Series-connected System Research Articles

Optimization of the operation of existing district heating systems

AbstractThis study examines the economic optimisation of existing district heating systems. A new approach has been taken to solving a long-standing problem. The authors describe the input-output model of the system, the balance equations for the thermal equilibrium of the system, and the heat transfer system. From the balance equations of the series-connected system elements, the resultant heat transfer balance equation and the resultant power transmission equation are derived. In an example, the authors detailed how perturbations in some input variables can be corrected with other variables. The equations presented and the concepts introduced form absolutely new scientific results.

Study on a direct-coupling thermoacoustic refrigerator using time-domain acoustic-electrical analogy method

Thermoacoustic refrigeration is a clean cooling technology with high reliability. In this study, a time-domain acoustic–electrical analogy (TDAEA) method is proposed and improved, then applied to explore the performance of a high-efficiency 2-stage looped direct-coupling heat-driven thermoacoustic refrigerator. The effectiveness of the method is verified by experiments. Transient evolutions of oscillating pressure and volume flow rate are first presented. System performance under different working gases is explored, and helium is chosen due to its much larger cooling power. The influences of cooling and ambient temperatures and cavity parameters on system performance are then investigated. The results show that a rise in ambient temperature leads to a dramatic decline in cooling power. Moreover, the influences of cavity parameters are complicated. When the diameter and length of the cavity are respectively 95 mm and 440 mm, the cooling power achieves a maximum of 3.65 kW with COP of 0.76; while with diameter and length reaching 90 mm and 360 mm, respectively, a peak COP of 0.82 with cooling power of 1.47 kW is obtained. Furthermore, a comparison between the presented direct-coupling system and a series-connection system is performed. The results show better performance of the direct-coupling system, which achieves a cooling power of 5.08 kW under air-conditioning case, 22.4 % higher than that of the series-connection system, implying its superiority in air-conditioning field for larger cooling capacity and more compact configuration. This study provides a new perspective for understanding ofthermoacoustic refrigerators.

Influence of operating conditions on solar energy utilization efficiency of flat plate solar collector

For the last 20 years, solar collectors have been developing rapidly in the use of energy in buildings. Under experimental conditions, the solar energy utilization efficiency (SEUE) of flat plate solar collectors (FPSC) can reach more than 80%, but the engineering application of SEUE is low, and even the collector heating cannot meet the design requirements. In this paper, based on the existing thermal performance of FPSC, the influence of ambient meteorological parameters and hot water system operation parameters on SEUE is studied using experimental tests and analytical calculations. The results reflected that the collectors connected to the auxiliary heaters will affect SEUE, with series-connected systems having greater SEUE than parallel-connected systems. When the solar radiation intensity was low, the SEUE of parallel-connected systems was more likely to be negative. Under calculated conditions, when the water inlet temperature was 20, 30, 40, and 50 °C, the SEUE of the collector was 0%, and the corresponding solar radiation intensity was 113, 184, 225, and 328 W/m2, respectively. Reducing the average water temperature of the collector can reduce the heat loss in the energy conversion process between the collector and the air and increase the SEUE. When the solar radiation intensity was 500 W/m2, the collector inlet temperature decreases from 50 °C to 30 °C, and the SEUE increased from 20.9% to 38.5%. The research results can provide a parameter basis for the design of the FPSC system, especially the connection mode of collector and auxiliary heat device, and the design of system water temperature.

Optimization and comparison of two improved very high temperature gas-cooled reactor-based hydrogen and electricity cogeneration systems using iodine-sulfur cycle

To enrich the existing research methods and content, two improved very high temperature gas-cooled reactor and iodine-sulfur (I–S) cycle-based nuclear hydrogen and steam and helium gas turbines electricity cogeneration systems, including the series connection system (SCS) and the parallel connection system (PCS), are proposed and studied. The energy and exergy analysis methods are used to model these two systems, and Aspen Plus is adopted to build the I–S hydrogen production system. The energy consumption and thermal efficiency of the I–S system are analyzed in detail, and the parametric optimization of two improved systems is performed using particle-swarm optimization (PSO) algorithm. Lastly, the performance comparison of the two systems under different operating conditions is conducted. The simulation results show that more than 99% of the energy consumption of the I–S system is occupied by H2SO4 section and HIx section, and the system's thermal efficiency is estimated to be in the range of 17.7%–43.3%. After using an internal heat exchange network, a conservative thermal efficiency of 23.7% is achieved. The optimization results show that under zero hydrogen production load, the proposed PCS and SCS can respectively achieve the net electrical power outputs of 172.8 MW and 125.7 MW, the global thermal efficiencies of 49.36% and 35.91%, and the global exergy efficiencies of 51.94% and 37.79%. With the increase of hydrogen production load, the global efficiencies of both systems decrease significantly, but the decreasing rate of PCS is faster than that of SCS. In addition, the performance comparison results indicate that when the hydrogen production load is small or the intermediate heat exchanger's primary side helium outlet temperature is close to the reactor inlet temperature, the PCS would be a better option than the SCS.

