Abstract:
Disclosed is an apparatus for changing a mode in a proportional integral differential (PID) controller, which removes an impact generated in a mode change and stably performs the mode change when the operational mode of the PID controller is changed from a manual mode into an automatic mode or vice versa. The apparatus includes a PID operator configured to generate a driving signal by performing a PID operation in an automatic mode or a manual mode based on a manual mode change signal or an automatic mode change signal; a manual mode buffer configured to process the generated driving signal and output the processed driving signal to a load driver when the manual mode change signal is generated; and a speed difference integral calculator configured to analyze the generated driving signal and output the analyzed driving signal to the PID operator when the automatic mode change signal is generated.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the benefit of Korean Patent Application No. 10-2010-0032914, filed on Apr. 9, 2010, the disclosure of which is hereby incorporated herein by reference in its entirety. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to an apparatus and a method for changing a mode in a proportional integral differential controller (hereinafter, referred to as a PID controller). More specifically, the present invention relates to an apparatus and a method for changing a mode in a PID controller, which can remove an impact generated in a mode change and stably perform the mode change when the operational mode of the PID controller is changed from a manual mode to an automatic mode or vice versa. 
         [0004]    2. Description of the Related Art 
         [0005]    In general, a PID controller is widely used to control the driving of various types of loads including an electric motor and the like. The operational modes of the PID controller that drives a load are divided into an automatic mode and a manual mode. 
         [0006]    In the automatic mode, the PID controller determines the current state of the load by inputting a speed detection signal to the load, and generates a driving signal for driving the load by PID-controlling the determined state of the load and a speed command signal set by a user. Then, the PID controller drives the load based on the generated driving signal. 
         [0007]    Thus, the automatic mode is used to drive the load in a state desired by the user according to the current operational state of the load, and the PID controller can stably drive the load by repeatedly performing an operation without a pause. 
         [0008]    In the manual mode, the PID controller drives the load by generating a driving signal based on the speed command signal set by the user, regardless of the state of the load fed back from a system. 
         [0009]    The automatic and manual modes of the PID controller can be changed when the user so desires. However, in a case where a mode change is performed in the state that the load is driven based on an output signal of the PID controller, an overload is applied to the system, and an impact is generated due to the mode change. 
         [0010]    For example, in a case where the operational mode of the PID controller is changed from the automatic mode to the manual mode, the PID controller outputs a driving signal based on only the speed command signal in the state that the PID controller outputs the driving signal according to the difference value between the speed detection signal and the speed command signal. 
         [0011]    If the value of the driving signal outputted from the PID controller is greatly changed, the driving state of the load is greatly changed, and the change in the driving state of the load is transferred to the system as it is. Therefore, an overload is applied to the system. 
         [0012]    Thus, in a case where the operational mode of the PID controller is changed from the automatic mode into the manual mode, the generation of an impact generated in the mode change is restricted by limiting the variation of a driving signal outputted from the PID controller, and accordingly, the overload of the system is prevented. 
         [0013]    However, if the variation of the driving signal outputted from the PID controller is limited in the mode change, a response speed is delayed. 
         [0014]    Further, in a case where the operational mode of the PID controller is changed from the manual mode into the automatic mode, the PID controller performs a PID control from an initial value, and hence it takes much time for the PID controller to drive a load in a stable state. Therefore, the driving speed of the load is not constantly stable, and accordingly, the system is vibrated. 
       SUMMARY OF THE INVENTION 
       [0015]    Embodiments of the present invention provide an apparatus for changing a mode in a PID controller capable of reducing an impact generated in a mode change while not limiting the variation of a driving signal, when the operational mode of the PID controller is changed from an automatic mode into a manual mode. 
         [0016]    Embodiments of the present invention also provide an apparatus for changing a mode in a PID controller capable of stably changing a mode while restricting the occurrence of a time delay, vibration or the like, when the operational mode of the PID controller is changed from an automatic mode into a manual mode. 
         [0017]    It is to be understood that technical problems to be solved by the present invention are not limited to the aforementioned technical problems and other technical problems which are not mentioned will be apparent from the following description to the person with an ordinary skill in the art to which the present invention pertains. 
