Motor control device and motor control method

Abstract

In an aspect, a motor control device and a motor control method according to the present invention are characterized by being configured to drive a three-phase brushless motor with a 120-degree square wave on the basis of a phase current obtained from a detection signal of a current sensor at current detection timing within a current acquisition period, and switching the current detection timing in response to regenerative operation and power running operation of the three-phase brushless motor. Thus, the phase current to be detected can be detected in both the regenerative operation and the power running operation.

Description

Motor control device and motor control method

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

[0002] The PWM inverter for motor control in Patent Document 1 has a current sensor provided on the DC bus of the inverter main circuit, and has a phase current calculation unit that calculates phase currents based on the detection value of the current sensor and PWM pulses output from PWM pulse generation means, and the PWM pulse generation means outputs the PWM pulses with the timing interval between the rise or fall of the PWM pulses between each phase set to a predetermined value or more.

[0003] Japanese Patent Application Laid-Open No. 2001-327173

[0004] However, when a three-phase brushless motor is driven with a 120-degree rectangular wave, the behavior of the phase current differs between regenerative operation and power running, so if the phase current is detected at a constant current detection timing regardless of whether the motor is in regenerative operation or power running, it may be impossible to detect the desired phase current (more specifically, the peak current). Since the desired phase current cannot be detected, if the actual phase current becomes larger than the detected phase current value, an overcurrent state occurs in which a current exceeding the command current flows, which may cause the inverter circuit or the motor to overheat.

[0005] The present invention has been made in consideration of the current situation, and its purpose is to provide a motor control device and a motor control method that can detect the desired phase current in both regenerative operation and power running when a three-phase brushless motor is driven by a 120-degree rectangular wave.

[0006] Therefore, in one aspect of the motor control device and motor control method according to the present invention, the current detection timing within the current acquisition period is switched depending on whether the three-phase brushless motor is in regenerative operation or power running operation.

[0007] According to the above invention, when a three-phase brushless motor is driven by a 120-degree rectangular wave, the phase current to be detected can be detected in both regenerative operation and power running.

[0008] FIG. 1 is a system diagram of an internal combustion engine for a vehicle. FIG. 2 is a diagram showing a control system for a three-phase brushless motor. FIG. 3 is a time chart showing the control operation of an inverter. FIG. 4 is a diagram showing the four quadrants of inverter control. FIG. 5 is a time chart showing changes in phase current during powering operation. FIG. 6 is a time chart showing changes in phase current during regenerative operation. FIG. 7 is a functional block diagram showing details of a current acquisition unit.

[0009] An embodiment of the present invention will now be described. Fig. 1 shows an internal combustion engine for a vehicle equipped with a three-phase brushless motor to which a motor control device and a motor control method according to the present invention are applied. The internal combustion engine 101 is provided with an intake air mass sensor 103 in an intake duct 102 that detects an intake air flow rate QA of the internal combustion engine 101. An intake valve 105 opens and closes an intake port of a combustion chamber 104 of each cylinder.

[0010] Fuel injection valves 106 inject fuel into intake ports 102a of each cylinder. The fuel injected by fuel injection valves 106 is drawn into combustion chambers 104 together with air through intake valves 105, and is ignited and burned by sparks from spark plugs 107. The combustion pressure then pushes pistons 108 down toward crankshafts 109, driving the crankshafts 109 to rotate.

[0011] An exhaust valve 110 opens and closes the exhaust port of the combustion chamber 104, and when the exhaust valve 110 opens, exhaust gas inside the combustion chamber 104 is discharged into an exhaust pipe 111. The exhaust pipe 111 is equipped with a catalytic converter 112 that contains a catalyst such as a three-way catalyst. The intake valve 105 opens and closes in accordance with the rotational position of an intake camshaft 115a that is rotationally driven by the crankshaft 109. The exhaust valve 110 opens and closes in accordance with the rotational position of an exhaust camshaft 115b that is rotationally driven by the crankshaft 109.

