CN107884634B - Self-circulation test method of back-to-back converter - Google Patents
Self-circulation test method of back-to-back converter Download PDFInfo
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Abstract
The invention relates to a self-circulation test method of a back-to-back converter, which comprises the following steps: step S1, connecting two alternating current ports of the back-to-back converter together to form an internal current path, and communicating with a control circuit in the back-to-back converter by adopting an upper computer; step S2, testing the internal electrical connection and control functions of the back-to-back converter; step S3, testing the current characteristics of the back-to-back converter; step S4, testing the insulation performance and voltage characteristic of the back-to-back converter; and step S5, testing the power characteristics of the back-to-back converter in a rated working state. The requirements on test conditions and measuring equipment are reduced, and internal errors and defects of the back-to-back converter are positioned and eliminated under safe and reliable conditions.
Description
Technical Field
The invention relates to the technical field of power electronics, in particular to a self-circulation test method for a back-to-back converter.
Background
The back-to-back converter is a common converter type, is formed by connecting two three-phase bridge converters together, can flexibly convert the voltage, frequency, phase number or other electrical characteristics of a power supply system, realizes a required electric energy form and a control strategy, and is widely applied to the fields of motor control, AC-AC frequency conversion, uninterruptible power supplies, wind power generation, power grid energy management and the like at present. A typical back-to-back converter includes two three-phase bridge converters, a dc bus capacitor, a control circuit, a sensor sampling circuit, and a drive protection circuit. A circuit topology of a typical back-to-back converter is shown in fig. 1. The patent back-to-back converter of brushless doubly-fed generator, the patent multilevel converter control system, the patent flexible multi-state switch device and the control method thereof and the like all adopt the back-to-back converter.
The back-to-back converter needs to perform a complex electric energy conversion process in operation, so that sufficient and effective tests must be performed to find internal defects of the converter and eliminate errors and hidden dangers in principle design or production and processing. There are two main types of conventional test methods. One type adopts a digital simulation or semi-physical simulation mode, simulates the working condition of the converter in a numerical calculation mode, and tests the control method and the algorithm strategy of the converter, for example, in the patent "testing method of a wind power converter controller based on dSPACE". However, this kind of test method can only test the control algorithm and the software code, the main circuit of the back-to-back converter (such as the three-phase bridge converter, the dc bus capacitor, etc.) is replaced by the simulation system, and the actual work is not performed, so the working state of the converter hardware cannot be checked, and the actual situation of the back-to-back converter cannot be fully tested.
The other type of the test is carried out according to the real working conditions of the back-to-back converter, for example, in the patent 'a field test and evaluation method of the double-fed converter', the converter is actually connected with the double-fed motor and the power grid according to the actual working state to carry out the test. The test can reflect the real software and hardware states of the converter, but has two disadvantages: firstly, measurement equipment such as a motor, a power grid and an alternating current power supply is needed, and the requirement on test conditions is high; secondly, if the converter is required to operate in a high-voltage and high-power rated working state, if errors, defects or hidden dangers exist in the principle design or production and processing of the back-to-back converter, the back-to-back converter or external measuring equipment is possibly broken down, and even dangers and accidents are caused, so that the personal safety is endangered.
Disclosure of Invention
In view of the foregoing analysis, the present invention aims to provide a self-circulation test method for a back-to-back converter, which is used to solve the problems that the digital simulation method in the prior art cannot sufficiently test the actual condition of the back-to-back converter and has a high requirement on the test condition when testing according to the actual working condition of the back-to-back converter.
The purpose of the invention is mainly realized by the following technical scheme:
the self-circulation test method of the back-to-back converter comprises the following steps:
step S1, connecting two alternating current ports of the back-to-back converter together to form an internal current path, and communicating with a control circuit in the back-to-back converter by adopting an upper computer;
step S2, testing the internal electrical connection and control functions of the back-to-back converter;
step S3, testing the current characteristics of the back-to-back converter;
step S4, testing the insulation performance and voltage characteristic of the back-to-back converter;
and step S5, testing the power characteristics of the back-to-back converter in a rated working state.
