Capacity control technique with motor temperature override

A method of performing capacity control in a chiller system, the method comprising:

• driving a compressor of the chiller system using a motor;
• cooling the motor using refrigerant supplied from a refrigeration circuit of the chiller system, the refrigeration circuit having the compressor, a condenser, and an evaporator in fluid communication;
• controlling an amount of the refrigerant provided to the motor for cooling using a motor cooling valve positioned fluidly between the motor and the condenser, wherein the motor cooling valve is electronically adjustable continuously between a fully open position and a fully closed position to regulate the amount of the refrigerant introduced into the motor between full refrigerant flow and no refrigerant flow, respectively;
• and
• controlling loading or unloading of the chiller system using a capacity control system according to a motor temperature-based capacity control scheme performed in response to determining that the motor cooling valve is in the fully open position, wherein the motor temperature-based capacity control scheme is performed as a function of a monitored temperature associated with the motor, a first temperature threshold corresponding to the monitored temperature, and a second temperature threshold corresponding to the monitored temperature higher than the first temperature threshold, wherein controlling the loading or unloading of the chiller system comprises:
• proportionally limiting loading of the chiller system based on an amount by which the monitored temperature has exceeded the first temperature threshold in response to determining that the monitored temperature is within a temperature range between the first temperature threshold and the second temperature threshold;
• or
• proportionally unloading the chiller system based on an amount by which the monitored temperature has exceeded the second temperature threshold in response to determining that the monitored temperature is within a temperature range between the second temperature threshold and a chiller shutdown temperature;
• or both.

A control system having processing circuitry and memory circuitry, the memory circuitry storing a temperature-based capacity control scheme for a chiller system and the processing circuitry being configured to perform the temperature-based capacity control scheme, wherein the temperature-based capacity control scheme is performed as a function of a monitored temperature in a motor configured to drive a compressor of the chiller system, a first temperature threshold corresponding to the monitored temperature, and a second temperature threshold corresponding to the monitored temperature higher than the first temperature threshold, wherein the temperature-based capacity control scheme comprises:

• a load limiting region corresponding to a temperature range between the first temperature threshold and the second temperature threshold, wherein the load limiting region is configured to proportionally limit loading of the chiller system based on an amount by which the monitored temperature has exceeded the first temperature threshold;
• or
• an override region associated with a temperature range above the second temperature threshold and below a chiller shutdown temperature, wherein the override region is configured to proportionally unload the chiller system based on an amount by which the monitored temperature has exceeded the second temperature threshold;
• or both.