WO2013010266A1

WO2013010266A1 - Method and system for providing local primary frequency response

Info

Publication number: WO2013010266A1
Application number: PCT/CA2012/000691
Authority: WO
Inventors: Malcolm Stuart Metcalfe; Andrew Ross GASSNER
Original assignee: Enbala Power Networks Inc.
Priority date: 2011-07-21
Filing date: 2012-07-20
Publication date: 2013-01-24

Abstract

A method for providing a local primary frequency response within a local region of an electrical power system uses one or more local load resources electrically coupled to the power system within the local region. The method comprises: determining one or more local frequency characteristics of the power system within the local region; determining an emulated inertial response for each local load resource based upon the local frequency characteristics; determining a desired local primary frequency response for each local load resource based upon the emulated inertial response determined for each local resource; determining operational setpoints for each local load resource to provide the desired local primary frequency response for the local resource; and directing the local load resources to operate at the selected operational setpoints for each local resource.

Description

Method and System for Providing Local Primary Frequency Response Field

[0001] This disclosure relates generally to a method and system for providing local primary frequency response in an electrical power system.

Background

[0002] Electricity is a currency, providing a convenient means of transporting energy from a source such as falling water, solar or wind to end users. Electricity is delivered at the speed of light and it is used the instant that it is created.

[0003] Utilities that generate and deliver electricity require a number of services, called Ancillary Services to achieve and maintain balance between supply and demand in the power system. These services include, but are not limited to:

System Regulation or Balancing: This service adjusts load or generation based on commands from an Automatic Generation Control (AGC) system at the System Control Centre of a utility to provide second by second balance between the power that is generated and the power that is consumed. The AGC system sends control signals every few seconds to continuously maintain this balance. System regulation has traditionally been provided by generators, but loads and storage devices are now being used to fulfill this role.

Operating Reserves: There are several types of reserves that fit into this category, and all are used to provide extra power at times when the power system is experiencing shortages or an unexpected loss of generation.

Demand Response: At peak load times, utilities may offer customers a payment to reduce their consumption for a period of time. Under Frequency Load and Generation Shedding: In cases where a system disturbance causes a decline in system frequency, large steam turbine generators may trip off-line to protect their machinery from damage caused by operations at speeds outside their intended design. To minimize the risk of generation shedding, there is a load shedding system that will operate at a higher frequency, with the intent of halting the decay in frequency and avoiding the need for generation shedding. Generation shedding is often the first stage of a cascading failure.

[0004] In addition to the Ancillary Services, there is another type of response that is essential in maintaining the reliable operation of the grid and is known as Primary Frequency Response (PFR). PFR is an autonomous and locally controlled action to either increase or decrease power output in response to a change in system frequency. PFR helps to arrest the change in frequency as other ancillary services are deployed to bring the power system back to the normal state. PRF is the first line of defence in maintaining stability after a system disturbance. PFR includes three different components:

Inertia response: provided by masses that rotate in generators and large synchronous motors. Any change in system frequency will autonomously cause these devices to either speed up or slow down, and the acceleration will cause them consume/generate either more or less power in a direction that will oppose a change in frequency. The short term power change is reflected in an increase or decrease in the rotating kinetic energy of the machine.

Generator Governor Droop Response: Most generators are equipped with speed governors that will increase or decrease the power input to the generator turbine with any change in the generator speed of rotation/ system frequency, thereby adjusting the generator's output accordingly as a droop response. Each generator has a specified droop setting, which is defined as the amount of speed (i.e. frequency) change that is necessary to cause the governor to cause the generator to change its droop response from 0 to 100%. The magnitude of the droop response change follows a droop line - e.g. a a generator with a 5% droop setting will change the power output by 100% when system frequency rises or falls by 5%.

Load response: Many loads will autonomously increase or reduce their consumption on a rise or fall in either voltage of frequency, such as, for example, motor loads, and driving HVAC systems.

