Showing papers on "Maximum power point tracking published in 1996"

Methodology for optimally sizing the combination of a battery bank and PV array in a wind/PV hybrid system

Abstract: In this paper, a methodology for calculation of the optimum size of a battery bank and the PV array for a standalone hybrid wind/PV power system is developed. Long term data of wind speed and irradiance recorded for every hour of the day for 30 years were used. These data were used to calculate the average power generated by a wind turbine and a PV module for every hour of a typical day in a month. A load of a typical house in Massachusetts, USA, was used as a load demand of the hybrid system. For a given load and a desired loss of power supply probability, an optimum number of batteries and PV modules was calculated based on the minimum cost of the power system.

Dynamic maximum power point tracker for photovoltaic applications

Abstract: A dynamic process for reaching the maximum power point of a variable power source such as a solar cell is introduced. The process tracks maximum power nearly cycle-by-cycle during transients. Information from the natural switching ripple instead of external perturbation is used to support the maximizing process. The method is globally stable for DC-DC power converters, provided that a switching action is present. A prototype boost power converter that uses this method for control can follow power transients on time scales of a few milliseconds. This performance can be achieved with a simple analog control structure, which supports power processing with minimum loss.

Influence of photovoltaic power generation on required capacity for load frequency control

Abstract: We developed a mathematical model to evaluate the impact of small (rooftop) photovoltaic (PV) power-generating stations on economic and performance factors for a larger scale power system, and applied this model to the Tokyo metropolitan area. We used solar radiation data from five local meteorological stations to estimate both the individual and aggregate contributions of the projected PV stations to the local power grid. We found that an electrical power system containing a 10% contribution from PV stations would require a 2.5% increase in load frequency control (LFC) capacity over a conventional system. The break-even cost for PV power generation was found to be relatively high for contribution levels of less than 10%. Higher proportions of PV power generation gave lower break-even costs, but economic and LFC considerations imposed an upper limit of about 10% on PV contributions to the overall power systems.

A new panel-integratable inverter concept for grid-connected photovoltaic systems

Abstract: This paper describes the problems of conventional inverter concepts for photovoltaic power systems and presents a new, panel-integratable inverter concept as a solution. This concept is advantageous regarding safety (no DC-lines), flexibility (modular concept), converted energy per year (no mismatch losses due to individual MPP tracking of each panel) and costs (no reinforced isolation due to AC distribution). Furthermore a 250 W DC to AC inverter is developed, which consists of a series resonant DC-DC power converter and a line inverter. The inverter has a high efficiency and consumes little power itself. Meeting international standards, sinusoidal line current with low distortion is achieved. The inverter has a built-in controller to operate the panel in the maximum power point. Above this, the concept allows the flexible use with many different combinations of solar panels. To realize an inexpensive system, the controller is built up using standard low-cost components.

A study of lead-acid battery efficiency near top-of-charge and the impact on PV system design

Abstract: Knowledge of the charge efficiency of Pb-acid batteries near top-of-charge is important to the design of small PV power systems. In order to know how much energy is required from the photovoltaic array in order to accomplish the task of meeting load, including periodic full battery charge, a detailed knowledge of the battery charging efficiency as a function of state of charge is required, particularly in the high state-of-charge regime, as PV power systems are typically designed to operate in the upper 20 to 30% of battery state-of-charge. This paper presents the results of a process for determining battery charging efficiency near top-of-charge and discusses the impact of these findings on the design of small PV power systems.

A study of equipment sizes and constraints for a unified power flow controller

Abstract: This paper provides a quantitative measurement of the benefit that a unified power flow controller (UPFC) can provide to increase firm power transfer between two large power systems Included is a complete model for a UPFC control system that contains bus voltage control by the shunt inverter, real power transfer between the shunt and series inverters, and real and reactive power control for the transmission line into which the series inverter is inserted A significant part of the model is representation of dynamic limits that coordinate injected current limits for the shunt inverter, power transfer limits between inverters, voltage injection limits for the series inverter, current limits for the series inverter and line voltage limits for the transmission line This paper contains a simple power system simulation to demonstrate the coordinated dynamic control and illustrate issues that power system planning engineers consider in defining applications for a UPFC

