CN115065230B - Three-phase bridgeless SEPIC type PFC converter - Google Patents
Three-phase bridgeless SEPIC type PFC converter Download PDFInfo
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- H—ELECTRICITY
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- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
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- H02M1/42—Circuits or arrangements for compensating for or adjusting power factor in converters or inverters
- H02M1/4208—Arrangements for improving power factor of AC input
- H02M1/4233—Arrangements for improving power factor of AC input using a bridge converter comprising active switches
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Abstract
The utility model provides a three-phase bridgeless SEPIC type PFC converter, has solved the problem of current distortion that current SEPIC type three-phase PFC converter topology components and parts utilization ratio is lower and power switch tube junction capacitance brings, belongs to the bridgeless PFC converter topology field of three-phase. The invention comprises three input filter inductors, three energy storage capacitors, three energy storage inductors, three groups of two-way switches, six switches and two output filter capacitors, wherein the six switches are divided into three groups of one-way switches, and each group of two switches; the single-phase conversion circuit in the three-phase conversion is the same, and shares two output filter capacitors; compared with the existing topology, the semiconductor power device, the inductance and the capacitance reach the optimal quantity, and the utilization rate of the components is higher. Meanwhile, critical conduction mode control is adopted, power factor correction of an input side is achieved according to a conduction time control equation, the problem of current distortion is effectively solved, conduction loss of the converter can be further reduced, and the efficiency of the converter is effectively improved.
Description
Technical Field
The invention relates to a novel wide-gain three-phase bridgeless SEPIC type PFC converter based on CRM (critical conduction mode) control, and belongs to the topological field of three-phase bridgeless PFC converters.
Background
The three-phase PFC converter topology based on the SEPIC circuit has the advantages of simple circuit structure, good power factor correction effect, wide output voltage regulation range and the like, and is widely applied to the fields of small and medium power such as LED driving power supplies, battery chargers and the like. The input side of a conventional SEPIC PFC converter typically incorporates a rectifier bridge formed of diodes to rectify the input voltage, so that there are always two diodes through which current flows during circuit operation. The diode loss of the input rectifier bridge is particularly serious in the case of low power and high current. In order to reduce or even eliminate the loss in the diode rectifier bridge, a three-phase bridgeless PFC converter topology based on a SEPIC circuit is sequentially proposed, and two types of totem-pole phase modular type three-phase PFC converters and bridgeless Dual SEPIC type three-phase PFC converters are mainly used at present.
The totem pole phase modular SEPIC type three-phase PFC converter topology can be considered as three parallel single phase totem pole bridgeless SEPIC type PFC converters with three independent output ports. In view of the coupling problem of the three-phase non-isolated structure, three independent outputs are not connectable together. Meanwhile, an input diode exists in each single-phase module of the converter to always work, so that the system efficiency is reduced. The bridge-free Dual SEPIC type three-phase PFC converter topology uses more semiconductor power devices, and for each alternating current input, two groups of inductors and capacitors are adopted to respectively work on a positive half shaft and a negative half shaft of an input voltage, so that the coupling problem caused by a non-isolation structure is solved, but the utilization rate of the devices is lower, and the power density of the system is lower.
In addition, due to the fact that the junction capacitance of the power switch tube exists in reality, during the follow current period of switching tube turn-off, the junction capacitance of the switch tube can resonate with the energy storage inductor, so that the filter inductance current and the energy storage inductance current are not equal when the next conduction signal of the switch tube comes, and therefore current distortion exists in the input current of the three-phase bridgeless PFC converter based on the SEPIC circuit under the control of the fixed duty ratio DCM.
Disclosure of Invention
Aiming at the problems of low utilization rate of topological components of the existing SEPIC type three-phase PFC converter and current distortion caused by junction capacitance of a power switch tube, the invention provides a three-phase bridgeless SEPIC type PFC converter.
The invention relates to a three-phase bridgeless SEPIC type PFC converter, which comprises three input filter inductors, three energy storage capacitors, three energy storage inductors, three groups of bidirectional switches, six switches and two output filter capacitors, wherein the six switches are divided into three groups of unidirectional switches, and each group of unidirectional switches comprises two switches; the single-phase conversion circuit is the same in three-phase conversion and shares two output filter capacitors, and comprises an input filter inductor, an energy storage capacitor, an energy storage inductor, a group of bidirectional switches, a group of unidirectional switches and two output filter capacitors;
in the single-phase conversion circuit, each phase of input power supply is respectively connected with an input filter inductor, a group of bidirectional switches and an energy storage inductor in series, two ends of the bidirectional switches connected with the energy storage inductor in series are connected with an energy storage capacitor in parallel, the connection point of the bidirectional switches and the energy storage inductor is M points, the connection point of the energy storage inductor and the energy storage capacitor is simultaneously connected with one ends of two switches in the group of unidirectional switches, and the other ends of the group of unidirectional switches are respectively X points 1 And X 2 Two output filter capacitors are respectively connected in series with X 1 Between points and M and X 2 Dots and dotsBetween M points.
