PCWM Motor Drive System Real-Time Sinusoidal Control
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Solution Overview
Problem
Existing motor drive systems, such as those described in U.S. Pat. Nos. 4,634,952 and 5,420,778, face limitations including inability to alter frequency or voltage during a signal output cycle, lack of load measurement, complex hardware requirements, and inefficient sinusoidal signal generation, which restrict their flexibility and performance in driving three-phase AC motors sinusoidally without rotor position sensing.
Innovation Solution
A pulse code width modulation (PCWM) technology is employed with real-time calculation capabilities using finite state machines and ultrasonic carrier frequencies to generate sinusoidal motor drive waveforms, incorporating a single ASIC with integrated sine function tables and V/F tables, enabling precise speed control and reduced hardware complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If RAM is used to store coded sinusoidal signals for the entire signal cycle, then the system can generate sinusoidal motor drive signals, but the frequency and voltage level cannot be altered during the current signal output cycle
Solution Approach 1:
The patent divides the signal generation into discrete pulse intervals rather than storing entire cycles. Each pulse can be independently controlled with its own width and timing, allowing frequency and voltage adjustments to take effect immediately in subsequent pulses without waiting for cycle completion.
Solution Approach 2:
The system transitions from static pre-stored waveforms to dynamic real-time pulse generation. The pulse width modulation allows continuous adjustment of voltage level and frequency by varying pulse characteristics on-the-fly, enabling adaptive control during operation.
2Ease of operation
If a synchronous signal with carrier frequency proportional to signal frequency is used, then the system can generate PWM signals, but a complicated variable step-down counter is required to select output signal frequency
Solution Approach 1:
The patent replaces complex mechanical/electrical counter circuits with a microprocessor-based software solution. The microprocessor calculates and generates PWM signals directly, eliminating the need for variable step-down counters and simplifying frequency selection through programmable control.
3Reliability
If at least three hardware chips and two microcomputers are used for encoding and decoding sine functions, then the system can generate PWM signals, but the hardware construction becomes complex
Solution Approach 1:
The patent combines multiple separate hardware components (chips for encoding, microcomputers for control, gate arrays for decoding) into a single integrated microprocessor system. The microprocessor performs all functions including sine wave generation, PWM encoding, and control logic, significantly reducing hardware complexity while maintaining signal accuracy.
Data Source
AI summary
A detailed architectural and operational characteristic of a pulse code width modulation (PCWM) motor drive system is presented. The system can drive a three phase permanent magnet AC (PMAC) motor sinusoidally without sensing its rotor position. The system employs an ultrasonic carrier frequency (e.g., of approximately 20 kHz) to avoid annoying acoustic noise problems. While keeping the hardware construction at a minimum, it can provide the highest possible motor performance by satisfying various motor operating requirements. The system may include an AC to DC converter, an application specific integrated circuit (ASIC), a DC to DC step-down chopper, and a gate drive and power transistor circuitry to drive a three phase AC motor.