AC-DC Power Converter Research Articles

A transformerless three‐level three‐phase boost PWM inverter for PV applications

Multilevel converters have seen rising demands in the past decades, due to their increased power ratings, enhanced power quality, low switching losses and reduced electromagnetic interference. Prominent among them are the three-level (3L) neutral point clamped and the flying capacitor inverter topologies along with their derivatives. Nevertheless, the main drawback of these topologies is the requirement of a front-end boost DC–DC converter to compensate the high dc-link voltage demand, which is usually twice the grid peak voltage. This multi-stage power conversion further pulls down the overall system efficiency. A single-stage dc–ac power converter with boost capability offer an interesting alternative compared to the two stage approach. Considering this aspect, a novel three-level three-phase boost type inverter is introduced in this paper for general-purpose applications (prominently grid-connected renewable energy). The proposed inverter would reduce the DC-link voltage requirement to half using the same or even less number of active and passive components, compared to the conventional three-level neutral point clamped and flying capacitor family. The principle of operation and theoretical analysis are discussed in detail. The design methodology along with simulation and experimental waveforms for a 5 kVA inverter are presented to prove the concept of the proposed inverter topology for practical applications.

Performance of Active Clamp and Interleaved Active Clamp Fly back DC-DC Converters for PV Systems

The Flyback converter topology is a well-known and widely used for AC-DC and DC-DC power converters that cover a broad-spectrum including switching power supplies, photovoltaic (PV) system, electric cars, and fuel cell-based generation systems, and among other applications. In this work, Active Clamp Flyback (ACF) and Interleaved Active Clamp (IACF) converters are designed and simulated for the use of DC-DC converters of PV system applications. Two control systems are used to control the output voltage of the DC-DC converters for various PV conditions, which are PID (proportional integral derivatives) and FLC (fuzzy logic controller). MATLAB/SIMULINK is used to model and simulate the proposed system, where the proposed control systems are developed to regulate the output voltage for the load requirements. The simulation results of the proposed PV systems indicate that the output voltage stabilizes effectively to the required voltage (24 V) for various loads/applications while the input voltage (output from the solar panel) to the converters is varying regrading to different sun radiation levels and other parameters. The efficiency of ACF and IACF converters are found to be 88% and 90%, respectively.

WITHDRAWN: Design and analysis of ML-VSC based SMES with improved power quality features

Now a days there is high demand of power. In the process of supplying the required amount of power, the power system become complex and transient stability has become a major challenging. In order to progress transient stability there are various measures identical as discrete control of excitation systems, ML-VSC (Multi Level Voltage Source Converter) based SMES (Super Conducting Magnetic Energy Storage System) etc., in that ML-VSC based Super Conducting Magnetic Energy Storage System has acknowledged much responsiveness in the power system application. As the inertia is little, if some distraction at load side will disturb frequency of a system and it will create electromechanical oscillations. The SMES controller which is using as a fast acting storage system, it be capable of supervise the electromechanical oscillations immediately and helps in plummeting the frequency deviancies underneath the limits. This paper is apprehensive by way of the control of ML-VSC based SMES for effective assistance of active and reactive power of a power system. Super Conducting Magnetic Energy Storage System is a device comprises of a superconducting coil, wherein ac power is converted into dc by ac-dc power conversion system and it will be stored in superconducting coil as magnetic energy, it can be charged and discharged very rapidly during the ac-dc conversion because of its high storage efficiency and fast response. Here, the ML (Multilevel inverter) provides more than two voltage levels due to this the harmonic contents are reduced and desired output voltage waveform can be obtained. The time domain parameters of the SMES are controlled by PID controller with the help of PID controller technique.

Hybrid Modular Multilevel Rectifier: A New High-Efficient High-Performance Rectifier Topology for HVDC Power Delivery

This letter presents a novel three-phase rectifier topology, namely hybrid modular multilevel rectifier (HMMR) for medium or high voltage ac-dc power conversion applications. Compared with modular multilevel converter (MMC), up to 50% of the IGBTs and submodules (SMs) including capacitors can be replaced by simple high-efficient high-voltage line-frequency diode stacks. HMMR can keep the key benefits of MMC, such as modularity, reliability, and excellent harmonic performance, while significantly reducing the power losses, costs, and volume. Unlike the thyristor-based line-commutated converter (LCC) rectifier, HMMR can operate under different grid conditions and can even provide reactive power support, making it a strong candidate of rectifier unit for point-to-point MV and HV power delivery. The feasibility of proposed converter is verified by the simulation as well as experimental results.

