JP2566579B2 - Power converter - Google Patents

Description

TECHNICAL FIELD The present invention relates to a power converter that converts three-phase AC power into DC power.

[Conventional technology]

Figure 4 shows, for example, the Conference Record of the
1986 IEE Industry Applications Society Annual Meeting Part 1 (Conference Record of the 1986 IEEE Industr
y Applications Sosiety Annual Meeting Part 1) P630
FIG. 6 is a circuit configuration diagram showing the most typical conventional power conversion device shown in FIG. In the figure, 1 is an AC power supply, 2 is a reactor connected in series to the circuit of the AC power supply 1, and 3 is a first
In the diode rectifier, the AC side is connected to the AC power source 1 via the reactor 2. A switch 4 is connected in parallel between the DC output terminals P and N of the first diode rectifier 3. Reference numeral 5 is an inverter, and switches S _{1 to} S _{4 form} a single-phase bridge, the direct current input side of which is connected in parallel to the switch 4. Reference numeral 6 denotes an insulating transformer, the primary side of which is connected to the AC terminal of the inverter 5 and the secondary side of which is provided with a midpoint tap. A second diode rectifier 7 is constituted by a single-phase center tap connection, and its AC input side is connected to the secondary side of this insulating transformer 6. Reference numeral 8 denotes a capacitor, which is connected between the direct current output terminal of the second diode rectifier 7 and the midpoint tap of the secondary side of the insulation transformer 6.

Next, the operation will be described. First, the switches 4 and the switches S _{1 to} S ₄ that compose the inverter 5 are specifically self-extinguishing type semiconductor elements such as transistors and GTOs, and at a high frequency about 10 times or more higher than the frequency of the AC power supply 1. The switching operation is performed, the waveform distortion of the current I _L of the AC power supply 1 is reduced, and the input power factor is controlled to be approximately 1. FIG. 5 shows the operation waveform of the switch 4. The figure shows an example of a waveform when the switch 4 is operated at a switching frequency of 12 times the power supply frequency. The switch 4 is an AC power supply voltage in which the DC output currents I _P and I _N of the first diode rectifier 3 are indicated by broken lines.
Pulse width modulation PWM control is performed so that the full wave rectified waveform of Va follows the similar waveform. For example, when the switch 4 is turned on during the period from time t _{1 to} t ₂ , the AC power supply 1 is passed through the reactor 2 through the path of the AC power supply 1-reactor 2-diode D ₁ -switch 4-diode D ₄ -AC power supply 1. A closed circuit that short-circuits is formed, the current I _{4 of the} switch 4 increases, and energy is stored in the reactor 2. When the instantaneous value of this current exceeds the current reference value shown by the broken line, the switch 4 is turned off. At this time, due to the energy storage action of the reactor 2, the AC power supply current I _L flows to the inverter 5 side in the route of the reactor 2-diode D ₁ -inverter 5-diode D ₄ -AC power supply 1, and the insulation transformer 6 and the second transformer. The capacitor 8 is charged via the diode rectifier 7 and electric power is supplied to a load (not shown) connected to the capacitor 8. Since the energy of the reactor 2 is released in this manner, the currents I _L , I _P , I _N and the input current I ₅ flowing through the inverter 5 decrease. When the instantaneous value of the DC output currents I _P and I _N becomes lower than the current reference value, the switch 4 is controlled to be turned on again, and the ON / OFF operation of the switch 4 is repeated. When the voltage polarity of the AC power supply 1 is reversed, the first
The current is similarly controlled via the diodes D ₂ and D ₃ of the diode rectifier 3 of.

