CN114156071B - Active noise reduction method and device for vibration reduction and noise reduction of urban distribution transformer - Google Patents
Active noise reduction method and device for vibration reduction and noise reduction of urban distribution transformer Download PDFInfo
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Abstract
The invention relates to an active noise reduction method and device for vibration reduction and noise reduction of urban distribution transformer. The system comprises a power grid voltage signal acquisition unit, a high-speed signal processing and harmonic analysis unit and an inverted harmonic generator PWM inversion unit; the power grid signal acquisition unit is used for detecting output voltage signals of the transformer, inputting the output voltage signals to the high-speed signal processing unit and the harmonic analysis unit after proportional amplification, carrying out Fourier transformation on the detected voltage signals, calculating main harmonic components contained in power grid voltage, solving an equation set of PWM inversion control moment after harmonic times of the main harmonic components are determined, calculating the moment of switching on and switching off of IGBT (insulated gate bipolar transistor) in one quarter of voltage cycle of the power grid, and outputting the moment to an IGBT driving circuit of the PWM inversion unit of the inverted harmonic generator in a PWM signal mode, wherein the inversion circuit formed by the IGBT is connected with the power grid in parallel to realize elimination of harmonic noise. The invention has high efficiency, can accurately eliminate the harmonic wave of set times and realizes the active noise reduction of the harmonic wave of the transformer.
Description
Technical Field
The invention belongs to the field of vibration reduction and noise reduction of transformers, and relates to an active noise reduction method and device for vibration reduction and noise reduction of urban distribution transformers.
Background
The power transformer has the advantages of safety, reliability, simple maintenance, low cost and the like, the development speed of the power transformer is indirectly accelerated, the share of the power transformer in practical engineering application is increased, but the noise problem is more prominent, and the power transformer gradually becomes a development bottleneck. Vibration noise is used as an important investigation index, and is the same as loss heating, and is more and more focused by researchers. The noise of the transformer is a kind of continuous noise generated by the vibration of the transformer body and the vibration of the cooling device.
In terms of the noise generation mechanism of the transformer body, the research results at home and abroad show that the source of the vibration of the transformer body is iron core vibration caused by magnetostriction of the silicon steel sheet. When the harmonic exists in the transformer, the harmonic is formed by overlapping a plurality of currents with similar or same frequencies, and when the harmonic current flows through the winding of the transformer, the iron core of the transformer is caused to stretch to generate vibration, which is the source of the noise of the transformer. Eliminating the harmonics of the transformer current can reduce transformer noise from the source.
In addition, the cooling device of the transformer also generates noise. The vibration of the cooling device is generated when the cooling fan and the transformer oil pump are operated; vibration of the transformer body is transmitted to the cooling device through insulating oil, pipe joints, assembly parts thereof and the like, so that the vibration of the cooling device is aggravated, and radiated noise is increased.
The noise reduction of the transformer is generally based on the noise generation mechanism, and technical measures for reducing the noise of the transformer body include: and a high-quality silicon steel sheet with small magnetostriction is selected, so that rated working magnetic density of the iron core is reduced, and the structure of the iron core is improved. Technical measures taken in terms of the mechanical structure of the transformer include: the mechanical connection mode of the iron core and the oil tank is improved, and vibration-proof rubber pads are arranged between the bottom foot of the body and the oil tank, between the oil tank and the foundation and between the busbar and the fixed structural member, so that the rigid connection is changed into elastic connection, and the purposes of reducing vibration, preventing resonance and reducing noise are achieved.
Further, from the viewpoint of improving the fuel tank and its structure, it is necessary to increase the rigidity of the entire fuel tank in order to reduce the vibration amplitude of the fuel tank wall. The method for improving the rigidity is to increase the thickness of the box wall and the number of the reinforcing irons, and select better reinforcing iron shapes and welding positions. The sound-producing body is isolated from the surrounding environment by a dense and heavy material which is commonly used in the acoustic technology. The performance of the sound insulation member is related to the weight per unit area, and the sound insulation effect is better as the weight is heavier. When the natural vibration frequency of the oil tank is the same as or close to the fundamental frequency and harmonic frequency of the noise of the transformer body, resonance occurs, the sound insulation effect is greatly reduced, and the oil tank can even become a noise amplifier in some cases.
