CN107332267B - Control method and system for avoiding continuous low of extra-high voltage direct current power - Google Patents
Control method and system for avoiding continuous low of extra-high voltage direct current power Download PDFInfo
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- H—ELECTRICITY
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
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Abstract
The invention discloses a control method and a system for avoiding the continuous low of extra-high voltage direct current power, which comprises the following steps: calculating a harmonic distortion rate of the voltage of the converter bus; judging whether the alternating voltage distortion is caused by the excitation inrush current or not according to the voltage harmonic distortion rate; judging whether the excitation surge current enters a descending trend or not according to the voltage harmonic distortion rate; when the alternating voltage distortion is caused by the magnetizing inrush current and the magnetizing inrush current enters a descending trend, the output value of the commutation failure prediction function is reduced. The technical scheme provided by the invention avoids the problem that the extra-high voltage direct current power is continuously low due to the magnetizing inrush current, not only supports small-range modification of programs, but also has universal applicability.
Description
Technical Field
The invention relates to the field of extra-high voltage direct current, in particular to a control method and a control system for avoiding the continuous low of extra-high voltage direct current power.
Background
The excitation inrush current can cause the voltage distortion of a converter bus, possibly causes the continuous action of a commutation failure prediction function in the extra-high voltage direct current control system, and the direct current power is maintained in a low state in a short time. In 2016, 3 and 21 days, excitation inrush current generated by charging of a transformer of an official transformer substation causes the commutation failure prediction function of a Tianshan-Zhongzhou extra-high voltage direct current system to continuously act, and the direct current power fluctuation time reaches 13 s.
In a direct-current power transmission control system, in order to reduce the risk of phase commutation failure caused by alternating-current fault, a phase commutation failure prediction function is introduced, and the direct-current power transmission control system comprises two parallel calculation parts. One part is to perform zero sequence detection of three-phase ac voltages to detect whether a single-phase ac fault occurs, and the other part is to use α β variation of ac voltages to detect a three-phase fault. After the alternating current fault is detected, an output value AMIN _ CFPREV of a commutation failure prediction function is increased, and the AMIN _ CFPREV is subtracted from an output firing angle command value of the inverter maximum firing angle regulator, so that the inverter is triggered in advance, and the capability of resisting commutation failure is improved.
For commutation bus voltage distortion caused by excitation inrush current, under the condition that the distortion is not serious but reaches a commutation failure prediction function fixed value, the commutation failure prediction function acts, the commutation failure caused by the excitation inrush current can be avoided, but the direct current power is continuously low, only after the excitation inrush current is attenuated to a certain degree, the commutation failure prediction function can be quitted, the excitation inrush current is generally attenuated slowly, so that the direct current low-power operation lasts for a long time, certain impact is generated on an alternating current system, and the stable operation of the alternating current and direct current system is influenced.
At present, a measure for inhibiting the magnetizing inrush current is to install a phase selection switching-on device or a switching-on resistor on a transformer, try to reduce the magnetizing inrush current from the source and avoid the problem that the magnetizing inrush current flows into a power grid to cause the operation of other equipment.
When the circuit breaker is closed to charge the large-capacity transformer, the generated surge current is called magnetizing inrush current. The magnetizing inrush current contains a large number of low harmonic components (mainly the second and third harmonics) and has a long decay time. The influence of the magnetizing inrush current on the special direct current transmission system is mainly reflected in that the magnetizing inrush current can cause voltage distortion of a converter bus, possibly leading to continuous action of a commutation failure prediction function in an extra-high voltage direct current control system, and direct current power is maintained in a low state in a short time, so that impact is caused on an accessed alternating current system, and the stable operation of the alternating current system is influenced.
Although the generation of the magnetizing inrush current can be inhibited by additionally installing the phase selection switching-on device or installing the switching-on resistor on the transformer, the range of the transformer substation where the switching-on magnetizing inrush current causes the disturbance of the direct current system cannot be determined due to the complex structure of the real power grid, and if the phase selection switching-on device or the switching-on resistor is installed in a large area, the operation cost can be greatly increased.
