A new topology has been recently proposed for grid-connected photovoltaic (PV) systems, using modular multilevel converters (MMCs) and distributing PV panels throughout the MMC cells. This topology has two main advantages: it reduces the power losses related to moving the energy into the MMC capacitors from an external source, and it removes the losses and costs related to the DC to DC converters used to track the maximum power point on string converters or central converters, because that task is delegated to MMC cells. However, traditional pulse width modulation (PWM) techniques have many problems when dealing with this application: the distortion at the output increases to unacceptable values when MMC cells target different voltages. This paper proposes a new modulation technique for MMCs with different cell voltages, taking into account the measured cell voltages to generate switching sequences with more accurate timing. It also adapts the modulator sampling period to improve the transitions from level to level, an important issue to reduce the internal circulating currents. The proposed modulation has been validated using simulations that show a consistent behavior in the output distortion throughout a wide operation range, and it also reduces the circulating currents and cuts the conduction losses by half. The behavior of this new topology and this new modulation has been compared to the mainstream topology with external PV panels and also to a fixed carrier modulation.

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In the research presented in this article, a procedure for determining student workload has been designed, tested, and validated. This procedure also makes it possible to analyze how different teaching variables are affected by workload and to visualize the learning environment generated in the course.Background: When the project-based learning (PBL) methodology is used in a course, if the students' workload is not properly planned and controlled, important variables in the educational environment, such as the teaching organization and the students' approach to learning, can be affected. The PBL methodology may even become unfeasible as it affects the other courses with which it shares year and semester. This justifies the need to know the student workload of a subject. The previous research has presented procedures for establishing student workload. However, they use questionnaires with a high number of questions. A questionnaire with many questions affects the reliability of students' answers. The questionnaire presented in this article reduces the number of questions without affecting the results obtained and it is easily applicable to other courses.Research Questions: The questions to be answered in this research are: 1) is the workload of the students, when using the PBL methodology in a course, in line with the one established in the syllabus? and 2) is the learning environment created in the course as expected?Methodology: The methodology used to obtain the necessary data is based on students completing weekly surveys, two critical incident questionnaires (CIQs), and a final survey. The aim was