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Building energy plays a significant role in total energy consumption in China. It is widely recognized that the insulation performance of the external envelops is a critical factor for energy consumption of building air conditioning system. In this study, the effects of building external wall’s insulation thickness and position on the heating and cooling loads of a commercial building studied for five cities from different climatic zones of China, namely, Harbin, Xi’an, Shanghai, Kunming and Guangzhou, are investigated numerically. The wall’s optimum insulation thicknesses of the building simulated in these cities are determined by the life cycle cost analysis (LCCA) method. Meanwhile, the different positions of insulation layer embedded in the wall are investigated in terms of the time lag and decrement factor. The results show that the increase of insulation thickness has a significant effect on the building heating load, inversely it exhibits a relatively small effect on the building cooling load. The analysis indicates that building energy savings vary from different climatic zones. For a given wall insulation and the same building conditions, the largest building energy savings are achieved in Harbin, and energy savings of other cities follow the order of Xi’an, Shanghai, Kunming and Guangzhou. The variation of building energy savings in Guangzhou is insignificant along with the increase of the insulation thickness. Using expanded polystyrene as insulation layer material, the optimum insulation layers of the building in Harbin, Xi’an, Shanghai, Kunming and Guangzhou are founded to be 80 mm, 60 mm, 40 mm, 40 mm, and 20 mm, respectively.

A novel single phase Phase-Locked Loop (PLL) is proposed in this paper to accurately and rapidly estimate the instantaneous phase angle of a grid. A conjugate rotating vector pair is proposed and defined to synthesize the single phase signal in the stationary reference frame. With this concept, the proposed PLL innovatively sets one phase input of the PARK transformation to a constant zero. By means of a proper cancellation, a zero steady state phase angle estimation error can be achieved, even under magnitude and frequency variations. The proposed PLL structure is presented together with guidelines for parameters adjustment. The performance of the proposed PLL is verified by comprehensive experiments. Satisfactory phase angle estimation can be achieved within one input signal cycle, and the estimation error can be totally eliminated in four input cycles for the most severe conditions.

Distributed air-gap inductors have the advantage of reducing winding loss in high switching frequency dc/dc converters. However, they also have the disadvantage of uneven distribution of flux density, which inevitably leads to uncompleted utilization of magnetic material. This paper proposes a horizontal-winding multipermeability low-temperature cofired ceramic (LTCC) inductor to increase inductance and improve efficiency without the necessity of increasing inductor volume. For the purpose of simplicity, a two-permeability LTCC inductor is taken as an example for analysis and comparison. Design of such an inductor is demonstrated with the aid of 2-D finite elementary analysis simulation. A two-permeability LTCC inductor together with a single-permeability LTCC inductor is fabricated for measuring and testing. The measured results show the two-permeability inductor has higher inductance than the single-permeability inductor. Both inductors are tested in a 5-V input, 3.3-V output dc/dc converter to test their performances. The testing results show the two-permeability LTCC inductor could further improve the efficiency of high-frequency dc/dc converters compared with the single-permeability LTCC inductor.

Optimal nonblocking modular supervisory control of discrete-event systems is developed using state tree structures to manage state explosion. The total specification of the system to be controlled is decomposed into several sub-specifications, and a separate optimal (maximally permissive) nonblocking supervisor designed for each. Under an additional global nonblocking condition we directly obtain an optimal nonblocking modular state feedback control for the full system. If that condition fails, i.e. the modular controlled system is blocking, an additional coordinator is adjoined which renders the global controlled behaviour, both nonblocking and optimal.

A novel switching table of direct power control (DPC) strategy for three-level NPC rectifier is proposed in this paper. With the theory of instantaneous reactive power, it gets the inner relationship between instantaneous power (active power and reactive power) and space voltage vectors. The dc-link voltages are maintained at the required level using hysteresis controller for the NP current exploiting the redundancy states of the rectifier. With the switching table proposed in this paper, the excellent dynamic and transient performances are achieved under unity power factor operation without abnormal instantaneous reactive power fluctuation. Simulation results verify the validity and feasibility of the proposed strategies.