As can be seen from the above analysis, the addition of the phase selection switching-on device or the installation of the switching-on resistor to the transformer can suppress the generation of the magnetizing inrush current, but the range of the transformer substation to be added cannot be determined, and the operation cost is increased; at present, the control logic of a direct current system does not consider the characteristic of magnetizing inrush current, and after the magnetizing inrush current enters a commutation bus, a commutation failure prediction function possibly acts for a long time, so that disturbance is caused to the alternating current and direct current system.
Therefore, in order to solve the above problems, the present invention provides a method and a system for controlling the continuous low of the extra-high voltage dc power.
Disclosure of Invention
In order to overcome the defects in the prior art, the invention provides a control method and a control system for avoiding the continuous low of extra-high voltage direct current power.
The technical scheme provided by the invention is as follows:
a control method for avoiding continuous low of extra-high voltage direct current power comprises the following steps:
calculating a harmonic distortion rate of the voltage of the converter bus;
judging whether the alternating voltage distortion is caused by the excitation inrush current or not according to the voltage harmonic distortion rate;
judging whether the excitation surge current enters a descending trend or not according to the voltage harmonic distortion rate;
when the alternating voltage distortion is caused by the magnetizing inrush current and the magnetizing inrush current enters a descending trend, the output value of the commutation failure prediction function is reduced.
Preferably, the harmonic distortion factor of the voltage of the commutation bus is calculated according to the following formula:
in the formula: THDv: the harmonic distortion rate of the voltage of the converter bus; u shapen: when n is>When 1, the voltage of the nth harmonic wave is expressed as an effective value; u shape1: the effective value of the fundamental voltage.
Preferably, the determining whether the alternating voltage distortion is caused by the magnetizing inrush current according to the voltage harmonic distortion rate includes:
and when the harmonic distortion duration time is larger than the time threshold and the commutation failure prediction function is continuously started, judging that the alternating voltage distortion is caused by the magnetizing inrush current.
Preferably, the harmonic distortion duration being greater than a time threshold includes:
and comparing the three-phase voltage harmonic distortion rate with a distortion rate threshold after taking the maximum value of the three voltage harmonic distortion rates, and if the three voltage harmonic distortion rates are greater than the radian threshold and the duration is greater than a time threshold, judging that the harmonic distortion duration is greater than the time threshold.
Preferably, the commutation failure prediction function is continuously started, and includes:
and judging whether the radian output by the commutation failure prediction function is larger than a radian threshold or not according to the radian output by the commutation failure prediction function, and if the radian is larger than the radian threshold and the duration is larger than a time threshold, judging that the commutation failure prediction function is continuously started.
Preferably, the determining whether the magnetizing inrush current enters the downward trend according to the voltage harmonic distortion rate includes:
if the value of the harmonic distortion rate of the three-phase voltage divided by the value of the harmonic distortion rate of the three-phase voltage after the filtering link is less than 1 and the value of the harmonic distortion rate of the three-phase voltage divided by the value of the harmonic distortion rate after the filtering link is delayed by a time threshold, the harmonic distortion caused by the existing excitation inrush current is judged to enter a descending trend.
Preferably, the reducing the output value of the commutation failure prediction function when the ac voltage distortion is caused by the magnetizing inrush current and the magnetizing inrush current goes into a downward trend includes:
when the alternating voltage distortion is caused by the magnetizing inrush current and the magnetizing inrush current enters a downward trend, the output value of the commutation failure prediction function is set to 0.
Preferably, the time threshold is 300 ms;
the distortion rate threshold is 0.02;
the radian threshold is 0.02.
A control system for avoiding sustained low of extra-high voltage dc power, the system comprising: the device comprises a calculation module, a first judgment module, a second judgment module and an output module;
the calculation module is used for calculating the voltage harmonic distortion rate of the current conversion bus;
the first judging module is used for judging whether the alternating voltage distortion is caused by the excitation inrush current or not according to the voltage harmonic distortion;
the second judging module is used for judging whether the excitation surge current enters a descending trend or not according to the voltage harmonic distortion;
and the output module is used for reducing the output value of the commutation failure prediction function when the alternating voltage distortion is caused by the excitation inrush current and the excitation inrush current enters a downward trend.
