Abstract
Distributed rooftop photovoltaic (PV) generators prospered distributed generation (DG) in recent years. Certain randomness of rooftop PV connection may lead to significant PV power imbalance across three phases, especially in low-voltage distribution systems. Due to interphase line coupling, traditional Var compensation methods which typically have competent voltage regulation performance may become less effective in such PV imbalance scenarios. In this paper, the limitation of traditional Var compensation methods in voltage regulation with unbalanced PV power integration is demonstrated and comprehensively analyzed. After describing the voltage regulation challenge, based on the voltage sensitivity analysis, it is revealed that PV power unbalanced level together with equivalent mutual impedance among phase conductors has a significant impact on the effectiveness of traditional Var compensation methods on voltage regulation. On this basis, to improve the performance of voltage regulation methods, some suggestions are proposed for both current system operation and future distribution system planning. Numerical studies demonstrate the effectiveness of the proposed suggestions. Future rooftop PV integration in LV systems can benefit from this research.
Highlights
In recent years, various distributed generation and storage systems including photovoltaic, wind power, electric vehicles, etc., have been developed vigorously [1,2,3,4,5,6]
Var compensation methods that only rely on local measurements (e.g., PV generation and local line-to-ground voltage) have already been widely implemented in centralized PV plants for the point of common coupling (PCC) voltage regulation [29,30,31]. e main advantage of these methods is their rapid response speed, which makes them suitable to counter fast voltage fluctuations caused by PV power variations and with more attractive options for distributed rooftop PV generators
Schematic diagram of a PV system with corresponding control loops is displayed in Figure 2 [34]. e main control task for a PV system is to regulate its DC-link voltage following a maximum power-point tracking (MPPT) scheme which is designed to maximize the electricity power harvested from PV panels
Summary
PV inverters may be required to generate a certain amount of reactive power for system voltage regulation. It is worth noting that the active power output PPV is controlled by id, while iq is responsible for adjusting the reactive power generation of a PV inverter. No matter which method is used, the power factor of grid-connected PV inverters is generally restricted within the range from 0.9 lagging to 0.9 leading by the utility [35]
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