Protection method and system for abnormal power supply of power unit of high-voltage frequency conversion device

Abstract

The invention relates to a power supply abnormity protection method and system for a power unit of a high-voltage frequency conversion device, and the method comprises the steps: employing a filter algorithm for a three-phase input current signal, and calculating the third and fifth harmonic contents; a primary winding of the phase-shifting transformer is connected with the wire inlet switch in a star connection mode, the input end of the wire inlet switch is connected with a high-voltage power grid, and the Hall current sensor is arranged between the output end of the wire inlet switch and the phase-shifting transformer. The method has the advantages that when the input power supply of the power units in the high-voltage frequency converter is abnormal, the problem that due to the fact that the number of power unit modules of the high-voltage frequency converter is large, extra detection devices such as current and voltage sensors do not need to be additionally arranged on each power unit, and power unit power supply abnormity protection can be achieved; according to the method, effective values of third harmonics, fifth harmonics and fundamental waves are calculated through filter design, the third harmonic content and the fifth harmonic content are further calculated, threshold value setting is carried out on the content ratio, and finally power supply abnormity protection is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of high-voltage frequency converter detection, and in particular to a method and system for protecting a power supply abnormality of a power unit of a high-voltage frequency converter. Background Art

[0002] The high-voltage inverter is mainly composed of a phase-shifting transformer, a power unit, a control system, a cooling system, etc. The phase-shifting transformer is mainly used to supply power to the power unit. Since the high-voltage inverter uses multiple power units in series and multiple levels for output, the number of secondary windings of the phase-shifting transformer is large and corresponds to the number of power units. Usually, the power supply abnormality of the power unit is as follows:

[0003] 1) Phase loss caused by the blowing of the power unit fuse;

[0004] 2) The rectifier bridge of the power unit is damaged, causing the fuse to blow and the phase to be lost;

[0005] 3) Power supply abnormality caused by transformer winding abnormality or damage to the cable from the transformer to the power unit;

[0006] 4) When a power unit is powered abnormally, it is sometimes difficult to protect it through input side overcurrent or imbalance detection.

[0007] The conventional detection method is to determine whether there is an abnormal power supply problem in the power unit by detecting the status of the fuse and the three-phase input current or voltage of each power unit. Due to the large number of power units, this detection method is complex, has low reliability and high cost. Summary of the invention

[0008] The purpose of the present invention is to provide a method and system for protecting the power unit of a high-voltage frequency conversion device from power supply anomaly, so as to solve the problem that the high-voltage frequency conversion device has a large number of power unit modules, each power unit has an input detection circuit and related detection circuits, which increases the cost of the power unit module, and the frequency conversion control system for monitoring the input side anomalies of each power unit module is complex.

[0009] To achieve the above object, the present invention is implemented through the following technical solutions:

[0010] A method for protecting power supply abnormality of a power unit of a high-voltage frequency conversion device is implemented based on a power unit controller. A filter algorithm is used for a three-phase input current signal to calculate the third and fifth harmonic contents:

[0011] When one phase is missing at the input end of a certain variable frequency power unit, the third harmonic content changes. If the calculated third harmonic content exceeds the set protection threshold, the incoming line switch is disconnected;

[0012] When two phases of a variable frequency power unit are short-circuited at the input end, the third harmonic content changes. If the calculated third harmonic content exceeds the set protection threshold, the incoming line switch is disconnected.

[0013] When two or three phases are missing at the input end of a power unit in the inverter, the third and fifth harmonic contents change. If the calculated third and fifth harmonic contents exceed the set protection threshold 1 or the set protection threshold 2, the incoming line switch is disconnected;

[0014] When one phase is missing at the input end of two power units in the inverter, the third harmonic content changes. If the calculated third harmonic content exceeds the set protection threshold, the incoming line switch is disconnected;

[0015] When two phases are missing at the input end of two power units in the inverter, the third and fifth harmonic contents change. If the calculated third and fifth harmonic contents exceed the set protection threshold 1 or the set protection threshold 2, the incoming line switch is disconnected;

[0016] When two phases are short-circuited at the input end of two power units in the inverter, the third harmonic content changes. When the calculated third harmonic content exceeds the set protection threshold, the incoming line switch is disconnected.

[0017] Set the protection threshold value to 1, and the calculation formula is as follows:

[0018] Set protection threshold 1 = third harmonic content × K ①

[0019] Set the protection threshold 2, the calculation formula is as follows:

[0020] Set protection threshold 2 = fifth harmonic content × K ②

[0021] In formulas ① and ②, K is a coefficient, and the range of K is 1.5-25.

[0022] The filter algorithm is the Fast Fourier Transform FFT algorithm.

