below respectively.

[0048] in,

[0049] The power and terminal voltage calculation module 1 includes: a voltage dq conversion unit 11, a current dq conversion unit 12, a power calculation unit 13 and a terminal voltage amplitude calculation unit 14; the input end of the voltage dq conversion unit 11 is connected to the three-phase voltage of the inverter, the input end of the current dq conversion unit 12 is connected to the three-phase current of the inverter, the output end of the voltage dq conversion unit 11 is connected to the input end of the terminal voltage amplitude calculation unit 14, the output end of the current dq conversion unit 12 is connected to the input end of the power calculation unit 13, and the dq rotation coordinate system angle position inputs of the voltage dq conversion unit 11 and the current dq conversion unit 12 are both the phase angle of the inverter modulation voltage.

[0050] The reactive link modulation voltage amplitude calculation module 2 includes: a first subtractor 21, a third subtractor 23, a first gain operator 25 and a first integral operator 26 connected in sequence, and a second subtractor 22 and a reactive droop controller 24 connected in sequence; the input end of the first subtractor 21 is connected to the output end of the terminal voltage amplitude calculation unit 14 and receives the inverter terminal voltage setting value; the input end of the second subtractor 22 is connected to the output reactive power output end of the power calculation unit 13 and receives the inverter output reactive power setting value; the output end of the reactive droop controller 24 is connected to the input end of the third subtractor 23; the first integral operator 26 outputs the reactive link modulation voltage amplitude.

[0051] The active link modulation voltage phase calculation module 3 includes: a fourth subtractor 31, an active droop controller 32, a fifth subtractor 33, a second gain operator 34, a second integrator 35, a multiplier 36 and a third integrator 37 connected in sequence, and a sixth subtractor 38 and a third gain operator 39 connected in sequence; the input end of the fourth subtractor 31 is connected to the active power output end of the power calculation unit 13 and receives the inverter output active power setting value; the input end of the sixth subtractor 38 is connected to the output end of the second integrator 35 and receives the input fixed value; the output end of the third gain operator 39 is connected to the input end of the fifth subtractor 33; the third integrator 37 outputs the active link modulation voltage phase.

[0052] The active power regulation module 4 includes: a comparator 41 and an active power regulation reference value generator 42 connected in sequence; the input end of the comparator 41 obtains the VSG active power increment; the output end of the active power regulation reference value generator 42 is connected to the input end of the fourth subtraction operator 31.

[0053] Example 2

[0054] Based on Example 1, the present invention proposes a method as follows Figure 2The grid-connected structure of the inverter 51 shown includes the above-mentioned inverter controller, the inverter 51, the LC filter 52, the transmission line 53 and the drive circuit 54. The input end of the inverter controller is connected to the terminal voltage and current measurement output end of the inverter 51, and the output end of the inverter controller is connected to the modulation signal input end of the inverter 51. The input end of the LC filter 52 is connected to the output end of the inverter 51, and the output end of the LC filter 52 is connected to the input end of the transmission line 53, and the output end of the transmission line 53 is connected to the grid side; the input end of the inverter controller is connected between the LC filter 52 and the transmission line 53; the drive circuit 54 is connected between the output end of the inverter controller and the input end of the inverter 51.

[0055] The three-phase voltage and three-phase current of the LC filter 52 at the inverter 51 end are input to the inverter controller, and after analysis and calculation, a PWM control signal is output to the drive circuit 54, and the drive circuit 54 drives the inverter 51 to realize the inverter function. The DC voltage output from the DC side is connected to the power grid after passing through the inverter 51, the LC filter 52 and the transmission line 53.

[0056] Example 3

[0057] This embodiment proposes a method for suppressing low-frequency oscillation of a power grid. Based on the VSG control strategy, the method reduces the interaction between various components of VSG transient energy, so that the power system can absorb more transient energy, thereby suppressing the low-frequency oscillation of the power grid and ensuring the safe and stable operation of the power system. The method specifically includes the following steps:

[0058] Step 1: Measure the three-phase voltage e from the DC side to the LC filter at the inverter end a 、e b 、e c and three-phase current i a 、i b 、i c ; Three-phase voltage e a 、e b 、e c and three-phase current i a 、i b 、i c After entering the power and terminal voltage calculation module, the voltage dq conversion unit decomposes the three-phase voltage e a 、e b 、e c Transformed to the dq axis of the synchronous rotating coordinate system, the dq axis component of the voltage is u a and u b Similarly, the current dq conversion unit decomposes the three-phase current i a 、i b 、ic Transformed to the dq axis of the synchronous rotating coordinate system, the dq axis component of the voltage is i a and i b .

