JPH10164862A - Power conversion apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to utilize regenerative power from a motor effectively by a simple circuit by a method wherein an inverter bridge by which DC power smoothed by a capacitor is converted into AC power so as to be supplied to the motor is installed and a power storage circuit is connected to the capacitor via a step-up and step-down circuit. SOLUTION: In an inverter device, an AC power supply 1 is converted into DC power supply by a rectifier 2. Since the power which is converted by the rectifier 2 contains voltage ripples depending on the frequency of the power supply, it is smoothed into a perfect DC voltage by a smoothing capacitor 3. The smoothed DC voltage is converted, by an inverter bridge 4, into an AC power supply having an arbitrary frequency and an arbitrary voltage, and it drives a motor 5. The main circuit power of the inverter bridge 4 is current- controlled by a step-up and step-down chopper circuit 9 so as to be shifted to a power storage circuit 10. The power storage circuit 10 is a circuit in which a current flowing out from the step-up and step-down chopper circuit 9 can be stored as power, and it is generally a capacitor, a battery or the like.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power conversion device which converts an AC power supply into a DC power supply once, further converts the power supply into an arbitrary AC power supply, and can effectively use regenerative power.

[0002]

2. Description of the Related Art Due to the rapid development of power control elements in recent years, inverter devices have been widely used in the field of variable speed motors. As shown in FIG. 3, the basic circuit of the main circuit of the inverter device converts an AC power supply 1 into a direct current by a rectifier 2. The power converted by the rectifier 2 has a voltage ripple depending on the frequency of the power supply, and is therefore smoothed by the smoothing capacitor 3 to a complete DC voltage. The smoothed DC voltage is converted by the inverter bridge 4 into an AC power supply having an arbitrary frequency and voltage, and drives the electric motor 5.

[0003] By operating the electric motor 5 at a variable speed by the inverter device, it is possible to improve the machining accuracy and machining efficiency of the workpiece. However, in the inverter device shown in FIG. 3, although it is possible to transfer power from the AC power supply 1 to the electric motor 5, it is not possible to consume regenerated electric power from the electric motor 5 or return it to the power supply side.

The electric power generated by the motor 5 is called regenerative electric power, and is generated when the rotation speed of the motor 5 exceeds a synchronous speed determined by the frequency of the electric power supplied from the inverter device. For example, in the case of a crane application, there is always a hoisting operation and a lowering operation, and in the case of a lowering operation, the regenerative operation state described above is set. This regenerative electric power increases the DC circuit voltage of the inverter device, and eventually leads to overvoltage protection of the inverter device and stops operation. Therefore, it is necessary to treat the regenerative electric power in some way.

Conventionally, methods for processing regenerative power include: (1) As shown in FIG.
A resistance discharge circuit composed of a series circuit of the switching element 6 and the resistor 7 is provided, and when the DC voltage of the inverter device rises and exceeds a certain value, the switching element 6 is turned on.
A method in which regenerative energy is converted to heat and consumed by the resistor 7.

(2) As shown in FIG. 5, there is a system in which the rectifier 2 of the inverter device is constituted by a converter bridge 8 which is the same circuit as the inverter bridge 4 to perform power regeneration.

[0007]

As a circuit configuration shown in FIG. 4, a resistor 7 and a switching element 6 each have one circuit.
It can be composed of simple circuits and is inexpensive. However, since all the regenerative power is converted into heat by the resistor 7 and discarded, it is wasteful of energy and goes backwards from the viewpoint of energy saving. In addition, since the size of the resistor is large, there is a problem that the mounting space and the ambient temperature are increased.

In the circuit configuration shown in FIG. 5, the power is returned to the power supply, so that there is an advantage that the regenerative power is effectively used. However, the circuit configuration requires six sets of switching elements and high-speed diodes, which is compared with a rectifier having only diodes. It is complicated and expensive. In addition, since the inverter DC voltage is converted into a pulsed voltage by the switching element and the power is returned to the power supply, the pulse voltage is superimposed on the power supply voltage, which may adversely affect other devices connected to the same power supply. . An object of the present invention is to provide a power converter that can effectively use regenerative power from a motor with a simple circuit.

