Motor control device and motor control method

Abstract

A motor control device according to the present invention has a control drive circuit (30) that supplies a drive signal to an inverter (20) that drives a motor (10), a timepoint setting circuit (31) that sets a first timepoint and a second timepoint within a period before the motor (10) is started during which the control drive circuit (30) selects and energizes two of three phases of the motor (10), and a not-energized phase voltage detection circuit (32) that compares the voltage of the not-energized phase of the motor (10) at the first timepoint and the voltage of the not-energized phase of the motor (10) at the second timepoint.

Description

Motor control device and motor control method

[0001] The present disclosure relates to a motor control device and a motor control method that detects the initial position of a rotor of a three-phase motor before the motor starts operating without using a sensor.

[0002] An example of a motor control device that detects the initial position without a sensor is disclosed in Patent Document 1. The motor control device in Patent Document 1 has a stopped phase rotor position detection circuit that applies a minute current to predetermined windings of the stator, just enough to prevent the stopped rotor from rotating, and detects the induced voltage generated in the non-energized phase to detect the position of the rotor relative to the stator.

[0003] Japanese Patent Application Laid-Open No. 2001-8490

[0004] However, in the above-mentioned conventional technology, the rotor position is estimated from the polarity of the detected induced voltage in the non-energized phase, and in the case of the permanent magnet motor assumed in Patent Document 1, there may be two candidates for the estimated position. Also, there is a method of detecting the zero-cross point where the polarity of the induced voltage changes, but there is a problem in that the zero-cross point does not exist in the induced voltage in the non-energized phase due to an offset in the induced voltage caused by a mismatch in the windings, making it impossible to detect.

[0005] Therefore, the present disclosure provides a motor control device and a motor control method that can perform sensorless and highly accurate position estimation before starting a three-phase motor.

[0006] The motor control device according to the present disclosure includes a control drive circuit that supplies a drive signal to an inverter circuit that drives a three-phase motor; a time point setting circuit that sets a first time point and a second time point during a period before the start of the three-phase motor during which the control drive circuit selects and energizes two of the three phases of the three-phase motor; and a non-energized phase voltage detection circuit that compares the voltage of a non-energized phase of the three-phase motor at the first time point with the voltage of the non-energized phase at the second time point.

[0007] The motor control method according to the present disclosure is a motor control method executed by a motor control device, and includes a control drive step of supplying a drive signal to an inverter circuit that drives a three-phase motor; a time point setting step of setting a first time point and a second time point during a period in which two of the three phases of the three-phase motor are selected and energized in the control drive step before starting the three-phase motor; and a non-energized phase voltage detection step of comparing the voltage of a non-energized phase of the three-phase motor at the first time point with the voltage of the non-energized phase at the second time point.

[0008] These comprehensive or specific aspects may be realized as a system, a method, an integrated circuit, a computer program, or a computer-readable recording medium such as a CD-ROM, or may be realized as any combination of a system, a method, an integrated circuit, a computer program, and a recording medium.

[0009] According to the present disclosure, it is possible to perform sensorless position estimation with high accuracy before starting a three-phase motor.

[0010] FIG. 1 is a circuit configuration diagram showing a motor control device according to a first embodiment. FIG. 2 is a circuit diagram showing a time point setting circuit of the motor control device according to the first embodiment. FIG. 3 is a circuit diagram showing a non-energized phase voltage detection circuit of the motor control device according to the first embodiment. FIG. 4 is a waveform diagram of a main part of the motor control device according to the first embodiment. FIG. 5 is a phase estimation table of the motor control device according to the first embodiment. FIG. 6 is a circuit diagram showing a time point setting circuit of the motor control device according to the second embodiment. FIG. 7 is a phase estimation table of the motor control device according to the second embodiment. FIG. 8 is a circuit configuration diagram showing a motor control device according to a third embodiment. FIG. 9 is a circuit diagram showing a time point setting circuit of the motor control device according to the third embodiment. FIG. 10 is a waveform diagram of a main part of the motor control device according to the third embodiment. FIG. 11 is a flowchart showing an example of a motor control method according to another embodiment.

[0011] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. Note that each of the embodiments described below represents a specific example of the present disclosure. Therefore, the numerical values, shapes, materials, components, and the arrangement and connection of the components shown in the following embodiments are merely examples and are not intended to limit the present disclosure.

[0012] Furthermore, each figure is a schematic diagram and is not necessarily an exact representation. Therefore, the scales and the like do not necessarily match in each figure. In each figure, the same reference numerals are used to denote substantially the same components, and redundant explanations will be omitted or simplified.

[0013] (First Embodiment) A motor control device according to a first embodiment will be described below.

[0014] 1 is a circuit diagram showing a motor control device according to embodiment 1. The motor control device is a device for controlling a sensorless motor. A motor 10, which is the object of control by the motor control device, is an example of a three-phase motor having star-connected three-phase windings of U, V, and W phases.

[0015] The inverter 20 is an example of an inverter circuit that drives the motor 10. The inverter 20 is a bridge circuit that has three pairs of high-side switch elements and low-side switch elements that are arranged between a power supply and ground. The inverter 20 supplies drive current to each phase of the motor 10 to control the operation of the motor 10.

