CN117811389A

CN117811389A - Bridgeless isolated AC-DC single-stage PFC converter and control method thereof

Info

Publication number: CN117811389A
Application number: CN202211171314.9A
Authority: CN
Inventors: 请求不公布姓名
Original assignee: Individual
Current assignee: Individual
Priority date: 2022-09-25
Filing date: 2022-09-25
Publication date: 2024-04-02
Also published as: WO2024060855A1

Abstract

The invention provides a bridgeless isolation type AC-DC single-stage PFC converter and a control method thereof, and belongs to the field of power electronics/new energy. The single transformer comprises an input filter circuit, a capacitor network, a conversion bridge, a transformer, a rectifier and a filter, and the two technical schemes of a single transformer and a double transformer are adopted, wherein the transformer and the rectifier are added on the basis of the input filter circuit, and the double transformer has various output modes. The control method corresponds to a single-bridge arm PWM and a double-bridge arm PWM, and the control method has two modulation modes of frequency multiplication and bipolar. In order to reduce the cost, a low-frequency bridge arm of the conversion bridge of the single transformer scheme adopts a diode. For bidirectional conversion or synchronous rectification, the rectifier adopts a switching tube. To reduce the direct current of the primary winding of the transformer, two derivative circuits are proposed. The advantages are: (1) the isolated single-stage conversion has low cost; (2) the power frequency rectifier bridge is omitted, and the efficiency is high; (3) the conversion power is high, and the output voltage is wide; (4) suitable for voltage and current source modes; (5) the control method is flexible and reliable.

Description

Bridgeless isolated AC-DC single-stage PFC converter and control method thereof

Technical Field

The invention relates to a bridgeless isolation type AC-DC single-stage PFC converter and a control method thereof, which are electric energy efficient conversion/switching power supply technology and belong to the technical field of power electronics/new energy.

Background

A single-stage PFC (Power Factor Correction) converter, which is an alternating-current input/direct-current output switching converter; the function is to stabilize the required DC output by only one power conversion and to realize the power factor correction at the AC side. The Power Factor Correction (PFC) is to track an ac voltage with an input ac current so that waveforms of the ac voltage and the ac voltage are identical in phase, thereby achieving a high power factor.

Currently, PFC (Power Factor Correction) converters are generally non-isolated, and Boost (Boost) topology, buck (Buck) topology, buck-Boost topology and totem pole topology are commonly used. The isolated single-stage PFC converter adopts flyback topology in most cases, and has half-bridge topology and the like. Flyback topologies are single ended conversions, where the power transmitted cannot be too great, and are generally suitable for low power applications. Although the half-bridge type topology can be applied to medium and high power, the rectification loss is larger when the power frequency rectification bridge exists.

The foregoing is provided to assist in understanding the principles of the invention and is not intended to be limiting.

Disclosure of Invention

The invention aims to overcome the defects of the prior art and provides a bridgeless isolation type AC-DC single-stage PFC converter and a control method thereof. The converter is an isolated single-stage PFC converter, has isolated input and output, stabilizes direct current output and realizes high power factor. The converter is an AC-DC circuit without a power frequency rectifier bridge, adopts full-bridge topology, belongs to double-end conversion, can transmit high power, and improves efficiency and reduces cost. The converter comprises two technical schemes of a single transformer and a double transformer, and the corresponding control method is also divided into two types: one is single leg PWM control, corresponding to a single transformer scheme; the other is double bridge arm PWM control, corresponding to a double transformer scheme.

The technical scheme of the invention is as follows.

A bridge-free isolated AC-DC single-stage PFC converter has two technical schemes; the first is a single transformer scheme and the second is a double transformer scheme. Both solutions have the same input filter circuit and transform bridge.

The input filter circuit comprises common mode and differential mode inductances, an X capacitor and a Y capacitor, and is provided with two alternating current output ends.

The conversion bridge comprises switching tubes Q1, Q2, Q3 and Q4, wherein the full-bridge topology is provided with two bridge arms, the switching tubes Q1 and Q2 form a first bridge arm, and the switching tubes Q3 and Q4 form a second bridge arm. The drain electrode of the switching tube Q1 is connected with the source electrode of the Q2 to serve as a node V1, and the drain electrode of the switching tube Q3 is connected with the source electrode of the Q4 to serve as a node V2; the drains of the switching tubes Q2 and Q4 are connected as the positive end Vd of the conversion bridge, and the sources of the switching tubes Q1 and Q3 are connected as the ground end GND of the conversion bridge.

The single transformer scheme comprises an input filter circuit, a capacitor network, a conversion bridge, a transformer, a rectifier and a filter, which are connected in sequence. The alternating current power supply Ua is connected with the input filter circuit, and two alternating current output ends of the input filter circuit provide stable alternating current voltage; the filter supplies the dc voltage with the high-frequency ripple removed as an output of the inverter to a load.

The capacitor network comprises capacitors Cd, cs, C1 and C2, which are thin film capacitors with smaller capacity instead of electrolytic capacitors with large capacity, in particular Cd. Two ends of the capacitor Cd are respectively connected with the positive end Vd and the ground end GND of the conversion bridge, and two ends of the capacitor Cs are respectively connected with two alternating current output ends of the input filter circuit; one end of the capacitor C1 and one end of the capacitor C2 are connected with one alternating current output end of the input filter circuit to serve as a node Vs, the other end of the capacitor C1 is connected with the ground end GND of the conversion bridge, the other end of the capacitor C2 is connected with the positive end Vd of the conversion bridge, and the node V2 of the conversion bridge is connected with the other alternating current output end of the filter circuit. Either the capacitors C1 and C2 or the capacitor Cs or the capacitor Cd are removed to simplify the circuit and reduce the cost, but the ripple current of each capacitor will change.

The transformer has a primary winding Np and at least one secondary winding Ns. The primary winding Np has two ends, the secondary winding Ns has two ends and a center tap, or the center tap is removed.

One end of the primary winding Np is connected with a node Vs of the capacitor network, and the other end is connected with a node V1 of the conversion bridge. Two ends of the secondary winding Ns are respectively connected with two alternating current input ends of the rectifier; when the rectifier adopts a full-wave rectification topology, the middle tap of Ns is used as a positive output end or a negative output end of the rectifier; when the rectifier adopts a full bridge rectification topology, then the center tap of Ns is removed.

The rectifier adopts full-wave rectification topology or full-bridge rectification topology, and has a positive output end, a negative output end and two alternating current input ends.

The full wave rectification topology includes diodes D1, D2 connected in two ways. The first connection is called common cathode connection, that is, the cathodes of the diodes D1 and D2 are connected together as the positive output terminal of the rectifier, the anode of the diode D1 and the anode of the diode D2 are used as the two ac input terminals of the rectifier, and the middle tap of the secondary winding Ns of the transformer is used as the negative output terminal of the rectifier. The second connection mode is called common anode connection, namely, the anodes of the diodes D1 and D2 are connected together to serve as the negative output end of the rectifier, the cathode of the diode D1 and the cathode of the diode D2 serve as two alternating current input ends of the rectifier, and the middle tap of the secondary winding Ns of the transformer serves as the positive output end of the rectifier.

The full-bridge rectification topology comprises diodes D1, D2, D3 and D4, wherein the anode of the diode D1 is connected with the cathode of the diode D2 to serve as one alternating current input end of the rectifier, the anode of the diode D3 is connected with the cathode of the diode D4 to serve as the other alternating current input end of the rectifier, the cathodes of the diodes D1 and D3 are connected to serve as the positive output end of the rectifier, and the anodes of the diodes D2 and D4 are connected to serve as the negative output end of the rectifier.

The filter comprises filter inductors Lo1 and Lo2 and a filter capacitor Co, forms a four-terminal network, and is provided with a positive input end, a negative input end, a positive output end and a negative output end. Two ends of the filter inductor Lo1 are respectively used as a positive input end and a positive output end of the filter, and two ends of the filter inductor Lo2 are respectively used as a negative input end and a negative output end of the filter; the positive pole and the negative pole of filter capacitor Co are connected with the positive output end and the negative output end of the filter respectively. The filter inductors Lo1 and Lo2 are independent or coupled, or Lo1 or Lo2 is removed to simplify the circuit; when Lo1 is removed, the positive input end and the positive output end of the filter are directly connected, and when Lo2 is removed, the negative input end and the negative output end of the filter are directly connected. Or the filter capacitor Co is removed to be suitable for the current source mode output. When Co is reserved, then it is the voltage source mode output.

The positive input end and the negative input end of the filter are respectively connected with the positive output end and the negative output end of the rectifier, and the positive output end and the negative output end of the filter are respectively used as the positive output end +vo and the negative output end-Vo of the converter.

For single transformer solutions, in order to reduce costs (but increase losses), the switching tubes Q3, Q4 of the conversion bridge can be replaced by diodes D01, D02, respectively, or the switching tubes Q3, Q4 of the conversion bridge can be replaced by unidirectional thyristors S1, S2, respectively; the replacement rule is that the anode and the cathode of the diode or the unidirectional thyristor respectively correspond to the source electrode and the drain electrode of the switching tube. Meanwhile, capacitors C1 and C2 of the capacitor network are reserved, one ends of the capacitors C1 and C2 are commonly connected with a node Vs or a node V2 of the conversion bridge, and the other ends of the capacitors C1 and C2 are respectively connected with a ground end GND and a positive end Vd of the conversion bridge.

The dual transformer scheme comprises an input filter circuit, a capacitor network, a transformation bridge, a first transformer, a second transformer, a rectifier X, a rectifier Y, one filter or two filters, namely a filter X and a filter Y. The alternating current power supply Ua is connected with an input filter circuit, and two alternating current output ends of the input filter circuit provide stable alternating current voltage. The rectifier X and the rectifier Y are respectively connected with the filter X and the filter Y to form two groups of outputs; alternatively, rectifier X and rectifier Y are jointly connected in combination with a filter to form a set of outputs.

