CN116388594A - Control method and controller for maximum power point tracking of flyback micro-inverter - Google Patents
Control method and controller for maximum power point tracking of flyback micro-inverter Download PDFInfo
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
- H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
- H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
- H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
- H02M7/53—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
- H02M7/537—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters
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- G—PHYSICS
- G05—CONTROLLING; REGULATING
- G05F—SYSTEMS FOR REGULATING ELECTRIC OR MAGNETIC VARIABLES
- G05F1/00—Automatic systems in which deviations of an electric quantity from one or more predetermined values are detected at the output of the system and fed back to a device within the system to restore the detected quantity to its predetermined value or values, i.e. retroactive systems
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- G05F1/67—Regulating electric power to the maximum power available from a generator, e.g. from solar cell
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- H—ELECTRICITY
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- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
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- H02M7/53—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
- H02M7/537—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters
- H02M7/5387—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters in a bridge configuration
- H02M7/53871—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters in a bridge configuration with automatic control of output voltage or current
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- H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
- H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
- H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
- H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
- H02M7/53—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
- H02M7/537—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters
- H02M7/539—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters with automatic control of output wave form or frequency
- H02M7/5395—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters with automatic control of output wave form or frequency by pulse-width modulation
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- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J2300/00—Systems for supplying or distributing electric power characterised by decentralized, dispersed, or local generation
- H02J2300/20—The dispersed energy generation being of renewable origin
- H02J2300/22—The renewable source being solar energy
- H02J2300/24—The renewable source being solar energy of photovoltaic origin
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- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
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Abstract
The invention relates to the field of distributed photovoltaic power generation, and aims to provide a control method and a controller for tracking a maximum power point of a flyback micro-inverter. The control method adopts peak current to control the inverter to work in a current critical intermittent mode; controlling the reference value i according to the peak current ref Generates an instantaneous value for controlling the main switching tube Q M On-off PWM signals; regulating the main switching tube Q by using the duty cycle control factor k M To achieve sinusoidal ac grid connection of current and to achieve maximum based on adjustment of duty cycle control factor kAnd (5) tracking power points. The inverter control method provided by the invention can realize the maximum power point tracking function of the micro inverter under the condition of realizing grid-connected current sinusoidal; the control logic is simple, the calculation is convenient, and the control logic can be realized by a very simple circuit; therefore, the hardware product has low cost and stable operation.
Description
Technical Field
The invention relates to the field of distributed photovoltaic power generation, in particular to a control method and a controller for tracking a maximum power point of a flyback micro-inverter.
Background
With the expansion of the application range of photovoltaic systems, distributed, consumer photovoltaic products will further develop. Current distributed photovoltaic product and control related devices mainly include micro-inverters, power optimizers, and the like.
Among the micro-inverters, the flyback micro-inverter is one of which the current commercialization is successful and the application is wide. The flyback micro-inverter uses a flyback circuit to convert direct current output by the photovoltaic module into alternating current and inject the alternating current into a power grid. Flyback inverters exhibit current source characteristics because they typically employ discontinuous or critical discontinuous modes of operation. At present, in a current critical intermittent mode (Boundary Conduction Mode, BCM), a disturbance observation method is often adopted for maximum power point tracking (Maximum Power Point Tracking, MPPT) of a flyback inverter product. The output voltage of the photovoltaic module is disturbed, a closed-loop control method is generally needed in the control process, the operation load of the controller is increased, and the complexity of the system is increased. To solve this problem, an improvement in the maximum power point tracking method is required.
Therefore, the maximum power point tracking control method capable of realizing open loop control, simple logic and convenient flyback micro-inversion is a current industry requirement.
Disclosure of Invention
The invention aims to solve the technical problem of overcoming the defects in the prior art and providing a control method and a controller for tracking the maximum power point of a flyback micro-inverter.
