Highly efficient three-phase grid-connected parallel inverter system

Abstract

In this paper, a new three-phase grid-connected inverter system is proposed. The proposed system includes two inverters. The main inverter, which operates at a low switching frequency, transfers active power to the grid. The auxiliary inverter processes a very low power to compensate for the grid current ripple. Thus, no active power is processed by the auxiliary inverter. The goal is to produce a grid current with a low total harmonic distortion (THD) and to obtain the highest efficiency from the inverter system. The main inverter is controlled via a space-vector pulse-width modulation owing to its optimum switching pattern, and the auxiliary inverter is controlled via a hysteresis current-control technique owing to the technique's fast dynamic response. The proposed system is analyzed in terms of different DC-link voltage, switching frequency, and filter inductance values. The optimum system parameters are selected that provide a THD value of less than 5%. A prototype inverter system at a 10-kW output power has been implemented. The main inverter operates at a 3-kHz switching frequency, and the auxiliary inverter compensates for the grid-current ripple. In total, a THD of 4.33% and an efficiency of 97.86% are obtained using the proposed inverter system prototype.

Comparative Study of Single-Phase PWM Rectifier Control Techniques

“…Unlike other control techniques, voltage-oriented control technique is carried out in d-q coordinate system [21]. As seen in Figure 14, firstly, the grid current is transformed to the α-β coordinate system.…”

Grid-Connected PV Generation System—Components and Challenges: A Review

“…The transformation from three-phase stationary reference frame into two-phase rotating reference frame has also been called as D-Q transformation and it is governed by Equations (9)- (11) respectively. = Transforming natural frame AC variable quantities into a DC quantity two-phase rotating reference frame makes filtering and controlling easily achievable [85].…”

“…These DC quantities are then transformed back into the ABC natural frame where they will be used as a reference signal for sinusoidal pulse-width modulation (SPWM) to generate proportional duty-cycle switching sequence to the three-phase inverter. By referring to Equation (11), the transformation of the reference frame from AC quantities into DC quantities require a value of α which is the information of phase angle of grid. There are numerous methods used to obtain the grid information especially phase angle value.…”

“…The challenges include the maximum power extraction from PV modules, rapid output variation, and daily variability of the output, the effect on power quality especially voltage and current harmonics, current backflow and a mismatch between PV output and grid demand. Contrary to single-phase system, the three-phase GPV generation system is commonly preferred in high-power applications as its ability to provide almost constant power flow and able to avoid excessive asymmetry in the grid current [11]. The maximum power transfer is the utmost objective regarding developing the GPV generation system.…”

Control Scheme and Performance Analysis of Dual-Frequency Single-Phase Grid-Connected Inverter Interfaced With Weak and Distorted Grids

“…High impedance and low inertia constant are typical features of a weak grid. The grid weakness is usually evaluated by the short-circuit ratio (SCR), which is the ratio of the short-circuit capacity of the grid to the rated capacity SN of the grid-connected inverter [41], [42], which can be expressed as…”