[0059] Step 2: In the power and terminal voltage calculation module, the terminal voltage amplitude calculation unit calculates the value of the terminal voltage according to the u a and u b The output voltage amplitude of the inverter is calculated according to the u a 、u b and i a 、i b The output active power P and output reactive power Q of the inverter are calculated. The calculation formulas for the output voltage amplitude, output active power and output reactive power are as follows: (1), where P is the active power output by the inverter, Q is the reactive power output by the inverter, and E t is the voltage amplitude at the inverter terminal.

[0060] Step 3: The reactive link modulation voltage amplitude calculation module calculates the output voltage amplitude E according to the output voltage amplitude E t and the output reactive power Q, the modulation voltage amplitude E is calculated q , the calculation formula is: E q =∫K e [(E * -E t )-n(QQ * )]dt(2), where E * is the set value of the inverter terminal voltage; Q * is the setting value of the inverter reactive power; K e is the amplification gain; n is the droop coefficient of the reactive voltage link; E q is the q-axis component of the inverter modulation wave signal, and the 0-axis and d-axis components of the modulation wave signal are both 0.

[0061] Step 4: According to the VSG transient energy flow model, the change rate of the damping component in the VSG transient energy flow is analyzed and obtained.

[0062] The specific analysis process is as follows:

[0063] According to the definition of transient energy flow, the transient energy flow of VSG and its components are calculated. The expression of energy function is:

[0064] Where W IN is the energy flowing into the port, E t and θ are the amplitude and phase values ​​of the terminal voltage, and P and Q represent the output active power and reactive power. x ,I y 、Vx 、V y are the components of the generator current and voltage in the xy coordinate system, I d ,I q 、V d 、V q They respectively represent the components of the generator current and voltage converted to the dq coordinate system through dq transformation.

[0065] The above formula (3) can be divided into two parts: Among them, W e Related to the reactive link, W g Related to the active link.

[0066] The energy W flowing into the port IN Applied to VSG, W e It can be further expanded to:

[0067] Among them, E q is the inverter output voltage, R s is the filter resistance, and X1 is the filter reactance. S The value is very small, and in the dynamic process, E q And it can quickly reach a steady state, that is, I d dE q ≈0, so the s The term is ignored, and the final simplified result of (5) above is obtained.

[0068] Since the research object is transient energy flow, it is necessary to study the change of energy in the transient process. However, since the amplitude of current change in the transient process is small, in this embodiment, W e Not considered.

[0069] Similarly, W g It can be further expanded to: The calculation formula combining the virtual angular frequency ω of the active link inverter and the phase angle δ of the modulation wave is:

[0070] Can get

[0071] (7) where J is the virtual moment of inertia of the inverter; m is the active droop coefficient; P * is the set value of the inverter output active power; ω * K is the setting value of the inverter output angular frequency; d is the virtual damping coefficient of the inverter; δ is the phase of the inverter modulation wave; ω0 is the angular frequency reference value.

[0072] Refer to W gPart of the expression (6) is used to derive W in the transient process g The variables are shown in formula (9):

[0073]

[0074] Referring to the synchronous generator, the components in equation (9) are defined as the potential energy components W of the transient energy. PE , damping component W D and the kinetic energy component W KE , as shown in formula (10):

[0075] Since the change of △ω is usually small, the kinetic energy component occupies a small proportion in the total transient energy flow. Therefore, the interaction of components in the transient energy flow is mainly concentrated between the potential energy component and the damping component. If the interaction between the potential energy component and the damping component can be reduced, the stability of the VSG grid-connected system can be improved from the energy perspective, thereby better suppressing the low-frequency oscillation of the power system. Therefore, the additional active power regulation module selects the damping component as the optimization object, that is, reducing the damping component W D changes.

[0076] To W D Find the inverted W D The rate of change is:

[0077] Next, the small signal analysis method is used to analyze the VSG active link to obtain:

[0078]

[0079] Where △P represents the increment of active power output P during oscillation relative to the steady-state value of active power P0, △ω represents the increment of angular frequency output ω relative to the steady-state value of active power ω0 during oscillation; for the virtual moment of inertia J and virtual damping coefficient K of the VSG active link d , its design condition meets the requirement that J is much smaller than K d , so J / K d The term can be ignored, that is, in expression (12), △P and △ω can be regarded as proportional links; as in the expression shown.

[0080] Substituting expression (13) into expression (12) yields: It is the expression of the rate of change of the damping component in the transient energy flow of VSG.

[0081] Step 5: The active power regulation module regulates the change rate of the damping component and outputs an active power regulation reference value.

