BACKGROUND

The present invention relates to elevator systems. More specifically, the present invention relates to energy management of an elevator system during marginal quality utility power conditions.

The power demands for operating elevators range from positive, in which externally generated power from a power utility is used, to negative, in which the load in the elevator drives the hoist motor so that the hoist motor produces electricity as a generator (i.e., regeneration). Elevator regenerative drives have been developed that return regenerated energy to the power utility grid, or store regenerated electrical energy in an electrical energy storage system.

An elevator system is typically designed to operate over a specific input voltage range. The components of the elevator drive have voltage and current ratings that allow the drive to continuously operate while power from the power utility grid remains within a designated input voltage range.

Transient overvoltage or undervoltage conditions have a potential to cause elevator shut downs. Sustained power undervoltage conditions, either sags or brownouts, cause conditions where the elevator cannot draw sufficient power from the grid to maintain required system operating voltages. These conditions occur when the grid voltage is below a certain level (usually 15% to 30% of the nominal line voltage), and can lead to costly recalls for service and repairs. When a utility power failure occurs or under poor quality conditions, the elevator may become stalled between floors in the elevator hoistway until the utility power on the grid returns to normal conditions.

Even under marginal conditions, in which the grid voltage is somewhat less than 15% below the nominal line voltage, the added current required from the grid to satisfy power demand of the elevator system, in particular peaks during startup, can cause voltage sag conditions.

SUMMARY

An elevator system includes an energy management controller and an energy storage system for operating an elevator during marginal quality power conditions (such as undervoltage or overvoltage conditions). The energy management controller, in response to sensed line undervoltage or overvoltage conditions, causes the elevator to operate in an off- grid mode using energy from the energy storage system. The energy management controller monitors state-of-charge of the energy storage system to maintain the energy storage system within state-of-charge limits.

During periods between elevator operation, the power management system harvests usable power from the line to trickle charge the energy storage system to extend operations. While line conditions may not be satisfactory for elevator operations at lower current demands, partial charging of the energy storage becomes possible.

During sustained marginal quality power conditions, the energy management controller uses power management strategies to maintain and extend operation of the elevator system. The power management strategies may include delaying elevator runs, reducing performance by reducing operating speeds of the elevator, shutting down the elevator temporarily to allow the energy storage system to be recharged using current from the grid, and adjusting state-of-charge operating limits of the energy storage system to extend elevator operation.

BRIEF DESCRIPTION OF THE DRAWINGS

The Figure is a block diagram of an elevator system including an energy management controller operating in conjunction with an elevator drive controller and an electrical energy storage system to provide operation of an elevator during marginal quality power conditions.

DETAILED DESCRIPTION

The Figure is a block diagram of elevator system 10, which includes elevator hoist motor 12, elevator car 14, counterweight 16, roping 18, elevator load sensor 20, elevator drive converter 22, DC power bus 24, smoothing capacitor 26, inverter 28, AC/DC converter 30, DC/DC converter 32, electrical energy storage (EES) system 34, state-of- charge (SOC) sensor 36, line voltage sensor 38, elevator electrical systems 40, elevator drive controller 42, energy management controller 44, and switches 46 and 48. During normal operation, elevator system 10 operates using AC electrical power delivered from primary power source 50, which is typically a utility power distribution grid. The grid power is shown in the Figure as three-phase AC power, although in some cases single phase AC power may be used. Hoist motor 12 controls the speed and direction of movement between elevator car 14 and counterweight 16. The power required to drive hoist motor 12 varies with the acceleration and direction of movement of elevator car 14, as well as the load in elevator car 14. For example, if elevator car 14 is being accelerated, run up with a load greater than the weight of counterweight 16 (i.e., heavy load), or run down with a load less than counterweight 16 (i.e., light load), electrical power is required to drive hoist motor 12. In this case, the power demand for hoist motor 12 is positive. If elevator car 14 runs down with a heavy load, or runs up with a light load, elevator car 14 drives hoist motor 12 and regenerates electrical energy. In this case of negative power demand, hoist motor 12 generates AC electrical power that is converted to DC power by inverter 28 under the control of elevator drive controller 42. The converted DC power may be returned to primary power supply 50, used to recharge EES system 34, and/or dissipated in a dynamic brake resistor (not shown) that can be connected across power bus 24.

