Abstract:
A bi-directional smooth transition switch with bumpless transfer is disclosed. It is composed of two feedback loops, each with feedback and forward-loop compensators. During loop operation, one feedback loop is active, while the other is inactive. The smooth transition switch operates in the following manner. The switch output is measured. Next, an error signal is formed as the difference between the forward-loop compensator output and the switch output, which is fed to the input of a high gain feedback compensator. The output of the feedback compensator is a feedback signal. When no switching occurs, the feedback signal remains zero in the active loop, and the output signal of the inactive loop will track the output signal of the active loop. When the switchover occurs, the inactive loop will replace the original active loop and provide smooth transition switch&#39;s output.

Description:
FIELD OF THE INVENTION 
     The present invention is related generally to the field of industrial switches and more particularly to the field of smooth transition switches. 
     BACKGROUND OF THE INVENTION 
     Switches are very popular components used in various industrial fields. Industrial process systems and devices often require switching among alternative modes or controllers to satisfy multiple optimal objectives. Such examples include switching from manual to automatic control states. Other examples include switching from one controller, such as a proportional controller, to another controller, such as a proportional-integrate controller for a process. 
     When switching between controllers or modes (switchover), the difference between the outputs of different controllers or modes produces a discontinuous bump in the process input. This, in turn, causes undesirable bumps in the controlled output variables. This difference or mismatch can deeply deteriorate the performance of the process. Such phenomenon is referred to as the bump transfer. The issue of avoiding process bump transfer is one of the most important issues in industry processes. A goal of switching is to realize a smooth transition of bumpless transfer between different controllers or process operating modes. Technology used to realize a smooth transition is referred to as bumpless transfer technology. 
     The purpose of bumpless transfer is to keep the control signal sent into the controlled plant continuous when the switching occurs. Most current bumpless transfer control devices in use today rely on the operating information of the system or specific system design technology. This method requires a designer to know the process mode or the controller states. Thus, it requires the controller states to always be computable. Therefore, it is a challenge for bumpless transfer devices to be applied in different processes and different areas of the industry. Another challenge for bumpless transfer devices is to be used easily by people who are not familiar with a special system or process. 
     SUMMARY OF THE INVENTION 
     The invention includes a smooth transition switch with bumpless transfer, comprising a switch with a control input, a first signal input, a second signal input and an output. In addition, the smooth transition switch also has a first feedback loop operably connected to the first signal input and the output of the switch, and a second feedback loop operably connected to the second signal input and the output of the switch. 
     In another embodiment, at least one of the feedback loops in the transition switch includes a summing junction having a plurality of inputs and at least one output operably connected to the first signal input of the switch. The loop also has a forward-loop compensator operably connected between the output of the summing junction and the first signal input of the switch. In addition, the loop has a comparator with a first input operably connected to an output of the forward-loop compensator and a second input operably connected to the output of the switch. 
     In yet another embodiment, the invention is directed to a method of smooth transition switching including the steps of reading a control signal, reading a plurality of input signals, reading at least one feedback signal, and generating at least one error signal. The method further includes forward-loop compensating the at least one error signal, and generating at least one input command signal for the switch. Furthermore, an output command signal is switched to the at least one input command signal. Next, another error signal is calculated and then feedback compensated. Finally, at least one feedback signal is generated from the compensated error signal. 
     Further scope of applicability of the present invention will become apparent from the following detailed description, claims, and drawings. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will become more fully understood from the detailed description given here below, the appended claims, and the accompanying drawings in which: 
         FIG. 1  shows a block diagram of a conventional switch; 
         FIG. 2  is a simplified block diagram of the bi-directional smooth transition switch in the present invention comprising two feedback loops; 
         FIG. 3  is a block diagram of the bi-directional smooth transition switch in the present invention; 
         FIG. 4  is a flowchart which discloses the steps taken by the present invention when switching between control (or command) signals; 
         FIG. 5  is an implementation of the smooth transition switch using a microprocessor; and 
         FIG. 6  is an implementation of the smooth transition switch using a microprocessor and a conventional analog switch. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The present invention comprises a bi-directional smooth transition switch with bumpless transfer which does not rely on system or controller models. Furthermore, specialized knowledge of the system is not required to operate the bi-directional smooth transition switch. Applications for the bi-directional smooth transition switch include the automobile industry, the aerospace industry, power electronics and the chemical industry. 
