Motor control device and motor control method

Abstract

A motor control device and a motor control method according to one aspect of the present invention involves: acquiring a detection signal of a current sensor for detecting current flowing in a conduction phase of a three-phase blushless motor; performing 120-degree rectangular wave driving on the three-phase blushless motor on the basis of a control current value based on the detection signal; and obtaining the control current value on the basis of a current value detected by the current sensor before switching of the conduction phase in the 120-degree rectangular wave driving, and a current value detected by the current sensor after said switching. This configuration makes it possible to suppress oscillation of a motor current.

Description

Technical Field

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

Background Art

[0002] The control device of the compressor in Patent Document 1 includes position detection means for detecting the rotational position of the rotor of a brushless motor, inverter control means for driving an inverter by energizing and sequentially switching specific two phases out of the three-phase stator windings of the brushless motor based on the signal of the position detection means, and current control means for controlling the current so that the current becomes a waveform similar to the waveform of the no-load induced voltage of the brushless motor within the two-phase energization section of the inverter.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] By the way, when driving a three-phase brushless motor with a 120-degree rectangular wave, the motor current temporarily drops when the energized phase is switched. Therefore, if the detected value of the current sensor that detects the current flowing through the energized phase of the three-phase brushless motor is directly used for energization control, the motor current vibrates, and there is a risk that overcurrent, torque control failure, etc. may occur due to the vibration of the motor current.

[0005] The present invention has been made in view of the conventional situation, and an object thereof is to provide a motor control device and a motor control method capable of suppressing vibration of the motor current in the 120-degree rectangular wave drive of a three-phase brushless motor.

Means for Solving the Problems

[0006] In one embodiment of the motor control device according to the present invention, the control unit of the motor control device is configured to acquire a detection signal from a current sensor that detects the current flowing through the energized phases of a three-phase brushless motor, and to drive the three-phase brushless motor with a 120-degree square wave based on a control current value based on the detection signal, and to determine the control current value based on the current value detected by the current sensor before the switching of the energized phases and the current value detected by the current sensor after the switching. Furthermore, in one embodiment, the motor control method according to the present invention is a motor control method for driving a three-phase brushless motor with a 120-degree square wave, performed by a control unit, and includes the steps of: acquiring a detection signal from a current sensor that detects the current flowing in the energized phase of the three-phase brushless motor; determining a control current value based on the detection signal; and outputting a control signal to the drive circuit of the three-phase brushless motor based on the control current value, wherein the step of determining the control current value is to determine the control current value based on the current value detected by the current sensor before the switching of the energized phase and the current value detected by the current sensor after the switching. [Effects of the Invention]

[0007] According to the above invention, it is possible to suppress motor current oscillations in 120-degree square wave driving of a three-phase brushless motor. [Brief explanation of the drawing]

[0008] [Figure 1] This is a system diagram of an internal combustion engine for a vehicle. [Figure 2] This is a block diagram showing a control system for a 3-phase brushless motor. [Figure 3] This is a time chart showing the PWM control pattern of the inverter. [Figure 4] This is a time chart illustrating the phase voltage and inter-phase voltage when complementary PWM is not implemented. [Figure 5] This is a time chart illustrating the phase voltage and inter-phase voltage when complementary PWM is implemented. [Figure 6] This is a time chart showing the phase voltage and shunt current when pulse shift control is not implemented. [Figure 7] This is a time chart showing the phase voltage and shunt current when pulse shift control is implemented. [Figure 8] This is a time chart showing how the phase current drops when the energized phase is switched. [Figure 9] This is a time chart showing the details of the response delay processing. [Figure 10] This is a time chart showing the state when response delay processing is performed in the low rotation range of the motor. [Figure 11] This is a time chart showing the state when response delay processing is performed in the high-speed range of the motor. [Figure 12] This is a time chart showing the effects of response delay processing. [Figure 13] This diagram illustrates the drop in phase current during power mode. [Figure 14] This diagram illustrates why the phase current does not drop in regenerative mode. [Modes for carrying out the invention]

[0009] Embodiments of the present invention will be described below. Figure 1 shows an internal combustion engine for a vehicle equipped with a three-phase brushless motor to which the motor control device and motor control method according to the present invention are applied.

[0010] The internal combustion engine 101 is equipped with an intake air volume sensor 103 in the intake duct 102 for detecting the intake air flow rate QA of the internal combustion engine 101. The intake valve 105 opens and closes the intake port of the combustion chamber 104 of each cylinder.

