Volume 47 Number 2 2006 83 Contributions to Optimization of the Functioning of Some In by vdr16883

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									                                        Volume 47, Number 2, 2006                                      83




            Contributions to Optimization of the
             Functioning of Some Inverters by
                        Simulation
                    Mircea GORDAN and Claudiu MICH-VANCEA
Abstract: Inductive electro-thermic heating installations must be characterized by specific parameters
(current, voltage, frequency), in comparison with those of industrial installation. To obtain these
parameters, can be used some modern devices, as the redress – inverter system with static commutation
elements. This system makes the conversion of the alternative voltage given by an industrial power supply
installation into a continuous one, with the redress device then this voltage is converted again in an
alternative one, with other parameters, with the inverter.
         The paper presents the alternative – continuous convention bridge (redressing device), continuous
– alternative convention bridge (inverter) containing different commutation elements. Also, describes the
semi-conductive elements, PWM command signal generation using “Matlab–Simulink” environment.
Redressing – inverter system was simulated for some R, L, C parameters obtained by a design calculus, in
the case of o cylindrical piece electromagnetic induction volume heating installation. The simulations
show which static commutation device is optimal for a proper behaviour of the inverter in the case of the
given charge. The Simulink simulated inverter is developed for a serial compensated charge, containing
three types of static commutation elements and some ideal static commutations (IGBT, MOSFET, GTO).

Keyword: inverter, Matlab-Simulink, charge RLC.


        1. Generalities                                 frequency. To modifier this voltage,
                                                        depending on the technological process
     The paper presents a simulation solution,          needs, can be used different methods to
in “Matlab–Simulink” environment, for an                modify the frequency multipliers and static
induction electro-thermic heating installations         converter. The development of power
power source. This power source contains a              electronics, based on different types of static
redressing circuit, an inverter and a command           commutation element, lead to a lower
circuit for the inverter with static                    economical costs and higher efficiencies of
commutation elements.                                   the alternative – continuous conversion
     Heating adjust inside the electromagnetic          installations. Because there exist many types
induction heating installation is developed             of static commutation elements, for this
especially according to the electromagnetic             simulation were used both AC – DC and DC
field penetration depth.                                – AC conversion installations. As a
     As it can be seen by modifying the                 conclusion, first of all the power industrial
frequency can be modified the penetration               voltage will be first of all redressed as a
depth and finally is modified the layer where           continuous voltage, and then will be
is developed the heat inside the piece. The             converted back in an alternative signal, with
low, medium and high voltage from the                   the help of the inverter.
industrial power installation has 50 Hz,
84                                                             ACTA ELECTROTEHNICA


     2. Conversion circuit and their
command

     To analyze the electric circuit of an
inductor, first of all was simplified the
original circuit to an R – L serial one. This
simplified circuit was adapted to a condenser
C, that can be connected serial or parallel.
Depending on the connection of the
condenser with the serial R – L elements, it is
obtained a serial or parallel resonant circuit.
    To obtain the scheme form figure 2.1 in
Matlab–Simulink environment is easy and                                                             Fig. 2.2. Alternative voltage redressing scheme
needs simple object oriented programming                                                                       simulated with Simulink.
knowledge, connected with the analyzed
phenomena.                                                                possibilities to store the information and
                   Lf
                                                   Inver ter              visualize the result, like: visualization on the
                                          T1                   T3
                                                                          oscilloscope, digital visualization device,
                                     D1                              D3
                                                                          storing the results in Matlab environment
R
S                        Cf
                                                   Load
                                                                          working space called “workspace” on storing
T                                              R          L     C         the data in a file on the hard disk.
                                     D2
                                          T2                    T4
                                                                     D4
                                                                               To design an inverting circuit with
         Bridge    Filter
                                                                          Simulink in the library must be introduced
         AC-DC                                                            the static switches which will be placed in a
                                                                          bridge. Between the arms of the bridge is
                        Control system                                    connected the charge, which can be an
                                                                          inductance of an inductive electro-thermic
    Fig. 2.1. Electric scheme of a power supply circuit                   heating installations. Usually, in the analyzed
                 of a serial R–L–C charge.                                system this charge is simplified to an R-L-C
                                                                          serial resonant circuit.
     Matlab offers the user a set of libraries
containing already defined blocks that can be                                            200




used to construct new phenomena. Pre-
                                                                                         100
                                                                          Voltage AC




