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Food safety problems occur frequently, and the food safety problems of major enterprises are continuously reported. Therefore, food safety quality and how to test food safety have become the focus of people’s attention. The technical testing of food safety is mainly achieved through chemical means, but with the continuous development of science and technology, the disadvantages of chemical testing technology continue to appear, so how to improve the chemical testing technology has become a difficult problem to be overcome in the technical field. The thesis focuses on various chemical technologies in food safety testing, such as electrochemical immunosensors, liquid chromatography detection, pigment rapid testing instruments, nucleic acid aptamers, etc., and selects several items for detailed description.

Direct bypass of DC-DC boost converter in traction inverter has many advantages including increased efficiency and pass-through capability. This paper explains different practical aspects of direct bypass of the boost stage of traction inverter using diode. Bypass diode enters into the linear operating region (DC Q-point) when the battery discharges through the bypass diode to drive the electric motors. Therefore, thermal stress of the DC-link capacitor is shared between the input and DC-link capacitors through the bypass diode. During battery charging operation, the inverters introduce voltage ripple in the DC-link terminal which results in unwanted energy circulation through the bypass diode. Both of these phenomena have been investigated in details. In addition, this paper proposes and validates a control strategy to eliminate the energy circulation during battery charging mode using minimum boosting at a reduced frequency to optimize the power loss of the boost converter.

The IGBTs are dominantly used in traction inverters for automotive applications. Because the Si-based device technology is being pushed to its theoretical performance limit in such applications during recent years, the gate driver design is playing a more prominent role to further improve the traction inverter loss performance. The conventional gate driver design in traction inverter application needs to consider worst case scenarios which adversely limit the semiconductor devices' switching speed in its most frequent operation regions. Specifically, when selecting the gate resistors, the IGBT peak surge voltage induced by di/dt and stray inductance must be limited below the device rated voltage rating under any conditions. The worst cases considered include both highest dc bus voltage and maximum load current. However, the traction inverter operates mainly in low current regions and at bus voltage much lower than the worst case voltage. This paper proposed a gate driver circuit that can mitigate the compromise between low switching loss and high device stresses. Compared with conventional gate driver circuits, only a low voltage PNP BJT, two Zener diodes and a resistor are added in the proposed circuit. The implementation is easy and the potential cost increase is low. The proposed gate driver can separately control the different phases of turn-off transient to achieve short turn-off delay, fast dv/dt and low surge voltage across IGBT. Because the proposed method does not require any feedback circuits, logic and control circuits which could limit the circuit bandwidth, this method can be used for fast switching applications.

With the increasing demand for environment-friendly and high fuel economy vehicles, most of the automotive manufacturers are working on the development of their electric and hybrid electric vehicles (EVs/HEVs). The traction inverter plays a significant role in EV/HEV system and converts energy between the battery and the electric motors. One of the key challenges during the traction inverter development is how to evaluate its performance in the lab. This paper proposes a method to evaluate the performance of traction inverter in EVs/HEVs. Comparing with the traditional lab test methods, the proposed method uses the real driving cycles of the vehicle and illustrates the traction inverter performance in real driving conditions. The experimental results show the benefits of the proposed method.

Based on field experiment, the yield and water use efficiency (WUE) of tobacco under different nitrogen levels were studied in Hunan province, China. The results show that the evaportranspiration (ET) of flue-cured tobacco dealt with N2 (90kg N fertilizers per ha) gets to the maximum. In addition, the vigorous period has the maximum ET due to the critical period of water requirement. The linear relationship is established among fertilization, yield and water use efficiency. Reasonable fertilizer application can increase water use efficiency and flue-cured tobacco yield.

The blossom-end rot (BER) induced by calcium deficiency will cause a great impact on tomato yield and quality. Aimed at the tomato physical barriers caused by calcium deficiency, the composite micro-organisms (EM) fermentation technology was applied to configure biological active calcium preparations of different calcium concentrations, with raw materials of calcium sulfate, lime and gypsum. The active calcium preparation with calcium concentration of 1 ‰ was sprayed on the fruits during the fruit development period in the field experiment. The results show that lime with highest solubility is the best raw material for the fermentation of EM active calcium preparations with the consideration of higher calcium concentration, reasonable pH and EC value, and the lowest cost. It also shows the incidence of blossom-end rot of the experimental group is 35.36 % lower than that of CK.

