CN109995229B

CN109995229B - PFC circuit

Info

Publication number: CN109995229B
Application number: CN201810001599.9A
Authority: CN
Inventors: 田龙祥; 周志健; 廖仁诠
Original assignee: Delta Electronics Shanghai Co Ltd
Current assignee: Delta Electronics Shanghai Co Ltd
Priority date: 2018-01-02
Filing date: 2018-01-02
Publication date: 2021-06-18
Anticipated expiration: 2038-01-02
Also published as: TW201931745A; TWI665856B; CN109995229A

Abstract

The invention discloses a PFC circuit, which comprises two conversion branches which are electrically connected, wherein each conversion branch comprises: the input inductor, the n switch units and the n-1 coupling inductors are arranged, and one end of the input inductor is connected with an input power supply; n switch units are connected in parallel, wherein n is a positive integer greater than or equal to 2; each coupling inductor comprises two windings, and the two windings form reverse coupling; and when the n switch units are conducted, the current flowing through the n switch units is equalized through the n-1 coupling inductors.

Description

PFC circuit

Technical Field

The present invention relates to a PFC circuit, and more particularly, to a PFC circuit based on a coupled inductor.

Background

With the continuous improvement of power grade of power electronic equipment, a single switch tube or a switch module is difficult to meet the power requirement, so that a plurality of switch tubes are often required to be connected in parallel for use in practical application, but a new problem is brought, namely, in practical application, the phenomenon of uneven current among the switch tubes is caused by the difference between the switch tubes and a loop, and the performances of reliability, safety and the like of the power electronic equipment are further reduced.

The current common method for solving the problem of non-uniform current among the parallel switch tubes is mainly to design symmetrical driving and main loops to achieve better uniform current among the switch tubes. However, the switching speed is fast and the loop parameters are difficult to control, so that the design difficulty is greatly increased, and the feasibility of the method is lower and lower as the speed of the switching device is increased day by day.

Referring to fig. 1, fig. 1 is a schematic structural diagram of a conventional PFC circuit, which is mainly used for converting ac power into dc power. As shown in fig. 1, the PFC circuit includes two switching branches Z1, each switching branch Z1 includes a switching unit a1, but in practical use, it is difficult for a single switching unit to satisfy high power requirements due to the limitation of the power of the switching unit.

Disclosure of Invention

In order to overcome the problems of the prior art, an object of the present invention is to provide a PFC circuit, which includes two converting branches electrically connected to each other, each of the converting branches including:

an input inductor, one end of which is connected with an input power supply;

n switching units connected in parallel, wherein n is a positive integer greater than or equal to 2;

n-1 coupling inductors, wherein each coupling inductor comprises two windings, and the two windings form reverse coupling;

at least one winding is connected in series between each switch unit and the other end of the input inductor, and when the n switch units are switched on, the current flowing through the n switch units is equalized through the n-1 coupling inductors.

In the PFC circuit, each of the conversion branches further includes:

one end of each diode is electrically connected with each switch unit in a one-to-one correspondence mode, and the other end of each diode is electrically connected with the output end of the PFC circuit.

In the PFC circuit, each of the conversion branches further includes:

the first coupling inductor comprises a first winding and a second winding, the first winding is provided with a first end and a second end, the second winding is provided with a third end and a fourth end, and the first end and the third end are electrically connected to the other end of the input inductor;

a first switch unit, one end of which is electrically connected to the second end;

the second switch unit is connected with the first switch unit in parallel, one end of the second switch unit is electrically connected with the fourth end, and the other end of the first switch unit is electrically connected with the other end of the second switch unit;

one end of the first diode is electrically connected with the second end and one end of the first switch unit;

a second diode, one end of which is electrically connected to the fourth end and one end of the second switch unit;

and one end of the first output capacitor is electrically connected to the other ends of the first diode and the second diode, and the other end of the first output capacitor is also electrically connected to the other ends of the first switch unit and the second switch unit.

