JPS6243436B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a torque detection device for an inverter-driven three-phase induction motor.

2. Description of the Related Art Conventionally, a torque detection device using a strain gauge as a torque measurement device for a rotating machine is known. However, these devices are expensive, require thin shafts, and have poor measurement accuracy. Furthermore, the detected torque is a shaft-transmitted torque and not an electromagnetic torque generated from the rotating machine itself. However, recently, as a way to compensate for these drawbacks, a torque detection device that directly determines electromagnetic torque from the voltage applied to the motor and its current has been considered. In other words, Figure 1 shows the conventional 3
This is an example of a circuit showing an electromagnetic torque detection device for a phase alternator. In the figure, 1ab and 1bc are voltage detectors between each line, 2a and 2b are phase current detectors, 3 is an electromotive force calculator, and 4 is a magnetic flux calculator that integrates the electromotive force calculated by the electromotive force calculator 3. Vessel, 6a, 6b, 6c
is a multiplier, 5 and 7 are adders, and 8 is a stator of the alternating current machine.

Next, the operation of the conventional device having the circuit configuration as described above will be explained below. The conventional torque detection device shown in Figure 1 calculates the magnetic flux that interlinks orthogonally to each phase winding of an alternating current machine, multiplies it by each phase current, and adds the obtained phase torque to generate an electromagnetic torque. This is what we seek. The respective magnetic fluxes that intersect orthogonally to each phase are Φ _bc in the case of the a phase, and Φ _ca and c in the case of the b phase.
In the case of a phase, it corresponds to Φ _ab . In order to obtain these magnetic fluxes, first the terminal voltage is detected by the voltage detectors 1ab and 1.
bc or the phase current is detected by each of the phase current detectors 2a and 2b and supplied to the electromotive force calculator 3. In the electromotive force calculator 3, the voltage drop due to the winding resistance and the induced voltage due to the leakage reactance are removed from the terminal voltages V _ab , V _bc , and the electromotive force E _ab , E
_bc is input to the magnetic flux calculator 4 from the output terminal. The electromotive forces E _ab and E _bc supplied to the magnetic flux calculator 4 are immediately integrated, and the calculated magnetic fluxes Φ _bc , Φ _ca , and Φ _ab orthogonal to each phase are outputted from the output terminal. Each phase torque is obtained by multiplying each phase current by the magnetic flux orthogonally interlinking each phase current using multipliers 6a, 6b, and 6c. The electromagnetic torque at this time is obtained as the sum of the torques of each phase using an adder 7.
Therefore, the functional configuration of the magnetic flux calculator 4 consists of an integrator and its calculator.

In this way, conventional torque detection devices have a method of determining torque by detecting magnetic flux from voltage and current, so it is necessary to provide multiple dedicated voltage and current detectors for torque detection. The device becomes complicated and expensive due to the fact that the magnetic flux calculator 4 requires an integrator, and drift of the integrator amplifier becomes a problem, and the amplifier saturates in the low speed range, making it difficult to detect torque. There were drawbacks such as measurement errors.

The present invention has been made in order to eliminate the above-mentioned drawbacks of the conventional art, and includes a DC current detector provided in advance to detect the electromagnetic torque of an induction motor driven by an inverter, particularly a current source inverter. By using a motor rotation angular velocity (slip frequency control) detector, inverter DC voltage detector, etc., and combining it with two operational amplifiers and two multipliers, the torque of an inverter-driven three-phase induction motor can be easily and inexpensively determined. The purpose is to provide a detection device.