Next, the operation of the inverter 5 will be described with reference to FIG. First, the switch 4 is the DC voltage Vd period t ₁ ~t ₂ the inverter 5 turned on becomes zero. Then, when the switch 4 is turned off in the period from time t ₂ to t ₃ , the switches S ₁ and S ₄ of the inverter 5 are turned on and the output current I _{I of the} inverter 5 is
Has a waveform with the illustrated polarity. When the switch 4 is turned on again during the period from time t _{3 to} t ₄ , the output current I _{I of the} inverter becomes zero. Subsequently, when the time t ₄ ~t switch 4 in the period of ₅ is turned off, the output current I _I is a period of time t ₂ ~t ₃ inverters 5 by turn to turn on the switch S _2, S ₃ of the inverter 5 A waveform having a polarity opposite to that of the waveform is obtained. Thus, every time the switch 4 is turned off, the switch of the inverter 5 is switched.
An alternating output current I _I is obtained at the output of the inverter 5 by alternately turning on S ₁ , S ₄ and S ₂ , S ₃ . The output current I _I of the inverter 5 is rectified by the second diode rectifier 7, and the output current I _O of the second diode rectifier 7 has a waveform as shown. In the DC voltage Vd of the inverter 5 when the switch 4 is in the off period, the winding ratio of the insulating transformer 6 is n,
If the terminal voltage Vc of the capacitor 8 is constant, it becomes nVc.

Based on the operations of the switch 4 and the inverter 5, the current ripple of the AC power supply current I _L is obtained with the inductance of the reactor 3 being L as follows.

Times of Day, Times of Day, Therefore, by controlling the switching time interval of the switch 4 and the inverter 5 by the PWM control circuit (not shown), the instantaneous current control can be performed following the current reference value.

[Problems to be solved by the invention]

Since the conventional power converter is configured as described above, the conduction period of each arm element that performs the step-up chopper operation via the second diode rectifier is 180 °, and the alternating current is controlled in the sine wave shape. It will be. However, when this is applied to a three-phase AC power supply, the conduction period of each arm becomes 120 ° and the AC current cannot be controlled in a sinusoidal shape simply by making the second diode rectifier into a three-phase bridge configuration. A large number of low-order harmonic components such as the 5th and 7th order are included, and a filter is required to remove these harmonics. Also, three sets of power converters are provided to provide a three-phase power converter. However, since the number of switching elements is large, there is a problem in that the cost of the device increases.

The present invention has been made to solve the above problems, and provides a three-phase AC power converter capable of controlling an alternating current in a sine wave shape and controlling a power factor of a power source to approximately 1. The purpose is to

[Means for solving problems]

A power converter according to the present invention includes a power converter including a three-phase bridge-connected thyristor rectifier and a single-phase bridge-connected inverter connected to a DC output side of the thyristor rectifier via a reactor. Two sets are provided in parallel, diode rectifiers are connected to the output sides of the respective inverters via insulating transformers, and the output sides of the respective diode rectifiers are connected to the same polarity and capacitors are connected.

[Action]

In the power conversion device according to the present invention, each thyristor rectifier provided with two sets of three-phase bridge-connected thyristor rectifiers controls the voltage of the three-phase AC power supply at different phase control angles to rectify the thyristor rectifiers, and each single-phase bridge connection. The output currents of the thyristor rectifiers are controlled by respective inverters in the latter stage so as to form a triangular current waveform having a phase difference of 180 ° with each other, and each inverter is controlled by periodically providing a DC short-circuit mode, The AC power output from the inverter is connected to each diode rectifier through each insulation transformer, and the DC output converted by the diode rectifier to the same polarity is connected to the capacitor terminal to connect the final DC power. To get

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. In the figure, the same parts as those in FIG. 4 are shown with the same reference numerals, and in FIG. 1, 10H and 10L are thyristor rectifiers connected to a three-phase bridge, and their AC ends have a three-phase AC power supply.
e _U, e _V, is connected to the e _W. 2H and 2L are reactors connected to the DC output terminals of the thyristor rectifiers 10H and 10L, 5
H, 5L is an inverter connected between the DC output terminals of the thyristor rectifiers 10H, 10L via the reactors 2H, 2L, 6
H, 6L is an insulation transformer connected to the output side of the inverters 5H, 5L, 7H, 7L is a diode rectifier connected to the secondary side of the insulation transformers 6H, 6L, and 8 is the diode rectifier 7H, 7
It is a capacitor commonly connected to the DC output side of L.