Preferably, the calculating module is configured to calculate the harmonic distortion rate of the voltage of the commutation bus according to the following formula:
in the formula: THDv: the harmonic distortion rate of the voltage of the converter bus; u shapen: when n is>When 1, the voltage of the nth harmonic wave is expressed as an effective value; u shape1: the effective value of the fundamental voltage.
Preferably, the first judging module comprises a duration judging submodule and a duration starting submodule;
the duration judgment submodule is used for comparing the three-phase voltage harmonic distortion rate after taking the maximum value of the three voltage harmonic distortion rates with a distortion rate threshold, judging that the harmonic distortion lasts more than a time threshold when the three voltage harmonic distortion rates are larger than the distortion rate threshold and the delay is larger than the time threshold;
and the continuous promoter module is used for judging that the radian is larger than a radian threshold value and the time delay is larger than a time threshold value according to the radian output by the commutation failure prediction function, and judging that the commutation failure prediction function is continuously started.
Preferably, the second judging module comprises a ratio judging submodule and a delay judging submodule;
the ratio judgment submodule is used for judging whether the value obtained by dividing the harmonic distortion rate of the three-phase voltage by the value obtained by the filtering link is less than 1 or not;
and the delay judgment submodule is used for judging whether the lasting time of the three-phase voltage harmonic distortion rate divided by the value of the three-phase voltage harmonic distortion rate passing through the filtering link is less than 1 is more than or equal to a time threshold value or not.
Compared with the prior art, the invention has the beneficial effects that:
the invention provides a method for calculating the voltage harmonic distortion of a converter bus to judge the attenuation trend of magnetizing inrush current and synchronously reducing the output value of a commutation failure prediction function, which avoids the problem that the ultrahigh voltage direct current power is continuously low due to magnetizing inrush current;
the technical scheme provided by the invention has no direct relation with specific engineering parameters, and has universal applicability to different direct current projects;
according to the technical scheme provided by the invention, the direct current transmission control system adopts a modularized full-graphical programming language, the small-range modification of the program is supported, and the newly added logic of the method can be started only under the condition that the continuous distortion of the converter bus voltage is caused by low-order harmonic waves, so that the control of the direct current system in a normal operation state and other fault states can not be influenced.
Drawings
FIG. 1 is a flow chart of a control method for continuously lowering extra-high voltage DC power;
FIG. 2 is a schematic diagram of the commutation failure prediction function control logic of the present invention;
FIG. 3 is a schematic diagram of a comparison of the power delivered by the improved front and rear dipoles of the present invention;
wherein, 1: harmonic distortion rate of a-phase voltage, 2: harmonic distortion rate of B-phase voltage, 3: harmonic distortion rate of C-phase voltage, 4: commutation failure prediction function, 5; radian output by commutation failure prediction function, 6: before improvement, 7: after the improvement.
Detailed Description
For a better understanding of the present invention, reference is made to the following description taken in conjunction with the accompanying drawings and examples.
In the current commutation failure prediction function, a zero sequence channel mainly acts after the occurrence of the excitation inrush current, but according to waveform analysis, a calculated value of the zero sequence channel is a discontinuous variable and does not visually reflect the harmonic change condition of the excitation inrush current. Therefore, the low-order harmonic component in the voltage of the current conversion bus in the FFT algorithm decomposition is considered, and the attenuation trend of the harmonic component in the excitation surge current is judged according to the voltage harmonic distortion rate. The voltage harmonic distortion rate is a continuous variable. The method determines the attenuation trend of the magnetizing inrush current by calculating the voltage harmonic distortion of the converter bus, synchronously reduces the output value of the commutation failure prediction function, and solves the problem that the ultrahigh voltage direct current power is continuously low due to the magnetizing inrush current on the premise of avoiding direct current commutation failure caused by the magnetizing inrush current.
