A capacitor testing device

Abstract

The present invention provides a capacitor testing device, wherein the secondary side of a multi-winding transformer includes n groups of three-phase AC windings, each group of three-phase AC windings being connected to the input ends of corresponding three power units respectively; the output ends of the n power units in each phase are cascaded to form a one-phase power branch; one end of each power branch is connected, and the other end is connected to a capacitor under test through the output end of the testing device; each power unit receives a corresponding driving signal so that the electrical parameter flowing through the capacitor under test reaches a target test value, thereby testing indicators such as the life and temperature rise of the capacitor under test at the target test value; and each phase power branch is formed by cascading the corresponding n power units, wherein the carrier phases of the power units are not completely the same, thereby increasing the output equivalent switching frequency. Therefore, high-order harmonics can be output by selecting a low-frequency power electronic switch.

Description

Technical Field

[0001] The present invention relates to the field of power electronics, and in particular to a capacitor testing device. Background Art

[0002] In the prior art, durability testing of AC filter capacitors uses an industrial frequency power supply, which increases the amplitude of its own output test voltage to simulate the heating caused by the superposition of fundamental and harmonic waves. However, this testing method is significantly different from the actual working conditions of the AC filter capacitors, and it is impossible to accurately determine the lifespan, temperature rise and other indicators of the AC filter capacitors in actual applications.

[0003] Moreover, the industrial frequency power supply in the form of existing power electronic devices has very high switching frequency requirements because it emits high-frequency harmonics, such as harmonics above 5kHz, which brings great difficulties to device selection. Summary of the Invention

[0004] In view of this, the present invention provides a capacitor testing device to reduce the switching frequency of a power electronic switch.

[0005] To achieve the above object, the present invention provides the following technical solutions:

[0006] A first aspect of the present invention provides a capacitor testing device, comprising: a controller, a multi-winding transformer, and 3n power units; n is an integer greater than 1, wherein,

[0007] The primary side of the multi-winding transformer is connected to the inner side of the input terminal of the testing device;

[0008] The secondary side of the multi-winding transformer includes n groups of three-phase AC windings, and each group of three-phase AC windings is connected to the input ends of the corresponding three power units respectively;

[0009] The output ends of n power units in each phase are cascaded to form a power branch of one phase;

[0010] One end of each of the power branches is connected;

[0011] The other end of each power branch is connected to the capacitor under test through the output end of the testing device;

[0012] The controller is used to send a corresponding driving signal to the control end of each power unit through the driving circuit, so that the carrier phase of each power unit in the power branch is not completely the same, and the electrical parameter flowing through the capacitor under test is the target test value.

[0013] Optionally, in each phase, the carrier phases of the power units are different.

[0014] Optionally, the power unit includes: a rectifier, a support capacitor and an output H-bridge;

[0015] The AC side of the rectifier serves as the input end of the power unit;

[0016] The DC side of the rectifier is connected to the DC side of the output H-bridge, and the support capacitor is provided between the positive and negative connection points;

[0017] The AC side of the output H-bridge serves as the output end of the power unit;

[0018] The control end of the output H-bridge at least serves as a part of the control end of the power unit.

[0019] Optionally, in each phase, the carrier waves of the output H-bridges are staggered by 180° / n.

[0020] Optionally, the rectifier is: a fully controlled rectifier circuit;

[0021] The control end of the fully-controlled rectifier circuit serves as the other control end of the power unit.

[0022] Optionally, the phases of the secondary windings of the multi-winding transformer are the same;

[0023] In each phase, the carrier waves of the fully-controlled rectifier circuits are staggered by 360° / 3n.

[0024] Optionally, the rectifier is an uncontrolled rectifier circuit.

[0025] Optionally, the multi-winding transformer is a phase-shifting transformer, in which the phases of the secondary windings of each phase are staggered by 60° / n.

[0026] Optionally, it also includes: a step-down transformer;

[0027] The step-down transformer is arranged between the three-phase power branch and the output end of the testing device.

[0028] Optionally, the source of the driving signal is a modulation module in the controller. When the modulation module outputs a modulation wave in a current control mode, the electrical parameter is current, and the target test value includes any one of the following:

[0029] The current command value under normal occurrence simulation conditions, the current command value under harmonic occurrence simulation conditions, the current command value under flicker occurrence simulation conditions, the current command value under current mutation simulation conditions, and the current command value under current imbalance simulation conditions.

[0030] Optionally, in the current control mode, the two control loops in the modulation module that respectively control the output side active current and the output side reactive current of the test device are both: negative feedback current loops;

[0031] The current regulator in the negative feedback current loop is a proportional-integral + repetitive controller with a limiting function.

