Motor control device

Abstract

To provide a motor control device in which noise and vibration at a startup time of a sensorless motor can be reduced.SOLUTION: In order to achieve the above object, a motor control device 1 of the present invention includes a drive unit 2 that supplies current to a sensorless motor M, and is configured to detect an induction voltage generated in a coil of the sensorless motor M to detect the position of a rotor of the sensorless motor M, and to control the sensorless motor M. During a startup operation period from startup of the sensorless motor M to a synchronous operation state, a current limited to be smaller than a current allowed to be supplied in the synchronous operation state is supplied from the drive unit 2 to the sensorless motor M.SELECTED DRAWING: Figure 1

Description

Technical Field

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

Background Art

[0002] A motor control device for driving and controlling a sensorless motor includes a driver that supplies current to the coils of each phase of the sensorless motor, and a controller that detects the rotational position of the rotor of the sensorless motor and gives a voltage command to the driver.

[0003] Such a motor control device detects the induced voltage generated in one phase coil that is not energized in order to detect the position of the rotor, and detects the position of the rotor by detecting the induced voltage generated in one phase coil that is not energized while energizing two of the three-phase coils to generate a rotating magnetic field to synchronize and rotate the sensorless motor (see, for example, Patent Document 1).

[0004] Since the induced voltage is generated when the magnetic flux passing through the coil changes as the rotor equipped with a permanent magnet rotates, the motor control device cannot detect the position of the rotor unless the rotor rotates. Therefore, when starting the sensorless motor, the motor control device energizes the coil in a state where the position of the rotor is not grasped, positions the rotor at a predetermined position, then sequentially energizes the three-phase coils to generate a rotating magnetic field to forcibly rotate the rotor, and gradually increases the rotational speed of the rotor by gradually advancing the switching of the energized coils little by little. Then, when the rotational speed of the rotor increases to such an extent that the induced voltage generated in the coil can be detected, the motor control device switches to a synchronous operation in which it energizes the coil at an appropriate timing while detecting the position of the rotor by the induced voltage and drives it.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] As described above, even though the conventional motor control device pre-excites the coil at the start of the sensorless motor to position the rotor at a predetermined position, the rotor is not always exactly at the predetermined position. When current is applied to the coil to rotate the rotor, the rotor may rotate reversely for a moment, or may not rotate smoothly due to the difficulty of rotating the load and may vibrate or rotate more than expected, resulting in noise and vibration.

[0007] Therefore, an object of the present invention is to provide a motor control device capable of reducing noise and vibration during the startup operation period of a sensorless motor.

Means for Solving the Problems

[0008] In order to achieve the above object, the motor control device of the present invention includes a drive unit that supplies current to a sensorless motor, detects an induced voltage generated in the coil of the sensorless motor to detect the position of the rotor of the sensorless motor, and is a motor control device that controls the sensorless motor. During the startup operation period from the start of the sensorless motor until the position of the rotor can be detected and the synchronous operation state in which the sensorless motor is controlled based on the position of the rotor is reached, a current that is smaller than and restricted by the current allowed to be supplied in the synchronous operation state is supplied from the drive unit to the sensorless motor.

[0009] According to the motor control device configured as described above, in the prior art, the current limit was the same during both the startup operation period and the synchronous operation state, but during the startup operation period, the current is restricted to be smaller than in the synchronous operation state. Therefore, the force for rotating the rotor during the startup operation period becomes smaller, and the rotor rotates once in the direction opposite to the rotation direction of the rotating magnetic field generated by energizing the three-phase coils at startup and then rotates in the rotation direction of the rotating magnetic field, or the angular acceleration acting on the rotor during the startup operation period becomes too large, so that the frequency of overshooting with respect to the rotating magnetic field can be reduced, and the vibration and noise during the startup operation period of the sensorless motor can be reduced.