In order to solve the technical problems, the invention adopts the following solutions:
provides a control method for tracking maximum power point of flyback micro-inverterThe flyback micro-inverter comprises a main switching tube Q which is positioned in a primary circuit and connected with a primary winding of a transformer T M ；
The control method adopts peak current to control the inverter to work in a current critical intermittent mode; controlling the reference value i according to the peak current ref Generates an instantaneous value for controlling the main switching tube Q M On-off PWM signals; regulating the main switching tube Q by using the duty cycle control factor k M To achieve sinusoidal ac grid connection of current, and to achieve maximum power point tracking based on adjustment of the duty cycle control factor k; wherein,,
the peak current control reference value i ref Is calculated according to the following formula
The duty cycle control factor k satisfies the following relation:
in the above formulae, i ref (t) is the instantaneous value of the reference value iref; k is a duty ratio control factor, and N is the duty ratio of the secondary side and the primary side in the transformer T; i pv V is the output current of the photovoltaic module pv Is the output voltage omega of the photovoltaic module g The angular speed of the grid voltage is represented by t; d (t) represents the main switching tube Q M An instantaneous value of the duty cycle, L m Is the exciting inductance of the transformer T, V g Is the effective value of the grid voltage.
As a preferred scheme of the invention, in order to realize maximum power point tracking, the duty ratio control factor k is continuously adjusted in the control process; the method specifically comprises the following steps:
(1) Setting the initial value of the duty ratio control factor k to be 0;
(2) Output current I of photovoltaic module pv And output voltage V pv Multiplication is carried out to obtain the output power P of the photovoltaic module in the period pv The method comprises the steps of carrying out a first treatment on the surface of the Comparing the value with the output power of the previous period to obtain the change direction of the output power;
(3) Calculating a duty ratio control factor k, and comparing the value of the duty ratio control factor k with a calculated value obtained in the previous period to obtain the change direction of the duty ratio control factor k;
(4) If the output power P in the present period pv And the duty ratio control factor k is increased or decreased simultaneously, and then the value of the duty ratio control factor k is increased in the next period; if the changing directions of the two are not consistent in the period, the lower period is reduced by the value of the duty ratio control factor k.
The invention further provides an inverter controller for realizing the control method for tracking the maximum power point of the flyback micro-inverter, which comprises a sampling module, an MPPT control module, a reference value calculation module and a PWM generation module which are electrically connected in sequence, wherein the sampling module is also electrically connected with the reference value calculation module and the PWM generation module respectively;
the sampling module is used for collecting the operation parameters of the inverter and the power grid and outputting the output current I of the photovoltaic module to the MPPT control module pv And output voltage V pv Output voltage V of the photovoltaic module is output to a reference value calculation module pv And the grid voltage effective value V g The method comprises the steps of carrying out a first treatment on the surface of the Outputting primary side current i of transformer to PWM generating module p And transformer secondary side current i s ；
The MPPT control module is used for calculating and obtaining a duty ratio control factor k and outputting the duty ratio control factor k to the reference value calculation module;
the reference value calculation module is used for calculating a reference value i for obtaining peak current control ref Outputting the real-time numerical value of the PWM signal to a PWM generation module;
the PWM generating module is used for calculating PWM signals and outputting the PWM signals to the main switching tube Q M To control the on-off of the electric motor.
The invention also provides a flyback micro inverter for realizing the maximum power point tracking control method, which comprises a primary circuit, a transformer T and a secondary circuit, wherein a main switching tube Q connected with a primary winding of the transformer T is arranged in the primary circuit M The method comprises the steps of carrying out a first treatment on the surface of the The input end of the inverter is connected with the output end of the photovoltaic module, and the output end of the inverter is connected with the power grid v g Are connected; the flyback micro inverter also comprises an inverter controller, wherein a PWM generating module in the controller is electrically connected to the main switching tube Q M 。
As a preferable scheme of the invention, the primary side circuit further comprises an input electrolytic capacitor C in The method comprises the steps of carrying out a first treatment on the surface of the Input electrolytic capacitor C in Parallel connected at two output ends of the photovoltaic module, C in The positive pole of the photovoltaic module is connected with the positive pole of the photovoltaic module, and the positive pole is connected with one end of the primary winding of the transformer; the other end of the primary winding of the transformer and a main switch tube Q M Drain electrode is connected with Q M The source electrode is connected to C in The negative electrode is connected with the grounding end.
As a preferable mode of the invention, the secondary side circuit comprises a rectifier diode D M Secondary side decoupling capacitor C o A bridge expansion circuit and a CL filter circuit; secondary winding of transformer T and rectifier diode D M The bridge type power grid is connected with a bridge type unfolding circuit after being connected in series, a CL filter circuit is connected in parallel between two bridge arms of the bridge type unfolding circuit, and the output of the CL filter circuit is connected with the input end of the power grid; secondary side decoupling capacitor C o Parallel to two ends of the bridge type unfolding circuit, and a secondary side decoupling capacitor C o One end connected with the secondary side ground is not connected with a rectifier diode D in a secondary side winding of the transformer M One end of the connection is connected.
