Output Current Harmonic Distortion Research Articles

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 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.

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.

H14 Three‐Level Inverter for Common‐Mode Voltage Suppression

This paper presents an H14 three‐level inverter topology and the corresponding control method for common‐mode voltage (CMV) suppression based on the three phase three‐level neutral‐point‐clamped inverter. Operation performance of the proposed H14 three‐level inverter is first analyzed under different switching patterns, and the corresponding CMV under each operation states is investigated. The control method of H14 inverter is presented by following a feasible minimal CMV output within the switching patterns, and the switching function is given which is very easy to be implemented. Furthermore, the operation performances of the proposed H14 inverter in terms of total harmonic distortion of output current, DC link neutral‐point voltage oscillation and CMV are investigated in simulation and hardware‐in‐the‐loop experiment. The verification results show that the proposed H14 three‐level inverter is able to suppress the CMV, the maximum amplitude of CMV is reduced from Vdc/3 to Vdc/6 especially with desirable operation performances of inverter. © 2020 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC.

Switching-Cell Four-Leg Current Source Inverter

Conventional current source inverter (CSI) suffers from open-circuit problem during switch transition. Thus, overlap-time should be inserted in the gate signals for safe commutation. The overlap-time distorts output current waveforms and increases total harmonic distortion of output current. Moreover, it reduces the current source utilization of the inverter. To solve these problems, this article proposes a new three-phase four-leg switching-cell (SC) CSI, abbreviated as H8-SC-CSI. With the help of the SC structure, the reliability of the proposed inverter is greatly enhanced as open-circuit concerns are eliminated. In addition, with the intrinsic voltage clamping action of the SC structure, switch voltage overshoot at turn-off is mitigated. In the proposed CSI, the switch overlap-time can be minimized or eliminated because the inductor current can flow through the SC capacitors. A 1.2 kW prototype inverter is designed and tested to verify the feasibility of the circuit.

DC-link loop bandwidth selection strategy for grid-connected inverters considering power quality requirements

DC-link voltage and output current control loops are two cascaded loops in the control structure of grid-connected inverters. A high DC-link voltage loop bandwidth (DCL-BW) provides more disturbance rejection capability for the control loop and is preferred from control system perspective. However, for stability issues, this BW is limited and must be sufficiently less than that of the current control loop. Among the different control schemes, instantaneous active reactive control (IARC) method provides the highest possible DCL-BW (i.e., 0.02 × switching frequency). Having this degree of freedom in the controller design, a proper methodology should be defined for selection of DCL-BW. In this paper, different factors including the output current harmonic distortion, low-order harmonics on DC link voltage, and the inverter nominal rating are introduced as affecting parameters for DCL-BW selection. Accordingly, a DCL-BW selection strategy based on output current harmonic distortion is proposed. The proposed method enhances the power quality indices of the grid-connected inverters, which especially is useful for few kVA power inverters. Finally, to validate the conducted analysis, experimental and simulation results are provided.

Resistorless Realization of First‐Order Current Mode Universal Filter

AbstractThis paper proposes a first‐order current mode universal filter employing single active building block, namely differential difference dual‐X second generation current conveyor. The proposed filter is designed to provide multiple filter responses simultaneously, namely low‐pass, high‐pass, and all‐pass on applying a current signal at its input terminal. The proposed work also enjoys the presence of metal oxide semiconductor transistors working as tunable resistors. Some of the key features of the proposed filter are as follows: use of single passive element (a grounded capacitor), ease of cascadability as all the outputs are available at highimpedance ports, low active and passive sensitivities, significantly high frequency of operation (3 MHz), low total harmonic distortion of output current (1.28%), low output current noise (10 pA/√Hz), and low power dissipation (2 mW). A detailed study of device nonidealities is also presented to show the satisfactory performance of the proposed structure under all practical considerations. PSPICE simulations effectively demonstrate the good performance of the proposed filter.

Advanced Variable Switching Frequency Control for Improving Weighted Efficiency of Distributed Renewable Generation Systems

Energy conversion efficiency and output current harmonic distortion are two key performance measures of small-scale grid-connected distributed generation (DG) systems. As the interface between renewable energy generators and the utility grid, dc-ac converters (i.e. inverters) have been increasingly used in recent years. In this paper, a novel control algorithm termed “variable switching frequency control (VSFC)” is proposed to increase the weighted efficiency of the inverter for renewable energy generators through selection of optimal switching frequencies of pulse width modulation (PWM) in real time, based on estimation of output current harmonic distortion. Both simulation and experimental results indicate the proposed VSFC algorithm ensures that the inverter can operate with maximum efficiencies at different output levels while satisfying standard requirements for grid current harmonic distortion. Furthermore, implementation of this method to improve the inverter efficiency has no impact on inverter costs or control complexity.

Compact Three Phase Multilevel Inverter for Low and Medium Power Photovoltaic Systems

A new three phase multilevel inverter with reduced number of components count is proposed in this paper. This inverter is designed using a single DC source per phase to generate multiple level output voltage which makes it suitable for low and medium voltage applications, including ac-coupled renewables or energy storages. A generalized circuit configuration is shown in this paper following which the number of output voltage level can be increased as per expectation. Although, each element endures the voltage stress equivalent to the input DC voltage, the value of total standing voltage (TSV) is reduced by the utilization of minimized number of components with respect to the number of series connected capacitors. Further, staircase modulation scheme is used to generate the switching signals. Hence, the proposed inverter can be operated at low switching frequency with optimal output current harmonic distortion which decreases switching losses and suppresses power factor falling. In order to validate the theoretical explanations and practical performances of the proposed inverter, the hypothesis is simulated for 9, 13 and 39 output voltage level inverters for three phase with a line voltage total harmonic distortion (THD) of 6.06%, 4.16% and 2.10% respectively in MATLAB/Simulink and a 5-level single phase laboratory prototype is implemented in the laboratory.

A Novel Model Predictive Control via Optimized Vector Selection Method for Common-Mode Voltage Reduction of Three-Phase Inverters

In this paper, a novel model predictive control (MPC) via a double vector optimized selection method is proposed. The main idea of this method is for decreasing the high common-mode voltage of two-level inverter under balance situation, improve the tracking performance of the output current and decrease the high output current harmonic distortion rate. To solve the problem of increasing the value of total harmonic distortion (THD) due to the reduction of the available voltage vector, this method controls two voltage vectors in each sampling period for getting a better tracking performance of the output current. Simultaneously, compared with the adding virtual vector MPC method, which results in excessive switching losses, the proposed method defining the selection range of the second voltage vector. Only two voltage vectors adjacent to the first voltage vector can be selected so that the switching frequency can be greatly reduced. An experimental control platform based on Simulink-Real-Time system is presented for the further verification of the effectiveness of the proposed control method. The simulation and experimental results showed that the proposed method could effectively reduce the output common-mode voltage of the inverter. Simultaneously, the THD value and the switching loss are greatly reduced.

A Novel Controller Design for Three-phase Voltage Source Inverter

Two-level three-phase voltage source inverter (VSI) with resistive-inductive load has been widely applied in the real life and production. Precise control and fast response are essential for the performance of two-level three-phase VSI with the resistive-inductive load. In this paper, a novel controller design which consists of discrete-time model predictive control (DMPC) based on Laguerre functions and space vector pulse width modulation (SVPWM) is proposed to satisfy these requirements. The inputs of the three-phase are transformed into stationary α-β coordinate for reducing calculation. In addition, the parameters of DMPC based on Laguerre functions are calculated during the offline period, which can reduce the burden of online calculation. With the voltage detection of resistive-inductive load and the current compensation, required reference voltage can be predicted. The required reference voltage is later applied to SVPWM to get the switch sequences. A modified DMPC based on Laguerre functions-SVPWM can achieve a very low total harmonic distortion of output current. Extensive simulation results demonstrate that the proposed approach has a fast dynamic response and perfect steady-state performance.

A New Compensation Control Strategy for Grid-connected Wind Turbine and Fuel Cell Inverters in a Microgrid

The use of a new control method for grid-connected inverters for reducing the output current harmonic distortion in a wide range of grid-connected distributed generation (DG) applications, including wind turbine (WT) and fuel cell (FC) inverters is proposed in this paper. The control method designed to eliminate main harmonics in a microgrid (MG) and between MG and point of common coupling (PCC) and responsible for the correction of the system unbalance. Another advantage of the proposed control method is that it can be easily adopted into the DG control system without the installation of extra hardware. The proposed control method is comprised of the synchronous reference frame method (SRF). Results from the proposed control method are provided to show the feasibility of the proposed approach.

A Survey of Low Switching Frequency Modulation Techniques for Medium-Voltage Multilevel Converters

Multilevel converters (MLCs) have emerged as standard power electronic converters for medium-voltage high-power industrial applications. Owing to dominating device switching losses in high-power applications, it is preferable to use low device switching frequency (LDSF) modulation techniques. Then, it is possible to achieve higher device utilization, higher converter efficiency, and reduced cooling requirements. However, there exists a tradeoff between device switching frequency and harmonic distortion of converter output currents. Therefore, the main challenge for LDSF modulation techniques is to minimize the harmonic distortion of the output currents. The goal of this paper is to provide a review of various LDSF modulation techniques proposed in the literature and also discuss in detail about one of the emerging LDSF control techniques known as synchronous optimal pulsewidth modulation. Finally, challenges to LDSF modulation techniques for emerging multilevel topologies and future trends in applications of MLCs are discussed to motivate further research, to enhance the proposed LDSF techniques, and to explore for new alternatives.

Power Control of Photovoltaic Inverter under Unbalanced Grid Faults Considering Limits of Its Current Harmonics

This paper studies the instantaneous output power characteristics of photovoltaic inverters and its flexible power control strategy under unbalanced grid faults. Then the optimal parameters model of the power control is established with minimum integrated fluctuation amplitude of the active and reactive power as a goal when the constraint of the output current harmonic distortion of photovoltaic inverters is taken into account. Finally, the optimal power control of photovoltaic inverters based on dead-beat current tracking is realized and the feasibility of the proposed control strategy is verified with the power system transient software PSCAD/EMTDC.

Design of Grid Connected Parallel Inverters with Interleaved Phase Shift by Using CAN Bus

A grid-connected parallel inverter with interleaved phase shift is proposed in this paper. The synchronous are generated by the master module to achieve interleaving phase shift PWM for the parallel inverters connected to grid-tied system that make the inverter to output current to the power line and share the load. TI TMS320F2812 DSP is used for system feedback control with voltage and current by using A/D converters to generate the output current close to sine wave. The expected output current values are determined by the master module and transmitted via CAN (Control area network) between inverter modules. The grid-tied system uses zero-voltage-detection circuit to synchronize the inverter currents with grid voltage. For each switching period, PWM voltage of two inverters are interleaved to reduce the total output current ripple so that the switching frequency can be reduced and the power system EMI problem can be alleviated as well. The experiment results are provided to verify the performance of the proposed system to reduce output current harmonic distortion.

Genetic fuzzy control applied to the inverter of solid oxide fuel cell for power quality improvement

The deregulation and unbundling of electricity markets in many countries worldwide bring new perspectives for fuel cells. The connection between the fuel cell and the load is through an inverter using pulse width modulation (PWM). This paper presents a new flux modulation approach for the closed-loop control of the output voltage of inverters for fuel cell power plants. A fuzzy logic control is proposed for this PWM converter and the fuzzy scaling factors are optimized by using genetic algorithms. The proposed control scheme can achieve fast transient responses and, at the same time, have low total harmonic distortion in output current during steady-state operation. This genetic fuzzy controller demonstrates improved response than conventional flux vector method.

A Fuzzy Flux Control to Reduce Harmonics in the Utility Interface of Fuel Cell Power Systems

The deregulation and unbundling of electricity markets in many countries worldwide brings new perspectives for fuel cells. This article presents a new flux modulation approach for the closed-loop control of the output voltage of inverters for fuel cells, using the flux vector control method. Criteria for designing a fuzzy controller are established, and a comparison with the conventional flux control method is shown. The proposed control scheme can achieve fast transient responses and, at the same time, have low total harmonic distortion in output current during steady-state operation. The performance of the new modulator has been verified in simulation.

Self-Tuning Dead-Time Compensation Method for Voltage-Source Inverters

A new method of dead-time compensation is proposed, capable of self-tuning to the inverter and load properties. The tuning, performed real-time, relies on parameter selection of a generic compensation characteristic. During the parameter search, the quality of compensation is being continuously assessed against the harmonic distortion of output currents. The method enjoys very effective compensation of both harmonic and linear distortion caused by dead time and other parasitic agents.

Fuzzy-tuning current-vector control of a three-phase PWM inverter for high-performance AC drives

This paper proposes a new discrete fuzzy-tuning current-vector control (FTC) scheme for three-phase pulsewidth modulation (PWM) inverters. The proposed current control scheme can achieve fast transient responses and, at the same time, have very low total harmonic distortion in output current during steady-state operation. The proposed FTC scheme generates quasi-optimum PWM patterns by using a closed-loop control technique with instantaneous current feedback. The proposed FTC scheme has been realized using a single-chip digital signal processor (TMS320C14) from Texas Instruments. Experimental results are given to verify the proposed fuzzy-tuning current control strategy for three-phase PWM inverters.