[0032] Optionally, the negative feedback current loop further includes: a summing connector; the summing connector is used to:

[0033] Using the actual value of the shaft voltage corresponding to the output side of the test device as a feedforward term, superimposing the output of the current regulator;

[0034] and / or,

[0035] When a step-down transformer is provided between the three-phase power branch and the output end of the test device, the product of the actual value of another current on the output side of the test device, the output electrical angular frequency and the equivalent inductance value on the output side is used as the decoupling term to superimpose the output of the current regulator; and the decoupling term corresponding to the active current on the output side is inverted and superimposed.

[0036] Optionally, the source of each of the driving signals is a modulation module in the controller. When the modulation module outputs a modulation wave in a voltage control mode, the electrical parameter is voltage, and the target test value includes any one of the following:

[0037] The voltage command value under normal simulated working conditions, the voltage command value under harmonic simulated working conditions, the voltage command value under flicker simulated working conditions, the voltage command value under voltage sudden change simulated working conditions, and the voltage command value under voltage unbalance simulated working conditions.

[0038] Optionally, in the voltage control mode, the two control loops in the modulation module that respectively control the d-axis voltage and the q-axis voltage of the output voltage of the test device in a 2-phase rotating coordinate system each include: a negative feedback voltage outer loop and a current inner loop;

[0039] The current inner loop is a current loop that uses the output side active current or the output side reactive current of the test device as negative feedback;

[0040] The voltage regulator in the negative feedback voltage outer loop is a proportional-integral + repetitive controller with a limiting function;

[0041] The current regulator in the current inner loop is a proportional controller or a proportional-integral controller with a limiting function.

[0042] Optionally, the current inner loop further includes: a summing connector; the summing connector is used to:

[0043] Using the actual value of the shaft voltage corresponding to the output side of the test device as a feedforward term, superimposing the output of the current regulator;

[0044] and / or,

[0045] When a step-down transformer is provided between the three-phase power branch and the output end of the test device, the product of the actual value of another current on the output side of the test device, the output electrical angular frequency and the equivalent inductance value on the output side is used as the decoupling term to superimpose the output of the current regulator; and the decoupling term corresponding to the active current on the output side is inverted and superimposed.

[0046] Optionally, also include:

[0047] A first controllable switch provided on each phase branch inside the output end of the test device;

[0048] and / or,

[0049] A second controllable switch provided on each phase branch inside the input end of the test device;

[0050] The first controllable switch and the second controllable switch are controlled by the controller.

[0051] Optionally, it further includes: a discharge circuit arranged outside the output end of the test device, controlled by the controller, and used to discharge the capacitor under test after the test of the capacitor under test is stopped.

[0052] Optionally, the discharge circuit includes: three third controllable switches and three discharge resistors;

[0053] One end of each of the third controllable switches is correspondingly connected to the output end of the testing device;

[0054] The other end of each of the third controllable switches is connected to the corresponding discharge resistor;

[0055] The other ends of the discharge resistors are connected;

[0056] Each of the third controllable switches is controlled by the controller.

[0057] The capacitor testing device provided by the present invention has a multi-winding transformer whose secondary side includes n groups of three-phase AC windings, each group of three-phase AC windings being connected to the input ends of corresponding three power units respectively; the output ends of the n power units in each phase are cascaded to form a single-phase power branch; one end of each power branch is connected, and the other end is connected to the capacitor under test through the output end of the testing device; each power unit receives a corresponding drive signal so that the electrical parameter flowing through the capacitor under test reaches a target test value, thereby testing indicators such as the life and temperature rise of the capacitor under test at the target test value; and each phase power branch is formed by cascading the corresponding n power units, wherein the carrier phases of the power units are not completely the same, thereby increasing the output equivalent switching frequency. Therefore, high-order harmonics can be output by selecting a low-frequency power electronic switch. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings to be used in the embodiments or the description of the prior art. Obviously, the drawings described below are merely embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying any creative work.

