Majid Pahlevani

An Adaptive Droop DC-Bus Voltage Controller for a Grid-Connected Voltage Source Inverter With LCL Filter

This paper presents a very fast dc-bus voltage controller for a single-phase grid-connected voltage-source inverter (VSI) with an LCL output filter used in renewable energy applications. In single-phase grid-connected inverters, the design of the dc-bus voltage control scheme is very challenging due to the presence of a second harmonic ripple across the dc-bus voltage. The proposed dc-bus voltage control scheme is able to address the difficulties introduced by the second-harmonic ripple. The dc-bus voltage controller is based on an adaptive droop control technique, which is able to provide a very fast transient response for the closed-loop system and ensures the optimal operation of the VSI during steady-state conditions. Also, the simple structure of the controller makes it very practical for grid-connected VSIs used in renewable energy power conditioning systems. Theoretical analysis and experimental results demonstrate the superior performance of the proposed control approach compared to conventional dc-bus voltage control schemes.

A Fast DC-Bus Voltage Controller for Bidirectional Single-Phase AC/DC Converters

This paper presents a new dc-bus voltage control technique for single-phase bidirectional ac/dc converters. The proposed controller is able to significantly improve the transient response of the dc-bus voltage control loop and provide a robust and reliable closed-loop control system. In the proposed approach, the dc value of the dc-bus voltage is precisely estimated through a specific adaptive filter. The structure of the proposed filter provides a very fast and robust estimation for the dc value of the dc-bus voltage. In particular, the proposed dc-extraction technique is able to precisely estimate the dc value in presence of double-frequency ripple mounted on top of the dc-bus voltage in single-phase ac/dc converters. Simulation and experimental results demonstrate the superior performance of the proposed closed-loop control system compared to the conventional ones.

A Hybrid Estimator for Active/Reactive Power Control of Single-Phase Distributed Generation Systems With Energy Storage

This paper presents a new active/reactive power closed-loop control system for a hybrid renewable energy generation system used for single-phase residential/commercial applications. The proposed active/reactive control method includes a hybrid estimator, which is able to quickly and accurately estimate the active/reactive power values. The proposed control system enables the hybrid renewable energy generation system to be able to perform real-time grid interconnection services such as active voltage regulation, active power control, and fault ride-through. Simulation and experimental results demonstrate the superior performance of the proposed closed-loop control system.

A Series–Parallel Current-Driven Full-Bridge DC/DC Converter

This paper presents a novel series-parallel current-driven (SPCD) full-bridge dc/dc converter, which is able to process and deliver power efficiently over a wide range of load variations. In order to guarantee reliable operation of high-frequency dc/dc converters, the converter should be able to sustain soft switching for a wide range of operating conditions. The SPCD full-bridge converter, proposed in this paper, is able to offer soft switching for the input power semiconductors and smooth commutations for the output diodes. Also, the particular structure of the proposed converter eliminates the need for extra auxiliary circuits to provide reactive current for soft switching at light loads. The proposed topology can fully eliminate voltage spikes across the output diodes by providing smooth and lossless commutations for the output diodes. Thus, the proposed converter can be an efficient and reliable solution for variety of applications with a high switching frequency and a high output voltage. The SPCD full-bridge converter has the ability to integrate all magnetic components into an integrated transformer in order to achieve a high power density. The integrated transformer is thoroughly analyzed using ANSYS high-frequency structure simulator. Simulation and experimental results confirm the superior performance of the proposed SPCD full-bridge dc/dc converter.

A novel digital peak-current-mode self-sustained oscillating control (PCM-SSOC) technique for a Dual-Active Bridge DC/DC converter

This paper presents a peak-current mode self-sustained oscillating control (SSOC) technique for a Dual-Active Bridge (DAB) DC/DC converter. The proposed control approach is able to significantly improve the performance of the bi-directional DAB DC/DC converter over a very wide range of operating conditions. Basically, the proposed PCM-SSOC scheme adaptively regulates the respective phase-shifts for each bridge, as well as the switching frequency of the converter for different operating conditions in order to achieve an optimal performance. In this control technique, the timing signal is produced based on the transformer primary current, which is a feedback to the control system to determine the switching instants of the power MOSFETs. Therefore, the control system automatically tunes the control variables for different operating conditions. Comprehensive mathematical analysis based on the geometric viewpoint of the control system of the proposed PCM-SSOC scheme is presented, which provides a very good insight into designing the control system. Experimental results provided from an experimental prototype confirm the superiority of the converter performance compared to the conventional fixed-frequency phase-shift control approach.

A D-Q rotating frame DC-bus voltage controller for bi-directional single-phase AC/DC converters

This paper presents a closed-loop control technique in D-Q rotating frame for bi-directional single-phase AC/DC converters. The proposed control system allows the active and reactive power control in both directions from grid to vehicle and vehicle to grid, while controlling the DC-bus voltage. Due to the lack of freedom degrees required for orthogonal systems, using the D-Q frame is a challenge in single-phase power conditioning systems. In this paper, an all-pass filter has been used to generate the orthogonal signals in the closed-loop control system. This method generates the orthogonal signals without degrading the dynamics of the closed-loop control system and with less noise in comparison to the other common methods such as differentiators. A DC-bus voltage estimator based on adaptive filter has also been used in this paper to remove the double frequency ripple and in turn increase the reliability and speed of the proposed controller. The proposed control scheme is used to implement the smart charging and power management strategies of the residential loads using electric vehicles as a storage system. Simulation and experimental results demonstrate the transient and steady-state performance of the proposed controller in different modes of operation. Also the performance of the proposed DC-bus voltage estimator in removing the double frequency ripple as well as the application of the proposed control scheme in implementation of power management strategies in a typical household, has been shown by using simulation results.

Frequency-adaptive current controller for grid-connected renewable energy systems

An adaptive proportional-resonant (APR) controller for current controller of grid-connected DC/AC systems for renewable energy applications is presented. The increase in renewable energy on the electricity grid poses stability risks to the network as the frequency and amplitude are not as tightly regulated as in previous years. The proposed APR controller is able to maintain high quality current at frequencies well beyond the IEEE1547 standard. The controller is constructed in two parts, a phase-locked loop (PLL) for synchronization and identification of the grid frequency, and a current controller based on the form of the well-known PR controller. The current controller is able to dynamically adjust to the shifting frequency of grid which ensures high quality, unity power-factor across the 59.3-60.5Hz spectrum set by IEEE1547, and beyond. The PLL implemented is an amplitude-decoupled adaptive notch filter (AANF) which provides a very fast, an accurate solution for frequency estimation as well as reference signal generation. The AANF and the APR controller are implemented digitally on an FPGA platform and verified experimentally on a 1kW DC/AC prototype.

A Hybrid Phase-Shift Modulation Technique for DC/DC Converters With a Wide Range of Operating Conditions

This paper presents a new hybrid phase-shift modulation technique which is able to provide soft switching for the entire operating conditions of dc/dc converters. The proposed phase-shift modulation technique does not require any extra active/passive circuitry to guarantee soft-switching. In addition, the proposed technique can be applied to the general category of power circuit topologies for dc/dc converters, which use a full-bridge inverter in their power circuit. The proposed hybrid phase-shift modulation technique includes two distinct modulation strategies based on the operating condition of the converter. Thus, it has a variable structure that can optimize the performance for various operating conditions. The main advantages of the proposed technique are the achievement of soft-switching independent of the load condition, and optimized performance. Theoretical analysis and simulation/experimental results demonstrate the superior performance of the proposed hybrid phase-shift modulation technique over the conventional one.

Observer-based control technique for a grid-connected DC/AC converter used in renewable energy applications

This paper presents sensorless techniques for a grid-connected voltage source inverter with an LCL-filter in order to improve the closed-loop control performance and reduce the overall cost of the converter through an observer-based control approach. The observability of the system is mathematically analyzed using the system state-space equations, and then two state observers are designed and the closed-loop performance of the observers is compared in detail. The observer-based controller is implemented on a grid-connected voltage source inverter. The experimental results demonstrate the feasibility of the proposed closed-loop control system and superior performance particularly in terms of noise susceptibility.

Power control of a bi-directional AC/DC rectifier used for telecom backup systems

This paper presents a novel control scheme to control the flow of active and reactive power through a single-phase bi-directional AC/DC converters used for telecom backup systems. The proposed controller enables the telecom facilities to control the power flow in both directions from grid to telecom and telecom to grid. In this paper the fuel cell system coupled with ultra-capacitors has been used as telecom backup system. By using 10% of the backup storage capacity, not only telecom companies can ensure their high standard reliability, but they can also benefit from their assets, as well as participating in ancillary services market. The main purpose of this paper is to achieve this feature by using the proposed converter configuration and its control scheme. So the proposed control scheme is implemented in D-Q rotating frame. Due to the lack of freedom degrees in single phase converters using the D-Q frame is challenging. In this paper, to cope with this problem the all-pas-filter has been used to generate the orthogonal system required for D-Q frame. Also A hybrid estimator has been used in this paper to estimate the real-time amount of active/reactive power. This estimator can estimate real-time power values very fast and reliable, which can improve the dynamic abilities of the proposed controller. The performance of the proposed controller is evaluated by using simulation and experimental results. Also the application of the proposed controller in implementation of energy management strategies in a typical telecommunication backup system has been proved by simulation results.