Control circuit, proportional coefficient acquisition method, inverter and energy storage device

Abstract

The application provides a control circuit of an inverter, which is used for obtaining a current of a filter inductor and a value set corresponding to the inductor; performing data fitting on the value set to obtain a fitting function of the inductor and the current of the filter inductor; obtaining a real-time current of the filter inductor, and obtaining a real-time inductance of the filter inductor according to the fitting function; and obtaining a proportional coefficient according to the real-time inductance of the filter inductor and a preset reference inductance. Thus, the control circuit, the proportional coefficient obtaining method, the inverter and the energy storage device provided by the application can guarantee the dynamic and steady-state performance of the inverter and improve the robustness of the inverter to the change of the filter inductor under the condition that the output current of the inverter changes.

Description

Technical Field

[0001] This application relates to the field of energy storage technology, and in particular to a control circuit, a method for obtaining the proportional coefficient, an inverter, and an energy storage device. Background Technology

[0002] With the development of energy storage technology, inverters have been more widely used, among which L-type inverters have become even more prevalent due to their simple structure and ease of control. L-type inverters typically filter the output current using a filter inductor and regulate the output current through a current loop feedback. The core inductance of the filter inductor may change with the current, thus causing the filter inductance to vary with the current.

[0003] However, the control parameters of the current loop controller in the current loop need to be determined based on the filter inductor. When the current of the filter inductor changes, the control parameters of the current loop controller in the current loop cannot follow the real-time inductance value of the filter inductor, which reduces the dynamic and steady-state performance of the inverter. Summary of the Invention

[0004] In view of the above problems, this application provides a control circuit, a proportional coefficient acquisition method, an inverter, and an energy storage device, which can ensure the dynamic and steady-state performance of the inverter under the condition of changes in the output current of the inverter and improve the robustness of the inverter to changes in the filter inductance.

[0005] In a first aspect, this application provides a control circuit for an inverter, which further includes an inverter circuit. The inverter circuit includes at least two switching bridge arms, each of which includes an upper bridge arm switch and a lower bridge arm switch. At least one of the switching bridge arms outputs AC power to the power grid through a filter inductor at its midpoint. The control circuit includes an amplifier, a current loop controller, a control signal generator, and a proportional gain regulator. The amplifier amplifies the error current according to the proportional gain, wherein the error current is the difference between a preset reference current and the current of the filter inductor; the current loop... The controller outputs a reference voltage based on the amplified error current; the control signal generator outputs a control signal based on the reference voltage and the grid voltage, which controls the switching of the upper and lower bridge arm switches; the proportional gain regulator is used to: obtain the set of values ​​for the current of the filter inductor and the corresponding inductance; perform data fitting on the set of values ​​to obtain a fitting function of the inductance and current of the filter inductor; obtain the real-time current of the filter inductor and obtain the real-time inductance of the filter inductor based on the fitting function; and obtain the proportional gain based on the real-time inductance of the filter inductor and a preset reference inductance. The control circuit provided in this application can construct a fitting function and then obtain the proportional gain based on the real-time inductance and a preset reference inductance. By adjusting the proportional gain of the amplifier, the inverter can adapt to the dynamic changes in the current of the filter inductor and adjust the overall transfer function of the current loop control circuit accordingly, thereby enhancing the inverter's robustness to inductance changes.

[0006] In conjunction with the first aspect, in one possible implementation, the reference inductor is the initial inductance of the filter inductor, and the scaling factor is the ratio of the real-time inductance of the filter inductor to the reference inductor.

[0007] In conjunction with the first aspect, in one possible implementation, the proportional coefficient regulator is further used to: obtain at least two corresponding inductance values ​​based on a preset function of the inductance and current of the filter inductor and at least two different current values; and obtain a set of values ​​for the current and corresponding inductance of the filter inductor based on the at least two different current values ​​and the corresponding at least two inductance values; wherein the degree of the highest-order term in the preset function is greater than the degree of the highest-order term in the fitting function. The control circuit provided in this application can obtain a set of values ​​through the preset function, and this set of values ​​can be used to construct a fitting function with a lower degree of the highest-order term, thereby simplifying the computational load of the control circuit and enhancing its operational efficiency.

[0008] In conjunction with the first aspect, in one possible implementation, the proportional gain regulator is further used to: detect the inductance value of the filter inductor under different current values; and obtain a set of values ​​for the filter inductor's current and corresponding inductance based on at least two different current values ​​and their corresponding inductance values. The control circuit provided in this application can obtain the set of values ​​by repeatedly detecting the filter inductor's current and corresponding inductance.

