Systems, apparatus, and methods are provided for maintaining the state of charge of energy storage devices such as batteries, flywheel, capacitors, or other technologies that are energetically coupled with the electricity grid to support ancillary services. To reliably respond to requests to regulate the grid, the charge on the energy storage device is sustained or restored to a specified range in a manner that optimizes the readiness of the energy storage device to supply ancillary services in light of the condition of the grid. A state of charge (SOC) of the energy storage device and the grid frequency may be monitored. When a request from the operator to regulate the grid frequency is not being serviced, the charge of the energy storage device may be increased or decreased so that the charge may be sustained within the specific range. Once the SOC falls outside of the first range, charge may be added to or removed from the energy storage device when the grid frequency has appropriate values, e.g. if the grid frequency is respectively above a first setpoint or below a second setpoint.

Frequency responsive charge sustaining control of electricity storage systems for ancillary services on an electrical power grid

An apparatus and method therefor transfers electric charge between a charge storage device (25) and a first power terminal (11) having a plurality of first-nodes. The method interchanges charge between the charge storage device and a first first-node of the plurality of first-nodes through an inductive section (22), and, when a predetermined charge has been interchanged between the charge storage device and the first first-node, replacing the first first-node by a second first-node of the plurality of first-nodes. Charge is interchanged between the charge storage device and the second first-node through the inductive section. Preferably, the ratio of the charge interchanged between the charge storage device and the first first-node and the charge interchanged between the charge storage device and the second first-node is equal to a ratio of the currents drawn from the first first-node and the second first-node. Charge can also be interchanged between the charge storage device and a second power terminal (12) using a similar method.

Charge transfer apparatus and method therefore

A transformerless photovoltaic system that may benefit from inverter topologies more suitable for ripple current cancellation techniques is provided. In one exemplary embodiment, the system may combine basic modules of straightforward inverter topologies to meet requirements for higher power applications and may comprise a bipolar photovoltaic array, and a full-bridge inverter electrically coupled to the bipolar photovoltaic array. The full bridge inverter may comprise first and second inverter legs that may be arranged to energize two phases of a grid electrically coupled to the photovoltaic system. In one exemplary embodiment, switching signals applied to switching devices in each of the first and second inverter legs may be adjusted relative to one other to reduce ripple current therein, thereby reducing the size of components used by the system.

Transformerless power conversion in an inverter for a photovoltaic system

Systems and methods are provided for reactive power regulation and voltage support for renewable energy plants. In one embodiment, a system and method are provided for coordinating voltage and reactive power output of a plant with one or more requirements associated with a utility. The method can include generating a VAR regulator output signal (132) based at least in part on a reactive power control signal (102) received from a utility, controlling reactive power and voltage output of the one or more power sources based at least in part on the generated VAR regulator output signal (132), aggregating reactive power output or the one or more power sources, and providing the aggregated reactive power to the utility.

Reactive power regulation and voltage support for renewable energy plants

Per-panel photovoltaic energy extraction with integrated converters can increase overall array tracking efficiency. Also, switched-capacitor (SC) converters have been evaluated for many applications because of the possibility for on-chip integration; applications to solar arrays are no exception. This paper presents a comprehensive system-level look at solar installations, finding possibilities for optimization at and between all levels of operation in an array. Specifically, this paper examines new arrangements and options for applying switched-capacitor circuits at 3 levels: for the panel and sub-panel level, as part of the overall control strategy, and for ensuring stable and robust interface to the grid with the possibility of eliminating or reducing the use of electrolytic capacitors.

A systems approach to photovoltaic energy extraction

The power conversion system (PCS) developed by the author is a new technology that efficiently transforms power between AC and DC. The conversion process permits the input voltage level to be stepped up or down without the use of magnetic core transformers. The transformation is accomplished using solid state switching devices, capacitors, air-core inductors and an intelligent control system. The technology is based on the property of resonance charging, thereby permitting the use of self commutating switches. The current through the switches, being sinusoidal in nature, has a low dI/dt. This permits the use of slower, less expensive thyristors, similar to those used in high voltage phase control applications. Using these components, a highly efficient inverter can be constructed for a variety of large utility applications.

R. Limpaecher

Papers

Compact and efficient transformerless power conversion system