Motor control device

Abstract

This technology prevents feedback control caused by inaccurate actual rotational speeds during motor startup, thereby reducing the possibility of step loss. [Solution] A motor control device that drives and controls a motor using a control mode that includes a startup mode executed when the motor is started and a normal mode executed when the motor is running normally after startup, comprising: an actual rotation speed acquisition unit that acquires the actual rotation speed of the motor; a control mode setting unit that sets the control mode; a target rotation speed setting unit that sets the target rotation speed of the motor in the process of bringing the actual rotation speed closer to the final target rotation speed; and an actual rotation speed control unit that controls the motor in the normal mode based on the difference between the actual rotation speed and the target rotation speed so that the actual rotation speed approaches the target rotation speed, wherein the conditions for the control mode setting unit to transition the control mode from the startup mode to the normal mode include the actual rotation speed of the motor in the startup mode being greater than a predetermined threshold.

Description

Technical Field

[0001] The present invention relates to a motor control device.

Background Art

[0002] Conventionally, in a sensorless control brushless motor that detects the magnetic pole position of a permanent magnet rotor by detecting the induced voltage induced in the stator winding, there is a technique for controlling at the time of switching from forced synchronization control to sensorless control (feedback synchronization control) at startup. For example, in Patent Document 1, when the phase difference between the forced synchronization control signal and the feedback synchronization control signal generated based on the zero-crossing point of the induced voltage becomes a predetermined value or less at the time of switching from forced synchronization control to feedback synchronization control (feedback control), switching is made to feedback synchronization control for maintaining a stable driving state, and thereafter, rated driving by feedforward is performed.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] An error can occur in detecting the actual rotational speed of the motor. In particular, it is inaccurate at the initial stage of startup. In feedback control, control is performed to bring the actual rotational speed closer to the target rotational speed according to the difference between the actual rotational speed and the target rotational speed. However, when performing feedback control based on an inaccurate actual rotational speed, the difference between the actual rotational speed and the target rotational speed becomes inaccurate. Therefore, even though the difference between the true rotational speed and the target rotational speed is not actually so large, the actual rotational speed may be adjusted excessively, resulting in detuning.

[0005] This invention has been made in view of the above problems, and aims to provide a technology that prevents feedback control due to inaccurate actual rotational speed during motor startup and reduces the possibility of step loss. [Means for solving the problem]

[0006] A motor control device according to one embodiment is a motor control device that drives and controls a motor by a control mode that includes a startup mode executed when the motor is started and a normal mode executed when the motor is running normally after startup, and comprises: an actual rotation speed acquisition unit that acquires the actual rotation speed of the motor; a control mode setting unit that sets the control mode; a target rotation speed setting unit that sets a target rotation speed of the motor in the process of bringing the actual rotation speed closer to the final target rotation speed; and an actual rotation speed control unit that controls the motor in the normal mode based on the difference between the actual rotation speed and the target rotation speed so that the actual rotation speed approaches the target rotation speed, wherein the conditions for the control mode setting unit to transition the control mode from the startup mode to the normal mode include the actual rotation speed of the motor in the startup mode being greater than a predetermined threshold.

[0007] Generally, the actual rotational speed of a motor is inaccurate immediately after startup, and becomes more accurate as the rotational speed increases. Therefore, the motor control device restricts the transition of the control mode from startup mode to normal mode only after the rotational speed has risen to a certain level. This configuration prevents feedback control due to the inaccurate actual rotational speed at motor startup and reduces the possibility of step loss. [Brief explanation of the drawing]

[0008] [Figure 1] This diagram shows the overall configuration of an electric pump, including the motor control device. [Figure 2] This is a system configuration diagram showing the detailed configuration of the motor control device. [Figure 3] This diagram schematically illustrates the control method used by the motor control device. [Figure 4]This diagram schematically illustrates the control method used by the motor control device. [Figure 5] This diagram schematically illustrates a conventional control method. [Modes for carrying out the invention]

[0009] Here, one embodiment of the present invention will be described with reference to the drawings in the following order. (1) Overall configuration of the electric pump: (2) Detailed configuration of the motor control device: (3) Control modes by motor control device: (4) Conventional control methods and effects of this embodiment: (5) Other embodiments:

[0010] (1) Overall configuration of the electric pump: Figure 1 shows the overall configuration of the electric pump WP1, including the motor control device 100. The electric pump WP1 comprises a motor 110, an inverter 120, a control circuit 130, and a zero-cross detection unit 140. The motor 110 is, for example, an AC electric motor that drives the electric pump WP1. The motor 110 is a sensorless controlled brushless motor that detects the magnetic pole position of the permanent magnet rotor 110a, which is rotationally driven by the driving magnetic field generated by the stator windings 110u, 110v, and 110w, by detecting the induced voltage induced in the stator windings 110u, 110v, and 110w.