As a preferable scheme of the invention, the bridge unfolding circuit comprises four MOS switching tubes Q 1 、Q 2 、Q 3 And Q 4 Wherein the switch Q 1 And Q 4 When the power grid voltage is in a positive half period, the power grid is turned on, and otherwise, the power grid is turned off; switch tube Q 2 And Q 3 And is turned on when the grid voltage is in a negative half cycle, and is turned off otherwise.
As a preferred embodiment of the present invention, the CL filter circuit includes a filter capacitor C f And a filter inductance L f The method comprises the steps of carrying out a first treatment on the surface of the Wherein, the filter capacitor C f Across the switching tube Q 1 Source and switching tube Q of (2) 3 Between the drains of (a), a filter inductance L f Connected with a filter capacitor C f And one side of the power grid input end, and the other side of the power grid input end and the filter capacitor C f Not with filter inductance L f The other ends of the connection are connected.
Compared with the prior art, the invention has the beneficial effects that:
1. the inverter control method provided by the invention can realize the maximum power point tracking function of the micro inverter under the condition of realizing grid-connected current sinusoidal;
2. the control logic is simple, the calculation is convenient, and the control logic can be realized by a very simple circuit; therefore, the hardware product has low cost and stable operation.
Drawings
Fig. 1 is a schematic circuit diagram of a flyback micro-inverter according to the present invention.
Fig. 2 is a schematic circuit diagram of the inverter controller according to the present invention.
Fig. 3 is a flowchart of a maximum power point tracking control method according to the present invention.
Fig. 4 shows primary and secondary side currents of a transformer in a critical intermittent mode of a flyback micro-inverter according to the present invention.
Fig. 5 is a derivative diagram of the principle of the flyback micro-inverse maximum power point tracking implementation of the present invention.
Detailed Description
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings to be used in the description of the embodiments or the prior art will be briefly described below.
Fig. 1 is a schematic diagram of a flyback micro-inverter according to the present invention. The flyback inverter comprises a primary side circuit, a high-frequency transformer T and a secondary side circuit. The input end of the inverter is connected with the photovoltaic module, and the output end of the inverter is connected with the power grid v g Are connected.
Wherein the primary circuit comprises an input electrolytic capacitor C in And main power MOS switch tubeQ M (hereinafter referred to as the main switching tube Q) M ). The connection mode is that an electrolytic capacitor C is input in Parallel connected at two output ends of the photovoltaic module, C in And the positive electrode of the photovoltaic module is connected with the positive electrode of the photovoltaic module, and the positive electrode of the photovoltaic module is connected with one end of the primary winding of the transformer. The other end of the primary winding of the transformer and a main switch tube Q M Drain electrode is connected with Q M The source electrode is connected to C in The negative electrode is connected with the grounding end.
The secondary circuit comprises a rectifying diode D M A secondary decoupling capacitor C o One is formed by MOS switch tube Q 1 ，Q 2 ，Q 3 And Q 4 Bridge-type unfolding circuit formed by filter capacitor C f And a filter inductance L f And a CL filter circuit is formed. The connection mode is that the secondary side and the primary side of the transformer and C in The synonym end of one end is connected with a rectifier diode D M Anode of rectifier diode D M Cathode and C of (2) o Is connected to one end of Q 1 And Q 4 Is connected with the drain electrode of the transistor; q (Q) 1 Source and Q of (2) 2 Is connected with the drain electrode of Q 4 Source and Q of (2) 3 Is connected with the drain electrode of the transistor; q (Q) 2 And Q 3 Source of (C) and capacitor C o Is connected to the other end of the secondary winding, while the other end is not connected to D M One end of the connection is connected. Filter capacitor C f Connected to Q 1 Source and Q 3 Between the drains, a filter inductance L f One end and Q 1 The source electrode is connected with the power grid v at the other end g Is connected to one end of the power grid v g And Q is the other end of (2) 3 Is connected to the drain of the transistor. For Q 1 、Q 2 、Q 3 、Q 4 When the grid voltage is in the positive half cycle, Q 1 And Q 3 Conducting, Q when the grid voltage is in the negative half cycle 2 And Q 4 Conducting.
The main circuit structure of the flyback inverter belongs to the known technology, and the circuit structure and the function implementation principle of the flyback inverter are described in a plurality of literature books, so that the invention is not repeated.
Fig. 2 is a schematic diagram of a controller of the flyback micro-inverter according to the present invention.