       FIG. 1  shows a block diagram of a conventional switch. It is a double throw, single pole switch. A control signal input at the control terminal connects the output terminal to either input terminal  1  or  2 . Assuming that input terminal  1  is connected to the output terminal, a signal on the control terminal would cause the input at input terminal  2  to be connected to the output terminal. If the value of the input at input  1  is not equal to the value at input  2 , a jump in the output signal will occur when switching from input  1  to input  2 . This jump represents a difference between the current and the desired output signal when the switchover is effected. This will cause a bump in the process being controlled. 
       FIG. 2  is an illustrated block diagram of the bi-directional smooth transition switch in the present invention. The differences between the inputs and the output of the switch are fed back to the inputs through dynamic compensators KC 1  and KC 2  to form two feedback loops L 1 , L 2 . The parameters KC 1  and KC 2  are chosen to optimize the switch&#39;s dynamic response characteristics. 
     When the control terminal CT causes switching from input terminals T 1  and T 2 , the output O 1  response of the switch SW 1  will be controlled by the feedback loop so as to minimize the jump in the output signal. Thus, the present invention utilizes feedback compensation to compensate for sudden signal changes. In a preferred embodiment, the compensation includes two feedback loops, L 1 , L 2 . Thus, by minimizing any effects caused by switching, the output signal will be kept continuous and smooth. 
     The block diagram of the smooth transition switch of the present invention is shown in  FIG. 3 . Two feedback loops are formed from two input reference signals r 1 , r 2  in the input terminal T 1 , T 2  to output signal c in the output terminal O 1  with the compensators K 1 , K 2  and forward-loop compensators (or forward compensators) C 1 , C 2 . At input terminal T 1 , input signal r 1  is input to summing junction or summer S 1 . Similarly, at input terminal T 2 , an input signal r 2  is input to summing junction S 2 . Feedback signals f 1 , f 2  are subtracted from the input reference signals r 1 , r 2  in the summing junctions S 1  and S 2  respectively to form the error signals e 1 , e 2 . Error signals e 1 , e 2  are passed through corresponding forward-loop compensators C 1 , C 2 , respectively, forming command signals a, b respectively. 
     Command signal a is input to input I 1  of switch SW 1  and to summing junction S 3 . Similarly, command signal b is input to input I 2  of switch SW 1  and to summing junction S 4 . A switch control signal s, input at the control terminal CT, is connected to the control input of switch SW 1 . The output of switch SW 1 , O 1 , comprises output command signal c which is input to both summing junctions S 3  and S 4 . The switch control signal s controls which input of switch SW 1 , I 1  or I 2 , is connected to the output of switch SW 1 , O 1 , and thus determines which command signal, a or b, is output as command signal c. 
     As stated earlier, the difference between the inputs and the output of the switch SW 1  is fed back to the inputs through feedback compensators K 1  and K 2  to form two feedback loops L 1 , L 2 . In summing junction S 3 , command signal a is subtracted from command signal c producing error signal e 3 . Error signal e 3  is then passed through feedback compensator K 1  creating feedback signal f 1  which is input to summing junction S 1 . Similarly, in summing junction S 4 , command signal b is subtracted from command signal c producing error signal e 4 . Error signal e 4  is then passed through feedback compensator K 2  creating feedback signal f 2  which is input to summing junction S 2 . 
