Method and system for determining the position of an electric motor

Abstract

Disclosed are methods and apparatus for determining the position of a rotor in an electric motor, such as a three-phase motor, by driving a pair of phases with complementary signals and examining the voltage of a floating phase in the phases to determine first and second sectors in which a first one of the magnetic poles of the rotor may be located. Embodiments may also include driving first and second currents to the first and second sectors, and analyzing the time at which each of the first and second currents reaches a threshold to identify the sector. Embodiments may also include applying torque to the motor to move the rotor by driving at least one phase pair with corresponding signals having the same phase and different duty cycles, for determining the rotor's position.

Description

[0001] This application is a divisional application of the invention patent application with the application date of May 30, 2017, entitled “Method and system for determining the position of an electric motor” and application number 201780037072.5. Background Art

[0002] Circuits for controlling and driving brushless DC (BLDC) motors are known. It is also known that it may be desirable to know the motor's position at startup. Conventional BLDC motor control techniques can use BEMF (back electromotive force) information for position estimation. However, at zero speed, such as when the motor is starting, BEMF information is unavailable. Another conventional starting technique is to drive the motor in open loop (e.g., align and run) without a position estimate, which can result in reverse rotation during startup. Furthermore, this technique can increase startup time if a relatively conservative startup profile is selected, or make motor starting unreliable if an aggressive startup profile is selected. A known alternative technique for motor starting is called Initial Position Detection (IPD), commonly used in hard disk drives, for example. Current is injected into six combinations of the three stator phases, with one of the six combinations having the minimum inductance indicating the rotor's north pole. However, due to the torque generated during current injection, conventional IPD techniques are noisy in practice. Furthermore, because six relatively close signals are compared, accuracy can be poor. Summary of the Invention

[0003] Embodiments of the present invention provide methods and apparatus for detecting motor position at zero or low motor speeds using complementary drive and sense (CDD) signals. Embodiments may be suitable for three-phase BLDC motors. Inductance differences are detected based on the motor position after which the inductor saturation will be detected from the magnet polarity. In an embodiment, the motor position relative to the magnet can be determined within a given range (e.g., thirty degrees) at zero torque. Conventional motor position techniques may have a significantly larger range, such as sixty degrees. In one embodiment, complementary drive and sense - polar axis current injection (CDD-PACI) provides motor position detection. In another embodiment, complementary drive and sense - slight movement (CDD-slight movement) provides motor position.

[0004] In an embodiment, acoustic noise and vibration are significantly reduced compared to conventional motor position detection techniques because a high frequency signal, such as 25 kHz, is used. In addition, the relatively high frequency signal reduces the time required to detect the motor position.

[0005] In one aspect of the present invention, a method for determining the position of a rotor in a three-phase motor having phase A, phase B, and phase C includes: determining first and second sectors in which a first one of the magnetic poles of the rotor may be located by driving phase pairs AB, AC, and BC with complementary signals and checking the voltage of a floating phase in the phases, wherein the first and second sectors are relatively positioned; and driving first and second currents to the first and second sectors, and analyzing the time at which each of the first and second currents reaches a threshold to identify which of the first and second sectors is aligned with the first one of the magnetic poles of the rotor.

[0006] A method also includes one or more of the following features: the time corresponds to a level of inductor saturation, the motor includes a BLDC motor, the sectors include twelve sectors, a first and a second of the sectors spanning approximately thirty degrees, driving phase pairs AB, AC, and BC with complementary signals having a duty cycle of approximately fifty percent, generating substantially zero torque by driving phase pairs AB, AC, and BC with the complementary signals, driving a first current in a first direction and a second current in a second direction opposite in phase to the first direction, encoding an output of a comparison of corresponding floating voltages and a voltage threshold during driving phase pairs AB, AC, and BC with the complementary signals, and / or determining a first and a second of sectors in which a first of the rotor poles may be located from the encoded output.

[0007] In another aspect of the present invention, a system for determining the position of a rotor of a three-phase motor includes: a first module that generates a drive signal for the three-phase motor; a second module that is configured to determine first and second sectors in which a first one of the magnetic poles of the rotor may be located by driving phase pairs AB, AC, and BC with complementary signals and checking the voltage of a floating phase in the phases, wherein the first and second sectors are relatively positioned; and a third module that generates signals to drive first and second currents to the first and second sectors and analyzes the time when each of the first and second currents reaches a threshold to identify which of the first and second sectors is aligned with the first one of the magnetic poles of the rotor.

