JPS633559B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a torque detection circuit for driving an induction motor using a static power converter.

In recent years, advances in semiconductor technology have been remarkable.
Since it has become easier to realize a variable frequency power source, static power converters, particularly induction motor drives using inverters, are attracting attention. Furthermore, with regard to electric vehicles in the railway field, active attempts are being made to replace the conventional DC motor drive with an induction motor drive using an inverter. In replacing the motor with an induction motor, a major problem is how accurately the torque of the motor can be detected and controlled. In other words, in a DC machine, the torque can be more easily controlled than the field current and armature which are individually controlled, and the desired operating performance can be guaranteed. However, in an induction motor, the current corresponding to the field current and armature current are inseparably integrated into the motor input current, so it is impossible to determine the torque from this. Various methods have been proposed for detecting the torque of this induction motor, but none have been realized that satisfy the requirements for high reliability and high precision as applied to electric vehicles. That is, the following content has been conventionally considered.

(1) Determine the rotor input power by subtracting the loss of the inverter and motor from the inverter's DC stage current, and divide this by the rotational speed to obtain the torque.

(2) Calculate the secondary current (I ₂ ) from the equivalent circuit of the motor, and calculate the secondary equivalent resistance {(1.−S)・r ₂ /S} (r ₂ ;
The generated power {(1-S) r ₂ ·(I ₂ ) ² /S} is determined as the copper loss during the secondary resistance (S; slipping), and this is divided by the rotational speed to obtain the torque.

In this way, conventional methods use motor constants everywhere and include operations to divide by rotational speed ω, making compensation for temperature changes in the primary and secondary resistances complicated, for example, during startup, etc. There is a possibility that low-speed torque cannot be obtained.

SUMMARY OF THE INVENTION In view of the above-mentioned problems, it is an object of the present invention to provide a torque detection circuit particularly suitable for configuring an electric vehicle control loop. The present invention will be explained below based on the drawings.

Figures 1 to 3 are shown to facilitate understanding of the basic technical idea of the present invention. Figure 1 shows an equivalent circuit of an induction motor, and Figure 2 shows voltage and current vectors in the circuit shown in Figure 1. FIG. 3 is a vector diagram showing the phase relationship of each current.

That is, in Figure 1a, V〓 is the terminal voltage between phases, E〓 ₀ is the gap induced voltage, E〓 _r is the rotor voltage, I〓 _n
is the stator current, I〓 _r is the rotor current, I〓 _p is the excitation current for providing gap magnetic flux, r ₁ , l ₁ are the primary resistances,
The primary leakage inductance, l ₂ indicates the secondary leakage inductance. Further shown in Figure 1b
I〓 is an equivalent excitation current that provides secondary interlinkage flux φ ₂ , and I _q is a torque component current orthogonal to the equivalent excitation current I〓. From I〓, _Iq , the torque T is expressed by equation (1), where m is the number of phases, n is the number of pole pairs, and M is mutual inductance.

T= _mnMI〓Iq ...(1) Here, ₁ is the phase angle between the terminal voltage V〓 and the gap induced voltage _E〓0 , and is called the primary voltage phase difference angle. According to the well-known Syuta-Teimets equation, ₁ = tan ^-1 C ₂ /C ₁ (2), where C ₁ and C ₂ are Syuta-Teimets constants. Further, ₂ is the phase angle between the gap induced voltage E〓 ₀ and the rotor voltage E〓 _r , which is called the secondary voltage phase difference angle, and is given as follows.

₂ = tan ^-1 (S・ω/r ₂ l ₂ ) ...(3) Now, assuming that the power factor angle seen from the motor terminal is θ, the active current (I _n cos θ), the reactive current (I _n sin θ), and the above I〓 , I _q
The relationship is shown in Figure 3. From this figure 3, if I〓 and I _q are expressed using I _n cosθ and I _n sinθ, (4),
It becomes as shown in equation (5).

I = I _n sin (θ−) = I _n sinθ・cos − I _n cosθ・sin
………(4) I _q = I _n cos(θ−) = I _n cosθ・cos−I _n sinθ・sin
......(5) As described above, the present invention inputs the active current (I _n cosθ) and reactive current (I _n sinθ) in equations (4) and (5) from the current detection circuit portion to be described later. At the same time, the sin and cos can be calculated according to equations (4) and (5) by referring to values suitable for the operating condition from among the data calculated in advance using equations (2) and (3). Furthermore, the idea is to obtain the torque from equation (1). Here, the torque T is given as follows according to the Schützheimets formula. However, ω ₀ is the synchronous angular velocity (2ω/n).

T=mS(E ₀ ) ² r ₂ /9.8ω ₀ {(r ₂ ) ² +(Sωl ₂ ) ² } This can be further transformed as follows.