Preferably, the bidirectional switch is two anti-series power switching tubes, the anti-series power switching tubes comprise anti-parallel diodes and junction capacitors, and the PFC converter works in a critical conduction mode;
when a group of unidirectional switch currents of the A phase and zero crossing, the bidirectional switch of the A phase is conducted, and the conduction time is shortened
After that, the A-phase bidirectional switch is turned off to finish a switching cycle;
when a group of unidirectional switch currents of the B phase and zero crossing, the B phase bidirectional switch is conducted, and the conduction time is shortened
After that, the B-phase bidirectional switch is turned off to finish one switching cycle;
when a group of unidirectional switch currents of the C phase and zero crossing, the C phase bidirectional switch is conducted, and the conduction time is shortened
After that, the C-phase bidirectional switch is turned off to finish one switching cycle;
v A 、v B 、v C three-phase input voltage instantaneous value V representing input power supply under power frequency dc Representing the output voltage of the PFC converter,
r A ＝r B ＝r C ，
r A 、r B 、r C represents A, B, C three-phase network side equivalent input resistance, L 2 Representing the inductance value of the energy storage inductor.
The invention also provides a four-wire system three-phase bridgeless SEPIC type PFC converter, wherein the central line of a three-phase input power supply is connected with an M point.
Preferably, the bidirectional switch is two anti-series power switching tubes, the anti-series power switching tubes comprise anti-parallel diodes and junction capacitors, and the PFC converter works in a critical conduction mode;
when a group of unidirectional switch currents of the A phase and zero crossing, the bidirectional switch of the A phase is conducted, and the conduction time is shortened
After that, the A-phase bidirectional switch is turned off to finish a switching cycle;
when a group of unidirectional switch currents of the B phase and zero crossing, the B phase bidirectional switch is conducted, and the conduction time is shortened
After that, the B-phase bidirectional switch is turned off to finish one switching cycle;
when a group of unidirectional switch currents of the C phase and zero crossing, the C phase bidirectional switch is conducted, and the conduction time is shortened
After that, the C-phase bidirectional switch is turned off to finish one switching cycle;
v A 、v B 、v C three-phase input voltage instantaneous value V representing input power supply under power frequency dc Representing the output voltage of the PFC converter,
r A ＝r B ＝r C ，r A 、r B 、r C represents A, B, C three-phase network side equivalent input resistance, L 1 Representing the inductance value, L, of the filter inductance 2 Representing the inductance value of the energy storage inductor.
As a preferred alternative to this,
alpha represents the current ripple coefficient, T A_min Represents the lowest switching frequency, V rms Representing the effective value of three-phase voltage, P o Representing PFCThe converter outputs power.
The invention has the beneficial effects that the input side of the topology is not provided with the diodes which work all the time, and compared with the existing topology, the semiconductor power device, the inductance and the capacitance are optimized in number, and the utilization rate of the components is higher. Meanwhile, aiming at the current distortion problem caused by the junction capacitance of the power switch tube, the critical conduction mode (CRM) control is adopted, the power factor correction of the input side is realized according to a conduction time control equation, the current distortion problem is effectively solved, the conduction loss of the converter can be further reduced, and the efficiency of the converter is effectively improved.
Drawings
Fig. 1 is a circuit diagram of a three-wire system three-phase bridgeless PFC converter;
fig. 2 is a circuit diagram of a four-wire three-phase bridgeless SEPIC PFC converter;
fig. 3 is a division diagram of different working intervals of three-phase input voltage, wherein the ordinate v represents the three-phase input voltage, and the abscissa t represents the working time;
FIG. 4 shows the input voltage at [ pi/3, pi/2]The three-phase bridgeless SEPIC type PFC converter in the interval is switched S in one switching period a1 、S b2 、S c2 Current, energy storage inductance L a2 、L b2 、L c2 Current and switch Q a1 、Q b2 、Q c2 A current waveform diagram;
fig. 5 is a working mode diagram of a three-wire system three-phase bridgeless SEPIC PFC converter with input voltage in [ pi/3, pi/2 ] intervals in different switching states, wherein fig. 5 (a) is a working mode diagram of a working stage (1), fig. 5 (b) is a working mode diagram of a working stage (2), fig. 5 (c) is a working mode diagram of a working stage (3), fig. 5 (d) is a working mode diagram of a working stage (4), and fig. 5 (e) is a working mode diagram of a working stage (5); fig. 5 (f) is an operational mode diagram of the operational phase (6); fig. 5 (g) is an operating mode diagram of the operating phase (7);
fig. 6 is a CRM control algorithm block diagram of a three-phase bridgeless SEPIC PFC converter;
fig. 7 shows a four-wire system three-phase bridgeless SEPIC PFC converter with a phase a switch in 4 different modes of operation in a single switching cycleS a1 Current, energy storage inductance L a2 Current and switch Q a1 、Q a2 A current waveform diagram;
fig. 8 is a diagram of a phase operation mode of a four-wire system three-phase bridgeless SEPIC PFC converter in different states, including fig. 8 (a) v A >0, bidirectional switch conduction mode, fig. 8 (b) is v A >0, bidirectional switch off mode, fig. 8 (c) v A <0, bidirectional switch conduction mode, fig. 8 (d) v A <0, a bidirectional switch turns off a mode;
fig. 9 is a waveform diagram of three-phase input voltage and current under the condition of three-phase input 110V/50Hz and output 270V/1500W, wherein fig. 9 (a) is the waveform of input voltage and current of the three-wire system three-phase bridgeless SEPIC PFC converter of example 1; fig. 9 (b) is an input voltage and current waveform of the four-wire system three-phase bridgeless SEPIC PFC converter of example 2.
