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 =  V_t =  3V_ml/2∏  * Cos  ɖ  for 0<  ɖ <  ∏

For converter 2 in the field circuit,

                                    V_f =  3V_ml/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  = 3V_ml/2∏ * (1 + Cos  ɖ  )  for 0 <  ɖ  <  ∏

For converter 2,    V_f   = 3V_ml/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 = V_t = V_m / 2∏ * ( 1+  Cos ɖ )    for 0 < ɖ <  ∏

Where V_m = maximum value of the source voltage

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

                                            V_f   =  V_m / ∏ * ( 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  = V_t is the same as shown in the figure.

                                             V₀ = V_t = V_m/∏ * ( 1+  Cos ɖ )    

   for field circuit, V_f = V_m / ∏ * ( 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 = V_f  =  (2V_m/∏ ) * 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,   V_f   =  (2V_m / ∏ ) * 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.

The three phase dc drive, as in single phase dc drive, may be subdivided an under :

• Three phase half wave converter drives
• Three phase semi-converter drive
• Three phase full converter drives
• Three phase dual converter drives

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,   V_t =  2V_m/∏ * Cos ɖ₁   for 0< ɖ₁ <  ∏

For the armature converter 2 in operation,   V_t =  2V_m/∏ * Cos ɖ₂   for 0< ɖ₂ <  ∏

Where  ɖ₁ +  ɖ₂ = ∏


For field converter V_f =  2V_m/∏ * 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 : 

• Direct sequence spread spectrum (DS/SS)
• Frequency hopping spread spectrum (FH/SS)

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.

Full form related to microprocessor X86 programming

Full form related to microprocessor X86 programming

DOS - Disk operating system

CPU - Central processing unit

HLL  - High level language

SSU - Secondary storage unit

IU - Input unit

OU - Output unit

FLOPS - Floating point operation per second

MIPS - Million instruction per second

CU - Control unit

ALU - Arithmetic logic unit

ROM - Read only memory 

RAM - Random access memory

BIU - Bus interface unit

IQ - Instruction queue

CSR - Code segment register 

DSR - Data segment register

ESR - Extra segment register

EU - Execution unit

CF - Carry flag

PF - Parity flag

IF - Interrupt flag

OF - Overflow flag

SF - Sign flag

ZF - Zero flag

TF - Trap flag

DF - Direction flag

U - Undefined 

IP - Instruction Pointer

LIFO - Last in first out

ENDP - End of procedure

EPDM - End of macro

EXTRN - External

PTR - Pointer

LEA - Load effective address

LDS - Load register and DS register

LES - Load register and ES register

LAHF - Load AH with flags

SAHF - Store AH in flag register

SHL - Shift logical left

SAR - Shift arithmetic right

SAL - Shift arithmetic left

POPF - Pop flag register

POPA - Pop all registers

POP - Pop register

PUSHA - Push all register\

ROL  - Rotate left

ROR - Rotate right

RCL - Rotate through carry left

RCR - Rotate through carry right

ADD - Addition

ADC - Addition with carry

INC  - Increment

SUB - Subtraction

SBB - Subtract with borrow

AAA - ASCII adjust for addition

AAS - ASCII adjust for subtraction

AAM - ASCII adjust for multiplication

AAD - ASCII adjust for division

DAA - Decimal adjust for addition

DAS - Decimal adjust for subtraction

MUL  - Multiplication

IMUL - Integer multiply

DIV - Division

IDIV - Integer division

CBW - Convert byte to word

CWD - Convert word to double word

TEST - Test and set flags

XOR - Logical exclusive OR

JMP - Jump

NOT - Logically not

JAE - Jump on above or equal 

JNB - Jump or not below

JNC- Jump on not carry

JNBE - Jump on not below or equal 

JB - Jump on below

JNAE - Jump or not above or equal

JC - Jump on carry

JE - Jump on equal

JZ - Jump on zero

JG - Jump on greater than

JNLE - Jump on not less or equal

JGE - Jump on grater or equal

JNL - Jump on not less

JL - Jump on less than

JNGE - Jump on not greater than or equal

JLE - Jump or less than or equal

JNG - Jump or not greater

JNE - Jump on not equal
JNZ - Jump or not zero
JNO - Jump on not overflow
JNP - Jump on not parity
JPO - Jump on parity odd
JNS - Jump on not sign
JO - Jump on overflow
JP - Jump on parity even
JPE - Jump on parity equal
JS - Jump on sign
IRET - Interrupt return
INTO - Interrupt on overflow
CLC - Clear carry
CMC - Complement carry
STC - set carry
CLD - Clear direction flag
STD - Set direction flag
CLL - Clear interrupt flag
STI - Set interrupt flag
HLT - Halt
NOP - No operation
WAIT/FWAIT - Wait or Floating wait

