CN113162451B - Control method and device for neutral point potential balance of multi-level inverter - Google Patents
Control method and device for neutral point potential balance of multi-level inverter Download PDFInfo
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- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
- H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
- H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
- H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
- H02M7/483—Converters with outputs that each can have more than two voltages levels
- H02M7/487—Neutral point clamped inverters
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
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Abstract
The invention discloses a method and a device for controlling the neutral point potential balance of a multi-level inverter, wherein the method comprises the following steps: s1, acquiring deviation voltage of a midpoint potential of an inverter; s2, sending the deviation voltage of the midpoint potential of the inverter into a deviation balancing controller, and automatically optimizing in real time by the deviation balancing controller according to the deviation voltage of the midpoint potential; s3, superposing the output of the deviation balancing controller to the expected output fundamental voltage; s4, estimating the midpoint voltage of the inverter at the next moment according to the superposed fundamental wave voltage; and S5, judging whether the midpoint voltage meets the set range of midpoint potential balance or not according to the estimated midpoint voltage, if so, directly outputting the superposed fundamental wave voltage, otherwise, dynamically adjusting the parameters of the deviation balance controller and transferring to the step S2. The control method and the device for the neutral point potential balance of the multi-level inverter have the characteristics of simple control, low cost and strong applicability.
Description
Technical Field
The invention relates to the technical field of power electronic multi-level inverters, in particular to a method and a device for controlling neutral point potential balance of a multi-level inverter.
Background
With the rapid development of modern power electronic technology and digital control technology, multi-level inverters in power electronic equipment are receiving wide attention and become hot spots of domestic and foreign research. The multi-level inverter is widely applied to the fields of alternating current-direct current electric energy conversion, motor frequency conversion speed regulation, electric energy quality control and the like. Compared with the traditional two-level inverter, the multi-level inverter has the advantages that the output voltage harmonic content is low, the voltage stress born by a switching device is small under the same frequency condition, the switching frequency is low, the system loss is small, and the inversion efficiency is high. However, in the diode-clamped multilevel inverter, the capacitor voltage may change due to unbalanced charging and discharging of the current flowing through the midpoint of the dc side to the capacitor, and when the difference between the capacitor voltages is too large, the output waveform may be deformed, which is a problem of unbalanced midpoint potential of the dc side and may threaten the system safety.
Aiming at the problem of unbalanced midpoint potential, the solution of the prior art mainly comprises a hardware method and a software method, wherein the hardware method is added with auxiliary hardware, so that the cost is higher, and meanwhile, because additional devices are added, the reliability of the system is reduced; the software method is to inject proper zero sequence component into the modulation wave to adjust the midpoint potential, and the method does not need to add extra hardware, so the method has higher practicability; however, the existing software control method has a problem that the optimal zero sequence component cannot be calculated in real time, which can only be realized by increasing the capacitance of the capacitor or increasing the switching frequency of the system in order to reduce the fluctuation of the midpoint potential to the maximum extent, and increasing the capacitance of the capacitor will cause the increase of the system cost, while increasing the switching frequency of the system will cause the increase of the system loss. Based on the above problems in the prior art, it is urgently needed to provide a new method and device for controlling the neutral point potential balance of a multilevel inverter.
Disclosure of Invention
The invention aims to provide a control method and a control device for neutral point potential balance of a multi-level inverter, which can improve the output performance of the inverter by introducing a deviation balance controller and inner loop control of neutral point voltage and have the characteristics of simple control, low cost and strong applicability.
In order to achieve the purpose, the invention provides the following scheme:
a control method for the neutral point potential balance of a multi-level inverter comprises the following steps:
s1, acquiring deviation voltage of a midpoint potential of an inverter;
s2, sending the deviation voltage of the midpoint potential of the inverter into a deviation balancing controller, and automatically optimizing in real time by the deviation balancing controller according to the deviation voltage of the midpoint potential;
s3, superposing the output of the deviation balancing controller to the fundamental voltage expected to be output;
s4, estimating the midpoint voltage of the inverter at the next moment according to the superposed fundamental wave voltage;
and S5, judging whether the midpoint voltage meets the set range of midpoint potential balance or not according to the estimated midpoint voltage, if so, directly outputting the superposed fundamental voltage, and if not, dynamically adjusting the parameters of the deviation balance controller and transferring to the step S2.
