Title of Invention

''A UNIVERSAL ADAPTIVE AUTO-TUNING CONTROLLER FOR INDUCTION MOTOR DRIVE CONTROL''

Abstract

A universal adaptive auto-tuning controller for induction motor drive control, said drive control system (9) comprises of a system (8) and a logic circuit (7) connected to a universal adaptive auto-tuning controller (1) characterized in that said AATC (1) comprises of a step input (2) connected to an ON/OFF controller (4) through the first error calculator (3), the output of said ON/OFF controller (4) is connected to an integrator (6) through the second error calculator (5) for an output of Vo and a biasing signal (Vbias) as input at the second error calculator (5).

Full Text

This invention relates to Universal Adaptive Auto-Tuning Controller (AATC) for induction motor drive control. Any control system has two major components, the process and the controller. The purpose of the controller is to keep the process variable close to the desired value as per the set point for changes in the set point and external disturbances. This is achieved by feedback in some control systems and by adaptation of the controller's gain constants in others. In adaptive controllers, pre-determined process response is used to compare it with the actual response of the process and then correct the process response. The pre-determined response of the process is obtained by prior estimation using a model of the process developed or based on observed response over a period of time. The accuracy of the pre-determined response of the process and the measured response decide the effectiveness of the adaptive controller. Controllers are used for various applications, especially in industrial and transportation systems. Controllers are of various types and they are broadly classified as classical controllers and modern controllers. Some of their applications are in process control, power supplies, drive control etc. In process control, the system parameters, like temperature, pressure, flow etc, are controlled to meet their set value and enable the process to reach the set point in a pre-determined pattern and time. In drives, the controllers are used for start-stop and speed control of the motor for various types of loads and loading patterns. In power supplies, controllers are used to maintain the required output parameters, like voltage, current etc. at the set values and to shut down the power supply in case of any fault or abnormal operation due to its input or load. A controller has several parameters that can be adjusted. The control loop performs well if the parameters are chosen properly. In some cases, improper selection of parameters may lead to unstable operatin of the system. The procedure of selecting the appropriate parameters of the controller is called "tuning" of the controller. The conventional adaptive controllers are classified into two major types.They are Model Reference Adaptive Controller (MRAC) and Self-Tuning Controller (STC). In MRAC, a mathematical model of the system to be controlled is developed such that it specifies the designed performance of the system. The values of parameters of the system being controlled is predetermined and kept ready as reference for comparison. Then, the actual parameters are measured for the system being controlled. These measured parameters of the system are compared with the predetermined values in the reference model developed. The deviation of the parameters are corrected by a pre-determined rule called "Adaptation rule". The overall aim of MRAC is to force the output of the controller to correspond to the model output. The Self-Tuning Controller's philosophy for obtaining an automatic adjustment mechanism is to identify the system to be controlled using measured input and output data of the system and then set the appropriate values for the parameters of the controller using a pre-determined rule called "Synthesis rule". The main disadvantage associated with the present system of manual tuning of parameters of the controler is that it requires services of specially trained skilled engineers. Another disadvantage associated with the present system of manual tuning is that any improper selection of parameters frequently lead to unstable operation of the system. Yet another disadvantage associated with the conventional adaptive controller is that the conventional adaptive controller is tailor-made to suit a specific system and the rules for tuning of controller parameters are system-specific. Hence an adaptive controller made for one system is not suitable for use in another system. Therefore, the main object of the present invention is to provide an auto tuning controller which does not require manual tuning of the controller parameters by specially trained skilled engineers. Another object of the present invention is to provide a universal adaptive auto-tuning controller for the induction motor drive control application which eliminates the costs and time involved for commissioning. Yet another object of the present invention is to provide an auto-tuning controller which considerably reduces the installation time for an induction motor drive in the chosen system. In accordance with the present invention there is provided a^ universal adaptive auto-tuning controller for induction motor drive control, said drive control system comprises a logic circuit and a system connected to the universal adaptive auto-tuning controller characterized in that said AATC comprise^ a step input connected to an ON/OFF controller through first error calculator, the output of said controller is fed to an integrator through a second error calculator for an output of Vo and a biasing signal ( V bias) as input at the second error calculator. The nature of the invention, its objective and further advantages residing in the same will be apparent from the following description made with reference to non-limiting exemplary embodiments of the invention represented in the accompanying drawings. Fig. 1- block schematic of adaptive auto-tuning controller Fig.2- The adaptive auto-tuning controller in a control system; Fig. 3 - Typical response of the adaptive auto-tuning controller to a step input with different V bias values. DETAILED DESCRIPTION In view of the limitations of the conventional adaptive controllers, a