Further, in step S1, the two three-phase ac outputs of the back-to-back converter are connected together via the LC filter circuit i and the LC filter circuit ii, and the dc power supply supplies power to the dc bus, thereby forming an internal self-circulation of electric energy.
Further, the step S3 specifically includes:
step S31, testing the power characteristic and the current sampling function of the rated current of the back-to-back converter;
and step S32, testing the current protection function of the back-to-back converter.
Further, the step S4 specifically includes:
step S41, testing the insulation performance and the voltage sampling function of the back-to-back converter;
and step S42, testing the voltage protection function of the back-to-back converter.
Further, in the step S2, the dc power supply outputs low-voltage dc power, and the open-loop inversion PWM algorithm 1 and the PWM algorithm 2 are loaded into the control circuit by the upper computer, where the two algorithms are completely the same, and the control circuit respectively controls the three-phase bridge converter i and the three-phase bridge converter ii to operate in the open-loop inversion state by using the PWM algorithm 1 and the PWM algorithm 2 and by using the driving protection circuit i and the driving protection circuit ii; measuring output voltages of the LC filter circuit I and the LC filter circuit II, and when the output voltages are three-phase sinusoidal alternating-current voltages, indicating that the driving protection circuit I, the driving protection circuit II, the three-phase bridge type converter I and the three-phase bridge type converter II are normal in electrical connection, and simultaneously indicating that the control circuit correctly executes a loaded PWM algorithm 1 and a loaded PWM algorithm 2, so that the control function of the back-to-back converter is verified; otherwise, the back-to-back converter should be checked, and subsequent steps are performed after the fault is found and eliminated.
Further, in step S31, the dc power supply keeps outputting low-voltage dc power unchanged, keeps PWM algorithm 1 unchanged, modifies PWM algorithm 2, and gradually adjusts the phase angle of the modulated wave, thereby increasing the output currents of the three-phase bridge converter i and the three-phase bridge converter ii until reaching the rated current of the back-to-back converter, measures the current at the ABC output terminal of the three-phase bridge converter, reads the current sampling result of the corresponding point in the control circuit through the upper computer, and if the current sampling result is consistent with the measured true current value of the corresponding point, the current sampling function is normal; otherwise, the back-to-back converter should be checked, and subsequent steps are performed after the fault is found and eliminated.
Further, in step S32, the output low-voltage dc power of the dc power supply is kept unchanged, the PWM algorithm 1 is kept unchanged, the PWM algorithm 2 is continuously modified, and the phase angle deviation of the modulation waves of the PWM algorithm 1 and the PWM algorithm 2 is continuously increased until the output currents of the three-phase bridge converter i and the three-phase bridge converter ii exceed the overcurrent protection threshold of the current; reading a protection result signal in the control circuit through an upper computer, and simultaneously measuring voltage waveforms of the driving signals 1 and 2; when the output current is lower than the overcurrent protection threshold value, the read protection result signal is at a high level, and the measured driving signal is in a chopping mode; when the output current exceeds the overcurrent protection threshold, the read protection result signal is at a low level, and the measured driving signal is at a high level, which indicates that the current protection function is normal; otherwise, the back-to-back converter should be checked, and subsequent steps are performed after the fault is found and eliminated.
Further, in the step S41, keeping the PWM algorithm 1 and the PWM algorithm 2 identical; slowly increasing the output voltage of the direct current power supply until the rated value of the direct current bus voltage is reached; measuring output voltages of the LC filter circuit I and the LC filter circuit II, when a sinusoidal alternating current voltage is normally output, proving that the insulation performance of the back-to-back converter is normal, simultaneously measuring a direct current bus voltage and alternating current voltages of the LC filter circuit I and the LC filter circuit II, which are connected with the back-to-back converter, and reading a voltage sampling result in the control circuit through an upper computer; when the voltage sampling result is consistent with the measured real voltage value of the corresponding point, the voltage sampling function is normal; otherwise, the back-to-back converter should be checked, and subsequent steps are performed after the fault is found and eliminated.
