Power Flow Control Solutions for a Modern Grid Using SMART Power Flow Controllers. Kalyan K. Sen
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to be reduced and dynamic voltage stability is required for critical loads. The final selection of a solution, however, depends on knowing the functional requirements and analyzing the cost and benefit of each available solution to determine the cost‐effective solution that provides the most features at the least total cost. In the case of a simple voltage regulation at a utility bus, a SC may be an adequate solution, whereas for an arc furnace type of constantly variable load, the power electronics VSC‐based STATCOM may be the best solution.
With the introduction of the first commercial STATCOM at TVA in 1995, it was anticipated that the power electronics VSC‐based voltage regulation technique would be the new wave of the future. Instead, rotating machinery‐based SynCons are being installed to provide some inertia to the power grid, since the grid is now becoming heavily loaded with IBRs that convert renewable wind and solar energy into usable AC electricity. Note that the IBRs do not have any mechanical inertia that is available in rotating machinery‐based conventional power grid. In the meantime, many of the nine inverters from the first‐generation FACTS Controllers were decommissioned prematurely due to component obsolescence and without much payback.
Table 1-3 Various compensators for utility applications.
| Compensators | Commercial names |
|---|---|
| Non‐power electronics‐based technology | Transformer and LTCs‐based Voltage‐Regulating Transformer (VRT) and Phase Angle Regulator (PAR), reactors/capacitors, Synchronous Condenser (SynCon), motor/generator, and Sen Transformer (ST) |
| Power electronics thyristor‐based technology | Static Var Compensator (SVC) and Thyristor‐Controlled Series Capacitor (TCSC) |
| Power electronics VSC‐based technology | STATic synchronous COMpensator (STATCOM), Static Synchronous Series Compensator (SSSC), and Unified Power Flow Controller (UPFC) |
Table 1-4 Features, advantages, and benefits of various solutions.
| Solutions | Feature(s) | Advantage | Benefit |
|---|---|---|---|
| Shunt Reactor/Shunt Capacitor, VRT, SynCon, TCR, TSC, SVC, STATCOM | Voltage regulation | Meets operating voltage requirement of the load | Higher asset utilization |
| PAR | Phase angle regulation | Power flow magnitude and direction control | |
| Series Reactor/Series Capacitor, TCSC, SSSC | Reactance regulation | ||
| ST, UPFC | Voltage regulation, phase angle regulation, and impedance regulation |
The power industry’s pressing need for the most economical ways to transfer bulk power along a desired path may relieve grid congestion in some markets during peak hours and integrate renewable energy from wind and solar sources. Apart from building new transmission lines that may take a decade or longer, there may be quicker and inexpensive options to utilize the existing transmission system infrastructure and harness the dormant capacity of the underutilized lines. This can only be possible through a dynamic line impedance management, which results in independent control of active and reactive power flows in the transmission lines. Independent control of active and reactive power flows leads to
Reduction in reactive power flow, resulting in a reduction of losses in generators, transformers, and transmission lines, which increases the overall efficiency of the grid, thus lowering GHG emissions and reducing global warming
Freeing up the generators, transformers, and transmission lines to carry more active power
Power flow through the desired transmission paths that have high impedances, low power flow, and low line utilization
Avoidance of grid congestion by redirecting excess power flow from an overloaded line to underloaded lines, instead of tripping the overloaded line and creating possible blackouts when power flow is needed the most, thus improving grid reliability and resiliency, and
Delayed construction of new, expensive, high‐voltage electric transmission lines.
The SPFC is proposed to enhance the controllability of the power flow in the power grid on the basis of functional requirements and cost‐effective solutions. The SPFC is derived from utilizing the best features of all the technical concepts that are developed in the power flow control area until now. In the simplest term, a SMART Controller is what one procures is based on what one needs. Utilities are recommended to choose a solution that meets their need in terms of reliability, cost‐effectiveness, component non‐obsolescence, efficiency, ease of relocation, and interoperability.
The Sen Transformer technology meets the immediate need of the utility in terms of maximizing the revenue‐generating active power flow while providing the highest efficiency. The ST uses transformers and mechanical LTCs and offers high reliability, high efficiency, low cost, component non‐obsolescence, high power density, small footprint, and ease of relocation. The ST allows the utilities to avoid the initial purchase of an expensive PFC, along with the equally high cost of replacing a power electronics inverter‐based system as it becomes obsolete. In addition to being a smaller, more dynamic, and customizable system that is less costly to maintain, the ST can be relocated to adapt to changing power system needs. Since ST uses existing transformer/LTCs‐based technology, it offers a high level of interoperability, enabling components from various suppliers to be used for its manufacturing, operation, and maintenance. This also ensures a baseline global manufacturing standard, which increases the confidence of the consumer about the end product.
The power electronics inverter‐based technology has the capability of providing fast (sub‐cycle) dynamic response for a given transmission line impedance, although in a PFC, the dynamic response of at least a few line cycles is necessary to operate safely under various contingencies. Most utility applications allow regulation of the power flow in the line(s) in a “slow” manner as permitted by the speed of operation of the mechanical LTCs. Applications that require faster response times can make use of TC LTCs, instead of mechanical LTCs as shown in Figure 2‐51. The STs with both types of LTCs (mechanical and TC) cover a wide range of requirements for power flow control in electric transmission lines. If the LTCs are too coarse for an IR, the number of taps on the winding may be increased.
The ST can be customized to operate in a limited‐angle range that is suitable for a particular application. This reduces the number of secondary windings from nine to six and the number of three‐phase LTCs from three to two. Consequently, the cost of an ST can be reduced due to its simpler design, whereas there is no such option for the reduction of cost in a power electronics inverter‐based FACTS controller. The inverter is always designed to operate in the entire 360°‐range of series‐injection of a compensating voltage whether a particular application needs it or not.
Compared to the UPFC, the ST has inherent advantages: less costly, component non‐obsolescence, portable, and reduced and easy maintenance along with many other features. The value proposition to the customer is that in comparison to a FACTS controller, a 5:1 reduction in equipment cost and a 10:1 reduction in operational/maintenance cost of an ST are expected. The ST provides 21st‐century power flow control solutions with an impedance regulation using 20th‐century power hardware, such as transformer/LTCs, which are proven to be reliable to the utilities worldwide and reduce the