Net-following inverter phase locking method and system based on composite voltage regulation

Abstract

The invention discloses a grid-following type inverter phase locking method and system based on composite voltage regulation, and belongs to the technical field of inverter control, and the method comprises the steps: detecting the current of a power grid and the voltage of a grid-connected point, and obtaining the current of the power grid and the output voltage under a dq coordinate system through coordinate transformation; according to the output voltage and the power grid current under the dq coordinate system, the active power of the grid-following type inverter is obtained; obtaining the reference current of the output current according to the active power of the following grid type inverter; obtaining a transformation angle under the dq coordinate system according to an error between the output voltage and a voltage reference value; establishing a model of a composite synchronous dominant loop to obtain composite synchronous loop gain; the conversion angle and the sampling current are updated according to the composite synchronous loop gain; and a PWM signal is generated through the current regulator to drive the IGBT. According to the method provided by the invention, the composite voltage synchronous control of the grid-connected inverter can be realized, and the robustness of the grid-connected inverter under strong and weak power grids is remarkably improved.

Description

Technical Field

[0001] The present invention relates to the technical field of inverter control, and in particular to a grid-following inverter phase locking method and system based on composite voltage regulation. Background Art

[0002] Distributed power generation systems based on renewable energy sources such as wind and solar energy are developing on a large scale. Grid-connected inverters, as the energy conversion interface between distributed power generation units and the power grid, play a vital role in the safe, stable and efficient operation of distributed power generation systems. Centralized new energy power generation clusters are mostly located at the end of the power grid (such as the Northwest Wind and Solar Base), lacking conventional power sources such as thermal power and hydropower, and showing weak power grid characteristics. The grid impedance cannot be ignored and may vary over a wide range. The grid-following inverter achieves synchronization with the grid voltage through a phase-locked loop. In a weak power grid, the phase-locked loop and the grid impedance are interactively coupled, which may cause synchronization stability problems. Summary of the invention

[0003] The purpose of this application is to overcome the defects of the prior art and provide a phase-locking method and system for a grid-following inverter based on composite voltage regulation, aiming to improve the stable operation of the grid-following inverter under a wide range of grid impedance.

[0004] In a first aspect, the present application provides a grid-following inverter phase locking method based on composite voltage regulation, comprising the following steps: Detect the grid current and perform coordinate transformation on the grid current to obtain dq The grid current in the coordinate system is dq The grid current in the coordinate system includes the d-axis grid current and the q-axis grid current; the grid connection point voltage is detected, and the grid connection point voltage is transformed into a coordinate system to obtain dq The output voltage in the coordinate system is dq The output voltage in the coordinate system includes the d-axis output voltage and the q-axis output voltage; according to dq The output voltage and grid current in the coordinate system are used to obtain the active power output by the grid-following inverter; Obtaining a reference current of a grid current according to the active power output by the grid-following inverter and the q-axis output voltage, wherein the reference current of the grid current includes a d-axis reference current and a q-axis reference current; The dq The output voltage in the coordinate system is compared with the corresponding output voltage reference value to obtain dq The error between the output voltage in the coordinate system and the corresponding output voltage reference value is obtained by passing the error through the phase-locked loop controller. dq Transformation angle in coordinate system; The model of the composite synchronous dominant loop is established to obtain the loop gain from the grid voltage phase angle to the grid-connected voltage phase angle, and the updated dq Transformation angle in coordinate system; The updated dq The transformed angle in the coordinate system is sent to the grid current coordinate transformation path to obtain a new sampling current, wherein the new sampling current includes a d-axis sampling current and a q-axis sampling current; The new sampling current and the error between the new sampling current and the reference current are sent to the current controller, and a PWM modulation signal is obtained through current regulation to realize the control of the grid-following inverter.

[0005] Optionally, the active power output by the grid-connected inverter is expressed as: Among them, P is the active power output by the grid-following inverter, is the d-axis output grid voltage, is the q-axis output voltage, i g_d is the d-axis grid current, i g_q is the q-axis grid current.

[0006] Optionally, the matrix expression of the reference current of the grid current is: in, i gref_d is the d-axis reference current of the grid current, i gref_q is the q-axis reference current of the grid current, is the active loop controller, is the voltage loop controller, P ref is the active power reference value, P is the active power output by the grid-following inverter, U ref_d is the d-axis output voltage reference value, U d is the d-axis output voltage The actual value of .

[0007] Optionally, the dq The output voltage in the coordinate system is compared with the voltage reference value to obtain dq The error between the output voltage and the voltage reference value in the coordinate system is obtained by passing the error through the phase-locked loop controller. dq Transformation angles in the coordinate system, including: The q-axis grid voltage is compared with the q-axis output voltage reference value to obtain a q-axis output voltage error, and the q-axis output voltage error is passed through a q-axis PI controller to obtain a q-axis angular frequency variation; Compare the d-axis grid voltage with the d-axis output voltage reference value to obtain a d-axis output voltage error, and pass the d-axis output voltage error through a d-axis PI controller to obtain a d-axis angular frequency variation; The q-axis angular frequency variation, the d-axis angular frequency variation, and the angular frequency rated value are added and multiplied by a Laplace integrator to obtain a phase angle of the output voltage.

[0008] Optionally, a model of the composite synchronous dominant loop is established to obtain the loop gain from the grid voltage phase angle to the grid-connected voltage phase angle, and an updated dq Transformation angles in the coordinate system, including: exist dq Establish the equivalent circuit of the grid-following inverter in the coordinate system; According to the equivalent circuit of the grid-following inverter, an LCL dynamic equation is obtained; Using the q-axis phase-locked loop controller, determine dq The rotation angular frequency of the coordinate system is dq The rotation angular frequency of the coordinate system transforms the grid voltage into dq In the coordinate system, the grid voltage is obtained dq Vector linearization expression, get the grid voltage dq Vector; According to the grid voltage dq Vector, get the simplified grid voltage; According to the simplified grid-connected voltage, a composite synchronous dominant loop gain transfer function is obtained; Using the composite synchronous dominant loop gain transfer function, the updated dq The transformation angle in the coordinate system.

