Smart Loads for Voltage Control in Distribution Networks

This paper shows that the smart loads (SLs) could be effective in mitigating voltage problems caused by photovoltaic (PV) generation and electric vehicle (EV) charging in low-voltage (LV) distribution networks. Limitations of the previously reported SL configuration with only series reactive compensator (SLQ) (one converter) is highlighted in this paper. To overcome these limitations, an additional shunt converter is used in back-to-back (B2B) configuration to support the active power exchanged by the series converter, which increases the flexibility of the SL without requiring any energy storage. Simulation results on a typical U.K. LV distribution network are presented to compare the effectiveness of an SL with B2B converters (SLBCs) against an SLQ in tackling under- and over-voltage problems caused by EV or PV. It is shown that SLBCs can regulate the main voltage more effectively than SLQs especially under overvoltage condition. Although two converters are required for each SLBC, it is shown that the apparent power capacity of each converter is required to be significantly less than that of an equivalent SLQ

Virtual inertia from smart loads

The inertia of future power systems is expected to decrease with increasing penetration of renewable energy resources. Sufficient inertia is required to avoid large fluctuations in grid frequency and also limit the excessive rate of change of frequency (RoCoF). Unlike many previous works focusing on virtual inertia on the power supply side, this paper studies and quantifies potential virtual inertia from the load side. The analysis shows that, voltage-dependent loads coupled with electric spring (ES) technology can be operated as smart loads (SL) within the +/- 5% tolerance of the ac mains voltage and offer virtual inertia. Following the U.K. National Grid frequency requirements, it is shown that the ES based SL can provide virtual inertia up to an inertia coefficient of HSL=2.5 s (when np=2) with respect to its load power rating. The effectiveness of such virtual inertia extraction from SL has been verified by the simulation study on a CIGRE benchmark microgrid with high-resolution domestic demand model. The value of HSL is shown to be around 1.3 s during the most part of the day and can increase the overall system inertia coefficient by 0.53 s if all the domestic loads are transformed into the proposed smart loads

DEVELOPMENT OF FORECASTING AND SCHEDULING METHODS AND DATA ANALYTICS BASED CONTROLS FOR SMART LOADS IN RESIDENTIAL BUILDINGS.

DEVELOPMENT OF FORECASTING AND SCHEDULING METHODS AND DATA ANALYTICS BASED CONTROLS FOR SMART LOADS IN RESIDENTIAL BUILDINGS

Distributed electric-spring-based smart thermal loads for overvoltage prevention in LV distributed network using dynamic consensus approach

Overvoltage arising from reverse power flow in low-voltage (LV) distribution network caused by surplus roof-top photovoltaic (PV) energy generation is a major challenge in the emerging smart grid. This paper reports a study on the use of distributed thermal Smart Loads (SLs) for overvoltage prevention along a LV feeder. The basic principle involves the combined use of electric springs (ESs) and storage-type electric water heaters (EWHs) as distributed smart loads. Through distributed control, these smart loads play the important roles of mitigating reverse power flow problems and maintaining local mains voltage within the specified tolerance. Detailed modeling of the combined ES and EWH including their practical electrical and thermal capacities and constraints is adopted and optional distributed energy storage system (ESS) is also considered in the evaluation. Based on the Sha Lo Bay residential LV network in Lantau Island, Hong Kong, these case studies confirm the feasibility of the proposed approach for overvoltage prevention. The proposed distributed SLs-plus-ESS method is proved to be a cost-effective and environmental friendly way for overvoltage prevention in LV distributed network with high PV penetration

Use of Smart Loads for Power Quality Improvement

Electric spring (ES) was originally proposed as a distributed demand-side management technology for making noncritical loads adaptive to the availability of intermittent renewable power generation. The second generation of ES, fed with batteries (ES-2) and associated with a noncritical load, can form a new kind of combined smart load and distributed energy storage technology for smart grids. With its four-quadrant operation, ES-2 is able to offer ancillary grid services in addition to its major functions of voltage and frequency regulation. This paper presents the operating principles and the input current control of ES-2 for power quality improvement such as power factor correction and harmonics reduction. The operating principles and the proposed input current control have been verified with the experimental results obtained from a small-scale power grid. Another weak single-phase power system fed by intermittent wind power is set up to prove the combined operation of ES-2 for power quality improvement and ES-1 (ES with capacitor storage) for voltage stabilization. The experimental results show that ES-2 with input current control can carry out power quality improvement as its ancillary function

Rapid Frequency Response From Smart Loads in Great Britain Power System

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