Control system concepts

 Open loop and closed loop control systems and their differences:-

Control systems are designed to manage the behavior of dynamic systems. They are categorized into open loop and closed loop systems, each with distinct characteristics and applications.

- Open Loop: No feedback, simpler, less accurate, handles disturbances poorly, stable, used in simple applications.

- Closed Loop: Feedback, complex, accurate, handles disturbances well, potential stability issues, used in critical applications.

Effects of positive and negative feedback:-

1. Negative Feedback

Effects:

Stability: Reduces system errors by correcting deviations from the desired output.

Accuracy: Improves tracking of the reference input.

Noise Reduction: Minimizes the impact of disturbances.

Bandwidth: Increases the system’s operating frequency range.

Gain Reduction: Lowers overall gain but enhances robustness.

2. Positive Feedback

Effects:

Amplification: Increases system gain (output grows over time).

Instability: Can lead to oscillations or runaway behavior.

Hysteresis: Creates switching thresholds (used in Schmitt triggers).

Reduced Accuracy: Output diverges from the reference input.

1.What is a Signal Flow Graph?

A graphical representation of a system’s variables and their dependencies.

Used to simplify complex systems (e.g., control systems, electrical circuits).

Components:

Nodes: Represent variables (e.g., inputs, outputs, signals).

Branches: Directed edges showing relationships between nodes (labeled with gains/transmittances).

Paths: Sequences of branches from one node to another.

Loops: Closed paths starting and ending at the same node.

2. Key Definitions

Forward Path:A path from input to output without repeating nodes.

Forward Path Gain: Product of branch gains along the path.

Loop:A closed path where no node is encountered more than once.

Loop Gain: Product of branch gains in the loop.

Non-Touching Loops:Loops with no common nodes.

3. Mason’s Gain Formula

The transfer function T of a system is given by:

4. Steps to Apply Mason’s Formula

 

DC Servo Motor

Principle of Operation

DC servo motors are closed-loop systems that use a DC motor (typically brushed) combined with feedback control to achieve precise positioning, speed, or torque.

Components:

DC Motor: Brushed or brushless.

Feedback Device: Encoder or potentiometer.

Control Circuit: Compares input command with feedback.

Gearbox: Reduces speed and increases torque.

Working Mechanism:

Input Signal: A control signal (e.g., PWM pulse) specifies the desired position/speed.

Feedback: The encoder/potentiometer measures the motor’s actual position.

Error Detection: The control circuit compares the input command and feedback to generate an error signal.

Correction: The error signal adjusts the armature voltage/current to drive the motor until the error is minimized.

AC Servo Motor

Principle of Operation

AC servo motors use AC induction or synchronous motors with advanced feedback control for high precision and efficiency.

Components:

AC Motor: Synchronous (permanent magnet rotor) or induction.

Feedback Device: Resolver or high-resolution encoder.

Inverter/Drive: Converts DC to variable-frequency AC for motor control.

Working Mechanism:

Input Signal: A reference command (position, speed, or torque).

Stator Magnetic Field: The inverter generates a rotating magnetic field by varying the frequency and phase of AC supply.

Rotor Interaction:

Synchronous Motor: Permanent magnet rotor locks to the stator’s rotating field.

Induction Motor: Induced currents in the rotor create torque.

Feedback Control: The encoder/resolver provides real-time rotor position/speed data.

Vector Control: Adjusts stator current magnitude and phase to control torque and flux independently.

Key Takeaways

DC Servo Motors:

Ideal for low-cost, low-speed applications.

Brushed types require maintenance; brushless are more efficient.

AC Servo Motors:

Excel in high-speed, high-precision tasks.

Use advanced control techniques (e.g., Field-Oriented Control).

Feedback is Critical: Both types rely on closed-loop control to minimize error.

Synchronous motor working and applications

 What is a Synchronous Motor?

