Advantages and disadvantages of cycloconverter

Cycloconverter is actually AC-AC converter. It converts a constant voltage and constant frequency AC waveform to another AC waveform. This article gives information about some advantages and disadvantages of cyclo-converter to know more details about cyclo-converter. 

Advantages of cyclo-converter :
  • Efficiency is very high compared to other converters
  • Four quadrant operation is possible because cyclo-converter is capable of power transfer in both the directions
  • AC power at one frequency is directly converted to a lower frequency in a single conversion
  • If one of the SCR fails, the cyclo-converter operates with a distorted output
  • In this converter, power transfer is possible from supply load and vice versa at any power factor
  • Dynamic response is good 
  • Smooth low-speed operation
Disadvantages of cyclo-converter :
  • Control circuit become complex so difficult to design
  • The output frequency of the cyclo-converter is 1/3th or 1/2th for responsible power output and efficiency
  • Power factor is too much poor at large values of α
  • More distortion at low frequencies
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Application of cycloconverter

Cyclo-converter is basically converted input power at one frequency to output power at a different frequency with one stage of conversion.

Basically, cyclo-converter is two types namely :  
  • Step down cyclo-converters
  • Step-up cyclo-converters
The application of cyclo-converters include the following :
  • Speed control of high power ac drives.
  • Static VAr compensation.
  • Induction heating.
  • Synchronous motor.
  • Rolling mill drives.
  • Mine winders.
  • Cement mill drives.
  • This converter also has used for converting variable speed alternator to constant frequency output with age for use as a power supply in aircraft or shipboards.
  • HVDC transmission system.
  • Grinding mills.
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Cycloconverter operation

A principle of cyclo-converter operation :
  • A cyclo-converter is a one types of device that converts AC power at a certain frequency into AC power but lower frequency.
  • The principle of cyclo-converter is described given below by using a single phase to single phase step-up converters and single phase to single phase step down converters.
Cyclo-converter operation
Types of cyclo-converter :
  1. Single phase to single phase cyclo-converter 
  2. Three phases to three phase cyclo-converter 
Single phase to single phase bridge type cyclo-converter 
  • The operation of bridge type cyclo-converter shown in the figure. It can be easily explained for both discontinuous and continuous load current. The voltage and current waveform would again be as shown in the figure. 
  • It consists of a total of eight thyristors, four for the positive group and four for the negative group. 

Bridge type single phase to single phase cyclo-converters
This converter having to back to back connection of full wave rectifier. We have to assume that get on forth of the input voltage as the output.  For the first two cycles of  VS the positive converters operate supplying current to the load and the input voltage get rectified. In the next two cycles, the other converter called the -ve converters, it will operate the current load in the opposite direction called a reverse direction. so we also conclude that one converter is an operation the other converter will be disabled conditions, therefore, there is no current circulating between rectifiers.

Three phases to three phase cyclo-converters 

Out of the several configurations of 3 phase to 3 phase cyclo-configuration as shown in the figure. Here only one important scheme used for a large industrial drive is presented. Each phase of the 3 phase output must have a displacement of 120 degrees. The figure shows the circuit arrangement of 3-phase to three phase cyclo-converter using three sets of three-phase half wave circuit employing a total of 18 thyristors. 

3-phase to 3-phase cyclo-converters
Applications :
The application of cyclo-converters include the following :
  • Speed control of high power ac drives.
  • Static VAr compensation.
  • Induction heating.
  • Synchronous motor.
  • Rolling mill drives.
  • Mine winders.
  • Cement mill drives.
  • For converting variable speed alternator to constant frequency output with age for use as a power supply in aircraft or shipboards.
  • HVDC transmission system.
  • Grinding mills.

CRT advantages and disadvantages

CRT full form stands for cathode ray tube also known as the picture tube. It is less bulky, as well as used in various applications. This article gives the advantages and disadvantages of CRT to give more information about CRT.

