Maximum Efficiency Point Research Articles

Maximum Efficiency Control of PMSM Drives Considering System Losses Using Gradient Descent Algorithm Based on DC Power Measurement

This paper proposes a novel method of efficiency improvement in a vector controlled permanent magnet synchronous motors (PMSM) through system level maximum efficiency point determination using current angle as a control variable. Loss models for the inverter and the motor fundamental and harmonic losses, which are capable of being solved online using available terminal measurements in the system are initially developed. The loss models and dc-link power measurement are then used to seek the maximum efficiency angle for different operating conditions using a gradient descent optimization algorithm. The developed method is robust against changes in inductances due to saturation and cross saturation with loading conditions as well as temperature effects. The effectiveness of the developed method in improving the system efficiency is verified and compared with conventional maximum torque per ampere method. The proposed strategy has been validated on a laboratory interior PMSM, and the efficiency has been calculated for different speed and torque conditions. The experimental validations confirm the effectiveness of the proposed solution in improving the motor drive system energy efficiency.

Investigations on the influence of ethanol and water injection techniques on engine's behavior of a hydrogen - biofuel based dual fuel engine

This work explores the influence of hydrogen and ethanol on improving engine's behavior of Maduca longifolia oil (MO) based dual fuel diesel engine. A mono cylinder diesel engine was tested in dual fuel mode of operation at the rated power output of 3.7 kW under variable hydrogen energy shares from 0 to the maximum allowable limit (until severe knocking i.e. upto 20%). The knock limit was further extended by injecting water and ethanol at the intake manifold and the engine's performance, emission and combustion characteristics were analyzed. In addition ethanol was also injected and introduced along with the intake air for comparison with hydrogen dual fuel mode. Dual fuel operation increased the BTE from 25.2% with neat MO to a maximum of 28.5% and 30% respectively with hydrogen and ethanol for the energy share of 15% and 38% where as the BTE was 30.8% with ND. The smoke opacity was reduced from 78% with neat MO to 58% for the hydrogen energy share of 15% which is the MEP (maximum efficiency point) whereas the smoke emission was noted as 51% with ND operation. However, hydrogen induction increased the NO (nitric oxide) emission. Injection of water and ethanol at the inlet was observed to extend the knocking limit with improved BTE. The BTE reached a maximum of 30.1% with 5% water and 30.8% with 10% ethanol injection. The MEPs were arrived as 31% and 30% hydrogen energy shares respectively with 5% water and 10% ethanol injection. It was concluded that hydrogen induction can be very effective in improving the diesel engine's performance when using MO as base fuel when operating on dual fuel mode. The performance could be improved by extending the knock limit by injecting ethanol and water along with hydrogen.

Optimal Performance Characteristics of Subcritical Simple Irreversible Organic Rankine Cycle

Based on the theory of finite time thermodynamics, a subcritical simple irreversible organic Rankine cycle (SSIORC) model considering heat transfer loss and internal irreversible losses is established in this paper. The total heat transfer surface area is taken as a constraint, and R245fa is adopted as working fluid of the cycle in the performance optimization. The evaporator heat transfer surface area and mass flow rate of the working fluid are optimized to obtain the maximum power output and thermal efficiency of the SSIORC, respectively. In addition, the influences of the internal irreversibilities on the optimal performances are also investigated. The results show that when the evaporator heat transfer surface area is varied, the relationship between power output and thermal efficiency is a loop-shaped curve, and there exist maximum power output and thermal efficiency points, respectively. However, the two maximum points are very close to each other. When the mass flow rate of the working fluid is varied, the relationship between power output and thermal efficiency is a parabolic-like curve. With the decreases of expander and pump irreversible losses, the performances of the irreversible SSORC are close to those of the endoreversible SSORC with the only loss of heat transfer loss.

