With the energy transition, electrical energy consumption is increasing heavily. Electric vehicles replace cars with internal combustion engines, and electric heating replaces gas-heated homes. The AC electricity grid becomes congested with the increase in load. Local electricity generation through PV panels or windmills also increases, but there is generally a mismatch in generation and demand. Besides, practically all electrical equipment uses DC directly or in the conversion process. This makes using DC grids much more efficient than AC grids. The distribution grid can not convert directly to AC. DC microgrids could prove an attractive solution to support the distribution grid and to move gradually to a DC grid. These locally operated grids combine load, generation, and energy storage. A bipolar DC microgrid further increases efficiency by providing an additional voltage level and doubling the power compared to a unipolar DC grid with the same pole voltage. A DC/AC converter will interface the LV AC grid and the DC grid to enable energy exchange between the grids.

Research is conducted to the design and modulation techniques for a transformerless bipolar 700 V DC grid interfacing converter. Mitigating the isolation transformer increases efficiency and reduces material usage, but will also provide a path for ground leakage current to flow. An NPC converter topology is selected and an 11-segment modulation scheme is implemented using sub-references and carriers. This scheme mitigates the oscillations in the DC neutral point, while simultaneously reducing the ground leakage current to acceptable levels. Furthermore, a novel dead time compensation method is implemented to reduce the ground leakage current further. Finally, a new concept to provide unbalanced power to the poles based on the pole voltages is introduced. Simulations and experimental tests show that the developed modulation technique can enable a transformerless connection.

This thesis presents a resonant sensor circuit design that converts the deformation of a load cell in a conveyor belt into a change in resonance frequency. The sensor is inductively coupled to a reader circuit using planar PCB inductor coils. A sensor circuit was designed, fitted on a square PCB with 14.14 mm side length. The circuit consists of a planar squared inductor and a planar interdigital capacitor. The inductor has an inductance of 0.66535 $\mu$H, and the capacitor has a capacitance of 5.157 pF. An additional SMD capacitor was added to reach a resonating frequency range around 27.2 MHz. The deformation of the load cell causes a bend in the sensor PCB, which is directly attached to the diaphragm of the load cell. The bend causes a change in capacitance of the interdigital capacitor, which shifts the resonance frequency of the sensor. The sensor components are designed in MATLAB and simulated and verified in CST studio.