AC Power Conversion Research Articles

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.

A Latency-Insensitive Design Approach to Programmable FPGA-Based Real-Time Simulators

This paper presents a methodology for the design of field-programmable gate array (FPGA)-based real-time simulators (RTSs) for power electronic circuits (PECs). The programmability of the simulator results from the use of an efficient and scalable overlay architecture (OA). The proposed OA relies on a latency-insensitive design (LID) paradigm. LID consists of connecting small processing units that automatically synchronize and exchange data when appropriate. The use of such data-driven architecture aims to ease the design process while achieving a higher computational efficiency. The benefits of the proposed approach is evaluated by assessing the performance of the proposed solver in the simulation of a two-stage AC–AC power converter. The minimum achievable time-step and FPGA resource consumption for a wide range of power converter sizes is also evaluated. The proposed overlays are parametrizable in size, they are cost-effective, they provide sub-microsecond time-steps, and they offer a high computational performance with a reported peak performance of 300 GFLOPS.

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.

전기추진선박의 제어전원 및 보조장치 전원공급용 DC/AC 인버터의 입력전압변동 시험평가 및 분석

The main power supply of electric vehicles and ships is generally composed of a battery, a generator and a fuel cell, and a propulsion motor and inverter are used as a driving device. In addition to the main power supply for electric power-driven driving, additional auxiliary power supply for control system and auxiliary system is required, and power conversion devices (inverters and converters) are used for this purpose. Power conversion devices for auxiliary power supply receives power from main power supply such as battery, generator and fuel cell and performs the AC or DC power conversion. The voltage variation of main power supply depends on the usage conditions of electric propulsion system. The power conversion devices for auxiliary power supply shall not cause output stop even if the voltage of main power supply suddenly changes to the allowable voltage range. The output of the power conversion devices for auxiliary power supply shall have an operating capability to produce a stable output within the permitted voltage range. This paper deals with the test evaluation and analysis for the input voltage fluctuation of the DC/AC inverter(power conversion devices) in auxiliary power supply of electric ship..

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.

An Isolated Bidirectional Microinverter Based on Voltage-in-Phase PWM-Controlled Resonant Converter

A single-stage single-phase isolated bidirectional microinverter based on a voltage-in-phase pulsewidth modulation (VIP-PWM)-controlled resonant converter is proposed in this article. With the VIP-PWM control, the voltage conversion ratio of the resonant converter can be regulated from zero to infinity, theoretically, which means the VIP-PWM is suitable for wide-voltage-range applications, such as single-stage isolated inverters. Moreover, the voltage conversion ratio of the resonant converter is only determined by the equivalent duty cycle and is independent of the value and the direction of the transferred power. Therefore, the value and the direction of the power flow can be changed smoothly, which makes the proposed converter suitable for bidirectional dc–ac power conversion. Accordingly, a simple unified current controller can be employed for both inverter and rectifier modes. In addition, soft switching can be achieved during most of the grid period, and high efficiency can be achieved with the proposed solution. Detailed operation principles, characteristics, design considerations, and control strategy of the proposed microinverter are presented. A 300-W prototype with an input voltage range of 25–40 V is established and tested to verify the effectiveness and feasibility of the proposed solution.

DFIG Model Suitable for SSR Research

The simulation model of doubly fed induction generator (DFIG) is the basis of the research on subsynchronous resonance (SSR) of DFIG. In this paper, the conditions that the model of DFIG is suitable for the research of subsynchronous oscillation (SSO) are analyzed firstly. Then, the drive system, doubly fed induction motor, AC / DC / AC power converter and control strategy of DFIG are modeled, and these models are unified as electromechanical model. At last, the validity of the model is verified by the example of SSR when the DFIG is sent out through series compensated transmission line.

Delta-Sigma Modulation Based Common-Mode Voltage Elimination in Direct Matrix Converter

The direct matrix converter (DMC) offers a compact and robust solution over typical ac–dc–ac converter, by enabling direct ac–ac power conversion without any energy storage requirements. Moreover, it offers enhanced source current quality, innate bidirectionality and power factor correction capabilities. Its industrial suitability is further advocated by the elimination of common-mode voltage through the DMC topology. Space vector modulation and model predictive control based approach to common-mode voltage elimination in matrix converter, are previously proposed. This article proposes the delta-sigma modulation for common-mode voltage elimination in matrix converter, which is computationally less cumbersome and performs better as compared to previously documented methods. This method utilizes only six most optimum states of DMC that yield zero common-mode voltage, and performs load voltage and source current control by computing each error variable (delta), integrating it (sigma) and further minimizing it within a hysteresis band. Source current control necessitates load current estimation, which is done through predictive model of the load, hence eliminating load current sensors.

