Method for detecting excitation position of motor

Abstract

The invention provides an excitation position detection method of a motor, which can reliably detect the excitation position of the motor and start the motor even if the driving voltage varies during sensing energization when a three-phase brushless motor is started in a sensorless driving mode through PWM control of 120-degree energization. When the MPU (51) senses a power supply voltage fluctuation during energization, if the inductance of the motor is Lm, the resistance value is Rm, the drive voltage before the fluctuation is Vb, and the energization time is tb, the MPU (51) sets the motor current as Im. The motor current (Im) is obtained according to the following formula: [mathematical formula 1] # imgabs0 # uses [mathematical formula 2] # imgabs1 # obtained by solving (formula 1) with respect to time: [mathematical formula 2] # imgabs1 #, the motor current (Im) obtained in (formula 1) and the changed drive voltage (Va) are substituted (formula 2), a new energization time (ta) is calculated, and the energization time (ta) is used for sensing energization to determine the permanent magnet excitation position.

Description

Technical Field

[0001] The present invention relates to a method for detecting the excitation position of a motor when starting the motor in a sensorless manner. Background Art

[0002] Traditionally, small DC motors used brushed DC motors. However, due to issues such as brush noise, electrical noise, and durability, brushless DC motors have emerged. Furthermore, sensorless motors, which lack position sensors, have recently gained attention for their compactness, lightweight, robustness, and cost-effectiveness. Initially adopted in hard disk drives and other applications in the information technology sector, they are now also gaining adoption in home appliances and automotive applications with the advancement of vector control technology.

[0003] Figure 6 The structure of a three-phase brushless DC motor, an example of a sensorless motor without a position sensor, is shown. A rotor 2 rotates about a rotor shaft 1, and a pair of permanent magnets 3 are provided at the south and north poles. The permanent magnet excitation has various magnetic pole configurations (IPM, SPM) and pole numbers. On a stator 4, armature windings (coils) U, V, and W are arranged on pole teeth spaced 120° apart in phase, connected in a star configuration via a neutral point (common point) C.

[0004] Figure 7 This is a block diagram showing an example of a conventional sensorless drive circuit. MOTOR is a three-phase sensorless motor. MPU51 is a microcontroller (control unit). INV52 is a three-phase half-bridge inverter circuit (output unit). RS53 is a current sensor. ADC54 is an A / D converter that converts current values into digital values. In an actual circuit, these components would also be required, including a power supply, a position sensor input, a zero-crossing comparator, a pseudo-common point generator, and a host interface. However, these components have been omitted to avoid complexity.

[0005] Figure 8 This diagram shows a 120-degree energization timing chart, a representative example of a three-phase brushless DC motor drive method. Section 1: Rectangular wave energization from phase U to phase V; Section 2: Rectangular wave energization from phase U to phase W; Section 3: Rectangular wave energization from phase V to phase W; Section 4: Rectangular wave energization from phase V to phase U; Section 5: Rectangular wave energization from phase W to phase U; and Section 6: Rectangular wave energization from phase W to phase V. The dashed line represents the induced voltage waveform. HU to HW are the output waveforms of the Hall effect sensor built into the motor. Conventional brushless DC motors with position sensors switch excitation based on these signals.

[0006] Because sensorless drive methods cannot detect the rotor position when stationary or rotating at low speeds, a widely used excitation starting method is to forcibly position the rotor using fixed excitation and then increase the speed in an open-loop manner. However, this method requires a large current for positioning and has the disadvantage of requiring a considerable amount of time, resulting in startup delays. Furthermore, depending on the stopping position, significant reversals occur during positioning, limiting its use and making it unsuitable for reciprocating mechanisms or applications that utilize external forces for rotation. Furthermore, there are issues with viscous loads or weak load fluctuations, which can easily lead to detuning.

