CN101834443B - Method for balancing three-level direct current midpoint voltage by using time factor - Google Patents
Method for balancing three-level direct current midpoint voltage by using time factor Download PDFInfo
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- CN101834443B CN101834443B CN2010101555396A CN201010155539A CN101834443B CN 101834443 B CN101834443 B CN 101834443B CN 2010101555396 A CN2010101555396 A CN 2010101555396A CN 201010155539 A CN201010155539 A CN 201010155539A CN 101834443 B CN101834443 B CN 101834443B
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Abstract
The invention discloses a method for balancing a three-level direct current midpoint voltage by using a time factor, which comprises the following steps of: 1, sampling a midpoint voltage and a midpoint current, and judging the midpoint voltage and the midpoint current; 2, executing a step 3 when the midpoint voltage is not zero, and jumping to a step 5 when the midpoint voltage is zero; 3, determining acting time of positive and negative small vectors according to the directions of the midpoint voltage and the midpoint current; 4, balancing the midpoint voltage after the positive and negative small vectors are counteracted; and 5, finishing the program. The value range of the time factor is experimental data and is adjusted according to the voltage value and the current value detected by an active filter and the running directions of the voltage and the current. The method has the advantages of prolonging service life of the capacitor, along with simple and convenient operation, low voltage fluctuation on a direct-current side capacitor, few sampling data and low requirement on software and hardware.
Description
Technical field
The present invention relates to a kind of balance method that is applied to Active Power Filter-APF three level system, particularly relate to a kind of method of utilizing time factor balancing three-level direct current mid-point voltage.
Background technology:
Three level voltage equilibrium problems of the DC side of Active Power Filter-APF are one of key technologies of active filter.When the mid point of Active Power Filter-APF DC side is uneven, to bring following harm: the first, current transformer output voltage waveforms distorted, be input to harmonic compensation current in the electrical network just with low-order harmonic, thereby make Active Power Filter-APF can not follow the tracks of well the harmonic current of load; The second, the voltage that bears of switching device is unbalanced, every mutually in a part of device to bear voltage higher, will affect normal operation when serious; Three, the voltage fluctuation on the dc bus capacitor has reduced the life-span of electric capacity.
For Active Power Filter-APF can be worked, should make great efforts to make mid-point voltage to keep balance.Especially when design current transformer control strategy, to consider the impact of vector alignment voltage, the fluctuation of mid-point voltage is dropped to minimum degree.The method of prior art control neutral point voltage balance mainly contains: one, open loop control, by the positive and negative small vector of alternate selection, do not need to detect DC bus-bar voltage and output end current, realize simple, but because the impact of vector alignment voltage in can't compensating, thus can only be by the symmetry of middle vector self, at a complete output voltage in the cycle, finish neutral point voltage balance, cause mid-point voltage to have very large low-frequency ripple; Two, detect the dc capacitor voltage size, then according to the offset direction of mid-point voltage, the PWM of the positive and negative small vector of the reasonable arrangement (abbreviation of Pulse Width Modulation, be pulse width modulation) action time of pulse, carry out the mid-point voltage compensation, but the method algorithm is very complicated; Three, detect dc capacitor voltage size and three-phase alternating current output current, the method obtains directivity function by real-time detection three-phase alternating current output current direction, utilize this function to select in the PWM cycle generating positive and negative voltage vector to control the mid point sense of current action time, realize the balance of voltage, this method is fine good in theory, and it can calculate the concrete time of compensation, but the data that the method will be sampled are many, amount of calculation is larger, to having relatively high expectations of software and hardware.
Summary of the invention:
The object of the invention is to overcome the deficiencies in the prior art, a kind of method of utilizing time factor balancing three-level direct current mid-point voltage is provided, realize simply and easily three level neutral point voltage balances.
In order to achieve the above object, the technical solution used in the present invention is:
A kind of method of utilizing time factor balancing three-level direct current mid-point voltage, step is as follows:
Step 1, beginning alignment voltage and mid point electric current are sampled, and alignment voltage and mid point electric current are judged;
Step 2, mid-point voltage are non-vanishing, execution in step 3, and mid-point voltage is zero, skips to step 5;
Step 3, mid-point voltage greater than zero and the mid point electric current greater than zero the time negative small vector according to time factor fine setting offset mid-point voltage greater than zero part,
Mid-point voltage less than zero and the mid point electric current less than zero the time positive small vector according to time factor fine setting offset mid-point voltage greater than zero part,
Mid-point voltage less than zero and the mid point electric current greater than zero the time positive small vector according to time factor fine setting offset mid-point voltage greater than zero part,
Mid-point voltage greater than zero and the mid point electric current less than zero the time negative small vector according to time factor k fine setting offset mid-point voltage greater than zero part;
Mid-point voltage after step 4, the positive and negative small vector of process are offset reaches balance;
Step 5, EP (end of program).
