Device and method for controlling brushless DC electric machine

The present invention relates to a device and a method for controlling a brushless DC electric machine, and more particularly to a device and a method for controlling an advance angle of the brushless DC electric machine.

A permanent magnetic electric machine is classified as a permanent sine-wave electric machine and a permanent trapezoidal-wave electric machine (brushless DC electric machine). Take a motor for example, the permanent sine-wave motor has a back electromotive force of a sine wave and fits a stator current of another sine wave for producing a constant torque. Otherwise, the brushless DC electric machine has a back electromotive force of a trapezoidal wave and fits a stator current of a square wave for producing a constant torque.

The brushless DC electric machine includes a rotor and a stator winding by at least a winding. Due to the existence of a winding inductance, a winding voltage must lead a back electromotive force by an angle known as an advance angle which is an important factor affecting the efficiency and the noise of the electric machine. An optimum advance angle is related to the rotating speed of the rotor. The higher the rotating speed is, the greater the optimum advance angle will be. A typical controller of the brushless DC electric machine does not control the advance angle, so that the performance of the electric machine is worse in the whole scope of the rotating speed.

At present, common methods are as follows. The first method uses software or a digital signal processor for controlling the advance angle and is disclosed in the US Publication No. 2006/0132076 A1. Good as the effect of this control method is, the cost is higher.

The second method uses hardware for controlling the advance angle and is disclosed in the U.S. Issuance Pat. No. 4,276,504. Please refer to FIG. 1( a ), which is a schematic block diagram disclosed in the U.S. Pat. No. 4,276,504 showing a conventional system for controlling an advance angle of a brushless DC electric machine. Afterward, please refer to FIG. 1( b ), which is a schematic diagram showing a relation between the advance angle and a motor rotating speed of the system in FIG. 1( a ). As shown in FIG. 1( b ), the used advance angle is a small fixed value while there is a low rotating speed (MOTOR SPEED<S 1 ), and the used advance angle is a large fixed value while there is a high rotating speed (MOTOR SPEED>S 1 ).

An optimum advance angle of the motor increases with the increment of the rotating speed in the whole scope of the rotating speed. Therefore, this control method cannot guarantee the advance angle to be optimum in the whole scope of the rotating speed. Besides, a tacho-generator is used in FIG. 1( a ), which makes the structure of the control circuit complicated, so that the cost increases.

The third method also uses hardware for controlling the advance angle and is disclosed in the WO Patent No. 97/33363. Please refer to FIG. 2( a ), which is a schematic diagram disclosed in the WO Patent No. 97/33363 showing a conventional circuit for controlling an advance angle of a brushless DC electric machine. Afterward, please refer to FIG. 2( b ), which is a waveform diagram showing signals obtained from the circuit in FIG. 2( a ). As shown in FIG. 2( b ), the advance angle φ increases with the increment of the rotating speed.

However, as the circuit structure in FIG. 2( a ) is a high-pass filter, the robustness of this control system is worse. Besides, only when position signals 48 and 50 are sine waves, the controlled advance angle is exact, but in general, the position signals 48 and 50 include many harmonic waves, so that the controlled advance angle is not exact.

In sum, in order to overcome the aforementioned defect, it is necessary to design a control system that the hardware circuit is stable, the cost is low, and the advance angle tends to be optimum in the whole scope of the rotating speed, which becomes the primary motive of the present invention.

It is an object of the present invention to provide a controller of a brushless DC electric machine and a method for controlling the brushless DC electric machine. Therefore, the advance angle of the electric machine tends to be optimum in the whole scope of the rotating speed, and a control module with high performance, low cost, good robustness is provided.

According to an aspect of the present invention, a controller of a brushless DC electric machine having a rotor and at least a stator winding powered by a driving voltage is provided, which includes a position sensor, an advance angle control circuit, and a driving circuit. The position sensor is moved along a reverse rotating direction of the rotor by a prepositioned angle for outputting a position signal. The advance angle control circuit receives the position signal and a driving voltage reproduction signal reproduced from the driving voltage and outputs a commutation control signal lagging the position signal by a first delay time. The driving circuit receives the commutation control signal for outputting a driving signal for controlling a commutation of the brushless DC electric machine.

