CN109188177B - High-power NPC three-level inverter short-circuit current on-line detection system - Google Patents
High-power NPC three-level inverter short-circuit current on-line detection system Download PDFInfo
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- G—PHYSICS
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
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Abstract
The invention provides a high-power NPC three-level inverter short-circuit current on-line detection system, which comprises: the device comprises a di/dt detection unit, a current reduction unit, a short circuit detection unit, a short circuit path identification unit and a current state display unit. When the inverter is short-circuited, the system can rapidly judge the short-circuit type according to the positive bus, the negative bus, the load current and the current change rate of each phase, identifies a fault line and is beneficial to analyzing the cause of the short-circuit fault. Compared with the existing current on-line detection method, the method reduces current detection units, and has better practical operability, stronger detection function and lower detection cost.
Description
Technical Field
The invention relates to the field of detection of power electronic devices, in particular to a high-power NPC three-level inverter short-circuit current on-line detection system.
Background
The Neutral Point Clamped (NPC) three-level inverter is the most widely used three-level topology, and a short circuit fault is an important factor affecting the reliable operation of the system, and when the system is in a short circuit fault, a conventional control system detects the short circuit fault according to a driving board of an IGBT module, and then performs a corresponding shutdown operation. However, the short-circuit fault generated by a certain module is a cause of the short-circuit fault, and especially in the case of secondary fault of the system, the fault association effect prevents the accurate judgment of the short-circuit fault factor.
Conventional short-circuit detection methods such as desaturation method, di/dt detection method, gate charge method, etc. are only used for realizing rapid short-circuit protection, and cannot provide specific short-circuit information. At present, the short circuit condition can be detected by extracting the current of the IGBT module, however, the NPC type three-level single-phase topology has 4 IGBT modules and 2 clamping diode modules, and if the current of each module is independently detected at the same time, 18 current detection units are required for the conventional three-phase high-power NPC three-level topology, so that the cost of system detection is increased undoubtedly.
Disclosure of Invention
The invention aims to provide a high-power NPC three-level inverter IGBT module current on-line detection system, and aims to solve the problems. The invention can reduce the current detection units and accurately judge the current path with short-circuit fault when the short-circuit fault occurs.
In order to achieve the above object, the technical scheme of the present invention is as follows: a high-power NPC three-level inverter short-circuit current on-line detection system comprises: the device comprises a di/dt detection unit, a current reduction unit, a short circuit detection unit, a short circuit path identification unit and a current state display unit; the first output end of the di/dt detection unit is connected with the first input end of the current reduction unit, the second output end of the di/dt detection unit is connected with the first input end of the short circuit detection unit, the first output end of the current reduction unit is connected with the second input end of the short circuit detection unit, the second output end of the current reduction unit is connected with the first input end of the current state display unit, the first output end of the short circuit detection unit is connected with the first input end of the short circuit path identification unit, and the first output end of the short circuit path identification unit is connected with the second input end of the current state display unit; wherein:
di/dt detecting unit for detecting a rate of change di of a current flowing through a single-phase positive bus + Rate of change di of negative bus current/dt - /dt and the rate of change of the load current di L /dt；
A current reduction unit for reducing the current change rate detected by the di/dt detection unit to a measured current value;
the short circuit detection unit is used for detecting a short circuit state, comparing the detected current signal and the current change rate signal with a reference value to judge whether a short circuit fault occurs or not, and outputting an output signal of a comparison result to the short circuit path identification unit;
the short-circuit path identification unit is used for judging a short-circuit path, and stores a relation table of the short-circuit path and the comparison output signal, and the short-circuit path can be obtained through table lookup;
and the current state display unit is used for displaying positive and negative buses and load current output by each phase and displaying a short circuit path when short circuit occurs.
As an improvement of the invention, the di/dt detection unit adopts a flexible Rogowski coil which is respectively sleeved at a positive bus, a negative bus and a load of the A-phase topology.
As an improvement of the invention, the current reduction unit adopts an integrating circuit to respectively carry out integral reduction on the positive bus, the negative bus and the load current change rate output by the di/dt detection unit.
As an improvement of the invention, the integrating circuit is a compound integrating circuit.
