Droop control method and device of inverter

Abstract

The invention relates to the field of inverter control, and provides a droop control method and device for an inverter, and the method comprises the steps: setting a droop control loop to be represented by a negative number of a ratio of a unit matrix to a voltage outer loop transfer function, and obtaining a droop coefficient of the droop control loop according to the voltage closed loop transfer function and the droop coefficient of the droop control loop; the current output impedance of the inverter is updated to the target output impedance, the output impedance is adjusted to be controlled and adjusted by the droop coefficient, the influence of the control loop parameter and the output power on the closed loop output impedance is eliminated, the adjustment conflict of the output impedance is reduced when the inverter realizes the dynamic performance and the power sharing capability between the inverters, and the power sharing performance of the inverter is improved. And the flexibility of adjusting the output impedance is improved.

Description

Technical Field

[0001] The present application relates to the field of inverter control, and in particular to a droop control method and device for an inverter. Background Art

[0002] An inverter is a converter that can convert direct current into alternating current. In the field of power electronics, inverters play an important industrial role. For example, in the field of renewable energy, such as solar photovoltaic power and wind farms, inverters can convert direct current obtained by energy conversion of solar or wind energy into alternating current and connect it to the grid or power local loads.

[0003] When the inverter processes DC power that is much larger than the inverter's conversion capacity, multiple inverters can be connected in parallel to output AC power. In the case of multiple inverters in parallel, in order to improve the stability of the output AC power, the inverter should have good dynamic performance and power sharing capabilities between inverters.

[0004] The dynamic performance of the inverter and the power sharing capability between inverters are both related to the output impedance of the inverter. In order to share power between parallel inverters, the output impedance of the inverter needs to be increased. However, improving the dynamic performance of the inverter requires reducing the output impedance of the inverter, which leads to conflicts in adjusting the output impedance of the inverter, and it is impossible to achieve both the dynamic performance of the inverter and the power sharing capability between inverters at the same time. Summary of the invention

[0005] In order to solve the problem of output impedance conflict when the inverter achieves dynamic performance and power sharing capability between inverters.

[0006] In a first aspect, some embodiments of the present application provide a droop control method for an inverter, including: Obtain the delay transfer function, the current inner loop transfer function and the duty cycle to inductor current transfer function; Performing product calculation on the delay transfer function, the current inner loop transfer function and the duty cycle to inductor current transfer function to obtain a current open loop transfer function; Calculating a current closed-loop transfer function based on a unit matrix and the current open-loop transfer function; Performing product calculation on the current closed-loop transfer function, the voltage outer-loop transfer function and the transfer function from the inductor current to the output voltage to obtain a voltage open-loop transfer function; Calculate a voltage closed-loop transfer function based on the unit matrix and the voltage open-loop transfer function; Setting the droop control loop of the inverter to a target representation, wherein the target representation is a negative representation of a ratio of a unit matrix to the voltage outer loop transfer function; By means of the target representation, the current output impedance of the inverter is updated to the target output impedance according to the voltage closed-loop transfer function and the droop coefficient of the droop control loop.

[0007] In some embodiments, before the step of setting the droop control loop to the target representation mode, the method further comprises: Calculating a voltage difference between a first voltage reference value and a second voltage reference value; wherein the first voltage reference value is a voltage reference value after the inverter performs droop control, and the second voltage reference value is a voltage reference value before the inverter performs droop control; Calculating a target ratio of the voltage difference to the output current of the inverter; The addition result of the droop coefficient and the target ratio is calculated to obtain the droop control loop.

[0008] In some embodiments, the voltage outer loop transfer function can be expressed by the following formula: ; in, is the voltage outer loop transfer function, is the ratio of the voltage outer loop of the inverter, is the integral parameter of the voltage outer loop of the inverter, s is the Laplace variable.

[0009] In some embodiments, the current inner loop transfer function can be expressed by the following formula: ; in, is the current inner loop transfer function, is the ratio of the current inner loop of the inverter, is the integral parameter of the current inner loop of the inverter.

[0010] In some embodiments, the step of setting the droop control loop to a target representation comprises: Obtaining a current output impedance of the inverter; the current output impedance is obtained by calculating the addition result of a first impedance result and a second impedance result, the first impedance result is obtained by calculating the product result of an open-loop output impedance and a difference between the unit matrix and the voltage closed-loop transfer function, and the second impedance result is obtained by calculating the addition result of the ratio of the droop coefficient, the droop control loop, and the transfer function from the output current to the inductor current to the voltage outer loop transfer function, and then calculating the product result of the addition result and the voltage closed-loop transfer function; A target representation of the droop control loop is calculated based on the first impedance result and the second impedance result.

[0011] In some embodiments, before the step of obtaining the current output impedance of the inverter, the method further includes: Obtaining a transfer function from output current to output voltage, a transfer function from output current to inductor current, and a transfer function from inductor current to output voltage; Calculate the product of the transfer function from the output current to the inductor current and the transfer function from the inductor current to the output voltage; The open-loop output impedance of the inverter is obtained by calculating the difference between the negative output current to output voltage transfer function and the product of the output current to inductor current transfer function and the inductor current to output voltage transfer function.

[0012] In some embodiments, the step of calculating the current closed-loop transfer function based on the identity matrix and the current open-loop transfer function includes: Calculating an addition result of the unit matrix and the current open-loop transfer function; The current closed-loop transfer function is obtained by calculating a ratio of the current open-loop transfer function to a sum of the unit matrix and the current open-loop transfer function.

[0013] In some embodiments, the step of calculating the voltage closed-loop transfer function based on the identity matrix and the voltage open-loop transfer function includes: Calculating an addition result of the unit matrix and the voltage open-loop transfer function; The voltage closed-loop transfer function is obtained by calculating a ratio of the voltage open-loop transfer function to a sum of the unit matrix and the voltage open-loop transfer function.

[0014] In some embodiments, the delay transfer function can be expressed by the following formula: ; in, is the delay transfer function, To control the delay time.

[0015] In a second aspect, some embodiments of the present application provide a droop control device for an inverter, including a control module, wherein the control module is configured to: Obtain the delay transfer function, the current inner loop transfer function and the duty cycle to inductor current transfer function; Performing product calculation on the delay transfer function, the current inner loop transfer function and the duty cycle to inductor current transfer function to obtain a current open loop transfer function; Calculating a current closed-loop transfer function based on a unit matrix and the current open-loop transfer function; Performing product calculation on the current closed-loop transfer function, the voltage outer-loop transfer function and the transfer function from the inductor current to the output voltage to obtain a voltage open-loop transfer function; Calculate a voltage closed-loop transfer function based on the unit matrix and the voltage open-loop transfer function; Setting the droop control loop of the inverter to a target representation, wherein the target representation is a negative representation of a ratio of a unit matrix to the voltage outer loop transfer function; By means of the target representation, the current output impedance of the inverter is updated to the target output impedance according to the voltage closed-loop transfer function and the droop coefficient of the droop control loop.

[0016] It can be seen from the above technical scheme that the present application provides a droop control method and device for an inverter, which sets the droop control loop to be represented by the negative number of the ratio of the unit matrix to the voltage outer loop transfer function, and updates the current output impedance of the inverter to the target output impedance according to the voltage closed-loop transfer function and the droop coefficient of the droop control loop, so that the output impedance is adjusted to be controlled and adjusted by the droop coefficient, eliminating the influence of the control loop parameters and the output power on the closed-loop output impedance, reducing the adjustment conflict of the output impedance when the inverter realizes dynamic performance and the power sharing capability between inverters, and improving the flexibility of adjusting the output impedance. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the technical solution of the present application, the drawings required for use in the embodiments are briefly introduced below. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0018] Figure 1 A schematic diagram of two inverters working in parallel in an embodiment of the present application; Figure 2 A flow chart of a droop control method performed by an inverter provided in an embodiment of the present application; Figure 3 The inverter droop control structure diagram provided in the embodiment of the present application; Figure 4 A loading voltage fluctuation diagram of the inverter provided in an embodiment of the present application without performing droop control; Figure 5 A load-free voltage fluctuation diagram of the inverter provided in an embodiment of the present application without performing droop control; Figure 6 A loading voltage fluctuation diagram of the inverter performing droop control provided in an embodiment of the present application; Figure 7 A load-free voltage fluctuation diagram of the inverter performing droop control provided in an embodiment of the present application. DETAILED DESCRIPTION

[0019] In order to make the purpose and implementation method of the present application clearer, the exemplary implementation method of the present application will be clearly and completely described below in conjunction with the drawings in the exemplary embodiments of the present application. Obviously, the described exemplary embodiments are only part of the embodiments of the present application, rather than all the embodiments.

[0020] It should be noted that the brief description of terms in this application is only for the convenience of understanding the embodiments described below, and is not intended to limit the embodiments of this application. Unless otherwise specified, these terms should be understood according to their common and usual meanings.

[0021] The terms "first", "second", "third", etc. in the specification and the above drawings of this application are used to distinguish similar or similar objects or entities, and do not necessarily mean to limit a specific order or sequence, unless otherwise specified. It should be understood that the terms used in this way can be interchangeable under appropriate circumstances.

[0022] The terms "comprises," "comprising," and "having," and any variations thereof, are intended to cover but not exclude inclusion, for example, a product or device comprising a list of components is not necessarily limited to all the components expressly listed but may include other components not expressly listed or inherent to such product or device.