In the PFC circuit, each of the conversion branches further includes:

a second coupling inductor, including a third winding and a fourth winding, where the third winding has a fifth end and a sixth end, the fourth winding has a seventh end and an eighth end, the fifth end is electrically connected to the first end, the third end, and the other end of the input inductor, and the seventh end is electrically connected to the second end;

a first switching unit, one end of which is electrically connected to the fourth end;

one end of the second switch unit is electrically connected to the eighth end;

one end of the third switch unit is electrically connected to the sixth end, and the other end of the first switch unit and the other end of the second switch unit are electrically connected with the other end of the third switch unit;

a first diode, one end of which is electrically connected to the fourth end and one end of the first switch unit;

one end of the second diode is electrically connected to the eighth end and one end of the second switch unit;

one end of the third diode is electrically connected to the sixth end and one end of the third switching unit;

and one end of the first output capacitor is electrically connected to the other end of the first diode, the other end of the second diode and the other end of the third diode, and the other end of the first output capacitor is electrically connected to the other end of the first switch unit, the other end of the second switch unit and the other end of the third switch unit.

In the PFC circuit, the first winding and the second winding have the same number of turns.

In the PFC circuit, the first terminal and the third terminal are different name terminals.

In the PFC circuit, the first winding and the second winding have the same number of turns, and the third winding and the fourth winding have the same number of turns.

In the PFC circuit, the first terminal and the third terminal are different name terminals, and the fifth terminal and the seventh terminal are different name terminals.

In the PFC circuit, when the n switching units of each conversion branch receive the driving signal and are turned on, the reverse recovery current generated by the diode electrically connected to the switching unit turned on later is output to the switching unit turned on earlier through the at least two windings connected in series, so as to equalize the transient on-current of each switching unit.

Aiming at the prior art, the invention has the advantages that the coupling inductor is arranged in the conversion branch circuit, so that the PFC circuit with the structure achieves good current sharing effect in both transient state and steady state, further the power density of the system is increased, and the safety and the reliability are better; meanwhile, the coupling inductor can be designed to be very small, so that the system cost cannot be increased.

Drawings

Fig. 1 is a schematic structural diagram of a conventional PFC circuit;

fig. 2 shows a schematic diagram of a current loop when the first switch unit a1 is turned on first in the PFC circuit;

FIG. 3 shows a graph of the current of two parallel switch cells of FIG. 2;

fig. 4 is a schematic structural diagram of a PFC circuit according to a first embodiment of the present invention;

FIG. 5 is a schematic diagram of a current loop when the first switch unit A1 in FIG. 4 is turned on first;

FIG. 6 is a graph of current flowing through two parallel switch cells of FIG. 4;

fig. 7 is a schematic structural diagram of a PFC circuit according to a second embodiment of the present invention;

fig. 8 is a schematic diagram of 1 winding turn of the coupling inductor.

Wherein the reference numerals are:

z1: switching branch

L: input inductor

R1: first winding

R2: second winding

R3: third winding

R4: the fourth winding

A1: first switch unit

A2: second switch unit

A3: third switch unit

D1: first diode

D2: second diode

D3: third diode

C1: first output capacitor

C: capacitor with a capacitor element

S: input power supply

SCR: silicon controlled rectifier

Detailed Description

The invention is described in further detail below with reference to specific embodiments and with reference to the following figures: the embodiment is implemented on the premise of the technical scheme of the invention, and the implementation mode and the operation process are given, but the protection scope of the invention is not limited by the following embodiments.

It should be noted that the numbers of the switch units and the coupling inductors described below are only one embodiment of the present invention, and those skilled in the art can fully adjust the numbers of the switch units and the coupling inductors according to the use requirement under the concept of the present invention, so the present invention does not limit the numbers of the switch units and the coupling inductors.

In order to be suitable for high-power application occasions, each conversion branch in the PFC circuit comprises two or more switching units which are connected in parallel, and in order to reduce the system cost, the switching units connected in parallel share one input inductor. However, in practical use, due to differences of the switch units, inconsistency of the driving circuits, and differences of parasitic inductance and resistance of the main loop, the switch units connected in parallel have an inconsistent current. Referring to fig. 2-3, fig. 2 is a schematic diagram illustrating a current loop when the first switch unit a1 in the PFC circuit is turned on first, and fig. 3 is a graph illustrating currents of two parallel switch units in fig. 2. When the first switch unit a1 is turned on before the second switch unit a2, the reverse recovery currents of the two diodes D1 and D2 flow into the first switch unit a1 at the same time, which results in the transient on-current of the first switch unit a1 being increased, and increases the current stress of the switch. When the switch unit is stably conducted, because the parasitic parameters of the main loops of the switch unit are very small, if the design of the two main loops has small difference, the currents on the two switch units have large difference. As a result, the parallel switch units have different losses, heat dissipation is difficult, and the turn-off stress of the switch unit having a large current is significantly increased, thereby reducing the reliability and safety of the system.

