Switched reluctance motor without rotor position sensor

Abstract: A sensorless 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 without providing separate sensors for identifying the position of the rotor, includes a motor driving part (90) for driving the motor by exciting phases of the motor in a predetermined sequence, an adding part (100) for adding the currents of each phase ; a low pass filtering part (110) for filtering the output signals from said adding parts (100) ; a first amplifying part (60a) for amplifying output voltages from said low pass filtering part (110) to first proper levels ; a first comparing part (70a) for comparing output voltages of said first amplifying part (60a) with first references voltages respectively, a delaying part (50) for delaying the output voltages from said low pass filtering part (110) 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, 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).

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 a 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. According to US-A-5 051 680, a sensorless reluctance motor (ie a reluctance motor having no rotor position sensor) can be controlled on the basis of the relative magnitude of the phase 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 ; an adding part for adding the currents of each phase; a low pass filtering part for filtering the output signals from said adding parts ; a first amplifying part for amplifying output voltages from said low pass filtering part to first 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 low pass filtering part for predetermined times ; a second amplifying part for amplifying the output voltages from said delaying part to second levels ; a second comparing part for comparing output voltages from said second amplifying part with second reference voltages respectively, to generate a high level signal in case the output voltage of said second amplifying part is higher than the second reference voltage and a 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 combining 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. FIG. 2B shows a sensor disc of the conventional SRM. FIG. 3A and 3B show the wave patterns of each part 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 a first embodiment of this invention. FIGs. 6A to 6E show wave patterns of each part of FIG. 5. FIG. 7 is a circuit diagram of a sensorless SRM according to a second embodiment of this invention. FIG. 8 is a circuit diagram of a sensorless SRM according to a third embodiment of this invention. DETAILED DESCRIPTION OF THE INVENTION FIG. 5 is a circuit diagram of a sensorless SRM according to a first embodiment of this invention. The sensorless SRM includes a motor driving part 90 for driving a motor through excitation of each phase of the motor in a predetermined sequence, an adding part 100 for adding the currents of each phase of the motor driving part 90, a low pass filtering part 110 for filtering the output signals from said adding part 100, a first amplifying part 60a for amplifying phase voltages V1', V2' and V3' transmitted from the filtering part 110 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 Vref1, 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 110 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 90 includes the first transistor Q1 having the collector connected to a supply voltage source Vdc and the emitter connected to the cathode of a diode D6 and one terminal of a coil La, the second transistor Q2 having the collector connected to the other terminal of the coil La and the anode of the diode D7 and the emitter connected to a resistor R17, and a transistor R16 connected to the anode of the diode D6. In this manner, the pairs of transistors Q3 and Q4, and Q5 and Q6 are connected with coils Lb and Lc, diodes D8 and D9, and D10 and D11, and resistors R18 and R19, and R20 and R21. When a high level signal of the pulse width modulation signal as shown in FIG. 6A is applied to the bases of the transistors Q1 and Q2, the transistors Q1 and Q2 are turned on. Then, the passage of current is formed in the sequence of the coil La and the resistor R17 and the current in the resistor R17 increases gradually while the transistors Q1 and Q2 are turning on. At this time, if the low level signal of the pulse width modulation signal is applied to the bases of the transistors Q1 and Q2, the transistors Q1 and Q2 are turned off to form a current discharge flow passage in the sequence of the resistor R16, diode D6, coil La and diode D7. Therefore, the current in the resistor R16 decreases gradually while the transistors Q1 and Q2 are turning off. When the high level signal of the pulse width modulation signal is applied again to the bases of the transistors Q1 and Q2 during the decrease of the current, the