阅读说明：本技术 用于控制电动机的方法和控制系统 (Method and control system for controlling an electric motor ) 是由 高扬 于 2018-07-25 设计创作，主要内容包括：用于控制电动机(16)的方法,该方法包括：确定电动机(16)的计划参考速度(32)；基于计划参考速度(32)来确定脉冲宽度调制(PWM)开关频率；以及通过交流电流(24)来控制电动机(16),该交流电流(24)通过具有所确定的PWM开关频率的PWM开关来产生。还提供了用于控制电动机(16)的控制系统(12)和包括控制系统(12)的工业机器人(10)。(Method for controlling an electric motor (16), the method comprising: determining a planned reference speed (32) of the electric motor (16); determining a Pulse Width Modulation (PWM) switching frequency based on a planned reference speed (32); and controlling the electric motor (16) by means of an alternating current (24), the alternating current (24) being generated by means of PWM switching having the determined PWM switching frequency. A control system (12) for controlling the electric motor (16) and an industrial robot (10) comprising the control system (12) are also provided.)

1. A method for controlling an electric motor (16), the method comprising:

-determining a planned reference speed (32) of the electric motor (16);

-determining a Pulse Width Modulation (PWM) switching frequency based on the planned reference speed (32); and

-controlling the electric motor (16) with an alternating current (24), the alternating current (24) being generated by PWM switching having the determined PWM switching frequency.

2. The method of claim 1, wherein the determination of the PWM switching frequency comprises: a higher PWM switching frequency is determined if the planned reference speed (32) is relatively high, or a lower PWM switching frequency is determined if the planned reference speed (32) is relatively low.

3. The method according to claim 1 or 2, wherein the determination of the PWM switching frequency comprises: when the planned reference speed (32) is above a high speed threshold, a predetermined high PWM switching frequency is set.

4. The method according to any of the preceding claims, wherein the determination of the PWM switching frequency comprises: when the planned reference speed (32) is below a low speed threshold, a predetermined low PWM switching frequency is set.

5. The method of claim 4, wherein the determination of the PWM switching frequency comprises: setting a PWM switching frequency proportional to the planned reference speed (32) when the planned reference speed (32) is above the low speed threshold.

6. The method according to any of the preceding claims, wherein the determination of the PWM switching frequency comprises:

-predicting a load on the electric motor (16) based on the planned reference speed (32); and

-determining the PWM switching frequency based on the load on the motor (16).

7. The method of claim 6, wherein the prediction of the load on the motor (16) is based on a mathematical model of the motor (16).

8. The method of any of the preceding claims, further comprising: adjusting one or more control parameters of a drive unit (22) for outputting the alternating current (24) based on the planned reference speed (32).

9. The method according to any one of the preceding claims, wherein the method comprises:

-determining planned reference speeds (32) of a plurality of motors (16) of an industrial robot (10);

-determining, for each of the electric motors (16), a PWM switching frequency based on the planned reference speed (32) of the electric motor (16); and

-controlling each of the electric motors (16) with an alternating current (24), the alternating current (24) being generated by PWM switching having the determined PWM switching frequency.

10. A control system (12) for controlling an electric motor (16), the control system (12) comprising a data processing device (28) and a memory (30), the memory (30) having stored thereon a computer program comprising program code which, when executed by the data processing device (28), causes the data processing device (28) to carry out the steps of:

-determining a planned reference speed (32) of the electric motor (16);

-determining a Pulse Width Modulation (PWM) switching frequency based on the planned reference speed (32) of the electric motor (16); and

-controlling a drive unit (22) to output an alternating current (24) to the electric motor (16), the alternating current (24) being generated by PWM switching with the determined switching frequency.

11. An industrial robot (10) comprising a control system (12) according to claim 10 and a manipulator (14) with at least one motor (16).

12. An industrial robot (10) according to claim 11, wherein the electric motor (16) comprises at least six poles.

13. An industrial robot (10) according to claim 11 or 12, wherein the control system (12) comprises a path planner configured to determine the planned reference speed (32) of the motor (16).

Technical Field

The present invention generally relates to a method and a control system for controlling an electric motor. In particular, a method for controlling an electric motor is provided, wherein a Pulse Width Modulation (PWM) switching frequency is determined based on a planned reference speed of the electric motor, a control system for controlling the electric motor and an industrial robot comprising the control system are provided.

Background

A PWM controlled motor with a large number of poles requires a high PWM switching frequency. Today, such motors are controlled by a constant high PWM switching frequency. With a constant high PWM switching frequency, the motor may overheat. High PWM switching frequencies also lead to switching losses, electromagnetic compatibility (EMC) problems and higher costs. In some drive unit applications, a 50% to 150% increase in PWM switching frequency results in 50% to 150% increase in switching losses, higher EMC problems, and more than 50% increase in cost. However, a higher PWM switching frequency is only required when the speed of the motor is higher.

CN 102384118A discloses a speed regulation control method, equipment, a system and engineering mechanical equipment of an electro-hydraulic proportional valve. The method comprises the following steps: acquiring an actual speed of the hydraulic actuator element; when the difference between the actual speed and the expected speed is larger than the preset value, adjusting the frequency and/or the duty ratio of a PWM signal applied to the electro-hydraulic proportional valve according to the difference; calculating the frequency and/or amplitude of the dither signal according to the adjusted frequency and/or duty ratio of the PWM signal, and adjusting the calculated amplitude of the dither signal; the adjusted dither signal and the adjusted PWM signal are input to the electro-hydraulic proportional valve together.

Disclosure of Invention

It is an object of the present disclosure to provide a method for controlling an electric motor, which method improves the performance of the electric motor.

It is another object of the present disclosure to provide a method for controlling an electric motor that provides robust and/or smooth control of the electric motor.

Another object of the present disclosure is to provide a method for controlling an electric motor which extends the service life of the electric motor and/or the drive unit of the electric motor.

It is another object of the present disclosure to provide a method for controlling an electric motor that reduces the costs associated with the electric motor.

It is another object of the present disclosure to provide a method for controlling an electric motor that reduces EMC problems associated with the electric motor.

It is another object of the present disclosure to provide a method for controlling an electric motor that addresses some or all of the above objects.

It is another object of the present disclosure to provide a control system for controlling an electric motor that addresses one, some, or all of the above objects.

It is another object of the present disclosure to provide an industrial robot comprising a control system for controlling an electric motor, which industrial robot solves one, some or all of the above objects.

According to an aspect, there is provided a method for controlling an electric motor, the method comprising: determining a planned reference speed of the motor; determining a PWM switching frequency based on the planned reference speed; and controlling the motor by means of an alternating current, which alternating current is generated by means of a PWM switch having the determined PWM switching frequency.

The method constitutes a dynamic PWM switching frequency control method. By determining the PWM switching frequency based on the planned reference speed, no feedback from the motor is required to determine the PWM switching frequency. For several reasons, it is advantageous to determine the PWM switching frequency based on a planned reference speed rather than based on feedback from the motor. For example, the method thus provides a more robust control, and the control of the motor is not lost. Furthermore, disturbances in the feedback signal from the motor (such as measurement errors) can be avoided when determining the PWM switching frequency.

The method is based on the principle that: the planned reference speed (i.e. the prediction of the reference speed of the motor) is good enough to be used for determining the appropriate PWM switching frequency. However, feedback from the motor may be used for servo control of the motor and/or for monitoring the performance of the motor. For example, feedback from the position sensor may be used to calculate the current speed of the motor for various purposes.

When the motor is driven at the planned reference speed, the PWM switching frequency corresponding to the planned reference speed is used. In the present disclosure, the planned reference speed of the motor may be constituted by a planned reference rotational speed. Further, in the present disclosure, the motor may be constituted by an electric servo motor.

The determination of the PWM switching frequency may include: a higher PWM switching frequency is determined if the planned reference speed is relatively high or a lower PWM switching frequency is determined if the planned reference speed is relatively low. By setting a higher PWM switching frequency at relatively higher speeds and a lower PWM switching frequency at relatively lower speeds, the problems associated with a constant or sustained high PWM switching frequency may be avoided while still supporting the use of high power density motors (e.g., motors having at least 16 poles) that require a high PWM switching frequency at high speeds.

The method further enables full use of the power cycle margin of the drive unit. That is, the method enables the motor to be driven at a high speed with a high PWM switching frequency without making the driving unit a bottleneck in terms of service life.

The determination of the PWM switching frequency may include: when the planned reference speed is above the high speed threshold, a predetermined high PWM switching frequency is set. The predetermined high PWM switching frequency may be, for example, 6kHz to 14kHz (such as 8kHz to 10 kHz). The high speed threshold may be, for example, 4000rpm to 8000rpm (such as 6000 rpm).

The determination of the PWM switching frequency may include: when the planned reference speed is below the low speed threshold, a predetermined low PWM switching frequency is set. The predetermined low PWM switching frequency may be, for example, 1kHz to 3kHz (such as 1.5kHz to 2.5kHz, such as 2 kHz). The low speed threshold may be, for example, 200rpm to 800rpm (such as 250 rpm).

The determination of the PWM switching frequency may further include: when the planned reference speed is above the low speed threshold, a PWM switching frequency is set that is proportional to the planned reference speed. The PWM switching frequency may be proportional to the planned reference speed, for example, when the planned reference speed is between the low speed threshold and the high speed threshold.

The determination of the PWM switching frequency may include: predicting a load on the motor based on the planned reference speed; and determining the PWM switching frequency based on the load on the motor. In this case, the prediction of the load on the motor may be made based on a mathematical model of the motor.

The method may further comprise: one or more control parameters of a drive unit for outputting an alternating current are adjusted based on the planned reference speed. Thus, the control parameters of the motor will also follow the planned reference speed of the motor. By adapting the control parameters to the planned reference speed of the motor, a stable and consistent control of the motor over the entire speed range of the motor may be ensured. This solution provides a smooth control of the motor, since variations in the PWM switching frequency can be avoided which negatively affect the control performance of the motor. Such smooth control is particularly useful for industrial robots, where the manipulator may perform many jerky (jerky) movements, for example, as compared to electric cars. This solution further improves the robustness of the control of the motor.

For example, in PI (proportional integral) control of the current of the motor, the high K of the control function_p(coefficient of proportionality) and Low K_v(integral coefficient) can be set during relatively high speed of the motor, and high K_vBut low K_pMay be set during relatively low speeds of the motor and thus depend on the control purpose of the application of the motor. Various types of non-linear control methods may be used in the drive unit to adjust K according to the PWM switching frequency_pAnd K_vFor outputting an alternating current having a desired electrical frequency.

The method can comprise the following steps: determining planned reference speeds of a plurality of motors of an industrial robot; determining, for each of the motors, a PWM switching frequency based on a planned reference speed of the motor; and controlling each of the motors by an alternating current generated by PWM switching having the determined PWM switching frequency. The method constitutes a dynamic PWM switching frequency control method which takes into account the dynamic behavior of the industrial robot.

The step of determining a planned reference speed for each motor may be performed by a path planner of the industrial robot. However, the method according to the present disclosure may be implemented in applications other than industrial robots. For example, the method may be implemented for controlling a motor or other industrial actuator of a conveyor belt.

According to another aspect, there is provided a method for controlling an electric motor, the method comprising: determining a PWM switching frequency for the motor; controlling the motor by means of an alternating current, which is generated by means of a PWM switch having the determined PWM switching frequency; and adjusting one or more control parameters of a drive unit for outputting an alternating current based on the PWM switching frequency.

According to another aspect, there is provided a control system for controlling an electric motor, the control system comprising a data processing device and a memory, the memory having stored thereon a computer program comprising program code which, when executed by the data processing device, causes the data processing device to perform the steps of: determining a planned reference speed of the motor; determining a Pulse Width Modulation (PWM) switching frequency based on a planned reference speed of the motor; and controlling the driving unit to output an alternating current to the motor, the alternating current being generated by PWM having the determined PWM switching frequency. The control system may be further configured to perform any method according to the present disclosure.

The control system may comprise at least one drive unit for generating an alternating current with a desired electrical frequency by means of a PWM technique. The control system may for example comprise one drive unit associated with each motor or one drive unit associated with a plurality of motors.

Each drive unit may for example comprise: an inverter electrically interposed between a Direct Current (DC) power source and the motor and converting power between direct current and Alternating Current (AC); a smoothing capacitor electrically interposed between the DC power supply and the inverter and connected between a positive electrode and a negative electrode on a DC side of the inverter; and an inverter control unit that controls switching of the switching elements of the inverter according to a predefined switching frequency.

According to another aspect, there is provided a control system for controlling an electric motor, the control system comprising a data processing device and a memory, the memory having stored thereon a computer program comprising program code which, when executed by the data processing device, causes the data processing device to perform the steps of: determining the PWM switching frequency; controlling the motor by means of an alternating current, which is generated by means of a PWM switch having the determined PWM switching frequency; and adjusting one or more control parameters of a drive unit for outputting an alternating current based on the PWM switching frequency.

According to another aspect, an industrial robot is provided, comprising a control system according to the present disclosure and a manipulator having at least one motor (such as a plurality of motors). Each motor may comprise at least six poles (such as at least ten poles, such as at least 16 poles).

The control system may include a path planner configured to determine a planned reference speed of the motor.

Drawings

Further details, advantages and aspects of the disclosure will become apparent from the following examples taken in conjunction with the accompanying drawings, in which:

FIG. 1: a block diagram of an industrial robot comprising a control system and a manipulator with a plurality of motors is schematically shown.

Detailed Description

Hereinafter, a method for controlling a motor in which a Pulse Width Modulation (PWM) switching frequency is determined based on a planned reference speed of the motor will be described, a control system for controlling the motor, and an industrial robot including the control system will be described. The same reference numerals will be used to refer to the same or similar structural features.

