Common-mode suppression method based on dc integrated power system of series hybrid ship

Abstract

The application relates to a common-mode suppression method based on a series hybrid ship direct-current integrated power system, common-mode inductance is adopted between a variable flow module and a motor, and a high-frequency variable flow module with a midpoint connected between alternating-current and direct-current sides is adopted to suppress common-mode voltage; common-mode inductance is adopted on the direct-current side of the variable flow module, and a high-frequency variable flow module with a midpoint connected between alternating-current and direct-current sides is adopted to suppress common-mode voltage, the motor side high-frequency variable flow module common-mode voltage can be suppressed; a magnetic ring is added in a battery side loop of a DC / DC module to suppress common-mode voltage, the high-frequency DC / DC module common-mode voltage can be suppressed; an isolation transformer is adopted on the battery variable flow side to suppress common-mode voltage. The application takes realizing safe and reliable operation of the direct-current integrated power system as a main target, reduces the common-mode interference of the system through the proposed common-mode suppression scheme, solves the reliability problem of the system, and thus guarantees normal power supply of the power system and improves the reliability of safe operation of the direct-current integrated power system.

Description

Technical Field

[0001] This invention relates to a power quality control method for power systems, and more particularly to a common-mode suppression method based on a series hybrid power ship DC integrated power system. Background Technology

[0002] With the widespread application of DC integrated power systems, numerous core devices such as energy storage systems and power equipment have been introduced. In particular, the electromagnetic interference and other negative effects caused by the large number of high-frequency harmonic components in the output voltage of bidirectional DC-DC converters and PWM inverters in energy storage systems seriously threaten the safe and stable operation of surrounding electrical equipment. Simultaneously, the high-frequency common-mode voltage output by the inverter can generate high-frequency ground leakage current through parasitic capacitance, leading to electromagnetic interference and affecting the normal operation of other electrical equipment within the system. The electromagnetic interference and other negative effects caused by the large number of high-frequency harmonic components in the AC voltage on the input or output side of high-frequency converter modules seriously threaten the safe and stable operation of surrounding electrical equipment. For example, during the trial operation of a certain ship, there were multiple instances of brief overcurrent in the diesel generator, causing a drop in speed and shutting down the AFE (Automatic Fusion Controller). Subsequent AVR testing revealed that after the diesel generator started, it was affected by common-mode voltage interference and three-phase voltage asymmetry. Severe interference could lead to a complete power outage on the ship, causing incalculable property damage. Common-mode voltage can damage motor insulation, introduce common-mode current, and cause motor bearings to fail due to current erosion. This can lead to increased motor vibration, rotor ring breakage, and other problems, significantly shortening the motor's lifespan. Furthermore, common-mode voltage has high-frequency characteristics and a large dv / dt ratio, resulting in extremely high-frequency common-mode leakage current oscillations, reaching hundreds of kHz. When these high-frequency common-mode leakage currents flow back to the power grid through the grounding wire, they generate strong common-mode electromagnetic interference, affecting the normal operation of other control systems or electronic equipment. Excessive common-mode leakage current amplitude can also cause protective circuit malfunctions, triggering relay trips and shutting down the system, thus affecting its normal operation. Common-mode voltage also affects battery life. Therefore, research on common-mode interference suppression technology for shipboard DC integrated power systems is of great significance. Summary of the Invention

[0003] This invention addresses the issue of unbalanced three-phase voltage output caused by the PWM modulation strategy employed in current ship DC integrated power systems, which generates high-frequency common-mode voltage at the motor and battery terminals. This high-frequency common-mode voltage poses a serious threat to the ship's DC integrated power system, as well as various motors and energy storage batteries on board. The invention proposes a common-mode suppression method based on a series hybrid power system for ship DC integrated power systems. This method can significantly reduce the amplitude of the common-mode voltage in the DC integrated power system, thereby mitigating its impact.

[0004] To achieve the above objectives, the technical solution of the present invention is as follows: a common-mode suppression method based on a series hybrid power ship DC integrated power system, wherein a common-mode inductor and a high-frequency converter module with a midpoint connection between the AC and DC sides are used to suppress common-mode voltage; a common-mode inductor and a high-frequency converter module with a midpoint connection between the AC and DC sides are used on the DC side of the converter module to suppress common-mode voltage, thereby suppressing the common-mode voltage of the high-frequency converter module on the motor side; a magnetic ring is added to the battery-side circuit of the DC / DC module to suppress common-mode voltage, thereby suppressing the common-mode voltage of the high-frequency DC / DC module; and an isolation transformer is used on the battery converter side to suppress common-mode voltage.