As an improvement of the invention, the comparison circuit respectively carries out short circuit detection on the forward current and the reverse current at the load, and carries out short circuit detection on the forward current of the positive bus and the negative bus and the change rate of the forward current.
As an improvement of the invention, an amplifier is additionally arranged at the front end of a comparison circuit of the current change rates of the positive bus and the negative bus in the short circuit detection unit.
As an improvement of the invention, the short-circuit path identification unit divides the short-circuit paths into two types, wherein one type is an inter-bridge arm short-circuit path, and the other type is an intra-bridge arm short-circuit path. The short circuit between bridge arms is that the inverter load is short-circuited, and short-circuit current flows through the load. The bridge arm internal short circuit is a short circuit caused by breakdown or misleading of a power device in the bridge arm, and short circuit current does not pass through a load.
As an improvement of the invention, the current state display unit adopts an AD chip to restore the current to the unitOutput signal VI L ，VI + And VI - Converted into digital signals and stored in a computer together with the short-circuit path identification unit output signals.
As an improvement of the invention, in order to further reduce the number of the current detection units and reduce the cost of the detection system, the load current of the other phase can be obtained by only measuring the load current of any two phases, and the load current of the other phase is the negative number of the sum of the load currents of the other two phases.
As an improvement of the invention, the current reduction unit consists of two composite integrating circuits and an adder.
Compared with the existing short circuit detection method, the invention does not need to detect the current of each module, only needs to detect the current of the positive bus, the negative bus and the load of each phase, not only reduces the current detection unit, but also reduces the number of Rogowski coils in the detection unit. The invention not only can identify the short-circuit fault, but also can determine the path of the short-circuit current flowing, provides more detailed reference for engineering personnel when diagnosing the cause of the short-circuit fault, and is beneficial to improving the efficiency of short-circuit fault diagnosis.
Drawings
The invention will be further described with reference to the accompanying drawings in which:
FIG. 1 is a short circuit current detection system;
FIG. 2 is a schematic diagram of the NPC three level inverter topology and Rogowski coil placement of the present invention;
FIG. 3 is a short circuit current path between legs;
FIG. 4 is a short circuit current path in a bridge arm;
FIG. 5 is a composite integration circuit;
fig. 6A phase load current sense circuit;
FIG. 7 is a modified phase A load current detection circuit;
fig. 8 short path identification rule table.
The specific embodiment is as follows:
in order that the invention may be more clearly understood, a detailed description of the invention will be rendered by reference to the appended drawings and specific embodiments thereof.
Example 1:
referring to fig. 1, a short-circuit current on-line detection system of a high-power NPC three-level inverter according to the present invention includes: the device comprises a di/dt detection unit, a current reduction unit, a short circuit detection unit, a short circuit path identification unit and a current state display unit. The first output end of the di/dt detection unit is connected with the first input end of the current reduction unit, the second output end of the di/dt detection unit is connected with the first input end of the short circuit detection unit, the first output end of the current reduction unit is connected with the second input end of the short circuit detection unit, the second output end of the current reduction unit is connected with the first input end of the current state display unit, the first output end of the short circuit detection unit is connected with the first input end of the short circuit path identification unit, and the first output end of the short circuit path identification unit is connected with the second input end of the current state display unit; wherein:
the di/dt detection unit is used for detecting the current change rate di of the single-phase positive bus + Rate of change di of negative bus current/dt - /dt and the rate of change of the load current di L /dt；
A current reduction unit for reducing the current change rate detected by the di/dt detection unit to a detected current value;
the short circuit detection unit is used for detecting a short circuit state, comparing the detected current signal and the current change rate signal with a reference value to judge whether a short circuit fault occurs or not, and outputting an output signal of a comparison result to the short circuit path identification unit;
the short circuit path identification unit is used for judging a short circuit path, the short circuit path identification unit stores a relation table of the short circuit path and the comparison output signal, and the short circuit path can be obtained through table lookup;
and the current state display unit is used for storing the positive bus, the negative bus and the load current output by each phase and displaying a corresponding short circuit path when short circuit occurs.
