Inverter Unit Pulse Integration for Low-Speed Motor Control
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Solution Overview
Problem
Two-phase modulation control inverter units for three-phase motors face challenges in maintaining controllability at low speeds due to reduced switching time and pulse width, leading to unreadable voltage signals and excessive switching device activation, which deteriorates motor performance.
Innovation Solution
The inverter unit incorporates a controller that integrates pulses across multiple signal cycles to ensure adequate pulse width for voltage reading, preventing excessive switching time and maintaining controllability by adjusting control signals to switch devices ON and OFF effectively, even at reduced voltage and speed conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If two-phase modulation control is used to reduce switching loss, then switching loss is reduced, but pulse width becomes too short for voltage reading at low speeds
Solution Approach 1:
The control circuit performs preliminary integration of control signals across multiple carrier signal cycles to accumulate sufficient pulse width before voltage reading occurs. This preliminary action ensures that even though individual switching pulses are narrow (for low switching loss), their integrated sum provides adequate width for accurate voltage measurement through the shunt resistor.
Solution Approach 2:
Multiple narrow control pulses from different carrier signal cycles are merged/integrated into a single wider pulse. This combining approach maintains the low switching loss benefit of narrow individual pulses while achieving the required pulse width for voltage reading by accumulating multiple pulses within the read cycle period.
2Measurement precision
If pulse width is increased to ensure voltage reading, then voltage reading becomes reliable, but switching devices remain ON for unnecessarily long time
Solution Approach 1:
The control circuit performs preliminary integration of control signals across multiple carrier signal cycles to accumulate sufficient pulse width before voltage reading occurs. This preliminary action ensures that even though individual switching pulses are narrow (for low switching loss), their integrated sum provides adequate width for accurate voltage measurement through the shunt resistor.
Solution Approach 2:
The system uses periodic carrier signals to generate control pulses that are integrated over multiple cycles. By reading voltage at specific periodic intervals (at the timing of integrated pulse output), the system achieves reliable measurement without requiring continuously extended pulse widths, thus avoiding excessive switching device activation.
3Speed
If voltage reading is performed at low speed operation, then motor control is maintained, but pulse width is insufficient for accurate reading
Solution Approach 1:
The control circuit performs preliminary integration of control signals across multiple carrier signal cycles to accumulate sufficient pulse width before voltage reading occurs. This preliminary action ensures that even though individual switching pulses are narrow (for low switching loss), their integrated sum provides adequate width for accurate voltage measurement through the shunt resistor.
Solution Approach 2:
The system dynamically adapts its reading strategy to low-speed operation by integrating pulses over multiple cycles. The integration process dynamically accumulates pulse width until the reading threshold is met, allowing accurate voltage reading at low speeds without requiring proportionally longer individual pulse widths that would increase switching loss.
Data Source
AI summary
The two-phase modulation control inverter unit includes a plurality of switching devices, a shunt resistor and a controller. The switching devices drive a three-phase motor. The shunt resistor is connected between a direct-current power supply and the switching devices. The controller reads a voltage applied to the shunt resistor in a read cycle, computes command voltages based on the read voltage, and uses the command voltages and carrier signals to compute three control signals. The read cycle corresponds to two or more signal cycles of each carrier signal. Each control signal has a pulse for each signal cycle of the corresponding carrier signal. The controller integrates a plurality of pulses of each control signal in the read cycle into one or more pulses. The controller reads a voltage applied to the shunt resistor at the time of outputting of the integrated one or more pulses in the next read cycle.