Effect of viscosity on the external characteristics and flow field of a molten salt pump in the view of energy loss

The performance of molten salt pump is affected by its geometrical structure and the physical properties of delivered fluids. In order to reveal the effects of these factors on pump performance, the performance curves were analyzed theoretically, the flow field was measured accurately by using high-speed photography, and the external characteristics were tested by using water as test medium. The numerical model was verified by the path lines, absolute velocity and performance curves obtained by experiment. Based on the verified model, the relationship among the fluid viscosity, external characteristics and flow field was investigated in the view of energy loss. The results show that reducing the blade outlet angle and outlet width as well as increasing the blade outlet thickness can avoid the unstable running. When delivering low viscosity fluids, since the impact loss is relatively large at low flow rate, the hump is easy to appear in the Head-Flow rate curve. When delivering high viscosity fluids, the opposite happens. With the increase of viscosity, the head and efficiency decrease monotonously, and the maximum efficiency point moves towards low flow rate. At the low flow rate, the shaft power decreases as the viscosity increases, while at the high flow rate, the shaft power increases as the viscosity increases. Compared with delivering water, when the viscosity is lower than 0.01453Pa⋅s, the drop of head and efficiency is less than 5%. The results of the study have reference significance on the development of high-performance molten salt pump and stable operation.

Maximum Efficiency Tracking in Inductive Power Transmission Using Both Matching Networks and Adjustable AC–DC Converters

The maximum efficiency point of an inductive power link depends on its load power consumption and the distance between the transmitter and the receiver. Matching networks (MNs) and adjustable ac–dc converters have been proposed in the literature as a means to achieve and track this maximum efficiency point. Most of the published papers in inductive power transmission only use one of these two methods without considering a joint design. In this paper, we analyze and compare both methods proposing a general joint design which exploits the advantages of each method. A proof-of-concept system was developed following the proposed flow, built and tested. This system, with a regulated output voltage, presents improvements in measured efficiencies of up to 80% (from 9.2% to 16%) at the largest distances, thus maximizing the distance range. The same approach can be used to maximize output dc voltage, instead of the link efficiency. The proposed system using our designed MN achieved a maximum output voltage that was 90% higher (from 1.36 to 2.59 V) than the case where only a step-up converter was used.

Numerical simulation of the performance of a low-head prototype Kaplan turbine

The opening degrees of guide vane and runner blade are adjustable for Kaplan units. Therefore, the prototype unit performance is evaluated by cam curves to ensure the maximum efficiency points at different runner blade or guide vane angles. In this paper, the numerical simulation method is used to obtain the cohesive curves. The gravity force term is not ignored in the calculation, of which the effects are analysed not only on prototype performances, but also on internal flow characteristics such as the streamlines around runner blades, the pressure distributions and the head losses of each part.

Low-Cost Maximum Efficiency Tracking Method For Wireless Power Transfer Systems

This paper presents a novel maximum efficiency point (MEP) tracking method for wireless power transfer (WPT) systems. It is proved that at the MEP for a typical system containing a boost converter on the receiving end, the derivative $dD/d{V_{{\text{in}}}}$ ( ${V_{{\text{in}}}}$ being the inverter's dc input and $D$ being the duty cycle of the converter) is equal to or smaller than a constant $\beta $ that is determined by system parameters. By tuning ${V_{{\text{in}}}}$ and comparing $dD/d{V_{{\text{in}}}}$ with $\beta $ , the MEP can be tracked without a power or current sensor, hence reducing the tracking cost. A WPT system is demonstrated experimentally to verify the method. When the diameters of and the vertical distance between the transmitting and receiving coils are 4.3 and 2.35 cm, respectively, without horizontal misalignment, high efficiency is maintained even when the load ranges from 5 to 100 Ω, and the efficiency improvement reaches 41.2% when compared to the measured efficiencies without the proposed method. The differences between the maximum efficiencies tracked by the proposed method and the manually searched maximum values are at most 1.8%. Extension of the proposed method to WPT systems employing other popular forms of inverter, dc/dc converter, and coil topology is also presented.

