Hitachi L100 instruction manual Characteristics

L100 Inverter

3–13

V/F Characteristics

When the motor load has a lot of inertia or starting friction, you may need to increase the low frequency starting torque charac- teristics by boosting the voltage above the normal V/F ratio (shown at right). The boost is applied from zero to 1/2 the base frequency. You set the breakpoint of the boost (point A on the graph) by using parameter A43. The manual boost is calcu- lated as an addition to the standard straight V/F line (constant torque curve).

V	A42 = 11
100%
	Torque boost
11.8%	A
0			frequency
	6.0Hz	30.0Hz	f base =
	A43 = 10.0%		60Hz

Be aware that running the motor at a low speed for a long time can cause motor overheating. This is particularly true when manual torque boost is on, or if the motor relies on a built-in fan for cooling.

Parameter A44 selects the inverter algorithm for generating the frequency output, as shown in the diagram to the right. The inverter generates the motor output according to the V/F algorithm selected. The V/F curve is oriented toward developing constant torque or reduced torque (see graph below, left). You can select either constant torque or reduced torque V/F control.

Inverter PWM Switching Algorithms

A44

Variable freq. control,

constant torque

Output

Variable freq. control,

reduced torque

V			V
100%	A44 = 00		100%
	Constant	A44 = 01		A45
	torque
		Reduced
			20%
		torque
0		frequency	0	frequency

Using parameter A45 you can modify the voltage gain of the inverter (see graph above, right). This is specified as a percentage of the full scale setting (Automatic Voltage Regulation) AVR level in parameter-F03. The gain can be set from 20% to 100%. It should be adjusted in accordance with the motor specifications.