CN114301314A

CN114301314A - Two-level three-phase boost-buck PFC (power factor correction) rectifier converter and control method thereof

Info

Publication number: CN114301314A
Application number: CN202111439883.2A
Authority: CN
Inventors: 刘斌; 李玲
Original assignee: Liu Sanying
Current assignee: Liu Sanying
Priority date: 2021-11-30
Filing date: 2021-11-30
Publication date: 2022-04-08
Also published as: WO2023098214A1

Abstract

The application relates to a two-level type three-phase boost-buck PFC rectifier converter and a control method thereof, wherein the two-level type three-phase boost-buck PFC rectifier converter comprises an input buck switch rectifier bridge arm group, an energy storage follow current unit and a boost switch unit; the energy storage follow current unit comprises a first follow current inductor, a second follow current inductor and a seventh diode; the boost switch unit comprises a seventh switch tube, eighth to ninth diodes and a first filter capacitor. According to the invention, the voltage-reducing PFC rectification conversion is realized by applying the PWM driving signals in the 'middle' mode and the 'high' mode to the switching tubes in the voltage-reducing switch rectification bridge arm group. When the boost output is needed, normally-on and 'middle' mode PWM driving signals are applied to the switching tubes in the buck switch rectifier bridge group, and the PWM driving signals are applied to the seventh switching tube to continue combined control, so that the boost can be realized, the turn-on times of devices are reduced, and the switching loss is reduced.

Description

Two-level three-phase boost-buck PFC (power factor correction) rectifier converter and control method thereof

Technical Field

The application relates to the technical field of three-phase rectification converters, in particular to a two-level three-phase boost-buck PFC rectification converter and a control method thereof.

Background

The power of the current electric equipment is larger and larger, the electric equipment adopting a three-phase power supply mode is more and more, the electric energy quality of the power grid is greatly damaged if the electric equipment does not have a Power Factor Correction (PFC) function, and even paralysis of the power grid can be caused in severe cases. In order to meet the quality requirement of a power grid and reduce harmonic pollution to the power grid or cause unnecessary transmission burden of a distribution network, three-phase electric equipment must have a PFC function or be additionally provided with a filter device so as to meet the requirements of relevant regulations.

Generally, a rectifier converter circuit for three-phase ac input is mainly of a two-level or three-level boost type if a PFC function is required. However, after boosting, the output voltage is high, and there is a limit to the use of the converter or load connected to the back end, such as inputting a 380V ac voltage of a nominal three-phase three-wire, the output is generally set at about 720V, even as high as 800V. When the rear-end output voltage needs to be adjusted by a converter, the conventional power tube with better performance is below 650V, and in recent years, novel switching devices such as SiC and the like with slightly higher voltage and better high-frequency switching performance are available, but the cost is high; in order to solve the limitation of the power device of the dc converter at the rear end of the rectifying converter and to take efficiency and other factors into consideration, a buck-type two-level rectifying converter has become a research focus in recent years, for example, fig. 1 shows a boost PFC, when the initial voltage is lower, a reduction process is required, fig. 2 shows a buck PFC, if the buck PFC is adopted, the rated voltage of the voltage peak voltage of the phase voltage of 1.5 times at most can be stably output theoretically, and if the output required voltage exceeds the voltage range, the output required voltage does not reach the voltage peak voltage

For the peak value of the multiplied phase voltage, a one-stage non-isolated DC/DC direct-current conversion circuit (such as a boost scheme) must be added at the rear end to convert the peak value into the required output voltage, and fig. 3 is implemented by adopting a boost or buck scheme and then performing one-stage DC/DC voltage stabilization conversion, so that the two-stage scheme has higher cost, and the efficiency is reduced due to the two-stage conversion.

Disclosure of Invention

The invention aims to provide a two-level three-phase buck-boost PFC rectifier converter and a control method thereof, and solves the technical problems that in the prior art, a two-level converter needs to be converted for many times, a control algorithm is relatively complex, a plurality of flow guide circuit devices are needed, and the flow guide capability of a buck switch device cannot be fully utilized, so that the loss is large, and the two-level three-phase buck-boost PFC rectifier converter is not suitable for being applied in places with limited volume, relatively high cost requirement or wide output variation range.

The invention adopts a technical scheme that: a two-level type three-phase boost-buck PFC rectification converter comprises an input buck switch rectification bridge arm group, an energy storage follow current unit and a boost switch unit; the input buck switch rectifying bridge arm group comprises a first buck switch rectifying bridge arm, a second buck switch rectifying bridge arm and a third buck switch rectifying bridge arm, each buck switch rectifying bridge arm comprises an alternating current input port, a positive output port and a negative output port, and equivalent controllable selection switches are arranged among the alternating current input port, the positive output port and the negative output port; the energy storage follow current unit comprises a first follow current inductor, a second follow current inductor and a seventh diode; the boost switch unit comprises a seventh switch tube, eighth to ninth diodes and a first filter capacitor;

the positive output ports of the first buck switch rectifying bridge arm, the second buck switch rectifying bridge arm and the third buck switch rectifying bridge arm are sequentially connected and then connected with the cathode of the seventh diode and one end of the first freewheeling inductor; the negative output ports of the first buck switch rectifying bridge arm, the second buck switch rectifying bridge arm and the third buck switch rectifying bridge arm are sequentially connected and then connected with the anode of the seventh diode and one end of the second freewheeling inductor; the other end of the first freewheeling inductor is connected with the anode of the eighth diode and the drain of the seventh switching tube; the other end of the second freewheeling inductor is connected with the cathode of the ninth diode and the source of the seventh switching tube; one end of the first filter capacitor is connected with the cathode of the eighth diode to form a positive output end of the rectifier converter, and the other end of the first filter capacitor is connected with the anode of the ninth diode to form a negative output end of the rectifier converter.