[0009] Optionally, the grid voltage dq The vector linearization expression is: in, is the grid voltage amplitude, The grid voltage dq Vector V gdq With grid voltage dq Vector U dq The steady-state value of the power angle between is the linearized power angle small signal quantity, is the linearized grid voltage d Axis component, is the linearized grid voltage q Axis component.

[0010] Optionally, the composite synchronous dominant loop gain transfer function for: in, The composite synchronous dominant loop gain transfer function is d Axis component, The composite synchronous dominant loop gain transfer function is q Axis component.

[0011] Optionally, the dq Rotational frequency of the coordinate system The expression is: in, is the grid-connected angular frequency small signal quantity, is the angular frequency rating.

[0012] Optionally, the grid-connected angular frequency small signal quantity The expression is: in, for q Axis phase-locked loop transfer function, is the q-axis component of the grid-connected voltage, for q Axis PI controller, s is the Laplace operator.

[0013] In a second aspect, the present application further provides a grid-following inverter phase-locking system based on compound voltage regulation, wherein the grid-following inverter phase-locking system based on compound voltage regulation performs the steps of the grid-following inverter phase-locking method based on compound voltage regulation as described in any one of the first aspects, including: A data acquisition module is used to detect the grid current and the grid connection point voltage, and perform coordinate transformation on the grid current and the grid connection point voltage to obtain the grid current and the output voltage; A power calculation module, used to calculate the active power output by the grid-following inverter according to the grid current and output voltage; A reference current calculation module, used to determine a reference current of the output current according to the active power and output voltage output by the grid-following inverter; The angle conversion module is used to obtain the output voltage and the voltage reference value according to the output voltage. dq Transformation angle in coordinate system; The composite synchronous dominant loop and loop gain module is used to construct a composite synchronous dominant loop model. The composite synchronous dominant loop model is used to obtain the loop gain and the new dq Coordinate system transformation angle; The sampling current updating module is used to update the current according to the new dq The coordinate system transforms the angle and updates the sampled current; The PWM modulation module is used to obtain a PWM modulation signal according to a new sampling current to control the grid-following inverter.

[0014] The present application provides a grid-following inverter phase locking method and system based on composite voltage regulation, by introducing d The shaft voltage control tracks the voltage phase of the grid connection point in real time. Combined with the q-axis voltage error correction, a composite synchronous dominant loop model is constructed, which can dynamically adjust the rotation angular frequency of the dq coordinate system, effectively suppress the influence of the LCL filter resonance on the stability, and improve the anti-interference ability of the phase-locked loop under weak power grids; by establishing the loop gain, a balance between the bandwidth and stability of the phase-locked loop is achieved, which can not only ensure the phase-locked accuracy, but also enhance the system's robustness to changes in grid impedance.

[0015] In order to make the above features and advantages of the invention more obvious and easy to understand, embodiments are given below and described in detail with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the related technologies, the drawings required for use in the embodiments or the related technical descriptions are briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0017] Figure 1 A control block diagram of a grid-following inverter phase-locking method based on composite voltage regulation provided in one embodiment of the present application.

[0018] Figure 2 This is a flow chart of a grid-following inverter phase-locking method based on composite voltage regulation provided in one embodiment of the present application.

[0019] Figure 3 This is a flowchart of step S4 in a grid-following inverter phase locking method based on composite voltage regulation provided in one embodiment of the present application.

[0020] Figure 4 This is a flowchart of step S5 in a grid-following inverter phase locking method based on composite voltage regulation provided in one embodiment of the present application.

[0021] Figure 5 An equivalent circuit diagram of a grid-following inverter in a grid-following inverter phase-locking method based on composite voltage regulation provided in one embodiment of the present application.

[0022] Figure 6 A block diagram of a transfer function of a composite synchronous dominant loop in a grid-following inverter phase-locking method based on composite voltage regulation provided in one embodiment of the present application.

[0023] Figure 7 It is a graph of the amplitude-frequency characteristic of the frequency sweep verification of the closed-loop transfer function of the synchronous dominant loop of the grid-following inverter before improvement in the grid-following inverter phase-locking method based on composite voltage regulation provided in one embodiment of the present application.

[0024] Figure 8 It is a graph of the amplitude-frequency characteristic of the frequency sweep verification of the closed-loop transfer function of the synchronous dominant loop of the improved grid-following inverter based on compound voltage regulation in the phase-locking method of the grid-following inverter based on compound voltage regulation provided in one embodiment of the present application.

[0025] Fig. 9 This is a simulation waveform diagram of grid-connected voltage, current and frequency of a grid-connected inverter in a weak power grid before improvement in a grid-connected inverter phase-locking method based on composite voltage regulation provided in another embodiment of the present application.

[0026] Fig.10 This is a simulation waveform diagram of grid-connected voltage, current and frequency of an improved composite synchronous grid-following inverter in a weak power grid in a grid-following inverter phase-locking method based on composite voltage regulation provided in another embodiment of the present application.

[0027] Fig.11 This is a structural schematic diagram of a grid-following inverter phase-locked system based on composite voltage regulation provided in another embodiment of the present application. DETAILED DESCRIPTION

[0028] In order to make the purpose and technical solution of the embodiment of the present application clearer, the technical solution of the embodiment of the present application will be clearly and completely described in conjunction with the drawings of the embodiment of the present application. Obviously, the described embodiment is a part of the embodiment of the present application, not all of the embodiments. Based on the described embodiment of the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0029] Figure 1 The control block diagram of the grid-following inverter phase-locking method based on composite voltage regulation provided in this application is as follows: Figure 1It can be seen that the grid-connected inverter includes: a power module 1, a three-phase inverter bridge module 2, an LCL filter module 3, a public grid module 4, and a control module 5. Among them, the power module 1 is connected to the first end of the three-phase inverter bridge module 2, the second end of the three-phase inverter bridge module 2 is connected to the first end of the LCL filter module 3, the second end of the LCL filter module 3 is connected to the public grid module 4 through the grid connection point PCC, the input end of the control module 5 is connected to the grid connection point PCC and the third end of the LCL filter module 3, and the output end of the control module 5 is connected to the third end of the three-phase inverter bridge module 2.

