JPS6264283A - Driver for motor - Google Patents

Abstract

PURPOSE:To protect a driver and a load against an overload state by limiting a shaft output in response to the product of the rotating speed and a current of a motor. CONSTITUTION:A rotating speed command generator 7 generates a rotating speed command on the base of temperature detected by a temperature detector 6. A rotating speed detector 11 counts and calculates the rotating speed of the rotor of a motor. A calculating and accelerating/decelerating circuit 8 compares to calculate the rotating speed command with the rotating speed of the rotor and outputs an acceleration/deceleration command to a driver 9. A multiplier 14 calculates the product of the amplitude of a winding current and the rotating speed. An overload discriminator 13 outputs an overload signal to the circuit 8 when the output value of the multiplier 14, i.e., the shaft output of a DC brushless motor 1 exceeds a set value.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a drive device for a motor for driving a compressor that is capable of controlling the rotational speed, and particularly relates to an operation suitable for protecting the drive device when the operating load increases. Concerning load reduction.

[Background of the invention]

A conventional electric motor drive device will be explained with reference to FIG. 1 is a DC brushless electric motor, 2 is a compressor, 3 is an evaporator, 4 is a condenser, and 5 is a pressure reducer, which together constitute a refrigeration cycle.

Further, 6 is a temperature detection circuit, 7 is a rotation speed command generation circuit, and 8 is a temperature detection circuit.
1 is a calculation/acceleration/deceleration circuit, 9 is a drive circuit, 1O is a commutator circuit, 11 is a rotation speed detection circuit, 12 is a rotor position detection circuit, 13 is an overload judgment circuit, and 15 is a current detection circuit. It constitutes the drive unit of the

Next, load reduction operation during overload according to the prior art will be explained. The heat load of the refrigeration cycle increases and the winding current of the motor 1 increases. The magnitude of this current is determined by the current detection circuit 15.
The detected value is manually input to the overload determination circuit 13. When the current exceeds a permissible value, an overload signal is manually input to the calculation/acceleration/deceleration circuit 8 to lower the rotational speed of the motor in an attempt to escape from the overload state. Therefore, for loads where the current is large during high speed rotation, and the current is reduced accordingly when the rotational speed of the motor is lowered, it is possible to effectively reduce the load during overload.

However, as shown in FIG. 4, the load on the refrigeration cycle is such that the current is larger in the medium speed rotation range than in the high speed rotation range, such as a refrigerator. In such a case, when the electric motor drive device according to the known technique is used to escape from an overload state that occurs in a high speed rotation range, an excessive current may flow in a medium speed rotation range and damage the circuit elements. Furthermore, if the set value is set small in advance to prevent damage to the element, the driving device will not be able to fully utilize its capabilities.

[Purpose of the invention]

An object of the present invention is to provide a motor drive device that reduces the operating load so that the motor can continue to operate stably and at its maximum operating capacity in the event that the operating load exceeds the allowable value.
It is about offering.

[Summary of the invention]

When the compressor is driven by an electric motor whose rotational speed can be controlled, the magnitude of the motor's winding current is not necessarily proportional to the rotational speed, and the current is maximum in the medium speed rotation range. On the other hand, there is a load reduction circuit to protect circuit elements from excessive current, but if the current is set at a level that will not damage the main elements of the drive unit due to heat generation in the high-speed rotation range, it will be necessary in the medium-speed rotation range. In some cases, it may become impossible to obtain a suitable drive output.

Therefore, we focused on the fact that the shaft output of an electric motor is given by the product of rotational speed and torque, and that torque and current are proportional.We calculated these products in the electric motor drive device, and by limiting it, we could prevent overloads. The purpose is to protect the drive device and load from the following conditions.

[Embodiments of the invention]

Hereinafter, one embodiment of the present invention will be described in detail using a refrigerator as an example. FIG. 1 is an overall configuration diagram of an embodiment of the present invention. l is a DC brushless motor, 2 is a compressor, 3 is an evaporator, 4
5 is a condenser, 5 is a pressure reducer, and these constitute a refrigeration cycle. Further, 6 is a temperature detection circuit, 7 is a rotational speed command generation circuit, 8 is a calculation/acceleration/deceleration circuit, 9 is a drive circuit, 1o is a commutator circuit, 11 is a rotational speed detection circuit, 12 is a rotor position detection circuit, and 13 is a An overload determination circuit, 14 a multiplication circuit, and 5 a current detection circuit constitute an electric motor drive device.

First, a mechanism for driving the electric motor 1 will be explained.

