CN111669043A

CN111669043A - Control device of PFC circuit, PFC circuit and control method thereof

Info

Publication number: CN111669043A
Application number: CN202010573918.0A
Authority: CN
Inventors: 刘文斌; 范胜全; 李洋; 范晓坤
Original assignee: Gree Electric Appliances Inc of Zhuhai
Current assignee: Gree Electric Appliances Inc of Zhuhai
Priority date: 2020-06-22
Filing date: 2020-06-22
Publication date: 2020-09-15

Abstract

The invention discloses a control device of a PFC circuit, the PFC circuit and a control method thereof, wherein the device comprises: the PFC auxiliary circuit is connected with the filtering module in parallel and is used for performing follow current on the filtering module under the control of the control unit and under the condition of self starting; the sampling unit is used for sampling the input parameters and the output parameters of the PFC circuit; the control unit is used for controlling the PFC auxiliary circuit and the PFC main switch circuit to be turned on or off according to the input parameter and the output parameter, so that the PFC circuit can work in a continuous conduction mode under the condition that the PFC auxiliary circuit is turned on; and under the condition that the PFC main switch circuit is started, enabling the PFC circuit to work in a zero-voltage conversion mode. The scheme of the invention can solve the problem of lower working efficiency of the PFC circuit and achieve the effect of improving the working efficiency of the PFC circuit.

Description

Control device of PFC circuit, PFC circuit and control method thereof

Technical Field

The invention belongs to the technical field of electronic circuits, and particularly relates to a control device of a PFC circuit, the PFC circuit and a control method thereof, and particularly relates to a control device of an alternating current Continuous Conduction Mode (CCM) totem-pole Power Factor Correction (PFC) circuit, the PFC circuit and a control method thereof based on a zero voltage conversion (ZVT) technology.

Background

With the increase of the load of the power grid, in order to meet the standard, the power factor and the total harmonic distortion become important indexes of equipment design, and the PFC circuit as a pre-converter can generate smooth sinusoidal input current, but the working efficiency of the PFC circuit is low.

The above is only for the purpose of assisting understanding of the technical aspects of the present invention, and does not represent an admission that the above is prior art.

Disclosure of Invention

The present invention provides a control device for a PFC circuit, the PFC circuit and a control method thereof, to solve the problem of low working efficiency of the PFC circuit, and achieve the effect of improving the working efficiency of the PFC circuit.

The invention provides a control device of a PFC circuit, comprising: the device comprises a PFC auxiliary circuit, a sampling unit and a control unit; the PFC circuit includes: the filter module and the PFC main switch circuit; the PFC auxiliary circuit is connected with the filtering module in parallel and used for performing follow current on the filtering module under the control of the control unit and under the condition of self starting; the sampling unit is used for sampling the input parameters and the output parameters of the PFC circuit; the control unit is used for controlling the PFC auxiliary circuit and the PFC main switch circuit to be turned on or off according to the input parameter and the output parameter, so that the PFC circuit can work in a continuous conduction mode under the condition that the PFC auxiliary circuit is turned on; and under the condition that the PFC main switch circuit is started, enabling the PFC circuit to work in a zero-voltage conversion mode.

Optionally, the PFC auxiliary circuit includes: the first auxiliary switch tube, the second auxiliary switch tube and the auxiliary inductor; the first auxiliary switching tube, the second auxiliary switching tube and the third auxiliary switching tube are arranged in series; the PFC main switch circuit includes: the PFC circuit comprises a first branch and a second branch, wherein the first branch is connected with a first switching tube and a second switching tube in series, the second branch is connected with a third switching tube and a fourth switching tube in series, and the central point of each branch is connected with a zero-fire line at the input end of the PFC circuit respectively.

Optionally, the first auxiliary switch tube, the second auxiliary switch tube, the first switch tube, the second switch tube, the third switch tube, and the fourth switch tube are all triodes with diodes; in the PFC auxiliary circuit, the first auxiliary switching tube and the second auxiliary switching tube are respectively used for freewheeling of the filtering module in a positive half-cycle and a negative half-cycle of an alternating current at the input end; the first auxiliary switch tube and the second auxiliary switch tube are respectively connected with a reverse diode in parallel to be used as body diodes, and each body diode freewheels with the switch tube connected with the body diode in parallel; in the PFC main switch circuit, each switch tube is connected with a body diode in the same direction in parallel, and each body diode is also connected with a parasitic capacitor in parallel.

Optionally, the filtering module includes: a filter inductor; and the inductance value of the auxiliary inductor is smaller than that of the filter inductor.

Optionally, wherein the input parameters include: an input voltage and an input current; the input voltage is specifically a voltage value of an input end of the PFC circuit; the input current is specifically a current value at a connection node of the filtering module and the PFC main switch circuit; the output parameters comprise: outputting the voltage; the output voltage is a voltage value of a load end of the PFC circuit.

Optionally, the controlling unit controls on or off of the PFC auxiliary circuit and the PFC main switching circuit, and includes: under the condition that the input parameters comprise input voltage and input current and the output parameters comprise output voltage, determining reference current according to the input voltage, the output voltage and preset reference voltage; determining a control signal according to the reference current and the input current; and controlling the on or off of the PFC auxiliary circuit and the PFC main switch circuit according to the control signal.

Optionally, the control signal includes: a PWM signal; the control unit determines a control signal including: determining a modulation wave; and outputting the PWM signal according to the modulation wave and the carrier wave so as to control the on or off of a switching tube in the PFC auxiliary circuit and/or the PFC main switching circuit.

