Yuba Raj Kafle

Improved peak shaving in grid-connected domestic power systems combining photovoltaic generation, battery storage, and V2G-capable electric vehicle

Strategic use of domestic battery storage in households with a V2G-capable electric vehicle and photovoltaic generation is shown to be capable of shaving the peak loading on the electricity distribution grid under realistic operating conditions by up to 37%. The additional degree of freedom provided by combining the EV and domestic storage is shown to enable additional reductions in peak grid load. A smart control algorithm is described for coordinating the system components to reduce peak grid load and improve power quality.

Bifurcation Analysis in a Digitally Controlled H-Bridge Grid-Connected Inverter

The bifurcation behavior of a digitally controlled H-bridge grid-connected inverter is studied in this paper. The discrete-time model of this time-varying system is derived for inherent time delay in a digitally controlled system. Theoretical analyses indicate that only Hopf bifurcation can take place when the system loses its stability. The analytical expression of oscillation frequency is also derived in this paper. Moreover, the stability and instability boundaries for all switching cycles within a line cycle are described by analytical expressions. Finally, the theoretical results are verified by numerical simulations, circuit simulations and experimental measurements. These aforementioned conclusions provide an insight into the design process of the inverter system in terms of stability behavior and instability phenomenon.

Control Strategy Based on Equivalent Fundamental and Odd Harmonic Resonators for Single-Phase DVRs

In this paper, a digital control strategy based on equivalent fundamental and odd harmonic resonators is proposed for single-phase DVRs. By using a delay block, which can be equivalent to a bank of resonators, it rejects the fundamental and odd harmonic disturbances effectively. The structure of the single closed-loop control system consists of a delay block, a proportional gain and a set of zero phase notch filters. The principle of the controller design is discussed in detail to ensure the stability of the system. Both the supply voltage and the load current feedforwards are used to improve the response speed and the ability to eliminate disturbances. The proposed controller is simple in terms of its structure and implementation. It has good performances in harmonic compensation and dynamic response. Experimental results from a 2kW DVR prototype confirm the validity of the design procedure and the effectiveness of the control strategy.

Towards an internet of energy

The current model of centralized electricity generation, transmission and distribution is under pressure to change for a variety of reasons; environmental concerns are driving a shift away from large coal-fired generation systems to increasing adoption of renewable energy sources, which tend to be distributed and not always available on demand, and hence requiring distributed storage support. Moreover, to support electric vehicles, energy needs to be provided as a service to consumers independent of location, rather than a product delivered and billed to a fixed location. In this work, we compare and contrast modern internet and energy networks and services, identifying key functionalities and the main technical challenges to be faced in transforming the electricity distribution system to a flexible yet reliable and robust platform for the exchange of electrical energy.

Performance comparison of single-phase transformerless PV inverter systems

Removing the isolation transformer in grid-connected photovoltaic (PV) inverters is desirable to increase efficiency and reduce the size, weight, and cost of these systems. However, it may also allow leakage current through the stray capacitance between the PV array and ground, causing a safety risk. Both efficiency and leakage current depend upon both inverter topology and modulation strategy. In this work three single-phase inverter topologies, i.e. the H-bridge, HERIC, and H5 inverters, are compared with respect to efficiency and leakage current to determine their suitability as transformerless PV inverter systems. Experimental results are presented for the most promising case, i.e. the HERIC inverter with standard sinusoidal pulse-width modulation.

A new PWM Shoot-through control for voltage-fed quasi-z-source DC/DC converters

This paper presents a new shoot-through control method applicable for an impedance source galvanically isolated DC/DC converter. In impedance source converters, the introduction of shoot-through states increases the switching speed of H-bridge switches about two to three times the switching frequency. This approach reduces the switching transient of all switches of inverters by commutating them once in a switching cycle. The shoot-through states are generated by alternatively switching the single leg of the inverter whereas, in baseline modulation approach, all the switches are turned on during shoot-through states. This method decreases the switching loss of front-end converters and independent controllability of active and shoot through states. This modulation technique is applied and validated to a voltage-feed Quasi-Z source isolated DC-DC converter with a voltage doubling rectifier.

A comparative study of two current-control techniques applied to a three-phase three-level active power filter

The active power filter (APF) has already established itself as a prominent means of addressing harmonic pollution and other power quality issues. Current control of an APF is a key in achieving a good compensation performance. Generally, PI control is used owing to its simplicity and ease of implementation. However, using a proportional resonant (PR) controller can give an added advantage in tracking of harmonics at higher frequencies. This paper presents a comparative study of current control when implemented using PI and PR controllers in a platform of a three-phase three-level shunt APF. The simulation results prove the effectiveness of PR control over PI control.

Aperiodic pulse-modulation technique to reduce peak EMI in impedance-source DC-DC converters

The use of wide-bandgap (WBG) devices in power converters provides several advantages in terms of efficiency, power density and low cooling requirements. However, a potential unwanted side-effect is the increased electromagnetic interference (EMI) noise, the basis of which is the high di/dt and dv/dt realized by the characteristic sharp rise and fall switching offered by the WBG power switches. To suppress the EMI, this paper presents a generic framework for the generation of an aperiodic carrier signal, which can be extended to drive multiple switched power converters. The aperiodic modulation scheme is implemented in a MATLAB Simulink environment and realized on a field-programmable gate array (FPGA) development board through an auto-code generation feature offered by a hardware description language (HDL) coder. Finally, the efficacy of the proposed aperiodic modulation methodology has been tested on a quasi-Z-source DC-DC converter. A 9 dB suppression in the peak conducted EMI emissions was demonstrated with no adverse impact on the voltage gain and efficiency of the power converter.

A new PWM shoot-through control technique to reduce switching losses in impendance source DC/DC converters

A simplified shoot-through pulse width modulation (PWM) technique is presented for reducing switching losses in impedance source DC-DC converters. The proposed PWM method alternates shoot-through state conduction in each leg of the H-bridge, thereby increasing controllability of the converter, reducing the number of switching transients, and reducing the dynamic loss of the converter through soft-switching. The proposed modulation method was verified using a GaN-based quasi-Z-source DC-DC converter. This method demonstrates better performance at low load and with high switching frequency.