JPH03218296A - inverter device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Detailed Description of the Invention [Field of Application in "Industry" 2] The present invention relates to a control system for an imperter device that controls the frequency of electric power supplied to an electric motor. The present invention relates to a method that can be suitably applied to an inverter device.

[Conventional technology] Conventional sky. The outline of the control device for rotating the drive motors of the eight refrigerant compressors is shown in FIG. In the figure, AC power of three-phase AC power g1 is converted to DC by a converter 2 such as a three-phase aftereffect rectifier circuit,
Next, the power switching section 3 of the inverter device converts the power into three-phase AC power of an arbitrary frequency and supplies it to the refrigerant compressor driving electric motor 4, which is a load. The inverter device is
The structure is such that the higher the frequency of the alternating current power supplied to the electric motor 4, the larger the output current thereof, and thereby the electric motor 4 is driven at a rotation speed corresponding to the frequency of the alternating current supplied from the inverter device. .

The current flowing through the motor 4 is detected by a current detector 5,
The current detection signal l1 is input to the microcomputer 6 provided in the 11U controller of the air conditioner. Is the microcomputer 6 an indoor temperature sensor? External information sources such as 7
The required frequency is reduced based on the information from the controller, and this frequency instruction is sent to the controller 1 and roller 8 of the inverter device. The controller 1-roller 8, in accordance with the instructions from the microcomputer 6, sends a drive signal of the frequency specified by the instruction to the electric insulating section 3. As a result, the inverter device switches the electric motor 4 at the frequency.
to drive.

In this way, in a normal case, that is, when the current flowing through the motor 4 is below a predetermined current (motor rated current), the operating frequency of the motor 4 is lowered by the microcomputer 6 that responds to information from the external information source 7. .

If the current detection signal ■■ from the current detector 5 is an overload signal (that is, it exceeds the rated current of the motor 4)
When , the microcomputer 6 performs frequency division under overload conditions and gives an instruction to reduce the frequency to the controller 8 of the input device. In response to the frequency reduction instruction from the microcomputer 6, the controller 8 sends the frequency-reduced motive signal to the power switching section 3!
j, er. In this way, when an overload current flows, the frequency of the power supplied to the motor 4 is reduced to suppress the overcurrent.

[Problems to be Solved by the Invention] However, in such a conventional device, a current detection signal of the current flowing in the motor is inputted to the microcomputer 6 of the controller of the air conditioner, and this microcomputer 6 detects overload. Alternatively, it is necessary to determine whether the motor is normal and to perform calculations to reduce the operating frequency of the electric motor by taking this determination result into consideration, which complicates the processing in the microcomputer 6. In addition, the controller 8 of the inverter device does not directly receive the overcurrent signal and performs frequency reduction control, but the controller 8 performs frequency reduction control in response to a frequency reduction command from the microcomputer 6. The frequency reduction speed and reduction width were not appropriate, which caused the problem of hunting in the operating frequency of the motor.

3 [Means for Solving the Problems] In order to solve these conventional problems, the present invention provides the following:
A current detection signal of the motor current is input to the inverter, and the inverter monitors the overload. When an overload condition occurs, the inverter directly controls the frequency reduction.

[Operation] The inverter side determines the state of motor overload and performs control to reduce the frequency of the power supplied to the motor, so the frequency can be reduced quickly by the desired amount in the event of an overload. On the other hand, on the control side of devices that use electric motors (air conditioners, etc.), control is simple because all that is required is to instruct the target frequency, and therefore stable operation for long periods of time is possible at frequencies below the rated load. can.

[Example] An example of the present invention will be described below with reference to FIGS. 1 and 2.

As shown in Figure 1, the controller of a device (such as an air conditioner that uses an electric motor to move a compressor) uses a signal corresponding to external information such as the detected room temperature and a setting ID. Calculate the required frequency and give this frequency instruction to the inverter. On the inverter side, the motor 4 is driven at a frequency according to this instruction, and the motor current is constantly monitored to determine whether or not there is an overload. When an overload condition is detected, an instruction is given from the controller. A predetermined constant frequency is subtracted from the above-mentioned frequency, and AC power at a frequency from which the constant frequency is subtracted is supplied to the electric motor. This frequency reduction control is continued until the current flowing through the motor becomes smaller than the rated value, that is, until there is no longer an overload.

FIG. 2 shows its control circuit, and in the figure, the same symbols as those shown in FIG. 3 indicate corresponding parts.

As can be seen from the figure, a current detection signal from a current detector 5 that detects the current flowing through the motor 4 is input to a controller 8 in the inverter device. The controller 8 always compares the sampled value of the current detector with the set value Io corresponding to the rated current of the motor 4, and L>
? When the state o appears, it is determined that an overcurrent state has occurred, and the frequency is decreased by a predetermined frequency F1 from the frequency Fc instructed by the controller 6 of the device (Fc-F■).
A shy motion signal is supplied to the electric power switching unit 3. Then, during the next sampling period, the sampling value of the current detection signal 1 remains the set value. If it is larger, the controller 6 of the device further changes the commanded frequency Fc to a predetermined frequency F. ×2
The power switching unit 3 is driven at a frequency (Fc-2F■) obtained by subtracting . Such frequency reduction control is performed for each zumbling period until the overcurrent condition disappears and the condition of ≦Io is satisfied. The predetermined frequency F to be subtracted here is determined as appropriate, but if it is set relatively low, the rotational frequency of the load 4 will not decrease sharply, and the device will become unstable due to frequency hunting. This action can be prevented. The power switching unit 3 is a conventional one consisting of a three-phase bridge circuit made up of switching semiconductor elements such as transistors and lances, and performs switching operations in response to the activation signal. Therefore, when the frequency of the electric motor is reduced, the on-duty ratio of the power switching unit 3 is reduced, and the current flowing through the motor 4 is naturally reduced.

As mentioned in the second section of ``Effects of the Invention'', in the present invention, the occurrence of an overcurrent condition is determined in the inverter device that supplies power to the electric motor, and when the occurrence of the overcurrent condition is determined, each sampling is performed until the overcurrent condition disappears. Since a predetermined frequency is subtracted from the frequency instructed by the controller of the electric motor device for each period to obtain the operating frequency of the inverter device, it is possible to simplify the processing in the controller of the electric motor device and also to prevent overload. Frequency reduction control under load can be performed appropriately and at high speed, and therefore the motor can operate stably for a long time without becoming unstable due to frequency hunting.

[Brief explanation of drawings]

1 and 2 are diagrams for explaining an embodiment of the inverter control method according to the present invention, and FIG. 3 is a diagram for explaining a conventional example. 1. Power supply 2. Converter 3. Power switching unit 4. Motor 5. Current detector 6.. Microcomputer 7. External information source 8. Controller [1 roller (1 other person) 8.

Claims (1)

[Claims] In a control method for an inverter device that drives an electric motor by receiving a frequency instruction from a controller of an electric motor device, the inverter device detects a current flowing through the electric motor and uses the current detection signal to control a power switching section in the inverter device. When the current detection signal exceeds a set value corresponding to the rated current of the motor, a predetermined frequency is subtracted from the frequency instruction in the control section in the inverter device, and the current detection signal An inverter control method characterized in that the power switching section is controlled by subtracting the predetermined frequency until the predetermined frequency falls within the set value.