[0007] Therefore, a method is proposed in which, when the motor is stationary, three-phase sensing pulse (constant voltage rectangular wave pulse) voltage is applied to the three-phase coil in sequence, and the energization time of the coil corresponding to the measured phase of the single-phase energization without divergence at the neutral point is measured, or by measuring the peak coil current and comparing the sizes, the stationary position of the permanent magnet excitation is instantaneously determined (Patent Document 1: Japanese Patent Gazette No. 2018-78695). Prior art literature Patent Literature

[0008] Patent Document 1: Japanese Patent Application Publication No. 2018-78695 Summary of the Invention Technical problem to be solved by the invention

[0009] According to the above-mentioned method for detecting the excitation position of the electric motor of Patent Document 1, the excitation position of the permanent magnet in a stationary state can be detected, and two-phase 120° rectangular wave power can be supplied to start the motor. Through a simple drive circuit and control software, the electric motor can be started from a stationary state with closed-loop control at low cost. However, in systems with fluctuating power supply voltages, such as battery systems, the drive voltage applied to the motor fluctuates, making it difficult to measure the energized time and peak coil current of the phase being measured, leading to a significant increase in coil current. If the drive circuit cannot cope with this significant increase in coil current, rotor position detection becomes impossible.

[0010] When measuring large coil currents, digital control technology relies on the performance of the A / D converter circuit that converts current into voltage. A / D converter circuits, with a typical resolution of 10 or 12 bits, measure current by quantizing it within a specific range. For example, when dividing a coil current from 0A to 3A by 12 bits, the resolution is 3 / 4096 ≈ 0.00073. However, when the coil current is from 0A to 30A, the resolution is 30 / 4096 ≈ 0.0073. As the measurement range increases, the resolution decreases. When using the technology disclosed in Patent Document 1 or its derivative technologies, a sensing current larger than the current normally used by the motor is often required to flow. Therefore, the coil current may not be measured due to fluctuations in the power supply voltage, or the measurement resolution of the A / D converter circuit may be reduced, resulting in poor controllability.

[0011] Figures 17 to 19 The waveform diagram shows the three-phase coil current relative to the rotor electrical angle when the drive voltage applied to a motor is 12V, 16V, and 20V and the power-on time (on-duty ratio) within the PWM cycle is 50 [μsec]. Figures 17 to 18 , it can be seen that as the driving voltage increases, the coil current also increases. Figure 19 As shown, when the drive voltage increases to 20 V, the overlapped portions of the three-phase coil current waveforms increase, making measurement difficult. When the measurement limit (dashed line portion) is exceeded, the coil current cannot be measured. Technical means for solving technical problems

[0012] The present invention is proposed to solve these problems, and its purpose is to provide a method for detecting the excitation position of an electric motor. When a three-phase brushless motor is started in a sensorless driving manner by PWM control through 120-degree power-on, the excitation position of the motor can be reliably detected even if the power supply voltage changes during the sensing power-on.

[0013] A method for detecting the excitation position of an electric motor, the electric motor including a rotor with permanent magnet excitation and a stator with three-phase coils connected in a star shape, and starting in a sensorless driving manner by performing 120° rectangular wave energization, characterized in that it includes: an output unit, which energizes the three-phase coils via a three-phase half-bridge inverter circuit; a control unit, which stores excitation position information and switches the excitation state by switching the output unit according to a rotation instruction from a host controller, wherein the excitation position information is used to specify a total of 6 energization directions in the three-phase coils and an excitation switching interval of 120° energization corresponding to each energization direction; a current detection unit, which is connected to the output unit and detects the coil current; a timer unit, which measures a specified sensing energization time; and a measuring unit, which measures the coil current value based on the output of the current detection unit. The excitation position detection method includes : a step of releasing the coil energy stored in the three-phase coil; a step of taking the total current supplied to the motor as a measurement object, the control unit sequentially selecting any one of the six energization directions, applying a constant voltage rectangular wave pulse for a specified time to the three-phase coil, and measuring the coil current value after the specified time by the measuring unit; a step of storing the coil current value as measurement data; and a step of selecting the energization direction with the largest measurement value from the measurement data of the six energization directions, determining the permanent magnet excitation position based on the excitation position information corresponding to the maximum energization direction, and starting the three-phase coil by applying a voltage for a specified time, the control unit, when sensing the power supply voltage change during energization, assumes that the motor current is Im when the inductance of the motor is Lm, the resistance is Rm, the drive voltage before the change is Vb, and the energization time is tb, and calculates the motor current Im according to the following formula: [Mathematical formula 1] Solving (Equation 1) for time yields: [Mathematical formula 2] The motor current Im and the changed drive voltage Va obtained in (Equation 1) are substituted into (Equation 2) to calculate a new energization time ta. This energization time ta is used for sensing energization to determine the permanent magnet excitation position.