[0009] In conjunction with the first aspect, in one possible implementation, the fitting function is: Where L′ is the real-time inductance of the filter inductor, and P(I) = I n +I n-1 +…+I0,Q(I)=I m +I m-1 +…+I0, where I is the real-time current of the filter inductor, m and n are both integers, and I0 is a preset current constant. The control circuit provided in this application can construct the fitting function as a rational fitting function, which can reduce the computational load of the control circuit without sacrificing significant accuracy.

[0010] In conjunction with the first aspect, in one possible implementation, n = 0 and m = 2.

[0011] Secondly, this application provides a method for obtaining a proportional coefficient, applied to an inverter. The inverter includes an inverter circuit and a control circuit. The inverter circuit includes at least two switching bridge arms, each including an upper bridge arm switch and a lower bridge arm switch. At least one of the switching bridge arms outputs AC power to the grid through a filter inductor at its midpoint. The control circuit includes an amplifier, a current loop controller, a control signal generator, and a proportional coefficient regulator. The amplifier amplifies the error current according to the proportional coefficient, wherein the error current is the difference between a preset reference current and the current of the inverter's output current filter inductor; the current loop controller... The device is used to output a reference voltage based on the amplified error current and the control parameters of the current loop controller; the control signal generator and proportional coefficient regulator are used to output corresponding control signals based on the reference voltage and the grid voltage. The control signal reference voltage is used to control the on / off state of the upper and lower bridge arm switches. The method includes: obtaining the current of the filter inductor and the corresponding inductance value set; performing data fitting on the value set to obtain the fitting function of the filter inductor's inductance and current; obtaining the real-time current of the filter inductor and obtaining the real-time inductance of the filter inductor based on the fitting function; and obtaining the proportional coefficient based on the real-time inductance of the filter inductor and the preset reference inductance.

[0012] In conjunction with the second aspect, in one possible implementation, obtaining the set of values ​​for the current and corresponding inductance of the filter inductor includes: obtaining at least two corresponding inductance values ​​based on a preset function of the inductance and current of the filter inductor and at least two different current values; obtaining the set of values ​​for the current and corresponding inductance of the filter inductor based on the at least two different current values ​​and the at least two corresponding inductance values; wherein the degree of the highest-order term in the preset function is greater than the degree of the highest-order term in the fitting function.

[0013] Thirdly, this application provides an inverter, including an inverter circuit and a control circuit provided by any possible implementation of the first aspect, wherein the control circuit is used to control the output current of the inverter circuit.

[0014] Fourthly, this application provides an energy storage device, including a battery and an inverter as provided in any possible implementation of the third aspect, wherein the battery is used to provide an input voltage to the inverter.

[0015] Furthermore, the beneficial effects of the various possible implementation methods in the second, third, and fourth aspects can be referred to the beneficial effects of the corresponding implementation methods in the first aspect, and will not be elaborated here. Attached Figure Description

[0016] Figure 1 A schematic diagram of the energy storage device provided in this application.

[0017] Figure 2 A schematic diagram of the inverter provided in this application.

[0018] Figure 3 A schematic diagram of the control circuit provided in this application.

[0019] Figure 4 The control block diagram of the inverter provided in this application.

[0020] Figure 5 Image of the preset function provided in this application.

[0021] Figure 6 A schematic diagram of the fitting function provided in this application.

[0022] Figure 7 The Bode plot of the inverter without an amplifier and proportional regulator.

[0023] Figure 8 Bode plot of the inverter provided in this application.

[0024] Figure 9 A flowchart illustrating the method for obtaining the proportional coefficient provided in this application. Detailed Implementation

[0025] The technical solutions in the embodiments of this application will be clearly described below with reference to the accompanying drawings.

[0026] It is understood that the connection relationships described in this application refer to direct or indirect connections. For example, the connection between A and B can be a direct connection between A and B, or an indirect connection between A and B through one or more other electrical components. For example, A can be directly connected to C, and C can be directly connected to B, thus achieving a connection between A and B through C. It is also understood that the "A connects to B" described in this application can be a direct connection between A and B, or an indirect connection between A and B through one or more other electrical components.

[0027] In the description of this application, unless otherwise stated, " / " means "or". For example, A / B can mean A or B. The "and / or" in this document is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent three cases: A exists alone, A and B exist simultaneously, and B exists alone.

[0028] In the description of this application, the words "first," "second," etc., are used only to distinguish different objects and do not limit the quantity or order of execution, nor do they imply that they must be different. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion.