Optionally, the control unit is configured to control on or off of a switching tube in the PFC auxiliary circuit and/or the PFC main switching circuit, and includes: under the condition that a first auxiliary switching tube and a second auxiliary switching tube in the PFC auxiliary circuit are both triodes with diodes, and a first switching tube, a second switching tube, a third switching tube and a fourth switching tube in the PFC main switching circuit are all triodes with diodes, and each body diode is connected with a parasitic capacitor in parallel, the control method comprises the following control conditions under any set state: in a first setting state, the first auxiliary switch tube and the second auxiliary switch tube are both closed, the first switch tube and the third switch tube are both conducted, and the third switch tube and the fourth switch tube are both closed; in a second set state, the body diode of the second auxiliary switch tube is turned off after the first time when the first switch tube is turned on and is turned on before the second switch tube is turned off; then, the filtering module charges an auxiliary inductor through a body diode of the first auxiliary switching tube; in a third setting state, when the current value at the connection node of the filter module and the main PFC switch circuit is zero, the first switch tube Q1 is closed, and the parasitic capacitance of the filter module and the main PFC switch circuit resonates; in a fourth setting state, when the parasitic capacitance of the filtering module and the PFC main switching circuit resonates and the grid voltage of the second switching tube is zero, the second switching tube is conducted; the power grid charges the filtering module and the auxiliary inductor through the second switching tube and the fourth switching tube; in a fifth set state, a body diode of a second auxiliary switching tube is turned off, and the filtering module and the auxiliary inductor are charged by the power grid through the second switching tube and the fourth switching tube; the first auxiliary switch tube and the second auxiliary switch tube are both closed, the first switch tube and the third switch tube are both switched on, and the third switch tube and the fourth switch tube are both closed.

In accordance with the above apparatus, another aspect of the present invention provides a PFC circuit, including: the control device of the PFC circuit described above.

In a matching manner with the PFC circuit, a further aspect of the present invention provides a method for controlling a PFC circuit, where the PFC circuit includes: the filter module and the PFC main switch circuit; the control method of the PFC circuit comprises the following steps: through a PFC auxiliary circuit connected with a filtering module in parallel, under the control of the control unit, the filtering module is subjected to follow current under the condition of self starting; sampling input parameters and output parameters of the PFC circuit through a sampling unit; controlling, by a control unit, on or off of the PFC auxiliary circuit and the PFC main switch circuit according to the input parameter and the output parameter, so that the PFC circuit can operate in a continuous conduction mode when the PFC auxiliary circuit is turned on; and under the condition that the PFC main switch circuit is started, enabling the PFC circuit to work in a zero-voltage conversion mode.

Optionally, controlling, by the control unit, on or off of the PFC auxiliary circuit and the PFC main switch circuit includes: under the condition that the input parameters comprise input voltage and input current and the output parameters comprise output voltage, determining reference current according to the input voltage, the output voltage and preset reference voltage; determining a control signal according to the reference current and the input current; and controlling the on or off of the PFC auxiliary circuit and the PFC main switch circuit according to the control signal.

Optionally, the controlling unit controls the on or off of a switching tube in the PFC auxiliary circuit and/or the PFC main switching circuit, including: under the condition that a first auxiliary switching tube and a second auxiliary switching tube in the PFC auxiliary circuit are both triodes with diodes, and a first switching tube, a second switching tube, a third switching tube and a fourth switching tube in the PFC main switching circuit are all triodes with diodes, and each body diode is connected with a parasitic capacitor in parallel, the control method comprises the following control conditions under any set state: in a first setting state, the first auxiliary switch tube and the second auxiliary switch tube are both closed, the first switch tube and the third switch tube are both conducted, and the third switch tube and the fourth switch tube are both closed; in a second set state, the body diode of the second auxiliary switch tube is turned off after the first time when the first switch tube is turned on and is turned on before the second switch tube is turned off; then, the filtering module charges an auxiliary inductor through a body diode of the first auxiliary switching tube; in a third setting state, when the current value at the connection node of the filter module and the main PFC switch circuit is zero, the first switch tube Q1 is closed, and the parasitic capacitance of the filter module and the main PFC switch circuit resonates; in a fourth setting state, when the parasitic capacitance of the filtering module and the PFC main switching circuit resonates and the grid voltage of the second switching tube is zero, the second switching tube is conducted; the power grid charges the filtering module and the auxiliary inductor through the second switching tube and the fourth switching tube; in a fifth set state, a body diode of a second auxiliary switching tube is turned off, and the filtering module and the auxiliary inductor are charged by the power grid through the second switching tube and the fourth switching tube; the first auxiliary switch tube and the second auxiliary switch tube are both closed, the first switch tube and the third switch tube are both switched on, and the third switch tube and the fourth switch tube are both closed.

Therefore, according to the scheme of the invention, the zero voltage switching (ZVT) of the switching tube of the main switching circuit is realized by adding the PFC auxiliary branch, so that the totem PFC works in a Continuous Conduction Mode (CCM), the problem of low working efficiency of the PFC circuit can be solved, and the effect of improving the working efficiency of the PFC circuit is achieved.

The problem of large operating switching loss of the totem PFC under CCM is solved by using ZVT; by adopting a Continuous Conduction Mode (CCM), the switching frequency of the switching tube can be increased, and the work efficiency of the PFC is further improved.

Additional features and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention.

The technical solution of the present invention is further described in detail by the accompanying drawings and embodiments.

Drawings

Fig. 1 is a schematic structural diagram of a control device of a PFC circuit according to an embodiment of the present invention;

fig. 2 is a schematic structural diagram of a PFC circuit according to an embodiment of the present invention;

fig. 3 is a flowchart of a positive half cycle operation of the PFC circuit of the present invention, wherein (a) is a schematic diagram of a current flow of the PFC circuit in a first stage, (b) is a schematic diagram of a current flow of the PFC circuit in a second stage, (c) is a schematic diagram of a current flow of the PFC circuit in a third stage, (d) is a schematic diagram of a current flow of the PFC circuit in a fourth stage, and (e) is a schematic diagram of a current flow of the PFC circuit in a fifth stage;

fig. 4 is a flowchart illustrating a control method of the PFC circuit according to an embodiment of the present invention;

fig. 5 is a schematic flowchart of an embodiment of controlling the on/off of the PFC auxiliary circuit and the PFC main switch circuit according to the method of the present invention;

FIG. 6 is a flowchart illustrating an embodiment of determining a control signal in the method of the present invention.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the technical solutions of the present invention will be clearly and completely described below with reference to the specific embodiments of the present invention and the accompanying drawings. It is to be understood that the described embodiments are merely exemplary of the invention, and not restrictive of the full scope of the invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

According to an embodiment of the present invention, there is provided a control apparatus of a PFC circuit. Referring to fig. 1, a schematic diagram of an embodiment of the apparatus of the present invention is shown. The control means of the PFC circuit may comprise: the device comprises a PFC auxiliary circuit, a sampling unit and a control unit. The PFC circuit may be a totem PFC circuit, and the totem PFC circuit may include: the circuit comprises a filtering module (such as a filtering inductor L) and a PFC main switch circuit, wherein the filtering module and the PFC main switch circuit can form a loop with an alternating current power supply. The PFC main switch circuit may be configured to rectify an input ac power into a dc power and provide the dc power to a load at a rear end of the PFC main switch circuit under the control of the control unit when the PFC main switch circuit is turned on. For example: the PFC main switch circuit realizes alternating current to direct current and improves the power factor by a control signal sent by the controller.