The invention provides a method and a system for controlling continuous low of extra-high voltage direct current power. The method for controlling the continuous low of the extra-high voltage direct current power specifically comprises the following steps:
(1) calculating the harmonic distortion rate of the voltage of the current conversion bus
The degree of Voltage waveform Distortion is measured by the Voltage sinusoidal wave Distortion rate, also known as the Voltage Harmonic Distortion rate (THDv). The voltage harmonic distortion rate is expressed as a percentage of the ratio of the root mean square value of each harmonic voltage to the effective value of the fundamental voltage. Considering that the magnetizing inrush current mainly contains low-order harmonics, and the high-order harmonics are too small to be ignored, the voltage harmonic distortion rate is only calculated to 13 th harmonic in the invention. The voltage harmonic distortion THDv calculation formula is as follows.
In the formula: u shapen: when n is>When 1, the voltage of the nth harmonic wave is expressed as an effective value; u shape1: the effective value of the fundamental voltage.
How to realize the control of the output value of the commutation failure prediction function CFPREV is further explained below with reference to the schematic control logic diagram of the commutation failure prediction function shown in fig. 2.
(2) Determining whether AC voltage distortion is caused by magnetizing inrush current
UA _ THDV, UB _ THDV and UC _ THDV are respectively the harmonic distortion rate 1 of the A-phase voltage, the harmonic distortion rate 2 of the B-phase voltage and the harmonic distortion rate 3 of the C-phase voltage of the commutation bus. Determination condition 1: after the maximum value of the three-phase voltage harmonic distortion is obtained, the three-phase voltage harmonic distortion is compared with 0.02, the delay time is more than 0.02 and 300ms, namely the harmonic distortion lasts for more than 300ms, and the harmonic distortion can be considered as the harmonic distortion caused by the excitation inrush current; determination condition 2: CFPREV _ RAD is radian 5 output by the commutation failure prediction function, and is judged to be more than 0.02 time delay 300ms, which indicates that the commutation failure prediction function is continuously started. If the phase of the determination conditions 1 and 2 is equal to 1, it is determined that the ac voltage distortion is caused by the magnetizing inrush current.
(3) Judging the descending trend of the magnetizing inrush current
Determination condition 3: after the harmonic distortion rates of the three-phase voltage are divided by the values of the three-phase voltage through the filtering link, the obtained values are smaller than 1, the harmonic distortion rates of the phase voltage are in a decreasing trend, after the 300ms delay link, the harmonic distortion rates of the three-phase voltage are judged to be continuously decreased for 300ms, and if the judgment value is 1, the harmonic distortion caused by the existing excitation inrush current enters a downward trend.
(4) When the alternating voltage distortion is caused by the excitation inrush current and the excitation inrush current enters a descending trend, the output value of the commutation failure prediction function is reduced
When the determination conditions 1, 2, and 3 are satisfied, the CFPREV _ SET variable is 1, and the commutation failure prediction function 4 is reset, so that the output value 5 of the commutation failure prediction function CFPREV is zero, and the output CFPREV _ RAD thereof gradually decreases to 0 due to the delay.
Commutation failure prediction function 4: comprises two parallel parts: one is zero sequence detection to detect whether a single phase ac fault occurs; another is to use the alpha/beta variation of the ac voltage to detect three-phase faults.
The specific detection principle comprises:
when a single-phase fault occurs, the sum of the three-phase voltages is not 0;
when three-phase faults occur, the vector obtained by alpha/beta change is smaller than a steady-state value;
the detection of the AC fault can increase the CFPREV _ RAD value and cause the inverter to trigger in advance, so that the probability of the occurrence of phase commutation failure is reduced.
Through the judgment logic, the commutation failure prediction continuous action caused under the continuous action of the excitation inrush current can be determined, when the harmonic wave caused by the excitation inrush current enters a reduction trend and reaches a threshold value, the output value of the commutation failure prediction function is reduced, and the direct-current system can be quickly restored to the original steady-state operation condition while the commutation failure is avoided.
