Non-inverting buck-boost derived hybrid converter

This paper proposes a family of novel flying capacitor transformerless inverters for single-phase photovoltaic (PV) systems. Each of the new topologies proposed is based on a flying capacitor principle and requires only four power switches and/or diodes, one capacitor, and a small filter at the output stage. A simple unipolar sinusoidal pulse width modulation technique is used to modulate the inverter to minimize the switching loss, output current ripple, and the filter requirements. In general, the main advantages of the new inverter topologies are: 1) the negative polarity of the PV is directly connected to the grid, and therefore, no leakage current; 2) reactive power compensation capability; and 3) the output ac voltage peak is equal to the input dc voltage (unlike neutral-point-clamped and derivative topologies, which requires twice the magnitude of the peak ac voltage). A complete description of the operating principle with modulation techniques, design guidelines, and comprehensive comparisons is presented to reveal the properties and limitations of each topology in detail. Finally, experimental results of 1-kVA prototypes are presented to prove the concept and theoretical analysis of the proposed inverter family for practical applications.

Transformerless inverters are becoming popular, especially in the field of renewable energy systems because of their compactness in size and higher efficiency. However these topologies are suffering from leakage currents and they can be reduced by clamping the neutral point during freewheeling modes. Two types of basic switching cells are introduced to build the proposed topology. They are positive neutral point clamping cell and negative neutral point clamping cell. Using these two cells proposed topology is clearly explained. In this paper unipolar sinusoidal pulse width modulation (UPSPWM) which is already existing and modified unipolar sinusoidal pulse width modulation (MUPSPWM) which is proposed to these topologies for getting an improved result. These two types used for creating switching pulse pattern for all topologies and then obtained results are compared in respect of THD. Existing topologies like OH5 and full bridge dc bypass (FB-DCBP) are also simulated with both PWM techniques and their results are compared to proposed topology in respect of total harmonic distortion (T.H.D) and number of switches. Results showing in this paper are validated by simulating with MATLAB.

This paper presents a comparative experimental study of bipolar and unipolar switching schemes of a single-phase inverter based stand-alone PV system. The single-phase inverter is connected with the PV string and DC-DC converter in subsequent arrangement along with maximum power point tracking (MPPT) for optimum power generation in autonomous mode despite of changing irradiance condition. The steady-state and transient behaviour of both incremental conductance (INC) and variable step-size incremental conductance (VSSINC) MPPT algorithms are analyzed thoroughly. The sinusoidal pulse width modulation (SPWM) technique is incorporated to create the proper gate signals for the inverter switches. The inherent harmonic component in output inverter voltage is somewhat reduced by choosing a high frequency carrier signal and an LC filter is designed to eliminate the higher order harmonics. A laboratory setup for the dual-stage stand-alone PV system is developed using a boost converter, 1 − ϕ inverter and the control schemes are implemented using the dSPACE RTI1103 digital controller. The INC and VSSINC MPPT results are presented at varying irradiation. The functionality of the bipolar and unipolar SPWM are observed at an irradiation of 210 W/m2 which confirms that the unipolar SPWM gives superior performance than bipolar SPWM switching.

This paper provides a comparative analysis of bipolar versus unipolar Sinusoidal Pulse Width Modulation (SPWM) in DC-AC inverters, focusing on Total Harmonic Distortion (THD) across modulation indices and the latter’s effects on the R-L loads. Using the PIC18F2431 microcontroller for its efficiency, a single-phase inverter accomplished to deliver a high-fidelity sine wave. This study discovered that while both SPWM methods reduce harmonics, the unipolar approach yields more uniform THD reduction and superior performance, particularly noticeable in RL load conditions, where minimal harmonic distortion is crucial. The bipolar inverter, despite a higher initial THD, shows a considerable improvement at higher indices, significantly enhanced by an LC low-pass filter. This filter is a key component in achieving sub-1% THD levels at full modulation, ensuring optimal sine wave quality. The findings highlight the operational differences between the SPWM techniques and the importance of the LC filters in ameliorating the inverter output for various power applications.

