Sensorless switched reluctance motor

Abstract: A sensorless Switched Reluctance Motor (=SRM) suitable to drive the SRM based on the position of a rotor detected through the detection of the variation of the current of each phase La, Lb, Lc (look at Fig.2a) without providing separate sensors for identifying the position of the rotor, includes a motor driving part (10) for driving the motor by exciting phases La, Lb, Lc of the motor in a predetermined sequence, a differentiating part (20) for differentiating the currents exciting the phases La, Lb, Lc of the motor respectively, an amplifying part (30) for amplifying output voltages from the differentiating part to proper levels, and a comparing part (40) for comparing output voltages of the amplifying part (30) with reference voltages vref1, vref2, vref3 respectively, to generate a high level signal ga, gb, gc in case the output voltage of said amplifying part is higher than the reference voltage vref1, vref2, vref3 and a low level signal ga, gb, gc in case the output voltage of said amplifying part (30) is lower than the reference voltage. The signals ga, gb, gc are applied to the gates G1 to G6 to foresee the position of the rotor. Another embodiment (see Figurs 7) includes a filter (40) instead of a differentiating part (20). A further embodiment (see Figurs 9 and 7b) includes an adding part (100) with a filter (110) instead of a differentiating part (20).

Description: FIELD OF THE INVENTION This invention relates to sensorless switched reluctance motors (hereinafter called "SRM"), more particularly to the sensorless SRMs suitable to drive the SRMs based on the position of a rotor detected through the detection of the variation of the current of each phase without providing separate sensors for identifying the position of the rotor. BACKGROUND OF THE INVENTION FIG. 1 shows rotor and sensors of a conventional SRM. A rotor 1 rotates on the generation of a magnetic field thereof by fixed magnetic poles. A sensor disc 2 is mounted on the same shaft with the rotor 1 to rotate together with the rotor 1. Position detection sensors S1, S2 and S3 detect the condition of the light passing or blocked by the sensor disc 2 on the rotation of the sensor disc 2. A logical circuit 5 generates phase excitation signals PH1, PH2 and PH3 on input of position detection signals from the position detection sensors S1, S2 and S3. The position detection sensors S1, S2 and S3 includes light emitter 3 emitting light and light receiver 4 receiving light respectively. FIG. 2A shows a typical stator and the rotor of the SRM and FIG. 2B shows construction of a sensor disc of a conventional SRM. As shown in FIG. 2B, the sensor disc 2 mounted on the rotor 1 and having projections 9 and cuts 10 rotates together with the rotor 1 when the rotor 1 rotates. The light emitters 3 of the position detection sensors S1, S2 and S3 emit light on the rotation of the sensor disc 2. The light is passed or blocked by the projections 9 and the cuts 10 in the sensor disc 2. Then the light receiver 4 of the position detection sensors S1, S2 and S3 detect the continuous intermission of light. On supply of power to the SRM, the rotor 1 rotates and the sensor disc 2 mounted on the rotor 1 is rotates. Then the emitted light according to the rotation of the sensor disc 2 is detected by the position detection sensors S1, S2 and S3. The light signals from above light emission are converted into a electrical signal. The converted electrical signals are as shown in FIG. 3A. In FIG. 3A, (a) is output wave of the first position detection sensor S1, (b) is output wave of the second position detection sensor S2 and (c) is output wave of the third position detection sensor S3. Referring to FIG. 2B, the output wave of the first position detection sensor S1 is explained. A low level signal is generated during the first 30 degrees because the light receiver 4 can receives no light. The light receiver 4 receives light during next 60 degrees because the light is passed, thus the position detection sensor S1 generates a high level signal. In this way the position detection sensor S1 generates the high or low level signal. When the signals as in FIG. 3A are supplied to the logical circuit 5 for generating phase excitation signals, signals as in FIG. 3B are generated from the logical circuit 5, which drive a gate of a transistor or a base of the transistor resulting in the rotation of the motor. Different signals with the signals as in FIG. 3B can be generated by control signals(not shown) in the logical circuit 5. FIG. 3B shows the rotor 1 rotating in counter clockwise direction. In this case, the power should be supplied to