scispace - formally typeset
Search or ask a question

Showing papers by "Huai Wang published in 2014"


Journal ArticleDOI
TL;DR: This review serves to provide a clear picture of the state-of-the-art research in this area and to identify the corresponding challenges and future research directions for capacitors and their dc-link applications.
Abstract: DC-link capacitors are an important part in the majority of power electronic converters which contribute to cost, size and failure rate on a considerable scale. From capacitor users' viewpoint, this paper presents a review on the improvement of reliability of dc link in power electronic converters from two aspects: 1) reliability-oriented dc-link design solutions; 2) conditioning monitoring of dc-link capacitors during operation. Failure mechanisms, failure modes and lifetime models of capacitors suitable for the applications are also discussed as a basis to understand the physics-of-failure. This review serves to provide a clear picture of the state-of-the-art research in this area and to identify the corresponding challenges and future research directions for capacitors and their dc-link applications.

882 citations


Journal ArticleDOI
TL;DR: In this article, the three major aspects of power electronics reliability are discussed, respectively, which cover physics-of-failure analysis of critical power electronic components, state-ofthe-art design for reliability process and robustness validation, and intelligent control and condition monitoring to achieve improved reliability under operation.
Abstract: Power electronics has progressively gained an important status in power generation, distribution, and consumption. With more than 70% of electricity processed through power electronics, recent research endeavors to improve the reliability of power electronic systems to comply with more stringent constraints on cost, safety, and availability in various applications. This paper serves to give an overview of the major aspects of reliability in power electronics and to address the future trends in this multidisciplinary research direction. The ongoing paradigm shift in reliability research is presented first. Then, the three major aspects of power electronics reliability are discussed, respectively, which cover physics-of-failure analysis of critical power electronic components, state-of-the-art design for reliability process and robustness validation, and intelligent control and condition monitoring to achieve improved reliability under operation. Finally, the challenges and opportunities for achieving more reliable power electronic systems in the future are discussed.

531 citations


Journal ArticleDOI
TL;DR: In this article, the LVRT capability of three mainstream single-phase transformerless PV inverters under grid faults is explored in order to map future challenges, and control strategies with reactive power injection are also discussed.
Abstract: Transformerless photovoltaic (PV) inverters are going to be more widely adopted in order to achieve high efficiency, as the penetration level of PV systems is continuously booming. However, problems may arise in highly PV-integrated distribution systems. For example, a sudden stoppage of all PV systems due to anti-islanding protection may contribute to grid disturbances. Thus, standards featuring with ancillary services for the next-generation PV systems are under a revision in some countries. The future PV systems have to provide a full range of services as what the conventional power plants do, e.g., low-voltage ride-through (LVRT) under grid faults and grid support service. In order to map future challenges, the LVRT capability of three mainstream single-phase transformerless PV inverters under grid faults is explored in this paper. Control strategies with reactive power injection are also discussed. The selected inverters are the full-bridge (FB) inverter with bipolar modulation, the FB inverter with dc bypass, and the Highly Efficient and Reliable Inverter Concept (HERIC). A 1-kW single-phase grid-connected PV system is analyzed to verify the discussions. The tests confirmed that, although the HERIC inverter is the best candidate in terms of efficiency, it is not very particularly feasible in case of a voltage sag. The other two topologies are capable of providing reactive current during LVRT. A benchmarking of those inverters is also provided in this paper, which offers the possibility to select appropriate devices and to further optimize the transformerless system.

307 citations


Journal ArticleDOI
TL;DR: In this article, a voltage source in series with the dc bus line is connected to compensate the ripple voltage on the dc-link capacitor, so as to make the output have a near zero ripple voltage.
Abstract: A technique for reduction of the dc-link capacitance in a capacitor-supported system is presented. The concept is based on connecting a voltage source in series with the dc bus line to compensate the ripple voltage on the dc-link capacitor, so as to make the output have a near zero ripple voltage. Since the voltage compensator processes small ripple voltage on the dc link and reactive power only, it can be implemented with low-voltage devices. The overall required energy storage of the dc-link, formed by a reduced value of dc-link capacitor and the voltage compensator, is reduced, allowing the replacement of popularly used electrolytic capacitors with alternatives of longer lifetime, like power film capacitors, or extending the system lifetime even if there is a significant reduction in the capacitance of electrolytic capacitors due to the aging effect. Comprehensive analysis on the static and dynamic characteristics of the system, and hold-up time requirement will be discussed. The proposed technique is exemplified on an ac-dc-dc power conversion system. Theoretical predictions are favorably verified by experimental results.

