A grid-connected control strategy, device and readable storage medium for micro inverter

Abstract

The embodiment of the present invention discloses a grid-connected control strategy, device and readable storage medium of a micro-inverter, wherein the grid-connected control strategy includes: obtaining the grid-connected output voltage and bus voltage of the target inverter; using a second-order generalized integrator to convert the grid-connected output voltage into α-axis and β-axis output voltages; using the converted α-axis and β-axis output voltages to determine the bus voltage reference value of the target inverter; using the bus voltage reference value and the bus voltage, determining the corresponding control law through an integral sliding mode voltage controller; using the determined control law, determining an initial modulation signal through a current controller; using a preset secondary modulation strategy to process the initial modulation signal to obtain a target modulation signal. The present invention solves the technical problems of large front-end and rear-end circuit losses and low energy conversion efficiency in the prior art due to a high bus voltage setting value, and achieves the technical effect of reducing the front-end and rear-end circuit losses of the inverter and improving the energy conversion efficiency of the inverter while ensuring the minimization of the bus voltage.

Description

Technical Field

[0001] The embodiments of the present invention relate to the technical field of inverter grid-connected control, and in particular to a grid-connected control strategy, device and readable storage medium for a micro inverter. Background Art

[0002] In a two-stage high-frequency link inverter, the size of the bus voltage often affects the energy conversion efficiency of the inverter. In order to obtain sufficient output capacity, it is necessary to consider factors such as switch duty cycle limitation, transformer ratio, grid voltage fluctuation, switch dead zone, etc. to increase the bus voltage, which is generally a constant value and may bear a certain double frequency fluctuation. However, a higher bus voltage will lead to the following efficiency losses:

[0003] (1) The switching duty cycle of the boost circuit increases, resulting in higher conduction losses and a significant reduction in the efficiency of the previous stage.

[0004] (2) The voltage stress of the subsequent switching tube increases significantly. If there is a high-ratio transformer, the voltage stress of the secondary switching tube will increase especially, and the switching loss will also increase.

[0005] (3) The setting of bus voltage needs to take into account the maximum grid voltage fluctuation of ±10%. However, in reality, most operating conditions still operate near the standard grid amplitude voltage. If designed according to the maximum margin, it will cause non-negligible voltage stress and increase in switching losses. Summary of the invention

[0006] The embodiments of the present invention provide a micro-inverter grid-connected control strategy, device and readable storage medium, which solve the technical problems in the prior art of large front-end and rear-end circuit losses and low energy conversion efficiency due to high bus voltage setting values.

[0007] An embodiment of the present invention provides a micro-inverter grid-connected control strategy, the grid-connected control strategy comprising:

[0008] Obtain the grid-connected side output voltage and bus voltage of the target inverter;

[0009] The grid-connected side output voltage is converted into α-axis and β-axis output voltages by using a second-order generalized integrator;

[0010] Determine the bus voltage reference value of the target inverter using the converted α-axis and β-axis output voltages;

[0011] Determining a corresponding control law by an integral sliding mode voltage controller using the bus voltage reference value and the bus voltage;

[0012] Using the determined control law, an initial modulation signal is determined by a current controller;

[0013] The initial modulation signal is processed using a preset secondary side modulation strategy to obtain a target modulation signal.

[0014] Further, determining the bus voltage reference value of the target inverter using the converted α-axis and β-axis output voltages includes:

[0015] The converted α-axis and β-axis output voltages are used to perform amplitude calculation to obtain the output amplitude voltage;

[0016] The bus voltage reference value is determined using the output amplitude voltage and transformer parameters of the target inverter, wherein the transformer parameters at least include a transformer step-up ratio, a duty cycle, and a switch tube dead zone margin.

[0017] Further, using the bus voltage reference value and the bus voltage, determining a corresponding control law through an integral sliding mode voltage controller includes:

[0018] The tracking error of the bus voltage is defined as a state variable of the integral sliding mode voltage controller, and the integral sliding mode surface is constructed using the state variable;

[0019] Introducing an exponential reaching law by using the differential of the integral sliding surface;

[0020] Constructing a power model between the bus voltage and the output active power;

[0021] The corresponding control law is determined by using the bus voltage reference value, the integral sliding mode surface, the reaching law and the power model.

[0022] Further, using the determined control law, determining an initial modulation signal through a current controller includes:

[0023] determining a current reference value using the control law;

[0024] Obtaining a secondary side filter current of the target inverter;

[0025] Inputting the current reference value and the secondary-side filter current into a current controller to obtain a first output;

[0026] The initial modulation signal is determined using the first output quantity, the grid voltage, the step-up transformation ratio of the transformer, and the bus voltage, wherein the grid voltage is the voltage of the grid to which the target inverter is to be connected.

[0027] Further, determining the initial modulation signal using the first output quantity, the grid voltage, the step-up transformation ratio of the transformer, and the bus voltage includes:

[0028] The first output quantity is added to the grid voltage, and the obtained sum is divided by the product of the step-up transformation ratio of the transformer and the bus voltage to obtain the initial modulation signal.

[0029] Further, determining the current reference value by using the control law includes:

[0030] The current reference value is determined by using the control law, the α-axis output voltage, the β-axis output voltage, and the reactive power reference value of the target inverter.