Optionally, in step S1, obtaining a deviation voltage of a midpoint potential of the inverter specifically includes:
s101, detecting the upper bus capacitor voltage, the lower bus capacitor voltage and the three-phase current output by the inverter;
s102, calculating a power factor output by the inverter according to the three-phase voltage and the three-phase current output by the inverter; the power factor is calculated by firstly obtaining the electrical angle psi v of three-phase voltage and the electrical angle psi A of three-phase current through a phase-locked loop, and then the power factor output by the inverter is cos (psi v-psi A);
s103, calculating the deviation voltage of the midpoint potential according to the obtained power factor, wherein when the power factor is larger than or equal to 0, the deviation voltage of the midpoint potential is obtained by subtracting the lower bus voltage from the upper bus voltage, and when the power factor is smaller than 0, the deviation voltage of the midpoint potential is obtained by subtracting the upper bus voltage from the lower bus voltage.
Optionally, in step S2, an ant colony algorithm is adopted in the process that the deviation balancing controller performs real-time automatic optimization according to the deviation voltage of the midpoint potential, and specifically includes:
s201, recording the step length of the ant movement as lambda, the number of ants as m, the correction direction as F, the correction direction being determined by the deviation value of the midpoint potential fluctuation at the current moment, when the deviation value is positive, the correction direction F =1, otherwise F = -1, effectively shortening the iteration times by increasing the correction direction, reducing the rolling optimization calculation amount, gradually reducing the step length along with the increase of the iteration times, and the kth iteration has
λ(k)＝F·λ 0 e -k (1)
In the formula, λ 0 ＝1；
S202, ant positions are parameter adjustment values of the deviation balancing controller in a period, in the control of the midpoint potential, the optimal value is searched, the solution space is one-dimensional, in the solution space, a feasible solution is defined as D epsilon (0,1), m ants are averagely and randomly distributed into each solution space, and the feasible solution is divided into one ant in each interval;
s203, when the midpoint potential control algorithm is activated, each ant can obtain the fluctuation value of the midpoint voltage, and the midpoint potential fluctuation corresponding to the position of each ant is regarded as the pheromone sediment of the position;
s204, the ant with the minimum corresponding pheromone precipitation is kept in the original position and the rest ants continue to update the positions according to the formula (2),
wherein D (k + 1) is the position of the kth iteration ant +1, D (k) is the position of the kth iteration ant, delta is the stability factor,
is a unit vector, the direction of the unit vector is that the ith ant points to the position of an ant with high pheromone content, and when all ants finish all movements, one iteration is finished;
and S205, continuously repeating the steps S203 and S204 until all ants gather at the minimum fluctuation point of the voltage.
Optionally, in step S3, the output of the deviation balancing controller is superimposed onto the fundamental wave voltage expected to be output, and a specific superimposing manner is to add the output of the deviation balancing controller to each phase of the three-phase fundamental wave voltage output by the inverter.
Optionally, when the superimposed fundamental voltage exceeds the set maximum and minimum range values of the modulation wave, overmodulation needs to be performed on the superimposed fundamental voltage, and the specific method includes: firstly, judging whether the generated three-phase fundamental wave voltage is overmodulation or not, and if not, directly outputting the overmodulation; if yes, the overmodulation of a specific phase needs to be determined, an overmodulation offset value of the overmodulation phase is calculated, and then the offset value is added or subtracted to the three-phase fundamental voltage simultaneously so as to achieve the purpose of eliminating the overmodulation.
Optionally, in step S4, estimating a midpoint voltage of the inverter at the next time according to the superimposed fundamental voltage, specifically including:
s401, establishing a mathematical model of the output quantity of the deviation balancing controller and the fluctuation of the output midpoint voltage of the inverter;
s402, substituting the output quantity of the deviation balance controller into the mathematical model to obtain the corresponding deviation voltage, thereby estimating the midpoint voltage of the next time.
Optionally, the setting range of the midpoint potential balance in step S5 is: the estimated midpoint voltage is less than a set voltage x the system midpoint imbalance k, wherein the set voltage is the bus voltage of the inverter, and the system midpoint imbalance k is determined according to the application requirements of different systems.
Optionally, the value range of the midpoint imbalance k in the system is (0,1), and the midpoint voltage fluctuation range required by the system is 1% -10%.
