Patent Description:
Air conditioning systems typically employ a motor that drives a compressor. The motor may be equipped with an active magnetic bearing assembly that supports a rotor of the motor. If power is lost or the motor drive experiences a fault, power to the active magnetic bearing assembly is disrupted. In such an event, the rotor of the motor can spin backwards due to refrigerant vapor backflow into the compressor. Rotation of the rotor when the active magnetic bearing assembly is unpowered can damage the active magnetic bearing assembly and/or the rotor.

<CIT> discloses a generator control device that can reliably brake a generator even when the device fails, wherein energy generated by the generator can be consumed by a power consumption resistor, thereby reducing the rotation speed of the generator.

<CIT> discloses methods for limiting reverse motor speeds for motor drive power loss events, in which a first power dissipation circuit is enabled at the motor drive output to limit reverse rotation of a driven motor load when motor drive power is lost.

According to a first aspect, there is provided an air conditioning system including a compressor having a motor; a condenser; an evaporator; a drive configured to be powered by an AC input voltage and to provide multiphase, AC output to the motor; an active magnetic bearing assembly supporting a rotor of the motor, the active magnetic bearing assembly configured to be powered by the AC input voltage; and a motor braking assembly electrically connected to the drive, the motor braking assembly including at least one switch and at least one braking resistor; wherein the at least one switch is held in an open state by power from the drive; and wherein upon disruption of the AC input voltage, the at least one switch assumes a closed state shorting windings of the motor through the at least one braking resistor.

Optionally, the at least one switch comprises three switches and the at least one braking resistor comprises three braking resistors.

Optionally, each switch of the three switches is connected to a respective phase of the multiphase, AC output of the drive and each resistor of the three resistors includes a first terminal connected to a respective switch of the three switches.

Optionally, each resistor of the three resistors includes a second terminal connected to a common point.

The air conditioning system may include at least one fuse connected in series between an AC output phase of the drive and the at least one switch.

The air conditioning system may include three fuses, each fuse connected in series between an AC output phase of the drive and a respective one of the three switches.

Optionally, the drive includes a DC bus between a converter and an inverter.

Optionally, the at least one switch is connected to a first side of the DC bus, a first terminal of the at least one resistor is connected to the at least one switch and a second terminal of the at least one resistor is connected to a second side of the DC bus.

The air conditioning system may include a fuse connected in series between first side of the DC bus and the at least one switch.

The air conditioning system may include a drive controller associated with the drive, the drive controller configured to verify that the at least one switch is open prior to powering the motor.

The air conditioning system may include a sensor configured to detect a test signal to verify that the at least one switch is open prior to powering the motor.

Technical benefits of embodiments of this disclosure include the ability to quickly brake a rotor of a motor during a power loss to protect components of an active magnetic bearing supporting the rotor.

Additional technical features and benefits are realized through the techniques of the present disclosure. Certain exemplary embodiments and aspects of the invention are described in detail herein by way of example only.

<FIG> is a block diagram of air conditioning system <NUM> in an example embodiment. The air conditioning system <NUM> may be configured to condition air in a building, such as a chiller, roof top unit, heat pump, etc. The air conditioning system <NUM> may be configured to condition air for refrigerated environments, such as a refrigerated container, a refrigerated trailer, refrigerator/freezer, etc..

The air conditioning system <NUM> includes a variable speed motor <NUM> that is coupled to a compressor <NUM>. The compressor <NUM> includes an impeller/rotor that rotates and compresses liquid refrigerant to a superheated refrigerant vapor for delivery to a condenser <NUM>. In the condenser <NUM>, the refrigerant vapor is liquefied at high pressure and rejects heat (e.g., to the outside air via a condenser fan in an air-cooled application). The liquid refrigerant exiting condenser <NUM> is delivered to an evaporator <NUM> through an expansion valve <NUM>. The refrigerant passes through the expansion valve <NUM> where a pressure drop causes the high-pressure liquid refrigerant to achieve a lower pressure combination of liquid and vapor. As fluid passes the evaporator <NUM>, the low-pressure liquid refrigerant evaporates, absorbing heat from the fluid, thereby cooling the fluid and evaporating the refrigerant. The low-pressure refrigerant is again delivered to compressor <NUM> where it is compressed to a high-pressure, high temperature gas, and delivered to condenser <NUM> to start the refrigeration cycle again. It is to be appreciated that while a specific air conditioning system is shown in <FIG>, the present teachings are applicable to any air conditioning system.

