JPH054737U - Inverter control power supply backup circuit - Google Patents

Abstract

(57) [Abstract] [Objective] In an inverter device that converts AC power into DC by a forward conversion unit RF, converts the DC power into AC by an inverse conversion unit INV, and supplies the DC power to a motor IM, a capacitor capacity for power failure backup is provided. Make it smaller. [Structure] A diode D ₂ and a backup capacitor C ₂ are connected in series between a positive and negative bus connecting the forward conversion unit RF and the inverse conversion unit INV, and a common connection point of the diode D ₂ and the backup capacitor C ₂ and a negative bus. The control circuit 1 is connected between them. When the AC input is normal, the backup capacitor C ₂ is charged as shown by the solid line arrow, and when the instantaneous power failure occurs, the charge stored in the capacitor C ₂ is discharged to the control circuit 1 as shown by the broken line arrow.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a control power supply backup circuit of an inverter device that supplies electric power to a load such as an electric motor.

[0002]

[Prior Art]

 Conventionally, in a standard inverter unit, as a backup method at the time of power failure, for example, an MG method, a capacitor method, a battery method, etc. have been adopted. In the MG method, as shown in FIG. 4A, when the AC power source is normal, the generator AG is driven through the electric motor IM and the flywheel (indicated by a dashed line in the figure), and the AC power source is used. When a momentary power failure occurs, the electromagnetic contactor is switched to perform backup with the output of the generator. As shown in Fig. 4 (b), the capacitor system has a large capacity of the main circuit smoothing capacitor (indicated by the dashed line in the figure) of the DC intermediate circuit that connects the forward conversion unit and the inverse conversion unit, so that when a momentary power failure occurs It backs up both the main circuit and the control circuit. As shown in FIG. 4 (c), the battery system stores electric power in a storage battery by a charger when AC power is normal (indicated by a dashed line in the figure), and backs up by discharging power of the storage battery when an instantaneous power failure occurs. It is a thing.

[0003]

[Problems to be solved by the device]

 The MG system shown in FIG. 4 (a) requires a large number of devices such as an electric motor, a flywheel, a generator, a transformer, and an AVR, which makes the device configuration very complicated and also requires maintenance of the rotating machine. Are required, and the price of the device rises.

Further, in the capacitor method of FIG. 4B, the capacity of the smoothing capacitor of the main circuit has to be made extremely large, resulting in a large installation area of the capacitor and a rise in the device price.

Further, in the battery system of FIG. 4 (c), devices such as a charger and a storage battery must be provided, and the device becomes complicated and the price rises, the installation area becomes large, and the storage battery is large. Will need to be maintained.

Here, in the capacitor system of FIG. 4B, the power source of the control circuit of the inverse converter is taken from the main circuit DC as shown in FIG. 5A. The circuit of FIG. 5 (a) is stopped because the control cannot operate normally when the DC voltage drops to 180 V when the DC voltage is 200 V and 360 V when the DC voltage is 400 V. Now, in the circuit of FIG. 5 (a), the capacity of the backup C that can continue operation for 1 second at 100% load will be calculated. However, the motor efficiency (η _M ) is 90% and the inverter efficiency (η _I ) is 98%.

(Calculation) In order to keep the motor output P _M for Δt time and Ed decrease, the following formula must be established.

[0008]

[Equation 1]

Here, since Ed ₁ = 1.35ei = 1.35 × 220V = 297V (about 300V) and Ed ₂ = 180V, C = 2 × 11KW × 1sec / 0.9 × 0.98 {300 ² −180 ² } = 43 3040 μF (about 0.43 F) As described above, the method of backing up both the main circuit and the control circuit by the capacitor requires a huge capacity of capacitor.

The present invention has been made in view of the above points, and an object thereof is to provide a control power supply backup circuit of an inverter device capable of performing backup at the time of power failure with a capacitor having an extremely small capacity.

[0011]

[Means for Solving the Problems]

 The present invention provides a control power supply for an inverter device including a forward conversion unit that converts the power of an AC power supply into DC power, and an inverse conversion unit that converts the direct current power of the forward conversion unit into AC power and supplies the load. In the backup circuit, a diode and a capacitor are connected in series between the positive and negative DC buses connecting the forward conversion unit and the inverse conversion unit, and the control circuit of the inverter device is connected between the common connection point of the diode and the capacitor and the negative bus. It is characterized by connecting.

