# US 2013/0155730 A1 · System and method for low speed control of polyphase ac machine

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- Number: US 2013/0155730 A1
- Document ID: US20130155730A1
- Status: Published application
- Kind: A1
- Application number: 13/720,510
- Filed: 2012-12-19
- Published: 2013-06-20
- Earliest claimed: 2011-12-19
- Assignees: ZBB Energy Corporation
- Inventors: Jeffrey A. Reichard; Nathan Jobe; Thomas Alan Laubenstein
- Web page: https://patentgrep.com/patent/US20130155730A1

## CPC

- A61K 33/24: Heavy metals; Compounds thereof
- A61K 41/0057: {Photodynamic therapy with a photosensitizer, i.e. agent able to produce reactive oxygen species upon exposure to light or radiation, e.g. UV or visible light; photocleavage of nucleic acids with an agent}
- A61K 49/005: {characterised by the carrier molecule carrying the fluorescent agent}
- A61N 5/062: {Photodynamic therapy, i.e. excitation of an agent}
- C09K 11/7773: {with alkali or alkaline earth metal}
- H02J 3/381: {Dispersed generators}
- H02M 5/453: using devices of a triode or transistor type requiring continuous application of a control signal
- H02M 7/219: in a bridge configuration
- H02P 23/03: specially adapted for very low speeds
- B82Y 5/00: Nanobiotechnology or nanomedicine, e.g. protein engineering or drug delivery
- B82Y 30/00: Nanotechnology for materials or surface science, e.g. nanocomposites
- B82Y 40/00: Manufacture or treatment of nanostructures
- H02J 3/44: with means for ensuring correct phase sequence
- H02J 2101/28: Wind energy
- H02P 6/182: using back-emf in windings
- H02P 2101/15: for wind-driven turbines
- Y02E 10/76: Power conversion electric or electronic aspects
- A61K: PREPARATIONS FOR MEDICAL, DENTAL OR TOILETRY PURPOSES (devices or methods specially adapted for bringing pharmaceutical products into particular physical or administering forms A61J3/00; chemical aspects of, or use of materials for deodorisation of air, for disinfection or sterilisation, or for bandages, dressings, absorbent pads or surgical articles A61L; soap compositions C11D)
- A61N: ELECTROTHERAPY; MAGNETOTHERAPY; RADIATION THERAPY; ULTRASOUND THERAPY (measurement of bioelectric currents A61B; surgical instruments, devices or methods for transferring non-mechanical forms of energy to or from the body A61B18/00; anaesthetic apparatus in general A61M; incandescent lamps H01K; infrared radiators for heating H05B)
- C09K: MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
- 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)
- H02P: CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
- B82Y: SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
- Y02E: REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION

## Abstract

A power converter configured to improve power capture in a wind turbine during low wind speed operation is disclosed. The power converter converts the power generated by the alternator of the wind turbine into a suitable AC current for delivery to a utility grid or to an electric load independent of the utility grid. The power converter is configured to operate in multiple operating modes, utilizing both synchronous and non-synchronous control methods, to extend the operating range of the power converter. During non-synchronous operation, the power converter utilizes a modulation routine that may either vary the dead-time compensation period during a constant modulation period or vary the modulation period with a constant on-time. A seamless transfer between non-synchronous and synchronous control methods with low total harmonic distortion (THD) improves the range of power generation for wind generators.

## Claims

### Claim 1

A power converter comprising:
an input configured to receive power from a multi-phase AC source;
a DC bus having a positive and a negative rail;
a plurality of positive switching devices, each positive switching device selectively connecting one phase of the AC source to the positive rail of the DC bus;
a plurality of negative switching devices, each negative switching device selectively connecting one phase of the AC source to the negative rail of the DC bus;
a memory device storing a series of instructions; and
a controller configured to execute the series of instructions to:
determine a magnitude of power generated by the AC source, and
execute a modulation module to generate a positive control signal for each positive switching device and a negative control signal for each negative switching device, wherein:
the control signals are generated in a first operating mode when the AC source is generating a magnitude of power greater than a first threshold,
the control signals are generated in a second operating mode when the AC source is generating a magnitude of power less than the first threshold, and
during the second operating mode, each of the positive switching devices are controlled to connect each phase of the AC source to the positive rail in tandem and each of the negative switching devices are controlled to connect each phase of the AC source to the negative rail in tandem.

### Claim 2 (depends on 1)

The power converter of claim 1 wherein during the first operating mode the controller executes the modulation module with a fixed modulation frequency and a fixed dead time.

### Claim 3 (depends on 2)

The power converter of claim 2 wherein during the second operating mode the controller executes the modulation module with a fixed on time and a varying modulation frequency.

### Claim 4 (depends on 3)

The power converter of claim 3 wherein the controller accesses a lookup table stored in the memory device, the lookup table defining a rate of change of the modulation frequency during the second operating mode as a function of the current modulation frequency.

### Claim 5 (depends on 4)

The power converter of claim 4 wherein the modulation frequency varies from about 10 kHz to about 50 Hz.