[0011] The fuel injector 106 injects fuel into the intake port 102a of each cylinder. The fuel injected by the fuel injector 106 is drawn into the combustion chamber 104 along with air via the intake valve 105, and ignited and combusted by a spark from the spark plug 107. Then, the combustion pressure pushes down the piston 108 toward the crankshaft 109, rotationally driving the crankshaft 109.

[0012] Also, the exhaust valve 110 opens and closes the exhaust port of the combustion chamber 104. When the exhaust valve 110 opens, the exhaust gas in the combustion chamber 104 is discharged into the exhaust pipe 111. The exhaust pipe 111 includes a catalytic converter 112 incorporating a catalyst such as a three-way catalyst.

[0013] The intake valve 105 opens and closes as the intake camshaft 115a rotated by the crankshaft 109 rotates. Also, the exhaust valve 110 opens and closes as the exhaust camshaft 115b rotated by the crankshaft 109 rotates.

[0014] The electric variable valve timing mechanism 114 (hereinafter referred to as the VVT mechanism 114) is a mechanism that continuously advances and retards the valve timing of the intake valve 105, which is an engine valve, by changing the rotational phase of the intake camshaft 115a with respect to the crankshaft 109 according to the rotational speed of the three-phase brushless motor 12 as an actuator. The VVT mechanism 114 has a known structure disclosed in, for example, Japanese Patent No. 7085629. Hereinafter, an aspect of the structure and operation of the VVT mechanism 114 will be outlined.

[0015] The VVT mechanism 114 is disposed between a timing sprocket (not shown) and the intake camshaft 115a, and includes a phase change mechanism that changes the relative rotational phase between the timing sprocket and the intake camshaft 115a. The phase change mechanism includes a three-phase brushless motor 12 and a reduction mechanism that reduces the rotational speed of the three-phase brushless motor 12 and transmits it to the intake camshaft 115a. When the three-phase brushless motor 12 is driven to rotate in both forward and reverse directions, a reduced rotational force is transmitted to the intake camshaft 115a. This causes the intake camshaft 115a to rotate in both forward and reverse directions relative to the timing sprocket, thereby changing the relative rotational phase between the intake camshaft 115a and the timing sprocket.

[0016] Furthermore, 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 power to the ignition coil.

[0017] The control system for controlling the operation of the internal combustion engine 101 includes an engine control module 201 (hereinafter referred to as ECM201) that controls fuel injection by the fuel injector 106 and ignition by the spark plug 107, and a VVT controller 202 that controls valve timing by the VVT ​​mechanism 114. The VVT ​​controller 202 is a motor control device that controls the three-phase brushless motor 12, which is the actuator of the VVT ​​mechanism 114.

[0018] ECM201 is an electronic control unit equipped with a microcomputer 201a, and VVT controller 202 is an electronic control unit equipped with a microcomputer 202a. The microcomputers 201a and 202a include a processor, non-volatile memory, volatile memory, and the like.

[0019] The ECM201 acquires signals output by various sensors and performs calculations according to a program pre-stored in non-volatile memory to calculate and output the control values ​​for the fuel injector 106, ignition module 116, etc. Furthermore, the VVT ​​controller 202 acquires signals transmitted by the ECM 201 and signals output by various sensors, and performs calculations according to a program pre-stored in non-volatile memory to calculate and output the control amount for the three-phase brushless motor 12 of the VVT ​​mechanism 114.

[0020] In addition to the intake air volume sensor 103, the internal combustion engine 101 is equipped with a crank angle sensor 203 that outputs a crank angle signal POS at predetermined angular positions of the crankshaft 109, an accelerator position sensor 206 that detects the amount of depression of the accelerator pedal 207, in other words, the accelerator opening degree ACC, a cam angle sensor 204 that outputs a cam angle signal CAM at predetermined angular positions of the intake camshaft 115a, a water temperature sensor 208 that detects the temperature TW of the coolant of the internal combustion engine 101, and an air-fuel ratio sensor 209 installed in the exhaust pipe 111 upstream of the catalytic converter 112 that detects the air-fuel ratio AF based on the oxygen concentration in the exhaust gas.

[0021] The crank angle signal POS output by the crank angle sensor 203 is a pulse signal for each unit crank angle, and the signal output pattern is set such that one or more consecutive pulses are missing for each crank angle corresponding to the stroke phase difference between cylinders. Here, the ECM201 detects the position of the missing pulse signal in the crank angle signal POS as the reference crank angle position.

[0022] Furthermore, the cam angle signal CAM output by the cam angle sensor 204 is output for each crank angle corresponding to the stroke phase difference between cylinders. The ECM201 acquires the signals output by these various sensors, and also acquires the on / off signal of the ignition switch 205, which is the main switch for starting and stopping the internal combustion engine 101.

