JP2002058254A - Current detector circuit for air conditioner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To overcome the problem such that a predetermined or more heating loss occurs due to a use of a resistor and a photocoupler as a means for detecting a DC pulse current of an inverter circuit. SOLUTION: A current detector circuit for an air conditioner comprises an AC current transformer (ACCT) 6 provided at any of an anode and a cathode of a power smoothing circuit to thereby detect the DC pulse current.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a PWM for an air conditioner.
The present invention relates to a current detection circuit of a device having an inverter power conversion circuit.

[0002]

2. Description of the Related Art A conventional current detection circuit of a product having a PWM inverter control circuit has a structure in which a detection resistor is attached between a power supply and a power element and a current flowing through the resistor is converted into a voltage as shown in FIG. Was common.

In order to incorporate the detected voltage into a low-voltage control signal, it is necessary to insulate the high DC voltage of the power section with an expensive photocoupler or the like.

Further, when controlling the air conditioner by detecting the current of the compressor, it is common to use DCCT which does not saturate even at a low frequency.

[0005]

However, in the above-described conventional configuration, even when the resistance value for obtaining the voltage for operating the photocoupler is selected to be the minimum, the heat loss due to the resistance during the operation of the air conditioner is about 3 to 4 W. This has resulted in a circuit configuration that is contrary to energy conservation in recent years. In addition, parts for insulating the circuit are always required, and a new alternative circuit is required.

As a component for solving this problem, there is a DCCT which incorporates a Hall element and does not saturate even with a direct current, but is not employed in an air conditioner due to its complicated and expensive circuit configuration. Similarly, detecting a compressor current to control an advanced air conditioner also has a problem with the cost of the detector.

The present invention has been made to solve the above-described problems, and has as its object to provide an energy-saving and inexpensive current detection circuit.

[0008]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention generally relates to a general-purpose current transformer (ACCT) for detecting an AC input current of 50/60 Hz.
Is attached to either the positive electrode or the negative electrode of the DC smoothing power supply circuit, and the DC pulse current PWM-controlled by the power conversion circuit is detected as a DC pulse current by ACCT.

Further, another invention of the present application is capable of detecting individual currents on the positive side and the negative side of a semiconductor power element, and thus also detecting a current such as a ground fault of a compressor motor operated by a PWM inverter power conversion circuit. It is.

According to another invention of the present application, two or three current transformers are mounted between a power conversion circuit and a compressor motor circuit, and a signal in a non-saturated region is ignored ignoring a signal in a low-frequency saturated region and controlling a current in a non-saturated region. This is detected as a signal.

[0011]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a general PWM inverter control device, 1 is an AC power supply, 2 is a rectifier circuit, 3 is a smoothing capacitor, 4 is a PWM power conversion circuit, 5 is a motor, 6 is a current transformer (ACCT) 7 Is a load resistance of the current transformer, and 8 is a current detection and PWM inverter control circuit.

FIG. 2 shows a current waveform flowing into the power conversion circuit 4 and the frequency is set to about 3 kHz by the PWM inverter control circuit 8 and the current value is set to several amperes depending on the operating conditions and the load motor rating. The current transformer No. 6 has a configuration in which the number of primary windings is one and the inductance is small, and the secondary is wound 3000 times. The loss when current flows through the primary winding is mainly copper loss of the winding loss, and the loss can be reduced.

In order to convert the secondary current of the current transformer into a voltage, a load resistance (RL) is attached to the current detection circuit 8. This resistance loss is hardly lost due to the secondary current of the current transformer (usually about 3 mA), and a general-purpose and inexpensive silicon steel plate can be used for the magnetic material of the core.

[0015] Since the withstand voltage between the primary and the secondary of the current transformer can be easily obtained as a single component with a safety standard corresponding to the AC power supply voltage, the secondary output can be directly connected to the low voltage control circuit.

When a DC pulse waveform is applied to a general-purpose current transformer designed for AC current, measures against DC excitation of the core are problematic. However, the PWM frequency of the harmonic machine of the embodiment is about 3 kHz, and 50/60 Hz. The pulse width is about 1/50 to 60 with respect to the current transformer frequency designed in the above, and the duty ratio of this pulse is usually 50 to 80%, and is not sufficiently saturated with respect to one cycle of AC current (18 to 20 ms). A DC pulse current is applied as shown in FIG.
The slope of the pulse current is determined by the impedance of the wiring and the motor winding. In the PWM inverter control method, the regenerative energy of the load motor is 4 immediately after the DC pulse is turned off at the timing of the upper and lower dead times of the power elements in the power conversion circuit 4 as a reset action for the DC excitation of the current transformer core. Diode →
It flows through the smoothing capacitor 3 to the current transformer for a moment in the reverse direction.

Accordingly, the core magnetic flux flows in a direction for resetting the excitation, so that the saturation of the core is not a problem. While the DC current is zero, the reverse potential corresponding to the excitation of the core remains as a secondary voltage, but this value is very small and does not pose a problem in control. Therefore, it is easy to select 1 by selecting the load resistance (RL).
A secondary voltage proportional to the secondary current can be detected.