LOCK - Lock shared resources
CLD - Clear direction flag
STD - Set direction flag
MOVS - Moves string
MOVSB - Moves string string byte
MOVSW - Moves string word
LODS - Load string
LODSB - Load string byte
LODSW - Load string word
CMPS - Compare string
CMPSB - Compare string byte
CMPSW - Compare string word
STOS - Store string
STOSB - Store string byte
STOSW - Store string word

Advantages and disadvantages of frequency hopping spread spectrum

There are some of the advantages of frequency hopping spread spectrum (FH-SS) given below :

• It has less distance effect.
• Provide the greatest amount of spreading.
• The bandwidth of these systems is large.
• It has a short acquisition time.
• Best discrimination against multi-path.
• Very large bandwidth.
• The synchronization is not greatly dependent on distance.
• This system can be programmed to avoid some part of the spectrum.

There are some of the disadvantages of Frequency hopping spread spectrum (FH-SS) given below :

• It needs complex and costly digital frequency synthesizers are required to be used.
• It needs error detection.
• The processing gain is higher than that of a direct sequence spread spectrum.
• This system is not useful for the range and range rate measurement.
• The modulation scheme has become obsolete.

Some more advantages of FH/SS compared to DS/SS is given below :

• FS/SS is less susceptible to be near-far problems than DS/SS.
• The processing gain is higher than that of system DS/SS.
• FH/SS can produce signals of wider bandwidth than DS/SS.
• In FS/SS the problem of a relative power level of co-channel signals is not critical as than DS/SS.

Explore more information:

1. Advantages and disadvantages of DSSS
2. What are the difference between DSSS and FHSS

Advantages and disadvantages of GSM

GSM is a cellular technology used for transmitting mobile voice and data services developed by European Telecommunications standards Institutes to describe the protocols for second generation digital cellular networks. 

GSM provides standard features like cell phone encryption, data networking, caller ID, call forwarding, call waiting, SMS and conferencing and it can be used in an application like home automation, mobile technology, toll collection, energy conversion etc. GSM has both advantages and disadvantages of which consumers should be aware of. 

Advantages of GSM :

• More suitable network with robust features.
• No roaming charges on International calls. 
• Worldwide connectivity and extensive coverage. 
• SAIC and DAIC techniques used in GSM provide very high transmission quality. 
• The phone works based on the SIM card so that it is easy to change the different varieties of phones by users. 
• GSM signals don't have any deterioration. 
• Easy to integrate GSM with other wireless technology such as CDMA and LTE.
• It has the ability to use repeaters. 
• Because of the pulse nature of transmission talk time is generally high.

Disadvantages of GSM :

• Bandwidth lag because of multiple users shares the same bandwidth so the transmission can encounter interface. 
• It can interfere with certain electronics, such as hearing aids that are due to pulse transmission technology. As a result, many locations, such as hospitals, airports and petrol pumps require cell phones to be turned off. 
• To increase coverage repeaters are required to be installed. 
• It provided limited data rate capability so for high data rate advanced version of GSM devices are used. 
• Many of GSM technology is patented by Qualcomm thus license needs to be obtained from them. 
• Manufacturers are not releasing IS-95 devices due to the lack of a big market so IS-95 is normally installed in the small tower. 
• GSM has fixed maximum call sites range up to 35 km that is very limited. 
• There is no end-to-end encryption of user data. 
• Several incompatibilities within the GSM standards. 
• Electromagnetic radiation is more with the use of GSM.
• Macrocells affected by the multipath signal loss.

Explore more information:

1. What are the difference between SMS and BBM
2. What are the difference between networking and telecommunication
3. What are the difference between SMS and IM

Static switch definition

A switch having no moving part called as a static switch. Power semiconductor devices which can be turned on and off within a few microseconds can be used as fast acting static switches.

Static switches can be also used for latching, current and voltage detection, a time delay circuit, transducers etc.

A static switch is two types :

1. AC switches
2. DC switches 

If we are using input is ac then ac SS are used while we are using input is DC, DC SS are used. Switching speed for AC switches is governed by the supply frequency and turn off time of thyristor (SCR). 

For DC static switches, the switches speed depends on the commutation circuitry and turn off time of fast thyristor. AC switches may be single phase or three phases. 

Static switches do not change or control the power delivered to load as it is done in a single phase voltage controller In a static switch, the semiconductor switches are turned on at zero crossing of the load current, whereas it is not so single-phase voltage controller.

Static switches are now replacing mechanical and electromechanical switches because of several advantages listed below.

