JP2003088126A - Ac-dc converter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an AC-DC converter which can design a light-weight and small size power supply facility of high power factor and high conversion efficiency. SOLUTION: A PWM control pulse which is outputted with a switching control unit 25 through variable control of duty depending on each phase-voltage waveform of the power supply is alternately supplied, without relation to the polarity of power supply detected with a polarity detection unit 29, to the FETs 5rp, 5sp, 5tp of the positive output terminal side (P side) and the FETs 5rn, 5sn, 5tn of the negative output terminal side (N side) to alternately turn ON and OFF the FETs in the P and N sides.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an AC-DC converter used as a power supply device for a load such as a battery mounted on a large battery vehicle or the like.

[0002]

2. Description of the Related Art Conventionally, an AC- which converts three-phase alternating current into direct current
An inverter type induction motor control device using a DC converter is configured as shown in FIG. 6, for example. In FIG. 6, reference numeral 51 is a three-phase AC power supply, 52 is a full-bridge connection of six diodes 53, and a three-phase bridge rectifier circuit connected to the R, S, and T phase terminals of the AC power supply 51, and 55 is A smoothing capacitor, which is connected in parallel to the positive and negative output terminals of the rectifier circuit 52 and constitutes an AC-DC converter together with the rectifier circuit 52, includes six insulated gate bipolar transistors (hereinafter referred to as IGBTs) 57rp, 5
7rn, 57sp, 57sn, 57tp, 57tn are full-bridge connected, and are inverter circuits connected to the positive and negative output terminals of the rectifier circuit 52. Each of the IGBTs 57rp, 57rn, 57sp, 5 of this inverter circuit 56 is
A flywheel diode 58 is connected in antiparallel to each of 7sn, 57tp, and 57tn, and a three-phase induction motor 59 is connected to three output terminals of the inverter circuit 56.

At this time, the connection points of the IGBTs 57rp and 57rn, the connection points of the IGBTs 57sp and 57sn, the IGBT
The connection point of T57tp and 57tn corresponds to the output terminal of the inverter circuit 56.

A quasi-constant voltage type battery charger using an AC-DC converter is constructed, for example, as shown in FIG. 7. In FIG. 7, 61 three-phase AC power supplies and 62 each input on the primary side. The terminal is a three-phase leakage transformer connected to the R, S, and T phase terminals of the AC power supply 61, and 63 is a full bridge connection of six diodes 64 to each output terminal on the secondary side of the leakage transformer 62. It is a three-phase bridge rectifier circuit that is connected to the leakage transformer 62 and constitutes an AC-DC converter. The positive and negative output terminals of the rectifier circuit 63 are connected to the positive and negative terminals of the battery 65, respectively. In this case, the output voltage is adjusted by switching the taps of the leakage transformer 62, but the output is adjusted to some extent by the leakage transformer 62 itself according to the state of charge of the battery 65.

[0005]

However, in the induction motor control device shown in FIG. 6, since a large pulsating current flows intermittently in the capacitor 55 on the output side of the rectifier circuit 52, the harmonics generated at that time are generated. However, there is a risk that it may adversely affect other power supply equipment as noise and cause malfunction of the power supply equipment.

Further, since this pulsating current is out of phase with the AC waveform of the power source, reactive power is generated due to the reduction in power factor, and as a result, the current capacity is larger than the capacity of the induction motor 59 as a load. Power supply equipment is required, and large-scale power supply equipment must be designed to supplement the reactive power.

Further, in the quasi-constant voltage type charging device shown in FIG. 7, in addition to the problems of harmonics and the increase in size of power supply equipment, due to the characteristics of the leakage transformer 62, that is, internal loss due to heat generation of the transformer itself is large. Therefore, there is a problem in that the efficiency is reduced, and the power supply facility is large and expensive.

Therefore, an object of the present invention is to provide an AC-DC converter capable of designing a light-weight and small-sized power supply facility having a high power factor, high efficiency.