A Novel DTC-SVPWM Technique for Symmetric 6 and 3 Phase PMSM Two-Motor Series-Connected Systems

A Novel DTC-SVPWM Technique for Symmetric 6 and 3 Phase PMSM Two-Motor Series-Connected Systems

A Digital Interconnected Bus Providing Voltage Synchronization for the Modular Series-Connected Inverters

The input port or the output port series-connected system is very suitable for medium- or high-voltage applications. For the output series-connected modular inverter system, the important issue is to guarantee that the phase angle of the different modules are exactly the same, otherwise, the total output voltage cannot meet the requirement. This letter proposes a digital synchronization strategy, which adopts a digital interconnected bus to provide the common reference signal for the composed modules. The operation principle, circuit schematic, and control design of the proposed strategy are explained in detail in this letter, and finally, the performance of the strategy is verified on a three-module series-connected inverter system.

A Synchronization Method for the Modular Series-Connected Inverters

The series-connected system is widely used in the medium or high voltage applications. For the series-connected inverter system, the phase angle synchronization should be guaranteed to ensure the total output voltage. Usually, a centralized controller is used to send the same voltage command to each module downstream. In order to improve the flexibility and scalability of the modular system, a decentralized synchronization method is proposed in this letter. The synchronization principle, control strategy, and control parameter design guidance are introduced step by step. Finally, the performance of the proposed strategy is verified by a series-connected three-module inverters system.

CONTROL OF DOUBLE THREE-PHASE PMSM SERIES-CONNECTED SYSTEM BASED ON ADAPTIVE BACK-STEPPING METHOD

To research space gap magnetic field harmonic influence on the decouple control and unknown parameters of double three-phase permanent magnet synchronous motor permanent magnet synchronous motor (PMSM) two-motor series-connected system, the nonlinear adaptive back-stepping control approach is presented.

Modeling and Decoupled Control of Series-Connected Split-Phase Synchronous Machines With Open-Circuit Fault

Split-phase motor drives have advantages such as lower torque ripple, enhanced fault tolerance, higher power-to-weight ratio, and lower dc-link voltage requirement, making it an attractive alternative to the conventional three-phase drives. In the proposed series-connected topology, both the motors are connected in different phase sequences, allowing the fundamental component of the winding current to produce torque in the first machine, and sixth-order harmonic currents to produce torque in the other machine. Both the motors used are synchronous machines, which have advantages such as higher power density and easier control. The proposed method can be easily extended to other synchronous machines such as permanent magnet machines and reluctance machines. In this article, a mathematical model for series-connected split-phase synchronous motors is developed and validated experimentally for decoupled field-oriented control of dual split-phase synchronous machines. Furthermore, the developed model (series-connected system) is extended for open-circuit fault operation, and experimental results are presented for the first time. Simulation results as well experimental results for steady state, transient conditions for normal, and fault operation are presented to validate the proposed scheme.

System simulation on refrigerant-based battery thermal management technology for electric vehicles

Progress in the higher requirements for battery thermal management system (BTMS), a new refrigerant-based BTMS of electric vehicles (EVs) is proposed and analyzed, especially designed for high ambient temperature and high speed dynamic conditions. Based on the vehicle system framework, the thermal response, energy efficiency and irreversibility of the system are discussed hereunder. As indicate by the results, the average temperature of battery module and temperature difference between cells are effectively controlled. In addition, energy analysis is performed under different conditions, including energetic coefficient of performance (COPen) and exergetic coefficient of performance (COPex). The intensification of driving conditions has a negative impact on both COPen and COPex, while the increase of ambient temperature reduces COPen and promotes COPex. Further, the effects of BTMS on the air conditioning (AC), and their consequences are explored. Through a cabin-prioritized control strategy and a series-connected system configuration, this paper aims to improve the system performance and make progresses on the whole vehicle thermal management system.