novel universal adaptive auto-tuning controller (AATC) is developed which can be used in any system. Figs. 1 and 2 show the principle of operation of the developed Novel Universal Adaptive Auto-Tuning Controlle (AATC). The developed AATC (1) has an integrator (6) as a sub-system, as shown in the Fig. 1. Normally, the AATC (1) output (Vo) rises linearly. By using a feedback mechanism, the integrator (6) output (Vo) stops changing on reaching the set value of the input signal (Vi). A novel biasing signal "Vbias" is incorporated in this Adaptive Auto-Tuning Controller (1) to regulate the output (Vo) of the AATC, as shown in Fig. 1. Hence, integral time "Ti" of the controller (l)(the reciprocal of which is the integral gain "Ki" of the controller) is also changed, as shown in Fig. 3. In this way the controller parameter - integral time "Ti" - is regulated by the biasing signal (V bias) used in this Adaptive Auto- Tuning Controller (1). A system variable that needs to be limited ( such as output Yo in Fig. 2 is linked through a logic circuit (7) and a signal conditioner to the biasing signal " V bias". Then, the error in the process variable regulates the biasing signal "Vbias". In this method, the system (8) automatically tunes the controller parameter - integral time "Ti" and continuously adapts it to adjust the AATC (1) output (Vo) to appropriately control the process output (Yo) in such a way that the chosen process parameters are within the set limits. Hence, in this controller (1), the gain parameters are tuned automatically on demand from an external signal (V bias),and also the parameters of the controller are continuously updated and this results in an Adaptive Auto-Tuning Controller (1). This AATC (1) can also be used for other applications, like process control, where there is requirement to control the process parameters, such as, temperature, level, flow, pressure etc. The controller (1) developed is an analog circuit based Adaptive Auto-Tuning Controller (1). This has the advantage of fast response, as there are no delay elements, like filters, sampling, etc. The performance of the Adaptive Auto-Tuning Controller (1) is studied by simulating it on a digital computer. In this simulation, the "Vbias" value is varied to study its effect on the output of the controller (1). These simulation results show that the integral time "Ti" of this controller can be tuned continuously by adjusting the value of "Vbias" dynamically and continuously. This dynamic variation feature of this controller due to continuous variation of the value of "Vbias" enables continuous automatic tuning of "Ti" and this results in the Adaptive Auto-Tuning Controller. It is observed from the simulation results that the integral time "Ti" of this AATC can be varied from 1 second to 50 seconds, i.e. 1:50 range, when the Vbias is changed from 10 volts to 0.1 volt. This gives a very good advantage of a wide operating range of integral time "Ti" for the AATC (1) developed. This range can be used on-line and dynamically. A hardware prototype of the Adaptive Auto-Tuning Controller (1) is developed and fabricated. The circuit of the AATC (1) consists of the five numbers of general purpose ICs, which are easily available in the Indian market. These ICs are assembled on a Printed Circuit Board (PCB) of industry standard single EURO size of 100mm (H) X 160mm (D). This industry standard single EURO size PCB enables the AATC to be fitted into industry-wise widely used 19 inch rack for control cards. This will also enable the develooped AATC (1) to be retrofitted into any existing industrial controller. The developed AATC (1) is highly reliable due to the low component count of five ICs only. The industry standard size PCB and connector used for mounting of this AATC in the industry standard 19-inch rack will enable it to withstand vibrations. One of the major advantages of this hardware prototype of AATC is its very low cost. _ Q The experimental tests on the AATC (1) are conducted by applying a step input (2) and measuring the output behaviour of the AATC (1). This step input (2) is of 10 volts magnitude and is applied through an ON/OFF switch from one of the dc voltage sources of adjustable output type. For various values of the"Vbias" Voltage, output of the AATC (1) is observed on the oscilloscope, and also it is measured and recorded. The experimental test results establish that the experimental results closely match with the simulation results, thus validating the theory of operation of the developed Adaptive Auto-Tuning Controller (1). In brief, the salient features of the developed Novel Universal Adaptive Auto-Tuning Controller are as follows: On-line continuous updating and Auto-Tuning of the parameters of the controller (1); Very low cost-The component cost is less than one hundred rupees (or $ US). (3) Eliminates manual tuning of parameters - no requirement of skilled engineers. (4) High reliability due to very few components - only 5 ICs are used. Simple control philosophy. Easy design. No complicated algorithms to be implemented. Fast response - no delay elements like sampling, filters etc. Wide operating range of 1:50 of the integral time "Ti". The use of this Novel Universal AATC to induction motor drive application is analyzed in detail. Performance of the 25 hp induction motor, when controlled with the developed Adaptive Auto-Tuning Controller, is simulated on a digital computer and the simulation results are analyzed in detail. Major observations from the simulation studies done on the AATC controlled motor drive, at the rated voltage input with different loads and step speed commands are as follows: The controller parameter - integral time "Ti" - of the AATC is effectively regulated by the biasing input signal "Vbias", which in-turn is regulated by the current error in the AATC controlled induction motor drive system, as seen from the effective operation of the current limiting action of the controller. Thus, the auto-tuning action of the controller is effectively implemented. The controller parameter, integral time "Ti", also continuously adapts to different load conditions and speed commands of the induction motor drive system. Hence, the adaptive action of the controller is effectively implemented. This establishes the theory and