Detailed Description
The following description of the embodiments of the present invention will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
It should be noted that, without conflict, the embodiments of the present invention and features of the embodiments may be combined with each other.
The invention is further described below with reference to the drawings and specific examples, which are not intended to be limiting.
The three-phase bridgeless SEPIC type PFC converter of the present embodiment includes three input filter inductors, L respectively a1 、L b1 、L c1 Three small-capacity energy storage capacitors, respectively C a1 、C b1 、C c1 Three small-inductance energy storage inductors, L respectively a2 、L b2 、L c2 Two output filter capacitors C dc1 、C dc2 Three sets of two-way switches, a first set S a1 、S a2 The method comprises the steps of carrying out a first treatment on the surface of the Second group S b1 、S b2 The method comprises the steps of carrying out a first treatment on the surface of the Third group S c1 、S c2 Six switches Q a1 —Q c2 The switch may be selected according to the operating mode of the circuit: the boost mode adopts a diode/synchronous rectifier tube; the buck-boost mode employs a unidirectional current-controlled switch with reverse blocking capability, such as a unidirectional current-controlled switch IGBT with reverse blocking capability or a standard IGBT series diode without reverse blocking capability.
Wherein the inductance values of the three input filter inductors are the same and L 1 The capacitance values of the three small-capacity energy storage capacitors are the same and are C 1 The inductance values of the three small-inductance energy storage inductors are the same and are L 2 The capacitance values of the two output filter capacitors are the same and are C dc Each group of bidirectional switches is realized by adopting reverse series switching tube switches, the actions are the same, and the bidirectional flow of energy can be realized.
The single-phase conversion circuit is the same in three-phase conversion and shares two output filter capacitors, and comprises an input filter inductor, an energy storage capacitor, an energy storage inductor, a group of bidirectional switches, a group of unidirectional switches and two output filter capacitors;
the circuit structure of the three-phase bridgeless SEPIC PFC converter may be divided into two types, three-phase three-wire system and three-phase four-wire system, according to whether a neutral line exists in the three-phase ac power supply.
Example 1: as shown in fig. 1, in the three-phase bridgeless SEPIC PFC converter according to the present embodiment, in an a-phase single-phase conversion circuit, an a-phase input power supply and an input filter inductance L are respectively connected a1 Two-way switch S a1 、S a2 Energy storage inductance L a2 Sequentially connected in series, two-way switch S a1 、S a2 And energy storage inductance L a2 Two ends of the series connection are connected in parallel with an energy storage capacitor C a1 Bidirectional switch S a1 、S a2 And energy storage inductance L a2 The connection point of (2) is M point, and the energy storage inductance L a2 And energy storage capacitor C a1 The connection point of the one-way switch is simultaneously connected with one end of two switches in a group of one-way switches, and the other end of the one-way switch is respectively X 1 And X 2 Two output filter capacitors C dc1 、C dc2 Respectively connected in series to X 1 Between points and M and X 2 Between point and point M.
Compared with 18 semiconductor power devices, 6 energy storage capacitors and 6 energy storage inductors of a three-phase PFC converter without a bridge Dual SEPIC, the semiconductor power device is fewer in number, the topology of the embodiment adopts 12 semiconductor power devices, 3 energy storage capacitors and 3 energy storage inductors, the number of the semiconductor power devices is reduced, the number of the inductors and the number of the capacitors are halved, the utilization rate of components is effectively improved, and the system efficiency and the power density are also improved.
The working condition of the three-phase bridgeless SEPIC type PFC converter of the embodiment and the three-phase input voltage v A 、v B 、v C Is related to the waveform change of the three-way bidirectional switch. According to the polarity relation of the three-phase input voltage, a power grid period is divided into 12 sections, and the relation between the positive value and the negative value of the three-phase voltage in each section is unchanged. In interval [ pi/3, pi/2]For example, the working process of the converter is specifically analyzed.
Before analyzing the working principle of the PFC converter, the following description is made:
1) The PFC converter operates in a critical conduction mode (CRM);
2) Output filter capacitor C dc1 、C dc2 Is large enough, the partial pressure of the two capacitors is equal, i.e. v Cdc1 ＝v Cdc2 ＝V dc /2；
3) The power switch tube of the two-way switch comprises an anti-parallel diode and a junction capacitor;
4) The switching frequency is far higher than the frequency of the input alternating current power supply, and the switching period T S The three-phase input voltage is considered as a fixed value V A 、V B 、V C The voltage of the energy storage capacitor is a fixed value V a1 、V b1 、V c1 。
In the interval of three-phase input voltage [ pi/3, pi/2 ], according to the conduction condition of three-way bidirectional switch, the converter has 7 working modes, the main current waveform of a circuit with one switching period in the interval of [ pi/3, pi/2 ] is shown in figure 4, and the corresponding working modes are shown in figure 5.
