Motor control device and motor control method

Abstract

The present invention rotates a rotor of an electric motor by sequentially switching between energization modes that designate, from among the three phases of the electric motor, two phases in which a pulse voltage is applied. The pulse voltage alternately generates first pulses for rotating the rotor in one direction and second pulses for rotating the rotor in the reverse direction, the second pulses having a polarity opposite to that of the first pulses. The energization modes are switched to one direction or the reverse direction on the basis of the comparison between a first threshold value and the value of a first open phase voltage resulting from the application of the first pulses and the comparison between a second threshold value and the value of a second open phase voltage resulting from the application of the second pulses. When switching to the reverse direction, the first threshold value is set on the basis of the value of the first open phase voltage and the first initial threshold value preset for each energization mode. When switching to the one direction, the second threshold value is set on the basis of the value of the second open phase voltage and the second initial threshold value preset for each energization mode.

Description

[Technical Field]

[0001] The present invention relates to a motor control device and a motor control method. [Background technology]

[0002] A known motor control method rotates the rotor of an electric motor by sequentially switching between conduction modes that specify two of the three-phase coils of the electric motor to which a pulse voltage is applied (see, for example, Patent Document 1). This pulse voltage alternates between forward rotation pulses for rotating the rotor in the forward direction and reverse rotation pulses with the opposite polarity to the forward rotation pulses for rotating the rotor in the reverse direction. Rotational drive is controlled in either the forward or reverse direction by reversing the length of the application time of the forward and reverse rotation pulses. The conduction mode is switched to the forward direction when a forward rotation open phase voltage induced in the open phase by application of a forward rotation pulse crosses a forward rotation threshold set for each conduction mode in a predetermined direction. On the other hand, the conduction mode is switched to the reverse direction when a reverse rotation open phase voltage induced in the open phase by application of a reverse rotation pulse crosses a reverse rotation threshold set for each conduction mode in a predetermined direction. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Republished Patent Publication WO2012 / 029451 Summary of the Invention [Problem to be solved by the invention]

[0004] When the rotor starts rotating in the reverse direction from a forward rotation state, it is assumed that the reverse rotation opening phase voltage has already crossed the reverse rotation threshold in the predetermined direction immediately after the most recent current conduction mode change before the rotor rotation changes from forward to reverse. In such a case, if the reverse rotation opening phase voltage does not change to the value before crossing the reverse rotation threshold in the predetermined direction before the rotor rotation changes from forward to reverse, even if the rotor starts rotating in the reverse direction, the reverse rotation opening phase voltage will not cross the reverse rotation threshold in the predetermined direction, causing a loss of synchronization. Naturally, a similar loss of synchronization can also occur when the rotor starts rotating in the forward direction from a reverse rotation state.

[0005] Furthermore, due to various factors such as individual differences between electric motors, the values ​​of the reverse rotation open phase voltage and forward rotation open phase voltage immediately after switching the current supply mode also vary, making it difficult to set the reverse rotation threshold and forward rotation threshold to constant values ​​in advance so as to prevent loss of synchronization due to reversal of the rotation direction.

[0006] The present invention has been made in consideration of the above-mentioned problems, and has as its object to provide a motor control device and a motor control method that suppress loss of synchronization of an electric motor. [Means for solving the problem]

[0007] Therefore, the motor control device and motor control method according to the present invention rotate the rotor of the electric motor by sequentially switching between current conduction modes that specify two-phase coils to which a pulse voltage is applied among the three-phase coils of the electric motor, and outputs a control signal to a drive circuit that drives the electric motor so that the pulse voltage alternately generates a first pulse for rotating the rotor in one direction and a second pulse having the opposite polarity to the first pulse for rotating the rotor in the direction opposite to the one direction, and by reversing the magnitude relationship between the application times of the first pulse and the second pulse, the rotor can be rotated in one direction or the reverse direction. and controls the rotational drive of the motor, detects a first open phase voltage induced in the open phase when a first pulse is applied, and a second open phase voltage induced in the open phase when a second pulse is applied, and for each current conduction mode, sets a first threshold value that specifies the value of the first open phase voltage when switching the current conduction mode in one direction, and sets a second threshold value that specifies the value of the second open phase voltage when switching the current conduction mode in the reverse direction, and switches the current conduction mode to either one direction or the reverse direction based on two comparison results: comparing the value of the first open phase voltage with the first threshold value, and comparing the value of the second open phase voltage with the second threshold value. When the current conduction mode is switched in the opposite direction, the first threshold value is set based on a first switching detection value, which is the value of the first open phase voltage immediately after the current conduction mode is switched, and a first initial threshold value preset for each current conduction mode, while when the current conduction mode is switched in one direction, the second threshold value is set based on a second switching detection value, which is the value of the second open phase voltage immediately after the current conduction mode is switched, and a second initial threshold value preset for each current conduction mode. [Effects of the Invention]

[0008] According to the motor control device of the present invention, it is possible to suppress loss of synchronization of the electric motor. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 2 is a schematic diagram illustrating an example of an electric motor and its drive control system. [Figure 2] FIG. 1 is a schematic diagram illustrating an example of a hardware configuration of a motor control device. [Figure 3] FIG. 10 is an explanatory diagram schematically illustrating an example of square wave driving during forward rotation. [Figure 4] FIG. 10 is an explanatory diagram illustrating an example of square wave driving during reverse rotation. [Figure 5] FIG. 10 is an explanatory diagram illustrating a schematic diagram of the open phase voltage in the conduction mode [3]. [Figure 6] FIG. 10 is an explanatory diagram schematically showing a change in a normal rotation open phase voltage with respect to a rotor rotation angle. [Figure 7] FIG. 10 is an explanatory diagram schematically showing a change in reverse rotation open phase voltage with respect to the rotor rotation angle. [Figure 8] FIG. 2 is a functional block diagram relating to low-speed sensorless control of the motor control device. [Figure 9] FIG. 3 is a functional block diagram showing a detailed configuration of a voltage command adjusting unit. [Figure 10] FIG. 3 is a functional block diagram showing a detailed configuration of a control signal generating unit. [Figure 11] 10 is a time chart showing a control signal waveform when an applied voltage command value is zero. [Figure 12] 10 is a time chart showing a control signal waveform when an applied voltage command value is a positive value. [Figure 13] 10 is a time chart showing a control signal waveform when the applied voltage command value is a negative value. [Figure 14] FIG. 4 is a functional block diagram showing a detailed configuration of an open phase voltage detection unit. [Figure 15] FIG. 4 is a functional block diagram showing a detailed configuration of a normal rotation threshold setting unit. [Figure 16] FIG. 4 is a functional block diagram showing a detailed configuration of a reverse rotation threshold setting unit. [Figure 17] 4 is a time chart showing an example of improved operation of the electric motor. [Figure 18] 18 is an explanatory diagram showing the change in the open phase voltage of FIG. 17 with respect to the rotor rotation angle. FIG. [Figure 19] FIG. 10 is an explanatory diagram illustrating the lower limit of the threshold value set in the energization mode [3]. [Figure 20] FIG. 10 is an explanatory diagram illustrating the upper limit of the threshold value set in the energization mode [4]. [Figure 21] 1 is a time chart showing an example of a conventional operation of an electric motor. [Figure 22] 22 is an explanatory diagram showing the change in the open phase voltage of FIG. 21 with respect to the rotor rotation angle. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0010] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 shows an example of an electric motor and its drive control system.

[0011] The electric motor 1 is driven by a drive circuit 2, and the drive of the electric motor 1 is controlled by a motor control device 3. The motor control device 3 can control the electric motor 1 to rotate in both forward and reverse directions, and the bidirectionally rotating electric motor 1 is used as a power source for various in-vehicle devices. For example, the electric motor 1 is used as a power source that can rotate in both forward and reverse directions in a variable compression mechanism of an internal combustion engine to adjust the top dead center position of the piston. The electric motor 1 can also be used as a power source that can rotate in both forward and reverse directions in an electric water pump that circulates engine coolant, an electronically controlled throttle that adjusts the amount of intake air for an internal combustion engine, an electric parking brake, and other devices.

[0012] [General configuration of electric motor] The electric motor 1 is a three-phase synchronous motor and includes a rotor 11 in which permanent magnets 11B with opposite polarities are alternately arranged in a rotor yoke 11A in the direction of rotation, and a stator 12 including a U-phase coil 12u, a V-phase coil 12v, and a W-phase coil 12w. Although not shown, the stator 12 is configured such that teeth that face the rotor 11 in the radial direction relative to the rotation axis are sequentially arranged along the direction of rotation of the rotor 11, and these multiple teeth are connected by a stator yoke. Three-phase coils 12u, 12v, and 12w are wound around the multiple teeth of the stator 12, and one end of each of the three-phase coils 12u, 12v, and 12w is Y-connected to form a neutral point 12N.

[0013] [Outline of the drive circuit] The drive circuit 2 receives a DC voltage V DC The inverter has a three-phase bridge circuit in which a U-phase arm, a V-phase arm, and a W-phase arm are connected in parallel between a positive-side bus 2A connected to the positive electrode of an in-vehicle battery 4 and a negative-side bus 2B connected to the negative electrode of the in-vehicle battery 4. The U-phase arm is configured by connecting an upper-arm switching element 21 and a lower-arm switching element 22 in series, and the two switching elements 21, 22 are connected to the other end 13 of the U-phase coil 12u. The V-phase arm is configured by connecting an upper-arm switching element 23 and a lower-arm switching element 24 in series, and the two switching elements 23, 24 are connected to the other end 14 of the V-phase coil 12v. The W-phase arm is configured by connecting an upper-arm switching element 25 and a lower-arm switching element 26 in series, and the two switching elements 25, 26 are connected to the other end 15 of the W-phase coil 12w.

[0014] In the drive circuit 2, the switching elements 21 to 26 each have an anti-parallel free-wheeling diode D and an externally controllable control electrode, and perform a switching operation of switching between an on state and an off state in accordance with a control signal input to the control electrode. The switching elements 21 to 26 are, for example, power semiconductor elements such as MOSFETs (Metal Oxide Semiconductor Metal Field Effect Transistors) and IGBTs (Insulated Gate Bipolar Transistors). In the following description, it is assumed that N-channel MOSFETs are used as the switching elements 21 to 26. When the switching elements 21 to 26 are turned on by a high-level gate signal equal to or greater than a threshold voltage, electrical conduction is established between the drain and source, and when the switching elements are turned off by a low-level gate signal below the threshold, electrical conduction is interrupted between the drain and source.

[0015] [Motor control device overview] The motor control device 3 has a built-in computer, as shown in Fig. 2, an example of its hardware configuration. Specifically, the motor control device 3 includes a processor 31 such as a CPU (Central Processing Unit) that performs arithmetic control. The motor control device 3 also includes volatile memory 32, such as SRAM (Static Random Access Memory) or DRAM (Dynamic Random Access Memory), that temporarily stores information, and non-volatile memory 33, such as flash memory, that permanently stores information. The motor control device 3 also includes an input / output interface 34 that inputs and outputs signals to and from the outside. These devices are connected to each other via a bus 35 so that they can communicate with each other.

[0016] Referring again to FIG. 1 , motor control device 3 receives a command signal including an applied voltage command value V* and inputs three-phase applied voltages Vu, Vv, and Vw. Based on these signals and voltages, motor control device 3 generates and outputs gate signals for switching elements 21-26. The applied voltage command value V* is calculated by a higher-level control device than motor control device 3 and can take positive or negative values, including zero. A positive applied voltage command value V* indicates a forward rotation command for rotating electric motor 1 forward; a negative applied voltage command for rotating electric motor 1 reversely; and a zero applied voltage command for stopping electric motor 1. Regarding the three-phase applied voltages Vu, Vv, and Vw, U-phase applied voltage Vu corresponds to the voltage at the other end 13 of U-phase coil 12u, V-phase applied voltage Vv corresponds to the voltage at the other end 14 of V-phase coil 12v, and W-phase applied voltage Vw corresponds to the voltage at the other end 15 of W-phase coil 12w. If the motor control device 3 can detect the operation or state of a system powered by the electric motor 1, the motor control device 3 may calculate the applied voltage command value V* so that the system reaches a target state. The gate signal may also be output via a pre-driver that adjusts the voltage to a voltage suitable for driving the switching elements 21-26.

[0017] The motor control device 3 uses sine wave drive (180° energization) in the high rotation speed range above a predetermined rotation speed, and square wave drive (120° energization) in the low rotation speed range below the predetermined rotation speed as a drive method for the electric motor 1. Sine wave drive is a method of driving the electric motor 1 by applying a pseudo-sine wave voltage to the three-phase coils 12u, 12v, and 12w. On the other hand, square wave drive is a method of driving the electric motor 1 by sequentially switching, in increments of 60 electrical degrees, the energization mode that specifies two-phase coils to which a pulse voltage is applied among the three-phase coils 12u, 12v, and 12w.

