Motor drive control method and system

Abstract

A motor drive control method for controlling a speed of a motor to follow a speed command value with a speed actual value of the motor. The method includes the steps of driving the motor based on the speed command value by repeating an on-interval in which a torque is generated in the motor and an off-interval in which the torque is not generated in the motor at a predetermined cycle, wherein in the driving step, a phase voltage is applied only to one of a plurality of phases of the motor by a pulse width modulation method in the on-interval.

Description

Technical Field

[0001] This invention relates to a motor drive control method and system. Background Technology

[0002] When fuel cell vehicles operate under conditions with low cooling performance, such as high-output operation during hot hill climbing, the fuel cell stack's operating temperature rises, and the moisture content of the supplied fuel decreases, causing the fuel cell stack to dry out. This results in a decrease in the stack's operating voltage at the same current. In this situation, a vicious cycle may occur where the decrease in stack voltage leads to an increase in the heat generated by the fuel cell stack, further raising the fuel cell's operating temperature.

[0003] To prevent a vicious cycle of rising fuel cell operating temperatures, a control technique has been applied in recent years to fuel cell systems used in vehicles to increase the relative humidity on the cathode side by increasing the air pressure supplied to the cathode. Therefore, it is necessary to further increase the compression ratio of the air compressor supplying air to the cathode side of the fuel cell stack.

[0004] Because a higher compression ratio of the air supplied to the cathode side of the fuel cell stack is required, the air compressor is designed to further increase its compression ratio and exhibit maximum efficiency at the maximum pressure operating point. This design improves compressor efficiency in the high-flow, high-compression-ratio range but results in reduced efficiency in the relatively low-flow range. Therefore, when driving in urban areas, the increased power consumption of the air compressor in the low-flow range, which is the primary driving range, negatively impacts the vehicle's fuel efficiency.

[0005] More specifically, since booster air compressors, which further increase the air compression ratio compared to existing atmospheric pressure blowers, require a further increase in the drive speed of the built-in motor, the difference in motor drive speed between the low and high flow ranges widens, making it difficult to improve the efficiency of the air compressor itself. Specifically, booster air compressors reduce motor inductance to ensure sufficient voltage margin as motor speed increases in the high-speed operating range, but this reduction in inductance leads to an increase in three-phase ripple current, thus reducing motor / inverter efficiency. Particularly in the low flow range where relatively low output is required, the increased current ripple due to the smaller three-phase current results in a significant reduction in efficiency. In other words, the three-phase ripple current, as a secondary component, does not contribute to motor torque; compared to the three-phase sinusoidal current component in the low flow range where motor torque is lower, the three-phase ripple current is relatively large, thus reducing motor / inverter efficiency compared to the high output range.

[0006] Furthermore, to achieve high-speed rotation, an airfoil bearing is used in the air compressor motor. This airfoil bearing needs to rotate at a speed above a predetermined speed to maintain lift. Therefore, if the airfoil bearing continuously drives the motor at a speed below the predetermined speed to maintain lift, there is a risk of the airfoil bearing burning out due to friction with the motor shaft. Therefore, to prevent the airfoil bearing from burning out, the air compressor has a minimum drive speed limit. Thus, even if the fuel cell needs to operate at low output, the air compressor is driven at a speed above the minimum drive speed to avoid unnecessary air supply, thereby reducing the efficiency of the fuel cell system itself.

[0007] To address these issues, Korean Patent Registration No. 10-1988088 (applicant: Hyundai Motor Co., Ltd.) proposes a technology for performing motor torque on / off control in the low-speed range. According to this patent, when the motor's drive torque is on, the inverter applies a control method: by controlling the pulse width modulation duty cycle determined by the controller, all phase switches of the motor are controlled, thereby applying a three-phase voltage to the motor. Compared to conventional methods that control the motor torque to be always on, the control method in this patent has a torque off range, thus preventing inverter switching losses, conduction losses, and current ripple losses, thereby improving efficiency.

[0008] The background description is provided only to enhance understanding of the background of this invention and should not be construed as an admission that it corresponds to prior art known to those skilled in the art. Summary of the Invention

[0009] This invention relates to a motor drive control method and system. Specific embodiments relate to a motor drive control method and system that can significantly improve motor efficiency by reducing inverter current ripple losses and switching losses in the low-speed drive range of a high-speed motor.

[0010] In view of the problems that have occurred in the prior art, embodiments of the present invention are proposed, and embodiments of the present invention provide a motor drive control method and system that can minimize the switching losses and current ripple losses of the inverter, perform control so that the motor designed to generate maximum efficiency at high speed repeatedly generates motor torque in an on-state interval and does not generate motor torque in a off-state interval at low speed, while controlling the inverter switching elements so that only a phase voltage corresponding to one phase of the motor is applied in the on-state interval.

[0011] An embodiment of the present invention provides a motor drive control method for controlling the motor speed so that the measured speed value of the motor follows the speed command value. The method includes the following steps: based on the speed command value, driving the motor by repeating an open interval in which torque is generated in the motor and a closed interval in which no torque is generated in the motor at a predetermined period, wherein in the driving step, during the open interval, a phase voltage is applied to only one phase of multiple phases of the motor by pulse width modulation.

[0012] According to an embodiment of the present invention, in the driving step, control can be performed to keep the phases of the motor in which no phase voltage is applied always on or always off during the on-extension interval.

[0013] According to an embodiment of the present invention, the start and end points of the opening interval can be determined before and after the time point when the q-axis in the rotating coordinate system of the motor intersects with the axis in the fixed coordinate system corresponding to a phase of the applied phase voltage.

[0014] According to an embodiment of the present invention, the driving step may include the following steps: determining a target phase among a plurality of phases of the motor that corresponds to a phase to which a phase voltage is to be applied during the opening interval; determining whether the q-axis in the rotating coordinate system of the motor is close to the axis corresponding to the target phase in the fixed coordinate system; and when the determination step determines that the q-axis in the rotating coordinate system of the motor is close to the axis corresponding to the target phase in the fixed coordinate system by a predetermined angle, applying a phase voltage to the target phase only by means of pulse width modulation during the time corresponding to the opening interval.

[0015] According to an embodiment of the present invention, in the step of applying phase voltage, control can be performed to keep the remaining phases other than the target phase always on or always off during the time corresponding to the on interval.

[0016] According to an embodiment of the present invention, the start and end points of the opening interval can be determined before and after the time point when the q-axis in the rotating coordinate system of the motor intersects with the axis in the fixed coordinate system corresponding to a phase of the applied phase voltage.

[0017] According to an embodiment of the invention, during the driving step, control can be performed to make the drive current supplied to the motor substantially zero during the off interval.

[0018] According to an embodiment of the present invention, during the driving step, the switching elements included in the inverter that supply drive current to the motor can be disconnected (off) during the off interval.

[0019] According to an embodiment of the present invention, in the driving step, the switching elements included in the inverter that apply the driving voltage to the motor can be controlled so that the driving voltage applied to the motor in the off interval is substantially equal to the back electromotive force of the motor.

[0020] Additionally, embodiments of the present invention provide a motor drive control system, comprising: a speed controller that determines a current command value for driving the motor so that a measured value of the motor speed follows the speed command value; a current controller that determines a voltage command value for driving the motor so that a measured value of the motor drive current actually supplied to the inverter of the motor follows the current command value; a voltage output converter that converts the voltage command value and performs on / off control of switching elements included in the inverter based on the voltage command value; and a torque on / off determiner that determines whether to execute a torque on / off mode by repeatedly performing an on-off interval that generates torque in the motor and a off interval that does not generate torque in the motor at a predetermined period, wherein when the torque on / off determiner determines to execute the torque on / off mode, the voltage output converter controls the inverter to apply a phase voltage to only one phase of multiple phases of the motor in the on-off interval using pulse width modulation.

[0021] According to an embodiment of the present invention, when the torque on / off determiner determines to execute the torque on / off mode, the voltage output converter can control the inverter to keep the phases of the motor in which no phase voltage is applied always on or always off during the on-off interval.

[0022] According to an embodiment of the present invention, the start and end of the opening interval can be determined before and after the time point when the q-axis in the rotating coordinate system of the motor intersects with the axis in the fixed coordinate system corresponding to a phase of the applied phase voltage.

[0023] According to an embodiment of the present invention, when the torque on / off determination device determines to execute the torque on / off mode, the voltage output converter can control the switching element included in the inverter to apply the phase voltage only to the target phase through pulse width modulation within a preset time corresponding to the on-off interval, starting from the time point when the q-axis in the rotating coordinate system of the motor approaches the axis corresponding to the target phase in the fixed coordinate system at a predetermined angle, which corresponds to a phase of the phase voltage applied in the on-off interval.

[0024] According to an embodiment of the present invention, when the torque on / off determiner determines to execute the torque on / off mode, the voltage output converter can control the switching elements included in the inverter to make the drive current supplied to the motor substantially zero in the off interval.

[0025] According to an embodiment of the present invention, when the torque on / off determiner determines that the torque on / off mode is to be executed, the voltage output converter can disconnect the switching elements included in the inverter during the off interval.

[0026] According to an embodiment of the present invention, when the torque on / off determiner determines to execute the torque on / off mode, the voltage output converter can control the switching elements included in the inverter so that the drive voltage applied to the motor in the off interval is substantially equal to the back electromotive force of the motor.

[0027] According to an embodiment of the present invention, when the torque on / off determiner determines to execute the torque on / off mode, the speed controller can determine the current command value to be zero when the motor torque is off.

[0028] According to an embodiment of the present invention, when the speed command value or the current command value is within a preset range, the torque on / off determiner can determine the torque on / off mode.

[0029] According to the motor drive control method and system, the efficiency of a system using a motor can be improved by reducing the power consumption of the motor. In particular, in a fuel cell vehicle that includes an air compressor that uses a motor, the efficiency of the fuel cell system and the vehicle's fuel efficiency can be improved by reducing the power consumption of the air compressor.

[0030] Furthermore, according to the motor drive control method and system, no cost is incurred due to the addition of additional hardware, and the power consumption of the motor can be easily reduced by performing on / off control of the motor torque in a specific speed range or a specific torque range.

[0031] In particular, according to the motor drive control method and system, when performing motor torque on / off control, the maximum torque is obtained in the corresponding phase by using only one phase of the motor among multiple phases in the on-off interval that generates motor torque, thereby ensuring a reduction in inverter switching losses and current ripple losses.

[0032] Furthermore, according to the motor drive control method and system, not only can the efficiency of the motor be improved in a constant speed drive state, but also the efficiency can be improved in an acceleration / deceleration drive state.

[0033] The effects obtained in the embodiments of the present invention are not limited to the effects described above, and those skilled in the art can clearly understand other effects not mentioned above from the following description. Attached Figure Description

[0034] The above and other objects, features and advantages of the invention will become clearer from the following detailed description taken in conjunction with the accompanying drawings, wherein:

[0035] Figure 1 This is a block diagram schematically illustrating an example of a fuel cell system applying a motor drive control method and system according to an embodiment of the present invention;

[0036] Figure 2This is a block diagram illustrating a motor drive control system according to an embodiment of the present invention;

[0037] Figure 3 This is a flowchart illustrating a motor drive control method according to an embodiment of the present invention;

[0038] Figure 4 This is a graph illustrating the motor torque on / off control state applied to a motor drive control method according to an embodiment of the present invention;

[0039] Figure 5 This is a flowchart illustrating in more detail the steps of executing the torque on / off mode in a motor drive control method according to an embodiment of the present invention;

[0040] Figure 6 This is a diagram illustrating the state of each phase in the motor torque on-off interval and the motor torque off-off interval applied in the motor drive control method and system according to an embodiment of the present invention; and

[0041] Figure 7 This is a graph showing the relationship between the q-axis of the motor in the rotating coordinate system during the motor torque opening range, and one of the three phase axes through which the phase voltage is applied by pulse width modulation, in the motor drive control method and system according to an embodiment of the present invention. Detailed Implementation

[0042] In the following, a motor drive control method and system according to exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0043] Figure 1 This is a block diagram schematically illustrating an example of a fuel cell system applying a motor drive control method and system according to an embodiment of the present invention.

[0044] like Figure 1 As shown, the fuel cell system may include: a fuel cell stack 100, comprising fuel cell units that receive hydrogen as fuel and air as oxidant to generate electricity through an oxidation / reduction reaction; an air compressor 10 that supplies compressed air to the cathode of the fuel cell stack 100; and a humidifier 200 that supplies moisture to the compressed air in the air compressor 10 and delivers the compressed air to the fuel cell stack 100. Here, the humidifier 200 receives highly humid unreacted air discharged from the fuel cell stack 100 and provides moisture to the air supplied to the fuel cell stack 100.

[0045] As described in the background art, in order to prevent hydrogen from drying out due to the heat generated by the fuel cell stack when high output is required in the fuel cell stack 100, the compression ratio of the air supplied to the fuel cell stack 100 is increased. That is, the air flow rate is increased by operating the air compressor 10 at a higher speed to further supply humidified air to the fuel cell stack 100, thereby avoiding the drying phenomenon.

[0046] In order to control the air compressor 10, a controller 20 may be provided in the fuel cell system for controlling the air compressor 10, or more precisely, for controlling the motor included in the air compressor 10.

[0047] In describing the various embodiments of the present invention, a motor control method implemented in controller 20 for controlling the motor of air compressor 10 included in a fuel cell system, and a motor control system including air compressor 10 and controller 20 are used as application examples. However, the described application examples are not limited to air compressors in fuel cell systems, and the technology of the present invention can be widely applied to the control of various motors in other technical fields outside the field of fuel cells.

[0048] Figure 2 This is a block diagram of a motor drive control system according to an embodiment of the present invention.

[0049] Reference Figure 2 According to an embodiment of the present invention, a motor drive control system may include a speed controller 21, a current controller 23, a voltage output converter 25, an inverter 27, and a torque on / off determiner 29. Figure 2 In the middle, the motor and Figure 1 The air compressor is referred to by the same reference numeral "10". This is because the various embodiments of the invention are for controlling the drive of a motor, and in particular for controlling the drive of a motor included in an air compressor in a fuel cell system. Therefore, controlling the air compressor can be understood as substantially the same as controlling the motor of the air compressor. Furthermore, throughout this specification, controlling the air compressor can be understood as referring to the motor that controls the air compressor.

[0050] Speed ​​controller 21 receives speed commands for controlling the motor speed from a host controller (not shown), and generates and outputs current command values ​​(Id*, Iq*) for driving the motor based on the measured motor speed obtained by actually detecting the motor speed. Here, the host controller can be a controller for controlling a fuel cell system or a vehicle controller for controlling a vehicle using a fuel cell system. The host controller can determine the output of the fuel cell stack 100 based on vehicle speed, vehicle climb angle, accelerator opening operated by the driver, etc., and can determine the motor speed considering the output and temperature of the fuel cell stack 100. The host controller provides the determined motor speed as a speed command value to speed controller 21. Speed ​​controller 21 compares the received speed command value with the measured motor speed corresponding to the actual motor speed to generate and output current command values ​​(Id*, Iq*) so that the motor speed follows the speed command value.

[0051] Here, the current command values ​​(Id*, Iq*) are command values ​​for the drive current of motor 10. Generally, when controlling a motor, a target torque is set and the drive current of the motor is controlled so that the motor follows its target torque. Since the embodiments of the present invention are applied to controlling the speed of a motor, the speed controller 21 determines the target torque that the measured speed value can follow the speed command value based on the measured speed value and the speed command value, and generates current command values ​​corresponding to the target torque to control the motor to follow the target speed command value. More specifically, the current command values ​​(Id*, Iq*) output from the speed controller 21 can be the d-axis current command value and the q-axis current command value of the motor.

[0052] The speed controller 21 can employ control techniques that accumulate the error between the command value and the measured value by integrating the error and reflecting it in the control quantity, such as a proportional-integral (PI) controller. That is, the speed controller 21 can employ control techniques that integrate and reflect the error between the speed command and the actual speed of the motor 10. Besides PI control, the speed controller 21 can employ techniques such as proportional-integral-differential (PID) control, integral-proportional (IP) control, or IP-PI hybrid control.

[0053] Meanwhile, the motor 10 is equipped with a sensor 13 for detecting the position of the motor rotor, such as a Hall sensor or a rotary transformer. The measured speed value obtained by the sensor 13 detecting the actual rotational speed of the motor 10 is provided to the speed controller 21, thereby generating a current command value.

[0054] The current controller 23 executes control to make the current supplied to the motor from the inverter 27 follow the current command values ​​(Id*, Iq*), and outputs the d-axis and q-axis voltage command values ​​(Vd*, Vq*). The current controller 23 detects part or all of the current supplied to the motor 10 from the inverter 27 for each phase, and executes control to receive feedback of the measured values ​​of the drive current converted into d-axis and q-axis currents, and makes the measured values ​​of the drive current follow the current command values, i.e., the d-axis current command values ​​and the q-axis current command values ​​(Id*, Iq*).

[0055] Similar to the speed controller 21 described above, the current controller 23 can use control techniques that include integral processing for accumulating the error between the actual current supplied to the motor from the inverter 27 and the current command value (Id*, Iq*), such as PI control, PID control, IP control, IP-PI hybrid control, etc.

[0056] The voltage output converter 25 converts the d-axis voltage command value and the q-axis voltage command value (Vd*, Vq*) into a three-phase voltage command value through coordinate transformation (DQ<-> three-phase (abc)). Based on the converted three-phase voltage command value, it generates drive signals for driving the switching elements in the inverter 27 and provides them to the inverter 27. As the drive signals control the switching elements in the inverter 27, the inverter 27 outputs a three-phase current for driving the motor 10.

[0057] In addition, the voltage output converter 25 can convert the measured value of the three-phase drive current of the inverter 27, which is fed back to the current controller 23 for control, back into DQ current and provide it to the current controller 23.

[0058] Specifically, when it is determined that motor 10 needs to be controlled in a torque-on / off mode that repeatedly generates motor 10 torque during the on-off interval and does not generate motor 10 torque during the off-off interval at a predetermined period, voltage output converter 25 can control motor 10 to repeat the on-off interval and off-off interval at a preset time interval. Whether to enter the torque-on / off mode can be determined by torque-on / off determiner 29.

[0059] The torque on / off determiner 29 receives the speed command value provided to the speed controller 21 or the current command value (Id*, Iq*) generated by the speed controller 21, and determines to perform torque on / off when the speed command value or the current command value (Id*, Iq*) is within a preset range.

[0060] When the torque on / off determination unit 29 determines that the torque on / off of the motor 10 needs to be repeatedly executed, it can provide the determination result to the voltage output converter 25 and the current controller 23. The voltage output converter 25, receiving the determination result from the torque on / off determination unit 29, transmits a signal to the inverter 27 to control the switching elements in the inverter 27, thereby enabling the torque on / off of the motor 10. Furthermore, the current controller 23, receiving instructions from the torque on / off determination unit 29, is able to perform appropriate control during the torque off range.

[0061] The torque on / off control of the motor will become clearer from the following description of the motor drive control method according to an embodiment of the present invention.

[0062] Figure 3 This is a flowchart illustrating a motor drive control method according to an embodiment of the present invention. Figure 3 The illustrated embodiment relates to an example of performing motor torque on / off control when the motor speed command value or current command value is within a preset range. The features of embodiments of the invention that apply a torque on / off mode that repeatedly generates an on-off interval of motor torque and a off-off interval without generating motor torque at a predetermined period are not limited to... Figure 3 The specific conditions used in the example shown can be applied to motor drives, regardless of the magnitude of the speed command value or the current command value.

[0063] Reference Figure 3 When the motor 10 is in a stopped state (S11), when a non-zero speed command value is input to the speed controller 21 (S12), control for generating motor torque begins.

[0064] When the speed command value is input to the speed controller 21, the speed controller 21 derives current command values ​​(Id*, Iq*) and outputs them to the current controller 23. The current command values ​​(Id*, Iq*) are used to execute control so that the measured speed value of the motor 10 follows the speed command value. The current controller 23 derives and outputs voltage command values ​​(Vd*, Vq*) so that the measured current value corresponding to the value of the drive current directly detected from the inverter 27 to the motor 10 follows the current command values ​​(Id*, Iq*). The voltage output converter 25 converts the voltage command values ​​(Vd*, Vq*) of the DQ coordinates into three-phase (u-phase, v-phase, and w-phase) voltages and generates PWM switching signals for controlling the switching elements in the inverter 27 and outputs them to the inverter 27 to output each three-phase voltage.

[0065] The motor drive begins through a series of processes. According to an exemplary embodiment of the present invention, after the motor 10 is driven, the torque on / off determiner 29 monitors the speed command value or current command value to determine whether to execute the torque on / off mode (S131, S132). That is, when the speed command value is within a preset range (… Figure 3 (S131) ​​where the value is greater than zero and less than A (positive number) or the current command value is within the preset range. Figure 3 When the value in S132 is greater than zero and less than B (a positive number), the torque on / off determination unit 29 can determine to execute the torque on / off mode. Considering the rapid decrease in efficiency of high-speed air compressors in low-speed or low-torque ranges as described in the background art, the preset range corresponds to the low-speed or low-torque range where efficiency decreases. However, according to another embodiment of the present invention, the motor torque on / off can be controlled across the entire torque and speed range within which the motor can be driven, without considering the aforementioned range.

[0066] When the torque on / off determination unit 29 determines that the torque on / off mode needs to be executed, the torque on / off determination unit 29 can instruct the voltage output converter 25 to output a drive signal for controlling the on / off state of the switching elements included in the inverter 27 to execute the torque on / off mode, and the voltage output converter 25 can control the switching elements in the inverter 27 according to the instruction (S14).

[0067] Figure 4 This is a graph illustrating the motor torque on / off control state applied to a motor drive control method according to an embodiment of the present invention.

[0068] like Figure 4 As shown, according to an embodiment of the present invention, in Figure 3 In step S14, a torque on / off mode can be executed, in which the motor torque is generated repeatedly in an on-off interval D1 and the motor torque is not generated in a off-off interval D2 at a predetermined period. The time interval of the on-off interval D1, the time interval of the off-off interval D2, and the period of repeating the on-off interval D1 and the off-off interval D2 can be determined in advance by experimental methods to be values ​​that minimize power consumption for each motor speed inverter and ensure operational stability.

[0069] This torque on / off mode is preferably applied even when the load affecting motor 10 is small and the speed change due to inertia is minimal. When the load on motor 10 is large, since deceleration mainly occurs in the torque off range, the acceleration / deceleration of motor speed due to repeated torque on / off is large, which may lead to unnecessary energy loss. Therefore, the effectiveness of repeated torque on / off control is significantly reduced when the motor load is large. In particular, when the acceleration / deceleration of motor speed due to torque on / off control exceeds a predetermined level, there is a problem of increased power consumption of motor 10.

[0070] Furthermore, as the moment of inertia of motor 10 increases, the impact of on / off control on motor torque may increase. That is, when the moment of inertia of motor 10 is large, speed fluctuations are smaller even in the torque off range, thereby improving the efficiency of torque on / off control.

[0071] According to an embodiment of the present invention, as a specific technique for repetitive control of motor torque on / off, a technique is to apply a phase voltage to only one phase of the multiple phases of the motor 10 via pulse width modulation during the on-off interval D1 where motor torque is generated. When a phase voltage is applied to only one phase of the motor during the on-off interval D1 instead of multiple phases, the switching frequency of the switching elements in the inverter 27 can be relatively reduced. Conversely, since only one phase is used to drive the motor, it is preferable to perform control to generate maximum torque in the corresponding phase.

[0072] Figure 5 This is a flowchart illustrating in more detail the steps of executing the torque on / off mode in a motor drive control method according to an embodiment of the present invention. Figure 6 This is a diagram illustrating the state of each phase in the motor torque on-off interval and the motor torque off-off interval applied in the motor drive control method and system according to an embodiment of the present invention. Additionally, Figure 7 This is a graph showing the relationship between the q-axis of the motor in the rotating coordinate system during the motor torque opening range, and one of the three phase axes through which the phase voltage is applied by pulse width modulation, in the motor drive control method and system according to an embodiment of the present invention.

[0073] Reference Figures 5 to 7 This will provide a clearer understanding of the torque on / off mode of the motor drive control method according to embodiments of the present invention.

[0074] Reference Figure 5 The steps for controlling the motor in torque-on / off mode ( Figure 3S14) includes: a step of determining a target phase among multiple phases (u phase, v phase, and w phase) of the motor 10 as the phase to which a phase voltage is to be applied in the opening interval D1 (S141); a step of determining whether the q-axis in the rotating coordinate system of the motor is close to the axis corresponding to the target phase in the fixed coordinate system (S142); a step of applying a phase voltage to only the target phase by pulse width modulation within a time Δt corresponding to the preset opening interval D1 when it is determined that the q-axis in the rotating coordinate system of the motor is close to the axis corresponding to the target phase in the fixed coordinate system by a predetermined angle (S143); and a step of entering the closing interval D2 after time Δt (S145).

[0075] Generally, when performing space vector pulse width modulation (SPWM) control for motor control, in the motor's rotating coordinate system, the q-axis is the point where maximum torque is generated, and the d-axis is the point where no torque is generated. Utilizing this motor characteristic, such as... Figure 6 As shown, in step S143, when the q-axis in the rotating coordinate system of the motor approaches the target phase in the fixed coordinate system corresponding to a phase selected from the u-phase, v-phase, and w-phase ( Figure 6 The shaft of the u-phase is set to generate the motor torque opening interval D1, and pulse width modulation control is performed on the selected phase in the opening interval D1, so that the maximum torque can be generated on the selected phase.

[0076] In this case, the remaining phases, except for the selected phase, can be controlled to be always on or always off.

[0077] That is, such as Figure 7 As shown, the start time of the opening interval D1 can be the time when the q-axis in the rotating coordinate system rotates to approach the axis in the selected fixed coordinate system corresponding to one of the three phases by a predetermined angle, and the end time of the opening interval D1 can be the time when the q-axis in the rotating coordinate system rotates and passes through the axis in the fixed coordinate system corresponding to one of the three phases, deviating by a predetermined angle. Therefore, the start and end points of the opening interval D1 can be determined before and after the time point when the q-axis in the rotating coordinate system of the motor 10 intersects the axis in the fixed coordinate system corresponding to the target phase.

[0078] As described above, according to embodiments of the present invention, inverter switching control based on a predetermined pulse width modulation duty cycle is performed only on one target phase to generate a phase voltage corresponding to that phase during the on-state interval, and switching control is not performed on the remaining phases, thereby preventing inverter switching losses, conduction losses, and current ripple losses. That is, compared to a method that performs switching control on all multiple phases of the motor during the on-state interval D1, the efficiency of embodiments of the present invention can be significantly improved. Furthermore, since the switching control timing of the target phase is controlled such that the axis of the target phase of the motor is synchronized with the q-axis in the motor's rotating coordinate system, the maximum torque that can be implemented as the target phase can be generated, thereby preventing a decrease in speed following performance.

[0079] Refer again Figure 3 During the range where the motor torque is set to off, all switching elements included in inverter 27 are disconnected (100% duty cycle) to block the drive current supplied to the motor. That is, during the range where the motor torque remains off, voltage output converter 25 can output a control signal to inverter 27 to disconnect all switching elements.

[0080] The inverter 27, which provides the torque (drive current) for driving the three-phase motor, typically uses six switching elements (such as IGBTs) to implement a three-phase switched full-bridge circuit. The current controller 23 compares the current command value with the measured motor drive current and outputs a voltage command value (DQ coordinate) that reduces its error. The voltage output converter 25 converts the voltage command value into a three-phase voltage and determines the duty cycle of the switching elements so that the converted three-phase voltage can be applied to the motor 10, thereby performing on / off control of the switching elements for each phase.

[0081] In the motor drive control method according to an embodiment of the present invention, torque on / off control repeats on-time and off-time intervals at a predetermined period. Here, in the torque on-time interval, the inverter switching elements are controlled to apply a phase voltage to one of the multiple phases of the motor as described above, and in the torque off-time interval, all inverter switching elements are disconnected, thereby executing the torque on / off mode.

[0082] As another method for controlling the switching elements of inverter 27 in the torque off-range D2, an on / off control method can be applied to the switching elements of each phase in inverter 27 to generate a drive voltage with a voltage magnitude substantially equal to the back electromotive force generated in motor 10. When the back electromotive force of motor 10 is the same as the three-phase drive voltage of inverter 27, no potential difference occurs, and therefore a zero-current control state may occur where inverter 27 does not supply current to motor 10, i.e., a state in which no motor torque is generated.

[0083] When motor torque on / off control is executed, i.e., torque on / off mode (S14), during the motor torque off interval (S15), it is preferable to stop the integral control executed by the current controller 23 (S161). When the current controller 23 allows integration of the error between the command value and the measured value during the motor torque off interval, the integral error causes a large output to be applied from each controller at the time point when the torque is turned on again, resulting in system instability. Due to the changes in the speed command value and the current command value, the effect of torque on / off control will be severely hindered. Of course, during the motor torque on interval (S15), it is preferable for the current controller 23 to execute integral control (S162).

[0084] As another example, instead of stopping the integral control of the current controller 23 during the motor torque off-state interval, a method can be applied whereby the entire control operation is stopped and the current command value is output as zero during the motor torque off-state interval when the speed controller 21 changes the motor torque from on to off. That is, by making the speed controller 21 output the current command as zero to block the three-phase output, the integral operation in the current controller 23 due to the error between the current command value and the measured current is interrupted during the torque off-state interval when no torque or output is generated. Therefore, excessive output due to accumulated errors at the point when the motor torque restarts can be prevented. Of course, normal speed controller operation can be resumed when the motor torque changes from off to on. Since the operation of the speed controller 21 is stopped during the motor torque off-state interval, when the motor torque restarts, the output of the speed controller 21 remains at the output value before the motor torque was turned off, thus ensuring the stability of speed control without unnecessary acceleration and deceleration.

[0085] Simultaneously, when the motor speed exceeds the preset range or the current command output from the current controller 23 exceeds the preset range, the torque on / off determination unit 29 activates a typical control method, in which the three-phase drive current of the inverter 27 is determined based on the current command value, without executing the torque on / off mode (S17). As described above, when the speed of the motor 10 is equal to or higher than the preset speed, the load torque on the motor side increases (for example, in a fuel cell system, when the speed increases, the load torque of the air compressor increases due to the increase in flow and pressure). Therefore, the deceleration generated in the torque off range of the motor 10 should be compensated in the torque on range, resulting in unnecessary acceleration and deceleration. The resulting losses exceed the switching losses and three-phase current ripple losses reduced by the torque on / off control. When the current command value is equal to or higher than the preset value, it can be regarded as a rapid acceleration range or a high-speed rotation state. Therefore, compared with the typical continuous torque application method, the repetitive control method of motor torque on / off is less efficient.

[0086] As one scenario where the current command exceeds the preset range, regenerative braking torque may be applied to the motor. When regenerative braking is performed, the torque is applied in the opposite direction to the rotation direction, which is considered a negative torque state. Therefore, this can be considered a situation where the current command value exceeds... Figure 3 In step S132, the range is greater than 0 and less than B (a positive number). Even when the motor is decelerated to perform regenerative braking, it is preferable to stop the motor torque on / off control. This is because, in regenerative braking mode, recovering energy through continuous motor torque control is advantageous in terms of efficiency.

[0087] As described above, the motor drive control method and system according to various embodiments of the present invention can improve the efficiency of the system using the motor by reducing the power consumption of the motor. In particular, in a fuel cell vehicle that includes an air compressor that uses a motor, the efficiency of the fuel cell system and the fuel efficiency of the vehicle can be improved by reducing the power consumption of the air compressor.

[0088] Furthermore, the motor drive control methods and systems according to various embodiments of the present invention do not incur costs due to the addition of separate hardware, and the power consumption of the motor can be easily reduced by performing motor torque on / off control in a specific speed range or a specific torque range.

[0089] In particular, in the motor drive control method and system according to various embodiments of the present invention, when performing motor torque on / off control, by using only one phase of the multiple phases of the motor in the interval where the motor torque is generated to obtain the maximum torque in the corresponding phase, it is possible to ensure a reduction in inverter switching losses and current ripple losses and significantly improve efficiency.

[0090] Furthermore, based on the motor drive control method and system, not only can the efficiency of the motor be improved under constant speed drive conditions, but also the efficiency of the motor under acceleration / deceleration drive conditions can be improved.

[0091] Although the invention has been shown and described with respect to specific embodiments, it will be apparent to those skilled in the art that various modifications and changes can be made to the invention without departing from the spirit of the invention as provided in the appended claims.

Claims

1. A motor drive control method for controlling a motor speed to follow a speed command value with a speed actual value of the motor, the method comprising the steps of: driving the motor by repeating, at a predetermined cycle, an ON period in which a torque is generated in the motor and an OFF period in which no torque is generated in the motor, based on the speed command value, wherein in the driving step, a phase voltage is applied only to one phase of a plurality of phases of the motor by pulse width modulation in the ON period to obtain a maximum torque in the corresponding phase, wherein the driving step includes determining a target phase corresponding to the one phase to which the phase voltage is to be applied in the ON period among the plurality of phases of the motor; wherein a switching control time point of the target phase is controlled so that a shaft of the target phase is synchronized with a q-axis in a rotating coordinate system of the motor.

2. The method according to claim 1, wherein in the driving step, control is performed to always turn ON or always turn OFF a phase to which the phase voltage is not applied among the plurality of phases of the motor in the ON period.

3. The method according to claim 1, wherein a start point and an end point of the ON period are determined before and after, respectively, time points at which a q-axis in a rotating coordinate system of the motor intersects with an axis corresponding to the one phase to which the phase voltage is applied in a fixed coordinate system.

4. The method according to claim 1, wherein the driving step further includes the steps of: determining a target phase corresponding to the one phase to which the phase voltage is to be applied in the ON period among the plurality of phases of the motor; determining whether a q-axis in a rotating coordinate system of the motor is close to an axis corresponding to the target phase in a fixed coordinate system; and when it is determined that the q-axis in the rotating coordinate system of the motor is close to the axis corresponding to the target phase in the fixed coordinate system by a predetermined angle, applying the phase voltage only to the target phase by the pulse width modulation in a time corresponding to the ON period.

5. The method according to claim 4, wherein in the step of applying the phase voltage, control is performed to always turn ON or always turn OFF the remaining phases except for the target phase in the time corresponding to the ON period.

6. The method according to claim 4, wherein a start point and an end point of the ON period are determined before and after, respectively, time points at which the q-axis in the rotating coordinate system of the motor intersects with the axis corresponding to the one phase to which the phase voltage is applied in the fixed coordinate system.

7. The method according to claim 1, wherein in the driving step, control is performed to make a drive current supplied to the motor zero in the OFF period.

8. The method according to claim 7, wherein in the driving step, a switching element included in an inverter that supplies the drive current to the motor is turned OFF in the OFF period.

9. The method according to claim 7, wherein In the driving step, a switching element included in an inverter that controls application of a driving voltage to the motor is controlled so that the driving voltage applied to the motor in the off interval is equal to the counter electromotive voltage of the motor.

10. A motor drive control system comprising: a speed controller that determines a current command value of a driving current for driving a motor so that a speed actual value of the motor follows a speed command value of the motor; a current controller that determines a voltage command value for driving the motor so that a motor driving current actual value supplied to an inverter of the motor follows the current command value; a voltage output converter that converts the voltage command value and performs on / off control of a switching element included in the inverter based on the voltage command value; and a torque on / off determiner that determines whether to execute a torque on / off mode of driving the motor by repeating an on interval in which torque is generated in the motor and an off interval in which torque is not generated in the motor at a predetermined cycle, wherein when the torque on / off determiner determines to execute the torque on / off mode, the voltage output converter controls the inverter to apply a phase voltage to only one phase of a plurality of phases of the motor in the on interval by a pulse width modulation method to obtain maximum torque in the corresponding phase, wherein a target phase corresponding to the one phase to which the phase voltage is to be applied in the on interval is determined among the plurality of phases of the motor; wherein a switching control time point of the target phase is controlled so that a shaft of the target phase is synchronized with a q-axis in a rotating coordinate system of the motor.

11. The system according to claim 10, wherein when the torque on / off determiner determines to execute the torque on / off mode, the voltage output converter controls the inverter to always turn on or always turn off a phase of the plurality of phases of the motor to which the phase voltage is not applied in the on interval.

12. The system according to claim 10, wherein a start point and an end point of the on interval are determined to be before and after, respectively, time points at which a q-axis in a rotating coordinate system of the motor and an axis in a fixed coordinate system corresponding to the one phase to which the phase voltage is applied intersect.

13. The system according to claim 10, wherein when the torque on / off determiner determines to execute the torque on / off mode, the voltage output converter controls the switching element included in the inverter to apply the phase voltage to only the target phase by the pulse width modulation method within a predetermined time corresponding to the on interval from a time point at which the q-axis in the rotating coordinate system of the motor approaches the axis in the fixed coordinate system corresponding to the target phase corresponding to the one phase to which the phase voltage is applied in the on interval to a predetermined angle.

14. The system according to claim 10, wherein When the torque on / off determiner determines to execute the torque on / off mode, the voltage output converter controls the switching element included in the inverter to make the drive current supplied to the motor zero in the off interval.

15. The system according to claim 14, wherein When the torque on / off determiner determines to execute the torque on / off mode, the voltage output converter turns off the switching element included in the inverter in the off interval.

16. The system according to claim 14, wherein When the torque on / off determiner determines to execute the torque on / off mode, the voltage output converter controls the switching element included in the inverter to make the application of the drive voltage to the motor in the off interval equal to the counter electromotive force of the motor.

17. The system according to claim 14, wherein When the torque on / off determiner determines to execute the torque on / off mode, the speed controller determines the current command value to be zero when the motor torque is off.

18. The system according to claim 10, wherein When the speed command value or the current command value is within a predetermined range, the torque on / off determiner determines to execute the torque on / off mode.

19. A motor drive control method, comprising: determining a current command value of a drive current for driving a motor so that a speed actual value of the motor follows a speed command value of the motor; determining a voltage command value for driving the motor so that a motor drive current actual value supplied to an inverter of the motor follows the current command value; converting the voltage command value, and performing on / off control of a switching element included in the inverter based on the voltage command value; determining whether to execute a torque on / off mode of driving the motor by repeatedly in a predetermined cycle an on interval in which torque is generated in the motor and an off interval in which torque is not generated in the motor; and when it is determined to execute the torque on / off mode, controlling the inverter so that in the on interval a phase voltage is applied only to one phase of a plurality of phases of the motor by a pulse width modulation method, and so that in the on interval a phase in which the phase voltage is not applied among the plurality of phases of the motor is always on or always off to obtain maximum torque in the corresponding phase, wherein a target phase corresponding to the one phase to which the phase voltage is to be applied in the on interval is determined among the plurality of phases of the motor; wherein a switching control time point of the target phase is controlled so that a shaft of the target phase is synchronized with a q-axis in a rotating coordinate system of the motor.

20. The method according to claim 19, further comprising: a start point and an end point of the on interval are determined to be before and after a time point at which a q-axis in a rotating coordinate system of the motor and an axis corresponding to the one phase to which the phase voltage is applied in a fixed coordinate system intersect, respectively.

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