JP2000002725A - Input current detection method of inverter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an input current detection method at the time of adjusting an alternating current outputted from an inverter, so that an input current from an alternating-current power source to the inverter will not exceed a prescribed value. SOLUTION: An inverter 1 is equipped with CT 15, a full-wave rectifier 16, a filter circuit 17, an alternating voltage detector 18, a direct current voltage detector 19 and a detection circuit 20, and a correction operation relative to an output of the filter circuit 17 is executed by the detection circuit 20, and consequently, a detection accuracy of an input current into the inverter 1 is improved, regardless of the frequency of the commercial power source, and the load to the inverter 1 relative to a digital control by a microcomputer is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for detecting an input current when an AC output from an inverter is adjusted such that a detected value of an input current from an AC power supply to the inverter does not exceed a specified value.

[0002]

2. Description of the Related Art For example, in an air conditioner comprising one outdoor unit and a plurality of indoor units, an inverter for supplying electric power to a motor for driving a compressor built in the outdoor unit has an AC power supply. Adjust the AC output from the inverter so that the input current from the commercial power supply to the inverter does not exceed a specified value set based on ambient temperature and the like, to prevent overload of the inverter and the motor,
The power consumption of air conditioning equipment is reduced.

Conventionally, as a method of detecting the input current of the inverter when performing the above-mentioned adjustment, for example, the following method is performed. . It detects whether or not the value obtained by rectifying and smoothing the secondary current of the current transformer (CT) inserted in the line from the commercial power supply to the inverter exceeds a predetermined value corresponding to the specified value.

[0004] An effective value is calculated from an instantaneous value of a secondary current of a current transformer (CT) inserted in a line from a commercial power supply to an inverter, and whether the effective value exceeds a predetermined value corresponding to the specified value or not. Or to detect.

[0005]

However, the above-described detection method has a simple circuit configuration, but has a disadvantage that a detection error accompanying a change in the frequency or voltage of the commercial power supply is large. In addition, the above detection method has a complicated circuit configuration, and in recent digital control of an inverter by a microcomputer, a sample value of the instantaneous value of the secondary current is converted into a digital value by a high-speed A / D converter. The microcomputer has a large burden in calculating the effective value from the digital value, and requires a microcomputer capable of performing a higher-speed calculation.

An object of the present invention is to solve the above-mentioned problems and to provide a method of detecting an input current of an inverter with a small load on a microcomputer.

[0007]

According to a first aspect of the present invention, a direct current obtained from an alternating current power supply via a rectifying circuit and a smoothing circuit is converted into an alternating current having a desired frequency and voltage by an inverse conversion circuit. An inverter for supplying power to the AC power supply, wherein the input current from the AC power supply does not exceed a specified value. A calculated value based on a value obtained by rectifying and smoothing a secondary current of a current transformer (CT) inserted in a line to a circuit and an output value of the smoothing circuit is used as a detected value of the input current. And

According to a second aspect of the present invention, in the method for detecting an input current of the inverter, a value obtained by rectifying and smoothing a secondary current of a current transformer (CT) inserted in a line from the AC power supply to the rectifier circuit is provided. And a calculation value based on the frequency of the AC power supply is used as the detection value of the input current. According to a third aspect of the present invention, in the method for detecting an input current of the inverter, a value obtained by rectifying and smoothing a secondary current of a current transformer (CT) inserted in a line from the AC power supply to the rectifier circuit; A calculation value based on the output value of the circuit and the frequency of the AC power supply is used as the detection value of the input current.

According to the present invention, a detection error of the input current can be reduced by using a corrected value as a detection value of the input current as described later with respect to a value obtained by rectifying and smoothing the secondary current. The burden on the microcomputer shared with the digital control of the above is also reduced.

[0010]

FIG. 1 is a circuit diagram showing an embodiment of an input current detecting method for an inverter according to the present invention, wherein 1 is an inverter, 2 is a single-phase commercial power supply as an AC power supply, and 3 is It is a three-phase motor. The inverter 1 has a rectifier circuit 11 in which diodes are connected in a two-phase bridge as shown in the figure, a smoothing circuit 12 having a reactor and an electrolytic capacitor as shown in FIG. An inverting circuit 13 in which a parallel circuit is connected in a three-phase bridge, and an inverter for turning on / off each transistor constituting the inverting circuit 13 to generate an alternating current of a desired frequency and voltage at the output of the inverting circuit 13 The control circuit 14, a CT 15 for detecting an input current from the commercial power supply 2, a full-wave rectifier 16 for rectifying a secondary current of the CT 15, and an output of the full-wave rectifier 16 are smoothed. A filter circuit 17 for outputting, an AC voltage detector 18 for detecting a voltage of the AC power supply 1, a DC voltage detector 19 for detecting an output voltage of the smoothing circuit 12, and Filter circuit 17, the AC voltage detector 18, the DC voltage detector 19 performs an operation described later based on the respective output values, and a value corresponding to the input current of the calculated value from the AC power supply 1,
When detecting that the calculated value exceeds a determination value corresponding to a specified value set based on the ambient temperature of the input current or the like, an adjustment signal output from the inversion circuit 13 for adjusting the AC is controlled by an inverter. And a detection operation circuit 20 to be sent to the circuit 14.

