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A novel railway power conditioner based on modular multilevel converter with integrated super capacitor energy storage system
Published in Rodolfo Dufo-López, Jaroslaw Krzywanski, Jai Singh, Emerging Developments in the Power and Energy Industry, 2019
MMC-RPC, though capable of solving the negative sequence current problem effectively, can’t completely solve the problem of regenerative braking energy and internal voltage fluctuations of MMC. In view of these problems, a new railway power conditioner based on MMC integrated super capacitor energy storage system is proposed. Firstly, the working mode of regenerative braking and the voltage fluctuation principle of the capacitor of SM are analyzed. Secondly, a combined control strategy is proposed to control the energy flow of ESS and eliminate the voltage fluctuation of the SM. Finally, the effectiveness of the control strategy was verified in matlab/simulink. The regenerative braking energy can be effectively utilized and the usage of large-capacity capacitors can be greatly reduced through controlling ESS effectively, followed by the comprehensive improvement of the economy .
Electric Vehicles
Published in Hussein T. Mouftah, Melike Erol-Kantarci, Smart Grid, 2017
The basic architecture of an inductive wireless PEV charging system is as follows. In the primary side, the 50/60 Hz utility AC input is converted to a regulated DC voltage by a power conditioner with a power factor correction just like a wired charger. A pulse width modulated (PWM) inverter can be used here. Then, a switching network converts the DC energy to high-frequency (HF) AC energy (square wave) at the required operating frequency. Usually, power flow regulation is also achieved through the modulation of this HF signal. Then, step-up or step-down high-frequency transformers are used to couple the energy to the next stage, which is the matching network. The key aspect of the matching network is a very low loss (high Q) energy storage element used for coupling, which shall reduce the volt-ampere (VA) rating of the power supply. This stage is also commonly referred to as an impedance matching network, or a resonant tank.
Power Conversion and Control for Fuel Cell Systems in Transportation and Stationary Power Generation
Published in Frede Blaabjerg, Dan M. Ionel, Renewable Energy Devices and Systems with Simulations in MATLAB® and ANSYS®, 2017
Kaushik Rajashekara, Akshay K. Rathore
A fuel cell propulsion system with a battery pack and a power conditioner is shown in Figure 12.7 [7]. Both the fuel cell stack and the battery provide the power required for propulsion. The power conditioner must be sized depending on the maximum power capacity of the fuel cell stack. To prevent the negative current from going into the stack, a diode is connected in series with the fuel cell stack. Negative current may cause cell reversal and damage the fuel cell stack. The power for the accessory loads of the fuel cell system is derived from the battery side of the converter to make sure that accessory loads are always powered even when the fuel cell stack is not producing any power. This would help to start the system faster. The battery power could also be used to initially warm up the system and bring the stack output voltage to a nominal level. Thus, in this kind of layout, starting the fuel cell system will not be a concern. The battery voltage has to be selected to be equal to the required DC input voltage to the power inverter. If the propulsion system is designed to be operated at a DC voltage above the fuel cell voltage, the power conditioner boosts the fuel cell stack voltage up to the battery voltage and also charges the propulsion batteries. If the fuel cell stack voltage is higher than the battery voltage, the power conditioner acts as a buck converter.