[0023] A three-phase inverter is a converter that can convert direct current into alternating current to access the power grid or power local loads. Taking a renewable energy power generation system as an example, such as a solar photovoltaic power station, a three-phase inverter can convert the direct current obtained from solar energy converted by the solar photovoltaic power station into alternating current, and output the alternating current to the load to supply power to the load. Another example is a wind farm, a three-phase inverter can convert the direct current generated by the wind farm through wind energy into alternating current. In these application scenarios, different environmental conditions and load performance require that the three-phase inverter needs to output alternating current accurately and stably. However, due to different application scenarios, the same inverter cannot be used for current conversion. Therefore, multiple three-phase inverters may be required to work in parallel. For example, for the first three-phase inverter, the direct current obtained by solar energy conversion can be converted into alternating current, and for the second three-phase inverter, the direct current generated by the wind farm through wind energy can be converted into alternating current. The first three-phase inverter can work in parallel with the second three-phase inverter to achieve the simultaneous conversion of direct current from different energy sources into alternating current available to the load.

[0024] In addition, as the magnitude of current conversion increases, when the inverter processes direct current that is much greater than the inverter's conversion capacity, multiple inverters can also be connected in parallel to output alternating current energy. Figure 1 Schematic diagram showing two inverters working in parallel in an embodiment of the present application. Figure 1, including an inverter 1 and an inverter 2 connected in parallel, wherein the structures and working principles of the inverter 1 and the inverter 2 are the same, and the inverter 1 is taken as an example for explanation, and the connection structure and working principle of the inverter 2 can refer to the structure and working principle of the inverter 1. V ac To input the DC power of inverter 1, through the control of switches S1, S2, S3 and S4, the four switches form an H-bridge structure to convert the DC power into AC power that can be used by the load. In the positive half cycle: S1 and S4 are turned on, the current is from P→S1→L→load→S4→N, and the output is a positive voltage. In the negative half cycle: S2 and S3 are turned on, the current is from P→S2→L→load→S3→N, and the output is a negative voltage.

[0025] P is the positive pole of the DC input terminal, N is the negative pole of the DC input terminal, V P The voltage of the positive terminal of the DC input, V N is the voltage of the negative pole of the DC input terminal, and O is the neutral point. A, B, C and N are the A-phase high-voltage line, B-phase high-voltage line, C-phase high-voltage line and ground line of the three-phase inverter respectively. After the DC enters the three high-voltage lines, it passes through the LC filter composed of capacitors and inductors. i La is the inductor current of the A-phase high-voltage line, i Lb is the inductor current of the B-phase high-voltage line, i Lc is the inductor current of the C phase high voltage line, i LN is the inductor current of the ground wire. i ca is the capacitive current filtered by the A-phase high-voltage line, i cb is the capacitive current filtered by the A-phase high-voltage line, i cc The capacitive current filtered out by the A-phase high-voltage line is finally obtained as the output current of the A-phase high-voltage line. i a , the output current of the B phase high voltage line i b , output current of phase C high voltage line i c , to provide AC power to the load.

[0026] In the scenario where multiple inverters are connected in parallel, in order to improve the stability of the output AC power, the three-phase inverter should have good dynamic performance and power sharing capability between inverters. Dynamic performance means that when the load increases or decreases, the voltage fluctuation of each three-phase inverter is reduced, and the stability of the output current between each three-phase inverter is improved. Power sharing capability means that during the current conversion process, the power distributed between each three-phase inverter working in parallel is the same.

[0027] However, there is a contradiction between dynamic performance and the power sharing capability between inverters. In order to achieve power sharing between each three-phase inverter, it is necessary to increase the output impedance of the three-phase inverter by adjusting the virtual impedance or by connecting an inductor to the output end of the inverter, so as to achieve power sharing between the three-phase inverters. To improve the dynamic performance of the three-phase inverter, it is necessary to reduce the output impedance of the three-phase inverter, which leads to conflicts in adjusting the output impedance of the three-phase inverter, and it is impossible to achieve both the dynamic performance of the inverter and the power sharing capability between the inverters.

[0028] In order to solve the problem of adjusting the output impedance conflict when the inverter realizes dynamic performance and the power sharing capability between the inverters, some embodiments of the present application provide a droop control method of the inverter, which is applied to the three-phase inverter. For the convenience of description, the three-phase inverter is referred to as the inverter below. Among them, the inverter can execute the droop control method through the control module set inside, that is, the execution subject in this embodiment is the control module of the inverter, and other electrical components in the inverter can perform other current conversion functions. Figure 2 Flow chart of the inverter droop control method provided in the embodiment of the present application. Figure 2 , the method comprising: S100: Obtaining a delay transfer function, a current inner loop transfer function, and a duty cycle to inductor current transfer function.

[0029] In the embodiment of the present application, the output impedance of the inverter is affected by the output power of the inverter and the control loop parameters when realizing the dynamic performance and the power sharing capability between the inverters, wherein the output power is used to maintain the power sharing capability of the inverter, and the dynamic performance is used to maintain the stability of the output voltage of the inverter when the load is increased or decreased. The control loop of the inverter includes a droop control loop, a current inner loop and a voltage outer loop, and the droop control loop parameters of the droop control loop, the current inner loop parameters of the current inner loop and the voltage outer loop parameters of the voltage outer loop are all control loop parameters.