[0029] With the development of energy storage technology, inverters have been more widely used, among which L-type inverters have become even more prevalent due to their simple structure and ease of control. L-type inverters typically filter the output current using a filter inductor and regulate the output current through current loop feedback. The core inductance of the filter inductor may vary with the current. For example, the inductance of a powder core may decrease as the current increases, and the inductance of the powder core exhibits a non-linear relationship with the current, thus causing the filter inductance to change with the current.

[0030] However, the control parameters of the current loop controller in the current loop, such as the proportional coefficient Kp and integral coefficient Ki of the proportional-integral (PI) controller, need to be determined based on the filter inductor. As a result, when the current of the filter inductor changes, the control parameters of the current loop controller in the current loop cannot follow the real-time inductance value of the filter inductor, which reduces the dynamic and steady-state performance of the inverter.

[0031] Therefore, this application provides a control circuit, a proportional coefficient acquisition method, an inverter, and an energy storage device, which can ensure the dynamic and steady-state performance of the inverter under the condition of changes in the output current of the inverter, and improve the robustness of the inverter to changes in the filter inductance.

[0032] Specifically, please refer to Figure 1 , Figure 1 This is a schematic diagram of the energy storage device 10 provided in this application. The energy storage device 10 includes a battery 11 and an inverter 12. The battery 11 is connected to the inverter 12. The battery 11 is used to output voltage, which is converted by the inverter 12 and then output to an external device. The external device can also output charging voltage, which is converted by the inverter 12 to charge the battery 11.

[0033] The inverter 12 can be a bidirectional inverter circuit, and external devices can include AC loads, other energy storage devices, battery devices, and the power grid. For example, when the inverter 12 is connected to an AC load, it can output the electrical energy provided by the battery 11 to the AC load to provide AC power. As another example, when the inverter 12 is connected to other energy storage devices, it can provide the electrical energy output from the battery 11 to those devices, or output the electrical energy stored in other energy storage devices to the battery 11, thus transferring electrical energy between different energy storage devices. Furthermore, when the inverter 12 is connected to the power grid, it can output the electrical energy provided by the grid to the battery 11 to charge it, or convert the electrical energy output from the battery 11 into AC power and feed it into the grid.

[0034] Please see Figure 2 , Figure 2 This is a schematic diagram of the inverter 12 provided in this application. The inverter 12 includes an inverter circuit 121 and a control circuit 122. The inverter circuit 121 includes an L-type single-phase inverter circuit. Specifically, the L-type single-phase inverter circuit includes a first switch arm and a second switch arm. The two ends of the first switch arm are connected to the two ends of the second switch arm, the two ends of the bus capacitor C, and the two ends of the battery 11 (not shown in the figure). The first switch arm includes a switch transistor Q1 and a switch transistor Q2, wherein switch transistor Q1 is the upper switch arm of the first switch arm, and switch transistor Q2 is the lower switch arm of the first switch arm. The second switch arm includes a switch transistor Q3 and a switch transistor Q4, wherein switch transistor Q3 is the upper switch arm of the second switch arm, and switch transistor Q4 is the lower switch arm of the second switch arm. The midpoint of the first switch arm is connected to the power grid through a filter inductor L, and the midpoint of the second switch arm is also connected to the power grid.

[0035] The inverter circuit 121 periodically turns on and off via switches Q1, Q2, Q3, and Q4 to convert the input voltage provided by the battery 11 into grid voltage and feed it into the power grid, or to convert the grid voltage into a charging voltage to charge the battery 11. The voltage across the battery 11 is V. dc The current in the filter inductor L is I. g The grid voltage is V g .

[0036] Control circuit 122 connects to switching transistors Q1, Q2, Q3, and Q4. Control circuit 122 outputs control signals to control the on / off state of switching transistors Q1, Q2, Q3, and Q4. By adjusting the parameters of the control signals, parameters such as the duty cycle and switching frequency of switching transistors Q1, Q2, Q3, and Q4 can be adjusted, thereby changing the output current parameters of inverter circuit 121. For example, by adjusting the duty cycle of the control signals, the magnitude of the current output at the midpoint of the first switching arm can be adjusted.

[0037] This embodiment uses the example of connecting the output terminal of inverter 12 to the power grid. In some embodiments, the output terminal of inverter 12 can also be connected to external devices, such as AC loads, other energy storage devices, battery devices, etc. Correspondingly, the grid voltage in this embodiment can be replaced by the voltage of the AC load, the voltage of other energy storage devices, the battery voltage, etc. This application does not limit the devices connected to the output terminal of inverter 12.

[0038] In some embodiments, the inverter circuit 121 may also include an L-type three-phase inverter circuit or other inverter circuits. This application does not limit the type of inverter circuit 121.