Further, in the step S42, the PWM algorithm 1 and the PWM algorithm 2 are continuously kept identical; continuously increasing the output voltage of the direct current power supply until the output voltage exceeds the overvoltage protection threshold of the direct current bus voltage, reading a protection result signal in the control circuit through the upper computer, and simultaneously measuring a driving signal 1 and a driving signal 2; when the output voltage is lower than the overvoltage protection threshold value, the read protection result signal is at a high level, and the measured driving signal is in a chopping mode; when the output voltage exceeds the overvoltage protection threshold, the read protection result signal is at a low level, and the measured driving signal is at a high level, which indicates that the voltage protection function is normal; otherwise, the back-to-back converter should be checked, and subsequent steps are performed after the fault is found and eliminated.
Further, in step S5, the output voltage of the dc power supply is reduced to the rated voltage of the dc bus, the PWM algorithm 1 is kept unchanged, the PWM algorithm 2 is modified, the phase angle deviation is gradually increased until the output current of the back-to-back converter reaches the rated value, and the current between the LC filter circuit i and the LC filter circuit ii is measured; when the measured current value is the same as the rated current; and the measurement continuously outputs rated current within a certain time, so that the converter is proved to normally work or work for a long time in a rated working state; otherwise, the back-to-back converter should be checked to find and remove the fault.
The invention has the following beneficial effects:
the invention provides a self-circulation test method of a back-to-back converter, which is used for testing the internal electrical connection, control function, sampling function, protection function, insulation performance and power characteristic of the back-to-back converter, reducing the requirements on test conditions and measurement equipment, and positioning and eliminating internal errors and defects of the back-to-back converter under safe and reliable conditions.
In the invention, the technical schemes can be combined with each other to realize more preferable combination schemes. Additional features and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
Drawings
The drawings are only for purposes of illustrating particular embodiments and are not to be construed as limiting the invention, wherein like reference numerals are used to designate like parts throughout.
Fig. 1 shows a schematic diagram of a typical back-to-back converter architecture;
fig. 2 shows a flow chart of an implementation of a self-loop test method of a back-to-back converter;
FIG. 3 is a wiring diagram illustrating a self-circulation test method of a back-to-back converter;
fig. 4 shows a typical circuit diagram of a three-phase bridge converter;
fig. 5 shows a circuit diagram of an LC filter circuit.
Detailed Description
The accompanying drawings, which are incorporated in and constitute a part of this application, illustrate preferred embodiments of the invention and together with the description, serve to explain the principles of the invention and not to limit the scope of the invention.
A specific embodiment of the present invention discloses a self-circulation test method for a back-to-back converter, as shown in fig. 2, comprising the following steps:
and step S1, connecting the two alternating current ports of the back-to-back converter together to form an internal current path, and communicating with a control circuit in the back-to-back converter by using an upper computer.
The wiring mode of the self-circulation test method of the back-to-back converter is shown in fig. 3, two paths of three-phase alternating current output of the back-to-back converter are connected together through an LC filter circuit I and an LC filter circuit II, a direct current power supply is connected in parallel at two ends of a direct current bus of the back-to-back converter to supply power to the back-to-back converter, internal self-circulation of electric energy is formed, and the back-to-back converter can normally work under the condition that no external equipment such as a power grid, a generator and a load exists (for the back-to-back converter internally comprising 1 or 2 LC filter circuits, only the LC filter circuit I or the LC filter circuit II added externally needs to be replaced by the LC filter circuit inside.
