A flyback micro-reverse critical discontinuous mode analog control method

Abstract

The present application relates to the field of distributed photovoltaic power generation, and aims to provide a flyback micro-inverter critical discontinuous mode simulation control method. The inverter comprises a flyback converter, a power frequency inverter filter circuit and an inverter control circuit; wherein the inverter control circuit comprises an MPPT control circuit and a PWM wave generation circuit; the former comprises a reference voltage V ref generation circuit, a PI regulation circuit and a peak current reference value i ref generation circuit, a peak current reference value i ref generation circuit contains two multipliers and a divider circuit, by collecting the output voltage V pv of the photovoltaic module and the output current I pv , the peak current reference value i ref is obtained; the latter outputs the WM signal as the input of the MOS tube Q s , which is used for realizing the control of the flyback converter. The present application realizes the simulation control of the critical discontinuous mode flyback micro-inverter, can save the digital chip commonly used in the existing control mode, and reduces the complexity and control cost of the system.

Description

Technical Field

[0001] This invention relates to the field of distributed photovoltaic power generation, and specifically to a flyback micro-inverter critical discontinuous mode simulation control method. Background Technology

[0002] With the expansion of photovoltaic (PV) system applications, distributed and residential PV products will further develop. Current distributed PV products mainly include components such as microinverters and power optimizers. Among microinverters, flyback microinverters are currently the most commercially successful and widely used. Flyback microinverters use flyback circuits to convert the direct current (DC) output from PV modules into alternating current (AC), which is then injected into the grid. Due to their intermittent or critically intermittent operating mode, they exhibit current source characteristics. Currently, most flyback inverter products use digital control; however, the high cost of the digital control chips (DSPs, FPGAs, etc.) and their peripheral circuits hinders the large-scale promotion of microinverters, necessitating cost control.

[0003] Therefore, the control method of micro-inverters that are low-cost and do not use or use few CNC chips is suitable for industry needs. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a flyback micro-inverse critical discontinuous mode simulation control method.

[0005] To solve the technical problem, the solution of the present invention is:

[0006] A flyback micro inverter is provided, which includes a flyback converter, a power frequency inverter filter circuit and an inverter control circuit. The AC input terminal and DC input terminal of the inverter control circuit are connected in parallel to the AC terminal and DC terminal of the inverter, respectively, and the output of the inverter is connected to the power grid.

[0007] (1) The flyback converter has the following circuit structure:

[0008] The primary winding of transformer T and MOSFET Q s and current sampling resistor R s After being connected in series, it is connected to the input electrolytic capacitor C. in It is connected in parallel across the two ends of the photovoltaic module, with the negative terminal grounded; the secondary winding of transformer T is connected to rectifier diode D. M It is connected in series and then in parallel with the power frequency inverter filter circuit, which is connected to the power grid.

[0009] The auxiliary winding of transformer T is connected to the auxiliary coil voltage limiting resistor R at both ends. ssAfter connecting the Zener diode, it is then connected to the inverting input of the hysteresis comparator 2; the two hysteresis comparator resistors R ss1 R ss2 After being connected in series, one end is connected to the output of hysteresis comparator 2, and the other end is connected to the comparator reference voltage V. refss And the midpoint is connected to the non-inverting input of the hysteresis comparator2;

[0010] (2) The inverter control circuit includes an MPPT control circuit and a PWM wave generation circuit; wherein,

[0011] The MPPT control circuit (MPPT stands for Maximum Power Point Tracking) includes a reference voltage V connected in sequence. ref Generation circuit, PI regulation circuit, and peak current reference value i ref Generation circuit, peak current reference value i ref The generator circuit contains two multipliers and one divider circuit (hereinafter also called the Divider circuit);

[0012] The PWM wave generation circuit includes a high-frequency current detection circuit, a comparator1, and an AND gate1.

[0013] The MPPT control circuit acquires the output voltage V of the photovoltaic module. pv With output current I pv The peak current reference value i is obtained. ref The high-frequency current detection circuit samples the primary current, with sampling resistor R. s The voltage across the current sensor is used to obtain the current detection value i. p The output signals of both are connected to comparator1. The outputs of comparator1 and hysteresis comparator2 are connected to logic gate AND1, and the PWM signal output by the latter is used as the MOSFET Q. s The input is used to control the flyback converter.

[0014] As a preferred embodiment of the present invention, the outputs of the PI regulation circuit and the Divider circuit in the MPPT control circuit are both connected to the peak current reference value i. ref The input of the first multiplier MUL1 in the generation circuit; the output of the latter, along with the grid phase sinusoidal half-wave signal, serves as the input of the second multiplier MUL2, whose output is the peak current reference value i. ref .

