Direct Current Motor with Permanent Magnet Energy Injection

Marius Constantin Georgescu Department of Electrical Engineering and Applied Physics

Transylvania University of Brasov Brasov, Romania

mgeorg2011@yahoo.com

Abstract—This paper presents an original dc motor concept and prototype based on a permanent magnets injection. It was built as an experimental model and certified by a patent of invention in Romania. This motor can be controlled by an adjustable dc supplying voltage as electric input source and by another adjustable magnetic device based on permanent magnets. The main original aspect is the same as a part of the permanent magnets (PM) are situated inside of the dc motor rotor (as armature) and the other part of them is outside of the motor. The outside permanent magnets are connected and grouped, constituting a magnetic device as adjustable magnetic energy source. Both the PM parts (armature and magnetic device) are related between them. As first application field has been identified the automotive propulsion.

Keywords—dc machine; efficiency; permanent magnet motor; magnetic device.

I. INTRODUCTION New researches and developments are focused to rise the

magnetic material performances in order to produce high efficiency PM electrical motors. Some of these magnetic materials are the rare earth based alloys ones. For example, NdFeB permanent magnets have good sensitivity with increasing operating temperature in suitable temperature conditions stability. Based on their improved magnetic properties, the dc motors used for automotive applications have traction characteristics with very good performances.

Some of the main requirements of the electrical automotive motors are the followings:

• fast response in propulsion system dynamics based on higher torque/weight and torque/inertia ratios,

• optimized magnetic circuit to obtain higher air-gap magnetic flux and good efficiency of electromechanical energy conversion,

• reduced weight/size ratio and compact structure,

• suitable traction characteristics,

• higher reliability (long life, safety in operation) and easy maintenance.

978-1-4799-2442-4/13/$31.00 ©2013 IEEE.

Since their higher efficiency at low/medium power applications, rotor low losses and availability in various geometrical configurations, the permanent magnets motors are quite promoted by research and fabrication as main vehicle propulsion sources. In this aim, the author proposes a dc motor with an original configuration based on adjustable permanent magnet energy injection.

II. MOTOR DESCRIPTION The presented dc motor is original as design and certified

by a patent of invention registered in Romania [1].

A general configuration of it is depicted in the Fig. 1 and consists in two main sub-assemblies mechanic and galvanic coupled between them.

A. First Sub-assembly This one provides the energy conversion and delivers the

electric/magnetic power in order to control the functional parameters of the motor. It contains the following main parts:

• the metal casing sustained and centered on two side shields. Inside to the casing is fixed a cylindrical stator made of ferromagnetic sheets and containing the main dc winding supplied by a system of collector-mobile rotating brushes. The magnetic circuit is to obtain higher air-gap magnetic flux and good efficiency of electromechanical energy conversion.

• the stator winding can be powered from two dc sources: one (V1) is the main fixed/controlled dc supply and the second (V2) is an auxiliary dc pulsating adjustable supply. The main dc supply is used to control the motor parameters (torque, speed, power, efficiency) and the auxiliary dc supply is used as a supplementary power one. On the stator exists an even number of teeth parallel and uniform axial, correlated with the number of rotor (armature) pole pairs.

• the motor armature consists of a non-magnetic metallic shaft centered in the two side shields. On the shaft are fixed the pole pairs with parallel sides regarding the stator pole pairs and the shaft.

• permanent magnets (NdFeB) radial situated between the poles of the armature. They are thus placed in order to concentrate the magnetic flux.

from the external PM device. In comparison with the classical dc motor, this motor has some main advantages as: very good

Fig. 1. General configuration of the dc motor with permanent magnet energy injection.

B. Second Sub-assembly It consists in a collector with adjustable positions. The

number of collector bars is correlated with the number of stator magnetic switching poles. It contains also a system of slip-ring brushes. The whole collector-brush system provides the dc motor supply with electric energy and is detailed in [1]. Outside the dc motor, there is a permanent magnet controlled device (as a battery). It contains permanent magnets with the same specific magnetic energy, connected between them and also with the armature permanent magnets. Connecting the permanent magnets is done in a certain order and without exceeding the dc motor magnetic saturation.

As results, this motor can be simultaneously powered from two different sources with two adjustable energy forms electric and magnetic ones. The permanent magnet device is outside of the dc motor situated in order to provide more magnetic energy, taking into account the limited space inside the motor. Outside location of PM device permits the transfer of magnetic energy only their fields inside, through magnetic injection (positions 0, 1, 2, 3, 4 as depicted in Fig.1.).

As supplying, the dc motor has the following possibilities: • fixed direct current and PM adjustable injection,

• adjustable direct current and fixed PM injection,

• both adjustable (direct currents and PM injection).

