KR20030063583A - Inductance Measurement Method for Sensorless Control of SRM - Google Patents

Abstract

PURPOSE: A method for detecting a position of a rotor in a switched reluctance motor is provided to generate the low level current and estimate the inductance by applying a pulse voltage regardless of a driving torque to a phase of the switched reluctance motor which is not excited. CONSTITUTION: A method for detecting a position of a rotor in a switched reluctance motor is to measure position information of a rotor necessary for driving the switched reluctance motor without using an additional position sensor such as an encoder. A pulse voltage regardless of a driving torque is applied to a phase of the switched reluctance motor which is not excited and the low level current is generated thereby. The inductance is estimated from a predetermined formula by using the low level current, the pulse voltage, and a sustain time of the pulse voltage.

Description

Inductance Measurement Method for Sensorless Control of SRM

The present invention has a simple structure, robust brushless motor, capable of high speed operation, has the speed-torque characteristic of a DC series motor, and has excellent control performance and high speed driving performance. The present invention relates to an inductance measuring technique and a method for detecting the position of a rotor for the sensorless control of SRM, which is expanding its application area throughout the aircraft and the industry.

Synchronized control to inductance profile is essential for high efficiency and high performance operation of SRM driven by pulsed excitation power source. Position detection device for detecting information on rotor position angle for proper switching operation according to rotor position Is essential. Rotor position angle detection generally uses encoders or resolvers. However, the higher the resolution of these mechanical external position sensors, the higher the cost. Therefore, research is being actively conducted on the use of a low-cost encoder or a sensorless drive for completely eliminating the burden on the installation cost.

SRM is a power device that generates rotational force by using reluctance torque. Reluctance torque is a torque that is generated depending on magnetic structure when applying excitation energy to only stator or rotor. It is caused by the change of the turn and the excitation energy, and is due to the characteristic that the reluctance of the phase to which the excitation energy is applied is minimized. 1 is a basic configuration of a dual salient SRM driving system.

Using the concept of coenergy to find the torque formula of a motor, torque on one phase of a double-pole type SRM Is the position angle of the rotor, The partial derivative of the nose energy with respect to

here Is the torque of the Hansang, Nose energy Is the current of the winding, Silver inductance, Denotes the rotor position angle. In this equation, since torque is proportional to the square of the current, it is irrelevant to the direction of the phase current, and since the polarity of the torque changes according to the inductance slope, there is a position angle of the rotor where negative torque occurs. Therefore, in order to suppress negative torque, the SRM must switch in synchronization with the position angle of the rotor.

In SRM, the solution to phase current is essential to generate the desired torque with the correct switching behavior. The phase voltage equation of SRM for analyzing phase current is as follows.

here Is the phase voltage, Silver winding resistance, Is the rotor angular velocity.

In the phase voltage equation of equation (2), the second term on the right side corresponds to the counter electromotive force. Therefore, the back EMF term is expressed by the following equation.

here to be.

As shown in equation (3), the counter electromotive force takes the same form as the direct current motor, and the torque equation in the equation (1) takes the same form as the direct current series motor. Therefore, it can be seen that the speed-torque characteristic of SRM has the same characteristics as the DC series motor.

SRM motor has simple structure and protruding magnetic pole, but it needs to get the position information of the rotor in order to operate in the optimal operation state. Hall elements, resolvers, encoders, and the like are used as sensors for detecting the position and speed of the rotor.

The Hall element is a sensor that changes the output signal every 180 ° according to the magnetic position of the rotor. In the case of a permanent magnet motor using three Hall elements, the rotor position is measured at 60 ° intervals. However, within 60 ° intervals, the position cannot be detected with more precision, the proper arrangement of the Hall elements for magnetic detection is difficult, and it is susceptible to external magnetic fields.

The resolver has the advantage of being able to detect the position and speed of the rotor research, but has the disadvantage of economical due to the high cost and complicated design and processing of the motor to secure the stability of the sensor.