[0059] Figure 1 A schematic structural diagram of a capacitor testing device provided in an embodiment of the present invention;

[0060] Figure 2 A schematic diagram of the structure of a power unit provided in an embodiment of the present invention;

[0061] Figure 3 A schematic diagram of the specific structure of a power unit provided in an embodiment of the present invention;

[0062] Figure 4 A schematic diagram of the specific structure of a capacitor testing device provided in an embodiment of the present invention;

[0063] Figure 5 Another specific structural diagram of a power unit provided by an embodiment of the present invention;

[0064] Figure 6 Another specific structural diagram of the capacitor testing device provided by an embodiment of the present invention;

[0065] Figure 7 and Figure 8 Two other specific structural schematic diagrams of the capacitor testing device provided by the embodiments of the present invention;

[0066] Figure 9a and Figure 9b They are two control logic block diagrams of the capacitor testing device provided by the embodiments of the present invention. DETAILED DESCRIPTION

[0067] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0068] In this application, the terms "comprises," "comprising," or any other variations thereof are intended to encompass non-exclusive inclusion, such that a process, method, article, or apparatus that includes a list of elements includes not only those elements but also other elements not explicitly listed, or elements inherent to such process, method, article, or apparatus. In the absence of further limitations, an element defined by the phrase "comprising a ..." does not preclude the presence of additional identical elements in the process, method, article, or apparatus that includes the element.

[0069] The present invention provides a capacitor testing device, such as Figure 1 As shown, it includes: a controller (not shown in the figure), a multi-winding transformer T1 and 3n power units (such as Figure 1 A1, B1, C1, A2, B2, C2, ..., An, Bn, Cn) shown in ; n is an integer greater than 1, wherein:

[0070] The primary side 01 of the multi-winding transformer T1 is connected to the inner side of the input end of the capacitor testing device 100; when the input end of the capacitor testing device 100 is connected to the power supply, the multi-winding transformer T1 converts the voltage on its primary winding to its respective secondary windings according to the corresponding transformation ratio.

[0071] The secondary side of multi-winding transformer T1 includes n groups of three-phase AC windings 02, each of which is connected to the input terminals of three corresponding power units. For example, the secondary windings in the first three-phase AC winding 02 are connected to the input terminals of power units A1, B1, and C1, respectively; the secondary windings in the second three-phase AC winding 02 are connected to the input terminals of power units A2, B2, and C2, respectively; and the secondary windings in the nth three-phase AC winding 02 are connected to the input terminals of power units An, Bn, and Cn, respectively.

[0072] The output ends of n power output units per phase are cascaded to form a single-phase power branch. For example, the output ends of power units A1, A2, ..., An are cascaded to form the A-phase power branch; the output ends of power units B1, B2, ..., Bn are cascaded to form the B-phase power branch; and the output ends of power units C1, C2, ..., Cn are cascaded to form the C-phase power branch. That is, every three power units form a group, and the input ends of each power unit in the group are respectively connected to the corresponding secondary winding of the multi-winding transformer T1. The single-phase output ends of each power unit in the group are respectively connected to a single-phase power branch, thereby forming the three-phase power branch of the test device 100. Each phase power branch is formed by cascading the single-phase output ends of multiple power units.

[0073] One end of each power branch is connected to each other, and the other end of each power branch is connected to the capacitor to be tested through the output end of the test device 100 .

[0074] During the specific operation, the controller is used to send a corresponding drive signal to the control end of each power unit through the drive circuit, so that the electrical parameters flowing through the capacitor under test are the target test values. That is, when the input end of the test device 100 is connected to the power supply, the secondary windings of the multi-winding transformer T1 will provide the target test value for the capacitor under test through the corresponding power unit, thereby testing the lifespan, temperature rise and other indicators of the capacitor under test at the target test value, thereby achieving durability and other tests. In addition, the drive signal received by the control end of each power unit will also make the carrier phases of each power unit in the power branch not completely the same, which is equivalent to increasing the equivalent switching frequency of the output. When the carrier phases of each power unit are different, that is, when the carriers of each power unit are staggered by 180° / n, the equivalent switching frequency of the output can be increased to 2n times that of a single tube, reducing the switching frequency of the power electronic switch, so that a low-frequency power electronic switch can be used to output relatively high-frequency harmonics.

[0075] The capacitor testing device 100 provided in this embodiment can not only test the lifespan, temperature rise, and other indicators of the capacitor under test at target test values, but also, since each phase power branch is composed of the corresponding n cascaded power units, by adjusting the carrier phase shift of each power unit, high-order harmonics can be output by selecting a low-frequency power electronic switch, thereby reducing the switching frequency of the power electronic switch.

[0076] On the basis of the above embodiment, optionally, the power unit in the test device 100 can be as follows Figure 2 As shown in , it specifically includes: a rectifier 10, a support capacitor C and an output H bridge 20; wherein:

[0077] The AC side of the rectifier 10 serves as the input end of the power unit; the DC side of the rectifier 10 is connected to the DC side of the output H-bridge 20, and the support capacitor C is provided between the positive and negative connection points; the AC side of the output H-bridge 20 serves as the output end of the power unit.