The capacitor network comprises capacitors Cs, cd, C1, C2, C3 and C4, which all adopt thin film capacitors with smaller capacity rather than electrolytic capacitors with large capacity, in particular Cd. Two ends of the capacitor Cs are respectively connected with two alternating current output ends of the input filter circuit, and two ends of the capacitor Cd are respectively connected with the positive end Vd and the ground end GND of the conversion bridge; one ends of the capacitors C1 and C3 are connected to one ac output end of the input filter circuit and serve as a node Vs1, one ends of the capacitors C2 and C4 are connected to the other ac output end of the input filter circuit and serve as a node Vs2, the other ends of the capacitors C1 and C2 are connected to the ground end GND of the conversion bridge, and the other ends of the capacitors C3 and C4 are connected to the positive end Vd of the conversion bridge. Either any two of C1, C2, C3, C4 are removed, either Cs or Cd are removed, or Cs and Cd are removed, to simplify the circuit and reduce cost, but circuit symmetry is reduced and ripple current of each capacitor will change.

The first transformer has a primary winding Np1 and at least one secondary winding Ns1; the primary winding Np1 has both ends, and the secondary winding Ns1 has both ends and an intermediate tap, or the intermediate tap is removed. The second transformer has a primary winding Np2 and at least one secondary winding Ns2; the primary winding Np2 has both ends, and the secondary winding Ns2 has both ends and an intermediate tap, or the intermediate tap is removed.

The two ends of the primary winding Np1 are respectively connected with a node Vs1 of the capacitor network and a node V1 of the conversion bridge, and the two ends of the primary winding Np2 are respectively connected with a node Vs2 of the capacitor network and a node V2 of the conversion bridge. Two ends of the secondary winding Ns1 are respectively connected with two alternating current input ends of the rectifier X; when the rectifier X adopts a full-wave rectification topology, the intermediate tap of Ns1 serves as a positive output terminal or a negative output terminal of the rectifier X; when rectifier X adopts a full bridge rectification topology, then the center tap of Ns1 is removed. Two ends of the secondary winding Ns2 are respectively connected with two alternating current input ends of the rectifier Y; when the rectifier Y adopts a full-wave rectification topology, the middle tap of the Ns2 is used as a positive output end or a negative output end of the rectifier Y; when rectifier Y adopts a full bridge rectification topology, then the center tap of Ns2 is removed.

The rectifier X and the rectifier Y adopt full-wave rectification topology or full-bridge rectification topology, and have a positive output end, a negative output end and two alternating current input ends. The internal diodes are connected in the same manner as the rectifiers described in the single transformer scheme, being two copies thereof.

The single filter, the filter X and the filter Y are all four-terminal networks and are provided with a positive input end and a negative input end, a positive output end and a negative output end. The internal network structure is the same as the filter described in the single transformer scheme.

The rectifier X is connected to the filter X and the rectifier Y is connected to the filter Y, constituting two sets of outputs, namely a first output and a second output. The concrete connection mode is as follows: the positive output end and the negative output end of the rectifier X are respectively connected with the positive input end and the negative input end of the filter X, and the positive output end and the negative output end of the filter X are respectively used as the positive end +Vo1 and the negative end-Vo1 of the first output of the converter. The positive output end and the negative output end of the rectifier Y are respectively connected with the positive input end and the negative input end of the filter Y, and the positive output end and the negative output end of the filter Y are respectively used as the positive end +Vo2 and the negative end-Vo2 of the second output of the converter. The first output and the second output can be supplied to the load independently, or in parallel or in series.

Alternatively, the rectifier X and the rectifier Y are connected together in a combined manner to form a set of outputs, and the positive output terminal and the negative output terminal of the filter are respectively used as the positive terminal +vo and the negative terminal-Vo of the output of the converter. The combination mode is divided into parallel combination and series combination. The parallel combination is as follows: the positive output ends of the rectifier X and the rectifier Y are commonly connected with the positive input end of the filter, and the negative output ends of the rectifier X and the rectifier Y are commonly connected with the negative input end of the filter; the series combination is as follows: the positive output end of the rectifier X and the negative output end of the rectifier Y are respectively connected with the positive input end and the negative input end of the filter.

To realize AC-DC bidirectional conversion or synchronous rectification, a switching tube is used for replacing the rectifier and diodes in the rectifier X and the rectifier Y; the replacement rule is that the source electrode and the drain electrode of the switch tube respectively correspond to the anode and the cathode of the diode. The bidirectional conversion means a switching conversion in which electric energy flows bidirectionally between an ac side and a dc side.

In order to reduce the direct current of the primary windings of the first and second transformers in the single and dual transformer schemes, two derivative circuits are proposed.

The first derivative circuit is that the primary windings of the transformer, the first transformer and the second transformer are connected in parallel with inductance, and the self inductance of the inductance connected in parallel is far smaller than that of the primary windings.

The second derivative circuit is to add an inductor at the primary winding position of the transformer and the primary windings of the first transformer and the second transformer, and the primary windings are connected with a capacitor in series.

Based on a single transformer scheme, the connection mode of the second derivative circuit is as follows: two ends of the inductor Lr are respectively connected with a node V1 of the conversion bridge and a node Vs of the capacitor network; one end of a primary winding Np of the transformer is connected with a node V1 of the conversion bridge, the other end of the primary winding Np is connected with one end of a capacitor Cr, and the other end of the capacitor Cr is connected with a node V2 or a positive end Vd or a ground end GND of the conversion bridge, or a node Vs of a capacitor network.

Based on the double-transformer scheme, the connection mode of the second derivative circuit is as follows: two ends of the inductor Lr1 are respectively connected with a node V1 of the conversion bridge and a node Vs1 of the capacitor network, one end of a primary winding Np1 of the first transformer is connected with the node V1 of the conversion bridge, the other end of the primary winding Np1 of the first transformer is connected with one end of the capacitor Cr1, and the other end of the capacitor Cr1 is connected with a positive end Vd or a ground end GND of the conversion bridge or a node Vs1 or a node Vs2 of the capacitor network; two ends of the inductor Lr2 are respectively connected with a node V2 of the conversion bridge and a node Vs2 of the capacitor network, one end of a primary winding Np2 of the second transformer is connected with the node V2 of the conversion bridge, the other end of the second transformer is connected with one end of the capacitor Cr2, and the other end of the capacitor Cr2 is connected with a positive end Vd or a ground end GND of the conversion bridge or is connected with a node Vs1 or a node Vs2 of the capacitor network.

There are two control methods for the bridgeless isolated AC-DC single-stage PFC converter. The first is single bridge arm PWM control, which is suitable for the single transformer scheme; the second type is double-bridge arm PWM control, which is suitable for the double-transformer scheme and is subdivided into two modes of frequency multiplication modulation and bipolar modulation.

Single bridge arm PWM control method

The second leg, which is formed by switching tubes Q3 and Q4, switches at a low frequency at the frequency of ac power supply Ua. In the positive half cycle of the ac power supply Ua, i.e. the voltage of the node Vs is higher than the voltage of the node V2, the upper switching tube Q4 is turned off and the lower switching tube Q3 is turned on; in the negative half cycle of the ac power supply Ua, i.e. the voltage at node Vs is lower than the voltage at node V2, the lower switching tube Q3 is turned off and the upper switching tube Q4 is turned on.

The first leg, which is formed by switching tubes Q1 and Q2, is high frequency converted under complementary PWM control. By complementary PWM is meant that the sum of the duty cycles of the switching transistors Q1 and Q2 is equal to 1, ignoring the dead time. Setting the on-duty ratio of the switching tubes Q1 and Q2 to be D respectively ₁ And D ₂ D is then ₁ +D ₂ ＝1。

Control law: during the positive half period of the ac power supply Ua, the output voltage of the converter is equal to D ₁ Is proportional to the average value of (a); during the negative half-cycle of the ac power supply Ua, the converterOutput voltage and D ₂ Is proportional to the average value of (a). And D is ₁ And D ₂ The instantaneous value of (2) is changed according to the power factor correction requirement, and the sinusoidal alternating voltage of the input current tracking power supply Ua is realized, so that the waveforms of the sinusoidal alternating voltage are consistent and the phases are the same.

The control flow is as follows:

on the direct current side, sampling an output variable, wherein the output variable is output voltage, output current or output power;

the output variable is filtered by a low-pass filter (bandwidth is less than 20 Hz) to remove second harmonic waves and high-frequency ripples;

comparing the filtered output variable with a given value to obtain an output variable error;

PID or PI adjustment is carried out on the output variable errors to obtain feedback variables;

and isolating the feedback variable and then negatively feeding back to the alternating current side.

Sampling alternating voltage and input current at the alternating side;

The alternating voltage sampling signal controls the low-frequency switching of the second bridge arm and is used as a waveform phase reference of the input current;

calculating the alternating voltage sampling signal and a feedback variable from an output side to obtain a reference value of input current;

comparing the reference value with an input current sampling signal to obtain an input current error;

PID or PI adjustment is carried out on the input current error, and a control quantity is obtained;

comparing the control quantity with the triangular wave to generate a pulse width modulation signal;

then dead time is inserted to form two paths of complementary PWM signals;

the two paths of complementary PWM signals drive the switching tubes Q1 and Q2 of the first bridge arm to perform high-frequency conversion.

Thus, the double closed loop feedback control is completed, so that the output variable is stably regulated and the power factor correction is realized.

Double bridge arm PWM control method

The first bridge arm and the second bridge arm of the conversion bridge are opened in the same wayThe off frequency is high frequency shifted under complementary PWM control. Setting the on duty ratio of the switching tubes Q1, Q2 and Q3, Q4 as D respectively ₁ 、D ₂ And D ₃ 、D ₄ . Ignoring dead time of switching transition, D ₁ +D ₂ ＝1＝D ₃ +D ₄ The method comprises the steps of carrying out a first treatment on the surface of the And requirement D ₄ ＝D ₁ And D ₃ ＝D ₂ 。

The bipolar modulation mode is that the switching tubes Q3 and Q4 are respectively synchronous (i.e. in phase) with the conduction driving pulse of the switching tubes Q2 and Q1; the frequency multiplication modulation mode is that the switching tubes Q3 and Q4 are respectively synchronous with the conduction driving pulse of the switching tubes Q1 and Q2. There are three alignment ways for PWM pulses in the frequency doubling modulation mode: center alignment, front edge alignment, back edge alignment.

Control law: the output voltage of the converter is equal to (D) ₁ ·D ₂ ) _min /|D ₁ -D ₂ | _max Proportional to (D) ₁ ·D ₂ ) _min Representation (D) ₁ ·D ₂ ) Is the minimum of, |D ₁ -D ₂ | _max Representation |D ₁ -D ₂ Maximum values of i, which occur at ac voltage u _a Positive and negative peak times of (a). And D is ₁ And D ₂ And the instantaneous value of (c) varies as required by power factor correction.