[0031] The embodiment of the present invention further provides a micro-inverter grid-connected control device, the grid-connected control device comprising:

[0032] A voltage acquisition unit, used to acquire the grid-connected side output voltage and bus voltage of the target inverter;

[0033] A voltage conversion unit, used for converting the grid-connected side output voltage into α-axis and β-axis output voltages by using a second-order generalized integrator;

[0034] A reference voltage determination unit, used to determine a bus voltage reference value of the target inverter using the converted α-axis and β-axis output voltages;

[0035] A control signal determination unit, configured to determine a corresponding control law by using the bus voltage reference value and the bus voltage through an integral sliding mode voltage controller;

[0036] A first modulation signal determination unit, configured to determine an initial modulation signal through a current controller using the determined control law;

[0037] The second modulation signal determination unit is used to process the initial modulation signal using a preset secondary side modulation strategy to obtain a target modulation signal.

[0038] The embodiment of the present invention further provides a micro-inverter grid-connected control device, the micro-inverter grid-connected control device comprising:

[0039] at least one processor; and

[0040] a memory communicatively connected to the at least one processor; wherein,

[0041] The memory stores a computer program executable by the at least one processor, and the computer program is executed by the at least one processor so that the at least one processor can execute the grid-connected control method of the micro-inverter described in any of the above embodiments.

[0042] An embodiment of the present invention further provides a computer-readable storage medium, wherein the computer-readable storage medium stores computer instructions, and the computer instructions are used to enable a processor to implement the grid-connected control method of the micro-inverter described in any of the above embodiments when executed.

[0043] An embodiment of the present invention further provides a computer program product, which includes a computer program. When the computer program is executed by a processor, the computer program implements the grid-connected control method of the micro inverter according to any of the above embodiments.

[0044] The embodiment of the present invention discloses a grid-connected control strategy, device and readable storage medium of a micro inverter, wherein the grid-connected control strategy includes: obtaining the grid-connected output voltage and bus voltage of the target inverter; converting the grid-connected output voltage into α and β axis output voltages by using a second-order generalized integrator; determining the bus voltage reference value of the target inverter by using the converted α and β axis output voltages; determining the corresponding control law by using the bus voltage reference value and the bus voltage through an integral sliding mode voltage controller; determining an initial modulation signal by using the determined control law through a current controller; and processing the initial modulation signal by using a preset secondary modulation strategy to obtain a target modulation signal. The present invention dynamically corrects the bus voltage by using the output voltage converted by a second-order generalized integrator, and improves the dynamic correction of the bus voltage by using the nonlinearity, robustness, no static error and dynamic following performance of the integral sliding mode voltage controller, thereby solving the technical problems of large front-end and rear-end circuit losses and low energy conversion efficiency in the prior art due to the high bus voltage setting value, and achieving the technical effect of reducing the front-end and rear-end circuit losses of the inverter and improving the energy conversion efficiency of the inverter while ensuring the minimization of the bus voltage. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 is a circuit diagram of a two-stage high-frequency chain inverter provided by an embodiment of the present invention;

[0046] Figure 2 It is a principle block diagram of the grid-connected control of a two-stage high-frequency chain inverter provided by an embodiment of the present invention;

[0047] Figure 3 is a flow chart of a grid-connected control strategy of a micro-inverter provided by an embodiment of the present invention;

[0048] Figure 4 It is a block diagram of the grid-connected control principle of a two-stage high-frequency chain inverter provided by an embodiment of the present invention;

[0049] Figure 5 It is a principle block diagram of the bus voltage sliding mode control law provided by an embodiment of the present invention;

[0050] Figure 6is a photovoltaic characteristic curve diagram provided by an embodiment of the present invention;

[0051] Figure 7 It is a comparison curve diagram among the bus voltage, SPWM modulation ratio, output voltage, and secondary voltage stress at the working condition 1 provided by an embodiment of the present invention;

[0052] Figure 8 is a comparison curve diagram of bus voltage, SPWM modulation ratio, output voltage, and secondary voltage stress under working condition 2 provided by an embodiment of the present invention;

[0053] Fig. 9 is a comparison curve diagram of bus voltage, SPWM modulation ratio, output voltage, and secondary voltage stress under working condition three provided by an embodiment of the present invention;

[0054] Fig.10 It is a comparison curve diagram of bus voltage, SPWM modulation ratio, output voltage, and secondary voltage stress under four working conditions provided by an embodiment of the present invention;

[0055] Fig.11 is a structural diagram of a micro-inverter grid-connected control device provided by an embodiment of the present invention;

[0056] Fig.12 It is a structural schematic diagram of a grid-connected control device of a micro-inverter provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0057] The present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It is to be understood that the specific embodiments described herein are only used to explain the present invention, rather than to limit the present invention. It should also be noted that, for ease of description, only parts related to the present invention, rather than all structures, are shown in the accompanying drawings.

[0058] It should be noted that the terms "first", "second", etc. in the specification, claims and drawings of the present invention are used to distinguish different objects, rather than to limit a specific order. The following embodiments of the present invention can be implemented separately, or in combination with each other, and the embodiments of the present invention do not impose specific limitations on this.

