Converter AC filter capacitor failure detection method, device and converter system

Abstract

The present invention relates to a method, a detection device and a converter system for detecting failure of an AC filter capacitor of a converter. When an internal circuit of the converter is not connected to a power grid, a power unit is controlled to output an AC voltage of a fixed amplitude to provide voltage support for an AC filter capacitor load, so that a current is generated in the system. The state of the AC filter capacitor is detected by collecting the current.

Description

Technical Field

[0001] The present invention relates to the technical field related to converter grid-connected control, and in particular to a converter AC filter capacitor failure detection method, device and converter system. Background Art

[0002] The converter is a device that realizes the conversion between direct current and alternating current. It mainly includes key components such as switch devices, control systems, sampling Hall, power devices, bus capacitors, filter inductors, and filter capacitors. The control system realizes four-quadrant operation and completes the conversion between AC and DC by controlling the conduction state of the power devices. At present, converters have been widely used in wind power, photovoltaics, energy storage, subway regenerative braking and other fields, providing strong support for the utilization of new energy and the stability of the power grid.

[0003] In order to improve the quality of grid-connected power of the converter, a filter is installed between the power unit and the grid. The filter includes filter inductors and filter capacitors. The high-frequency components in the grid-connected current are filtered out by the filter. The operating environment of the converter is generally harsh. The filter capacitor will decay or fail after long-term operation. At this time, the harmonics of the grid-connected current will increase, which will affect the quality of grid power and the stable operation of the converter, and increase the safety risk of the system. Therefore, it is necessary to detect the failure of the converter filter capacitor to ensure the safe and reliable operation of the system. Summary of the invention

[0004] Based on the above situation of the prior art, the purpose of the present invention is to provide a method, device and converter system for detecting failure of the AC filter capacitor of an inverter. When the internal circuit of the inverter is not connected to the power grid, the power unit is controlled to output an AC voltage of a fixed amplitude to provide voltage support for the AC filter capacitor load, so that current is generated in the system, and the state of the AC filter capacitor is detected by collecting the current.

[0005] To achieve the above object, according to one aspect of the present invention, a method for detecting failure of an AC filter capacitor of a converter is provided, comprising the steps of:

[0006] Collect the DC bus voltage U of the converter dc ;

[0007] According to the DC bus voltage U dc and rated AC voltage value, calculate the open-loop control modulation index m;

[0008] Performing open-loop control on a power unit in the converter according to the open-loop control modulation index m, so that the power unit outputs a rated AC voltage;

[0009] Collect the instantaneous value I of the three-phase current output by the power unit a ,Ib ,I c ;

[0010] According to the instantaneous value of the output current I a ,I b ,I c , calculate the effective value of current I abc_rms , and the effective value of the current I abc_rms With the preset current threshold I abc_threshold For comparison, if I abc_rms Greater than I abc_threshold , the AC filter capacitor is normal, otherwise, the AC filter capacitor is invalid.

[0011] Furthermore, the open-loop control modulation index m is obtained by the following formula:

[0012]

[0013] Among them, U p-p It is the peak value of the rated AC voltage.

[0014] Further, open-loop control is performed on the power unit in the converter according to the open-loop control modulation index m, including controlling the modulation index to increase from zero ramp to m during the switch control process.

[0015] Furthermore, the preset current threshold I abc_threshold It is obtained by the following formula:

[0016] Q C =3×U 线 2 ×ω×C △

[0017]

[0018] Among them, Q C is the reactive power of the AC filter capacitor, U 线 is the rated AC voltage value, C △ is the capacitance of the AC filter capacitor connected in a triangle.

[0019] Furthermore, before the converter is started, the AC contactor is disconnected and the detection method is implemented; based on the detection result, if the AC filter capacitor is normal, the normal startup operation logic is executed.

[0020] According to a second aspect of the present invention, there is provided a device for detecting failure of an AC filter capacitor of a converter, comprising an analog quantity acquisition unit and a control unit;

[0021] The analog quantity acquisition unit acquires the DC bus voltage U of the converter. dcAnd the instantaneous value of the three-phase current output by the converter power unit I a ,I b ,I c , and output to the control unit;

[0022] The control unit calculates an open-loop control modulation index m according to the DC bus voltage Udc and the rated AC voltage value, and performs open-loop control on a power unit in the converter according to the open-loop control modulation index m so that the power unit outputs the rated AC voltage; and

[0023] According to the instantaneous value of the output current I a ,I b ,I c , calculate the effective value of current I abc_rms , and the effective value of the current I abc_rms With the preset current threshold I abc_threshold For comparison, if I abc_rms Greater than I abc_threshold , the AC filter capacitor is normal, otherwise, the AC filter capacitor is invalid.