The inverter controller comprises a sampling module, an MPPT control module, a reference value calculation module and a PWM generation module which are electrically connected in sequence, wherein the sampling module is also electrically connected with the reference value calculation module and the PWM generation module respectively.
The sampling module is used for collecting the operation parameters of the inverter and the power grid, and obtaining the output voltage V of the photovoltaic module through sampling pv Photovoltaic module output current I pv Primary current i of transformer p Secondary side current i of transformer s Grid voltage v g Sampled values of the signal. The sampling module outputs current I pv And output voltage V p And outputting the output to an MPPT module, and generating a duty ratio control factor k by the MPPT module. The main switching tube Q can be regulated by using the duty ratio control factor k M The sine alternating current grid connection of the current is realized.
The duty cycle control factor k satisfies the following relation:
wherein V is g Is the effective value of the voltage of the power grid, I pv V is the output current of the photovoltaic module pv Is the output voltage of the photovoltaic module, L m Is the excitation inductance of the transformer T.
Duty cycle control factor k and output voltage V of photovoltaic module pv And the grid voltage effective value V g Is input to a reference value calculation module together, and a peak current control reference value i is calculated according to the following formula ref Is the instantaneous value of (a):
wherein i is ref (t) is the current reference value i ref Is a real-time value of (2); k is a duty ratio control factor, N is the duty ratio of the secondary side and the primary side in the transformer T, omega g The angular speed of the grid voltage is represented by t; d (t) represents the main switching tube Q M An instantaneous value of the duty cycle of (a).
The instant value i of the reference value is then used ref With primary current i of transformer p And transformer secondary side current i s Commonly input to a PWM generation module to calculate and obtain a control Q M On-off PWM signal. The functional implementation manner of the PWM generation module belongs to a well-known technology, and since the generation manner of the PWM signal is already described in many literature books, the invention will not be repeated.
Fig. 3 is a flowchart of a maximum power point tracking control method according to the present invention.
In order to realize maximum power point tracking, the invention needs to continuously adjust the duty ratio control factor k in the control process; the method specifically comprises the following steps:
firstly, setting the initial value of a duty ratio control factor k to be 0; by V pair pv And I pv Multiplication is carried out to obtain the output power P of the real-time photovoltaic module pv And comparing the value with the power value obtained in the previous period to obtain the change direction of the power. If the size is larger, the value is marked as 1, otherwise, the value is marked as 0; the same applies to the direction of change of the duty control factor k. If in the present period, P pv And k increases or decreases simultaneously, the lower period increases the value of k; if P in the present period pv And the changing direction of k is inconsistent, the lower period is reduced by the value of k, and it is obvious that an exclusive-OR relationship exists between the values.
Specific examples are shown in the following table:
| the period P pv Direction of change | The direction of change of the period k | Lower period k direction of change |
| 1 (increase) | 1 (increase) | 1 (increase) |
| 1 (increase) | 0 (decrease) | 0 (decrease) |
| 0 (decrease) | 0 (decrease) | 1 (increase) |
| 0 (decrease) | 1 (increase) | 0 (decrease) |
The duty ratio control factor k can be continuously adjusted in the control process, so that the duty ratio control factor k can track the running parameter change conditions of the photovoltaic module and the power grid in real time, and the adjustment of PWM control signals is influenced by the change of the numerical value of the duty ratio control factor k. And finally, the photovoltaic module can operate in a maximum power output state by adjusting the operation of the flyback micro-inverter.
Fig. 4 shows the primary and secondary side currents of the transformer in the critical interrupt mode of the flyback micro-inverter according to the present invention.
The implementation principle of the control method according to the present invention will be described in more detail with reference to fig. 1 to 5:
due to the main switching tube Q M The switching frequency of (2) is much higher than the grid frequency, so for simplicity of analysis it is assumed that the grid voltage remains unchanged during one switching period. Combining with the self working characteristics of flyback micro-inversion in BCM mode, it can be obtained that Q M The on-time of (c) is:
wherein i is ref (t) is the current reference value i ref Is a real-time value of (2);
because the bridge type unfolding circuit adopted by the secondary side only plays a role in converting steamed bread waves into sine waves, the average value of the secondary side current of the transformer T can be considered as grid-connected current:
wherein I is g V is the effective value of the grid-connected current g The voltage is an effective value of the power grid voltage, and t represents time;
meanwhile, it is derived that:
wherein d (t) represents the main switching tube Q M An instantaneous value of the duty cycle of (a).