205 citations


Journal ArticleDOI
TL;DR: In this paper, reactive power injection (RPI) strategies for single-phase photovoltaic (PV) systems are explored in light of this, and the design and implementation considerations for the characterized RPI strategies are also discussed.
Abstract: As the development and installation of photovoltaic (PV) systems are still growing at an exceptionally rapid pace, relevant grid integration policies are going to change consequently in order to accept more PV systems in the grid. The next-generation PV systems will play an even more active role like what the conventional power plants do today in the grid regulation participation. Requirements of ancillary services like low-voltage ride-through (LVRT) associated with reactive current injection and voltage support through reactive power control have been in effectiveness in some countries, e.g., Germany and Italy. Those advanced features can be provided by next-generation PV systems and will be enhanced in the future to ensure an even efficient and reliable utilization of PV systems. In light of this, reactive power injection (RPI) strategies for single-phase PV systems are explored in this paper. The RPI possibilities are as follows: 1) constant average active power control; 2) constant active current control; 3) constant peak current control; and 4) thermal optimized control strategy. All those strategies comply with the currently active grid codes but are with different objectives. The proposed RPI strategies are demonstrated first by simulations and also tested experimentally on a 1-kW singe-phase grid-connected system in LVRT operation mode. Those results show the effectiveness and feasibilities of the proposed strategies with reactive power control during LVRT operation. The design and implementation considerations for the characterized RPI strategies are also discussed.

195 citations


Proceedings ArticleDOI
16 Mar 2014
TL;DR: In this paper, the authors explored reactive power injection (RPI) strategies for single-phase photovoltaic (PV) systems in low-voltage ride-through (LVRT) operation.
Abstract: As the development and installation of photovoltaic (PV) systems are still growing at an exceptionally rapid pace, relevant grid integration policies are going to change consequently in order to accept more PV systems in the grid. The next generation PV systems will play an even more active role like what the conventional power plants do today in the grid regulation participation. Requirements of ancillary services like Low-Voltage Ride-Through (LVRT) associated with reactive current injection and voltage support through reactive power control, have been in effectiveness in some countries. Those advanced features can be provided by next-generation PV systems, and will be enhanced in the future to ensure an even efficient and reliable utilization of PV systems. In the light of this, Reactive Power Injection (RPI) strategies for single-phase PV systems are explored in this paper. The RPI possibilities are: a) constant average active power control, b) constant active current control, c) constant peak current control and d) thermal optimized control strategy. All those strategies comply with the currently active grid codes, but are with different objectives. The thermal optimized control strategy is demonstrated on a 3 kW single-phase PV system by simulations. The other three RPI strategies are verified experimentally on a 1 kW singe-phase system in LVRT operation mode. Those results show the effectiveness and feasibilities of the proposed strategies with reactive power control during LVRT operation. The design and implementation considerations for the characterized strategies are also discussed.

150 citations


Journal ArticleDOI
TL;DR: The essence of the proposed concept lies in the selection of an appropriate power limit for the CPG control to achieve an improved thermal performance and an increased utilization factor of PV inverters, and thus, to cater for a higher penetration level of PV systems with intermittent nature.
Abstract: This letter proposes a hybrid power control concept for grid-connected photovoltaic (PV) inverters. The control strategy is based on either a maximum power point tracking control or a constant power generation (CPG) control depending on the instantaneous available power from the PV panels. The essence of the proposed concept lies in the selection of an appropriate power limit for the CPG control to achieve an improved thermal performance and an increased utilization factor of PV inverters, and thus, to cater for a higher penetration level of PV systems with intermittent nature. A case study on a single-phase PV inverter under yearly operation is presented with analyses of the thermal loading, lifetime, and annual energy yield. It has revealed the trade-off factors to select the power limit and also verified the feasibility and the effectiveness of the proposed control concept.