[0010] Furthermore, the motor control device includes a determination unit that determines whether the current flowing through the sensorless motor is an overcurrent, and during the startup operation period, a bias voltage may be added to the detection signal corresponding to the current flowing through the sensorless motor and input to the determination unit. According to the motor control device configured in this way, since a bias voltage is added to the detection signal given to the determination unit that determines whether the current supplied to the sensorless motor is an overcurrent, it is possible to cause the determination unit to misrecognize that a current larger than the actual current is flowing due to the addition of the bias voltage, and the function of the determination unit originally provided in the motor control device can be utilized to limit the current, and it is also not necessary to prepare a program for controlling the current of the sensorless motor only during the startup operation period.

[0011] Also, the motor control device may include a power supply for adding a bias voltage to the detection signal and a switching element provided between the power supply and the determination unit to adjust the height of the bias voltage. In the motor control device configured in this way, when PWM controlling the switching element, the height of the bias voltage can be adjusted by adjusting the on-duty ratio of the switching element. Therefore, according to the motor control device, since the upper limit value of the current that can be supplied to the sensorless motor during the startup operation period can be adjusted according to the load driven by the sensorless motor, the vibration and noise of the sensorless motor during the startup operation period can be reduced according to the load.

[0012] Furthermore, the motor control device may adjust the height of the bias voltage based on the temperature of the load. In the motor control device configured in this way, since the height of the bias voltage is adjusted based on the temperature of the load, even when driving a load whose rotational resistance changes due to a change in temperature, the current supplied to the sensorless motor during the startup operation period is adjusted according to the temperature to be suitable for driving the load, and the vibration and noise of the sensorless motor can be reduced, making it optimal for use with a load whose resistance changes due to a change in temperature.

Advantages of the Invention

[0013] According to the motor control device of the present invention, noise and vibration during the startup operation of the sensorless motor can be reduced.

Brief Description of the Drawings

[0014]

Figure 1

Figure 2

Figure 3

Embodiments for Carrying Out the Invention

[0015] Hereinafter, the present invention will be described based on the embodiments shown in the drawings. As shown in FIG. 1, the motor control device 1 includes a drive unit 2 that supplies current to a sensorless motor M, a control unit 3 that gives commands to the drive unit 2, a position detection unit 4 that detects the induced voltage of a coil (not shown) of the sensorless motor M to detect the position of a rotor (not shown) of the sensorless motor M, a determination unit 5 that determines whether the current flowing through the sensorless motor M is an overcurrent, and an addition circuit 6 that adds a bias voltage Bv to a detection signal V corresponding to the current flowing through the sensorless motor M and inputs it to the determination unit 5.

[0016] Hereinafter, each part of the motor control device 1 of the present embodiment will be described in detail. The motor control device 1 supplies current to a sensorless motor M, which is the control target, to drive the sensorless motor M. In the present embodiment, the sensorless motor M, which is the control target, drives a hydraulic pump P.

[0017] The sensorless motor M is a three-phase brushless motor, although not shown in detail, and includes a rotor (not shown). The drive unit 2 includes three legs each having two sets of switching elements corresponding to the three-phase coils of the sensorless motor M. By turning on and off the switching elements of each leg, a three-phase output inverter 21 that connects the power supply 23 and a coil of any phase to supply current to the coil, and a PWM modulator 22 that outputs a signal for turning on and off each switching element of the three-phase output inverter 21 are provided. When the PWM modulator 22 receives a signal instructing the voltage to be applied to each phase coil of the sensorless motor M from the control unit 3, it generates a PWM signal with a duty ratio corresponding to the signal and applies it to the switching element. When receiving the PWM signal, the three-phase output inverter 21 turns on and off the switching elements to apply the voltage instructed by the control unit 3 to each phase coil for driving, for example, with 120-degree conduction, and supplies current to the coil. Further, a shunt resistor 7 for detecting the current flowing through each phase coil of the sensorless motor M is provided between the drive unit 2 and the ground.