The invention also provides a midpoint potential balance device of the multi-level inverter, which is applied to the control method of the midpoint potential balance of the multi-level inverter, and the device comprises the following components: the device comprises a deviation voltage acquisition module, a midpoint potential balance controller and a PWM controller module, wherein the input end of the deviation voltage acquisition module is electrically connected with the capacitor input end and the midpoint of a diode clamp type multi-level inverter circuit, the output end of the deviation voltage acquisition module is electrically connected with the input end of the midpoint potential balance controller, the output end of the midpoint potential balance controller is electrically connected with the input end of the PWM controller module, and the output end of the PWM controller module is electrically connected with the diode clamp type multi-level inverter of the diode clamp type multi-level inverter circuit; the device comprises a neutral point potential balance controller, a deviation voltage acquisition module, a neutral point potential balance controller, a PWM controller module and a diode clamp type multi-level inverter, wherein the deviation voltage acquisition module is used for acquiring deviation voltage of neutral point potential of the inverter and transmitting the deviation voltage to the neutral point potential balance controller, the neutral point potential balance controller is used for generating optimal neutral point potential balance control quantity in real time according to the neutral point deviation voltage, the obtained control quantity is superposed with three-phase fundamental wave voltage expected to be output and then output to the PWM controller module, and the PWM controller module is used for generating corresponding driving pulse according to the fundamental wave voltage output by the neutral point potential balance controller and controlling the diode clamp type multi-level inverter to generate PWM waves.
Optionally, the midpoint potential balance controller includes a deviation voltage calculation module, a deviation balance controller module, an expected output fundamental wave voltage module, a midpoint voltage estimation module, and a midpoint voltage judgment module, an input end of the deviation voltage calculation module is electrically connected to an output end of the deviation voltage acquisition module, an output end of the deviation voltage calculation module is electrically connected to an input end of the deviation balance controller module, output ends of the deviation balance controller module and the expected output fundamental wave voltage module are both electrically connected to an input end of the midpoint voltage estimation module, an output end of the midpoint voltage estimation module is electrically connected to an input end of the midpoint voltage judgment module, and an output end of the midpoint voltage judgment module is electrically connected to input ends of the deviation balance controller module and the PWM controller module, respectively; the deviation voltage calculation module is used for receiving deviation voltage of the midpoint potential and sending the deviation voltage of the midpoint potential of the inverter to the deviation balance controller module, the deviation balance controller module is used for generating a midpoint potential balance control quantity according to actual deviation voltage of the midpoint potential, the fundamental wave voltage module expected to be output is used for producing three-phase fundamental wave voltage expected to be output, the midpoint voltage estimation module is used for estimating the midpoint voltage of the inverter at the next moment according to the superposed fundamental wave voltage, the midpoint voltage judgment module is used for judging whether the midpoint voltage meets the set range of midpoint potential balance or not according to the estimated midpoint voltage, and if the midpoint voltage meets the set range, the superposed fundamental wave voltage is directly transmitted to the PWM controller module; and if the voltage does not meet the requirement, adjusting the parameters of the deviation balance controller, re-estimating the deviation of the midpoint voltage until the estimated midpoint voltage meets the set range of midpoint potential balance, and transmitting the fundamental voltage to the PWM controller module.
According to the specific embodiment provided by the invention, the invention discloses the following technical effects: according to the control method and device for the neutral point potential balance of the multi-level inverter, the deviation balance controller is introduced, so that the dynamic response of the whole adjusting system is quickened, neutral point voltage errors are eliminated, and the dynamic and static performances of neutral point potential adjustment are improved; by introducing inner loop control of the midpoint voltage, whether the midpoint voltage obtained by internal calculation and evaluation of the deviation balancing controller can meet the system requirements or not is judged, and if the midpoint voltage cannot meet the system requirements, recalculation is carried out, and the midpoint voltage cannot be output until the midpoint voltage meets the system requirements, so that compared with the traditional midpoint control method that whether the midpoint voltage meets the requirements or not can be judged after the midpoint voltage is output by an actual system, the deviation of the midpoint voltage can be effectively reduced; by introducing a rapid method of overmodulation treatment, the harmonic waves of three-phase voltage output by the inverter can be effectively improved, and the output performance of the inverter is improved; the invention effectively reduces the deviation of the midpoint voltage on the premise of not increasing the system loss, reduces the cost, is suitable for diode-clamped three-level inverters in the current market, is also suitable for other types of inverters with single midpoint structures, and has wide application prospect. The control method and the device for the neutral point potential balance of the multi-level inverter have the characteristics of simple control, low cost and strong applicability.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required in the embodiments will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art that other drawings can be obtained according to the drawings without creative efforts.