[0016] The control drive circuit 30 is a circuit that supplies drive signals to the inverter 20. To control the inverter 20, the control drive circuit 30 generates a drive signal UH for a high-side switch element that supplies power to the U phase, a drive signal VH for a high-side switch element that supplies power to the V phase, a drive signal WH for a high-side switch element that supplies power to the W phase, a drive signal UL for a low-side switch element that supplies power to the U phase, a drive signal VL for a low-side switch element that supplies power to the V phase, and a drive signal WL for a low-side switch element that supplies power to the W phase, and outputs these signals to the gates of the respective switch elements. The current flowing from the power supply to ground via the inverter 20 is designated as current Im. In the present disclosure, when the control drive circuit 30 detects that the motor 10 is in a pre-start state, it supplies a current to the other two phases of the motor 10 such that each phase is sequentially de-energized so as to prevent rotation, in order to detect the pre-start initial position of the rotor of the motor 10, and activates the time setting circuit 31. The state before motor 10 is started refers to the state before power is supplied to motor 10 to rotate the rotor, and is basically a state in which the rotor is stopped. However, a state in which power is not supplied to motor 10 to rotate the rotor and the rotor is rotating by inertia or due to external disturbances such as wind is also included in the state before motor 10 is started in this disclosure, as long as motor 10 is rotating at a low rotation speed of, for example, 100 rpm or less.

[0017] For example, the control drive circuit 30 is a computer including a processor (microprocessor) and a memory. The memory may be a read-only memory (ROM) or a random access memory (RAM), and can store a program to be executed by the processor. The control drive circuit 30 is realized by the processor that executes the program stored in the memory.

[0018] The time point setting circuit 31 sets a first time point and a second time point during a period before the start of the motor 10, during which the control drive circuit 30 selects two of the three phases of the motor 10 and energizes them (specifically, energizes them with a current that is not large enough to rotate the rotor). The time point setting circuit 31 sets the first time point and the second time point during the current supply period in accordance with instructions from the control drive circuit 30 and transmits them to the non-energized phase voltage detection circuit 32.

[0019] The non-energized phase voltage detection circuit 32 compares the voltage of the non-energized phase of the motor 10 at a first time point with the voltage of the non-energized phase at a second time point. The non-energized phase voltage detection circuit 32 detects and compares the voltage of the non-energized phase at two time points set in the time point setting circuit 31, determines whether the voltage increases or decreases between the two time points, and transmits the determination result (i.e., the result of the comparison by the non-energized phase voltage detection circuit 32) to the control drive circuit 30.

[0020] For example, the control drive circuit 30 estimates the rotor initial position based on the determination result of the non-energized phase voltage detection circuit 32 and starts rotation control. For example, the control drive circuit 30 has the function of a position estimation circuit that estimates the rotor position of the motor 10 based on the comparison result by the non-energized phase voltage detection circuit 32. Note that the time point setting circuit 31 may have the function of the position estimation circuit, or the non-energized phase voltage detection circuit 32 may have the function of the position estimation circuit. Furthermore, the motor control device does not have to have the function of a position estimation circuit. For example, the comparison result by the non-energized phase voltage detection circuit 32 may be output to a position estimation circuit external to the motor control device, and the rotor position of the motor 10 may be estimated by the position estimation circuit external to the motor control device.

[0021] Next, the circuit configurations of the time point setting circuit 31 and the non-energized phase voltage detection circuit 32 will be described with reference to FIGS. 2A and 2B.

[0022] Figure 2A is a circuit diagram showing a time point setting circuit 31 of the motor control device according to embodiment 1. Figure 2B is a circuit diagram showing a non-energized phase voltage detection circuit 32 of the motor control device according to embodiment 1. Figures 2A and 2B show the time point setting circuit 31 and the non-energized phase voltage detection circuit 32 that are used when the U phase is selected as the non-energized phase. A time point setting circuit and a non-energized phase voltage detection circuit that are used when the V phase or the W phase is selected as the non-energized phase also exist, but are not shown in the figures because their circuit configurations are similar to those shown in Figures 2A and 2B.

[0023] 2A, a drive signal UH for the high-side switch element of the U-phase and a drive signal UL for the low-side switch element are input to the NOR gate 310. Therefore, when the output of the NOR gate 310 is at an H level, all of the switch elements of the inverter 20 corresponding to the U-phase are in an off state, and therefore the H level output of the NOR gate 310 indicates that the U-phase is a non-conductive phase.

[0024] The output of the NOR gate 310, the drive signal VH for the V-phase high-side switch element, and the drive signal WL for the W-phase low-side switch element are input to the AND gate 311. Therefore, when the output signal U (V → W) of the AND gate 311 is at the H level, this indicates that the U-phase is a non-conductive phase, the V-phase high-side switch element and the W-phase low-side switch element are in the ON state, and a current flows from the V-phase to the W-phase.

[0025] The output of the NOR gate 310, the drive signal WH for the W-phase high-side switch element, and the drive signal VL for the V-phase low-side switch element are input to the AND gate 312. Therefore, when the output signal U (W→V) of the AND gate 312 is at the H level, this indicates that the U-phase is a non-conductive phase, the V-phase low-side switch element and the W-phase high-side switch element are in the ON state, and a current flows from the W-phase to the V-phase.

[0026] The OR gate 313 receives the outputs of the AND gate 311 and the AND gate 312. Therefore, when the output signal U (V-W) of the OR gate 313 is at the H level, this indicates that the U phase is a non-conductive phase and the V and W phases are conductive phases.

[0027] The time point setting circuit 31 sets the first time point to a timing that is a first predetermined time after the control drive circuit 30 selects two of the three phases of the motor 10 and starts energizing them, and sets the second time point to a timing that is a second predetermined time after the first time point. To achieve this function, the time point setting circuit 31 has delay circuits 314 and 315. The delay circuits 314 and 315 output signals that are generated by delaying the signal U(V-W) by a predetermined time. Specifically, the delay signal UD1 of the delay circuit 314 becomes high a short time after the signal U(V-W) becomes high and the state of the inverter 20 is determined. The delay signal UD2 of the delay circuit 315 becomes high before the signal U(V-W) falls to low. For example, if the period during which the U phase is a non-energized phase and the V and W phases are energized phases (i.e., the period during which the signal U(V-W) is at H level) is set to 100 μsec, the delay time of delay circuit 314 is set to 10 μsec, and the delay time of delay circuit 315 is set to 80 μsec. This allows delay signal UD1 to go to H level 10 μsec after signal U(V-W) goes to H level, and delay signal UD2 to go to H level 10 μsec before signal U(V-W) falls to L level. In this way, the first and second points in time can be set by delay circuits or the like.