[0008] A system may also include one or more of the following features: the system includes an IC package having first, second, and third outputs for providing the drive signal for each of the three phases, the time corresponding to the level of inductor saturation, the motor including a BLDC motor, the sectors including twelve sectors, the first and second of the sectors spanning approximately thirty degrees, the system is further configured to drive phase pairs AB, AC, and BC using complementary signals having a duty cycle of approximately fifty percent, generating substantially zero torque by driving phase pairs AB, AC, and BC using the complementary signals, the system is further configured to drive a first current in a first direction and a second current in a second direction opposite to the first direction, the system is further configured to encode an output of a comparison of corresponding floating voltages and voltage thresholds during driving phase pairs AB, AC, and BC using the complementary signals, and / or the system is further configured to determine, from the encoded output, a first and second sector in which a first one of the rotor poles may be located.

[0009] In another aspect, embodiments of the present invention provide methods and apparatus for detecting motor position at zero or low motor speeds using complementary drive and sense (CDD) signals. Embodiments may be suitable for three-phase BLDC motors. Inductance differences are detected based on the motor position after which the inductor saturation will be detected from the magnet polarity. In an embodiment, the motor position relative to the magnet can be determined within a given range (e.g., thirty degrees) at zero torque. Conventional motor position techniques may have a significantly larger range, such as sixty degrees. In one embodiment, complementary drive and sense - polar axis current injection (CDD-PACI) provides motor position detection. In another embodiment, complementary drive and sense - slight movement (CDD-slight movement) provides motor position.

[0010] In an embodiment, acoustic noise and vibration are significantly reduced compared to conventional motor position detection techniques because a high frequency signal, such as 25 kHz, is used. In addition, the relatively high frequency signal reduces the time required to detect the motor position.

[0011] In one aspect of the present invention, a method for determining the position of a rotor in a three-phase motor having phase A, phase B, and phase C includes: determining first and second sectors in which a first one of the magnetic poles of the rotor may be located by driving phase pairs AB, AC, and BC, respectively, with complementary signals and checking the voltage of a floating phase in the phases, wherein the first and second sectors are relatively positioned; and applying torque to the motor by driving at least one phase pair with corresponding signals having the same phase and different duty cycles to move the rotor by a given amount from the rotor position in the first or second sector for determining the position of the rotor.

[0012] A method also includes one or more of the following features: moving the rotor a given amount by determining when a voltage of a floating phase of the phases is less than a threshold, driving the phase pairs with complementary signals to confirm the rotor position after the rotor is moved the given amount, the motor comprising a BLDC motor, the sectors comprising twelve sectors, a first and a second of the sectors spanning approximately thirty degrees, driving the phase pairs AB, AC, and BC with complementary signals having a duty cycle of approximately fifty percent, encoding an output of a comparison of the corresponding floating voltages and a voltage threshold during driving the phase pairs AB, AC, and BC with the complementary signals, the given amount corresponding to approximately 45 degrees, determining the rotor position within thirty degrees, and / or moving the rotor clockwise by the given amount from the rotor position in the first of the sectors, or moving the rotor counterclockwise by the given amount from the rotor position in the second of the sectors.

[0013] In another aspect of the present invention, a system for determining the position of a rotor of a three-phase motor includes: a first module that generates a drive signal for the three-phase motor; a second module configured to determine a first and a second sector in which a first one of the magnetic poles of the rotor may be located by driving phase pairs AB, AC, and BC with complementary signals and checking the voltage of a floating phase in the phases, wherein the first and the second in the sectors are relatively positioned; and a third module configured to apply torque to the motor by driving at least one phase pair with corresponding signals of the same phase and different duty cycles to move the rotor by a given amount from the rotor position in the first or second of the sectors for determining the position of the rotor.

[0014] A system may also include one or more of the following features: the system is further configured to move the rotor a given amount by determining that the voltage of the floating phase in the phases is less than a threshold, the system is further configured to drive the phase pair using complementary signals to confirm the rotor position after the rotor moves the given amount, the motor includes a BLDC motor, the sectors include twelve sectors, the first and second of the sectors span approximately thirty degrees, the system is further configured to encode the output of the comparison of the corresponding floating voltage and the voltage threshold during driving the phase pairs AB, AC and BC using complementary signals, the given amount corresponds to approximately 45 degrees, the rotor position is determined within thirty degrees, and / or the system is further configured to move the rotor clockwise by the given amount from the rotor position in the first of the sectors, or to move the rotor counterclockwise by the given amount from the rotor position in the second of the sectors. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The foregoing features of the present invention, as well as the invention itself, may be more fully understood from the following description of the accompanying drawings, in which:

[0016] Figure 1 is a schematic representation of a motor control circuit that can determine the position of a motor according to an exemplary embodiment of the present invention;

[0017] Figure 1A An exemplary equivalent circuit for a portion of a three-phase electric motor is shown;

