JPS60139185A - Torque detector of ac machine - Google Patents

Abstract

PURPOSE:To accurately detect a torque to a low frequency by relatively cancelling the phase error of a voltage detection due to a transformer by the phase compensation of a current. CONSTITUTION:A phase leading compensator 8 for compensating the phase lead having the same time constant as the phase leading characteristic of a transformer is provided in a line current detector. Thus, when the phase of current detection signal is lead in the amount (delta) that the phase is led by the frequency characteristic of an insulated transformer 4 at a magnetic flux vector phid, the relative position relationship between the current and the magnetic flux is maintained, and a torque can be calculated accurately to a low frequency.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a torque detection device that includes a phase lead compensation circuit for a current detection signal of an AC motor.

[Prior art and its problems]

Conventionally, there is a method of calculating torque from the terminal voltage and current of an AC motor, but the detection phase characteristics of the transformer used to isolate the extra voltage deteriorate at low frequencies.
There was a problem that satisfactory torque detection could not be performed.

Generally, the torque generated by an induction motor can be expressed as a vector cross product of secondary magnetic flux and motor current. That is,
Torque T is T=K −4Xφ・・・・・・・−・・−・−・−・−
...-... (Formula 11, where L: Phase current vector. Secondary flux linkage vector: Constant. Therefore, the two-phase current and secondary flux linkage vector can be expressed as It is possible to detect the electrical torque by detecting the Accuracy in phase difference detection is required. - Here, an example of the configuration of a conventional torque detector is shown in Figure 1. In Figure 1, (11) is a motor, (12) is a motor control device, and (13) is a motor control device. , torque detector, (14) is an isolation transformer for voltage detection, (15) is a current detector, (16) is a magnetic flux vector calculation circuit, (17) is an orthogonal conversion that converts current and magnetic flux from three phases to two phases. (The magnetic flux vector calculation circuit (16) in FIG. 1 is generally composed of a phase voltage integration circuit and an impedance drop compensation circuit.

A drawback of the conventional torque enhancer (13) shown in FIG. 1 is that the detection accuracy is reduced at low frequencies. The reason for this is the transformer (14
This is because the frequency characteristics of ) deteriorate at low frequencies. The transformer is equivalently shown in Figure 2 (a)! be able to. Here, for the input voltage 51 when almost no load current flows in the secondary side (secondary open circuit), Tt - Lt /Rs (lance primary time constant), and the voltage ratio of the transformer is 1:1. shall be. (Ls = L2) (see FIG. 2(b)), and as is clear from the Bode diagram, when the frequency becomes low, the phase of the detected voltage 102 advances with respect to the input voltage L1. Therefore, the calculated magnetic flux, Betator, is
An error in phase lead will occur with respect to the true magnetic flux vector, and an error i will occur in the phase difference between the detected current and the detected magnetic flux, resulting in +1
As can be seen from equation 1, calculation □ results in torque error.

Figure 3 shows this calculated torque error in a vector diagram; t is the true secondary magnetic flux, td is the current detection signal (=true current - Lt), and the true torque error is 3. A in the diagram
As shown in , it is expressed as the area of a rectangle with diagonals t and d, whereas the induced voltage signal (the secondary voltage signal of the isolation transformer (14) side) ad is advanced by δ from the true induced voltage et, and the detected torque calculated by the magnetic flux vector calculation circuit (13) is detected as shown in B in Fig. 3. The area corresponds to the Torr product, and the error is larger than the area of A.

[Purpose of the invention]

It is an object of the present invention to solve these conventional problems and perform phase compensation on a current detection signal to detect torque with high accuracy even at low frequencies.

[Structure of the invention]

The torque detection device of the present invention is characterized in that it is configured to calculate a secondary magnetic flux linkage by performing phase lead compensation on the line current detection signal with a time constant equivalent to the phase lead characteristic of the transformer. It is.

[Example] □ Hereinafter, the present invention will be explained based on embodiments shown in the drawings.

FIG. 4 is a block diagram showing the configuration of the torque detector of the present invention, in which (1) is the electric motor, (2) is the electric motor control device, (
3) is a torque detector, (4) is an isolation transformer, (5) is a current detector, (6) is a magnetic flux vector calculation circuit, (7) is an orthogonal conversion circuit, and (8) is a phase lead compensation circuit.

Here, the phase lead compensation circuit (8) plays the role of maintaining a correct relative phase relationship between the magnetic flux detection signal and the current detection signal even at low frequencies. That is, as shown in the vector diagram of FIG. 5, if the magnetic flux vector Jd advances the phase of the current detection signal by the amount δ that the phase advances due to the frequency characteristics of the isolation transformer, then
The relative phase relationship between current and magnetic flux is maintained, and torque can be calculated correctly. That is, δ=δ' in Figure 5
, (δ' is the phase difference caused by the phase lead compensation circuit (8)), then the detected torque represented by the area of section A and the true torque represented by section B are equal.

From the above, when the primary winding time constant of the transformer is Tt, the input/output transfer function of the phase lead compensation circuit is sTt /
By setting (1+sTt), δ=δ', and calculations can be made with high accuracy up to low frequencies.

Since this phase lead compensator does not pass a DC component, it also has the effect of cutting off the offset of a current detector (such as a CT using a Hall element).

〔Effect of the invention〕

As described above, according to the present invention, 1. This has the effect that phase errors in voltage detection by the transformer can be relatively canceled out by phase compensation of the current, and torque can be detected with high accuracy up to low frequencies.

[Brief explanation of the drawing]

Figure 1 is a block diagram showing the configuration of a conventional torque detector.
Fig. 2 is an explanatory diagram showing the equivalent circuit and transfer function of an isolation transformer, Fig. 3 is an explanatory diagram showing the relationship between true torque and detected torque at low frequencies, and Fig. 4 is an explanatory diagram showing the configuration of the torque detector of the present invention. The block diagram shown in FIG. 5 is an explanatory diagram showing the relationship between true torque and detected torque according to the present invention. (l): Electric motor (2): Motor control device (31:) Lux detector (4): Insulation transformer (5): Current detector
(6): Magnetic flux vector calculation circuit (7): Orthogonal transformation circuit
(8): Phase lead compensation circuit patent applicant Yaskawa Electric Co., Ltd. Agent Masu Kobori (and 2 others) Figure 2 Tt”L1/R1 Figure 3

Claims (1)

[Claims] 1. In a device that detects the +lux of an alternating current machine based on the voltage vector of the alternating current machine detected via a transformer and the secondary linkage magnetic flux vector obtained from the line current of the alternating current machine, the line current detection signal is ζ A torque detection device for an alternating current machine, characterized in that it is configured to calculate a secondary cross-interrupting magnetic flux by performing phase lead compensation having a time constant equivalent to the phase lead characteristic of the transformer.