Harmonic Current Control Strategy Research Articles

VSC control strategy for HVDC compensating harmonic components

This paper proposes a voltage source converter (VSC) control strategy for the high voltage direct current (HVDC) transmission systems compensating the harmonic components. For VSC-HVDC AC system accounted for a relatively large share of the 5th, 7th, 11th, 13th and other low harmonics. A selective harmonic current control strategy based on vector proportional integral (VPI) regulator in dq coordinate system is proposed on the basis of PI control. In which, PI is used to control the DC component of the current error, while VPI is used to suppress the multiplicative fluctuations of the current error. Unlike the proportional-integral resonant (PIR) regulator, the VPI contains a second-order numerator that achieves the ideal 0° phase delay of the closed-loop transfer function of the control system at the set resonant frequency point, so its control accuracy for harmonic currents is better than that of the PIR. A two-terminal VSC-HVDC system is built using Simulink software, and current compensation simulations are performed for three control methods: conventional PI, PIR and PI parallel VPI schemes. The superior harmonic suppression performance of VPI is verified by comparing the harmonic content.

Torque Improvement of Spoke-type Permanent Magnet Motor with Auxiliary Stator Using Harmonic Current Control Strategy

The spoke-type permanent magnet motor with auxiliary stator exhibits high torque performance owing to the flux focus effects. To further improve its torque density, this paper proposes a control method by using harmonic current strategy. Based on the theoretical analysis, a 3-D torque look-up table by dq-axis current and electrical angle is established with the aid of the finite element method (FEM). The maximum torque per ampere curve at each rotor position is identified and summarized to adequately indicate the relationship between torque and current amplitude of the motor. Through theoretical derivation, it is concluded that the minimum torque cost curve is the contour line of ∂Te/∂i <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , which can be employed to identify the harmonic current for torque density improvement. Compared to traditional strategies, the proposed control strategy can increase torque density of forward and reverse torque by 1.22% and 1.40%, respectively. The experimental results verify the analysis and simulation results, as well as prove the effectiveness of the proposed strategy.

Direct current control strategy of LCL‐type converter for harmonic suppression under distorted grid condition

The grid voltage distortion represents a significant cause of the grid quality degradation when a renewable energy system is incorporated into the traditional grid. In this paper, a direct harmonic current control strategy is proposed for an LCL converter under distorted grid conditions. The proposed strategy improves the power quality and enhances the converter robustness under the non-ideal grid conditions. Traditionally, in the harmonic suppression strategy, the capacitor current is commonly used as a harmonic information source to control and suppress harmonics, which not only realises active damping, but also provides harmonic current suppression. Unlike the existing technologies, the proposed strategy realises the closed-loop control and harmonic current suppression by sampling the converter-side current. The proposed strategy can achieve a more efficient harmonic suppression than the traditional methods without requiring additional sensors and hidden danger of resonance. The impedance characteristics of multi loops are analysed when a distorted voltage is applied to the LCL converter. Then, the corresponding control strategy is proposed. The similarities and differences in harmonic suppression and stability between the proposed strategy and the traditional strategies are presented and discussed. Finally, the effectiveness and feasibility of the proposed strategy are verified by the simulation and experimental results.

An Improved Harmonic Suppression Control Strategy for the Hybrid Microgrid Bidirectional AC/DC Converter

The nonlinear load in AC/DC hybrid microgrid seriously affects the power transmission quality of bidirectional AC/DC interlinking converter (BIC). In this article, an improved Fryze-Buchholz-Depenbrock (FBD) harmonic current detection method combined with droop control is designed to suppress harmonic current control strategy. The decoupled double synchronous reference frame phase locked loop (DDSRF-PLL) with self decoupled network is used to eliminate the negative sequence fundamental frequency component, and the accurate phase detection can also be realized when affected by nonlinear load. The least mean square (LMS) algorithm adaptive filter can enhance the dynamic response ability when the load current suddenly changes. To solve the problem that the cut-off frequency of low pass filter (LPF) can not take into account the detection accuracy and response speed of FBD harmonic current detection method. Finally, Matlab/Simulink is used for simulation verification. The simulation results show that the improved control strategy not only realizes the bidirectional flow of power and maintains the DC bus voltage stability, but also reduces the total harmonic distortion (THD) at point of common coupling (PCC) by 0.45% compared with the traditional FBD control strategy. And the effectiveness and feasibility of the design method are proved.

Dual-Loop-Based Harmonic Current Control Strategy and Admittance Modeling for a Multimodular Parallel SAPFs System

A large-capacity harmonic current widely exists in low-voltage distribution networks, which seriously affects the operation reliability and the efficiency of power system and related equipment. Due to its excellent controllability and dynamic response performance, the full-controlled semiconductor-device-based multimodular shunt active power filter is considered as the optimal choice to compensate the distorted current from large-scale nonlinear loads. However, due to the increase of parallel modules, comprehensive compensation performance needs to be improved and the system stability analysis is required. In this article, based on the comprehensive comparison and the analysis of the traditional parallel operation, a novel dual-loop-based harmonic control strategy that features the comprehensive filtering performance through combining feedforward power splitting and feedback frequency splitting control is proposed, which realizes a comprehensive optimization of capacity utilization, compensation precision, and dynamic response performance. In addition, for the system stability analysis, by establishing the two-port Norton equivalent circuit of a multi-inverter parallel system in the admittance form, the response expressions of each part of parallel system are obtained, and the essential reason for the instability is revealed from the perspective of the frequency-domain characteristics of global admittance. Finally, simulation and experimental results are presented to support the reasonability and effectiveness of the proposed method.

A Method for Improving Compensation Performance of the Active Power Filter

Distributed renewable energy connected to the power grid in the form of micro-grid, which makes a great impact on the power quality of the grid. Active Power Filter (APF) is a kind of effective device, which can improve the power supply quality and purify the power pollution. It‘s particularly significant to improve the APF’s performance. Based on the selective harmonic current control strategy, which is used to solve the problem, that the main times of the harmonic current is not sufficiently compensated, this paper considers to adopt the LCL filter on the grid-side to further improve the compensation performance of active power filter. This improvement can reduce the high frequency harmonics caused by the way of PWM high frequency modulation. Finally a case study simulated by PSIM software verifies the superiority of the proposed measure.