CN110768558A - Inverter midpoint voltage balancing method based on time distribution factor method - Google Patents

Inverter midpoint voltage balancing method based on time distribution factor method Download PDF

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CN110768558A
CN110768558A CN201910909368.2A CN201910909368A CN110768558A CN 110768558 A CN110768558 A CN 110768558A CN 201910909368 A CN201910909368 A CN 201910909368A CN 110768558 A CN110768558 A CN 110768558A
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distribution factor
time distribution
voltage
time
midpoint
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戴宁
辛瑞芝
张洪波
刘鼎立
徐悦
李圣
刘树通
薛铭
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Shandong Electrical Engineering & Equipment Group Xinneng Technology Co Ltd
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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
    • 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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Abstract

The invention relates to an inverter midpoint voltage balancing method based on a time distribution factor method, which realizes the control of the midpoint voltage balancing by the time distribution factor method: introducing a small vector time distribution factor k for distributing the action time of the positive and negative small vectors in a switching period to realize the balance of the midpoint voltage; and introducing a parameter self-adaptive PI controller to obtain a small vector time distribution factor k and obtain the action time of the positive and negative small vectors to balance the midpoint voltage. The invention adopts a parameter self-adaptive adjustment PI control strategy to generate a time distribution factor k to dynamically adjust the action time of the positive and negative small vectors, thereby controlling the balance of the midpoint voltage on the direct current side. The method only needs capacitor voltage, the control algorithm is simple and easy to implement, and the digitization is favorably realized.