[0030] When the inverter responds to the control signal for performing current conversion, there will be a certain delay time, that is, the time between the time when the inverter receives the control signal and the time when the inverter responds to the control signal and starts to perform current conversion is the delay time. Therefore, it is necessary to obtain the delay transfer function.

[0031] The delay transfer function can be expressed as follows: ; in, is the delay transfer function, To control the delay time, the droop coefficient can be adjusted through the delay transfer function to offset the effect of the delay time on the current conversion in the subsequent droop control process.

[0032] In order to facilitate the description of the dynamic performance of the inverter, the following transfer function relationship of the inverter working state can be obtained through the physical working relationship of the inverter: ; in, is the inductor current of the inverter, is the output current of the inverter, d is the output duty cycle of the inverter, is the transfer function from output current to inductor current, is the transfer function from duty cycle to inductor current.

[0033] ; in, is the output voltage, is the transfer function from inductor current to output voltage, is the transfer function from output current to output voltage. is the small signal component of the variable, for example, is the small signal component of the inductor current, is the small signal component of the output current, is the small signal component of the output duty cycle, is the small signal component of the output voltage. In the above transfer function relationship, the transfer function from duty cycle to inductor current can be obtained, that is, It should be noted that the transfer functions in the embodiments of the present application are all based on the Laplace variables. s Calculated as a variable.

[0034] The current inner loop transfer function, that is, the transfer function of the current inner loop PI controller (proportional-integral controller), can be calculated by the current inner loop. The current inner loop can be expressed by the following formula: ; in, is the current reference value, that is, the current value of the inverter before droop control is performed. is the current inner loop transfer function. According to the formula of the current inner loop and the small signal component of the output duty cycle , the current inner loop transfer function can be calculated , the current inner loop transfer function It can be expressed as follows: ; in, is the ratio of the current inner loop of the inverter, is the integral parameter of the inverter's current inner loop, as well as All are current inner loop parameters.

[0035] S200: Perform product calculation on the delay transfer function, the current inner-loop transfer function, and the duty cycle to inductor current transfer function to obtain a current open-loop transfer function.

[0036] After obtaining the delay transfer function, the current inner loop transfer function, and the duty cycle to inductor current transfer function, the control module can calculate the current open loop transfer function , the current open-loop transfer function can be expressed as: ; Therefore, the control module may perform a product calculation on the delay transfer function, the current inner-loop transfer function, and the duty cycle-to-inductor current transfer function to obtain the current open-loop transfer function.

[0037] S300: Calculating a current closed-loop transfer function according to a unit matrix and the current open-loop transfer function.

[0038] The current open-loop transfer function is the basis for designing the current closed-loop transfer function. By analyzing the open-loop characteristics, the parameters of the inverter compensator, such as proportional gain, integration time, etc., can be determined to optimize the closed-loop dynamic response.

[0039] In this embodiment, the control module can calculate the addition result of the unit matrix and the current open-loop transfer function, where the unit matrix is ​​a conventional matrix in the field of mathematics. After obtaining the addition result, the ratio of the current open-loop transfer function to the addition result of the unit matrix and the current open-loop transfer function can be calculated to obtain the current closed-loop transfer function.

[0040] In this embodiment, based on the generation relationship between the current open-loop transfer function and the current closed-loop transfer function, the current closed-loop transfer function can be calculated by the current open-loop transfer function and the unit matrix, as shown in the following formula: ; in, is the current open-loop transfer function, E is the identity matrix.

[0041] S400: Perform product calculation on the current closed-loop transfer function, the voltage outer-loop transfer function, and the transfer function from the inductor current to the output voltage to obtain a voltage open-loop transfer function.

[0042] The voltage open-loop transfer function can be defined as follows: ; in, is the voltage open-loop transfer function, is the voltage outer loop transfer function, that is, the transfer function of the voltage outer loop PI controller. The voltage outer loop transfer function can be expressed as follows: ; in, is the ratio of the voltage outer loop, The integral parameter of the voltage outer loop. The ratio of the voltage outer loop and the integral parameter of the voltage outer loop are both voltage outer loop parameters. Therefore, it is necessary to adjust the droop coefficient of the droop control loop in the subsequent steps to eliminate the influence of the voltage outer loop parameters on the output impedance. Among them, the voltage outer loop transfer function can be derived from the voltage outer loop, and the voltage outer loop can be expressed by the following formula: ; in, Indicates the reference value of the inductor current.

[0043] S500: Calculating a voltage closed-loop transfer function according to a unit matrix and the voltage open-loop transfer function.

[0044] The voltage open-loop transfer function is the basis for designing the voltage closed-loop transfer function. In this embodiment, based on the generation relationship between the voltage open-loop transfer function and the voltage closed-loop transfer function, the control module can calculate the addition result of the unit matrix and the voltage open-loop transfer function. After the addition result is calculated, the ratio of the voltage open-loop transfer function to the addition result of the unit matrix and the voltage open-loop transfer function can be calculated to obtain the voltage closed-loop transfer function. The voltage closed-loop transfer function can be calculated by the voltage open-loop transfer function and the unit matrix, as shown in the following formula: ; in, is the voltage closed-loop transfer function.

