KR100967665B1 - Motor speed control system and speed control method in low speed area - Google Patents

Abstract

A motor speed control system and a speed control method in a low speed region are provided. The motor speed control system includes a measuring unit that measures the time delay in the speed control loop and the bandwidth of the speed controller in the low speed region of the motor, sets a closed loop pole according to the speed of the motor, and selects a phase at the closed loop pole. Determines whether the PID gain of the speed controller is selected for the compensation of the closed loop pole considering the position change and phase condition of the phase selection unit and the closed loop pole, and if the PID gain of the speed controller is selected, the PID of the speed controller It includes a control unit for adjusting the gain of the speed controller according to the speed change of the motor through the gain.

Speed controller, PID gain, electric motor

Description

Motor speed control system and speed control method in low speed region {System and method for motor speed control in the low speed region}

The present invention relates to a motor speed control system and a speed control method in a low speed region, and through a PID gain selected in consideration of a measurement time delay according to the low speed region operation, in a low speed region to improve the speed control performance in the low speed region operation. The present invention relates to an electric motor speed control system and a speed control method.

In industrial motor drive applications, high precision and fast response to position tracking in all operating areas are absolutely required. This problem of speed response and precision for position tracking must be considered in connection with the characteristics of the speed controller. Most industrial electric motor drive systems have a current or torque controller in the form of a PI (Proportional and Integral) at the bottom, followed by a speed controller in the form of P (Proportional) or PI, followed by a P-position position controller as the highest controller. Control structure. That is, the characteristics of the position control in such a structure depend on the speed response and the precision of the speed controller. Consequently, the response of the position control is determined by the selection of the maximum frequency band of the speed control loop. The maximum frequency band of such a speed controller is limited by the speed detection time by the variable sampling method and the interaction with the internal current control loop, but in general, the exact selection method considering this is not known. Therefore, during the initial installation of the motor drive device in the industrial field, a lot of time is wasted to set the maximum frequency band of the speed controller in a trial and error method by experiment for each machine.

1 illustrates a motor driving system using a conventional variable sampling method.

In the block diagram of FIG. 1 composed of a variable sampling method (M / T method) for speed detection, the motor drive system 10 includes a speed controller 12, a current controller 14, an (SVPWM) inverter 16, The encoder 20 installed on the motor shaft, and the M / T calculator 22 for calculating the speed by a variable sampling method.

The speed controller 12 detects the actual speed with respect to the command speed of the electric motor 18 by using the closed loop controller and finally performs the speed control of the electric motor 18. Then, the current controller 14 receives the output current of the electric motor 18 according to the current command which is the output of the speed controller 12 and performs current control. In addition, the inverter 16 (for example, a PWM inverter) simultaneously modulates the magnitude and frequency of the output voltage from the input power source of the DC voltage source to modulate the three-phase command voltage represented by the space vector in the complex space. In addition, the motor 18 corresponds to the control object, the encoder 20 is a device for measuring the speed of the motor 18 to measure the increase in the rotation angle, generally an incremental encoder (Incremental Encoder) is used. The measurement time Ts is synchronized to the encoder pulse that is generated for the first time after the given sampling time Tc, and the M / T calculator 22 performs the speed calculation through this.

2 is a conceptual diagram illustrating output characteristics of a variable sampling method according to an operating speed range of an electric motor. 3 is a conceptual diagram illustrating output characteristics of a variable sampling method according to a low speed region operation of an electric motor.

As shown in Fig. 2, the variable sampling scheme has good characteristics in the general speed range, but does not calculate the speed until the next encoder pulse arrives in the region in which no encoder pulse is input for a given sampling time Tc. Done. Therefore, a delay time Td by Ts-Tc occurs in the speed control loop, and its value is inversely proportional to the speed.

Here, as shown in FIG. 3, it can be seen that the delay time Td increases during the low speed region operation. Within the speed control loop, the delay time is inversely proportional to speed, which limits the frequency bandwidth of the speed controller.

As described above, due to the problem caused by the variable sampling method, the frequency bandwidth of the speed controller during the low speed region operation is changed, and if it is not reflected in the speed controller design, it may adversely affect the low speed region operation performance of the motor.

Accordingly, there is a need to improve the performance of the conventional motor drive system by reflecting the change of the speed measurement time delay and the frequency bandwidth that are involved in the low speed region operation of the motor.

An object of the present invention is to provide a motor speed control system and a speed control method to improve speed control performance in low speed region operation through a PID gain selected in consideration of a measurement time delay caused by low speed region operation.

