Output Current Distortion Research Articles

Modulation Strategy with Minimum Switching Losses for Three-Phase Non-Isolated AC–DC Matrix Converters

This paper presents an analysis of the operational characteristics of three-phase AC–DC matrix converters, which operate as rectifiers but possess a range of additional capabilities. These include the ability to reverse the power flow, control the input power factor, and generate a multilevel output voltage. The analysis yields a modulation strategy that minimizes switching losses. The proposed modulation strategy is compared with seven well-known space vector modulation strategies in terms of efficiency and distortion of input and output current. The performance is experimentally validated.

An optimal parameter design method for cascaded H‐bridge multi‐level converter in wind farm

AbstractThe cascaded H‐bridge multi‐level converter is the main topology of high‐voltage and high‐capacity converter in renewable energy power generation, energy storage system and reactive power compensation equipment. The parameter design of cascaded H‐bridge multi‐level converters directly determines the material cost and performance. Taking the output current distortion rate and the ripple voltage of the capacitor of the cascaded H‐bridge multi‐level converter as the constraint conditions, this paper proposes an overall parameter optimal design method of the cascaded H‐bridge multi‐level converter based on the optimization of the total material cost. Finally, the effectiveness of the proposed parameter design method is verified by the simulation result.

Development of Various Types of Independent Phase Based Pulsewidth Modulation Techniques for Three-Phase Voltage Source Inverters

Discontinuous pulse-width-modulation (DPWM) methods have been extensively used in the industrial area to reduce overall losses, which decreases the corresponding thermal stress on the power switches of converters. However, local thermal overload can arise due to different aging conditions of semiconductor devices or failure in the cooling system. This leads to reduced reliability of the converter system due to the low expected lifespan of the most aged switches or phase legs. In this paper, the modified DPWM strategies for independent control of per-phase switching loss are introduced to deal with this matter. The proposed per-phase DPWM techniques are generated by modifying the conventional three-phase DPWM methods for reducing the switching loss in a specific leg, whereas the output performance is not degraded. This paper reports on output performance, including output current total harmonic distortion (THD) and power loss of switching devices, analysis for the various modified DPWM strategies for independent control of per-phase switching loss, which is applicable in 2-level 3-phase voltage source inverters (2L3P VSIs). The results are compared to the corresponding continuous PWM technique to verify and analyze the effectiveness and accuracy of the modified DPWM strategies for independent control of per-phase switching loss.

Output current harmonic analysis and suppression method for PMSM drive system with modular multilevel converter

AbstractAiming at the output current distortion problem in the low frequency operation of permanent magnet synchronous motor (PMSM) drive system of modular multilevel converter (MMC), the essential relationship between the output current distortion and the injected components is analyzed in this paper. A current harmonic suppression method combining feedforward and feedback compensation is proposed. Firstly, the feedback control method is applied to transform the MMC three‐phase output current into the dq rotating coordinate system at fundamental frequency ω. The harmonics of the AC terms to be suppressed are filtered out. The dominant fundamental frequency component turned into the DC term is retained. Then combined with feedforward control, the control performance of the system is improved. Secondly, the deadbeat predictive current control is improved by introducing an integral link in it. System disturbances caused by parameter changes can be compensated in real time. The design of the control system is simplified and the static error is reduced. Meanwhile, the system has the advantages of small torque pulsation and fast speed response. Finally, the PMSM drive system model of the 11‐level MMC is built in MATLAB/Simulink. The correctness and effectiveness of the proposed suppression method are verified.