In the case of using an encoder, one side of the shaft needs to be allocated for the encoder, so it is difficult to attach a heat dissipation fan, and the problem of heat dissipation must be considered in the design when used for a long time. In addition, when attaching the sensor, it must be attached to the rotating shaft very precisely, so mass production is difficult and the attached sensor is affected by the use environment, so the reliability of the sensor in high ambient temperature, high humidity, or high vibration environment Decreases. Therefore, in consideration of these problems, the sensorless method without a position detector or a speed sensor of a rotor has been studied in recent years.

Conventional sensorless method indirectly measures inductance by using voltage and current. The merchant inductance of the motor varies with the rotor position. Normally, the inductance of SRM is more than 3 when the maximum / minimum value is more than 10, and it is more than 10 when it is well designed, so it is possible to know the inductance indirectly if this value can be calculated using voltage and current.

The stator voltage equation of the SRM is shown in equation (4).

Where V is the applied voltage and L is the motor inductance. If you sum up L in equation (4)

Where A = (di / d) / i, B = (V / i) -R Is the value from the previous sample.

Equation (5) can be used to know rotor position indirectly, but it is difficult to calculate inductance in real time. In addition, it is in a state in which reliability is not secured to compensate for errors caused by measurement errors or noise.

The present invention proposes a method for detecting the position of the rotor by applying a pulse voltage to a phase that is not generating torque in a new manner different from the above and measuring the phase inductance of the SRM from the generated current. . The proposed rotor position detection method can detect the position of the rotor even during stop and start, which solves the problem of the conventional start. Therefore, not only stable speed control is possible in a wide range of speeds by on / off angle control, but also the possibility of practical use of SRM is enhanced by realizing low price of controller by eliminating the existing encoder, and proved through experiments.

Figure 1 SRM drive system

Fig. 2 Linear Inductance / Periodic Converter

Fig. 3 A phase equivalent circuit of SRM when a small current is applied

Fig. 4 Phase voltage and phase current waveforms when pulsed voltage is applied

5 is a block diagram of the entire system

6 Inductance profile and current for inductance detection

(a) Inductance profile according to the change of electric angle

(b) Inductance detection current according to the change of electric angle

Figure 7 Current peak value change according to the rotor position

Figure 8 Pulse current, sample hold value and calculated inductance according to rotor position

Fig. 9 Phase B current, phase A signal, and phase A current for inductance estimation

When the phase voltage is applied to the SRM and the phase current as a torque component is detected, the phase inductance can be theoretically calculated to obtain information about the position of the rotor. Since the SRM is driven by applying an intermittent exciting power to each phase winding sequentially, there is always a phase in which phase current for torque generation is not conducted. Thus, inductance can be measured from a phase in which no phase current is conducted in SRM. The phase inductance can be measured by applying a voltage to the phase in which the phase current is not conducting and detecting the current, but the back electromotive force cannot be ignored during operation, and the voltage drop caused by the resistance cannot be ignored. In particular, the phase current for inductance detection should not cause torque pulsations. To meet this limitation, the current for inductance measurement must be very small. For this purpose, if a small current is generated by applying a very narrow pulse voltage, the voltage drop and the counter electromotive force component of the resistance can be ignored by the small current, and the phase voltage equation may be simply viewed as an inductance term. Therefore, if the phase current is very small in SRM, the voltage equation of Eq. (2) is simply expressed as Eq. (6).

Equation (6) is expressed as an electrical equivalent circuit as shown in FIG.

The phase inductance of SRM is simply expressed as a function of position. In the circuit of FIG. 3, the inductance can be estimated by turning on SW1 and detecting and calculating the current flowing at this time.

At this time, the inductance detection current should be set to a time that is small enough not to affect torque generation. 4 is a phase current waveform when a phase voltage of SRM is applied to calculate inductance.

At this time, if the current solution is obtained when the phase switch is turned off, equation (7) is given as below.

From the equation (7), as shown in Fig. 4, the peak current at which the switch is turned off when given the switch-on time is as follows.

The inductance is obtained from the peak current obtained from Equation (8) as follows.

In Eq. (9), if the applied voltage and the switch-on time are defined as set values, it can be treated as a constant. Equation (9) is simply expressed as follows.

here, to be.