[0015] As a preferred embodiment of the present invention, the reference voltage V ref The generation circuit includes: multiplier MUL3, sample-and-hold circuit, comparator 3, XNOR gate XNOR1, D flip-flop, and DC voltage source V. d Two switches S c and S dc Two resistors R c and R dc NOT gate (NOT1) and capacitor C c ;in,

[0016] The voltage V at the output of the photovoltaic module pv With current I pv Connect it to the input of multiplier MUL3, and the output P of the latter... pv The circuit is divided into two paths, connected to the non-inverting input of comparator 3 and the input of the sample-and-hold circuit, respectively. The output of the sample-and-hold circuit is connected to the inverting input of comparator 3, and the output of comparator 3 is connected to one input of the XNOR gate XNOR1. The output of XNOR1 is connected to the D input of the D flip-flop, and the Q output of the D flip-flop is denoted as V. flag ;

[0017] DC voltage source V d The negative terminal is grounded, and its positive terminal is connected to switch S. c With resistance R c One end is connected; resistor R c The other end is connected to capacitor C. c The positive terminal and the switch S dc One end is connected, switch S dc The other end is connected to resistor R dc With capacitor C c The negative terminal and DC voltage source V d The negative terminal is connected; the output V of the D flip-flop flag It is divided into three paths. The first path is connected to the other input of the XNOR gate XNOR1, and the second path is connected to the switch S. c Connected, the third path is connected to switch S via NOT1. dc Connected.

[0018] As a preferred embodiment of the present invention, the Divider circuit includes: a 1V DC voltage source, two switches S1 and S2, and a capacitor C. D Two resistors R a and R b One operational amplifier, OPA1; among which,

[0019] The negative terminal of the DC voltage source is grounded, and its positive terminal is connected to the non-inverting input of op-amp OPA1; the inverting input of op-amp OPA1 is divided into three paths, all of which are connected to capacitor C. D negative terminal, switch S 1 and resistor R b The other end of resistor R6 is connected to the negative terminal of a DC voltage source via switch S2; the other end of switch S1 is connected to resistor R a With capacitor C D The positive terminal is connected to the positive terminal, which is also connected to the output terminal of OPA1; the output terminal of OPA1 uses the voltage to ground as the output of the Divider circuit.

[0020] As a preferred embodiment of the present invention, the MPPT control circuit further includes a DC current detection circuit, a DC voltage detection circuit, and an AC voltage detection circuit; wherein,

[0021] Both the DC voltage detection circuit and the DC current detection circuit are connected in parallel to the output terminal of the photovoltaic module. They respectively collect the voltage V at the output terminal of the photovoltaic module. pv With current I pv The output signal is connected to the reference voltage V in the MPPT control circuit. ref Generation circuit;

[0022] The AC voltage detection circuit is located on the mains side, and its output signals are clock signals clock1 and clock2; the outputs of this circuit are respectively connected to the reference voltage V. ref The sample-and-hold circuit and D flip-flop in the generation circuit are used to provide the clock signal.

[0023] As a preferred embodiment of the present invention, the DC current detection circuit, the DC voltage detection circuit, and the AC voltage detection circuit each include a sampling filter circuit and a proportional amplifier circuit.

[0024] As a preferred embodiment of the present invention, the MPPT control circuit further includes an auxiliary power supply for supplying power to the control circuit and serving as a reference voltage V. ref V of the generation circuit d It is used as a DC voltage source in the divider circuit.

[0025] This invention further provides a method for implementing critical discontinuous mode simulation control of a flyback micro-inverter using the aforementioned flyback micro-inverter, comprising:

[0026] (1) Maximum power point tracking control of photovoltaic modules:

[0027] When the system is working normally, the DC voltage detection circuit and the DC current detection circuit detect the voltage V output by the photovoltaic module panel. pv and current i pv Samples are taken and output to the sampling signal input reference voltage V.ref Generation circuit; in this circuit, the power value P of the current cycle is first obtained by multiplier MUL3. pv Comparator 3 will assign the power value P pv The power value of the previous cycle is compared with the power value stored in the sample-and-hold circuit to determine the direction of power change in the current cycle. A high output from comparator3 indicates an increase in power, recorded as 1; conversely, a low output indicates a decrease, recorded as 0. A high output from the D flip-flop is recorded as 1, and a low output as 0. The output of the D flip-flop from the previous cycle and the direction of power change in the current cycle are simultaneously input into the XNOR gate XNOR1, and the XNOR gate XNOR2... l The output will serve as the input to the D flip-flop in the next cycle; the reference voltage V ref The output signal V of the generation circuit ref It is controlled by the output of a D flip-flop: when the D flip-flop outputs a high level, the output signal V... ref Gradually increase, and vice versa;

[0028] An AC voltage detection circuit is used to detect the AC voltage on the grid side, and its output signals are clock signals clock1 and clock2; these signals are then connected to a reference voltage V. ref After the generation circuit is completed, it serves as the operating clock for the sample-and-hold circuit and the D flip-flop, respectively.

[0029] The MPPT circuit generates a reference value Vref, which is subtracted from the photovoltaic panel's voltage Vpv. The main function of the PI regulation circuit is to adjust the output voltage V of the photovoltaic module based on the IV curve relationship. pv Control the output voltage V to make this difference zero. pv For reference voltage V ref The tracking enables the photovoltaic module to operate in maximum power point tracking control mode. Since PI control is a commonly used control method in the industry, it will not be described in detail in this invention.

