Electronic control transformer using DC link voltage

• US 20070151272A1
• Filed: 01/03/2006
• Published: 07/05/2007
• Est. Priority Date: 01/03/2006
• Status: Abandoned Application

• Current Assignee: York International Corporation (Johnson Controls International plc)
• Original Assignee: York International Corporation (Johnson Controls International plc)
• Inventors: Schnetzka, Harold, Cosan, Muhammet
• Application Number:
  US11/324,368
• Publication Number:
  US 20070151272A1
• Time in Patent Office: Days
• US Class Current: 62/228.100
• CPC Class Codes: F25B 2600/021 Inverters therefor
• CPC Class Codes: F25B 49/025 Motor control arrangements
• CPC Class Codes: Y02B 30/70 Efficient control or regulation technologies, e.g. for control of refrigerant flow, motor or heating

Abstract

In a chiller system, an electronic control transformer is powered by the DC link of a variable speed drive that drives a compressor motor. The electronic control transformer converts the DC voltage to a constant 120 VAC at 60 Hz, for providing power to auxiliary electrical devices associated with the chiller system. The electronic transformer includes four semiconductor switches to convert the DC voltage to AC. The energy stored in the compressor motor is transferred to the DC link of the VSD during an input voltage sag. The electronic control transformer maintains the control voltage and prevents the system auxiliary loads from dropping out during a voltage sag. The chiller system is able to ride through the input voltage sag or interruption. A boost converter may be provided at the input of the VSD to increase ride through capability.

Claims

1. A drive system to power a plurality of components of a chiller system having different voltage requirements, the drive system comprising:

a converter stage connected to an AC power source to receive an input AC power at a fixed input AC voltage and a fixed input frequency, the converter stage being configured to convert the fixed input AC voltage to a boosted DC voltage, the boosted DC voltage being greater than the fixed input AC voltage;

a DC link connected to the converter stage, the DC link being configured to filter the boosted DC voltage and store energy from the converter stage; and

a first inverter stage connected to the DC link, the first inverter stage being configured to convert the boosted DC voltage from the DC link to provide an output power at a variable voltage and variable frequency to a motor of a chiller system, the variable voltage having a maximum voltage greater in magnitude than the fixed input AC voltage and the variable frequency having a maximum frequency greater than the fixed input frequency;

wherein the first inverter stage is configured to reverse power flow through the first inverter stage to the DC link stage to transfer electrical power from energy stored in a rotating mass of a motor connected to the first inverter stage to maintain a voltage level of the DC link in response to a decreasing fixed input AC voltage; and

a second inverter stage connected to the DC link, the second inverter stage being configured to convert the boosted DC voltage from the DC link into an auxiliary output power source having a fixed output AC voltage and a fixed output frequency for at least one component of a chiller system, the fixed output AC voltage being less than the fixed input AC voltage; and

, wherein the fixed output AC voltage and fixed output frequency of the second inverter stage is maintained in the event of a temporary decrease in the fixed input AC voltage.

2. The drive system of claim 1, wherein the converter stage is controllable to precharge the DC link.

3. The drive system of claim 1, wherein the second inverter stage is comprised of at least four power semiconductor switches configured to invert the boosted DC voltage to the fixed output AC voltage and fixed output frequency.

4. The drive system of claim 1, wherein the first inverter stage and the second inverter stage are disposed in a single enclosure.

5. The drive system of claim 1, wherein the first inverter stage and the second inverter stage are disposed in separate enclosures.

6. The drive system of claim 1, wherein the auxiliary output power source fixed output AC voltage is 120 VAC and the fixed output frequency is 60 Hz.

7. The drive system of claim 1, wherein the second inverter stage provides the fixed output AC power to a control panel and to a power distribution panel, and at least one auxiliary electrical component is connected to the power distribution panel.

9. The drive system of claim 3, wherein the second inverter stage also comprises a circuit for providing a DC power source directly from the input AC power while the converter stage is precharging the DC link.

10. The drive system of claim 9, wherein the circuit of the second inverter stage includes a plurality of diodes connected to the input AC power and a diode connected to the DC link.

8. The drive system of claim 8, wherein the at least one auxiliary electrical component is selected from the group consisting of:

pumps, relays, solenoids, heaters, contactors, fans, and combinations thereof.

