KR20040008005A - Control system and method based on neutral voltage compensation of brushless dc motor - Google Patents

Abstract

PURPOSE: A neutral voltage compensation-based BLDC motor control system and a controlling method thereof are provided to control correctly the rotation of the BLDC motor by estimating accurately a position of a rotor and compensating a neutral point voltage on the basis of the position of the rotor. CONSTITUTION: A neutral voltage compensation-based BLDC motor control system includes a plurality of switches(Q1-Q6), a position estimation information generator(500), and a controller(600). The switches(Q1-Q6) are used for switching the current applied to the BLDC motor. The position estimation information generator(500) is used for generating the position estimation information to compensate a position of a rotor on the basis of output signals of the switches(Q1-Q6) and an output signal of the rotor of the BLDC motor. The controller(600) is used for controlling operations of the switches(Q1-Q6).

Description

CONTROL SYSTEM AND METHOD BASED ON NEUTRAL VOLTAGE COMPENSATION OF BRUSHLESS DC MOTOR}

The present invention relates to a control system and a method of a BC motor based on the neutral point voltage compensation, in particular by using the neutral voltage generated by the rotation of the BC motor to estimate the position of the rotor and compensate for the estimation error The present invention relates to a control system and a method of controlling a BC motor.

In general, a brushless DC motor (BLDC) removes mechanical contacts such as a brush and a commutator from a DC motor, and instead installs an electronic commutator. Refers to a DC motor. The stator of the BCD motor uses an armature that forms a current through a coil, and the rotor uses a permanent magnet formed by repeating the N pole and the S pole. As is well known, in order for the BCD motor to rotate continuously, a continuous rotating magnetic field must be formed in the BCD motor. In order to form a continuous rotating magnetic field, the commutation (or current) of the current flowing in the coil of each armature of the armature must be performed at an appropriate time. For proper commutation, the position of the rotor must be recognized. . Here, the commutation means to change the current direction of the motor stator coil so that the rotor can rotate. Usually, a Hall sensor or a resolver element is used as a device for recognizing the position of the rotor. The advantages of BCD motors are that they do not require worn brush exchanges, have less noise from EMI, and the heat transfer characteristics are improved, resulting in greater power than other motors of the same size.

In general, a control system for controlling such a BC motor includes a converter, an inverter, a BC motor, and a controller. In more detail, when the converter converts the AC power supplied from the power supply device into DC power and transfers it to the inverter, the inverter receives DC power from the converter and switches according to a switching operation signal from the controller. The BLC motor rotates the rotor by the switching operation of the inverter, and the controller receives the signals detected from various sensors for detecting the position and speed of the rotor and performs commutation at an appropriate time to control the switching cycle of the inverter. do. The controller performs drive control to rotate the rotor by applying a three-phase current to the stator of the BCD motor. The controller supplies a three-phase voltage to the BCD motor and controls the voltage and current using the switching elements of the inverter. At this time, the proper torque of the inverter must be switched according to the exact position of the rotor permanent magnet so that the torque generated by the BCD motor has a uniform value. The BCD motor needs the position information of the rotor to supply the proper current in synchronization with the position of the rotor instead of the mechanical brush and commutator. The position sensor of the rotor causes various problems such as price increase of BCD motor, increase of volume, decrease of reliability and limitation of use environment. Therefore, studies to drive BCD motors without a position sensor have been steadily progressed to overcome this problem. At this time, when the rotation position of the rotor is not known accurately, torque ripple occurs, which has a problem of generating vibration and noise of the BCD motor.

As a method used to reduce such torque ripple, there is a terminal voltage processing method of a BC motor based on the fact that some information of back EMF can be obtained from the terminal voltage applied to the BC motor. The terminal voltage processing method passes a terminal voltage of a BCD motor through a phase shifter (for example, a low pass filter) to produce a signal having a 90 degree phase difference, and zero-crossing a signal having a 90 degree phase difference. By considering the signal logic relationship with respect to the signal, the phase position of the 120 degree flat-top portion with respect to the counter electromotive force of each phase (a, b, c phase) of the BCD motor can be known. . The controller switches the switch of the inverter so that current flows in each phase of the BCD motor by matching the phase to the flat-top portion described above.

