Unipolar Modulation Research Articles

A New Transformer-Less Single-Phase Photovoltaic Inverter to Improve the Performance of Grid-Connected Solar Photovoltaic Systems

Photovoltaic (PV) energy systems have found diverse applications in fulfilling the increasing energy demand worldwide. Transformer-less PV inverters convert the DC energy from PV systems to AC energy and deliver it to the grid through a non-isolated connection. This paper proposes a new transformer-less grid-connected PV inverter. A closed-loop control scheme is presented for the proposed transformer-less inverter to connect it with the power grid. The proposed transformer-less inverter reduces extra leakage current and holds the common-mode voltage at a constant point. To eliminate extra leakage current, as well as achieve constant common-mode voltage, a midpoint clamping method is utilized to operate the inverter. The proposed transformer-less inverter is formed of seven insulated gate bipolar transistors (IGBTs) employing a unipolar sinusoidal pulse width modulation (SPWM) technique for switching purposes. An LCL filter is employed to reshape the two-level inverter output voltage and current to obtain closer sinusoidal waveforms. The output voltage and current total harmonic distortion (THD) of the proposed transformer-less inverter were found to be 1.25% and 0.94%, respectively, in the grid-connected mode. The leakage current elimination mechanism with the proposed transformer-less inverter is deeply analyzed in this paper. The performances of the proposed transformer-less inverter were evaluated with MATLAB/Simulink simulation and validated in a laboratory scale experiment.

Assessment of Total Harmonic Distortion in Buck-Boost DC-AC Converters using Triangular Wave and Saw-Tooth based Unipolar Modulation Schemes

This paper presents an assessment of the levels of total harmonic distortion (THD) in buck-boost DC-AC converters using triangular wave and saw-tooth unipolar based-modulation schemes. This paper seeks to identify a better technique for mitigating the total harmonic distortion on buck-boost DC-AC converters under unipolar carrier-based modulation schemes. This was achieved by subjecting the buck-boost DC-AC converter under triangular wave-based and saw-tooth based-unipolar modulation schemes. The voltage and current output of the buck- boost DC-AC converter under each scheme was analysed using a power GUI Fast Fourier Transform (FFT) analytical tool resident in the MATLAB Simulink environment unlike with the conventional scheme of computing the percentage of THD. The test system was obtained by a combination of DC-DC buck-boost converter, H-bridge based-insulated unipolar gate transistors, and a logic control unit. It was realized that THD of 0.2865%, peak output voltage of 294.1V and current of 9.805A were obtained by using the saw-tooth based-unipolar modulation scheme, whereas a THD of 0.1479%, peak output voltage of 297.4V and current of 9.53A were obtained by using the triangular wave based-bipolar modulation scheme on the same Buck-boost DC-AC converter circuit. The results imply a high power factor utilization and low power loss in the triangular wave based-unipolar modulation scheme compared to the saw-tooth based-unipolar modulation technique for improving the performance characteristics of the buck-boost converter system. This study showed that power drives and heavy load machines based-power electrical loads are required to use the saw-tooth based-unipolar modulation (STBUM) scheme for high current and low THD%, whereas sensitive power electrical loads such as hospital equipment and communication industries based-power electronic devices are required to use the triangular wave-based unipolar modulation (TWBUM) scheme due to low current and THD%.

Passivity-Based Multisampled Converter-Side Current Control of LCL-Filtered VSCs

With the gradually decreasing cost of high-performance digital processors, multisampling current control is a potential method to reduce the control delay and improve the stability in <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LCL</i> -filtered grid-connected converters. In the practical implementation, an antialiasing filter is required to remove the sampled switching harmonics and suppress the low-order aliasing. However, due to the phase lag from the antialiasing filter, the dissipative region of converter output admittance still cannot be lifted to switching frequency, which leads to a risk of system instability under wide grid admittance variation. In order to tackle this challenge, a filter capacitor voltage feedforward scheme using multisampling is proposed in this article. Consequently, the dissipation below the switching frequency is harvested for a three-phase converter. Furthermore, by doubling the multisampling rate, the proposed method can extend the dissipative region to the apparent switching frequency for a single-phase converter using unipolar modulation. The experimental results validate the effectiveness of the proposed method on a down-scaled single/three-phase converter.

