JP2000092857A - Power conversion device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To miniaturize a capacitor and to prolong life by setting the switching frequencies of a converter circuit and an inverter circuit to be the same, and drive-controlling the switching element of the converter circuit so that it is turned off when the switching element of the inverter circuit is in an on-state. SOLUTION: A drive circuit 23 drives the switching elements of a converter main circuit 21 and an inverter main circuit 22. The converter main circuit 21 is provided with a switching element 25. In the inverter main circuit 22, switching elements 28a-28d and diodes 29a-29d are connected in parallel and they are connected in series. Then, more than two of them are connected to a power source in parallel. The drive circuit 23 generates the gate command pulse of the switching element 25 of the converter main circuit 21 and the gate command pulses of the switching elements 28a-28d of the inverter main circuit 22. A comparator generates a command for tuning on/off the switching elements 25 and 28a-28d.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a DC power source obtained by rectifying a photovoltaic power generation device, a fuel cell power generation device or an AC power source, a load such as a motor or the like which requires inverter drive, or a commercial power source. The present invention relates to a power conversion device used for the purpose of an inverter or the like required for system interconnection.

[0002]

2. Description of the Related Art FIG. 4 shows a conventional example of a power converter used for the above purpose. A converter circuit 11 connected to a DC power source 13 and an AC load (or commercial power source) 14 connected to the converter circuit 11 are shown. , And an inverter circuit 12 for outputting the output. The converter circuit 11
The inverter circuit 12 includes an inductor 15 connected to the DC power supply 13, a switching element 16 and a diode 17 connected to the inductor 15, and a capacitor 18 connected to the diode 17. The inverter circuit 12 includes switching elements 19a to 19d. Diodes 20a-2
0d are connected in series, each connected in parallel,
Further, two or more power supplies are connected in parallel to a power supply. Here, the number of parallel connections is two when the output AC is single-phase and three when the output AC is three-phase.

In the power conversion circuit configured as described above, the voltage from the DC power supply 13 is converted by driving the switching element 16 of the converter circuit 11 for switching, and the switching elements 19a to 19d of the inverter circuit 12 are switched. By driving, AC conversion is performed and power is supplied to an AC load (or commercial power supply) 14. Converter circuit 11 and inverter circuit 1
In many cases, each of the switching elements 2 is driven by providing a drive circuit (not shown). As a result, even if the switching frequency is different or the frequency is the same, the switching is turned on and off independently. ing.

[0004]

However, in the conventional switching method, the switching element of the converter circuit 11 may be turned off when the switching elements 19a to 19d of the inverter circuit 12 are turned off.
At this time, all the current stored in the inductor 15 of the converter circuit 11 is stored in the capacitor 18 through the diode 17 because the switching elements 19a to 19d of the inverter circuit 12 are in an off state. Therefore, in order to cope with this, a capacitor having a large ripple current is required, and there has been a problem that the capacity of the capacitor becomes larger than necessary or the life is shortened.

An object of the present invention is to provide a power converter capable of reducing the size of a capacitor and extending the life thereof in consideration of such a conventional problem of switching drive.

[0006]

According to the present invention, there is provided a converter circuit for converting a DC voltage from a DC power supply to a predetermined DC voltage by driving a switching element on and off;
An inverter circuit that converts the output of the converter circuit into an alternating current having a predetermined frequency by driving the switching element on and off, the switching frequency of the converter circuit and the switching frequency of the inverter circuit are the same, and the switching element of the inverter circuit is And a drive control circuit that drives and controls a switching element of the converter circuit to be turned off when it is turned on.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings showing an embodiment.

FIG. 1 is a block diagram showing a configuration of a power converter according to an embodiment of the present invention. In FIG. 1, reference numeral 21 denotes a converter main circuit, 22 denotes an inverter main circuit, and 23 denotes a drive circuit 23 as a drive control circuit for driving the switching elements of the converter main circuit 21 and the inverter main circuit 22. Converter main circuit 21
Is a switching element 25 connected between the inductor 24 and the common pole;
And a capacitor 27 connected between the diode 26 and a common pole. The inverter main circuit 22 includes switching elements 28a to 28d and diodes 29a to 29d. 29d are connected in series, each being connected in parallel, and two or more are connected in parallel to a power supply. Here, the number connected in parallel is
As in the conventional example, when the output AC is single-phase, the output is two, and when the output is three-phase, the output is three. The drive circuit 23 includes a gate command pulse of the switching element 25 of the converter main circuit 21 and a switching element 28a of the inverter main circuit 22.
This circuit generates gate command pulses of .about.28d. Wiring is connected to the drive circuit 23 at both ends of the capacitor 27 in order to detect the output voltage of the converter main circuit 21.

FIG. 2 is a block diagram showing a function of the drive circuit 23 for generating a converter gate command pulse and an inverter gate command pulse. In FIG. 2, reference numeral 31 denotes a sawtooth voltage generating means, and 32 denotes a triangular wave voltage generating means. As shown in FIG. To generate voltage.

