Johan Enslin

Network impacts of high penetration of photovoltaic solar power systems

The impacts of PV power plants are associated with voltage profiles, electrical losses, power factor, capacity planning, power quality, system operations and protection. Currently utility-scale solar PV plants have nominal capacities that are compatible with distribution substation MVA ratings e.g., between 1 MVA and 10 MVA, plans are to develop transmission interconnected PV plants in the 50 – 100 MW power range. These distribution network impacts are discussed and mitigation solutions are provided. A case study of a feeder fully loaded with PV power plants will be discussed.

Doubly Fed Induction Generator (DFIG)-Based Wind Farm Control Framework for Primary Frequency and Inertial Response Application

This paper presents a new wind farm control framework for inertial and primary frequency response for a high wind integrated power system. The proposed architecture is unique in the sense that the methodology can be used for frequency regulation support during subsynchronous and super-synchronous operation of the wind turbines (farm). The architecture work with existing wind farm controllers thus avoiding any additional replacement or tuning. The methodology depends on reduced order modeling based on model order reduction (MOR) and subsequent online controller design. The approach is tested on a smaller wind farm and further evaluated on a larger reduced power grid with 39 buses and ten generators. The results show that the proposed architecture provides greater flexibility in wind farm control towards frequency oscillations.

Generator emulation controls for photovoltaic inverters

State-of-the-art inverter controls for grid-tied photovoltaic (PV) systems pose a number of challenges to grid stability if deployed on a large scale. This paper addresses large-scale integration of PV and other distributed generation (DG) into the grid. A new control scheme for grid-tied DG inverters is proposed to embed various load-following functions. This control scheme, dubbed Generator Emulation Controls (GEC), allows DG inverters to perform voltage regulation support, reactive power compensation, and fault ride-through. GEC also allows DG inverters to form scalable inverter-dominated micro-grids. These micro-grids are capable of operating in grid-tied mode or of separating and supporting an islanded load. Dynamic modeling of synchronous generators is presented, and used to guide GEC implementation. Experimental results are presented to demonstrate some of the main features of GEC.∗

Dynamic reactive power and energy storage for integrating intermittent renewable energy

The role and application of energy storage and dynamic reactive power support is discussed in this paper. A well-engineered energy storage plant can help alleviate some of the problems encountered with the integration of intermittent renewable resources and at the same time make renewable power plants more cost effective in existing traditional power system. The intent of this paper is to demonstrate these features by means of a planned application of a STATCOM and Battery Energy Storage System (BESS) in a region with high penetration levels of wind and solar integration. Firstly, the paper describes the integration challenges of integrating intermittent renewable energy, followed by possible mitigation measures. Thirdly, a specific application of a STATCOM with a BESS is included and the different possible revenue streams are calculated.

Application of STATCOM with energy storage for wind farm integration

The application of a STATCOM and Battery Energy Storage System (BESS) can help alleviate some of the problems encountered with wind farm integration to the existing power system. The intent of this paper is to demonstrate the benefits obtained with STATCOM and BESS for this purpose. First, the paper identifies the power quality and some other issues in the Southern California Edison system where there is abundant wind generation. Computer simulations (e.g. load flow and transient stability) show that the application of a STATCOM with BESS can help the system survive under the most severe contingencies occurring in the area. The analysis also demonstrates that the BESS can help dispatch an individual wind farm in the area during steady state. The BESS can help reduce local wind generation curtailment, necessary during high generation and low local system load that causes transmission overloading, by absorbing the excess energy generated by the wind farms.

Clustering and cooperative control of distributed generators for maintaining microgrid unified voltage profile and complex power control

To meet several power objectives, the idea of organizing DGs into several clusters in a microgrid is proposed in this paper. Power objectives include maintaining active power flow to the main grid at a predetermined level, minimizing the reactive power flow to the main grid and maintaining a unified voltage profile across the microgrid. DGs are organized differently for active and reactive power control. All DGs realize active power objective in one group. As reactive power is used to maintain the unified voltage, DGs are grouped in several clusters to regulate multiple critical point voltages. The closest cluster to the point of common coupling, minimizes the reactive power flow and others manage their reactive power to regulate their critical points. Each cluster has a virtual leader which other DGs follow, utilizing the cooperative control. The cooperative law is also derived, based on the dynamics of the inverters.

Grid impacts and mitigation measures for increased PV penetration levels using advanced PV inverter regulation

As part of the Renewable Systems Interconnection (RSI), exploring the impact of high levels of PV penetration on standard utility system planning methodologies is critical. In this paper, in order to evaluate the potential impacts on representative distribution feeders for a south-eastern utility that is facing the interconnection of increasing levels of Photovoltaic (PV) generation; detailed steady-state and dynamic modeling and simulation of the integrated systems are performed. The study was conducted on two representative feeders: an almost exclusively residential feeder, and a predominantly rural feeder. Multiple PV penetration levels based on Spring loading were considered: 33.3% and 75% of total feeder loading, and 75% of total connected capacity as extreme case. Steady-state and dynamic analyses were performed. Procedures used to evaluate these impacts and results and observations are discussed. Moreover, possible impact mitigation strategies and evaluation of PV inverter controllers for mitigating the negative impacts are assessed.

Application of STATCOM for power quality improvement

The application of a STATCOM can help to alleviate some of the power quality issues encountered within a refinery consisting of large induction machine loads. The intent of this paper is to demonstrate the improvements obtained with STATCOM for this purpose and also to evaluate economical benefits obtained with it. First, the paper identifies the power quality and other issues around the refinery in the Southern California Edison system. Computer simulations show that the application of a STATCOM can help the big motor load to survive under the most severe contingencies occurring in the area. The analysis also demonstrates that the STATCOM with appropriate controller can be very effective in harmonic reduction.

Layout study of contactless magnetoresistor current sensor for high frequency converters

In this paper, we present a new technique to unify and intensify the magnetic fields that results in higher performance of Anisotropic Magneto-Resistive (AMR) current sensors and consequently develop a closed loop controller for 100W synchronous GaN buck converter at 1MHz. The closed loop operation of high switching frequency converters at high power has always been a big challenge due to lack of access to current information. The proposed method that also intensifies the magnetic fields through the sensor, significantly improves the bandwidth limits, and reduces electromagnetic interference (EMI) on AMR sensors, making them applicable for high switching frequency and high current power electronics converters. After verifying uniform distribution concept through simulation, we also implemented a prototype of AMR current sensors onto Printed Circuit Board (PCB) for verification of the concept at high frequency converter. We then present the design procedure and associated challenges of an integrated analogue peak current controller for creating the closed loop operation of a GaN buck converter at high switching frequency.

On reactive power injection control of distributed grid-tied AC-stacked PV inverter architecture

In this paper, two different Reactive Power Injection (RPI) methods for a fully distributed PV inverter architecture are investigated. RPI methods are parts of ancillary service requirements for modern PV systems to play a more active role in grid regulation and control in future high penetrated PV generation networks. The main objective of this paper is to demonstrate and test RPI methods on a panel-level AC-stacked PV-inverter string which is controlled with distributed control scheme with minimum communication requirements and propose a combined RPI method. Effectiveness and feasibility of distributed control architecture and RPI methods are verified by experimental results during normal operation and voltage disturbance conditions using a lab-scale PV inverter string setup.