JP2000184746A - Inverter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an inverter of a high power factor of a low cost by alleviating a withstand burden of a capacitor for an arm. SOLUTION: The inverter comprises fly-wheel diodes 31, 32 connected in antiparallel with switching elements 21, 22, and a rectifying power source 10 connected in parallel with a circuit of the elements 21, 22. An AC load 40 is connected from a connecting mid-point of the elements 21, 22 to a connecting mid-point of capacitors 51, 52 for arms. The inverter also comprises three auxiliary diodes 72, 73, 74 connected forward in series, and a smoothing capacitor 71 crossing over two sides 73, 74 of the diodes 72, 73, 74. The inverter also comprises an auxiliary circuit 70 having the diodes 72, 73, 74 and the smoothing capacitors 71, 75 connected in parallel with the circuit of the elements 21, 22.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inverter device for converting a rectified power supply voltage to a high frequency and supplying the same to an AC load.

[0002]

2. Description of the Related Art A conventional apparatus will be described with reference to FIG. The inverter device of FIG. 3 includes a rectified power supply 10 that rectifies an AC power supply 11 voltage. It has a pair of switching elements 21 and 22 which are controlled so as to be turned on and off alternately. Flywheel diodes 31 and 32 are connected in anti-parallel to the switching elements 21 and 22, respectively. It has a pair of series-connected arm capacitors 51 and 52. The circuit of the rectified power supply 10, the circuits of the switching elements 21 and 22, and the circuits of the capacitors 51 and 52 for the arms are connected in parallel with each other. An AC load 40 is provided between a connection point between the switching elements 21 and 22 and a connection point between the arm capacitors 51 and 52. It has three auxiliary diodes 72, 73 and 74 connected in series. Two 7 on one side of each auxiliary diode 72, 73, 74
A smoothing capacitor 71 that straddles 3.74 is provided. Each auxiliary diode 72, 73, 74 includes a smoothing capacitor 75 that straddles the other two 72, 73. Each auxiliary diode 72, 73, 74 and each smoothing capacitor 71, 75
Are connected in parallel to the circuits of the switching elements 21 and 22. Each switching element 21/22
And the auxiliary diodes 72, 73, and 74 are in a serial relationship with each other. The arm capacitor 51 has a large capacity, and the arm capacitor 52 has a small capacity. Although it is also known to use arm capacitors 51 and 52 having the same capacity, it is assumed here that there is a difference between a large capacity and a small capacity. The auxiliary circuit 70 serves to increase the power factor. When the large capacity and the small capacity are set as described above, the power factor is further increased.

The operation of the circuit shown in FIG. 3 will be described. Each of the switching elements 21 and 22 and each of the flywheel diodes 31 and 32 are turned on in the order of 21 → 32 → 22 → 31 → 21. (1) When the switching element 21 is on, a current flows through the closed circuit of the large-capacity arm capacitor 51 → the switching element 21 → the inductive AC load 40 → the large-capacity arm capacitor 51, and the large-capacity arm capacitor 51 Discharge occurs, and electromagnetic energy accumulates in the inductive AC load 40. This operation continues until the switching element 21 is turned off. (2) When the flywheel diode 32 is on,
Inductive AC load 40 → small-capacity arm capacitor 52 →
A current flows in the closed circuit of the flywheel diode 32 → the inductive AC load 40, the electromagnetic energy of the inductive AC load 40 is released, and the small-capacity arm capacitor 52 is charged. This operation continues until the electromagnetic energy of the inductive AC load 40 becomes empty. At the end of the ON period of the flywheel diode 32, the voltage of the small-capacity arm capacitor 52 becomes a high voltage. The voltage obtained by adding the voltage of the large-capacity arm capacitor 51 to the voltage of the small-capacity arm capacitor 52 is applied to the auxiliary circuit 70, and charges the smoothing capacitors 71 and 75 belonging to the auxiliary circuit 70.