[0012] The electric variable valve timing mechanism 114 (hereinafter referred to as the VVT ​​mechanism 114) continuously changes the valve timing of the intake valve 105, which is an engine valve, in the advance or retard direction by changing the rotational phase of the intake camshaft 115a relative to the crankshaft 109 by controlling the rotational speed of the three-phase brushless motor 12. One aspect of the structure and operation of the VVT ​​mechanism 114 will be outlined below. The VVT ​​mechanism 114 includes a phase change mechanism that is disposed between a timing sprocket (not shown) and the intake camshaft 115a and changes the relative rotational phase between the timing sprocket and the intake camshaft 115a.

[0013] The phase change mechanism includes three-phase brushless motor 12 and a speed reduction mechanism that reduces the rotational speed of three-phase brushless motor 12 and transmits the reduced rotational force to intake camshaft 115a. When three-phase brushless motor 12 is rotated forward or backward, the reduced rotational force is transmitted to intake camshaft 115a. As a result, intake camshaft 115a rotates forward or backward relative to the timing sprocket, and the relative rotational phase between intake camshaft 115a and the timing sprocket is changed.

[0014] The ignition module 116 is directly attached to the spark plug 107 and supplies ignition energy to the spark plug 107. The ignition module 116 includes an ignition coil and a power transistor that controls the supply of electricity to the ignition coil.

[0015] The control system that controls the operation of the internal combustion engine 101 includes an engine control module 201 (hereinafter referred to as ECM 201) that controls fuel injection by the fuel injection valves 106 and ignition by the spark plugs 107, and a VVT controller 202 that controls the VVT ​​mechanism 114. The VVT ​​controller 202 corresponds to a motor control device that controls the three-phase brushless motor 12 of the VVT ​​mechanism 114.

[0016] The ECM 201 and the VVT ​​controller 202 are electronic control devices, and the ECM 201 includes a microcomputer 201a, and the VVT ​​controller 202 includes a microcomputer 202a. The microcomputers 201a and 202a include a processor, a nonvolatile memory, a volatile memory, and the like.

[0017] The ECM 201 acquires signals output by the various sensors and performs arithmetic processing in accordance with programs stored in a nonvolatile memory to calculate and output manipulated variables for the fuel injection valve 106, ignition module 116, etc. The VVT ​​controller 202 acquires signals sent by the ECM 201 and signals output by the various sensors and performs arithmetic processing in accordance with programs stored in a nonvolatile memory to calculate and output manipulated variables for the VVT ​​mechanism 114, specifically the three-phase brushless motor 12.

[0018] As the various sensors, the internal combustion engine 101 is equipped with the aforementioned intake air amount sensor 103, a crank angle sensor 203 that outputs a crank angle signal POS for each predetermined angular position of the crankshaft 109, an accelerator opening sensor 206 that detects the depression amount of the accelerator pedal 207, in other words, the accelerator opening ACC, a cam angle sensor 204 that outputs a cam angle signal CAM for each predetermined angular position of the intake camshaft 115a, a water temperature sensor 208 that detects the temperature TW of the cooling water of the internal combustion engine 101, and an air-fuel ratio sensor 209 that is installed in the exhaust pipe 111 upstream of the catalytic converter 112 and detects the air-fuel ratio AF based on the oxygen concentration in the exhaust.

[0019] The crank angle signal POS output by the crank angle sensor 203 is a pulse signal for each unit crank angle, and its signal output pattern is set so that one or a series of multiple pulses are missing for each crank angle corresponding to the stroke phase difference between the cylinders. Here, the position of the missing pulse signal in the crank angle signal POS is detected as a reference crank angle position.

[0020] The cam angle sensor 204 outputs a cam angle signal CAM for each crank angle corresponding to the stroke phase difference between the cylinders. The ECM 201 acquires the signals output by these various sensors and also acquires an on / off signal from an ignition switch 205, which is the main switch for operating and stopping the internal combustion engine 101.