[0023] Furthermore, the three-phase brushless motor 12 of the VVT ​​mechanism 114 is equipped with Hall sensors 12u, 12v, and 12w as motor rotation position sensors for detecting the positional relationship between the three phase coils (U-phase coil, V-phase coil, and W-phase coil) and the rotor. The VVT ​​controller 202 then acquires the signals output by the Hall sensors 12u, 12v, and 12w.

[0024] The ECM201 calculates a target rotational phase, which is the target value of the rotational phase of the intake camshaft 115a relative to the crankshaft 109, based on the engine operating conditions such as engine load and engine rotational speed obtained from the output signals of the various sensors mentioned above. It also calculates the actual rotational phase based on the crank angle signal POS and the cam angle signal CAM. The ECM201 then calculates the target rotational speed Nt of the three-phase brushless motor 12 of the VVT ​​mechanism 114 so that the actual rotational phase approaches the target rotational phase, and transmits the signal of the target rotational speed Nt to the VVT ​​controller 202.

[0025] The VVT ​​controller 202, having acquired the signal for the target rotational speed Nt, determines the command current value CCV, which is the target value of the motor current, so that the actual rotational speed of the three-phase brushless motor 12 approaches the target rotational speed Nt. The controller then controls the manipulated variable of the three-phase brushless motor 12 so that the actual motor current approaches the command current value CCV. In other words, the VVT ​​controller 202 controls the current supplied to the three-phase brushless motor 12 of the VVT ​​mechanism 114 by speed feedback control.

[0026] Figure 2 is a block diagram showing the drive circuit 210 for the three-phase brushless motor 12 provided by 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 3-phase brushless motor 12 using a 120-degree square wave drive, which sequentially switches between two of the three phases to which voltage is applied. In other words, the microcomputer 202a is a control unit that executes a motor control method for driving the three-phase brushless motor 12 with a 120-degree square wave.

[0027] In 120-degree square wave driving, for example, the following patterns can be switched every 60 degrees of rotation: the first pattern where current flows from the U phase to the V phase, the second pattern where current flows from the U phase to the W phase, the third pattern where current flows from the V phase to the W phase, the fourth pattern where current flows from the V phase to the U phase, the fifth pattern where current flows from the W phase to the U phase, and the sixth pattern where current flows from the W phase to the V phase. By switching the energizing pattern, for example in the case of the U phase, energization is performed for 120 degrees between the first and second patterns, then de-energized for 60 degrees between the third pattern, and then energized again for 120 degrees between the fourth and fifth patterns. Note that 120-degree square wave driving is also referred to as 120-degree energization or square wave driving.

[0028] The 3-phase brushless motor 12 is equipped with three phase coils of U-phase, V-phase, and W-phase connected in a star configuration on a cylindrical stator, and a rotor made of permanent magnets is rotatably mounted in a space formed in the center of the stator. The Hall sensors 12u, 12v, and 12w are positioned around the rotor at 120-degree intervals, and by combining the sensor signals from these Hall sensors 12u, 12v, and 12w, the timing for switching the energization pattern every 60 degrees is detected.

[0029] The drive circuit 210 for the three-phase brushless motor 12 includes an inverter 211, a DC power supply 212 for the inverter 211, and an inverter drive circuit 213. The inverter 211 is configured by connecting semiconductor switching elements 211a-211f, such as FETs, in a three-phase bridge configuration and supplies AC power to the three-phase brushless motor 12.

[0030] The gate terminals of the semiconductor switching elements 211a-211f of the inverter 211 are connected to the output ports of the inverter drive circuit 213. Then, the on / off state of the semiconductor switching elements 211a-211f is switched according to the gate control signals that the inverter drive circuit 213 outputs to each gate terminal of the semiconductor switching elements 211a-211f. Furthermore, a shunt resistor 214 (in other words, a current sensor) for detecting motor current is placed on the DC bus between the inverter 211 and ground GND.

[0031] Figure 3 shows one embodiment of the PWM control pattern of semiconductor switching elements 211a-211f in 120-degree square wave driving. In the example shown in Figure 3, the semiconductor switching elements 211a, 211c, and 211e on the upper arm are fixed in the ON position, while the semiconductor switching elements 211b, 211d, and 211f on the lower arm are controlled by PWM, employing a lower arm chopper control system.