Performance of a 10 kW power electronic interface for combined wind/PV isolated generating systems

Abstract: The hoped exploitation of pollution-free, low cost, renewable energy resources has always stirred up interest and inventiveness. The double-input single-output DC/DC power converter discussed in this paper, developed for combined wind-photovoltaic generating systems, aims to mitigate the output power fluctuations due to the intermittent nature of both solar and wind energy. Digital control of the whole apparatus also contributes to optimise the converter modes of operation, running both the energy input circuits at their maximum power level. The paper reports an overall description of the power interface characteristics and experimental results recorded in extensive laboratory tests of a 10 kW rated prototype.

A novel on-line MPP search algorithm for PV arrays

Abstract: A novel maximum power point (MPP) search algorithm for photovoltaic (PV) array power systems is introduced. The proposed algorithm determines the maximum power point of a PV array for any temperature and solar irradiation level using an online procedure. The method needs only the online values of the PV array output voltage and current, which can be obtained easily by using just current and voltage transducers. The algorithm requires neither the measurement of temperature and solar irradiation level nor a PV array model that is mostly used in look-up table based algorithms. Satisfactory results were obtained with the proposed algorithm in a laboratory prototype implementation scheme consisting of a PV array computer emulation model, a chopper controlled permanent magnet DC motor, and a DT2827 data acquisition board with the ATLAB software drivers for interfacing.

Novel grid-connected photovoltaic inverter

Abstract: Detailed analysis and simulation results of a novel solar photovoltaic inverter configuration interconnected to the grid are presented. From the simulation results it is confirmed that the harmonic distortion of the output current waveform of the inverter fed to the grid is within the stipulated limits laid down by the utility companies. Typical hardware aspects are also discussed in detail and the applicability of the design is verified.

Cellular communication system with remote power source for providing power to access points

Abstract: A cellular communication system which eliminates high costs and difficulties associated with providing electrical power to the access points. The cellular communication system includes a remote power source which obviates the need to install an AC power outlet in close proximity to each access point. The remote power source transforms AC power to DC power at a central remote location, and provides as its output one or more low voltage DC power lines. By performing the AC/DC power transformation at a central location, only the low voltage DC power lines need to be fed to each access point. The remote power source also includes a backup power supply feature and an alarm to draw attention to system malfunctions.

PV water pumping with a peak power tracker using a simple six step square wave inverter

Abstract: The application of photovoltaics (PV) has been increasingly popular, especially in remote areas where power from a utility is not available or is too costly to install. PV powered water pumping is frequently used for agriculture and in households. Among many available schemes, the system under study consists of a PV array, a variable-frequency inverter, an induction motor, and a water pump. The inverter feeds the induction motor, which drives the water pump. To seek the optimum power output of the PV array, the inverter is operated at variable frequency to vary the output of the water pump. The inverter is operated to generate a six-step quasi-square wave instead of a pulse width modulated (PWM) voltage output to reduce the switching losses. The inverter acts as both a variable-frequency source and a peak-power tracker of the system, thus having the number of switches minimized. The system is a low-cost design with a simple control strategy. The direct current (DC) bus is supported by a DC capacitor; thus, a balance-of-power flow must be maintained to avoid the collapse of the DC bus voltage. Another advantage of the system is that the current is limited to an upper limit of the PV array current. Thus, in case a short circuit is developed, the motor winding and the power semiconductor switches can be protected against excessive current flow.

DSP-based controller application in battery storage of photovoltaic system

Abstract: Photovoltaic power systems normally use maximum power point tracking (MPPT) to continuously deliver the highest possible power to the load when changes in insolation and temperature occur. This overcomes the problem of mismatch between the solar cells and the given load. The solar array is normally treated as a voltage source, but it is treated as a current source in this paper. A simple method of tracking the maximum power point (MPP) and forcing the PV power system to operate near this point is also presented. The effect of the negative impedance of power converters on the MPPT process is also considered. As to the system equivalent circuit model, the principle of energy conservation is used to develop large- and small-signal models and the transfer function. By using this model, the drawbacks of the state-space-averaging method can be overcome. A TI320C25 digital signal processor (DSP) was used to implement the proposed MPPT controller; simulations and experimental results show its excellent performance.

