CN111082688B - Carrier reverse phase laminated PWM midpoint potential balance control method - Google Patents

Carrier reverse phase laminated PWM midpoint potential balance control method Download PDF

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CN111082688B
CN111082688B CN201911353333.1A CN201911353333A CN111082688B CN 111082688 B CN111082688 B CN 111082688B CN 201911353333 A CN201911353333 A CN 201911353333A CN 111082688 B CN111082688 B CN 111082688B
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pwm
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CN111082688A (en
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李耀华
高瞻
葛琼璇
赵鲁
张波
王晓新
张树田
吕晓美
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Institute of Electrical Engineering of CAS
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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
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02P—CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
    • H02P27/00—Arrangements or methods for the control of AC motors characterised by the kind of supply voltage
    • H02P27/04—Arrangements or methods for the control of AC motors characterised by the kind of supply voltage using variable-frequency supply voltage, e.g. inverter or converter supply voltage
    • H02P27/06—Arrangements or methods for the control of AC motors characterised by the kind of supply voltage using variable-frequency supply voltage, e.g. inverter or converter supply voltage using dc to ac converters or inverters
    • H02P27/08—Arrangements or methods for the control of AC motors characterised by the kind of supply voltage using variable-frequency supply voltage, e.g. inverter or converter supply voltage using dc to ac converters or inverters with pulse width modulation
    • H02P27/12—Arrangements or methods for the control of AC motors characterised by the kind of supply voltage using variable-frequency supply voltage, e.g. inverter or converter supply voltage using dc to ac converters or inverters with pulse width modulation pulsing by guiding the flux vector, current vector or voltage vector on a circle or a closed curve, e.g. for direct torque control

Abstract

A carrier reverse phase laminated PWM midpoint potential balance control method. Aiming at the condition that a three-level converter uses carrier inversion lamination PWM as a modulation strategy, when the midpoint potential deviation exceeds a limit value, firstly determining a middle vector used by the carrier inversion lamination PWM in a current phase angle region; then detecting the midpoint potential deviation value and the modulation wave and midpoint current corresponding to the medium vector, judging the product direction of the three, and sending the product direction to a PI controller to obtain a medium vector time adjustment factor delta Uneu; and controlling the action time of the medium vector by superposing the medium vector time adjustment factor delta Uneu on a modulation wave corresponding to the medium vector, thereby controlling the neutral point potential balance under the action of carrier inversion lamination PWM. The control method can control the midpoint potential deviation under the action of the carrier reverse phase laminated PWM method within a limited range, and improves the reliability of the three-level converter.

Description

Carrier reverse phase laminated PWM midpoint potential balance control method
Technical Field
The invention relates to a neutral point potential balance control method, in particular to a carrier reverse phase laminated PWM neutral point potential balance control method.
Background
A typical three-level converter, such as a three-level Neutral Point Clamped (NPC) converter, has a main circuit topology as shown in fig. 1. Compared with the traditional two-level converter, the three-level NPC converter can output three different level states by controlling the on and off of each switching device of a three-phase bridge arm, and has the advantages of high output power, low device voltage stress and the like; compared with a cascaded H-bridge multi-level topology, the cascaded H-bridge multi-level topology has the advantages of simple circuit structure, convenience in back-to-back operation and the like. Based on the advantages, the three-level NPC converter is generally applied to the speed regulation occasion of the medium-high voltage high-power motor at present.
The common-mode voltage is zero-sequence voltage with high-frequency and high-amplitude characteristics between a load neutral point and a reference potential point. The document entitled "a method for predicting common-mode voltage suppression by a voltage source inverter model based on optimized voltage vector selection" (Guo Lei, Jinnan, Shen Yongpeng [ J ]. the report of electrotechnical science 2018,33(6):1347-2355.) indicates that when a three-level converter is applied to the speed regulation field of a medium-high voltage high-power motor, the common-mode voltage can have adverse effects on the service life and the insulation performance of a bearing of a traction motor and cause electromagnetic interference. To extend traction motor life, one must try to reduce the common mode voltage of the three-level converter.
The carrier reverse phase laminated PWM is a modulation strategy based on carrier comparison, and generates a corresponding PWM control signal by comparing two triangular carriers with the same frequency, the same phase and the same amplitude and reverse direction with a three-phase modulation wave, thereby controlling the on or off of each bridge arm power switching device of the three-level converter. The carrier inversion lamination PWM principle is simple and easy to realize, and the specific principle schematic diagram is shown in FIG. 2.
Document "Pulse width modulation for power converters" and "capacitors" in Holmes d.g., Lipo T a M. New York: IEEE Press,2003.) indicates that, compared to conventional SPWM and SVPWM, carrier-inverting stacked PWM can reduce the common-mode voltage of the three-level converter from one third to one sixth of the dc voltage. Therefore, the carrier inversion stacked PWM is more suitable for the requirement of the three-level converter on reducing the common-mode voltage.
Besides reducing the common mode voltage, the three-level converter also needs to pay attention to maintaining the midpoint potential balance, that is, maintaining the deviation value of the upper end voltage and the lower end voltage of the direct current side of the three-level converter within a limited range. Unbalanced midpoint potential can generate low-order harmonic in output voltage and cause power devices of a certain half bridge arm of the three-level converter to bear overhigh voltage, so that the operation safety is endangered, and therefore measures must be taken to ensure balanced midpoint potential of the three-level converter.
Defining the dc side voltage of the three-level converter to be 2E, the three level states from high to low output of which are P, O, N respectively, and the corresponding output voltages are E, 0, -E respectively, the voltage space vectors of the three-level converter can be summarized in fig. 3. Each voltage space vector in fig. 3 can be classified into a zero vector, a P-type small vector, an N-type small vector, a medium vector, and a large vector according to the magnitude and the corresponding level state. And the P-type small vector and the N-type small vector at the same phase angle are mutually redundant small vectors. Table 1 summarizes the specific classification of the voltage space vectors of the three-level converter.