[0018] Figure 1B Is used to measure Figure 1 A schematic representation of a circuit for phase signals in a circuit;

[0019] Figure 2 is a schematic representation of the rotor associated with phases A, B and C;

[0020] Figure 2A is a schematic representation of the sector in which the rotor position is located;

[0021] Figure 3 is a schematic representation of the magnets and flux associated with phases A, B, and C;

[0022] Figure 4A is a schematic representation of a switching element that can provide a phase signal;

[0023] Figure 4B is a waveform diagram of an exemplary signal capable of driving phases A and B while leaving phase C floating;

[0024] Figure 5A is a schematic representation of a switching element that can provide polar current injection and a comparator;

[0025] Figure 5B is a schematic representation of the sectors corresponding to the north or south poles aligned with the phases of the motor;

[0026] Figure 6 is a waveform diagram of a signal for complementary drive and detection (CDD) of a motor position;

[0027] Figure 7A It shows Figure 6 Further details of the signals in the waveform diagram and quadrant representation for possible rotor positions;

[0028] Figure 7B It shows Figure 6 Further details of the signals in the waveform diagram and quadrant representation for possible rotor positions;

[0029] Figure 8 is a waveform diagram of a signal used for complementary drive and detection (CDD) to detect the position of the motor;

[0030] Figure 9 is a waveform diagram of the signal used for polar axis current injection to determine the motor position after CDD;

[0031] Figure 10 is a flow chart of an exemplary sequence of steps for determining motor position;

[0032] Figure 11 is a schematic representation of determining the position of a motor including moving the rotor by applying torque from known possible positions;

[0033] Figure 12 is a waveform diagram illustrating signals used to determine possible motor positions, apply torque to move the motor, and determine the motor position;

[0034] Figure 13 is a flow chart of an exemplary sequence of steps for determining possible motor positions, applying torque to move the motor, and determining the motor position; and

[0035] Figure 14 is a schematic diagram of an exemplary computer that can perform at least a portion of the processes described herein. DETAILED DESCRIPTION

[0036] Figure 1 An exemplary motor control circuit 102 is shown in accordance with an exemplary embodiment of the present invention, coupled to a motor 104 for providing BLDC motor starting using complementary drive and detection (CDD). The motor 104 is shown to include three windings 104a, 104b, 104c, which can be depicted as respective equivalent circuits having an inductor in series with a resistor and in series with a back electromotive force (BEMF) voltage source. For example, winding A 104a is shown to include an inductor 130 in series with a resistor 131 and in series with a back electromotive force voltage source VA 136. Detailed description of the exemplary motor control circuit 102 is provided below in conjunction with FIG. Figure 1A Exemplary equivalent circuits are more fully described.

[0037] The motor control circuit 102 includes a speed demand generator 107 that is coupled to receive an external speed demand signal 106 from outside the motor control circuit 102. The external speed demand signal 106 can be in one of a variety of formats. Typically, the external speed demand signal 106 indicates a speed of the motor 104 requested from outside the motor control circuit 102.

[0038] The speed demand generator 107 is configured to generate a speed demand signal 107a. The pulse width modulation (PWM) generator 108 is coupled to receive the speed demand signal 107a and is configured to generate a PWM signal having a duty cycle controlled by the speed demand signal 107a. The PWM generator 108 is also coupled to receive a modulation waveform from the modulation signal generation module 146. The PWM signal is generated to have modulation characteristics (i.e., a relatively time-varying duty cycle) according to the modulation waveform.

[0039] The motor control circuit 102 also includes a gate driver circuit 110 coupled to receive a PWM signal and configured to generate PWM gate drive signals 110a, 110b, 110c, 110d, 110e, 110f to drive six transistors 112, 114, 116, 118, 120, 122 arranged as three half-bridge circuits 112 / 114, 116 / 118, 120 / 122. The six transistors 112, 114, 116, 118, 120, 122 operate in saturation to provide three motor drive signals VoutA 124, VoutB 126, and VoutC 128 at nodes 102d, 102c, and 102b, respectively. It will be appreciated that any suitable configuration of switching elements may be used to provide the motor drive signals.

[0040] The motor control circuit 102 may also include a signal processing module 143, which may include a CDD module 145 for processing signals from a sensor module 147. As described more fully below, the effects of various applied phase signals may be used to determine rotor position. For example, the sensor module 147 may be configured to receive a back EMF signal (e.g., may be coupled to receive one or more of the motor drive signals 124, 126, 128, including a back EMF signal that may be directly observed when the motor windings 104a, 104b, 104c are not driven and the corresponding winding currents are zero).