[0021] The three-phase brushless motor 12 of the VVT ​​mechanism 114 is equipped with Hall sensors 12u, 12v, and 12w as motor rotational position sensors for detecting the positional relationship between the rotor and the three-phase coils, i.e., the U-phase coil, the V-phase coil, and the W-phase coil. The VVT ​​controller 202 acquires the motor rotational position signals output by the Hall sensors 12u, 12v, and 12w.

[0022] The ECM 201 calculates a target rotational phase, which is a target value of the rotational phase of the intake camshaft 115a relative to the crankshaft 109, based on engine operating conditions such as the engine load and engine rotational speed obtained from output signals from the various sensors described above, and also calculates an actual rotational phase based on the crank angle signal POS and the cam angle signal CAM. The ECM 201 then calculates a target rotational speed of the three-phase brushless motor 12 so that the actual rotational phase approaches the target rotational phase, and sends a target rotational speed signal (in other words, a rotational speed command signal) to the VVT ​​controller 202. The VVT ​​controller 202 calculates a target value of the motor current based on the actual rotational speed and the target rotational speed of the three-phase brushless motor 12, and controls the AC power supplied to the three-phase brushless motor 12 based on the actual motor current and the target value.

[0023] 2 is a diagram showing a drive circuit 210 for the three-phase brushless motor 12 provided in the VVT ​​controller 202, and the control function of the three-phase brushless motor 12 by the microcomputer 202a of the VVT ​​controller 202. The microcomputer 202a of the VVT ​​controller 202 drives the three-phase brushless motor 12 with 120-degree rectangular wave drive that sequentially switches two of the three phases to which a voltage is applied. In other words, the microcomputer 202a is a control unit that executes each step of a motor control method for 120-degree rectangular wave drive of the three-phase brushless motor 12.

[0024] In 120-degree rectangular wave driving, for example, a first pattern in which current flows from the U phase to the V phase, a second pattern in which current flows from the U phase to the W phase, a third pattern in which current flows from the V phase to the W phase, a fourth pattern in which current flows from the V phase to the U phase, a fifth pattern in which current flows from the W phase to the U phase, and a sixth pattern in which current flows from the W phase to the V phase are switched every 60 electrical degrees. Taking the U phase as an example, by switching the conduction patterns, the U phase is energized for 120 degrees in the first and second patterns, is de-energized for the subsequent 60 degrees in the third pattern, and is then energized for a further 120 degrees in the fourth and fifth patterns. Note that 120-degree rectangular wave driving is also referred to as 120-degree conduction or simply rectangular wave driving.

[0025] The three-phase brushless motor 12 has a cylindrical stator and a rotor equipped with a permanent magnet. The stator has three-phase coils, U-phase, V-phase, and W-phase, that are star-connected. The rotor is rotatably mounted in a space formed in the center of the stator. Hall sensors 12u, 12v, and 12w are arranged around the rotor at 120-degree intervals. The microcomputer 202a determines the rotor's rotational position from the sensor signals of the Hall sensors 12u, 12v, and 12w, and switches the selection pattern for the two phases to be energized every 60 electrical degrees depending on the rotor's rotational position.

[0026] Drive circuit 210 for three-phase brushless motor 12 includes inverter 211 that supplies AC power to three-phase brushless motor 12, DC power supply 212 for inverter 211, and inverter drive circuit 213. Inverter 211 is formed by connecting semiconductor switching elements 211a-211f such as FETs in a three-phase bridge configuration.

[0027] The gate terminals of the semiconductor switching elements 211a to 211f of the inverter 211 are connected to the output ports of the inverter drive circuit 213. The semiconductor switching elements 211a to 211f are switched on and off by gate control signals output from the inverter drive circuit 213 to the gate terminals of the semiconductor switching elements 211a to 211f.

