Search

Renewable Distributed Energy Resources (DERs) are on track to dominate in near future, mitigating the ever-growing energy demand. DERs mostly interact with the grid through power electronic converters, whereas traditional power grid’s power operations are controlled by Synchronous Machines (SMs). With more DERs coming into the picture and contributing an increasing portion of power flow, the power control architecture of the grid must be revisited. There are many benefits of using a Voltage Controlled-Virtual Synchronous Machine (VC-VISMA) controller, such as communication-less cooperation between power sources achieving tight regulation of grid voltage and frequency. But a major disadvantage of this controller is it cannot operate under conditions where the central grid is absent, such as black-start. In this paper, a modified VC-VISMA or Dropped VISMA (DVSM) is proposed aiming to control voltage and frequency even under black start. The performance of this modified controller is validated in MATLAB/Simulink.

The supercascode configurations demonstrate significant benefits over the monolithic medium voltage SiC MOSFETs in terms of cost, commercial viability and thermal dissipation capability. However, this feature can produce an unexpected phenomenon in power electronics applications called self-sustained oscillation during turn-off. This paper presents a comprehensive root-cause analysis of this behavior in a 6.5 kV - 50 A SiC JFET supercascode circuit. A theoretical analysis is carried out based on a turn-off switching equivalent circuit which facilitates the determination of criteria for self-sustained oscillations. The analysis is verified with a SPICE simulation (LTSpice), which also provides a platform to test the countermeasure to suppress the self-sustained oscillation. Finally, the feasibility of an oscillation suppression method is verified by both simulations and experimental set up.

There has been an increase in the decentralization of electrical power generation with the introduction of Inverter Based Distributed Generation (IBDG). This restructuring of the grid system achieves a resilient and closer to carbon-free grid. Despite the growing integration of IBDG, there has been operational challenges such as power quality deterioration and mis-operation of grid protection equipment, caused by the power electronic interface of inverters along with wind, solar intermittency and grid bidirectionality. Several mitigation techniques have been proposed in the literature. However, this paper focuses on the problem of the maloperation of traditional protection relays due to increased IBDG penetration. Many studies in protection of IBDG networks have been conducted, yet protection equipment exclusively for IBDG applications are not yet developed. This paper will focus on the mis-operation of the Negative Sequence Voltage Polarized (NSVP) directional element caused by IBDG, which will be investigated using a Typhoon Inc. Virtual test bed (real-time simulation platform), running with a Hardware in the Loop (HIL) protection relay. The simulation is conducted on a modified IEEE 13-node system while the IBDG is modelled to have Dynamic VAR control.

With higher penetration of Distributed Energy Resources (DERs) into the utility power grid, the power control architecture of the grid must be revisited. The main reason for this is that DERs mostly interface with the grid through power electronics (i.e. inverters), whereas traditional centralized grid-forming has been majorly achieved by Synchronous Generators (SG). By employing a Virtual Synchronous Machine (VISMA) controller, benefits such as communication-less and independent power control can be achieved concurrently with maintaining power grid standards (stable voltage and frequency constraints). However, the VISMA controller cannot operate under conditions where the central grid is absent, especially for the black-start condition. In this paper, a modified VISMA (called Mod-Visma) is proposed, which incorporates the missing voltage and frequency regulation outer loops into the baseline VISMA control architecture. The performance of this modified controller is validated in MATLAB/Simulink.

In this paper, a new solid-state circuit breaker for medium voltage applications is proposed named Diode Clamped Solid-State Circuit Breaker (SSCB). Unlike the conventional medium-voltage SSCBs using simultaneously operated switches in series to block medium level voltage, Diode Clamped SSCB utilizes a novel diode clamped topology to extend its operating voltage. In the breaking process, the switches in the Diode Clamped SSCB are tripped sequentially to interrupt fault current and do not incur dynamic voltage unbalancing issues. After the breaking operation, the voltage across the switches is clamped to the capacitor voltage. In addition, with asymmetric configuration, Diode Clamped SSCB can effectively limit the increase of fault current and reduce the volume of metal oxide varistors (MOVs). PLECS simulation software as well as an experimental prototype have been used to prove the plausibility and superiority of the Diode Clamped SSCB.

SiC based Solid State Circuit Breakers (SSCBs) have recently entered into the market at the low voltage end of the network, and their adoption is slowly moving upstream as higher voltage offerings mature. Unavailability of commercial medium voltage SiC devices and their low current handling capability and high dv/dt hinder medium voltage SSCB designs. However, series connection of low voltage devices can meet the required voltage level if dynamic and static voltage balancing is possible. In this paper, an active voltage clamping method is proposed to achieve balanced dynamic turn-off voltage sharing between cascaded devices (CREE 1.2kV/30A SiC MOSFETs). Also, this method minimizes the number of components, overall switching losses and delay time by avoiding bulky and expensive RC snubbers. Different possible reasons behind dynamic voltage unbalancing and the proposed balancing technique have been verified in the LTspice simulation software. In addition, experimental results have been carried out to validate the effectiveness of the proposed technique.

