JP2020141477A - Work machine - Google Patents

Abstract

To provide a work machine in which, in a case where a sensorless control technology for estimating a rotational angle of an electric motor by using a voltage command value is adopted, the influence of a dead time of an inverter can be suppressed.SOLUTION: A work machine (shovel) according to one embodiment of the present invention includes a motor generator 12, and an inverter 18A that controls the motor generator 12. A control circuit of the inverter 18A performs control such that the voltage of the motor generator 12 becomes relatively high even in a low-speed state in which the speed is relatively low. Further, a work machine (shovel) according to another embodiment of the present invention includes a motor generator 12. The current phase of the motor generator 12 varies between a low-speed state in which the speed is relatively low and a high-speed state in which the speed is relatively high.SELECTED DRAWING: Figure 3

Description

The present invention relates to a working machine.

For example, a work machine including an electric motor for driving a hydraulic pump or the like is known (see, for example, Patent Document 1).

Japanese Unexamined Patent Publication No. 2013-028962

By the way, instead of mounting a sensor for detecting the rotation angle of the electric motor, a sensorless control technique for controlling the electric motor while estimating the rotation angle from the current value and the voltage value of the electric motor may be applied to the work machine. In this case, the rotation angle of the electric motor may be estimated by using the voltage command value generated in the control process instead of the actual voltage value of the electric motor without using the sensor that detects the voltage of the electric motor.

However, an error due to the dead time of the inverter (hereinafter, “dead time error”) is included between the actual voltage value of the electric motor and the voltage command value. In particular, when the voltage of the motor is very small (that is, when the load of the motor is low), the influence of the dead time error becomes relatively remarkable. Therefore, there is a possibility that the estimated value of the rotation angle of the electric motor deviates significantly from the actual rotation angle, and the electric motor cannot be controlled appropriately.

Therefore, in view of the above problems, it is necessary to provide a work machine capable of suppressing the influence of the dead time of the inverter when the sensorless control technology for estimating the rotation angle of the electric motor using the voltage command value is adopted. With the goal.

In order to achieve the above object, in one embodiment of the present invention,
With an electric motor
A control device for controlling the electric motor is provided.
The control device controls so that the voltage of the electric motor becomes relatively high even in a low speed state where the speed is relatively low.
Work machines are provided.

Further, in other embodiments of the present invention,
Equipped with an electric motor
The electric motor has a different current phase between a low speed state in which the speed is relatively low and a high speed state in which the speed is relatively high.
Work machines are provided.

According to the above-described embodiment, when a sensorless control technique for estimating the rotation angle of an electric motor using a voltage command value is adopted, a work machine capable of suppressing the influence of dead time of an inverter is provided. be able to.

It is a side view of the excavator which concerns on one Embodiment. It is a block diagram which shows typically an example of the structure of the excavator which concerns on one Embodiment. It is a figure explaining the current state of the motor generator in both the high speed / high load state and the low speed / low load state. It is a flowchart which shows typically an example of the control processing about the motor generator by an inverter.

Hereinafter, modes for carrying out the invention will be described with reference to the drawings.

[Outline of excavator]
First, an outline of an excavator as an example of a work machine will be described with reference to FIG.

FIG. 1 is a side view showing an example of a shovel according to the present embodiment.

The excavator (an example of a work machine) according to the present embodiment includes a lower traveling body 1, an upper rotating body 3 mounted on the lower traveling body 1 so as to be able to turn via a turning mechanism 2, and a boom 4 as a working device. It includes an arm 5, a bucket 6, and a cabin 10 on which an operator is boarded.

The lower traveling body 1 includes, for example, a pair of left and right crawlers, and each crawler is hydraulically driven by traveling hydraulic motors 1A and 1B (see FIG. 2) to self-propell.

The upper swivel body 3 is electrically driven by a swivel electric motor 21 (see FIG. 2), which will be described later, to swivel with respect to the lower traveling body 1.

The boom 4 is pivotally attached to the center of the front portion of the upper swing body 3 so as to be vertically movable, an arm 5 is pivotally attached to the tip of the boom 4 so as to be vertically rotatable, and a bucket 6 is vertically attached to the tip of the arm 5. It is rotatably pivoted. The boom 4, arm 5, and bucket 6 are hydraulically driven by the boom cylinder 7, arm cylinder 8, and bucket cylinder 9 as hydraulic actuators, respectively.