Modality I: as shown in fig. 5 (a), the three groups of bidirectional switches are all on at this stage. A-phase input filter inductance L a1 Forward charging, inductance L a1 The current rises linearly in the forward direction; B. c-phase input filter inductance L b1 、L c1 Reverse charging, inductance L b1 、L c1 The current rises inversely linearly. Energy storage inductance L a2 、L b2 、L c2 The voltage at two ends is respectively equal to the energy storage capacitor C a1 、C b1 、C c1 Voltage across, i.e. v La2 ＝V a1 、v Lb2 ＝V b1 、v Lc2 ＝V c1 . Energy storage capacitor C a1 、C b1 、C c1 Respectively to energy storage inductance L a2 、L b2 、L c2 Discharge, L a2 、L b2 、L c2 Stored energy. At the same time, output filter capacitor C dc1 、C dc2 Together, provide energy to the load.
Modality II: as shown in fig. 5 (B), the A, C phase bidirectional switch is on and the B phase bidirectional switch is off. A. C-phase input filter inductance L a1 、L c1 Linear charging; energy storage inductance L a2 、L c2 The voltages at the two ends are respectively the energy storage capacitor voltage V a1 、V c1 Inductance L a2 、L c2 And (5) linear charging. The B-phase bidirectional switch is turned off, and the voltage at two ends of the bidirectional switch is clamped to be V b1 -V dc /2. Input filter inductance L b1 Discharging to the output side, the current linearly drops; energy storage inductance L b2 The reference direction of the voltage at two ends is opposite to the current, the inductance L b2 Energy is also released to the output side. At the same time, switch Q b2 Lead to filter capacitor C dc2 And the load providing energy, the current of which decreases linearly from the peak value until the switch Q b2 The current drops to 0 and the b-phase bi-directional switch begins to conduct.
Modality III: as shown in fig. 5 (c), the a-phase bidirectional switch is on, and the B, C-phase bidirectional switch is off. A-phase input filter inductance L a1 Energy storage inductance L a2 And (5) linear charging. B. The C-phase bidirectional switch is turned off, and the voltage at two ends of the B-phase bidirectional switch is clamped to be V b1 -V dc Clamping voltage at two ends of 2/C phase bidirectional switch to V c1 -V dc /2. Input filter inductance L b1 、L c1 Releasing energy to the output side. Energy storage inductance L b2 、L c2 The reference direction of the voltage at two ends is opposite to the current, the inductance L b2 、L c2 Energy is also released to the output side. At the same time, switch Q b2 、Q c2 Lead to filter capacitor C dc2 And the load is supplied with energy until the switch Q b2 、Q c2 The current drops to 0, and the B-phase and C-phase bidirectional switches start to conduct.
Modality IV: as shown in fig. 5 (d), the a-phase bidirectional switch is turned off, and the B, C-phase bidirectional switch is turned on. B. C-phase input filter inductance L b1 、L c1 Linear charging; energy storage inductance L b2 、L c2 The voltages at two ends are respectively the voltage V of the energy storage capacitor b1 、V c1 Inductance L b2 、L c2 And (5) linear charging. The A-phase bidirectional switch is turned off, and the voltage at two ends of the bidirectional switch is clamped to be V a1 +V dc /2. Input filter inductance L a1 Discharging to the output side, the current linearly drops; energy storage inductance L a2 The reference direction of the voltage at two ends is opposite to the current, the inductance L a2 Energy is also released to the output side. At the same time, switch Q a1 Lead to filter capacitor C dc1 And the load providing energy, the current of which decreases linearly from the peak value until the switch Q a1 The current drops to 0 and the a-phase bi-directional switch begins to conduct.
Modality V: as shown in fig. 5 (e), the A, C phase bi-directional switch is off and the B phase bi-directional switch is on. The voltage at two ends of the A-phase bidirectional switch is clamped to be V a1 +V dc Clamping voltage at two ends of 2/C phase bidirectional switch to V c1 -V dc /2. A-phase input filter inductance L a1 Energy storage inductance L a2 Releasing energy to the output side, switch Q a1 Lead to filter capacitor C dc1 And the load provides energy. B-phase input filter inductance L b1 Energy storage inductance L b2 And (5) linear charging. C-phase input filter inductance L c1 Energy storage inductance L c2 Releasing energy to the output side, switch Q c2 Lead to filter capacitor C dc2 And the load provides energy.
