Systems and methods for mitigating harmonics in electrical systems by using active and passive filtering techniques

Abstract

Systems and methods of the present disclosure involve passive, hybrid, and active filtering configurations to mitigate current harmonics for various electrical loads. One hybrid filtering configuration is medium voltage (MV) active filtering using a DC-DC converter and a multi-level inverter, and low voltage (LV) passive filtering. Another hybrid filtering configuration is MV passive filtering and LV active filtering using a two-level inverter. An active filtering configuration includes both MV and LV active filtering. The present disclosure also features power distribution unit (PDU) transformers electrically coupled to respective power supplies on the LV side of an electrical system. Each PDU transformer includes primary coils in a delta configuration and secondary coils in a wye configuration. The secondary coils are in series with respective leakage inductance coils. The secondary coils and the leakage inductance coils are integrated together into a single unit or module.

1 . (canceled) 
     
     
         2 . A system, comprising:
 an active filter configured to electrically couple to transformers including secondary coils in a wye configuration;   an uninterruptible power supply (UPS) including:
 a multi-level inverter electrically coupled to the transformers; and 
 a DC-DC converter electrically coupled to the multi-level inverter and configured to electrically couple to an energy storage device; and 
   a controller operably coupled to the DC-DC converter and the multi-level inverter of the UPS, the controller configured to operate the DC-DC converter and the multi-level inverter of the UPS in an active filtering mode to supply a harmonic current from the UPS to compensate for a harmonic portion of a load current and in a UPS mode to supply power from the UPS if an interruption in power is detected.   
     
     
         3 . The system of  claim 2 , further comprising a line reactor electrically coupled between an electrical grid and the transformers. 
     
     
         4 . The system of  claim 3 , wherein the line reactor is electrically coupled between the electrical grid and a cooling system, and
 wherein the UPS is electrically coupled to the cooling system.   
     
     
         5 . The system of  claim 4 , wherein the cooling system is selected from the group consisting of fans for drawing hot air through evaporator coils, a cooling distribution unit (CDU) having a pump, a cooling system pump, a fluid cooler having fans, a chiller having a compressor, and combinations thereof. 
     
     
         6 . The system of  claim 2 , further comprising a current sensor configured to sense a load current,
 wherein the controller filters the load current to obtain a harmonic portion of the load current and controls the DC-DC converter and the multi-level inverter of the UPS to generate the harmonic current based on the harmonic portion of the load current.   
     
     
         7 . The system of  claim 2 , wherein the transformers are electrically coupled to respective server power supplies and fan variable frequency drives. 
     
     
         8 . The system of  claim 2 , further comprising an LCL filter coupled to an output of the multi-level inverter of the UPS. 
     
     
         9 . The system of  claim 2 , wherein each transformer includes primary coils in a delta configuration. 
     
     
         10 . The system of  claim 2 , wherein the secondary coils are electrically coupled to leakage inductance coils, respectively. 
     
     
         11 . The system of  claim 2 , further comprising a line reactor electrically coupled to the transformers. 
     
     
         12 . The system of  claim 2 , wherein the active filter includes an energy storage device and a two-level inverter. 
     
     
         13 . The system of  claim 12 , wherein the active filter includes an LCL filter. 
     
     
         14 . The system of  claim 12 , wherein the energy storage device includes an ultracapacitor, a battery, or a combination of an ultracapacitor and a battery. 
     
     
         15 . A system, comprising:
 an active filter configured to electrically couple to transformers including secondary coils in a wye configuration;   an uninterruptible power supply (UPS) including:
 a multi-level inverter electrically coupled to the transformers; and 
 a DC-DC converter electrically coupled to the multi-level inverter and configured to electrically couple to an energy storage device; and 
   a controller coupled to the DC-DC converter and the multi-level inverter of the UPS, the controller configured to operate the DC-DC converter and the multi-level inverter of the UPS to supply a harmonic current from the UPS to compensate for a harmonic portion of a load current and to supply power from the UPS if an interruption in power is detected.   
     
     
         16 . The system of  claim 15 , wherein the active filter includes an energy storage device and a two-level inverter. 
     
     
         17 . The system of  claim 16 , wherein the active filter includes an LCL filter. 
     
     
         18 . The system of  claim 16 , wherein the energy storage device includes an ultracapacitor, a battery, or a combination of an ultracapacitor and a battery. 
     
     
         19 . The system of  claim 15 , further comprising a line reactor electrically coupled between an electrical grid and the transformers. 
     
     
         20 . The system of  claim 19 , wherein the transformers are electrically coupled to respective server power supplies and fan variable frequency drives,
 wherein the line reactor is electrically coupled between the electrical grid and a cooling system, and   wherein the UPS is electrically coupled to the cooling system.   
     
     
         21 . The system of  claim 20 , wherein the cooling system is selected from the group consisting of fans for drawing hot air through evaporator coils, a cooling distribution unit (CDU) having a pump, a cooling system pump, a fluid cooler having fans, a chiller having a compressor, and combinations thereof.