[0009]

In order to achieve the above-mentioned object, the present invention is an AC-DC converter for converting an alternating current of a three-phase alternating current power supply into a direct current and supplying it to a load. A bridge circuit having three series circuits connected in parallel and having positive and negative output terminals connected to the load, and a booster connecting a connection point of the switching elements in each series circuit and each phase of the power supply. Reactor, a polarity detection unit that detects the polarity of each phase voltage of the power supply, and when each phase voltage of the power supply detected by the polarity detection unit is positive, in the series circuit of the bridge circuit The switching elements on the negative output terminal side are switched at a predetermined frequency and a predetermined duty when the phase voltage of the power supply is negative. And a switching control unit for controlling the switching control, short-circuiting the power supply through the reactor by turning on each of the switching elements, the voltage due to the energy stored in the reactor during this on is turned off by turning off the switching elements. It is characterized in that it is superimposed on the power supply voltage and supplied to the load through a diode connected in parallel with the switching element.

With such a configuration, the voltage due to the energy stored in the reactor while each switching element is on is superimposed on the power supply voltage via the diode when the switching element is off, and the power supply voltage is boosted. Supplied to the load. At this time, according to the positive and negative of each phase voltage of the three-phase AC power supply detected by the polarity detection unit, by the switching control unit, each switching element on the negative output terminal side in each series circuit of the bridge circuit, and each The switching element on the positive output terminal side is switching-controlled at a predetermined frequency and a predetermined duty.

As a result, a current having a waveform substantially similar to the waveform of the power supply voltage is supplied to the load, and since a smoothing capacitor is not used as in the prior art, the generation of harmonics due to a large pulsating current is also generated. In addition, a high power factor of about 98% can be secured, and the power supply voltage is boosted by superimposing the voltage due to the electromagnetic energy of the reactor due to switching, so that it is as expensive as a conventional leakage transformer. It is not necessary to use an inefficient transformer, the power supply voltage can be boosted with a high efficiency of 93% or more, and the power supply equipment can be reduced in weight and size. In particular, when the on-vehicle battery is 288 V DC or more as in a battery-powered vehicle and the crest value is higher than the battery voltage as in a three-phase AC power supply and a high voltage transformer is not required, the efficiency at that time is 98. It becomes very high as a percentage. On the other hand, DC48V
When the battery is used to charge the battery, a transformer is required, so multiplying the transformer efficiency gives a total efficiency of 93.
Although it is ~ 95%, it still exceeds the efficiency of the leakage transformer.

Further, according to the present invention, there is provided a waveform detecting section for detecting a waveform of each phase voltage of the power source, and the switching control section is based on each phase voltage waveform of the power source detected by the waveform detecting section. The control duty of the switching element is variable.

With such a configuration, the waveform of the load current can be made closer to the waveform of each phase voltage detected by the waveform detector, and the power factor and efficiency can be further improved.

Further, the present invention comprises a load voltage detecting section for detecting a load voltage supplied to the load, and a load current detecting section for detecting a load current flowing through the load, wherein the switching control section has the load voltage. And feedback control of the load current.

With such a configuration, the load voltage and the load current are feedback-controlled by the switching control section, so that the load voltage and the load current can be controlled at high speed and with high accuracy.

Further, the present invention is characterized in that each of the switching elements is constituted by a field effect transistor formed by integrating the diode. According to such a configuration, since the parasitic diode of the field effect transistor can be used, it is not necessary to separately prepare a diode, simplification and miniaturization can be achieved in terms of circuit arrangement, and 100 tens of volts or less can be achieved. It is very effective as a power supply facility for small capacity.