[0005] Furthermore, the specific method for suppressing common-mode voltage in a high-frequency converter module that uses a common-mode inductor and a neutral point connection between the AC and DC sides is as follows: A common-mode inductor of a certain inductance is configured for each phase of the AC line on the AC side of the converter module, before the motor input terminal; in the AC line between the common-mode inductor and the motor, Y capacitors of a certain capacitance are connected to the three-phase circuit in a star connection, and the star-connected neutral point of the Y capacitors is connected to the voltage neutral point on the DC side of the converter module via a copper busbar or cable.

[0006] Furthermore, the specific method for suppressing common-mode voltage in a high-frequency converter module with a common-mode inductor on the DC side and a neutral point connected between the AC and DC sides is as follows: a common-mode inductor of a certain value is configured for each DC line on the DC side of the converter module, between the DC support capacitor and the converter module; in the AC line between the AC side of the converter module and the motor, Y capacitors of a certain capacitance are connected to the three-phase circuit in a star connection manner, and the star connection neutral point of the Y capacitor is connected to the voltage neutral point of the DC side of the converter module through a copper busbar or cable.

[0007] Furthermore, the common-mode inductance value on the DC side is greater than the differential-mode AC filter inductance value.

[0008] Furthermore, after determining the DC-side common-mode inductor, the filter capacitor value at the midpoint of the DC-side structure is calculated according to the calculation method for the differential-mode filter capacitor.

[0009] Furthermore, an isolating switch or protection switch is configured between the star-connected neutral point of the Y capacitor and the midpoint of the DC side voltage of the converter module.

[0010] Furthermore, the output of the high-frequency converter module adopts a differential-mode LC filter. The differential-mode LC filter is a low-pass filter composed of inductors and capacitors. In order to make the load voltage closer to the sine wave, minimize the fundamental wave loss, and avoid resonance, the resonant frequency of the differential-mode LC filter is lower than the lowest harmonic frequency contained in the PWM voltage, but higher than the fundamental wave frequency.

[0011] Furthermore, the specific method for using magnetic rings to suppress common-mode voltage on the battery side is as follows: a certain number of magnetic rings are connected in series in the circuit between the DC / DC chopper module and the battery side to suppress common-mode voltage.

[0012] The beneficial effects of this invention are as follows: Based on the common-mode voltage suppression method of DC integrated power system, this invention can significantly reduce the common-mode voltage on the motor side and battery side, thereby improving the service life of the motor and battery and enhancing the safety and reliability of DC integrated power system operation. Attached Figure Description

[0013] Figure 1 This is a schematic diagram of the common-mode voltage suppression scheme for the AC side of the converter module of the present invention, which uses a common-mode inductor and connects the AC and DC sides at the midpoint.

[0014] Figure 2 This is a schematic diagram of the common-mode voltage suppression scheme using a common-mode inductor on the DC side and a midpoint connection between the AC and DC sides in the converter module of the present invention;

[0015] Figure 3 This is a schematic diagram of the magnetic ring suppression scheme of the present invention;

[0016] Figure 4 This is a schematic diagram of the isolation transformer scheme of the present invention. Detailed Implementation

[0017] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0018] like Figures 1 to 4 As shown, this invention provides a common-mode suppression method for a ship's integrated DC power system. This method employs a common-mode inductor and a high-frequency converter module with a midpoint connection between the AC and DC sides to suppress common-mode voltage. It also employs a common-mode inductor and a high-frequency converter module with a midpoint connection between the AC and DC sides on the DC side of the converter module to suppress common-mode voltage. Both methods can suppress the common-mode voltage of the high-frequency converter module on the motor side. On the battery side, a magnetic ring is added to the battery-side circuit of the DC / DC module to suppress common-mode voltage; this method can suppress the common-mode voltage of the high-frequency DC / DC module.

[0019] The design method for suppressing common-mode voltage in a high-frequency converter module that uses a common-mode inductor and a neutral point connection between the AC and DC sides is as follows: On the AC side of the converter module and before the motor input terminal, a common-mode inductor with a certain inductance value is configured for each phase of the AC line; in the AC line between the common-mode inductor and the motor, a high-frequency capacitor (Y capacitor) with a certain capacitance value is connected to the three-phase circuit in a star connection. The star connection neutral point of the Y capacitor is connected to the voltage neutral point of the DC side of the converter module through a copper busbar (or cable), etc. Depending on the actual needs, an isolating switch (or protection switch) can be configured between the star connection neutral point of the Y capacitor and the voltage neutral point of the DC side of the converter module.

[0020] The design method for suppressing common-mode voltage in a high-frequency converter module with a common-mode inductor on the DC side and a neutral point connected to the AC and DC sides is as follows: A common-mode inductor of a certain value is configured for each DC line on the DC side of the converter module, between the DC support capacitor and the converter module; In the AC line between the AC side of the converter module and the motor, Y capacitors of a certain capacitance are connected to the three-phase circuit in a star connection. The star-connected neutral point of the Y capacitor is connected to the voltage neutral point of the DC side of the converter module through a copper busbar (or cable), etc. Depending on the actual needs, an isolating switch (or protection switch) can be configured between the star-connected neutral point of the Y capacitor and the voltage neutral point of the DC side of the converter module.