[0023] The power supply abnormality protection system of the power unit of the high-voltage frequency conversion device includes a phase-shifting transformer and a frequency conversion power unit. The input terminal U / V / W of the corresponding frequency conversion power unit adopts the extended triangle connection method and is connected to the corresponding secondary winding of the phase-shifting transformer through the port. All the corresponding frequency conversion power units of the secondary winding of each phase are connected in series to form a single-phase frequency conversion power unit group. The three single-phase total frequency conversion power unit groups are connected to the load through the port in a star connection method; the primary winding of the phase-shifting transformer is connected to the incoming switch in a star connection method, the input end of the incoming switch is connected to the high-voltage power grid, and a Hall current sensor is arranged between the output end of the incoming switch and the phase-shifting transformer. The Hall current sensor is used to transmit the three-phase input current signal data to the power unit controller.

[0024] The primary winding of the phase-shifting transformer corresponds to n sets of secondary windings.

[0025] Optical fiber communication is adopted between the variable frequency power unit and the power unit controller. The power unit controller includes: PWM control module, AD control module, fault processing module, input control module, output control module and communication module.

[0026] The power unit controller is a field programmable gate array FPGA or a complex programmable logic device CPLD.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] 1. By collecting and analyzing the three-phase input current signal at the front end of the phase-shifting transformer of the high-voltage inverter, when the power unit input power supply in the high-voltage inverter is abnormal, the high-voltage inverter can be protected from power unit power supply abnormality without adding additional detection devices such as current and voltage sensors to each power unit due to the large number of power unit modules;

[0029] 2. Calculate the effective values ​​of the third harmonic, fifth harmonic and fundamental wave through filter design, and then calculate the third harmonic content and fifth harmonic content. Set the threshold of the content ratio to finally achieve protection against power supply abnormality.

[0030] 3. The protection method is simple and easy to implement. There is no need to add input detection circuits and related detection lines to each power unit, and there is no need to monitor the input side abnormalities of each power unit module, which saves costs and reduces the complexity of the frequency conversion control system. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is a topological diagram of the power unit of a high-voltage frequency conversion device.

[0032] Figure 2 It is the third harmonic content of the input current harmonic when the inverter power unit is powered normally.

[0033] Figure 3 It is the third harmonic content of the input current harmonic when one phase of the input power supply of a power unit of the inverter is missing.

[0034] Figure 4 It is the third harmonic content of the input current harmonic when two phases of the input power supply of a power unit of the inverter are short-circuited.

[0035] Figure 5 It is the third and fifth harmonic content of the input current harmonic when two or three phases of the input power supply of a power unit of the inverter are missing.

[0036] Figure 6It is the third harmonic content of the input current harmonic when one phase of the input power supply of two power units of the inverter is missing.

[0037] Figure 7 It is the third and fifth harmonic content of the input current harmonic when two or three phases of the input power supply of two power units of the inverter are missing.

[0038] Figure 8 It is the third harmonic content of the input current harmonic when two phases of the input power supply of two power units of the inverter are short-circuited.

[0039] Fig. 9 The invention discloses a method and a system flow chart for protecting a power supply abnormality of a power unit of a high-voltage frequency conversion device.

[0040] In the figure: 1- Power unit DETAILED DESCRIPTION

[0041] The present invention is described in detail below in conjunction with the accompanying drawings, but it should be noted that the implementation of the present invention is not limited to the following embodiments.

[0042] The following examples are implemented on the premise of the technical solution of the present invention, and provide detailed implementation methods and specific operation processes, but the protection scope of the present invention is not limited to the following examples. The methods used in the following examples are conventional methods unless otherwise specified.

[0043] [Example 1]

[0044] See Figure 1 A method and system for protecting power supply abnormality of a power unit of a high-voltage frequency conversion device, comprising a phase-shifting transformer and a frequency conversion power unit. The primary winding of the phase-shifting transformer is connected to an incoming line switch in a star connection. The input end of the incoming line switch is connected to a high-voltage power grid. A Hall current sensor is arranged between the output end of the incoming line switch and the phase-shifting transformer. The Hall current sensor is used to transmit three-phase input current signal data to a power unit controller. Optical fiber communication is adopted between the frequency conversion power unit and the power unit controller. The power unit controller comprises: a PWM control module, an AD control module, a fault processing module, an input control module, an output control module, and a communication module. The power unit controller is a field programmable gate array FPGA or a complex programmable logic device CPLD.