Specifically, the PFC auxiliary circuit, connected in parallel to the filtering module, may be configured to freewheel the filtering module when the PFC auxiliary circuit is turned on under the control of the control unit, that is, when the PFC auxiliary circuit is turned on, so that the PFC circuit can operate in a continuous conduction mode. For example: the PFC auxiliary circuit can be used for freewheeling on an inductor L in the main circuit, so that the totem PFC can work in a Continuous Conduction Mode (CCM).

Specifically, the sampling unit, such as a sampling resistor, a voltage sensor, a current sensor, and the like, is respectively connected to the input terminal and the load terminal of the PFC circuit, and may be configured to sample input parameters and output parameters of the PFC circuit, specifically, may be configured to sample input voltage and input current at the input terminal (i.e., a power grid terminal) of the PFC circuit, and sample output parameters at the load terminal of the PFC circuit. For example: and the sampling unit can be used for sampling the input voltage and the input current.

Specifically, the control unit, such as an MCU controller, may be configured to control, according to the input parameter and the output parameter, on or off of the PFC auxiliary circuit and the PFC main switch circuit, so that when the PFC auxiliary circuit is turned on, the PFC auxiliary circuit freewheels the filtering module, so that the PFC circuit can operate in a continuous conduction mode. Under the condition that the PFC main switch circuit is started, the PFC main switch circuit rectifies input alternating current into direct current and provides the direct current to a load at the rear end of the PFC main switch circuit, so that the PFC circuit works in a zero-voltage conversion mode (namely a ZVT mode). For example: and the MCU controller can be used for obtaining PWM waves for controlling the switching tube according to the input voltage, the input current value and the voltage of the load end which are obtained by sampling.

For example: the PFC circuit may include: a main switching circuit and an auxiliary PFC circuit. The follow current of the auxiliary PFC circuit is used for enabling the PFC circuit to work in a continuous current mode, peak voltage is reduced, the switching tube works in a ZVT mode through reasonable switching-on time, and switching loss is reduced. The PFC circuit is provided with an auxiliary circuit, the output current is in a continuous mode, and the switching mode is zero-voltage switching.

Therefore, the PFC auxiliary circuit is arranged, the input parameters and the output parameters of the PFC circuit are sampled, and then the on-off of the PFC main switching circuit and the PFC auxiliary circuit are controlled according to the input parameters and the output parameters of the PFC circuit, so that the PFC circuit can work in a continuous conduction mode under the condition that the PFC auxiliary circuit is turned on, and the input alternating current can be rectified into direct current and then provided for a load under the condition that the PFC main switching circuit is turned on, so that the switching frequency of a switching tube can be increased by adopting the Continuous Conduction Mode (CCM), and the working efficiency of the PFC can be improved; the problem of large operating switch loss of totem PFC under CCM is solved by using ZVT.

In an optional example, the PFC auxiliary circuit may include: the first auxiliary switch tube (i.e., the first auxiliary switch tube gs1), the second auxiliary switch tube (i.e., the second auxiliary switch tube gs2), and the auxiliary inductor (i.e., the inductor La). The first auxiliary switch tube, the second auxiliary switch tube and the third auxiliary switch tube are arranged in series.

For example: two auxiliary switches and an auxiliary inductor are adopted to form a PFC auxiliary circuit, a switch device has three conduction modes, namely 1, a continuous mode/2, a discontinuous mode/3 and an intermittent mode, and the switching loss is as follows: 3>1 ═ 2, the maximum allowed switching frequency 3>2> 1. The application of the auxiliary circuit increases the allowed maximum switching frequency of 1 and reduces the switching losses.

For example: the auxiliary circuit is composed of a first auxiliary switch tube gs1, a second auxiliary switch tube gs2, a first auxiliary diode S1, a second auxiliary diode S2 and an inductor La. The switching tube of the main switching circuit realizes zero voltage switching (ZVT) through the PFC auxiliary branch, so that the totem PFC works in a Continuous Conduction Mode (CCM).

The PFC main switching circuit may include: the PFC circuit comprises a first branch and a second branch, wherein the first branch is connected with a first switching tube (namely a first switching tube Q1) and a second switching tube (namely a second switching tube Q2) in series, the second branch is connected with a third switching tube (namely a third switching tube Q3) and a fourth switching tube (namely a fourth switching tube Q4) in series, and the central point of each branch is respectively connected with a zero line and a live line of the input end of the PFC circuit.

For example: the PFC main switch circuit is formed by four switch tubes, compared with a diode used by a general rectifying circuit, the switch tubes have controllable characteristics, and the rectifying circuit formed by the diodes outputs pulsating direct current, so that the power supply characteristics are poor, and the PFC main switch circuit also does not have a boosting function. The totem PFC formed by the controllable switching devices can output stable direct-current voltage, and the voltage value can be set within a certain range.

That is, the PFC main switch circuit may include two branches, each branch is connected in series with two switching tubes, for example, a first branch is connected in series with a first switching tube Q1 and a second switching tube Q2, a second branch is connected in series with a third switching tube Q3 and a fourth switching tube Q4, a central point of each branch is respectively connected to a zero-fire line of an input terminal, and the PFC main switch circuit is configured to rectify an ac input power into a dc power and provide the dc power to a back-end load.

The first auxiliary switch tube, the second auxiliary switch tube, the first switch tube, the second switch tube, the third switch tube and the fourth switch tube are all triodes with diodes.

