The three-phase voltage source PWM rectifier is highly valued for its bidirectional energy flow, sinusoidal grid currents, low input current harmonics, constant DC voltage control, compact filtering, and high power factor (nearly unity). It has become a popular choice in various industries such as four-quadrant drives, active power filters, superconducting energy storage, and renewable energy generation, replacing traditional rectifiers that suffer from high input current harmonic content and low power factor.
Among the many control strategies for PWM rectifiers, direct current control and indirect current control are primary methods. These strategies rely on complex algorithms and modulation modules. However, the direct power control (DPC) approach has gained significant attention recently due to its simplicity, strong interference resistance, excellent dynamic performance, and decoupled active/reactive power control. Extensive studies and practical implementations have validated its effectiveness.
This article explores the main circuit topology of the three-phase voltage-source PWM rectifier and the DPC-based control strategy, comparing and analyzing their features. Building on this foundation, future developments in PWM rectifier control strategies are anticipated.
The two-level and three-level PWM rectifier topologies are currently the most established designs. Two-level configurations are simpler and more widely adopted, whereas three-level configurations offer greater conversion power despite their more complex structure and midpoint potential balancing issues. Recent research has focused on minimizing power switches for low-power applications and exploring multi-level converters and soft-switching techniques for high-power scenarios.
Direct power control systems operate on a double closed-loop structure with DC-side voltage as the outer loop and instantaneous power as the inner loop. By controlling the active and reactive power, the system achieves the desired power factor and power flow direction. Among various DPC methods, the voltage-based DPC (V-DPC) is notable for its straightforward algorithm, lack of need for PWM modulation, and faster dynamic response. However, it suffers from non-fixed switching frequencies and high dependency on sensor accuracy.
Virtual flux linkage-based DPC (VF-DPC) offers advantages such as lower sampling frequencies and reduced total harmonic distortion (THD) under non-ideal grid voltages. Yet, it still struggles with non-fixed switching frequencies. The instantaneous power theory-based DPC provides more precise active and reactive power calculations without relying on system switching states, but it requires a higher sampling frequency.
Space vector-based DPC (SVM-DPC) improves upon traditional DPC by integrating space vector PWM modulation and PI controllers, offering fixed switching frequencies and reduced current distortion. Despite these benefits, its control algorithm is complex, and the system's accuracy depends on the current switching state.
Fixed-frequency power prediction-based DPC (P-DPC) maintains traditional DPC's advantages while introducing a novel method for achieving fixed switching frequencies. However, its power prediction algorithm is relatively intricate.
Power decoupling DPC separates active and reactive powers, enhancing tracking capabilities and static performance. Nevertheless, its algorithm complexity and reliance on estimated parameter accuracy remain challenges. Dual switch table DPC improves active/reactive power coupling by independently adjusting each power component.
Other improvements include fuzzy logic control integration, reactive power adjustment for active power enhancement, and dead-zone settings for sector boundaries. Phase-locked loops have also been introduced to improve voltage vector positioning.
Looking ahead, advancements in power electronics and control theories will deepen research into PWM rectifier control strategies. Future trends include enhanced current distortion reduction, minimized DC ripple, and further improved power factors. Researchers are also focusing on robustness under wide disturbances, unbalanced grids, multi-level converters, and intelligent control methods like neural networks and fuzzy logic.
In conclusion, this article has outlined the advantages of DPC in three-phase voltage-source PWM rectifiers, explored their topologies, explained key control methods, and forecasted future developments. As technology progresses, DPC will continue to evolve, meeting the stringent demands of modern industrial applications.
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