The common measures for reducing the noise of the cooling device include selecting a low-noise cooling fan, reducing the noise of a self-cooling radiator, reducing the noise design of a transformer body, and the like.
The scholars also put forward an electromagnetic-vibration-noise coupling calculation method, reduce noise to corresponding mechanical vibration, and then establish a mechatronic control system, so that the integrated control of the mechanical vibration and electromagnetic harmonic wave is realized, and the method has good prospect.
The transformer is in the middle link of electric energy transmission in the power grid system, and abundant harmonic components exist in the process of connecting the transformer with the bus due to the existence of large nonlinear loads such as a calcium carbide furnace, an electrolytic furnace, various types of motors and the like, and the harmonic components can be greatly changed along with the change of the loads. The harmonic wave not only appears as distortion of the voltage waveform of the power grid, but also causes additional loss and noise of the transformer, so that the equipment is overheated and electromagnetic interference is brought to the communication equipment.
In conclusion, the harmonic elimination of the transformer has very important significance, not only can simply reduce the transformer noise caused by electromagnetic harmonic, but also lays a foundation for realizing electromechanical integrated noise reduction control in the future.
Disclosure of Invention
The invention aims to provide an active noise reduction method and device for vibration reduction and noise reduction of urban distribution transformer, which utilize a high-speed digital signal processor to sample voltage signals of a transformer at high speed, solve harmonic amplitudes in the transformer through a rapid digital signal processing technology, and finally invert same-frequency harmonic waves with the same amplitude and opposite phases through a PWM power electronic technology to realize dynamic sequencing of the harmonic amplitudes and dynamic harmonic elimination.
In order to achieve the above purpose, the technical scheme of the invention is as follows: the active noise reduction method for urban distribution transformer vibration reduction and noise reduction comprises the steps of detecting an output voltage signal of a transformer, carrying out proportional amplification, carrying out Fourier transformation on the amplified voltage signal, calculating main harmonic components contained in power grid voltage, determining harmonic times of the main harmonic components, solving an equation set of PWM inversion control moment, calculating the moment of IGBT on and off in one quarter of voltage cycle of the power grid, and outputting the moment to an IGBT driving circuit in a PWM signal mode, so that elimination of harmonic noise is realized.
The invention also provides an active noise reduction device for urban distribution transformer vibration reduction and noise reduction, which comprises a power grid voltage signal acquisition unit, a high-speed signal processing and harmonic analysis unit and an inverse harmonic generation unit; the power grid signal acquisition unit is used for detecting output voltage signals of the transformer, inputting the output voltage signals to the high-speed signal processing and harmonic analyzing unit after proportional amplification, the high-speed signal processing and harmonic analyzing unit is used for carrying out Fourier transformation on the detected voltage signals, calculating main harmonic components contained in the power grid voltage, solving an equation set of PWM inversion control moments after harmonic times of the main harmonic components are determined, calculating the moment of on and off of IGBT in one quarter of voltage cycle of the power grid, and outputting the moment to an IGBT driving circuit of a PWM inversion unit of the inversion harmonic generating unit in a PWM signal mode to eliminate harmonic noise.
In an embodiment of the invention, the power grid voltage signal acquisition unit comprises a high-precision voltage transformer and a signal amplification circuit, wherein the measurement range of the high-precision voltage transformer is 50V-4200V, the primary nominal current of the measurement precision is less than 0.9%, the nonlinearity is less than 0.3%, the bandwidth is-3 dB <13kHz, the signal amplification circuit consists of an operational amplifier with a high gain bandwidth product, and the working frequency is between 27 GHz and 31.5 GHz.
In one embodiment of the invention, the frequency of the high-speed signal processing and harmonic analysis unit is more than 400MHz, the storage space is more than 500k, and the maximum sampling point number is N max The power supply system frequency is f, and the maximum sampling interval is required
In an embodiment of the present invention, the high-speed signal processing and harmonic analysis unit can implement ordering of harmonic duty ratios by using a signal processing technology, and when the ratio k between the amplitude of the lowest order harmonic and the amplitude of the higher order harmonic reaches 100, the requirement can be satisfied, and the noise influence of the higher order harmonic is automatically ignored.