The di/dt detection unit adopts a flexible rogowski coil, which is applicable to the installation and measurement of the current of a conductor with a large surface area due to the variable shape. Rogowski coilRespectively sleeved at the positive bus, the negative bus and the load of the A-phase topology, the placement position of the Rogowski coil is shown in figure 2 and Q A1 ~Q A3 For A Xiang Luoshi coil placement, Q B1 ~Q B3 For B Xiang Luoshi coil placement, QC 1 ~Q C3 For the placement position of the C Xiang Luoshi coil, because of the three-level topological three-phase symmetry of the NPC, only one phase is analyzed, and the A-phase topology is taken as an example for analysis.
And the current reduction unit adopts three composite integrating circuits to respectively carry out integral reduction on positive and negative buses and the change rate of load current output by the Rogowski coil. The composite integrating circuit comprises a passive integrating circuit and an active integrating circuit, and can restore high-frequency current through the passive integrating circuit and low-frequency current through the active integrating circuit, thereby being beneficial to improving the measurement precision of short-circuit current. As shown in fig. 5 of the present embodiment, the composite integrating circuit includes a discharge resistor R S Five resistors R 1 ~ R 5 Two capacitors C 1 ~C 2 Two operational amplifiers U 1 ~U 2 . Discharge resistor R S One end and resistor R 2 One end of the discharging resistor R is connected with and receives the output signal of the flexible Rogowski coil S The other end is grounded; resistor R 2 One end, capacitor C 2 One end and an operational amplifier U 1 The positive input end is connected; capacitor C 2 The other end is grounded; resistor R 1 One end, capacitor C 1 One end, resistor R 3 One end and an operational amplifier U 1 The negative input end is connected; resistor R 1 The other end is grounded; capacitor C 1 Another end, resistance R 3 Another end, operational amplifier U 1 Output terminal and amplifier U 2 The positive input end is connected; resistor R 4 One end, resistor R 5 One end and an amplifier U 2 The negative input end is connected; resistor R 4 Grounding; resistor R 5 The other end and amplifier U 2 The output end is connected with and outputs a current reduction signal.
R 2 And C 2 Form a passive integrating circuit, U 1 、R 1 、R 3 And C 1 An active integrating circuit is formed.
Three composite integrating circuits in the current reduction unit output reduction signals which are positive bus current signals VI respectively A+ Negative bus current signal VI A- And a load current signal VI LA 。
The schematic diagram of the short circuit detection unit is shown in fig. 6, and the comparison circuit is used to detect the output values of the di/dt detection unit and the current reduction unit respectively, and the threshold parameter is set to determine whether a short circuit is generated. And comparing the forward current and the reverse current of the load respectively by adopting a double comparator. Because the current and the current change rate on the positive bus and the negative bus are in the positive direction during short circuit, short circuit detection is only needed for the positive current of the positive bus and the negative bus and the positive current change rate thereof. Because the output value of the di/dt detection unit is too small, an operational amplifier is additionally arranged at the front end of the comparison circuit of the current change rates of the positive bus and the negative bus to amplify the detection value.
