Transformerless inverters are widely used in different photovoltaic nonisolated ac module applications, mainly in grid-tied photovoltaic (PV) generation systems, due to the benefits of achieving high efficiency over a wide load range, and low cost. Various transformerless inverter topologies have been proposed to meet the safety requirement of low ground leakage currents, such as specified in the VDE-4105 standard and low-output ac-current distortion. Topology modifications of transformerless full bridge inverters are designed to balance and maintain a constant common mode output voltage, thereby eliminating or reducing leakage currents. This article reviews and compares the different methods for limiting leakage currents in known topologies of the full-bridge transformerless inverters, such as: H4, H5, H6, HERIC, and their improvements. The main topologies and strategies used to reduce the leakage current in transformerless schemes are summarized, highlighting advantages and disadvantages and establishing points of comparison with similar topologies. To compare the properties of different medium to high power inverters, PV inverter topologies were implemented using IGBTs and tested with the same components, same simulation parameters in PSPICE to evaluate their performance in terms of energy efficiency and leakage current characteristics. The detailed power stage operating principles, extended PWM modulator, and integrated universal gate driver with galvanic isolation in the transmission path of control signal for all IGBTs of the inverter, as well isolated and floating bias power supply for gate drivers are described.

This paper presents new and original architectures and implementations of two filterless, open-loop digital Class-BD audio amplifiers with constant common mode (CM) output voltage. The first, low-power amplifier consists of four ultrahigh-current EL7158 pin drivers, the OUT pins of which form the H bridge. The drivers are controlled from the extended LBDD PWM modulator and have appropriately set voltage levels on the VL and VH pins. The second proposed amplifier consists of two cooperating H-bridge power stages (HBS) implemented on complementary MOSFET pairs and powered by two different voltages. Both HBSs are driven by four EL7158 pin drivers having appropriately adjusted voltage levels on the VL and VH pins and controlled by an extended LBDD PWM modulator. The hybrid 9 bit DPWM modulator uses a linearized Class-BD double-sided modulation scheme with pre-compensation, enabling the most faithful emulation of natural NBDD PWM and, thus, providing attractive spectral characteristics at the DM output. Basic SPICE simulations and experimental results of the proposed digital Class-BD amplifiers were compared with the conventional digital Class-BD amplifiers. The elimination of CM signals significantly contributes to the reduction in electromagnetic interference (EMI), particularly those produced on the cables connecting the loudspeaker to the HBS terminal. Proposed Class-BD amplifiers with original and new topologies, due to their simple design and easy control (no galvanic isolation of control signals and no floating bias power supplies), which generate no CM voltage and feature excellent DM performance, similar to conventional Class-BD amplifiers, are very attractive solutions for filterless Class-BD amplifiers.

This paper presents new architectures and implementations of original open-loop Class-BD audio amplifiers with balanced Common-Mode output. The output stage of each proposed amplifier includes the typical H-bridge with four MOSFETs and four additional MOSFET switches that balance and keep the Common-Mode output constant. The presented amplifiers employ the extended NBDD PWM or PSC PWM modulation scheme. When the output stage is built only on NMOSFET transistors, gate drivers require a floating power supply, using a self-boost charge pump with capacitive isolation of the control signal. The use of complementary MOSFETs in the output stage greatly simplifies gate control systems. The proposed amplifiers were compared to the typical Class-BD configuration, using the optimal NBDD modulation with respect to audio performance of the Differential-Mode (DM) and Common-Mode (CM) outputs. Basic SPICE simulations and experimental studies have shown that the proposed Class-BD amplifiers have similar audio performance to the prototype with the optimal NBDD modulation scheme, while at the same time having a balanced constant voltage CM output, thus eliminating the main contributor to radiation emission. As a result, the filtering of the DM output signals can be greatly simplified, while the filtering of the CM output signals can be theoretically eliminated. Practically, due to the timing errors added by the gate drivers, spikes are generated at the CM output, which are very easy to filter out by the reduced LC output filter, even at very low L.

The paper proposes an original single-phase transformerless three-level (S-PT) photovoltaic (PV) inverter in the cascade H bridge (CHB) configuration. The DC-link voltage of the inverter is created by two serial voltage sources with a voltage twice as low as the DC-link voltage. An appropriate V_CC DC-link voltage is generated by a two-phase DC-DC boost converter, fed from the string panel output at a level determined by the maximum power point tracking (MPPT) algorithm. Two symmetrical sources with V_CC/2 are formed by a divider of two series-connected capacitors of large and the same capacitance. The common mode (CM) voltage of the proposed inverter is constant, and the voltage stresses across all switches, diodes and gate drive circuits are half of the DC-link voltage. The principles of operation of the S-PT inverter, an implementation of a complete gate control system with galvanic isolation for all IGBTs, are also presented. The proposed inverter topologies have been implemented using high-speed IGBTs and simulated in PSPICE, as well as being experimentally validated.