In this paper, Design and development of control circuit algorithm of 3-Φ Voltage Source Inverter (VSI) using Unipolar Sinusoidal Pulse Width Modulation (SPWM) techniques is proposed using STM32F407VGTx discovery board interfaced with MATLAB Simulink Environment. For implementing 3-Φ VSI, this method is most useful as it will eliminate complexity of control circuit algorithm occurred due to analog circuit, reduces cost, size of filter required, and improved overall inverter efficiency. Pulse width modulated voltage source inverter is preferred for high performance AC drives. The proposed control scheme and the result obtained by embedded simulations interfaced with STM32F4 microcontroller are presented and discussed. A simple hardware implementation is proposed and experimental results of SPWM based VSI are also shown. The Simulation results of the proposed scheme have excellent performance and compared with hardware results.

A novel zero-voltage and zero-current soft-switching PWM DC-DC converter with low voltage and current stresses is presented in this paper. A new interleaved two switch forward converter topology is developed to minimize circulating current with no additional auxiliary circuits. This converter has many advantages such as less components, better efficiency, high power density and cost effectiveness for high power applications. The principle of operation is illustrated together with steady-state analysis. Moreover the effectiveness of the proposed converter topology is verified by simulation and experiments.

This paper presents a simple method for the microcontroller implementation of a noninverting buck-boost converter. The converter requires two switches, but only one set of controls. As compared to a cascaded buck converter/boost converter topology, the noninverting buck-boost converter requires one less capacitor and inductor. The system operates as a buck converter for duty cycles between 0-50% in the microcontroller, and as a boost converter (up to a gain of twice the input voltage) for duty cycles between 50-100%. The system is therefore also advantageous because the microcontroller algorithm prevents a dead short from occurring during operation in the boost converter mode. Experimental and PSpice results prove that both buck and boost operation are possible using this topology. The effect of the load resistance on the results is discussed.

This paper describes an application of the space vector modulation (SPM) technique to a photovoltaic assisted single-phase line-interactive inverter operating as an uninterruptible power supply (UPS). The performance of this inverter is comparable to a unipolar sinusoidal pulse width modulation (SPWM) operating at higher switching frequencies. Preliminary experimental results using a DSP-based system and simulation using Matlab/Simulink confirm the validity of the proposal. This UPS has built in features such as active filtering, demand side management and integration of renewable energy sources such as photovoltaic (PV). In this paper, comparison of SVM and SPWM in single-phase together with simulation and experimental results are also included.

In the transformerless photovoltaic (PV) system, the common mode ground leakage current may appear due to the galvanic connection between the PV array and the ground, which causes the safety issues and reduces the efficiency. To solve this problem, a novel inverter topology with switched capacitors is proposed in this paper. By connecting one pole of the PV cell directly to the neutral line of the grid, the common mode current is eliminated. Meanwhile, the switched capacitor technology is applied to increase the DC voltage utilization rate. Furthermore, a modified unipolar sinusoidal pulse width modulation (SPWM) strategy is proposed to reduce the pulsating current caused by the charging and discharging operations of the switched capacitors. Also, several optimization principles are put forward to further reduce the pulsating current to improve the efficiency and reliability. Finally, the proposed topology and modulation strategy are verified with simulation and a 250W experimental prototype.

A novel zero-voltage and zero-current soft-switching PWM DC-DC converter with low conduction losses is presented in this paper. A new interleaved two switch forward converter topology is developed to minimize circulating current with no additional auxiliary circuits. This converter has many advantages such as less components, better efficiency, high power density and cost effectiveness for high power applications. The principle of operation is illustrated together with steady-state analysis. Moreover, the effectiveness of the proposed converter topology is verified by implementing a 500 W-100 kHz breadboard.