A synchronous motor is a type of AC motor that operates on the principle of synchronism. It consists of stator and rotor. When the stator is energised it creates a magnetic field and interacts with the rotor, causing it to rotate at a synchronous speed. Once synchronous motors are synchronized, they operate efficiently.

A synchronous motor is a type of AC motor that operates at a speed directly proportional to the frequency of current supplied. It helps the synchronous motor to maintain synchronous speed regardless of changes in load.

Unlike induction motors, which rely on the principle of electromagnetism and experience a change in speed due to a change in load. However, synchronous motors maintain their synchronous speed with the frequency supply irrespective of changes in load making them ideal for applications that require constant speed control such as clocks, timers, and various industrial processes.

The construction of a synchronous motor includes two main components: stator and rotor. The stator is the stationary part of the motor and consists of three-phase windings similar to the induction motor. While the rotor is the rotating part of the motor, it can be either a salient pole or cylindrical. 

Synchronous motor works on the principle of interaction between the stator and rotor. When a three-phase AC supply is provided to windings of stator, they generate a rotating magnetic field (RMF) which interacts with the magnetic field of the rotor, locks the rotor and causes it to rotate at synchronous speed. 

However, unlike induction motors, synchronous motors are not self-starting. At idle conditions, the rotor’s magnetic field experiences alternating torque due to the rotating magnetic field (RMF) of the stator which is insufficient to initiate the rotation of the rotor. To start the rotation, auxiliary methods such as damper windings or an external motor are used to bring the rotor up to synchronous speed before DC excitation is applied.

Working of Synchronous Motor:-

The working of a synchronous motor is based on the principle of synchronism. In this principle, the rotation of the rotor is synchronised with the frequency of the alternating current (AC) supply. Similar to other AC motors, synchronous motors also consist of a stationary part called the stator.

The stator contains wire coils, supplied with alternating current (AC) supply. When these coils are energised with an AC supply, it produces a rotating magnetic field. This rotating magnetic field helps the rotor to rotate. 

The rotor is the rotating part of the motor. It contains either electromagnets or permanent magnets arranged in specific patterns. These magnets are then arranged with a rotating magnetic field produced by the stator. As a result of this interaction, the rotor starts to rotate. 

The most important feature of synchronous motors is their ability to maintain constant speed. They have the ability to synchronize the rotation of the rotor with the frequency of AC supply. 

When the rotor rotates with the magnetic field produced by the stator, an electromotive force (EMF) is induced in rotor windings. This EMF creates a magnetic field in the rotor, which aligns itself with the magnetic field of the stator. As a result, the rotor rotates at the same speed as the rotating magnetic field.

The synchronous speed (Ns) of the synchronous motor is determined by the formula Ns = 120xf/P where f is the frequency of the AC supply and P is the number of poles in the motor. This formula shows that the speed of a synchronous motor is inherently related to the frequency of the AC power supply, typically 50Hz or 60Hz.

These synchronous motors are used in various industrial machinery, pumps, compressors, wind turbines, and daily live applications.

However, precise speed control is achieved by adjusting the frequency of AC supply. By increasing or decreasing, the frequency of supply the motor speed can be adjusted to meet the requirements of specific applications. 

In some synchronous motors, an additional DC supply is required for rotor winding to create the magnetic field produced for synchronisation. This process is known as excitation. It helps synchronous motors to maintain their synchronization with the AC power supply. However synchronous motors are not self-starting.

Unlike other AC motors, which can start and operate without any external source, synchronous motors require an external source for initial rotation to synchronise with the magnetic field produced by the stator. Once synchronous motors are synchronised, they operate efficiently. 

However synchronous motors are not self-starting. Unlike other AC motors, which can start and operate without any external source, synchronous motors require an external source for initial rotation to synchronise with the magnetic field produced by the stator. Once synchronous motors are synchronised, they operate efficiently.

Applications of Synchronous Motor:-

A synchronous motor is an electric motor that operates at a constant speed with the frequency of AC supply irrespective of change in load, which makes it ideal for various applications. 