The back-to-back converter includes: the three-phase bridge type converter I, the three-phase bridge type converter II, direct current bus capacitor, control circuit, sampling circuit, drive protection circuit I, drive protection circuit II. The three-phase bridge type converter I, the three-phase bridge type converter II and the direct current bus capacitor are connected in parallel at two ends of the direct current bus. The sampling circuit samples current and voltage in the circuit and transmits a sampling result to the control circuit; the driving protection circuit I and the driving protection circuit II respectively receive a modulation signal 1 and a modulation signal 2 sent by the control circuit, and respectively send a driving signal 1 and a driving signal 2 to the three-phase bridge type converter I and the three-phase bridge type converter II; the control circuit receives the sampling result of the sampling circuit (the control circuit, the sampling circuit and the drive protection circuit can be applied to the test method provided by the text only by completing corresponding functions, the specific circuit design can be different, and the interface is changed along with the specific design).
The three-phase bridge converter i is identical to the three-phase bridge converter ii, as shown in fig. 4, and includes: a switch tube T1, a switch tube T2, a switch tube T3, a switch tube T4, a switch tube T5 and a switch tube T6. The switch tubes T1-T6 of the three-phase bridge converter can adopt power electronic power devices such as IGBT, MOS tube and thyristor, and the specific element models of the three-phase bridge converter can be reasonably selected according to the specification parameters such as voltage, current and power of the back-to-back converter and are not fixed.
The LC filter circuit i and the LC filter circuit ii are identical, as shown in fig. 5, and include: an inductor L1, an inductor L2, an inductor L3, a capacitor C1, a capacitor C2 and a capacitor C3; one ends of the inductor L1, the inductor L2 and the inductor L3 are respectively the 1, 2 and 3 ends of the LC filter circuit; the other ends of the inductor L1, the inductor L2 and the inductor L3 are respectively the 4, 5 and 6 ends of the LC filter circuit; the other ends of the inductor L1, the inductor L2 and the inductor L3 are grounded through a capacitor C1, a capacitor C2 and a capacitor C3 respectively to serve as a 7 terminal of the LC filter circuit. The inductance and the capacitance in each LC filter circuit should be ensured to be the same as inductance L1, inductance L2 and inductance L3, and the same as capacitance C1, capacitance C2 and capacitance C3 (the specific parameters such as inductance, capacitance and the like can be reasonably selected according to the specification parameters such as the power level and the output frequency of the back-to-back converter, and are not fixed). The ends 1, 2 and 3 of the LC filter circuit I are respectively connected to the A, B, C end of the three-phase bridge current transformer I; the ends 1, 2 and 3 of the LC filter circuit II are respectively connected to the A, B, C end of the three-phase bridge current transformer II; the ends 4, 5 and 6 of the LC filter circuit I are respectively connected to the ends 4, 5 and 6 of the LC filter circuit II; terminals 7 of the two LC filter circuits are both grounded.
The upper computer is connected with the back-to-back converter through a CAN bus and CAN write and read data into and from the control circuit. The upper computer and the back-to-back converter communicate through a CAN bus, and other communication modes (such as JTAG and Ethernet) CAN also be adopted.
And step S2, testing the internal electrical connection and control functions of the back-to-back converter.
The direct-current power supply outputs low-voltage direct current (in the embodiment, the low voltage is selected to be 24V, and the specific voltage value meets the low-voltage level), an open-loop inversion PWM algorithm is loaded into the control circuit through the upper computer, the PWM algorithm comprises a PWM algorithm 1 and a PWM algorithm 2, the two algorithms are completely the same, modulation waves of the algorithms have the same voltage amplitude, the same frequency and the same phase, and the control circuit respectively controls the three-phase bridge converter I and the three-phase bridge converter II to work in an open-loop inversion state through the drive protection circuit I and the drive protection circuit II by utilizing the PWM algorithm 1 and the PWM algorithm 2. Measuring output voltages of an LC filter circuit I and an LC filter circuit II through measuring equipment, if the LC filter circuit I and the LC filter circuit II normally output three-phase sinusoidal alternating-current voltages, the driving protection circuit I, the driving protection circuit II, the three-phase bridge type converter I, the three-phase bridge type converter II and electrical connection of the driving protection circuit I, the driving protection circuit II, the three-phase bridge type converter I and the three-phase bridge type converter II are normal, meanwhile, a control circuit correctly executes a loaded PWM algorithm, and the control function of the back-to-back converter is verified; otherwise, the back-to-back converter should be checked, and subsequent steps are performed after the fault is found and eliminated.
