KR101466341B1 - Apparatus and method of controlling motor - Google Patents

Abstract

A motor control apparatus and method are disclosed. The motor control apparatus determines the polarity of the compensation voltage based on the current polarity of either the phase current or the estimated current to compensate for the output voltage distortion of the inverter, The polarity of the compensation voltage can be accurately determined by indirectly discriminating the polarity of the phase current through the current.

Inverter, Voltage Compensation, Dead Time, Current Polarity

Description

[0001] APPARATUS AND METHOD OF CONTROLLING MOTOR [0002]

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

In an inverter including a plurality of switching elements, a dead time is applied to control signals of a pair of switching elements in order to prevent an electrical short due to simultaneous turn-on of the pair of switching elements. This dead time causes distortion of the phase current, and the distortion of the phase current hinders the stable speed control of the motor. Therefore, in the motor control apparatus including the inverter, compensation of the dead time is very important for the stable speed control of the motor.

The dead time compensation method includes a method using a voltage applied to both ends of a switching transistor constituting an inverter for driving a motor and a method using an output current of the inverter. A method using a voltage across the switching element requires a separate voltage detection device and is influenced by noise in actual implementation so that the output current of the inverter is used instead.

The motor controlled by the inverter is typically a brushless direct current motor (BLDC motor). Since this BLDC motor can instantaneously generate a large rotational force and can control the rotational speed precisely, it is possible to rapidly rotate the rotary tub instantaneously in the rinse cycle of the washing machine and to control the rotational speed of the rotary tub rotating at high speed Suitable.

In using a BLDC motor in a washing machine, the influence of the inverter's dead time must also be considered. In order to minimize the influence of the dead time of the inverter, the polarity of the dead time compensation voltage is determined in consideration of the polarity of the current flowing through the BLDC motor. If the rotation speed of the rotating group is relatively low, It is difficult to detect an accurate zero crossing point of the phase current, and therefore, there is a large possibility that the polarity of the dead time compensation voltage is erroneous. Due to the polarity error of the dead-time compensation voltage, dead-time compensation is not properly performed, which causes distortion of the current waveform flowing through the BLDC motor, resulting in torque ripple. This torque ripple does not greatly affect the rotation speed of the rotating tappet while the rotating tappet rotates at a high speed. However, in the case that the rotating tappet rotates at a relatively low speed, the torque ripple causes vibration and noise in the rotating tappet rotating. As a result, accurate dead time compensation of the inverter must be performed in order to reduce the vibration and noise of the washing machine and realize stable operation of the washing machine.

A motor control apparatus according to the present invention comprises: an inverter for generating a phase current to supply to a 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 determines 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 above-described estimated current is a current when modeling a motor and inputting a command voltage to the modeled motor.

A 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; The polarity of the compensation voltage is determined according to the estimated polarity of the estimated current based on the modeling of the motor when the magnitude of the phase current is within the preset reference range.

The above-described estimated current 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. FIG. 1 is a block diagram of a BLDC motor control apparatus according to an embodiment of the present invention. 1, the converter 104, the DC-link capacitor 108, and the inverter 106 constitute a power conversion apparatus. The converter 104 converts the AC power supplied from the AC power supply 102 to DC. The inverter 106 converts the DC power to three-phase alternating current power (U, V, W) and supplies it to the BLDC motor 110.

Information about 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 control unit 114. The control unit 114 refers to the information on the current ia (ib) (ic) of each phase of the three-phase AC power and the position / speed information F / G of the rotor of the BLDC motor 110, The inverter control signal S for controlling the rotational speed of the inverter 110 is generated. The inverter control signal S generated by the control unit 114 controls the switching point and amount of each phase of the three-phase AC power A (B) (C) output from the inverter 106 to the BLDC motor 110 And its purpose is to allow the rotational speed of the BLDC motor 110 to follow a 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 / indicates the invert of the phase.

2 is a view showing an inverter of the BLDC motor control apparatus shown in Fig. As shown in FIG. 2, the inverter 106 switches six transistors of power supplied to the BLDC motor 110 by switching six switching elements, that is, transistors Q1 to Q6, respectively, by an inverter control signal S Three transistors Q1, Q3 and Q5 located at the upper side among the transistors Q1 to Q6 are switched by the inverter control signals of Sa, Sb and Sc respectively and three transistors Q2 and Q4 located at the lower side are switched, (Q6) are switched by inverter control signals of / Sa, / Sb and / Sc, respectively. As a result, the upper three transistors Q1, Q3, and Q5 and the three lower transistors Q2, Q4, and Q6 have opposite switching states (on / off). Diodes D1, D2, D3, D4, D5 and D6 connected in parallel to the respective transistors Q1, Q2, Q3, Q4, Q5 and Q6 are connected to a freewheeling diode Free Wheel Diode.

FIG. 3 is a graph showing voltage distortion of the inverter according to the polarity of the phase current. The signals shown in FIG. 3 represent the case of "A", which is one of the three-phase powers, and the other cases of "B" and "C" are controlled in the same manner. 3, the switching signal Sa and the switching signal / Sa having phases opposite to each other are generated on the basis of the command voltage VaN * generated in the control unit 114. [ A dead time tdead is provided in the front portion of the switching signal Sa and a rear portion of the switching signal Sa to generate a section in which the switching signal Sa and the switching signal / Do not. If a period in which the two switching signals Sa and the switching signal / Sa overlap occurs, the transistor Q1 and the transistor Q4 of the inverter 106 shown in FIG. 2 are simultaneously turned on and the current flows to the ground The normal switching operation of the inverter 106 can not be performed. The dead time (tdead) is to prevent this.