operation of the developed Adaptive Auto-Tuning Controller (1). In the AATC controlled 25 hp induction motor drive, the current error signal effectively controls the controller output signal under different loads on the motor and even for different step inputs of the speed command, like 0 to 100 per cent, 50 to 100 per cent etc. c) The AATC output signal effectively regulates the frequency of the output voltage ( which in-turn decides the operating speed of the motor) of the PWM voltage source inverter, whenever the stator peak current exceeds the set current limit, for various loads on the motor and also for various step speed commands to the AATC. d) The AATC has a wide operating range and fast response, as it limits even the fast changing instantaneous peak currents of the induction motor drive at starting conditions and for step speed commands. The performance of the developed Adaptive Auto-Tuning Controller is studied using an experimental set-up for an induction motor drive. A hardware prototype of 25 hp induction motor drive with the Adaptive Auto - Tuning Controller is developed and fabricated. This drive uses an IGBT-based pulse-width-modulated (PWM) voltage source inverter (VSI). This developed Adaptive Auto-Tuning Controller is tested for start-stop and for adjusting the speed setting of a variable speed squirrel cage induction motor using the simple V/f control scheme. The experimental test results with the AATC controlled 25 hp induction motor drive establish that the experimental results closely match with the simulation results, thus validating the theory of operation of the developed Adaptive Auto-Tuning Controller for induction motor drive control application. In brief, the salient features of operation of the developed Adaptive Auto-Tuning Controller for the control of induction motor drive control application are as follows: (1) On-line continuous updating and auto-tuning of the controller parameters are done while continuously meeting the induction motor drive requirement of maintaining the stator current within the set limit of 1.5 times the rated peak current of the motor. The developed AATC is suitable for different load conditions on the motor and even for step inputs in speed commands, as seen from the results of the above investigations. (2) Very low cost drive controller - the cost of the components in the developed AATC is less than one hundred rupees and the cost of the total drive control circuits is also very low. This cost includes the PWM waveform generation, protection and gate signal generation circuits and gate drives. The cost of total control circuits is considered very low, especially because of providing advanced features in the drive, like the Adaptive Auto-Tuning Controller. (3) Eliminates manual tuning of parameters by using the Adaptive Auto-Tuning Controller for the induction motor drive control application. This is a major advantage, as it eliminates the costs involved for commissioning and for utilizing specially trained skilled engineers. This also considerably reduces the installation time for an induction motor drive in the chosen system. (4) High reliability, as very few components are used. The total control circuit consists of four PCBs, including the PWM waveform generation, protection and gate signal generation circuits. Simple control philosophy even for controlling a complex system like the induction motor drive. Easy design, as the circuits and components used are easyto understand and implement, especially for an induction motor drive without using a speed feedback scheme. (7) No complicated algorithms are to be implemented even with advanced features, like Adaptive Auto-Tuning Controller, incorporated for the induction motor drive control. (8) Fast response- no delay elements like sampling, filters etc. Also, this Adaptive Auto- Tuning Controller for induction motor drive control provides a quick speed response without any speed overshoots for different load conditions on the motor and even for step inputs in speed commands, as seen from the results of the above investigations. (9) Wide operating range of the integral time "Ti" of the Adaptive Auto-Tuning Controller incorporated for the induction motor drive control provides for meeting different load conditions and sudden variations in speed command. Some applications of the Novel Adaptive Auto-Tuning Controller: The developed AATC controlled induction motor drive control using V/f controlled PWM voltage source inverter based open loop speed control scheme has many applications in like Roller Table Drives, Conveyor belts, Cranes, Hoists, Elevators, Lifts, Locomotives, Electric Vehicles etc. In these applications, the closed-loop speed control method is seldom used since the drive speed is always varied depending on the road and track conditions. The given applications are only illustrative and are not exhaustive. The invention described hereinabove is in relation to a non-limiting embodiment and as defined by the accompanying claims. WE CLAIM: 1. A universal adaptive auto-tuning controller for induction motor drive control, said drive control system (9) comprises a system (8) and a logic circuit (7) connected to a universal adaptive auto-tuning controller (1), characterized in that said AATC (1) comprises of a step input (2) connected to an ON/OFF controller (4) through a first error calculator 2. The universal adaptive auto-tuning controller as claimed in claim 1 wherein said AATC hardware implemented circuit of the AATC (1) comprises of fine general purpose ICs, and assembled on a printed circuit board. 3. The universal adaptive auto-turning controller as claimed in claim 1 wherein said AATC (1) has a wide operating range of 1:50 of the integral time (Ti) when the biasing signal (Vbias) is changed from 10 Volts to 0.1 Volt. 4. A universal adaptive auto-tuning controller for induction motor drive control as herein described and a® illustrated with reference to the accompanying drawings.

Documents:

150-del-2001-abstract.pdf

150-del-2001-claims.pdf

150-del-2001-correspondence-others.pdf

150-del-2001-correspondence-po.pdf

150-del-2001-description (complete).pdf

150-del-2001-drawings.pdf

150-del-2001-form-1.pdf

150-del-2001-form-19.pdf

150-del-2001-form-2.pdf

150-del-2001-form-3.pdf

150-del-2001-gpa.pdf