Inverter Carrier Cycle Correction for Ripple Current Cancellation
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Solution Overview
Problem
Conventional inverter devices using PWM systems face challenges in accurately detecting phase currents due to ripple currents caused by ON-period corrections, leading to noise and vibration issues, which affect the reliability and compactness of the device.
Innovation Solution
The inverter device employs a single current sensor with a control circuit that applies first and second corrections to the carrier cycle, ensuring opposite polarity ripple currents cancel each other out, reducing high-frequency noise and vibration, and allowing for a compact, lightweight structure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If ON-period correction is applied to enable phase current detection, then current detection capability is improved, but ripple current and noise increase
Solution Approach 1:
The patent applies periodic correction to the ON-period of switching elements in a carrier cycle, where the correction amount varies periodically across different phases. This periodic action enables current detection by creating sufficient time intervals while the ripple current effects cancel out over complete cycles, resolving the contradiction between detection capability and noise generation.
Solution Approach 2:
The patent converts the harmful ripple current effects into a beneficial cancellation mechanism. By designing the ON-period correction such that ripple currents in different phases have opposite polarities and cancel each other over complete carrier cycles, the harmful effect of ripple current is transformed into a neutralizing force, allowing both current detection and low noise operation.
2Measurement precision
If multiple current sensors are used for accurate phase current detection, then measurement precision is improved, but device complexity and size increase
Solution Approach 1:
The patent makes a single current sensor perform the function of detecting all three phase currents by utilizing the cancellation effect of ripple currents. The correction mechanism enables one sensor to capture information about multiple phases through strategic timing and ripple cancellation, eliminating the need for multiple dedicated sensors and reducing device complexity.
Solution Approach 2:
The system uses the inherent ripple current effects and their cancellation properties to enable a single sensor to serve multiple detection purposes. The correction mechanism is designed so that the sensor naturally captures the necessary information through the periodic cancellation of ripple effects, without requiring additional sensors or complex external measurement systems.
3Reliability
If ON-period is extended to ensure sufficient detection time, then detection reliability is improved, but ripple current effects worsen
Solution Approach 1:
The patent introduces asymmetric correction amounts for different phases within the carrier cycle. By making the ON-period extension unequal across phases (with different correction amounts for U, V, W phases), the system achieves sufficient detection time for reliable measurement while creating ripple current patterns that cancel out when summed over complete cycles, thus reducing net ripple effects.
Data Source
AI summary
The inverter device contains the following structure: an inverter circuit which has upper-arm switching elements that are connected on a positive side of a DC power source and lower-arm switching elements that are connected on a negative side of the DC power source; a current sensor that detects current flowing between the DC power source and the inverter circuit; and a control circuit that controls the inverter circuit by a PWM driving so that the inverter circuit outputs AC current to the motor. The control circuit provides a carrier cycle with a first correction and provides the successive cycle with a second correction, by which the current sensor can detect phase current of the motor. A ripple current caused by the first correction and a ripple current caused by the second correction are opposite in polarity.