Furthermore, the equivalent controllable selection switch consists of a switch tube and four diodes, or consists of two switch tubes and two diodes;

when the equivalent controllable selection switch consists of a switch tube and four diodes, the source electrode of the switch tube is connected with the anodes of the first diode and the second diode, and the source electrode of the switch tube is connected with the cathodes of the third diode and the fourth diode; the cathode of the first diode is connected with the positive output port; the cathode of the second diode and the anode of the third diode are connected with the alternating current input port; the anode of the fourth diode is connected with the negative output port;

when the equivalent controllable selection switch is composed of two switch tubes and two diodes, after the first switch tube and the first diode are connected in series to form a first branch circuit, one end of the first branch circuit is connected with the alternating current input port, the other end of the first branch circuit is connected with the positive output port, after the second switch tube and the second diode are connected in series to form a second branch circuit, one end of the second branch circuit is connected with the alternating current input port, the other end of the second branch circuit is connected with the negative output port, and the first branch circuit and the second branch circuit are symmetrical about the alternating current input port.

Furthermore, the switch tube and the seventh switch tube are both high-frequency switch tubes provided with a reverse diode or equivalent high-frequency switch tubes with the same function, and the reverse diode is an integrated diode, a parasitic diode or an additional diode; the first filter capacitor is a polar capacitor or a non-polar capacitor.

The input filter is connected with the alternating current input ports of the first buck switch rectifying bridge arm, the second buck switch rectifying bridge arm and the third buck switch rectifying bridge arm.

The control method of the two-level type three-phase buck-boost PFC rectification converter comprises the following steps:

s100: analyzing the phase and the interval of each phase power supply at the current moment according to the phase lock of the input three-phase three-wire power supply voltage signal;

s200: analyzing the instantaneous value of the voltage of each phase power supply in each interval according to the phase-locked phase in the step S100;

s300: judging whether the working mode of the rectifying converter is a buck mode or a boost mode according to the instantaneous value of the voltage of each phase power supply and the output voltage setting in the step S200, determining whether a high mode driving signal applied to an input buck switch rectifying bridge arm group is a PWM driving signal or a normally-on signal, and performing PWM driving control on a seventh switch tube; if the maximum value of the interphase instantaneous value pressure difference of the two phases is greater than the set value of the output voltage, the voltage reduction mode is adopted, a seventh switching tube is not required to be switched on, and the driving signal of the high mode is a PWM driving signal; if the maximum value of the interphase instantaneous value pressure difference of the two phases is equal to or less than the set value of the output voltage, the boosting mode is adopted, a seventh switching tube needs to be switched on, and the high mode driving signal is a normally-on signal;

s400: applying a driving signal to an input buck switch rectifier bridge arm group in the current interval to carry out PWM driving control, so that two-phase current with higher instantaneous value is firstly conducted; switching off a switching tube on the conducted instantaneous value secondary high-phase alternating current circuit, and continuing conducting the current of the phase with the highest instantaneous value and the phase with the lowest instantaneous value; the specific method comprises the following steps: simultaneously applying high-mode PWM driving signals with the same duty ratio to the switching tubes corresponding to the buck switch rectifying bridge arms in the two-phase alternating current circuit with the highest instantaneous value and the lowest instantaneous value, and simultaneously applying middle-mode PWM driving signals to the switching tubes corresponding to the buck switch rectifying bridge arms in the current circuit with the next-highest amplitude value, so that the switching tubes applying the high-mode PWM driving signals are turned off in each section, and the switching tubes applying the middle-mode PWM driving signals are turned off firstly; enabling each phase current to conduct during each switching cycle;

s500: after each phase current is conducted according to the set requirement, follow current is conducted through the energy storage follow current unit; and if the current loop is in the voltage reduction mode, all driving signals input into the voltage reduction switch rectifying bridge arm group are turned off, and if the current loop is in the voltage boosting mode, all driving signals of the corresponding voltage reduction switch rectifying bridge arm in the seventh switch and the current loop with the next highest amplitude instantaneous value are turned off.

Further, in steps S300 to S500, the same driving signal as the "high" mode PWM driving signal or the driving signal that is turned off earlier than the "medium" mode and is turned off at the same time as the "high" mode PWM driving signal is applied to the step-down switching rectifying bridge arm of the phase having the lowest ac input instantaneous value.

Further, in steps S300 to S500, when the seventh switching tube is in the PWM operating state, the PWM switching frequency of the seventh switching tube is consistent with the PWM switching frequency for controlling the first buck switch rectifying bridge arm, the second buck switch rectifying bridge arm, and the third buck switch rectifying bridge arm.

Further, the time of conducting current of each phase is in direct proportion to the instantaneous value of the phase voltage, and the current conducting time of the phase with the maximum instantaneous value is equal to the sum of the current conducting times of the other two phases.

The invention adopts another technical scheme that; a three-phase rectification converter comprises at least two-level three-phase boost-buck PFC rectification converters in the technical scheme, each two-level three-phase boost-buck PFC rectification converter is connected in parallel, the working phases of PWM driving signals of each two-level three-phase boost-buck PFC rectification converter are staggered according to 1/N high-frequency switching periods, wherein N is the total number of the two-level three-phase boost-buck PFC rectification converters.

The invention has the beneficial effects that:

(1) from the structure and performance, the defect of high voltage at the rear end of the traditional boost three-phase rectification conversion circuit is overcome, the conversion complexity of a multi-stage circuit is simplified, the limitation of a direct-current converter power device at the rear end is reduced, and the selectable space is larger;

(2) the traditional boost or buck three-phase rectification conversion circuit is changed, the output voltage has smaller limitation compared with the alternating current input, can be boost, buck and even the voltage with a phase difference amplitude, namely the output voltage is between

Is multiplied by

The advantages of replacing the traditional passive PFC are obvious in a multiple input phase voltage range, in particular toThe traditional three-phase passive PFC with the power factor of less than 30kW is replaced;

(3) when the output voltage is greater than

When the input voltage is within the range of multiple input voltages, or the fluctuation amplitude of the input voltage range is much larger than that of the input voltage range

Is multiplied by

Compared with the traditional two-stage direct current voltage stabilizing circuit, the invention can work in a voltage reduction or voltage boosting state according to the requirement, the high-frequency switching of a switch device is less, the loss is reduced, the switching loss of the invention is less than half of the prior known scheme from the visual angle, the efficiency is higher, and the invention is suitable for occasions with high efficiency and high power density requirements;

(4) due to the structural simplification, only the conduction of a rectification bridge arm of the buck switch or the boost switch needs to be controlled, so that the control difficulty is reduced, and in terms of the switching operation of the PFC function, a regular or logic combined PWM driving signal is applied to a switching tube of each phase, so that the control method is simplified.

Drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings needed to be used in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present application, and it is obvious for those skilled in the art that other drawings can be obtained according to these drawings without creative efforts.

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

FIG. 2 is a schematic diagram of a classical six-switch buck rectifier circuit;

FIG. 3 is a schematic diagram of a prior art DC output block;

fig. 4 is a schematic diagram of a two-level three-phase buck-boost PFC rectifier converter according to embodiment 1 of the present invention;

fig. 5 is a schematic diagram of a three-phase ac voltage waveform and a schematic diagram of an intersection point definition according to embodiment 1 of the present invention;

fig. 6 is a schematic diagram of a specific embodiment of an equivalent controllable selection switch in a buck switch bridge arm in embodiment 1 of the present invention;

fig. 7 is a schematic diagram of another modified example of the converter according to embodiment 1 of the present invention;

fig. 8 is a schematic diagram 1 of an AB phase conduction loop in an AC-BC interval according to embodiment 1 of the present invention, which is in a buck inductor energy storage mode;

FIG. 9 is a schematic diagram of a BC-phase continuous flow loop in an AC-O interval in embodiment 1 of the present invention;

FIG. 10 is a schematic diagram of an O-BC interval AC phase-continuous flow loop according to embodiment 1 of the present invention;

fig. 11 is a schematic diagram of an AC-BC interval inductor current freewheeling circuit according to embodiment 1 of the present invention;

fig. 12 is a schematic diagram 2 of an AB phase conduction loop in an AC-BC interval according to embodiment 1 of the present invention, which is in a boost inductor energy storage mode;

FIG. 13 is a simplified diagram of an equivalent transformation of embodiment 1 of the present invention;

FIG. 14 is a schematic diagram of the relationship between the driving waveforms of the switch groups in the step-down mode in the three-phase AC cycle in embodiment 1 of the present invention;

FIG. 15 is a schematic diagram showing the relationship between the driving waveforms of the switch groups in the boost mode in the three-phase AC cycle in embodiment 1 of the present invention;

fig. 16 is a schematic structural view of embodiment 2 of the present invention.

The reference signs explain: KB 1-first buck switch rectifying bridge arm, KB 2-second buck switch rectifying bridge arm, KB 3-third buck switch rectifying bridge arm, D1-first diode, D2-second diode, D3-third diode, D4-fourth diode, D7-seventh diode, D8-eighth diode, D9-ninth diode, T1-first switch tube, T2-second switch tube, T7-seventh switch tube, T8-eighth switch tube, L1-first freewheeling inductor, L2-second freewheeling inductor, C1-first filter capacitor, C2-second filter capacitor, Phase A-A Phase input, Phase B-B Phase input, Phase C-C Phase input, 1-AC input port, 2-positive output port, 3-negative output port.

Detailed Description

In order that the above objects, features and advantages of the present invention can be more clearly understood, a more particular description of the invention will be rendered by reference to the appended drawings. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention, however, the present invention may be practiced in other ways than those specifically described herein, and thus the present invention is not limited to the specific embodiments disclosed below.

Unless defined otherwise, technical or scientific terms used herein shall have the ordinary meaning as understood by one of ordinary skill in the art to which this application belongs. The use of "first," "second," and similar terms in the description and claims of this patent application do not denote any order, quantity, or importance, but rather the terms are used to distinguish one element from another. Also, the use of the terms "a" or "an" and the like do not denote a limitation of quantity, but rather denote the presence of at least one. The terms "connected" or "coupled" and the like are not restricted to physical or mechanical connections, but may include electrical connections, whether direct or indirect. "upper", "lower", "left", "right", and the like are used merely to indicate relative positional relationships, and when the absolute position of the object being described is changed, the relative positional relationships are changed accordingly.

Example 1:

as shown in fig. 4, a two-level three-phase buck-boost PFC rectifier converter includes an input buck switch rectifier bridge arm set, an energy storage freewheeling unit, and a boost switch unit; the input buck switch rectifying bridge arm set comprises a first buck switch rectifying bridge arm KB1, a second buck switch rectifying bridge arm KB2 and a third buck switch rectifying bridge arm KB3, each buck switch rectifying bridge arm comprises an alternating current input port 1, a positive output port 2 and a negative output port 3, and an equivalent controllable selection switch is arranged among the alternating current input port 1, the positive output port 2 and the negative output port 3; the energy storage freewheeling unit comprises a first freewheeling inductor L1, a second freewheeling inductor L2 and a seventh diode D7; the boosting switch unit comprises a seventh switch tube T7, eighth to ninth diodes D8-D9 and a first filter capacitor C1;

the positive output ports 2 of the first buck switch rectifying bridge arm KB1, the second buck switch rectifying bridge arm KB2 and the third buck switch rectifying bridge arm KB3 are sequentially connected, and then connected to the cathode of the seventh diode D7 and one end of the first freewheeling inductor L1; the negative output ports 3 of the first buck switch rectifying bridge arm KB1, the second buck switch rectifying bridge arm KB2 and the third buck switch rectifying bridge arm KB3 are sequentially connected, and then connected to the anode of the seventh diode D7 and one end of the second freewheeling inductor L2; the other end of the first freewheeling inductor L1 is connected with the anode of the eighth diode D8 and the drain of the seventh switching tube T7; the other end of the second freewheeling inductor L2 is connected to the cathode of the ninth diode D9 and the source of the seventh switching tube T7; one end of the first smoothing capacitor C1 is connected to the cathode of the eighth diode D8 to form the positive output end of the rectifier converter, and the other end of the first smoothing capacitor C1 is connected to the anode of the ninth diode D9 to form the negative output end of the rectifier converter.

The equivalent controllable selection switch consists of a switch tube and four diodes, or consists of two switch tubes and two diodes; the high-frequency PWM driving signal can be applied to the high-frequency switching tube according to the requirement of alternating current rectification conduction to control the on and off, so that the conduction connection with direction selectivity is realized, namely, the high-frequency pulse type rectification conduction of alternating current positive half waves or the high-frequency pulse type rectification conduction of alternating current negative half waves is formed.

