Parallel Frequency Converter Power Balance via Pulse Timing
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Solution Overview
Problem
In high-power motor control applications, parallel-connected frequency converters experience uneven power distribution and non-simultaneous control pulses, leading to current peaks and potential short-circuits due to disparities in firing and extinguishing delays of power modules.
Innovation Solution
The solution involves synchronizing the firing controls by delaying the falling edge of the control pulse for IGBTs, ensuring simultaneous power switch activation and regulating power balance without shortening the safety time, while increasing inductance between output terminals to manage current peaks and disbalances.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If frequency converters are connected in parallel to increase power handling ability, then the power capacity is improved, but uneven power distribution and current peaks occur due to non-simultaneous control pulses
Solution Approach 1:
The control system performs preliminary detection of current values before switching operations, and adjusts the falling edge timing of control pulses in advance to prevent current peaks from occurring, rather than reacting after the problem arises
Solution Approach 2:
The control system continuously monitors current values from each frequency converter and uses this feedback information to dynamically adjust the falling edge timing of control pulses, ensuring balanced current distribution and preventing current peaks in parallel-connected converters
2Reliability
If the falling edge of control pulse is delayed to regulate power balance, then power distribution is improved, but the safety time margin is reduced
Solution Approach 1:
The control system applies only the necessary degree of delay to the falling edge of control pulses - just enough to achieve current balance between parallel converters, rather than excessive delay that would compromise safety time margins. The delay amount is precisely controlled based on current measurements
Solution Approach 2:
The system dynamically adjusts the timing parameter of the control pulse falling edge based on measured current values, changing the delay amount adaptively to achieve optimal power balance while maintaining adequate safety time margins under different operating conditions
3Reliability
If inductance between output terminals is increased to manage current peaks, then current balance is improved, but the device complexity and size increase
Solution Approach 1:
The control system replaces the need for complex passive inductance matching networks with an active control approach that uses electronic timing adjustment of control pulses to achieve current balance, thereby managing current peaks without adding substantial inductance components
Solution Approach 2:
Instead of changing the physical parameter of inductance values in the circuit, the system changes the timing parameter of control pulses to achieve the same effect of current peak management, avoiding the need for additional inductance components and reducing device complexity
Data Source
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AI summary
A method and a parallel connection arrangement for equalizing the output powers of power converter units (INU11,INU12), which power converter units comprise semiconductor switch bridges controlled with pulse width modulation, and which comprise a control unit arrangement (CU1,CU2) for forming control pulses, with which the semiconductor switches are controlled. The control unit arrangement delays the falling edge of the control pulses of at least one semiconductor switch of at least one power converter unit.