Feedback And Stability Lab Report Essay Samples

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Abstract

DC motor consists of a stator which generates magnetic field and a rotor. In this lab-report PMDC motor is considered which generates electro-magnetic field through the permanent magnet. As far as the control systems are concerned there are 2 basic control systems Open Loop and closed Loop. Any time, the closed loop systems are considered better, however with partially degraded performance. The object of this lab is therefore to ascertain the efficacy of closed loop systems and compare its performance with the open loop system. This was done by comparison between output signal and ref signal. The stability of the system and the cost of performance are noted. The comparison charts and the graph are drawn to make it clear that the motor experienced a better stability when used in the closed loop system. The details of the experiment, standard procedures and the results are presented in the prescribed report format.

Introduction

We have 2 basic control systems known as closed Loop & open loop systems. Both of these are known to use the signals called reference, r(t), & control, u(t). However, the difference between the two is that whilst Open loop systems don’t use feedback, closed loop systems do. (Celcelja,2013).
As an example one may think of some assembly plant & one controller that control assembly plant operations. For open loop system controller doesn’t distinguish that the plant may generate an output other than expected when it is set for u(t) signal. Hence, it is not feasible for the controller to alter u(t) so as to account-for variation in y(t) signal. y(t) may vary as compare to u(t) as mathematical model of the plant will not account for the state or event in the plant. In this case u(t) & y(t) are not correlated. External, uncontrolled event that affects the plant output is other reason. (Celcelja,2013).
Figure: Open-Loop System outline
Above figure display r(t) & u(t), while y(t) is the output signal and h(t) is plant transfer function . r(t) is controlled by human indicating the expected outcome from controller. This is for instance common volume controller we see everyday.
The Proportional Controller can dynamically adjust u(t) in close loop systems with the help of e(t) which is error term.
Figure: Close Loop System outline
Criticism empowers a framework to end up steady and to come back to a stable condition when outer occasions disturb or annoy a framework. Consequently for being steady a framework shows an abated reaction to changes in a reference signal or to outer occasions. The systems for a control framework utilizing criticism are: relative, subordinate, essential or of these instruments consolidated into a PID controller. The PID controller is exceptionally normal in industry. (Franklin, Powell & Emami-Naeini A 2010).
The decision of a controller relies on upon the application's prerequisites. This lab assembles an application that uses the obligation cycle of the PWM sign to alterably alter encompassing light levels. The controller builds the obligation cycle of the PWM with a specific end goal to apply more power to the LED and subsequently build its force. The PWM is the control, u(t), that is nourished into the plant (that is, LED).
This specific item encounters bothers all the time. Somebody may open a drapery or turn on an alternate light. The controller ought to react to increments in encompassing light by diminishing the PWM signal's obligation cycle which thus diminishes the LED (plant) such that the aggregate surrounding light matches the reference signal.
Changes to the LED's force can happen as quick as the mcu processes and redesigns the PWM obligation cycle register (OCR2). For this application one upgrade each 100 milliseconds is more than sufficient. One milli-second is moderate contrasted with how quick surrounding light fills a room. At paces of human discernment 100 milliseconds is quick however noticeable. These timing contemplations drive the necessity for just expecting to utilize a corresponding controller. Indication. A greatest change of 2% to 4% to the obligation cycle each 50 - 100 ms actualizes a decent smooth move of the LED's power.
As you can envision this is simply the surface of a profound subject. On the off chance that this material is fascinating consider taking different courses that examine input and particularly control frameworks, for example, ECE4510 or ECE4520 (ECE3510 is an essential for both courses). Notwithstanding, this lab is a down to earth active methodology. We require simply enough data to realize that the outline is grounded on hypothesis. (Franklin, Powell & Emami-Naeini A 2010).
Figure: Close Loop System having “K” as Feedback and w(t) as Perturbation
There are other complicated feedback systems as shown in above Figure. Indispensable or differential controllers perform their individual scientific capacities on the blunder term, e(t) when processing a redesigns to u(t). These controllers have distinctive piece charts than the relative controller indicated in Figure 5-3. Nonetheless, from the purpose of the equipment hardware just the yield term y(t) is sustained once again into the equipment, ordinarily through an A/D converter.
In this lab, the plant's capacity is to produce a coveted level of encompassing light. The sensor measures surrounding light with a Cadmium Sulfide (CdS) photocell. The sensor measures the plant's execution. Nonetheless, it additionally measures outside irritations, for example, light from different sources that are not controlled by the plant.
A relative control framework figures the mistake term or distinction of the reference flag, r(t) and yield, y(t), to powerfully change u(t). That is, e(t)=r(t)-y(t) and u(t)=u(t)+e(t). In the event that a client conforms r(t) then the lapse term displays the same change and the re-count of u(t) still works.
Circuit 5-1 portrays how we will be actualizing a shut circle framework with the AVR mcu. Port D, bit 7 controls the PWM to the LED and the criticism is controlled by the inherent ADC on Port A, bit 0.Circuit 5-1 – A Closed-Loop Control System

