Hitachi WJ200-001S Instruction Manual page 42

Torque and Constant Volts/Hertz Operation
In the past, AC variable speed drives used
an open loop (scalar) technique to control
speed. The constant-volts-hertz operation
maintains a constant ratio between the
applied voltage and the applied frequency.
With these conditions, AC induction motors
inherently delivered constant torque across
the operating
applications, this scalar technique was
adequate.
Today, with the advent of sophisticated microprocessors and digital signal processors
(DSPs), it is possible to control the speed and torque of AC induction motors with
unprecedented accuracy. The WJ200 utilizes these devices to perform complex
mathematical calculations required to achieve superior performance. You can choose
various torque curves to fit the needs of your application. Constant torque applies the
same torque level across the frequency (speed) range.
reduced torque
setting will add additional torque in the lower half of the frequency range for the
constant and variable torque curves. With the
can specify a series of data points that will define a custom torque curve to fit your
application.
Inverter Input and Three-phase Power
The Hitachi WJ200 Series of inverters includes two sub-groups: the 200V class and the
400V class inverters. The drive described in this manual may be used in either the
United States or Europe, although the exact voltage level for commercial power may be
slightly different from country to country. Accordingly, a 200V class inverter requires
(nominal) 200 to 240VAC, and 400V class inverter requires from 380 to 480VAC.
The 200V class inverters having a suffix of –SF accept single-phase 200V class input
voltage, those with a suffix –LF three-phase power only. All 400V class inverters
require three-phase power supply.
TIP: If your application only has single phase power available, refer to WJ200 inverter TIP
TIP TIP
of 3HP or less (European version with a suffix of -SFE); they can accept single phase
input power. Note: Larger models may be able to accept single-phase with derating.
Contact your Hitachi distributor for assistance.
The common terminology for single phase power is line (L) and Neutral (N).
Three-phase power connections are usually labeled Line 1 [R/L1], Line 2 [S/L2] and
Line 3 [T/L3]. In any case, the power source should include an earth ground connection.
That ground connection will need to connect to the inverter chassis and to the motor
frame (see "Wire the Inverter Output to Motor" on page 2-21).
speed range. For
, lowers the torque delivered at mid-level frequencies. A torque boost
Output
voltage
V
Constant torque
0
some
Variable torque
free-setting torque
f
100%
Output frequency
, also called
curve feature, you
1− − − − 19