FIG. 1 is a flow chart of a method for controlling the neutral point potential balance of a multilevel inverter according to the present invention;
FIG. 2 is a block diagram of a circuit system of the midpoint potential balancing apparatus of the multi-level inverter of the present invention;
FIG. 3 is a diagram of a midpoint voltage ripple of an inverter using a conventional midpoint voltage control method, using a diode clamped three-level inverter as an example;
FIG. 4 is a diagram illustrating a midpoint voltage fluctuation of an inverter employing the control method of the present invention, for example, a diode clamped three-level inverter;
description of reference numerals: 1. a deviation voltage acquisition module; 2. a midpoint potential balance controller; 3. a PWM controller module; 4. a diode clamp type multi-level inverter; 201. a deviation voltage calculation module; 202. a deviation balancing controller module; 203. a fundamental voltage module of desired output; 204. a midpoint voltage estimation module; 205. and a midpoint voltage judging module.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The invention aims to provide a control method and a control device for neutral point potential balance of a multi-level inverter, which can improve the output performance of the inverter by introducing a deviation balance controller and inner loop control of neutral point voltage and have the characteristics of simple control, low cost and strong applicability.
In order to make the aforementioned objects, features and advantages of the present invention more comprehensible, the present invention is described in detail with reference to the accompanying drawings and the detailed description thereof.
As shown in fig. 1, the method for controlling the neutral point potential balance of the multilevel inverter according to the present invention includes:
s1, acquiring deviation voltage of a midpoint potential of an inverter; the method specifically comprises the following steps:
s101, detecting the upper bus capacitor voltage, the lower bus capacitor voltage and the three-phase current output by the inverter;
s102, calculating a power factor output by the inverter according to the three-phase voltage and the three-phase current output by the inverter; the power factor is calculated by firstly obtaining the electrical angle psi v of three-phase voltage and the electrical angle psi A of three-phase current through a phase-locked loop, and then the power factor output by the inverter is cos (psi v-psi A);
s103, calculating the deviation voltage of the midpoint potential according to the obtained power factor, wherein when the power factor is larger than or equal to 0, the deviation voltage of the midpoint potential is obtained by subtracting the lower bus voltage from the upper bus voltage, and when the power factor is smaller than 0, the deviation voltage of the midpoint potential is obtained by subtracting the upper bus voltage from the lower bus voltage;
s2, sending the deviation voltage of the midpoint potential of the inverter into a deviation balancing controller, and automatically optimizing in real time by the deviation balancing controller according to the deviation voltage of the midpoint potential; the ant colony algorithm is adopted in the process that the deviation balance controller carries out real-time automatic optimization according to the deviation voltage of the midpoint potential, and the method specifically comprises the following steps:
s201, recording the step length of the ant movement as lambda, the number of ants as m, the correction direction as F, the correction direction being determined by the deviation value of the midpoint potential fluctuation at the current moment, when the deviation value is positive, the correction direction F =1, otherwise F = -1, effectively shortening the iteration times by increasing the correction direction, reducing the rolling optimization calculation amount, gradually reducing the step length along with the increase of the iteration times, and the kth iteration has
λ(k)＝F·λ 0 e -k (1)
In the formula, λ 0 ＝1；
S202, ant positions are parameter adjustment values of the deviation equalization controller in a period, in the control of midpoint potential, an optimal value is searched, a solution space is one-dimensional, in the solution space, a feasible solution is defined as D e (0,1), m ants are averagely and randomly distributed into each solution space, and the feasible solution is divided into intervals so that one ant exists;
s203, when the midpoint potential control algorithm is activated, each ant can obtain the fluctuation value of the midpoint voltage, and the midpoint potential fluctuation corresponding to the position of each ant is regarded as pheromone precipitation of the position;
s204, the ant with the minimum corresponding pheromone deposition is kept in the original position and the other ants continue to carry out position updating according to the formula (2),
wherein D (k + 1) is the position of the kth iteration ant +1, D (k) is the position of the kth iteration ant, delta is the stability factor,
is a unit vector with the direction that the ith ant points to the ant with high pheromone contentThe positions of ants, and when all ants finish all movements, one iteration is finished;
s205, continuously repeating the steps S203 and S204 until all ants gather at the minimum fluctuation point of the voltage;