Multioutput Hybrid Solar Inverter With No Right Half-Plane Zero and Reduced Common-Mode Leakage Current

In this article, a multioutput-based transformerless hybrid solar inverter (TLHSI) with no right half-plane zero (RHPZ) and reduced common-mode leakage/ground current is presented for photovoltaic (PV) based microgrid applications. In the proposed multioutput TLHSI, two magnetically coupled inductor coils are placed between the input and dc output sides along with a dc-link capacitor to continuously provide the stored energy to the dc load so that the RHPZ is eliminated and, thus, makes it a minimum phase system. Furthermore, a hybrid unipolar sinusoidal pulsewidth modulation technique is established to nullify the high-frequency components of common-mode voltage across the PV to ground stray capacitor. Also, it normalizes both dc and ac loads at the same instant from a single dc input during each operating state of the proposed TLHSI. The shoot-through issue is resolved in the proposed TLHSI, which increases the system reliability. Furthermore, as the deadtime is not required in between the switching pulses, the quality of the inverter output voltage improves. The performance analysis of the proposed TLHSI is compared with the existing topologies. To validate the performance of TLHSI, a scaled down 340 W laboratory prototype is developed.

A Novel Application of Random Hysteresis Current Control: Acoustic Noise and Vibration Reduction of a Permanent Magnet Synchronous Motor Drive

This article presents a novel application of the random hysteresis current control (RHCC) technique on a permanent magnet synchronous motor (PMSM) drive to reduce acoustic noise and vibration (ANV). The proposed RHCC approach brings a significant reduction in torque ripples and ANV in the motor, thereby enhancing the performance of the complete drive system under operation. Among various available spread-spectrum techniques, RHCC has recently applied to unipolar and bipolar pulsewidth modulation (PWM)-fed power electronics converters to reduce harmonics in voltage and currents, with promising results. Furthermore, in-depth theoretical background and analysis of the performance of RHCC in reducing the torque ripples, vibration, and acoustic noise of a PMSM drive are presented. Appropriate simulation as well as experimental analysis have been carried out. The results show a substantial reduction of ANV in a PMSM drive through the proposed RHCC technique. The performance of the proposed method is compared with pseudorandom triangular PWM, hysteresis current control (HCC), and sinusoidal PWM (SPWM) techniques.

Zero Leakage Current Single-Phase Quasi-Single-Stage Transformerless PV Inverter With Unipolar SPWM

Power inverters for distributed photovoltaic (PV) power generation systems usually need to fulfill several requirements, e.g., the safety, the voltage boost capability, and the reduced volume and the cost. An improved transformerless single-phase quasi-single-stage common-mode PV inverter with four switches and an improved unipolar modulation strategy are proposed in this article. The inverter features double-grounded to solve potential safety issues caused by the leakage current. In addition, its voltage boosting is accomplished by a quasi- single-stage conversion structure so that PV system efficiency can be improved. Meanwhile, it benefits continuous input current so is suitable for PV application. In this article, the operation principle of the proposed inverter, the improved modulation strategy, and two grid-tied control strategies are introduced. The voltage and current stresses of the components are analyzed, and parameter design guideline is further given. Both the off-grid and grid-tied experiments were conducted to verify the theoretical analysis.

