Line-commutated Rectifier Research Articles

Novel Average Value Model for Faulty Three-Phase Diode Rectifier Bridges

Rectifiers are widely used in industrial applications. Although detailed models of rectifiers are usually used to evaluate their performance, they are complex and time-consuming. Therefore, the Average Value Model (AVM) has been introduced to meet the demand for a simple and accurate model. This type of rectifier modeling can be used to simplify the simulations of large systems. The AVM of diode rectifiers has been an area of interest for many electrical engineers. However, healthy diode rectifiers are only considered for average value modeling By contrast, faults occur frequently on diodes, which eventually cause the diodes to open-circuit. Therefore, it is essential to model bridge rectifiers under this faulty condition. Indeed, conventional AVMs are not appropriate or accurate for faulty rectifiers. In addition, they are significantly different in modeling In this paper, a novel application of the parametric average value of a three-phase line-commutated rectifier is proposed in which one diode of the rectifier is considered open-circuited. In order to evaluate the proposed AVM, it is compared with experimental and simulation results for the application of a brushless synchronous generator field. The results clearly demonstrate the accuracy of the proposed model.

Coordinated Control for Large-Scale Wind Farms with LCC-HVDC Integration

Wind farms (WFs) controlled with conventional vector control (VC) algorithms cannot be directly integrated to the power grid through line commutated rectifier (LCR)-based high voltage direct current (HVDC) transmission due to the lack of voltage support at its sending-end bus. This paper proposes a novel coordinated control scheme for WFs with LCC-HVDC integration. The scheme comprises two key sub-control loops, referred to as the reactive power-based frequency (Q-f) control loop and the active power-based voltage (P-V) control loop, respectively. The Q-f control, applied to the voltage sources inverters in the WFs, maintains the system frequency and compensates the reactive power for the LCR of HVDC, whereas the P-V control, applied to the LCR, maintains the sending-end bus voltage and achieves the active power balance of the system. Phase-plane analysis and small-signal analysis are performed to evaluate the stability of the system and facilitate the controller parameter design. Simulations performed on PSCAD/EMTDC verify the proposed control scheme.

Real‐time gating signal generation and performance analysis for fully controlled five‐phase, ten‐pulse, line‐commutated rectifier

Fossil fuel prices and air pollution impel many countries to concentrate on renewable energy sources, of which wind energy is considered to be a pillar. Owing to the numerous advantages when compared with its three-phase counterpart, five-phase direct-drive permanent magnet (PM) generators are a key area of focus in power generation with renewable and wind energy systems. The generator output requires a converter, such as an AC–DC rectifier, to match load requirements. The objective of this work is to generate in real time the gating signals of a fully controlled five-phase, line-commutated rectifier, fed from a five-phase PM generator. A mixed-reality environment is used to implement the gating signal generation algorithm for the five-phase rectifier, where the required gating signals are successfully generated, even with some distorted prototype generator voltage waveforms. The performance of the rectifier is investigated practically and validated by using the MATLAB/SIMULINK platform. Moreover, a comparison with a five-phase pulse-width modulated current source rectifier in terms of losses, size, weight, and cost is presented.

Model Predictive Control in the Multi-Megawatt Range

This paper presents an application of model predictive control to a variable-speed drive system operating in the multi-megawatt range. The variable-speed drive system comprises a synchronous machine fed by a line-commutated rectifier and a load-commutated inverter. The control task is to regulate the dc-link current, and hence the machine torque, to ensure the machine speed follows a given reference. The proposed control approach is model predictive control, where both the rectifier- and inverter-firing angles are considered as control inputs. The nonlinear model predictive torque controller has been implemented on an embedded system and applied in an industrial-scale pilot plant installation. The experiments show the successful operation of model predictive control on a plant with more than 48 MW power.

Model Predictive Control of Load Commutated Inverter-fed Synchronous Machines

This paper considers torque regulation of a variable-speed synchronous machine fed by a line-commutated rectifier and a load-commutated inverter. The proposed control approach is model-predictive control where both the rectifier and inverter firing angles are considered as control inputs. Conventional controllers assign different tasks to the rectifier and inverter firing angle. In contrast, the model-predictive controller coordinates the firing angles and this improves the dynamic performance and disturbance rejection. In particular, the proposed controller handles line side under voltage conditions better than a conventional PI controller. The nonlinear model-predictive torque controller has been implemented on an embedded system and applied in an experimental test bed. The experiments confirm that the controller is able to successfully ride through line side under voltage conditions.

Direct Interfacing of Dynamic Average Models of Line-Commutated Rectifier Circuits in Nodal Analysis EMTP-Type Solution

Dynamic average-value models (AVMs) for AC-DC rectifier circuits are generally formulated in state-space form and hence are straightforward to implement in state-variable-based simulation languages. In the nodal analysis-based approach used in electromagnetic transient (EMTP-type) simulation packages, the development of AVMs requires additional effort to reformulate and interface the models with the external ac and dc networks. This paper proposes a new averaged-circuit model for three-phase line-commutated rectifiers which is directly interfaced with the ac and dc networks, thereby achieving a simultaneous solution of the respective variables in EMTP-type solution. The proposed model is verified against conventionally interfaced model, as well as detailed switching model of the original rectifier circuit. A significant improvement of numerical accuracy and stability of the solution is demonstrated even at fairly large time steps.

Transformer-Less Series Reactive/Harmonic Compensation of Line-Commutated HVDC for Offshore Wind Power Integration

Experimental validation in addition to detailed modeling and simulation of a new transformer-less series compensator for line-commutated HVDC rectifier terminal is presented. The compensator employs very small capacitors compared to those in conventional shunt compensators or fixed series capacitors for reactive power compensation of such links. The proposed device demonstrates fundamental-frequency reactive power and harmonic-current compensation.

A Transformerless Series Reactive/Harmonic Compensator for Line-Commutated HVDC for Grid Integration of Offshore Wind Power

This paper introduces, explains, and investigates the application of a transformerless series-connected reactive/harmonic compensator. The proposed compensator is applied to compensate the high reactive-power/harmonic demand of a 12-pulse line-commutated HVDC rectifier terminal. Simulation results reveal that the proposed strategy compensates the reactive power and harmonics of the HVDC converter satisfactorily. All of this is achieved using significantly smaller capacitance at the compensator dc link than the capacitance required in the state-of-the-art shunt compensators employing passive components. The compensator thus would eliminate the need of fundamental-frequency reactive power supply and minimize (or eliminate altogether) the requirement of passive shunt harmonic compensation. This would result into smaller shunt passive filters, smaller or no shunt capacitor banks, and smaller converter transformers, leading to a more compact HVDC terminal, the current size of which is considered to be the main hurdle in its application for integration of large-scale offshore wind energy. Experimental results from a small-scale setup validate the effectiveness observed in the simulations.

Modeling, Analysis, and Control for the Rectifier of Hybrid HVdc Systems for DFIG-Based Wind Farms

In order to improve the dynamic performance of the hybrid HVdc system for doubly fed induction generator wind farms, this paper presents the modeling, analysis, and control methods for its line-commutated rectifier. First, the state variable model of the rectifier subsystem on the reference frame is derived considering different control modes of the current source inverter subsystem. Then, the ac current dynamic of the rectifier subsystem is quantitatively analyzed based on the eigenvalue analysis method. According to the analysis results, a double loop control scheme is designed: the inner loop utilizes the inverse system control technique plus a switchable phase-lead compensator, and the outer loop implements an ordinary propotional-integral controller. Finally, the validity of the quantitative analysis method and the superiority of the proposed control scheme are verified by Simulink/SimPowerSystems simulations.

Simple Modeling and Identification Procedures for “Black-Box” Behavioral Modeling of Power Converters Based on Transient Response Analysis

Today, black-box behavioral models of power converters are becoming interesting for system level simulation of power electronics systems. These models can be used to evaluate the response of systems that are composed of commercial converters, since they can be fully parameterized by analyzing the actual converter response. To optimize the required computational resources, these models should be as simple as possible. Furthermore, the identification of the parameters should be carried out easily, looking for simple experiments and straightforward adjusting algorithms. Easy modeling and identification procedures, based on a transient response analysis, are proposed in this paper. Using this method, a large-signal black-box behavioral model of a power converter is composed of reduced-order transfer functions, which are identified by analyzing the step response of the converter. Both an actual commercial dc-dc converter and a line-commutated rectifier have been modeled and identified by means of this approach, in order to validate the proposed procedures.

Design of a 400 MW power supply for a 60 T pulsed magnet

The National High Magnetic Field Laboratory at Los Alamos designs a magnet that produces magnetic fields of up to 60 T for as long as 100 ms. The power and energy to operate the magnet is provided by a 1430 MVA, 24 kV energy storage generator. Three modular design power supplies convert the AC-power produced by the generator into controlled DC-power needed by the three coil groups of the eight coil magnet. The modules are rated at 4 kV no-load voltage and 20 kA full-load current for up to 2 seconds once every hour, each including a 12-pulse, line-commutated rectifier designed to operate in the 66 Hz to 42 Hz pulse operation range of the generator. A short description of the overall 60 T/100 ms magnet system is given, followed by a detailed description of the the power converter system design.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Application of GTO voltage source inverter in a hybrid HVDC link

This paper investigates the application of a GTO voltage source inverter in a two-terminal HVDC link, which is fed at the sending end by a line-commutated rectifier. This type of HVDC link may be applied when power transfer is predominantly unidirectional, especially to a weak AC system. The investigations are based on analytical studies and digital time-domain simulations with the Electromagnetic Transient program for DC systems (EMTDC). Control method and protection requirements are studied, together with dynamic behavior of the system following disturbances, e.g. DC fault, AC fault, start-up etc. The studies are aimed at exhibiting the technical feasibility of the proposed HVDC scheme. Need for further studies is pointed out when necessary.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>