Power System Demands Demand-side Control

and

The electric power system, being influenced by economic market
forces, is moved towards higher utilization. To maintain
reliability, system operators look towards non-traditional options;
i.e., beyond transmission and generation solutions. Demand-side
management (DSM)
is emerging as a viable option with
significant technical and financial benefits derived from utilizing
various forms of demand-side control.

A recent power system event involved the usage of demand-side
control to regain reliable power system operation [1]. DSM effectively
and quickly restored the power system from localized problems and
potential system-wide imbalance.

Demand-side Categories

Demand-side control types in the North American electricity industry
can be categorized in the order of contribution to power system security
and electricity market efficiency as follows.

  • Time of Use Pricing (TOU) – this approach shifts power
    consumption from peak periods where the probability of high market
    prices and transmission congestion are high.
  • Real Time Pricing (RTP) – this demand-side control
    strategy allows the load to reallocate energy utilization to lower
    market price hours and when power transmission usage is lower.
  • Demand-side Bidding – this category assists the system
    operator in maintaining generation-load balance and in managing of
    zonal congestion; tends to lower the operating cost of the consumer
    and demand-side assists in alleviating generation resource shortage.
  • DSM as Ancillary Service – DSM is utilized as system
    reserve for emergencies especially when no other possible option
    provides solution to mitigate existing system-wide operating
    concerns. In this case, DSM can be called upon to support the system
    operation as Responsive Reserve, Non-spinning Reserve, Regulating
    Reserve, or as a Replacement Reserve. Most often, the demand is
    reduced during periods of critical generation reserve margins and
    when electricity market prices are high due to generation shortage.
  • Direct Load Control – this strategy employs the usage of
    automated controls to reduce or curtail demand consumption during
    the occurrence of price spikes or during summer peak periods.
  • Interruptible Load Program (ILP) – demand is reduced or
    cut-off from the grid to maintain secured system operation during
    emergencies where system continuous service can be put at risk.
    System operators can utilize interruptible load for economic benefit
    and eliminating system operating constraints.

The Demand for
Demand-side Management

Following are some reasons why there is a demand for DSM.

  1. Efficient Market Operation – Allowing for demand
    elasticity in a locational marginal price (LMP) market results in a
    more efficient market. Figure 1 below illustrates this concept.

    Figure
    1. Locational marginal price computation and adjustment due to
    demand-side management.

    The figure gives us a higher LMP, P1, when demand is not taking
    advantage of TOU or RTP. When demand-side utilizes TOU or RTP, the
    LMP, P2, is “kicked” downwards as the demand curve shifts to the
    left.

  2. System-wide recovery – DSM as an ancillary service in the
    form of interruptible load provides corrective and preventive action
    to restore system-wide equilibrium. Figure 2 is an example of system
    frequency response with and without utilizing demand-side control.

    Figure 2. System
    frequency plot with and without interruptible load.

  3. Solution to voltage problems – dynamic voltage support
    can be derived from demand-side control. This is specifically more
    valuable in areas where voltage is depressed and reactive power
    compensation is lacking. Figure 3 presents the utilization of
    interruptible load as voltage support.

Conclusions

As utilization increases, the electric power system needs all the
resources available to maintain reliable and secure operation.
Demand-side control provides an alternative to conventional system
resources in restoring power system frequency and in supporting voltage
recovery. Additionally, DSM helps in make electric markets more
efficient. The power system demands demand-side management for the many
benefits it has to offer.

References:

  1. ERCOT Demand Response Program Helps Restore Frequency Following
    Grid Event (on-line :

    http://tdworld.com/customer_service/ercot-demand-response-grid-event/
    )
  2. “A Survey of Load Control Programs for Price and System
    Stability”, P. Jazayeri, et al, IEEE Transactions on Power Systems,
    Vol. 20, No. 3, August 2005
  3. “Classification of Control for Demand-side Participation”, Y. T.
    Tan and D. S. Kirschen, Technical Report, 2007 (on-line :

    http://www.supergen-networks.org.uk/publications/publications_softcopies/Report%20-%20Classification%20of%20controls.pdf
    )
  4. “Demand-Side View of Electricity Markets”, D. S. Kirschen, IEEE
    Transactions on Power Systems, Vol. 18, No. 2, May 2003