Procedures & Equipment

Equipment
Different control setups can be made through diverse wiring plan and hence distinctive circuits on the simple unit. This unit incorporates a four data lapse speaker.
This unit join with the mechanical unit, and is utilized to execute the control framework. It permits an information to be produced and by means of the sign being altered, yield values from the engine can be acquired. (Basak,1996)The simple unit gives pick up potentiometers, demonstrated on the board as P1, P2 and P3. Potentiometer P1 and P2 can be utilized to give framework increase control furthermore permit the tacho-generator sign to be balanced. P3 is imperative in the trial then again, and it can be connected to any information, to furnish the slip enhancer with a flexible data. (Henslee & Ward, 2013)
The unit gives an engine based physical framework, and additionally speed and position sensing abilities. (Basak,1996)The brake plate and magnet on the mechanical unit give the customizable burden to the engine, and the brake lever interprets this.

Procedures

Open Loop:
At first, the open circle plan was tried, keeping in mind the end goal to see the impact of burden torque. The data of the P3 was joined with the + 10V sign attachment, while the showcase was made to peruse the velocity esteem in RPM through the utilization of the RPM/DVM switch indicated at the base of the mechanical unit. The handle P3 was then moved appropriately, until the presentation read an estimation of 40rpm. This worth relates to 1280rpm of the engine shaft, and was then recorded. The switch at the base of the mechanical unit was then flicked with a specific end goal to attain to the DVM setting. The current estimation indicated on the showcase was recorded. The same system took after, as the brake lever on the mechanical unit was moved from its introductory position downwards six times. For every position the brake step was connected, the worth for the engine speed and the armature current was recorded. This system was rehashed three times and accordingly the normal of the three sets of information could be figured. The outcomes were classified.

Closed Loop:

Before commencing the testing of the closed loop system configuration, the RPM/DVM switch was set to DVM and the main power was turned off. The output of the P3 and reversed tacho-generator signal were connected to the left hand side input sockets of the error amplifier on the analogue unit. The error amplifier feedback loop was then closed. This was done by connecting it via the 1MΩ resistor and by connecting the output signal of the error amplifier to the input terminal of the power amplifier. The P3 knob as set to zero, and the circuit configuration was checked to ensure no human error had been made in the set up. The P3 adjusting knob was then moved until it read a value of 40rpm, and this value was then recorded. The switch at the bottom of the mechanical unit was then flicked in order to achieve the DVM setting. The current measurement shown on the display was recorded. Results
After carrying out the setup process as illustrated above. Two experiments are to be carried out to obtain the motor speed as well as the armature current values for the open loopand the closed loop systems. These values obtained are shown in Table 1 and Table 2.Averages were also calculated for each set of results, this was done using equation (7) shown in
Speed (ω) and current (I) results from the Open Loop control system, at various brake positionsTable 2. Speed (ω) and current (I) results from the Closed Loop control system, at various brake positions (Shinners,1998).
A plot of ω versus I, for the open-loop system and closed-loop system can be seen below in the Figure. Both plots are shown with standard error bars along with the equation of the line, shown on the figure itself.
The theoretical calculation to find output voltage of the error amplifier uses equation (6), derived earlier. Substitute values of VA and VB into equation (6)- using the values for the resistors as R2= 100KΩ and R1=1MΩ. Using equation (8), shown on the next page, the error between the theoretical and the experimental VOUT can be calculated at each brake position. Table 4 shows this percentage error at every brake position. The accuracy of the experiment can therefore be commented on after obtaining these percentage error values.
Voltages of the reference signal, the tacho-generator signal and the theoretic and experimental outputs of the error amplifier, for the closed loop system.
Error= calculated value-experimental valuecalculated valuex 100% (8)
The percentage error at each break position shows that there is a slight difference between the actual value of the output voltage and the theoretical (or calculated) value. The average error across all the brake positions is equal to 2.04%, calculated by summing all the errors together and dividing by the number of brake positions. The discussion will provide reasoning for the experimental values and the error involved.

Discussion

The clearest perception from the rate and current after-effects of the open circle framework is that the plot (Figure 9) demonstrates a steeper slant, when contrasted with the shut circle framework bend. This means the way that an increment in present will mean pace will change more, general a more prominent angle is being indicated (slope is demonstrated to be equivalent to 37.579). There is an unlucky deficiency of regulation, and as a result of the absence of input in the open circle framework; it gets to be clear that the framework is inclined to aggravation. The way that there is no connection between the yield flag once more into the info implies that there is a constant increment in yield, at last bringing about the framework to be greatly inclined to disturbances.The shut circle framework demonstrates a little inclination in correlation (3.8364), must not exactly the open circle plot. The line is very nearly even, portraying almost no change in engine speed with armature current. By and large, the outcomes are steadier as a consequence of input, and because of abrogations, unsettling influence did not assume a part in the shut circle framework results. An increment in the armature current would imply that a restoring torque is created in this way importance the rate ought to be kept steady. While there was no vacillation when measuring the voltages in the shut circle framework, an approach to expand comprehension of the outcomes would have been to take voltage estimations for the open circle framework.
In this specific lab, the most unmistakable mistake could just originate from the wellspring of off base alignment of the instruments. This lab utilized a computerized framework, so guaranteeing adjustment of these instruments is a key element of getting exact results. By not resetting the simple unit for instance, implies there may have been an irregular lapse that happened amid the examination. This is quickly figured out by the way that rehashes were taken of every framework setup, and midpoints were likewise computed to recognize any invalid results that may have happened. To enhance further on the examination, considerably more values could have been taken, expanding the measure of information sets to five.In the lion's share of tests notwithstanding, there will me a component of human lapse. The most evident human blunder would originate from wrongly altering the brake, prompting invalid and off base results. From tables 1 and 2, there are no abnormalities amid both the open circle and shut circle classification of results. Subsequently it is protected to say that each position of the brake was connected effectively and reliably. By allocating set parts inside the lab appeared well and good, as every member would stay on the same undertaking for instance moving the brake lever. This implied that everybody got used to the part given, at last expanding the precision of the investigation.

Conclusion

Two basic type of control systems were demonstrated for PMDV Motor -- Open Loop and closed Loop. The advantage of using closed loop system was observed. It was highlighted that the close loop takes the output into the system as feedback. This was done so that the comparison between output signal and ref signal may be made. It was observed that by doing this, stability was in-built to the system at the cost of system performance. From the chart and the graph, it is clear that the motor experienced a better stability when used in the closed loop system, This was judged from the parameters like RPM, I(A) and V/A. The parameters show steady results with lesser fluctuations, smooth changing for the 6 braking positions and better stability. The second graph's gradient as shown for the closed loop system as a gradual gradient. Therefore, the closed loop is preferable as in the open loop it was observed that the current was unsteady and was increasing with RPM, which is not a desirable condition. References
Basak, A.(1996)..Permanent-magnet DC linear motors. Oxford:Clarendon Press.
Celcelja, F.(2013), Concept of Control: Lecture Notes, University of Surrey
Franklin F.G, Powell J. D and Emami-Naeini A.(2010). Feedback Control of Dynamic Systems, Sixth Edition, Pearson
Henslee,E. and Ward, S.(2013).Numerical and Experimental Methods:Background Documents and Methods, University of Surrey.
Shinners, S. M.(1998).Modern control system theory and design. New York: J. Wiley.
Sivanagaraju, S. and Devi, L.(2012). Control Systems Engineering. Tunbridge Wells, UK: NewAcademic Science.
Hughes M.(2012), Electronic Instrumentation:Amplifiers Lecture Notes, University of Surrey.
Distefano, J.,Stubberud A. R and Williams, I. J.(1995).Schaum’s outline of theory and problems of feedback and control systems.New York:McGraw- Hill.

Appendix

Open Loop Data
Close Loop Data:
Eg=KEω (1)
VS=IaRa+Eg (2)
IaEg=P=TLω=Tm ω (3)
ω= ω0 -bTm (4)
ω= VsKE-Tm KE2Ra (5)
Output voltage of a summing amplifier:VOUT= -R2R1 (VA + VB) (6)
mean= xinumber of data sets (7)
Where:xi = total motor speed/ total armature current
Error= calculated value-experimental valuecalculated valuex 100% (8)