Humanitarian engineering and vulnerable communities: hydropower applications in localised flood response and sustainable development
Published in International Journal of Sustainable Energy, 2020
Spyros Schismenos, Garry John Stevens, Dimitrios Emmanouloudis, Nichole Georgeou, Surendra Shrestha, Michail Chalaris
It should be noted that there is a large variety of turbines for both types. In this study we focus on turbines that do not require high head and can operate under both low flow (often, normal conditions) and high flow (rare, extreme conditions). Besides the type and design of the hydro-turbine, an appropriate generator is important when designing PHYS. Turbines that rotate at slow speeds may require a gearbox or pulley system. In general, the most preferred choice for small-scale hydropower systems is the permanent magnet synchronous generator. This is an electrical generator that converts mechanical/rotational energy to electricity and can be used without a gearbox. It offers high efficiency with low maintenance and can also be used by other renewable energy types (wind energy) (Acharya, Papadakis, and Shaikh 2016; Smith 1994). Small hydropower generators can be categorised as direct current (DC) and alternating current (AC) generators. Specifically: DC Generators: Depending on their size, they can produce more than 3 kW. Dynamos, that are permanent magnet DC generators, are perhaps the most popular option. For slow water speed, diesel dynamos that were used in trucks or buses are preferred as they focus on the energy generation efficiency. They can generate up to 500 W and power energy storage units (batteries) similarly to car battery charging. However, the batteries should be very close to the generator in order to avoid energy loss due to distance. Besides dynamos, car and automotive alternators are also an option, however, they may lack in efficiency. Car alternators, for instance, require high rpm speed; whereas, automotive alternators require an external power supply to create a magnetic field. Most DC generators use rectifiers to convert the low-voltage DC electricity into AC electricity. The AC electricity is required for powering home appliances (120 or 240 volts) (Smith 1994).AC Generators: Depending on their size, they can produce from 500W to 10kW. They are mainly used for powering energy grids or home appliances if connected directly to houses. When connected with a power conditioner, they can maintain steady energy output, voltage and frequency regardless the speed of the hydro-turbine (Smith 1994).
Decoupled State-Feedback Based Control Scheme for the Distributed Generation System
Published in Electric Power Components and Systems, 2018
The IEEE Std. 1547-2003 and the IEEE Std. 929-1995 state explicitly that the DGU within the DGS is not used to regulate the voltage of the distribution system, however the most recent draft for the IEEE Std. 1547.7-2013 [29] endorses a good potential of the DGS to regulate the voltage at a non-stiff distribution system. Another merit of the developed control scheme is its ability to operate the DGU as a power conditioner to mitigate some voltage problems that emanate from a remote disturbance in the power grid. It is known that a single-line to ground fault produces a voltage dip in one phase and a voltage-change in the other phases [34]. In this work, the arbitrary choice for the voltage threshold is 0.8 p.u.; meaning that if the voltage at the PCC is less than 0.90 and greater than 0.8 p.u., then the control scheme operates the DGU as a power conditioner to regulate the voltage at the PCC. The control scheme adjusts the power references so as to inject considerable reactive power (with a minor change in active power). The distribution system experiences many instantaneous voltage sags, which propagate everywhere in the distribution system [34]. To ride-through this sag, the control scheme continuously detects the voltage at the PCC. If the voltage at the PCC is less than 0.90, the selector switch of Figure 3 changes to the ride-through mode, at which the power references are set such that the active power remains almost constant at its pre-set value, while the reactive power reference becomes proportion to the value of the sagged voltage through a proportional gain as shown in Figure 3. A single line to ground fault is initiated at t = 5 s. As a result of this fault, Figure 9a demonstrates injected active power (with a positive sign) and injected reactive power (with a negative sign) for two different conditions, which are the DGU without a ride-through mode and the DGU with a ride-through mode. First for the DGU without a ride-through mode, the reactive power almost does not change during the voltage sag, it stays around its pre-set value and consequently the voltage is slightly raised from 0.7 p.u. to almost 0.83 p.u. as shown in Figures 9a and 9b. For the DGU with a ride-through mode, its performance indicates a considerable injection of reactive power to raise the voltage at the PCC; and consequently the voltage is raised from 0.7 to 0.95 p.u. as shown in Figures 9a and 9b. When the disturbance is cleared, the voltage at the PCC goes back to its original value. Eventually, the control scheme normally operates the DGU in a grid-connected mode to inject normal active and reactive power as before the occurrence of this disturbance. The transient in voltage shown immediately after t = 5 s stems from the response of the control scheme so as to keep the system voltage constant. Eventually, these curves clarify the impact of operation of the DGU in a ride-through mode on the voltage profile at the PCC.