Load Shed Module

• US 20160204651A1
• Filed: 01/09/2015
• Published: 07/14/2016
• Est. Priority Date: 01/09/2015
• Status: Active Grant

• Current Assignee: Generac Power Systems Incorporated (Generac Holdings Incorporated)
• Original Assignee: Generac Power Systems Incorporated (Generac Holdings Incorporated)
• Inventors: lles, Robert, Phillips, Andy, Yu, Taesik, Lee, Sungmin, Pancheri, Brendan, Wischstadt, Greg
• Granted Patent: US 10,069,331 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: G01R 11/04 Housings; Supporting racks; Arrangements of terminals
• CPC Class Codes: G01R 11/06 Magnetic circuits of induction meters
• CPC Class Codes: H02J 2310/12 The local stationary network supplying a household or a building
• CPC Class Codes: H02J 2310/14 The load or loads being home appliances
• CPC Class Codes: H02J 3/14 by switching loads on to, or off from, network, e.g. progressively balanced loading
• CPC Class Codes: H02J 9/061 for DC powered loads
• CPC Class Codes: Y02B 70/30 Systems integrating technologies related to power network operation and communication or information technologies for improving the carbon footprint of the management of residential or tertiary loads, i.e. smart grids as climate change mitigation technology in the buildings sector, including also the last stages of power distribution and the control, monitoring or operating management systems at local level
• CPC Class Codes: Y02B 70/3225 Demand response systems, e.g. load shedding, peak shaving
• CPC Class Codes: Y04S 20/222 Demand response systems, e.g. load shedding, peak shaving
• CPC Class Codes: Y04S 20/242 Home appliances
• CPC Class Codes: Y04S 20/248 UPS systems or standby or emergency generators

Abstract

A load shed module configured to be connected in series between a power supply and a load is disclosed. A separate load shed module is connected in series between each load and the power supply. The load shed module determines the frequency of the voltage supplied from the power supply. Based on the frequency, the load shed module determines if utility power is connected or if a generator is connected. If the generator is connected and the frequency of the voltage goes outside of a desired operating range for a preset time, the load shed module disconnects the load from the power supply. Each load shed module includes a priority setting and reconnects its corresponding load after a predetermined time corresponding to the priority setting.

Claims

1. A load shed module configured to be connected in series between a power source and a load, the load shed module comprising:

an input configured to receive a first electrical connection from the power source;

an output configured to provide a second electrical connection for the load;

a switch operatively connected in series between the input and the output, wherein the switch receives a control signal to selectively open and close the switch;

a sensor configured to generate a feedback signal corresponding to an alternating current (AC) voltage present at the input;

a priority selector operable to generate a priority signal for the load shed module,

a controller connected to the sensor to receive the feedback signal, connected to the priority selector to receive the priority signal, and connected to the switch to supply the control signal, wherein the controller is operable to;

determine whether the power source is a utility power source or an alternate power source as a function of the feedback signal,

compare the feedback signal to a threshold when the power source is the alternate power source,

generate the control signal to open the switch when the feedback signal exceeds the threshold for a first predetermined time, and

generate the control signal to close the switch when the power source is the alternate power source and when a second predetermined time has passed, wherein the second predetermined time is selected as a function of the priority signal.

2. The load shed module of claim 1 wherein the controller is further operable to:

determine a frequency of the AC voltage present at the input from the feedback signal, and

determine whether the power source is the utility power source or the alternate power source as a function of the frequency of the AC voltage.

3. The load shed module of claim 2 wherein the controller is further operable to:

store a minimum frequency of the AC voltage,

store a maximum frequency of the AC voltage,

determine a difference between the minimum frequency and the maximum frequency, wherein the threshold is a maximum difference between the minimum frequency and the maximum frequency, and

generate the control signal to open the switch when the difference exceeds the maximum difference for the first predetermined time.

4. The load shed module of claim 2 wherein the controller is further operable to:

determine a difference between the frequency of the AC voltage present at the input and an expected frequency of the AC voltage present at the input, wherein the threshold is a maximum difference between the frequency of the AC voltage present at the input and the expected frequency of the AC voltage present at the input, and

generate the control signal to open the switch when the difference exceeds the maximum difference for the first predetermined time.

5. The load shed module of claim 1 wherein:

the controller is configured to operate in a first operating mode and in a second operating mode;

during the first operating mode, the controller generates the control signal to open the switch when the feedback signal exceeds the threshold for the first predetermined time;

during the second operating mode, the controller generates the control signal to open the switch when the feedback signal exceeds the threshold for a third predetermined time; and

the third predetermined time is less than the first predetermined time.

6. The load shed module of claim 5 wherein during the second operating mode, the controller is further operable to enter a lock out operating mode when the feedback signal exceeds the threshold for the third predetermined time.