When the equivalent controllable selection switch consists of one switch tube and four diodes, the source electrode of the switch tube is connected with the anodes of the first diode D1 and the second diode D2, and the source electrode of the switch tube is connected with the cathodes of the third diode D3 and the fourth diode D4; the cathode of the first diode D1 is connected to the positive output port 2; the cathode of the second diode D2 and the anode of a third diode D3 are connected with the alternating current input port 1; the anode of the fourth diode D4 is connected to the negative output port 3;

when the equivalent controllable selective switch is composed of two switch tubes and two diodes, after a first switch tube T1 and a first diode D1 are connected in series to form a first branch, one end of the first branch is connected to the ac input port 1, and the other end of the first branch is connected to the positive output port 2, after a second switch tube T2 and a second diode D2 are connected in series to form a second branch, one end of the second branch is connected to the ac input port 1, and the other end of the second branch is connected to the negative output port 3, wherein the first branch and the second branch are symmetrical with respect to the ac input port 1.

In embodiment 1, during operation, ac input ports 1 of the first buck switching rectifier bridge KB1, the second buck switching rectifier bridge KB2, and the third buck switching rectifier bridge KB3 are respectively connected to a three-phase ac power supply. In embodiment 1, the switch tube and the seventh switch tube T7 are both high-frequency switch tubes provided with a merged diode or equivalently high-frequency switch tubes with the same function, and the merged diode is an integrated diode, a parasitic diode or an extra diode; the first filter capacitor C1 is a polar capacitor or a non-polar capacitor. Embodiment 1 may further include an input filter, one end of the input filter is connected to the ac input port 1 of the first buck switch rectifier bridge KB1, the second buck switch rectifier bridge KB2, and the third buck switch rectifier bridge KB3, and the other end of the input filter is connected to a three-phase ac power supply, so as to filter the input power supply, and also filter and attenuate internal noise reflected to the input end.

s300: judging whether the working mode of the rectifying converter is a buck mode or a boost mode according to the instantaneous value of the voltage of each phase power supply and the output voltage setting in the step S200, determining whether a high mode driving signal applied to an input buck switch rectifying bridge arm group is a PWM driving signal or a normally-on signal, and performing PWM driving control on a seventh switch tube T7; if the maximum value of the interphase instantaneous value pressure difference of the two phases is greater than the set value of the output voltage, the voltage reduction mode is adopted, the seventh switching tube T7 is not required to be switched on, and the driving signal of the high mode is a PWM driving signal; if the maximum value of the interphase instantaneous value pressure difference of the two phases is equal to or less than the set value of the output voltage, the boosting mode is adopted, the seventh switching tube T7 needs to be switched on, and the driving signal of the high mode is a normally-on signal;

The method for judging the magnitude of the instantaneous value is to compare the magnitude of the absolute value of the instantaneous value of each phase. In steps S300 to S500, the same drive signal as the "high" mode PWM drive signal or a drive signal that is turned off earlier than the "medium" mode and is turned off at the same time as the "high" mode PWM drive signal is applied to the step-down switching rectifier bridge arm of the phase having the lowest ac input instantaneous value. When the seventh switching tube T7 is in the PWM operating state, the PWM switching frequency of the seventh switching tube T7 is the same as the PWM switching frequency for controlling the first buck switch rectifying bridge arm KB1, the second buck switch rectifying bridge arm KB2, and the third buck switch rectifying bridge arm KB 3. The time of conducting current of each phase is in direct proportion to the instantaneous value of the phase voltage, and the current conducting time of the phase with the maximum instantaneous value is equal to the sum of the current conducting times of the other two phases.

As shown in fig. 6, the equivalent controllable selection switch has three internal structures. Fig. 6(b) is composed of a switching tube and four diodes, wherein the source of the switching tube is connected to the anodes of the first diode D1 and the second diode D2, and the source of the switching tube is connected to the cathodes of the third diode D3 and the fourth diode D4; the cathode of the first diode D1 is connected to the positive output port 2; the cathode of the second diode D2 and the anode of a third diode D3 are connected with the alternating current input port 1; the anode of the fourth diode D4 is connected to the negative output port 3; fig. 6(c) is composed of two switching tubes or two diodes, when the first switching tube T1 is connected in series with the first diode D1, the anode of the first diode D1 is connected to the ac input port 1, the source of the first switching tube T1 is connected to the positive output port 2, when the second switching tube T2 is connected in series with the second diode D2, the cathode of the second diode D2 is connected to the ac input port 1, and the drain of the second switching tube T2 is connected to the negative output port 3; fig. 6(d) can be obtained by adjusting the series connection sequence of the switching tube and the diode in fig. 6 (c).

In addition, in fig. 6, after the switching tube is applied with the on-driving signal, the whole buck switch rectifying bridge arm can also be equivalent to two series diodes connected from the negative output port 3 to the positive output port 2, except that the connection point of the two diodes is clamped by the ac of the ac input port 1. The present invention is not limited to the connection method of the high-frequency switching tube and the diode to realize the connection between the ac input port 1, the positive output port 2, and the negative output port 3 of the buck switch rectifying bridge arm, and other combinations that can realize the functions of the controllable selection switch of the present invention also belong to the protection scope of the present invention.

Assuming that an ac positive half-wave is applied to the ac port and a forward rectification pulse conduction control is required, when a PWM signal of on is applied to the first switch tube T1 in fig. 6, the first switch tube T1 is turned on, the third diode D3 is connected in series with the first diode D1 between the ac input port 1 and the positive output port 2 in fig. 6(b), which is equivalent to a diode having an anode connected to the ac input port 1 and a cathode connected to the positive output port 2, so that forward rectification can be performed, the anode of the first diode D1 is connected to the ac input port 1 between the ac input port 1 and the positive output port 2 in fig. 6(c) and fig. 6(D), and the cathode of the first diode D1 is connected to the positive output port 2, so that forward rectification can be performed. On the contrary, if an ac negative half-wave is applied to the ac port and negative-direction rectification pulse conduction control is required, when a PWM signal of turning on is applied to the first switching tube T1 in fig. 6(b) or the second switching tube T2 in fig. 6(c) and 6(D), the corresponding switching tube is turned on, the second diode D2 and the fourth diode D4 are connected in series between the ac input port 1 and the negative output port 3 in fig. 6(b), which is equivalent to a diode having a cathode connected to the ac input port 1 and an anode connected to the negative output port 3, so that negative-direction rectification can be performed, the anode connected to the negative output port 3, which is equivalent to the second diode D2, between the ac input port 1 and the negative output port 3 in fig. 6(c) and 6(D), and the cathode connected to the ac input port 1 of the second diode D2, so that negative-direction rectification can be performed; when the output ends of a plurality of buck switch rectifying bridge arms are connected in parallel, if the controllable switch tubes are simultaneously switched on, the voltage bias effect of the diodes is small due to the equivalent property of the diodes of the channels, so that the highest voltage is preferentially switched on in a positive direction or the lowest voltage is preferentially switched on in a negative direction, and the voltage of the other channels cannot be switched on due to the fact that the equivalent diodes are switched off.

