Regenerative Frequency Converter With Buck-Boost DC Link Control
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Solution Overview
Problem
Current regenerative frequency converters for elevator hoisting motors require high DC link voltages to maintain control margins, leading to increased voltage stress on components and common mode voltage in motor windings, limiting their reliability and efficiency, and necessitating bulky EMI filters.
Innovation Solution
A frequency converter design featuring phase-specific bidirectional buck-boost converters that adjust the DC link voltage between 300 V to 700 V, eliminating the need for additional EMI filters and reducing common mode voltage, while enabling bidirectional power supply between the AC supply network and motor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a high DC link voltage (at least 620 V) is adopted to maintain control margin for the regenerative line bridge, then the control performance is improved, but the voltage stress on IGBT transistors and common mode voltage in motor windings increase, adversely affecting component lifetime
Solution Approach 1:
The patent changes the voltage parameter by using phase-specific bidirectional buck-boost converters to actively regulate DC link voltage, allowing operation at lower voltages (300-700V range) while maintaining adequate control margins through precise voltage control, thereby reducing stress on power electronic components
2Object-affected harmful factors
If a separate LCL filter is connected between the supply network and input terminals of the regenerative line bridge to meet EMI and THD standards, then the electromagnetic compatibility is improved, but the device becomes heavy and bulky
Solution Approach 1:
The patent merges the EMI filtering function with the regenerative line bridge by using the phase-specific bidirectional buck-boost converters to inherently suppress EMI and THD through their switching operation and control strategy, eliminating the need for a separate bulky LCL filter
Solution Approach 2:
The regenerative line bridge is given multiple functions: it performs power conversion, regenerative braking, and EMI filtering simultaneously through the phase-specific bidirectional buck-boost converters, which can operate in different modes to achieve various objectives
3Reliability
If a high DC link voltage is used to ensure adequate control margin, then the regenerative line bridge control is improved, but the inverter side would have excessive voltage (450V would be adequate)
Solution Approach 1:
The patent implements independent voltage control for different parts of the system by using phase-specific bidirectional buck-boost converters on the line bridge side and a standard inverter on the motor side, allowing the DC link voltage to be optimized separately for each function rather than using a single high voltage for both
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 design enhances the reliability and power density of the system, reduces weight and size, and achieves high-quality sinusoidal current waveforms, resulting in improved ride quality and up to 35% reduction in converter weight and size compared to traditional systems.
Implementation Method 1
Each of the buck-boost converters is configured to be connected to a different phase of the supply network to enable bidirectional supply of power between the supply network and the DC link
Data Source
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AI summary
The present invention discloses a regenerative frequency converter (1) and an elevator system comprising such a frequency converter. The frequency converter (1) is operable for bidirectional supply of power between an alternating current supply network (2) and an alternating current electric motor (3). The frequency converter comprises a regenerative line bridge (6) and an inverter (7) interconnected by a DC link (8). The inverter (7) comprises phase legs (9A, 9B, 9C) for supplying a variable-amplitude, variablefrequency voltage to the motor phases. The regenerative line bridge (6) comprises buckboost converters (13A,14A,15A,16A,18A; 13B,14B,15B,16A,18A; 13C,14C,15C,16C,18C) connected between different input terminals (4A,4B,4C) and the DC link (8).