Control Strategy of Intergrated Photovoltaic-UPQC System for DC-Bus Voltage Stability and Voltage Sags Compensation

Abstract

Power quality problem, because of its various forms and occurrence frequency, has become one of the most critical challenges confronted by a power system. Meanwhile, the development of renewable energy has led to more demands for an integrated system that combines both merits of sustainable energy generation and power quality improvement. In this context, this paper discusses an integrated photovoltaic-unified power quality conditioner (PV-UPQC) and its control strategy. The system is composed of a series compensator, shunt compensator, dc-bus, and photovoltaic array, which conducts an integration of photovoltaic generation and power quality mitigation. The fuzzy adaptive PI controller and the improved Maximum Power Point Tracking (MPPT) technique are proposed to enhance the stability of dc-bus voltage, which is aimed at the power balance and steady operation of the whole system. Additionally, the coordinate control strategy is studied in order to ensure the normal operation and compensation performance of the system under severe voltage sag condition. In comparison to the existing PV-UPQC system, the proposed control method could improve the performance of dc-bus stability and the compensation ability. The dynamic behavior of the integrated system were verified by simulation in MATLAB and PLECS. Selected results are reported to show that the dc-bus voltage was stable and increased under severe situations, which validates the effectiveness of the proposed integrated PV-UPQC system and its control strategy.

Indirect Matrix Converter-Based Grid-Tied Photovoltaics System for Smart Grids

“…Energies 2020, xx, 5 17 of 19 constant, with small transients due to the 'dc link' controller dynamics. The flows are reversed in case active power is flowing from the grid to the load in standard conditions (P PV < P load ).…”

“…These include Power Quality (PQ) issues such as low-order current harmonics, due to the use of non-linear loads, resulting in additional losses and voltage distortion in the point of connection to the grid (Point of Common Coupling-PCC) [1]. Also, voltage-related disturbances on the LV grid, such as voltage sag/swell and permanent undervoltage/overvoltage, are PQ issues that are of great concern for 2 of 18 most critical loads, as they may lead to equipment malfunction and degradation, short-time interruptions and an overall decrease in efficiency [2][3][4][5].…”

“…With the latter solution, the PV system injects series voltages on the grid to control the voltages at the PCC, where the sensitive loads are connected. This naturally leads to a Unified Power Quality Conditioner (UPQC) topology including current and voltage compensation with shunt and series converters, respectively [1,5,[21][22][23].…”

DC Bus Voltage Influence and Stabilization Technology Under Servo Loading for Aerospace Combined Power Supply

“…On the other hand, in order to solve the power fluctuation and bus voltage instability caused by changes in the external environment of a photovoltaic grid-connected system, a performance-based adaptive Backstepping controller has been proposed to adjust the bus voltage and inverter current [20]. In [21], a fuzzy adaptive PI controller and an improved maximum power point tracking (MPPT) technology have been proposed to enhance the stability of the DC bus voltage to achieve power balance and stable operation of the system, but it has not been verified in practice. In [22], a load management method has been proposed to maintain system stability in a critical DC power system.…”

Impedance Matching-Based Power Flow Analysis for UPQC in Three-Phase Four-Wire Systems

“…Correspondingly, the amplitudes and directions of the power flows will be changed with the SC/PC's operation state changes. According to the phase angle difference between system output voltage (i.e., load voltage) and grid voltage, the common analysis methods of the UPQC's operation principle are as follows: (1) UPQC-P: the difference is 0 or π, the SC only transmits active powers in the forward or reverse direction [5,6]; (2) UPQC-Q: the difference is π/2, the SC only transmits reactive powers for loads [7,8]; (3) UPQC-VAmin: the difference range is 0-π/2, the SC transmits active and reactive powers at the same time. This method attempts to minimize the volt-ampere (VA) loading, thereby reducing the design cost of UPQC [9,10]; (4) UPQC-S: it has the same range of the angle difference as UPQC-VAmin, but the difference is that the SC operates at maximum capacity to enhance the UPQC's utilization [11,12].…”