[0005] In recent years, new technology has changed the characteristics of both generation and loads in the power system. Many large generators operate without effective governor response. Load characteristics have changed. The percentage of motor loads has decreased and many of the remaining large motors are equipped with Variable Frequency Drives (VFDs), which make the motors insensitive to system frequency changes. Additionally, most electronic equipment (including computers) is frequency and voltage independent. The available amount of PFR has fallen and the rate of decline appears to be increasing. At present, a large contingent loss of generation can result in a decrease in system frequency that may come close to or exceed the automatic load shedding levels.

Summary

[0006] According to one aspect of the present disclosure, there is provided a method for providing a local primary frequency response within a local region of an electrical power system, using one or more local load resources electrically coupled to the power system within the local region. The method comprises:

(a) determining one or more local frequency characteristics of the power system within the local region;

(b) determining an emulated inertial response for each local load resource based upon the local frequency characteristics; (c) determining a desired local primary frequency response for each local load resource based upon the emulated inertial response determined for each local resource;

(d) determining operational setpoints for each local load resource to provide the desired local primary frequency response for the local resource; and

(e) directing the local load resources to operate at the selected operational setpoints for each local resource.

[0007] The method may further comprise determining an emulated droop response for each local load resource based upon the local frequency characteristics; and the desired local primary frequency response for each local load resource may be determined based upon the emulated droop response and the emulated inertial response determined for the local resource.

[0008] The local frequency characteristics may comprise (a) the deviation between the local frequency of the power system at the location from a nominal frequency of the power system and (b) the rate of change of the local frequency of the power system within the local region.

[0009] The emulated droop response may be determined based upon the deviation of the local frequency from the nominal frequency scaled by a local droop setting. Also, the emulated droop response may be set to zero if the difference between the local frequency and the nominal frequency does not exceeds a local droop deadband. Further, the emulated droop response may be applied based upon an adjustable time constant.

[0010] The emulated inertial response may be determined based upon the rate of change of the local frequency of the power system within the local region. Also, the emulated inertial response may be determined by scaling the rate of change of the local frequency by a local inertial setting. [0011] The method may further comprise determining a total local primary frequency response provided by the local load resources, and communicating the total local primary frequency response to an independent system operator or an integrated electricity provider.

[0012] In another aspect of the present disclosure there is provide a system for implementing the foregoing method. The system may comprise a local controller in communication with one or more local load resources, the system configured to receive operational state information from the local load resources and direct the local load resources to operate at operational setpoints. The local controller may comprise a local master controller and one or more local load resource controllers. The system may communicate select information to a remote server which then communicates the total local primary frequency response to an independent system operator or an integrated electricity provider.

Brief Description of Figures

[0013] Figure 1 is a block diagram of a system for providing local primary frequency response in an electrical power system according to one embodiment.

[0014] Figure 2 is a flow diagram of a method of providing local primary frequency response in an electrical power system according to one embodiment.

Detailed Description

[0015] The embodiments described herein generally relate a method and system for providing local primary frequency response in an electrical power system using at least one load resource. Unlike loads that autonomously react to a change in system frequency (as is known in the art), the embodiments here employ a method that pro-actively determines a desired local primary frequency response for each local load resource based upon the emulated inertial response and optionally droop response determined for each local resource, then controls the output of those load resources to provide the determined local primary frequency response.

[0016] Throughout the disclosure where a server or controller is referenced it may include one or more servers or controllers in communication with each other through one or more networks or communication mediums. Each server and controller generally comprises one or more processors and one or more computer readable mediums in communication with each other through one or more networks or communication mediums. The one or more processors may comprise any suitable processing device known in the art, such as, for example, application specific circuits, programmable logic controllers, field programmable gate arrays, microcontrollers, microprocessors, virtual machines, and electronic circuits. The one or more computer readable mediums may comprise any suitable memory devices known in the art, such as, for example, random access memory, flash memory, read only memory, hard disc drives, optical drives and optical drive media, or flash drives. In addition, where a network is referenced it may include one or more suitable networks known in the art, such as, for example, local area networks, wide area networks, intranets, and the Internet. Further, where a communication to a device or a direction of a device is referenced it may be communicated over any suitable electronic communication medium and in any suitable format known to in the art, such as, for example, wired or wireless mediums, compressed or uncompressed formats, encrypted or unencrypted formats.

