This paper describes the design procedure and performance of an LCL grid filter for a medium-voltage neutral-point clamped converter to be adopted for a multimegawatt (multi-MW) wind turbine. The unique filter design challenges in this application are driven by a combination of the medium-voltage converter, a limited allowable switching frequency, component physical size and weight concerns, and the stringent limits for allowable injected current harmonics. Traditional design procedures of grid filters for lower power and higher switching frequency converters are not valid for a multi-MW filter connecting a medium-voltage converter switching at low frequency to the electric grid. This paper demonstrates a frequency-domain-model-based approach to determine the optimum filter parameters that provide the necessary performance under all operating conditions given the necessary design constraints. To achieve this goal, new concepts, such as virtual-harmonic content and virtual filter losses are introduced. Moreover, a new passive-damping technique that provides the necessary damping with low losses and very little degradation of the high-frequency attenuation is proposed.

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Grid-Filter Design for a Multimegawatt Medium-Voltage Voltage-Source Inverter

This paper presents a linear direct-quadrature current control strategy for voltage source converters (VSCs) in a rotating reference frame (RRF). The described method is based on multivariable-proportional-integral (PI) regulators and provides fast dynamics and a zero steady-state error. Contrary to the well-known conventional PI-based control strategies in RRFs, the presented method provides practically decoupled axes with a superior disturbance rejection capability. Moreover, its implementation is relatively simple and does not impose excessive structural complexity compared to its conventional PI-based competitors. The method is applicable to both single- and three-phase systems and also to anisotropic three-phase systems, e.g., synchronous motors with different direct and quadrature impedances driven by VSCs. Implementing a three-phase test system, the performance of the presented method is experimentally evaluated.

/pdf/multivariable-pi-based-dq-current-control-of-voltage-source-2my7he8rbt.pdf

Multivariable-PI-Based $dq$ Current Control of Voltage Source Converters With Superior Axis Decoupling Capability

A self-tuning proportional-integral (PI) controller in which the controller gains are adapted using the particle swarm optimization (PSO) technique is proposed for a static synchronous compensator (STATCOM). An efficient formula for the estimation of system load impedance using real-time measurements is derived. Based on the estimated system load, a PSO algorithm, which takes the best particle gains, the best global gains, and previous change of gains into account, is employed to reach the desired controller gains. To demonstrate the effectiveness of the proposed PSO self-tuning PI controller for a STATCOM, experimental results for a system under different loading conditions are presented. Results from the self-tuning PI controller are compared with those from the fixed-gain PI controllers.

Design of a Self-Tuning PI Controller for a STATCOM Using Particle Swarm Optimization

This paper presents a linear current control scheme for single-phase active power filters. The approach is based on an outer voltage loop, an inner current loop, and a resonant selective harmonic compensator. The design of the control parameters is carried out using conventional linear techniques (analysis of loop gain and other disturbance-rejection transfer functions). The performance of the proposed controller is evaluated and compared with two reference controllers: a basic control and an advanced repetitive control. In comparison with these controllers, the proposed control scheme provides additional attenuation to the harmonics coming from the load current, the grid voltage, and the reference signal, resulting in a grid current with lower harmonic distortion. Experimental results are reported in order to validate this paper.

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Selective Harmonic-Compensation Control for Single-Phase Active Power Filter With High Harmonic Rejection

In medium-/high-power inverters, optimal pulse-width modulation (OPWM) is often used to reduce the switching frequency and at the same time, realize selective harmonic elimination (SHE). For both two-level and multilevel inverters, most selective harmonic elimination (SHE) studies are based on solving multiple variable high-order nonlinear equations. Furthermore, for multilevel inverters, SHE has been often studied based on the assumption of balanced dc levels and single switching per level. In this paper, the authors further developed harmonics injection and equal area criteria-based four-equation method to realize OPWM for two-level inverters and multilevel inverters with unbalanced dc sources. For the cases, where only small number of voltage levels are available, weight oriented junction point distribution is utilized to enhance the performance of the four-equation method. A case study of multilevel inverter at low-modulation index is used as an example. Compared with existing methods, the proposed method does not involve complex equation groups and is much easier to be utilized in the case of large number of switching angles, or multiple switching angles per voltage level in multilevel inverters.

A Universal Selective Harmonic Elimination Method for High-Power Inverters

The problem of reactive power and harmonics in the medium voltage level of a power distribution system is considered in this paper. Reconfiguration of the power delivery network imposes new constraints in a distribution substation so that the reactive compensation should be increased. The alternative of a shunt hybrid active filter connected to the 13.8-kV level to enhance the power quality is analyzed in this paper. This proposal uses the existing capacitor bank to build a hybrid filter in which the complementary compensation is performed by the active filter. The performance of the hybrid filter is evaluated with extensive simulations considering reactive power, harmonics, and unbalance compensation. It shows very good behavior in steady-state and transient conditions.

/pdf/hybrid-active-filter-for-reactive-and-harmonics-compensation-3yu605mjft.pdf

Hybrid Active Filter for Reactive and Harmonics Compensation in a Distribution Network

This paper deals with the problem of reactive power and harmonics in a standard medium-voltage (MV) distribution network. It proposes a simple and inexpensive solution to enhance power quality when a particular connection to the high-voltage transmission network is required. It presents the design of a hybrid active filter topology connected to the MV level of a power distribution system. Its main task is to regulate a 132-kV voltage level. Reconfiguration of the power delivery network imposes new constraints in a distribution substation so that the reactive compensation should be increased. The topology of a shunt hybrid active filter is analyzed. It is built with the series connection of a passive filter and a low-rated active filter. The proposed filter is directly connected to a 13.8-kV level with no need of a step-down transformer. The possibility of different levels of reactive power compensation is implemented. The proposal shows very good performance for different load demands.

/pdf/hybrid-power-filter-to-enhance-power-quality-in-a-medium-5ckqckilff.pdf

Hybrid Power Filter to Enhance Power Quality in a Medium-Voltage Distribution Network

This paper presents the design of different topologies of active power filters to compensate reactive power and harmonics in the medium voltage level of a distribution power system. One pure active filter and two hybrid topologies, are implemented. A pure active compensation is obtained with a Shunt active power filter (SAPF). The shunt combination of SAPF and passive filter, form one of the hybrid topologies implemented, named shunt hybrid active power filter (SHAPF). The other hybrid topology, called hybrid shunt active power filter (HSAPF), connects the active filter in series with two shunt passive filters. Simulation for different load demands and distortions are performed. Finally a comparative evaluation of the different filters is carried out.

/pdf/comparison-of-active-filters-topologies-in-medium-voltage-dnp0xcyu98.pdf

Comparison of active filters topologies in medium voltage distribution power systems

Futaleufu hydropower plant has 4 Francis turbines rated 118 MW and it is connected to the power system by 2times330 kV lines. Studies carried out in the past did not predict the instable operation of Futaleufu after a 330 kV line fault, when some Futaleufu turbines are automatically disconnected as a consequence of the faulted line tripping. Load rejection caused by disconnected turbines generate large transients in the remaining turbines due to hydraulic coupling through the common conduits. Then, to improve related models and, therefore, to improve studies results of such a line fault it was necessary to make several tests in Futaleufu power plant. Finally, these models were used to conduct studies to design a new automatism, like the gate partial closing of the remaining turbines, to obtain a dynamically stable operation of Futaleufu after the disconnection by fault of a line of 330 kilovolts.

/pdf/hydraulic-transients-in-hydropower-plant-impact-on-power-3heqejb26v.pdf

Hydraulic transients in hydropower plant impact on power system dynamic stability

This paper presents the application of a hybrid active power filter for reactive and harmonic compensation at the level of Medium Voltage (MV) of an electrical network of an industrial plant. It is considered as control algorithm, the application of the d-q theory and performing the current measuring in the system, establishing a feedback control loop (feedback). It is analyzed a hybrid topology called Shunt Hybrid Active Power Filter SHAPF. This proposal uses an existing capacitor bank, transformed into a passive filter, and connected in series with the Active Filter to build a hybrid filter in which the compensation supplement is made by the active filter. We analyze different scenarios of operation. The topology has very good performance under steady state and transient.

/pdf/compensation-with-hybrid-active-power-filter-in-an-4a8svffi7f.pdf

Patricia Liliana Arnera

Papers

Hybrid Active Filter for Reactive and Harmonics Compensation in a Distribution Network

Hybrid Power Filter to Enhance Power Quality in a Medium-Voltage Distribution Network

Comparison of active filters topologies in medium voltage distribution power systems

Hydraulic transients in hydropower plant impact on power system dynamic stability

Compensation with Hybrid Active Power Filter in an Industrial Plant