Modular Energy Storage in M2C Converters for Voltage Dip Ride-Through
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Solution Overview
Problem
Existing power converter circuits in electric drives face issues with voltage dips leading to shutdowns, reduced output power, and active braking, particularly in modular converter topologies like M2C, where restarting is difficult without precharging, and integrating energy storage devices into intermediate circuits reduces voltage swing and is challenging.
Innovation Solution
A power converter design incorporating supercapacitors or accumulators with higher energy density in a series connection to the intermediate circuit, allowing for robust shutdowns with residual torque, and enabling energy storage and voltage regulation during network disturbances.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If energy storage devices are directly integrated into the module's intermediate circuits, then energy storage capability is improved, but the available voltage swing of the storage device is reduced because the minimum module voltage is limited
Solution Approach 1:
The patent extracts the energy storage function from the module-level intermediate circuits and places it at the converter-level intermediate circuit. This allows the energy storage devices to operate independently of the minimum module voltage constraints, enabling full voltage swing capability while maintaining energy storage functionality.
Solution Approach 2:
The patent moves the energy storage deployment from a vertical integration within modules to a horizontal deployment at the converter level. This dimensional shift allows energy storage devices to bypass the voltage limitations imposed by individual module architectures and operate with the full voltage range of the converter system.
2Quantity of substance
If the size of the capacitor bank is increased for energy storage purposes, then energy storage capacity is improved, but extremely high discharge currents flow from the capacitor array on the DC side which can cause damage due to extremely high mechanical forces and/or arcing
Solution Approach 1:
The patent introduces semiconductor switches as intermediary components between the capacitor bank and the load. These switches control the discharge current, preventing direct short-circuit-like charging and limiting the current to safe levels while still enabling energy storage functionality.
Solution Approach 2:
The patent implements pre-charging circuits that charge the capacitor bank in advance under controlled conditions before commissioning. This preliminary action prevents uncontrolled, short-circuit-like charging from occurring and ensures safe operation from the start.
3Reliability
If a current-limited pre-charging of the capacitor array is performed before commissioning, then safety is improved, but auxiliary circuits for pre-charging become complex as they must be designed for the high operating voltage
Solution Approach 1:
The patent uses semiconductor switches as intermediary components that simplify the pre-charging circuit design. These switches provide current limiting and control functions, allowing the pre-charging circuits to be designed with lower voltage ratings while still handling high-voltage systems safely.
4Productivity
If voltage dips occur in the supply network, then power conversion continues, but the output voltage at the motor is reduced resulting in loss of output power or even active braking of the motor load
Solution Approach 1:
The patent stores energy in advance in the capacitor bank during normal operating conditions. When voltage dips occur, this pre-stored energy is released to maintain the output voltage and power level, preventing loss of output power or active braking of the motor load.
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
Maintains residual torque and prevents shutdowns during voltage dips, avoiding power loss and active braking, with scalable and redundant energy storage that adapts to voltage requirements.
Implementation Method 1
It is known to provide a capacitor or a series connection of capacitor banks in the intermediate circuit of a so-called U-converter having a DC voltage intermediate circuit
Implementation Method 2
A power converter design incorporating supercapacitors or accumulators with higher energy density in a series connection to the intermediate circuit
Data Source
Figure 1
Figure 2
Figure 3~4
AI summary
The invention relates to a power converter circuit (4), in particular an M2C converter with at least two partial converters, a first partial converter, in particular a rectifier bridge, and a second partial converter, in particular an inverter bridge, wherein at least the second partial converter has at least one phase module (8) having an upper and lower branch, the plus terminals (P) of which are electrically connected to a positive busbar (PS) and the minus terminals (N) of which are electrically connected to a negative busbar (NS), and thus form an intermediate circuit, in particular a DC intermediate circuit (7), wherein a connection point of the electrically series-connected branches of each phase module (8) forms an AC voltage connection (L), wherein each branch of the phase module (8) has two or more two-pole submodules (12) electrically connected in series, wherein each two-pole submodule (12) has a storage capacitor (17),in which a series circuit of two controllable electronic semiconductor switches (13, 14), each with an anti-parallel connected diode (15, 16), is electrically connected in parallel, and wherein a connection of the storage capacitor (17) and a connection point of these two controllable electronic switches (13, 14) each form a terminal (I, II or II, I), wherein the intermediate circuit, in particular DC intermediate circuit (7) has at least one storage branch (9) with at least two submodules (12), wherein these submodules (12) each have an energy store (10) which is electrically connected in parallel to the, in particular internal, energy store (17) of the submodule (12).