Because the driving protection circuit I and the driving protection circuit II are completely the same, the three-phase bridge converter I and the three-phase bridge converter II are completely the same, the LC filter circuit I and the LC filter circuit II are completely the same, and two paths of PWM algorithms in the control circuit are also completely the same, so the three-phase driving signal 1 and the three-phase driving signal 2 are the same, the pulse width modulation waveform 1 and the pulse width modulation waveform 2 are also the same, fundamental waves have the same voltage amplitude, the same frequency and the same phase, the output of the LC filter circuit I and the LC filter circuit II is three-phase sine alternating current voltage, and no current exists on a connecting line between the three-phase sine alternating current voltage. Namely, the back-to-back converter works under the low-voltage no-load safety condition, so that even if a fault occurs, the equipment cannot be damaged or destroyed excessively, and the test process is safe and reliable.
Step S3, testing the current characteristics of the back-to-back converter.
The current characteristics of the back-to-back converter tested in the low-voltage state of the embodiment comprise the power characteristics of rated current, a current sampling function and a current protection function.
And step S31, testing the power characteristic and the current sampling function of the rated current of the back-to-back converter.
The direct current power supply keeps the low-voltage direct current output in the step S2 unchanged, an open-loop inversion PWM algorithm in a control circuit is modified, a PWM algorithm 1 is kept unchanged, a PWM algorithm 2 is modified, the phase angle of a modulation wave is adjusted step by step, so that the modulation waves of the PWM algorithm 1 and the PWM algorithm 2 have certain phase angle deviation (0-180 degrees), the larger the phase angle deviation is, the larger the three-phase current output by the converter is, and the output currents of the three-phase bridge converter I and the three-phase bridge converter II are increased until the rated current of the back-to-back converter is achieved (for the back-to-back converter, the phase angle deviation of the modulation waves of the two driving algorithms has a direct corresponding relation with the output current of the converter, and the output current can be adjusted until the rated current of the back-to-back converter.
And measuring the current between the LC filter circuit I and the LC filter circuit II by using measuring equipment. If the measured current value is the same as the rated current; and the measurement can continuously output rated current within a certain time (such as 12 hours), so that the back-to-back converter can normally work (or work for a long time) under the rated current; otherwise, the back-to-back converter should be checked, and subsequent steps are performed after the fault is found and eliminated.
The current of the ABC output end of the three-phase bridge type current transformer is measured through measuring equipment (the back-to-back current device comprising the LC filter circuit can also measure the current output by the 456 end of the LC filter circuit), and the current sampling result of the corresponding point in the control circuit is read through an upper computer. If the current sampling result in the control circuit is read by the upper computer to be consistent with the measured real current value of the corresponding point, the current sampling function is normal; otherwise, the back-to-back converter should be checked, and subsequent steps are performed after the fault is found and eliminated.
And step S32, testing the current protection function of the back-to-back converter.