Advantages of CRT :
  • Less expensive than other display technology
  • Fast response time
  • It can operate at any resolution, geometry and also for aspect ratio without the need for rescaling the image
  • Highest pixel resolutions generally available
  • They produce more colours
  • CRT also suitable for use even in dim or dark light
  • Produce a very dark black and grayscale and are the reference standard for all professional calibrations
  • Easily increases the monitor's brightness by reflecting the light
  • Fast response times and no motion artifacts
Disadvantages of CRT :
  • Big back and take up space on a desk
  • Not suitable for very bright environments because less bright than LCD
  • They are large, heavy and bulky
  • Consume a lot of electricity and  also produce a lot of heat
  • Geometrical error at edges
  • Flickering at 50-80 Hz
  • Harmful DC and AC electric and magnetic fields
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What is electric drive

  • In many of industrial applications, electricity is one of the most important components. 
  • An electric motor is the most important part,  it is an energy transmitting device and the working machine.
  • An electric motor is the source of the motive power. An energy transmitting device delivers power from electric motor to the driven machine, it usually consists of a shaft, belt, rope, etc. 
  • An electric drive together with its working machine constitute is an electric drive system.
  • A ceiling drives together with its speed regulator but without blades is an example of an electric drive.
  • In short, a drive is a combination of the various system combined together for the purpose of motion control, so it is many more benefits of electric drive to motion control.
  • Electric drive is mainly two types: AC drive and DC drive In that drive motive power in dc and AC drive is provided by dc motors and ac motors respectively. This electric drive uses many devices like pumps, fans, robots, etc.
DC drives :

 DC motors are used extensively in adjustable speed drive and position control applications. It can be also used conjunction with power electronic converters are dc separately excited motor or dc series motor. So depending upon the type of AC source or the method of voltage control, dc drive classified as under :
Advantages and disadvantages of an electrical drive :

The following advantages of electrical drive given below :
  • It has a very large range of torque, speed, and power.
  • It is very free from pollution.
  • It can operate on all the quadrants of speed torque plane.
  • Their working is independent of the environment condition.
  • The efficiency of the drive is high.
  • The drive can easily be started and it does not require any refueling.
The following disadvantages of electrical drive given below :
  • It can cause noise pollution.
  • The initial cost of the system is high.
  • The application of the drive is limited.
  • It has a poor dynamic response.
  • The output power obtained of conductor or a short circuit device so the system may get damaged due to which several problems occur.
  • The output power obtained from the drive is low.
Application of electrical drive :
  • A ceiling fan motor with a regulator.
  • A motor and conveyor belt with material on its belt.
  • Food mixer without food is processed.
  • It is also used as a large number of industrial and domestic applications.
  • It is also used Rolling mills and textile mills as well as some machine tools.
  • Some other applications like pumps, robots, washing, etc.
  • It can also use various traction like an electric train, electric buses, trams, trolleys, battery-driven solar power vehicles.

Single phase DC drives feature

Electric drive is designed to convert electrical energy into mechanical energy and provide electrical control.  Let we check features of single-phase DC drives one by one below :
  • Linear torque control
  • Adjustable current limit
  • Maximum speed settings
  • Stall relay contact
  • Armature voltage
  • Speed reference 0-10V 
  • Ramp single output
  • Current single output
  • Speed single output
  • Control fuses fitted
  • Stability adjustment
  • Suitable for shunt
  • Calibration range switches
  • Total demand signal output
  • Zero speed relay contact
  • IR compensation
  • Total demand signal output
  • Speed signal output
  • Current signal output
  • Power on and stall indicator LEDs

Single phase DC drives

  • Electric drive is a combination of the various system combined together for the purpose of motion control, so it is many more benefits of electric drive to motion control.
  • Some basic features of single-phase DC drives is that speed single output, control fuses fitted,  and it can provide stability adjustment etc.
  • The general circuit arrangement for single phase dc drives as shown in the figure.
  • The arrangement for the speed control of a separately excited for dc motor from single phase source.
  • In this circuit to shown in the figure, it can insert inductor in series with the armature circuit to reduce the ripple in the armature current and also to make the armature current continuous for low values of motor speed to shown in the figure. 
Single phase DC drives 
Single phase dc drive may be subdivided as under :

