Motor drive apparatus, refrigeration cycle apparatus, and air conditioner
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Solution Overview
Problem
When multiple inverter modules with small capacities are connected to form a large-capacity inverter, the increased wiring inductance leads to surge voltages and malfunctions in peripheral circuits, particularly due to the high current flow and di/dt effects, which can damage switching elements and cause demagnetization of motors.
Innovation Solution
The motor drive apparatus employs parallelized switching elements in each phase, with a control unit generating PWM signals to manage the on/off states of these elements, and includes a protection circuit to stop the inverter modules when an overcurrent fault is detected, using a coreless current detector to reduce impedance and suppress surge voltages. The inverter modules are connected to a common earth point to minimize induced voltages and di/dt effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If multiple inverter modules are connected in parallel to increase current capacity, then the current handling capability is improved, but the wiring inductance increases causing surge voltages and peripheral circuit malfunctions
Solution Approach 1:
The patent divides the single inverter system into multiple independent inverter modules (first inverter module and second inverter module), each handling a portion of the total current. This segmentation allows the system to achieve high current capacity while keeping individual module wiring inductance low, thereby reducing surge voltages in each module.
Solution Approach 2:
The patent introduces a new dimensional approach by connecting multiple inverter modules in parallel across different phases (U-phase, V-phase, W-phase), transforming the single-module serial structure into a multi-module parallel structure. This dimensional change enables current distribution across multiple pathways, reducing the current burden and associated surge voltages on any single wiring path.
2Power
If multiple inverter modules are used to achieve large capacity, then the current handling is improved, but the voltage occurring in wiring patterns and lead frame increases threefold
Solution Approach 1:
Each inverter module is designed as an independent unit with its own wiring patterns and lead frames handling only a fraction of the total current. This segmentation reduces the current through each individual wiring path, thereby reducing the voltage stress (V=L×di/dt) on each module's internal wiring and lead frame connections.
Solution Approach 2:
The patent incorporates protection circuits in each inverter module that detect overcurrent conditions and generate stop signals before damage occurs. This beforehand cushioning prevents voltage stress from exceeding safe limits by actively monitoring and responding to current conditions, protecting the wiring and components from excessive voltage stress.
3Object-affected harmful factors
If inverter modules are separately connected to reduce wiring inductance, then the surge voltage is reduced, but the device complexity increases
Solution Approach 1:
The patent merges multiple inverter modules into a unified inverter system where the modules work together to drive a three-phase motor. The modules share common elements such as the motor connection point and control architecture, which simplifies the overall system integration while maintaining the benefits of reduced individual wiring inductance and surge voltage.
Solution Approach 2:
Each inverter module is designed as a universal, interchangeable unit that can be independently connected to handle different phase currents. This universality allows the same module design to be replicated and connected in various configurations, reducing the complexity of custom wiring designs while achieving the desired current distribution and surge voltage reduction.
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 configuration effectively suppresses malfunctions in peripheral circuits and enhances the reliability of the motor drive apparatus by reducing surge voltages and current stress on switching elements, allowing for a large current capacity while maintaining cost-effectiveness and preventing damage from overcurrents.
Implementation Method 1
a coreless current detector to reduce impedance and suppress surge voltages
Data Source
Figure 1
Figure 2~3
Figure 4
AI summary
A motor drive apparatus includes: inverter modules equivalent in number to phases of a motor 15; and a control unit 5 that generates a PWM signal for driving the inverter modules 2, 3, and 4 by using PWM. Each of the inverter modules 2, 3, and 4 includes: a plurality of pairs of switching elements, each pair of switching elements including two switching elements connected in series; a drive circuit 7 that drives the plurality of pairs of switching elements in accordance with an input signal of the control unit; and a protection circuit 8 that stops the drive circuit 7 when a first threshold voltage value is exceeded regardless of the input signal from the control unit 5. The plurality of pairs of switching elements is connected in parallel, and power GNDs 28 that are reference terminals of the plurality of pairs of switching elements, a control GND 30 that is a reference terminal of the drive circuit 7, and a terminal 26 for overcurrent fault input in the protection circuit 8 are independently exposed to the outside. The power GNDs 28 and the control GND 30 are connected to a single point on a printed circuit board by a wiring pattern.