Large-scale wind farms connect to the grid and deliver electrical energy to the load center. When a short-circuit fault occurs on the transmission line, there will be an excess of electric power, but the power demand will increase instantaneously once the fault is removed. The conventional additional frequency control strategies of wind farms can effectively reduce the frequency fluctuation caused by load mutation, but still there are some limitations for the frequency fluctuation caused by the whole process of occurrence, development and removal of a short-circuit fault on the transmission line. Therefore, this paper presents an improved additional frequency control strategy for wind farms. According to the variation law of system frequency during the whole process of a short-circuit fault, the proposed strategy revises the parameters in conventional additional frequency control of the doubly-fed induction generator (DFIG) to have effective damping characteristics throughout the entire process from failure to removal, thereby the output power of DFIGs could respond to frequency fluctuation rapidly. MATLAB/ Simulink is used to build a four-machine two-area model for simulation analysis. The results show that the control strategy can effectively reduce the frequency fluctuation of DFIGs, and enhance the stability of the system.

A surface plasmon resonance (SPR) biosensor was applied to detect influenza-A virus in human. The detection scheme was based on the measurement of SPR response unit resulting from the hybridization of biotinylated DNA probe immobilized on the SPR chip modified with streptavidin and the product of polymerase chain reaction reversed from the influenza-A virus RNA segment (AB514942). The prepared biosensor demonstrated optimum performance in 200 mM phosphate buffered saline (PBS) with a pH value of 7.5 and exhibited good sensitivity with a detection limit of 0.5 pM for perfect complementary hybridization. In addition, the prepared biosensor can effectively discriminate perfect complementary and other three types of mismatch: base substitute, base insertion and base deletion in 200 mM phosphate buffered saline (PBS) with a pH value of 7.5. Furthermore, the influenza-A virus in throat swab samples was directly (without RNA extraction, and amplification) detected with the prepared machine, and the result showed that the SPR response unit was in response to the dilution factor of throat swabs. Better sensitivity and specificity based on Surface Plasmon Resonance biosensor were obtained which demonstrated a promising potentiality in detecting influenza-A virus

Facing the environment problems, the improvement on the efficiency of the construction machinery is highly demanded, meanwhile, large energy wasted in hydraulic slewing systems, reaching the desired speed slowly and vibration in braking are widespread. In this paper, a closed-loop control swing system (CCSS) is proposed. In this system, bidirectional variable pump controls the change of oil flow by programmed software algorithm, instead of pilot actuated reversing valve, which significantly improves the efficiency of hydraulic circuit. Based on the model structures, we develop a hydraulic swing prototype and verify the advantages of our design means of theoretical calculation and simulation. It verifies that CCSS and based on accumulator slewing system(BASS) can respectively save 875.5 KJ and 347.2 KJ more than OCSS with operational weight of 100 tons grasp steel machine, which can support theoretical basis for energy conservation and environmental protection to study the new type of engineering machinery.

Workpiece placing and removing for stretcher operated by hand have low precision, low efficiency and poor security. The workpiece automatic placing and removing manipulator of stretcher driven by pneumatic is introduced in this paper，in which two control methods: electric-pneumantic control and PLC program control are advanced to realize stepless speed regulation, overload protection and to complete complex actions easily. The design shows the advantages such as simple structure, low cost, easy to operate and maintenance, high efficiency and reliability, which can also improve safety, reduce the labor intensity, ensure product quality and process stability.

Gripper with two claws of automatic placing and removing manipulator is designed in this paper, and structure characteristics, working theory and positional error analysis are introduced. This gripper has the function of automatic center aligning and size control. The chucking size of gripper can be modified automatically in order to be adaptable when clamping different work pieces and this gripper, which could shorten the time and improve the efficiency, is designed to place and remove workpiece at one time beat. The gripper has a virtue of better ability to locate and move, improving the precision of automatic feeding manipulator and lathe cutting. The grippers have the advantages of simple structure, small volume and weight, which can solve the problems of complicated structure and massive volume for typical translational gripper. They also could simplify the control system of manipulator; meet the demand of placing and removing workpiece instead of complicated and heavy manual work.