The present invention adopts time factor to distribute the action time of the positive and negative state of a pair of small vector in the sampling period, the control mid-point voltage.Be Tx the action time of supposing positive and negative small vector, k represents time factor, be kTx the negative small vector action time when then beginning, be (1-k) Tx the action time of positive small vector, the mid-point voltage value is the poor of DC side dividing potential drop capacitance voltage Vdc1 and Vdc2, mid point outflow of bus current direction is for just, and concrete control law is:
Vdc1-Vdc2＞h and I0＞0 a k value is got (1-k), and the time of positive small vector effect is (1-k) Tx;
Vdc1-Vdc2＞h and I0＜0 a k value is constant, and the time of negative small vector effect is kTx;
Vdc1-Vdc2＜-h and I0＞0 a k value are constant, and the time of negative small vector effect is kTx;
Vdc1-Vdc2＜-h and I0＜0 a k value get (1-k), and the time of positive small vector effect is (1-k) Tx.
H is that the stagnant endless belt of voltage is wide, I0 is the mid point electric current, k is experimental data, traffic direction according to the magnitude of voltage that detects in active power filter, current value and voltage and current is adjusted size, decide positive and negative small vector pwm pulse to act on the time of system, the size of adjustment is according to the size of the wide h of stagnant endless belt in 4 relational expressions.
Find out from above four formulas, need not to judge the balance that just can keep mid-point voltage through the logic of complexity, simultaneously owing to the wide existence of endless belt that stagnates, so that k value amplitude of variation is little, control by the real-time alignment magnitude of voltage of negative feed back control system, reach the balance of mid-point voltage.
Compared with prior art, the invention has the beneficial effects as follows: the first, utilize time factor k that the positive and negative small vector of three level mid-point voltages is finely tuned, reach neutral point voltage balance, easy and simple to handle; The second, the voltage fluctuation on the dc bus capacitor is little, has prolonged the life-span of electric capacity; Three, sampled data is few, to software and hardware require low.
Description of drawings:
Fig. 1 is theory diagram of the present invention;
Fig. 2 is the three dimensional vector diagram of three level of the present invention.
Embodiment:
Central idea of the present invention is to overcome the deficiencies in the prior art, and a kind of method of utilizing time factor balancing three-level direct current mid-point voltage is provided, can simple and effective realization three level neutral point voltage balances.Be elaborated with reference to accompanying drawing below in conjunction with embodiment, in order to technical characterictic of the present invention and advantage are carried out more deep annotation.
Theory diagram of the present invention as shown in Figure 1, a kind of method of utilizing time factor balancing three-level direct current mid-point voltage, step is as follows:
Step 1, beginning alignment voltage and mid point electric current are sampled, and alignment voltage and mid point electric current are judged;
Step 2, mid-point voltage are non-vanishing, execution in step 3, and mid-point voltage is zero, skips to step 5;
Step 3, mid-point voltage greater than zero and the mid point electric current greater than zero the time negative small vector according to time factor fine setting offset mid-point voltage greater than zero part,
Mid-point voltage less than zero and the mid point electric current less than zero the time positive small vector according to time factor fine setting offset mid-point voltage greater than zero part,
Mid-point voltage less than zero and the mid point electric current greater than zero the time positive small vector according to time factor fine setting offset mid-point voltage greater than zero part,
Mid-point voltage greater than zero and the mid point electric current less than zero the time negative small vector according to time factor k fine setting offset mid-point voltage greater than zero part;
Mid-point voltage after step 4, the positive and negative small vector of process are offset reaches balance;
Step 5, EP (end of program).
The present invention adopts time factor to distribute the action time of the positive and negative state of a pair of small vector in the sampling period, the control mid-point voltage.Be Tx the action time of supposing positive and negative small vector, k represents time factor, be kTx the negative small vector action time when then beginning, be (1-k) Tx the action time of positive small vector, the mid-point voltage value is the poor of DC side dividing potential drop capacitance voltage Vdc1 and Vdc2, mid point outflow of bus current direction is for just, and concrete control law is:
Vdc1-Vdc2＞h and I0＞0 a k value is got (1-k), and the time of positive small vector effect is (1-k) Tx;
Vdc1-Vdc2＞h and I0＜0 a k value is constant, and the time of negative small vector effect is kTx;
Vdc1-Vdc2＜-h and I0＞0 a k value are constant, and the time of negative small vector effect is kTx;
Vdc1-Vdc2＜-h and I0＜0 a k value get (1-k), and the time of positive small vector effect is (1-k) Tx.
