JPH08182342A - Power converter - Google Patents

Abstract

PURPOSE: To provide a power converter which has a capacity and function equivalent to those of a power converter using elements with the same loss characteristic and is suitable for reducing the loss of the whole converter. CONSTITUTION: A power converter is constituted by using elements with different loss characteristics on a phase bases, such as low on-loss elements GTO3 and GTO4 and low switching-loss elements IGBT5-IGBT8 and constituting the x-phase constituted of the GTOs in two-level output and y-phase constituted of the IGBTs in three-level output, and then, changing the number of output levels of each phase. The low on-loss elements are switched to each other by using long-period signals based on the reference wave of output voltage and the low switching-loss elements are switched to each other at high speeds by performing PWM control. Therefore, the withstand voltages of the elements can be used efficiently and the distortion of the output waveform of the converter resulting from the x-phase constituted of the low on-loss elements can be corrected by performing PWM control, because the element loss in each phase can be reduced and the withstand voltage in each phase can be made equal to that in another phase.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power converter for converting alternating current into direct current, and more particularly to a power converter with pulse width modulation control using a self-turn-off device.

[0002]

2. Description of the Related Art As an example of a conventional converter circuit for performing pulse width modulation (hereinafter referred to as PWM) control, there is a converter shown in FIG. 4 of Japanese Patent Laid-Open No. 1-259758. This performs switching by comparing a reference wave for generating a voltage waveform to be output to the AC side with a carrier wave, and thereby a pulsed voltage is output to the AC side.
In this case, the arbitrary voltage fundamental wave is obtained by changing the reference wave. In addition, the phase difference between the AC power supply voltage and the AC output voltage of the converter is adjusted to bidirectionally control the power flow.
Therefore, a converter circuit in which the number of parts is reduced and the price is reduced is disclosed in FIG. 1 of the publication. This is a converter in which one phase is composed only of diodes and the other phase is a switching element, and the required switching element is 2
In general, an inexpensive general rectifier diode can be used for the diode-only phase. This allows the device to be inexpensive. In addition, P that combines different elements for each phase
As a WM inverter circuit, Japanese Patent Laid-Open No. 63-26206
As shown in FIG. This is a single-phase inverter circuit configured by using high-speed type and low-speed type switching elements for each phase, and performs switching using PWM signals of different frequencies according to the element characteristics of each. This makes it possible to obtain a high-speed switching inverter having the same function as that in the case where all the elements used are not high-speed switching elements, and the cost of the device can be reduced.

[0003]

Of the above-mentioned conventional techniques,
A converter configured with all the same elements as shown in FIG. 4 of Japanese Patent Laid-Open No. 1-259758 uses four high-speed switching elements, so that the number of components is large, the apparatus is expensive, and all Since the switching element switches at high speed, there is a problem that switching loss is large. A converter having one diode only for one phase and a switching element for the other phase described in FIG. 1 of the same publication has a low switching loss, but regenerative operation is not possible because there is only a diode phase, and a regenerative brake is provided. Cannot be used. In addition, JP-A-63-262
In an inverter using a switching element different for each phase described in No. 062, when it is applied to a large capacity such as a vehicle converter, a high speed switching element generally has a low breakdown voltage and a low speed switching element. Has a high withstand voltage, the withstand voltage of the entire converter is limited by the high-speed switching element, and it is impossible to apply it to a large capacity one, and there is a problem that the withstand voltage of each phase is not balanced.

An object of the present invention is to provide a power converter which has the same capacity and function as a power converter using elements having the same loss characteristics, and which is suitable for reducing the generated loss of the entire converter. To provide.

[0005]

In a power converter for converting AC to DC or vice versa by pulse width modulation control using self-arc-extinguishing elements, elements having different loss characteristics are used for each phase. However, one phase uses a low on-loss element 2
The level output configuration is used, and the other phases are configured as a 3-level output configuration using low switching loss elements. Further, the number of output levels of each phase and the number of serial multiple connections of the elements of each phase are different.

[0006]