7. A method of connecting a load to a power source in a power distribution system, comprising the steps of:

reading a feedback signal corresponding to a voltage received at an input of a load shed module from the power source;

determining a frequency of the voltage from the feedback signal with a controller in the load shed module;

comparing the frequency to a threshold frequency;

generating a control signal with the controller to open a switch connected in series between the input and an output of the load shed module when the frequency of the voltage at the input is outside of the threshold frequency for a first predetermined time, wherein the output of the load shed module is connected to the load;

determining a priority level of the load shed module; and

generating the control signal with the controller to close the switch connected in series between the input and the output of the load shed module after a second predetermined time when the frequency of the voltage is within the threshold frequency, wherein the second predetermined time is a function of the priority level of the load shed module.

8. The method of claim 7 further comprising the step of determining whether the voltage at the input of the load shed module is from a utility power source or from a backup generator as a function of the frequency of the voltage.

9. The method of claim 7 wherein:

the load shed module is operable in a first operating mode and in a second operating mode,

the first predetermined time is a first duration in the first operating mode,

the first predetermined time is a second duration in the second operating mode, and

the first duration is longer than the second duration.

10. The method of claim 9 further comprising the step of entering a lock out operating mode when the frequency of the voltage at the input is outside of the threshold frequency for the first predetermined time during the second operating mode.

11. The method of claim 7 further comprising the steps of:

determining a minimum frequency of the voltage at the input of the load shed module with the controller;

determining a maximum frequency of the voltage at the input of the load shed module with the controller;

determining a difference between the minimum frequency and the maximum frequency with the controller, wherein the threshold frequency is a maximum difference between the minimum frequency and the maximum frequency, and

generating the control signal to open the switch when the difference exceeds the maximum difference for the first predetermined time.

12. The method of claim 7 further comprising the steps of:

determining a difference between the frequency of the voltage present at the input and an expected frequency of the voltage present at the input, wherein the threshold is a maximum difference between the frequency of the voltage present at the input and the expected frequency of the voltage present at the input, and

generating the control signal to open the switch when the difference exceeds the maximum difference for the first predetermined time.

13. A load shed system configured to be connected in series between an output of a transfer switch and a plurality of loads, wherein the transfer switch selectively connects one of a utility power source and an alternate power source to the output of the transfer switch, the load shed system comprising:

a plurality of load shed modules, each load shed module electrically connected between the output of the transfer switch and one of the plurality of loads, wherein each load shed module includes;

a housing configured to be mounted independently of each of the other load shed modules;

an input configured to receive a first electrical connection from the transfer switch;

an output configured to provide a second electrical connection for the corresponding load;

a switch operatively connected in series between the input and the output, wherein the switch receives a control signal to selectively open and close the switch;

a sensor configured to generate a feedback signal corresponding to an alternating current (AC) voltage present at the input;

a priority selector operable to generate a priority signal for the load shed module; and

a controller connected to the sensor to receive the feedback signal, connected to the priority selector to receive the priority signal, and connected to the switch to supply the control signal, wherein

the controller is operable to determine whether the power source is the utility power source or the alternate power source as a function of the feedback signal and to generate the control signal to close the switch when the power source is the alternate power source and when an initial predetermined time has passed,

the initial predetermined time is selected as a function of the priority signal; and

each of the plurality of load shed modules has no communication with the other of the plurality of load shed modules.

14. The load shed system of claim 13 wherein the controller is further operable to compare the feedback signal to a threshold when the power source is the alternate power source and to generate the control signal to open the switch when the feedback signal exceeds the threshold for a running mode predetermined time.

15. The load shed system of claim 14 wherein the controller is further operable to:

determine a frequency of the AC voltage present at the input, and

determine whether the power source is the utility power source or the alternate power source as a function of the frequency of the AC voltage.

16. The load shed system of claim 15 wherein each load shed module further includes a memory device and the controller is further operable to

store a minimum frequency of the AC voltage in the memory device,

store a maximum frequency of the AC voltage in the memory device,

determine a difference between the minimum frequency and the maximum frequency, wherein the threshold is a maximum difference between the minimum frequency and the maximum frequency, and

generate the control signal to open the switch when the difference exceeds the maximum difference for the running mode predetermined time.

17. The load shed system of claim 15 wherein the controller is further operable to:

determine a difference between the frequency of the AC voltage present at the input and an expected frequency of the AC voltage present at the input, wherein the threshold is a maximum difference between the frequency of the AC voltage present at the input and an expected frequency of the AC voltage present at the input, and

generate the control signal to open the switch when the difference exceeds the maximum difference for the running mode predetermined time.

18. The load shed system of claim 13 wherein:

the controller is configured to operate in a first operating mode and in a second operating mode;

during the first operating mode, the controller generates the control signal to open the switch when the feedback signal exceeds the threshold for a running mode predetermined time;

during the second operating mode, the controller generates the control signal to open the switch when the feedback signal exceeds the threshold for a transitional mode predetermined time; and

the transitional mode predetermined time is less than the running mode predetermined time.

19. The load shed system of claim 18 wherein during the second operating mode, the controller is further operable to enter a lock out operating mode when the feedback signal exceeds the threshold for the transitional mode predetermined time.

20. The load shed system of claim 13 wherein the load shed module is configured to be mounted either proximate to the transfer switch or proximate to the corresponding load.