JP2001352775A - Rotational speed detector for induction motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To facilitate highly accurate detection of the rotational speed of an induction motor through a simple arrangement. SOLUTION: An arrangement comprising an up/down counter 10 for detecting the number of pulse signals by receiving output pulse signals from a PG sensor 4 for detecting the rotational speed of an induction motor 3, a clock counter 11 for detecting the period of a constant period clock generator 14, a rotational speed operating section 15 for reading out the values from the up/down counter and the clock counter synchronously and operating a rotational speed Fr from the ratio of the number (N) of these pulse signals and the period (T), and an adder 17 for determining the output frequency Fi of the induction motor from the sum of the slip frequency command Fs and the output frequency Fi of the induction motor is further provided with a sampling period setting section 22 for setting the calculation period (Ts) of the rotational speed based on the magnitude of the output frequency, and a system timer generator 16 outputting an operation period varying command and the operational period of the rotational speed is prolonged as the output frequency of the induction motor increases.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rotation speed detecting device for an induction motor for controlling the running of an electric vehicle by a variable voltage and variable frequency inverter.

[0002]

2. Description of the Related Art In an electric vehicle in which a traveling induction motor is driven by a variable voltage and variable frequency inverter, it is necessary to accurately detect the rotation speed of the induction motor for vector control and adhesion control of the induction motor. Generally, for detecting the rotation speed, a rotation speed detector (PG sensor) connected to the induction motor and outputting a pulse signal having a cycle inversely proportional to the rotation speed of the induction motor is used. From the ratio of N) to the period (T), a digital controller (for example, a microcomputer) performs an operation to calculate the rotation speed of the induction motor. As a method for accurately detecting the rotation speed of an induction motor, Japanese Patent Application Laid-Open
There is a system disclosed in Japanese Patent Application Laid-Open No. 2-7383. This method uses a pulse encoder in which the frequency of a pulse signal in one rotation of an induction motor is at least two orders of magnitude higher than that of a PG sensor used in an electric vehicle. Since there is a possibility that a torque response may occur due to a speed response delay accompanying the above, the calculation cycle is shortened with an increase in the rotation speed to improve the accuracy. However, in the case of an electric car of the inverter type, as described above, if the frequency of the pulse signal of the PG sensor is low and the operation cycle of the microcomputer is shortened, the accuracy of the rotational speed deteriorates, and the induction motor is controlled. Has a shortcoming that the processing time is insufficient.
As another method for accurately detecting the rotation speed of an induction motor, there is a method disclosed in Japanese Patent Application Laid-Open No. 60-82077. In this method, a reference time for calculating the rotation speed is set, and an interrupt is generated by a pulse signal of the PG sensor. When the reference time exceeds a certain time obtained by dividing the clock of the microcomputer, the rotation speed is calculated. It is a method that
The process for controlling the induction motor is performed in the remaining time after the interruption process. If the rotation speed increases, the interrupt cycle becomes shorter, and if the reference time is constant, the calculation time is insufficient, and the range of the rotation speed that can be processed is limited. Longer to extend the control range of the rotational speed. However, in the case of an electric vehicle of the inverter type, it is required that the delay of the control response be small as well as the accuracy of the rotational speed. In this method, the reference time is compensated for by the increase of the reference time, but the control response is delayed.

[0003]

SUMMARY OF THE INVENTION An object of the present invention is to provide an induction motor rotation speed detecting apparatus which can easily detect the rotation speed of an induction motor with high accuracy with a simple structure in view of the above circumstances. is there.

[0004]

In order to solve the above problems, a pulse signal output from a PG sensor connected to an induction motor is input, and the number of pulse signals is detected by counting rising edges of the pulse signals. / Counter, a clock counter for detecting the period of the clock generator with a fixed period, and the values of the up / down counter and the clock counter are read in synchronization, and the number (N) and period (T) of these pulse signals are The rotation frequency calculating means for calculating the rotation speed from the ratio, and the calculation means for obtaining the output frequency of the induction motor by the sum of the slip frequency command of the induction motor and the calculated rotation speed, the magnitude of the output frequency A sampling cycle setting means for setting a calculation cycle of the rotation speed on the basis of a clock signal, and a system timer for outputting a variable command of the calculation cycle. Means provided to increase the operation period of the rotation speed with an increase in the output frequency of the induction motor.