According to another aspect of the present invention, a method for controlling a brushless DC electric machine having a rotor and at least a stator winding powered by a driving voltage is provided, which includes the following steps. Firstly, a position signal of the rotor is obtained by leading a position sensor with respect to a first commutation position. Next, a driving voltage reproduction signal of the driving voltage is obtained. Next, a commutation control signal lagging the position signal by a delay time based on the position signal and the driving voltage reproduction signal being inversely proportional to the delay time is output. Next, a commutation of the stator winding is driven according to the commutation control signal.

The above objects and advantages of the present invention will become more readily apparent to those ordinarily skilled in the art after reviewing the following detailed descriptions and accompanying drawings, in which:

FIG. 1( a ) is a schematic block diagram disclosed in the U.S. Pat. No. 4,276,504 showing a conventional system for controlling an advance angle of a brushless DC electric machine;

FIG. 1( b ) is a schematic diagram showing a relation between the advance angle and a motor rotating speed of the system in FIG. 1( a );

FIG. 2( a ) is a schematic diagram disclosed in the WO Patent No. 97/33363 showing a conventional circuit for controlling an advance angle of a brushless DC electric machine;

FIG. 2( b ) is a waveform diagram showing signals obtained from the circuit in FIG. 2( a );

FIG. 3 is a schematic structural diagram showing a circuit for a controller of a brushless DC electric machine according to the first embodiment of the present invention;

FIG. 4 is a schematic diagram showing the position relation of the position sensor according to the present invention;

FIG. 5 is a schematic data diagram showing the relation between a needed delay time and the driving voltage reproduction signal under an optimum state for the advance angle according to the present invention;

FIG. 6 is a schematic diagram showing a circuit for the advance angle control circuit according to the present invention;

FIG. 7( a ) and FIG. 7( b ) are waveform diagrams showing signals obtained from the circuit in FIG. 6 according to the present invention;

FIG. 8 is a schematic diagram showing a comparison between a needed delay time in FIG. 5 and a circuit delay time according to the present invention;

FIG. 9 is a schematic diagram showing another circuit for the advance angle control circuit according to the present invention; and

FIG. 10 is a schematic structural diagram showing a circuit for a controller of a brushless DC electric machine according to the second embodiment of the present invention.

The present invention will now be described more specifically with reference to the following embodiments. It is to be noted that the following descriptions of preferred embodiments of this invention are presented herein for the purposes of illustration and description only; it is not intended to be exhaustive or to be limited to the precise form disclosed.

In the present invention, a tacho-generator is not used for obtaining a rotating speed of an electric machine, and a signal provided directly or indirectly from a winding voltage of the electric machine is used for obtaining the information of the rotating speed of the electric machine. Because the rotating speed of the electric machine increases with the increase of the winding voltage of the electric machine, illustrated in a technical term, the rotating speed is proportional to the winding voltage on the characteristic. Therefore, an optimum advance angle increases with the increase of the winding voltage. The subsequent description is illustrated for a single-phase electric machine; however, the present invention is also effective for a three-phase electric machine.

Please refer to FIG. 3 , which is a schematic structural diagram showing a circuit for a controller of a brushless DC electric machine according to the first embodiment of the present invention. In FIG. 3 , a brushless DC electric machine system 30 includes the controller 31 of the brushless DC electric machine and a brushless DC motor 32 , wherein the brushless DC motor 32 is an applicable device belonging to the brushless DC electric machine. The brushless DC motor 32 includes a rotor 321 and at least a stator winding 322 and 323 powered by a driving voltage V CC , wherein the stator winding includes a first stator winding 322 and a second stator winding 323 . The controller 31 of the brushless DC electric machine includes a position sensor 311 , an advance angle control circuit 312 , and a driving circuit 313 .