[0014] A method for detecting the excitation position of an electric motor, wherein the electric motor includes a rotor with permanent magnet excitation and a stator with three-phase coils connected in a star shape, and is started in a sensorless driving manner by performing 120° rectangular wave energization, and is characterized in that it includes: an output unit, which energizes the three-phase coils via a three-phase half-bridge inverter circuit; a control unit, which stores excitation position information and switches the excitation state by switching the output unit according to a rotation instruction from a host controller, wherein the excitation position information is used to specify a total of 6 energization directions in the three-phase coils and an excitation switching interval of 120° energization corresponding to each energization direction; a current detection unit, which is connected to the output unit and detects the coil current; a timer unit, which measures a specified sensing energization time; and a measuring unit, which measures the coil current value based on the output of the current detection unit. The detection method includes: a step of releasing the coil energy accumulated in the three-phase coil; a step of measuring the total current supplied to the motor, wherein the control unit selects any one of the six power-on directions one by one in sequence, applies a constant-voltage rectangular wave pulse for a specified time to the three-phase coil, and the measuring unit measures the coil current value after the specified time; a step of storing the coil current value as measurement data; and a step of the control unit determining the permanent magnet excitation position based on the power-on direction with the largest measurement value and the power-on direction with the second largest measurement value in the measurement data of the six power-on directions, applying a voltage to the three-phase coil for a specified time to start the motor, and the control unit, when sensing the power supply voltage change during power-on, assumes the motor current is Im when the inductance of the motor is Lm, the resistance is Rm, the drive voltage before the change is Vb, and the power-on time is tb, calculates the motor current Im according to the following formula: [Mathematical formula 1] Solving (Equation 1) for time yields: [Mathematical formula 2] The motor current Im and the changed drive voltage Va obtained in (Equation 1) are substituted into (Equation 2) to calculate a new energization time ta. This energization time ta is used for sensing energization to determine the permanent magnet excitation position.

[0015] Therefore, when the control unit senses the change in the driving voltage during power-on, it calculates the motor current Im according to the following formula: [Mathematical formula 1] Using [Formula 2] obtained by solving (Formula 1) with respect to time Substituting the motor current Im and the changed drive voltage Va obtained in (Equation 1) into (Equation 2) calculates a new energization time ta. This energization time ta is then used to apply the constant-voltage rectangular wave pulse voltage to determine the permanent magnet excitation position. This allows the motor's excitation position to be detected and started without being affected by fluctuations in the drive voltage during sensing. Effects of the Invention

[0016] The present invention can provide a method for detecting the excitation position of an electric motor. When a three-phase brushless motor is started in a sensorless driving manner by PWM control through 120-degree energization, the excitation position of the motor can be reliably detected and started even if the driving voltage fluctuates during sensing energization. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a schematic diagram of the coil current waveform when a constant voltage rectangular wave pulse is applied to the coil. Figure 2 This is a coil current waveform diagram when measuring in six energizing directions. Figure 3 This is an approximate waveform diagram showing the change in the peak current arrival time at the excitation position when the current is low. Figure 4 This is an approximate waveform diagram showing the change in the peak current arrival time at the excitation position when a large current is applied. Figure 5 This is a diagram showing the peak current arrival times in the three energizing directions of a star connection. Figure 6 This is the structural diagram of a three-phase brushless DC motor with star connection. Figure 7 This is a block diagram of a conventional motor drive circuit. Figure 8 This is the 120° power-on timing diagram. Figure 9 This is a graph showing actual current measurements using the method for measuring the peak current value when the pulse time is constant. Figure 10 This is a circuit diagram for implementing a star connection method for measuring the peak current value when the pulse time is constant. Figure 11 This is a circuit diagram for implementing a delta connection method for measuring the peak current value when the pulse time is constant. Figure 12 This is a waveform diagram of the coil current during sensing energization when the energization time is updated from 12V driving voltage and 50 μsec to 16V driving voltage and 28 μsec. Figure 13This is a waveform diagram of the coil current during sensing energization when the energization time is updated from 12V driving voltage and 50 μsec to 20V driving voltage and 19 μsec. Figure 14 This is a waveform diagram of the coil current during sensing energization with a drive voltage of 12 V and an energization time of 29 [μsec]. Figure 15 This is a waveform diagram of the coil current during sensing energization when the energization time is updated from 29 μsec for a driving voltage of 12 V to 19 μsec for a driving voltage of 16 V. Figure 16 This is a waveform diagram of the coil current during sensing energization when the energization time is updated from 12V driving voltage and 29 [μsec] to 20V driving voltage and 14 [μsec] after the energization time is updated. Figure 17 This is a waveform diagram of the coil current during sensing energization with a drive voltage of 12 V and an energization time of 50 [μsec]. Figure 18 This is a waveform diagram of the coil current during sensing energization with a drive voltage of 16 V and an energization time of 50 [μsec]. Figure 19 This is a waveform diagram of the coil current during sensing energization with a drive voltage of 20 V and an energization time of 50 [μsec]. DETAILED DESCRIPTION