Implementation of cascaded H-bridge DC-link inverter for marine electric propulsion drives

Abstract This paper presents a single-phase seven level Cascaded H-Bridge DC-Link (CHBDCL) inverter for marine electric propulsion drives. The speed of propulsion drive can be changed by CHBDCL inverter by converting DC output from the rectifier to variable output voltage with or without change in frequency. The proposed CHBDCL inverter generates more output voltage with minimum harmonic content than classical Multilevel Inverters (MLIs). The CHBDCL inverter necessitates only ‘m + 3’ power devices for ‘m’ number of levels, although the classical MLIs requires ‘(2m − 1)’ power devices. CHBDCL inverter can have the effective performance by utilizing unipolar Sine Pulse Width Modulation (SPWM) and unipolar Space Vector PWM (SVPWM) with sine carrier. The effectiveness of the proposed CHBDCL inverter topology has been verified by using MATLAB/SIMULINK for various modulation indices in terms of voltage levels and harmonic analysis. Furthermore, an experimental setup involving pulse generation from a Field Programmable Gate Array (FPGA) has been used to test the performance of the proposed CHBDCL inverter.

Simple and Seamless PWM Scheme of Isolated Bidirectional AC–DC Converter for Reducing Voltage Spike

This article proposes an improved modulation scheme based on unipolar sinusoidal pulsewidth modulation for a single-phase single-stage isolated bidirectional ac&#x2013;dc converter. A direct ac&#x2013;ac conversion system connected with a high-frequency transformer typically suffers from high-voltage spikes because of the leakage inductors of the high-frequency transformer and the grid filter inductors, resulting in reduced reliability and large power losses. The proposed modulation scheme can eliminate the high-voltage spikes in bidirectional power flow without the use of additional circuits while realizing zero-voltage switching. In addition, because the proposed method does not require individual gate control of the bidirectional power switches, the generation of gate signals can be simplified using the proposed modulation scheme. A simulation model and a 1.2 kW grid-connected ac&#x2013;dc converter based on silicon-carbide metal&#x2013;oxide&#x2013;semiconductor field-effect transistors are implemented to validate the effectiveness of the proposed modulation scheme.

A kind of ZVS quasi impedance source inverter with high voltage transmission ratio

A kind of zero-voltage switching (ZVS) quasi impedance source inverter (qISI) with high voltage transmission ratio is proposed, and critical conclusions are drawn by analysing of the circuit structure, modulation method, high-frequency working modes, voltage transmission ratio, resonant processes and ZVS conditions, and the design guideline of primary parameters. A novel impedance network, a ZVS auxiliary branch, a single-phase inverter bridge, and an output LC filter make up the inverter, the unipolar SPWM modulation method is introduced, and dynamic response of output voltage and energy storage capacitor voltage is realized. The impedance network consists of an inductor and two inductor-capacitor-capacitor-diode (LCCD) cells. The ZVS auxiliary branch includes a resonant inductor, a clamping capacitor, and an auxiliary switch, providing the ZVS conditions for all switches. 1 KVA prototype is built and the experimental results proved that the proposed inverter features high voltageboosting, ZVS of all switches, high power density, output waveform with small THD, and strong load capacity and applies to single-phase inversion with low input voltage or wide input voltage range.

Review and design of modular multilevel inverter with modified multicarrier PWM techniques for solar PV applications

PurposeThese implementations not only generate excessive voltage levels to enhance the quality of power but also include a detailed investigating of the various modulation methods and control schemes for multilevel inverter (MLI) topologies. Reduced harmonic modulation technology is used to produce 11-level output voltage with the production of renewable energy applications. The simulation is done in the MATLAB/Simulink for 11-level symmetric MLI and is correlated with the conventional inverter design.Design/methodology/approachThis paper is focused on investigating the different types of asymmetric, symmetric and hybrid topologies and control methods used for the modular multilevel inverter (MMI) operation. Classical MLI configurations are affected by performance issues such as poor power quality, uneconomic structure and low efficiency.FindingsThe variations in both carrier and reference signals and their performance are analyzed for the proposed inverter topologies. The simulation result compares unipolar and bipolar pulse-width modulation (PWM) techniques with total harmonic distortion (THD) results. The solar-fed 11-level MMI is controlled using various modulation strategies, which are connected to marine emergency lighting loads. Various modulation techniques are used to control the solar-fed 11-level MMI, which is connected to marine emergency lighting loads. The entire hardware system is controlled by using SPARTAN 3A field programmable gate array (FPGA) board and the least harmonics are obtained by improving the power quality.Originality/valueThe simulation result compares unipolar and bipolar PWM techniques with THD results. Various modulation techniques are used to control the solar-fed 11-level MMI, which is connected to marine emergency lighting loads. The entire hardware system is controlled by a SPARTAN 3A field programmable gate array (FPGA) board, and the power quality is improved to achieve the lowest harmonics possible.

