Passive diode bridge (B6) rectifiers are widely used in industry for three-phase AC-to-DC conversion due to simplicity of circuit and design, high efficiency as well as robustness and low cost. For applications which require high input current quality (low THDi and high power factor) active three-phase rectifiers have to be used which in general are dedicated systems fully replacing the passive rectifier stage. For specific applications (e.g., AC drives) now a concept is attractive which opens the opportunity that an existing B6 rectifier optionally can be upgraded to high quality mains currents if required. This paper provides a concise topology survey and proposes several new circuits regarding such DC-side located add-on options for standard B6 rectifiers. All proposed topologies (introduced and also new circuits) are based on the third harmonic injection principle. The most attractive concepts are analyzed in detail concerning injection inductor design, DC- link capacitor design and voltage/current stress of the required switching semiconductor devices. Measurements of a laboratory prototype finally illustrate good stationary and dynamic performance of the implemented system.
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