                                                                                           0

defined blocks have standard functional                                                  -100

parameters, but they can be modified                                                     -200


depending on the application. The                                                               0       0.05   0.1   0.15    0.2
                                                                                                                            Time
                                                                                                                                   0.25   0.3   0.35   0.4



modification of these parameters can be done                                             100

using a special window.                                                                   80


     In figure 2.2 is presented a redressing
                                                                            Voltage DC




                                                                                          60


circuit Simulink simulated scheme, which has                                              40



the target to redress and filter an                                                       20




approximately 100V alternative voltage. The
                                                                                           0
                                                                                                0       0.05   0.1   0.15    0.2   0.25   0.3   0.35   0.4
                                                                                                                            Time


redressing circuit contains 4 semi-conductive                                               Fig. 2.3. Sinusoidal, redressed and filtered signal.
diodes connected in a bridge. After the
voltage is redressed with the above-                                           R, L, C circuit parameters were obtained
mentioned bridge, this voltage is double –                                with a design calculus in the case of an
alternance redressed and filtered with an Lf –                            inductor for an induction heating technologic
Cf filter. This way is obtained a continuous                              process, for which the input are: heating
voltage.                                                                  temperature, working frequency imposed for
     To visualize the parameters of the                                   the inductor and the material processing time.
simulated scheme, Matlab offers many                                      Knowing the frequency imposed for the
                                       Volume 47, Number 2, 2006                                         85


power supply of the inductor and the values           the power stored in inductor and must find a
of R, L, C parameters, can be implemented a           proper discharge way. One solution is given
Simulink scheme for the real inductor power           by using with modulator impulses (PWM) for
supply circuit. The inverter is developed with        the commutation elements commands. The
commanded static commutation elements.                charge voltage contains PWM impulses and
Depending on the imposed technological                the current will be sinusoidal, depending on
frequency can be used different types of static       the number of PWM impulses and of the
commutation elements: GTO tyristors, IGBT             modulation.
transistors, MOSFET transistors.                           PWM command with sinusoidal
     MOSFET        transistors    are   power         modulation is used to eliminate the
electronics devices very often used in power          harmonics superior to a given order. As the
commutation sources building. MOSFET                  number of impulses in a period is bigger,
offers much more advantage than bipolar               more harmonics can be eliminated.
transistors, like: big commutations speed,                 The width of the impulses must be a
commutation time is independent of the                sinusoidal function depending on their
charge circuit and temperature variation,             position angle, measured starting with the
input impedance is very big.                          beginning of a half-alternance. Switches
                                                      command is obtained by using 2 function:
                                                             - a sinusoidal function with f
                                                      frequency (charge voltage fundamental
                                                      frequency), with a variable A amplitude;
                                                             - a triangular function, with a constant
                                                      A, amplitude and a frequency f t = 2 Nf Hz .




      Fig. 2.4. Bridge inverter with MOSFET
               commutation elements.

     To be sure that the charge current is
alternative, the positive alternance is obtained
by activating MOSFET and MOSFET-3
elements. The negative alternance is given by
activating MOSFET-1 and MOSFET-2                          Fig. 2.5. Simulink scheme of the PWM signals
elements. It’s better that, between the                       generator with sinusoidal modulations.
impulses, the charge voltage to avoid random
variation determined by the inductor self                     The closing and opening impulses
induced voltage. For this it is necessary to          depend on the fundamental harmonic value
create a discharge way, because the charge            that is obtained at the inverter output. This
voltage is close to zero volt. The most               one must annihilated the harmonics with
performant commutation elements contain a             order smaller then 2N. The impulses
diode     place     anti-parallel   with     the      maximum number N, existing in a half-
commutation element. The diode is the one             period, limited by the maximal frequency of
who assures the discharge way, as it can be           the switches functional process. It must be
seen in figure 2.1.                                   underlined that the commutations losses grow
     A correct command for a bridge inverter          vary fast with the frequency growing.
with R, L, C charge must take into account
86                                          ACTA ELECTROTEHNICA