[0041] Figure 1B An exemplary sensor module 147 is shown having a first comparator 160 having a first input coupled to a switching element pair and a second input coupled to a threshold. As described more fully below, the first comparator output 162 determines whether the threshold is exceeded. As described more fully below, a second comparator 164 has a first input, such as VBB / 2, and a floating phase in phase.

[0042] Reference again Figure 1The signal processing module 143 is configured to generate a position reference signal indicating a rotational reference position of the motor 104. The modulation signal generation module 146 is coupled to receive the position reference signal and is configured to change the phase of the modulation waveform provided to the PWM generator 108.

[0043] The motor control circuit 102 may be coupled to receive a motor voltage VMOT, or VM for short, at a node 102 a. During the time when the upper transistors 112 , 116 , 120 are on, the motor voltage VMOT is supplied to the motor through the transistors 112 , 116 , 120 . It should be understood that when the transistors 112 , 116 , 120 are on and supplying current to the motor 104 , there may be a small voltage drop (e.g., 0.1 volt) across the transistors 112 , 116 , 120 .

[0044] In one aspect of the present invention, signal processing module 143 controls motor startup, including complementary drive and detection (CDD). In one embodiment, the position of the rotor in a three-phase motor having phases A, B, and C can be located within the first and second of a plurality of sectors by sequentially driving phase pairs AB, AC, and BC using complementary signals and examining the voltage of the floating phase in the phases. In one embodiment, CDD-PACI determines motor position. Following CDD, once the rotor position is determined to be within one of two sectors, the system drives corresponding first and second phase currents toward the first and second sectors and analyzes the time at which each of the first and second currents reaches a threshold to identify which of the first and second sectors is aligned with the first of the rotor's magnetic poles. The driving current generates magnetic flux such that, depending on the rotor polarity, the permanent magnet flux increases or decreases the flux generated by the current. This enhances or prevents inductance saturation, which can be used to determine the rotor position between two oppositely positioned sectors. In one embodiment, the time at which the drive current reaches the threshold can be measured to identify the rotor position.

[0045] Figure 1B An exemplary equivalent circuit for the windings of a three-phase motor is shown. At zero rotor speed, the sum of the BEMFs is zero. The sum of the phase currents is always zero, i.e., I A +I B +I C = 0. If the system is driven as follows: U A =VBB, V B = GND and C phase floating (I A =-I B =I and Ic=0), then Uc=VBB / 2+I*(R B -R A ) / 2+dI / dt*(L B -LA ) / 2. If R A = R B and L A = L B , then Uc = VBB / 2. However, if L A ≠ L B , U C will be higher or lower than VBB / 2. If a current with a higher frequency and zero average amplitude is selected, then a zero average drive torque will be generated. Since the di / dt associated with the inductor can be large, the signal of interest can be detected as:

[0046] If L A > L B , then UC < VBB / 2, if L A < L B , then U C > VBB / 2.

[0047] Figure 2 Illustrates the rotor magnet 200 divided into four sectors / quadrants I, II, III, IV, relative to three phases A, B, C, which can have a first pair I, III and a second pair II, IV. In an embodiment, the four quadrants I, II, III, IV are defined by the midline between phase A and phase B. The inductance difference between phase A and phase B will be successively positive and negative. By measuring the voltage polarity between Uc (floating) and VBB / 2, for example, a specific quadrant pair corresponding to the rotor position relative to the magnet can be identified. That is, it can be determined that the rotor position is within the quadrant pair I, III or within the pair II, IV. In a similar manner, phases A and C can be driven and then phases B and C to determine additional information by detecting the voltage of the floating phase. Figure 2A Illustrates the possible rotor positions divided by quadrants for each of the three phases, resulting in 12 sectors, each sector spanning 30 degrees. That is, the quadrants for each of the three phases are offset from each other to provide 12 sectors. The rotor position can be determined to be within one of the 12 sectors, as described more fully below.

[0048] Figure 3 Illustrates an exemplary position of the magnetic pole / rotor relative to the motor phases A, B, C. For the illustrated position, the system is capable of driving current from phase A to phase C, which generates a magnetic flux 301 from A to C. The permanent magnet flux then increases the flux in phases A and C, which results in earlier inductance saturation. The system can drive current from C to phase A, which generates a magnetic flux from C to A. The permanent magnet flux then decreases the flux 302 in phases A and C, which results in later inductance saturation.

[0049] It should be understood that magnetic saturation refers to the state reached when increasing the applied winding current can no longer further increase the magnetization of the material, so the total magnetic flux density B tends to be more or less stable. Note that it may continue to increase very slowly due to the magnetic permeability of the vacuum. As the current approaches the saturation current, the equivalent inductance decreases significantly. Therefore, the current will increase significantly when approaching the saturation current.

