The diode rectifier offers several desirable features such as a unity displacement-factor and a high efficiency with low complexity and high reliability, but the utility line-current is significantly distorted. The traditional multi-pulse (e.g., 12-pulse, 18-pulse and so on) PAM concept by means of multiple rectifier units and phase-shifting isolation-transformers is a well-known scheme to improve the input line-current waveform and reduce dc-current/voltage ripple. Though, the necessity of the isolation-transformer is a great weak point especially for applications in low to medium power range. To mitigate the problem, several investigations have been done. The PWM rectifier is a modern and effective alternative, although it results in a higher initial cost, lower efficiency and EMI noise problems due to high frequency switching.
To solve the problem, we have two alternatives without PWM and are so called “Passive” schemes. One is the multi-pulse/multi-phase scheme without the isolation transformer but with an autotransformer. This scheme results in a simplified multi-pulse PAM rectifier. The other is the Third-Harmonic-Current Injection and the expanded schemes. Although these two schemes have been studied independently in most cases, new types of diode PFC rectifier obtained by combining the two schemes have been studied recently. Additionally, further new topologies, so called “Hybrid” type, have been proposed very recently. The rectifiers with the new concept consist of an autotransformer-connected double 3-phase bridge 12-pulse rectifier and a PWM dc-dc converter on the dc-side to perform the current injection. The Hybrid rectifiers offer output voltage controllability and sinusoidal input currents similarly to the PWM rectifiers.
To show the current trends and remaining possibilities of the Passive and Hybrid rectifiers, this paper gives a survey and historical review of the rectifiers. Then, some new topologies in the category are investigated. Simulation and experimental results of the rectifiers are described to explore the operating mechanism and to obtain hints to achieve new topologies.