Mode VI: as shown in fig. 5 (f), the A, B phase bi-directional switch is off and the C phase bi-directional switch is on. The voltage at two ends of the A-phase bidirectional switch is clamped to be V a1 +V dc Clamping voltage at two ends of 2, B-phase bidirectional switch to V b1 -V dc /2. A-phase input filter inductance L a1 Energy storage inductance L a2 Releasing energy to the output side, switch Q a1 Lead to filter capacitor C dc1 And the load provides energy. B-phase input filter inductance L b1 Energy storage inductance L b2 Releasing energy to the output side, switch Q b2 Lead to filter capacitor C dc2 And the load provides energy. C-phase input filter inductance L c1 Energy storage inductance L c2 And (5) linear charging.
Mode VII: as shown in fig. 5 (g), the three sets of bidirectional switches are all turned off at this stage. The voltage at two ends of the A-phase bidirectional switch is clamped to be V a1 +V dc Clamping voltage at two ends of 2, B-phase bidirectional switch to V b1 -V dc Clamping voltage at two ends of 2/C phase bidirectional switch to V c1 -V dc /2. Three-way input filter inductance L a1 、L b1 、L c1 Energy storage inductance L a2 、L b2 、L c2 Releasing energy to the output side while switching Q a1 、Q b2 、Q c2 All are conducted to the filter capacitor C dc1 、C dc2 、C dc2 And the load provides energy.
As can be seen from the analysis of the 7 working modes, A, B, C three phases work relatively independently, and the conduction signals of each phase of the two-way switch A, B, C come from the respective switch Q a1 、Q b2 、Q c2 Zero crossing detection signal of current. When the switch Q a1 The A-phase bidirectional switch is turned on when the current drops to 0, and the switch Q b1 B-phase bidirectional switch is conducted when current drops to 0, and when switch Q c1 And when the current drops to 0, the C-phase bidirectional switch is conducted.
According to the analysis of the working mode of the three-phase PFC converter, taking the A phase as an example, in order to realize the power factor correction function, a switch Q is required to be switched on during the conduction period of the A phase bidirectional switch a2 And (5) switching off. In double pairsDuring the switch-on period, switch Q a2 The voltage at both ends is V A -V dc 2, when the converter is operated in the boost mode, i.e. the output voltage is greater than 2 times the peak value of the single-phase input voltage, the switch Q a1 The voltage across the switch Q is negative a1 The power factor correction function can be realized by adopting a diode/synchronous rectifying tube. When the converter operates in the buck-boost mode, i.e. the output voltage is 2 times less than the peak value of the single-phase input voltage, the switch Q a2 The PFC function of the converter needs to be implemented with a unidirectional current-controlled switch with reverse blocking capability, such as a unidirectional current-controlled switch IGBT with reverse blocking capability or a standard IGBT series diode without reverse blocking capability. When the standard IGBT series diode without reverse blocking capability is adopted, the working frequency of the standard IGBT without reverse blocking capability is the frequency of a three-phase input power supply.
The average voltage is 0 in the switching period of the voltages at the two ends of the three-phase input filter inductor, so that:
v A 、v B 、v C three-phase input voltage instantaneous values v of input power source under power frequency AM 、v BM 、v CM Respectively represent the instantaneous value, v, of the voltage between the power frequency lower node A, B, C and the M point MN The instantaneous value of the voltage between the midpoint M of the output capacitor and the midpoint N of the three-phase power supply under the power frequency is represented;
three-phase ac voltage balance, v A +v B +v C =0, from which:
substitution of formula (2) into formula (1) yields:
this can be achieved by:
taking into account the energy storage inductance L a2 、L b2 、L c2 Average voltage is 0 in two-end voltage switching period, and energy storage capacitor C is used under power frequency a1 、C b1 、C c1 Instantaneous value v of voltage across Ca1 、v Cb1 、v Cc1 Can be expressed as:
energy storage capacitor C a1 、C b1 、C c1 The voltage at the two ends is equal to A, B, C three-phase voltage respectively. Thus within the switching cycle there are:
as can be seen from the analysis of the 7 working modes, the turn-off time of the bidirectional switch is the switch Q a1 、Q b2 、Q c2 The peak instant of the current. Taking into account L 1 >>L 2 Neglecting the current variation on each phase of input filter inductor, switch Q a1 、Q b2 、Q c2 Is the current peak i of (2) Qa_peak 、i Qb_peak 、i Qc_peak Can be expressed as:
wherein d A 、T A Respectively an A-phase bidirectional switch duty ratio and a switch period, d B 、T B Respectively B-phase bidirectional switch duty ratio and switch period, d C 、T C Duty cycle and switching period of C-phase bidirectional switch respectively。
Energy storage inductance L a2 、L b2 、L c2 The two-terminal voltage switching period satisfies volt-second balance, namely:
the switch Q in the switching period can be obtained according to the formula (7) and the formula (8) a1 、Q b2 、Q c2 Average value i of current Qa_avg 、i Qb_avg 、i Qc_avg ：
In other intervals of the three-phase alternating voltage, the working condition of the converter is similar to the [ pi/3, pi/2 ] intervals, and according to the input-output power conservation condition under ideal conditions, the expression of the three-phase input current under CRM control is obtained:
wherein T is A_ON 、T B_ON 、T C_ON The on time of the A, B, C three-phase bidirectional switch respectively.
