CN108696144A - The modulation compensated circuit of interleaving inverse excitation type DC/DC hardware - Google Patents

Abstract

The invention relates to an interleaved flyback DC/DC hardware modulation compensation circuit, including a photovoltaic panel, a DC side capacitor, an interleaved flyback DC/DC converter, an inverter bridge, an output filter, a power grid and a hardware compensation module; The invention has the function of insulating and isolating the input side and the output side, which can deal with the situation that the circuit is greatly affected by electromagnetic interference and the circuit components are different in practice. It has a wide range of applicable voltage and wide range of applicable temperature, which improves the existing interleaved flyback The working status of the switching tubes of the conventional converter is inconsistent; the present invention only adds a modulation signal compensation circuit, does not increase the volume of the existing topological structure, ensures that the output waveform of the converter is more stable, and provides a smoother output for the subsequent inverter circuit. Voltage can also effectively reduce the fluctuation of output power.

Description

Interleaved Flyback DC/DC Hardware Modulation Compensation Circuit

technical field

The invention relates to the technical field of solar power generation, and in particular proposes an interleaved flyback DC/DC hardware modulation compensation circuit in the design of a two-stage photovoltaic grid-connected system.

Background technique

As a clean energy source, solar energy is widely used in the power industry. In the research of two-stage low-power photovoltaic power generation systems, the interleaved flyback inverter is often used as the boost part of the primary DC/DC circuit, while the interleaved The output voltage fluctuation of the flyback DC/DC circuit directly affects the efficiency and conversion performance of the subsequent inverter circuit, so the control of the interleaved flyback circuit is one of the difficulties in system design. The commonly used interleaved flyback converter control strategy is related to its working mode. The control of DCM mode mainly depends on the MPPT link. The input current obtained by MPPT is compared with the triangular carrier to obtain the SPWM drive signal. This control strategy is simple. However, it is only limited to DCM mode; the control of BCM mode adopts current peak control, but this control is more complicated than the control strategy of DCM mode, which is not conducive to popularization.

Literature T.Lodh, N.Pragallapati and V.Agarwal, "An improved control scheme for interleaved flyback converter based micro-inverter to achieve high efficiency," 2016 IEEE 1st International Conference on Power Electronics, Intelligent Control and Energy Systems (ICPEICES), Delhi, 2016, pp.1-6. An optimal control strategy based on an interleaved flyback micro-inverter is proposed, which matches the appropriate operation mode for various instantaneous powers, thereby improving the working efficiency of the circuit, but this This control strategy has a high requirement on the operating speed of the processor, which increases the cost of the detection circuit, and the control method is relatively complicated, which is not conducive to wide-scale use.

Contents of the invention

The invention proposes an interleaved flyback DC/DC hardware modulation compensation circuit, which solves the problems of unbalanced output voltage and output power fluctuation of the interleaved flyback in the prior art.

In order to achieve the above object, technical scheme of the present invention is as follows:

The interleaved flyback DC/DC hardware modulation compensation circuit is characterized in that it includes a photovoltaic panel, a DC side capacitor, an interleaved flyback DC/DC converter, an inverter bridge, an output filter, a power grid, and a hardware compensation module;

The photovoltaic panel is connected in parallel with the DC side capacitor and the interleaved flyback DC/DC converter;

The interleaved flyback DC/DC converter includes two independent first flyback converters and second flyback converters with the same parameters; the first flyback converter includes a transformer T1, and the primary transformer T1 is The main power switch SW11 on the main power switch SW11 side, the body diode D11 in anti-parallel connection with the main power switch SW11, the rectifier diode D1 on the secondary side of the transformer T1, and the snubber capacitor C1; the second flyback converter includes a transformer T2 and a main The power switch SW21, the body diode D21 connected in antiparallel with the main power switch SW21, the rectifier diode D2 on the secondary side of the transformer T2, and the snubber capacitor C2;

The inverter bridge includes a single-phase full-bridge inverter circuit, the input side of the single-phase full-bridge inverter circuit is connected to the output of the interleaved flyback DC/DC converter, and the output is connected to the output filter and the power grid;

The hardware compensation module includes a double closed loop module, a current correction module, a load sharing compensation module and a signal modulation module; the input of the current correction module is the current of the interleaved flyback DC/DC converter, and the output of the current correction module is connected to the load sharing compensation module The input, the output of the load sharing compensation module and the output of the double closed-loop loop are connected to the input of the signal modulation module, and the output of the signal modulation module is finally used to control the duty cycle of the switching tube.

Further, the double closed-loop module includes a current compensation link and a voltage feedforward link, the input of the current compensation link is connected to the current acquisition circuit, and the input of the voltage feedforward link is connected to the voltage acquisition circuit.