The cabin 10 is mounted on the left side of the front portion of the upper swing body 3, and inside the cabin 10, a driver's seat on which the operator sits, an operation device 26 described later, and the like are provided.

[Excavator configuration]
Next, the configuration of the excavator according to the present embodiment will be described with reference to FIG. 2 in addition to FIG.

FIG. 2 is a block diagram showing an example of a configuration centered on the drive system of the excavator according to the present embodiment.

In the figure, the mechanical power line is indicated by a double line, the high-pressure hydraulic line is indicated by a thick solid line, the pilot line is indicated by a broken line, and the electric drive / control line is indicated by a thin solid line.

<Hydraulic drive system of excavator>
As described above, the hydraulic drive system according to the present embodiment includes hydraulic actuators that drive various driven elements. The hydraulic actuator includes traveling hydraulic motors 1A and 1B, boom cylinder 7, arm cylinder 8 and bucket cylinder that hydraulically drive each of the lower traveling body 1 (that is, the left and right crawlers), the boom 4, the arm 5, and the bucket 6. Including 9 mag. The hydraulic drive system of the excavator according to the present embodiment includes an engine 11, a speed reducer 13, a main pump 14, and a control valve 17.

The engine 11 is the main power source in the hydraulic drive system and is mounted on the rear part of the upper swing body 3. The engine 11 rotates constantly at a predetermined target rotation speed under the control of an engine controller (ECM: Engine Control Module) 30C described later. The engine 11 is, for example, a diesel engine that uses light oil as fuel, and drives the main pump 14 and the pilot pump 15 via a speed reducer 13. Further, the engine 11 drives the motor generator 12 via the speed reducer 13 to cause the motor generator 12 to generate electricity.

The speed reducer 13 is mounted on the rear part of the upper swing body 3, for example, and the main pump 14 and the pilot pump 15 are coaxially connected in series with two input shafts to which the engine 11 and the motor generator 12 described later are connected. It has one output shaft. The speed reducer 13 can transmit the power of the engine 11 and the motor generator 12 to the main pump 14 and the pilot pump 15 at a predetermined reduction ratio. Further, the speed reducer 13 can distribute and transmit the power of the engine 11 to the motor generator 12, the main pump 14, and the pilot pump 15 at a predetermined reduction ratio.

The main pump 14 (an example of a hydraulic pump) is mounted at the rear of the upper swing body 3 and supplies hydraulic oil to the control valve 17 through the high-pressure hydraulic line 16. The main pump 14 is driven by the engine 11, or the engine 11 and the motor generator 12. The main pump 14 is, for example, a variable displacement hydraulic pump, and a regulator (not shown) controls the angle (tilt angle) of the swash plate under the control of the excavator controller 30A described later. As a result, the main pump 14 can adjust the stroke length of the piston and control the discharge flow rate (discharge pressure).

The control valve 17 is a hydraulic control device mounted in the central portion of the upper swing body 3 and controls the hydraulic drive system in response to the operation of the operating device 26 by the operator. As described above, the control valve 17 is connected to the main pump 14 via the high-pressure hydraulic line 16, and the hydraulic oil supplied from the main pump 14 is used as a hydraulic actuator for the traveling hydraulic motors 1A (for right) and 1B (for left). ), The boom cylinder 7, the arm cylinder 8, and the bucket cylinder 9 can be supplied. Specifically, the control valve 17 is a valve unit including a plurality of hydraulic control valves (direction switching valves) that control the flow rate and flow direction of hydraulic oil supplied from the main pump 14 to each of the hydraulic actuators.

<Electric drive system of excavator>
The electric drive system of the excavator according to the present embodiment includes a motor generator 12, a current sensor 12s1, a voltage sensor 12s2, and an inverter 18A. Further, the electric drive system of the excavator according to the present embodiment includes a turning electric motor 21, a current sensor 21s, a resolver 22, a mechanical brake 23, a turning reducer 24, and an inverter 18B.

