Content uploaded by Zohaib Akhtar

Author content

All content in this area was uploaded by Zohaib Akhtar on Oct 01, 2015

Content may be subject to copyright.

Smart Loads for Voltage Control in Distribution Networks

Zohaib Akhtar*, Balarko Chaudhuri, Ron Hui

2015 IEEE PES General Meeting

*Acknowledgement: Funded by the Commonwealth Scholarship.

A. STUDY SYSTEM

•Low voltage (LV) side is modelled

in detail while the medium voltage

(MV) bus is considered to be

tightly regulated at 1.0 p.u.

•Eight equally spaced single-phase

loads connected to each phase of

the LV feeder.

•To simulate voltage disturbances,

a photovoltaic (PV) panel with a

peak power of 5.2 kW, and an

electric vehicle (EV) charging

facility of 3.0 kW are included at

each load terminal. Fig. 2: Segment of aLV distribution

network [2].

4. SIMULATION RESULTS

Fig. 1: (a) Smart load with reactive compensation (SLQ), (b) Smart load with

back-to-back converters (SLBC)

1. BACKGROUND

•Increasing use of distributed generation (DGs) like rooftop photovoltaic

(PV) generation would cause over-voltage problem in low-voltage and/or

medium voltage (LV/MV) distribution networks

•Charging the growing fleet of electric vehicles (EVs) during the night

could lead to under-voltage problem even during otherwise off-peak

hours

•Such voltage problems could potentially become unacceptable with

increasing penetration of PVs/EVs

•Reactive shunt compensators on their own are not very effective in

controlling the voltage at the LV level due to high R/X ratio of the system

2. RESEARCH OBJECTIVES

•Validate the effectiveness of smart loads (SLs) [1] through system

studies in mitigating voltage problems caused by photovoltaic (PV)

generation and electric vehicle (EV) charging, using realistic low voltage

(LV) distribution network models

•Estimating required SL ratings for effective voltage control

•Comparison between different types of SLs in terms of compensator

rating, costs and performance under different system conditions

3. SMART LOAD (SL) TYPES

Fig. 3: Hourly variation in load, PV

output and EV charging power

•A typical PV output profile is

generated using a half-hourly

average solar irradiation data.

•The EV charging power is

assumed to be constant.

•Over-voltage occurs during the

day time when the PV generation

is close to its peak value

•Under-voltage occurs at EV

charging near peak load

•50% loads are considered to be

non-critical

REFERENCES

[1] Z. Akhtar, B. Chaudhuri, and S. Y. R. Hui, “Primary frequency control

contribution from smart load with reactive compensation,” IEEE

Transactions

on Smart Grid, 2015

[2] “The impact of small scale embedded generation on the operating

parameters of distribution networks,” Department of Trade and Industry, UK,

Report, 2003.

6. FUTURE WORK

•Design of an optimal control to minimize the control effort.

•Load characterization and identification of loads that can serve as non-

critical loads.

Fig. 4: Variation of (a) supply voltage

at L8, (b) voltage across non-critical

load, (c) compensator voltage

magnitude and (d) phase angle over

24 hours

Fig. 5: Variation of (a) active and (b)

reactive power of smart load, (c)

active and (d) reactive power of the

compensator over a 24 hours

Fig. 7: Box plots for voltage across

(a)-(b) supply/mains, and (c)-(d)

noncritical loads for under-and

over-voltage events.

Fig. 6: Total reactive capacity of the

converters for SLQ and SLBC

expressed as a percentage of the

smart load (SL) rating

5. CONCLUSION

•Smart loads with back-to-back converters (SLBCs) can be used to

effectively control the voltage in aLV network.

•SLBCs perform better compared to smart loads with reactive only

compensation (SLQs) especially, in case of over-voltage events caused

by photovoltaic (PV) generation.

•While the performance of SLQs depend on the R/X ratio of the network,

SLBCs can ensure acceptable voltage regulation over a wider range of

R/X ratios.

•Moreover, SLBCs can achieve better voltage regulation with less total

converter power capacity than SLQs. An SLBC would require one

additional power converter compared to an SLQ.

B. OVER- AND UNDER-VOLTAGE CONDITIONS