Constant Power Operation Research Articles

An Electric Vehicle-Oriented Approach for Battery Multi-Constraint State of Power Estimation Under Constant Power Operations

An Electric Vehicle-Oriented Approach for Battery Multi-Constraint State of Power Estimation Under Constant Power Operations

D-Q-axis magnetic field design and investigation of asymmetrical multi-layer flux barriers PM motor for speed regulation enhancement

In this paper, an asymmetrical multi-layer flux barriers permanent magnet (AMFB-PM) motor is proposed. The key of this study is to design the d-q-axis magnetic field reasonably. Firstly, the influence of d-axis inductance on the constant power speed range is analyzed. To optimize the constant power speed regulation performance, an asymmetric flux barrier is employed to adjust the saturation degree of the d-axis magnetic circuit under flux-weakening state. Additionally, the introduction of the asymmetrical flux barrier enables directional deflection of reluctance torque, thereby enhancing the output torque. The analysis results verify the effectiveness of the asymmetrical flux barrier design, which provide a wide speed regulation with constant power operation and high torque density for PM motors.

Multi-condition operating characteristics and optimization of a small-scale ORC system

The multi-condition operating characteristics of an organic Rankine cycle (ORC) are crucial to the development of the practical unit. This work developed a steady-state model of a small-scale ORC prototype built and tested in the lab. The influence of heat source/sink parameters, component design, and operation strategies are analyzed. It is found that the optimal output power and thermal efficiency correspond to the similar expander rotating speed but diverse working fluid mass flow rate. The higher mass flow rate is beneficial to the output power whereas deteriorates the thermal efficiency. Heat source temperature and flow rates mainly affect the unit output power while the ambient temperature and humidity influence both the output power and thermal efficiency. The condenser fouling resistance leads to a significant reduction of expander output power and system thermal efficiency. However, the effect of the evaporator fouling resistance could be neglected due to its sufficient redundant area. The long-term climate conditions and operating strategies profoundly impact the unit's off-design performance. The annual constant output power operation can be achieved by adjusting the working fluid mass flow rate. The thermal efficiency of the unit is damaged while pursuing the output power stability in winter and spring.

Research on Grid-Connected Control Strategy of Photovoltaic (PV) Energy Storage Based on Constant Power Operation

In order to effectively mitigate the issue of frequent fluctuations in the output power of a PV system, this paper proposes a working mode for PV and energy storage battery integration. To address maximum power point tracking of PV cells, a fuzzy control-based tracking strategy is adopted. The principles and corresponding mathematical models are analyzed for the three-phase voltage PWM converter and bidirectional DC/DC converter, while feedforward decoupling double closed loop, constant power (PQ), and constant voltage charge/discharge control strategies are proposed. Space vector pulse width modulation (SVPWM) technology is utilized to generate power switching tube driver signals. Finally, a simulation model is developed in MATLAB/Simulink for system analysis. The results demonstrate that the proposed method enables constant grid-connected power generation and constant voltage charging of the energy storage battery when the PV cell’s power generation exceeds that of the grid. When insufficient solar power generation occurs, both the PV system and energy storage battery work together to achieve constant grid-connected power.

Optimal design and performance assessment of a proposed constant power operation mode for the constant volume discharging process of advanced adiabatic compressed air energy storage

A power operation mode of constant volume discharging process for advanced adiabatic compressed air energy storage (AA-CAES), called compensation mode (C mode), is proposed. The dynamic model of the proposed C mode discharging process is established based on the conservations of mass, momentum, and energy. The reliabilities of compressor, air tank, and air turbine are verified separately. The optimal design is carried out to reduce the power consumed by the compressor. The optimal design pressure ratio and reduced flow rate are 2.48 and 9.292 × 10−5 m·s·K0.5, respectively. This finding proves that the proposed dynamic model obeys the first and second laws of thermodynamics. The exergy distribution of the entire discharging process is studied. Results show that the two largest exergy losses occur in MT and MR. The performance of the proposed C mode is compared with that of the two other operation modes. The proposed C mode enhances the energy storage efficiency of the AA-CAES system by 14.71 %. This study provides a relatively efficient and feasible technical solution for the constant power operation of AA-CAES.