[0005]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a rotation speed detecting device for an induction motor according to an embodiment of the present invention. In FIG. 1, a power converter 1 supplied with power from an overhead wire 2 has a variable voltage,
The variable frequency controlled output is supplied to the induction motor 3.
The induction motor 3 is mechanically connected to wheels (not shown) of the electric vehicle, and the electric vehicle is controlled according to the output of the power converter 1. The rotation speed of the induction motor 3 is detected by a PG sensor 4 connected to the induction motor 3, and is obtained by calculating a pulse signal having a cycle inversely proportional to the rotation speed of the induction motor 3. That is, the output of the PG sensor 4 is input to the up / down counter 10, and the rising edge of the pulse signal is detected to count the number of pulses (N). The clock counter 11 divides the output of the clock generator 14 and counts it as a T counter value (T). Rotation speed calculator 1
5 outputs the read signal RD to the latches 12 and 13 every sampling period Ts. Latch 12, Latch 1
3 receives the read signal RD, the clock counter 1
The count value of T counted by 1 is latched by the latch 12, and the count value of N counted by the up / down counter 10 is latched by the latch 13, and is synchronously input to the rotation speed calculator 15. The rotation speed calculation unit 15 calculates the rotation speed Fr of the induction motor 3 from the ratio (N / T) between the N counter value and the T counter value within the same sampling cycle that outputs the read signal RD. Here, the sampling period Ts is generated from the system timer generator 16.

FIG. 2 shows an example of the relationship between the N count value, the T count value, and the read timing of the count value of the rotation speed calculator 15. The N count value is the count value of the output of the PG sensor 4, and the T count value is the count value of the output of the clock generator 14. That is, the rotation speed calculation unit 15
Then, the read signal RD is output at the timings of the read timings t1, t2, and t3.
At 1, T1, and t2, the count values N2, T2, and t3 are input in synchronization with the count values N3 and T3, respectively. Then, a difference from each count value in the previous sampling process is obtained, and the rotation speed Fr is calculated. For example, t
The calculation of the rotational speed Fr at 2 is as shown in equation (1). Here, T ₀ indicates a read timing time width. Fr = k × (ΔN / ΔT) = k × (N2−N1) / (T2−T1) (1) where, k: operation coefficient

On the other hand, a three-phase output current of the power converter 1 is detected by a current transformer (CT) 23, input to a coordinate conversion unit 21 to vector-decompose the three-phase current, and output the slip frequency calculation unit 19. To calculate the slip frequency Fs.
From this, the adder 17 adds the rotational speed Fr calculated above and the slip frequency Fs to obtain the output frequency Fi. The output frequency Fi is input to the voltage calculator 18 and calculates an instantaneous voltage command value of the power converter 1 together with a voltage command value (not shown). The obtained instantaneous voltage command value is PWM
It is converted into a PWM signal by the control unit 20 and controls the power converter 1. Here, N counter 10, T counter 1
1, the latches 12, 13 and the like can be easily configured by a programmable hard logic 100. The rotation speed calculator 15, the adder 17, the voltage calculator 18, the slip frequency calculator 19, the PWM controller 20, the coordinate converter, etc. 21 is suitable for processing by a microcomputer 110 using software.

In such a configuration, the sampling period Ts of the rotation speed calculation unit 15 needs to be processed at, for example, about Ts = 1 ms in consideration of the influence of a delay in calculation. On the other hand, as the clock frequency of the T counter 11, it is practical to adopt a value of 1 MHz or less in order to divide the frequency of the clock generator 14 for operating the logic. Assuming 400 kHz as an example, the time resolution of the T counter is 2.5 μs. In this case, the error of the speed calculation is 2.5 μs / 1 ms = 0.25%. Here, if the sampling period Ts is kept constant, the resolution of the calculated rotational speed Fr decreases as the speed increases. Output frequency F of inverter type electric car
If i is about 200 Hz at the maximum, Fi = 200 Hz
Is 200Hz x 0.25% = 0.5H
z, and when using a low-slip induction motor,
This discontinuity in the output frequency cannot be ignored as a cause of current ripple. Therefore, the output frequency F
Sampling period Ts of rotation speed calculation with increase of i
If the error of the speed calculation is made to be within a certain value by lengthening, the ripple of the current can be suppressed even in the low slip induction motor. That is, in FIG. 1, the sampling cycle setting unit 22 determines the magnitude of the output frequency Fi, and as shown in FIG. 3, changes the sampling cycle Ts from the sampling cycle initial value Ts0 to the maximum frequency F1.
The characteristic is set to be s1, and a Ts variable command is given to the system timer generator 16. Here, Ts0 = 1m
Assuming that s, Ts1 = 3 ms and F1 = 200 Hz, Ts
The speed calculation error at 1 = 3 ms is 2.5 μs / 3 ms ≒
Since it is 0.083%, the resolution of the calculation of Fr is 200
Hz × 0.083% ≒ 0.17 Hz, the frequency discontinuity can be suppressed to about 抑制 す る of the conventional frequency, and the current ripple can be reduced.