[0059] Figure 1 is a circuit diagram of a two-stage high-frequency chain inverter provided by an embodiment of the present invention. Figure 1 As shown, the inverter includes a front-stage boost circuit and a high-frequency link inverter circuit for rear-stage transformer boost (i.e. Figure 1 The high-frequency boost circuit shown in the figure), bus capacitor C d At the same time, it serves as a double frequency power decoupling capacitor. The front stage boost circuit includes input capacitor C in, diode D, boost inductor L b And the switch tube T that controls its boost level b The front-stage boost circuit is used to boost the voltage converted by the photovoltaic module (PVModule); the rear-stage primary circuit mainly includes the full-bridge circuit switch tubes T1-T4, and the high-frequency transformer adopts three windings (respectively winding N p , Winding N s1 , Winding N s2 , whose transformation ratio is 1:n:n), the secondary winding is a double winding with taps, and the secondary circuit is a cycloconverter with a split-phase structure composed of switch tubes Q1-Q8 and an inductor L f1 , capacitor C o1 、Inductance L f2 , capacitor C o2 The secondary circuit is the grid-connected side, which is connected to the grid to be connected.

[0060] Figure 2 1 is a principle block diagram of the grid-connected control of a two-stage high-frequency chain inverter provided by an embodiment of the present invention. Figure 2 As shown in the figure, for the front-stage boost circuit, its control adopts a control scheme of photovoltaic voltage and inductor current dual closed-loop control, using the photovoltaic voltage output by the MPPT (Maximum Power Point Tracking) module as the reference instruction of the voltage outer loop, the output of the voltage outer loop as the reference instruction of the inductor current inner loop, and the output of the inductor current inner loop as the modulation wave for generating the PWM (Pulse Width Modulation) signal for controlling the boost circuit switch tube. At this time, the modulation wave generated by the inductor current inner loop output is only used for the front-stage boost and decoupling. After comparing this modulation wave containing double frequency fluctuations with the carrier, a PWM signal for controlling the switch tube is generated, thereby realizing the input capacitor C in The double frequency voltage ripple on the photovoltaic voltage is transferred to the bus capacitor C d The function of the inductor current inner loop is mainly to suppress the DC side inductance L b When the double frequency fluctuation of the inductor current is suppressed, the DC side input capacitor C in No double frequency pulsating voltage ripple will be generated at both ends. At this time, the double frequency pulsating part of the AC side output power will be transmitted to the bus capacitor C d On the bus capacitor C d The voltage ripple with double frequency is presented on the in The double frequency ripple on the bus is transferred to the bus capacitor Cd.

[0061] Specifically, the above implementation method is: the photovoltaic voltage reference value V pvref And the actual value of photovoltaic voltage V pv After subtraction, the deviation value enters the voltage controller, and the voltage controller outputs the inductor current reference value I Lbref , the inductor current reference value I Lbref and the inductor current feedback value I Lb After subtraction, the deviation value enters the current controller and outputs a reference signal d containing a double frequency ripple. The reference signal d is modulated to obtain the driving signal e of the front-stage boost switch tube, which is used to modulate the front-stage boost switch tube T b .

[0062] See also Figure 2 For the high-frequency link boost circuit at the rear stage, a dual closed-loop control scheme of capacitor voltage and grid-connected current is adopted. d The average voltage of is used as the reference instruction of the voltage outer loop. In order to achieve the control of active and reactive output, that is, to meet the requirement of reactive support capability, the output of the voltage outer loop is used as the command value of active power. At this time, the reference instruction of the current inner loop is calculated by the active power command value and the reactive power command value. Among them, the command value of active power is obtained through the output of the voltage inner loop, and the command value of reactive power is obtained through the output of the voltage outer loop. After the current inner loop command value is calculated, it is controlled by the current inner loop, and its output is added with the grid voltage V g and bus capacitor voltage V Cd The modulation wave is calculated and compared with the carrier wave to obtain the PWM signal for controlling the switch tube. When designing the bus voltage, the average value is obtained by the reference value of the post-stage bus capacitor voltage V Cdref Therefore, it should be noted that when decoupling is achieved, the voltage valley value should meet the requirements of the subsequent AC output.

[0063] Specifically, the above implementation is as follows: bus capacitor C d The voltage reference value V Cdref and bus capacitor voltage V Cd Subtract, the deviation value enters the voltage controller to output the power reference command P ref , then based on the power reference command P ref And reactive power reference value O ref Calculate the current reference value I ref , current reference value I ref and filter current I Lf1 After the difference is made, it is output by the current controller, and the output value is then compared with the grid voltage v g After adding, with N s V CdThe modulation signal m is obtained by division; the final modulation signal m is processed by a preset secondary side modulation strategy to obtain the modulation signals of the secondary side switch tubes T1-T4 and Q1-Q8.

[0064] On the basis of the above technical scheme, by adding a bus voltage correction strategy, the bus voltage is dynamically adjusted to ensure that the bus voltage is minimized while reducing the circuit losses of the front and rear stages of the inverter and improving the energy conversion of the inverter. At the same time, the voltage controller is converted into an integral sliding mode voltage controller. The dynamic control process of the bus voltage correction strategy can be improved by utilizing the nonlinearity, robustness, zero static error and dynamic following performance of the integral sliding mode controller.

[0065] Figure 3 The present invention provides a flow chart of a micro-inverter grid-connected control strategy. Figure 4 The invention provides a two-stage high-frequency chain inverter grid-connected control principle block diagram.