The motor generator 12 (an example of the motor) is an assist power source for the hydraulic drive system, and is mounted on the rear portion of the upper swing body 3. The motor generator 12 is, for example, an IPM (Interior Permanent Magnet) motor. Further, the motor generator 12 is not equipped with a predetermined sensor, specifically, a sensor for detecting the rotation angle of the rotating shaft (for example, a rotary encoder, a resolver, etc.). The motor generator 12 is connected to the power storage system 120 including the capacitor 19 and the turning electric motor 21 via the inverter 18A. The motor generator 12 is driven by three-phase AC power supplied from the capacitor 19 and the turning electric motor 21 via the inverter 18A, and assists the engine 11, and the main pump 14 and the pilot via the speed reducer 13. Drive the pump 15. Further, the motor generator 12 is driven by the engine 11 to perform power generation operation, and the generated power can be supplied to the capacitor 19 and the turning electric motor 21. The switching control between the power running operation and the power generation operation of the motor generator 12 may be realized by the inverter 18A under the control of the hybrid controller (hereinafter, “HB controller”) 30B described later.

The current sensor 12s1 detects the current of each of the three phases (U phase, V phase, W phase) of the motor generator 12. The current sensor 12s1 is provided, for example, in the power path between the motor generator 12 and the inverter 18A. The detection signals corresponding to the currents of each of the three phases of the turning motor 21 detected by the current sensor 12s1 are directly taken into the inverter 18A through a one-to-one communication line or an in-vehicle network such as CAN (Controller Area Network). Is done. Further, the detection signal may be taken into the HB controller 30B through a one-to-one communication line or an in-vehicle network such as CAN, and input to the inverter 18A via the HB controller 30B.

The inverter 18A (an example of a control device) drives and controls the motor generator 12 under the control of the HB controller 30B. The inverter 18A is, for example, a conversion circuit that converts DC power into three-phase AC power or converts three-phase AC power into DC power, a drive circuit that switches the conversion circuit, and a control that defines the operation of the drive circuit. It includes a control circuit that outputs a signal (for example, a PWM (Pulse Width Modulation) signal).

Specifically, the control circuit of the inverter 18A sequentially bases the motor generator 12 based on the detection signal of the current sensor 12s1 (that is, the current measurement value of the motor generator 12) and the voltage command value Vcom of the motor generator 12. The rotation angle of the rotation axis of the above may be estimated. For example, the control circuit estimates the rotation angle, rotation speed, and the like of the rotation shaft of the motor generator 12 based on a known Extended Electromotive Force (EEFM) model. Further, the control circuit performs the known dead time compensation for compensating for the dead time error between the voltage command value Vcom of the motor generator 12 and the actual voltage value of the motor generator 12, while performing the motor generator 12 Estimate the rotation angle, rotation speed, etc. Then, the control circuit controls the drive of the motor generator 12 (hereinafter, "sensorless control") while grasping the operating state of the motor generator 12 based on the estimated values of the rotation angle and the rotation speed that are sequentially derived. You may go. As a result, the motor generator 12 does not need to be provided with a sensor (for example, a rotary encoder or the like) for detecting the rotation angle and the rotation position. Therefore, the number of sensors can be reduced, the cost of the excavator can be suppressed, and detection defects due to dirt on the sensor can be suppressed. Further, in the sensorless control, since the voltage command value Vcom is used instead of the voltage measurement value of the motor generator 12, the number of sensors can be further reduced, the cost of the excavator can be suppressed, and the detection failure due to the dirt on the sensor can be suppressed. Etc. can be suppressed.

At least one of the drive circuit and the control circuit of the inverter 18A may be provided outside the inverter 18A (for example, the HB controller 30B (an example of a control device)).

The turning electric motor 21 is provided in a turning mechanism 2 that connects between the lower traveling body 1 and the upper turning body 3, and under the control of the HB controller 30B, power running operation and regenerative power for turning and driving the upper turning body 3 Is generated to perform a regenerative operation in which the upper swing body 3 is swiveled and braked. The swivel motor 21 is connected to the power storage system 120 via the inverter 18B, and is driven by the three-phase AC power supplied from the capacitor 19 and the motor generator 12 via the inverter 18B. Further, the turning motor 21 supplies regenerative power to the capacitor 19 and the motor generator 12 via the inverter 18B. As a result, the capacitor 19 can be charged and the motor generator 12 can be driven by the regenerative power. The switching control between the power running operation and the regenerative operation of the turning electric motor 21 may be realized by the inverter 18B under the control of the HB controller 30B. A resolver 22, a mechanical brake 23, and a turning speed reducer 24 are connected to the rotating shaft 21A of the turning electric motor 21.