[0021] The integrated design method for suppressing common-mode voltage using magnetic rings on the battery side is as follows: a certain number of magnetic rings are connected in series in the circuit between the DC / DC chopper module and the battery side to suppress common-mode voltage.

[0022] The integrated design method for suppressing common-mode voltage using an isolation transformer on the battery converter side is as follows: An isolation transformer is connected in series in the circuit between the energy storage inverter module DC / AC and the ship's AC main grid (such as a 6.6kV AC grid) to suppress common-mode voltage.

[0023] Example:

[0024] The integrated design method for common-mode voltage suppression of a high-frequency converter module with common-mode inductors on the motor side and AC / DC sides connected at the midpoint is as follows:

[0025] (1) Parameter design of the output differential LC filter of the high-frequency converter module

[0026] A typical differential-mode LC filter is a low-pass filter, mainly composed of inductors and capacitors, which suppresses high-frequency components and allows low-frequency components to pass. Its design is primarily based on the inverter's switching frequency and fundamental frequency. The inverter's higher harmonics are concentrated near integer multiples of the switching frequency.

[0027] The performance of an LC filter is mainly determined by the resonant frequency between the reactance L and the capacitance C.

[0028] To make the load voltage closer to a sine wave, minimize fundamental frequency loss, and avoid resonance, the resonant frequency must be much lower than the lowest harmonic frequency in the PWM voltage, but much higher than the fundamental frequency. After determining the cutoff frequency, the LC product is essentially fixed; the values ​​of inductor L and capacitor C need to be further determined. The basis for determining inductor L is generally that, under rated current, the voltage drop across inductor L should be less than the required value, ideally controlled within 3% to 5%. Then, the value of the filter capacitor C can be determined.

[0029] The capacitor of the differential-mode LC filter is Y-connected, which may be the midpoint of the AC side. Its impedance at the switching frequency is very small, and it can be used as the midpoint for constructing a common-mode suppressor.

[0030] (2) Design of DC-side common-mode inductor and filter capacitor for high-frequency converter module

[0031] Based on the analytical analysis, the common-mode voltage suppression effect is best when the equivalent common-mode inductance of the AC-side differential-mode filter of the high-frequency converter module is equal to the DC-side common-mode inductance. Referring to the design value of the differential-mode filter inductance, the value of the DC-side common-mode inductance is designed. After determining the DC-side common-mode inductance, the filter capacitor value at the midpoint of the DC-side structure is calculated according to the calculation method for the differential-mode filter capacitor.

[0032] The differential-mode filter in a high-capacity high-frequency converter module has a smaller inductance. To prevent excessive current in the connection between the midpoint of the AC and DC sides and to suppress the influence of switching frequency harmonics on the control current, the common-mode inductance on the DC side should be greater than that of the differential-mode AC filter.

Claims

1. A common-mode suppression method based on a series hybrid power ship DC integrated power system, characterized in that: A high-frequency converter module with a common-mode inductor and a midpoint connection between the AC / DC converter module and the motor is used to suppress common-mode voltage. This method also suppresses common-mode voltage on the motor side. Adding a magnetic ring to the battery-side circuit of the DC / DC module further suppresses common-mode voltage. An isolation transformer is used on the AC side of the battery DC / AC converter to suppress common-mode voltage. Specifically, the method involves configuring a common-mode inductor of a certain value for each phase of the AC line on the AC side of the converter module, before the motor input. In the AC line between the common-mode inductor and the motor, Y capacitors of a certain capacitance are connected to the three-phase circuit in a star configuration. The star-connected neutral point of the capacitor is connected to the voltage midpoint of the DC side of the converter module via a copper busbar or cable. Specific methods for suppressing common-mode voltage in high-frequency converter modules using common-mode inductors on the DC side and AC / DC side midpoint connections include: configuring a common-mode inductor of a certain value for each DC line on the DC side of the converter module, between the DC support capacitor and the converter module. The common-mode inductance value on the DC side is greater than the inductance value of the differential-mode AC filter. After determining the common-mode inductance on the DC side, the filter capacitor value at the DC side midpoint is calculated according to the calculation method for the differential-mode filter capacitor. In the AC line between the AC side of the converter module and the motor, Y capacitors of a certain capacitance value are connected to the three-phase circuit in a star connection manner. The star-connected neutral point of the Y capacitor is connected to the voltage midpoint of the DC side of the converter module via a copper busbar or cable. A disconnecting switch or protection switch is configured between the star-connected neutral point of the Y capacitor and the voltage midpoint of the DC side of the converter module.

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