Fig. 1 schematically shows a block diagram of an example of an industrial robot 10 comprising a control system 12 and a manipulator 14 with a plurality of motors 16. The industrial robot 10 according to fig. 1 constitutes one of many possible implementations of a method for controlling an electric motor 16 according to the present disclosure.

In fig. 1, the motor 16 of the manipulator 14 is used to control the movement (e.g., rotation or translation) of a plurality of links (not shown) relative to each other. Each motor 16 is arranged to drive a joint (not shown) between two adjacent links. In the non-limiting example of fig. 1, each electric motor 16 is constituted by a rotary electric servomotor having 16 poles. The manipulator 14 is shown as including six motors 16, but the number of motors 16 may be increased or decreased.

The manipulator 14 further includes a plurality of position sensors 18 (e.g., resolvers) associated with the electric motors 16. Each position sensor 18 is arranged to detect the rotational position of the associated motor 16 in real time. Signals indicative of the measured position 20 of each motor 16 are sent to the control system 12. Optionally, manipulator 14 further includes one or more speed detection sensors (not shown) for detecting the rotational speed of each motor 16 in real time.

The control system 12 includes a plurality of drive units 22. Each drive unit 22 is configured to generate an alternating current 24 having a certain electrical frequency generated by a PWM technique. In the example of fig. 1, the control system 12 includes one drive unit 22 associated with each motor 16. However, one driving unit 22 may alternately drive a plurality of motors 16.

Each drive unit 22 may include a rectifier for converting AC to DC, a frequency converter (inverter), and a DC bus connected between the rectifier and the inverter. The inverter converts the DC current into a variable alternating current 24. Each drive unit 22 may further comprise an inverter control unit which controls the switching of one or more switching elements of the inverter in accordance with the commanded switching frequency. Variable alternating current 24 from the inverter of the drive unit 22 is provided to the associated motor 16.

The inverter of the driving unit 22 may further include an IGBT (insulated gate bipolar transistor) module. The lifetime of an IGBT module depends on the power cycle. The lifetime of the IGBT module may be reduced if a high PWM switching frequency is also used at the lower speed of the associated motor 16.

The control system 12 of this example further includes a host computer 26. The host computer 26 includes a data processing device 28 (e.g., a central processing unit CPU) and a memory 30. The computer program is stored in the memory 30. The manipulator program, the model of the manipulator 14, and the path planner are implemented in the host computer 26 (e.g., in the memory 30). The path planner plans the path of the manipulator 14. For each motor 16 of the manipulator 14, the path planner generates a signal representing the planned reference velocity 32 based on motion instructions from the manipulator program and a model of the manipulator 14. The control system 12 is thus configured to determine a planned reference speed 32 of the motor 16.

The path planner may further generate a signal representing the reference position 34 for each motor 16 based on the motion instructions from the manipulator program and the model of the manipulator 14. The planned reference speed 32 and the optional reference position 34 for each motor 16 are sent to the associated drive unit 22.

The planned reference speed 32 for each motor 16 and the measured position 20 for each motor 16 are used by the associated drive unit 22 for closed-loop PID control of the motors 16. PID controlled control parameter (K)_p、K_i、K_d) Adjustments may be made based on the projected reference speed 32 and the PWM switching frequency.

The alternating current 24 can be generated, for example, by means of SVPWM (space vector PWM) and current loop PI control implemented in each drive unit 22. Control parameter (K) of PI control_p、K_i) Adjustments may be made based on the projected reference speed 32 and the PWM switching frequency.

The control system 12 is further configured to determine the PWM switching frequency based on the planned reference speed 32 of the associated motor 16. When the planned reference speed 32 is high, a high switching frequency may be set, and when the planned reference speed 32 is low, a low switching frequency may be set. When the motor 16 is driven at the planned reference speed 32, the alternating current 24 generated by the PWM switching having the determined PWM switching frequency is output to the motor 16.

When the planned reference speed 32 is below a low speed threshold (e.g., 250rpm), the PWM switching frequency may be set to a predetermined low value (e.g., 2 kHz). When the planned reference speed 32 is above a high speed threshold (e.g., 6000rpm), the PWM switching frequency may be set to a predetermined high value (e.g., 10 kHz). When the planned reference speed 32 is between the low speed threshold and the high speed threshold, the PWM switching frequency may be set to an intermediate value (between a predetermined low value and a predetermined high value) that is proportional to the planned reference speed 32.

While the present disclosure has been described with reference to exemplary embodiments, it should be understood that the invention is not limited to what has been described above. For example, it should be understood that the dimensions of the components may be varied as desired.