Li-Dan Zhou

A novel synchronization scheme for grid-connected converters by using adaptive linear optimal filter based PLL (ALOF–PLL)

Abstract This paper proposes a novel grid synchronization scheme using a new phase-locked loop (PLL) scheme based on the adaptive linear optimal filtering (ALOF) technique. The problem formulation of the proposed ALOF is based on decomposing grid voltage signal into inner product of two vectors, namely, the vector of trigonometric functions and the vector of coefficients, corresponding to the input vector and the weight vector of the closed-loop adaptation algorithm by using least-mean-square (LMS) optimization algorithm. The coefficient of the fundamental component of the grid voltage is used as input signal for the PLL and the phase angles of the trigonometric functions are obtained from the output of the PLL recursively. The mathematical derivation of the weights updating law and the stability analysis of the ALOF–PLL are presented. Besides, the parameter selection for optimal performance is also discussed in terms of continuous domain (s-domain) analysis, discrete domain (z-domain) analysis and time domain simulations. The proposed ALOF–PLL shows the characteristic of band-pass filter at fundamental frequency and a notch filter at the harmonic frequencies. Finally, a detailed comparison with the existing single-phase and three-phase grid synchronization methods is also presented, and the proposed ALOF–PLL is found to have overwhelming advantages over the existing grid synchronization methods in terms of tracking accuracy, dynamic response and immunity to grid voltage disturbances, such as voltage sag/swell, phase-angle jump, harmonics, unbalance, random noises and frequency jump, etc. The validity and effectiveness of the ALOF–PLL is substantially confirmed by the extensive simulation results obtained from Matlab/Simulink.

Robust Deadbeat Control Scheme for a Hybrid APF With Resetting Filter and ADALINE-Based Harmonic Estimation Algorithm

A novel hybrid active power filter (HAPF) topology is proposed, which shows advantages of the conventional HAPF and the LCL filter in terms of reduced dc-link voltage, lower switching ripples, and less electromagnetic interference injection. To enhance the noise rejection capability of the digital controller, the resetting filters (RFs) are utilized as prefilters before the analog/digital sampling stage. A robust deadbeat current control law is derived based on the average current tracking scheme, where the effect of the RFs is favorably incorporated. To alleviate the difficulties in current controller design, the ac-side capacitor voltage of the HAPF is estimated by using the adaptive linear neural network identifier in the load current feedforward loop. Hence, a simple proportional controller is utilized in the inner current loop. Moreover, the grid current feedback and load current feedforward strategies are used to achieve precise current tracking and fast dynamic response. A 75-kVA prototype system is built for verification. The validity of the proposed HAPF and its control algorithms are confirmed by the experimental results.

A novel harmonic-free power factor corrector based on T-type APF with adaptive linear neural network (ADALINE) control

Abstract A novel harmonic-free power factor correction (PFC) topology based on T-type active power filter (APF) is proposed in this paper. The proposed system has better stability characteristics compared to conventional shunt APF topologies and it is a natural filter for the non-linear load harmonic disturbances. The tuned passive filters are connected at the ac-side of the rectifier load, which are designed to provide fundamental reactive power compensation and eliminate majority of load harmonics in order to minimize the power rating and heat dissipation of the voltage source inverter (VSI). The control scheme is based on a decoupled state-space equations of the T-type APF using separate proportional-integral controllers in d-axis and q-axis of rotating reference frame synchronized with grid voltages, respectively. The fundamental components of load-side currents are feed-forwarded in the current control loop using two groups of synchronous frame adaptive linear neural networks (ADALINEs) to ensure a fast dynamic response. A proportional-integral controller is adopted in the outer voltage loop for balancing the active power flow of the dc-side capacitor of the VSI. The proposed power factor corrector topology is studied analytically and by simulation under various scenarios using Matlab/Simulink. The validity and effectiveness of the proposed topology as well as its control schemes are substantially confirmed by the simulation results.

Analysis and effective controller design for the cascaded H-bridge multilevel APF with adaptive signal processing algorithms

The cascaded H-bridge (CHB) multilevel inverter is being recognized as the most suitable topology for high-power medium-voltage power quality conditioning applications. This paper presents mathematical modeling and effective controller design methodology for the CHB-based active power filters (APFs), which achieves dynamic reactive power and harmonic compensation. The most crucial problems in CHB-APF control are the simultaneous requirements of both accurate harmonic current compensation and the dc-link voltage stabilization among the H-bridges, which is the prerequisite for the stable operation of CHB-APF. To achieve dc-link stabilization, a novel voltage balancing algorithm is proposed by splitting the dc-link voltage control task into two parts, namely, the average voltage control and the voltage balancing control, where the sine and cosine functions of the phase angle of the fundamental component of the grid voltage are used, respectively. To ensure accurate phase tracking, a novel phase-locked loop (PLL) is proposed by using the adaptive linear neural network (ADALINE), where the grid voltage background distortion is also taken into account. The superior performance of the ADALINE-PLL is validated by comparison with the existing PLLs in literatures. Furthermore, the proportional-resonant (PR) controller is used for the reference current tracking. A separate ADALINE algorithm is applied for reference current generation (RCG) for the CHB-APF. The excellent performance of the ADALINE-based RCG scheme is verified by comparison with the existing RCG schemes, namely, the low-pass filter approach and the single-phase p − qmethod. The experimental results on the three modules CHB-APF are presented, which verifies the effectiveness of the proposed control algorithms. Copyright

Design, implementation and field test of a novel hybrid active power filter

This paper proposes an LCL-filter-based hybrid active power filter for harmonic mitigation of a 10/0.4 kV residential distribution system. Adaptive linear neuron network (ADALINE) is applied for individual harmonic component extraction from distorted nonlinear load currents, and the estimated signals are used for the selective harmonic elimination (SHE) purpose in the current-loop controller. A robust deadbeat current control law is derived based on the low frequency model of the presented topology. By using the ADALINE based SHE strategy, the current-loop controller bandwidth is significantly reduced thus the stability of whole system is ensured. Both the laboratory experiments and field tests are implemented. The feasibility and effectiveness of the proposed system have been substantially confirmed by the experimental results.

ON USING LINEAR PERIODICALLY RESETTING FILTER IN CURRENT CONTROL LOOP FOR ACTIVE POWER FILTER

Among linear control techniques, deadbeat control has been widely accepted as a feasible current control technique as far as the digital signal processor (DSP) implementation of active power filter (APF) is concerned. This control technique uses high gain on the error measured at one sample, to control the error ideally to zero by the next sample. The high gain makes the control very sensitive to any error or noise in the measurements, which is always there in electrical systems. Especially, the periodic noise in parallel implementation of an inverter or APF demands a higher order filter at the current transducer output, which affects the dynamic response of the system. Recently, few papers have reported the results about the use of linear periodically resetting integrators (LPRI) as filter in some electronic applications. This paper is an attempt to generalize the idea of LPRI and here we introduce the notion of linear periodically resetting filter (LPRF). The frequency characteristics of an LPRF are analyzed. Possible application of these filters in current control is studied. It is shown that these filters can be adopted to improve the performances of a current loop in APF.

Modeling, Control and Experimental Investigation of a Novel DSTATCOM Based on Cascaded H-bridge Multilevel Inverter

A novel static synchronous compensator for reactive power compensation of distribution system (DSTATCOM) is proposed, based on the cascaded H-bridge multilevel inverter configuration. The mathematical formulation of the multilevel DSTATCOM is presented using state-space representations. A new software phase-locked loop (SPLL) is presented for grid synchronization and the obtained phase angle of the fundamental component of the grid voltage is utilized for deriving the active and reactive power balancing equations of the multilevel DSTATCOM. The proportional-resonant (PR) controller scheme is adopted for the current tracking control of the inverter, and the average dc-link voltage is controlled using a proportional-integral (PI) controller to regulate the active power flow of the DSTATCOM. Besides, the voltage balancing (VB) control among individual H-bridges is achieved by using separate PI regulators to control the difference voltage between the individual dc-link voltage and the average dc-link voltage. The validity of the proposed multilevel DSTATCOM and its control strategies is substantially confirmed by the extensive simulation results and the experimental results from the prototype system.

Experimental investigation of the operation characteristics of 3-phase 3-wire active power filter

The conventional passive filtering has been outdated since it detune with age and the performance of passive filters is affected by the grid impedance, which may cause resonance problems. Active power filters (APFs) are attractive solutions to solve harmonics-related power quality problems due to the development of power semiconductors, control theory and digital signal processors (DSP), and they have become the first choice for power quality solutions. This paper systematically investigated 3-phase 3-wire active filter in 3-phase 3-wire and 3-phase 4-wire systems, and both the balanced and unbalanced situations are considered. It was found by various experiments, that 3-phase 3-wire active filter works quite well in 3-phase 3-wire system, however, its performance in 3-phase 4-wire system is unsatisfactory, and it may even inject unwanted harmonics to the grid under certain situations, which deteriorates power quality at the point of common coupling (PCC).

On using resetting integrator in current control loop for active power filter

Current control loops is the key element in the control structure of active power filter systems. Among linear control techniques, deadbeat control has widely been accepted as a feasible current control technique as far the DSP implementation of APF is concerned. This control technique that uses high gains on the errors measured at one sample is very sensitive to any error or noise in the measurements, which is always there in electrical systems. Especially, the periodic noise in parallel implementation of an inverter or APF demands a higher order filter at the current transducer output, which affects the system dynamic response. Recently few papers have reported the results about the use of resetting integrators as filter in some electronic applications. This paper is an attempt to show possible application of resetting integrator as filter to current control for APF, where linear control methods have better frequency characteristics and current response than general deadbeat control. Simulation and experiment verify that these filters can be adopted to improve the performances of a current loop in APF

A New Power Factor Correction Scheme Based on T-type Active Power Filter Using Neural Algorithmic Approach

Abstract A novel power factor corrector (PFC) topology based on T-type active power filter (APF) is proposed in this paper. The control scheme is based on a decoupled state-space equations of the T-type APF using proportional-integral (PI) controllers in the synchronous reference frame. The fundamental components of load currents are feed-forwarded in the current-loop controller by using synchronous frame adaptive linear neural networks to ensure a fast dynamic response. A separate PI controller is adopted in the outer voltage-loop for balancing the active power flow of the APF DC-side capacitor. The simulation and experimental results are presented, which demonstrate the validity and effectiveness of the proposed system.