JPH0251390A - Brushless dc motor - Google Patents

Abstract

PURPOSE:To improve reliability by directly utilizing back electromotive voltage generated in a stator winding and obtaining optimum conduction timing to a switching element. CONSTITUTION:A brushless DC motor and a driver circuit for the motor are composed of a four-pole permanent magnet rotor 1, stator windings A to C arranged in three-phase and winding driving transistors(Trs) 2a-2c driving the stator windings. The motor is driven by applying successively changing over base currents to the base terminals 3a-3c of the winding driving Trs 2a-2c in response to the rotational position angle of a rotor 1. Accordingly, when the peaks of the crest values of windings A to C are shown respectively by points a to c, the conduction time of the A phase is shown by Ta between points b and c, the conduction time of the B phase by Tb between c-a', and the conduction time of the C phase by Tc between a'-b', and the time of the peaks of the windings of other phase is detected, thus acquiring pulses for performing optimum conduction.

Description

Detailed Description of the Invention (a) Industrial Application Field The present invention relates to a brushless DC motor, in particular, it does not have a position detection mechanism and is capable of detecting back electromotive force generated in the stator windings during operation of the motor. The present invention relates to a brushless DC motor which is used to detect the position of a permanent magnet rotor.

(B) Prior Art Conventionally, Japanese Patent Publication No. 62-20791 discloses a brushless DC motor in which the position of a permanent magnet rotor is detected using a back electromotive force generated in a stator winding. this is,
a rectifier circuit that individually extracts all or part of the non-current-carrying region of the back electromotive force generated in each of the plurality of stator windings;
It is equipped with discharge type and suction type voltage-current conversion circuits that convert the outputs of the rectifier circuits into currents, respectively, and an arithmetic circuit composed of a plurality of time-integrating capacitors that are charged and discharged by both the conversion circuits. All or part of the non-current-carrying region of the back electromotive force generated in each of the plurality of stator windings is taken out individually, and this is integrated and subtracted in time, and the result of the integral operation is calculated as the rotation of the permanent magnet rotor. This signal is used as a position signal to sequentially energize a plurality of stator windings to drive an electric motor.

(8) Problems to be Solved by the Invention However, according to the above configuration, the back electromotive force is rectified by the rectifier circuit, so if the rectifier circuit is configured with general rectifying elements such as diodes, the order of the rectifying elements A directional voltage drop occurs, and this voltage drop causes the rectified waveform to be different from the back electromotive voltage waveform (the peak value of the rectified waveform becomes lower than the peak value of the back electromotive voltage waveform by the voltage drop). For this reason, the peak value of the time-integrated waveform based on the rectified waveform described above may not be constant, and the rotational position signal calculated based on this may be affected to some extent, and the switching Stable switching of elements (switching at constant timing) may not be performed. This problem becomes particularly noticeable when the rotational speed of the permanent magnet rotor is low, since the peak value of the back electromotive force is low and the influence on the rectified waveform becomes large. In addition, in the above configuration, multiple time-integrating capacitors are used when charging and discharging the output of the heavy voltage current conversion circuit, so it is difficult to set the charging and discharging cycles, and if the settings are incorrect, the switching elements will not be able to switch properly. There were problems with reliability.

The present invention has been completed in view of the above points, and includes a three-phase stator winding and a switching element for driving a permanent magnet rotor connected in series with each of the windings, and is integrated into the series circuit. In a brushless DC motor that is directionally energized (hereinafter referred to as a 3-phase one-way energized brushless DC motor), there are problems such as the forward voltage drop of the rectifying element, its adverse effect on the rotational position signal, and the complexity of the time-integrating capacitor. The purpose is to provide a highly reliable brushless DC motor that eliminates the need for repetitive charge/discharge cycle settings, is unaffected by the rotation speed of the permanent magnet rotor, and is capable of energizing optimal switching elements from low to high speeds. shall be.

(d) Means for Solving the Problems The present invention provides a three-phase stator winding and switching for driving windings connected in series to each of the windings in a three-phase one-way energizing type brushless DC motor. A peak time detection circuit detects the peak time of the back electromotive force generated in each of the stator windings and outputs a signal in the brushless DC motor, which is equipped with an element and is configured to unidirectionally conduct current through the series circuit. established,
The switching element is switched when a signal is output from this circuit.

Further, in the brushless DC motor according to claim 1, the stator windings are always energized in such a manner that one phase is ON and the second phase is OFF, and the induced back electromotive force and power supply voltage of one phase that is the OFF phase are provided. A first detection circuit detects the difference between the two phases and outputs a signal, and a second detection circuit detects the difference between the induced back electromotive voltage of the other phase and the power supply voltage and outputs a signal. By comparing the output signals from both circuits, the peak time of the back electromotive voltage of the OFF phase winding is detected.

