JPH027893A - Current detection and current detection circuit in inverter driving system of ac machine - Google Patents

Abstract

PURPOSE:To find the current of each phase with a single current detector by finding a corrected waveform from a current command signal and by multiplying it by an actual value of current to find the amplitude of winding current of each phase. CONSTITUTION:The current refluxed from an inverter INV to a power source side is detected (b) by a current detector S. With a corrected waveform generation circuit CORR a waveform signal (c) is formed in proportion to the inverse number of the current waveform to be measured with a current detector S when the amplitudes of the current of each phase are equal. With an arithmetic circuit FUNC the current waveform (b) actually measured with the current detector S is multiplied by the waveform (c) formed through the corrected waveform generation circuit CORR to find the winding current of each phase. The winding current of each phase from the arithmetic circuit FUNC is fed back to a current control section CONT and compared with a current command signal CCS, so that a PWM pulse generation circuit is controlled.

Description

DETAILED DESCRIPTION OF THE INVENTION a. Field of Industrial Application The present invention relates to a current detection method and circuit in an inverter drive system of an alternating current machine. In particular, the present invention relates to a current detection method and circuit that can detect the current of each phase without providing a current detector for each phase.

b. Prior Art FIG. 4 shows a conventional method for detecting current in an inverter drive system of an alternating current machine.

The inverter INV is controlled by the signal from the FILM pulse generating circuit Pl, and each phase winding (1°, 2...
−・−・・m) is supplied with current. The current of each phase is detected by a current detector (Sl, S2.-・-
3m). The detected current values of each phase are fed back to the current control unit C0NT. Current command signal CCS
Based on the detected current value, the pulse generation circuit PWM
is controlled.

C9 Problems to be Solved by the Invention In the current detection method or circuit according to the prior art, it is necessary to provide a current detector for each phase.

Therefore, it is necessary to have an equal number of amplifier circuits, and it is also necessary to precisely match the gains of the current detectors for each phase.

An object of the present invention is to provide a current detection method and circuit that can determine the current of each phase using a single current detector.

d. Means for solving the problem The above problem is a current detection method and circuit in an inverter drive system of an AC machine that uses an inverter to control each phase current. When the amplitude of each phase current is equal, a correction waveform generation circuit forms a signal with a waveform proportional to the reciprocal of the current waveform to be measured by the current detector, and the current waveform actually measured by the current detector is Current detection in an inverter drive system of an AC machine, characterized by multiplying a current waveform and a waveform formed by a correction waveform generation circuit using an arithmetic circuit, and determining the amplitude of the winding current of each phase from the output of the arithmetic circuit. solved by the method and circuit.

e. Operation FIG. 1 is a block diagram of a current detection circuit in an inverter drive system of an AC machine according to the present invention, and FIG. 2 is a main diagram for explaining the operation of the method and apparatus according to the present invention in the case of three-phase drive. The signal waveform at the point is shown.

The inverter INV is controlled TJ by the signal from the PWM pulse generation circuit PWP, and each phase winding (1°2
, . . . m).

Hereinafter, in order to make the explanation concrete, it will be referred to as m-3.

The current in each phase is given by a time equation with equal amplitude.

1lI=i@5in(ωt) L ”'l@SIn'(ωt-2π/3)tw=j
o 5in (ωt + 2π/3) inverter I
The current flowing back from the NV to the power supply PS is the sum of the solid line portion (lower half) of each phase winding current shown in Fig. 2(a), so if the sign is reversed, the waveform shown in Fig. 2(b) is obtained. becomes.

Here, the function A(y) is defined as follows.

A (y) = y (y≧O) A (y) = 0 (y < 0) At this time, the waveform Ka (t) in FIG. 2(b) is expressed by the following equation.

Ko(t) = io (A(-sin ωt)+A
(-sin(ωt-2+r/3))+A(-sin(ω
t + 2z/3))) Specifically, the sections (A, B), (B, C), (C, D), (D, E) on the horizontal axis in Figure 2
(E, F), (F, G), (G, H) are the following functions.

Ko(t) =-1o 5in(ωt-2π/3)
(A, B)Ko(t) −1s(sin(ω
t 2 z /3) 5in(ω t)+
2+r/3)) (B, C)Ko(t) =
-4o(sin(a+t)+2z/3)) (C,D
)Ko(t) =-i@5in(ωt)+2
z/3) +sin(wt))(D, E) Ko(t) = is sin ωL
(E, F). (t) =
1o(sin ωt +sin (ωt−2π
/3)) (F, G) Ko(t) --io(sin(ωt -2z/3
)) (G, H) The signal detected by the current detector S provided on the return line from the inverter INV to the power supply is proportional to the above function KO(t).

On the other hand, the correction waveform generation circuit C0RR generates a signal L(t) proportional to the reciprocal of Ko(t).

L(t)=(A(sin a+t)+A(-sin(
ωL 2/3)) + A(-sin (ωt +
2z/3))) -'Specifically, for example, the section (A) on the horizontal axis in FIG.

B) and (B, C) are the following functions.

L(t) = (-5in (ωt -2π/3)) -
' (A, B)L(t)= (-5in (ωt
−2π/3)+sin (ωL + 2z/3) −
' (B, C) Figure 2 (C) shows the correction waveform generation circuit C0RI? The output waveform of is shown.