[0030] (2) Analog circuit control based on critical discontinuous mode of peak current:

[0031] Reference voltage V ref The reference voltage V output by the generation circuit ref With the output voltage V of the photovoltaic module panel pv The circuit is connected to a PI control circuit, with the output of the PI control circuit serving as one input to the first multiplier MUL1, and the output of the Divider circuit serving as the other input; the AC voltage sampling circuit acquires the sinusoidal half-wave signal sin(θ) of the grid phase. gThe output of the first multiplier MUL1, together with the output of the second multiplier MUL2, serves as the input to the second multiplier MUL2. The output of the second multiplier MUL2 is the current reference value i. ref ;

[0032] The primary current i is detected using a high-frequency current detection circuit targeting the current sampling resistor Rs. p When input to the inverting input of comparator1, the current reference value will be i ref The input is the non-inverting input; the output of comparator1 is connected to one input of the AND gate, and the other input is connected to the comp2o signal output by the hysteresis comparator2; the PWM signal output by the AND gate is used as the MOSFET Q in the flyback converter. s The input is used to control the peak current of the flyback converter, enabling the flyback micro-inverter to operate in critical discontinuous inductor current mode (BCM), and ultimately achieve sinusoidal AC grid connection.

[0033] As a preferred embodiment of the present invention, when the secondary current of transformer T is not zero, the comp2o signal output by hysteresis comparator2 is at a low level; when the secondary current of transformer T is zero, the signal changes to a high level.

[0034] Compared with the prior art, the beneficial effects of the present invention are:

[0035] 1. This invention realizes analog control of critical discontinuous mode flyback micro inverter, which can eliminate the digital chips commonly used in existing control methods, reducing system complexity and control costs.

[0036] 2. This invention lays the foundation for further integration of this control method into a dedicated control chip, which is conducive to further reducing costs. Attached Figure Description

[0037] Figure 1 This is the circuit diagram of the flyback micro-inverter in this invention.

[0038] Figure 2 V is the reference voltage in the MPPT control circuit. ref Schematic diagram of the generation circuit.

[0039] Figure 3 It is the reference voltage V ref Timing diagram of the generation circuit.

[0040] Figure 4 This is an internal structure diagram of the divider circuit in the MPPT control circuit.

[0041] Figure 5This is the main waveform diagram of the flyback microinverter in this invention.

[0042] Figure 1 The reference numerals in the figures are as follows: MPPT control circuit 100; PI regulation circuit output 101; Divider circuit output 102; PWM wave generation circuit 200; flyback converter 300; power frequency inverter filter circuit 400; Detailed Implementation

[0043] The specific implementation of the present invention will now be described with reference to the accompanying drawings:

[0044] I. Circuit Structure Description

[0045] like Figure 1 As shown, the flyback micro-inverter provided by this invention includes a flyback converter, a power frequency inverter filter circuit, and an inverter control circuit. The inverter control circuit includes an MPPT control circuit and a PWM wave generation circuit. The AC input terminal and DC input terminal of the inverter control circuit are connected in parallel to the AC terminal and DC terminal of the inverter, respectively, and the output of the inverter is connected to the power grid.

[0046] 1. The flyback converter 300 has the following circuit structure:

[0047] The primary winding of transformer T and MOSFET Q s and current sampling resistor R s After being connected in series, it is connected to the input electrolytic capacitor C. in It is connected in parallel across the two ends of the photovoltaic module, with the negative terminal grounded; the secondary winding of transformer T is connected to rectifier diode D. M After being connected in series, it is then connected in parallel with the power frequency inverter filter circuit, which is connected to the power grid. The auxiliary winding of transformer T is connected to the auxiliary coil voltage-limiting resistor R at both ends. ss After connecting the Zener diode, it is then connected to the inverting input of the hysteresis comparator 2; the two hysteresis comparator resistors R ssl R ss2 After being connected in series, one end is connected to the output of hysteresis comparator 2, and the other end is connected to the comparator reference voltage V. refss And the midpoint is connected to the non-inverting input of the hysteresis comparator2.

[0048] Specifically, the flyback converter includes an input electrolytic capacitor C. in A high-frequency transformer T, and a main power MOSFET Q s A primary-side current sampling resistor R s A secondary rectifier diode D M Auxiliary coil voltage limiting resistor R ssZener diode, hysteresis comparator 2, and two hysteresis comparator resistors R ss1 R ss2 Its connection method is: C in C is connected in parallel at both ends of the photovoltaic module. in The positive terminal is connected to the positive terminal of the photovoltaic module, and at the same time, this terminal is connected to one end of the primary winding of the transformer, while the other end of the primary winding of the transformer is connected to Q. s Source and pole connected, Q s Drain and R s One end is connected, R s The other end is connected to the photovoltaic panel and C in The negative terminal, i.e., the grounding terminal, is connected. The secondary winding of the transformer is connected to the primary winding and C. in The non-same-name terminal of the connected terminal and D M The anode is connected. The transformer auxiliary winding is connected to the primary winding and C. in The terminals with the same name as the connected terminals are grounded, and the terminals with different names are connected to R. ss One end is connected, R ss The other end is connected to both the cathode of Zener and the inverting input of comparator 2, while the anode of Zener is grounded. The non-inverting input of comparator 2 is simultaneously connected to R... ss1 and R ss2 One end is connected, R ss1 The other end is connected to the comparator reference voltage V. refss Connected, R ss2 The other end is connected to the output of comparator2, and the output of comparator2 is denoted as comp2o.

