KR20100034079A - Apparatus and method of controlling motor - Google Patents

Abstract

PURPOSE: A motor controller and a method thereof are provided to compensate the distortion of an output voltage of an inverter by deciding the polarity of a compensation voltage based on one polarity among a phase current and an estimated current. CONSTITUTION: A motor controller comprises an inverter(106) and a controller(114). The inverter supplies phase current to the motor(110). The controller comprises a compensation current generating part. The compensation current generating part decides the polarity of the compensation voltage according to one polarity among an estimated current and a phase current. The compensation current generating part decides the polarity of the compensation voltage according to the polarity of the estimated current when the size of the phase current is within a criteria range.

Description

Motor control device and method {APPARATUS AND METHOD OF CONTROLLING MOTOR}

The present invention relates to a motor control device, and more particularly, to dead time compensation of an inverter of a motor control device including an inverter.

In an inverter including a plurality of switching elements, a dead time is applied to a control signal of a pair of switching elements to prevent an electrical short circuit caused by simultaneous turn-on of a pair of switching elements. This dead time causes distortion of the phase current, which distorts the stable speed control of the motor. Therefore, in the motor control apparatus including the inverter, the compensation of this dead time is very important for stable speed control of the motor.

Dead time compensation methods include a method using a voltage across the switching transistors constituting the inverter for driving the motor and a method using the output current of the inverter. Since the method of using the voltage across the switching element requires a separate voltage detection device and is affected by noise in actual implementation, the output current of the inverter may be used instead.

The motor controlled by the inverter is typically a brushless direct current motor (BLDC motor). This BLDC motor not only generates a large rotational force in a moment, but also enables precise rotational speed control, so that it is possible to instantaneously rotate the rotating tank in a rinsing cycle of a washing machine and to control the rotating speed of the rotating tank rotating at high speed. Suitable.

In using a BLDC motor in a washing machine, the effect of the dead time of the inverter must also be fully considered. In order to minimize the influence of the dead time of the inverter, the polarity of the dead time compensation voltage is determined by considering the polarity of the current flowing through the BLDC motor. If the rotation speed of the rotating tank is relatively low, the phase current of the BLDC motor is Because of its small size, accurate zero crossing point detection of phase current is difficult, and therefore, there is a high possibility of error in polarity of the dead time compensation voltage. Dead time compensation Due to the polarity error of the dead voltage compensation voltage, dead time compensation is not performed properly, which causes distortion of the current waveform flowing in the BLDC motor, which causes torque ripple. While the torque ripple does not greatly affect the rotation of the rotating tub at high speed, the torque ripple causes vibration and noise to the rotating tub while the rotating tub rotates at a relatively low speed. As a result, accurate dead time compensation of the inverter must be made to reduce the vibration and noise of the rotating tub of the washing machine to realize stable operation of the washing machine.

The motor control apparatus according to the present invention includes: an inverter for generating a phase current and supplying the motor; And a compensation voltage generator for determining the polarity of any one of the estimated current and the phase current, and determining the polarity of the compensation voltage according to the determined polarity.

The compensation voltage generator may determine the polarity of the compensation voltage according to the polarity of the estimated current when the magnitude of the phase current is within a preset reference range.

In addition, the estimated current described above is a current when modeling a motor and inputting a command voltage to the modeled motor.

The motor control method according to the present invention comprises: detecting a phase current; Determining whether the magnitude of the phase current is within a preset reference range; When the magnitude of the phase current is within a preset reference range, the polarity of the compensation voltage is determined according to the estimated polarity of the estimated current based on the modeling of the motor.

In addition, the estimated current described above is a current when modeling a motor and inputting a command voltage to the modeled motor.

A preferred embodiment of the present invention will be described with reference to FIGS. 1 to 8. 1 is a view showing a BLDC motor control apparatus according to an embodiment of the present invention. As shown in Fig. 1, the converter 104, the DC-link capacitor 108, and the inverter 106 constitute a power converter. The converter 104 converts AC power provided from the AC power source 102 into direct current. The inverter 106 converts the DC power back into three-phase AC power U, V, and W and supplies it to the BLDC motor 110.

Information on the current (ia) (ib) (ic) of each phase of the three-phase AC power supplied from the inverter 106 to the BLDC motor 110 is provided to the controller 114. The control unit 114 refers to the information on the current (ia) (ib) (ic) of each phase of the three-phase alternating current power and the position / speed information (F / G) of the rotor of the BLDC motor 110 with reference to the BLDC motor ( An inverter control signal S for controlling the rotation speed of 110 is generated. The inverter control signal S generated by the control unit 114 controls the switching time and the amount of current of each phase of the three-phase AC power (A) (B) (C) output from the inverter 106 to the BLDC motor 110. The purpose is to allow the rotational speed of the BLDC motor 110 to follow the speed command H input from the outside. The inverter control signal S is composed of six signals Sa, Sb, Sc, / Sa, / Sb, and / Sc, where "/" means inverting phase (level).