the real-time automatic optimization is realized through an intelligent algorithm (such as an artificial neural network, an ant colony algorithm and the like), so that the deviation equilibrium controller mainly plays the following roles: firstly, the dynamic response is fast, and the deviation of the midpoint potential can be quickly reflected to the expected output fundamental wave; secondly, static error is eliminated, and steady-state error generated by midpoint potential can be effectively eliminated; thirdly, improving the dynamic and static performance of the midpoint potential adjustment;
s3, superposing the output of the deviation balancing controller to the fundamental voltage expected to be output; the specific superposition mode is that the output quantity of the deviation balance controller is added to each phase of three-phase fundamental voltage output by the inverter; when the superimposed fundamental voltage exceeds the maximum and minimum range values set by the modulation wave, the superimposed fundamental voltage needs to be overmodulating, and the specific method comprises the following steps: firstly, judging whether the generated three-phase fundamental voltage is overmodulation or not, and if not, directly outputting the overmodulation; if yes, determining which phase has overmodulation, calculating an overmodulation deviation value of the overmodulation phase, and adding or subtracting the deviation value to or from three-phase fundamental wave voltages simultaneously to achieve the purpose of eliminating the overmodulation; through the implementation of the step, steady-state errors generated by the midpoint potential can be further effectively eliminated, the fluctuation deviation of the midpoint potential is minimized, and meanwhile, the harmonic waves of output voltage and current are reduced;
s4, estimating the midpoint voltage of the inverter at the next moment according to the superposed fundamental wave voltage; the method specifically comprises the following steps:
s401, establishing a mathematical model of the output quantity of the deviation balancing controller and the voltage fluctuation of the output midpoint of the inverter;
s402, substituting the output quantity of the deviation balancing controller into the mathematical model to obtain corresponding deviation voltage, thereby estimating the midpoint voltage of the next time;
s5, judging whether the midpoint voltage meets the set range of midpoint potential balance or not according to the estimated midpoint voltage, if so, directly outputting the superposed fundamental voltage, and if not, dynamically adjusting the parameters of the deviation balance controller and transferring to the step S2;
the setting range of the midpoint potential balance is as follows: the estimated midpoint voltage is less than a set voltage multiplied by a system midpoint unbalance degree k, wherein the set voltage is a bus voltage of the inverter, and the system midpoint unbalance degree k is determined according to application requirements of different systems; the value range of the neutral point unbalance degree k in the system is (0,1), and the neutral point voltage fluctuation range required by the system is 1-10%; when the system requires that the fluctuation of the midpoint voltage is smaller, the value of the corresponding midpoint unbalance degree k is smaller, namely the midpoint unbalance degree k of the system can achieve the purpose of adjusting the fluctuation amplitude of the midpoint voltage, the larger k is, the larger the fluctuation of the finally output midpoint voltage is, and the smaller k is, the smaller the fluctuation of the finally output midpoint voltage is; specifically, if the estimated midpoint voltage does not meet the requirement of being less than the set voltage x the system midpoint imbalance k, the deviation balance controller dynamically adjusts the parameters of the controller until the estimated midpoint voltage meets the requirement of being less than the set voltage x the system midpoint imbalance k, and the control of the multilevel inverter midpoint potential balance is realized according to the output superposed fundamental wave voltage;
as shown in fig. 2, the midpoint potential balancing apparatus for a multilevel inverter provided in the present invention specifically includes: the voltage-stabilizing circuit comprises a deviation voltage acquisition module 1, a midpoint potential balance controller 2 and a PWM controller module 3, wherein the input end of the deviation voltage acquisition module 1 is electrically connected with the capacitor input end and the midpoint of a diode clamp type multilevel inverter circuit, the output end of the deviation voltage acquisition module 1 is electrically connected with the input end of the midpoint potential balance controller 2, the output end of the midpoint potential balance controller 2 is electrically connected with the input end of the PWM controller module 3, and the output end of the PWM controller module 3 is electrically connected with a diode clamp type multilevel inverter 4 of the diode clamp type multilevel inverter circuit; the midpoint potential balance controller 2 includes a deviation voltage calculation module 201, a deviation balance controller module 202, an expected output fundamental wave voltage module 203, a midpoint voltage estimation module 204, and a midpoint voltage judgment module 205, an input end of the deviation voltage calculation module 201 is electrically connected to an output end of the deviation voltage acquisition module 1, an output end of the deviation voltage calculation module 201 is electrically connected to an input end of the deviation balance controller module 202, output ends of the deviation balance controller module 202 and the expected output fundamental wave voltage module 203 are both electrically connected to an input end of the midpoint voltage estimation module 204, an output end of the midpoint voltage estimation module 204 is electrically connected to an input end of the midpoint voltage judgment module 205, and an output end of the midpoint voltage judgment module 205 is electrically connected to input ends of the deviation balance controller module 202 and the PWM controller module 3, respectively;
