This paper presents an optimized sliding mode control (SMC) strategy to maximize existence region for single-phase dynamic voltage restorers. It is shown analytically that there exists an optimum ...sliding coefficient which enlarges the existence region of the sliding mode to its maximum. Also, it is pointed out that the optimum sliding coefficient improves the dynamic response. In addition, a double-band hysteresis control which ensures the switching of a transistor in the voltage source inverter during a half-cycle while it remains either on or off in the other half cycle is used to mitigate the switching frequency. The theoretical considerations and analytical results are verified through computer simulations and experimental results. Simulation and experimental results show that the proposed SMC strategy not only compensates the undesired voltage disturbances and maintains the load voltage at desired level with low total harmonic distortion, but also exhibits fast dynamic response and operates at reasonably low switching frequency.
This paper presents time-varying and constant switching frequency based sliding-mode control (SMC) methods for three-phase transformerless dynamic voltage restorers (TDVRs) which employ half-bridge ...voltage source inverter. An equation is derived for the time-varying switching frequency. However, since the time-varying switching frequency is not desired in practice, a smoothing operation is applied to the sliding surface function within a narrow boundary layer with the aim of eliminating the chattering effect and achieving a constant switching frequency operation. The control signal obtained from the smoothing operation is compared with a triangular carrier signal to produce the pulse width modulation signals. The feasibility of both SMC methods has been validated by experimental results obtained from a TDVR operating under highly distorted grid voltages and voltage sags. The results obtained from both methods show excellent performance in terms of dynamic response and low total harmonic distortion (THD) in the load voltage. However, the constant switching frequency-based SMC method not only offers a constant switching frequency at all times and preserves the inherent advantages of the SMC, but also leads to smaller THD in the load voltage than that of time-varying switching frequency-based SMC method.
This article presents an indirect sliding mode control (SMC) for single-ended primary-inductor converters (SEPIC). Unlike the conventional SMC methods, the proposed SMC method employs a sliding ...surface function based on the input current error only. The use of such sliding surface function not only simplifies the implementation but also reduces the cost of implementation. It is shown that the output voltage control can be achieved indirectly. The input current reference is generated by a proportional-integral (PI) regulator. The existence condition and the region of the closed-loop system are determined for all possibilities of the PI gains. The performance of the proposed SMC method is investigated on a laboratory prototype converter, operated in buck and boost modes, in terms of the voltage regulation ability under abrupt changes in the input voltage and load resistance. Simulation and experimental results are presented and discussed.
In this article, a model predictive control (MPC) method for dc-dc single-ended primary-inductor converters with autotuning weighting factor capability is presented. The conventional MPC requires ...retuning of the weighting factor when the operating condition of the converter is changed. The effect of this change is observed as inability of the controller in maintaining the switching frequency constant. The weighting factor avoids excessive switching frequency in the dc-dc converters. Based on the relation between the inductor current ripple and switching frequency, an autotuning weighting factor based MPC is proposed. The effect of the weighting factor on the switching frequency is investigated. The proposed MPC eliminates the need for retuning the weighting factor when the operating point of the converter is changed. The proposed control strategy is verified experimentally under input voltage, load, and parameter variations. The results obtained from conventional and proposed MPC methods are compared. It is shown that the proposed MPC method controls the average switching frequency when the operating mode of the converter is changed. Furthermore, parameter mismatch results are presented for both conventional and proposed MPC methods.
This article presents an enhanced frequency adaptive demodulation technique for grid-synchronization of grid-connected converters in variable frequency condition. Demodulation works by generating ...demodulated voltages which contain undesired double frequency components. As a result, high-order low-pass filters with high cutoff frequency are required to eliminate the undesired components. This reduces the dynamic performance. Frequency adaptive demodulation technique enhances the dynamic performance by rejecting the double frequency components as opposed to filtering, however, at the cost of additional computational complexity. This article overcomes this problem by using double demodulation without recreating the double frequency component for rejection purposes. This reduces the computational complexity significantly. Suitability of the proposed method is verified through numerical simulation and experimental study. Comparative study with existing frequency adaptive demodulation and second-order generalized integrator phase-locked loop techniques demonstrate the validity and performance improvement by the proposed technique.
Grid synchronization techniques play a significant role in integrating renewable energy sources to the electric power grid. In this context, estimating the phase and frequency of the grid voltage ...signal is an interesting problem. Out of various techniques available in the literature, linear Kalman filter (LKF) is one of the most popular one. In this article, we propose an alternative implementation of the LKF for grid synchronization application. The proposed implementation uses a linear parametric model of the grid voltage signal including dc offset. It does not involve any quadrature signal generation, rather it works by estimating the phase angle. This helps to estimate the unknown grid frequency directly from the phase angle. This clearly differentiates the proposed alternative implementation with respect to the existing implementations. Performance improvement by the proposed technique is verified extensively through comparative numerical simulation and experimental studies. Comparative results demonstrate the suitability of the proposed technique with respect to other state-of-the-art techniques namely second-order generalized integrator phase-locked loop and enhanced phase-locked loop.
This article presents a super twisting sliding-mode control (ST-SMC) for single-phase dynamic voltage restorers (DVRs). Unlike the conventional first-order sliding-mode controller, the proposed ...ST-SMC technique eliminates the need for differentiating the compensation voltage in the sliding surface function while keeping the merits of first-order SMC. As a consequence of employing ST-SMC, a continuous control signal is achieved from which the pulsewidth modulation (PWM) signals can be generated. In this case, the inverter operates at a constant switching frequency. The stability analysis of ST-SMC is also presented. The reference compensation voltage needed in ST-SMC is estimated by using Brockett oscillator-based frequency-locked loop. Theoretical considerations are verified through experimental results under ideal and distorted grid voltage conditions. The obtained results show that the ST-SMC has good dynamic performance and can maintain the load voltage at a desired level under voltage sag, swell, and harmonically distorted grid voltages.
A grid-synchronization-based fundamental frequency positive-sequence (FFPS) and negative-sequence (FFNS) amplitudes estimation technique is proposed for unbalanced and distorted grid. In this ...technique, the sequence amplitudes are extracted by extracting the phase-angle of the FFPS and FFNS components. The extracted phase-angles have DC and double frequency AC components. The AC component is filtered out by using a Moving Average Filter (MAF) of appropriate window length. From the extracted phase-angle, the unknown frequency can be estimated by using a suitable controller. A frequency-fixed equidistant samples-based pre-loop filter is also applied to eliminate the effect of measurement offset. The proposed technique has a very simple structure and is easy to tune. Small-signal modeling-based stability analysis and gain tuning procedure are also provided. The proposed technique strikes a good balance between fast convergence and disturbance rejection capability. Comparative numerical simulation and experimental results with similar other techniques demonstrate the suitability and performance enhancement by the proposed technique.
Development of advanced grid‐synchronization technique for unbalanced and distorted grid is considered in this paper. In this context, self‐tuning filter (STF) is considered to extract the ...fundamental component from the measured unbalanced and distorted voltages. Standard STF considers balanced grid voltages which is not always possible to ensure in the actual power grid. To mitigate this issue, an extended STF is proposed by analyzing the standard STF in the state‐space framework. To make the proposed ESTF grid‐following, a robust open‐loop frequency estimator is also applied. The closed‐loop system enjoys excellent filtering benefit from the extended STF side while taking advantage of the fast convergence speed property of the open‐loop frequency estimation technique. Numerical simulation and experimental results with double second‐order generalized integrator phase‐locked loop are provided to validate the theoretical developments.
Bu çalışmada, fotovoltaik (PV) sistemler için hem şebeke bağlantılı hem de ada durumda güç akışını sağlayabilen bir eviricinin tasarımı ve kontrolü sunulmuştur. Şebekede kesinti olması durumunda, ...önerilen güç ve kontrol yapısı güneş panellerinden dâhili yüklere güç akışı sağlamaktadır. Böylece, ışınlama süresi boyunca, kesintilerin yükler üzerindeki etkisi azaltılmış ve PV’de üretilen güç maksimum seviyede kullanılmıştır. Ayrıca, PV panellerden maksimum seviyede güç transferi için Maksimum Güç Noktası Takip (MPPT) algoritması kullanılmıştır. MPPT algoritması evirici için bir referans akım üretecek biçimde uyarlanmıştır. Şebeke kesintisi durumunda sistem gerilim kontrollü olarak çalışmaktadır ve referans akım yük gerilimi ile nominal gerilim arasındaki hataya bağlı olarak bir çıkış üreten PI kontrolör tarafından belirlenmektedir. Önerilen sistem, MATLAB/Simulink ortamında modellenmiş ve doğrulanmıştır. Sonuçlar, önerilen sistemin her iki çalışma durumunda da güç akışını başarıyla sağladığını göstermektedir.
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