Next, the operation will be described with reference to the operation waveforms shown in FIG. In the figure, e _Uo , e _Vo , and e _Wo are three-phase AC power supplies e _U and e
The phase voltage waveforms of _V and e _W are shown. Thyristor rectifier 10H, 10L arm elements U _H , V _H , W _H , X _H , Y _H , Z _H , _UL , V _L , W _L , X _L ,
Conduct control of Y _L and Z _L as shown in each thyristor rectifier 10
It is switched every 120 ° for H and 10L. Such a phase control method for the thyristor rectifiers 10H and 10L is disclosed in, for example, Japanese Patent Publication No.
No. 9-20274 is shown as an example of application to an AC motor inverter, so details are omitted. Vd _H and Vd _L represent DC output voltage waveforms of the thyristor rectifiers 10H and 10L, and each has a voltage ripple with a frequency three times the power supply frequency. Id _H and Id _L represent DC output current waveforms of the thyristor rectifiers 10H and 10L, and the waveforms are controlled by the inverters 5H and 5L in a triangular wave shape for each conduction period of each arm element of the thyristor rectifiers 10H and 10L. Where the actual DC output current waveform
The current ripple component of the switching frequency component of each inverter 5H, 5L is superimposed on Id _H , Id _L , but for simplicity,
It is omitted in the waveform of FIG. In addition, the inverter 5H, 5
By forcing the zero points of the DC output current waveforms Id _H and Id _L by L, the conduction of the arm elements of the thyristor rectifiers 10H and 10L is switched, and the waveforms of these DC output current waveforms Id _H and Id _L Have a 180 ° phase difference (60 ° phase difference when referenced to the power supply frequency). I _U , I _V , and I _W represent the current waveforms of the three-phase AC power supplies e _U , e _V , and e _W , and the DC output current waveform Id for the conduction period of the arm element of each thyristor rectifier 10H, 10L. It is obtained by synthesizing _H and Id _L , and has a sinusoidal shape. And 3-phase AC power supply
e _U, e _V, the phase voltage waveform e _Uo of e _W, e _Vo, to become e _Wo and phase, can be operated at a power factor of 1. For example, the current waveform I _U of the U-phase three-phase alternating current is obtained as follows. Phase 0 ° ~ 60 °
Becomes Id _L through the thyristor U _L during the period of and the phase is 60 ° to 1
Id _H and Id _L are combined through the thyristors U _H and U _L during the 20 ° period, and through the thyristor U _H during the phase 120 ° to 180 ° period.
Id _H next, during a phase 180 ° to 240 ° becomes a synthesis of Id _H and Id _L via the id _H next, during a phase 240 ° to 300 ° thyristors X _H and X _L via the thyristor X _H, Phase 300 °
During the period of ~ 360 °, it becomes Id _L via the thyristor X _L , and an alternating sinusoidal current is obtained. Here, the peak values of the current waveforms I _U , I _V , and I _W of this three-phase AC power supply are If so, the peak values of the triangular output current waveforms Id _H and Id _L of the thyristor rectifiers 10H and 10L are The inverters 5H and 5L are controlled so that

Next, the operation of the inverters 5H and 5L will be described with reference to the operation waveforms in FIG. The inverters 5H and 5L are configured as a single-phase bridge and perform the same operation. FIG. 3 shows the operation of the switches SH _{1 to} SH ₄ , which are arm elements of the inverter 5H, corresponding to FIG. 6 showing the operation waveform of the conventional power converter. During the period from t _{1 to} t ₂ , by turning on the switches SH ₁ and SH ₃ , the DC output end of the thyristor rectifier 10H is short-circuited via the reactor 2H, and the DC output current waveform Id _H is shown in the above formula (1). Increase by ΔI _A according to the relational expression. Here, Va in the equation (1) corresponds to the DC output voltage waveform Vd _H of the thyristor rectifier 10H. By period t ₂ ~t ₃ is to turn on the switch SH ₄ instead of turning off the switch SH ₃ Next, to obtain an output current I _{the IH} inverter 5H illustrated polarity, the DC output current waveform Id _H above ( According to the relational expression shown in the equation (2), it decreases by ΔI _B. Then switch SH ₁
By turning on the switch SH ₂ instead of turning off
DC output current waveform when switches SH ₂ and SH ₄ are turned on at the same time
Id _H increases again. During the next period t ₄ to t ₅ , the switch SH ₄
By turning on the switch SH ₃ instead of turning off
Output current of inverter 5H through switches SH ₂ and SH ₃ I _IH
Flows and has a polarity opposite to that of I _IH during the period of t _{2 to} t ₃ . The output current I _IH of the inverter 5H is rectified by the diode rectifier 7H via the insulating transformer 6H, and the output current I _OH of the diode rectifier 7H has a waveform as shown in the figure. Time t ₁ ~t ₂ and t ₃ each switch in ~t ₄ corresponds to the operation of the switch 4 for operation of the thus conventional step-up chopper
By simultaneously turning on SH ₁ and SH ₃ and switches SH ₂ and SH ₄ , the same operation as the conventional switch 4 is performed.
The operation of the inverter 5L is similar to the operation of the inverter 5H, and by turning on the switches SL ₁ and SL ₃ and the switches SL ₂ and SL ₄ at the same time, the same operation as the conventional switch 4 is performed. Since the ripple current flowing into the capacitor 8 is the sum of the ripple components of the output currents I _OH and I _OL of the diode rectifiers 7H and 7L, the switching timing of the inverters 5H and 5L must be reduced in order to reduce this ripple component. It is preferable to operate the motors by shifting them (for example, having a phase difference of 180 ° with each other).