         [0018]    According to one general aspect of the present invention, there is provided an apparatus for changing a mode in a PID controller, the apparatus comprising: a PID operator configured to generate a driving signal by performing a PID operation in an automatic mode or a manual mode based on a manual mode change signal or an automatic mode change signal; a manual mode buffer configured to process the driving signal generated by the PID operator and output the processed driving signal to a load driver when the manual mode change signal is generated; and a speed difference integral calculator configured to analyze the driving signal generated by the PID operator and output the analyzed driving signal to the PID operator when the automatic mode change signal is generated. 
         [0019]    The manual mode buffer may include a timer configured to generate a switching signal during a predetermined time when the manual mode change signal is generated, a filter configured to buffer the driving signal generated by the PID operator, and a plurality of switches configured to input the driving signal generated by the PID operator to the filter or bypass the driving signal generated by the PID operator to the load driver, based on the switching signal. 
         [0020]    The filter may be a lag filter that performs high-frequency filtering on the driving signal outputted by the PID operator. 
         [0021]    The speed difference integral calculator may calculate a speed difference integral signal included in the driving signal generated by the PID operator when the automatic mode change signal is generated. The PID operator may generate a driving signal by replacing a speed difference integral signal of a driving signal to be generated with the speed difference integral signal calculated by the speed difference integral calculator at an initial stage in which the automatic mode change signal is generated. 
         [0022]    According to an aspect of the present invention, there is provided a method for changing a mode in a proportional integral differential (PID) controller, the method comprising: generating a driving signal by performing a PID operation in an automatic mode or a manual mode based on a manual mode change signal or an automatic mode change signal; processing the driving signal and outputting the processed driving signal to a load driver when the manual mode change signal is generated; and analyzing the driving signal and outputting the analyzed driving signal when the automatic mode change signal is generated. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0023]    These and/or other aspects and advantages of the invention will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which: 
           [0024]      FIG. 1  is a block diagram showing a configuration of a speed control apparatus of an electric motor using a PID control; 
           [0025]      FIGS. 2 and 3  are graphs showing changes in output signal of the PID controller when a mode is changed in the speed control apparatus of  FIG. 1 ; 
           [0026]      FIG. 4  is a block diagram showing a configuration of an apparatus for changing a mode in a PID controller according to an embodiment of the present invention; and 
           [0027]      FIGS. 5 and 6  are graphs showing changes in output signal when a mode is changed in the apparatus. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0028]    The present invention is described more fully hereinafter with reference to the accompanying drawings, in which embodiments of the present invention are shown. This present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure is thorough, and will fully convey the scope of the present invention to those skilled in the art. 
         [0029]      FIG. 1  is a block diagram showing a configuration of a speed control apparatus of an electric motor using a PID control. The speed control apparatus may include a PID controller  120 , a load driver  130 , a load  100 , a speedometer  110 , and the like. The load  100  may include, for example, an electric motor. The speedometer  110  generates a speed detection signal PV by detecting the rotation speed of the load  100 . The PID controller  120  generates a driving signal MV for driving the load  100  by PID-controlling a speed command signal SV inputted under an operation of a user and the speed detection signal PV of the electric motor  100 . The load driver  130  drives the load  100  by generating driving power based on the driving signal MV outputted by the PID controller  120 . 
         [0030]    In a case where the electric motor that is the load  100  is driven in the speed control apparatus configured as described above, the speed command signal SV set under the operation of the user is inputted to the PID controller  120 . 
         [0031]    The speedometer  110  generates a speed detection signal PV by detecting the rotation speed of the load  100 , and the generated speed detection signal PV is inputted the PID controller  120 . 
         [0032]    In a case where the currently set operational mode of the PID controller  120  is an automatic mode, the PID controller  120  determines a difference value between the speed command signal SV and the speed detection signal PV and generates a driving signal MV for driving the load  100  based on the determined difference value. The generated driving signal MV is inputted to the load driver  130 . 
         [0033]    Then, the load driver  130  generates driving power corresponding to the driving signal MV, and the electric motor  100  is driven and rotated by the generated driving power. 