[0039] Please see Figure 3 , Figure 3 This is a schematic diagram of the control circuit 122 provided in this application. The control circuit 122 includes a current loop control circuit, which specifically includes an adder 122a, an amplifier 122b, a current loop controller 122c, an adder 122d, a control signal generator 122e, and a proportional coefficient adjuster 122f.

[0040] Adder 122a is used to receive a preset reference current I ref and the current I of the filter inductor L g and set the preset reference current I ref and the current I of the filter inductor L g The error current is obtained by subtracting the two.

[0041] Amplifier 122b is connected to adder 122a. Amplifier 122b is used to amplify the error current according to a proportional coefficient.

[0042] A current loop controller 122c is connected to an amplifier 122b. The current loop controller 122c outputs a reference voltage based on the amplified error current. Specifically, the current loop controller 122c obtains the reference voltage from the amplified error current according to control parameters. These control parameters can be inherent parameters of the controller. For example, when the current loop controller 122c is a PI controller, the control parameters include the proportional coefficient Kp, integral coefficient Ki, and derivative coefficient Kd of the PI controller. Alternatively, when the current loop controller 122c is a PR controller, the control parameters include the proportional coefficient Kp, integral coefficient Ki, and resonant coefficient Kr of the PR controller.

[0043] Adder 122d is used to receive the reference voltage and the grid voltage, and to superimpose the grid voltage and the reference voltage to obtain the superimposed voltage.

[0044] It is understandable that the adder 122d can achieve grid voltage feedforward, which can offset the impact of grid voltage disturbances on the current loop control circuit and enhance the stability of the current loop control circuit and the inverter.

[0045] Control signal generator 122e is connected to adder 122d. Control signal generator 122e outputs corresponding control signals to switches Q1, Q2, Q3, and Q4 based on the superimposed voltage. These control signals are used to control the on / off state of switches Q1, Q2, Q3, and Q4. Specifically, control signal generator 122e uses the superimposed voltage as the modulation wave and a preset triangular carrier wave as the carrier wave to modulate the control signal. When the voltage of the preset triangular carrier wave is greater than the modulation wave, the control signal is high; when the voltage of the preset triangular carrier wave is less than the modulation wave, the control signal is low. Thus, control signal generator 122e can generate a pulse width modulation (PWM) signal, i.e., the control signal, which controls the on / off state of switches Q1, Q2, Q3, and Q4 according to a specific duty cycle, causing the output voltage waveform of inverter circuit 121 to follow the modulation wave. The proportional gain regulator 122f is connected to the amplifier 122b. The proportional gain regulator 122f is used to determine the proportional gain of the amplifier 122b. Specifically, the proportional gain regulator 122f is used to obtain the current of the filter inductor L and the corresponding set of inductance values.

[0046] The set of values ​​includes at least two combinations of the current and corresponding inductance values ​​of the filter inductor L. For example, when the current of the filter inductor L is 10A, the corresponding inductance is 0.43mH, then 10A and 0.43mH constitute one combination in the set of values. As another example, when the current of the filter inductor L is 50A, the corresponding inductance is 0.24mH, then 50A and 0.24mH constitute another combination in the set of values. These two combinations of values ​​can constitute one set of values, and a set of values ​​can also include more combinations, such as three or more combinations. This application limits the number of combinations of values ​​included in the set to at least two, without imposing any other limitations.

[0047] Obtaining the set of values ​​for the current and corresponding inductance of the filter inductor L can include: obtaining the set of values ​​based on a preset function relating the inductance and current of the filter inductor L. Specifically, the preset function can be a function derived from multiple equations or formulas such as the DC bias curve equation of the filter inductor L, Ampere's law, and the inductance equation. The DC bias curve equation of the filter inductor L can be expressed as formula (1) as follows:

[0048]

[0049] Where a, b, c, and d are preset equation parameters, μ is the permeability of the filter inductor L, μ0 is the initial permeability of the filter inductor L, and H is the magnetic field strength. a, b, c, and d can be determined based on the material of the magnetic core in the filter inductor L.

[0050] Ampere's law can be expressed as formula (2) as follows:

[0051]

[0052] Where H is the magnetic field strength, N is the number of turns of the filter inductor L, I is the current in the filter inductor L, and l is the effective magnetic path length.

[0053] The inductance equation can be expressed as formula (3) as follows:

[0054]

[0055] Where A is the effective core cross-sectional area.

[0056] Thus, the preset function can be derived from formulas (1) to (3) as shown in formula (4):

[0057]

[0058] At this point, by substituting the two preset current values ​​A1 and A2 into formula (4), the inductances L1 and L2 of the corresponding filter inductor L can be calculated. A1 and L1 can form a value combination, and A2 and L2 can form a value combination. The two value combinations can form a value set, and thus the value set can be obtained according to the preset function.