[0011] The inverter 120 is connected to the DC power supply 210 and also to the motor 110, and is a power conversion device that converts power between the DC power supply 210 and the multi-phase AC power supply of the motor 110 (in this case, three-phase AC consisting of U-phase, V-phase, and W-phase).

[0012] The DC power supply 210 supplies power to the electric pump WP1. The DC power supply 210 that supplies power to the motor 110 is a high-voltage, high-capacity DC power supply. The DC power supply 210 can supply power to the motor 110 via the inverter 120.

[0013] The inverter 120 is a circuit that converts power between a DC power supply 210 and an AC motor 110 by comprising multiple series circuits of upper switching elements 11a to 11c and lower switching elements 11d to 11f. Specifically, among the multiple switching elements, the switching elements electrically connected to the positive terminal of the DC power supply 210 are called upper switching elements 11a, 11b, and 11c. Also, among the multiple switching elements, the switching elements electrically connected to the negative terminal of the DC power supply 210 are called lower switching elements 11d, 11e, and 11f.

[0014] It is preferable that power semiconductor elements capable of high-frequency operation be used for the upper switching elements 11a to 11c and the lower switching elements 11d to 11f. Examples of such elements include IGBTs (Insulated Gate Bipolar Transistors), power MOSFETs (Metal Oxide Semiconductor Field Effect Transistors), SiC-MOSFETs (Silicon Carbide - Metal Oxide Semiconductor FETs), SiC-SITs (SiC - Static Induction Transistors), and GaN-MOSFETs (Gallium Nitride - MOSFETs). In this embodiment, the upper switching elements 11a to 11c and the lower switching elements 11d to 11f are IGBTs.

[0015] The inverter 120 is composed of a bridge circuit having a number of arms corresponding to each of the multiple phases. The inverter 120 has arms for three AC phases, and each arm is composed of a series circuit of one of the upper switching elements 11a to 11c and one of the lower switching elements 11d to 11f. Specifically, as shown in Figure 1, in the inverter 120, two switching elements are connected in series between the positive and negative terminals of the DC power supply 210 to form one arm.

[0016] For example, the upper-side switching element 11a and the lower-side switching element 11d form a series circuit to constitute one arm. Similarly, the upper-side switching element 11b and the lower-side switching element 11e form a series circuit to constitute one arm, and the upper-side switching element 11c and the lower-side switching element 11f form a series circuit to constitute one arm. In the case of three-phase alternating current, these series circuits (one arm) are connected in parallel in three lines (three phases). That is, a bridge circuit is formed in which a set of series circuits (arms) corresponds to each of the coils corresponding to the U phase, V phase, and W phase of the motor 110.

[0017] The midpoints of the series circuits (arms) formed by the switching elements of the corresponding phases, that is, the connection points between the upper-side switching elements 11a to 11c and the lower-side switching elements 11d to 11f, are electrically connected to each of the three-phase coils of the motor 110. In addition, for each switching element, the direction from the negative electrode to the positive electrode (the direction from the lower side to the upper side) is defined as the forward direction, and diodes 13a to 13f (freewheel diodes) are electrically connected in parallel to each switching element.

[0018] The control circuit 130 is a circuit that controls the inverter 120. The control circuit 130 includes a motor control device 100 and a drive circuit 131. In addition to the motor control device 100 and the drive circuit 131, the control circuit 130 may also include various circuits for controlling the inverter 120. The control circuit 130 causes the switching elements constituting the inverter 120 to perform a switching operation. The drive circuit 131 is a circuit for operating the power switching elements constituting the inverter 120 belonging to the high-voltage system circuit. On the other hand, the motor control device 100 is an integrated circuit that performs various information processes. The motor control device 100 is, for example, a processor. The motor control device 100 is an IC circuit that controls each part according to a predetermined procedure and is constituted by, for example, a microcomputer, a DSP (Digital Signal Processor), or the like.