TABLE 1 three-level converter voltage space vector types
Figure BDA0002335239520000021
The existing midpoint potential balance control method mainly utilizes the principle that the directions of midpoint currents corresponding to P-type small vectors and N-type small vectors at the same phase angle are opposite, when the midpoint potential imbalance phenomenon occurs, the directions of three-phase currents are judged, then redundant small vector action time beneficial to midpoint potential balance is added, and therefore the upper end voltage and the lower end voltage on the direct current side are controlled to restore balance again. The principle of the method is described in detail in the document 'hybrid three-level neutral-point potential balance control strategy' (Zhoujinghua, [ J ]. Chinese electro-mechanical engineering, 2013,33(24): 82-89.).
Fig. 4 is a three-phase voltage waveform of the carrier reverse phase laminated PWM at a carrier ratio of 12. From the analysis, the equivalent voltage space vector sequence of the carrier-inverted stacked PWM in the phase angle region of 0 degree to 60 degrees is PNP → ONP → ONO → OOO → ONO → ONP, PNP → PNO → ONO → OOO → ONO → PNO → PNN, and only a small vector ONO is used in each carrier period, and the corresponding redundant small vector POP is not used. Because the carrier inversion lamination PWM only uses one small vector in each carrier period, the traditional method for redistributing the action time of the redundant small vector cannot be utilized to regulate and control the neutral point potential balance.
The carrier reverse phase laminated PWM can effectively reduce the common mode voltage of the three-level converter, but the method cannot utilize the existing method for redistributing the action time of the redundant small vector to regulate and control the neutral point potential balance. In order to better apply carrier inversion lamination PWM in a three-level converter, a midpoint potential balance control method suitable for the carrier inversion lamination PWM needs to be designed.
Disclosure of Invention
In order to overcome the defect that the carrier reverse phase laminated PWM can not utilize the existing method for redistributing the action time of the redundant small vectors to carry out neutral point potential balance control, the invention provides a carrier reverse phase laminated PWM neutral point potential balance control method. The invention can control the midpoint potential deviation under the action of the carrier reverse phase laminated PWM within a limited range, thereby improving the reliability of the three-level converter when the carrier reverse phase laminated PWM is used as a modulation strategy.
Aiming at the condition that a three-level converter uses carrier inversion lamination PWM as a modulation strategy, when the deviation of the midpoint potential exceeds a limit value, a middle vector used by the carrier inversion lamination PWM in a current phase angle area is determined; then detecting the midpoint potential deviation value and the modulation wave and midpoint current corresponding to the medium vector, judging the product direction of the three, and sending the product direction to a PI controller to obtain a medium vector time adjustment factor delta Uneu; and controlling the action time of the medium vector by superposing the medium vector time adjustment factor delta Uneu on a modulation wave corresponding to the medium vector, thereby controlling the neutral point potential balance under the action of carrier inversion lamination PWM.
When the midpoint potential deviation exceeds a limit value, the carrier reverse phase laminated PWM midpoint potential balance control method specifically comprises the following steps:
1. determining a medium vector used by carrier phase inversion lamination PWM in a current phase angle area;
when the midpoint potential deviation exceeds a limit value, determining a medium vector used by carrier reversed phase laminated PWM in a current phase angle area; defining the three level states of the three-level converter from high to low output as P, O, N, the medium vectors used by the carrier inversion lamination PWM in different phase angle regions are respectively as follows:
1) for a phase angle region of 30 degrees to 90 degrees, the medium vector used by the carrier inversion lamination PWM is PNO;
2) for a phase angle region of 90 degrees to 150 degrees, a middle vector used by the carrier inversion lamination PWM is PON;
3) for the phase angle region of 150 degrees to 210 degrees, the middle vector used by the carrier phase inversion lamination PWM is OPN;
4) for a phase angle region from 210 degrees to 270 degrees, the middle vector used by the carrier inversion lamination PWM is NPO;
5) for a phase angle region of 270 degrees to 330 degrees, the middle vector used by the carrier inversion lamination PWM is NOP;
6) for the 330 degree to 30 degree phase angle region, the medium vector used by the carrier inversion stacked PWM is ONP.
2. Detecting a modulation wave corresponding to the middle vector and a midpoint current;
the control method of the invention judges the product direction of the midpoint potential deviation value and the modulation wave and the midpoint current corresponding to the midpoint vector by detecting the midpoint potential deviation value and the midpoint vector, and sends the product direction to the PI controller to obtain a midpoint vector time adjustment factor delta Uneu; the modulation wave and the midpoint current corresponding to the vector in the definition are respectively UxAnd ixThe method for detecting the modulation wave and the midpoint current corresponding to the medium vector comprises the following steps:
1) when the middle vector is PNO or NPO, there is Ux＝Umc，ix＝ic；
2) When the middle vector is PON or NOP, there is Ux＝Umb，ix＝ib；
3) When the middle vector is OPN or ONP, there is Ux＝Uma，ix＝ia；
In the above detection method, Uma、Umb、UmcModulated waves i representing A, B and C phases, respectivelya、ib、icThe currents of the A phase, the B phase and the C phase are respectively. Three-phase modulated wave Uma、UmbAnd UmcThe definition is as follows:
Figure BDA0002335239520000041
to Uma、UmbAnd UmcIn definition, Ua、Ub、UcRepresents sine waves of A phase, B phase and C phase, U0Is a zero sequence component. U shapea、Ub、UcAnd U0Is defined as follows:
Figure BDA0002335239520000042
to Ua、Ub、UcAnd U0In the definition, M is the amplitude of the modulated wave after per unit, ωbIs angular frequency, UmaxAnd UminRespectively represents Ua、Ub、UcMaximum and minimum values of (a).