An optimized synchronous approach to DC/DC droop backstepping control considering voltage compensation in DC microgrids

This paper addresses the impact of widely distributed power electronic loads and their constant power operations on the stability of DC microgrids. A backstepping controller, based on droop control, is proposed as a solution for mitigating the issues of constant power load in these grids. The unique feature of this controller is its independence from inter-device communication, which enhances the expandability and scalability of the DC microgrid. To tackle the challenge of power side converters needing a subsequent level DC/DC converter for voltage adjustment, a synchronous optimization method is introduced. This method, incorporating voltage compensation, keeps track of local output power during system transients. It identifies when the droop coefficient ratio deviates from proportionality, using this deviation as the initiation point for algorithm optimization. This approach modifies the local droop curve, enabling synchronous optimization. Before being optimized, the controller under heavy load conditions cannot meet the requirements of maintaining bus voltage and accurately allocating power simultaneously. However, after optimization, the system can maintain bus voltage while still ensuring accurate power allocation after disturbances. Moreover, the controller before optimization requires a secondary DC/DC converter to transfer electrical energy from the variable DC bus to the main bus. The optimized controller can effectively eliminate voltage offset and directly connect the DC/DC converter to the main bus, eliminating the cost problem caused by the secondary converter.

Design and analysis of marine permanent magnet synchronous motor based on Motor-cad

In the marine electric propulsion system, the motor is an important part to ensure safe navigation, which should have the characteristics of low noise, low vibration, high performance protection level, etc. The permanent magnet synchronous motor (PMSM) has the advantages of rapid dynamic response, stable operation, strong overload capacity, high efficiency and small size, which is especially suitable for electric propulsion systems in marine environments. According to the performance requirements of marine motors and the permanent magnet synchronous motor structural characteristics, an electromagnetic design and simulation of a 120kW marine permanent magnet synchronous motor is completed in this paper. Meanwhile, the stator skewed slot is used to reduce the amplitude of harmonic distortion and the additional torque caused by tooth harmonic. At same time, the rotor structure with U-shaped magnetic steel groove is used to enhance the density of power and overload capacity of the motor, expand the scope of motor constant power operation effectively. A prototype with high efficiency, reliability and a small volume has been developed. According to the simulation results, the marine permanent magnet synchronous motor designed in this paper fully meets the design requirements.

Voltage Differential Analysis during Power Discharge Operation in Energy Storage Systems

Constant Power Discharge (CPD) is a lucrative operating mode for grid-tied ESS in many energy markets. The CPD mode corresponds to an increasing current drawn as the ESS discharges. The operation can be modeled with an aged anode and cathode open circuit potentials (OCPn/p+RRC) model that can let us identify electrode-level (eSOH) parameters and resistance growth even though we do not have slow discharge with Constant Current. This identification process from realistic ESS field data, namely constant power discharge, will enable continuous eSOH diagnostics and lead to real-time and operando quantification of loss of active material and loss of lithium inventory (LAM and LLI, respectively).In addition, the timing of when the cell groups' differential voltage peaks occur when the battery system is under constant power operations inform us about the imbalance among cell groups in a module of a battery system, as shown in the figure. Using the time separation among cell differential voltage peaks as a metric of cell imbalance can improve cell balancing algorithms that measure cell imbalance using maximum or minimum voltage, which can be directly affected by the power limits of the battery system.The efficacy of the proposed algorithms is evaluated for multi-cell modules consisting of NMC/graphite cells, operating as part of a large-scale grid-connected energy storage system. Ultimately, by enabling improved diagnostics of the state of health of individual cells in a battery system and improved cell balancing algorithms, this work will enhance the performance and safety of large-scale lithium-ion battery systems. Figure 1

A novel constant power operation mode of constant volume expansion process for AA-CAES: Regulation strategy, dynamic simulation, and comparison

A novel operation mode of constant volume discharging process for advanced adiabatic compressed air energy storage (AA-CAES) is proposed, which achieves a constant output power by throttling and air supplementation. The dynamic model of the expansion process was developed based on the conservation of mass and energy of the open system. The reliability of the turbine and air storage tank models was verified. The results of the energy and exergy analysis of the expansion process show.