[0078] Specifically, the rectifier 10 rectifies the received current, inverts the rectified electric energy through the output H-bridge 20, and outputs it to the capacitor under test from its AC side, so as to test the life, temperature rise and other indicators of the capacitor under test at the target test value.

[0079] The control end of the output H-bridge 20 serves as at least part of the control end of the corresponding power unit; that is, if the rectifier 10 is controllable, the control end of the rectifier 10 serves as the other control end of the corresponding power unit; if the rectifier 10 is controllable, the control end of the output H-bridge 20 serves as all the control ends of the corresponding power unit.

[0080] In practical applications, the controller may stagger the carrier waves of the output H-bridges 20 in each phase by 180° / n, thereby staggering the carrier waves of the power units by 180° / n.

[0081] It should be noted that, in order to realize the carrier phase shifting function under the above-mentioned power unit cascade, the rectifier 10 can be optionally Figure 3 As shown in , the rectifier 10 is a fully controlled rectifier circuit; including a first switch tube S1, a second switch tube S2, a third switch tube S3, a fourth switch tube S4, a fifth switch tube S5 and a sixth switch tube S6; wherein:

[0082] The first switching tube S1 and the second switching tube S2 are connected in series, and the series connection point serves as one phase of the AC side of the rectifier 10; the third switching tube S3 and the fourth switching tube S4 are connected in series, and the series connection point serves as another phase of the AC side of the rectifier 10; the fifth switching tube S5 and the sixth switching tube S6 are connected in series, and the series connection point serves as the third phase of the AC side of the rectifier 10; the first switching tube S1, the third switching tube S3, and the fifth switching tube S5 serve as the upper bridge arm of each phase; the second switching tube S2, the fourth switching tube S4, and the sixth switching tube S6 serve as the lower bridge arm of each phase; the bridge arms of each phase are connected in parallel to obtain the positive and negative poles of the DC side of the rectifier 10.

[0083] The output H-bridge 20 and the control terminals of the switches in the rectifier 10 serve together as all the control terminals of the corresponding power units.

[0084] In actual applications, all switching tubes can be IGBTs (Insulated Gate Bipolar Transistors) or MOSFETs (Metal-Oxide-Semiconductor Field-Effect Transistors), depending on their specific application environment, and are all within the scope of protection of this application.

[0085] When each power unit uses Figure 3 In the structure shown, in the test device 100, the phases of the secondary windings of the multi-winding transformer T1 are the same, and the carriers of the fully controlled rectifier circuits in each phase are staggered by 360° / 3n. Figure 4 The structure shown is used as an example for explanation. Each phase power branch is formed by cascading the corresponding five power units. The carrier phase shifts of the grid-side power units are staggered by 24°, and the carriers of the output H-bridges 20 are staggered by 36°.

[0086] The testing device 100 provided in this embodiment can achieve a higher power factor and lower current harmonics on the input side by adopting a multi-winding transformer + active rectification + carrier phase shifting approach.

[0087] In addition, in order to realize the carrier phase shifting function under the above-mentioned power unit cascade, there is another optional solution: the rectifier 10 in the test device 100, such as Figure 5 As shown in the figure, the rectifier 10 is: an uncontrolled rectifier circuit; which specifically includes: a first diode N1, a second diode N2, a third diode N3, a fourth diode N4, a fifth diode N5 and a sixth diode N6; the connection method of each diode is as follows Figure 5 As shown in , no further description is given here.

[0088] At this time, in the capacitor testing device 100, the phases of the secondary windings of the multi-winding transformer T1 are staggered by 60° / n. Figure 6 The structure shown is used as an example for explanation. Each phase power branch is formed by cascading the corresponding 8 power units. The phases of the secondary windings of the multi-winding transformer T1 are staggered by 7.5 degrees, and the carriers of the output H bridges 20 are staggered by 22.5 degrees.

[0089] The capacitor testing device 100 provided in this embodiment can also achieve a higher power factor and lower current harmonics on the input side by adopting a phase-shifting transformer.

[0090] It is worth noting that both of the above two methods can realize the carrier phase shifting function under the cascade of power units. At the same time, the input side can also achieve a higher power factor and lower current harmonics through a phase shifting transformer, or a multi-winding transformer + active rectification + carrier phase shifting method. However, in actual applications, it is not limited to the above two implementation forms, and the structure of each power unit is not limited to Figure 2 For the structure shown, any solution that can achieve an increase in the equivalent switching frequency through cascading + carrier phase shifting is within the protection scope of this application.

[0091] In practical applications, the large current flowing through power electronic devices usually results in very large losses in the main switches of the power electronic devices, which brings great difficulties to the selection of devices.

