A UPFC for Voltage Regulation in LV Distribution Feeders With a DC-Link Ripple Voltage Suppression Technique

The large-scale integration of distributed photovoltaic generation causes several power quality issues in low voltage (LV) distribution networks. Network voltage profile variations severely affect the LV distribution networks. The four-leg unified power flow controller (4L-UPFC) has series and shunt converters that can address the power quality issues. However, instantaneous power theory shows that second-order harmonic voltage (2ωHV) appears at the dc-link capacitor of the 4L-UPFC during any unbalanced operations. This article proposes control strategies for series and shunt converters that will simultaneously regulate the load voltages of a distribution feeder while suppressing the 2ωHV term on the dc-link of the UPFC. A controlled negative sequence current from the shunt converter is used to suppress the 2ωHV term on the dc-link. The active suppression of the 2ωHV term allows electrolytic capacitors to be replaced with small long life ceramic or film capacitors, and this does not require additional passive compensation. Stability analysis of the control loops demonstrates the overall stability of the converter system. The proposed control methods have been implemented on a Texas DSP (F28377D). An experimental demonstration on a laboratory scale prototype shows that the proposed control methods can effectively regulate the load voltages at LV distribution feeders and suppress the 2ωHV on the dc-link of UPFC during unbalanced loads and supply conditions. © 1972-2012 IEEE

Matrix converter based voltage regulator for managing smart microgrid with high renewable energy penetrations

This thesis examines the use of matrix converter (MC) in voltage regulators intended for use in the low voltage (LV) distribution network. Voltage balance and voltage regulation can be controlled by adding a series compensation voltage with a transformer. The MC supplies the injection transformer with an appropriate voltage which may be significantly unbalanced. Prior-art MCs have been predominantly applied in motor drives which have relatively balanced voltages and currents. This thesis shows the existing methods are not ideal for very unbalanced situations. It is shown that a traditional MC supplying an unbalanced load develops current harmonics at its input terminal. This thesis provides an improved MC modulation method that can eliminate input harmonics. This result is confirmed by simulation and experimental work. The thesis extends the traditional 3× 3 matrix into four wire compatible MC topologies including 3×4, 4×3 and 4×4 converters. For these cases, and generalised cases, solutions are presented for switch commutation. These are implemented with a field programmable gate array (FPGA). An experimental study is made of switch commutation for silicon and silicon carbide metal oxide semiconductor field-effect transistors (MOSFETs)

Matrix converter based voltage regulator for managing smart microgrid with high renewable energy penetrations

This thesis examines the use of matrix converter (MC) in voltage regulators intended for use in the low voltage (LV) distribution network. Voltage balance and voltage regulation can be controlled by adding a series compensation voltage with a transformer. The MC supplies the injection transformer with an appropriate voltage which may be significantly unbalanced. Prior-art MCs have been predominantly applied in motor drives which have relatively balanced voltages and currents. This thesis shows the existing methods are not ideal for very unbalanced situations. It is shown that a traditional MC supplying an unbalanced load develops current harmonics at its input terminal. This thesis provides an improved MC modulation method that can eliminate input harmonics. This result is confirmed by simulation and experimental work. The thesis extends the traditional 3× 3 matrix into four wire compatible MC topologies including 3×4, 4×3 and 4×4 converters. For these cases, and generalised cases, solutions are presented for switch commutation. These are implemented with a field programmable gate array (FPGA). An experimental study is made of switch commutation for silicon and silicon carbide metal oxide semiconductor field-effect transistors (MOSFETs)

An improved modulation method for matrix converters with unbalanced output loading

In this paper Instantaneous Reactive Power (IRP) theory is applied to develop an improved modulation method for Matrix Converters (MCs) operating with unbalanced loads. IRP theory shows that, for unbalanced loading conditions, the instantaneous power contains a constant component and a component that fluctuates at twice the fundamental frequency. In conventional modulation schemes the power fluctuation results in input current harmonics. The new method removes the harmonic distortion by synthesizing an input current vector that contains positive and negative sequence components that satisfy the power balance requirements but have only fundamental frequency components. The paper shows that the conventional modulation method may be converted to produce the required input current vector by phase modulation of the input current vector

A UPFC topology for LV feeder voltage regulation and current balance in high PV penetration applications

Haque, M ORCiD: 0000-0002-7615-7982; Wolfs, PJ ORCiD: 0000-0001-7048-1231The integration of large scale photovoltaic (PV) generation causes several power quality issues in low voltage (LV) distribution networks. Among them, network voltage profile variation and voltage unbalance are the two severe issues that affect the normal operation of distribution feeders and restrict the further expansion of PV units. The unified power flow controller (UPFC) is generally used in transmission and sub-transmission to provide power balance for series and shunt compensation, however, their use in distribution networks for voltage management is rare. The paper proposes a four leg (4L) UPFC-like topology with a small dc-link capacitor as a regulatory device to mitigate voltage issues in LV distribution networks. Instantaneous power theory (IPT) is applied to analyze the proposed 4L-UPFC for LV distribution networks. Real and instantaneous power balance of the UPFC is achieved by controlling the input positive and negative sequence current of the shunt converter. Detailed analysis and simulation studies are conducted to show the operation of the 4L-UPFC with a small dc-link capacitor within Australian LV distribution networks. The simulation results show that the UPFC can regulate the sequence voltages to maintain the far end load voltages within the allowable voltage boundaries under high PV penetrations. The results also show that the shunt converter can zero sequence compensation at the input side of the LV feeder

