Inherent Short-circuit Protection Research Articles

DC-Link Current Optimal Control of Current Source Converter in DFIG

In this paper, a novel control strategy of current source converter (CSC) is proposed for doubly-fed induction generator (DFIG) wind energy conversion system (WECS). Most of the studies on wind forms are based on voltage source converter, nevertheless, with the development of semiconductor technology and high switching frequency reverse block insulated gate bipolar transistor (RB-IGBT) devices being used in CSCs, the shortcomings of conventional CSCs including low switching frequency, large passive devices and slow dynamic performance can be overcome. Furthermore, WECS based on CSCs has various advantages, such like robustness, inherent short-circuit protection, fault ride through capability and so on. To implement the CSCs in DFIG wind energy conversion system, this paper analyzes the system configuration, operation principles, modulation strategy and control strategy. In addition, a novel control strategy based on DC-Link current optimal control is proposed. The simulation and prototype experiments verily the validity of system configuration and control strategy.

Real-time performance evaluation of two-quadrant z-source DC-DC converter for DC drive

This paper contributes to real-time performance evaluation of two-quadrant z-source DC-DC converter drive for industrial application. Regulating the switching duty ratio of the converter produces the desired output voltage level. Z-source DC-DC converter has additional qualities over a traditional buck-boost converter such as higher boost factor at low switching duty ratio, more reliable, inherent short circuit protection and impedance network that behaves as a second-order filter. Z-source converter-fed separately excited DC-drive model is developed in MATLAB/Simulink and executed in field programmable gate array (FPGA)-based real-time digital simulator (RTDS) at fixed-time step of 10 μs and the constant switching frequency is 5 KHz. The real-time simulation results present the real-time performance of the z-source converter-fed DC-drive system during motoring and regenerative braking mode. Small signal analysis is done using state space averaging approach to design a suitable controller for closed-loop drive system. A laboratory-based low voltage hardware prototype of z-source DC-DC converter system is developed utilising a real-time digital simulator (OP5600) as a rapid control prototype.

Multilevel CSC System Based on Series–Parallel Connected Three-Phase Modules With Optimized Carrier-Shift SPWM

Current source converter (CSC) is widely used in high power applications. To increase the system power rating, both series and parallel connections can be adopted and implemented easily. In this article, a mixed series-parallel CSC structure is proposed for high power application. An optimized carrier-shift sinusoidal pulsewidth modulation (SPWM) is adopted for the mixed system to simultaneously improve the dc-link voltage quality and achieve multilevel ac output, which can potentially reduce the size of dc- and ac-side filters. Meanwhile, the system reliability can be significantly improved due to the modular design with carrier-shift SPWM and inherent short-circuit protection of CSC. With these advantages, the proposed mixed series-parallel CSC structure can be an attractive candidate for medium-voltage drives, high-voltage direct current, and offshore wind power applications. Simulation and experimental results verify the effectiveness of the novel mixed series-parallel CSC system with optimized carrier-shift SPWM.

Multilevel current source converters for high power medium voltage applications

In medium voltage high power applications, multi-level current source converters (CSCs) are good candidate to increase system power region, reliability, and the quality of output waveforms. Compared with widely researched voltage source multi-level converters (MLCs), the current source MLCs have the advantages of inherent short-circuit protection, high power capability and high quality of output current waveforms. The main features of MLCs include reduced harmonics, lower switching frequency and reduced current stress on each device which is a particularly important for high power application with low voltage and high current requirements. This paper conducts a general review of the current research about MLCs in higher power medium voltage application. The different types of parallel structure based MLCs and the modulation methodologies will be introduced and compared. Specifically, the circuit analysis of the common-mode (CM) loop for parallel structures will be conducted, the common-mode voltage (CMV) and circulating current suppression methods developed on the base of multilevel modulations will be addressed.