In order to achieve the above object, the motor speed control system according to an embodiment of the present invention, the measurement unit for measuring the time delay and the bandwidth of the speed controller in the speed control loop in the low speed region of the motor, and the closed loop according to the speed of the motor Determines whether the PID gain of the speed controller is selected to set the pole, and to determine the phase in the closed loop pole and the compensation of the closed loop pole in consideration of the position change and phase condition of the closed loop pole, If the PID gain of the controller is selected, and includes a control unit for adjusting the gain of the speed controller according to the speed change of the motor through the PID gain of the speed controller.

According to another aspect of the present invention, there is provided a method of controlling a speed of a motor, the method comprising the steps of (a) measuring a time delay and a bandwidth of a speed controller in a speed control loop in a low speed region of the motor, and setting a closed loop pole according to the speed of the motor. (B) selecting a phase at the closed loop pole, and (c) determining whether the PID gain of the speed controller is selected for the compensation of the closed loop pole in consideration of the positional change and the phase condition of the closed loop pole. And (d) if the PID gain of the speed controller is selected, adjusting the gain of the speed controller according to the speed change of the motor through the PID gain of the speed controller.

According to the motor speed control system and the speed control method of the present invention has the following advantages.

First, there is an advantage that can improve the performance of the conventional motor drive system by reflecting the speed measurement time delay and the change in the frequency bandwidth accompanying the low speed region operation of the motor.

Second, there is an advantage that the fast dynamic characteristics (selected maximum frequency band) according to the speed command change can be obtained by applying the PID gain of the speed controller according to the speed during the low speed region operation.

Third, there is an advantage that can improve the performance of the conventional motor drive system by maintaining the robustness against disturbance torque by applying the PID gain considering the bandwidth of the speed controller.

Advantages and features of the present invention and methods for achieving them will be apparent with reference to the embodiments described below in detail with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, but can be implemented in various different forms, and only the embodiments make the disclosure of the present invention complete, and the general knowledge in the art to which the present invention belongs. It is provided to fully inform the person having the scope of the invention, which is defined only by the scope of the claims. Like reference numerals refer to like elements throughout.

The pole function and zero point of the transfer function can be obtained from the transfer function of the system in which the current controller and the motor are combined. Here, the pole and the zero refer to the root of which the denominator of the transfer function becomes zero, and the zero refers to the root of which the numerator becomes zero. When such a system is controlled through a speed controller, the system is affected by the gain of the speed controller. To do this, calculate the poles and zeros of each transfer function as a method for selecting the speed controller gains, and then calculate the phases corresponding to each point and adjust the angles to compensate for the calculated phases to satisfy the stable conditions. Is given. To do this, a phase condition is required, and the value obtained from the calculated phase condition is derived to determine the gain of the corresponding unknown by obtaining a polynomial from which the speed controller gain can be obtained. It will be described in more detail below.

4 shows a block diagram of an industry standard speed control structure.

,

및

은 각각 전동기 속도 지령, 실제 속도, 토크 상수, 관성 및 마찰 계수를 나타낸다. 또한,

및

는 전동기 고정자 저항과 인덕턴스 및 전류제어 루프의 지연 시간이다.

는 평균 속도 검출에 의한 속도 검출 지 연과 속도 제어 루프 계산에 의한 지연 시간을 의미한다.As shown in Fig. 4, the speed controller C (S) 12 generates the torque component current command i ^* _q (s) . Then, the motor torque component current i _q (s) is controlled by the current controller 14 PI gains K _p and K _i corresponding to the bandwidth ω _c . In Figure 4,

,

And

Denotes the motor speed command, actual speed, torque constant, inertia and friction coefficient, respectively. Also,

And

Is the stator resistance and delay time of the inductance and current control loop.

Means the speed detection delay by average speed detection and the delay time by speed control loop calculation.

로 설정하면 전류 제어기(14)의 개루프 전달함수(

)는 수식 1과 같이 정의될 수 있다. Ignoring the delay time τ _c of the current control loop in the current controller 14 of FIG.

If set to, the open-loop transfer function of the current controller 14 (

) May be defined as in Equation 1.

[Equation 1]

는 전류 제어기(14)의 대역폭을 나타내며, 앞서 기술된 수식 1의 개루프 전달함수를 전류 지령과 실제 전류 사이의 폐루프 전달 함수(

)로 나타내면 수식 2와 같이 정의할 수 있다.In Equation 1,

Denotes the bandwidth of the current controller 14, and the open loop transfer function of Equation 1 described above is converted to the closed loop transfer function between the current command and the actual current.