Three phase half wave converter drives

  • Three phases half wave converter drive consisting of two converts and a separately excited dc motor.
  • The armature circuit of the motor is fed through a three-phase half wave converter whereas its field is energized through a three-phase semi-converter.
  • Two quadrant operation can also be obtained from three phases half wave converter drive in case motor field winding is energized from a single phase or three phases full converter.
Three phases half wave converter drive 


 V0 = Vt =  3Vml / 2∏ * Cos ɖ  for the  0< ɖ <  ∏

The voltage expression is valid only for the contentious armature current. for three phase semi-converter, the average value field voltage from the equation given by this equation given below,

                                        Vf =  3Vml/2∏ * (1+Cos  ɖ1 ) for 0<  ɖ1 <  ∏


  Vml = Is the maximum value of line voltage and ɖ is the firing angle for converter 1.

Application :

A three-phase half wave converter drive is not normally used in the industrial application as introduce dc component in the ac supply lines.

Three phase dual converter drive

  • The schematic diagram of three phases dual converter d drive as shown in the figure.
  • As per the circuit diagram converter, 1 allows motor control 1 and 4 quadrants whereas with converter 2 the operation in 2 and 3 quadrants obtained
  • For reversing the polarity of motor generated emf for regeneration purpose, field circuit must be energized from a single phase or three phases full converter.
Three phases dual converter dc drive
When converter 1 or 2 is in operation

Average output voltage,

V0 =  Vt is =  3Vm l/ 2∏  * Cos  ɖ1  for 0<  ɖ1 <  ∏

With a 3 phase full converter in the filed circuit,

Vf  =  3Vml/2∏ * Cos  ɖf  for 0<  ɖf <  ∏

In case of circulating types of dual converter, ɖ1  + ɖ2 =180 degree

Application :

  • Direction and speed control dc motors.
  • Applicable wherever the reversible dc is required.
  • Industrial variable speed dc drive.

Three phase full converter drive

The circuit diagram of one three phase full converter in the armature circuit and 1 phase full converter in the field circuit, is as shown in figure.

 Three phase full converter dc drive

For converter 1 in the armature circuit, the average output voltage from given by, 

                                V0 =  Vt =  3Vml/2∏  * Cos  ɖ  for 0<  ɖ <  ∏
For converter 2 in the field circuit,

                                    Vf =  3Vml/2∏  * Cos ɖ1  for 0< ɖ1  <  ∏ 

Three phase semi converter drive

  • The circuit diagram of 3 phase semi-converter feeding a separately excited dc motor is shown in the figure.
  • Shown in the figure, the field winding of the motor is also connected to the three-phase semi-converter. 
  • This drive offers one quadrant operation and is used up to about 115 kW ratings.

Figure - 3-phase semi converter feeding a separately excited dc motor



For converter 1,     V0  = V t  = 3Vml/2∏ * (1 + Cos  ɖ  )  for 0 <  ɖ  <  ∏

For converter 2,    Vf   = 3Vml/2∏ * (1 + Cos  ɖ1  )    for 0 <  ɖ1 <  ∏

Single phase half wave converter drives

  • A single phase half wave converter drive a shown in the figure. A separately excited dc motor, fed through single phase half wave converter, as shown in the figure.
  • In this converters, motor field circuit is fed through a single phase semiconductor in order to reduce the ripple content in the field circuit.
  • So in a single phase, half wave converter feeding a dc motor offers one quadrant drive.
  • For a single phase half wave converter, average output voltage of converter the voltage V0  = armature terminal voltage. Vt is given by,
                              V0 = Vt = Vm / 2∏ * ( 1+  Cos ɖ )    for 0 < ɖ <  ∏
Where Vm = maximum value of the source voltage

For single phase semi converter in the field circuit, the average output voltage is given by 

                                            Vf   =  Vm / ∏ * ( 1+  Cos ɖ )  0 < ɖ1  <  ∏
Single phase half wave converter drive

Advantages and disadvantages of AC drive

AC drive is devices for controlling motor speed by converting DC to AC. AC drive has improved productivity and also have made a huge contribution to the development in electronics industries. This article gives information about some advantages and disadvantages of AC drive to know more details about AC drive.