An embodiment of the present invention will be described below. First, FIG. 2 is a block diagram of a device for detecting electromagnetic torque of a three-phase induction motor driven by a current source inverter. In FIG. 2, the control device is omitted because it is not directly related. In Figure 2, 11 is a three-phase AC power supply.
2 is an AC/DC converter, 13 is a DC reactor that smoothes the current, 14 is an inverter that converts DC to rectangular wave AC current, 15 is a three-phase induction motor, and 16 is a rotational angular velocity detector that detects the speed of the motor. be. Next, as a torque detection device, 17 is an inverter DC voltage detector, 18 is a spike voltage cut circuit that removes the spike voltage superimposed on the inverter DC voltage during commutation, 19 is a DC current detector, and 20 is a motor winding. An arithmetic circuit that calculates the voltage drop due to resistance (stator winding resistance, rotor winding resistance), 21 is a subtracter that subtracts the resistance drop from the DC voltage, and 22 is a multiplier that multiplies the output of the subtracter by the DC current id. The multiplier 23 is an absolute value bias circuit that outputs the absolute value of the rotational angular velocity detector 16 to prevent the velocity from becoming negative, and provides a bias so that the velocity does not become zero even if the output of the rotational angular velocity detector 16 is zero. , 24 is a divider that divides the output of the multiplier 22 by the output of the absolute value bias circuit 23, 25 is a gain corresponding to the number of opposite poles, and the output of the gain 25 becomes torque τ ₀ , and the sign determination circuit 28 determines the sign of the torque. give.

In the present invention having such a configuration, in order to detect the torque of an induction motor driven by an inverter, the instantaneous power P ₀ supplied from the DC intermediate circuit to the three-phase induction motor 15, that is, the inverter DC voltage e _Id, is determined from the winding. Focusing on the fact that the product of the voltage drop due to resistance and the spike voltage generated during commutation and the inverter DC input current id divided by the rotational angular speed ω _r can be approximated as the generated torque of an induction motor, this principle was developed. This is used to detect the torque of a three-phase induction motor. In the following, we will theoretically explain in detail how instantaneous torque can be derived using the basic equations of an induction motor whose d-q axis coordinates have been transformed, and how instantaneous torque can basically be approximated using the above concept. That is, the basic equations converted to the d-q axis coordinates for the stator of the induction motor with the secondary inductor short-circuited are given by equations (1) and (2). FIG. 3 shows the positional relationship between the dq axes and the a, b, and c phases of the stator winding axes. It is assumed that the q-axis is in the same direction as the a-phase winding axis, and the d-axis is in a phase delayed by 90 degrees from the q-axis.

τ=M/L ₂ (3/2)・P・(i _qs Φ _dr −i _ds Φ _qr )
...(2) Here, V _ds : Stator d-axis voltage, V _qs : Stator q
Axis voltage, i _ds : Stator d-axis current, i _ds : Stator q
Axial current, Φ _dr : Rotor d-axis magnetic flux, Φ _qr : Rotor q
Axial magnetic flux, τ: torque, P: number of counter poles, M: stator-rotor mutual inductance, L ₁ : stator self-inductance, L ₂ : rotor self-inductance,
r ₁ : Stator winding resistance, r ₂ : Rotor winding resistance, ω _r :
Motor rotation angular velocity (electrical angle), p: differential operator,
Also, the relationship between the d and q axes and each phase axis is shown in Figure 3 (3)
It is expressed as the formula.

Here, f corresponds to voltage, current, magnetic flux, etc.
It shows the relationship between three phases and two phases. The equation (1) is
When the coordinates are transformed using equation (4), the equations between each vector become as shown in equations (5) and (6).

V〓=[r ₁ +Lσp]I〓+M/L ₂ PΦ〓 _r …(5) P〓Φ _r [−r ₂ /L ₂ +jω _r ]〓Φ _r +r ₂ /L ₂
M〓I...(6) However, Lσ=L ₁ −M ² /L ₂ When formula (6) is substituted into formula 5 to find magnetic flux 〓Φ _r , formula (7) is obtained.

Now, if we pay attention to the fact that the secondary time constant T ₂ (=L ₂ /r ₂ ) of an induction motor is generally as large as 0.5 to 1 second,
When the motor rotational angular frequency (electrical angle) ω _r is sufficiently larger than the reciprocal of the quadratic time constant 1/T ₂ (=r ₂ /L ₂ ), (7
) is approximated as shown in equation (8), and the d-axis and q-axis components are expressed as shown in equations (9) and (10).