[0049] 2. The power frequency inverter filter circuit 400 has the following circuit structure:

[0050] The rectifier diode D in the flyback converter M The cathode is connected to the input of the power frequency inverter filter circuit, and the output of the power frequency inverter filter circuit is connected to the power grid. The power frequency inverter filter circuit includes a filter capacitor C. o And four thyristors Q1, Q2, Q3, and Q4, and a filter capacitor C. f and filter inductor L f The CL filter is composed of C o One end and D M Connected, this terminal is also connected to the anodes of Q1 and Q4, the cathode of Q1 is connected to the anode of Q2, the cathode of Q4 is connected to the anode of Q3, and the anodes of Q2 and Q3 are connected to capacitor C. o The other end is connected, and this end is not connected to the secondary winding of D. M One end is connected. Filter capacitor C f The filter inductor L is connected between the cathodes of Q1 and Q3.f One end is connected to the cathode of Q1, and the other end is connected to the power grid v. g One end is connected, the power grid v g The other end is connected to the anode of Q3.

[0051] 3. Auxiliary power supply (not shown in the diagram) is used to supply power to the electrical components in each circuit and serves as a reference voltage V. ref V of the generation circuit d Used with a 1V DC voltage source in the Divider circuit.

[0052] 4. The MPPT control circuit has the following circuit structure:

[0053] The MPPT control circuit includes a reference voltage V connected in sequence. ref Generation circuit, PI regulation circuit, peak current reference value i ref The circuit includes a generation circuit, a DC current detection circuit, a DC voltage detection circuit, and an AC voltage detection circuit.

[0054] Figure 2 It is the reference voltage V ref The schematic diagram of the generation circuit, which specifically includes: multiplier MUL3, sample-and-hold circuit, comparator 3, and XNOR gate. i D flip-flop, DC voltage source V d Two switches S c and S dc Two resistors R c and R dc NOT gate (NOT1) and capacitor C c Among them, the voltage V at the output terminal of the photovoltaic module pv With current I pv Connect to the input of multiplier MUL3, the output of which is P. pv The circuit is divided into two paths, connected to the non-inverting input of comparator 3 and the input of the sample-and-hold circuit, respectively. The output of the sample-and-hold circuit is connected to the inverting input of comparator 3, and the output of comparator 3 is connected to one input of the XNOR gate XNOR1. The output of XNOR1 is connected to the D input of the D flip-flop, and the Q output of the D flip-flop is denoted as V. flag DC voltage source V d The negative terminal is grounded, and its positive terminal is connected to switch S. c With resistance R c One end is connected; resistor R c The other end is connected to capacitor C. c The positive terminal and the switch S dc One end is connected, switch S dcThe other end is connected to resistor R dc With capacitor C c The negative terminal and DC voltage source V d The negative terminal is connected; the output V of the D flip-flop flag It is divided into three paths. The first path is connected to the other input of the XNOR gate XNOR1, and the second path is connected to the switch S. c Connected, the third path is connected to switch S via NOT1. dc Connected.

[0055] Figure 3 It is the reference voltage V ref The timing diagram of the generation circuit, Q in the diagram 1O Q 2O Q 3O Q 4O These represent the gate-level drive signals for thyristors Q1, Q2, Q3, and Q4, respectively. clock1 and clock2 represent... Figure 2 The operating clock of the sample hold devices and the D flip-flops.

[0056] Peak current reference value i ref The generating circuit contains two multipliers and a Divider circuit.

[0057] Figure 4 This is an internal structure diagram of the Divider circuit in the MPPT control circuit. The circuit includes: a 1V DC voltage source, two switches S1 and S2, and a capacitor C. D Two resistors R a and R b One operational amplifier (OPA1); the negative terminal of the DC voltage source is grounded, and its positive terminal is connected to the non-inverting input of OPA1; the inverting input of OPA1 is divided into three paths, all connected to capacitor C. D The negative terminal, switch S1 and resistor R b resistance R b The other end is connected to the negative terminal of a DC voltage source via switch S2; the other end of switch S1 is connected to resistor R. a With capacitor C D The positive terminal is connected to the positive terminal, which is also connected to the output terminal of OPA1; the output terminal of OPA1 uses the voltage to ground as the output of the Divider circuit.

[0058] Both the DC voltage detection circuit and the DC current detection circuit are connected in parallel to the output terminal of the photovoltaic module. The output of the DC voltage detection circuit is V. pv The output of the DC current detection circuit is I. pv Both outputs are input to the MPPT control circuit and connected to the reference voltage V. refThe input to the generation circuit. The AC voltage detection circuit is located on the mains side, and its output signals are clock signals clock1 and clock2; the outputs of this circuit are respectively connected to the reference voltage V. ref The sample-and-hold circuit and D flip-flop in the generation circuit are used to provide the clock signal. Each of the aforementioned detection circuits (not shown in the figure) includes a sampling filter circuit and a proportional amplifier circuit.