The control flow is as follows:

Sampling an alternating voltage and an input current on an alternating side, wherein the alternating voltage and the input current are used as waveform phase references of the input current;

Then dead time is inserted, phase shift is expanded, and four complementary PWM signals are formed;

the four paths of PWM signals respectively drive the switching tubes of the first bridge arm and the second bridge arm to carry out high-frequency conversion.

Compared with the prior art, the invention has the following advantages.

1) The invention relates to an isolated single-stage PFC conversion, which adopts a full-bridge topology, belongs to double-end conversion and can transmit high power.

2) The invention is divided into two schemes, a single transformer and a double transformer, the latter can output more power in various combination modes.

3) The invention has the advantages of simplified topology, no power frequency rectifier bridge, reduced cost, improved efficiency and enhanced reliability.

4) The invention has a wide output voltage range, and is suitable for both a voltage source mode and a current source mode.

5) The invention can adopt a plurality of control methods such as single-bridge arm PWM, double-bridge arm frequency multiplication or bipolar PWM, etc.

Drawings

Fig. 1 is a schematic diagram of a single transformer scheme for a bridgeless isolated AC-DC single stage PFC converter.

Fig. 2 is a schematic diagram of a rectifier employing a full wave rectification topology common cathode connection.

Fig. 3 is a schematic diagram of a rectifier employing a full wave rectification topology common anode connection.

Fig. 4 is a schematic diagram of a rectifier employing a full bridge rectifying topology.

Fig. 5 is a schematic diagram of a network topology of a filter.

Fig. 6 is a schematic diagram of two sets of outputs of a two-transformer scheme for a bridgeless isolated AC-DC single stage PFC converter.

Fig. 7 is a schematic diagram of the parallel output of a two-transformer scheme for a bridgeless isolated AC-DC single stage PFC converter.

Fig. 8 is a schematic diagram of a dual transformer scheme series output of a bridgeless isolated AC-DC single stage PFC converter.

Fig. 9 is a schematic diagram of the switching tubes of the conversion bridge of the single transformer scheme replaced by diodes.

Fig. 10 is a schematic diagram of a rectifier with diodes replaced by switching tubes for a single transformer scheme.

Fig. 11 is a schematic diagram of a first derivative circuit of a single transformer scheme.

Fig. 12 is a schematic diagram of a second derivative circuit of a single transformer scheme.

Reference numerals illustrate:

reference numerals	Name of the name	Reference numerals	Name of the name
				1	Input filter circuit	Cd、Cs、C1、C2、C3、C4、Cr	Capacitance device
2、20	Capacitor network	Lr	Inductance
				3	Conversion bridge	Np、Np1、Np2	Primary winding
4、41、42	Transformer	Ns、Ns1、Ns2	Secondary winding
				5、51、52	Rectifier device	Q1、Q2、Q3、Q4、Q5、Q6、Q7、Q8	Switch tube
6、61、62	Filter	D1、D2、D3、D4、D01、D02	Diode
				Lo1、Lo2	Filtering inductance	Vs、Vs1、Vs2、V1、V2、Vd、GND	Node symbol
Co	Filter capacitor	Ua	AC power supply

Detailed Description

The invention will be described and analyzed in detail below with reference to the drawings, in which preferred embodiments are shown. The described embodiments are only some, but not all, embodiments of the invention.

1. Preferred embodiments of the invention

There are two kinds of technical schemes of bridge-free isolated type AC-DC single-stage PFC converter. The first is a single transformer scheme, see fig. 1; the second is a double transformer solution, see fig. 6, 7, 8. The two technical schemes have the same input filter circuit (1) and a conversion bridge (3).

The input filter circuit (1) comprises common mode and differential mode inductances, an X capacitor and a Y capacitor, and is provided with two alternating current output ends.

The conversion bridge (3) comprises switching tubes Q1, Q2, Q3 and Q4, wherein the full-bridge topology is provided with two bridge arms, the switching tubes Q1 and Q2 form a first bridge arm, and the switching tubes Q3 and Q4 form a second bridge arm. The drain electrode of the switching tube Q1 is connected with the source electrode of the Q2 to serve as a node V1, and the drain electrode of the switching tube Q3 is connected with the source electrode of the Q4 to serve as a node V2; the drains of the switching tubes Q2 and Q4 are connected as the positive end Vd of the conversion bridge (3), and the sources of the switching tubes Q1 and Q3 are connected as the ground end GND of the conversion bridge (3). The switching tube is not limited to MOSFET or IGBT.

As shown in fig. 1, the single transformer scheme comprises an input filter circuit (1), a capacitor network (2), a conversion bridge (3), a transformer (4), a rectifier (5) and a filter (6), which are connected in sequence. The alternating current power supply Ua is connected with the input filter circuit (1), and two alternating current output ends of the input filter circuit (1) provide stable alternating current voltage; the filter (6) supplies the DC voltage with the high-frequency ripple filtered as the output of the inverter to a load.

The capacitor network (2) comprises capacitors Cd, cs, C1 and C2, which are thin film capacitors with smaller capacity instead of electrolytic capacitors with large capacity, in particular Cd. Two ends of a capacitor Cd are respectively connected with a positive end Vd and a ground end GND of the conversion bridge (3), and two ends of the capacitor Cs are respectively connected with two alternating current output ends of the input filter circuit (1); one end of the capacitor C1 and one end of the capacitor C2 are connected with one alternating current output end of the input filter circuit (1) to serve as a node Vs, the other end of the capacitor C1 is connected with the ground end GND of the conversion bridge (3), the other end of the capacitor C2 is connected with the positive end Vd of the conversion bridge (3), and the node V2 of the conversion bridge (3) is connected with the other alternating current output end of the filter circuit (1). Either the capacitors C1 and C2 or the capacitor Cs or the capacitor Cd are removed to simplify the circuit and reduce the cost, but the ripple current of each capacitor will change.

The transformer (4) has a primary winding Np and at least one secondary winding Ns. The primary winding Np has two ends, the secondary winding Ns has two ends and a center tap, or the center tap is removed.

One end of the primary winding Np is connected with a node Vs of the capacitor network (2), and the other end is connected with a node V1 of the conversion bridge (3). Two ends of the secondary winding Ns are respectively connected with two alternating current input ends of the rectifier (5); when the rectifier (5) adopts a full-wave rectification topology, the middle tap of Ns is used as a positive output end or a negative output end of the rectifier (5); when the rectifier (5) adopts a full bridge rectification topology, then the center tap of Ns is removed.

The rectifier (5) adopts a full-wave rectification topology or a full-bridge rectification topology and is provided with a positive output end, a negative output end and two alternating-current input ends. As shown in fig. 2, 3 and 4.

The full wave rectification topology includes diodes D1, D2 connected in two ways. The first type is called common cathode connection (see fig. 2), i.e. the cathodes of the diodes D1, D2 are connected together as the positive output of the rectifier (5), the anode of the diode D1 and the anode of the diode D2 are used as the two ac inputs of the rectifier (5), and the intermediate tap of the secondary winding Ns of the transformer (4) is used as the negative output of the rectifier (5). The second type is called common anode connection (see fig. 3), i.e. the anodes of the diodes D1, D2 are connected together as the negative output of the rectifier (5), the cathode of the diode D1 and the cathode of the diode D2 are used as the two ac inputs of the rectifier (5), and the intermediate tap of the secondary winding Ns of the transformer (4) is used as the positive output of the rectifier (5).

The full-bridge rectification topology (see fig. 4) comprises diodes D1, D2, D3 and D4, wherein the anode of the diode D1 is connected with the cathode of the diode D2 to serve as one alternating current input end of the rectifier (5), the anode of the diode D3 is connected with the cathode of the diode D4 to serve as the other alternating current input end of the rectifier (5), the cathodes of the diodes D1 and D3 are connected to serve as the positive output end of the rectifier (5), and the anodes of the diodes D2 and D4 are connected to serve as the negative output end of the rectifier (5).

The filter (6) comprises filter inductors Lo1 and Lo2 and a filter capacitor Co, forms a four-terminal network, and is provided with a positive input end, a negative input end, a positive output end and a negative output end, as shown in fig. 5. The two ends of the filter inductor Lo1 are respectively used as a positive input end and a positive output end of the filter (6), and the two ends of the filter inductor Lo2 are respectively used as a negative input end and a negative output end of the filter (6); the positive pole and the negative pole of the filter capacitor Co are respectively connected with the positive output end and the negative output end of the filter (6). The filter inductors Lo1 and Lo2 are independent or coupled, or Lo1 or Lo2 is removed to simplify the circuit; when Lo1 is removed, the positive input end and the positive output end of the filter (6) are directly connected, and when Lo2 is removed, the negative input end and the negative output end of the filter (6) are directly connected. Or the filter capacitor Co is removed to be suitable for the current source mode output. When Co is reserved, then it is the voltage source mode output.

The positive input end and the negative input end of the filter (6) are respectively connected with the positive output end and the negative output end of the rectifier (5), and the positive output end and the negative output end of the filter (6) are respectively used as the positive output end +vo and the negative output end-Vo of the converter.

As shown in fig. 9, for a single transformer solution, the switching tubes Q3, Q4 of the conversion bridge (3) can be replaced with two diodes D01, D02 in order to reduce costs (but increase losses). The anode of the diode D01 is connected with the ground end GND, the cathode of the diode D02 is connected with the positive end Vd, and the cathode of the diode D01 is connected with the anode of the diode D02 to serve as a node V2; meanwhile, the capacitors C1 and C2 of the capacitor network (2) are reserved, one ends of the capacitors C1 and C2 are commonly connected with the node Vs or the node V2, and the other ends of the capacitors C1 and C2 are respectively connected with the ground end GND and the positive end Vd.