[0059] Obtaining the current and corresponding inductance value set of the filter inductor L can further include: detecting the inductance value of the filter inductor L under different current values, and obtaining the current and corresponding inductance value set of the filter inductor based on at least two different current values ​​and their corresponding inductance values. For example, a preset first current and a second current, A1 and A2, can be passed into the filter inductor L, and the corresponding real-time inductance values ​​L1 and L2 of the filter inductor L can be detected. A1 and L1 can form a value combination, and A2 and L2 can form a value combination. These two value combinations can form a value set, thereby obtaining the value set based on the detected inductance value of the filter inductor L under different current values.

[0060] The proportional coefficient regulator 122f is also used to perform data fitting on the acquired set of values ​​to obtain the fitting function of the inductance of the filter inductor to the current. Among them, data fitting refers to approximately connecting multiple two-dimensional coordinate points through a smooth curve, and the function satisfied by the equation of this smooth curve is the fitting function. For example, the set of values ​​includes multiple combinations of values, each combination of values ​​is equivalent to a two-dimensional coordinate point, the horizontal axis is the current and the vertical axis is the inductance. All the combinations of values ​​are approximately connected through a curve, and the equation of the curve is the fitting function. Data fitting methods can include polynomial fitting, exponential fitting, logarithmic fitting, power function fitting, rational function fitting, etc., which are not limited in this application. Taking rational function fitting as an example, after performing data fitting on the combination of values ​​in the set of values ​​through the rational function fitting method, a rational fitting function can be obtained. The rational fitting function can be expressed as formula (5) as follows:

[0061]

[0062] Where L′ is the real-time inductance of the filter inductor L, I is the real-time current of the filter inductor L, and I0 is the preset current constant. m and n are positive integers and can be set as needed.

[0063] Since the highest term c in the preset function represented by formula (4) is relatively high, it may affect the calculation efficiency and performance of the proportional coefficient regulator 122f. However, the highest term m or n in the rational fitting function represented by formula (5) can be set by the user. Therefore, by setting a smaller m or n, the complexity of the function of inductance versus current of the filter inductor can be reduced, thereby improving the calculation efficiency and performance of the proportional coefficient regulator 122f and saving the CPU resources occupied by the proportional coefficient regulator 122f.

[0064] The proportional gain regulator 122f is also used to obtain the real-time current of the filter inductor L and to obtain the real-time inductance of the filter inductor according to the fitting function. For example, the proportional gain regulator 122f can detect the real-time current of the filter inductor L and substitute the detected real-time current of the filter inductor L into the fitting function shown in formula (5) to obtain the real-time inductance of the filter inductor L.

[0065] The proportional coefficient regulator 122f is also used to obtain the proportional coefficient based on the real-time inductance of the filter inductor L and the preset reference inductance. The preset reference inductance is the inductance value of the filter inductor L corresponding to the control parameters of the current loop controller, or the initial inductance of the filter inductor L. It can be understood that the control parameters of the current loop controller 122c can be determined based on the inductance value of the filter inductor L, and the inductance value of the filter inductor L corresponding to the determined control parameters of the current loop controller 122c is the preset reference inductance. Specifically, the relationship between the real-time inductance of the filter inductor L, the preset reference inductance, and the proportional coefficient satisfies formula (6) as follows:

[0066]

[0067] Where λ is the proportionality coefficient and L0 is the preset reference inductance.

[0068] Therefore, the control circuit 122 provided in this application can construct a fitting function by acquiring the set of current and inductance values ​​of the filter inductor L, and obtain the real-time inductance from the real-time current of the filter inductor L through the fitting function. Then, it obtains the proportional coefficient based on the real-time inductance and a preset reference inductance. By adjusting the proportional coefficient of the amplifier 122b, without changing the control parameters of the current loop controller 122c, the inverter 12 can adapt to the dynamic changes in the current of the filter inductor L and adjust the overall transfer function of the current loop control circuit accordingly. This reduces the adverse effects of the inductance of the filter inductor L decreasing with increasing current on the current loop control circuit, so that the frequency characteristics exhibited by the inverter 12 when the current of the filter inductor L is different are consistent with the frequency characteristics designed based on the initial inductance of the filter inductor L, thus enhancing the robustness of the inverter 12 to inductance changes.