[0092] Therefore, this embodiment provides a more preferred solution, which is as follows Figure 7 As shown, the test device 100 , based on the above embodiment, further includes: a step-down transformer T2 ; the step-down transformer T2 is arranged between the three-phase power branch and the output end of the test device 100 .

[0093] The step-down transformer T2 can reduce the high voltage achieved by each power branch to a lower level. At this time, due to the conservation of energy, the current on the primary side of the step-down transformer T2 will be smaller, while the current on the secondary side will be larger.

[0094] In other words, this embodiment reduces the current flowing through the power electronic switches within each power unit by cascading high voltage and then reducing the voltage, achieving low current and low switching frequency, thereby reducing device switching losses. Furthermore, this embodiment not only reduces the switching frequency of the power electronic switches, but also reduces the current flowing through the power electronic switches, thereby reducing system losses and improving efficiency.

[0095] In practical applications, the step-down transformer T2 may be a multi-tap transformer to output multiple levels of voltage, thereby broadening its scope of application.

[0096] In addition, the testing device 100 may further include Figure 7 As shown in FIG: a first controllable switch K1 provided on each phase branch inside the output terminal of the test device 100, and (as shown in FIG Figure 7 ) or (not shown), a second controllable switch K2 is provided on each phase branch inside the input end of the testing device 100 .

[0097] The first controllable switch K1 and the second controllable switch K2 are both controlled by a controller.

[0098] In practical applications, by controlling the on and off of the first controllable switch K1, access tests for different capacitors under test can be safely implemented; moreover, by controlling the on and off of the second controllable switch K2, the power supply can be connected and disconnected without the need for plugging and unplugging, which is safer.

[0099] On the basis of the above embodiments, preferably, Figure 8 (In Figure 7 As shown in the figure, the capacitor testing device 100 also includes: a discharge circuit 101 arranged outside the output end of the capacitor testing device 100, which is controlled by the controller and is used to discharge the capacitor under test after the test of the capacitor under test is stopped to ensure the safety of the operation.

[0100] In practical applications, the discharge circuit 101 can be Figure 8 As shown in , it specifically includes: three third controllable switches (such as K3 shown in the figure) and three discharge resistors (such as R shown in the figure); wherein:

[0101] One end of each third controllable switch is connected to the output end of the test device 100 , and the other end of each third controllable switch is connected to one end of the corresponding bleeder resistor, and the other end of each bleeder resistor is connected.

[0102] Each third controllable switch is controlled by the controller.

[0103] In practical applications, each bleeder resistor can be implemented by connecting multiple resistors in series or in parallel, or other devices can be used to replace the bleeder resistor; the discharge circuit 101 can also adopt other structures as long as it can achieve the above-mentioned discharge function, which is within the protection scope of this application.

[0104] On the basis of the above embodiments, the driving signal received by each power unit in the test device 100 is sourced from the modulation module ( Figure 9a or Figure 9b The modulation waves output by the modulation module, after passing through the corresponding drive circuit, can generate corresponding drive signals to realize the control of each power unit.

[0105] In actual applications, the modulation module can output a modulated wave under the current control mode; at this time, under the corresponding driving signal, the function of the test device 100 is to adjust the current flowing through the capacitor under test (that is, the above-mentioned electrical parameters) to the current command value (that is, the above-mentioned target test value) under any working condition such as normal occurrence simulation, harmonic occurrence simulation, flicker occurrence simulation, current mutation simulation and current imbalance simulation.

[0106] See also Figure 9aIn this current control mode, the output side active current and the output side reactive current of the test device are mainly controlled respectively. The corresponding two control loops in the modulation module are both: negative feedback current loop; the current regulator ACR in the negative feedback current loop is: proportional integral + repetitive controller with limiting function, that is, the current regulator ACR adopts proportional integral control and repetitive control at the same time, and has limiting function. Figure 9a In the example, PLL refers to a phase-locked loop, which can detect the output voltage u of the test device. oa 、u ob 、u oc Get the actual value u of the d-axis voltage in the 2-phase rotating coordinate system od and the actual value of the q-axis voltage u oq And the output electrical angle θ; 3S refers to the 3-phase stationary coordinate system, 2R refers to the 2-phase rotating coordinate system, the coordinate transformation link from 3S to 2R can convert the output side current i of the test device into oa 、i ob 、i oc Convert the actual value of the active current on the output side of the test device i od and the actual value of reactive current i on the output side oq ; Refers to the given value of the active current on the output side of the test device. Refers to the reactive current given value on the output side of the test device; u oa Refers to the actual value of the A-phase voltage on the output side of the test device, u ob Refers to the actual value of the B-phase voltage on the output side of the test device, u oc Refers to the actual value of the C-phase voltage on the output side of the test device, i oa Refers to the actual value of the A-phase current on the output side of the test device, i ob Refers to the actual value of the B-phase current on the output side of the test device, i oc Refers to the actual value of the C-phase current on the output side of the test device; Refers to the d-axis voltage adjustment amount, Refers to the q-axis voltage regulation. After the coordinate transformation from 2R to 3S, the voltage regulation of each phase on the output side of the test device can be obtained. Finally, the PWM module generates the driving signal for each switch tube in each power unit.

