# US 2014/0192567 A1 · Methods for controlling electrical inverters and electrical inverters and systems using the same

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- Number: US 2014/0192567 A1
- Document ID: US20140192567A1
- Status: Published application
- Kind: A1
- Application number: 14/141,715
- Filed: 2013-12-27
- Published: 2014-07-10
- Earliest claimed: 2013-01-07
- Assignees: Aeg Power Solutions B.V.
- Applicants: AEG Power Solutions BV
- Inventors: Didier Balocco
- Web page: https://patentgrep.com/patent/US20140192567A1

## CPC

- H02J 3/46: Controlling the sharing of generated power between the generators, sources or networks
- H02J 3/1814: having reactive elements actively controlled by bridge converters, e.g. unified power flow controllers [UPFC] or controlled series voltage compensators
- H02J 3/1835: with stepless control
- H02J 3/381: {Dispersed generators}
- H02J 3/40: Synchronisation of generators for connection to a network or to another generator
- H02J 3/48: Controlling the sharing of active power
- H02J 3/50: Controlling the sharing of reactive power
- H02M 1/12: Arrangements for reducing harmonics from AC input or output
- H02M 7/48: using discharge tubes with control electrode or semiconductor devices with control electrode
- H02J 2101/24: Photovoltaics
- H02J 2101/25: {involving maximum power point tracking control for photovoltaic sources}
- H02J 2101/28: Wind energy
- H02J 2101/40: Hybrid power plants, i.e. a plurality of different generation technologies being operated at one power plant
- Y02E 10/56: Power conversion systems, e.g. maximum power point trackers
- Y02E 10/76: Power conversion electric or electronic aspects
- Y02E 40/30: Reactive power compensation
- Y02P 80/20: using renewable energy
- 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)
- Y02E: REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02P: CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS

## Abstract

A system for generating a duty cycle control signal for controlling an inverter power train providing an output current waveform to a grid operating with a grid voltage waveform compares a reference current waveform shaped to the grid voltage waveform with the output current waveform to generate an error signal. The error signal is used to generate a corrective control action signal, which is combined with a feed-forward signal representing a nominal duty cycle generated with a feed-forward function. The combination of the feed-forward signal and the corrective control action signal provide the duty cycle control signal.

## Claims

### Claim 1

A method of controlling an electrical inverter including an inverter power train for outputting power to an electrical grid comprising:
generating a reference current waveform in response to a request for power, the reference current waveform shaped by a shape of a grid voltage waveform on the electrical grid;
comparing an inverter output current waveform with the reference current waveform to generate an error signal;
generating a corrective control action signal from the error signal;
generating a nominal duty cycle operating point signal with a feed-forward function; and
adding the nominal duty cycle operating point signal and the corrective control action signal to generate a duty cycle control signal for controlling the duty cycle of the inverter power train and thereby provide an output current waveform with a shape substantially matching the shape of the grid voltage waveform.

### Claim 2 (depends on 1)

The method of claim 1, wherein the inverter power train outputs multiple-phase power and the duty cycle control signal controls the generation of an output current waveform of one selected phase such that a shape of the output current waveform of the selected phase substantially matches a shape of the voltage waveform of the selected phase on the electrical grid.

### Claim 3 (depends on 1)

The method of claim 1, wherein generating the reference current waveform comprises:
receiving a set point value proportional to the power requested;
multiplying the set point value and the grid voltage waveform to generate a waveform substantially matching the grid voltage waveform of the electrical grid;
calculating a square of a root-mean-square voltage of the grid voltage waveform; and
generating the reference current waveform shaped by the grid voltage waveform by dividing the waveform by the square of the root-mean-square voltage of the grid voltage waveform.

### Claim 4 (depends on 3)

The method of claim 3, further comprising:
shifting a phase of the grid voltage waveform prior to multiplication with the set point value to vary a phase difference between grid voltage waveform and the output current waveform and thereby vary a corresponding amount of reactive power output from the electrical inverter to the electrical grid.

### Claim 5 (depends on 1)

The method of claim 1, wherein comparing an inverter output current waveform with the reference current waveform to generate an error signal comprises:
scaling and filtering the inverter output current waveform to generate an image of the inverter output current waveform; and
taking a difference between the image of inverter output current waveform and the reference waveform to generate the error signal.

### Claim 6 (depends on 1)

The method of claim 1, wherein comparing an inverter output current waveform with the reference current waveform to generate an error signal comprises:
scaling and low pass filtering the inverter output current waveform to generate an image of the inverter output current waveform;
scaling and high pass filtering an inverter input current waveform to generate an image of the inverter input current waveform;
adding the images of the input and output current waveforms to generate a sum;
taking a difference between the sum and the reference waveform to generate the error signal.