Background: The aim of this study was to explore whether serum baseline tryptase (sBT) levels might be a useful marker not only for the accurate diagnosis of childhood asthma, but also for the prediction of disease severity. Methods: A total of 114 asthmatic children were enrolled in this study, 36 of whom had mild intermittent asthma, 38 had mild persistent asthma, and 40 had moderate to severe persistent asthma. Additionally, 34 age-matched healthy children were enrolled as controls. The sBT levels of these populations were measured using a fluoroenzymeimmunoassay kit. The diagnostic performance of sBT levels and their correlation with asthma severity were systematically investigated using receiver operating characteristic (ROC) analysis and correlation analysis. Results: Children with mild and moderate to severe persistent asthma had significantly increased sBT levels as compared to those with mild intermittent asthma and healthy controls. ROC analysis further demonstrated that sBT levels not only appear to be highly sensitive and specific for distinguishing asthmatic children from healthy controls, but also show good accuracy for the differentiation of various asthmatic subgroups. Correlation analysis revealed that in all asthmatic subgroups sBT levels were significantly correlated with a variety of key markers that reflect the disease severity of asthma, including childhood asthma control test scores, serum IgE and interleukin-13 levels, blood eosinophil counts, and pulmonary test parameters. Conclusions: sBT levels may have a potential use in supporting a diagnosis of asthma in children and as a predictor of disease severity.

Conventional hysteresis current controllers have the disadvantage of a variable switching frequency. This paper presents a novel hysteresis current control method which uses the adjacent current error zero-crossing time to calculate the upper/lower hysteresis bandwidth after the measured half current error period. This strategy makes the algorithm independent of load parameters and thus it can achieve a stable switching frequency. An improved switching scheme has been successfully applied to a single-phase three-level H-bridge voltage source inverter driving a vibration test bench based on the novel hysteresis current. It can select appropriate switching states to overcome dead-time effects without dead-time compensation according to the relation of the current switching state, the current error, and the upper/lower hysteresis bandwidth. Field-programmable gate array has enough computational power to allow multiple sampling within a current error period and logic control power to implement state machine transitions. The simulation and experimental results are given to demonstrate the validity and features of the novel hysteresis current controller with the improved switching scheme.

In recent years, multilevel technology has become an effective and practical solution in the field of moderate and high voltage applications. This paper discusses an APF with a three-level NPC inverter. Obviously, the application of such converter to APFs is hindered by the problem of the voltage unbalance of DC capacitors, which leads to system instability. This paper comprehensively analyzes the theoretical limitations of the neutral-point voltage balancing problem for tracking different harmonic currents utilizing current switching functions from the space vector PWM（SVPWM）point of view. The fluctuation of the neutral point caused by the load currents of certain order harmonic frequency is reported and quantified. Furthermore, this paper presents a close-loop digital control algorithm of the DC voltage for this APF. A PI controller regulates the DC voltage in the outer-loop controller. In the current-loop controller, this paper proposes a simple neutral-point voltage control method. The neutral-point voltage imbalance is restrained by selecting small vectors that will move the neutral-point voltage in the direction opposite the direction of the unbalance. The experiment results illustrate that the performance of the proposed approach is satisfactory.

The squirrel-cage induction machine (IM) has been widely employed in microgrid. Accurate electrical parameters are necessary for the field-oriented control of the IM to achieve excellent performance. In this paper, a new offline identification scheme is presented based on the vector constructing method. The IM parameters are estimated using the recursive least squares (RLS) algorithm, which is applied to the continuous-time model of the IM at standstill. A single-phase ac test is used to make the machine standstill. The main feature of the proposed scheme is that the stator voltage, stator current and their derivatives, which are normally needed for the RLS algorithm, are constructed by the vector constructing method. The constructing rules are elaborated, which indicate that the phase shift and the amplitude ratio between the fundamental components of the voltage and the current have to be unchanged. This feature can avoid the analog or digital differentiators and greatly increase the noise immunity. Furthermore, the digital low-pass filter is not required for the proposed scheme, which can reduce the complexity of the identification scheme. Simulation and experimental results have been presented to demonstrate the validity and the feasibility of the proposed scheme.