Design a 25-level inverter topology with less switching devices fed by PV systems

<span lang="EN-US">Multilevel inverter (MLI) technology has lately emerged as one of the most popular solutions for high power and medium voltage energy management. MLIs have many benefits and require more switches for higher levels, which are considered disadvantaged. This could result in large size and extremely expensive cost for the MLI. So, in order to overcome this problem, a new MLI topology is proposed with reduced number of switches. A 25‐level inverter fed by isolated unequal photovoltaic panels as DC sources is chosen in this study. The structure of DC voltages is chosen as (1:1:5:5) Vdc. The proposed approach, which is created using twelve switches, is ideally suited for a high-power application. Multi-carrier with a sinusoidal PWM technique is programmed as a controller. According to the simulation findings, a single-phase system's output voltage and current total harmonic distortion (THD) values are 1.2% and 0.462%, respectively, while a three-phase system's values are 1.07% and 0.342%. These findings prove that the power circuit and investigation were successful.</span>

Modular Modeling and Statistical Validation for Grid-Connected FS-MPC-Controlled Matrix Converters

In recent publications statistical model checking (SMC) has been proposed as a method for verifying the performance of finite-set model predictive control (FS-MPC) algorithms applied to power electronics converters. One of the reasons the full potential of the method in the power electronics systems (PES) has not yet been explored is the time consuming modelling process. In this paper we propose a modular method of modelling the power electronics system components by providing simple building blocks, which can be connected to build different PES. The modelling method is here demonstrated on a direct matrix converter, which operates in a stochastic grid with different harmonic distortion levels and voltage sags. By applying the SMC, the performance of the control algorithm in terms of the output current distortion, effects of the weighting factor selection and grid distortions on the device utilization can be evaluated. The obtained results confirm, that high grid distortions and voltage sags will increase the stress of several devices. This information can be of great importance to identify the most stressed components and how the control algorithm can be adapted to extend the lifetime of the components and thereby the system during different grid conditions. The verified FS-MPC algorithm has also been implemented in an experimental set-up.

Dual randomized discontinuous pulse width modulation for three-phase inverter

ABSTRACT The discontinuous PWM technique, with its advantage over the continuous PWM technique in reducing switching losses in power converters, is gaining popularity. However, its deterministic nature results in discrete harmonics with significant amplitudes, which leads to electromagnetic interference (EMI) emissions. The randomised PWM technique is gaining more interest because of its effectiveness in spreading the harmonic spectrum and thus reducing EMI problems in power converters. This paper presents a carrier-based dual randomised discontinuous PWM (DRDPWM) method for a three-phase voltage inverter. The DRDPWM method combines the random carrier frequency (RCF-DPWM) and random pulse position (RPP-DPWM) schemes. In addition to reducing switching losses, DRDPWM can achieve a broad spread of the voltage spectrum with significantly smaller amplitudes. Furthermore, it produces less inverter output current distortion when compared to traditional DPWM and simple random (RCF-DPWM and RPP-DPWM) schemes. Simulations and experimental results confirm the effectiveness of the suggested method for spreading the voltage spectrum compared to simple random schemes. Additionally, an evaluation of the performance of all randomised discontinuous schemes is conducted based on a number of assessment metrics, including the switching loss factor (SLF), the power spectral density (PSD), the harmonic spread factor (HSF), and the quality factor (QF).

An improved active islanding detection method for grid-connected solar inverters with a wide range of load conditions and reactive power

Islanding occurs when a utility-interactive distributed generator (DG) is disconnected from the utility grid and continues to supply power to local loads. This condition has several consequences including damage to the equipment and personnel safety risks. Therefore, it is required by utility interconnection standards for the DG to stop energizing local loads in the case of islanding. In this paper, an active islanding detection method (IDM) based on injecting a disturbance into the phase-locked loop (PLL) of a grid-connected photovoltaic (PV) inverter and monitoring the harmonic components of the point of common coupling (PCC) is proposed. A modified Goertzel algorithm is utilized to detect the injected harmonic which is effective for a wide range of load conditions in terms of load quality factor, resonant frequency, and reactive power. The simulation results in MATLAB/Simulink show that the proposed technique is fast with minimum side effects on power quality features such as output current total harmonic distortion (THD). This method is implemented on a single phase 5 kW grid-tied PV inverter and is tested experimentally. The experimental results verify that the proposed technique is fast with zero non-detection zone (NDZ) which is effective for a variety of load conditions.

Modulated Model-Free Predictive Current Control for Voltage Source Inverters With Stagnation Elimination and Sampling Disturbance Suppression

Model-free predictive current control (MFPCC) has been widely used in voltage source inverters (VSIs). The output current performance of look-up-table-based MFPCC is affected by the number of the applied voltage vectors (VVs), the current gradient updating and the sampling disturbance. To improve the current performance, a novel modulated MFPCC is proposed for VSI, while real-time current gradient updating and sampling disturbance suppression can be achieved. First, three basic VVs are picked, whose duration time are computed according to the current gradients. Second, an advanced current gradient updating method is presented by establishing the equations of different current gradients under different VVs. Furthermore, the sampling disturbance effect on MFPCC is analyzed and an extended state observer is designed to suppress such effect. Simulation model and experimental platform of the VSI system are structured to verify the preponderance of the proposed MFPCC in reducing the total harmonic distortion of output current.

A Quasi-Z-Source Four-Switch Three-Phase Inverter With Null Vector Capability

In this paper, a novel structure for a four-switch three-phase inverter with the ability of creating a null vector is proposed. This structure utilizes a symmetrical quasi-Z-source network and generates zero output voltage during the shoot-through state, which is similar to the null vector in the conventional six- switch inverter. This vector is used for the remaining time for each switching period. This means that the proposed structure has several advantages over the conventional four-switch inverter, in which two active vectors with opposite directions are necessary for synthesizing a null vector. These two vectors increase the switching losses due to the current circulation through these active states. Moreover, the number of switching states increases because of applying two opposite vectors. However, this problem does not exist in the proposed topology. To decrease the output current distortion and to minimize the number of switching events per each cycle, a new switching pattern is proposed, too. Also, fluctuations of the two split capacitors in the dc-link are considered in the closed-loop modulation method, which balances the output voltages and decreases current THD by 0.7%. To validate the proposed topology and the given pulse width modulation approach, its mathematical analyses are given here. Also, simulations and experimental verification have been performed on a 1 kW prototype inverter.

Total harmonic distortion reduction based energy harvesting using grid-based three phase system and integral-derivative

Distributed generation (DG) and solar photovoltaic (PV) systems are just two of the many places multilevel inverters have found a home. The total harmonic distortion (THD) of an inverter's output voltage or current is widely regarded as a useful quality indicator. In order to lessen THD while enhancing the performance of the network, the authors of this research presented a unified controller.An integrated controller consisting of PID (Proportional-Integral-Derivative),Fuzzy,and Artificial Neural Network (ANN) controllers is used in the 31-level multilevel inverter to reduce THD in the PV system. The fundamental frequency of the suggested integrated controller is 50 Hz,and the simulation results show that the THD is reduced to 0.94 percent. The proposed controller's performance shown a considerable decrease in 5th order harmonics for the Cascaded H-bridge Multilevel Inverter,as well as an average percentage reduction in line voltage total harmonic distortion of 17.04 compared to the existing approach.

A modulation strategy for eliminating zero-crossing distortion of dual buck high-precision resonant converter

Due to no current distortion caused by blanking time, the resonant pole dual buck soft-switching power converter (RPDBSPC) can be applied to ultra-precision motor drive. The soft-switching operation can expand the switching frequency and improve the current response. Based on the resonant pole soft-switching topology, this paper proposes an in-phase modulation strategy. By analyzing the output voltage characteristics of switching nodes under different inductance current states, it reveals the mechanism of in-phase modulation to achieve nonlinear voltage suppression by adjusting the common conduction region. According to the correlation of modulated signals, the mathematical model of modulation algorithm is established, then the strategy feasibility and system stability are researched. Finally, the total harmonic distortion of output current can reach to 0.134% by applying the in-phase modulation when the bus voltage is 500V and the switching frequency is 100 kHz.

A Novel Analytical Formulation of SiC-MOSFET Losses to Size High-Efficiency Three-Phase Inverters

This paper presents a novel analytical loss formulation to predict the efficiency of three-phase inverters using silicon carbide (SiC) metal—oxide—semiconductor field-effect transistors (MOSFETs). The proposed analytical formulation accounts for the influence of the output current harmonic distortion on the conduction losses as well as the impact of the output parasitic capacitances and the deadtime on the switching losses. The losses are formulated in balanced conditions to select suitable SiC MOFETs for the desired target efficiency. To validate the proposed methodology, a 3-phase inverter is designed to present full load efficiency in excess of 99% when built using SiC MOSFETs antiparalleled with SiC Schottky diodes selected for the specified full load efficiency. Experimental assessment of the designed inverter efficiency is compared with the expected values from the proposed analytical formulation and shown to match or exceed the predicted results for loads ranging from 40% to 100% of full load.

AC-DC Fuzzy Linear Active Disturbance Rejection Control Strategy of Front Stage of Bidirectional Converter Based on V2G

Aiming at the problems of output voltage fluctuation and current total harmonic distortion (THD) in the front stage totem-pole bridgeless PFC of two-stage V2G (Vehicle to Grid) vehicle-mounted bi-directional converter, a fuzzy linear active disturbance rejection control strategy for V2G front-stage AC-DC power conversion system is proposed. Firstly, the topological working mode of the totem-pole bridgeless PFC is analyzed, and the mathematical model is established. Combined with the system model and the linear active disturbance rejection theory, a double closed-loop controller is designed with the second-order linear active disturbance rejection control as the voltage outer loop and PI control as the current inner loop. The controller can realize self-adaptive tuning of the proportional gain coefficient of the active disturbance rejection controller through fuzzy reasoning and realize self-adaptive control. Simulation and experimental results show that this method can better solve the problems of slow system response and high total harmonic distortion rate of input current and effectively improve the system’s robustness.

Data Driven Model Predictive Control for Modular Multilevel Converters With Reduced Computational Complexity

Model predictive control (MPC) has become increasingly popular among researchers for modular multilevel converters (MMCs) due to its ability to incorporate multiobjective control and provide superior dynamic response. However, it is computationally challenging to implement it on MMCs when the number of submodules is increased. This paper proposes a finite control set (FCS) model predictive control (MPC) with reduced computational complexity for modular multilevel converters (MMCs). To accomplish this goal, a reduced order data-driven model is obtained using sparse identification of nonlinear systems (SINDy) by incorporating the input terms in the load current and circulating current dynamics. As a result, the need to use the arm voltages or the submodule capacitor voltages dynamic equations as in the case of a conventional FCS-MPC is eliminated. To improve the output current total harmonic distortion (THD) and reduce the effect of higher switching frequencies caused by the FCS-MPC, an updated cost function is proposed. The effectiveness of the proposed technique is validated by simulation and experimental results.

Mitigation of power oscillations for energy harvesting capability improvement of grid-connected renewable energy systems

The increasing penetration of renewable energy sources in the power system raises several challenges from the power quality and output power fluctuations point of view. However, the output power oscillations and power quality problems caused by the low order harmonic oscillations at the second-order frequency of the utility grid on the dc-link capacitor are emerging as major issues for the efficient operation of power converters. In this manner, a novel method based on modification in the control algorithm to alleviate the output power oscillation and reduce the output current total harmonic distortion is proposed. The proposed control approach seems as a promising solution for the satisfactory grid operation of renewable energy sources regarding not requiring any additional circuit and increment in the capacity of the dc-link capacitor. Moreover, mitigation of oscillations enhances the active power reference tracking capability of the controller that enables the overall efficiency improvement of the system. The performed case studies reveal that the overall efficiency rate of the system is increased by 1.3%. On the other hand, the output current harmonic distortion is decreased below 3% even under low power operating conditions. Also, the complexity level of the control algorithm is quite low for real-time implementation.

