Common terms for frequency converters (1)

1. Rectifier/Converter:

 The first major section of the frequency converter main power circuit and the first part of the power flow. The incoming AC line voltage is rectified to DC voltage in the converter section, which consists of diodes, silicon-controlled rectifiers (SCRs), or insulated gate bipolar transistors (IGBTs) connected in a full-wave bridge configuration.

2. DC bus:

 The second major section of the frequency converter main power circuit, consisting primarily of capacitors that store the power rectified by the converter.

3. Inverter: 

The third major section of the frequency converter main power circuit. The inverter section consists of an IGBT that uses a pulsed DC bus voltage or pulse width modulation to produce a sinusoidal output current. The inverter is the main difference between frequency converters and DC drives, so frequency converters are sometimes also called inverters.

4. Insulated gate bipolar transistor (IGBT): 

A high-speed semiconductor switch that is driven by electronics. By applying a small positive voltage between the gate and emitter points of the IGBT, current is allowed to flow from the collector point to the emitter point.

5. Carrier frequency:

 In a PWM-based inverter, the rate at which the output transistors are turned off or on, typically 2 to 15 kHz. The higher the rate, the better the current waveform, but the greater the inverter losses.

6. Common bus: 

A method of connecting the DC bus segments of separate inverters, or running multiple independent inverter segments from a common DC power source.

7. Ground: 

Ground is the reference point for the incoming AC power. If the power conductor accidentally touches the ground, the AC power protection circuit immediately electrically isolates the AC power from the contact point. To create the ground point, a ground rod is usually connected to the earth, and all ground circuits are connected to this ground point. When the inverter chassis is connected back to this ground, a safe conduction path is created to prevent the conductor from accidentally shorting to the metal part of the enclosure.

8. KW / hp : 

A measure of the power of a motor, where k W = hp X0.746. Due to the reactive current component produced by an induction motor, the power capacity of the motor is not V×A, but hp.

9. Line Reactor: 

A device consisting of a conductor wound around an iron core. When current flows through the coil, a magnetic field is generated in the core. Any change in the magnitude or direction of the current opposes the existing magnetic field in the core until equilibrium is reached. Line reactors reduce the current discontinuity caused by the variable frequency converter. Reducing this discontinuity reduces the harmonic currents generated by the variable frequency drive. Since the line reactor is installed before the variable frequency drive, it also helps protect the drive from most voltage transients by reducing the voltage proportional to the current flowing through the drive. The terms reactor and inductor are often used interchangeably to refer to the same device.

10. Link Choke: 

In a variable frequency drive, a single reactor placed before the DC bus capacitor. Link chokes reduce harmonics generated by VFDs in the same way as line reactors, but provide less protection against voltage transients.

11. Constant Torque and Variable Torque Loads:

· Constant Torque: Torque requirements do not vary with speed, sometimes requiring intermittent overloading.

· Variable Torque: Torque requirements naturally increase with speed (such as fans or pumps), and intermittent overloading is not required.