the neutral point potential balance controller module 2 is provided with a neutral point potential balance controller, the deviation voltage acquisition module 1 is used for acquiring deviation voltage of neutral point potential of the inverter and transmitting the deviation voltage to the neutral point potential balance controller 2, the neutral point potential balance controller 2 is used for generating optimal neutral point potential balance control quantity according to the neutral point deviation voltage in real time, and the optimal neutral point potential balance control quantity is superposed with three-phase fundamental wave voltage expected to be output and then output to the PWM controller module 3; the PWM controller module 3 is used for generating corresponding driving pulses according to the fundamental voltage output by the midpoint potential balance controller 2 and controlling the diode-clamped multilevel inverter to generate PWM waves; the deviation voltage calculation module 201 is configured to receive a deviation voltage of a midpoint potential, and send the deviation voltage of the midpoint potential of the inverter to the deviation equalization controller module 202, the deviation equalization controller module 202 is configured to generate a midpoint potential equalization control amount according to an actual deviation voltage of the midpoint potential, the fundamental wave voltage module 203 expected to be output is configured to produce a three-phase fundamental wave voltage expected to be output, the midpoint voltage estimation module 204 is configured to estimate a midpoint voltage of the inverter at a next time according to the superimposed fundamental wave voltage, the midpoint voltage judgment module 205 is configured to judge whether the midpoint voltage satisfies a set range of midpoint potential balance according to the estimated midpoint voltage, and if the midpoint voltage satisfies the set range, the superimposed fundamental wave voltage is directly transmitted to the PWM controller module 3; if the neutral point voltage does not meet the set neutral point potential balance range, the parameters of the deviation balance controller are adjusted, the deviation of the neutral point voltage is re-estimated until the estimated neutral point voltage meets the set neutral point potential balance range, and then the fundamental wave voltage is transmitted to the PWM controller module 3;
as shown in fig. 3 to 4, the amplitude of the midpoint voltage fluctuation of the diode-clamped three-level inverter adopting the control method of the present invention is significantly lower than that of the inverter adopting the conventional midpoint control method, which results in the advantages that the output performance of the inverter is improved under the condition that the hardware condition and the software condition of the device are the same, and simultaneously, the overvoltage of the power device in the inverter is small due to the small voltage fluctuation, and the reliability of the device is improved.
According to the control method and device for the neutral point potential balance of the multi-level inverter, the deviation balance controller is introduced, so that the dynamic response of the whole adjusting system is quickened, neutral point voltage errors are eliminated, and the dynamic and static performances of neutral point potential adjustment are improved; by introducing inner ring control of the midpoint voltage, whether the midpoint voltage obtained by internal calculation and evaluation of the deviation balancing controller can meet the system requirements or not is judged, if the midpoint voltage can not meet the system requirements, the midpoint voltage is recalculated and can not be output until the midpoint voltage meets the system requirements, and compared with the traditional midpoint control method that whether the midpoint voltage meets the requirements or not can be judged after the actual system output, the deviation of the midpoint potential can be effectively reduced; by introducing a rapid method of overmodulation treatment, the harmonic waves of three-phase voltage output by the inverter can be effectively improved, and the output performance of the inverter is improved; the invention effectively reduces the deviation of the midpoint voltage on the premise of not increasing the system loss, reduces the cost, is suitable for diode-clamped three-level inverters in the current market, is also suitable for other types of inverters with single midpoint structures, and has wide application prospect. The control method and the device for the neutral point potential balance of the multi-level inverter have the characteristics of simple control, low cost and strong applicability.
The principles and embodiments of the present invention have been described herein using specific examples, which are provided only to help understand the method and the core concept of the present invention; meanwhile, for a person skilled in the art, according to the idea of the present invention, the specific embodiments and the application range may be changed. In view of the above, the present disclosure should not be construed as limiting the invention.
