TRANSISTOR IGBT
Bipolar transistors insulated gate commonly called IGBT's are the result of many investigations carried out by manufacturers of electronic components in order to get a device high switching speed, low power consumption of control and great ability to support voltage and high currents. The symbol of the German standard IGBT as shown in Figure 3-6.
Note that the collector-emitter terminals typically come with a diode "Damper" installed in that position for protection against inductive loads.
To activate an IGBT (turn on), apply a voltage set value to their control terminals Gate-emitter. The current consumption of the control terminal is virtually zero, so it is said that no current IGBT. This avoids the time delays associated with devices that draw power control such as bipolar transistors BJT.
IGBT transistor responds quickly to signal changes (less than 1 us), reducing motor audible levels in the AC while it is controlling the torque and speed. And, large switching frequency (carrier frequency) provides a current control dynamic response. Also, an IGBT losses are very small as a result of arranged in compact encapsulated inside the drive. The IGBT corrective action by a digital multimeter LED scale (Damper Diode Transistor IGBT) is shown in Figure 3-7. The value "OL" in the table (3-1) represents maximum scale.
PHASE BRIDGE INVERTER
Figure 3-8 shows the circuit that can meet the requirements stipulated by the equation (3-4). Therefore the AC motor can be controlled at different rates at face value and still retain the characteristics of its nominal torque.
The only way to achieve a voltage wave that meets the requirement of changing voltage and frequency proportionally at the same time, through an inverter circuit.
Figure 3-8 shows the parts that make up the power section of all types of variable speed AC motor today.
The input power is VAC single or three phase depending on the power of AC motor control. This AC voltage is rectified by a diode bridge.
Then we have the stage line filter with power filter (coil) and voltage filter (capacitor), with the aim of having a DC voltage bar as continuously as possible (terminals + DC /-DC).
This bar is the entrance to DC inverter circuit, which work through switched IGBTs makes an output voltage (terminals U, V, W) called "Sine-PWM," which meets the requirement of maintaining V / F ratio constant.
BREAST-PWM VOLTAGE
Figure 3-9 shows in detail the wave "Sine-PWM" output three-phase inverter bridge. The amplitude (Vd) of the wave is equal to bar DC voltage (terminals + DC /-DC inverter circuit input).
The engine receives this wave voltage output terminals U, V, W and filtrate streams (IU, IV. IW) nearly sinusoidal. The average effective voltage "V" depends on the width of the pulses and the effective frequency "f" seen by the motor is 1 / T. The switching speed IGBT transistors is 1 / t called "carrier frequency".
The result is that the motor is the relationship "V / f" proportional to their nominal values, getting their work to develop even smaller than normal speeds without loss of torque.
