Active Voltage Control Research Articles

Adaptive active voltage control system’s emergency response

Adaptive active voltage control system’s emergency response

Investigation of the trade‐off between switching losses and EMI generation in Gaussian S‐shaping for high‐power IGBT switching transients by active voltage control

Over three decades of development effort has brought insulated gate bipolar transistor (IGBT) technology to a high-level of maturity. IGBT converters have been widely used in industry. However, the high-speed switching transient of the IGBT-freewheel diode chopper cell causes high-level electromagnetic interference (EMI). Electromagnetic compatibility requirements are normally taken into account by utilising costly EMI filters or shielding on the load and supply side. The risk of this traditional method is to incur a delay in commercialising the converters since identification of the failure causes, modifications, and successfully re-testing are required. A promising alternative is to constrain the EMI at source by introducing active voltage control technique and shaping the IGBT switching transient into a sophisticated ‘S’-shape. Previously, IGBT switching waveforms have been successfully shaped into an advanced Gaussian ‘S’-shape with the EMI greatly reduced. In this study, the authors further investigated the trade-off between EMI generation and switching losses in such an S-shaping method. The investigation was carried out in an accurate physical IGBT/diode model that is able to accurately simulate the device switching transient. From the results, it can be seen that by using the Gaussian S-shaping method the trade-off between EMI and switching losses could be much improved.

Robust Stability Analysis of Active Voltage Control for High-power IGBT Switching by Kharitonov's Theorem

The main idea of active voltage control (AVC) is to employ classic feedback-control methods forcing the IGBT collector voltage transient to follow a predefined trajectory. This feedback control of IGBTs has great advantages in guaranteeing that IGBTs remain in safe operating area (SOA), restricting EMI, mitigating the voltage/current stress, minimizing/predicting their power losses, and balancing voltages of IGBTs in series. Inevitably, however, AVC introduces stability issues. Based on the assumption that accurate IGBT small-signal model parameters are available, an analogue proportional-derivative and multiloop feedback control was proposed to achieve stable performance in previous work. Due to nonlinearities and uncertainties in IGBT parameters, previous stability analysis methods have important limitations. This work uses Kharitonov's theorem during the IGBT controlled turn-off to assess the system's stability and guide the AVC design to account for model uncertainties and varying parameters. We conducted experiments to investigate the system's robust stability due to these uncertainties in the IGBT parameters, which confirm the validity of the proposed theoretical analysis. With the use of wide bandwidth op-amps, it is shown that the feedback design may be simplified.

Modeling and simulation of parallel DC/DC converters for online AC impedance estimation of PEM fuel cell stack

The electrochemical impedance spectroscopy (EIS) technique is now widely used in the study of the hydrogen polymer electrolyte membrane fuel cell (PEMFC), especially the diagnosis of flooding and drying. Though the working conditions of fuel cell vehicles is fairly rough with large electromagnetic interference and ever-changing environment, lots of efforts have been made to prompt the online EIS analysis of PEMFC stack in vehicles, such as using a DC/DC converter based on the ripple currents or active voltage control and so on. Considering the practical topologies of fuel cell powertrain systems, their researches inspire us to put forward a simpler approach in terms of applicability and controllability. For this reason, a topology of two parallel boost DC/DC converters for online AC impedance estimation of PEMFC stack is proposed. This topology is modeled using Matlab/Simulink. To better understand the electrical characteristic of PEMFC, equivalent circuits are utilized to model the PEMFC based on the electrochemical reactions and mass transport properties in the fuel cell. Fluctuation signals produced by a DC/DC converter are injected into the stack. The other DC/DC converter is used to adjust the output characteristic of the stack to the output voltage and current requirements of the external power devices and load. In this way, the fluctuation signal generation and power conversion are decoupled, which is more suitable for different applications of PEMFC stack. To effectively control these converters, closed-loop PI controllers are adopted and coefficients are regulated according to the frequency of disturbance signals. Based on this model, simulation results show that fluctuation signals are well generated and injected into the stack with low total harmonic distortion (THD). After analysis of the output voltage and current of the stack using FFT technique, AC impedance calculated is in consistent with the impedance characteristic of the equivalent circuits with high accuracy.

Shaping High-Power IGBT Switching Transitions by Active Voltage Control for Reduced EMI Generation

High-performance power switching devices [insulated-gate bipolar transistors (IGBTs)] realize high-performance power converters. Unfortunately, with a high switching speed of the IGBT-freewheel diode chopper cell, the circuit becomes intrinsic sources of high-level electromagnetic interference (EMI). Therefore, costly EMI filters or shielding is normally demanded on the load and supply sides. An S-shaped voltage transient with a high-order time derivative eliminates the discontinuity in the switching transient and can suppress high-frequency spectrum of EMI emissions. More importantly, it provides an improved tradeoff between EMI generation and switching time, therefore switching losses. This promising tradeoff can be explored further for better high-frequency EMI suppression by using the infinitely differentiable characteristics of Gaussian S-shaped transients. However, current gate drive schemes cannot achieve the S shaping. In this paper, active voltage control is applied and improved successfully to define IGBT switching dynamics with a smoothed Gaussian waveform.