FIG. 3 shows a graph of the current of two parallel switch cells of FIG. 2; the horizontal axis is time T, the vertical axis is current I, curves S1 and S2 are current curves of the first switch unit a1 and the second switch unit a2 tested under the double-pulse condition, respectively, and E is a transient current difference. At time T1, the first switch unit a1 and the second switch unit a2 are turned on, and the difference between the turned-on times is small, which is not shown in the figure. In the figure, the transient current of the first switch unit a1 which is turned on first is 81.4A, the transient current of the second switch unit a2 which is turned on later is 70.4A, and the transient current difference E at the turn-on moment of the first switch unit a1 and the second switch unit a2 which are connected in parallel is 11A. At time T2, the first switch unit a1 and the second switch unit a2 reach steady state, and there is also a significant difference in current during steady state conditions.

The present application proposes a PFC circuit that overcomes the above-mentioned drawbacks. Referring to fig. 4, fig. 4 is a schematic structural diagram of a PFC circuit according to a first embodiment of the present invention. It should be noted that each conversion branch includes two switch units and one coupling inductor in this example, but the invention is not limited thereto. As shown in fig. 4, the PFC circuit of the present invention includes two switching branches Z1 electrically connected to each other, and each switching branch Z1 includes: an input inductor L, a first switch unit A1, a second switch unit A2 and a first coupling inductor; one end of the input inductor L is connected with an input power supply S; the first switching unit a1 is connected in parallel with the second switching unit a 2; the first coupling inductor comprises a first winding R1 and a second winding R2 which have the same number of turns, and the first winding R1 and the second winding R2 form reverse coupling; when the two switching units a1 and a2 are turned on, the currents flowing through the first switching unit a1 and the second switching unit a2 are equalized through the first winding R1 and the second winding R2 of the first coupling inductor.

The first winding R1 has a first end 1 and a second end 2, the second winding R2 has a third end 3 and a fourth end 4, and the first end 1 and the third end 3 are different name ends; the first end 1 and the third end 3 are electrically connected to the other end of the input inductor L; one end of the first switch unit a1 is electrically connected to the second end 2; one end of the second switch unit a2 is electrically connected to the fourth terminal 4, and the other end of the first switch unit a1 is electrically connected to the other end of the second switch unit a 2.

Further, each conversion branch Z1 includes a first diode D1, a second diode D2 and a first output capacitor C1; one end of the first diode D1 is electrically connected to the second end 2 and one end of the first switch unit a 1; one end of the second diode D2 is electrically connected to the fourth terminal 4 and one end of the second switch unit a 2; one end of the first output capacitor C1 is electrically connected to the other ends of the first diode D1 and the second diode D2, and the other end of the first output capacitor C1 is also electrically connected to the other ends of the first switch unit a1 and the second switch unit a 2.

When the switching branch Z1 is connected between the positive output terminal of the PFC circuit and the neutral point N, the switching units a1 and a2 are IGBTs, and the connection relationship between the devices in the switching branch Z1 is further described as follows. The source of the first switch unit a1 is electrically connected to the second terminal 2; the source of the second switch unit a2 is electrically connected to the fourth terminal 4; the drain of the first switch unit a1 is electrically connected to the drain of the second switch unit a2 and to the neutral point N. An anode of the first diode D1 is electrically connected to the second terminal 2 and the source of the first switch unit a1, and a cathode of the first diode D1 is electrically connected to the positive output terminal of the PFC circuit; an anode of the second diode D2 is electrically connected to the fourth terminal 4 and the source of the second switch unit a2, and a cathode of the second diode is electrically connected to the positive output terminal of the PFC circuit. One end of the first output capacitor C1 is electrically connected to the positive output end of the PFC circuit, and the other end of the first output capacitor C1 is electrically connected to the neutral point N.