transistors Q1 and Q2 are turned on again making the current in the resistor R17 flow again. Repetition of this operation results in the voltage on the resistor R17 as shown in FIG. 6B and the voltage on the resistor R16 as shown in FIG. 6C. Accordingly, due to the direction of the current, the resistor R16 develops negative voltage as shown in FIG. 6C, and the resistor R17 develops positive voltage as shown in FIG. 6B. The adding part 100 includes an inverter 101 connected to the cathode of the diode D6 of the motor driving part 90 for inverting the current in the resistor R16 and the adder 104 for adding the currents flowing through the resistor R22 connected to the inverter 101 and the resistor R23 connected to the emitter of the transistor Q2 of the motor driving part 90. In the same manner, adders 105 and 106 are connected with inverters 102 and 103 and resistors R24 and R25, and R26 and R27. The inverter 101 inverts the voltage on the resistor R16 and transmits the inverted voltage to the adder 104. The adder 104 adds the output signal from the inverter 101 and the voltage on the resistor R17. The output signal of the adder 104 is as shown in FIG. 6D. The filtering part 110 has three low pass filters 111 to 113. The low pass filter 111 filters the output signal of the adder 104 in order to make no discontinuity in the shape of current flowing through the winding of the SRM. The resultant wave pattern is as shown in FIG. 6E. The output signals V1', V2' and V3' of the low pass filters 111 to 113 are 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 110 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 Vref1, Vref2 and Vref3 and generates high level signals in case the output signal is higher than the reference voltages Vref1, 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 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 applied to the gates of the each pair of transistors Q1 and Q2, Q3 and Q4, and Q5 and Q6 of the motor driving part 90. 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 capacitances of the capacitors C4 to C6, of the delaying part 50. FIG. 7 is a circuit diagram of a motor driving part 120 of a sensorless SRM according to a second embodiment of this invention. In FIG. 7, pairs of transistors Q1 and Q2, Q3 and Q4 and Q5 and Q6 are connected in series, the emitters of the transistors Q1, Q3 and Q5 and the collectors of the transistors Q2, Q4 and Q5 and the collectors of the resistors R28, R29 and R30 and coils La, Lb and Lc are connected in series, respectively, the diodes D6, D8 and D10 are connected to the emitters of the transistors, Q1, Q3 and Q5 and the diodes D7, D9 and D11 are connected to the collectors of the transistors Q2, Q4 and Q6 and connected to the voltage supply source Vdc. The collectors of the transistors Q1, Q2 and Q3 are also connected to the voltage supply source Vdc. It is shown that it is possible to detect the current flowing in each phase with only one current detection resistor R28, R29 or R30 during the turn on and off of the pairs of transistors Q1 and Q2, Q3 and Q4, and Q5 and Q6. For example, if the bases of the transistors Q1 and Q2 are applied with high level of the pulse width modulation signals, the transistors Q1 and Q2 are turned-on making the current flow passage in the sequence of the current detection resistor R28 and the coil La. Therefore, the current wave pattern can be detected from the current detection resistor R28 while the transistors Q1 and Q2 are turning on. In this time, if the bases of the transistors Q1 and Q2 are applied with low level of the pulse width modulation signals, the transistors Q1 and Q2 are turned off making the current discharge flow passage in the sequence of the diode D6, the current detection resistor R28, the coil La and the diode D7. Therefore, the current wave pattern can be detected from the current detection resistor R28 while the transistors Q1 and Q2 are turning off. In conclusion, the current wave pattern for the windings of each phase can be detected while one pair of transistors Q1 and Q2 are turning on and off. FIG. 8 is a circuit diagram of a motor driving part 130 of a sensorless SRM according to a third embodiment of this invention. Up to now, the projected part of the stator 6 is wound with single winding as shown in FIG. 2A, but the projected part of the stator 6 having two windings is described in the third embodiment. As shown in FIG. 8, transistors Q7, Q8 and Q9, coils L1, L3 and L5, and current detection resistors R28, R30 and R32 connected in series, and diodes D11, D12 and D13, coils L2, L4 and L6, and current detection resistors R29, R31 and R33 connected in series, are connected between the plus terminal and minus terminal of the supply voltage source Vdc in parallel, and transistors Q7, Q8 and Q9 have the collectors connected with