Pulse Density Modulation for Maximum Efficiency Point Tracking of Wireless Power Transfer Systems

Maximum efficiency point tracking (MEPT) control has been adopted in state-of-the-art wireless power transfer (WPT) systems to meet the power demands with the highest efficiency against coupling and load variations. Conventional MEPT implementations use dc/dc converters on both transmitting and receiving sides to regulate the output voltage and maximize the system efficiency at the expense of increased overall complexity and power losses on the dc/dc converters. Other implementations use phase-shift control or on-off control of the transmitting side inverter and the receiving side active rectifier instead of dc/dc converters but cause new problems, e.g., hard switching, low average efficiency, and large dc voltage ripples. This paper proposes a pulse density modulation (PDM) based implementation for MEPT to eliminate all the mentioned disadvantages of existing implementations. Delta-sigma modulators are used as an example to realize the PDM. A dual-side soft switching technique is proposed for the PDM. The ripple factor of the output voltage with PDM is derived. A 50 W WPT system is built to validate the proposed method. The system efficiency is maintained higher than 70% for various load resistances when the power transfer distance is 0.5 m, which is 1.67 times the diameter of the coils.

Modeling and Dynamics of HTS Motors for Aircraft Electric Propulsion

In this paper, the methodology of how a dynamic model of a conventional permanent magnet synchronous motor (PMSM) may be modified to model the dynamics of a high-temperature superconductor (HTS) machine is illustrated. Simulations of a typical PMSM operating under room temperature conditions and also at temperatures when the stator windings are superconducting are compared. Given a matching set of values for the stator resistance at superconducting temperature and flux-trapped rotor field, it is shown that the performance of the HTS PMSM is quite comparable to a PMSM under normal room temperature operating conditions, provided the parameters of the motor are appropriately related to each other. From these simulations, a number of strategies for operating the motor so as to get the propeller to deliver thrust with maximum propulsive efficiency are discussed. It is concluded that the motor–propeller system must be operated so as to deliver thrust at the maximum propulsive efficiency point. This, in turn, necessitates continuous tracking of the maximum propulsive efficiency point and consequently it is essential that the controller requires a maximum propulsive efficiency point tracking (MPEPT) outer loop.

Decoupled control of wireless power transfer: Eliminating the interdependence of load resistance and coupling to achieve a simple control framework with fast response times

Wireless power transfer (WPT) is an exciting technology that attempts to transfer energy via loosely coupled inductors. This paper suggests an automated system in which load side impedance matching is utilized to regulate power to a variable load. Such a scheme requires proper selection of topology and component values so that reactance is not a function of load resistance or coupling. Since the maximum power point (MPP) and maximum efficiency point (MEP) do not arise at the same load resistance, careful selection of resistance must be made so efficiency is maximized while target power is maintained. The result is a system that is quick, accurate, simple, robust, and operates without the need of a backward communications link.

High efficiency design of an impulse turbine used in oscillating water column to harvest wave energy

Abstract Wave energy harvesting systems mostly have low power production capability because of unoptimized design of the system components. A bidirectional flow impulse-turbine used in such a system has efficiency less than 40%, and it is required to design the turbine for a higher efficiency. Present work finds an optimal design and shows design-variable sensitivity to the turbine efficiency. The problem is solved using numerical analysis technique. The flow through the turbine was analyzed by solving the Reynolds-averaged Navier-Stokes equations (RANSE). The design variables; namely number of rotor blades and number of guide vane, guide vane angle and guide vane profile were modified to maximize the turbine efficiency. Using the Latin hypercube sampling technique, sample points were selected from a design space defined by lower and upper limits of the variables. Then, several surrogates were constructed using the RANSE calculated results, and the turbine performance was optimized. The results show that guide vane angle is the most sensitive parameter, while the guide vane profile has negligible effect on efficiency. A hybrid genetic algorithm searched the optimal design point. The relative mean efficiency enhancement over a wide range of flow coefficient was approximately 24%, while it was 28% at maximum efficiency point.