T=m(E ₀ /ω) ² (Sω/r ₂ )/9.8(2/η) {1
+(Sω/r ₂ ) ² (l ₂ ) ² } In this way, the secondary voltage phase difference angle ₂ is determined using the above formula, if the torque T is determined, (Sω/r ₂ ) is constant, so
Since the right side of equation (3) is constant, it is possible to set it to a constant value in advance. Note that this value is the secondary resistance
It is clear that it is not affected by changes in r ₂ .

In addition, the primary voltage phase difference angle ₁ can be obtained from the following Scheduling constant and equation (2). however
G ₀ is the excitation conductance, and B ₀ is the excitation susceptance.

a ₁ = Sr ₂ / (r ₂ ) ² + (Sωl ₂ ) ² a ₂ = S ² ωl ₂ / (r ₂ ) ² + (Sωl ₂ ) ² b ₁ = G ₀ + a ₁ b ₂ = B ₀ + a ₂ C ₁ = 1 + r ₁ b ₁ + ωl ₁ b ₂ c ₂ = r ₁ b ₂ −ωl ₁ b ₁ c In the calculation for determining the primary voltage phase difference angle ₁ , the primary resistance that changes depending on the temperature is included. becomes. However, when this value is specifically determined from the motor constants and operating conditions, ( ₁ = -4° ~
+7°), and in practical terms it is a primary resistance.
Even when looking at the temperature change of r ₁ (-10° to +110°), the variation is within 2° at most. This variation has a very small influence as an error on the detection of the torque T determined by the above equation (1), and there is no problem in obtaining a highly accurate torque detection method using this torque detection method.

Next, detection of active current and reactive current will be explained with reference to FIGS. 4 and 5. That is, FIG. 4 is a system diagram of an inverter drive device showing an example of a current detection circuit, and FIG. 5 is a waveform diagram showing the principle of effective current detection.

In Fig. 4, 1 is a DC power supply, and 2 is six switches 2a, 2b, 2, which employ semiconductor switching elements such as transistors and thyristors.
A three-phase inverter configured with 2c, 2d, 2e, and 2f as main control elements, 3 an induction motor, and 4 a control device that applies a control signal 101 to the switch so that the output of the three-phase inverter 2 becomes a desired voltage and frequency. In the apparatus, 5 is a current detection circuit, and 6a, 6b, 6c are current transformers for taking out a current detection signal 102 proportional to the motor input current. Here, current detection circuit 5 detects active current and reactive current, receives voltage phase signal 103 from control device 4, combines it with current detection signal 102, and sends current signal 104 to control device 4. The current detection circuit 5 as described above provides a special input signal for performing torque calculation, as will be described later.

Now, in Fig. 5, if the control signal to switch 2a is given as shown, the U-phase interphase voltage generated at the output of three-phase inverter 2 matches this, so the U-phase current I _U has a force against it. The waveform will be delayed by the rate angle θ as shown in the example below. Here I _U = I _n sin
Taking the average value I _a of a half cycle for the voltage phase as (ωt−θ), we get Therefore, I _a becomes a signal proportional to the effective current (I _n cosθ). Therefore, if the above-mentioned I _a is determined from the voltage phase signal 101 based on the switch control signal and the detected load current for all three phases, a signal proportional to the effective current can be easily obtained. Also(6)
When calculating the equation, the switch 2a control signal was used, but by extracting it from the control device 4 as a signal delayed by (π/2), it is possible to obtain (π/2) from this signal.
2) If we take the average value of the current I _R from (3π/2), we get Therefore, the reactive current ( _In sinθ) can be easily obtained.

FIG. 6 is a system diagram of main parts showing an embodiment according to the present invention, in which 7 is a torque detection circuit, 8 is a speed detector coupled to the induction motor 3 and sends out a rotation speed signal 801, and 41 and 43 are comparisons. 42 and 44 are amplifiers, 45 is an adder, 46 is an oscillator, 47 is a frequency divider, 48 is a modulator, and 49 is a logic amplifier circuit.
In the figure, the same reference numerals as in FIG. 4 indicate parts having the same functions.

Here, the torque detection circuit 7 includes, for example, a semiconductor lead-on memory storage device 7e, a microcomputer 7f, latch circuits 7g to 7h, digital-to-analog converters (DA) 7a to 7d, and an adder/subtractor 7i.
7j and a multiplier 7K, one input is given the active current signal 501 and the reactive current signal 502 of the output of the current detection circuit 5 as explained in FIG. 4 and FIG. A torque command 401, an inverter frequency command 451, and signal data 700 of the voltage of the DC power supply 1 as shown in FIG.
is generated.

In other words, in the torque detection circuit 7, DA7
a, 7b, 7c, and 7d each receive an active current signal 501 and a reactive current signal 502 at their analog input terminals as shown in the example, and the storage device 7e stores cos data and sin data corresponding to the internal phase difference angle described above.
The data is stored and sent to the microcomputer 7f for holding the cos data 701.
Latch circuits 7g and 7 for holding sin data 702
h. Here, the microcomputer 7f receives the signal data 700, searches the data, performs interpolation control if necessary, and supplies the output to the latch circuits 7g and 7h while correcting the data.