As can be seen from the comparison diagram of the improved front and rear bipolar transmission powers shown in fig. 3, by adding the magnetizing inrush current determination logic, the connection between the dc control system and the magnetizing inrush current harmonic is accurately established, and after the harmonic caused by the magnetizing inrush current enters the attenuation trend, the commutation failure prediction function is exited, so that the dc system is more quickly restored to the original steady-state operation condition. By improving the comparison of the transmission power of the front and the rear double poles, the transmission power of the rear double pole is improved by 1s before the improvement and is recovered to the original operation condition.
Correspondingly, the invention also provides a control system for continuously reducing the extra-high voltage direct current power, which comprises: the device comprises a calculation module, a first judgment module, a second judgment module and an output module;
the calculation module is used for calculating the voltage harmonic distortion rate of the current conversion bus;
the first judgment module is used for judging whether the alternating voltage distortion is caused by the excitation inrush current or not according to the voltage harmonic distortion rate;
the second judgment module is used for judging whether the excitation surge current enters a descending trend or not according to the voltage harmonic distortion rate;
and the output module is used for reducing the output value of the commutation failure prediction function when the alternating voltage distortion is caused by the excitation inrush current and the excitation inrush current enters a downward trend.
The calculation module is used for calculating the harmonic distortion rate of the voltage of the commutation bus according to the following formula:
in the formula: THDv: the harmonic distortion rate of the voltage of the converter bus; u shapen: when n is>When 1, the voltage of the nth harmonic wave is expressed as an effective value; u shape1: the effective value of the fundamental voltage.
The first judgment module comprises a duration judgment submodule and a duration starting submodule;
the duration judgment submodule is used for comparing the maximum value of the three-phase voltage harmonic distortion rate with a radian threshold value, judging that the harmonic distortion lasts more than a time threshold value when the maximum value is larger than the radian threshold value and the delay is larger than the time threshold value;
and the continuous promoter module is used for judging that the radian is larger than a radian threshold value and the time delay is larger than a time threshold value according to the radian output by the commutation failure prediction function, and judging that the commutation failure prediction function is continuously started.
The second judgment module comprises a ratio judgment submodule and a delay judgment submodule;
the ratio judgment submodule is used for judging whether the value obtained by dividing the harmonic distortion rate of the three-phase voltage by the value obtained by the filtering link is less than 1 or not;
and the delay judgment submodule is used for judging whether the lasting time of the three-phase voltage harmonic distortion rate divided by the value of the three-phase voltage harmonic distortion rate passing through the filtering link is less than 1 is more than or equal to a time threshold value or not.
As will be appreciated by one skilled in the art, embodiments of the present application may be provided as a method, system, or computer program product. Accordingly, the present application may take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment combining software and hardware aspects. Furthermore, the present application may take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, and the like) having computer-usable program code embodied therein.
The present application is described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the application. It will be understood that each flow and/or block of the flow diagrams and/or block diagrams, and combinations of flows and/or blocks in the flow diagrams and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instruction means which implement the function specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
The present invention is not limited to the above embodiments, and any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention are included in the scope of the claims of the present invention which are filed as the application.
Claims (7)
1. A control method for avoiding continuous low of extra-high voltage direct current power is characterized by comprising the following steps:
calculating a harmonic distortion rate of the voltage of the converter bus;
judging whether the alternating voltage distortion is caused by the excitation inrush current or not according to the voltage harmonic distortion rate;
judging whether the excitation surge current enters a descending trend or not according to the voltage harmonic distortion rate;
when the alternating voltage distortion is caused by excitation inrush current and the excitation inrush current enters a descending trend, reducing an output value of a commutation failure prediction function;
the method for determining whether the alternating voltage distortion is caused by the magnetizing inrush current according to the voltage harmonic distortion rate comprises the following steps: when the duration time of harmonic distortion is longer than a time threshold and the commutation failure prediction function is continuously started, judging that the alternating voltage distortion is caused by excitation inrush current;
the step of judging whether the excitation surge current enters a descending trend according to the voltage harmonic distortion rate comprises the following steps:
if the harmonic distortion rate of the three-phase voltage is divided by the value of the harmonic distortion rate of the three-phase voltage passing through the filtering link and is less than 1, and the time is delayed by a time threshold, it is judged that the harmonic distortion caused by the current excitation inrush current enters a descending trend;
when alternating voltage distortion is caused by excitation inrush current and the excitation inrush current enters a downward trend, the output value of the commutation failure prediction function is reduced, and the commutation failure prediction method comprises the following steps:
when the alternating voltage distortion is caused by the magnetizing inrush current and the magnetizing inrush current enters a downward trend, the output value of the commutation failure prediction function is set to 0.