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

In this way, an error occurs between the command voltage VaN * and the actual output voltage VaN + (VaN-) due to the dead time tdead. Particularly when the polarity of the current is positive, the output voltage VaN + And the output voltage VaN- when the polarity of the current is negative (-). Therefore, this error can be compensated to prevent the distortion of the output voltage of the inverter 106 due to the dead time. However, in order to accurately compensate the output voltage distortion of the inverter 106 due to the dead time, it is necessary to accurately detect the polarity and polarity switching point of the phase current, that is, the zero crossing point, .

If the polarity of the phase current and the zero crossing point are not accurately detected, a compensating voltage of an inappropriate size is generated, and the compensation result using this is unreliable. Fig. 4 is a diagram showing the inaccurate compensation of the output voltage of the inverter and distortion of the phase current accordingly. Fig. As shown in FIG. 4, in detecting the zero crossing point in the low current section near 0A, an error occurs due to noise, a filter or the like between the actual current 402 and the measuring current 404, It can be seen that the inaccurate zero crossing point detection is performed and the value of the polarity discrimination signal 406 (+) (406 (-)) is also significantly different from the actual zero crossing point.

5 is a diagram illustrating a compensation voltage generator according to an 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 preferable to arrange such a compensation voltage generating unit 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 shown in FIG. 5, the compensation voltage generator according to an embodiment of the present invention includes a current polarity determination unit 502 for determining the polarity of the phase current ias and generating a polarity determination signal 504. The polarity determination 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 compensated voltage Vdis whose polarity is determined in this manner is added to the command voltage Vas of A to become the final command voltage Vasdis.

6 is a view showing the current polarity determination unit shown in Fig. 6, the current polarity determination unit 502 according to an exemplary embodiment of the present invention uses a zero crossing detection unit 602 to calculate a zero crossing point (ies) And a polarity discriminating signal 504 is generated. One of the two phase currents ias is an estimated current iase obtained through modeling of the BLDC motor 110 with the command voltage Vas as an input and the other is an actual phase current ias . The zero crossing detection unit 602 discriminates 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. On the other hand, if the magnitude of the phase current ias is smaller than the predetermined If it is 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 because the magnitude of the phase current ias in the low current section is too small to accurately detect the zero crossing point so that the polarity of the phase current ias can be determined more accurately through the polarity discrimination using the estimated current iase .

6, the modeling of the BLDC motor 110 causes the inductance component (L) 602 and the resistance component (R) 604 to form an open loop. If open-loop configuration is used, zero delay does not occur and accurate zero-crossing point detection is possible.

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

In the above equation, ω can be ignored because it is close to zero in the low current section. In the above equation, the remaining terms excluding the term including ω are subjected to a Laplace Transform.

To summarize,

7 is a diagram 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 to generate the compensation voltage Vasdis. If the magnitude of the phase current ias is within the reference range (example 704), an estimated current iase through modeling of the BLDC motor 110 for a more accurate zero crossing point and polarity detection of current is generated 706 ) Detects the zero crossing point and polarity of the estimated current (iase) (708). Conversely, if the phase current ias exceeds the reference range (NO in 704), the zero crossing point and polarity of the phase current ias is detected (710). Thus, when the zero crossing point and the polarity of the current are detected, the polarity of the compensation voltage Vdis is determined based on the current polarity (712). That is, the polarity of the compensation voltage Vdis is determined to be negative when the current polarity is negative, and the polarity of the compensation voltage Vdis is determined to be positive when the current polarity is positive. When the polarity of the compensation voltage Vdis is determined, the compensation voltage Vdis is reflected in the command voltage Vas to perform voltage compensation (714).

FIG. 8 is a diagram illustrating a phase current and a phase current polarity discrimination state in the case where a voltage distortion of an inverter is compensated by applying a voltage distortion correcting apparatus and method according to an embodiment of the present invention. 8, in detecting the zero crossing point in the low current section in the vicinity of 0A, since there is almost no error between the actual current 802 and the measuring current 804, accurate zero crossing point detection is performed and the polarity determination signal 806 (+)) (806 (-)) also have accurate values.

1 is a block diagram of 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.

Fig. 3 is a diagram showing voltage distortion of the inverter by the polarity of the phase current. Fig.

4 is a diagram showing an inaccurate compensation of an output voltage of an inverter and thus distortion of a phase current.

5 illustrates a compensation voltage generator according to an embodiment of the present invention.

6 is a view showing the current polarity determination unit shown in Fig.

FIG. 7 illustrates a voltage distortion correction method of an inverter according to an embodiment of the present invention. FIG.

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

Description of the Related Art [0002]

102: AC power source

104: Converter

106: inverter

108: DC-link capacitor

110: BLDC motor

114:

502:

602: Zero crossing detection section

Claims (5)

An inverter for generating a phase current and supplying it to the motor; And a compensation voltage generating unit 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 polarity of the compensation voltage is determined according to the polarity of the estimated current. delete The method according to claim 1, Wherein the estimated current is a current when modeling the motor and inputting a command voltage to the modeled motor. Detecting a phase current; Determining whether the magnitude of the phase current is within a preset reference range; Wherein the polarity of the compensation voltage is determined 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 predetermined reference range. 5. The method of claim 4, Wherein the estimated current is a current when modeling the motor and inputting a command voltage to the modeled motor.

Images