Claims (9)
1. A control method for the neutral point potential balance of a multilevel inverter is characterized by comprising the following steps:
s1, acquiring deviation voltage of a midpoint potential of an inverter;
s2, sending the deviation voltage of the midpoint potential of the inverter into a deviation balancing controller, and automatically optimizing in real time by the deviation balancing controller according to the deviation voltage of the midpoint potential;
s3, superposing the output of the deviation balancing controller to the expected output fundamental voltage;
s4, estimating the midpoint voltage of the inverter at the next moment according to the superposed fundamental wave voltage;
s5, judging whether the midpoint voltage meets the set range of midpoint potential balance or not according to the estimated midpoint voltage, if so, directly outputting the superposed fundamental voltage, and if not, dynamically adjusting the parameters of the deviation balance controller and transferring to the step S2;
in the step S2, the ant colony algorithm is adopted in the process that the deviation balancing controller performs real-time automatic optimization according to the deviation voltage of the midpoint potential, and specifically includes:
s201, recording the step length of the ant movement as lambda, the number of ants as m, the correction direction as F, the correction direction being determined by the deviation value of the midpoint potential fluctuation at the current moment, when the deviation value is positive, the correction direction F =1, otherwise F = -1, effectively shortening the iteration times by increasing the correction direction, reducing the rolling optimization calculation amount, gradually reducing the step length along with the increase of the iteration times, and the kth iteration has
λ(k)＝F·λ 0 e -k (1)
In the formula, λ 0 ＝1；
S202, ant positions are parameter adjustment values of the deviation equalization controller in a period, in the control of midpoint potential, an optimal value is searched, a solution space is one-dimensional, in the solution space, a feasible solution is defined as D e (0,1), m ants are averagely and randomly distributed into each solution space, and the feasible solution is divided into intervals so that one ant exists;
s203, when the midpoint potential control algorithm is activated, each ant can obtain the fluctuation value of the midpoint voltage, and the midpoint potential fluctuation corresponding to the position of each ant is regarded as the pheromone sediment of the position;
s204, the ant with the minimum corresponding pheromone precipitation is kept in the original position and the rest ants continue to update the positions according to the formula (2),
wherein D (k + 1) is the position of the kth iteration ant +1, D (k) is the position of the kth iteration ant, delta is the stability factor,
is a unit vector, the direction of the unit vector is that the ith ant points to the position of the ant with high pheromone content, and when all ants finish all movements, one iteration is finished;
and S205, continuously repeating the steps S203 and S204 until all ants gather at the minimum fluctuation point of the voltage.
2. The method for controlling the neutral point potential balance of the multilevel inverter according to claim 1, wherein the step S1 of obtaining the offset voltage of the neutral point potential of the inverter specifically comprises:
s101, detecting the upper bus capacitor voltage, the lower bus capacitor voltage and the three-phase current output by the inverter;
s102, calculating a power factor output by the inverter according to the three-phase voltage and the three-phase current output by the inverter; the power factor is calculated by firstly obtaining the electrical angle psi v of three-phase voltage and the electrical angle psi A of three-phase current through a phase-locked loop, and then the power factor output by the inverter is cos (psi v-psi A);
s103, calculating the deviation voltage of the midpoint potential according to the obtained power factor, wherein when the power factor is larger than or equal to 0, the deviation voltage of the midpoint potential is obtained by subtracting the lower bus voltage from the upper bus voltage, and when the power factor is smaller than 0, the deviation voltage of the midpoint potential is obtained by subtracting the upper bus voltage from the lower bus voltage.
3. The method according to claim 1, wherein the step S3 superimposes the output of the deviation-equalizing controller on the fundamental wave voltage desired to be output, in such a manner that the output of the deviation-equalizing controller is added to each of the three fundamental wave voltages output from the inverter.
4. The method for controlling the neutral point potential balance of a multilevel inverter according to claim 3, wherein when the superimposed fundamental wave voltage exceeds the maximum and minimum range values set by the modulation wave, the superimposed fundamental wave voltage is required to be overmodulatied, and the method is specifically:
firstly, judging whether the generated three-phase fundamental voltage is overmodulation or not, and if not, directly outputting the overmodulation; if yes, the overmodulation of a specific phase needs to be determined, an overmodulation offset value of the overmodulation phase is calculated, and then the offset value is added or subtracted to the three-phase fundamental voltage simultaneously so as to achieve the purpose of eliminating the overmodulation.
