A–3

L100 Inverter

DC Braking

The inverter DC braking feature stops the AC commutation to the

 

motor, and sends a DC current through the motor windings in order

 

to stop the motor. Also called “DC injection braking,” it has little

 

effect at high speed, and is used as the motor is nearing a stop.

Deadband

In a control system, the range of input change for which there is no

 

perceptible change in the output. In PID loops, the error term may

 

have a dead band associated with it. Deadband may or may not be

 

desirable; it depends on the needs of the application.

Digital Operator Panel For Hitachi inverters, “digital operator panel” (DOP) refers first to the operator keypad on the front panel of the inverter. It also includes hand-held remote keypads, which connect to the inverter via a cable. Finally, the DOP Professional is a PC-based software simulation of the keypad devices.

Diode

A semiconductor device that has a voltage-current characteristic

 

that allows current to flow only in one direction, with negligible

 

leakage current in the reverse direction. See also Rectifier.

Duty Cycle

1. The percent of time a square wave of fixed frequency is ON

 

(high) versus OFF (low). 2. The ratio of operating time of a motor,

 

braking resistor, etc. to its resting time. This parameter usually is

 

specified in association with the allowable thermal rise for the

 

device.

Dynamic Braking

The inverter dynamic braking feature shunts the motor-generated

 

EMF energy into a special braking resistor. The added dissipation

 

(braking torque) is effective at higher speeds, having a reduced

 

effect as the motor nears a stop.

Error

In process control, the error is the difference between the desired

 

value or setpoint (SP) and the actual value of a the process variable

 

(PV). See also Process Variable and PID Loop.

EMI

Electromagnetic Interference - In motor/drive systems, the switch-

 

ing of high currents and voltages creates the possibility of generat-

 

ing radiated electrical noise that may interfere with the operation of

 

nearby sensitive electrical instruments or devices. Certain aspects of

 

an installation, such as long motor lead wire lengths, tend to

 

increase the chance of EMI. Hitachi provides accessory filter

 

components you can install to decrease the level of EMI.

A Appendix

Four-quadrant operation

Free-run Stop

Referring to a graph of torque versus direction, a four-quadrant drive can turn the motor either forward or reverse, as well as decelerate in either direction (see also reverse torque). A load that has a relatively high inertia and must move in both directions and change directions rapidly requires four-quadrant capability from its drive.

A method of stopping a motor, caused when the inverter simply turns OFF its motor output connections. This may allow the motor and load to coast to a stop, or a mechanical brake may intervene and shorten the deceleration time.