Power Conversion Device Switching Circuit for Motor Drive
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Solution Overview
Problem
Conventional power conversion devices suffer from power loss due to continuous connection between the power supply and inverters, and inability to form a closed loop for drive current, especially in motors with neutral points, leading to inefficiencies in both low-speed and high-speed operations.
Innovation Solution
A power conversion device with a switching circuit that disconnects the power supply from one inverter and connects it to ground, allowing for neutral point formation in low-speed operation and n-phase energization control using both inverters during high-speed operation, thereby managing current flow effectively across the motor windings.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the power supply is continuously connected to both inverters, then the motor can operate at high speed with both inverters, but power loss increases and a closed loop for drive current cannot be formed
Solution Approach 1:
The patent applies dynamics by making the connection state of the first inverter changeable: during low-speed operation, the first inverter is disconnected from the power supply to form a closed loop and reduce power loss; during high-speed operation, the first inverter is connected to enable both inverters to work. This dynamic switching resolves the contradiction between speed range and power loss.
Solution Approach 2:
The patent segments the power conversion function into two independent inverters with different operational roles. The first inverter handles low-speed operation with closed-loop current flow, while the second inverter handles high-speed operation. This segmentation allows each inverter to be optimized for its specific speed range, resolving the contradiction between wide speed range and power loss.
2Loss of energy
If the first inverter is disconnected from the power supply and connected to ground, then a closed loop for drive current is formed reducing power loss, but the motor cannot operate at high speed requiring both inverters
Solution Approach 1:
The switching circuit dynamically changes the connection state of the first inverter based on operating conditions. At low speeds, it disconnects the first inverter from power supply and connects to ground to form closed loop. At high speeds, it reconnects the first inverter to power supply. This dynamic adaptation resolves the contradiction between power loss reduction and speed range.
Solution Approach 2:
The patent changes the electrical connection parameters of the first inverter (connection to power supply vs. ground) based on motor speed requirements. This parameter change enables the system to switch between closed-loop operation (low power loss) and dual-inverter operation (high speed capability), resolving the contradiction.
3Manufacturing precision
If neutral point formation is used for low-speed operation, then current control is improved, but the system cannot provide high-speed operation with both inverters
Solution Approach 1:
The patent segments the operational modes: neutral point formation through the first inverter is dedicated to low-speed precise current control, while the second inverter handles high-speed operation. This segmentation allows neutral point formation to improve current control precision without limiting the overall speed range of the motor.
Solution Approach 2:
The system dynamically switches between neutral point formation mode (first inverter connected to ground) for low-speed precise control and dual-inverter mode for high-speed operation. This dynamic switching enables the system to achieve both precise current control and wide speed range.
4Speed
If both inverters are connected to the power supply, then high-speed operation is enabled, but heat generation increases and torque control at low speed deteriorates
Solution Approach 1:
The switching circuit dynamically controls the connection state of the first inverter based on speed and thermal conditions. During low-speed operation, it disconnects the first inverter from power supply to reduce heat generation and enable closed-loop current flow. During high-speed operation, it connects the first inverter to provide sufficient power. This dynamic control resolves the contradiction between speed range and heat generation.
Solution Approach 2:
The patent segments the power delivery function: the second inverter provides power for high-speed operation, while the first inverter provides closed-loop current path for low-speed operation with reduced heat generation. This segmentation allows the system to achieve wide speed range while minimizing heat generation at each operating point.
Data Source
AI summary
A power conversion device includes a first inverter connected to first ends of windings of each phase of a motor, a second inverter connected to second ends of the windings of each phase, and a first switching circuit including at least one of a first switch to switch between whether the first inverter and a power supply are connected or disconnected and a second switch to switch between whether the first inverter and a ground are connected or disconnected. The power conversion device has a first operation mode when the motor is driven at a low speed, and a second operation mode when the motor is driven at a high speed.