One kind of common position sensor is a Hall sensor. A practical commutation position of the brushless DC motor 32 is predetermined. The position sensor 311 is installed on the stator of the brushless DC motor 32 and produces a position signal V SIG1 having position information of the rotor 321 , wherein the position signal V SIG1 is in advance of the practical commutation position of the brushless DC motor 32 is predetermined.

The common connection point of the first stator winding 322 and the second stator winding 323 receives the driving voltage V CC supplying power to the first stator winding 322 and the second stator winding 323 .

The advance angle control circuit 312 receives the position signal V SIG1 and a driving voltage reproduction signal V M . In the present embodiment, because the input terminal of the driving voltage reproduction signal V M is coupled to the driving voltage V CC , the driving voltage reproduction signal V M is identical to the driving voltage V CC . Therefore, the rotating speed is proportional to the driving voltage V CC applied to the stator windings 322 and 323 on the characteristic; that is, the driving voltage reproduction signal V M is proportional to the rotating speed of the brushless DC motor 32 . The advance angle control circuit 312 delays the position signal V SIG1 by a delay time T DA and produces a commutation control signal V SIG2 ; that is, the commutation control signal V SIG2 lags the position signal V SIG1 by the delay time T DA .

The driving circuit 313 receives the commutation control signal V SIG2 for outputting a driving signal V DRV . The driving signal V DRV is for controlling a commutation of the stator windings 322 and 323 of the brushless DC motor 32 .

In FIG. 3 , the brushless DC motor 32 further includes a first transistor TR 1 and a second transistor TR 2 . The first transistor TR 1 controls a first winding current I A1 flowing through the first stator winding 322 , and the second transistor TR 2 controls a second winding current I A2 flowing through the second stator winding 323 . The driving signal V DRV further includes a first driving sub-signal V SDRV1 controlling the first winding current I A1 and a second driving sub-signal V SDRV2 controlling the second winding current I A2 .

Afterward, the optimum of the advance angle of the brushless DC motor 32 is described. Please refer to FIG. 4 , which is a schematic diagram showing the position relation of the position sensor according to the present invention. In FIG. 4 , the position sensor 311 is on the stator side of the brushless DC motor 32 . Relative to the condition that the advance angle is suitable and that the brushless DC motor 32 has a fit commutation position, the position sensor 311 is moved along a reverse rotating direction (as shown by an arrow) of the rotor by a prepositioned angle Δα and is fixed. Afterward, under a corresponding rotating speed (or driving voltage V CC ), the advance angle is made optimum through control of the advance angle control circuit 312 and the driving circuit 313 according to the position signal V SIG1 , the driving voltage reproduction signal V M , and the delay time T DA . The optimum of the advance angle is implemented through delaying the position signal V SIG1 by the delay time T DA .

Please refer to FIG. 5 , which is a schematic data diagram showing the relation between a needed delay time and the driving voltage reproduction signal under an optimum state for the advance angle according to the present invention. The data source in FIG. 5 is described as follows. On condition that the position sensor 311 has the prepositioned angle Δα, a known commutation control signal V SIG2F is received by the driving circuit 313 controlling the brushless DC motor 32 , so that the advance angle of the brushless DC motor 32 is made optimum. The relation between a needed delay time T DF and the driving voltage reproduction signal V M can be obtained and is shown as multiple-point data in FIG. 5 , wherein the commutation control signal V SIG2F lags the position signal V SIG1 by the needed delay time T DF . As shown in FIG. 5 , the driving voltage reproduction signal V M is inversely proportional to the needed delay time T DF .

Please refer to FIG. 6 , which is a schematic diagram showing a circuit for the advance angle control circuit according to the present invention. It is the object of a circuit 70 in FIG. 6 that a rising edge of the commutation control signal V SIG2 lags a corresponding rising edge of the position signal V SIG1 by a first delay time T DP1 , a falling edge of the commutation control signal V SIG2 lags a corresponding falling edge of the position signal V SIG1 by a second delay time T DP2 , and the first delay time T DP1 and the second delay time T DP2 are made equal to the delay time T DA . Therefore, the produced delay time T DA tends to coincide with the data in FIG. 5 and the advance angle being optimum can be guaranteed. Besides, the present circuit 70 can resist interference of noise and its system is also stable and reliable.