     Comparing this smooth transition switch with a conventional switch in the same condition, assume that switch SW 1  input I 1  with signal a is connected to switch SW 1  output O 1  with signal c before switching. There is no difference between signal a and signal c in this case. That is, command signal a=output signal c, a=c. As a result, the error signal e 3 =c−a. Consequently, the feedback signal f 1  is equal to zero. Thus, the input signal r 1  is forwarded to output signal c directly. Because the switch is on in this loop, this loop, L 1 , that consists of error signal e 3 =c−a, feedback compensator K 1 , error signal e 1 =r 1 −f 1  and forward-loop compensator C 1 , is called the active loop. 
     When L 1  is the active loop, the other loop, L 2 , is off and is call the inactive loop. It consists of error signal c 4 =c−b, feedback compensator K 2 , error signal e 2 =r 2 −f 2 , and froward-loop compensator C 2 . In the same period of time that the active loop is on, the inactive loop will generate an error signal c 2 =r 2 −f 2  and feedback error signal c 4 =c−b. By the suitable choice for the parameters of compensators K 2 , C 2 , the input signal b of switch SW 1  will be forced to track the signals a and c in the active loop L 1 . 
     When switching from I 1  with signal a to I 2  with signal b, the inactive loop L 2  will replace the original active loop L 1  to be the active loop in the smooth transition switch of the present invention. The response of command signal b of switch SW 1  will be controlled by the present active feedback loop L 2  such that the bump in the output signal c is controlled when output O 1  of the switch with command signal c is switched from I 1  with signal a to I 2  with signal b. Since the output of present active loop L 2  is always tracking the original active loop L 1  before switching, the inactive loop becomes the active loop without an abrupt bump. As a result, the smooth transition switch output, output signal c, will remain in a continuous state, thus ensuring that the output control signal used to control a plant is continuous when the switching occurs. 
     In the same period of time, the original active loop, L 1 , becomes the inactive loop. It will generate an error signal e 1 =r 1 −f 1  and feedback error signal e 3 =c−a. By the suitable choice for the parameters of compensators K 1 , C 1 , the input signal a of switch SW 1  will be forced to track signals b and c in at the current active loop L 2 . 
     Therefore, the bump incurred during switchover between two input signals is minimized when the smooth transition switch is applied in processes and devices. In other words, the smooth transition switch introduces feedback control to compensate for the sudden signal changes during switchover. As a result, the output of the switch will be kept continuous and smooth, and effect of switching is minimized. 
     The parameters of two feedback compensators K 1 , K 2  and forward-loop compensators C 1 , C 2  can be chosen to control the dynamic response characteristics. In a preferred embodiment, the principle of parameter choice used is to track the output signal of the active loop in the smooth transition switch of the present invention. Thus, parameters can be chosen empirically. Generally, the compensators K 1 , K 2  can be chosen to have high constant gains such that the error signal e 3 , e 4  are reduced to zero quickly. 
     The forward-loop compensators C 1 , C 2  can be chosen to be simple proportional-integrate compensators. In addition, they can be chosen to have a general compensator form with a transfer function of C(s)=b 1 *s+b 0 )/(a 1 *s+1) where the coefficients a 1 , and b 0 , b 1  are constant coefficients and s is the switch control signal. 
     This method of the smooth transition switch is based on measuring or estimating the actual switch output variable c. It can be realized by using suitable sensor measurement technology or state estimation technology to obtain the solution for output signal c. 
     Generally, the mismatching that can occur during switchover between the process input and the controller output can produce very detrimental effects in the industrial process. This can occur when switching from manual to automatic control and switching between two controllers in parallel. The switching apparatus and method of the present invention can keep the control signal transmitted into the controlled plant or process continuous when the switching occurs. Thus, this invention for a smooth transition switch is a very significant improvement for industrial processes and devices. 