[0066] like Figure 3 As shown, the grid-connected control strategy of the micro-inverter specifically includes the following steps:

[0067] S101, obtaining the grid-connected side output voltage and bus voltage of the target inverter.

[0068] Specifically, see Figure 4 , grid-connected output voltage v o is the capacitance C o1 and capacitor C o2 The voltage at both ends, bus voltage V cd Refers to the bus capacitance C d The voltage across both ends.

[0069] S102, using a second-order generalized integrator to convert the grid-connected side output voltage into α-axis and β-axis output voltages.

[0070] Specifically, after obtaining the grid-connected output voltage v o After that, the α-axis output voltage v is converted using a second-order generalized integrator. oα And the β-axis output voltage v oβ .

[0071] S103, determining a bus voltage reference value of a target inverter using the converted α-axis and β-axis output voltages.

[0072] Specifically, when the α-axis output voltage v is obtained oα And the β-axis output voltage v oβ Then, the α-axis output voltage v oα And the β-axis output voltage v oβPerform amplitude calculation to obtain the amplitude voltage, and then use the amplitude voltage to calculate the bus voltage reference value V cdref .

[0073] S104, using the bus voltage reference value and the bus voltage, determine a corresponding control law through an integral sliding mode voltage controller.

[0074] Specifically, during the bus voltage correction process, when the bus voltage reference value V cdref When the bus voltage changes too fast and causes overshoot, it will reduce the bus voltage during the dynamic correction process, which will directly lead to the failure to meet the output voltage requirements. Therefore, when obtaining the bus voltage reference value V cdref and bus voltage V cd Afterwards, the integral sliding mode voltage controller is used to improve the process of dynamic correction of bus voltage. The integral sliding mode voltage controller is used to take advantage of its nonlinearity, robustness, zero static error and dynamic following performance to obtain a control law that can meet the requirements, that is, the above output power reference instruction P ref .

[0075] S105, using the determined control law, determine an initial modulation signal through a current controller.

[0076] S106, using a preset secondary side modulation strategy to process the initial modulation signal to obtain a target modulation signal.

[0077] Specifically, after obtaining the control law P ref Then, based on the control law P ref Calculate the current reference value I ref , the current reference value I ref and filter current I Lf1 After the difference is made, it is output by the current controller, and the output value is the same as the grid voltage v g After adding, add N s V Cd The modulation signal m is obtained by division; finally, the modulation signal m is processed by a preset secondary side modulation strategy to obtain the modulation signals of the secondary side switch tubes T1-T4 and Q1-Q8.

[0078] The embodiment of the present invention dynamically corrects the bus voltage by using the output voltage converted by a second-order generalized integrator, and improves the dynamic correction of the bus voltage by utilizing the nonlinearity, robustness, zero static error and dynamic following performance of an integral sliding mode voltage controller, thereby solving the technical problems of large front-end and rear-end circuit losses and low energy conversion efficiency due to high bus voltage setting values ​​in the prior art, and achieving the technical effect of reducing the front-end and rear-end circuit losses of the inverter and improving the energy conversion efficiency of the inverter while ensuring the minimization of the bus voltage.

[0079] Based on the above technical solutions, S103 specifically includes: using the converted α-axis and β-axis output voltages to perform amplitude calculation to obtain the output amplitude voltage; using the output amplitude voltage and the transformer parameters of the target inverter to determine the bus voltage reference value, wherein the transformer parameters include at least the transformer's step-up transformation ratio, duty cycle and switch tube dead zone margin.

[0080] Specifically, Figure 4 As shown, the α-axis output voltage v oα And the β-axis output voltage v oβ Then, the α-axis output voltage v oα And the β-axis output voltage v oβ Perform amplitude calculation to obtain the amplitude voltage V oamp , and then use the amplitude voltage V oamp By formula V cdref =V oamp *N s / 0.9+V mar Calculate the bus voltage reference value V cdref , where N s is the step-up ratio of the transformer, the duty cycle is 0.9, V mar is the dead zone margin of the switch tube.

[0081] However, simulation verification shows that if V cbref Changes faster, increase the K of the PI voltage controller p Although the following speed is improved, it is easy to cause overshoot, affecting the dynamic performance of the grid-connected current, and even the bus voltage is reduced during the dynamic process, which cannot meet the output voltage requirements. The integral sliding mode is to reasonably set the initial state of the integrator so that the initial state of the system is on the sliding mode surface from the beginning, thereby eliminating the arrival section to improve the robustness of the control system. Therefore, by using the integral sliding mode voltage controller, the sliding mode control has nonlinearity, robustness, no static error and dynamic following performance, and the above control dynamic process is improved.

[0082] On the basis of the above technical solutions, S104 specifically includes:

[0083] S1, the tracking error of the bus voltage is defined as the state variable of the integral sliding mode voltage controller, and the integral sliding mode surface is constructed using the state variable.

[0084] Specifically, the bus voltage V cd The tracking error is defined as the state variable of the bus voltage controller: cd =V cd * -V cd , where V cd *is the reference voltage; define x cd is the state variable of the integral sliding mode voltage controller, that is, the bus voltage V cd The tracking error of cd The integral sliding surface s is constructed to eliminate static errors and reduce the influence of high-frequency noise caused by differentiation. The integral sliding surface s is:

[0085] ;

[0086] Among them, s is the integral sliding surface and c is the integral coefficient.