[0018] An embodiment of the method for detecting the excitation position of an electric motor according to the present invention is described below with reference to the accompanying drawings. This invention is described using a sensorless motor as an example of an electric motor having a permanent magnet excitation on the rotor, a stator with windings arranged with a 120° phase difference and connected in a star configuration, and phase terminals connected to a motor output unit.

[0019] Hereinafter, as an example, a method for detecting the permanent magnet excitation position of a sensorless motor that drives a three-phase DC brushless motor in a sensorless manner will be described together with the structure of a sensorless motor driving device. Figure 6 An embodiment of a three-phase brushless DC motor according to the present invention is shown. As an example, a three-phase brushless DC motor having a two-pole permanent magnet rotor and a stator 4 with three slots is shown. The motor can be either an inner rotor type or an outer rotor type. Furthermore, the permanent magnet excitation can be either an embedded permanent magnet (IPM) motor or a surface permanent magnet (SPM) motor.

[0020] exist Figure 6In the figure, a rotor 2 is integrally mounted on a rotor shaft 1, and a two-pole permanent magnet 3 is provided as an excitation field. On a stator 4, pole teeth U, V, and W are arranged opposite the permanent magnet 3 with a phase difference of 120°. Windings u, v, and w are provided on each of the pole teeth U, V, and W of the stator 4, and the phases are connected in a star configuration at a common point C, forming a three-phase brushless DC motor that is wired to the motor drive device described below. Since common wires are not required, they are omitted.

[0021] Here, the principle of detecting the exciting position of the permanent magnet will be described. When a constant voltage pulse is applied to the coil, the current increases according to the following formula. I(t)=(L / R)·(1-e (-t·R / L) ) Where I is the coil current, L is the coil inductance, and R is the coil resistance. Figure 1 The figure shows the current waveform when a constant-voltage rectangular pulse is applied to the coil. If the coil resistance R is constant and the energization time t is a specified value, the peak current value I(t) reflects the change in inductance L.

[0022] Next, we will explain the excitation position detection method for measuring the peak current by setting the pulse time t to a specified value. The current increase rate is greater at positions with smaller inductance, and smaller at positions with larger inductance. Therefore, the current change corresponding to the rotor position is opposite to the pulse time change when the peak current is constant. The peak current values I1 to I6 when a short-time pulse is applied vary depending on the excitation position due to the influence of magnetic resistance. The peak current change relative to the excitation position has two periods, and can be approximated by the following formula for one phase: ΔIa=cos2θ, cos(2θ+π) (where θ=excitation position). For the other two phases, the values of θ can be set to +120° and -120°.

[0023] When applying a longer pulse, the peak currents I1 to I6 vary depending on the excitation position because the magnetic resistance changes with the excitation polarity. The current variation with respect to the excitation position has a periodicity and can be approximated by the following equation for one phase: ΔIb=cos2θ, cos(2θ+π) (where θ=excitation position: when θ is 0 to π / 2 and 3π / 2 to 2π, ΔIb=-1). For the other two phases, the values of θ can be set to +120° and -120°.