For single transformer solutions, in order to reduce costs (but increase losses), the switching tubes Q3, Q4 of the conversion bridge (3) can be replaced with diodes D01, D02, respectively (see fig. 9), or the switching tubes Q3, Q4 of the conversion bridge (3) can be replaced with unidirectional thyristors S1, S2, respectively; the replacement rule is that the anode and the cathode of the diode or the unidirectional thyristor respectively correspond to the source electrode and the drain electrode of the switching tube. Meanwhile, the capacitors C1 and C2 of the capacitor network (2) are reserved, one ends of the capacitors C1 and C2 are commonly connected with the node Vs or the node V2, and the other ends of the capacitors C1 and C2 are respectively connected with the ground end GND and the positive end Vd. Supplementary explanation: the diode is an uncontrolled element, the unidirectional thyristor is a half-controlled and low-frequency element, and the switching tube is a full-controlled and high-frequency element.

As shown in fig. 6, 7, 8, the two-transformer scheme comprises an input filter circuit (1), a capacitor network (20), a conversion bridge (3), a first transformer (41), a second transformer (42), a rectifier X (51), a rectifier Y (52), a filter (6), or two filters, namely a filter X (61) and a filter Y (62). The alternating current power supply Ua is connected with the input filter circuit (1), and two alternating current output ends of the input filter circuit (1) provide stable alternating current voltage. Rectifier X (51) and rectifier Y (52) are connected with filter X (61) and filter Y (62) respectively to form two groups of outputs; alternatively, rectifier X (51) and rectifier Y (52) are jointly connected in combination with filter (6) to form a set of outputs.

The capacitor network (20) comprises capacitors Cs, cd, C1, C2, C3, C4, which all use thin film capacitors with smaller capacity rather than electrolytic capacitors with larger capacity, in particular Cd. Two ends of the capacitor Cs are respectively connected with two alternating current output ends of the input filter circuit (1), and two ends of the capacitor Cd are respectively connected with the positive end Vd and the ground end GND of the conversion bridge (3); one ends of the capacitors C1 and C3 are connected with one alternating current output end of the input filter circuit (1) to serve as a node Vs1, one ends of the capacitors C2 and C4 are connected with the other alternating current output end of the input filter circuit (1) to serve as a node Vs2, the other ends of the capacitors C1 and C2 are connected with the ground end GND of the conversion bridge (3), and the other ends of the capacitors C3 and C4 are connected with the positive end Vd of the conversion bridge (3). Either any two of C1, C2, C3, C4 are removed, either Cs or Cd are removed, or Cs and Cd are removed, to simplify the circuit and reduce cost, but circuit symmetry is reduced and ripple current of each capacitor will change.

The first transformer (41) has a primary winding Np1 and at least one secondary winding Ns1; the primary winding Np1 has both ends, and the secondary winding Ns1 has both ends and an intermediate tap, or the intermediate tap is removed. The second transformer (42) has a primary winding Np2 and at least one secondary winding Ns2; the primary winding Np2 has both ends, and the secondary winding Ns2 has both ends and an intermediate tap, or the intermediate tap is removed.

The two ends of the primary winding Np1 are respectively connected with a node Vs1 of the capacitor network (20) and a node V1 of the conversion bridge (3), and the two ends of the primary winding Np2 are respectively connected with a node Vs2 of the capacitor network (20) and a node V2 of the conversion bridge (3). Two ends of the secondary winding Ns1 are respectively connected with two alternating current input ends of the rectifier X (51); when the rectifier X (51) adopts a full-wave rectification topology, the center tap of Ns1 serves as a positive output terminal or a negative output terminal of the rectifier X (51); when rectifier X (51) adopts a full bridge rectification topology, then the center tap of Ns1 is removed. Two ends of the secondary winding Ns2 are respectively connected with two alternating current input ends of the rectifier Y (52); when the rectifier Y (52) adopts a full-wave rectification topology, the center tap of Ns2 serves as a positive output terminal or a negative output terminal of the rectifier Y (52); when rectifier Y (52) adopts a full bridge rectification topology, then the center tap of Ns2 is removed.

The rectifier X (51) and the rectifier Y (52) adopt a full-wave rectification topology or a full-bridge rectification topology, and have a positive output terminal, a negative output terminal and two ac input terminals.

The full-wave rectification topology comprises diodes D1 and D2, and the connection modes of the diodes D1 and D2 are two; the first connection mode is called common cathode connection, namely, the cathodes of the diodes D1 and D2 are connected together to serve as the positive output end of the rectifier, the anode of the diode D1 and the anode of the diode D2 serve as two alternating current input ends of the rectifier, the middle tap of the secondary winding Ns1 of the first transformer (41) serves as the negative output end of the rectifier X (51), and the middle tap of the secondary winding Ns2 of the second transformer (42) serves as the negative output end of the rectifier Y (52); the second connection mode is called common anode connection, that is, the anodes of the diodes D1 and D2 are connected together to serve as the negative output end of the rectifier, the cathode of the diode D1 and the cathode of the diode D2 serve as two alternating current input ends of the rectifier, the middle tap of the secondary winding Ns1 of the first transformer (41) serves as the positive output end of the rectifier X (51), and the middle tap of the secondary winding Ns2 of the second transformer (42) serves as the positive output end of the rectifier Y (52).

The filter X (61), the filter Y (62) and the filter (6) are four-terminal networks, and are provided with a positive input end, a negative input end, a positive output end and a negative output end, and comprise filter inductors Lo1 and Lo2 and a filter capacitor Co. Two ends of the filter inductor Lo1 are respectively used as a positive input end and a positive output end of the filter, and two ends of the filter inductor Lo2 are respectively used as a negative input end and a negative output end of the filter; the positive pole and the negative pole of filter capacitor Co are connected with the positive output end and the negative output end of the filter respectively. The filter inductors Lo1 and Lo2 are independent or coupled, or Lo1 or Lo2 is removed to simplify the circuit; when Lo1 is removed, the positive input end and the positive output end of the filter are directly connected, and when Lo2 is removed, the negative input end and the negative output end of the filter are directly connected. Or the filter capacitor Co is removed to be suitable for the current source mode output.

Rectifier X (51) and rectifier Y (52) are connected to filter X (61) and filter Y (62), respectively, to form two sets of outputs, namely rectifier X (51) is connected to filter X (61) to form a first output of the converter, and rectifier Y (52) is connected to filter Y (62) to form a second output of the converter, see fig. 6. The specific description is as follows: the positive output end and the negative output end of the rectifier X (51) are respectively connected with the positive input end and the negative input end of the filter X (61), and the positive output end and the negative output end of the filter X (61) are respectively used as a positive end +Vo1 and a negative end-Vo1 of the first output. The positive output end and the negative output end of the rectifier Y (52) are respectively connected with the positive input end and the negative input end of the filter Y (62), and the positive output end and the negative output end of the filter Y (62) are respectively used as a positive end +Vo2 and a negative end-Vo2 of the second output. The first output and the second output can be supplied to the load independently or in parallel or in series.

Alternatively, rectifier X (51) and rectifier Y (52) are jointly connected in combination with filter (6) to form a set of outputs, the positive and negative outputs of filter (6) being the positive +vo and negative-Vo of the converter output, respectively. The combination mode is divided into parallel combination and series combination. The parallel combination (see fig. 7) is: the positive output ends of the rectifier X (51) and the rectifier Y (52) are commonly connected with the positive input end of the filter (6), and the negative output ends of the rectifier X (51) and the rectifier Y (52) are commonly connected with the negative input end of the filter (6); the series combination (see fig. 8) is: the negative output end of the rectifier X (51) is connected with the positive output end of the rectifier Y (52), the positive output end of the rectifier X (51) is connected with the positive input end of the filter (6), and the negative output end of the rectifier Y (52) is connected with the negative input end of the filter (6).

To achieve AC-DC bi-directional conversion or synchronous rectification, the rectifier (5) and the diodes in the rectifier X (51) and the rectifier Y (52) are used by a switch Guan Tihuan, and the switch tube adopts, but is not limited to, a MOSFET or an IGBT; the replacement rule is that the source electrode and the drain electrode of the switch tube respectively correspond to the anode and the cathode of the diode. An example of a single transformer scheme is shown in fig. 10.

In order to reduce the direct current of the primary windings of the transformer (4) and the first (41) and second (42) transformers, two derivative circuits are proposed.

The first derivative circuit is characterized in that the primary windings of the transformer (4), the first transformer (41) and the second transformer (42) are connected in parallel by inductance, and the self inductance of the inductance connected in parallel is far smaller than that of the primary windings.

Based on a single transformer scheme, an inductor Lr is connected in parallel with a primary winding Np of a transformer (4), so that the self-inductance of the inductor Lr is far smaller than that of the primary winding Np. See fig. 11.

Based on a double-transformer scheme, an inductor Lr1 is connected in parallel with a primary winding Np1 of a first transformer (41), so that the self-inductance of the inductor Lr1 is far smaller than that of the primary winding Np 1; an inductor Lr2 is connected in parallel with the primary winding Np2 of the second transformer (42) so that the self inductance of the inductor Lr2 is much smaller than the self inductance of the primary winding Np 2.

The second derivative circuit is to add an inductor at the primary winding position of the transformer (4), the first transformer (41) and the second transformer (42), and the primary winding is connected with a capacitor in series.

Based on a single transformer scheme, the connection mode of the second derivative circuit is as follows: two ends of the inductor Lr are respectively connected with a node V1 of the conversion bridge (3) and a node Vs of the capacitor network (2); one end of a primary winding Np of the transformer (4) is connected with a node V1 of the conversion bridge (3), the other end of the primary winding Np is connected with one end of a capacitor Cr, and the other end of the capacitor Cr is connected with a node V2 or a positive end Vd or a ground end GND of the conversion bridge (3) or a node Vs of the capacitor network (2). See fig. 12.

Based on the double-transformer scheme, the connection mode of the second derivative circuit is as follows: two ends of the inductor Lr1 are respectively connected with a node V1 of the conversion bridge (3) and a node Vs1 of the capacitor network (20), one end of a primary winding Np1 of the first transformer (41) is connected with the node V1 of the conversion bridge (3), the other end of the primary winding Np1 is connected with one end of the capacitor Cr1, and the other end of the capacitor Cr1 is connected with a positive end Vd or a ground end GND of the conversion bridge (3) or is connected with the node Vs1 or a node Vs2 of the capacitor network (20); two ends of the inductor Lr2 are respectively connected with a node V2 of the conversion bridge (3) and a node Vs2 of the capacitor network (20), one end of a primary winding Np2 of the second transformer (42) is connected with the node V2 of the conversion bridge (3), the other end of the primary winding Np2 is connected with one end of the capacitor Cr2, and the other end of the capacitor Cr2 is connected with a positive end Vd or a ground end GND of the conversion bridge (3) or a node Vs1 or a node Vs2 of the capacitor network (20).