Analytical Calculation of the Residual ZVS Losses of TCM-Operated Single-Phase PFC Rectifiers

Triangular-current-mode (TCM) modulation guarantees zero-voltage-switching across the mains cycle in AC-DC power converters, eliminating hard-switching with a minor ${\approx} {30}{\%}$ penalty in conduction losses over the conventional continuous current mode (CCM) modulation scheme. TCM-operated converters, however, include a wide variation in both switching frequency and switched current across the mains cycle, complicating an analytical description of the key operating parameters to date. In this work, we derive an analytical description for the semiconductor bridge-leg losses in a TCM AC-DC converter, including the rms current and/or conduction losses, switching frequency, and switching losses. For SiC mosfet s, we introduce a new loss model for switching losses under zero-voltage-switching, which we call “residual ZVS losses”. These losses include the constant $C_\text{oss}$ losses found in previous literature but must also add, we find, turn-off losses that occur at high switched currents. The existence and modeling of these turn-off losses, which are due to currents flowing through the Miller capacitance and raise the inner gate source voltage to the threshold level and accordingly limit the voltage slew rate, are validated on the IMZA65R027M1H 650V SiC mosfet . The complete loss model – and the promise of TCM for high power density and high efficiency – is validated on a 2.2 kW hardware bridge-leg demonstrator, which achieves a peak 99.6 $\%$ semiconductor efficiency at full load. The proposed, fully-analytical model predicts bridge-leg losses with only 12 $\%$ deviation at the nominal load, accurately including residual ZVS losses across load, modulation index, and external gate resistance.

Systematization of a Multilevel-Topology-Based Linear Amplifier Family for Noiseless DC–AC Power Conversion

Electrical power converters use semiconductor switching devices for larger loss reduction compared with non-switching power linear amplifier such as a class-B amplifier. However, it is well known that the switching operation produces harmonics and EMI noise, thus passive components are usually required for the suppression of these harmful sub-products. Use of recent fast power devices such as silicon carbide (SiC) and gallium nitride (GaN) devices produce larger dv/dt and di/dt than that of Si power devices and as a result above mentioned problem becomes more tangible. In this paper, the authors propose a concept of a family of multi-level linear amplifier (MLLA), which makes no switching power conversion possible. MLLA consist of series-connected switching devices and only one of them operates as a linear amplifier and the loss is much less than that of the class-B amplifier. The concept of the family is very useful when a proper MLLA topology might be selected for applications. In this paper, three kinds of MLLA—diode-clamped linear amplifier (DCLA), flying-capacitor linear amplifier (FCLA), and novel modular-cascaded linear amplifier (MCLA)—with four series connection of devices are investigated for the viewpoint of merits and demerits clarification and the efficiency over 82 % is demonstrated in the experiments.

A Single-Stage Multi-Port Buck-Boost Inverter

This article presents a novel inverter topology with a multi-port structure, which aims to connect two independent dc sources to a three-phase load by using single-stage power conversion. The proposed inverter has been developed to be used in hybrid renewable energy applications such as photovoltaic (PV), fuel cell (FC), and battery energy storage systems. Compared to the conventional hybrid dual-source inverters that use a multi-input dc-dc converter to provide a dc-link voltage at the input of the inverter stage, the proposed dual-source inverter uses an integrated dc-ac power conversion stage. The conventional topologies use bulky electrolytic capacitors at the input of the inverter stage, which leads to lower voltage gain and reliability due to high parasitic ESR/ESL and short lifetime of these capacitors. Moreover, compared to existing multi-port voltage source inverters, the proposed topology uses lower semiconductors, cost, and weight and has higher voltage gain. Besides, the proposed topology draws continuous current from both input ports and there is magnetic isolation between the input sources, which makes it suitable for hybrid PV and FC systems. In the proposed topology, two interlocked impedance networks are used, which are connected by coupled inductors, diodes, and capacitors. The proposed topology uses a simple switching method that is implemented with low-cost microcontrollers. The analysis and performance of the proposed inverter are verified through both computer simulations and experimental results of a 600 W-50 Hz laboratory prototype using the simple boost-SPWM modulation method.