Combining the above formulas, if the grid-connected current is to be ensured to be sine value, the Q is obtained easily M The on-time of (c) must satisfy the following relationship:
wherein k is the duty cycle control factor, and the value of k is generated by the MPPT control circuit.
If Q M Satisfying the above relation, the average value of the secondary side current at this time can be found as:
meanwhile, neglecting the losses of the converter itself, it is assumed that the input power is equal to the output power:
P pv ＝V g I g ＝V pv I pv
the following relationship can be derived:
as can be readily seen from this relationship, I is now pv Is V pv Drawing the proportional function and the I-V, P-V curves of the photovoltaic module into the same graph to obtain the graph 5. As can be readily seen from fig. 5, as the k value increases, the slope of the scaling function increases, and at the same time the scaling function has a uniquely defined intersection with the I-V characteristic of the photovoltaic module, which means that each k value corresponds to an operating point.
If the MPPT is to be controlled by controlling the k value, the correlation logic relationship can be described as follows: if the k value is increased in the period, the output power P of the photovoltaic module is simultaneously pv Also increases, the next control period continues to increase the k value, otherwise P increases with the k value in the present period pv Decreasing, the next control period requires decreasing the k value; if the k value is reduced in the present period, P is the same time pv Decreasing, the next control period requires decreasing the k value, and otherwise increasing the k value. If the k value is added to P pv If the increase of (1) is recorded as logic 1 and the decrease is recorded as logic 0, the logic relation table shown in the table 4-1 can be obtained according to the above description, and it is easy to see that the change direction of the k value of the next control period is equal to the k value and P of the present period pv Is the same or a relationship between the directions of change, which also corresponds to the flow chart described in fig. 3. As long as the value of k is controlled according to the above procedure, there must be a certain value k mpp The working point of the photovoltaic module is positioned at the voltage V corresponding to the maximum power point mpp And power P mpp Where it is located.
On the premise of adopting peak current control, the instant value of the primary current reference value which needs to be obtained at the moment can be obtained as follows:
meanwhile, according to the formula, the further analysis is not difficult to obtain:
it can be seen that the larger k, the larger the duty cycle, and thus the value of k can be named the duty cycle control factor.
In summary, under the control of the analog control circuit, the flyback micro-inverter can finally realize the maximum power point tracking function on the premise of ensuring the sine of the grid-connected current. Meanwhile, the control mode is simple to realize, and can also be realized in an analog control mode, and details are not repeated here.
The foregoing detailed description of the embodiments and advantages of the invention will be apparent from the following more particular description of the invention, as illustrated in the accompanying drawings, wherein like reference characters refer to the same parts throughout the different views.
Claims (8)
1. A control method for tracking maximum power point of flyback micro inverter includes main switch tube Q connected with primary winding of transformer T in primary circuit M The method comprises the steps of carrying out a first treatment on the surface of the It is characterized in that the method comprises the steps of,
the control method adopts peak current to control the inverter to work in a current critical intermittent mode; controlling the reference value i according to the peak current ref Generates an instantaneous value for controlling the main switching tube Q M On-off PWM signals; regulating the main switching tube Q by using the duty cycle control factor k M To achieve sinusoidal ac grid connection of current, and to achieve maximum power point tracking based on adjustment of the duty cycle control factor k; wherein,,
the peak current control reference value i ref Is a function of the instantaneous value of (a),obtained by calculation according to
The duty cycle control factor k satisfies the following relation:
in the above formulae, i ref (t) is the instantaneous value of the reference value iref; k is a duty ratio control factor, and N is the duty ratio of the secondary side and the primary side in the transformer T; i pv V is the output current of the photovoltaic module pv Is the output voltage omega of the photovoltaic module g The angular speed of the grid voltage is represented by t; d (t) represents the main switching tube Q M An instantaneous value of the duty cycle, L m Is the exciting inductance of the transformer T, V g Is the effective value of the grid voltage.
