Randomized PWM Variable Speed Drive for Low-Noise PMSM Chillers
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Solution Overview
Problem
Permanent magnet synchronous motor (PMSM) drives in HVAC&R systems face limitations due to low performance requirements, high system costs, and complex control system designs, restricting their application in commercial and industrial scales.
Innovation Solution
A variable speed drive system utilizing a converter, DC link, and inverter with a controller applying randomized Pulse-Width Modulation (PWM) to vary the switching frequency of transistors, enabling output AC power with variable voltage and frequency, and powering a PMSM motor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If randomized pulse width modulation is applied to vary switching frequency, then electromagnetic interference and acoustic noise are reduced, but control system complexity increases
Solution Approach 1:
The patent applies randomized pulse width modulation that dynamically varies the switching frequency of transistors in the converter and inverter at each switching cycle. This dynamic approach prevents the generation of consistent electromagnetic interference patterns and reduces acoustic noise by avoiding resonant frequencies, while the randomization itself becomes the control mechanism rather than adding separate noise reduction components.
Solution Approach 2:
The controller changes the switching frequency parameter randomly at each switching cycle instead of maintaining a fixed frequency. This parameter variation effectively reduces electromagnetic interference and acoustic noise by preventing harmonic buildup and resonant conditions, while the randomization algorithm provides a structured approach to managing the complexity.
2Use of energy by moving object
If permanent magnet synchronous motors are used in HVAC&R systems, then motor efficiency and power density are improved, but system cost and control complexity increase
Solution Approach 1:
The system employs randomized pulse width modulation that dynamically adjusts switching frequencies to optimize motor performance across different operating conditions. This dynamic control approach maximizes the efficiency benefits of permanent magnet synchronous motors while the randomization technique simplifies the control algorithm compared to traditional fixed-frequency PWM methods.
Solution Approach 2:
The randomized PWM control system allows the motor to self-optimize its performance by varying switching frequencies in response to load conditions without requiring complex external control interventions. The randomization inherently adapts to prevent resonance and optimize efficiency across varying operating points.
3Device complexity
If fixed switching frequency is used in PWM control, then control system is simpler, but electromagnetic interference and acoustic noise increase
Solution Approach 1:
The patent implements a dynamic switching frequency approach where the controller varies the switching frequency randomly at each switching cycle. This dynamic variation prevents the formation of consistent electromagnetic interference patterns and reduces acoustic noise by avoiding resonant frequencies, while the randomization algorithm itself provides a relatively simple control mechanism compared to traditional fixed-frequency PWM.
Solution Approach 2:
The switching frequency parameter is changed randomly at each cycle instead of remaining fixed. This parameter variation effectively reduces electromagnetic interference and acoustic noise by preventing harmonic buildup and resonant conditions, while the randomization approach maintains control system simplicity through a straightforward implementation method.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution enhances motor performance, reduces system costs by minimizing filter sizes, decreases electromagnetic interference and acoustic noise, and improves system stability by optimizing torque and minimizing losses.
Implementation Method 1
The converter is arranged to convert the input AC voltage to a DC voltage
Implementation Method 2
A DC link is connected to the converter and configured to filter and store the DC voltage from the converter
Implementation Method 3
The controller is arranged to apply randomized pulse width modulation to vary the switching frequency of transistors in the converter and the inverter
Implementation Method 4
The controller is arranged to apply randomized pulse width modulation to vary the switching frequency of transistors in the converter and the inverter at each switching cycle
Implementation Method 5
The use of a permanent magnet to generate a substantial air gap magnetic flux makes it possible to design highly efficient PMSMs
Implementation Method 6
The PMSM is a rotating electric machine in which the stator might be similar to a stator of an induction motor and the rotor has surface-mounted or interior permanent magnets
Data Source
AI summary
A drive system for a compressor of a chiller system includes a variable speed drive. The variable speed drive receives an input AC power at a fixed input AC voltage and a fixed input frequency, and provides an output AC power at a variable voltage and variable frequency. The variable speed drive includes a converter connected to an AC power source. The converter is arranged to convert the input AC voltage to a DC voltage. A DC link is connected to the converter and configured to filter and store the DC voltage from the converter. An inverter is connected to the DC link. A motor is connectable to the compressor for powering the compressor. A controller is arranged to control switching in the converter and the inverter. The controller is arranged to apply randomized pulse width modulation to vary the switching frequency of transistors in the converter and the inverter at each switching cycle. The motor may be a permanent magnet synchronous motor.