In one embodiment of the invention, the on and off time of the IGBT in one quarter of the voltage cycle of the power grid is calculated by a high-speed digital signal processor, and harmonics below k times are eliminated by inversion of a PWM (pulse width modulation) technology.
In an embodiment of the present invention, a calculation formula of the moment when the IGBT is turned on and off is:
wherein alpha is i For the i-th switching instant, i=1, 2, p, p=0, 1,2,.. 3 、U 5 ……U (2p+1) Harmonic amplitude of … … p+1 times 3 times 5, U d The voltage is the DC bus voltage of the PWM inverter circuit.
Compared with the prior art, the invention has the following beneficial effects: the invention utilizes a high-speed digital signal processor to sample the voltage signal of the transformer at a high speed, solves the harmonic amplitude in the transformer by a rapid digital signal processing technology, and finally inverts the same-frequency harmonic with the same amplitude and opposite phases by a PWM power electronic technology to realize the dynamic sequencing of the harmonic amplitude and the dynamic harmonic elimination.
Drawings
Fig. 1 is an output PWM waveform of the harmonic cancellation method.
Fig. 2 is a block diagram of an active noise reduction device for vibration damping and noise reduction of urban distribution transformer according to the present invention.
Fig. 3 is a system configuration diagram of the present invention.
Fig. 4 is a flow chart of the signal processing according to the present invention.
Detailed Description
The technical scheme of the invention is specifically described below with reference to the accompanying drawings.
As shown in fig. 2 and 3, the active noise reduction device for urban distribution transformer vibration reduction and noise reduction of the invention comprises three parts: 1. the power grid voltage signal acquisition unit; 2. a high-speed signal processing and harmonic analysis unit; 3. an inverted harmonic generation unit. The unit selection devices are as follows:
the power grid voltage signal acquisition unit comprises a high-precision voltage transformer, a signal amplifying circuit and the like. The measurement range of the high-precision voltage transformer is 50V to 4200V, the primary nominal current of the measurement precision is less than 0.9%, the nonlinearity is less than 0.3%, the bandwidth is-3 dB <13kHz, and the dielectric strength can reach 12kV at most. The signal amplifying circuit consists of an operational amplifier with a high gain-bandwidth product, the working frequency is between 27 and 31.5GHz, and the amplifier provides a gain of up to 19dB and a +5V power supply of 230mA under the maximum gain. Providing a gain control voltage allows for variable gain control up to 13dB, excellent gain flatness, and compatibility with high volume surface mount manufacturing in 4x4mm plastic QFN leadless packages that are compliant with RoHS standards. The gain can be automatically adjusted along with the amplitude change of the input signal, and the gain has extremely high gain bandwidth product, so that the high-frequency signal is effectively ensured not to be lost. The collected voltage signals are amplified to an amplitude range suitable for digital signal processing through a proportionality coefficient k and then input to an analog-digital conversion port of the CPU.
The high-speed signal processing and harmonic analysis unit comprises a singlechip, voltage signal analog acquisition and PWM signal output. Wherein, the CPU system frequency can reach 800MHz. The system comprises a 2MB system memory SRAM, can store a large amount of voltage analog quantity data in real time, can realize rapid whole-period expansion after voltage analog quantity data in a quarter period are acquired, and performs rapid discrete Fourier transform on positive period voltage signal sampling values after expansion, then orders the amplitude of each subharmonic, and finally obtains an inversion unit for driving an inversion harmonic generator at the turn-off moment of a PWM signal switch box after solving a multivariable nonlinear equation.
The reverse harmonic generation unit comprises a high-power high-frequency IGBT module, an IGBT driving circuit, overcurrent protection and the like. PWM signals output by the high-speed signal processing and harmonic wave analysis unit can be processed by the IGBT driving circuit at the calculated opening and closing sequence time alpha of the switch i The IGBTs are turned on or off, inverting the desired inverted harmonics.
Working principle:
1) The output voltage of the transformer is sampled, and the symmetry of the voltage signal shows that the waveform of the 0-pi/2 interval of the output voltage of the transformer is antisymmetric with the waveform of the pi-3 pi/2 interval, and the waveform of the pi/2-pi interval is antisymmetric with the waveform of the 3 pi/2-2 pi interval. Therefore, only the waveform of the output voltage of the transformer in the interval of 0-pi/2 is acquired, and the waveform in the whole 2 pi period can be obtained through prolongation.
2) The digital processor has a 12-bit ADC module with a sampling rate of 4M samples per second (4 MSPS), and can be implemented up to sampling the 0-800kHz harmonic components.
3) In order to increase the operation speed and avoid harmonic sampling leakage, a sampling speed of 50KHz is adopted, namely the sampling N is carried out in the power frequency period of each power grid voltage max And (3) a point, according to a harmonic voltage calculation formula:
wherein U represents harmonic voltage amplitude, and x (n) is grid voltageN in one period max Sample point voltage values of each. f (n, k) is a calculation factor.
4) K harmonics eliminated by the PWM inverter circuit.
Fig. 1 is a waveform of a U-phase voltage in a three-phase bridge PWM inverter circuit. Wherein the rectangular wave is a DC voltagePWM waveform obtained after chopping. The PWM waveform may be equivalently a sinusoidal voltage waveform shown by a dotted line according to the equal area principle.
Because the PWM switch control time sequence is in mirror symmetry with a quarter period, even harmonic is not contained in the harmonic wave, and alpha in the first quarter period only needs to be found 1 、α 2 And alpha 3 Is provided for the switching time of the three switches. For waveform a in the figure n Is formula (1)
Wherein n=3, 5,7, …
If the number of times the IGBT turns on and off is p in a quarter period of the voltage signal, all harmonics lower than 2p+1 times in the transformer can be eliminated, and a system of equations consisting of p equations can be established as follows:
p＝0,1,2,...
solving the above equation set to obtain a set of alpha 1 、α 2 …α p P switching moments of (a).
For harmonic amplitude U needing to be eliminated by 3 times and 5 times … … 2p+1 times 3 、U 5 ……U (2p+1) Only the corresponding switch combination with the corresponding opposite amplitude value is required to be obtained, and the corresponding harmonic wave is eliminated, so that the purpose of reducing harmonic wave noise of the transformer is achieved.
In the process of calculating the amplitude values of the subharmonics by the high-speed digital signal processor, the ratio k of the amplitude value of the lowest subharmonic to the amplitude value of the higher subharmonic is recorded and compared at the same time, and when k is more than 100, the requirement of harmonic suppression is considered to be met, and the calculation of the higher subharmonic is not continued.
1) The high-precision transformer may be a high-precision voltage transformer VS series transformer not limited to ABB company. The model can be JDZ-3Q, 6Q, 10Q, or JDZJ series but not limited to the above high voltage transformer
2) The signal amplification circuit may employ, but is not limited to, variable gain operational amplifiers HMC6187, ADL5246, etc. from nannoc analog corporation, where HMC6187 is a gallium arsenide analog variable gain amplifier.
3) The CPU adopts, but is not limited to, AM243x series dual-core Arm Cortex-R5F microprocessor of Texas instrument TI company, its SRAM partition and special low delay channel of configuration provide the best real-time performance in the same kind of singlechip for real-time on-line operation and data processing.
Specifically taking a JDZ-3Q voltage transformer as an example, rated input voltage is 3kV, rated output is 15VA-100VA, the primary side of the voltage transformer is connected to the outlet of the transformer, and the secondary side of the voltage transformer is connected to the proportional amplifying circuit. The voltage signal output by the secondary side of the voltage transformer is regulated to be smaller than 5V in peak-to-peak value through the variable gain proportional operational amplifier circuit. And 2.5V standard direct current is superimposed in the signal to be sampled, the voltage signal is raised to be within 0-5V, and the average voltage value of 2.5V is the 0V position of the voltage signal. The voltage analog signal acquisition and analog-to-digital conversion are carried out by the ADC port, and the voltage signal of 0-5V is converted into a digital value of 0-4096. In order to ensure the safety of the equipment of the digital signal processing DSP, a limiting circuit is added between the input signal and the digital signal processing DSP, so that the digital signal processing DSP is prevented from being burnt due to overhigh voltage signal.
The sampling and holding time is set to be 1 microsecond, the sampling mode is timing sampling, the sampling interval is set to be 20 microseconds, the ADCAM64x/AM243x series DSP internally contains a 2MB flash memory, and an analog sampling value array U of the voltage signal can be stored in the DSP internal flash memory.