        Simulink scheme for PWM command                                     20

                                                                            15

signal generation using sinusoidal modulation




                                                                  PWM
                                                                            10



is presented in figure 2.5. In figure 2.6 is                                 5

                                                                             0


shown the modulation of the two signals to                                       0             0.5                1                    1.5          2                 2.5                 3
                                                                                                                                      Time                                               -3
                                                                                                                                                                                  x 10
                                                                           100

obtain the PWM. Modifying the triangular                                    50




                                                           Voltage
signal frequency is also modified the number                                 0

                                                                           -50

of impulses applied to static commutation                             -100
                                                                                 0             0.5                1                    1.5          2                 2.5                 3

elements.                                                                                                                             Time                                               -3
                                                                                                                                                                                  x 10


                                                                     1000




                                                        Curent
                                                                             0


                                                                   -1000


                                                                                 0                           0.005                                 0.01                              0.015
                                                                                                                                      Time



                                                                          Output signals forms of the inverter with ideal
                                                                          commutation elements for a 1500 Hz resonant
                                                                       frequency and 5000 Hz modulator signal frequency.
                                                                           20

                                                                           15



                                                                  PWM
                                                                           10

                                                                            5

                                                                            0
                                                                                 0                           0.005                                 0.01                             0.015
                                                                                                                                      Time

                                                                           100

                                                                           50
                                                          Voltage




                                                                            0

                                                                           -50


     Fig. 2.6. PWM signal with sinusoidal modulation.                 -100
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                                                                                                                                      Time


                                                                     1000


           3. Results. Conclusions
                                                        Curent




                                                                            0


                                                                  -1000



     The Matlab simulator inverter has the                                       0                           0.005
                                                                                                                                      Time
                                                                                                                                                   0.01                             0.015




following characteristic:                                                Output signals forms of the inverter with ideal
        -     resonant   circuit    parameters:                          commutation elements for a 1500 Hz resonant
             −2                  −6                                   frequency and 1000 Hz modulator signal frequency.
 R = 4,8 ⋅ 10 [Ω] ; L = 50,51⋅10 [ H ] ;
C = 222.88 ⋅10 −6 [ F ] ,                                                    20

                                                                             15


        - working fundamental frequency f =
                                                                      PWM




                                                                             10

                                                                                 5

1500 [Hz].                                                                       0
                                                                                     0   0.2         0.4   0.6           0.8            1    1.2          1.4   1.6         1.8          2

     The inverter is simulated for 4 different                              100
                                                                                                                               Time                                                  -3
                                                                                                                                                                                  x 10



types of static switches (ideal, GTO, IGBT,                                  50
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                                                                                 0

MOSFET) and for 3 different values of the                                   -50


modulating frequency (1000 Hz, 5000 Hz,                                    -100
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                                                                                                                                        1    1.2          1.4   1.6         1.8
                                                                                                                                                                                     -3
                                                                                                                                                                                         2



10000 Hz). This way, are eliminated
                                                                                                                                                                                  x 10


                                                                           1000


harmonics numbers 1, 8, 12. The following
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                                                                                 0


figures present the simulated inverter output                         -1000



signals forms.                                                                       0                           0.005
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                                                                                                                                                   0.01                             0.015




     The obtained results confirm the idea                            Output signals forms of the inverter with ideal
that more and more harmonics are eliminated                           commutation elements for a 1500 Hz resonant
when the modulator signal frequency is                            frequency and 10000 Hz modulator signal frequency.
growing. In the same time, the charge current            GTO commutation elements (advantage: a
will have a form close to a sinusoid. But                strong current, but small commutation
when this frequency is growing, also grows               frequency).
the commutation frequency but the amplitude                   In the case of the inverter with ideal
of the charge current is smaller. This process           commutation elements the charge voltage
is important in the case of the inverter with            follows very well the PWM commutation
                                                                                             Volume 47, Number 2, 2006                                                                                                                  87


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               20
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               15