[0045] The input terminal U / V / W of the corresponding variable frequency power unit adopts the extended triangle connection method, and is connected to the corresponding secondary winding of the phase-shifting transformer through the port. The secondary winding adopts the triangle connection method. The transformer adopts multi-pulse rectification to achieve the effect of mutual cancellation of third, fifth, seventh and other harmonics. All corresponding variable frequency power units of each phase secondary winding are connected in series to form a single-phase variable frequency power unit group. The three single-phase total variable frequency power unit groups are connected to the load through the port in a star connection method; the primary winding of the phase-shifting transformer corresponds to n groups of secondary windings, n≥1; since the secondary winding of the phase-shifting transformer is connected to the corresponding power unit, when the power supply of the power unit is abnormal, such as unit phase loss, abnormality of the secondary side of the phase-shifting transformer causing problems in the power supply of the power unit, the third, fifth and seventh harmonics on the secondary side of the high-voltage inverter will not be able to cancel each other, thereby causing changes in the harmonic indicators of the primary winding of the high-voltage transformer.

[0046] See Figure 6 , a method and system for protecting power supply abnormality of power unit of high-voltage frequency conversion device is implemented based on power unit controller, and the contents are as follows:

[0047] 1) The three-phase input current signal is calculated through the fast Fourier transform FFT algorithm to obtain the third and fifth harmonic contents;

[0048] Taking n=8 as an example, under normal circumstances, the harmonic content is as follows: Figure 2 , 8 power units are connected in series per phase, Figure 1 When n=8, the power supply frequency is 50 Hz, the third harmonic content is the ratio of the 150 Hz current to the effective value of the fundamental current, and the fifth harmonic content is the ratio of the 250 Hz current to the effective value of the fundamental current;

[0049] 2) When the power supply of the power unit is abnormal, the content is as follows:

[0050] a. When one phase is missing at the input end of a certain frequency conversion power unit, the third harmonic content in the three-phase input current signal data will change. When the calculated third harmonic content exceeds the set protection threshold, the incoming line switch will be disconnected for a while, cutting off the power supply to the frequency converter, thus protecting the frequency converter power unit from abnormal input power supply.

[0051] See Figure 3 ,It can be seen from the figure that the third harmonic (150hz harmonic) content increases from 0.2% to more than 5%;

[0052] b. When two phases of a variable frequency power unit are short-circuited at the input end, the effective value of the third harmonic in the three-phase input current signal data changes, and the calculated third harmonic content exceeds the set protection threshold, and the incoming line switch is temporarily disconnected;

[0053] See Figure 4,It can be seen from the figure that the third harmonic (150hz harmonic) content increases from 0.2% to more than 9%;

[0054] c. When two phases are missing at the input end of a certain variable frequency power unit, the incoming line switch is disconnected when the calculated third harmonic content or fifth harmonic content exceeds the set protection threshold by one or two;

[0055] See Figure 5 , it can be seen from the figure that the third harmonic (150hz harmonic) content increased from 0.2% to more than 1.4%; the fifth harmonic (250hz harmonic) content increased from 0.7% to more than 1.4%;

[0056] d. When one phase is missing at the input end of two frequency conversion power units, the calculated third harmonic content exceeds the set protection threshold and the incoming line switch is disconnected for three times;

[0057] See Figure 6 ,It can be seen from the figure that the third harmonic (150hz harmonic) content increases from 0.2% to more than 9%;

[0058] e. When two or three phases are missing at the input end of two frequency conversion power units, the incoming line switch is disconnected when the calculated third or fifth harmonic content exceeds the set protection threshold by one or two;

[0059] See Figure 7 , it can be seen from the figure that the third harmonic (150hz harmonic) content increased from 0.2% to more than 1%; the fifth harmonic (250hz harmonic) content increased from 0.7% to more than 3.5%;

[0060] f. When two phases of the input end of two variable frequency power units are short-circuited, the effective value of the third harmonic in the three-phase input current signal data changes, and the calculated third harmonic content exceeds the set protection threshold, and the incoming line switch is temporarily disconnected;

[0061] See Figure 8 , it can be seen from the figure that the effective value of the third harmonic (150hz harmonic) increases from 0.2% to more than 9%;

[0062] The calculation formula for setting the protection threshold is as follows:

[0063] Set protection threshold 1 = third harmonic content or effective value × K ①

[0064] Set protection threshold 2 = fifth harmonic content or effective value × K ②

[0065] In formulas ① and ②, the set protection threshold is set protection threshold 1 and set protection threshold 2, K is a coefficient, and the range of K is 1.5-25.

[0066] Working process Fig. 9, the content is as follows:

[0067] Depend on Figure 2 to Figure 8 It can be seen that under normal and abnormal conditions, the third and fifth harmonic contents change significantly compared with other harmonics. The more power supply abnormalities there are in the power unit modules, the more obvious the changes in the third and fifth harmonic contents are. Since the large deviation in the amplitude of the third and fifth harmonic contents can be identified through detection, the scheme is feasible. By using harmonic extraction methods such as Fourier transform FFT algorithm or filtering algorithm to extract the third or fifth harmonic from the input current data, calculate the effective value or the proportion of the fundamental content and set the protection threshold, the power supply abnormality problems in the power supply of the power unit modules can be identified. Due to the different high-voltage frequency conversion voltage levels and the different number of power unit modules in series, the relevant threshold settings are adjusted according to the actual situation when an abnormality occurs.