This paper reports the humidity sensitive properties of NaTaO3 nanocrystalline. The NaTaO3 nanocrystalline was synthesized by a simple hydrothermal method, and characterized by X-ray diffraction and scanning electron microscope. Then NaTaO3 humidity sensor was fabricated by coating the nanocrystalline materials on interdigitated electrodes. The device shows good impedance-RH (relative humidity) linearity, narrow hysteresis and rapid time response characteristic. The impedance decreases about three orders of magnitude when the relative humidity (%RH) increases from 33% to 95%RH. The maximum hysteretic value of the sensor is 1%RH and the response time is about 3 s in the operated humidity scope. Moreover, the sensing mechanism was discussed by the complex impedance spectra in detail. These results indicate the potential application of NaTaO3 in humidity sensors.

Raising nitrogen utilization efficiency could not only cut the fertilizer costs, but also reduce the N loss and residual, which benefits a lot to agricultural production and environmental protection. In this experiment, the 15N tracing technique was employed in order to clear the accumulation and whereabouts of fertilizer N in flue-cured tobacco plants, besides, the tobaccos were treated by six different water-nitrogen modes, for the sake of finding out the best design with the highest nitrogen utilization efficiency. The results showed that more N application contributed to more fertilizer N accumulation, also increased the content of total N; Excess irrigation restrained the tobacco plants' absorption of fertilizer N, ultimately leading to the low utilization efficiency of nitrogen fertilizer; After apex pruning, the N offering ability of the soil was much stronger than that of nitrogen fertilizer, and the fertilizer N accounts a relatively small part for the total N in tobacco plants, the highest nitrogen utilization efficiency was 24.16%, recorded in the design of 800mm irrigation amount and 6g/plant pure N application(T2), Meanwhile, the agronomic characters and crop yield was observed, tobaccos in T2 design performed better than the average level of field-cultivated tobaccos, the conclusions could be obtained that T2 design was preferable, which achieved the highest nitrogen utilization efficiency when ensured the normal growth and good harvest of flue-cured tobacco.

A novel dead-time elimination method is presented in this paper for voltage source inverters. This method is based on decomposing of a generic phase-leg into two basic switching cells, which are configured with a controllable switch in series with an uncontrollable diode. Therefore, dead-time is not needed. In comparison to using expensive current sensors, this method precisely determines the load current direction by detecting which anti-parallel diode conducts in a phase-leg. A low-cost diode-conduction detector is developed to measure the operating state of the anti-parallel diode. In comparison with complicated compensators, this method features simple logic and flexible implementation. This method significantly reduces the output distortion and regains the output RMS value. The principle of the proposed dead-time elimination method is described in detail. Simulation and experimental results are given to demonstrate the validity and features of this new method.

This paper presents a Z-source inverter system and control for general-purpose motor drives. The Z-source inverter system employs a unique LC network in the dc link and a small capacitor on the ac side of the diode front end. By controlling the shoot-through duty cycle, the Z-source can produce any desired output ac voltage, even greater than the line voltage. As a result, the new Z-source inverter system provides ride-through capability during voltage sags, reduces line harmonics, improves power factor and reliability, and extends output voltage range. Analysis, simulation, and experimental results will be presented to demonstrate these new features.

The application of cross-links at the cable joints and the arrester-groundings at the cable terminals undoubtedly reduces the ground potential and the sheath current in a cable system, however, such configuration builds an open circuit in the grounding conductor and stops the partial discharges (PD) pulses to travel. Thus very few pulse energy goes into the grounding wire, which is an industrial accepted checkpoint for PD defects through conventional sensors such as high frequency current transformers. To solve the problem, this paper introduced an innovative broadband PD sensor by using a capacitive jumper to bridge the PD propagation path. In this way, the problem of impedance mismatch at PD frequency is avoided, while an `open circuit' is maintained at power frequency. The sensor is tested in the laboratory with an oscilloscope for its sensitivity and detection bandwidth, while the latter reaches about 200 kHz ~ 87MHz. Such sensor was tested in a real 110 kV cable and shown the convenience and effectiveness in PD detection.

In this work, an innovative and feasible solution is proposed for a Variable Voltage Converter (VVC) with direct bypass for traction drive inverters in HEVs. With the proposed method, the VVC capability is significantly increased and power loss is dramatically reduced. The advantages associated with this method include 1) Mitigation of VVC oscillation issues occurring during fast power flow transients, since the VVC output minimum voltage is directly clamped to the HV battery voltage anytime the output side voltage is lower than that of the HV battery voltage. 2) A significant increase in VVC pass-through operation capability; as a result, both vehicle EV drive maximum speed and duration are increased, 3) significantly reduced VVC power loss and noticeably increased vehicle fuel economy. This solution has been proved to be very useful and feasible especially for Plug-in HEV applications.

