Shared DC Bus Inverter Control for Regenerative Energy Loss
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Solution Overview
Problem
Existing systems with shared DC buses experience energy loss due to the dissipation of regenerative energy as heat through shunt resistors, leading to inefficiency and additional thermal management costs.
Innovation Solution
A controller monitors the DC voltage and current flow on a shared DC bus, adjusting the operation of inverters to balance motoring and regenerative modes, and optionally adding capacitance to manage energy without shunt resistors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a shunt resistor is connected to the shared DC bus to dissipate regenerative energy, then the DC bus voltage can be controlled to prevent component damage, but substantial thermal energy is generated requiring additional thermal management equipment and reducing system efficiency
Solution Approach 1:
The patent converts the harmful regenerative energy that would otherwise be dissipated as heat into useful energy by capturing it through the capacitor bank. The capacitor stores the regenerative energy from motors during braking or deceleration, preventing voltage spikes while recovering energy for later use, thus transforming a harmful effect into a beneficial one.
Solution Approach 2:
The patent changes the electrical parameters of the DC bus by introducing a capacitor bank that dynamically adjusts the bus impedance characteristics. This allows the system to absorb regenerative energy without the need for resistive dissipation, fundamentally changing how energy is managed on the DC bus from a resistive to a reactive approach.
2Reliability
If a shunt resistor is used to manage regenerative energy, then DC bus voltage can be maintained within safe limits, but additional thermal management equipment such as fans and heatsinks is required
Solution Approach 1:
The patent converts the harmful regenerative energy that would otherwise be dissipated as heat into useful energy by capturing it through the capacitor bank. The capacitor stores the regenerative energy from motors during braking or deceleration, preventing voltage spikes while recovering energy for later use, thus transforming a harmful effect into a beneficial one.
Solution Approach 2:
The patent extracts the thermal management subsystem (shunt resistors, heatsinks, fans) from the overall system by replacing it with a capacitor bank that handles regenerative energy without generating heat. This removal of the thermal management chain simplifies the system architecture and eliminates associated complexity.
3Ease of operation
If inverters draw power from the shared DC bus during motoring mode, then motors can operate normally, but the DC bus voltage may droop requiring the rectifier to supply sufficient power
Solution Approach 1:
The patent employs periodic energy exchange between the capacitor bank and the DC bus. During motoring mode, the capacitor bank periodically supplements the rectifier output to maintain bus voltage, and during regenerative mode, it absorbs excess energy. This periodic action smooths out voltage fluctuations and stabilizes the DC bus throughout the motor operation cycle.
Solution Approach 2:
The capacitor bank is pre-charged during periods when motors are drawing power (motoring mode), storing energy in advance. When motors switch to regenerative mode, this pre-stored energy can be quickly exchanged, preventing voltage droop and maintaining stability without requiring the rectifier to immediately respond to changing load conditions.
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
Reduces energy loss by optimizing inverter operations and potentially eliminating the need for shunt resistors, enhancing system efficiency and reducing thermal management expenses.
Implementation Method 1
A capacitor bank is connected between the shared DC bus and a neutral reference of the multiple inverters
Implementation Method 2
The shunt resistor establishes an electrical conduction path from the DC bus through the shunt resistor. The power dissipated in the shunt resistor is equal to the square of the amplitude of current flowing through the resistor times the resistance value of the shunt resistor
Data Source
AI summary
A system and method for reducing energy loss in a multiple inverter system provides a DC voltage to multiple inverters via a shared DC bus. Each inverter is configured to control operation of a motor operatively connected to a corresponding inverter. An amplitude of the DC voltage present on the DC bus is monitored, and each inverter selectively draws current from or delivers current to the DC bus. An amplitude of the current drawn from or delivered to the DC bus is monitored by each inverter. A level of energy delivered by at least one of the inverters to the DC bus is determined when the amplitude of the DC voltage exceeds a predefined threshold during a first operation of the multiple inverter system. At least one subsequent operation of the multiple inverter system is adapted responsive to the level of energy delivered to the DC bus.