To achieve unity power factor correction at the three-phase input side, the on-time of each phase bi-directional switch control needs to be:
wherein r is A 、r B 、r C A, B, C three-phase network side equivalent input resistance, r when three-phase voltage and power are balanced A ＝r B ＝r C 。
Order the
The deformation of formula (11) can be obtained:
the formula (12) is the CRM control equation of the proposed three-phase bridgeless SEPIC type PFC converter, the structural block diagram of the control method is shown in figure 6, wherein V m Can be obtained from a closed voltage loop of the output voltage. The CRM control method based on the formula (12) is timing conduction, and is controlled to be turned off, wherein a conduction signal depends on zero crossing detection signals of the sum of currents of each phase of switch, namely, the conduction moment of A phase is i Qa1 +i Qa2 The current and zero crossing time of (2), the B phase conduction time is i Qb1 +i Qb2 The current and zero crossing time of (2), the C phase conduction time is i Qc1 +i Qc2 And zero crossing times. The current sum is selected because the stage of positive input voltage of each phase is the upper switch work and the lower switch is turned off, the stage of negative input voltage is the lower switch work and the upper switch is turned off, and the judgment of the input voltage can be omitted when the current sum is subjected to zero crossing detection. The integrator is reset and starts to perform V on each phase of bidirectional switch on time m And (3) starting integration until the output of each phase integrator meets a CRM control equation shown in a formula (12), turning over the comparator, turning off the bidirectional switch, and completing one switching cycle. By adopting the CRM control method based on the formula (12), the three-phase PFC converter can work in a critical conduction state, the problem that the bidirectional switch junction capacitor resonates in the follow current stage to cause input current distortion is effectively solved.
As can be seen from equation (8), the three-phase PFC converter has a wide output gain, which can be expressed as:
when the input voltage of a certain phase is in the vicinity of zero crossing, the duty ratio of the phase is larger; at the peak of the input voltage, the duty cycle of this phase is relatively small. A wide range of variation of the output voltage can be achieved by closed loop regulation of the output voltage.
Example 2: as shown in fig. 2, in the four-wire three-phase bridgeless SEPIC PFC converter according to the present embodiment, in the a-phase single-phase conversion circuit, a-phase input power supply and input filter inductance L are respectively connected a1 Two-way switch S a1 、S a2 Energy storage inductance L a2 Sequentially connected in series, two-way switch S a1 、S a2 And energy storage inductance L a2 Two ends of the series connection are connected in parallel with an energy storage capacitor C a1 Bidirectional switch S a1 、S a2 And energy storage inductance L a2 The connection point of (2) is M point, and the energy storage inductance L a2 And energy storage capacitor C a1 The connection point of the one-way switch is simultaneously connected with one end of two switches in a group of one-way switches, and the other end of the one-way switch is respectively X 1 And X 2 Two output filter capacitors C dc1 、C dc2 Respectively connected in series to X 1 Between points and M and X 2 And the center line of the three-phase input power supply is connected with the M point. At this time, the three-phase bridgeless SEPIC type PFC converter realizes decoupling on the circuit structure, and each phase of circuit works completely independently. Three-phase input voltage and power balance, and output current of each phase is I dc /3. Taking phase a as an example, according to the positive and negative of the alternating voltage of phase a and the switching state of a bidirectional switch, 4 different working modes exist in a single-phase model of the three-phase bridgeless SEPIC PFC converter based on CRM control, the main current waveform of a circuit in a switching period is shown in fig. 7, and the corresponding working modes are shown in fig. 8.
Modality I: as shown in FIG. 8 (a), this stage v A >The 0, A phase bidirectional switch is conducted, and the filter inductance L is input in the switching period a1 The voltage at both ends is V A The inductor current rises linearly in the forward direction. Energy storage inductance L a2 The voltage at two ends is the voltage V of the energy storage capacitor a1 Energy storage capacitor C a1 Energy storage inductor L through bidirectional switch a2 Discharging, energy storage inductance L a2 The current rises linearly. At this time, the load is formed by the output filter capacitor C dc1 、C dc2 Providing energy.
Modality II: as shown in FIG. 8 (b), this stage v A >The 0, A phase bidirectional switch is turned off, and the filter inductance L is input in the switching period a1 Voltage across the terminalsIs V (V) A -V a1 -V dc /2<0, the inductor current begins to drop linearly. Energy storage inductance L a2 The voltage at two ends is the output filter capacitor C dc1 Voltage, reference direction of voltage is opposite to current, energy storage inductance L a2 Releasing energy to the output side, energy storage inductance L a2 The current drops linearly. At this time, switch Q a1 Conducting and directing to filter capacitor C dc1 And the load providing energy, the current of which decreases linearly from the peak value until the switch Q a1 The current drops to 0 and the a-phase bi-directional switch is turned on.