[0030] As an example, the power supply module 1 may include a DC power supply V dc ; The three-phase inverter bridge module 2 may include a switch tube and a freewheeling diode; LCL The filter module 3 may include a filter resistor R f 、Filter inductor L f1 , L f2 and filter capacitors C ; The public grid module 4 may include a three-phase voltage source v g and equivalent grid impedance Z g , the equivalent grid impedance Z g By the grid resistance R g and grid inductance L g The controller module 5 may include a phase-locked loop controller, an output current controller, a capacitor current controller, an active loop controller, a voltage loop controller, a power calculation, and an abc / dq converter.

[0031] In one embodiment, see Figure 2 The present application provides a grid-following inverter phase-locking method based on compound voltage regulation. The grid-following inverter phase-locking method based on compound voltage regulation may include the following steps: step S1 to step S7.

[0032] Step S1: Detect the grid current and perform coordinate transformation on the grid current to obtain dq The grid current in the coordinate system is dq The grid current in the coordinate system includes the d-axis grid current and the q-axis grid current; the grid connection point voltage is detected, and the grid connection point voltage is transformed into a coordinate system to obtain dq The output voltage in the coordinate system is dq The output voltage in the coordinate system includes a d-axis output voltage and a q-axis output voltage.

[0033] Step S2: According to dq The output voltage and grid current in the coordinate system are used to obtain the active power output by the grid-following inverter.

[0034] Step S3: Obtain a reference current of the grid current according to the active power output by the grid-following inverter and the d-axis output voltage. The reference current of the grid current includes: d Axis reference current and q Axis reference current.

[0035] Step S4: dq The output voltage in the coordinate system is compared with the corresponding output voltage reference value to obtain dq The error between the output voltage in the coordinate system and the corresponding output voltage reference value is obtained by passing the error through the phase-locked loop controller. dq The transformation angle of the coordinate system.

[0036] Step S5: Establish a model of the composite synchronous dominant loop, obtain the loop gain from the grid voltage phase angle to the grid voltage phase angle, and obtain the updated dq The transformation angle in the coordinate system.

[0037] Step S6: Update the dq The transformed angle in the coordinate system is sent to the grid current coordinate transformation path to obtain a new sampling current. The new sampling current includes d Axis sampling current and q Axis sampling current.

[0038] Step S7: sending the new sampled current and the error between the new sampled current and the reference current to the current controller, obtaining a PWM modulation signal through current regulation, and realizing control of the grid-following inverter.

[0039] In the grid-following inverter phase-locking method based on composite voltage regulation of the present application, the coordinate transformation angle is corrected in real time by the phase-locked loop controller, which can effectively eliminate the grid-connected impact current; the reference current is calculated by the active power and the d-axis voltage to establish a direct power-current mapping relationship; by introducing the phase-locked loop d The shaft voltage control tracks the voltage phase of the grid-connected point in real time, generates the reference angle of the synchronous rotating coordinate system, and combines with the power calculation module to generate the reference signal of the current loop to realize the composite voltage synchronization control of the grid-connected inverter. It can achieve higher power density and lower loss while ensuring the stability of the power grid, and significantly improve the robustness of the grid-connected inverter under strong and weak power grids, which has significant engineering application value.

[0040] In step S1, see Figure 2 Step S1 in the embodiment of the present invention is to detect the grid current and to transform the grid current into a coordinate system. dqThe grid current in the coordinate system is dq The grid current in the coordinate system includes the d-axis grid current and the q-axis grid current; the grid connection point voltage is detected, and the grid connection point voltage is transformed into a coordinate system to obtain dq The output voltage in the coordinate system is dq The output voltage in the coordinate system includes a d-axis output voltage and a q-axis output voltage.

[0041] Specifically, the grid current is detected by a current sensor i g , for the grid current i g Perform coordinate transformation to obtain dq The grid current in the coordinate system is dq The grid current in the coordinate system includes the d-axis grid current i g_d and q-axis grid current i g_q .

[0042] Furthermore, the voltage sensor is used to detect the grid voltage. (ie output voltage ), for the output voltage Perform coordinate transformation to obtain dq The output voltage in the coordinate system is dq The output voltage in the coordinate system includes the d-axis output voltage and q-axis output voltage .

[0043] As an example, a synchronous sampling technique may be used to ensure that the current and voltage signals are phase aligned.

[0044] In step S2, see Figure 2 In step S2, according to dq The output voltage and grid current in the coordinate system are used to obtain the active power output by the grid-following inverter.

[0045] Specifically, according to dq D-axis output voltage in the coordinate system , q-axis output voltage , d-axis grid current i g_d and q-axis grid current i g_q , we can get the active power P output by the grid-following inverter. The expression is: in, for d Shaft output voltage, for q Shaft output voltage,i g_d for d Shaft grid current, i g_q for q Axis grid current.

[0046] In step S3, see Figure 2 In step S3, a reference current of the grid current is obtained according to the active power output by the grid-following inverter and the d-axis output voltage, wherein the reference current of the grid current includes d Axis reference current and q Axis reference current.

[0047] Specifically, according to the active power P, the d-axis output voltage , d-axis output voltage reference value U ref_d , Active power reference value P ref , obtain the reference current of the grid current, the reference current of the grid current includes d Axis reference current i gref_d and q Axis reference current i gref_q .

