JPH08205560A - Power converter - Google Patents

Abstract

(57) [Abstract] [Purpose] To provide a power conversion device that has a power supply side transistor bridge that operates only in a regenerative state and that can suppress circulating current even when the switching pattern of the power supply side transistor bridge changes. To do. [Structure] An element or circuit for suppressing the circulating current is connected between a DC connection terminal of a diode bridge and a DC connection terminal of a power supply side transistor bridge. Then, the circulating impedance is suppressed by increasing the transient impedance of the loop formed by the diode bridge, the power supply side transistor bridge, and the AC reactor.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to improvement of an economical power conversion device using a self-turn-off device and a high speed diode.

[0002]

2. Description of the Related Art With the development of self-turn-off devices such as transistors and gate turn-off thyristors, pulse width modulation (hereinafter referred to as PWM) inverters are widely used in a wide range of fields. Generally, the DC voltage of the PWM inverter does not need to be changed, and thus the AC power supply is used after full-wave rectification. However, when it is necessary to regenerate power to the AC power supply side in an application field where the load motor is in the regenerative state, the circuit exactly the same as the inverter side conversion bridge is connected to the AC side of the inverter and PWM control is performed. A method of regenerating electric power to a power source is used.

In this system, the diode connected in parallel with the switching element of the conversion bridge connected to the AC side must be a high speed diode. This is because when current flows in one diode of two arms connected in series in the transistor bridge and the other transistor turns on, the main circuit smoothing capacitor is short-circuited by transistor operation until the diode recovers the reverse direction. A large short-circuit current flows and the loss increases.

To prevent this, a high speed diode having a short recovery time is used. However, since a high-speed diode has a higher forward voltage than a rectifier diode, most of the current flows to the diode when the transistor bridge on the power supply side operates as a forward converter, which causes a forward voltage drop and There is a drawback in that the efficiency of the converter is reduced because the flow loss becomes large.

When the power source side transistor bridge operates as a forward converter, there is a method of stopping switching of the transistor to operate as a diode bridge. In this case, the switching loss is reduced and the efficiency is improved, but the conduction angle of the current flowing through the diode is 6
The peak current increases to about 0 degree. Therefore, it is necessary to use a high-speed diode having a large current rating with respect to the rated current of the transistors connected in parallel.

To solve the above problems,
Japanese Patent Publication No. 7950 proposes the following method. This method will be described with reference to FIG. The AC power supply 1 is connected to the AC connection terminal of the diode bridge 3 via the high speed fuse 2. From the DC side connection terminal of the diode bridge 3, the smoothing capacitor 5 is passed through the current limiting resistor 4 for initial charging.
Is charged, and after the charging is completed, the contact 6 is closed and converted into alternating current by the inverter bridge 7 to supply alternating current power to the alternating current motor 8. Further, the AC side connection terminal of the transistor bridge 9 in the same circuit as the inverter bridge 7 is connected to the AC connection terminal of the diode bridge 3 via the AC reactor 10, and the DC side connection terminal thereof is also connected to the DC connection terminal of the diode bridge 3.

With the circuit configuration shown in FIG. 3, the diode bridge 3 is passed during forward conversion, and the power source side transistor bridge 9 is PWM synchronized with the phase of the power source only when the DC voltage rises and enters the regenerative state. By switching, power can be regenerated to an AC power supply with a power factor of approximately 1, and the above-mentioned problem can be solved.

[0008]

In the circuit shown in FIG. 3, the switching element of the transistor bridge 9 on the power supply side operates, that is, the AC reactor 10 in the regenerative state.
The discharge current of is considered using FIG. FIG. 4 shows FIG.
For the two phases of the diode bridge 3 and the power supply side transistor bridge 9 of the circuit of (3), the DC part is rewritten on the same line.

When the U-phase switching element 9u-t and the V-phase element 9v-t of the power source side transistor bridge 9 are turned on, the regenerative current Iu is generated by the smoothing capacitor 5 from the element 9u-t, the input reactor 10u, and the input reactor 10u. It returns to the smoothing capacitor 5 through the AC power source 1, the AC reactor 10v, and the element 9v-t. In this state, when the switching pattern is switched and the switching element 9u-t is turned off, the current flowing in the input reactor 10u tends to continue flowing. That is, the reactor 10u is in the power supply state.

At this time, the reactor 10u is discharged in a loop composed of the U-phase diode 3u-d of the diode bridge 3 and the U-phase switching element 9u-t of the power source side transistor bridge 9. On the contrary, the energy accumulated in the AC reactor 10v flows to the AC power supply 1 through the W-phase diode 9v-d of the power supply side transistor bridge 9 and the U-phase switching element 9u-t of the power supply side transistor bridge 9. That is, the stored energy of the AC reactor 10 may circulate through the diode of the diode bridge 3 at the moment when the switching pattern of the switching element of the power source side transistor bridge 9 changes. In other words, the circulating current due to the stored energy of the AC reactor 10 flows between the diode bridge 3 and the power supply side transistor bridge 9 without flowing into the AC power supply 1.