The low on-loss element performs switching with a long-period signal based on the output voltage reference wave, reduces the number of times of switching, and operates so that the on state continues for a long time. The ratio of ON loss is larger than that of switching loss. Therefore, when the low ON loss element is operated in this way, almost no switching loss occurs, and the ON loss can be suppressed due to the characteristics of the element. Therefore, the generated loss of the element can be reduced. On the other hand, the low switching loss element is P
When high-speed switching by WM control is performed to increase the number of times of switching and operate so as to generate many pulses in one cycle, the switching loss accounts for a larger proportion than the ON loss in the generated loss of the element. . Therefore, when the low switching loss element is operated in this manner, almost no on loss occurs, and the switching loss can be suppressed due to the characteristics of the element. Therefore,
The generated loss of the element can be reduced. as a result,
Compared to a power converter using switching elements that all have the same loss characteristics, it has the same capacity and function as this,
In addition, it is possible to reduce the generated loss of the entire power converter. Further, the PWM control by the low switching loss element can correct the distortion of the converter output waveform generated in the phase configured by the low on-loss element. In addition, the breakdown voltage of the low switching loss element is generally lower than that of the low on-loss element. Therefore, by making the number of output levels of the phase configured by the low switching loss element or the number of serial multiple connections of the elements larger than the number of output levels of the phase configured by the low on-loss element or the number of serial multiple connections of the elements, The breakdown voltage of each phase can be balanced, and the high breakdown voltage of the low on-loss element can be effectively utilized.

[0007]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an embodiment of the present invention. Generally, GTO and IGBT are used as elements used in vehicle power converters.
As shown in FIG. 5, the GTO has a low ON loss characteristic and the IGBT has a low switching loss characteristic. Here, there is a BJT as a low on-loss element and an FET as a low-switching loss element. Further, as shown in FIG. 6, an element having a small switching loss, such as an IGBT or an FET, has a high operating frequency and a low breakdown voltage. In FIG. 1, 1 is an AC power supply, 2 is a reactor, 3 to 4 are GTOs,
9 to 10 are freewheel diodes antiparallel connected to the GTO, 5 to 8 are IGBTs, 11 to 14 are freewheel diodes antiparallel connected to the IGBT, 15 to 1
6 is a clamp diode, and 17 to 18 are filter capacitors. The elements used for each phase are GTO and IGBT, and the x-phase composed of GTO is a two-level output, IGBT.
The y-phase configured in (3) constitutes a single-phase PWM converter as a 3-level output. Further, 19 to 20 are comparators, 21
Is a multiplier, 22 is a subtractor, 23 is a carrier generation circuit, 24
Reference numerals 25 to 25 respectively represent drive circuits for controlling the x-phase GTO and the y-phase IGBT, and constitute a PWM control circuit.

The operation of the embodiment circuit shown in FIG. 1 will be described with reference to FIG. 2, the ec * reference waveform is the converter voltage command value ec * of FIG. 1, and the ex * reference waveform is the multiplier 2
1 output voltage, ey * reference waveform is output voltage command value ey * to y phase, ex output waveform is output voltage from x phase, ey output waveform is output voltage from y phase, ec output waveform is converter output voltage ec is shown. When the converter voltage command value ec * is issued, the pulse signal Px according to the polarity is obtained by the comparator 19. This pulse signal Px is applied to the drive circuit 24
Drive to the x phase and output waveform ex from the x phase
Is output. Also, the multiplier 20 multiplies the pulse signal Px by half the value of the DC stage voltage Ed to obtain the output voltage e.
x * is obtained, and this is subtracted from the converter voltage command value ec * by the subtracter 21 to output the y-phase output voltage command value ey *.
Get. The pulse signal Py is obtained by comparing this with the carrier wave yc generated by the carrier wave generation circuit 23 by the comparator 22. When the pulse signal Py is input to the drive circuit 25 to drive the y phase, the output waveform e from the y phase to the three levels
y is output. The converter output voltage ec is obtained by subtracting the ey output waveform from the ex output waveform, and the converter output waveform ec becomes a 3-level output as shown in FIG.

