Kishore Chatterjee

Solar PV micro-inverters are typically designed to be operated in grid-connected mode. By interfacing a battery with a micro-inverter, it is possible to minimize the wide variations in power drawn from solar PV module. In this article a battery-integrated transformer-less solar PV micro-inverter is proposed which can integrate a battery having voltage lower than that of the PV module. Depending on the available solar irradiation and the battery's state of charge, it simultaneously regulates the battery current and the current drawn from the PV module. Although it is suitable for getting interfaced with a 220 V ac grid, it can also operate in a standalone mode in the absence of the grid. The proposed micro-inverter has inherent power decoupling capability, and the existence of double grounding ensures that there is no leakage current flow. In-depth analysis of the proposed scheme is carried out. An appropriate control algorithm is developed for operating the micro-inverter under different conditions. The feasibility of the proposed scheme is validated by performing detailed experimental studies on the prototype developed for the purpose.

This article proposes a multifunctional onboard charger (MOC) for electric vehicles (EVs) that facilitates main battery charging (MBC) from a single-phase grid. It can also feed power to single-phase load or back to the grid, and as an auxiliary power module (APM), supplying low-voltage dc (LVDC) power to the vehicle's auxiliary system. The proposed charger is a two-stage converter wherein the first-stage consists of front-end Totem-pole power factor correction (PFC) circuit with an integrated ripple power compensation (RPC) circuit to absorb the second harmonic ripple power. The second-stage is a dual active bride (DAB), used to control the power to/from the main battery. To facilitate the APM mode of operation, the first-stage circuitry is reconfigured to form an interleaved buck converter to supply high current to the LVDC bus. In addition, the dc conversion ratio of DAB is maintained near unity by adjusting the winding configuration of the transformer ensuring soft-switching in all the operating modes. The high dc link voltage requirement of the integrated RPC is addressed by using a novel RPC control methodology, thereby facilitating the use of 650 V GaN switches in the converter. Detailed simulation studies are carried out to predict the performance of the converter for all the modes of operation, and these results are experimentally validated on a 7.2 kW laboratory prototype.

Dc microgrid experiences a high magnitude of fault current during a pole-to-pole (PP) fault. It is difficult to interrupt such a current due to the absence of natural current zeros. In this article, the authors propose a current limiting type fault ride-through (FRT) scheme for converters in the dc microgrid, which reduces the steady-state fault current during a PP fault. The steady-state fault current reduction is achieved by setting the power fed by each converter to a minimum value using control. The reduced fault current further reduces the voltage and current stress on the circuit breaker (CB) for clearing the fault. The proposed scheme also ensures fast voltage restoration of the network voltage without having to go through the startup process. The proposed scheme uses locally available converter data to detect and limit the fault current. The performance of the proposed scheme is compared with systems in which converters do not have an FRT scheme or have an existing power sequence method as an FRT scheme. The viability of the proposed scheme is confirmed through detailed simulations on a 380 V low voltage dc (LVDC) microgrid model. The performance of the proposed scheme is experimentally validated on a laboratory prototype network.

A boost/buck-boost derived solar PV micro-inverter suitable for interfacing a 35 V 220 W PV module to a 220 V single phase ac grid is proposed in this paper. It employs only six switches, out of which two switches operate at high frequency, two at line frequency and rest of the two switches at high frequency during either positive half cycle or in the negative half cycle of the grid voltage. In order to achieve high gain as well as negligible turn on losses for the high frequency switches, the micro-inverter is operated in discontinuous mode of conduction for all possible operating conditions. The negative terminal of the PV module is directly connected to the grid neutral, and hence the the magnitude of leakage flow is zero. The instantaneous power mismatch between the dc side and the ac side is addressed by achieving inherent power decoupling in the proposed topology without incorporating any additional active power decoupling circuit. The detailed analyses of the proposed micro-inverter is carried out. A 220 W laboratory prototype of the proposed micro-inverter is fabricated, and experimental studies are carried out in detail to confirm the viability of the proposed scheme.

A SEPIC-Ćuk-based transformerless micro inverter capable of interfacing a 35 V, 250 W solar PV module to a single-phase 220–230 V ac grid is proposed in this article. The circuit employs only one high-frequency switch and four line-frequency switches thereby reducing the switching losses. This also enhances the overall reliability of the system. The circuit is made to operate in discontinuous conduction mode (DCM) under all possible operating conditions to achieve high gain and at the same time ensure negligible turn on loss for the high-frequency switch. The direct connection existing between the PV neutral and the utility ground makes the magnitude of the leakage current to be zero. In order to reduce the size of the capacitor across the PV module, an active power decoupling circuit is employed. Hence, this capacitor can be realized by a thin film capacitor instead of an electrolytic capacitor thereby improving the reliability of the system. Detailed analysis of the proposed microinverter is carried out. The effectiveness of the proposed scheme is verified by performing detailed simulation studies. A 250 W laboratory prototype of the inverter is fabricated, and detailed experimental studies are carried out to confirm the viability of the proposed scheme.