As shown in <FIG>, the compressor <NUM> is driven by a variable speed motor <NUM> from power supplied from a multiphase, AC input voltage <NUM> (grid or mains) through a drive <NUM> including an AC-DC converter <NUM> and a DC-AC inverter <NUM>. The drive <NUM> may be a variable frequency drive that controls speed of motor <NUM> using a varying multiphase, AC output voltage. The AC-DC converter <NUM> includes solid-state electronics to convert the AC input voltage <NUM> to a DC voltage across a DC bus <NUM>. Such converters <NUM> are known in the art. The inverter <NUM> includes solid-state electronics to produce multiphase, AC output voltage. In an embodiment, inverter <NUM> converts the DC voltage from the converter <NUM> into a multiphase, AC output voltage, at a desired frequency and/or magnitude in order to drive the multiphase motor <NUM>. Such inverters <NUM> are known in the art.

<FIG> depicts a motor braking assembly <NUM> for use with the motor <NUM> and drive <NUM>. The rotor of motor <NUM> is supported by an active magnetic bearing assembly <NUM>. The active magnetic bearing assembly <NUM> is powered by the AC input voltage <NUM>. In situations where power to the motor <NUM> is interrupted, it is desirable to stop rotation of the rotor of motor <NUM> promptly. The motor braking assembly <NUM> provides for quickly stopping rotation of the rotor of motor <NUM> when power to the motor <NUM> is interrupted. The interruption of power to the motor <NUM> may be a result of loss of the AC input voltage <NUM>, a fault in the drive <NUM> or another cause.

The motor braking assembly <NUM> includes a plurality of switches <NUM>. The switches <NUM> are moved by an open, non-conductive state and a closed, conductive state in response to power from the drive <NUM>. The switches <NUM> may be implemented using relays, transistors, etc. Each switch <NUM> is connected to a respective phase of the multiphase, AC output of the drive <NUM> through a fuse <NUM>. As such, each switch <NUM> is also connected to one phase winding of the motor <NUM>. The motor braking assembly <NUM> includes a plurality of braking resistors <NUM>. Each braking resistor <NUM> has a first terminal connected to a respective one of the switches <NUM>. The second terminal of each braking resistor <NUM> is connected to a common point <NUM>.

Each switch <NUM> is normally closed, and is held in an open, non-conductive state during normal operation by power from the drive <NUM>. Upon a disruption of power to the motor <NUM>, power to the switches <NUM> is interrupted. The disruption of power to the motor <NUM> may be caused by a fault at the AC input voltage <NUM> or by a fault in the drive <NUM>. This causes the switches <NUM> to assume a closed, conductive state. This shorts the multiphase windings of motor <NUM> through the braking resistors <NUM> to cause the rotor of motor <NUM> to stop rotating.

Fuses <NUM> protect the motor windings of motor <NUM> from being inadvertently shorted through the braking resistors <NUM> due to a fault in one or more switches <NUM>. Fuses <NUM> are connected in series between one phase of the drive <NUM> and a respective one of the switches <NUM>.

The drive <NUM> may include a drive controller <NUM>. The drive controller <NUM> may be implemented using a general-purpose microprocessor executing a computer program stored on a storage medium to perform the operations described herein. Alternatively, the drive controller <NUM> may be implemented in hardware (e.g., ASIC, FPGA) or in a combination of hardware/software. The drive controller <NUM> may also be part of an air conditioning control system.