3. Detecting a midpoint potential deviation value;
the control method of the invention judges the product direction of the midpoint potential deviation value and the modulation wave and the midpoint current corresponding to the midpoint vector by detecting the midpoint potential deviation value and the midpoint vector, and sends the product direction to the PI controller to obtain a midpoint vector time adjustment factor delta Uneu; the detection method of the midpoint potential deviation value comprises the following steps:
ΔU＝Udc1-Udc2
in the above formula, Δ U represents a midpoint potential deviation value, Udc1For the upper voltage, U, of the DC side of the three-level converterdc2The voltage is the lower end voltage of the direct current side of the three-level converter.
4. Superposing the medium vector time adjustment factor delta Uneu to a modulation wave corresponding to a medium vector;
the control method controls the action time of the medium vector by superposing the medium vector time adjustment factor delta Uneu to the modulation wave corresponding to the medium vector, thereby controlling the neutral point potential balance under the action of carrier reverse phase laminated PWM; the specific way of superimposing the medium vector time adjustment factor Δ unneu to the medium vector corresponding modulation wave is as follows:
1) for the phase angle regions of 30 degrees to 90 degrees, 210 degrees to 270 degrees, there is Uma＝Uma，Umb＝Umb，Umc＝Umc+ΔUneu；
2) For phase angle regions of 90 degrees to 150 degrees, 270 degrees to 330 degrees, there is Uma＝Uma，Umb＝Umb+ΔUneu，Umc＝Umc；
3) For the phase angle regions of 150 degrees to 210 degrees and 330 degrees to 30 degrees, there is Uma＝Uma+ΔUneu，Umb＝Umb，Umc＝Umc；
In the above mode, Uma、Umb、UmcThe modulation waves respectively represent A phase, B phase and C phase, and the delta Uneu is a medium vector time adjustment factor.
5. Limiting the range of the modulation wave corresponding to the middle vector to be-1 to 1;
the control method controls the action time of the medium vector by superposing the medium vector time adjustment factor delta Uneu to the modulation wave corresponding to the medium vector, thereby controlling the neutral point potential balance under the action of carrier reverse phase laminated PWM; the range of the modulation wave corresponding to the intermediate vector after the intermediate vector time adjustment factor Δ unneu is superimposed should be limited to-1 to 1, and the specific limiting method is as follows:
1) for the 30 degree to 90 degree, 210 degree to 270 degree phase angle regions, there are:
Figure BDA0002335239520000051
2) for the phase angle regions of 90 degrees to 150 degrees, 270 degrees to 330 degrees, there are:
Figure BDA0002335239520000052
3) for the phase angle region of 150 degrees to 210 degrees, 330 degrees to 30 degrees, there are:
Figure BDA0002335239520000053
in the above limiting method, Uma、Umb、UmcThe modulated waves of the A phase, B phase and C phase are represented respectively.
6. When the midpoint potential deviation value of the three-level converter is within a limited range, enabling a middle vector time adjustment factor delta Uneu to be 0;
the control method of the invention is only put into use when the midpoint potential deviation exceeds a limit value. And when the midpoint potential deviation value of the three-level converter is within a limited range, enabling the delta Uneu to be 0, and not adjusting the modulation wave. Δ unneu is the medium vector time adjustment factor.
Drawings
FIG. 1 three-level NPC converter topology;
FIG. 2 is a carrier-reversed phase stacked PWM schematic;
FIG. 3 is a voltage space vector diagram of a three-level converter;
FIG. 4 shows three-phase voltages under the action of carrier inversion lamination PWM in a phase angle region from 0 to 60 degrees at a carrier ratio of 12;
fig. 5 is a schematic diagram of the influence of upward or downward shift of the medium vector on the acting time of the medium vector corresponding to the modulation wave used by the carrier inversion stacked PWM in the phase angle region from 90 degrees to 120 degrees;
fig. 6 is a schematic diagram of the influence of upward or downward shift of the medium vector on the acting time of the medium vector corresponding to the modulation wave used by the carrier inversion stacked PWM in the phase angle region of 120 to 150 degrees;
FIG. 7 is a detailed schematic diagram of a carrier inversion stacking PWM midpoint potential balance control method according to the present invention;
FIG. 8 shows the variation of the upper and lower voltages on the DC side without the midpoint potential balance protection, with the fundamental frequency of 50Hz and the modulation ratio fixed at 0.8;
FIG. 9 shows the fundamental frequency of 50Hz, the modulation ratio of 0.8, and the results of the point potential balance control method of the present invention; fig. 9a is a variation of the voltage at the upper end and the voltage at the lower end of the dc side, and fig. 9b is a comparison of the midpoint potential deviation value and the limit value;
FIG. 10 shows the variation of the upper and lower voltages on the DC side without the midpoint potential balance protection, with a fundamental frequency of 50Hz and a modulation ratio of 0.1 to 1 cyclically;
FIG. 11 shows the results of an example in which the fundamental frequency of the example is 50Hz, the modulation ratio is varied cyclically from 0.1 to 1, and the point potential balance control method according to the present invention is applied; FIG. 11a is the variation of the voltage at the upper end and the voltage at the lower end of the DC side, and FIG. 11b is the comparison of the midpoint potential deviation value and the limit value; fig. 11c shows a modulation ratio that varies cyclically.
Detailed Description
The invention is further described with reference to the following figures and detailed description.
Aiming at the condition that a three-level converter uses carrier inversion lamination PWM as a modulation strategy, when the deviation of the midpoint potential exceeds a limit value, a middle vector used by the carrier inversion lamination PWM in a current phase angle area is determined; then detecting the midpoint potential deviation value and the modulation wave and midpoint current corresponding to the medium vector, judging the product direction of the three, and sending the product direction to a PI controller to obtain a medium vector time adjustment factor delta Uneu; and controlling the action time of the medium vector by superposing the medium vector time adjustment factor delta Uneu on a modulation wave corresponding to the medium vector, thereby controlling the neutral point potential balance under the action of carrier inversion lamination PWM.