[0018] From the viewpoint of reducing product costs and size, the motor control device 3 controls the driving of the electric motor 1 using sensorless control that estimates the rotation angle of the rotor 11 (hereinafter referred to as the "rotor rotation angle") without using a position detection sensor such as a Hall element. In sensorless control using sinusoidal wave drive, the rotor rotation angle is detected based on the induced voltage (speed electromotive force) generated by the rotation of the rotor 11. On the other hand, in sensorless control using square wave drive, the timing to switch the current conduction mode is detected based on a comparison between the value of the pulse induced voltage (hereinafter referred to as the "open phase voltage") generated in a non-energized open phase coil by applying a pulse voltage to the two-phase coil and a predetermined threshold. This is because it may be difficult to detect the speed electromotive force with high accuracy at rotation speeds below a predetermined speed.

[0019] Note that if the system using the electric motor 1 as a power source is not intended for use in the high rotational speed range, the motor control device 3 may drive the electric motor 1 only with square wave drive. Below, we will omit the explanation of sine wave drive control and instead explain square wave drive control (low speed sensorless control) that detects the timing to switch the current supply mode based on the value of the open phase voltage and a predetermined threshold value.

[0020] Next, the square wave drive of the electric motor 1 will be described with reference to Figures 3 and 4. Figure 3 shows an example of square wave drive when rotating the rotor 11 forward, and Figure 4 shows an example of square wave drive when rotating the rotor 11 reversely. The current conduction modes for square wave drive are composed of six current conduction modes [1] to [6].

[0021] As shown in Fig. 3, when the rotor 11 is rotated in the forward direction, the energization modes [1] to [6] are switched sequentially in this order. On the other hand, as shown in Fig. 4, when the rotor 11 is rotated in the reverse direction, the energization modes [1] to [6] are switched sequentially in the reverse order to when the rotor 11 is rotated in the forward direction.

[0022] The energization modes [1] to [6] are switched when the rotor rotation angle matches a predetermined angle (energization switching angle). The energization switching angle is determined in increments of 60 degrees in electrical angle corresponding to the energization modes [1] to [6], and is set to six angles, for example, 210 degrees, 270 degrees, 330 degrees, 30 degrees, 90 degrees, and 150 degrees. When set in this manner, during forward rotation, the mode switches to energization mode [1] at 210 degrees, to energization mode [2] at 270 degrees, to energization mode [3] at 330 degrees, to energization mode [4] at 30 degrees, to energization mode [5] at 90 degrees, and to energization mode [6] at 150 degrees. Also, when rotating in reverse, it switches to conduction mode [6] at 210°, switches to conduction mode [5] at 150°, switches to conduction mode [4] at 90°, switches to conduction mode [3] at 30°, switches to conduction mode [2] at 330°, and switches to conduction mode [1] at 270°.

[0023] 3 and 4, the pulse voltages applied to the two-phase coils in the current conduction modes [1] to [6] are shown as the U-phase to V-phase line voltage Vuv, the V-phase to W-phase line voltage Vvw, and the W-phase to U-phase line voltage Vwu. Here, the line voltage Vuv is the difference [Vu-Vv] obtained by subtracting the V-phase applied voltage Vv from the U-phase applied voltage Vu, the line voltage Vvw is the difference [Vv-Vw] obtained by subtracting the W-phase applied voltage Vw from the V-phase applied voltage Vv, and the line voltage Vwu is the difference [Vw-Vu] obtained by subtracting the U-phase applied voltage Vu from the W-phase applied voltage Vw.

[0024] 3 and 4, the line voltages Vuv, Vvw, and Vwu include forward rotation pulses (first pulses) that cause a line current to flow so as to rotate the rotor 11 in the forward direction, and reverse rotation pulses (second pulses) that have the opposite polarity to the forward rotation pulses and cause a line current to flow so as to reverse the rotor 11. In the line voltages Vuv, Vvw, and Vwu, forward rotation pulses and reverse rotation pulses are generated alternately.

[0025] As shown in Fig. 3, when the rotor 11 is rotated forward, the pulse width of the forward rotation pulse in the conduction modes [1] to [6] is larger than the pulse width of the reverse rotation pulse. The difference between the two pulse widths is minimum (for example, zero) when the applied voltage command value V* is zero, and increases as the applied voltage command value V* increases in the positive direction. The forward rotation pulse is generated by the DC voltage V DC On the other hand, in the case of the line voltage Vwu in the conduction mode [2], the forward pulse flows a line current from the U phase to the W phase, so the absolute value of the DC voltage V DCThe forward pulse is a pulse (negative pulse) with an amplitude of a negative value corresponding to the line voltage Vvw in conduction mode [3]. Similarly, the forward pulse is a positive pulse to cause a line current to flow from the V phase to the W phase in the line voltage Vvw in conduction mode [3], while it is a negative pulse to cause a line current to flow from the V phase to the U phase in the line voltage Vuv in conduction mode [4]. Also, the forward pulse is a positive pulse to cause a line current to flow from the W phase to the U phase in the line voltage Vwu in conduction mode [5], while it is a negative pulse to cause a line current to flow from the W phase to the V phase in the line voltage Vvw in conduction mode [6]. Note that the reverse pulse is a positive or negative pulse of the opposite polarity to the forward pulse in conduction modes [1] to [6].

[0026] As shown in Figure 4, when the rotor 11 is rotated in the reverse direction, the pulse width of the reverse rotation pulse in the conduction modes [1] to [6] is larger than the pulse width of the forward rotation pulse. The difference between the two pulse widths is minimum (e.g., zero) when the applied voltage command value V* is zero, and increases as the applied voltage command value V* decreases in the negative direction. Furthermore, when the rotor 11 is rotated in the reverse direction, the direction of the line current in the conduction modes [1] to [6] is opposite to that in Figure 3. Therefore, the reverse rotation pulse is a negative pulse in the line voltage Vuv in the conduction mode [1] to pass a line current from the V phase to the U phase, whereas the reverse rotation pulse is a positive pulse in the line voltage Vwu in the conduction mode [2] to pass a line current from the W phase to the U phase. Similarly, the forward rotation pulse is a positive pulse to cause a line current to flow from the V phase to the W phase in the line voltage Vvw in the conduction mode [3], while it is a negative pulse to cause a line current to flow from the V phase to the U phase in the line voltage Vuv in the conduction mode [4]. Also, the forward rotation pulse is a positive pulse to cause a line current to flow from the W phase to the U phase in the line voltage Vwu in the conduction mode [5], while it is a negative pulse to cause a line current to flow from the W phase to the V phase in the line voltage Vvw in the conduction mode [6]. Note that the forward rotation pulse is a positive or negative pulse of opposite polarity to the reverse rotation pulse in the conduction modes [1] to [6].

[0027] In conduction mode [1] and conduction mode [4], a pulse voltage is applied to the V and W phases in both forward and reverse rotation, causing an open phase voltage to be generated in the W phase, which is a non-conductive open phase. In conduction mode [2] and conduction mode [5], a pulse voltage is applied to the U and W phases in both forward and reverse rotation, causing an open phase voltage to be generated in the V phase, which is a non-conductive open phase. In conduction mode [3] and conduction mode [6], a pulse voltage is applied to the V and W phases in both forward and reverse rotation, causing an open phase voltage to be generated in the U phase, which is a non-conductive open phase.

[0028] Next, a method for detecting the timing of switching the conduction mode in rectangular wave drive of the electric motor 1 will be described with reference to Figs. 5 to 7. Fig. 5 shows an example of the change in the open phase voltage induced by application of a forward rotation pulse in conduction mode [3] and the open phase voltage induced by application of a reverse rotation pulse in conduction mode [3] with respect to the rotor rotation angle. Fig. 6 shows the open phase voltage generated by application of a forward rotation pulse in each conduction mode. Fig. 7 shows the open phase voltage generated by application of a reverse rotation pulse in each conduction mode. Note that the open phase voltage in each conduction mode is a relative value between the potential of the neutral point 12N and each value of the three-phase applied voltages Vu, Vv, and Vw, and can take either a positive or negative value. Furthermore, the potential of the neutral point 12N is a value relative to the DC voltage V DC It may be half the value.

[0029] As shown in FIG. 5, in conduction mode [3], pulse voltages are applied to the V and W phases, making the U phase an open phase, but the forward pulse is a positive pulse while the reverse pulse is a negative pulse. Therefore, the open phase voltage E1 induced by the application of the forward pulse (hereinafter referred to as the "forward rotation open phase voltage") and the open phase voltage E2 induced by the application of the reverse pulse (hereinafter referred to as the "reverse rotation open phase voltage") change differently with respect to the rotor rotation angle. Conduction mode [3] is set in the range of 330° to 30° (shaded area in the figure) where the forward rotation open phase voltage E1 monotonically decreases in the forward rotation direction and the reverse rotation open phase voltage E2 monotonically decreases in the reverse rotation direction. Therefore, the forward rotation open phase voltage E1 is set to the forward rotation threshold (first threshold) V, which determines the value of the forward rotation open phase voltage E1 at the forward rotation switching angle of 30°.FW_th When the reverse rotation open phase voltage E2 falls below the reverse rotation threshold (second threshold) V , which defines the value of the reverse rotation open phase voltage E2 at the reverse rotation direction current switching angle of 330 degrees, the timing for switching from the current conduction mode [3] to the current conduction mode [4] is detected. RV_th When the voltage drops below 0 V, the timing to switch from conduction mode [3] to conduction mode [2] is detected.

[0030] In this document, the value of the forward open phase voltage E1 is the forward threshold V FW_th When the value of the forward rotation open phase voltage E1 falls below the forward rotation threshold V FW_th From the above, the forward rotation threshold V FW_th When the value of the forward rotation open phase voltage E1 is less than the forward rotation threshold V FW_th When the value of the forward open phase voltage E1 exceeds the forward threshold V FW_th The following is the forward rotation threshold V FW_th This means that the reverse open phase voltage E2 increases to a value greater than the reverse threshold V RV_th When the reverse open phase voltage E2 is below the reverse threshold V RV_th The same applies when it exceeds .

[0031] As described above, in conduction mode [3], the forward rotation pulse is a positive pulse and the reverse rotation pulse is a negative pulse. However, as shown in Figures 3 and 4, the forward rotation pulse and reverse rotation pulse in conduction modes [1] to [6] alternate between positive and negative pulses as the conduction mode changes one by one. Therefore, as shown in Figure 6, as the conduction mode changes sequentially, a monotonically increasing section in which the forward rotation open phase voltage E1 monotonically increases in the forward rotation direction and a monotonically decreasing section in which the forward rotation open phase voltage E2 monotonically decreases in the forward rotation direction alternate. Furthermore, as shown in Figure 7, as the conduction mode changes sequentially, a monotonically increasing section in which the reverse rotation open phase voltage E2 monotonically increases in the reverse rotation direction and a monotonically decreasing section in which the reverse rotation open phase voltage E2 monotonically decreases in the reverse rotation direction alternate. Specifically, the forward rotation open phase voltage E1 is a monotonically decreasing section in the forward rotation direction in the conduction modes [1], [3], and [5], while it is a monotonically increasing section in the forward rotation direction in the conduction modes [2], [4], and [6]. Also, the reverse rotation open phase voltage E2 is a monotonically decreasing section in the reverse rotation direction in the conduction modes [1], [3], and [5], while it is a monotonically increasing section in the reverse rotation direction in the conduction modes [2], [4], and [6]. Therefore, the forward rotation threshold V FW_th The upper normal threshold (first upper threshold) V FW_th1 is the normal rotation threshold V FW_th On the other hand, in conduction modes [1], [3], and [5] where the normal rotation open phase voltage E1 is in the monotonically decreasing section, the upper normal rotation threshold V FW_th1 Lower forward threshold (first lower threshold) V FW_th2 is the normal rotation threshold V FW_th In addition, the aforementioned reversal threshold V RV_th contains two thresholds that are different from each other in the monotonically increasing section and the monotonically decreasing section. That is, in the conduction modes [1], [3], and [5] where the reverse open phase voltage E2 is in the monotonically increasing section, the upper reverse threshold (second upper threshold) V RV_th1 is the reversal threshold V RV_th On the other hand, in the conduction modes [2], [4], and [6] where the reverse open phase voltage E2 is in the monotonically decreasing section, the upper reverse threshold V RV_th1A lower reversal threshold (second lower threshold) V RV_th2 is the reversal threshold V RV_th This becomes:

[0032] In this way, the motor control device 3 detects not only the forward rotation open phase voltage E1 but also the reverse rotation open phase voltage E2 even when the rotor 11 is rotating in the forward direction. On the other hand, the motor control device 3 detects not only the reverse rotation open phase voltage E2 but also the forward rotation open phase voltage E1 even when the rotor 11 is rotating in the reverse direction. This is to detect the reversal of the rotation direction of the rotor 11 and switch the conduction mode to the reverse direction, particularly when the applied voltage command value V* is reversed.