It should be noted that while a single hoist motor 12 is shown in the Figure, elevator system 10 can be modified to power multiple hoist motors 12. In that case, multiple power inverters 28 may be connected in parallel across power bus 24 to provide conditioned power to each of the multiple hoist motors 12.

Elevator drive converter 22, power bus 24, smoothing capacitor 26, and inverter 28 form a regenerative elevator drive that controls the flow of electrical power between hoist motor 12, primary power supply 50, and EES system 34 as a function of power demand (positive or negative) of elevator hoist motor 12, the quality of power being delivered by primary power supply 50 (as sensed by line voltage sensor 38), and state-of- charge of EES system 34 (as determined by SOC sensor monitor 36). Operation of elevator drive converter 22, inverter 28, AC/DC converter 30, and DC/DC converter 32 is controlled by elevator drive controller 42 in conjunction with energy management controller 44.

Elevator drive converter 22 receives three-phase power from primary power supply 50, and converts the three-phase AC power to DC power that is delivered to DC power bus 24. In one embodiment, elevator drive converter 22 comprises a plurality of power transistor circuits that can be driven to either convert three-phase AC power from primary power supply 50 to DC output power, or to convert DC power from power bus 24 to three-phase AC power that is delivered back to primary power supply 50. The operation of elevator drive converter 22 is controlled by control signals Cl supplied by elevator drive controller 42. In one embodiment, elevator drive controller 42 employs pulse width modulation (PWM) to produce control signals Cl as gating pulses that periodically switch the power transistor circuits of elevator drive controller 42. It should be noted that primary power supply 50 could also be a single phase source.

Inverter 28 is a three-phase power inverter capable of inverting DC power from power bus 24 to three-phase AC power delivered to hoist motor 12. In addition, inverter 28 can rectify AC power regenerated by hoist motor 12 to produce DC power that is delivered to power bus 24. Inverter 28 may include a plurality of power transistor circuits driven by PWM gating pulse control signals C2 produced by elevator drive controller 42. Drive controller 42 may vary the speed and direction of movement of elevator car 14 by adjusting the frequency, phase, and magnitude of the gating pulses to inverter 28.

EES system 34 may include one or more devices capable of storing electrical energy that are connected in series or parallel. In some embodiments, EES system 34 includes at least one supercapacitor, which may include symmetric or asymmetric supercapacitors. In other embodiments, EES system 34 includes at least one secondary or rechargeable battery, which may include any of nickel-cadmium (NiCd), lead acid, nickel- metal hydride (NiMH), lithium ion (Li-ion), lithium ion polymer (Li-Poly), iron electrode, nickel-zinc, zinc/alkaline/manganese dioxide, zinc-bromine flow, vanadium flow, and sodium-sulfur batteries. In other embodiments, other types of electrical or mechanical devices, such as flywheels, can be used to store energy. EES system 34 may include one type of storage device or may include combinations of storage devices.

EES system 34 interfaces with DC power bus 24 through DC/DC converter 32, which is a bi-directional DC/DC converter. When EES system 34 is called upon to deliver power to operate hoist motor 12, DC/DC converter 32 converts the power from EES system 34 to a DC power level compatible with DC power bus 24. When EES system 34 is being charged from power bus 24, DC/DC converter 32 converts the DC power from bus 24 to a voltage compatible with EES system 34. Charging of EES system 34 from power bus 24 can occur using regenerated electrical energy from hoist motor 12, or from rectified electrical power from primary power source 50 during a period when power demand of elevator hoist motor 12 is neutral. DC/DC converter 32 is controlled by control signals C4 from elevator drive controller 42. The power could also come from alternative energy sources. This may be the case, for instance, if back-up generators are running.

AC/DC converter 30 converts AC power from primary power source 50 to DC voltage that can be used to charge EES system 34, as well as provide power to elevator electrical systems 40 through switch 48. Elevator electrical systems 40, which include the systems that provide ventilation, lighting, and control functions for elevator cab 14, can also be powered by AC power derived from primary power source 50 through switch 46. Elevator drive controller 42 provides control signals C3 to AC/DC converter 30, and switch control signals Sl and S2 to switches 46 and 48, respectively.

