MULTI-LEVEL MEDIUM VOLTAGE DATA CENTER STATIC SYNCHRONOUS COMPENSATOR (DCSTATCOM) FOR ACTIVE AND REACTIVE POWER CONTROL OF DATA CENTERS CONNECTED WITH GRID ENERGY STORAGE AND SMART GREEN DISTRIBUTED ENERGY SOURCES

• US 20150155712A1
• Filed: 09/09/2014
• Published: 06/04/2015
• Est. Priority Date: 09/09/2013
• Status: Active Grant

• Current Assignee: Inertech IP LLC
• Original Assignee: Inertech IP LLC
• Inventors: Mondal, Subrata K.
• Granted Patent: US 9,774,190 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: H02J 3/1857 wherein such bridge converter is a multilevel converter
• CPC Class Codes: H02J 3/32 using batteries with converting means
• CPC Class Codes: H02J 7/345 using capacitors as storage or buffering devices
• CPC Class Codes: H02M 1/007 Plural converter units in cascade push-pull DC/DC converters with pre-regulator H02M3/3374; DC-AC converters following a DC-DC stage including a high frequency transformer H02M7/4807; DC-AC converters following a DC-DC conversion stage generating periodically varying voltages H02M7/4826
• CPC Class Codes: H02M 7/483 Converters with outputs that each can have more than two voltages levels
• CPC Class Codes: H02M 7/4837 Flying capacitor converters
• CPC Class Codes: Y02E 40/10 Flexible AC transmission systems [FACTS]
• CPC Class Codes: Y02E 40/20 Active power filtering [APF]
• CPC Class Codes: Y02E 60/10 Energy storage using batteries
• CPC Class Codes: Y02E 60/13 Energy storage using capacitors

Abstract

Systems and methods for supplying power (both active and reactive) at a medium voltage from a DCSTATCOM to an IT load without using a transformer are disclosed. The DCSTATCOM includes an energy storage device, a two-stage DC-DC converter, and a multi-level inverter, each of which are electrically coupled to a common negative bus. The DC-DC converter may include two stages in a bidirectional configuration. One stage of the DC-DC converter uses a flying capacitor topology. The voltages across the capacitors of the flying capacitor topology are balanced and switching losses are minimized by fixed duty cycle operation. The DC-DC converter generates a high DC voltage from a low or high voltage energy storage device such as batteries and/or ultra-capacitors. The multi-level, neutral point, diode-clamped inverter converts the high DC voltage into a medium AC voltage using a space vector pulse width modulation (SVPWM) technique.

Claims

1. A transformerless DCSTATCOM for an IT electrical load, comprising:

an energy storage device;

a two-stage bi-directional DC-DC converter;

a multi-level inverter outputting a medium AC inverter voltage; and

a controller configured to control the magnitude of the medium AC inverter voltage of the multi-level inverter to generate or absorb reactive power to achieve a power factor equal to or approximately equal to unity at PCC, the controller further configured to charge or discharge the energy storage device by adjusting the angle of the medium AC inverter voltage with respect to a medium AC grid voltage,

wherein a negative terminal of the energy storage device, a negative terminal of the two-stage DC-DC converter, and a negative terminal of the multi-level inverter are electrically coupled to a common negative bus.

2. The transformerless DCSTATCOM according to claim 1, wherein the medium AC voltage is between about 3.3 kV and about 18 kV.

3. The transformerless DCSTATCOM according to claim 1, wherein the two-stage DC-DC converter includes a first stage that generates a first output DC voltage and a second stage that generates a second output DC voltage higher than the first output DC voltage.

4. The transformerless DCSTATCOM according to claim 3, wherein a positive terminal of the second stage of the DC-DC converter and a positive terminal of the multi-level inverter are electrically coupled to a common positive bus.

5. The transformerless DCSTATCOM according to claim 3, wherein the first stage includes two levels and the second stage includes more than two levels.

