Multiple Resonant Controllers Research Articles

Current Harmonic Compensation for $n$ -Phase Machines With Asymmetrical Winding Arrangement and Different Neutral Configurations

Low-order current harmonics arise in ac drives due to nonlinearities, producing torque ripple and extra losses. In multiphase machines, which offer advantages over three-phase ones, the latter is aggravated because some harmonics map in low-impedance no-torque subspaces. A multiple-resonant-controller (MRC) structure, combining resonant controllers and synchronous frames, was proposed for harmonic cancellation. It permits substantial computational saving over the multiple-synchronous-frame (MSF) strategy, which includes proportional-integral control in one synchronous frame per harmonic. However, such MRC method is only suitable for symmetrical winding arrangements (SWAs), while asymmetrical winding arrangements (AWAs) are also widespread. Adapting the MRC for AWAs is not straightforward, since the harmonic mapping differs significantly from SWAs, and the effect of neutral configurations on it is more complicated and has hardly been studied. In this paper, an MRC strategy for multiphase machines with AWA is developed. Different neutral configurations are considered; particularly, it is shown and taken into account that for a single isolated neutral, unlike with SWAs, certain subspaces are coupled and unbalanced. The optimum frequencies of the resonant controllers and synchronous frames are assessed. The computational burden of the MRC and MSF schemes is compared, and the differences with SWAs are established. Experimental results are provided.

Discrete-time multiple resonant controller design for uninterruptible power supplies

This paper casts the design problem of multiple resonant controllers for uninterruptible power supplies in a robust discrete-time framework. Euler and Adams-Bashforth discretization methods are considered to describe the uncertain open-loop plant and periodic reference tracking/disturbance rejection is guaranteed by the introduction of a discrete-time resonant controller in the control loop. Controller parameters are determined by the solution of a convex optimization problem subject to linear matrix inequality constraints. Simulation results in 3.5kVA power inverter are considered to illustrate the method.

Frequency-Varying Current Harmonics for Active Magnetic Bearing via Multiple Resonant Controllers

The rotating machinery suspended by an active magnetic bearing (AMB) system always suffers from rotor mass imbalance and sensor runout disturbances, which lead to the periodic fluctuations in control currents. This paper presents a novel multiple resonant controllers (MRC) for an AMB system to suppress the multifrequency current harmonics in the presence of variable rating speed. The principle and structure of the plug-in MRC used for current harmonics suppression in the AMB system is discussed. The design of the proposed MRC, using the progressively tuning and segmentation switch strategy, is given. The proposed design method for the MRC can achieve the balance between good stability and harmonics suppression precision. As well, the robustness of the overall system is systematically analyzed for the entire operational speed range. Simulation and experimental results for current fluctuations and multifrequency vibration forces on a magnetically suspended flywheel validate the effectiveness of the proposed method.

Design approach of discrete‐time resonant controllers for uninterruptible power supply applications through frequency response analysis

A new methodology to design discrete-time multiple resonant controllers for single-phase uninterruptible power supply inverters is proposed in this study. This methodology is based on classical linear tools and consists on the synthesis of the inverter output impedance according to standard specifications. This synthesis is performed using a multi-loop control strategy composed of an inner current control loop using a proportional controller, and an outer voltage control loop using the multiple resonant controller. A prototype was built to demonstrate the practical feasibility of the theoretical proposal. A significant reduction of the output impedance at determined harmonic frequencies resulted in a low-voltage total harmonic distortion of the output voltage of about 1.76%, for IEC 62040-3 reference non-linear load.

Active Power Quality Improvement Strategy for Grid-Connected Microgrid Based on Hierarchical Control

When connected to a distorted grid utility, droop-controlled grid-connected microgrids (DCGC-MGs) exhibit low equivalent impedance. The harmonic and unbalanced voltage at the point of common coupling (PCC) deteriorates the power quality of the grid-connected current (GCC) of DCGC-MG. This paper proposes an active, unbalanced, and harmonic GCC suppression strategy based on hierarchical theory. The voltage error between the bus of the DCGC-MG and the grid’s PCC was transformed to the dq frame. On the basis of the grid, an additional compensator, which consists of multiple resonant voltage regulators, was then added to the original secondary control to generate the negative fundamental and unbalanced harmonic voltage reference. Proportional integral and multiple resonant controllers were adopted as voltage controller at the original primary level to improve the voltage tracking performance of the inverter. Consequently, the voltage difference between the PCC and the system bus decreased. In addition, we established a system model for parameter margin and stability analyses. Finally, the simulation and experiment results from a scaled-down laboratory prototype were presented to verify the validity of the proposed control strategy.

Internal-Model-Principle-Based Specific Harmonics Repetitive Controller for Grid-Connected PWM Inverters

This paper analyzes the general properties of IMP-based controller and presents an internal-model-principle-based (IMP-based) specific harmonics repetitive control (SHRC) scheme. The proposed SHRC is effective for specificnk±morder harmonics, withn>m≥0andk=0,1,2,…. Using the properties of exponential function, SHRC can also be rewritten into the format of multiple resonant controllers in parallel, where the control gain of SHRC isn/2multiple of that of conventional RC (CRC). Therefore, including SHRC in a stable closed-loop feedback control system, asymptotic disturbance eliminating, or reference tracking for any periodic signal only including these specific harmonic components atn/2times faster error convergence rate compared with CRC can be achieved. Application examples of SHRC controlled three-phase/single-phase grid-connected PWM inverters demonstrate the effectiveness and advantages of the proposed SHRC scheme.

Harmonic voltage resonant compensation control of a three-phase inverter for battery energy storage systems applied in isolated microgrid

The aim of this paper is to propose a sinusoidal voltage signals tracking control strategy, adaptive for frequency of a three-phase inverter for a battery energy storage system (BESS) applied to an isolated microgrid. To support the normal operation of distributed renewable energy and feed the critical loads under the isolated mode, the BESS generally works in voltage control mode (VCM). The proposed control strategy, which transforms the tracking control problem into a state feedback control problem, includes two terms, one of which is state feedback control used to stabilize system while another employs multiple resonant controllers applied to achieve harmonics compensation control. The optimal linear-quadratic (LQ) control approach in which the root locus method is used for optimization selection of weight matrix Q is adopted to tune the control parameters of multiple resonant controllers. The proposed control strategy performs outstanding voltage control performance to maintain an excellent voltage level such as zero steady-state error and low total harmonic distortion (THD) under the situation of sudden load changes, back power flow of renewable energy such as photovoltaic and nonlinear load in an isolated microgrid. Finally, the validity of the proposed approach is verified through simulations and a three-phase experiment prototype of BESS with TMS320F28335 DSP.

Current Harmonics Compensation Based on Multiresonant Control in Synchronous Frames for Symmetrical <inline-formula> <tex-math notation="TeX">$n$</tex-math></inline-formula>-Phase Machines

Low-order odd current harmonics arise in practical multiphase drives due to machine and converter nonlinear behavior (e.g., deadtime and flux saturation). If the windings are distributed, some harmonics cause torque ripple, whereas others produce losses. The latter is aggravated by the small impedance in the no-torque subspaces. Current harmonics can be compensated without steady-state error by proportional-integral controllers in multiple synchronous frames (SFs); however, a heavy computational load is required. In three-phase systems, the computational burden of this multiple SF (MSF) scheme is often avoided by implementing instead resonant controllers (RCs) tuned at the harmonics that are multiples of six in an SF rotating with the fundamental frequency. A similar structure has been proposed for nonlinearities compensation in asymmetrical six-phase machines. This paper extends this multiple RC (MRC) strategy to symmetrical machines of any phase number. The optimum frequencies for the RCs and for the SF in each plane, so that the number of RCs is minimized, are established. Then, the computational load of the resulting generic MRC scheme is assessed and compared with that of the MSF structure. The conditions in which the former is particularly preferable over the latter are identified. Experimental results are provided.

불평형부하 시 독립형 인버터의 데드타임 보상기법

Stand-alone inverter supplies constant voltage to loads. However, when a three-phase stand-alone inverter supplies unbalanced load, the generated output voltages also become unbalanced. The nonlinear characteristics of inverter dead time cause a more serious distortion in the output voltage. With unbalanced load, voltage distortion caused by dead time differs from voltage distortion under balanced load. Phase voltages in the stationary reference frame include unbalanced odd harmonics and then, d-q axis voltages in the synchronous reference frame have even harmonics with different magnitude, which are mitigated by the proposed multiple resonant controller. This study analyzes the voltage distortion caused by unbalanced load and dead time, and proposes a novel dead time compensation method. The proposed control method is tested on a 10-kW stand-alone inverter system, and shows that total harmonic distortion (THD) is reduced to 1.5% from 4.3%.

Modeling, Analysis, and Design of Multifunction Grid-Interfaced Inverters With Output LCL Filter

The purpose of this paper is to investigate the model, control, and implementation of a multifunction grid-interfaced inverter with output LCL filter, which can provide high performance active power current and compensate the existent harmonics simultaneously in a distributed network. Equipped with LCL filter, the proposed multifunction inverter offers reduced switching harmonics and superior output current shapes. However, the multifunction inverter with output LCL filter brings some challenges, including LCL resonance, phase lag, and complexity in system design. To address these issues, this paper analyzes and develops general Thevenin/Norton models for the multifunction grid inverters with LCL filter. Based on the general models of system, this paper presents guidelines of the control and the procedure of filter design for this application. In particular, a proportional-resonant (PR) plus odd-harmonic repetitive control (OHRC) scheme is designed for the outer current loop. The phase compensation method and detailed design criteria for the proposed control scheme are presented. Furthermore, the proposed OHRC scheme is compared with the previous multiple resonant control (MRC) based on their internal relationship. Simulation and experimental results are provided to validate the effectiveness and advantages of the proposed control strategy.

Multiple Resonant Controllers for Uninterruptible Power Supplies—A Systematic Robust Control Design Approach

This paper deals with the synthesis problem of multiple resonant controllers for uninterruptible-power-supply systems in a robust control framework. The controller parameters aiming the tracking of sinusoidal reference signals (with zero steady-state error) and the rejection of harmonic components of the output voltage (when supplying energy to time-varying nonlinear loads) are determined by means of a convex optimization problem subject to a set of linear-matrix-inequality constraints. Results from a 5.0-kVA experimental setup are considered to illustrate and validate the proposed approach.

A Comparative Analysis of Repetitive and Resonant Controllers to a Servo-Vision Ball and Plate System

This paper presents a comparative analysis of two alternative control strategies based on the Internal Model Principle: the Repetitive Controller and the Multiple Resonant Controller. The proposed implementations are evaluated experimentally in a servo-vision ball and plate balancing system. The plant is composed by an orientable platform with a free rolling sphere on top, where the controlled variable is the ball position. The methodology considered to synthesize the associated state gains parameters is the Linear Quadratic Regulator approach. The experimental results compare characteristics such as steady-state error, transient response and input signal for each implemented control strategy.

Sinusoidal Voltage Shaping of Inverter Equipped Stand-Alone Generating Units

Voltage-source inverters in microgrid stand-alone applications need the accurate control of the filter output voltages. Most of the time, supplied loads are not constant along daily based period; they change the total power consumption, the power factor, the current harmonic content of nonlinear equipment, and the power balancing among the phases. Consequently, the control dynamic behavior is affected, and the effectiveness of harmonic controllers is reduced. In this paper, the very sinusoidal shaping of inverter output voltage is achieved through a multiple resonant controller, which is adaptively tuned online according to the output power filter and load behavior. Resonant compensators are placed in the loop to achieve low total harmonic distortion of output voltage waveforms.

Phase Compensation Multiresonant Control of CVCF PWM Converters

In this paper, phase compensation is proposed for a multiple resonant control (MRSC) scheme to compensate system delays on the basis of phase compensation repetitive control (RC). The inherent relationship between RC and resonant control (RSC) is comprehensively developed: the partial equivalence between RC and MRSC, the advantages and disadvantages of MRSC over RC-much faster convergence rate at the cost of heavier parallel computation burden. Stability criterion of MRSC systems, zero-phase compensation at each harmonic frequency, and rules of thumb for choosing RSC gains are developed for synthesis of phase compensation MRSC. The proposed phase compensation scheme enables MRSC to independently choose compensation phase angle and control gain at each resonant frequency. Accurate phase compensations and optimal weighted control gains at each selected harmonic frequency enable MRSC systems to significantly improve the control performance: wide stability range, high tracking accuracy, and fast error convergence rate. Experimental results of a three-phase PWM inverter illustrate the validity of the phase compensation MRSC scheme.

Vibration control of a cantilever beam using multiple model adaptive resonant control

In this paper, a multiple model approach is utilised to improve the transient performance of an adaptive resonant controller. The proposed controller, Multiple Model Adaptive Resonant Controller (MMARC), is applied to attenuate vibrations in a cantilever beam structure with large varying parameters. On-line estimation of the structure’s natural frequencies is used to up-date the adaptive resonant controller’s parameters. A very simple supervisor scheme based on the system’s vibration frequency measurement is proposed to reduce the computation burden of the multiple model strategy. Simulation results show that the proposed MMARC strategy can achieve better transient response than a single adaptive controller.