[0069] Please see Figure 4 , Figure 4This is a control block diagram of the inverter 12 provided in this application. The formula within each block represents the transfer function of the corresponding electronic component. For example, for amplifier 122b, the proportional gain λ is its transfer function. For current loop controller 122c, taking a PI controller as an example, Kp + Ki / s is the transfer function of current loop controller 122c, where Kp is the proportional gain, Ki is the integral gain, and s is a complex number in the Laplace transform. For another example, for inverter circuit 121, Kpwm is the transfer function of inverter circuit 121, or equivalent gain coefficient, and after per-unit scaling, Kpwm = 1. For yet another example, for filter inductor L, 1 / Ls is the transfer function of filter inductor L, where L is the real-time inductance of filter inductor L, and s is a complex number in the Laplace transform.

[0070] The beneficial effects of the control circuit 122 of this application will be explained in detail below with reference to test data. It should be understood that all physical quantities involved in this application are example values, used only to illustrate the beneficial effects of the control circuit 122, and this application does not impose any limitations on the values ​​of any physical quantities.

[0071] Please see Figure 5 , Figure 5 An image of the preset function provided in this application. For example... Figure 5 As shown, the initial inductance of the filter inductor L is approximately 441.6 μH. When the current flowing through the filter inductor L reaches the peak full-load current of 70 A, the real-time inductance of the filter inductor L is approximately 155.5 μH, which is 35% of the initial inductance. Therefore, if the control parameters of the current loop controller 122c are designed based on a fixed preset reference inductance, the real-time inductance of the filter inductor L changes with the current, resulting in poor dynamic stability of the inverter 12.

[0072] Please see Figure 6 , Figure 6 A schematic diagram of the fitting function provided in this application. For example... Figure 6 As shown, with Figure 5 The fitting function is constructed by taking at least two points on the graph of the preset function as the set of values. For example, for ease of calculation, m=2 and n=2 are taken, and the fitting function is shown in formula (7):

[0073]

[0074] Calculate the coefficient of determination R between the fitted function and the preset function based on their graphs. 2 =0.999, Root Mean Square Error (RMSE) = 8.687 * 10 -7 The coefficient of determination represents the proportion of the total variation of the dependent variable that can be explained by the independent variable through the regression relationship. In this embodiment, R02 A value close to 1 indicates a high degree of fit between the fitted function and the preset function, suggesting a strong correlation between them. The root mean square error (RMSE) characterizes the average deviation between the predicted and actual values; in this embodiment, RMSE is close to 0, indicating a small average deviation between the fitted function and the preset function. In summary, constructing the fitted function using the preset function not only reduces the computational load of the control circuit 122 but also ensures high computational accuracy and low computational deviation.

[0075] Please see Figure 7 , Figure 7 The Bode plot of inverter 12 is shown without amplifier 122b and proportional regulator 122f. Figure 5 Taking the initial inductance of the filter inductor L (441.6 μH) as an example, the control parameters of the current loop controller 122c are designed. The initial inductance of the filter inductor L (441.6 μH) is then used as the preset reference inductance. Following the design principles of a phase margin of not less than 45°, an amplitude margin of not less than 10 dB, and a current loop bandwidth of 2 kHz, after designing the control parameters of the current loop controller 122c, the amplitude-frequency characteristic curve and phase-frequency characteristic curve of the inverter 12 are shown as solid lines P11 and P12 in the figure, respectively. When the real-time inductance of the filter inductor L decays to 155.5 μH, the amplitude-frequency characteristic curve and phase-frequency characteristic curve of the inverter 12 are shown as dashed lines P21 and P22 in the figure, respectively.

[0076] The method for determining the phase margin of inverter 12 based on the Bode plot includes: determining the frequency value corresponding to zero gain on the amplitude-frequency response curve, i.e., taking the point with a vertical coordinate of 0 on the amplitude-frequency response curve, determining the horizontal coordinate of that point, and then determining the phase corresponding to that frequency value on the phase-frequency response curve, i.e., taking the point with the horizontal coordinate of that frequency value on the phase-frequency response curve, and determining the vertical coordinate of that point. The absolute value of the difference between this vertical coordinate and 180° is then the phase margin of inverter 12.

[0077] For example, as shown by solid lines P11 and P12, the inverter 12 has a phase margin of 58° when the real-time inductance of the filter inductor L is the initial inductance of 441.6μH. As another example, as shown by dashed lines P21 and P22, the inverter 12 has a phase margin of 26.1° when the control parameters of the current loop controller 122c remain unchanged and the real-time inductance of the filter inductor L is 155.5μH.

[0078] The method for determining the gain margin of inverter 12 based on the Bode plot includes: determining the frequency value corresponding to a phase of -180° on the phase frequency response curve, i.e., taking the point on the phase frequency response curve with a vertical coordinate of -180°, determining the horizontal coordinate of that point, and then determining the gain corresponding to that frequency value on the amplitude frequency response curve, i.e., taking the point on the amplitude frequency response curve with the horizontal coordinate of that frequency value, and determining the vertical coordinate of that point. The absolute value of this vertical coordinate is then the gain margin of inverter 12.