And continuously keeping the low-voltage direct current output by the direct-current power supply unchanged, modifying an open-loop inversion PWM algorithm in the control circuit, keeping the PWM algorithm 1 unchanged, modifying the PWM algorithm 2, and continuously increasing the phase angle deviation (0-180 degrees) of the modulation waves of the PWM algorithm 1 and the PWM algorithm 2, so that the output currents of the three-phase bridge type converter I and the three-phase bridge type converter II are increased until the overcurrent protection threshold value of the current is exceeded. And reading a protection result signal in the control circuit through an upper computer in the process of continuously increasing the current, and simultaneously measuring the voltage waveforms of a driving signal 1 output by the driving protection circuit I and a driving signal 2 output by the driving protection circuit II through measuring equipment (such as an oscilloscope and a voltage probe). When the output current is lower than the overcurrent protection threshold value, the read protection result signal is at a high level, and the measured driving signal is in a chopping mode (namely, the driving signal continuously jumps between the high level and the low level); when the output current exceeds the overcurrent protection threshold, the read protection result signal is at a low level, and the measured drive signal is at a high level, which indicates that the current protection function is normal (in this embodiment, for the protection result signal, the low level represents fault protection, and the high level represents normal; otherwise, the back-to-back converter should be checked, and subsequent steps are performed after the fault is found and eliminated.
And step S4, testing the insulation performance and the voltage characteristic of the back-to-back converter.
The voltage characteristics of the back-to-back converter tested by the embodiment comprise a voltage sampling function and a voltage protection function.
And step S41, testing the insulation performance and the voltage sampling function of the back-to-back converter.
Modifying an open-loop inversion PWM algorithm in a control circuit, and keeping a PWM algorithm 1 and a PWM algorithm 2 completely the same; the output voltage of the dc power supply is slowly increased until the nominal value of the dc bus voltage is reached (typically 700V). And measuring the output voltages of the LC filter circuit I and the LC filter circuit II through measuring equipment, and if the sinusoidal alternating voltage is normally output, the insulation performance of the back-to-back converter is proved to be normal. Meanwhile, the voltage of the direct current bus and the alternating current voltages of the ends 1, 2 and 3 of the LC filter circuit I and the LC filter circuit II can be measured through measuring equipment (the back-to-back current device comprising the LC filter circuit can also measure the voltage output by the end 456 of the LC filter circuit), and the voltage sampling result in the control circuit is read through an upper computer. If the voltage sampling result in the control circuit is read by the upper computer to be consistent with the measured real voltage value of the corresponding point, the voltage sampling function is normal; otherwise, the back-to-back converter should be checked, and subsequent steps are performed after the fault is found and eliminated.
And step S42, testing the voltage protection function of the back-to-back converter.
Continuously keeping the PWM algorithm 1 and the PWM algorithm 2 to be completely the same; and continuously increasing the output voltage of the direct-current power supply on the basis of the rated value of the direct-current bus voltage until the output voltage exceeds the overvoltage protection threshold value of the direct-current bus voltage, reading a protection result signal in the control circuit through an upper computer in the process of continuously increasing the voltage, and measuring a driving signal 1 output by the driving protection circuit I and a driving signal 2 output by the driving protection circuit II through measuring equipment. If the read protection result signal is at a high level when the output voltage is lower than the overvoltage protection threshold value, the measured driving signal is in a chopping mode (namely, the driving signal continuously jumps between the high level and the low level); when the output voltage exceeds the overvoltage protection threshold, the read protection result signal is at a low level, and the measured driving signal is at a high level, which indicates that the voltage protection function is normal (in this embodiment, for the result protection signal, the low level represents fault protection, and the high level represents normal; otherwise, the back-to-back converter should be checked, and subsequent steps are performed after the fault is found and eliminated.
And step S5, testing the power characteristics of the back-to-back converter in a rated working state.
Reducing the output voltage of the direct current power supply to the rated voltage of the direct current bus, modifying an open-loop inversion PWM algorithm in a control circuit, keeping a PWM algorithm 1 unchanged, modifying a PWM algorithm 2, and gradually increasing phase angle deviation (0-180 degrees) until the output current of the back-to-back converter reaches the rated value. At the moment, the back-to-back power converter works at rated voltage and rated current, and the current between the LC filter circuit I and the LC filter circuit II is measured through measuring equipment. When the measured current value is the same as the rated current; and the rated current is continuously output within a certain time (such as 12 hours) by measurement, so that the fact that the converter can normally work (or work for a long time) in a rated working state is proved; otherwise, the back-to-back converter should be checked to find and remove the fault.
