Abstract: A method includes operating a microsource in a grid mode in which the microsource is connected to a utility grid. The microsource is located in a microgrid and is configured to deliver a power P1 at a frequency ?1. During operation in the grid mode ?1 is a first frequency and P1 is a first power. The first frequency is an operating frequency of the utility grid. The microsource is transferred from the grid mode to an island mode, causing a frequency change such that ?1 changes to a second frequency and a power change such that P1 changes to a second power. The frequency change occurs at a first rate with respect to the power change while ?1 is less than a slope switch frequency. The frequency change occurs at a second rate with respect to the power change while ?1 is greater than the slope switch frequency.

Abstract: A microsource is provided, which includes an energy storage device, a power generation device, and a controller. The energy storage device is operably coupled for power transfer to a load through a first power bus. The power generation device is operably coupled for power transfer to the load through a second power bus. The controller determines a mode of operation for the energy storage device and the power generation device based on an energy level of the energy storage device and on the load; determines minimum power set points and maximum power set points for the energy storage device and the power generation device based on the determined mode of operation, on a storage output power measured at the first power bus, and on a generation output power measured at the second power bus; and controls an output power of the energy storage device and an output power of the power generation device based on the determined minimum and maximum power set points.

Abstract: A microsource is provided, which includes an inverter, an energy storage device, and a controller. The controller calculates a maximum frequency change for the inverter based on a first comparison between a first power set point and a measured power from the inverter. The first power set point is defined based on a charge level of the energy storage device. A minimum frequency change for the inverter is calculated based on a second comparison between a second power set point and the measured power from the inverter. An operating frequency for the inverter is calculated based on a third comparison between a power set point and a measured power flow. A requested frequency for the inverter is calculated by combining the maximum frequency change, the minimum frequency change, and the operating frequency. The requested frequency is integrated to determine a phase angle of a voltage of the inverter to control a frequency of an output power of the inverter.

Abstract: A method includes operating a microsource in a grid mode in which the microsource is connected to a utility grid. The microsource is located in a microgrid and is configured to deliver a power P1 at a frequency ?1. During operation in the grid mode ?1 is a first frequency and P1 is a first power. The first frequency is an operating frequency of the utility grid. The microsource is transferred from the grid mode to an island mode, causing a frequency change such that ?1 changes to a second frequency and a power change such that P1 changes to a second power. The frequency change occurs at a first rate with respect to the power change while ?1 is less than a slope switch frequency. The frequency change occurs at a second rate with respect to the power change while ?1 is greater than the slope switch frequency.

Abstract: A microsource is provided, which includes a generator, a prime mover, and a controller. The prime mover includes a shaft connected to drive the generator to generate power at a frequency controlled by a rotation rate of the shaft. The controller calculates an operating frequency for the generator based on a comparison between a power set point and a measured power flow. A requested shaft speed for the prime mover is calculated by combining a maximum frequency change, a minimum frequency change, and the calculated operating frequency. A shaft speed adjustment is calculated for the prime mover based on a comparison between the requested shaft speed and a measured shaft speed of the prime mover. A fuel command for the prime mover is calculated based on the shaft speed adjustment. A rotation rate of the shaft of the prime mover is adjusted based on the calculated fuel command to control the frequency.

Abstract: A method of controlling the output inverter of a microsource in a distributed energy resource system is disclosed. Embodiments of the invention include using unit or zone power controllers that reduce the operating frequency of the inverter to increase its unit output power. Preferred embodiments includes methods wherein the inverter reaches maximum output power and minimum operating frequency at the same time, and further comprising using a voltage controller implementing a voltage vs. reactive current droop. Other aspects of this embodiment relate to an inverter that implements such methods, and a microsource containing such an inverter. These methods can be extended to control inverters in a plurality of microsources, organized in a single zone or in a plurality of zones.

Abstract: A microsource is provided, which includes an energy storage device, a power generation device, and a controller. The energy storage device is operably coupled for power transfer to a load through a first power bus. The power generation device is operably coupled for power transfer to the load through a second power bus. The controller determines a mode of operation for the energy storage device and the power generation device based on an energy level of the energy storage device and on the load; determines minimum power set points and maximum power set points for the energy storage device and the power generation device based on the determined mode of operation, on a storage output power measured at the first power bus, and on a generation output power measured at the second power bus; and controls an output power of the energy storage device and an output power of the power generation device based on the determined minimum and maximum power set points.