[0018] The position detection unit 4 detects the induced voltage generated in a non-energized coil among the three-phase coils when the rotational speed of the rotor of the sensorless motor M is equal to or higher than a predetermined rotational speed, and detects the zero-crossing point of the induced voltage to detect the position of the rotor. When the sensorless motor M makes one electrical rotation, there are timings when each phase coil is not energized twice. Therefore, the position detection unit 4 performs position detection six times in total at 60-degree intervals for the three-phase coils. Specifically, the position detection unit 4 monitors the terminal voltage of each of the three-phase coils and detects the zero-crossing point of the non-energized coil to detect the position of the rotor. Since the zero-crossing point of the induced voltage appears at the 30-degree point of the 60-degree non-energized period, the position detection unit 4 may, for example, measure the time from the zero-crossing point of one coil to the zero-crossing point of the next coil to create a time corresponding to 30 degrees and generate a signal notifying the energization timing for each coil.

[0019] The position of the rotor detected by the position detector 4 is input to the control unit 3. The position detector 4 outputs the position of the rotor to the control unit 3 when the rotational speed of the rotor becomes equal to or higher than a predetermined rotational speed and the induced voltage generated in the non-energized coil can be stably detected. However, when the rotational speed of the rotor is lower than the predetermined rotational speed, the induced voltage cannot be stably detected, so the position of the rotor is not output to the control unit 3.

[0020] The control unit 3 includes a control command generation unit 31 that obtains the speed of the sensorless motor M from the electrical angle of the rotor obtained from the position detector 4, obtains a current command from the deviation between the obtained speed and the speed command, obtains a voltage command from the deviation between the current of each phase coil detected by the potential difference of the shunt resistor 7 and the current command, and converts the voltage command into three-phase voltage commands using the electrical angle of the rotor. Then, the control unit 3 inputs the obtained voltage command of each phase to the drive unit 2 as a command. Note that the configuration of the control unit 3 described above is an example, and design changes can be made as long as the sensorless motor M can be driven. Note that the control unit 3 may receive an input of a speed command from a higher-level control device and generate a voltage command to be applied to the sensorless motor M when obtaining the voltage command from the speed command, or may obtain a voltage command from a torque command when control regarding speed is not required.

[0021] The determination unit 5 uses, as a final signal, the voltage signal that is the sum of the detection signal V for detecting the current flowing through the sensorless motor M and the bias voltage Bv added to the detection signal V, and determines whether the current flowing through the sensorless motor M is an overcurrent in response to the input of the final signal. When the determination unit 5 determines that the current flowing through the sensorless motor M is an overcurrent, it outputs a stop signal that is a high-level signal to the drive unit 2, and when the current is not an overcurrent, it outputs a drive signal that is a low-level signal to the drive unit 2. The drive unit 2 includes, for example, a switch (not shown) between the power supply 23 and the three-phase output inverter 21, and when a stop signal is input from the determination unit 5, the switch opens to stop the current supply to the sensorless motor M. Note that the drive unit 2 may turn off the switching elements of each arm to stop the current supply to the sensorless motor M when it receives the stop signal.

[0022] Specifically, the determination unit 5 is a comparator in which the final signal, which is a voltage obtained by adding the detection signal V, which is the potential difference between both ends of the shunt resistor 7 provided between the drive unit 2 for detecting the current flowing through the sensorless motor M and the ground, and the bias voltage Bv applied by an additional circuit 6 described later, is input to the plus terminal, and the threshold voltage to be compared with the final signal is input to the minus terminal. The potential difference between both ends of the shunt resistor 7 is proportional to the current flowing through the sensorless motor M, and the threshold voltage is set to the potential difference between both ends of the shunt resistor 7 when an overcurrent flows through the sensorless motor M. Therefore, when the input detection signal V exceeds the threshold voltage, the determination unit 5 outputs a stop signal, which is a high-level signal, to the drive unit 2, and when the input detection signal V is equal to or lower than the threshold voltage, outputs a drive signal, which is a low-level signal, to the drive unit 2. When the stop signal is input, the drive unit 2 stops the current supply to the sensorless motor M as described above, while when the drive signal is input, the drive unit 2 supplies current to the sensorless motor M.