[0009]

According to a first aspect of the present invention, there is provided a power converter, comprising: a rectifier for converting AC power to DC power; a capacitor for smoothing DC power output from the rectifier; And a power storage circuit connected to a capacitor via a step-up / step-down circuit.

According to the above means, the regenerative power stored in the power storage circuit can be used effectively. Claim 2
The described power converter includes a rectifier for converting AC power to DC power, a capacitor for smoothing DC power output from the rectifier, and an inverter bridge for converting the smoothed DC power to AC power of an arbitrary frequency and voltage. And a voltage detection circuit connected to both ends of the capacitor, and a power storage circuit connected to the capacitor via a buck-boost circuit, wherein the buck-boost circuit has the capacitor voltage greater than a predetermined reference voltage. In this case, the DC power is transferred from the capacitor side to the power storage circuit, and when the reference voltage becomes small, the DC power is transferred from the power storage circuit to the capacitor side.

According to the above means, the regenerative electric power flowing into the inverter rich from the motor can be stored in the power storage circuit, and the power stored during the regeneration is supplied from the power storage circuit to the electric motor via the inverter rich during power running. In addition, the regenerative power at the time of regeneration can be effectively used at the time of power running, and a power converter suitable for energy saving can be provided.

According to a third aspect of the present invention, a step-down / step-up chopper circuit is used as the step-up / step-down circuit.
The power converter according to claim 4 uses a capacitor as the power storage circuit. A power converter according to a fifth aspect uses a battery as a power storage circuit.

[0013]

FIG. 1 is a main circuit configuration diagram showing an embodiment of a power converter according to the present invention. The basic circuit of the main circuit of the inverter device converts an AC power supply 1 into a direct current by a rectifier 2. The power converted by the rectifier 2 has a voltage ripple depending on the frequency of the power supply, and is therefore smoothed by the smoothing capacitor 3 to a complete DC voltage. The smoothed DC voltage is converted by the inverter bridge 4 into an AC power supply having an arbitrary frequency and voltage, and drives the electric motor 5.

Reference numeral 9 denotes a step-up / step-down chopper circuit, and reference numeral 10 denotes a power storage circuit for storing power. Step-up / step-down chopper circuit 9
Consists of two sets of switching elements 9a and 9b, flywheel diodes 9c and 9d, and a reactor 9e. The switching element 9a and the flywheel diode 9c constitute a step-down chopper, and the switching element 9b and the flywheel diode 9d constitute a step-up chopper. Is configured.

The current detector 11 detects a pulse current IDC flowing from the inverter device into the step-up / step-down chopper circuit 9. FIG. 2 is a configuration diagram of a control circuit of the step-up / step-down chopper circuit 9 of FIG. Hereinafter, the circuit will be described.

In the figure, VDC is a DC voltage signal of the main circuit of the inverter device, and is detected from both ends of the smoothing capacitor 3. VR is a voltage reference signal for starting power transfer with the inverter device, and is a value higher than the peak value of the normal power supply voltage.

Reference numeral 9f denotes a state determination circuit. For example, in a lowering operation for a crane, the DC voltage of the inverter rises due to the regenerative power, and the DC voltage signal VDC>
When the state of the voltage reference signal VR is reached, the state determination circuit 9
f enables the gate circuit 9g1 that operates the step-down chopper circuit including the switching element 9a so that the power is transferred from the inverter rich 4 to the power storage circuit 10.

Reference numeral 9h denotes an arithmetic unit, which is a voltage reference signal VR.
And the DC voltage signal VDC, and calculates the current reference signal I
Output R. 9j is a smoothing circuit for averaging the pulse current IDC flowing into the step-up / step-down chopper circuit 9 from the inverter bridge 4 detected by the current detector 11, and outputting it as a signal IF. This signal IF is compared with the current reference signal IR, and further compared with the triangular wave of the triangular wave transmitter 9k to become the gate signal of the gate circuit 9g1.
Drive a.

As described above, the inverter DC voltage is monitored, and a gate signal is applied to the switching element 9a of the step-down chopper circuit so that a large amount of current flows when the deviation from the reference voltage VR increases. Therefore, the main circuit power of the inverter bridge 4 is current-controlled by the chopper circuit 9 and moves to the power storage circuit 10. The power storage circuit 10 is a circuit that can store the current flowing out of the chopper circuit 9 as power, and is generally a capacitor, a battery, or the like.

