Wednesday, 25 December 2013

What is VFD Control?Why it is used in Solar Water Pumping System?


VFD(Variable frequency Drive), an old technology but most efficient one for solar power water pumping system,It is also known as Variable Speed Drive(VSD).Almost 65% of the electrical energy utilized in America which are from Pumps,Compressors,Fans,Blowers etc..,which are driven by constant speed motors or synchronous motors where the speed of the motors are constant till the end and in which the option to control the running speed will be using resistive devices which will dissipate more heat ,the efficiency of the system is low due to the wastage of power through dissipation of heat.

vfd circuit


History.

In the early days of VFD technology, it was used for some typical application in process control for manufacturing synthetic fiber,steel bars,and aluminum foil. Because it improves process performance and reduces maintenance costs, they replaced motor generator sets and DC drives. When the energy crisis occurred in the early 1970s, saving energy became a critical goal, and the use of VFDs quickly spread into large pump applications.

What is VFD Control?.
Variable frequency control of AC induction motors provides an economically sound and operationally effective solution for speed control and reduced power consumption,the converter develops a voltage 
directly proportional to the frequency, which produces a constant magnetic flux in the motor.This electronic control can match the motor speed to the load requirement. This eliminates a number of costly and energy inefficient ancillaries to throttle the speed of the motor.

Types of Variable Frequency Drives(VFD).

VFD types



Why VFD used in Solar Pumping System?.
The principle of this method of VFD is to supply DC from the PV array directly into the DC bus inside the VFD. The normal AC input is not used. As the sun rises,the PV voltage and current will increase,when the power is high enough, it will start the pump. The PV array must be large enough to provide enough power to start the pump with including the head of water. The size of the PV array required for this method can be very expensive.

vfd drives for motors and pumpsA VFD reduces the actual motor speed, which reduces the amps drawn by the motor,This reduces the amount of energy used and saves you energy costs. By ramping up the motor speed slowly, VFDs also help customers save energy by reducing the in-rush and mechanical issues associated with starting of motors.




The first and most obvious way a VFD can save you money is through increasing the efficiency of your AC motors and decreasing electricity use. The amount of energy that a VFD can save depends on the average load of the motor and the number of hours per day it is turned on. While average energy savings varies, it’s safe to say that most AC motors do not need to be running at full capacity for most hours of their use. Furthermore, the initial cost of a motor or VFD is generally only a fraction of the cost of operating the motor over its life span. This means that a VFD system usually pays for itself in a matter of months or years.

Advantages of VFD:
  1. A VFD may be used for control of process temperature, pressure, or flow without the use of a separate controller. Suitable sensors and electronics are used to interface the driven equipment with the VFD.
  2. Lower maintenance costs, as lower operating speeds result in longer life for bearings and motors.
  3. The motor does not require a starter.
  4. The ability of a VFD to limit torque to a user-selected level ,protects driven equipment that cannot tolerate excessive torque.
  5. Users can utilize multi-motor applications, such as pumps or fans, with one control unit.
  6. High-speed applications for the wood-finishing industry ,approx 30-40% energy is saved