[0024] Furthermore, the open-loop control modulation index m is obtained by the following formula:

[0025]

[0026] Among them, U p-p is the peak value of the rated AC voltage.

[0027] Further, open-loop control is performed on the power unit in the converter according to the open-loop control modulation index m, including controlling the modulation index to increase from zero ramp to m during the switch control process.

[0028] Furthermore, the preset current threshold I abc_threshold It is obtained by the following formula:

[0029] Q C =3×U 线 2 ×ω×C △

[0030]

[0031] Among them, Q C is the reactive power of the AC filter capacitor, U 线 is the rated AC voltage, C △ is the capacitance of the AC filter capacitor connected in a triangle.

[0032] According to a third aspect of the present invention, there is provided a converter system, the converter system comprising a converter and an AC filter capacitor failure detection device; wherein:

[0033] The converter comprises a power unit and an AC filter, the input of the power unit is connected to a DC source via a DC circuit breaker, and the output of the power unit is connected to an AC grid via an AC filter and an AC switch; the AC filter comprises an AC filter capacitor;

[0034] The AC filter capacitor failure detection device includes the AC filter capacitor failure detection device as described above in the second aspect of the present invention, and detects the AC filter capacitor in the converter.

[0035] In summary, the present invention provides a method, a detection device and a converter system for detecting failure of an AC filter capacitor of a converter. When the internal circuit of the converter is not connected to the power grid, the power unit is controlled to output an AC voltage of a fixed amplitude to provide voltage support for the AC filter capacitor load, so that current is generated in the system, and the state of the AC filter capacitor is detected by collecting the current. The present invention has the following beneficial technical effects:

[0036] (1) A filter capacitor failure detection is performed before the converter is started, and the AC filter capacitor is disconnected from the grid during the detection process. This is to avoid affecting the normal control logic of the converter and to avoid affecting the filter capacitor failure detection due to power interaction between the AC filter capacitor and the grid.

[0037] (2) The converter calculates the open-loop modulation index m based on the current DC bus voltage and the rated AC voltage, and controls the power unit to output the rated AC voltage through the control unit to provide voltage for the AC filter capacitor load, thereby generating current interaction in the system and providing data support for filter capacitor failure detection.

[0038] (3) When the converter performs open-loop control on the power unit, the open-loop modulation index is ramped from zero to m, realizing soft-start charging of the filter capacitor to avoid the generation of impact current.

[0039] (4) The implementation of this detection method does not require any changes to the inverter system hardware. The system's standard current Hall sensor is used in conjunction with the corresponding detection logic to detect the state of the filter capacitor, which facilitates the function upgrade of the inverter. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 It is a flow chart of the method for detecting failure of AC filter capacitor of converter according to the present invention;

[0041] Figure 2 The present invention is a schematic diagram of the circuit structure of the converter AC filter capacitor failure detection device and the converter system. DETAILED DESCRIPTION

[0042] In order to make the purpose, technical scheme and advantages of the present invention clearer, the present invention is further described in detail below in conjunction with specific embodiments and with reference to the accompanying drawings. It should be understood that these descriptions are only exemplary and are not intended to limit the scope of the present invention. In addition, in the following description, the description of well-known structures and technologies is omitted to avoid unnecessary confusion of the concept of the present invention.

[0043] The technical solution of the present invention is described in detail below with reference to the accompanying drawings. According to one embodiment of the present invention, a method for detecting failure of an AC filter capacitor of a converter is provided. The flow chart of the detection method is shown in FIG. Figure 1 As shown, Figure 2 The present invention shows a circuit structure diagram of the converter AC filter capacitor failure detection device and the converter system. Figure 1 and Figure 2 This embodiment is described in detail. The detection method comprises the following steps:

[0044] When the converter is DC-powered, the control unit controls the AC contactor to be in a disconnected state before the converter is started, so that the AC filter is disconnected from the AC power grid.

[0045] The analog quantity acquisition unit acquires the DC bus voltage U of the converter dc and output the collected values ​​to the control unit.

[0046] According to the DC bus voltage U dc and the rated AC voltage value, calculate the open-loop control modulation index m, and perform open-loop control on the power unit in the converter according to the open-loop control modulation index m, so that the power unit outputs the rated AC voltage. In this process, the modulation index needs to be ramped from zero to m; when the converter adopts the SVPWM modulation algorithm, the calculation method of the modulation index m is as follows:

[0047]

[0048] Among them, U p-p It is the peak value of the rated AC voltage.

