Dictionary of Electrical Engineering

Commonly used terms in the Electrical industry.

DC servo drive
a feedback, speed control drive system used for position control. Servos are used for applications such as robotic actuators, disk drives, and machine tools.
DC test
tests that measure a static parameter, for example, leakage current.
DC voltage constant
voltage with no variation over time. This can be considered in general terms as an alternating current (AC) with a frequency of variation of zero, or a zero frequency signal. For microwave systems, DC voltages are provided by batteries or AC/DC converters required to "bias" transistors to a region of operation where they will either amplify, mix or frequency translate, or generate (oscillators) microwave energy.
DC-AC inverter

See inverter
DC-DC converter
a switching circuit that converts direct current (DC) of one voltage level to direct current (DC) of another voltage level. A typical DC-DC converter includes switches, a low pass filter (to attenuate the switching frequency ripple), and a load. The size of magnetic components and capacitors can be reduced and bandwidth can be increased when operating at high frequency. Most DC-DC converters are pulse-width modulated (PWM), while resonant or quasi-resonant types are found in some applications. Commonly used topologies include the buck converter, boost converter, buck-boost converter, and Cuk converter. Isolation can be achieved by insertion of a high frequency transformer.
definite time DC motor acceleration
when DC motors accelerate during their starting sequence, starting resistors are removed from the armature circuit in steps. In definite time DC motor acceleration (also referred to as open loop DC motor acceleration), the starting resistors are removed in definite time increments, whether the motor is actually accelerating or not.
high-voltage DC (HVDC)
transmission transmission of electric power (at typically 500-1500 kV) using DC rather than AC. This can be desirable for several reasons:

1. For economic reasons when a large amount of power is to be transmitted over a long distance, i.e., 300-400 miles, or via
underwater cables;

2. For the connection of asynchronous AC systems; and

3. Improved transient stability and dynamic damping of the electrical system oscillations.
HVDC transmission

See high-voltage DC transmission
IDC
DC current in amperes.
PDC
common symbol for DC power in watts.
permanent magnet brushless DC machine
a machine that is similar in structure to a permanent magnet synchronous machine, containing armature windings on the stator and permanent magnets on the rotor. The permanent magnet brushless DC machine, however, is characterized by a trapezoidal flux density distribution in the airgap instead of the sinusoidal distribution of the synchronous machine. In operation, a DC voltage is applied sequentially to the stator coils to create a rotating field that pulls the rotor with it. To correctly operate, the brushless DC machine requires sensors to determine the rotor position so that the proper stator phases may be excited.
permanent magnet DC machine
a DC machine in which the field excitation in the stator is provided by permanent magnets instead of electromagnets.
permanent magnet DC motor

See permanent magnet DC machine
shunt DC machine
a DC machine with the field winding connected in shunt with the armature. In shunt generators, residual magnetism must be present in the machine iron in order to initiate the generation process. These machines are also known as self-excited, since they supply their own excitation.
sinewave brushless DC
a permanent magnet brushless motor with sinusoidally distributed stator phase windings. More
commonly known as permanent magnet synchronous machine.
variable speed DC drive
a DC motor controller that allows the DC motor to operate over a wide speed range. A common type of variable speed DC drive uses a separately excited DC motor. Armature voltage control is used to provide operation below base speed, and field weakening is used to provide operation above base speed.
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