JPH089684A - Inverter control apparatus - Google Patents

Abstract

PURPOSE:To operate a compressor motor with maximum efficiency by changing an operating current which is given to the compressor motor by a method wherein an inverter power supply is controlled on the basis of an operating current value from a current detector. CONSTITUTION:In the case of an air conditioner, an inverter 2 supplies drive electric power to a compressor motor 3 at a frequency corresponding to a load according to a PWM control signal from a microcomputer 8a for a controller 8, and a current detector CT5 is installed at a power-supply interconnection at any one arbitrary phase out of windings U, V, W on the AC side of the inverter 2. As a result, a secondary current can be changed largely irrespective of the operating frequency of the compressor motor 3. However, since a detection signal is an alternating current, it is converted into a DC voltage via a rectifier circuit 6 so as to be given to an input port for the controller 8 as the detection signal. Consequently, the compressor motor can be operated with maximum efficiency by changing an operating current which is given to the compressor motor from an inverter power supply.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control technique for an air conditioner such as a room air conditioner, and more particularly to an inverter control device capable of performing maximum efficiency operation control using an inverter power supply.

[0002]

2. Description of the Related Art In an air conditioner of a variable frequency control system using an inverter power supply, a converter constituting the inverter power supply rectifies three-phase AC power supplies R, S, T into DC power, and this DC power is converted into an inverter power supply. Is supplied to the inverter constituting the.

In this type of conventional air conditioner, a CT (current transformer) for current detection is arranged between a converter and an inverter, and an AC signal detected by the CT for current detection is passed through a rectifier circuit. Then, it is converted into a DC voltage and applied as a detection signal to the microcomputer.

[0004]

However, when the CT for current detection is arranged between the converter and the inverter in this way, the change in the operating current of the converter motor is small,
Even if the operating frequency changes, it is difficult for the microcomputer to grasp the change in the load state of the converter motor.

As shown in FIG. 5, the output voltage to the compressor motor with respect to the inverter operating frequency has a constant output voltage / operating frequency relationship (referred to as output voltage / operating frequency constant control). In open loop control, it is not related to changes in the load of the compressor motor.

[0006] Therefore, the applicant of the present invention, in such an open loop control, operates efficiently in a certain specific load range (ie, efficient motor drive), but as shown in FIG. 6, the load is considerably light. In this case, a lower voltage is applied as the output voltage at that time as shown in lines L1 to L3, and conversely, when the load becomes considerably heavy, the output voltage at that time is as shown in lines L1 to L2. We came to think that efficient operation could be achieved by applying a higher voltage.

The present invention has been made to solve the above problems, and provides an inverter control device capable of operating a compressor motor at maximum efficiency by changing the operating current supplied from the inverter power supply to the compressor motor. It is intended to be provided.

[0008]

In order to solve the above-mentioned problems, the present invention according to claim 1 provides an inverter power supply in an inverter control device for variably controlling an operating frequency of a compressor by an inverter power supply according to a refrigeration load. A current detector that detects the operating current flowing in the one-phase winding of the motor winding between the motor of the compressor and the compressor, and controls the inverter power supply based on the operating current value from this current detector. And a controller that operates.

[0009]

According to the present invention, the operating current (secondary current) flowing in one phase winding of the motor winding between the inverter power supply and the compressor motor is detected by the current detector. Compared to detecting the current between the inverter-powered converter and the inverter-powered inverter, operation can be performed at maximum efficiency.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 shows a preferred embodiment of an air conditioner incorporating the inverter control device of the present invention.

In FIG. 1, a converter 1 which constitutes an inverter power supply rectifies three-phase AC power supplies R, S and T into DC power and supplies this DC power to an inverter 2 which constitutes the inverter power supply. There is.

The inverter 2 is a PWM (Pulse-Wav) from the microcomputer 8a of the controller 8.
In accordance with an e-Modulation) control signal, driving power (three phases, u, v, w) having a frequency corresponding to a refrigeration (or air conditioning) load (hereinafter, simply referred to as a load) is supplied to the compressor motor 3, and the compressor motor 3 The circulation amount of the refrigerant in the air conditioning unit 4 is controlled by the change in the compression capacity of the air conditioning unit 4, and the air conditioning operation according to the load is performed.