Interactive Grid Interfacing System by Matrix-Converter-Based Solid State Transformer With Model Predictive Control

The back-to-back connection of two three-to-single-phase matrix converters (MCs) through a high-frequency transformer to create the so called MC-based solid state transformer (SST) for interactive grid interfacing is proposed in this paper. The solution provides single-stage bidirectional ac–ac power conversion. There are advantages of no lifetime-limited storage capacitors, light weight, and compact volume. The conventional modulation methods of this MC-SST system require additional control design for power management. Besides, space vector modulation contains sophisticated voltage and current vectors computation and duty cycle composition, considering the two back-to-back connected three-to-single-phase MCs. In this paper, a model predictive control (MPC) is proposed for this MC-SST linking different ac grids. The proposed MPC predicts the state variables based on the discrete model of MC-SST system and the present circuit variables, and then selects an optimal switching state that ensures the smallest value of a cost function, for the next sampling time. Simulation and experimental studies are carried out to demonstrate effectiveness and simplicity of the proposed MPC for such MC-SST grid-interfacing system.

PENGELOMPOKAN SEBARAN TRANSFORMATOR DISTRIBUSI BERDASARKAN KAPASITAS DAYA MENGGUNAKAN METODE NAÏVE BAYES Studi Kasus: PT. PLN RAYON KOTA SAMARINDA

Human needs for energy are mostly obtained from electrical energy, both for daily needs and for industrial needs. PT. PLN (Persero) is one of the state electricity companies that serves the community's need for electricity. Transformer or better known as "transformer" or "transformer" is actually an electrical device that converts AC power at one voltage level to one voltage level based on the principle of electromagnetic induction without changing its frequency. Because of the lack of distribution of transformers around the Samarinda area, it can result in electricity demand services to the community. Therefore we need a method that can facilitate the distribution of PT. PLN Rayon Kota Samarinda, one of the methods is by applying Naïve Bayes. The purpose of this study is to facilitate the distribution in each region and the type of transformer used. The results of calculations using the Naïve Bayes method, the results obtained the probability of grouping training data is P (160) = 0.006441224, P (100) = 0.016304348, P (80) = 0.001610306, P (50) = 0.001610306, P (40) = 0.000402576, P P (20) = 0,000679348. From the calculation results, it appears that the probability value P (100) is more dominant, then 100 is recommended for real consumption which is used as training data. The Naïve Bayes method produces an accuracy rate of 92%.

Novel Active-Neutral-Point-Clamped Inverters With Improved Voltage-Boosting Capability

Conventional active-neutral-point-clamped (ANPC) inverters exhibit low voltage gain that inherently leads to a high dc-link voltage requirement. An improved ANPC inverter that is capable of generating five voltage levels has recently reduced the dc-link voltage twofold to achieve unity gain. This led to the development of a single-stage dc–ac power converter with no frontend boost dc–dc converter. This article proposes novel ANPC inverters capable of unity or boosted voltage gain while generating higher voltage levels. The first topology can provide a voltage gain of 1.5 and extends the number of levels to seven by incorporating only one additional switch. The topology can also be extended by adding three switches and one floating capacitor to generate nine levels with unity voltage gain, or 11 levels with a voltage gain of 2.5. The proposed ANPC inverters and their operations are comprehensively discussed. Experimental results are provided to validate the feasibility of the proposed ANPC inverters.

A Highly Reliable and Efficient Class of Single-Stage High-Frequency AC-Link Converters

This paper proposes a new class of topologies of single-stage high-frequency ac-link power converters, which is capable of providing both voltage step up/down within a wide frequency and voltage ranges. The proposed family, which supports bidirectional power flow, can interface various single/multi-port dc and/or single/multi-phase ac systems to provide dc–dc, dc–ac, ac–dc, or ac–ac power conversion. In this family of converter, which offers a very modular structure, a small inductor that forms the link exchanges power entirely or partially between the source and load. The proposed family can function in buck, boost, and/or buck–boost modes of operation, and a combination of these modes of operation is also feasible. In comparison to the parallel inductive four-quadrant link converters, the proposed family features a significantly reduced link peak current, reduced switch ratings, and reduced total number of power switches. These features enhance the efficiency, reduce the total cost, and increase the power density of the system. In order to further improve the overall efficiency of the system, minimize the current/voltage stress over all utilized semiconductor devices, and lower electromagnetic interference (EMI), a small capacitor is placed in parallel with the link inductor to realize soft-switching operation for the proposed configurations. Moreover, the proposed converters have the potential to incorporate a lightweight single-phase high-frequency transformer for electrical isolation. The proposed circuit topologies prevent reverse recovery issues and eliminate losses corresponding to body diodes of power switching devices via utilizing power switches in conjunction with external fast recovery diodes. The proposed family offers a very high level of reliability owing to its immunity from short circuit of input and output terminals and open circuit of the link inductor, which may occur in other power converters due to commutation problem resulting from a short deadtime or an overlap time between switches, unwanted control command, delay in electronic circuits, or EMI noise's misgating on or off , in addition to the absence of electrolytic capacitors in the power circuit. A control approach is also developed to regulate input and output currents in one stage of power conversion. A detailed theoretical analysis, operation, design methodology, and control strategy of the proposed family are provided in this paper, and the effectiveness and performance of the proposed converter family are verified via simulation results and experimentally.

Two-Stage Isolated Bidirectional DC–AC Converters With Three-Port Converters and Two DC Buses

A novel two-stage structure with two dc buses is proposed for isolated bidirectional dc–ac power conversion. A variable dc-link voltage plus a constant dc-link voltage operation is adopted for the proposed two-stage structure. One of the dc-link voltages is regulated adaptively according to the variation of dc-side voltage, so that the dc–dc power stage can always work at its optimized point. New families of three-port (TP) bidirectional dc–dc converters and TP bidirectional inverter/rectifier (TP-BIR) are proposed to implement the proposed two-stage dc–ac power conversion structure. A bidirectional dc–ac converter composed of a TP-CLLC resonant converter and a T-type TP-BIR is taken as an example to verify the effectiveness of the proposed structure. Operation principles of both the TP-CLLC resonant converter and the T-type TP-BIR are analyzed in detail. Modulation and control strategies are proposed for the TP-BIR to achieve voltage regulation and power distribution between the two dc buses. A 1.5-kW prototype is built and tested to verify the feasibility and advantages of the proposed solution.

PV Micro-Inverter Topology Using LLC Resonant Converter

In this paper, a DC–single-phase AC power converter with an LLC resonant converter is presented for a photovoltaic (PV) micro-inverter application. This application requires the leakage current suppression capability. Therefore, an isolated power converter is usually combined for DC/AC systems. The LLC resonant converter is the one of the isolated power converter topologies, and it has good performance for conversion efficiency with easy control. On the other hand, a double-line frequency power ripple has to be compensated for in order to improve the performance of the maximum power point tracking (MPPT). Therefore, a bulky electrolytic capacitor is usually necessary for the power converter. However, the electrolytic capacitor may limit the lifetime of the micro-inverter. This paper introduces the PV micro-inverter with a LLC resonant converter. In addition, the active power decoupling circuit is applied in order to compensate the double-line frequency power ripple by the small capacitor in order to eliminate the electrolytic capacitor. Finally, the transformer design is considered in order to reduce the transformer losses. As a result, the conversion efficiency of the LLC converter is improved by 1% when the litz wire has many strands.

Switched capacitors 9‐level module (SC9LM) with reduced device count for multilevel DC to AC power conversion

Switched capacitors (SCs)-based modules are being increasingly used for multilevel DC to AC power conversion, especially for low input voltage applications. Many of these topologies operate in two stages involving H-bridge switches, which endure high-voltage stress. The SC 9-level module (SC9LM) presented here operates in a single stage with one DC source and two capacitors. In addition, the peak inverse voltage of all power switches is confined to the voltage of the input DC source. The proposed 9-level module ensures a reduced number of power switches. In addition, with appropriate utilisation of states, two of the eleven switches in the module operate at fundamental switching frequency, thereby minimising the switching losses. A single SC9LM achieves a voltage gain of two. The proposed module is validated through circuit analysis followed by simulation and experimental results.

Generalized Formulations and Solving Techniques for Selective Harmonic Elimination PWM Strategy: A Review

Multilevel inverters (MLIs) are widely recommended for DC to AC power conversion as per the load requirements. The MLIs are preferred over other types of multilevel and conventional converters due to their ability to produce staircase output voltage waveforms with superior harmonics profile. However, the performance of MLIs largely depends on the modulation strategy employed. Among the various modulation techniques, the selective harmonic elimination (SHE) method is more efficient in eliminating low-order harmonics from the voltage waveform produced by MLIs. Proper mitigation of the dominant low-order harmonics results in reduction in switching losses in the semiconductor devices and improves the efficiency of the inverter. However, the analytical solution of the nonlinear SHE equations constitutes the main challenge. Over last few decades, various solving algorithms and techniques such as algebraic methods such as resultant theory, numerical techniques and optimization algorithms have been developed and proposed for selective elimination of unwanted harmonics. This review paper presents the various aspects of the problem formulations for SHE technique. Moreover, the detailed principle operation for five different SHE problem-solving techniques is also discussed in this paper. Solution trajectories corresponding to multiple solutions, PWM waveforms with single and multiple transitions at each voltage level and also for pulse-width-amplitude modulation are evaluated and presented to help the researchers gain better insight into the SHE problem and its solution.

