JPH05111291A - Frequency control method for air-conditioner provided with inverter - Google Patents

Abstract

PURPOSE:To realize fine frequency control by determining a slip at the time of compressor operation from the torque component of the primary current of a motor and feeding the difference between a frequency command value and the slip to a comparator for making a decision of the necessity of skip thereby minimizing the frequency width to be skipped. CONSTITUTION:A voltage type PWM inverter 17 drives a motor 18 and a current sensor 19 detects u-phase and v-phase currents Iu and Iv. A primary current operating means 11 outputs a current having maximum instantaneous value among three phase currents as Imax. A coordinates converting means 10 outputs an exciting current component Id and a torque current component Iq. The torque current component Iq is then multiplied by a slip frequency gain constant Ks9 to produce a slip amount which is subtracted from a frequency command value f' fed from a frequency control section 12 thus determining an actual operating frequency 4 of the motor 18. A comparing section 3 compares the actual rotational frequency 4 with a frequency to be skipped and produces a regulated frequency when they matches each other.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control method which does not continuously operate at a resonance point by operating a compressor, and more particularly to a method for finely controlling an operation frequency around the resonance point.

[0002]

2. Description of the Related Art A conventional frequency control method for an air conditioner with an inverter will be described with reference to FIGS.

In FIG. 2, there is a comparison unit 3 for determining whether or not the input frequency 1 is a skip frequency. In FIG. 3, there is a curve 5 showing the characteristic of speed change with respect to a load of a certain constant frequency command value, and this frequency command value is equal to the rotation speed 7. The resonance point 6 exists in the air conditioner. Now, if slip 2 occurs when the compressor is operating at a rotational speed of 7, the compressor will continue to operate at a rotational speed of 4 which is the same as the resonance point. Therefore, it is necessary to give the skip frequency a certain width. Therefore, the following problems can be raised.

In order to skip the resonance point 6, the slip 2 must be taken into consideration and frequencies other than the resonance point 6 must be skipped.

[0005]

The problem to be solved by the present invention is that, in the conventional frequency control method, in order to skip the resonance point, the slip amount is taken into consideration and the frequencies other than the resonance point must be skipped. I couldn't.

An object of the present invention is to perform fine control up to the operating frequency around the resonance point without skipping frequencies other than the resonance point.

[0007]

The present invention accomplishes its objectives by an apparatus and method as shown in FIG. The means will be described below with reference to FIGS. 1 to 4. First, the amount of slip 2 during operation of the compressor is obtained, and the amount of slip 2 is subtracted from the frequency command value, and then input to the comparison unit 3 which determines whether or not to skip.

[0008]

By subtracting the slip amount 2 which can be obtained from the torque current component of the primary current of the electric motor from the frequency command value 1, the frequency 4 at which the electric motor is actually operating can be known. It is determined whether the operating frequency 4 and the resonance point 6 are equal to each other to decide whether to skip. With this device and method, the width of the frequency range other than the resonance point 6 that must be skipped can be reduced, and fine frequency control can be performed around the skip frequency.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a control system to which the present invention is applied will be described with reference to FIGS.

A dotted line 16 is a block diagram showing a control method, which is software stored in the microcomputer ROM. (However, FIG. 4 is a block diagram of only the portion related to the present invention, and does not show the control method of all the software stored in the ROM.) Voltage type PWM
The inverter 17 is driving the motor 18, and the current at this time is detected by the current sensor 19 as the u-phase current and the v-phase currents Iu, I.
v13 is detected, and this is taken into the microcomputer as data by the A / D converter. Regarding the values of Iu and Iv, the maximum instantaneous value is selected from the three phases of u phase v phase w phase in the primary current calculation 11 and is output as Imax15. Further, the value 13 of Iu and Iv is coordinate-converted and Id and Iq14 are output as an exciting current component and a torque current component.

The frequency command value f ₀ * 8 is input to the frequency control unit 12 from the outdoor control board. In addition, the frequency controller 12
A value 14 of Id and Iq and a value 15 of Imax are also input to the device to execute overload protection control, overcurrent protection control, stabilization control, etc., and output a frequency command value f * 1 inside the microcomputer. Here, the slip frequency gain K is added to the torque current component Iq.
The slip amount S2 is obtained by multiplying the constant s9, and the actual frequency 4 of the motor is obtained by subtracting this from the frequency command value f * 1.

The comparison section 3 compares the frequency 4 with the frequency to be skipped, and outputs f * 1 as they are if they are not equal, and outputs the frequency to be skipped if they are equal. The output from the comparison unit 3 is used as it is in the PWM waveform shaping. Further, by feeding back the output from the comparison unit 3 to the frequency control unit, the frequency command value f ₀ * from the outside is output.
From the difference with 8, it is determined whether to accelerate or decelerate.

By this control method, the frequency skip range can be compared with the actual frequency of the motor, so that the slip amount does not have to be taken into consideration in the skip range and the skip range can be minimized. As a result, only the resonance point that should be originally skipped can be skipped, and the unnecessary range other than the resonance point is not skipped. Therefore, fine frequency control can be performed near the resonance point.

[0014]

According to the present invention, since the width of the frequency to be skipped can be minimized, fine frequency control can be performed.

[Brief description of drawings]

FIG. 1 is a control block diagram of the present invention.

FIG. 2 is a control block diagram of a conventional technique.

FIG. 3 is an operation explanatory diagram according to the present invention.

FIG. 4 is an explanatory diagram of an embodiment in which the present invention is applied to an inverter device.

[Explanation of symbols]

1 ... Frequency command value, 2 ... Slip amount, 3 ... Comparison part, 4 ... Operating frequency, 5 ... Curve showing characteristics of speed and load, 6 ... Resonance point.

Claims (1)

[Claims] 1. A speed command signal from the outside, an internal speed command value of a microcomputer, a primary current component value of a motor input from a current sensor, and an exciting current component and a torque current derived by coordinate conversion of the primary current component value. A frequency command value calculated based on the component, a slip amount calculated based on the torque current component value of the electric motor and a constant specific to the electric motor, and a frequency control of an air conditioner with an inverter controlled by a frequency skip range. In the method, the value to be compared with the frequency skip range is a value obtained by subtracting a slip amount from the frequency command value, the frequency control method for an air conditioner with an inverter.