Active power conditioner for reactive and harmonic compensation having PWM and stepped-wave inverters

Abstract: An active power quality conditioner for compensating reactive power and harmonic distortion in power systems. A pulse width modulated (PWM) inverter (70) for each phase is controlled to produce a harmonic distortion compensation signal that is coupled to an inductor. The inductor is connected in series between a stepped-wave inverter (84) and one phase of the power line. A current produced by the stepped-wave inverter compensates for the reactance of a load coupled to the power line. The PWM inverter operates at a frequency that is substantially greater than the fundamental frequency of the power line and is not exposed to the full power line voltage; it can be constructed using components of relatively low power and voltage rating. In contrast, the stepped-wave inverter, which is decoupled from the PWM inverter, operates at the fundamental frequency and is subjected to most of the stress. Both shunt coupled and series coupled compensators are described. Compensation for an unbalanced load is provided using a compensator (364) that includes a 24-pulse stepped-wave inverter (366).

Fault tolerant power distribution system

Abstract: A power distribution circuit is provided that isolates both power source and load faults. In one embodiment, the power distribution circuit includes two power MOSFETs connected with the channels of the power MOSFETs in series and having their gates electrically connected together. The body diode of one power MOSFET is aligned with the opposite polarity with respect to polarity of the body diode of the second power MOSFET. The power MOSFETs are adapted to be coupled between a first power source and a load. The power distribution circuit also includes a first sensor that detects when the power MOSFETs conduct too much current and switches the power MOSFETs off by discharging the gate voltage of both power MOSFETs during such overcurrent conditions. Accordingly, when both power MOSFETs are switched off, the opposing polarity of the body diodes in the power MOSFETs ensures that one of the body diodes will be reversed biased in case of a short circuit failure in either the load or the power source. Incorporating N such power circuits in a power distribution module for distributing power from N power sources to a single load provides a fault tolerant power distribution module that can tolerate up to N-1 power source faults.

Delay and power expressions for a CMOS inverter driving a resistive-capacitive load

Abstract: A delay and power model of a CMOS inverter driving a resistive-capacitive load is presented. The model is derived from Sakurai's alpha power law and exhibits good accuracy. The model can be used to design and analyze those inverters that drive a large RC load when considering both speed and power. Expressions are provided for estimating the propagation delay, transition time, and short circuit power dissipation for a CMOS inverter driving resistive-capacitive interconnect lines.

A new peak power tracker for cost-effective photovoltaic power system

Abstract: Solar arrays are the most expensive components in photovoltaic power systems. Thus solar arrays should be operated at their maximum power point in order to reduce the overall cost of the power system. This paper presents a new peak power tracker (PPT) which forces a PV power system to extract the maximum power from solar arrays, regardless of the change of load demand, insolation and temperature. The benefits of the PPT are simplicity, cost-effectiveness and flexibility.

A bifunctional utility connected photovoltaic system with power factor correction and UPS facility

Abstract: In this paper, a novel utility connected photovoltaic power generation system with unity power factor and uninterruptable power system facility and its control strategy are proposed. The proposed photovoltaic (PV) system is connected in parallel between the utility and load. The PV system provides an uninterruptable voltage to the load, a maximum power tracking to solar array, and power factor correction to the utility. The proposed system has the following advantages compared with the conventional utility connected PV system: harmonic elimination function; feeding the photovoltaic energy to the utility; and providing the uninterruptible power source battery to the load. In the case where the photovoltaic array system is in a state of poor power generation, the battery and capacitor of the PV system are charged by a three phase utility source and the inverter in the PV system only provides the reactive current to eliminate the harmonic current exited on the utility. In the normal operation mode, the PV system supplies active power to the load and reactive power to the utility in order to maintain the unity power factor and to regulate AC load voltage.

