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Under normal circumstances, power electronics circuitry does not contain one single power semiconductor component but is composed of several components. When discrete devices are used, several of them, including their corresponding heat sinks, must be combined into one assembly to create a bundle of semiconductors that serve to compliment one another.
Since the heat sinks are connected to one terminal, each of the corresponding semiconductor components must be electrically isolated during assembly. The electrical connections are made using cables or busbars. This construction is very costly in terms of the material, volume, and labor involved. A completely different method of constructing power modules is opened up by the idea of putting the necessary insulation of the individual components into the component itself rather than into the mechanical structure of the module.
Such power modules are characterized by the separation of the paths for current and heat flow. Internal insulation with good heat dissipation capability ensures that the metal base is electrically isolated from the circuit which is connected to the outer terminals and that the heat from several components can be dissipated without losing any potential energy to a common cooling device.
Figure 1. Principle behind power module construction
Modules may contain line rectifier diodes, fast diodes, thyristors, MOSFETs, or IGBTs as semiconductors. The complexity of the internal circuitry ranges from a single semiconductor to as many as 20 semiconductor functions. In addition, some modules comprise passive components such as temperature sensors, resistors, and capacitors. Power modules with integrated driver functions are referred to as Intelligent Power Modules (IPM).
Power Module Applications
Very common are halfbridge modules (dual modules, phase modules) with the connection sequence ~/+/-/ for the main terminals. This configuration allows for many circuits typical in power electronics to be created from several of these modules and simple connection elements. Figure 2 demonstrates in an exemplary drawing the layout of such a halfbridge module integrating thyristors by means of solder technology.
Figure 2. Schematic layout of a thyristor-halfbridge module
A plastic case is glued on the module body and enough silicon gel is applied that insulation requirements are met permanently. It should be noted that most casing materials are not fully impermeable to infrared light. This means that the off-state current has a higher value in a bright environment, e.g. sunshine, than in complete darkness. This does not affect module functionality or reliability.
Besides halfbridge circuits, modules with 1-phase and 3-phase bridge circuits are very common both as rectifiers and inverters. Modules containing a rectifier bridge plus inverter and brake chopper are normally referred to as CIB modules (Converter Inverter Brake, the rectifier here being called a "converter"). Other module configurations are available for special applications.
Single Phase Bridge Rectifier
Single phase bridge rectifier applications include battery chargers and 2 quadrant DC drives.
Figure 2. Single Phase bridge rectifiers
The advantages of using a single phase bridge rectifier are quite obvious:
- Both modules can be mounted on 1 heat sink since the base plates of the modules are insulated
- Simple bus for direct current and alternating current (e.g. SEMIPACK port configuration)
3-Phase Bridge Rectifier
Figure 3. Three phase rectifier
Three-phase controlled rectifiers have a wide range of applications, from small rectifiers to large High Voltage Direct Current (HVDC) transmission systems. They are used for electro-chemical processes, many kinds of motor drives, traction equipment, controlled power supplies, and many other applications.
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