6. The transformerless DCSTATCOM according to claim 5, wherein the second stage includes three levels or five levels.

7. The transformerless DCSTATCOM according to claim 5, wherein the two-stage DC-DC converter includes a plurality of switches that form the levels of the first and second stages and a plurality of capacitors coupled together in a flying capacitor topology having a common negative bus.

8. The transformerless DCSTATCOM according to claim 5, wherein the medium AC output is a three-phase AC output,

wherein the multi-level inverter includes three sets of switches, each of which corresponds to one of the three phases of the three-phase AC output, and

wherein each set of switches is configured in a diode-clamped multi-level topology.

9. The transformerless DCSTATCOM according to claim 3, wherein the multi-level inverter converts the second output DC voltage into a third output voltage that is an AC voltage smaller than the second output DC voltage.

10. The transformerless DCSTATCOM according to claim 3, further comprising a DC-DC converter controller configured to control the first stage with pulse width modulation control signals and configured to control the second stage in a flying mode configuration with fixed duty cycle control signals,

wherein the controller is further configured to control the multi-level inverter using space vector PWM control signals so as to perform neutral point voltage balancing.

11. The transformerless DCSTATCOM according to claim 1, wherein the two-stage DC-DC converter is a bidirectional converter configured to allow the flow of both active and reactive power in a first direction from the energy storage device to the AC output of the multi-level inverter and in a second direction from the AC output of the multi-level inverter to the energy storage device.

12. The transformerless DCSTATCOM according to claim 1, wherein the energy storage device is a low voltage energy storage device.

13. The transformerless DCSTATCOM according to claim 12, wherein the low voltage is between about 700 V and about 1200 V.

14. The transformerless DCSTATCOM according to claim 1, wherein the energy storage device is a battery, an ultra-capacitor, or a battery and an ultra-capacitor electrically coupled to one another.

15. The transformerless DCSTATCOM according to claim 1, wherein the multi-level inverter includes more than two levels.

16. A method for supplying power from a transformerless DCSTATCOM to an electrical load when an interruption in power occurs, the method comprising:

supplying a first DC voltage from a low voltage energy storage device to a DC-DC converter;

converting the first DC voltage into a second DC voltage;

providing the second DC voltage to a multi-level inverter;

generating an AC inverter voltage from the second DC voltage, wherein the AC inverter voltage is a medium voltage less than the second DC voltage;

controlling the AC inverter voltage of the multi-level inverter to generate or absorb reactive power to achieve a power factor at PCC equal to or approximately equal to unity; and

charging or discharging the energy storage device by adjusting the angle of the AC inverter voltage with respect to an AC grid voltage.

17. The method according to claim 16, further comprising:

measuring the AC grid voltage and an AC grid current;

calculating a phase angle (⊖

) between the measured AC grid voltage and the measured AC grid current;

calculating reactive power based on the phase angle, the measured AC grid voltage, and the measured AC grid current;

determining whether the measured AC grid current is leading or lagging with respect to the measured AC grid voltage;

if the measured AC grid current is leading with respect to the measured AC grid voltage, generating the calculated reactive power by adjusting the magnitude of the AC inverter voltage so it is greater than the magnitude of the AC grid voltage; and

if the measured AC grid current is leading with respect to the measured AC grid voltage, absorbing the calculated reactive power by adjusting the magnitude of the AC inverter voltage so it is less than the magnitude of the AC grid voltage.

18. The method according to claim 16, further comprising:

measuring AC grid voltage, AC grid current, and phase angle between the AC grid voltage and the AC grid current;

calculating power factor based on measured phase angle;

calculating active power demand at grid PCC based on the measured AC grid voltage, the measured AC grid current, and the calculated power factor;

determining whether to charge or discharge the energy storage device based on the calculated active power demand at the grid PCC;

charging the energy storage device by adjusting the angle of the AC inverter voltage so that it lags with respect to the AC grid voltage; and

discharging the energy storage device by adjusting the angle of the AC inverter voltage so that it leads with respect to the AC grid voltage.