[0028] As shown in FIG. 2B , resistors 320 and 321 divide the U-phase voltage Vu and apply the divided voltage VU to the input terminal of switch 322. Switch 322 is controlled by signal UD1; when signal UD1 is H level, the input terminal is connected to the upper terminal, and when signal UD1 is L level, the input terminal is connected to the lower terminal. Capacitor 323 is connected to the upper terminal of switch 322, and capacitor 324 is connected to the lower terminal. Capacitor 323 is short-circuited by switch 325, and capacitor 324 is short-circuited by switch 326. Switches 325 and 326 are driven by an inverted signal of signal U(V-W) output by inverter 327. That is, when signal U(V-W) is H level, switches 325 and 326 are turned off, and capacitors 323 and 324 are able to charge. The voltage Vinp of the capacitor 323 and the voltage Vinn of the capacitor 324 are input to a comparator 328, and the output CmpU of the comparator 328 is input to a D terminal of a D flip-flop 329. A signal UD2 is input to the D flip-flop 329 as a clock signal, and the output CmpU of the comparator 328 when the signal UD2 rises is output from the D flip-flop 329 as a result U_UD of determining whether the U-phase voltage is increased or decreased.

[0029] 3 is a waveform diagram of essential parts of the motor control device according to embodiment 1. This diagram shows drive signals UH, UL, VH, VL, WH, and WL output by control drive circuit 30, current Im flowing through inverter 20, U-phase voltage Vu, output signal U(V-W) from time point setting circuit 31, delay signals UD1 and UD2, voltages Vinp and Vinn of capacitors 323 and 324, output CmpU from comparator 328, and determination output U_UD from non-energized phase voltage detection circuit 32.

[0030] First, the operation of determining whether or not the non-energized phase voltage increases or decreases when the U-phase voltage Vu of the motor control device according to embodiment 1 shown in FIGS. 1, 2A, and 2B becomes a non-energized phase will be described with reference to the waveform diagram of essential parts in FIG. 3.

[0031] 3, all signals except for the U-phase voltage Vu and the output CmpU of comparator 328 are at zero potential (L level). Because all switches of inverter 20 are off, U-phase voltage Vu remains near the midpoint potential between the power supply and ground. Furthermore, switches 325 and 326 are on, causing capacitors 323 and 324 to be grounded, and input voltages Vinp and Vinn are both at zero potential, so the output CmpU of comparator 328 is indefinite.

[0032] At time t0, when the drive signals VH and WL rise, the V-phase high-side switch element and the W-phase low-side switch element are turned on, and current Im begins to flow from the V-phase to the W-phase. Current Im increases at a slope determined by the inductances of the V and W-phases and the power supply voltage, and a voltage proportional to current Im is superimposed on the non-conductive U-phase. The polarity of this proportionality constant is determined by the rotor position. This is because the mutual inductance is determined by the rotor position, and the non-conductive phase voltage is determined according to the mutual inductance and current Im. The rotor position can be estimated as follows: if the U-phase voltage Vu increases, the rotor position (i.e., the rotor phase) is 180°±90°; if it decreases, it is 0°±90°. In time point setting circuit 31, signal U (V-W) rises, and in non-energized phase voltage detection circuit 32, delay signal UD1 is still at L level, so the input terminal and lower terminal of switch 322 are connected, and capacitor 324 is charged to divided voltage VU. Therefore, voltage Vinn becomes higher than voltage Vinp, and output CmpU of comparator 328 becomes L level.

[0033] At time t1, when delay signal UD1 from time point setting circuit 31 rises, switch 322 connects the input terminal to the upper terminal, and capacitor 323 is charged to divided voltage VU. Because voltage Vinn maintains the initial divided voltage VU, when U-phase voltage Vu increases, voltage Vinp becomes higher than voltage Vinn, and output CmpU of comparator 328 switches to H level. Conversely, when U-phase voltage Vu decreases, voltage Vinp remains lower than voltage Vinn, and output CmpU of comparator 328 remains L level.

[0034] At time t2, when the delay signal UD2 from the time point setting circuit 31 rises, a clock signal is input to the D flip-flop 329, and the output CmpU of the comparator 328 at that time is output as the determination signal U_UD. That is, if the U-phase voltage Vu has increased, the determination signal U_UD is fixed at the H level, and if it has decreased, the determination signal U_UD is fixed at the L level. At time t3, the signal U(V-W) falls, returning to the state before time t0.

[0035] The above operation is also performed when the V phase is a non-energized phase and when the W phase is a non-energized phase, to determine the determination signal V_UD for the V phase and the determination signal W_UD for the W phase. If the determination signal V_UD is at H level, the rotor phase is 300±90°, if it is at L level, the rotor phase is 120±90°, if the determination signal W_UD is at H level, the rotor phase is 60±90°, if it is at L level, the rotor phase is 240±90°.

[0036] The non-energized phase voltage detection circuit 32 outputs to the position estimation circuit (e.g., the control drive circuit 30) combinations (specifically, 2 cubed = 8 combinations) of the comparison results made by the non-energized phase voltage detection circuit 32 for each combination (specifically, three combinations) of selecting two phases from the three phases of the motor 10. Because the phase of the non-energized phase can be determined in advance for each combination of the comparison results of the induced voltages at two points in time when the V and W phases are selected as energized phases, the comparison results of the induced voltages at two points in time when the W and U phases are selected as energized phases, and the comparison results of the induced voltages at two points in time when the U and V phases are selected as energized phases, a phase estimation table such as that shown in FIG.