Further, the load sharing compensation module includes a filter module and a compensation quantization module, the input side of the filter module is connected to the current correction module, and the output side is connected to the compensation quantization module.

Further, the interleaved flyback DC/DC hardware modulation compensation circuit is externally connected with an electrical parameter acquisition module, a protection circuit, an alarm module and a microprocessor;

The electrical parameter acquisition module includes an input voltage and input current acquisition module, an output voltage and output current acquisition module, a grid voltage and grid current acquisition module, and the electrical parameter acquisition module is respectively connected to the photovoltaic panel input, the interleaved flyback converter output and the grid side;

The protection circuit includes a relay and an electromagnetic drive. The relay is used to connect the filter circuit and the power grid. When the relay is closed, the system is connected to the grid. When the relay is disconnected, the system is off the grid. The electromagnetic drive is connected to the microprocessor. Beneficial effects of the present invention:

1. The interleaved flyback DC/DC hardware modulation compensation circuit of the present invention has the function of insulating and isolating the input side and the output side, and can deal with the actual situation that the circuit is subject to large electromagnetic interference and there are differences in circuit components. Its applicable voltage range Wide temperature range and wide applicable temperature range, which improves the current situation of inconsistent work of the switch tubes of the existing interleaved flyback converter.

2. The interleaved flyback DC/DC hardware modulation compensation circuit of the present invention only adds a modulation signal compensation circuit, does not increase the volume of the existing topological structure, and ensures that the output waveform of the converter is more stable. It provides a smoother voltage and can effectively reduce output power fluctuations.

Description of drawings

Fig. 1 is a block diagram of a photovoltaic grid-connected system with an interleaved flyback DC/DC hardware modulation compensation circuit of the present invention;

Fig. 2 is a schematic diagram of the main circuit of a photovoltaic grid-connected system with an interleaved flyback DC/DC hardware modulation compensation circuit of the present invention;

Fig. 3 is a schematic diagram of the interleaved flyback DC/DC hardware modulation compensation circuit of the present invention;

Fig. 4 is a circuit schematic diagram of a photovoltaic grid-connected system with an interleaved flyback DC/DC hardware modulation compensation circuit of the present invention;

Detailed ways

The present invention will be further described in detail below through specific embodiments in conjunction with the accompanying drawings. Wherein, similar elements in different implementations adopt associated similar element numbers. In the following implementation manners, many details are described for better understanding of the present application. However, those skilled in the art can readily recognize that some of the features can be omitted in different situations, or can be replaced by other elements, materials, and methods. In some cases, some operations related to the application are not shown or described in the description, this is to avoid the core part of the application being overwhelmed by too many descriptions, and for those skilled in the art, it is necessary to describe these operations in detail Relevant operations are not necessary, and they can fully understand the relevant operations according to the description in the specification and general technical knowledge in the field.

The names of the symbols in Figure 2, Figure 3, and Figure 4 are as follows:

Vpv - photovoltaic panel output voltage;

Cdc - DC side capacitance;

T1, T2—the transformers corresponding to the first flyback converter and the second flyback converter;

SW11, SW21 - the main power tubes corresponding to the first flyback converter and the second flyback converter;

SW12, SW22 - auxiliary power tubes corresponding to the first flyback converter and the second flyback converter;

D11, D21 - body diodes connected in antiparallel with the main power tube;

D12, D22 - body diodes in anti-parallel connection with the auxiliary power tube;

D1, D2 - rectifier diodes on the secondary sides of transformers T1 and T2;

C1, C2 - the buffer capacitance of the secondary side of the transformer T1, T2;

S1, S2, S3, S4——Inverter bridge switch tube;

Lac, Cac - AC side filter inductor, AC side filter capacitor;

Vo - the output voltage of the interleaved flyback through the buffer capacitor;

d, △d——Flyback main switching tube duty cycle reference value, duty cycle compensation amount;

d1, d2——the duty cycle corresponding to the main power tubes of flyback 1 and flyback 2;

im1, im2 - the current flowing through the inductor in the converter;

ipv1, ipv2 - input branch current after correction;

△ipv, △ipvref——error between input currents, reference error;

The present invention will be further described below in conjunction with the accompanying drawings. Referring to Figures 1-4, the interleaved flyback DC/DC hardware modulation compensation circuit includes a photovoltaic panel, a DC side capacitor, an interleaved flyback DC/DC converter, Inverter bridge, output filter, grid (or load) and hardware compensation module;

The photovoltaic panel is used as the input of the entire circuit, and is connected in parallel with the DC side capacitor and the interleaved flyback DC/DC converter;