Here are the most common applications of synchronous motor

Industrial Drives

 Synchronous motor plays an important role in driving industrial machinery such as conveyor systems, mixers, extruders, machine tools, printing presses, and packaging machinery, where constant speed operation is essential for efficiency. 

Power Generation Pump

Synchronous motors are used in power plants to drive large generators or pumps and improve the power factor correction to enhance the efficiency of the power generation plants. 

Pumps

Synchronous motors are used in the pump system to drive the rotor of the pump and maintain constant fluid flow. 

Clock and Timer

Synchronous motors are used in clocks and timers to ensure accurate time-keeping over extended periods without any fluctuations. 

Hydro Electric Powerplant

Hydro Electric Powerplant

Hydroelectric power is obtained from the potential energy of a water body located at a certain height above a river channel, which is converted into kinetic energy, and finally into electrical energy at the lowest point in the river channel.

1 . Hydroelectric power plant

A hydroelectric power plant comprises a set of facilities and electromechanical equipment used to transform water's potential energy into electrical energy, and can operate constantly. The available electrical energy is proportional to the flow rate and the drop in elevation.

2 . Parts of a hydroelectric power plant

A hydroelectric power plant has the following parts:

• Dam or weir: it contains the river water, forming a reservoir behind it and thus creating a water drop that is used to produce energy. Dams can be made of earth or concrete (the latter is the most common one).

• Spillways: They release part of the impounded water without passing through the turbines; water can then be used for irrigation purposes. They are located on the main wall of the dam and can be at the top or at the bottom. Most of the water goes into a plunge pool at the toe of the dam, to prevent scour damage by the falling water.

• Water intakes: they let in the impounded water towards the turbines through a penstock. Water intakes have gates to control the amount of water that reaches the turbines and grids to filter out any debris such as trunks, branches, etc.

• Powerhouse: it houses the hydraulic and electrical equipment (turbines, generators, transformers) and the service area with control and testing rooms. It has inlet and outlet gates to ensure the equipment area can be dry in case of repairs or disassembling equipment.

• Turbines: they harness the energy of the water that goes through them to rotate around a shaft. There are three main types of turbines: Pelton, Francis and Kaplan turbines (propeller type).

• Transformers: electrical devices to increase or decrease the voltage in an alternating current circuit, while maintaining the electric power.

• Electrical power transmission lines: cables to transmit the electricity generated.

HYDRO ELECTRIC POWER PLANT

3 . Types of hydroelectric power plants

There are three types of hydroelectric power plants:

• Run-of-the-river power plants: these hydroelectric power plants withdraw water from the river based on the available water flow, which depends on environmental conditions, and run it through the turbines. The drop in elevation is small and these power plants require a constant water flow.

• Hydroelectric power plants with a reservoir: they are hydroelectric power plants that use an upstream water impoundment with a dam. The reservoir regulates the amount of water going through the turbines and producing electrical energy year-round, independently of the water flow in the river. This type of plants allows using most of the energy produced and the kilowatts hour are usually cheaper.

• Pumped-storage hydroelectric power plants: they are hydroelectric power plants with two reservoirs at different elevations, which are operated when there is an extra demand of electrical energy. Water in the upper reservoir goes through the turbine and flows into the lower reservoir, and is later pumped back up to the upper reservoir at the time of day when there is not such a high demand of energy.

This is the over view about HYDRO ELECTRIC POWER PLANT 

If any Query comment me below, THANK YOU, ALL THE BEST.

INDUCTION AND SYNCHRONOUS MACHINES

 

Construction of Three Phase Induction Motor

The three phase induction motor is the most widely used electrical motor. Almost 80% of the mechanical power used by industries is provided by three phase induction motors because of its simple and rugged construction, low cost, good operating characteristics, the absence of commutator and good speed regulation. In three phase induction motor, the power is transferred from stator to rotor winding through induction. The induction motor is also called a synchronous motor as it runs at a speed other than the synchronous speed. 

Like any other electrical motor induction motor also have two main parts namely rotor and stator. 