[0037] FIG. 4 is a phase estimation table for the motor control device according to the first embodiment. As shown in the rotor phase estimation table in FIG. 4, phase estimation is possible in 60° increments depending on the levels of the three-phase determination signals. For example, when determination signal U_UD is low, determination signal V_UD is high, and determination signal W_UD is high, the rotor phase ranges from 0°±90°, 300±90°, and 60±90°, i.e., from -30° to 30°. For example, the rotor phase can be estimated as 0°, midway between -30° and 30°. In this way, the position estimation circuit (e.g., control drive circuit 30) can estimate the rotor position of motor 10 based on the comparison results (specifically, a combination of comparison results such as (L, H, H)) made by non-energized phase voltage detection circuit 32.

[0038] There are 2^3 = 8 possible combinations of increase / decrease determination results, but Figure 3 excludes cases where a determination cannot be made (specifically, when all are at H level or when all are at L level). In such cases, it is advisable to improve the estimation accuracy by performing the detection operation again.

[0039] 2B , the de-energized phase voltage detection circuit 32 includes a comparator 328 that compares the voltage of the de-energized phase at a first time point with the voltage of the de-energized phase at a second time point. However, the comparator 328 is not limited to an analog circuit such as a comparator. The comparator 328 only needs to have the function of determining whether the voltage of the de-energized phase at the first time point has increased or decreased at the second time point. For example, the comparator 328 may be configured as an arithmetic circuit that stores digital values ​​obtained by AD-converting the voltage of the de-energized phase at each time point and determines whether the voltage has increased or decreased depending on whether each digital value is positive or negative when subtracted.

[0040] As described above, by comparing the induced voltage at two points in time in the non-energized phase during the energized period, it is possible to detect whether the induced voltage increases or decreases with the passage of energization time, and to accurately determine the phase of the non-energized phase. Therefore, the position of the motor 10 can be estimated accurately without a sensor before it is started.

[0041] Second Embodiment Next, a motor control device according to a second embodiment will be described.

[0042] In the motor control device according to the first embodiment, there is no limitation on the direction of current Im flowing through the energized phases (for example, V-phase and W-phase when the non-energized phase is U-phase). For example, in FIG. 4, when the rotor position is near 30°, which is midway between 0° and 60°, there is little change in phase voltage Vv when V-phase is the non-energized phase, which may result in uncertain increase / decrease determination. Therefore, in the motor control device according to the second embodiment, the time point setting circuit is a time point setting circuit 31A as shown in FIG. 5.

[0043] 5 is a circuit diagram showing a time point setting circuit 31A of a motor control device according to embodiment 2. For example, when the non-energized phase is the U phase, the time point setting circuit 31A determines whether the phase voltage Vu increases or decreases when a current Im flows from the V phase to the W phase, and whether the phase voltage Vu increases or decreases when a current Im flows from the W phase to the V phase.

[0044] In Figure 5, the same components as those of time setting circuit 31 shown in Figure 2A are assigned the same numbers, and their description will be omitted. The difference from time setting circuit 31 shown in Figure 2A is that OR gate 313 is omitted, and delay circuit 316, which receives signal U (V → W) and outputs delayed signal UD1 (V → W), and delay circuit 317, which outputs delayed signal UD2 (V → W), are provided, and delay circuit 318, which receives signal U (W → V) and outputs delayed signal UD1 (W → V), and delay circuit 319, which outputs delayed signal UD2 (W → V), are provided. The functions of delay circuits 316 and 318 are equivalent to those of delay circuit 314 in Figure 2A, and the functions of delay circuits 317 and 319 are equivalent to those of delay circuit 315 in Figure 2A.

[0045] Although not shown, the motor control device according to the second embodiment is equivalent to the non-energized phase voltage detection circuit 32 shown in FIG. 2B and includes a non-energized phase voltage detection circuit that receives the signal U (V→W), the delayed signal UD1 (V→W), and the delayed signal UD2 (V→W) and determines whether the U-phase voltage is increasing or decreasing, and a non-energized phase voltage detection circuit that receives the signal U (W→V), the delayed signal UD1 (W→V), and the delayed signal UD2 (W→V) and determines whether the U-phase voltage is increasing or decreasing. Furthermore, the motor control device according to the second embodiment also includes a time point setting circuit and a non-energized phase voltage detection circuit that determine whether the phase voltage Vv will increase or decrease when a current Im flows from the U phase to the W phase when the non-energized phase is the V phase, and whether the phase voltage Vv will increase or decrease when a current Im flows from the W phase to the V phase, and a time point setting circuit and a non-energized phase voltage detection circuit that determine whether the phase voltage Vw will increase or decrease when a current Im flows from the V phase to the U phase when the non-energized phase is the W phase, and whether the phase voltage Vw will increase or decrease when a current Im flows from the U phase to the V phase.

[0046] The operation of each is the same as in embodiment 1, and therefore detailed description will be omitted. The non-energized phase voltage detection circuit outputs combinations (specifically, 2 to the power of 6 = 64 combinations) of the results of comparison by the non-energized phase voltage detection circuit for each permutation (specifically, six permutations) that selects two phases from the three phases of motor 10 to a position estimation circuit (e.g., control drive circuit 30). The permutation that selects two phases from the three phases of motor 10 is a combination that selects two phases from the three phases of motor 10 while also taking into consideration the direction of flow of current Im. Comparison result of induced voltages at two points in time when V phase and W phase are selected as energized phases and the direction of current flow is selected from V phase to W phase; comparison result of induced voltages at two points in time when V phase and W phase are selected as energized phases and the direction of current flow is selected from W phase to V phase; comparison result of induced voltages at two points in time when W phase and U phase are selected as energized phases and the direction of current flow is selected from W phase to U phase; comparison result of induced voltages at two points in time when W phase and U phase are selected as energized phases and the direction of current flow is selected from W phase to U phase; Since the phase of the non-energized phase can be determined in advance for each combination of the results of comparing the induced voltages at two points in time when the U-phase to W-phase direction is selected, the results of comparing the induced voltages at two points in time when the U-phase and V-phase are selected as the energized phases and the U-phase to V-phase direction is selected as the current flow direction, and the results of comparing the induced voltages at two points in time when the U-phase and V-phase are selected as the energized phases and the V-phase to U-phase direction is selected as the current flow direction, a phase estimation table such as that shown in FIG. 6 can be created in advance.