Specifically, in the PFC auxiliary circuit, the first auxiliary switching tube and the second auxiliary switching tube may be respectively configured to freewheel the filter module (i.e., the main circuit inductor L) in a positive half-cycle and a negative half-cycle of the alternating current at the input end. The first auxiliary switch tube and the second auxiliary switch tube are respectively connected with a reverse diode in parallel to be used as a body diode, and each body diode freewheels with the switch tube connected with the body diode in parallel.

For example: the PFC auxiliary circuit is formed by two auxiliary switches with anti-parallel diodes, and the anti-parallel diodes are a common mode of a switching device and can provide a current path when the switching device is closed, namely follow current.

For example: the PFC auxiliary circuit is connected in parallel to the filter inductor L, and can comprise an auxiliary inductor connected in series with a switching tube, wherein the two switching tubes respectively follow current for the main circuit inductor L in the positive half period and the negative half period of the alternating current, the two switching tubes are respectively connected in parallel with a reverse diode, and the diodes follow current for the parallel switching tubes.

In the PFC main switch circuit, each switch tube is connected with a body diode in the same direction in parallel, and each body diode is also connected with a parasitic capacitor in parallel.

For example: four switching tubes, a strip diode and a parasitic capacitor are adopted, the parasitic capacitor is the circuit characteristic of the switching tubes, the parasitic capacitor does not exist in an actual circuit, and the characteristic is ideal as a parasitic capacitor. The main switching circuit can change alternating current into a stable direct current power supply.

Optionally, the filtering module may include: and a filter inductor. And the inductance value of the auxiliary inductor is smaller than that of the filter inductor.

For example: the auxiliary circuit inductance La should be much smaller than the filter inductance L to reduce its rms current value, reduce unnecessary losses and reduce size. The net current at the switch node A is influenced by the on-off of the PFC auxiliary circuit, so that the current at the switch node A is quickly reset to zero, the gate voltage drops to zero before the second switch tube Q2 is switched on in a positive half period and the gate voltage drops to zero before the first switch tube Q1 is switched on in a negative half period by utilizing the resonance of an inductor and the parasitic capacitance of a main switch, and therefore zero voltage conduction is achieved, and the switching loss is reduced.

In an alternative example, the input parameters may include: an input voltage and an input current. The input voltage is specifically a voltage value of an input end of the PFC circuit. The input current is specifically a current value at a connection node of the filter module and the PFC main switch circuit. The output parameters may include: and outputting the voltage. The output voltage is a voltage value of a load end of the PFC circuit.

For example: the sampling unit samples the voltage of a load end, the voltage of an input end and the current at a connection node of the PFC main switch circuit.

Therefore, the on/off of the switch tubes in the PFC main switch circuit and the PFC auxiliary circuit is controlled through various input parameters, output parameters and the like, different parameters can be used for controlling in different occasions, and convenience and flexibility of control are improved.

In an optional example, the controlling unit controls the PFC auxiliary circuit and the PFC main switch circuit to be turned on or off according to the input parameter and the output parameter, and may include: under the condition that the input parameters can comprise input voltage and input current and the output parameters can comprise output voltage, determining reference current according to the input voltage, the output voltage and preset reference voltage; determining a control signal according to the reference current and the input current; and controlling the on or off of the PFC auxiliary circuit and the PFC main switch circuit according to the control signal.

For example: the sampling unit samples the voltages of the input end and the load end and inputs the voltages into the controller MCU, and the controller MCU controls the switching tubes of the PFC main switching circuit and the PFC auxiliary switching circuit through the output PWM to realize the AD-DC conversion of high power factor. The Continuous Conduction Mode (CCM) is adopted firstly, and then the zero voltage conversion (ZVT) technology is adopted, so that the problem that the switching frequency in the Discontinuous Conduction Mode (DCM) and the critical conduction mode (CRM) cannot be improved can be solved, the problem that the switching loss is large due to the fact that the Continuous Conduction Mode (CCM) is used independently can also be solved, and the effects of improving the power factor and increasing the working efficiency of the totem PFC are achieved.

Therefore, the PFC auxiliary circuit and the PFC main switching circuit are controlled to be turned on or turned off according to the input parameters and the output parameters, the working efficiency of the PFC circuit can be improved, and the switching loss is small.

Optionally, the control signal may include: a PWM signal.

The determining, by the control unit, a control signal according to the reference current and the input current may include: determining a modulation wave; and outputting the PWM signal according to the modulation wave and the carrier wave so as to control the on or off of a switching tube in the PFC auxiliary circuit and/or the PFC main switching circuit.

For example: the method comprises the steps of determining reference current according to input voltage, output voltage and preset reference voltage of a totem-type PFC circuit, determining a modulation wave according to the reference current and current on a totem-type PFC inductor L, and outputting a switching tube in a PWM signal control unit through the modulation wave and a carrier by an MCU.

Therefore, the control signal is determined according to the reference current and the input current, and the PFC main switch circuit and the PFC auxiliary circuit can be reliably controlled based on the reference current and the input current.

More optionally, the controlling unit outputs the PWM signal according to the modulation wave and the carrier to control on or off of a switching tube in the PFC auxiliary circuit and/or the PFC main switching circuit, and may include: under the condition that the input current is larger than a set PFC overcurrent threshold, a switching tube in the PFC main switching circuit is controlled to be closed; and under the condition that the input current is less than or equal to a set PFC overcurrent threshold, controlling a switching tube in the PFC main switching circuit to be alternately switched on.

For example: the MCU controller determines a reference current through the voltage of the input end, the voltage of the load end and a preset reference voltage, and the reference current and the node current at the joint of the sampling PFC main switch determine a modulation wave. The sampling unit transmits the sampled current value to the MCU, the MCU compares the sampled current value with a PFC overcurrent threshold value I1, and if the sampled current value is larger than the PFC overcurrent threshold value I1, the MCU closes the switch tube through outputting PWM, so that the effect of protecting the circuit is achieved.

Specifically, in a case that the first auxiliary switching tube and the second auxiliary switching tube in the PFC auxiliary circuit are both triodes with diodes, and the first switching tube, the second switching tube, the third switching tube and the fourth switching tube in the PFC main switching circuit are all triodes with diodes, and each body diode is connected in parallel with a parasitic capacitor, the on or off of the switching tubes in the PFC auxiliary circuit and/or the PFC main switching circuit is controlled, which may include a control situation in any one of the following setting states:

the first control scenario: in a first setting state, the first auxiliary switch tube and the second auxiliary switch tube are both closed, the first switch tube and the third switch tube are both conducted, and the third switch tube and the fourth switch tube are both closed.