[0045] S600: Setting the droop control loop to a target representation mode.

[0046] In order to decouple the output impedance from the output power of the inverter and the control loop parameters of the inverter, it is necessary to reset the target representation of the droop control loop. To this end, the control module can first set the final representation of the output impedance, as shown in the following formula: ; in, The final representation of the inverter's output impedance is is the droop coefficient. Since the voltage closed-loop transfer function is a fixed function formula, when the output impedance is finally expressed, when the output impedance is controlled solely by the droop coefficient, that is, the inverter can determine the output impedance of the inverter by adjusting the droop function, so that the output impedance is decoupled from the output power of the inverter and the control loop parameters of the inverter, thereby avoiding the influence of power and control loop parameters on the output impedance.

[0047] Based on the final representation of the output impedance, the target representation of the droop control loop can be reversely derived through the calculation formula of the output impedance.

[0048] To this end, the control module needs to first calculate the current output impedance of the inverter. The calculation formula for the current output impedance can be expressed as follows: ; in, is the current output impedance of the inverter, is the droop control loop. When the negative number of the ratio of the unit matrix to the voltage outer loop transfer function is expressed, the voltage outer loop transfer function including the control loop parameters can be eliminated by calculation. , the transfer function from output current to inductor current and The impact of The open-loop output impedance of the inverter, i.e., the output impedance of the inverter when current control is not performed. By simplifying and eliminating the influence of control parameters on the output impedance, the flexibility of output impedance adjustment is improved.

[0049] In some embodiments, the droop control loop can be expressed as: ; in, is the first voltage reference value, that is, the first voltage reference value after the inverter performs droop control, is the set second voltage reference value, i.e., the voltage reference value of the inverter before droop control, is the droop coefficient.

[0050] After derivation, the control module can calculate the voltage difference between the first voltage reference value and the second voltage reference value, the first voltage reference value is the voltage difference after the inverter performs droop control, and the second voltage reference value is the voltage reference value before the inverter performs droop control. After calculating the voltage difference, the target ratio of the voltage difference to the output current is calculated, and then the sum of the droop coefficient and the target ratio is calculated to obtain the droop control loop, that is, the current representation of the droop control loop. After substituting the current representation of the droop control loop into the calculation formula of the current output impedance, the target representation of the droop control loop can be calculated.

[0051] Among them, after substituting the final representation of the output impedance into the calculation formula of the current output impedance, the following formula can be derived: ; Then the transfer function from inductor current to output voltage is and the transfer function of output current to output voltage After substituting, the target expression of the droop control loop can be obtained. That is, the target expression of the droop control loop is as follows: ; When the target representation of the droop control loop is a negative representation of the ratio of the unit matrix to the voltage outer loop transfer function, the output impedance of the inverter can be controlled separately by the droop coefficient. , and The control loop parameters in the corresponding transfer function cannot affect the output impedance. Therefore, the inverter can adjust the output impedance by changing the droop coefficient alone to balance the power sharing capability and dynamic adjustment capability of the inverter when working in parallel, thereby improving the application flexibility of the inverter.

[0052] The current output impedance can be obtained by calculating the sum of the first impedance result and the second impedance result, wherein the control module can first calculate the difference between the unit matrix and the voltage closed-loop transfer function, and then calculate the product result of the open-loop output impedance and the difference between the unit matrix and the voltage closed-loop transfer function to obtain the first impedance result. The control module can calculate the sum of the droop coefficient, the droop control loop, and the ratio of the transfer function from the output current to the inductor current to the voltage outer loop transfer function, and calculate the product result of the sum and the voltage closed-loop transfer function to obtain the second impedance result.

[0053] The current output impedance can be obtained by adding the first impedance result and the second impedance result, and the target representation of the droop control loop is reversely calculated by the current output impedance and the final representation of the output impedance set in step S600.

[0054] In some embodiments, the open-loop output impedance of the inverter can obtain the transfer function of the output current to the output voltage, the transfer function of the output current to the inductor current, and the transfer function of the inductor current to the output voltage based on the functional relationship in step S100. The control module can first calculate the product result of the transfer function of the output current to the inductor current and the transfer function of the inductor current to the output voltage, and then calculate the difference between the transfer function of the output current to the output voltage in the form of a negative number and the above product result to obtain the open-loop output impedance of the inverter. The open-loop output impedance of the inverter can be expressed by the following formula: ;

[0055] S700: updating the current output impedance of the inverter to a target output impedance according to the voltage closed-loop transfer function and the droop coefficient of the droop control loop through the target representation method.

