Vs Vs Shunt Converter Series Converter Load Shunt Converter (a) Load (b) fig 6 A typical diagram of low-voltage (a) series and (b) shunt devices used for voltage regulation. ENGO-V Smart Switch Setpoint Input Historical Data Output Smart Switch f Smart Switch Controller Communication Module (a) Smart Switch Command and Health Status Input Power Terminal ENGO-V10 (b) fig 7 (a) The internal architecture of the ENGO-V10 device. (b) The distributed shunt var injection device realized with an ENGO-V10 device capable of injecting up to 10 kvar of vars on a single-phase basis at 240 V. (Image courtesy of Varentec.) ENGO-V10 is installable on a pole-top next to the service transformer. With ENGOs LTC Tap at 1.0 pu 250 245 Voltage 240 235 230 225 220 11 :0 0 p. m 12 . :0 0 a. m 1: 00 . a. m . 2: 00 a. m . 3: 00 a. m . 4: 00 a. m . 5: 00 a. m . 6: 00 a. m . 7: 00 a. m . 215 Time of Day Substation Voltage on 240-V Base Secondary Voltage at 24 Locations ANSI Low Limit fig 8 The impact of a fleet of 24 ENGO devices on a single phase of a feeder with a voltage set point of 240 V and LTC tap set at 1 pu. 20 IEEE PowEr ElEctronIcs MagazInE z December 2014 In addition, this must all be compatible with specific utility processes and must happen at a price point that provides an attractive return on investment for the utility. Many in the research community have proposed the use of SSTs that can provide the ultimate level of gridedge control. Figure 5 shows a block schematic of an exemplary galvanically isolated SST system for a single-phase 12-kV-120/120-V application. Even without the cost constraint of US$25/kVA, the aforementioned SST specifications are extremely challenging. The wide-bandgap high-voltage semiconductor devices necessary for the front-end converter are beginning to be commercially available but are still too expensive, except in certain niche applications. Meeting the thermal-management, fault-current, and no-field-service objectives is very challenging using the current design approaches. As a result, even though the concept of the SST continues to be very appealing and is the focus of much research, its translation into real products has not yet occurred [10]. Finally, the need to conform to the 100-kV BIL requirement dramatically impacts the size and cost of low-power converters (under current technology) to impractical levels. At the system level, distributed control poses a unique set of challenges. Most power converters are designed with the