DC microgrids and distribution systems: An overview

Reliability is one of the key issues for the application of Insulated Gate Bipolar Transistors (IGBTs) in power electronic converters. Many efforts have been devoted to the reduction of IGBT wear out failure induced by accumulated degradation and catastrophic failure triggered by single-event overstress. The wear out failure under field operation could be mitigated by scheduled maintenances based on lifetime prediction and condition monitoring. However, the catastrophic failure is difficult to be predicted and thus may lead to serious consequence of power electronic converters. To obtain a better understanding of catastrophic failure of IGBTs, the state-of-the-art research on their failure behaviors and failure mechanisms is presented in this paper. Moreover, various fault-tolerant design methods, to prevent converter level malfunctions in the event of IGBT failure, are also reviewed.

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Catastrophic failure and fault-tolerant design of IGBT power electronic converters - an overview

In order to interface one photovoltaic (PV) port, one bidirectional battery port, and one load port of a PV-battery dc power system, a novel nonisolated three-port dc/dc converter named boost bidirectional buck converter (B3C) and its control method based on three-domain control are proposed in this paper. The power flow and operating principles of the proposed B3C are analyzed in detail, and then, the dc voltage relation between three ports is deduced. The proposed converter features high integration and single-stage power conversion from both PV and battery ports to the load port, thus leading to high efficiency. The current of all three ports is continuous; hence, the electromagnetic noise can be reduced. Furthermore, the control and modulation method for B3C has been proposed for realizing maximum power point tracking (MPPT), battery management, and bus voltage regulation simultaneously. The operation can be transited between conductance mode and MPPT mode automatically according to the load power. Finally, experimental verifications are given to illustrate the feasibility and effectiveness of the proposed topology and control method.

A Nonisolated Three-Port DC–DC Converter and Three-Domain Control Method for PV-Battery Power Systems

A novel dc-dc switching converter consisting of a boost stage cascaded with a buck converter with their coils magnetically coupled is presented. The disclosed converter has the same step-up or step-down voltage conversion properties than the single inductor noninverting buck-boost converter but exhibits nonpulsating I/O currents. The converter control-to-output transfer function is continuous between operation modes if a particular magnetic coupling is selected. The addition of a damping network improves the dynamics and results in a control-to-output transfer function that has, even in boost mode, two dominant complex poles without right-half-plane zeros. An example shows that an output voltage controller can be designed with the same well-known techniques usually applied to the second-order buck regulator. Details of a prototype and experimental results including efficiency, frequency, and time domain responses are presented. The experimental results validate the theoretical expected advantages of the converter, namely, good efficiency, wide bandwidth, and simplicity of control design.

A Noninverting Buck–Boost DC–DC Switching Converter With High Efficiency and Wide Bandwidth

This paper deepens in the study of the recently described coupled-inductor buck-boost converter. The output voltage of this dc-dc converter can be regulated above and/or below its input voltage with high efficiency and wide bandwidth. The control of the input and/or output nonpulsating converter currents is addressed in this paper. The small-signal control-to-input/output-current transfer functions in open-loop permits the design of the respective average current-mode controllers. The combination of the input- and output-current controllers with an additional output voltage limiter loop is proposed as a method to regulate one of the currents while limiting the maximum values of the other two variables. The theoretical analyses have been validated by means of simulations and also experimentally on a 48-V 800-W purpose built-prototype. In particular, the frequency response measurements that have been carried out for a representative set of the converter operating points are in good agreement with the simulations.

Current-Mode Control of a Coupled-Inductor Buck–Boost DC–DC Switching Converter

Solar Array Regulators (SAR) in a satellite Power Conditioning Unit (PCU) are implemented to transfer the power during sunlight from the solar arrays to the power bus. The objective of this paper is to present how Buck Boost Regulators (B2R) could be used as Step-Up, Direct Energy Transfer and Step-Down Solar Array Regulators. Control circuitries of a new kind are introduced for regulated and unregulated buses, illustrated by practical results demonstrating that such regulators can be used in satellite power systems.

Buck Boost Regulator (B 2 R) for spacecraft Solar Array Power conversion

When a DC/DC converter is used to control the power on the main bus of a spacecraft it needs to comply with highly demanding requirements from the dynamic point of view. Hence, converters with very good dynamic performance, i.e. with no zero on the right-half plane are typically used. The conventional boost converter has not been used in European space applications mainly because of its poor dynamics. This paper addresses the way of using a boost converter in this application and demonstrates that this converter can cope with the very demanding requirements needed. A prototype has been built and tested to proof it.

Battery discharge regulator for space applications based on the boost converter

In a satellite, the main function of a Power Conditioning Unit (PCU) is to manage the energy coming from several power sources (usually solar arrays and battery) and to deliver it continuously to the users in an appropriate form during the overall mission. The objective of this paper is to present an electronic switching DC-DC converter called Buck-Buck-Boost Regulator (B³R) that could be used as a modular and recurrent solution for regulated satellite power bus classes. The power conversion stages of the B³R topology are first described. Then theoretical equations and practical tests illustrate how the converter operates in term of power conversion, control loops performances and efficiency. The paper finally provides some examples of single point failure tolerant implementation using the B³R.

Multiple port DC DC converter for spacecraft Power Conditioning Unit

A solar array system includes at least one solar array and at least one solar array regulator. The solar array regulator has an input port to be connected to the solar array, and an output port to be connected to a power bus. The solar array comprises a switching voltage converter comprising a step-down (PC 1 ) and a step-up (PC 2 ) power cell connected in cascade; and a control circuit for driving said voltage converter in a step-up, a step-down or a direct energy transfer mode, depending on an input control signal and on at least one feedback signal (S IL F ) indicative of an operating condition of said switching voltage converter; characterized in that said at least one feedback signal (S IL F ) is indicative of an intensity of an electrical current (I L ) flowing between said step-down and said step-up power cells, whereby the control circuit implements an internal current feedback control.

Solar array regulator based on step-up and down conversion and solar power system comprising the same

The compliance to the fault tolerant operation requirement for power electronics is commonly assessed with reference to fault models applicable at component level. For switching MOSFET, the fault models include the short-circuit and open-circuit failures, implicitly assuming that the Gate open failure is equivalent to a switch open or short failure. MOSFET Gate open failure, also called floating Gate failure, may however entail a Drain to Source channel conduction with non-zero impedance and the subsequent power dissipation in the failed device may prove critical because of the thermal failure propagation risk. The present paper is dedicated to that question. It is shown that a power MOSFET with floating Gate is driven by leakage current from whatever initial conduction status either into a steady-state dissipative status or into run-away due to thermal instability. The analysis is confirmed by practical tests. As a conclusion, provisions to mitigate the MOSFET Gate open failure are proposed to be implemented at MOSFET level and/or at converter design level.

Olivier Mourra

Papers

Buck Boost Regulator (B 2 R) for spacecraft Solar Array Power conversion

Battery discharge regulator for space applications based on the boost converter

Multiple port DC DC converter for spacecraft Power Conditioning Unit

Solar array regulator based on step-up and down conversion and solar power system comprising the same

MOSFET gate open failure analysis in power electronics