[0033] [Specific functions of the motor control device] 8 shows an example of functional blocks related to low-speed sensorless control of motor control device 3. Functionally, motor control device 3 has a voltage command adjuster 301, a control signal generator including a PWM (Pulse Width Modulation) signal generator 302 and a gate signal generator 303, a current conduction mode determiner 304, and a mode switching trigger generator 305. These functions are basically realized by processor 31 reading a control program from non-volatile memory 33 into volatile memory 32 and executing it. However, this does not exclude the possibility that some or all of the above functions of motor control device 3 are realized by hardware rather than by software processing.

[0034] The voltage command adjusting unit 301 adjusts the applied voltage command value V* to obtain an adjustment command value. By adjusting the applied voltage command value V*, a PWM signal can be generated that can apply a pulse voltage including a forward rotation pulse and a reverse rotation pulse, regardless of whether the applied voltage command value V* is a positive or negative value. The voltage command adjusting unit 301 will be described in detail later.

[0035] The PWM signal generation unit 302 generates the PWM signals PX and PY based on the adjustment command value obtained by the voltage command adjustment unit 301. The PWM signal generation unit 302 also generates a line voltage signal [PX-PY] based on the generated PWM signals PX and PY. The PWM signal generation unit 302 will be described in detail later.

[0036] The gate signal generator 303 outputs the energization mode signal S generated by the energization mode determination unit 304 as described later. MODE Based on this, the gate signal generating unit 303 determines two phases to which the PWM signals PX and PY are applied, and generates gate signals for the switching elements 21 to 26. The gate signal generating unit 303 will be described in detail later.

[0037] The power supply mode determination unit 304 determines whether the normal rotation switch trigger signal S is generated by the mode switch trigger generation unit 305 as described later. FW_SW or reverse switch trigger signal S RV_SW A new conduction mode is determined based on the MODE For example, when the current conduction mode is the conduction mode [3], the conduction mode determination unit 304 generates the forward rotation switching trigger signal S FW_SW On the other hand, when the current conduction mode is the conduction mode [3], the conduction mode determination unit 304 determines the conduction mode [4] as the new conduction mode. RV_SW When this occurs, the new conduction mode is determined to be conduction mode [2].

[0038] The mode switching trigger generating unit 305 generates signals related to the three-phase applied voltages Vu, Vv, and Vw, and the conduction mode signal S generated by the conduction mode determining unit 304. MODE Based on this, the forward rotation switching trigger signal S FW_SW or reverse switch trigger signal S RV_SW Generates a forward rotation switch trigger signal S FW_SW occurs when the energization mode is switched in the forward direction, and the reverse direction switching trigger signal S RV_SWis generated at the timing of switching the conduction mode in the reverse direction. More specifically, the mode switching trigger generating unit 305 has an open phase voltage detecting unit 306, a forward rotation threshold setting unit 307, a reverse rotation threshold setting unit 308, a comparing unit 309, and a comparing unit 310.

[0039] The open phase voltage detection unit 306 detects the three-phase applied voltages Vu, Vv, and Vw, and the conduction mode signal S MODE , and the line voltage signal [PX-PY], the open phase voltage is detected by distinguishing between a forward rotation open phase voltage E1 and a reverse rotation open phase voltage E2. Details of the open phase voltage detection unit 306 will be described later.

[0040] The forward rotation threshold setting unit 307 receives the energization mode signal S MODE Based on this, the upper normal rotation threshold V is set as the normal rotation initial threshold (first initial threshold). FW_th1 and the lower normal threshold V FW_th2 Either one of these is set as the forward rotation threshold V FW_th The reverse rotation threshold setting unit 308 sets the energization mode signal S MODE Based on this, an upper reversal threshold V is set as a reversal initial threshold (second initial threshold). RV_th1 and the lower reversal threshold V RV_th2 Either one of them is set to the reversal threshold V RV_th Set as.

[0041] The comparison unit 309 compares the normal rotation open phase voltage value E1 with the normal rotation threshold value V FW_th and based on the comparison result, a forward rotation switching trigger signal S FW_SW The comparison unit 310 compares the reverse open phase voltage value E2 with the reverse threshold value V RV_th and based on the comparison result, a reverse switching trigger signal S RV_SW Generates.

[0042] 9 shows a detailed configuration example of voltage command adjusting unit 301. Voltage command adjusting unit 301 includes multiplying units 311 and 312, a sign inverting unit 313, adding units 314 and 315, a correction pulse generating unit 316, an adding unit 317, and a subtracting unit 318.

[0043] The multiplication unit 311 multiplies the applied voltage command value V* by 0.5 to calculate [V* / 2]. The multiplication unit 312 multiplies the DC voltage V of the in-vehicle battery 4 by 0.5. DC Multiply the detected value by 0.5 to get [V DC The sign inverting unit 313 inverts the sign of [V* / 2] to obtain [-V* / 2]. The adding unit 314 calculates [V DC / 2] to obtain the offset command value VX0, and the adder 315 adds [V DC / 2] to obtain an offset command value VY0. A correction pulse generation unit 316 generates a correction pulse signal that reflects a correction amount ΔV for correcting the offset command values ​​VX0 and VY0 so that forward rotation pulses and reverse rotation pulses are generated in the line voltages Vuv, Vvw, and Vwu in each conduction mode. An adder 317 adds the correction amount ΔV of the correction pulse signal to the offset command value VX0 to obtain an adjustment command value VX1, and a subtracter 318 subtracts the correction amount ΔV of the correction pulse signal from the offset command value VY0 to obtain an adjustment command value VY1. These adjustment command values ​​VX1 and VY1 become the final applied voltage command values.

[0044] FIG. 10 shows a detailed configuration example of the PWM signal generating unit 302 and the gate signal generating unit 303.

[0045] The PWM signal generation unit 302 includes a triangular wave generation unit 319 that generates a triangular wave carrier signal TC, a comparison unit 320 that compares the adjustment command value VX1 with the triangular wave carrier signal TC, and a comparison unit 321 that compares the adjustment command value VY1 with the triangular wave carrier signal TC. The comparison unit 320 generates a PWM signal PX as a result of comparing the adjustment command value VX1 with the triangular wave carrier signal TC, and the comparison unit 321 generates a PWM signal PY as a result of comparing the adjustment command value VY1 with the triangular wave carrier signal TC. Both PWM signals PX and PY are rectangular pulse signals represented by two potential levels: a high potential (H) level and a low potential (L) level.

[0046] The PWM signal generating unit 302 also includes a [PX-PY] signal generating unit 322. The [PX-PY] signal generating unit 322 generates a line voltage signal [PX-PY] by subtracting the potential of the PWM signal PY from the potential of the PWM signal PX. The line voltage signal [PX-PY] is a bipolar pulse signal represented by three potentials, in descending order: a positive level (P level), a zero level, and a negative level (N level).

[0047] The gate signal generating unit 303 includes a U-phase switching unit 323, a V-phase switching unit 324, a W-phase switching unit 325, a zero signal generating unit 326, and inverting units 327, 328, and 329. The U-phase switching unit 323, the V-phase switching unit 324, and the W-phase switching unit 325 generate a conduction mode signal S MODE Based on this, the PWM signal PX, the PWM signal PY, and a zero signal of zero potential (e.g., ground potential) generated by the zero signal generating unit 326 are selected from among the PWM signal PX, the PWM signal PY, and a mutually different signal. Specifically, the U-phase switching unit 323 selects the PWM signal PX in conduction modes [1] and [2], the PWM signal PY in conduction modes [4] and [5], and the zero signal in conduction modes [3] and [6]. The V-phase switching unit 324 selects the PWM signal PX in conduction modes [3] and [4], the PWM signal PY in conduction modes [1] and [6], and the zero signal in conduction modes [2] and [5]. The W-phase switching unit 325 selects the PWM signal PX in conduction modes [5] and [6], the PWM signal PY in conduction modes [2] and [3], and the zero signal in conduction modes [1] and [4]. In other words, when the applied voltage command value V* is a positive value, the PWM signal PX is used as the gate signal for the upstream phase switching element and the PWM signal PY is used as the gate signal for the downstream phase switching element in the two phases through which line current flows in each conduction mode. On the other hand, when the applied voltage command value V* is a negative value, the PWM signal PY is used for the upstream phase switching element and the PWM signal PX is used for the downstream phase switching element in the two phases through which line current flows in each conduction mode.

[0048] The signal selected by the U-phase switching unit 323 is output as the gate signal Pup for the switching element 21 of the upper arm of the U-phase, and is also output via the inverter 327 as the gate signal Pun for the switching element 22 of the lower arm of the U-phase. The signal selected by the V-phase switching unit 324 is output as the gate signal Pvp for the switching element 23 of the upper arm of the V-phase, and is also output via the inverter 328 as the gate signal Pvn for the switching element 24 of the lower arm of the U-phase. The signal selected by the W-phase switching unit 325 is output as the gate signal Pwp for the switching element 25 of the upper arm of the W-phase, and is also output via the inverter 329 as the gate signal Pwn for the switching element 26 of the lower arm of the U-phase. The inverters 327, 328, and 329, except for the zero signal, interchange the potential levels of the PWM signals PX and PY to generate complementary PWM signals.

[0049] The control signal waveforms in voltage command adjustment unit 301 and PWM signal generation unit 302 will be described with reference to Fig. 11 to Fig. 13. Fig. 11 shows an example of the control signal waveform when applied voltage command value V* is zero, Fig. 12 shows an example of the control signal waveform when applied voltage command value V* is a positive value, and Fig. 13 shows an example of the control signal waveform when applied voltage command value V* is a negative value. In each of Fig. 11 to Fig. 13, (A) is the applied voltage command value V*, (B) is the correction pulse signal, (C) is the triangular wave carrier TC and adjustment command values ​​VX1, VY1, (D) is the PWM signal PX, (E) is the PWM signal PY, and (F) is the line voltage signal [PX-PY].

[0050] As shown in FIG. 11(A), when the applied voltage command value V* is zero, the offset command values ​​VX0 and VY0 are [V DC / 2]. As shown in FIG. 11(B), the correction pulse signal is synchronized with the period of the triangular wave carrier TC (see FIG. 11(C)). The correction amount ΔV is positive in the first half of the period before the peak of the triangular wave carrier TC, and negative in the second half of the period after the peak of the triangular wave carrier TC, resulting in a bipolar pulse signal with a rectangular waveform. The correction amount ΔV of such a correction pulse signal is added to the offset command value VX0 and subtracted from the offset command value VY0 to generate adjustment command values ​​VX1 and VY1, respectively, as shown in FIG. 11(C). The adjustment command values ​​VX1 and VY1 have the same pulse width as the correction pulse signal and are pulse signals with waveforms that are inverted from each other. However, the timing at which the pulse signal of the adjustment command value VX1 coincides with the triangular wave carrier TC and the timing at which the pulse signal of the adjustment command value VY1 coincides with the triangular wave carrier TC are shifted from each other. 11(D) and (E), there are periods where the H level period of PWM signal PX overlaps with the L level period of PWM signal PY, and periods where the L level period of PWM signal PX overlaps with the H level period of PWM signal PY. As a result, as shown in FIG. 11(F), the line voltage signal [PX-PY] is at the P level when PWM signal PX is at the H level and PWM signal PY is at the L level, and is at the N level when PWM signal PX is at the L level and PWM signal PY is at the H level.

[0051] The waveform of the line voltage signal [PX-PY] shown in Fig. 11(F) corresponds to the waveform when the pulse width of the forward rotation pulse is the same as the pulse width of the reverse rotation pulse in the line voltages Vuv, Vvw, and Vwu in Fig. 3. Alternatively, the waveform of the line voltage signal [PX-PY] shown in Fig. 11(F) corresponds to the waveform when the pulse width of the reverse rotation pulse is the same as the pulse width of the forward rotation pulse in the line voltages Vuv, Vvw, and Vwu in Fig. 4.