         [0034]    In a case where the currently set operational mode of the PID controller  120  is a manual mode, the PID controller  120  generates a driving signal MV based on the speed command signal SV regardless of the amplitude of the speed detection signal PV fed back from the speedometer  110 , and the generated driving signal MV is inputted to the load driver  130 . 
         [0035]    Then, the load driver  130  generates driving power corresponding to the driving signal MV, and the electric motor  100  is driven and rotated by the generated driving power. 
         [0036]    That is, if the PID controller  120  is operated in the automatic mode at times t 10  and t 20  as shown in  FIGS. 2 and 3 , the PID controller  120  initially generates a vibrating driving signal MV. As time elapses, the PID controller  120  generates the driving signal MV in a stable state, so that the load driver  130  stably drives the load  100 . 
         [0037]    If the operational mode of the PID controller  120  is changed into the manual mode at times t 11  and t 21  in the state that the PID controller  120  is operated in the automatic mode, the value of the driving signal MV outputted by the PID controller  120  may be rapidly decreased as shown in  FIG. 2  or may be rapidly increased as shown in  FIG. 3 . 
         [0038]    That is, in the automatic mode, the PID controller  120  calculates a difference value between the speed detection signal PV fed back from the speedometer  110  and the speed command signal SV set by the user, and generates a driving signal MV based on the calculated difference value. 
         [0039]    If the operational mode of the PID controller  120  is changed into the manual mode in the state described above, the PID controller  120  generates a driving signal MV based on the speed command signal SV set by the user regardless of the speed detection signal PV. Therefore, the value of the driving signal MV outputted by the PID controller  120  may be rapidly decreased or may be rapidly increased. 
         [0040]    If the value of the driving signal MV is rapidly decreased as described above, a low-load impact is generated which allows the load driver  130  to rapidly decrease the driving speed of the load  100 . If the value of the driving signal MV is rapidly increased as described above, a high-load impact is generated which allows the load driver  130  to rapidly increase the driving speed of the load  100 . 
         [0041]    If the low-load impact or high-load impact is generated, a heavy burden is imposed on the load  100 . In the low-load impact or high-load impact is repeated for a long period of time, the lifetime of the load  100  is shortened. 
         [0042]    If the operational mode of the PID controller  120  is changed into the automatic mode at times t 12  and t 22  in the state that the PID controller  120  is operated in the manual mode, the PID controller  120  generates a driving signal MV by performing a PID control from an initial value, and therefore, it takes much time until the load  100  is driven at a stable speed. Further, the PID controller  120  generates a vibrating driving signal MV until the load  100  is driven at the stable speed, and the load driver  130  drives the load  100  based on the vibrating driving signal MV. Therefore, the driving speed of the load  100  is vibrated, and a system operated according to the driving of the load  100  is also vibrated. 
         [0043]      FIG. 4  is a block diagram showing a configuration of an apparatus for changing a mode in a PID controller according to an embodiment of the present invention. The apparatus may include a PID operator  400 , a manual mode buffer  410 , a lag filter  412 , a timer  414  and a speed difference integral calculator  420 . 
         [0044]    The PID operator  400  is operated in a manual or automatic mode based on a manual or automatic mode change signal. In the automatic mode, the PID operator  400  generates a driving signal MV 1  by performing a PID control according to the difference value between a speed detection signal PV and a speed command signal SV. In the manual mode, the PID operator  400  generates a driving signal MV 1  by performing a PID control according to the speed command signal SV. The PID operator  400  also generates a driving signal MV 1  based on a speed difference integral signal MVi fed back from the speed difference integral calculator  420  at an initial stage in which the operational mode of the PID operator  400  is changed from the manual mode into the automatic mode. 
         [0045]    The manual mode buffer  410  buffers the driving signal MV 1  outputted by the PID operator  400  using high-frequency filtering and outputs the buffered driving signal MV 2  to a load driver during a time predetermined at an initial stage in which the operational mode of the PID operator  400  is changed from the automatic mode into the manual mode. 
         [0046]    The manual mode buffer  410  includes the lag filter  412  that is a high-frequency filter, the timer  414  and switches  416  and  418 . 
         [0047]    The lag filter  412  buffers the driving signal MV 1  outputted by the PID operator  400  using the high-frequency filtering. 
         [0048]    The timer  414  is triggered based on a manual mode change signal so as to generate a switching signal during a predetermined time. 
         [0049]    The switches  416  and  418  are switched based on the switching signal outputted by the timer  414  so that an output signal of the PID operator  400  is buffered through the lag filter  412  and then outputted to the load driver during the predetermined time of the timer  414 . In a case where the predetermined time of the timer  414  elapses, the output signal of the PID operator  400  is immediately outputted to the load driver. 