When the switching branch Z1 is connected between the negative output terminal of the PFC circuit and the neutral point N, the switching units a1 and a2 are IGBTs, and the connection relationship between the devices in the switching branch Z1 is further described as follows. The drain of the first switch unit a1 is electrically connected to the fourth terminal 4; the drain of the second switch unit a2 is electrically connected to the second terminal 2; the source of the first switch unit a1 is electrically connected to the source of the second switch unit a2, and is connected to the neutral point N. The cathode of the first diode D1 is electrically connected to the fourth terminal 4 and the drain of the first switch unit a1, and the anode of the first diode D1 is electrically connected to the negative output terminal of the PFC circuit; the cathode of the second diode D2 is electrically connected to the second terminal 2 and the drain of the second switch unit a2, and the anode of the second diode is electrically connected to the negative output terminal of the PFC circuit. One end of the first output capacitor C1 is electrically connected to the negative output terminal of the PFC circuit, and the other end of the first output capacitor C1 is electrically connected to the neutral point N.

Referring to fig. 5-6, fig. 5 is a schematic diagram of a current loop when the switch unit a1 in fig. 4 is turned on first; fig. 6 is a graph of the current flowing through two parallel switch units of fig. 4, and the operation of the PFC circuit of the present invention will be described in detail with reference to fig. 4-6. Taking one conversion branch as an example, the inductance of the two windings of the first coupling inductor is L1 and L2, respectively, the mutual inductance is M, and L1, L2 and M are approximately equal under the condition that the winding of the inductor is good. Since the first switching unit a1 is first turned on by the difference of the driving signal and the switching units, the reverse recovery current of the first diode D1 flows through the first switching unit a1, while the reverse recovery current of the second diode D2 flows through the first switching unit a1 via the second winding R2 and the first winding R1, since the existence of the first coupling inductor is equivalent to forming a loop as in fig. 5, when the first winding R1 and the second winding R2 are connected in series, the inductance L1 and the inductance L2 are superposed, the reverse recovery current of the second diode D2 is resisted, since the rate of change of the diode reverse recovery current di/dt is large, the impedance (L1+ L2) di/dt of the first coupling inductor to the reverse recovery current of the second diode D2 is large, the reverse recovery current flowing into the first switch unit a1 from the second diode D2 is blocked, and the transient on-state current between the parallel-connected switch units can be balanced. When the second switching unit a2 is turned on, the reverse recovery current of the second diode D2 flows through the second switching unit a2, and finally the transient turn-on current in the first switching unit a1 and the second switching unit a2 substantially coincide.

When the first switch unit a1 and the second switch unit a2 are stably turned on, the current in the input inductor L respectively flows through the first switch unit a1 and the second switch unit a2 through the two windings R1 and R2 of the first coupling inductor, assuming that the currents flowing through the first switch unit a1 and the second switch unit a2 are i1 and i2 respectively, and the voltages at the two ends of the first switch unit a1 and the second switch unit a2 are U1 according to kirchhoff's law:

the following formula (3) can be obtained from the formulas (1) and (2):

since L1, L2, and M are approximately equal, it can be found that di1 is di2, and i1 and i2 have the same initial current, so i1 is i2 when they are stably turned on. By clamping two windings in the coupling inductor, the currents when the parallel switch units are stably conducted are basically equal, and the current equalizing effect is achieved.

Referring to fig. 6, fig. 6 is a graph illustrating the current flowing through the two parallel switch units shown in fig. 4; the horizontal axis is time T, the vertical axis is current I, and the curves S3 and S4 are curves of currents flowing through the first switch unit a1 and the second switch unit a2, respectively. At time T1, the first and second switching units a1 and a2 are turned on, and at time T2, the first and second switching units a1 and a2 are stably turned on. The difference between the on times of the first switch unit a1 and the second switch unit a2 is small and cannot be shown in the figure, but for clarity, the intervals are artificially shifted. As shown in fig. 6, the currents flowing through the first and second switching units a1 and a2 are substantially identical at time T1 and time T2. Compared with the curves S1 and S2 in fig. 3, the switching tube current sharing degree in fig. 3 is 7.3%, and the switching tube current sharing degree in fig. 6 is 1.9%, so that the PFC circuit of the present invention can achieve good current sharing effect in both transient state and steady state. It should be noted that the present invention is not limited to the above experimental values.

