Multiphase Current Source Inverters for Grid Synchronization
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Solution Overview
Problem
Existing power conversion systems face challenges in converting unstable direct current (dc) power from renewable sources like wind turbines and photovoltaic arrays into stable alternating current (ac) power suitable for injection into the electric grid, particularly due to high harmonic distortion and limited power capacity.
Innovation Solution
The use of multiphase regulated current source inverters with phase-shifting transformers to convert dc power from wind and solar sources into ac power with reduced harmonic distortion, allowing for synchronized injection into the grid, and incorporating step-up and step-down pulsed dc current regulators to maintain optimal output levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional voltage source inverters are used to convert DC power from renewable sources, then the system can operate with simpler circuit topology, but the output power contains high harmonic distortion and limited power capacity
Solution Approach 1:
The patent divides the power conversion system into multiple independent current source inverter modules, each processing a portion of the total power. By segmenting the conversion process across multiple parallel modules with different phase shifts, the system achieves reduced harmonic distortion in the aggregated output while maintaining manageable circuit complexity at each module level.
Solution Approach 2:
The patent combines multiple inverter outputs with different phase characteristics (e.g., 0°, 30°, 60° phase shifts) to create a composite AC output waveform. This composite approach synthesizes a cleaner sine wave with reduced harmonics by leveraging the complementary characteristics of each phase-shifted component.
2Device complexity
If single-phase or three-phase inverters are used for power conversion, then the device complexity remains low, but the power capacity is limited
Solution Approach 1:
The patent merges multiple current source inverter modules in parallel operation, each contributing a portion of the total power capacity. By combining the outputs of these modules with different phase shifts, the system achieves scalable power capacity while keeping each individual module's complexity manageable.
Solution Approach 2:
The patent extends the conventional single-phase or three-phase architecture by introducing multiple phase dimensions (e.g., five-phase, six-phase, or twelve-phase systems). This dimensional expansion allows the system to handle higher power capacities while distributing the complexity across multiple phase legs rather than overloading a single phase structure.
3Speed
If direct DC-to-AC conversion is performed without intermediate regulation, then the conversion process is faster, but the output stability and synchronization with the grid are compromised
Solution Approach 1:
The patent implements preliminary DC current regulation before the inversion process. Each current source inverter module receives pre-regulated DC current input, ensuring stable and controlled conversion to AC output. This preliminary regulation step establishes consistent operating conditions that enable reliable grid synchronization and stable output characteristics.
Solution Approach 2:
The patent incorporates feedback control mechanisms that monitor the AC output and grid conditions, then adjust the DC current input and switching patterns accordingly. This closed-loop feedback ensures the inverter output remains synchronized with the grid frequency and phase while maintaining stable voltage and current levels despite variations in renewable source output.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution effectively reduces total harmonic distortion and increases power capacity, enabling efficient integration of renewable energy sources into the grid with improved stability and efficiency.
Implementation Method 1
converting direct current (dc) power from a plurality of typically unstable sources to alternating current (ac) power
Implementation Method 2
multiphase regulated current source inverters with phase-shifting transformers to convert dc power from wind and solar sources into ac power with reduced harmonic distortion, allowing for synchronized injection into the grid
Data Source
AI summary
Power from the dc outputs of wind-generated power collection nodes is converted to ac power of suitable quality for injection into an electric power grid. Conversion is accomplished by current regulation of the dc outputs of the wind-generated power collection nodes to the input of each one of multiple inverters in a system, with each inverter outputting multiple phase currents that are out of phase with the multiple phase currents outputted from all other inverters in the system. The multiple phase currents from all of the inverters in a system are connected to the secondary windings of a phase transformation network that produces a three phase current output having a step-shaped waveform for injection into the electric power grid. Alternatively the dc input to each one of the multiple inverters may be a combination of the dc outputs of wind-generated power collection nodes and the dc outputs of solar photovoltaic power collection nodes.