Here, the operation of the circuit when the output waveform ey of three levels is output will be described. Output waveform ey +
As for the output, the IGBT5 and the IGBT6 are turned on, and the earth-filter capacitor 17-IGBT5-IGBT6-(e
y) -Owing to the circuit operation of ground, the 0 ₍₊₎ output of the output waveform ey is obtained by the circuit operation of the ground-clamp diode 15-IGBT6- (ey) -ground when the IGBT 6 is turned on, and the output waveform ey -Output is IGBT
7, IGBT8 is turned on, ground-IGBT7-IGB
A circuit operation of T8-filter capacitor 18-ground, and a 0 _(-) output of the output waveform ey is obtained by circuit operation of ground- (ey) -IGBT7-clamp diode 16-ground when the IGBT 7 is turned on. Similarly, the operation on the circuit when the 3-level converter output waveform ec is output will be described. Converter output waveform ec
Is the highest + output of the AC power supply 1-reactor 2-freewheel diode 9-filter capacitor 17-filter capacitor 18-freewheel diode 14
-Freewheel diode 13-AC power supply 1 operates as a circuit, and subsequently, IGBT5 and IGBT6 are turned on, AC power supply 1-reactor 2-freewheel diode 9-
IGBT5-IGBT6--the AC power supply 1 is operated to increase the current value, and then the IGBT5 and the IGBT6 are turned off,
The IGBT 6 is turned on to obtain the + output of 1/2 of the converter output waveform ec, which is obtained by returning to the circuit operation described above.
AC power supply 1-Reactor 2-Freewheel diode 9-Filter capacitor 17-Clamp diode 15
-IGBT6-The 0 ₍₊₎ output of the converter output waveform ec obtained by the circuit operation of the AC power supply 1 is the IGBT5, I
The GBT 6 is turned on and is obtained by the circuit operation of the AC power supply 1-reactor 2-freewheel diode 9-IGBT 5-IGBT 6-AC power supply 1. The highest-output of the converter output waveform ec is: AC power supply 1-freewheel diode 12-freewheel diode 11
-Filter capacitor 17-Filter capacitor 18-
The freewheel diode 10-reactor 2-AC power supply 1 operates as a circuit, subsequently the IGBT7 and the IGBT8 are turned on, and the AC power supply 1-IGBT7-IGBT8-freewheel diode 10-reactor 2-AC power supply 1 is operated, Increase the current value, then IGBT7, IGB
The negative output of 1/2 of the converter output waveform ec is obtained by turning off T8 and returning to the circuit operation described above.
BT7 is turned on and is obtained by the circuit operation of AC power supply 1-IGBT7-clamp diode 16-filter capacitor 18-freewheel diode 10-reactor 2-AC power supply 1. The 0 _(-) output of converter output waveform ec is IGBT7. , IGBT8 turns on, AC power supply 1-I
GBT7-IGBT8-Freewheel diode 10
-Reactor 2-obtained by the circuit operation of the AC power supply 1. The operation on the circuit has been described as operating as a converter. However, when conversion (inverter operation) reverse to that of the converter is performed to perform regenerative control, the GTO can be similarly turned on and off.

In this way, the output ex of the x phase is 18
The pulse is 0 ° current, and the GTO switching frequency is small. Further, the y-phase output ey becomes a pulse switched at the carrier frequency, and the number of switching times of the IGBT becomes large. That is, a GTO having a low on-loss characteristic is used for the x phase, the number of times of switching is reduced, and the operation is performed so that the on-state continues for a long time, thereby increasing the ratio of the on-loss to the loss generated in the GTO. Therefore, the switching loss hardly occurs, and the ON loss can be suppressed due to the characteristics of the GTO. Therefore, the GTO generated loss can be reduced. Further, by using an IGBT having a low switching loss characteristic for the y phase and operating so as to increase the number of times of switching and output a large number of pulses within one cycle, the switching loss accounts for the ON loss among the ON loss. Since the ratio is increased, almost no ON loss occurs, and the switching loss can be suppressed due to the characteristics of the IGBT.
It is possible to reduce the generated loss. In the present embodiment, as a result, the generated loss of the entire converter can be reduced as compared with the case where a switching element having the same loss characteristic such as only GTO or only IGBT is used. Further, although a distorted output waveform including a harmonic component is generated in the x phase configured by the GTO, the distortion of the x phase output waveform can be corrected by the PWM control by the y phase IGBT. Further, in this embodiment, the output ex of the x phase is
Is obtained by a pulse of 180 ° current flow, the circuit configuration for the x phase of the PWM control circuit can be the comparator 19 and the drive circuit 24, and the PWM control circuit can be simplified as a whole. As a result, the cost can be reduced.

Next, in FIG. 1, for simplification, a structure in which the number of parallel connection of GTO and IGBT elements is the same for each phase is shown, but as shown in FIG. 5, the withstand voltage of the IGBT of the low switching loss element is as follows. It is smaller than GTO, which is a low on-loss element. Therefore, in consideration of the current balance of each phase depending on the allowable current value of the element, the number of serial multiple connections of the IGBT element together with the number of y-phase output levels configured by the IGBT element is
It is set to be larger than the number of x-phase output levels composed of GTOs and the number of GTO elements connected in series (not shown). With this configuration, the breakdown voltage of each phase can be balanced, and the high breakdown voltage of the low on-loss element can be effectively utilized. Therefore, the present embodiment can be applied to a large-capacity converter such as a vehicular converter, and also has a problem that the withstand voltage of the converter as a whole is limited by the high-speed switching element. Resolve. Although the GTO and the IGBT are used in the present embodiment, the FET may be used instead of the BJT and the IGBT instead of the GTO.