Maximum power point tracking with temperature compensation of photovoltaic for air conditioning system with fuzzy controller

Abstract: Fuzzy control has received a great deal of attention due to its excellent behavior when applied to complex and nonlinear system. As fuzzy theory is close to human reasoning, fuzzy controllers are easy to design and cheap to produce. In this paper, we investigate the possibilities of P/sub max/ control using the fuzzy controller, and we also examine the optimal power converter using a step-up chopper circuit to operate the solar cell at an optimal voltage of compensated voltage (i.e. of determined transducer by temperature (-40/spl deg/C/spl sim/+100/spl deg/C)). The proposed step-up maximum power point tracking (MPPT) system is studied by simulation and is implemented by using a microcomputer which controls the duty ratio of an IGBT boost converter.

Advantage of boost vs. buck topology for maximum power point tracker in photovoltaic systems

Abstract: Electrical systems employing solar cells as the energy source are designed to be operated at the point of maximum power of the solar cells. To track this point as the solar radiation and temperature vary, a maximum-power-point-tracker (MPPT) is used. Most MPPT are based on a DC to DC converter of the buck or boost types. In this article we compare the energy efficiency of these converters and show that an MPPT based on the boost converter configuration results in higher output power, thus better utilizing the solar cells.

The AC photovoltaic module

Abstract: This paper describes the design, development and performance of a large-area photovoltaic module whose electrical output is AC power suitable for direct connection to the utility grid. The AC PV module, developed with support from the US DOE and NREL under the PV:BONUS Program, incorporates a dedicated, integrally mounted, high-efficiency 250 Watt DC-to-AC inverter that is fully compatible with 120 V, 60 Hz utility power. We call this concept an AC photovoltaic module or in context, simply an AC Module. Because of its ease of use and wide appeal, the AC PV module may be considered the first photovoltaic appliance. The module's output may be connected directly to a building's conventional AC distribution system without need for DC wiring, string combiners, DC ground-fault protection or additional power-conditioning equipment. The AC module has the potential to become the first photovoltaic power "building product", as it can be marketed as a complete, packaged solution for the emerging residential rooftop and commercial demand-side management markets.

Uninterruptible power supplies having cooled components

Abstract: Methods and apparatus for uninterruptible power supply (UPS) systems (30) are provided. The UPS systems (30) are configured to provide the advantages of an in-line device, and operate in a quasi-standby mode. The UPS (30) includes a rectifier unit (44) and inverter (48) arranged to nominally deliver a portion (38, 46, 50) (e.g. up to about 20 %) of the primary AC power supply (32) to a critical load (52) through an output transformer (42). The rectifier unit (44) preferably includes internal energy storage capabilities, such as a capacitor and inductor. The remaining portion (36) of the AC power supply is nominally supplied directly to the critical load (52) and is controlled by a transfer switch (40) and the output transformer (42). When a fault is detected in the main AC power supply (32), the transfer switch (40) switches to a faulted position and power is supplied from the rectifier inductor and capacitor or from a battery (56) to the load through the inverter (48). Electronic switches (54) such as MOSFETs are provided in the system to control the supply of power from the battery (56) (or other energy storage device) to the inverter (48) and to control the charging and discharging of the battery. The inverter (48) and MOSFETs (54) are designed to withstand transient overpower and overcurrent operation without deleterious consequences by liquid cooling the inverter (48) or the inverter (48) and the MOSFETs (54) under predetermined conditions to temperatures between about 60 K and 270 K.

Photovolatic power converter

Abstract: PROBLEM TO BE SOLVED: To provide a power converter which can use a safe small-sized filter for system interconnection, because the input and output of the converter are insulated from each other, and can be used for low-voltage solar batteries. SOLUTION: A photovoltaic power converter is constituted to convert the power generated from a solar battery 12 into three-phase AC power and provided with a first power converter 11 which converts DC power from the battery 12 into AC power, a transformer 10 which inputs the output of the converter 11 through its primary side and outputs an insulated output from the secondary side, and (3×n) sets of second power converters 1 which convert the insulated power from the transformer 10 into single-phase AC power. The single-phase AC output terminals of the converters 1 are divided into three units, with each unit being composed of (n) sets of output terminals connected in series, and the units are connected in star connection by using any terminal of the output lines of the units as a neutral point. The other terminals of the three output lines are connected to a system power source 19 and the AC outputs among the three units are subjected to multiplex PWM pulse width modulation so that the AC outputs can be shifted from each other by electrical angles of 120 deg. and regenerated to the source 19.