In the event of a ground fault or the like on the motor load side, the timing of the negative polarity of the AC power supply (motor → lower power element of power conversion circuit → ACCT (lower) → lower side of rectifier circuit in FIG. 1) Current detection is performed only in the element → AC power supply → motor, but by inserting a similar current transformer also in the positive polarity side, the positive polarity timing of the AC power supply (AC power supply → upper element of rectifier circuit → ACCT (upper side) ) → upper power element of the power conversion element → motor → AC power supply).

FIG. 3 shows an embodiment in which the ACCT is mounted at the position of claim 3, and FIG. 4 shows the characteristics of the ACCT. General-purpose current transformer (ACCT) is 50 / 60H
motor current is low frequency f1
In the following, the core of the current transformer is saturated and its output signal cannot be used. However, the compressor cannot perform its function unless it is operated at an operation frequency higher than a certain frequency, so that the minimum frequency can be limited for control. If detection by ACCT is possible under these minimum conditions, it can be used as a current detector.

In the embodiment of the present invention,
Although FIG. 1-1 shows a single-phase AC power supply, a three-phase AC power supply, DC
The same operation and effect can be obtained with an input power supply.

Although FIGS. 1-2 and 3 show a single-phase full-wave rectifier circuit configuration, a voltage-doubler rectifier circuit, a power factor correction circuit with PFC, and other input power factor correction circuit configurations of passive, active, and partial SW systems. However, the same operation and effect can be obtained.

Further, although two current transformers are arranged in the U and W phases in FIG. 3-6, three current transformers may be mounted in the U, V and W phases.

[0023]

As is apparent from the above embodiment, the present invention proposes a current detecting circuit in which a loss in a current detecting means flowing through a PWM inverter control device is greatly reduced as compared with a conventional resistance type. According to this, the use of a general-purpose current transformer eliminates the need for expensive insulating parts, and provides an effect of low cost and energy saving.

In the present invention, two current detection circuits are arranged on the positive and negative sides of the power supply smoothing circuit to detect a ground fault current of a load device. According to this configuration, the loss of the current detector is minimized. In this way, it is possible to provide an inexpensive ground fault detection protection.

Further, the present invention proposes a current detection circuit outside the saturation region of a general-purpose current transformer (ACCT) by arranging a current transformer in a compressor motor current detection circuit. By adopting the method, an expensive DCCT is not required, and an effect that inexpensive current detection can be performed is achieved.

[Brief description of the drawings]

FIG. 1 is a block diagram showing the configuration of the present invention.

FIG. 2 is a waveform diagram of a current flowing through a current transformer (ACCT).

FIG. 3 is a block diagram showing the configuration of the present invention.

FIG. 4 is an output characteristic diagram of an input current frequency of ACCT.

FIG. 5 is a block diagram showing a configuration of a conventional current detection circuit.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 AC power supply 2 Rectifier circuit 3 Smoothing capacitor 4 Power conversion circuit 5 Motor 6 Current transformer (ACCT) 7 Load resistance 8 Current detection + drive circuit

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (Reference) H02P 7/36 303 H02P 7/36 303U 5H576 7/63 302K 7/63 302 303V 303 6/02 371D (72) Inventor Yohei Suzuki 1006 Kazuma Kazuma, Kadoma City, Osaka Prefecture F-term (reference) 3L060 AA01 CC10 DD02 EE04 3L061 BA01 BA07 5H007 AA06 BB06 CA01 CB02 CB05 CC01 DA05 DC02 EA02 FA03 FA13 FA14 HA01 5H560 EB12 DC JJ01 JJ02 RR10 UA03 XA02 XA12 5H575 AA06 BB02 BB06 BB10 DD06 DD10 GG04 HA08 HB20 LL22 MM02 MM20 5H576 AA10 BB02 BB06 BB10 CC05 DD02 DD07 EE11 GG04 HA02 HB02 LL22 MM02 MM20

Claims (3)

[Claims] A compres- sor motor and a circuit for rectifying an ac power supply for driving the compressor motor into a direct current,
A PWM inverter power conversion circuit for converting the direct current into a three-phase alternating current;
In an air conditioner in which the number of revolutions of the compressor motor is changed by controlling the inverter power conversion circuit, the capacity of the air conditioner is variable, and the overcurrent protection for the semiconductor power element used in the PWM inverter power conversion circuit is performed. ,
An AC current transformer (ACCT) is provided at a positive electrode or a negative electrode of a power supply smoothing circuit as a current detecting element for protecting the permanent magnet inside the compressor motor from over-excitation, and a DC pulse current is generated by the ACCT. A current detection circuit for an air conditioner characterized by detecting. 2. An AC current transformer (ACCT) is connected to a positive electrode of a power supply smoothing circuit as a current detecting element for overcurrent protection of a semiconductor power element of a power conversion circuit from a ground fault to a power supply circuit of a compressor motor. 2. The current detection circuit for an air conditioner according to claim 1, wherein the current detection circuit is provided on a negative electrode and detects a ground fault current by the ACCT. 3. An AC current transformer (ACCT) is provided in a motor circuit as a current detecting element for taking in an operating current of a compressor motor as a control signal, and the control current is detected by the ACCT. Item 2. The current detection circuit for an air conditioner according to Item 1.