JPH07167928A - Measuring device for instantaneous characteristic value of three-phase ac motor - Google Patents

Abstract

PURPOSE:To measure instantaneous characteristic values by calculating the maximum values of phase voltage and phase current instantaneously from the voltage and current detected by a voltage/current detector. CONSTITUTION:Two line voltages Vab and Vbc among three-phase line voltages Vab, Vbc, and Vca of a stator are inputted into the maximum value calculator 1 for phase voltage, and the maximum value Em of the phase voltage is calculated. On the other hand, two line currents Ia and Ib among three-phase line currents Ia, Ib, and Ic are inputted into calculators for sum and product of line currents 2 and 3, respectively, for calculation of Ia+Ib and IaXIb, and the output is inputted into a calculator 4 for calculation of (Ia+Ib)<2>-IaXIb. Also, using the output from the calculator 4, the maximum value Im of phase current is calculated by a maximum calculator 5. The effective value of phase voltage can be obtained by K3Em at a calculator 6 for effective value of phase voltage based on the output from the maximum value calculator 1. The effective value of phase current is obtained by K3Im, at a calculator 1 for effective value of phase current based on the output from the maximum value calculator 5.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention instantaneously detects a voltage applied to a stator winding of a three-phase AC motor and a line current, and instantaneously calculates each maximum value and each effective value of the phase voltage and current. Input, secondary input (output in case of synchronous motor),
The present invention relates to a device for measuring instantaneous characteristic values of a three-phase AC motor, which is a synchronous motor, characterized by instantaneously calculating the torque and the efficiency of the synchronous motor. The present invention relates to a device for measuring instantaneous characteristic values of a three-phase AC motor, which is an induction motor, for detecting and calculating a secondary copper loss and a secondary output, and then performing an instantaneous calculation of the efficiency of the induction motor. Furthermore, a device for calculating the instantaneous torque quickly and easily is also proposed.

In this measuring device, calculation is performed during normal operation in which there is no zero-phase value, and two line voltages and two line currents on the stator side of a three-phase AC motor are instantaneously detected, and Performs instantaneous calculation of characteristic values.

[0003]

2. Description of the Related Art Up to now, in order to obtain each characteristic value of a three-phase AC motor, a conventional measuring instrument is often used, and instantaneous measurement is impossible. Although a digital measuring device enables high-speed measurement, it is not commercially available for instantaneous measurement of each characteristic value described in claim 1, claim 2 and claim 3. The maximum value of the sine wave voltage and the sine wave current is the maximum value of the half cycle time, and the power factor is often the phase difference between the voltage and the current.In this case, it is not possible to calculate the maximum value and the power factor instantaneously. It is possible.

Various methods have been developed and used for measuring the torque of an electric motor, but the most general method is a mechanical method, in which the amount of torsional strain of the shaft is measured and the torque is then measured. It is a method of indirectly knowing the quantity. However, this method requires a torque measuring device to be directly connected between the electric motor and the load.

[0005]

SUMMARY OF THE INVENTION The present invention measures instantaneous characteristic values of a three-phase AC motor by instantaneously detecting two line voltages and two line currents on the stator side of the three-phase AC motor. An attempt is made to provide a measuring device capable of performing the measurement.

[0006]

SUMMARY OF THE INVENTION In the case of a synchronous machine, a device for measuring instantaneous characteristic values of a three-phase AC motor according to the present invention detects a stator winding applied voltage and a line current of the three-phase AC motor. A voltage / current detection device, a maximum value calculator for instantaneously calculating the maximum values of the phase voltage and the phase current from the voltage and current detected by the voltage / current detection device, and the instantaneous value of the three-phase AC motor An input calculator for calculating an input, and a power factor calculator for calculating an instantaneous power factor from each maximum value of the phase voltage and phase current calculated by the maximum value calculator and the input, and the alternating current A secondary input (output) calculator for instantaneous calculation of the secondary input (output in the case of a synchronous motor) of the motor and a secondary input (output) calculated by the secondary input (output) calculator Torque calculator that calculates instantaneous torque and voltage / current detection device It is equipped with a torque calculator that calculates the instantaneous torque from the current detected by and the magnetic flux calculated by the magnetic flux calculator, and an efficiency calculator that calculates the efficiency of the synchronous motor from the input and output of the synchronous motor. And