Predictive DTC Strategy With Fault-Tolerant Function for Six-Phase and Three-Phase PMSM Series-Connected Drive System

On the one hand, with the use of direct torque control (DTC) for a six-phase permanent magnet synchronous motor (PMSM) and a three-phase PMSM series-connected system supplied by a six-phase inverter, it is possible to realize fast torque control for two PMSMs. On the other hand, because the number of inverter output voltage vectors (VVs) is increased to 64, it is difficult to divide sectors for traditional switching table DTC (ST-DTC). Furthermore, it is difficult to choose an optimal switching vector to reduce torque and flux ripples of two PMSMs in ST-DTC. A predictive control strategy of torque and stator flux is introduced into a two-PMSM series-connection DTC system, including winding fault, in this paper. Based on the principle of minimum errors of torque and stator flux amplitude and minimum zero-sequence current, an optimal VV is predicted. In order to realize uninterrupted torque control before and after open-phase fault, open-phase winding flux is considered in stator flux, and the inverter VV considering open-phase voltage is constructed in an open-phase control strategy. The experimental results show that the steady-state torque and stator flux ripples of a series-connected drive system are greatly reduced, and the drive system can operate without interruption from failure-free to failure operation.

A Markov decision process model case for optimal maintenance of serially dependent power system components

Purpose – Using a case study for electrical power equipment, the purpose of this paper is to investigate the importance of dependence between series-connected system components in maintenance decisions. Design/methodology/approach – A continuous-time Markov decision model is formulated to find a minimum cost maintenance policy for a circuit breaker as an independent component while considering a downstream transformer as a dependent component. Maintenance of the dependent component is included implicitly in terms of the costs associated with certain state-action pairs. For policy and cost comparisons, a separate model is also formulated that considers only the circuit breaker as the independent component. After uniformizing the continuous-time models to discrete time, standard methods are used to solve for the average-cost-optimal policies of each model. Findings – The optimal maintenance policy and its cost differ significantly depending on whether or not the dependent component is considered. Research limitations/implications – Data used are from manufacturer databases; additional model validation could be conducted if applied to an electric utility asset fleet within their generation, transmission, and/or distribution system. This model and methodology are already being applied in other contexts such as industrial machinery and equipment, jet engines, amusement park rides, etc. Practical implications – The outcome of this model can be utilized by asset and operations managers to make maintenance decisions based on prediction rather than more traditional time- or condition-based maintenance methodologies. This model is being developed for use as a module in a larger maintenance information system, specifically linking condition monitor data from the field to a predictive maintenance model. Similar methods are being applied to other applications outside the electrical equipment case detailed herein. Originality/value – This model provides a structured approach for managers to decide how to best allocate their resources across a network of inter-connected equipment. Work in this area has not fully considered the importance of dependency on systems maintenance, particularly in applications with highly variable repair and replacement costs.

Study on Series Control Method for Dual Three-Phase PMSM based on Space Vector Pulse Width Modulation

Decoupling control of two-motor dual three-phase permanent-magnet synchronous motor (PMSM) series-connected system can be realized by using proper phase transposition rules with a single supply from a six-phase voltage source inverter (VSI), which solved the control problem of two motors in series. Since the traditional two-vector SVPWM strategy, which is commonly used in three-phase system, exists 5 th and 7 th harmonics in x-y plane, making it hard to realize decoupling control of two-motor dual three-phase PMSM series-connected system. Meanwhile, the DC bus voltage utilization of carrier-based PWM strategy is lower. Thus one method, which adopted a TBTSB-SVPWM strategy with two modulators, was proposed in this paper. It ensures the inverter output voltage only contains two kinds of fundamental components required by the two seriesconnected motors with a single VSI, making it possible to realize decoupling control of two-motor dual three-phase PMSM series-connected system. Simulation results indicate that there is no influence on the other motor while the speed/load of any one motor changed, achieving the decoupling control of series-connected system, and the feasibility and validness of the proposed approach are verified.

A Markov Decision Process Model Case for Optimal Maintenance of Dependent Components

This paper is a case study of electrical power equipment to investigate the importance of dependence between series-connected system components in maintenance decisions. A continuous-time Markov decision model is formulated to find a minimum cost maintenance policy for a circuit breaker as independent component while considering a downstream transformer as a dependent component. Maintenance of the dependent component is included implicitly in terms of the costs associated with certain state-action pairs. For policy and cost comparisons, a separate model is also formulated that considers only the independent component. The optimal maintenance policy and its cost differ significantly depending on whether or not the dependent component is considered. Data used are from manufacturer databases; additional model validation could be conducted if applied to an electric utility generation, transmission and/or distribution system. This model and methodology could be applied in other contexts such as industrial mach...