[0059] In the MPPT control circuit, the outputs of the PI regulation circuit and the Divider circuit are both connected to the peak current reference value i. ref The input of the first multiplier MUL1 in the generation circuit; the output of the latter, along with the grid phase sinusoidal half-wave signal, serves as the input of the second multiplier MUL2, whose output is the peak current reference value i. ref .

[0060] 5. The PWM wave generation circuit has the following circuit structure:

[0061] The PWM wave generation circuit includes a high-frequency current detection circuit (not shown in the diagram), comparator1, and AND gate1. The MPPT control circuit acquires the output voltage V of the photovoltaic module. pv With output current I pv The peak current reference value i is obtained. ref The high-frequency current detection circuit samples the primary current, with sampling resistor R. s The voltage across the current sensor is used to obtain the current detection value i. p The output signals of both are connected to comparator1. The outputs of comparator1 and hysteresis comparator2 are connected to logic gate AND1, and the PWM signal output by the latter is used as the MOSFET Q. s The input is used to control the flyback converter.

[0062] II. Explanation of Circuit Working Principle

[0063] By utilizing the aforementioned flyback microinverter, this invention realizes a method based on peak current critical discontinuous mode control, which includes two parts:

[0064] 1. Maximum power point tracking control of photovoltaic modules:

[0065] When the system is working normally, the DC voltage detection circuit and the DC current detection circuit detect the voltage V output by the photovoltaic module panel. pv and current i pv Samples are taken and output to the sampling signal input reference voltage V. refGeneration circuit; in this circuit, the power value P of the current cycle is first obtained by multiplier MUL3. pv Comparator 3 will assign the power value P pv The power value of the current cycle is compared with the power value stored in the sample-and-hold circuit of the previous cycle to determine the direction of power change in the current cycle; a high output of comparator3 indicates an increase in power, recorded as 1; conversely, a low output indicates a decrease, recorded as 0; a high output of the D flip-flop is recorded as 1, and a low output is recorded as 0; the output of the D flip-flop of the previous cycle and the direction of power change in the current cycle are simultaneously input to the XNOR gate XNOR1, and the output of the XNOR gate XNOR1 will be used as the input of the D flip-flop in the next cycle; reference voltage V ref The output signal V of the generation circuit ref It is controlled by the output of a D flip-flop: when the D flip-flop outputs a high level, the output signal V... ref Gradually increase, and vice versa;

[0066] An AC voltage detection circuit is used to detect the AC voltage on the mains side, and its output signals are clock signals clock1 and clock2; these signals are then connected to a reference voltage V. ref After the generation circuit is completed, it serves as the operating clock for the sample-and-hold circuit and the D flip-flop, respectively.

[0067] The PI control circuit adjusts the output voltage V of the photovoltaic module based on the IV curve relationship of the photovoltaic module panel. pv Control is performed to achieve the output voltage V pv For reference voltage V ref The tracking enables the photovoltaic modules to operate in maximum power point tracking control mode;

[0068] 2. Analog circuit control based on critical discontinuous mode of peak current:

[0069] Reference voltage V ref The reference voltage V output by the generation circuit ref With the output voltage V of the photovoltaic module panel pv The circuit is connected to a PI control circuit, with the output of the PI control circuit serving as one input to the first multiplier MUL1, and the output of the Divider circuit serving as the other input; the AC voltage sampling circuit acquires the sinusoidal half-wave signal sin(θ) of the grid phase. g The output of the first multiplier MUL1, together with the output of the second multiplier MUL2, serves as the input to the second multiplier MUL2. The output of the second multiplier MUL2 is the current reference value i. ref ;

[0070] The primary current i is detected using a high-frequency current detection circuit targeting the current sampling resistor Rs. pInputting it into the inverting input of comparator1 will cause the current reference value to be i ref The input is the non-inverting input; the output of comparator1 is connected to one input of the AND gate, and the other input is connected to the comp2o signal output by the hysteresis comparator2; the PWM signal output by the AND gate is used as the MOSFET Q in the flyback converter. s The input is used to control the peak current of the flyback converter, enabling the flyback micro-inverter to operate in critical discontinuous inductor current mode (BCM), and ultimately achieve sinusoidal AC grid connection.

[0071] The working principle of MPPT will be described in more detail below with reference to the accompanying diagram:

[0072] V obtained through voltage and current sampling circuit pv with I pv As the input signal to multiplier MUL3, multiplier MUL3 calculates the power P of the photovoltaic panel in this cycle. pv The voltage value is compared with the power value of the previous cycle stored in the sample-and-hold circuit. If comparator3 outputs a high level, it indicates that the power has increased in the current cycle, recorded as 1; otherwise, it indicates that the power has decreased in the current cycle, recorded as 0. Simultaneously, the output signal of this comparator and the output signal of the D flip-flop are used as input signals to the XNOR gate XNOR1. The output of the XNOR gate XNOR1 serves as the input for the next cycle of the D flip-flop. If the D flip-flop outputs a high level, then V... ref Increase, V ref The increase in voltage will control the output voltage V of the photovoltaic panel through subsequent control circuitry. pv Increase, or decrease (V) pv Decrease. That is, the output of the D flip-flop represents V in the next cycle. pv The direction of change, outputting a high level indicates V pv An increase is denoted as 1, and a decrease is denoted as 0. The rationale for choosing an XNOR gate can be represented by the following table:

[0073] <![CDATA[This cycle P pv Change direction]]> <![CDATA[This cycle V pv Change direction]]> <![CDATA[Next cycle V pv Change direction]]> 1 (Added) l (increase) 1 (Added) 1 (Added) 0 (decrease) 0 (decrease) 0 (decrease) 0 (decrease) 1 (Added) 0 (decrease) 1 (Added) 0 (decrease)

[0074] According to the IV characteristic curve of photovoltaic cells, V pv The direction of change is from the previous cycle V pv and P pv Jointly decided. If V pv and P pv Simultaneously increasing or decreasing, the next period V pv The change needs to be increased; conversely, if the two changes are not synchronized, then V in the next period... pv It needs to be reduced. The trigger time of the sample-and-hold circuit and the clock of the D flip-flop are both as follows: Figure 3 The timing diagram described is shown below. Figure 2 When V flag When it is high, it indicates that V re The capacity needs to be increased; at this point, Sc is activated, and S... dc Off, C c Charging, V ref Rise; conversely, V flag When S is low, c Shutdown, S dc On, C c Discharge, V ref The temperature drops. Through the above control, the V value in the MPPT control of the system can be achieved. ref generate.

[0075] Figure 5 This is a diagram showing the main waveforms of the flyback microinverter described in this invention. In this invention, the flyback converter is controlled by the primary-side peak current and operates in critical discontinuous current mode (BCM).

[0076] Combination Figure 1 , 5 The principle and process of achieving critical discontinuous mode control in the aforementioned micro-inverter are described below:

[0077] When the flyback converter is controlled by the primary-side peak current and operates in discontinuous inductor current mode, the peak primary-side current is:

[0078]

[0079] In the formula L m For the magnetizing inductance of the transformer, t on-BCM Indicates the on-time of the switching transistor, i ref-BCM That is, i in the schematic diagram ref θ g This represents the phase of the power grid, assuming the power grid voltage is:

[0080]

[0081] In the formula V g The effective value of the grid voltage can be used to calculate the turn-off time:

[0082]

[0083] In the formula, N represents the turns ratio of the secondary winding to the primary winding of the transformer, and t off Representing the turn-off time, the average secondary current of the microinverter described in this paper under BCM mode is calculated as follows:

[0084]

[0085] Furthermore, the average secondary current at this time can be derived as follows:

[0086]

[0087] It should be noted that since the inverter in this control scheme is a power frequency inverter, the average value of the secondary current is the grid-connected current. Therefore, the goal of this control scheme is to achieve sinusoidalization of the grid-connected current, that is, sinusoidalization of the average value of the secondary current. If i at this time... ref If the current is a standard sine wave, then according to the above formula, the grid-connected current will no longer be a sine wave and will not meet the grid connection conditions. Therefore, other calculations must be introduced. The average value of the secondary current is expressed as follows:

[0088]

[0089] Among them I g This indicates the effective value of the grid-connected current.

[0090] For the main power MOSFET Q s The value obtained by subtracting the duty cycle from 1 is:

[0091]

[0092] At this point, the required current reference value i can be calculated. ref The size is:

[0093]

[0094] Generated by the MPPT control circuit, i.e. Figure 1 The output of the PI circuit ( Figure 1 (101), this value determines the magnitude of the peak value of the current reference value.

[0095] When the primary current reference value satisfies the above relationship, the average value of the secondary current can be guaranteed to be a sinusoidal current. After passing through the full-bridge power frequency inverter circuit, the sinusoidal full-wave current is injected into the power grid.

[0096] To achieve peak current control, V needs to be adjusted. ref V generated by the generation circuit ref Perform PI regulation. The output of the PI regulator and the output of the Divider circuit are multiplied by the MUL. l Multiply, the output of multiplier MUL1 is then multiplied by the phase of the power grid sin(θ). g The reference current value i is obtained by multiplying the two values ​​by multiplier MUL2. ref The grid phase is obtained by an AC voltage sampling circuit.

[0097] Based on the aforementioned method of sinusoidal injection of grid-connected current into the grid, a divider circuit is required. Figure 4 The described internal structure of the Divider circuit shows that the input of the circuit is a 1V DC voltage, and the output is... Its specific working principle can be described as follows:

[0098] The circuit is divided into two operating stages. In stage 1, when the PWM signal is low, S1 is turned on and S2 is turned off, resulting in the following expression:

[0099] v C (t)=-i C (t)·R

[0100] v in +v C (t)=v out (t)

[0101] Where v c Indicates capacitance C D voltage, i c Indicates that current flows through capacitor C D The current, v in This indicates a 1V DC input, v out This indicates the output of the Divider circuit.