The carrier reverse phase laminated PWM midpoint potential balance control method specifically comprises the following steps:
firstly, judging whether the midpoint potential deviation exceeds a limit value, if so, executing the following steps, and if not, setting the middle vector time adjusting factor delta Uneu to be 0.
When the midpoint potential deviation exceeds a limit value, the control method of the invention comprises the following steps:
1. determining a medium vector used by carrier phase inversion lamination PWM in a current phase angle area;
when the midpoint potential deviation exceeds a limit value, the control method firstly determines a medium vector used by the carrier inversion lamination PWM in the current phase angle area. The reason why the in-use vector of the carrier inversion lamination PWM needs to be determined is as follows:
if the product of the current flowing into the midpoint and the time is not equal to the product of the current flowing out of the midpoint and the time in one sampling period, the charging voltage and the discharging voltage of the upper end capacitor and the lower end capacitor on the direct current side are not equal, and further the midpoint potential is unbalanced. Only the small vector and the medium vector can generate the midpoint current, namely only the small vector and the medium vector can influence the midpoint potential, so that the balance of the midpoint potential can be controlled by adjusting the action time of the small vector and the medium vector.
As shown in fig. 4, the equivalent voltage space vector sequence of the carrier-inverted stacked PWM within one sampling period is PNP → ONP → ONO → OOO. Setting the sampling period as T, and the action time of PNP, ONP, ONO and OOO in one sampling period as TL、TM、TSAnd TZFrom volt-second equivalent principle, it can be known that:
Figure BDA0002335239520000061
in the formula (1), m represents a modulation ratio, theta represents a phase angle, T is a sampling period, and T isLActing time, T, of large vector PNPMTime of action of the medium vector ONP, TSTime of action, T, of the small vector ONOZThe action time of the zero vector OOO. As can be seen from the analysis formula (1), as the modulation ratio m increases, the action time of the medium vector and the large vector increases, and the action time of the zero vector and the small vector decreases.
The modulation ratio is proportional to the fundamental wave amplitude of the output line voltage of the three-level converter, so that the midpoint current gradually increases along with the increase of the modulation ratio. From the above results, it can be seen that the influence of the medium vector on the center potential is larger than that of the small vector for the carrier-inverted stacked PWM. Therefore, the neutral point potential balance under the action of the carrier reverse phase laminated PWM can be controlled by controlling the action time of the vector corresponding to the carrier reverse phase laminated PWM.
In different phase angle regions, the medium vectors used by the carrier inversion lamination PWM are respectively as follows:
1) for the phase angle area of 0-30 degrees, the carrier phase inversion lamination PWM equivalent voltage space vector sequence is PNP → ONP → ONO → OOO, and the corresponding middle vector is ONP;
2) for a phase angle area of 30-60 degrees, the carrier phase inversion lamination PWM equivalent voltage space vector sequence is PNP → PNO → ONO → OOO, and the corresponding middle vector is PNO;
3) for a phase angle area of 60 degrees to 90 degrees, the carrier phase inversion laminated PWM equivalent voltage space vector sequence is PNN → PNO → POO → OOO, and the corresponding used medium vector is PNO;
4) for a phase angle area of 90 degrees to 120 degrees, the carrier phase inversion lamination PWM equivalent voltage space vector sequence is PNN → PON → POO → OOO, and the corresponding middle vector is PON;
5) for the phase angle region of 120 degrees to 150 degrees, the carrier phase inversion lamination PWM equivalent voltage space vector sequence is PPN → PON → OON → OOO, and the corresponding middle vector is PON;
6) for the phase angle region of 150 degrees to 180 degrees, the carrier phase inversion laminated PWM equivalent voltage space vector sequence is PPN → OPN → OON → OOO, and the middle vector used correspondingly is OPN;
7) for a phase angle region of 180 degrees to 210 degrees, the carrier phase inversion laminated PWM equivalent voltage space vector sequence is NPN → OPN → OPO → OOO, and the middle vector used correspondingly is OPN;
8) for a phase angle region from 210 degrees to 240 degrees, the carrier phase inversion laminated PWM equivalent voltage space vector sequence is NPN → NPO → OPO → OOO, and the corresponding used middle vector is NPO;
9) for the phase angle area from 240 degrees to 270 degrees, the carrier phase inversion laminated PWM equivalent voltage space vector sequence is NPP → NPO → NOO → OOO, and the corresponding used middle vector is NPO;
10) for a phase angle region of 270 degrees to 300 degrees, the carrier phase inversion laminated PWM equivalent voltage space vector sequence is NPP → NOP → NOO → OOO, and the middle vector used correspondingly is NOP;
11) for the phase angle area of 300 degrees to 330 degrees, the carrier phase inversion laminated PWM equivalent voltage space vector sequence is NNP → NOP → OOP → OOO, and the middle vector used correspondingly is NOP;
12) for the 330-360 degree phase angle region, the carrier phase inversion laminated PWM equivalent voltage space vector sequence is NNP → ONP → OOP → OOO, and the corresponding middle vector is ONP.