2. The control method of the invention

Single bridge arm PWM control method

The second leg, which is formed by switching tubes Q3 and Q4, is switched at a low frequency at the frequency of the sinusoidal ac power supply Ua. In the positive half period of the sinusoidal alternating current power supply Ua, that is, the voltage of the node Vs is higher than the voltage of the node V2, the switching tube Q4 at the upper part is turned off and the switching tube Q3 at the lower part is turned on; in the negative half cycle of the sinusoidal ac power supply Ua, i.e. the voltage at node Vs is lower than the voltage at node V2, the lower switching tube Q3 is turned off and the upper switching tube Q4 is turned on.

Control law: at the position ofThe positive half period of the sinusoidal alternating current source Ua, the output voltage of the converter being equal to D ₁ Is proportional to the average value of (a); during the negative half period of the sinusoidal ac power supply Ua, the output voltage of the converter is equal to D ₂ Is proportional to the average value of (a). And D is ₁ And D ₂ The instantaneous value of (2) is changed according to the power factor correction requirement, and the sinusoidal alternating voltage of the input current tracking power supply Ua is realized, so that the waveforms of the sinusoidal alternating voltage are consistent and the phases are the same.

The control flow is as follows:

On the AC side, an AC voltage u is sampled _a And input current i _a ；

then dead time is inserted to form two paths of complementary PWM signals;

Double bridge arm PWM control method

The first bridge arm and the second bridge arm of the conversion bridge (3) are subjected to high-frequency conversion under complementary PWM control at the same switching frequency. Setting the on duty ratio of the switching tubes Q1, Q2 and Q3, Q4 as D respectively ₁ 、D ₂ And D ₃ 、D ₄ . Ignoring dead time of switching transition, D ₁ +D ₂ ＝1＝D ₃ +D ₄ The method comprises the steps of carrying out a first treatment on the surface of the And requirement D ₄ ＝D ₁ And D ₃ ＝D ₂ 。

When the switching transistors Q3, Q4 are synchronized (i.e., in phase) with the on-drive pulses of Q2, Q1, respectively, they are called bipolar modulation; when the switching transistors Q3, Q4 are synchronized with the on driving pulses of Q1, Q2, respectively, it is called frequency doubling modulation. The frequency multiplication modulation PWM pulse has three alignment modes, namely center alignment, front edge alignment and back edge alignment.

The control flow is as follows:

On the AC side, an AC voltage u is sampled _a And input current i _a The former is used as a waveform phase reference of the input current;

For synchronous rectification, the rectifier is required to be synchronized with the driving pulse of the switching tubes in the conversion bridge, and the on-duty ratio of the former is slightly smaller than that of the latter. That is, the rising edge of the driving pulse of the former is slightly delayed from the latter, and the falling edge of the driving pulse of the former is slightly advanced from the latter, and the delay/advance time is precisely controlled and kept stable.

For AC-DC bidirectional conversion, two working conditions of rectification and inversion are divided. If the electric energy flows from AC to DC, the electric energy is in a rectification working condition; and if the electric energy flows from DC to AC, the electric energy is in an inversion working condition.

Under the rectifying working condition, the switching tube of the rectifier works in a synchronous rectifying state, and the requirements of driving pulses of the rectifier and the conversion bridge are the same as those of the synchronous rectification.

Under inversion conditions, the roles of the rectifier and the conversion bridge are exchanged, namely, the function of the rectifier is conversion, and the function of the conversion bridge is rectification. Because the rectifier is connected with the inductor in the filter at first, the direct-current side input of the inversion working condition is a current source, and the conduction driving pulse of the upper pipe and the lower pipe of the bridge arm needs to have overlapping time. And the overlapping time is opposite to the rule of dead time, the upper and lower tubes of the bridge arm are turned off in the dead time, and the upper and lower tubes of the bridge arm are turned on in the overlapping time. Therefore, new requirements are placed on the driving pulses of the rectifier and the conversion bridge.

For the inversion conditions, the rectifier is required to be synchronized with the driving pulse of the switching tube in the conversion bridge, and the conduction duty ratio of the former is slightly larger than that of the latter. That is, the rising edge of the driving pulse of the former leads the latter, and the falling edge of the driving pulse of the former lags the latter. The lead/lag time is precisely controlled and kept stable so that the overlap time of the legs of the rectifier is equal to (or slightly less than) the dead time of the legs of the conversion bridge.

3. Working principle of single transformer scheme

The single-transformer scheme of the converter adopts single-bridge arm PWM control, and the working principle is described in detail below.

3.1 average value of transformation ratio and output voltage of transformer

As shown in FIG. 1, voltages between nodes Vs, V1, V2, vd and GND are set to be u, respectively _s 、u ₁ 、u ₂ 、u _d 。u _d Referred to as bus voltage; the voltage between nodes Vs and V2 is denoted as u _a ，u _a The sinusoidal alternating voltage of the alternating current power supply Ua on the capacitor Cs after the alternating current power supply Ua passes through the input filter circuit; the voltage between nodes Vs and V1 is denoted as u _p ，u _p I.e. the voltage of the primary winding Np of the transformer.

After the power supply Ua passes through the input filter circuit, a stable sinusoidal alternating voltage u is formed on the capacitor Cs _a 。

In U _R Is u _a Is effective value of omega is u _a A kind of electronic device angular frequency.

The second bridge arm formed by the switching tubes Q3 and Q4 is switched at a low frequency by the frequency of the sinusoidal alternating current power supply Ua; the first leg, which is formed by switching tubes Q1 and Q2, is high frequency converted under complementary PWM control. u (u) _p And u is equal to _a The relation of (2) is:

u _p ＝u _a +(u ₂ -u ₁ ) (E-2)

in the positive half period of the sinusoidal alternating current power supply Ua, namely 0 < ωt less than or equal to pi, u _a > 0, switch Q4 is off and Q3 is on, u ₂ =0. U when the switching tube Q2 is off and Q1 is on ₁ =0, then u _p ＝u _a The method comprises the steps of carrying out a first treatment on the surface of the U when the switching tube Q1 is turned off and Q2 is turned on ₁ ＝u _d U is _p ＝u _a -u _d 。

In the negative half period of the sinusoidal AC power supply Ua, i.e. pi < ωt.ltoreq.2pi, u _a < 0, switch Q3 is off and Q4 is on, u ₂ ＝u _d . U when the switching tube Q2 is off and Q1 is on ₁ =0, then u _p ＝u _a +u _d The method comprises the steps of carrying out a first treatment on the surface of the U when the switching tube Q1 is turned off and Q2 is turned on ₁ ＝u _d U is _p ＝u _a 。

In order to simplify analysis, the conduction voltage drops of the switching tubes Q1, Q2, Q3 and Q4 are ignored, and the dead time of on-off switching of the switching tubes Q1 and Q2 is ignored. Setting the on duty ratio of the switching tube Q1 as D ₁ The on duty ratio of the switch tube Q2 is D ₂ D is then ₁ +D ₂ =1. According to the balance principle of the voltage second value of the switch transformation, the voltage u is obtained _a And u is equal to _d Is a relation of (3).

Taking a full-bridge rectification topology of a rectifier as an example (see FIG. 4), the DC output voltage V is analyzed _o With sinusoidal alternating voltage u _a Is a relationship of (3). V (V) _o The voltage between +vo and-Vo is the voltage on the filter capacitor Co of the filter. Let the transformation ratio of the secondary winding Ns and the primary winding Np of the transformer be n.

Ignoring the voltage drop of the rectifier, the average value V of the positive and negative output voltages (i.e. the rectified voltage) _R The method comprises the following steps:

the combination of formula (E-3), formula (E-4) and formula (E-1) gives V _R And u _d Is a unified parsing formula of (1).

Output voltage V of rectifier _R After passing through the filter, the DC output voltage V is obtained _o 。V _o Can be decomposed into DC components (i.e. average)And AC component->

As can be seen from equation (E-5), after the transformation ratio n is determined, the voltage V _R And u is equal to _a Two variables are related to D. If V is to be made _R For pure direct current, it is required that D is inversely proportional to |sin (ωt) |; and D varies in the range of 0 < D < 1, V _R And cannot be pure direct current, which contains a certain alternating current component. The converter therefore needs to adjust the average value of D to stabilize V _o While the instantaneous value of D is controlled in accordance with the requirements of Power Factor Correction (PFC).

How does n determine then? This requires a constraint-defining the bus voltage u _d Maximum peak of (2)Because the capacitance network adopts a small capacitance, the capacitor network is +.>Appears at an alternating voltage u _a Peak time of (2). The voltage withstand value of the switching tubes Q1 to Q4 is V _DS Let->A is referred to as a pressure-resistant utilization ratio, and a=0.85 to 0.8 is generally taken.

Derived from formula (E-5) and formula (E-1):

theoretical analysis and simulation experiments prove that: when outputting (keeping Co) with a voltage source, the alternating voltage u _a V corresponding to peak time _R Instantaneous value equal to average value of output voltageWhen outputting (Co removal) with a current source, the alternating voltage u _a V corresponding to peak time _R Instantaneous value is equal to peak value of output voltage +.>

Setting an alternating voltage u _a Is in the range of [ U ] _R-m ,U _R-M ]，U _R-m And U _R-M U respectively _a A minimum significant value and a maximum significant value of (a). A unified relation of the transformation ratio n and the output voltage is obtained according to the formula (E-7) and the formula (E-5):

in the method, in the process of the invention,and->Respectively the average value and the peak value of the output voltage, +.>And->Respectively the maximum average value and the maximum peak value of the output voltage; d (D) _m Is a valid value U _R The corresponding minimum characterizing duty cycle, which occurs at u _a Peak time. />

Description: considering diode drop, dead time, efficiency, etc., the actual value of the transformation ratio n should be slightly greater than the theoretical value given by equation (E-8).

Similar analytical conclusions can be drawn when the rectifier adopts a full wave rectification topology.