[0032] For example, when flowing current from the V phase to the W phase, the semiconductor switching element 211c, which is the upper arm of the V phase, is fixed in the ON position, while the on / off state of the semiconductor switching element 211f, which is the lower arm of the W phase, is controlled by PWM. At this time, when the semiconductor switching element 211c is turned on, the terminal voltage of the V phase becomes the power supply potential, and when the semiconductor switching element 211f is turned on, the terminal voltage of the W phase becomes the ground potential, creating a potential difference between the energized phases, and causing current to flow from the V phase to the W phase.

[0033] In other words, during the ON period of the PWM-controlled semiconductor switching element of the lower arm, the energized phase current flows through the shunt resistor 214. Therefore, the microcomputer 202a samples the current flowing through the shunt resistor 214 during the ON period of the semiconductor switching element in the lower arm, which is the timing when current in the energized phase flows through the shunt resistor 214, and detects the current value of the energized phase. Furthermore, an upper arm chopper control can be employed, in which the semiconductor switching element of the lower arm is fixed in the ON position, while the on / off state of the semiconductor switching element of the upper arm is controlled by PWM.

[0034] Furthermore, the microcomputer 202a can perform complementary PWM (in other words, complementary up and down switching) when driving a 120-degree square wave. Complementary PWM is a switching control method that turns the semiconductor switching elements of the lower arm and the upper arm on and off in opposite phases to each other.

[0035] Figure 4 shows an example of switching operation when current flows from the U phase to the V phase without complementary PWM. In Figure 4, the semiconductor switching element 211a, which is the upper arm of the U-phase, is held ON, and the semiconductor switching element 211b, which is the lower arm of the U-phase, is held OFF.

[0036] Furthermore, the on / off state of the semiconductor switching element 211d, which is the lower arm of the V phase, is controlled by PWM with the duty cycle being "command voltage / power supply voltage VB", while the semiconductor switching element 211c, which is the upper arm of the V phase, is kept off. If complementary PWM as shown in Figure 4 is not implemented, the phase-to-phase voltage during periods of de-energization becomes equivalent to the induced voltage, resulting in a state where the average voltage differs from the command voltage, and the controllability of the current and rotational speed of the 3-phase brushless motor 12 decreases.

[0037] On the other hand, Figure 5 shows an example of switching operation when current is passed from the U phase to the V phase when complementary PWM is implemented. In Figure 5, the on / off switching of the semiconductor switching element 211a, which is the upper arm of the U phase, is controlled by PWM with a duty cycle of "50% + command voltage / power supply voltage VB / 2", and the semiconductor switching element 211b, which is the lower arm of the U phase, is switched on and off in the opposite phase to the semiconductor switching element 211a, which is the upper arm.

[0038] Furthermore, the on / off switching of the semiconductor switching element 211c, which is the upper arm of the V phase, is controlled by PWM with a duty cycle of "50% - command voltage / power supply voltage VB / 2", and the semiconductor switching element 211d, which is the lower arm of the V phase, is switched on and off in the opposite phase to the semiconductor switching element 211c, which is the upper arm. When implementing complementary PWM as shown in Figure 5, there is no period of no power supply except for the dead time, and the phase-to-phase voltage is fixed at 0V or the power supply voltage VB, so the average voltage becomes the command voltage, resulting in good controllability of the current and rotational speed of the 3-phase brushless motor 12.

[0039] Furthermore, when the duty cycle of the PWM control is small, the microcomputer 202a can perform pulse shift control, which is a process that ensures the current detection period by the shunt resistor 214 by shifting the phase of the PWM pulse. Figure 6 shows the phase voltage and shunt current when current is passed from the U phase to the V phase during switching operation, without pulse shift control. In this case, if the duty cycle is small, the time during which the shunt current flows will fall below the predetermined minimum time (lower limit) for which current detection is possible, making current detection impossible.

[0040] In contrast, Figure 7 shows the phase voltage and shunt current when pulse shift control is implemented during the switching operation when current flows from the U phase to the V phase. The microcomputer 202a uses pulse shift control to advance the phase of the PWM pulse that controls the U-phase voltage, while delaying the phase of the PWM pulse that controls the V-phase voltage. This makes the period during which the U-phase-V-phase voltage is positive (+ power supply voltage VB) longer than when pulse shift control is not performed. At the same time, it generates a period during which the U-phase-V-phase voltage is negative (- power supply voltage VB) by the amount of time the voltage is positive (+ power supply voltage VB), so that the average voltage does not change. This allows the time during which the shunt current flows to be maintained for longer than the minimum time required for current detection by pulse shift control, even when the duty cycle is small, thus enabling current detection.