In the case of a three-phase induction motor, in addition to the above, a rotation speed detecting device for detecting the rotation speed is further provided, and the rotation speed detected by the rotation speed detecting device and the secondary input (output).
It further comprises a calculator of secondary copper loss and secondary output obtained by calculation with the secondary input calculated by the calculator, and an efficiency calculator for calculating the efficiency of the three-phase induction motor from the input and the secondary output. It is characterized by that.

[0008]

The operation of the device for measuring the instantaneous characteristic values of the three-phase AC motor according to the present invention will be described in detail with reference to FIGS. 1 and 2. FIG. 1 is a diagram showing each line voltage and each line current of the three-phase AC motor. In the measuring apparatus for instantaneous characteristic values of the three-phase AC motor of the present invention, the three-phase system of a, b, and c is connected. In addition, the three-phase line voltage V _ab on the stator side of the three-phase AC motor,
V _bc, two line voltages V _ab in V _ca, V _bc and the line current I
_a, I _b, two line currents I _a in I _c, detects the instantaneous value of the I _b.

On the other hand, the space vector will be described with reference to FIG. V _S is a space rotation voltage vector, I _S is a space rotation current vector, Ψ _S is a space rotation magnetic flux vector, and each component Vα, Vβ, Iα on the α, β two-phase axis,
It can be decomposed into Iβ and Ψα, Ψβ, respectively. The magnitudes of the spatial rotation voltage vector V _S and the current vector I _S of the phase voltage and the phase current of the three-phase AC motor are as follows: voltage components Vα and Vβ on the α and β two-phase axes and currents on the two-phase axis. It can be expressed by the components Iα, Iβ, the maximum value E _m of the phase voltage and the maximum value I _{m of the} phase current, and the formula (1) is obtained.

[Equation 1]

Further, each voltage component V on the two-phase axis of the equation (1)
α and Vβ and the current components Iα and Iβ on the two-phase axis are in normal operation with no zero-phase value, in the case of a star connection, from the following equation (2), and in the case of a triangle connection, (3) Each is obtained from the formula.

In case of star connection

[Equation 2] However, the coefficients C ₁ = (6) ^-1/2 , C ₂ = (2) ^-1/2 C ₃ = (3/2) ^1/2 , C ₄ = 2 ^1/2

In case of triangular connection

[Equation 3]

In the case of star connection, each voltage component and each current component on the two-phase axis of equation (2) is substituted into equation (1), and in the case of triangular connection, each component of equation (3) is substituted into equation (1). Then, the maximum value E _m of the phase voltage and the maximum value I _m of the phase current of each connection can be obtained, and the equation (4) is obtained.

[Equation 4] Here, the coefficients K ₁ and K _{2 in the} equation (4) are K ₁ = 2/3, K ₂ = 2 / (3) ^{1/2 in a} star connection.
And in the case of triangular connection, K ₁ = 2 / (3) ^1/2 , K ₂ = 2/3
Becomes

The input P ₁ of the three-phase AC motor can be calculated and calculated based on the equation (5) during normal operation without the zero phase.

[Equation 5]

Since the following equation holds between the input P _{1 of the} motor and the power factor cosφ,

[Equation 6] The power factor cosφ of the motor is given by equation (7). Here, φ indicates the phase difference between the voltage vector V _S and the current vector I _{S in} FIG. 2 or the phase difference between the phase voltage and the phase current.

[0016] Thus the two line voltages of the three-phase AC motor and two line currents and instantaneous detection, (4), (5) and (3/2) performs the instantaneous calculation of E _m I _m , By substituting the calculation result into the equation (7), the instantaneous power factor cosφ can be obtained.

