Supply Unit for Electric Drives with Asymmetric Power Control
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Solution Overview
Problem
Existing supply units are limited in providing higher motor power during feed-in operation compared to regenerative power in feedback operation, and they suffer from power losses due to parasitic circulating currents when connected directly in parallel.
Innovation Solution
The supply unit allows power to be fed into the DC voltage intermediate circuit via both the mains rectifier and the freewheeling diodes of the mains inverter, with controlled activation of electronic switches based on phase-to-phase voltages and intermediate circuit voltage to avoid parasitic currents, and uses balanced impedance in the mains rectifier and inverter branches to distribute current equally, enabling 200% motor power and 100% inverter power for feedback.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the inverter and rectifier are connected directly in parallel, then the device complexity is reduced, but parasitic circulating currents occur causing power losses
Solution Approach 1:
The patent introduces an intermediary control mechanism that coordinates the switching of electronic switches in the inverter with the rectifier operation. This control intermediary prevents parasitic circulating currents by ensuring proper timing and sequencing of switch operations, thereby resolving the contradiction between simple parallel connection and energy losses.
2Device complexity
If the available power for motor and generator operation is made equal at 100% rated power, then the system is symmetric and simple to control, but it cannot provide higher motor power during feed-in operation as required by practical applications
Solution Approach 1:
The patent implements dynamic power capability where the available motor power can exceed the generator power. The system transitions from a static symmetric power configuration to a dynamic asymmetric configuration, allowing 200% motor power capability while maintaining 100% generator power capability, thus adapting to practical application requirements.
Solution Approach 2:
The patent changes the power parameters of the system by enabling the motor power capability to be doubled relative to the generator power capability. This parameter change is achieved through controlled activation of electronic switches and coordination between the inverter and rectifier, allowing the system to provide 200% rated power for motor operation while maintaining 100% for generator operation.
3Ease of operation
If electronic switches are activated independently of current in 120° block operation, then the control is simplified, but parasitic circulating currents occur when the intermediate circuit voltage rises
Solution Approach 1:
The patent implements feedback control by monitoring the intermediate circuit voltage and using this information to control the activation of electronic switches. The switching decisions are based on feedback from voltage sensors that detect when the intermediate circuit voltage rises, preventing parasitic circulating currents while maintaining simplified control through automatic voltage-based triggering.
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 configuration achieves a power ratio of 2:1 for motor power to generator power, reducing parasitic circulating currents and associated losses, thereby enhancing operational efficiency.
Implementation Method 1
The drive power required during motor operation is transmitted via the freewheeling diodes of the mains inverter, which function as a bridge rectifier
Implementation Method 2
a controlled inverter controlled by the three-phase network as an additional unit parallel to a mains rectifier integrated into a frequency converter
Data Source
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AI summary
The invention relates to a supply unit for electric drives, having a three-phase voltage power supply input (L1, L2, L3) and a direct current voltage output (U2+, U2) which is supplied in case of a motor load. In case of a generator load, the supply is returned to the three-phase voltage power supply. A power supply inverter (WR) having electronic switches (T1, T6) for the return supply and anti-parallel free-wheeling diodes (D7, D12) therefor are provided, wherein the latter are utilized as bridge rectifiers during the supply operation. In order to be able to provide more motor power than generator power, a power supply rectifier (GR) is disposed parallel to the power supply inverter, wherein balancing units (X1, X6) are provided for the supply operation at the power supply output of the power supply inverter, and at the power supply input of the power supply rectifier. The electronic switches (T1, T6) of the inverter (WR) are activated in pairs in a chronologically alternating manner during the return supply operation until the voltage on the side of the direct current voltage exceeds a predetermined reference value. The activation and deactivation is carried out in sectors, wherein the number of sectors (S1, S6) is derived from twice the number of power supply phases (L1, L2, L3).