[0050] If current is driven from C to A, this generates magnetic flux from C to A, and the permanent magnet flux reduces the flux 302 from C to A. This results in a reduction in flux from phases A and C, delaying inductor saturation. It should be understood that if the rotor polarity is opposite to that shown, i.e., S pole is on top, then the conclusions about delayed / earlier inductor saturation are also opposite to those described above.

[0051] In an embodiment, when the rotor position has two possible positions 180 degrees apart, current can be injected into the phase to generate a magnetic flux that is aligned with or opposite to the permanent magnet flux. By detecting the difference in saturation levels, the two possible positions can be resolved. In an embodiment, the time it takes for each current to reach a given threshold can be used to determine the rotor position. It should be noted that these current drive modes do not generate any significant motor torque.

[0052] Figure 4A and 4B An exemplary embodiment of complementary drive and detection (CDD) implementing zero torque position detection according to an exemplary embodiment of the present invention is shown. Figure 4A shows a simplified circuit which can be similar to Figure 1 A switching configuration having corresponding pairs of switching elements is used to generate signals for phases A, B and C. It will be appreciated that the phase signals may be generated using any suitable configuration of switching elements.

[0053] exist Figure 4B As can be seen from FIG, complementary drive signals DrA, DrB with a 50% duty cycle (phase difference of 180 degrees) are applied to phases A and B. Figure 4A As shown, the comparator CC has a first input as the floating phase C and a second input as VBB / 2. With this arrangement, the voltage of the floating phase C can be compared with VBB / 2 for use in the quadrant pair ( Figure 2A ) defines the rotor position. It should be understood that the solid and dashed lines indicating the current flowing through the switches and the complementary drive signals DrA and DrB correspond to each other. For example, when the drive signal DrA decreases and is low, current flows through the lower switch of the Phase A switch pair and through the upper switch of the Phase B switch pair. Since Phase C is floating, no current is generated from the drive signals DrA and DrB.

[0054] Then by successively driving phases AC and then BC, and measuring the floating phase, the rotor position can be located within two of the twelve sectors. As mentioned above, the twelve sectors are formed by three quadrants offset by 120 degrees, where Figure 2 The four quadrants I, II, III, and IV are defined by the midline between phases A and B. Figure 2A The additional sectors are bounded by the midlines of phases B and C and the midlines of phases A and C.

[0055] Figure 5A A polar current injection circuit 500 and a comparator 502 are shown having a first input as a threshold and a second input as a drive current. Figure 5B The position of the rotor's north (or south) pole relative to a phase, such as phase A, is shown as being within one of first and second sectors S0, S6, which can span 30 degrees, with the first and second sectors S0, S6 being 180 degrees apart from each other. Current can be driven toward two possible positions (sectors S0, S6). One of the currents will reach the threshold of comparator 502 first. The current that reaches the threshold at comparator 502 faster corresponds to the rotor being aligned with the magnet's north pole because saturation will be reached earlier due to alignment with the north pole.

[0056] Figure 6 Exemplary waveforms for implementing complementary drive and detection (CDD) and polar axis current injection (PACI) according to an exemplary embodiment of the present invention are shown. During CDD, in the exemplary waveforms, as described above, first phases A and B are driven in a complementary manner, then phases B and C are driven in a complementary manner (phase C voltage is not shown), and then phases A and C are driven to determine which of two opposing sectors of twelve sectors the rotor is located in. In the illustrated example, during the AB portion of CDD, phase C is floating and the phase A and phase B voltages are energized. The phase A voltage waveform includes a high frequency signal during the AB and AC portions of CDD. The phase B voltage waveform includes a high frequency signal during the AB and BC portions of CDD. It will be understood that substantially zero torque is generated during CDD.

[0057] Once the CDD is complete, PACI can determine which of the two sectors identified in the CDD the rotor is located in. During the first portion of PACI, the Phase A current is driven in a first direction until the VBB current reaches the PACI threshold TH. The time it takes for the VBB current to reach the PACI threshold TH is measured. During the second portion of PACI, the Phase A current is driven in the opposite direction, and the time it takes for the VBB current to reach the PACI threshold TH is measured. The minimum time for the VBB current to reach the PACI threshold TH corresponds to the sector where the magnet's north pole is close to the Phase A sector.

[0058] Figure 7A and 7B shows more details of the CDD that drives the phase A and B voltages in a complementary manner as described above. In Figure 7A , the floating phase C voltage is below VBB / 2 when the phase A voltage is high, and above VBB / 2 when the phase B voltage is high. The phase A current rises when the phase A voltage is high and falls when the phase A voltage is low. In Figure 7B , the phase C voltage is above VBB / 2 when the phase A voltage is high, and below VBB / 2 when the phase B voltage is high. When phase A is driven high, if Uc > VBB / 2, the N pole of the rotor is in quadrant I or III ( Figure 7B [[ID=⑨]]). If Uc < VBB / 2, then the N pole of the rotor is in quadrant II or IV ( Figure 7A ).