[0082] From expression (14), it can be seen that the damping component WD The rate of change of W is related to ω and △P. The effect caused by the change of ω can be ignored. D The rate of change of is mainly affected by △P. Therefore, in order to make W D The rate of change of is reduced, therefore, the output active power regulation reference value of the additional active power regulation module can be determined in the following manner:

[0083] When △P is greater than 0 and greater than the set upper threshold △P up , in order to reduce W D The rate of change of active power needs to be increased * To reduce △P;

[0084] When △P is less than 0 and less than the set upper threshold △P down , in order to reduce W D The rate of change of active power needs to be reduced * To reduce △P;

[0085] Therefore, the output active power regulation reference value can be determined according to the following expression:

[0086]

[0087] In the formula, is the initial active power reference value; K p1 and K p2 is the active power reference value adjustment coefficient, its value is positive; △P up is the upper limit of the set threshold, and its value is positive; △P down It is the lower limit of the set threshold, and its value is negative.

[0088] Step 6: The active link modulation voltage phase calculation module calculates the active power P according to the output active power P and the active power adjustment reference value P * , the inverter modulation wave phase is calculated according to expression (7).

[0089] Step 7: The reactive link modulation voltage amplitude calculation result and the active link phase calculation result are transformed by dq inverse transformation to obtain the modulation voltage signal u a 、u b 、u c , and then generate PWM control signals according to the PWM algorithm to drive the three-phase inverter bridge to realize the inverter function.

[0090] It should be noted that, in this embodiment,

[0091] The rated voltage of the inverter is 380V, the rated frequency is 50Hz, and the rated power is 50kW. Correspondingly, the rated voltage of the inverter DC terminal is U dc=600V. The power electronic device of the three-phase full-bridge inverter circuit is IGBT (Insulated Gate Bipolar Transistor), model Infineon F150R12RT4. The PWM carrier frequency is 10kHz. The inductance L of the LC filter is 2.8mH and the capacitance is 40μF. The control parameters related to the active link of the virtual synchronous generator are selected as m=0.01, virtual moment of inertia J=0.1, and virtual damping coefficient K d =1.0, initial reference active power The upper threshold value △P is set up =0.01, the lower limit of the threshold is set to △P down =-0.01, active power reference value adjustment coefficient K p1 =0.8, K p2 =0.8. The changes in the active power reference value correction during the control process are as follows: Figure 3 As shown in the figure, the suppression effect of the low-frequency oscillation of the system before and after the controller is applied is as follows: Figure 4 As shown. It can be seen that under the action of this controller, the low-frequency oscillation of the system is well suppressed.

[0092] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. An inverter controller, characterized in that: include: A power and terminal voltage calculation module (1), a reactive link modulation voltage amplitude calculation module (2), an active link modulation voltage phase calculation module (3), an active power regulation module (4) and a PWM modulation module (5); the input end of the power and terminal voltage calculation module (1) is connected to the measured values ​​of the three-phase voltage and three-phase current at the output end of the inverter, and the output end is connected to the input ends of the reactive link modulation voltage amplitude calculation module (2) and the active link modulation voltage phase calculation module (3); the input end of the active power regulation module (4) obtains the VSG active power increment, and the output end is connected to the active link modulation voltage phase calculation module (4) The input end of the modulation voltage phase calculation module (3) is used to determine the active power regulation reference value based on the increment of the active power relative to the active power steady-state value, so that the active link modulation voltage phase calculation module (3) calculates the inverter modulation wave phase according to the active power regulation reference value; the output ends of the reactive link modulation voltage amplitude calculation module (2) and the active link modulation voltage phase calculation module (3) are connected to the input end of the PWM modulation module (5), and the output end of the PWM modulation module (5) outputs a PWM control signal for driving the inverter to suppress low-frequency oscillation of the power grid.

2. An inverter controller according to claim 1, characterized in that: It comprises a dq inverse transformation module (6), the input end of the dq inverse transformation module (6) is connected to the output ends of the reactive link modulation voltage amplitude calculation module (2) and the active link modulation voltage phase calculation module (3), and the output end of the dq inverse transformation module (6) is connected to the input end of the PWM modulation module (5).

3. The inverter controller according to claim 1, characterized in that: The power and terminal voltage calculation module (1) comprises: a voltage dq conversion unit (11), a current dq conversion unit (12), a power calculation unit (13) and a terminal voltage amplitude calculation unit (14); the input end of the voltage dq conversion unit (11) is connected to the three-phase voltage of the inverter, the input end of the current dq conversion unit (12) is connected to the three-phase current of the inverter, the output end of the voltage dq conversion unit (11) is connected to the input end of the terminal voltage amplitude calculation unit (14), the output end of the current dq conversion unit (12) is connected to the input end of the power calculation unit (13), and the dq rotation coordinate system angle position inputs of the voltage dq conversion unit (11) and the current dq conversion unit (12) are both the phase angle of the inverter modulation voltage.

