Discrete Time Oscillator PWM for Sine Wave Motor Drive
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Solution Overview
Problem
Conventional motor driving circuits fail to generate a motor driving current that follows a sine wave form, resulting in undesired noise due to the inability to vary the pulse width of the driving voltage accordingly.
Innovation Solution
A pulse width modulator using a discrete time oscillator generates a pulse width modulation signal with a pulse width that varies according to a sine wave form, comprising a discrete time oscillator, data storage device, data processing block, counter, and comparator, which sequentially changes the first address bits and digital count to produce a PWM signal that mimics a sine wave form.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If a conventional triangular wave-based PWM signal generator is used, then the circuit structure is simple, but the motor driving current cannot follow a sine wave form resulting in noise
Solution Approach 1:
The patent pre-calculates and stores sine wave form data in a lookup table during the design phase. The DTO generates addresses that sequentially access this pre-stored data, allowing the motor driving current to follow a sine wave form without requiring complex real-time calculations, thus reducing noise while keeping the circuit relatively simple
Solution Approach 2:
The patent uses a discrete time oscillator to generate addresses that copy the pattern of a sine wave. By storing sine wave data in advance and using the DTO to sequentially access this stored data, the system creates a digital copy of the sine wave form that drives the motor, achieving smooth current variation without the complexity of analog sine wave generation circuits
2Manufacturing precision
If the pulse width is kept constant in conventional PWM generation, then the control is simple, but the driving current cannot vary according to sine wave form
Solution Approach 1:
The patent makes the pulse width dynamic by using the discrete time oscillator to generate sequentially changing addresses that access different values from the stored sine wave data. This causes the PWM signal's pulse width to vary dynamically according to the sine wave form, achieving precise current waveform control while using relatively simple digital circuitry
Solution Approach 2:
The patent changes the pulse width parameter of the PWM signal based on the discrete time oscillator output. By varying the pulse width according to pre-stored sine wave data, the system achieves accurate sine wave form current control, transforming a static parameter into a dynamically changing one that follows the desired waveform
Data Source
AI summary
A pulse width modulator includes a discrete time oscillator, a data storage device, a data processing block, a counter, and a comparator. The discrete time oscillator generates a first address of bits used by the data processing block for reading first data from the data storage device. The data processing block generates second data from the first data and at least one bit of the first address bits. The comparator generates a pulse width modulation signal by comparing the second data and a digital count generated by the counter.