[0023] Although not shown in the figure, an RC circuit composed of a resistor and a capacitor may be provided between the drive side of the shunt resistor 7 and the plus terminal in the determination unit 5, and the detection signal V with noise removed by the RC circuit may be input to the determination unit 5.

[0024] The additional circuit 6 includes two resistors 63 and 64 installed in series on a line 62 connecting the power supply 61 to the anti-ground side of the shunt resistor 7, a signal line 65 connecting between the resistors 63 and 64 to the plus terminal of the determination unit 5, and a switching element 66 provided between the resistor 63 on the line 62 and the power supply 61. The additional circuit 6 adds a voltage corresponding to the voltage drop of the resistor 64 as the bias voltage Bv to the detection signal V, which is the potential difference of the shunt resistor 7, and inputs the result to the plus terminal of the determination unit 5.

[0025] In addition, since the additional circuit 6 can adjust the current flowing through the resistor 64 by changing the on-duty ratio of the switching element 66, it can adjust the bias voltage Bv added to the detection signal V. When the bias voltage Bv is added to the detection signal V by the additional circuit 6, the final signal input to the determination unit 5 becomes a voltage that is higher than the voltage corresponding to the current flowing through the sensorless motor M by the amount of the bias voltage Bv. Therefore, when a current smaller than the current corresponding to the bias voltage Bv by the amount of the current corresponding to the threshold voltage flows through the sensorless motor M, the determination unit 5 detects an overcurrent and outputs a stop signal to the drive unit 2.

[0026] The switching element 66 is controlled by a bias voltage adjustment unit 32 provided in the control unit 3. The bias voltage adjustment unit 32 turns on and off the switching element 66 by PWM control only during the startup operation period from the startup when current starts to be supplied to the sensorless motor M to start it until it reaches the synchronous operation state where synchronous operation is possible, and adjusts the bias voltage Bv added to the detection signal V. However, when the position detection unit 4 can detect the position of the rotor of the sensorless motor M, the switching element 66 is turned off, and thereafter, the switching element 66 is maintained in the off state during the drive of the sensorless motor M. Therefore, the bias voltage adjustment unit 32 turns on the switching element 66 at a predetermined duty ratio in a state where the rotational speed of the rotor is less than a predetermined rotational speed and the input of the rotor position cannot be received from the position detection unit 4. Thus, the additional circuit 6 adds the bias voltage Bv to the detection signal V and inputs the final signal to the determination unit 5. On the other hand, when the rotational speed of the rotor becomes equal to or higher than the predetermined rotational speed and the input of the rotor position can be received from the position detection unit 4, the bias voltage adjustment unit 32 turns off the switching element 66. Therefore, the additional circuit 6 inputs the detection signal V as it is to the determination unit 5 as the final signal without adding the bias voltage Bv to the detection signal V.

[0027] Therefore, the additional circuit 6 adds the bias voltage Bv to the detection signal V only during the startup operation period of the sensorless motor M, and stops adding the bias voltage Bv to the detection signal V when the sensorless motor M enters the synchronous operation state where it operates in synchronous operation.

[0028] Note that, in order to mitigate the variation of the final signal input to the determination unit 5 due to the on / off operation of the switching element 66 in the determination unit 5, the line 62 of the addition circuit 6 may be grounded to the ground between the resistors 63 and 64 via a capacitor.