[0019] A master control device 220 is connected to the motor control device 100. The master control device 220 is a control device that overall controls a plurality of control devices including the motor control device 100. When a command from the master control device 220 is input, the motor control device 100 performs various controls based on that command.

[0020] The motor control device 100 controls the motor 110 via the inverter 120 based on the final target rotational speed Nco of the motor 110 provided as a request signal from the master control device 220 or the like via CAN (Controller Area Network) or the like. Specifically, the motor control device 100 performs switching control of the upper-stage switching elements 11a to 11c and the lower-stage switching elements 11d to 11f of the inverter 120 by PWM control via the drive circuit 131. In PWM (Pulse Width Modulation) control, the motor control device 100 generates a rectangular pulse wave for turning on or off the switching elements 11a to 11f of each phase by comparing a carrier wave (triangular wave) of the carrier frequency with a constant voltage command calculated by rotational speed feedback control. The motor control device 100 can change the duty ratio by changing the value of the voltage command. The duty ratio means the value obtained by dividing the pulse width by the pulse period (cycle). When the duty ratio is large, the torque of the motor 110 is larger than when it is small. Therefore, increasing the duty ratio increases the rotational speed of the motor 110, and decreasing the duty ratio decreases the rotational speed of the motor 110. In this embodiment, the motor control device 100 controls the rotation of the motor 110 in a 120-degree conduction method.

[0021] The drive circuit 131 is a circuit for switching the on and off states of the upper switching elements 11a to 11c and the lower switching elements 11d to 11f, respectively. The drive circuit 131 only needs to be able to control the on and off states of each switching element. When each switching element is an IGBT or FET, the control terminal is the gate terminal, so the drive circuit 131 generates a drive signal that is applied to the gate terminal of each switching element. Here, this drive signal is called the gate drive signal.

[0022] The motor control device 100 identifies the switching elements to be turned on or off and instructs the drive circuit 131 corresponding to each switching element to turn each switching element on or off. In response to this instruction, the drive circuit 131 generates gate drive signals UH, UL, VH, VL, WH, WL to drive the upper switching elements 11a to 11c and the lower switching elements 11d to 11f, respectively.

[0023] In addition to the series circuits of the upper switching elements 11a to 11c and the lower switching elements 11d to 11f, the inverter 120 has a series circuit including neutral potential generating resistors 12a and 12b that generate the neutral point potential (hereinafter referred to as neutral potential Vn) of the voltage generated at the terminals of the stator windings 110u, 110v, and 110w.

[0024] The zero-cross detection unit 140 generates zero-cross detection signals Vu0, Vv0, and Vw0 by comparing the drive terminal voltages Vu, Vv, and Vw generated at terminals U, V, and W of the stator windings 110u, 110v, and 110w with the neutral potential Vn, and outputs them to the motor control device 100. The zero-cross detection unit 140 has comparators 140u, 140v, and 140w. Comparators 140u, 140v, and 140w receive the drive terminal voltages Vu, Vv, and Vw and the neutral potential Vn as inputs, respectively, and output zero-cross detection signals Vu0, Vv0, and Vw0 to the motor control device 100. The zero-crossing detection signals Vu0, Vv0, and Vw0 are signals that indicate the zero-crossing points where the drive terminal voltages Vu, Vv, and Vw of each stator winding 110u, 110v, and 110w intersect with the neutral potential Vn.

[0025] The motor control device 100 controls the rotational speed of the permanent magnet rotor 110a by switching the upper switching elements 11a to 11c and the lower switching elements 11d to 11f of the inverter 120 via the drive circuit 131 using PWM control. In this embodiment, the rotational speed is the number of motor rotations per unit time (rpm).