However, if the speed of the BCD motor is variable, the frequency of the terminal voltage of the BCD motor is changed, which causes the phase shifter to make a phase difference of exactly 90 degrees. That is, when a terminal voltage signal having a wide band frequency passes through the phase shifter, a signal having a phase difference of exactly 90 degrees is not produced, and a phase error with respect to the rotor position of the BC motor occurs. FIG. 1 is a graph showing a torque ripple generation relationship appearing in a BCD motor with time when a conventional phase error occurs. When a phase error occurs for a rotor of a BCD motor, as shown in FIG. Back EMF of each phase of DC motor ( ) And phase current ( ), The phase error occurs, and the torque ripple component is included in the torque generated by the BCD motor due to the phase error. As a result, the rotation of the BCD motor cannot be accurately controlled.

In order to solve this problem, the technical problem of the present invention is to accurately estimate the rotor position irrespective of the speed change of the BCD motor and to compensate for the neutral point voltage of the BCD motor based on the BCD motor. The present invention provides a system and method capable of precisely controlling rotation.

Another object of the present invention is to provide a BLC motor control system that can be implemented without using a position sensing element, reducing the manufacturing cost, simplifying the driving circuit, and does not break even when used for a long time.

1 is a graph showing a torque ripple occurrence relationship shown in a BCD motor with time when a conventional phase error occurs.

2 is a block diagram showing a BCD motor control system according to an embodiment of the present invention.

3 is a block diagram illustrating a position estimator in more detail according to an embodiment of the present invention.

4 is a graph showing the phase angle between the counter electromotive force and the current waveform of the BCD motor.

5 is a graph showing a neutral voltage waveform generated by a difference in phase angles.

6 is a graph showing the neutral point voltage measured in the BCD motor and the neutral point voltage waveform estimated by the embodiment of the present invention.

7 is a graph illustrating a neutral point voltage compensation result according to a compensation of a position estimation error.

8 is a graph illustrating a phase relationship between a counter electromotive force and a current after the position estimation error is compensated according to an embodiment of the present invention, and a neutral point voltage according thereto.

<Description of Symbols for Major Parts of Drawings>

100: power supply

200: inverter

300: BLC motor

400: terminal voltage detector

500: location estimation unit

600: current controller

In order to achieve the above object, a control system using a neutral point voltage of a BLC motor according to an aspect of the present invention includes a plurality of switches for switching a current applied to each of a plurality of coils constituting an armature of the BLC motor. Switching means including a switch; Obtaining the first position signal of the rotor based on the output value of the switching means, that is, the motor terminal voltage, and compensating the neutral point voltage estimated by using the counter electromotive force and inverter DC current supplied to the BCD motor Position estimating means for estimating a position of the rotor by obtaining a second position signal of; And control means for controlling opening and closing of the switches of the switching means, based on the output of the position estimating means, so that the BCD motor can rotate.

The BCD motor control method according to another aspect of the present invention is a BLC motor control method for use in a BLC motor control system having a plurality of switches for switching a current applied to a BLC motor. Generating a position estimation signal to compensate for the position of the rotor using the terminal voltage of the DC motor and the outputs from the plurality of switches; And controlling switching of a current applied to the BC motor based on the position estimation signal of the rotor.

DETAILED DESCRIPTION Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

2 is a block diagram illustrating a control system of a BCD motor according to an embodiment of the present invention. As shown in FIG. 2, the BCD motor control system based on the neutral point voltage compensation according to an embodiment of the present invention includes a power supply unit 100, an inverter 200, a BCD motor 300, and a terminal voltage detector. 400, the position estimator 500, and the current controller 600.

The power supply unit 100 converts AC power input from commercial power into DC power Vd and supplies the same to the inverter 200. For convenience of explanation, it has been described that the conversion from the AC power source to the DC power source Vd is performed by the power supply unit 100, but is actually performed by a converter (not shown) connected to the power supply unit 100. Inverter 200 receives a DC power supply (Vd) required for operation from the converter to switch the switch (Q1 ~ Q6) by a drive signal from the current control unit 600 to convert to three-phase AC power. The inverter 200 further includes a single DC current sensor 210 for sensing current flowing in each phase. Since the switching order of the inverter 200 is the same as that of a general three-phase inverter, a description of the switching order thereof will be omitted herein. In the exemplary embodiment of the present invention, the switches Q1 to Q6 have been described using bipolar transistors as examples, but other switching elements for performing a switching operation may be used. The BCD motor 300 is a phase current flowing into each phase (a phase, b phase, c phase) by the switching operation of the inverter 200 ( Rotate the rotor (not shown). In general, the BCD motor 300 has a neutral point n formed by a three-phase coil having a winding resistance R and an inductance L, and a description of the structure of a general BCD motor 300 will be omitted. . The terminal voltage detector 400 is connected to a lead wire connected between the inverter 200 and the BC motor 300 to measure the voltage at this point. The terminal voltage detector 400 generally includes a three-phase resistance divider circuit, and a description of general terminal voltage detection will be omitted below.

The position estimator 500 obtains a rough position signal of the rotor based on the terminal voltages Va, Vb, and Vc measured by the terminal voltage detector 400, and the intermediate point o of the power supply unit 100. And obtain a rotor position signal based on the neutral point voltage Vno which appears according to the operation of the inverter 200 between the neutral point n of the BCD motor 300 and the final rotor position estimation signal θ. Get The method for obtaining the position signal of the rough rotor is an open loop rotor position estimation method, and the method for obtaining the rotor position signal based on the neutral point voltage Vno is a closed loop. Rotor position estimation method. The position estimator 500 may add these two signals to complementarily function to obtain a final precise position estimation signal θ.

3 is a block diagram illustrating the position estimator 500 of FIG. 2 in more detail. The position estimator 500 according to an embodiment of the present invention is a low pass filter unit. 510, a zero-crossing position detector 520, a neutral voltage estimator 530, a first adder 540, a PI controller 550, and a second adder 560. .

The low pass filter 510 receives the three-phase terminal voltages Va, Vb, and Vc measured from the terminal voltage detector 400 and filters the terminal voltages V'a, V'b, and V 'having a phase difference of 90 degrees. c) convert to a signal. The zero crossing position detector 520 receives a terminal voltage V'a, V'b, V'c having a phase difference of 90 degrees made from the low pass filter 510, and passes the zero voltage signal waveform through zero. Is detected and the position is generated as the first rotor position value θ ₁ . The neutral point voltage estimator 530 rotates the DC current (| id |) obtained by rectifying the DC terminal current waveform measured by the DC current sensor 210 by the rectifier 700 and the BCD motor 300. The magnitude E of the back EMF of each phase determined according to the speed is received to generate an estimated neutral point voltage Vnop. The first adder 540 receives the neutral point voltage Vnop estimated from the neutral point voltage estimator 530 and compensates for the difference of the phase angles to be zero, and the neutral point voltage reference value Vno = 0. The estimated neutral point voltage Vnop is added. In other words, the preset neutral point voltage reference value (Vno = 0) is a value for compensating that the neutral point voltage does not occur in the normal operation section of the inverter 200 over the entire speed range of the BCD motor 300. The PI (Proportional and Integral) control unit 550 receives the neutral point voltage error signal added from the first adder 540 and performs proportional integration control. The second adder 560 is configured to compensate the first rotor position value θ ₁ detected by the zero crossing position detector 520 and the estimated neutral point voltage Vnop, and the second rotor position value θ. _{After 2} ) is added, the position estimation signal θ is finally generated and transmitted to the current controller 600.

The current controller 600 receives a direct current (| id |) from the rectifier 700 that converts the current detected by the direct current sensor 210 into a positive value, and the rotor estimated from the position estimator 500. Receiving a position estimation signal θ and generating a pulse width modulated gate driving signal for driving each of the switches S1 to S6 of the inverter 200, thereby switching the switching timing to the generated gate driving signal. By adjusting, the switches S1 to S6 of the inverter 200 are driven.

Hereinafter, the operation of the BCD motor control system based on the neutral point voltage compensation according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

The low pass filter 510 of the position estimator 500 receives and filters the terminal voltages Va, Vb, and Vc of each phase of the BCD motor 300, and outputs a terminal voltage signal V having a phase difference of 90 degrees. 'a, V'b and V'c are outputted to the zero crossing position detector 520. The zero crossing position detector 520 is a first rotor of the BC motor 300 from the terminal voltages V'a, V'b, and V'c having a phase difference of 90 degrees received from the low pass filter 510. The position value θ ₁ is generated.

On the other hand, the neutral point voltage estimator 530 zeros the counter electromotive force E generated by the DC current (| id |) detected from the DC current sensor 210 and the rotational speed of the rotor of the BC motor 300. The neutral point voltage is received from the crossing position detector 520. Hereinafter, the principle for generating the estimated neutral point voltage Vnop will be described.

FIG. 4 is a graph showing the phase angle between the counter electromotive force and the current waveform of the BCD motor. As shown in FIG. 4, the counter electromotive force of each phase induced by the rotation of the rotor ( The waveform of) has a trapezoid of 120 degree flat-top shape. In Fig. 4, the counter electromotive force of each phase induced by the rotation of the rotor ( Is the flat-top waveform portion E of the counter electromotive force through the inverter 200 and the current of each phase (120 degrees square wave current) ) Are supplied to match each other so that torque generated in the BCD motor 300 becomes a uniform value without ripple. At this time, when the phase current difference α is smaller than zero (0) when the current of each phase, which is a 120-degree square wave current, flows ahead of the flat-top waveform portion E of the counter electromotive force of each phase, This is called the leading α. Back EMF of each phase Current in each phase that is 120 degrees square wave current than the flat-top waveform portion (E) of ) Is a case where the phase angle difference α is larger than zero (0), and the phase angle difference at this time is called lagging α. As shown in Fig. 4, the counter electromotive force of each phase ( ) And accurately estimate the phase current ( Phase of the back EMF ( Torque ripple does not occur in the BCD motor 300 to be matched with the phase of).

FIG. 5 is a graph showing a neutral voltage waveform generated by a difference in phase angles. FIG. 5A illustrates a phase angle difference of zero in FIG. 4 and a phase angle difference of FIG. 5B. 5 (c) shows the neutral point voltage waveform of the BCD motor 300 for each of the phase angle differences in the ground. In FIG. 5 (a), since the terminal voltage when the phase angle difference is zero is generated once in each commutation section at 60 degree intervals, the six commutation section neutral point voltage pulses at 360 degrees in which the BC motor 300 rotates once Occurs. If the phase angle difference of FIG. 5 (b) is true, a new neutral point voltage component is additionally shown in the normal operation section of the inverter 200 immediately after the commutation period neutral point pulse as shown in FIG. 5 (a). When the phase angle difference of 5 (c) is the ground, it can be seen that a new neutral point voltage component is additionally displayed in the normal operation section of the inverter 200 immediately before the commutation period neutral voltage pulse as shown in FIG. 5 (a). . Thus, comparing the case where the phase angle difference does not occur with the case where the phase angle difference is true and ground, it can be seen that the neutral point voltage component in the normal operation section of the inverter 200 occurs when the phase angles do not coincide with each other. Can be. In three cases, the section in which the neutral point voltage having the same pulse type appears is a section in which the inverter 200 operates in a commutation mode.

In order to explain the calculation of the neutral point voltage, the normal mode section in which the switches Q1 and Q6 of FIG. 3 perform the pulse width modulation PWM operation is considered. The above-described normal operation section refers to a section in which no commutation occurs, that is, a section in which only two arbitrary switches of the inverter 200 operate. For example, a description will be given of the operation of the normal operation mode in which the current flows to the b phase when the switch Q1 and the Q6 of the inverter 200 are in an on state, that is, through the BC motor 300 on a. . In contrast, the commutation mode section refers to a transition section in which three arbitrary switches operate simultaneously to change the flow of current.

The neutral point voltage Vno generated in the normal operation section of the inverter 200, for example, the normal operation section in which current flows from the a phase to the b phase, is calculated as in Equation 1 below.

= counter electromotive force on a, : back electromotive force on b.

The above Equation 1 is not suitable for use because it is difficult to accurately determine the counter electromotive force, so a neutral point voltage estimation equation that can be easily calculated is required. In order to estimate the neutral point voltage that may appear in the normal operation period of the inverter, the neutral point voltage estimator 530 calculates an estimated neutral point voltage Vnop from the following equation.

(S: switching function of the inverter (1 or -1), R: winding resistance of the motor, L: winding inductance of the motor, E: magnitude of counter electromotive force on the motor, Vd: DC input voltage, id: DC current).

In Equation 2, the DC input voltage (Vd) is a constant voltage source, the winding resistance (R) and inductance (L) of the BCD motor 300 is a predetermined value, the switching function (S) is the inverter 200 In the case of 1 (the switch is turned on) according to the operating characteristic of the above), the necessary information for calculating the estimated value of the neutral point voltage according to Equation 2 described above includes the direct current (| id |) and the BC motor (300). Only the value E of the back EMF is determined by the rotational speed of. Therefore, the neutral point voltage estimator 530 may calculate the estimated neutral point voltage Vnop from the DC current | id | detected from the DC current sensor 510 and the counter electromotive force magnitude E of each phase. The switching function S is a function value according to the states of the switches Q1 to Q6, and the value of the switching function S is 1 in which the switches Q1 to Q6 of the inverter 200 are turned on. When the switching function (S) is -1, the switch means that the switch of the inverter 200 is turned off. The definition of the switching function S is not limited to the embodiment of the present invention. FIG. 6 is a graph showing a neutral point voltage measured by a BCD motor and a neutral point voltage waveform estimated by an embodiment of the present invention. FIG. 6A illustrates a BDC motor 300 driven by an inverter 200. Referring to FIG. FIG. 6B illustrates the neutral point voltage waveform calculated by Equation 2, which is an estimation equation in the normal operation of the inverter 200. Referring to FIG.

The first adder 540 receives the estimated neutral point voltage Vnop from the neutral point voltage estimator 530 and estimates the neutral point voltage reference value Vno = 0 so that the difference in phase angle becomes zero. The neutral point voltage Vnop is added. The neutral point voltage reference value Vno = 0 may be supplied through any compensation value providing means included in the position estimator 500 or may be a compensation value supplied from an external device (not shown) such as a microcomputer. The present invention is not limited only to the examples. The PI controller 550 receives an error signal value between the estimated neutral point voltage Vnop and the neutral point voltage reference value (Vno = 0) added from the first adder 540 to perform a proportional integral control to perform a second integral control. The rotor position value θ ₂ is generated The second adder 560 is the first rotor position value θ ₁ generated by the zero crossing position detector 520 and the first generated by the PI controller 550. After adding the two rotor position values θ ₂ , a final rotor position estimation signal θ is generated, and the generated position estimation signal θ is transmitted to the current control unit 600. Current control unit 600 ) Receives a position estimation signal (θ) that is an output value of the position estimator 500, and performs timing control on the switches Q1 to Q6 of the inverter 200.

7 is a graph illustrating a neutral point voltage estimation result according to compensation of a position estimation error. FIG. 7A is a graph showing the rotor position estimate of the BCD motor 300 over time. When the rotor position estimation error is greater than zero, the ground and the position estimation error are zero. The smaller (-) case indicates the truth. FIG. 7A illustrates a case where the initial position estimation error is 20 degrees of phase difference, and the position estimation error is reduced while finally performing the position estimation and the compensation of the neutral point voltage according to an embodiment of the present invention. It indicates that the position estimation error is zero. 7B illustrates a phenomenon in which the neutral point voltage component generated in the normal operation section of the inverter 200 estimated by Equation 2 is compensated and removed by the position estimator 500.

8 is a graph illustrating a phase relationship between a counter electromotive force and a current and a neutral point voltage according to the current after compensating for a position estimation error, according to an exemplary embodiment of the present invention. ) And back EMF on a ) Has a ground phase difference, so a position estimation error occurs. 8B illustrates the timing of the switches Q1 to Q6 of the inverter 200 by the current controller 600 based on the compensated position estimation result after the position estimator 500 compensates for the position estimation error. The phase relationship between the counter electromotive force and the current after the control and the neutral point voltage according thereto are shown.

The embodiments of the present invention described above are not limited to the one embodiment only, and are not limited by the above-described contents and the accompanying drawings, and various substitutions, modifications, and changes without departing from the spirit and scope of the present invention. Of course, change is possible.

As described above, the BCD motor control system and its method based on the neutral point voltage compensation of the present invention accurately estimate the rotor position using the neutral point voltage of the BLC motor regardless of the speed change of the BLC motor. The rotation of the BCD motor can be controlled. In addition, the present invention can reduce the position estimation error by extracting the position information of the rotor more stable and precise over the entire speed range of the BCD motor compared to the conventional BCD motor control method. In addition, the present invention can estimate the position of the rotor using the terminal voltage without a position detection sensor such as a Hall sensor that recognizes the position of the rotor of the BCD motor, it is possible to reduce the weight and volume of the BCD motor In addition, the power density can be improved, and the manufacturing cost competitiveness of the system can be enhanced. As such, the present invention provides a simple and reliable system by implementing the control of the BCD motor using the terminal voltage without additional sensors or additional devices, and for miniaturization and precision of home appliances, robots, industrial equipment, etc. Can be used.

Claims (7)

In the control system of the BCD motor, A plurality of switches for switching a current applied to the BC motor; Means for generating position estimation information for compensating the position of the rotor based on output signals from the plurality of switches and output signals from the rotor of the BC motor; And Control means for controlling the operation of the plurality of switches based on the position estimation information BCD motor control system comprising a. The method of claim 1, wherein the position estimation information generating means A filter unit for filtering terminal voltages output from the plurality of switches to terminal voltages having a phase difference of a first angle; A rotor position detector for detecting first position information of the rotor from a terminal voltage having a phase difference of the first angle; A neutral point voltage estimator for estimating a neutral point voltage based on a direct current output from the plurality of switches and a counter electromotive force from the rotor; A neutral point voltage compensator for generating second position information of the rotor by compensating the neutral point voltage of each phase by using the estimated neutral point voltage and a predetermined neutral point voltage reference value; And An adder configured to generate position estimate information of the rotor by adding the first position information and the second position information; BCD motor control system comprising a. The method of claim 2, wherein the neutral voltage compensator An adder for adding the estimated neutral point voltage and the neutral point voltage reference value; And And a proportional integral controller configured to generate the second position information by proportionally integral controlling the output of the adder. The neutral point voltage estimator of claim 2, wherein the neutral point voltage estimator (S: switching function of the switching means, R: winding resistance of the BCD motor, L: winding inductance of the BCD motor, E: magnitude of counter electromotive force on each BLC motor, Vd: supplied to the switching means) And the estimated neutral point voltage (Vnop) is calculated using a formula of DC input voltage, id: DC current supplied to the switching means. In the BCD motor control method for use in a BCD motor control system having a plurality of switches for switching the current applied to the BCD motor, Generating a position estimation signal for compensating the position of the rotor using the terminal voltage of the BC motor and the outputs from the plurality of switches; And Controlling switching of a current applied to the BC motor based on the position estimation signal of the rotor. BCD motor control method comprising a. The method of claim 5, wherein the generating of the position estimation signal Filtering terminal voltages output from the plurality of switches to terminal voltages having a phase difference of a first angle; Detecting first position information of the rotor from a terminal voltage having a phase difference of the first angle; Estimating a neutral point voltage based on a direct current output from the plurality of switches and a counter electromotive force from the rotor; Generating second position information of the rotor by compensating the neutral point voltage of each phase by using the estimated neutral point voltage and a predetermined neutral point voltage reference value; And Generating location estimation information of the rotor by adding the first location information and the second location information; BCD motor control method comprising a. The method of claim 5, wherein the generating of the position estimation signal (S: switching function of the switching means, R: winding resistance of the BCD motor, L: winding inductance of the BCD motor, E: magnitude of counter electromotive force on each BLC motor, Vd: supplied to the switching means) And the estimated neutral point voltage (Vnop) is calculated using a formula of DC input voltage, id: DC current supplied to the switching means.