[0107] Preferably, the negative feedback current loop may further include: a summing connector; the summing connector is used to: use the actual value of the shaft voltage corresponding to the output side of the test device (such as Figure 9a The u shown in od or u oq) as a feedforward term to superimpose the output of the current regulator ACR; and / or, a step-down transformer (such as Figure 7 and Figure 8 When T2 is shown in FIG, the actual value of the output current of the test device is taken as Figure 9a The i shown in od or i oq ), output electrical angular frequency ω o The product of the output side equivalent inductance L is used as the decoupling term to superimpose the output of the current regulator ACR; and the decoupling term ω corresponding to the output side active current o Li oq Need to be inverted to get -ω o Li oq Then overlay.

[0108] More preferably, the test voltage of the test device 100 is programmable. By setting the modulation wave that controls the output voltage, the frequency, amplitude and phase of the fundamental wave, higher harmonics and interharmonics output by the test device 100 can be adjusted, and voltage surges and dips, three-phase imbalance, flicker and other working conditions can be simulated.

[0109] That is, the modulation module can also output a modulated wave under the voltage control mode; at this time, under the corresponding driving signal, the function of the test device 100 is to adjust the voltage flowing through the capacitor under test (that is, the above-mentioned electrical parameter) to the voltage command value (that is, the above-mentioned target test value) under any working condition such as normal occurrence simulation, harmonic occurrence simulation, flicker occurrence simulation, voltage mutation simulation and voltage imbalance simulation.

[0110] See also Figure 9b In this voltage control mode, the d-axis voltage and q-axis voltage of the output voltage of the test device in the two-phase rotating coordinate system are mainly controlled. The two corresponding control loops in the modulation module include: a negative feedback voltage outer loop and a current inner loop; wherein, the current inner loop is: based on the output side active current of the test device (such as Figure 9b The i shown in od ) or output side reactive current (such as Figure 9b The i shown in oq ) As the current loop of negative feedback, its current regulator ACR can be a proportional controller or a proportional-integral controller with a limiting function; the voltage regulator AVR in the negative feedback voltage outer loop is: a proportional-integral + repetitive controller with a limiting function, that is, the voltage regulator AVR adopts proportional-integral control and repetitive control at the same time, and has a limiting function. Figure 9b middle, Refers to the d-axis voltage command value, Refers to the q-axis voltage command value. The definitions of other modules and symbols are the same as Figure 9a The same as in the previous section, no further description is given here.

[0111] Preferably, the current inner loop may further include: a summing connector; the summing connector is used to: use the output side of the test device to correspond to the actual value of the shaft voltage (such as Figure 9b The u shown in od or u oq ) as a feedforward term to superimpose the output of the current regulator ACR; and / or, a step-down transformer (such as Figure 7 and Figure 8 When T2 is shown in FIG, the actual value of the output current of the test device is taken as Figure 9b The i shown in od or i oq ), output electrical angular frequency ω o The product of the output side equivalent inductance L is used as the decoupling term to superimpose the output of the current regulator ACR; and the decoupling term ω corresponding to the output side active current o Li oq Need to be inverted to get -ω o Li oq Then overlay.

[0112] In the voltage control mode, the test device 100 can be enabled to simulate actual working conditions such as harmonic generation, flicker generation, voltage sudden rise and fall, and voltage imbalance, and can truly simulate the actual working conditions of the capacitor.

[0113] In practical applications, in order to make the driving signal received by the control end of each power unit come from a modulation wave in either the current control module or the voltage control mode, a mode selection module can be added to the control logic of the test device 100, such as Figure 9b As shown in , when the mode selection is 0, the corresponding control mode is the voltage control mode, and when the mode selection is 1, the corresponding control mode is the current control mode.

[0114] (1) When the voltage control mode is selected, the d-axis component of the given voltage under the corresponding simulation condition (i.e. ) and the q-axis component (i.e. ), respectively with the actual sampled output voltage (i.e. u od or u oq ) and the resulting error enters the automatic voltage regulator (AVR). The AVR uses a proportional-integral + repetitive control method to control the output voltage harmonics and has a limiting function.