Φ _dr =L ₂ /M〓 _r (V _qs −(r ₁ + (M/L ₂ ) ² r ₂ +Lσp)ids) ...(9) Φ _qr = −L ₂ /M〓 _r (V _ds −( r ₁ + (M/L ₂ ) ² r ₂ +Lσp)ids)...(10) Now, in an induction motor driven by a current source inverter, due to the switching action of the inverter,
120 degree conduction square wave current flows. Therefore, there is one stator winding in which no current flows except for a short time during commutation, and a, b, c, a, b
...They should be in order with the phase windings. The present invention utilizes this fact to determine torque. That is, in Fig. 2, if the thyristors of phase B and C of the thyristor are conducting, DC current i _d flows from the stator winding phase B to c phase, and the stator winding current is i _a =0, i _b = i _d , i _c =-
It is written as _id . When the d- and q-axis current components of this three-phase stator current are determined using equation (3), the equations (11) and (12) are obtained, and the q-axis component current becomes zero. That is, The generated torque τ is rearranged from equation (2) using the relationship of equations (11) and (12), and by substituting equation (10), it becomes equation (13).

From equation (13), the torque τ is obtained by multiplying the terminal voltage of the two conducting phases minus the leakage inductance and stator/rotor resistance drop by the DC current i _d , dividing by the rotational angular velocity ω _r , and multiplying by the polar logarithm. Become something.

In a current source inverter, commutation is performed every 60°. The winding phases of the stator through which direct current flows are b, c phase, b, a phase, c, a phase, c, b phase, a,
The phase shifts from phase b, phase a, c, phase b, c, etc., (11)
Although the relationship shown in equation (11) is no longer maintained, if the d- and q-axes are advanced in steps of 60 degrees with commutation as shown by the broken lines of the d and q axes in Figure 3, the relationship of equation (11) can be obtained. is maintained. In that case, the d-axis voltages V _ds necessary to calculate the torque are V _bc , V _ba , V _ca , V _cb ,
When we pay attention to the switching of the inverter by changing to V _ab , V _ac , V _{bc .} . . , we notice that these voltages are equal to the instantaneous value of the inverter DC voltage. In other words, the inverter DC voltage e _Id is always equal to the terminal voltage of the two phases from which the DC current i _d is leaking. Therefore, e _ds in equation (12) can be expressed as equation (14), and torque τ can be expressed as equation (15) _.
and the inverter DC voltage e _Id .

τ=P・id/ω _r (e _Id −2(r ₁ +(M/L ₂ ) ² r ₂ +pLσ) i _d ) ... (15) In reality, during the short time e _Id during commutation, A spike voltage is generated, and a spike voltage of 2Lσd _td /dt is also generated. Therefore, since these spike voltages are an exchange of reactive power with the commutating capacitor, they do not affect the torque and can be ignored.
Therefore, when the leakage inductance Lσ is ignored and a low-pass filter is used to remove the spike voltage superimposed on the inverter DC voltage e _Id , the time constant T is such that there is no effect of time delay. FIG. 2 is a configuration diagram of a torque detection circuit based on equation (15). Here, FIG. 4 shows waveforms of essential parts of the circuit of FIG. 2. First, a is the motor phase current i _a ,
b is the inverter DC voltage e _Id and c is the DC current i
_a and d represent the output τ ₀ of the torque detector, and e represents the waveform of the generated torque τ determined strictly from equation (2). As can be easily seen from the configuration, the output d of the torque detector is obtained by removing the spike voltage from the DC voltage at b, multiplying it by the DC current at c, and dividing by the rotation angle ω _r to determine the generated torque. It agrees very well with e. It can be seen from the above results that the instantaneous torque can be approximated.

In FIG. 2, the DC voltage e _Id detected by the inverter DC voltage 17 is passed through the spike voltage cut circuit 18 to remove the spike voltage, and the DC current _{i d} detected by the DC current detector 19 is
The subtractor 21 calculates the resistance drop caused by the stator and rotor.
The multiplier 22 and the divider 24 respectively multiply by i _d and divide by ω _r , multiply by the pole logarithm, and finally a special judgment circuit gives a sign to obtain the torque τ. Since the rotation speed is constant when ω _r <<1/T ₂ and the divider can only calculate positive values, the absolute value circuit 23 is provided.

