Hitachi SJ100 Instruction Manual page 38

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-per-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
speed range. For some applications, this scalar
technique was adequate.
Today, with the advent of sophisticated micro-
processors and digital signal processors (DSPs),
it is possible to control the speed and torque of AC induction motors with unprecedented
accuracy. The SJ100 utilizes these devices to perform complex mathematical calcula-
tions required to achieve superior performance. The technique is referred to as sensorless
vector control. It allows the drive to continuously monitor its output voltage and current,
and their relationship to each other. From this it mathematically calculates two vector
currents. One vector is related to motor flux current, and the other to motor torque
current. The ability to separately control these two vectors is what allows the SJ100 to
deliver extraordinary low-speed performance and speed control accuracy.
Inverter Input and Three-Phase Power
The Hitachi SJ100 Series of inverters includes two sub-groups: the 200V class and the
400V class inverters. The drives 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 a 400V class inverter requires from 380 to 460VAC.
Some 200V class inverters will accept single-phase or three-phase power, but all 400V
class inverters require a three-phase power supply.
TIP: If your application only has single phase power available, refer to SJ100 inverters
of 3HP or less; they can accept single phase input power.
The common terminology for single phase power is Line (L) and Neutral (N). Three-
phase power connections are usually labeled Line 1 (L1), Line 2 (L2) and Line 3 (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
the Inverter Output to Motor" on page
Output
voltage
V
Constant torque
0
Output frequency
2–18).
1–19
SJ100 Inverter
f
100%
"Wire