[0012]

[Action]

 When the AC power supply is normal, the output power of the forward conversion unit is supplied to the control circuit via the diode and is supplied to the reverse conversion unit for normal operation of the inverter device. Further, at this time, the output current of the forward converter flows through the diode to the capacitor, so that the capacitor is charged. When an instantaneous power failure occurs in the AC power supply, the power supply from the forward converter is cut off to the control circuit, but instead of this, power is supplied by discharging the charge stored in the capacitor. Therefore, the control of the inverter device can be continued even if an instantaneous power failure occurs. In this way, the capacity of the capacitor that backs up the instantaneous power failure is very small because it backs up only the control circuit. The device is extremely simple and inexpensive to construct, since only a diode and a small-capacitance capacitor need be provided in the standard inverter device.

[0013]

【Example】

 An embodiment of the present invention will be described below with reference to the drawings. In FIG. 1, RF is a forward conversion unit that converts AC power introduced from an AC power supply (not shown) into DC power, and is configured by, for example, connecting three-phase bridges of diodes or thyristors. The positive side output end of the forward converter RF has a resistor R₁And the inverse converter INV via a parallel circuit composed of the electromagnetic contactor MC. The inverse conversion unit INV is for converting DC power into AC power, and is composed of, for example, three-phase bridge-connected transistors. A diode D is provided between the positive and negative bus lines that connect the forward conversion unit RF and the inverse conversion unit INV.₂ And backup capacitor C₂Series circuit consisting of the main circuit smoothing capacitor C₁And are connected in parallel. Diode D₂And backup capacitor C ₂ The control circuit 1 is connected between the common connection point and the negative bus. An induction motor IM is connected to the output side of the inverse conversion unit INV.

In the circuit configured as described above, when the AC power supply is normal, the direct-current output power of the forward converter RF is supplied to the control circuit 1 and is also AC-converted by the inverse converter INV, and the forward converter is also provided. The RF output current flows to the backup capacitor C ₂ via the diode D ₂ as shown by the solid line arrow. As a result, the backup capacitor C ₂ is charged when the AC power supply is normal. When a momentary power failure occurs in the AC power supply, the power supply from the forward conversion unit RF to the control circuit 1 is cut off, but instead of this, the discharge current of the backup capacitor C ₂ is as shown by the broken line arrow in the figure. It flows and power is supplied. Therefore, control of the inverter device can be continued when an instantaneous power failure occurs.

A specific circuit of the above embodiment is configured as shown in FIG. 2, for example. 2, the same parts as those in FIG. 1 are denoted by the same reference numerals.

The capacity of the backup capacitor C ₂ is very small because it backs up only the control circuit. For example, if an attempt is made to back up the operation of a 5 kW electric motor for 0.1 second, there are the following differences between the conventional main circuit backup method and the method of the present invention.

(1) In case of main circuit backup C = 2 × 5 × 10 ³ × 0.1 / 0.87 × 0.95 (300 ² −180 ² ) = 0. 021F = 21000 μF {however, motor efficiency (η _M ) = 0.87 and inverter efficiency (η _I ) = 0.95. } (2) In case of only control circuit (backup method of the present invention) As shown by the characteristic line L ₁ in FIG. 3, C is 40 μF.

[0018]

[Effect of the device]

 As described above, according to the present invention, the backup capacitor is charged when the AC power supply is normal, and the charge of the backup capacitor is discharged to the control circuit when an instantaneous power failure occurs. It can be extremely small. Therefore, the cost of the device can be reduced and the installation area can be reduced.

[Brief description of drawings]

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

FIG. 2 is a circuit diagram showing a specific configuration of the embodiment.

FIG. 3 is a characteristic diagram showing the relationship between the capacity of a backup capacitor and backup time.

FIG. 4 shows a backup method of a conventional inverter device, FIG. 4 (a) is a circuit diagram of an MG system, FIG. 4 (b) is a circuit diagram of a capacitor system, and FIG. 4 (c) is a circuit of a battery system. Fig.

FIG. 5 shows a control method of a conventional inverter device, and FIG.
5A is a circuit diagram and FIG. 5B is a voltage characteristic diagram.

[Explanation of symbols]

1 ... Control circuit, RF ... Forward conversion unit, INV ... Inverse conversion unit, C
₁ ... main circuit smoothing capacitor, C ₂ ... backup capacitor, D ₂ ... diode.

Claims (1)

[Claims for utility model registration] 1. A forward conversion unit for converting the power of an AC power supply into a DC power, and an inverse conversion unit for converting the DC power of the forward conversion unit into an AC power and supplying the load. In a control power supply backup circuit of an inverter device comprising: a diode and a capacitor are connected in series between the positive and negative DC buses connecting the forward conversion unit and the inverse conversion unit, and the common connection point of the diode and the capacitor and the negative bus. A control power supply backup circuit for an inverter device, characterized in that a control circuit for the inverter device is connected in between.