[0028] A shunt resistor 214A for detecting the motor current is disposed on the DC bus between the inverter 211 and ground GND. The shunt resistor 214A and an operational amplifier 214B that amplifies the voltage drop across the shunt resistor 214A constitute a current sensor 214 that detects the motor current. The shunt current signal output by the operational amplifier 214B, i.e., the phase current detection signal, is an analog signal of the potential difference [V] generated across the shunt resistor 214A.

[0029] The microcomputer 202a of the VVT ​​controller 202 acquires the shunt current signal output by the current sensor 214 and the target rotation speed signal output by the ECM 201, and outputs a PWM (Pulse Width Modulation) signal to the inverter drive circuit 213. Below, a functional unit provided in the microcomputer 202a that generates a PWM signal from the shunt current signal and the target rotation speed will be described.

[0030] The current acquiring unit 221 acquires the shunt current signal, which is an analog voltage signal, from the current sensor 214, and outputs the shunt current signal sampled at a predetermined current detection timing (in other words, current sampling timing) within a current acquiring period as a signal of a real-phase current. Here, the current acquiring period (in other words, sampling period or current detection period) during which the current acquiring unit 221 performs the sampling process of the shunt current signal will be described.

[0031] 3 illustrates an example of PWM control of the semiconductor switching elements 211a-211f in 120-degree rectangular wave drive. Here, the microcomputer 202a employs lower-arm chopper control, in which the semiconductor switching elements in the upper arm of the inverter 211 are fixed on and the semiconductor switching elements in the lower arm are PWM-controlled to be turned on and off.

[0032] For example, when current flows from the DC power supply 212 to the W phase via the V phase, the microcomputer 202a fixes the semiconductor switching element 211c, which is the upper arm of the V phase, to ON, and PWM-controls the ON / OFF of the semiconductor switching element 211f, which is the lower arm of the W phase, based on a command voltage. At this time, when the semiconductor switching element 211c is turned ON, the terminal voltage of the V phase becomes the power supply potential. On the other hand, when the semiconductor switching element 211f is turned ON, the terminal voltage of the W phase becomes the ground potential. As a result, a potential difference occurs between the V phase and the W phase, and current flows from the V phase to the W phase.

[0033] Therefore, during the on-period of the PWM-controlled lower-arm semiconductor switching element, a phase current appears in the shunt resistor 214A. Therefore, during the on-period of the lower-arm semiconductor switching element, which is the timing at which the phase current appears in the shunt resistor 214A, the microcomputer 202a samples the current flowing through the shunt resistor 214A to detect the current value of the energized phase, i.e., the actual phase current. In other words, when lower-arm chopper control is adopted, the on-period of the lower-arm semiconductor switching element becomes the current acquisition period.

[0034] The microcomputer 202a can employ upper-arm chopper control for PWM control of the semiconductor switching elements 211a-211f, in which the lower-arm semiconductor switching elements are fixed on and the upper-arm semiconductor switching elements are PWM-controlled to be turned on and off. The microcomputer 202a can also implement complementary PWM (in other words, upper and lower complementary switching) in 120-degree rectangular wave drive. Complementary PWM is a switching control that turns on and off the lower-arm semiconductor switching elements and the upper-arm semiconductor switching elements in opposite phases.

[0035] The current control unit 222 acquires the signal of the actual phase current obtained by the current acquisition unit 221 through sampling processing during the current acquisition period. The current control unit 222 sets a command voltage so that the actual phase current approaches the target phase current. The rotational speed control unit 223 acquires the target rotational speed signal and the actual rotational speed signal output by the ECM 201, and sets a target current so that the actual rotational speed approaches the target rotational speed. The rotational speed control unit 223 then outputs the target current signal to the current control unit 222.

[0036] The rotational speed calculation unit 224 acquires the motor rotational position signals output from the Hall sensors 12u, 12v, and 12w, and calculates the actual rotational speed of the three-phase brushless motor 12 based on the motor rotational position signals. The rotational speed calculation unit 224 then outputs a signal representing the actual rotational speed of the three-phase brushless motor 12 to the rotational speed control unit 223.