[0026] (2) Detailed configuration of the motor control device: Figure 2 is a system configuration diagram showing the detailed configuration of the motor control device 100. The motor control device 100 drives and controls the motor 110 using control modes that include a startup mode executed when the motor 110 is started and a normal mode executed during normal operation after the motor 110 has started. Specifically, the motor control device 100 includes an actual rotation speed acquisition unit 10, a control mode setting unit 20, an actual rotation speed control unit 30, a target rotation speed setting unit 30a, and a PWM generation unit 40. In this embodiment, the target rotation speed setting unit 30a is one of the functions of the actual rotation speed control unit 30.

[0027] The actual rotational speed acquisition unit 10 acquires the actual rotational speed of the motor 110. For example, the actual rotational speed acquisition unit 10 estimates the rotational speed of the motor 110 based on the zero-cross detection signals Vu0, Vv0, and Vw0 input from the zero-cross detection unit 140, and outputs the actual rotational speed Nca, obtained by passing the estimated rotational speed through a low-pass filter, to the control mode setting unit 20 and the actual rotational speed control unit 30. For example, the actual rotational speed acquisition unit 10 determines the number of zero-crossings from the zero-cross detection signals Vu0, Vv0, and Vw0, and identifies the signal period from the number of zero-crossings. The actual rotational speed acquisition unit 10 determines the rotation period from the signal period, the number of poles of the motor 110, and the number of slots, and estimates the rotational speed of the motor 110.

[0028] The control mode setting unit 20 sets the control mode of the motor 110. In this embodiment, the conditions for transitioning the control mode from the startup mode to the normal mode are predetermined (details will be described later). The control mode setting unit 20 transitions the control mode based on these conditions. The control mode setting unit 20 outputs the set control mode to the actual rotation speed control unit 30 and the PWM generation unit 40. The control mode setting unit 20 also outputs the final target rotation speed Nco, instructed by the CAN signal, to the actual rotation speed control unit 30. In addition to the startup mode and normal mode, other control modes may include a stop mode when the motor 110 has stopped operating and an abnormal mode when an abnormality has occurred in the motor 110.

[0029] The target rotation speed setting unit 30a sets the target rotation speed Nta of the motor 110 during the process of bringing the actual rotation speed Nca closer to the final target rotation speed Nco. In this embodiment, the target rotation speed setting unit 30a sets the target rotation speed Nta of the motor 110 based on the actual rotation speed Nca input from the actual rotation speed acquisition unit 10 and the final target rotation speed Nco output from the control mode setting unit 20. The method for setting the target rotation speed Nta will be described later.

[0030] In normal mode, the actual rotation speed control unit 30 controls the motor 110 so that the actual rotation speed Nca approaches the target rotation speed Nta, based on the difference between the actual rotation speed Nca and the target rotation speed Nta. Specifically, the actual rotation speed control unit 30 instructs the PWM generation unit 40 so that the rotation speed of the motor 110 using the 120-degree energization method described above changes according to the target rotation speed Nta. Furthermore, the actual rotation speed control unit 30 generates a duty cycle command Dco with a reduced duty cycle ratio depending on whether the actual rotation speed Nca is greater than the target rotation speed Nta, or generates a duty cycle command Dco with a higher duty cycle ratio depending on whether the target rotation speed Nta is greater than the actual rotation speed Nca. For example, the actual rotation speed control unit 30 controls the actual rotation speed Nca of the motor 110 based on the actual rotation speed Nca input from the actual rotation speed acquisition unit 10, the target rotation speed Nta set by the target rotation speed setting unit 30a, and the control mode. The actual rotational speed control unit 30 determines, for example, the duty cycle δD to be increased or decreased from the current duty cycle D0, according to the magnitude and sign of the Nta-Nca value. Then, the actual rotational speed control unit 30 increases or decreases the duty cycle δD from the current duty cycle D0 and generates a duty cycle command Dco. The actual rotational speed control unit 30 outputs the generated duty cycle command Dco to the PWM generation unit 40.

[0031] The PWM generation unit 40 identifies the switching elements to be turned on or off and instructs the drive circuit 131 corresponding to each switching element to turn each switching element on or off. In response to this instruction, the drive circuit 131 generates gate drive signals UH, UL, VH, VL, WH, WL to drive the upper switching elements 11a to 11c and the lower switching elements 11d to 11f, respectively, and outputs them to each switching element 11a to 11f. For example, based on the duty cycle command Dco input from the actual rotational speed control unit 30 and the control mode input from the control mode setting unit 20, the PWM generation unit 40 identifies the switching elements to be turned on or off and instructs the drive circuit 131 corresponding to each switching element to turn each switching element on or off.

