JPH05328611A - Two-way converter device - Google Patents

Abstract

PURPOSE:To prevent a semiconductor element in a two-way converter device from being damaged due to a resonance current by opening a filter capacitor when a two-way converter is operated as a converter. CONSTITUTION:A switch 46 is provided in series to a capacitor 44 of a filter 40. The load voltage is picked up from the output of a two-way converter 38 by a detecting circuit 48 and input to a comparator circuit 54. When the load voltage is smaller than reference voltage of a reference voltage source 58, by a signal of high level output from the comparator circuit 54, the switch 46 is turned off to open the capacitor 44. Accordingly, resonance due to the capacitor 44 and line impedance is no more generated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bidirectional converter device, and more particularly to, for example, a converter function of converting AC from a system into DC and supplying it to a load, and conversely converting DC from a solar cell or the like into AC. The present invention relates to a bidirectional converter device including a bidirectional converter having an inverter function of regenerating into a grid.

[0002]

2. Description of the Related Art This type of bidirectional converter device is used for an air conditioner using a solar cell as one of power sources, so-called solar air conditioner.

[0003]

Generally, in such a bidirectional converter device, the bidirectional converter is connected to the system through a noise filter, but when the bidirectional converter is operating as the above-mentioned converter. Resonance may occur between the system impedance and the filter capacitor. In such a case, a resonance current is superimposed on the bidirectional converter, and a semiconductor element such as an IGBT (Insulated Gate Bipolar T
The heat of the ransistor) increases and there is a danger that it will be damaged.

Therefore, a main object of the present invention is to provide a bidirectional converter device capable of preventing damage to a semiconductor element due to a resonance phenomenon during converter operation.

[0005]

The present invention provides a bidirectional converter and a bidirectional converter having a function of converting an alternating current from a system to a direct current and supplying it to a load, and a function of converting a direct current into an alternating current to regenerate the system. In a bidirectional converter device provided with a filter capacitor inserted between the converter and the system, the filter capacitor is opened when the load voltage is lower than a predetermined reference value,
It is a bidirectional converter device.

[0006]

The load voltage of the bidirectional converter is taken out, and when the load voltage is equal to or higher than the predetermined reference value, the bidirectional converter operates as an inverter, and resonance between the filter capacitor and the system impedance does not occur. Make the filter capacitor function as it is.
When the load voltage is below the reference value, the bidirectional converter is operating as a converter. For example, by activating a switch according to the output from the converter,
Open the filter capacitor. Therefore, the aforementioned resonance no longer occurs. Therefore, an excessive current due to resonance does not flow in the semiconductor element used in the bidirectional converter.

[0007]

According to the present invention, resonance can be prevented during the converter operation of the bidirectional converter, so that damage to the semiconductor element forming the bidirectional converter can be prevented. The above-mentioned objects, other objects, features and advantages of the present invention will become more apparent from the following detailed description of the embodiments with reference to the drawings.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, bidirectional converter device 10 of this embodiment is used particularly in, for example, a so-called solar air conditioner, and therefore includes a solar cell 12. The DC voltage from the solar cell 12 is input to the DC / DC converter 14. This DC voltage is accumulated in the capacitor 16, converted into an AC voltage by the switching of the FETs 18a and 18b, and taken out from the transformer 20 as an AC voltage according to a predetermined transformation ratio. The alternating voltage is then applied to the four diodes 22a, 22b, 22c and 2
After being rectified by a diode bridge circuit including 2d and passing through a filter 24 including a coil 26 and a capacitor 28,
It is smoothed in the smoothing capacitor 30. Further, this DC voltage is converted into a three-phase AC by the air conditioner inverter 32, and the motor 34 is driven thereby.

A bidirectional converter 38 is interposed between the air conditioner inverter 32 and the commercial power supply 36. The bidirectional converter 38 operates as the converter or the inverter described above. Therefore, when the solar cell 12 has surplus power, the DC voltage generated by the solar cell 12 and output from the smoothing capacitor 30 is input to the bidirectional converter 38. A filter 40 is inserted between the bidirectional converter 38 and the commercial power supply 36, and the filter 40 includes coils 42a, 42b,
42c and 42d and a capacitor 44 are included to shape the waveform of the AC voltage output from the bidirectional converter 38 for regeneration to the system. When the power generated by solar cell 12 is insufficient, AC power from commercial power supply 36 is input to bidirectional converter 38 via filter 40.
The bidirectional converter 38 converts alternating current into direct current, and the converted direct current is smoothed by the smoothing capacitor 30 and input to the air conditioner inverter 32.

Further, in the filter 40, a switch 46 is inserted in series with the capacitor 44. The switch 46 operates in response to a signal from a comparator 62 described later and is turned on (closed) or turned off (open). A detection circuit 48 for detecting the load voltage is arranged on the positive side of the above-mentioned capacitor 30. In the detection circuit 48, the voltage corresponding to the load voltage is taken out through the transformer 52 by the switching operation of the transistor 50 and input to the comparison circuit 54. The comparison circuit 54 includes an inverter 56, and the load voltage extracted by the voltage detection circuit 48 is inverted by the inverter 56. The inverted load voltage is added to the reference voltage of the reference voltage source 58. That is, the load voltage is subtracted from the reference voltage, and the result is passed through the inverting amplifier 60 and the comparator 6
2 to the (-) input. The (+) input of the comparator 62 is grounded. Therefore, the comparator 6
2 outputs a high level signal when the output voltage of the inverting amplifier 60 is zero (ground potential) or less, that is, when the load voltage is higher than the unit voltage. Comparator 6
This signal from 2 is provided as a control signal for the switch 46.

During the inverter operation, the load voltage from the transformer 52 becomes higher than the reference voltage, and as shown in FIG. 2, the inverting amplifier 60 outputs a positive value. And Figure 3
As can be seen from the above, a low level signal is output from the comparator 62. In response to the signal, the switch 46 is turned on and the capacitor 44 is not opened. On the other hand, during the converter operation, the load voltage becomes lower than the reference voltage, and as can be seen from FIG. 2, the inverting amplifier 60 outputs a negative value. Then, as can be seen from FIG. 3, a high level signal is output from the comparator 62. In response to that signal, switch 46 is turned off and capacitor 44 is opened. Therefore, resonance does not occur due to the capacitor 44 and the impedance of the system, and a large resonance current does not flow in each element of the bidirectional converter 38. Therefore, even when the bidirectional converter 38 is operating as a converter, they do not operate. Will not be destroyed.

[Brief description of drawings]

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

FIG. 2 is a graph showing the output of the inverting amplifier of this embodiment.

FIG. 3 is a waveform diagram showing a comparator output of this embodiment.

[Explanation of symbols]

 38 ... Bidirectional converter 44 ... Capacitor 46 ... Switch 48 ... Detection circuit 54 ... Comparison circuit 56 ... Inverter 58 ... Reference voltage source 60 ... Inversion amplifier 62 ... Comparator

Claims (1)

[Claims] 1. A bidirectional converter having a function of converting an alternating current from a system to a direct current and supplying it to a load, and a function of converting a direct current to an alternating current to regenerate the system, and between the bidirectional converter and the system. A bidirectional converter device comprising a filter capacitor inserted in the bidirectional converter device, wherein the filter capacitor is opened when the load voltage is lower than a predetermined reference value.