1. Stator: As its name indicates stator is a stationary part of induction motor. A stator winding is placed in the stator of induction motor and the three phase supply is given to it. 

2. Rotor: The rotor is a rotating part of induction motor. The rotor is connected to the mechanical load through the shaft. 

1. Squirrel cage rotor, 

2. Slip ring rotor or wound rotor or phase wound rotor. 

Depending upon the type of rotor construction used the three phase induction motor are classified as: 

1. Squirrel cage induction motor, 

2. Slip ring induction motor or wound induction motor or phase wound induction motor.

Stator of Three Phase Induction Motor:

 The stator of the three-phase induction motor consists of three main parts : 

1. Stator frame, 

2. Stator core, 

3. Stator winding or field winding. 

Stator Frame:

It is the outer part of the three phase induction motor. Its main function is to support the stator core and the field winding. It acts as a covering, and it provides protection and mechanical strength to all the inner parts of the induction motor. The frame is either made up of die-cast or fabricated steel. The frame of three phase induction motor should be strong and rigid as the air gap length of three phase induction motor is very small. Otherwise, the rotor will not remain concentric with the stator, which will give rise to an unbalanced magnetic pull. 

Stator Core:

The main function of the stator core is to carry the alternating flux. In order to reduce the eddy current loss, the stator core is laminated. These laminated types of structure are made up of stamping which is about 0.4 to 0.5 mm thick. All the stamping are stamped together to form stator core, which is then housed in stator frame. The stamping is made up of silicon steel, which helps to reduce the hysteresis loss occurring in the motor. 

Stator Winding or Field Winding:

The slots on the periphery of the stator core of the three-phase induction motor carry three phase windings. We apply three phase ac supply to this three-phase winding. The three phases of the winding are connected either in star or delta depending upon which type of starting method we use. We start the squirrel cage motor mostly with star-delta stator and hence the stator of squirrel cage motor is delta connected. We start the slip ring three-phase induction motor by inserting resistances so, the stator winding of slip ring induction motor can be connected either in star or delta. The winding wound on the stator of three phase induction motor is also called field winding, and when this winding is excited by three phase ac supply, it produces a rotating magnetic field

Types of Three Phase Induction Motor:

1. Squirrel Cage Three Phase Induction Motor:

The rotor of the squirrel cage three phase induction motor is cylindrical and have slots on its periphery. The slots are not made parallel to each other but are bit skewed (skewing is not shown in the figure of squirrel cage rotor besides) as the skewing prevents magnetic locking of stator and rotor teeth and makes the working of the motor more smooth and quieter. The squirrel cage rotor consists of aluminum, brass or copper bars (copper bras rotor is shown in the figure beside). These aluminum, brass or copper bars are called rotor conductors and are placed in the slots on the periphery of the rotor. The rotor conductors are permanently shorted by the copper, or aluminum rings called the end rings. To provide mechanical strength, these rotor conductors are braced to the end ring and hence form a complete closed circuit resembling like a cage and hence got its name as squirrel cage induction motor. The squirrel cage rotor winding is made symmetrical. As end rings permanently short the bars, the rotor resistance is quite small, and it is not possible to add external resistance as the bars get permanently shorted. The absence of slip ring and brushes make the construction of Squirrel cage three-phase induction motor very simple and robust and hence widely used three phase induction motor. These motors have the advantage of adopting any number of pole pairs. The below diagram shows a squirrel cage induction rotor having aluminum bars short circuit by aluminum end rings.