The Dual-Current Control Strategy of Grid-Connected Inverter With LCL Filter

In the renewable energy generation systems, the grid-connected inverter with LCL filter (GCI- LCL ) is an important device to realize dc–ac power conversion and connect the distributed power generation system and power grid. However, the resonance problems of the LCL filter may bring instability to GCI- LCL . Besides, the grid impedance and the time delay in digital controllers also have a harmful influence on the stability of GCI- LCL . To solve these problems, a dual-current active damping control strategy based on the inverter-side current and grid-connected current feedback for GCI- LCL is proposed in this paper, and the systematic parameters design process is investigated. Compared with the conventional damping strategies, a resonance suppression for the LCL filter, a larger stability margin, and a better anti-interference capability in a weak grid can be achieved under the proposed strategy. In addition, by analyzing the active damping effect of the proposed strategy, a simplified model in a low-frequency band for GCI- LCL is proposed to enhance the anti-interference capability in the weak grid and simplify the parameters design process. Finally, a GCI- LCL prototype is constructed and the experiment results verify the correctness and feasibility of the analysis and proposed strategy.

Guidelines to Classical Frequency-Domain Disturbance Observer Redesign for Enhanced Rejection of Periodic Uncertainties and Disturbances

The paper suggests a method aimed to improve the performance of dynamical systems with periodic uncertainties and disturbances (ac power converters are typical representatives of such systems) utilizing frequency-domain disturbance observer (DOB)-based control structure. In such control arrangement, DOB filter is the key component and should be designed so that its magnitude (phase) is as close to unity (zero) as possible at frequencies where the total uncertainty and disturbance exists. The methodology for designing DOB filters is well established mostly for systems with slow-varying uncertainties/disturbances and has been barely extended to systems with periodic excitation (such as grid-connected or stand-alone ac power converters). In this study, systematic enhancement of DOB filters, designed according to the classical methodology, is suggested based on appropriate mixing with a series multiresonant term. The proposed approach allows attaining improved periodic signals rejection capability while significantly sacrificing neither the dc gain nor the crossover frequency. Quantitative design guidelines are provided, and possible tradeoffs are revealed. The proposed methodology is validated by application to current control of LCL -filter-based inverter connected to a distorted ac grid. Feasibility and performance of the suggested approach are well supported by simulations and experiments.

A Family of Single-Stage High-Gain Dual-Buck Split-Source Inverters

In this paper, a family of single-phase single-stage high-gain dual-buck split-source inverters (SSIs) is proposed. The proposed inverters have the combine benefits of SSI, dual-buck inverter (DBI), and high-gain dc–dc converters. Similar to the DBI, they provide high reliability by eliminating shoot-through issues, increase switching frequency and efficiency by using power MOSFETs without leading the body diodes to reverse recovery issues, and decrease pulsewidth modulation (PWM) dead-time. In addition, voltage boost operation is achieved in a single stage without using any additional active switch, which is in favor of lower control complexity and lower cost. On the other hand similar to the SSI, buck–boost dc–ac power conversion is realized in a single stage. However, compared to the SSI, the proposed inverters have no shoot-through issues, MOSFETs can be used without reverse recovery issues, dead-time can be minimized, switching frequencies can be increased, and external fast recovery diodes can be used to improve efficiency. In addition, four different high-gain dual-buck SSIs are presented. As an example, the proposed switched-coupled-inductor split-source DBI is analyzed and compared with the other proposed structures. To validate the theoretical analysis, a 300-W experimental prototype is designed and tested at 25–35-V input voltage, $155~V_{\text {peak}}$ output voltages and 50 kHz.

A VEN Condition Monitoring Method of DC-Link Capacitors for Power Converters

The dc-link capacitors are important components that tend to be one of the weakest part of power converters. Thus, it is necessary to monitor the aging parameters of dc-link capacitors in valuable power electronic systems. This paper proposes a simple yet effective variable electrical network (VEN) condition monitoring method for dc-link capacitors in three-phase pulsewidth modulation (PWM) ac–dc–ac power converters. The capacitance ( C ) and equivalent series resistance of dc-link capacitors are estimated through the designed VEN unit during the discharging process. This VEN method does not need the current sensor or injecting signals into the control loop. The above property is favorable for the hardware and controller design. Besides, the designed monitoring circuit can be an external unit or a built-in unit which offers a flexible solution for electrical devices. When the designed VEN is used as an external unit, neither the hardware design nor the programs in the controller needs to change, which is practical and economic for electrical devices in use. Experiments are carried out in a 55 kW ac–dc–ac inverter with different capacitors. The experiment results prove the method to be effective and accurate.