If only the current for estimating the inductance in the phase where no phase current is conducting is detected, the position of the rotor can be estimated simply from equation (10).

A block diagram of the entire system created on the basis of the above theory is shown in FIG. The block diagram of FIG. 5 is a speed command value as an input, sends information of a phase to which pulse power is applied from an angle controller to a current selector, calculates an angle from an inductance table through a peak current detector, and enters a signal from the angle predictor to the angle controller again. It is designed to generate a phase signal.

6 shows an inductance profile and current waveform for estimating inductance according to the electrical position angle of the rotor. As shown in FIG. 6 (a), since the inductance for the rotor position angle does not become a shear yarn function, when the inductance is calculated, two rotor position angles satisfying the inductance exist. Among these two values, the value corresponding to the current rotor position angle can be obtained by using the previous phase switch information and the inductance profile. Since each phase of the SRM is sequentially excited, the current rotor position angle can be known by referring to the previous phase switch information.

The rotor position angle at initial startup can be determined by calculating the inductance of all phases. During operation, the rotor position is detected by the phase switch information and the estimated inductance of the previous phase to be excited.

In order to verify the sensorless operation and reliability of SRM by the proposed inductance inference technique, the characteristics of the fabricated SRM were verified through experiments. The motor tested was a 12 / 8-pole SRM with a class of 400 W.

The processor used in the controller is the DSP320F241. The DSP320F241 has six PWM terminals and a PWM interrupter. It has a built-in EEPROM, 10-bit A / D converter, and a self-monitoring function by a watchdog timer. To detect the inductance by the board, pulses are generated by the PWM terminal and current is sampled by the PWM interrupter. The position angle of the rotor is estimated by referring to the state of the switch, and the SRM is controlled by determining the operation mode based on the command speed and the speed by estimating the speed based on this.

The change of the current peak value for estimating inductance according to the rotor position is shown in FIG. 7. According to the electric angle of the rotor 360 degrees, the magnitude of the peak current changes as shown in the figure.

The width of the pulse voltage applied to the phase for inductance detection The peak value of the current changes as the rotor rotates. At the alignment position, the current peak value is minimum and at the non-alignment position, it is maximum. By detecting this current value, inductance can be obtained.

FIG. 8 shows the current for inductance measurement and the inductance calculated on the basis of the continuous pulse voltage applied in the SRM. As can be seen from the waveform, it can be seen that the inductance for the electrical angle 360 degrees is good. Therefore, it can be said that the validity of the sensorless control of the SRM by the inductance measuring method is verified to some extent. Even if the calculated inductance is different from the actual inductance, the position angle is estimated by using the calculated inductance and the position angle at that time.

9 shows the B-phase current, the A-phase switching signal, and the A-phase current for inductance measurement while driving the SRM in the sensorless mode. Since the A phase signal is determined by the micro current value by the pulse voltage applied to the previous phase B, the phase A switch is turned on when the micro current of the phase B for the inductance calculation exceeds a predetermined value. As shown in the figure, the current for inductance estimation applies a pulse voltage at the rotor position angle that does not affect the generation of drive torque thereon.

The present invention proposes a position angle sensorless operation method of SRM based on inductance estimation. In this method, a small current is generated by the pulse voltage so as not to influence the driving torque generation on the unexcited phase. Inductance was calculated from this current, and the position angle was estimated. As a result of experiments by implementing the proposed set of experiments, it can be seen that not only the rotor position can be estimated at standstill but also the rotor position angle is well estimated during operation.

The proposed rotor position detection method can detect the position of the rotor even during stop and start, which solves the problem of the conventional start. Therefore, not only stable speed control is possible in a wide range of speeds by on / off angle control, but also the possibility of practical use of SRM is enhanced by realizing low price of controller by eliminating the existing encoder, and proved through experiments.

Claims (1)

By measuring the rotor position information necessary for driving the SRM without attaching an additional position sensor such as an encoder, a pulse voltage that does not affect the driving torque is applied on the motor that is not excited and a micro current is detected. do. A method of estimating inductance using Equation (9) using this current, voltage, and duration of voltage.