Therefore, in the following discussion, the operation principle and the path are represented by positive rectification conduction or negative rectification conduction of the buck switch rectification bridge arm, and the corresponding path is denoted as "KB positive" or "KB negative".

As shown in fig. 5, the three-Phase ac power supply of embodiment 1, including Phase a, Phase B and Phase C, has a standard voltage waveform as reference for convenience of description since there may be transient or distortion in the ac voltage actually input. For convenience of description, the three-phase voltages are different by 120 degrees and are sinusoidal voltages, and each 360 degrees is a cycle; in consideration of intuitive convenience, the convergence points are respectively defined as AC (30 °), BC (90 °), BA (150 °), CA (210 °), CB (270 °), AB (330 °), AC (30 ° or 390 °), with 30 ° to 390 °, i.e., a 30 ° point of the next cycle as one complete cycle; the zero crossing point is marked as "0".

As shown in fig. 4, a load or a circuit equivalent to a load may be connected between the positive output terminal and the negative output terminal. According to the basic principle of circuit voltage reduction, the output voltage is lower than the input voltage to form the voltage reduction. Therefore, in embodiment 1, two phases with larger instantaneous values in the three phases are turned on, and the opposite output terminals form a voltage difference, which is referred to as 0 ° or the origin of the phase a in fig. 5, where the lowest instantaneous difference value of the voltage difference should be the 30 °, 90 °, 150 °, 210 °, 270 °, 330 ° point of the phase a, or a similar periodic phase difference relationship point, and the lowest value at this time is the phase voltage highest amplitude value 1+1/2 times; the highest point of the instantaneous difference of the voltage difference is the point of 60 degrees, 120 degrees, 180 degrees, 240 degrees, 300 degrees and 360 degrees of the phase A or the similar periodic phase difference relation point, and the highest value at this time is

The maximum amplitude of the phase voltage is multiplied. When the output voltage is set to be less than

Wherein V is an effective value of the phase voltage, and is smaller than a minimum voltage difference value between two phases of the three-phase voltage at any time, and the output operating state of embodiment 1 is a full step-down mode. When the output voltage is set to be greater than

It is higher than the maximum voltage difference between the three phases at any time, and the output operation state of embodiment 1 is the step-up mode. When in transfusionVoltage between

And

in between, the operation mode of embodiment 1 has both step-up and step-down.

(1) Determining a buck mode based on output voltage requirements

As shown in fig. 8, in the AC-BC section from the AC point to the BC point, the absolute value of the instantaneous value of the phase voltage of a phase and the instantaneous value of the phase voltage of B is higher than that of the phase C, and according to the above-mentioned KB conduction principle, if the PWM driving on signal is applied to the first buck switch rectifying arm KB1, the second buck switch rectifying arm KB2 and the third buck switch rectifying arm KB3 at the same time, the second buck switch rectifying arm KB2 connected to a is conducting, and the voltage is marked as Va; a first buck switch rectifying bridge arm KB1 connected with B is in negative conduction, and the voltage is recorded as Vb; the output end of the "KB 3 positive" path of the third buck switch rectifying bridge arm KB3 connected to C cannot be conducted due to reverse bias of the voltage Va, and the current of the a phase can flow through the "KB 2 positive" path, the first freewheeling inductor L1, the eighth diode D8, the first filter capacitor C1, the external load, the ninth diode D9, the second freewheeling inductor L2, and then returns to the ac source of the B phase through the "KB 1 negative" path. At this time, the first freewheeling inductor L1 and the second freewheeling inductor L2 are in a step-down energy storage state, that is, because the output voltage is lower than the input voltage "Va-Vb", the redundant voltage is dropped across the first freewheeling inductor L1 and the second freewheeling inductor L2, so that the first freewheeling inductor L1 and the second freewheeling inductor L2 store energy and are in a forward series relationship with the output voltage.

As shown in fig. 9, in the AC-0 interval, when the drive of the "KB 2 positive" path is turned off, the current cannot be reversed immediately at this time due to the presence of the first freewheeling inductor L1 and the second freewheeling inductor L2 in the circuit, and the "KB 3 positive" path is turned on due to the disappearance of the bias voltage Va, and the voltage is denoted as Vc, but since Vc is lower than the instantaneous value of Va, the electromotive force of the inductor reverses, and the inductor releases a free wheel. The phase C current flows through a first freewheeling inductor L1, an eighth diode D8, a first filter capacitor C1, an external load, a ninth diode D9 and a second freewheeling inductor L2 from a positive KB3 path, and then returns to the phase B alternating current source through a negative KB1 path. At this time, the first freewheel inductor L1 and the second freewheel inductor L2 are in a boost enabled state, and are in a forward series relationship with the input voltage Vcb.

As shown in fig. 10, in the 0-BC interval, the output terminal of the "KB 3 negative" path connected to C is not turned on due to reverse bias by the voltage Vb, and when the drive of the "KB 1 negative" path is turned off, the current cannot be immediately reversed due to the presence of the first freewheel inductor L1 and the second freewheel inductor L2 in the loop, and the "KB 3 negative" path is turned on due to disappearance of the bias voltage Vb, and the voltage is denoted as Vc, but since Vc is lower than the instantaneous value of Vb, the electromotive force of the inductor reverses, and the inductor releases a free-wheeling. The phase A current flows through a first freewheeling inductor L1, an eighth diode D8, a first filter capacitor C1, an external load, a ninth diode D9 and a second freewheeling inductor L2 from a positive KB2 path and returns to the phase C alternating current source through a negative KB3 path. At this time, the first freewheel inductor L1 and the second freewheel inductor L2 are in a boost enabled state, and are in a forward series relationship with the input voltage Vac.

