State-Space Modeling Techniques of Emerging Grid-Connected Converters

In modern power electronics-based power systems, accurate modeling is necessary in order to analyze stability and the interaction between the different elements, which are connected to it. State space modeling seems a valid approach to study the modes of a certain system and their correlation with its states. Unfortunately, this approach may require complicated calculations and it is difficult to model advanced or emerging control techniques for grid-tied converters, such as cascaded controllers (e.g., voltage and current) and virtual synchronous generators (VSGs). Moreover, this approach does not allow an easy reconfiguration of the modeled system by adding, removing of modifying certain elements. To solve such problems, this paper presents a step-by-step approach to the converter modeling based on the Component Connection Method (CCM). The CCM is explained in detail and a practical example is given, by modeling one exemplary VSG model available in the literature. The obtained model is finally validated experimentally to demonstrate the practical accuracy of such approach.

Individualized Generation of Appropriate Assistance Timings for Active Lower Limb Robots via Machine Learning

Background: Obtaining appropriate assistance timings for individual users of active lower limb assistant robots (ALLARs) is one of the major challenges that limit the practical application of robots since very small assistance timing errors greatly affect the robot's assistance effect. However, neither theoretical nor experimental methods can currently generate appropriate assistance timings due to their respective availability or accuracy limitations. Method: In this paper, we proposed a new method to generate appropriate assistance timings for individual users of ALLARs via machine learning. The method has the accuracy of theoretical methods and the availability of experimental methods. We established a database of ten static physiological parameters, three dynamic parameters, and theoretical appropriate assistance timings, and mapped the static physiological parameters and the dynamic parameters to the theoretical assistance timings using multilayer neuron networks. Fold-cross validation and determination efficient were used to test the fit of the model. The root mean square error between generated values and true values of each subject was compared to that between the mean of the sample and the true values of each subject to evaluate the data accuracy of our method. We also set ±2% error as the boundary of the practical accuracy and compared the practical accuracy when using our method to that when using the mean generally. Result: The model achieved a small standard deviation of the square root error in the 10-fold cross-validation experiment and a large determination coefficient. We reduced the data error of starting and ending assistance timing from 0.0265 and 0.0172 to 0.014±0.000429 and 0.0079±0.000875, respectively, and improved the practical accuracy of starting and ending assistance timing from 54.93% and 75.49% to 89.54% and 99.95%, respectively.Conclusion: The proposed method can generate an appropriate assistance timings for different users of ALLARs walking at different speeds. Moreover, a new reference for ending assistance timings is provided and the database can be used as a reference for futer research. The practical effect of the method will be tested in future work.

ON PRACTICAL ACCURACY ASPECTS OF UNMANNED AERIAL VEHICLES EQUIPPED WITH SURVEY GRADE LASER SCANNERS

Unmanned aerial vehicles (UAVs) equipped with image sensors, which have been widely used in various fields such as construction, agriculture, and disaster management, can obtain images at the millimeter to decimeter scale. Useful tools that produce realistic surface models using 3D reconstruction software based on computer vision technologies are generally used to produce datasets from acquired images using UAVs. However, it is difficult to obtain the feature points from surfaces with limited texture, such as new asphalt or concrete, or detect the ground in areas such as forests, which are commonly concealed by vegetation. A promising method to address such issues is the use of UAV-equipped laser scanners. Recently, low and high performance products that use direct georeferencing devices integrated with laser scanners have been available. Moreover, there have been numerous reports regarding the various applications of UAVs equipped with laser scanners; however, these reports only discuss UAVs as measuring devices. Therefore, to understand the functioning of UAVs equipped with laser scanners, we investigated the theoretical accuracy of the survey grade laser scanner unit from the viewpoint of photogrammetry. We evaluated the performance of the VUX-1HA laser scanner equipped on a Skymatix X-LS1 UAV at a construction site. We presented the theoretical values obtained using the observation equations and results of the accuracy aspects of the acquired data in terms of height.

Comparison of Different On-Site Measurement Methods and Their Practical Accuracy

Turbines or pumps in hydropower plants achieve peak efficiencies of far more than 90% depending on the specific speed and the type of machine. Based on model tests or numerical simulations, the efficiency of a prototype machine has to be guaranteed and measured with the best measurement technique available. The choice of the appropriate efficiency measurement method does not only depend on the expected measurement uncertainties and tolerances set in a contract, it is also a question of the effort required for such a measuring campaign and of technical challenges, e.g., limitations imposed by plant operating conditions as draining of the system or constant load operation. Concerning hydraulic turbomachines, modern measuring technology offers different methods for efficiency measurements at a turbine unit. Primarily through the development of real-time capable data acquisition systems, it is possible to perform high-precision measurements rather quickly, whereby minimal downtimes can be achieved. In the first part, the specific measurement methods available in different standards are presented in an overview, and then in the second part, the achieved accuracies of a very complex thermodynamic measurement are compared with a low-cost clamp-on acoustic Doppler measurement using a concrete example.