[0037] The command voltage / duty converter 225 acquires a command voltage signal from the current controller 222, and also acquires the voltage of the DC power supply 212, i.e., a power supply voltage signal. Then, the command voltage / duty converter 225 calculates, from the command voltage and the power supply voltage, a command duty ratio for applying the command voltage to the three-phase brushless motor 12. The energization phase determiner 226 acquires motor rotation position signals output by the Hall sensors 12u, 12v, and 12w, and combines the motor rotation position signals to create and output energization phase switching information (in other words, energization mode command information) for every 60-degree rotation.

[0038] The PWM signal generation unit 227 acquires a command duty ratio signal from the command voltage / duty conversion unit 225, and acquires current conduction phase switching information from the current conduction phase determination unit 226. Then, based on the command duty ratio signal and the current conduction phase switching information, the PWM signal generation unit 227 generates a PWM signal for each of the semiconductor switching elements 211a-211f of the inverter 211. The inverter drive circuit 213 acquires the PWM signal generated by the PWM signal generation unit 227, and generates and outputs gate signals (in other words, on / off control signals) for each of the semiconductor switching elements 211a-211f of the inverter 211 based on the PWM signal.

[0039] The microcomputer 202a enables highly responsive control of the valve timing by implementing four-quadrant operation, which causes the three-phase brushless motor 12 to perform powering (in other words, driving) and regenerative (in other words, braking) operations in both forward and reverse rotation. The current acquisition unit 221 has a function of switching the current detection timing within the current acquisition period between when the three-phase brushless motor 12 is in powering operation and when the three-phase brushless motor 12 is in regenerative operation.

[0040] 4 shows the correlation between each operation mode of four-quadrant operation and the motor rotation speed and motor current (in other words, motor torque). Quadrant 1 is a mode of forward rotation and powering operation, quadrant 2 is a mode of forward rotation and regenerative operation, quadrant 3 is a mode of reverse rotation and powering operation, and quadrant 4 is a mode of reverse rotation and regenerative operation.

[0041] Here, powering operation is a mode in which current flows from DC power supply 212 to three-phase brushless motor 12, and regenerative operation is a mode in which power is returned from three-phase brushless motor 12 to DC power supply 212, with powering operation occurring when the power is positive and regenerative operation occurring when the power is negative. In other words, current acquiring unit 221 can determine whether the operation is powering or regenerative operation based on the direction of the motor voltage and the direction of the motor current, and switch the current detection timing within the current acquiring period.

[0042] Next, the reason why the current acquisition unit 221 switches the current detection timing between powering operation and regenerative operation will be explained. The time chart in Figure 5 illustrates an example of changes in the actual phase current when the operation mode of the three-phase brushless motor 12 is powering operation, i.e., the current flowing through the shunt resistor 214A. When the operation mode of the three-phase brushless motor 12 is powering operation, the actual phase current monotonically increases within the current acquisition period. Therefore, when the operation mode is powering operation, the current acquisition unit 221 can acquire the peak current, which is the peak value of the phase current, by setting the current detection timing based on the end timing of the current acquisition period.

[0043] 6 illustrates an example of the change in the actual phase current, i.e., the current flowing through shunt resistor 214A, when three-phase brushless motor 12 is in regenerative operation. When three-phase brushless motor 12 is in regenerative operation, the actual phase current monotonically decreases within the current acquisition period. Therefore, when current acquisition unit 221 is in regenerative operation, if it sets the current detection timing based on the end timing of the current acquisition period, as is the case when current acquisition unit 221 is in powering operation, it will not be able to acquire the peak current, and will instead detect a phase current lower than the peak current.