FIG. 5 shows an actual circuit configuration of the torque detection circuit based on the above-mentioned principle. In the figure, parts that are the same as those in FIG. 2 are indicated by the same reference numerals, so a description of overlapping parts will be omitted. That is, the direct current i _d
is determined by detecting the converter input current by the current transformer 19a and rectifying it by the full-wave rectifier circuit 19b. This DC current detection circuit is usually always included in the inverter control device 26, so no new device is required to detect the DC current. The inverter DC voltage e _Id is obtained by amplifying the voltage divided by the resistor 17a with a differential amplifier.
The spike voltage cut circuit 18 is composed of a low-frequency RC filter circuit, and the subtracter 21 is implemented by an operational amplifier, and by changing the input resistance of the operational amplifier, the resistance drop of the arithmetic circuit 20 shown in FIG. 2 can be subtracted. It will be done. The rotational angular velocity detector 16 is realized by a velocity generator, and is provided from the beginning when performing slip frequency control. Further, the sign determination circuit 28 gives a sign to the torque based on the sign of the rotational angular velocity detector, and can be realized by a simple logic circuit. In order to realize a torque detection device in this way,
It can be seen that the circuit can be configured easily since it only requires two operational amplifiers and two multipliers.

Further, in the above embodiment, a device for detecting the torque of an induction motor driven by a current source inverter has been described, but the torque of an induction motor driven by a voltage source inverter can be similarly determined. In other words, if we focus on inverter switching and advance the d-q coordinates in 60 degree steps for each commutation, the d-axis component voltage V _ds will always be zero, V _qs will be constant, 2/3e _Id , and the torque will be If we approximate the resistance drop part, it becomes the same as equation (15).

Therefore, a torque detection device for an induction motor driven by a voltage source inverter can also be realized using the same principle as shown in FIG. That is, FIG. 6 shows an induction motor driven by a voltage source inverter, and the main circuit differs from the current source inverter shown in FIG. 5 in that it includes a smoothing capacitor 27 for smoothing the voltage. Further, only a shaft resistor 19c for detecting direct current and an isolation amplifier 19d for insulating the main circuit and the control circuit are added as a detection circuit.

Therefore, according to the present invention, when detecting the torque of an induction motor driven by an inverter, it is possible to detect the torque of an induction motor driven by an inverter in advance using the detectors normally provided in the inverter circuit, that is, the DC current, the inverter DC voltage, and the rotation angle detector (slip frequency). The device is inexpensive because only two multiplier circuits are used (during control), no other detectors are required, and the torque of a three-phase induction motor driven by an inverter can be detected with a simple circuit. This has the effect of Furthermore, since the torque detected by this device is an instantaneous torque, it can also be treated as a control target, and has the advantage that it can be used as a feedback signal when performing torque control.

[Brief explanation of the drawing]

Figure 1 is a configuration diagram of a conventional torque detection device, Figure 2
The figure is a configuration diagram of the torque detection device according to the present invention,
Figure 4 is an explanatory diagram for explaining the principle of the present invention.
The figure is a waveform diagram showing the output of the torque detecting device according to the present invention and the waveforms of various parts. Figure 5 is a circuit diagram when the present invention is applied to an induction motor driven by a current source inverter. FIG. 2 is a circuit diagram when the present invention is implemented in an induction motor driven by a type inverter. 14... Inverter, 15... Three-phase induction motor, 16... Rotation angular velocity detector, 17... Inverter DC voltage detector, 18... Spike voltage cut circuit, 19... DC current detector, 20... Calculation Circuit, 21... Subtractor, 22... Multiplier, 23...
... Absolute value bias circuit, 24 ... Divider, 28 ...
...Sign determination circuit. Note that the same reference numerals in the figures indicate the same or equivalent parts.

Claims (1)

[Claims] 1. An inverter DC voltage detector that detects the inverter DC voltage of a three-phase induction motor driven by an inverter, and a spike voltage cut circuit that removes spike voltage from the inverter DC voltage detected by the inverter DC voltage detector. , a DC current detector that detects the inverter DC current;
an arithmetic circuit that calculates the voltage drop due to the winding resistance of the motor; a subtracter that subtracts the voltage drop due to the winding resistance from the output of the spike voltage cut circuit;
a multiplier that multiplies the output of the subtracter and the output of the DC current detector; a rotational angular velocity detector that detects the rotational angular velocity of the three-phase induction motor; and an output of the rotational angular velocity detector that is zero or negative. an absolute value bias circuit that detects torque by dividing the output of the multiplier by the output of the absolute value bias circuit, and a sign determination circuit that determines the sign of the rotational angular velocity and assigns a sign to the torque. A torque detection device for an inverter-driven three-phase induction motor, comprising: