Harmonic Suppression Strategy Research Articles

DC-Biased Sinusoidal Current Excited Switched Reluctance Motor Drives Based on Flux Modulation Principle

This article proposes a novel current control technique for three-phase switched reluctance motor (SRM) drives with harmonic current suppression, based on developed flux modulation principle. For conventional SRM control systems, the unsmooth and discontinuous stator current cause serious torque ripple, vibration, and noise, due to the doubly salient motor structure. In order to overcome shortcomings in conventional drives, the developed flux modulation principle is employed for the SRM in this article, where the working principle is investigated in detail, including the excitation magnetic field, flux modulator, and armature magnetic field. Then, a new control strategy is presented to generate the dc-biased sinusoidal current, by employing the modular open-winding converter. Furthermore, a harmonic current suppression strategy is put forward for the new drive to improve the motor performance, by employing a developed vector proportional integral control scheme. Compared to existing SRM drives, the torque ripple and motor vibration can be both significantly reduced, the motor structure and winding arrangement do not need to be changed, and the robustness of the motor system is improved. Finally, experiments are carried out on a three-phase 12/8 SRM prototype to verify the effectiveness of the proposed SRM drive and control strategy.

Research on harmonic cooperative suppression strategy of hybrid parallel DC transmission system

Hybrid parallel DC transmission system has both flexible control characteristics of MMC-HVDC and large capacity transmission capacity of LCC-HVDC, which has good economy and practicability. However, the connection of hybrid parallel DC transmission system will bring a series of harmonic problems, so harmonic suppression measures must be taken. This paper firstly introduces the generation mechanism and basic characteristics of LCC-HVDC characteristic and non-characteristic harmonics. Then the causes of MMC-HVDC circulation are analysed. Finally, based on the parallel connection of LCC-HVDC and MMC-HVDC in the same AC bus, a harmonic co-suppression strategy of hybrid parallel DC transmission system is proposed and the simulation verification is carried out. The results show that the strategy can use MMC-HVDC to assist in absorbing the harmonics generated by LCC-HVDC.

Current Harmonic Suppression in Dual Three-Phase Permanent Magnet Synchronous Machine With Extended State Observer

Dual three-phase (DTP) permanent magnet synchronous machines (PMSM) have been utilized in many applications due to their outstanding performance. However, large stator current harmonics limit the further application of the DTP-PMSM due to the low impedance in the harmonic subspace. To solve this problem, this article proposes a current harmonic suppression strategy based on an extended state observer (ESO). A detailed analysis is carried out to demonstrate the disturbance rejection ability and robustness of the proposed method. The theoretical analysis also shows that the ESO strategy outstands the conventional proportional-integral controller and advanced proportional resonance (PR) controller in terms of harmonic reduction. The advantages are verified by simulation and experimental results under different operating conditions. The proposed strategy still works well when considering other factors that may cause harmonic distortion, such as magnetic circuit saturation, saliency ratio, over-modulation of the inverter, the voltage drop caused by electric devices, and dead time. Meanwhile, some limitations are also pointed out. The proposed strategy can also be easily applied to other multiphase PMSM types.

Selective Harmonic Current Rejection for Virtual Oscillator Controlled Grid-Forming Voltage Source Converters

Virtual oscillator control (VOC) is a nonlinear grid-forming controller that simultaneously achieves the functionality of output voltage control and primary control layers in a power electronics interfaced distributed generation (DG) unit. Unlike conventional phasor-based primary control methods such as the droop control and virtual synchronous machine control, VOC is a time-domain controller that can guarantee almost global asymptotic synchronization. However, the high-frequency dynamics has largely been ignored in the analysis of VOC in prior art; as a result, VOC-based DGs fail to suppress harmonic current in the presence of harmonic distortion in the network-side voltage. In this work, we demonstrate that frequency-domain method can be used for oscillator-based converters in the high-frequency range, specifically, for harmonic mitigation in the converter output current. We propose a virtual impedance-based selective harmonic current suppression method, and demonstrate that it is better to use the network-side current feedback rather than that of the converter-side current for VOC implementation with virtual impedance control. Established harmonic rejection strategies for grid-following and conventional grid-forming converters are compared with the proposed method for VOC. Through impedance-based analysis, we demonstrate that the proposed method augments the passivity range of the converter terminal response with a much simpler implementation. The proposed harmonic suppression strategy is validated through hardware experiments using a single-phase inverter prototype.

