Frequency control and power balancing in disturbed power inverter system and method thereof
First Claim
1. An electrical power control system comprising:
- a first inverter;
an electrical power grid;
a first inductive member connecting said first inverter to said electrical power grid; and
,a first inverter control system having a phase locked loop including a transfer function providing a predetermined phase shift between 0.5 to 500 degrees per Hz during nearly steady operation, whereby the input of said phase locked loop is a voltage on said electrical power grid side of said first inverter and the output of said phase locked loop is a sine wave corresponding to the desired fundamental value and phase at the output of said first inverter.
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Accused Products
Abstract
A system and method are disclosed for controlling DC to AC power converters (inverters) that are operated as voltage sources and are paralleled on the AC side. This method allows for controlling frequency while sharing real power. The disclosed method requires no communication between inverters for proper load sharing, thus enhancing reliability of a system of parallel inverters. The only signals required for control are the AC voltage and frequency and their reaction to the inverter output current. The present invention allows a multiplicity of inverters or active rectifiers to share power in relation to their share of the available power capacity of the system. This makes it possible to parallel DG sources with various response times while they are connected to either a utility grid or in a stand-alone power network with no communications required between inverters. The addition of communications to the system allows the dispatch of energy for economic reasons and to fine tune load balance. Communications can be used for systems status and maintenance but is not required for reliable short-term operation.
42 Citations
17 Claims
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1. An electrical power control system comprising:
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a first inverter; an electrical power grid; a first inductive member connecting said first inverter to said electrical power grid; and
,a first inverter control system having a phase locked loop including a transfer function providing a predetermined phase shift between 0.5 to 500 degrees per Hz during nearly steady operation, whereby the input of said phase locked loop is a voltage on said electrical power grid side of said first inverter and the output of said phase locked loop is a sine wave corresponding to the desired fundamental value and phase at the output of said first inverter. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. A phase lock loop comprising:
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a phase detector having at least one input voltage from an electrical grid and an output; a loop filter electrically having an input and an output, said loop filter being connected on said loop filter input to said phase detector output; a voltage controlled oscillator having an input and a first and second output, said voltage controlled oscillator input being electrically connected to said loop filter; a phase shift electrically connected to said loop filter output; and a low pass filter electrically connected to said phase shift and said loop filter. - View Dependent Claims (9, 10)
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11. A method of controlling power output from a control system, comprising the steps of:
- receiving a signal representative of voltage from an electrical grid;
receiving a signal representative of voltage from an inverter; obtaining a phase error signal that represents the difference between the inverter and electrical grid voltages; generating a frequency error signal that is a function of the phase error signal, wherein said phase error signal and frequency error signals are voltage signals; and
,adjusting the phase error signal via a feedback loop that includes a phase shift and low pass filter of the frequency error signal; and
,shifting the phase between 0.5 to 500 degrees per Hz during nearly steady operation. - View Dependent Claims (12, 13, 14, 15, 16, 17)
- receiving a signal representative of voltage from an electrical grid;
Specification