In the example shown in FIG. 3, the sampling period Ts is continuously changed with respect to the output frequency Fi. However, in the case of an inverter type electric vehicle, control is performed even in a region equal to or higher than the maximum output voltage Em of the induction motor, and its speed is controlled. The control range is more than twice the synchronization speed. Therefore, the characteristics of the sampling period as shown in FIG. 4 may be used. That is, the sampling period Ts0 is constant in the speed region up to the maximum output voltage Em (synchronous speed F0), and the sampling period is continuously varied from Ts0 to Ts1 in the region above the maximum output voltage Em. In an induction motor with a synchronous speed of about 70 Hz,
As before, Ts0 = 1 ms, Ts1 = 3 ms, F1 =
If the frequency is 200 Hz, the speed calculation error up to Fi = 70 Hz is 2.5 μs / 1 ms = 0.25%.
Is at most 70Hz x 0.25% ≒ 0.175
Hz. In addition, when Fi = 200 Hz, the resolution is ≒ 0.17 Hz as in the above case, and this method also has the effect of reducing the current ripple as in the example of FIG.

FIG. 5 shows a flowchart of a calculation process of the rotation speed Fr and the sampling period Ts. This process is started for each sampling period Ts, and the N count value and the T count value are read for both (a) and (b), and the differences ΔN and ΔT from the previous sampling are obtained to calculate the rotational speed Fr. Finally, the calculation of the next sampling period Ts is performed. Although the calculated Ts is not shown in the flowchart, the next timer Ts
Replaced with the startup data. Note that FIG.
In the example, the sampling period Ts is obtained, and the next calculation of Ts is as shown in equation (2). Ts = Ts0 + (Ts1−Ts0) × (Fi / F1) (2) Further, (b) is a process for obtaining the characteristics of the sampling period Ts in the example of FIG. 4, and when Fi ≦ F0, the next Ts
Is Ts = Ts0, and when Fi> F0, the next T
The calculation of s is as shown in equation (3). Ts = Ts0 + (Ts1−Ts0) × {(Fi−F0) / (F1−F0)} (3)

[0011]

As described above, according to the present invention,
With a simple configuration, the rotational speed of the induction motor can be detected over a wide range with high accuracy, and thereby the vector control and the adhesion control of the induction motor in the inverter-type electric vehicle can be performed with high accuracy. Further, since the calculation error of the induction motor in the high-speed range can be made equal to that in the low-speed range, discontinuity of the output frequency of the induction motor can be suppressed, and ripple of the motor current can be reduced.

[Brief description of the drawings]

FIG. 1 shows a rotation speed detecting device for an induction motor according to an embodiment of the present invention.

FIG. 2 is a diagram showing a relationship between a rotation speed calculation and an N counter and a T counter according to the present invention.

FIG. 3 is a diagram illustrating an example of a relationship between a sampling cycle and a rotation speed of a rotation speed calculation unit according to the present invention.

FIG. 4 is a diagram showing another example of the relationship between the sampling period and the rotation speed of the rotation speed calculation unit of the present invention.

FIG. 5 is a flowchart illustrating processing of a rotation speed calculation unit and a sampling cycle setting unit according to the present invention;

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1: Power converter, 2: Overhead wire, 3: Induction motor, 4: PG
Sensor, 10 up / down counter, 11 clock counter, 12, 13 latch, 14 clock generator, 15 rotational speed calculator, 16 system timer generator, 17 adder, 18 voltage calculator , 19 ... Slip frequency calculator, 20 ... PWM converter, 21 ... Coordinate converter,
22: sampling cycle setting unit, 23: current transformer (CT)

Claims (3)

[Claims] 1. An induction motor for controlling the running of an electric vehicle by a variable voltage, variable frequency inverter, rotation speed detection means for generating a signal having a period inversely proportional to the rotation speed of the induction motor, and the periodic signal, A counter that counts the number of periodic signals, a counter that counts clocks of a fixed period, a counter that inputs the number of the periodic signals and the output of the clock counter at a fixed period, and calculates the ratio of the number of the periodic signals and the clock period A rotation speed calculating means for obtaining a rotation speed of the induction motor, and a calculation means for obtaining an output frequency of the induction motor by a sum of a slip frequency command of the induction motor and the rotation speed, wherein an output frequency of the induction motor is calculated. A rotation speed detection device for an induction motor, wherein a calculation cycle of the rotation speed calculation means is lengthened with an increase. 2. The method according to claim 1, wherein a calculation cycle of the rotation speed calculation means is constant up to a maximum output voltage of the induction motor, and is increased in a maximum output voltage region with an increase in an output frequency of the induction motor. A rotation speed detecting device for an induction motor, characterized in that: 3. The method according to claim 1, wherein a sampling cycle setting means for setting a calculation cycle of the rotation speed based on the magnitude of the output frequency, and a system timer for outputting a command to change the calculation cycle. Means for detecting a rotational speed of an induction motor.