A temperature detection circuit 6 detects the temperature inside the refrigerator, and a rotation speed command generation circuit 7 generates a rotation speed command based on the temperature. Further, the rotor position detection circuit 12 detects the position of the rotor and outputs it to the drive circuit 9.

The rotational speed detection circuit 11 counts and calculates the rotational speed of the rotor of the electric motor. The calculation/acceleration/deceleration circuit 8 compares and calculates the rotational speed command and the rotational speed of the rotor. If the commanded rotational speed and the actual rotational speed are equal, the rotational speed is maintained; if the commanded rotational speed and the actual rotational speed are not equal, the rotational speed is made equal to the commanded rotational speed. A command to accelerate/decelerate is output to the drive circuit 9. The drive circuit 9 outputs a drive signal to the commutator circuit 10 based on the acceleration/deceleration command and the rotor position signal. The commutator circuit 10 is a DC brushless motor 1
Rotation is maintained by sequentially switching the energized windings.

The electric motor is operated as described above. Further, the current detection circuit 15 detects the winding current, and the multiplication circuit 14 calculates the product of the thickness of the winding current and the rotation speed. The overload determination circuit 13 generates an overload signal and outputs it to the calculation/acceleration/deceleration circuit 8 when the output value of the multiplication circuit, that is, the shaft output of the DC brushless motor exceeds a set value. When this overload signal is generated, the calculation/acceleration/deceleration circuit 8 decelerates the speed according to a preprogrammed procedure regardless of the rotational speed command to protect the motor drive device from the overload condition.

Next, the principle of the present invention will be explained using FIG. 2.

FIG. 2 shows the operating range of the electric motor drive device according to the present invention. The region 9 is a region limited by the maximum rotation speed, and the drive device does not drive the electric motor above a preset maximum rotation speed.

Region 17 is a region limited by current, and when a current larger than a preset current is detected, an overload signal is generated and the above-described load reduction process is performed.

Further, in this case, the rotation speed is in a low to medium speed range, and the heat generated by the drive device and load is not so large that the device and load are not damaged by heat.

Region 16 is a normal operating region where the rotational speed and current are within the rated range. However, if the current increases close to the allowable value in the high-speed rotation range, the heat generated in the drive device and load increases and operation cannot be maintained (this is region 18). Even if the current is below the allowable value, if the product of these, i.e. the shaft output of the motor, exceeds a certain value, an overload signal is generated even if the current is below the allowable value, and load reduction operation is performed to lower the rotation speed.This is a feature of the present invention. It is.

According to this embodiment, it is possible to always maintain operation to the limit of the smaller of the current capacity and heat dissipation capacity of the main element of the motor drive device.

Although this embodiment has been described using a DC brushless motor as the motor, it goes without saying that the present invention can be applied regardless of the type of motor.

〔Effect of the invention〕

According to the present invention, since the maximum output of the electric motor drive device can be limited, it is possible to continue operation with less notching at the maximum output that can be operated. There is an effect of expanding the range.

[Brief explanation of the drawing]

FIG. 1 is an overall configuration diagram of an electric motor drive device according to the present invention;
FIG. 2 is an explanatory diagram of the operating principle of load limiting according to the present invention, and FIG. 3 is an overall configuration diagram of a motor drive device according to a known technique.
FIG. 4 is an explanatory diagram of the load on the refrigerator. 1... Electric motor, 2... Compressor, 3... Evaporator, 4
... Condenser, 5... Pressure reducer, 6... Temperature detection circuit, 7... Rotation speed command generation circuit, 8... Calculation/acceleration/deceleration circuit, 9... Drive circuit, 10. ... Commutator circuit, 11... Rotation speed detection circuit, 12... Rotor position detection circuit, 13... Overload determination circuit, 14... Multiplication circuit, 15... Current detection circuit, 16. ... Steady operation region, 17... Current limit region, 18... Output limit region, 19... Rotation speed limit region. C) Agent: Patent Attorney Katsutoshi Ogawa''- ¥2 GO Date and Time: ¥3 Picture Tea 4 Mouth O Rotation Fun

Claims (1)

[Claims] 1. A refrigeration cycle is composed of a compressor, an evaporator, a condenser, a pressure reducer, etc., and a motor for driving the compressor whose rotational speed can be controlled, a temperature detection circuit, a motor rotational speed command generation circuit, a motor drive control circuit, A motor drive device equipped with a commutator circuit, characterized by being provided with a multiplication circuit for multiplying the rotational speed of the motor or the output frequency of the drive control circuit by the load current, an overload operation determination circuit, and a rotational speed acceleration/deceleration circuit. A drive device for an electric motor.