146 citations


Journal ArticleDOI
TL;DR: In this paper, a robust passive damping method for LLCL-filter-based grid-tied inverters is proposed, which effectively can suppress the possible resonances even if the grid inductance varies in a wide range.
Abstract: In order to minimize the effect of the grid harmonic voltages, harmonic compensation is usually adopted for a grid-tied inverter. However, a large variation of the grid inductance challenges the system stability in case a high-order passive filter is used to connect an inverter to the grid. Although in theory, an adaptive controller can solve this problem, but in such a case the grid inductance may need to be detected online, which will complicate the control system. This paper investigates the relationship between the maximum gain of the controller that still keeps the system stable and the Q-factor for a grid-tied inverter with an RL series or an RC parallel damped high-order power filter. Then, a robust passive damping method for LLCL-filter-based grid-tied inverters is proposed, which effectively can suppress the possible resonances even if the grid inductance varies in a wide range. Simulation and experimental results are in good agreement with the theoretical analysis.

125 citations


01 Jan 2014
TL;DR: In this paper, the authors proposed a hybrid power control for grid-connected PV inverters based on either a Maximum Power Point Tracking (MPPT) control or a Constant Power Generation (CPG) control depending on the instantaneous available power from the PV panels.
Abstract: This letter proposes a hybrid power control con- cept for grid-connected Photovoltaic (PV) inverters. The control strategy is based on either a Maximum Power Point Tracking (MPPT) control or a Constant Power Generation (CPG) control depending on the instantaneous available power from the PV panels. The essence of the proposed concept lies in the selection of an appropriate power limit for the CPG control to achieve an improved thermal performance and an increased utilization factor of PV inverters, and thus to cater for a higher penetration level of PV systems with intermittent nature. A case study on a single-phase PV inverter under yearly operation is presented with analyses of the thermal loading, lifetime, and annual energy yield. It has revealed the trade-off factors to select the power limit and also verified the feasibility and the effectiveness of the proposed control concept. may severely exceed the initial project outlay. The energy storage elements are mostly installed at the substation side instead of in the individual inverters also considering cost and maintenance. Since the above solutions introduce considerable investments, two kinds of hybrid control concepts have been proposed in prior-art research. In (3), an MPPT control with a reduced power mode control has been introduced to avoid dynamic overloading in a stand-alone wind-PV generation system. The selection of the power limit for the reduced power mode control is dynamically in accordance to the power oscillations during wind turbine soft stalling. The reduced power mode operation is achieved by modifying the MPPT algorithm based on a virtual MPPT. In (8) , an MPPT control with power curtailment control is proposed to prevent over- voltage of low voltage feeders by limiting the excessive power injection to the grid from PV inverters. The selection of the power limit for the power curtailment control depends on the upper voltage limit of the low voltage feeders. These control concepts can effectively avoid the over-loading issue with an acceptable reduction of the overall energy generation (9). However, the issue on the utilization of PV inverter remains and the thermal performance of the PV inverters is still unknown.

101 citations


Proceedings ArticleDOI
16 Mar 2014
TL;DR: In this article, a constant power generation (CPG) control concept of PV inverters is proposed to meet the need of this emerging ancillary service provided by future PV systems, which can contribute to a weakened requirement of grid expansion and at the same time an increased penetration level.
Abstract: With an imperative demand of clean and reliable electricity generation in some countries, the increasing adoption of new photovoltaic (PV) systems pushes the Distribution System Operators (DSOs) to expand the transmission/distributed lines. However, the potential cost brought by such extensions and increased maintenances introduce new obstacles. In view of this concern, the DSOs starts to reduce PV installations in order to avoid an extension of the power infrastructure. Besides, another alternative solution is to limit the maximum feed-in power of the existing PV systems to a certain level. It can contribute to a weakened requirement of grid expansion and at the same time an increased penetration level. Therefore, to meet the need of this emerging ancillary service provided by future PV systems, a Constant Power Generation (CPG) control concept of PV inverters is proposed in this paper. Accordingly, it is worth investigating into two main issues: a) analyzing the reduction of the energy yield due to CPG control to study its feasibility from an economic point of view and b) developing robust CPG control methods, otherwise, it may introduce instabilities. Thereby, the implementation possibilities for PV systems in CPG operation mode are also discussed in this paper. Additionally, the loss of energy is calculated to reveal the viability of the proposed CPG control method. Operation examples of a PV system are presented to show the effectiveness of the CPG control method to unload the distributed grid.

