Abstract
This paper presents a method for improving the reliability of DC nanogrids by decreasing the input capacitance requirement. The nanogrid DC bus capacitance requirement is reduced by utilizing the zero-sequence operation mode of the solid state converter (SSC). This SSC is often considered as the main DC nanogrid energy control unit that is linking the nanogrid with the main utility AC grid and managing the nanogrid elements. The proposed method injects a zero-sequence voltage in the SSC AC filter capacitors to compensate the low frequency power ripples that are imposed on the DC bus. The proposed method compensates power ripple due to non-linear loads, linear loads, distorted grids, and load variations. Moreover, the compensation method does not require additional components that are commonly used with the existing power ripple compensators. Furthermore, practical considerations of the proposed control are discussed in the paper regarding stabilization of the nanogrid in case of lack of critical damping. The analysis and results demonstrated that a 50 μF total capacitance is sufficient at the DC bus for 500V/5kW DC nanogrid to achieve negligible DC bus voltage ripple. Thereby, with such small DC nanogrid input capacitance, the DC link capacitor can be a film type capacitor to enhance the reliability of the nanogrid.
Highlights
Given the DC nature of photovoltaic (PV), energy storage systems (ESS), electric vehicles (EV), etc., DC nanogrids have risen as attractive, efficient and reliable solutions for their interconnection [1, 2]
The instantaneous power exchanged between the utility network and the DC nanogrid is oscillating at twice the utility grid frequency [6, 7]
Consider the harmonically distorted AC node that is linked to the DC nanogrid through the proposed solid state converter (SSC); this system is equivalent to a grid connected bi-directional DC/AC converter with an LCL filter
Summary
Given the DC nature of photovoltaic (PV), energy storage systems (ESS), electric vehicles (EV), etc., DC nanogrids have risen as attractive, efficient and reliable solutions for their interconnection [1, 2]. - Independent ripple mitigation control of other elements - Used for several kilowatt applications. - Two additional switches - Additional inductor is needed - Additional capacitor is needed - Ripple mitigation control reference requires computation. The control dependent compensation methods (i.e., cluster (VI) in Table I) are not robust to system parameters mismatch, and operation setpoint variations This makes their operation even further problematic with nonideal conditions or nanogrid operation change such as load increase or decrease, etc. The working principle of Battery Storage i LfBat Bat v SBat Bat
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