[0052] As shown in FIG. 12(A), the applied voltage command value V*, which is a positive value, is expressed as [V DC The offset command value VX0 is the value obtained by adding [V* / 2] to [V DCIt is indicated by the difference [VX0 - VY0] of the offset command value VY0 (<VX0) obtained by subtracting [V* / 2] from [V* / 2]. To the offset command value VX0, the correction amount ΔV of the correction pulse signal in Fig. 12(B) (common to Fig. 11(B)) is added to generate the pulse signal of the adjustment command value VX1 in Fig. 12(C). Also, from the offset command value VY0, the correction amount ΔV of the correction pulse signal in Fig. 12(B) is subtracted to generate the pulse signal of the adjustment command value VY1 in Fig. 12(C). The timing at which the pulse signal of the adjustment command value VX1 coincides with the triangular wave carrier TC is closer to the peak timing of the triangular wave carrier TC when compared with the pulse signal of the adjustment command value VX1 in Fig. 11(C). Also, the timing at which the pulse signal of the adjustment command value VY1 coincides with the triangular wave carrier TC is away from the peak timing of the triangular wave carrier TC when compared with the pulse signal of the adjustment command value VY1 in Fig. 11(C). For this reason, as shown in Figs. 12(D) and (E), the period during which the H-level period of the PWM signal PX and the L-level period of the PWM signal PY overlap becomes longer, and the period during which the L-level period of the PWM signal PX and the H-level period of the PWM signal PY overlap becomes shorter. Therefore, as shown in Fig. 12(F), when the line voltage signal [PX - PY] is compared with the line voltage signal [PX - PY] in Fig. 11(F), the P-level period during which it becomes the P level becomes longer, and the N-level period during which it becomes the N level becomes shorter.

[0053] The waveform of the line voltage signal [PX - PY] shown in Fig. 12(F) corresponds to the waveforms of the line voltages Vuv, Vvw, Vwu in the energization modes [1], [3], [5] in Fig. 3, and corresponds to the waveforms obtained by inverting the line voltages Vuv, Vvw, Vwu in the energization modes [2], [4], [6]. That is, a forward rotation pulse is applied during the P-level period of the line voltage signal [PX - PY], and a reverse rotation pulse is applied during the N-level period of the line voltage signal [PX - PY].

[0054] As shown in Fig. 13(A), the applied voltage command value V* which is a negative value is DC the offset command value VX0 obtained by adding [V* / 2] to [V DCThis is represented by the difference [VX0-VY0] between the offset command value VY0 (>VX0) obtained by subtracting [V* / 2] from [V* / 2]. A correction amount ΔV of the correction pulse signal of FIG. 13(B) (common to FIG. 11(B)) is added to the offset command value VX0 to generate the pulse signal of the adjustment command value VX1 of FIG. 13(C). Furthermore, a correction amount ΔV of the correction pulse signal of FIG. 13(B) is subtracted from the offset command value VY0 to generate the pulse signal of the adjustment command value VY1 of FIG. 13(C). The timing at which the pulse signal of the adjustment command value VX1 coincides with the triangular wave carrier TC is further away from the peak timing of the triangular wave carrier TC than the pulse signal of the adjustment command value VX1 of FIG. 11(C). The timing at which the pulse signal of adjustment command value VY1 coincides with the triangular wave carrier TC is closer to the peak timing of the triangular wave carrier TC compared to the pulse signal of adjustment command value VY1 in Figure 11(C). Therefore, as shown in Figures 13(D) and 13(E), the period during which the H level period of PWM signal PX overlaps with the L level period of PWM signal PY is shorter, and the period during which the L level period of PWM signal PX overlaps with the H level period of PWM signal PY is longer. Therefore, as shown in Figure 13(F), the P level period of line voltage signal [PX-PY] is shorter and the N level period is longer compared to the line voltage signal [PX-PY] in Figure 11(F).

[0055] The waveform of the line voltage signal [PX-PY] shown in Figure 13(F) corresponds to the waveforms of the line voltages Vuv, Vvw, Vwu in the conduction modes [1], [3], and [5] in Figure 4, and corresponds to the inverted waveforms of the line voltages Vuv, Vvw, and Vwu in the conduction modes [2], [4], and [6]. In other words, a forward pulse is applied during the P level period of the line voltage signal [PX-PY], and a reverse pulse is applied during the N level period of the line voltage signal [PX-PY].

[0056] As explained with reference to Figures 11 to 13, during the P level period of the line voltage signal [PX-PY], forward pulses are applied as the line voltages Vuv, Vvw, and Vwu, and during the N level period of the line voltage signal [PX-PY], reverse pulses are applied as the line voltages Vuv, Vvw, and Vwu.

[0057] 14 shows a detailed configuration example of the open phase voltage detection unit 306. The open phase voltage detection unit 306 includes a three-phase applied voltage selection unit 330, a trigger signal generation unit 331, sampling units 332 and 333, and open phase voltage calculation units 334 and 335.

[0058] The three-phase applied voltage selection unit 330 outputs the conduction mode signal S MODE In other words, the three-phase applied voltage selector 330 selects the U-phase applied voltage Vu in the conduction modes [3] and [6], selects the V-phase applied voltage Vv in the conduction modes [2] and [5], and selects the W-phase applied voltage Vw in the conduction modes [1] and [4].

[0059] Based on the line voltage signal [PX-PY], the trigger signal generation unit 331 generates a trigger signal that serves as the sampling timing for the applied voltage of the phase selected by the three-phase applied voltage selection unit 330 (U-phase applied voltage Vu in the figure). Specifically, when the trigger signal generation unit 331 detects that the line voltage signal [PX-PY] is in the P level period (for example, a fall from the P level), it generates a forward rotation pulse trigger signal S TRG1 Furthermore, when the trigger signal generating unit 331 detects that the line voltage signal [PX-PY] is in the N level period (for example, rising from the N level), it generates the reverse pulse trigger signal S TRG2 Generate.

[0060] The sampling unit 332 receives the normal rotation pulse trigger signal S generated by the trigger signal generating unit 331. TRG1 In response to the signal, the sampling unit 333 samples the applied voltage selected by the three-phase applied voltage selection unit 330 from among the three-phase applied voltages Vu, Vv, and Vw by A / D (Analog to Digital) conversion or the like. TRG2In response to the above, the applied voltage selected by the three-phase applied voltage selection unit 330 from among the three-phase applied voltages Vu, Vv, and Vw is sampled by A / D conversion or the like. The sampling units 332 and 333 may each include a capacitor that holds the applied voltage to be sampled for a certain period of time.

[0061] An open phase voltage calculation unit 334 calculates the value of the open phase voltage based on the applied voltage sampled by the sampling unit 332 and the potential of the neutral point 12N, and detects this value as a forward rotation open phase voltage E1. An open phase voltage calculation unit 335 calculates the value of the open phase voltage based on the applied voltage sampled by the sampling unit 333 and the potential of the neutral point 12N, and detects this value as a reverse rotation open phase voltage E2.

[0062] Here, the conventional problems with the motor control device 3 configured as above will be described with reference to Figures 21 and 22. Figure 21 shows a typical example of the conventional operation of the electric motor 1 under low-speed sensorless control by the motor control device 3, where (A) shows the time variation of the applied voltage command value V* and (B) shows the rotor rotation angle range R detected by the motor control device 3. θ (C) is the time change of the forward rotation open phase voltage E1, and (D) is the time change of the reverse rotation open phase voltage E2. Figure 22 shows the changes in the forward rotation open phase voltage E1 and the reverse rotation open phase voltage E2 with respect to the rotor rotation angle from time t5 to t6 in Figure 21.

[0063] As shown in Figure 21(A), the applied voltage command value V* is a positive value indicating a forward rotation drive command until time t2, changes to zero at time t2 indicating a drive stop command, and changes to a negative value indicating a reverse rotation drive command at time t4.

[0064] Immediately before time t1, as shown in FIG. 21(B), the motor control device 3 sets the rotor rotation angle range R θThe angle is detected as 330-30 deg, and a pulse voltage is applied to the electric motor 1 in conduction mode [3] (see Figures 3 and 6). Because the P level period in the line voltage signal [PX-PY] is longer than the N level period, the pulse width of the forward rotation pulse in the line voltage Vvw is longer than the pulse width of the reverse rotation pulse, and line current flows from the V phase to the W phase, causing forward rotation (see Figure 3). The forward rotation open phase voltage E1 is calculated based on the U phase applied voltage Vu when the forward rotation pulse is applied, and decreases monotonically as shown in Figure 21(C) (see Figures 3, 6, and 14).

[0065] At time t1, as shown in FIG. 21(C), the value of the forward rotation open phase voltage E1 becomes equal to or exceeds the lower forward rotation threshold V FW_th2 At this time, the motor control device 3 determines whether the rotor rotation angle range R θ When it is determined that the angle has shifted from 330 to 30 degrees to 30 to 90 degrees, the conduction mode [3] is switched to the conduction mode [4] (see Figure 6). As a result, the forward rotation open phase voltage E1 is calculated based on the W-phase applied voltage Vw when the forward rotation pulse is applied, and increases monotonically as shown in Figure 21(C) (see Figures 3, 6, and 14).

[0066] At time t2, when the applied voltage command value V* becomes zero, the P level period and the N level period in the line voltage signal [PX-PY] become the same length (see FIG. 11(F)). As a result, the pulse width of the forward rotation pulse in the line voltage Vuv becomes shorter until it becomes the same as the pulse width of the reverse rotation pulse, the line current from the V phase to the U phase becomes substantially zero, and the forward rotation drive stops. Even after the forward rotation drive stops, the forward rotation of the rotor 11 continues due to inertia, and the current supply mode switching control continues to be performed while the drive is stopped.

[0067] At time t3, as shown in FIG. 21(C), the value of the forward rotation open phase voltage E1 exceeds the upper forward rotation threshold V FW_th1 When the rotation angle of the rotor exceeds the predetermined value, the motor control device 3 sets the rotation angle of the rotor within the range R θThe motor control device 3 determines that the rotational angle has shifted to 90-150 degrees and switches the conduction mode [4] to the conduction mode [5]. After this, the forward rotation of the rotor 11 continues due to inertia, and the motor control device 3 switches the conduction mode in the order of [6], [1], [2], ...

[0068] When the rotor 11 is rotating forward, as shown in FIG. 21(D), the upper reverse threshold V RV_th1 is the reversal threshold V RV_th In the conduction mode set as above, the value of the reverse open phase voltage E2 is equal to the upper reverse threshold V RV_th1 (See FIG. 7.) When the rotor 11 is rotating forward, as shown in FIG. 21(D), the lower reverse rotation threshold V RV_th2 is the reversal threshold V RV_th In the conduction mode set as above, the value of the reverse open phase voltage E2 is equal to the lower reverse threshold V RV_th2 (See FIG. 7.) Therefore, while the rotor 11 is rotating in the forward direction, the current supply mode is not switched to the reverse direction.

[0069] At time t4, as shown in FIG. 21(B), the motor control device 3 sets the rotor rotation angle range R θ is detected as 270 to 330 deg, and a pulse voltage is applied to the electric motor 1 in conduction mode [2]. When the applied voltage command value V* becomes negative at time t4, the N-level period in the line voltage signal [PX-PY] becomes longer than the P-level period. As a result, the pulse width of the reverse rotation pulse in the line voltage Vwu becomes longer than the pulse width of the forward rotation pulse, and line current flows from the W phase to the U phase, starting reverse rotation (see Figure 4). At this time, it is assumed that the forward rotation of the rotor 11 is still continuing due to the influence of inertia.

[0070] At time t5, the forward rotation of the rotor 11 causes the value of the forward rotation open phase voltage E1 to exceed the upper forward rotation threshold V FW_th1 When the rotation angle of the motor controller 3 exceeds the rotor rotation angle range R θis determined to be between 330 and 30 degrees, and the conduction mode [2] is switched to the conduction mode [3]. Then, when the pulse voltage is applied in the conduction mode [3], the rotation of the rotor 11 is switched from forward rotation to reverse rotation.

[0071] As shown in FIG. 21(D) and FIG. 22, when the motor control device 3 switches the conduction mode [2] to the conduction mode [3] at time t5, the value of the reverse rotation opening phase voltage E2 has already reached the lower reverse rotation threshold value V RV_th2 This is a phenomenon that can occur due to individual differences between electric motors 1, physical variations within the electric motor 1, electrical noise, etc. When this phenomenon occurs, as shown in Figures 21(D) and 22, the value of the reverse opening phase voltage E2 becomes smaller than the lower reverse threshold value V RV_th2 When the rotor 11 starts to rotate in reverse in a state where the value of the reverse opening phase voltage E2 is smaller than the lower reverse threshold V RV_th2 Therefore, when the rotor 11 starts to rotate in the reverse direction from the forward rotation state, the motor control device 3 cannot correctly detect the timing to switch from the current supply mode [3] to [2], and a loss of synchronization occurs due to the reversal of the rotation direction.