[0115] The output of the voltage regulator AVR enters the current inner loop and is compared with the actual current (i.e., i od or i oq ) is compared, and the resulting error enters the automatic current regulator (ACR). In voltage control mode, the current regulator (ACR) is a proportional or proportional-integral controller with a limiting function.

[0116] The output of the current regulator ACR is added with the decoupling term -ω o Li oq Or ω o Li od , and the voltage feedforward term u od or u oq After that, it goes through the 2R to 3S coordinate transformation link and enters the PWM module to generate various drive signals. Moreover, the decoupling term and the feedforward term are optional and do not necessarily need to exist.

[0117] (2) When the current control mode is selected, the voltage loop does not work. The d-axis component (i.e. ) and the q-axis component (i.e. ), and the actual current (i od or i oq ) is compared, and the resulting error enters the automatic current regulator (ACR). In current control mode, the ACR is a proportional-integral + repetitive controller with a limiting function.

[0118] The output of the current regulator ACR is added with the decoupling term -ω o Li oq Or ω o Li od , and the voltage feedforward term u od or u oq After that, it goes through the 2R to 3S coordinate transformation link and enters the PWM module to generate various drive signals. Both the decoupling term and the feedforward term are optional.

[0119] Depend on Figure 9b It can be seen that in different control modes, the control method of the test device 100 is different, specifically, the reference value source of the current is different, and the controller of the current loop is different, both of which can be set through the mode selection module.

[0120] The test device 100 provided in this embodiment can realize the control switching of the output current and output voltage, so that it emits the fundamental wave and harmonics with rich frequency bands. It also has the ability to produce various working conditions such as instantaneous voltage drop, imbalance, and flicker, thereby simulating the actual working environment of the capacitor and accurately obtaining indicators such as the life and temperature rise of the capacitor in actual application.

[0121] The same or similar parts between the various embodiments in this specification can be referred to each other, and each embodiment focuses on the differences from other embodiments. In particular, for the system or system embodiment, since it is basically similar to the method embodiment, the description is relatively simple, and the relevant parts can be referred to the partial description of the method embodiment. The system and system embodiments described above are merely schematic, wherein the units described as separate components may or may not be physically separated, and the components displayed as units may or may not be physical units, that is, they may be located in one place, or they may be distributed on multiple network units. Some or all of the modules can be selected according to actual needs to achieve the purpose of the solution of this embodiment. Ordinary technicians in this field can understand and implement it without making any creative efforts.

[0122] Professionals may further appreciate that the units and algorithm steps of each example described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, computer software, or a combination of the two. In order to clearly illustrate the interchangeability of hardware and software, the above description has generally described the components and steps of each example according to their functions. Whether these functions are performed in hardware or software depends on the specific application and design constraints of the technical solution. Professionals and technicians may use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of the present invention.

[0123] With respect to the above description of the disclosed embodiments, the features described in the various embodiments in this specification may be interchanged or combined to enable those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not limited to the embodiments shown herein, but is intended to conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A capacitor testing device, characterized in that: include: controller, a multi-winding transformer, and 3n power units; n is an integer greater than 1, where The primary side of the multi-winding transformer is connected to the inner side of the input terminal of the testing device; The secondary side of the multi-winding transformer includes n groups of three-phase AC windings, and each group of three-phase AC windings is connected to the input ends of the corresponding three power units respectively; The output ends of n power units in each phase are cascaded to form a power branch of one phase; One end of each of the power branches is connected; The other end of each power branch is connected to the capacitor under test through the output end of the testing device; The controller is used to send a corresponding driving signal to the control end of each power unit through the driving circuit, so that the carrier phase of each power unit in the power branch is not completely the same, and the electrical parameter flowing through the capacitor under test is a target test value; The power unit includes: a rectifier, a supporting capacitor and an output H-bridge; The AC side of the rectifier serves as the input end of the power unit; The DC side of the rectifier is connected to the DC side of the output H-bridge, and the support capacitor is provided between the positive and negative connection points; The AC side of the output H-bridge serves as the output end of the power unit; The control end of the output H-bridge at least serves as a part of the control end of the power unit.

2. The capacitor testing device according to claim 1, wherein: In each phase, the carrier phases of the power units are different.

3. The capacitor testing device according to claim 1, wherein: In each phase, the carrier waves of the output H-bridges are staggered by 180° / n.

4. The capacitor testing device according to claim 1, wherein: The rectifier is: a fully controlled rectifier circuit; The control end of the fully-controlled rectifier circuit serves as the other control end of the power unit.