[0102] In the second stage, when the PWM signal is high, S1 is off and S2 is on, resulting in the following expression:

[0103] v in =i C (t)·R

[0104] v in +v C (t)=v out (t)

[0105] Based on the ampere-second balance principle of capacitor voltage:

[0106]

[0107] In the formula, d represents the duty cycle, d' = 1 - d, which simplifies to:

[0108]

[0109] so:

[0110]

[0111] Therefore, we can conclude that:

[0112]

[0113] It can perform voltage boosting calculations. Since the Divider circuit has a fixed input voltage of 1V, its output voltage is... Using phase instead of time, it can be expressed as:

[0114] Furthermore, combined Figure 1 The working principle of the PWM wave generation circuit can be described as follows:

[0115] The high-frequency current detection circuit detects the primary current i through Rs. p This value is connected to the inverting input of comparator1, while the i generated by the aforementioned circuit... ref The input is connected to the non-inverting input of comparator1, and the output of comparator1 is connected to one input of the AND gate AND1. The other input of AND1 is connected to the comp2o signal. The output of the AND gate AND1 is the PWM signal.

[0116] It should be noted that for the comp2o signal, the signal is low when the secondary current is not zero; and the signal becomes high when the secondary current is zero.

[0117] Under the control of analog control circuits, flyback microinverters ultimately achieve maximum power point tracking and sinusoidal current grid connection.

[0118] The specific embodiments described above illustrate the technical solution and beneficial effects of the present invention in detail. It should be understood that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, additions, and equivalent substitutions made within the scope of the principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A flyback microinverter, characterized in that, The inverter includes a flyback converter, a power frequency inverter filter circuit, and an inverter control circuit. The AC input terminal and DC input terminal of the inverter control circuit are connected in parallel to the AC terminal and DC terminal of the inverter, respectively. The output of the inverter is connected to the power grid. (1) The flyback converter has the following circuit structure: The primary winding of transformer T and MOSFET Q s and current sampling resistor R s After being connected in series, it is connected to the input electrolytic capacitor C. in It is connected in parallel across the two ends of the photovoltaic module, with the negative terminal grounded; the secondary winding of transformer T is connected to rectifier diode D. M It is connected in series and then in parallel with the power frequency inverter filter circuit, which is connected to the power grid. The auxiliary winding of transformer T is connected to the auxiliary coil voltage limiting resistor R at both ends. ss After connecting the Zener diode, it is then connected to the inverting input of the hysteresis comparator 2; the two hysteresis comparator resistors R ss1 R ss2 After being connected in series, one end is connected to the output of hysteresis comparator 2, and the other end is connected to the comparator reference voltage V. refss And the midpoint is connected to the non-inverting input of the hysteresis comparator2; (2) The inverter control circuit includes an MPPT control circuit and a PWM wave generation circuit; wherein, The MPPT control circuit includes a reference voltage V connected in sequence. ref Generation circuit, PI regulation circuit, and peak current reference value i ref Generation circuit, peak current reference value i ref The generator circuit contains two multipliers and one divider circuit. The PWM wave generation circuit includes a high-frequency current detection circuit, a comparator1, and an AND gate1. The MPPT control circuit acquires the output voltage V of the photovoltaic module. pv With output current I pv The peak current reference value i is obtained. ref The high-frequency current detection circuit samples the primary current, with sampling resistor R. s The voltage across the current sensor is used to obtain the current detection value i. p The output signals of both are connected to comparator1. The outputs of comparator1 and hysteresis comparator2 are connected to logic gate AND1, and the PWM signal output by the latter is used as the MOSFET Q. s The input is used to control the flyback converter.

2. The flyback microinverter according to claim 1, characterized in that, The outputs of the PI adjustment circuit and the divider circuit in the MPPT control circuit are both connected to the peak current reference value i. ref The input of the first multiplier MUL1 in the generation circuit; the output of the latter, along with the grid phase sinusoidal half-wave signal, serves as the input of the second multiplier MUL2, whose output is the peak current reference value i. ref .

3. The flyback microinverter according to claim 1, characterized in that, The reference voltage V ref The generation circuit includes: multiplier MUL3, sample-and-hold circuit, comparator 3, XNOR gate XNOR1, D flip-flop, and DC voltage source V. d Two switches S c and S dc Two resistors R c and R dc NOT gate (NOT1) and capacitor C c ;in, The voltage V at the output of the photovoltaic module pv With current I pv Connect to the input of multiplier MUL3, the output of which is P. pv The circuit is divided into two paths, connected to the non-inverting input of comparator 3 and the input of the sample-and-hold circuit, respectively. The output of the sample-and-hold circuit is connected to the inverting input of comparator 3, and the output of comparator 3 is connected to one input of the XNOR gate XNOR1. The output of XNOR1 is connected to the D input of the D flip-flop, and the Q output of the D flip-flop is denoted as V. flag ; DC voltage source V d The negative terminal is grounded, and its positive terminal is connected to switch S. c With resistance R c One end is connected; resistor R c The other end is connected to capacitor C. c The positive terminal and the switch S dc One end is connected, switch S dc The other end is connected to resistor R dc With capacitor C c The negative terminal and DC voltage source V d The negative terminal is connected; the output V of the D flip-flop. flag It is divided into three paths. The first path is connected to the other input of the XNOR gate XNOR1, and the second path is connected to the switch S. c Connected, the third path is connected to switch S via NOT1. dc Connected.