The interleaved flyback DC/DC converter includes two independent first flyback converters and second flyback converters with the same parameters; the first flyback converter includes a transformer T1, and the primary transformer T1 is The main power switch SW11 on the main power switch SW11 side, the body diode D11 in anti-parallel connection with the main power switch SW11, the rectifier diode D1 on the secondary side of the transformer T1, and the snubber capacitor C1; the second flyback converter includes a transformer T2 and a main The power switch SW21, the body diode D21 connected in antiparallel with the main power switch SW21, the rectifier diode D2 on the secondary side of the transformer T2, and the snubber capacitor C2;

The inverter bridge includes a single-phase full-bridge inverter circuit. The input side of the single-phase full-bridge inverter circuit is connected to the output of the interleaved flyback DC/DC converter, and the output is connected to the output filter and the grid to realize grid-connected operation. ;

The hardware compensation module includes a double closed-loop module, a current correction module, a load sharing compensation module and a signal modulation module; the input of the current correction module is the current of the interleaved flyback DC/DC converter, and the output of the current correction module is connected to the input of the load sharing compensation module. The output of the load sharing compensation module and the output of the double closed-loop loop are connected to the input of the signal modulation module, and the output of the signal modulation module is the duty cycle of the final control switch tube.

The double closed-loop module includes a current compensation link and a voltage feedforward link. The input of the current compensation link is connected to the current acquisition circuit, and the input of the voltage feedforward link is connected to the voltage acquisition circuit. The current compensation link and the voltage feedforward link jointly determine the modulation signal and control the switch. The tube is turned on to meet the output waveform requirements.

The current rectification module performs single-period average processing on the current during the turn-on period of the switch tube of the interleaved flyback DC/DC converter, and the current detection of the interleaved flyback DC/DC converter is connected with the input current rectification module.

The load sharing compensation module includes a filter module and a compensation quantization module. The input side of the filter module is connected to the current correction module, and the output side is connected to the compensation quantization module. The error of the input current of the two branches is used to compensate the modulation signal of the switching tube of each branch. , to ensure the consistency of the conduction time of the input switch tube, and to stabilize the output voltage of the converter.

The signal modulation module is a modulation circuit, which compensates the duty cycle reference value by using the duty cycle compensation amount, and finally outputs a new modulation signal to control the interleaved flyback converter to work.

The interleaved flyback DC/DC hardware modulation compensation circuit is also externally connected to an electrical parameter acquisition module, a protection circuit, an alarm module and a microprocessor; the electrical parameter acquisition module includes an input voltage and input current acquisition module, an output voltage and output current acquisition module, and a grid The voltage and grid current acquisition module, and the electrical parameter acquisition module are respectively connected to the input of the photovoltaic panel, the output of the interleaved flyback converter, and the grid side;

The protection circuit includes a relay and an electromagnetic drive. The relay is used to connect the filter circuit and the power grid. When the relay is closed, the system is in the grid-connected state, and when the relay is disconnected, the system is in the off-grid state; the electromagnetic drive is connected to the microprocessor.

As shown in Figure 3, the schematic diagram of the hardware modulation compensation circuit of the present invention, current compensation and voltage feed-forward are used to generate the duty cycle reference value, and the current rectifier is based on the current and the inductor current flowing through the two single-ended flyback converters The corresponding duty ratio is recalculated for the input branch current. The error between the input currents and the reference error is obtained through the load compensator to obtain a duty ratio compensation amount. Combined with the duty ratio base value, the output of the signal modulation module is the final control switch tube duty cycle.

Introduce the working process of the present invention below:

The invention realizes the compensation for the conduction signal of the switch tube of the interleaved flyback converter, so that the fluctuation of the output voltage is small. Firstly, the current compensation circuit and the voltage feedforward circuit generate the duty cycle reference value d; secondly, the current rectifier recalculates the input branch current according to the current im1, im2 flowing through the inductor in the converter and the duty cycle d1, d2, and obtains For ipv1 and ipv2, the error △ipv and the reference error △ipvref between the input currents of ipv1 and ipv2 are used to obtain a duty ratio compensation amount △d through the load compensator; finally, combined with the duty ratio base value d and the compensation amount △d, The microcontroller will output the duty ratios d11, d12, d21, and d22 of the flyback converter; when there is overvoltage or overcurrent in the circuit, the microcontroller will output an electromagnetic disconnection signal, and the grid-connected operation will no longer be performed. Protect the stable operation of the power grid.

