Method and system for determining instantaneous peak power consumption in elevator banks

• US 7,743,890 B2
• Filed: 06/12/2007
• Issued: 06/29/2010
• Est. Priority Date: 06/12/2007
• Status: Active Grant

• Current Assignee: Mitsubishi Electric Research Laboratories, Inc. (Mitsubishi Electric Corporation)
• Original Assignee: Mitsubishi Electric Research Laboratories, Inc. (Mitsubishi Electric Corporation)
• Inventors: Nikovski, Daniel N., Brand, Matthew E.
• Primary Examiner(s): SALATA, ANTHONY J
• Application Number:
  US11/761,683
• Publication Number:
  US 20080308361A1
• Time in Patent Office: 1,113 Days
• Field of Search: 187/247, 187280-287, 187380-388
• US Class Current: 187/382
• CPC Class Codes: B66B 1/2458 For elevator systems with multiple shafts and a single car per shaft
• CPC Class Codes: B66B 2201/102 Up or down call input
• CPC Class Codes: B66B 2201/211 Waiting time, i.e. response time
• CPC Class Codes: B66B 2201/212 Travel time
• CPC Class Codes: B66B 2201/216 Energy consumption
• CPC Class Codes: B66B 2201/222 Taking into account the number of passengers present in the elevator car to be allocated
• CPC Class Codes: Y02B 50/00 Energy efficient technologies in elevators, escalators and moving walkways, e.g. energy saving or recuperation technologies

Abstract

A method and system determine peak power consumption over time by a bank of elevator for servicing a set of passenger hall calls and delivery requests, and selecting elevator schedules that keep peak power consumption below a predetermined threshold. For each car in response to receiving a hall call, a set of all possible paths to service all hall calls assigned to the car are determined, in which each path includes a set of all possible segments. A peak power consumption for each possible segment is also determined. The peak power consumptions for the set of all possible segments for each time instant are added to determine a total peak power consumption for each time instant, and a particular path is selected as a schedule to operate the bank of elevator cars, if the total peak power consumption for any instant in time while operating according to the selected schedule is below a predetermined threshold.

Claims

1. A method for determining, for any instant in time, total peak power consumption for a bank of elevator cars, comprising;

determining, for each car in response to receiving a hall call, a set of all possible paths to service all hall calls assigned to the ear, in which each path includes a set of all possible segments;

determining a peak power consumption for each possible segment;

adding the peak power consumptions for the set of all possible segments for each time instant to determine a total peak power consumption for each time instant; and

selecting a particular path as a schedule to operate the bank of elevator cars, if the total peak power consumption for any instant in time while operating according to the selected schedule is below a predetermined threshold.

2. The method of claim 1 wherein the set of all possible paths of each car depend on a current state of the elevator system, and further comprising:

defining the current state of the elevator system by passengers having assigned cars, and for each car a direction of travel, a position, and a velocity of the car.

3. The method of claim 1 further comprises:

organizing the set;

of all possible states in a corresponding dynamic programming trellis, and wherein transitions between the states correspond to the set of all possible path segments.

4. The method of claim 1 further comprising:

associating each segment with a power profile.

5. The method of claim 1, in which the bank of elevator cars includes traction sheave elevators without counterweights.

6. The method of claim 1, in which a destination associated with the hall call is unknown.

7. The method of claim 1, in which the peak power consumed when following a particular path p is ƒ

_p(t), and the total peak power is F(t)=max<sub>pε

P</sub>ƒ

_p(t), where P is the set of all possible paths.

8. The method of claim 1, further comprising:

modeling the set of all possible segments with a phase-space diagram.

9. The method of claim 8, in which the total peak power consumption. F(t) at a particular instant in time t is a nested maximization.

F(t)=max_sε

Smax<sub>τ

ε

γ

s</sub>ƒ

_s(t, τ

), where S is a set of all possible segments of the phase-space diagram, and γ

_s is the set of all possible starting times τ

for realizations of a particular segment s.

10. The method of claim 9, in which the realization of the particular segment s depends on the starting time τ

of the realization, and a profile of the total peak power consumption is time-invariant

ƒ

_s(t, τ

)=ƒ

_s(t+Δ

t, τ

+Δ

τ

),

for any time interval Δ

t,

11. The method of claim 10, in which the peak power profile F_s(t) of the segment s is approximated by a first part:

for tε

[t_min, t*), F_s(t)=ƒ

_s(t, t_min), a second part;

for tε

[t_min+t*, t_max+t*]), F_s(t)=ƒ

_s(t_min+t*, t_min)=ƒ

_s(t*,

     0), and a third part;

for tε

(t_max+t*, t_max+t₁]), F_s(t)=ƒ

_s(t, t_max), where t* is a time of peak power consumption, and t_min is an earliest time and t_max is a latest time when traversal of segment s can start, respectively.

12. The method of claim 11, in which the earliest time t_min and the latest time t_max when a traversal of segment s can start are determined by means of dynamic programming, using recurrent equalities

t^q_min=min_rε

R[t^r_min+Δ

t(r, q)], and

t^q_max=max<sub>rε

R</sub>[t^r_max+Δ

t(r, q)], and

where q is the state of the trellis at the beginning of segment s, and R is the set of states at the beginning of segments which end with state q, and Δ

t(r, q) is a duration of the segment between state r and state q.

13. The method of claim 12, in which the determination of the earliest and the latest start times for each segment is performed in a single pass over the state of the trellis, starting from an upper right end of the trellis and proceeding row-by-row towards a bottom row of the trellis, while proceeding right to left within each consecutive row.

14. The method of claim 13, in which the earliest:

time t_min and the latest time t_max, as well as maximization of the peak power for any moment in time between the earliest time t_min and the latest time t_max is updated during the same pass over the trellis, such that F(t) is assigned a value of F_s(t), if the previous estimate of F(t) is lower than F_s(t).

15. The method of claim 14, in which the update is performed for a discrete set of time moments t⁽ⁱ⁾=iΔ

t, i=0, I, for a selected time step Δ

t, such that F⁽ⁱ⁾=F(t⁽ⁱ⁾)=F(iΔ

t), and F⁽ⁱ⁾ is assigned a value of F_s(iΔ

t)s if a previous estimate of F⁽ⁱ⁾ is lower than F_s(iΔ

t).

16. The method of claim 15, where all peak power profiles F⁽ⁱ⁾ for each car are added up separately for each time instance t⁽ⁱ⁾, and the schedule is accepted only if the sums of the total peak power for all time instances t⁽ⁱ⁾ is below a predetermined threshold,

17. The method of claim 1, in which the bank of elevator cars includes traction sheave cars with counterweights.

18. A system determines, for any instant in time, total peak power consumption for a bank, of elevator cars, comprising:

means for determining, for each car in response to receiving a hall, call, a set of all possible paths to service all hall calls assigned to the car, in which each path includes a set of all possible segments;

means for determining a peak power consumption for each possible segment;

means for adding the peak power consumptions for the set of all possible segments for each time instant to determine a total peak power consumption for each time instant; and

means for selecting a particular path as a schedule to operate the bank of elevator cars, if the total peak power consumption for any instant in time while operating according to the selected schedule is below a predetermined threshold.

19. The system of claim 18 wherein, the set of all possible paths of each car depend on a current state of the elevator system, and further comprising:

means for defining the current state of the elevator system by passengers having assigned cars, and for each car a direction of travel, a position, and a velocity of the car.