Advantages of AC drive :
  • It can use conventional, low cost, 3 phase AC induction motor for most applications
  • Require very less maintenance
  • AC drive save energy during the part load operation
  • Smaller, lighter, more commonly available 
  • Works better in high-speed operation 
  • A back up is available in the controller fails 
  • Work in a hazardous area like factory area chemical, petrochemical etc whereas DC motors are unsuitable for such environment because of commutator sparking in a device.
Disadvantages of AC drive :
  • Power converter for the control of AC motors are more complex compared to other drives
  • Power converters for AC drives are more expensive
  • Power converters for AC drives generate harmonics in the supply system and also load circuit

Single phase semicoverter drive

  • To show in the figure, a separately excited dc motor, fed through two single-phase semi-converter, one for the armature circuit and the other for the field circuit, is shown in the figure. 
  • Both converter 1, as well as converter 2, are connected to the same single phase source.
  • This converter also offers one quadrant drive and it can be used up to about 15 kW dc drives.
  • The waveform for current and voltage are sketched in the figure on the assumption of ripple-free armature current.
  • Load voltage waveform for V0  = Vt is the same as shown in the figure.
                                             V0 = Vt = Vm/∏ * ( 1+  Cos ɖ )    

    for field circuit, Vf = Vm / ∏ * ( 1+  Cos ɖ1 ) 
Single phase semi converter drive

Single phase full converter drive

  • In single phase full converter, there are two full converters, one converter feeding the armature circuit and the other converter feeding the field circuit of a separately excited dc motor are shown in circuit diagram. 
  • For regenerative braking of the motor, the power must flow from the motor to be AC source and also this is feasible only if motor counter emf is reversed because then ea it would be negative, shown in the figure.
  • So the direction of the current can not be reversed as SCR are a unidirectional device.
  • In order that current in field winding can be reversed, the field winding must be energized through single phase full converter as shown in the figure.
For the armature converter 1,   V0 = Vf  =  (2Vm/∏ ) * Cos ɖ   for 0 < ɖ <  ∏

For single phase semi converter in the field circuit, the average output voltage is given by the following formula, 
      
           Same way for the field converter 2,   Vf   =  (2Vm / ∏ ) * Cos ɖ1   for 0 < ɖ1  <  ∏

Single phase full converter drives

Three phase dc drives

  • Large dc motor are always three phase converters for their speed control.
  • A three phase controlled converters feed power to the armature circuit for containing speeds below base speed.
  • Another three phase controlled converter is inserted in the field circuit for getting speeds above base speed.
  • The output frequency of three phase converter is higher than those single phase converter.
  • Therefore, for  reducing the armature current ripple, the inductor in a three phase dc drive is of lower value than that in a single phase dc drive.
  • As the armature current is mostly continuous, the motor performance in 3 phase dc drives is superior to those in single phase dc drive.

Single phase dual converter drive

  • A single phase dual converter drive, obtained by connecting two full converters in anti parallel, as shown in figure. The feeding is a separately excited dc motor.
  • It uses is limited to about 15 kW dc drive.
  • It offers four quadrant operation.
  • For working in first and fourth quadrant, converter 1 is in operation.
  • For operation in second and third quadrant, converter 2 is energized.
  • For the four quadrant operation demands that field winding of the motor is emerged from the single phase or three phase full converter.
For the armature converter 1 in operation,   Vt =  2Vm/∏ * Cos ɖ1   for 0< ɖ1 <  ∏
For the armature converter 2 in operation,   Vt =  2Vm/∏ * Cos ɖ2   for 0< ɖ2 <  ∏

Where  ɖ1 +  ɖ2 = ∏
For field converter Vf =  2Vm/∏ * Cos ɖ3   for 0< ɖ3 <  ∏
Single phase dual converter

What is spread spectrum

Overview :

Spread spectrum is a one types of techniques it can be used for transmitting radio or telecommunication signal. The increasing demand of wireless communication have faced problems because of limited spectrum capacity and multi-path propagation. These problems can be minimized by spread spectrum communication.