Description

Inverter midpoint voltage balancing method based on time distribution factor method
Technical Field
The invention belongs to the technical field of power electronic control, and particularly relates to a method for balancing midpoint voltage of a T-shaped three-level inverter based on a time distribution factor method.
Background
Compared with the traditional two-level inverter, the three-level inverter has obvious advantages in the aspects of output voltage harmonic content, output waveform, Total Harmonic Distortion (THD) and the like, so that the three-level inverter is widely applied to the field of medium-high voltage high-power inverters. At present, diode clamping type, flying capacitor type, H-bridge cascade type and the like are common in a topology structure of a three-level inverter, wherein a T-type neutral point clamped ("TNPC") three-level inverter is a new topology structure obtained by improving and optimizing the topology structure of the diode neutral point clamped three-level inverter. Compared with the traditional diode clamp type inverter, the neutral point clamping function in the T-shaped inverter is realized by the switching tubes of each phase of bridge arms which are reversely connected in series, and the neutral point clamping function has wide research and application because fewer devices are used, the loss of a circuit is reduced, and output voltage harmonics are smaller and the efficiency is higher.
There is an inherent problem in three-level inverters, namely the midpoint voltage balancing problem. When the midpoint voltage of the inverter fluctuates, the capacitors connected in series with the direct-current side bus cannot enable the voltages on the two sides to reach an accurate balanced state, so that the output waveform of the inverter is greatly influenced, the direct-current side capacitors are damaged, and even the inverter can possibly fail to work, and corresponding measures are needed to be taken to stabilize the midpoint voltage balance of the inverter. Regarding the neutral point voltage balance problem of the three-level inverter, common solutions include constructing a virtual space vector, reasonably selecting an action sequence of a redundant vector and injecting a zero-sequence voltage component, but the calculation is complex, the realization of a control system is difficult, and the online realization is not facilitated.
Disclosure of Invention
Aiming at the defects of the existing method for balancing the midpoint voltage of the T-type three-level inverter, the method analyzes the characteristics and the rules of the voltage space vector of the T-type three-level inverter, considers that the midpoint voltage balance can be realized by a small vector in an SVPWM (space pulse width modulation) algorithm, and provides a method for obtaining a time distribution factor k by adopting parameter self-adaptive PI control so as to adjust the action time of positive and negative small vectors. The improved SVPWM method is adopted to realize the control of the midpoint voltage balance of the T-type three-level inverter, the control of a balance circuit is not required to be added, the complicated calculation is simplified, and the calculation time and the response speed of the system are shortened.
The technical scheme adopted by the invention for solving the technical problems is to provide a method for balancing the midpoint voltage of the inverter based on a time distribution factor method, wherein the method for controlling the midpoint voltage balance is realized by the time distribution factor method, and comprises the following steps:
step 1, introducing a small vector time distribution factor k for distributing the action time of the positive and negative small vectors in a switching period to realize the balance of the midpoint voltage.
And 2, introducing a parameter self-adaptive PI controller to obtain a small vector time distribution factor k and obtain the action time of the positive and negative small vectors to balance the midpoint voltage.
And a parameter self-adaptive PI regulation method is adopted to calculate the time distribution factor k of the small vector, so that the calculation of parameters such as midpoint current, capacitance and the like can be avoided. The difference value of the two capacitor voltages is input into a parameter self-adaptive PI controller, the output quantity is a time distribution factor k, the current generated under the action of a small vector is added with the current generated by a middle vector to obtain a midpoint current, and the midpoint current is subjected to an integration link of a capacitor to finally obtain the actual deviation value of the upper capacitor and the lower capacitor. The inverter dynamically adjusts the action time of the positive and negative small vectors by adjusting the generated time distribution factor k through the parameter self-adaptive PI controller, thereby controlling the balance of the midpoint voltage on the direct current side.
Preferably, the input parameters of the parameter adaptive PI controller may be expressed as:
Figure BDA0002212737550000021
in the formula:
Figure BDA0002212737550000022
and
Figure BDA0002212737550000023
respectively a DC capacitor C in a T-type three-level inverter1And C2A voltage across; e is the voltage deviation, i.e. x1；x2Means for integrating the voltage deviation e; x is the number of3Indicating that the voltage deviation e is differentiated.
The time allocation factor k is calculated as:
k＝KPx1+KIx2。
the weighting coefficient of the parameter adaptive PI controller is a proportionality coefficient KPAnd integral coefficient KIAccording to the capacitor voltageAnd
Figure BDA0002212737550000025
deviation pair K ofPAnd KIAnd carrying out real-time online adjustment.
Preferably, the action time of positive and negative small vectors is (1+ k) t respectively by the time distribution factor k obtained by the parameter adaptive PI controllersT 2 and (1-k)s/2。
The invention has the beneficial effects that:
on the premise of not changing the total action time of the small vectors, the change of the two midpoint capacitor voltages needs to be detected and tracked in real time, the parameters of the traditional PI controller are difficult to select, the value of a time distribution factor k is inaccurate, the time distribution of the small vectors is influenced, and the adjustment effect of the midpoint voltage balance is further influenced. The invention adopts a parameter self-adaptive adjustment PI control strategy to generate a time distribution factor k to dynamically adjust the action time of the positive and negative small vectors, thereby controlling the balance of the midpoint voltage on the direct current side. The method only needs capacitor voltage, the control algorithm is simple and easy to implement, and the digitization is favorably realized.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below. It should be apparent that the drawings in the following description are specific embodiments of the invention, and that other drawings within the scope of the present application can be obtained by those skilled in the art without inventive effort.
Fig. 1 is a diagram of a midpoint voltage balance control structure according to an embodiment of the present invention.
Detailed Description
The present invention will be described in detail below with reference to the drawings and examples, including but not limited to the following examples.
A method for balancing the midpoint voltage of an inverter based on a time distribution factor method realizes the control of the midpoint voltage balance by the time distribution factor method, and comprises the following steps:
step 1, introducing a small vector time distribution factor k, and distributing the action time of positive and negative small vectors in a switching period to realize the balance of the midpoint voltage.