[0072] Even if a step-out occurs due to a reversal of the rotation direction, the rotor 11 rotates in the reverse direction by applying a pulse voltage in the conduction mode [3], and the forward rotation open phase voltage E1 and the reverse rotation open phase voltage E2 change in the reverse direction in the conduction mode [3] state as shown in Figure 22. The motor control device 3 controls the rotor rotation angle range R θ Since it is still recognized that the angle is 330 to 30 degrees, the lower forward threshold V corresponding to the energization mode [3] is still set. FW_th2 and the lower reversal threshold V RV_th2 21(C), (D) and 22, at time t6, the actual rotation angle range R of the rotor 11 is θ When the reverse open phase voltage E2 is between 210 and 270 degrees, the value of the reverse open phase voltage E2 exceeds the lower reverse threshold V RV_th2 Before the value of the forward open phase voltage E1 falls below the lower forward threshold V FW_th2Therefore, the motor control device 3 is configured to set the rotor rotation angle range R θ The controller 10 judges that the angle is between 30 and 90 degrees and switches the energization mode [3] to the energization mode [4]. As a result, the rotation of the rotor 11 changes from reverse to forward, and this time the value of the reverse rotation opening phase voltage E2 becomes equal to or exceeds the upper reverse rotation threshold V RV_th1 Before the value of the positive open phase voltage E1 falls below the upper positive threshold V FW_th1 When the current exceeds the threshold voltage, the motor control device 3 switches from conduction mode [4] to conduction mode [5]. When a step-out occurs due to a reversal of the rotation direction, the rotor 11 may rotate forward even though the motor control device 3 has received a reverse drive command, or, depending on the conditions, the rotor 11 may stop rotating.

[0073] The loss of synchronism due to the reversal of the rotation direction occurs when the reverse open phase voltage E2 immediately after switching the conduction mode from [2] to [3] in the forward direction exceeds the lower reverse threshold V RV_th2 In other words, the loss of synchronism due to the reversal of the rotation direction is not limited to the occurrence of a loss of synchronism due to the reverse open phase voltage E2 being smaller than the lower reverse threshold V RV_th2 On the other hand, the loss of synchronism due to the reversal of the rotation direction mentioned above is caused by the reverse open phase voltage E2 immediately after the conduction mode is switched to the forward rotation direction becoming smaller than the lower reverse threshold V RV_th2 In other words, the loss of synchronism due to the reversal of the rotation direction is not limited to the occurrence of a loss of synchronism due to the reverse open phase voltage E2 becoming smaller than the upper reverse threshold V RV_th1 This also includes causes that are greater than

[0074] In addition, the above-mentioned step-out due to the reversal of the rotation direction has been described as occurring when the rotor 11 starts to rotate in the reverse direction from the forward rotation state, but it can also occur when the rotor 11 starts to rotate in the forward direction from the reverse rotation state. That is, step-out due to the reversal of the rotation direction occurs when the forward rotation open phase voltage E1 immediately after the conduction mode is switched from [1] to [6], from [3] to [2], or from [5] to [4] in the reverse direction exceeds the upper forward rotation threshold V FW_th1 In addition, the loss of synchronization due to the reversal of the rotation direction may occur when the forward rotation open phase voltage E1 is greater than the lower forward rotation threshold V immediately after switching the conduction mode from [2] to [1], from [4] to [3], or from [6] to [5]. FW_th2 This also includes cases that occur due to phenomena where the value is smaller than

[0075] In consideration of the conventional problems with the motor control device 3 configured as described above, in this embodiment, the motor control device 3 is configured as follows. That is, as shown in FIG. 8, the forward rotation threshold setting unit 307 receives the energization mode signal S MODE In addition, the value of the forward rotation open phase voltage E1 detected by the comparison unit 309 immediately after switching the conduction mode (first switching detection value E1 SW ) based on the normal threshold V FW_th As shown in FIG. 8, the reverse rotation threshold setting unit 308 sets the energization mode signal S MODE In addition, the value of the reverse opening phase voltage E2 detected by the comparison unit 310 immediately after switching the current supply mode (second switching detection value E2 SW ) based on the reversal threshold V RV_th is set.

[0076] Next, referring to FIGS. 15 and 16, the forward rotation threshold V FW_th and the reversal threshold V RV_th 15 shows an example of the detailed functional configuration of the forward rotation threshold setting unit 307, and FIG.

[0077] 15, the normal rotation threshold setting unit 307 includes an initial threshold selection unit 336, comparison units 337 and 338, a comparison result selection unit 339, and a switching unit 340. The initial threshold selection unit 336 selects a current conduction mode signal S MODE Based on this, the upper normal rotation threshold V FW_th1 and the lower normal threshold V FW_th2 Specifically, the initial threshold value selection unit 336 selects one of the upper normal rotation threshold values ​​V FW_th1 While selecting the lower forward threshold V FW_th2 The comparison unit 337 selects the lower normal threshold V FW_th2 and the first switching detection value E1 SW Specifically, the comparator 337 compares the lower normal threshold V FW_th2 is the first switching detection value E1 SW On the other hand, the comparator 337 generates a high potential (H) output signal when the lower normal threshold V FW_th2 is the first switching detection value E1 SW The comparator 338 generates a low potential (L) output signal when the first switching detection value E1 SW and the upper normal threshold V FW_th1 Specifically, the comparator 338 compares the first switching detection value E1 SW is the upper normal threshold V FW_th1 On the other hand, the comparator 338 generates a high potential (H) output signal when the first switching detection value E1 SW is the upper normal threshold V FW_th1 The comparison result selection unit 339 generates a low potential (L) output signal when the conduction mode signal S MODE Based on the output signal selected by the comparison result selection unit 339, the switching unit 340 selects either the comparison result of the comparison unit 337 or the comparison result of the comparison unit 338. Specifically, the comparison result selection unit 339 selects the output signal of the comparison unit 337 in the energization modes [1], [3], and [5], and selects the output signal of the comparison unit 338 in the energization modes [2], [4], and [6]. Based on the output signal selected by the comparison result selection unit 339, the switching unit 340 selects the first switching detection value E1SW Alternatively, the initial threshold value selection unit 336 selects either one of the normal rotation initial threshold values, and sets the selected value as the normal rotation threshold value V FW_th Specifically, when the output signal selected by the comparison result selection unit 339 is at a high potential (H), the switching unit 340 sets the first switching detection value E1 SW is the normal rotation threshold V FW_th On the other hand, when the output signal selected by the comparison result selection unit 339 is at a low potential (L), the switching unit 340 sets the normal initial threshold selected by the initial threshold selection unit 336 as the normal threshold V FW_th Set as.

[0078] In other words, when the energization mode is [1], [3], or [5], the normal rotation threshold setting unit 307 sets the normal rotation threshold V FW_th That is, the normal rotation threshold setting unit 307 sets the first switching detection value E1 SW is the lower normal threshold V FW_th2 If it is less than the first switching detection value E1 SW is the normal rotation threshold V FW_th On the other hand, the forward rotation threshold setting unit 307 sets the first switching detection value E1 SW is the lower normal threshold V FW_th2 If it is equal to or greater than the lower normal threshold V FW_th2 is the normal rotation threshold V FW_th Set as.

[0079] In addition, when the energization mode is [2], [4], or [6], the normal rotation threshold setting unit 307 sets the normal rotation threshold V FW_th That is, the normal rotation threshold setting unit 307 sets the first switching detection value E1 SW is the upper normal threshold V FW_th1 If it is greater than the first switching detection value E1 SW is the normal rotation threshold V FW_th On the other hand, the forward rotation threshold setting unit 307 sets the first switching detection value E1 SW is the upper normal threshold V FW_th1 If it is less than or equal to the upper normal threshold V FW_th1 is the normal rotation threshold V FW_th Set as.

[0080] 16, the reverse threshold setting unit 308 includes an initial threshold selection unit 341, comparison units 342 and 343, a comparison result selection unit 344, and a switching unit 345. The initial threshold selection unit 341 receives a conduction mode signal S MODE Based on this, the upper reversal threshold V is set as the initial reversal threshold. RV_th1 and the lower reversal threshold V RV_th2 Specifically, the initial threshold value selection unit 341 selects one of the upper reverse threshold values ​​V RV_th1 While selecting the lower reverse threshold V RV_th2 The comparator 342 selects the lower inversion threshold V RV_th2 and the second switching detection value E2 SW Specifically, the comparator 342 compares the lower inversion threshold V RV_th2 is the second switching detection value E2 SW On the other hand, the comparator 342 generates a high potential (H) output signal when the lower inversion threshold V RV_th2 is the second switching detection value E2 SW The comparator 343 generates a low potential (L) output signal when the second switching detection value E2 SW and the upper reversal threshold V RV_th1 Specifically, the comparator 343 compares the second switching detection value E2 SW is the upper reversal threshold V RV_th1 When the second switching detection value E2 is greater than the first switching detection value E1, a high potential (H) output signal is generated. SW is the upper reversal threshold V RV_th1 The comparison result selection unit 344 generates a low potential (L) output signal when the conduction mode signal S MODE , and selects either the comparison result of the comparison unit 342 or the comparison result of the comparison unit 343. Specifically, the comparison result selection unit 344 selects the output signal of the comparison unit 342 in the energization modes 1, 3, and 5, and selects the output signal of the comparison unit 343 in the energization modes 2, 4, and 6. The switching unit 345 selects the second switching detection value E2 based on the output signal selected by the comparison result selection unit 344. SWAlternatively, the initial threshold value selection unit 341 selects either one of the inversion initial threshold values, and sets the selected value as the inversion threshold value V RV_th Specifically, when the output signal selected by the comparison result selection unit 344 is at a high potential (H), the switching unit 345 sets the second switching detection value E2 SW The inversion threshold V RV_th On the other hand, when the output signal selected by the comparison result selection unit 344 is at a low potential (L), the switching unit 345 sets the reverse initial threshold selected by the initial threshold selection unit 341 as the reverse threshold V RV_th Set as.

[0081] In other words, when the energization mode is [1], [3], or [5], the reverse rotation threshold setting unit 308 sets the reverse rotation threshold V as follows: RV_th That is, the reverse rotation threshold setting unit 308 sets the second switching detection value E2 SW is the lower reversal threshold V RV_th2 If it is less than the second switching detection value E2 SW The inversion threshold V RV_th On the other hand, the reverse rotation threshold setting unit 308 sets the second switching detection value E2 SW is the lower reversal threshold V RV_th2 If it is greater than or equal to the lower reversal threshold V RV_th2 The inversion threshold V RV_th Set as.

[0082] In addition, when the energization mode is [2], [4], or [6], the reverse rotation threshold setting unit 308 sets the reverse rotation threshold V RV_th That is, the reverse rotation threshold setting unit 308 sets the second switching detection value E2 SW is the upper reversal threshold V RV_th1 If it is greater than the second switching detection value E2 SW The inversion threshold V RV_th On the other hand, the reverse rotation threshold setting unit 308 sets the second switching detection value E2 SW is the upper reversal threshold V RV_th1 If it is less than or equal to the upper reversal threshold V RV_th1 The inversion threshold V RV_th Set as.

[0083] FIG. 17 shows a schematic example of an improved operation of the electric motor 1 by the low-speed sensorless control of the motor control device 3, where (A) shows the time change of the applied voltage command value V* and (B) shows the rotor rotation angle range R detected by the motor control device 3. θ (C) is the time change of the forward rotation open phase voltage E1, and (D) is the time change of the reverse rotation open phase voltage E2. Figure 22 shows the changes in the forward rotation open phase voltage E1 and the reverse rotation open phase voltage E2 with respect to the rotor rotation angle from time t5 to t6 in Figure 21.

[0084] As shown in Figure 17(A), the applied voltage command value V* is a positive value indicating a forward rotation drive command until time t2, changes to zero at time t2 indicating a drive stop command, and changes to a negative value indicating a reverse rotation drive command at time t4.

[0085] Immediately before time t1, as shown in FIG. 17(B), the motor control device 3 sets the rotor rotation angle range R θ The angle is detected as 330 to 30 degrees, and a pulse voltage is applied to the electric motor 1 in the energization mode [3], causing it to rotate in the forward direction (see Figures 3 and 6).