[0087] S2, the exponential reaching law is introduced by using the differential of the integral sliding surface.

[0088] Specifically, after obtaining the integral sliding surface s, the integral sliding surface s is differentiated to obtain: ,in, is the differential of s, For x cd The differential of x cd When its differential term converges to 0, the state variable is on the sliding surface. The sliding motion successively goes through two stages: reaching and stabilizing on the sliding surface. In order to improve the dynamic performance of the approaching process, the exponential approaching law is introduced. , the exponential reaching law consists of a constant speed term and an exponential reaching term, where , k i is the constant speed approach coefficient, also called the sliding mode switch gain; k e Exponential approximation coefficient; sign(s) is the sign function.

[0089] S3, construct a power model between bus voltage and output active power.

[0090] Specifically, the bus voltage V cd The power model between the output active power P is: .

[0091] S4, determine the corresponding control law using the bus voltage reference value, integral sliding surface, reaching law and power model.

[0092] Specifically, Figure 5 As shown, Figure 5 The bus voltage sliding mode control law provided by the embodiment of the present invention is a principle block diagram, and the output active power reference value P is used as the control law P ref , then the control law P ref for:

[0093] .

[0094] On the basis of the above technical solutions, S105 specifically includes:

[0095] S1051, determining a current reference value using a control law;

[0096] S1052, obtaining a secondary side filter current of a target inverter;

[0097] S1053, inputting the current reference value and the secondary side filter current into the current controller to obtain a first output value;

[0098] S1054: Determine an initial modulation signal using the first output quantity, the grid voltage, the step-up transformation ratio of the transformer, and the bus voltage, wherein the grid voltage is the voltage of the grid to which the target inverter is to be connected.

[0099] Optionally, S1054 specifically includes: adding the first output quantity to the grid voltage, and dividing the obtained sum by the product of the transformer step-up transformation ratio and the bus voltage to obtain an initial modulation signal.

[0100] Specifically, Figure 4 As shown, after determining the control law P ref Then, we use the control law P ref Calculate the current reference value I ref , and then obtain the secondary filter current I of the target inverter Lf1 , using the current reference value I ref and the secondary filter current I Lf1 The difference is taken as the input value and input into the current controller. The output value is the first output quantity. The first output current is compared with the grid voltage v g Add them together and get the sum s V Cd The initial modulation signal m is obtained by division; finally, the initial modulation signal m is processed by a preset secondary side modulation strategy to obtain modulation signals of the secondary side switch tubes T1-T4 and Q1-Q8.

[0101] Optionally, S1051, determining the current reference value by using a control law includes:

[0102] The current reference value is determined using the control law, the α-axis output voltage, the β-axis output voltage, and the reactive power reference value of the target inverter.

[0103] Specifically, Figure 4 As shown, in order to make the current reference value I ref The determination is more accurate, and the α-axis output voltage v can also be added oα , β-axis output voltage v oβ , and the reactive power reference value Q of the target inverter ref Participating current reference value I ref of determination.

[0104] Alternatively, if Figure 4 As shown, in order to make the first output flow of the current controller more accurate, the α-axis output voltage v oα , β-axis output voltage v oβ The calculated value of are fed into the current controller as input values.

[0105] It should be noted that, in the embodiment of the present invention, the grid-connected control strategy of the micro-inverter proposed in the present invention is not only applicable to a specific inverter topology, but also applicable to two-stage inverters.

[0106] The effect of the grid-connected control method of the micro-inverter provided by the present invention is described below with reference to a specific embodiment.

[0107] For example, the maximum output power of the micro photovoltaic inverter is 600W, and the input voltage V pv 22~55V, input capacitor C in The decoupling capacitor C is 100uF d (i.e. bus capacitance) is 13.2mF, grid voltage v g 240Vac±10%, transformer ratio N s For example, the secondary side modulation strategy is adopted in the latter stage. The corresponding photovoltaic characteristic curve is as follows: Figure 6 As shown, the maximum power point voltage is 48.52V, the maximum power point current is 12.66A, and the maximum power is 614.09W.

[0108] The proposed micro-inverter grid-connected control strategy is applied to verify the switch tube voltage stress, boost switch tube duty cycle, grid-connected current, bus voltage, etc. At 0.2s and 0.35s, the grid-connected voltage is transiently changed from 0.9 times to 1 times, and then from 1 times to 0.9 times, and the photovoltaic voltage is in MPPT operation. The sliding mode controller parameters are selected as: k i = 0.1, k e =0.1, c=0.4. Then:

[0109] Working condition 1: When the constant bus voltage is 65V, under the control of the PI bus voltage outer loop control, the comparison curves between bus voltage, SPWM modulation ratio, output voltage, and secondary voltage stress are as follows: Figure 7 shown.

[0110] Working condition 2: Using the variable DC bus voltage algorithm, under the control of the PI bus voltage outer loop, set K p =0.7, the comparison curves among bus voltage, SPWM modulation ratio, output voltage and secondary voltage stress are shown in Figure 8 shown.

[0111] Condition 3: Using the variable DC bus voltage algorithm, under the control of the PI bus voltage outer loop, set K p =5.6, the comparison curves among bus voltage, SPWM modulation ratio, output voltage and secondary voltage stress are shown in Fig. 9 shown.