[0047] FIG. 6 is a phase estimation table for the motor control device according to the second embodiment. The phase estimation table shown in FIG. 6 shows 18 possible combinations of increase / decrease determination results and was created with the possibility of erroneous detection near the boundary of the estimated phase as described above in mind. For example, when the rotor position is near 30°, which is midway between 0° and 60°, the determination of an increase / decrease in the phase voltage Vv when a current Im flows from the U phase to the W phase with the V phase being a non-energized phase often does not match the determination of an increase / decrease in the phase voltage Vv when a current Im flows from the W phase to the V phase. This is because the change in the direction of the current Im changes the likelihood of magnetic saturation at rotor positions such as 30°, which is midway between 0° and 60°, making the increase / decrease in the phase voltage more likely to be reversed. Therefore, when the determination of the increase or decrease in the phase voltage Vv when the current Im flows from the U phase to the W phase with the V phase being a non-energized phase does not match the determination of the increase or decrease in the phase voltage Vv when the current Im flows from the W phase to the V phase, it is possible to estimate that the rotor position is at 0° (specifically, between 0° and 30°). In other words, in such a case, it is possible to prevent the rotor position from being erroneously estimated as being at 60°.

[0048] There are 2 to the power of 6 = 64 possible combinations of increase / decrease determination results, but Figure 6 excludes cases where a determination cannot be made (for example, all are at H level) and cases where the possibility of erroneous detection is low. In such cases, the estimation accuracy may be improved by performing the detection operation again.

[0049] As described above, according to this embodiment, by taking the current direction into consideration and increasing the number of determination criteria, it is possible to reduce the possibility of erroneous detection and improve the accuracy of position estimation.

[0050] Note that the motor 10 may not necessarily be stationary before startup, such as when the motor 10 is vibrating irregularly due to cogging, when the motor 10 has not completely stopped since its last operation, or when the rotor is rotating due to an external factor (e.g., wind). In such cases, an accurate comparison result may not be obtained. Therefore, the position estimation circuit (e.g., the control and drive circuit 30) may estimate the rotor position of the motor 10 based on the comparison result by the non-energized phase voltage detection circuit if the comparison result by the non-energized phase voltage detection circuit is the same a predetermined number of times in succession. This also applies to the first embodiment and the third embodiment described below. If the motor 10 is rotating forward before startup, it is sufficient to transition to steady-state operation. However, if the motor is rotating backward or is operating irregularly, it is desirable to apply a forced brake and repeat the initial position estimation operation before startup as disclosed herein until the same comparison result is obtained a predetermined number of times in succession (e.g., three times). If the comparison result is the same a predetermined number of times in succession, it is considered that a correct comparison result has been obtained, and the rotor position of the motor 10 can be accurately estimated.

[0051] In addition, in typical sensorless motor control, to detect the rotor phase during rotation, the differential voltage between the voltage of the non-energized phase and the voltage of the motor neutral point (the connection point of the U-, V-, and W-phase windings) is detected as the induced voltage (BEMF), and the zero-crossing point of this voltage is detected. If the motor neutral point is not external to the motor 10, the voltage at the connection point connecting each phase with three resistors or the midpoint between the power supply and ground is used as the virtual neutral point voltage. In the above embodiment, an example is described in which the induced voltage is detected by resistively dividing the voltage of the non-energized phase. However, what is required for phase estimation is not the absolute value of the voltage, but whether it is increasing or decreasing. Therefore, the differential voltage between the phase voltage and a reference potential such as the neutral point potential may also be detected. Therefore, the comparator 328 in the non-energized phase voltage detection circuit can also be used as the comparator used in the BEMF zero-crossing detection circuit during steady-state operation. In other words, the comparator 328 may perform comparisons to detect the zero-crossing points of the induced voltage used to detect the rotor position after the motor 10 is started. This is similar to the first embodiment and the third embodiment described below. The same applies when AD conversion and digital processing are performed as described above, and the non-energized phase voltage detection circuit of the present disclosure can share its components with the BEMF zero-cross detection circuit during steady-state operation. As described above, the motor control device of the present disclosure can use a comparator that performs comparisons to detect zero-crossing points of the induced voltage used to detect the rotor position after start-up of the motor 10, and also use comparator 328 that estimates the position before start-up of the motor 10, thereby reducing the number of components required for initial position estimation. In other words, the motor control device can be made smaller and less expensive.

[0052] Third Embodiment Next, a motor control device according to a third embodiment will be described.

[0053] In the first and second embodiments, examples have been described in which the timing for detecting the voltage of the non-energized phase is set from the drive signal using a delay circuit in the time point setting circuits 31 and 31A, but the present disclosure is not limited to this method, and the timing for detecting the voltage of the non-energized phase may also be set using the inverter current Im.

[0054] Figure 7A is a circuit diagram showing a motor control device according to embodiment 3. Figure 7B is a circuit diagram showing a time point setting circuit 31B of the motor control device according to embodiment 3. In both figures, the same numbers are used to designate components with the same functional configuration as those in Figures 1 and 2A shown in embodiment 1, and their description will be omitted.