It has been addressed that light and intermediate load efficiencies of high-frequency buck converters in portable electronic devices are very important for extending lifetime of batteries. This paper proposes to utilize wide range, gradually changeable nonlinear inductors with variable on time control to improve light and intermediate load efficiencies. Integrated multipermeability magnetic cores are advanced to realize the nonlinear inductors. And based on the nonlinear inductors, variable on-time control scheme is proposed to reduce the frequency-dependent loss. The theoretical loss reduction is demonstrated by comparing loss of a converter employing conventional constant on-time control scheme and employing the proposed control scheme. A two-permeability nonlinear inductor prototype is fabricated. Its inductance could vary from 0.13 μH at full load to 0.66 μH at no load. The nonlinear inductor is employed in a 12 V input, 1.6 V output buck converter to evaluate its performance. With the purpose of comparison, other two commercial chip inductors are also tested in the converter. The results show the nonlinear inductor with variable on time control could effectively improve efficiencies of light and intermediate load conditions as theoretical analysis does.

In this paper, a novel Active Voltage Quality Regulator (AVQR) topology with a thyristor rectifier and an adaptive dclink voltage control strategy are proposed. The proposed AVQR can efficiently mitigate the long duration variations (e.g. undervoltages/overvoltages), voltage imbalances and voltage harmonics. Compared with conventional AVQRs, it can regulate the load voltage very well with a much lower dc-link voltage. This is accomplished by replacing the diode rectifier with a thyristor rectifier. Moreover, its dc-link voltage can vary with the deviations of the supply voltage through the proposed adaptive dc-link voltage control strategy. All of these contribute to its significantly higher efficiency for online operating, which is very important and attractive for many applications. The proposed topology and control strategy are theoretically analyzed in detail. Simulation results are also provided in the paper. Finally, the feasibility and effectiveness of the proposed method are verified by means of experimental results from a 2kVA prototype. Both of the simulation and experimental results show that the proposed AVQR can achieve a much higher efficiency and similar regulation performance when compared with the conventional ones.

It is found out that using reverse coupled inductors could effectively improve power density and dynamic performance of multiphase interleaved point of load converters. Thus, it is of great significance to conduct a research about design and fabrication of ultrathin coupled inductors for system 3-D integration. The aim of this paper is to explore the structures, modeling, and fabrication of ultrathin coupled inductors based on low-temperature cofired ceramic (LTCC) technology. Four structures classified by shapes and relative positions of windings are introduced and compared. Simple but effective analytic models are set up to calculate self-inductance, leakage inductance, and coupling coefficient for quick design, and a design guideline is summarized according to the models. We made a 1.3-mm-thick LTCC coupled inductor and two competing coil coupled inductors, and compared their characteristics and performance. They are tested in a 12-V input and 1.2-V/40-A output two-phase interleaved buck converter at three different switching frequencies. Core loss and winding loss of the inductors are quantified by simulation. Compared with conventional coil coupled inductors, the LTCC coupled inductor has higher power density and light load efficiency. Besides, it could also help to improve the transient performance of converters for its higher coupling coefficient.

Three-level NPC inverters have been put into practical use for years especially in high voltage high power grids. This paper researches three-level active power filters (APFs). In this paper a mathematical model in the d-q coordinates is presented for 3-phase 3-wire NPC APFs. The deadbeat control scheme is obtained by using state equations. Canceling the delay of one sampling period and providing the predictive value of the harmonic current is a key problem of the deadbeat control. Based on this deadbeat control, the predictive output current value is obtained by the state observer. The delay of one sampling period is remedied in this digital control system by the state observer. The predictive harmonic command current value is obtained by the repetitive predictor synchronously. The repetitive predictor can achieve a better prediction of the harmonic current with the same sampling frequency, thus improving the overall performance of the system. The experiment results indicate that the steady-state accuracy and the dynamic response are both satisfying when the proposed control scheme is implemented.

This paper presents a novel hybrid common-mode (CM) electromagnetic interference filter for a military power supply. The proposed filter is composed of an active impedance multiplication circuit cascaded with a benchmark CM inductor. The active impedance multiplication circuit is very effective in boosting the impedances of both the benchmark CM inductor and the noise source. Thus, the total equivalent impedance of the filter is enlarged by the active booster to a great extent. An important advantage of the approach is that only a small-size CM choke is used as the passive filter instead of a traditional CLC filter. Furthermore, the noise source is turned to be an inevitable part of the hybrid filter by the impedance multiplication effect. Experimental results were carried out according to MIL-STD-461. It is shown that the proposed approach can acquire good noise attenuation performance within a wide frequency range.