Referring to fig. 7, fig. 7 is a schematic structural diagram of a PFC circuit according to a second embodiment of the present invention. The PFC circuit shown in fig. 7 has substantially the same structure as the PFC circuit shown in fig. 4, and therefore, the same parts are not repeated herein, and different parts will be described below. In the present embodiment, each switching branch Z1 includes: an input inductor L, a first coupling inductor, a second coupling inductor, a first switch unit a1, a second switch unit a2, and a third switch unit A3; the first coupling inductor comprises a first winding R1 and a second winding R2, the number of turns of the first winding R1 is the same as that of the second winding R2, the first winding R1 is provided with a first end 1 and a second end 2, the second winding R2 is provided with a third end 3 and a fourth end 4, and the first end 1 and the third end 3 are different name ends; the second coupling inductor comprises a third winding R3 and a fourth winding R4, the number of turns of the third winding R3 is the same as that of the fourth winding R4, the third winding R3 is provided with a fifth end 5 and a sixth end 6, the fourth winding R4 is provided with a seventh end 7 and an eighth end 8, the fifth end 5 and the seventh end 7 are different name ends, the fifth end 5 is electrically connected with the first end 1, the third end 3 and the other end of the input inductor L, and the seventh end 7 is electrically connected with the second end 2; one end of the first switch unit a1 is electrically connected to the fourth end 4; one end of the second switch unit a2 is electrically connected to the eighth end 8; one end of the third switch unit A3 is electrically connected to the sixth end 6, and the other end of the first switch unit a1, the other end of the second switch unit a2 and the other end of the third switch unit A3 are electrically connected.

A second winding R2 is connected in series between the first switch unit A1 and the other end of the input inductor L; a first winding R1 and a fourth winding R4 are connected in series between the second switch unit A2 and the other end of the input inductor L; a fourth winding R3 is connected in series between the third switching unit a3 and the other end of the input inductor L. When the three switch units a1, a2 and A3 are turned on, the currents flowing through the first switch unit a1, the second switch unit a2 and the third switch unit A3 are equalized through the first winding R1 and the second winding R2 of the first coupling inductor and the third winding R3 and the fourth winding R4 of the second coupling inductor.

Further, each switching branch Z1 further includes: a first diode D1, a second diode D2, a third diode D3; one end of the first diode D1 is electrically connected to the fourth terminal 4 and one end of the first switch unit a 1; one end of the second diode D2 is electrically connected to the eighth end 8 and one end of the second switch unit a 2; one end of the third diode D3 is electrically connected to the sixth terminal 6 and one end of the third switching unit A3; one end of the first output capacitor C1 is electrically connected to the other end of the first diode D1, the other end of the second diode D2, and the other end of the third diode D3, and the other end of the first output capacitor C1 is electrically connected to the other end of the first switch unit a1, the other end of the second switch unit a2, and the other end of the third switch unit A3.

Taking a switching branch as an example, the inductance of the two windings of the first coupling inductor is L1 and L2, respectively, and the inductance of the two windings of the second coupling inductor is L3 and L4, respectively. The first switch unit a1 is first turned on due to the difference of the driving signal and the switch units, and the reverse recovery current of the first diode D1 flows through the first switch unit a 1. Meanwhile, the reverse phase recovery current of the second diode D2 flows through the first switch unit a1 via the third winding R3, the first winding R1 and the second winding R2, at this time, the first winding R1, the second winding R2 and the third winding R3 form a series connection, inductance values L1, L2 and L3 are superimposed, and the reverse phase recovery current of the second diode D2 is resisted, and since the change rate di/dt of the diode reverse phase recovery current is large, the impedance (L1+ L2+ L3) di/dt of the first coupling inductor and the second coupling inductor to the reverse phase recovery current of the second diode D2 is large, and the reverse phase recovery current flowing into the first switch unit a1 from the second diode D2 is resisted. Meanwhile, the reverse recovery current of the third diode D3 flows through the first switch unit a1 via the fourth winding R4 and the second winding R2, at this time, the second winding R2 and the fourth winding R4 are connected in series, the inductance L2 is superposed with the inductance L4, and the reverse recovery current of the third diode D3 is resisted, and since the change rate di/dt of the diode reverse recovery current is large, the resistance (L2+ L4) di/dt of the first coupling inductor and the second coupling inductor to the reverse recovery current of the third diode D3 is large, and the reverse recovery current flowing into the first switch unit a1 from the third diode D3 is resisted. Finally, the first coupling inductor and the second coupling inductor play a role in balancing transient switching-on current between the switch units connected in parallel.

