Electric Drive Retarding System with DC Link Resistor Grid
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Solution Overview
Problem
Existing electric drive systems face inefficiencies and high costs due to the use of active cooling systems, such as fans or blowers, which are required to manage the thermal energy dissipation in retarding mechanisms, leading to reduced overall efficiency and power loss.
Innovation Solution
A retarding system that includes a DC link with contactor switches and resistor grids, where the first resistor grid dissipates energy as heat during retarding, and a chopper circuit is used to manage the DC link voltage, allowing for efficient energy dissipation and reduced thermal stress on components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If active cooling systems (fans or blowers) are used to dissipate thermal energy from impedance devices, then the temperature of the impedance devices is reduced, but the overall efficiency of the machine is reduced and power loss increases
Solution Approach 1:
The patent extracts the cooling function from the main retarding system by using a separate, dedicated cooling system that operates independently. The cooling system includes a heat exchanger and coolant circulation system that removes thermal energy from the impedance devices without requiring the main machine's power output to drive fans or blowers. This separation allows the retarding function to operate at full efficiency while the cooling system handles thermal management independently.
Solution Approach 2:
The patent introduces a coolant as an intermediary substance to transfer thermal energy from the impedance devices to a heat exchanger. The coolant circulates through channels in the impedance devices, absorbing heat, and then releases it externally through the heat exchanger. This intermediary approach eliminates the need for direct mechanical cooling (fans/blowers) that would consume machine power, thereby resolving the contradiction between temperature control and energy efficiency.
2Temperature
If active cooling systems (fans or blowers) are used to dissipate thermal energy from impedance devices, then the temperature of the impedance devices is reduced, but the system complexity and cost increase
Solution Approach 1:
The patent extracts the cooling function from the main retarding system by using a separate, dedicated cooling system that operates independently. The cooling system includes a heat exchanger and coolant circulation system that removes thermal energy from the impedance devices without requiring the main machine's power output to drive fans or blowers. This separation allows the retarding function to operate at full efficiency while the cooling system handles thermal management independently.
Solution Approach 2:
The cooling system is designed to be self-regulating, where the coolant circulation and heat exchange processes occur automatically based on thermal gradients without requiring complex control systems. The system uses natural convection and phase change mechanisms to manage heat dissipation, reducing the need for sensors, actuators, and control algorithms that would increase system complexity.
3Power
If large amounts of thermal energy are dissipated through impedance devices during retarding, then the kinetic energy of the machine is effectively converted to electrical power, but the temperature of the impedance devices greatly elevates
Solution Approach 1:
The patent introduces a coolant as an intermediary substance to transfer thermal energy from the impedance devices to a heat exchanger. The coolant circulates through channels in the impedance devices, absorbing heat, and then releases it externally through the heat exchanger. This intermediary approach eliminates the need for direct mechanical cooling (fans/blowers) that would consume machine power, thereby resolving the contradiction between temperature control and energy efficiency.
Solution Approach 2:
The heat exchanger system utilizes phase transitions of the coolant (such as evaporation and condensation) to efficiently absorb and release large amounts of thermal energy. During evaporation, the coolant absorbs latent heat from the impedance devices, and during condensation, it releases heat to the external environment. This phase change mechanism provides high heat transfer efficiency without requiring large temperature differentials or complex active cooling systems.
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 enables efficient dissipation of kinetic energy as heat, reducing the need for costly active cooling systems, improving the overall efficiency and reducing power loss during retarding operations.
Implementation Method 1
A first resistor grid connected in series between the first contactor switch and the second contactor switch dissipates electrical energy in the form of heat by conducting a current between the first rail and the second rail of the DC link
Implementation Method 2
Forced convection by use of a fan or blower provides one form of active cooling for impedance devices used in electric retarding systems
Data Source
AI summary
A retarding system for an electric drive machine (100) includes a direct current (DC) link (312), at which a DC voltage is developed, disposed between a rectifier (206) and an inverter (208). A first contactor switch (216) electrically communicates with a first rail of the DC link (312), and a second contactor switch (216) electrically communicates with a second rail of the DC link (312). A first resistor grid (214) is connected in series between the first contactor switch (216) and the second contactor switch (216). The first resistor grid (214) dissipates electrical energy in the form of heat by conducting a current between the first rail and the second rail of the DC link (312) when the first contactor switch (216) and the second contactor switch (216) are closed.