) Can be defined as in Equation 2.

[Equation 2]

)와 인덕턴스(

) 및 대역폭(

)에 의해 전류 제어기(14)의 비례 이득과 적분 이득을 결정하면, 오버슈 트(Overshoot) 없는 전류 제어기(14)를 설계할 수 있다.Through equation 1 and equation 2, stator resistance of the motor (

) And inductance (

) And bandwidth (

By determining the proportional gain and the integral gain of the current controller 14 by using a), the current controller 14 without overshoot can be designed.

)를 정의한 것이다. Hereinafter, Equation 3 ignores the speed detection delay due to the average speed detection and the delay τ _s due to the speed control loop calculation.

) Is defined.

[Equation 3]

는 전류 제어기(14)의 대역폭,

,

및

은 토크 상수, 관성 및 마찰 계수를 나타내며, 속도 제어 구조는 수식 3과 같이 간략한 전달함수로 정의할 수 있다.In Equation 3,

Is the bandwidth of the current controller 14,

,

And

Represents torque constant, inertia and friction coefficient, and the speed control structure can be defined as a simple transfer function as shown in Equation 3.

5 is a block diagram of a speed control structure after the conversion to the Z-region according to an embodiment of the present invention. It can be seen that i ^* _q (s) ) occurs.

In the following description, the open loop transfer function of the current controller 14 and the motor in the Z-region may be defined as Equation 4 below. For reference, the Z-transformation is a mathematical tool for the analysis of linear discrete systems.

[Equation 4]

,

는

,

로 전류 제어기(14)의 대역폭(

)과 전동기의 토크 상수(

) 및 관성(

)으로 정의될 수 있으며,

는 속도 제어기(12)의 샘플링 주기로 정의될 수 있다. 수식 4에 나타난 바와 같이, 저속 영역에서 가변 샘플링 방식을 사용할 경우, 속도에 따라 속도 제어기(14)의 샘플링 주기(T)가 변한다는 것을 알 수 있다.In Equation 4, the variable

,

Is

,

The bandwidth of the furnace current controller 14

) And the torque constant of the motor (

) And inertia (

) Can be defined as

May be defined as the sampling period of the speed controller 12. As shown in Equation 4, when the variable sampling method is used in the low speed region, it can be seen that the sampling period T of the speed controller 14 changes according to the speed.

)는 수식 5와 같으며, 수식 5를 Z-영역으로 변환한 속도 제어기(12)의 이득은 수식 6과 같이 정의될 수 있다.Transfer function of the speed controller 12 shown in FIG.

) Is the same as Equation 5, and the gain of the speed controller 12 obtained by converting Equation 5 to the Z-region can be defined as Equation 6.

[Equation 5]

[Equation 6]

,

및

는 각각 속도 제어기(12)의 비례 이득, 적분 이득 및 미분 이득을 나타낸다.In the above formula 6,

,

And

Denotes the proportional gain, the integral gain and the derivative gain of the speed controller 12, respectively.

The proportional gain, the integral gain and the derivative gain of the speed controller 12 of Equation 6 can be used to design a gain that satisfies the stability in the Z-transformation.

,

,

를 통해 전동기의 속도 제어를 수행하며 전류 지령을 출력한다.As described in Equation 5, the speed controller 12 is a transfer function of the speed controller 12 composed of PID.

,

,

Speed control of the motor is carried out and the current command is output.

The transfer function 52 of the Zero Order Hold ( ZOH ) holds a continuously changing signal in the digital system as a sampled discrete signal during the sampling period.

In addition, the open loop transfer function 54 of the current controller / motor ignores the internal time delay of the current controller 14, and the internal time delay of the speed controller 12 is reflected in the sampling period. Here, it is assumed that the friction coefficient is very small.

Meanwhile, when the position of the closed loop pole in the Z-region is calculated, it may be preferably defined as in Equation 7.

[Formula 7]

과

는 (

), (

)로 표현할 수 있으며, 여기서

은 고유 진동수,

은 감쇠비를 의미하며, 매우 작은 감쇠의 경우 시스템 응답은 요동하고, 대단히 큰 감쇠의 경우 응답은 요동이 없다. 또한

,

는 각각 속도 제어기의 샘플링 주기 및 주파수 대역폭을 나타낸다.In the above formula 7,

and

Is (

), (

), Where

Silver natural frequency,

Is the damping ratio. For very small attenuation, the system response fluctuates. For very large attenuation, the response is oscillatory. Also

,

Denotes the sampling period and the frequency bandwidth of the speed controller, respectively.