[0041] Next, we will explain in detail the control functions of the three-phase brushless motor 12 provided by the microcomputer 202a, as shown in Figure 2. The microcomputer 202a has the following functional units: a phase current detection unit 222, a response control unit 223, a current control unit 224, a command voltage / duty cycle conversion unit 225, an energized phase determination unit 226, and a PWM signal generation unit 227.

[0042] The phase current detection unit 222 converts the potential difference across the shunt resistor 214 into a current value, thereby determining the detected current value DCV (in other words, the raw current value before processing), which is the current value of the current flowing through the energized phases of the three-phase brushless motor 12. In other words, the shunt resistor 214 and the phase current detection unit 222 constitute a current sensor that detects the current flowing through the energized phases of the three-phase brushless motor. As described above, the phase current detection unit 222 samples the current value based on the potential difference across the shunt resistor 214 as the detected current value DCV during the ON control period of the PWM-controlled semiconductor switching element among the semiconductor switching elements 211a-211f that constitute the inverter 211.

[0043] The response control unit 223 is a functional unit that processes the detected current value DCV detected by the phase current detection unit 222 to obtain the control current value ACV (in other words, the recognized current value of the microcomputer 202a), which is the actual phase current value used to control the inverter 211. When the energized phase is switched, it performs a process to delay the response of the control current value ACV to the detected current value DCV. The functions of the response control unit 223 will be explained in detail later.

[0044] The current control unit 224 obtains the control current value ACV (in other words, the actual phase current) output by the response control unit 223 and the command current value CCV (in other words, the target phase current) based on the rotational phase control error, and calculates the command voltage value CVV. The command voltage / duty cycle conversion unit 225 converts the command voltage value CVV obtained from the current control unit 224 into the duty cycle for PWM control of the semiconductor switching elements 211a-211f that constitute the inverter 211.

[0045] The energized phase determination unit 226 combines the sensor signals from the Hall sensors 12u, 12v, and 12w to create energized phase switching information (in other words, energized phase designation information) every 60 degrees of rotation. The PWM signal generation unit 227 acquires a duty cycle signal from the command voltage / duty cycle conversion unit 225 and also acquires power phase switching information from the power phase determination unit 226.

[0046] Then, the PWM signal generation unit 227 generates PWM signals for each of the semiconductor switching elements 211a-211f that constitute the inverter 211, based on the acquired duty cycle signal and the power supply phase switching information. The inverter drive circuit 213 acquires the PWM signal generated by the PWM signal generation unit 227 and outputs gate signals for each of the semiconductor switching elements 211a-211f of the inverter 211 based on the acquired PWM signal.

[0047] The functions of the response control unit 223 will be described in detail below. Figure 8 is a time chart showing how the detected current value DCV, detected by the shunt resistor 214, temporarily drops as the energized phase switches, and how the controlled motor current oscillates as a result.

[0048] In 120-degree square wave drive, the energized phase is switched every 60 degrees the 3-phase brushless motor 12 rotates. However, because the switching of the energized phase causes current to start flowing in the phase that was previously not carrying current, a drop in phase current occurs immediately after the switching of the energized phase. The microcomputer 202a increases the command voltage by sampling the phase current that drops due to the switching of the energized phase. As the command voltage increases, the phase current increases, causing the phase current to oscillate immediately after the switching of the energized phase. Oscillation of the phase current can cause overcurrent or torque control failure, potentially leading to damage to the motor drive circuit or the mechanical parts of the VVT ​​mechanism 114.

[0049] Therefore, when the energized phase is switched, the response control unit 223 performs a process to delay the response of the control current value ACV to the detected current value DCV (hereinafter referred to as the response delay process). This suppresses the oscillation of the phase current by preventing the control current value ACV used for motor control from falling similarly even if the detected current value DCV temporarily drops due to the energized phase switching. Furthermore, by suppressing phase current oscillations through response delay processing, overcurrent and torque control failures can be prevented, thereby preventing damage to the motor drive circuit or the mechanical parts of the VVT ​​mechanism 114.

[0050] The response control unit 223 determines the control current value ACV as a response delay process, based on the detected current value DCV before the switching of the energized phase and the detected current value DCV after the switching. Figure 9 is a time chart illustrating the details of the response delay processing. The microcomputer 202a (response control unit 223) updates and records the detected current value DCV in its built-in memory each time it samples the detected current value DCV.

[0051] Then, when the power supply phase is switched, the microcomputer 202a reads the detected current value DCV sampled immediately before the switch from memory as the first step of response delay processing, and holds the control current value ACV at the detected current value DCV immediately before the switch during the first interval until the first time T1 has elapsed from the power supply phase switch. Furthermore, after the first time T1 has elapsed since the switching of the energized phase, the microcomputer 202a performs the second step of response delay processing, gradually bringing the control current value ACV closer to the detected current value DCV over a second time T2. Then, after the microcomputer 202a matches the control current value ACV to the detection current value DCV, it maintains this state until the next phase switch occurs.