A Five-Level Current-Source Inverter for Grid-Connected or High-Power Three-Phase Wound-Field Synchronous Motor Drives

Simple converter structure, inherent short-circuit protection and regenerative capability are the most important advantages of current-source inverters (CSI’s) which have made them suitable for medium-voltage high-power drives. Usually in grid-connected gas turbine generators or pumped storage hydro power plants, efficient and reliable current-source load-commutated inverters (LCI’s) with thyristor switches are employed. Also, this type of CSI is widely used in very large drives with power ratings of tens of megawatts to supply wound-field synchronous motors (WFSM’s). However, LCI’s suffer from some disadvantages such as large torque pulsations, poor power factor, and start-up criticalities. In this paper, a novel multilevel-based CSI is proposed. The proposed converter consists of one LCI and one CSI bridge with self-turn-off switches along with a voltage clamping circuit. The CSI switches are forced commutated; hence, a voltage clamping circuit is employed to limit voltage spikes caused by current variations in inductive paths during commutation transients. Drastic reduction in harmonic distortion of stator current and improved fundamental power factor are achieved by the proposed topology. In addition, torque pulsations are reduced remarkably for normal and starting operating conditions. Comprehensive analysis of the proposed structure is presented and the design of converter components is elaborated.

Modular symmetric and asymmetric reduced count switch multilevel current source inverter

Current source inverters (CSIs) have prominent features compared to voltage source inverters. The CSIs are less affected by grid voltage fluctuations, their control is simple and they have inherent short-circuit protection. This study proposes a novel multilevel CSI based on modular cells. The proposed topology is performed based on the parallel connection of two-switch modules. According to the value of current sources in each module, the proposed configuration can be operated in two modes of operation: symmetric and asymmetric. A comparison study is carried out between the proposed topology, the cascaded H-bridge and a recently developed topology in terms of the number of switches, the number of sources, total switch device power, and power losses. The comparison study shows a great improvement in performance of the proposed symmetric and asymmetric topologies compared to conventional structures. In addition, the proposed circuit shows an interesting feature which is the common emitter connection of the main switches. This arrangement leads to simple gate drive circuits. Finally, seven-level symmetric topology and fifteen-level asymmetric topology are simulated and the laboratory prototypes of them are implemented. The presented simulation and experimental results validate the feasibility of proposed topologies.

Design of buck‐type current source inverter fed brushless DC motor drive and its application to position sensorless control with square‐wave current

Owing to the widely used brushless DC motors (BDCMs) in high-efficiency applications, many position sensorless control methods based on voltage source inverters had been developed in the literature. Recently, current source inverters (CSIs) are receiving more and more attention because of their inherent short-circuit protection characteristics. But no position sensorless control for buck-type CSI with square-wave current had been found in the literature. In this study, the buck-type CSI-fed BDCM drive is designed and its application to the square-current position sensorless control is first proposed. The provided simulation and experimental results verify the effectiveness of the proposed CSI-based position sensorless control.

An Improved $LLC$ Resonant Inverter for Induction-Heating Applications With Asymmetrical Control

This paper proposes a modified <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LLC</i> resonant load configuration of a full-bridge inverter for induction-heating applications. The <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LLC</i> load configuration is a combination of a series inductor, a matching transformer, and an inductor and a capacitor connected in parallel. The output power is controlled using the asymmetrical voltage-cancellation technique. With the use of a phase-locked loop control, the operating frequency is automatically adjusted to maintain a small constant lagging phase angle under load-parameter variation during the heating process. The proposed configuration has the benefit of smaller inductance and inherent short-circuit protection capability in case a short circuit occurs at the induction coil or from transformer saturation. The validity of the proposed method is verified through computer simulation and hardware experiment at an operating frequency range of 108.7-110.6 kHz.

A Direct Converter for High-Energy Physics Applications

This paper describes the development of a high-frequency resonant-power converter for high-energy physics (CW) applications. The proposed converter topology has been demonstrated by the construction of a laboratory demonstrator that produces 25 kV with less than 1% ripple at 1 A (25 kW). The converter is a direct converter topology operating without the use of a dc link, significantly reducing the size and weight of the converter and resulting in a relatively high-energy density converter. A high-frequency (20 kHz) resonant circuit is employed which provides inherent short-circuit protection of the converter from the output, while reducing the turns ratio of the transformer. The transformer is integrated into the resonant circuit and operates at the same frequency as the resonant circuit (20 kHz). To achieve high-frequency and high-flux operation of the transformer, an amorphous (nanocrystalline) core is used, further reducing the physical size of the converter. Use of the resonant circuit also allows for soft switching of the IGBTs. High-frequency operation allows for a reduction in size of both the transformer and output filters, thereby removing the need for operation with a crowbar. All of the techniques implemented in the prototype converter may be extended to higher voltage higher power systems.