A picture of the dc motor prototype is presented in the Fig. 2.

The magnetic injection is performed by inserting in the motor armature circuit, progressively, the permanent magnets

Fig. 2. Prototype of the DC motor with PM device.

power/size ratio, very good volume/mass ratio, easy starting in load and overload conditions, high torque at starting (suitable for automotive applications), good efficiency in wide speed ranges, adjustable electric and mechanic powers in different adjustable magnetic injections, availability to deliver electric power within the grid and also to storage it in batteries.

III. EXPERIMENTS AND PRACTICAL RESULTS The experiments and practical results have been carried out

at S.C. Electroprecizia S.A. Săcele (an electric motor plant near Bra�ov) and are official certified.

Are presented the results referring to the dc motor behavior at dc constant voltage supply of V1=30V, in the following magnetic injections, as shown in the Fig.1:

Device with PM energy 1200g / 182 Ws

Control of magnetic energy

• position/injection 0,

• position/injection 1, for a magnetic energy of 52Ws,

• position/injection 2, for a magnetic energy of 89Ws,

• position/injection 3, for a magnetic energy of 127Ws,

• position/injection 4, for a magnetic energy of 182 Ws.

In laboratory conditions, the experiments can be extended until a magnetic energy of 457Ws. To obtain an increased magnetic energy, the permanent magnet mass is progressively increased by magnetic injection from the magnetic device. Thus, for example, for 182Ws of magnetic energy results a PM mass of 1.2kg and for 457Ws results a 3kg of PM mass. The magnetic parameters and characteristics for the PM used (NdFeB) are presented in [2, 3].

A synthesis of motor test results at constant supply voltage of V1 =30V dc and a constant shaft torque of T = 1.37Nm is given the Table I.

TABLE I. TESTS AT CONSTANT VOLTAGE AND TORQUE

Magnetic energy

injection stages

Current I [A]

Electric power

absorbed P1 [W]

Speed n

[rpm]

Output useful power

P2 [W]

Efficiency [%]

Stage 0 13.2 396 490 70 17.7 Stage 1 12.0 360 599 86 23.9 Stage 2 11.0 330 650 93 28.2 Stage 3 10.0 300 703 101 33.7 Stage 4 8.3 249 735 105 42.1

It remarks that, by increasing of magnetic injection, in

constant supply voltage conditions, the electrical power P1 decreases (by current decreasing) and the output power P2 and the efficiency increase. That means a substitution of electric energy absorbed, with an equal amount of magnetic energy and a compensation for loss of electromagnetic energy. It is the explanation for the increasing efficiency.

Taking into account that all, for each stage, ten tests are accomplished. Below are presented the whole experiment results as tables and waveforms.

For the case of constant dc voltage V1=30V, a synthesis is presented, as follows:

• position 0 (see Fig. 3 and Table II)

Fig. 3. Motor waveforms at position zero.

TABLE II. MOTOR TESTS AT POSITION ZERO

Test sets

Torque [Nm]

Speed [rpm]

Current [A]

Output useful power [W]

Electric power

[W]

Effi-ciency [%]

1 0.00 1392 2.4 0 72 0 2 0.32 1245 4.3 42 129 32.5 3 0.44 1180 5.3 54 159 34 4 0.58 1100 6.5 67 195 34.3 5 0.70 1035 7.4 76 222 34.2 6 0.82 960 8.25 82 247 33,2 7 0.97 856 9.55 87 286 30.4 8 1.08 772 10.5 87 315 27.6 9 1.20 655 11.6 82 348 23.6

10 1.37 490 13.2 70 396 17.7

• position 1 (see Fig. 4 and Table III)

Fig. 4. Motor waveforms at position one.

TABLE III. MOTOR TESTS AT POSITION ONE

Test sets

Torque [Nm]

Speed [rpm]

Current [A]

Output useful power [W]

Electricpower

[W]

Effi-ciency [%]

1 0.00 1365 2.2 0 66 0 2 0.32 1230 4 41 120 34.2 3 0.44 1173 4.8 54 144 37.5 4 0.58 1098 5.7 67 171 39.2 5 0.70 1046 6.6 77 198 38.9 6 0.82 979 7.5 84 225 37.3 7 0.97 881 8.7 89 261 34.1 8 1.08 802 9.7 91 291 31.3 9 1.20 733 10.6 91 318 28.9

10 1.37 599 12 86 360 23.9

• position 2 (see Fig. 5 and Table IV)

Fig. 5. Motor waveforms at position two.