Advantages of Squirrel Cage Induction Rotor:

1. Its construction is very simple and rugged. 

2. As there are no brushes and slip ring, these motors requires less maintenance. 

Applications of Squirrel Cage Induction Rotor:

We use the squirrel cage induction motors in lathes, drilling machine, fan, blower printing machines, etc

2. Slip Ring or Wound Rotor Three Phase Induction Motor:

In this type of three phase induction motor the rotor is wound for the same number of poles as that of the stator, but it has less number of slots and has fewer turns per phase of a heavier conductor. The rotor also carries star or delta winding similar to that of the stator winding. The rotor consists of numbers of slots and rotor winding are placed inside these slots. The three end terminals are connected together to form a star connection. As its name indicates, three phase slip ring induction motor consists of slip rings connected on the same shaft as that of the rotor. The three ends of three-phase windings are permanently connected to these slip rings. The external resistance can be easily connected through the brushes and slip rings and hence used for speed controlling and improving the starting torque of three phase induction motor. The brushes are used to carry current to and from the rotor winding. These brushes are further connected to three phase star connected resistances. At starting, the resistance is connected to the rotor circuit and is gradually cut out as the rotor pick up its speed. When the motor is running the slip ring are shorted by connecting a metal collar, which connects all slip ring together, and the brushes are also removed. This reduces the wear and tear of the brushes. Due to the presence of slip rings and brushes the rotor construction becomes somewhat complicated therefore it is less used as compare to squirrel cage induction motor.

Advantages of Slip Ring Induction Motor:

1. It has high starting torque and low starting current. 

2. Possibility of adding additional resistance to control speed. 

Application of Slip Ring Induction Motor:

Slip ring induction motor are used where high starting torque is required i.e in hoists, cranes, elevator etc

Difference between Slip Ring and Squirrel Cage Induction Motor:

Production of Rotating Magnetic Field: 

The production of Rotating magnetic field in 3 phase supply is very interesting. When a 3-phase winding is energized from a 3-phase supply, a rotating magnetic field is produced. This field is such that its poles do no remain in a fixed position on the stator but go on shifting their positions around the stator. For this reason, it is called a rotating field. It can be shown that magnitude of this rotating field is constant and is equal to 1.5 fm where fm is the maximum flux due to any phase. 

A three phase induction motor consists of three phase winding as its stationary part called stator. The three phase stator winding is connected in star or delta. The three phase windings are displaced from each other by 120°. The windings are supplied by a balanced three phase ac supply

The three phase currents flow simultaneously through the windings and are displaced from each other by 120° electrical. Each alternating .phase current produces its own flux which is sinusoidal. So all three fluxes are sinusoidal and are separated from each other by 120°. If the phase sequence of the windings is R-Y-B, then mathematical equations for the instantaneous values of the three fluxes ΦR , ΦY , ΦB can be written as, 

ΦR = Φmsin(ωt) 

ΦY = Φmsin(ωt - 120) 

ΦB = Φmsin(ωt - 240) 

As windings are identical and supply is balanced, the magnitude of each flux is Φm .

Case 1 : 

ωt = 0 

ΦR = Φmsin(0) = 0 

ΦY = Φmsin(0 - 120) = -0.866 Φm 

ΦB = Φmsin(0 - 240) = +0.866 Φm 

Case 2 : 

ωt = 60 

ΦR = Φmsin(60) = +0.866 Φm 

ΦY = Φmsin(- 60) = -0.866 Φm 

ΦB = Φmsin(- 180) = 0 

Case 3 : 

ωt = 120 

ΦR = Φmsin(120) = +0.866 Φm 

ΦY = Φmsin(0) = 0 

ΦB = Φmsin(- 120) = -0.866 Φm 

Case 4 : 

ωt = 180 

ΦR = Φmsin(180) = 0 

ΦY = Φmsin(60) = +.866 Φm

ΦB = Φmsin(- 60) = -0.866 Φm

By comparing the electrical and phasor diagrams we can find the the flux rotates one complete 360 degree on the 180 degree displacement of flux. 

Effect of Frequency on Rotor Parameter in the Three Phase Induction Motor:

Rotor emf 

When the three phase supply is given to the three phase induction motor, the rotating magnetic field is produced which rotates at synchronous speed. 