[0068] The present invention collects and analyzes the three-phase input current signal at the front end of the phase-shifting transformer of the high-voltage inverter. When the input power supply of the power unit in the high-voltage inverter is abnormal, the problem of a large number of power unit modules in the high-voltage inverter is solved. There is no need to add additional detection devices such as current and voltage sensors to each power unit, so as to achieve protection against power supply abnormality of the power unit; a filter design is adopted to calculate the effective values ​​of the third harmonic, the fifth harmonic and the fundamental wave, and then calculate the third harmonic content and the fifth harmonic content, and finally achieve protection against power supply abnormality by setting a threshold for the content ratio; the protection method is simple and easy to implement, and there is no need to add an input detection circuit and related detection circuits to each power unit, and there is no need to monitor the input side abnormality of each power unit module, thereby saving costs and reducing the complexity of the frequency conversion control system.

Claims

1. A method for protecting power supply abnormality of a power unit of a high-voltage frequency conversion device, implemented based on a power unit controller, characterized in that: The three-phase input current signal uses a filter algorithm to calculate the third and fifth harmonic content: When one phase is missing at the input end of a certain variable frequency power unit, the third harmonic content changes. If the calculated third harmonic content exceeds the set protection threshold, the incoming line switch is disconnected; When two phases of a variable frequency power unit are short-circuited at the input end, the third harmonic content changes. If the calculated third harmonic content exceeds the set protection threshold, the incoming line switch is disconnected. When two or three phases are missing at the input end of a power unit in the inverter, the third and fifth harmonic contents change. If the calculated third and fifth harmonic contents exceed the set protection threshold 1 or the set protection threshold 2, the incoming line switch is disconnected; When one phase is missing at the input end of two power units in the inverter, the third harmonic content changes. If the calculated third harmonic content exceeds the set protection threshold, the incoming line switch is disconnected; When two phases are missing at the input end of two power units in the inverter, the third and fifth harmonic contents change. If the calculated third and fifth harmonic contents exceed the set protection threshold 1 or the set protection threshold 2, the incoming line switch is disconnected; When two phases are short-circuited at the input end of two power units in the inverter, the third harmonic content changes. When the calculated third harmonic content exceeds the set protection threshold, the incoming line switch is disconnected.

2. A method for protecting a power supply abnormality of a power unit of a high-voltage frequency conversion device according to claim 1, characterized in that: The calculation formula for setting the protection threshold value 1 is as follows: Set protection threshold 1 = third harmonic content × K ① Set protection threshold 2, the calculation formula is as follows: Set the protection threshold value 2 = fifth harmonic content × K ② In formulas ① and ②, K is the coefficient, and the range of K is 1.5-25.

3. A method for protecting a power supply abnormality of a power unit of a high-voltage frequency conversion device according to claim 1, characterized in that: The filter algorithm is a Fast Fourier Transform (FFT) algorithm.

4. A high-voltage frequency conversion device power unit power supply abnormality protection system for implementing the method described in any one of claims 1 to 3, comprising a phase-shifting transformer and a frequency conversion power unit, wherein the input terminal U / V / W of the corresponding frequency conversion power unit adopts a Yanbian triangle connection method and is connected to the corresponding secondary winding of the phase-shifting transformer through a port, and all corresponding frequency conversion power units of each phase of the secondary winding are connected in series to form a single-phase frequency conversion power unit group, and three single-phase total frequency conversion power unit groups are connected to the load through a port in a star connection method; characterized in that The primary winding of the phase-shifting transformer is connected to the incoming switch in a star connection. The input end of the incoming switch is connected to the high-voltage power grid. A Hall current sensor is arranged between the output end of the incoming switch and the phase-shifting transformer. The Hall current sensor is used to transmit the three-phase input current signal data to the power unit controller.

5. A high-voltage frequency conversion device power unit power supply abnormality protection system according to claim 4, characterized in that: The primary winding of the phase-shifting transformer corresponds to n groups of secondary windings.

6. A high-voltage frequency conversion device power unit power supply abnormality protection system according to claim 4, characterized in that: The variable frequency power unit and the power unit controller use optical fiber communication, and the power unit controller includes: a PWM control module, an AD control module, a fault processing module, an input control module, an output control module, and a communication module.

7. A high-voltage frequency conversion device power unit power supply abnormality protection system according to claim 4, characterized in that: The power unit controller is a field programmable gate array FPGA or a complex programmable logic device CPLD.

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