[Equation 7]

The instantaneous apparent power is obtained from the calculation of (3/2) E _m I _m , and the instantaneous reactive power is obtained from P _{1 in the} equation (5) and this apparent power.

The secondary input P ₂ of the three-phase induction motor, which is a three-phase AC motor, or the output P ₂ of the three-phase synchronous motor can be expressed by equation (8).

[Equation 8] Here, P ₁₀ shows the iron loss and mechanical loss at no load,

[Equation 9] And I _a0 and I _bo represent the line currents I _a and I _b under no load, respectively.

P _ab0 is an input of the electric motor during no-load operation, and two line voltages and two line currents I _a and I under no load.
_b (that is, I _a0 and I _bo ) is measured and determined by the equation (5). R _Y represents one-phase stator winding resistance of the electric motor star connection, and the coefficient K _{4 in} this case is 2.

Further, if one-phase stator winding resistance of the triangular connection is represented by RΔ and R _Y of the equations (8) and (9) is represented by RΔ, the coefficient K ₄ becomes (2/3). .

The P ₂ when the three-phase AC motor is loaded is determined in advance by instantaneously detecting the two line voltages and the two line currents when the load is applied and obtaining P ₁ by the equation (5). It is obtained by substituting P _{10 under} no load into the equation (8).

The instantaneous torque τ of the electric motor is obtained by substituting the power source frequency f, the number of pole pairs n, and P ₂ obtained by the equation (8) into the following equation which is a well-known torque equation.

[Equation 10]

The efficiency η _sy of the synchronous motor is expressed by equations (5) and (8).
It is obtained by substituting the values of P ₁ and P ₂ obtained by the equation into the equation (11).

[Equation 11]

Further, in the case of the three-phase induction motor as set forth in claim 2, in addition to the voltage / current detection device of the device described above, a rotation speed detection device for detecting the rotation speed is provided and detected. The slip S is obtained from the rotational speed and the synchronous speed, and the well-known secondary copper loss P _C2 is calculated as the secondary input of the equation (8) and this S
From equation (12), the secondary output P is obtained from equation (13).
You get ₀ .

[Equation 12]

[Equation 13]

Therefore, the efficiency η _IM of the three-phase induction motor is obtained by substituting the values of P ₁ and P ₀ obtained by the equations (5) and (13) into the equation (14).

[Equation 14]

Next, the calculation for obtaining the instantaneous torque more quickly and easily will be described. Instantaneous torque τ of a three-phase induction motor or a three-phase AC motor that is a three-phase synchronous motor
Is written as a vector product of the spatial rotation magnetic flux vector Ψ _S and the spatial rotation current vector I _S, and is expressed by the following equation (15).

[Equation 15]

Further, each magnetic flux component Ψ on the two-phase axis shown in FIG.
It can be represented by α, Ψβ and the respective current components Iα, Iβ, and is given by equation (16).

[Equation 16]

The respective phase currents of the stator windings of the three-phase AC motor are represented by i _a , i _b and i _c , and the magnetic fluxes of each phase are Ψ _a , Ψ _b and Ψ _c.
If the normal zero phase does not exist, each magnetic flux component and each current component can be expressed by the equation (17).

[Equation 17] Substituting each component of equation (17) into equation (16), equation (18) is obtained.

[Equation 18]

Each phase voltage v of the stator winding of the three-phase AC motor
_a, v _b, v voltage equation of (19) between the _c and the phase flux is established.

[Formula 19] Here, R is the winding resistance of each phase of the stator winding.

Therefore, the phase magnetic fluxes Ψ _a and Ψ _b of the stator winding shown in the equation (18) can be obtained by calculating the equation (20) derived from the equation (19).

[Equation 20]

If the equation (20) is expressed by the line voltages V _ab and V _bc of the three-phase AC motor and the line currents I _a and I _b , the formula (21) is used for the star connection and the triangle connection is used. Can be expressed by equation (22).