[0032] (3) Control modes by motor control device: Figures 3 and 4 are schematic diagrams illustrating the control modes of the motor control device 100. The upper diagrams of Figures 3 and 4 show the control modes set by the control mode setting unit 20. The middle diagrams of Figures 3 and 4 show the changes in rotational speed N. The lower diagrams of Figures 3 and 4 show the changes in the duty cycle command Dco output from the actual rotational speed control unit 30. Note that these figures do not strictly represent the control modes of the motor control device 100.

[0033] First, when the control mode setting unit 20 receives a CAN signal including the final target rotational speed Nco from the overall control device 220, it sets the control mode, which was set to stop mode, to start mode. The control mode setting unit 20 also outputs the final target rotational speed Nco to the actual rotational speed control unit 30. In the initial stage of the start mode (0 to t11), the target rotational speed setting unit 30a sets the target rotational speed Nta to 0. In the initial stage of the start mode (0 to t11), the motor 110 is performing initial alignment, and no zero crossing occurs. Therefore, the actual rotational speed control unit 30 obtains information that the actual rotational speed Nca is 0 from the actual rotational speed acquisition unit 10 and maintains 0 as the actual rotational speed Nca of the motor 110. In the initial stage of the start mode (0 to t11), the actual rotational speed control unit 30 outputs a constant duty cycle command Dco to the PWM generation unit 40 in order to perform initial alignment of the motor 110. At t11, the initial alignment of the motor 110 is completed. At the end of the startup mode (t11~t13), the actual rotation speed control unit 30 sets the duty cycle command Dco to a predetermined value so that the motor 110 rotates, and outputs it to the PWM generation unit 40.

[0034] The actual rotational speed acquisition unit 10 estimates the rotational speed based on the zero-cross detection signals Vu0, Vv0, and Vw0 input from the zero-cross detection unit 140. Because the estimation process takes time, the estimated rotational speed is input to the control mode setting unit 20 and the actual rotational speed control unit 30 with a time delay compared to the true rotational speed. In this embodiment, the rotational speed obtained by passing the estimated rotational speed through a low-pass filter is used as the actual rotational speed Nca for feedback control. Therefore, the filtering process takes time, and the actual rotational speed Nca is input to the control mode setting unit 20 and the actual rotational speed control unit 30 with a time delay compared to the estimated rotational speed. Thus, an error occurs between the true rotational speed and the actual rotational speed.

[0035] In this embodiment, the conditions for transitioning the control mode from the startup mode to the normal mode are predetermined. The control mode setting unit 20 transitions the control mode based on these conditions. In this embodiment, these conditions include the continuous detection of zero crossings by the zero crossing detection unit 140, and the fact that the actual rotational speed Nca of the motor 110 in the startup mode is greater than a predetermined threshold Nt. Specifically, in this embodiment, if the zero crossing detection unit 140 detects zero crossings a predetermined number of times, the rotation of the motor 110 is considered to be continuing, and one of the conditions for transitioning to the normal mode is considered to be satisfied. Also, if the actual rotational speed Nca of the motor 110 in the startup mode is greater than a predetermined threshold Nt, one of the conditions for transitioning to the normal mode is considered to be satisfied. In this embodiment, when these conditions are satisfied, the control mode setting unit 20 transitions the control mode from the startup mode to the normal mode. The threshold Nt is set, for example, within a range in which accurate estimation of the rotational speed by zero crossing is possible (a range in which step loss does not occur). The signal period is determined by the number of zero-crossings, so a higher rotational speed results in a more accurate signal period, and consequently, a more accurate estimation of the rotational speed.

[0036] The threshold Nt can be set to a larger value as the starting rotational speed Nb in the motor 110's startup mode increases. As described above, at the end of the startup mode (t11~t13), the actual rotational speed control unit 30 sets the duty cycle command Dco to a predetermined value. When this predetermined value is set, the motor 110 rotates at the starting rotational speed Nb. Therefore, the starting rotational speed Nb represents the rotational speed at which the torque generated in the motor 110 and the load torque applied to the electric pump are balanced by applying a predetermined value of duty cycle command Dco.