[0079] For example, as shown by solid lines P11 and P12, the inverter 12 has a gain margin of 16.4 dB when the real-time inductance of the filter inductor L is the initial inductance of 441.6 μH. As another example, as shown by dashed lines P21 and P22, the inverter 12 has a gain margin of 7.32 dB when the control parameters of the current loop controller 122c remain unchanged and the real-time inductance of the filter inductor L is 155.5 μH.

[0080] It can be seen that without amplifier 122b and proportional coefficient regulator 122f, the phase margin and amplitude margin of inverter 12 will decrease as the inductance of filter inductor L decays. The reduction in phase margin and amplitude margin will lead to adverse consequences such as decreased operating stability of inverter 12 and signal oscillation.

[0081] Please see Figure 8 , Figure 8 The Bode plot of the inverter 12 provided in this application is shown. That is, the Bode plot of the inverter 12 when using amplifier 122b and proportional coefficient regulator 122f. When the real-time inductance of the filter inductor L decays to 155.5μH, the amplitude-frequency characteristic curve and phase-frequency characteristic curve of the inverter 12 are shown as solid lines P31 and P32 in the figure, respectively.

[0082] As shown by solid lines P11 and P12, when amplifier 122b and proportional coefficient regulator 122f are used, with the control parameters of current loop controller 122c remaining unchanged, when the real-time inductance of filter inductor L is 155.5μH, the phase margin of inverter 12 is 58.2° and the amplitude margin is 16.5dB, which are almost the same as the phase margin and amplitude margin when the real-time inductance of filter inductor L is the initial inductance value.

[0083] Therefore, by adjusting the proportional gain of amplifier 122b without changing the control parameters of current loop controller 122c, this application enables inverter 12 to adapt to the dynamic changes in the current of filter inductor L and adjust the overall transfer function of current loop control circuit accordingly. This reduces the adverse effects of the inductance of filter inductor L decreasing with increasing current on current loop control circuit, ensuring that the frequency characteristics exhibited by inverter 12 are basically consistent with the frequency characteristics designed based on the initial inductance of filter inductor L when the current of filter inductor L is different, thus enhancing the robustness of inverter 12 to inductance changes.

[0084] Please see Figure 9 , Figure 9 A flowchart illustrating the proportional gain acquisition method provided in this application. The proportional gain acquisition method provided in this application is applied to the inverter 12 provided in this application. The proportional gain acquisition method provided in this application includes the following steps:

[0085] Step S1: Obtain the current of the filter inductor L and the set of values ​​for the corresponding inductor.

[0086] The process of obtaining the set of values ​​for the current and corresponding inductance of the filter inductor L may include: obtaining the set of values ​​based on a preset function of the inductance and current of the filter inductor L; detecting the inductance value of the filter inductor L under different current values; and obtaining the set of values ​​for the current and corresponding inductance of the filter inductor based on at least two different current values ​​and their corresponding inductance values. For details, please refer to the above description regarding the proportional coefficient regulator 122f obtaining the set of values ​​for the current and corresponding inductance of the filter inductor L, which will not be repeated here.

[0087] Step S2: Perform data fitting on the set of values ​​to obtain the fitting function of inductance and current of the filter inductor L.

[0088] Data fitting can include polynomial fitting, exponential fitting, logarithmic fitting, power function fitting, rational function fitting, etc. For details, please refer to the above description regarding data fitting using the proportional coefficient adjuster 122f; it will not be repeated here.

[0089] Step S3: Obtain the real-time current of the filter inductor L, and obtain the real-time inductance of the filter inductor L according to the fitting function.

[0090] Specifically, the real-time inductance of the filter inductor L can be obtained by detecting the real-time current and substituting it into a fitting function. For details, please refer to the above description regarding the proportional gain regulator 122f obtaining the real-time inductance of the filter inductor based on the fitting function; further elaboration will not be repeated here.

[0091] Step S4: Obtain the scaling factor based on the real-time inductance of the filter inductor L and the preset reference inductance.

[0092] The preset reference inductance is the inductance value of the filter inductance L corresponding to the control parameters of the current loop controller. The proportional gain is the amplification factor of amplifier 122b. For details, please refer to the above description regarding the proportional gain adjuster 122f obtaining the proportional gain based on the real-time inductance of the filter inductance L and the preset reference inductance; it will not be repeated here.