Between the converter 1 and the inverter 2, D
CL (DC detector) and capacitor 7 are provided.

A characteristic of the embodiment of the present invention is that any one of the windings u, v, w of the AC side (output side) of the inverter 2 in the preceding stage of the compressor motor 3, for example, the v phase. The current detector CT (current transformer) 5 is provided in the power supply wiring of.

As described above, the current detector CT for detecting the current value is provided in any one-phase winding of the windings u, v, w on the AC side (output side, secondary side) of the inverter 2. By setting, as will be described later with reference to FIG. 4, the secondary current can be largely changed regardless of the operating frequency of the compressor motor 3. That is, the current detector C on the secondary side
By setting T and monitoring the secondary current by the microcomputer 8a, it is easy to grasp the change in the operating load state of the compressor motor 3. On the other hand, when the current detector CT is arranged between the converter 1 and the inverter 2 as in the conventional case, the change in the primary current is small even if the operating frequency changes, and the operating load state of the compressor motor 3 changes. I can't figure out.

The current detector CT is for taking in the operating current in the one-phase v between the compressor motor 3 and the inverter 2 into the microcomputer 8a. Since the detection signal of the current detector CT5 is AC, the rectifier circuit 6 is used. Is converted into a direct current voltage via and is supplied to the input port of the controller 8 as a detection signal.

The controller 8 uses the detection signal as input data and makes a determination as shown in FIG. 2 by the built-in microcomputer 8a.

This abnormality judgment is made by the microcomputer 8
It is executed by the operation control program stored in the ROM or the like in a.

As described above, FIG. 6 shows the relationship between the output voltage and the inverter frequency.

In the conventional inverter operation, the output voltage / operating frequency relationship is always constant (referred to as output voltage / operating frequency constant control) as described with reference to FIG. 6, but as shown in FIG. The line L1 showing the output voltage / operating frequency relationship is sometimes raised as L2, and the line L1 showing the output voltage / operating frequency relationship is lowered as L3 when the load is light.

As a means for realizing this, the secondary current minimum control is performed according to the flowchart shown in FIG. According to the actually obtained data, this secondary current minimum control is what is called primary efficiency maximum control, which can reduce the annual power consumption. That is, it is possible to reduce the power consumption and realize the operation with the maximum efficiency.

Here, the maximum efficiency operation control (Max Ef
fincycy drive control (hereinafter referred to as MED control) will be described.

This maximum-efficiency operation control is to perform fine adjustment of the output voltage according to the outside air temperature, the operation frequency, and the current condition for the purpose of energy-saving operation. By performing this control, it is possible to always perform the operation with the maximum efficiency on the primary side (minimum input power) according to the operation load.

Under the conditions other than the MED control condition, the operation is always performed based on the predetermined basic output voltage, and in the case of the MED control, the operation is performed based on the correction table of the predetermined basic output voltage.

The conditions for entering the MED control are, for example, an operating frequency of 30 to 60 Hz and an outside air temperature of 35 ° C.
Below (when cooling) / 14 ° C or below (when heating) and the temperature of the coil of the indoor heat exchanger is 46 ° C or below and the secondary side current is 8
A or less (A / D input detected by CT) and the same operating frequency continued for 10 seconds or more.

The allowable range of change in the output voltage during MED control is limited to a certain value or less. This is to prevent runaway of the microcomputer 8a.

Next, the secondary current minimum control will be described with reference to FIG.

First, the microcomputer 8a determines whether or not the above MED control condition is satisfied (step S1). When this MED control condition is not satisfied, the compressor motor 3 of FIG.
To drive.

When this MED control condition is satisfied, the microcomputer 8a adjusts the output voltage and once reduces the output voltage (step S2). Then, for example, after waiting for 5 to 10 seconds, it is determined whether or not the average current value thereafter increases while monitoring the effect of lowering the output voltage (step S3).