81 citations


Journal ArticleDOI
TL;DR: This paper introduces a real field mission profile oriented design tool for the new generation of grid-connected photovoltaic (PV)-inverter applications based on silicon carbide devices that considers the mission profile from the real field where the converter will operate.
Abstract: This paper introduces a real field mission profile oriented design tool for the new generation of grid-connected photovoltaic (PV)-inverter applications based on silicon carbide devices. The proposed design tool consists of a grid-connected PV-inverter model, an electrothermal model, a converter safe operating area (SOA) model, a mission profile model, and an evaluation block. The PV-system model involves a three-level bipolar switch neutral point clamped (3L-BS NPC) inverter connected to the three-phase grid through an LCL filter. Moreover, the SOA model calculates the required converter heatsink thermal impedance Z th_ H in order to perform in a safe mode for the whole operating range. Furthermore, the proposed design tool considers the mission profile (the measured solar irradiance and ambient temperature) from the real field where the converter will operate. Thus, a realistic loading of the converter devices is achieved. To consider one-year real field measurements of the mission profile, an accurate long-term simulation model is developed. The model predicts the junction and case temperature of the converter devices, for three different case scenarios. In the first case, a one-year mission profile is used into the model with a sampling rate of 5 min. For the second and third case, a more detailed analysis is performed for a one-week mission profile (in the winter-summer time) with a sampling rate of 25 s. The simulation results shows the thermal loading distribution among the converter devices (MOSFET, IGBT+FD) in terms of junction (average, peak, ΔT) and case (average) temperature for all three simulation cases. Finally, the evaluation block is used to analyze the results in order to perform a thermal-loading-based classification of the converter devices.

Journal ArticleDOI
TL;DR: In this paper, a junction temperature control concept for the switching devices in a single-phase PV inverter is proposed to reduce the junction temperature stress, and thus to achieve improved reliability of a PV inverters.
Abstract: Future photovoltaic (PV) inverters are expected to comply with more stringent grid codes and reliability requirements, especially when a high penetration degree is reached, and also to lower the cost of energy. A junction temperature control concept is proposed in this study for the switching devices in a single-phase PV inverter in order to reduce the junction temperature stress, and thus to achieve improved reliability of a PV inverter. The thermal stresses of the switching devices are analysed during low-voltage ride-through operation with different levels of reactive power injection, allowing an optimal design of the proposed control scheme with controlled mean junction temperature and reduced junction temperature swings. The effectiveness of the control method in terms of both thermal performance and electrical performance is validated by the simulations and experiments, respectively. Both test results show that single-phase PV inverters with the proposed control approach not only can support the grid voltage recovery in low-voltage ride-through operation but also can improve the overall reliability with a reduced junction temperature.

Proceedings ArticleDOI
18 Sep 2014
TL;DR: In this article, the authors investigated the ways of reducing ripple current stresses of DC-link capacitors in back-to-back converters and proposed control strategies to achieve either an extended lifetime for a designed DClink or a reduced DClink size for fulfilling a specified lifetime target.
Abstract: Three-phase back-to-back converters have a wide range of applications (e.g. wind turbines) in which the reliability and cost-effectiveness are of great concern. Among other com- ponents and interconnections, DC-link capacitors are one of the weak links influenced by environmental stresses (e.g. ambient temperature, humidity, etc.) and operating stresses (e.g. voltage, ripple current). This paper serves to investigate the ways of reducing ripple current stresses of DC-link capacitors in back-to- back converters. The outcome could benefit to achieve either an extended lifetime for a designed DC-link or a reduced DC-link size for fulfilling a specified lifetime target. The proposed control strategies have been demonstrated on a study case of a 1.5 kW converter prototype. The experimental verifications are in well agreement with the theoretical analyses.