Firstly, the influence of small vectors in SVPWM on the midpoint voltage of the T-type three-level inverter is analyzed. The T-type three-level inverter comprises 12 switching devices (IGBT) in total, and 27 switching states can occur, wherein the effective space vector is 19. According to the difference of the voltage vector magnitude, the effective space vector is divided into a zero vector, a small vector, a medium vector and a large vector. Because the number of times of small vectors in the basic space vector in each sampling period is large, each large area is divided into 6 small areas so as to ensure the accuracy of a midpoint voltage balance control algorithm and simulation.
According to the working principle of the T-type three-level inverter, the midpoint voltage is not subjected to large vector summationThe influence of zero vector, and the change of the middle vector and the small vector which generate the midpoint current can cause the unbalance of the midpoint voltage, wherein the switching state corresponding to the middle vector is an uncontrollable quantity, but the small vectors which cause the change of the midpoint voltage are in pairs, namely, a positive small vector and a negative small vector, and the positive small vector and the negative small vector can have opposite influence on the midpoint voltage. When the T-type three-level inverter works in a P-type small vector, namely a positive small vector switching state (POO)]When the three-phase load is connected between the positive direct current bus and the midpoint O, the current flows into the midpoint I of the midpoint OoWill result in a midpoint voltage voAnd (4) rising. When the T-type three-level inverter operates in the N-type switching state [ ONN ] as opposed to the P-type small vector switching state]Will result in a midpoint voltage voAnd decreases. Therefore, the control of the midpoint voltage can be realized by controlling the action time of the P-type and the N-type, namely the positive and negative small vector switches, so that the midpoint voltage reaches an equilibrium state.
The time distribution factor method is a method capable of realizing accurate control of midpoint voltage balance, and small vector time distribution factors are introduced to calculate the action time of positive and negative small vectors in a switching period, so that the midpoint voltage balance is realized. Setting the time distribution factor as k, and after introducing the action of the time distribution factor k, the total action time of the negative small vectors becomes (1+ k) T1(2) the total action time of the positive small vector becomes (1-k) T1And/2, the action time of the medium vector, the large vector and the zero vector is kept unchanged.
And 2, introducing a parameter self-adaptive PI controller to obtain a small vector time distribution factor k and obtain the action time of the positive and negative small vectors to balance the midpoint voltage.
Midpoint current i generated by small vectorsoSMidpoint current i generated by the sum vectoromThe midpoint current i can be composedoNamely:
io＝ios+iom
due to iomI.e. the midpoint current generated by the medium vector action is an uncontrollable quantity, so that the midpoint voltage can be balanced by controlling tosI.e. the current generated by the small vector action.
Defining the action time of P-type small vector, namely positive small vector as tPsThe action time of the N-type small vector, i.e. the negative small vector is tNsTotal action time of small vector is tsIt is possible to obtain:
Figure BDA0002212737550000041
iOs＝tPsiP+tNsiN
in the formula iPAnd iNRespectively representing the currents generated when a positive small vector and a negative small vector act, and iP＝-iN。
From the above equation it follows:
iOs＝ktsiN
the time distribution factor k is calculated by adopting a parameter self-adaptive PI regulation method, the calculation of parameters such as midpoint current, capacitance and the like can be avoided, the analysis is combined, and according to the formula, the midpoint voltage balance control structure of the embodiment of the invention is shown in figure 1. Reference voltage deviation value in the figure
Figure BDA0002212737550000043
And actual voltage deviation value DeltaUCThe output quantity is a time distribution factor k, and the current generated by the small vector action and the current i generated by the medium vector action are addedomThereby obtaining a midpoint current ioThen passing through the integration link of the capacitor
Figure BDA0002212737550000044
Finally, the actual deviation value of the upper and lower capacitors can be obtained. The T-type three-level inverter dynamically adjusts the action time of the positive small vector and the negative small vector by adjusting the generated time distribution factor k through the parameter self-adaptive PI controller, thereby controlling the balance of the midpoint voltage on the direct current side.
The inputs of the parameter adaptive PI controller are as follows:
Figure BDA0002212737550000045
in the formula:
Figure BDA0002212737550000046
and
Figure BDA0002212737550000047
are respectively a DC capacitor C1And C2A voltage across; and e is the voltage deviation.
The time allocation factor k is calculated as:
k＝KPx1+KIx2
the weighting coefficient of the parameter adaptive PI controller is a proportionality coefficient KPAnd integral coefficient KICan be based on the capacitor voltage
Figure BDA0002212737550000051
And
Figure BDA0002212737550000052
coefficient of deviation from comparative example KPAnd integral coefficient KIAnd carrying out real-time online adjustment.
Setting e (K) to represent the deviation value between the DC side capacitor voltages at the sampling moment, and when | e (K) | is less than a given error limit, KP＝kmax(ii) a/M; when | e (K) | is greater than a given error bound, KP(n+1)＝KP(n)+η1x1x3And KI(n+1)＝KI(n)+η2x1x2η denotes the adjustment rate, according to the obtained PI adjustment coefficient, the time distribution factor k is obtained, and then the total action time of the negative small vector becomes (1+ k) ts(2) the total action time of the positive small vector becomes (1-k) ts/2。
On the premise of not changing the total action time of the small vectors, the change of the two midpoint capacitor voltages needs to be detected and tracked in real time, the parameters of the traditional PI controller are difficult to select, the value of a time distribution factor k is inaccurate, the time distribution of the small vectors is influenced, and the adjustment effect of the midpoint voltage balance is further influenced. The invention adopts a parameter self-adaptive adjustment PI control strategy to generate a time distribution factor k to dynamically adjust the action time of the positive and negative small vectors, thereby controlling the balance of the midpoint voltage on the direct current side. The method only needs capacitor voltage, the control algorithm is simple and easy to implement, and the digitization is favorably realized.
Finally, it is to be noted that: the above examples are only specific embodiments of the present invention, and are not intended to limit the technical solutions of the present invention, and the scope of the present invention is not limited thereto. Those skilled in the art will understand that: any person skilled in the art can modify or easily conceive the technical solutions described in the foregoing embodiments or equivalent substitutes for some technical features within the technical scope of the present disclosure; such modifications, changes or substitutions do not depart from the spirit and scope of the embodiments of the present invention, and they should be construed as being included therein.