Analysis of Photovoltaic Plants with Battery Energy Storage Systems (PV-BESS) for Monthly Constant Power Operation

Photovoltaic generation is one of the key technologies in the production of electricity from renewable sources. However, the intermittent nature of solar radiation poses a challenge to effectively integrate this renewable resource into the electrical power system. The price reduction of battery storage systems in the coming years presents an opportunity for their practical combination with utility-scale photovoltaic plants. The integration of properly sized photovoltaic and battery energy storage systems (PV-BESS) for the delivery of constant power not only guarantees high energy availability, but also enables a possible increase in the number of PV installations and the PV penetration. A massive data analysis with long-term simulations is carried out and indicators of energy unavailability of the combined system are identified to assess the reliability of power production. The proposed indicators allow to determine the appropriate sizing of the battery energy storage system for a utility-scale photovoltaic plant in a planning stage, as well as suggest the recommended operating points made for each month through a set of graphs and indicators. The presence of an inflection zone has been observed, beyond which any increase in storage does not generate significant reductions in the unavailability of energy. This critical zone is considered the sweet spot for the size of the storage, beyond which it is not sensible to increase its size. Identifying the critical point is crucial to determining the optimal storage size. The system is capable of providing reliable supply of constant power in monthly periods while ensuring capacity credit levels above 95%, which increases the penetration of this renewable resource. Despite the fact that the study focuses exclusively on the analysis from an energy perspective, it is important to consider the constraints associated to real storage systems and limit their oversizing.

In-Depth Analysis of Smooth and Nonsmooth Bifurcations for an Open-Loop Boost Converter Feeding Constant Power Loads in Discontinuous Conduction Mode

This paper presents a study of the existence conditions of limit cycles and mechanisms when losing their stability in an open-loop DC–DC boost converter loaded with a constant power load and operating in discontinuous conduction mode. First, the existence conditions are determined. Then, boundaries associated with different kinds of instabilities such as the classical smooth fold and period-doubling bifurcations and nonsmooth border-collision bifurcations such as fold border-collision bifurcations are elucidated. To perform the stability analysis, an implicit 1D map for the system is derived. From this model, it is obtained that smooth period-doubling and fold bifurcations may occur at certain values of the circuit parameters. Some results from numerical simulations performed on the circuit-based switched model are provided showing consistency with the theoretical analysis from the derived model.

회전속도와 간극 폭에 따른 모터의 열전달 특성에 대한 수치적 연구

Three-dimensional computations are performed to investigate the flow and thermal characteristics of a synchronous reluctance motor, which is capable of wide range of constant power and variable speed operation required for industrial applications such as control devices. This work focuses on the effects of rotational speed and rotor-stator gap width on the flow and thermal characteristics. The present computations show that thermal generation and convection changes with rotational speed have a significant effect on the motor temperature distribution, and that the flow and temperature fields in the rotor-stator gap strongly depends on the rotational speed and gap width relative the critical conditions. The heat transfer path in the motor is comparatively analyzed according to the rotational speed and rotor-stator gap.

Research on Robust Model Predictive Control Strategy of Wind Turbines to Reduce Wind Power Fluctuation

• Establish a robust model predictive control (RMPC) strategy for wind turbines based on wind speed uncertainty. • The error model of the nominal system and actual system is constructed and Lyapunov stability is used to prove that the error system tends to be stable. • Simulation analysis of the influence of RMPC strategy on wind turbine operation at different stable operating points. In the process of wind power generation, the random fluctuation of wind speed affects the smooth operation of the wind turbine and the stability of the output power of the wind turbine. Aiming at the influence of wind speed random fluctuation on the stable operation of wind turbines, this paper regards wind speed random fluctuation as bounded disturbance and adopts Robust Model Predictive Control (RMPC) strategy to divide the actual wind power system with wind speed disturbance into two parts: undisturbed nominal system and perturbed parts. As for the mismatch between the actual wind power system and the nominal system, the state of the actual wind power system is limited to a constant set by a certain feedback control law. The feedback control law and robust invariant set are then solved off-line via linear matrix inequalities (LMI). The 5MW wind turbine model developed by Nrel is used to simulate the feasibility of the algorithm on the MATLAB platform. RMPC control strategy can achieve the control goals of maximum wind energy capture at low wind speed and constant power operation at high wind speed. RMPC can effectively reduce the influence of wind speed uncertainty on stable operation of wind turbines, reduce output power fluctuation and improve power generation quality.

Analysis of the Hybridization of PV Plants with a BESS for Annual Constant Power Operation

The electrical generation of photovoltaic systems is variable and non-dispatchable. Energy storage systems can provide the system with energy management capabilities. In particular, with a hybrid system that combines a photovoltaic system and an energy storage system, it is possible to deliver firm power to the grid, if it is correctly dimensioned and operated. The objective of this work is to study the most appropriate relationship between the capacity of the battery energy storage system (BESS) and the peak power of the photovoltaic generator that enables the delivery of constant power throughout the year. Analysis parameters are presented that help to decide the most convenient energy injection constant value (PV-CPG set point) and the size of the storage system. As a case study, the most suitable battery capacity for a 1 MWp photovoltaic system with a battery located in Zaragoza (Spain), and the most convenient annual setpoint values for its operation are analyzed.

Optimal Design of Hybrid Rocket Small Satellite Launchers: Ground Versus Airborne Launch

A three-stage hybrid rocket is considered as a small satellite launcher. The same engine is used in different numbers in each stage: six, three, and one in the first, second, and third stages, respectively. This design choice aims at an overall reduction of the launcher cost. The propellants are liquid oxygen and a paraffin-based fuel. The performance of different feed systems and launch options are evaluated: the feasibility of a ground launch is analyzed and compared to similar three-stage launchers with airborne launch using both a gas pressurized feed system and an electric turbopump feed system. The optimization procedure exploits a direct method to evaluate the best values of engine design parameters, whereas an indirect method optimizes the ascent trajectory once the engine design is given. Constant power and blowdown operation are, respectively, assumed for the electrical feed system and the gas pressurized feed system. The initial mass of the launcher is given (5000 kg), and the payload mass is maximized for a given insertion orbit. The initial thrust is fixed in order to have an initial acceleration equal to . The nozzle expansion ratio in the first-stage engines is reduced to avoid separation at liftoff in the ground case, and the third-stage engines are used at a lower vacuum thrust level to satisfy maximum acceleration constraints. The results show that the proposed small satellite launcher concepts are able to deliver payload masses in the range of 40–100 kg into the desired orbit.

High efficiency single‐pulse controlled switched reluctance motor drive based on novel multilevel converter

Due to the high back electromotive force and short commutation time at high speed, the phase current of switched reluctance motor (SRM) is difficult to reach a large value, which limits the output performance of the motor in high-speed operation. This paper proposes a novel multilevel converter (MLC) with fast excitation and fast demagnetisation capability, which allows each phase to control independently even in overlapping conduction operation and is suitable for SRM with any number of phases. The excitation current in the rising inductance region is increased by high-voltage fast excitation, thus increasing the phase current level of the motor at high speed; the current tailing in the falling inductance region is suppressed by high-voltage fast demagnetisation, thereby reducing the generation of negative torque. Based on the novel MLC, a maximum torque per ampere (MTPA) control strategy is designed, and closed-loop control of the boost capacitor voltage is developed. By optimising control, the output torque and efficiency of switched reluctance motor drive (SRD) are greatly improved, and the constant power operation range is extended. Simulation study and experimental results verify the effectiveness of the proposed scheme.

