Conventional Current Regulators Research Articles

Current Control of Single-Phase VSC Systems With Inductor Saturation Using Inverse Dynamic Model-Based Compensation

In voltage-source converter (VSC) systems, utilization of filter inductors with deep saturation characteristics is often advantageous due to the improved size, cost, and efficiency. However, with the use of conventional current regulation (CCR) methods, the inductor saturation results in significant dynamic performance loss and poor steady-state current waveform quality. This paper proposes the inverse dynamic model (IDM)-based compensation method to overcome these performance issues. The method converts the nonlinear inductor of the plant to a fictitious linear inductor such that linear current regulators can perform satisfactorily. In conjunction, identification of L–R parameters is performed to obtain IDM of the system within an acceptable range of sensitivity yielding satisfactory performance. The performance issues of CCR methods with saturable inductor are demonstrated by simulations and experiments. Then, the proposed method is experimentally verified on a single-phase 1.5-kW grid-connected VSC. The performance improvement over the CCR methods is verified by a detailed comparison of experimental waveforms.

Inductor Saturation Compensation With Resistive Decoupling for Single-Phase Controlled VSC Systems

In voltage-source converter systems, utilization of filter inductors with deep saturation characteristics is often advantageous because of the improved size, cost, and efficiency. However, with the use of conventional current regulation methods, the inductor saturation results in significant dynamic performance loss and poor steady-state current waveform quality. This paper proposes the saturation compensation with resistive decoupling (SCRD) method to overcome these performance issues. The method converts the nonlinear inductor of the plant to a fictitious linear inductor such that linear current regulators can perform satisfactorily. The steady-state and dynamic performances of SCRD are investigated in detail in comparison with other methods and advantageous performance attributes of SCRD are demonstrated on a 1.5-kW grid-connected system via simulations and laboratory experiments. In addition, identification of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L–R</i> parameters is performed, parameter sensitivity issues are addressed, and satisfactory performance is demonstrated.

Current control based power management strategy for distributed power generation system

The integration of renewable energy sources (RES) based distributed generation (DG) systems into electric grid has many challenges such as synchronization, control, power management (PM) and power quality problems. This paper proposes a references current generator (RCG) based PM strategy to control three phase inverter and manage power flow among the DG energy sources, electric grid and load demand under balanced and unbalanced grid conditions. The amplitudes of active and reactive power oscillations are also eliminated and controlled through only one flexible control parameter (FCP) under grid faults and harmonic distortions. Compared with previous similar studies, one of the important contributions is capable to inject maximum active power and minimum reactive power into electric grid and load at inverter power capacity under grid faults Another contribution is to extract the positive and negative sequence (PNS) voltage and current components with the improved fast and robust dual adaptive filters based phase locked loop (DAF-PLL). Fractional order proportional integral (FOPI) is selected as an attractive solution for AC current regulation to exhibit fast transient response and to achieve zero steady-state errors as compared with conventional current regulation controllers in synchronous or stationary frames.

Specially Designed Driver Circuits to Stabilize LED Light Output Without a Photodetector

This study proposes a novel light-emitting diode (LED) driver circuit that stabilizes the lighting output without a photodiode. The LED driver circuit is composed of a self-alignment circuit to compensate for the photo-power deviation and a feedback control system instead of a conventional photodetector to maintain the electrical power of the LED. The LED characteristics, based on electrical and optical measurements that varied with temperature, were built to be a lookup reference of the generated LED photopower, which serves as a compensator. A commercial full color LED system, which comprises red, green, and blue (RGB) LED chips, was implemented according to the novel concept. The impact of a conventional current regulator, a proposed electrical-power stabilization circuit, and a self-aligned photo-power stabilization circuit was studied graphically, followed by experimental verification. The maximal and minimal rate of change of the radiant flux Φ driven by the proposed LED drivers are 3.467% in a red LED, and 2.848% in green LED, respectively, over the ambient temperature range of 0.5-85 °C. The experimental results verified the implementation of a lighting power stabilization control system without the use of a photodiode for RGB LEDs.

Feed-Forward Transient Current Control for Low-Voltage Ride-Through Enhancement of DFIG Wind Turbines

High penetration of wind power requires reliable wind energy generation. A successful low-voltage ride-through (LVRT) scheme is a key requirement to achieve reliable and uninterrupted electrical power generation for wind turbines equipped with doubly fed induction generators (DFIGs). This paper proposes a feed-forward transient current control (FFTCC) scheme for the rotor side converter (RSC) of a DFIG to enhance its LVRT capability. This new control scheme introduces additional feed-forward transient compensations to a conventional current regulator. When three phase faults occur, these compensation terms correctly align the RSC ac-side output voltage with the transient-induced voltage, resulting in minimum transient rotor current and minimum occurrence of crowbar interruptions. With little additional computational effort, the proposed control scheme helps relieve the transient current stress on the RSC and helps maintain an uninterrupted active and reactive power supply from the wind turbines to the power grid. Simulation results are shown to demonstrate the effectiveness of the proposed FFTCC scheme in suppressing transient rotor currents.

D. C. Power system for excitation of large current superconducting coils for fusion plasma experimental facility

The Large Helical Device (LHD), that is a fusion plasma experimental facility, has three sets of supercon-ducting helical coil blocks and three sets of superconducting poloidal coils. To excite these coils, dc power supplies with large output current are constructed. For these power supplies, high accuracy of current control is required to make the plasma experiment condition. Also low voltage output ripple is required for diagnostics and protection of superconducting coils. In the control of these coil currents, the coil current is affected by the changing of the other coil currents if a conventional current regulation method is adapted because these coils have strong mutual coupling to each other. To resolve this problem, the LHD power system uses a state variable based regulator for the current control. This paper introduces this dc power system for LHD.

The use of voltage feedback in HVDC converter control

The use of combined voltage and current feedback for converter control was investigated. A simplified linear model for a monopolar dc link was developed for analysis of large and small disturbances. Using parameters from the proposed EPRI - Consolidated Edison 100 MW dc link, an eigenvalue analysis was performed, in which a compensated current feedback control was compared with the system using voltage feedback. Results of the linearized analysis showed that the use of voltage feedback appears to offer greater damping of system oscillations and considerably faster large-signal response than the use of a conventional current regulator. A detailed hybrid computer simulation of the 100 MW dc link was also used in the investigation. The ac system, individual converter valves, converter controls, and the dc line are fully represented in the simulation. Computer studies were made for various operations and disturbances, in which the current control was compared with the system using voltage feedback. Generally the results of the simulation agree with the basic conclusions reached from the linear analysis, however, the use of the simplified linear model for selecting optimum control parameters was in several cases shown to be somewhat inaccurate.