When the average current value has not increased in step S3, the microcomputer 8a proceeds to step S4 and determines whether or not the average current value has reached the lower limit value. When the average current value reaches the lower limit value as shown in step S5, the process proceeds to step S6. On the other hand, when the average current value has not reached the lower limit value, the process returns to step S2 so that the average current value reaches the lower limit value (the secondary current value becomes the secondary current final value). The loop of steps S2, S3, S4 and S5 is
It corresponds to the zone ZL on the left side of FIG. 3, and moves in the direction of arrow X1.

On the other hand, when the average current value increases in step S3, the process proceeds to step S7 and the output voltage is increased. However, in this case, the secondary current value becomes the secondary current final value. The loop of steps S2, S3 and S7 corresponds to the zone ZR on the right side of FIG. 3, and moves in the direction of arrow X2.

When the actual secondary current value increases by 1.5 A (when the operating load increases and the output voltage deviates from the optimum value), the output voltage is returned to the reference output voltage (step S8).

The secondary current minimum control is adopted as a means for performing the most efficient inverter drive according to the load state. As a method of adjusting the secondary current to the minimum, the operating current of the compressor motor 3 is read by the microcomputer 8a by the current detector CT, and the microcomputer 8a minimizes the secondary current in a certain load state. Such an output voltage (Vave) is output (closed loop control is performed).

When the minimum secondary current value under a certain operating load (torque) is selected and controlled, as a result, it is operated under the condition that the primary efficiency is maximum (see FIG. 4). This also means choosing the operation where the input power on the primary side is always the minimum. This point is shown in FIG.

FIG. 4 shows an example of the relationship between the primary efficiency, the primary current, the secondary current and the torque (load) in the secondary current minimum control.

The primary efficiency curve is a curve for achieving the same efficiency with the smallest electric energy.

Conventionally, the primary efficiency curves PL1 to PL are used.
It was controlled only by PL2 out of 5. On the other hand, in the present invention, control is performed using the primary efficiency maximum operation envelope PL (indicated by a thick line) that connects the uppermost portions of these primary efficiency curves PL1 to PL5. The smaller the torque, the smaller the current used.

The line connecting the lowermost portions of the secondary current curves SL1 to SL5 is called the secondary current envelope SL, and the current value greatly changes according to the change in torque.

When this secondary current is monitored by the current detector CT shown in FIG. 1, since the change in the secondary current is larger than that of the primary current, load followability is good and optimum control can be performed.

On the other hand, since the change in the primary current PC is very small, it is only a change within the detection error range of the current detector CT, and the monitoring accuracy is poor. Therefore, more complex control is required. Particularly in a small air conditioner, since the method of monitoring the primary current is adopted, the change in the load cannot be grasped.

By the way, the present invention can be variously modified without departing from the scope of the claims.

[0043]

As described above, according to the present invention, the operating current (secondary current) flowing in the one-phase winding of the motor winding between the inverter power supply and the compressor motor is Since the current is detected by the current detector, the operation can be performed with the maximum efficiency as compared with the case where the current is detected between the converter of the inverter power supply and the inverter of the inverter power supply.

Therefore, the compressor motor can be operated at maximum efficiency due to the change in the operating current supplied from the inverter power supply to the compressor motor.

[Brief description of drawings]

FIG. 1 is a block diagram showing a preferred embodiment of an air conditioner incorporating an inverter control device of the present invention.

FIG. 2 is a flow chart for explaining secondary current minimum control in the present invention.

FIG. 3 is a diagram showing a relationship between an output voltage and a secondary current in FIG.

FIG. 4 is a diagram showing a primary efficiency, a primary current, and a secondary current curve in the present invention.

FIG. 5 is a diagram showing a conventional relationship between an output voltage and an operating frequency.

FIG. 6 is a diagram showing an example of changes in output voltage under heavy load and light load in FIG.

[Explanation of symbols]

 1 Converter that constitutes an inverter power supply 2 Inverter that constitutes an inverter power supply 3 Compressor motor 8 Controller

Claims (1)

[Claims] 1. An inverter control device for variably controlling an operating frequency of a compressor according to a refrigeration load by an inverter power supply, wherein one phase winding of a winding of the motor between the inverter power supply and the motor of the compressor. An inverter control device comprising: a current detector that detects an operating current flowing through the controller; and a controller that controls an inverter power supply based on an operating current value from the current detector.