[0086] At time t1, as shown in FIG. 17(C), the value of the forward rotation open phase voltage E1 becomes equal to or exceeds the lower forward rotation threshold V FW_th2 At this time, the motor control device 3 determines whether the rotor rotation angle range R θ The controller 100 determines that the rotational angle has shifted from 330° to 30° to 30° to 90°, and switches the conduction mode [3] to the conduction mode [4] (see FIG. 6). As a result, the forward rotation open phase voltage E1 is calculated based on the W-phase applied voltage Vw when the forward rotation pulse is applied, and the first switching detection value E1 is calculated based on the W-phase applied voltage Vw when the forward rotation pulse is applied, as shown in FIG. 17(C). SW (See Figures 3, 6, and 14.) First switching detection value E1 SW is the upper forward rotation threshold V that is preset as the initial forward rotation threshold for the energization mode [4]. FW_th1 , the normal rotation threshold setting unit 307 sets the upper normal rotation threshold V FW_th1 is the normal rotation threshold V FW_thOn the other hand, the reverse rotation open phase voltage E2 is calculated based on the W-phase applied voltage Vw when the reverse rotation pulse is applied, and is set as the second switching detection value E2 as shown in FIG. 17(D). SW (See Figures 4, 7, and 14.) Second switching detection value E2 SW is the upper reverse threshold V that is preset as the initial reverse threshold for the energization mode [4]. RV_th1 Since the reverse rotation threshold value setting unit 308 sets the second switching detection value E2 SW is the reversal threshold V RV_th is set as

[0087] At time t2, when the applied voltage command value V* becomes zero, the forward rotation drive stops. Even after the forward rotation drive stops, the forward rotation of the rotor 11 continues due to inertia, and the switching control of the current supply mode continues while the drive is stopped.

[0088] At time t3, as shown in FIG. 17(C), the value of the forward rotation open phase voltage E1 exceeds the upper forward rotation threshold V FW_th1 When the rotation angle of the rotor exceeds the predetermined value, the motor control device 3 sets the rotation angle of the rotor within the range R θ The controller 10 determines that the rotational angle has shifted to 90 to 150 degrees, and switches the energization mode [4] to the energization mode [5]. Meanwhile, the reverse rotation open phase voltage E2 reaches the second switching detection value E2 due to the forward rotation of the rotor 11. SW The second switching detection value E2 SW , the current conduction mode is not switched to the reverse direction. After this, the forward rotation of the rotor 11 continues due to inertia, and the motor control device 3 switches the current conduction mode in the order of [6], [1], [2], ...

[0089] At time t4, as shown in FIG. 17(B), the motor control device 3 sets the rotor rotation angle range R θ is detected as 270 to 330 deg, and a pulse voltage is applied to the electric motor 1 in the energization mode [2]. In the energization mode [2], the forward rotation open phase voltage E1 is calculated based on the V-phase applied voltage Vv when the forward rotation pulse is applied, and the reverse rotation open phase voltage E2 is calculated based on the V-phase applied voltage Vv when the reverse rotation pulse is applied. In addition, the forward rotation threshold setting unit 307 sets the upper forward rotation threshold VFW_th1 is the normal rotation threshold V FW_th On the other hand, the reverse rotation threshold value setting unit 308 sets the second switching detection value E2 SW is the reversal threshold V RV_th At time t4, when the applied voltage command value V* becomes negative, reverse driving is started (see FIG. 4). At this time, it is assumed that the forward rotation of the rotor 11 is still continuing due to the influence of inertia.

[0090] At time t5, the forward rotation of the rotor 11 causes the value of the forward rotation open phase voltage E1 to exceed the upper forward rotation threshold V FW_th1 When the rotation angle of the motor controller 3 exceeds the rotor rotation angle range R θ The reverse rotation open phase voltage E2 is determined to be between 330 and 30 degrees, and the conduction mode [2] is switched to the conduction mode [3]. Meanwhile, the reverse rotation open phase voltage E2 is set to the second switching detection value E2 SW The second switching detection value E2 SW Since the current flow rate does not exceed , the current flow mode is not switched to the reverse direction.

[0091] In the conduction mode [3], the forward rotation open phase voltage E1 is calculated based on the U-phase applied voltage Vu when the forward rotation pulse is applied, and when the rotor 11 continues to rotate forward, the first switching detection value E1 SW As shown in FIG. 17(C), the first switching detection value E1 SW is the lower forward rotation threshold V that is preset as the forward rotation initial threshold for the energization mode [3]. FW_th2 , the normal rotation threshold setting unit 307 sets the lower normal rotation threshold V FW_th2 is the normal rotation threshold V FW_th On the other hand, in the conduction mode [3], the reverse rotation open phase voltage E2 is calculated based on the U-phase applied voltage Vu when the reverse rotation pulse is applied, and when the rotor 11 continues to rotate forward, the second switching detection value E2 is set as shown in FIG. SW As shown in FIG. 17(D) and FIG. 18, the second switching detection value E2 SW is the lower reverse threshold V that is preset as the initial reverse threshold for the energization mode [3]. RV_th2Since the reverse rotation threshold value setting unit 308 sets the second switching detection value E2 SW is the reversal threshold V RV_th is set as

[0092] After time t5, as shown in FIG. 17(D) and FIG. 18, when the rotation of the rotor 11 changes from forward to reverse due to the start of reverse driving (time t4), the reverse opening phase voltage E2 becomes equal to or lower than the lower reverse threshold V RV_th2 If the reversal threshold V RV_th as the lower reversal threshold V RV_th2 When this is set, the reverse open phase voltage E2 is lower than the lower reverse threshold V RV_th2 As described above, it is difficult to switch from the energization mode [3] to the energization mode [2] because the second switching detection value E2 cannot be lowered below this value. SW is the reversal threshold V RV_th Therefore, when the rotor 11 starts to rotate in the reverse direction and the reverse rotation open phase voltage E2 changes in the reverse direction in FIG. 18, the second switching detection value E2 SW will fall below this.

[0093] At time t6, as shown in FIG. 17(D), the value of the reverse rotation opening phase voltage E2 becomes equal to the second switching detection value E2 SW When the rotation angle of the motor falls below the predetermined value, the motor control device 3 sets the rotor rotation angle range R θ The controller 10 determines that the rotational speed of the rotor 11 has shifted from 270 to 330 degrees, and switches the conduction mode [3] to the conduction mode [2]. Meanwhile, the normal rotation open phase voltage E1 is lower than the lower normal rotation threshold V FW_th2 Since the voltage does not decrease to the normal rotation direction, the current supply mode is not switched to the normal rotation direction.

[0094] The main points of the improved operation of the electric motor 1 through the low-speed sensorless control of the motor control device 3 described above can be expanded as follows.

[0095] In principle, the motor control device 3 sets the forward rotation threshold V as follows: FW_th and the reversal threshold VRV_th In other words, in the conduction modes [2], [4], and [6], the upper forward rotation threshold V FW_th1 is the normal rotation threshold V FW_th The upper reversal threshold V RV_th1 is the reversal threshold V RV_th In addition, in the energization modes [1], [3], and [5], the lower forward rotation threshold V FW_th2 is the normal rotation threshold V FW_th The lower reversal threshold V RV_th2 is the reversal threshold V RV_th is set to

[0096] However, the first switching detection value E1 immediately after switching to the energization mode [1], [3], [5] due to the reverse rotation of the rotor 11 SW is the lower normal threshold V FW_th2 When the value is less than the normal rotation threshold V FW_th is the first switching detection value E1 SW In addition, the first switching detection value E1 immediately after switching to the energization mode [2], [4], or [6] due to the reverse rotation of the rotor 11 is set to SW is the upper normal threshold V FW_th1 When it is larger than the normal threshold V FW_th is the first switching detection value E1 SW As a result, when the rotation of the rotor 11 changes from reverse to forward, the value of the forward rotation open phase voltage E1 becomes equal to or greater than the upper forward rotation threshold value V FW_th1 Greater than or lower forward threshold V FW_th2 This is because, when the rotation of the rotor 11 changes from reverse to forward, the value of the forward rotation open phase voltage E1 becomes equal to or exceeds the forward rotation threshold value V FW_th The first switching detection value E1 is set as SW This is because the value returns to the value below or above this value.

[0097] On the other hand, the second switching detection value E2 immediately after switching to the energization mode [1], [3], [5] due to the forward rotation of the rotor 11 SW is the lower reversal threshold V RV_th2 When theRV_th is the second switching detection value E2 SW In addition, the second switching detection value E2 immediately after switching to the energization mode [2], [4], or [6] due to the forward rotation of the rotor 11 is set to SW is the upper reversal threshold V RV_th1 When it is larger than the reversal threshold V RV_th is the second switching detection value E2 SW As a result, when the rotation of the rotor 11 changes from forward to reverse, the value of the reverse opening phase voltage E2 is set to the upper reverse threshold value V RV_th1 Greater than or lower reversal threshold V RV_th2 This is because the value of the reverse opening phase voltage E2 exceeds the reverse threshold value V when the rotation of the rotor 11 changes from forward to reverse. RV_th The second switching detection value E2 is set as SW This is because the value returns to the value below or above this value.

[0098] Such a motor control device 3 can accurately detect the timing for switching the current conduction mode to the reverse direction even if the rotation direction of the rotor 11 is reversed, thereby significantly reducing loss of synchronism of the electric motor 1. This makes it possible to prevent the rotor 11 from rotating in a direction opposite to the drive command (forward rotation drive command or reverse rotation drive command) received by the motor control device 3, or to prevent the rotor 11 from stopping rotation.

[0099] [First Modification] Next, a first modification of the motor control device 3 will be described. In this modification, after the rotor 11 changes from reverse rotation to forward rotation, the value of the forward rotation open phase voltage E1 becomes the first switching detection value E1. SW This modification improves the reliability of detecting the timing for switching the conduction mode to the forward rotation direction, assuming that the time it takes for the rotor 11 to return to the forward rotation direction is extremely short. Also, in this modification, when the rotation of the rotor 11 changes from forward to reverse, the value of the reverse rotation open phase voltage E2 is equal to the second switching detection value E2. SW This improves the reliability of detecting the timing to switch the current conduction mode to the reverse direction, assuming that the time it takes for the current conduction mode to return to the reverse direction is extremely short.

[0100] Specifically, the motor control device 3 detects the first switching detection value E1 SW is the normal rotation threshold V FW_th When setting the first switching detection value E1 as follows: SW That is, the motor control device 3 corrects the first switching detection value E1 SW a positive offset value ΔEp (>0) added to the first switching detection value E1 SW The value obtained by adding a negative offset value ΔEn(<0) to the forward rotation threshold V FW_th In addition, the motor control device 3 determines the second switching detection value E2 SW The inversion threshold V RV_th When setting the second switching detection value E2 as follows: SW That is, the motor control device 3 corrects the second switching detection value E2 SW a positive offset value ΔEp (>0) added to the second switching detection value E2, or a negative value SW The value obtained by adding a negative offset value ΔEn(>0) to the reverse threshold V RV_th In short, the first switching detection value and E1 SW and second switching detection value E2 SW A predetermined offset value ΔEp or ΔEn is added to each value to obtain the forward rotation threshold V FW_th and the reversal threshold V RV_th The absolute values ​​of each of these are made larger.

[0101] According to the first modification, the first switching detection value E1 SW By correcting as described above, after the rotor 11 changes from reverse rotation to forward rotation, the value of the forward rotation open phase voltage E1 becomes equal to the corrected first switching detection value E1 SW The time required for the normal rotation open phase voltage E1 to return to the first switching detection value E1 can be made longer than when the correction is not performed. SW When comparing with the forward open phase voltage E1, the value of the forward threshold V FW_th This can prevent the electric motor 1 from losing synchronism due to the temperature falling below or exceeding the reference temperature.

[0102] Furthermore, according to the first modified example, the second switching detection value E2 SW By correcting as described above, after the rotor 11 changes from forward rotation to reverse rotation, the value of the reverse rotation open phase voltage E2 becomes the corrected second switching detection value E2 SW The time required for the reverse open phase voltage E2 to return to the second switching detection value E2 can be made longer than when no correction is performed. SW When comparing with the reverse open phase voltage E2, the value of the reverse open phase voltage E2 has already exceeded the reverse threshold V RV_th This can prevent the electric motor 1 from losing synchronism due to the temperature falling below or exceeding the reference temperature.

[0103] [Second Modification] Next, a second modification of the motor control device 3 will be described. In this modification, the first switching detection value E1 SW and second switching detection value E2 SW Assuming that each value of shows an abnormal value due to the influence of electrical noise, etc., the normal rotation threshold V FW_th and the reversal threshold V RV_th This limits the range of values ​​that can be taken.

