阅读说明：本技术 一种模块化多电平变换器的传感器故障综合诊断及穿越方法 (Sensor fault comprehensive diagnosis and ride-through method of modular multilevel converter ) 是由 张莉 王连强 熊永圣 于 2020-12-08 设计创作，主要内容包括：本发明属于电力电子设备故障诊断和故障穿越技术领域,一种模块化多电平变换器的传感器故障综合诊断及穿越方法,通过对比交流输出侧电流传感器测得值与输出电流参考值来检测和定位交流输出侧电流传感器故障；通过对比上一控制周期的开关状态、子模块电容充放电情况和桥臂电流传感器测得值来检测和定位桥臂电流传感器故障；通过对比同一桥臂上不同子模块电压传感器的差值来检测和定位子模块电压传感器故障。本发明实现了MMC传感器的故障诊断和故障穿越,在不增加原有MMC拓扑结构的基础上,实现多传感器和多类型传感器快速、准确的检测和定位,同时可以完成多传感器和多类型传感器的故障穿越,使MMC在传感器故障状态下也能长时间平稳运行。(The invention belongs to the technical field of fault diagnosis and fault ride-through of power electronic equipment, and discloses a sensor fault comprehensive diagnosis and ride-through method of a modular multilevel converter, which detects and positions faults of a current sensor at an alternating current output side by comparing a value measured by the current sensor at the alternating current output side with an output current reference value; detecting and positioning the faults of the bridge arm current sensors by comparing the switching state of the previous control period, the charging and discharging conditions of the sub-module capacitors and the values measured by the bridge arm current sensors; and detecting and positioning faults of the voltage sensors of the sub-modules by comparing difference values of the voltage sensors of different sub-modules on the same bridge arm. The invention realizes the fault diagnosis and fault ride-through of the MMC sensor, realizes the rapid and accurate detection and positioning of a plurality of sensors and a plurality of types of sensors on the basis of not increasing the original topological structure of the MMC, and can complete the fault ride-through of the plurality of sensors and the plurality of types of sensors, so that the MMC can stably operate for a long time under the fault state of the sensors.)

1. A sensor fault comprehensive diagnosis and ride-through method of a modular multilevel converter is characterized by comprising the following steps:

(1) sensor feedback system under normal operation state established according to MMC topological structure

The MMC control feedback system mainly comprises three alternating current side output current sensors, three bridge arm current sensors and a sub-module capacitance voltage sensor; and obtaining electrical information of each sensor for diagnosis including three-phase AC side current value i_joThree lower bridge arm current values i_NjOr upper bridge arm current value i_PjAnd the voltage value of each sub-module capacitor; current value of upper bridge arm passes through i_Pj＝i_jo+i_NjObtaining a structure;

(2) diagnosing the fault position of the AC side output current sensor and carrying out fault ride-through

By setting reference value of output currentAnd the AC side current value i_joComparing, if the deviation value isIf the current is greater than the set threshold value, the AC side output current sensor fails, the threshold value depends on the precision of the AC side output current sensor and the parameter values of each device of the main circuit, wherein j is three-phase power of a, b and c, and I_joThe maximum value of the three-phase output currents a, b and c; simultaneously according to kirchhoff's law i_ao+i_bo+i_coWhen the current value is equal to 0, the actual value of the fault sensor is constructed by using the other two-phase alternating-current side output current sensors;

(3) diagnosing fault positions of sub-module capacitance voltage sensors and performing fault ride-through

Under the condition that the sub-module capacitance voltage sensor works normally, the capacitance voltage of the same bridge armThe values are almost equal, and the capacitance voltage value of a certain submodule and the capacitance voltage deviation value of other submodules are expressed asIn the formula of U_dcFor the DC side voltage value, N is the number of sub-modules of each bridge arm, u_cPjyIs the capacitance voltage u of the y-th sub-module of the j-phase upper and lower bridge arms_cNjYThe capacitor voltage of other sub-modules of the same bridge arm; if the deviation value g is_cIf the sub-module capacitance voltage sensor is larger than a set threshold value, the sub-module capacitance voltage sensor breaks down, and the threshold value depends on the precision of the sub-module capacitance voltage sensor and the parameter values of all devices of the main circuit; meanwhile, the capacitance voltage value of the submodule is replaced by the average value of the voltage sensor values of other submodules of the same bridge arm, the input times of the fault submodule is kept equal to those of other submodules, the capacitance voltage balance is ensured as much as possible, and the fault ride-through is completed;

(4) diagnosing fault positions of bridge arm current sensors and performing fault ride-through

Bridge arm current i_XjAnd sub-module capacitor voltage u on bridge arm thereof_cThe relationship is

Discretizing according to an Euler formula to obtain a discrete equation of a bridge arm current k moment as

Where C is the sub-module capacitance, G_cFor the sub-module, the value 1 is the input state, the value 0 is the cut-off state, T_sIs a sampling period; measured value i of bridge arm current sensor at time k_Xj(k) And calculating a value referenceComparing, and if the symbols are different, judging that the current sensor of the bridge arm of the phase has a fault; judging the type of fault, and judging whether a fault signal continuously occurs for multiple times so as to avoid misdiagnosis of the current value of the bridge arm near the zero point; meanwhile, the bridge arm current only acts on the sub-module capacitor voltage balance control, only the direction needs to be provided, and according to the characteristics of the bridge arm current and the output current, the upper bridge arm current value is replaced by an alternating-current side current value, the lower bridge arm current value is replaced by a negative value of the alternating-current side current value, and fault ride-through is completed.

2. The method for comprehensively diagnosing and traversing sensor faults of the modular multilevel converter according to claim 1, wherein in the step (4), whether the fault signal continuously occurs or not is judged n times to avoid misdiagnosis of bridge arm current values near a zero point, and the magnitude of the n value depends on sampling frequency and output current frequency.

Technical Field

The invention belongs to the technical field of fault diagnosis and fault ride-through of power electronic equipment, and particularly relates to a comprehensive diagnosis and ride-through method of voltage and current sensor faults of a modular multilevel converter.

Background

The modular multilevel converter has the advantages of modular design, strong expansibility, small operation loss, high output waveform and the like, and is more and more widely applied to occasions with high voltage level and large transmission capacity in recent years. The MMC sensor fault diagnosis and fault ride-through technology can improve the reliability and safety of the operation of the MMC sensor due to the large number of voltage and current sensors.

At present, the sensor diagnosis and ride-through technology for the power electronic converter is limited to the traditional bridge topology structure, and diagnosis and ride-through for the sensor fault of the topology structure of the MMC are not carried out at present, so that a comprehensive diagnosis and ride-through method for the MMC sensor is provided, and has certain significance.

Disclosure of Invention

In view of the above, the present invention provides a method for comprehensively diagnosing and traversing sensor faults of a modular multilevel converter, which can simultaneously diagnose and locate a plurality of and different types of sensor faults and realize fault traversing without redundancy, and the method improves the comprehensiveness of fault diagnosis of an MMC sensor and has the characteristics of rapidness, reliability and practicability.

The invention provides the following technical scheme:

the sensor failure described in the present invention is a hard failure, i.e., a complete failure of the sensor.

A sensor fault comprehensive diagnosis and ride-through method of a modular multilevel converter comprises the following steps:

(1) sensor feedback system under normal operation state established according to MMC topological structure

The MMC control feedback system mainly comprises three alternating current side output current sensors, three bridge arm current sensors and a sub-module capacitance voltage sensor; and obtaining electrical information of each sensor for diagnosisAt a current value i including three-phase AC side_joThree lower bridge arm current values i_Nj(or upper arm current value i)_Pj) And the voltage value of each sub-module capacitor; current value of upper bridge arm passes through i_Pj＝i_jo+i_NjObtaining a structure;

(2) diagnosing the fault position of the AC side output current sensor and carrying out fault ride-through

By setting reference value of output currentAnd the AC side current value i_joComparing, if the deviation value isIf the current is greater than the set threshold value, the AC side output current sensor fails, the threshold value depends on the precision of the AC side output current sensor and the parameter values of each device of the main circuit, wherein j is three-phase power of a, b and c, and I_joThe maximum value of the three-phase output currents a, b and c; simultaneously according to kirchhoff's law i_ao+i_bo+i_coWhen the current value is equal to 0, the actual value of the fault sensor is constructed by using the other two-phase alternating-current side output current sensors;

(3) diagnosing fault positions of sub-module capacitance voltage sensors and performing fault ride-through

Under the condition that the sub-module capacitance-voltage sensor works normally, the capacitance voltage values of the same bridge arm are almost equal, and the capacitance voltage values of a certain sub-module and the capacitance voltage deviation values of other sub-modules are expressed asIn the formula of U_dcFor the DC side voltage value, N is the number of sub-modules of each bridge arm, u_cPjyIs the capacitance voltage u of the y-th sub-module of the j-phase upper and lower bridge arms_cNjYThe capacitor voltage of other sub-modules of the same bridge arm; if the deviation value g is_cIf the voltage is greater than a set threshold value, the submodule capacitor voltage sensor is in failure, and the threshold value is determined by the submoduleThe precision of the capacitance voltage sensor and the parameter values of each device of the main circuit; meanwhile, the voltage value of the submodule is replaced by the average value of the voltage sensor values of other submodules of the same bridge arm, the input times of the fault submodule is kept equal to those of other submodules, the capacitor voltage balance is ensured as much as possible, and the fault ride-through is completed;

(4) diagnosing fault positions of bridge arm current sensors and performing fault ride-through

Bridge arm current i_XjAnd sub-module capacitor voltage u on bridge arm thereof_cThe relationship is

Discretizing according to an Euler formula to obtain a discrete equation of a bridge arm current k moment as

Where C is the sub-module capacitance, G_cFor the sub-module, the value 1 is the input state, the value 0 is the cut-off state, T_sIs a sampling period; measured value i of bridge arm current sensor at time k_Xj(k) And calculating a value referenceComparing, and if the symbols are different, judging that the current sensor of the bridge arm of the phase has a fault; judging the type of fault, and judging whether a fault signal continuously occurs for multiple times so as to avoid misdiagnosis of the current value of the bridge arm near the zero point; meanwhile, the bridge arm current only acts on the sub-module capacitor voltage balance control, only the direction needs to be provided, and according to the characteristics of the bridge arm current and the output current, the upper bridge arm current value is replaced by an alternating-current side current value, the lower bridge arm current value is replaced by a negative value of the alternating-current side current value, and fault ride-through is completed.

The invention has the beneficial effects that:

(1) the method realizes the comprehensive diagnosis of the fault of the MMC sensor for the first time.

(2) The method of the invention realizes the fault ride-through of various MMC sensors for the first time.

(3) The method only needs the original electronic device, thereby avoiding adding an additional hardware circuit and saving the cost.

(4) The method can realize rapid diagnosis, the diagnosis time is as short as a plurality of sampling periods, and the stable operation of the MMC can be kept for a long time after the fault crossing.

Drawings

FIG. 1 is a diagram of an MMC map structure and sensor configuration of the present invention.

Fig. 2 is a fault diagnosis signal diagram of the MMC sensor of the present invention, wherein fig. 2(a) is a diagnosis signal diagram of a three-phase ac side current sensor and a three-phase lower bridge arm current sensor, and fig. 2(b) is a diagnosis signal diagram of all six sub-module voltage sensors of an a-phase upper and lower bridge arm.

Fig. 3 is a schematic diagram of an experimental result of fault diagnosis and fault ride-through of the MMC sensor of the present invention, wherein fig. 3(a) is a graph of an experimental result of three-phase current at the ac side, fig. 3(b) is a graph of an experimental result of current of an upper bridge arm and a lower bridge arm at a phase a, and fig. 3(c) is a graph of an experimental result of capacitance and voltage of all 6 sub-modules at the upper bridge arm and the lower bridge arm at a phase a.

Detailed Description

The invention is further explained below with reference to the drawings and the embodiments. It will be readily apparent to those skilled in the art that various modifications to the above-described embodiments may be made, and the generic principles defined herein may be applied to other embodiments without the use of inventive faculty. Therefore, the present invention is not limited to the above embodiments, and those skilled in the art should make improvements and modifications to the present invention based on the disclosure of the present invention within the protection scope of the present invention.

The embodiment provides a submodule fault positioning method of a modular multilevel converter based on correlation analysis, which comprises the following steps:

(1) establishing a sensor feedback system in a normal operation state according to the MMC topological structure;

(2) diagnosing the fault position of the current sensor at the alternating current side, and performing fault ride-through;

(3) diagnosing the fault position of the sub-module capacitance voltage sensor, and performing fault ride-through;

(4) and diagnosing the fault position of the bridge arm current sensor and performing fault ride-through.