For example: state a: the first switch Q1 and the third switch Q3 are turned on, and the current flows from the inductor L through the first switch Q1, then through the load and back to the grid through the third switch Q3.

The second control scenario: in a second set state, the body diode of the second auxiliary switch tube is turned off after the first time when the first switch tube is turned on and is turned on before the second switch tube is turned off; and then, the filtering module charges the auxiliary inductor through the body diode of the first auxiliary switching tube.

For example: state b: the switch S2 is turned off most of the time that the first switch Q1 is on, and turned on before the second switch Q2 is turned off, and the large inductor L begins to charge the auxiliary inductor La through the anti-parallel diode of the first auxiliary switch gs 1.

The third control scenario: in a third setting state, when the current value at the connection node of the filter module and the PFC main switch circuit is zero, the first switch tube Q1 is turned off, and the parasitic capacitance of the filter module and the PFC main switch circuit resonates.

For example: and c, state c: since the value of the auxiliary inductor La is small and the charging time is short, when the net current at the switching node a is zero, the first switching tube Q1 is turned off, and the inductor resonates with the parasitic capacitance of the main switch.

The fourth control scenario: in a fourth setting state, when the parasitic capacitance of the filtering module and the PFC main switching circuit resonates and the grid voltage of the second switching tube is zero, the second switching tube is conducted; and the power grid charges the filtering module and the auxiliary inductor through the second switching tube and the fourth switching tube.

For example: and a state d: when resonance occurs, the gate voltage of the second switch Q2 will be zero, and at this time, the second switch Q2 is turned on, and the power grid charges the inductor L and the auxiliary inductor La through the second switch Q2 and the fourth switch Q4.

Fifth control scenario: in a fifth set state, a body diode of a second auxiliary switching tube is turned off, and the filtering module and the auxiliary inductor are charged by the power grid through the second switching tube and the fourth switching tube; the first auxiliary switch tube and the second auxiliary switch tube are both closed, the first switch tube and the third switch tube are both switched on, and the third switch tube and the fourth switch tube are both closed.

For example: and a state e: s2 is turned off, and the grid charges the inductor L through the second switching tube Q2 and the fourth switching tube Q4. Since the current in the inductor L is present throughout the entire cycle, the circuit operates in CCM mode.

Therefore, the on or off of the switching tube in the PFC auxiliary circuit and/or the PFC main switching circuit is controlled by the PWM signal, so that the on or off of the switching tube is reliably and safely controlled.

Through a large number of tests, the technical scheme of the invention is adopted, and the switching tube of the main switching circuit realizes zero voltage switching (ZVT) by adding the PFC auxiliary branch, so that the totem PFC works in a Continuous Conduction Mode (CCM), the problem of low working efficiency of the PFC circuit can be solved, and the effect of improving the working efficiency of the PFC circuit is achieved.

According to an embodiment of the present invention, there is also provided a PFC circuit corresponding to the control device of the PFC circuit. The PFC circuit may include: the control device of the PFC circuit described above.

Compared with the traditional boost-PFC device, the totem PFC device has the advantages of higher utilization rate, low loss, small common-mode noise interference and the like, and meanwhile, the application of a Wide Band Gap (WBG) device enables the totem bridgeless power factor correction circuit to work above high frequency 100kHz, and the improvement of the switching frequency is beneficial to improving the power factor.

Some totem PFC circuits are formed by an inductor and 4 switching tubes, the 4 switching tubes form two branches in pairs, and a zero-fire line passes through the inductor and then is connected with the central points of the two branches. If the switch tube adopts a continuous conduction mode (DCM) or a critical conduction mode (CRM), the method is helpful to reduce the switching loss; but will limit the increase in switching frequency. If Continuous Conduction Mode (CCM) is used, the switching frequency can be increased, but at the same time the switching losses are increased.

In an optional embodiment, the present disclosure provides a totem-pole Power Factor Correction (PFC) circuit based on an ac Continuous Conduction Mode (CCM) of a zero voltage conversion technology (ZVT technology), and the Continuous Conduction Mode (CCM) is adopted to increase the switching frequency of a switching tube, thereby improving the PFC working efficiency; the problem of large operating switch loss of totem PFC under CCM is solved by using ZVT.

In an alternative example, in an aspect of the present invention, an ac continuous conduction mode totem-pole power factor correction circuit based on a zero-voltage conversion technology may include: the device comprises an MCU controller, a sampling unit, a PFC auxiliary circuit and a PFC main switch circuit.

Optionally, a sampling unit may be used to sample the input voltage and the input current.

Optionally, the MCU controller may be configured to obtain a PWM wave for controlling the switching tube according to the sampled input voltage, input current value, and voltage at the load terminal.

Specifically, the sampling unit samples a voltage at a load terminal, a voltage at an input terminal, and a current at a connection node of the PFC main switch circuit.

The MCU controller determines a reference current through the voltage of the input end, the voltage of the load end and a preset reference voltage, and the reference current and the node current at the joint of the sampling PFC main switch determine a modulation wave. The sampling unit transmits a sampled current value (namely node current at the connection position of the PFC main switch) to the MCU, the MCU compares the sampled current value with a PFC overcurrent threshold value I1, and if the sampled current value is larger than the PFC overcurrent threshold value I1, the MCU closes a switch tube through outputting PWM, so that the effect of protecting a circuit is achieved.

For example: the over-current threshold is set to protect the circuit, and the threshold is higher than the reference current and smaller than the maximum current borne by the circuit and the devices thereof. Fig. 2 shows the positive half cycle of the ac input and the two switching devices of the auxiliary circuit operating in the positive and negative half cycles of the ac input, respectively.

Optionally, the PFC auxiliary circuit may be configured to freewheel the inductor L in the main circuit, so that the totem PFC may operate in a Continuous Conduction Mode (CCM), and the PFC main switching circuit implements ac-to-dc conversion and improves the power factor by a control signal sent by the controller.

