John D. Kueck

Adaptive Voltage Control With Distributed Energy Resources: Algorithm, Theoretical Analysis, Simulation, and Field Test Verification

Distributed energy resources (DE) or distributed generators (DG) with power electronics interfaces and logic control using local measurements are capable of providing reactive power related ancillary system services. In particular, local voltage regulation has drawn much attention in regards to power system reliability and voltage stability, especially from past major cascading outages. This paper addresses the challenges of controlling DEs to regulate local voltage in distribution systems. An adaptive voltage control method has been proposed to dynamically modify control parameters to respond to system changes. Theoretical analysis shows that there exists a corresponding formulation of the dynamic control parameters; hence the adaptive control method is theoretically solid. Both simulation and field experiment test results at the Distributed Energy Communications and Controls (DECC) Laboratory confirm that this method is capable of satisfying the fast response requirement for operational use without causing oscillation, inefficiency, or system equipment interference. Since this method has a high tolerance to real-time data shortage and is widely adaptive to variable power system operational situations, it is quite suitable for broad utility application.

Demand Response Spinning Reserve Demonstration

The Demand Response Spinning Reserve project is a pioneeringdemonstration of how existing utility load-management assets can providean important electricity system reliability resource known as spinningreserve. Using aggregated demand-side resources to provide spinningreserve will give grid operators at the California Independent SystemOperator (CAISO) and Southern California Edison (SCE) a powerful, newtool to improve system reliability, prevent rolling blackouts, and lowersystem operating costs.

Adaptive voltage control with distributed energy resources: Algorithm, theoretical analysis, simulation, and field test verification

Distributed energy resources (DE) or distributed generators (DG) with power electronics interfaces and logic control using local measurements are capable of providing reactive power related ancillary system services. In particular, local voltage regulation has drawn much attention in regards to power system reliability and voltage stability, especially from past major cascading outages. This paper addresses the challenges of controlling DEs to regulate local voltage in distribution systems. An adaptive voltage control method has been proposed to dynamically modify control parameters to respond to system changes. Theoretical analysis shows that there exists a corresponding formulation of the dynamic control parameters; hence the adaptive control method is theoretically solid. Both simulation and field experiment test results at the Distributed Energy Communications and Controls (DECC) Laboratory confirm that this method is capable of satisfying the fast response requirement for operational use without causing oscillation, inefficiency, or system equipment interference. Since this method has a high tolerance to real-time data shortage and is widely adaptive to variable power system operational situations, it is quite suitable for broad utility application.

The Distribution System of the Future

Abstract Utility engineers have complained that distributed energy resources are a control and protection nightmare, but with local control agents DER will be an integral and valuable player in distribution reliability.

The Demand Response Spinning Reserve Demonstration--Measuring the Speed and Magnitude of Aggregated Demand Response

Spinning reserves are an electricity grid operators first strategy for maintaining system reliability following a major disturbance. The Demand Response Spinning Reserve project has demonstrated that it is technologically feasible to provide spinning reserves using aggregations of small, controllable residential appliances. This paper addresses two concerns stemming from the high cost of real-time telemetry, which makes it impractical to monitor individual, small appliances comprising an aggregated demand-response resource. First, time-stamped information taken at each stage in a load curtailment sequence, starting with the grid operators initial dispatch command and ending with the receipt of the command by the residential appliances, is analyzed to measure the speed of demand response. Second, load information from distribution feeders serving aggregations of controlled appliances along with end-use monitoring information collected from a sample of the appliances are analyzed to estimate and understand the influencing the magnitude and statistical significance of the amount of load curtailed.

Properly understanding the impacts of distributed resources on distribution systems

The subject paper discusses important impacts of distributed resources on distribution networks and feeders. These include capacity, line losses, voltage regulation, and central system support (such as volt/var control via central generators and substation) as the number, placement and penetration levels of distributed resources are varied. Typically, the impacts of distributed resources on the distribution system are studied by using steady-state rather than dynamic analysis tools. However, the response time and transient impacts of both system equipment (such as substation/feeder capacitors) and distributed resources needs to be taken into account and only dynamic analysis will provide the full impact results. ORNL is completing a study of distributed resources interconnected to a large distribution system considering the above variables. A report of the study and its results will be condensed into a paper for this panel session. The impact of distributed resources will vary as the penetration level reaches the capacity of the distribution feeder/system. The question is how high of a penetration of distributed resource can be accommodated on the distribution feeder/system without any major changes to system operation, system design and protection. The impacts will most surely vary depending upon load composition, distribution and level. Also, it is expected that various placement of distributed resources will impact the distribution system differently.

A tariff for reactive power

This paper describes a suggested tariff or payment for the local supply of reactive power from distributed energy resources. The authors consider four sample customers, and estimate the cost of supply of reactive power for each customer. The power system savings from the local supply of reactive power are also estimated for a hypothetical circuit. It is found that reactive power for local voltage regulation could be supplied to the distribution system economically by customers when new inverters are installed. The inverter would be supplied with a power factor of 0.8, and would be capable of local voltage regulation to a schedule supplied by the utility. Inverters are now installed with photovoltaic systems, fuel cells and microturbines, and adjustable-speed motor drives.

Interaction of multiple distributed energy resources in voltage regulation

Distributed energy resources (DE) with power electronics (PE) interfaces with the right control are capable of providing reactive power related ancillary services; voltage regulation in particular has drawn much attention. In this paper the problem of how to coordinate control multiple DEs to regulate the local voltage in the distribution system is addressed. A control method for voltage regulation using the DE PE controller is presented and based on the proposed control scheme; the voltage regulation of a distribution system with one DE and two DEs are tested, respectively. The factors affecting the gain parameters of the PE controller are investigated. The simulation results show that the parameters of the controller determine its dynamic response for voltage regulation and the factors associated with the network characteristics, such as locations of DEs and the amount of load, affect the impact range of the controller. The research work presented in this paper can be potentially used for the control system design of Smart Grid or Utility of the Future.

Nuclear Generating Stations and Transmission Grid Reliability

Nuclear generating stations have historically been susceptible to transmission system voltage excursions. When nuclear generating stations trip because of voltage excursions, the resulting loss in real and reactive power support can exacerbate transmission events. New standards are being developed which should help improve nuclear plant and transmission system reliability. This paper provides a brief historical perspective. Nuclear plants do not provide automatic generation control in response to frequency decay and are also limited in providing voltage support. As 28 new nuclear plants are being considered for connection to an already highly stressed transmission grid, consideration must be given to nuclear plant design features that will enhance transmission system reliability.

Utility-Side Voltage and PQ Control with Inverter-Based Photovoltaic Systems

Abstract Distributed energy resources (DER) are relatively small-scale generators or energy storage units that are located in close proximity to load centers. The DERs that are integrated to the grid with the power electronic converter interfaces are capable of providing nonactive power in addition to active power. Hence, they are capable of regulating the voltages of weak electrical buses in distribution systems. This paper discusses voltage control capability of photovoltaic (PV) systems as compared to the traditional capacitor banks. The simulation results prove the effectiveness of dynamic voltage control capability of inverter-based PVs. With proper control algorithms, active and nonactive power supplied from DERs (e.g., solar PVs or micro-turbines) can be controlled independently. This paper also presents the scenario of controlling active and nonactive power supplied from a PV array to track and supply the local load.