Harmonic voltage excess problem test and analysis in UHV and EHV grid particular operation mode

An improved controller design method for an inverter operating with extra functions to suppress current harmonics or voltage harmonics is proposed. When at least two of this-type inverters are operating in a micro-grid, they can collaboratively bear current harmonics and voltage harmonics suppression tasks respectively. This would benefit the micro-grid further wide applications. In this paper, firstly, the principles of harmonics comprehensive suppression are analyzed. Then, two kinds of inverter controllers with different harmonics suppression purposes are designed. Finally, the effectiveness of the above control strategies is verified by Matlab/Simulink simulation results. The total harmonic distortion (THD) values of current and voltage are obviously reduced when these two inverters are connected in parallel with the micro-grid.

When the power system is disturbed or the operation mode is changed, the electromagnetic transient process will occur, which will lead to the high frequency transient component and affect the protection and control of the power system. Therefore, attention should be paid to the analysis of high-frequency transient components when modeling and analyzing the system model. In view of the fact that the symmetrical-component theory is not suitable for asymmetric transmission lines and the phasor method is not suitable for transient analysis and calculation, this paper uses the phase coordinate approach and Laplace transform to derive the node voltage equation of three-phase π type transmission lines in frequency domain, which can be used to calculate the transient response of transmission lines caused by the change of operation mode or disturbance. And vectorized NILT is used to calculate the time domain solution, which greatly improves the calculation speed. The calculated results are basically consistent with those of ATP-EMTP, and can fully reflect the transient characteristics. This method lays a foundation for analyzing the influence of high frequency transient components on power system and fault analysis considering transient process.

The variation of background harmonics, system harmonic impedance and load characteristics will affect the harmonic voltage and current at the point of common coupling(PCC), which will lead to large estimation error of harmonic contribution if ignored. In this paper, a simple and effective method is proposed to identify the abrupt transition points in the harmonic parameter data, then the harmonic voltage and current data are divided into several stable data sections, in which the background harmonic and system harmonic impedance are basically unchanged, and the load characteristics are relatively stable. On this basis, the harmonic contribution of the harmonic source is discussed and evaluated by using the robust regression method in the data segment, and the dynamic variation of the harmonic contribution parameter in the time period is obtained. The simulation results show that the proposed method can accurately identify the variation of harmonic parameters and divide the harmonic information into several stable data segments. The robust regression method has higher accuracy than other linear regression methods. The accuracy and effectiveness of the proposed method are proved.

Flexible heat exchanger network design for chemical processes with operation mode changes

The harmonic transfer characteristics in the distribution network were analyzed from two aspects of harmonic current and harmonic voltage in this paper. The analysis results show that the harmonic current mainly flows into the upper system when the filter device is not input. The transmission coefficient is related to the transformer ratio when the harmonic current is injected into the upper system and transmitted from the low pressure side to the high pressure. The harmonic voltage of the higher-level power grid is mainly concentrated on the load equivalent impedance of the current-level power grid when passing through the distribution network. When the harmonic filter voltage of the upper-level power grid is mainly transmitted, the system is mainly concentrated on the system of the current-level power grid.

Self-optimization enables technical systems to adapt their behavior to varying environmental conditions and changing operation modes. Objective functions serve as evaluation criteria for the system behavior. In this paper we present a novel approach of an objective-based controller. This controller is based on Pareto sets, which are solutions of multiobjective optimization problems and computed offline. The controller can be used to continuously adjust the system behavior by computing optimal configurations out of the Pareto sets without solving an optimization problem at runtime. The goal of the controller is to drive the objective values toward a desired relative weighting. Furthermore, the controller is able to cope with varying operation modes, which arise in case of component faults, for example. For each operation mode an entire Pareto set is computed separately. For designing the objective-based controller we use a simplified model of the closed-loop system. The objective values are approximated at runtime by means of a lowpass filter. An active suspension system affected by unknown track excitations serves as an application example. We use a particular control reconfiguration approach in case of an actuator fault as a change of the operation mode. Finally, simulations with a nonlinear model of the system validate our approach.

This paper proposes a triple-phase-shift (TPS) control strategy for the full-bridge three-level (FBTL) DC/DC converter to reduce the voltage stress and harmonics on the transformer. The proposed control strategy is composed of three phase-shift delays to keep the maximum voltage changes (ΔV) on the transformer's primary side at only half of the input voltage (Vin/2) , which is different from the conventional control strategies causing the higher voltage changes with value of Vin . Therefore, the proposed control strategy can effectively reduce the voltage change rate (dv/dt) and voltage harmonics on the transformer due to the benefits of multi-level voltage produced by the three phase-shift delays. Additionally, the proposed TPS control strategy has two working modes, which can thus have wide voltage gain. Finally, the experimental results are presented to verify the proposed control strategy.

It must need to take off the cause of nonlinearity if someone needs a good resistor. The 3 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">rd</sup> harmonic distortion voltages of three types of resistors were measured. In the next stage, the 3 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">rd</sup> harmonic voltage is tested using by a bridge made on a printed circuit board (PCB) occurs current constriction effectively. It is very simple structure without contact barriers to consider the cause of nonlinear distortion. It is obvious that the short bridge causes the high distortion voltage. It seems that heat oscillation for power dissipation and propagation of one cycle of AC current from both bride edges to wide areas of PCB would cause the 3 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">rd</sup> harmonic distortion voltage. In this study, further testing with very low frequency current is superposed to check the AC heating effect is prevented by the low frequency current.

This paper presents a Norton model for modelling distribution networks where the system configuration is not fully known. Traditionally harmonic studies use complex distribution networks modelled by harmonic current sources for specific frequencies. Although this model has been proved to be adequate for some studies, this may not be adequate for other applications. When changing the operating conditions of the supply-side system, the harmonic currents injected by the distribution network might change and to investigate these harmonic currents, the Norton model is used. The change of operating condition is obtained by switching shunt capacitors. The estimated model can be used to analyze, for example, the effect of harmonic filters under different supply system configurations or operating conditions. The method of estimating the Norton models is illustrated on a test system, simulated on the well-known simulation program EMTP-ATPDraw. Key words : Norton model; Distribution network; Operating conditions; Harmonic currents and voltages

A novel control strategy for mode seamless switching of PV converter in DC microgrid based on double integral sliding mode control

The paper presents the basic concepts of power quality considerations, especially when current, voltage or both present nonsinusoidal waveforms. The use of shunt compensator for current harmonic or unbalance compensation or the use of series compensator for voltage harmonic or unbalance compensations is discussed. Then the advantage of using hybrid passive and active power filter is also discussed. The association of shunt and series active filter composing the UPQC (universal power quality conditioner) which can guarantee perfect voltage and current harmonic compensation is presented. As a result of the generalization of the concept of the UPFC (unified power flow controller) associated with the concept of UPQC, the UPLC (universal active power line conditioner) is presented, which can compensate voltage and current harmonics as well as control the power flow in a transmission line.

Fault detection and diagnosis based on particle filters combined with interactive multiple-model estimation in dynamic process systems

This paper focuses on the islanded operation of microgrids. In this mode of operation, the microsources are required to cooperate autonomously to regulate the local grid voltage and frequency. Droop control is typically used to achieve this autonomous voltage and frequency regulation. Inverters having LCL output filters would cause voltage distortion to be present at the PCC of the local load when non-linear current is supplied to the load due to the voltage drop across the grid side inductor. Techniques to reduce the output voltage distortion typically consist of installing either passive or active filters to selectively compensate harmonic frequencies. However, by adding suitable control strategies to the inverters connected to the microgrid, the power quality of the microgrid can be improved without the installation of any additional equipment. In this paper, a capacitive virtual impedance loop, implemented in each of the microsource inverters, is proposed so as to dampen the voltage harmonics at the PCC of the local load. Simulation results are presented showing the suitability of the proposed algorithm in dampening the PCC voltage harmonics.

The implementation of maximum power point tracking (MPPT) schemes by the ripple correlation control (RCC) algorithm is presented in this paper. A reference is made to single-phase single-stage multilevel photovoltaic (PV) generation systems, when the inverter input variables (PV voltage and PV current) have multiple low-frequency (ripple) harmonics. The harmonic analysis is carried out with reference to a multilevel configuration consisting of an H-bridge inverter and level doubling network (LDN) cell, leading to the multilevel inverter having double the output voltage levels as compared to the basic H-bridge inverter topology (i.e., five levels vs. three levels). The LDN cell is basically a half-bridge fed by a floating capacitor, with self-balancing voltage capability. The multilevel configuration introduces additional PV voltage and current low-frequency harmonics, perturbing the basic implementation of the RCC scheme (based on the second harmonic component), leading to malfunctioning. The proposed RCC algorithm employs the PV current and voltage harmonics at a specific frequency for the estimation of the voltage derivative of power dP/dV (or dI/dV), driving the PV operating point toward the maximum power point (MPP) in a faster and more precise manner. The steady-state and transient performances of the proposed RCC-MPPT schemes have been preliminarily tested and compared using MATLAB/Simulink. Results have been verified by experimental tests considering the whole multilevel PV generation system, including real PV modules, multilevel insulated-gate bipolar transistor (IGBT) inverters, and utility grids.

There is a certain amount of current harmonics in interior permanent magnet synchronous motor. In order to accurately control the current harmonic, this article focuses on three aspects: establishing current harmonic calculation model, extracting current harmonic, and designing current harmonic regulator. A current harmonic calculation model, which considers the effect of voltage harmonics induced by current controllers and digital control delay on the initial phase angle of voltage harmonics, is established for the first time. With the help of multiple synchronous rotating frame transformation, a current harmonic extraction method more suitable for motor drive field, which aims to extract the current harmonic characteristics of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</i> -axis and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">q</i> -axis currents, is proposed. On this basis, the controlled quantity and control quantity are unified in <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d–q</i> coordinate frame for analyzing the coupling relationship of current harmonic characteristics. And then a PI current harmonic regulator, including current harmonic decoupling and voltage harmonic initial phase angle compensation, is constructed, so as to realize the effective control of current harmonics. Finally, the effectiveness and superiority of the proposed method are verified by simulation and experiments.