[0059] Figure 8 shows the phase A, B, and C voltage signals and the phase A current signal for the CDD. During the first (AB) part, the phase A and B voltage signals are complementary, and the phase C voltage floats, as described above. During the second (BC) part of the CDD, the phase B and C voltage signals are driven in a complementary manner, and the phase A signal floats. During the third (AC) part of the CDD, the phase A and C voltage signals are driven in a complementary manner, and the phase B voltage signal floats. As described above, the floating signal during each CDD part can be compared with a threshold (e.g., VBB / 2).

[0060] In the waveform diagram shown, during the AB CDD part, when the phase A voltage is high, it can be seen that Uc < VBB / 2, encoded as 0. Similarly, during the BC part, when the phase B voltage is high, U A < VBB / 2 is encoded as 0, and during the AC part, when the phase C voltage is high, U B > VBB / 2 is encoded as 1. In an embodiment, a floating voltage below VBB / 2 can be encoded as logical "0", and a floating voltage greater than VBB / 2 can be encoded as logical "1". In the illustrated example, Uc < VBB / 2, U A < VBB / 2, and U B > VBB / 2 correspond to "001", where a six-line look-up table can be used to check the rotor position in degrees. Table 1 below is an exemplary look-up table. For Figure 8 example, the code 001 corresponds to the rotor position at 30 degrees or 210 degrees relative to phase A in the sector.

[0061] Table 1

[0062] 001 30 or 210 011 60 or 240 010 90 or 270 110 120 or 300 100 150 or 330 101 180 or 0

[0063] Figure 9 shows Figure 8 an exemplary waveform for PACI after the CDD waveform of. Phase C (not shown) is driven high, and phase A is driven low. The phase A current decreases while the phase C current (not shown) increases. The VBB current increases until the PACI threshold is reached. The time when the VBB current reaches the PACI threshold is time T1. After the current stabilizes to the default level, the phase A voltage is driven high and phase C is driven low. The phase A current, contrary to before, e.g., increases, and the VBB current increases until the PACI threshold is reached at time T2. In the illustrated embodiment, T1 < T2, which indicates that the N pole is closer to phase A and opposite to phase C.

[0064] Figure 10 shows an exemplary sequence of steps for determining the position of a motor according to an exemplary embodiment of the present invention. In step 1000, the first pair of phase voltages in a three-phase motor are driven in a complementary manner while the other phase voltage is floating and being monitored. In step 1002, the second pair of phase voltages are driven in a complementary manner while the other phase voltage is floating and being monitored. In step 1004, the third pair of phase voltages are driven in a complementary manner while the other phase voltage is floating and being monitored. In step 1006, it is determined that the position of the rotor is within two of a plurality of sectors. In an embodiment, the two possible sector positions of the rotor are 180 degrees apart. In step 1008, a first current is driven in a first direction corresponding to the first of the two possible sector positions. In step 1010, the first time when the current of the floating phase reaches the threshold is determined. In step 1012, a second current is driven in a direction corresponding to the other of the two possible sector positions. In step 1014, the second time when the current of the floating phase reaches the threshold is determined. In step 1016, the first time and the second time are compared with each other. In step 1018, the sector position of the rotor is determined based on whether the first time or the second time is less. As described above, the current that takes less time to reach the threshold corresponds to being aligned with the N pole of the rotor due to earlier saturation.

[0065] Exemplary embodiments of the present invention can provide advantages over conventional motor position techniques. For example, exemplary embodiments are relatively quiet and fast and do not generate any significant acoustic noise or vibration because a higher frequency signal, such as 25kHz, is used. The high frequency signal also reduces the time required for position detection. In addition, in an embodiment, the PACI phase conducts two pulses, where a conventional IPD requires six pulses, thereby generating less torque. In an exemplary embodiment, in the worst case, only 26% (15 degrees) of the maximum torque (sin 15=0.26) is achieved using the same amount of current. In addition, a higher position resolution, such as 30 degrees, is provided compared to the 60-degree resolution of a conventional IPD. Moreover, embodiments of the present invention can provide better accuracy because the two pulses aligned with or opposite to the rotor's N pole provide a distinction for inductor saturation. In addition, embodiments of the present invention can accept larger motor tolerances because the two pulses are applied to the same winding, thereby offsetting unbalanced motor winding errors.