Thermodynamic analysis of a combined power/refrigeration cycle: Combination of Kalina cycle and ejector refrigeration cycle

In the present study, a new power and refrigeration cycle is investigated which is a combination of a Kalina cycle and an ejector refrigeration cycle (ERC). In the proposed configuration of the combined cycle, an ejector refrigeration cycle is inserted into the Kalina cycle to recover heat from ammonia poor solution which leaves the separator at high temperature/pressure and does not contribute to power generation in Kalina cycle Working fluid of the Kalina cycle and ERC are ammonia-water solution and R134a, respectively. The combined cycle is simulated by EES software and details of the applied mathematical model and developed simulation program are extensively reported. The effect of five key operational parameters of the combined cycle (i.e. turbine inlet pressure, turbine inlet temperature, concentration of ammonia-water basic solution, condenser outlet temperature and pressure of refrigerant in heat exchanger) on the combined cycle performance parameters (refrigeration capacity, power production, thermal efficiency, exergy of produced power, exergy of refrigeration and exergy efficiency) is analyzed and physical mechanisms behind the determined results are reported. Additionally, variation of performance parameters with heat exchanger pressure is examined with different refrigerants (R134a, R152a and R290) to determine the effect of refrigerants on system performance. The results show that thermal efficiency of the combined cycle increases with increasing turbine inlet temperature and concentration of ammonia-water solution but decreases with rising condenser outlet temperature and heat exchanger pressure. A maximum thermal efficiency point is determined in the analyzed range of the turbine inlet pressure. Exergy efficiency increases with rising turbine inlet pressure, turbine inlet temperature and concentration of ammonia-water solution but decreases with increasing condenser outlet temperature and heat exchanger pressure. Refrigeration capacity and thermal efficiency results of the combined cycle are the highest for the operation of ERC with R290 and the lowest with R134a. Exergy efficiency is the lowest for ERC operation with R290 and the highest with R134a.

Achieving Efficiencies Exceeding 99% in a Super-Junction 5-kW DC–DC Converter Power Stage Through the Use of an Energy Recovery Snubber and Dead-Time Optimization

A highly efficient 5-kW bidirectional dc–dc converter power stage operating from a 400-V supply implementing super-junction (SJ) metal–oxide–semiconductor field-effect transistor (MOSFETs) is presented. SJ MOSFETs have low on-state resistances and low switching losses. However, their application in voltage-source converters can be compromised by the reverse recovery behavior of their intrinsic diodes and their highly nonlinear output capacitances. A series switching-aid circuit is used to control the output capacitance charging current. The dead times between switching transitions are assessed and optimized in order to deactivate the intrinsic diodes. The combination of these techniques enables very high efficiencies to be attained. Calorimetric measurements indicate a full-load efficiency of 99.1% for the prototype 5-kW dc–dc converter power stage. A loss reduction of approximately 50% is achieved with the prototype converter power stage when compared to an equivalent insulated-gate bipolar transistor (IGBT)-based power stage. Lastly, a loss versus duty cycle function is experimentally determined, which can be used to inform the design of a maximum efficiency point tracking system.

Impact of oxygen enrichment on the engine's performance, emission and combustion behavior of a biofuel based reactivity controlled compression ignition engine