The short circuit detection unit includes: eight operational amplifiers U 3 ~U 10 Eight resistors R 6 ~R 13 . Operational amplifier U 3 The negative input end is connected with a reference value V REF1 Positive input terminal and operational amplifier U 4 The negative input terminal is connected to and receives the load current signal VI LA The output signal of the output end is V X1 The method comprises the steps of carrying out a first treatment on the surface of the Operational amplifier U 4 The positive input end is connected with a reference value V REF2 The output signal of the output end is V X2 The method comprises the steps of carrying out a first treatment on the surface of the Operational amplifier U 5 The positive input end receives a positive bus current signal VI A+ The negative input end is connected with a reference value V REF3 The output signal of the output end is V X3 The method comprises the steps of carrying out a first treatment on the surface of the Operational amplifier U 8 The positive input end receives the negative bus current signal VI A- The negative input end is connected with a reference value V REF5 The output signal of the output end is V X4 The method comprises the steps of carrying out a first treatment on the surface of the Resistor R 8 One end, resistor R 9 One end and an operational amplifier U 6 The positive input end is connected; resistor R 8 The other end receives a positive bus current change rate signal di A+ Dt, resistance R 9 The other end is grounded; resistor R 6 One end and resistor R 7 One end, operational amplifier U 6 The negative input end is connected with the resistor R 6 The other end is grounded; resistor R 7 The other end and operational amplifier U 6 Output terminal, operational amplifier U 7 The positive input end is connected with an operational amplifier U 6 The output signal is VDI A+ The method comprises the steps of carrying out a first treatment on the surface of the Operational amplifier U 7 The negative input end is connected with a reference value V REF4 The output signal of the output end is VDI 1 The method comprises the steps of carrying out a first treatment on the surface of the Resistor R 12 One end, resistor R 13 One end and an operational amplifier U 9 The positive input end is connected; resistor R 12 The other end receives the positive bus current change rate signal di-/dt and the resistor R 13 The other end is grounded; resistor R 10 One end and resistor R 11 One end, operational amplifier U 9 The negative input end is connected with the resistor R 10 The other end is grounded; resistor R 11 The other end and operational amplifier U 9 Output terminal, operational amplifier U 10 The positive input end is connected with an operational amplifier U 9 The output signal is VDI A- The method comprises the steps of carrying out a first treatment on the surface of the Operational amplifier U 10 The negative input end is connected with a reference value V REF6 The output signal of the output end is VDI 2 。
V X1 When the voltage is high level 1, the positive short circuit current appears at the load, V X2 When the voltage is high level 1, the reverse short circuit current appears at the load, V X3 When the voltage is high level 1, the short circuit current appears in the positive bus, V X4 When the voltage is high-level 1, the short-circuit current appears at the negative bus, and VDI 1 When the voltage is high level 1, the change rate of the short circuit current of the positive bus is higher, and VDI is higher 2 When the voltage is at a high level 1, the change rate of the negative bus short-circuit current is high.
The short circuit path recognition unit adopts an FPGA or CPLD digital chip, and a logic program is arranged in the chip to perform path recognition. The invention divides the short circuit paths into two types, wherein one type is a short circuit path between bridge arms, which is set as a path 1-a path 4, as shown in figure 3; the second type is an internal short-circuit path of the bridge arm, which is set as a path 5 to a path 9, as shown in fig. 4.
In the short-circuit path between bridge arms, the path 1 is that short-circuit current flows from the positive bus to the A-phase first IGBT module T 1 Second IGBT module T 2 And a load L A The method comprises the steps of carrying out a first treatment on the surface of the Path 2 is current flowing from zero bus through first clamp diode modeBlock D 1 Second IGBT module T 2 And a load L A The method comprises the steps of carrying out a first treatment on the surface of the Path 3 is the current from load L A Flow through third IGBT module T 3 Second clamping diode module D 2 Reaching a zero bus; path 4 is the current from load L A Flow through third IGBT module T 3 Fourth IGBT module T 4 Reaching the negative bus.
In the bridge arm internal short-circuit path, the path 5 is that current flows from the positive bus to the first IGBT module T 1 Second IGBT module T 2 Third IGBT module T 3 And a second clamping diode D 2 . Path 6 is current flowing from the positive bus through the first IGBT module T 1 And a first clamping diode D 1 . Path 7 is current flowing from zero bus through first clamp diode D 1 Second IGBT module T 2 Third IGBT module T 3 And a fourth IGBT module T 4 . Path 8 is current flowing from zero bus through second clamping diode D 2 And a fourth IGBT module T 4 . Path 9 is current flowing from the positive bus through the first IGBT module T 1 Second IGBT module T 2 Third IGBT module T 3 And a fourth IGBT module T 4 。
The short circuit path recognition principle is as follows: because the short-circuit current tends to pass through one or two of the positive bus, the negative bus and the load, and the change rate of the short-circuit current is different according to the quantity of the flowing power devices, the short-circuit path is judged by detecting whether the short-circuit current passes through the positive bus, the negative bus and the load and detecting the change rate of the short-circuit current of the positive bus and the negative bus.