2. Detecting a modulation wave corresponding to the middle vector and a midpoint current;
the control method of the invention detects the midpoint potential deviation value and the corresponding adjustment of the medium vectorAnd (3) wave making and midpoint current, judging the product direction of the wave making and the midpoint current, and sending the product direction to a PI (proportional integral) controller to obtain a middle vector time adjustment factor delta Uneu. The modulation wave and the midpoint current corresponding to the vector in the definition are respectively UxAnd ixThe method for detecting the modulation wave and the midpoint current corresponding to the vector in the control method comprises the following steps:
1) for the phase angle region of 30 degrees to 90 degrees, the middle vector used by the carrier inversion laminated PWM is PNO, the inflow and outflow midpoints correspond to C phase, and U is arrangedx＝Umc，ix＝ic；
2) For the phase angle region of 90-150 degrees, the middle vector used by the carrier inversion lamination PWM is PON, the inflow and outflow midpoints correspond to the B phase, and U is arrangedx＝Umb，ix＝ib；
3) For the phase angle region of 150 degrees to 210 degrees, the middle vector used by the carrier inversion laminated PWM is OPN, the inflow and outflow midpoints correspond to A phase, and U is arrangedx＝Uma，ix＝ia；
4) For a phase angle region of 210 degrees to 270 degrees, the middle vector used by the carrier inversion laminated PWM is NPO, the inflow and outflow midpoints correspond to the C phase, and U existsx＝Umc，ix＝ic；
5) For the phase angle region of 270 degrees to 330 degrees, the middle vector used by the carrier inversion laminated PWM is NOP, the inflow and outflow midpoints correspond to the B phase, and U is arrangedx＝Umb，ix＝ib；
6) For the phase angle region of 330 degrees to 30 degrees, the middle vector used by the carrier inversion laminated PWM is ONP, the inflow and outflow midpoints correspond to A phase, and U is arrangedx＝Uma，ix＝ia。
In the above detection method, Uma、Umb、UmcModulated waves i representing A, B and C phases, respectivelya、ib、icThe currents of the A phase, the B phase and the C phase are respectively. Three-phase modulation wave U of carrier reverse phase laminated PWM (pulse-width modulation) for improving direct-current voltage utilization rate under action of carrier reverse phase laminated PWMma、UmbAnd UmcFrom three phases positiveSine wave Ua、Ub、UcSuperimposing a specific zero sequence component U0Specifically defined as follows:
Figure BDA0002335239520000081
to Uma、UmbAnd UmcIn definition, Ua、Ub、UcRepresents sine waves of A phase, B phase and C phase, U0Is a zero-sequence component, M is the amplitude of the modulated wave after each unit, omegabIs angular frequency, UmaxAnd UminRespectively represents Ua、Ub、UcMaximum and minimum values of (a).
3. Detecting a midpoint potential deviation value;
the control method of the invention judges the product direction of the midpoint potential deviation value and the modulation wave and the midpoint current corresponding to the midpoint vector by detecting the midpoint potential deviation value and the midpoint vector, and sends the product direction to the PI controller to obtain the middle vector time adjustment factor delta Uneu. And further detecting a midpoint potential deviation value on the basis of detecting a modulation wave and a midpoint current corresponding to a vector in the carrier reverse phase laminated PWM equivalent. The specific detection method comprises the following steps:
ΔU＝Udc1-Udc2(3)
in the above formula, Δ U represents a midpoint potential deviation value, Udc1For the upper voltage, U, of the DC side of the three-level converterdc2The voltage is the lower end voltage of the direct current side of the three-level converter.
4. Superposing the medium vector time adjustment factor delta Uneu to a modulation wave corresponding to a medium vector;
the control method controls the action time of the medium vector by superposing the medium vector time adjustment factor delta Uneu to the modulation wave corresponding to the medium vector, thereby controlling the neutral point potential balance under the action of carrier reverse phase laminated PWM. The principle of controlling the neutral point potential balance by using the medium vector time adjustment factor delta unneu is as follows:
for the phase angle region of 30 degrees to 90 degrees, the middle vector used by the carrier inversion lamination PWM is PNO, and the corresponding middle point current is C phase current ic. When the point is electrifiedDifference in bit offset value Δ U<At 0, in order to restore the neutral point potential balance, the upper end voltage U of the DC side of the three-level converter is requireddc1And (4) rising. At this time if ic>0, increasing the PNO action time can make Udc1Rising; if ic<0, reducing the PNO action time can make Udc1Rising; current midpoint potential deviation value delta U>At 0, to restore midpoint potential balance, U should be madedc1And (4) descending. At this time if ic>0, reducing the PNO action time can make Udc1Descending; if ic<0, increasing the PNO action time can make Udc1Descending;
for a phase angle region of 90 degrees to 150 degrees, the middle vector used by the carrier inversion lamination PWM is PON, and the corresponding middle point current is B phase current ib. Current midpoint potential deviation value delta U<At 0, in order to restore the neutral point potential balance, the upper end voltage U of the DC side of the three-level converter is requireddc1And (4) rising. At this time if ib>0, increasing the PON action time can make Udc1Rising; if ib<0, reducing PON action time can make Udc1Rising; current midpoint potential deviation value delta U>At 0, to restore midpoint potential balance, U should be madedc1And (4) descending. At this time if ib>0, reducing PON action time can make Udc1Descending; if ib<0, increasing the PON action time can make Udc1Descending;
for the phase angle region of 150 degrees to 210 degrees, the middle vector used by the carrier phase inversion lamination PWM is OPN, and the corresponding middle point current is A phase current ia. Current midpoint potential deviation value delta U<At 0, in order to restore the neutral point potential balance, the upper end voltage U of the DC side of the three-level converter is requireddc1And (4) rising. At this time if ia>0, increasing the OPN action time can make Udc1Rising; if ia<0, decreasing the OPN action time allows Udc1Rising; current midpoint potential deviation value delta U>At 0, to restore midpoint potential balance, U should be madedc1And (4) descending. At this time if ia>0, decreasing the OPN action time allows Udc1Descending; if ia<0, increasing the OPN action time can make Udc1Descending;
for a phase angle region of 210 degrees to 270 degrees, the carrier inversion layerThe middle vector used by the stacked PWM is NPO, and the corresponding midpoint current is C phase current ic. Current midpoint potential deviation value delta U<At 0, in order to restore the neutral point potential balance, the upper end voltage U of the DC side of the three-level converter is requireddc1And (4) rising. At this time if ic>0, increasing the NPO action time can make Udc1Rising; if ic<0, decreasing the NPO action time can make Udc1Rising; current midpoint potential deviation value delta U>At 0, to restore midpoint potential balance, U should be madedc1And (4) descending. At this time if ic>0, decreasing the NPO action time can make Udc1Descending; if ic<0, increasing the NPO action time can make Udc1Descending;
