Electricity: motive power systems – Switched reluctance motor commutation control
Reexamination Certificate
1999-12-16
2001-04-17
Nappi, Robert E. (Department: 2837)
Electricity: motive power systems
Switched reluctance motor commutation control
C318S132000, C318S434000
Reexamination Certificate
active
06218795
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a rotor magnetic pole position detection device in a DC brushless motor drive control apparatus for performing a sensorless drive control under a pulse width modulation (PWM).
2. Description of the Related Art
A conventional DC brushless motor is generallyarranged so that an output circuit including switching elements and so forth chops a DC power to sequentially pass a current through stationary windings of a plurality of phases, whereby a rotary magnetic field is generated to rotate a rotor. A control signal applied to the output circuit at this time is required to be an appropriate signal corresponding to a rotary state of the rotor. To this end, a positional sensor such as a Hall-effect element is provided to detect the rotational position of the rotor. However, recent study and development has been directed to a brushless motor which has a structure of detecting the rotary position of the rotor without using such a positional sensor as a Hall-effect element.
Explanation will be made below as to a principle of detecting the rotary position of the rotor with use of FIG.
12
.
FIG. 12
shows voltage waveforms corresponding to one phase under no PWM control in the prior art. In
FIG. 12
, reference numeral
43
denotes a reference voltage,
44
denotes a waveform of a terminal voltage,
45
denotes an output of a comparator for comparing the reference voltage
43
and the terminal voltage, and
54
denotes a zero-cross point. The principle of detecting the rotary position of the rotor is as follows. The terminal voltage generated in the stationary winding by rotation of the rotor is detected. A phase of the induced voltage in the stationary winding at the zero-cross point (i.e., a positional signal indicative of a predetermined rotary position of the rotor) is detected based on the timing at which the detected terminal voltage coincides with the preset reference voltage.
In the above case, when a continuous ON signal is output during its energization period of the stationary winding as a control signal, the terminal voltage of the stationary winding can be continuously detected. In the PWM control system, however, it becomes impossible to detect the terminal voltage of the stationary winding as it is. In other words, when the PWM control signal which repeats ON/OFF at a fast period during the energization period of the stationary winding is applied, the terminal voltage of the stationary winding can also be detected intermittently as to cross the reference voltage many times as shown in FIG.
13
A. Therefore, it is impossible to detect the zero-cross point
54
of the induced voltage, just as it is.
FIG. 13A
shows waveforms of voltages corresponding to one phase under the PWM control in which a conventional lower arm is switched and waveforms under the PWM control.
FIG. 13B
shows waveforms of voltages corresponding one phase under the PWM control in which a conventional upper arm is switched.
FIG. 15
is a major part of a conventional DC brushless motor drive control device.
The above will be more detailed. As shown in
FIG. 15
, a DC brushless motor includes a stator having stator coils SU, SV and SW of three phases U, V and W, and a rotor R of a permanent magnet. The DC brushless motor includes a unit (which is called as “upper arm” hereinafter) which has three PNP-type transistors Tr
1
, Tr
2
and Tr
3
as switching elements and three flywheel diodes D
1
, D
2
and D
3
connected in parallel to these transistors, and a unit (which is called as “lower arm” hereinafter) which has three NPN-type transistors Tr
4
, Tr
5
and Tr
6
and three flywheel diodes D
4
, D
5
and D
6
connected in parallel to these transistors, as driving circuit for performing the PWM control. The ends of the stator coils SU, SV and SW of the phases U, V and W are connected. The other ends of the stator coils SU, SV and SW are connected to the common connection points between the pairs of the PNP-type transistors Tr
1
, Tr
2
and Tr
3
and the NPN-type transistors Tr
4
, Tr
5
and Tr
6
, respectively. The collectors and emitters of the arms are connected to two bases, and a common connection point ON to the both arms is arranged to output ½ of a voltage between the buses.
When such a DC brushless motor is controlled in the PWM manner, this can be realized by performing the PWM control by switching either one of the upper and lower arms using logical operating means such as a micro-computer. The terminal voltage waveform
46
shown in
FIG. 13A
shows a waveform which is obtained when the lower arm is subjected to the PWM control. When the upper arm is subjected to the PWM control, on the contrary, the terminal voltage waveform shown in
FIG. 13B
is obtained. To put it simply, these two terminal voltages are inverted mutually with respect to the reference voltage, so that they are basically the same. Accordingly, in view of the fact that the zero-cross point
54
of the induced voltage can not be detected by intermittently detecting the reference voltage crossed many times under the PWM control, the PWM control in which the upper arm is switched is the same as the PWM control in which the lower arm is switched.
Though the above explanation has been briefly made, more detailed explanation will be directed to the waveforms generated when the upper and lower arms are switched. Explanation will first be made as to when the upper arm is subjected to the PWM control. When one (e.g., Tr
1
) of the three PNP-type transistors as the switching elements in the upper arm is switched (ON/OFF) under the PWM control, a current flows through the stator coils SU and SV during an ON state of the NPN-type transistor Tr
5
in the lower arm. At this time, the voltage waveform becomes one shown in duration {circle around (1)} of the terminal voltage waveform in FIG.
13
B. That is, when the switching element is turned ON under the PWM control, a voltage lower by a voltage drop of the element Tr
1
than a (+) power voltage of a power source E appears as a U-phase terminal voltage. When the switching element is turned OFF under the PWM control, the electric energy accumulated in the stator coils SU and SV is discharged through the flywheel diode D
4
. Next, while either one of the remaining two switching elements in the upper arm is in its ON state, the voltage waveform becomes either one of the voltage waveforms in two duration {circle around (2)} in FIG.
13
B. That is, when either one of the PNP-type transistors Tr
2
and Tr
3
as the switching elements is switched (turned ON or OFF) and is in its ON state and when either one of the NPN-type transistors Tr
5
and Tr
6
not connected to the elements Tr
2
and Tr
3
is in its ON state, the induced voltage appears in the terminal of the stator coil SU. When the above switching element is switched to its OFF state, the U-phase terminal voltage shows a neutral point of the terminal voltage between the V- and W-phase terminal voltages (i.e., a value nearly equal to a (−) power voltage of the power source E), so that the voltage in duration {circle around (2)} has such a shape that its pulse height increases or decreases with time. Further, when the NPN-type transistor Tr
4
in the lower arm is turned ON and the PNP-type transistor Tr
2
is turned ON or OFF, a voltage higher by a voltage drop of the element than the (−) power voltage appears and has such a waveform shown in duration {circle around (3)} in FIG.
13
B.
Explanation will then be made as to a case where the lower arm is subjected to the PWM control. When one (e.g., Tr
4
) of the three NPN-type transistors as switching elements in the lower arm is switched (turned ON or OFF) under the PWM control, a current flows through the stator coils SU and SV during the ON state of the PNP-type transistor Tr
2
in the upper arm. At this time, a voltage waveform becomes one shown in duration {circle around (1)} of the terminal voltage waveform in FIG.
13
A. That is, when this switching element is turned ON under th
Duda Rina I.
Matsushita Electric - Industrial Co., Ltd.
Nappi Robert E.
Stevens Davis Miller & Mosher LLP
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