Performance Comparison between Series-Connected and Parallel-Connected Thermoelectric Generator Systems

The connections between the thermoelectric modules are crucial importance for the performance of the thermoelectric power system. Many studies have been done to improve the output of thermoelectric system, but very little specific to the connections between the modules. A mathematical model of a module has been established, and based on this model, the performance of two systems composed of 6 pieces of thermoelectric modules, one in series connection and the other in parallel connection, is simulated with MATLAB software and then compared. The results can be used as reference for the design and prediction of thermoelectric system.

Impact of Skin Effect, Resistive and Dielectric Losses on Current Estimation and Reliability of ULSI Interconnects

In this study, a series connection system of interconnects and gates is studied. In the system, we focus on skin effect, resistive and dielectric losses in previous level interconnects and the impact of their variations on the fast current estimation and the lifetime calculation of the post level interconnects. The changes in cross-section dimensions of interconnects are used to represent their differences in resistances, dielectric losses and skin effect in actual circuits or to represent the process of Electro Migration (EM). Through the analysis of the voltage transfer function of interconnects, the different roles of skin effect, resistive and dielectric losses in signal attenuation for interconnects of various cross-sections are pointed out. The study shows that the input voltage waveforms of the post level interconnects will change if the cross-section sizes of the previous level interconnects vary. By means of showing the changing tendencies of current and lifetime estimation results affected by the cross-section dimensions of the previous interconnects, we indicate that the fast current and reliability estimation results will not be accurate enough if these effects are not included.

Research of Backstepping Control for Multiphase Permanent Magnet Synchronous Motor of Two-Motor Series System

The double Y shift 3 0 PMSM two-motor series-connected system is a novel multi-machines system, which PMSM1 operates on d q plane and PMSM2 operates on 1 2 z z plane. To overcome the poor robustness and static and dynamic performances of PI controller, the backstepping control approach suitable for the two-motor series-connected system is researched. And the backstepping controller of PMSM1 is deduced on d q plane. The simulation contrasting with PI controller show that backstepping can realize the decouple control of the two series-connected motors and improve the dynamic and static performances.

Research on BFV-SVPWM Control Strategy for Two Double-Y Shift 30° PMSM Series-Connected System

Multi-motor drive system is one important area of the motion control research. In this paper, the working principle of single-inverter driving the series-connected system of two double Y-shift 30 ° PMSM is proposed. In order to achieve the better decouple operating of the two series-connected motors and improving the DC bus utilization, a novel control method of BFV-SVPWM for the system is presented. In Matlab/Simulink environment, variable-speed operations are simulated to verify that the proposed BFV-SVPWM control is strategy feasibility and superiority.

Simulation of Vector Control for Two Double Y Shift 30° PMSMs Series-Connected System

A number of multi-phase motors can be series-connected and driven by a single inverter via the appropriate phase transformation rules, and all motors in series-connected can be independently controlled . In this paper, the working principle of two six-phase permanent magnet synchronous motor series-connected system is proposed, the vector control strategy of id=0 and the carrier-wave modulation PWM technology are adopted to make the decoupled running of the two motors. Simulation of the two motors series system is obtained based on Matlab/simulink. The feasibility of the series system is proved by analysis the independently operating of one motor when the speed of the other motor is changed.

The Modeling and Simulation of DFIM Based on Auto Disturbance Rejection Controller

In order to solve the coupling of rotor current of d axis and q axis, a new kind of control scheme for double-fed induction machine (DFIM) speed regulation system is proposed based on the theory of auto disturbance rejection controller (ADRC). The ADRC is composed of three parts: tracking-differentiator (TD), extended state observer (ESO) and nonlinear state feedback controller (NSFC). In the ADRC scheme, the coupling of rotor current is regarded as the inner disturbance of DFIM, inputting this disturbance to the input port of the speed regulation system by the feedforward compensation, the speed regulation system can change to the simple integral series connection system or simple linear system. This controller can realize decoupling of rotor current of d axis and q axis, obtaining a good speed tracking performance with small overshoot and fast setting time. Simulation results indicate the rationality and validity of the ADRC.