[0056] Through the target representation of the droop control loop, the output impedance of the inverter can be controlled according to the voltage closed-loop transfer function and the droop coefficient of the droop control loop to update the current output impedance of the inverter to the target output impedance. In the process of updating the target output impedance, the control module can adjust the droop coefficient according to the dynamic performance requirements corresponding to the parallel connection of the inverters and the accuracy requirements of the power sharing, so as to configure the target output impedance suitable for the current working condition within the bandwidth range, thereby solving the problem of output impedance adjustment conflict when realizing the dynamic performance of the inverter and the power sharing capability between the inverters.

[0057] Figure 3 This is a control flow chart of the inverter parallel operation provided in the embodiment of the present application. Figure 3 , wherein the inverter 1 and the inverter 2 are in parallel relationship, and both execute control strategies in the dq coordinate system. Firstly, the control structure and connection relationship of the inverter 1 are described. , are the voltage and current in the d coordinate system, , The voltage and current in the q coordinate system are input into inverter 1. w The power P obtained through power calculation is input into the Pf-Droop module. The Pf-Droop module is an active power-frequency droop control module, which is used to adjust the power sharing capability of inverter 1 and inverter 2.

[0058] After passing through the Pf-Droop module, the power P and the voltage of the three-phase high-voltage line The coordinate transformation module is input together to perform coordinate transformation through s / 1 to convert direct current into alternating current, and the voltage part after coordinate transformation, that is, and After passing through the abc / Dq module, i.e. the Park conversion module, the Park conversion is obtained. and , Parker converted and Input voltage outer loop. The current part after coordinate conversion is the same as the current of three-phase high voltage Input into the Park conversion module together to perform Park conversion to obtain and , in and Input current inner loop to output to the load.

[0059] The inverter 1 also includes a QV-Droop module and a first dynamic control module connected in parallel with the Pf-Droop module, wherein the QV-Droop module is a reactive power-voltage droop control module, and the QV-Droop module and the first dynamic control module can respectively perform dynamic adjustment capabilities. Since the two are connected in parallel, they do not affect each other when performing dynamic adjustment capabilities. The first dynamic control module includes a droop control loop of a d-axis coordinate system arranged in parallel. and virtual impedance , where the virtual impedance The dynamic adjustment capability of inverter 1 can be adjusted to droop the control loop That is, the output impedance of the inverter 1 is adjusted to achieve dynamic adjustment and power sharing capabilities at the same time. The inputs of the QV-Droop module and the first dynamic control module are , thus calculating the voltage reference value in the d coordinate system , and through the voltage outer loop, according to the voltage reference value , output the current reference value in the d coordinate system to the current inner loop The inverter 1 is also provided with a second dynamic control module connected in series with the voltage outer loop, namely, a dynamic control module in the q coordinate system. The second dynamic control module also includes a droop control loop arranged in parallel and virtual impedance .

[0060] It should be noted that the present application only performs dynamic adjustment on the active part, that is, the output impedance in the d coordinate system. Therefore, the droop control loop in the second dynamic control module There is no adjustment effect on the output impedance of the inverter. The second dynamic control module input is , the output of the current inner loop is the current reference value .

[0061] The connection structure and control principle of inverter 2 are the same as those of inverter 1, that is, the input of inverter 2 is , , , .in, , are the voltage and current in the d coordinate system, , The voltage and current in the q coordinate system are input into the inverter 2, and the power P and frequency are calculated by power operation. wInput Pf-Droop module, which is an active power-frequency droop control module used to adjust the power sharing capability of inverter 1 and inverter 2.

[0062] Power P and voltage of three-phase high-voltage line The coordinate transformation module is input together to perform coordinate transformation through s / 1 to convert direct current into alternating current, and the voltage part after coordinate transformation, that is, and After the Park conversion module, the converted and , the converted and Input voltage outer loop. The current part after coordinate conversion is the same as the current of three-phase high voltage The Park conversion module is input together to perform Park conversion to obtain the converted and , that is, converted into alternating current, and then and Input current inner loop to output to the load.

[0063] The inverter 2 also includes a QV-Droop module and a first dynamic control module connected in parallel with the Pf-Droop module, wherein the QV-Droop module is a reactive power-voltage droop control module, and the QV-Droop module and the first dynamic control module can respectively perform dynamic adjustment capabilities without affecting each other. The first dynamic control module includes a droop control loop arranged in parallel. and virtual impedance , where the virtual impedance The dynamic adjustment capability of inverter 2 can be adjusted to droop the control loop The output impedance of the inverter 2 can be adjusted to achieve dynamic adjustment and power sharing capabilities at the same time. The inputs of the QV-Droop module and the first dynamic control module are , thus calculating the voltage reference value in the d coordinate system , and through the voltage outer loop, according to the voltage reference value , output the current reference value in the d coordinate system to the current inner loop The inverter 2 is also provided with a second dynamic control module connected in series with the voltage outer loop, namely, a dynamic control module in the q coordinate system. The second dynamic control module also includes a droop control loop arranged in parallel and virtual impedance .