[0093] Therefore, the control circuit 100, proportional coefficient acquisition method, inverter 12 and energy storage device 10 provided in this application can ensure the dynamic and steady-state performance of inverter 12 under the condition of output current variation, and improve the robustness of inverter 12 to filter inductor L variation.

[0094] Those skilled in the art should recognize that the above embodiments are only used to illustrate this application and are not intended to limit this application. Any appropriate changes and variations made to the above embodiments within the essential spirit and scope of this application fall within the scope of protection claimed in this application.

Claims

1. A control circuit for an inverter, the inverter further comprising an inverter circuit, the inverter circuit comprising at least two switching transistor bridge arms, each switching transistor bridge arm comprising an upper bridge arm switch and a lower bridge arm switch, wherein the midpoint of at least one of the switching transistor bridge arms outputs AC current to an output terminal through a filter inductor, characterized in that, The control circuit includes an amplifier, a current loop controller, a control signal generator, and a proportional coefficient adjuster. The amplifier is used to amplify the error current according to the proportional coefficient, wherein the error current is the difference between a preset reference current and the current of the filter inductor. The current loop controller is used to output a reference voltage based on the amplified error current; The control signal generator is used to output a control signal based on the reference voltage and the voltage at the output terminal. The control signal is used to control the on / off state of the upper bridge arm switch and the lower bridge arm switch. The proportional coefficient adjuster is used for: Based on the preset function of the inductance and current of the filter inductor and the at least two different current values, at least two corresponding inductance values ​​are obtained. The set of values ​​for the current of the filter inductor and the corresponding inductor values ​​is obtained based on the at least two different current values ​​and the at least two corresponding inductance values. By performing data fitting on the set of values, a fitting function for the inductance and current of the filter inductor is obtained, and the fitting function is: ,in, The real-time inductance of the filter inductor is... , , Let m and n be the real-time current of the filter inductor, where m and n are both integers. The current constant is a preset value; wherein the degree of the highest-order term in the preset function is greater than the degree of the highest-order term in the fitted function; Obtain the real-time current of the filter inductor, and obtain the real-time inductance of the filter inductor according to the fitting function; The scaling factor is obtained by comparing the real-time inductance of the filter inductor with a preset reference inductance, wherein the reference inductance is the initial inductance of the filter inductor, and the scaling factor is the ratio of the real-time inductance of the filter inductor to the initial inductance.

2. The control circuit as described in claim 1, characterized in that, The output terminal is connected to the power grid or a load.

3. The control circuit as described in claim 1, characterized in that, Where n=0 and m=2.

4. A method for obtaining a proportional coefficient, applied to an inverter, the inverter including an inverter circuit and a control circuit, the inverter circuit including at least two switching bridge arms, each switching bridge arm including an upper bridge arm switch and a lower bridge arm switch, the midpoint of at least one of the switching bridge arms outputting AC current to the power grid through a filter inductor, the control circuit including an amplifier, a current loop controller, a control signal generator, and a proportional coefficient adjuster, the amplifier being used to amplify the error current according to the proportional coefficient, wherein... The error current is the difference between a preset reference current and the current of the filter inductor. The current loop controller is used to output a reference voltage based on the amplified error current and the control parameters of the current loop controller; the control signal generator proportional coefficient regulator is used to output a corresponding control signal based on the reference voltage and the grid voltage, the control signal reference voltage being used to control the on / off state of the upper bridge arm switch and the lower bridge arm switch, characterized in that the method includes: Based on the preset function of the inductance and current of the filter inductor and the at least two different current values, at least two corresponding inductance values ​​are obtained. The set of values ​​for the current of the filter inductor and the corresponding inductor values ​​is obtained based on the at least two different current values ​​and the at least two corresponding inductance values. By performing data fitting on the set of values, a fitting function for the inductance and current of the filter inductor is obtained, and the fitting function is: ,in, The real-time inductance of the filter inductor is... , , Let m and n be the real-time current of the filter inductor, where m and n are both integers. The current constant is a preset value; wherein the degree of the highest-order term in the preset function is greater than the degree of the highest-order term in the fitted function; Obtain the real-time current of the filter inductor, and obtain the real-time inductance of the filter inductor according to the fitting function; The scaling factor is obtained by comparing the real-time inductance of the filter inductor with a preset reference inductance, wherein the reference inductance is the initial inductance of the filter inductor, and the scaling factor is the ratio of the real-time inductance of the filter inductor to the initial inductance.

5. An inverter, characterized in that, It includes an inverter circuit and a control circuit as described in any one of claims 1 to 3, wherein the control circuit is used to control the output current of the inverter circuit.

6. An energy storage device, characterized in that, Includes a battery and an inverter as described in claim 5, wherein the battery is used to provide an input voltage to the inverter.

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