Further, the present invention is characterized in that each of the switching elements is composed of an insulated gate bipolar transistor. With such a configuration, the insulated gate bipolar transistor is relatively inexpensive and capable of high-speed switching, so that a power supply facility for large capacity exceeding 100 tens of volts can be realized with an inexpensive configuration.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS (Principle of Boosting) Prior to the description of the embodiments, the principle of boosting in the present invention will be described.
The basic principle of a DC circuit and a single-phase AC circuit is as follows: Japanese Patent Application Laid-Open No. 10-32937 filed by the applicant of the present application, page 2, left column, line 39 to page right column, line 14 (also in FIGS. 1 to 5). See).

That is, to explain using a single-phase AC circuit, as shown in FIG.
The bridge rectifier circuit BR of the individual diodes D1 to D4 is connected, and the switching elements S1 and S2 are connected in parallel only to the upper and lower two-stage diodes D1 and D2, respectively, and a capacitor is provided between the positive and negative output terminals of the rectifier circuit BR. Connect C (or DC load).

Then, as shown in FIG. 4A, when the voltage polarity of the AC power source VB is positive, as shown in FIG. 4B, the lower switching element S2 is driven by the chopper signal of a predetermined frequency. When the switching element S2 is repeatedly turned on and off, a current flows through the path of the reactor L, the switching element S2, and the diode D4 during the on period of the switching element S2 to accumulate inductive energy in the reactor L. When the switching element S2 is turned off, the reactor is turned on. The induced current due to the energy stored in L is diverted to the diode D1 to charge the capacitor C, the charging current causes the voltage across the capacitor C to become higher than the power supply voltage, and the boosted voltage V2 across the capacitor C. (> V1) appears.

On the other hand, when the voltage polarity of the AC power supply VB is negative as shown in FIG. 4A, the upper switching element S1 is turned on by a chopper signal of a predetermined frequency as shown in FIG. 4C. By turning off, current flows through the path of the diode D3, the switching element S1, and the reactor L during the ON period of the switching element S1, and inductive energy is accumulated in the reactor L. When the switching element S1 turns off, the reactor L The induced current due to the stored energy is diverted to the diode D3 to charge the capacitor C, the charging current causes the voltage across the capacitor C to become higher than the power supply voltage, and the boosted voltage V2 (>) across the capacitor C. V1) appears.

As a result, the waveform of the current flowing through the capacitor C becomes a waveform that is sagged as shown in FIG. 4D, but is generally similar to the voltage waveform of the AC power source VB. And, it is difficult to reduce the jaggedness of the current waveform by the feedback control system, but it is possible to suppress the change (distortion) of the current waveform due to the fluctuation on the AC side power supply voltage or the load side by the feedback control system, In order to suppress such a change (distortion) in the current waveform and bring it closer to the voltage waveform, the switching element S
It suffices to perform variable control according to the voltage waveform of the power supply without fixing the ON / OFF duty of 1 and S2. In the present invention,
The duty is variably controlled by feedback controlling the load voltage and the load current while detecting the voltage waveform of the AC power supply.

Further, when this is expanded to a three-phase AC circuit,
As shown in FIG. 5, rectifier circuits BRr, BR similar to those in FIG.
s, BRt, etc. may be provided and connected to each phase of the three-phase AC power supply VB3 via the reactors Lr, Ls, Lt. Depending on whether the voltage polarity of the three-phase AC power supply VB3 is positive or negative, the lower side (negative Side) switching elements Srn, Ssn, Stn or upper side (positive side) switching elements Srp, Ssp, St
p By switching at a predetermined frequency, a voltage V4 (> V3) obtained by boosting the power supply voltage V3 can be supplied to the capacitor C (or DC load).

Here, the rectifier circuit BRr is a diode Dr.
1, Dr2, Dr3, Dr4 are configured by bridge connection, and similarly, the rectifier circuit BRs includes a diode Ds.
1, Ds2, Ds3, Ds4, and the rectifier circuit BRt is configured by bridge-connecting the diodes Dt1, Dt2, Dt3, Dt4.

(First Embodiment) A first embodiment of the present invention based on the above principle will be described with reference to FIG.

