System and method for using a photovoltaic power source with a secondary coolant refrigeration system

Abstract

A secondary coolant refrigeration system powered primarily by a photovoltaic source and by an alternating current (AC) source as a backup is disclosed. The secondary coolant refrigeration system has a pump for pumping secondary coolant fluid through a secondary coolant fluid loop. The system includes a variable frequency drive for controlling the speed of the pump. The variable frequency drive includes drive circuitry configured to provide variable frequency power to the pump via an output interface. The variable frequency drive also includes a first interface configured to receive power from the photovoltaic source and a second interface configured to receive power from the AC source. The variable frequency drive further includes a circuit configured to switch between providing power to the drive circuitry from the first interface and providing power to the drive circuitry from the second interface. The circuit is further configured to cause the variable speed drive to be powered by the photovoltaic source when the power received from the first interface is adequate and by the AC source when the power received from the first interface is not adequate.

1 . A secondary coolant refrigeration system powered primarily by a photovoltaic source and by an alternating current (AC) source as a backup, the secondary coolant refrigeration system having a pump for pumping secondary coolant fluid through a secondary coolant fluid loop, the system comprising:
 a variable frequency drive for controlling the speed of the pump, the variable frequency drive comprising:
 drive circuitry configured to provide variable frequency power to the pump via an output interface; 
 a first interface configured to receive power from the photovoltaic source; 
 a second interface configured to receive power from the AC source; and 
 a circuit configured to switch between providing power to the drive circuitry from the first interface and providing power to the drive circuitry from the second interface, wherein the circuit is further configured to cause the variable speed drive to be powered by the photovoltaic source when the power received from the first interface is adequate and by the AC source when the power received from the first interface is not adequate. 
   
   
   
       2 . The secondary coolant refrigeration system of  claim 1 , wherein the circuit is configured to cause the switch between the first interface and the second interface to be smooth so that operation of the pump is not interrupted. 
   
   
       3 . The secondary coolant refrigeration system of  claim 1 , wherein the switching is automated and does not require human input before each switch. 
   
   
       4 . The secondary coolant refrigeration system of  claim 1 , wherein the circuit is configured to determine whether the power received from the first interface is adequate by comparing the power received at the first interface to the power received at the second interface. 
   
   
       5 . The secondary coolant refrigeration system of  claim 1 , wherein the circuit is configured to determine that the power received from the first interface is adequate when voltage at the first interface is equal to or greater than the voltage at the second interface. 
   
   
       6 . The secondary coolant refrigeration system of  claim 1 , wherein the circuit is configured to determine that the power received from the first interface is adequate when voltage at the first interface is at least 1.35 times higher than the voltage at the second interface. 
   
   
       7 . The secondary coolant refrigeration system of  claim 1 , wherein the circuit determines whether the power received from the first interface is adequate for driving the pump by comparing voltage from the first interface to a threshold value. 
   
   
       8 . The secondary coolant refrigeration system of  claim 7 , wherein the variable frequency drive further comprises an input for receiving a signal from a user interface and wherein the controller is further configured to adjust the threshold value based on the received signal. 
   
   
       9 . The secondary coolant refrigeration system of  claim 1 , further comprising:
 wherein the pump is one of a plurality of pumps for pumping secondary coolant fluid; and   wherein the variable frequency drive is one of a plurality of variable frequency drives, each variable frequency drive configured to drive one of the plurality of pumps,   wherein each variable frequency drive is configured to receive power from the photovoltaic source or another photovoltaic source by default.   
   
   
       10 . The secondary coolant refrigeration system of  claim 1 , wherein the circuit comprises a diode connected to the photovoltaic power source, the diode configured to have an on-voltage of at least the normal output voltage from the AC source. 
   
   
       11 . The secondary coolant refrigeration system of  claim 10 , wherein the circuit further comprises a rectifier configured to receive power from the second interface and to provide power to a direct current (DC) bus, the DC bus couples the second interface to inverter circuitry of the variable frequency drive, and wherein the output from the cathode of the diode is connected to the DC bus. 
   
   
       12 . The secondary coolant refrigeration system of  claim 1 , wherein the circuit comprises a programmable controller. 
   
   
       13 . A method for controlling a pump used in a secondary coolant refrigeration system, the speed of the pump controlled using a variable frequency drive configured to selectively receive power from an AC source and a photovoltaic source, the method comprising:
 using the variable frequency drive to determine whether power received from the photovoltaic source is adequate for driving the pump;   configuring the variable frequency drive to use the power received from the photovoltaic source when the power is adequate for driving the pump; and   using the variable frequency drive to switch from using the power received from the photovoltaic source to power received from the AC source when the power received from the photovoltaic source is inadequate for driving the pump.   
   
   
       14 . The method of  claim 13 , wherein the variable frequency drive is configured to use power from the photovoltaic source when the voltage available from the photovoltaic source is equal to or greater than the voltage available at the AC source. 
   
   
       15 . The method of  claim 13 , wherein the variable frequency drive is configured to use power from the photovoltaic source when the voltage available from the from the photovoltaic power source at least 1.35 times higher than the voltage available at the AC source when the AC source is a three phase AC source and at least 0.9 times higher than the voltage available at the AC source when the AC source is a single phase AC source. 
   
   
       16 . The method of  claim 13 , further comprising:
 comparing a measurement of voltage of the power received from the photovoltaic source to a threshold value.   
   
   
       17 . The method of  claim 16 , further comprising:
 receiving an input from a user interface; and   adjusting the threshold value based on the received input.   
   
   
       18 . The method of  claim 13 , further comprising:
 configuring the variable frequency drive to receive power from the photovoltaic source by default and the AC source as a backup.   
   
   
       19 . The method of  claim 13 , further comprising:
 wherein the switch is smooth and the operation of the pump is not interrupted.   
   
   
       20 . The method of  claim 13 , further comprising:
 comparing the power received from the photovoltaic source to the power available from the AC source.   
   
   
       21 . A system for cooling a plurality of refrigeration loads, the system comprising:
 a plurality of secondary coolant fluid loops configured to cool the plurality of refrigeration loads;   a plurality of coolant pumps, each coolant pump associated with at least one secondary coolant fluid loop;   a plurality of variable frequency drives, each variable frequency drive configured to control and drive one of the plurality of coolant pumps; and   at least one photovoltaic power source;   wherein the plurality of variable frequency drives are configured to receive power from the photovoltaic power source and to use the power from the photovoltaic power source to drive the coolant pumps when the power from the photovoltaic power source meets a threshold requirement, and wherein each variable frequency drive is also configured to receive power from a second power source and to use the power received from the second power source when the power from the photovoltaic power source does not meet the threshold requirement.   
   
   
       22 . The system of  claim 21 , wherein the threshold requirement is a minimum voltage requirement and wherein the second power source is one of grid power and a battery backup source. 
   
   
       23 . The system of  claim 21 , wherein a separate photovoltaic power source is provided for each of the variable frequency drives.