Power Conversion Circuit With Sequential Relay Startup
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional solid-state transformers experience high contact power and reliability risks due to large currents during startup, leading to increased component volume and cost.
Innovation Solution
A power conversion circuit design where relays on each phase line are sequentially closed with resistors in parallel, limiting current increments and reducing contact power, and a method for controlling the sequential closure and opening of relays to manage startup and shutdown processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If all relays T1, T2, and T3 are closed simultaneously during startup, then the SST can be powered on quickly, but large impact currents are generated causing high contact power and reliability risks
Solution Approach 1:
The patent divides the simultaneous relay closing action into sequential stages. Multiple relays are closed one after another rather than all at once, segmenting the current impact over time. This is achieved through a controller that generates staged closing signals for relays T1, T2, and T3, ensuring that at least one relay remains open to limit total current while still enabling power-on functionality.
Solution Approach 2:
The patent implements preliminary action by closing certain relays before others in a predetermined sequence. The controller pre-plans the closing order of relays based on circuit requirements, closing relays that can safely handle current first, then progressively closing others. This preliminary sequencing prevents sudden large current impacts while ensuring the system can still be powered on effectively.
2Ease of operation
If resistors R1, R2, and R3 are used to charge bus capacitors, then the bus capacitors can be charged during startup, but the resistors consume power and generate heat
Solution Approach 1:
The patent makes the resistor connection dynamic by using relays to control whether resistors are connected to the circuit during charging. The relays can switch the resistors in and out of the circuit based on charging progress or system state, transforming a static power-consuming component into a dynamically controlled element that only consumes power when necessary for charging.
Solution Approach 2:
The relays serve as intermediaries between the resistors and the bus capacitors. Instead of resistors directly and continuously charging capacitors, the relays mediate the charging process by controlling the connection timing and duration. This intermediary control allows the system to achieve capacitor charging while minimizing unnecessary power consumption and heat generation from the resistors.
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 design reduces relay contact power and volume, minimizing current impact and enhancing system reliability by gradually increasing current during startup and reducing contact ratings during shutdown.
Implementation Method 1
a resistor and a relay (which may also be referred to as a contactor) that are connected in parallel are disposed to start the SST
Implementation Method 2
a capacitance of a bus capacitor in the power converter is 0, and mains electricity charges the bus capacitor
Implementation Method 3
A solid-state transformer (SST) is a still electrical device that combines a power electronics conversion technology and an electromagnetic induction principle-based high-frequency electric energy conversion technology to convert electric energy of one power characteristic into electric energy of another power characteristic
Data Source
Figure 1
Figure 2
Figure 3
AI summary
Embodiments of this application provide a power conversion circuit, a method for controlling a power conversion circuit, and a transformer, to reduce a volume of a component in the power conversion circuit and improve system reliability. The power conversion circuit includes at least one first power conversion unit connected in series to a first phase line, at least one second power conversion unit connected in series to a second phase line, at least one third power conversion unit connected in series to a third phase line, a plurality of first start circuits connected in series to the first phase line, and a plurality of second start circuits connected in series to the second phase line. Each first start circuit includes a first relay and a first resistor that are connected in parallel, and first relays in all the first start circuits are sequentially closed after the power conversion circuit is powered on, to start the power conversion circuit. Each second start circuit includes a second relay and a second resistor that are connected in parallel, and second relays in all the second start circuits are sequentially closed after the power conversion circuit is powered on, to start the power conversion circuit.