5. The method for controlling the midpoint potential balance of the multilevel inverter according to claim 1, wherein in the step S4, the estimating of the midpoint voltage of the inverter at the next time according to the superimposed fundamental voltage specifically comprises:
s401, establishing a mathematical model of the output quantity of the deviation balancing controller and the voltage fluctuation of the output midpoint of the inverter;
s402, substituting the output quantity of the deviation balance controller into the mathematical model to obtain the corresponding deviation voltage, thereby estimating the midpoint voltage of the next time.
6. The method according to claim 1, wherein the setting range of the midpoint potential balance in step S5 is: the estimated midpoint voltage is less than a set voltage x the system midpoint imbalance k, wherein the set voltage is the bus voltage of the inverter, and the system midpoint imbalance k is determined according to the application requirements of different systems.
7. The method for controlling the neutral point potential balance of the multilevel inverter according to claim 6, wherein the value range of the neutral point unbalance k in the system is (0,1), and the neutral point voltage fluctuation range required by the system is 1% -10%.
8. A neutral point potential balancing apparatus for a multilevel inverter, which is applied to the method for controlling neutral point potential balancing of a multilevel inverter according to any one of claims 1 to 7, the neutral point potential balancing apparatus comprising: the device comprises a deviation voltage acquisition module, a midpoint potential balance controller and a PWM controller module, wherein the input end of the deviation voltage acquisition module is electrically connected with the capacitor input end and the midpoint of a diode clamp type multi-level inverter circuit, the output end of the deviation voltage acquisition module is electrically connected with the input end of the midpoint potential balance controller, the output end of the midpoint potential balance controller is electrically connected with the input end of the PWM controller module, and the output end of the PWM controller module is electrically connected with the diode clamp type multi-level inverter of the diode clamp type multi-level inverter circuit; the device comprises a neutral point potential balance controller, a deviation voltage acquisition module, a neutral point potential balance controller, a PWM controller module and a diode clamp type multi-level inverter, wherein the deviation voltage acquisition module is used for acquiring deviation voltage of neutral point potential of the inverter and transmitting the deviation voltage to the neutral point potential balance controller, the neutral point potential balance controller is used for generating optimal neutral point potential balance control quantity in real time according to the neutral point deviation voltage, the obtained control quantity is superposed with three-phase fundamental wave voltage expected to be output and then output to the PWM controller module, and the PWM controller module is used for generating corresponding driving pulse according to the fundamental wave voltage output by the neutral point potential balance controller and controlling the diode clamp type multi-level inverter to generate PWM waves.
9. The midpoint potential balancing device of the multi-level inverter according to claim 8, wherein the midpoint potential balancing controller comprises a deviation voltage calculation module, a deviation balancing controller module, a desired output fundamental voltage module, a midpoint voltage estimation module and a midpoint voltage judgment module, an input terminal of the deviation voltage calculation module is electrically connected to an output terminal of the deviation voltage acquisition module, an output terminal of the deviation voltage calculation module is electrically connected to an input terminal of the deviation balancing controller module, output terminals of the deviation balancing controller module and the desired output fundamental voltage module are electrically connected to an input terminal of the midpoint voltage estimation module, an output terminal of the midpoint voltage estimation module is electrically connected to an input terminal of the midpoint voltage judgment module, and output terminals of the midpoint voltage judgment module are electrically connected to input terminals of the deviation balancing controller module and the PWM controller module, respectively; the deviation voltage calculation module is used for receiving deviation voltage of the midpoint potential and sending the deviation voltage of the midpoint potential of the inverter to the deviation balance controller module, the deviation balance controller module is used for generating a midpoint potential balance control quantity according to actual deviation voltage of the midpoint potential, the fundamental wave voltage module expected to be output is used for producing three-phase fundamental wave voltage expected to be output, the midpoint voltage estimation module is used for estimating the midpoint voltage of the inverter at the next moment according to the superposed fundamental wave voltage, the midpoint voltage judgment module is used for judging whether the midpoint voltage meets the set range of midpoint potential balance or not according to the estimated midpoint voltage, and if the midpoint voltage meets the set range, the superposed fundamental wave voltage is directly transmitted to the PWM controller module; and if the voltage does not meet the requirement, adjusting the parameters of the deviation balance controller, re-estimating the deviation of the midpoint voltage until the estimated midpoint voltage meets the set range of midpoint potential balance, and transmitting the fundamental voltage to the PWM controller module.
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| CN102710163B (en) * | 2012-05-22 | 2014-08-27 | 华中科技大学 | Neutral-point voltage control method of NPC (neutral-point converter) type three-level inverter based on interval selection |
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