[0055] The motor control device according to embodiment 3 shown in FIG. 7A differs from the motor control device according to embodiment 1 shown in FIG. 1 in that it adds a resistor 33 for detecting the inverter current Im and inputs the voltage across resistor 33 to a time point setting circuit 31B. The time point setting circuit 31B shown in FIG. 7B differs from the time point setting circuit 31 shown in FIG. 2A in that, instead of the delay circuit 315, it includes a comparator 331 that compares the voltage across resistor 33 with a voltage source 330, an AND gate 332, and generates a signal UD2 by logically multiplying a signal U(V-W) and the output CmpI of the comparator 331. The resistance of resistor 33 is Rs, and the voltage of voltage source 330 is Vs. That is, the inverter current Im is compared with a threshold value Vs / Rs by the comparator 331. The non-energized phase voltage detection circuit 32 has the same configuration as that shown in FIG. 2B, and therefore a description thereof will be omitted.

[0056] 8 is a waveform diagram of essential parts of the motor control device according to embodiment 3. Fig. 8 shows output signal U(V-W) and delay signal UD1 of time point setting circuit 31B, current Im and threshold value VS / Rs flowing through inverter 20, output CmpI of comparator 331, output signal UD2, voltages Vinp and Vinn of capacitors 323 and 324, output CmpU of comparator 328, and determination output U_UD of non-energized phase voltage detection circuit 32.

[0057] The operation of determining whether the phase voltage is increased or decreased when the U-phase voltage Vu of the motor control device according to the third embodiment is a non-energized phase will be described below with reference to the waveform diagram of essential parts in Figure 8. Note that the operation before time t0 in Figure 8 and the process of generating the signal U(V-W) are the same as those in the first embodiment, and therefore will not be described here.

[0058] At time t0, current Im begins to flow from the V phase to the W phase, and signal U (V-W) rises. Current Im increases at a rate determined by the inductances of the V and W phases and the power supply voltage, and a voltage proportional to current Im is superimposed on the de-energized U phase. In de-energized phase voltage detection circuit 32, voltage Vinn is higher than voltage Vinp, and output CmpU of comparator 328 goes low.

[0059] At time t1, when delay signal UD1 from time point setting circuit 31B rises, switch 322 connects the input terminal to the upper terminal, and capacitor 323 is charged to divided voltage VU. Because voltage Vinn maintains the initial divided voltage VU, when U-phase voltage Vu increases, voltage Vinp becomes higher than voltage Vinn, and output CmpU of comparator 328 switches to H level. Conversely, when U-phase voltage Vu decreases, voltage Vinp remains lower than voltage Vinn, and output CmpU of comparator 328 remains L level.

[0060] At time t2, when inverter current Im exceeds threshold value Vs / Rs, output signal CmpI of comparator 331 of time point setting circuit 31B is inverted to H level. When signal UD2, which is the logical product of signal CmpI and signal U(V-W), rises, a clock signal is input to D flip-flop 329, and output CmpU of comparator 328 at that time is output as determination signal U_UD. In other words, if U-phase voltage Vu has increased, determination signal U_UD is fixed at H level, and if it has decreased, determination signal U_UD is fixed at L level. At time t3, signal U(V-W) falls, returning to the state before time t0.

[0061] The above operation is also performed when the V phase is the non-energized phase and when the W phase is the non-energized phase, and a determination signal V_UD for the V phase and a determination signal W_UD for the W phase are determined. As shown in the rotor phase estimation table of Figure 4, similar to the first embodiment, phase estimation in 60° increments is possible according to the levels of the three-phase determination signals.

[0062] In this way, the motor control device may include a current detection circuit (e.g., resistor 33) that detects the current Im of the inverter 20, and the time point setting circuit 31B may set the first time point to a timing that is a first predetermined time after the control drive circuit 30 selects two of the three phases of the motor 10 and starts energizing them, and may set the second time point to a time point when the current Im of the inverter 20 detected by the current detection circuit reaches a predetermined value. Because the current Im of the inverter 20 gradually increases over time, the first and second time points can be set by utilizing the change in the current Im of the inverter 20 over time. Note that the first and second time points may also be set in the second embodiment as in the third embodiment.

[0063] The current detection circuit may also detect overcurrent in the inverter 20. In this embodiment, the current detection circuit detects the inverter current Im and compares it with a threshold value, but by adjusting the threshold value, the current detection circuit can also be used as an overcurrent detection circuit for the inverter 20. In other words, the inverter current detection circuit used in the overcurrent protection circuit can be used as part of the time point setting circuit 31B. Therefore, the motor control device of the present disclosure can reduce the number of components used for initial position estimation. In other words, the motor control device can be made smaller and less expensive.

[0064] (Other Embodiments) As described above, the embodiments have been described as examples of the technology according to the present disclosure. However, the technology according to the present disclosure is not limited to these, and can be applied to embodiments in which modifications, substitutions, additions, omissions, etc. are made as appropriate. For example, the following modifications are also included in one embodiment of the present disclosure.

[0065] For example, the present disclosure can be realized not only as a motor control device, but also as a motor control method including steps (processing) performed by components that make up the motor control device.

[0066] FIG. 9 is a flowchart showing an example of a motor control method according to another embodiment.

[0067] The motor control method is a motor control method executed by a motor control device, and as shown in FIG. 9 , includes a control drive step (step S11) of supplying a drive signal to an inverter circuit that drives a three-phase motor, a time point setting step (step S12) of setting a first time point and a second time point during a period before the start of the three-phase motor in which two of the three phases of the three-phase motor are selected and energized in the control drive step, and a non-energized phase voltage detection step (step S13) of comparing the voltage of a non-energized phase of the three-phase motor at the first time point with the voltage of the non-energized phase at the second time point.