[0066] In another aspect of the present invention, the motor position is determined to be within a number of sectors. The motor position is then modified by applying torque to the motor to move the rotor from an initial position, referred to herein as a CDD slight shift. In one example, the applied torque moves the rotor 45 degrees or 135 degrees from the initial position. In an embodiment, the drive signals that generate the torque are phase-complementary, but rather than having a 50% duty cycle as described above, they are floating in the third phase. The asymmetric nature of the complementary signals generates the torque. The voltage on the floating phase can be monitored, allowing the different floating phases to be evaluated once a zero crossing is detected. The rotor position can then be determined from the two possible sector positions.

[0067] Figure 11An example of applying torque to a motor to determine rotor position is shown. In an embodiment, CDD is used to identify the initial first and second possible sectors IS0 and IS1 where the rotor may be located. The rotor position can be slightly shifted by driving the motor to different positions. For example, the Phase C voltage signal can be driven to 55%, the Phase B voltage can be driven to 45%, and Phase A can be left floating. As shown in the illustrative example, the motor is driven to the 2 o'clock position DP1. When the output of a comparator with the floating Phase A voltage and VBB / 2 as inputs crosses zero, the rotor position is either the first position DP1 or the second position DP2. In an embodiment, the first and second positions DP1 and DP2 are 90 degrees apart. As can be seen, if the rotor is initially located in the first possible sector IS0, the rotor is driven to the first position DP1. If the rotor is initially located in the second possible sector IS1, the rotor is driven to the second position DP2. For example, as described above, by driving Phases A and B or Phases A and C with complementary signals, rotor position can be confirmed. The motor position has been determined, and a quiet and efficient motor start-up can begin.

[0068] Figure 12 The "slightly shifted" waveforms are shown for Phase A voltage, Phase B voltage, Phase C voltage, and Phase B current, where A is the floating phase. It can be seen that the Phase B voltage is driven at a 55% duty cycle. Since Phases B and C are complementary, Phase C is driven at a 45% duty cycle. During the slight shift, the average value of the Phase B current is no longer zero because it has a small DC offset, which is how the rotor is driven to move slightly. The floating phase (Phase A) voltage envelope becomes closer and closer until there is a zero crossing, which corresponds to, for example, Figure 11 The position of DP1 / DP2 in.

[0069] Figure 13An exemplary sequence of steps for providing CDD slightly shifted motor position detection according to an embodiment is shown. In step 1300, complementary drive and detection (CDD) is performed as described above to determine the motor's position within two sectors. In step 1302, torque is applied to the motor by a drive signal having a duty cycle other than 50%. For example, the phase C voltage signal is driven at 55% and the phase B voltage signal is driven at 45%. In step 1304, the voltage of the floating phase is measured. If phases B and C are driven and phase A is floating, the voltage of phase A is measured. In step 1306, the floating phase voltage is monitored. In step 1308, the floating phase voltage is compared to a threshold. In one embodiment, the floating phase A voltage is compared to VBB / 2. Continuing with this example, when the floating phase A voltage is less than VBB / 2, while the phase C voltage is active, the motor is moved a given amount, such as 45 degrees. The applied torque is then removed. In optional step 1310, the motor position can be confirmed, for example, by performing a partial CDD process (e.g., one phase).

[0070] Figure 14 An exemplary computer 1400 is shown that can perform at least a portion of the processes described herein. Computer 1400 includes a processor 1402, volatile memory 1404, non-volatile memory 1406 (e.g., a hard disk), an output device 1407, and a graphical user interface (GUI) 1408 (e.g., a mouse, keyboard, display). Non-volatile memory 1406 stores computer instructions 1412, an operating system 1416, and data 1418. In one example, computer instructions 1412 from volatile memory 1404 are executed by processor 1402. In one embodiment, article 1420 includes non-transitory computer-readable instructions.

[0071] The processes may be implemented in hardware, software, or a combination of both. The processes may be implemented in a computer program executed on a programmable computer / machine, each of which includes a processor, a storage medium or other article of manufacture readable by the processor (including volatile and non-volatile memory and / or storage elements), at least one input device, and one or more output devices. The program code may be applied to data input using the input device to perform the process and generate output information.

[0072] The system can perform processing at least in part via a computer program product (e.g., in a machine-readable storage device) for execution or control of the operation of a data processing device (e.g., a programmable processor, a computer, or multiple computers). Each such program can be implemented in a high-level flow or object-oriented programming language to communicate with the computer system. However, the program can be implemented in assembly or machine language. The language can be assembly or compiled and can be deployed in any form, including as a stand-alone program or as a module, component, subroutine, or other unit suitable for use in a computing environment. The computer program can be deployed to be executed by a single computer or multiple computers at one location or distributed across multiple locations and interconnected by a communication network. The computer program can be stored on a storage medium or device (e.g., a CD-ROM, hard disk, or magnetic disk) that can be read by a general-purpose or special-purpose programmable computer, for configuring and operating the computer when the computer reads the storage medium or device. The processing can also be implemented as a machine-readable storage medium configured with a computer program, and when executed, the instructions in the computer program cause the computer to perform the operation.