As can be seen from the above, the on-state of each phase current can be realized in each switching period, and the key to realize the high PF value and the low THDI is to first conduct two phases with higher instantaneous values and opposite polarities, form the step-down energy storage on the inductance of the loop, and then turn off the conducting loop of the next-highest phase with the absolute value of the instantaneous value, so that the follow current passes through the lowest phase with the instantaneous value. Therefore, in each switching period, the current loop of the next highest phase of the instantaneous value is firstly switched off, the PWM driving signal mode of the switching tube which is firstly switched off is marked as "medium", and the PWM driving signal mode of the switching tube which is then switched off is marked as "high". Although the switching tube driving of the phase with the lowest instantaneous value can also apply the PWM driving signal in the high mode, the channel of the phase with the lowest instantaneous value can be conducted only after the PWM driving signal in the medium mode is switched off, and the PWM driving signal mode is marked as the low mode. Therefore, in the practical control of embodiment 1, although there may be three duty ratios of the on-state of the switching tube, there are two duty ratios of the PWM driving signal per cycle under normal conditions to satisfy the control.

As shown in fig. 11, when all the PWM on-voltages applied to the rectifying legs of the buck switch are turned off, the ac input current loop is cut off, and since the current of the inductor cannot be transited, the first freewheeling inductor L1 and the second freewheeling inductor L2 must keep freewheeling, so that the seventh diode D7 is forward biased to conduct. The current forms a current freewheeling loop by the first freewheeling inductor L1, the eighth diode D8, the first filter capacitor C1, the external load, the ninth diode D9, the second freewheeling inductor L2 and the seventh diode D7.

According to the operation principle of the embodiment 1, in the step-down switching unit, in the same switching period, the PWM driving signal mode in which the PWM driving signal for turning on the switching tube on the circuit is turned off first is referred to as the "middle" mode, and the PWM driving signal mode in which the PWM driving signal is turned off later is referred to as the "high" mode. According to the control method, two phases with relatively high instantaneous values and opposite polarities are firstly conducted in each switching period, the inductance of a conducting loop generates voltage drop and energy storage, and then a switching tube in a passage of the next-highest phase with the instantaneous values is turned off, so that follow current passes through the lowest phase of the absolute value of the instantaneous values. Therefore, in each switching period, current flows in the three phases, the duty ratio of the PWM driving signal is well modulated according to real-time control, the current waveform and the voltage waveform can be consistent, a high PF value is obtained, and the PFC correction function is achieved.

Furthermore, in the case where the same effect is to be achieved without considering the complexity of control, another control mode may be adopted: and applying a driving signal to the switching tube of each buck switch rectifying bridge arm at different times, firstly applying signals to two phases with higher instantaneous values and opposite polarities to enable the two phases to be conducted, then turning off the switching tube of the next-highest phase current path of the two phases which are conducted, applying a driving signal to the switching tube on the alternating current circuit with the lowest instantaneous value to enable the switching tube to be conducted, so that the follow current passes through the lowest instantaneous value phase, and then controlling to turn off the switching tube in the buck switching unit. Therefore, in each switching period, the current loops of the two phases with the same amplitude and the same direction of the higher phase are firstly switched off, the PWM driving signal mode which is firstly switched off is marked as a 'middle' mode, the PWM driving signal mode which is then switched on is marked as a 'low' mode, and the PWM driving signal mode which is firstly switched on and is finally switched off is marked as a 'high' mode. This approach does not depart from our previously described "high" and "medium" control strategy and will not be described in detail.

(2) Determining boost mode based on output voltage demand

The buck switching rectifier bridge arm paths connected to the respective cross currents are controlled by the PWM driving shown in fig. 15, and in addition to the PWM driving corresponding to the "high" mode, a PWM driving signal is applied to the seventh switching transistor T7. That is, as shown in fig. 12, when the seventh switch transistor T7 is turned on, the current will be directly short-circuited by the seventh switch transistor T7 to form a loop, and the voltage of the ac source is completely applied to the first freewheeling inductor L1 and the second freewheeling inductor L2, so that the inductors store energy. As shown in fig. 11, when the seventh switching transistor T7 is turned off, the current cannot be reversed and the current continues to be in the original direction due to the presence of the first freewheeling inductor L1 and the second freewheeling inductor L2, but since Va-Vb is lower than the output voltage, the inductor electromotive force is caused to release energy in the reverse direction and follow a current, which is connected in series with the input voltage, and releases energy to the output or load terminal together with the input power source Vab. In the interval of AC-BC, when the rectification path of the A phase or the B phase is switched off, the C phase automatically carries out follow current conduction;

from the above, the buck switch rectifier bridge arms of the highest amplitude phase and the lowest amplitude phase form a first rectified voltage after being conducted, the buck switch rectifier bridge arms of the highest amplitude phase and the next highest amplitude phase form a second rectified voltage after being conducted, and the second rectified voltage is higher than the first rectified voltage. Therefore, the switching of the input rectification voltage loop can be realized by performing PWM switching on the switching tube of the rectification bridge arm of the secondary high-phase step-down switch, so that three-phase current can be conducted by matching with the conduction of the seventh switching tube T7 at the rear end. Therefore, the control mode reduces the switching of two-phase buck switch rectifying bridge arms, also reduces the switching loss of switching off and switching on the switching tube, and simultaneously only switches the buck switch rectifying bridge arm with the second-highest alternating current, so that the voltage borne by the switching tube of the buck switch rectifying bridge arm is only the voltage difference between the first voltage and the second voltage, thereby avoiding the highest-phase voltage difference when three buck switch rectifying bridge arms are all switched on under the drive of PWM, and further reducing the switching loss of the switching tube of the buck switch rectifying bridge arm. For the sake of unifying the description of the control method with the buck mode, we refer to the transition normally-on drive signal as a special "high" drive signal, i.e. the "high" in this mode has another special meaning.

According to the foregoing working principle analysis, the circuit of embodiment 1 in each operating mode can be simplified by conversion, in each channel transient state, an ac source can be equivalent to a dc source after being rectified by a diode, or an ac source plus a diode can be regarded as a dc source in a transient circuit, and a switching tube in an ac circuit can also be simplified and equivalent to a switch, and a plurality of series circuits in the circuit can be simplified into one, so that the circuit of embodiment 1 can be regarded as a buck-boost circuit after the above equivalence, as shown in fig. 13. Therefore, the circuit has a typical voltage reduction function and a typical voltage boosting function. Considering the conduction loss of devices in the circuit, the loss of duty ratio conduction angles such as dead zones and drive time delay and the necessary power factor correction function, compared with the traditional two-stage conversion mode, the amplitude range of the output voltage in the embodiment 1 is optimally the effective value of the input three-phase voltage

The ratio may be slightly more than this range.

