Moshe Averbukh

Issues in Modeling Amorphous Silicon Photovoltaic Modules by Single-Diode Equivalent Circuit

In this paper, the applicability of the well-known single-diode equivalent circuit to modeling amorphous silicon photovoltaic modules is questioned. It is shown that, unlike in mono- and polycrystalline modules, all of the equivalent circuit parameters are irradiation dependent. This dependence may be derived from either manufacturer-provided or measured I-V curves for different irradiation levels. In order to extract the equivalent circuit parameters, the suggested approach combines numerical solution of two transcendental and two regular algebraic equation systems with single-parameter fitting procedure. Two additional parameters are introduced to describe temperature dependence of photocurrent and diode reverse saturation current. As result, a set of seven parameters is obtained, comprehensively describing the panel performance for arbitrary ambient conditions. It is shown that characteristic curves obtained using the proposed approach match well the manufacturer-provided data for various values of temperature and irradiation.

Portable Ultracapacitor-Based Power Source for Emergency Starting of Internal Combustion Engines

An original ultracapacitor (UC) based compact electric power source is introduced in the paper. The device employs the synergy between rich energy content of vehicle lead-acid batteries and power capabilities of UCs to allow emergency starting of internal combustion engine in case of a weak battery. The UC-based power source is capable of charging at low rate from the battery and then providing current burst required for proper engine starting. A prototype is designed employing original power circuitry, and a dedicated algorithm for optimal UC charging is developed. The device is successfully used for diesel engine starting, as shown by experimental results.

Average Modeling and Performance Analysis of Voltage Sensorless Active Supercapacitor Balancer With Peak Current Protection

In this paper, average modeling and analysis of a dual-supercapacitor bank, actively balanced by a bidirectional buck-boost converter, is presented. In such a system, natural balancing is achieved when the converter is operated in open loop with 50% duty cycle, eliminating the need for measuring the voltage of each storage device. Nevertheless, excessive currents arise even for slight voltage misbalance because of the highly underdamped nature of the system. In order to remedy this drawback, bidirectional pulse-by-pulse inductor current limitation is introduced, which is equivalent to adding a peak-current-mode-like control loop to the system. Since the duty cycle never exceeds 50%, compensation ramp is not required to maintain stability. On the other hand, while the uncontrolled system dynamics is linear, introducing the current limit mechanism turns the closed-loop dynamics into a nonlinear one, burdening the analysis task and thus calling for suitable average model to perform fast simulations for system analysis. Therefore, dynamical equations of the system are developed in order to derive the switching-cycle-averaged model and reveal the tradeoff between current limit level, balancing time and efficiency for the worst case of imbalance. Simulations and experiments support the presented findings.

Enhancing Low-Throttle-Operation Robustness of ICE-Based APU by Supercapacitor-Realized Virtual Inertia

Low throttle operation of internal combustion engine-based auxiliary power units is desirable under light load to decrease specific fuel consumption. Unfortunately, sudden load increase may lead to voltage collapse and consequent stability lost due to limited total inertia and slow prime mover dynamics. This letter demonstrates that connecting a supercapacitor across auxiliary power unit output terminals is equivalent to increasing total inertia and may enhance low throttle operational robustness. Proposed findings are validated by experimental results.

Active voltage sensorless supercapacitor bank balancer with peak current protection

In this paper, average modeling of a dual-supercapacitor bank, actively balanced by a bidirectional buck-boost converter is presented. In such a system, natural balancing is achieved when the converter is operated in open loop with 50% duty cycle, eliminating the need for measuring the voltage of each storage device. Nevertheless, excessive currents arise even for slight voltage misbalance because of the highly underdamped nature of the system. In order to remedy this drawback, bidirectional pulse-by-pulse inductor current limitation is introduced, which is equivalent to adding a peak-current-mode-like control loop to the system. Since the duty cycle never exceeds 50%, compensation ramp is not required to maintain stability. On the other hand, while the uncontrolled system dynamics is linear, introducing the current limit mechanism turns the closed loop dynamics into a nonlinear one, burdening the analysis task and thus calling for suitable average model to perform fast simulations for system analysis. Dynamical equations of the system are developed in order to derive the switching-cycle-averaged model. Simulations support the presented findings.