The Closed-Loop Sideband Harmonic Suppression for CHB Inverter With Unbalanced Operation

For <i>N</i>-cells cascaded H-bridge (CHB) inverters based on unipolar double frequency phase-shifted pulsewidth modulation (PS-PWM), the output voltage is distorted and its harmonics are difficult to be suppressed under unbalanced conditions (different dc voltages and&#x002F;or modulation indices). This article proposes a closed-loop harmonic suppression scheme based on the PS-PWM, and the scheme is easily implemented in the <i>dq</i> frame to adaptively adjust the displacement angles of the triangular carriers. The harmonic content can be suppressed to its possible minimum value without the limitation of the operational point by the proposed method. The adjustment rules of displacement angles and the harmonic suppression principle are presented in detail. This method can effectively restrain harmonic magnitudes without the limitation of the cells number and does not require complicated trigonometric function calculations or optimization algorithms. Moreover, the principle of symmetrical sideband harmonic suppression is also discussed. The effectiveness of the proposed method is verified by a downscale test platform of the single-phase CHB inverter.

Simulation of Boost Derived Hybrid Converter Using Fuzzy Logic Controller for EV Application

Abstract: A new control technique for hybrid converter topologies with a single DC input that simultaneously supplies DC and AC to appropriate DC and AC loads is presented in this paper. This is achieved by using Voltage Source Inverter (VSI) bridge instead of single step-up switch in a boost converter. This converter is known as Boost Derived Hybrid Converter (BDHC) because it is derived from the basic boost converter. Unipolar sinusoidal pulse width modulation (PWM) is used to control the BHDC. This BDHC utilizes less number of switches and furnishes DC and AC yield with higher reliability. Fuzzy logic controllers (FLC) are being used to replace the conventional PID controllers in this control technique. Since fuzzy controller is the best option for non-linear control technique, it is used to control BDHC which is has nonlinear dynamics. The input to the fuzzy logic controller is error and change in error from two different comparators which contrasts AC and DC voltages with their respective reference voltages. The simulation results of BDHC are done using MATLAB/SIMULINK. Keywords: Boost Derived Hybrid Converter (BDHC), Voltage Source Inverter (VSI), Pulse Width Modulation (PWM), Fuzzy Logic Controller (FLC)

An Improved Conventional Diode-Clamped Multilevel Inverter Using Non-Zero Triangular- Based Unipolar Modulation Scheme

This paper presents an improved conventional diode-clamped multilevel inverter using non-zero triangular-based unipolar modulation scheme. The proposed scheme is meant to reduce the number of carrier waves, minimize the circuits of modulation scheme and obtain stabilized output voltage waveforms. Non-zero triangular-based unipolar modulation scheme is actualized by using two zero-free triangular wave carriers and two modulating sinewaves for line-to- line five level output voltage waveforms in single phase full bridge diode-clamped multilevel inverter unlike conventional multicarrier sinusoidal pulse width modulation that uses four triangular waves and one modulating sinewave for the same inverter type. The proposed system also used microcontroller in the combinational of its wave signals in order to generate the appropriate triggering signals for switching the power semiconductor switches. The proposed system has the following features: (i) It produces two distinct triggering trains (W1 and W2) meant to reduce the low and high harmonics unlike conventional modulation techniques (ii) All its carrier waves operate in continuous current mode which makes it unique from other multicarrier and other related modulation schemes (iii) it has low component counts. The proposed scheme on the conventional diode-clamped inverter produced the following results: voltage and current with total harmonic distortions of 0.4547%, stabilized 400V output voltage and 20A output current, probability results at each level of voltage and current occurrences are 0.10, 0.25, 0.25, 0.75 and 0.90; power output of 80kW, low component counts of modulation circuit scheme and experimental prototype.

An Effective Spatial Modulation Based Scheme for Indoor VLC Systems

We propose an enhanced spatial modulation (SM)-based scheme for indoor visible light communication systems. This scheme enhances the achievable throughput of conventional SM schemes by transmitting higher order complex modulation symbol, which is decomposed into three different parts. These parts carry the amplitude, phase, and quadrant components of the complex symbol, which are then represented by unipolar pulse amplitude modulation (PAM) symbols. Superposition coding is exploited to allocate a fraction of the total power to each part before they are all multiplexed and transmitted simultaneously, exploiting the entire available bandwidth. At the receiver, a two-step decoding process is proposed to decode the active light emitting diode index before the complex symbol is retrieved. It is shown that at higher spectral efficiency values, the proposed modulation scheme outperforms conventional SM schemes with PAM symbols in terms of average symbol error rate (ASER), and hence, enhancing the system throughput. Furthermore, since the performance of the proposed modulation scheme is sensitive to the power allocation factors, we formulated an ASER optimization problem and propose a sub-optimal solution using successive convex programming (SCP). Notably, the proposed algorithm converges after only few iterations, whilst the performance with the optimized power allocation coefficients outperforms both random and fixed power allocation.

Three-phase inverter with a variable control algorithm

The paper presents the construction of a three-phase frequency converter with the possibility of choosing the type of PWM modulation and a smooth change of the frequency of the modulated signal. In a practical way, various inverter control algorithms were implemented in the same hardware system using the STM ARM Cortex M3 processor. The use of THIPWM modulation allowed to reduce the harmonic content in the output signal and effectively use the possibilities of the power source. The system can choose one of two scalar control algorithms, with the option of compensation for the influence of the stator resistance on the motor shaft torque in the initial range of the linear control characteristic at a constant voltage to frequency ratio. The research confirmed that the most advantageous type of PWM in this system is unipolar double-edge modulation. The use of the THIPWM method resulted in a gain in the amplitude of the fundamental harmonic of the output voltage for the three-phase inverter operation mode compared to the SPWM method. The appropriate precision of the frequency control step was also obtained, and the test results confirmed the functionality of the converter.

Mirror-Bridge Phase-Shift Modulation With Low Common-Mode Noise for Single-Phase CHB PFC

For ac/dc power conversion applications like server power supply, telecom power supply, and on-board charger of an electric vehicle, the rising electricity demand has presented challenges toward high efficiency and high power density. The cascaded H-bridge (CHB) based multilevel power factor correction (PFC) converter has much higher power density than that of traditional boost PFC converter. However, the CHB-PFC converter has multiple floating dc outputs, which leads to a common mode (CM) electromagnetic interference (EMI) issue due to the parasitic capacitance of cascaded dc/dc stages and layouts and distributed noise sources existing in the ac/dc system. Thus, a large EMI filter is necessary for the PFC system that sharply degrades the system's power density. In order to quantify the CM noise caused by the floating outputs and cascaded parasitic capacitance, a unified equivalent CM circuit model is derived in this article, which decouples the effects among the multiple CM noise sources in the CHB converter. Based on the derived circuit model, a mirror-bridge phase-shift modulation is proposed to cancel the CM noise within the CHB converter itself. A single-phase 2-kW CHB PFC prototype has been built up to verify the analysis, and 40-dB CM noise reduction compared with conventional unipolar modulation is achieved by the proposed modulation scheme.