The current sensor 21s detects the currents of the three phases (U phase, V phase, and W phase) of the swivel motor 21. The current sensor 21s is provided, for example, in the power path between the turning electric motor 21 and the inverter 18B. The detection signal corresponding to the current of each of the three phases of the turning electric motor 21 detected by the current sensor 21s may be directly taken into the inverter 18B through a one-to-one communication line or an in-vehicle network such as CAN. Further, the detection signal may be taken into the HB controller 30B through a one-to-one communication line or an in-vehicle network such as CAN, and input to the inverter 18B via the HB controller 30B.

The resolver 22 detects the rotation position (rotation angle) of the turning electric motor 21 and the like. The detection signal corresponding to the rotation angle detected by the resolver 22 may be directly taken into the inverter 18B through a one-to-one communication line, an in-vehicle network such as CAN, or the like. Further, the detection signal may be taken into the HB controller 30B through a one-to-one communication line or an in-vehicle network such as CAN, and input to the inverter 18B via the HB controller 30B.

The mechanical brake 23 mechanically generates a braking force with respect to the rotating shaft 21A of the turning electric motor 21 under the control of the HB controller 30B. As a result, the mechanical brake 23 can perform turning braking of the upper turning body 3 and maintain the stopped state of the upper turning body 3.

The swivel reducer 24 is connected to the rotating shaft 21A of the swivel motor 21 and reduces the output (torque) of the swivel motor 21 at a predetermined reduction ratio to increase the torque and swivel the upper swivel body 3. Drive. That is, during the power running operation, the turning electric motor 21 turns and drives the upper turning body 3 via the turning speed reducer 24. Further, the turning speed reducer 24 increases the inertial rotational force of the upper turning body 3 and transmits it to the turning electric motor 21 to generate regenerative power. That is, during the regenerative operation, the turning electric motor 21 regenerates power by the inertial rotational force of the upper turning body 3 transmitted via the turning speed reducer 24, and turns and brakes the upper turning body 3.

The inverter 18B drives and controls the turning electric motor 21 under the control of the HB controller 30B. The inverter 18B is, for example, a conversion circuit that converts DC power into three-phase AC power or converts three-phase AC power into DC power, a drive circuit that switches the conversion circuit, and a control that defines the operation of the drive circuit. It includes a control circuit that outputs a signal (for example, a PWM signal).

Specifically, the control circuit of the inverter 18B performs speed feedback control and torque feedback control on the turning electric motor 21 based on the detection signals of the current sensor 21s and the resolver 22.

<Excavator storage system>
The excavator storage system 120 according to the present embodiment includes a capacitor 19, a buck-boost converter 100, and a DC bus 110. The power storage system 120 is mounted on the front right side of the upper swing body 3 together with the inverters 18A and 18B of the electric drive system, for example.

The capacitor 19 is an example of a power storage device that supplies electric power to the motor generator 12 and the turning electric motor 21 and charges the generated electric power of the motor generator 12 and the turning electric motor 21. Further, a relay (hereinafter referred to as “breaking relay”) that cuts off between the capacitor 19 and the main circuit on the load side including the buck-boost converter 100 is provided. As a result, the capacitor 19 is disconnected from the main circuit under the control of the HB controller 30B when the excavator is stopped or when the excavator is abnormal (for example, when an accident such as a fall occurs). Therefore, it is possible to suppress a situation in which a very large short-circuit current flows through the capacitor 19 due to an abnormality when the operator is absent or an abnormality when the operator is present. The cutoff relay is provided, for example, in the power paths on both the positive electrode side and the negative electrode side between the capacitor 19 and the buck-boost converter 100.

