Application of electric drives

In many of the industrial application, an electric motor is one of the most important components. An electric motor is a most important part, it is an energy transmitting device and the working machine. Here this article gives the application of electric drives to know more details about it. 

• A ceiling fan motor with regulator.
• A motor and also have conveyor belt with material on its belt.
• Food mixer without food is processed.
• It is also used a large number of industrial as well as domestic application.
• It is also used rolling mills, textile mills as well as some machine tools.
• Some other application like pumps, robots, washing etc.
• It can also use various traction like an electric train, electric buses, trams, trolleys, battery driven solar power vehicles.
• Electric propulsion.
• Cement kilns.
• Elevators, escalators, and lift.
• Automotive applications.
• Spindles and servos.
• Plant automation.

Advantages and disadvantages of electric drive

The machining equipment designed to convert electrical energy into mechanical energy and provide electrical control is called electric drive. This article gives information about the advantages and disadvantages of the electrical drive to know more details about the electrical drive. 

Advantages of electric drive :

• Very large range torque, speed, and power
• Free from pollution
• It can operate on all the quadrants of speed torque plane side
• Working is independent of the environment condition
• The efficiency of the drive is high
• No starting problem easily start so not require any refueling

Disadvantages of electric drive :

• Cause noise pollution
• An initial cost of the system is high
• Application of the drive is limited
• Poor dynamic response
• The output power obtained from the drive is too much low
• The output power obtained of conductor or short circuit, the system may get damaged due to which several problems occur

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 :

• Single phase dc drives
• Three phase dc drives
• Chopper drives 

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 :

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

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 = V_t =  3V_ml / 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,

                                        V_f =  3V_ml/2∏ * (1+Cos  ɖ₁ ) for 0<  ɖ₁ <  ∏

  V_ml = 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 =  V_t is =  3V_{m l}/ 2∏  * Cos  ɖ₁  for 0<  ɖ₁ <  ∏

With a 3 phase full converter in the filed circuit,

V_f  =  3V_ml/2∏ * Cos  ɖ_f  for 0<  ɖ_f <  ∏

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 =  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