[0017] Referring to Figure 1 , an embodiment is shown of a system 100 for providing local primary response in an electrical power system 150. The system 100 generally comprises a local portion and a remote portion: the local portion comprising a local master controller 110, a plurality of local resource controllers 120A-C, and a plurality of local resources 140A-C; and the remote portion comprising a remote server 160. [0018] The system 100 is generally configured to provide a local primary frequency response by monitoring local frequency characteristics of the electrical power system 150 within a local region of the electrical power system 150 (hereinafter referred to as the "local region"), determining a desired local primary frequency response based on the measured local frequency characteristics, and directing select local resources 140A-C to operate at specific setpoints determined to provide the desired local primary frequency response.

[0019] The local resources 140A-C comprise electrical devices that are electrically connected to the electrical power system 150 within the local region. The local resources 140A-C comprise one or more electrically-powered devices having capacity to consume a load ("load resources"). The local resources can also include electrical generators having capacity to generate power ("generation resources"), and storage devices having capacity to store energy and later release it back to the electrical power system 50 ("storage resources").

[0020] In this embodiment, the load resource can for example be a multiple single-speed water pump, an analog electrical boiler, and an analog electrical blower. These electrically-powered devices are normally intended to serve a primary process other than providing a local primary frequency response, and the system 100 is configured to operate one or more of these devices as a load resource to provide local primary frequency response services only within the operational constraints defined by the original primary processes of these devices. For example, the water pump can be used primarily to regulate the water level in a municipal water supply tank, each electrical boiler can be used primarily to provide heat and domestic hot water for a building as part of a hybrid electric-gas heating system, and each blower can be used primarily to aerate a waste water treatment tank. An enable switch (not shown) can be provided which is actuated by an operator to place the load resource on-line to be available provide local primary frequency response, or off-line to provide services to its primary process. Alternatively, the master controller 110 can be programmed with an algorithm that can determine when a load resources operational constraint is reached and then automatically take a load resource off line; a similar such algorithm is disclosed in Applicant's PCT application WO 2011/085477 for using load resources in providing ancillary services.

[0021] The local resources 140A-C are monitored and controlled by local resource controllers 120A-C located within or in close proximity to the local region. Local resource controllers 120A-C are configured to receive control signals from the local master controller 110 comprising operational setpoints for each of the local resources 140A-C determined to provide a desired local primary frequency response, and direct the local resources 140A-C to operate at the operational setpoints. In addition, resources controllers 120A-C are configured to monitor the operational state of the local resources 140A-C and communicate the operational state of the resources 140A-C to the local master controller 110 (for example, setpoints, change in setpoints, electrical demand, voltage, etc.). In the alternative, the plurality of local resource controllers 120A-C may comprise a single controller. In the further alternative, each local resource controller 120A-C may comprise multiple controllers in communication with one another.

[0022] The local master controller 110 is located within or in close proximity to the local region and is generally configured to: measure local frequency characteristics of the electrical power system 150 within the local region, determine a desired local primary frequency response based on the measured local frequency characteristics, determine operational setpoints of select local resources 140A-C that will provide the desired local primary frequency response, and direct the resources controllers 120A-C to operate the select local resources 140A-C at the setpoints. In addition, the local master controller 110 is configured to receive information respecting the operational state of the local resources 140A-C from the resources controllers 120A-C (for example, setpoints, change in setpoints, electrical demand, voltage, etc.), determine the individual and total local primary frequency responses actually provided by the local resources 140A-C, and communicate to the remote server 160 the local frequency and the individual and total local primary frequency responses provided by the local resources 140A-C. Such communications from the local master controller 110 to the remote server 160 may occur periodically (for example, every 2-4 seconds) or upon the occurrence of predefined events (for example, upon a predefined local frequency deviation). Alternatively, the local master controller 110 may communicate to the remote server 160 other information received from the local resources 140A-C or determined based upon information received from the local resources 140A-C.