[0112] Working condition 4: Using the variable DC bus voltage algorithm, under the control of the integral sliding mode voltage controller, the comparison curves between bus voltage, SPWM modulation ratio, output voltage, and secondary voltage stress are shown in the figure below: Fig.10 shown.

[0113] The above simulation process analysis is shown in Table 1. From the comparison in Table 1, it can be seen that the grid-connected control method of the micro-inverter provided by the embodiment of the present invention can make the modulation ratio of the inverter relatively constant and the dynamics good.

[0114] Table 1. Comparison of simulation analysis results

[0115]

[0116] Fig.11 It is a structural diagram of a grid-connected control device for a micro-inverter provided in an embodiment of the present invention.

[0117] like Fig.11 As shown, the micro-inverter grid-connected control device specifically includes:

[0118] A voltage acquisition unit 61 is used to acquire the grid-connected side output voltage and bus voltage of the target inverter;

[0119] A voltage conversion unit 62, used to convert the grid-connected side output voltage into α-axis and β-axis output voltages using a second-order generalized integrator;

[0120] A reference voltage determination unit 63, used to determine a bus voltage reference value of a target inverter using the converted α-axis and β-axis output voltages;

[0121] A control signal determination unit 64, configured to determine a corresponding control law by an integral sliding mode voltage controller using a bus voltage reference value and a bus voltage;

[0122] A first modulation signal determination unit 65 is used to determine an initial modulation signal through a current controller using the determined control law;

[0123] The second modulation signal determination unit 66 is used to process the initial modulation signal using a preset secondary side modulation strategy to obtain a target modulation signal.

[0124] Optionally, the reference voltage determination unit 63 specifically always:

[0125] The converted α-axis and β-axis output voltages are used to perform amplitude calculation to obtain the output amplitude voltage;

[0126] The bus voltage reference value is determined by using the output amplitude voltage and transformer parameters of the target inverter, wherein the transformer parameters at least include a step-up transformation ratio, a duty cycle, and a switch tube dead zone margin of the transformer.

[0127] Optionally, the control signal determination unit 64 specifically always:

[0128] The tracking error of bus voltage is defined as the state variable of integral sliding mode voltage controller, and the integral sliding mode surface is constructed by using the state variable;

[0129] The exponential reaching law is introduced by using the differential of the integral sliding surface;

[0130] Construct a power model between bus voltage and output active power;

[0131] The corresponding control law is determined using the bus voltage reference value, integral sliding surface, reaching law and power model.

[0132] Optionally, the first modulation signal determining unit 65 is specifically configured to:

[0133] Determine the current reference value by using the control law;

[0134] Obtain the secondary filter current of the target inverter;

[0135] Inputting the current reference value and the secondary side filter current into the current controller to obtain a first output value;

[0136] An initial modulation signal is determined using the first output quantity, the grid voltage, the step-up transformation ratio of the transformer, and the bus voltage, wherein the grid voltage is the voltage of the grid to which the target inverter is to be connected.

[0137] Optionally, the first modulation signal determining unit 65 is further configured to:

[0138] The first output quantity is added to the grid voltage, and the obtained sum is divided by the product of the transformer step-up transformation ratio and the bus voltage to obtain an initial modulation signal.

[0139] Optionally, the first modulation signal determining unit 65 is further configured to:

[0140] The current reference value is determined using the control law, the α-axis output voltage, the β-axis output voltage, and the reactive power reference value of the target inverter.

[0141] The micro-inverter grid-connected control device provided in the embodiment of the present invention can execute the micro-inverter grid-connected control method provided in any embodiment of the present invention, and has the corresponding functional modules and beneficial effects of the execution method.

[0142] Fig.12 1 is a schematic diagram of the structure of a micro-inverter grid-connected control device provided by an embodiment of the present invention. The grid-connected control device of the micro-inverter is intended to represent various forms of digital computers, such as laptop computers, desktop computers, workbenches, personal digital assistants, servers, blade servers, mainframe computers, and other suitable computers. The electronic device can also represent various forms of mobile devices, such as personal digital processing, cellular phones, smart phones, wearable devices (such as helmets, glasses, watches, etc.) and other similar computing devices. The components shown herein, their connections and relationships, and their functions are merely examples and are not intended to limit the implementation of the present invention described and / or required herein.

[0143] like Fig.12 As shown, the electronic device 10 includes at least one processor 11, and a memory connected to the at least one processor 11, such as a read-only memory (ROM) 12, a random access memory (RAM) 13, etc., wherein the memory stores a computer program that can be executed by at least one processor, and the processor 11 can perform various appropriate actions and processes according to the computer program stored in the read-only memory (ROM) 12 or the computer program loaded from the storage unit 18 to the random access memory (RAM) 13. In the RAM 13, various programs and data required for the operation of the electronic device 10 can also be stored. The processor 11, the ROM 12, and the RAM 13 are connected to each other through a bus 14. The input / output (I / O) interface 15 is also connected to the bus 14.