(*) Effect The brushless DC motor of the present invention has the above-mentioned former configuration, and directly utilizes the back electromotive force generated in the stator windings to determine the optimal timing for energizing the switching elements (at the point when the rotational torque is large). This eliminates the need for a rectifier circuit or time-integrating capacitor, eliminates the forward voltage drop of the rectifying element and its negative effect on the rotational position signal, and eliminates the complicated charging/discharging cycle settings of the time-integrating capacitor. Moreover, since the peak value of the back electromotive force is not directly used, but the ratio is used, the switching element can be energized at the optimal timing from low to high speeds without being affected by the rotation speed of the permanent magnet rotor. It becomes possible to do
This can improve reliability.

Furthermore, the latter configuration allows the back electromotive force of the two-phase windings that are always OFF to be used, thereby providing more reliable energization timing, further improving reliability, and simplifying the circuit configuration.

(f) Example Embodiments of the present invention will be described below based on the drawings.

FIG. 1 is a schematic diagram of a brushless DC motor and a switching element for driving windings according to the present invention. 1 is a 4-pole permanent magnet rotor; A, B, and C are stator windings arranged in three phases; 2
A, 2b, and 2c are winding drive transistors that drive the windings A, B, and C, respectively, and 3a, 3b, and 3c are their base terminals.

4 is a terminal connected to a positive DC power supply VCC.

The motor is driven by the base terminals 3a of the winding drive transistors 2B, 2b, 2c depending on the rotational position angle of the rotor 1.
, 3b, and 3c by applying base currents that are switched sequentially.

FIG. 2 shows the basic energization timing according to the present invention.

Here, the back electromotive force of each winding A, B, and C generated when the permanent magnet rotor 1 rotates is vA.

V, VC. In this case, the optimal energization timing is Ta and Tb in each of the three-phase windings A, B, and C, respectively.
, Tc. That is, if the peak values of the windings A, B, and C are respectively a, b', and c,
The energizing time of A phase is Ta between b and c, the energizing time of B phase is Tb between c and a', and the energizing time of C phase is T between a゛ and b'.
c, and by detecting the peak time of the windings of the other phases, a pulse for performing the above-mentioned optimum energization is obtained.

Next, a basic method for detecting the peak time of the OFF phase will be explained with reference to FIG. The waveforms of the back electromotive force generated in each winding A, B, and C are vA, Vs, and Vc, respectively, and the energization state is always such that one phase is ON and the second phase is OFF. Considering the peak point of the electromotive voltage, up to this point the C phase is ONL as shown in FIG. Here, the peak value from +VCC at point b is E, b
If the peak value of VA of phase A at the same time as the point is KE, the peak value E changes depending on the rotation speed, but K is a constant that does not change depending on the rotation speed. For example, if VA-Esinθ, it becomes -1/2. Therefore, [vi-(+vcc):l and [(+Vcc)-VA)
If we compare the value multiplied by 1/1 and detect the time when this becomes 1:1, this will be the peak point of V. That is, as shown in FIG. 4, (Vl-(+Vcc)) and t
Since the point where the peak values of both pressures of /x((+vcc)-va) coincide is the peak point of v3, a pulse is generated at this point b. In addition, in the case of other phases, (V C+ (+ V CC”) ) and
By comparing 1/K((+Vcc)-Vm), the peak time C of Vc is determined as (VA-(+Vcc)3 to 1/K((+
Vcc)-Vc) is compared to detect the peak point a of Va.

Specific examples will be described below based on the above basic logic.

FIG. 5 is an example of a circuit of a brushless DC motor, with stator windings A and B connected in a three-phase one-way energization system.

The back electromotive voltages vA, v, , Vc and +VCC of each phase of C are divided by resistors R8 to R6 and taken out as signals,
Convert to a level that can be handled. Here, Rt-Rs
=Rs, Rs-R--Rs, the damping ratio will be constant. Furthermore, this voltage is divided by R7-R14 to a level that allows voltage comparison. Here −Rγ −Rψ −R1
1"'R11l R#"R1.-R11"Rt4, signal voltage levels V at V b yvc having the same peak value with respect to V as shown in FIG. 6 can be obtained.

The signal voltages va, vb, vC obtained in this way
is input to two differential amplifiers 5 and 6 as shown in FIG. Here, the amplification degree of the differential amplifier 5 is set to 1, and the amplification degree of the differential amplifier 6 is set to 1/K. When the respective outputs are compared by the voltage comparator 7, at the peak of Vm, the winding A
It is possible to generate a pulse a for energizing. At this time, when the back electromotive voltage vA in the A phase and the generated pulse a from the voltage comparator 7 are viewed in terms of time, a time chart as shown in FIG. 8 is obtained. Similarly, a pulse 51 for energizing the winding 11B from the other B-phase and C-phase is also applied to the winding 11.
A pulse C for energizing Ac can be obtained.

