Variable frequency drives (VFD) types

       Variable frequency drives (VFD), all using their output devices (IGBTs, transistors, thyristors) is switched on or off only. The use of devices such as transistors in linear mode, the linear drive is not for the Variable frequency drives (VFD), since the energy lost during the training is about as much as they are delivered to the load.

The reader can be classified as follows.

•       Constant voltage.

•       Constant current.

•       cycloconverter.

Convert the voltage to the DC link voltage is constant during each cycle. The current drive is an important inducer is located between the rectifier and the output of the bridge so that current is almost constant. cycloconverter with no input rectifier and DC link and connect to the station's output in each step of entering the appropriate information.

Variable frequency drives (VFD) is the most common type of packaging is a kind of constant voltage. using pulse width modulation to control both the frequency and effective voltage applied to the motor load

The benefits of variable frequency drives (VFD) systems

                         

       

Energy Conservation of variable frequency drives (VFD) systems 

      If an AC-motor application that does not need to run at full speed, then you can reduce your energy costs by controlling the motor with variable speed. Energy savings with variable torque distribution can be significant, often pays the cost of the VFD in a few months. In variable torque applications, the torque required varies roughly with the square of the speed and power demand varies roughly with the cube of speed, resulting in a higher power reduction for a small reduction in speed. The engine consumes only 25% of energy compared to 50% rate is 100% speed. This is known as affinity laws, which define the relationships described between speed, flow, torque and power

The Variable frequency drives (VFD) motor control

•  Start : The frequency of the Variable frequency drives (VFD) with the starting frequency. Motor to supply torque. The Variable frequency drives (VFD) will gradually increase the frequency up. the upper torque of the motor load torque motor began to rotate.

• Speed ​​and engine speed constant : when the starter motor and frequency Variable frequency drives (VFD) and also the output can gradually increase till the specified frequency. the rise in frequency is that the time to accelerate when the output frequency is equal to the specified frequency. Acceleration is complete. Variable frequency drives (VFD) enters the amount of operation. With a continuing velocity.

• To reduce speed: To do this, set the frequency to lower frequency output. Variable frequency drives (VFD) are less frequent from time to time to reduce speed to be set. At the lower frequencies. The motor speed is greater than the frequency output of the Variable frequency drives (VFD). Motor is running. The generator manufacturer. Power to the Variable frequency drives (VFD). (Regeneration) and also the voltage (voltage across the condenser) were increased. Thus, the Variable frequency drives (VFD) could be a circuit that receives energy from the regeneration, which can cause the brake motor. this is often referred to as a cycle. Circuit brake energy recovery. during the slow work of this nature repeatedly, if the energy is less. (Torque needed to reduce Speed ​​is small) rate of the brake circuit will be low. typically it doesn't work at it. Break this cycle usage. Designed to be thought-about in terms of cooling at 2-3% as long as the brakes are used frequently. Or use the brakes too long. can cause a cooling of the resistor and also the device acts as a switch Chss degeneration.
• Stop: Inverter to reduce the frequency down to a certain extent. And will produce power to the motor to operate the brakes. The motor is braking, with direct light.

How does the variable frequency drives (VFD) work ?

      The basic block diagram of a simple can consist of variable frequency drives (VFD), the most important and works as follows.

• Reetifier circuit :   Rectifier circuit: instead of conversion or amendment of voltage alternating current to direct current voltage. Circuits embody Power diode 4, the input is single section. The 6-power diode when the input is 3 section (for a definite variety of SCR variable frequency drives (VFD) circuits act as a record, contact the provider, which enables agents to manage the voltage in the circuit. DC link it). 

• DC Link :  DC link or a link to the DC circuit. Integrated circuit is connected between this and therefore the variable frequency drives (VFD) circuit. (Which are going to be described in next section), that consists of very little capacitor with an oversized vary of voltage four hundred VDC or 800 VDC reckoning on the voltage input to one section or 3 section, the filter pressure. DC incorporates a record comments by the Fort to flatten it. And serves to store electrical charge. The motor works as a generator within the short term thanks to the brake or bog down the speedy. (For use with masses that have lots of inertia and therefore the got to stop quickly. High pressure can drop back to his cab and a capacitor. Kappa Exeter harm, therefore in observe there's a Shoppers by a resistance in series with the transistor. And a capacitor in parallel with the caps. The transistor are going to be converted to regulate this through the resistor to cut back power consumption happens.

• Inverter Circuit : Inverter circuit that performs conversion of DC voltage. (Through the filter of a DC link) is an AC voltage. Power transistor circuit is comprised of a six pack (currently mainly used IGBT) acts as a switch, cutting power to convert it to AC power. Techniques commonly utilized by the PWM (Pule width modulation). 

• Control circuit : The control circuit will receive data from the user, for instance. The speed you would like to method. and therefore the output from the transistor to regulate the voltage and frequency in line with the speed and torque. The user desires. 

        Why is that the conversion of AC and DC conversion from DC to AC again? (FAQ).
       Since the conversion from AC to AC. Go on to it. The high frequency output will live up to the frequency of the input it's not possible to regulate the motor speed is quicker than the speed at that it left on the plate of the motor. however switching from AC to DC and converted back to AC once more, the variable frequency drives (VFD) will generate a frequency above the input frequency. 

How do speed control of the motor cycle ?

       The speed of the induction motor or induction motors. will modification with the speed or the equation of synchronous speed (Ns)

Synchronous speed  (Ns) = (120 * f ) / P

                                                        f   = frequency electrical current.

                                                        P = number of pole

Equation of synchronous Nas - Speed ​​is the speed of the motor can be adjusted by two routes.
          1. the number of poles (P) and
          2. The frequency of electrical equipped to the electric motor (f)

      Table summarizes the relationship of the speed of the motor with variety of different polarity can be seen that how to control the speed by changing the amount of magnetic poles. Speed ​​will vary every time so as to change from 3000 rpm to 1500 rpm or 1500 rpm to 3000 rpm (the change of the 2-pole into a 4-pole, or from 4 pole down to 2 pole), which changes the speed in this method, speed changes aren't subtle. , As in the no-load. The key is to use a specially designed motor that may change the amount of magnetic poles solely. It does not suit the requirements of many. sorts who want to regulate the speed of the load to speed with the speed of the production process. the process is usually employed in inverter control motor speed, instead of due to the merger. control the motor speed constant. The speed at completely different speeds, quick and a lot of accurate.

What is the variable frequency drive ?

 

      Variable frequency drive (VFD) or the AC drive is used for controlling the speed of electronic devices. Motors or AC induction motors. (Which is usually noted as "A synchronous motor Nassau or squirrel-cage").