As shown in FIG. 1, an inverter rectifier circuit 2 is connected to each phase R, S, T of a three-phase AC power source via a boosting reactor 1. This inverter rectifier circuit 2
Is a kind of active filter called SMR (Switching Moded Rectifier), which boosts the power supply voltage without using L, C and a leakage transformer, and includes six IGBTs 3rp, 3rn, 3s which are switching elements.
p, 3sn, 3tp, 3tn are full bridge connection bridge circuits, and each IGBT 3rp, 3rn, 3sp,
Flywheel diodes 4rp, 4rn, and 4s connected in parallel in opposite directions to 3sn, 3tp, and 3tn, respectively.
p, 4sn, 4tp, 4tn.

Then, the IGBTs 3rp, 3 for the R phase
IGBT3rp, 3rn connection point in the rn series circuit, IGBT3sp, 3sn connection point in the S-phase IGBT3sp, 3sn series circuit, IGBT3tp, 3tn IGBT3 in the T-phase series circuit
The connection point of tp, 3tn is connected to each phase R, S, T of the power supply via the boosting reactor 1. Further, a battery 6 as a DC load is connected to the positive and negative output terminals of the inverter rectifier circuit 2.

Further, each IGBT of the inverter rectifier circuit 2
3rp, 3rn, 3sp, 3sn, 3tp, 3tn are
It is controlled by the switching control unit 8. The switching control unit 8 includes an R, C filter 10, constant voltage diodes 11r, 11s, 11t and a photo coupler 12r,
A polarity detection unit 13 composed of 12s and 12t for detecting the polarity of each phase voltage of the power supply, a load voltage Vb of the battery 6 detected by the load voltage detection unit 15, and a load current detection unit 1
The load current Ib flowing through the battery 6 detected by 6 is feedback controlled to perform PWM (Pulse Width Modulatio).
n) A PWM control unit 18 that generates a control pulse, a gate unit 19 that performs a logical product of the output of the polarity detection unit 13 and the output of the PWM control unit 18, the gate unit 19 and each IGBT 3
rp, 3rn, 3sp, 3sn, 3tp, 3tn are electrically insulated from each other, and the output of the gate unit 19 is set to each IGBT 3rp,
3rn, 3sp, 3sn, 3tp, 3tn and the isolation part 20 which outputs to the control terminal.

By the way, the PWM control section 18 includes a reference voltage generating section 18a, a voltage regulator 18b having a limiter function, a current regulator 18c, a reference duty setting section 18d, an adder 18e, and a pulse output section 18.
and f.

Then, the reference voltage Vs from the reference voltage generator 18a and the load voltage Vb from the load voltage detector 16 are error-amplified by the voltage regulator 18b, and the error current Iref obtained by this is amplified and the load current from the load current detector 16 is obtained. Ib and Ib are error-amplified by the current regulator 18c, and the error signal obtained thereby and the duty signal set by the reference duty setting unit 18d are added by the adder 18e, and the reference duty setting unit 1
A PWM control pulse is output from the pulse output unit 18f to variably control the constant duty by 8d.

This PWM control pulse passes through the gate section 19 described above, so that when the phase voltage of each power source detected by the polarity detection section 13 is positive, the IGBTs 3rn, 3sn on the negative output terminal side of the inverter rectifier circuit 2 are formed. , 3tn
In addition, when each phase voltage of the power source detected by the polarity detection unit 13 is negative, I on the positive output terminal side of the inverter rectifier circuit 2
It is adapted to be supplied to GBT3rp, 3sp, 3tp.

Then, as explained in the above-mentioned boosting principle, the IGBTs 3rn, 3sn, 3tn on the negative output terminal side.
ON, OFF, and each IGBT3r on the positive output terminal side
By turning on / off p, 3sp, and 3tp, the power supply voltage is boosted, and the boosted charging voltage is supplied to the battery 6,
The battery 6 is charged. Although not shown in FIG. 1, a smoothing capacitor for flowing a surge current is connected in parallel to the unit of the battery 6,
Measures have been taken to prevent a current that fluctuates significantly from flowing in. At this time, as a current waveform flowing through the reactor 1,
A waveform similar to the power supply voltage can be obtained.

