TECHNICAL FIELD

The present invention relates to power generation facilities. More specifically, the present invention provides methods and systems for operating a power generation facility such as a photovoltaic (PV) solar farm.

BACKGROUND

Power systems worldwide need to ensure voltage regulation, stability, allow high levels of power transmission capacity in the lines to transfer power from existing or new generating sources, and regulate system frequency, despite various system disturbances. These disturbances could be slow and gradual variations in loads and generation, or large and sudden variations, such as faults, line switching, equipment outages, etc.

There are primarily two types of stability:

Angle Stability: This relates to maintaining synchronism of generators. It has two main components:a) Small Signal Stability—caused by small disturbances and insufficient damping in power systems with respect to different oscillatory modesb) Transient Stability—This is affected by large disturbances in power systems

Voltage Stability: This relates to the system's ability to maintain acceptable voltages, and is typically caused by lack of adequate reactive power support both during steady state and during disturbances such as faults.

Another major problem being increasingly encountered is the lack of power transfer capacity in transmission and distribution lines. Increasing stability significantly increases the power transmission capacity of transmission lines. On the other hand, the power transfer capacity in distribution lines is typically limited by thermal limits of the line.

A third problem being faced by power systems is the regulation of system frequency despite the ongoing system disturbances. Frequency deviations occur due to imbalances between the generation and the loads during disturbances. Maintaining frequency is an important issue in isolated power systems, such as microgrids.

Another issue with current technology is the lack of power carrying capacity in power transmission lines. With the ever-growing number of renewable generating sources in power transmission and distribution grids, there is an imminent need for providing capacity on existing lines to carry the real power generated by them.

The existing technology for compensating for reactive power flows in the lines is through passive devices such as capacitors and inductors, which are fixed in rating, and hence not controllable. Therefore, this method is not widely employed due to these limitations.

The other option is to install very expensive dynamic reactive power compensators such as Static Var Compensator (SVC) or Static Synchronous Compensator (STATCOM). These may not be cost-effective for the objective to be achieved.

Based on the above, there is therefore a need for systems, methods, and devices which mitigate if not overcome the issues noted above. More specifically, since photovoltaic (PV) solar farms conventionally only produce real power, and do not contribute to increasing system stability, enhancing power transfer capacity, or providing frequency control, methods and systems which would allow PV energy farms to perform these functions would be desirable.

SUMMARY

The present invention provides systems, methods, and devices relating to operating a power generation facility to contribute to the overall stability of the power transmission system. A controller operates on the power generation facility to modulate real power or reactive power, or both real and reactive power in a decoupled (independent) control mode to contribute to the overall stability of the power transmission system. Real or reactive power, or both, can be injected into the power transmission system as necessary. As well, the real power produced or the reactive power produced by the power generation facility can be increased or decreased as required by the power transmission system. For solar farms, the solar panels can be connected or disconnected to add or subtract real power. Also, the real power output from the solar panels can be modulated by varying its output direct current (DC) voltage. The inverter can further be controlled to inject or absorb reactive power with the power transmission system.

In a first aspect, this document discloses a method for enhancing stability in a power grid system to which is coupled a power generation facility, the method comprising:a) detecting a need for enhancing system stability in said power grid system;b) modulating at least one of reactive power, real power, and a combination of real and reactive power from said power generation facility; andc) providing at least one of modulated reactive power, modulated real power, and a combination of said modulated reactive power and said modulated real power from said power generation facility to said power grid system; wherein a modulation of a combination of real and reactive power is performed simultaneously in a decoupled manner,wherein step b) further comprises adjusting at least one inverter of said power generation facility to thereby use at least a portion of said at least one inverter's capacity to provide at least one of said modulated reactive power, said modulated real power, and said combination of modulated real and modulated reactive power; andwherein at least one of said modulated reactive power, said modulated real power, and said combination of modulated real and modulated reactive power increases said stability of said power grid system by performing at least one of:damping system oscillations;increasing transient stability;regulating power system frequency;improving voltage stability and voltage regulation;increasing power transmission capacity in transmission lines; andincreasing power transmission capacity in distribution lines.

In a second aspect, this document discloses a method for enhancing stability in a power grid system to which is coupled a power generation facility, the method comprising:a) detecting a need for enhancing system stability in said power grid system;b) modulating at least one of reactive power, real power, and a combination of real and reactive power from said power generation facility; andc) providing at least one of modulated reactive power, modulated real power and a combination of said modulated reactive power and said modulated real power from said power generation facility to said power grid system;

wherein said combination of real and reactive power is modulated simultaneously in a decoupled manner,

wherein step b) further comprises adjusting at least one inverter of the power generation facility to thereby use at least a portion of said at least one inverter's capacity to provide at least one of said modulated reactive power, said modulated real power, and said combination of said modulated reactive power and said modulated real power,

wherein at least one of said modulated reactive power, said modulated real power, and said combination of said modulated real power and said modulated reactive power increases said stability of said power grid system by performing at least one of:damping system oscillations;increasing transient stability;regulating power system frequency;improving voltage stability and voltage regulation;increasing power transmission capacity in transmission lines; andincreasing power transmission capacity in distribution lines, and

wherein said power generation facility is operated such that any remaining inverter capacity in said power generation facility after real power production is used for reactive power exchange.

