Technical sciences/Electronics and radio electronics

Meshkov A.S., Susdorf D.V.

“Komsomolsk-na-Amure’s state technical university”, “S.-Petersburg’s state polytechnic university”, Russia

Improving of energy efficiency factor of low power electric drives

Energy saving is the priority line of the technical policy for all of the developed countries. An analysis of the structure of energy losses shows that between production, distribution and consumption of the electricity the consumption has the most significant part of missing energy (it can reach 90%). An electric drive is one of the biggest consumers of the electric power in the whole world. Of course, mainly all the attention of many engineers is focused on the powerful engines. However, these engines have a big amount of efficiency is about 95-99% and that's difficult to raise it more. On the other, hand we have an electric drive of low power. As a result of its massive using in construction tools, medicine equipment and different home appliances small raising of its efficiency is able to safe megawatts of energy. Besides, the efficiency of these engines is 30-60%. So, it gives a big field of work to improve this amount, particularly in the adjustable speed drive. So it's a big electric energy economy reserve.

Single-phase collector engines of low power with a serial excitement is widespread in modern equipment. Main causes of this are soft mechanical characteristics and high overload capacity at the moment, for the most part, and determine the wide application of these motors.

To ensure optimum operation of electrified instruments and household appliances in terms of energy needed synthesis of the control law, which allows to obtain the required mechanical characteristics of the electric power consumption and optimize the work cycle.

Optimal control problem in terms of electric energy successfully realizes future can be formulated as follows: change the speed of the engine from the values v1 to v2, so that would be for any time of the transient energy consumed by the transducer, was minimal. The basic equation of motion in the EP system of relative units is as follows:

To ensure maximum dynamic efficiency:

where - is a loss in the EP: electrical and mechanical.

Necessary to satisfy the following conditions:

In cases where a function of speed and does not depend explicitly on time and way, the minimum of the definite integral is achieved, provided that for each value of the velocity on the time interval of the motor provides a minimum of the integrand:

Then, at a constant speed and neglecting mechanical losses, the solution has the form:

Thus, the effective value of the supply voltage must increase to a parabolic law. This function changes the current value of the supply voltage will be optimal in terms of energy performance criteria.

To solve the problem of stabilizing the rate, as well as an indirect control of dynamic torque is proposed to use the structure, forming a feedback signal as a function inversely depending on engine speed. To do this, measure the time decay of the self-induction EMF output to zero. This time with a high degree of accuracy is proportional to the armature current and inversely proportional to engine speed. The advantage of this method is the ability to take into account the large number of perturbations, including the heating of the motor, changing the voltage.

The time constant of the motor is given by:

From the presented equations can be seen that to maintain a stable engine speed to maintain a constant decay time of self-induction EMF to zero. This is done by regulating the width of the pulse voltage.

Conclusions:

- the optimal law of variation of the input voltage of the electric motor, according to the criterion of minimum loss, is its quadratic dependence on the electromagnetic torque;

- with variable torque load on the shaft of the single-phase commutator motor is advisable to use the concept of dynamic efficiency of the proposed control method and the structure of the electric drive can improve the dynamic efficiency by up to 20%, while improving the quality of the spectrum of current that affects the external current network, more than 3%.

Publications:

1. Krause P.C., Analysis of electric machinery and drive systems / Krause P.C., Wasynczuk O., Sudhoff S.D., - IEEE Press 2002, с. 76-84.

2. Барков В.А. Полупроводниковые устройства для управления электрическими машинами постоянного тока / Учебное пособие, Ленинград, 1982.