H is that the stagnant endless belt of voltage is wide, I0 is the mid point electric current, the span of time factor k is experimental data, adjust the size of k according to the traffic direction of the magnitude of voltage that detects at active power filter, current value and voltage and current, decide the time of the system that acts on of positive and negative small vector pwm pulse, the size of adjustment is according to the size of the wide h of stagnant endless belt in 4 relational expressions.
Find out from above four formulas, need not to judge the balance that just can keep mid-point voltage through the logic of complexity, simultaneously owing to the wide existence of endless belt that stagnates, so that k value amplitude of variation is little, control by the real-time alignment magnitude of voltage of negative feed back control system, reach the balance of mid-point voltage.
The three dimensional vector diagram of three level as shown in Figure 2, A, B, C are three level voltages, synthetic vector voltage can be divided three classes among the figure:
6 of long vectors: PNN, PNP, NNP, NPP, NPN, PPN, be positioned at orthohexagonal summit, three switches all only have P, N two states.
6 of middle vectors: PON, OPN, NPO, NOP, ONP, OPN are positioned at the mid point on every limit of regular hexagon.
6 pairs of short vectors: POO, ONN, PPO, OON, OPO, NON, OPP, NOO, OOP, NNO, POP, ONO are the small voltage vector of 12 2DOFs, are positioned at regular hexagon center and summit line mid point.
Short vector voltage is three level DC mid-point voltage of the present invention, when mid-point voltage value and theoretical value have deviation, controls the time fine tuning mid-point voltage value of positive and negative small vector effect by time factor k, reaches the balance of three level mid-point voltages.
Claims (1)
1. method of utilizing time factor balancing three-level direct current mid-point voltage, be Tx the action time of supposing positive and negative small vector, k represents time factor, be kTx the negative small vector action time when then beginning, be (1-k) Tx the action time of positive small vector, the mid-point voltage value is the poor of DC side dividing potential drop capacitance voltage Vdc1 and Vdc2, and mid point outflow of bus current direction is for just, and concrete control law is:
Vdc1-Vdc2＞h and I0＞0 a k value is got (1-k), and the time of positive small vector effect is (1-k) Tx;
Vdc1-Vdc2＞h and I0＜0 a k value is constant, and the time of negative small vector effect is kTx;
Vdc1-Vdc2＜-h and I0＞0 a k value are constant, and the time of negative small vector effect is kTx;
Vdc1-Vdc2＜-h and I0＜0 a k value get (1-k), and the time of positive small vector effect is (1-k) Tx;
H is that the stagnant endless belt of voltage is wide, I0 is the mid point electric current, the span of time factor k is experimental data, adjust the size of k according to the traffic direction of the magnitude of voltage that detects at active power filter, current value and voltage and current, decide the time of the system that acts on of positive and negative small vector pwm pulse, the size of adjustment is according to the size of the wide h of stagnant endless belt in 4 relational expressions.
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| CN103095166B (en) * | 2013-01-30 | 2015-03-18 | 华为技术有限公司 | Modulating method and modulating equipment of space vector pulse width |
| CN103178737A (en) * | 2013-03-25 | 2013-06-26 | 江苏宝丰新能源科技有限公司 | Hysteresis control method for keeping midpoint voltage balance of three-level photovoltaic inverter |
| CN104167947B (en) * | 2014-07-18 | 2017-04-12 | 山东大学 | Z-source three-level T-type inverter and neutral-point balance control method thereof |
| CN104158422A (en) * | 2014-07-30 | 2014-11-19 | 华南理工大学 | Mid-point voltage control method for midpoint clamping type three-level inverter |
| CN105610339B (en) * | 2015-12-22 | 2018-03-02 | 国家电网公司 | A kind of three-level modulation method of Virtual Space vector |
| CN106533230A (en) * | 2016-12-15 | 2017-03-22 | 东南大学 | Three-level virtual space vector voltage equalizing modulation method based on simplified balance factor |
| CN106787917B (en) * | 2017-01-16 | 2019-05-14 | 华南理工大学 | A kind of NP complementary type SVPWM control method of three-phase tri-level inverter |
| CN108270367A (en) * | 2017-10-17 | 2018-07-10 | 天津铁科运通轨道技术有限公司 | A kind of three-level current transformer neutral balance control method |
| CN109617440B (en) * | 2018-12-12 | 2021-03-12 | 上海电机学院 | SVPWM-based three-level inverter direct-current side midpoint voltage balancing method |
| CN111224573B (en) * | 2020-01-20 | 2021-08-03 | 北京瑞盈同创智能技术研究院有限公司 | Current polarity-based midpoint potential balance control method and device |
| CN113395008B (en) * | 2021-07-27 | 2022-08-23 | 盾石磁能科技有限责任公司 | Midpoint balance control method of flywheel energy storage motor driving circuit in charging process |
| 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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