The drive controller <NUM> may verify that the switches <NUM> are in the correct position prior to powering the motor <NUM>. For example, prior to providing power to the motor <NUM>, the drive controller <NUM> may generate a test signal on one phase of the multiphase, AC output of the drive <NUM>. If the test signal is not detected by a sensor at the remaining phases of the multiphase, AC output of the drive <NUM>, then the switches <NUM> are in the open, non-conductive state. This indicates it is safe to provide power to the motor <NUM>. Otherwise, the drive controller <NUM> can attempt to reset the switches <NUM> (e.g., provide power on and off signals to the switches <NUM>) and then verify that the switches <NUM> are in the correct position prior to powering the motor <NUM>.

In another embodiment, the drive controller <NUM> determines the status of the normally closed, or back contact, of a relay serving as a switch <NUM>. Under normal operation, the resistors <NUM> should be out of the circuit and the normally closed contact of the relay in an open position. Only in a power loss condition are the resistors <NUM> in circuit.

<FIG> depicts a motor braking assembly <NUM> in another embodiment. The motor braking assembly <NUM> is connected across the positive and negative sides of the DC bus <NUM>, between the AC-DC converter <NUM> and the DC-AC inverter <NUM>. The motor braking assembly <NUM> includes a switch <NUM>. The switch <NUM> may be implemented using a relay, transistor, etc. The switch <NUM> is connected to a first side of the DC bus (e.g., positive) through a fuse <NUM>. The motor braking assembly <NUM> includes a braking resistor <NUM>. The braking resistor <NUM> has a first terminal connected to the switch <NUM>. The second terminal of the braking resistor <NUM> is connected to a second side of the DC bus <NUM> (e.g., negative).

Switch <NUM> is normally closed, and is held in an open, non-conductive state during normal operation by power from the drive <NUM>. Upon a disruption of power to the motor <NUM>, power to the switch <NUM> is interrupted. The disruption of power to the motor <NUM> may be caused by a fault at the AC input voltage <NUM> or by a fault in the drive <NUM>. This causes the switch <NUM> to assume the closed, conductive state. This shorts the multiphase windings of motor <NUM> through the braking resistor <NUM> to cause the rotor of motor <NUM> to stop rotating.

A fuse <NUM> protects the motor windings of motor <NUM> from being inadvertently shorted through the braking resistors <NUM> due to a fault in the switch <NUM>. The fuse <NUM> is connected in series between one side of the DC bus <NUM> and the switch <NUM>.

The drive controller <NUM> may verify that the switch <NUM> is in the correct position prior to powering the motor <NUM>. For example, prior to providing power to the motor <NUM>, the drive controller <NUM> may generate a test signal on one side of the DC bus <NUM>. If the test signal is not detected by a sensor at the other side of the DC bus, then the switch <NUM> is in the open, non-conductive state. This indicates it is safe to provide power to the motor <NUM>. Otherwise, the drive controller <NUM> can attempt to reset the switch <NUM> (e.g., provide power on and off signals to the switch <NUM>) and then verify that the switch <NUM> is in the correct position prior to powering the motor <NUM>.

Claim 1:
An air conditioning system (<NUM>) comprising:
a compressor (<NUM>) having a motor (<NUM>);
a condenser (<NUM>);
an evaporator (<NUM>);
a drive (<NUM>) configured to be powered by an AC input voltage and to provide multiphase, AC output to the motor; and
a motor braking assembly (<NUM>; <NUM>) electrically connected to the drive, the motor braking assembly including at least one switch (<NUM>; <NUM>) and at least one braking resistor (<NUM>; <NUM>);
wherein the at least one switch is held in an open state by power from the drive;
characterised in that the air conditioning system comprises an active magnetic bearing assembly (<NUM>) supporting a rotor of the motor, the active magnetic bearing assembly configured to be powered by the AC input voltage;
wherein upon disruption of the AC input voltage (<NUM>), the at least one switch (<NUM>; <NUM>) assumes a closed state shorting windings of the motor through the at least one braking resistor (<NUM>; <NUM>).