The buck-boost converter 100 boosts the power of the capacitor 19 and outputs it to the DC bus 110, or lowers the power supplied to the DC bus 110 and stores it in the capacitor 19. The buck-boost converter 100 switches between a step-up operation and a step-down operation so that the voltage value of the DC bus 110 falls within a certain range according to the operating state of the motor generator 12 and the turning electric motor 21. The switching control between the step-up operation and the step-down operation of the step-up / down converter 100 may be realized by the HB controller 30B based on the voltage detection value of the DC bus 110, the voltage detection value of the capacitor 19, and the current detection value of the capacitor 19.

The DC bus 110 is provided between the inverters 18A and 18B and the buck-boost converter 100, and controls the transfer of electric power between the capacitor 19, the motor generator 12, and the turning motor 21.

<Excavator operation system>
The shovel operation system according to the present embodiment includes a pilot pump 15, an operation device 26, a pressure sensor 29, and the like.

The pilot pump 15 is mounted on the rear portion of the upper swing body 3 and supplies the pilot pressure to the operating device 26 via the pilot line 25. The pilot pump 15 is, for example, a fixed-capacity hydraulic pump, and is driven by the engine 11, or the engine 11 and the motor generator 12.

The operating device 26 includes, for example, levers 26A and 26B and a pedal 26C. The operation device 26 is provided near the driver's seat of the cabin 10, and the operator operates each driven element (for example, the lower traveling body 1, the upper turning body 3, the boom 4, the arm 5, the bucket 6, and the like). It is an operation input means for. In other words, the operating device 26 is a hydraulic actuator (for example, traveling hydraulic motors 1A and 1B, boom cylinder 7, arm cylinder 8, bucket cylinder 9, etc.) and an electric actuator (swivel electric motor 21) for driving each driven element. Etc.) is an operation input means for performing the operation. The operating device 26 (lever 26A, 26B, and pedal 26C) is connected to the control valve 17 via the hydraulic line 27. As a result, a pilot signal (pilot pressure) corresponding to the operating state of the lower traveling body 1, the boom 4, the arm 5, the bucket 6, and the like in the operating device 26 is input to the control valve 17. Therefore, the control valve 17 can drive each hydraulic actuator according to the operating state of the operating device 26. Further, the operating device 26 is connected to the pressure sensor 29 via the hydraulic line 28.

The operating device 26 may be of an electric type. In this case, in the figure, the pressure sensor 29 is replaced with an electric operating device 26, and the hydraulic pilot operating device 26 is replaced with a proportional valve that operates in response to a control command from the excavator controller 30A. The electric operation device 26 outputs an electric signal corresponding to the operation content (for example, the operation direction and the operation amount), and the electric signal is taken into the excavator controller 30A. Then, the excavator controller 30A outputs a control command corresponding to the electric signal input from the operation device 26, that is, a control command corresponding to the operation content of the operation device 26 to the proportional valve. As a result, the pilot pressure corresponding to the operation content of the operation device 26 is input to the control valve 17 from the proportional valve.

As described above, the pressure sensor 29 is connected to the operating device 26 via the hydraulic line 28, and the pilot pressure on the secondary side of the operating device 26, that is, the pilot pressure corresponding to the operating state of each operating element in the operating device 26. Is detected. The pressure sensor 29 is connected to the excavator controller 30A, and the pressure signal (pressure detection value) according to the operating state of the lower traveling body 1, the upper swinging body 3, the boom 4, the arm 5, the bucket 6 and the like in the operating device 26 is displayed. , Is taken into the excavator controller 30A.

<Excavator control system>
The shovel control system according to this embodiment includes a control device 30 and a starter motor 11st.

The control device 30 includes an excavator controller 30A, an HB controller 30B, and an engine controller 30C.

The functions of the excavator controller 30A, the HB controller 30B, the engine controller 30C, and the like may be realized by arbitrary hardware or a combination of hardware and software. For example, the excavator controller 30A, the HB controller 30B, the engine controller 30C, and the like include a CPU (Central Processing Unit), a memory device (main storage device) such as a RAM (Random Access Memory), and a ROM (Read Only Memory). It may be composed mainly of a non-volatile auxiliary storage device and a microcomputer including an I / O (Input-Output) interface device and the like.

The excavator controller 30A cooperates with various controllers including the HB controller 30B and the engine controller 30C to perform various controls related to the excavator. For example, the excavator controller 30A may integrally control the operation of the entire excavator (various devices mounted on the excavator) based on bidirectional communication with various controllers such as the HB controller 30B and the engine controller 30C.

The HB controller 30B controls the drive of the electric drive system based on various information input from the excavator controller 30A (for example, the detected value of the pressure sensor 29 corresponding to the operating state of the operating device 26). For example, the HB controller 30B drives the inverter 18A based on the detection value corresponding to the operating state of the operating device 26 detected by the pressure sensor 29, and determines the operating state (power running operation and power generation operation) of the motor generator 12. Perform switching control. Further, for example, the HB controller 30B drives the inverter 18B based on the detection value corresponding to the operating state of the operating device 26 detected by the pressure sensor 29, and drives the operating state (power running operation and regenerative operation) of the turning electric motor 21. ) Is switched. Further, for example, the HB controller 30B drives the buck-boost converter 100 based on the detection value corresponding to the operating state of the operating device 26 detected by the pressure sensor 29, and the step-up / down operation of the buck-boost converter 100 and the step-down operation. In other words, switching control between the discharged state and the charged state of the capacitor 19 is performed.

The engine controller 30C drives the engine 11 based on various information input from the excavator controller 30A (for example, a control command including the set rotation speed of the engine 11 and the operation mode of the excavator corresponding to the set rotation speed of the engine 11). Take control. Specifically, the engine controller 30C realizes drive control of the engine 11 by outputting a control command to an actuator such as a starter motor 11st to be controlled or a fuel injection device of the engine 11.

The starter motor 11st is operated by electric power from an auxiliary battery (for example, a lead storage battery) (not shown), and under the control of the engine controller 30C, the crankshaft of the engine 11 is forcibly rotated to start the engine 11. Specifically, the starter motor 11st does not perform detailed control regarding the rotation speed, the rotation position, etc. as in the case of the motor generator 12, and assists the engine 11 with a relatively smaller assist level than the motor generator 12. By doing so, the engine 11 is started.

[Details of motor generator control method]
Next, with reference to FIG. 3, the details of the control method of the motor generator 12 by the inverter 18A (control circuit) will be described.

FIG. 3 shows a high-speed state in which the rotation speed is relatively high, a high-load state in which the load is relatively high (hereinafter, collectively referred to as “high-speed / high-load state”), and a low-speed state and load in which the rotation speed is relatively low. It is a figure explaining the current state of the motor generator 12 in both the relatively low low load states (hereinafter collectively, "low speed and low load states"). Specifically, FIG. 3 shows the current vector of the dq axis (hereinafter, simply “current vector”) (graph 310), the low speed state, and the low speed state of the motor generator 12 in both the high speed / high load state and the low speed / low load state. It is a figure which shows the time change (graph 320) of the current (hereinafter, "phase current") of each phase (U phase, V phase, W phase) of the motor generator 12 in both high speed states.

In the graph 310, the current vector 312 represents the high speed / high load state of the motor generator 12, and the current vector 313 represents the low speed / low load state of the motor generator 12. Further, in the graph 320, the time series 322 represents the time change of the phase current in the high speed and high load state of the motor generator 12, and the time series 323 is the time of the phase current in the low speed and low load state of the motor generator 12. Represents change.

Like the current vectors 312 and 313, the inverter 18A (control circuit) generates electric power in a manner of changing the magnitude of the current vector defined in a certain direction, that is, the magnitudes of the d-axis current and the q-axis current. Drive control of the machine 12 is performed. In other words, as in the time series 322 and 323, the inverter 18A (control circuit) usually controls the drive of the motor generator 12 in a manner of changing the amplitude of the phase current in a certain phase. Hereinafter, the control mode will be referred to as "normal control" for convenience.

When the phase current and the phase voltage become relatively small corresponding to the low speed and low load state of the motor generator 12, the effect of dead time compensation is generally relatively low. For example, the region 321 of the graph 320 corresponds to the amplitude of the phase current in which the effect of the dead time compensation is relatively low and the accuracy as the sensorless control using the voltage command value Vcom cannot be ensured by the normal dead time compensation. ..