Partial shading problem solution for solar arrays fed by MPPT via permanent monitoring of individual panels

Todays PV solar power plants would be unimaginable without Maximum Power Point Tracker (MPPT) electronic scheme increasing significantly energy production. Partial shading of PV panels in a big solar plant including hundreds and thousands those items becomes important problem for MPPT. The results of shading may not be only the proportional diminishing of the total electrical power but that is more seriously the generating multi-extreme power-current (P-I); power-voltage (P-V) curves, disturbing meaningfully the search algorithms of MPPT. Present work proposes the solution for determination of the global maximum position on the operating P-I or P-V curves providing for MPPT algorithm precision information which prevent missteps during optimization procedure. The developed method based on permanent monitoring of PV panels with the subsequent assessment of their solar irradiation and estimation of the global maximum location for the entire group of solar panels.

Energy losses modeling in induction motors fed by Danfoss VF micro drive FC51

The correct selection of appropriate induction motor for a specific electric drive represents an important issue, especially when VFD is applied for the motor supply. A number of different approaches were suggested for this aim. Methods of motors selection that founded on assessment and minimization of energy losses in the motor are preferable, since they provide optimal selection of a motor with a prolonged service time and maximum energy efficiency. There are three different kinds of losses in the motor: cooper resistive losses, mechanical and iron (core) losses. The present work describes the approach of iron losses estimation for a VFD FC51 of Danfoss Company. The method is based on the representation of supplied voltage (current) by the Fourier Transform and analytical description of iron losses by interpolation polynomials.

Optimal control of micro-grid autonomous hybrid power stations based on modeling of stochastic energy consumption

Micro-grid power system becomes today vital reality for many of energy applications including remote habitations areas, military bases, and retranslation and communication equipment and so on. One on the central problem during developments of such systems represents the pressing need to optimize a) the structural design of all facilities including renewable sources (solar), controllable sources (diesel-generator), electrical storage (batteries) and b) control of energy flows inside a system providing optimal efficiency and minimum of fossil fuel consumption. Present works provides the simulation modeling of entire micro-grid system having various parameters of all system components. The special accent was made on the simulation of electrical power consumption models, which was developed taking into account significantly stochastic behavior of energy demands. Simulation modeling was realized by the application of MATLAB/Simulink program software. Stochastic models of energy demands and solar energy possibilities were developed on the base of real data were registered during prolonged period of time in the Negev region of Israel.

Compact energy source for emergency engine staring based synergetic battery-ultracapacitor circuit

The present article presents an original, compact and powerful electric source, synergistically combining ESB and UC for emergency starting of internal combustion engines. The prototype of this device was created on the basis of an original circuit solution; also, a special algorithm for optimal charging of the UC was developed. The prototype was successfully tested with a diesel engine.

Combining Diesel Generators With Ultracapacitors to Enhance Stability and Reliability

Diesel generator based auxiliary power units (DG-APU) are widely used in different civil and military applications. Fuel economy and service life are probably the most important issues concerning their operation. Controlling engine throttle position in accordance with the load power allows regulating fuel supply to the engine to optimize fuel consumption. Despite the advantage of the method, control stability is sacrificed in case of light load operation as follows. When the DG-APU is running with a light load, engine throttle position should be nearly closed in order to minimize fuel consumption. If a load step is applied in such situation, engine velocity may drop sharply until complete stop because of insufficient control system bandwidth. This is why velocity and throttle position of a DG-APU should not be decreased below some level even if load power is low to maintain reliability at the expense of increased specific fuel consumption. Moreover, for small diesel-generators the throttle position is usually fixed. Thereby, relatively wide range load power variations (typical for many of diesel-generator applications) cause excessive fuel consumption.The situation may be sufficiently improved by connecting ultracapacitors (UC) on the DG-APU output terminals, introducing additional inertia allowing smoothing engine velocity decrease during a sudden load increase thus providing more time to the control system to regulate throttle position. As a result, DG-APU would be operated much more efficiently at light loads without sacrificing stability. Moreover, the UC may be used at as starter motor power source, removing starting stress from electrochemical batteries. Present work investigates the improvements in UC-supported DG-APU fuel efficiency and stability compared to conventional technical solutions. The research is based on mathematical modeling of the entire system, verified by experiments. The results support the presented ideas and quantitatively demonstrate the improved fuel economy and reliability of small DG-APUs.Copyright