Maximising low voltage grid hosting capacity for PV and electric mobility by distributed voltage control

European low voltage grids host an increasing amount of energy from rooftop PV installations. Experience in Germany has shown that PV installations do not grow uniformly but with regional hot spots. Meanwhile it is widely agreed that low voltage grids should only be updated to accommodate some 90 % or less of available PV power in peak times in order to avoid extensive costs for grid reinforcement. The main limiting factor in rural distribution grids is the grid voltage. In the Austrian research project “DG DemoNet—Smart LV Grid” new approaches to deal with restricted grid capacities are analysed using active voltage control. In three pilot regions, the actual amount of installed PV is increased to reach physical limits. Voltage control schemes are developed, tested in simulations and then validated in the field. In one pilot region, electric mobility as additional future load in low voltage grids and its integration into the overall system is considered. This paper analyses the performance of the developed control approaches in simulation.

Coordinated Voltage Control in Distribution Networks Including Several Distributed Energy Resources

Connecting distributed generation (DG) to weak distribution networks can often cause voltage rise problems. Traditionally, these voltage rise problems have been mitigated by passive methods such as reinforcing the network. This can, however, lead to high connection costs of DG. The connection costs can in many cases be lowered if active voltage control methods are used instead of the passive approach. In this paper, two coordinated voltage control algorithms suitable for usage in distribution networks including several distributed energy resources are proposed and studied. The first algorithm uses control rules to determine its control actions and the second algorithm utilizes optimization. The operation of the implemented algorithms is, at first, studied using time domain simulations. Thereafter, the network effects and costs of both algorithms are compared using statistical distribution network planning and also practical implementation issues are discussed.

Aiding Power System Support by Means of Voltage Control With Intelligent Distribution Substation

AC power systems have to continuously balance generation and consumption in order to maintain a stable system frequency. The mismatches between the electricity generated and consumed have to be compensated by means of ancillary services, usually provided by conventional power plants. However, the recent developments in power distribution and automation will allow some of those services to be provided by distribution networks. Therefore, in this paper voltage control, at distribution substations, is used in connection with demand response (DR) for aiding system support in the Netherlands. The available capacity, which could be accessible by applying active voltage control, is evaluated and quantified as a function of supplied load over time. The DR capacity is estimated and the implications on power system imbalances are demonstrated in a case study for the Netherlands. In addition, the impact on the network losses is addressed and evaluated.

Dynamic Stability of a Microgrid With an Active Load

Rectifiers and voltage regulators acting as constant power loads form an important part of a microgrid’s total load. In simplified form, they present a negative incremental resistance and beyond that, they have control loop dynamics in a similar frequency range to the inverters that may supply a microgrid. Either of these features may lead to a degradation of small-signal damping. It is known that droop control constants need to be chosen with regard to damping, even with simple impedance loads. Actively controlled rectifiers have been modeled in nonlinear state-space form, linearized around an operating point, and joined to network and inverter models. Participation analysis of the eigenvalues of the combined system identified that the low-frequency modes are associated with the voltage controller of the active rectifier and the droop controllers of the inverters. The analysis also reveals that when the active load dc voltage controller is designed with large gains, the voltage controller of the inverter becomes unstable. This dependence has been verified by observing the response of an experimental microgrid to step changes in power demand. Achieving a well-damped response with a conservative stability margin does not compromise normal active rectifier design, but notice should be taken of the inverter–rectifier interaction identified.

Modeling the Biological Nanopore Instrument for Biomolecular State Estimation

The nanopore is a powerful tool for probing biomolecular interactions at the single-molecule level, and shows great promise commercially as a next-generation deoxyribonucleic acid (DNA) sequencing technology. Coupling active voltage control with the nanopore has expanded its capabilities, for example, by allowing precise manipulation of DNA-enzyme complexes at millisecond timescales. However, any change in voltage excites capacitance in the system and results in masking the molecule's contribution to the measured current. To improve active control capabilities, a method is needed for continuous monitoring of the molecule's contribution to the current during voltage-varying experiments. The method must be able to separate the capacitive effects from the channel conductance, which is the parameter that can be used to infer the state of the molecule in the pore. The contributions of this paper are: 1) to develop a dynamic model of the nanopore instrument which includes capacitance and conductance parameters and 2) to develop model-based algorithms for estimating the conductance parameter during voltage varying experiments. First, grey- and black-box state-space models are estimated and compared using nanopore experimental data and system identification tools. Next, a validated grey-box model is used to derive two methods for estimating the channel conductance under voltage-varying conditions: one based on least-squares, and one based on the extended Kalman filter. In simulations and experiments, the Kalman filter outperforms the simpler least-squares method.