Abstract: A method and apparatus for an interface switch having an external terminal electrically connected to an AC voltage ? at a frequency ?0 (for example a utility supply), and an internal terminal electrically connected to an AC voltage V at a selectable frequency ? (for example a microsource). In one embodiment, the interface switch is closed when the voltage difference between ? and V and the relative phase angle ?EV between ? and V are both small, and when the higher frequency voltage (as between ? and V) leads the lower frequency voltage. In another embodiment, the interface switch is closed when the envelope of the voltage difference between ? and V reaches a local minimum at a point of inflection.

Abstract: A microsource is provided, which includes a generator, a prime mover, and a controller. The prime mover includes a shaft connected to drive the generator to generate power at a frequency controlled by a rotation rate of the shaft. The controller calculates an operating frequency for the generator based on a comparison between a power set point and a measured power flow. A requested shaft speed for the prime mover is calculated by combining a maximum frequency change, a minimum frequency change, and the calculated operating frequency A shaft speed adjustment is calculated for the prime mover based on a comparison between the requested shaft speed and a measured shaft speed of the prime mover. A fuel command for the prime mover is calculated based on the shaft speed adjustment. A rotation rate of the shaft of the prime mover is adjusted based on the calculated fuel command to control the frequency.

Abstract: A microsource is provided, which includes an inverter, an energy storage device, and a controller. The controller calculates a maximum frequency change for the inverter based on a first comparison between a first power set point and a measured power from the inverter. The first power set point is defined based on a charge level of the energy storage device. A minimum frequency change for the inverter is calculated based on a second comparison between a second power set point and the measured power from the inverter. An operating frequency for the inverter is calculated based on a third comparison between a power set point and a measured power flow. A requested frequency for the inverter is calculated by combining the maximum frequency change, the minimum frequency change, and the operating frequency. The requested frequency is integrated to determine a phase angle of a voltage of the inverter to control a frequency of an output power of the inverter.

Abstract: A power electronics interface in a microsource controller allows efficient connection in a power system of small, low cost and reliable distributed generators such as microturbines, fuel cells and photovoltaic. Power electronics provide the control and flexibility to insure stable operation for large numbers of distributed generators. The power electronics controls are designed to insure that new generators can be added to the system without modification of existing equipment. A collection of sources and loads can connect to or isolate from the utility grid in a rapid and seamless fashion, each inverter can respond effectively to load changes without requiring data from other sources, and voltage sag and system imbalances can be corrected.

Abstract: A power electronics interface in a microsource controller allows efficient connection in a power system of small, low cost and reliable distributed generators such as microturbines, fuel cells and photovoltaic. Power electronics provide the control and flexibility to insure stable operation for large numbers of distributed generators. The power electronics controls are designed to insure that new generators can be added to the system without modification of existing equipment. A collection of sources and loads can connect to or isolate from the utility grid in a rapid and seamless fashion, each inverter can respond effectively to load changes without requiring data from other sources, and voltage sag and system imbalances can be corrected.

Abstract: A method and apparatus is provided for restoring a sagging voltage signal on a power transmission line, caused by a remote fault in the utility power system, to a balanced three-phase condition at the pre-fault voltage level. Voltage restoration is provided by injecting a voltage signal in series with the power transmission line which restores the load voltage vectors to the pre-fault condition. The restored load voltage vectors are rotated by a selected phase angle such that zero real power flow is associated with the voltage restoration. The voltage compensation signal may be injected into the power transmission line by connecting a voltage compensator inverter in series with the transmission line. The voltage compensator inverter may be controlled to provide the desired injected voltage signal using a synchronous reference frame based controller.

Abstract: A high voltage d.c. power transmission system utilizes a metallic return conductor for carrying return current between converters at opposite ends of the system. The return conductor is connected to earth ground at one end of the system and is otherwise insulated from earth ground so that its opposite end is floating with respect to d.c. The return conductor has no capacitor connected from earth ground thereto of a size capable of limiting the voltage thereon. But connected between said opposite end of the return conductor and earth ground is a valve-type surge arrestor having a primarily zinc-oxide valve element and no gap in series therewith. This surge arrestor has a protective level that is reached by the overvoltages produced by the normal operating transients of the system, such as those produced by system start-up and commutation failures.