PWM Control Part Optimizing Phase Current Detection Timing
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Solution Overview
Problem
In motor drive control systems using PWM inverters, detecting phase currents accurately is challenging due to unstable detection signals and close time intervals of rising edges, which can result in insufficient time for detecting currents, especially in sinusoidal three-phase AC voltage scenarios.
Innovation Solution
A motor drive control device that controls the turning on-off of upper and lower arm switching elements in a PWM inverter using PWM pulses, generating pulses based on carrier signals and phase voltage commands to ensure timely detection of phase currents by adjusting the high-level periods of PWM pulses, particularly for the largest and smallest phases, allowing for accurate current detection across all phases.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If different phase currents are detected in accordance with a combination of turning on a low voltage side transistor in each of the rows constituted of two transistors connected in parallel, then current error correction can be performed, but the time for detecting phase currents may not be able to be ensured when time intervals of rising edges become closer
Solution Approach 1:
The patent applies preliminary action by pre-determining the detection timing of phase currents based on the timing of rising edges of PWM pulses. The control device is configured to detect phase currents at specific timings that are determined in advance, ensuring that detection is performed at optimal moments before the rising edges occur, thus preventing detection time insufficiency while maintaining accurate current measurement for error correction.
2Reliability
If phase currents are detected during a short period of time excluding the rising edge within a pulse width, then unstable detection signals are avoided, but the time for detecting phase currents may not be able to be ensured
Solution Approach 1:
The patent applies preliminary action by pre-determining the detection timing of phase currents based on the timing of rising edges of PWM pulses. The control device is configured to detect phase currents at specific timings that are determined in advance, ensuring that detection is performed at optimal moments before the rising edges occur, thus preventing detection time insufficiency while maintaining accurate current measurement for error correction.
Data Source
AI summary
A motor drive control device controls driving of a motor by performing PWM control of turning on-off of an arm switching element of a PWM inverter outputting a three-phase AC voltage to the motor, and detects current values of respective phases of the three-phase AC voltage. The motor drive control device turns off a lower arm switching element for a largest phase by causing a first PWM pulse based on a largest phase voltage command and a carrier signal throughout an entire first period during which the carrier signal rises or falls to be at a low level. The motor drive control device turns on a lower arm switching element for a smallest phase by causing a second PWM pulse based on a smallest phase voltage command and the carrier signal throughout an entire second period during which the carrier signal rises or falls to be at a high level.