5,668 research outputs found
Fast Adaptive Robust Differentiator Based Robust-Adaptive Control of Grid-Tied Inverters with a New L Filter Design Method
In this research, a new nonlinear and adaptive state feedback controller with a fast-adaptive robust differentiator is presented for grid-tied inverters. All parameters and external disturbances are taken as uncertain in the design of the proposed controller without the disadvantages of singularity and over-parameterization. A robust differentiator based on the second order sliding mode is also developed with a fast-adaptive structure to be able to consider the time derivative of the virtual control input. Unlike the conventional backstepping, the proposed differentiator overcomes the problem of explosion of complexity. In the closed-loop control system, the three phase source currents and direct current (DC) bus voltage are assumed to be available for feedback. Using the Lyapunov stability theory, it is proven that the overall control system has the global asymptotic stability. In addition, a new simple L filter design method based on the total harmonic distortion approach is also proposed. Simulations and experimental results show that the proposed controller assurances drive the tracking errors to zero with better performance, and it is robust against all uncertainties. Moreover, the proposed L filter design method matches the total harmonic distortion (THD) aim in the design with the experimental result
Distributed control of a fault tolerant modular multilevel inverter for direct-drive wind turbine grid interfacing
Modular generator and converter topologies are being pursued for large offshore wind turbines to achieve fault tolerance and high reliability. A centralized controller presents a single critical point of failure which has prevented a truly modular and fault tolerant system from being obtained. This study analyses the inverter circuit control requirements during normal operation and grid fault ride-through, and proposes a distributed controller design to allow inverter modules to operate independently of each other. All the modules independently estimate the grid voltage magnitude and position, and the modules are synchronised together over a CAN bus. The CAN bus is also used to interleave the PWM switching of the modules and synchronise the ADC sampling. The controller structure and algorithms are tested by laboratory experiments with respect to normal operation, initial synchronization to the grid, module fault tolerance and grid fault ride-through
PI-based controller for low-power distributed inverters to maximise reactive current injection while avoiding over voltage during voltage sags
This paper is a postprint of a paper submitted to and accepted for publication in
IET Power Electronics and is subject to Institution of Engineering and Technology Copyright. The copy of record is
available at the IET Digital Library.In the recently deregulated power system scenario, the growing number of distributed generation sources should be considered as an opportunity to improve stability and power quality along the grid. To make progress in this direction, this work proposes a reactive current injection control scheme for distributed inverters under voltage sags. During the sag, the inverter injects, at least, the minimum amount of reactive current required by the grid code. The flexible reactive power injection ensures that one phase current is maintained at its maximum rated value, providing maximum support to the most faulted phase voltage. In addition, active power curtailment occurs only to satisfy the grid code reactive current requirements. As well as, a voltage control loop is implemented to avoid overvoltage in non-faulty phases, which otherwise would probably occur due to the injection of reactive current into an inductive grid. The controller is proposed for low-power rating distributed inverters where conventional voltage support provided by large power plants is not available. The implementation of the controller provides a low computational burden because conventional PI-based control loops may apply. Selected experimental results are reported in order to validate the effectiveness of the proposed control scheme.Peer ReviewedPostprint (updated version
Suppression of line voltage related distortion in current controlled grid connected inverters
The influence of selected control strategies on the level
of low-order current harmonic distortion generated by an inverter
connected to a distorted grid is investigated through a combination
of theoretical and experimental studies. A detailed theoretical
analysis, based on the concept of harmonic impedance, establishes
the suitability of inductor current feedback versus output
current feedback with respect to inverter power quality. Experimental
results, obtained from a purpose-built 500-W, three-level,
half-bridge inverter with an L-C-L output filter, verify the efficacy of inductor current as the feedback variable, yielding an
output current total harmonic distortion (THD) some 29% lower
than that achieved using output current feedback. A feed-forward
grid voltage disturbance rejection scheme is proposed as a means to
further reduce the level of low-order current harmonic distortion.
Results obtained from an inverter with inductor current feedback
and optimized feed-forward disturbance rejection show a THD of
just 3% at full-load, representing an improvement of some 53% on
the same inverter with output current feedback and no feed-forward
compensation. Significant improvements in THD were also
achieved across the entire load range. It is concluded that the use
of inductor current feedback and feed-forward voltage disturbance
rejection represent costâeffect mechanisms for achieving improved
output current quality
Sensorless multi-loop control of phase-controlled series-parallel resonant converter
This paper proposes a multi-loop controller for the phase-controlled series-parallel resonant converter. Output voltage is solely measured for control and inner loop is used to enhance closed loop stability and dynamic performance compared to single-loop control. No additional sensors are used for inner loop variables. These are estimated using a Kalman filter, based on a linearized converter model. The advantage of this sensorless scheme is not only reducing the number of sensors but more significantly providing an alternative to sensing high frequency resonant tank variables which require high microcontroller resolution in real time. First, the converter non-linear large signal behavior is linearized using a state feedback based scheme. Consequently, the converter preserves its large signal characteristics while modeled as a linear system. Comparison is made between the most suitable state variables for feedback, according to a stability study. Finally, simulation and experimental results are demonstrated to validate the improved system performance in contrast with single-loop control
DSOGI-PLL based power control method to mitigate control errors under disturbances of grid connected hybrid renewable power systems
The control of power converter devices is
one of the main research lines in interfaced renewable
energy sources, such as solar cells and wind turbines.
Therefore, suitable control algorithms should be
designed in order to regulate power or current properly
and attain a good power quality for some disturbances,
such as voltage sag/swell, voltage unbalances and fluctuations,
long interruptions, and harmonics. Various
synchronisation techniques based control strategies
are implemented for the hybrid power system applications
under unbalanced conditions in literature studies.
In this paper, synchronisation algorithms based
Proportional-Resonant (PR) power/current controller
is applied to the hybrid power system (solar cell + wind
turbine + grid), and Dual Second Order Generalized
Integrator-Phase Locked Loop (DSOGI-PLL) based PR
controller in stationary reference frame provides a solution
to overcome these problems. The influence of
various cases, such as unbalance, and harmonic conditions,
is examined, analysed and compared to the PR
controllers based on DSOGI-PLL and SRF-PLL. The
results verify the effectiveness and correctness of the
proposed DSOGI-PLL based power control method
A multifunctional dynamic voltage restorer for power quality improvement
Power quality is a major concern in electrical power systems. The power quality disturbances such as sags, swells, harmonic distortion and other interruptions have an impact on the electrical devices and machines and in severe cases can cause serious damages. Therefore it is necessary to recognize and compensate all types of disturbances at an earliest time to ensure normal and efficient operation of the power system. To solve these problems, many types of power devices are used. At the present time, one of those devices, Dynamic Voltage Restorer (DVR) is the most efficient and effective device used in power distribution systems. In this paper, design and modeling of a new structure and a new control method of multifunctional DVRs for voltage quality correction are presented. The new control method was built in the stationary frame by combining Proportional Resonant controllers and Sequence-Decouple Resonant controllers. The performance of the device and this method under different conditions such as voltage swell, voltage sag due to symmetrical and unsymmetrical short circuit, starting of motors, and voltage distortion are described. Simulation result show the superior capability of the proposed DVR to improve power quality under different operating conditions and the effectiveness of the proposed method. The proposed new DVR controller is able to detect the voltage disturbances and control the converter to inject appropriate voltages independently for each phase and compensate to load voltage through three single-phase transformers.Web of Science116art. no. 135
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