Like this, cos data 701 is DA7a,7
The sin data 702 is input to the digital input terminal of b.
These signals are applied to the digital input terminals of DA7c and DA7d, respectively. Therefore, the DA7a output 703 has (I _n sinθ・cos), and the DA7b output 704 has (I _n cosθ
×cos), DA7c output 705 (I _n cosθ・
sin), and (I _n sinθ·sin) is obtained at the DA7d output 706. Further, the adder/subtractor 7i performs a subtraction operation, and the adder/subtractor 7j performs an addition operation, so that these outputs 707 and 708 become the output 707.
becomes (I _n sinθ・cos−I _n cosθ・sin), that is, I〓, and the output 708 becomes (I _n cosθ・cos + I _n sinθ・sin)
In other words, it becomes I _q . The output signal generated by multiplying these signals by the multiplier 7k, that is, the torque detection signal 709, is expressed by equation (1).

Further, to explain the circuit configuration step by step, a comparator 41 and an amplifier 42 amplify the signal from the deviation between the torque command 401 and the torque detection signal 709 to give an effective current command 421, and a comparator 43 and an amplifier 44 Further, a slip command signal 441 is generated by amplifying the difference between the effective current command 421 and the effective current signal 501. The rotation speed signal 801 is added to this slipping command signal 441 by an adder 45 to obtain an inverter frequency command 451. Furthermore, an output signal 461 given via the oscillator 46 is input to a frequency divider 47, which divides the frequency and supplies it to a logic amplifier circuit 49, which generates a pulse train synchronized with the inverter switch signal.
The voltage phase signal 103 as described above is sent to the current detection circuit 5 as a pulse train delayed by 90 degrees. The modulator 48 inputs the output 472 from the frequency divider 47 and the inverter frequency command 451 as a voltage command, and generates a pulse train signal 481 having a desired pulse width.
occurs. From this, the logic amplifier circuit 49 sends out the control signal 101 as explained in FIG.

According to this embodiment, it is possible to input the torque command 401 and obtain an effective feedback value, thereby accelerating or decelerating the induction motor with a torque commensurate with the torque command 401, and ultimately an electric vehicle that exhibits the desired driving performance. drive can be realized. In the control system of this embodiment, even if the secondary resistance changes, the change is compensated for by increasing or decreasing the slip from the torque control system such that (Sω/r ₂ ) remains constant.
This enables a highly accurate drive system that could not be achieved with conventional constant slip control systems.

As explained above, according to the present invention, special torque calculation is performed using the sine value and cosine value corresponding to the voltage phase difference angle of the induction motor, and the optimum torque can be detected with high precision by suitable slip compensation etc. A torque detection circuit for an induction motor can be provided.

[Brief explanation of the drawing]

Figure 1 shows the equivalent circuit of an induction motor, and Figure 2 shows the equivalent circuit of the induction motor.
Figure 3 is a vector diagram showing the phase relationship of each current in Figures 1 and 2. Figures 4 and 5 explain detection examples of active and reactive currents. FIG. 6 is a system diagram and a waveform diagram of an inverter drive device for use in the present invention. 2...Three-phase inverter, 3...Induction motor, 4
...Control device, 5...Current detection circuit, 7...Torque detection circuit, 101...Control signal, 102...Current detection signal, 103...Voltage phase signal, 401...
... Torque command, 421 ... Effective current command, 441
...Slip command signal, 451...Inverter frequency command, 501...Active current signal, 502...Reactive current signal.

Claims (1)

[Scope of Claims] 1. A static power conversion device that supplies a variable voltage/variable frequency power source to an induction motor to drive it, comprising: a current detection circuit that detects an active current and a reactive current of the induction motor; From the detection signal of the reactive current and the sine and cosine values corresponding to the internal voltage phase difference angle of the induction motor, using the following formula, T=mnMI〓I _q ...(1) I〓=I _n sin(θ −) =I _n sinθ・cos−I _n cosθ−I _n cosθ・
sin ……(4) I _q = I _n cos (θ−) = I _n cosθ・cos−I _n sinθ・sin
...(5) However, T: Torque m: Number of phases n: Number of pole pairs M: Mutual inductance I〓: Equivalent exciting current I _q : Torque component current θ: Power factor angle seen from the motor terminals I _n cosθ: Effective current I _n sin θ: A torque detection circuit for an induction motor, characterized by comprising a calculation circuit that performs reactive current torque calculation. 2. The torque detection circuit for an induction motor according to claim 1, wherein the sine value and cosine value are stored values in a storage device calculated in advance. 3. The torque detection circuit for an induction motor according to claim 2, wherein the stored value is retrieved by a signal indicating the operating state of the static power converter and corrected by interpolation calculation.