### Claim 7 (depends on 6)

The method of claim 6, further comprising:
generating a signal predicting a crossing point of the resulting product with the reference waveform; and
taking a difference between signal predicting the crossing point and the reference waveform to generate the error signal.

### Claim 8 (depends on 1)

The method of claim 1, wherein the power train generates a half-cycle of a phase of an output voltage waveform with an instantaneous phase voltage VPhasex by switching between a voltage VPlus and a voltage VMiddle with a duty-cycle controlled by the duty cycle control signal, and wherein the feed-forward function provides the nominal duty cycle operating point signal as:
Nominal Duty Cycle=(VPhaseX−VMiddle)/(VPlus−VMiddle)
where the second voltage VMiddle is determined by a minimum-maximum shaping of the output voltage waveform as:
VMiddle=(Maximum(VPhaseX)−Minimum(VPhasex))/2.

### Claim 9 (depends on 1)

The method of claim 1, wherein the power train generates a half-cycle of a phase of an output voltage waveform with an instantaneous phase voltage VPhaseX by switching between a voltage VPlus and a voltage VMiddle with a duty-cycle controlled by the duty cycle control signal, and wherein the feed-forward function provides the nominal duty cycle operating point signal as:
Nominal Duty Cycle=(VPhaseX−VMiddle)/(VPlus−VMiddle)
where the second voltage VMiddle is determined by third harmonic shaping as:
V
2
=
∏
X

V
Phase


X
[
Maximum


(
V
Phase


X
)
)
]
2

### Claim 10

A system for generating a duty cycle control signal for controlling an inverter power train providing an output current waveform to a grid operating with a grid voltage waveform comprising:
a control loop operable to:
generate a reference current waveform shaped to the grid voltage waveform;
generate an error signal representing a difference between the reference current waveform and the output current waveform;
generate an corrective control action signal from the error signal;
generate a feed-forward signal representing a nominal duty cycle using a feed-forward function; and
generate the duty cycle control signal by combining the corrective control action signal and the feed-forward signal.

### Claim 11 (depends on 10)

The system of claim 10, wherein the control loop comprises a selected on of a plurality of like control loops, wherein each control loop controls the output current waveform of a corresponding phase of multi-phase power being provided by the power train to the grid.

### Claim 12 (depends on 11)

The system of claim 11, wherein the control loop further comprises set point circuitry for generating the reference current waveform and operable to:
generate a signal representing a square of a root-mean-square value of the grid voltage waveform;
scaling the grid voltage with a value representing power to be provided to the grid; and
generate the reference current waveform by dividing the scaled grid voltage waveform by the square of the root-mean-square value of the grid voltage waveform.

### Claim 13 (depends on 12)

The system of claim 12, wherein the set point circuitry is further operable to shift the phase of the grid voltage waveform prior to scaling with a value representing power to be provided to the grid.

### Claim 14 (depends on 10)

The system of claim 10, wherein at least a portion of the control loop is implemented with a digital signal processor.

### Claim 15 (depends on 10)

The system of claim 10, wherein at least a portion of the control loop is implemented in an analog integrated circuit.

### Claim 16 (depends on 10)

The system of claim 10, further comprising a current sensor for sensing the output current waveform and filtering and scaling circuitry for generating a signal representing the output current waveform for comparison with the reference current waveform to generate the error signal.

### Claim 17 (depends on 16)

The system of claim 16, further comprising another current sensor for sensing a power train input current waveform and filtering and scaling circuitry for generating a signal representing the power train input current waveform for combination with the signal representing the output current waveform to generate a signal for comparison with the reference current waveform to generate the error signal.

### Claim 18 (depends on 10)

The system of claim 10, wherein:
the system further comprises:
a current sensor for sensing the output current waveform; and
another current sensor for sensing a power train input current waveform; and
the control loop is further operable to:
filter and scale the output of the current sensor to generate a first signal representing the output current waveform;
filter and scale and output of the another current sensor to generate a second signal representing the power train input current waveform;
combine the first and second signals;
implement an anticipation function to predict the crossing point of the combination of the first and second signals and the reference current waveform; and
in response to a result of the anticipation function, compare the combination of the first and second signals with the reference current waveform to generate the error signal.

### Claim 19 (depends on 18)

The system of claim 18, wherein the anticipation function is implemented with a one-pole, one-zero function.

### Claim 20 (depends on 10)

The system of claim 10, wherein generating a corrective control action comprises implementing a selected one of a proportional integral derivative function and a two-poles, two-zeros function.