When the positive bus and the load simultaneously detect a positive short-circuit current, i.e. VI A+ >V REF3 、VI LA >V REF1 When a short-circuit current flows through the path 1; when a forward short circuit current is detected at only the load, i.e. VI LA >V REF1 At all times, a short-circuit current flows through path 2; when only a load detects a reverse short-circuit current, i.e. VI LA <V REF2 When a short-circuit current flows through the path 3; when a positive short circuit current is detected at the negative bus and a reverse short circuit current is detected at the load, VI A- >V REF5 、VI LA <V REF2 At this time, a short-circuit current flows through the path 4. When a forward short-circuit current is detected at only the positive bus, i.e. VI A+ >V REF3 At the same time, the short-circuit current change rate is smaller, i.e. VDI A+ <V REF4 When the short-circuit current flows through the path 5, and when the short-circuit current change rate is large, i.e. VDI A+ >V REF4 When a short-circuit current flows through the path 6; when a positive short-circuit current is detected at only the negative bus, i.e. VI A- >V REF5 At the same time, the short-circuit current change rate is smaller, i.e. VDI A- <V REF6 When the short-circuit current flows through the path 7, and when the short-circuit current change rate is large, i.e. VDI A- >V REF6 When a short-circuit current flows through the path 8; when I+ and I-detect short-circuit current at the same time, i.e. VI A+ >V REF3 And VI A- >V REF5 At this time, a short-circuit current flows through the path 9.
The path recognition rule table shown in fig. 8 is formulated according to the principle of short-circuit path recognition, and the short-circuit path recognition unit outputs a 4-bit binary signal. When V is X1 -V X4 ，VDI 1 ，VDI 2 A low level 0, a normal state, and a corresponding output signal 0000; when V is X1 And V X3 Meanwhile, when the signal is at a high level 1, the signal is at a short circuit path 1, and the corresponding output signal is 0001; when only V X1 When the signal is at a high level 1, the signal is a short circuit path 2, and the corresponding output signal is 0010; when V is X2 And V X4 Meanwhile, when the signal is at a high level 1, the signal is a short circuit path 3, and the corresponding output signal is 0011; when only V X2 When the signal is at a high level 1, the signal is a short circuit path 4, and the corresponding output signal is 0100; when only V X3 When the signal is at a high level 1, the signal is a short circuit path 5, and the corresponding output signal is 0101; when V is X3 And VDI 1 When the signal is sequentially high level 1 in a short time, the signal is short circuit path 6, and the corresponding output signal is 0110; when only V X4 When the signal is at a high level 1, the signal is a short circuit path 7, and the corresponding output signal is 0111; when V is X4 And VDI 2 When the signal is sequentially high level 1 in a short time, the signal is short-circuit path 8, and the corresponding output signal is 1000; when V is X3 And V X4 At the same time, when the voltage is at high level 1, the voltage is at short circuit path 9, corresponding toIs 1001.
The current state display unit adopts an AD chip to restore the output signal VI of the current reduction unit L ，VI + And VI - The digital signal is converted into a digital signal, and the digital signal is stored in a computer together with a 4-bit binary signal output by a short circuit path identification unit, and waveforms of positive buses, negative buses and load currents of each phase are displayed through an oscilloscope. When a short circuit fault occurs, the short circuit current path displays the corresponding path in the form of a nixie tube; the engineering personnel can judge the cause of the short circuit fault according to the data waveform stored in the computer and the current path displayed by the nixie tube.
Example 2:
because the sum of the three-phase load currents is zero, in order to further reduce the number of the current detection units and reduce the cost of the detection system, only any two-phase load current needs to be measured, and the load current of the other phase is the negative number of the sum of the load currents of the other two phases. Thus, Q in FIG. 1 can be eliminated A3 、Q B3 、Q C3 Rogowski coil and its composite integrating circuit at any position to remove Q A3 For example, the Rogowski coil detects the load current I by the A-phase current reduction unit LA Instead of the composite integration circuit as shown in fig. 7.
The circuit is an adder, which can directly add the input signals and take the negative number. The adder includes: three resistors R 14 ~R 16 An operational amplifier U 11 The method comprises the steps of carrying out a first treatment on the surface of the Wherein the resistance R 14 One end of (a) receives a B-phase load current signal VI LB Resistance R 15 Is connected to one end of the circuit for receiving C-phase load current signal VI LC Operational amplifier U 11 Negative input terminal of (a) and resistor R 14 Another end, resistance R 15 Another end, resistance R 16 One end is connected with an operational amplifier U 11 Is grounded, operational amplifier U 11 Output terminal of (d) and resistor R 16 And the other end is connected with the output signal VI LA 。
It should be noted that the above-mentioned embodiments are merely preferred embodiments of the present invention, and are not intended to limit the scope of the present invention, and equivalent substitutions or alternatives made on the basis of the above-mentioned technical solutions are all included in the scope of the present invention.
