JPH09140186A - Current controller for ac motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To employ a film capacitor by reducing the capacity of a power supply capacitor connected with the power supply side. SOLUTION: The current controller for AC motor comprises a battery 1, an inverter 7 conducting through a gate drive circuit 13, a power supply capacitor C1 connected with the power supply side of inverter 7, an AC motor 11, a control circuit 14 including a microcomputer, an accelerator 19, a drive/reverse switch 20, motor current sensors 9, 10, and a battery current sensor 8. The current controller for AC motor is further provided with a control circuit comprises means for control current waveform where the current level is sustained at a substantially constant level for the electrical angle of basic sine wave in the range of 60-120 deg., and a duty factor control means for inverter where the motor current is fed back from the current sensor and equalized to the control current wave.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to reducing the capacity of a power supply capacitor connected to a power supply side of a device for controlling a three-phase AC motor from a battery, and more particularly to a current control device for an AC motor suitable for a battery forklift.

[0002]

2. Description of the Related Art Conventionally, a device for controlling a three-phase AC motor has generally been focused on flowing a sinusoidal current.

For example, as described in Japanese Patent Application Laid-Open No. 6-296395, a sinusoidal current is passed through the electric motor and the overload output wave is increased in the electrical angle range of 0 to 180 degrees. .

Further, in general, a power supply capacitor is connected to the power supply side so as to absorb a surge when the switching element constituting the inverter is off and a ripple current.

[0005]

The problem to be solved is to reduce the capacity of the power supply capacitor connected to the power supply side. As the power supply capacitor, an electrolytic capacitor is usually used, but the electrolytic capacitor has a relatively short life due to use time and requires maintenance.

Therefore, a film capacitor is used to facilitate maintenance and inspection.

[0007]

When a sinusoidal wave current is supplied to a three-phase AC motor, a ripple current flows in the battery current. A current including the ripple current is supplied to the AC motor so that this ripple current disappears.

That is, the current supplied to the AC motor is made to be near DC.

When a current obtained by combining a sine wave current and a ripple current is supplied to the motor as shown in FIG. 2 (c), the battery current is almost constant as shown by the dotted line in FIG. 2 (b). Flows.

To explain further, (a) of FIG. 2 shows a current waveform flowing from the battery to the inverter. IU (+) shows a U phase, IV (+) shows a V phase, and IW (+) shows a W phase. . FIG. 2B shows the total current value of each phase shown in FIG. The solid and dotted currents are the ripple currents.

FIG. 2C shows the sine wave shown in FIG. 2A added with the ripple current shown in FIG. 2B in order to make the ripple current shown in FIG. 2B zero. . The waveform on the negative side is a waveform of a current flowing through the electric motor 11, and includes ripple currents of IV and IW.

The capacity of the power supply capacitor connected to the power supply side is
Although the ripple current is eliminated, it may be small, but it is necessary to prevent the surge voltage when the semiconductor element forming the inverter is turned on / off from increasing.

The surge voltage is greatly affected by the inductances L1 and L2 due to the connection between the power supply capacitor and the inverter shown in FIG. Normally, if only this surge voltage is absorbed, a film capacitor is used, and the inductance L2 can be made smaller to make it smaller. The capacity of the power supply capacitor may be approximately several hundred microfarads.

[0014]

DETAILED DESCRIPTION OF THE INVENTION The present invention will be described below with reference to FIG.

FIG. 1 shows a block diagram of a control device according to the present invention.

The battery 7 has a wiring inductance L1 and is connected to a power source capacitor C1 and is connected to a power source line C5 and a power source line 6 via an element side inductance L2, and an inverter 7 is provided.
Connect to The battery current sensor 8 is connected to the-power supply line 6, and the current sensor 9 and the current sensor 10 for detecting the current of the electric motor 11 are connected to the U-phase and V-phase electric motor wirings of the electric motor. The semiconductor element 12 of the inverter 7 uses a transistor (IGBT here) in which a diode is reversely connected. The two semiconductor elements 12 form an arm, and the three arms are connected to the U, V, and W phase terminals of the electric motor 11.

The gate drive circuit 13 turns on / off the semiconductor element 12 of the inverter 7. The control circuit 14 receives a signal from the input circuit 15 and operates the inverter. The signals from the forward / reverse switch 20 of the accelerator 19 and the current sensor are input and processed by the microcomputer 17 of the control circuit.

FIG. 2 is a waveform diagram for explaining the operation of the present invention.

The electrical angle is almost constant from 60 to 120 degrees. This is because the current of each phase bears the ripple current.

Electrical angles 30 to 60 degrees and 120 to 1
50 degrees may be added to the U-phase current as shown in FIG. Alternatively, it may be added to the V and W phase currents.

FIG. 3 shows a software flowchart.

The operation mode (power running,
Judgment of regeneration, coasting, stop).

When the battery current is small, the ripple current is small and general sine wave current control is performed. When the battery current is large, the current waveform shown in FIG.

When the battery current cannot be measured, the magnitude of the battery current can be determined by the current value of the current sensor 9 or the current sensor 10 for detecting the current of the electric motor 11.

The inductance L1 in FIG. 1 is about several microhenries, and the inductance L2 is about several tenths of microhenries.

Since the frequency applied to the motor is about 1 to 150 Hertz, the voltage drop due to the inductance L1 is small and there is no problem.

The inductances L1 and L2 are semiconductor elements 1
It appears as a jump voltage when 2 turns on and off. In order to prevent this, the power supply capacitor C1 may have several hundred microfarads. With such a value, the film capacitor can be stored in the space when the conventional electrolytic capacitor is used. Therefore, it is only necessary to look at the appearance during maintenance and inspection.

[0028]

According to the present invention, the capacity of the power supply capacitor can be reduced. Then the film condenser became usable and the maintenance and inspection period became long.

[Brief description of the drawings]

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

FIG. 2 is an operation waveform diagram according to the present invention.

FIG. 3 is a software flowchart.

[Explanation of symbols]

1 ... Battery, 2 ... Power source inductance, 3 ... Power source capacitor, 4 ... Element side inductance, 5 ... + Power source line, 6
...- Power line, 7 ... Inverter, 8 ... Battery current sensor, 9, 10 ... Current sensor, 11 ... AC electric motor, 12 ...
Semiconductor element, 13 ... Gate drive circuit, 14 ... Control circuit, 15 ... Input circuit, 19 ... Accelerator, 20 ... Forward / backward switch.

Claims (1)

[Claims] 1. A battery, an inverter energized by a gate drive circuit, a power supply capacitor connected to the power source side of the inverter, an AC electric motor, a control circuit including a microcomputer, an accelerator, a forward / reverse selector switch, and an electric motor for detecting electric motor current. In a current control device for an AC motor composed of a current sensor, a traveling mode is judged from the forward / reverse selector switch and an accelerator signal, and a peak value proportional to the frequency and current of the basic sine wave is calculated to calculate the electrical angle of the basic sine wave. Inverter conduction ratio control means for calculating a control current waveform in which the current value from 60 degrees to 120 degrees is a substantially constant value and feeding back the current value from the electric motor current sensor so as to be equal to the control current waveform. A current control device for an AC electric motor, comprising a control circuit having the same.