As described above, despite the fact that regenerative electric power flows from the motor 5 into the DC circuit of the inverter to increase the DC voltage, the DC voltage is kept constant and the crane is stable without overvoltage protection operation. The lowering operation can be continued.

In the crane operation, the lowering, that is, the regenerative operation does not continue, and when the lowering is completed, the hoisting, that is, the powering operation is performed next. The power running operation refers to a state in which the current flows from the inverter device to the electric motor 5 in view of the current flow, and is an operation as a normal electric motor.

When the power stored in the previous regenerative operation remains in the power storage circuit 10, the operation of supplying the power of the main circuit of the inverter device from the power storage circuit 10 is performed in reverse to the case of the regenerative operation.

In the case of the power running operation, the DC voltage of the inverter device is high and is the peak value of the power supply voltage. Therefore, DC voltage signal VDC <voltage reference signal VR. Therefore, the control circuit enables the gate circuit 9g2 to operate the boost chopper circuit including the switching element 9b so as to transfer power from the power storage circuit 10 to the inverter device.

In the operation of the boost chopper circuit, when the switching element 9b is turned on, a current flows from the power storage circuit 10 via the reactor 9e. Next, the switching element
When the FF is performed, the energy stored in the reactor 9e passes through the flywheel diode 9c and charges and circulates the smoothing capacitor 3 of the inverter device.

As in the operation during regeneration, the DC voltage signal VD
A current command signal is generated based on the deviation signal between C and the voltage reference signal VR, and is compared with the current signal IF.
By controlling the ON / OFF ratio of the power storage circuit 10, the power of the power storage circuit 10 can be returned to the inverter device, and the stored regenerative power can be effectively used as power for powering. By releasing the power, the next regenerative power can be absorbed.

[0026]

As described above, according to the power conversion device of the present invention, in the case of repeated operation of powering / regenerative operation such as for a crane, it is possible to temporarily store the regenerative electric power from the electric motor and use it for the next powering operation. As a result, a significant energy saving effect can be obtained as compared with the conventional resistive discharge method, and the number of current control elements in the main circuit can be reduced to 1/3 of that of the conventional PWM converter method. It is possible to provide an inexpensive power converter.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a main circuit of a power converter according to an embodiment of the present invention.

FIG. 2 is a configuration diagram of a control circuit of the power converter shown in FIG.

FIG. 3 is a configuration diagram of a main circuit of a conventional power converter.

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

FIG. 5 is a configuration diagram of a main circuit of a conventional power converter.

[Explanation of symbols]

1 is an AC power supply, 2 is a rectifier, 3 is a smoothing capacitor, 4 is an inverter bridge, 5 is an electric motor, 6 is a switching element, 7 is a resistor, 8 is a converter bridge, 9 is a buck-boost chopper, 10 is a power storage circuit, 11 is a current detector.

Claims (5)

[Claims] 1. A rectifier for converting AC power into DC power, a capacitor for smoothing DC power output from the rectifier, and converting the smoothed DC power into AC power having an arbitrary frequency and voltage and supplying the AC power to a motor. An inverter bridge,
A power converter having a power storage circuit connected to the capacitor via a step-up / step-down circuit. 2. A rectifier for converting AC power to DC power, a capacitor for smoothing DC power output from the rectifier, and converting the smoothed DC power to AC power of an arbitrary frequency and voltage and supplying the AC power to a motor. An inverter bridge,
A voltage detection circuit connected to both ends of the capacitor, and a power storage circuit connected to the capacitor via a step-up / step-down circuit, wherein the step-up / step-down circuit is such that the capacitor voltage is higher than a predetermined reference voltage. Transferring the DC power from the capacitor side to the power storage circuit, and transferring the DC power from the power storage circuit to the capacitor side when the capacitor voltage becomes smaller than the reference voltage. Power converter. 3. The power converter according to claim 1, wherein said step-up / step-down circuit is a step-down / step-up chopper circuit. 4. The power converter according to claim 1, wherein said power storage circuit is a capacitor. 5. The power converter according to claim 1, wherein the power storage circuit is a battery.