Unlocking the Hidden Capacity of the Electrical Grid Through Smart Transformer and Smart Transmission

Abstract

Power systems are experiencing a rapid and dramatic transformation driven by the massive integration of nondispatchable renewable energy sources such as wind and solar and highly variable loads such as electric vehicles and air conditioning. This challenges existing grid assets eventually leading to update them which in turn increase significantly the costs of the sustainable technologies. Power electronics is a pivotal technology for electrical power processing for renewable energies and sustainable transportation. By means of "smart" functionalities power electronics converters already embedded in such applications, can also contribute to guaranteeing the overall system stable operation. Anyway this cooperative contribution from distributed devices may be not enough leading to the need in the voltage transformation and power transmission of "system level" power electronics solutions. In the case of large charging stations a Smart Transformer while in the case of large solar and wind parks integration Medium or High Voltage Direct Current Transmission are system level solutions. This paper wants to review the potential of using such infrastructures to increase the capacity of existing grid assets avoiding or deferring their upgrade and hence reducing the overall costs of renewables integration and of the electrification of transport sector. In fact the power converters embedded in Smart Transformer (ST) and High Voltage Direct Current (HVDC) can provide fast frequency and voltage response and precise control of power flow acting at system level much more effectively and feasibly for system operators as the distributed power converters embedded in several small sources and users. This paper reviews for the first time these two key power electronics "system level" solutions together -Smart Transformer and High Voltage Direct Current -starting from their basic functionalities and showings how they can go beyond them showing how with grid forming functionalities they can offer new "Smart Grid" tools to enhance the capability of the existing electric grid infrastructures.

Analysis and Design of Independent DC Bus Structure Multiport Power Electronic Transformer Based on Maximum Power Transmission Capability of Low-Voltage DC Ports

“…The structures of Port 1 to 6 are shown in Figure 12. Each of Port 1 and Port 2 consists of four DABs and both of them can be constructed as asymmetrical T-Ports (i.e., T (2,1,1) ) or symmetrical D-Ports (i.e., D (2,2) ). Each of Port 3 and Port 4 consists of three DABs and both of them will be constructed as symmetrical T-Ports (i.e., T (1,1,1) ).…”

“…A multiport power electronic transformer (MPET) provides a competitive solution for the networking of hybrid AC/DC distribution systems due to its compatibility and advanced functionalities [1,2]. Most of the existing MPETs provide at least a mediumvoltage AC port, a low-voltage AC port and a low-voltage DC port [3].…”

New single‐stage bidirectional three‐phase ac‐dc solid‐state transformer

“…Note further that the output dc voltage U DC already begins to increase at t = t 2 when the first phase (phase b) releases clamping and starts 50% PWM duty cycle operation, as the primary-side transformer voltage pulses are rectified by the secondaryside MOSFET body diodes. At t = t 3 , that is, once all phases operate with DPWM, the SVM of the secondary-side rectifier is enabled, and the output voltage U DC and/or power transfer P can be regulated by the PWM carrier phase shift ϕ according to (1).…”

“…Conventionally, a low-frequency, that is, grid-frequency transformer (LFT) provides galvanic separation and steps down the MVac voltage to low-voltage ac (LVac) levels like 400 or 690 V. The subsequent power-factor-correction (PFC) rectifier is then not exposed to MV, but, on the other hand, the LFT's relatively large volume might limit the overall power density. To enable more compact system realizations and/or to provide extended functionality [1], MVac-LVdc solid-state transformers (SSTs) employing medium-frequency transformers (MFTs) instead of LFTs are considered for applications like EV charging [2][3][4][5][6][7][8][9][10][11], electrolyzers [12], and future datacenters [13][14][15].…”

Overview of Talkative Power Conversion Technologies

“…The information from different energy sources, loads, and storage can be shared on the grid and therefore the power flow within the grid can be controlled optimally. It is in particular can enable μ-grids interfaced to main grid by a Smart Transformer (ST) [68].…”