[0023] The local master controller 110 generally comprises a processor communicative with the local resource controllers, a memory having encoded thereon a local primary frequency response program executable by the processor, and a frequency meter. The frequency meter is electrically coupled to the electrical power system 150 within the local region and is capable of accurately and rapidly measuring the local frequency of the electrical power system 150 within the desired primary frequency control period of the electrical power system 150. In the present embodiment, the frequency meter is configured to measure the local frequency at 10 times per second. Alternatively, the frequency meter may be configured to measure the local frequency at any desired rate within the desired primary frequency control period of the electrical powers system 150. In the further alternative, the local master controller 110 may comprise multiple controllers in communication with one another. In the yet further alternative, the local master controller 1 0 and local resource controllers 120A-C may comprise a single controller.

[0024] The remote server 160 is generally configured to receive information from the local master controller 110 (for example, the local frequency characteristics and the total local primary frequency responses provided by the local resources 140A-C) and communicate the local frequency characteristics (or a subset thereof) and the total local primary frequency response to an independent system operator (ISO), integrated electricity provider or other desired recipient. Alternatively, the remote server 160 may communicate to the ISO, integrated electricity provider or other desired recipient other information received from the local master controller 110 or determined based upon such information received from the local master controller 110. The remote server 160 may be located at any desirable location within or remote from the local region. In the alternative, the remote server 160 may be eliminated from the system 100 and the local master controller may communicate information directly to the ISO, integrated electricity provider or other desired recipient.

[0025] Referring to Figure 2, one embodiment is shown of a method 200 of providing local primary frequency response in an electrical power system 50 which utilizes at least one load resource in providing the local primary frequency response. The method 200 is encoded in the local primary frequency response program and executed by the system 100 to control the local resources to provide a suitable local primary frequency response. In block 202, the frequency meter of the local master controller 110 measures the local frequency of the power system 150 and the processor of the local master controller 110 determines local frequency characteristics of the power system 150. In the alternative, the frequency meter may determine the local frequency characteristics. In the present embodiment, the frequency characteristics comprise the deviation of the local frequency from the nominal frequency of the electrical power system 150 (e.g. 60 Hz in North America) and the rate of change of the local frequency. In the alternative, the local master controller 110 may determine other local frequency characteristics, such as, for example, higher order derivatives of the local frequency.

[0026] In block 206, the local master controller 110 determines an emulated droop response for each selected local resource 140A-C on the measured local frequency characteristics wherein at least one of the selected local resources is a load resource. In the present embodiment, the emulated droop response is determined based upon the deviation of the local frequency from the nominal frequency scaled by an adjustable local droop setting, and regulated by an adjustable local droop deadband (LDD) such that the emulated droop response will be zero unless the deviation of the local frequency from the nominal frequency exceeds the local droop deadband. This may be mathematically expressed as:

EDR =

if ft- ft, > LDD, (1) f_N LDs yioo

otherwise EDR - 0 where EDR for the selected local resource is the emulated droop response expressed as the target percentage reduction (or increase in the case of over frequency) in power consumption when the resource is a load (or increase in power generation when the resource is a generator) of the selected local load and optionally other resource 140A-C, ft is the local frequency, ft/ is the nominal frequency, LDS is the local droop setting for the selected local load and optionally other resource 140A-C (which may vary between local resources 140A-C) expressed as a percentage droop of local frequency from the nominal frequency after which the power consumption of the selected local load resource 140A-C should be reduced by 100% (for example, a 1 % reduction in local frequency with a 5% local droop setting would result in a steady state EDR of 20%, that is, a target reduction in power consumption of the selected local load resource 140A-C by 20%), f is the time measured from when ft- ft_/ exceeds the local droop deadband (t is set to zero when ft- ft, is less than the local droop deadband), r is an adjustable time constant, and LDD is the local droop deadband.

