Motor Drive Inverter Control to Reduce Capacitor Current and Heat
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Solution Overview
Problem
Existing motor drive devices face reliability issues in high load ranges and high outside temperature environments due to increased current flowing through capacitors, leading to potential failures and decreased performance.
Innovation Solution
A motor drive device with a control unit that performs load pulsation compensation, power supply pulsation compensation, and overload compensation to reduce capacitor charge and discharge currents, while prioritizing constant current load control, using a rectifier unit, capacitor, and inverter to manage inverter input current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a small-capacitance capacitor is used to reduce size and cost, then device complexity and cost are reduced, but reliability decreases due to temperature rise and capacitor failure under high load and high outside temperature conditions
Solution Approach 1:
The control unit dynamically changes operating parameters by adjusting the drive pattern of the motor to reduce charge and discharge currents of the capacitor. This includes modifying current commands to account for capacitor temperature and state, thereby reducing thermal stress on the capacitor while maintaining acceptable device size
Solution Approach 2:
The control unit implements feedback control by monitoring the power state of the capacitor and adjusting the drive pattern accordingly. The control unit performs power supply pulsation compensation control based on capacitor state information, creating a closed-loop system that prevents capacitor overheating and failure while using small-capacitance components
2Power
If inverter current is increased to meet high load range requirements, then motor performance is improved, but capacitor charge and discharge current increases leading to temperature rise and potential failure
Solution Approach 1:
The control unit applies periodic pulsation to the drive pattern that corresponds to the capacitor's charge and discharge cycle. By superimposing this pulsation, the control unit reduces the amplitude of charge and discharge currents while maintaining the average power transmission required for high load operation, thereby reducing capacitor temperature rise
Solution Approach 2:
The control unit dynamically adjusts current commands based on capacitor power state to reduce charge and discharge currents while maintaining motor performance. This parameter adjustment allows high power operation without proportionally increasing capacitor stress and temperature
Data Source
AI summary
A motor drive device includes a rectifier unit that rectifies first AC power supplied from a commercial power supply, an inverter that generates second AC power and output the second AC power to a motor, and a control unit that controls the operation of the inverter such that pulsation according to the power state of a capacitor is superimposed on a drive pattern of the motor, to reduce a charge and discharge current of the capacitor. The control unit performs load pulsation compensation control to compensate for load pulsation, power supply pulsation compensation control to reduce the charge and discharge current of the capacitor, and overload compensation control to reduce an inverter input current input to the inverter, while preferentially performing constant current load control to control the rotational speed of the motor.