Signal detected by current detector S and correction waveform generation circuit C0
The output signal of RR is multiplied in the arithmetic circuit FUNC. As shown in FIG. 2(a), when the amplitudes of the phase currents are equal, the output of the arithmetic circuit FUNC becomes constant and its value is equal to the amplitude io of the current.

The amplitude of each phase current iu, iv, iw is 11
゜.

iw. + iw. When , the current detected by the current detector S is the sum of the solid line portion (lower half) of each phase winding current shown in Fig. 2 (dl), so if the sign is reversed, the current detected by the current detector S is as shown in Fig. 2 ( The waveform is shown in e).

The waveform K(t) in FIG. 2(e) is expressed by the following equation.

K(t) = IuoA(sin(IJ t)+1
voA(-sin(ωt-2π/3))++wo^(
−sin (ωt + 2π/3)) Specifically, the sections (A, B), (B, C), (C, D), (
D, E), (E, F) (F, G), (G, H) are the following functions.

K(t)=-iVo 5in(ωt 2π/3)
(A, B) K(t) Tomivo 5in(ωt-
2π/3)-iwo 5in(ωt+2 to/3)
(B, C) (t)=-i, o (sin(
ωt + 2π/3)) (C, D) (t)=-fw@5in(ωt + 2π/3
) −iwo 5in(act) (D, E) K(t)= iws sin ωt
(E, F)K(t)=-iuo
sin ωt −Lo gin(ωL −
2π/3)(F, G) to (t)=-4,o (sin (ωt −2π
/3)) (G, H) The other correction waveform generation circuit C0RR generates the same waveform as the waveform L(t) in FIG. 2(C). Since the output of the arithmetic circuit FUNC is the product of the functions K(t) and L(t), the sections (A, B) and (
The outputs of the arithmetic circuit FUNC at C, D) and (E, F) are each proportional to the winding current t Wet1110+l t of each phase.

The winding current of each phase detected in this way is controlled by the current control section C.
0NT, and the PHI pulse generating circuit P-gate is controlled based on the current command signal CCS and the detected current value.

r, Embodiment The correction waveform generation circuit C0RR can be realized using a known analog function generation circuit that generates a predetermined analog waveform in synchronization with the current command signal CCS. Further, the arithmetic circuit can be realized using an analog multiplication circuit.

Furthermore, each phase current value can be determined by subjecting the respective outputs of the current detector S and the correction waveform generating circuit C0R to analog/digital conversion and multiplying the outputs using a digital multiplication circuit. It is possible within the technical scope of the present invention to store the amplitude of each phase current in a memory or the like and obtain a time average over a relatively long period of time, or to obtain these values using a known technique such as a multiplexer. be.

FIG. 3 shows another example of a circuit that implements the current detection method according to the present invention.

A correction waveform is read out from the first read-only memory ROMI based on a signal from the central control unit CPU,
It is sent to the digital arithmetic circuit FUNC. A current signal detected by a current detector S, amplified by an amplifier circuit A, and further converted from analog to digital is sent to the digital arithmetic circuit FUNC. Note that the current detector S detects the return current from the inverter INV to the power supply in the same manner as in FIG. From the output of the arithmetic circuit FUNC, each phase winding current can be determined as explained in the section of the operation.

On the other hand, the output of the central control unit 1 CPU reads the current value, pulse width, current rise speed, etc. for each phase winding from the second read-only memory ROM 2, and this signal is sent to the conversion circuit T. A conversion circuit T generates a current command signal.

g. Effects of the Invention Each phase winding current can be detected using a single current detector.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a current detection circuit in an inverter drive system of an AC machine according to the present invention, and FIG. 2 is a signal at main points for explaining the operation of the method and circuit according to the present invention in the case of three-phase drive. FIG. 3 shows another example of a circuit implementing the current detection method according to the present invention, and FIG. 4 shows an example of a current detection circuit for an inverter drive system of an alternating current machine according to the prior art. A...Amplification circuit, CCS...Current command signal,
C0NT...Current control unit, C0RP...Correction waveform generation circuit, F[INC...Arithmetic circuit, INV・
...Inverter, M...Electric motor, ps...
Power supply, PWM...PWM pulse generation circuit, ROMI, ROM2...Read only memory, S
...Current detector, ゛T...Conversion circuit. Patent applicant Oriental Motor Co., Ltd. (and 2 others)

Claims (1)

[Claims] (1) In a current detection method in an inverter drive system of an AC machine that uses an inverter to control each phase current, a current detector is used to detect the current flowing back from the inverter to the power supply side, and the amplitude of each phase current is equal. A correction waveform generation circuit generates a signal with a waveform proportional to the reciprocal of the current waveform to be measured by the current detector, and the current waveform actually measured by the current detector and the waveform formed by the correction waveform generation circuit are generated. 1. A current detection method in an inverter drive system of an alternating current machine, characterized in that the amplitude of the winding current of each phase is obtained from the output of the arithmetic circuit by multiplying by using an arithmetic circuit. (2) In a current detection circuit in an inverter drive system of an AC machine that uses an inverter to control each phase current, a current detector that detects the current flowing back from the inverter to the power supply side and the above when the amplitude of each phase current is equal. A correction waveform generation circuit forms a signal with a waveform proportional to the reciprocal of the current waveform to be measured by the current detector, and the current waveform actually measured by the current detector is multiplied by the waveform formed by the correction waveform generation circuit. Equipped with an arithmetic circuit that
A current detection circuit in an inverter drive system of an alternating current machine, characterized in that the amplitude of the winding current of each phase is determined from the output of an arithmetic circuit.