[0037] In the example shown in the center diagram of Figure 3, the timing at which the zero-cross detection unit 140 continuously detects a zero-cross is t12. The timing at which the actual rotational speed Nca of the motor 110 in the startup mode becomes greater than a predetermined threshold Nt is t13. Therefore, the control mode setting unit 20 transitions the control mode from startup mode to normal mode at t13.

[0038] When transitioning the control mode from startup mode to normal mode, the target rotational speed setting unit 30a sets the target rotational speed Nta to be equal to or greater than the actual rotational speed Nca. By setting the target rotational speed Nta at the time of mode transition to be equal to or greater than the actual rotational speed Nca, a situation where the target rotational speed Nta at the time of mode transition is excessively low compared to the actual rotational speed Nca does not occur. Therefore, it is possible to suppress an excessive reduction in the duty cycle immediately after mode transition, and consequently suppress an excessive reduction in the actual rotational speed, thereby reducing the possibility of losing synchronism.

[0039] The target rotational speed Nta in the initial stage of normal mode (t13~t15) is determined based on the actual rotational speed Nca at the transition timing t13 and a predetermined slope (change in target rotational speed Nta with respect to time). Specifically, at timing t13, the actual rotational speed Nca is set to the initial value of the target rotational speed Nta of the motor 110. Between timings t13 and t15, the target rotational speed Nta is set to increase gradually over time at a predetermined slope, starting from the initial value. The actual rotational speed control unit 30 instructs the PWM generation unit 40 to change the rotational speed of the motor 110 using the 120-degree energization method described above according to the target rotational speed Nta. Furthermore, the actual rotational speed control unit 30 acquires the actual rotational speed Nca from the actual rotational speed acquisition unit 10 and outputs a duty cycle command Dco to the PWM generation unit 40, which indicates a duty cycle that can be controlled so that the actual rotational speed Nca approaches the target rotational speed Nta. For example, between t13 and t14, the actual rotational speed Nca is higher than the target rotational speed Nta. Therefore, control is applied to reduce the duty cycle, and consequently, the actual rotational speed decreases. However, within the range where accurate rotational speed estimation by zero crossing is possible (the range where step-out does not occur), for example, up to the threshold Nt, a decrease in the actual rotational speed does not cause any problems.

[0040] On the other hand, at t14-t15, the target rotational speed Nta is higher than the actual rotational speed Nca. Therefore, control is performed to increase the duty cycle, and consequently, the actual rotational speed Nca rises to the final target rotational speed Nco. In normal mode, the target rotational speed Nta from t15 onwards is the final target rotational speed Nco. Since the target rotational speed Nta and the actual rotational speed Nca are the same, the actual rotational speed control unit 30 outputs a duty cycle command Dco, which is the same constant duty cycle as the duty cycle at t15, to the PWM generation unit 40, and maintains a constant actual rotational speed.

[0041] In the example described above, the actual rotational speed Nca at the time of transition to normal mode was used as the initial value of the target rotational speed Nta, but a larger value may also be used as the initial value of the target rotational speed Nta. Figure 4 shows an example in which the threshold Nt is smaller than in Figure 3, with the same configuration as in Figures 1 and 2. In the example shown in Figure 4, the timing at which the zero-cross detection unit 140 continuously detects zero-crossing is t12, and the timing at which the actual rotational speed Nca in the motor 110's startup mode becomes greater than the predetermined threshold Nt is t13. Therefore, the control mode setting unit 20 transitions the control mode from startup mode to normal mode at t13. However, in the example shown in Figure 4, the threshold Nt is smaller than in the example shown in Figure 3.