11. A chiller system comprising:

a refrigerant circuit comprising compressor, a condenser, and an evaporator connected in a closed refrigerant loop;

a motor connected to the compressor to power the compressor;

a variable speed drive connected to the motor, the variable speed drive being configured to receive an input AC power at a fixed input AC voltage and a fixed input frequency and provide an output power at a variable voltage and variable frequency to the motor, the variable voltage having a maximum voltage greater in magnitude than the fixed input AC voltage and the variable frequency having a maximum frequency greater than the fixed input frequency, the variable speed drive comprising;

a converter stage connected to an AC power source providing the input AC power, the converter stage being configured to convert the input AC voltage to a boosted DC voltage, the boosted DC voltage being greater than the fixed input AC voltage;

a DC link connected to the converter stage, the DC link being configured to filter the boosted DC voltage and store energy from the converter stage; and

a first inverter stage connected to the DC link, the first inverter stage being configured to convert the boosted DC voltage from the DC link into the output power for the motor, the first inverter stage also being configured to reverse power flow through the first inverter stage to the DC link stage to transfer electrical power from energy stored in a rotating mass of the motor to maintain the voltage level of the DC link stage in response to a decreasing input AC voltage; and

an electronic control transformer connected to the DC link, the electronic control transformer being configured to convert the boosted DC voltage from the DC link into an auxiliary output power source having a fixed output AC voltage and a fixed output frequency, the fixed output voltage being less than the fixed input AC voltage, wherein the fixed output AC voltage and fixed output frequency of the electronic control transformer is maintained in the event of a temporary decrease in the input AC voltage.

12. The chiller system of claim 11, wherein the converter stage is controllable to precharge the DC link.

13. The chiller system of claim 11, wherein the electronic control transformer is comprised of at least four power semiconductor switches configured to invert the boosted DC voltage to the fixed output AC voltage and fixed output frequency.

14. The chiller system of claim 11, wherein the first inverter stage and the electronic control transformer are disposed in a single enclosure.

15. The chiller system of claim 11, wherein the first inverter stage and the electronic control transformer are disposed in separate enclosures.

16. The chiller system of claim 11, wherein the auxiliary output power source fixed output AC voltage is 120 VAC and the fixed output frequency is 60 Hz.

17. The chiller system of claim 12, wherein the electronic control transformer provides the fixed output AC power to a control panel and to a power distribution panel, and at least one auxiliary electrical component is connected to the power distribution panel.

18. The drive system of claim 17, wherein the at least one auxiliary electrical component is selected from the group consisting of:

pumps, relays, solenoids, heaters, contactors, fans, and combinations thereof.

19. The drive system of claim 12, wherein the electronic control transformer also comprises a circuit for providing a DC power source directly from the input AC power while the converter stage is precharging the DC link.

20. The drive system of claim 11, wherein the circuit of the electronic control transformer includes a plurality of diodes connected to the input AC power and a diode connected to the DC link.

21. An electronic control transformer for powering at least one auxiliary device associated with a chiller system, the electronic control transformer comprising:

an inverter module to convert a DC voltage to provide a fixed output AC voltage and fixed frequency to power the at least one auxiliary device;

the inverter module comprising a plurality of pairs of power switches, wherein each pair of power switches includes an insulated gate bipolar transistor connected in anti-parallel to a diode;

an input DC connection for connecting the electronic control transformer to a DC link of a variable speed drive; and

an output AC connection for connecting the at least one auxiliary device to the inverter module.

22. The electronic control transformer of claim 21 wherein the inverter module is controllable by a pulse width modulation technique.

23. The electronic control transformer of claim 21 wherein the plurality of pairs of power switches comprises two pairs of power switches.

24. The electronic control transformer of claim 21, further comprising an input AC connection for connecting to an input AC power source used to power the variable speed drive, the input AC connection also including a pair of converter diodes and a reverse blocking diode, the converter diodes configured to rectify an input AC voltage from the input AC power source to a DC voltage and the reverse blocking diode being connected between the converter diodes and the input DC connection to prevent short-circuiting a precharge circuit of the variable speed drive.

25. The electronic control transformer of claim 24, also comprising an input capacitor connected across the input DC connection for filtering the DC input and for storing electrical energy.

26. The electronic control transformer of claim 21, also comprising an input capacitor connected across the input DC connection for filtering the DC input and for storing electrical energy.

27. The electronic control transformer of claim 21, also comprising an isolation transformer connected to the output AC connection for electrical isolation of the load.

28. The electronic control transformer of claim 27, also comprising a filter circuit in series with the isolation transformer, wherein the filter circuit comprises at least one series-connected inductor, at least one parallel connected capacitor, and combinations thereof.