This paper focuses on the non-inverting buck- boost converter operated as either buck or boost converter. It is shown that a pulse-width modulation (PWM) discontinuity around buck/boost mode transition can result in substantial increases in output voltage ripple. The effect of the PWM nonlinearity is studied using periodic steady state analysis to quantify the worst case ripple voltage in terms of design parameters. Furthermore, a bifurcation analysis shows that the PWM discontinuity leads to quasi- periodic route to chaos, which results in erratic operation around the buck/boost mode transition. The increased ripple is a very significant problem when the converter is used as a power supply for an RF power amplifier, as is the case in WCDMA handsets. An approach is proposed to remove the discontinuity which results in reduced output voltage ripple, at the expense of reduced efficiency, as demonstrated on an experimental prototype.

With the advent of battery-powered portable devices and mandatory adoption of power factor correction, noninverting buck-boost converters are garnering lots of attention. Conventional two-switch or four-switch noninverting buck-boost converters choose their operation modes by measuring input and output voltage magnitude. The criterion for the selection of the operation mode can cause higher output voltage transients in the neighborhood, where input and output are close to each other. For the mode selection, due to the voltage drops raised by the parasitic components, it is not enough just to compare the magnitude of input and output voltages. In addition, the difference in the minimum and maximum effective duty cycles between controller output and switching device yields discontinuity at the instant of mode change. Moreover, the different properties of output voltage versus a given duty cycle of buck and boost operating modes contribute to the output voltage transients. In this paper, the effect of the discontinuity due to the effective duty cycle derived from the device switching time at the mode change is analyzed. A technique to compensate the output voltage transient due to this discontinuity is proposed. In order to attain additional mitigation of output transients and a linear input/output voltage characteristic in buck and boost modes, the linearization of DC gain of the large-signal model in boost operation is analyzed as well. Analytical, simulation, and experimental results are presented to validate the proposed theory.

This paper proposes a new single-phase H-Bridge transformerless inverter with common ground for grid-connected photovoltaic systems (hereafter it is called `Siwakoti-H' inverter). The inverter works on the principle of flying capacitor and consists of only four power switches (two reverse blocking IGBT's (RB-IGBT) and two MOSFET's), a capacitor and a small filter at the output stage. The proposed topology share a common ground with the grid and the PV source. A Unipolar Sinusoidal Pulse-Width Modulation (SPWM) technique is used to modulate the inverter to minimize switching loss, output current ripple and filter requirements. The main advantages of the new inverter topology are the elimination of the leakage current and ability to provide reactive power to the grid. Further, the peak of output ac voltage is equal to input dc-voltage (unlike NPC and ANPC type which requires two times of the peak ac-voltage magnitude). Simulation as well as experimental results from a 1 kW prototype are presented at the end of the paper to prove the concept and also the theoretical analysis presented.

IGCTs are especially adapted for high-power applications. In Voltage Source Converter (VSC) IGCT applications a series di/dt limiting inductor and a clamp circuit must be used, in order to protect freewheel diodes from excessive current derivatives. The main parameter to be considered in the clamping circuit design is the characteristics of the DC bus current, which may depend both on the converter topology and the chosen modulation strategy. In this paper a current di/dt limiter circuit for a H-Bridge with Bipolar and Unipolar modulation is designed and experimentally validated. It is shown that if the same clamp parameters are used for both modulations strategies, the semiconductor current di/dt in the Bipolar case is 50% smaller than in the Unipolar one. In addition, the turn-on overcurrent and the turn off overvoltage with the Bipolar modulation are twice with respect to the Unipolar ones. Thus, if the aim is to obtain the same overvoltage in both cases, the maximum output current for the Bipolar case will have to be 50% smaller.

The FC sources are unregulated voltage sources and require power converter devices to get a regulated output voltage. When these devices are used in low voltage low power applications DC-DC buck-boost converters (BBC) are required to get the regulated voltage on load side. The multi device multi switch operation of the buck-boost converters are usually employed for successful operation of the FC stacks. In this paper, the different non-inverting type of buck-boost converters i.e., buck-boost converter (BBC), multi-device buck-boost converter (MDBBC), interleaved buck-boost converter (IBBC), and multi-device interleaved buck-boost converters (MDIBBC) are analysed and comparative study among them are presented with respect to the parameters like, ripple current, component size, power losses and efficiency. The comparative study demonstrates that the multi device converter topologies are more efficient than the other converter topologies employed in low voltage low power applications.