Bootstrap Capacitor Recharge via Voltage Regulator
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Solution Overview
Problem
Inverter circuits with bootstrap capacitors face challenges in maintaining charge at low switching speeds or during stall conditions, leading to potential loss of power and torque, especially when motor loads are unable to provide sufficient current, and existing solutions like p-channel MOSFETs result in higher power losses or complex multi-winding power supplies.
Innovation Solution
The implementation of a circuit that uses controllable switching devices to recharge bootstrap capacitors, allowing operation at 100% duty cycle and resisting steady-state conditions, powers multiple phases from a shared power supply, and includes a voltage regulating device to manage power flow between the high side power bus and the bootstrap capacitor, ensuring continuous operation and preventing catastrophic failures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a bootstrap capacitor is used to drive the high side switch gate, then the gate voltage can be boosted above the high side power bus voltage, but the capacitor will discharge at low switching speeds or steady-state conditions without opportunity to recharge
Solution Approach 1:
A voltage regulating device is introduced as an intermediary component between the high side power bus and the bootstrap capacitor. This device actively manages charge transfer, allowing the capacitor to be recharged from the high side power bus when the switching device is off, preventing discharge at low switching speeds while maintaining the voltage boost capability.
Solution Approach 2:
The voltage regulating device enables the bootstrap capacitor to self-recharge during the off-state of the switching device. The system automatically manages the charge-discharge cycle without external intervention, with the regulator detecting when the capacitor voltage drops below a threshold and initiating recharge from the high side power bus.
2Reliability
If control schemes force the high side driver off for minimum time to allow capacitor recharge, then the capacitor can be recharged, but the circuit must operate at less than 100% duty cycle sacrificing performance
Solution Approach 1:
The voltage regulating device acts as an intermediary that decouples the capacitor recharge process from the switching cycle requirements. It can recharge the capacitor continuously or periodically from the high side power bus without requiring the high side driver to be forced off, enabling true 100% duty cycle operation while maintaining capacitor charge.
3Productivity
If external conditions cause 100% or near-100% operating condition such as motor stall, then the inverter can maintain performance, but the bootstrap capacitor may discharge without recharge opportunity leading to loss of control
Solution Approach 1:
The voltage regulating device serves as a protective intermediary that continuously monitors bootstrap capacitor voltage and intervenes to recharge it from the high side power bus when voltage drops below thresholds. This prevents loss of control during motor stall conditions where the high side driver would otherwise remain continuously on without recharge opportunity.
Solution Approach 2:
The voltage regulating device provides beforehand cushioning by maintaining the bootstrap capacitor voltage above critical thresholds through proactive recharge. This prevents the catastrophic failure mode of gate drive voltage collapse during stall conditions, cushioning against the adverse effects of extended on-states.
4Reliability
If p-channel MOSFETs are used to address bootstrap capacitor discharge, then the capacitor can be recharged, but power losses increase
Solution Approach 1:
The voltage regulating device replaces the mechanical/current-dependent recharge mechanism of p-channel MOSFETs with an active voltage-regulated control system. This substitution enables precise control of recharge timing and amount, minimizing energy losses while ensuring adequate capacitor recharge even at 100% duty cycle operation.
5Reliability
If complex multi-winding power supplies are used to provide isolated power to high side driver, then the driver can be powered independently, but device complexity increases
Solution Approach 1:
The voltage regulating device provides multi-functionality by serving both as a power distribution element and as a bootstrap capacitor recharge mechanism. It draws from the existing high side power bus (shared infrastructure) and provides regulated power to the bootstrap capacitor, eliminating the need for separate multi-winding power supplies while maintaining independent driver operation.
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 extends the operability of inverter circuits to 100% duty cycle, prevents loss of control during stall conditions, and reduces power losses, enabling the top switch to turn on promptly and operate in linear mode, thus enhancing the reliability and efficiency of inverter circuits.
Implementation Method 1
a voltage regulating device configured to receive power from the high side power bus and controllably supply power to the bootstrap capacitor based on a regulator input voltage received at a regulator input port, the regulator input voltage based on a voltage difference between a voltage present on the output port and a voltage present on the high side power bus
Implementation Method 2
a bootstrap capacitor coupled between the voltage regulating device and the output port
Data Source
AI summary
The subject matter of this specification can be embodied in, among other things, a phase circuit having an output port, and a high side circuit having a first input port, a high side switching device configured to receive power from a high side power bus and switch power to the output port based on a first input signal received at the first input port, a voltage regulating device having a regulator input port, and a bootstrap capacitor coupled between the voltage regulating device and the output port, wherein the regulating device is configured to receive power from the high side power bus and controllably supply power to the bootstrap capacitor based on a regulator input voltage received at the regulator input port, the regulator input voltage based on a voltage difference between a voltage present on the output port and a voltage present on the high side power bus.