[0048] As an example, the matrix expression of the reference current of the grid current is: in, is the active loop controller, is the voltage loop controller, P ref is the active power reference value, U ref_d is the d-axis output voltage reference value, U d is the d-axis output voltage P is the actual value of the grid-following inverter output.

[0049] As an example, the active loop controller The expression is: in, is the proportionality coefficient, is the integral coefficient, and s is the Laplace operator.

[0050] As an example, a voltage loop controller The expression is: in, is the proportionality coefficient, is the integral coefficient, and s is the Laplace operator.

[0051] As an example, the active power reference value P ref Can be set to 10KW.

[0052] As an example, the d-axis output voltage reference value U ref_d Can be set to 311V.

[0053] In step S4, see Figure 2 In step S4, the dq The output voltage in the coordinate system is compared with the corresponding output voltage reference value to obtain dq The error between the output voltage in the coordinate system and the corresponding output voltage reference value is obtained by passing the error through the phase-locked loop controller. dq The transformation angle of the coordinate system.

[0054] As an example, see Figure 3 , step S4 may include the following steps: step S41 to step S43.

[0055] Step S41: q Shaft output voltage and q The shaft output voltage reference value is compared to obtain q The shaft output voltage error will q The shaft output voltage error is q axis PI controller, get q The change in shaft angular frequency.

[0056] Step S42: d Shaft output voltage and d The shaft output voltage reference value is compared to obtain d The shaft output voltage error will d The shaft output voltage error is d axis PI controller, get d The change in shaft angular frequency.

[0057] Step S43: q Shaft angular frequency change, d The phase angle of the output voltage is obtained by adding the shaft angular frequency change and the angular frequency rating and multiplying by 1 / s.

[0058] Specifically, in step S41, q Shaft output voltage and q Shaft output voltage reference value U ref_q By comparison, we get q The shaft output voltage error will q The shaft output voltage error is qAxis Phase Locked Loop Controller F q (s), get q Shaft angular frequency change .

[0059] As an example, the q Axis Phase Locked Loop Controller F q The expression of (s) is: in, is the proportionality coefficient, is the integral coefficient, and s is the Laplace operator.

[0060] As an example, q Shaft output voltage reference value U ref_q Can be set to 0V.

[0061] Further, in step S42, d Shaft output voltage and d Shaft output voltage reference value U ref_d By comparison, we get d Shaft output voltage error. d The shaft output voltage error is d Axis Phase Locked Loop Controller F d (s), get d Shaft angular frequency change .

[0062] As an example, the d Axis Phase Locked Loop Controller F d The expression of (s) is: in, is the proportionality coefficient.

[0063] As an example, d Shaft output voltage reference value U ref_d Can be set to 311V.

[0064] Further, in step S43, q Shaft angular frequency change , d Shaft angular frequency change , angular frequency rating Adding and multiplying by the Laplace integrator 1 / s gives dq Transformation angle in coordinate system θ .

[0065] As an example, the angular frequency rating The expression is: in, is the rated frequency of the power grid, which can be set to 50Hz.

[0066] As an example, the angular frequency rating Can be set to 100p rad / s.

[0067] In step S5, refer to Figure 2 In step S5, a model of the composite synchronous dominant loop is established to obtain a loop gain from the grid voltage phase angle to the grid-connected voltage phase angle, and an updated dq The transformation angle in the coordinate system.

[0068] As an example, see Figure 4 , step S5 may include the following steps: step S51 to step S56.

[0069] Step S51: dq The equivalent circuit of the grid-following inverter is established in the coordinate system.

[0070] Step S52: Obtain the LCL dynamic equation according to the equivalent circuit of the grid-following inverter.

[0071] Step S53: Using the q-axis phase-locked loop controller, determine dq The angular frequency of rotation of the coordinate system is based on dq The rotation angular frequency of the coordinate system transforms the grid voltage into dq In the coordinate system, the grid voltage is obtained dq Vector.

[0072] Step S54: According to the grid voltage dq Vector, get the grid voltage dq The vector linearization representation is used to obtain the simplified grid-connected voltage.

[0073] Step S55: obtaining a composite synchronous dominant loop gain transfer function according to the simplified grid-connected voltage.

[0074] Step S56: Using the composite synchronous dominant loop gain transfer function, obtain an updated dq The transformation angle in the coordinate system.

[0075] Specifically, in step S51, the circuit topology of the grid-following inverter is simplified to obtain dq The simplified circuit of the grid-following inverter in the coordinate system is as follows: Figure 5 The simplified circuit of the grid-following inverter includes: the output voltage of the grid-following inverter port U* , machine side inductance impedance Z f1 , grid-side inductance impedance Z f2 , grid side impedance Z g , three-phase voltage source v g , Capacitive Admittance Y c Among them, the machine side inductor impedance Z f1 The first end is connected to the grid inverter port output voltage U * , machine side inductor impedance Z f1 The second end of the inductor is connected to the grid side impedance Z f2 The first end, the grid-side inductor impedance Z f2 The second end is connected to the grid side impedance Z g The first end, grid side impedance Z g The second end is connected to a three-phase voltage source v g Capacitive Admittance Y c The first end of the machine side inductor impedance Z f1 The second end of the capacitive admittance Y c The second end is grounded.

[0076] As an example, the machine-side inductor impedance Z f1 Can include filter inductors L f1 and filter resistor R f , filter resistor R f The first end is connected to the grid inverter port output voltage U * , filter resistor R f The second end of the filter inductor is connected L f1 The first end of the grid side inductor impedance Z f2 Can include filter inductors L f2 , filter inductor L f2 The first end of the filter inductor is connected L f1 The second end of the filter inductorL f2 The second end is connected to the grid side impedance Z g The first end; grid side impedance Z g Can include grid resistance R g and grid inductance L g , grid resistance R g The first end of the filter inductor is connected L f2 The second end of the grid resistance R g The second end of the grid inductor is connected L g The first end, the grid inductance L g The second end is connected to a three-phase voltage source v g ; Capacitive admittance Y c Can include filter capacitors C , filter capacitor C The first end of the filter inductor is connected L f1 The second end of the filter capacitor C The second end of the filter capacitor is grounded. C The capacitor voltage is U c , filter capacitor C The capacitor current is I c , grid side impedance Z g The grid current is I g , the output current of the grid-following inverter is I .