Claims (8)
1. An online detection system for short-circuit current of a high-power NPC three-level inverter, which is characterized by comprising: the device comprises a di/dt detection unit, a current reduction unit, a short circuit detection unit, a short circuit path identification unit and a current state display unit;
the first output end of the di/dt detection unit is connected with the first input end of the current reduction unit, the second output end of the di/dt detection unit is connected with the first input end of the short circuit detection unit, the first output end of the current reduction unit is connected with the second input end of the short circuit detection unit, the second output end of the current reduction unit is connected with the first input end of the current state display unit, the first output end of the short circuit detection unit is connected with the first input end of the short circuit path identification unit, and the first output end of the short circuit path identification unit is connected with the second input end of the current state display unit; wherein: the di/dt detection unit is used for detecting the current change rate di+/dt of the single-phase positive bus, the current change rate di-/dt of the negative bus and the current change rate di of the load L /dt；
The di/dt detection unit is used for detecting the current change rate di of the single-phase positive bus + Rate of change di of negative bus current/dt - /dt and the rate of change of the load current di L /dt；
The current reduction unit adopts an integrating circuit to respectively integrate and reduce the positive bus, the negative bus and the load current change rate output by the di/dt detection unit to obtain a measured current value;
the short circuit detection unit is used for detecting output values of the di/dt detection unit and the current reduction unit respectively by adopting a comparison circuit, judging whether a short circuit is generated or not by comparing the output values with a set threshold parameter so as to judge whether a short circuit fault occurs or not, and outputting an output signal of a comparison result to the short circuit path identification unit;
the short circuit path identification unit is used for judging a short circuit path, and the short circuit path identification unit stores a relation table of the short circuit path and the comparison output signal, and can obtain the short circuit path through table lookup;
the current state display unit is used for storing and displaying positive and negative buses and load current output by each phase and displaying a short circuit path when short circuit occurs.
2. The high-power NPC three-level inverter short-circuit current online detection system according to claim 1, wherein the di/dt detection unit adopts a flexible Rogowski coil and is sleeved at a positive bus, a negative bus and a load of an A-phase topology respectively.
3. The high power NPC three level inverter short circuit current online detection system of claim 2, wherein the integration circuit is a composite integration circuit.
4. The system for online detection of short-circuit current of high-power NPC three-level inverter according to claim 3, wherein the comparison circuit performs short-circuit detection on the forward current and the reverse current at the load, and performs short-circuit detection on the forward current of the positive bus and the negative bus and the change rate of the forward current thereof.
5. The system for online detection of short-circuit current of high-power NPC three-level inverter according to claim 4, wherein an amplifier is additionally arranged at the front end of a comparison circuit of current change rates of a positive bus and a negative bus in the short-circuit detection unit.
6. The system for detecting the short-circuit current of the high-power NPC three-level inverter according to claim 1, wherein the current state display unit converts output signals VIL, VI+ and VI < - > of the current reduction unit into digital signals by adopting an AD chip, and stores the digital signals in a computer together with the output signals of the short-circuit path identification unit.
7. The system of claim 1, wherein the detection system only needs to measure the load current of any two phases to obtain the load current of another phase, and the load current of another phase is the negative of the sum of the load currents of other two phases.
8. The system for online detection of short-circuit current of high-power NPC three-level inverter according to claim 7, wherein said current reduction unit is composed of two composite integration circuits and an adder.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
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| CN201811163568.XA CN109188177B (en) | 2018-10-01 | 2018-10-01 | High-power NPC three-level inverter short-circuit current on-line detection system |
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| CN113138354B (en) * | 2021-04-15 | 2023-02-10 | 广东友电新能源科技有限公司 | Self-checking method and system of I-type three-level inverter |
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