Design and implementation of a CSI inverter with unipolar SPWM modulation and PR controller for lineal loads

This paper presents a detailed implementation of a current source inverter using unipolar sinusoidal pulse width modulation. This method is uncommon in these types of inverters and the semiconductor devices, integrated circuits, sensors, and filters used in conjunction with the TMS320F28379D microcontroller will be discussed. The inverter was tested in both an open and closed loop with a proportional resonant controller. Satisfactory results in terms of the harmonic distortion factor at the voltage output and the regulation indices for lineal loads were obtained. The response circuit demonstrated its viability for the subsequent connection to an electrical distribution network.

Highly Efficient Transformerless Inverter with Flying-Capacitor Buck–Boost for Single-Phase Grid-Connected PV Systems

Grid-connected inverters (GCI) are commonly used in PV system applications to generate a regulated AC current to feed into the grid. Transformerless inverters are the most advanced inverters that are used in industry, which provide efficiency with smaller size and lower cost. This paper proposes a grid-connected single-phase transformerless inverter with the technology of common ground and the virtual DC bus concept. In this topology, the grid neutral is connected directly to the PV ground, which generates a constant common mode voltage (CMV), thus leading to the elimination of the leakage current caused by the PV array’s parasitic capacitance. The proposed inverter has a buck–boost circuit with a flying capacitor to generate the DC bus for a negative power cycle, four switches, and two diodes. A unipolar sinusoidal pulse width modulation (SPWM) technique is used which reduces the output filter requirements. In addition, only one switch carries the load current during the active states of both the negative and positive power cycle, thus minimizing the conduction losses. One more advantage presented in the proposed inverter is its ability to charge the flying capacitor during all operation states due to the existence of the buck–boost circuit. Design and theoretical calculations were conducted in this paper to optimize the losses. Moreover, the PSIM simulation was used to validate the proposed topology inverter, verify the performance by showing leakage current elimination, and achieve unipolar voltage in the output bus. The simulation results show a peak efficiency of 98.57% for a 2 kW inverter, which agrees with the theoretical calculations.

Analysis and Design Based on the Operation Mode of Power Electronic Transformer in Smart Grid

Power electronic transformers(PET) are the key energy conversion equipment in the operation of modern smart grids, the main function of PET is to achieve the conversion of AC voltage to AC voltage, while taking into account the DC ports. This article mainly studies three-stage power electronic transformers based on three-phase uncontrolled rectifier, full-bridge isolated DC-DC converter and three-phase inverter. The operation mechanism and actual working process of the three parts of the PET are analyzed respectively, and the transformer is simulated and analyzed based on the Matlab/Simulink simulation platform. The rectifier converts the AC voltage on the grid side into a rippled DC voltage; the DC-DC converter transforms the obtained DC voltage, taking into account the access of the DC ports; the inverter converts the obtained DC voltage into AC voltage through unipolar modulation and connects to the grid. The experimental results show that the PET constructed in this way can operate safely and stably, which has good voltage conversion and electrical isolation functions, and can be connected to DC loads.

Performances of Photovoltaic System Using Grid Tied Transformerless Inverter

In order to eliminate the common-mode (CM) leakage current in the transformer less photovoltaic (PV) systems, the concept of the virtual dc bus is proposed in this paper. By connecting the grid neutral line directly to the negative pole of the dc bus, the stray capacitance between the PV panels and the ground is bypassed. As a result, the CM ground leakage current can be suppressed completely. Meanwhile, the virtual dc bus is created to provide the negative voltage level for the negative ac grid current generation. Consequently, the required dc bus voltage is still the same as that of the full-bridge inverter. Based on this concept, a novel transformer less inverter topology is derived, in which the virtual dc bus is realized with the switched capacitor technology. It consists of only five power switches, two capacitors, and a single filter inductor. Therefore, the power electronics cost can be curtailed. This advanced topology can be modulated with the unipolar sinusoidal pulse width modulation (SPWM) and the double frequency SPWM to reduce the output current ripple. As a result, a smaller filter inductor can be used to reduce the size and magnetic losses.