for the phase angle region of 270 degrees to 330 degrees, the middle vector used by the carrier inversion lamination PWM is NOP, and the corresponding middle point current is B phase current ib. Current midpoint potential deviation value delta U<At 0, in order to restore the neutral point potential balance, the upper end voltage U of the DC side of the three-level converter is requireddc1And (4) rising. At this time if ib>0, increasing the NOP action time can make Udc1Rising; if ib<0, reducing the NOP action time can make Udc1Rising; current midpoint potential deviation value delta U>At 0, to restore midpoint potential balance, U should be madedc1And (4) descending. At this time if ib>0, reducing the NOP action time can make Udc1Descending; if ib<0, increasing the NOP action time can make Udc1Descending;
for the phase angle region of 330 degrees to 30 degrees, the middle vector used by the carrier inversion lamination PWM is ONP, and the corresponding middle point current is A phase current ia. Current midpoint potential deviation value delta U<At 0, in order to restore the neutral point potential balance, the upper end voltage U of the DC side of the three-level converter is requireddc1And (4) rising. At this time if ia>0, increasing the ONP action time can make Udc1Rising; if ia<0, decreasing the ONP action time can make Udc1Rising; current midpoint potential deviation value delta U>At 0, to restore midpoint potential balance, U should be madedc1And (4) descending. At this time if ia>0, decreasing the ONP action time can make Udc1Descending; if ia<0, increasing the ONP action time can make Udc1And (4) descending.
Summarizing the above analysis, it can be seen that:
for any phase angle region, the midpoint potential deviation value delta U and the midpoint current ixWhen the product of the carrier phase inversion lamination PWM is less than zero, the action time of the vector corresponding to the carrier phase inversion lamination PWM is increased, so that the neutral point potential can be recovered and balanced more conveniently; when Δ U and ixWhen the product of the carrier inversion lamination PWM is larger than zero, the action time of the vector corresponding to the carrier inversion lamination PWM is reduced, and the neutral point potential recovery balance is facilitated.
And further analyzing the influence of the upward movement or downward movement of the medium vector corresponding to the modulation wave on the action time of the medium vector. Taking the phase angle range from 90 degrees to 120 degrees as an example, the middle vector used by the carrier inversion lamination PWM is PON, and the middle vector corresponds to the modulation wave Umb<0, the effect of shifting up or down the middle vector corresponding modulation wave on the action time of the middle vector is shown in fig. 5: the upward movement of the modulated wave results in the increase of the medium vector action time, and the downward movement of the modulated wave results in the decrease of the medium vector action time. Taking the phase angle region of 120 degrees to 150 degrees as an example, the middle vector used by the carrier inversion lamination PWM is PON, and the middle vector corresponds to the modulation wave Umb>0, the influence of shifting up or down the middle vector corresponding modulation wave on the action time of the middle vector is shown in fig. 6: the upward movement of the modulated wave results in the increase of the medium vector action time, and the downward movement of the modulated wave results in the decrease of the medium vector action time.
Similarly, the thought analysis shows that for phase angle regions from 60 degrees to 120 degrees, from 180 degrees to 240 degrees and from 300 degrees to 360 degrees, the values of the modulation waves corresponding to the medium vectors are less than zero, at the moment, the upward movement of the modulation waves can cause the action time of the medium vectors to be increased, and the downward movement can cause the action time of the medium vectors to be reduced; for phase angle regions from 0 degree to 60 degrees, from 120 degrees to 180 degrees and from 240 degrees to 300 degrees, the value of the modulation wave corresponding to the medium vector is larger than zero, at the moment, the modulation wave is moved upwards to reduce the acting time of the medium vector, and the moving downwards to increase the acting time of the medium vector.
The superposition of a positive value on the modulation wave corresponding to the medium vector can cause the modulation wave to move upwards, and the superposition of a negative value can cause the modulation wave to move downwards, and the following conclusion can be obtained by combining all the analyses:
for any phase angle regionThe midpoint potential deviation value delta U and the midpoint current ixModulated wave U corresponding to medium vectormxWhen the product of the two phases is less than zero, the modulation wave corresponding to the vector in the carrier reverse phase laminated PWM is shifted down to be more beneficial to the recovery balance of the midpoint potential; the midpoint potential deviation value delta U and the midpoint current ixModulated wave U corresponding to medium vectormxWhen the product of the two-dimensional space vector multiplication is larger than zero, the modulation wave corresponding to the vector in the carrier reverse phase laminated PWM is shifted up to be more beneficial to restoring balance of the midpoint potential.
Based on the conclusion, the midpoint potential deviation value and the product direction of the modulation wave corresponding to the midpoint vector and the midpoint current are sent to the PI controller to obtain the middle vector time adjustment factor delta Uneu, and the middle vector time adjustment factor delta Uneu is superposed on the modulation wave corresponding to the middle vector to control the action time of the middle vector, so that the midpoint potential balance can be controlled under the action of carrier reverse phase laminated PWM.
5. Limiting the range of the modulation wave corresponding to the middle vector to be-1 to 1;
the control method controls the action time of the medium vector by superposing the medium vector time adjustment factor delta Uneu to the modulation wave corresponding to the medium vector, thereby controlling the neutral point potential balance under the action of carrier reverse phase laminated PWM; the carrier reverse phase laminated PWM obtains PWM signals of each power device based on comparison of a three-phase modulation wave and a triangular carrier, and the value range of the triangular carrier is-1 to 1, so that in order to prevent overmodulation, the range of a modulation wave corresponding to a middle vector after a middle vector time adjustment factor delta Uneu is superposed is limited to-1 to 1.