[0024] Considering that both reactance change and magnetoresistance change are reflected when a long-term pulse is applied, the current change is approximately expressed as ΔI=ΔIa+ΔIb. Figure 9 This waveform shows the measured current changes when a long pulse is applied. Pulses are applied for a specified time in each of the six three-phase current directions every 1°, and the peak current is measured. A total of 2160 data points are plotted. The motor used is a spindle motor for a hard disk drive.

[0025] Depend on Figure 9 As can be seen, the current direction with the highest peak current value switches within the 120° energization excitation interval, i.e., within a 60° interval. Therefore, by identifying the current direction with the highest peak current value, the rotor position can be uniquely determined, enabling startup with 120° energization. As will be described later, the relationship between the current direction with the highest peak current value and the excitation position information can be determined using the maximum energization patterns in Tables 3 and 4.

[0026] The three-phase current supply directions of a three-phase motor differ depending on the connection method. In the case of star connection, there are 6 directions as shown in Table 1, and in the case of delta connection, there are 6 directions as shown in Table 2.

Table 1

Table 2

[0027] Table 3 below shows the relationship between the maximum energization pattern and permanent magnet excitation position information for star connection. In Table 3, the maximum energization pattern is labeled "W-UV" for example, when the W phase is connected to the positive power supply and the U and V phases are connected to the ground (negative) side. For reference, the corresponding excitation pattern for the 120° energization method is also noted. In addition, the following Table 4 shows the relationship between the maximum power-on mode, the second-largest power-on mode, and the permanent magnet excitation position information when the triangle connection is made. In Table 4, the power-on mode is marked as "WU" for example when the W phase is connected to the positive power supply and the U phase is connected to the ground side (negative side). The power-on mode is marked as "WU" for example when the W phase is connected to the positive power supply and the U phase is connected to the ground side (negative side). If the two phases are energized according to the recorded excitation mode, the rotation is forward, and if the energization direction is reversed, the rotation is reversed.

[0028]

Table 3

Table 4

[0029] First, the specific method for determining the rotor position using the star connection shown in Table 3 will be described. When stationary, energize the three-phase circuit for a certain period of time in each of the six directions, and measure the peak current. As a result, for example, if the coil current value is maximum when the U-VW circuit is energized, Table 3 shows that the excitation is located in the range of 150° to 210° in electrical angle. Then, if VW excitation is performed using a 120° rectangular wave circuit, connecting the V phase to the positive power supply and the W phase to the ground, the rotor starts to rotate in the forward direction. If WV excitation is performed in the reverse direction, the rotor rotates in the reverse direction. Thus, according to this scheme, position detection can be performed extremely easily.

[0030] At rest, three-phase current is applied in each of the six directions for a specified period of time, and the peak current is measured. Refer to Table 1 for the order of the power supply patterns. As a result, for example, if the peak current value is maximum during U-VW energization, Table 2 shows that the excitation is in the range of 150° to 210°. Then, if VW excitation is performed with 120° energization, connecting the V phase to the power supply's + (positive) side and the W phase to ground, the rotor starts rotating in the forward direction. If WV excitation is performed in the reverse direction, the rotor rotates in the reverse direction.

[0031] Next, we'll explain how to determine the rotor position using the delta connection shown in Table 4. When stationary, energize the two-phase circuit in each of the six directions for a specified period of time, and measure the peak current. Refer to Table 2 for the order of the energization patterns. For example, if the peak current value is the highest during UW energization, Table 4 indicates that the excitation position is between 180° and 240°. Furthermore, if the next highest energization pattern is the UV energization pattern, the excitation position is between 180° and 210°. In this case, if VW excitation is performed with 120° energization, connecting the V phase to the + (positive) side of the power supply and the W phase to ground, the rotor starts rotating in the forward direction. If WV excitation is performed in the reverse direction, the rotor rotates in the reverse direction.

