Three-phase

About: Three-phase is a research topic. Over the lifetime, 16801 publications have been published within this topic receiving 159477 citations.

Power sharing control strategies for a three-phase microgrid in different operating condition with droop control and damping factor investigation

Abstract: In this study, a microgrid with two voltage source inverters (VSIs), operating in islanded or grid-connected mode is analysed. The active power control by droop coefficients and reference frequencies is demonstrated. In addition, the inductive and resistive droop strategies are compared by considering the complex line impedance. By measuring the line impedance in the prototype, it was found that, even for the low-voltage microgrid, the line impedance was not predominantly resistive, but complex. For this line impedance condition, an investigation to determine the best droop control law considering the partial derivatives. Observing the partial derivatives and the experimental results obtained it is demonstrated that inductive droop control is better to control the active power for complex line impedance. For a scenario with resistive unbalanced loads and different power sharing between the inverters, the proposed control, implemented in the a–b–c reference frame, was validated. A novel absolute damping factor is developed to improve the transient response and reduce the reactive power flow. The VSIs are connected to the grid without transformers to reduce the connection costs. Simulation and experimental results are presented to confirm the improvements achieved using the implemented control method.

New Stationary Frame Control Scheme for Three Phase PWM Rectifiers under Unbalanced Voltage Dips Conditions

Abstract: A new stationary frame control scheme for three-phase pulse width modulation (PWM) rectifiers operating under unbalanced voltage dips conditions is proposed in this paper. The proposed control scheme regulates the instantaneous active power at the converter poles to minimize the harmonics of the input currents and the output voltage. The paper novelty is the development of a new current-reference calculation implemented directly in stationary reference frame. This allows using proportional - sinusoidal signal integrators (P-SSI) controllers for simultaneous compensation of both positive and negative current sequence components. No phase locked loop (PLL) strategies and coordinate transformations are needed. A comparison with two other existing control techniques is also performed. Experimental results are presented for a 20 kVA AC/DC converter prototype to demonstrate the effectiveness of the proposed control scheme. Fast dynamic performance with small DC-link voltage ripple and input sinusoidal currents are obtained with this control scheme even under severe voltage dips operating conditions.

An Optimized Third Harmonic Injection Method for Reducing DC-Link Voltage Fluctuation and Alleviating Power Imbalance of Three-Phase Cascaded H-Bridge Photovoltaic Inverter

Abstract: Due to different solar radiation, temperature, and other reasons of modules in the three-phase cascaded H-bridge (CHB) photovoltaic (PV) inverter, the output power among PV modules will be unequal and lead to unbalanced grid currents, which cannot meet the requirements of grid codes. On the other hand, the second-order voltage ripple is aroused in the dc-link capacitor since each phase-leg of the CHB inverter is made up of a single-phase inverter. Concerning these two issues, this paper proposes an optimized third harmonic injection method based on fundamental frequency zero sequence injection (FFZSI), which is a conventional method to handle the slight power imbalance problem. In this paper, the FFZSI is adopted to redistribute the power among three phases, and then the third harmonic is injected into the three-phase combined reference waveforms according to the two requirements: all modules are free from overmodulation and the dc-link voltage fluctuation is mostly reduced. Therefore, the proposed method can reduce the dc-link voltage fluctuation and extend the power balance range of FFZSI at the same time. The validity and effectiveness of the proposed method are verified by simulation and experimental results.

Model Predictive Direct Power Control of Three-Phase Grid-Connected Converters With Fuzzy-Based Duty Cycle Modulation

Abstract: An improved model predictive direct power control (MPDPC) for three-phase grid-connected converters is proposed. In the proposed method, two voltage vectors are applied during a control period and their duty cycles are determined by a fuzzy logic-based modulator. The inputs to the modulator are the active and reactive power errors and the output is the duty cycle of the first (main) voltage vector. The fuzzy rules are developed based on expert knowledge and the fact that small/large power errors can be compensated by applying the main voltage vector for a small/large portion of the switching period. The candidate voltage vector pairs are examined on a control Lyapunov function and the pair that satisfy the closed-loop stability criteria are selected. The voltage vector pairs are then applied following a proposed switching pattern through which reduced average switching frequency is achieved. Comparative simulation and hardware-in-the-loop studies between the proposed method and a most recently introduced duty cycle-based MPDPC confirm that in addition to lower average switching frequency, better quality currents and active and reactive powers can be achieved under the proposed MPDPC.

Control of unbalanced voltage PWM converter using instantaneous ripple power feedback

Abstract: The voltage unbalance can impair a PWM converter system because the input active and reactive power ripples are generated by the cross products of line currents and unbalanced voltages. In this paper, effects of voltage unbalance in a three phase PWM converter are analyzed and a new control scheme to suppress input power ripple and DC link voltage ripple caused by unbalances is presented. The proposed method is based on the instantaneous power theory to compute compensation currents which cancel the power ripple. The simulation and experimental results are presented to verify the feasibility and effectiveness of the proposed method.