Proportional Feedforward Control Research Articles

Control of Active Power Decoupling Circuit Based on Parametric Oscillator

In this paper, we tested the buck-plus-unfolder bidirectional converter as the active power decoupling circuit to suppress the unknown low frequency ripples on the dc bus. Due to its bipolar operation, the buffering capacitor voltage needs to be half of the frequency of the disturbance. We exploit the parametric resonance phenomenon to build a virtual oscillator controller for the converter. Unlike direct resonance, the parametric one occurs when the parameter of the reactive element of the oscillator varies around twice of the resonance frequency. The dc bus voltage ripple is chosen as the modulation signal for the oscillator. A frequency adaptive mechanism is embedded in the controller to update the resonance frequency. With the references constructed from the states of the oscillator, a proportional-feedforward controller is designed to track the reference for the buffering capacitor voltage. The proposed control algorithm has been verified by both simulation and experiments.

An improving control strategy for grid -connected current in weak grid

The traditional proportional feedforward control strategy can suppress the low order harmonics in the strong power grid, but in the weak power grid environment, the grid impedance will have an adverse impact on the stability of the system, resulting in the proportional feedforward control can not suppress the low order harmonics well. In order to solve this problem, a control strategy combining resonant feedforward and new repetitive proportional controller is proposed. Firstly, the stability of traditional proportional feedforward and resonant feedforward systems is analyzed and compared by impedance analysis method. Then, a new repetitive controller is added to suppress low order harmonics based on resonant feedforward control, and the stability of single-phase LCL grid connected inverter system is analyzed Matlab / Simulink is used to simulate and verify the system. The results show that the system stability and the ability to suppress low order harmonics are significantly improved.

Adaptive Virtual Impedance of Grid-Tied Inverters to Enhance the Stability in a Weak Grid

In a weak grid, especially with a grid-voltage proportional feedforward controller, the grid-tied inverter tends to interact with the grid impedance and thus suffers from poor power quality and even instability. In order to improve the stability, serial-parallel virtual impedance based on the derivative controllers of grid current and voltage is proposed in this paper. With the aim of optimizing the performance of the inverter for a variety of grid impedance, these derivative coefficients are adaptively tuned by the constraint of a minimum leading phase which is determined by the phase margin and the current tracking response. With this proposed adaptive virtual impedance, the grid-tied inverter can operate stably under a wide variety of grid impedance and voltage harmonic rejection performance is also improved. Simulation and experimental results validate the effectiveness of the proposed method and design methodology.

Optimization Algorithm for Selective Compensation in a Shunt Active Power Filter

This paper proposes an optimization algorithm based on linear matrix inequalities (LMIs) to be implemented in a shunt active power filter (SAPF) enabling it to perform a selective compensation of nonefficient powers when the rated power of the SAPF is limited. The system uses the IEEE Standard 1459 to identify the different power terms (active, reactive, unbalance, and harmonics) demanded by local loads in a three-phase four-wire system. Then, the algorithm solves a quadratically constrained quadratic program by means of an LMI formulation and calculates the optimal reference currents that allow the SAPF to cancel a selection of the previously identified nonefficient power terms. For this selection, the algorithm presents different weighting coefficients in the cost index to be optimized. These coefficients assign a relative importance to each different nonefficient power term, giving priority to some over the others. Moreover, the optimization performed in this work to calculate the reference currents considers that the SAPF presents a power limitation. Finally, the reference currents' tracking has been implemented using a proportional feedforward controller which assures a constant commutation frequency of the SAPF. Experimental results demonstrate the validity of the proposal.

PI control based on fuzzy set-point weighting tracking for hydraulic crane boom system

A PI control strategy based on fuzzy set-point weighting following was proposed for the active damping control of a hydraulic crane boom system (HCBS). Two valve-controlled PI controllers, which include a proportional feedforward controller based on fuzzy set-point weighting following and a limited semi-integrator(LSI), are designed respectively. LSI is used to limit output signal and to prevent wind up at the low frequency of the spectrum. By using a range camera and an electronic feedback control, the tip damping on the HCBS can be adjusted artificially. A collaborative control simulation technique of HOPSAN and MATLAB/SIMULINK is applied to the controller design. Simulation results show that the proposed PI control system has less overshoot as well as faster response. The tip damping on the HCBS during operation is improved.

State estimation-based control of a coal gasifier

On-line state estimation techniques provide a means of inferring real-time values for key process variables that cannot themselves be measured directly. Such state estimates can then form a basis for improved process control. Accordingly, Kalman filtering (KF) is applied to a non-linear coal gasifier system operated initially under a conventional feedback control strategy. Key unmeasured disturbances to gasifier operation arise in discharge pressure and coal feed ‘quality’. The fact that by treating both of these variables as unknown process parameters, they can be included in an augmented state and parameter vector and estimated reliably by KF is shown. A proportional feedforward control strategy, acting on these disturbance estimates and linked into the existing conventional feedback control system, is then shown to enhance system performance to both step and sinusoidal discharge pressure changes and to steps of up to 18% around normal coal feed quality. No significant performance difference relative to conventional feedback control is shown in ramping the downstream-generated power output. An important future outcome may be enhanced operation and control of upstream coal preparation plant based on the capability demonstrated here to obtain reliable real-time estimates of coal quality by KF.

Comment on Point:Counterpoint “Supraspinal locomotor centers do/do not contribute significantly to the hyperpnea of dynamic exercise in humans”

The following letters are in response to the Point:Counterpoint series “Supraspinal locomotor centers do/do not contribute significantly to the hyperpnea of dynamic exercise in humans” that appeared in the March issue (vol. 100: 1087–1083, 2006; <http://jap.physiol.org/content/vol100/issue3/