Proceedings ArticleDOI
18 May 2014
TL;DR: In this paper, a comparison study between a Si-based 3L-Diode Neutral Point Clamped (DNPC) and a SiC-based 2L-Full Bridge (FB) three-phase PV-inverter topologies in terms of efficiency, thermal loading distribution and costs was conducted.
Abstract: The recent developments in wide band-gap devices based GaN and SiC is showing a high impact on the PV-inverter technology, which is strongly influenced by efficiency, power density and cost. Besides the high efficiency of PV inverters, also the mechanical size, the compactness and simple structure have an important role in the cost reduction. To increase the efficiency of PV systems, most of solutions for PV inverters have moved to three-level (3L) structures reaching typical efficiencies of 98% due to low switching losses of 600V Si IGBT or MOSFET and reduced core losses in the filter. With the appearance of SiC 1200V MOSFETs, it becomes possible to return to more simple two-level (2L) structure with comparable efficiency but high potential to reduce the overall cost. This paper deals with a comparison study between a Si-based 3L-Diode Neutral Point Clamped (DNPC) and a SiC-based 2L-Full Bridge (FB) three-phase PV-inverter topologies in terms of efficiency, thermal loading distribution and costs. Moreover the above mentioned PV-inverters are built and tested in laboratory in order to validate the obtained results.

Proceedings ArticleDOI
13 Nov 2014
TL;DR: In this article, a reliability-oriented design tool for a new generation of grid connected PV-inverters is presented, which consists of a real field Mission Profile (MP) model (for one year operation in USA-Arizona), a PV-panel model, a grid-connector model, an Electro-Thermal model and the lifetime model of the power semiconductor devices.
Abstract: This paper introduces a reliability-oriented design tool for a new generation of grid connected PV-inverters. The proposed design tool consists of a real field Mission Profile (MP) model (for one year operation in USA-Arizona), a PV-panel model, a grid connected PV-inverter model, an Electro-Thermal model and the lifetime model of the power semiconductor devices. A simulation model able to consider a one year real field operation conditions (solar irradiance and ambient temperature) is developed. Thus, one year estimation of the converter devices thermal loading distribution is achieved and is further used as an input to a lifetime model. The proposed reliability oriented design tool is used to study the impact of MP-variation, Gate-Driver (GD) parameters variation and device degradation in the PV- inverter lifetime. The obtained results indicate that in order to improve the accuracy of the lifetime estimation it is crucial to consider also the device degradation feedback. Moreover the MP of the field where the PV-inverter is operating and the GD- parameters selection has an important impact in the converter reliability and it should be considered from the design stage to better optimize the converter design margin.

Proceedings ArticleDOI
13 Nov 2014
TL;DR: In this paper, the authors translate real-field mission profiles (i.e., solar irradiance and ambient temperature) into voltage, current, and temperature stresses of the DC capacitors under both normal and abnormal grid conditions.
Abstract: DC capacitors are widely adopted in grid-connected PhotoVoltaic(PV) systems for power stabilization and control decoupling. They have become one of the critical components in grid-connected PV inverters in terms of cost, reliability and volume. The electrical and thermal stresses of the DC capacitors are varying along with the intermittent solar PV energy (i.e. of weather-dependency) and also the grid conditions (e.g. voltage fault transients). This paper serves to translate real-field mission profiles (i.e. solar irradiance and ambient temperature) into voltage, current, and temperature stresses of the DC capacitors under both normal and abnormal grid conditions. As a con- sequence, this investigation provides new insights into the sizing and reliability prediction of those capacitors with respect to prior- art studies. Two study cases on a single-stage PV inverter and a two-stage PV inverter are demonstrated by simulations and experiments. The results have verified the discussions.