Fig. 4 is a flow chart of the signal processing according to the present invention.
The voltage signal acquisition needs to start from a voltage zero crossing point, and the specific steps are as follows:
1) The voltage signal sampling value is assigned to a variable A, whether A is larger than 2048 is compared, if A is larger than 2048, a sign s is recorded as 1, if A is smaller than 2048, a sign s= -1 is recorded to continue the circulating step 1 until the sign s is changed from-1 to 1, a zero crossing point is found, and the A at the moment is assigned to U [0];
2) The variable i is self-added, interval t max Microsecond, resampling the analog value of the voltage signal, converting the analog value into a digital value and assigning the digital value to the variable U [ i ]]Step 2 is cycled until i=n max And/4, completing sampling.
3) Then the 250 data of the array U are rearranged in reverse order according to the sequence number and added in the array U [ N ] max /4]-U[N max /2]Is a kind of medium.
4) Array U []N of (2) max 2 data inversions are added to the array U [ N ] max /2+1]-U[N max ]In (1) to obtain N max Sampling values of the voltage signals.
The harmonic analysis stage comprises the following specific steps:
the magnitude of each k harmonics is calculated as follows.
And so on.
The calculation stage of PWM inversion switch time comprises the following specific steps:
1) The switching time of the anti-phase harmonic generation unit is calculated, and U is calculated according to the following formula (3) 、U (5) ……U (2p+1) Substituting into equation set to solve alpha 1 、α 2 ……α p P switching moments of (a).
Wherein alpha is i For the i-th switching instant, i=1, 2, p, p=0, 1,2,.. 3 、U 5 ……U (2p+1) Harmonic amplitudes of the order of 3 and 5 … … p+1.
2) The high-speed digital signal processor continues to detect the voltage zero crossing point, when the voltage signal passes through zero from positive to negative, when the voltage signal is about to enter the negative half cycle, namely from 180 degrees, the high-speed digital signal processor timer is cleared, and the time is delayed to alpha 1 Turning on IGBT and delaying to alpha at moment 1 +α 2 Turning off IGBT, alpha 1 +α 2 +α 3 Turning on IGBT again until alpha 1 +α 2 +…α p At the moment, the quarter-cycle PWM control is completed.
3) Continuing with the previous a during one-fourth to one-half of the voltage signal, starting with the moment of one-fourth period of the voltage as the time start p The IGBT is turned on at the moment, and then sequentially delays alpha p-1 ，α p-2 …α 1 And the switching state is symmetrical to the switching state of the first quarter of the voltage signal.
4) In the latter half period of the voltage signal, the turn-on and turn-off sequence and duration of the IGBT are identical to those of the former half period.
Through voltage type inversion of one period, the outlet of the PWM inverter is connected with the corresponding phase of the power grid, so that all corresponding times of harmonic waves in the power grid can be eliminated, and the ignored high-frequency harmonic waves occupy less than 0.2%.
The above is a preferred embodiment of the present invention, and all changes made according to the technical solution of the present invention belong to the protection scope of the present invention when the generated functional effects do not exceed the scope of the technical solution of the present invention.
Claims (7)
1. The active noise reduction method for urban distribution transformer vibration reduction and noise reduction is characterized in that output voltage signals of a transformer are detected, after proportional amplification, main harmonic components contained in power grid voltages are calculated through Fourier transformation on the amplified voltage signals, after harmonic times of the main harmonic components are determined, an equation set of PWM inversion control moment is solved, the moment of IGBT on and off in one quarter of voltage cycle of the power grid is calculated, and the moment is output to an IGBT driving circuit in a PWM signal mode, so that elimination of harmonic noise is realized;
the specific implementation process of solving the equation set of PWM inversion control time, calculating the time of IGBT on and off in one quarter of voltage cycle of the power grid, and outputting the time to the IGBT driving circuit in a PWM signal mode is as follows:
because the PWM switch control time sequence is in mirror symmetry with a quarter period, even harmonic is not contained in the harmonic wave, and alpha in the first quarter period only needs to be found 1 、α 2 And alpha 3 Is provided with three switching moments; for waveform a n The formula is:
wherein n=3, 5,7, …
If the number of times the IGBT is turned on and off is p in a quarter period of the voltage signal, all harmonics lower than 2p+1 times in the transformer can be eliminated, and an equation set consisting of the following p equations is established:
p＝0,1,2,...