terminal A-A' first, to B-B' next and to C-C' third in FIG. 2A. But, in order to rotate the rotor 1 in clockwise direction, the power should be supplied to terminal A-A', and to C-C' and B-B' in sequence continuously thereafter. FIG. 4 shows changes of inductance of a coil wound on a stator 6 according to change of phase. The inductance of the coil is the largest when there in no difference in phase ie, when the coil wound part of the stator 6 is matched with the projections 9 of the rotor, 1 and the smallest when the coil wound part of the stator 6 is positioned in 45 degrees by the phase difference with the projections 9 of the rotor 1. Generally, excitation occurs in a degrees by the phase difference in the SRM, starting the excitation at the point of inductance increase of the coil. The motor will be braked, if the excitation is started at the point of inductance decrease. In another word, when the signals detected by the light receivers 4 are transmitted to the logical circuit 5, the logical circuit 5 generates the phase excitation signals PH1, PH2, and PH3 as shown in 3B and transmits these signals to terminals A-A', B-B' and C-C' shown in FIG. 2A, respectively to excite A phase winding La, B phase winding Lb and C phase winding Lc in sequence to rotate the rotor 1. However, it has problems in conventional SRM as follow. Various machining processes to mount the position detection sensors on the motors are required in order to detect the position of the rotor, Thus the production processes are complicated that much. And more space to mount the position detection sensors inside or outside of the motors makes the motors larger. Special sensors are required in case the motor should be operated in high temperature where ordinary sensors are not operative. Sensors like photo-interrupt element are unable to operate when the motors contain refrigerant or lubrication oil like compressors. In the prior art disclosed in US-A-4 074 179 the position of a stepping motor is determined by detecting and processing the winding currents. SUMMARY OF THE INVENTION The object of this invention is to provide sensorless SRMs suitable for controlling of the operation of the SRMs through the detection of the changes of the current in each phase without employing the sensor disc and position detection sensors for the detection of the position of a rotor. This and other objects of this invention can be achieved by providing a sensorless switched reluctance motor comprising: a motor driving part for driving the motor by exciting phases of the motor in a predetermined sequence; a filtering part for filtering currents exciting the phases of the motor respectively; a first amplifying part for amplifying output voltages from said filtering part to first proper levels, a first comparing part for comparing output voltages of said first amplifying part with first references voltages respectively, to generate a high level signal in case the output voltage of said first amplifying part is higher than the first reference voltage and a low level signal in case the output voltage of said first amplifying part is lower than the first reference voltage; a delaying part for delaying the output voltages from said filtering part for predetermined times; a second amplifying part for amplifying the output voltages from said delaying part to second proper levels; a second comparing part for comparing output voltages from said second amplifying part with second reference voltages respectively, to generate the high level signal in case the output voltage of said second amplifying part is higher than the second reference voltage and the low level signal in case the output voltage of said second amplifying part is lower than the second reference voltage; and an OR gating part for logically operating the output signals from said first comparing part and the output signals from said second comparing part. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows a rotor and sensors of a conventional SRM. FIG. 2A shows a stator and the rotor of the conventional SRM. and FIG. 2B shows a sensor disc of the conventional SRM. FIG. 3A and 3B show the wave patterns of each parts of FIG. 2. FIGs. 4A, 4B and 4C show changes of inductance of each phase according to the changes of rotation angle. FIG. 5 is a circuit diagram of a sensorless SRM according to this invention. FIGs. 6A to 6I show wave patterns of each parts of FIG. 5. DETAILED DESCRIPTION OF THE INVENTION FIG. 5 is a circuit diagram of a sensorless SRM according to this invention. The sensorless SRM includes a motor driving part 10 for driving a motor through excitation of each phase of the motor in a predetermined