Crossing behaviors at intersections are conventionally described through the gap acceptance theory; however, many gap-forcing behaviors exist at Chinese urban intersections. In this study, gap-forcing behaviors were analyzed and modeled from the perspective of conflict avoidance using a new modeling methodology called virtual field graph. After providing the definition of the preemptive status and the method to calculate the preemptive level, a new driving behavior model that differentiates from the conventional gap acceptance model was established. Analysis of collected field conflict data indicates that 82.2% of drivers’ decisions are normal decisions, while 17.8% are abnormal decisions. This suggests that there should be a physiological critical preemptive level while the drivers are making decisions. The driving population’s critical preemptive level was calibrated with the collected field conflict data through the logistic regression method and maximum likelihood approach.

The interference between the power stage and the driving circuit is one of the key issues of power module design, especially for those with high power densities, where couplings become more severe. This paper focuses on suppression techniques for inductive coupling. As a demonstration, a 2 kW single phase power factor correction active integrated power electronic module consisting of full bridge rectifiers, a current sensing resistor, and boost converter, is developed employing CoolMOS FET and SiC diodes. The electromagnetic interference mechanism in the module is analyzed and illustrated. In order to reduce the voltage spike of the power devices, three different design patterns of the power stage layout are presented and compared with regard to the reduction of parasitic self-inductance of the critical loop in the power stage. The approaches to reducing the inductive interference between the high di/dt loop in the power stage and the driving loop are investigated, including the proposed flux cancellation pattern for the layout of the high power di/dt loop, reduction of electromagnetic interference sources, and the insertion of a copper shielding layer between them. Finally, the design guidelines are built and verified by the simulation and experimental results.

Grid-connected wind turbines are fluctuating power sources that may produce flicker during continuous operation.This paper presents a simulation model of a megawatt-level variablespeed wind turbine with a full-scale back-to-back power converter developed in the simulation tool of PSCAD/EMTDC. Flicker emission of this system is investigated. Reactive power compensation is mostly adopted for flicker mitigation. However, the flicker mitigation technique shows its limits, when the grid impedance angle is low in some distribution networks. A new method of flicker mitigation by controlling active power is proposed. It smoothes the 3p active power oscillations from wind shear and tower shadow effects of the wind turbine by varying the dc-link voltage of the full-scale converter. Simulation results show that damping the 3p active power oscillation by using the flicker mitigation controller is an effective means for flicker mitigation of variable-speed wind turbines with full-scale back-to-back power converters during continuous operation. Udgivelsesdato: September Grid-connected wind turbines are fluctuating power sources that may produce flicker during continuous operation.This paper presents a simulation model of a megawatt-level variablespeed wind turbine with a full-scale back-to-back power converter developed in the simulation tool of PSCAD/EMTDC. Flicker emission of this system is investigated. Reactive power compensation is mostly adopted for flicker mitigation. However, the flicker mitigation technique shows its limits, when the grid impedance angle is low in some distribution networks. A new method of flicker mitigation by controlling active power is proposed. It smoothes the 3p active power oscillations from wind shear and tower shadow effects of the wind turbine by varying the dc-link voltage of the full-scale converter. Simulation results show that damping the 3p active power oscillation by using the flicker mitigation controller is an effective means for flicker mitigation of variable-speed wind turbines with full-scale back-to-back power converters during continuous operation.

Most reported compensation schemes for active electromagnetic interference filters (AEFs) use either voltage canceling or current canceling to deal with high-frequency noise interference. The purpose of this paper is to investigate the compensation characteristics of these two kinds of AEFs for different types of noise sources, i.e., common mode (CM) and differential mode (DM) noise source. This is examined by experimental identification and theoretical analysis of the insertion losses of AEF with voltage- or current-cancellation scheme. It is demonstrated that current-canceling AEFs are effective in eliminating high-impedance CM noise, while voltage-canceling AEFs are good compensation solutions for low-impedance DM noise. The results reported in the paper enable the choice of optimized compensation schemes, using the aforementioned indicated aspects.