3.3 Power factor correction and AC component of output Voltage

Meanwhile, the converter also realizes PFC function (Power Factor Correction-power factor correction). PFC is the alternating current i _a Tracking ac voltage u _a So that the waveforms are identical and phase-identical, thereby achieving a high power factor. In theory, the power factor PF is less than or equal to 1. When pf=1, there are:

In the formula (E-13), I _R For alternating current i _a Is effective. Assuming the efficiency of the converter is eta, the AC input power P is _a And DC output power P _o The method comprises the following steps of:

will output power P _o Into DC componentsAdd ac component->The form of (2):

the output voltage V is analyzed by taking the voltage source output and the resistor load as examples _o Is included in the power supply. Because the load containing the reactance component (inductive reactance or capacitive reactance) is connected in parallel with the filter capacitor, the parallel model of the capacitor and the resistor can be equivalent.

DC output voltage V _o Can be decomposed into DC componentsAdd ac component->In the form of (a), namely:

according to the law of conservation of energy, the linear superposition theorem and the circuit theory, the following differential equation is obtained:

wherein C is _o R is filter capacitance _o Is the load resistance. Taking into account thatThe formula (E-17) is simplified as:

solving for (E-18)Differential equation, can obtain AC componentThe expression of (2) is as follows:

as can be seen from (E-19), the AC component of the output voltage of a single stage PFC converterIs 2 times the angular frequency of the input ac voltage and is therefore called the second harmonic. Increasing the filter capacitance Co can reduce the second harmonic but cannot be completely eliminated. If the second harmonic is to be completely eliminated, additional technical means are required. / >

4. Working principle of double-transformer scheme

The double-transformer scheme of the converter adopts double-bridge arm frequency multiplication PWM control or double-bridge arm bipolar PWM control, and the working principle is described in detail below.

4.1 bus voltage, rectified voltage vs. duty cycle

As shown in fig. 6 to 8, voltages between the nodes Vs1, vs2, V1, V2, vd and GND are denoted as u, respectively _s1 、u _s2 、u ₁ 、u ₂ 、u _d 。u _d Referred to as bus voltage; the voltage between nodes Vs1 and Vs2 is denoted as u _a ，u _a I.e. the sinusoidal ac voltage of the ac power supply Ua after filtering. The voltage between nodes Vs1 and V1 is denoted as u _p1 ，u _p1 Namely the voltage of the primary winding Np1 of the first transformer; the voltage between nodes Vs2 and V2 is denoted as u _p2 ，u _p2 I.e. the voltage of the primary winding Np2 of the second transformer. U is then _a 、u _p1 、u _p2 And u is equal to _s1 、u _s2 The relation of (2) is:

u _a ＝u _s1 -u _s2 ,u _p1 ＝u _s1 -u ₁ ,u _p2 ＝u _s2 -u ₂ (E-20)

introducing a virtual midpoint voltage u _m The following relationship is given:

the first bridge arm and the second bridge arm are subjected to high-frequency conversion under complementary PWM control at the same switching frequency. First, the working conditions of the first bridge arm and the first transformer are analyzed. U when the switching tube Q2 is off and Q1 is on ₁ =0, then u _p1 ＝u _s1 The method comprises the steps of carrying out a first treatment on the surface of the U when the switching tube Q1 is turned off and Q2 is turned on ₁ ＝u _d U is _p1 ＝u _s1 -u _d 。

To simplify the analysis, the conduction voltage drops of the switching transistors Q1, Q2 are ignored, and the dead time of the bridge arm conversion is ignored. Setting the on duty ratio of the switching tube Q1 as D ₁ The on duty ratio of the switch tube Q2 is D ₂ D is then ₁ +D ₂ =1. According to the principle of the switching transformed volt-second value balance, the primary winding Np1 of the first transformer satisfies the following relation.

u _s1 ·D ₁ +(u _s1 -u _d )·D ₂ ＝0 (E-22)

The analysis is performed below using a full bridge rectifier topology (see fig. 4) for rectifier X as an example. Let the transformation ratio of the secondary winding Ns1 and the primary winding Np1 of the first transformer be n ₁ 。

Neglecting the voltage drop of the rectifier X, the average value V of the rectified output voltage thereof _R1 The method comprises the following steps:

V _R1 ＝(u _s1 ·D ₁ +(u _d -u _s1 )·D ₂ )·n ₁ (E-23)

the combination of formula (E-23), formula (E-22) and formula (E-21) gives:

and then analyzing the working conditions of the second bridge arm and the second transformer. When the switch tubeU when Q4 is off and Q3 is on ₂ =0, then u _p2 ＝u _s2 The method comprises the steps of carrying out a first treatment on the surface of the U when the switching tube Q3 is off and Q4 is on ₂ ＝u _d U is _p2 ＝u _s2 -u _d 。

Likewise, the conduction voltage drop of the switching transistors Q3, Q4 and the dead time of the bridge arm conversion are ignored. Setting the on duty ratio of the switching tube Q3 as D ₃ The on duty ratio of the switch tube Q4 is D ₄ D is then ₃ +D ₄ =1. According to the principle of the switching transformed volt-second value balance, the primary winding Np2 of the second transformer satisfies the following relation.

u _s2 ·D ₃ +(u _s2 -u _d )·D ₄ ＝0 (E-25)

Likewise, rectifier Y also employs a full bridge rectification topology, see FIG. 4. Let the transformation ratio of the secondary winding Ns2 and the primary winding Np2 of the second transformer be n ₂ 。

Similarly, ignoring the voltage drop of the rectifier Y, the average value V of the rectified output voltage thereof _R2 The method comprises the following steps:

V _R2 ＝(u _s2 ·D ₃ +(u _d -u _s2 )·D ₄ )·n ₂ (E-26)

the combination of formula (E-26), formula (E-25) and formula (E-21) gives:

setting the same rectified voltage average value V _R And a transformation ratio n.

V _R2 ＝V _R1 ＝V _R ,n ₁ ＝n ₂ ＝n (E-28)

The union formula (E-28) and the formulas (E-27) and (E-24) are derived:

solving a quadratic equation of (E-29), only D ₃ ＝1-D ₁ Meets the actual engineering requirements, namely:

substituting formula (E-30) into formulas (E-27) and (E-24) to derive:

u _m ＝u _d /2 (E-31)

4.2 combination of outputs and transformation ratio n of transformer

The rectifier X and rectifier Y may be connected to the filter X and filter Y, respectively, to form two sets of outputs, see fig. 6. The two sets of dc outputs can be supplied to the loads independently, or in parallel or in series.

The rectifier X and the rectifier Y can be connected with a filter together in a combined mode to form a group of outputs; the combination mode is divided into parallel combination and serial combination, and is shown in fig. 7 and 8.

Rectified voltage V _R Or a combination thereof, after passing through the filter, a DC output voltage V is obtained _o ；V _o Can be decomposed into DC components (i.e. average)And AC component->

As can be seen from formula (E-32), the converter requires adjustment of D ₁ To stabilize the output voltage V _o D, D ₁ And is controlled in accordance with the Power Factor Correction (PFC) requirements.

The same idea as the single transformer scheme is based on limiting the maximum peak value of the bus voltage The constraint of "determines the transformation ratio n of transformer X and transformer Y. Because the capacitance network adopts a small capacitance, the capacitor network is +.>Appears at an alternating voltage u _a Is a peak time of (a). Here again, the withstand voltage values of the switching transistors Q1 to Q4 are set to V _DS Let->A is referred to as a pressure-resistant utilization ratio, and a=0.85 to 0.8 is generally taken.

From formula (E-32) and formula (E-1):

/>

simulation analysis and theoretical derivation prove that: when outputting (keeping Co) with a voltage source, the alternating voltage u _a V corresponding to peak time _R Instantaneous value equal to average value of output voltageWhen outputting (Co removal) with a current source, the alternating voltage u _a V corresponding to peak time _R Instantaneous value is equal to peak value of output voltage +.>

The unified formula of the time-varying ratio n and the output voltage is independently or in parallel output, which is obtained by the formulas (E-33) and (E-32).

In the method, in the process of the invention,and->Respectively the average value and the peak value of the output voltage, +.>And->Respectively the maximum average value and the maximum peak value of the output voltage; u (U) _R-M Is an alternating voltage u _a Is the maximum effective value of (2); (D) ₁ ·D ₂ ) _min And |D ₁ -D ₂ | _max Respectively represent (D) ₁ ·D ₂ ) Sum of minima of (D) ₁ -D ₂ Maximum value of i, which occurs at u _a Positive and negative peak times of (a).

Description 1: considering dead time, diode drop, and efficiency, the actual value of the transformation ratio n should be slightly greater than the theoretical value given by equation (E-34).

Description 2: the formulas (E-34) and (E-35) are values when they are outputted independently or in parallel. When output in series, the transformation ratio n of the formula (E-34) is halved, the formula (E-35)And->Doubling.

When rectifier X and rectifier Y employ a full wave rectification topology, they can be analyzed similarly.

The power factor correction and the ac component of the output voltage of the dual transformer scheme can be concluded to be similar to the single transformer scheme.

5. Description of two derived circuits

The primary winding of the transformer has the function of boosting inductance, and the current i of the primary winding _p Not only has an alternating current component but also has a direct current component, the direct current component and the alternating current componentThe components are approximately half of each other. In order to reduce the direct current component of the primary winding current of the transformer, two derivative circuits are proposed.

The first derivative circuit is that the primary winding of the transformer is connected with an inductor in parallel, and the self inductance of the inductor in parallel is far smaller than that of the primary winding. Fig. 11 is an example of a single transformer scheme shunt inductance. The quantitative relation of the self-inductance is as follows:

wherein L is _r Is the self-inductance of the parallel inductance,for the self inductance of the primary winding required after the inductance is connected in parallel, L _p Is the self inductance of the primary winding required when no inductance is connected in parallel.

The first derivative circuit may reduce the dc component of the primary winding current of the transformer to approximately one tenth of the original. To further reduce the dc component, a second derivative circuit may be used.

The second derivative circuit is to add an inductor at the position of the primary winding of the transformer, and the primary winding is connected with a capacitor in series. Fig. 12 is an example of a second derivative circuit of a single transformer scheme. The quantitative relation between inductance and capacitance is:

wherein C is _r Is the capacity of the series capacitance,is the capacity of the capacitor Cs required after the series capacitance, C _s Is the capacity of the capacitor Cs required without a series capacitance.