[0077] As an example, in step S52, in order to suppress the influence of the LCL filter resonance on the stability, the capacitive current active damping is added to control the LCL filter module 3, and the LCL dynamic equation expression can be obtained as follows: in, is the capacitor voltage U c of dq Vector, Grid voltage U of dq Vector, Output voltage of the grid-following inverter port U * of dq Vector, is the grid current I g of dq Vector, Output current for grid-following inverter I of dq Vector, is the capacitor current I c of dq Vector.

[0078] As an example, the capacitor voltage U c of dq Vector The expression is: in, is the capacitor voltage U c of d Axis component, is the capacitor voltage U c of q Axis component.

[0079] As an example, the grid voltage U of dq Vector The expression is: in, Grid voltage U of d Axis component, Grid voltage U of q Axis component.

[0080] As an example, the output voltage of the grid-following inverter port U * of dq Vector The expression is: in, Output voltage of the grid-following inverter port U * of d Axis component, Output voltage of the grid-following inverter port U * ofq Axis component.

[0081] As an example, the grid current I g of dq Vector The expression is: in, is the grid current I g of d Axis component, is the grid current I g of q Axis component.

[0082] As an example, the grid-following inverter output current I of dq Vector The expression is: in, Output current for grid-following inverter I of d Axis component, Output current for grid-following inverter I of q Axis component.

[0083] As an example, the capacitor current I c of dq Vector The expression is: in, is the capacitor current I c of d Axis component, is the capacitor current I c of q Axis component.

[0084] Furthermore, according to the active damping of the capacitor current G AD (s) And the LCL dynamic equation, the output voltage of the grid-following inverter port can be obtained dq Vector , the expression is: in, is the PWM gain of the grid-following inverter, The reference voltage for the output voltage of the grid-following inverter port dq Vector, is the grid current I g Reference value dq Vector, is the grid current I g of dq Vector, is the capacitor current I c of dq Vector, It is a 1.5 beat digital control delay. It is the output current controller of the grid-following inverter. is the capacitor current controller.

[0085] As an example, the output reference voltage of the grid-following inverter dq Vector The expression is: in, The reference voltage of the grid voltage d Axis component, The reference voltage of the grid voltage q Axis component.

[0086] As an example, the PWM gain of a grid-following inverter The expression is: in, is the triangular carrier amplitude, For DC power supply.

[0087] As an example, the triangular carrier amplitude Can be set to 3V or 4.58V.

[0088] As an example, 1.5 beats digital control delay The transfer function expression is: in, T s is the sampling period, s is the Laplace operator, Represents the approximate continuous domain of a 1.5-beat digitally controlled delay.

[0089] As an example, the grid-following inverter output current controller The expression is: in, is the proportionality coefficient, is the integral coefficient, and s is the Laplace operator. As an example, the capacitor current controller The expression is: in, is the proportionality coefficient, is the integral coefficient, and s is the Laplace operator.

[0090] Further, in step S53, the q-axis phase-locked loop controller is used to determine dq Rotational frequency of the coordinate system for: in, is the grid-connected angular frequency small signal quantity, is the angular frequency rating.

[0091] As an example, the grid-connected angular frequency small signal The expression is: in, for q Axis phase-locked loop transfer function, is the q-axis component of the grid-connected voltage, for q Axis PI controller, s is the Laplace operator.

[0092] As an example, q Axis PLL transfer function The expression is: in, is the proportional gain, is the integral gain, for q Axis PI controller, s is the Laplace operator.

[0093] Furthermore, in order to form a closed-loop dynamic of the entire system, the grid voltage (i.e., the three-phase voltage source v g ) to dq In the coordinate system, the grid voltage is obtained dq Vector V gdq The expression is: in, The grid voltage d Axis component, The grid voltage q Axis component.

[0094] Further, in step S54, the grid voltage can be obtained. dq Vector V gdq , grid-connected voltage dq Vector U dq , grid current dq Vector I gdq The relationship between them is: in, R g is the grid resistance, L g is the grid inductance, for dq The rotation angular frequency of the coordinate system, s is the Laplace operator.

[0095] Furthermore, the grid voltage can be obtained dq Vector V gdq The linearization expression at the steady-state operating point of the system is: in, is the grid voltage amplitude, The grid voltage dq Vector V gdq With grid voltage dq Vector U dq The steady-state value of the power angle between is the linearized power angle small signal quantity, is the linearized grid voltage d Axis component, is the linearized grid voltage q Axis component.

[0096] As an example, the linearized power angle small signal The expression is: in, is the small signal of grid voltage phase angle, It is the small signal quantity of grid voltage phase angle.

[0097] As an example, the simplified grid voltage is: in, For simplified grid voltage d Axis component, For simplified grid voltage q Axis component, R g is the grid resistance, L g is the grid inductance, is the angular frequency rating, for q Axis PI controller, The grid voltage dq Vector V gdq With grid voltage dq Vector U dq The steady-state value of the power angle between is the grid voltage amplitude, Grid-connected current q Steady-state value of the axis component, The grid voltage dq Vector V gdq With grid voltage dq Vector U dq The power angle between the small signal, , is the identity matrix.

[0098] As an example, the matrix The expression is: in, is the PWM gain of the grid-following inverter, is the filter capacitor, is the filter inductor, is the filter inductor, is the filter resistor, For filter inductance L f1 The equivalent resistance of For filter inductance L f2 The equivalent resistance of is the angular frequency rating, It is a 1.5 beat digital control delay. is the Laplace operator, Grid voltage d Steady-state value of the axis component, is the active loop controller, It is the output current controller of the grid-following inverter. is the capacitor current controller.

