Fault Handling Methods and Comparison for Different DC Breaker Topologies and MMC Topologies of the HVDC System

The HVDC system has many significant benefits and is widely used around the world. The protection of HVDC system is always an issue, which should be solved. This paper presents the working principle of different protection schemes. The advantages and disadvantages of these protection schemes are also introduced. In order to solve the HVDC fault, two protection strategies are proposed. One design focusses on the topologies of the HVDC breaker in the HVDC line, such as all-solid HVDC breaker, resonant HVDC breaker, and hybrid HVDC breaker. The other design is from the viewpoint of converter topology, which has two types. One type generates the counter-emf in arms, such as full bridge MMC, hybrid MMC, and clamp-double MMC. The other type cuts off the current path from the AC side to the DC side, which is also introduced in this paper. Some performances of these topologies are compared, such as switching time and efficiency.

A Novel Analog Circuit Design for Maximum Power Point Tracking of Photovoltaic Panels

A new analog technique is proposed in order to track the maximum power point (MPP) of PV panels. The proposed technique uses the well-known simple functions of electronic circuits. The proposed technique is validated by applying it to boost based off grid PV system. The simulation of the PV system was done on the circuit oriented simulator Proteus-ISIS. A good efficiency of the analog technique (more than 98%) was registered. The variation of irradiation was introduced in order to study the robustness of the proposed analog MPPT technique.

Quantitative Analysis of Efficiency Improvement of a Propulsion Drive by Using SiC Devices: A Case of Study

One of the emerging research topics in the propulsion drive of the electric vehicles is the improvement in the efficiency of its component parts, namely, the propulsion motor and the associated inverter. This paper is focused on the efficiency of the inverter and analyzes the improvement that follows from the replacement of the silicon (Si) IGBT devices with silicon carbide (SiC) MOSFETs. To this end, the paper starts by deriving the voltage-current solicitations of the inverter over the working torque-speed plane of the propulsion motor. Then, a proper model of the power losses in the inverter over a supply period of the motor is formulated for the two types of device, including the integrated freewheeling diode. By putting together the voltage-current solicitations and the device power losses, the efficiency maps of the Si IGBT and SiC MOSFET inverters are calculated and compared over the torque-speed plane. The results for the Si IGBT inverter are supported by measurements executed on a marketed C-segment compact electric car, while the SiC MOSFET loss model is validated by an on-purpose built test bench. Finally, the overall efficiency of the propulsion drive is calculated by accounting for the motor efficiency. Main outcomes of the paper is a quantitative evaluation of both the improvement in the efficiency achievable with the SiC MOSFETs and the ensuing increase in the electric car range.

Experimental Verification of a Battery Energy Storage System for Integration with Photovoltaic Generators

This paper presents the experimental verification of a 2 kW battery energy storage system (BESS). The BESS comprises a full-bridge bidirectional isolated dc-dc converter and a PWM converter that is intended for integration with a photovoltaic (PV) generator, resulting in leveling of the intermittent output power from the PV generator at the utility side. A phase-shift controller is also employed to manage the charging and discharging operations of the BESS based on PV output power and battery voltage. Moreover, a current controller that uses the d-q synchronous reference frame is proposed to regulate the dc voltage at the high-voltage side (HVS) to ensure that the voltage ratio of the HVS with low-voltage side (LVS) is equivalent to the transformer turns ratio. The proposed controllers allow fast response to changes in real power requirements and results in unity power factor current injection at the utility side. In addition, the efficient active power injection is achieved as the switching losses are minimized. The peak efficiency of the bidirectional isolated dc-dc converter is measured up to 95.4% during battery charging and 95.1% for battery discharging.

Sensorless Control of Nonsinusoidal Permanent Magnet Brushless Motor Using Selective Torque Harmonic Elimination Control Method Based on Full-Order Sliding Mode Observer

Nowadays, due to excellent advantages of permanent magnet brushless (PMBL) motors such as high efficiency and high torque/power density, they are used in many industrial and variable-speed electrical drives applications. If the fabricated PMBL motor has neither ideal sinusoidal nor ideal trapezoidal back-EMF voltages, it is named nonideal (or nonsinusoidal) PMBL motor. Employing conventional control strategies of PMSMs and BLDCMs lowers the efficiency and leads to unwanted torque ripple, vibration, and acoustic noises. Moreover, in many applications to reduce the cost and enhance the reliability of drive, sensorless control techniques are used. This paper proposes a novel sensorless control for a nonsinusoidal PMBL motor with minimum torque ripple. To develop smooth torque, the selected torque harmonic elimination strategy is employed. Furthermore, to estimate the rotor position and speed, a novel full-order sliding mode observer is designed. Proposed observer estimates the position and speed of motor from standstill to final speed. The proposed observer is robust to uncertainty of harmonic contents in phase back-EMF voltage and able to run the motor from standstill with closed-loop control scheme. The capabilities of torque ripple minimization and sensorless strategies are demonstrated with some simulations.