FIG. 3 shows another embodiment of the present invention. In the present embodiment, the y-phase, which has a three-level output structure using an IGBT in the embodiment shown in FIG. 1, has a simple structure in which the clamp diodes 15 and 16 are removed, and a two-level output is provided. The control method is the same as that of the embodiment of FIG. 1, and FIG. 4 shows the operation waveform of this embodiment. It differs from the embodiment of FIG. 1 in that the output waveform ey has two levels. Therefore, the converter output waveform ec is a two-level output as shown in FIG. Also in this embodiment, two GTOs of x-phase low on-loss elements are connected in series and four y-phase low switching loss elements are connected in series. However, depending on the allowable current value of each element, The number of series multiple connections of the elements of each phase may be changed in consideration of the phase current balance. In this case, it can be applied to a large-capacity one such as a converter for a vehicle. The problem that the breakdown voltage of the entire converter is limited by the high speed switching element is solved. Although the GTO and the IGBT are used also in the present embodiment, the FET may be used instead of the BJT and the IGBT instead of the GTO. Although the embodiments shown in FIGS. 1 and 3 are all shown for the converters, the same can be said for the inverters which perform the inverse conversion operation when regenerative controlling these embodiments.

[0013]

As described above, according to the present invention, it is possible to obtain a power converter having the same capacity and function as a power converter using elements having the same characteristics and having low loss. it can. By changing the number of output levels or changing the number of elements connected in series for each phase, the withstand voltage of each phase can be balanced and the withstand voltage performance of the high withstand voltage element can be effectively used. Further, the PWM control by the low switching loss element can correct the distortion of the converter output waveform generated in the phase configured by the low on-loss element. Further, since the output of a certain phase is obtained by the pulse of 180 ° conduction, the circuit configuration of the PWM control circuit for the phase is simplified, and the cost of the device can be reduced.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention.

FIG. 2 is a voltage output waveform diagram showing a switching operation according to an embodiment of the present invention.

FIG. 3 is a circuit diagram showing another embodiment of the present invention.

FIG. 4 is a voltage output waveform diagram showing a switching operation according to another embodiment of the present invention.

FIG. 5 is a device distribution regarding ON loss and switching loss.

FIG. 6 is a device distribution regarding breakdown voltage and operating frequency.

[Explanation of symbols]

 1 Single-phase AC power source 2 Reactor 3-4 GTO 5-8 IGBT 9-14 Freewheel diode 15-16 Clamp diode 17-18 Filter capacitor 19-20 Comparator 21 Multiplier 22 Subtractor 23 Carrier wave generation circuit 24-25 Drive circuit

Claims (7)

[Claims] 1. A power converter for converting alternating current into direct current by pulse width modulation control using a self-extinguishing element, or vice versa, in one phase, an on loss is smaller than a switching loss (hereinafter, referred to as an element). , Low on-loss element.)
A power converter having a two-level output configuration using the above and a three-level output configuration using an element whose switching loss is smaller than the on loss (hereinafter referred to as a low switching loss element) in the other phases. 2. A power converter for converting alternating current to direct current by pulse width modulation control using a self-extinguishing element, or vice versa, wherein a certain phase uses a low on-loss element.
A power converter having a level output configuration and a three-level output configuration using low switching loss elements for the other phases, wherein the number of output levels of each phase and the number of series multiple connections of the elements of each phase are different. 3. The low on-loss element according to claim 1 or 2, wherein the low on-loss element performs switching in a long cycle based on an output voltage reference wave, and the low switching loss element performs a high-speed switching operation by PWM control to reduce a low on-loss. A power converter characterized in that an output voltage is obtained by subtracting a 3-level output using a low switching loss element from a 2-level output using an element to obtain an output voltage by a converter or a conversion reverse thereto. 4. The low on-loss element according to claim 1, claim 2 or claim 3, and at least two sets of free wheel diodes connected in antiparallel to the low on-loss element, and a low switching loss element on another phase. At least four sets of anti-freewheel diodes connected in anti-parallel to each are provided, and at least two sets of clamps are provided between the connection points of two sets of the low switching loss elements and the connection points of the other two sets of the low switching loss elements. A power converter characterized by connecting a diode. 5. A power converter for converting alternating current to direct current by pulse width modulation control using a self-extinguishing element, or vice versa, wherein one phase is a low on-loss element and the other phase is A power converter having a two-level output configuration using low switching loss elements. 6. A power converter for converting AC to DC or vice versa by pulse width modulation control using a self-extinguishing element, wherein one phase is a low on-loss element and the other phase is A power converter characterized by having a two-level output configuration using low switching loss elements and having different numbers of series multiple connections of elements of each phase. 7. The low on-loss element according to claim 5, wherein the low on-loss element performs switching in a long cycle based on the output voltage reference wave, and the low switching loss element performs high-speed switching operation by PWM control to reduce low on-loss. A power converter characterized in that an output voltage is obtained by subtracting a two-level output using a low switching loss element from a two-level output using an element to obtain an output voltage by conversion of a converter or vice versa.