Real Time Power Control in a High Voltage Power Supply for Dielectric Barrier Discharge Reactors: Implementation Strategy and Load Thermal Analysis

Atmospheric-pressure plasma treatments for industrial and biomedical applications are often performed using Dielectric Barrier Discharge reactors. Dedicated power supplies are needed to provide the high voltage frequency waveforms to operate these nonlinear and time-dependent loads. Moreover, there is a growing technical need for reliable and reproducible treatments, which require the discharge parameters to be actively controlled. In this work, we illustrate a low-cost power supply topology based on a push–pull converter. We perform experimental measurements on two different reactor topologies (surface and volumetric), showing that open loop operation of the power supply leads to a temperature and average power increase over time. The temperature increases by ΔTvol~120 °C and ΔTsup~70 °C, while the power increases by ΔPvol~78% and ΔPsup~60% for the volumetric (40 s) and superficial reactors (120 s), respectively. We discuss how these changes are often unwanted in practical applications. A simplified circuital model of the power supply–reactor system is used to infer the physical relation between the observed reactor thermal behavior and its electrical characteristics. We then show a control strategy for the power supply voltage to ensure constant average power operation of the device based on real-time power measurements on the high voltage side of the power supply and an empirical expression relating the delivered power to the power supply output voltage. These are performed with an Arduino Due microcontroller unit, also used to control the power supply. In a controlled operation the measured power stays within 5% of the reference value for both configurations, reducing the temperature increments to ΔTvol~80 °C and ΔTsup~44 °C, respectively. The obtained results show that the proposed novel control strategy is capable of following the transient temperature behavior, achieving a constant average power operation and subsequently limiting the reactor thermal stress.

Identification of Control Parameters for Converters of Doubly Fed Wind Turbines Based on Hybrid Genetic Algorithm

The accuracy of doubly fed induction generator (DFIG) models and parameters plays an important role in power system operation. This paper proposes a parameter identification method based on the hybrid genetic algorithm for the control system of DFIG converters. In the improved genetic algorithm, the generation gap value and immune strategy are adopted, and a strategy of “individual identification, elite retention, and overall identification” is proposed. The DFIG operation data information used for parameter identification considers the loss of rotor current, stator current, grid-side voltage, stator voltage, and rotor voltage. The operating data of a wind farm in Zhangjiakou, North China, were used as a test case to verify the effectiveness of the proposed parameter identification method for the Maximum Power Point Tracking (MPPT), constant speed, and constant power operation conditions of the wind turbine.

Analysis of Pv Plants with Bess for Annual Constant Power Operation

Analysis of Pv Plants with Bess for Annual Constant Power Operation

A Novel DC-Biased Current Dual PM Vernier Machine

In this article, a novel electric machine having permanent magnets (PMs) in both stator and rotor parts, and fed with dc biased phase current is proposed. The innovative characteristic of the proposed machine is that it contains multiple field excitation sources including stator PM, rotor PM. and dc component in the phase current. Thus, the exciting field can be greatly strengthened. What is more, the exciting field is flexible and adjustable thanks to the variable dc component. Therefore, the proposed machine is expected to exhibit high torque density, wide constant power operation range. This article first illustrates the basic operation principle, slot/pole combination equation, and the topology. Then, performance of six machines with different slot/pole combination is analyzed. After that, effects of several key design parameters on machine performance are researched theoretically and by finite-element method and genetic algorithm. And neural network is applied to verify the correctness of torque and torque ripple. Finally, the electromagnetic performance including flux density, back electromotive force, torque quality of an optimized machine is illustrated.