Reference numeral 33 denotes a circuit for detecting the output voltage of the converter main circuit 21 and controlling the pulse width of a gate command pulse for driving the switching element 25 of the converter main circuit 21 so that the output voltage becomes a predetermined voltage. It is a converter command voltage generating means. That is, when the converter output voltage is lower than the predetermined value, the voltage generated from converter command voltage generating means 33 is increased, and when the converter output voltage is higher than the predetermined value, converter command voltage generating means 33 is increased. To reduce the voltage generated from

Reference numeral 34 denotes a comparator as a converter drive pulse generating means for comparing the sawtooth voltage from the sawtooth voltage generating means 31 with the command voltage from the converter command voltage generating means 33. When the voltage is higher than the voltage, switching element 25 of converter main circuit 21
Is turned on, and when the sawtooth voltage is lower than the command voltage, a command to turn off the switching element 25 is generated. As a result, a gate command pulse subjected to PWM modulation as shown in FIG. 3 is generated.

Reference numeral 35 denotes an inverter output command voltage generating means for controlling the pulse width of a command pulse for commanding the output voltage or output current of the inverter main circuit 22.

Reference numeral 36 denotes a comparator serving as an inverter driving pulse generating means for comparing the triangular wave from the triangular wave voltage generating means 32 with the output value from the inverter output command voltage generating means 35. When the voltage is too high, a command to turn on the switching elements 28a to 28d of the inverter main circuit 22 is generated. Conversely, when the triangular wave voltage is lower than the output command voltage, a command to turn off the switching elements 28a to 28d of the inverter main circuit 22 is generated. (Here, the switching element 28a
As a matter of course, the on-off timing of each of the elements 28 to 28d is controlled to output an AC voltage. Therefore, when the switching elements 28a and 28d are on, the switching elements 28b and 28c are off, and when the switching elements 28a and 28d are off, the switching elements 28b and 28c are controlled to be on.) As a result, a gate command pulse subjected to PWM modulation as shown in FIG. 3 is generated. As a result, when the gate command pulse for the converter is turned off, the gate command pulse for the inverter is always turned on.

It is needless to say that the logic may be reversed even if the directions of the triangular wave and the sawtooth wave described in the above embodiment are opposite.

In the above embodiment, the sawtooth wave and the triangular wave are output by hardware. However, the present invention is not limited to this, and the same function may be realized by software using a microcomputer or the like. .

[0016]

As apparent from the above description, the present invention makes the switching frequency of the converter circuit and the inverter circuit the same, and ensures that the switching of the inverter is always turned on when the switching of the converter is turned off. By doing so, there is an advantage that the ripple current flowing into the capacitor is reduced, so that the capacitor can be downsized and the life can be extended.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of a power conversion device according to an embodiment of the present invention.

FIG. 2 is a functional block diagram of a drive circuit in the embodiment.

FIG. 3 is a waveform diagram schematically showing output values from each functional block of the drive circuit according to the embodiment.

FIG. 4 is a block diagram showing a configuration of a conventional power converter.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Converter circuit 12 Inverter circuit 13 DC power supply 14 AC load 21 Converter main circuit 22 Inverter main circuit 23 Drive circuit 31 Saw wave voltage generating means 32 Triangular wave voltage generating means 33 Command voltage generating means for converter 34, 36 Comparator 35 Output command for inverter Voltage generation means

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Yoshiro Tsuchiyama 1006 Kazuma Kadoma, Kadoma City, Osaka Prefecture F-term in Matsushita Electric Industrial Co., Ltd. (reference) 5G053 AA01 CA08 EB01 5H007 AA06 BB06 BB07 CA02 CB02 CB04 CB05 CC12 CC23 DA03 DA05 DA06 DC05 EA02 FA04 5H576 BB06 CC03 CC04 DD01 DD02 HA03 HB02 JJ01 JJ03 LL24

Claims (2)

[Claims] A converter circuit for converting a DC voltage from a DC power supply to a predetermined DC voltage by driving a switching element on and off, and an output of the converter circuit at a predetermined frequency by driving the switching element on and off. An inverter circuit that converts the AC power into the AC power, the switching frequency of the converter circuit and the switching frequency of the inverter circuit are the same frequency, and the switching element of the converter circuit is turned on when the switching element of the inverter circuit is on. A power conversion device, comprising: a drive control circuit that controls off driving. 2. The driving control circuit according to claim 1, further comprising: a sawtooth wave generating means for generating a sawtooth wave voltage; A triangular wave generating means, a converter command voltage generating means for generating a command voltage for controlling a pulse width of a gate command pulse for driving a switching element of the converter circuit, and an output of the converter command voltage generating means. Based on the output of the sawtooth wave generating means, a drive pulse generator for the converter for generating a drive pulse for the switching element of the converter circuit and a pulse width of a gate command pulse for driving the switching element of the inverter circuit are controlled. Command voltage generating means for generating a command voltage for the inverter, the output of the command voltage generating means for the inverter and 2. The power conversion device according to claim 1, further comprising an inverter drive pulse generator that generates a drive pulse for a switching element of the inverter circuit based on an output of the triangular wave generator.