Diesel engine with RCCI (Reactivity Controlled Compression Ignition) finds the next generation technology in engine research for combusting slow burning fuels such as vegetable oils and arriving extremely lower levels of smoke and NO (Nitric Oxide) emissions simultaneously. An attempt was made to operate a diesel engine on RCCI mode by injecting ethanol as low reactivity fuel at the intake manifold of the engine using sunflower based Waste Cooking Oil (WCO) as high reactivity fuel under oxygen enriched intake air. The influence of the combined effect of oxygen enrichment and RCCI mode on engine's behavior was studied using WCO as the high reactivity (main) fuel. Significant improvement (upto 33.5% with RCCI mode from 29.1% with neat WCO at peak power) in BTE (brake thermal efficiency) with drastic reduction in smoke (upto 48% with RCCI at the maximum efficiency point from 69% with neat WCO at peak power) and NO were achieved with injection of ethanol under RCCI mode when using WCO as base fuel mainly at high loads (power outputs). Combining oxygen enrichment with RCCI resulted in further improvement in BTE (upto 36.2%) and reduction in smoke (upto 37% at the maximum efficiency point), HC and CO emissions at all power outputs. Peak pressure and energy release rate were found to be superior with RCCI mode with EF (electronic fuel) injection of ethanol associated with oxygen enriched combustion. It is concluded that RCCI operation with injection of ethanol combined with oxygen enrichment could be preferred for very high BTE, lowest smoke and NO emissions using WCO as base fuel. The optimal level of low reactivity fuel blending with high reactivity WCO could be at the ethanol energy share of 25% for the highest thermal efficiency at peak load. The optimal oxygen concentration of 23% by volume could be preferred for best performance of the engine fueled with WCO as main fuel.

Automatic tuning of the switching frequency for efficiency maximization in an ESS-PV hybrid PCS

An automatic switching frequency tuning algorithm (ASTA) for a real-time condition is proposed. The primary aim is to maximize the power efficiency of a power electronic system. The power loss of a hard-switched power converter is determined by the power loss in power semiconductor devices, magnetic devices, capacitors, etc. Switching frequency of a power converter is one of the parameters which influence the power loss. The parameters which determine the maximum-efficiency point can vary with the ageing of devices and the change in environmental conditions. In this paper, a PWM-carrier frequency is utilized for efficiency maximization of a power conversion system. By varying the PWM-carrier frequency from the minimum to maximum value to search for the switching frequency associated with the point of maximum efficiency, this algorithm is designed for a hybrid-energy power conversion system which consists of DC/DC converters and a DC/AC inverter. For the realization of this algorithm, real-time power metering for efficiency calculations is realized by software, which requires no cost increase as the method shares the voltage-and-current sensing circuits with the converter control unit. The metering algorithm has tolerance of less than 1% over a wide load range. The experimental results present efficiency data captured during the operation of the ASTA algorithm in wide ranges of switching frequencies.

Megahertz Multiple-Receiver Wireless Power Transfer Systems With Power Flow Management and Maximum Efficiency Point Tracking

This paper presents systematic analysis and design of a megahertz multiple-receiver (RX) wireless power transfer (WPT) system driven by a Class E power amplifier. Both circuit-level and system-level analyses are conducted to discuss the characteristics of the WPT system. In order to simultaneously manage the power flow and maximize the overall system efficiency, a new control scheme is proposed that combines maximum efficiency point tracking and time-division multiplexing. Through the proposed scheme, RXs with different loading and coupling conditions can be charged by the same transmitter with simplified design and control strategy. Finally, the proposed control scheme is validated using an example 6.78-MHz three-RX WPT system. The experimental results show that various power requirements can be quickly and stably satisfied, and the overall average system efficiency can reach as high as 71.7%.

Maximum Efficiency Point Tracking (MEPT) for Variable Speed Small Hydropower Plant With Neural Network Based Estimation of Turbine Discharge

The paper presents the control system of a small hydropower plant (SHP) working at variable speed operation (VSO). In general, VSO increases the turbine operating discharge and gives higher efficiency over a wide operating range. It is particularly advantageous under conditions different from the original design conditions. Changing of the hydrological conditions requires adjustments to the control system; therefore, the new maximum efficiency point tracking (MEPT) algorithm is proposed. The MEPT algorithm implemented in the load controller employs the gradient method. The water level governor based on the PI controller combined with the adaptive load controller is analyzed. The troublesome measurement of the turbine discharge is replaced by the neural-network-based estimator. The correlation analysis of the system parameters was performed by using principal component analysis. The proposed algorithm was implemented in the programmable logic controller and tested on a real low-head SHP of 150 kW power with two single-regulated propeller turbines.