Computer Generated Forces (CGF) lacks an effective collaboration method. As a result of this, Based on the traditional contract net protocol, a integrated contract net protocol suitable for CGF collaboration is proposed in which strategies such as interaction trust, witness trust and threshold value are integrated. In order to ensure integrity, correctness and reliability of integrated contract net protocol, formalized method colored net is used to model integrated contract net protocol and liveness, accessibility and bound ness of protocol are analyzed and validated. Finally, integrated contract net protocol is applied to collaboration simulation of missile attack and defense CGF system. Simulation results show that integrated contract net protocol effectively reduces communication cost of collaboration and increases completion task rate of system.

In this work, an innovative and feasible evaluation method is proposed to fully verify the Variable Voltage Converter (VVC) functionality for vehicle electrification applications. With the proposed method, the VVC can be fully tested for all four operation modes which can occur during vehicle real driving conditions. The proposed method provides a solution which allows hardware self-evaluation with HEV drive cycles during development stages in the laboratory. The advantages associated with this method includes 1) the capability of testing the VVC up to full power under all operating modes, 2) minimal external power demand and energy savings; 3) enable hardware to be tested with real drive conditions and significantly reduces costs and resources which are required by vehicle road tests.

In applications where batteries work together with power electronic circuits, the current ripple generated by the power electronics will be shared by both the battery and passive components in the circuit. The amount of ripple absorbed by the battery depends on its impedance at the switching frequency of power electronics. This paper presents an impedance based high frequency battery model derived from test results of a NiMH battery using a novel battery impedance tester. The possible reasons for the battery impedance characteristics in high frequency region, including skin effect and proximity effect, are also discussed. This battery model can be directly used in current ripple analysis, passive components design and control strategy optimization of power electronic circuits. The effect of the passive component values on the battery current ripple is analyzed using the ac equivalent circuit of the test setup.

To overcome the drawbacks of the conventional gate drive, in this paper a closed-loop gate control method is proposed. In this novel method, the switching speed, specifically di/dt, is measured from the voltage across the parasitic inductance of the IGBT module and a closed-loop control is employed to adaptively adjust the gate drive voltage to control the switching speed according to a preset control reference. As a result, both the voltage overshoot and current overshoot can be effectively controlled. This new gate drive method enables programmable control of switching speed and allows full use of the capability of the power devices. The oscillations during IGBT switching are also reduced and associated EMI problems can be mitigated. The relationships between the controlled voltage overshoot, current overshoot and associated energy losses are derived and can provide guidelines for practical design. Also, the proposed gate drive fully utilizes gate drive signal information of amplitude and duty cycle, and provides a new capability for the system modulator to effectively control both the power electronic circuit's steady-state and transient behaviors simultaneously.

An active fault protection method is proposed to prevent the IGBTs from being damaged should they be under over-current and short circuit fault conditions. A closed-loop gate drive method is used to effectively control the IGBT turn-off switching speed independent of the fault type or resultant over-current level. Compared with conventional solutions, the proposed method can limit fault current level, minimize energy loss with fast shut down transient, and control voltage overshoot. Also, no additional hardware circuit or soft shut down process is need. Even if an over-current fault condition can not be effectively detected, the automatically controlled IGBT turn-off switching speed can avoid a dangerous voltage overshoot across the power device. This new feature can significantly improve the robustness of the power system and cannot be achieved with the conventional approaches.

A full-bridge dc-dc converter employing diode rectifier in the output experiences severe voltage overshoot and oscillation problem across the diode rectifier caused by the interaction between the junction capacitance of the rectifier diode and the leakage inductance of transformer. The pronounced reverse-recovery current of high power diodes enforces these issues significantly by increasing power loss and voltage overshoot. Conventional energy recovery clamping circuits suffer from high voltage overshoot if the input voltage of converter is wide. In this work, a novel energy recovery clamp circuit is proposed to overcome this problem. Performance of the proposed circuit is verified both theoretically and experimentally with a 70 kW dc-dc converter.

A dead-time elimination method is presented in this paper for PWM controlled inverters. In comparison to using expensive current sensors, this method precisely determines the load current direction by detecting the operating conditions of active devices and their anti-parallel diodes. A low-cost diode-conducting detection circuit is developed to measure the operating status of the anti-parallel diode. In comparison with complicated compensators, this method features with simple logic and flexible implementation. This method significantly reduces the output distortion and regains the RMS value. The principle of proposed dead-time elimination method is described. Simulation and experimental results are given to demonstrate the validity and features of the dead-time elimination method.

A 260 kVA inverter has been developed with a passive soft-switching snubber. The main circuit configuration and prototyping are described. Optimization of the passive soft-switching snubber parameters has been made to control the voltage overshoot across the switches, minimize snubber and inverter losses, and effectively limit dv/dt and di/dt during activation. An efficiency higher than 98.5% has been achieved as well as other prospected features. Experimental results are given to demonstrate the validity and features of the inverter.