[0029] When starting the sensorless motor M configured as described above, since the position of the rotor cannot be detected, first, two predetermined phases of the three-phase coils are excited for a predetermined time in a state where the position of the rotor is not grasped, and the permanent magnet of the rotor is attracted to position the rotor at a predetermined position. Subsequently, when the predetermined time has elapsed, the motor control device 1 sequentially energizes the three-phase coils to perform 120-degree energization to generate a rotating magnetic field and forcibly rotate the rotor, and gradually advances the switching of the energized coils little by little to gradually increase the rotational speed of the rotor.

[0030] During the startup operation period from the startup of this sensorless motor M to the synchronous operation state, since the rotational speed of the sensorless motor M is low in the position detection unit 4, the position of the rotor cannot be detected using the induced voltage, and since there is no signal input from the position detection unit 4, the control unit 3 turns on the switching element 66 of the addition circuit 6 at a predetermined duty ratio. Therefore, during the startup operation period of the sensorless motor M, the addition circuit 6 adds a predetermined bias voltage Bv to the detection signal V of the potential difference between both ends of the shunt resistor 7 and inputs it to the determination unit 5.

[0031] Then, according to the height of the bias voltage Bv added to the detection signal V, the determination unit 5 determines that an overcurrent is flowing through the sensorless motor M even when no overcurrent corresponding to the threshold voltage is flowing through the sensorless motor M. That is, when the bias voltage Bv is added to the detection signal V, although actually only a current corresponding to the potential difference across both ends of the shunt resistor 7 flows through the sensorless motor M, the determination unit 5 determines that an apparent current obtained by adding the current corresponding to the bias voltage Bv to the actually flowing current is flowing. Therefore, when the finally input signal becomes equal to or higher than the threshold voltage, the determination unit 5 regards it as an overcurrent and inputs a stop signal to the drive unit 2. Thus, the current supplied from the drive unit 2 to the sensorless motor M is limited to an upper limit value obtained by subtracting the current corresponding to the bias voltage Bv (the value obtained by dividing the bias voltage Bv by the resistance value of the shunt resistor 7) from the current at which the potential difference across both ends of the shunt resistor 7 becomes equal to the voltage threshold value.

[0032] As shown by line A in FIG. 2, the upper limit value is a current value at which the potential difference across both ends of the shunt resistor 7 becomes equal to the threshold voltage and is smaller than the upper limit of the current (line B in FIG. 2) that can be supplied to the sensorless motor M in the synchronous operation state. Therefore, by thus limiting the current supplied to the sensorless motor M by the determination unit 5, during the starting operation period of the sensorless motor M, the motor control device 1 supplies a current (line D in FIG. 2) that is limited to be smaller than the current (line C in FIG. 2) supplied to the sensorless motor M when the additional circuit 6 is not provided, as shown in FIG. 2. FIG. 2 is a diagram showing the transition of the current of one phase of the coil during energization when limiting the current when the three-phase output inverter 21 energizes two-phase coils. In FIG. 2, it shows a situation where the current flowing through the coil reaches the upper limit value and the supply of the current is stopped, the current flowing through the coil is limited to the upper limit value and decreases, after the current decreases, the next PWM signal is turned on and the current is supplied, and again, the state where the current supply is stopped when the current reaches the upper limit value continues.

[0033] In this way, when the motor control device 1 limits the current to be smaller than that in the synchronous operation state during the startup operation period and supplies a current smaller than that of the prior art to the sensorless motor M during the startup operation period of the sensorless motor M, the force for rotating the rotor becomes smaller, and the rotor rotates once in the direction opposite to the rotation direction of the rotating magnetic field generated by energizing the three-phase coils during startup and then rotates in the rotation direction of the rotating magnetic field, or the angular acceleration acting on the rotor becomes too large, reducing the frequency of overshooting with respect to the rotating magnetic field, and reducing the vibration and noise during the startup operation period of the sensorless motor M.

[0034] As described above, the motor control device 1 of the present embodiment includes a drive unit 2 that supplies current to the sensorless motor M, detects an induced voltage to detect the position of the rotor of the sensorless motor M, and controls the sensorless motor M. When starting the sensorless motor M, a current limited to be smaller than the current allowed in the synchronous operation state is supplied from the drive unit 2 to the sensorless motor M until the position of the rotor can be detected.