Therefore, according to the first embodiment, a current having a waveform substantially similar to the waveform of the power supply voltage is supplied to the reactor 1, so that a high power factor of about 98% can be secured and Since the power supply voltage is boosted by using the induced current due to the electromagnetic energy of the reactor 1 due to switching, it is not necessary to use an expensive and inefficient transformer such as a conventional leakage transformer, and it is 98%.
The power supply voltage can be boosted with the above high efficiency, and each IG
The controllability of BT is high, and it is possible to reduce the weight and size of power supply equipment.

In this case, the IGBT is used as the switching element.
Since T is used, it is very effective for large-capacity power supply equipment of 100 tens of volts or more.

(Second Embodiment) A second embodiment of the present invention will be described with reference to FIG.

As shown in FIG. 2, the inverter rectifier circuit 2
The basic configuration of is similar to that of FIG. 1, and a field effect transistor (hereinafter referred to as FET) 5rp, 5rn, 5sp, 5s is used as a switching element instead of the IGBT.
The difference from the first embodiment is that n, 5tp, and 5tn are used. In this case, FETs 5rp, 5rn, 5s
By using p, 5sn, 5tp, and 5tn, the parasitic diode of the FET can be used as the flywheel diode. Therefore, as in the first embodiment, the flywheel diodes 4rp, 4rn, 4sp, 4sn, and 4t are separately provided.
It is not necessary to provide p and 4tn.

Further, as shown in FIG. 2, the switching control section 25 in the present embodiment includes a three-phase transformer 26 corresponding to a waveform detection section for detecting a voltage waveform of each phase of the power source, a comparator 27 and a volume 28. Polarity detection unit 29 that detects the polarity of each phase voltage of the actual power supply, and load voltage detection unit 1
5, the load voltage Vb of the battery 6 detected by the load current Ib flowing through the battery 6 detected by the load current detector 16 is feedback-controlled to generate a PWM control pulse, and the duty of the PWM control pulse is changed. It is configured by a PWM control unit 30 for controlling.

The PWM control section 30 includes a reference voltage generating section 30a and a voltage regulator 30 having a limiter function.
b and multipliers 30cr, 30cs, 30ct for each phase
And current regulators 30dr, 30ds, 3 for each phase
0dt and adders 30er, 30es, 30e for each phase
t, the pulse output units 30fr, 30fs, 30ft,
It is composed of isolation portions 30gr, 30gs, and 30gt.

Then, the reference voltage Vs from the reference voltage generator 30a and the load voltage Vb from the load voltage detector 16 are error-amplified by the voltage regulator 30b, and the output voltage VE of the voltage regulator 30b as an error signal and the three-phase transformer. The secondary voltages VR, VS, VT of 26 are respectively multiplied by multipliers 30cr, 30cs, 30ct to obtain phase current command signals Icr, Ics, Ict.
Here, the R-phase multiplier 30cr is (VE × VR / 1
0) is performed, and S-phase and T-phase multipliers 30cs, 30
The same applies to ct.

Subsequently, these phase current command signals Icr, I
Each of cs and Ict and each of the phase currents IR, IS and IT detected in the latter stage of the reactor 1 are error-amplified by the current regulators 30dr, 30ds and 30dt, and the respective error signals which are the respective outputs,
The respective phase voltage reference rate setting signals output from the polarity detection unit 29 are added by the adders 30er, 30es and 30et, whereby the FETs 5rp, 5rn and 5s are added.
The duty of the PWM control pulse to p, 5sn, 5tp, 5tn is corrected according to the power supply voltage waveform, and the adder 30
er, 30es, 30et, the PWM control pulse of the duty based on the output of the pulse output unit 30fr,
Isolation unit 3 from each of 30fs and 30ft
It is output via 0 gr, 30 gs, and 30 gt.

