Switched Three-Phase Power Inverter

The previous section considers a simple DC to DC boost converter with two switches controlled by two complementary signals. The healthy boost converter thus may be in one of two feasible modes. Reference [18] studies switch faults in a simple single phase half-bridge inverter. In [17], bond graph-based FDI is applied to a single phase H-bridge inverter. Both works represent switches by means of controlled junctions, i.e. use hybrid bond graphs. 

The power switches suggest to capture the dynamic behaviour of a three-phase inverter by a hybrid model and to study the effect of switch failures on the behaviour of this type of power converter. Three-phase inverters are a common component in many power electronic systems. They are used, for instance, 

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. 

The switch state independent conductance causality of the non-ideal switches results in an undetermined causality at 0-junctions Oa, 0, Oc representing the potentials Va,Vb, Vc of the nodes between upper and lower switches in the half-bridges. The causal conflicts have been removed by attaching an auxiliary C-storage element to each of these 0-junctions. Equations derived from the bond graph are formulated such that the auxiliary eapacitances can be set to zero. Consequently, the small ON-resistance of the switches and the node capacitances do not lead to small time constants. 

The three half-bridges are denoted by an index a, b, c respectively. Moreover, an index p is used for the upper switch of a half-bridge. An index n indicates the lower switches. Accordingly, map(t) denotes the discrete state of the upper switch in the half-bridge with the index a at time instant t. 

---

Fig. 8.20 Circuit schematic of a switched three-phase DC to AC power inverter with an RL-load in delta configuration [27]...

A relatively new innovation for use in electric motor compressor drives is the variable frequency power source. Fundamentally, the power source converts an existing three-phase source into DC then uses an inverter to convert back to a variable frequency supply. Thyristors or transistors are used to switch the output at the required frequency. 

AC electric drives require more sophisticated converters when they are supplied with DC sources, because electric machines requires periodic voltage and current waves with a variable frequency depending on the load requirements. In Fig. 5.8, the scheme of an example of three-phase induction motor driven by a pulse-width-modulated inverter is reported. In this scheme a three-phase bridge connection with six power modules is shown to form the so-called inverter. Each power module can be composed by a number of power switches connected in parallel to carry higher currents. Across each power switch (IGBT) a parallel diode is connected to provide a return path for the phase current when the power module is switched off. 

Clearly, a bond graph approach to FDI of systems modelled as a hybrid system is not limited to switched power electronic systems but may be applied to other engineering systems as well for which a hybrid model is appropriate. In the following, the case studies consider faults in a DC to DC boost-converter, in a three-phase DC to AC inverter and in a three-phase rectifier AC to DC. In some motor drives, a rectifier and an inverter are used back-to-back [8], Computations have been performed by means of the open source software program Scilab [21],... 

The structural information of the ARRs has been captured in an all-mode FSM. With the sensors used, all faults can be detected but cannot be isolated by analysing ARRs. It depends on how a system to be considered is built up whether further sensors can be added so that voltages across switches and currents through them can be measured. For instance, if there is a fault in one leg of the three-phase inverter or the rectifier, it can be due to a fault in one of the two switches in that leg. As to open circuit faults in switching cells, characteristic trajectories can be obtained after application of the dq-transformation that allow to isolate open switch faults. This technique not based on ARRs but often used in power electronics has been illustrated in Sect. 8.2.4 for an open circuit fault in the lower switch Sw4 of inverter leg a . 

Primary-Chopped Switching Power Supply Inverters for Ascertained Power Supply of Three-Phase... 

---