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THREE PHASE CONTROLLED RECTIFIERS

2 THREE PHASE CONTROLLED RECTIFIERS 2.1 Introduction

In the following part, we will see some topologies for 3 phase rectifiers. But we can start to explain why those topologies appeared. The high harmonic content and a low power factor cause some problems in power distribution system. New standards have been introduced by governments or organizations to limit the harmonic content of the current drawn from the power line by rectifiers. Consequently, new topologies have been deployed for rectification applications [9] .

We can introduced five topologies (Figure 2.1).

The figure a) present a simple solution of Boost converter. The main drawback of this solution is stress on the components and low frequency distortion of the input current.

The topologies b) and c) use PWM rectifier modules with a very low current rating (20 25% level of RMS current comparable with e) topology). Hence they have a low cost potential and provide only the possibility of regenerative braking mode b) or active filtering c).

Figure d) presents a converter called a Vienna rectifier. The main advantage is low switch voltage, but non typical switches are required.

Figure e) presents the most popular topology. This universal topology has the advantage of using a low cost three phase module with a bidirectional energy flow capability, and it can also provide a unity power factor (UPF). However, its disadvantages are a high per unit current rating, poor immunity to shoot through faults, and high switching losses [9] .

Topologies are compared in a table (see Table 2.1). A diode rectifier is also included to the table for comparison.

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