In this way, the duty is variably controlled according to the voltage waveform of each phase of the power source, and the pulse output units 30fr, 3fr.
PWM control pulses output from 0fs and 30ft are FETs 5rp and 5s on the P side (positive output terminal side) regardless of the polarity of the power source detected by the polarity detection unit 29.
p, 5tp and FET 5rn on the N side (negative output terminal side)
Alternately supplied to 5sn and 5tn, P-side and N-side FET
Are alternately turned on and off. The reason is, for example, R
When the polarity of the phase voltage is positive, the FET 5rn is turned on, and the current flowing by turning on the FET 5rn is
This is because turning off 5rn only causes commutation to the parasitic diode, but turning on FET5rp with a delay of 1 to 2 μs causes further commutation to the source and drain of FET5rp. At this time, the ON voltage of the FET is lower (0.1 V or less) than the parasitic diode loss (ON voltage≈1 V), and therefore the loss is extremely small.
Further, in the case of the IGBT as in the first embodiment, when the polarity of the current waveform is inverted, the control operation delay causes a non-energized state, which causes distortion. However, in the case of the FET, the switching speed is high. There is no delay and the non-energized state is resolved.

Therefore, according to the second embodiment, the FET 5r on the negative output terminal side (N side) is based on the voltage waveform of each phase of the power source.
n, 5sn, 5tn and positive output terminal side (P side) FET
By varying the control duty of 5 rp, 5 sp, and 5 tp, the waveform of the load current can be made more similar to the waveform of each phase voltage as compared with the above-described first embodiment, and the power factor and efficiency can be improved. Further improvement can be aimed at. Furthermore, in the case of the IGBT as in the first embodiment,
The switching frequency is considered to be 20 kHz as an upper limit, but in the case of the FET as in the present embodiment, it is possible to be up to about 1 MHz, and the switching frequency of the FET is 10 kHz.
When set to 0 kHz to 200 kHz, by design,
The inductance of the boosting reactor 1 can be reduced to 1/5 to 1/10 of that of the reactor used in the IGBT, the weight and cost of the device can be reduced, and improvement in control response can be expected.

In the second embodiment, the FETs 5rp, 5rn, 5sp, 5sn and 5t are used as switching elements.
Since p and 5tn are used, it is very effective as a power supply facility for a relatively small capacity of 100 tens of volts or less, and the FETs on the P and N sides are alternately turned on and off 1-2 μ
FETs 5rp, 5rn, 5sp, 5s only for a time of about s
Since it is only necessary to perform commutation (flywheel) using the parasitic diodes of n, 5tp, and 5tn, it is not necessary to separately prepare a diode as the flywheel diode as in the first embodiment. It is possible to achieve simplification and miniaturization.

As a specific application example of the present invention, in an inverter facility of an automatic warehouse, etc., instead of providing an AC main circuit power source for each facility, a collective inverter system in which DC is integrated (common) In this case, by using the battery together, it is possible to significantly reduce the equipment capacity by smoothing the power of the battery. Furthermore, it can be applied to the charging equipment when floating charging is performed by mounting an AC generator in a hybrid battery work vehicle, etc., and it is expected to have the effect of reducing the weight and speed, and eliminating the need for return charging. it can.

The present invention is not limited to the above-described embodiments, and various modifications other than those described above can be made without departing from the spirit of the invention.

[0046]

As described above, according to the first aspect of the present invention, a current having a waveform substantially similar to the waveform of the power supply voltage is supplied to the load, and the harmonics caused by the large pulsating current are generated. It is possible to secure a high power factor of about 98% without any occurrence, and because the power supply voltage is boosted by superimposing the voltage due to the electromagnetic energy of the reactor due to switching, it is possible to use a conventional leakage transformer. There is no need to use an expensive and inefficient transformer, the power supply voltage can be boosted at a high efficiency of 98% or more, the controllability is high, and it is possible to reduce the weight and size of the power supply equipment. It is possible to provide an AC-DC converter capable of reducing the installation capacity by about half as compared with the voltage system, and having a high power factor, high efficiency, and lightweight and compact power supply equipment design.