coils L1, L3 and L5 and the emitters connected with the current detection resistors R28, R30 and R32. The coil L1 and coil L2 are in mutual induction, the coil L3 and the coil L4, and the coil L5 and the coil L6, are in mutual induction. The transistor Q7 is turned on when the transistor Q7 is applied with high level of the pulse width modulation signal. The current flow passage is formed in the sequence of the coil L1 and the current detection resistor R28 on the turn on of the transistor Q7. Even though current flows in the coil L2 by the self-induction thereon, current does not flow in the coil L2 due to the diode 11 positioned in the reverse direction. In this condition, if the base of the transistor Q7 is applied with low level of the pulse width modulation signal to turn off the transistor Q7, the current discharge flow passage is formed in the sequence of the current detection resistor R29, the coil L2 and the diode D11. According to this invention, the sensorless SRM has the advantages of enabling proper operation in unfavourable 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. Although the invention has been described in conjunction with specific embodiments, it is evident that many alternatives and variations will be apparent to those skilled in the art in light of the foregoing description. Accordingly, the invention is intended to embrace all of the alternatives and variations that fall within the scope of the appended claims.

Claims: A sensorless switched reluctance motor comprising: a motor driving part (90) for driving the motor by exciting phases of the motor in a predetermined sequence ; an adding part (100) for adding the currents of each phase ; a low pass filtering part (110) for filtering the output signals from said adding parts (100) ; a first amplifying part (60a) for amplifying output voltages from said low pass filtering part (110) to first levels ; a first comparing part (70a) for comparing output voltages of said first amplifying part (60a) with first references voltages (Vref1 ... Vref3), 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 low pass filtering part (110) for predetermined times ; a second amplifying part (60b) for amplifying the output voltages from said delaying part (50) to second levels ; a second comparing part (70b) for comparing output voltages from said second amplifying part (60b) with second reference voltages (Vref4 ... Vref6), respectively, to generate a high level signal in case the output voltage of said second amplifying part (60b) is higher than the second reference voltage and a 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 combining 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 adding part (100) includes a plurality of blocks, each block having an inverter (101) for inverting the current flowing through a first current detecting resistor (R16), said inverter (101) being connected with a cathode of a diode (D6) of said motor driving part (90), and an adder (104) for adding the output signal of said inverter (101) and a voltage applied to a second current detecting resistor (R17) of said motor driving part (90). A sensorless switched reluctance motor as claimed in claim 1, wherein said low pass filtering part (110) includes a plurality of low pass filters (111, 112, 113). A sensorless switched reluctance motor as claimed in claim 1, wherein said motor driving part (90) includes a plurality of blocks (120), each block having one pair of switching means (Q1-Q6) connected in series, current detection resistors (R28-R30) and a coil (La, Lb, Lc) connected in parallel between said one pair of switching means (Q1-Q6). A sensorless switched reluctance motor as claimed in claim 2, wherein said one pair of switching means (Q1, Q2) are positioned between a plus terminal and a minus terminal of a supply voltage source. A sensorless switched reluctance motor as claimed in claim 5, further including a first diode (D6) which has a first anode connected to the minus terminal of the supply voltage source and a first cathode connected to the current detection resistor (R16), and a second diode (D7) which has a second anode connected to a coil (La) and a second cathode connected to the plus terminal of the supply voltage source. A sensorless switched reluctance motor as claimed in claim 1, wherein said motor driving part (90) includes a plurality of blocks (130), each block having a first coil (L1, L3, L5), a switching means (Q7, Q8, Q9) and a first current detection resistor (R28, R30, R32) connected in series between the plus terminal and the minus terminal of the supply voltage source, and a diode (D11, D12, D13), a second coil (L2, L4, L6) and a second current detection resistor (R29, R31, R33) connected in series, to be thereby connected in parallel.

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