In addition, the relationship between the frequency bandwidth and the attenuation ratio may be defined as Equation 8 through Equation 7.

[Equation 8]

In Equation 8, ω _BW , T means the bandwidth of the speed controller 12, the sampling period of the speed controller, respectively.

Equation 8 may determine the damping ratio of the speed control structure associated with the bandwidth ω _BW of the speed controller 12, and the bandwidth and the damping ratio of the speed controller according to the driving speed and the calculated closed loop pole may be represented as shown in FIG. 6. have.

Meanwhile, the PID of the speed controller 12 for satisfying the stability condition by measuring the phase of each pole and zero point in the closed loop pole considering the phase condition through the closed-loop pole calculated in Equation 7 above. It is necessary to determine whether the gain is selected and compensate for it by selecting the gain of the speed controller 12. Accordingly, the polynomials considering the phases to be compensated by the PID gain of the final speed controller 12 by calculating the phases of the poles and zeros of Equation 4 and the phases of the poles and zeros of Equation 6 are represented by Equations 9 and 10. Can be defined.

[Equation 9]

[Equation 10]

인 관계를 만족하는 이득을 선정하여야 안정된 제어기를 설계할 수 있기 때문에 위의 조건을 적용하여 안정된 제어기 이득 선정을 위한 실시예는 수식 11과 같이 정의 될 수 있다.Here, in order to select the gain of the speed controller 12 of Equation 6, the unit circle in the Z-region which is the stability boundary condition

Since a stable controller can be designed only by selecting a gain that satisfies the relation, the embodiment for selecting a stable controller gain by applying the above conditions can be defined as shown in Equation 11.

[Equation 11]

6 shows a closed loop pole and speed controller bandwidth according to speed in accordance with an embodiment of the present invention.

와

의 비(64) 및 Z-변환하였을 때의 폐루프 극점(65)을 나타낸다. 여기서, 수식 7과 수식 8이 사용될 수 있으며, 수식 7을 통해 폐루프 극점(65)을 구할 수 있고, 수식 8을 통해 속도 제어기의 대역폭(62)과 감쇠비(63)가 산출될 수 있다. 그리고, 속도가 낮아질수록 속도 측정 지연 시간 증가에 의해 속도 제어기의 샘플링 주기(T)가 변화하며 이로 인해 속도 제어기(12)의 주파수 대역폭이 감소하고 있음을 알 수 있다.For example, based on 3600 pulses per machine rotation of the motor, the bandwidth 62 and the damping ratio 63 of the speed controller according to the time delay measured at the predetermined motor speed 61,

Wow

The ratio 64 and the closed loop pole 65 at the time of Z-conversion are shown. Equations 7 and 8 may be used, and the closed loop pole 65 may be obtained through Equation 7, and the bandwidth 62 and the damping ratio 63 of the speed controller may be calculated through Equation 8. In addition, as the speed decreases, the sampling period T of the speed controller changes due to an increase in the speed measurement delay time, thereby reducing the frequency bandwidth of the speed controller 12.

7 shows the PID gain of the final speed controller calculated by applying Equations 9 to 11 according to the speed in the low speed region according to an embodiment of the present invention.

More specifically, FIG. 7 is a speed controller calculated to compensate each closed loop pole when the Z-converted closed loop pole summarized in FIG. 6 is compensated using the PID controller of the speed controller 12. PID gain 72 is shown.

8 is a flowchart illustrating a speed control method considering a M / T speed measurement time delay according to an embodiment of the present invention. 9 is a motor speed control system 100 for performing the steps of FIG. 8.

The measuring unit 110 measures the time delay and the bandwidth of the speed controller 12 in the speed control loop in the low speed region of the motor (S61). In this case, the measuring unit 110 may measure a frequency when the phase delay is -45 degrees by measuring a phase delay of the actual speed output after applying a speed command including a predetermined frequency component.

Next, the phase selector 120 sets a closed loop pole in the Z-region according to the speed of the motor (S62). Here, Equations 7 and 8 may be used, and the phase selector 120 calculates a phase at a closed loop pole and selects a phase to be compensated by a PID controller (not shown) of the speed controller 12. Done.

Next, the controller 130 controls the PID of the speed controller 12 to satisfy the condition for the system to be stable in the Z-region in consideration of the positional change and the phase condition of the closed loop pole in the Z-region. By selecting the gain, it is determined whether the PID gain of the speed controller 12 for compensating the phase corresponding to the stable condition is selected (S63). Here, Equations 9 to 11 may be applied, and the controller 130 selects a final gain that satisfies a stability condition that should be 1 when the phase condition and the closed loop pole are 1.