[0052] The microcomputer 202a determines the control current value ACV in the second time interval T2 (second interval) according to the following formula. ACV = (DCV before switching * G) + (DCV * (1 - G)) Here, the microcomputer 202a gradually decreases the gain G in the above equation from 1 to 0 over a second time T2, thereby gradually bringing the control current value ACV closer to the latest detected current value DCV over a second time T2, from the detected current value DCV before switching.

[0053] The first time interval T1 is determined based on, for example, the time it takes for the phase current to recover from a state where it has dropped due to the switching of the energized phase to within the allowable current fluctuation range (for example, ±5A) when the target value of the phase current is the maximum current (hereinafter referred to as the recovery time), and is stored as a constant in non-volatile memory. In other words, the first time T1 can be defined as the time it takes for the detected current value DCV after switching the energized phase to return to [(detected current value DCV before switching) - 5A], even when the commanded value of the phase current is the maximum current.

[0054] Furthermore, since the recovery time varies depending on the magnitude of the phase current before switching, the microcomputer 202a can set the first time T1 to be variable based on the current value before switching, instead of acquiring the first time T1 as a fixed value. In other words, the microcomputer 202a can determine the time until the detected current value DCV becomes within the allowable current fluctuation range relative to the control current value ACV, based on the detected current value DCV before switching or the command current value CCV before switching, and set the first time T1 variably based on the determined time.

[0055] Here, the motor current response is the response of a first-order lag system due to the motor phase resistance and inductance, and the difference ΔDC between the detected current value DCV before switching and the detected current value DCV after switching is expressed by Equation 1.

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[0056] The microcomputer 202a calculates the time t required for the difference ΔDC to become the allowable current fluctuation range according to Equation 1, and sets the calculated time t as the first time T1. With this configuration, it is possible to prevent the control current value ACV from being excessively held at the detected current value DCV immediately before switching, and to maintain control responsiveness to the command current value CCV.

[0057] Furthermore, if the second time interval T2 is short, the current response improves but the current fluctuation becomes larger, while conversely, if it is long, the current fluctuation becomes smaller but the current response deteriorates. Therefore, the second time interval T2 is set to achieve both current responsiveness and suppression of current fluctuations, and is stored as a constant in non-volatile memory. Furthermore, the microcomputer 202a can change the gain G at a constant rate in the second time period T2, and can also increase the rate at which the gain G decreases over time.

[0058] The following explains how the response delay processing by the response control unit 223 can be applied to both low-speed and high-speed rotation of the three-phase brushless motor 12. Figure 10 shows the state in which response delay processing by the response control unit 223 is applied when the 3-phase brushless motor 12 is rotating at a low speed, with the relationship between the magnitude of the energizing phase switching period, motor control period, and current drop period being such that the energizing phase switching period >> motor control period > current drop period.

[0059] For motor control, it is required that the control current value ACV does not take into account the phase current that drops due to the switching of the energized phase. Here, during the first time interval T1 from the switching of the energized phase, the control current value ACV is maintained at the detected current value DCV before the switching of the energized phase. Then, during the second time interval T2, the control current value ACV approaches the detected current value DCV. Therefore, at low rotation speeds, the control current value ACV is prevented from taking in the phase current that has dropped due to the switching of the energized phase.

[0060] Furthermore, for motor control, it is required that the motor current value be controlled to the commanded current value CCV except during the phase current drop period associated with the switching of energized phases. Here, after the phase current drop associated with the switching of the energized phase has subsided, the control current value ACV matches the detected current value DCV, and motor control is effectively performed based on the detected current value DCV. Therefore, at low rotation speeds, the motor current value can be controlled to the command current value CCV except during the phase current drop period. In other words, by applying response delay processing by the response control unit 223 when the 3-phase brushless motor 12 is rotating at a low speed, the motor current value can be controlled to the command current value CCV while suppressing the reflection of the phase current that has dropped due to the switching of the energized phase into the control.

[0061] Figure 11 shows the state in which response delay processing by the response control unit 223 is applied when the 3-phase brushless motor 12 is rotating at high speed, where the relationship between the energization phase switching period and the control period is such that the energization phase switching period < motor control period, and the energization phase switching period is less than or equal to the first time T1. In motor control at high rotational speeds, it is required to implement current limiting that prevents the actual phase current from exceeding the commanded current value (CCV). Here, the microcomputer 202a uses the phase current before the switching of the energized phase, which is the peak current, for energization control, and does not use the phase current that drops due to the switching of the energized phase for energization control. Therefore, it is possible to achieve current limiting that prevents the actual phase current from being greater than the commanded current value CCV.

