Harmonic Distortion Caused by Single-Phase Grid-Connected PV Inverter

Due to the fast growth of photovoltaic (PV) installations, concerns are rising about the harmonic distortion generated from PV inverters. A general model modified from the conventional control structure diagram is introduced to analyze the harmonic generation process. Causes of the current harmonics are summarized, and its relationship with output power levels is analyzed. In particular for two-stage inverter, unlike existing models that assume the direct current (DC)-link voltage is constant, the DC-link voltage ripple is identified as the source of a series of odd harmonics. The inverter is modeled as a time-varying system by considering the DC-link voltage ripple. A closed-form solution is derived to calculate the amplitude of the ripple-caused harmonics. The theoretical derivation and analysis are verified by both simulation and experimental evaluation

Control of a single-switch two-input buck converter for MPPT of two PV strings

© 2014 ACPE. In this paper, the configuration composed by a Two-Input Buck (TIBuck) converter and a boost inverter is proposed for low-voltage grid-connected PV systems. This configuration is attractive for this application because it has high efficiency and can achieve dual maximum power point tracking (MPPT) with only one active switch. However, in this system, the nonlinear characteristics of the converter and the two PV arrays complicate the control. By means of a small-signal modeling, the control theme of the two PV voltages is formulated and the effect of the nonlinearities is presented. Simulation results are reported to validate the theoretical analysis, showing the dual MPPT capability

Advanced multi-functional model predictive control for three-phase AC/DC converters

© 2016 The Institute of Electrical Engineers of Japan. With the conventional model predictive control (MPC) based direct power control of three-phase AC/DC converters, the active and reactive powers can be simultaneously controlled by a single cost function. A change in parameters of either the active or reactive power within the cost function will affect the other, leading to poor dynamic performance of transient response. Besides, the steady state performance of the conventional MPC is affected by one-step-delay of digital implementation. This paper proposes an advanced multi-functional MPC of three-phase full-bridge AC/DC converter for high power applications. It has multiple functions such as one-step-delay compensation, power ripple reduction, switching frequency reduction, and dynamic mutual influence elimination. Using the proposed modified cost function, both the steady state and dynamic performances of the converter can be improved. Finally, the simulation results are reported to validate the advancement of the proposed control strategy in comparison with other control methods

Low-complexity dual-vector-based predictive control of three-phase PWM rectifiers without duty-cycle optimization

© 2013 IEEE. The conventional model-predictive-based direct power control (MPDPC) of the three-phase full-bridge AC/DC converters chooses the best single voltage vector for the following control period, which results in variable switching frequency and power distortion, and thus a relatively higher sampling frequency is needed to achieve acceptable results. This paper proposes a simplified dual-vector-based predictive direct duty-cycle-control (SPDDC) with an additional zero vector implemented in contrast to the MPDPC. With the same best vector selection method, the proposed strategy has retained the control simplicity with just one more step added and much better control performance as well as a fixed switching frequency in comparison to the MPDPC. On the other hand, the duty-cycle optimization procedure is eliminated while the negative duration issue is essentially resolved compared with the conventional dual-vector-based model predictive duty-cycle-control (MPDCC). Comprehensive comparisons of various control methods by numerical simulation and experimental testing show that the SPDDC can achieve better steady state and dynamic performance than the MPDPC and simpler algorithms than the MPDCC

Analysis of a shunt maximum power point tracker for PV-battery system

© 2015 IEEE. This paper first presents a maximum power point efficiency analysis of the conventional direct connection of PV panels to a battery. Next, an improved shunt maximum power point tracking (MPPT) which integrated a half-bridge converter with a full-bridge load is proposed. The configuration is designed such that the PV panel voltage equals the sum of capacitor voltage and battery. This capacitor voltage is controlled to achieve the MPPT of the PV panels. Some experimental results are reported to verify the proposed concept and analysis

Review of battery cell balancing techniques

© 2014 ACPE. A highly reliable and efficient battery management system (BMS) is crucial for applications that are powered by electrochemical power. Cell balancing is one of the most important features of a BMS. Cell balancing techniques help to distribute energy evenly among battery cells. Without cell balancing, a portion of the capacity or energy in the battery bank will be wasted, especially for long battery string which operates in frequent recycling condition. In this paper, some popular cell balancing techniques are described and categorized according to the way of processing redundant energy in battery cells