Studies on performance, combustion and emission of a single cylinder diesel engine fuelled with rubber seed oil and its biodiesel along with ethanol as injected fuel

Alcohols are gaining interest as an alternate biofuel for compression ignition engines because they contain oxygen and are produced using biomass. Since they have lower cetane number, they are suitable for premixed combustion applications. In this investigation, the authors have tried to improve a single cylinder diesel engine’s performance by injecting ethanol into the intake port during the suction stroke. Rubber seed oil (RSO), rubber seed oil methyl ester (RSOME) and diesel are the primary fuels injected directly into the combustion chamber. The injection timing and duration of ethanol injection were optimized for dual fuel operation. The results indicate that increasing ethanol quantity with RSO and RSOME lead to an increase in brake thermal efficiency and reduction in smoke emissions. The maximum brake thermal efficiency achieved at full load is 31%, 29.9% and 29.3% with diesel, RSOME and RSO at ethanol energy shares of 35.2%, 33.5% and 31.6%, respectively. Smoke reduces by 44.26% with RSO, 43.63% with RSOME and 26.47% with diesel at maximum thermal efficiency point. However, HC, CO, and NOx emissions increases with increase in ethanol energy share at all loads. Peak pressure and maximum rate of pressure rise increases with increase in ethanol injection. Combustion duration reduces with ethanol injection, which in turn contributes to a higher heat release rate.

Standalone fuel cell generation system with different tracking techniques: economic analysis

The proton exchange membrane fuel cell (PEMFC) can be operated at different points such as the maximum power point (MPP) to extract maximum power and the maximum efficiency point (MEP) to operate at maximum efficiency. However, the different tracking techniques influence the cost of electricity (COE) of the fuel cell generation system. In this paper, the economic analysis of the PEMFC with the MPP tracking (MPPT) and MEP tracking (MEPT) techniques using the HOMER energy system analysis software is presented. A detailed comparison of the economic impact of the tracking techniques for ten load configurations of a standalone fuel cell generation system, which includes combined heat and power (CHP) loads is presented and discussed. Finally, based on economic considerations, a procedure to select a suitable tracking technique for particular requirements of the standalone PEMFC application is proposed. It is found that in the case of CHP configuration, the MPPT technique is the preferred technique to achieve low COE.

Sub-system level numerical simulation investigation of the S-shaped inlet and the rear subsonic fan-stage

For investigating the evolution process of a half flush-mounted air intake exit distortion in the downstream flow field and also its effects on the fan-stage performance, sub-system level numerical simulation of the whole structure of the air intake and the fan-stage was carried out. Considering large boundary layer ingestion, a scheme that bleeding air from stator for blowing control in the front air intake was also proceeded. At the same time, both the single fan-stage with uniform air admission and the single airintake without fan-stage are researched for comparison. The results show that giving a real exit boundary or not has significant impact on the airintake numerical simulation results, especially to the circumferential total pressure distortion and the swirl distortion at the airintake exit. Due to large boundary layer ingesting, the aerodynamic performance of the fan-stage declines a lot. As comparing with the homogeneous air admission condition, the maximum isentropic efficiency and the choked mass flow of the fan-stage decrease about 4.17% and 1.31%, respectively. After bleeding air from the stator, the overall performance of the fan-stage changes significantly. It improves a lot when the fan-stage works between the maximum efficiency point and the stall margin while decreases under other conditions. The distorted low energy fluid from upstream always covers several passages as it goes through the fan-stage. And in the meanwhile, severe flow separation appears at suction side of stator blades, no matter the bleed air flow control executed or not. Impact of the design of the bleed air pipe on the control effect is large, and the best bleed air pipe for flow control is needed to further research in the future.