In summary, the embodiment of the present invention provides a self-circulation testing method for a back-to-back converter. According to the testing method provided by the text, two paths of three-phase alternating current outputs of the back-to-back converter are connected together through two LC filter circuits to form an internal current path, so that the back-to-back converter can output rated current in the circuit topology and can be tested, the requirements on equipment such as a power grid, a motor and an actual load are saved, and the testing cost is reduced. The testing is carried out according to the testing sequence from low voltage to high voltage and from no load to rated working condition, the internal electrical connection, the control function, the sampling function, the protection function, the insulation performance and the power characteristic of the back-to-back converter are tested, the internal hardware errors and defects of the back-to-back converter are positioned and eliminated under safe and reliable conditions, the risk of damage to the back-to-back converter or external measuring equipment in the testing process is greatly reduced and even avoided, and serious faults or safety accidents are prevented.
Those skilled in the art will appreciate that all or part of the flow of the method implementing the above embodiments may be implemented by a computer program, which is stored in a computer readable storage medium, to instruct related hardware. The computer readable storage medium is a magnetic disk, an optical disk, a read-only memory or a random access memory.
The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are included in the scope of the present invention.
Claims (8)
1. A self-circulation test method of a back-to-back converter is characterized by comprising the following steps:
step S1, connecting two alternating current ports of the back-to-back converter together to form an internal current path, and communicating with a control circuit in the back-to-back converter by adopting an upper computer;
step S2, testing the internal electrical connection and control functions of the back-to-back converter;
step S3, testing the current characteristics of the back-to-back converter;
step S4, testing the insulation performance and voltage characteristic of the back-to-back converter;
step S5, testing the power characteristics of the back-to-back converter in a rated working state;
in the step S1, two paths of three-phase ac outputs of the back-to-back converter are connected together through the LC filter circuit i and the LC filter circuit ii, and the dc power supply supplies power to the dc bus, thereby forming internal self-circulation of electric energy;
in the step S2, the direct-current power supply outputs low-voltage direct current, an open-loop inversion PWM algorithm 1 and a PWM algorithm 2 are loaded into the control circuit by the upper computer, the two algorithms are completely the same, and the control circuit respectively controls the three-phase bridge converter i and the three-phase bridge converter ii to operate in an open-loop inversion state by the drive protection circuit i and the drive protection circuit ii by using the PWM algorithm 1 and the PWM algorithm 2; measuring output voltages of the LC filter circuit I and the LC filter circuit II, and when the output voltages are three-phase sinusoidal alternating-current voltages, indicating that the driving protection circuit I, the driving protection circuit II, the three-phase bridge type converter I and the three-phase bridge type converter II are normal in electrical connection, and simultaneously indicating that the control circuit correctly executes a loaded PWM algorithm 1 and a loaded PWM algorithm 2, so that the control function of the back-to-back converter is verified; otherwise, the back-to-back converter should be checked, and subsequent steps are performed after the fault is found and eliminated.
2. The self-circulation test method of the back-to-back converter according to claim 1, wherein the step S3 specifically comprises:
step S31, testing the power characteristic and the current sampling function of the rated current of the back-to-back converter;
and step S32, testing the current protection function of the back-to-back converter.
3. The self-circulation test method of the back-to-back converter according to claim 1, wherein the step S4 specifically comprises:
step S41, testing the insulation performance and the voltage sampling function of the back-to-back converter;
and step S42, testing the voltage protection function of the back-to-back converter.