The operation principle of the PFC circuit shown in fig. 7 is the same as that of the PFC circuit shown in fig. 4, and is not described herein again.

In summary, the PFC circuit of the present invention includes two electrically connected converting branches Z1, and each converting branch Z1 includes: the circuit comprises an input inductor L, n switch units and n-1 coupling inductors, wherein the n switch units are connected in parallel, and n is a positive integer greater than or equal to 2; when the n switch units are conducted, the current flowing through the n switch units is equalized through the n-1 coupling inductors. Therefore, based on the structure that the coupling inductor is arranged in the conversion branch circuit, the PFC circuit with the structure has good current-sharing performance in transient state and steady state, the power density of the system is increased, and the safety and the reliability are better.

In the PFC circuit of the present application, each conversion branch Z1 further includes: one end of each diode is electrically connected with each switch unit in a one-to-one correspondence mode, and the other end of each diode is electrically connected with the output end of the PFC circuit.

Meanwhile, the coupling inductor can be designed to be very small, for example, the number of turns of each winding in the coupling inductor can be very small, and even the coupling inductor can be formed by only winding 1 coil. Referring to fig. 8, fig. 8 is a schematic diagram illustrating that the winding turns of the coupling inductor are 1 turn. In fig. 8, the number of winding turns of the coupling inductor is 1, but the invention is not limited to this, and the coupling inductor can be flexibly designed according to actual needs. The coupling inductor has smaller volume design, and can not increase the system cost and occupy the circuit space.

It should be noted that the above embodiments are only used for illustrating the present invention, and do not limit the technical solutions described in the present invention; meanwhile, although the present invention has been described in detail with reference to the above embodiments, it will be understood by those skilled in the art that the present invention may be modified and equivalents may be substituted; therefore, all technical solutions and modifications which do not depart from the spirit and scope of the present invention should be construed as being included in the scope of the appended claims.

Claims

1. A PFC circuit comprising two conversion branches electrically connected to each other, each of the conversion branches comprising:

an input inductor, one end of which is connected with an input power supply;

when the n switch units are switched on, transient currents flowing through the n switch units are equalized through the n-1 coupling inductors, and the number of turns of the winding of the at least one coupling inductor is 1 turn.

2. The PFC circuit of claim 1, wherein each of the conversion legs further comprises:

3. The PFC circuit of claim 2, wherein each of the conversion legs further comprises:

4. The PFC circuit of claim 2, wherein each of the conversion legs further comprises:

one end of the second switch unit is electrically connected to the eighth end;

5. The PFC circuit of claim 3, wherein the first winding and the second winding have the same number of coil turns.

6. The PFC circuit of claim 3, wherein the first terminal and the third terminal are synonym terminals.

7. The PFC circuit of claim 4, wherein the first winding and the second winding have the same number of coil turns, and wherein the third winding and the fourth winding have the same number of coil turns.

8. The PFC circuit of claim 4, wherein the first terminal and the third terminal are synonym terminals, and the fifth terminal and the seventh terminal are synonym terminals.

9. The PFC circuit of claim 2, wherein when the n switching units of each of the converting branches are turned on by receiving a driving signal, a reverse recovery current generated by the diode electrically connected to a switching unit turned on later is outputted to a switching unit turned on earlier through at least two windings connected in series to equalize transient on-currents of the switching units.