Starting condition:

• The speed of the rotor during starting condition is zero therefore the relative speed between stator rotating magnetic field and rotor speed is Ns – N = Ns 
• When the rotor conductors cut the rotating magnetic field, an emf will be induced in it. 
• Let us consider that the induced emf in the rotor is E2

Running condition:

• Let us assume that the induced emf in the rotor is E2’. The relative speed between stator rotating magnetic field and rotor speed is Ns – N. 
• The induced emf in the rotor condition is

Relative speed                                                 Rotor emf

    Ns                                                                           E2

    Ns – N                                                                    E2’                                             

    E2’ = [ Ns – N / Ns ] E2

    E2’ = s E2

• The slip at starting is unity therefore the rotor induced emf is same as that of starting condition.
• However the rotor induced emf decreases as the speed increases or slip decreases.

DC Biasing of BJT'S

Biasing of BJT'S

DC Biasing of BJT'S:

Objectives:

 To Understand : 

• Concept of Operating point and stability 

• Analyzing Various biasing circuits and their comparison with respect to stability 

BJT – A Review 

• Invented in 1948 by Bardeen, Brattain and Shockley 

• Contains three adjoining, alternately doped semiconductor regions: Emitter (E), Base (B), and Collector (C) 

• The middle region, base, is very thin

 • Emitter is heavily doped compared to collector. So, emitter and collector are not interchangeable. 

Three operating regions:

• Linear – region operation: 

– Base – emitter junction forward biased – Base – collector junction reverse biased 

• Cutoff – region operation: 

– Base – emitter junction reverse biased – Base – collector junction reverse biased 

• Saturation – region operation: 

– Base – emitter junction forward biased – Base – collector junction forward biased

Introduction - Biasing:

The analysis or design of a transistor amplifier requires knowledge of both the dc and ac response of the system. In fact, the amplifier increases the strength of a weak signal by transferring the energy from the applied DC source to the weak input ac signal 

• The analysis or design of any electronic amplifier therefore has two components: 

• The dc portion and 

• The ac portion 

During the design stage, the choice of parameters for the required dc levels will affect the ac response.

What is biasing circuit? 

• Once the desired dc current and voltage levels have been identified, a network must be constructed that will establish the desired values of IB, IC and VCE, Such a network is known as biasing circuit. A biasing network has to preferably make use of one power supply to bias both the junctions of the transistor.

Purpose of the DC biasing circuit:

• To turn the device “ON” 

• To place it in operation in the region of its characteristic where the device operates most linearly, i.e. to set up the initial dc values of IB, IC, and VCE

Biasing circuits: 

• Fixed – bias circuit 

• Emitter bias 

• Voltage divider bias 

• DC bias with voltage feedback 

• Miscellaneous bias

Diode Clippers, Definition and Classification

clippers:

Diode Clipping Circuit:-

    The diode clipper is an electronic circuit consisting of a diode and resistor. That Clip's (or) Cut's of an input signal. The output of the clipping circuit is depends on the Diode orientation and input signal, Such a circuit is termed as diode clipper.

    The clipped-off signal produced at the output becomes flat when a certain voltage limit has reached and due to this it is also termed as diode limiter.

    The half-wave rectifier is an example of a diode clipping circuit because when the diode is forward biased any voltage below zero is clipped off and, similarly, when the diode is reverse biased any voltage above zero is clipped off.

Clippers are classified by the orientation of the diode as shown in below:

1. series clipper
• Series POSITIVE Clipper
1. Series POSITIVE Clipper with POSITIVE Bias
2. Series PSITIVE Clipper with NEGATIVE Bias
• Series NEGATIVE Clipper
1. Series NEGATIVE Clipper with POSITIVE Bias
2. Series NEGATIVE Clipper with NEGATIVE Bias
2. Parallel Clipper
• Parallel POSITIVE Clipper
1. Parallel POSITIVE Clipper with POSITIVE Bias
2. Parallel POSITIVE Clipper with NEGATIVE Bias
• Parallel NEGATIVE Clipper
1. Parallel NEGATIVE Clipper with POSITIVE Bias
2. Parallel NEGATIVE Clipper with NEGATIVE Bias