                                                                                                                                  PWM
                                                                                                                                         10
         PWM




               10
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                5
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                0
                                                                                                                                                 0   0.002   0.004   0.006         0.008   0.01   0.012      0.014     0.016   0.018    0.02
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              300
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             1000                                                                                                                      1000

              500




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                0

             -500                                                                                                                  -1000

         -1000                                                                                                                                   0                         0.005                          0.01                          0.015
                     0                        0.005                            0.01                         0.015                                                                          Time
                                                              Time



               Output signals forms of the inverter with GTO                                                                         Output signals forms of the inverter with IGBT
             commutation elements for a 1500 Hz frequency and                                                                        commutation elements for a 1500 Hz resonant
                   1000 Hz modulator signal frequency.                                                                            frequency and 1000 Hz modulator signal frequency.

                                                                                                                                       20
               20
                                                                                                                                       15
               15




                                                                                                                             PWM
                                                                                                                                       10
         PWM




               10
                                                                                                                                        5
                 5
                                                                                                                                        0
                 0
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                0.035    0.0355   0.036   0.0365      0.037   0.0375   0.038      0.0385   0.039   0.0395   0.04
                                                                                                                                                                                           Time                                           -3
                                                               Time                                                                                                                                                                    x 10
              150                                                                                                                  100

              100
                                                                                                                                       50
               50
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   Voltage




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                 0
               -50                                                                                                                     -50
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               0.035     0.0355   0.036   0.0365      0.037   0.0375   0.038      0.0385   0.039   0.0395   0.04
                                                                                                                                                                                           Time                                           -3
                                                               Time                                                                                                                                                                    x 10
             1000
                                                                                                                                 1000
              500
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Curent




                                                                                                                                        0
                 0

             -500                                                                                                             -1000

         -1000                                                                                                                               0                             0.005                          0.01                           0.015
                     0                        0.005                            0.01                         0.015
                                                                                                                                                                                           Time
                                                              Time



               Output signals forms of the inverter with GTO                                                                         Output signals forms of the inverter with IGBT
             commutation elements for a 1500 Hz frequency and                                                                        commutation elements for a 1500 Hz resonant
                   5000 Hz modulator signal frequency.                                                                            frequency and 5000 Hz modulator signal frequency.

               20                                                                                                                      20

               15                                                                                                                      15
                                                                                                                             PWM
         PWM




               10                                                                                                                      10

                5                                                                                                                       5

                0                                                                                                                       0

               0.035     0.0355   0.036   0.0365      0.037   0.0375   0.038      0.0385   0.039   0.0395   0.04                             0       0.2     0.4     0.6           0.8       1     1.2           1.4     1.6     1.8           2
                                                               Time                                                                                                                        Time                                               -3
                                                                                                                                                                                                                                       x 10
                                                                                                                                   100
             100
                                                                                                                                       50
               50
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  Voltage




                                                                                                                                        0
                0
                                                                                                                                       -50
               -50
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             -100
               0.035     0.0355   0.036   0.0365      0.037   0.0375   0.038      0.0385   0.039   0.0395   0.04                             0       0.2     0.4     0.6           0.8       1     1.2           1.4     1.6     1.8           2
                                                               Time                                                                                                                        Time                                               -3
                                                                                                                                                                                                                                       x 10
             1000
                                                                                                                                 1000
             500
                                                                                                                    Curent
Curent




                0                                                                                                                       0


             -500                                                                                                             -1000

         -1000
                     0                        0.005                            0.01                         0.015                            0                             0.005                          0.01                           0.015
                                                              Time                                                                                                                         Time



               Output signals forms of the inverter with GTO                                                             Output signals forms of the inverter with IGBT
             commutation elements for a 1500 Hz frequency and                                                            commutation elements for a 1500 Hz resonant
                  10000 Hz modulator signal frequency.                                                                   frequency and 10000 Hz modulator signal frequency.

 signals. This means that this commutation                                                                            disadvantage: when the commutation
 elements have zero opening/closing time                                                                              frequencies are high appear some voltage
 intervals.                                                                                                           peaks, which can destroy the commutation
      Also can be concluded that MOSFET                                                                               elements.
 elements have the smallest commutation                                                                                   As a conclusion, can be said that
 time's intervals, but are characterized by a                                                                         MOSFET commutation elements have a good
  88                                                                                         ACTA ELECTROTEHNICA