[0032] When the MPU 51 detects that the power supply voltage fluctuates during energization, the drive voltage applied to the motor also fluctuates. However, the MPU 51 performs the following processing to update the energization time. If the motor's inductance is Lm, its resistance is Rm, the previous drive voltage is Vb, and the energization time for one cycle is tb, let the motor current be Im. Calculate the motor current Im using the following formula: [Mathematical formula 1] Solving (Equation 1) for time yields: [Mathematical formula 2] The motor current Im and the changed drive voltage Va obtained in (Formula 1) are substituted into (Formula 2) to calculate a new energization time ta.

[0033] Specifically, in actual measurement or simulation, the appropriate energization time tb is substituted into (Equation 1) to obtain the motor current Im. Figure 17 In the graph, based on the motor's inductance Lm, resistance Rm, the previous drive voltage Vb = 12V, and the power-on time tb in the previous cycle = 50 [μsec], (Equation 2) is used to calculate the new power-on time ta when the changed drive voltage Va changes to 16V and 20V. When the changed drive voltage Va = 16V, the new power-on time ta = approximately 28 [μsec], and when the changed drive voltage Va = 20V, the new power-on time ta = approximately 19 [μsec]. The MP U51 applies a constant-voltage rectangular wave pulse voltage for the new power-on time ta to determine the permanent magnet excitation position.

[0034] Figure 12 and Figure 13 The waveform of the coil current measured during the new energization time ta is shown. As the drive voltage Va increases, the coil current also increases, but remains within the measurement limit (dashed line). The current waveforms overlap, and there is no range where the peak current value is difficult to discern. Furthermore, the reason the coil current increases with increasing drive voltage Va is due to changes in the magnetic circuit due to magnetic saturation. However, this cannot be avoided due to the structure that uses magnetic circuit changes to detect rotor position. Conversely, by setting the energization time ta, which is updated after magnetic saturation, to the minimum energization time required to detect the induced current, the increase in coil current caused by rising changes in drive voltage Va can be minimized.

[0035] For the same motor, if the coil current value measured when the drive voltage Vb was 12V and the current-carrying time in one cycle was 29 [μsec] is calculated using (Equation 2) in the same way when the drive voltage Va changes to 16V and 20V, then ta = about 19 [μsec] when the drive voltage Va = 16V and ta = about 14 [μsec] when the drive voltage Va = 20V. Their curves are shown in the figure below. Figures 14 to 16Even in this case, when the drive voltage Va increases, the coil current value also increases, but it converges within the measurement limit range, the current waveforms overlap, and there is no range where it is difficult to determine the peak current value. As described above, a method for detecting the excitation position of an electric motor can be provided. When a three-phase brushless motor is started in a sensorless driving manner by PWM control through 120° energization, the excitation position of the motor can be reliably detected and started even if the driving voltage fluctuates during the sensing energization.

[0036] In addition, the distribution of the measured data intersects at the excitation switching point. Therefore, the detection of the excitation switching point can be performed by periodically sensing in the current section and the rotation direction through two energization patterns and comparing the two obtained measured data. Figure 5 For example, when the rotor is in interval 1 of 30° to 90°, according to Table 3, it can be seen that the power-on direction of the current interval is W-UV power-on. In addition, if the power-on direction of the adjacent interval in the rotation direction is the forward direction, it can also be determined as UW-V power-on in interval 2. If sensing is performed in these two directions, the size of the measured data changes when the rotor exceeds 90°. Therefore, it is possible to detect that the rotor has rotated to interval 2, and the excitation mode can be switched at this moment. Similarly, if the switching points of the excitation intervals are detected one by one and the excitation mode is switched, it is possible to start seamlessly from a standstill, or to continuously generate low-speed rotation or stall torque. While sensing time must be minimized during rotation, the aforementioned sensing method reduces the six current-carrying directions at rest to just two, reducing measurement time to one-third. While the measurement time varies depending on the motor and drive circuit conditions, it's generally around 300µs.

[0037] Furthermore, the direction of rotation can be determined by measuring the three current-carrying directions. The three current-carrying directions corresponding to the current interval, the forward direction, and the reverse direction are periodically sensed. By comparing the magnitudes of the respective measurement data, the boundary point of the next forward or reverse excitation interval is detected. The direction of rotation can also be determined based on which excitation boundary point is detected first.