Electromagnetic interference of using 24Vdc current control buck converter for medical light emitting diode

Recently, there has been an increasing demand for low-power LED lighting fixtures that can contribute to a low-carbon society, however because AC voltage cannot be used directly for LEDs, an ACDC power converter is required for the LED equipment. Therefore, a buck converter as an ACDC power converter is applied to the LED equipment, but the effect of electromagnetic interference (EMI) becomes an issue which cannot be ignored in wireless communication equipment. In particular, because EMI radiated emission becomes a significant problem of communication signal discontinuations, the input of the buck converter has to be installed the EMI reduction filter equipment. This research shows EMI disturbance characteristics when a buck type current control DCDC converter circuit is used for an LED lighting equipment, and reports experimental results of EMI radiated emission characteristics improvement by changing the input and output circuit constants. Moreover, it is shown that can reduce to the floor noise level (background noise) when an output chip capacitor is inserted without an input filter.

Non-visible transformations of chaotic attractors due to their ultra-low density in AC–DC power factor correction converters

Recently, it has been shown that DC–AC and AC–DC power converters whose dynamics is governed by two vastly different frequencies lead to a special class of piecewise smooth models characterized by a practically unpredictable number of switching manifolds between partitions in the state space associated with different dynamics. In the previous publications, we have shown that transformations of chaotic attractors in such models can be caused by their interactions with unstable cycles occurring in the regions of the attractors associated with an ultra-low invariant density, which is beyond a practical observability in physical or numerical experiments. The appearance of such low-density regions has been explained by the so-called spiking phenomenon. In the present paper, we make the next step and ask the natural question what are the reasons behind the appearance of spikes. Applying a novel technique (cobweb diagrams for non-autonomous maps), we explain a connection between spiking and the presence of two vastly different frequencies.

A Novel Single-Stage Five-Level Common-Ground-Boost-Type Active Neutral-Point-Clamped (5L-CGBT-ANPC) Inverter

The conventional active neutral-point-clamped (ANPC) inverter inherits excellent high-frequency common mode voltage (CMV) mitigation ability but with a restricted voltage gain. This letter proposes a novel five-level ANPC inverter that is able to accomplish voltage-boosting within a single-stage dc–ac power conversion. A common ground in the proposed topology not only mitigates the high-frequency CMV but also enhances the dc-link voltage utilization. The proposed topology exhibits lower voltage stresses and higher compactness when compared with a conventional two-stage five-level ANPC inverter. The proposed inverter saves three power switches and one capacitor while enhancing the overall efficiency. Simulations and experimental tests have validated the overall operation, efficacy, and practicality of the proposed ANPC inverter.

Topology and Control of Four-Quadrant Dual-DC-Port Dual-Buck Inverters For Semi-Two-Stage DC–AC Power Conversion

A method to derive topologies of four-quadrant dual-dc-port dual-buck inverter (DDP-DBI) is proposed in this article. A new family of DDP-DBIs is obtained by replacing one of the switching legs in a four-quadrant dual-buck half-bridge switching cell with a dual-input buck type switching leg. With the proposed DDP-DBIs, both the low voltage dc source and the high voltage intermediate dc-bus can be used as the inputs of the inverter. Therefore, in comparison with the conventional two-stage dc-ac power system, a semi-two-stage dc-ac power conversion system with reduced power losses and enhanced conversion efficiency is achieved. A unipolar sinusoidal pulse width-modulation strategy is presented for the DDP-DBI. In each line cycle, all the power devices and filter inductors only operate within half line cycle, and only one active switch is operated at high frequency. Moreover, no freewheeling current flows through the body diodes of the active switches. As a result, the conversion efficiency of the overall dc-ac power conversion system is improved. Operation principles, characteristics, modulation and control strategies of one of the proposed DDP-DBI are analyzed in detail. Effectiveness and feasibility of the proposed DDP-DBI are verified with experimental results.

Three-Phase Mission Profile Emulator for Multiple Submodules in Modular Multilevel Converter

This article proposes a highly efficient mission profile emulator (MPE) for submodules (SM) in modular multilevel converter (MMC), with respect to its basic circuit topology, control method and design. By using a common three-phase dc-ac power converter, as well as some analytical equations of MMC, the proposed MPE is capable of emulating operating conditions of multiple SMs in the MMC system. Compared with existing single-phase testing methods, the proposed three-phase structure achieves better testing efficiency. In the proposed MPE, two testing units of SMs, including four different mission profiles of submodule, are tested simultaneously with low requirements on dc power supply voltage. The comparisons between the complete MMC system and the MPE in the simulation, as well as experimental measurements, are given to verify the validity and accuracy of the proposed testing approach.