As can be seen from the above analysis, in the above boost control mode, in embodiment 1, unnecessary boost or buck and intermediate capacitor energy storage processes in the conventional two-stage converter shown in fig. 3 are omitted, and at the same time, compared with switching devices of other three-phase voltage stabilizing converters, the switching frequency is greatly reduced, the switching loss is reduced, and the system efficiency is improved.

For other intervals, the control method is similar to the AC-BC interval. For a BC-BA interval, in a BC-0 interval, a driving signal of a switching tube of an A, B two-phase current path is a high mode PWM driving signal, a driving signal of a switching tube of a C-phase current path is a middle mode PWM driving signal, namely a C-phase loop is firstly turned off; in the interval 0-BA, the driving signal of the switch tube of the C, B two-phase current path is a high mode PWM driving signal, and the driving signal of the switch tube of the A-phase current path is a middle mode PWM driving signal, namely, the A-phase loop is firstly turned off.

For a BA-CA interval, in a BA-0 interval, a driving signal of a switching tube of an A, C two-phase current path is a high mode PWM driving signal, a driving signal of a switching tube of a B-phase current path is a middle mode PWM driving signal, namely a B-phase loop is firstly turned off; in the interval 0-CA, the driving signal of the switching tube of the A, B two-phase current path is a high mode PWM driving signal, and the driving signal of the switching tube of the C-phase current path is a medium mode PWM driving signal, i.e. the C-phase loop is firstly turned off.

For the CA-CB interval, in the CA-0 interval, the driving signal of the switching tube of the B, C two-phase current path is a high mode PWM driving signal, the driving signal of the switching tube of the A-phase current path is a middle mode PWM driving signal, namely, the A-phase loop is firstly turned off; in the interval 0-CB, the driving signal of the switching tube of the A, C two-phase current path is the "high" mode PWM driving signal, and the driving signal of the switching tube of the B-phase current path is the "medium" mode PWM driving signal, that is, the B-phase loop is turned off first.

For a CB-AB interval, in a CB-0 interval, a driving signal of a switching tube of an B, A two-phase current path is a high mode PWM driving signal, a driving signal of a switching tube of a C-phase current path is a middle mode PWM driving signal, namely a C-phase loop is firstly turned off; in the interval 0-AB, the driving signal of the switch tube of the B, C two-phase current path is the high mode PWM driving signal, and the driving signal of the switch tube of the A-phase current path is the middle mode PWM driving signal, i.e. the A-phase loop is firstly turned off.

For an AB-AC interval, in an AB-0 interval, a driving signal of a switching tube of an C, A two-phase current path is a high mode PWM driving signal, a driving signal of a switching tube of a B-phase current path is a middle mode PWM driving signal, namely a B-phase loop is firstly turned off; in the 0-AC interval, the driving signal of the switching tube of the B, A two-phase current path is the high mode PWM driving signal, and the driving signal of the switching tube of the C-phase current path is the middle mode PWM driving signal, i.e. the C-phase loop is firstly turned off.

In reality, three-phase voltage is not completely ideal, and changes of phase, amplitude and direction exist, so that the driving waveform of each section can be judged and generated only according to actual phase locking, and therefore the instantaneous waveform of each alternating-current voltage of each section is judged according to the characteristics of the instantaneous waveform, but not expressed by an ideal angle. According to the characteristics of the three-phase power signal, the three-phase power signal can be divided into twelve segments, the twelve segments are based on the above principle, and the waveform logic table of the driving signals of the first to third buck switch rectifying bridge arms KB1 to KB3 is shown in table 1.

TABLE 1 Driving state logic table for switching tube

The "low" mode indicates that the same drive signal as the buck switching rectifier arm having the maximum instantaneous value can be applied by the control method described above, or the drive signal that makes a freewheeling with the switching tube having the maximum instantaneous value is applied at the latest before the drive signal of the switching tube of the other phase having the same direction as the instantaneous value is turned off, and the duty ratio is described as "high-medium". Therefore, in consideration of simplification and normalization of control, the "low" mode can apply a drive signal in accordance with the "high" mode without affecting the function implementation. In this case, table 1 can be simplified into a logic table of driving states of the switching tube as shown in table 2:

TABLE 2 simplified logic table of driving states of switching tubes

According to the driving state logic table of the switching tube shown in table 2, a control cycle is divided into 12 sections in total, and the following control method is executed:

detecting input alternating voltage, judging whether each index of the input voltage meets a working condition or not, and continuing waiting when the index does not meet the condition; if the current phase of the three-phase three-wire power supply meets the conditions, starting working, judging according to the phase locking of the input three-phase three-wire power supply voltage signals, and analyzing the phase and the interval of each phase power supply at the current moment; analyzing the absolute value of the instantaneous value of the voltage of each phase power supply; and judges whether embodiment 1 operates in the step-up mode or the step-down mode according to the absolute value of the instantaneous value of the input inter-phase voltage and the set value of the output voltage. If the voltage boosting mode is adopted, a PWM driving signal is applied according to an operation result to turn on a seventh switching tube T7; if the voltage reduction mode is selected, the seventh switch tube T7 does not need to be turned on. And simultaneously, applying a middle mode PWM driving signal to a corresponding descending switching tube in a current loop of a second-highest phase with the absolute value of the instantaneous value, applying high mode PWM driving signals with the same duty ratio to the other switching tubes, enabling a two-phase power supply with a higher instantaneous value to form a current path, and simultaneously forming boosting energy storage or voltage division energy storage on an inductor of an energy storage follow current unit, wherein after the middle mode PWM driving signals are closed, the other two switching tubes which originally apply the high mode PWM driving signals provide follow current paths for the inductor to be continuously conducted, and if the switching tubes are in a boosting mode, after a seventh switching tube T7Q7 is closed, the inductor electromotive force is reversely connected with input voltage in series, so that the energy release follow current mode is entered. The specific duty ratio of the PWM driving signals in the high mode and the middle mode is determined by the real-time control operation result of the controller. When the drive of all the switch tubes in the buck switch bridge arm group is turned off, the inductance electromotive force is reversed, and the inductance current is formed into a path by a seventh diode D7. In general, the time for inputting the conduction current of each phase is in a relative relationship with the instantaneous value of the phase voltage, that is, the higher the instantaneous value is, the longer the current conduction time is, the larger the duty ratio is, the current conduction time of the phase with the maximum instantaneous value is equal to the sum of the current conduction times of the other two phases with relatively low instantaneous values and is less than the total time of the switching period, and the relevant waveform driving is as shown in fig. 14.

