Matrix AC-AC Converter Control Without a DC Link Capacitor
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Solution Overview
Problem
In industrial motor drive applications, the conversion of AC power to DC and then back to AC results in a larger volume and decreased efficiency due to the need for a DC capacitor as an energy relay buffer.
Innovation Solution
A matrix power conversion device using bidirectional switches directly converts AC power to AC power without a DC capacitor, employing a controller to generate a control carrier wave that determines the turning-on time of each switch for efficient power conversion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a DC capacitor is used as an energy relay buffer in AC-DC-AC power conversion, then the power conversion can be achieved, but the volume increases and efficiency decreases
Solution Approach 1:
The patent removes the DC capacitor from the power conversion system, extracting the energy buffering function to the motor's own inductance. This eliminates the need for a separate DC link capacitor, reducing device volume and improving efficiency by removing the associated losses.
Solution Approach 2:
The motor inductance is made to serve dual purposes: both as the load inductance for motor operation and as the energy buffering element traditionally provided by a DC capacitor. This multi-functionality eliminates the need for dedicated buffering components, reducing overall system volume.
2Reliability
If a DC capacitor is used as an energy relay buffer, then power conversion is enabled, but the lifespan decreases
Solution Approach 1:
By removing the DC capacitor from the system, the patent eliminates the reliability issues associated with capacitor degradation, leakage, and limited lifespan. The system now relies on the motor's inherent inductance, which has no such degradation issues.
3Ease of operation
If bidirectional switches are controlled using carrier wave comparison, then output voltage and current synthesis is achieved, but switching losses occur
Solution Approach 1:
The patent employs periodic carrier wave comparison for PWM control of bidirectional switches, enabling precise synthesis of output voltage and current. The periodic switching allows for controlled energy transfer while maintaining the ability to synthesize desired output waveforms through duty cycle modulation.
Data Source
AI summary
A matrix power conversion device including a plurality of three-phase switching modules and a controller is provided. Each three-phase switching module includes a plurality of bidirectional switches connected to the input phase voltages of the three-phase input power respectively and outputs a corresponding output phase voltage of the three-phase output power. The controller determines a maximum voltage, an intermediate voltage and a minimum voltage among all the input phase voltages to acquire a waveform of a control carrier wave in a switching cycle. The controller acquires output expected values corresponding to all output phase voltages and compares them with the waveform of the control carrier wave for acquiring a turning-on time of each of the plurality of bidirectional switches. Accordingly, the controller controls the matrix power conversion device to switch the three-phase input power so as to change the three-phase output power for driving the motor.