(1990). ENERGY FUNCTION ANALYSIS FOR POWER SYSTEM STABILITY. Electric Machines & Power Systems: Vol. 18, No. 2, pp. 209-210.

Energy function analysis for power system stability

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.

/pdf/reliability-of-capacitors-for-dc-link-applications-in-power-2b0em1025t.pdf

Reliability of Capacitors for DC-Link Applications in Power Electronic Converters—An Overview

Pulsewidth modulation (PWM) voltage source converters are becoming a popular interface to the power grid for many applications. Hence, issues related to the reduction of PWM harmonics injection in the power grid are becoming more relevant. The use of high-order filters like LCL filters is a standard solution to provide the proper attenuation of PWM carrier and sideband voltage harmonics. However, those grid filters introduce potentially unstable dynamics that should be properly damped either passively or actively. The second solution suffers from control and system complexity (a high number of sensors and a high-order controller), even if it is more attractive due to the absence of losses in the damping resistors and due to its flexibility. An interesting and straightforward active damping solution consists in plugging in, in cascade to the main controller, a filter that should damp the unstable dynamics. No more sensors are needed, but there are open issues such as preserving the bandwidth, robustness, and limited complexity. This paper provides a systematic approach to the design of filter-based active damping methods. The tuning procedures, performance, robustness, and limitations of the different solutions are discussed with theoretical analysis, selected simulation, and experimental results.

Filter-Based Active Damping of Voltage Source Converters With $LCL$ Filter

Computer Controlled Systems: Theory and Design

This paper deals with various active damping approaches for PI-based current control of grid-connected pulsewidth-modulation (PWM) converters with LCL filters, which are based on one additional feedback. Filter capacitor current, as well as voltage feedback for the purpose of resonance damping, are analyzed and compared. Basic studies in the continuous Laplace domain show that either proportional current feedback or derivative voltage feedback yields resonance damping. Detailed investigations of these two approaches in the discrete z-domain, taking into account the discrete nature of control implementation, sampling, and PWM, are carried out. Several ratios of LCL resonance frequency and control frequency are considered. At high resonance frequencies, only current feedback stabilizes the system. At medium resonance frequencies, both approaches have good performance. At low resonance frequencies, stability gets worse, even though voltage feedback offers slightly better damping properties. Measurements validate the theoretical results.

https://www.tf.uni-kiel.de/etit/LEA-download/dl-open/veroeff_2010/ias_dannehl.pdf

Investigation of Active Damping Approaches for PI-Based Current Control of Grid-Connected Pulse Width Modulation Converters With LCL Filters

Design and analysis of PI state space control for grid-connected pulsewidth modulation (PWM) converters with LCL filters based on pole placement approach is addressed. State space control offers almost full controllability of system dynamic. However, pole placement design is difficult and usually requires much experience. In this paper, a suitable pole placement strategy is proposed, which ensures fulfilling the requirements, which are commonly specified with respect to rise time, overshoot, and proper resonance damping. Controller parameter expressions are derived in terms of system parameters and specified poles and zeros. Hence, straightforward controller tuning for a particular system setting is possible. Performance is analyzed by means of transfer function-based calculations, simulations with MATLAB, and experimental tests. Dynamic performance and robustness against grid impedance variations are addressed as well as harmonic rejection capability and other practical issues.

PI State Space Current Control of Grid-Connected PWM Converters With LCL Filters

Design and analysis of PI state space control for grid-connected PWM converters with LCL filters based on pole placement approach is addressed. State space control offers almost full controllability of system dynamic. However, pole placement design is difficult and usually requires much experience. In this paper a suitable pole placement strategy is proposed, that ensures fulfilling the requirements, which are commonly specified with respect to rise time, overshoot, and proper resonance damping. Controller parameter expressions are derived in terms of system parameters and specified poles and zeros. Hence straightforward controller tuning for a particular system setting is possible. Performance is analyzed by means of transfer function-based calculations, simulations with Matlab, and experimental tests.

https://www.tf.uni-kiel.de/etit/LEA-download/dl-open/veroeff_2009/ecce_dannehl.pdf

PI state space current control of grid- connected PWM converters with LCL filters

This paper proposes a decision tree (DT) based systematic approach for cooperative online power system dynamic security assessment (DSA) and preventive control. This approach adopts a new methodology that trains two contingency oriented DTs on daily basis by the databases generated from power system simulations. Fed with real-time wide area measurements, one DT about measurable variables is employed for online DSA to identify potential security issues and the other DT about controllable variables provides online decision support on preventive control strategies against those issues. A cost effective algorithm is adopted in this proposed approach to optimize the trajectory of preventive control. The paper also proposes an importance sampling algorithm on database preparation for efficient DT training for power systems with high penetration of wind power and distributed generation. The performance of the approach is demonstrated on a 400-bus, 200-line operational model of western Danish power system.

/pdf/a-systematic-approach-for-dynamic-security-assessment-and-42rp5k9ah5.pdf

A Systematic Approach for Dynamic Security Assessment and the Corresponding Preventive Control Scheme Based on Decision Trees

A simple Vce online monitoring circuit is presented in this paper. It allows an accurate wear out prediction of IGBT modules, in high-power applications, during normal converter operation. Bipolar measurement allows monitoring of both IGBT and antiparallel diode. The circuit uses two serial connected diodes to sense the Vce voltage with millivolt accuracy. One diode acts as a protection to block high DC voltage present on input terminals. When the device is conducting the voltage on the second diode is measured to compensate for the voltage drop on the protection diode thus eliminating voltage offset due to diodes' forward voltage temperature dependency. Using four diodes one can monitor voltages on all power devices in a converter leg.

/pdf/online-vce-measurement-method-for-wear-out-monitoring-of-4fjh451pth.pdf

Paul Bach Thøgersen

Papers

Investigation of Active Damping Approaches for PI-Based Current Control of Grid-Connected Pulse Width Modulation Converters With LCL Filters

PI State Space Current Control of Grid-Connected PWM Converters With LCL Filters

PI state space current control of grid- connected PWM converters with LCL filters

A Systematic Approach for Dynamic Security Assessment and the Corresponding Preventive Control Scheme Based on Decision Trees

Online Vce measurement method for wear-out monitoring of high power IGBT modules