Multilevel Chopper Boost Control for High-Capacity AC Compressors
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Solution Overview
Problem
High-capacity air-conditioning compressor systems face inefficiencies due to increased cost and size issues with existing booster circuits, particularly when boosting DC voltage for high-capacity compressors, leading to higher reactor energy demands, semiconductor losses, and harmonic current generation.
Innovation Solution
A power conversion apparatus with a multilevel chopper circuit that includes a booster mode switching unit allowing for selection among three boost modes based on motor operation status, using wide bandgap semiconductors and a smoothing capacitor to control voltage and reduce reactor size and semiconductor losses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a booster circuit is used to boost DC voltage for high-capacity compressors, then the output voltage of the inverter circuit is increased and the operating range is expanded, but the reactor requires a large amount of energy, increasing cost and size
Solution Approach 1:
The booster circuit is divided into multiple independent switching devices (first switching device and second switching device) that operate in different modes. This segmentation allows the circuit to achieve high voltage boosting without requiring a single large reactor, as each switching device handles a portion of the boosting function independently.
Solution Approach 2:
The circuit dynamically switches between different operating modes (first boosting mode and second boosting mode) based on the required output voltage. The control unit adjusts the switching patterns of the switching devices to match the load requirements, optimizing the use of the reactor and reducing unnecessary energy consumption and heat generation.
2Power
If a booster circuit is used to boost DC voltage for high-capacity compressors, then the output voltage of the inverter circuit is increased and the operating range is expanded, but semiconductor loss increases and cost increases
Solution Approach 1:
The control unit dynamically selects between different boosting modes based on the required output voltage. In the first boosting mode, the first switching device operates with a specific duty cycle while the second switching device remains off. In the second boosting mode, both switching devices operate with coordinated duty cycles. This dynamic mode selection optimizes semiconductor utilization and reduces unnecessary switching losses.
Solution Approach 2:
The switching devices operate in periodic cycles with controlled duty ratios. The first switching device switches at a first duty ratio while the second switching device switches at a second duty ratio, creating a periodic action pattern that reduces peak current stresses and distributes switching losses over time, thereby reducing overall semiconductor loss.
3Object-generated harmful factors
If the booster circuit is stopped to suppress harmonic current generation, then harmonic current is reduced, but the operating range of the motor is limited
Solution Approach 1:
The circuit dynamically switches between different boosting modes and operational states based on the motor's operating requirements. When high voltage boosting is needed, the circuit enters boosting modes with appropriate duty cycles. When the motor operates in regions where harmonic current is a concern, the control unit can transition to non-boosting operation or use the second boosting mode with lower ripple characteristics, thus maintaining adaptability while managing harmonic current.
Solution Approach 2:
The control unit changes operating parameters (duty ratios, switching frequencies, and boosting modes) based on the motor's operating conditions. By adjusting these parameters, the circuit can suppress harmonic current generation in certain operating regions while maintaining full operating range capability through parameter optimization in other regions.
4Object-generated harmful factors
If a large reactor is used to suppress harmonic current when the booster circuit is stopped, then harmonic current is reduced, but the size and cost of the reactor increases
Solution Approach 1:
The reactor is segmented into multiple smaller reactors, each associated with a specific switching device. This segmentation eliminates the need for a single large reactor to suppress harmonic current, as each smaller reactor handles a portion of the current and harmonic suppression function independently.
Solution Approach 2:
The switching devices and control unit act as intermediaries to manage harmonic current generation. Rather than relying solely on a large reactor for passive harmonic suppression, the active control of switching patterns and duty cycles serves as an intermediary mechanism to dynamically suppress harmonics while using smaller reactor components.
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 reduces the cost and size of the reactor and power module, increases the boost ratio, and expands the operating range of the motor while minimizing harmonic current generation and semiconductor losses.
Implementation Method 1
a three-phase full-wave rectifier circuit generates a DC voltage for driving the inverter
Implementation Method 2
In the booster circuit, energy is accumulated in the reactor during an ON period of the switching device, and the accumulated energy is released during an OFF period thereof to boost the DC voltage
Implementation Method 3
a smoothing capacitor configured to smooth an output of the booster circuit
Data Source
AI summary
A power conversion apparatus, including: an MLC circuit configured to boost an input voltage from a three-phase rectifier; a smoothing capacitor configured to smooth an output of the MLC circuit; an inverter control unit configured to generate a PWM signal; an inverter circuit configured to convert a DC voltage of the smoothing capacitor into an AC voltage based on an input of the PWM signal and to supply the AC voltage to a motor; a boost mode switching unit having at least three boost modes in which a boost level of the input voltage is selected and configured to switch among the at least three boost modes depending on an operation status of the motor determined for the purpose of controlling a refrigeration cycle; and an MLC control unit configured to control the MLC circuit based on the switching by the boost mode switching unit.