Proceedings ArticleDOI
13 Nov 2014
TL;DR: In this paper, the authors investigated the reliability performance of the power devices (e.g. IGBTs) used in PV inverters with the constant power generation (CPG) control under different feed-in power limits.
Abstract: Grid operation experiences have revealed the neces- sity to limit the maximum feed-in power from PV inverter systems under a high penetration scenario in order to avoid voltage and frequency instability issues. A Constant Power Generation (CPG) control method has been proposed at the inverter level. The CPG control strategy is activated only when the DC input power from PV panels exceeds a specific power limit. It enables to limit the maximum feed-in power to the electric grids and also to improve the utilization of PV inverters. As a further study, this paper investigates the reliability performance of the power devices (e.g. IGBTs) used in PV inverters with the CPG control under different feed-in power limits. A long-term mission profile (i.e. solar irradiance and ambient temperature) based stress analysis approach is extended and applied to obtain the yearly electrical and thermal stresses of the power devices, allowing a quantitative prediction of the power device lifetime. A study case on a 3 kW single-phase PV inverter has demonstrated the advantages of the CPG control in terms of improved reliability.

Proceedings ArticleDOI
Rui Wu1, Huai Wang1, Ke Ma1, Pramod Ghimire1, Francesco Iannuzzo1, Frede Blaabjerg1 
13 Nov 2014
TL;DR: In this article, a Cauer thermal model for a 1700 V/1000 A IGBT module with temperature-dependent thermal resistances and thermal capacitances is proposed for circuit-level simulation.
Abstract: Thermal impedance of IGBT modules may vary with operating conditions due to that the thermal conductivity and heat capacity of materials are temperature dependent. This paper proposes a Cauer thermal model for a 1700 V/1000 A IGBT module with temperature-dependent thermal resistances and thermal capacitances. The temperature effect is investigated by Finite Element Method (FEM) simulation based on the geometry and material information of the IGBT module. The developed model is ready for circuit-level simulation to achieve an improved accuracy of the estimation on IGBT junction temperature and its relevant reliability aspect performance. A test bench is built up with an ultra-fast infrared (IR) camera to validate the proposed thermal impedance model.

Proceedings ArticleDOI
16 Mar 2014
TL;DR: In this article, a new method to selectively control the amount of dc-link voltage ripple by processing the desired reactive power by a DC/DC converter in an isolated AC/DC or AC/AC/DC/AC system is proposed.
Abstract: A new method to selectively control the amount of dc-link voltage ripple by processing the desired reactive power by a DC/DC converter in an isolated AC/DC or AC/DC/AC system is proposed. The concept can reduce the dc-link capacitors used for balancing the input and output power and thereby limiting the voltage ripple. It allows the use of a smaller dc-link capacitor and hence a longer lifetime and at the same time high power density and low cost can be achieved. The isolated DC/DC converter is controlled to process the desired reactive power in addition to the active power. The control system to achieve this selective degree of compensation is proposed and verified by Simulations.

Journal ArticleDOI
TL;DR: The obtained results indicate that the MP of the field where the PV-inverter is operating has an important impact in the converter lifetime expectation, and it should be considered in the design stage to better optimize the converter design margin.

Proceedings ArticleDOI
08 Apr 2014
TL;DR: In this article, the authors describe an unprecedented fast and accurate approach to electro-thermal simulation of power IGBTs suitable to simulate normal as well as abnormal conditions based on an advanced physics-based PSpice model together with ANSYS/Icepak FEM thermal simulator in a closed loop.
Abstract: A basic problem in the IGBT short-circuit failure mechanism study is to obtain realistic temperature distribution inside the chip, which demands accurate electrical simulation to obtain power loss distribution as well as detailed IGBT geometry and material information. This paper describes an unprecedented fast and accurate approach to electro-thermal simulation of power IGBTs suitable to simulate normal as well as abnormal conditions based on an advanced physics-based PSpice model together with ANSYS/Icepak FEM thermal simulator in a closed loop. Through this approach, significantly faster simulation speed with respect to conventional double-physics simulations, together with very accurate results can be achieved. A case study is given which presents the detailed electrical and thermal simulation results of an IGBT module under short circuit conditions. Furthermore, thermal maps in the case of non-uniform threshold voltage/ solder resistance/ gate resistance among the cells are presented in comparison with the case of uniform distribution, evidencing the capabilities of studying short-circuit of aged devices by the presented technique.