       FIG. 4  is a flowchart which discloses the steps taken by the present invention when switching between input command signals. First, read switch control signal s ( 100 ). Next, read input signals r 1  and r 2  ( 110 ). Then, read feedback signals f 1  and f 2  ( 120 ). 
     Next, the output signal from summing junction S 1 , error signal e 1 , is calculated by taking the difference between input signal r 1  and feedback signal f 1  ( 200 ), e 1 =r 1 −f 1 . Similarly, the output signal from summing junction S 2 , error signal e 2 , is calculated by taking the difference between input signal r 2  and feedback signal f 2  ( 210 ), e 2 =r 2 −f 2 . 
     Next, execute compensator C 1  algorithm based on error signal e 1  and generate input signal a ( 220 ). Execute compensator C 2  algorithm based on error signal e 2  and generate input signal b ( 230 ). 
     Next, determine switch output signal c=a or c=b ( 310 ) according to the value of switch control signal s. 
     In step  400  and  410 , the errors e 3 , e 4  between output signal and input signals of switch SW 1  are calculated. e 3  is the difference between c and a, e 3 =c−a ( 400 ). e 4  is the difference between c and b, e 4 =c−b ( 410 ). 
     In step  500 , compensator K 1  algorithm is executed based on the error signal e 3  creating feedback signal f 1  ( 510 ). Similarly, in step  520 , compensator K 2  algorithm is executed based on the error signal e 4  creating feedback signal f 2  ( 530 ). In a preferred embodiment, compensators K 1  and K 2  are dynamic compensators. 
     Implementation of the Smooth Transition Switch Using a Microprocessor 
     This smooth transition switch with bumpless transfer can be implemented using both software and hardware.  FIG. 5  illustrates an embodiment of the present invention using a microprocessor with A/D and D/A converters (analog to digital signal conversion and digital to analog signal conversion devices).  FIG. 6  illustrates another embodiment of the present invention which uses a microprocessor with A/D and D/A converters and a conventional analog switch. Because  FIGS. 5 and 6  include all of the elements for the controller illustrated in  FIG. 3 , a detailed description of the identical elements will not be provided in connection with  FIGS. 5 and 6 . 
     In  FIG. 5 , two analog switch input signals r 1  and r 2  are converted to digital signals by using analog/digital converters A/D 1  and A/D 2 . The switch control signal s is also converted to a digital signal using analog/digital converter A/D 3 . The smooth transition switch of the present invention is implemented by executing software SF stored in the digital control unit (DCU) which is located in microprocessor M 1 . The software can be stored in RAM, ROM or any of storage medium compatible with the present invention. The digital output signal c of the digital control unit is then converted to an analog signal using digital/analog converter D/A 1  to be an analog output of the switch. 
     In  FIG. 6 , two analog switch signals r 1  and r 2  are converted to digital signals by using analog/digital converters A/D 1 , A/D 2 . An analog switch output signal c is converted to the digital signals by using analog/digital converters A/D 3 , A/D 4 . Part of the smooth transition switch of the present invention is implemented by using software SF stored in the digital control unit DCU in the microprocessor M 1 . This part includes feedback compensators K 1 , K 2 , and forward-loop compensators C 1 , C 2  as well as their signal summing junctions S 1 , S 2 , S 3  and S 4 . The output signals of compensators C 1 , C 2  are then converted to the analog signals using digital/analog converters D/A 1  and D/A 2  to be the input signals of a conventional analog switch SW 1 . The analog switch control signal s is forwarded directly to the conventional switch SW 1 . As it is mentioned above, the analog output signal c of the conventional switch SW 1  is then converted to a digital signal using two analog/digital converter A/D 3  and A/D 4  to be input signals of summing junctions S 3  and S 4 . 
     The foregoing discussion discloses and describes an exemplary embodiment of the present invention. One skilled in the art will readily recognize from such discussion, and from the accompanying drawings and claims that various changes, modifications and variations can be made therein without departing from the true spirit and fair scope of the invention as defined by the following claims.