General circuit description

STEVAL-IHM006V1

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General circuit description

Currently, the most widely used method to vary the AC mono-phase load voltage in applications

such as refrigerators, hydraulic pumps, fans and lamps consists in using the phase

partialization technique via a triac device. Although this simple and low cost solution has been

used for several years, it creates excessive harmonic distortion and has a consequent low

efficiency. Typical applications used to solve this problem are systems based on a complex

inverter drive, which are quite expensive.

The presented patented solution can solve third harmonic problems thanks to its switching

work mode. The induction motor is driven in high frequency mode by an innovative switch

topology, which delivers a silent and cost effective variable speed drive. The speed is controlled

by the motor voltage: the power switch runs in PWM mode and its duty cycle changes linearly

to control the speed versus the torque.

The base circuit can be viewed as a double chopper that operates on a sinusoidal busdirectly

from the 50-60Hz mains, without a preliminary AC-DC conversion type.

The double chopper is able to energize the load from any level of the sinusoidal voltagewave

and demagnetize it via a free-wheeling current system, obtaining the voltage regulation and the

current. This means that the circuit operates as an AC-AC converter or transformer and the

form of the current load is a perfect sinusoidal shape. The proposed circuit does not have any

load type limitations. It works with any inductive-ohmic load with notable angles between the

current and the voltage.

The power can be controlled by varying the duty cycle of the PWM signal where the shape of

the current is sinusoidal due to the filtering effect of the inductive nature of the load.

If the load has a reactive power, it can transit between load and line grid independently from the

power level and is not blocked or dissipated in any electronic parts of the circuit.

The control parameters (PWM modulation, reference signal and current sensing) are controlled

through an MCU. The AC/AC chopper driver evaluation board is based on the ST7FLITE05

microcontroller (8-bit MCU with single voltage flash memory, ADC, timers, SPI, 1% internal RC

oscillator)

Obsolete

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- Obsolete

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