According to the second aspect of the present invention, the waveform of the load current can be made closer to the waveform of each phase voltage detected by the waveform detection unit, and the power factor and efficiency are further improved. It will be possible.

According to the third aspect of the invention, the load voltage and the load current are feedback-controlled by the switching control unit, so that the load voltage and the load current can be controlled at high speed and with high accuracy. become.

According to the invention described in claim 4, since the characteristics of the field effect transistor can be effectively utilized,
It is not necessary to separately prepare a diode, and it is possible to achieve simplification and miniaturization in terms of circuit arrangement, which is very effective as a power supply facility for small capacity of 100 tens of volts or less.

According to the invention of claim 5, the insulated gate bipolar transistor is relatively inexpensive and capable of high-speed switching. Therefore, a large capacity power supply facility exceeding 100 tens of volts is inexpensive. It can be realized by the configuration.

[Brief description of drawings]

FIG. 1 is a connection diagram of a first embodiment of the present invention.

FIG. 2 is a wiring diagram of a second embodiment of the present invention.

FIG. 3 is an explanatory diagram of a boosting principle of the present invention.

FIG. 4 is an explanatory diagram of a boosting principle of the present invention.

FIG. 5 is an explanatory diagram of a boosting principle of the present invention.

FIG. 6 is a wiring diagram of a conventional induction motor control device using a general AC-DC converter.

FIG. 7 is a connection diagram of a conventional charging device using a general AC-DC converter.

[Explanation of symbols]

1 Boosting Reactor 2 Inverter Rectifier Circuit 3rp, 3rn, 3sp, 3sn, 3tp, 3tn I
GBT (switching element) 4rp, 4rn, 4sp, 4sn, 4tp, 4tn Flywheel diode 5rp, 5rn, 5sp, 5sn, 5tp, 5tn F
ET (switching element) 6 battery (load) 8,25 switching controller 13, 29 polarity detector 15 load voltage detector 16 load current detector 26 three-phase transformer (waveform detector)

Claims (5)

[Claims] 1. An AC-DC converter for converting an alternating current of a three-phase alternating current power supply into a direct current and supplying it to a load, wherein three series circuits of two switching elements are connected in parallel, and the positive and negative output terminals are the above-mentioned. A bridge circuit connected to a load, a boosting reactor that connects each connection point of both switching elements in each series circuit and each phase of the power supply, and polarity detection that detects the polarity of each phase voltage of the power supply. Section, when each phase voltage of the power source detected by the polarity detection section is positive, the switching element on the negative output terminal side in each series circuit of the bridge circuit, the phase voltage of the power source Is negative, a switching control unit that controls switching of the switching elements on the positive output terminal side at a predetermined frequency and a predetermined duty is provided. When the switching element is turned on, the power supply is short-circuited via the reactor, and the voltage due to the energy stored in the reactor during this turning on is turned off by the switching element, and the power supply is supplied via a diode connected in parallel to the switching element. An AC-DC converter, which is superimposed on a voltage and supplied to the load. 2. A waveform detection unit that detects a waveform of each phase voltage of the power supply, wherein the switching control unit controls the switching element based on each phase voltage waveform of the power supply detected by the waveform detection unit. The AC-DC converter according to claim 1, wherein the duty is variable. 3. A load voltage detection unit for detecting a load voltage supplied to the load, and a load current detection unit for detecting a load current flowing through the load, wherein the switching control unit includes the load voltage and the load current. Is feedback-controlled, The AC-DC converter according to claim 1 or 2. 4. The switching element is formed of a field effect transistor formed by integrating the diodes.
The AC-DC converter according to any one of 1. 5. The AC-D according to claim 1, wherein each of the switching elements is composed of an insulated gate bipolar transistor.
C converter.