[0044] If current acquiring unit 221 acquires a current lower than the peak current during regenerative operation and inverter 211 is driven and controlled based on the phase current, an overcurrent state occurs in which a current exceeding the command current flows, which may cause overheating of inverter 211 and three-phase brushless motor 12. Therefore, current acquiring unit 221 switches the current detection timing between powering operation and regenerative operation, thereby making it possible to acquire the peak current during both powering operation and regenerative operation and preventing inverter 211 and three-phase brushless motor 12 from overheating.

[0045] That is, during powering operation in which the actual phase current monotonically increases during the current acquisition period, the current acquisition unit 221 acquires the peak current by sampling the shunt current signal based on the end timing of the current acquisition period. Also, during regenerative operation in which the actual phase current monotonically decreases during the current acquisition period, the current acquisition unit 221 acquires the peak current by sampling the shunt current signal based on the start timing of the current acquisition period. This allows the current acquisition unit 221 to acquire the peak current during both powering operation and regenerative operation, and can prevent an overcurrent state in which a current exceeding the command current flows.

[0046] The following describes in detail the function of the current acquisition unit 221 to switch the current detection timing between powering operation and regenerative operation. Fig. 7 is a functional block diagram of the current acquisition unit 221. The powering / regenerative determination unit 221A acquires a command voltage signal from the current control unit 222, and also acquires a real-phase current signal that is a sampling result during the current acquisition period.

[0047] The powering / regenerative determination unit 221A determines whether the operation is regenerative or powering based on the direction of the command voltage (in other words, the motor voltage) and the direction of the actual phase current (in other words, the motor current), and outputs a signal indicating whether the operation is regenerative or powering, that is, an operation mode signal or a powering / regenerative determination signal. Here, when the direction of the voltage and the direction of the current are expressed by positive and negative signs, the powering / regenerative determination unit 221A can determine whether the operation is regenerative or powering based on the positive or negative sign of the power (power = current × voltage).

[0048] Large fluctuations in the actual phase current can cause hunting, in which the powering / regenerative determination unit 221A repeatedly determines whether the motor is in powering operation or regenerative operation. This can lead to hunting in the current detection timing, which can exacerbate fluctuations in the motor current. Therefore, the powering / regenerative determination unit 221A can prevent hunting by determining whether the motor is in powering operation or regenerative operation based on the target phase current instead of the actual phase current. Furthermore, the powering / regenerative determination unit 221A can prevent hunting by providing hysteresis to the threshold value used for comparison with the actual phase current in the sign determination process, thereby providing hysteresis in the determination of switching the current detection timing. Furthermore, the powering / regenerative determination unit 221A can prevent hunting by determining whether the motor is in powering operation or regenerative operation after a predetermined number of consecutive determinations.

[0049] The current acquisition period determination unit 221B acquires a command duty ratio signal from the command voltage / duty conversion unit 225 and outputs signals indicating the start and end timings of the current acquisition period. Here, when the PWM control is lower-arm chopper control, the current acquisition period is the on-period of the lower-arm semiconductor switching element. The start timing of the current acquisition period is the timing when the lower-arm semiconductor switching element switches from off to on, and the end timing of the current acquisition period is the timing when the lower-arm semiconductor switching element switches from on to off.

[0050] The adder 221C adds a predetermined time required for the shunt current signal to rise to the start timing of the current acquisition period output by the current acquisition period determination unit 221B, and outputs the result as the current detection timing during regenerative operation. In other words, the current detection timing during regenerative operation is set based on the start timing of the current acquisition period, and is the point in time when the predetermined time (first set time) required for the shunt current signal to rise has elapsed from the start timing of the current acquisition period. Here, the predetermined time required for the shunt current signal to rise is determined based on the allowable current detection error and the response speed of the shunt current signal (in other words, the time constant).