6. When the midpoint potential deviation value of the three-level converter is within a limited range, enabling a middle vector time adjustment factor delta Uneu to be 0;
the control method of the invention is only put into use when the midpoint potential deviation exceeds a limit value. When the midpoint potential deviation value of the three-level converter is within a limited range, in order to improve harmonic performance, the medium vector time adjustment factor delta Uneu is made to be 0, and the modulation wave is not adjusted.
The specific principle of the carrier inversion lamination PWM midpoint potential balance control method is shown in FIG. 7.
The invention overcomes the defect that the carrier reverse phase laminated PWM can not utilize the existing method for redistributing the action time of the redundant small vector to carry out midpoint potential balance control, and provides the midpoint potential balance control method suitable for the carrier reverse phase laminated PWM by shifting up or down the modulation wave corresponding to the medium vector. The control method can control the midpoint potential deviation under the action of the carrier reverse phase laminated PWM within a limited range, thereby improving the reliability of the three-level converter when the carrier reverse phase laminated PWM is used as a modulation strategy.
The following examples are provided to illustrate the effects of the present invention.
According to the embodiment of the invention, a three-level converter model is built by means of PSIM software, and the effectiveness of the carrier reverse phase laminated PWM midpoint potential balance control method provided by the invention is verified by utilizing simulation. The simulation conditions were as follows:
the modulation strategy used by the three-level converter is carrier reverse phase laminated PWM, the simulation step length is 10us, the sampling frequency is 1200Hz, the carrier frequency is 750Hz, three phases at the output side are respectively connected with a 1 omega resistor in series connection with a 5mH inductor, the voltage at the direct current side is 500V, the initial voltage value at the upper end of the direct current side is 400V, the initial voltage value at the lower end of the direct current side is 100V, and the limit value of the midpoint potential deviation is set to be 30V.
FIG. 8 shows the variation of the upper and lower voltages on the DC side without adding the midpoint potential balancing protection measure, with the fundamental frequency of 50Hz and the modulation ratio fixed at 0.8. As can be seen from fig. 8, when the three-level converter uses carrier-inverting stacked PWM as a modulation strategy, if a midpoint potential imbalance problem occurs at a fixed modulation ratio, the midpoint potential imbalance problem may exist without adding a midpoint potential balance control method, which may adversely affect the safe and reliable operation of the three-level converter.
FIG. 9 shows the fundamental frequency of 50Hz, the modulation ratio of 0.8, and the results of the point potential balance control method of the present invention; fig. 9a shows the variation of the voltage at the upper end and the voltage at the lower end of the dc side, and fig. 9b shows the comparison between the midpoint potential deviation value and the limit value. The results of the embodiment of fig. 9 show that when the three-level converter uses carrier-inverting stacked PWM as the modulation strategy, when the midpoint potential imbalance problem occurs at a fixed modulation ratio, the midpoint potential balance control method of the present invention can reduce the deviation value of the upper-end voltage and the lower-end voltage of the dc bus to within the limit value, so that the midpoint potential is restored to balance again.
FIG. 10 shows the variation of the upper and lower voltages on the DC side without adding the midpoint potential balance protection measure, in the case of the embodiment in which the fundamental frequency is 50Hz and the modulation ratio is varied cyclically from 0.1 to 1. As can be seen from fig. 10, when the three-level converter uses carrier-inversion stacked PWM as a modulation strategy, if a middle-point potential imbalance problem occurs under a modulation ratio that changes cyclically, the middle-point potential imbalance problem will always exist unless a middle-point potential balance control method is added, and thus, the safe and reliable operation of the three-level converter is adversely affected.
FIG. 11 shows the results of an example in which the fundamental frequency of the example is 50Hz, the modulation ratio is varied cyclically from 0.1 to 1, and the point potential balance control method according to the present invention is applied; FIG. 11a is the variation of the voltage at the upper end and the voltage at the lower end of the DC side, and FIG. 11b is the comparison of the midpoint potential deviation value and the limit value; fig. 11c shows a modulation ratio that varies cyclically. The results of the embodiment of fig. 11 show that when the three-level converter uses carrier-inverting stacked PWM as the modulation strategy, when the midpoint potential imbalance problem occurs under the modulation ratio of cyclic variation, the midpoint potential balance control method of the present invention can reduce the deviation value of the upper end voltage and the lower end voltage of the dc bus to within the limit value, so that the midpoint potential is restored to balance again.
As shown in fig. 8 to fig. 11, the results of the embodiment verify the effectiveness of the method for controlling the midpoint potential balance in the carrier inversion lamination PWM according to the present invention. Aiming at the condition that the three-level converter uses carrier inversion lamination PWM as a modulation strategy, the invention can effectively control the neutral point potential to restore balance again no matter whether the modulation ratio is changed. The invention overcomes the defect that the carrier reverse phase laminated PWM can not utilize the existing method for redistributing the redundant small vector action time to carry out neutral point potential balance control, and can control the neutral point potential deviation under the action of the carrier reverse phase laminated PWM within a limited range, thereby improving the reliability of the three-level converter when the carrier reverse phase laminated PWM is used as a modulation strategy.

