Drive circuit for brushless motor

Abstract: A driving circuit for a brushless motor can change the rotation stably by switching a target rotation speed and the gain of a speed difference compensation filter. This driving circuit comprises a speed detection means for detecting a rotor speed; a speed difference detecting means for outputting a difference between the detected actual rotation speed of the rotor and a target rotation speed as a speed difference signal; and a speed difference compensation filter comprised of the a proportion - integration (P/I) filter (460) connected in parallel with a first order delay filter (461), the input of parallel circuit is the speed difference signal, the outputs of the parallel circuit are added and further supplied in series to another first order delay filter (464), the output of the another first order delay filter is supplied to the armature windings of the motor as a current indication value.

Description: Fie1d of the Invention The invention relates to drive circuit for the brushless motor. Description of the Prior Art The rotation driving control of a brushless motor can be classified roughly into two functions. One of which is a commutation control for controlling the timing of respective phase current which flows through respective armature winding. Another is a speed control which maintains the rotation speed constant. In the commutation control, a rotor location signal is necessary which indicates the relative position of the armature winding and the rotor. On the other hand, in the speed control, a speed signal is necessary for indicating rotation speed of the rotor. In a speed control of the brushless motor, it is generally used a system for maintaining the rotating speed constant by controlling the current quantity flowing in the armature winding. FIG. 11 shows a block diagram of a speed control system of the driving circuit for conventional brushless motor. In FIG. 11, 530 is a speed detecting circuit which detects actual rotation speed of the rotor and outputs a speed signal, 531 is a speed difference detecting circuit which outputs a speed difference signal having a pulse width corresponding to the speed difference by counting the speed signal period using reference clock. A speed difference compensation filter 532 outputs a current indication value to a current supplying circuit 533 so that a speed difference becomes zero according to the speed difference signal. The current supplying circuit 533 regulates a current quantity supplied to the armature winding of the brushless motor 534 according to the current indication value. In the driving circuit of such conventional brushless motor, the speed difference compensation filter is constituted of an analog filter in which a PI filter 460 and a first order delay filter 464 are connected serially as shown in FIG. 12. In the driving circuit of the conventional brushless motor, the speed signal period is counted by the reference clock an therefore the reference clock frequency inputted into the speed difference detecting circuit is switched in proportion to the indicated rotation speed when the indicated rotation speed to the motor is switched. Regarding the system which detects the speed similar for controlling the rotation speed of the brushless motor, there are a system which is popularly called a FG system which exclusively use a frequency generator for speed detection and a system which detects speed according to a feature that a magnitude of the counter electromotive voltage signal induced in the armature winding is in proportion to the rotation speed. In the detection system for detecting a speed by a private frequency generator, it is necessary to provide a frequency generator having a high machining accuracy. Therefore, it is necessary to provide a wide space for installing the private detecting apparatus and then there is a cost disadvantage. In the detecting system for detecting a speed by an amplitude of the counter electromotive voltage, since the voltage generated by the current flowing in the armature winding is superpose to the counter electromotive voltage, it is difficult to detect only the amplitude of the counter electromotive voltage, and also the magnitude is followed by a change of environment. US 4 605 885 discloses a method of controlling the rotation speed of a motor to maintain a desired value in which a deviation between the detected rotation speed and the desired value is obtained and the gain of the feedback loop is changed to a value lower than a predetermined one during a period in which the deviation is smaller than a preset maximum ripple value. It is the object of the present invention to provide a driving circuit for the brushless motor for obtaining a speed signal without providing a private speed detecting circuit. Further, it is the object of the present invention to provide a driving circuit for the brushless motor for providing a high accurate rotation mode with fully compressed disturbance even if the disturbance at low pass area is large. SUMMARY OF THE INVENTION The brushless motor driving circuit of the present invention comprises a speed detection means for detecting a rotor speed; a speed difference detecting means for outputting a difference between the detected actual rotation speed of the rotor and a target rotation speed as a speed difference signal; and a speed difference compensation