[0038] exist Figure 5For example, assuming that the rotor is in interval 1 of 30° to 90°, the excitation boundary point in the forward direction is 90°, which is the intersection of the W-UV energization direction and the UW-V energization direction. Similarly, the excitation boundary point in the reverse direction is 30°, which is the intersection of the W-UV energization direction and the WV-U energization direction. If the 90° intersection on the forward side is detected before the 30° intersection on the reverse side, it is judged that the rotor is rotating forward. Similarly, if the 30° intersection is detected before the 90° intersection, it can be known that the rotor is reversing. Therefore, if the three energization directions in the current interval and the adjacent intervals before and after are periodically sensed, the excitation interval boundary points and the rotation direction can be known. This eliminates rotational restrictions and allows both forward and reverse rotation. Furthermore, even when forced to rotate by an external force, position detection and torque generation in any direction are possible. Using this sensing method reduces the current flow direction from six at rest to three, reducing measurement time by half.

[0039] then, Figure 10 This example shows a sensorless motor drive circuit using star connection, which applies pulses for a predetermined time and measures the peak current value of the coil. The output of the current sensor 53 (current detection unit) is sent to the A / D converter 55 (ADC: Analog-to-Digital Converter, analog-to-digital conversion circuit, A / D converter unit). The A / D converter 55 measures the coil current value based on the output of the current sensor 53. The A / D converter 57 does not need to be high-performance, and an inexpensive converter built into the MPU 51 can be practical. For example, a 12-bit ADC with a data activation time of 1 μs and a conversion time of approximately 20 μs is installed in a general-purpose MPU microprocessor unit, which is sufficient for the purpose of the present invention. According to the above structure, in the case of star connection, the peak coil current value is measured for the six energization directions of the three-phase power supply according to Table 1, and the excitation position is detected from the measured data of the maximum energization direction according to Table 3. The corresponding excitation position information pre-stored in the MPU 51 is determined as the rotor position.

[0040] in addition, Figure 11 This example shows a sensorless motor drive circuit using delta connection by applying pulses for a specified time and measuring the peak current value of the coil. Figure 10 The same components are marked with the same numbers and reference descriptions. Six energization patterns for the two-phase coils and information on the permanent magnet excitation position are pre-stored in the memory of the MPU 51. The sensing time is set by the timer circuit 56. Position detection begins in response to a rotation command from the host controller 50. When position detection begins, all outputs to the three-phase coils are turned off, and the system waits for a specified time.

[0041] Next, constant-voltage rectangular wave energization begins in the two-phase coils from inverter circuit 52 in a predetermined two-phase energization pattern, and measurement by A / D converter 55 begins. The peak coil current value immediately before the end of the sensing energization is measured by A / D converter 55 and stored as measurement data. Furthermore, when energization of the three-phase coils by inverter circuit 52 is cut off, the stored energy in the coils begins to be released.

[0042] After the forward energization mode for the two-phase coil to be measured, the reverse energization mode is selected and energized. For the remaining two phases, the reverse energization mode is also selected after the forward energization mode. For a total of 6 energization modes, constant voltage rectangular wave energization and peak coil current value measurement by the A / D converter 55 are repeated. When the measurement is completed, the MPU 51 detects the excitation position from the measurement data of the maximum energization direction and the second maximum energization direction according to Table 4, and determines the corresponding excitation position information pre-stored in the MPU 51 as the rotor position.

[0043] The following briefly describes the actual measurement procedure. First, all three phases are deenergized and the coil current is allowed to reach zero. Next, in the case of a star connection, one of the six energization directions is selected one by one according to Table 1 (in the case of a delta connection, according to Table 2). A constant-voltage rectangular wave pulse is applied to the three-phase coils, and sensing of energization begins. Timer circuit 56 waits for a specified time. After the specified time has elapsed, A / D converter 55 measures the coil peak current value based on the output of current sensor 53 and stores it as measurement data. All three phases are deenergized again, and the coil current is allowed to reach zero.

[0044] When the driving voltage Vb changes during constant-voltage rectangular wave power-on, the following operations are repeatedly performed: the coil current Im is calculated according to the above (Formula 1), constant-voltage rectangular wave power-on is performed during the new power-on time ta under the changed driving voltage Va calculated according to the above (Formula 2), and the peak coil current value is measured.