In this article, a modified BLdc motor having a wide flat-topped back EMF waveform of around 169 $^{0}$ is designed and presented. This motor when excited with an appropriate current waveform as proposed in this article provides around 13.8% improvement in torque density while ensuring that the torque ripple remains the same as that of a conventional BLdc motor drive. Further, the proposed drive can be realized by employing only three hall sensors, and the control configuration remains to be simple as that of a conventional BLdc motor drive involving two-phase conduction. The proposed motor of a 3.6 kW rating has been designed, and its various design parameters are verified on an FEM-based platform, MAGNET. A 3.6 kW motor has been fabricated and a conventional three-leg inverter is employed to drive the motor. The controller for the drive has been realized by utilizing a TMS320F28335 dsp board. The efficacy of the proposed drive is verified by performing detailed simulation and experimental studies.

A single phase, single stage, non-isolated microinverter scheme is proposed in this paper which can address the issues that are commonly associated with flyback derived microinverters, such as i) the appearance of high voltage turn OFF spikes across the high frequency switch, ii) the requirement of lossy snubbers to control these voltage spikes, iii) the necessity for high turns ratio of the transformer and iv) poor efficiency due to the involvement of a higher number of components. The proposed topology involves only one high frequency switch. A resonance capacitor is employed which not only controls the turn OFF voltage spikes across this power switch but also ensures zero voltage turn ON (ZVS) for this switch. A coupled inductor based Ćuk configuration is incorporated in this topology wherein the energy trapped in the transformer leakage inductance is fed back to the grid, thereby improving the overall efficiency. Implementation of a dedicated boundary conduction control (BCM) strategy effectively limits the value of overall system ohmic losses and thereby ensures performance with enhanced efficiency. The inverter operating principle, the process for deriving the reference current expression, and the optimum design strategy for the inverter parameters are discussed in detail. A 220 W laboratory prototype is fabricated to validate the efficacy of the proposed scheme.

A seven bus ac-dc hybrid nanogrid system for futuristic buildings (FBs), and its related control strategy are proposed in this paper. The nanogrid has one ac bus and six dc buses which can be operated simultaneously, and power from any bus can be transferred seamlessly to the other buses. Further, two dc buses and the ac bus are designed to operate both in the grid connected as well as in standalone mode. The other two dc buses are meant for interfacing solar photo voltaic (PV) system, and the battery storage. The remaining two dc buses are configured to negotiate loads at medium voltage levels. The reconfigurable feature of some of the buses enhances the applicability of the nanogrid for powering wide range of home appliances. The battery bus and the PV bus are designed for low voltage rating to minimize the series connection of batteries and PV modules respectively. Further, the requirement of lower number of series connected modules for the PV array minimizes the effect of shading. The viability of the proposed nanogrid system is validated by performing detailed experimental studies on a laboratory scale 1.2 kW nanogrid system developed for the purpose.

In high-power industrial installations, instead of a single shunt active harmonic filter (SAHF), parallel-connected multiple modular units of SAHF having lower current rating are generally preferred. In order to ensure that these modules share the compensating current in proportion to their individual current ratings, an intermodular communication network is generally being employed. This intermodular communication network reduces the overall reliability of the system, and it can be avoided if every individual module can autonomously estimate the compensating current to be shared by it. In case of voltage-source inverters operating in parallel, a droop-based current control scheme is generally employed to achieve the aforesaid requirement. However, in the SAHF, the inverters are operated in the current control mode, and hence, the existing droop-based control scheme needs appropriate modification. In this article, a modified droop-based scheme is proposed for a multimodular SAHF operating in the current control mode. The principle of operation of the proposed control scheme and its detailed mathematical analysis are presented. The feasibility of the scheme is verified by performing detailed simulation studies. A laboratory prototype having two SAHF modules, each having a VA rating of 30 kVA, is fabricated. Detailed experimental studies are carried out utilizing the laboratory prototype to confirm the viability of the proposed scheme.

In this paper, a novel multiport converter (MPC) to interface different Solar-Photovoltaic Modules (SPM), and the battery with a 380 V dc microgrid is proposed. It is ensured that all the SPMs are operated at their respective Maximum-Power Points (MPP). The boosting of the low voltages of the SPMs, and that of the battery to 380 V is accomplished by involving a DC-DC converter along with a high-frequency transformer. The battery banks are charged directly from the power of the SPM without involving the high-frequency transformer. This significantly reduces the power flow path within the system. The MPC can operate in stand-alone mode or in microgrid connected mode as and when required. As per the system demand, the MPC is capable of tracking the MPP, controlling the battery charging current, and regulating the voltage across the local loads. The proposed MPC is modeled using the first component approximation method to facilitate the design of the appropriate controllers. The effectiveness of the proposed scheme is established by performing detailed simulation studies. A hardware prototype of the MPC is fabricated. Detailed experimental studies are carried out utilizing the developed prototype to confirm the viability of the proposed scheme.