Single-Shunt SVPWM Shifting Pattern for Low-Speed Current Sensing
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Solution Overview
Problem
In power inverter systems using single-shunt current sensing, narrow pulses during motor start or low running speeds lead to inaccurate motor current measurement due to insufficient sensing time, affecting motor control performance.
Innovation Solution
Implementing a fixed shifting pattern in the space vector pulse width modulation (SVPWM) scheme to enlarge the pulse width between time t_on and t_off, allowing for accurate current sensing without altering the output voltage, and reducing acoustic noise by maintaining a consistent shifting pattern across all sectors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If standard SVPWM scheme is used with single shunt resistor, then system cost is reduced, but current measurement precision deteriorates during narrow pulse conditions
Solution Approach 1:
The patent applies dynamics by making the PWM scheme adaptive rather than fixed. The control unit dynamically adjusts the PWM generation based on detected narrow pulse conditions, switching between standard SVPWM and modified SVPWM schemes. This dynamic adaptation allows the system to maintain measurement precision when needed while preserving cost benefits during normal operation.
Solution Approach 2:
The patent changes the timing parameters of the PWM scheme by introducing a time advance offset (TOA) that shifts the sampling window. This parameter modification enlarges the effective sensing window during narrow pulses, allowing accurate current measurement to be achieved through parameter adjustment rather than hardware changes.
2Measurement precision
If PWM sampling window is enlarged to allow accurate current sensing, then measurement precision improves, but output voltage accuracy deteriorates
Solution Approach 1:
The patent applies preliminary action by pre-calculating and storing voltage compensation values in lookup tables before runtime. When narrow pulse conditions are detected, the control unit retrieves pre-computed compensation values that correct for the PWM shifting effects, thereby maintaining output voltage accuracy while benefiting from the enlarged sensing window.
Solution Approach 2:
The patent implements feedback by continuously monitoring the actual output voltage and using this information to adjust PWM generation. The control unit compares measured voltage against target values and applies corrective adjustments, ensuring that the output voltage remains accurate even when PWM timing is modified for improved current sensing.
3Device complexity
If PWM pattern is modified to enable single shunt current sensing, then device complexity is reduced, but motor control performance deteriorates during start and low-speed operation
Solution Approach 1:
The patent makes the PWM scheme dynamic by detecting operating conditions (narrow pulse identification) and automatically switching between different PWM generation modes. During motor start and low-speed operation when narrow pulses occur, the system transitions to a modified SVPWM mode that ensures reliable current measurement, thereby maintaining control performance while keeping the overall device simple.
Solution Approach 2:
The patent applies preliminary anti-action by proactively detecting narrow pulse conditions before they degrade control performance and preemptively adjusting the PWM scheme. The control unit monitors pulse widths and, upon detecting conditions that would lead to measurement failure, switches to an alternative PWM mode that prevents the performance degradation from occurring in the first place.
Data Source
Figure 1A~1B
Figure 2A~2B
Figure 3
AI summary
A power module configured to supply a multi-phase current to a multi-phase load is provided. The power module includes an inverter circuit configured to generate a plurality of phase currents that contribute to the multi-phase current and an output voltage based on a plurality of pulse width modulation (PWM) signals; and a control unit configured to generate the plurality of PWM signals to control a plurality of phases based on space vector modulation and modulate the multi-phase current to generate a voltage space vector that is representative of the output voltage and which rotates through a plurality of PWM sectors of a space vector coordinate system. The control unit is configured to regulate a shifting pattern of the plurality of PWM signals during a zero vector switching period such that the shifting pattern is fixed for all of the plurality of PWM sectors as the voltage space vector rotates therethrough.