Buck–boost thyristor-based PWM current-source inverter

The traditional thyristor-based current-source inverter (CSI) has been reported for use in synchronous motor drives and utility-grid-interfacing systems, where its inherent output short-circuit protection and direct-current control have been added advantages. Despite these advantages, the thyristor-based CSI is known to suffer from poor waveform quality owing to its low-frequency six-step switching and only step-up (boost) operation. Both disadvantages severely constrain the use of thyristor-based CSI for utility interfacing, especially when the inverter input is fed from renewable-energy sources whose outputs vary continuously. To address the above limitations, the paper proposes the design of a buck–boost thyristor-based CSI with pulse-width-modulated (PWM) control. This CSI uses a unique X-shaped LC impedance network connected to its DC link for current-boosting and a controlled switch for actively commutating its main thyristor devices using an appropriately designed digital PWM scheme. The inverter is tested experimentally using a laboratory prototype, and is shown to perform smooth DC–AC current conversion, making it a competitive solution for both utility and industry applications.

Resonant converter with inherent short-circuit protection

Using a systematic procedure for classifying resonant converters, we have synthesized a zero-voltage switching resonant structure with inherent short-circuit protection. We analyze the operating modes of the disclosed converter and derive the control characteristic curve. Experimental verification is presented in a 100-W prototype.

Series–parallel resonant converter for an EDM power supply

A new EDM impulse generator based on a HF-switched dc to dc series–parallel resonant converter is presented. The converter generates the necessary voltage, first to ionize the dielectric and then to maintain the discharge and, provided that it operates in constant current mode, the impulse generator has inherent short-circuit protection. As the switches turn on at zero voltage the converter presents minimum switching losses. The characteristics of this power electronic system are high speed control of the quality of each pulse, small size and light weight suitable for on-site machining. The EDM power supply has been validated to perform operations in a nuclear power plant application. The design and results are described in this paper.

Wide-load-range resonant converter supplying the SAE J-1773 electric vehicle inductive charging interface

The recommended practice for electric vehicle battery charging using inductive coupling (SAE J-1773), published in January 1995 by the Society of Automotive Engineers, Inc., outlines values and tolerances for critical vehicle inlet parameters which must be considered when selecting a coupler driving topology. The inductive coupling vehicle inlet contains a significant discrete capacitive component in addition to low magnetizing and high leakage inductances. Driving the vehicle interface with a variable-frequency series-resonant power converter results in a four-element topology with many desirable features: unity transformer turns ratio; buck/boost voltage gain; current-source operation; monotonic power transfer characteristic over a wide load range; throttling capability down to no load; high-frequency operation; narrow modulation frequency range; use of zero-voltage-switched MOSFETs with slow integral diodes; high efficiency; inherent short-circuit protection; soft recovery of output rectifiers; and secondary d/spl nu//dt control and current waveshaping for the cable, coupler and vehicle inlet, resulting in enhanced electromagnetic compatibility. In this paper, characteristics of the topology are derived and analyzed using two methods. Firstly, the fundamental mode AC sine-wave approximation is extended to battery loads and provides a simple, yet insightful, analysis of the topology. A second method of analysis is based on the more accurate, but complex, time-based modal approach. Finally, typical experimental results verify the analysis of the topology presented in the paper.

A capacitor charging power supply utilizing a Ward converter

A prototype capacitor-charging power supply (CCPS) that utilizes a Ward converter is presented. This converter is a member of the family of resonant converters and is capable of zero-current switching. It is applicable to capacitor charging because of its inherent short-circuit protection and its insensitivity to the value of the load capacitance. The converter is controlled using a constant on-time constant frequency scheme that allows the utilization of zero-current switching techniques. The prototype CCPS is capable of charging various values of load capacitors up to 1000 V DC. Waveforms that show single- and repetitive-charge operation of the CCPS are presented. >

A current fed inverter with inherent short circuit protection and suppression of ringing

A qualitative analysis of an inverter that has inherent short circuit protection and suppression of ringing is described. The inverter feeds into a resonant tank circuit such as used for induction-heating at 100 kHz. An experimental unit is described and waveforms are given.

Inherent Overload Protection for the Series Resonant Converter

The overload characteristics of the full bridge series resonant power converter are considered. This includes analyses of the two most common control methods presently in use. The first of these uses a current zero crossing detector to synchronize the control signals and is referred to as the σ controller. The second is driven by a voltage controlled oscillator and is referred to as the γ controller. It is shown that the γ controller has certain reliability advantages in that it can be designed with inherent short circuit protection. Experimental results are included for an 86 kHz converter using power metal-oxide-semiconductor field-effect transistors (MOSFETs).