[0042] Immediately after a mode transition, as shown in the center diagram of Figure 4, the actual rotational speed Nca increases rapidly. Therefore, if the target rotational speed Nta is excessively small immediately after a mode transition, the actual rotational speed Nca tends to become excessively large relative to the target rotational speed Nta. In this case, control is performed to abruptly reduce the duty cycle, which was constant from t11 to t13, at t13, making it easy to lose synchronism. Therefore, as shown in the center diagram of Figure 4, the control mode setting unit 20 may set the reference value Nr to the initial value of the target rotational speed of the motor 110 when the actual rotational speed Nca when transitioning the control mode from the startup mode to the normal mode is smaller than a predetermined reference value Nr. By setting the reference value Nr (> threshold Nt) to the initial value of the target rotational speed Nta of the motor 110, the difference between the target rotational speed Nta and the actual rotational speed Nca can be reduced after the mode transition (t16 to t17). This suppresses excessive reductions in the duty cycle, and consequently, suppresses excessive reductions in the actual rotational speed, thereby reducing the possibility of losing synchronism.

[0043] In the above configuration, at timing t13 as shown in the center and lower diagrams of Figure 4, the reference value Nr is set to the initial value of the target rotational speed Nta of the motor 110. Between timings t13 and t18, the target rotational speed Nta is set to increase gradually over time at a predetermined rate, starting from the initial value. The actual rotational speed control unit 30 acquires the actual rotational speed Nca from the actual rotational speed acquisition unit 10 and outputs a duty cycle command Dco to the PWM generation unit 40, which indicates a duty cycle ratio that can be controlled so that the actual rotational speed Nca approaches the target rotational speed Nta. For example, between t13 and t16, the target rotational speed is higher than the actual rotational speed. Therefore, control is performed to increase the duty cycle ratio, and consequently, the actual rotational speed increases. On the other hand, between t16 and t17, the actual rotational speed is higher than the target rotational speed. Therefore, control is performed to decrease the duty cycle ratio, and consequently, the actual rotational speed decreases.

[0044] Between t17 and t18, the target rotational speed is higher than the actual rotational speed. Therefore, control is performed to increase the duty cycle, and consequently, the actual rotational speed rises to the final target rotational speed Nco. In normal mode, the target rotational speed Nta from t18 onwards is the final target rotational speed Nco. Since the target rotational speed Nta and the actual rotational speed Nca are the same, the actual rotational speed control unit 30 outputs a duty cycle command Dco, which is the same constant duty cycle as the duty cycle at t18, to the PWM generation unit 40, thereby maintaining a constant actual rotational speed.

[0045] (4) Conventional control methods and effects of this embodiment: Figure 5 is a schematic diagram illustrating a conventional control method. In conventional technology, during forced synchronous control (start mode), initial motor alignment is first performed between 0 and t1, and once the initial alignment is complete, the motor starts rotating at t1. Then, when zero crossing is continuously detected at t2, the system transitions to feedback synchronous control (normal mode). In this case, since sensorless control cannot detect the true rotational speed, the internal target rotational speed cannot be set using the true rotational speed at the time of mode transition (start rotational speed Nb) as the initial value. For this reason, the rotational speed is estimated by zero crossing, and furthermore, the rotational speed obtained by passing this estimated rotational speed through a low-pass filter (actual rotational speed) is used in the control. In conventional technology, during mode transition, the target rotational speed is set using the actual rotational speed Na at the time of mode transition as the initial value.

[0046] However, the rotational speed estimated by zero-crossing lags behind the true rotational speed, and the rotational speed after the low-pass filter used in control (actual rotational speed) lags even further behind the rotational speed estimated by zero-crossing. Consequently, the actual rotational speed Na at the time of mode transition may be significantly lower than the true rotational speed at the time of mode transition (starting rotational speed Nb). Even in such cases, conventionally, the target rotational speed was set using the actual rotational speed Na at the time of mode transition as the initial value. On the other hand, the slope of the target rotational speed must be set within a controllable range, and it is not possible to set a slope steeper than a predetermined value. Therefore, in t2~t3, the difference between the actual rotational speed and the target rotational speed becomes large, which may lead to the duty cycle being controlled to be excessively low. Consequently, if the rotational speed becomes excessively low, it becomes difficult to estimate the rotational speed by zero-crossing, which may lead to overshoot, undershoot, or loss of synchronism due to rotational speed fluctuations.

[0047] In addition, while the above-described conventional technique involves controlling the duty cycle to be excessively low, given that the actual rotational speed of the motor 110 is inaccurate immediately after startup, it is also conceivable that control may be performed to excessively increase the duty cycle.

