Switching-Transistor Model

In this section, a simulation method of basic switching circuit by the EMTP is explained. The technique can be applicable to a power-switching device. 

The base-emitter characteristic can be expressed by a nonlinear resistor model installed in the EMTP. Although both TYPE-92 and -99 models accept point-by-point data expressing its current-voltage characteristic, the true nonlinear resistor model (TYPE-92) is suitable for the simulation from the viewpoint of stability. The characteristic is easily obtained from the data sheet of the transistor. 

If saturation voltage between the collector and the emitter cannot be negligible, a resistor is inserted in series with the switch. The resistor and the capacitor Qj represent a base spreading resistance and a base input capacitance, respectively. 

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The simplest switching transistor model of the EMTP is the TACS-controlled switch model (TYPE-13) illustrated in Figure 4.5. 

Flow chart for the simplest switching transistor model. 

The key point of our transistor model is the negative differential heat resistance as we observed in the diode model(Li Wang Casati, 2004). It provides the possibility that when Ta changes both Js and Jd change simultaneously in the same way. Therefore Js = Jd (or Js Jd) can be achieved for several different values of T0 or even in a wide region of T0 as shown in Figs.10 and 11. In this situation heat switch and heat modulator/amplifier are possible. In the ideal, limiting... 

The component providing a signal b(t) that externally controls the pass transistor modelled as a switch is denoted as switch control. Its output signal b(t) is an input to the switched network and may be subject to disturbances. 

The small example systems considered in this chapter are widely used basic components of power electronic systems. In power electronics, it is common to model the fast switching semiconductor devices that use various types of transistors, diodes, or thyristors simply as ideal or non-ideal switches although more sophisticated transistor models can be used and are used depending on the application and the purpose of a simulation study. 

The transistor model described in Section 4.2.3.1 is simple and useful for low-frequency switching circuits. However, the accuracy of the model is reduced as the switching frequency increases. A modified MOSFET model is illustrated in Figure 4.14. 

Simulation models of a switching transistor and a MOSFET are also explained in this chapter. The model parameters of the device are easily obtained from a data sheet supplied by its manufacturer or from a simple experiment without complicated physical parameters of the semiconductor. The proposed model also enables temperature estimation. The accuracy of the models is satisfactory for the design of a switching circuit, such as a DC/DC converter and an inverter. 

Limitation The logic system defined In this package may be insufficient for modelling switched transistors,... 

We first demonstrate the switch function of our transistor, namely we show that the system can act like a good heat conductor or an insulator depending on the control temperature. This is illustrated in Fig.lO(b), where we plot JG, Js, and Jd versus Trj. When TG increases from 0.03 to 0.135, both Jd and Js increase. In particular, at three points TG 0.04,0.09 and 0.135, Jd = Js thus JG is exactly zero. These three points correspond to off , semi-on and on states, at which Jd is 2.4 x 10-6,1.2 x 10-4 and 2.3 x 10-4, respectively. The ratio of the heat current at the on state and that at the off state is about 100, hence our model displays one important function - switch -just like the function of a MOSFET used in a digital circuit. 

Finally we have shown the possibility to build a thermal diode which exhibits a very significant rectifying effect in a very wide range of system parameters. Moreover, based on the phenomenon of negative differential thermal resistance observed in the thermal diode, we have built a theoretical model for a thermal transistor. The model displays two basic functions of a transistor switch and modulator/amplifier. Although at present it is just a model we believe that, sooner or later, it can be realized in a nanoscale system experiment. After all the Frenkel-Kontorova model used in our simulation is a very popular model in condensed matter physics(Braun and Kivshar, 1998). 

H. Shichman andD. Hodges. Modelling and simulation of insulated-gate field effect transistor switching circuits , IEEE Journal of Solid-State Circuits SC3 (1968), 285-289. 

Semiconductor switches in power electronic inverters are commonly made up of a transistor together with a diode in anti-paraUel connection as depicted in Fig. 2.13a for a bipolar transistor to provide a path for an inductive load current when conducting switches are turned off and thus to avoid damage of the transistors in an inverter. MOSFET transistors have a built-in diode. Figure2.13b shows a bond graph model of such a transistor-diode pair. 

In this book, switching devices such as electrical diodes and transistors, or hydraulic valves are modelled as non-ideal switches represented by a bond graph component model Sw that is composed of a switched MTF and a resistor in fixed conducfance causality. The choice of fixed conductance causality is motivated by the fact that it is the flow through the element that is determined by the discrete switch state. 

Junco et al. use this power inverter as an example for the application of their implementation of the non-standard switched power junctions (SPJs) (Chap. 2) in the modelling language of the 20sim modelling and simulation software [28]. In [29], and [30, Chap. 8], they model the transistor-diode pair in each half-bridge by means of a SPJ and address the dynamic behaviour of the healthy system. 

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