The advance angle control circuit 70 shown in FIG. 6 includes a first comparing circuit 71 , a second comparing circuit 72 , a third comparing circuit 73 , a fourth comparing circuit 74 , a NOT gate, and a controllable switch. The first delay time T DP1 is formed through control of the magnitude of the potential of the driving voltage reproduction signal V M by a first resistor R 1 and a first capacitor C 1 coupled to the first comparing circuit 71 . The second delay time T DP2 is formed through control of the magnitude of the potential of the driving voltage reproduction signal V M by a second resistor R 2 and a second capacitor C 2 coupled to the third comparing circuit 73 .

The first comparing circuit 71 has a non-inverting input terminal receiving the position signal V SIG1 , an inverting input terminal receiving a first reference potential V REF1 , and an output terminal receiving the driving voltage reproduction signal V M through the first resistor R 1 and coupled to a ground potential GND through the first capacitor C 1 , and compares the position signal V SIG1 with the first reference potential V REF1 for outputting a first comparing signal V COMP1 at the output terminal. When the position signal V SIG1 starts to be greater than the first reference potential V RF1 , the first delay time T DP1 starts and the driving voltage reproduction signal V M starts to charge the first capacitor C 1 through the first resistor R 1 , wherein a charging voltage of the first capacitor C 1 is equal to the first comparing signal V COMP1 .

The second comparing circuit 72 has a non-inverting input terminal receiving the first comparing signal V COMP1 , and an inverting input terminal receiving a second reference potential V REF2 , and compares the first comparing signal V COMP1 with the second reference potential V REF2 for outputting a second comparing signal V COMP2 . When the first comparing signal V COMP1 starts to be greater than the second reference potential V REF2 , the second comparing signal V COMP2 is inverted to a high logical level and the first delay time T DP1 stops.

The third comparing circuit 73 has an inverting input terminal receiving the position signal V SIG1 , an non-inverting input terminal receiving a third reference potential V REF3 , and an output terminal receiving the driving voltage reproduction signal V M through the second resistor R 2 and coupled to a ground potential GND through the second capacitor C 2 , and compares the position signal V SIG1 with the third reference potential V REF3 for outputting a third comparing signal V COMP3 at the output terminal. When the position signal V SIG1 starts to be less than the third reference potential V REF3 , the second delay time T DP2 starts and the driving voltage reproduction signal V M starts to charge the second capacitor C 2 through the second resistor R 2 , wherein a charging voltage of the second capacitor C 2 is equal to the third comparing signal V COMP3 .

The fourth comparing circuit 74 has a non-inverting input terminal receiving the third comparing signal V COMP3 , and an inverting input terminal receiving a fourth reference potential V REF4 , and compares the third comparing signal V COMP3 with the fourth reference potential V REF4 for outputting a fourth comparing signal V COMP4 . When the third comparing signal V COMP3 starts to be greater than the fourth reference potential V REF4 , the fourth comparing signal V COMP4 is inverted to a high logical level.

The NOT gate receives the fourth comparing signal V COMP4 and inverts the fourth comparing signal V COMP4 for outputting a fifth comparing signal V COMP5 . When the fifth comparing signal V COMP5 is inverted to a low logical level, the second delay time T DP2 stops.

The controllable switch 76 has a first selection terminal receiving the second comparing signal V COMP2 , a second selection terminal receiving the fifth comparing signal V COMP5 , a control terminal receiving the position signal V SIG1 , and an output terminal, and selectively switches one of the first selection terminal and the second selection terminal to the output terminal for outputting the commutation control signal V SIG2 . When the position signal V SIG1 is at a high logical level, the commutation control signal V SIG2 is identical to the second comparing signal V COMP2 , and when the position signal V SIG1 is at a low logical level, the commutation control signal V SIG2 is identical to the fifth comparing signal V COMP5 .