filter comprised of a proportion - integration (P/I) filter connected in parallel with a first order delay filter, the input of parallel circuit is the speed difference signal, the outputs of the parallel circuit are added and further supplied in series to another first order delay filter, the output of the another first order delay filter is supplied to the armature windings as a current indication value. Since the speed difference compensation filter is comprised of serial connection of a parallel connection of a PI filter and a first order delay filter, and a first order delay filter, a good low pass compression characteristics for disturbance can be obtained. Further, the brushless motor driving circuit of the present invention comprises a speed detection means for detecting a rotor speed; a speed difference detection means for outputting a difference between the detected actual rotation speed of the rotor and a target rotation speed as a speed difference signal; and a speed difference compensation filter comprised of a serial circuit of a proportion - integration (P/I) filter and a first order delay filter, the input of circuit is the speed difference signal, the serial circuit is further supplied in parallel to another first order delay filter, the parallel output is added and supplied to the armature windings as a current indication value. Since the speed difference compensation filter is comprised of parallel connection of a serial connection of a PI filter, a good low pass compression characteristics for disturbance can be obtained. Since a target of the speed difference detector and a gain of the speed difference compensation filter are switched according to the indicated rotation speed, it is not necessary to change the reference clock inputted into the speed difference detector. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of an embodiment which shows a general construction a brushless motor driving device. FIG. 2 is a block diagram of a speed difference compensation filter of an embodiment 1. FIG. 3 shows frequency characteristic of a speed difference compensation filter of the embodiment 1. FIG. 4 is a block diagram of a speed difference compensation filter for digital system of an embodiment 1. FIG. 5 is a block diagram of a speed difference compensation filter of an embodiment 2. FIG. 6 shows frequency characteristic of a speed difference compensation filter of the embodiment 2. FIG. 7 is a block diagram of a speed difference compensation filter of the embodiment 2. FIG. 8 is a block diagram of a third embodiment of the present invention which shows a general construction a brushless motor driving device. FIG. 9 shows a construction of a speed difference detecting circuit of an embodiment 3. FIG. 10 is a block diagram of a PI filter of an embodiment 4. FIG. 11 Is a block diagram which shows a speed control system of a conventional brushless motor driving device. FIG. 12 is a block diagram which shows a speed difference compensation filter of a conventional brushless motor driving device. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1 FIG. 1 is a block diagram of a general construction of a brushless motor driving device. In FIG. 1, the numeral 406 denotes a starting circuit, the numeral 409 denotes a speed difference detecting circuit for counting a period of the speed signal 3d by the counter and for outputting a period difference between the indicated value and the measured value as a speed difference detection signal 409a. The numeral 410 denotes a speed difference compensation filter for supplying a current indication value 410a to a current supplying circuit 411 so that the speed difference detection signal 409a become zero. A current supplying circuit 411 comprises a resistor 10, a bridge circuit 11, a buffer amplifier 212, a resistor 213 and a driving transistor 214, and supplies a predetermined driving current to the armature windings 12, 13 and 14 according to the driving signals 9a ~ 9f. A terminal voltage compensation circuit, a comparator 2 and a waveform shaping circuit 3 constitute the rotor location signal generating circuit 4. In this embodiment, a brushless motor having a speed difference compensation filter in which a low pass gain characteristics is improved in comparison with the conventional speed difference compensation filter is explained below. A construction of the speed difference compensation filter which is important for realising the invention is explained below. FIG. 2 is transfer block diagram in which the speed difference compensation filter is comprised of analog filter. In FIG. 2, the numeral 460 denotes a proportion - integration (PI) filter, the numeral 461 denotes a first order delay filter, the numeral 462 denotes a gain element or coefficient multiplier, the numeral 463 denotes an adder, the numeral 464 denotes a first order delay filter. A speed difference detection signal 409a which is outputted from the speed difference detecting circuit 409 is inputted on an input terminal X of the speed difference compensation filter. An output signal outputted from the terminal Y is supplied to the current supplying circuit 411 as a current indication value 410a for the armature winding. This speed difference compensation filter 410 is different from the conventional speed difference compensation filter shown FIG. 12 in that the present filter adds the speed difference