The modeling of small power bridge by Simulink program.

Gordan, Mircea ; Pop, Adrian Petru ; Gordan, Cornelia 等

1. INTRODUCTION

The paper presents a simulation solution by Matlab-Simulink program of feed source for an electro-thermal heating installation by induction, which consists from rectifier-inverter circuit and a command circuit for inverter with static switch elements. The fit of heat into heating installations by electromagnetic induction is doing in dependence of penetration depth of electromagnetic field (Biloteanu, 2008):

[delta] = 1/[square root of [pi] x f x [mu] x [sigma]] (1)

Where: [delta]-is penetration depth, f-current frequency, [mu]-magnetic permeability, f-current frequency, [sigma]-electrical conductivity.

By change the frequency due to altering of penetration depth and in final the layer in which is development the heat. The feed current frequency is 50 Hz, and for its altering is used some methods such as rotated convertors, multipliers of ferromagnetic frequency and static convertors. It has selected for simulation static convertors from direct current in alternating current, in function of technological process demands (Munteanu, 1998; Rombaut, 2001).

2. CONVERSION CIRCUITS AND COMMANDS

For analyzing of inductor electric circuit has done of R-L-C series circuit for using Matlab-Simulink program, presented in Fig.1.

[FIGURE 1 OMITTED]

[FIGURE 2 OMITTED]

The Simulink diagram of rectifier circuit for an alternating voltage of 100V is presenting in Fig.2. The rectifier is composed from four semiconductors diodes by a bridge connection, which able rectifying of alternating voltage and than being filtrated by L-C filer to get a signal of direct voltage.

Realizing of inverter circuit by Simulink program is doing by get in from libraries of static switches that would be connected bridge, and the bridge is charge with an inductor of electro-thermal heating installation by induction.

The parameters of R-L-C circuit were resulted by a design calculus of heating process by induction, where enter data are heating temperature, predictable operation frequency of inductor and processing time of material. By knowing these data can be implemented the Matlab program by Simulink, which simulation of feed inductor circuit with real values. The inverter is build up from static switch elements commended, which may be used in function of technological demand frequency the following static commutations such as GTO, IGBT and MOSFET (Popa, 2005; Book Matlab, 2001).

The power transistor-MOSFET has high performances as great commutation speed, independent commutation time from charge circuit and temperature variations, great enter impedances values. For assuring of alternative current character on charge is obtain by activation of MOSFET and MOSFET3 elements for positive alternation, or MOSFET1 and MOSFET2 for negative alternation. The performed switch elements contain a diode located anti-parallel with commutation element, which assuring a demand flowing way similar with from Fig.1.

An adequate command of inverter in bridge with RLC charge recommends a performance command such as modulation in time (PWM) of impulses for command of commutation elements. The voltage on charge is forming by PWM impulses and sinusoidal current depends by number of PWM impulses and modulation. The sinusoidal PWM command is used for avoid of superior harmonics unit a predictable order. The width impulses must to be a sin function of position angle measured at the beginner of semi-alternation.

The command of switches is doing by two functions: a sinusoidal frequency function-f, which has adjustable amplitude-A, and a triangle function of amplitude At=const. and frequency [f.sub.t]=2Nf.

[FIGURE 3 OMITTED]

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The open and end impulses are function of fundamental value demand of output inverter, which assured avoid of inferior harmonics of 2N order. The maximal number of impulses-N obtain of semi-period is limited by maxim working frequency of switches, considering fast growing of commutation loses in same time with frequency rising.

The Simulink diagram for generation of PWM command signal with sinusoidal modulation is showing in Fig.4.

3. RESULTS OF TEST

The inverter used of simulation by Matlab-Simulink program has the following characteristics: parameters of resonant circuit-R=4.8 x [10.sup.-2] [OMEGA], L=50.51 x [10.sup.-6] H, f=1500 Hz. It's used 4 static commutations: ideals, GTO, IGBT and MOSFET, for 3 frequency of modulation of 1000Hz, 5000Hz, and 10000Hz (avoid harmonics of 1, 8 and 12 order).

The results confirm again that once with rising of modulator signal frequency there are eliminated the harmonics and the current through charge tends to perfect sin-wave form.

[FIGURE 5 OMITTED]

[FIGURE 6 OMITTED]

[FIGURE 7 OMITTED]

However, once with frequency rising is going diminish of current amplitude through charge, in special at inventers with GTO. At inverters with ideal switches can be observed that voltage on charge is following perfect the PWM commutation signals, which indicated that these elements have zero times of open/end, and other inventers with GTO, IGBT and MOSFET presented time of open/end different of zero. From all of them, the MOSFET has smaller commutation times, but presents disadvantage that at great commutation frequencies occurring voltage peaks, which in working can damage the elements.

4. CONCLUSIONS

These simulation tests have emphasized a good working of MOSFET switches for high frequencies of commutation, but in same time with rise commutation frequency occur important loses. An excellent working were at IGBT that have a greater commutation times as MOSFET, which didn't present tops of voltage on charge during frequency rising, represented only voltage and current attenuation on charge.

The PWM command technique presents advantages as avoid harmonics and power adjustment with large using.

Simulation using of inverters circuit working can be prevented the perturbation currents and voltages, avoid distortions about feed network, found optimal solutions without much money, reducing premature defects, etc.

5. REFERENCES

Biloteanu, A. & Mihai, D. (2008). Static converter and performing structural command, Technical Ed., Bucharest

Muntean, N. (1998). Static convertor, Technical Ed., Bucharest

Popa D. (2005). Static Convertor. Simulation on PC, EDP Editor, Bucharest

Rombaut, C. (2001). Power electronic converters, Technical Ed., Bucharest

***(2001). Handbook Matlab-Simulink