Active closed‐loop gate voltage control method to mitigate metal‐oxide semiconductor field‐effect transistor turn‐off voltage overshoot and ring

Voltage overshoot and ring will occur during metal-oxide semiconductor field-effect transistor (MOSFET) turn-off, when it is embedded in circuits with inductive load and operates in pulse width modulation mode. The voltage overshoot and ring not only increase the system voltage stress, but also produce radiated and conducted electromagnetic interference. Based on the analysis of the influence of the gate voltage on the MOSFET turn-off behaviour, this study presents an active closed-loop gate voltage control method to mitigate the voltage overshoot and ring. The proposed method senses the instant when the MOSFET drain current starts to fall by comparing the drain voltage with the bus voltage. Once the instant has been detected, a turn-off assistance voltage with proper amplitude and adjustable duration is generated and applied to the gate to mitigate the overshoot and ring. The delay of the gate control loop, including the delay of the comparator, can be compensated by proper choice of the components. Both simulations and experiments results indicate that the MOSFET turn-off voltage overshoot is largely reduced and the ring is almost completely eliminated. At the same time, the turn-off loss and EMI are also minimised.

Series-Connected IGBTs Using Active Voltage Control Technique

With series insulated-gate bipolar transistor (IGBT) operation, well-matched gate drives will not ensure balanced dynamic voltage sharing between the switching devices. Rather, it is IGBT parasitic capacitances, mainly gate-to-collector capacitance Cgc, that dominate transient voltage sharing. As Cgc is collector voltage dependant and is significantly larger during the initial turn-off transition, it dominates IGBT dynamic voltage sharing. This paper presents an active control technique for series-connected IGBTs that allows their dynamic voltage transition dVce/dt to adaptively vary. Both switch ON and OFF transitions are controlled to follow a predefined dVce/dt. Switching losses associated with this technique are minimized by the adaptive dv/dt control technique incorporated into the design. A detailed description of the control circuits is presented in this paper. Experimental results with up to three series devices in a single-ended dc chopper circuit, operating at various low voltage and current levels, are used to illustrate the performance of the proposed technique.

Evaluation of Uncertainty in Hybrid Plants, Including Wind Turbine, Photovoltaic, Fuel Cell, and Battery System using Fuzzy Logic

This paper examines the possibility of hybrid plants with a variable consumption in necessary conditions. The use of an adaptive controller includes fuzzy controller with increasing the high-reliability of system as an appropriate option. In his study inputs are voltage conditions and power; output variables include the operation of fuel cell and renewable energies. In this investigation, the objective function is the possibility and the ability of working in low and full load conditions along with the changes in renewable energies conditions. These controllers help to use a controller for hybrid systems. Consequently, communication of this situation by a central controller would be possible. Changes in wind speed and also the inherent changes in photovoltaic system are created during the simulation process. The system should be able to comply with the existing abnormal terms in addition to providing the electricity to the load. In a way that it can provide the required power through the commands which are transmitted from system controllers to AC and DC subsystems and eventually the system reach to a stable condition in a short period of time. In this case it is so important that the essential parameters of the network remain stable. This stability will be illustrated through the stabilization of the line voltage in 1 p.u and also restoring the frequency to its pervious condition. The active power control and voltage controller transmit the commands to the other controlling part which is an interface between two AC and DC systems in order to control the network values. A PID controller was used for controlling parameters in active power regulator. These parameters are designed with fuzzy logic algorithm.

Automated forward and reverse ratcheting of DNA in a nanopore at 5-Å precision

Single-molecule techniques have been developed for commercial DNA sequencing1,2. One emerging strategy uses a nanopore to analyze DNA molecules as they are driven electrophoretically in single file order past a sensor3-5. However, uncontrolled DNA strand electrophoresis through nanopores is too fast for accurate base reads6. A proposed solution would employ processive enzymes to deliver DNA through the pore at a slower average rate7. Here, we describe forward and reverse ratcheting of DNA templates through the α–hemolysin (α-HL) nanopore controlled by wild-type phi29 DNA polymerase (phi29 DNAP). DNA strands were examined in single file order at one nucleotide spatial precision in real time. The registry error probability (either an insertion or deletion during one pass along a template strand) ranged from 10% to 24.5% absent optimization. This general strategy facilitates multiple reads of individual template strands and is transferrable to other nanopore devices for implementation of DNA sequence analysis.

