System and method for managing AC power using auxiliary DC-to-AC inversion

Patent metadata

Field	Value
Publication number	US-9847643-B2
Application number	US-201414446092-A
Country	US
Kind code	B2
Filing date	Jul 29, 2014
Priority date	Jul 29, 2014
Publication date	Dec 19, 2017
Grant date	Dec 19, 2017

Abstract

A system and method are provided for managing demand for a client with a fluctuating AC power grid demand, using DC-to-AC power inversion as an auxiliary source of power. The inverter has a selectable inversion power output levels connected to the AC client to supply auxiliary power for a portion of the AC power demand. The AC grid demand is averaged. In each of a series of periodic time intervals, a current AC grid demand average in a current time interval is compared to a demand goal, which is the highest AC grid demand average, as measured at an end of a time interval, and selected from a plurality of time intervals. The inverter output power level is selected so that the current AC grid demand average is less than or equal to the demand goal by the end of the current time interval.

First claim

We claim:

1. A method for managing demand for an alternating current (AC) client using direct current (DC)-to-AC power inversion as an auxiliary source of power, the method comprising:
providing an AC client with a fluctuating AC grid demand, a DC-to-AC inverter having an input connected to a DC power auxiliary source and selectable inversion power output levels connected to the AC client to supply auxiliary power for a portion of the AC power demand;
averaging the AC grid demand;
in each of a series of periodic time intervals, comparing a current AC grid demand average in a current time interval to a demand goal, which is a highest AC grid demand average as measured at an end of a time interval, and selected from a plurality of time intervals; and,
selecting the DC-to-AC inverter output power level so that the current AC grid demand average is less than or equal to the demand goal by the end of the current time interval.

2. The method of claim 1 further comprising:
establishing an efficient power trigger level equal to the demand goal;
establishing a continuous power trigger level equal the demand goal plus a leeway margin;
wherein selecting the inverter output power level so that the current AC grid demand average is less than or equal to the demand goal by the end of the current time interval includes:
selecting at least a first DC-to-AC inverter output power level, having a first efficiency, when the current AC grid demand average exceeds the efficient power trigger level; and,
selecting at least a second DC-to-AC inverter output power level greater than the first DC-to-AC inverter output power level, and having a second efficiency less than the first efficiency, when the current AC grid demand average exceeds the continuous power trigger level.

3. The method of claim 2 wherein providing the DC-to-AC inverter includes the DC-to-AC inverter having a limited availability, selectable third DC-to-AC inverter output power level, greater than the second DC-to-AC inverter output power level, with a third efficiency less than the second efficiency; and,
wherein selecting the DC-to-AC inverter output power level so that the current AC grid demand average is less than or equal to the demand goal by the end of the current time interval includes using the third DC-to-AC inverter output power level when required to make the current AC grid demand average less than or equal to the demand goal by the end of the current time interval.

4. The method of claim 3 further comprising:
calculating the availability of the third DC-to-AC inverter output power level in the current time interval;
in response to calculating the availability of the third DC-to-AC inverter output power level, establishing a maximum power trigger level; and,
wherein using the third DC-to-AC inverter output power level when required includes using the third DC-to-AC inverter output power level when the current AC grid demand average exceeds the maximum power trigger level.

5. The method of claim 4 wherein calculating the availability of the third DC-to-AC inverter output power level includes calculating a “B” segment of time immediately preceding the end of the current time interval, in which the third DC-to-AC inverter output power level is available; and,
wherein establishing the maximum power trigger level includes calculating a negative slope, from the end of the current time interval, equal to the third DC-to-AC inverter output power level minus the second DC-to-AC inverter output power level, divided by the duration of the time interval, and ending at a beginning of the “B” segment of time.

6. The method of claim 5 wherein calculating the availability of the third DC-to-AC inverter output power level includes calculating an “A” segment of time between the end of a previous time interval and the beginning of the “B” segment of time in the current time interval; and,
wherein establishing the maximum power trigger level includes establishing a constant value maximum power trigger level in the “A” segment of time equal to the value of the negative slope at the beginning of the “B” segment of time.

7. The method of claim 6 wherein calculating the availability of the third DC-to-AC inverter output power level in the current time interval includes calculating the availability in response to DC-to-AC inverter temperature and time of use.

8. The method of claim 7 wherein calculating the “B” segment of time in which the third DC-to-AC inverter output power level is available includes calculating a heating time, which is a function of the time expected for the DC-to-AC inverter to reach a maximum threshold temperature, from a current temperature, when running at the third DC-to-AC inverter output level.

9. The method of claim 5 wherein calculating the availability of the third DC-to-AC inverter output power level includes calculating an “A” segment of time between the end of a previous time interval and the beginning of the “B” segment of time in the current time interval; and,
wherein using the third DC-to-AC inverter output power level when required includes using the third DC-to-AC inverter output power level only in the “B” segment of time.

10. The method of claim 5 wherein establishing the maximum power trigger level includes establishing a conservative maximum power trigger level by calculating a negative slope, from the end of the current time interval as offset by a safety time margin, equal to the third DC-to-AC inverter output power level minus the second DC-to-AC inverter output power level, divided by the duration of the time interval, minus a safety power margin and ending at the beginning of the “B” segment of time.

11. The method of claim 4 wherein establishing the maximum power trigger level includes establishing a maximum power trigger level less than the continuous power trigger level;
wherein selecting the DC-to-AC inverter output power level so that the current AC grid demand average is less than or equal to the demand goal by the end of the current time interval includes using the second DC-to-AC inverter output power level when the current AC grid demand average is greater than the maximum power trigger level.

12. The method of claim 2 wherein establishing the efficient power trigger level equal to the demand goal includes establishing the efficient power trigger level equal to the demand goal minus a jitter margin.

13. A system for managing demand for an alternating current (AC) client using direct current (DC)-to-AC power inversion as an auxiliary source of power, the system comprising:
a DC-to-AC inverter having an input connected to a DC power auxiliary source and selectable inversion power output levels connected to an AC client to supply auxiliary power for a portion of a fluctuating AC grid demand;
a measurement module having an interface connected to the AC client, the measurement module averaging the AC grid demand, and in each of a series of periodic time intervals, comparing a current AC grid demand average in a current time interval to a demand goal, which is a highest AC grid demand average as measured at an end of a time interval, and selected from a plurality of time intervals; and,
a controller having an interface connected to the DC-to-AC inverter and measurement module, the controller selecting the DC-to-AC inverter output power level so that the current AC grid demand average is less than or equal to the demand goal by the end of the current time interval.

14. The system of claim 13 wherein the measurement module establishes an efficient power trigger level equal to the demand goal, and a continuous power trigger le

Assignees

• Sharp Laboratories America Inc

Inventors

• Park Daniel

Classifications

• H02J3/381 Primary

  Dispersed generators · CPC title

• Y04S20/222

  Demand response systems, e.g. load shedding, peak shaving · CPC title

• Y02B70/3225

  Demand response systems, e.g. load shedding, peak shaving · CPC title

• H02J2105/12

  supplying households or buildings · CPC title

• H02J3/14

  by switching loads on to, or off from, the networks, e.g. progressively balanced loading · CPC title