4. An inverter controller according to claim 3, characterized in that: The reactive link modulation voltage amplitude calculation module (2) comprises: a first subtractor (21), a third subtractor (23), a first gain operator (25) and a first integral operator (26) connected in sequence, and a second subtractor (22) and a reactive droop controller (24) connected in sequence; the input end of the first subtractor (21) is connected to the output end of the terminal voltage amplitude calculation unit (14) and receives the inverter terminal voltage setting value; the input end of the second subtractor (22) is connected to the output reactive power output end of the power calculation unit (13) and receives the inverter output reactive power setting value; the output end of the reactive droop controller (24) is connected to the input end of the third subtractor (23); and the first integral operator (26) outputs the reactive link modulation voltage amplitude.

5. The inverter controller according to claim 3, characterized in that: The active link modulation voltage phase calculation module (3) comprises: a fourth subtractor (31), an active droop controller (32), a fifth subtractor (33), a second gain operator (34), a second integral operator (35), a multiplier (36) and a third integral operator (37) connected in sequence, and a sixth subtractor (38) and a third gain operator (39) connected in sequence; the input end of the fourth subtractor (31) is connected to the active power output end of the power calculation unit (13) and receives the inverter output active power setting value; the input end of the sixth subtractor (38) is connected to the output end of the second integral operator (35) and receives the input fixed value; the output end of the third gain operator (39) is connected to the input end of the fifth subtractor (33); and the third integral operator (37) outputs the active link modulation voltage phase.

6. The inverter controller according to claim 5, characterized in that: The active power regulation module (4) comprises: a comparator (41) and an active power regulation reference value generator (42) connected in sequence; the input end of the comparator obtains the VSG active power increment; the output end of the active power regulation reference value generator (42) is connected to the input end of the fourth subtraction operator (31).

7. An inverter grid-connected structure, characterized in that: include: An inverter controller and an inverter (51) as claimed in any one of claims 1 to 6; the input end of the inverter controller is connected to the terminal voltage and current measurement output end of the inverter (51), and the output end of the inverter controller is connected to the modulation signal input end of the inverter (51); the DC voltage output from the DC side is connected to the power grid after passing through the inverter (51).

8. The inverter grid-connected structure according to claim 7, characterized in that: include: An LC filter (52), a transmission line (53) and a drive circuit (54); the input end of the LC filter (52) is connected to the output end of the inverter (51), the output end of the LC filter (52) is connected to the input end of the transmission line (53), and the output end of the transmission line (53) is connected to the power grid side; the input end of the inverter controller is connected between the LC filter (52) and the transmission line (53); and the drive circuit (54) is connected between the output end of the inverter controller and the input end of the inverter (51).

9. A method for suppressing low-frequency oscillation of a power grid of an inverter controller according to any one of claims 1 to 6, characterized in that: The following steps are involved: Obtain the three-phase voltage and three-phase current of the inverter; The power and terminal voltage calculation module calculates the output terminal voltage amplitude of the inverter according to the three-phase voltage, and calculates the output active power and output reactive power of the inverter according to the three-phase current; The reactive link modulation voltage amplitude calculation module calculates the modulation voltage amplitude according to the output terminal voltage amplitude and the output reactive power; According to the VSG transient energy flow model, the change rate of the damping component in the VSG transient energy flow is analyzed and obtained; The active power regulation module regulates the change rate of the damping component and outputs an active power regulation reference value; The active link modulation voltage phase calculation module calculates the inverter modulation wave phase according to the output active power and the active power adjustment reference value; The PWM modulation module generates a PWM control signal according to the modulation voltage amplitude and the inverter modulation wave phase, which is used to drive the inverter to suppress low-frequency oscillation of the power grid.

10. A method for suppressing low-frequency oscillation of a power grid according to claim 9, characterized in that: The method for obtaining the active power regulation reference value comprises the following steps: Obtaining the increment △P of the output active power P of the inverter relative to the active power steady-state value P0; Set the upper threshold value △P of the increment △P up and the lower threshold △P down ; When the increment ΔP is greater than the upper threshold ΔP up When the active power adjustment reference value is set to: When the increment ΔP is less than the lower threshold ΔP down When the active power adjustment reference value is set to: In the formula, is the initial active power reference value; Kp1 and Kp2 are the active power reference value adjustment coefficients.

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