Please refer to FIG. 7( a ) and FIG. 7( b ), which are waveform diagrams showing signals obtained from the circuit in FIG. 6 according to the present invention. Waveforms in FIG. 7( a ) are those of the position signal V SIG1 , the first comparing signal V COMP1 , and the commutation control signal V SIG2 . Besides, a waveform (not shown) of the third comparing signal V COMP3 is similar to the waveform of the first comparing signal V COMP1 . As shown in FIG. 7( a ), the magnitude of the first delay time T DP1 is determined according to magnitudes of three quantities, which are a product of the first resistor R 1 and the first capacitor C 1 , the second reference potential V REF2 , and the driving voltage reproduction signal V M . The magnitude of the second delay time T DP2 is determined according to magnitudes of three quantities, which are a product of the second resistor R 2 and the second capacitor C 2 , the fourth reference potential V REF4 , and the driving voltage reproduction signal V M . Therefore, the produced delay time T DA of the circuit 70 in FIG. 6 has a tendency to coincide with the data in FIG. 5 for guaranteeing the advance angle optimum.

In FIG. 7( b ), there are two multiple-period waveforms of the position signal V SIG1 and the commutation control signal V SIG2 , and the time relation between the position signal V SIG1 and the commutation control signal V SIG2 is shown therein.

Please refer to FIG. 8 , which is a schematic diagram showing a comparison between a needed delay time in FIG. 5 and a circuit delay time according to the present invention. Dotted data points in FIG. 8 come from FIG. 5 . A curve in FIG. 8 expresses the relation between a produced circuit delay time and the driving voltage reproduction signal V M , wherein the produced circuit delay time corresponds to one of the first delay time T DP1 and the second delay time T DP2 . As shown in FIG. 8 , the circuit delay time produced by the advance angle control circuit 70 has a tendency to coincide with the practical needed delay time T DF through the establishment of at least a time constant (a product of a resistance and a capacitance) and reference potentials.

Please refer to FIG. 9 , which is a schematic diagram showing another circuit for the advance angle control circuit according to the present invention. It is the object of a circuit 80 in FIG. 9 that a rising edge of the commutation control signal V SIG2 lags a corresponding rising edge of the position signal V SIG1 by a first delay time T DQ1 , a falling edge of the commutation control signal V SIG2 lags a corresponding falling edge of the position signal V SIG1 by a second delay time T DQ2 , and the first delay time T DQ1 and the second delay time T DQ2 are made equal to the delay time T DA . Therefore, the produced delay time T DA tends to coincide with the practical needed delay time T DF .

The circuit 80 in FIG. 9 includes a first controllable switch 81 , a second controllable switch 82 , and a comparing circuit 83 . The first controllable switch has a first selection terminal receiving the driving voltage reproduction signal V M through a third resistor R 3 , a second selection terminal coupled to a ground potential GND through a fourth resistor R 4 , and an output terminal coupled to the ground potential GND through a third capacitor C 3 , and selects one of the first selection terminal and the second selection terminal to be connected to the output terminal according to the position signal V SIG1 for outputting a first selection signal V SLT1 at the output terminal. When the position signal V SIG1 is inverted to a high logical level, the first delay time T DQ1 starts and the driving voltage reproduction signal V M starts to charge the third capacitor C 3 by the third resistor R 3 . When the position signal V SIG1 is inverted to a low logical level, the second delay time T DQ2 starts and the first selection signal V SLT1 on the third capacitor C 3 is discharged by the fourth resistor R 4 .

The second controllable switch has a first selection terminal receiving a fifth reference potential V REF5 , a second selection terminal receiving a sixth reference potential V REF6 , a control terminal receiving the position signal V SIG1 , and an output terminal, and selectively switches one of the first selection terminal and the second selection terminal to the output terminal for outputting the commutation control signal V SIG2 at the output terminal. The sixth reference potential V REF6 is a difference between the driving voltage reproduction signal V M and the fifth reference potential V REF5 . When the position signal V SIG1 is at the high logical level, the second selection signal V SLT2 is identical to the fifth reference potential V REF5 , and when the position signal V SIG1 is at the low logical level, the second selection signal V SLT2 is identical to the sixth potential V REF6 .