Hybrid Modulation and Power Decoupling Control on Single-Phase Bridge Inverter With Buck-Boost Converter

Single-phase H-bridge inverters provide a convenient and flexibly modulated solution to the dc–ac power conversion at once undergoing an inherent power mismatch between dc and ac sides. This article introduces a novel hybrid modulation technique that combines conventional sinusoidal pulsewidth modulation (SPWM) with pulse energy modulation (PEM) for a new single-phase bridge inverter with active power decoupling based on the front-end buck-boost converter. The proposed single-phase bridge inverter diverts the second-order ripple power into a small film capacitor at the buck-boost converter. The proposed hybrid modulation technique modulates the bridge inverter with PEM under discontinuous conduction mode (DCM) and with SPWM under continuous conduction mode (CCM), thus achieving zero-current turn-on compared with SPWM under DCM and removes a sampling circuit as compared with PEM under CCM. A 400-W single-phase inverter system has been built in Power Simulation (PSIM 11.0) to validate the theoretical analysis. Both hybrid modulation and active power decoupling control have been implemented in the experimental prototype using DSP TMS320F28335. The simulation and experimental results show that the second-order ripple power has been successfully mitigated with active power decoupling control, and the bridge inverter is able to work under both DCM and CCM with hybrid modulation.

Control of Single-Phase Electrolytic Capacitor-Less Isolated Converter for DC Low Voltage Residential Networks

In recent years, there has been a desire to improve electricity generation and consumption, to reach sustainability. Technological solutions today allow a rational use of electricity with good overall performance. Traditionally, from production to distribution, electrical energy is AC-supported for compatibility reasons and easy voltage level transformation. However, nowadays most electric loads need DC power to work properly. A single high-efficiency central AC-DC power converter may be advantageous in eliminating several less efficient AC-DC embedded converters, distributed all over a residential area. This paper presents a new single-phase AC-DC converter using one active bridge (most isolated topologies are based on the dual active bridge concept) and a high-frequency isolation transformer with low-value non-electrolytic capacitors, together with its control system design. The converter can be introduced into future low-voltage DC microgrids for residential buildings, as an alternative to several embedded AC-DC converters. Non-linear control techniques (sliding mode control and the Lyapunov direct method) are employed to guarantee stability in the output DC low voltage with near unity power factor compensation in the AC grid. The designed converter and controllers were simulated using Matlab/Simulink and tested in a lab experimental prototype using digital signal processing (DSP) to evaluate system performance.

New Multifunctional Isolated Microinverter with Integrated Energy Storage System for PV Applications

This paper proposes a novel multifunctional isolated microinverter which is able to extract the maximum available power from a solar photovoltaic module and inject it into the power grid, while simultaneously charging a battery energy storage system (BESS). The proposed microinverter integrates a novel DC–DC power converter and a conventional DC–AC power converter. The DC–DC power converter is able to send electrical energy to the secondary side of a high-frequency transformer and to the BESS, using only two power switches. Throughout this paper, the converter topology, the operation modes, the control algorithms, and the development of a laboratory prototype of the proposed microinverter are described in detail. Moreover, simulation and experimental results are presented to demonstrate the feasibility of the proposed solution.

AC–DC boost converter based on T-type multi-state switching cell and output voltage balancing

A novel topology of the ac–dc power converter to supply neutral-point-clamped inverters used in ac motor drives and wind offshore power grids is proposed. It is based on the T-type multi-state switching cell, which allows obtaining a five-level voltage waveform downstream of the input filter inductor. The converter presents a high voltage gain due to the transformer secondary windings associated with series-connected diode rectifiers. Prominent main characteristics of this topology include power factor correction, operation of the filter inductor at twice the switching frequency, reduced conduction losses in the semiconductors, and voltage balance across the output capacitors. To verify the operating principle of the converter a design example is described, considering that the converter specifications are: output power of 3 kW; rms input voltage of 110 V; total output voltage of 1 kV, which is equally divided among four capacitors and switching frequency of 20 kHz. Simulation results are shown to validate the theoretical assumptions and verify the behaviour of the rectifier in terms of dynamic response while also supplying unbalanced loads.