(3) When the switching element 22 is on, the capacitor 52 for the small-capacity arm → the inductive AC load 4
0 → switching element 22 → current flows through the closed circuit of the small-capacity arm capacitor 52, the small-capacity arm capacitor 52 is discharged, and electromagnetic energy is accumulated in the inductive AC load 40. This operation continues until the voltage obtained by adding the voltage of the capacitor 51 for the large-capacity arm to the voltage of the capacitor 52 for the small-capacity arm drops to a value equal to the rectified power supply 10 voltage (instantaneous value). Thereafter, the rectified power supply 10 → the capacitor 51 for the large-capacity arm → the inductive AC load 40 → the switching element 22
→ A current flows through the closed circuit of the rectifier power supply 10 →
Power is supplied from Accordingly, the large-capacity arm capacitor 51 is charged, and the electromagnetic energy of the inductive load circuit 40 is released. When the voltage (instantaneous value) of the rectified power supply 10 is appropriately low, the rectified power supply 10 is not fed, and the large-capacity arm capacitor 51 → the inductive AC load 40 → the switching element 22 → (the auxiliary diode 72 → the smoothing capacitor 71) or (Smoothing capacitor 75 → auxiliary diode 74) → A current flows through the closed circuit of the large-capacity arm capacitor 51, and the smoothing capacitors 71 and 75 are discharged. (4) When the flywheel diode 31 is turned on, a current flows through the closed circuit of the inductive AC load 40 → the flywheel diode 31 → the capacitor 51 for the large-capacity arm → the inductive AC load 40, and the electromagnetic force of the inductive AC load 40 The energy is released, and the large-capacity arm capacitor 51 is charged.
This operation continues until the electromagnetic energy of the inductive AC load 40 becomes empty. Here, returning to the above item (1), the operation is repeated. With the above operation, the power supply from the rectified power supply 10 is performed almost continuously, so that the power factor is improved.

[0005]

A voltage of at least a half of the maximum voltage of the rectified power supply 10 is applied to the large-capacity arm capacitor 51 and the small-capacity arm capacitor 52 of FIG. Considering voltage oscillation, a higher voltage is applied. A high-voltage capacitor that can withstand it must be used. SUMMARY OF THE INVENTION It is an object of the present invention to provide an inexpensive inverter device that enables use of a low-withstand-voltage arm capacitor.

[0006]

According to the present invention, a circuit for each arm capacitor is connected in parallel with a circuit including each switching element via at least one smoothing capacitor. For convenience of explanation, if the conventional arm capacitor is an old arm capacitor, the old arm capacitor corresponds to a series circuit (composite capacitor) of the arm capacitor and the smoothing capacitor. For this reason, the arm capacitor voltage is lower than the old arm capacitor voltage by the amount of the smoothing capacitor voltage, and a low-voltage capacitor can be used.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to FIG. The component codes and the like in FIG. 3 described above are diverted as much as possible, and redundant description is omitted as appropriate. 1 includes a rectified power supply 10 for rectifying an AC power supply 11 voltage.
It has a pair of switching elements 21 and 22 which are controlled so as to be turned on and off alternately. Flywheel diodes 31 and 32 are connected in anti-parallel to the switching elements 21 and 22, respectively. The circuit of the rectified power supply 10 and the circuits of the switching elements 21 and 22 are connected in parallel. An AC load 40 is provided between a connection midpoint between the switching elements 21 and 22 and a connection midpoint between the arm capacitors 51 and 52. It has three auxiliary diodes 72, 73 and 74 connected in series. Auxiliary diodes 72 and 73
A smoothing capacitor 71 that straddles the two 73 and 74 on one side of 74 is provided. Each auxiliary diode 72, 73, 74 includes a smoothing capacitor 75 that straddles the other two 72, 73. An auxiliary circuit 70 including each of the auxiliary diodes 72, 73 and 74 and each of the smoothing capacitors 71 and 75 is connected in parallel to the circuit of each of the switching elements 21 and 22. Each switching element 21/22 and each auxiliary diode 72.7
3.74 are in a serial relationship with each other. The circuit of each of the arm capacitors 51 and 52 is connected in parallel with the circuit including each of the switching elements 21 and 22 via at least one smoothing capacitor 71.