[0104] Now, referring to FIG. 19, the forward rotation threshold V FW_th and the reversal threshold V RV_th 19 shows an example of the change in the forward rotation open phase voltage E1 and the reverse rotation open phase voltage E2 with respect to the rotor rotation angle in the conduction mode [3].

[0105] As shown in Figure 19, the rotor rotation angle range R of 330 to 30 degrees corresponds to the energization mode [3]. θ In this case, the forward rotation open phase voltage E1 is in a monotonically decreasing section in the forward direction, and the reverse rotation open phase voltage E2 is in a monotonically decreasing section in the reverse direction. If the conduction mode is not switched, the forward rotation open phase voltage E1 will continue to monotonically decrease between 30 and 90 degrees, and then change to a monotonically increasing state. The voltage value at which the forward rotation open phase voltage E1 changes from a monotonically decreasing state to a monotonically increasing state is called the forward rotation switching limit value E1. MINOn the other hand, if there is no switching of the conduction mode, the reverse rotation open phase voltage E2 continues to decrease monotonically between 270 and 330 degrees, and then changes to increase monotonically. The voltage value at which the reverse rotation open phase voltage E2 changes from a monotonous decrease to a monotonous increase is called the reverse rotation switching limit value E2. MIN If the normal rotation threshold V FW_th forward rotation switching limit value E1 MIN If it is set to less than this, even if the rotor 11 rotates forward up to 30 to 90 degrees, the value of the forward rotation open phase voltage E1 will not exceed the forward rotation threshold V FW_th In addition, the reverse threshold V RV_th Reverse switching limit value E2 MIN If it is set to less than this, even if the rotor 11 reverses up to 270 to 330 degrees, the value of the reverse open phase voltage E2 will not exceed the reverse threshold V RV_th It may not be possible to fall below this level.

[0106] For this reason, the motor control device 3 sets the lower forward rotation threshold V FW_th2 Instead of the first switching detection value E1 SW The forward rotation threshold V is set using FW_th The lower limit of the forward rotation threshold V FW_th2 Less than forward rotation switching limit value E1 MIN The motor control device 3 also sets the lower reverse rotation threshold V RV_th2 Instead, the second switching detection value E2 SW The reversal threshold V is set using RV_th The lower limit of V is the lower reversal threshold V RV_th2 Less than reverse switching limit value E2 MIN In the conduction modes [1] and [5], in which the forward rotation open phase voltage E1 and the reverse rotation open phase voltage E2 monotonically decrease in each direction, the forward rotation threshold V FW_th and the reversal threshold V RV_th As a result, the lower limit values ​​of the first switching detection value E1 SW The forward rotation threshold V is set using FW_th When it is below the lower limit, the normal rotation threshold V FW_th is corrected to the lower limit value. SW The reversal threshold V is set to RV_thWhen it falls below the lower limit, the reversal threshold V RV_th is corrected to the lower limit.

[0107] Next, referring to Figure 20, the forward rotation threshold V FW_th and the reversal threshold V RV_th 20 shows an example of the change in the forward rotation open phase voltage E1 and the reverse rotation open phase voltage E2 with respect to the rotor rotation angle in the conduction mode [4].

[0108] As shown in Figure 20, the rotor rotation angle range R of 30 to 90 degrees corresponds to the energization mode [4]. θ In this case, the forward rotation open phase voltage E1 is in a monotonically increasing section in the forward direction, and the reverse rotation open phase voltage E2 is in a monotonically increasing section in the reverse direction. If the conduction mode is not switched, the forward rotation open phase voltage E1 will continue to increase monotonically between 90 and 150 degrees, and then will change to a monotonically decreasing state. The voltage value at which the forward rotation open phase voltage E1 changes from a monotonically increasing state to a monotonically decreasing state is called the forward rotation switching limit value E1. MAX On the other hand, if there is no switching of the conduction mode, the reverse rotation open phase voltage E2 continues to increase monotonically between 330 and 30 degrees, and then changes to a monotonous decrease. The voltage value at which the reverse rotation open phase voltage E2 changes from a monotonous increase to a monotonous decrease is called the reverse rotation switching limit value E2. MAX If the normal rotation threshold V FW_th forward rotation switching limit value E1 MAX If the value is set larger than this, even if the rotor 11 rotates forward up to 90 to 150 degrees, the forward rotation open phase voltage E1 will exceed the forward rotation threshold V FW_th In addition, the reverse threshold V RV_th Reverse switching limit value E2 MAX If it is set larger, even if the rotor 11 reverses up to 330 to 30 degrees, the reverse opening phase voltage E2 will be greater than the reverse threshold V RV_th It may not be possible to exceed this.

[0109] For this reason, the motor control device 3 sets the upper forward rotation threshold V FW_th1 Instead of the first switching detection value E1 SW The forward rotation threshold V is set using FW_th The upper limit of the forward rotation switching limit value E1MAX Below the upper normal threshold V FW_th1 The motor control device 3 also sets the upper reverse rotation threshold V RV_th1 Instead, the second switching detection value E2 SW The reversal threshold V is set using RV_th The upper limit of the reverse rotation limit E2 MAX Below and above the reversal threshold V RV_th1 In the conduction modes [2] and [6], in which the forward rotation open phase voltage E1 and the reverse rotation open phase voltage E2 increase monotonically in each direction, the forward rotation threshold V FW_th and the reversal threshold V RV_th As a result, the upper limit values ​​of the first switching detection value E1 SW The forward rotation threshold V is set using FW_th becomes larger than the upper limit, the forward rotation threshold V FW_th is corrected to the upper limit value. SW The reversal threshold V is set using RV_th becomes larger than the upper limit, the reversal threshold V RV_th is corrected to the upper limit.

[0110] According to the second modification, the first switching detection value E1 SW and second switching detection value E2 SW Even if each value shows an abnormal value due to the influence of electrical noise, etc., the normal rotation threshold V FW_th and the reversal threshold V RV_th The lower and upper limits of the respective values ​​are set within the above-mentioned predetermined ranges, thereby further reducing the possibility of the electric motor 1 losing synchronization.

[0111] [Third Modification] Next, we will explain a third modified example of the motor control device 3. This modified example focuses on the fact that the loss of synchronism of the electric motor 1 described with reference to Figures 21 and 22 occurs when the rotation direction of the rotor 11 is reversed, and reduces the processing load of the motor control device 3.

[0112] Specifically, when the rotor rotation speed N is less than a predetermined value Nc, the motor control device 3 sets the normal rotation initial threshold value or the first switching detection value E1 SW Either one of these is set to the forward threshold V FW_th When the rotor rotation speed N is less than the predetermined value Nc, the motor control device 3 sets the reverse rotation initial threshold value or the second switching detection value E2 SW Either one of the two is the reversal threshold V RV_th In other words, when the rotor rotation speed N is equal to or greater than the predetermined value Nc, the motor control device 3 sets the first switching detection value E1 SW Without using the upper normal threshold V FW_th1 and the lower normal threshold V FW_th2 The value corresponding to the current conduction mode is set as the forward rotation threshold V FW_th Furthermore, when the rotor rotation speed N is equal to or greater than the predetermined value Nc, the motor control device 3 sets the second switching detection value E2 SW Without using the upper inversion threshold V RV_th1 and the lower reversal threshold V RV_th2 The value corresponding to the conduction mode is used as the reverse threshold V RV_th The rotor rotation speed N is set as follows: MODE The change rate can be obtained based on the rate of change (for example, based on the reciprocal of the switching interval of the energization mode).

[0113] According to the third modification, in a situation where there is a low possibility that the electric motor 1 will lose synchronism, the motor control device 3 sets the first switching detection value E1 SW Without using the normal threshold V FW_th Set the second switching detection value E2 SW Without using the inversion threshold V RV_th Therefore, the forward rotation threshold V FW_th and the reversal threshold V RV_th This reduces the processing load on the motor control device 3 associated with the setting of the parameter.

[0114] [Fourth Modification] Next, we will explain a fourth modified example of the motor control device 3. Like the third modified example, this modified example reduces the processing load of the motor control device 3 by focusing on the fact that the loss of synchronization of the electric motor 1 described with reference to Figures 21 and 22 occurs when the rotation direction of the rotor 11 is reversed.

[0115] Specifically, the motor control device 3 starts driving the rotor 11 to reverse the rotation direction, and then detects the first switching detection value E1 SW The normal threshold V FW_th Setting of the second switching detection value E2 SW The inversion threshold V RV_th Setting of the applied voltage command value V* is started. For example, when the applied voltage command value V* reverses its positive and negative polarities, in other words, when the magnitude relationship between the pulse width of the forward rotation pulse and the pulse width of the reverse rotation pulse is reversed, it can be determined that driving to reverse the rotation direction of the rotor 11 has started. Furthermore, when driving to reverse the rotation direction of the rotor 11 has started, it can also be determined that driving to reverse the rotation direction of the rotor 11 has started when the rotor 11 is rotating in one direction due to inertia and is then driven in the reverse direction. This is because, even if the applied voltage command value V* is zero, the rotor 11 may be rotating due to inertia caused by the rotation drive based on the previous applied voltage command value V* or the influence of an external force. Therefore, if the rotation direction of the rotor 11 when the applied voltage command value V* is zero can be detected, it can be determined that driving to reverse the rotation direction of the rotor 11 has started when the applied voltage command value V* changes from zero to a positive or negative value. Furthermore, if the rotation direction of the rotor 11 when the pulse widths of the forward rotation pulse and the reverse rotation pulse are equal can be detected, it can be determined that driving to reverse the rotation direction of the rotor 11 has started when the pulse widths of the forward rotation pulse and the reverse rotation pulse change in magnitude. The direction of rotation of the rotor 11 is determined by the energization mode signal S MODE It can be detected based on changes in

[0116] First switching detection value E1 SW The normal threshold V FW_th Setting of the second switching detection value E2 SW The inversion threshold V RV_thThe setting of the first switching detection value E1 ends when a predetermined time Tc has elapsed since the start of driving to reverse the rotation direction of the rotor 11. SW The normal threshold V FW_th Setting of the second switching detection value E2 SW The inversion threshold V RV_th The setting of the first switching detection value E1 ends when the number of switching of the current supply mode reaches a predetermined value Sc after the start of driving to reverse the rotation direction of the rotor 11. SW The normal threshold V FW_th Setting of the second switching detection value E2 SW The inversion threshold V RV_th The setting of is completed when the rotor rotation speed N reaches or exceeds the predetermined value Nc, as described above.

[0117] According to the fourth modification, in a situation where the possibility of the electric motor 1 losing synchronism is low, the forward rotation threshold V FW_th and the reversal threshold V RV_th This reduces the processing load on the motor control device 3 associated with the setting of the parameter.

[0118] [Fifth Modification] Next, we will explain a fifth modified example of the motor control device 3. Like the third modified example, this modified example reduces the processing load of the motor control device 3 by focusing on the fact that the loss of synchronization of the electric motor 1 described with reference to Figures 21 and 22 occurs when the rotation direction of the rotor 11 is reversed.

[0119] In one aspect, the electric motor 1 loses synchronism when the rotation of the rotor 11 changes from forward to reverse and the reverse opening phase voltage E2 exceeds the upper reverse threshold V RV_th1 or the lower reversal threshold V RV_th2 In addition, as another aspect of the loss of synchronism of the electric motor 1, when the rotation of the rotor 11 changes from reverse to forward, the forward rotation open phase voltage E1 does not fall below the upper forward rotation threshold V FW_th1 or the lower forward threshold V FW_th2Therefore, the motor control device 3 continuously detects the second switching detection value E2 only when the rotor 11 is rotating in the forward direction. SW Using the inversion threshold V RV_th On the other hand, the motor control device 3 may set the first switching detection value E1 only when the rotor 11 is rotating in the reverse direction. SW Using the normal threshold V FW_th may be set.

[0120] According to the fifth modification, in a situation where the electric motor 1 is unlikely to lose synchronism, the forward rotation threshold V FW_th and the reversal threshold V RV_th This reduces the processing load on the motor control device 3 associated with the setting of the parameter.

[0121] [Sixth Modification] Next, a description will be given of a sixth modified example of the motor control device 3. This modified example shortens the time required to switch the current conduction mode when the rotation direction of the rotor 11 is reversed.