[0073] The processing can be performed by one or more programmable processors executing one or more computer programs to perform the functions of the system. All or part of the system can be implemented as special-purpose logic circuitry (e.g., FPGA (field programmable gate array) and / or ASIC (application-specific integrated circuit)).

[0074] Having described exemplary embodiments of the present invention, it will now be apparent to those skilled in the art that other embodiments incorporating the concepts herein may also be used. The embodiments contained herein should not be limited to the disclosed embodiments, but should be limited only by the spirit and scope of the appended claims. All publications and references cited herein are expressly incorporated herein by reference in their entirety.

[0075] The elements of the different embodiments described herein can be combined to form other embodiments not specifically set forth above. The various elements described in the context of a single embodiment can also be provided individually or in any suitable sub-combination. Other embodiments not specifically described herein are also within the scope of the following claims.

Claims

1. A method for determining a position of a rotor in a three-phase electric motor having phase A, phase B, and phase C, comprising: determining first and second sectors of sectors in which a first magnetic pole of the rotor may be located by driving phase pairs AB, AC, and BC with complementary signals, respectively, and comparing a voltage of a floating phase of the phases with a voltage threshold, wherein the first and second sectors of the sectors are relatively positioned; and Torque is applied to the electric motor by driving at least one phase pair with respective signals having complementary phases and unequal duty cycles, wherein a respective third phase is floated to move the rotor by a given amount from a rotor position in a first sector or a second sector of the sectors for determining a position of the rotor. 2 . The method of claim 1 , further comprising moving the rotor by the given amount by determining when a voltage of the floating ones of the phases is less than a threshold. 3 . The method of claim 1 , further comprising driving a phase pair with complementary signals to confirm the rotor position after the rotor moves the given amount.

4. The method according to claim 1, wherein The motor includes a BLDC motor.

5. The method according to claim 1, wherein The sectors include twelve sectors.

6. The method according to claim 1, wherein A first sector and a second sector of the sectors span thirty degrees.

7. The method of claim 1, further comprising driving phase pairs AB, AC, and BC with complementary signals having a fifty percent duty cycle.

8. The method of claim 1, further comprising encoding an output of a comparison of the corresponding floating voltage and a voltage threshold during driving phase pairs AB, AC, and BC with complementary signals.

9. The method according to claim 1, wherein The given amount corresponds to 45 degrees.

10. The method according to claim 1, wherein The rotor position is determined to within thirty degrees.

11. The method of claim 1 , further comprising moving the rotor clockwise by the given amount from the rotor position in a first one of the sectors, or moving the rotor counterclockwise by the given amount from the rotor position in a second one of the sectors.

12. A system for determining a position of a rotor of a three-phase electric motor, comprising: A first module is configured to generate a drive signal for the three-phase motor; a second module configured to determine a first sector and a second sector in which a first magnetic pole of the rotor may be located by driving phase pairs AB, AC, and BC with complementary signals and comparing a voltage of a floating phase of the phases with a voltage threshold, wherein the first sector and the second sector are relatively positioned; as well as and a third module configured to apply torque to the electric motor by driving at least one phase pair with respective signals having complementary phases and unequal duty cycles, wherein a respective third phase is floated to move the rotor by a given amount from a rotor position in a first sector or a second sector of the sectors for determining a position of the rotor.

13. The system according to claim 12, wherein: The system is further configured to move the rotor by the given amount by determining when a voltage of the floating one of the phases is less than a threshold.

14. The system according to claim 12, wherein: The system is further configured to drive the phase pair with complementary signals to confirm the rotor position after the rotor moves the given amount.

15. The system according to claim 12, wherein: The motor includes a BLDC motor.

16. The system of claim 12, wherein: The sectors include twelve sectors.

17. The system of claim 12, wherein: A first sector and a second sector of the sectors span thirty degrees.

18. The system of claim 12, wherein: The system is further configured to encode the output of the comparison of the corresponding floating voltage and the voltage threshold during driving of phase pairs AB, AC, and BC with complementary signals.

19. The system of claim 12, wherein: The given amount corresponds to 45 degrees.

20. The system of claim 12, wherein: The rotor position is determined to within thirty degrees.

21. The system of claim 12, wherein: The system is further configured to move the rotor clockwise by the given amount from the rotor position in a first one of the sectors, or to move the rotor counterclockwise by the given amount from the rotor position in a second one of the sectors.

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