The foregoing description is only of the preferred embodiments of the present invention, and is not intended to limit the scope of the invention, but rather, the equivalent topology changes made by the description and drawings of the present invention, or the direct or indirect application in other related technical fields, are included in the scope of the invention.

Claims

1. A bridgeless isolated AC-DC single-stage PFC converter is a single transformer scheme, and comprises an input filter circuit (1), a capacitor network (2), a conversion bridge (3), a transformer (4), a rectifier (5) and a filter (6), which are sequentially connected; the input filter circuit (1) comprises a common mode inductance, a differential mode inductance, an X capacitor and a Y capacitor, and is provided with two alternating current output ends; the alternating current power supply Ua is connected with the input filter circuit (1), and two alternating current output ends of the input filter circuit (1) provide stable alternating current voltage; the filter (6) supplies the DC voltage with the high-frequency ripple filtered as the output of the converter to the load; the method is characterized in that:

The conversion bridge (3) comprises switching tubes Q1, Q2, Q3 and Q4, wherein the conversion bridge is of a full-bridge topology and is provided with two bridge arms, the switching tubes Q1 and Q2 form a first bridge arm, and the switching tubes Q3 and Q4 form a second bridge arm; the drain electrode of the switching tube Q1 is connected with the source electrode of the Q2 to serve as a node V1, and the drain electrode of the switching tube Q3 is connected with the source electrode of the Q4 to serve as a node V2; the drains of the switching tubes Q2 and Q4 are connected to serve as the positive end Vd of the conversion bridge (3), and the sources of the switching tubes Q1 and Q3 are connected to serve as the ground end GND of the conversion bridge (3);

the capacitor network (2) comprises capacitors Cd, cs, C1 and C2, and the capacitors adopt thin film capacitors with smaller capacity instead of electrolytic capacitors with large capacity; two ends of a capacitor Cd are respectively connected with a positive end Vd and a ground end GND of the conversion bridge (3), and two ends of the capacitor Cs are respectively connected with two alternating current output ends of the input filter circuit (1); one end of the capacitor C1 and one end of the capacitor C2 are connected with one alternating current output end of the input filter circuit (1) to serve as a node Vs, the other end of the capacitor C1 is connected with the ground end GND of the conversion bridge (3), the other end of the capacitor C2 is connected with the positive end Vd of the conversion bridge (3), and the node V2 of the conversion bridge (3) is connected with the other alternating current output end of the filter circuit (1); either capacitances C1 and C2, or capacitance Cs, or capacitance Cd;

the transformer (4) has a primary winding Np and at least one secondary winding Ns; the primary winding Np has two ends, the secondary winding Ns has two ends and a center tap, or the center tap is removed; one end of the primary winding Np is connected with a node Vs of the capacitor network (2), and the other end is connected with a node V1 of the conversion bridge (3); two ends of the secondary winding Ns are respectively connected with two alternating current input ends of the rectifier (5); when the rectifier (5) adopts a full-wave rectification topology, the middle tap of Ns is used as a positive output end or a negative output end of the rectifier (5); when the rectifier (5) adopts a full-bridge rectification topology, removing a middle tap of Ns;

The rectifier (5) adopts full-bridge rectification topology or full-wave rectification topology and is provided with a positive output end, a negative output end and two alternating current input ends; the full-bridge rectification topology adopted by the rectifier (5) comprises diodes D1, D2, D3 and D4, wherein the anode of the diode D1 is connected with the cathode of the diode D2 to serve as one alternating current input end of the rectifier (5), the anode of the diode D3 is connected with the cathode of the diode D4 to serve as the other alternating current input end of the rectifier (5), the cathodes of the diodes D1 and D3 are connected to serve as the positive output end of the rectifier (5), and the anodes of the diodes D2 and D4 are connected to serve as the negative output end of the rectifier (5);

the full-wave rectification topology adopted by the rectifier (5) comprises diodes D1 and D2, and the connection modes of the diodes D1 and D2 are two; the first connection mode is called common cathode connection, namely, the cathodes of the diodes D1 and D2 are connected together to serve as the positive output end of the rectifier (5), the anode of the diode D1 and the anode of the diode D2 serve as two alternating current input ends of the rectifier (5), and the middle tap of the secondary winding Ns of the transformer (4) serves as the negative output end of the rectifier (5); the second connection mode is called common anode connection, namely the anodes of the diodes D1 and D2 are connected together to serve as the negative output end of the rectifier (5), the cathode of the diode D1 and the cathode of the diode D2 serve as two alternating current input ends of the rectifier (5), and the middle tap of the secondary winding Ns of the transformer (4) serves as the positive output end of the rectifier (5);

The filter (6) comprises filter inductors Lo1 and Lo2 and a filter capacitor Co to form a four-terminal network, and is provided with a positive input end, a negative input end, a positive output end and a negative output end; the two ends of the filter inductor Lo1 are respectively used as a positive input end and a positive output end of the filter (6), the two ends of the filter inductor Lo2 are respectively used as a negative input end and a negative output end of the filter (6), and the positive pole and the negative pole of the filter capacitor Co are respectively connected with the positive output end and the negative output end of the filter (6); the filter inductors Lo1 and Lo2 are independent or coupled, or Lo1 or Lo2 is removed; when Lo1 is removed, the positive input end and the positive output end of the filter (6) are directly connected, and when Lo2 is removed, the negative input end and the negative output end of the filter (6) are directly connected; or the filter capacitor Co is removed so as to be suitable for current source mode output;

2. A bridgeless isolated AC-DC single stage PFC converter according to claim 1, wherein: in the single transformer scheme, diodes D01 and D02 are used for respectively replacing switching tubes Q3 and Q4 of a conversion bridge (3), or unidirectional thyristors S1 and S2 are used for respectively replacing switching tubes Q3 and Q4 of the conversion bridge (3), and the replacement rule is that the anode and the cathode of the diodes or the unidirectional thyristors respectively correspond to the source electrode and the drain electrode of the switching tubes; meanwhile, capacitors C1 and C2 of the capacitor network (2) are reserved, one ends of the capacitors C1 and C2 are commonly connected with a node Vs of the capacitor network (2) or a node V2 of the conversion bridge (3), and the other ends of the capacitors C1 and C2 are respectively connected with a ground end GND and a positive end Vd of the conversion bridge (3).

3. A bridgeless isolated AC-DC single stage PFC converter according to claim 1, wherein: in the single transformer scheme, a diode in the rectifier (5) is replaced by a switching tube, and the replacement rule is that the source electrode and the drain electrode of the switching tube respectively correspond to the anode and the cathode of the diode.

4. A bridgeless isolated AC-DC single stage PFC converter according to claim 1, wherein: there are two derivative circuits based on a single transformer scheme; the first derivative circuit is that a primary winding Np of a transformer (4) is connected with an inductor Lr in parallel, and the self-inductance of the inductor Lr is far smaller than that of the primary winding Np; the second derivative circuit is to add an inductance Lr at the position of the primary winding Np of the transformer (4), and the primary winding Np is connected with a capacitor Cr in series, and the specific connection mode is as follows: two ends of the inductor Lr are respectively connected with a node V1 of the conversion bridge (3) and a node Vs of the capacitor network (20), one end of the primary winding Np is connected with the node V1 of the conversion bridge (3), the other end of the primary winding Np is connected with one end of the capacitor Cr, and the other end of the capacitor Cr is connected with a node V2 or a positive end Vd or a ground end GND of the conversion bridge (3) or the node Vs of the capacitor network (20).

5. A bridgeless isolated AC-DC single-stage PFC converter is a double-transformer scheme, and comprises an input filter circuit (1), a capacitor network (20), a conversion bridge (3), a first transformer (41), a second transformer (42), a rectifier X (51), a rectifier Y (52), a filter (6) or two filters, namely a filter X (61) and a filter Y (62); the input filter circuit (1) comprises a common mode inductance, a differential mode inductance, an X capacitor and a Y capacitor, and is provided with two alternating current output ends; the alternating current power supply Ua is connected with the input filter circuit (1), and two alternating current output ends of the input filter circuit (1) provide stable alternating current voltage; the method is characterized in that:

the capacitor network (20) comprises capacitors Cs, cd, C1, C2, C3 and C4, which are thin film capacitors with smaller capacity instead of electrolytic capacitors with large capacity; two ends of the capacitor Cs are respectively connected with two alternating current output ends of the input filter circuit (1), and two ends of the capacitor Cd are respectively connected with the positive end Vd and the ground end GND of the conversion bridge (3); one ends of the capacitors C1 and C3 are connected with one alternating current output end of the input filter circuit (1) to serve as a node Vs1, one ends of the capacitors C2 and C4 are connected with the other alternating current output end of the input filter circuit (1) to serve as a node Vs2, the other ends of the capacitors C1 and C2 are connected with the ground end GND of the conversion bridge (3), and the other ends of the capacitors C3 and C4 are connected with the positive end Vd of the conversion bridge (3); either any two of the capacitances C1, C2, C3, C4 are removed, either the capacitance Cs is removed, or the capacitance Cd is removed, or both the capacitances Cs and Cd are removed;

The first transformer (41) has a primary winding Np1 and at least one secondary winding Ns1; the primary winding Np1 has both ends, the secondary winding Ns1 has both ends and an intermediate tap, or the intermediate tap is removed; the second transformer (42) has a primary winding Np2 and at least one secondary winding Ns2; the primary winding Np2 has both ends, the secondary winding Ns2 has both ends and an intermediate tap, or the intermediate tap is removed;

two ends of the primary winding Np1 are respectively connected with a node Vs1 of the capacitor network (20) and a node V1 of the conversion bridge (3), and two ends of the primary winding Np2 are respectively connected with a node Vs2 of the capacitor network (20) and a node V2 of the conversion bridge (3); two ends of the secondary winding Ns1 are respectively connected with two alternating current input ends of the rectifier X (51); when the rectifier X (51) adopts a full-wave rectification topology, the center tap of Ns1 serves as a positive output terminal or a negative output terminal of the rectifier X (51); when the rectifier X (51) adopts a full-bridge rectification topology, the middle tap of the Ns1 is removed; two ends of the secondary winding Ns2 are respectively connected with two alternating current input ends of the rectifier Y (52); when the rectifier Y (52) adopts a full-wave rectification topology, the center tap of Ns2 serves as a positive output terminal or a negative output terminal of the rectifier Y (52); when the rectifier Y (52) adopts a full-bridge rectification topology, the middle tap of the Ns2 is removed;

