Output LC Filter Research Articles

Repetitive neurocontroller with disturbance feedforward path active in the pass-to-pass direction for a VSI inverter with an output LC filter

Abstract An enhancement to the previously developed repetitive neurocontroller (RNC) is discussed and investigated in the paper. Originally, the time-base generator (TBG) has been used to produce the only input signal for the neural approximator. The resulting search space makes the dynamic optimization problem (DOP) of shaping the control signal solvable with the help of a function approximator such as the feed-forward neural network (FFNN). The plant under consideration, i.e. a constant-amplitude constant-frequency voltage-source inverter (CACF VSI) with an output LC filter, is assumed to be equipped with the disturbance load current sensor to enable implementation of the disturbance feed-forward (pDFF) path as a part of the non-repetitive subsystem acting in the along the pass p-direction. An investigation has been undertaken to explore potential benefits of using this signal also as an additional input for the RNC to augment the approximation space and potentially enhance the convergence rate of the real-time search process. It is numerically demonstrated in the paper that the disturbance feed-forward path active in the pass-to-pass k-direction (kDFF) improves the dynamics of the repetitive part as well indeed.

Control of Power and Voltage of Solar Grid Connected

Renewable energy is high on international agendas. Currently, grid-connected photovoltaic systems are a popular technology to convert solar energy into electricity. Control of power injected into the grid, maximum power point, high efficiency, and low total harmonic distortion of the currents injected into the grid are the requirements for inverter connection into the grid. Consequently, the performance of the inverters connected to the grid depends largely on the control strategy applied. In this paper the simulation and design of grid connected three phase photovoltaic system using Matlab/Simulink has examined. The proposed system consists photovoltaic panels, boost and inverter the PV system convert the sun irradiation into direct current, thereafter we have used a boost to track the maximum power point of the PV system, three-phase inverter and LC output filter. A VOC control strategy based on the phase shifting of the inverter output voltage with respect to the grid voltage. The proposed control strategy requires few hardware and computational resources. As a result, the inverter implementation is simple, and it becomes an attractive solution for low power grid connected applications.

Fundamental Study of Influence of Ripple Noise From DC–DC Converter on Spurious Noise of Wireless Portable Equipment

Power supply noise is a serious concern in noise-sensitive radio frequency or analog circuits. This paper presents an analysis of the influence of the synchronous rectification buck-type dc–dc converters for power amplifiers. An output ripple noise equation of the converter and a spurious noise equation of the carrier output voltage of the class-A amplifier powered by the converter are derived to analyze fundamental characteristics of these noise components theoretically. The amplifier's output spurious noise is calculated by these equations and measured by the evaluation circuit board. The spurious noise variation caused by the parameter variations of the amplifier or the converter is discussed based on these experimental and theoretical results. The spurious noise can be suppressed by decreasing the channel length modulation coefficient of the n-channel MOSFET constituting the amplifier and the natural frequency of the converter output LC filter. The spurious noise is reduced to low level below − 60 dB compared to the carrier signal by setting the channel length modulation coefficient below 0.1 V−1 and the natural frequency below 120 kHz. Furthermore, when the natural frequency is below 40 kHz, the spurious noise is − 80 dB below the carrier signal.

Control of power and voltage of solar grid connected

Renewable energy is high on international agendas. Currently, grid-connected photovoltaic systems are a popular technology to convert solar energy into electricity. Control of power injected into the grid, maximum power point, high efficiency, and low total harmonic distortion of the currents injected into the grid are the requirements for inverter connection into the grid. Consequently, the performance of the inverters connected to the grid depends largely on the control strategy applied. In this paper the simulation and design of grid connected three phase photovoltaic system using Matlab/Simulink has examined. The proposed system consists photovoltaic panels, boost and inverter the PV system convert the sun irradiation into direct current, thereafter we have used a boost to track the maximum power point of the PV system, three-phase inverter and LC output filter. A VOC control strategy based on the phase shifting of the inverter output voltage with respect to the grid voltage. The proposed control strategy requires few hardware and computational resources. As a result, the inverter implementation is simple, and it becomes an attractive solution for low power grid connected applications.

Control of Power and Voltage of Solar Grid Connected

Renewable energy is high on international agendas. Currently, grid-connected photovoltaic systems are a popular technology to convert solar energy into electricity. Control of power injected into the grid, maximum power point, high efficiency, and low total harmonic distortion of the currents injected into the grid are the requirements for inverter connection into the grid. Consequently, the performance of the inverters connected to the grid depends largely on the control strategy applied. In this paper the simulation and design of grid connected three phase photovoltaic system using Matlab/Simulink has examined. The proposed system consists photovoltaic panels, boost and inverter the PV system convert the sun irradiation into direct current, thereafter we have used a boost to track the maximum power point of the PV system, three-phase inverter and LC output filter. A VOC control strategy based on the phase shifting of the inverter output voltage with respect to the grid voltage. The proposed control strategy requires few hardware and computational resources. As a result, the inverter implementation is simple, and it becomes an attractive solution for low power grid connected applications.

Effect of state feedback coupling and system delays on the transient performance of stand-alone VSI with LC output filter

The influence of state feedback coupling in the dynamics performance of power converters for stand-alone microgrids is investigated. Computation and pulsewidth-modulated (PWM) delays are the main factors that limit the achievable bandwidth of current regulators in digital implementations. In particular, the performance of state feedback decoupling is degraded because of these delays. Two decoupling techniques to improve the transient response of the system are investigated, named nonideal and ideal capacitor voltage decoupling, respectively. In particular, the latter solution consists in leading the capacitor voltage on the state feedback decoupling path in order to compensate for system delays. Practical implementation issues are discussed with reference to both the decoupling techniques. A design methodology for the voltage loop that considers the closed-loop transfer functions developed for the inner loop is also provided. A proportional resonant voltage controller is designed according to Nyquist criterion taking into account application requirements. For this purpose, a mathematical expression based on root locus analysis is proposed to find the minimum value of the fundamental resonant gain. Experimental tests performed in accordance to UPS standards verify the theoretical analysis.

Robust Tracking Control of a Three-Phase DC-AC Inverter for UPS Application under Unbalanced Load Conditions

Abstract: This paper describes a robust control technique for three-phase uninterruptible power supply (UPS) with output LC filter under unbalanced load conditions. The proposed control scheme consists of a combination of two robust controllers for the positive- and negative-sequence in order to provide balanced sinusoidal output voltages by eliminating the negative-sequence which caused by unbalanced loads. The gains of controller are determined by a linear matrix inequality (LMI)-based optimization so that the convergence rate to the steady state is maximized in the presence of the uncertainties in the LC filter. The uncertainties of the system are expressed as the possible ranges of inductor and capacitor values. The effectiveness of the proposed control technique has been validated and illustrated by the simulation result under unbalanced load conditions.

Soft Switching PWM Cascaded Three-Level Combined DC–DC Converters With Reduced Filter Size and Wide ZVS Load Range

Two soft switching cascaded three-level (TL) combined dc–dc converters are proposed in this paper. The first converter is composed of a half-bridge cascaded TL dc–dc converter (CTLC) and a full-bridge (FB) CTLC, and the other one is composed of two FB CTLCs. The presented topologies have following common advantages: off-state voltage on all switches is only half of the input voltage; the structure of the primary circuit is simple and compact; all primary switches are directly clamped by the input capacitors and no added clamping devices are required; and the voltage across the output LC filter is a TL waveform, which results lower output filter volume and faster system dynamic response. In addition, the input filter can also be minimized. All power switches in the proposed converters can obtain zero-voltage switching in wide load range; furthermore, less conduction loss is added. The operation and technical analysis of the proposed converters are given. Experiments are carried out to validate the proposed converters, and efficiency curves are tested and given.

Plug-in direct particle swarm repetitive controller with a reduced dimensionality of a fitness landscape – a multi-swarm approach

Abstract The paper describes a modification to the recently developed plug-in direct particle swarm repetitive controller (PDPSRC) for the sine-wave constant-amplitude constant-frequency (CACF) voltage-source inverter (VSI). The original PDPSRC algorithm assumes that the particle swarm optimizer (PSO) takes into account a performance index defined over the whole reference signal period. Each particle stores all the samples of the control signal, e.g. α = 200 samples for a controller working at 10 kHz and the reference frequency equal to 50 Hz. Therefore, the fitness landscape (i.e. the performance index) is -dimensional ( D), which makes optimization challenging. That solution can be categorized as the single-swarm one. It has been previously shown that the swarm controller does not suffer from long-term stability issues encountered in the classic iterative learning controllers (ILC). However, the convergence of the swarm has to be kept at a relatively low rate to enable successful exploitation in the D search space, which in turn results in slow responsiveness of the PDPSRC. Here a multi-swarm approach is proposed in which we divide a dynamic optimization problem (DOP) among less dimensional swarms. The reference signal period is segmented into shorter intervals and the control signal is optimized in each interval independently by separate swarms. The effectiveness of the proposed approach is illustrated with the help of numerical experiments on the CACF VSI with an output LC filter operating under nonlinear loads.

Comparative Study of Wind Turbine Power Converters Based on Medium-Frequency AC-Link for Offshore DC-Grids

This paper considers an offshore wind turbine modular power converter (ac/dc) with permanent magnet synchronous generator based on three stages: an ac–ac converter, a medium-frequency transformer, and a full-bridge diode rectifier with LC output filter. Six converter topologies are compared; three of them are based on back-to-back (B2B) topology: the conventional B2B with three-phase sinusoidal waveform, the B2B with three-phase squared waveform, and the B2B with single-phase squared waveform. The other solutions are based on matrix topologies: the direct matrix converter, the indirect matrix converter, and the reduced matrix converter (RMC). A systematic methodology and main component models are introduced to evaluate the power loss, volume, and mass of the wind energy conversion system for all considered topologies as a function of the medium-frequency transformer operational frequency and the number of modules parallel connected. The comparison involves a tradeoff study between total power losses, size and weight of 10 MW modular converters. It was found that when Metglas alloy 2605SA1 is the transformer core material, the RMC topology leaves the best tradeoff between the considered performance indicators with an extra benefit in reducing the semiconductor devices cost of the modular converter.

High performance operation for a four-leg NPC inverter with two-sample-ahead predictive control strategy

In this paper is proposed a finite control-set model predictive control (FCS-MPC) strategy which uses a two-sample-ahead prediction horizon to achieve high-performance operation for a three-phase four-leg neutral-point-clamped (NPC) inverter with an output LC filter. The control strategy is proposed in order to minimize the error between the output voltages and their references, maintain equal voltage among the dc-link capacitors, and reduce the overall switching frequency of the inverter. One-sample-ahead and two-sample-ahead prediction horizon are evaluated and compared in terms of reference tracking error and THD, under steady-state and transient operating conditions with linear and non-linear loads. The experimental results demonstrate that the proposed two-sample-ahead prediction horizon is more suitable for high power applications where lower switching frequency operation is mandatory.

Improved model predictive control for three-phase inverter with output LC filter

The control of inverters with output LC filter has a special importance in applications where a high quality voltage is needed. However, the controller design becomes more difficult. A model predictive control (MPC) is used for voltage control of a three-phase inverter with output LC filter. The controller uses a model of the system to predict the behaviour of the variables for a given voltage vector sequence until a certain horizon of time, then a cost function is used as a criterion for selecting the switching state that will be applied during the next sampling interval. This paper presents the effect of considering different numbers of prediction steps in terms of THD and the number of cycles or the settling time to reach steady state operation. The simulation results for MPC with only one prediction step and the improved MPC with two prediction steps are presented and compared, under linear and nonlinear loads, using MATLAB/Simulink tools. The simulation results show that the improved MPC improves the THD for nonlinear loads and makes it constant for different resistive loads. Moreover, the settling time can be considered constant for various linear and nonlinear loads.

Particle Swarm Optimization of the Multioscillatory LQR for a Three-Phase Four-Wire Voltage-Source Inverter With an <inline-formula> <tex-math notation="TeX">$LC$</tex-math></inline-formula> Output Filter

This paper presents evolutionary optimization of the linear quadratic regulator (LQR) for a voltage-source inverter with an LC output filter. The procedure involves particle-swarm-based search for the best weighting factors in the quadratic cost function. It is common practice that the weights in the cost function are set using the guess-and-check method. However, it becomes quite challenging, and usually very time-consuming, if there are many auxiliary states added to the system. In order to immunize the system against unbalanced and nonlinear loads, oscillatory terms are incorporated into the control scheme, and this significantly increases the number of weights to be guessed. All controller gains are determined altogether in one LQR procedure call, and the originality reported here refers to evolutionary tuning of the weighting matrix. There is only one penalty factor to be set by the designer during the controller synthesis procedure. This coefficient enables shaping the dynamics of the closed-loop system by penalizing the dynamics of control signals instead of selecting individual weighting factors for augmented state vector components. Simulational tuning and experimental verification (the physical converter at the level of 21 kVA) are included.

A Performance Study on Synchronous and Asynchronous Update Rules for A Plug-In Direct Particle Swarm Repetitive Controller

Abstract In this paper two different update schemes for the recently developed plug-in direct particle swarm repetitive controller (PDPSRC) are investigated and compared. The proposed approach employs the particle swarm optimizer (PSO) to solve in on-line mode a dynamic optimization problem (DOP) related to the control task in the constant-amplitude constant-frequency voltage-source inverter (CACF VSI) with an LC output filter. The effectiveness of synchronous and asynchronous update rules, both commonly used in static optimization problems (SOPs), is assessed and compared in the case of PDPSRC. The performance of the controller, when synthesized using each of the update schemes, is studied numerically.

Five-Level T-Type Inverter Based on Multistate Switching Cell

In this paper, a new T-type inverter topology based on multistate switching cell is proposed. The topology presents five-level voltage before the output LC filter, providing high-order harmonics that are easily filtered. In this topology, the output filter ripple frequency is twice the switching frequency, therefore reducing the magnetic weight and volume. Other characteristics of the inverter are current sharing through the devices, facilitating its losses' dissipation, due to increased contact area and few involved components in the current flow path. In order to verify its feasibility, a design example, as well as experimental results, for a 5-kW prototype is presented in this paper.

Intelligent voltage control strategy for three-phase UPS inverters with output LC filter

This paper presents a supervisory fuzzy neural network control (SFNNC) method for a three-phase inverter of uninterruptible power supplies (UPSs). The proposed voltage controller is comprised of a fuzzy neural network control (FNNC) term and a supervisory control term. The FNNC term is deliberately employed to estimate the uncertain terms, and the supervisory control term is designed based on the sliding mode technique to stabilise the system dynamic errors. To improve the learning capability, the FNNC term incorporates an online parameter training methodology, using the gradient descent method and Lyapunov stability theory. Besides, a linear load current observer that estimates the load currents is used to exclude the load current sensors. The proposed SFNN controller and the observer are robust to the filter inductance variations, and their stability analyses are described in detail. The experimental results obtained on a prototype UPS test bed with a TMS320F28335 DSP are presented to validate the feasibility of the proposed scheme. Verification results demonstrate that the proposed control strategy can achieve smaller steady-state error and lower total harmonic distortion when subjected to nonlinear or unbalanced loads compared to the conventional sliding mode control method.

Model Predictive Approach for a Simple and Effective Load Voltage Control of Four-Leg Inverter With an Output <inline-formula> <tex-math notation="TeX">$LC$</tex-math></inline-formula> Filter

This paper presents a finite control set model predictive strategy and its application to the load voltage control of two-level four-leg inverters. The proposed approach uses the novel discrete-time model of the inverter and output LC filter in order to predict the variables to be controlled. These predictions are carried out for the 16 switching states of the inverter and are evaluated using a cost function. The switching state that forces the load voltages to be closest to their respective references is chosen and applied to the inverter. The behavior of the predictive controller has been investigated, and the changes to both inductive and capacitive filter parameters have been considered. In order to improve the reliability of the fourth leg as well as the overall inverter efficiency, a solution is proposed, which combines hardware and software reconfigurations. The feasibility of the proposed method is verified through simulation and experimental results considering single-/three-phase, balanced/unbalanced, and linear/nonlinear loads.

Galvanic Isolation and Output LC Filter Design for the Low-Voltage DC Customer-End Inverter

In this paper the need for a better design of the galvanic isolation and the output filter inductor in the customer-end inverter (CEI) of the low voltage DC (LVDC) network is discussed. The galvanic isolation can be implemented either with a 50 Hz transformer after the CEI or with an isolated DC-DC converter between the DC network and the CEI. However, the 50 Hz transformer solution adds a significant amount of volume and mass to the system. Based on calorimetric measurements conducted with the current system in which the galvanic isolation is implemented with the former method, the minimum requirements for the isolated DC-DC converter are presented and a comparison is carried out. For the system to be cost efficient the DC-DC converter should result in reduced lifetime cost compared with the transformer solution. In the output filter part a design method for an amorphous core filter inductor based on minimization of the lifetime cost is presented.

Robust Tracking Control of a Three-Phase DC–AC Inverter for UPS Applications

This paper describes a combination of robust control techniques applied to an offset-free robust tracking control of a three-phase dc-ac inverter with an output LC filter for application to uninterruptible power supply (UPS). The control law, which employs state feedback and integration of the tracking error, is described in a synchronous dq frame and is implemented using a space vector modulation technique. The controller is designed by a linear matrix inequality (LMI)-based optimization so that the convergence rate to the steady state is maximized in the presence of the uncertainties in the LC filter. These uncertainties are expressed as possible ranges of the capacitor and inductor values. In the absence of uncertainties, the designed controller will become a deadbeat controller, whereas in the presence of uncertainties, it provides the shortest possible settling time. Thus, the proposed design method provides a systematic tool to combine the robustness to model uncertainties with the deadbeat control. The use of a one-step-ahead predictor is considered to compensate for the computation delay, and an LMI-based method to obtain an optimal gain of the state estimator is also proposed. The efficacy of the proposed approach was experimentally confirmed on a three-phase 10-kVA prototype UPS system.

Nonlinear Robust Control of 3 Phase Inverter with Output LC Filter

Three phase inverters are commonly used to transfer energy from a source to the power grid. The quality of the power delivered to the grid, can be ensured via the use of an output LC filter. However inserting an output filter to an inverter circuitry would introduce new challenges to the controller design due to the additional parametric uncertainties imposed. In this study we present a new model based robust controller for a three phase inverter with output LC filter under the constraint that the output filter parameters are not exactly known. Specifically, d-q reference frame model of an inverter with output LC filter is used to develop a nonlinear robust controller that ensures the 3-phase output voltage with desired amplitude and frequency and with lowest harmonic distortion. Stability of the proposed method and the boundedness of the closed–loop system, is established via Lyapunov based tools in conjunction with a robust backstepping procedure. Simulation results are given in order to demonstrate performance and effectiveness of the proposed robust controller.