4. The self-circulation test method of the back-to-back converter according to claim 2, wherein in the step S31, the dc power supply keeps outputting the low voltage dc current unchanged, keeps the PWM algorithm 1 unchanged, modifies the PWM algorithm 2, gradually adjusts the phase angle of the modulation wave, thereby increasing the output current of the three-phase bridge converter i and the three-phase bridge converter ii until reaching the rated current of the back-to-back converter, measures the current at the ABC output terminal of the three-phase bridge converter, reads the current sampling result of the corresponding point in the control circuit through the upper computer, and if the current sampling result is consistent with the measured true current value of the corresponding point, the current sampling function is normal; otherwise, the back-to-back converter should be checked, and subsequent steps are performed after the fault is found and eliminated.
5. The self-circulation test method of the back-to-back converter according to claim 4, wherein in the step S32, the output low voltage dc of the dc power supply is kept unchanged, the PWM algorithm 1 is kept unchanged, the PWM algorithm 2 is continuously modified, and the phase angle deviation of the modulation waves of the PWM algorithm 1 and the PWM algorithm 2 is continuously increased until the output currents of the three-phase bridge converter i and the three-phase bridge converter ii exceed the overcurrent protection threshold of the current; reading a protection result signal in the control circuit through an upper computer, and simultaneously measuring voltage waveforms of the driving signals 1 and 2; when the output current is lower than the overcurrent protection threshold value, the read protection result signal is at a high level, and the measured driving signal is in a chopping mode; when the output current exceeds the overcurrent protection threshold, the read protection result signal is at a low level, and the measured driving signal is at a high level, which indicates that the current protection function is normal; otherwise, the back-to-back converter should be checked, and subsequent steps are performed after the fault is found and eliminated.
6. The self-circulation test method of the back-to-back converter according to claim 3, wherein in the step S41, the PWM algorithm 1 and the PWM algorithm 2 are kept identical; slowly increasing the output voltage of the direct current power supply until the rated value of the direct current bus voltage is reached; measuring output voltages of the LC filter circuit I and the LC filter circuit II, when a sinusoidal alternating current voltage is normally output, proving that the insulation performance of the back-to-back converter is normal, simultaneously measuring a direct current bus voltage and alternating current voltages of the LC filter circuit I and the LC filter circuit II, which are connected with the back-to-back converter, and reading a voltage sampling result in the control circuit through an upper computer; when the voltage sampling result is consistent with the measured real voltage value of the corresponding point, the voltage sampling function is normal; otherwise, the back-to-back converter should be checked, and subsequent steps are performed after the fault is found and eliminated.
7. The self-circulation test method of the back-to-back converter according to claim 6, wherein in the step S42, the PWM algorithm 1 and the PWM algorithm 2 are continuously kept identical; continuously increasing the output voltage of the direct current power supply until the output voltage exceeds the overvoltage protection threshold of the direct current bus voltage, reading a protection result signal in the control circuit through the upper computer, and simultaneously measuring a driving signal 1 and a driving signal 2; when the output voltage is lower than the overvoltage protection threshold value, the read protection result signal is at a high level, and the measured driving signal is in a chopping mode; when the output voltage exceeds the overvoltage protection threshold, the read protection result signal is at a low level, and the measured driving signal is at a high level, which indicates that the voltage protection function is normal; otherwise, the back-to-back converter should be checked, and subsequent steps are performed after the fault is found and eliminated.
8. The self-circulation test method of the back-to-back converter according to claim 1, wherein in step S5, the output voltage of the dc power supply is decreased to the rated voltage of the dc bus, the PWM algorithm 1 is kept unchanged, the PWM algorithm 2 is modified, the phase angle deviation is gradually increased until the output current of the back-to-back converter reaches the rated value, and the current between the LC filter circuit i and the LC filter circuit ii is measured; when the measured current value is the same as the rated current; and the measurement continuously outputs rated current within a certain time, so that the converter is proved to normally work or work for a long time in a rated working state; otherwise, the back-to-back converter should be checked to find and remove the fault.
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