[0049] The analog quantity acquisition unit acquires the instantaneous value I of the three-phase current output by the power unit. a ,I b ,I c The control unit generates an output current instantaneous value I a ,I b ,I c , calculate the effective value of current I abc_rms , and the effective value of the current I abc_rms With the preset current threshold I abc_threshold For comparison, if I abc_rms Greater than Iabc_threshold , the AC filter capacitor is normal, otherwise, the AC filter capacitor fails. abc_threshold It can be obtained by the following formula:

[0050] Q C =3×U 线 2 ×ω×C △

[0051]

[0052] Among them, Q C is the reactive power of the AC filter capacitor, U 线 is the rated AC voltage value, C △ is the capacitance of the AC filter capacitor connected in a triangle.

[0053] According to the above detection results, if the AC filter capacitor is detected to be in normal state, the control unit executes the normal startup operation logic; if the AC filter capacitor is detected to be in failure state, the control unit executes the fault reporting and shutdown logic and issues a filter capacitor failure alarm prompt.

[0054] According to a second embodiment of the present invention, a device for detecting failure of an AC filter capacitor of a converter is provided. The circuit structure diagram of the detection device is shown in FIG. Figure 2 The detection device includes an analog quantity acquisition unit and a control unit.

[0055] The analog quantity acquisition unit acquires the DC bus voltage U of the converter. dc And the instantaneous value of the three-phase current output by the converter power unit I a ,I b ,I c , and output to the control unit.

[0056] The control unit calculates the open-loop control modulation index m according to the DC bus voltage Udc and the rated AC voltage value, and performs open-loop control on the power unit in the converter according to the open-loop control modulation index m, so that the power unit outputs the rated AC voltage. In this process, the modulation index needs to be ramped from zero to m. When the converter adopts the SVPWM modulation algorithm, the open-loop control modulation index m can be obtained by the following formula:

[0057]

[0058] Among them, U p-p is the peak value of the rated AC voltage.

[0059] And, according to the instantaneous value of the output current I a ,I b ,I c, calculate the effective value of current I abc_rms , and the effective value of the current I abc_rms With the preset current threshold I abc_threshold For comparison, if I abc_rms Greater than I abc_threshold , the AC filter capacitor is normal, otherwise, the AC filter capacitor is invalid.

[0060] Preset current threshold I abc_threshold It is obtained by the following formula:

[0061] Q C =3×U 线 2 ×ω×C △

[0062]

[0063] Among them, Q C is the reactive power of the AC filter capacitor, U 线 is the rated AC voltage, C △ is the capacitance of the AC filter capacitor connected in a triangle.

[0064] According to the above detection results, if the AC filter capacitor is detected to be in normal state, the control unit executes the normal startup operation logic; if the AC filter capacitor is detected to be in failure state, the control unit executes the fault reporting and shutdown logic and issues a filter capacitor failure alarm prompt.

[0065] The third embodiment of the present invention provides a converter system, which includes a converter and an AC filter capacitor failure detection device. The converter includes a power unit and an AC filter. The input of the power unit is connected to a DC source via a DC circuit breaker, and the output of the power unit is connected to an AC grid via an AC filter and an AC switch. The AC filter includes an AC filter capacitor. The AC filter capacitor failure detection device includes the AC filter capacitor failure detection device as described in the second embodiment above, which detects the AC filter capacitor in the converter.

[0066] In summary, the present invention relates to a method for detecting failure of an AC filter capacitor of a converter, a detection device, and a converter system including the detection device. The detection method adopts a detection strategy as follows: before the converter is started, when the converter is not connected to the AC power grid, the control unit controls the power unit to output an AC voltage of a specific amplitude, the AC filter capacitor as a capacitive load absorbs reactive power, the analog quantity acquisition unit detects the corresponding current, the analog quantity acquisition unit transmits the detected current signal to the control unit, the control unit compares the collected current value with the set threshold value, and when the current value is lower than the threshold value, the AC filter capacitor is considered to be failed. The method is simple to implement and does not require additional hardware cost of the system. When the DC side of the converter is connected to a photovoltaic panel or an energy storage battery, an AC voltage is established by the converter itself to provide voltage support for the AC filter capacitor, thereby generating reactive current in the system, and the control unit uses the current size to detect the state of the filter capacitor. Through the above-mentioned technical solution provided by the present invention, the detection accuracy is improved, and no changes are needed to the hardware of the converter system. The current Hall of the system standard is used to cooperate with the corresponding detection logic to detect the state of the filter capacitor, which is convenient for the function upgrade of the converter.

