Torque and Constant Volts/Hertz Operation

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Getting Started

Introduction to Variable-Frequency Drives

An inverter, in general, is a device that converts DC power to AC power. The popular consumer power inverter is designed for powering an AC appliance from a car battery; put 12VDC in, and get 115VAC 50/60 Hz out, for example. The figure below shows how the variable-frequency drive employes an internal inverter. The drive first converts incoming AC power to DC through a rectifier circuit, creating a high-voltage internal DC bus. Then the inverter circuit inverts the DC back to AC again to power the motor. However, this special inverter varies its output frequency and voltage according to the desired motor speed.

Power		Variable-frequency Drive
Power
Input	Converter	High-voltage		Inverter
L1	Converter	High-voltage		Inverter
L1		DC Bus	+	Motor
		DC Bus	+	Motor
L2		+		U/T1
	Rectifier			U/T1
	Rectifier
L3				V/T2
				W/T3
			–

The simplified drawing of the inverter shows three double-throw switches. Usually implemented with six power transistors, outputs U/T1, V/T2, and W/T3 may switch positively or negatively. Using a commutation algorithm, the microprocessor in the drive switches the power transistors on and off at a very high speed to create the desired output waveforms. The reactance of the motor windings helps smooth out the pulses.

Torque and Constant Volts/Hertz Operation

In working with industrial motors we often discuss the motor torque. That is simply the rotational force the motor exerts at any given time. The goal of the inverter is to control motor speed, but the L100 inverter only has direct control over the output frequency and voltage. The no-load speed will be equal to the inverter output frequency minus a small amount of slip in the motor (slip is the difference between theoretical motor speed and actual speed). As the load increases, the slip and the delivered torque also increase . If the inverter can create strong motor torque over most or all of the speed range, then it is relatively easy for the system to achieve any desired speed. Speed regulation is a measure of the accuracy speed control, given as a percent difference from a fixed value. The L100 delivers speed regulation (no load to full load) within 3% of the (full scale) motor nameplate speed value.

When varying the output frequency, the inverter drive also must vary the output voltage in propor- tion to the frequency. It does so because of the motor’s characteristic inductive reactance. If the drive maintains a constant volts-per-hertz ratio, the motor will have constant torque characteristics. Constant torque is desirable for most applications, because it transfers power to the load consistently across the entire speed range.

Output
voltage
V
100%
	Constant torque
		f
0	Output frequency	100%
	Output frequency	100%

L100 specifications

The Hitachi L100 series is a versatile range of variable frequency drives (VFDs) designed to enhance performance in various industrial applications. Known for their reliability and efficiency, these drives are widely used in motors for pumps, fans, compressors, and conveyors.

One of the main features of the Hitachi L100 is its impressive control capabilities. The drive supports both scalar and vector control modes, allowing for precise speed and torque management. This flexibility ensures optimal motor performance across different load conditions. Additionally, the L100 series offers an impressive speed range, which can accommodate a wide variety of applications, from low-speed to high-speed requirements.

The L100 is equipped with built-in functionality for energy saving. By utilizing advanced control algorithms and auto-tuning features, the drive optimizes energy consumption, reducing operational costs and contributing to improved overall system efficiency. The energy-saving mode is particularly beneficial in applications where load conditions frequently change.

Another hallmark of the Hitachi L100 is its robust communication capabilities. The drive supports various communication protocols including Modbus and Ethernet, making it easy to integrate into existing control systems. This connectivity allows for real-time monitoring and diagnostics, which aids in predictive maintenance and minimizes downtime.

In terms of user-friendliness, the L100 series includes a clear, intuitive keypad that simplifies programming and operation. The drive also features a wide range of customizable parameters, enabling users to easily tailor the settings to suit specific application requirements. Additionally, the inclusion of a customizable PID controller allows users to refine process control automatically.

Safety is a priority in the design of the Hitachi L100. The drive comes with various built-in safety features such as overvoltage, overload, and short-circuit protection, ensuring reliable operation in challenging environments. Furthermore, it complies with global safety standards, making it suitable for international applications.

Lastly, the L100's compact design ensures easy installation and minimizes the space required in control cabinets. This is especially advantageous in facilities where space is at a premium. Overall, the Hitachi L100 series represents a combination of advanced technology, user-friendly features, and reliable performance, making it a popular choice for industrial automation solutions.

Hitachi L100 Torque and Constant Volts/Hertz Operation, Introduction to Variable-Frequency Drives

Models: L100

Introduction to Variable-Frequency Drives

Torque and Constant Volts/Hertz Operation

L100 specifications