[0064] It should be noted that the inverter 2 only performs dynamic adjustment on the active part, that is, the output impedance in the d coordinate system. Therefore, the droop control loop in the second dynamic control module There is no adjustment effect on the output impedance of inverter 2. The second dynamic control module input is , the output of the current inner loop is the current reference value .

[0065] In order to achieve power sharing, inverter 2 is provided with a phase-locked loop, which can obtain the voltage of the three-phase high-voltage line input by inverter 1 from the Pf-Droop module of inverter 1. v c,abc,1 , and inside the phase-locked loop, the inverter 2 pairs v c,abc,1 Perform the Park transform, which outputs and and through the PI controller according to and Calculate the phase angle of inverter 2 , and performs current conversion at the phase angle of inverter 1. When inverter 2 maintains the same phase angle as inverter 1, that is, The phase angle in inverter 1 When the two are the same, the same allocated power can be maintained, thus improving the consistency of power allocation.

[0066] It should be noted that the embodiment of the present application only takes two inverters working in parallel as an exemplary illustration. In actual application, the number of inverters can be increased according to the situation of DC power. The working principles and connection relationships of the parallel inverters can refer to the aforementioned embodiments, and this application will not elaborate on them. This application does not make any specific restrictions on the number of parallel inverters.

[0067] Figure 4 A loading voltage fluctuation diagram of the inverter provided in an embodiment of the present application without executing the droop control method. Figure 5 The inverter provided in the embodiment of the present application does not implement the droop control method. Figure 4 and Figure 5 It can be seen that before the droop control method disclosed in the embodiment of the present application is executed, the fluctuating voltage of the inverter is 22.3V when the voltage is loaded, and the fluctuating voltage is 23.5V when the voltage is unloaded. Figure 6 A voltage loading fluctuation diagram of the inverter executing the droop control method provided in an embodiment of the present application. Figure 7 The voltage unloading fluctuation diagram of the inverter performing the droop control method provided in the embodiment of the present application. Figure 6 and Figure 7It can be seen that after the droop control method disclosed in the embodiment of the present application is not executed, the fluctuating voltage of the inverter when the voltage is loaded is 8.8V, and the fluctuating voltage when the voltage is unloaded is 14.6V. It can be seen from the experimental data that the droop control method provided by the present application can effectively reduce the voltage fluctuation amplitude of the inverter when the voltage is loaded and the voltage is unloaded, and improve the dynamic performance of the inverter.

[0068] Some embodiments of the present application also provide a droop control device for an inverter, which is applied to an inverter and used to perform a droop control method for the inverter. The device includes a control module, which can be connected to a dynamic control module in the inverter to perform calculations on a droop control loop in the dynamic control module. The control module is configured to: S100: Obtaining a delay transfer function, a current inner loop transfer function, and a duty cycle to inductor current transfer function.

[0069] S200: Perform product calculation on the delay transfer function, the current inner-loop transfer function, and the duty cycle to inductor current transfer function to obtain a current open-loop transfer function.

[0070] S300: Calculating a current closed-loop transfer function according to a unit matrix and the current open-loop transfer function.

[0071] S400: Perform product calculation on the current closed-loop transfer function, the voltage outer-loop transfer function, and the transfer function from the inductor current to the output voltage to obtain a voltage open-loop transfer function.

[0072] S500: Calculating a voltage closed-loop transfer function according to a unit matrix and the voltage open-loop transfer function.

[0073] S600: Setting the droop control loop to a target representation mode.

[0074] The target representation is a negative representation of the ratio of a unit matrix to the voltage outer loop transfer function.

[0075] S700: updating the current output impedance of the inverter to a target output impedance according to the voltage closed-loop transfer function and the droop coefficient of the droop control loop through the target representation method.

[0076] It can be seen from the above technical scheme that the present application provides a droop control method and device for an inverter, which sets the droop control loop to be represented by the negative number of the ratio of the unit matrix to the voltage outer loop transfer function, and updates the current output impedance of the inverter to the target output impedance according to the voltage closed-loop transfer function and the droop coefficient of the droop control loop, so that the output impedance is adjusted to be controlled and adjusted by the droop coefficient, eliminating the influence of the control loop parameters and the output power on the closed-loop output impedance, reducing the adjustment conflict of the output impedance when the inverter realizes dynamic performance and the power sharing capability between inverters, and improving the flexibility of adjusting the output impedance.

[0077] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit it. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present application.

[0078] For the convenience of explanation, the above description has been made in conjunction with specific embodiments. However, the above exemplary discussion is not intended to be exhaustive or limit the embodiments to the specific forms disclosed above. Based on the above teachings, various modifications and variations can be obtained. The selection and description of the above embodiments are intended to better explain the present disclosure, so that those skilled in the art can better use the embodiments.