[0048] According to this embodiment, the control mode setting unit 20 transitions the control mode from the startup mode to the normal mode on the condition that the actual rotational speed Nca in the startup mode of the motor 110 is greater than a predetermined threshold Nt. That is, since the actual rotational speed Nca is inaccurate immediately after the motor 110 starts up and becomes more accurate as the rotational speed increases, the control mode is restricted to transition from the startup mode to the normal mode only after the rotational speed has increased to a certain extent. This prevents feedback control due to the inaccurate actual rotational speed at the start of the motor and reduces the possibility of losing synchronism.

[0049] (5) Other embodiments: The embodiments described above are merely examples for carrying out the present invention, and various other embodiments can be adopted. For example, in the above embodiments, in a sensorless type without a rotation sensor, the rotation speed is estimated from the zero-crossing of the U-phase, V-phase, and W-phase voltages of the motor 110. However, the present invention can also be applied to a motor 110 that is equipped with a rotation sensor 42 such as a resolver for detecting the rotation angle of the rotor, and the rotation speed is calculated from the detected rotation angle to obtain the actual rotation speed of the motor 110.

[0050] The control method for the motor 110 is not limited to the 120-degree energization method. For example, the motor control device 100 may control the motor 110 by vector control. In this case, the motor control device 100 adjusts the rotational speed of the motor 110 by adjusting the AC voltage command signal. Furthermore, in the above embodiment, the rotational speed is estimated by zero crossing, and the rotational speed obtained by passing that estimated rotational speed through a low-pass filter is used as the actual rotational speed for control. However, the rotational speed estimated by zero crossing may also be used as the actual rotational speed for control.

[0051] In the above embodiment, the conditions for determining whether or not to transition the control mode from the startup mode to the normal mode were described as the continuous detection of zero crossings by the zero-crossing detection unit 140 and the actual rotational speed of the motor 110 in the startup mode being greater than a predetermined threshold Nt. However, the transition determination conditions only need to include at least the condition that the actual rotational speed of the motor 110 in the startup mode is greater than a predetermined threshold Nt. Furthermore, the transition determination conditions may include other conditions.

[0052] In the above embodiment, the function of the target rotation speed setting unit 30a was implemented as one of the functions of the actual rotation speed control unit 30. However, the setting of the target rotation speed only needs to be calculated immediately before the deviation calculation with respect to the actual rotation speed in the rotation speed feedback. For example, the function of the target rotation speed setting unit 30a may be implemented in the control mode setting unit 20, as part of another function, or as an independent function. [Explanation of symbols]

[0053] 10...Actual rotation speed acquisition unit, 20...Control mode setting unit, 30...Actual rotation speed control unit, 30a...Target rotation speed setting unit, 100...Motor control device, 110...Motor, Nb...Starting rotation speed, Nco...Final target rotation speed, Nr...Reference value, Nt...Threshold, Nca...Actual rotation speed, Nta...Target rotation speed

Claims

1. A motor control device that drives and controls a motor using a control mode that includes a startup mode executed when the motor is started and a normal mode executed during normal operation after the motor has started, A unit for acquiring the actual rotational speed of the motor, A control mode setting unit for setting the aforementioned control mode, A target rotation speed setting unit sets the target rotation speed of the motor in the process of bringing the actual rotation speed closer to the final target rotation speed, In the normal mode, the system includes an actual rotation speed control unit that controls the motor so that the actual rotation speed approaches the target rotation speed based on the difference between the actual rotation speed and the target rotation speed. A motor control device in which the conditions for the control mode setting unit to transition the control mode from the startup mode to the normal mode include the actual rotational speed of the motor in the startup mode being greater than a predetermined threshold.

2. The motor control device according to claim 1, wherein the target rotation speed setting unit sets the target rotation speed to be equal to or greater than the actual rotation speed when transitioning the control mode from the startup mode to the normal mode.

3. The motor control device according to claim 2, wherein the threshold value increases as the predetermined starting rotation speed in the starting mode of the motor increases.

4. The motor control device according to any one of claims 1 to 3, wherein the target rotation speed setting unit sets the reference value to the initial value of the target rotation speed of the motor when the actual rotation speed when the control mode is transitioned from the startup mode to the normal mode is smaller than a predetermined reference value.

Images