[0099] As an example, the matrix The expression is: in, Grid-connected current d Steady-state value of the axis component, is the PWM gain of the grid-following inverter, is the filter capacitor, is the filter inductor, is the filter inductor, is the filter resistor, For filter inductance L f1 The equivalent resistance of For filter inductance L f2 The equivalent resistance of is the angular frequency rating, It is a 1.5 beat digital control delay. is the Laplace operator, is the active loop controller, It is the output current controller of the grid-following inverter. is the capacitor current controller and E is the unit matrix.

[0100] Further, in step S55, according to the simplified grid-connected voltage, As input, the simplified grid-connected voltage can be obtained q Axis Component The transfer function for: in, For simplified grid voltage q Axis component, R g is the grid resistance, L g is the grid inductance, is the angular frequency rating, for q Axis PI controller, The grid voltage dq Vector V gdq With grid voltage dq Vector U dq The steady-state value of the power angle between is the grid voltage amplitude, Grid-connected current q Steady-state value of the axis component, The grid voltage dq Vector V gdq With grid voltage dq VectorU dq The power angle between the small signal, , is the identity matrix.

[0101] Similarly, the simplified grid-connected voltage can be obtained d Axis Component The transfer function .

[0102] Furthermore, the composite synchronous dominant loop gain transfer function can be obtained: for: in, The composite synchronous dominant loop gain transfer function is q Axis component, The composite synchronous dominant loop gain transfer function is d Axis component.

[0103] Specifically, the composite synchronous dominant loop gain transfer function is q Axis Component The expression is: in, Grid voltage q Axis Component The transfer function of for q Axis phase-locked loop transfer function.

[0104] As an example, q Axis PLL transfer function The expression is: in, for q Axis PI controller, s is the Laplace operator.

[0105] As an example, the composite synchronous dominant loop gain transfer function is d Axis Component The expression is: in, Grid voltage d Axis Component The transfer function of for d Axis phase-locked loop transfer function.

[0106] As an example, d Axis PLL transfer function The expression is: in, for d Axis PI controller, s is the Laplace operator.

[0107] As an example, d Axis PI controller The proportional coefficient value can be obtained by parameter root locus analysis under different grid strength conditions. K PLLdpmax , K PLLdpmin The region enclosed by the constraint curve, where K PLLdpmax , K PLLdpmin They represent the maximum and minimum values ​​of this SCR (short circuit ratio), namely K PLLdpmax , K PLLdpmin They represent the maximum and minimum values ​​that the proportional term of the d-axis phase-locked loop controller can take, respectively.

[0108] As an example, the d-axis phase-locked loop controller may be a proportional controller.

[0109] at this time, dq Coordinate system rotation angular frequency for: in, is the grid-connected angular frequency small signal quantity, is the angular frequency rating.

[0110] Specifically, the grid-connected angular frequency The expression is: in, Grid voltage q Axis component, Grid voltage d Axis component, for q Axis phase-locked loop transfer function, for d Axis phase-locked loop transfer function, for q Axis PI controller, for d Axis PI controller, s is the Laplace operator.

[0111] Further, in step S56, Figure 6 The block diagram of the composite synchronous dominant loop transfer function is shown in Figure 2. Figure 6It can be seen that the input grid voltage phase angle small signal , after the composite synchronization dominates the loop gain transfer function , get the grid voltage phase angle small signal Based on the composite synchronous dominant loop gain and according to the Nyquist stability criterion, the parameters of the phase-locked loop controller can be optimized to obtain an updated dq Transformation angle in coordinate system θ' ,in, θ' is the composite synchronous dominant loop gain transfer function Get the small signal of grid voltage phase angle Superimpose steady-state quantities to control abc / dq conversion.

[0112] In step S6, refer to Figure 2 Step S6 in the above example, dq The transformed angle in the coordinate system is sent to the grid current coordinate transformation path to obtain a new sampling current. The new sampling current includes d Axis sampling current and q Axis sampling current.

[0113] Specifically, the updated dq Transformation angle in coordinate system θ The current is sent to the grid coordinate transformation path to control the transformation angle of the abc / dq converter, and the dq New sampling current in coordinate system. It can improve sampling accuracy, and the real-time updated transformation angle ensures the accuracy of coordinate transformation, provides high-precision input for current loop control, and enhances current tracking capability.

[0114] As an example, the dq The new sampled current in the coordinate system includes: the new current reflecting the active component d Axis sampling current i gd and new reactive components q Axis sampling current i gq .

[0115] In step S7, refer to Figure 2 In step S7, the new sampling current and the error between the new sampling current and the reference current are sent to the current controller, and a PWM modulation signal is obtained through current regulation to realize the control of the grid-following inverter.

[0116] Specifically, the new d Axis sampling current i gd ,new q Axis sampling current i gq , newd Axis sampling current i gd and d Axis reference current i ref_d The error, new q Axis sampling current i gq and q Axis reference current i ref_q The error is fed into the current controller G i ( s ), and then with the capacitor current I c of d Axis Component and capacitor current I c of q Axis Component Active damping of the capacitor current G AD (s) , combined with the updated dq Transformation angle in coordinate system θ' The modulation signal is generated by the dq current decoupling quantity, and the PWM control signal is generated by sinusoidal pulse width modulation to realize the control of the grid-following inverter.

[0117] In one example, in order to verify the accuracy of the method of the present application, the frequency scanning method was used on the PLECS platform to perform frequency scanning verification on the closed-loop transfer function of the synchronous dominant loop of the grid-following inverter, and a comparison diagram of the amplitude and phase curves before and after the improvement was obtained. Figure 7 In order to improve the amplitude-frequency characteristic curve of the closed-loop transfer function sweep verification of the synchronous leading loop of the front-following grid inverter, Figure 8 The amplitude-frequency characteristic curve of the frequency sweep verification of the closed-loop transfer function of the synchronous dominant loop of the improved grid-type inverter.