         [0050]    The speed difference integral calculator  420  calculates a speed difference integral signal MVi based on the driving signal MV 2  outputted to the load driver, the speed detection signal PV and the speed command signal SV and feeds back the calculated speed difference integral signal MVi to the PID operator  400  at the initial stage in which the operational mode of the PID operator  400  is changed from the manual mode into the automatic mode. 
         [0051]    According to the apparatus configured as described above, in the automatic mode, the PID operator  400  generates a driving signal MV 1  by performing a PID control based on a speed command signal SV set by a user and a fed-back speed detection signal PV, and the generated driving signal MV 1  is outputted to the load driver through the switches  416  and  418 . Thus, the load driver drives a load based on the driving signal MV 1 . 
         [0052]    In a case where a manual mode change signal is inputted in this state, the PID operator  400  is operated in the manual mode. That is, the PID operator  400  generates the driving signal MV 1  by performing the PID control based on the speed command signal SV set by the user. 
         [0053]    The manual mode change signal is inputted to the timer  414  of the manual mode buffer  410 . Then, the timer  414  is triggered to generate a switching signal while counting a predetermined time, so that the operational terminals of the switches  416  and  418  are connected to one fixed terminals a 1  and a 2 , respectively. After the predetermined time, the operational terminals of the switches  416  and  418  are connected to the other fixed terminals b 1  and b 2 , respectively. 
         [0054]    Then, the driving signal MV 1  outputted by the PID operator  400  is inputted to the lag filter  412  through the switch  416  so that a variation of the driving signal MV 1  is buffered using high-frequency filtering. A driving signal MV 2  obtained by buffering the variation of the driving signal MV 1  is outputted to the load driver through the switch  418  so that the load driver drives the load based on the driving signal MV 2 . 
         [0055]    That is, in the state that the PID operator  400  is operated in the automatic mode at times t 30  and t 40  as shown in  FIGS. 5 and 6 , a manual mode change signal is inputted to the timer  414  at times t 31  and t 41  so that the timer  414  operates at an initial stage in which the manual mode of the PID operator  400  is started and generates a switching signal during the predetermined time. 
         [0056]    Thus, a variation of the driving signal MV 1  outputted by the PID operator  400  is buffered using the high-frequency filtering through the lag filter  412  as shown in  FIGS. 5 and 6 , and the driving signal MV 2  obtained by buffering the variation of the driving signal MV 1  is outputted to the load driver. 
         [0057]    Accordingly, although the value of the driving signal MV 1  outputted by the PID operator  400  is greatly changed when the operational mode of the PID operator  400  is changed from the automatic mode into the manual mode, the value of the driving signal MV 1  is buffered, so that the load driver slowly varies the driving speed of the load. As a result, an impact caused by a mode change is not generated. 
         [0058]    In a case where an automatic mode change signal is inputted at times t 32  and t 42  in the state that the PID operator  400  is operated in the manual mode, the PID operator  400  is operated in the automatic mode. 
         [0059]    In this state, the speed difference integral calculator  420  calculates a speed difference integral signal MVi, and the calculated speed difference integral signal MVi is inputted to the PID operator  400 . 
         [0060]    Then, the PID operator  400  operating in the automatic mode replaces a speed difference integral signal of a driving signal MV 1  to be generated with the speed difference integral signal MVi outputted by the speed difference integral calculator  420 , thereby generating a driving signal MV. 
         [0061]    Thus, the driving signal MV outputted by the PID operator  400  at the initial stage in which the operational mode of the PID operator  400  is changed from the manual mode into the automatic mode is changed starting from the value of the driving signal MV that has been outputted in the manual mode as shown in  FIGS. 5 and 6 . Accordingly, the value of the driving signal MV outputted by the PID operator  400  is not vibrated. 
         [0062]    Hereinafter, the operation will be described in detail, in which as the PID operator  400  generates the driving signal MV by replacing the speed difference integral signal MVi outputted by the speed difference integral calculator  420 , the value of the driving signal MV outputted by the PID operator  400  is changed starting from the value of the driving signal MV that has been outputted in the manual mode. 
         [0063]    The driving signal MV outputted from the PID operator  400  by performing a PID operation contains a proportional operation element, an integral operation element and a differential operation element. In a case where a variation in error occurs among the elements contained in the driving signal MV, only the proportional operation element and the integral operation element are remained by excluding the differential operation element that instantaneously appears and disappears. 
         [0064]    When considering only the proportional operation element and the integral operation element, the proportional operation element and the integral operation element can be restored using the driving signal MV outputted by the PID operator  400 . 
         [0065]    The value of the driving signal MV outputted by the PID operator  400  may be defined by the following Equation 1. 
         [0000]        MV=MVp+MVi+MVd   Equation 1
 