Modality III: as shown in FIG. 8 (c), this stage v A <The 0, A phase bidirectional switch is conducted, and the filter inductance L is input in the switching period a1 The voltage at both ends is V A The inductor current rises in a reverse linear fashion. Energy storage inductance L a2 The voltage at two ends is the voltage V of the energy storage capacitor a1 Energy storage capacitor C a1 Energy storage inductor L through bidirectional switch a2 Discharging, energy storage inductance L a2 The current rises linearly. At this time, the load is formed by the output filter capacitor C dc1 、C dc2 Providing energy.
Modality IV: as shown in FIG. 8 (d), this stage v A <The 0, A phase bidirectional switch is turned off, and the filter inductance L is input a1 The voltage at both ends is V A -V a1 -V dc /2<0, the inductor current begins to drop linearly. Energy storage inductance L a2 The voltage at two ends is the output filter capacitor C dc2 Voltage, reference direction of voltage is opposite to current, energy storage inductance L a2 Releasing energy to the output side, energy storage inductance L a2 The current drops linearly. At this time, switch Q a2 Conducting and directing to filter capacitor C dc2 And the load providing energy, the current of which decreases linearly from the peak value until the switch Q a2 The current drops to 0 and the a-phase bi-directional switch is turned on.
From the previous analysis, the operation modes of the circuit are basically the same when the input voltage is positive or negative, and are mainly two modes of inductive charging and discharging. v A >0 and the turn-off time of the bidirectional switch, switch Q a1 The current of (2) reaches the current peak value; v A <0 and the turn-off time of the bidirectional switch, switch Q a2 The current of (a) reaches the current peak value, the current peak value i Qa_max Can be expressed as:
thereby obtaining the switch Q in the switching period under the control of CRM a1 /Q a2 The average value of the current can be expressed as:
conservation of input and output power under the power frequency condition, and the input current of the phase A can be expressed as:
wherein T is A_on Is the on time of the a-phase bi-directional switch.
The three-phase bridgeless SEPIC type PFC converter under the three-phase four-wire system works completely independently and has basically the same working process. Thereby obtaining a three-phase input current wave expression under the control of three-phase four-wire CRM:
wherein T is A_on 、T B_on 、T C_on The on time of the A, B, C three-phase bidirectional switch respectively.
According to the input side unity power factor correction requirement, the three-phase four-wire CRM control equation can be expressed as:
in the method, in the process of the invention,
as can be seen by comparing equation (12) with equation (17), the CRM control equation for the three-wire system is substantially the same as that for the four-wire system, illustrating that the proposed three-phase bridgeless SEPIC PFC converter does not have the problem of current coupling between the three phases, and the converter can be controlled using a single-phase control algorithm.
Combining equation (8) with equation (11) can obtain the switching cycle of the three-phase double-on switch operation:
wherein P is o Output power of the three-phase bridgeless SEPIC type PFC converter, V rms Is the effective value of the three-phase voltage.
Under CRM control, the switching period of the three-phase bridgeless SEPIC type PFC converter is directly related to the working index of a circuit. From an observation of equation (18), it is clear that, where the input voltage, output power, and energy storage inductance are fixed, the switching period is maximized at the three-phase input voltage peak and minimized near the three-phase input voltage zero crossing. In designing the energy storage inductance parameters in the embodiments 1 and 2, the variation range of the switching period needs to be defined, and the inductance value of the energy storage inductance is designed according to the condition.
The design of the three-phase input filter inductance mainly considers the current ripple of the three-phase input current. As can be seen from the foregoing working principle, taking phase a as an example, the current ripple of the input filter inductor of phase a is:
filter inductance L with determination of the size of the energy storage inductance and of the current ripple coefficient α a1 Can be obtained from formula (20):
from the above formula, the larger the input filter inductance value is, the smaller the input current ripple is. Taking the power frequency 50Hz three-phase input voltage of 110V, output 270V constant voltage and output power of 1500W as an example, the design and description of circuit parameters are carried out.
Design the lowest switching frequency T A_min Based on the given operation index, the inductance value of the energy storage inductance can be obtained according to equation (18) at 50 kHz:
taking the input current ripple coefficient α=0.2, determining the input filter inductance L according to equation (20):
the power factor correction of the three-phase bridgeless SEPIC PFC converter according to the above circuit parameters is shown in fig. 9, in which fig. 9 (a) is a three-phase three-wire system and fig. 9 (b) is a three-phase four-wire system. From simulation results, the CRM controls the input current of the down-converter to be sine wave, can track the input voltage waveform in real time, and has good power factor correction effect.
The method is applied to the fields of small and medium power such as LED driving power supplies and battery chargers.
Although the invention herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims. It should be understood that the different dependent claims and the features described herein may be combined in ways other than as described in the original claims. It is also to be understood that features described in connection with separate embodiments may be used in other described embodiments.