[0118] In another example, a simulation model of a three-phase grid-connected inverter was built based on the PLECS simulation platform to verify the correctness of the concept of the present application and the rationality of the closed-loop parameter design. Fig. 9 In order to improve the grid-connected voltage, current and frequency simulation waveforms of the front-following inverter under weak grid conditions, Fig.10 The improved composite synchronous grid-following inverter is connected to the grid in a weak grid. The composite synchronization coefficient of the composite synchronous grid-following inverter is K PLLd Can be set equal to 0.85, combined with Fig. 9 and Fig.10It can be seen that the composite voltage regulation grid-following inverter phase-locking method proposed in this application can improve the stability of the grid-following inverter under weak power grids, indicating the effectiveness of the composite synchronous grid-following inverter control strategy and verifying the accuracy of the parameter design.

[0119] In the phase-locking method of the grid-connected inverter based on composite voltage regulation of the present application, the d-axis voltage control is introduced to track the grid connection point voltage phase in real time, and the composite synchronous dominant loop model is constructed in combination with the q-axis voltage error correction; the rotation angular frequency of the dq coordinate system is dynamically adjusted by the composite synchronous dominant loop model, which can effectively suppress the influence of the LCL filter resonance on the stability and improve the anti-interference ability of the phase-locked loop under weak power grid; through the cascade control of the active loop and the voltage loop, the accurate calculation of the reference current is realized, and the stability and dynamic response speed of the power output are significantly improved; by correcting the coordinate transformation angle in real time, the grid connection impact current is eliminated and the current sampling accuracy is improved; the updated transformation angle ensures the phase alignment of the current and voltage signals in the dq coordinate system, provides high-precision input for the current loop control, and significantly improves the current tracking ability. While ensuring the stability of the power grid, the method of the present application reduces the switching loss and improves the power density, especially showing stronger adaptability under weak power grid conditions, significantly improving the phase-locking accuracy, power control capability and system robustness of the grid-connected inverter under different power grid strengths, and providing an efficient and stable solution for the grid connection of new energy.

[0120] It should be understood that, although the steps in the flowchart of the accompanying drawings are displayed in sequence as indicated by the arrows, these steps are not necessarily executed in sequence in the order indicated by the arrows. Unless otherwise specified herein, there is no strict order restriction on the execution of these steps, and these steps can be executed in other orders. Moreover, at least a portion of the steps in the accompanying drawings may include multiple sub-steps or multiple stages, and these sub-steps or stages are not necessarily executed at the same time, but can be executed at different times, and the execution order of these sub-steps or stages is not necessarily sequential, but can be executed in turn or alternately with other steps or at least a portion of the sub-steps or stages of other steps.

[0121] In another embodiment, see Fig.11The present application also provides a grid-following inverter phase-locking system based on composite voltage regulation, which may include: a data acquisition module 10, a power calculation module 20, a reference current calculation module 30, a transformation angle module 40, a composite synchronous dominant loop and loop gain module 50, a sampling current update module 60, and a PWM modulation module 70. Among them, the data acquisition module 10 is used to detect the grid current and the grid-connected point voltage, and perform coordinate transformation on the grid current and the grid-connected point voltage to obtain the grid current and the output voltage; the power calculation module 20 is used to obtain the active power output by the grid-following inverter according to the grid current and the output voltage; the reference current calculation module 30 is used to determine the reference current of the output current according to the active power output by the grid-following inverter and the output voltage; the transformation angle module 40 is used to obtain the output voltage according to the output voltage and the voltage reference value. dq The composite synchronous dominant loop and loop gain module 50 is used to construct a composite synchronous dominant loop model, and the composite synchronous dominant loop model is used to obtain the loop gain and the new dq Coordinate system transformation angle; sampling current update module 60 is used to update the current according to the new dq The coordinate system transforms the angle and updates the sampled current; the PWM modulation module 70 is used to obtain a PWM modulation signal according to the new sampled current to control the grid-following inverter.

[0122] In the above-mentioned grid-following inverter phase-locked system based on composite voltage regulation, the grid current and output voltage are accurately obtained through the data acquisition module 10, providing a basis for subsequent calculations; the power calculation module 20 and the reference current calculation module 30 cooperate to establish an accurate mapping of power and current; the coordinate transformation angle is corrected in real time through the transformation angle module 40 to eliminate the grid-connected impact current; the model is constructed through the composite synchronous dominant loop and the loop gain module 50 to optimize the phase-locked loop parameters; the sampling accuracy is ensured through the sampling current update module 60; and the modulation signal is generated through the PWM modulation module 70 to control the inverter. The system of this application can improve the robustness of the grid-following inverter under strong and weak power grids, reduce losses, and improve power density, and has significant engineering application value.

[0123] The technical features of the above embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0124] Although the present application has been disclosed as above with the embodiments, it is not intended to limit the present application. Any person with ordinary knowledge in the technical field can make some changes and modifications without departing from the spirit and scope of the present application. Therefore, the scope of protection of the present application shall be determined by the scope of the attached patent application.

