Motor Drive Capacitor Reduction via Input Voltage Parameter Change
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Solution Overview
Problem
Existing motor drive systems face challenges in reducing peak power supplied from a power source when actuating a motor and peak power regenerated when decelerating, due to limitations in capacitor capacitance, which can lead to increased costs and space requirements for capacitors, as well as potential damage to PWM converters if the capacitor voltage falls short of the input voltage peak value.
Innovation Solution
A motor drive system that includes a PWM converter and an inverter, with a capacitor connected between the PWM converter and the inverter, where the PWM converter operates to limit input and output currents or power, and uses a step-down transformer or low voltage AC power source to increase the potential difference between charged and discharged capacitor states, thereby reducing the required capacitance of the capacitor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the capacitance C is reduced to reduce peak power supplied from the power source, then the capacitor size and cost are reduced, but the capacitor voltage V2 after supplying power may be reduced to the input voltage peak value, causing current to flow through diodes and disabling power limitation
Solution Approach 1:
The invention changes the voltage parameters by using a lower input voltage than traditionally used. By supplying the PWM converter with a lower voltage AC power source (e.g., 200V instead of 400V), the capacitor voltage after discharge remains above the input voltage peak value, maintaining diode blocking capability while allowing reduced capacitance. This parameter change resolves the contradiction between reducing capacitor size and maintaining power limitation reliability.
2Volume of stationary object
If the capacitance C is reduced to reduce installation space, then the space requirement is reduced, but the potential difference V1-V2 must increase which conflicts with voltage constraints
Solution Approach 1:
The invention changes the operating voltage parameters by using a lower input voltage AC power source. This creates a larger allowable potential difference range for the capacitor (from input peak voltage to maximum capacitor voltage), enabling reduced capacitance and smaller installation space while maintaining safe operating voltages for all components.
3Reliability
If the PWM converter is supplied with standard voltage to drive the motor, then the motor can be driven reliably, but the potential difference of the capacitor is limited, requiring larger capacitance
Solution Approach 1:
The invention uses a two-stage voltage approach: first supplying the PWM converter with a lower voltage AC power source to enable larger capacitor voltage swing and reduced capacitance, then using the PWM converter's voltage boosting capability to generate the higher DC link voltage required for reliable motor driving. This resolves the contradiction between motor driving reliability and capacitance reduction.
4Quantity of substance
If the capacitance C is reduced, then the cost of the capacitor is reduced, but the risk of PWM converter damage increases if capacitor voltage falls short
Solution Approach 1:
The invention changes the voltage parameters by using a lower input voltage AC power source, which ensures that even when the capacitor is fully discharged, its voltage remains above the input voltage peak value. This maintains the blocking capability of the input diodes and prevents harmful current flow that could damage the PWM converter, thereby reducing capacitance without increasing damage risk.
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 approach allows for a reduction in capacitor capacitance by 43-49% while ensuring the motor can be driven with a lower voltage, increasing the potential difference and reducing the risk of PWM converter damage, thus efficiently managing power supply and regeneration.
Implementation Method 1
a capacitor (4) connected between the PWM converter (2) and the inverter (3)... the power of the capacitor is used for making up a shortage of power to drive a motor
Implementation Method 2
PWM converters that can boost a DC link voltage to a desired voltage of an input voltage peak value or more at a power factor of approximately 1 by a PWM switching operation of power semiconductor elements
Implementation Method 3
an inverter (3) for receiving the DC power and converting the DC power into AC power to drive a motor (8)
Data Source
AI summary
A motor drive of an embodiment of the present invention includes a PWM converter for converting AC power inputted from a low voltage AC power source into DC power by PWM control, an inverter for converting the received DC power to AC power to drive a motor, and a capacitor connected between the PWM converter and the inverter. The PWM converter is operated so as to limit input and output currents or input and output power to predetermined values, and supplied from the low voltage AC power source with a lower voltage than a voltage required to drive the motor. The PWM converter boosts a DC link voltage being an output voltage to the voltage able to drive the motor, and thereby serves to increase the potential difference of the capacitor between charged and discharged states to reduce the capacitance of the capacitor.