On the other hand, in this example, as shown in Graph 310, the inverter 18A is a motor generator corresponding to the torque command value Tcom generated in the control process when the phase current and the phase voltage reach the level of entering the region 321. The direction of the current vector is adopted so that the phase current and the phase voltage become relatively large while maintaining the torque of 12. Specifically, the inverter 18A is desired so that the phase voltage (maximum value) becomes equal to or higher than the predetermined threshold voltage Vth (in other words, a larger phase current corresponding to the predetermined threshold voltage Vth flows). The d-axis current is increased with reference to the current vector (for example, current vector 313) during normal control along the equal torque line 311 corresponding to the torque, that is, the torque command value Tcom of the motor generator 12, and the q-axis. Reduce the current (eg, current vector 314). In other words, as shown in Graph 320, the inverter 18A usually keeps the desired torque (that is, the torque command value Tcom) so that the phase voltage (maximum value) becomes equal to or higher than the predetermined threshold voltage Vth. The phase of the phase current is changed with reference to the time of control (time series 323) (time series 324). As a result, it is possible to secure an accuracy equal to or higher than the minimum dead time compensation required for sensorless control even at low speed and low load. Therefore, for example, at low speeds and low loads, the motor generator in sensorless control does not need to adopt a complicated dead time compensation algorithm or improve the hardware of the inverter 18A to shorten the dead time itself. It is possible to suppress a decrease in the estimation accuracy of the rotation angle of 12. Hereinafter, the control mode will be referred to as "low speed / low load control" for convenience.

The equal torque line 311 represents the case where the motor generator 12 is an IPM motor, and when the motor generator 12 is an SPM (Surface Permanent Magnet) motor, the equal torque line 311 is substantially parallel to the d-axis. .. That is, when the motor generator 12 is an SPM motor, the inverter 18A only needs to increase the d-axis current with reference to the current vector during normal control when shifting from normal control to low-speed / low-load control.

For example, when the charge amount of the capacitor 19 approaches a predetermined target value to some extent, the applied voltage of the motor generator 12 relatively decreases, and its torque (that is, current) approaches zero. In this case, if the above-mentioned normal control is continued, the estimation error of the rotation angle becomes relatively large, so that the motor generator 12 can output a desired torque (that is, a torque corresponding to the torque command value Tcom). However, there is a possibility that the speed of the motor generator 12 will pulsate. As a result, the motor generator 12 is in an unstable state in which the charge amount of the capacitor 19 cannot be quickly reached to the target value, the motor generator 12 makes a roaring sound, and the like. Can occur. On the other hand, in the inverter 18A, when the charge amount of the capacitor 19 approaches the target value to some extent and the applied voltage of the motor generator 12, that is, the voltage command value Vcom falls below the threshold voltage Vth, the motor generator Twelve control modes are switched from normal control to low-speed / low-load control. As a result, it is possible to suppress the occurrence of an unstable state of the motor generator 12 as described above.

[Control processing related to motor generator]
Next, the control process of the motor generator 12 by the inverter 18A (control circuit) will be described with reference to FIG.

FIG. 4 is a flowchart schematically showing an example of control processing relating to the electric generator 12 by the inverter 18A (control circuit). Specifically, FIG. 4 is a specific example of a control process for switching between the above-mentioned normal control and low-speed / low-load control. The process according to this flowchart may be repeatedly executed at predetermined control cycles, for example, from the start of the shovel (specifically, after the initial process after the start is completed) to the stop.

In step S102, the inverter 18A (control circuit) determines whether or not the voltage command value Vcom generated in the control process is equal to or higher than the predetermined threshold voltage Vth. The inverter 18A proceeds to step S104 when the voltage command value Vcom is equal to or higher than the predetermined threshold voltage Vth, and proceeds to step S106 in other cases (that is, when the voltage command value Vcom is lower than the predetermined threshold voltage Vth). ..

In step S104, the inverter 18A sets the control mode of the motor generator 12 to normal control, and ends the current process.

On the other hand, in step S106, the inverter 18A sets the control mode of the motor generator 12 to low speed / low load control, and ends the current process.

[Action of the present embodiment]
Next, the operation of the excavator (inverter 18A) according to the present embodiment will be described.

