Bjørn Rannestad

Improving Power Converter Reliability: Online Monitoring of High-Power IGBT Modules

The real-time junction temperature monitoring of a high-power insulated-gate bipolar transistor (IGBT) module is important to increase the overall reliability of power converters for industrial applications. This article proposes a new method to measure the on-state collector-emitter voltage of a high-power IGBT module during converter operation, which may play a vital role in improving the reliability of the power converters. The measured voltage is used to estimate the module average junction temperature of the high and low-voltage side of a half-bridge IGBT separately in every fundamental cycle of the current by calibrating them at load current. The measurement is very accurate and also measures the voltage at the middle of a pulse-width modulation (PWM) switching. A major objective is that this method is designed to be implemented in real applications. The performance of this technique is measured in a wind power converter at a low fundamental frequency. To illustrate more, the test method as well as the performance of the measurement circuit are also presented. This measurement is also useful to indicate failure mechanisms such as bond wire lift-off and solder layer degradation. The measurements of and rise in the junction temperature after five million cycles of normal operation of the converter are also presented.

A review on real time physical measurement techniques and their attempt to predict wear-out status of IGBT

Insulated Gate Bipolar Transistors (IGBTs) are key component in power converters. Reliability of power converters depend on wear-out process of power modules. A physical parameter such as the on-state collector-emitter voltage (Vce) shows the status of degradation of the IGBT after a certain cycles of operation. However, the Vce mainly shows the wear-out of bond wire lift-off and solder degradation. The Vce is normally used to estimate the junction temperature in the module. The measurement of Vce is sensitive to the converter power level and fluctuations in the surrounding temperature. In spite of difficulties in the measurement, the offline and online Vce measurement topologies are implemented to study the reliability of the power converters. This paper presents a review in wear-out prediction methods of IGBT power modules and freewheeling diodes based on the real time Vce measurement. The measurement quality and some practical issues of those measurement techniques are discussed. Furthermore, the paper proposes the requirements for the measurement and prognostic approach to determine wear-out status of power modules in field applications. The online Vce measurement for a selected topology is also shown in the paper.

Reliability Improvement of Power Converters by Means of Condition Monitoring of IGBT Modules

Power electronic systems have gradually gained an important status in a wide range of industrial applications such as renewable generation, motor drives, automotive, and railway transportation. Accordingly, recent research makes an effort to improve the reliability of power electronic systems to comply with more stringent constraints on safety, cost, and availability. The power devices are one of the most reliability-critical components in power electronic systems. Therefore, its condition monitoring plays an important role to improve the reliability of power electronic systems. This paper proposes a condition monitoring method of insulated-gate bipolar transistor (IGBT) modules. In the first section of this paper, a structure of a conventional IGBT module and a related parameter for the condition monitoring are explained. Then, a proposed real-time on-state collector–emitter voltage measurement circuit and condition monitoring strategies under different operating conditions are described. Finally, experimental results confirm the feasibility and effectiveness of the proposed method.

Test setup for accelerated test of high power IGBT modules with online monitoring of V ce and V f voltage during converter operation

Several accelerated test methods exist in order to study the failures mechanisms of the high power IGBT modules like temperature cycling test or power cycles based on DC current pulses. The main drawback is that the test conditions do not represent the real performance and stress conditions of the device in real application. The hypothesis is that ageing of power modules closer to real environment including cooling system, full dc-link voltage and continuous PWM operation could lead to more accurate study of failure mechanism. A new type of test setup is proposed, which can create different real load conditions like in the field. Furthermore, collector-emitter voltage (Vce) has been used as indicator of the wear-out of the high power IGBT module. The innovative monitoring system implemented in the test setup is capable of measure the Vce and forward voltage of the antiparallel diode (Vf) during converter operation, which is also demonstrated.

Condition monitoring of IGBT module for reliability improvement of power converters

Power electronic systems have gradually gained an important status in a wide range of industrial applications such as automotive, motor drives, railway transportation and renewable generation. Accordingly, recent research makes an effort to improve the reliability of power electronic systems to comply with more stringent constraints on safety, cost and availability. The power devices are the one of the most reliability-critical components in power electronic systems. Therefore, its condition monitoring plays an important role to improve the reliability of power electronic systems. This paper proposes a condition monitoring method of an IGBT module. In the first section of this paper, the structure of a conventional IGBT module and related parameter for the condition monitoring are explained. Then, an intelligent on-state collector-emitter voltage measurement circuit and condition monitoring strategies depending on converter operating conditions are described. Finally, experimental results confirm the feasibility and effectiveness of the proposed method.