[0051] Furthermore, the subtraction unit 221D subtracts a predetermined time required for analog-to-digital conversion (AD conversion) of the shunt current signal from the end timing of the current acquisition period output by the current acquisition period determination unit 221B, and outputs the result as the current detection timing during powering operation. In other words, the current detection timing during powering operation is set based on the end timing of the current acquisition period, and is a point in time that predates the end timing of the current acquisition period by the predetermined time (second set time) required for AD conversion of the shunt current signal. In this way, the current acquisition unit 221 sets the current detection timing during powering operation to be later than the current detection timing during regenerative operation.

[0052] During regenerative operation, the actual phase current monotonically decreases within the current acquisition period, so peak currents can be detected by setting the current detection timing based on the start timing of the current acquisition period.On the other hand, during powering operation, the actual phase current monotonically increases within the current acquisition period, so peak currents can be detected by setting the current detection timing based on the end timing of the current acquisition period.

[0053] Current detection timing switching unit 221E acquires the current detection timing during regenerative operation output by adder 221C and the current detection timing during powering operation output by subtractor 221D, and further acquires a determination signal for powering operation or regenerative operation output by powering / regeneration determination unit 221A. When powering / regeneration determination unit 221A determines that three-phase brushless motor 12 is in regenerative operation, current detection timing switching unit 221E outputs the current detection timing during regenerative operation determined by adder 221C. On the other hand, when powering / regeneration determination unit 221A determines that three-phase brushless motor 12 is in powering operation, current detection timing switching unit 221E outputs the current detection timing during powering operation determined by subtractor 221D.

[0054] That is, current detection timing switching unit 221E selects current detection timing based on the start timing of the current acquisition period when three-phase brushless motor 12 is in regenerative operation, and selects current detection timing based on the end timing of the current acquisition period when three-phase brushless motor 12 is in powering operation. Therefore, when three-phase brushless motor 12 is switched from regenerative operation to powering operation, the current detection timing is changed to a later timing within the current acquisition period, and conversely, when three-phase brushless motor 12 is switched from powering operation to regenerative operation, the current detection timing is changed to an earlier timing within the current acquisition period.

[0055] The AD converter 221F acquires the current detection timing output by the current detection timing switching unit 221E and the shunt current signal (analog voltage signal) output by the current sensor 214. Then, the AD converter 221F performs analog-to-digital conversion (AD conversion) on the shunt current signal, which is an analog voltage signal, at the current detection timing, and outputs the digital voltage signal obtained by the AD conversion. In other words, the AD converter 221F samples the output of the current sensor 214 at the current detection timing.

[0056] The voltage-current converter 221G converts the digital voltage signal acquired from the AD converter 221F into a digital current signal, i.e., a digital signal of the real current, based on conversion characteristics according to the resistance value of the shunt resistor 214A and the gain of the operational amplifier 214B. The voltage-current converter 221G then outputs the digital signal of the real current obtained by the conversion process to the current controller 222.

[0057] As described above, the current acquisition unit 221 switches the current detection timing between regenerative operation and power running operation of the three-phase brushless motor 12, and samples the shunt current signal at the current detection timing. This allows the microcomputer 202a to detect the peak current, which is the phase current to be detected, in both regenerative operation and power running operation. Therefore, the microcomputer 202a acquires a phase current that is lower than the peak current during regenerative operation and controls the inverter 211 to prevent an overcurrent state from occurring, which would otherwise cause the inverter 211 and the three-phase brushless motor 12 to overheat.

[0058] The technical ideas described in the above embodiments can be used in appropriate combinations as long as no contradictions arise. Furthermore, although the contents of the present invention have been specifically described with reference to preferred embodiments, it is obvious that a person skilled in the art can adopt various modified embodiments based on the basic technical ideas and teachings of the present invention.

[0059] For example, although the three-phase brushless motor 12 in the above embodiment is equipped with Hall sensors 12u, 12v, and 12w as rotational position sensors that detect the motor position, the motor control device and motor control method of the present invention can also be applied to a sensorless three-phase brushless motor that does not have a rotational position sensor. In sensorless 120-degree conduction, for example, the motor rotational position is detected by detecting the zero-cross point of the induced voltage that appears in the non-energized phase.