Proceedings ArticleDOI
13 Nov 2014
TL;DR: In this paper, an electro-thermal simulation approach was proposed to analyze the impact of the bond wires fatigue on the current and temperature distribution on IGBT chip surface under short-circuit.
Abstract: Bond wires fatigue is one of the dominant failure mechanisms of IGBT modules. Prior-art research mainly focuses on its impact on the end-of-life failure, while its effect on the short-circuit capability of IGBT modules is still an open issue. This paper proposes a new electro-thermal simulation approach enabling analyze the impact of the bond wires fatigue on the current and temperature distribution on IGBT chip surface under short-circuit. It is based on an Icepack- PSpice co-simulation by taking the advantage of both a finite element thermal model and an advanced PSpice-based multi- cell IGBT model. A study case on a 1700 V/1000 A IGBT module demonstrates the effectiveness of the proposed simulation method.

Proceedings ArticleDOI
01 Oct 2014
TL;DR: The design and development of a 6 kA/1.1 kV non-destructive testing system, which aims for short circuit testing of high-power IGBT modules, and the capability and the effectiveness of the proposed setup in the short-circuit aspect reliability studies of MW-scale power modules are described.
Abstract: This paper describes the design and development of a 6 kA/1.1 kV non-destructive testing system, which aims for short circuit testing of high-power IGBT modules. An ultra-low stray inductance of 37 nH is achieved in the implementation of the tester. An 100 MHz FPGA supervising unit enables 10 ns level control accuracy of the short-circuit duration, protection triggering, and acquisition of the electrical waveforms. Moreover, a protection circuit avoids explosions in case of failure, making the post-failure analysis possible. A case study has been carried out on an aged 1.7 kV IGBT power module. The case study shows the current and voltage waveforms during short-circuit, as well as the current mismatch among six inner sections, which demonstrate the capability and the effectiveness of the proposed setup in the short-circuit aspect reliability studies of MW-scale power modules.

01 Nov 2014
TL;DR: A flexible power controller is developed in this study, which can be configured in the PV inverter and flexibly change from one to another mode during operation, and offers the possibilities to generate appropriate references for the inner current control loop.
Abstract: This study explores the integration issues of next-generation high-penetration photovoltaic (PV) systems, where the grid is becoming more decentralised and vulnerable. In that case, the PV systems are expected to be more controllable with higher efficiency and reliability. Provision of ancillary and intelligent services, such as fault ride-through and reactive power compensation, is the key to attain higher utilisation of solar PV energy. Such functionalities for the future PV inverters can contribute to reduced cost of energy, and thus enable more cost-effective PV installations. To implement the advanced features, a flexible power controller is developed in this study, which can be configured in the PV inverter and flexibly change from one to another mode during operation. Based on the single-phase PQ theory, the control strategy offers the possibilities to generate appropriate references for the inner current control loop. The references depend on system conditions and also specific demands from both system operators and prosumers. Besides, this power control strategy can be implemented in commercial PV inverters as a standardised function, and also the operation modes can be achieved online in predesigned PV inverters. Case studies have verified the effectiveness and flexibilities of the proposal to realise the advanced features.

Book ChapterDOI
15 May 2014
TL;DR: This chapter will show the basics of power electronics technology for renewable energy systems, describe the mission profile of the technology and demonstrate how the power electronics is loaded under different stressors.
Abstract: Power electronics is the enabling technology for maximizing the power captured from renewable electrical generation, e.g., the wind and solar technology, and also for an efficient integration into the grid. Therefore, it is important that the power electronics are reliable and do not have too many failures during operation which otherwise will increase cost for operation, maintenance and reputation. Typically, power electronics in renewable electrical generation has to be designed for 20–30 years of operation, and in order to do that, it is crucial to know about the mission profile of the power electronics technology as well as to know how the power electronics technology is loaded in terms of temperature and other stressors relevant, to reliability. Hence, this chapter will show the basics of power electronics technology for renewable energy systems, describe the mission profile of the technology and demonstrate how the power electronics is loaded under different stressors. Further, some systematic methods to design the power electronics technology for reliability will be given and demonstrated with two cases—one is a wind power and the other is photovoltaic application.

