JP3549078B2 - Drive device for brushless motor - Google Patents

Description

[0001]
[Industrial applications]
The present invention relates to a motor drive device for improving the noise and efficiency of a polyphase brushless DC motor, particularly at low speed.
[0002]
[Prior art]
FIG. 3 is a circuit diagram of a driving device for a three-phase brushless DC motor according to the prior art, and is a circuit configuration diagram in which the number of revolutions of the motor is varied by changing a speed command voltage. In FIG. Magnetized rotor magnet, 2 is a group of magnetic pole position sensors built in the motor, 3 is a group of amplifiers for amplifying the signal of 2, 4 is a logic circuit for energizing 3 phase signals of 120 degrees with a phase difference of 120 degrees. 5 is a transistor group for energizing the motor coil by the signal of 4, 6 is a motor coil group, 7 is a speed command voltage, 8 is a sawtooth generation circuit, 9 is a comparator, 10 is a switching transistor, and 11 is a 10 The pre-drivers 12, 13, and 14 are choke coils, capacitors, and diodes, respectively, and the DC-DC converter 15 is configured by these 10, 11, 12, 13, and 14. To have a 16 in the power supply voltage Vcc is stepped down to a motor coil supply voltage Vm of 17 in accordance with the command voltage. The frequency of the sawtooth wave generating circuit 8 is set sufficiently higher than the switching frequency for energizing the motor coil, and the constants of the choke coil 12 and the capacitor 13 are selected so that the output becomes smooth.
[0003]
FIG. 4 is a time chart showing signal waveforms at various parts of the circuit of FIG. Next, the operation will be described with reference to FIG. In FIG. 4, reference numeral 18 denotes an output of the amplifier group 3, which is a three-phase sinusoidal signal whose phase is shifted by 120 electrical degrees. Reference numeral 19 denotes a signal inside the logic circuit, and reference numerals 20 and 21 denote outputs of the logic circuit 4 which are energized by an electrical angle of 120 degrees. Reference numeral 22 denotes a speed command voltage, and reference numeral 23 denotes a comparator output which is a PWM output. Reference numeral 17 denotes the output of the DC-DC converter, the broken line represents the Vcc level, and the solid line represents the voltage level according to the speed command value. Reference numeral 24 denotes a current waveform of a certain phase of the motor coil group 6, and a switching waveform having a sharp rise and fall at the time of phase switching is generated every 120 electrical degrees.
[0004]
[Problems to be solved by the invention]
In the above-described conventional circuit configuration, switching noise is large at each phase switching, and noise and vibration are generated. In particular, at low speed, noise due to mechanical causes in the motor is reduced, and switching noise at each phase switching becomes noticeable. An object of the present invention is to solve the above problems in principle.
[0005]
[Means for Solving the Problems]
The present invention synchronizes a motor voltage supplied by a DC-DC converter with a motor energizing cycle and superimposes a sine-wave-like waveform to smooth a waveform at the time of phase switching of a motor coil to reduce switching noise. For this purpose, full-wave synthesis and PWM conversion of the sine-wave output of the magnetic pole position sensor group built in the motor are performed. However, the frequency component of the synthesized sensor output does not have a phase shift, and the PWM carrier frequency has a sufficient filtering effect. A DC-DC converter is needed which can be obtained by setting a choke coil, a capacitor, and a PWM carrier frequency appropriately.
[0006]
【Example】
Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a circuit diagram showing an embodiment of a driving device for a three-phase brushless motor according to the present invention. In FIG. 1, reference numeral 30 denotes a full-wave synthesizing circuit of a sine wave output of the magnetic pole position sensor group, 33 denotes an adding circuit of the output of the full-wave synthesizing circuit and the speed command voltage 7, and 34 denotes a triangular wave generating circuit. The circuit configuration is the same as the conventional one, but the frequency of the triangular wave generating circuit 34, the inductance of the choke coil 12 of the DC-DC converter 15, and the capacitance of the capacitor 13 are changed to meet the following conditions.
The full-wave composite waveform frequency fm of the sine wave output of the magnetic pole position sensor group 2 is
Assuming that the number of magnetic poles P of the rotor magnet, the number of motor rotations N (rpm), and the number of phases of the motor coil are n, fm = (2 npN) / 120 (Hz).
As the number of phases increases and the number of rotations increases, fm also increases, and approaches the resonance frequency fc of the choke coil 12 and the capacitor 13 of the DC-DC converter 15. Becomes larger. Here, assuming that the inductance of the choke coil 12 is L and the capacitance of the capacitor 13 is C, the resonance frequency fr is
fr = 1 / 2π√LC is calculated.
Further, the PWM carrier frequency fc is determined by the frequency of the triangular wave generating circuit 34, and must be sufficiently large with respect to fr, and it is necessary to minimize the influence of the ripple voltage due to PWM on the motor coil voltage Vm.
From the above, a five-fold margin is expected for fm, and 5fm <fr, that is, 5 (2npN) / 120 <1 / 2π√LC, and a five-fold margin is expected for fc, 5fr <fc or 5 (1 / 2π√LC) <fc
By doing so, a motor voltage without waveform distortion can be supplied.
It is well known that the inductance of the choke coil is limited by the duty of the PWM.
In the above description, when the energization control circuit is unipolar energization, the half-wave composite waveform of the sine wave output of the magnetic pole position sensor group is obtained, so that fm becomes 1/2 and 5 (npN) / 120 <1 / 2π. √LC
And 5 (1 / 2π√LC) <fc.
[0007]
FIG. 2 is an operation timing chart in the circuit diagram of FIG. 31 is an output of the full-wave synthesizing circuit 30, 32 is an output of the adding circuit 33, 35 is a motor coil voltage, and is a full-wave synthesizing of a sine wave-like output of the magnetic pole position sensor group in synchronization with the three-phase electrical angle of 120 degrees. The waveform is superimposed on the DC voltage. As a result, the waveform 36 is a one-phase current waveform of the motor coil. During phase switching, the rising and falling waveforms of the current become smooth, and no switching noise occurs.
[0008]
FIG. 5 shows the frequency characteristics of the low-pass filter using the choke coil 12 and the capacitor 13 of the present embodiment. 40 is a gain, 41 is a phase, 42 is the maximum value of fm, 43 is fr, and 44 is fc. Frequency.
[0009]
【The invention's effect】
As described above in detail, according to the present invention, the supply voltage of the polyphase brushless DC motor is selected by selecting the frequency characteristics and the PWM frequency of the low-pass filter constituting the DC-DC converter so as to match the motor characteristics. The vibration and noise are greatly reduced by changing the phase of the energization each time and by making the switching waveform of the motor coil current rise and fall smoothly.
[Brief description of the drawings]
FIG. 1 is a circuit diagram showing an embodiment of a brushless motor driving device according to the present invention.
FIG. 2 is an operation timing chart of the brushless motor driving device shown in FIG. 1 and waveform diagrams of respective parts.
FIG. 3 is a circuit configuration diagram of a brushless motor driving device according to the related art.
FIG. 4 is an operation timing chart of the brushless motor driving device shown in FIG. 3 and waveform diagrams of respective parts.
FIG. 5 is a characteristic diagram of a filter using a choke coil and a capacitor used in one embodiment of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Rotor magnet 2 Magnetic pole position sensor group 3 Amplifier group 4 Logic circuit 5 Transistor group 6 Motor coil group 7 Speed command voltage 8 Saw wave generation circuit 9 Comparator 10 Transistor 11 Predriver 12 Choke coil 13 Capacitor 14 Diode 15 DC-DC converter 16 Power supply voltage 17 Conventional motor coil voltage waveform 18 Output waveform of amplifier group 3 19 Internal signal of logic circuit 4 Output waveform 21 of logic circuit 4 Output waveform 22 of logic circuit 4 Voltage waveform of speed command voltage 7 Voltage waveform of comparator 9 Output waveform 24 One-phase current waveform 30 of motor coil 6 Full-wave synthesis circuit 31 Output waveform 33 of full-wave synthesis circuit 30 Addition circuit 32 Output waveform of addition circuit 33 Triangular wave generation circuit 35 Motor coil voltage waveform of the present invention 36 Motor coil according to the invention One-phase current waveform