In this embodiment, the step (1) specifically includes the following steps: as shown in fig. 1, the MMC control feedback system is composed of three ac side output current sensors, three bridge arm current sensors, and a sub-module capacitance voltage sensor. And obtaining electrical information of each sensor for diagnosis including three-phase AC side current value i_joCurrent value i of three lower bridge arms_NjAnd the capacitor voltage value of each submodule; current value of upper bridge arm passes through i_Pj＝i_jo+i_NjAnd (5) obtaining the structure.

In this embodiment, the step (2) specifically includes the following steps: taking the fault of the current sensor at the side of the a-phase current as an example, the reference value is set through the output currentMeasured value i of AC side current sensor_aoComparing, if the deviation value isGreater than 10%, the sensor fails. Simultaneously according to kirchhoff's law i_ao+i_bo+i_coAnd (5) constructing an actual value of the a-phase sensor by using the b and c two-phase current sensors, wherein the actual value is 0.

In this embodiment, the step (3) specifically includes the following steps: capacitive voltage sensor u of 1 st sub-module of a-phase lower bridge arm_cNa1For example, when the sub-module voltage sensors work normally, the capacitance and voltage values of 3 sub-modules of the a-phase lower bridge arm are almost equal, and the capacitance and voltage sensor u of the 1 st sub-module of the a-phase lower bridge arm is almost equal_cNa1Capacitive voltage sensor u with other submodules_cNayHas a deviation value of

Such as deviation value g_cNa1And if the voltage is more than 10%, the 1 st voltage sensor of the a-phase lower bridge arm fails. At the same time u_cNa1The value of (A) is the average value of the voltage sensor values of other submodules of the lower bridge arm of the phaseAnd replacing, and keeping the input times of the fault sub-module equal to those of other sub-modules, ensuring the voltage balance of the capacitor as much as possible, and completing fault ride-through.

In this embodiment, the step (4) specifically includes the following steps: taking the fault of the a-phase lower bridge arm current sensor as an example, the a-phase lower bridge arm current value i_NaAnd the 1 st sub-module capacitor voltage u of the a-phase lower bridge arm_cPa1The relationship is

Wherein C is a sub-module capacitance value, discretizing according to an Euler formula to obtain a discrete equation of a bridge arm current k moment

G_cNa1For the sub-module, the value 1 is the input state, the value 0 is the cut-off state, T_sIs the sampling period. Measured value i of bridge arm current sensor at time k_Nj(k) And calculating a value referenceAnd comparing, and if the symbols are different, judging that the current sensor of the phase bridge arm has a fault. Meanwhile, the bridge arm current only acts on the sub-module capacitor voltage balance control, only the direction needs to be provided, and according to the characteristics of the bridge arm current and the output current, the bridge arm current value i on the a phase is adjusted_PaBy AC side current value i_aoInstead, lower arm current value i_NaBy negative values-i of the value of the AC side current_aoInstead, complete the breakdownThe more.

To describe this embodiment more clearly, fig. 2 and 3 show the simulation experiment results under this embodiment. The parameters used in this experiment are shown in table 1.

Fig. 2 is a diagnostic result of a sensor failure. The 2 nd sub-module voltage sensor of the a-phase upper bridge arm fails at 0.3s, the a-phase cross current side current sensor and the 1 st sub-module voltage sensor of the lower bridge arm fail at 0.4s, the a-phase lower bridge arm current sensor fails at 0.5s, and other sensors have no fault signals and have no misdiagnosis.

Fig. 3 is a waveform of each physical quantity measured by the oscilloscope and the physical quantity measured by the sensor. In fig. 3(a), the actual output current of the three-phase ac side does not change significantly before and after the fault, and the a-phase current sensor has a fault at 0.4s, which is a valueBecomes 0; in fig. 3(b), the actual a-phase upper and lower bridge arm currents do not change significantly before and after the fault, and the a-phase lower bridge arm current sensor has a fault at 0.5s, and the value thereofBecomes 0; in fig. 3(c), the voltage waveforms of all 6 sub-modules of the upper and lower bridge arms of the phase a are not obviously changed before and after the fault, and the voltage sensor of the 2 nd sub-module of the upper bridge arm of the phase a has a fault at 0.3s, and the value of the fault isThe voltage sensor of the 1 st sub-module of the lower bridge arm which becomes 0, a fails at 0.4s, and the value thereofBecomes 0.

The simulation experiment results show that the implemented scheme can quickly and accurately realize fault diagnosis and well realize fault ride-through to ensure stable operation of the system.

TABLE 1