DC Bus Impedance Research Articles

The impact of DC-bus impedance on the switching performance of low-voltage silicon power MOSFETs

Typical DC-bus stabilization for low-voltage power circuits consists primarily of ceramic capacitors due to the capacity density and low equivalent series resistance (ESR) resulting in low conduction losses. Particularly in hard-switching and hard-commutation operation, the low ESR and high equivalent series inductance (ESL) of the capacitors in the commutation path restrict the damping of the switch node voltage overshoot and introduce high-frequency ringing, reducing the voltage margin of the transistor. Therefore, this paper analyzes the impact of the DC-bus impedance and proposes a DC-bus snubber based on an RC network to form the DC-bus impedance’s characteristic, which minimizes the overshoot voltage. A comprehensive simulation using measurement-derived component models is shown, which is verified by an in-situ measurement on a test PCB. Furthermore, transient measurements using a double pulse test setup show the effectiveness of the proposed approach.

Power Model Free Voltage Ripple Suppression Method of Three-Phase PWM Rectifier Under Unbalanced Grid

Under the condition of the unbalanced grid, the second-order harmonic voltage ripple exists on the dc bus of the three-phase PWM rectifier. In this article, the internal relationship between the dc bus voltage ripple and the dc bus impedance is revealed. In addition, this article proposes a voltage ripple suppression method free from the power model, which can improve the system robustness against the parameter variations. By shaping the dc bus impedance, the voltage ripple is effectively suppressed without adding additional devices. In addition, the design criterion and the implementation of the virtual capacitor are analyzed in detail. Finally, experimental results show the accuracy of the theoretical analysis and the effectiveness of the proposed method.

A Loop Gain-Based Technique for Online Bus Impedance Estimation and Damping in DC Microgrids

In modern dc microgrids, several feedback-controlled power electronic converters are connected to the common dc bus. Although the control loops of each individual converter are designed with good stability margins, the interconnection of multiple source and load converters can cause stability and performance concerns, due to potential interactions. Therefore, in order to ensure the desired dynamic performance of the interconnected power converter system, an interesting approach is to perform online stability monitoring of the dc bus, and to properly damp the dc bus impedance, which has been demonstrated to ensure system-level stability and performance. In order to accomplish that, this article first derives a representation of the dc bus impedance in terms of voltage (or droop) loop gain of the source-side converter. Second, under certain simplifying assumptions it provides an estimate for the peak value of bus impedance-an indicator of system dynamic behavior- based on the phase margin. Third, it proposes to continuously monitor the peak value of bus impedance by only injecting a single sinusoid in the voltage (or droop) loop. The monitored value can then be used to autotune the voltage regulator, in order to keep the bus impedance in a well-known allowable impedance region. The proposed monitoring and stabilization technique eliminates the need for the time consuming and memory intensive impedance measurement tasks. This technique is verified by simulation and experimental results on a laboratory prototype system of interconnected power converters.

A DC Power System Stabilizer Based on Passivity-Oriented DC bus Impedance Shaping

High penetration of Power Electronic (PE) converters in DC power grids has caused new stability challenges due to dynamic interactions among a network’s subsystems. Dynamic interactions can be avoided by the impedance coordination between the subsystems through the modification of control loops or passive elements inside a grid. Impedance coordination is a very complex and time-consuming task with no adaptations to dynamic changes in a power grid. In this paper, the concepts of dynamic interaction and passivity are explained and combined together to provide an online stability measure in terms of the DC bus impedance characteristics. A novel DC Power System Stabilizer (PSS) is proposed which is connected to a DC bus as a separate module passivizing the bus impedance at non-passive interaction frequencies. The interaction frequencies are detected through a broadband online identification process. The PSS working principle, topology, modeling, and control designs are explained in detail. Finally, the functionality and performance of the proposed stabilizer are validated by simulation results.

Adaptive sliding mode control of interleaved parallel boost converter for fuel cell energy generation system

This paper deals with the problem of controlling energy generation systems including fuel cells (FCs) and interleaved boost power converters. The proposed nonlinear adaptive controller is designed using sliding mode control (SMC) technique based on the system nonlinear model. The latter accounts for the boost converter large-signal dynamics as well as for the fuel-cell nonlinear characteristics. The adaptive nonlinear controller involves online estimation of the DC bus impedance ‘seen’ by the converter. The control objective is threefold: (i) asymptotic stability of the closed loop system, (ii) output voltage regulation under bus impedance uncertainties and (iii) equal current sharing between modules. It is formally shown, using theoretical analysis and simulations, that the developed adaptive controller actually meets its control objectives.

DC bus voltage control for a distributed power system

This paper addresses voltage control of distributed DC power systems. DC power systems have been discussed as a result of the introduction of renewable, small-scale power generation units. Also, telecommunication power systems featuring UPS properties might benefit from a broader introduction of DC power systems. Droop control is utilized to distribute the load between the source converters. In order to make the loading of the source converters equal, in per unit, the voltage control algorithm for each converter has to be designed to act similar. The DC side capacitor of each converter, needed for filtering, is also determined as a consequence. The root locus is investigated for varying DC bus impedance. It is found that the risk of entering converter over-modulation is a stronger limitation than stability, at least for reasonable DC bus cable parameters. The stationary and dynamic properties during load variations are also investigated.