sequence, a filtering part 20 for filtering the currents of each phase of the motor driving part 10, a first amplifying part 60a for amplifying phase voltages V1, V2 and V3 transmitted from the filtering part 20 to a proper level, a first comparing part 70a for generating high level signals in case the output voltages VA, VB and VC of the first amplifying part 60a are higher than reference voltages Vrefl, Vref2 and Vref3 through the comparison of the output voltages VA, VB and VC of the first amplifying part 60a with the reference voltage, a delaying part 50 for delaying the phase voltages V1, V2 and V3, transmitted from the filtering part 20 for certain times, a second amplifying part 60b for amplifying the output voltages from the delay part 50 to proper levels, a second comparing part 70b for generating high level signals in case the phase voltages VA', VB' and VC' transmitted from the second amplifying part 60b are higher than reference voltages Vref4, Vref5 and Vref6 through the comparison of the phase voltages with the reference voltages Vref4, Vref5 and Vref6 and low level signals in other cases, and an OR gating part 80 for OR gating the output signals from the first comparing part 70a and the second comparing part 70b. The motor driving part 10 has transistors M1 and M2, M3 and M4, and M5 and M6, diodes D1 to D5, and coils La, Lb and Lc. The transistor M1 and the transistor M2 are connected in series, the drain of transistor M1 is connected with a cathode of the diode D1 of which an anode is earthen and one terminal of the coil La, and a source of the transistor M2 is connected with an anode of the diode D2 of which cathode is connected to a source of the transistor M1 and another terminal of the coil La. In this manner, the pairs of transistors M3 and M4, M5 and M6 are connected with the diodes D3 and D4, and D5 and D6, and coils Lb and Lc respectively. The transistors M1 and M2, M3 and M4, and M5 and M6 are turned on when predetermined signals are applied to gates G1 and G2, G3 and G4, and G5 and G6 of the transistors M1 and M2, M3 and M4, and M5 and M6. In the coils La, Lb and Lc, current flows through the transistors M1 to M6 on the turn-on of these transistors M1 to M6. Changes of inductances of each phase following the rotation of the rotor 1 is occurred as shown in FIG. 4 on the flow of the current in the coils La, Lb and Lc. The filtering part 20 consists of one block having an amplifier OP1 of which inversion terminal(-) is connected with a resistor R10 and a capacitor C5, connected in parallel and non-inversion terminal(-) is earthen, and a high pass filter including a phase current detection resistor R7 connected with a capacitor C4 in series, other block having an amplifier OP2 connected with a capacitor C5, a resistor R11 and a phase current detection resistor R8 connected in the same way as above block, and another block having an amplifier OP3 connected with a capacitor C6, a resistor R12 and a phase current detection resistor R8. Of the motor driving part 10, the drain of the transistor M2 is connected at a node between the capacitor C4 and the phase current detection resistor R7, connected in series in the filtering part 20, the drain of the transistor M4 is connected at a node between the capacitor C5 and the phase current detection resistor R, connected in series, and the drain of the transistor M6 is connected at a nod between the capacitor C6 and the phase current detection resistor R9, connected in series. Upon the operation of each pairs of transistors M1 and M2, M3 and M4, and M5 and M6 in the motor driving part 10, the phase currents iA, iB and iC flow in the phase current detection resistors R7 to R9 of the filtering part 20 as shown in FIGS. 6(A), 6(B) and 6(C), respectively. The currents flowing through the drains of the transistors M2, M4 and M6 are distributed respectively to be filtered by the high pass filters each having a amplifier, a resistor and a capacitor. The output signals -V1, -V2 and -V3 of the amplifiers OP1 to OP3 are inverted through separate inversion process and transmitted to the first amplifying part 60a and the delaying part 50, respectively. The first amplifying part 60a has the amplifiers AMP1 to AMP3, which amplify the output signals of the filtering part 20 to proper levels to transmit it to the first comparing part 70a. The first comparing part 70a has comparators CP1 to CP3, and compares the output signals of the first amplifier 60a with reference voltages Vrefl, Vref2 and Vref3 and generates high level signals in case the output signal is higher than the reference voltages Vrefl, Vref2 and Vref3. The delaying part 50 being an integrator type