solving the equation set to obtain a set of alpha 1 、α 2 …α p P switching moments of (a);
for harmonic amplitude U needing to be eliminated by 3 times and 5 times … … 2p+1 times 3 、U 5 ……U (2p+1) Only the corresponding switch combination with the corresponding amplitude value opposite to the corresponding number is required to be obtained, and the corresponding harmonic wave is eliminated, so that the transformer can reduce the harmonic wave noiseThe purpose is that;
in the process of calculating the amplitude values of all the subharmonics by the high-speed digital signal processor, the ratio k of the amplitude value of the lowest subharmonic to the amplitude value of the higher subharmonic is recorded and compared at the same time, and when k is more than 100, the requirement of harmonic suppression is considered to be met, and the calculation of higher subharmonic is not continued;
the harmonic analysis stage comprises the following specific steps:
calculating the amplitude of each k harmonic according to the following formula;
the calculation stage of PWM inversion switch time comprises the following specific steps:
1) The switching time of the anti-phase harmonic generation unit is calculated, and U is calculated according to the following formula (3) 、U (5) ……U (2p+1) Substituting into equation set to solve alpha 1 、α 2 ……α p P switching moments of (a);
wherein alpha is i For the i-th switching instant, i=1, 2, p, p=0, 1,2,.. 3 、U 5 ……U (2p+1) Harmonic amplitudes of the order of 3 and 5 … … p+1;
2) The high-speed digital signal processor continues to detect the voltage zero crossing point, when the voltage signal passes through zero from positive to negative, when the voltage signal is about to enter the negative half cycle, namely from 180 degrees, the high-speed digital signal processor timer is cleared, and the time is delayed to alpha 1 Turning on IGBT and delaying to alpha at moment 1 +α 2 Turning off IGBT, alpha 1 +α 2 +α 3 Turning on IGBT again until alpha 1 +α 2 +…α p At the moment, the PWM control of a quarter period is completed;
3) Continuing with the previous a during one-fourth to one-half of the voltage signal, starting with the moment of one-fourth period of the voltage as the time start p The IGBT is turned on at the moment, and then sequentially delays alpha p-1 ，α p-2 …α 1 And the switch state is symmetrical with the switch state of the front quarter of the voltage signal;
4) In the latter half period of the voltage signal, the turn-on and turn-off sequence and duration of the IGBT are identical to those of the former half period.
2. The active noise reduction device for urban distribution transformer vibration reduction and noise reduction is characterized by comprising a power grid voltage signal acquisition unit, a high-speed signal processing and harmonic analysis unit and an anti-phase harmonic generation unit; the power grid signal acquisition unit is used for detecting output voltage signals of the transformer, inputting the output voltage signals to the high-speed signal processing and harmonic analyzing unit after proportional amplification, carrying out Fourier transformation on the detected voltage signals by the high-speed signal processing and harmonic analyzing unit, calculating main harmonic components contained in the power grid voltage, solving an equation set of PWM inversion control moment after determining harmonic times of the main harmonic components, calculating the moment of on and off of IGBT in one quarter of voltage cycle of the power grid, and outputting the moment to an IGBT driving circuit of a PWM inversion unit of the inverted harmonic generating unit in a PWM signal mode to eliminate harmonic noise;
the specific implementation process of solving the equation set of PWM inversion control time, calculating the time of IGBT on and off in one quarter of voltage cycle of the power grid, and outputting the time to the IGBT driving circuit in a PWM signal mode is as follows:
because the PWM switch control time sequence is in mirror symmetry with a quarter period, even harmonic is not contained in the harmonic wave, and alpha in the first quarter period only needs to be found 1 、α 2 And alpha 3 Is provided with three switching moments; for waveform a n The formula is:
wherein n=3, 5,7, …
If the number of times the IGBT is turned on and off is p in a quarter period of the voltage signal, all harmonics lower than 2p+1 times in the transformer can be eliminated, and an equation set consisting of the following p equations is established:
p＝0,1,2,...