2. The control method for avoiding the ultra-high voltage direct current power from being continuously low as claimed in claim 1, wherein the calculating of the harmonic distortion rate of the converter bus voltage is calculated according to the following formula:
in the formula: THDv: the harmonic distortion rate of the voltage of the converter bus; u shapen: when n is>When 1, the voltage of the nth harmonic wave is expressed as an effective value; u shape1: the effective value of the fundamental voltage.
3. The control method for avoiding the ultra-high voltage direct current power from being continuously low as claimed in claim 1, wherein the specific judgment step that the harmonic distortion duration is greater than the time threshold is as follows:
and comparing the three-phase voltage harmonic distortion rate with a distortion rate threshold after taking the maximum value of the three voltage harmonic distortion rates, and if the three voltage harmonic distortion rates are greater than the distortion rate threshold and the duration is greater than a time threshold, determining that the harmonic distortion duration is greater than the time threshold.
4. The control method for avoiding the continuous low of extra-high voltage direct current power as claimed in claim 3, wherein the specific steps of the commutation failure prediction function in the continuous start are as follows:
and judging whether the radian output by the commutation failure prediction function is larger than a radian threshold or not according to the radian output by the commutation failure prediction function, and if the radian is larger than the radian threshold and the duration is larger than a time threshold, judging that the commutation failure prediction function is continuously started.
5. The control method for avoiding the continuous low of extra-high voltage direct current power as claimed in claim 4, wherein the time threshold is 300 ms;
the distortion rate threshold is 0.02;
the radian threshold is 0.02.
6. A control system for avoiding continuous low of extra-high voltage direct current power, which is characterized in that the system comprises: the device comprises a calculation module, a first judgment module, a second judgment module and an output module;
the calculation module is used for calculating the voltage harmonic distortion rate of the current conversion bus;
the first judging module is used for judging whether the alternating voltage distortion is caused by the excitation inrush current or not according to the voltage harmonic distortion;
the second judging module is used for judging whether the excitation surge current enters a descending trend or not according to the voltage harmonic distortion;
the output module is used for reducing the output value of the commutation failure prediction function when the alternating voltage distortion is caused by the excitation inrush current and the excitation inrush current enters a downward trend;
the first judgment module comprises a duration judgment submodule and a duration starting submodule;
the duration judgment submodule is used for comparing the three-phase voltage harmonic distortion rate after taking the maximum value of the three voltage harmonic distortion rates with a distortion rate threshold, judging that the harmonic distortion lasts more than a time threshold when the three voltage harmonic distortion rates are larger than the distortion rate threshold and the delay is larger than the time threshold;
the continuous promoter module is used for judging that the radian is larger than a radian threshold value and the time delay is larger than a time threshold value according to the radian output by the commutation failure prediction function, and judging that the commutation failure prediction function is continuously started;
the second judgment module comprises a ratio judgment submodule and a delay judgment submodule;
the ratio judgment submodule is used for judging whether the value obtained by dividing the harmonic distortion rate of the three-phase voltage by the value obtained by the filtering link is less than 1 or not;
and the delay judgment submodule is used for judging whether the lasting time of the three-phase voltage harmonic distortion rate divided by the value of the three-phase voltage harmonic distortion rate passing through the filtering link is less than 1 is more than or equal to a time threshold value or not.
7. The control system for avoiding continuous low of extra-high voltage direct current power as claimed in claim 6, wherein the calculating module is configured to calculate the harmonic distortion rate of the commutation bus voltage according to the following formula:
in the formula: THDv: the harmonic distortion rate of the voltage of the converter bus; u shapen: when n is>When 1, the voltage of the nth harmonic wave is expressed as an effective value; u shape1: the effective value of the fundamental voltage.
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