VSD Motor Control for Global MPPT in PV-Powered Drives
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Solution Overview
Problem
Controlling an electric motor driven by a variable speed drive (VSD) directly connected to a photovoltaic panel (PV panel) is challenging due to the varying power supply from the PV panel, as conventional maximum power point tracking (MPPT) techniques often stabilize at local maxima rather than global maxima, and there is no direct control mechanism for the PV panel's output voltage without a DC/DC converter.
Innovation Solution
Implementing a global maximum power point tracking (GMPPT) technique by controlling the electric motor's speed to manage the PV panel's output voltage, utilizing a variable speed drive (VSD) to identify and reach the maximum power point without a DC/DC converter, by monitoring power and voltage variations and adjusting the motor's speed to optimize power transfer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional MPPT techniques are used to control PV panel output voltage, then the control system is simple, but the system stabilizes at local maxima rather than global maxima, reducing power transfer efficiency
Solution Approach 1:
The patent implements a dynamic control approach where the VSD continuously adjusts the electric motor speed based on real-time monitoring of PV panel voltage and power. This dynamic adjustment allows the system to track the global maximum power point by actively responding to changes in irradiance and load conditions, rather than settling at static local maxima. The controller modifies motor speed references to induce voltage variations that enable identification and convergence to the global MPP.
Solution Approach 2:
The electric motor driven by the VSD serves as an intermediary element between the PV panel and the load. By controlling the motor speed, the system indirectly controls the PV panel output voltage without requiring a direct DC/DC converter. This intermediary approach allows the VSD to manipulate the operating point of the PV panel and achieve global MPP tracking through motor speed adjustments.
2Productivity
If a DC/DC converter is added to directly control PV panel output voltage, then maximum power point tracking is improved, but system cost and complexity increase
Solution Approach 1:
The VSD performs multiple functions: it controls the electric motor speed for mechanical work and simultaneously acts as a control mechanism for the PV panel output voltage. By leveraging the existing VSD infrastructure, the system achieves MPP tracking functionality without requiring a separate DC/DC converter. The same control electronics that manage motor operation are utilized to indirectly regulate PV panel voltage and track the maximum power point.
Solution Approach 2:
The system uses its own existing components (the VSD and electric motor) to achieve the function of a DC/DC converter. The VSD self-adjusts the motor operating conditions to create the necessary voltage variations at the PV panel output, enabling the system to track maximum power using its inherent capabilities rather than requiring external dedicated hardware.
3Productivity
If the electric motor speed is controlled to manage PV panel output voltage, then global maximum power point is achieved, but motor speed variations may affect mechanical load performance
Solution Approach 1:
The control method employs periodic perturbations in motor speed reference to induce corresponding voltage variations in the PV panel output. By applying small, periodic speed adjustments and monitoring the resulting power changes, the system can identify the direction toward the global maximum power point. This periodic action enables the extraction of system characteristics without causing large, disruptive speed variations that would significantly impact mechanical load performance.
Solution Approach 2:
The system continuously monitors PV panel voltage, current, and power, and uses this feedback to adjust the motor speed reference. The controller integrates power measurements and compares them against reference values to generate corrective speed adjustments. This feedback mechanism allows the system to achieve global MPP tracking while minimizing speed variations by making only the necessary adjustments to maintain optimal operating conditions.
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
Enhances power transfer from the PV panel to the electric motor by stabilizing the output voltage at the global maximum power point, improving energy efficiency and maintaining motor control without additional converter costs.
Implementation Method 1
An electric motor driven by a variable speed drive (hereinafter referred as VSD) may be supplied by a photovoltaic panel (hereinafter referred as PV panel or solar panel). The power provided by a photovoltaic panel varies with the irradiance of the PV panel.
Data Source
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AI summary
Examples include methods for supplying a power from a photovoltaic panel to an electric motor; a computer-readable storage medium, a computer program product, a processor and a control circuit comprising instructions allowing carrying out the methods; and a VSD adapted to implement the methods.