[0060] Furthermore, the current sensors for detecting the phase currents are not limited to a single sensor using a shunt resistor arranged on the DC bus of inverter 211, but may include a U-phase current sensor, a V-phase current sensor, and a W-phase current sensor that individually detect the currents of each phase. Here, the U-phase current sensor is arranged between the U-phase midpoint and the U-phase coil of inverter 211, the V-phase current sensor is arranged between the V-phase midpoint and the V-phase coil of inverter 211, and the W-phase current sensor is arranged between the W-phase midpoint and the W-phase coil of inverter 211.

[0061] Furthermore, the current acquisition unit 221 can select either the actual phase current sampled at a current detection timing based on the end timing of the current acquisition period or the actual phase current sampled at a current detection timing based on the start timing of the current acquisition period, based on the result of determining whether the operation is regenerative or powering. Furthermore, the microcomputer 202a (powering / regenerative determination unit 221A) can determine whether the operation is regenerative or powering based on the motor rotation speed and motor torque. Furthermore, the three-phase brushless motor 12 is not limited to a motor used as an actuator for the VVT ​​mechanism 114. The motor control device and motor control method according to the present invention can be applied to a three-phase brushless motor that is operated in regenerative or powering mode using 120-degree rectangular wave drive.

[0062] 12... Three-phase brushless motor, 202... VVT controller (motor control device), 202a... Microcomputer (control unit), 211... Inverter, 213... Inverter drive circuit, 214... Current sensor, 214A... Shunt resistor, 221... Current acquisition unit, 221A... Powering / regeneration determination unit, 221B... Current acquisition period determination unit, 221E... Current detection timing switching unit

Claims

1. A motor control device configured to acquire a detection signal from a current sensor that detects the current flowing through a current-carrying phase of a three-phase brushless motor, and drive the three-phase brushless motor with a 120-degree rectangular wave based on the phase current calculated from the detection signal at the current detection timing within a current acquisition period, wherein the current detection timing is switched depending on whether the three-phase brushless motor is in regenerative operation or power operation.

2. A motor control device according to claim 1, wherein regenerative operation and power running are determined based on the direction of the motor voltage and the direction of the motor current.

3. A motor control device according to claim 1, wherein the current detection timing is set based on the start timing of the current acquisition period during regenerative operation, and based on the end timing of the current acquisition period during power running.

4. A motor control device according to claim 3, wherein the current detection timing is set to a timing when a first set time has elapsed from the start timing of the current acquisition period during regenerative operation, and is set to a timing that is a second set time prior to the end timing of the current acquisition period during powering operation.

5. A motor control device according to claim 1, wherein the current detection timing during power running is set to be later than the current detection timing during regenerative running.

6. A motor control device according to claim 1, wherein the current detection timing switching decision has hysteresis.

7. A motor control method executed by a control unit, comprising: acquiring a detection signal from a current sensor that detects a current flowing through a current-carrying phase of a three-phase brushless motor; determining a phase current from the detection signal at a current detection timing within a current acquisition period; and driving the three-phase brushless motor with a 120-degree rectangular wave based on the phase current, wherein the step of determining the phase current includes a step of switching the current detection timing depending on whether the three-phase brushless motor is in regenerative operation or power operation.

8. A motor control method as claimed in claim 7, wherein the step of switching the current detection timing includes a step of distinguishing between regenerative operation and power running operation based on a direction of the motor voltage and a direction of the motor current.

9. A motor control method as claimed in claim 7, wherein the step of switching the current detection timing comprises setting the current detection timing based on the start timing of the current acquisition period during regenerative operation, and setting the current detection timing based on the end timing of the current acquisition period during power running.

10. A motor control method according to claim 7, wherein the step of switching the current detection timing comprises setting the current detection timing during power running operation to a timing later than the current detection timing during regenerative operation.

Images