5. The capacitor testing device according to claim 4, characterized in that: The phases of the secondary windings of the multi-winding transformer are the same; In each phase, the carrier waves of the fully-controlled rectifier circuits are staggered by 360° / 3n.

6. The capacitor testing device according to claim 1, wherein: The rectifier is an uncontrolled rectifier circuit.

7. The capacitor testing device according to claim 6, characterized in that: The multi-winding transformer is a phase-shifting transformer, and the phases of the secondary windings of each phase are staggered by 60° / n.

8. The capacitor testing device according to claim 1, wherein: Also includes: step-down transformer; The step-down transformer is arranged between the three-phase power branch and the output end of the testing device.

9. The capacitor testing device according to any one of claims 1 to 8, characterized in that: The source of the driving signal is a modulation module in the controller. When the modulation module outputs a modulation wave in a current control mode, the electrical parameter is current, and the target test value includes any one of the following: The current command value under normal occurrence simulation conditions, the current command value under harmonic occurrence simulation conditions, the current command value under flicker occurrence simulation conditions, the current command value under current mutation simulation conditions, and the current command value under current imbalance simulation conditions.

10. The capacitor testing device according to claim 9, characterized in that: In the current control mode, the two control loops in the modulation module that respectively control the output side active current and the output side reactive current of the test device are both: negative feedback current loops; The current regulator in the negative feedback current loop is a proportional-integral + repetitive controller with a limiting function.

11. The capacitor testing device according to claim 10, characterized in that: The negative feedback current loop further includes a summing connector; the summing connector is used to: Using the actual value of the shaft voltage corresponding to the output side of the test device as a feedforward term, superimposing the output of the current regulator; and / or, When a step-down transformer is provided between the three-phase power branch and the output end of the test device, the product of the actual value of another current on the output side of the test device, the output electrical angular frequency and the equivalent inductance value on the output side is used as the decoupling term to superimpose the output of the current regulator; and the decoupling term corresponding to the active current on the output side is inverted and superimposed.

12. The capacitor testing device according to any one of claims 1 to 8, characterized in that: The source of each of the driving signals is a modulation module in the controller. When the modulation module outputs a modulation wave in a voltage control mode, the electrical parameter is voltage, and the target test value includes any one of the following: The voltage command value under normal simulated working conditions, the voltage command value under harmonic simulated working conditions, the voltage command value under flicker simulated working conditions, the voltage command value under voltage sudden change simulated working conditions, and the voltage command value under voltage unbalance simulated working conditions.

13. The capacitor testing device according to claim 12, wherein: In the voltage control mode, the two control loops in the modulation module that respectively control the d-axis voltage and the q-axis voltage of the output voltage of the test device in a two-phase rotating coordinate system each include: a negative feedback voltage outer loop and a current inner loop; The current inner loop is a current loop that uses the output side active current or the output side reactive current of the test device as negative feedback; The voltage regulator in the negative feedback voltage outer loop is a proportional-integral + repetitive controller with a limiting function; The current regulator in the current inner loop is a proportional controller or a proportional-integral controller with a limiting function.

14. The capacitor testing device according to claim 13, characterized in that: The current inner loop further includes a summing connector; the summing connector is used to: Using the actual value of the shaft voltage corresponding to the output side of the test device as a feedforward term, superimposing the output of the current regulator; and / or, When a step-down transformer is provided between the three-phase power branch and the output end of the test device, the product of the actual value of another current on the output side of the test device, the output electrical angular frequency and the equivalent inductance value on the output side is used as the decoupling term to superimpose the output of the current regulator; and the decoupling term corresponding to the active current on the output side is inverted and superimposed.

15. The capacitor testing device according to any one of claims 1 to 8, characterized in that: Also includes: A first controllable switch provided on each phase branch inside the output end of the test device; and / or, A second controllable switch provided on each phase branch inside the input end of the test device; The first controllable switch and the second controllable switch are controlled by the controller.

16. The capacitor testing device according to any one of claims 1 to 8, characterized in that: Also includes: A discharge circuit is provided outside the output end of the test device and is controlled by the controller, and is used to discharge the capacitor under test after the test of the capacitor under test is stopped.

17. The capacitor testing device according to claim 16, wherein: The discharge circuit includes: three third controllable switches and three discharge resistors; One end of each of the third controllable switches is correspondingly connected to the output end of the testing device; The other end of each of the third controllable switches is connected to the corresponding discharge resistor; The other ends of the bleeder resistors are connected; Each of the third controllable switches is controlled by the controller.

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