Claims (3)

1. A method for balancing the midpoint voltage of an inverter based on a time distribution factor method is characterized by comprising the following steps:
step 1, introducing a small vector time distribution factor k for distributing the action time of positive and negative small vectors in a switching period to realize the balance of the midpoint voltage;
step 2, introducing a parameter self-adaptive PI controller to obtain a small vector time distribution factor k, and obtaining positive and negative small vector action time to balance midpoint voltage;
the difference value of the two capacitor voltages is input into a parameter self-adaptive PI controller, the output quantity is a time distribution factor k, the current generated under the action of a small vector is added with the current generated by a middle vector to obtain a midpoint current, and the midpoint current is subjected to an integration link of a capacitor to finally obtain the actual deviation value of the upper capacitor and the lower capacitor; the inverter dynamically adjusts the action time of the positive and negative small vectors by adjusting the generated time distribution factor k through the parameter self-adaptive PI controller, and controls the balance of the midpoint voltage on the direct current side.
2. The inverter midpoint voltage balancing method based on the time distribution factor method according to claim 1, wherein the input of the parameter adaptive PI controller is as follows:
Figure FDA0002212737540000011
in the formula:
Figure FDA0002212737540000012
and
Figure FDA0002212737540000013
are respectively a DC capacitor C1And C2A voltage across; e is the voltage deviation;
the time allocation factor k is calculated as:
k＝KPx1+K1x2；
the weighting coefficient of the parameter adaptive PI controller is a proportionality coefficient KPAnd integral coefficient KIAccording to the capacitor voltage
Figure FDA0002212737540000014
And
Figure FDA0002212737540000015
deviation pair K ofPAnd KIAnd carrying out real-time online adjustment.
3. The inverter neutral-point voltage balancing method based on the time distribution factor method according to any one of claims 1 or 2, wherein the action time of positive and negative small vectors obtained by the time distribution factor k obtained by the parameter adaptive PI controller is (1+ k) tsT 2 and (1-k)s/2。
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CN111865126A (en) * 2020-07-23 2020-10-30 珠海格力电器股份有限公司 Neutral point potential balance control method, device, medium and motor of three-level inverter
CN114614693A (en) * 2022-05-11 2022-06-10 深圳库马克科技有限公司 Balancing method and balancing device for midpoint voltage
CN116032138A (en) * 2023-03-29 2023-04-28 深圳市首航新能源股份有限公司 Driving method, driving device, inverter circuit and inverter

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CN114614693A (en) * 2022-05-11 2022-06-10 深圳库马克科技有限公司 Balancing method and balancing device for midpoint voltage
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Application publication date: 20200207