Advanced Materials Research Vols. 614-615

Abstract: In this paper, a comparative study on control strategies of parallel hybrid active power filters (PHAPF) is presented. A universal electric model of three different PHAPF is proposed. The principle for the harmonic current elimination of PHAPF when different control strategies are adopted is analyzed. As the performance of the PHAPF will be influenced by the fluctuation of the power system parameters, a comparative study of the influences when different control strategies are adopted is carried out. The conclusions can help in the choice of an optimal basic control strategy, and guarantee the secure operation of the PHAPF system. Experiments have been carried out to verify the validity of the theoretical analysis in this paper.

Abstract: This paper introduces a new mixing equipment. The numerical simulation and experiment have been done on the internal flow field and mixing effect of the new mixer and for a conventional Kenics static mixer. The exit mixing uniformity is used as an indicator to evaluate the two mixers’ mixing effect. For the adjustable mixer, when the blades angle increases, the mixing uniformity increases. But when absolute value of the angle passed 30°, the rate of increasing begins to slow down. For avoiding too much flow resistance in high workload, the new mixer’s blades rotating angle should be within ±30°. The production of high strength large scale shear eddies on the wake behind the swirl blades in the adjustable mixer is the key for the effective mixing of flocculant and raw water. According to the numerical simulation and industrial experiments, the new adjustable mixer not only can adjust blade angle to fit different working conditions, but also can quickly mix the raw water with flocculant in the pipe behind the blades. The new mixer’s mixing speed and mixing effect are both obviously better than the conventional Kenics static mixer.

Abstract: This paper contraposes 300MW CFB boiler of Shanxi certain coal-fired power plant, then optimize the control system of desulfurization and remake limestone transmission system. Collect the signal to establish knowledge base for judging starting or stalling control of feeding machine through lots of experiments. Adopt feedback control strategy to adjust the speed of feeding machine. Achieve the purpose of automatically controling the starting or stalling of feeding machine and the speed of feeding machine finally.

Abstract: Distributed Generation may be located far away from load centers due to their use of new energy resource distribution characteristics. In this case, Long distance transmission lines will introduce an equivalent impedance to the grid, so that the grid showing the characteristics of a weak grid. In this paper, the interaction between grid-connected inverter and weak grid is studied by means of impedance analysis in the frequency domain. The experimental results are used to evaluate the stability of grid-connected inverter under different grid impedance condition. In a weak grid system, the increasing grid inductance results in a smaller stability margin of impedances ration. To improve the stability of the grid-connected inverter, the paper introduces a kind of active damping method with a virtual resistor in parallel with the capacitor. The new active damping control scheme without differential factor has a simple algorithm. The experimental results are depicted to demonstrate the correctness of theoretical analysis and the feasibility of the active damping algorithm.

Abstract: In order to overcome the drawbacks of the conventional SPWM for three-phase CSC, this paper presents a generic novel PWM scheme. In the novel PWM scheme, one line cycle is divided into six 60° intervals, and during each interval, only two references are used to compare with the carriers to directly generate the required switching patterns. Because of the optional modulation signal, the modulation technique has the advantages of flexible and easy digital implementation. It is shown that, compared with the conventional SPWM, the novel PWM scheme has lower switching frequency, higher dc current utilization ratio and in-phase transfer between the three-phase line currents and the reference signals. Finally, the propositions are verified by the experimental results.

Abstract: This paper describes a SRAM design using the pipelining technique which has been used in many microprocessors extensively. The main purpose to design SRAM with the technique of pipelining is to improve the whole performance of the SRAM based on the characteristic of the pipelining technique that it can incease exponentially the circuit performance. A 2-stage pipelining 4K SRAM has been verified by simulation, and the results demonstrate that the performance of the read operation can be improved twice if the pipelining technique has been used compared with the conventional SRAM operation.

Abstract: This paper introduces a selective harmonic elimination (SHE) PWM method based on neutral-point potential balancing applied to a three-level Photovoltaic NPC Inverter. The method combines the SHE with neutral-point potential balancing， and introduces a method based on multi-objective ant colony algorithm to solve the SHE-PWM non-linear equations. SHE-PWM control method of multi-objective ant colony algorithm considering about neutral-point potential balancing, there is no need to solve the initial value of the equation when solving the SHEPWM equations. Experimental results demonstrate the validity of SHE-PWM method based on neutral-point potential balancing.

Abstract: Compared to the traditional dual Z-source inverter, Z-source inverter with a signal X-shaped LC impedance network has advantages of lower cost and an easier modulating algorithm. Based on the three-level single Z-source inverters, this paper proposed a suitable SVPWM scheme, which include vector region judgment, send order determine, and synthetic time calculation. It is available to achieve inductive voltage boosting by inserting the shoot-through vectors appropriately, while simultaneously provide a good performance on output with a correct volt-second average. The theoretical concepts discussed are verified by simulation results.

Abstract: This paper presents an analysis and improvement of self-oscillation electronic ballast for local emergency light. The improvement circuit has been presented by replacing the original BJTs with MOSFETs as a switching device. Also, 555-timer has been used to drive the MOSFETs instead of the ballast feedback in the original circuit. This electronic ballast start and regulate fluorescent lamps by converting a DC supply to high ignition AC voltage by a rectifier circuit with switching frequency in the range of 20 kHz -1MHz. Operation at high frequency has two advantages; an improved efficiency and elimination of flickering in the lamps. The simulation has been done by using PSIM Simulink software and its results have been compared with experimental results. The results shows that by using MOSFETs as a switching device, the Total Harmonic Distortion (THD) has been reduced and the brightness of lamp tube has been increased greatly.

Abstract: Laser cleaning is a non-contact, green and environmental cleaning method, which can effectively remove particulate contaminations of sizes as small as 0.1 μm without damage to the optics. But most laser cleaning devices are large and heavy, also expensive due to using large lasers such as CO2 laser, YAG Laser etc. In this work a low power LD was tried to clean fingerprint and dust contaminated on the surface of the attenuator glasses plates. In the laser cleaning experiment with low power diode the fingerprint grease can be efficient to be cleaned, but there is no evident effect for cleaning inorganic dust. The cleaning different degree of fingerprint contaminations was investigated at the variable laser parameters, including laser power and irradiation time. An optical microscope was used to analyze the cleaning effect. The results show that low power LD can effectively remove the fingerprint on the surface of absorptive-type attenuator glass plates. On the premise that the attenuator optics glasses are not damaged, the cleaning area increases with the increase of radiation time and laser power. The cleaning area doesn't change much with the variation of laser frequency when the other parameters are the same.