Table 1 Compensation amount status in different situations

It can be seen from Table 1 that the magnitude relationship between ipv1 and ipv2 determines the change direction of the compensation amount, so the working process is:

If the corrected current ipv1>ipv2, then △ipv>0, after calculating with the reference error value △ipvref, △ipv'<0, the load sharing compensator calculates the appropriate compensation amount △d according to the value of △ipv', And there is △d<0, indicating that the output voltage difference between the flyback 1 converter and the flyback 2 converter is large at this time. When the switch is switched, the output voltage fluctuation increases, so the flyback 1 converter should be reduced The conduction of the flyback 2 converter is increased, combined with the reference value d, the d11 is reduced, and the d21 is increased;

2) The corrected current ipv1=ipv2, then △ipv=0, after calculation with the reference error value △ipvref, △ipv'=0, compensation △d=0, indicating that the output voltage of the flyback converter fluctuates at this time Small, the current switch state should be kept, so that both d11 and d21 remain unchanged;

3) If the corrected current ipv1<ipv2, then △ipv<0, after calculating with the reference error value △ipvref, △ipv'>0, the load sharing compensator calculates the appropriate compensation amount△ according to the value of △ipv' d, and △d>0, it can be obtained from 1) in the same way. At this time, the output difference between flyback 1 and flyback 2 converters is large. When the switch is switched, the output voltage fluctuation increases, and the flyback should be reduced. Turn off the 1 converter, increase the turn off of the flyback 2 converter, combined with the reference value d, make d11 decrease and d21 increase.

The above uses specific examples to illustrate the present invention, which is only used to help understand the present invention, and is not intended to limit the present invention. For those skilled in the technical field to which the present invention belongs, some simple deduction, deformation or replacement can also be made according to the idea of the present invention.

Claims (4)

1. the modulation compensated circuit of interleaving inverse excitation type DC/DC hardware, it is characterised in that:Including photovoltaic panel, DC bus capacitor, interlock instead Swash formula DC/DC converters, inverter bridge, output filter, power grid and hardware compensating module;

The photovoltaic panel is in parallel with DC bus capacitor, interleaving inverse excitation type DC/DC converters;

The interleaving inverse excitation type DC/DC converters include two the first inverse excitation type converters and second independent, parameter is consistent Inverse excitation type converter;First inverse excitation type converter includes transformer T1, the master power switch SW11 of transformer T1 primary sides and master The antiparallel body diode D11 of power switch SW11, rectifier diode D1, the buffering capacitance C1 of transformer T1 secondary sides;Second Inverse excitation type converter includes transformer T2, the master power switch SW21 of transformer T2 primary sides, with master power switch SW21 instead simultaneously The body diode D21 of connection, rectifier diode D2, the buffering capacitance C2 of transformer T2 secondary sides;

The inverter bridge includes single-phase full bridge formula inverter circuit, the input side and interleaving inverse excitation type of single-phase full bridge formula inverter circuit The output connection of DC/DC converters, output are connect with output filter, power grid;

The hardware compensating module includes two close cycles return circuit module, electric current rectification module, the shared compensating module of load and signal tune Molding block;The input of electric current rectification module is the electric current of interleaving inverse excitation type DC/DC converters, the output connection load of electric current rectification module Shared compensating module input loads and shares compensating module output and two close cycles circuit output connection signal modulation module input, letter The output of number modulation module for final control switching tube duty ratio.

2. the modulation compensated circuit of interleaving inverse excitation type DC/DC hardware according to claim 1, which is characterized in that described pair is closed Loop back path module includes current compensation link and electric voltage feed forward link, and the input of current compensation link is connect with current collection circuit, The input of electric voltage feed forward link is connect with voltage collection circuit.

3. the modulation compensated circuit of interleaving inverse excitation type DC/DC hardware according to claim 2, it is characterised in that:The load Shared compensating module includes filter module and compensation quantization modules, and filter module input side is connect with electric current rectification module, is exported Side is connect with compensation quantization modules.

4. a kind of modulation compensated circuit of interleaving inverse excitation type DC/DC hardware according to claim 1, it is characterised in that:It is described The external electric parameter acquisition module of the modulation compensated circuit of interleaving inverse excitation type DC/DC hardware, protection circuit, alarm module and miniature place Manage device;

The electric parameter acquisition module includes input voltage and input current acquisition module, output voltage and output current acquisition Module, network voltage and power network current acquisition module, electric parameter acquisition module are separately connected photovoltaic panel input, interleaving inverse excitation type Converter exports and grid side;

The protection circuit includes relay and electromagnetic drive, and for connecting filter circuit and power grid, relay closes relay When conjunction, system grid connection, when relay disconnects, system off-network;Electromagnetic drive is connect with microprocessor.