4. The flyback microinverter according to claim 1, characterized in that, The divider circuit includes: a 1V DC voltage source, two switches S1 and S2, and a capacitor C. D Two resistors R a and R b One operational amplifier, OPA1; among which, The negative terminal of the DC voltage source is grounded, and its positive terminal is connected to the non-inverting input of op-amp OPA1; the inverting input of op-amp OPA1 is divided into three paths, all of which are connected to capacitor C. D The negative terminal, switch S1 and resistor R b resistance R b The other end is connected to the negative terminal of a DC voltage source via switch S2; the other end of switch S1 is connected to resistor R. a With capacitor C D The positive terminal is connected to the positive terminal, which is also connected to the output terminal of OPA1; the output terminal of OPA1 uses the voltage to ground as the output of the divider circuit.

5. The flyback microinverter according to claim 1, characterized in that, The MPPT control circuit further includes a DC current detection circuit, a DC voltage detection circuit, and an AC voltage detection circuit; wherein... Both the DC voltage detection circuit and the DC current detection circuit are connected in parallel to the output terminal of the photovoltaic module. They respectively collect the voltage V at the output terminal of the photovoltaic module. pv With current I pv The output signal is connected to the reference voltage V in the MPPT control circuit. ref Generation circuit; The AC voltage detection circuit is located on the mains side, and its output signals are clock signals clock1 and clock2; the outputs of this circuit are respectively connected to the reference voltage V. ref The sample-and-hold circuit and D flip-flop in the generation circuit are used to provide the clock signal.

6. The flyback microinverter according to claim 5, characterized in that, Each of the DC current detection circuit, DC voltage detection circuit, and AC voltage detection circuit includes a sampling filter circuit and a proportional amplifier circuit.

7. The flyback microinverter according to claim 1, characterized in that, The MPPT control circuit also includes an auxiliary power supply for powering the control circuit and serving as a reference voltage V. ref V of the generation circuit d It is used as a DC voltage source in the divider circuit.

8. A method for implementing critical discontinuous mode simulation control of a flyback micro-inverter using the flyback micro-inverter as described in claim 1, characterized in that, include: (1) Maximum power point tracking control of photovoltaic modules: When the system is working normally, the DC voltage detection circuit and the DC current detection circuit detect the voltage V output by the photovoltaic module panel. pv and current i pv Samples are taken and output to the sampling signal input reference voltage V. ref Generation circuit; in this circuit, the power value P of the current cycle is first obtained by multiplier MUL3. pv Comparator 3 will assign the power value P pv The power value of the current cycle is compared with the power value stored in the sample-and-hold circuit of the previous cycle to determine the direction of power change in the current cycle; a high output of comparator3 indicates an increase in power, recorded as 1; conversely, a low output indicates a decrease, recorded as 0; a high output of the D flip-flop is recorded as 1, and a low output is recorded as 0; the output of the D flip-flop of the previous cycle and the direction of power change in the current cycle are simultaneously input to the XNOR gate XNOR1, and the output of the XNOR gate XNOR1 will be used as the input of the D flip-flop in the next cycle; reference voltage V ref The output signal V of the generation circuit ref It is controlled by the output of a D flip-flop: when the D flip-flop outputs a high level, the output signal V... ref Gradually increase, and vice versa; An AC voltage detection circuit is used to detect the AC voltage on the grid side, and its output signals are clock signals clock1 and clock2; these signals are then connected to a reference voltage V. ref After the generation circuit is completed, it serves as the operating clock for the sample-and-hold circuit and the D flip-flop, respectively. The PI control circuit adjusts the output voltage V of the photovoltaic module based on the IV curve relationship of the photovoltaic module panel. pv Control is performed to achieve the output voltage V pv For reference voltage V ref The tracking enables the photovoltaic modules to operate in maximum power point tracking control mode; (2) Analog circuit control based on critical discontinuous mode of peak current: Reference voltage V ref The reference voltage V output by the generation circuit ref With the output voltage V of the photovoltaic module panel pv The circuit is connected to a PI control circuit, with the output of the PI control circuit serving as one input to the first multiplier MUL1, and the output of the divider circuit serving as the other input; the AC voltage sampling circuit acquires the sinusoidal half-wave signal sin(θ) of the grid phase. g The output of the first multiplier MUL1, together with the output of the second multiplier MUL2, serves as the input to the second multiplier MUL2. The output of the second multiplier MUL2 is the current reference value i. ref ; The primary current i is detected using a high-frequency current detection circuit targeting the current sampling resistor Rs. p Inputting it into the inverting input of comparator1 will cause the current reference value to be i ref The input is the non-inverting input; the output of comparator1 is connected to one input of the AND gate, and the other input is connected to the comp2o signal output by the hysteresis comparator2; the PWM signal output by the AND gate is used as the MOSFET Q in the flyback converter. s The input is used to control the peak current of the flyback converter, enabling the flyback micro-inverter to operate in the critical discontinuous inductor current mode, and ultimately achieve sinusoidal AC grid connection.

9. The method according to claim 8, characterized in that, It should be noted that when the secondary current of transformer T is not zero, the comp2o signal output by hysteresis comparator2 is low; when the secondary current of transformer T is zero, the signal changes to high.

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