Selective Current Harmonic Suppression for High-Speed PMSM Based on High-Precision Harmonic Detection Method

Winding currents contain lots of harmonics if motors rotate at a high speed. This paper addresses two key challenges on the harmonic suppression: 1) using the multiple synchronous rotating frame transformations (MSRFTs) to get the primary signals, and 2) proposing the closed-loop detection system (CDS) to extract the harmonics accurately. First, the mathematical model containing the harmonics was built. Second, the MSRFTs were introduced and the high-precision detection method called the CDS was analyzed. The CDS has a higher harmonic detection accuracy than the open-loop method and can enhance the disturbance rejection capability of the system. Third, the parameter-independent compensation algorithm was proposed to enhance the robustness against the motor parameter variations, which was combined with the compensation calculated by the mathematical model to suppress the harmonics. The effectiveness of the proposed harmonic suppression strategy was verified by the experiments on the turbo molecular pump.

Harmonic Suppression Strategy in Single-phase SPWM Based on Mixed Integer Nonlinear Programming

In single-phase bipolar SPWM inverter circuit, the output voltage contains high content of harmonic components. To solve this problem, we build a model of output voltage in single-phase SPWM bipolar inverter based on SPWM theory and Fourier series theory. Through theoretical analysis, calculation and plotting, we work out the distribution of harmonic in output voltage, investigate the relationship between amplitude modulation (AM) depth and harmonic components and finally determine a proper amplitude modulation depth to efficiently reduce harmonic components. To further reduce harmonic components of output voltage, we use LC low-pass filter. Then, based on the mathematical model of the filter and the distribution law of harmonics, we establish a mixed integer nonlinear programming to fully suppress harmonics and reduce switching losses. After searching for two times based on genetic algorithm, we work out the best frequency-modulation ratio and LC low-pass filter parameter. Finally in simulation, total harmonic distortion is reduced from 213.47 percent to 0.16 percent after harmonic suppression strategy implemented. The result has proved the effectiveness of the harmonic suppression strategy we applied, which can be used as a reference for output voltage harmonic elimination in single-phase SPWM inverter.

Analysis and Study of the Influence on the Train Side Harmonic as a SMES Fabricated Into the EMU Converter System

Due to the dynamic performance and continuous function of superconducting magnetic energy storage (SMES), the SMES was fabricated into the electrical multiple unit (EMU) high-speed train traction converter system. The pollution of harmonic current from ac drive electric locomotives was an essential problem to analyze. To settle this problem, first, the influence of SMES technology in the current harmonic of train grid side was studied, in which the current analysis method was used and a harmonic suppression scheme was proposed. Next, the effects of harmonic frequency characteristics and amplitude characteristics on the current harmonic were analyzed, with adjusting the carrier frequency and increasing the leakage inductance of the traction transformer. Finally, the accuracy of the theoretical analysis method is verified by the simulation analysis and experimental verification. The results showed that the new type superconductivity technology proposed could optimize the train side harmonic current remarkably.

Harmonic Current Suppression Strategy for Grid-Connected PWM Converters With LCL Filters

As for a grid-connected PWM converter with LCL filter, harmonic current can flow freely into the grid-side inductor and filter capacitor, when the connected power grid is harmonically distorted. The fact lies in that the conventional control scheme has a little ability to suppress the grid current harmonics. Though the harmonics can be suppressed by the capacitor current compensation method, it may lead to system stability issues. This paper proposes an improved harmonic suppression scheme with the partial capacitor current feedforward, which can effectively suppress the specified grid current harmonics on the premise of ensuring the system stability. Since the partial capacitor current is obtained as the differential output of a multi-second-order generalized integrator, no extra current sensors are needed. The effectiveness and feasibility of the proposed strategy are verified by detailed experimental results.

Harmonic Coupling Analysis and Suppression Strategy of Grid-connected Photovoltaic Inverter

For the complex harmonic coupling problem caused by the parallel connection of grid-connected photovoltaic inverters to the grid, the mathematical models of a single three-phase inverter and two three-phase inverters connected in parallel are established in this paper. The transfer function is derived and the resonant characteristics of grid-connected single inverter and parallel grid-connected multi-inverters are analyzed by using Bode diagram. On the basis of the maximum power tracking link, This paper proposes a control strategy which combines the double closed-loop of current by using grid-connected voltage and capacitive current with the proportional feedforward compensation of grid voltage, which maximizes the use of solar energy and has a better harmonic resonance suppression capability at the same time. The effectiveness and correctness of the proposed control strategy are verified by Matlab/Simulink system simulation.

Research on Multi - Resonant LCL Harmonic Suppression Strategy

Abstract Aiming at the resonance problem in the process of grid connection of LCL filter microgrid inverter, a multi-resonance LCL harmonic suppression strategy is proposed. On the basis of analyzing the principle and establishing the mathematical model in detail, the realization process of the multi-resonance constant power compound control strategy is studied emphatically. Through the simulation, the validity of the control strategy is verified, The results show that the scheme stabilizes the output power and reduces the total harmonic distortion of the grid-connected inverter to 0.12%, and the corresponding phase current distortion rate drops to 0.02%.The suppression effect is obvious, it is an effective harmonic suppression method.

Active Suppression of Selected DC Bus Harmonics for Dual Active Bridge DC–DC Converters

AC coupled dual active bridge (DAB) dc–dc converters typically use phase shifted square wave (PSSW) modulation to manage the power flow between two dc sources. With this scheme, the current flowing between the converter bridges injects high-magnitude current harmonics into each dc port at multiples of the primary switching frequency, which can excite resonances in the $LC$ circuits created by parasitic second-order impedances such as wiring inductances in the dc-link connections. This can cause substantial dc bus voltage and current oscillations, particularly with the higher switching frequencies that are used with wide bandgap devices, leading to excessive electromagnetic interference, significant filter stress, and eventual component operational failure. Conventionally, a relatively large dc bus filter capacitor (or inductor) helps to suppress these dc bus harmonic dynamics. However, the use of adaptive three-level modulation for a single phase DAB provides a much greater solution space to achieve a desired power transfer condition, with the three PSSW control angles that are available. This paper now explores the additional use of these angles to selectively suppress particular dc bus current harmonics across the entire operating range of the converter and thus allow the size of the DAB dc bus bridge capacitors to be minimized. This new active harmonic suppression (AHS) strategy is validated by theory, simulation, and matching experimental results.

A Harmonic Resonance Suppression Strategy for a High-Speed Railway Traction Power Supply System with a SHE-PWM Four-Quadrant Converter Based on Active-Set Secondary Optimization

Pulse width modulation (PWM) technology is widely used in traction converters for high-speed railways. The harmonic distribution caused by PWM is quite extensive, and increases the possibility of grid–train coupling resonance in the traction power supply system (TPSS). This paper first analyzes the mechanism of resonance, when the characteristic harmonic frequency of a four-quadrant converter (4QC) current that injects into the traction grid matches the resonant frequency of the traction grid, which may result in resonance in the system. To suppress resonance, this paper adopts specific harmonic elimination–pulse width modulation (SHE-PWM) technology combined with a transient direct current control strategy to eliminate the harmonics in the resonant frequency, which may suppress the grid–train coupling resonance. Due to the fact that the SHE-PWM process with multiple switching angles contains complex transcendental equations, the initial value is difficult to provide, and is difficult to solve using ordinary iterative algorithms. In this paper, an active-set secondary optimization method is used to solve the equation. The algorithm has the benefits of low dependence on initial values, fast convergence and high solution accuracy. Finally, the feasibility of the resonant suppression algorithm is verified by means of Matlab simulation.

A Harmonic Suppression Scheme for Full Speed Range of a Two-Level Inverter Fed Induction Motor Drive Using Switched Capacitive Filter

This paper proposes a novel harmonic suppression scheme for two-level inverter fed three-terminal induction motor drives using switched capacitive filter. Capacitor fed H-bridges used as filters are cascaded to conventional two-level inverter to eliminate fifth-and seventh-order harmonics for the full modulation range including a six-step operation. For the first time, two-level dodecagonal voltage space vector is implemented with single dc supply for three-terminal induction motor drive. Enabling the switched capacitive filtering at low-voltage domain and shifting the high frequency switching to the switched capacitive filter is shown. A uniform pulse width modulation technique is shown which charges and maintains the capacitor voltages while eliminating the fifth-and seventh-order harmonics for the full speed range.

Selective harmonic suppression strategy by SAPF in power distribution system

Selective harmonic suppression strategy by SAPF in power distribution system

Active Power Quality Improvement Strategy for Grid-Connected Microgrid Based on Hierarchical Control

When connected to a distorted grid utility, droop-controlled grid-connected microgrids (DCGC-MGs) exhibit low equivalent impedance. The harmonic and unbalanced voltage at the point of common coupling (PCC) deteriorates the power quality of the grid-connected current (GCC) of DCGC-MG. This paper proposes an active, unbalanced, and harmonic GCC suppression strategy based on hierarchical theory. The voltage error between the bus of the DCGC-MG and the grid’s PCC was transformed to the dq frame. On the basis of the grid, an additional compensator, which consists of multiple resonant voltage regulators, was then added to the original secondary control to generate the negative fundamental and unbalanced harmonic voltage reference. Proportional integral and multiple resonant controllers were adopted as voltage controller at the original primary level to improve the voltage tracking performance of the inverter. Consequently, the voltage difference between the PCC and the system bus decreased. In addition, we established a system model for parameter margin and stability analyses. Finally, the simulation and experiment results from a scaled-down laboratory prototype were presented to verify the validity of the proposed control strategy.

Three-Phase Series-Connected Modular Multilevel Converter for HVDC Application

The three-phase series-connected modular multilevel converter (SC-MMC) is presented as one option for high-voltage direct current (HVDC) tap to reduce the cost of an HVDC station. Compared with conventional three-phase parallel-connected MMC, the number of semiconductor switches in SC-MMC is reduced by one-third to withstand the same dc voltage. First, the paper studies the operating principle of SC-MMC, and then presents an interspacing phase-shifted pulsewidth-modulated method which could improve the waveform of the output ac voltage for a given switching frequency. Next, the control strategy based on the identical real power input of each phase is proposed to balance the dc voltage of each phase under an unbalanced grid condition. The current limit of switching devices is also taken into consideration to protect SC-MMC from overcurrent. Furthermore, a universal zero-sequence current controller is developed as one part of the control strategy. In addition, an innovative method to suppress the third harmonics of ac current is presented. With the third harmonic suppression strategy, the SC-MMC can operate with much smaller SM capacitors without deteriorating the ac current, which contributes to the cost reduction further. Finally, simulation results obtained in PSCAD/EMTDC are provided to validate the proposed control strategies.

Analysis and Suppression Strategy of Harmonics for SPWM Inverter

The three-phase voltage type SPWM inverter output voltage and current harmonic and its generation rule is discussed. And put forward a new easy to implement harmonic suppression strategy, the method through the correct choice of the carrier frequency and the sinusoidal wave superimposed on a three wave makes saddle shaped wave, to produce a corresponding SPWM waveform control inverter switch on-off thus improving the output waveform. Mathematical analysis shows that is helpful to reduce the output voltage THD ( waveform distortion factor ), improved harmonic current loss and torque characteristics, the simulation results prove the validity of these measures and practical.

Acceleration Harmonic Cancellation of Electro-hydraulic Servo Shaking Table

Nonlinearities are inherent in electro-hydraulic servo shaking table. Some nonlinearities are dead zone of servo valve, backlash and friction between joints, and friction in hydraulic cylinder. Nonlinearities cause harmonic distortion of the output acceleration signal corresponding to a sinusoidal input. On the basis of extensive studies on literature related to dead zone, backlash and friction compensation scheme, an adaptive harmonic suppression strategy based on adaptive notch filter technology is proposed. The task is accomplished by generating reference signals with frequency to be suppressed from the output. According to the error between the input acceleration and the feedback acceleration, the weights of filter are adjusted on-line by least mean square adaptive filtering algorithm in real-time. The reference inputs are weighted by the adaptive filter in such a way that it closely matches the harmonic. The output of the adaptive filter is a harmonic replica and is injected to the fundamental signal such that the output harmonic is suppressed, and the total harmonic distortion is greatly reduced. The above course is used as a basis for the development of adaptive harmonic cancellation algorithm.

A harmonic elimination and suppression scheme for an open-end winding induction motor drive

In this paper, a harmonic elimination and suppression scheme for a dual-inverter-fed open-end winding induction motor drive is presented. Two isolated dc-link sources with voltage ratio of approximately 1 : 0.366 are required for the present drive. These two isolated do links feeding two inverters to drive the open-end winding induction motor eliminate the triplen harmonic currents from the motor phase. The pulsewidth-modulation scheme proposed enables the cancellation of all the 5th- and 7th-order (6n /spl plusmn/ 1, where n = 1, 3, 5, 7, etc.) harmonic voltages and suppresses the 11th- and 13th-order harmonic voltage amplitudes in the motor phase voltage, in all modulation ranges. The next higher order harmonics present in the motor phase voltages are 23rd, 25th, 35th, 37th etc. (6n /spl plusmn/ 1, n = 4, 6, etc.). By using triangular carrier wave and proper modulating waves for each inverter, the open-end winding induction motor can be operated in the entire modulation range, eliminating all the 6n /spl plusmn/ 1 harmonics (n = 1, 3, 5, 7, etc.) coupled with 11th and 13th harmonic suppression. The proposed scheme also gives a smooth transition to the overmodulation region.

A pole sensitivity method for analyzing harmonic magnification in a power system

Harmonic resonance caused by the compensation capacitor banks in electric power systems is discussed in this paper. A method used to study the harmonic resonance and the harmonic magnification is presented. In this method, the calculation of system poles is combined with the calculation of pole sensitivities respective to the system's branch parameters. As a result, the information referring to the power system's harmonic resonance, the harmonic current magnification and the harmonic suppression strategy can be obtained by using this method.