VSD Terms & Definitions

VSD Terms and Definitions

The strength of the magnetizing field between the rotor and

stator .Flux density1.

The ratio at which constant torque is provided.2. v IHz ratio

Base frequency3.

4. In-rush current:

The front end section of the VSD, which changes AC to DC.

A diode bridge rectifier, or and SCR rectifier can be used5. Converter

Area of the drive that smoothes the DC voltage before

applying it to the inverter .DClink6.

The last section of the VSD that inverts DC into a variable

frequency and variable voltage signal.

7. Inverter

A silicon controlled rectifier is a three junction, four layer

semiconductor which exhibits the following circuit

characteristics:

8. SCR

.Current can flow from the anode to the cathode when the

voltage exceeds approximately 1 volt (plus to minus) and the

gate lead is made positive with respect to the cathode by a

suitable gate signal.

.Similar to the diode, no current can flow from the cathode

to the anode. ~

.Unlike the diode, the SCR can block current flow in the

forward direction ( snode to cathode) by keeping the gate

negative with respect to the cathode.

Diode9. The diode is a single junction, two layer semiconductor which

exhibits the following circuit characteristics:

.Current can flow from the anode to the cathode when the

voltage exceeds approximately 0.5 volts with the proper

polarity (plus to minus ). ".No appreciable current can flow from the cathode to the

anode regardless of. the polarity or voltage magnitude as

long as the diode is operated within its reverse voltage

rating.

VSD Terms and Definitions

IGBT0. The IGBT is a two junction, three layer device. IGBT's

provide a high switching speed necessary for PWM inverteroperation. IGBT's are capable of switching on and off several

thousand times a second. An IGBT can turn on in less than

400 nanoseconds and off in approximately 500 nanoseconds.

An IGBT consists of a gate"collector and an emitter. When a

positive voltage is applied to the gate of the IGBT, it will turn

on. This is similar to a switch. Current will flow between the

collector and emitter. An IGBT is turned off by removing the

positive voltage from the gate. During the off state, the IGBT

gate voltage is normally held at a small negative voltage to

prevent the device from turning on.

Harmonics: Any waveform that is not equal to the fundamental sinusoidal

waveform is considered to be a harmonic. Terms used to

describe these waveforms are as multiples of the

fundamental. Such as a Sth harmonic is S times the

fundamental.

11.