Dual-PLL Phase Tracking for Active Converter Line Dropout
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Solution Overview
Problem
Variable speed drives (VSDs) with active converters generate high common mode voltage, leading to premature bearing failures and harmonic distortion, and require accurate phase angle tracking for proper operation and synchronization during power outages.
Innovation Solution
A VSD system with a converter stage, DC link, and inverter stage, including phase angle tracking using two Phase-Locked-Loops (PLLs) and a liquid- or refrigerant-cooled inductor for reduced size and weight, along with a contactor bypass for loss reduction, and a filter for common and differential mode voltage reduction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If active converter technology is used to provide power factor correction and reduced input current harmonics, then input current quality is improved, but common mode voltage increases causing bearing fluting and premature bearing failures
Solution Approach 1:
A common mode choke is introduced as an intermediary component between the active converter and the motor to filter common mode voltage. The choke acts as a mediator that blocks high-frequency common mode currents while allowing differential mode power transmission, thus protecting the motor bearings from fluting and premature failures while maintaining the power factor correction benefits of the active converter
Solution Approach 2:
The patent modifies the operating parameters of the active converter by implementing a synchronized PWM technique that maintains a fixed phase relationship between the converter switching frequency and the input voltage frequency. This parameter control reduces the generation of common mode voltage while preserving the harmonic reduction capabilities, effectively changing the electrical parameters to minimize harmful effects
2Measurement precision
If synchronous d-q reference frame control is used for active converter operation, then control precision is improved, but system complexity increases requiring accurate phase angle tracking during power outages
Solution Approach 1:
The patent implements a preliminary action by storing the last known valid phase angle value in a register before power outage occurs. When voltage is detected as absent, the system switches to using this stored phase angle information, allowing the synchronous control to continue operating with previously acquired data rather than requiring complex real-time tracking during the outage
Solution Approach 2:
The control system dynamically adapts its operation mode based on the presence or absence of input voltage. During normal operation, it uses real-time phase angle tracking from the input voltage. During power outage, it transitions to using stored phase angle data. This dynamic switching simplifies the overall system by providing different operational modes rather than requiring a single complex solution for all 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
The solution reduces common and differential mode voltage stress, preventing premature bearing and insulation failures, and enhances synchronization during power outages, while reducing EMI/RFI emissions and the size, weight, and cost of inductive components.
Implementation Method 1
liquid- or refrigerant-cooled inductor
Implementation Method 2
liquid- or refrigerant-cooled inductor
Implementation Method 3
phase angle tracking using two Phase-Locked-Loops (PLLs)
Implementation Method 4
converter stage connected to an AC power source providing the input AC voltage, the converter stage being configured to convert the input AC voltage to a boosted DC voltage
Implementation Method 5
DC link connected to the converter stage, the DC link being configured to filter and store the boosted DC voltage
Implementation Method 6
inverter stage connected to the DC link, the inverter stage being configured to convert the boosted DC voltage from the DC link into the output AC power having the variable voltage and the variable frequency
Implementation Method 7
filter for common and differential mode voltage reduction
Implementation Method 8
filter for common and differential mode voltage reduction
Data Source
AI summary
Systems and methods for synchronous operation of variable speed drives having active converters include extending the synchronous operation of an active converter to the AC mains voltage during complete line dropout. A phase angle control circuit includes a squaring amplifier, a first phase-lock loop circuit associated and a second phase-lock loop circuit. The squaring amplifier receives the AC power source and outputs a rectangular output signal to a pair of phase lock loop (PLL) circuits. The first PLL circuit with a first lag-lead filter is configured with a high cutoff frequency to provide the converter stage with a phase angle parameter; and the second phase-lock loop circuit including a second lag-lead filter configured to have a low cutoff frequency to provide the lag-lead filter the capability of storing the phase angle of the mains voltage during mains interruption.