Energy management controller 44 functions in cooperation with elevator drive controller 42 to allow elevator system 10 to maintain and extend operation during time periods when power from primary power source 50 is in a sustained undervoltage condition, but has not yet reached the level of a brownout condition. Energy management controller 44 receives inputs from line voltage sensor 38 representing the sensed line voltage, a signal or signals from SOC sensor 36 (such as voltage, current, and temperature signals) from which the state-of-charge of EES system 34 can be determined, and a load signal from load sensor 20 associated with elevator car 14. Elevator drive controller 42 may also receive power requirement information from energy management controller 44. The power requirement information may include, for example, request for service from building occupants that elevator drive controller 42 will be servicing.

Elevator system 10 operates in a normal (grid-powered) operating mode using power from primary power source 50 to operate hoist motor 12 when line voltage sensed by sensor 38 indicates normal quality power. During the normal operating mode, EES system 34 may be used to improve energy utilization by storing regenerative power.

When sustained or transient undervoltage or overvoltage conditions occur, energy management controller 44 can initiate a marginal quality power (off-grid) operating mode in which use of elevator drive converter 22 is minimized, and elevator system 10 operates using stored power from EES system 34. Between runs of elevator car 14, low current level charging of EES system 34 from the primary power source 50 is provided through AC/DC converter 30 (or converter 22) to maintain at least a minimum state-of- charge in EES system 34 that will allow extended elevator operation.

Energy management controller 44 detects the occurrence and severity of the quality power issue. Based upon a determination of the severity of the quality power issue, energy management controller 44 may increase the maximum state-of-charge limit for EES system 34 from that used during normal operating mode in order to ensure enough stored energy for sustained operation of elevator system 10. Energy management controller 44 may also receive other inputs, such as inputs from authorized building or rescue personnel, that may call for an increase in the maximum state-of-charge limit.

Energy management controller 44 may also take elevator system 10 temporarily out of service if the state-of-charge of EES system 34 drops below a minimum level. After trickle charging EES system 34 using AC/DC converter 30, energy management controller 44 may allow elevator system 10 to return to service once the state- of-charge has reached at least a minimum level.

Energy management controller 44 can provide a number of different commands to elevator drive controller 42. First, in response to an undervoltage condition, energy management controller 44 provides an off-grid mode command that causes elevator drive controller 42 to operate hoist motor 12 from power supplied by EES system 34, rather than power from primary power supply 50. While in an off-grid mode, energy management controller 44 may cause elevator drive controller 42 to delay an elevator run, to reduce performance (e.g., reducing hoist motor speed), or shutting down elevator system 10 for a period until EES system 34 has a state-of-charge (SOC) sufficient to permit off-grid mode operation of elevator car 14. Energy management controller 44 can also provide commands to elevator drive controller 42 to adjust the operating limits of EES system 34, which will affect the charging of EES system 34 using converters 30 and 32, as well as the delivery of power from EES system 34 through DC power bus 24 and inverter 28 to hoist motor 12.

Although energy management controller 44 and elevator drive controller 42 are shown separately in the Figure, functions of controllers 42 and 44 may be combined in a single controller unit. Conversely, functions performed by elevator drive controller 42 and energy management controller 44 may be divided among more than two components.

Elevator system 10 is capable of continuing operation during periods of reduced grid quality power. As a result, the chance of passenger entrapment caused by undervoltage conditions is reduced, and overall customer satisfaction is increased.

When EES system 34 is in a marginal state-of-charge, elevator system 10 may still be able to function under some circumstances. For example, although elevator car 14 may be unavailable for power consuming runs, it could still be available for runs that provide regenerative power that can be used to maintain or increase the state-of-charge of EES system 34. This function can be used to sustain building evacuations during emergencies, during which empty upward runs and full downward runs, with evacuees filling the elevator cars, would be regenerating operations. By operating in an off-grid mode during marginal quality power conditions, critical components of elevator system 10 are not subjected to potentially damaging current levels. As a result, recalls for costly service or repair can be reduced. Transitions between the normal (grid-powered) and marginal quality power (off-grid) operating modes can be seamless as far as the users of the elevator system are concerned.

Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.