Feature of spread spectrum :
  • Capability of multiple access
  • Resistant to jamming
  • It has the ability to resist multi path propagation 
  • Because of multi-path propagation. It provide  immunity to distortion
  • Higher channel capacity
  • It can not be intercepted by any unauthorized person
Spread spectrum model :

Figure shows the general block diagram of a spread spectrum digital communication system. so not let us talk about one by one block in spread spectrum model in detail.

To shown in figure the input is given to a channel encoder that produces the analog signal with narrow bandwidth at the center frequency.

The the signal is modulated by a spreading code or sequence. The spreading code is generated by pseudo noise or pseudo random number generator. 

Modulation increases the bandwidth of the signal to be transmitted. At the receiver end the digit sequence is used to demodulate the spread signal. The signal is sent to the recover the data.
Spread spectrum model
Advantages of spread spectrum :
  • Reduced cross talk interference
  • Inherent security
  • Hard to detect
  • Longer operating distance
  • Better voice quality 
  • Harder to jam
  • Interception of signal will be difficult
  • Privacy due to pseudo-random code
  • Co-existence
  • Less multi path fading
Processing gain of spread spectrum :

 The processing gain is defined as the factor by which the bandwidth of the message signal is increased.

 Processing gain : N = Bss / B

 Where, 
B = Message signal bandwidth
Bss = Spread spectrum signal bandwidth

 Types of spread spectrum : 
Application of Spread spectrum :
  • Prevent signal jamming
  • Cellular technology
  • Cell phones
  • Global positioning system
  • Wireless local are network security
  • Prevent Interference at specific frequency
  • In obtaining the message signal
You may also check it out difference between DSSS and FHSS

Uninterruptible power supplies

Before we learn about UPS system first let we check out what is full form of UPS. There are several applications of UPS where even a temporary power failure can cause a great deal of public inconvenience leading to large economic losses. UPS can be used in electrical equipment where unexpected power disruption could cause injuries, serious business, or data losses, and also some many more advantages of the UPS system. Earlier UPS systems were based on an arrangement shown in the figure. 

 Working of rotating type UPS system :
  • This scheme is usually called rotating types UPS. This arrangement consists of DC motor driven alternator, the shaft of which is also coupled to a diesel engine. 
  • The UPS system needed is taken from the alternator output terminals. When the main supply fails, the diesel engine is run to take over the load. 
  • The battery bank is able to maintain the alternator speed through the dc motor and the flywheel, thus giving a no break supply to the critical load.
  • Static UPS system is two types, short break UPS and no break UPS. 
Short  break UPS :
  • In a situation where short interruption in supply can be tolerated, the short break UPS showed in the figure. In this system, the main ac supply is rectified to dc.
  • This dc output from the rectifier charges the batteries and is also converted to ac by an inverter. After passing through the filter, AC can be delivered to load in case normally off contacts are closed.
 No break UPS  :
  • When no break UPS supply is required, the static UPS system shown in the figure. In this supply is rectified and the delivered power to maintain the required charge on the batteries. 
When users no break UPS system has the following advantages :
  • The inverter can be used to condition the supply delivered to load
  • Load gets protected from transients in the main ac supply
  • The inverter output frequency can be maintained at the desired value In case of inverter failure is detected, the load is switched on the main ac supply directly by turning on the normally off static switch and opening the normally on a static switch.
The standby batteries in the UPS system are either nickel-cadmium or lead-acid types. NC battery has the following advantages :
  • Their electrolyte is non-corrosive. 
  • Their electrolyte does not emit an explosive gas when charging
  • NC batteries cannot be damaged by overcharging or discharging, these have therefore longer life
  • Cost of  NC  batteries is like, however, two or three times that of lead acid batteries.

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