Inverter Parallel Control via Cable Impedance Identification
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Solution Overview
Problem
Existing methods for suppressing cross current in motor drive systems with reactor-less parallel connection of inverters require empirical gain setting, which is often inaccurate and necessitates real-time adjustment due to varying cable impedance, leading to suboptimal control performance.
Innovation Solution
A power conversion apparatus that identifies cable impedance using a test pulse before motor operation and adjusts the cross current suppression control gain, optimizing control performance and eliminating the need for real-time gain tuning.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If empirical gain setting methods are used for cross current suppression control, then the control system can be implemented with existing methods, but the control performance is suboptimal and requires real-time adjustment due to varying cable impedance
Solution Approach 1:
The patent applies preliminary action by identifying cable impedance before motor operation using test pulses. The system measures the actual cable impedance between the inverter and motor, then pre-calculates the optimal cross current suppression control gain based on this measured impedance. This preliminary identification and gain calculation eliminates the need for real-time adjustment during operation, as the gain is already optimized for the specific installation conditions.
2Device complexity
If fixed cross current suppression control gain is used, then the control system is simpler to implement, but the gain is incompatible with varying cable impedance leading to increased current imbalance
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting the cross current suppression control gain based on the identified cable impedance. Instead of using a fixed gain, the system calculates the optimal gain as a function of the measured cable impedance parameters. This allows the control system to adapt to different cable lengths and impedances in various installation scenarios, maintaining current balance without requiring complex real-time adjustment mechanisms during operation.
Data Source
AI summary
In a motor drive system with inverter parallel connection, a laying cable impedance is identified by a test pulse, and a cross current suppression control gain is optimized to provide a power conversion apparatus that does not require a coupling reactor. In the motor drive system 1 in which the outputs of A-bank and B-bank inverters 20A and 20B are connected in parallel, a test pulse is outputted from the drive control unit 30 provided with the PWM controller 33 to the A and B bank inverters before operation. The laying cable impedance is identified from the DC voltage Vdc at the time of test pulse output and the response currents IA and IB. An adjustment gain is calculated from the ratio of installed cable impedance to specified cable impedance. Then, the proportional gain KP is multiplied to optimize the adjustment gain, and an on-delay time based on the optimized adjustment gain GL×KP is calculated during operation. The gate signal corrected by the calculated on-delay time is outputted to the corresponding inverter gate.