[Equation 21]

[Equation 22]

[0032]

EXAMPLE A concrete apparatus will be described below. Figure 3
FIG. 3 is a block diagram of an embodiment of a measuring device for measuring instantaneous characteristic values of a three-phase AC motor according to the present invention, which is different from the block diagram in the case of a three-phase AC motor in broken lines. A case is added and shown. First, the case of a three-phase AC motor not including the part inside the broken line will be described.

Two line voltages V _ab , V _bc among the three-phase line voltages V _ab , V _bc , V _ca of the stator are input to the maximum value calculator 1 of phase voltage, and equation (4) is used. The maximum value E _m of the phase voltage is calculated using this. On the other hand, the two line currents I _a and I _b among the three-phase line currents I _a , I _b and I _c are input to the calculator 2 of the sum of the line currents and the calculator 3 of the product of the line currents, respectively I _a + I _b and I _a × I _b are calculated, their outputs are input to the calculator 4, (I _a + I _b ) ² −I _a × I _b is calculated, and the phase current is calculated using the output of the calculator 4. The maximum value calculator 5 calculates the maximum value I _m of the phase current by the equation (4).

From the output of the maximum value calculator 1 of the phase voltage, the effective value 6 of the phase voltage is obtained by K ₃ E _m in the calculator 6 of the effective value of the phase voltage. Further, the effective value of the phase current is obtained from K ₃ I _m in the effective value calculator 7 of the phase current from the output of the maximum value calculator 5 of the phase current. Here, K ₃ is 2 ^-1/2 . Furthermore, from the maximum value output of the arithmetic unit 5 of the maximum value calculator 1 output and the phase current of the phase voltage, apparent power (3/2) in the calculating unit 8 of apparent power E _m I _m is determined.

In the input computing unit 9 for computing the instantaneous input,
The outputs of the calculator 2 of the sum of the line voltages V _ab and V _bc and the line current I _a and the line current are input, and the input P of the motor is calculated by the equation (5).
₁ is calculated. In the reactive power calculator 10, the instantaneous reactive power is obtained from the output of the apparent power calculator 8 and the output of the input calculator 9. In the power factor calculator 11, similarly, from the apparent power calculator 8 and the output of the input calculator 9,
Calculate the instantaneous power factor cosφ by performing the calculation according to the equation (7).

Next, the no-load input P _ab0 during no-load operation is obtained by the input computing unit 9, and the line current I _a0 and I _bo at no load are used to calculate the square of the sum of the line currents and the product of the line currents. The difference calculator 4 calculates (I _a0 + I _b0 ) ² −I _a0 × I _b0 , and the output and the input output P _ab of the calculator 9 calculate the iron loss and mechanical loss at no load. The loadless loss P ₁₀ is calculated in advance by calculating the equation (9) in the device 12. Secondary input (output)
The arithmetic unit 13 outputs to the arithmetic unit 9 of the input and the arithmetic unit 4 of the difference between the square of the sum of the line currents and the product of the line currents, and the no-load loss P ₁₀
Is input, and the output (which is the secondary input in the three-phase induction motor) is calculated by the equation (8).

The output of the secondary input (output) calculator 13 is input to the torque calculator 14 and the number of poles n and the frequency f are used (10).
The torque τ is calculated by the equation. Further, in the efficiency calculator 15 of the synchronous motor, the outputs of the input calculator 9 and the secondary input (output) calculator 13 are input, and the synchronous motor efficiency η _sy is calculated by the equation (11).

In the case of the three-phase induction motor, a rotation speed detecting device for detecting the rotation speed is added, and the arithmetic units 16 to 20 which are inside the broken line in FIG. 3 are added. That is, the rotation speed N _r, which is a detection signal from the rotation speed detection device that detects the rotation speed, is input to the slip calculator 16 and the synchronous speed N _S
Is used to calculate the slip S. In the secondary copper loss computing unit 17, the secondary copper loss P is calculated from the slip S and the secondary input P ₂ which is the output of the secondary input (output) computing unit 13 by the equation (12).
_C2 is calculated. The slip S output from the slip calculator 16 is also input to the calculator (18) (1-S), which is (1-S).
Is carried out and is sent to the computing device 19 for the secondary output, and the secondary output P ₀ is computed by the equation (13). In the efficiency calculator 20 of the induction motor, the input P ₁ which is the output of the calculator 9 of the input and the secondary output P ₀ which is the output of the calculator 19 of the secondary output are input, and the induction motor is expressed by the equation (14). Efficiency η _IM
Is required.