Claims (5)
1. The three-phase bridgeless SEPIC type PFC converter is characterized by comprising three input filter inductors, three energy storage capacitors, three energy storage inductors, three groups of two-way switches, six switches and two output filter capacitors, wherein the six switches are divided into three groups of one-way switches, and each group of two switches; the single-phase conversion circuit is the same in three-phase conversion and shares two output filter capacitors, and comprises an input filter inductor, an energy storage capacitor, an energy storage inductor, a group of bidirectional switches, a group of unidirectional switches and two output filter capacitors;
in the single-phase conversion circuit, each phase of input power supply is respectively connected with an input filter inductor, a group of bidirectional switches and an energy storage inductor in series, two ends of the bidirectional switches connected with the energy storage inductor in series are connected with an energy storage capacitor in parallel, the connection point of the bidirectional switches and the energy storage inductor is M points, the connection point of the energy storage inductor and the energy storage capacitor is simultaneously connected with one ends of two switches in the group of unidirectional switches, and the other ends of the group of unidirectional switches are respectively X points 1 And X 2 Two output filter capacitors are respectively connected in series with X 1 Between points and M and X 2 Between points and M;
the bidirectional switch is two reverse series power switching tubes, each reverse series power switching tube comprises an anti-parallel diode and a junction capacitor, and the PFC converter works in a critical conduction mode;
when the sum of the currents of a group of unidirectional switches of the A phase is zero, the bidirectional switch of the A phase is conducted, and the conduction time is shortened
After that, the A-phase bidirectional switch is turned off to finish a switching cycle;
when the sum of the currents of a group of unidirectional switches of the B phase is zero, the bidirectional switch of the B phase is conducted, and the conduction time is shortened
After that, the B-phase bidirectional switch is turned off to finish one switching cycle;
when the sum of currents of a group of unidirectional switches of the C phase crosses zero, the bidirectional switch of the C phase is conducted, and the bidirectional switch of the C phase is conductedTime
After that, the C-phase bidirectional switch is turned off to finish one switching cycle;
v A 、v B 、v C three-phase input voltage instantaneous value V representing input power supply under power frequency dc Representing the output voltage of the PFC converter,
r A ＝r B ＝r C ，
r A 、r B 、r C represents A, B, C three-phase network side equivalent input resistance, L 2 Representing the inductance value of the energy storage inductor.
2. The three-phase bridgeless SEPIC PFC converter of claim 1, wherein the switches are unidirectional current controllable switching IGBTs or standard IGBT series diodes.
3. The three-phase bridgeless SEPIC PFC converter of claim 1, wherein the switches employ diodes or synchronous rectifiers.
4. The three-phase bridgeless SEPIC type PFC converter is characterized by comprising three input filter inductors, three energy storage capacitors, three energy storage inductors, three groups of two-way switches, six switches and two output filter capacitors, wherein the six switches are divided into three groups of one-way switches, and each group of two switches; the single-phase conversion circuit is the same in three-phase conversion and shares two output filter capacitors, and comprises an input filter inductor, an energy storage capacitor, an energy storage inductor, a group of bidirectional switches, a group of unidirectional switches and two output filter capacitors;
in the single-phase conversion circuit, each phase of input power supply is respectively connected with an input filter inductor, a group of bidirectional switches and an energy storage inductor in series in sequence, and two ends of the bidirectional switches connected with the energy storage inductor in series are connected with an energy storage capacitor in parallelThe connection point of the two-way switch and the energy storage inductor is M point, the connection point of the energy storage inductor and the energy storage capacitor is connected with one end of two switches in a group of one-way switches at the same time, and the other end of one group of one-way switches is X point respectively 1 And X 2 Two output filter capacitors are respectively connected in series with X 1 Between points and M and X 2 Between points and M;
the neutral line of the three-phase input power supply is connected with the M point;
the bidirectional switch is two reverse series power switching tubes, each reverse series power switching tube comprises an anti-parallel diode and a junction capacitor, and the PFC converter works in a critical conduction mode;
when the sum of the currents of a group of unidirectional switches of the A phase is zero, the bidirectional switch of the A phase is conducted, and the conduction time is shortened
After that, the A-phase bidirectional switch is turned off to finish a switching cycle;
when the sum of the currents of a group of unidirectional switches of the B phase is zero, the bidirectional switch of the B phase is conducted, and the conduction time is shortened
After that, the B-phase bidirectional switch is turned off to finish one switching cycle;
when the sum of currents of a group of unidirectional switches of the C phase crosses zero, the bidirectional switch of the C phase is conducted, and the conduction time is shortened
After that, the C-phase bidirectional switch is turned off to finish one switching cycle;
v A 、v B 、v C three-phase input voltage instantaneous value V representing input power supply under power frequency dc Representing the output voltage of the PFC converter,
r A ＝r B ＝r C ，r A 、r B 、r C representing A, B, C three-phase network side equivalent input powerResistance, L 1 Representing the inductance value, L, of the filter inductance 2 Representing the inductance value of the energy storage inductor.
5. A three-phase bridgeless PFC converter according to claim 4, wherein,
alpha represents the current ripple coefficient, T A_min Represents the lowest switching frequency, V rms Representing the effective value of three-phase voltage, P o Representing PFC converter output power.
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