27.1: Integrated pMOS Gate Driver for a 3D AMOLED Display

AbstractSimultaneous Emission with Active Voltage control (SEAV) is a strong candidate for crosstalk‐free driving of 3D Active Matrix Organic Light Emitting Diode (AMOLED) displays. A gate driver for a SEAV 3D AMOLED panel needs two operating modes: the simultaneous switching mode and the progressive scanning mode. However, conventional gate drivers can operate in only progressive scanning mode. In this paper, a new integrated gate driver to support both of these modes is proposed and applied to a prototype 3D AMOLED display panel.

27.2: 31_inch FHD AMOLED 3‐D TV using Emission‐Switch Control Method

Abstract31_inch FHD AMOLED 3‐D TV using the Emission‐Switch Control for 3‐D driving was developed. The Emission‐Switch Control used here is that EM switches of each pixel are controlled simultaneously so that all pixels are emission and non‐emission at the same time. In order to use this control method, we developed and adopted EM driver which have 2‐D/3‐D switch‐able block between shift register and buffer. By using this method, we fabricated and demonstrated 31_inch AMOLED TV that achieved great viewing angle and on‐off 3‐D Cross‐talk with 0.39 % level. Also, compared to Active Voltage Control this method helps reducing the load on the system.

Measuring Single-Molecule DNA Hybridization by Active Control of DNA in a Nanopore

We present a novel application of active voltage control of DNA captured in a nanopore to regulate the amount of time the DNA is available to molecules in the bulk phase that bind to the DNA. In this work, the control method is used to measure hybridization between a single molecule of DNA captured in a nanopore and complementary oligonucleotides in the bulk phase. We examine the effect of oligonucleotide length on hybridization, and the effect of DNA length heterogeneity on the measurements. Using a mathematical model, we are able to deduce the binding rate of complementary oligonucleotides, even when DNA samples in experiments are affected by heterogeneity in length. We analyze the lifetime distribution of DNA duplexes that are formed in the bulk phase and then pulled against the pore by reversing the voltage. The lifetime distribution reveals several dissociation modes. It remains to be resolved whether these dissociation modes are due to DNA heterogeneity or correspond to different states of duplex DNA. The control method is unique in its ability to detect single-molecule complex assembly in the bulk phase, free from external force and with a broad (millisecond-to-second) temporal range.

Replication of individual DNA molecules under electronic control using a protein nanopore

Nanopores can be used to analyse DNA by monitoring ion currents as individual strands are captured and driven through the pore in single file order by an applied voltage. Here we show that serial replication of individual DNA templates can be achieved by DNA polymerases held at the α-hemolysin nanopore orifice. Replication is blocked in the bulk phase, and is initiated only after the DNA is captured by the nanopore. We used this method, in concert with active voltage control, to observe DNA replication catalyzed by bacteriophage T7 DNA polymerase (T7DNAP) and by the Klenow fragment of DNA polymerase I (KF). T7DNAP advanced on a DNA template against an 80 mV load applied across the nanopore, and single nucleotide additions were measured on the millisecond time scale for hundreds of individual DNA molecules in series. Replication by KF was not observed when this enzyme was held atop the nanopore orifice at 80 mV applied potential. Sequential nucleotide additions by KF were observed upon controlled voltage reversals.

Analysis, Design, and Control of Bidirectional Cascoded Configuration for a Fuel Cell Hybrid Power System

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> This paper presents a cascoded configuration combining a fuel cell (FC), a battery, and an ultracapacitor module (UCM) to create a hybrid power system. A cascoded configuration is constructed using a modified bidirectional flyback converter, which connects the battery and UCM in cascode to efficiently provide hybrid power. An active FC voltage control strategy is presented to manage the power flows of the proposed cascoded system. In this paper, the simulated hybrid power of the motion of an electric vehicle is illustrated in different situations. The experimental results show that the power flows using the proposed control strategy verify the theoretical analysis. In addition, the overall efficiency of the proposed hybrid power system at overload operation is much higher than the conventional one, and it can achieve 96%. </para>

Research of Supercapacitor Voltage Equalization Strategy on Rubber-Tyred Gantry Crane Energy Saving System

A model for supercapacitor voltage equalization strategy is analyzed, and on this basis a supercapacitor voltage equalization method for Rubber Tyred Gantry Crane (RTG) energy saving system is proposed, namely active voltage equalization method based on Buck-Boost converter. The equalizing speed of the proposed method is fast. Firstly, the working principle and process of the voltage equalization circuit is analyzed in detail. In addition, design of active voltage equalization circuit parameters and control strategy are given. Finally, simulation analysis of the series connection of supercapacitors module is performed. Results show that this method for equalizing voltage can avoid over-voltage of each cell and possess practicable and high value for supercapacitor RTG energy saving system.