includes resistors R13 to R15 and capacitors C7 to C9. The signals delayed in the delaying part 50 are transmitted to the second amplifying part 60b. The second amplifying part 60b has amplifiers AMP4 to AMP6. In the second amplifier 60b, the output signals of the delaying part 50 are amplified to proper levels and transmitted to the second comparing part 70b thereafter. The outputs of the first and the second amplifying parts 60a and 60b are as shown in FIGs. 6D, 6E and 6F in which waves with solid line represent the output signals of the first amplifying part 60a and waves with dotted line represent the output signals of the second amplifying part 60b. The second comparing part 70b has comparators CP4 to CP6. The second comparing part 70b, compares the output signals of the amplifying part 60b with reference voltages Vref4 to Vref6 to generate high level signals in case the output voltages are higher than the reference voltages Vref4 to Vref6 and low level signals in case the output voltages are lower than the reference voltages Vref4 to Vref6. The OR gating part 80 has OR gates OR1 to OR3 and receives the output signals from the first and the second comparing parts 70a and 70b. The OR gate OR1 receives the output signals of the comparator CP1 and the comparator CP4, the OR gate OR2 receives the output signals of the comparator CP2 and the comparator CP5, and the OR gate receives the output signals of the comparator CP3 and the comparator CP6. The output signals generated in the OR gates OR1 to OR3 are as shown in FIGS. 6G, 6H and 6I, respectively, and applied to the gates G1 and G2, G3 and G4, and G5 and G6 of the each pairs of transistors M1 and M2, M3 and M4, and M5 and M6 of the motor driving part 10. Thus, the position of the rotor 1 can be detected utilizing the output signals of the OR gates OR1 to OR3. The advance angle of the SRM can be adjusted through the adjustment of the resistances of the resistors R7 to R9 and the capacitances of the capacitors C4 to C6, of the delaying part 50. According to this invention, the sensorless SRM has the advantages of enabling proper operation in unfavorable conditions such as high temperature and the like as well as making the product compact by identifying the position of rotor through the detection of the change of each phase current without providing separate sensors for identifying the position of the rotor of the SRM.

Claims: A sensorless switched reluctance motor comprising: a motor driving part (10) for driving the motor by exciting phases of the motor in a predetermined sequence; a filtering part (20) for filtering currents exciting the phases of the motor respectively; a first amplifying part (60a) for amplifying output voltages from said filtering part (20) to first proper levels, a first comparing part (70a) for comparing output voltages of said first amplifying part (60a) with first references voltages respectively, to generate a high level signal in case the output voltage of said first amplifying part (60a) is higher than the first reference voltage and a low level signal in case the output voltage of said first amplifying part (60a) is lower than the first reference voltage; a delaying part (50) for delaying the output voltages from said filtering part (20) for predetermined times; a second amplifying part (60b) for amplifying the output voltages from said delaying part (50) to second proper levels; a second comparing part (70b) for comparing output voltages from said second amplifying part (60b) with second reference voltages respectively, to generate the high level signal in case the output voltage of said second amplifying part (60b) is higher than the second reference voltage and the low level signal in case the output voltage of said second amplifying part (60b) is lower than the second reference voltage; and an OR gating part (80) for logically operating the output signals from said first comparing part (70a) and the output signals from said second comparing part (70b). A sensorless switched reluctance motor as claimed in claim 1, wherein said first amplifying part (60a) and said second amplifying part (60b) include a plurality of amplifiers (AMP1-AMP6). A sensorless switched reluctance motor as claimed in claim 1, wherein said first comparing part (70a) and said second comparing part (70b) include a plurality of comparators (CP1-CP6). A sensorless switched reluctance motor as claimed in claim 1, wherein said OR gating part (80) includes a plurality of OR gates (OR1, OR2, OR3).

Inventors: LIM JUNG YOUNG, LIM, JUNG YOUNG
Applicants: LG ELECTRONICS INC, LG ELECTRONICS INC.
Application year: 1993
Main classification: H02P8
IPC codes: H02P25, H02P6