The operation of the rectifier circuit 11, the smoothing circuit 12, the inverting circuit 13, and the inverter control circuit 14 provided in the inverter 1 shown in FIG. 1 during normal operation is performed by a well-known technique. The description of the operation is omitted. FIG. 2 is a detailed circuit configuration diagram of the detection operation circuit 20 shown in FIG. 1, 21 is a power supply frequency detection circuit that detects the frequency of the commercial power supply 2 from the detection value of the AC voltage detector 18,
22 is a first input current correction circuit that outputs a first input current correction value obtained by correcting the output value of the filter circuit 17 with the frequency of the commercial power supply 2 detected by the power supply frequency detection circuit 21;
Reference numeral 23 denotes an input voltage estimating circuit that performs an operation based on the detected value of the DC voltage detector 19, the first input current correction value, the frequency of the commercial power supply 2, and a determination value to be described later, and outputs an input voltage estimated value. (1) A second input current correction circuit that calculates and outputs a second input current correction value based on an input current correction value and an input voltage estimation value, and 25 sets a determination value based on the ambient temperature of the input current of the commercial power supply 2 and the like. The judgment value setting circuit 26 is an adjustment signal generation circuit that outputs an adjustment signal to the inverter control circuit 14 when the second input current correction value exceeds the judgment value.

In the detection operation circuit 20, when the time constant of the filter circuit 17 is fixed, the frequency of the commercial power supply 1 (50 Hz or 60 Hz) is used.
Are slightly different even when the effective value of the input current to the inverter 1 is the same value. Therefore, the first input current correction circuit 2
In 2, a correction operation based on the frequency detected by the power supply frequency detection circuit 21 according to a known technique is performed, and the operation expression is the following expression (1).

[0013]

I _D1 = K _A · I _D0 (1) where I _D1 is a first input current correction value output from the first input current correction circuit 22, I _{D0 is} an output value of the filter circuit 17, K _A : a constant. The constant K _A in the above equation (1)
Can be obtained by inserting an AC ammeter in the path to the commercial power supply 2 and the inverter 1 and making the indicated values of the AC ammeter the same when the frequency of the commercial power supply 2 is 50 Hz and when the frequency is 60 Hz. it can.

In the input voltage estimating circuit 23 of the detecting operation circuit 20, the detection value (V _DC ) of the DC voltage detector 19 and the first
Input current correction value (I _D1) and the determination of the frequency and the determination value setting circuit 25 of the commercial power source 2 (I _S) following equation by (2)
To (6) to obtain an input voltage estimated value (V _E ).

[0015]

[Number 2] _{V E = V DC / K B} ... (2) where, K _B are constants obtained by any of the formulas (3) to (6) below.

[0016]

## EQU3 ## K _B = −K ₁ · I _D1 + C ₁ (3) where K ₁ and C ₁ are the frequencies of the commercial power supply 2 of 50 Hz.
In, and the determination value I _S is a constant when the following switching value _{I R (I R ≧ I S} ).

[0017]

K _B = −K ₂ · I _D1 + C ₂ (4) where K ₂ and C ₂ are the frequencies of the commercial power supply 2 of 50 Hz.
In, and the determination value I _S is a constant when the above switching value _{I R (I S ≧ I R} ).

[0018]

K _B = −K ₃ · I _D1 + C ₃ (5) where K ₃ and C ₃ are 60 Hz in frequency of the commercial power supply 2.
In, and the determination value I _S is a constant when the following switching value _{I R (I R ≧ I S} ).

[0019]

K _B = −K ₄ · I _D1 + C ₄ (6) where K ₄ and C ₄ are the frequencies of the commercial power supply 2 of 60 Hz.
In, and the determination value I _S is a constant when the above switching value _{I R (I S ≧ I R} ). The formula (2) constant in to Formula _{(6) (K B, K} 1 ~K 4, C 1 ~C 4) is inserted a an AC voltmeter and AC ammeter path to the commercial power source 2 and the inverter 1 And when the frequency of the commercial power source 2 is 50 Hz, and
The indicated value of the AC voltmeter and AC ammeter when the 0 Hz, can be determined as a value derived from piecewise linear approximation equation that an intersection of the switching value I _R.