[0027] In practice, the droop setting will typically be set between 0-10%, however, any desired droop setting may be selected between 0-100%. In addition, the local droop deadband is ideally set at a value intended to avoid (or at least assist in avoiding) system load or generator power changes in normal operating conditions in the electrical power system 150 (for example, the local droop deadband is typically set between 0-0.5Hz) In other words, the local droop deadband serves to filter out normal power system frequency variations and cause the resource to respond only where there is a material change in system frequency. Further, the adjustable time constant will typically be set to between 5 seconds to one minute, however, the time constant may be set to any desired value. In the alternative, the emulated droop response may be determined based upon other techniques known on the art.

[0028] In block 210, the local master controller 1 10 determines an emulated inertial response for each selected local load and optionally other resource 140A-C based upon the rate of change of the local frequency. In the present embodiment, the emulated inertial response is determined by scaling the rate of change of the local frequency by an adjustable local inertial setting. This may be mathematically expressed as:

EIR = LIS -^- (2) dt where EIR is the emulated inertial response expressed as the target percentage reduction in power consumption when the resource is a load (or increase in power generation when the resource is a generator) of the selected local resource 140A-C, f_L is the local frequency, LIS is the local inertial setting for the selected local resource 140A-C (which may vary between local resources 140A- C) expressed as the percentage reduction in power consumption for a selected local load resource (or increase in power generation for a generator resource) 140A-C per Hertz per second, and df dt is the first derivative of the local frequency over time, f. The local inertial setting may be selected to be any desired value. In the alternative, the emulated inertial response may be determined based upon other techniques known on the art.

[0029] In block 214, the local master controller 110 determines the desired local primary frequency response for each selected local resource 140A-C based upon the emulated droop response and the emulated inertial response calculated for the selected local resource 140A-C. In the present embodiment, the desired local primary frequency response is determined as the sum of the emulated droop response and the emulated inertial response. In the alternative, the desired local primary frequency response may be determined solely based upon the emulated inertial response. In the further alternative, the desired local frequency response may be determined based upon other methods based on one or both of the emulated droop response and the emulated inertial response.

[0030] In block 218, the local master controller 110 determines operational setpoints for each selected local resource 140A-C that will provide the desired local primary frequency response. In the present embodiment, the selected local resources 140A-C are predetermined as local load and optionally other resources 140A-C that are capable or desired to participate in providing local primary frequency response. In the alternative, the specific local resources 140A-C are may be selected dynamically by taking into account the operational state of the local resources 140A-C (for example, if a local resource 140A-C is offline, unavailable or being used for a higher priority application) and ensuring that at least one of the dynamically selected resources is a load resource.

[0031] In block 222, the local master controller 110 directs the applicable local resource controllers 120A-C to operate the selected local load and optionally other resources 140A-C at the operational setpoints determined to provide the desired local primary frequency response for each selected local resource 140A-C. The applicable local resource controllers 120A-C then direct the selected local load and optionally other resources 140A-C to operate at the operation setpoints for their associated selected local resources 140A-C.

[0032] In block 226, the local master controller 110 determines the total local primary frequency response that actually has been provided by the selected local load and optionally other resources 140A-C based upon operational state information communicated from the local resource controllers 120A-C to the local master controller 110.

[0033] In block 230, the local master controller 110 communicates to the remote server 160 the local frequency and the individual and total local primary frequency responses provided by the local load and optionally other resources 140A-C.

[0034] While the present invention is illustrated by description of several embodiments and while the illustrative embodiments are described in detail, it is not the intention of the applicants to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications within the scope of the appended claims will readily appear to those sufficed in the art. The invention in its broader aspects is therefore not limited to the specific details, representative apparatus and methods, and illustrative examples shown and described. Accordingly, departures may be made from such details without departing from the spirit or scope of the general concept.