If the circulating current is too large, the regenerative current to the power source decreases and the distortion current of the regenerative current to the power source increases. An object of the present invention is to provide a power conversion device that has a power supply side transistor bridge that operates only in a regenerative state and that can suppress a circulating current even when the switching pattern of the power supply side transistor bridge changes. is there.

[0012]

According to the present invention, in order to achieve the above object, an element or circuit for suppressing the circulating current is connected between a DC connection terminal of a diode bridge and a DC connection terminal of a power supply side transistor bridge. Is characterized by.

[0013]

The circulating current is suppressed by increasing the transient impedance of the loop formed by the diode bridge, the power source side transistor bridge, and the AC reactor.

[0014]

Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 1 is a circuit diagram showing an embodiment of the present invention. The same parts as those shown in FIG. 3 are designated by the same reference numerals and the description thereof will be omitted.

Between the DC connection terminal of the smoothing capacitor 5, that is, the diode bridge 3 and the DC connection terminal of the power source side, that is, the transistor bridge 9 for power regeneration, a reactor 11 wound around the same iron core with the winding polarity reversed. Connecting. Also, a transistor bridge 9 for power regeneration
The capacitor 12 is connected to the DC connection terminal of.

By the change in the switching pattern of the power source side, that is, the transistor bridge 9 for power regeneration,
The stored energy of one input reactor 10 flows through the AC power supply 1, but the stored energy of the other AC reactor 10 does not flow into the AC power supply 1 and circulates through the diode bridge 3. At this time, the currents flowing through the positive and negative lines between the diode bridge 3 and the DC connection terminals of the power regeneration transistor bridge 9 have a difference corresponding to the circulating current.

When this current difference occurs, the reactor 11
Since a magnetic flux is generated in the coil and functions as an inductance, it acts to suppress the difference in current. Therefore, the circulating current is suppressed. Further, the condenser 12 is the reactor 1
This is for absorbing the voltage surge that occurs when 1 operates as an inductance.

Further, since the magnetic flux generated in the reactor 11 is the difference in current flowing in the positive and negative lines between the diode bridge 3 and the DC connection terminal of the transistor bridge 9 for power regeneration, the iron loss is small and the reactor is small. Can be measured. During the forward conversion operation, a current flows from the AC power supply 1 to the smoothing capacitor 5 via the diode bridge 3, so that a circuit related to power regeneration (input reactor 1
0, the transistor bridge 9 for power regeneration, the capacitor 12, and the circulating current suppressing reactor 11) are separated from each other to form a general inverter device circuit. Therefore, since there is no voltage drop due to the circuit related to power regeneration, efficient inverter operation becomes possible.

(Other Embodiments) As shown in FIG. 2, even if the DC reactor 13 is inserted in each of the positive and negative lines of the DC connection terminal instead of the reactor 11, the circulating current suppressing effect can be obtained. is there.

[0020]

As described above, according to the present invention, in a power conversion device in which a circuit can be configured by connecting a general inverter device and a power regeneration unit having a capacity corresponding to the amount of regeneration of a load, the inverter device and the power regeneration device are used. By inserting the reactor at the connection point of the unit, it is possible to suppress the circulating current due to the discharge of the stored energy of the input reactor when the switching pattern of the bridge for power regeneration is switched, and stable power regeneration is possible. Become.

[Brief description of drawings]

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

FIG. 2 is a circuit diagram of another embodiment,

FIG. 3 is a circuit diagram of a conventional power conversion device,

FIG. 4 is a circuit diagram of a conventional power converter.

[Explanation of symbols]

1 ... AC power supply, 3 ... Diode bridge, 7 ... Inverter bridge, 9 ... Transistor bridge, 10 ... AC reactor, 1
1 ... Reactor, 13 ... DC reactor.

Claims (3)

[Claims] 1. A first bridge having a plurality of self-arc-extinguishing switching elements connected in parallel and a plurality of arms composed of high-speed diodes, and a second bridge having a plurality of arms composed of high-speed or general rectifying diodes. The AC side connection terminals of the first bridge are respectively connected to an AC power supply via an AC reactor, and the AC connection terminals of the second bridge are connected to an AC power supply directly or via an AC reactor. A power converter comprising a current suppressing circuit connected between the DC side connection terminals of the first and second bridges. 2. The power conversion device according to claim 1,
A power converter characterized in that two reactor windings wound on the same iron core are connected between the DC connection terminals of the first and second bridges so that the winding directions (polarities) are opposite. 3. The power conversion device according to claim 1,
A power converter in which a DC reactor is connected between the DC connection terminals of the first and second bridges.