(In FIG. 7, the configurations of the differential amplifier and voltage comparator for the B phase and C phase are the same, so they are omitted.)
The output pulses a, b, and c from each (three) voltage comparators 7 (the other two are not shown) are as shown in FIG. d, e, f are obtained. Here, the arithmetic circuit 8 obtains the optimum energizing pulse by sequentially turning on the phases in which pulses are generated until the other phases are turned on.

Based on the optimum energizing pulse obtained above, each winding A, B, C
When electricity is applied, the back electromotive voltage waveform of each phase is VA shown in Figure 10.
' , V, ', VC' (7). As a result, the waveform obtained by comparison from the back electromotive force also changes, so the generated pulses also change to a', b', and c in Figure 10.
', and the time width of the pulse becomes longer. However, since there is no equivalent effect at the time of pulse generation, the arithmetic circuit 8 performs the above-mentioned calculation again (calculation in which the phases in which pulses are generated are sequentially turned on, and the energizing pulse is made until the other phases are turned on). By doing this, optimal energizing pulses d', e similar to the above-mentioned pulses d, e, f' are obtained.
'.

r゛ is obtained.

In the above explanation, the amplification degrees of the differential amplifiers 5 and 6 are assumed to be 1 and 1.
/K, but other settings may be used depending on the relationship with the voltage comparator 7.

Furthermore, in this embodiment, a method of comparing the voltage difference between the OFF phase and +VCC was explained, but the method is not limited to this, and for example, one phase is the voltage of the back electromotive voltage itself, such as (Vl-VA). An optimal energizing pulse can be obtained even if the difference is detected and the time point when the value becomes 1+ is detected, and the present invention is equivalent to that provided that the peak time of the back electromotive force is detected.

(G) Effects of the Invention As described above, according to the present invention, it is possible to directly utilize the back electromotive force generated in the OFF-phase stator winding to obtain the optimum timing for energizing the winding drive switching element. , eliminates the need for a rectifier circuit or time-integrating capacitor, eliminates the forward voltage drop of the rectifying element and its negative effect on the rotational position signal, and eliminates the complicated charging/discharging cycle setting of the time-integrating capacitor, thereby reducing the rotational speed of the permanent magnet rotor. This makes it possible to energize the switching elements at optimal timing from low to high speeds without being affected by the effects of turbulence, resulting in a highly reliable brushless DC motor.

In addition, by always turning 1 phase ON and 52 phases OFF and using the back electromotive force of 0FF and 2 phases, it is possible to easily detect the peak time of the back electromotive voltage of each phase, and further improve reliability. Furthermore, by changing the constant K, the present invention can be easily applied to electric motors where the magnetization waveform of the permanent magnet rotor is different.

[Brief explanation of the drawing]

Fig. 1 is a conceptual diagram of a brushless DC motor and a winding drive switching element according to the present invention, Fig. 2 is a waveform diagram showing optimum energization switching timing using a back electromotive force, and Fig. 3 is a waveform diagram showing the optimum energization switching timing using a back electromotive voltage. Figure 4 is a waveform diagram showing the principle of voltage comparison for OFF-time detection using back electromotive voltage. Figure 5 is for brushless DC motors and winding drive. Actual circuit diagram of the switching element. Figure 6 is a waveform diagram showing the input and output when detecting back electromotive force in the circuit shown in Figure 5. Figure 7 is an example of a circuit for detecting OFF/OFF of back electromotive force. FIG. 8 is a waveform diagram showing the output of the peak detection circuit in FIG. 7, FIG. 9 is a diagram showing the relationship between the back electromotive voltage waveform, the output of the peak detection circuit, and the optimal energization pulse, and FIG. 10 is a relationship diagram between the back electromotive voltage waveform, the output of the peak time detection circuit, and the optimum energization pulse when the winding is energized by the optimum energization pulse. 1... Permanent magnet rotor, A, B, C... Stator winding, 2a, 2b, 2c... Winding drive transistor,
5, 6... Differential amplifier, 7... Voltage comparator,
8... Arithmetic circuit.

Claims (2)

[Claims] (1) A brushless DC motor comprising three-phase stator windings and a switching element for driving the windings connected in series with each of the windings, the series circuit being energized in one direction. A peak time detection circuit is provided to detect the peak time of the back electromotive force generated in each of the stator windings and output a signal, and the switching element is switched when the signal is output from this circuit. brushless DC motor. (2) The energization state of the stator windings is always set to one phase ON and two phases OFF, and the difference between the induced back electromotive force of one phase, which is the OFF phase, and the power supply voltage is detected and a signal is output. A first detection circuit that detects the difference between the induced back electromotive voltage of the other phase and the power supply voltage and outputs a signal is provided, and the output signals from both circuits are compared. OFF by
2. The brushless DC motor according to claim 1, wherein a peak time of a back electromotive voltage of a phase winding is detected.