Claims

A method for providing a local primary frequency response within a local region of an electrical power system, using one or more local load resources electrically coupled to the power system within the local region, the method comprising:

(b) determining an emulated inertial response for each local load resource based upon the local frequency characteristics;

(c) determining a desired local primary frequency response for each local load resource based upon the emulated inertial response determined for each local resource;

(d) determining operational setpoints for each local load resource to provide the desired local primary frequency response for the local load resource; and

The method as claimed in claim 1 , wherein:

(a) the method further comprises determining an emulated droop response for each local load resource based upon the local frequency characteristics; and

(b) the desired local primary frequency response for each local load resource is determined based upon the emulated droop response and the emulated inertial response determined for the local load resource. The method as claimed in any one of claims 1 to 2, wherein the local frequency characteristics comprise (a) the deviation between the local frequency of the power system at the location from a nominal frequency of the power system and (b) the rate of change of the local frequency of the power system within the local region.

The method as claimed in claim 2, wherein:

(a) the local frequency characteristics comprise (a) the deviation between the local frequency of the power system at the location from a nominal frequency of the power system and (b) the rate of change of the local frequency of the power system within the local region; and

(b) the emulated droop response is determined based upon the deviation of the local frequency from the nominal frequency scaled by a local droop setting.

The method as claimed in claim 4, wherein the emulated droop response is set to zero if the difference between the local frequency and the nominal frequency does not exceed a local droop deadband.

The method as claimed in claim 5, wherein the emulated droop response is applied based upon an adjustable time constant.

The method as claimed in any one of claims 3 to 6, wherein the emulated inertial response is determined based upon the rate of change of the local frequency of the power system within the local region.

The method as claimed in claim 7, wherein the emulated inertial response is determined by scaling the rate of change of the local frequency by a local inertial setting.

The method as claimed in any one of claims 1 to 8, further comprising: (a) determining a total local primary frequency response provided by the local load resources; and

(b) communicating the total local primary frequency response to an independent system operator or an integrated electricity provider.

10. The method as claimed in claim 1 wherein the power system further comprises at least one local generation resource and local storage resource and the method further comprises determining an emulated inertial response for the at least one local generation resource and local storage resource based upon the local frequency characteristics; determining a desired local primary frequency response for the at least one local generation resource and local storage resource based upon the emulated inertial response determined for the at least one local generation and local storage resource; determining operational setpoints for the at least one local generation resource and local storage resource to provide the desired local primary frequency response for the at least one local generation resource and local storage resource; and directing the at least one local generation resource and local storage resource to operate at the selected operational setpoints for each local resource.

11. A computer readable medium having encoded thereon instructions executable by a processor to perform the method as claimed in any of claims 1 to 9.

12. A power system for providing a local primary frequency response within a local region of an electrical power system, the power system comprising: at least one local load resource electrically coupled to the power system within the local region; a controller communicative with the at least one local load resource, and comprising a processor and a memory having encoded thereon instructions executable by the processor to perform the method as claimed in any of claims 1 to 9 and to send operational setpoints to each load resource.

13. A power system as claimed in claim 12 wherein the controller comprises at least one local load resource controller communicative with the at least one local load resource and; a local master controller communicative with the local load resource controller and comprising the processor and the memory having encoded thereon instructions executable by the processor to perform the method as claimed in any of claims 1 to 9 and to send selected operational setpoints to each local load resource controller to operate each local load resource at the selected operational setpoints.

14. A power system as claimed in claim 12 wherein the local master controller further comprises a frequency meter electrically coupled to the electrical power system for measuring the local frequency of the electrical power system.

15. A power system as claimed in claim 13 further comprising a remote server communicative with the local master controller and with an independent service operator (ISO) or integrated electricity provider or other recipient to provide information from the local master controller to the ISO, integrated electricity provider or other recipient including a total local primary frequency response.