Next, with reference to FIG. 4, a calculator of the instantaneously generated torque τ will be described in detail.

Two line voltages V _ab and V a of the three-phase AC motor
_bc and the two line currents I _a and I _b are instantly detected, and in the star connection, the calculator 21 performs (1/3) (2V _ab + V _bc ) and the calculator 22 calculates (1/3). 3) ( _Vbc- V
_ab ) is calculated.

Based on the output of the calculator 21 and the line current I _a, and from the output of the calculator 22 and the line current I _b , the magnetic flux calculator 23 calculates the equation (21), and the magnetic flux Ψ _{a of} each phase is calculated. Ψ
ask for _b and. The torque calculator 24 calculates the equation (18) from each phase magnetic flux and each line current to obtain the instantaneous torque τ of the star connection.

In the triangular connection, the calculator 25 (1/3)
The operation of (I _a −I _b ) is performed, and in the operation unit 26, (1
/ 3) (I _a + 2I _b ) is calculated.

By the output of the calculator 25 and the line voltage V _ab ,
Also, the magnetic flux calculator is calculated by the output of the calculator 26 and the line voltage V _bc .
In (27), each magnetic flux is obtained by performing the calculation of equation (22). In the torque calculator 28, each phase magnetic flux Ψ _a , Ψ _b and each phase current (1/3) (I _a −I _b ), (1/3) (I _a +2
_Ib ) and the equation (18) are calculated to find the instantaneous torque τ of the triangular connection.

As described in detail above, the instantaneous torque τ can be obtained by the torque calculator 14 in FIG. 3, but in order to obtain only the instantaneous torque τ, the method according to FIG. Can be calculated to.

[0045]

As described above, in the device for measuring the instantaneous characteristic value of the three-phase AC motor according to the present invention, the instantaneous line voltage and the two line current of the motor are used for instantaneous detection.
Maximum value of voltage and current, input, power factor, output of synchronous motor,
Instantaneous calculations are possible for the values of torque and efficiency, and the secondary input and secondary output of the induction motor, torque, and efficiency, and instantaneous values are obtained.

[Brief description of drawings]

FIG. 1 is a diagram showing line voltages and line currents of a three-phase AC motor.

FIG. 2 is a spatial rotation voltage vector V _S of a phase voltage and a phase current of a three-phase AC motor, a current vector I _S, and a magnetic flux vector Ψ.
It is a vector diagram showing _S and.

FIG. 3 is a block diagram of an embodiment of an apparatus for measuring instantaneous characteristic values of a three-phase AC motor according to the present invention.

FIG. 4 is a block diagram of an embodiment for quickly and simply calculating an instantaneous torque of a device for measuring instantaneous characteristic values of a three-phase AC motor according to the present invention.

[Explanation of symbols]