Solid State Circuit Breakers (SSCB) are a growing applications of Wide-Band-Gap (WBG) semiconductor devices, because of their ability to perform arc-less interruption of high DC currents. However, a necessary exercise before applying any novel switching device to the breaker space is the evaluation of its switching characteristics at the breaker's rated voltage and current. The turn ON and turn OFF losses have been accepted as two key parameters for performance evaluation. Since SSCB's are normally closed in their nominal operational state and are opened in fault conditions, this makes conduction losses the dominant form of thermal stress. However, characterizing the switching performance of an SSCB is also very useful to validate protection functionality, speed and ability to perform within its safe operating area. Towards that end, Double Pulse Testing (DPT) which is a testing apparatus intended for characterizing single semiconductor devices, has been adopted in this paper as a platform for SSCB testing of switching losses and dynamics, off-state voltage blocking and on-state current interruption. Such a platform provides a basis for comparative analysis of different SSCB implementations without having to expend energy by continuously operating at rated power. The DPT platform was used to validate an SSCB package from ATOMPower Inc, and the data obtained from the test was further post-processed in Python. MATLAB/Simulink software has been used for demonstration purposes and experimental results are included in this paper.

A novel approach for mitigation of power quality issues have been presented in the paper. This paper introduces a Center-Point-Clamped AC-AC Buck-Boost Converter based power quality device for industrial and residential customers at the leaf end of the distribution network. This converter utilizes the principle of center-point-clamping to reduce the voltage stress on the power semiconductor switches. It can buck, boost and eliminate unwanted line frequency harmonics from the input voltage by controlling the duty ratio of the switches, thereby providing desired voltage at the customer side with minimal THD. A closed loop strategy has also been presented in the paper. This feedback regulator improves the steady state and transient performance of the converter. Simulation results displayed in the paper verify the feasibility and effectiveness of the proposed power quality device in mitigation of power quality issues like voltage sag, voltage swell and harmonics at multiple order of line frequency, have been displayed in the paper. A small scale experimental prototype rated at 120V, 1-kW has been constructed in the laboratory. Experimental results further corroborate the theoretical and simulated analysis, and demonstrate the merits of the proposed approach.

A Virtual Power Plant (VPP) composed of distributed energy resources (DER) with load and generation forecasting is presented in this paper. The large-scale integration of renewable energy and energy storage systems have introduced many technical and economic challenges to both customers and utilities. High levels of renewable power injection might reduce grid stability due to intermittencies. The proposed VPP mitigates these issues and can function as a major component of a utility grid with high levels of DER penetration. The VPP has two components: a forecast and analytics component, and an electrical systems control component. The forecaster generates the dispatch schedule for each player in the VPP e.g. a PV station, and the loads. This is done by taking historical load and weather data, models of the VPP players, and the weather forecast as inputs. The electrical systems controllers use the dispatch schedule to regulate power flows from each individual player and to the loads. Grid frequency and voltage support are also provided by the control, thereby improving system stability. An example VPP with three solar photovoltaic and two battery energy storage systems is presented and implemented using a real-time digital simulator. The results validate the VPP performance in load forecasting, power flow control and grid support. A dispatch schedule is generated for a 24-hour period and the VPP controller operation to service the loads and supply the power sold on the day-ahead market was verified.

The significant mechanical inertia of the rotor in a synchronous generator is crucial for facilitating the cooperative grid forming capability of multiple such generators on the transmission and distribution network. This paper demonstrates that the DC link capacitance in a PV inverter is the analogous form of inertia for such a system, albeit having much smaller magnitude. Furthermore it proposes using storage integrated on the DC link to synthesize extra inertia by programming the storage power electronics controller to achieve an emulated capacitance. Inertia added to distributed energy resources (DERs) in this manner is the first step towards mitigating the power quality issues arising from increased renewable penetration on the network. Demonstration of the acquired inertia dynamics and verification of the required controller design is shown through a detailed simulation model.

Proliferation of distributed energy resources (DERs) on the low voltage network comes with a myriad of power quality problems such as voltage fluctuations and poor harmonic performance. Distributed mitigation solutions are being proposed for the low voltage network which are similar to state-of-the-art solutions in medium voltage networks. This paper presents a μ-STATCOM device as a distributed solution to interface with DER's at the leaf end of the network to achieve fine-tuned voltage regulation and mitigation of voltage harmonics. This solution combines the operation of low voltage grid-tied inverters (for both PV and battery systems) and passive or active voltage regulation devices. A general analysis of the effectiveness this solution along with simulation and experimental results are presented in this paper. A benchmark control algorithm has been designed to achieve the desired features of the proposed μ-STATCOM. The experimental setup consisted of a proof of concept hardware prototype rated at 5kW.