[0045] The MPU 51 selects the energizing direction that results in the maximum value from the six measured data. Next, in the case of a star connection, the excitation position information corresponding to the maximum energizing pattern in Table 3 is determined as the permanent magnet excitation position. (In the case of a delta connection, the excitation position information is determined as the permanent magnet excitation position based on the measured data for the maximum energizing direction and the next largest energizing direction according to Table 4.)

Claims

1. A method for detecting the excitation position of an electric motor, wherein the electric motor comprises a rotor with permanent magnet excitation and a stator with three-phase coils connected in a star configuration, and is started in a sensorless driving manner by applying 120° rectangular wave power. The method for detecting the excitation position of the electric motor is characterized in that: include: an output unit that energizes the three-phase coils via a three-phase half-bridge inverter circuit; a control unit that stores excitation position information and switches the excitation state by switching the output unit according to a rotation command from a host controller, the excitation position information being used to specify a total of six energization directions in the three-phase coils and an excitation switching interval of 120° energization corresponding to each energization direction; a current detection unit that is connected to the output unit and detects coil current; and a timer unit that measures a specified sensing energization time. and a measuring unit for measuring a coil current value based on an output of the current detecting unit. The excitation position detection method includes: releasing coil stored energy stored in the three-phase coil; The control unit sequentially selects one of six current-carrying directions, applies a constant-voltage rectangular wave pulse for a predetermined time to the three-phase coil, and the measurement unit measures the coil current value after the predetermined time has elapsed. a step of storing the coil current value as measurement data; and The control unit selects the energizing direction with the largest measured value from the measurement data of the six energizing directions, determines the permanent magnet excitation position based on the excitation position information corresponding to the largest energizing direction, and applies voltage to the three-phase coil for a predetermined time to start the operation. When the control unit senses a change in the power supply voltage during power-on, the motor current Im is calculated using the following formula, assuming that the motor's inductance is Lm, its resistance is Rm, the drive voltage before the change is Vb, and the power-on time is tb: [Mathematical formula 1] Solving (Equation 1) for time yields: [Mathematical formula 2] The motor current Im and the changed drive voltage Va obtained in (Equation 1) are substituted into (Equation 2) to calculate a new energization time ta, which is then used to perform sensing energization to determine the permanent magnet excitation position.

2. A method for detecting the excitation position of an electric motor, the electric motor comprising a rotor with permanent magnet excitation and a stator with three-phase coils connected in a star configuration, and started in a sensorless drive mode by applying 120° rectangular wave energization, The method for detecting the excitation position of the electric motor is characterized in that: include: an output unit that energizes the three-phase coils via a three-phase half-bridge inverter circuit; a control unit that stores excitation position information and switches the excitation state by switching the output unit according to a rotation command from a host controller, the excitation position information being used to specify a total of six energization directions in the three-phase coils and an excitation switching interval of 120° energization corresponding to each energization direction; a current detection unit that is connected to the output unit and detects coil current; and a timer unit that measures a specified sensing energization time. and a measuring unit for measuring a coil current value based on an output of the current detecting unit. The excitation position detection method includes: releasing coil stored energy stored in the three-phase coil; The control unit sequentially selects one of six current-carrying directions, applies a constant-voltage rectangular wave pulse for a predetermined time to the three-phase coil, and the measurement unit measures the coil current value after the predetermined time has elapsed. a step of storing the coil current value as measurement data; and The control unit determines the permanent magnet excitation position based on the current-carrying direction with the largest measured value and the current-carrying direction with the second largest measured value among the measurement data of the six current-carrying directions, and applies voltage to the three-phase coil for a predetermined time to start the coil. When the control unit senses a change in the power supply voltage during power-on, the motor current Im is calculated using the following formula, assuming that the motor's inductance is Lm, its resistance is Rm, the drive voltage before the change is Vb, and the power-on time is tb: [Mathematical formula 1] Solving (Equation 1) for time yields: [Mathematical formula 2] The motor current Im and the changed drive voltage Va obtained in (Equation 1) are substituted into (Equation 2) to calculate a new energization time ta, which is then used to perform sensing energization to determine the permanent magnet excitation position.

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