The PFC auxiliary circuit is connected in parallel to the filter inductor L, and can comprise an auxiliary inductor connected in series with a switching tube, wherein the two switching tubes respectively follow current of the main circuit inductor L in the positive half period and the negative half period of the alternating current, the two switching tubes are respectively connected in parallel with a reverse diode, and the diodes follow current for the parallel switching tubes.

The PFC main switching circuit can comprise two branches, each branch is connected with two switching tubes in series, the central point of each branch is respectively connected with a zero line and a live line of the input end, and the PFC main switching circuit is used for rectifying alternating-current input electricity into direct current to be supplied to a rear-end load.

Therefore, according to the scheme of the invention, the continuous conduction mode (namely CCM) is adopted firstly, and then the zero voltage conversion (namely ZVT) technology is adopted, so that the problem that the switching frequency cannot be increased in the Discontinuous Conduction Mode (DCM) and the critical conduction mode (CRM) can be solved, the problem of large switching loss caused by singly using the Continuous Conduction Mode (CCM) can also be solved, and the effects of increasing the power factor and increasing the working efficiency of the totem PFC are achieved.

In an alternative embodiment, a specific implementation process of the scheme of the present invention may be exemplarily described with reference to the examples shown in fig. 2 and fig. 3.

In an aspect of the present invention, a CCM totem PFC for ZVT is provided, and a PFC circuit may include: a main switching circuit and an auxiliary PFC circuit. The follow current of the auxiliary PFC circuit is used for enabling the PFC circuit to work in a continuous current mode, peak voltage is reduced, the switching tube works in a ZVT mode through reasonable switching-on time, and switching loss is reduced. The PFC circuit is provided with an auxiliary circuit, the output current is in a continuous mode, and the switching mode is zero-voltage switching.

Compared with some totem PFC circuits, the scheme of the invention adds an auxiliary PFC branch, and the auxiliary circuit consists of a first auxiliary switch tube gs1, a second auxiliary switch tube gs2, a first auxiliary diode S1, a second auxiliary diode S2 and an inductor La. The switching tube of the main switching circuit realizes zero voltage switching (ZVT) through the PFC auxiliary branch, so that the totem PFC works in a Continuous Conduction Mode (CCM).

Fig. 2 is a schematic structural diagram of a PFC circuit according to an embodiment of the present invention. As shown in fig. 2, the CCM totem PFC provided by the present invention based on ZVT may include: the device comprises a control module (such as an MCU), a sampling unit, a PFC auxiliary circuit and a PFC main switch circuit, wherein the sampling unit samples voltages at an input end and a load end and inputs the voltages into the MCU, and the MCU controls switch tubes of the PFC main switch circuit and the PFC auxiliary switch circuit by outputting PWM (pulse width modulation), so that AD-DC (analog-to-digital) conversion of high power factors is realized.

The sampling unit can select a sampling resistor, and can also adopt a voltage sensor, a current sensor and the like.

In a preferred embodiment, the auxiliary circuit inductance La should be much smaller than the filter inductance L to reduce its rms current value, reduce unnecessary losses and reduce bulk. The net current at the switch node A is influenced by the on-off of the PFC auxiliary circuit, so that the current at the switch node A is quickly reset to zero, the gate voltage drops to zero before the second switch tube Q2 is switched on in a positive half period and the gate voltage drops to zero before the first switch tube Q1 is switched on in a negative half period by utilizing the resonance of an inductor and the parasitic capacitance of a main switch, and therefore zero voltage conduction is achieved, and the switching loss is reduced.

Fig. 3 is a flow chart of the operation of the positive half cycle of the PFC circuit of the present invention. Fig. 3 is a flow chart showing the operation of the positive half cycle, and the graphs (a), (b), (c), (d) and (e) in fig. 3 represent the current flow direction of each stage of the circuit.

Wherein, the state a: the first switch Q1 and the third switch Q3 are turned on, and the current flows from the inductor L through the first switch Q1, then through the load and back to the grid through the third switch Q3.

State b: the switch S2 is turned off most of the time that the first switch Q1 is on, and turned on before the second switch Q2 is turned off, and the large inductor L begins to charge the auxiliary inductor La through the anti-parallel diode of the first auxiliary switch gs 1.

And c, state c: since the value of the auxiliary inductor La is small and the charging time is short, when the net current at the switching node a is zero, the first switching tube Q1 is turned off, and the inductor resonates with the parasitic capacitance of the main switch.

And a state d: when resonance occurs, the gate voltage of the second switch Q2 will be zero, and at this time, the second switch Q2 is turned on, and the power grid charges the inductor L and the auxiliary inductor La through the second switch Q2 and the fourth switch Q4.

And a state e: s2 is turned off, and the grid charges the inductor L through the second switching tube Q2 and the fourth switching tube Q4. Since the current in the inductor L is present throughout the entire cycle, the circuit operates in CCM mode.

In summary, in the scheme of the present invention, the reference current is determined according to the input voltage, the output voltage, and the preset reference voltage of the totem PFC circuit, the modulation wave is determined according to the reference current and the current on the totem PFC inductor L, and the MCU outputs the switching tube in the PWM signal control unit through the modulation wave and the carrier.

Since the processing and functions implemented by the PFC circuit of this embodiment substantially correspond to the embodiments, principles, and examples of the apparatus shown in fig. 1, reference may be made to the related descriptions in the foregoing embodiments without being detailed in the description of this embodiment.

Through a large number of tests, the technical scheme of the invention is adopted, and the problem of large operating switching loss of totem PFC under CCM is solved by adding the PFC auxiliary branch and utilizing ZVT.

According to an embodiment of the present invention, a method for controlling a PFC circuit is also provided, as shown in fig. 4, which is a schematic flow chart of an embodiment of the method of the present invention. The control method of the PFC circuit may be specifically a totem PFC circuit, and the totem PFC circuit may include: the circuit comprises a filtering module (such as a filtering inductor L) and a PFC main switch circuit, wherein the filtering module and the PFC main switch circuit can form a loop with an alternating current power supply. The PFC main switch circuit may be configured to rectify an input ac power into a dc power and provide the dc power to a load at a rear end of the PFC main switch circuit under the control of the control unit when the PFC main switch circuit is turned on. For example: the PFC main switch circuit realizes alternating current to direct current and improves the power factor by a control signal sent by the controller. The control method of the PFC circuit can comprise the following steps: step S110 to step S130.

