A variable-frequency drive (VFD) (also termed adjustable-frequency drive, variable-speed drive, AC drive, micro drive or inverter drive) is a type of adjustable-speed drive used in electro-mechanical drive systems to control AC motor speed and torque by varying motor input frequency and voltage.ariable-frequency drives are also categorized by the following load torque and power characteristics: 1  Variable torque, such as in centrifugal fan, pump, and blower applications. 2  Constant torque, such as in conveyor and positive-displacement pump applications.
For example, the UK is a unitary state (for the most part) whereas the US is a federation. A parliamentary form of government simply means that the executive branch/ministers/cabinet are part of the legislative body. Both unitary and federal states can have parliaments. For example, India is a federation with a parliamentary system where as the UK is a unitary state with a parliamentary system. m200220232
Under representative democracy, substantive representation (in contrast to descriptive representation) is the tendency of elected legislators to advocate on behalf of certain groups. Conflicting theories and beliefs exist regarding why constituents vote for representatives.