Claims

1. A grid-following inverter phase-locking method based on composite voltage regulation, characterized in that: The following steps are involved: Detect the grid current and perform coordinate transformation on the grid current to obtain dq The grid current in the coordinate system is dq The grid current in the coordinate system includes the d-axis grid current and the q-axis grid current; the grid connection point voltage is detected, and the grid connection point voltage is transformed into a coordinate system to obtain dq The output voltage in the coordinate system is dq The output voltage in the coordinate system includes the d-axis output voltage and the q-axis output voltage; according to dq The output voltage and grid current in the coordinate system are used to obtain the active power output by the grid-following inverter; Obtaining a reference current of a grid current according to the active power output by the grid-following inverter and the q-axis output voltage, wherein the reference current of the grid current includes a d-axis reference current and a q-axis reference current; The dq The output voltage in the coordinate system is compared with the corresponding output voltage reference value to obtain dq The error between the output voltage in the coordinate system and the corresponding output voltage reference value is obtained by passing the error through the phase-locked loop controller. dq Transformation angle in coordinate system; The model of the composite synchronous dominant loop is established to obtain the loop gain from the grid voltage phase angle to the grid-connected voltage phase angle, and the updated dq Transformation angle in coordinate system; The updated dq The transformed angle in the coordinate system is sent to the grid current coordinate transformation path to obtain a new sampling current, wherein the new sampling current includes a d-axis sampling current and a q-axis sampling current; The new sampling current and the error between the new sampling current and the reference current are sent to the current controller, and a PWM modulation signal is obtained through current regulation to realize the control of the grid-following inverter.

2. The grid-following inverter phase-locking method based on composite voltage regulation according to claim 1, characterized in that: The active power output of the grid-following inverter is expressed as: Among them, P is the active power output by the grid-following inverter, is the d-axis output voltage, is the q-axis output voltage, i g_d is the d-axis grid current, i g_q is the q-axis grid current.

3. The grid-following inverter phase locking method based on composite voltage regulation according to claim 2, characterized in that: The matrix expression of the reference current of the grid current is: in, i gref_d is the d-axis reference current of the grid current, i gref_q is the q-axis reference current of the grid current, is the active loop controller, is the voltage loop controller, P ref is the active power reference value, P is the active power output by the grid-following inverter, U ref_d is the d-axis output voltage reference value, U d is the d-axis output voltage The actual value of .

4. The grid-following inverter phase locking method based on composite voltage regulation according to claim 3 is characterized in that: The dq The output voltage in the coordinate system is compared with the voltage reference value to obtain dq The error between the output voltage and the voltage reference value in the coordinate system is obtained by passing the error through the phase-locked loop controller. dq Transformation angles in the coordinate system, including: The q-axis output voltage is compared with the q-axis output voltage reference value to obtain a q-axis output voltage error, and the q-axis output voltage error is passed through a q-axis PI controller to obtain a q-axis angular frequency variation; The d-axis output voltage is compared with the d-axis output voltage reference value to obtain a d-axis output voltage error, and the d-axis output voltage error is passed through a d-axis PI controller to obtain a d-axis angular frequency change; The q-axis angular frequency variation, the d-axis angular frequency variation, and the angular frequency rated value are added and multiplied by a Laplace integrator to obtain a phase angle of the output voltage.

5. The grid-following inverter phase-locking method based on composite voltage regulation according to claim 4, characterized in that: The model of the composite synchronous dominant loop is established to obtain the loop gain from the grid voltage phase angle to the grid-connected voltage phase angle, and the updated dq Transformation angles in the coordinate system, including: exist dq Establish the equivalent circuit of the grid-following inverter in the coordinate system; According to the equivalent circuit of the grid-following inverter, an LCL dynamic equation is obtained; Using the q-axis phase-locked loop controller, determine dq The rotation angular frequency of the coordinate system is dq The rotation angular frequency of the coordinate system transforms the grid voltage into dq In the coordinate system, the grid voltage is obtained dq Vector; According to the grid voltage dq Vector, get the grid voltage dq Vector linearization is used to obtain the simplified grid-connected voltage; According to the simplified grid-connected voltage, a composite synchronous dominant loop gain transfer function is obtained; Using the composite synchronous dominant loop gain transfer function, the updated dq The transformation angle in the coordinate system.

6. The grid-following inverter phase locking method based on composite voltage regulation according to claim 5, characterized in that: Grid voltage dq The vector linearization expression is: in, is the grid voltage amplitude, The grid voltage dq Vector V gdq With grid voltage dq Vector U dq The steady-state value of the power angle between is the linearized power angle small signal quantity, is the linearized grid voltage d Axis component, is the linearized grid voltage q Axis component.

7. The grid-following inverter phase-locking method based on composite voltage regulation according to claim 5, characterized in that: The composite synchronous dominant loop gain transfer function for: in, The composite synchronous dominant loop gain transfer function is d Axis component, The composite synchronous dominant loop gain transfer function is q Axis component.

8. The grid-following inverter phase locking method based on composite voltage regulation according to claim 5, characterized in that: Said dq Rotational frequency of the coordinate system The expression is: in, is the grid-connected angular frequency small signal quantity, is the angular frequency rating.

9. The grid-following inverter phase locking method based on composite voltage regulation according to claim 8, characterized in that: The grid-connected angular frequency small signal The expression is: in, for q Axis phase-locked loop transfer function, is the q-axis component of the grid-connected voltage, for q Axis PI controller, s is the Laplace operator.

10. A grid-following inverter phase-locking system based on composite voltage regulation, characterized in that: The grid-following inverter phase-locking system based on compound voltage regulation performs the steps of the grid-following inverter phase-locking method based on compound voltage regulation as claimed in any one of claims 1 to 9, including: A data acquisition module is used to detect the grid current and the grid connection point voltage, and perform coordinate transformation on the grid current and the grid connection point voltage to obtain the grid current and the output voltage; A power calculation module, used to obtain the active power output by the grid-following inverter according to the grid current and output voltage; A reference current calculation module, used to determine a reference current of the output current according to the active power and output voltage output by the grid-following inverter; The angle conversion module is used to obtain the output voltage and the voltage reference value according to the output voltage. dq Transformation angle in coordinate system; The composite synchronous dominant loop and loop gain module is used to construct a composite synchronous dominant loop model. The composite synchronous dominant loop model is used to obtain the loop gain and the new dq Coordinate system transformation angle; The sampling current updating module is used to update the current according to the new dq The coordinate system transforms the angle and updates the sampled current; The PWM modulation module is used to obtain a PWM modulation signal according to a new sampling current to control the grid-following inverter.

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