                  20

                  15
                                                                                                                     of MOSFET elements. But when the
                                                                                                                     commutation frequency grows, the charge
         PWM




                  10

                  5

                  0
                                                                                                                     voltage peaks do not exist any more. The
                       0   0.002    0.004   0.006       0.008   0.01
                                                                Time
                                                                         0.012      0.014   0.016   0.018     0.02
                                                                                                                     only one effect is that the charge voltage and
                                                                                                                     current present a small alternation.
              100

                  50


                                                                                                                          PWM command techniques have
  Voltage




                  0

               -50

              -100
                       0   0.002    0.004   0.006       0.008   0.01     0.012      0.014   0.016   0.018     0.02
                                                                                                                     advantages concerning the harmonics
                                                                Time
                                                                                                                     elimination and power adjustment. This
             1000
                                                                                                                     important advantage proves why this type of
Curent




                                                                                                                     command is often used, in spite of the fact
                  0


         -1000


                       0                        0.005                            0.01                        0.015
                                                                                                                     that needs a more complicated command
                                                                                                                     device and quick semi-conductor devices (the
                                                                Time



               Output signals forms of the inverter with MOSFET
                                                                                                                     costs are bigger). Technical progress obtained
                 commutation elements for a 1500 Hz resonant
              frequency and 1000 Hz modulator signal frequency.                                                      concerning the command parts (specialized
                                                                                                                     integrated circuits) and the power semi-
                  20                                                                                                 conductor devices make this technique more
                                                                                                                     and more attractive.
                  15
         PWM




                  10

                   5

                   0
                                                                                                                          Using the PC inverter circuits behavior
              200
                  0.02     0.021    0.022   0.023       0.024   0.025
                                                                Time
                                                                         0.026      0.027   0.028   0.029    0.03
                                                                                                                     simulation can be prevented the disturbing
              100                                                                                                    voltages and currents, can be eliminated the
                                                                                                                     distortions from the power supply network,
   Voltage




                   0



                                                                                                                     can be found optimal solution without high
              -100

              -200


                                                                                                                     costs for any application, etc.
                 0.02      0.021    0.022   0.023       0.024   0.025    0.026      0.027   0.028   0.029    0.03
                                                                Time


             1000
Curent




                   0
                                                                                                                             References
          -1000


                       0                        0.005                            0.01                        0.015

                                                                                                                     1. Bookmark MATLAB – Simulink.
                                                                Time



               Output signals forms of the inverter with MOSFET                                                      2. Rombaut Christian – Power electronic
                 commutation elements for a 1500 Hz resonant                                                            converters.
              frequency and 5000 Hz modulator signal frequency.
                                                                                                                     3. Al. Bitoleanu, Dan Mihai – Convertoare
                  20
                                                                                                                        statice şi structuri de comandă performante.
                  15                                                                                                 4. Nicolae Muntean – Convertoare statice.
            PWM




                  10

                   5

                   0
                  0.035    0.0355   0.036   0.0365      0.037   0.0375   0.038     0.0385   0.039   0.0395   0.04
                                                                                                                     Mircea GORDAN
                                                                 Time
               200
                                                                                                                     Claudiu MICH-VANCEA
               100

                                                                                                                     Universitatea din Oradea
    Voltage




                   0

              -100

              -200
                0.035      0.0355   0.036   0.0365      0.037   0.0375   0.038     0.0385   0.039   0.0395   0.04
                                                                 Time


              1000
 Curent




                   0


             -1000


                       0                        0.005                            0.01                        0.015
                                                                Time



           Output signals forms of the inverter with MOSFET
              commutation elements for a 1500 Hz resonant
          frequency and 10000 Hz modulator signal frequency.

  behavior for high commutation frequencies,
  in spite of the fact that exist important losses.
       Also, IGBT elements have a good
  behavior, but their commutation time
  intervals are a little bit bigger than in the case

								
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