Device and method for detecting unbalanced current of AC / DC filter of converter station based on digital frequency conversion

Abstract

The invention discloses a converter station AC / DC filter unbalance current detection device and method based on digital frequency conversion. The device comprises a voltage signal acquisition unit, a small signal current acquisition signal unit, an unbalance current calculation unit, a digital frequency generation unit and a high-voltage power unit. The digital frequency generating unit drives the high-voltage power unit to generate a variable-frequency high-voltage alternating-current source, the unbalanced current calculating unit controls the amplitude output by the high-voltage alternating-current source, the voltage signal collecting unit collects the voltage applied to the alternating-current and direct-current filter, and the small-signal current collecting signal unit collects unbalanced current. The unbalanced current calculation unit calculates an unbalanced current value under an actual working condition by measuring the voltage, the current and the frequency; the unbalanced current of the AC / DC filter can be accurately measured, the applied voltage is measured through the voltage signal acquisition unit, and the actual on-site unbalanced current value is converted.

Description

Technical Field

[0001] The invention relates to the field of devices of ultra-high voltage direct current converter stations, and in particular to a device and method for detecting unbalanced current of an AC / DC filter of a converter station based on digital frequency conversion. Background Art

[0002] When the UHV DC converter station is commutating between AC and DC, a large number of characteristic harmonics will be generated, and a large amount of harmonic current will enter the AC system. The AC filter is an important part of the converter station. It can effectively control the harmonics generated by the converter and control the system harmonics within a reasonable range. In addition, the AC filter can also provide the reactive power required for phase switching. There are two main structures of filter capacitors. The first is a bridge structure, and the second is a two-group parallel structure. If one of the components has a problem, the blown fuse will automatically isolate the faulty component. This process will generate a small unbalanced current. The more faulty components, the more unbalanced current will be generated, preventing small faults from spreading and affecting the operation of the entire filter. The converter station widely uses AC filters for harmonic filtering and reactive compensation. The excessive unbalanced current of the C1 capacitor in the AC filter has become an important factor that seriously affects the progress of the commissioning of the converter station and the equipment fault handling time after the unbalanced protection of the AC filter is activated.

[0003] At present, the unbalanced detection of AC and DC filters in domestic UHV DC converter stations mainly has the following shortcomings: 1. For the low-voltage and high-frequency method or the low-frequency and high-voltage method used to pressurize the two ends of the AC and DC filter capacitor, the low-voltage and high-frequency method has a voltage of at most 100V, and the low-frequency and high-voltage method has a voltage of 500V but a frequency of only 30HZ. For these two methods of pressurization, the actual unbalanced current is at the microampere level. Since the unbalanced current is too small, the measurement result has a large error with the unbalanced current in the actual operation on site; 2. The transformer is used to boost the voltage to the industrial frequency high voltage, and the equipment is bulky; therefore, it is necessary to design an unbalanced current detection device and method for the converter station AC and DC filter based on digital frequency conversion to solve the above problems. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide an unbalanced current detection device and method for an AC / DC filter in a converter station based on digital frequency conversion, which can generate a high-frequency and high-voltage voltage signal and apply it to the AC / DC filter in a UHV converter station, and can accurately measure the unbalanced current of the AC / DC filter through the built-in small signal current detection, and measure the applied voltage through a voltage signal acquisition unit, and convert the actual unbalanced current value on site.

[0005] In order to solve the above technical problems, the technical solution adopted by the present invention is: a converter station AC / DC filter unbalanced current detection device based on digital frequency conversion, including an unbalanced current calculation unit arranged inside the device, the unbalanced current calculation unit is respectively communicated with the high-voltage power unit, the digital frequency generating unit, the voltage signal acquisition unit and the small-signal current acquisition signal unit; the high-voltage power unit is communicated with the digital frequency generating unit; the high-voltage power unit, the voltage signal acquisition unit and the small-signal current acquisition signal unit are all electrically connected to the AC / DC capacitor filter of the converter station.

[0006] Preferably, the high-voltage power unit is provided with a short-circuit protection interface and an overload protection interface.

[0007] Preferably, the digital frequency generating unit drives the high voltage power unit with a variable frequency sinusoidal wave signal.

[0008] Preferably, the unbalanced current calculation unit and the digital frequency generation unit are connected via Ethernet.

[0009] Preferably, the unbalanced current calculation unit is connected to the high-voltage power unit via a 485 bus.

[0010] Preferably, the unbalanced current calculation unit and the voltage signal acquisition unit are connected via an SPI bus.

[0011] Preferably, the unbalanced current calculation unit and the small signal current acquisition signal unit are connected via an SPI bus.