detection signal 409a to the output of the PI filter 460 through the first order delay filter 461. In this configuration, the transfer function G C (s)of the speed difference compensation filter is given by an equation 1. G C (s) = {Kp (1+1/T 1 s) + K W /(1+T A s)} x 1/ (1+T L s) FIG. 3 shows a simulation result of open loop characteristics of the speed difference compensation filter when Kp=1, T I =1/(2πx10), K W =1, T A = 1/(2πx5), T L =1/(2πx60). The broken line in FIG. 3 shows a simulation result of the conventional speed difference compensation filter when Kp = 1, T I = 1/(2πx10), T L = 1/(2πx60). This FIG 3 shows that the filter of the present invention provides a improved low pass gain characteristic. FIG 2 shows an example comprised of an analog filter, but it is possible to be comprised of digital filter. FIG. 4 shows a transfer block diagram in which the speed difference compensation filter is comprised of the digital filter: In FIG. 4, the numerals 470 ~ 472 denote delay elements which causes the signal to delay by one sampling period, the numerals 473 ~ 479 denote gain elements, the numerals 480 ~ 483 denote adder. The delay element 471, the gain elements 476, 477 and the adders 481, 482 constitute a PI filter 484. The delay element 470, the gain elements 473 ~ 475, the adder 480 constitutes a first order delay filter 485. The delay element 472, the gain elements 478, 479, the adder 483 constitutes a first order delay filter 486. In this configuration, the transfer function G c (z) of the speed difference compensation filter is given by an equation (2). G c (z) = {Kp+K I /(1-z- 1 ) + K W (1-K A )/(1- K A z - 1 )} x (1-K L )/ (1-K L z- 1 ) Embodiment 2 In the embodiment, another speed difference compensation filter which has a improved low pass gain characteristics in comparison with the conventional speed difference compensation filter is explained. FIG. 5 is a transfer block diagram where a speed difference compensation filter is comprised of analog filter. In FIG. 5, the same elements as those in FIG. 2 are indicated by the same numerals. This speed difference compensation filter is different from the conventional speed difference compensation filter in that the output of the first order delay filter 461 which is supplied by the speed difference detection signals 405a is applied to an output of serial circuit of the PI filter 460 and the first order delay filter 464. In this configuration, the transfer function G C (s) of the speed difference compensation filter is given by an equation (3) . G C (s) = Kp(1+1/T 1 s)x1/(1+T L s)+K W /(1+T A s) FIG. 6 shows a simulation result of open loop characteristics of the speed difference compensation filter when Kp=1, T I =1(2πx10), K W =1, T A =1/(2πx5), T L =1/(2πx60). The broken line in FIG. 6 shows a simulation result of the conventional speed difference compensation filter when Kp=1, T I =1/(2πx10), T L =1/(2πx60). This FIG. 4 shows that the filter of the present invention provides a improved low pass gain characteristic. FIG. 5 shows an example comprised of an analog filter, but it is possible to be comprised of digital filter. FIG. 7 shows a transfer block diagram in which the speed difference compensation filter is comprised of the digital filter. In FIG. 7, the same elements as those in FIG. 1 are indicated by the same numerals. The numerals 487, 488 denote adders. In this configuration, the transfer function G C (z) of the speed difference compensation filter is given by an equation (4). G C (z) = {Kp+K I /(1-z- 1 )}x(1-K L )/(1-K L z -1 ) + K W (1-K A )/(1- K A z - 1 ) (2) Embodiment 3 In this embodiment, a brushless motor driving circuit which switches a target rotation speed of the speed difference detecting circuit and a gain of the gain element in the speed difference compensation filter when the indicated rotation speed has changed is explained. FIG. 8 is a block diagram which shows a general construction of a brushless motor driving circuit of the embodiment 3. In FIG. 8, the same elements as those in FIG. 1 are indicated by the same numerals. The numeral 490 denotes an input terminal where a mode switching signal 490a is inputted. A. mode switching signal 490a is inputted from outside of the brushless motor driving circuit and is comprised of binary signal for switching the motor rotation speed. In the above mentioned waveform shaping circuit 3, the logic pulse signal 3d outputted from OR circuit is supplied for a predetermined period at a normal rotation. Accordingly, this logic pulse signal 3d can be used as a speed signal for controlling the rotation speed. FIG. 9 is concrete construction example of the speed difference detecting circuit 409. In FIG. 9, the numerals 491, 492 denote initial value registers, the numeral 493 denotes a selector, the numeral 494 denotes a counter. The initial value registers 491, 492 provide initial values of target rotation speeds. In this embodiment, there are two initial value registers in order to respond to two kinds of indicated rotation speed. The selector 493 switches the two kinds of initial registers 491, 492 according to the logic level of the mode switching signal 490a. The counter 494 loads an initial value selected by these selector 493 at the timing of rising edge of the logic pulse signal 3d, and counts up in synchronism with the clock. For example, a period of the logic pulse signal 3d which is 1 (m sec) or 0,5 (m sec) at normal rotation is explained in correspondence with the two indicated rotation speed (the indicated rotation speeds are expressed A and B, respectively). Here, assume that the clock frequency is 1 (MHz), and the indicated rotation speed A corresponds to H level of the mode switching signal 490a and the indicated rotation speed B corresponds to L level of the mode switching signal 490a. -1000 is set to the initial value register 491, and -500 is set to the initial value register 492. In such construction, when the mode switching signal 490a is at H level, the selector 493 selects the initial value register 491 and the counter 494 loads -1000 for a initial value at a timing of rising edge of logic pulse signal 3d. Then, the counter 494 counts up in synchronism with to the clock and outputs a negative value when the period of logic pulse signal 3d is less than 1 (m sec) and positive value when the period of logic pulse signal 3d is larger than 1 (m sec) as a speed difference detection signal 409a. On the other hand, the mode switching signals 490a is at L level, the selector 493 selects the initial value register 492 and the counter 494 loads -500 for a initial value at a timing of rising edge of logic pulse signal 3d. Then, the counter 494 counts up in synchronism with to the clock and outputs a negative value when the period of logic pulse signal 3d is less than 0.5 (m sec) and positive value when the period of logic pulse signal 3d is larger than 0,5 (m sec) as a speed difference detection signal 409a). Embodiment 4 In the above embodiments, an operation of the speed difference detecting circuit 409 in case of the indicated rotation speed is changed is explained. But, since the target rotation speed is switched, there is a problem that the detection sensitivity varies by the difference of indicated rotation speed. In this embodiment, in order to solve the above problem, the gain element of the speed difference compensation filter is also switched. FIG. 10 is a block diagram of PI filter 484A when the speed difference compensation filter is switched. In FIG. 10, the same elements as those in Fig. 4 of the embodiment 1 are indicated by the same numerals. The numerals 495, 496 denote new gain elements which respond to the other indicated rotation speed, the numerals 497, 498 denote selectors. The selectors 497, 498 select gain element 476 or 495 and gain element 477 or 496, respectively, according to the logic level of the mode switching signal 490a. In the same way, the gain elements of the first order delay filters 485, 486 are also switched by the mode switching signal 490a. Of course, other general methods for switching the gain may be used. Further, in this embodiment, an example for switching the indicated rotation speed by binary signal of one bit, but it is possible to switch the indicated rotation speed by the binary signal of N bit when a plurality of indicated rotation speeds are used.

Claims: A brushless motor driving circuit comprising: a speed detection means for detecting a rotor speed; a speed difference detecting means (409) for outputting a difference between the detected actual rotation speed of the rotor and a target rotation speed as a speed difference signals; characterized by a speed difference compensation filter (410) comprised of a proportion - integration (P/I) filter (460) connected in parallel with a first order delay filter (461), the input of parallel circuit is the speed difference signal (409a), the outputs of the parallel circuit are added and further supplied in series to another first order delay filter (464), the output of the another first order delay filter (464) is supplied to the armature windings as a current indication value. A brushless motor driving circuit comprising: a speed detection means for detecting a rotor speed, a speed difference detecting means for outputting a difference between the detected actual rotation speed of the rotor and a target rotation speed as a speed difference signal; characterized by a speed difference compensation filter (410) comprised of the a serial circuit of a proportion - integration (P/I) filter (460) and a first order delay filter (464), the input (409a) of circuit is the speed difference signal, the serial circuit is further supplied in parallel to another first order delay filter (461), the parallel output is added and supplied to the armature windings as a current indication value. A brushless motor driving circuit according to claim 1 or 2, characterized in that said target rotation speed of the speed difference detecting means and a gain of the speed difference compensation filter are changed according to the indicated rotation speed which is supplied to the driving circuit of the brushless motor.

Inventors: HOSHI KIYOTAKA, IZUMI YUKIO, NAGAOKA HIDETAKA, NISHIKAWA KEICHI, ONODA ATSUO, OOMURA YUUJI, SUZUKI MITINAGA, HOSHI, KIYOTAKA, IZUMI, YUKIO, NAGAOKA, HIDETAKA, NISHIKAWA, KEICHI, ONODA, ATSUO, OOMURA, YUUJI, SUZUKI, MITINAGA, Hoshi, Kiyotaka, Mitsubishi Denki K.K., Izumi, Yukio, Mitsubishi Denki K.K., Nagaoka, Hidetaka, Mitsubishi Denki K.K., Nishikawa, Keichi, Mitsubishi Denki K.K., Onoda, Atsuo, Mitsubishi Denki K.K., Oomura, Yuuji, Mitsubishi Denki K.K., Suzuki, Mitinaga, Mitsubishi Denki K.K.
Applicants: MITSUBISHI ELECTRIC CORP, MITSUBISHI DENKI KABUSHIKI KAISHA
Application year: 1995
Main classification: H02P5
IPC codes: H02P6