FIG. 2 is a view showing an inverter of the BLDC motor control device shown in FIG. 1. As shown in FIG. 2, the inverter 106 has six switching elements, that is, six transistors of power supplied to the BLDC motor 110 by switching the transistors Q1 to Q6 respectively by the inverter control signal S. FIG. The three transistors Q1, Q3, and Q5 located above Q1 to Q6 are switched by inverter control signals of Sa, Sb, and Sc, respectively, and three transistors Q2 and Q4 located below. Q6 is switched by inverter control signals of / Sa, / Sb, and / Sc, respectively. As a result, the upper three transistors Q1, Q3 and Q5 and the lower three transistors Q2 and Q4 and Q6 have opposite switching states (on / off). The diodes D1, D2, D3, D4, D5, and D6 connected in parallel to each of the transistors Q1, Q2, Q3, Q4, Q5 and Q6 are freewheel diodes. Wheel Diode).

3 is a diagram illustrating voltage distortion of an inverter for each polarity of phase current. The signals shown in FIG. 3 show a case of “A” phase, which is one of three-phase power, and the other cases of “B” and “C” phases are controlled in the same manner. As shown in FIG. 3, the switching signal Sa and the switching signal / Sa of opposite phases are generated based on the command voltage VaN * generated by the control unit 114. However, a dead time (tdead) is placed at the front of the switching signal Sa and the rear of the switching signal / Sa, respectively, so that a section in which the switching signal Sa and the switching signal / Sa overlap each other is generated. Do not do it. If a section in which these two switching signals Sa and the switching signal / Sa overlap each other occurs, the transistors Q1 and Q4 of the inverter 106 shown in FIG. 2 are turned on at the same time, and current flows to the ground. Because of this, the normal switching operation of the inverter 106 is not achieved. Dead time is to prevent this.

This dead time (tdead) causes an error between the command voltage VaN * and the actual output voltage VaN + and VaN-, especially when the polarity of the current is positive and An error also occurs between the output voltage VaN- when the current polarity is negative. In FIG. 3, Ts is the switching frequency, Vdc is the voltage across the capacitor 108, Vsat is the falling voltage of transistors Q1 and Q4, and VFWD is the threshold voltage of diodes D1 and D4. ton and toff are the turn on delay time and the turn off delay time, respectively.

As described above, an error occurs between the command voltage VaN * and the actual output voltage VaN + and VaN− due to the dead time tdead, and especially when the polarity of the current is positive. ) And the output voltage VaN- when the polarity of the current is negative, compensate for this error, thereby preventing distortion of the output voltage of the inverter 106 due to dead time. However, in order to accurately compensate the output voltage distortion of the inverter 106 due to dead time, the polarity of the phase current and the switching point of the polarity, that is, the zero crossing point, are accurately detected, and the compensation voltage of the appropriate magnitude corresponding to the polarity of the phase current is detected. Should be generated.

If the polarity and zero crossing point of the phase current cannot be correctly detected, an incorrect magnitude of compensation voltage is generated, and the compensation result using the phase current is unreliable. 4 is a diagram illustrating inaccurate compensation of an output voltage of an inverter and thus distortion of a phase current. As shown in FIG. 4, in detecting the zero crossing point in the low current section near 0A, an error due to the influence of noise, a filter, etc. occurs between the actual current 402 and the measured current 404, Inaccurate zero crossing point detection results in a significant difference between the values of the polarity discrimination signals 406 (+) and 406 (−).

5 is a diagram illustrating a compensation voltage generator according to an exemplary embodiment of the present invention. The compensation voltage generator shown in FIG. 5 is provided in the controller 114 to generate a compensation voltage for the A phase of the three-phase power. It is desirable to provide such a compensation voltage generator for each phase of the three-phase power so that the compensation is performed in the same manner for the remaining B and C phases.

As illustrated in FIG. 5, the compensating voltage generator according to an exemplary embodiment of the present invention includes a current polarity discriminator 502 that determines the polarity of the phase current ias and generates a polarity discrimination signal 504. The polarity discrimination signal 504 determines the polarity of the compensation voltage Vdis. Therefore, the polarity of the compensation voltage Vdis is determined according to the polarity of the current. The compensation voltage Vdis having the polarity determined in this manner is added to the command voltage Va of the phase A to be the final command voltage Vadis.