TABLE IV. MOTOR TESTS AT POSITION TWO

Test sets

Torque [Nm]

Speed [rpm]

Current [A]

Output useful power

[W]

Electric power

[W]

Effi-ciency [%]

1 0.00 1319 2 0 60 0 2 0.32 1201 3.8 40 114 35.1 3 0.44 1149 4.5 53 135 39.2 4 0.58 1094 5.2 66 156 42.3 5 0.70 1036 6.2 76 186 40.9 6 0.82 974 6.9 84 207 40.5 7 0.97 892 8.2 91 246 37 8 1.08 822 9 93 270 34.4 9 1.20 764 9.7 96 291 33

10 1.37 650 11 93 330 28.2

• position 3 (see Fig.6 and Table V)

Fig. 6. Motor waveforms at position three.

TABLE V. MOTOR TESTS AT POSITION THREE

Test sets

Torque [Nm]

Speed [rpm]

Current [A]

Output useful power [W]

Electric power

[W]

Effi-ciency [%]

1 0.00 1273 2 0 60 0 2 0.32 1156 3.6 39 108 36.1 3 0.44 1110 4.2 51 126 40.5 4 0.58 1053 5.1 64 153 41.8 5 0.70 1005 5.7 74 171 43.3 6 0.82 962 6.4 83 192 43.2 7 0.97 901 7.3 92 219 42 8 1.08 859 7.8 97 234 41 9 1.20 791 8.7 99 261 37.9

10 1.37 703 10 101 300 33.7

• position 4 (see Fig. 7 and Table VI)

Fig. 7. Motor waveforms at position four.

TABLE VI. TABLE VI MOTOR TESTS AT POSITION FOUR

Test sets

Torque [Nm]

Speed [rpm]

Current [A]

Output useful power [W]

Electric power

[W]

Effi-ciency [%]

1 0.00 1135 1.9 0 57 0 2 0.32 1047 3.3 35 99 35.3 3 0.44 1013 3.9 47 117 40.2 4 0.58 977 4.5 59 135 43.7 5 0.70 933 5 68 150 45.3 6 0.82 902 5.7 77 171 45 7 0.97 851 6.4 86 192 44.8 8 1.08 827 7 93 210 44.3 9 1.20 785 7.5 99 225 44

10 1.37 735 8.3 105 249 42.1

IV. CONCLUSION This paper presents a prototype of a dc motor with PM

which is supplied by two adjustable energy sources: electric energy source and magnetic energy source which delivers energy by magnetic injection. This one is provided by PM grouped within a magnetic device (situated outside of the motor) related with the PM placed in the machine armature. It was demonstrated that by magnetic injection it is possible to control the motor functional parameters (torque, power, energy and efficiency).

The tests have been made in constant voltage of 30V dc and T=0÷1.37Nm conditions, for a motor prototype with a maximum power of 20kW.

Taking into account the motor advantages, the authors wish to improve its performances. In this aim a co-operation with some electrical machine manufacturers will be suitable.

ACKNOWLEDGMENT The prototype of the dc motor with PM energy injection

was realized by Mr. Gabriel DIACONU and officially certified by the Patent of Invention nr. 122470/30.06.2009 at OSIM Bucharest-Romania.

REFERENCES [1] G. Diaconu, “DC motor with permanent magnets” in Monitorul Oficial,

RO 126006 A2, Bucharest, Romania, published in 28.01.2011. [2] C. Lungoci, M. Georgescu, M.D. Călin, “Electrical Motor Types for

Vehicle Propulsion”, Proceedings of the 13th International Conference on Optimization of Electrical and Electronic Equipment OPTIM 2012, 24-26 May 2012, Brasov, nr. RD-00724, ISSN 1842-0133, pp. 635-641.

[3] M.D. Călin, M. Georgescu, C. Lungoci, “Influence of the Magnetic Materials on the Behavior of Traction Motors for Vehicle Propulsion”, Annals of the University of Craiova, Serie: Electrical Engineering, Year 36, No. 36, The 11th International Conference on Applied and Theoretical Electricity - ICATE 2012, 25-27 October 2012, Craiova, pp. 216-220, ISSN 1842 – 4805, Ed. Universitaria.

[4] M. Georgescu, “DC Brushless Drive System Suitable for Vehicle Propulsion”, TMT'2007 International Conference, Hammamet, Tunis, pp.1131-1134, ISBN 978-9958-617-34-8, sept. 2007.

[5] M. Georgescu, “Laboratory Test Bench for Vehicle Propulsion Permanent Magnet Motors”, Proceedings of the 9th International Conference on Challenges in Higher education and Research in the 21st Century, June 5-8, 2012, Sozopol, Bulgaria, pp. 204-207, Heron Press, Sofia, ISBN 978-954-580-318-5.