[0035] According to the motor control device 1 configured in this way, in the prior art, the current limit allowed during both the startup operation period and the synchronous operation state was the same. However, during the startup operation period of the sensorless motor M, a current smaller than that of the prior art is supplied to reduce the force for rotating the rotor during the startup operation period. Therefore, the rotor rotates once in the direction opposite to the rotation direction of the rotating magnetic field generated by energizing the three-phase coils during startup and then rotates in the rotation direction of the rotating magnetic field, or the angular acceleration acting on the rotor becomes too large, reducing the frequency of overshooting with respect to the rotating magnetic field, and reducing the vibration and noise during the startup operation period of the sensorless motor M.

[0036] Further, the motor control device 1 of the present embodiment includes a determination unit 5 that determines whether the current flowing through the sensorless motor M is an overcurrent. At startup, a bias voltage Bv is added to a detection signal V corresponding to the current flowing through the sensorless motor M and input to the determination unit 5. According to the motor control device 1 configured in this way, since the bias voltage Bv is added to the detection signal V given to the determination unit 5 that determines whether the current supplied to the sensorless motor M is an overcurrent, it is possible to cause the determination unit 5 to misrecognize that a current larger than the actual current is flowing due to the addition of the bias voltage Bv. The function of the determination unit 5 corresponding to the overcurrent protection circuit originally provided in the sensorless motor M can be used to limit the current, and there is no need to prepare a program for controlling the current of the sensorless motor M only during the startup operation period. Furthermore, by simply providing an additional circuit 6 and a simple control unit for the additional circuit 6 in the motor control device 1 including the determination unit 5 corresponding to the overcurrent protection circuit, the vibration and noise during startup of the sensorless motor M can be reduced.

[0037] Furthermore, the motor control device 1 of the present embodiment includes a power supply 61 for adding a bias voltage to a signal, and a switching element 66 provided between the power supply 61 and the determination unit 5 to adjust the magnitude of the bias voltage. According to the motor control device 1 configured in this way, when PWM - controlling the switching element 66, the magnitude of the bias voltage Bv can be adjusted by adjusting the on - duty ratio of the switching element 66. Therefore, according to the motor control device 1, since the upper limit value of the current that can be supplied to the sensorless motor M during the startup operation period can be adjusted according to the load driven by the sensorless motor M, the vibration and noise of the sensorless motor M during the startup operation period can be reduced according to the load. Also, according to the motor control device 1 configured in this way, an expensive amplifier circuit using an operational amplifier is not used to input the final signal to the determination unit 5, and the bypass voltage Bv can be easily added with an inexpensive circuit configuration. Moreover, since it includes the power supply 61, it can be installed as a retrofit to the existing motor control device 1.

[0038] Note that instead of the power supply 61, a step-down circuit that steps down the voltage of the power supply 23 and supplies it to the line 62 may be used. Further, in the motor control device 1 described above, in addition to the power supply 23 of the sensorless motor M, a power supply 61 for adding a bias voltage is provided separately. However, when the control unit 3 can output a signal capable of adding the bias voltage Bv to the line 62, like the motor control device 1A of the first modification of the embodiment shown in FIG. 3, the power supply 61 and the switching element 66 may be abolished, and the control unit 3 may output a signal to the line 62 by turning it on and off, or the control unit 3 may output a PWM signal.