A matrix converter based voltage regulator for MV rural feeders

In this paper a Matrix Converter (MC) has been used with a series voltage injection transformer to regulate the voltages on a Medium-Voltage (MV) rural distribution feeder. This approach is well suited to pole top regulator applications as DC bus capacitors are avoided. The MC is controlled using a space vector modulation (SVM) method that is capable of regulating the positive-sequence voltage on a feeder while simultaneously cancelling negative sequence voltages produced by high levels of load or distributed generation unbalance or by the use of non-transposed lines. The study of the MC modulation processes is undertaken with an exact switching model for the higher frequency behaviours of the converter while a small signal Instantaneous Reactive Power (IRP) based average signal model is used to study the multi-cycle dynamic regulatory performances

Matrix converter switching and commutation strategies for grid integration of distributed generation

For the practical implementation of MCs, one of the challenges is the commutation process. In this chapter. solutions for the commutation process are developed. Two switching topologies are available. These are classified as the one degree of freedom topology (with one active device) and the two degrees of freedom topology with two active devices. Different types of commutation processes are explored in this chapter as shown in Fig. 6. 1. Initially. the discussion focusses on the overlap and dead-band commutations and then, based on their limitations, examines two-, three- and four-step commutation processes.However, as these existing procedures still have limitations, an improved four-step current sensing-based commutation process is proposed. The commutation process is extended on the 'n' -lime switching arrangement. For a clear demonstration of the proposed improved commutation methods, the stale machines and switching tables are shown in two- to 'N'-leg commutations, with a set of logical agreements developed for safe switching commutation [I]. The industrial success of the MC will depend not only on the commutation but also be contingent on the connection between them and the switches

A review of topological ordering based voltage rise mitigation methods for LV distribution networks with high levels of photovoltaic penetration

In the past five years substantial amounts of rooftop photovoltaic (PV) generation have been installed across the low voltage distribution networks. These networks often have design lifetimes of 40 years. Most of the existing distribution networks were constructed, and the voltage profiles set, prior to the rapid uptake of PV. When power quality difficulties arise reconstruction or some other form of intervention is required. This review will focus on power electronic options for voltage profile management in networks with high penetrations of PV. A voltage profile improvement can be achieved with a range of series or shunt connected devices. The traditional voltage regulator adds a series compensation voltage and electronic and electro-mechanical variations exist. Shunt devices attempt to influence voltage with reactive or real power flows when storage is allowed. A shunt device is additionally capable of phase balancing which may substantially raise the allowable PV fraction. In addition to the topological choices, the converter choice will impact upon capability. This paper will examine full converter solutions which incorporate meaningful energy storage at a DC bus and reduced energy storage scenarios or storage free solutions such as matrix converter (MC) based devices. © 2019 Elsevier Lt

Dynamic Stability Analysis in Distribution Networks with Dynamic Loads and Renewable Energy Sources

The main focus of this thesis is the modelling, control and stability analysis ofdistribution networks with distributed generators and dynamic loads in which thedynamic loading effects in standard distribution networks are taken into consideration. Different case studies are considered, such as fault effects, a worst-casescenario and nodal voltage analyses of different network configurations. The dynamic modelling includes line resistance, which has been neglected in the existingliterature, but which the case studies show is a critical parameter affecting systemstability. An LQR controller is proposed for minimising the effect of resistance inthe distribution network. A novel linear zero dynamic controller (LZDC) is designto maintain the voltage and angle stability for distributed generators. Some elementary notions for the LZDC are introduced such as relative degree, Lie derivativeand exact linearization. This thesis also presents a new concept of a multiple inputmultiple output (MIMO) LZDC for a three-phase grid-connected photovoltaic (PV)system to enhance its stability and robustness under different weather conditions.Grid-connected PV systems are highly nonlinear systems in which most of the non-linearities occur due to the intermittency of sunlight and the switching functions oftheir converters and inverters. The proposed controller overcomes the limitations ofother controllers, such as the PI, hysteresis, predictive and sliding-mode controllers,and it is proven that this system operates at unity power factor. The effectiveness ofthe proposed control strategies are demonstrated through time-domain simulationstudies conducted using the standard industry-based software environment

Net-metering and Feed-in-Tariff policies for the optimum billing scheme for future industrial PV systems in Bangladesh

In this paper, the economic sustainability of net billing and feed-in-tariff (all energy buy/sell) method is analyzed in comparison with the current net-metering for the industrial PV systems in Bangladesh. Three billing methods are compared according to plant capacity factor, excess energy transfer, levelized cost of energy (LCOE), net present value (NPV), payback period, and profitability index (PI) for the analysis of optimum billing scheme. The highest plant capacity factor and minimum LCOE are found for the large PV system in Chattogram. Out of three methods, all energy buy/sell exhibits the NPV which is USD 5.85 million and PI of 2.54 at the minimum 4.9 years discounted payback time for the large PV system in Chattogram. The sensitivity analysis of solar irradiation at six other regional areas, bill escalation rate, and discount factor is performed to observe the impact on annual energy production and NPV. For both systems, all three assessed methods are found economically feasible, but the net metering is attained as the least profitable in comparison with net billing and all energy buy/sell schemes. From various analyses, it is found that the adaption of these two schemes in the present guideline can enhance industrial PV production in Bangladesh