[0067] It should be understood that the above specific embodiments of the present invention are only used to illustrate or explain the principles of the present invention, and do not constitute a limitation of the present invention. Therefore, any modifications, equivalent substitutions, improvements, etc. made without departing from the spirit and scope of the present invention should be included in the protection scope of the present invention. In addition, the appended claims of the present invention are intended to cover all changes and modifications that fall within the scope and boundaries of the appended claims, or the equivalent forms of such scope and boundaries.

Claims

1. A method for detecting failure of AC filter capacitor of a converter, characterized in that: Includes steps: Collect the DC bus voltage U of the converter dc ; Calculating the open-loop control modulation index m according to the DC bus voltage Udc and the rated AC voltage value; Performing open-loop control on a power unit in the converter according to the open-loop control modulation index m, so that the power unit outputs a rated AC voltage; Collect the instantaneous value I of the three-phase current output by the power unit a ,I b ,I c ; According to the instantaneous value of the output current I a ,I b ,I c , calculate the effective value of current I abc_rms , and the effective value of the current I abc_rms With the preset current threshold I abc_threshold For comparison, if I abc_rms Greater than I abc_threshold , the AC filter capacitor is normal, otherwise, the AC filter capacitor is invalid.

2. The detection method according to claim 1, characterized in that: The open-loop control modulation index m is obtained by the following formula: Among them, U p-p It is the peak value of the rated AC voltage.

3. The detection method according to claim 2, characterized in that: Open-loop control is performed on the power unit in the converter according to the open-loop control modulation index m, including ramping the control modulation index from zero to m during the switch control process.

4. The detection method according to claim 3, characterized in that: The preset current threshold I abc_threshold It is obtained by the following formula: Q C =3×U 线 2 ×ω×C Δ Among them, Q C is the reactive power of the AC filter capacitor, U 线 is the rated AC voltage value, C Δ is the capacitance of the AC filter capacitor connected in a triangle.

5. The detection method according to claim 4, characterized in that: Before the converter is started, the AC contactor is disconnected and the detection method is implemented; according to the detection result, if the AC filter capacitor is normal, the normal startup operation logic is executed.

6. A converter AC filter capacitor failure detection device, characterized in that: It includes an analog quantity acquisition unit and a control unit; The analog quantity acquisition unit acquires the DC bus voltage U of the converter. dc And the instantaneous value of the three-phase current output by the converter power unit I a ,I b ,I c , and output to the control unit; The control unit calculates an open-loop control modulation index m according to the DC bus voltage Udc and the rated AC voltage value, and performs open-loop control on a power unit in the converter according to the open-loop control modulation index m, so that the power unit outputs the rated AC voltage; as well as According to the instantaneous value of the output current I a ,I b ,I c , calculate the effective value of current I abc_rms , and the effective value of the current I abc_rms With the preset current threshold I abc_threshold For comparison, if I abc_rms Greater than I abc_threshold , the AC filter capacitor is normal, otherwise, the AC filter capacitor is invalid.

7. The detection device according to claim 6, characterized in that: The open-loop control modulation index m is obtained by the following formula: Among them, U p-p is the peak value of the rated AC voltage.

8. The detection device according to claim 7, characterized in that: Open-loop control is performed on the power unit in the converter according to the open-loop control modulation index m, including ramping the control modulation index from zero to m during the switch control process.

9. The detection device according to claim 8, characterized in that: The preset current threshold I abc_threshold It is obtained by the following formula: Q C =3×U 线 2 ×ω×C Δ Among them, Q C is the reactive power of the AC filter capacitor, U 线 is the rated AC voltage, C Δ is the capacitance of the AC filter capacitor connected in a triangle.

10. A converter system, characterized in that: The converter system includes a converter and an AC filter capacitor failure detection device; wherein, The converter comprises a power unit and an AC filter, the input of the power unit is connected to a DC source via a DC circuit breaker, and the output of the power unit is connected to an AC grid via an AC filter and an AC switch; the AC filter comprises an AC filter capacitor; The AC filter capacitor failure detection device comprises the AC filter capacitor failure detection device as claimed in any one of claims 6 to 9, and detects the AC filter capacitor in the converter.

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