The comparing circuit 83 has a non-inverting input terminal receiving the first selection signal V SLT1 , and an inverting input terminal receiving the second selection signal V SLT2 , and compares the first selection signal V SLT1 with the second selection signal V SLT2 for outputting the commutation control signal V SIG2 . When the commutation control signal V SIG2 is at the high logical level, the first delay time T DQ1 is performed, and when the commutation control signal V SIG2 is at the low logical level, the second delay time T DQ2 is performed.

Besides the aforementioned two embodiments, as long as the circuit where the relation between the delay time T DA and the driving voltage reproduction signal V M for a circuit can be implemented as the inverse proportional relation shown in FIG. 8 , it belongs to the embodiment of the present invention.

Please refer to FIG. 10 , which is a schematic structural diagram showing a circuit for a controller of a brushless DC electric machine according to the second embodiment of the present invention. A brushless DC electric machine system 90 in FIG. 10 is a deformation of the brushless DC electric machine system 30 in FIG. 3 , and the identical reference numerals therein have the same functions. In FIG. 10 , the driving circuit 313 of the controller 31 of the brushless DC electric machine uses a pulse width modulation (PWM) for regulating speed. The driving signal V DRV includes pulses widths of which are variable; that is, the width of the pulse in the driving signal V DRV expresses the magnitude of the rotating speed. Therefore, a voltage signal produced by filtering the driving signal V DRV can be used for controlling a delay time T DA produced by the advance angle control circuit 312 and for reproducing a driving voltage reproduction signal V M .

In FIG. 10 , a driving voltage reproduction signal V M derives from the driving signal V DRV and is not directly coupled to the driving voltage V CC of stator windings 322 and 323 . The controller 36 of the brushless DC electric machine in the present embodiment further includes a voltage sensing circuit 314 having a driving signal sensor 3141 and a low-pass filter 3142 . The driving signal sensor 3141 senses the driving signal V DRV for outputting a driving sensing signal V DRV — T . The low-pass filter 3142 having a fifth resistor R 5 and a fourth capacitor C 4 receives the driving sensing signal V DRV — T for outputting the driving voltage reproduction signal V M , so that a corresponding relation of reproduction is present between the driving voltage reproduction signal V M and the driving voltage V CC .

The aforementioned embodiments are illustrated for a single-phase electric machine. However, the control principle therein is also effective for a three-phase electric machine.

Afterward, referring to FIG. 3 again, a method for controlling a brushless DC electric machine is provided according to the present invention. There is a brushless DC motor 32 having a rotor 321 and at least a stator winding 322 and 323 powered by a driving voltage V CC , and the method includes the following steps. Firstly, a position signal V SIG1 of the rotor 321 is obtained by leading a position sensor with respect to a first commutation position. Next, a driving voltage reproduction signal V M of the driving voltage V CC is obtained. Next, a commutation control signal V SIG2 lagging the position signal V SIG1 by a delay time based on the position signal and the driving voltage reproduction signal being inversely proportional to the delay time T DA is output. Next, a commutation of the stator windings 322 and 323 based on the commutation control signal V SIG2 is driven.

The device and the method for controlling the brushless DC electric machine have the main feature that the commutation control signal is produced based on the position signal and the driving voltage reproduction signal V M and lagging the position signal by the delay time. Therefore, the advance angle of the brushless DC electric machine tends to be optimum in the whole scope of the rotating speed, and control architecture with high performance, low cost, good robustness is provided.

While the invention has been described in terms of what is presently considered to be the most practical and preferred embodiments, it is to be understood that the invention needs not be limited to the disclosed embodiments. On the contrary, it is intended to cover various modifications and similar arrangements included within the spirit and scope of the appended claims, which are to be accorded with the broadest interpretation so as to encompass all such modifications and similar structures.