solving the equation set to obtain a set of alpha 1 、α 2 …α p P switching moments of (a);
for harmonic amplitude U needing to be eliminated by 3 times and 5 times … … 2p+1 times 3 、U 5 ……U (2p+1) Only the corresponding switch combination with the corresponding opposite amplitude value is required to be obtained, and the corresponding harmonic wave is eliminated, so that the transformer achieves the purpose of reducing harmonic wave noise;
in the process of calculating the amplitude values of all the subharmonics by the high-speed digital signal processor, the ratio k of the amplitude value of the lowest subharmonic to the amplitude value of the higher subharmonic is recorded and compared at the same time, and when k is more than 100, the requirement of harmonic suppression is considered to be met, and the calculation of higher subharmonic is not continued;
the harmonic analysis stage comprises the following specific steps:
calculating the amplitude of each k harmonic according to the following formula;
the calculation stage of PWM inversion switch time comprises the following specific steps:
1) The switching time of the anti-phase harmonic generation unit is calculated, and U is calculated according to the following formula (3) 、U (5) ……U (2p+1) Substituting into equation set to solve alpha 1 、α 2 ……α p P switching moments of (a);
wherein alpha is i For the i-th switching instant, i=1, 2, p, p=0, 1,2,.. 3 、U 5 ……U (2p+1) Harmonic amplitudes of the order of 3 and 5 … … p+1;
2) The high-speed digital signal processor continues to detect the voltage zero crossing point, when the voltage signal passes through zero from positive to negative, when the voltage signal is about to enter the negative half cycle, namely from 180 degrees, the high-speed digital signal processor timer is cleared, and the time is delayed to alpha 1 Turning on IGBT and delaying to alpha at moment 1 +α 2 Turning off IGBT, alpha 1 +α 2 +α 3 Turning on IGBT again until alpha 1 +α 2 +…α p At the moment, the PWM control of a quarter period is completed;
3) Continuing with the previous a during one-fourth to one-half of the voltage signal, starting with the moment of one-fourth period of the voltage as the time start p The IGBT is turned on at the moment, and then sequentially delays alpha p-1 ，α p-2 …α 1 And the switch state is symmetrical with the switch state of the front quarter of the voltage signal;
4) In the latter half period of the voltage signal, the turn-on and turn-off sequence and duration of the IGBT are identical to those of the former half period.
3. The active noise reduction device for urban distribution transformer vibration attenuation and noise reduction according to claim 2, wherein the power grid voltage signal acquisition unit comprises a high-precision voltage transformer and a signal amplification circuit, the measurement range of the high-precision voltage transformer is 50V-4200V, the primary nominal current of the measurement precision is less than 0.9%, the nonlinearity is less than 0.3%, the bandwidth is-3 dB <13kHz, the signal amplification circuit is composed of an operational amplifier with a high gain bandwidth product, and the working frequency is between 27 GHz and 31.5 GHz.
4. The active noise reduction device for urban distribution transformer vibration reduction and noise reduction according to claim 2, wherein the frequency of the high-speed signal processing and harmonic analysis unit is more than 400MHz, the storage space is more than 500k, and the maximum sampling point number is N max The power supply system frequency is f, and the maximum sampling interval is required
5. The active noise reduction device for urban distribution transformer vibration reduction and noise reduction according to claim 2, wherein the high-speed signal processing and harmonic analysis unit can realize the ordering of harmonic duty ratios through a signal processing technology, and when the ratio k of the lowest harmonic amplitude to the amplitude of the higher harmonic reaches 100, the requirement can be met, and the noise influence of the higher harmonic is automatically ignored.
6. The active noise reduction device for urban distribution transformer vibration reduction and noise reduction according to claim 2, wherein the moment of switching on and switching off the IGBT in one quarter of voltage cycle of the power grid is calculated by a high-speed digital signal processor, and harmonic waves below k times are eliminated by inversion of a PWM (pulse width modulation) technology.
7. The active noise reduction device for urban distribution transformer vibration reduction and noise reduction according to claim 6, wherein the calculation formula of the on and off time of the IGBT is:
wherein alpha is i For the i-th switching instant, i=1, 2, p, p=0, 1,2,.. 3 、U 5 ……U (2p+1) Harmonic amplitude of … … p+1 times 3 times 5, U d The voltage is the DC bus voltage of the PWM inverter circuit.
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