Variable Speed Operation of Permanent Magnet Alternator Wind Turbines Using a Single Switch Power Converter

Abstract: Advantages of operating wind turbine generators at variable speed are well known. Various approaches have been proposed to extract maximum power from the turbines by operating them at the optimum tip-speed ratio. Often, they feature a three-phase controlled rectifier d-c link followed by a three-phase inverter type of power converter topology to deliver constant frequency a-c output power from a variable speed generator coupled to the turbine. However, in stand-along power supply applications for remote sites, where the power level is a few kW or less, this approach is economically unjustifiable. This paper presents a single switch power electronic converter to regulate the power output of a permanent magnet alternator driven turbine feeding a battery, featuring minimal additional costs suitable for low power applications. Power converter operation and a control strategy to maintain optimum tip-speed ratio are discussed in the paper. Computer simulations of the complete system verifying the proposed concepts are presented.

Development and testing of a 20 kW grid interactive photovoltaic power conditioning system in Western Australia

Abstract: A prototype current controlled power conditioning system has been developed and is being tested on a weak rural feeder line at Kalbarri, about 600 kilometers north-west of Perth in Western Australia. This system sources 20 kW of power from three photovoltaic arrays with a maximum power point tracking control. In addition, it provides voltage support for the grid at Kalbarri by varying its reactive power in response to the measured voltage at the point of connection. This paper describes the development and testing of the power conditioning system.

Performance analysis of a solar water pumping system

Abstract: The performance of a solar water pumping system is discussed in this paper, The system consists of a photovoltaic (PV) array, a permanent magnet (PM) DC motor and a helical rotor pump. The operation of the PV array is analysed using PSPICE. The efficiency of the system is improved with a maximum power point tracker (MPPT) and a sun-tracker. Simulation and field test results are presented.

Power generation controller for hybrid vehicle

Abstract: PROBLEM TO BE SOLVED: To control generated power of a engine-drive generator so that the power may always satisfy the required power performance of a vehicle, while preventing the overcharge and overdischarge of a battery. SOLUTION: A power generation controller for hybrid vehicle which makes power supply and regeneration between a battery 4 and a running motor 5, and, at the same time, supplies the electric power generated from an engine- driven generator 2 to the battery 4 and motor 5, discriminates the state of the battery 4 based on the chargeable and dischargeable power of the battery 4, the maximum driving force and maximum regenerated power of the motor 5, and the maximum generated power of the generator 2. The controller further decides the generated power of the generator 2 based on the discriminated results of the state of the battery 4. Therefore, the controller can decide the optimum generated power of the generator 2 in accordance with the state of the battery 4, and can satisfy the driving force required for a vehicle while preventing the overcharge and overdischarge of the battery 4.

Power generation method and power generator using a piezoelectric element, and electronic device using the power

Abstract: A power generator using a piezoelectric element is provided which generates electric power at a high efficiency. It has been determined that the efficiency of power generation varies as a function of the ratio of an initial unloaded value of the power generator to a prescribed voltage of the input of an electric power system. A high power generation efficiency can be obtained when the voltage ratio is in the range of approximately two to twenty. In particular, when the voltage ratio is in the range of approximately four to six, a maximum power generation efficiency can be obtained. The invention provides a small-sized, high performance power generator which can be used in practice in portable electronic devices or the like.

Evaluation of converter topologies for improved power quality in DC traction substations

Abstract: A high power converter is developed for improved power quality in DC traction substation applications. The proposed converter can be used as both an inverter and an active power filter (APF). As an inverter, it can recycle regenerative energy caused by decelerating trains and as an APF, it can compensate for harmonic distortion produced by the rectifier substations. This paper evaluates the different topologies which can be used to implement this converter. A multilevel topology for the converter is considered because of the high power and high dynamic bandwidth requirements. A comparison is made between using a multilevel inverter and using a combination of a multilevel chopper and a lower voltage inverter.