### Claim 6 (depends on 3)

The power converter of claim 3 wherein the control signals are generated in an intermediate operating mode when the AC source is generating a magnitude of power less than the first threshold and greater than a second threshold, wherein the second threshold is less than the first threshold and wherein the second operating mode executes below the second threshold.

### Claim 7 (depends on 6)

The power converter of claim 6 wherein during the intermediate operating mode the controller executes the modulation module with a blanking time periodically disabling the control signals.

### Claim 8

A power converter comprising:
an input configured to receive power from a multi-phase AC source;
a DC bus having a positive and a negative rail;
a plurality of positive switching devices, each positive switching device selectively connecting one phase of the AC source to the positive rail of the DC bus;
a plurality of negative switching devices, each negative switching device selectively connecting one phase of the AC source to the negative rail of the DC bus;
a memory device storing a series of instructions; and
a controller configured to execute the series of instructions to:
determine a magnitude of power generated by the AC source, and
execute a modulation module to generate a positive control signal for each positive switching device and a negative control signal for each negative switching device, wherein:
the control signals are generated in a first operating mode when the AC source is generating a magnitude of power greater than a first threshold,
the control signals are generated in a second operating mode when the AC source is generating a magnitude of power less than the first threshold, and
during the second operating mode, the controller periodically disables the control signals for a blanking time.

### Claim 9 (depends on 8)

The power converter of claim 8 wherein during the first operating mode the controller executes the modulation module with a fixed modulation frequency and a fixed dead time.

### Claim 10 (depends on 9)

The power converter of claim 9 wherein the control signals are generated in a third operating mode when the AC source is generating a magnitude of power less than a second threshold, wherein the second threshold is less than the first threshold and wherein during the third operating mode, each of the positive switching devices are controlled to connect each phase of the AC source to the positive rail in tandem and each of the negative switching devices are controlled to connect each phase of the AC source to the negative rail in tandem.

### Claim 11 (depends on 10)

The power converter of claim 10 wherein the memory device stores a lookup table defining a rate of change of the modulation frequency during the third operating mode as a function of the current modulation frequency.

### Claim 12 (depends on 11)

The power converter of claim 11 wherein the modulation frequency varies from about 10 kHz to about 50 Hz.

### Claim 13

A method of converting power from a renewable energy source having variable power generation capability, the method comprising the steps of:
monitoring a level of power generated by the renewable energy source;
controlling a power converter in a first operating mode via pulse width modulation having a fixed modulation frequency and a fixed dead time compensation when the level of power generated is above a first predetermined threshold; and
controlling the power converter in a second operating mode via pulse width modulation having a periodic blanking time, wherein the blanking time is repeated at a periodic interval during each cycle of a fundamental frequency of a voltage generated by the renewable energy source and wherein during the blanking time the pulse width modulation is disabled.

### Claim 14 (depends on 13)

The method of converting power of claim 13 further comprising the step of controlling the power converter in a third operating mode when the level of power generated is below a second predetermined threshold via pulse width modulation having a variable modulation frequency and a fixed on time, wherein the second predetermined threshold is less than the first predetermined threshold.

### Claim 15 (depends on 14)

The method of converting power of claim 14 wherein the renewable energy source generates a multi-phase AC input voltage and wherein controlling the power converter in the third operating mode further comprises the steps of:
connecting each of the phases from the AC input voltage to a positive rail of a DC bus in the power converter in tandem, and
connecting each of the phases from the AC input voltage to a negative rail of a DC bus in the power converter in tandem, wherein each of the phases are alternately connected to the positive and negative rails.

### Claim 16

A power converter comprising:
an input configured to receive power from an AC source;
a DC bus having a positive rail and a negative rail;
at least one positive switching device selectively connecting the input to the positive rail of the DC bus as a function of a corresponding positive gating signal;
at least one negative switching device selectively connecting the input to the negative rail of the DC bus as a function of a corresponding negative gating signal;
a memory device storing a series of instructions; and
a controller configured to execute the series of instructions to:
execute a modulation routine to generate each of the positive and negative gating signals;
determine a magnitude of power generated by the AC source,
generate the positive and negative gating signals for each of the positive and negative switching devices in a first operating mode when the magnitude of power generated by the DC source exceeds a first predefined threshold, and
generate the positive and negative gating signals for each of the positive and negative switching devices in a second operating mode when the magnitude of power generated by the DC source is less than the first predefined threshold, wherein
during the first operating mode, the controller periodically inserts a blanking time in the modulation routine, disabling the positive and negative gating signals during the blanking time, and
during the second operating, mode each of the positive switching devices connects the input to the positive rail in tandem and each of the negative switching devices connects the input to the negative rail in tandem.

### Claim 17 (depends on 16)

The power converter of claim 16 wherein during the second operating mode, the controller executes a current controller that varies the dead-time as a function of the current transferred between the AC source and the DC bus.

### Claim 18 (depends on 16)

The power converter of claim 16 wherein during the second operating mode, the controller executes the modulation routine with a varying modulation period and a fixed on time.

### Claim 19 (depends on 18)

The power converter of claim 18 wherein the memory device stores a lookup table defining a rate of change of the modulation period during the third operating mode as a function of the current modulation period.