[0012] Preferably, the high-voltage power unit is electrically connected to both ends of the AC / DC capacitor filter to provide voltage; and the voltage signal acquisition unit is electrically connected to both ends of the AC / DC capacitor filter to acquire voltage signals.

[0013] Preferably, the small signal current acquisition signal unit is connected in series with both ends of the unbalanced measurement CT of the AC / DC capacitor filter.

[0014] Preferably, a method for detecting unbalanced current of AC / DC filter in a converter station based on digital frequency conversion comprises: S1, the digital frequency generating unit drives the high voltage power unit with a variable frequency sine wave signal to generate high voltage, and the high voltage power unit is the output voltage of the AC / DC capacitor filter; S2, the unbalanced measurement CT of the AC / DC capacitor filter is disconnected and connected in series with the small signal current acquisition signal unit; S3, based on the fact that the unbalanced current is proportional to the voltage and frequency, the unbalanced current calculation formula under working conditions is: ; Where F is the frequency of the applied voltage, VN is the voltage level, V is the collected voltage, FN is the rated frequency, F is the output frequency, I is the collected current, and If is the unbalanced current at the rated voltage of the substation; Furthermore, the unbalanced current calculation unit includes TMS320F28377, which controls the test process and calculates the unbalanced current according to the collected signal and converts it into a high-voltage unbalanced current.

[0015] Furthermore, the voltage signal acquisition unit includes AD7616, which acquires the voltage applied to the AC / DC filter.

[0016] Furthermore, the small signal current acquisition signal unit includes AD7616, which acquires unbalanced current.

[0017] Furthermore, the digital frequency generating unit includes XC7S50, which generates a variable frequency sinusoidal wave signal to drive the high voltage power unit.

[0018] Furthermore, the high voltage power unit includes AD5781, which generates a 500V sinusoidal AC voltage with a frequency of 20HZ-1000HZ.

[0019] The beneficial effects of the unbalanced current detection device for AC / DC filter of a converter station based on digital frequency conversion provided by the present invention are as follows: 1. The present invention applies high frequency and high voltage to the AC and DC filters of the converter station. During the test, the unbalanced current reaches a current of more than mA, which greatly improves the current collection accuracy; 2. The present invention can realize synchronous sampling of voltage and unbalanced current. The actual measured voltage and unbalanced current values ​​can be converted into the unbalanced current value of the actual working condition, so that the test personnel can easily judge the correctness of the unbalanced current; 3. The present invention adopts a high frequency and high voltage method to miniaturize the test device, which is more conducive to carrying out work. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The present invention will be further described below in conjunction with the accompanying drawings and embodiments: Figure 1 It is a schematic diagram of a connection block diagram of the present invention; Figure 2 A schematic diagram of the connection relationship of the main control unit of the present invention; Figure 3 It is a schematic diagram of the process of the present invention. DETAILED DESCRIPTION

[0021] Embodiment 1: like Figure 1~Figure 2As shown, a converter station AC / DC filter unbalanced current detection device based on digital frequency conversion includes an unbalanced current calculation unit arranged inside the device, the unbalanced current calculation unit is respectively communicated with the high-voltage power unit, the digital frequency generating unit, the voltage signal acquisition unit and the small-signal current acquisition signal unit; the high-voltage power unit is communicated with the digital frequency generating unit; the high-voltage power unit, the voltage signal acquisition unit and the small-signal current acquisition signal unit are all electrically connected to the AC / DC capacitor filter of the converter station.

[0022] Preferably, the high-voltage power unit is provided with a short-circuit protection interface and an overload protection interface.

[0023] Preferably, the digital frequency generating unit drives the high voltage power unit with a variable frequency sinusoidal wave signal.

[0024] Preferably, the unbalanced current calculation unit and the digital frequency generation unit are connected via Ethernet.

[0025] Preferably, the unbalanced current calculation unit is connected to the high-voltage power unit via a 485 bus.

[0026] Preferably, the unbalanced current calculation unit and the voltage signal acquisition unit are connected via an SPI bus.

[0027] Preferably, the unbalanced current calculation unit and the small signal current acquisition signal unit are connected via an SPI bus.

[0028] Preferably, the high-voltage power unit is electrically connected to both ends of the AC / DC capacitor filter to provide voltage; and the voltage signal acquisition unit is electrically connected to both ends of the AC / DC capacitor filter to acquire voltage signals.

[0029] Preferably, the small signal current acquisition signal unit is connected in series with both ends of the unbalanced measurement CT of the AC / DC capacitor filter.

[0030] Furthermore, the unbalanced current calculation unit includes TMS320F28377, which controls the test process and calculates the unbalanced current according to the collected signal and converts it into a high-voltage unbalanced current.

[0031] Furthermore, the voltage signal acquisition unit includes AD7616, which acquires the voltage applied to the AC / DC filter.

