Hitachi X200 Series instruction manual 13, Torque and Constant Volts/Hertz Operation

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 speed range. For some applications, this scalar technique was adequate.

Output voltage

V

Constant torque

0f

100%

Output frequency

1−13

Getting started

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 X200 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. Variable torque, also called reduced torque, lowers the torque delivered at mid-level frequencies. A torque boost setting will add additionally torque in the lower half of the frequency range for the constant and variable torque curves. With the free-setting torque curve feature, you 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 X200 Series of inverters includes two sub-groups: the 200V class and the 400V class inverters. The drive describes 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.

For 200V class inverters having a suffix of –SFE accepts single phase 200V class input voltage, and three-phase for –LFU. All 400V class inverters require three-phase power supply.

TIP: If your application only has single phase power available, refer to X200 inverter of 3HP or less (European version with a suffix of -SFE); they can accept single phase input power.

The common technology 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).