Claims (8)

1. A carrier reverse phase laminated PWM midpoint potential balance control method is characterized in that: aiming at the condition that a three-level converter uses carrier inversion lamination PWM as a modulation strategy, when the midpoint potential deviation exceeds a limit value, firstly determining a middle vector used by the carrier inversion lamination PWM in a current phase angle region; then detecting the midpoint potential deviation value delta U and the modulation wave U corresponding to the medium vectorxMidpoint current i corresponding to the middle vectorxModulated wave U corresponding to vector in calculationxMidpoint current i corresponding to the middle vectorxThe product of the intermediate point potential deviation value delta U and the intermediate point potential deviation value delta U is obtained, the direction of the product of the three is judged, the direction of the product is input into a PI controller, and the output of the PI controller is the intermediate vector time adjustment factor delta Uneu; and controlling the action time of the medium vector by superposing the medium vector time adjustment factor delta Uneu on a modulation wave corresponding to the medium vector, thereby controlling the neutral point potential balance under the action of carrier inversion lamination PWM.
2. The carrier inversion lamination PWM midpoint potential balance control method according to claim 1, wherein: when the midpoint potential deviation exceeds a limit value, firstly determining a middle vector used by carrier inversion lamination PWM in a current phase angle area; defining three level states of the three-level converter from high to low output to be P, O, N respectively, in different phase angle regions, the medium vectors used by the carrier phase inversion lamination PWM are respectively as follows:
1) for a phase angle region of 30 degrees to 90 degrees, the medium vector used by the carrier inversion lamination PWM is PNO;
2) for a phase angle region of 90 degrees to 150 degrees, a middle vector used by the carrier inversion lamination PWM is PON;
3) for the phase angle region of 150 degrees to 210 degrees, the middle vector used by the carrier phase inversion lamination PWM is OPN;
4) for a phase angle region from 210 degrees to 270 degrees, the middle vector used by the carrier inversion lamination PWM is NPO;
5) for a phase angle region of 270 degrees to 330 degrees, the middle vector used by the carrier inversion lamination PWM is NOP;
6) for the 330 degree to 30 degree phase angle region, the medium vector used by the carrier inversion stacked PWM is ONP.
3. The carrier inversion lamination PWM midpoint potential balance control method according to claim 1, wherein: the method for detecting the modulation wave and the midpoint current corresponding to the medium vector comprises the following steps:
1) when the middle vector is PNO or NPO, there is Ux＝Umc，ix＝ic；
2) When the middle vector is PON or NOP, there is Ux＝Umb，ix＝ib；
3) When the middle vector is OPN or ONP, there is Ux＝Uma，ix＝ia；
In the above detection method, Uma、Umb、UmcModulated waves i representing A, B and C phases, respectivelya、ib、icThe currents of the A phase, the B phase and the C phase are respectively.
4. The carrier inversion lamination PWM midpoint potential balance control method according to claim 3, wherein: modulated wave Uma、UmbAnd UmcThe definition is as follows:
Figure FDA0002662485580000021
to Uma、UmbAnd UmcIn definition, Ua、Ub、UcRepresents sine waves of A phase, B phase and C phase, U0Is a zero sequence component; u shapea、Ub、UcAnd U0Is defined as follows:
Figure FDA0002662485580000022
to Ua、Ub、UcAnd U0In the definition, M is a labelAmplitude, omega, of the modulated wave after unitarybIs angular frequency, UmaxAnd UminRespectively represents Ua、Ub、UcMaximum and minimum values of (a).
5. The carrier inversion lamination PWM midpoint potential balance control method according to claim 3, wherein: the detection method of the midpoint potential deviation value comprises the following steps:
ΔU＝Udc1-Udc2
in the above formula, Δ U represents a midpoint potential deviation value, Udc1For the upper voltage, U, of the DC side of the three-level converterdc2The voltage is the lower end voltage of the direct current side of the three-level converter.
6. The carrier inversion lamination PWM midpoint potential balance control method according to claim 1, wherein: the control method controls the action time of the medium vector by superposing the medium vector time adjustment factor delta Uneu to the modulation wave corresponding to the medium vector, thereby controlling the neutral point potential balance under the action of carrier reverse phase laminated PWM; the specific way of superimposing the medium vector time adjustment factor Δ unneu to the medium vector corresponding modulation wave is as follows:
1) for the phase angle regions of 30 degrees to 90 degrees, 210 degrees to 270 degrees, there is Uma＝Uma，Umb＝Umb，Umc＝Umc+ΔUneu；
2) For phase angle regions of 90 degrees to 150 degrees, 270 degrees to 330 degrees, there is Uma＝Uma，Umb＝Umb+ΔUneu，Umc＝Umc；
3) For the phase angle regions of 150 degrees to 210 degrees and 330 degrees to 30 degrees, there is Uma＝Uma+ΔUneu，Umb＝Umb，Umc＝Umc；
In the above mode, Uma、Umb、UmcThe modulation waves respectively represent A phase, B phase and C phase, and the delta Uneu is a medium vector time adjustment factor.
7. The carrier inversion lamination PWM midpoint potential balance control method according to claim 6, wherein: the range of the modulation wave corresponding to the intermediate vector after the intermediate vector time adjustment factor Δ unneu is defined as-1 to 1, and the specific defining method is as follows:
1) for the 30 degree to 90 degree, 210 degree to 270 degree phase angle regions, there are:
Figure FDA0002662485580000023
2) for the phase angle regions of 90 degrees to 150 degrees, 270 degrees to 330 degrees, there are:
Figure FDA0002662485580000024
3) for the phase angle region of 150 degrees to 210 degrees, 330 degrees to 30 degrees, there are:
Figure FDA0002662485580000031
in the above limiting method, Uma、Umb、UmcThe modulated waves of the A phase, B phase and C phase are represented respectively.
8. The carrier inversion lamination PWM midpoint potential balance control method according to claim 1, wherein: the control method is only put into use when the midpoint potential deviation exceeds a limit value, when the midpoint potential deviation value of the three-level converter is within a limit range, delta Uneu is made to be 0, and the modulation wave is not adjusted; Δ unneu is the medium vector time adjustment factor.
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