FIG. 1 shows an arm condenser 51.5.
The circuit No. 2 is connected to a circuit including the switching elements 21 and 22 via a smoothing capacitor 71 near the arm capacitor 51 side. A series circuit (composite capacitor) of the arm capacitor 51 and the smoothing capacitor 71 corresponds to the old arm capacitor 51 of FIG. In the case of the old arm capacitor 51, the voltage is borne by the old arm capacitor 51 alone. In the case of FIG. 1, the corresponding voltage is shared by the arm capacitor 51 and the smoothing capacitor 71. Old arm condenser 51
The voltage of the arm capacitor 51 is lower than the voltage, and the withstand voltage load is reduced. FIG. 1 is supplemented.
The rectification power supply 10 includes rectification diodes 12 to 15. The AC load 40 is a lighting circuit, and includes a discharge lamp (fluorescent lamp) 41, a ballast inductor 42 in series with the discharge lamp 41, and a preheating capacitor 43 in parallel with the discharge lamp 41. Switching elements 21 and 22 and flywheel diode 31
The 32 and arm capacitors 51 and 52 constitute a half-bridge type inverter. The characteristics of the entire auxiliary circuit 70 are similar to those of a smoothing capacitor, but more precisely, the charging voltage /
This is a partial smoothing circuit having a discharge voltage ratio of 2. A control circuit for controlling the switching elements 21 and 22 to be turned on and off alternately is omitted. During the ON period of the switching element 21, the arm capacitor 51 and the smoothing capacitor 71 are discharged. The arm capacitors 51 and 52 may have the same capacity, but here, as in FIG.
1 is a large capacity, and the latter 52 is a small capacity. It has a higher power factor.

The embodiment shown in FIG. 2 will be described. The inverter device shown in FIG.
Of each switching element 2 via one smoothing capacitor 71 and the other smoothing capacitor 72.
1 and 22 connected in parallel. A series circuit (composite capacitor) of the arm capacitor 51 and the smoothing capacitor 71 corresponds to the old arm capacitor 51 of FIG. A series circuit (composite capacitor) of the arm capacitor 52 and the smoothing capacitor 72 corresponds to the old arm capacitor 52 of FIG. In the case of the old arm capacitor 52, the voltage is borne by the old arm capacitor 52 alone. In the case of FIG. 2, the corresponding voltage is shared by the arm capacitor 52 and the smoothing capacitor 75. The voltage of the arm capacitor 52 is lower than the voltage of the old arm capacitor 52,
The pressure resistance burden is reduced.

[0010]

In the present invention, the circuit of the arm capacitor is connected as required via the smoothing capacitor belonging to the auxiliary circuit. According to this, the withstand voltage load of the arm capacitor is reduced. Therefore, an inexpensive high power factor inverter device can be obtained.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of the device of the present invention.

FIG. 2 is another circuit diagram of the device of the present invention.

FIG. 3 is a circuit diagram of a conventional device.

[Explanation of symbols]

 10: Rectifying power supply 11: AC power supply 12-15: Rectifying diode 21 ・ 22: Switching element 31 ・ 32: Flywheel diode 40: Inductive AC load 41: Discharge lamp 42: Ballast inductor 43: Preheating capacitor 51 ・ 52 : Capacitor for arm 70: Auxiliary circuit 71 ・ 75: Capacitor for smoothing 72 ・ 73 ・ 74: Auxiliary diode

Claims (1)

[Claims] A rectifying power supply for rectifying an AC power supply voltage;
A switching element that is controlled to be turned on and off alternately in a series of pairs is provided, and a flywheel diode is connected in anti-parallel to each of the switching elements, and a circuit of the rectified power supply and a circuit of each of the switching elements are arranged in parallel. An AC load disposed between a connection midpoint of each of the switching elements and a connection midpoint of each of the arm capacitors; three auxiliary diodes connected in series; and one side of the auxiliary diode. A smoothing capacitor that straddles two of the auxiliary diodes, a smoothing capacitor that straddles the other two of the auxiliary diodes, and an auxiliary circuit including each of the auxiliary diodes and each of the smoothing capacitors. Connected in parallel to each other, and the switching elements and the auxiliary diodes are in a serial connection with each other. Inverter device is characterized in that connected in parallel with the circuit including the switching elements via at least one of said smoothing capacitor circuit for use capacitors.