1 calculator of maximum value of phase voltage 2 calculator of sum of wire current 3 calculator of product of wire current 4 calculator of difference between square of sum of wire current and product of wire current 5 calculator of maximum value of phase current 6 RMS value calculator for phase voltage 7 RMS value calculator for phase current 8 Apparent power calculator 9 Input calculator 10 Reactive power calculator 11 Power factor calculator 12 No-load loss calculator 13 Secondary Input (output) calculator 14 Torque calculator 14 15 Synchronous motor efficiency calculator 16 Slip calculator 16 17 Secondary copper loss calculator 18 (1-S) calculator 19 Secondary output calculator 20 Induction motor Efficiency calculator 21 (1/3) (2V _ab + V _bc ) calculator 22 (1/3) (V _bc −V _ab ) calculator 23 Flux calculator 24 Torque calculator 25 (1/3) ( I _a -I _b) computing unit _{26 (1/3) (I a +} 2I b) of the arithmetic unit 27 the flux calculator 28 torque unit a, b, and c three-phase system cosφ motor Maximum value f supply frequency I _a rate E _m-phase voltage, I _b, space rotating current vector Iα phase current I _c line current I _S three-phase AC motor, I beta alpha, each current component on the β two-phase axis I Maximum value of _m- phase current K ₃ Coefficient N _r Speed P ₀ Secondary output of induction motor P ₁ Input of motor P ₂ Output of synchronous motor or secondary input of induction motor P ₁₀ No load loss P _ab0 No load operation Input of the motor of P _C2 Secondary copper loss S Slip V _ab , V _bc , V _ca Three-phase line voltage V _S Space rotation voltage vector of phase voltage of three-phase AC motor V α, V β α, β on two-phase axis Each voltage component η _sy Synchronous motor efficiency η _IM Three-phase induction motor efficiency τ Motor instantaneous torque φ Phase difference between voltage vector and current vector Ψ _s Space rotation magnetic flux vector Ψ _a , Ψ _b a, b Magnetic flux of each phase Ψα, Ψβ α, β Magnetic flux components on the two-phase axis

Claims (3)

[Claims] 1. A voltage / current detection device for detecting a voltage applied to a stator winding of a three-phase AC motor and a line current, and a phase voltage instantaneously derived from the voltage and current detected by the voltage / current detection device. A maximum value calculator that calculates each maximum value of the phase current, an input calculator that calculates the instantaneous input of the three-phase AC motor, and a maximum of the phase voltage and phase current calculated by the maximum value calculator A power factor calculator for calculating an instantaneous power factor from a value and an input, and a secondary input (output) calculator for instantaneously calculating the output of the three-phase AC motor, which is a synchronous motor, and the secondary A torque calculator that calculates the instantaneous torque of the electric motor from the output calculated by the input (output) calculator, an input of the synchronous motor that is the output of the input calculator, and an output of the secondary input (output) calculator. The effect of calculating efficiency from the output of the synchronous motor Apparatus for measuring the instantaneous characteristic values of the three-phase AC motor is a synchronous motor, characterized in that it comprises a calculator. 2. A three-phase AC motor comprising a voltage / current detecting device for detecting a voltage applied to a stator winding and a line current, and a rotation speed detecting device for detecting a rotation speed, which are detected by the voltage / current detection device. The maximum value calculator that calculates each maximum value of the phase voltage and the phase current instantaneously from the voltage and the current, the input calculator that calculates the instantaneous input of the three-phase AC motor, and the maximum value calculator A power factor calculator for calculating an instantaneous power factor from each maximum value of the calculated phase voltage and phase current and an input is provided, and an instantaneous calculation of a secondary input of the three-phase AC motor, which is an induction motor, is performed. A secondary input (output) computing unit to perform, a torque computing unit that computes the instantaneous torque of the electric motor from the output computed by the secondary input (output) computing unit, and a rotation speed detected from the rotation speed detecting device. Calculated by the secondary input (output) calculator It is characterized by comprising a calculator of secondary copper loss and secondary output obtained by calculation with the secondary input, and an efficiency calculator for calculating the efficiency of the three-phase induction motor from the input and the secondary output. A device for measuring the instantaneous characteristic values of a three-phase AC motor, which is an induction motor. 3. A voltage / current detecting device for detecting a voltage applied to a stator winding of a three-phase AC motor and a line current is provided, and a magnetic flux is instantaneously generated from the voltage and the current detected by the voltage / current detecting device. A magnetic flux calculator for calculating, and a torque calculator for calculating an instantaneous torque from the current detected by the voltage / current detection device and the magnetic flux calculated by the magnetic flux calculator, and calculating an instantaneous torque. An apparatus for measuring instantaneous characteristic values of a three-phase AC motor, which is a synchronous motor or an induction motor.