[0144] A number of components in the electronic device 10 are connected to the I / O interface 15, including: an input unit 16, such as a keyboard, a mouse, etc.; an output unit 17, such as various types of displays, speakers, etc.; a storage unit 18, such as a disk, an optical disk, etc.; and a communication unit 19, such as a network card, a modem, a wireless communication transceiver, etc. The communication unit 19 allows the electronic device 10 to exchange information / data with other devices through a computer network such as the Internet and / or various telecommunication networks.

[0145] The processor 11 may be a variety of general and / or dedicated processing components with processing and computing capabilities. Some examples of the processor 11 include, but are not limited to, a central processing unit (CPU), a graphics processing unit (GPU), various dedicated artificial intelligence (AI) computing chips, various processors running machine learning model algorithms, a digital signal processor (DSP), and any appropriate processor, controller, microcontroller, etc. The processor 11 executes the various methods and processes described above, such as a grid-connected control method for a micro inverter.

[0146] In some embodiments, the grid-connected control method of the micro-inverter can be implemented as a computer program, which is tangibly contained in a computer-readable storage medium, such as a storage unit 18. In some embodiments, part or all of the computer program can be loaded and / or installed on the electronic device 10 via the ROM 12 and / or the communication unit 19. When the computer program is loaded into the RAM 13 and executed by the processor 11, one or more steps of the grid-connected control method of the micro-inverter described above can be performed. Alternatively, in other embodiments, the processor 11 can be configured to execute the grid-connected control method of the micro-inverter in any other appropriate manner (for example, by means of firmware).

[0147] Various implementations of the systems and techniques described above herein can be implemented in digital electronic circuit systems, integrated circuit systems, field programmable gate arrays (FPGAs), application specific integrated circuits (ASICs), application specific standard products (ASSPs), systems on chips (SOCs), load programmable logic devices (CPLDs), computer hardware, firmware, software, and / or combinations thereof. These various implementations can include: being implemented in one or more computer programs that can be executed and / or interpreted on a programmable system including at least one programmable processor, which can be a special purpose or general purpose programmable processor that can receive data and instructions from a storage system, at least one input device, and at least one output device, and transmit data and instructions to the storage system, the at least one input device, and the at least one output device.

[0148] Computer programs for implementing the methods of the present invention may be written in any combination of one or more programming languages. These computer programs may be provided to a processor of a general-purpose computer, a special-purpose computer, or other programmable data processing device, so that when the computer program is executed by the processor, the functions / operations specified in the flow chart and / or block diagram are implemented. The computer program may be executed entirely on the machine, partially on the machine, partially on the machine and partially on a remote machine as a stand-alone software package, or entirely on a remote machine or server.

[0149] In the context of the present invention, a computer-readable storage medium may be a tangible medium that may contain or store a computer program for use by or in conjunction with an instruction execution system, device, or equipment. A computer-readable storage medium may include, but is not limited to, electronic, magnetic, optical, electromagnetic, infrared, or semiconductor systems, devices, or equipment, or any suitable combination of the foregoing. Alternatively, a computer-readable storage medium may be a machine-readable signal medium. A more specific example of a machine-readable storage medium may include an electrical connection based on one or more lines, a portable computer disk, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), an optical fiber, a portable compact disk read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination of the foregoing.

[0150] To provide interaction with a user, the systems and techniques described herein may be implemented on an electronic device having: a display device (e.g., a CRT (cathode ray tube) or LCD (liquid crystal display) monitor) for displaying information to the user; and a keyboard and a pointing device (e.g., a mouse or trackball) through which the user can provide input to the electronic device. Other types of devices may also be used to provide interaction with the user; for example, the feedback provided to the user may be any form of sensory feedback (e.g., visual feedback, auditory feedback, or tactile feedback); and input from the user may be received in any form (including acoustic input, voice input, or tactile input).

[0151] The systems and techniques described herein may be implemented in a computing system that includes backend components (e.g., as a data server), or a computing system that includes middleware components (e.g., an application server), or a computing system that includes frontend components (e.g., a user computer with a graphical user interface or a web browser through which a user can interact with implementations of the systems and techniques described herein), or a computing system that includes any combination of such backend components, middleware components, or frontend components. The components of the system may be interconnected by any form or medium of digital data communication (e.g., a communication network). Examples of communication networks include: a local area network (LAN), a wide area network (WAN), a blockchain network, and the Internet.

[0152] A computing system may include a client and a server. The client and the server are generally remote from each other and usually interact through a communication network. The client and server relationship is generated by computer programs running on the corresponding computers and having a client-server relationship with each other. The server may be a cloud server, also known as a cloud computing server or cloud host, which is a host product in the cloud computing service system to solve the defects of difficult management and weak business scalability in traditional physical hosts and VPS services.

[0153] An embodiment of the present invention further provides a computer program product, which includes computer executable instructions. When the computer executable instructions are executed by a computer processor, they are used to execute the grid-connected control method of the micro inverter provided by any embodiment of the present invention.

[0154] In the process of implementation, the computer program product can be written in one or more programming languages ​​or a combination thereof to perform the computer program code of the present invention, including object-oriented programming languages, such as Java, Smalltalk, C++, and conventional procedural programming languages, such as "C" language or similar programming languages. The program code can be executed entirely on the user's computer, partially on the user's computer, as an independent software package, partially on the user's computer and partially on a remote computer, or completely on a remote computer or server. In the case of a remote computer, the remote computer can be connected to the user's computer through any type of network, including a local area network (LAN) or a wide area network (WAN), or can be connected to an external computer (for example, using an Internet service provider to connect through the Internet).