The rectifier X (51) and the rectifier Y (52) adopt full-wave rectification topology or full-bridge rectification topology, and are provided with a positive output end, a negative output end and two alternating current input ends; the full-bridge rectification topology adopted by the rectifier X (51) and the rectifier Y (52) comprises diodes D1, D2, D3 and D4, wherein the anode of the diode D1 is connected with the cathode of the diode D2 to serve as one alternating current input end of the rectifier, the anode of the diode D3 is connected with the cathode of the diode D4 to serve as the other alternating current input end of the rectifier, the cathodes of the diodes D1 and D3 are connected to serve as the positive output end of the rectifier, and the anodes of the diodes D2 and D4 are connected to serve as the negative output end of the rectifier;

the full-wave rectification topology adopted by the rectifier X (51) and the rectifier Y (52) comprises diodes D1 and D2, and the connection modes of the diodes D1 and D2 are two; the first connection mode is called common cathode connection, namely, the cathodes of the diodes D1 and D2 are connected together to serve as the positive output end of the rectifier, the anode of the diode D1 and the anode of the diode D2 serve as two alternating current input ends of the rectifier, the middle tap of the secondary winding Ns1 of the first transformer (41) serves as the negative output end of the rectifier X (51), and the middle tap of the secondary winding Ns2 of the second transformer (42) serves as the negative output end of the rectifier Y (52); the second connection mode is called common anode connection, namely, anodes of diodes D1 and D2 are connected together to serve as negative output ends of a rectifier, a cathode of the diode D1 and a cathode of the diode D2 serve as two alternating current input ends of the rectifier, a middle tap of a secondary winding Ns1 of a first transformer (41) serves as a positive output end of a rectifier X (51), and a middle tap of a secondary winding Ns2 of a second transformer (42) serves as a positive output end of a rectifier Y (52);

The filter X (61) and the filter Y (62) are four-terminal networks as the filter (6) and are provided with a positive input end and a negative input end, a positive output end and a negative output end; all comprise filter inductors Lo1 and Lo2 and a filter capacitor Co; two ends of the filter inductor Lo1 are respectively used as a positive input end and a positive output end of the filter, and two ends of the filter inductor Lo2 are respectively used as a negative input end and a negative output end of the filter; the positive electrode and the negative electrode of the filter capacitor Co are respectively connected with the positive output end and the negative output end of the filter; the filter inductors Lo1 and Lo2 are independent or coupled, or Lo1 or Lo2 is removed to simplify the circuit; when Lo1 is removed, the positive input end and the positive output end of the filter are directly connected, and when Lo2 is removed, the negative input end and the negative output end of the filter are directly connected; or the filter capacitor Co is removed so as to be suitable for current source mode output;

rectifier X (51) and rectifier Y (52) are connected with filter X (61) and filter Y (62) respectively to form two groups of outputs; or rectifier X (51) and rectifier Y (52) are jointly connected in combination with filter (6) to form a set of outputs.

6. A bridgeless isolated AC-DC single stage PFC converter according to claim 5, wherein: rectifier X (51) is connected with filter X (61) to form a first output of the converter, and rectifier Y (52) is connected with filter Y (62) to form a second output of the converter; the specific description is as follows: the positive output end and the negative output end of the rectifier X (51) are respectively connected with the positive input end and the negative input end of the filter X (61), and the positive output end and the negative output end of the filter X (61) are respectively used as a positive end +Vo1 and a negative end-Vo1 of the first output; the positive output end and the negative output end of the rectifier Y (52) are respectively connected with the positive input end and the negative input end of the filter Y (62), and the positive output end and the negative output end of the filter Y (62) are respectively used as a positive end +Vo2 and a negative end-Vo2 of the second output; the first output and the second output can be supplied to the load independently or in parallel or in series.

7. A bridgeless isolated AC-DC single stage PFC converter according to claim 5, wherein: the rectifier X (51) and the rectifier Y (52) are connected with the filter (6) in a combined mode to form a group of outputs, and the positive output end and the negative output end of the filter (6) are respectively used as a positive end +vo and a negative end-Vo of the output of the converter; the combination mode is divided into parallel combination and series combination; the parallel combination is that positive output ends of the rectifier X (51) and the rectifier Y (52) are commonly connected with a positive input end of the filter (6), and negative output ends of the rectifier X (51) and the rectifier Y (52) are commonly connected with a negative input end of the filter (6); the series combination is that the negative output end of the rectifier X (51) is connected with the positive output end of the rectifier Y (52), and the positive output end of the rectifier X (51) and the negative output end of the rectifier Y (52) are respectively connected with the positive input end and the negative input end of the filter (6).

8. A bridgeless isolated AC-DC single stage PFC converter according to claim 5, wherein: in the double transformer scheme, diodes in rectifier X (51) and rectifier Y (52) are replaced with switching tubes with the rule that the sources and drains of the switching tubes correspond to the anodes and cathodes of the diodes, respectively.

9. A bridgeless isolated AC-DC single stage PFC converter according to claim 5, wherein: there are two derivative circuits based on the dual transformer scheme; the first derivative circuit is: the primary winding Np1 of the first transformer (41) is connected with an inductor Lr1 in parallel, and the self-inductance of the inductor Lr1 is far smaller than that of the primary winding Np 1; the primary winding Np2 of the second transformer (42) is connected with an inductor Lr2 in parallel, and the self-inductance of the inductor Lr2 is far smaller than that of the primary winding Np 2; the second derivative circuit is: an inductor Lr1 is added at the position of a primary winding Np1 of the first transformer (41), the primary winding Np1 is connected with a capacitor Cr1 in series, an inductor Lr2 is added at the position of a primary winding Np2 of the second transformer (42), and the primary winding Np2 is connected with a capacitor Cr2 in series; the concrete connection mode is as follows: two ends of the inductor Lr1 are respectively connected with a node V1 of the conversion bridge (3) and a node Vs1 of the capacitor network (20), one end of the primary winding Np1 is connected with the node V1 of the conversion bridge (3), the other end of the primary winding Np1 is connected with one end of the capacitor Cr1, and the other end of the capacitor Cr1 is connected with a positive end Vd or a ground end GND of the conversion bridge (3) or connected with the node Vs1 or the node Vs2 of the capacitor network (20); two ends of the inductor Lr2 are respectively connected with a node V2 of the conversion bridge (3) and a node Vs2 of the capacitor network (20), one end of the primary winding Np2 is connected with the node V2 of the conversion bridge (3), the other end of the primary winding Np2 is connected with one end of the capacitor Cr2, and the other end of the capacitor Cr2 is connected with a positive end Vd or a ground end GND of the conversion bridge (3) or connected with the node Vs1 or the node Vs2 of the capacitor network (20).

10. A control method of a bridgeless isolation type AC-DC single-stage PFC converter adopts single-bridge arm PWM control, and is suitable for a single-transformer scheme of the converter; the method is characterized in that:

a second bridge arm formed by switching tubes Q3 and Q4 is switched at low frequency by the frequency of the alternating current power supply Ua; in the positive half cycle of the ac power supply Ua, i.e. the voltage of the node Vs is higher than the voltage of the node V2, the upper switching tube Q4 is turned off and the lower switching tube Q3 is turned on; in the negative half cycle of the ac power supply Ua, i.e. the voltage of the node Vs is lower than the voltage of the node V2, the lower switching tube Q3 is turned off and the upper switching tube Q4 is turned on;

the first bridge arm formed by the switching tubes Q1 and Q2 is subjected to high-frequency conversion under complementary PWM control; by complementary PWM is meant that the sum of the duty cycles of the switching transistors Q1 and Q2 is equal to 1, ignoring dead time; setting the on-duty ratio of the switching tubes Q1 and Q2 to be D respectively ₁ And D ₂ D is then ₁ +D ₂ =1; during the positive half period of the ac power supply Ua, the output voltage of the converter is equal to D ₁ Is proportional to the average value of (a); during the negative half period of the ac power supply Ua, the output voltage of the converter is equal to D ₂ Is proportional to the average value of (a); and D is ₁ And D ₂ And the instantaneous value of (2) is changed according to the power factor correction requirement;

The control flow is as follows:

isolating the feedback variable and then negatively feeding back to the alternating current side;

sampling alternating voltage and input current at the alternating side;

then dead time is inserted to form two paths of complementary PWM signals;

11. A control method of a bridgeless isolation type AC-DC single-stage PFC converter adopts double bridge arm PWM control, is divided into two modes of frequency multiplication modulation and bipolar modulation, and is suitable for a double transformer scheme of the converter; the method is characterized in that:

the first bridge arm and the second bridge arm of the conversion bridge (3) are subjected to high-frequency conversion under complementary PWM control at the same switching frequency; setting the on duty ratio of the switching tubes Q1, Q2 and Q3, Q4 as D respectively ₁ 、D ₂ And D ₃ 、D ₄ The method comprises the steps of carrying out a first treatment on the surface of the Neglecting dead switchingZone time, then D ₁ +D ₂ ＝1＝D ₃ +D ₄ The method comprises the steps of carrying out a first treatment on the surface of the And requirement D ₄ ＝D ₁ And D ₃ ＝D ₂ ；

The bipolar modulation mode is that the switching tubes Q3 and Q4 are respectively synchronous (i.e. in phase) with the conduction driving pulse of the switching tubes Q2 and Q1; the frequency multiplication modulation mode is that the switching tubes Q3 and Q4 are respectively synchronous with the conduction driving pulse of the switching tubes Q1 and Q2; there are three alignment ways for PWM pulses in the frequency doubling modulation mode: center alignment, front edge alignment, back edge alignment;

control law: the output voltage of the converter is equal to (D) ₁ ·D ₂ ) _min /|D ₁ -D ₂ | _max Proportional to (D) ₁ ·D ₂ ) _min Representation (D) ₁ ·D ₂ ) Is the minimum of, |D ₁ -D ₂ | _max Representation |D ₁ -D ₂ Maximum values of i, which occur at ac voltage u _a Is a positive and negative peak time of (2); and D is ₁ And D ₂ And the instantaneous value of (2) is changed according to the power factor correction requirement;

the control flow is as follows: