Sajjad M. Kaviri

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.

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.

A hierarchical control scheme to integrate the telecom backup systems into microgrid

This paper presents a novel hierarchical control scheme to integrate the telecom backup systems into power grid through microgrid. The proposed scheme employs hierarchical control system to correctly control the system in both grid-connected and islanded modes. The conventional hierarchical control system is highly dependent on communication links. With no communication link, the reliability and efficiency of the system degrades significantly. This paper proposes a novel hierarchical control scheme that is less relies om communication links and performs adequately even with no communication link. For the secondary control level, an innovative adaptive droop control scheme that regulates microgrid parameters locally is proposed. This approach needs neither an extra controller nor a communication link. To reduce the voltage measurement errors, the effect of line impedance between converter and Point of Common Coupling (PCC) has been taken into account in voltage adaptive droop controller. In addition, the proposed scheme offers two operation modes of autonomous and non-autonomous. In autonomous mode, the active/reactive power is controlled based on the grid parameters and available storage capacity without a need to communication link. While in non-autonomous mode the active/reactive power reference is provided by tertiary controller. With no tertiary controller in service, the proposed controller operates in the autonomous mode and controls the active/reactive power itself to ensure the stability of the power grid. The performance of the proposed controller is evaluated by using simulation results.

A New Slip Mode Frequency Shift Islanding Detection Method for single phase grid connected inverters

This paper presents a new slip mode frequency shift islanding detection method (SMS IDM). This new method uses a non-sinusoidal function for drifting the inverter phase angle. The Non-Detection Zone (NDZ) of the SMS IDM with sinusoidal function has been calculated and it has been shown that if the quality factor and/or the resonance frequency of the load changes during the inverter operation time, SMS IDM with sinusoidal function fails to detect islanding for a specific range of variation. It is shown in the paper that SMS IDM with the new function has a smaller NDZ area compared to the SMS IDM with sinusoidal function. Simulation and experimental results verify the results of the proposed new method.

Modified window, recursive least square estimator for active and reactive powers in single-phase AC systems

In this paper, an Instantaneous Power Signal (IPS) has been used to extract amount of active/reactive power in real-time. Estimation of real-time power is challenging in single-phase systems due to the presence of double-frequency ripple in IPS. In conventional methods the low bandwidth filters are used to remove this ripple. In this paper the real-time power estimation is obtained first by presenting the problem in terms time dependent linear optimization and then solved by using a least square (LS) method. In order to tackle the drawbacks associated with the conventional methods based on dq rotating frames and grid synchronization algorithms, the proposed algorithm is modified to be recursive and windows type to reduce the computational time. It is mathematically shown that by adding one additional parameter the active and reactive power estimation can be made independent of the initial time value. Simulation and experimental results prove the superior performance of the proposed estimator in comparison with the conventional estimators and the other least square algorithms, such as Kalman filters and forgetting factor, in term of convergence time and the amount of undershoot/overshoot in estimation of active and reactive power from instantaneous power signal.

Advanced slip mode frequency shift islanding detection method for single phase grid connected PV inverters

This paper presents an active islanding detection method which has zero non-detection zone. This method is the advanced version of the conventional slip mode frequency shift islanding detection method (SMS IDM). In this method the parameters of SMS IDM change based on the local load impedance value. The parameters value are calibrated periodically by measuring the impedance of the local load. The local load impedance can be calculated by injecting harmonic currents to the point of common coupling (PCC) and measuring its voltage during the calibration period. Simulation and experimental results show the accuracy of the proposed method in detection of islanding in any loading conditions.

Islanding detection for a single phase bidirectional converter in telecommunication power systems

Telecommunications is a rapidly growing field in global technology and it has a significant social, cultural, and economic impact on modern society. As such, ensuring reliability of these systems should be highly prioritized and involve sophisticated standards. Due to the highly sensitive nature of Telecom loads, it is vital that failure of the utility power be detected quickly. In this paper, Slip Mode Frequency Shift Islanding Detection Method is proposed for islanding detection of a single phase bidirectional converter in Telecommunication power systems. The proposed method uses an orthogonal system generation based PLL and an adaptive all pass filter for control of the converter. Simulation results verify the accuracy of the proposed method in detecting islanding in the required time frame.

Hybrid modulation technique for Dual-Active-Bridge DC-DC converters to achieve full ZVS over wide range of operating conditions

This paper presents a hybrid modulation scheme for DC-DC Dual Active Bridge (DAB) converters over a wide range of operating conditions. The proposed hybrid modulation scheme combines the Phase-Shift-Modulation (PSM) and the variable duty cycle into a hybrid modulation in order to maintain Zero Voltage Switching (ZVS). A simple method will be provided to calculate the moment of transition between these two modulations based on the ZVS Regions. The proposed hybrid modulation offers simple structure, high efficiency, and reduction of voltage stress on switches. It is also easy to implement in digital controllers (FPGA, DSP, etc.), which is a big advantage compared to the complex approaches in the literature. Simulation and experimental results of a 0–3.3 kW DAB converter are provided to demonstrate the feasibility and satisfactory performance of the proposed control.

A review of AC microgrid control methods

The concept of microgrid (MG) has been introduced as a solution to future electrical grid challenges such as the rapid increase of electrical demand, harvesting energy from renewable energy sources, and ensuring the quality and reliability of electricity supply. Distributed energy sources, as well as energy storage systems are interfaced with MGs through power electronic inverters. Control systems of the power electronic inverters in MGs play a key role in ensuring the perfect performance of MGs. This paper presents a comprehensive review of various control systems used in MGs. In particular, different levels of MG control systems have been investigated and corresponding control strategies at each level have been compared in detail. This paper categorizes MG control systems into four levels: 1- The converter output control that shapes the output current in order to control the flow of output power, 2- The power sharing algorithm that guarantees the even distribution of the load between parallel inverters, 3- The MG supervisory controller (secondary level) that deals with the supervisory control of the converters within the MG, and 4- The grid supervisory controller (tertiary level) that controls the flow of power between the main grid and the MG.