Power Conversion Device Parasitic Diode Blocking
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Solution Overview
Problem
Existing power conversion devices face challenges in safely interrupting motor operation during faults, particularly with parasitic diodes causing regenerative braking and limited magnetic field vector control, leading to reliability and efficiency issues in electric power steering systems.
Innovation Solution
A power conversion device using semiconductor switching elements connected to each phase and neutral point of a motor, with diodes oriented to prevent current paths to ground or the power source, ensuring safe operation and minimizing regenerative braking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a MOSFET is used as a relay to interrupt phase output when an abnormality occurs, then high reliability and fast protective operation are improved, but current still flows due to parasitic diode causing regenerative braking
Solution Approach 1:
A charge pump circuit is introduced as an intermediary component between the MOSFET and the motor phase. The charge pump generates a negative voltage relative to the source terminal, creating a potential barrier that prevents current flow through the parasitic diode. This intermediary mechanism effectively blocks the harmful regenerative braking current while maintaining the MOSFET's fast switching capabilities.
Solution Approach 2:
The charge pump circuit proactively generates a negative voltage bias before abnormality occurs, establishing a preventive barrier against parasitic diode conduction. By maintaining this negative voltage potential under normal operating conditions, the system preemptively counteracts the potential harmful effect of regenerative braking that would occur during fault conditions.
2Reliability
If operation is stopped upon occurrence of a failure to ensure safety, then safety is improved, but large steering effort using manual force is required
Solution Approach 1:
The system dynamically adjusts its operational state based on the type and severity of detected abnormalities. Instead of a static all-or-nothing approach, the control unit selectively manages different phases or winding sets, allowing the motor to continue operating in a degraded mode for certain fault conditions while maintaining safety. This dynamic response enables continued assisted steering with reduced capability rather than complete shutdown.
Solution Approach 2:
The motor control system is segmented into independently controllable phases or winding sets. When an abnormality is detected in one phase, the control unit can isolate and disable only the affected segment while maintaining operation of healthy segments. This segmentation allows partial continuation of motor function, providing sufficient steering assistance to avoid excessive manual effort while maintaining safety through isolation of the faulty portion.
3Object-generated harmful factors
If two MOSFETs are connected in series with opposite diode directions to block parasitic diode current, then regenerative braking is prevented, but device complexity increases
Solution Approach 1:
Instead of using two MOSFETs in series, a charge pump circuit is introduced as an intermediary component that achieves the same current-blocking function with a single MOSFET. The charge pump generates the necessary negative voltage potential to prevent parasitic diode conduction, eliminating the need for the complex series configuration while maintaining the protective function.
Solution Approach 2:
The system changes the voltage parameter by generating a negative voltage relative to the source terminal through the charge pump circuit. This parameter change (creating a negative voltage bias) fundamentally alters the electrical conditions to prevent parasitic diode forward conduction, achieving the protective function through voltage manipulation rather than through complex circuit topology.
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
The solution enables continued motor operation during faults, improving reliability and safety by preventing regenerative braking and maintaining magnetic field control, thus enhancing the performance and safety of electric power steering systems.
Implementation Method 1
a semiconductor element interrupts the phase output of the power converter so as to separate the motor from the inverter
Implementation Method 2
even when the MOSFET has been turned off, current flows due to a parasitic diode of the MOSFET
Implementation Method 3
a current path (closed circuit) is formed, the current path in which any route of from an FET 4 to the FET 7, from an FET 5 to the FET 8, and from FET 6 to the FET 9, leads to the ground fault point (ground) through a winding of the motor. That is, when the regenerative current flows in the motor through the current path, the motor receives regenerative braking.
Data Source
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AI summary
A first object of the present invention is to provide high reliability, a long lifetime, miniaturization, and high speed protective operation of a unit for separating a phase in which a failure has occurred upon failure and for connecting a drive circuit to a motor terminal to be driven. For a semiconductor replaced from an unit for separating the phase in which the failure has occurred upon failure and for connecting the drive circuit to the motor terminal to be driven, a second object of the present invention is to provide interruption of output that causes regenerative braking to a motor even when any of phase output lines is short-circuited to the ground or short-circuited to a power source, in addition to a short fault of a MOSFET included in an inverter. In order to achieve the first object of the present invention, in a power conversion device according to the present invention, a semiconductor element is used as an unit that is connected to each phase and a neutral point of a four-phase motor or a three-phase motor and that separates the phase and connects a drive circuit to a motor terminal to be driven. In order to achieve the second object of the present invention, the semiconductor switching element included in the power conversion device according to the present invention is connected so that a diode connected in parallel with the semiconductor switching element is connected in a direction in which a current path is not formed between a power source and a ground and so that the diode is further connected in a direction in which a current path is formed neither between a winding of the motor and the power source nor between the winding of the motor and the ground.