We describe a method for determining the split winding distribution for coupled inductors in interleaved converters. Our method greatly reduces the footprint and copper losses of the magnetic component. We discuss the analysis and design method for the coupled inductors in detail. We use a geometrical method to solve problems such as uneven fluxes of different legs and magnetic core selection criteria and optimizations. We use a flowchart to design the coupled inductor, and constructed a 400-W prototype by following it. We present some comparisons between our method and those presented in the literature. Simulation and experimental results demonstrate that our method is effective and straightforward.

The hybrid active electromagnetic interference filter (HAEF) is considered one of the best options for improving power quality for a number of considerations. A systematic classification and identification of HAEF configurations is given, including their insertion losses, impedance compatibilities, potential applications, and comparative features. It is aimed at providing a broad perspective on the status of HAEF technology to researchers and application engineers dealing with EMI issues. The basis of discussion is an equivalent circuit model that includes all possible combinations of active and passive elements and matches these to the desirable attributes. The evaluation indicates those topologies that are known and those topologies that are relatively new.

Reactive power control through the static compensator (STATCOM) has gained wide attentions due to its outstanding performance. But for a STATCOM with traditional control strategies, unbalanced utility voltages will greatly affect the performance of the STATCOM and, in severe cases, may even cause the shutdown of the STATCOM for overcurrent protection. This paper proposes novel control strategies to ensure normal operation of STATCOM in three-phase three-wire systems when severe system voltage unbalance occurs and, furthermore, to mitigate voltage unbalance at the point of common coupling (PCC) whether it is caused by the utility or load. The control laws, operation principles, compensation characteristics, and operating point optimization of the proposed control strategies are analyzed and compared in detail. The power flow in the STATCOM and corresponding dc-side voltage-control schemes for these control strategies are also introduced. It is shown that the proposed voltage-controlled current source (VCCS) strategy and modified voltage-controlled voltage source strategy are valid for voltage unbalance compensation, especially the VCCS strategy for low rating under the same performance. Finally, the simulation and experimental investigations were carried out with these three parameter-optimized control strategies, respectively, for light and heavy load conditions. The results verified that the current passing through the STATCOM is under control and the voltage at the PCC is more balanced than before compensation. The compensation performance of the STATCOM is thus proven satisfactory

A novel switching table of direct power control (DPC) strategy for three-level NPC rectifier is proposed in this paper. With the theory of instantaneous power, it gets the inner relationship between instantaneous power (active power and reactive power) and space voltage vectors. The dc-link voltages are maintained at the required level using hysteresis controller for the NP current exploiting the redundancy states of the rectifier. With the switching table proposed in this paper, the excellent dynamic and transient performances are achieved under unity power factor operation without abnormal instantaneous reactive power fluctuation. Simulation results verify the validity and feasibility of the proposed strategies.

The cooling storage ring of the heavy ion research facility in Lanzhou (HIRFL-CSR) is one of the five mega-science projects undertaken by Chinese Academy of Science within its ninth and tenth five-year plan period. The HIRFL-CSR facility can providing heavy ion beams in wide energy range, manifold and with high quality. This paper presents a hybrid filter structure consisting of a passive filter and a parallel dc active power filter (DCAPF) for a sample magnet power supply in HIRFL-CSR. The configuration of the power system with the DCAPF is introduced. Then a novel feedback control scheme for the DCAPF is proposed with detecting the output ripple voltage across the magnet load. For detailed discussion, a simple model of the whole system has been derived and the stability characteristic is analyzed. Through simulation and experiment investigation, the DCAPF is successfully applied in a 120-kW magnet power supply in HIRFL-CSR finally. The ripple factor and tracking accuracy of the output current through the load achieve 8.87 ppm and 100 ppm, respectively. Therefore, the rigor requirements of low output current ripple and fast ramp rate are both satisfied with the DCAPF proposed.

