JP2008271656A - Method of detecting initial magnetic pole position of permanent magnet motor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To exactly detect the initial magnetic pole position of a permanent magnet motor at a high speed. <P>SOLUTION: The method for detecting initial magnetic pole position in permanent-magnet motor first determines a PWM pulse width D<SB>t</SB>applied to a stator, where the PWM pulse width D<SB>t</SB>depends on motor parameters. Six voltage vectors are then successively applied to the stators and the associated current rising time are calculated. The position of a rotor is determined based on the shortest current rising time. The voltage vectors are again successively applied to the stators to recalculate the position of the rotor. The position of rotor can be precisely determined when the two calculations are consistent. When the two calculations are not consistent, the voltage vectors are again successively applied to the stators to recalculate the position of rotor until the calculations are consistent. The set current level is made to be larger than the motor rated current, for example, 160% motor rated current, to facilitate the determination of current rising time. The set current level can be 160% drive rated current when the motor rated current is larger than the drive rated current. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

Detailed Description of the Invention

(Technical field)
The present invention relates to a method for detecting an initial magnetic pole position of a permanent magnet motor, and more particularly to a method for detecting an initial magnetic pole position of a permanent magnet motor by a voltage pulse related to a motor parameter.

(Background technology)
As the industry has advanced and automated, servo motors have become widely used. For example, CNC machines, robot arms, industrial machines, elevators, and air conditioners generally require precise control over the motor. With the rapid development of microprocessors and power electronics, motors can be implemented with complex control theories to enhance their performance.

  Permanent magnet AC servo motors use an inverter pulse width modulation (PCM) signal to generate a rotating magnetic field in the stator. The rotating magnetic field of the stator interacts with the permanent magnetic field of the rotor to generate rotational torque. When the permanent magnet motor is controlled, the inverter switch is controlled to generate a rotating electric field suitable for smoothly operating the motor. However, the initial position of the rotor permanent magnet is usually unknown. This is because the rotor may rotate in both forward and reverse directions when the motor starts. However, indefinite rotation direction is not desirable in certain applications such as elevators. Therefore, the initial magnetic pole position of the permanent magnet motor should be accurately determined to prevent malfunction.

  As prior art methods for determining the initial magnetic pole position of a permanent magnet motor, there are a high frequency injection method (HFI) and a voltage pulse injection method. The HFI method has the disadvantages of complicated calculations, a priori information on dq axis inductance, and non-decomposition of ± 180 ° electrical angle. The conventional voltage pulse injection method uses the principle that the inductance is different when the rotational position is different, and the current gradient is different accordingly when the inductance is different. However, such conventional voltage pulse injection methods are excessively dependent on motor parameters. The motor coil can be damaged if the rise time is not set correctly. The measured value of the initial magnetic pole position becomes inaccurate if the rise time is too short.

  It would be desirable to provide a method for detecting the initial magnetic pole position of a fast and accurate permanent magnet motor to improve and stabilize the performance of the permanent magnet motor. The method of detecting the initial magnetic pole position of the permanent magnet motor is preferably less dependent on parameters and can be applied to any motor.

(Disclosure of the Invention)
An object of the present invention is to provide a method for accurately detecting the initial magnetic pole position of a permanent magnet motor.

Accordingly, the present invention provides a method for detecting the initial magnetic pole position of a permanent magnet motor. While applying a PWM pulse width _{D t} first stator, the PWM pulse width _{D t} varies by a motor parameter. Six voltage vectors are then sequentially applied to the stator and their associated current rise times are calculated. The rotor position is determined based on the shortest current rise time.

  According to one aspect of the invention, the voltage vector is again applied to the stator to recalculate the rotor position. If these two calculation results match, it can be said that the rotor position has been accurately determined. If these two calculation results do not match, the voltage vector is again applied to the stator again, and the rotor position is recalculated until the calculation results match.

  According to another aspect of the present invention, in the method for detecting the initial magnetic pole position of a permanent magnet motor, the current rise time can be easily determined by setting the set current level to be larger than the motor rated current, for example, 160% of the motor rated current. it can. The set current level can be 160% of the drive rated current when the motor rated current is larger than the drive rated current.

(Best Mode for Carrying Out the Invention)
Features that are considered novel of the invention are set forth in the appended claims. The invention itself, however, may best be understood by reference to the following detailed description of the invention. In the following, specific exemplary embodiments relating to the present invention will be described with reference to the accompanying drawings.