FIG. 6 is a diagram illustrating the current polarity discriminating unit illustrated in FIG. 5. As illustrated in FIG. 6, the current polarity determining unit 502 according to an embodiment of the present invention uses a zero crossing detection unit 602 to zero crossing points for any one of two phase currents (ias). And the polarity is discriminated to generate a polarity discrimination signal 504. One of the two phase currents (ias) is an estimated current (iase) obtained by modeling the BLDC motor 110 by inputting the command voltage Vas, and the other is the actual phase current (ias). . The zero crossing detection unit 602 determines the polarity of any one of the estimated current iase and the phase current ias according to the magnitude of the phase current ias. If the magnitude of the phase current ias exceeds a predetermined reference range, the zero crossing point of the phase current ias is detected to determine the polarity of the phase current ias, and conversely, the magnitude of the phase current ias is predetermined. If within the reference range, the zero crossing point of the estimated current iase is detected to determine the polarity of the phase current ias. This is to accurately determine the polarity of the phase current ias through the polarity determination using the estimated current iase because the magnitude of the phase current ias is too small in the low current section. .

In FIG. 6, modeling of the BLDC motor 110 allows the inductance component (L) 602 and the resistance component (R) 604 to form an open loop. Open loop configuration ensures accurate zero crossing point detection because no delay occurs.

Generation of the estimated current iase based on the modeling of the BLDC motor 110 is performed as follows.

In the above equation, ω is negligible because it is close to zero in the low current section. In the above equation, except for the term containing ω, the other terms are Laplace Transform.

In summary,

7 is a view illustrating a voltage distortion correction method of an inverter according to an embodiment of the present invention. As shown in FIG. 7, the magnitude of the phase current ias is first detected in order to generate the compensation voltage Vadis. If the magnitude of the phase current ias is within the reference range (Yes of 704), an estimated current is generated through modeling of the BLDC motor 110 for more accurate zero crossing point and polarity detection of the current (706). In step 708, the zero crossing point and the polarity of the estimated current are detected. Conversely, if the phase current ias exceeds the reference range (NO in 704), the zero crossing point and polarity of the phase current ias are detected (710). When the zero crossing point and the polarity of the current are detected as described above, the polarity of the compensation voltage Vdis is determined based on the current polarity (712). In other words, if the current polarity is negative, the polarity of the compensation voltage Vdis is determined to be negative, and if the current polarity is positive, the polarity of the compensation voltage Vdis is determined to be positive. When the polarity of the compensation voltage Vdis is determined, voltage compensation is performed by reflecting the compensation voltage Vdis in the command voltage Va.

8 is a diagram illustrating phase current and phase current polarity discrimination states when voltage distortion of an inverter is compensated by applying a voltage distortion correcting apparatus and method according to an exemplary embodiment. As shown in FIG. 8, in detecting the zero crossing point in the low current section near 0A, there is almost no error between the actual current 802 and the measured current 804, so that accurate zero crossing point detection is performed to obtain a polarity discrimination signal ( It can be seen that 806 (+)) and 806 (-) also have correct values.

1 is a view showing a BLDC motor control apparatus according to an embodiment of the present invention.

FIG. 2 is a diagram showing the configuration of the inverter shown in FIG. 1; FIG.

3 is a diagram illustrating voltage distortion of an inverter for each polarity of phase current.

4 shows inaccurate compensation of the output voltage of the inverter and thus distortion of the phase current.

5 is a diagram illustrating a compensation voltage generator according to an exemplary embodiment of the present invention.

FIG. 6 is a diagram illustrating a current polarity discriminating unit shown in FIG. 5. FIG.

7 is a view showing a voltage distortion correction method of an inverter according to an embodiment of the present invention.

8 is a view illustrating phase current and phase current polarity discrimination states when voltage distortion of an inverter is compensated by applying a voltage distortion correcting apparatus and method according to an exemplary embodiment of the present invention.

* Description of the symbols for the main parts of the drawings *

102: AC power

104: Converter

106: inverter

108: DC-link capacitor

110: BLDC Motor

114: control unit

502: voltage compensation unit

602: zero crossing detection unit

Claims (5)

An inverter for generating a phase current and supplying it to the motor; And a compensation voltage generator for determining the polarity of any one of the estimated current and the phase current and determining the polarity of the compensation voltage according to the determined polarity. The method of claim 1, wherein the compensation voltage generator, And determining the polarity of the compensation voltage according to the polarity of the estimated current when the magnitude of the phase current is within a preset reference range. The method of claim 1, And the estimated current is a current when modeling the motor and inputting a command voltage to the modeled motor. Detect phase current; Determining whether the magnitude of the phase current is within a preset reference range; And determining the polarity of the compensation voltage according to the polarity of the estimated current estimated based on the modeling of the motor when the magnitude of the phase current is within a preset reference range. The method of claim 4, wherein And the estimated current is a current when modeling the motor and inputting a command voltage to the modeled motor.

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