[0062] Furthermore, the motor control system is required to be able to follow changes in the commanded current value (CCV). Here, the microcomputer 202a performs motor control using the phase current before the switching of the energized phase, which is the latest value among the reliable current values, so that the motor current value can follow the command current value CCV.

[0063] Figure 12 is a time chart showing the effect of the response delay processing by the response control unit 223. Prior to time t1 in Figure 12, the motor is in a power mode where the direction of rotation of the 3-phase brushless motor 12 and the direction of the applied voltage to the 3-phase brushless motor 12 are the same, and the response control unit 223 performs response delay processing to determine the control current value ACV.

[0064] In power mode, a drop in current occurs due to the switching of the energized phase, and the detected current value DCV, which is the AD conversion value of the detection signal from the current sensor, fluctuates in response to the drop in current due to the switching of the energized phase. In contrast, the control current value ACV used for motor control is determined based on the detected current value DCV, but it is processed in a way that does not pick up on current drops due to the switching of energized phases. Therefore, by controlling the motor based on the control current value ACV, it is possible to keep motor current fluctuations within an acceptable range.

[0065] On the other hand, from time t1 onwards in Figure 12, the regenerative mode is in which the rotation direction of the 3-phase brushless motor 12 and the direction of the applied voltage to the 3-phase brushless motor 12 are opposite, and no current drop occurs due to the switching of the energized phase. Therefore, in regenerative mode, the microcomputer 202a stops the response delay processing by the response control unit 223 and sets the control current value ACV to the detected current value DCV (i.e., the raw current value detected by the current sensor), including immediately after the switching of the energized phase.

[0066] Figure 13 shows the currents in each phase, the voltages in each phase immediately after switching, the current flowing through the shunt resistor 214, and the current path immediately after switching, when a switch is performed from a pattern in which current flows from the U phase to the W phase to a pattern in which current flows from the V phase to the W phase in the power mode in which the motor current is a positive current. In power mode, when switching occurs from a pattern where current flows from the U phase to the W phase to a pattern where current flows from the V phase to the W phase, while a return current flows through the body diode (in other words, the parasitic diode) of the semiconductor switching element 211b on the lower arm of the U phase, the terminal voltage of the U phase is stuck at ground potential (Low) due to the back electromotive force. Therefore, during the current sampling interval, which is the period in which a potential difference occurs between the energized V-phase and W-phase, only the V-phase current Iv immediately after the start of energization flows through the shunt resistor 214, causing a drop in current.

[0067] On the other hand, Figure 14 shows the currents in each phase, the voltages in each phase immediately after switching, the current flowing through the shunt resistor 214, and the current path immediately after switching when switching is performed from a pattern in which current flows from the U phase to the W phase to a pattern in which current flows from the V phase to the W phase in the regenerative mode in which the motor current is a negative current. In regenerative mode, when the energizing pattern switches from one in which current flows from the U phase to the W phase to one in which current flows from the V phase to the W phase, the terminal voltage of the U phase remains at the power supply potential (High) due to the back electromotive force while a return current flows through the body diode (parasitic diode) of the semiconductor switching element 211a on the upper arm of the U phase. Therefore, during the current sampling interval, which is the period in which a potential difference occurs between the energized V-phase and W-phase, the current Iw of the W-phase, which was energized before the switching of the energized phases, flows through the shunt resistor 214, and no current drop occurs.

[0068] Thus, in the power mode and the regenerative mode, the path through which the return current of the open phase (U phase in Figures 13 and 14) flows changes, resulting in a difference in the current flowing through the shunt resistor 214. In the power mode, a drop in current occurs with the switching of the energized phase, whereas in the regenerative mode, there is no drop in current with the switching of the energized phase. Therefore, the microcomputer 202a performs response delay processing by the response control unit 223 in the power mode, and stops the response delay processing by the response control unit 223 in the regenerative mode, thereby suppressing a decrease in current responsiveness in the regenerative mode and reducing the computational load for the response delay processing.

[0069] The technical concepts 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 will be obvious to those skilled in the art that various modifications can be taken based on the basic technical concept and teachings of the present invention.