  1A and 1B are schematic views showing a magnetic field of a stator and a rotor in a permanent magnet motor, where the rotor magnetic field is provided by a permanent magnet and the stator magnetic field is provided by an external current. Yes. Therefore, the stator magnetic field can be treated as a known parameter. When the rotor magnetic field and the stator magnetic field are in opposite directions, the resultant magnetic field is in an unsaturated state (linear). On the other hand, when the rotor magnetic field and the stator magnetic field are in the same direction, the combined magnetic field is saturated (non-linear). The saturation of the combined magnetic field affects the magnitude of the stator inductance. By utilizing this characteristic, the initial magnetic pole position of the permanent magnet motor can be determined.

  FIG. 2 shows the relationship between the magnetic flux and the current in the permanent magnet motor, and it is possible to observe the influence of the saturation of the combined magnetic field on the magnitude of the stator inductance. When the combined magnetic field is saturated, the inductance is small. On the other hand, when the combined magnetic field is unsaturated, the inductance increases. The greater the stator inductance, the greater the circuit time constant. As a result, the current gently slopes even at the same applied voltage.

  FIG. 3 shows the relationship between current and time for different stator inductances. These stator inductances differ for saturated and unsaturated combined magnetic fields. The time for the current to rise to a certain level is also different between different inductances. By utilizing this characteristic, the initial magnetic pole position of the permanent magnet motor can be determined.

In other words, the stator inductance is different if the rotor is present at different positions. The initial magnetic pole position of the permanent magnet motor can be determined by measuring the current rise time. FIG. 4 shows six bias methods relating to the three-phase winding before the permanent magnet motor is operated. As shown in the figure, a bias voltage V _dc is applied to the three-phase windings U, V, and W, and positive and negative pulses are generated by the three-phase windings U, V, and W, respectively. The rising edge of the current generated with the bias voltage V _dc is measured by these six methods to obtain the initial magnetic pole position of the permanent magnet motor.

FIG. 5 shows an equivalent circuit for a permanent magnet motor. FIG. 6 shows a current waveform after exciting the motor coil, where R is the coil resistance, L is the inductance, V _dc is the bus voltage, I _rating is the motor rated current, and I _level = I _rating × 160%. It is. As if i _{(t) = I level,} it can be calculated rise time _{t r.}

As can be seen from FIG. 6, the smaller the inductance, the faster the current rises, that is, with a short rise time. Therefore, a pulse signal is applied by six bias methods as shown in FIG. 6, and the current rise time is measured. The rotational position with the shortest rise time is aligned with the stator. Regarding the setting of the current level I _level , if the rising current level is not sufficient, it is difficult to resolve the rising time. The current level I _level can be set as 160% of the motor rated current. When the motor rated current is larger than the inverter rated current, the current level I _level can be set as 160% of the inverter rated current.

In order to simplify the calculation, the voltage drop across resistor R was reduced to yield:
The slope of the current becomes difficult to measure with a computer program if the current rises too quickly. Therefore, the voltage is preferably injected by pulse width modulation (PWM) instead of turning on / off. FIG. 7 shows waveforms in the PWM method. Different motors have different motor parameters and their rise times are also different. The PWM method should also be changed according to the motor parameters. FIG. 8 shows the relationship between the PWM interrupt time T _s and the PWM pulse width D _t . Aliquoted PWM interrupt time _{T s} to 256, splitting the rise time _{t r} to 32PWM interrupt (also see FIG. 7 to _{be), t r = t 1 +} t 2 +. . + T ₃₁ + t ₃₂ and the PWM pulse width D _t can be calculated as follows:

  In the above formula, DB is a dead time (for example, 4 μS) for preventing a short circuit between the upper and lower arms, and CF is a maximum carrier frequency of the inverter for driving the motor.