         [0066]    In the Equation 1, MVp denotes a speed difference signal subjected to proportional operation, MVi denotes a speed difference integral signal subjected to integral operation, and MVd denotes a speed difference differential signal subjected to differential operation. The MVp, MVi and MVd are defined by the following Equations 2 to 4, respectively. 
         [0000]    
       
         
           
             
               
                 
                   MVp 
                   = 
                   
                     Kp 
                      
                     
                       ( 
                       
                         SV 
                         - 
                         PV 
                       
                       ) 
                     
                   
                 
               
               
                 
                   Equation 
                    
                   
                       
                   
                    
                   2 
                 
               
             
             
               
                 
                   MVi 
                   = 
                   
                     
                       
                         Ti 
                         A 
                         @ 
                       
                        
                       
                         ( 
                         
                           SV 
                           - 
                           PV 
                         
                         ) 
                       
                     
                      
                     
                        
                       t 
                     
                   
                 
               
               
                 
                   Equation 
                    
                   
                       
                   
                    
                   3 
                 
               
             
             
               
                 
                   MVd 
                   = 
                   
                     Td 
                      
                     
                        
                       
                          
                         t 
                       
                     
                      
                     
                       ( 
                       
                         SV 
                         - 
                         PV 
                       
                       ) 
                     
                   
                 
               
               
                 
                   Equation 
                    
                   
                       
                   
                    
                   4 
                 
               
             
           
         
       
     
         [0067]    Here, Kp, Ti and Td denote predetermined gain values, respectively. 
         [0068]    In the Equation 2, the gain value Kp, the speed command signal SV and the speed detection signal PV are previously known values, and the speed difference signal can be calculated using these values. 
         [0069]    When assuming that the value of the speed difference differential signal MVd is ‘0,’ it is possible to calculate the speed difference integral signal MVi included in the driving signal MV outputted by the PID operator  400 . 
         [0070]    In this embodiment, the speed difference integral calculator  420  calculates the speed difference integral signal MVi included in the driving signal MV outputted by the PID operator  400  as described above, and the calculated speed difference integral signal MVi is inputted to the PID operator  400  so as to be included in the driving signal MV. 
         [0071]    Thus, according to this embodiment, in a case where the operational mode of the PID operator  400  is changed from the manual mode into the automatic mode, the PID control is not performed from the initial operation of the PID operator  400  to obtain the driving signal MV in the automatic mode, but the PID control can be performed from the value of the driving signal MV that has been finally outputted in the manual mode. 
         [0072]    Further, the operational mode of the PID operator  400  is smoothly changed from the manual mode to the automatic mode through the PID operation of the PID operator  400  without an error such as a response delay, so that it is possible to prevent vibration of the driving signal MV. 
         [0073]    In the apparatus for changing a mode in a PID controller according to the present invention, a driving signal outputted by the PID controller is filtered using a high-frequency filter when the operational mode of the PID controller is changed from the automatic mode to the manual mode, so that it is possible to reduce an impact caused in the mode change and to drive a load by stably changing the automatic mode into the manual mode. 
         [0074]    Further, when the operational mode of the PID controller is changed from the manual mode into the automatic mode, a speed difference integral signal is extracted from elements contained in a PID control signal and then included in the driving signal, so that it is possible to smoothly change the manual mode into the automatic mode, to stably drive the load by preventing the situation of a rapid low load or rapid high load, and to induce the speed to rapidly approach a desired speed. 
         [0075]    Although a few embodiments of the present invention have been shown and described, it would be appreciated by those skilled in the art that changes may be made in this embodiment without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents.