KR101000121B1 - A pwm method for controlling bldc motors and a system thereof - Google Patents

Abstract

The present invention relates to a PWM switching method for controlling a BLDC motor and a system device therefor. The present invention is to simultaneously control the on / off of the four switching elements of the switching elements provided in the PWM inverter for controlling the three-phase BLDC motor, and among the switching elements corresponding to each other to control the opposite switching state. In particular, the switching element is controlled according to whether the phase current direction and the voltage direction of the BLDC motor match, and on / off of the PWM signal. That is, when the voltage and current are the same direction, 'Vs' is applied to the BLDC motor when the PWM is on, and when the PWM is off, a current loop is formed inside the PWM inverter to apply the voltage of '0'. In addition, the direction of voltage and current is different and '-Vs' is applied when PWM is on, and when the PWM is off, a current loop is formed inside the PWM inverter so that a voltage of '0' is applied. According to the present invention as described above, '-Vs' is not applied to the BLDC motor in the PWM off period, thereby reducing the current ripple, thus reducing the vibration and noise of the BLDC motor.

BLDC, Current Ripple, Pulse Width Modulation, PWM Inverter, Switching Device

Description

PCB switching method for controlling DC motor and system device for it {A PWM METHOD FOR CONTROLLING BLDC MOTORS AND A SYSTEM THEREOF}

The present invention relates to the control of the BLDC motor, and more particularly, when the voltage and current direction are different when the BLDC motor is driven, '0' (Zero) voltage is applied to the BLDC motor by changing the switching state in the PWM OFF section. The present invention relates to a PWM switching method for controlling a BLDC motor and a system device therefor.

Recently, the use of brushless DC (BLDC) motors, which are advantageous for miniaturization of motors, has become popular. This requires the precise and miniaturized electric motor due to the development of the robot industry, and this is in accordance with the tendency to miniaturize the motor and driver.

Unlike the DC motor, the BLDC motor does not need to be repaired due to brush wear, unlike a DC motor, and is supplied in proportion to the current in the same manner as a DC motor when an ideal square wave current flows to the stator winding in synchronism with the position of the rotor. To generate a constant torque. Thus, the BLDC motor has been increasingly used in the robot industry requiring a small motor or driver.

The BLDC motor is controlled by a pulse width modulation (PWM) technique to date, and in particular, is controlled by a bipolar PWM scheme or a unipolar PWM scheme using the PWM technique.

However, the prior art of controlling the BLDC motor has the following problems.

That is, the bipolar PWM method and the unipolar PWM method cause the opposite directions of voltage and current due to the inductance component of the motor. At this time, the motor cannot be controlled at the moment the current direction is changed. do.

More specifically, the bipolar PWM method and the unipolar PWM method will be described.

Here, the BLDC motor in the prior art and the embodiment of the present invention will be described as an example of a three-phase BLDC motor that is generally used.

In addition, the characteristics of the bipolar PWM method and the unipolar PWM method used for driving control of the three-phase BLDC motor will be described with reference to FIGS. 1 and 2.

FIG. 1 shows a bipolar PWM method for controlling a general three-phase BLDC motor, and the phase current and counter electromotive force of the BLDC motor.

Referring to FIG. 1, the bipolar PWM method is a mode of turning off a switch when off. Therefore, the power loss of the switching element is large.

Here, in the bipolar PWM scheme, a '-Vs' voltage is applied depending on the direction of the voltage and current and the PWM state, which causes current ripple.

This is shown in the following [Table 1].

When the direction of voltage and current is the same When the direction of voltage and current is different PWM status PWM ON PWM OFF PWM ON PWM OFF Applied voltage Vs -Vs -Vs -Vs

That is, the bipolar PWM method causes the current ripple and control performance because the '-Vs' voltage is applied to the motor when the direction of voltage and current is different, when PWM is ON or OFF. Will be degraded.

Next, FIG. 2 shows a unipolar PWM method for controlling a general three-phase BLDC motor and the phase current and counter electromotive force of the BLDC motor accordingly.

Referring to FIG. 2, the unipolar PWM method is a method in which only a switching element in front of the motor is turned off and a switching element in the rear of the motor is always on when the OFF. For example, when the current is to flow from the A phase to the C phase, it can be seen that the switching element Q1 is turned on / off and the switching element Q6 is always on during the period.

Similarly to the bipolar PWM method, the unipolar PWM method has a difference in voltage applied to the motor depending on the direction of the voltage and current and the PWM state.

This is shown in the following [Table 2].

When the direction of voltage and current is the same When the direction of voltage and current is different PWM status PWM ON PWM OFF PWM ON PWM OFF Applied voltage Vs 0 -Vs -Vs

In other words, in the unipolar PWM method, when the direction of voltage and current is different, the voltage of '-Vs' is applied to the BLDC motor regardless of whether the PWM is on or off. This also causes current ripple and degrades control performance.

In other words, the BLDC motor is designed to be controlled under the assumption that the voltage is '0' at the time of PWM OFF. When the '-Vs' voltage is applied, it causes the current ripple. Considering this, even if the voltage is applied during PWM ON, it is higher than the required voltage in the motor control process and '-Vs' is applied again when it is OFF, so the current ripple cause cannot be solved. .

As such, when the current ripple occurs when the BLDC motor is driven, it causes vibration and noise when the motor rotates, thereby significantly reducing the control performance.

As a result, the BLDC motor has a limitation in applying to a high performance control such as an intelligent robot, despite the advantages of the BLDC motor, that is, its volume-to-torque characteristics are good, and its high efficiency, long operating life, low noise, and fast operation speed. It was.

Accordingly, an object of the present invention is to solve the above problems, a PWM switching method and a system for controlling a BLDC motor to reduce the current pulsation in the phase current switching period and the PWM switching when the motor is driven. It is to provide a device.

Another object of the present invention is to control the voltage applied to the motor by controlling the state of the switching element in the PWM off section when the motor is driven.

According to a feature of the present invention for achieving the above object, a BLDC electric motor; First to sixth switching elements are provided to supply three-phase power to the BLDC motor through a PWM signal, wherein the two switching elements are connected in series to form a pair, and these pairs are three pairs, each pair connected in parallel with each other. PWM inverter; A current direction detector for detecting a current direction flowing to the BLDC motor; When the BLDC motor is driven by a pulse width modulation (PWM) method, if the current direction detected by the current direction detection unit and the voltage direction supplied to the PWM inverter in the PWM off section are different, And a controller configured to select four switching elements associated with the current direction and the current loop from among the first to sixth switching elements so as to form a current loop according to the current direction.

When a current loop is formed in the PWM inverter, the voltage applied to the BLDC motor is 'zero'.

According to another feature of the present invention, two switching elements are connected in series to form a pair, and these pairs are three pairs, and each pair is BLDC through the switching operation of the first to sixth switching elements provided in the PWM inverter connected in parallel with each other. Supplying three-phase power to the motor to drive the BLDC motor; Detecting whether a current transient occurs in the driving BLDC motor; If a current transient occurs and the current direction flowing to the BLDC motor is different from the voltage direction supplied to the PWM inverter, the current loop is formed in the PWM inverter according to the current direction during the PWM off period. And driving on / off four of the first to sixth switching elements associated with the current direction and the current loop.

When the current loop is formed, a zero voltage is applied to the BLDC motor.

In the controlling step, even though the voltage and current directions are the same due to the non-occurrence of the transient state of the current during the PWM off period, a current loop is formed inside the PWM inverter, so that the zero voltage is zero to the BLDC motor. Allow voltage to be applied.

In the PWM switching method and system apparatus for controlling the BLDC motor according to the present invention configured as described above can obtain the following effects.

First, in the control of BLDC motor drive, if the direction of voltage and current is the same, 'Vs' voltage is applied when PMW is on and '0' is applied when PWM is off, and the direction of voltage and current is different. In this case, by applying a voltage of '0' at the time of PWM off, the current ripple is reduced, thereby reducing the vibration and noise of the motor.

 Accordingly, the speed response and the current response can be expected to be improved by reducing the current ripple when the motor is driven.

Hereinafter, a PWM switching method and a system device for controlling the BLDC motor according to the present invention will be described in detail with reference to a preferred embodiment shown in the accompanying drawings.

3 is a block diagram of a system device for controlling a BLDC motor according to a preferred embodiment of the present invention, Figure 4 shows the internal circuit of the PWM inverter of Figure 3, Figure 5 is a preferred embodiment of the present invention The waveform diagram showing the phase current and the counter electromotive force state by the PWM method according to the present invention is shown. 6 to 9 are circuit diagrams showing current flow according to a voltage / current direction and a PWM state.

First, the configuration of FIG. 3 will be described.

A brush-less DC (BLDC) motor 100 is provided. The BLDC motor 100 of the present embodiment uses a three-phase BCD motor (hereinafter referred to as a "BLDC motor") 100 that is driven by receiving a three-phase power.

First, a power supply unit 200 for supplying general power to the system device of the present invention is provided. The power supply unit 200 refers to a general AC power.

The converter 210 receives the AC power from the power supply unit 200 and converts the AC power into a power suitable for the BLDC motor 100.

The output of the converter 210 is connected to a PWM inverter 220 which converts the power into a three-phase power source for driving the actual BLDC motor 100 and outputs it to the BLDC motor 100. The PWM inverter 220 is preferably a three-phase full bridge inverter (Full Bridge Inverter) consisting of six switching elements to apply the three-phase power to the BLDC motor 100 through a PWM signal. The PWM inverter 220 will be described in detail below with reference to FIG. 4.

Next, the current direction detection unit 230 is provided so as to know the current direction flowing to the BLDC motor 100 according to the rotor of the BLDC motor 100 driven by the PWM signal in the state where the three-phase power is supplied. do. The current direction detection unit 230 will be described as using the Hall sensor signal of the BLDC motor 100. However, it may be configured by using a sensor for detecting the voltage difference caused by the line term.

And a control unit 240 for controlling switching of the switching elements provided in the PWM inverter 220 according to the current direction and voltage direction detected by the current direction detection unit 230 and the PWM signal output from the PWM inverter 220. Is provided. The controller 240 applies a voltage of 'Vs' at the time of PWM ON and a voltage of '0' at the time of PWM OFF when the directions of voltage and current are the same, and at a time of PWM ON when the directions of voltage and current are different. When '-Vs' voltage and PWM off, the voltage of '0' is applied to the motor.

In addition, the position sensor 250 for detecting the position of the rotor in the BLDC motor 100, and the speed sensor 260 for detecting the speed of the BLDC motor 100 is provided. The results detected by the position sensor 250 and the speed sensor 260 are referenced when the BLDC motor 100 is driven through the control unit 240.

Next, an internal circuit configuration of the PWM inverter 220 will be described with reference to FIG. 4.

The PWM inverter 220 serves to control the BLDC motor 100.

The PWM inverter 220 includes six switching elements, that is, 'Q1', 'Q2', 'Q3', 'Q4', 'Q5' and 'Q6', and on / off is performed according to each control signal. do. That is, in order to apply a desired voltage to the winding of the BLDC motor 100, the Hall sensor signals generated differently according to the position of the rotor of the BLDC motor 100 are input to the 'Q1', 'Q2', 'Q3', ' The switching states of Q4 ',' Q5 'and' Q6 'are controlled.

Referring to the drawings, 'Q1' and 'Q4', 'Q3' and 'Q6', 'Q5' and 'Q2' are each connected in series to form a pair, and each pair is configured in parallel. Here, the 'Q1', 'Q3', 'Q5' is located in front of the BLDC motor 100, the 'Q2', 'Q4', 'Q6' is located in the rear end of the BLDC motor 100. .

The stator windings A, B, and C of the BLDC motor 100 are connected between 'Q1' and 'Q4', 'Q3' and 'Q6', 'Q5' and 'Q2'.

Reference numerals 'D1 to D6' are reverse current protection diodes.

Next, a PWM switching method for reducing current ripple by using a system device for controlling a BLDC motor having the above configuration will be described in detail.

First, the present invention allows the four switching elements of the six switching elements provided in the PWM inverter 220 to be turned on and off at once. A phase current and counter electromotive force waveform by a PWM method for controlling the four switching elements is shown in FIG. 5.

Referring to FIG. 5, the controller 240 selects only four switching elements related to the direction of the current detected by the current direction detector 230 among the six switching elements.

For example, when the current flows from the A phase to the C phase, the 'Q1', 'Q4', 'Q3', and 'Q6' can be seen to be turned on or off at once. . At this time, the 'Q1' and 'Q4', the 'Q3' and 'Q6' so that the switching state is reversed. That is, when 'Q1' is on, 'Q4' is off. This is to form a current loop inside the circuit of the system device so that a voltage of '0' is applied to the motor in the 'Q6' off section, which is a PWM off section.

Referring to FIGS. 6 to 9, voltages of 'Vs', '-Vs', and '0' are applied to the BLDC motor 100 according to the direction of voltage, current, and PWM state using the PWM method. Do it.

For reference, when the voltage supplied to the PWM inverter 220 and the direction of the current flowing in the PWM inverter 220 coincide with each other, the inductance component of the BLDC motor 100 does not affect the control to provide a desired control voltage. The state that can be applied, that is, the steady state of the current flowing in the desired direction. On the other hand, when the voltage supplied to the PWM inverter 220 and the direction of the current flowing through the PWM inverter 220 do not match, when the current is to be changed immediately due to the inductance component of the BLDC motor 100. It is the transient state of the current when it keeps its original direction instantaneously without changing.

Iii) the voltage and current are the same PWM  If on.

In this case, the controller 240 is a state in which 'Q1' and 'Q2' of the PWM inverter 200 is on, the 'Q4' and 'Q5' is off to apply a voltage to the BLDC motor 100 To be controlled.

At this time, the flow of the current i is as shown in FIG.

In addition, the voltage equation in FIG. 6 is the same as Equation 1.

Here, 'L' represents inductance components of the A and B phases, 'R' represents a resistance, 'i' represents a current, 'Vs' represents a direct current voltage source, and 'E' represents back EMF generated from the A and B phases.

That is, when the state of the detected PWM signal is ON while the voltage supplied to the PWM inverter 220 and the direction of the current flowing through the PWM inverter 220 are on, the positive DC voltage to the BLDC motor 100, That is, 'Vs' is applied.

Ii) the voltage and current are the same PWM Off-in  Occation.

In this case, '-Vs' is conventionally applied, which causes a current ripple phenomenon.

Therefore, even if the voltage and the current direction is the same, a voltage of '0' should be applied to the BLDC motor 100 in the PWM off period.

For this purpose, the controller 240 controls the 'Q1' and 'Q5' to be in an on state, and the 'Q4' and 'Q2' to be in an off state.

At this time, the flow of the current (i) is as shown in FIG.

In addition, the voltage equation in FIG. 7 may be expressed as Equation 2.

That is, when the state of the detected PWM signal is off while the voltage supplied to the PWM inverter 220 and the direction of the current flowing through the PWM inverter 220 match, the BLDC motor 100 has a value of '0'. By applying a voltage, the current ripple phenomenon can be reduced.

Next, a case in which the directions of voltage and current are different will be described. This case occurs due to the inductance component of the stator winding as described above.

Iii) different voltage and current directions PWM  If on.

In this case, as in the conventional bipolar PWM method and the unipolar PWM method, the controller 240 controls the 'Q1' and 'Q2' to be in an on state and the 'Q4' and 'Q5' to be in an off state.

At this time, the flow of the current i is as shown in FIG.

As shown in this case, the current must flow from the A phase to the B phase because the original 'Q1' and 'Q2' are on, but due to the inductance component of the winding of the BLDC motor 100, The current flows from the phase B to the phase A. The voltage equation in this case is as shown in [Equation 3].

That is, when the state of the detected PWM signal is ON while the direction of the voltage supplied to the PWM inverter 220 and the current flowing through the PWM inverter 220 is on, a negative DC voltage is applied to the BLDC motor 100. That is, '-Vs' is applied.

Iii) different voltage and current directions PWM Off-in  Occation.

In this case, the controller 240 should allow a voltage of '0' to be applied to the BLDC motor 100. For this purpose, the controller 240 controls the 'Q1' and 'Q5' to be in an on state and the 'Q4' and 'Q2' to be in an off state.

At this time, the flow of the current (i) is as shown in FIG.

Referring to FIG. 7, since a current loop is formed in the PWM inverter 220 circuit, a voltage of '-Vs' is not applied to the BLDC motor 100.

Therefore, the voltage applied to the BLDC motor 100 becomes '0'. Of course, due to the inductance component of the winding of the BLDC motor 100, current flows from the B phase to the A phase. The voltage equation in this case is the same as that of [Equation 2] above.

That is, when the state of the detected PWM signal is off while the direction of the voltage supplied to the PWM inverter 220 and the current flowing through the PWM inverter 220 is off, the BLDC motor 100 has a value of '0'. Voltage is applied.

As described above, the voltages applied to the BLDC motor 100 are summarized in the following [Table 3] according to whether the direction of voltage and current is the same and the PWM state in this state as in the case of i) to i).

When the direction of voltage and current is the same When the direction of voltage and current is different PWM status PWM ON PWM OFF PWM ON PWM OFF Applied voltage Vs 0 -Vs 0

In other words, in the PWM method according to the present embodiment, the directions of voltage and current are the same and 'Vs' is applied when the PWM is turned on, and a current loop is formed inside the PWM inverter 220 when the PWM is turned off, thereby providing a voltage of '0'. Is applied. In addition, the voltage and the current direction is different and '-Vs' is applied when the PWM is on, and when the PWM is off, a current loop is formed inside the PWM inverter 220 to apply a voltage of '0'.

In this way, in the conventional bipolar PWM method and the unipolar PWM method, when the voltage and current directions that cause the greatest current ripple are different, the phenomenon of '-Vs' being applied to the BLDC motor 100 when the PWM is turned off is solved. do. Therefore, it is possible to reduce the current ripple and further reduce vibration and noise of the BLDC motor 100. This means that the BLDC motor 100 can be applied to high performance control such as a robot industry and an intelligent robot requiring a small motor or a driver.

Although described with reference to the illustrated embodiment of the present invention as described above, this is merely exemplary, those skilled in the art to which the present invention pertains various modifications without departing from the spirit and scope of the present invention. It will be apparent that other embodiments may be modified and equivalent. Therefore, the true technical protection scope of the present invention will be defined by the technical spirit of the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a waveform diagram showing the phase current and the counter electromotive force of a bipolar PWM method for controlling a three-phase BLDC motor and a BLDC motor.

Figure 2 is a waveform diagram showing the phase current and counter electromotive force of the unipolar PWM method for controlling a general three-phase BLDC motor, and thus the BLDC motor.

3 is a block diagram of a system device for controlling a BLDC motor according to an embodiment of the present invention.

4 is an internal circuit diagram of the PWM inverter of FIG. 3.

5 is a waveform diagram illustrating a phase current and a counter electromotive force state by a PWM method according to an exemplary embodiment of the present invention.

6 to 9 are circuit diagrams showing current flow according to voltage / current directions and PWM states.

Explanation of symbols on the main parts of the drawings

100: BLDC motor 200: power supply

210: converter 220: PWM inverter

230: current direction detection unit 240: control unit

250: position sensor 260: speed sensor

Claims (5)

BLDC electric motor; First to sixth switching elements are provided to supply three-phase power to the BLDC motor through a PWM signal, wherein the two switching elements are connected in series to form a pair, and these pairs are three pairs, each pair connected in parallel with each other. PWM inverter; A current direction detector for detecting a current direction flowing to the BLDC motor; And When the BLDC motor is driven in a pulse width modulation (PWM) method, if the current direction detected by the current direction detection unit and the voltage direction supplied to the PWM inverter in the PWM off section are different, the current direction inside the PWM inverter. And a control unit configured to control on / off by selecting four switching elements related to the current direction and the current loop among the first to sixth switching elements to form a current loop according to the present invention. System unit. The method of claim 1, When the current loop is formed inside the PWM inverter, the voltage applied to the BLDC motor is a system device for controlling a BLDC motor, characterized in that the zero (zero). Two switching elements are connected in series to form a pair, and these pairs are three pairs, and the three phase power is supplied to the BLDC motor through the switching operation of the first to sixth switching elements provided in the PWM inverter connected in parallel to each other. Driving the BLDC motor; Detecting whether a current transient occurs in the driving BLDC motor; And, When the current transient occurs and the current direction flowing to the BLDC motor is different from the voltage direction supplied to the PWM inverter, the current loop is formed in the PWM inverter according to the current direction during the PWM off period. Driving on / off four switching elements associated with the current direction and the current loop among the sixth switching elements. The method of claim 3, wherein When the current loop is formed, a PWM switching method for controlling a BLDC motor, characterized in that the zero voltage is applied to the BLDC motor. The method of claim 3, wherein In the control step, During the PWM off period, even if the voltage and the current direction are the same due to the non-occurrence of the transient state of the current, a current loop is formed inside the PWM inverter so that a 'zero' voltage is applied to the BLDC motor. PWM switching method for controlling a BLDC motor, characterized in that.

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