In the present embodiment, the control circuit of the inverter 18A controls so that the voltage of the motor generator 12 becomes relatively high even in a low speed state where the speed is relatively low. Further, under the control of the control circuit of the inverter 18A, the motor generator 12 operates so that the current phases are different between the low speed state where the speed is relatively low and the high speed state where the speed is relatively high. To do.

As a result, the control circuit of the inverter 18A can prevent the voltage of the motor generator 12 from becoming too low. Therefore, the control circuit of the inverter 18A can suppress the influence of the dead time of the conversion circuit of the inverter 18A. This is because, as described above, the influence of the dead time of the conversion circuit of the inverter 18A becomes large when the phase current and the phase voltage of the motor generator 12 are relatively low and in a low speed / low load state.

Further, in the present embodiment, the control circuit of the inverter 18A may control the current of the motor generator 12 so that the voltage of the motor generator 12 becomes equal to or higher than a predetermined threshold voltage Vth.

As a result, the control circuit of the inverter 18A can specifically prevent the voltage of the motor generator 12 from becoming lower than the predetermined threshold voltage Vth.

Further, in the present embodiment, the control circuit of the inverter 18A may control the d-axis current of the motor generator 12 so as to be relatively large when the voltage of the motor generator 12 falls below the threshold voltage Vth.

As a result, the control circuit of the inverter 18A can keep the voltage of the motor generator 12 high to some extent while suppressing the influence on the torque.

Further, in the present embodiment, the control circuit of the inverter 18A corresponds to the torque to be output by the motor generator 12 (that is, the torque command value Tcom) when the voltage of the motor generator 12 falls below a predetermined threshold voltage Vth. The d-axis current of the motor generator 12 may be controlled to be relatively large while maintaining the torque).

As a result, the control circuit of the inverter 18A can specifically keep the voltage of the motor generator 12 high to some extent while preventing the influence on the torque.

Further, in the present embodiment, the control circuit of the inverter 18A makes the d-axis current of the motor generator 12 relatively large when the voltage of the motor generator 12 falls below a predetermined threshold voltage Vth, and The q-axis current may be controlled to be relatively small.

As a result, when the motor generator 12 is an IPM motor, the inverter 18A can keep the voltage of the motor generator 12 high to some extent while specifically preventing the influence on the torque.

[Transform / Change]
Although the embodiments for carrying out the present invention have been described in detail above, the present invention is not limited to such specific embodiments, and various aspects are within the scope of the gist of the present invention described in the claims. Can be transformed / changed.

Further, in the above-described embodiments and modifications, an arbitrary electric motor (for example, an arbitrary work machine (for example, an industrial vehicle, a forklift, a crane, etc.) including an electric motor as a power source of a hydraulic drive system) is adopted instead of the excavator. You may.

Further, in the control method of the motor generator 12 (that is, the method of switching between low speed / low load control and normal control, etc.) in the above-described embodiment and modification, the voltage command value is used instead of the voltage measurement value. It may be applied to any motor in which the sensorless control is implemented. For example, the above-mentioned control method may be adopted for a drive motor mounted on a hybrid vehicle.

11 Engine 12 Motor generator (motor)
12s1 Current sensor 14 Main pump 18A Inverter (control device)
30 Controller 30A Excavator Controller 30B Hybrid Controller 30C Engine Controller

Claims (6)

With an electric motor
A control device for controlling the electric motor is provided.
The control device controls so that the voltage of the electric motor becomes relatively high even in a low speed state where the speed is relatively low.
Work machine. The control device controls the current of the electric motor so that the voltage of the electric motor becomes equal to or higher than a predetermined threshold value.
The work machine according to claim 1. The control device controls the d-axis current of the electric motor to be relatively large when the voltage of the electric motor falls below the predetermined threshold value.
The work machine according to claim 2. When the voltage of the electric motor falls below the predetermined threshold value, the control device controls the d-axis current of the electric motor so as to be relatively large while maintaining the torque to be output by the electric motor.
The work machine according to claim 3. When the voltage of the electric motor falls below the predetermined threshold value, the control device controls the d-axis current of the electric motor to be relatively large and the q-axis current to be relatively small.
The work machine according to claim 3 or 4. Equipped with an electric motor
The electric motor has a different current phase between a low speed state in which the speed is relatively low and a high speed state in which the speed is relatively high.
Work machine.

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