[0068] For example, the present disclosure can be realized as a program for causing a computer (processor) to execute steps included in a motor control method. Furthermore, the present disclosure can be realized as a non-transitory computer-readable recording medium, such as a CD-ROM, on which the program is recorded.

[0069] For example, when the present disclosure is realized as a program (software), each step is performed by running the program using hardware resources such as a computer's CPU, memory, input / output circuitry, etc. In other words, each step is performed by the CPU acquiring data from memory or input / output circuitry, etc., performing calculations, and outputting the calculation results to memory or input / output circuitry, etc.

[0070] In the above-described embodiments, each component included in the motor control device may be configured with dedicated hardware, or may be realized by executing a software program suitable for each component. Each component may be realized by a program execution unit such as a CPU or processor reading and executing a software program recorded on a recording medium such as a hard disk or semiconductor memory.

[0071] Some or all of the functions of the motor control devices according to the above embodiments are typically realized as an LSI, which is an integrated circuit. These functions may be individually integrated into single chips, or some or all of them may be integrated into a single chip. Furthermore, the integrated circuit is not limited to an LSI, and may be realized using a dedicated circuit or a general-purpose processor. It is also possible to use an FPGA (Field Programmable Gate Array), which can be programmed after LSI manufacturing, or a reconfigurable processor, which allows the connections and settings of circuit cells within an LSI to be reconfigured.

[0072] Furthermore, if an integrated circuit technology that can replace LSI emerges due to advances in semiconductor technology or other derivative technologies, it is natural that each component included in the motor control device can be integrated using that technology.

[0073] In addition, this disclosure also includes forms obtained by making various modifications to the embodiments that a person skilled in the art would think of, and forms realized by arbitrarily combining the components and functions in each embodiment within the scope that does not deviate from the intent of this disclosure.

[0074] (Additional Notes) The above description of the embodiments discloses the following techniques.

[0075] (Technology 1) A motor control device having a control drive circuit that supplies a drive signal to an inverter circuit that drives a three-phase motor; a time point setting circuit that sets a first time point and a second time point during a period before the start of the three-phase motor when the control drive circuit selects and energizes two of the three phases of the three-phase motor; and a non-energized phase voltage detection circuit that compares the voltage of a non-energized phase of the three-phase motor at the first time point with the voltage of the non-energized phase at the second time point.

[0076] This allows for accurate position estimation of a three-phase motor before it is started, without using a sensor, by detecting whether the induced voltage increases or decreases with the passage of time between the energized and de-energized phases.

[0077] (Technology 2) A motor control device according to Technology 1, wherein the non-energized phase voltage detection circuit outputs a combination of the comparison results by the non-energized phase voltage detection circuit for each combination of two phases selected from the three phases of the three-phase motor.

[0078] This allows the phase of the non-energized phase to be determined in advance for each combination of the results of comparing the induced voltages at two points in time when the V and W phases are selected as the energized phases, the results of comparing the induced voltages at two points in time when the W and U phases are selected as the energized phases, and the results of comparing the induced voltages at two points in time when the U and V phases are selected as the energized phases. Therefore, based on these combinations, the position of the three-phase motor can be estimated accurately without a sensor before it is started.

[0079] (Technology 3) The motor control device according to Technology 1, wherein the non-energized phase voltage detection circuit outputs a combination of the results of the comparison by the non-energized phase voltage detection circuit for each permutation of selecting two phases from the three phases of the three-phase motor.

[0080] This makes it possible to determine in advance the phase of the non-energized phase for each combination of the following: a comparison result of induced voltages at two points in time when the V phase and the W phase are selected as the energized phases and the direction from the V phase to the W phase is selected as the current flow direction; a comparison result of induced voltages at two points in time when the V phase and the W phase are selected as the energized phases and the direction from the W phase to the V phase is selected as the current flow direction; a comparison result of induced voltages at two points in time when the W phase and the U phase are selected as the energized phases and the direction from the W phase to the U phase is selected as the current flow direction; a comparison result of induced voltages at two points in time when the W phase and the U phase are selected as the energized phases and the direction from the U phase to the W phase is selected as the current flow direction; a comparison result of induced voltages at two points in time when the U phase and the V phase are selected as the energized phases and the direction from the U phase to the V phase is selected as the current flow direction; and a comparison result of induced voltages at two points in time when the U phase and the V phase are selected as the energized phases and the direction from the V phase to the U phase is selected as the current flow direction. Therefore, based on these combinations, it is possible to perform sensorless position estimation with higher accuracy before starting the three-phase motor.

[0081] (Technology 4) The motor control device according to any one of Technologies 1 to 3, further comprising a position estimation circuit that estimates a rotor position of the three-phase motor based on the result of the comparison by the non-energized phase voltage detection circuit.

[0082] In this way, the motor control device may have a position estimation circuit that estimates the rotor position of the three-phase motor based on the comparison result by the non-energized phase voltage detection circuit.

[0083] (Technology 5) A motor control device according to Technology 4, wherein the position estimation circuit estimates the position of the rotor of the three-phase motor based on the result of the comparison by the non-energized phase voltage detection circuit when the result of the comparison by the non-energized phase voltage detection circuit is the same a predetermined number of times in succession.

[0084] For example, there are cases where the three-phase motor is vibrating irregularly due to cogging, where the three-phase motor has not completely stopped since its last operation, or where the rotor is rotating due to an external factor (e.g., wind). In such cases, there is a risk that a correct comparison result will not be obtained. Therefore, if the same comparison result is obtained a predetermined number of times in succession, it is considered that a correct comparison result has been obtained, and the rotor position of the three-phase motor can be accurately estimated based on the correct comparison result.

[0085] (Technology 6) A motor control device according to any one of Technologies 1 to 5, wherein the non-energized phase voltage detection circuit has a comparator that compares the voltage of the non-energized phase at the first time point with the voltage of the non-energized phase at the second time point, and the comparator performs a comparison to detect a zero-crossing point of an induced voltage that is used to detect the position of the rotor of the three-phase motor after startup of the three-phase motor.