[0032] Furthermore, the small signal current acquisition signal unit includes AD7616, which acquires unbalanced current.

[0033] Furthermore, the digital frequency generating unit includes XC7S50, which generates a variable frequency sinusoidal wave signal to drive the high voltage power unit.

[0034] Furthermore, the high voltage power unit includes AD5781, which generates a 500V sinusoidal AC voltage with a frequency of 20HZ-1000HZ.

[0035] Embodiment 2: like Figure 3 As shown, a method for detecting unbalanced current of AC / DC filter in a converter station based on digital frequency conversion includes: S1, the digital frequency generating unit drives the high voltage power unit with a variable frequency sine wave signal to generate high voltage, and the high voltage power unit is the output voltage of the AC / DC capacitor filter; S2, the unbalanced measurement CT of the AC / DC capacitor filter is disconnected and connected in series with the small signal current acquisition signal unit; S3, based on the fact that the unbalanced current is proportional to the voltage and frequency, the unbalanced current calculation formula under working conditions is: ; Where F is the frequency of the applied voltage, VN is the voltage level, V is the collected voltage, FN is the rated frequency, F is the output frequency, I is the collected current, and If is the unbalanced current at the rated voltage of the substation; The above embodiments are only preferred technical solutions of the present invention and should not be regarded as limiting the present invention. The protection scope of the present invention shall be the technical solutions recorded in the claims, including equivalent replacement solutions of the technical features in the technical solutions recorded in the claims. That is, equivalent replacement improvements within this scope are also within the protection scope of the present invention.

Claims

1. A converter station AC / DC filter unbalanced current detection device based on digital frequency conversion, characterized in that: The device comprises an unbalanced current calculation unit arranged inside the device, which is respectively connected to the high-voltage power unit, the digital frequency generating unit, the voltage signal collecting unit and the small-signal current collecting signal unit for communication; the high-voltage power unit is connected to the digital frequency generating unit for communication; the high-voltage power unit, the voltage signal collecting unit and the small-signal current collecting signal unit are all electrically connected to the AC / DC capacitor filter of the converter station.

2. According to claim 1, a converter station AC / DC filter unbalanced current detection device based on digital frequency conversion is characterized in that: The high-voltage power unit is provided with a short-circuit protection interface and an overload protection interface.

3. The unbalanced current detection device for AC / DC filter in a converter station based on digital frequency conversion according to claim 1 is characterized in that: The digital frequency generating unit drives the high voltage power unit with a variable frequency sinusoidal wave signal.

4. The unbalanced current detection device for AC / DC filter in a converter station based on digital frequency conversion according to claim 1 is characterized in that: The unbalanced current calculation unit is connected to the digital frequency generation unit via Ethernet.

5. The unbalanced current detection device for AC / DC filter in a converter station based on digital frequency conversion according to claim 1, characterized in that: The unbalanced current calculation unit is connected to the high voltage power unit via a 485 bus.

6. The unbalanced current detection device for AC / DC filter in a converter station based on digital frequency conversion according to claim 1, characterized in that: The unbalanced current calculation unit is connected to the voltage signal acquisition unit via an SPI bus.

7. The unbalanced current detection device for AC / DC filter in a converter station based on digital frequency conversion according to claim 1, characterized in that: The unbalanced current calculation unit is connected to the small signal current acquisition signal unit via an SPI bus.

8. The unbalanced current detection device for AC / DC filter in a converter station based on digital frequency conversion according to claim 1, characterized in that: The high-voltage power unit is electrically connected to both ends of the AC / DC capacitor filter to provide voltage; and the voltage signal acquisition unit is electrically connected to both ends of the AC / DC capacitor filter to acquire voltage signals.

9. The unbalanced current detection device for AC / DC filter in a converter station based on digital frequency conversion according to claim 1, characterized in that: The small signal current acquisition signal unit is connected in series with both ends of the unbalanced measurement CT of the AC / DC capacitor filter.

10. A method for detecting unbalanced current of AC / DC filters in converter stations based on digital frequency conversion according to any one of claims 1 to 9, characterized in that: include: S1, the digital frequency generating unit drives the high voltage power unit with a variable frequency sine wave signal to generate high voltage, and the high voltage power unit is the output voltage of the AC / DC capacitor filter; S2, the unbalanced measurement CT of the AC / DC capacitor filter is disconnected and connected in series with the small signal current acquisition signal unit; S3, based on the fact that the unbalanced current is proportional to the voltage and frequency, the unbalanced current calculation formula under working conditions is: ； Where F is the frequency of the applied voltage, VN is the voltage level, V is the collected voltage, FN is the rated frequency, F is the output frequency, I is the collected current, and If is the unbalanced current at the rated voltage of the substation.

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