JP2006029938A - Current offset compensation circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a current offset compensating circuit capable of restraining offset changes in a current sensor for precisely controlling the current. <P>SOLUTION: This current offset compensating circuit is provided with a first current sensor 1 for detecting a first phase current, a second current sensor 3 having polarity reverse to the polarity of the offset change caused by environmental changes in the first current sensor 1 and for detecting a second phase current, and a voltage conversion means 2 for converting the voltage signals output from the respective sensors into current values, and restrains an offset of a third phase current by A/D-converting the first phase current and the second phase current by the voltage conversion means 2 to calculate the current. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a circuit that detects each phase current of three-phase power that supplies power to a motor or the like using two current sensors.

As a conventional current detection method, there is a method of individually detecting currents of two phases in three phases and performing offset compensation with an output signal of a current sensor when the current value is 0. A circuit that compensates an output signal of a current sensor by correcting a voltage is known (see, for example, Patent Document 1).
Japanese Patent Laid-Open No. 10-300798

  However, in the conventional offset compensation method, the compensation amount is determined only when the current value before supplying power to the three phases is 0. For example, the ambient temperature changes while the current is not 0. As a result, the current detection accuracy is deteriorated without being able to cope with the offset change caused by this, and as a result, for example, current control is disturbed.

  SUMMARY OF THE INVENTION The present invention solves the above-described conventional problems, and an object thereof is to provide a current offset compensation circuit capable of controlling current with high accuracy by suppressing an offset change of a current sensor.

  In order to solve the above problem, a first current sensor for detecting a first phase current and a second phase having a polarity opposite to a polarity of an offset change due to an environmental change of the first current sensor. A second current sensor for detecting current; and voltage conversion means for converting a voltage signal output from each sensor into a current value. The voltage conversion means includes a first phase current and a second phase current. A / D conversion is performed to calculate the current, thereby suppressing the offset of the third phase current.

  In the offset compensation circuit of the current sensor of the present invention, it is possible to maintain the accurate current detection by suppressing the offset change when the current is not 0. Therefore, even when the offset of the current sensor changes due to the temperature or the change over time. The influence can be suppressed.

  Moreover, since the same component as the conventional method can be used, it can be suppressed at a low cost.

A first current sensor for detecting a first phase current, and a second current sensor for detecting a second phase current having a polarity opposite to the polarity of an offset change due to an environmental change of the first current sensor And voltage conversion means for converting the voltage signal output from each sensor into a current value, and the voltage conversion means performs A / D conversion on the first phase current and the second phase current to calculate a current. This suppresses the offset of the third phase current.

  The first embodiment converts each phase current into a voltage signal using two current sensors having different polarities of offset changes due to environmental changes, and obtains a current value of each phase from the voltage signal by the voltage conversion means. A description will be given with reference to FIG. 1 and FIG.

  In FIG. 1, the first current sensor 1 changes the U-phase current to the voltage conversion means 2 while changing the voltage signal Vu. The second current sensor 3 changes the W-phase current to the voltage signal Vw and outputs the voltage signal Vw. The voltage conversion means 2 includes a first A / D converter 4, a second A / D converter 5, and a current calculator 6, and the first A / D converter 4 and the second A / D The D converter 5 converts Vu and Vw into digital numerical values Iu and Iw, respectively. The current calculator 6 calculates each phase current Ium, Ivm, Iwm from Iu, Iw.

  The calculation performed by the current calculator 6 is Equation 1, and the three-phase currents Ium, Ivm, Iwm are calculated.

Next, the characteristics of the first current sensor and the second current sensor are shown in FIG. As shown in FIG. 2, the first current sensor 1 and the second current sensor 3 have offsets of opposite polarities such as Δe and −Δe with respect to the same environmental change. Here, in order to simplify the explanation, the absolute values are assumed to be equal.

Here, assuming that the amount of change in the current value after A / D conversion with respect to the offset change amount Δe of each current sensor is IE, the current detection values Ium, Ivm, and Iwm of each phase by the calculation of Equation 1 are true values Iut, For Iuv and Iwt,
Ium = Iut + IE
Ivm = Ivt
Iwm = Iwt-IE
Thus, the U-phase, V-phase, and W-phase current detection values include offsets of + IE, 0, and −IE, respectively, and the root mean square is √2 · IE.

Next, in the case of the conventional example shown in FIG. 3, the current detection values Ium, Ivm, and Iwm of the respective phases obtained by the calculation of Equation 1 are as follows.
Ium = Iut + IE
Ivm = Ivt-2 · IE
Iwm = Iwt + IE
Thus, the U-phase, V-phase, and W-phase current detection values include offsets of + IE, -2 · IE, and + IE, respectively, and the mean square is √6 · IE.

  That is, in the first embodiment, the influence on the current value with respect to the current offset change amount is suppressed to 1 / √3 as compared with the conventional example, and a more accurate current value can be detected.

  Note that the polarities of the offset changes in the first current sensor and the second current sensor need only be in opposite directions, and the effect does not change.

The offset compensation circuit of the current sensor of the present invention is useful for driving current control of a three-phase motor.

Explanatory drawing of the current offset compensation circuit in Example 1 of this invention FIG. 6 is a graph showing the change in offset characteristics of the current sensor according to the first embodiment of the present invention. Current sensor offset variation characteristics in the conventional example

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 1st current sensor 2 Voltage conversion means 3 2nd current sensor 4 1st A / D converter 5 2nd A / D converter 6 Current calculator

Claims (1)

A first current sensor for detecting a first phase current in offset compensation of a current sensor for detecting each phase current of three-phase power for supplying power to a motor or the like using two current sensors; and A second current sensor having a polarity opposite to the polarity of the offset change due to the environmental change of the current sensor for detecting the second phase current, and a voltage for converting the voltage signal output from each sensor into a current value Conversion means, and the voltage conversion means performs A / D conversion of the first phase current and the second phase current to calculate a current, thereby suppressing an offset of the third phase current. Current offset compensation circuit.