• A static switch has no moving parts, It maintenance is therefore very low
• A static switch has a long operational life
• A static switch has no bouncing at the time of turning on
• On time of a static switch is of the order of 3 microseconds, it has therefore very high switching speed
• Inbuilt AC overvoltage protection
• High-performance AC line quality monitoring

Advantages of static switches

Static switches are now replacing mechanical and electromechanical switches  both because of several advantages are listed below :

• A static switch has no moving parts, therefore, maintenance cost  is very low
• A static switch has a long operational life
• A static switch has no bouncing at the time of when is turning on
• On time of a static switch is of the order microseconds, it has therefore very high switching speed
• Inbuilt AC overvoltage protection
• High-performance AC line quality monitoring

What is frequency hopping spread spectrum

Frequency hopping spread spectrum is a method of transmitting radio signals by rapidly switching a carrier.  

In FHSS among many frequency channels using pseudorandom sequence known to both transmitter and receiver. 

Overview :

In FHSS the data bits that are transmitted in the different frequency slots are changed by the PN sequence.

FHSS is often used as a method to allow multiple transmitter and receiver pairs, it can operate in the same space on he same broad channel at the same time.

In FHSS the data sequence is spread over small frequency slots of the spread spectrum signal.

FHSS is a wireless technology that spreads its signal over rapidly changing frequencies. 

Advantages and disadvantages :

The advantages of Frequency hopping spread spectrum given below :

• It has less distance effect.
• Provide greatest amount of spreading.
• The bandwidth of these system is large.
• It has a short acquisition time.
• Best discrimination against multi-path.
• Very large bandwidth.
• The synchronization is not greatly dependent on distance.
• It can be programmed to avoid some part of the spectrum.

Disadvantages of Frequency hopping spread spectrum given below :

• It needs complex and costly digital frequency synthesizers are required to be used.
• It need error detection.
• The processing gain is higher than that of direct sequence spread spectrum.
• It is not useful for range and range rate measurement.

Application :

• Wireless local area network standard for Wi-Fi.
• Military communication equipment.
• Wireless personal area network standard for bluetooth.

Difference between DSSS and FHSS

DSSS and FHSS both are spread spectrum techniques. There is some difference between spreading the data into the wider bandwidth. FHSS using frequency hopping while DSSS using pseudo noise to modify the phase of the signal. So in this article, you can check some difference between these two spread spectrum. 

Difference :

• Over the complete bandwidth of the spread spectrum signal, the data sequence is spread in DSSS but in FHSS the data sequence is spread over small frequency slots of the spread spectrum signal.
• Cost is more in DSSS compare to FHSS.
• DSSS is relative distance and the system, FHSS is less affected by distance change.
• DSSS used the BPSK method and FHSS used many FSK methods.
• The acquisition time of  DSSS is long while in short in case of FHSS.
• Dwell time is 400 ms in FHSS but in DSSS has no dwell time. 
• Used density is less in DSSS but in more in FHSS.
• Chip rate Rc = 1 /  Tc in DSSS and Chip rate for FHSS is Rc = max (Rh,Rs).
• Interoperability is high in DSSS while low in FHSS. 
• DSSS changes the phase wheres FHSS changes the frequency being used. 
• FHSS is easier to synchronize than DSSS.
• DSSS used in positioning systems while FHSS is not.
• DSSS delivers capacity up to 11 Mbps but in FHSS supports up to 3 Mbps.
• DSSS is a very sensitive technology while FHSS is a robust one. 
• DSSS ideal for point to point applications while in FHSS can be used in point to multi-point deployment with better performance. 
• DSSS systems use a carrier that remains fixed to a specific frequency band while FHSS systems use a radio carrier that 'hops' from frequency to frequency in a pattern known as transmitter and receiver. 
• Frequencies are randomized in case of FHSS but in constant in case of DSSS. 
• Data is constant is the case of FHSS while randomize in case of DSSS.
• FHSS spreads the signal by hopping with a bandwidth of 83 MHz while in using DSSS spreads the signal by adding redundant with a bandwidth of 22 MHz.
• DSSS prone to errors but at a low level as compared to FHSS system. FHSS produces strong bursty errors. 

Explore more information:

1. Advantages and disadvantages of frequency hopping spread spectrum

2. Advantages and disadvantages of Direct sequence spread spectrum

Application of direct spread spectrum sequence

• Cordless phones operating in the 900 MHz, 2.4 GHz and 5.8 GHz bands. 
• United status GPS technology, European Galileo and Russian GLONASS satellite navigation systems used DS/SS system with a single PN code in conjunction with FDMA and later it is used to achieve CDMA with multiple PN code.  
• Used in the low probability of intercept signal.
• It obtain message privacy.
• Used military and many commercial application.
• The unique spreading codes support code division multiple access.
• Support various decision making level.
• To reject unintentional  interference.
• To minimize self interference due to the multi-path propagation.
• It is used in automatic meter reading. 
• Used in IEEE 802 11b and Zigbee network. 
• Radio controlled model automotive vehicles.