Direct Torque Control (DTC) of Frequency Converters (ac drives, frequency changers) (part 1)
As we know now, there are some disadvantages for frequency changers (ac drives, adjustable frequency drives) with one of these two commonly used control techniques: vector control (indirect torque control) & scalar control (v/f control) . Compared to vector contorl, which has another name - indirect torque control, we introduce another control technique for frequency inverters: direct torque control (DTC).
The difference between the traditional vector control (indirect torque control) and the direct torque control (DTC) is that the direct torque control (DTC) has no fixed switching pattern.
The direct torque control (DTC) switches the inverter according to the load needs. Due to elimination of the fixed switching pattern (characteristic of the vector and the scalar control), the direct torque control (DTC) response is extremely fast during the instant load changes. Although the speed accuracy up to 0.5 percent is ensured with this complex technology, DTC eliminates the requirement of any feedback device.
The block diagram of the direct torque control (DTC) implementation for ac drives (variable frequency drives, VFDs) is shown in the figure below.
(to be continued)