Proceedings ArticleDOI
13 Nov 2014
TL;DR: In this paper, the effect of series dynamic breaking resistor (SDBR) sizing on a Doubly Fed Induction Generator (DFIG) based wind power conversion system is evaluated by simulation.
Abstract: This paper investigates the effect of Series Dynamic Breaking Resistor (SDBR) sizing on a Doubly Fed Induction Generator (DFIG) based wind power conversion system. The boundary of the SDBR value is firstly derived by taking into account the controllability of the rotor side converter and the maximum allowable voltage of the stator. Then the impact of the SDBR value on the rotor current, stator voltage, DC-link voltage, reactive power capability and introduced power loss during voltage sag operation is evaluated by simulation. The presented study enables a trade-off sizing of the SDBR among the above performance factors. I. INTRODUCTION There are several types of the wind turbine generators (WTGs), one of which is the Doubly Fed Induction Generator (DFIG). In the last decades, the DFIG has been widely applied in the variable speed - constant frequency wind power technology. This is due to its simple control strategy, low losses, and it being capable of regulating the active and reactive power separately. However, the DFIG suffers from its sensitivity to grid faults, as a result of its direct connection to the grid. The stator of the DFIG is connected to the grid directly, whereas the rotor is connected to the grid through the back to back converter. Voltage sag in one of the dominant type of grid faults. It causes a transient stator flux in the generator, along with an increase in the rotor current due to the mutual coupling between the stator and rotor (1). The increased rotor current flowing through the Rotor Side Converter (RSC) may exceed the maximum allowable one, inducing damage to the converter and DC-link. The DC-link voltage rises as its capacitors are charged above their nominal voltage. Some means of protection is required to prevent the converter from high inrush current faults. Therefore, prior art research has been devoted to analyzing the behavior of wind turbines during faults and presenting Fault Ride-Through (FRT) solutions for wind turbines. Generally the solutions can be divided into two categories. The first one is by introducing additional hardware components or circuits, either in the stator side, rotor side, or on the DC-link of the RSC. The second one is by additional control schemes, e.g., demagnetization current or flux compensation to the DFIG system. The existing solutions to improve the performance and the FRT capability of DFIG systems are reviewed as follows. 1) Crowbar circuit

01 Jan 2014
TL;DR: In this paper, a robust passive damping method for LLCL-filter-based grid-tied inverters is proposed, which effectively can suppress the possible resonances even if the grid inductance varies in a wide range.
Abstract: In order to minimize the effect of the grid harmonic voltages, harmonic compensation is usually adopted for a grid-tied inverter. However, a large variation of the grid inductance challenges the system stability in case a high-order passive filter is used to connect an inverter to the grid. Although in theory, an adaptive controller can solve this problem, but in such a case the grid inductance may need to be detected online, which will complicate the control system. This paper investigates the relationship between the maximum gain of the controller that still keeps the system stable and the Q-factor for a grid-tied inverter with an RL series or an RC parallel damped high-order power filter. Then, a robust passive damping method for LLCL-filter-based grid-tied inverters is proposed, which effectively can suppress the possible resonances even if the grid inductance varies in a wide range. Simulation and experimental results are in good agreement with the theoretical analysis.

01 Oct 2014
TL;DR: In this article, the authors present a comprehensive investigation on the short circuit capability of wind-turbine-scale IGBT power modules by means of a 6 kA/1.1 kV non-destructive testing system.
Abstract: This paper presents a comprehensive investigation on the short circuit capability of wind-turbine-scale IGBT power modules by means of a 6 kA/1.1 kV non-destructive testing system. A Field Programmable Gate Array (FPGA) supervising unit is adopted to achieve an accurate time control for short circuit tests, which enables to define the driving signals with an accuracy of 10ns. Thanks to the capability and the effectiveness of the constructed setup, oscillations appearing during short circuits of the new-generation 1.7 kV/1 kA IGBT power modules have been evidenced and characterized under different collector voltage.