Brushless Motor Control Fixed State Sequence
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Solution Overview
Problem
Existing PWM control methods for multi-phase brushless motors experience discontinuities in di/dt measurements due to changes in the sequence of inverter states, leading to unreliable rotor position estimation, especially at low speeds and high magnetic saturation conditions.
Innovation Solution
A drive system with a control means that defines a fixed sequence of active states for each PWM period, allocates state times to required states, and omits unnecessary states, ensuring a consistent order of states throughout various operating parameters, including zero net voltage states to minimize state time differences and reduce acoustic noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a variable PWM pattern is used to adapt to different operating conditions, then the motor control flexibility is improved, but discontinuities in di/dt measurements occur due to changes in inverter state sequence
Solution Approach 1:
The PWM period is segmented into fixed sequence slots, each designed to accommodate specific inverter states. This segmentation allows the system to maintain a consistent state sequence while adapting to different operating conditions by selectively including or excluding states within the fixed framework.
Solution Approach 2:
The invention changes the parameter of state sequence ordering from variable to fixed, while allowing parameter changes in state duration and state selection. This resolves the contradiction by maintaining measurement consistency through fixed sequencing while preserving adaptability through flexible state allocation.
2Productivity
If all active states are included in each PWM period, then complete voltage coverage is achieved, but state time differences increase causing acoustic noise
Solution Approach 1:
The invention extracts and removes unnecessary active states from the PWM sequence when they are not required for the current operating condition. This reduces state time differences and minimizes acoustic noise while maintaining complete voltage coverage through selective state inclusion.
Solution Approach 2:
Instead of always applying all possible active states, the invention applies only the partial set of states necessary for the current operating condition. This partial action approach reduces harmful acoustic noise while achieving sufficient voltage coverage for motor control.
3Measurement precision
If PWM edges are shifted to enable di/dt measurements, then position estimation capability is improved, but acoustic noise increases
Solution Approach 1:
The invention performs preliminary allocation of inverter states within a fixed sequence framework before PWM generation. This preliminary arrangement ensures that di/dt measurement opportunities are built into the fixed sequence structure itself, eliminating the need for additional edge shifting that would generate acoustic noise.
Data Source
Figure 1~2
Figure 3~3a
Figure 4a~4c
AI summary
A drive system, for a multi-phase brushless electric motor comprising a plurality of phases, comprises: a drive circuit including switch means (26) arranged to vary the phase voltage applied to each of the phases (12, 14, 6) so as to switch the motor between a plurality of active states; and control means (33). The control means is arranged to control the switch means so as to provide PWM control of the phase voltages to control the mechanical output of the motor. The control means is arranged to define a sequence for all of the active states and, for each PWM period, to allocate state times for the states required for that period to generate a desired net voltage, and to order the required states in the same order as they occur in the sequence.