[0122] As mentioned above, the first switching detection value E1 SW is the upper normal threshold V FW_th1 If it is greater than the first switching detection value E1 SW is the normal rotation threshold V FW_th Instead, the first switching detection value E1 SW is the upper normal threshold V FW_th1 If it is greater than the first switching detection value E1 SW and the upper normal threshold V FW_th1 Both of these are set to the forward threshold V FW_th According to this, when the rotation of the rotor 11 changes from reverse to forward, the forward rotation open phase voltage E1 becomes equal to or exceeds the upper forward rotation threshold V FW_th1 If the value is equal to or less than the first switching detection value E1, the forward rotation open phase voltage E1 will be equal to or less than the first switching detection value E1 SW The upper forward threshold V FW_th1 Therefore, the normal rotation open phase voltage E1 exceeds the upper normal rotation threshold V FW_th1 The time until the forward rotation open phase voltage E1 exceeds the first switching detection value E1 SW, and the conduction mode can be switched quickly. FW_th1 If the value is larger than the first switching detection value E1, as described above, the forward rotation open phase voltage E1 increases with the forward rotation of the rotor 11. SW , and the conduction mode is switched to the forward direction normally. Similarly, the first switching detection value E1 SW is the lower normal threshold V FW_th2 If it is less than the first switching detection value E1 SW and the lower normal threshold V FW_th2 Both of these are set to the forward threshold V FW_th As a result, when the rotation of the rotor 11 changes from reverse to forward, the forward rotation open phase voltage E1 becomes equal to or exceeds the lower forward rotation threshold V FW_th2 If it is equal to or greater than this, the forward rotation open phase voltage E1 is equal to or greater than the first switching detection value E1 SW The lower forward threshold V FW_th2 This allows for quick switching of the power supply mode.

[0123] As mentioned above, the second switching detection value E2 SW is the upper reversal threshold V RV_th1 If it is greater than the second switching detection value E2 SW The inversion threshold V RV_th Instead, the second switching detection value E2 SW is the upper reversal threshold V RV_th1 If it is greater than the second switching detection value E2 SW and the upper reversal threshold V RV_th1 Both of these are inverted threshold V RV_th According to this, when the rotation of the rotor 11 changes from forward to reverse, the reverse opening phase voltage E2 becomes equal to or exceeds the upper reverse threshold value V RV_th1 If the reverse rotation opening phase voltage E2 is equal to or less than the second switching detection value E2 SW The upper reversal threshold V RV_th1 Therefore, the reverse open phase voltage E2 exceeds the upper reverse threshold V RV_th1 The time until the reverse open phase voltage E2 exceeds the second switching detection value E2 SWWhen the rotation of the rotor 11 changes from forward to reverse, the reverse opening phase voltage E2 exceeds the upper reverse threshold V RV_th1 If the reverse rotation opening phase voltage E2 is larger than the second switching detection value E2 as the rotor 11 rotates in the reverse direction, as described above, SW , and the conduction mode is switched to the reverse direction normally. Similarly, the second switching detection value E2 SW is the lower reversal threshold V RV_th2 If it is less than the second switching detection value E2 SW and the lower reversal threshold V RV_th2 Both of these are inverted threshold V RV_th As a result, when the rotation of the rotor 11 changes from forward to reverse, the reverse opening phase voltage E2 becomes equal to or exceeds the lower reverse threshold value V RV_th2 If the reverse rotation opening phase voltage E2 is equal to or greater than the second switching detection value E2 SW Lower reversal threshold V RV_th2 The current supply mode can be switched quickly below this value.

[0124] According to the sixth modification, when the rotation direction of rotor 11 is reversed, the time required for switching the current supply mode when the rotation of rotor 11 is reversed can be shortened.

[0125] The present invention has been specifically described above with reference to preferred embodiments and modifications thereof. However, it is obvious that a person skilled in the art can adopt various modifications based on the technical ideas and teachings of the present invention.

[0126] As the initial forward rotation threshold, in conduction modes [2], [4], and [6], the upper forward rotation threshold V FW_th1 is uniform, and in conduction modes [1], [3], and [5], the lower forward rotation threshold V FW_th2 was set uniformly, but the upper normal threshold V FW_th1 and the lower normal threshold V FW_th2 may be preset to a different value for each conduction mode. Similarly, as the initial reverse threshold, the upper reverse threshold V RV_th1is set to a uniform value, and the lower reverse threshold V RV_th2 was set uniformly, but the upper reversal threshold V RV_th1 and the lower reversal threshold V RV_th2 may be preset to a different value for each power supply mode.

[0127] The value of the forward open phase voltage E1 is the forward threshold V FW_th When the value of the forward rotation open phase voltage E1 falls below the forward rotation threshold V FW_th From the larger range, the forward threshold V FW_th This may include, or may be substituted for, the case where the value of the forward rotation open phase voltage E1 falls below the forward rotation threshold V FW_th When the value of the forward rotation open phase voltage E1 exceeds the forward rotation threshold V FW_th From the range below the normal threshold V FW_th This may include, or may be substituted for, the case where the reverse open phase voltage E2 increases to the reverse threshold V RV_th When the reverse open phase voltage E2 is below the reverse threshold V RV_th The same applies when it exceeds .

[0128] Furthermore, the technical ideas described in the above embodiments and modifications based thereon can be used in appropriate combinations as long as no contradictions arise. For example, the first to sixth modifications can be used in appropriate combinations as long as no contradictions arise. [Explanation of symbols]

[0129] 1...electric motor, 2...drive circuit, 3...motor control device, 11...rotor, 12u, 12v, 12w...three-phase coil, 301...voltage command adjustment unit, 302...PWM signal generation unit, 303...gate signal generation unit, 304...conduction mode determination unit, 306...open phase voltage detection unit, 307...forward rotation threshold setting unit, 308...reverse rotation threshold setting unit, 309, 310...comparison unit, [1], [2], [3], [4], [5], [6]...conduction mode, E1...forward rotation open phase voltage (first open phase voltage), E2...reverse rotation open phase voltage (second open phase voltage), E1 SW …1st switching detection value, E2 SW…2nd switching detection value, E1 MIN ,E1 MAX …Forward rotation switching limit value, E2 MIN ,E2 MAX ...reverse switching limit value, ΔEp, ΔEn...offset value, N...rotor rotation speed, Nc...predetermined value, Sc...predetermined value, Tc...predetermined time, Vuv, Vvw, Vwu...three-phase line voltage (pulse voltage), V FW_th … forward rotation threshold (first threshold), V RV_th …reverse threshold (second threshold), V FW_th1 …Upper forward threshold (first initial threshold), V FW_th2 …Lower forward threshold (first initial threshold), V RV_th1 …Upper reversal threshold (second initial threshold), V RV_th2 …Lower reversal threshold (second initial threshold)

Claims

1. 1. A motor control device that rotates a rotor of an electric motor by sequentially switching current conduction modes that specify two-phase coils to which a pulse voltage is applied among three-phase coils of the electric motor, a computer, the computer comprising: a control signal is output to a drive circuit that drives the electric motor so that the pulse voltage alternately generates a first pulse for rotating the rotor in one direction and a second pulse having an opposite polarity to the first pulse for rotating the rotor in a direction opposite to the one direction, and the rotation drive in either the one direction or the reverse direction is controlled by reversing the length relationship between the application times of the first pulse and the second pulse; Detecting a first open phase voltage induced in the open phase when the first pulse is applied, and a second open phase voltage induced in the open phase when the second pulse is applied; a first threshold value that defines a value of the first open phase voltage when the current conduction mode is switched in one direction, and a second threshold value that defines a value of the second open phase voltage when the current conduction mode is switched in the reverse direction, for each of the current conduction modes; the power supply mode is switched to either the one direction or the reverse direction based on two comparison results of comparing the value of the first open phase voltage with the first threshold value and comparing the value of the second open phase voltage with the second threshold value, The motor control device is configured such that, as a threshold setting process, when the current conduction mode is switched to the reverse direction, the computer sets the first threshold based on a first switching detection value, which is the value of the first open phase voltage immediately after the current conduction mode is switched, and a first initial threshold value that is preset for each current conduction mode, and when the current conduction mode is switched to one direction, the computer sets the second threshold based on a second switching detection value, which is the value of the second open phase voltage immediately after the current conduction mode is switched, and a second initial threshold value that is preset for each current conduction mode.

2. the first initial threshold is set to either a first upper threshold or a first lower threshold that is smaller than the first upper threshold for each of the current conduction modes, and the second initial threshold is set to either a second upper threshold or a second lower threshold that is smaller than the second upper threshold for each of the current conduction modes; 2. The motor control device of claim 1, wherein, when the current conduction mode is switched in the reverse direction, the first threshold value is set using the first switching detection value when the first switching detection value is greater than the first upper threshold value and when the first switching detection value is less than the first lower threshold value, while, when the current conduction mode is switched in one direction, the second threshold value is set using the second switching detection value when the second switching detection value is greater than the second upper threshold value and when the second switching detection value is less than the second lower threshold value.

3. 3. The motor control device of claim 2, wherein, when the current conduction mode is switched in the reverse direction, the first threshold value is set by adding a positive offset value to the first switching detection value that is greater than the first upper threshold value, or by adding a negative offset value to the first switching detection value that is less than the first lower threshold value, while, when the current conduction mode is switched in one direction, the second threshold value is set by adding a positive offset value to the second switching detection value that is greater than the second upper threshold value, or by adding a negative offset value to the second switching detection value that is less than the second lower threshold value.

4. 4. The motor control device according to claim 2, wherein upper limits are set in advance for the first threshold value, which is set based on the first switching detection value that is greater than the first upper threshold value, and the second threshold value, which is set based on the second switching detection value that is greater than the second upper threshold value, and lower limits are set in advance for the first threshold value, which is set based on the first switching detection value that is less than the first lower threshold value, and the second threshold value, which is set based on the second switching detection value that is less than the second lower threshold value.

5. 4. The motor control device according to claim 1, wherein the threshold value setting process is performed when the absolute value of the rotation speed of the rotor is less than a predetermined value.

6. The motor control device according to any one of claims 1 to 3, wherein the threshold setting process is performed until a predetermined time has elapsed since the start of driving to reverse the rotation direction of the rotor, or until the number of times the current flow mode is switched reaches a predetermined value.

7. 2. The motor control device according to claim 1, wherein the computer is configured to continuously set the first threshold value based on the first switching detection value and the first initial threshold value while the rotor is rotating in the reverse direction, and to continuously set the second threshold value based on the second switching detection value and the second initial threshold value while the rotor is rotating in one direction.

8. the first initial threshold is set to either a first upper threshold or a first lower threshold that is smaller than the first upper threshold for each of the current conduction modes, and the second initial threshold is set to either a second upper threshold or a second lower threshold that is smaller than the second upper threshold for each of the current conduction modes; When the current conduction mode is switched to the reverse direction, if the first switching detection value is greater than the first upper threshold, the first threshold is set to the first upper threshold and the first switching detection value, and if the first switching detection value is less than the first lower threshold, the first threshold is set to the first lower threshold and the first switching detection value, 2. The motor control device according to claim 1, wherein when the current conduction mode is switched in the one direction, if the second switching detection value is greater than the second upper threshold, the second threshold is set to the second upper threshold and the second switching detection value, and if the second switching detection value is less than the second lower threshold, the second threshold is set to the second lower threshold and the second switching detection value.

9. 1. A motor control method for rotating a rotor of an electric motor by sequentially switching current conduction modes that identify two-phase coils to which a pulse voltage is applied among three-phase coils of the electric motor, the method comprising: a computer outputs a control signal to a drive circuit that drives the electric motor so that the pulse voltage alternately generates a first pulse for rotating the rotor in one direction and a second pulse having a polarity opposite to that of the first pulse for rotating the rotor in a direction opposite to the one direction; the computer controls rotational driving in either the one direction or the reverse direction by inverting the magnitude relationship between the application times of the first pulse and the second pulse; The computer detects a first open phase voltage induced in the open phase when the first pulse is applied, and a second open phase voltage induced in the open phase when the second pulse is applied; the computer sets, for each of the conduction modes, a first threshold value that defines a value of the first open phase voltage when the conduction mode is switched in one direction, and a second threshold value that defines a value of the second open phase voltage when the conduction mode is switched in the reverse direction; the computer switches the conduction mode to either the one direction or the reverse direction based on two comparison results of comparing the value of the first open phase voltage with the first threshold value and comparing the value of the second open phase voltage with the second threshold value; Including, The computer sets the first threshold value based on a first switching detection value, which is the value of the first open phase voltage immediately after the current conduction mode is switched, and a first initial threshold value that is preset for each current conduction mode, when the current conduction mode is switched to the reverse direction, and sets the second threshold value based on a second switching detection value, which is the value of the second open phase voltage immediately after the current conduction mode is switched, and a second initial threshold value that is preset for each current conduction mode, when the current conduction mode is switched to one direction.

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