At step S110, the PFC auxiliary circuit connected in parallel with the filtering module freewheels the filtering module under the control of the control unit when the PFC auxiliary circuit is turned on, that is, when the PFC auxiliary circuit is turned on, so that the PFC circuit can operate in a continuous conduction mode. For example: the PFC auxiliary circuit can be used for freewheeling on an inductor L in the main circuit, so that the totem PFC can work in a Continuous Conduction Mode (CCM).

In step S120, a sampling unit, such as a sampling resistor, a voltage sensor, a current sensor, etc., is connected to the input terminal and the load terminal of the PFC circuit, respectively, to sample input parameters and output parameters of the PFC circuit, specifically, input voltage and input current at the input terminal (i.e., the grid terminal) of the PFC circuit, and to sample output parameters at the load terminal of the PFC circuit. For example: and the sampling unit can be used for sampling the input voltage and the input current.

In step S130, a control unit, such as an MCU controller, controls the PFC auxiliary circuit and the PFC main switch circuit to be turned on or off according to the input parameter and the output parameter, so that when the PFC auxiliary circuit is turned on, the PFC auxiliary circuit freewheels the filtering module, so that the PFC circuit can operate in a continuous conduction mode. Under the condition that the PFC main switch circuit is started, the PFC main switch circuit rectifies input alternating current into direct current and provides the direct current to a load at the rear end of the PFC main switch circuit, so that the PFC circuit works in a zero-voltage conversion mode (namely a ZVT mode). For example: and the MCU controller can be used for obtaining PWM waves for controlling the switching tube according to the input voltage, the input current value and the voltage of the load end which are obtained by sampling.

The input parameters may include: an input voltage and an input current. The input voltage is specifically a voltage value of an input end of the PFC circuit. The input current is specifically a current value at a connection node of the filter module and the PFC main switch circuit.

The output parameters may include: and outputting the voltage. The output voltage is a voltage value of a load end of the PFC circuit.

In an alternative example, in step S130, the control unit controls the specific processes of turning on or off the PFC auxiliary circuit and the PFC main switch circuit according to the input parameter and the output parameter, which may be referred to in the following exemplary description.

The following further describes, with reference to a schematic flow chart of an embodiment of controlling the on or off of the PFC auxiliary circuit and the PFC main switching circuit in the method of the present invention shown in fig. 5, a specific process of controlling the on or off of the PFC auxiliary circuit and the PFC main switching circuit in step S130, which may include: step S210 to step S230.

Step S210, determining a reference current according to the input voltage, the output voltage and a preset reference voltage under the condition that the input parameter may include an input voltage and an input current and the output parameter may include an output voltage.

Step S220, determining a control signal according to the reference current and the input current.

And step S230, controlling the on or off of the PFC auxiliary circuit and the PFC main switch circuit according to the control signal.

Wherein, the control signal may include: a PWM signal.

Optionally, in step S230, the control unit determines a specific process of the control signal according to the reference current and the input current, which may be referred to in the following exemplary description.

The following further describes a specific process of determining the control signal in step S230, with reference to a flowchart of an embodiment of determining the control signal in the method of the present invention shown in fig. 6, where the specific process may include: step S310 and step S320.

In step S310, a modulated wave is determined.

Step S320, outputting the PWM signal according to the modulation wave and the carrier wave to control the on/off of the switching tube in the PFC auxiliary circuit and/or the PFC main switching circuit.

More optionally, outputting, by the control unit, the PWM signal according to the modulation wave and the carrier to control on or off of a switching tube in the PFC auxiliary circuit and/or the PFC main switching circuit may include: under the condition that the input current is larger than a set PFC overcurrent threshold, a switching tube in the PFC main switching circuit is controlled to be closed; and under the condition that the input current is less than or equal to a set PFC overcurrent threshold, controlling a switching tube in the PFC main switching circuit to be alternately switched on.

The fourth control scenario: in a fourth setting state, when the parasitic capacitance of the filtering module and the PFC main switching circuit resonates and the grid voltage of the second switching tube is zero, the second switching tube is conducted. And the power grid charges the filtering module and the auxiliary inductor through the second switching tube and the fourth switching tube.

Fifth control scenario: and in a fifth set state, a body diode of a second auxiliary switching tube is closed, and the filtering module and the auxiliary inductor are charged by the power grid through the second switching tube and the fourth switching tube. The first auxiliary switch tube and the second auxiliary switch tube are both closed, the first switch tube and the third switch tube are both switched on, and the third switch tube and the fourth switch tube are both closed.

Since the processing and functions implemented by the method of the present embodiment substantially correspond to the embodiments, principles and examples of the PFC circuit, reference may be made to the related descriptions in the foregoing embodiments without being detailed in the description of the present embodiment.

Through a large amount of tests verification, adopt the technical scheme of this embodiment, through increasing PFC auxiliary branch road, adopt Continuous Conduction Mode (CCM), can increase the switching frequency of switch tube, and then promote PFC work efficiency.

In summary, it is readily understood by those skilled in the art that the advantageous modes described above can be freely combined and superimposed without conflict.

The above description is only an example of the present invention, and is not intended to limit the present invention, and it is obvious to those skilled in the art that various modifications and variations can be made in the present invention. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the claims of the present invention.

Claims

1. A control device for a PFC circuit, comprising: the device comprises a PFC auxiliary circuit, a sampling unit and a control unit; the PFC circuit includes: the filter module and the PFC main switch circuit; wherein the content of the first and second substances,

the PFC auxiliary circuit is connected with the filtering module in parallel and is used for performing follow current on the filtering module under the control of the control unit and under the condition of self starting;

the sampling unit is used for sampling the input parameters and the output parameters of the PFC circuit;

the control unit is used for controlling the PFC auxiliary circuit and the PFC main switch circuit to be turned on or off according to the input parameter and the output parameter, so that the PFC circuit can work in a continuous conduction mode under the condition that the PFC auxiliary circuit is turned on; and under the condition that the PFC main switch circuit is started, enabling the PFC circuit to work in a zero-voltage conversion mode.