In the above embodiment, an example in which a transistor is used as an arm element of the inverters 5H and 5L is shown, but a diode is connected in antiparallel to the transistor to prevent application of a reverse voltage during switching. It may be configured as described above. Instead of transistors, other self-turn-off type semiconductor devices (eg GTO, SIT, SI
(TH, MOSFET, etc.) also has the same effect as in the above embodiment.

Further, although the diode rectifiers 7H and 7L are configured by a single-phase full-wave bridge, the same effects as those of the above-described embodiment can be obtained even if the diode rectifiers have a single-phase bridge connection configuration as in the conventional example. Also, in the above embodiment, a three-phase AC power supply is used.
e _U, e _V, describes to convert the DC power insulated AC power e _W, have been omitted for the load of the power converter, and a DC load or a battery on the output side of the capacitor 8 It may be provided, or an inverter may be provided to convert this DC power into AC power.
In this case, the value of the AC input current may be PWM-controlled by the inverters 5H and 5L of the power converter so that the voltage of the capacitor 8 becomes constant.

Further, a filter for suppressing the harmonic component of the alternating current depending on the switching frequency of the inverters 5H, 5L may be provided on the AC power supply side.

〔The invention's effect〕

As described above, according to the present invention, the phase of the DC current output by each thyristor rectifier is configured so that each inverter is controlled to have a phase difference of 60 ° with respect to the power supply frequency, As a result of the current waveform of the three-phase AC power supply being in phase with the phase voltage waveform of the three-phase AC power supply, there is an effect that the power factor of the three-phase AC power supply can be controlled to approximately 1. Further, since the switching timings of the respective inverters are shifted from each other for operation, there is an effect that the high frequency current output from each diode rectifier can be reduced.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram of a power converter according to an embodiment of the present invention, FIGS. 2 and 3 are waveform diagrams of essential parts showing the operation of FIG. 1, and FIG. 4 is a conventional power converter. The circuit configuration diagram shown in FIG. 5, and FIGS. 5 and 6 are operation waveform diagrams of FIG. In the figure, e _U , e _V , and e _W are three-phase AC power supplies, 2H and 2L are reactors, 7H and 7L are diode rectifiers, 5H and 5L are inverters, 6H and 6L are isolation transformers, 8 is a capacitor, 10H, 10L is a thyristor rectifier. In the drawings, the same reference numerals indicate the same or corresponding parts.

Claims (1)

(57) [Claims] 1. Two sets of three connected in parallel to a three-phase AC power supply.
Phase-bridge-connected thyristor rectifiers, single-phase bridge-connected inverters connected to the output side of each of the thyristor rectifiers via reactors, and diodes connected to the output side of each of the inverters via insulating transformers In a power conversion device including a rectifier and a capacitor connected to the terminals that couple the output sides of the diode rectifiers to each other, the phase of the DC current output by each thyristor rectifier is 60 based on the power supply frequency. The power converter is characterized in that the respective inverters are controlled so as to have a phase difference of 10 degrees, and the switching timings of the respective inverters are shifted from each other to operate.