[0070] For example, the three-phase brushless motor 12 in the above embodiment is equipped with Hall sensors 12u, 12v, and 12w as rotational position sensors for detecting the motor position. However, the motor control device and motor control method according to the present invention can also be applied to sensorless three-phase brushless motors that do not have rotational position sensors such as Hall sensors. In sensorless 120-degree energization, for example, the motor rotation position can be detected by detecting the zero-crossing point of the induced voltage appearing in the unenergized phase.

[0071] Furthermore, in the above embodiment, the microcomputer 202a maintains the control current value ACV at the detected current value DCV before the switching of the energized phase until a first time T1 has elapsed from the switching of the energized phase. However, by setting the first time T1 during which the control current value ACV is maintained at the detected current value DCV before the switching of the energized phase to zero, the control current value ACV can be gradually brought closer to the detected current value DCV from the detected current value DCV before the switching over a predetermined period of time from the start of the switching of the energized phase.

[0072] Furthermore, the microcomputer 202a can obtain the control current value ACV by applying a low-pass filter to the detected current value DCV. In other words, the response control unit 223 only needs to be able to suppress the change in the control current value ACV in response to the drop in the detected current value DCV when the energized phase is switched. Furthermore, the 3-phase brushless motor is not limited to the motor used for the VVT ​​mechanism 114, nor is it limited to motors operated in power mode and regenerative mode. [Explanation of Symbols]

[0073] 12...3-phase brushless motor, 114...VVT mechanism, 202...VVT controller (motor control device), 202a...microcomputer (control unit), 211...inverter, 213...inverter drive circuit, 214...shunt resistor (current sensor), 222...phase current detection unit, 223...response control unit, 224...current control unit, 225...command voltage / duty cycle conversion unit, 226...energized phase determination unit, 227...PWM signal generation unit

Claims

1. A motor control device, The control unit included in the motor control device is The system is configured to acquire a detection signal from a current sensor that detects the current flowing through the energized phases of a three-phase brushless motor, and to drive the three-phase brushless motor with a 120-degree square wave based on a control current value derived from the detection signal. The control current value is determined based on the current value detected by the current sensor before the switching of the energized phase in the 120-degree square wave drive and the current value detected by the current sensor after the switching. Motor control device.

2. A motor control device according to claim 1, The control unit is, The control current value is maintained at the current value detected by the current sensor before the switching of the energized phase until a first time has elapsed since the switching of the energized phase, and after the first time has elapsed, it is gradually brought closer to the current value detected by the current sensor over a second time. Motor control device.

3. A motor control device according to claim 2, The control unit is The first time is changed according to the motor current value or command current value. Motor control device.

4. A motor control device according to claim 1, The control unit is, When the rotation direction of the three-phase brushless motor and the direction of the applied voltage to the three-phase brushless motor are opposite, the control current value shall be set to the current value detected by the current sensor. Motor control device.

5. A motor control device according to claim 1, The current sensor is configured to include a shunt resistor placed on the DC bus of the inverter that supplies AC power to the three-phase brushless motor. Motor control device.

6. A motor control device according to claim 5, The control unit is, The inverter that supplies AC power to the three-phase brushless motor is PWM controlled to drive the three-phase brushless motor with a 120-degree square wave. The time for which current flows through the shunt resistor is set to be greater than or equal to the minimum time for which current detection is possible by implementing pulse shift control that shifts the phase of the PWM pulse. Motor control device.

7. A motor control device, The control unit included in the motor control device is The detection signal from the current sensor that detects the current flowing through the energized phase of a three-phase brushless motor is acquired. Based on the detection signal, the control current value, which is the actual phase current value for control, is determined. The three-phase brushless motor is configured to drive a 120-degree square wave based on the control current value, When the energizing phase is switched in the 120-degree rectangular wave drive, the response of the control current value to the current value detected by the current sensor is delayed. Motor control device.

8. A motor control method for driving a three-phase brushless motor with a 120-degree square wave, which is executed by a control unit, The steps include: acquiring a detection signal from a current sensor that detects the current flowing through the energized phase of the three-phase brushless motor; The steps include determining the control current value based on the detection signal, The steps include: outputting a control signal to the drive circuit of the three-phase brushless motor based on the control current value; Includes, The step of determining the control current value is: The control current value is determined based on the current value detected by the current sensor before the switching of the energized phase in the 120-degree square wave drive and the current value detected by the current sensor after the switching. Motor control method.

9. A motor control method according to claim 8, The step of determining the control current value is: The steps include: maintaining the control current value at the current value detected by the current sensor before the switching of the energized phase until a first time has elapsed since the switching of the energized phase; The steps include gradually bringing the control current value closer to the current value detected by the current sensor over a second period of time after the first period of time has elapsed, including, Motor control method.

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