Estimation of Parasitic Resistance of Electrolytic Capacitor and Filter Inductor and Prediction of Input Filter Induced Oscillations in a Switch-Mode Magnet Power Supply

In switch-mode power converters with large ratings, it is important to be able to predict the parasitic resistances associated with circuit elements such as electrolytic capacitor and filter inductor in the initial converter design stage itself to avoid the cost and time associated with actual design, prototype fabrication, and testing of these components. Knowing the values of parasitic elements is also important as they decide the possibility of closed-loop instability, besides affecting the other circuit parameters. In this paper, a way to estimate the equivalent series resistance of electrolytic capacitor and the winding resistance of filter inductor is proposed leading to their closed form expressions in terms of system parameters. Using these, procedure to predict the closed-loop instability induced due to the input filter is exemplified with illustrative calculations.

An Improved Control Strategy for a Four-Leg Grid-Forming Power Converter under Unbalanced Load Conditions

This paper proposes an improved multiloop control strategy for a three-phase four-leg voltage source inverter (VSI) operating with highly unbalanced loads in an autonomous distribution network. The main objective is to balance the output voltages of the four-leg inverter under unbalanced load conditions. The proposed control strategy consists of a proportional-integral (PI) voltage controller and a proportional current loop in each phase. The voltage controller and the current control loop are, respectively, used to regulate the instantaneous output voltage and generate the pulse width modulation (PWM) voltage command with zero steady-state tracking error and fast transient response. A voltage decoupling feedforward path is also used to enhance the system robustness. Since the outer voltage loop operates in the synchronous reference frame, tuning and stability analysis of the PI controller is far from being straightforward. In order to cope with this challenge, the stationary reference frame equivalent of the voltage controller in the rotating frame is derived. Subsequently, a systematic design based on a frequency response approach is provided. Simulation results are also carried out using the DIgSILENT PowerFactory software to verify the effectiveness of the suggested control strategy.

Space Vector Modulation Technique for 3-Level NPC Converter with Constant Switching Frequency

This paper presents a simple Space Vector Modulation (SVM) methodology for a three-level NPC converter. Nearest three vectors (NTV) and corresponding duty cycles are deduced through simple generic mathematical expressions. Extra degrees of freedom of NPC converter are used to fully benefit from SVM advantages and to control the switching frequency. Simulation and experimental results are presented and discussed to validate the proposed methodology.

Optimal Method for Catastrophic Faults Diagnosis in RC Ladder Network

The RC ladder network has been analyzed for various catastrophic fault detection using minimal number of measurements. Generally, electronic circuit testing procedure is very exhaustive and includes higher cost; the presented approach will save fault diagnosis time. It is not possible to analyze the big RC ladder network to give the good fault coverage, so the ladder network has been broken into segments of different sizes. However, if segment size is small, it will cause more area overhead compared to bigger step size in terms of the interconnections and pins on the integrated circuit. A systematic and detailed analysis for one-step, two-step, three-step, and four-step RC ladder networks has been carried out for various faults and optimal step size is proposed. It has been investigated that three measurements are optimal to localize different catastrophic faults in a RC ladder network.

High-Voltage Converter for the Traction Application

High-voltage converter employing IGCT switches (VDC=2800 V) for traction application is presented. Such a power traction drive operates with an unstable input voltage over 2000⋯4000 V DC and with an output power up to 1200 kW. The original power circuit of the high-voltage converter is demonstrated. Development of the attractive approach to designing the low-loss snubber circuits of the high-frequency IGCT switches is proposed. It is established on the complex multilevel analysis of the transient phenomena and power losses. The essential characteristics of the critical parameters under transient modes and the relation between the snubber circuit parameters and the losses are discussed. Experimental results for the prototype demonstrate the properties of new power circuit. The test results confirm the proposed high-voltage converter performance capability as well as verifying the suitability of the conception for its use in the Russian suburban train power system and other high-voltage applications.