Claims (2)

A stator having a multi-phase winding wound thereon, a magnet rotor rotatably supported opposite to the stator, a position detecting element for detecting a position of the magnet rotor, and an output signal for the position detection. speed wherein consists energization control circuit for energization angle of 120 degrees sequentially energizing the polyphase winding, it was added to the DC-DC converter interposed between the power reception unit and the power supply of the vent electric control circuit in the Ru good bipolar energization In a brushless motor driving device configured to vary a motor supply voltage by a command voltage to change a motor speed, a circuit for full-wave rectifying and synthesizing the position detection signal of the magnet rotor, and an output of the synthesizing circuit and the speed. A circuit for adding a command voltage, and an output smoothing circuit having a low-pass filter comprising a series choke coil and a parallel capacitor, which constitutes the DC-DC converter. The numbers are n for the number of motor phases, P for the number of magnetic poles of the magnet rotor, N (rpm) for the maximum rotation speed of the motor, L (H) for the inductance of the series choke coil, and C (F for the capacitance of the parallel capacitor. ), When the switching frequency is fc (Hz),
A drive device for a brushless motor, wherein 5 (2nPN / 120) <(1 / 2π√LC) and 5 (1 / 2π√LC) <fc are satisfied. A stator having a multi-phase winding wound thereon, a magnet rotor rotatably supported opposite to the stator, a position detecting element for detecting a position of the magnet rotor, and an output signal of the position detection. A speed command voltage applied to a DC-DC converter inserted between a power receiving unit and a power supply of a power supply receiving unit of the power supply control circuit. A brushless motor driving device configured to vary a motor supply voltage to change a motor speed by a full-wave rectifying and synthesizing a position detection signal of the magnet rotor; and an output of the synthesizing circuit and the speed command voltage. and a circuit for adding the bets, and constituting the DC-DC converter, the output smoothing circuit having a low pass filter comprising more series choke coils and the parallel capacitor The numbers are n for the number of motor phases, P for the number of magnetic poles of the magnet rotor, N (rpm) for the maximum rotation speed of the motor, L (H) for the inductance of the series choke coil, and C (F for the capacitance of the parallel capacitor. ), When the switching frequency is fc (Hz),
A drive device for a brushless motor, characterized by satisfying a relationship of 5 (nPN / 120) <(1 / 2π√LC) and 5 (1 / 2π√LC) <fc.

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