Online chip temperature monitoring using υ ce -load current and IR thermography

This paper presents on-state collector-emitter voltage (υce, on)-load current (Ic) method to monitor chip temperature on power insulated gate bipolar transistor (IGBT) modules in converter operation. The measurement method is also evaluated using infrared (IR) thermography. Temperature dependencies of υce, on at load current is measured and temperature dependency calibration factor is formulated. This method needs a correction to compensate a deviation in the interconnection resistance from homogeneous temperature field in calibration to non-homogeneous field in loading. The correction parameter is obtained from a static calibration and the method is proposed in the paper. Ageing compensation in estimating the temperature is illustrated. The correction parameter is also analysed in finite element model and also investigated experimentally superimposing heat by conducting device for a longer time in the calibration.

Converter Monitoring Unit for Retrofit of Wind Power Converters

A converter monitoring unit (CMU), which will enable condition monitoring of wind turbine converters is presented in this paper. Reducing the cost of corrective maintenance by means of condition monitoring is a way of lowering operation and maintenance costs for wind turbine systems. The CMU must be able to detect a broad range of failure modes related to Insulated Gate Bipolar Transistor (IGBT) power modules and associated gate drives. IGBT collector-emitter on-state voltage (vceon) and current (ic) is sampled in the CMU and used for detection of emerging failures. A new method for compensation of unwanted inductive voltage drop in the vceon measurement path is presented, enabling retrofitting of CMUs in existing wind turbines. Finally, experimental results obtained on a prototype CMU are presented. Experimentally the vceon dependency to IGBT junction temperature and deterioration of gate drive voltage is investigated. The proposed method shows good detectability of both thermally related degradations of the power module and detectability of deterioration of gate drive voltage. It is also expected that the proposed method will enable detectability of other failure mechanisms.

Novel screening techniques for wind turbine power converters

Power converters represent one of the highest failure rates in the wind turbine. Therefore converter manufacturers perform burn-in tests to prevent shipping of faulty converters. Recent developments in junction temperature estimation, based on accurate online IGBT collector-emitter voltage measurements, allow for thermal stress estimation of the IGBT modules. This is utilized to detect infant mortalities in power converters, by comparing thermal responses of IGBTs for faulty and non-faulty converters. The method proves to be a time and cost efficient candidate to replace burn-in tests of power converters for wind turbines applications.

On-state voltage drop based derating/uprating on a MW converter to improve reliability

Abstract Power semiconductor devices are the most fragile components limiting reliability of power converters, where major stresses are temperature dependent parameters. Typically, the operating virtual maximum junction temperature is specified by a manufacturer for each individual device. The thermal system and operating load are designed based on this number. Online monitoring of an on-state collector–emitter voltage (υce,on) and a junction temperature is necessary to ensure the design performance within a safe limit and also to make this method applicable for derating/uprating power. This paper presents the real time measurement of υce,on and thereby the junction temperature estimation in high power converters. Knowing these parameters online, the maximum power capability can be detected. The operating maximum junction temperature is selected and thereby based on the operating condition the derating of power is shown for a megawatt (MW) converter. An experimental setup including online monitoring is described and the measurement of power derating is presented at the specified conditions.

On-state voltage drop based power limit detection of IGBT inverters

Power density is a key performance factor in order to reduce the cost and size of a power converter. Because of the unknown junction temperature, todays design margins are relatively high to ensure safe and a reliable operation. In this paper, the on-state voltage drop is measured online for all insulated gate bipolar transistors (IGBTs) in the inverter, using advanced gate driver. The die temperature is estimated and monitored on each device during power converter operation. Based on the monitored temperature in real time, the maximum power capability is detected. The output power is increased until a safe operating temperature of power modules. This enable a power density is increased by 11.16 kW /litre to 19.13 kW /litre in a low voltage power stack which is typically used in wind power converters. Experiment results are shown for safe operation of converter at around 1.2 MW, which is built in a standard size for the 600-700 kW. Furthermore, the 1700 V, 1000 A power module is replaced with a 1400 A module to increase the load current.