[0086] This allows the comparator to perform comparisons to detect the zero-crossing points of the induced voltage used to detect the rotor position after the three-phase motor is started, and also to estimate the position of the three-phase motor before it is started, making it possible to make the motor control device smaller and less expensive.

[0087] (Technology 7) A motor control device described in any of Technologies 1 to 6, wherein the time point setting circuit sets the first time point to a timing that is a first predetermined time after the control drive circuit selects two of the three phases of the three-phase motor and starts to energize them, and sets the second time point to a timing that is a second predetermined time after the first time point.

[0088] According to this, the first and second points in time can be set by a delay circuit or the like.

[0089] (Technology 8) A motor control device according to any one of Technologies 1 to 6, further comprising a current detection circuit that detects the current of the inverter circuit, wherein the time point setting circuit sets the first time point to a timing that is a first predetermined time after the control drive circuit selects two of the three phases of the three-phase motor and starts energizing them, and sets the second time point to a time point when the current of the inverter circuit detected by the current detection circuit reaches a predetermined value.

[0090] According to this, since the current of the inverter gradually increases with time, the first and second points in time can be set by utilizing the change in the current of the inverter over time.

[0091] (Technology 9) The motor control device according to Technology 8, wherein the current detection circuit detects an overcurrent in the inverter circuit.

[0092] This allows the current detection circuit to be used both as a current detection circuit for detecting overcurrent in the inverter and as a current detection circuit for setting the first and second points in time, making it possible to reduce the size and cost of the motor control device.

[0093] (Technology 10) A motor control method executed by a motor control device, the motor control method including: a control drive step of supplying a drive signal to an inverter circuit that drives a three-phase motor; a time point setting step of setting a first time point and a second time point during a period before starting the three-phase motor, during which two of the three phases of the three-phase motor are selected and energized in the control drive step; and a non-energized phase voltage detection step of comparing the voltage of a non-energized phase of the three-phase motor at the first time point with the voltage of the non-energized phase at the second time point.

[0094] This provides a motor control method that can accurately estimate the position of a three-phase motor before it is started without using a sensor.

[0095] The present disclosure can be applied to a motor control device that detects the initial position of a rotor of a three-phase motor before the start of operation without using a sensor.

[0096] 10 Motor 20 Inverter 30 Control drive circuit 31, 31A, 31B Time point setting circuit 32 Non-energized phase voltage detection circuit 33, 320, 321 Resistor 310 NOR gate 311, 312, 332 AND gate 313 OR gate 314, 315, 316, 317, 318, 319 Delay circuit 322, 325, 326 Switch 323, 324 Capacitor 327 Inverter 328, 331 Comparator 329 D flip-flop 330 Voltage source

Claims

1. A motor control device comprising: a control drive circuit that supplies a drive signal to an inverter circuit that drives a three-phase motor; a time point setting circuit that sets a first time point and a second time point during a period before the start of the three-phase motor during which the control drive circuit selects and energizes two of the three phases of the three-phase motor; and a non-energized phase voltage detection circuit that compares the voltage of a non-energized phase of the three-phase motor at the first time point with the voltage of the non-energized phase at the second time point.

2. A motor control device according to claim 1, wherein the non-energized phase voltage detection circuit outputs a combination of the results of the comparison by the non-energized phase voltage detection circuit for each combination of two phases selected from the three phases of the three-phase motor.

3. The motor control device according to claim 1, wherein the non-energized phase voltage detection circuit outputs a combination of the results of the comparison by the non-energized phase voltage detection circuit for each permutation of selecting two phases from the three phases of the three-phase motor.

4. A motor control device according to any one of claims 1 to 3, further comprising a position estimation circuit that estimates the rotor position of the three-phase motor based on the result of the comparison by the non-energized phase voltage detection circuit.

5. A motor control device as described in claim 4, wherein the position estimation circuit estimates the rotor position of the three-phase motor based on the result of the comparison by the non-energized phase voltage detection circuit when the result of the comparison by the non-energized phase voltage detection circuit is the same a predetermined number of times in succession.

6. A motor control device according to any one of claims 1 to 5, wherein the non-energized phase voltage detection circuit has a comparator that compares the voltage of the non-energized phase at the first time point with the voltage of the non-energized phase at the second time point, and the comparator performs a comparison to detect a zero-crossing point of an induced voltage used to detect the rotor position of the three-phase motor after startup of the three-phase motor.

7. A motor control device as claimed in any one of claims 1 to 6, wherein the time point setting circuit sets the first time point to a timing that is a first predetermined time after the control drive circuit selects two of the three phases of the three-phase motor and starts energizing them, and sets the second time point to a timing that is a second predetermined time after the first time point.

8. A motor control device according to any one of claims 1 to 6, further comprising a current detection circuit that detects the current in the inverter circuit, wherein the time point setting circuit sets the first time point to a timing that is a first predetermined time after the control drive circuit selects two of the three phases of the three-phase motor and starts to energize them, and sets the second time point to a time when the current in the inverter circuit detected by the current detection circuit reaches a predetermined value.

9. The motor control device according to claim 8, wherein the current detection circuit detects an overcurrent in the inverter circuit.

10. A motor control method executed by a motor control device, comprising: a control drive step of supplying a drive signal to an inverter circuit that drives a three-phase motor; a time point setting step of setting a first time point and a second time point during a period before the start of the three-phase motor during which two of the three phases of the three-phase motor are selected and energized in the control drive step; and a non-energized phase voltage detection step of comparing the voltage of a non-energized phase of the three-phase motor at the first time point with the voltage of the non-energized phase at the second time point.

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