Design And Implementation Of A Novel High Power Factor Hybrid Rectifier

In virtue of the advantage of high-power variable frequency technology which can realize a significant power-saving effect, its research has developed into one of the national leading direction of power saving. With the rapid development of variable frequency technology, the inverter technology, PWM technology, and other relevant areas also have a considerable development. But rectifier technology which serves as the input unit of the high-power converters has developed slowly. Currently, the majority products of converter manufacturers use uncontrolled 12-pulse rectifier, of which the character is simple and low cost. Compared to the regular uncontrolled rectifier, its line-side current harmonics has been noticeably reduced. Its shortcomings, however, are still evident. For example, the value of THD remains high and power factor is low, both of which can lead directly to the high harmonics of power system and increasing reactive power. In order to inhibit harmonic current and improve the power factor, this paper proposes a novel type of hybrid high power factor rectifier, and researches its topology and control strategy.Compared to the traditional topology of multi-pulse rectifier, this novel hybrid rectifier realizes a lower THD, which is less than 5% required by the power system, and its power factor is above 0.95. Moreover, when used as an input unit of three-level converter, it can achieve the NPC (neutral-point clamp) control, which is important to improve the performance of three-level converter. To prove the practicability of the topology, the paper first analyzes the main circuit of the rectifier, and then presents a harmonic detection method based on the instantaneous reactive power theory and PWM hysteresis current control strategy.Neutral-point potential balancing, which influences the performance of three-level converter, is also important. In order to achieve the optimal output voltage of converter, this paper presents a control strategy for the NPC on rectifier side. Compared to the traditional ones, this method alleviates the burden of control on inverter side, reduces the output voltage and current harmonics of converter and improves the performance of three-level converter. Finally, a low voltage and low power hybrid rectifier, which is based on the control chip TMS320F2812, is designed and applied. Simulation and experiment results show that the proposed novel hybrid rectifier topology and control strategy can achieve power transformation of the high power factor and low input harmonic current under high voltage.