[0039] In the motor control device 1 described above, a predetermined bias voltage is added to the detection signal V and the final signal is input to the determination unit 5. However, the bias voltage Bv can be adjusted by adjusting the on-duty ratio of the switching element 66. When the bias voltage can be adjusted in this way, the bias voltage Bv may be adjusted according to the temperature of the hydraulic pump P as a load. When adjusting the bias voltage according to the outside air temperature or the temperature of the hydraulic pump P as a load, for the motor control device 1 in FIG. 1, as shown by the broken line in FIG. 1, a temperature sensor 40 for detecting the temperature of the hydraulic pump P as a load is provided, and the temperature detected by the temperature sensor 40 is input to the bias voltage adjustment unit 32 in the control unit 3, and the on-duty ratio of the signal of the bias voltage adjustment unit 31 may be adjusted according to the temperature.

[0040] The bias voltage adjuster 31 adjusts the on-duty ratio of the switching element 66 so that the bias voltage Bv is proportional to the temperature detected by the temperature sensor 40, and increases the bias voltage Bv as the temperature rises. When the temperature of the hydraulic pump P is high, the temperature of the hydraulic oil in the hydraulic pump P is also high, and the viscosity of the hydraulic oil becomes low. Therefore, the higher the temperature of the hydraulic pump P, the lower the viscosity of the hydraulic oil, and when the rotor is rotationally driven at the start of the sensorless motor M, the resistance received by the sensorless motor M from the hydraulic pump P is small, making it easier for the rotor to rotate. If the current during the startup operation period is large, the sensorless motor M is likely to overshoot. On the other hand, in the motor control device 1 capable of adjusting the current according to the temperature, the temperature sensor 40 detects the temperature of the hydraulic pump P, increases the bias voltage Bv as the temperature rises, and increases the degree of reduction of the current flowing through the sensorless motor M, enabling the sensorless motor M to start. Therefore, according to the motor control device 1 capable of adjusting the current according to the temperature, the temperature sensor 40 detects the temperature of the hydraulic pump P, increases the bias voltage Bv as the temperature rises, and can reduce the overshoot of the sensorless motor M. Further, when the temperature of the hydraulic pump P decreases, the viscosity of the hydraulic oil increases, and the resistance exerted by the hydraulic pump P on the rotation of the sensorless motor M increases, the motor control device 1 reduces the bias voltage Bv and reduces the degree of reduction of the current supplied to the sensorless motor M during the startup operation period, thereby enabling the sensorless motor M to start promptly.

[0041] As described above, since the motor control device 1 of the present embodiment adjusts the height of the bias voltage Bv based on the temperature of the hydraulic pump P, which is the load, even when driving a load whose rotational resistance changes due to a temperature change, the current supplied to the sensorless motor M during the startup operation period is adjusted according to the temperature to be suitable for driving the load, reducing the vibration and noise of the sensorless motor M, and making it optimal for use in a load whose resistance during the startup operation period changes due to a temperature change.

[0042] Note that the temperature sensor 40 is configured to detect the temperature of the hydraulic pump P as a load. However, since the motor control device 1 and the load are installed adjacent to each other, if the temperature of the atmosphere surrounding the motor control device 1A is substantially equal to the temperature of the hydraulic pump P which is the load, the outside air temperature of the motor control device 1 may be detected. During the startup operation period of the sensorless motor M, since the hydraulic pump P is in a stopped state, the temperature of the hydraulic pump P often becomes equal to the outside air temperature. Even in the case where the hydraulic pump P is used as a load in this way, the sensorless motor M can be started while reducing the vibration and noise of the sensorless motor M.

[0043] Also, when changing the bias voltage Bv according to the change in temperature, one or both of the resistors 63 and 64 in the line 62 of the additional circuit 6 of the motor control device 1 of the embodiment shown in FIG. 1 may be a resistor such as a thermistor whose resistance value changes according to the temperature change.

