# US 10,873,208 B2 · Transformerless multi-level medium-voltage uninterruptable power supply (UPS) systems and methods

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- Number: US 10,873,208 B2
- Document ID: US10873208B2
- Status: Granted
- Kind: B2
- Application number: 15/991,700
- Filed: 2018-05-29
- Published: 2019-05-09
- Granted: 2020-12-22
- Earliest claimed: 2012-07-09
- Assignees: Inertech IP LLC
- Applicants: Inertech IP LLC
- Inventors: Subrata K. Mondal
- Web page: https://patentgrep.com/patent/US10873208B2

## CPC

- H02J 9/062: {for AC powered loads}
- H02M 3/156: with automatic control of output voltage or current, e.g. switching regulators
- H02J: ELECTRIC POWER NETWORKS; CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02M: APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF (transformers H01F; dynamo-electric converters H02K47/00; controlling transformers, reactors or choke coils, control or regulation of electric motors, generators or dynamo-electric converters H02P)

## Abstract

Systems and methods for supplying power at a medium voltage from an uninterruptible power supply (UPS) to a load without using a transformer are disclosed. The UPS includes an energy storage device, a single stage DC-DC converter or 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 unidirectional or 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. The UPS may also include a small filter to remove harmonics in the AC voltage output from the multi-level inverter.

## Claims

### Claim 1

A transformerless uninterruptible power supply for an electrical load, comprising:
an energy storage device;
a single stage DC-DC converter configured to convert a first DC voltage output from the energy storage device into a second DC voltage higher than the first DC voltage using fixed duty cycle control signals; and
a multi-level inverter configured to generate a medium AC voltage using space vector PWM control signals so as to perform neutral point voltage balancing,
wherein a negative terminal of the energy storage device, a negative terminal of the single stage DC-DC converter, and a negative terminal of the multi-level inverter are electrically coupled to a common negative bus.

### Claim 2 (depends on 1)

The transformerless uninterruptible power supply according to claim 1, wherein the single stage DC-DC converter includes a plurality of switches that form the levels of the single stage DC-DC converter and a plurality of capacitors coupled together in a flying capacitor topology having a common negative bus.

### Claim 3 (depends on 1)

The transformerless uninterruptible power supply according to claim 1, wherein the energy storage device is a high voltage energy storage device.

### Claim 4 (depends on 3)

The transformerless uninterruptible power supply according to claim 3, wherein the high voltage energy storage device has a high voltage between about 4 kV and about 7 kV.

### Claim 5 (depends on 1)

The transformerless uninterruptible power supply 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.

### Claim 6

A method for supplying power from a transformerless uninterruptible power supply 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 higher than the first output DC voltage using fixed duty cycle control signals;
providing the second DC voltage to a multi-level inverter; and
generating an AC voltage from the second DC voltage using space vector PWM control signals so as to perform neutral point voltage balancing, wherein the AC voltage is a medium voltage less than the second DC voltage.