2. The method according to claim 1, characterized in that for maximum power point tracking, the duty cycle control factor k is continuously adjusted during the control process; the method specifically comprises the following steps:
(1) Setting the initial value of the duty ratio control factor k to be 0;
(2) Output current I of photovoltaic module pv And output voltage V pv Multiplication is carried out to obtain the output power P of the photovoltaic module in the period pv The method comprises the steps of carrying out a first treatment on the surface of the Comparing the value with the output power of the previous period to obtain the change direction of the output power;
(3) Calculating a duty ratio control factor k, and comparing the value of the duty ratio control factor k with a calculated value obtained in the previous period to obtain the change direction of the duty ratio control factor k;
(4) If it isOutput power P in the present period pv And the duty ratio control factor k is increased or decreased simultaneously, and then the value of the duty ratio control factor k is increased in the next period; if the changing directions of the two are not consistent in the period, the lower period is reduced by the value of the duty ratio control factor k.
3. An inverter controller for implementing the control method for maximum power point tracking of a flyback micro-inverter according to claim 1, wherein the controller comprises a sampling module, an MPPT control module, a reference value calculation module and a PWM generation module which are electrically connected in sequence, and the sampling module is also electrically connected with the reference value calculation module and the PWM generation module respectively;
the sampling module is used for collecting the operation parameters of the inverter and the power grid and outputting the output current I of the photovoltaic module to the MPPT control module pv And output voltage V pv Output voltage V of the photovoltaic module is output to a reference value calculation module pv And the grid voltage effective value V g The method comprises the steps of carrying out a first treatment on the surface of the Outputting primary side current i of transformer to PWM generating module p And transformer secondary side current i s ；
The MPPT control module is used for calculating and obtaining a duty ratio control factor k and outputting the duty ratio control factor k to the reference value calculation module;
the reference value calculation module is used for calculating a reference value i for obtaining peak current control ref Outputting the real-time numerical value of the PWM signal to a PWM generation module;
the PWM generating module is used for calculating PWM signals and outputting the PWM signals to the main switching tube Q M To control the on-off of the electric motor.
4. A flyback miniature inverter for realizing a maximum power point tracking control method comprises a primary circuit, a transformer T and a secondary circuit, wherein a main switching tube Q connected with a primary winding of the transformer T is arranged in the primary circuit M The method comprises the steps of carrying out a first treatment on the surface of the The input end of the inverter is connected with the output end of the photovoltaic module, and the output end of the inverter is connected with the power grid v g Are connected; the flyback micro-inverter is characterized by further comprising an inverter controller as claimed in claim 4, wherein a PWM generation module in the controller is electrically connected withConnected to the main switching tube Q M 。
5. The flyback micro-inverter of claim 4 wherein the primary side circuit further comprises an input electrolytic capacitor C in The method comprises the steps of carrying out a first treatment on the surface of the Input electrolytic capacitor C in Parallel connected at two output ends of the photovoltaic module, C in The positive pole of the photovoltaic module is connected with the positive pole of the photovoltaic module, and the positive pole is connected with one end of the primary winding of the transformer; the other end of the primary winding of the transformer and a main switch tube Q M Drain electrode is connected with Q M The source electrode is connected to C in The negative electrode is connected with the grounding end.
6. The flyback micro-inverter of claim 4 wherein the secondary side circuit comprises a rectifier diode D M Secondary side decoupling capacitor C o A bridge expansion circuit and a CL filter circuit; secondary winding of transformer T and rectifier diode D M The bridge type power grid is connected with a bridge type unfolding circuit after being connected in series, a CL filter circuit is connected in parallel between two bridge arms of the bridge type unfolding circuit, and the output of the CL filter circuit is connected with the input end of the power grid; secondary side decoupling capacitor C o Parallel to two ends of the bridge type unfolding circuit, and a secondary side decoupling capacitor C o One end connected with the secondary side ground is not connected with a rectifier diode D in a secondary side winding of the transformer M One end of the connection is connected.
7. The flyback micro-inverter of claim 6, wherein the bridge development circuit comprises four MOS switch transistors Q 1 、Q 2 、Q 3 And Q 4 Wherein the switch Q 1 And Q 4 When the power grid voltage is in a positive half period, the power grid is turned on, and otherwise, the power grid is turned off; switch tube Q 2 And Q 3 And is turned on when the grid voltage is in a negative half cycle, and is turned off otherwise.
8. The flyback micro-inverter of claim 7 wherein the CL filter circuit comprises a filter capacitor Cf and a filter inductor L f The method comprises the steps of carrying out a first treatment on the surface of the Wherein, the filter capacitor C f Across the switching tube Q 1 Source and switching tube Q of (2) 3 Between the drains of (a), a filter inductance L f Connected with a filter capacitor C f And one side of the power grid input end, and the other side of the power grid input end and the filter capacitor C f Not with filter inductance L f The other ends of the connection are connected.
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