A VHF Wide-Input Range CMOS Passive Rectifier With Active Bias Tuning

Tiny implantable medical devices in millimeter size demand advanced wireless power solutions that operate at hundreds of megahertz and mainly use passive rectifiers for ac–dc power conversion. A conventional cross-connected (CC) rectifier can operate with high frequency and low input voltage but only achieves good efficiencies in a very narrow input power range, due to the shoot-through and reverse currents. This work presents a CMOS passive rectifier with active bias tuning (ABT), allowing a widely extended input range with high power conversion efficiency (PCE). In addition, we compensate for the process, voltage, and temperature variations with the ABT scheme that leads to a robust design for very-high-frequency (VHF) operation. Meanwhile, we propose a peak $V_{\mathrm {OUT}}$ searching scheme to indicate the charging/discharging directions for the ABT. We obtain a bias-voltage balancing among stacked rectifier stages with a switched-capacitor network. The proposed rectifier is fabricated in a 65-nm CMOS process. Measurement results of three chips show that the proposed rectifier improves the PCE over a wide input range, with an average maximum PCE of 64.4%.

Single-Phase Step-Up Switched-Capacitor-Based Multilevel Inverter Topology With SHEPWM

Multilevel inverter (MLI) topologies play a crucial role in the dc-ac power conversion due to their high-quality performance and efficiency. This article aims to propose a new switched-capacitor-based boost multilevel inverter topology (SCMLI). The proposed topology consists of nine power semiconductor switches with one dc voltage source and two capacitors, capable of generating a nine-level output voltage waveform with twice voltage gain. With the addition of two switches, the proposed topology can be used for higher voltage-gain applications. Other features of the proposed topology include the self-voltage balancing of the capacitors, parallel operation of the capacitors, lower voltage stress across the switches, along with the inherent polarity changing capability. To obtain the high-quality output waveform, a selective harmonic elimination pulsewidth modulation technique is applied. In this technique, the detrimental low-order harmonics can easily be regulated and eliminated from the output voltage of MLI. The proposed topology is compared with the recently introduced SCMLI topologies considering various parameters to set the benchmark of the proposed topology. The performance of the proposed MLI is investigated through various experimental results using a laboratory prototype setup.

A Three-Level Isolated AC–DC PFC Power Converter Topology With a Reduced Number of Switches

The main objective of this research work is to develop a new low-cost isolated three-level ac–dc power converter topology with a reduced number of switches. Existing three-level converter topologies change ac power to dc power while maintaining requirements set by international standards for power conversion. These types of converters have significant conduction losses due to high currents in the low-voltage side and high costs, mainly when using several active devices in series or in parallel to achieve high-voltage and high-power levels. The proposed topology replaces the conventional three-level converters in the secondary side by only two controlled devices and four diodes while still maintaining the basic functionality of a three-level converter. Furthermore, simulation results for a 25-kW case study and experimental results on a 900-W scale-down prototype demonstrate the feasibility of the proposed ideas.

A Novel Power Decoupling Control Method to Eliminate the Double Line Frequency Ripple of Two Stage Single-Phase DC-AC Power Conversion Systems

In two-stage single-phase inverters, inherent double line frequency ripple is present at both the input and output of the front-end converter. Generally, large electrolytic capacitors are used to eliminate this double line frequency ripple. It is well known that low frequency ripple shortens the lifespan of capacitors. Hence, the system reliability can get worse. In order to eliminate the double line frequency ripple, additional hardware combined with an energy storage device is required in most of the methods developed so far. In this paper, a novel power-decoupling control method is proposed to eliminate the double line frequency ripple at the front-end converter of two-stage single phase DC/AC power conversion systems. The proposed control algorithm is composed of two loops, a ripple compensation loop and an average voltage control loop, and no extra hardware is required. Since the proposed method does not require information from the phase-locked-loop (PLL) of the inverter, it is independent of inverter control. In order to verify the validity and feasibility of the proposed algorithm a 5 kW Dual Active Bridge (DAB) DC/DC converter and a single-phase inverter are implemented. The effectiveness of the proposed method is verified through the simulation and experimental results.