Improved space vector modulation algorithm of 5-level three-phase z-source based cascaded inverter

The integration of a Z-source network with a 5-Level three-phase inverter based cascaded to provide voltage step-up function is proposed in this paper. The system is controlling by an improved space vector modulation (SVM) the implantation of algorithm and innovative virtual automated solutions can be considered, very fast and very simple. The main objective of the proposed system is to achieve an output voltage twice the applied input voltage, and to eliminate the largest amount of excess harmonic. This proposed model is characterized by the ease of boosting the output voltage twice the input voltage, depending on the characteristics of the Z-source network without the need for a DC-DC rectifier. Furthermore, the proposed algorithm for this system is characterized by improving the output voltage and eliminating a large number of harmonics while greatly simplifying the calculations compared to its conventional SVM. This makes the proposed system and its algorithm an interesting alternative to classical systems and algorithms. The simulation was processed using MATLAB/Simulink. The results obtained prove and verify the effectiveness of the proposed system. From the results, of the output current total harmonic distortion (THD), it was reduced to 1.05% which is very low compared to the other algorithms in the literature.

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.

Interleaved operation of parallel three-level inverter and suppression of circulating current

Circulating current suppression has been a key problem for non-isolated photovoltaic grid-connected parallel inverters, but traditional circulating current suppression method cannot meet the aims of reducing circulating current and output current harmonic at the same time. This paper analyzes the five-level voltage output capability based on the interleaved parallel three-level inverter through the interaction of the two parallel inverters, then proposes the interleaved operation idea based on Model Predictive Control Strategy. Futhermore, based on the basic vector of zero common-mode voltage in this system, this paper proposes a method of suppressing circulating current suitable for interleaved parallel three-level inverters, and derives a detailed modulation implementation process. Simulation shows that while suppressing the circulating current, the proposed method can greatly reduce the harmonic distortion of the parallel output current, which achieves the goals of suppressing the circulating current and reduce output current harmonics simultaneously in the non-isolated parallel photovoltaic inverter.

An approach to the utilization of grid integration to analyze the performance and quality of solar photovoltaic model

Photovoltaic power is most important cause of energy subsequently it is simultaneously clean and limitless. PV power conversion devices must be maintained at MPP there to maximize the energy production of Solar array. To get the most energy out of the Solar array, MPPT monitoring is necessary. In recent times, a slew of strategies for controlling the voltage was presented. Power electronic devices developments for the combination of wind and solar power generation are discussed. Based on the dependability and development of each technology, conversations concerning developments and trends in sustainable source systems are provided. The consumption of electricity generated is increasing exponentially, and as a result, the incorporation of photovoltaic panels into distribution companies is increasing rapidly as well, even though it has a substantial impact on the show’s voltage stability. The purpose of this report is to look at how solar PV integration affects distribution transmission energy reliability. The analysis is carried out using RSCAD software, with one of the radial distribution networks with the lowest voltage profile accessible during the maximum of linked loads. Furthermore, the influence of current and voltage on the transmission or distribution system is compared by analyzing distribution system configuration with various solar PV system penetration rates. The simulated findings show that as the penetrating capability of the PV system increases, large harmonic distortion levels are injected, indicating that the solar photo system should only integrate corresponding to the highest capability the connection can sustain. When a PV technology is connected further than this maximum penetration of renewable energy sources, it produces considerable harmonic components, which harms the system that improves. Total voltage output frequency and current consumption distortion are determined to be 4.98 percent and 14.99 percent, correspondingly, at the maximum diffusion way that enables the permissible harmonic distortion limitation. Thus, the research presents the uses of Grid Integration to estimate the performance and the quality of the solar PV model.