Further, the second input current correction circuit 24 of the detection calculation circuit 20 calculates the following equation (7) based on the first input current correction value (I _D1 ) and the input voltage estimated value (V _E ), The calculation result is output as a second input current correction value ( _ID2 ).

[0021]

I _D2 = K _C · I _D1 (7) where K _C is a coefficient corresponding to the estimated input voltage (V _E ), and is an AC voltmeter on the path to the commercial power supply 2 and the inverter 1. And an AC ammeter, and furthermore, the voltage of the commercial power supply 2 is varied by known means, and the value of the coefficient K _C is calculated from the indicated value of the AC voltmeter when the indicated value of the AC ammeter is the same. You can ask.

For example, a home air conditioner comprising one outdoor unit and four indoor units, and a motor 3 (output: 3.7K) for driving a compressor built in the outdoor unit
W), the input value from the commercial power supply 2 (rated output voltage 200 V, 50 Hz) to the inverter 1 is low when the ambient temperature of the place where the outdoor unit is installed is low. 26A,
When it is determined that the input current exceeds 26 A as a result of the calculation of the above equations (1), (2), (4), and (7), an adjustment signal is output from the detection calculation circuit 20, and this adjustment is performed. In each case, the inverter control circuit 14 sets the frequency of the alternating current output from the inverse conversion circuit 13 to 2 Hz from the immediately preceding value based on the signal.
Lower it one by one.

As the ambient temperature increases, the specified value is reduced from 26 A to about 15 A. At this time, when the specified value is set to 20 A (= switching value) or less, equation (4) is used.
Instead, the calculation of equation (3) is performed.

[0024]

According to the present invention, the value obtained by rectifying and smoothing the secondary current of the CT inserted in the path from the commercial power supply to the inverter is determined by the constant of the above formulas (1) to (6). And the coefficients of equation (7) are set to optimal values based on the above-described experimental results, and the value calculated by performing correction based on these equations is used as the detected value of the input current. The detection error can be reduced to almost zero, and the correction operation cycle of the microcomputer used for the digital control of the inverter, which is on the order of 0.1 second, is sufficient. Therefore, the load on the microcomputer is small.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention.

FIG. 2 is a partial detailed circuit configuration diagram of FIG. 1;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Inverter 2 Commercial power supply 3 Motor 11 Rectifier circuit 12 Smoothing circuit 13 Inverting circuit 14 Inverter control circuit 15 CT 16 Full-wave rectifier 17 Filter circuit 18 AC voltage detector 19 DC voltage detector 20 Detection operation circuit 21 Power supply frequency detection circuit 22 First input current correction circuit 23 Input voltage estimation circuit 24 Second input current correction circuit 25 Judgment value setting circuit 26 Adjustment signal generation circuit

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2G035 AA13 AA15 AB08 AC03 AC16 AD02 AD04 AD14 AD19 AD23 AD28 AD55 AD57 AD58 AD65 5H007 AA06 BB06 CA01 CB05 CC01 DB02 DB12 DC02 DC05

Claims (3)

[Claims] An inverter for converting a direct current obtained from an alternating current power supply via a rectifier circuit and a smoothing circuit into an alternating current of a desired frequency and voltage by an inverting circuit and supplying power to the electric motor, wherein In the input current detection method for adjusting the alternating current output by the inverter so that the detected value of the input current from the inverter does not exceed a specified value, a current transformer inserted in a line from the AC power supply to the rectifier circuit is provided. A method for detecting an input current of an inverter, wherein a calculated value based on a value obtained by rectifying and smoothing a secondary current of a transformer (CT) and an output value of the smoothing circuit is used as the detected value of the input current. 2. An inverter for converting a DC obtained from an AC power supply through a rectifier circuit and a smoothing circuit into an AC having a desired frequency and voltage by an inverse conversion circuit and feeding the AC power to a motor, the inverter comprising: In the input current detection method for adjusting the alternating current output by the inverter so that the detected value of the input current from the inverter does not exceed a specified value, a current transformer inserted in a line from the AC power supply to the rectifier circuit is provided. A method for detecting an input current of an inverter, wherein a calculated value based on a value obtained by rectifying and smoothing a secondary current of a transformer (CT) and a frequency of the AC power supply is used as the detected value of the input current. 3. An inverter for converting a DC obtained from an AC power supply through a rectifier circuit and a smoothing circuit to an AC having a desired frequency and voltage by an inverse conversion circuit and feeding the AC power to a motor, the inverter comprising: In the input current detection method for adjusting the alternating current output by the inverter so that the detected value of the input current from the inverter does not exceed a specified value, a current transformer inserted in a line from the AC power supply to the rectifier circuit is provided. A value obtained by rectifying and smoothing a secondary current of a transformer (CT), an output value of the smoothing circuit, and a calculated value based on a frequency of the AC power supply, as a detected value of the input current. Current detection method.