[0044] When the motor control device 1 configured in this way has the resistor 63 as a thermistor whose resistance decreases as the temperature rises and the resistor 64 as a resistor whose change in resistance value due to temperature change is small, the resistance value of the resistor 63 decreases as the temperature rises, so the bias voltage Bv increases as the temperature rises. When the temperature of the hydraulic pump P rises, the motor control device 1 can reduce the resistance value of the resistor 63, increase the bias voltage Bv, and start the sensorless motor M while increasing the degree of reduction of the current flowing through the sensorless motor M. Therefore, according to the motor control device 1, overshoot of the sensorless motor M can be reduced when the temperature is high, and when the temperature drops and the viscosity of the hydraulic oil increases, the bias voltage Bv is lowered to reduce the reduction ratio of the current supplied to the sensorless motor M at startup, enabling prompt startup of the sensorless motor M.

[0045] Furthermore, when the motor control device 1 uses the resistor 63 as a resistor with a small change in resistance value due to temperature change and the resistor 64 as a thermistor whose resistance increases as the temperature rises, the resistance value of the resistor 64 increases as the temperature rises, so the bias voltage Bv increases when the temperature rises. When the temperature of the hydraulic pump P rises, the motor control device 1 increases the resistance value of the resistor 64, increases the bias voltage Bv, and can start the sensorless motor M while increasing the degree of reduction of the current flowing through the sensorless motor M. Therefore, according to the motor control device 1, when the temperature is high, overshoot of the sensorless motor M can be reduced, and when the temperature decreases and the viscosity of the hydraulic oil increases, the bias voltage Bv is lowered to reduce the degree of reduction of the current supplied to the sensorless motor M during the starting operation period, enabling rapid starting of the sensorless motor M.

[0046] Also, when the motor control device 1 uses the resistor 63 as a thermistor whose resistance decreases as the temperature rises and the resistor 64 as a thermistor whose resistance increases as the temperature rises, the resistance value of the resistor 63 decreases and the resistance value of the resistor 64 increases as the temperature rises, so the bias voltage Bv increases when the temperature rises. When the temperature of the hydraulic pump P rises, the motor control device 1 decreases the resistance value of the resistor 63 while increasing the resistance value of the resistor 64, increases the bias voltage Bv, and can start the sensorless motor M while increasing the degree of reduction of the current flowing through the sensorless motor M. Therefore, according to the motor control device 1, when the temperature is high, overshoot of the sensorless motor M can be reduced, and when the temperature decreases, the bias voltage Bv is lowered to reduce the degree of reduction of the current supplied to the sensorless motor M during the starting operation period, enabling rapid starting of the sensorless motor M.

[0047] As described above, the preferred embodiments of the present invention have been described in detail, but modifications, deformations, and changes are possible without departing from the scope of the claims.

Explanation of Reference Numerals

[0048] 1,1A ··· Motor control device, 2 ··· Driving unit, 5 ··· Judgment unit, 6 ··· Additional circuit, 61 ··· Power supply, 66 ··· Switching element, Bv ··· Bias voltage, M ··· Sensorless motor, V ··· Detection signal

Claims

1. A motor control device that includes a drive unit for supplying current to a sensorless motor, detects an induced voltage generated in a coil of the sensorless motor to detect a position of a rotor of the sensorless motor, and controls the sensorless motor, wherein, during a startup operation period from startup of the sensorless motor until a synchronous operation state is reached in which the position of the rotor can be detected and the sensorless motor is controlled based on the position of the rotor, a current that is smaller than and restricted from a current that is allowed to be supplied during the synchronous operation state is supplied from the drive unit to the sensorless motor The motor control device is characterized by the above.

2. A determination unit that determines whether or not a current flowing through the sensorless motor is an overcurrent is provided, During the startup operation period, a bias voltage is added to a detection signal for detecting a current flowing through the sensorless motor and input to the determination unit The motor control device according to claim 1, characterized by the above.

3. A power source for adding the bias voltage to the detection signal, and A switching element provided between the power source and the determination unit to adjust the magnitude of the bias voltage The motor control device according to claim 2, characterized by the above.

4. Adjusting the magnitude of the bias voltage based on the temperature of the load The motor control device according to claim 2 or 3, characterized by the above.

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