In many Chinese cities, pedestrian’s road crossing behavior is different from that of pedestrians in developed countries. This paper presents a pedestrian model for traffic system micro-simulation in China. Considering the high rate of signal non-compliance, we classify pedestrians into two types: law-obeying ones and opportunistic ones. Opportunistic ones decide whether to violate traffic signal during red man, depending on the states of some external factors (like policeman, vehicle flow and other pedestrians’ behaviors). Questionnaires were used to determine the proportions of these two types of pedestrians under different circumstances. In addition, a time gap distribution extracted from videotape were used to determine the criterion for pedestrians to decide whether to walk or wait when they conflict with vehicle flows. However, simulation results deviate from the data extracted from videotape in some degree. By adjusting the parameters on the basis of analyzing the occurrence of the deviations, the simulation results agree with the field results better. This model has represented the high rate of pedestrians’ red light running and the mixed characteristics of traffic flows in Chinese cities, and it may be applicable in the micro-simulation of traffic system in other developing cities.

In recent years, there has been considerable interest in the development and applications of active electromagnetic interference (EMI) filters. An active EMI filter (AEF) for integrated power electronics module (IPEM) is proposed in this paper, where large passive EMI filter is replaced by small passive components and active op-amp circuit. The technique is appropriated when improved attenuation is required at relatively low frequencies and the high-frequency filtering requirements are easily met. The effectiveness of the proposed circuit has been verified by experimental results. It is demonstrated that the proposed approach is most effective in a case where it is desirable to minimize the amount of passive components in the filter

For high power three-level Neutral Point Clamped (NPC) converter widely used in medium voltage speed regulation system, which has the characteristics of low switching frequency and complex harmonic distribution of output current waveform, output filter is needed in order to protect AC-side device. Normally, LC filter is used for its good performance. However, the low switching frequency and complex harmonic distribution lead to the design difficulties of the output LC filter. In this paper, on the basis of theoretical analysis, a novel design method of the output LC filter used in three-level NPC converter basing on minimum reactive power is proposed and the parameter design formula is deduced. Simulation results are given to demonstrate the validity of this new method.

A new multilevel matrix converter that can be applied to medium or high voltage ac drives is presented to alleviate harmonic components in the output voltage. The proposed converter contains six flying capacitors to balance the voltage distribution of series connection bidirectional switch modules and provide middle voltage levels. Stable flying capacitors voltage must be maintained to facilitate the operation of the converter. When the converter is working, the voltage of flying capacitors can be controlled by swapping two switching modes with opposite charging current corresponding to each middle voltage levels. A simple output voltage vector synthesis method is described and utilized. The operation and commutation strategies are discussed. Simulations and experiments are carried out to validate the proposed converter. Comparisons are made between proposed converter and conventional matrix converter.

A novel current-detection algorithm based on the time-domain approach for three-phase shunt active power filters (APFs) to eliminate harmonics, and/or correct power factor, and/or balance asymmetrical loads is analyzed in this paper. A basic overview and evaluation of the performance of existing current-detection algorithms for active power filters are presented. According to different complicated power quality issues and various compensation purposes, a novel current-detection algorithm is then proposed. Comparing with existing algorithms, this algorithm has shorter response time delay and clearer physical meaning. Different compensating current references can, thus, be accurately and easily obtained by adopting the proposed algorithm. It ensures that the shunt APF can very well achieve different compensation purposes. Moreover, it is very easy to implement this algorithm in a digital signal processor (DSP). Simulation results obtained with MATLAB and testing results on an experimental shunt APF are presented to validate the proposed algorithm.

This paper proposes a Monte Carlo model to estimate pedestrian delays at signalized intersections adopting pre-timed two-phase control in developing cities like Xi'an, China. In the model, the signal cycle is divided into a series of subphases, and each subphase lasts 1s. The model includes four parts: vehicle generator, pedestrian generator, pedestrian model, and statistical module. Vehicle generator is used to generate a vehicle sequence traversing the crosswalk. Pedestrian generator is used to generate a pedestrian sequence arriving at the crosswalk. Pedestrian model includes a set of rules pedestrians follow at signalized intersections. And statistical module calculates the average delay of pedestrians arriving during each subphase, and the overall average delay as well. Finally, field data collected from an intersection in Xi'an are used to validate the model, and the validation results indicate that the proposed model is able to estimate accurately the average delay of pedestrians arriving during each subphase.