Claims

1. A droop control method for an inverter, characterized in that: Applied to inverters, including: Obtain the delay transfer function, the current inner loop transfer function and the duty cycle to inductor current transfer function; Performing product calculation on the delay transfer function, the current inner loop transfer function and the duty cycle to inductor current transfer function to obtain a current open loop transfer function; Calculating a current closed-loop transfer function based on a unit matrix and the current open-loop transfer function; Performing product calculation on the current closed-loop transfer function, the voltage outer-loop transfer function and the transfer function from the inductor current to the output voltage to obtain a voltage open-loop transfer function; Calculate a voltage closed-loop transfer function based on the unit matrix and the voltage open-loop transfer function; Setting the droop control loop of the inverter to a target representation, wherein the target representation is a negative representation of a ratio of a unit matrix to the voltage outer loop transfer function; By means of the target representation, the current output impedance of the inverter is updated to the target output impedance according to the voltage closed-loop transfer function and the droop coefficient of the droop control loop.

2. The droop control method of the inverter according to claim 1, characterized in that: Before the step of setting the droop control loop to the target representation mode, the method further comprises: Calculating a voltage difference between a first voltage reference value and a second voltage reference value; wherein the first voltage reference value is a voltage reference value after the inverter performs droop control, and the second voltage reference value is a voltage reference value before the inverter performs droop control; Calculating a target ratio of the voltage difference to an output current of the inverter; The addition result of the droop coefficient and the target ratio is calculated to obtain the droop control loop.

3. The droop control method of the inverter according to claim 1, characterized in that: The voltage outer loop transfer function can be expressed by the following formula: ； in, is the voltage outer loop transfer function, is the ratio of the voltage outer loop of the inverter, is the integral parameter of the voltage outer loop of the inverter, s is the Laplace variable.

4. The droop control method of the inverter according to claim 3, characterized in that: The current inner loop transfer function can be expressed by the following formula: ； in, is the current inner loop transfer function, is the ratio of the current inner loop of the inverter, is the integral parameter of the current inner loop of the inverter.

5. The droop control method of the inverter according to claim 1, characterized in that: The steps to set up the droop control loop to target representation include: Obtaining a current output impedance of the inverter; the current output impedance is obtained by calculating the addition result of a first impedance result and a second impedance result, the first impedance result is obtained by calculating the product result of an open-loop output impedance and a difference between the unit matrix and the voltage closed-loop transfer function, and the second impedance result is obtained by calculating the addition result of the ratio of the droop coefficient, the droop control loop, and the transfer function from the output current to the inductor current to the voltage outer loop transfer function, and then calculating the product result of the addition result and the voltage closed-loop transfer function; A target representation of the droop control loop is calculated based on the first impedance result and the second impedance result.

6. The droop control method of the inverter according to claim 5, characterized in that: Before the step of obtaining the current output impedance of the inverter, the method further includes: Obtaining a transfer function from output current to output voltage, a transfer function from output current to inductor current, and a transfer function from inductor current to output voltage; Calculate the product of the transfer function from the output current to the inductor current and the transfer function from the inductor current to the output voltage; The open-loop output impedance of the inverter is obtained by calculating the difference between the negative output current to output voltage transfer function and the product of the output current to inductor current transfer function and the inductor current to output voltage transfer function.

7. The droop control method of the inverter according to claim 1, characterized in that: The step of calculating the current closed-loop transfer function according to the unit matrix and the current open-loop transfer function comprises: Calculating an addition result of the unit matrix and the current open-loop transfer function; The current closed-loop transfer function is obtained by calculating a ratio of the current open-loop transfer function to a sum of the unit matrix and the current open-loop transfer function.

8. The droop control method of the inverter according to claim 1, characterized in that: The step of calculating the voltage closed-loop transfer function according to the unit matrix and the voltage open-loop transfer function comprises: Calculating an addition result of the unit matrix and the voltage open-loop transfer function; The voltage closed-loop transfer function is obtained by calculating a ratio of the voltage open-loop transfer function to a sum of the unit matrix and the voltage open-loop transfer function.

9. The droop control method of the inverter according to claim 1, characterized in that: The delay transfer function can be expressed by the following formula: ； in, is the delay transfer function, To control the delay time.

10. A droop control device for an inverter, characterized in that: The invention comprises a control module, wherein the control module is configured to: Obtain the delay transfer function, the current inner loop transfer function and the duty cycle to inductor current transfer function; Performing product calculation on the delay transfer function, the current inner loop transfer function and the duty cycle to inductor current transfer function to obtain a current open loop transfer function; Calculating a current closed-loop transfer function based on a unit matrix and the current open-loop transfer function; Performing product calculation on the current closed-loop transfer function, the voltage outer-loop transfer function and the transfer function from the inductor current to the output voltage to obtain a voltage open-loop transfer function; Calculate a voltage closed-loop transfer function based on the unit matrix and the voltage open-loop transfer function; Setting the droop control loop of the inverter to a target representation, wherein the target representation is a negative representation of a ratio of a unit matrix to the voltage outer loop transfer function; By means of the target representation, the current output impedance of the inverter is updated to the target output impedance according to the voltage closed-loop transfer function and the droop coefficient of the droop control loop.

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