Voltage optimisation

About: Voltage optimisation is a research topic. Over the lifetime, 13831 publications have been published within this topic receiving 201336 citations.

Voltage and Power Balance Control for a Cascaded H-Bridge Converter-Based Solid-State Transformer

Abstract: The solid-state transformer (SST) is an interface device between ac distribution grids and dc distribution systems. The SST consists of a cascaded multilevel ac/dc rectifier stage, a dual active bridge (DAB) converter stage with high-frequency transformers to provide a regulated 400-V dc distribution, and an optional dc/ac stage that can be connected to the 400-V dc bus to provide residential 120/240 V $_{\rm ac}$ . However, due to dc-link voltage and power unbalance in the cascaded modules, the unbalanced dc-link voltages and power increase the stress of the semiconductor devices and cause overvoltage or overcurrent issues. This paper proposes a new voltage and power balance control for the cascaded H-Bridge converter-based SST. Based on the single-phase dq model, a novel voltage and the power control strategy is proposed to balance the rectifier capacitor voltages and the real power through parallel DAB modules. Furthermore, the intrinsic power constraints of the cascaded H-Bridge voltage balance control are derived and analyzed. With the proposed control methods, the dc-link voltage and the real power through each module can be balanced. The SST switching model simulation and the prototype experiments are presented to verify the performance of the proposed voltage and power balance controller.

Dynamic voltage scaling with links for power optimization of interconnection networks

Abstract: Originally developed to connect processors and memories in multicomputers, prior research and design of interconnection networks have focused largely on performance. As these networks get deployed in a wide range of new applications, where power is becoming a key design constraint, we need to seriously consider power efficiency in designing interconnection networks. As the demand for network bandwidth increases, communication links, already a significant consumer of power now, will take up an ever larger portion of total system power budget. In this paper we motivate the use of dynamic voltage scaling (DVS) for links, where the frequency and voltage of links are dynamically adjusted to minimize power consumption. We propose a history-based DVS policy that judiciously adjusts link frequencies and voltages based on past utilization. Our approach realizes up to 6.3/spl times/ power savings (4.6/spl times/ on average). This is accompanied by a moderate impact on performance (15.2% increase in average latency before network saturation and 2.5% reduction in throughput.) To the best of our knowledge, this is the first study that targets dynamic power optimization of interconnection networks.

Harmonic and reactive power compensation based on the generalized instantaneous reactive power theory for three-phase four-wire systems

Abstract: This paper presents harmonic and reactive power compensation based on a generalized theory of instantaneous reactive power for three-phase power systems. This new theory gives a generalized definition of instantaneous reactive power, which is valid for sinusoidal or nonsinusoidal and balanced or unbalanced three-phase power systems with or without zero-sequence currents and/or voltages. The properties and physical meanings of the newly defined instantaneous reactive power are discussed in detail. A harmonic and reactive power compensator based on the new theory for a three-phase harmonic-distorted power system with zero-sequence components in the load current and/or source voltage is then used as an example to show harmonic and reactive power measurement and compensation using the new theory. Simulation and experimental results are presented.

Local Reactive Power Control Methods for Overvoltage Prevention of Distributed Solar Inverters in Low-Voltage Grids

Abstract: The main objective of this study is to increase the penetration level of photovoltaic (PV) power production in low-voltage (LV) grids by means of solar inverters with reactive power control capability. This paper underlines weak points of standard reactive power strategies which are already imposed by certain grid codes, and then, the study introduces a new reactive power control method that is based on sensitivity analysis. The sensitivity analysis shows that the same amount of reactive power becomes more effective for grid voltage support if the solar inverter is located at the end of a feeder. Based on this fundamental knowledge, a location-dependent power factor set value can be assigned to each inverter, and the grid voltage support can be achieved with less total reactive power consumption. In order to prevent unnecessary reactive power absorption from the grid during admissible voltage range or to increase reactive power contribution from the inverters that are closest to the transformer during grid overvoltage condition, the proposed method combines two droop functions that are inherited from the standard cos φ(P) and Q(U) strategies. Its performance comparison in terms of grid losses and voltage variation with different reactive power strategies is provided by modeling and simulating a real suburban LV network.

Design and Analysis of a Grid-Connected Photovoltaic Power System

Abstract: A grid-connected photovoltaic (PV) power system with high voltage gain is proposed, and the steady-state model analysis and the control strategy of the system are presented in this paper. For a typical PV array, the output voltage is relatively low, and a high voltage gain is obligatory to realize the grid-connected function. The proposed PV system employs a ZVT-interleaved boost converter with winding-coupled inductors and active-clamp circuits as the first power-processing stage, which can boost a low voltage of the PV array up to a high dc-bus voltage. Accordingly, an accurate steady-state model is obtained and verified by the simulation and experimental results, and a full-bridge inverter with bidirectional power flow is used as the second power-processing stage, which can stabilize the dc-bus voltage and shape the output current. Two compensation units are added to perform in the system control loops to achieve the low total harmonic distortion and fast dynamic response of the output current. Furthermore, a simple maximum-power-point-tracking method based on power balance is applied in the PV system to reduce the system complexity and cost with a high performance. At last, a 2-kW prototype has been built and tested to verify the theoretical analysis of the paper.