[0155] Of course, the computer program product provided in the embodiments of the present application, whose computer executable instructions are not limited to the method operations described above, can also execute related operations in the method provided in any embodiment of the present application.

[0156] It should be understood that the various forms of processes shown above can be used to reorder, add or delete steps. For example, the steps recorded in this application can be executed in parallel, sequentially or in different orders, as long as the desired results of the technical solution of the present invention can be achieved, and this document is not limited here.

[0157] The above specific implementations do not constitute a limitation on the protection scope of the present invention. It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and substitutions can be made according to design requirements and other factors. Any modification, equivalent substitution and improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A grid-connected control strategy for a micro-inverter, characterized in that: The grid-connected control strategy includes: Obtain the grid-connected side output voltage and bus voltage of the target inverter; The grid-connected side output voltage is converted into α-axis and β-axis output voltages by using a second-order generalized integrator; Determine the bus voltage reference value of the target inverter using the converted α-axis and β-axis output voltages; Determining a corresponding control law by an integral sliding mode voltage controller using the bus voltage reference value and the bus voltage; Using the determined control law, an initial modulation signal is determined by a current controller; Processing the initial modulation signal using a preset secondary side modulation strategy to obtain a target modulation signal; The using the determined control law to determine an initial modulation signal through a current controller comprises: determining a current reference value using the control law; Obtaining a secondary side filter current of the target inverter; Inputting the current reference value and the secondary-side filter current into a current controller to obtain a first output; Determine the initial modulation signal using the first output, grid voltage, a step-up ratio of a transformer, and the bus voltage, wherein the grid voltage is the voltage of a grid to which the target inverter is to be connected; The determining of the initial modulation signal by using the first output quantity, the grid voltage, the step-up transformation ratio of the transformer and the bus voltage comprises: The first output quantity is added to the grid voltage, and the obtained sum is divided by the product of the step-up transformation ratio of the transformer and the bus voltage to obtain the initial modulation signal.

2. The grid-connected control strategy of the micro-inverter according to claim 1, characterized in that: Determining the bus voltage reference value of the target inverter using the converted α-axis and β-axis output voltages includes: The converted α-axis and β-axis output voltages are used to perform amplitude calculation to obtain the output amplitude voltage; The bus voltage reference value is determined using the output amplitude voltage and transformer parameters of the target inverter, wherein the transformer parameters at least include a transformer step-up ratio, a duty cycle, and a switch tube dead zone margin.

3. The grid-connected control strategy of the micro-inverter according to claim 1, characterized in that: Using the bus voltage reference value and the bus voltage, determining a corresponding control law through an integral sliding mode voltage controller includes: The tracking error of the bus voltage is defined as a state variable of the integral sliding mode voltage controller, and the integral sliding mode surface is constructed using the state variable; Introducing an exponential reaching law by using the differential of the integral sliding surface; Constructing a power model between the bus voltage and the output active power; The corresponding control law is determined by using the bus voltage reference value, the integral sliding mode surface, the reaching law and the power model.

4. The grid-connected control strategy of the micro-inverter according to claim 1, characterized in that: Determining the current reference value by using the control law includes: The current reference value is determined by using the control law, the α-axis output voltage, the β-axis output voltage, and the reactive power reference value of the target inverter.

5. A micro-inverter grid-connected control device, characterized in that: The grid-connected control device comprises: A voltage acquisition unit, used to acquire the grid-connected side output voltage and bus voltage of the target inverter; A voltage conversion unit, used for converting the grid-connected side output voltage into α-axis and β-axis output voltages by using a second-order generalized integrator; A reference voltage determination unit, used to determine a bus voltage reference value of the target inverter using the converted α-axis and β-axis output voltages; A control signal determination unit, configured to determine a corresponding control law by using the bus voltage reference value and the bus voltage through an integral sliding mode voltage controller; A first modulation signal determination unit, configured to determine an initial modulation signal through a current controller using the determined control law; A second modulation signal determination unit, configured to process the initial modulation signal using a preset secondary side modulation strategy to obtain a target modulation signal; The first modulation signal determination unit is also used to: determine the current reference value using the control law, obtain the secondary filter current of the target inverter, input the current reference value and the secondary filter current into the current controller, obtain the first output quantity, add the first output quantity to the grid voltage, and divide the sum by the product of the transformer's step-up transformation ratio and the bus voltage to obtain an initial modulation signal.

6. A micro-inverter grid-connected control device, characterized in that: The grid-connected control device of the micro-inverter comprises: at least one processor; and a memory communicatively connected to the at least one processor; wherein, The memory stores a computer program executable by the at least one processor, and the computer program is executed by the at least one processor so that the at least one processor can execute the grid-connected control method for the micro-inverter according to any one of claims 1 to 4.

7. A computer-readable storage medium, characterized in that: The computer-readable storage medium stores computer instructions, and the computer instructions are used to enable a processor to implement the grid-connected control method of the micro-inverter according to any one of claims 1 to 4 when executed.

8. A computer program product, characterized in that The computer program product comprises a computer program, and when the computer program is executed by a processor, the computer program implements the grid-connected control method of the micro inverter according to any one of claims 1 to 4.

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