By the control method, current circulation of three phases in each switching period is effectively guaranteed, and meanwhile, the duty ratio of the PWM driving signal is well modulated according to real-time control, so that the current waveform and the voltage waveform can be consistent, a high PF value can be obtained, and the PFC correction function is realized. In high power density, the advantages are very obvious, and the requirements of high-precision products can be met.

The modification of the embodiment 1 is shown in fig. 7, and fig. 7 is added with an eighth switch tube T8 and a second filter capacitor C2 on the basis of the embodiment 1. In some cases with relatively high output voltage, the boost switch tube and the filter capacitor may be connected in series in consideration of the selection of the boost switch tube and the back-end filter voltage, but there is no essential difference from embodiment 1. In embodiment 1, the first flywheel inductor L1, the second flywheel inductor L2, the eighth diode D8, and the ninth diode D9 are connected in series in the circuit, and may be equivalent to one flywheel inductor or one diode. Under the condition that the output is not connected with the isolation converter, the two inductance modes of the positive end and the negative end are favorable for stabilizing the equivalent potential of the output voltage, or when the multi-channel converters are connected in parallel in a staggered mode, the potentials between phases interfere and conduct due to the phase error, so that the inductors continue to flow at intervals between the output end and the rectification bridge arm of the buck switch. Normally, therefore, two inductors are preferably used. In embodiment 1, the seventh diode D7 may be omitted and driven to conduct up and down in place of the diode in the step-down switching rectifier arm. However, according to the above description and analysis of the operation principle of the buck switching rectifier arm, the equivalent impedance of the circuit is much larger than that of the seventh diode D7 alone, and the potential is clamped at the input ac voltage when the buck switching rectifier arm is turned on, so it is preferable to use the seventh diode D7 alone.

Example 2:

as shown in fig. 16, a three-phase rectification converter includes at least two-level three-phase buck-boost PFC rectification converters according to embodiment 1, each two-level three-phase buck-boost PFC rectification converter is connected in parallel, and the operating phases of the PWM driving signals of each two-level three-phase buck-boost PFC rectification converter are staggered according to 1/N high-frequency switching periods, where N is the total number of the two-level three-phase buck-boost PFC rectification converters.

The control method of embodiment 2 is the same as that of embodiment 1, and the "high" and "medium" mode PWM driving signal control method described in embodiment 1 can control N parallel-connected non-isolated three-phase buck-boost rectifier converters, respectively, and the operating phases of the first to third buck switch rectifier legs KB1 to KB3 and the seventh switch tube T7 of the N parallel-connected three-phase rectifier converters are staggered by 1/N high frequency switching period, so that the current at the ac input end can form a multiphase staggered parallel connection, thereby improving the discontinuous input current of the buck-type power supply.

The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A two-level type three-phase boost-buck PFC rectification converter is characterized by comprising an input buck switch rectification bridge arm group, an energy storage follow current unit and a boost switch unit; the input buck switch rectifying bridge arm group comprises a first buck switch rectifying bridge arm, a second buck switch rectifying bridge arm and a third buck switch rectifying bridge arm, each buck switch rectifying bridge arm comprises an alternating current input port, a positive output port and a negative output port, and equivalent controllable selection switches are arranged among the alternating current input port, the positive output port and the negative output port; the energy storage follow current unit comprises a first follow current inductor, a second follow current inductor and a seventh diode; the boost switch unit comprises a seventh switch tube, eighth to ninth diodes and a first filter capacitor;

2. The two-level three-phase buck-boost PFC rectifier converter according to claim 1, wherein the equivalent controllable selection switch is composed of one switching tube and four diodes, or two switching tubes and two diodes;

3. The two-level three-phase buck-boost PFC rectifier converter according to claim 2, wherein the switch tube and the seventh switch tube are both high-frequency switch tubes provided with a diode inverter or equivalent high-frequency switch tubes with the same function, and the diode inverter is an integrated diode, a parasitic diode or an extra diode; the first filter capacitor is a polar capacitor or a non-polar capacitor.

4. The two-level three-phase buck-boost PFC rectifier converter according to claim 1, further comprising an input filter connected to AC input ports of the first, second and third buck-switch rectifier legs.

5. A three-phase rectifying converter comprising at least two-level three-phase buck-boost PFC rectifying converters as claimed in any one of claims 1 to 4, wherein each two-level three-phase buck-boost PFC rectifying converter is connected in parallel, and the operating phases of the PWM driving signals of each two-level three-phase buck-boost PFC rectifying converter are staggered according to 1/N high-frequency switching periods, where N is the total number of the two-level three-phase buck-boost PFC rectifying converters.

6. A control method for a two-level three-phase buck-boost PFC rectifier converter, which is used for controlling the two-level three-phase buck-boost PFC rectifier converter as claimed in any one of claims 1 to 4, comprising the following steps:

7. The method as claimed in claim 6, wherein in steps S300-S500, the same driving signal as the "high" mode PWM driving signal or a driving signal that is turned off earlier than the "medium" mode and is turned off simultaneously with the "high" mode PWM driving signal is applied to the buck switch rectifying bridge arm of the phase with the lowest AC input instantaneous value.

8. The method as claimed in claim 6, wherein in steps S300 to S500, when the seventh switch tube is in a PWM operating state, the PWM switching frequency of the seventh switch tube is consistent with the PWM switching frequency for controlling the first buck switch rectifying bridge arm, the second buck switch rectifying bridge arm and the third buck switch rectifying bridge arm.

9. The method as claimed in claim 6, wherein the conducting time of each phase is proportional to the instantaneous value of the phase voltage, and the conducting time of the phase with the largest instantaneous value is equal to the sum of the conducting times of the other two phases.