FIG. 9 shows a flowchart regarding a method of detecting the initial magnetic pole position of the permanent magnet motor. First, the PWM pulse width _Dt is determined according to the motor parameter and the maximum carrier frequency of the inverter (step 100). Six voltage vectors having the configuration shown in FIG. 4 are sequentially applied to the stator (step 102). The current rise time for each voltage vector is calculated (step 104). The current rise times for the calculated voltage vectors are compared to obtain a rotor position determination value (step 106). Steps 102 to 106 are performed again to obtain another determination value of the rotor position. The two determination values are compared to check whether they match (step 108). If the two determination values match, the detection of the initial magnetic pole position of the permanent magnet motor is terminated. In the above steps, steps 102-106 are repeated to minimize the effects of noise. If the two determination values do not match, the six voltage vectors are sequentially applied again to the stator, and the rotor position is determined again. If the two consecutive determination values match, this flow is finished, and the initial magnetic pole position of the permanent magnet motor can be ensured.

  Although the present invention has been described with reference to its preferred embodiments, it should be understood that it is not intended to limit the invention to that detail. Various substitutions and modifications have been suggested in the foregoing description, but others will occur. Accordingly, all such substitutions and modifications are intended to be included within the scope of the present invention as defined in the appended claims.

It is the schematic shown about the stator magnetic field and rotor magnetic field of a permanent magnet motor. It is the schematic shown about the stator magnetic field and rotor magnetic field of a permanent magnet motor. The relationship between the magnetic flux and electric current in a permanent magnet motor is shown. The relationship between current and time for different stator inductances is shown. Six bias methods for the three-phase winding before the permanent magnet motor is operated will be described. An equivalent circuit for a permanent magnet motor is shown. The current waveform after exciting the motor coil is shown. The waveform in the PWM method is shown. PWM interrupt time showing the relationship between _{T s} and the PWM pulse width _{D t.} 3 shows a flowchart relating to a method for detecting an initial magnetic pole position of a permanent magnet motor.

Claims (13)

A method for detecting an initial magnetic pole position of a permanent magnet motor, wherein the permanent magnet motor is driven by an inverter, the motor including a rotor and a stator, and the stator including a three-phase winding. And the method includes:
(A) determining the PWM pulse width “D _t ” applied to the stator;
(B) sequentially outputting six voltage vectors to the stator;
(C) calculating the current rise time in response to each voltage vector;
(D) determining the rotor position decision value by composing the rise time resulting from the six voltage vectors;
A method comprising the steps of: Repeating steps (b)-(d); and
Check whether the two judgment values of the rotor position match,
The method of claim 1, further comprising: The method according to claim 1, wherein one PWM interrupt time “T _s ” is divided into 256 equal parts. 4. The method according to claim 3, characterized in that one rise time “t _r ” is divided into 32 interrupts. The PWM pulse width “D _t ” is _expressed by the following formula:
5. In the formula, “DB” is a dead time for preventing a short circuit between upper and lower arms, and “CF” is a maximum carrier frequency of an inverter for driving a motor. The method described in 1. The method according to claim 1, characterized in that the current level I _level is set as 160% of the motor rated current. 7. The method of claim 6, wherein if the motor rated current is greater than the inverter rated current, the current level I _level is set as 160% of the inverter rated current. A method for detecting an initial magnetic pole position of a permanent magnet motor, wherein the permanent magnet motor is driven by an inverter, and the motor includes a rotor and a stator, and the stator includes a three-phase winding. And the method includes:
(A) determining the PWM pulse width “D _t ” applied to the stator;
(B) sequentially outputting six voltage vectors to the stator;
(C) calculating the current rise time in response to each voltage vector;
(D) determining the first determination value of the rotor position by composing the rise time resulting from the six voltage vectors;
(E) repeating steps (b) to (d) to obtain a second determination value of the rotor position and checking whether the determination values of these two rotor positions match;
(F) knowing that the rotor position is correct when the two determination values of the rotor position match; and
(G) If the two determination values of the rotor do not match, repeating steps (b) to (e);
A method comprising the steps of: The method according to claim 8, wherein one PWM interrupt time “T _s ” is divided into 256 equal parts. The method according to claim 9, wherein one rise time “t _r ” is divided into 32 interrupts. The PWM pulse width “D _t ” is _expressed by the following formula:
11. The calculation according to claim 10, wherein "DB" is a dead time for preventing a short circuit between upper and lower arms, and CF is a maximum carrier frequency of an inverter for driving a motor. the method of. _9. The method according to claim 8, wherein the current level I _level is set as 160% of the motor rated current. 13. The method of claim 12, wherein if the motor rated current is greater than the inverter rated current, the current level I _level is set as 160% of the inverter rated current.