Browsing by Author "Pinto, S. F."
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- Direct Power Control of Matrix Converter Based Unified Power Flow ControllersPublication . Monteiro, Joaquim; Silva, J. Fernando; Pinto, S. F.; Palma, João Carlos Pires daThis paper presents the Direct Power Control of Three-Phase Matrix Converters (DPC-MC) operating as Unified Power Flow Controllers (UPFC). Since matrix converters allow direct AC/AC power conversion without intermediate energy storage link, the resulting UPFC has reduced volume and cost, together with higher reliability. Theoretical principles of DPC-MC method are established based on an UPFC model, together with a new direct power control approach based on sliding mode control techniques. As a result, active and reactive power can be directly controlled by selection of an appropriate switching state of matrix converter. This new direct power control approach associated to matrix converters technology guarantees decoupled active and reactive power control, zero error tracking, fast response times and timely control actions. Simulation results show good performance of the proposed system.
- Fast optimum-predictive control and capacitor voltage balancing strategy for bipolar back-to-back NPC converters in high-voltage direct current transmission systemsPublication . Chaves, Miguel; Margato, Elmano; Silva, J. F.; Pinto, S. F.; Santana, J.Multilevel power converters have been introduced as the solution for high-power high-voltage switching applications where they have well-known advantages. Recently, full back-to-back connected multilevel neutral point diode clamped converters (NPC converter) have been used inhigh-voltage direct current (HVDC) transmission systems. Bipolar-connected back-to-back NPC converters have advantages in long-distance HVDCtransmission systems over the full back-to-back connection, but greater difficulty to balance the dc capacitor voltage divider on both sending and receiving end NPC converters. This study shows that power flow control and dc capacitor voltage balancing are feasible using fast optimum-predictive-based controllers in HVDC systems using bipolar back-to-back-connected five-level NPC multilevel converters. For both converter sides, the control strategytakes in account active and reactive power, which establishes ac grid currents in both ends, and guarantees the balancing of dc bus capacitor voltages inboth NPC converters. Additionally, the semiconductor switching frequency is minimised to reduce switching losses. The performance and robustness of the new fast predictive control strategy, and its capability to solve the DC capacitor voltage balancing problem of bipolar-connected back-to-back NPCconverters are evaluated.
- Matrix converter-based active distribution transformerPublication . Pinto, S. F.; Alcaria, P.; Monteiro, Joaquim; Silva, J.F.This paper proposes a matrix converter-based active distribution transformer (MC-ADT) with enhanced control functionalities to be used in smart grids (SG). The proposed MC-ADT uses a matrix converter (MC) connected to a transformer inserted in series with the grid, and allows: 1) real-time voltage regulation of the low-voltage side of the MC-ADT, based on an adjustable reference value defined by the SG requirements and bounded by the standard values; 2) capability to regulate the LV grid voltage even in case of sags, voltage rises, and overvoltages in the transformer medium-voltage side; and 3) contribution to power factor correction in the MV side. The MC-ADT grid voltage regulators are synthesized, establishing the MC reference currents. To guarantee the tracking of the MC input and output reference currents, the space vector representation, together with sliding-mode direct control techniques, are used. The obtained experimental and simulation results show that the proposed system is able to regulate the LV grid voltages even for sags and overvoltages up to 20% in the MV side, and contributes to power factor correction in MV, while presenting fast dynamic response, without overshoot and almost zero steady-state error.
- Matrix Converter-Based Unified Power-Flow Controllers: Advanced Direct Power Control MethodPublication . Monteiro, Joaquim; Silva, J. Fernando; Pinto, S. F.; Palma, João Carlos Pires daThis paper presents a direct power control (DPC) for three-phase matrix converters operating as unified power flow controllers (UPFCs). Matrix converters (MCs) allow the direct ac/ac power conversion without dc energy storage links; therefore, the MC-based UPFC (MC-UPFC) has reduced volume and cost, reduced capacitor power losses, together with higher reliability. Theoretical principles of direct power control (DPC) based on sliding mode control techniques are established for an MC-UPFC dynamic model including the input filter. As a result, line active and reactive power, together with ac supply reactive power, can be directly controlled by selecting an appropriate matrix converter switching state guaranteeing good steady-state and dynamic responses. Experimental results of DPC controllers for MC-UPFC show decoupled active and reactive power control, zero steady-state tracking error, and fast response times. Compared to an MC-UPFC using active and reactive power linear controllers based on a modified Venturini high-frequency PWM modulator, the experimental results of the advanced DPC-MC guarantee faster responses without overshoot and no steady-state error, presenting no cross-coupling in dynamic and steady-state responses.