Here, when the PID gain of the speed controller is selected, the controller 130 automatically adjusts the gain of the speed controller 12 according to the speed change through the relationship between the time delay and the PID gain according to the speed of FIG. 7 ( S64). More specifically, the controller 130 functions to change the gain PID of the speed controller according to the time delay, so that the gain change of the speed controller 12 according to the speed change is automatically changed. Thereafter, the speed controller performs speed control of the motor through the proportional gain, the integral gain, and the derivative gain as the transfer function of the speed controller, and outputs a current command.

Therefore, in FIG. 10 showing the electric motor drive system, the gain (PID) change of the speed controller according to the time delay is functionalized through the process of FIG. 9, so that the gain change of the speed controller according to the speed change is automatically changed. Speed control performance in area operation is improved.

Each component illustrated in FIG. 9 may be configured as a kind of 'module'. The 'module' refers to a hardware component such as software or a field programmable gate array (FPGA) or an application specific integrated circuit (ASIC), and the module plays a role. However, modules are not meant to be limited to software or hardware. A module may be configured to reside on an addressable storage medium and may be configured to execute one or more processors. The functionality provided by the components and modules may be combined into a smaller number of components and modules or further separated into additional components and modules.

Although embodiments of the present invention have been described above with reference to the accompanying drawings, those skilled in the art to which the present invention pertains may implement the present invention in other specific forms without changing the technical spirit or essential features thereof. I can understand that. Therefore, it should be understood that the embodiments described above are exemplary in all respects and not restrictive.

1 illustrates a motor driving system using a conventional variable sampling method.

2 is a conceptual diagram illustrating output characteristics of a variable sampling method according to an operating speed range of an electric motor.

3 is a conceptual diagram illustrating output characteristics of a variable sampling method according to a low speed region operation of an electric motor.

4 shows a block diagram of an industry standard speed control structure.

5 is a block diagram of a speed control structure after converting to a Z-region in accordance with an embodiment of the present invention.

FIG. 6 illustrates closed loop pole and speed controller bandwidth according to speed in accordance with an embodiment of the present invention.

7 shows a speed controller PID gain in accordance with an embodiment of the present invention.

8 is a flowchart illustrating a speed control method considering a M / T speed measurement time delay according to an embodiment of the present invention.

9 is a block diagram of a speed control system according to an embodiment of the present invention.

10 illustrates an electric motor drive system according to an embodiment of the present invention.

<Explanation of symbols on main parts of the drawings>

12: speed controller 14: current controller

16: inverter 18: electric motor

20: Encoder 22: M / T Calculator

110: measuring unit 120: phase selector

130: control unit

Claims (7)

(a) measuring the time delay and bandwidth of the speed controller in the speed control loop in the low speed region of the motor, (b) setting a closed loop pole according to the speed of the motor and selecting a phase at the closed loop pole; (c) determining whether the PID gain of the speed controller for compensation of the closed loop pole is selected in consideration of the positional change and the phase condition of the closed loop pole; and (d) if the PID gain of the speed controller is selected, performing gain adjustment of the speed controller according to the speed change of the motor through the PID gain of the speed controller. The method of claim 1, wherein step (d) And functionalizing that the PID gain of the speed controller changes with the time delay, such that a gain change of the speed controller in response to a speed change of the motor is automatically changed. The method of claim 2, wherein step (d) And performing a speed control of the electric motor through a proportional gain, an integral gain, and a differential gain as a transfer function of the speed controller and outputting a current command. The method of claim 3, wherein And a PID gain of the speed controller whose unit circle size in the Z-region at the closed loop pole is 1. A measuring unit for measuring the time delay in the speed control loop in the low speed region of the motor and the bandwidth of the speed controller; A phase selector which sets a closed loop pole corresponding to the speed of the motor and selects a phase at the closed loop pole; Detects whether the PID gain of the speed controller for the compensation of the closed loop pole is selected in consideration of the positional change and the phase condition of the closed loop pole and, if the PID gain of the speed controller is selected, the PID of the speed controller. And a control unit that performs gain adjustment of the speed controller in accordance with a speed change of the motor through gain. The method of claim 5, wherein the control unit And a function of changing the PID gain of the speed controller according to the time delay so that the gain change of the speed controller according to the speed change of the motor is automatically changed. The method of claim 6, wherein the control unit And a PID gain of the speed controller whose unit circle size in the Z-region at the closed loop pole is 1.

Images