2. The control device of the PFC circuit of claim 1, wherein the PFC auxiliary circuit comprises: the first auxiliary switch tube, the second auxiliary switch tube and the auxiliary inductor; the first auxiliary switching tube, the second auxiliary switching tube and the third auxiliary switching tube are arranged in series;

the PFC main switch circuit includes: the PFC circuit comprises a first branch and a second branch, wherein the first branch is connected with a first switching tube and a second switching tube in series, the second branch is connected with a third switching tube and a fourth switching tube in series, and the central point of each branch is connected with a zero-fire line at the input end of the PFC circuit respectively.

3. The control device of the PFC circuit of claim 2, wherein,

the first auxiliary switch tube, the second auxiliary switch tube, the first switch tube, the second switch tube, the third switch tube and the fourth switch tube are all triodes with diodes; wherein the content of the first and second substances,

in the PFC auxiliary circuit, the first auxiliary switching tube and the second auxiliary switching tube are respectively used for freewheeling of the filter module in a positive half-cycle and a negative half-cycle of the alternating current at the input end; the first auxiliary switch tube and the second auxiliary switch tube are respectively connected with a reverse diode in parallel to be used as body diodes, and each body diode freewheels with the switch tube connected with the body diode in parallel;

4. The apparatus of claim 2, wherein the filtering module comprises: a filter inductor; and the inductance value of the auxiliary inductor is smaller than that of the filter inductor.

5. The control device for the PFC circuit according to any one of claims 1 to 4, wherein,

the input parameters comprise: an input voltage and an input current; the input voltage is specifically a voltage value of an input end of the PFC circuit; the input current is specifically a current value at a connection node of the filtering module and the PFC main switch circuit;

the output parameters comprise: outputting the voltage; the output voltage is a voltage value of a load end of the PFC circuit.

6. The apparatus according to any one of claims 1 to 4, wherein the control unit controls turning on or off of the PFC auxiliary circuit and the PFC main switching circuit, and includes:

under the condition that the input parameters comprise input voltage and input current and the output parameters comprise output voltage, determining reference current according to the input voltage, the output voltage and preset reference voltage;

determining a control signal according to the reference current and the input current;

and controlling the on or off of the PFC auxiliary circuit and the PFC main switch circuit according to the control signal.

7. The control device of the PFC circuit of claim 6, wherein the control signal comprises: a PWM signal;

the control unit determines a control signal including:

determining a modulation wave;

and outputting the PWM signal according to the modulation wave and the carrier wave so as to control the on or off of a switching tube in the PFC auxiliary circuit and/or the PFC main switching circuit.

8. The control device of the PFC circuit of claim 7, wherein the control unit controls on or off of a switching tube in the PFC auxiliary circuit and/or the PFC main switching circuit, and comprises:

under the condition that a first auxiliary switching tube and a second auxiliary switching tube in the PFC auxiliary circuit are both triodes with diodes, and a first switching tube, a second switching tube, a third switching tube and a fourth switching tube in the PFC main switching circuit are all triodes with diodes, and each body diode is connected with a parasitic capacitor in parallel, the control method comprises the following control conditions under any set state:

in a first setting state, the first auxiliary switch tube and the second auxiliary switch tube are both closed, the first switch tube and the third switch tube are both conducted, and the second switch tube and the fourth switch tube are both closed;

in a second set state, the body diode of the second auxiliary switch tube is turned off after the first time when the first switch tube is turned on and is turned on before the second switch tube is turned off; then, the filtering module charges an auxiliary inductor through a body diode of the first auxiliary switching tube;

in a third setting state, when the current value at the connection node of the filter module and the main PFC switch circuit is zero, the first switch tube Q1 is closed, and the parasitic capacitance of the filter module and the main PFC switch circuit resonates;

in a fourth setting state, when the parasitic capacitance of the filtering module and the PFC main switching circuit resonates and the grid voltage of the second switching tube is zero, the second switching tube is conducted; the power grid charges the filtering module and the auxiliary inductor through the second switching tube and the fourth switching tube;

in a fifth set state, a body diode of a second auxiliary switching tube is turned off, and the filtering module and the auxiliary inductor are charged by the power grid through the second switching tube and the fourth switching tube; the first auxiliary switch tube and the second auxiliary switch tube are both closed, the first switch tube and the third switch tube are both switched on, and the third switch tube and the fourth switch tube are both closed.

9. A PFC circuit, comprising: control means for a PFC circuit according to any one of claims 1 to 8.

10. A control method of a PFC circuit, the PFC circuit comprising: the filter module and the PFC main switch circuit; the control method of the PFC circuit comprises the following steps:

through a PFC auxiliary circuit connected with a filtering module in parallel, under the control of the control unit, the filtering module is subjected to follow current under the condition of self starting;

sampling input parameters and output parameters of the PFC circuit through a sampling unit;

controlling, by a control unit, on or off of the PFC auxiliary circuit and the PFC main switch circuit according to the input parameter and the output parameter, so that the PFC circuit can operate in a continuous conduction mode when the PFC auxiliary circuit is turned on; and under the condition that the PFC main switch circuit is started, enabling the PFC circuit to work in a zero-voltage conversion mode.

11. The method of claim 10, wherein the step of controlling the PFC circuit further comprises the step of,

12. The method according to claim 10 or 11, wherein controlling the PFC auxiliary circuit and the PFC main switch circuit to be turned on or off by the control unit comprises:

13. The method of claim 12, wherein the control signal comprises: a PWM signal;

the control unit determines a control signal including:

determining a modulation wave;

14. The method according to claim 13, wherein the controlling the on or off of the switching tube in the PFC auxiliary circuit and/or the PFC main switching circuit by the control unit comprises:

in a first setting state, the first auxiliary switch tube and the second auxiliary switch tube are both closed, the first switch tube and the third switch tube are both conducted, and the third switch tube and the fourth switch tube are both closed;

in a fourth setting state, when the parasitic capacitance of the filtering module and the PFC main switching circuit resonates and the grid voltage of the second switching tube is zero, the second switching tube is conducted;

the power grid charges the filtering module and the auxiliary inductor through the second switching tube and the fourth switching tube;