MMC Submodule Voltage Control for Passive Filter Resonance
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Solution Overview
Problem
Multi-phase multi-stage converters with passive frequency filters face challenges in controlling resonance points, especially when the resonance frequency is close to the sampling frequency, leading to excitation of resonance points and increased component stress due to aliasing effects and weak damping.
Innovation Solution
The control system switches on and off submodule voltages in a time-delayed manner within a sampling interval, with specific periods (T1 and T2) tailored to the resonant frequency, to minimize excitation of the passive frequency filter's resonance point, using time-delayed switching of submodule voltages to dampen interference effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the resonance frequency of the passive frequency filter is set above the sampling frequency, then high-frequency interference is strongly attenuated, but the resonance point is excited further due to aliasing effects
Solution Approach 1:
The invention applies periodic switching actions within the sampling interval by switching on and off submodule voltages in a time-delayed manner. This periodic switching creates a switching pattern that avoids exciting the resonance frequency of the passive frequency filter, thereby preventing resonance point excitation while maintaining effective attenuation of high-frequency interference.
Solution Approach 2:
The invention changes the timing parameters of the switching operations by introducing time delays T1 and T2 within the sampling interval. By adjusting these time delay parameters, the switching frequency and pattern are modified to avoid resonance excitation, allowing the system to maintain effective interference attenuation without triggering the resonance point of the filter.
2Object-generated harmful factors
If the resonance point is lowered below the switching frequency, then excitation of the resonance point is dampened, but very large and expensive filter components are required
Solution Approach 1:
The invention changes the operational parameters of the switching system by introducing time delays within the sampling interval, rather than changing the physical parameters of the filter components. This allows effective resonance dampening to be achieved through control strategy modification, avoiding the need for large and expensive filter components.
Solution Approach 2:
The invention replaces the mechanical approach of lowering the resonance point through larger physical filter components with a control-based approach. By using time-delayed switching patterns, the system achieves resonance dampening through electronic control rather than mechanical enlargement of filter components, thereby reducing device complexity and cost.
3Manufacturing precision
If submodule voltages are switched on and off rapidly to regulate connection voltage, then voltage regulation precision is improved, but resonance points are excited and component stress increases
Solution Approach 1:
The invention uses periodic switching actions with specific time delays T1 and T2 within each sampling interval. This periodic pattern allows rapid switching for voltage regulation while avoiding resonance excitation by synchronizing the switching pattern with the filter's resonant characteristics, thereby maintaining voltage precision without excessive component stress.
Solution Approach 2:
The invention applies preliminary time delay adjustments to the switching pattern before the actual switching occurs. By pre-calculating and applying time delays T1 and T2, the system prepares the switching pattern to avoid resonance excitation in advance, allowing rapid switching for regulation while preventing harmful resonance effects and component stress.
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 approach significantly reduces the excitation of the passive frequency filter, improves damping, lowers component stress, and enhances noise emission behavior, while reducing project risks related to electromagnetic compatibility (EMC) acceptance.
Implementation Method 1
A passive frequency filter, in particular as an LCL passive filter, is provided for each phase module to dampen higher-frequency components of the connection voltage. Such frequency filters have a resonant frequency which is expediently above the sampling frequency.
Implementation Method 2
The control system switches on and off submodule voltages in a time-delayed manner within a sampling interval, with specific periods (T1 and T2) tailored to the resonant frequency, to minimize excitation of the passive frequency filter's resonance point
Implementation Method 3
The control system switches on and off submodule voltages in a time-delayed manner within a sampling interval, with specific periods (T1 and T2) tailored to the resonant frequency, to minimize excitation of the passive frequency filter's resonance point, using time-delayed switching of submodule voltages to dampen interference effectively.
Data Source
Figure 1~2
Figure 3
Figure 4~5
AI summary
Multiphase multilevel power converter having a drive and a passive frequency filter, and method for driving the multiphase multilevel power converter. The invention relates to a multiphase multilevel power converter (MMC) having a phase module (210) formed from a plurality of submodules (610) which have an energy store (1020), wherein the energy store voltage (Uzk) can be connected and disconnected as a submodule voltage (UDC) between the two submodule poles (ACP1, ACP2), and wherein, in order to attenuate higher-frequency components of the connection voltage (21), a passive frequency filter (F) is provided for each phase module (210), the resonant frequency (fr) of which frequency filter is above a sampling frequency (ft) of a digital regulating system (15a) which connects disconnected submodule voltages (UDC) and disconnects connected submodule voltages (UDC) at successive sampling times (ti) in each case. In order to avoid exciting the point of resonance of the frequency filter (F), it is proposed that the drive (15) has a controller (15b) which briefly connects and again disconnects at least one of the disconnected submodule voltages (UDC) at least once within a sampling interval (Ti) of the regulating system (15a) in each case for a submodule voltage (UDC) which is connected by the regulating system (15a). The invention also includes a method for driving the multiphase multilevel power converter (MMC).