Co-simulation is a versatile technique for splitting a large system model into multiple components that can then be solved in parallel on interconnected simulation platforms. This is most useful for interconnecting diverse Real-Time platforms (possibly from different vendors). A challenge emerges from the discrepancy of the time base between the systems. Even a minute difference in the frequencies of the forcing functions (i.e. stiff voltage and current sources in simulations of electrical systems) will cause spurious drifting and low frequency oscillations in the simulation results. A resolution is proposed in this paper based on a synchronization signal originating from one platform called the master and sent to the others. The effectiveness of this approach is demonstrated through implementation on actual hardware, namely an interconnection between RTDS™ and Typhoon HIL platforms.

A conventional Counter-Comparator Digital Pulse Width Modulator (DPWM) with a fixed slope is dynamically and linearly shifted upwards or downwards by a value proportional to the error signal. The shift is done through applying a positive or negative offset (shift) value depending on the direction of the transient. This control approach aims to improve the transient response and efficiency of an FPGA-based digitally controlled DC-DC converters in terms of shorter settling time with optimal over-and undershoots. The dynamic Ramp Shift design method presented in this work is a linear DC shift control achieving a better dynamics response through reducing the time required by the compensator to reach back to the steady state during a transient condition. Moreover, it utilizes existing system digital controller, and does not require any additional circuitry. This shifting will only occur during transients for the reason that the error (which basically formulates the shift value) is almost zero during steady state, while during transients; the positive or negative value of the error will shift the ramp downwards or upwards. The proposed digital technique is validated by computer simulation. Experimental result of a prototype on a Xilinix FPGA platform verifies the concept.

This paper thoroughly analyzes various linear control loop designs of DC-AC inverters. First, the PI and P+Resonant controllers for current mode of operation are investigated. Then a detailed analysis of the various inverter control techniques for voltage mode operation is performed and the most promising technique is further analyzed. Finally simulation and experimental results are presented.

A piecewise digital control method is presented in this paper to improve the converter characteristics especially the efficiency. By combining more than one control method or/and compensators in a single converter controller, improved performance may be achieved. Piecewise control opens the possibility of combining advantages of different control schemes and preventing or minimizing their disadvantages. In this paper, by combining the asymmetric control and the duty-cycle-shifted control in a new piecewise control scheme, the performance and efficiency of half-bridge DC-DC converter with high switching frequency and wide input voltage range can be improved, without adding additional components. The proposed control is theoretically analyzed and its implementation considerations are discussed. Experimental results are also presented

Digital controllers are increasingly being used especially in complex systems, including power electronics systems, because of their advantages. In this paper, design, simulation, and experimental results of a fully digitally controlled half-bridge converter with current-doubler are presented. Digital system blocks effects are considered in the digital compensator design to achieve sufficient closed loop gain and phase margins and verified experimentally. Moreover, additional necessary functions are integrated in this digital controller, such as OVP/OCP functions and dead time optimizing function

In this paper, a discrete model is developed for DCS controlled half-bridge topology with current-doubler to facilitate digital controller design when operating at high switching frequencies. The discrete model is derived and then compared with the classical continuous model. The model is represented in the versatile state-space form, which allows the application of a wide range of modern and classical control theories. The pulse transfer function for the modulator input to converter output voltage is derived for use in voltage mode control. To verify the theoretical frequency response predicted by the presented model, a laboratory prototype is built

The interactive technical electronic book, TechEBook, currently under development at the University of Central Florida (UCF), introduces a paradigm shift by replacing the traditional electrical engineering course with topic-driven modules that provide a useful tool for engineers and scientists. The TechEBook comprises the two worlds of classical circuit books and interactive operating platforms such as iPads, laptops and desktops. The TechEBook provides an interactive applets screen that holds many modules, each of which has a specific application in the self learning process. This paper describes one of the interactive techniques in the TechEBook known as Symbolic Circuit Solver (SymCirc). The SymCirc develops a versatile symbolic based linear circuit with a switches solver. The solver works by accepting a Netlist and the element that the user wants to find the voltage across or current on, as input parameters. Then it either produces the plot or the time domain expression of the output. Frequency domain plots or Symbolic Transfer Functions are also produced. The solver gets its input from a Web-based GUI circuit drawer developed at UCF. Typical simulation tools that electrical engineers encounter are numerical in nature, that is, when presented with an input circuit they iteratively solve the circuit across a set of small time steps. The result is represented as a data set of output versus time, which can be plotted for further inspection. Such results do not help users understand the ultimate nature of circuits as Linear Time Invariant systems with a finite dimensional basis in the solution space. SymCirc provides all simulation results as time domain expressions composed of the basic functions that exclusively include exponentials, sines, cosines and/or t raised to any power. This paper explains the motivation behind SymCirc, the Graphical User Interface front end and how the solver actually works. The paper also presents some examples and results to better explain the concept.