CN113937986B - Method, device and equipment for detecting direct-current voltage of cascaded H-bridge power module - Google Patents

Method, device and equipment for detecting direct-current voltage of cascaded H-bridge power module Download PDF

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CN113937986B
CN113937986B CN202111536646.8A CN202111536646A CN113937986B CN 113937986 B CN113937986 B CN 113937986B CN 202111536646 A CN202111536646 A CN 202111536646A CN 113937986 B CN113937986 B CN 113937986B
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power module
current
voltage
direct current
direct
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CN113937986A (en
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张扬
李三苹
盛敬
许惠君
饶繁星
黄志开
刘剑冰
彭世健
穆阳
毛忠坤
胡志文
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Nanchang Institute of Technology
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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
    • H02M1/00—Details of apparatus for conversion
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R19/00—Arrangements for measuring currents or voltages or for indicating presence or sign thereof
    • 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
    • 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
    • H02M7/53—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 using devices of a triode or transistor type requiring continuous application of a control signal
    • H02M7/537—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 using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters
    • H02M7/5387—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 using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters in a bridge configuration

Abstract

The invention provides a method, a device and equipment for detecting direct-current voltage of a cascaded H-bridge power module, wherein the method comprises the following steps: acquiring alternating current of a current conversion chain acquired by a current transformer on the current conversion chain of the cascaded H bridge, and acquiring the current stage of a power module on the current conversion chain; when the power module is in an uncontrolled stage, calculating the direct current of the power module according to the alternating current of the converter chain; when the power module is in a control stage, acquiring a switch state matrix of each switch of the power module, and calculating direct current of the power module according to the switch state matrix and alternating current of a current conversion chain; and calculating the direct current voltage of the power module according to the direct current of the power module. The invention provides a new method for indirectly detecting the direct-current voltage of the power module of the cascaded H bridge based on the alternating current of the converter chain, the calculation precision of the method is irrelevant to the number of the power modules, the method is not influenced by the number of the power modules, and the method can be applied to a high-voltage system and has wider applicability.

Description

Method, device and equipment for detecting direct-current voltage of cascaded H-bridge power module
Technical Field
The invention relates to the technical field of electric power, in particular to a method, a device and equipment for detecting direct-current voltage of a cascaded H-bridge power module.
Background
The chain type STATCOM is an advanced reactive power compensation device and is widely applied to power quality compensation of a new energy power station. Cascaded H-bridges are the most common structure of chain STATCOM. The dc voltage of each power module is guaranteed to be stable, which is a necessary condition for the operation of the device, and therefore, the dc voltage of the power module generally needs to be detected during specific operation.
The traditional scheme is that a direct current voltage sensor is often additionally arranged on each power module, so that the chain-type STATCOM is often required to be additionally provided with dozens of sensors. The additional sensors add to the cost of the equipment and introduce additional measurement losses. And when a sensor of a certain power module breaks down, the whole device can be shut down. Therefore, the indirect detection technology without the direct-current voltage sensor has great effect on improving the economy and the reliability of the chain-type STATCOM.
In the prior art, the dc voltage of the cascaded H-bridge power module is usually detected indirectly based on a voltage transformer (PT for short) on a converter chain, but a PT sampling error may cause a large detection error when the number of power modules is large, and if the number of power modules is increased, the calculation time will be increased rapidly, which causes a large delay. Therefore, the calculation accuracy of the existing indirect detection method is greatly influenced by the number of power modules and the sampling accuracy, and the method is difficult to be applied to a high-voltage system.
Disclosure of Invention
Accordingly, the present invention is directed to a method, an apparatus, and a device for detecting a dc voltage of a cascaded H-bridge power module, so as to solve at least one technical problem in the background art.
According to the embodiment of the invention, the method for detecting the direct-current voltage of the cascaded H-bridge power module comprises the following steps:
acquiring alternating current of a current conversion chain acquired by a current transformer on the current conversion chain of the cascaded H bridge, and acquiring the current stage of a power module on the current conversion chain;
when the power module is in an uncontrolled stage, calculating the direct current of the power module according to the alternating current of the current conversion chain;
when the power module is in a control stage, acquiring a switch state matrix of each switch of the power module, and calculating direct current of the power module according to the switch state matrix and alternating current of the converter chain;
and calculating the direct current voltage of the power module according to the direct current of the power module.
In addition, the method for detecting the dc voltage of the cascaded H-bridge power module according to the above embodiment of the present invention may further have the following additional technical features:
further, when the power module is in an uncontrolled stage, the direct current of the power module satisfies a conditional expression:
i cj （t）=| i r （t）|
wherein the content of the first and second substances,i cj （t) Represents the direct current of the power module,i r （t) Representing the alternating current of said converter chain.
Further, when the power module is in the control phase, the direct current of the power module satisfies the conditional expression:
Figure 497065DEST_PATH_IMAGE001
wherein the content of the first and second substances,
Figure 124356DEST_PATH_IMAGE002
，ΔTin order to calculate the step size,Cis the capacity of the dc capacitor in the power module,R 1-R 4the resistance values of the four switches of the power module are respectively, and when the switches are switched on, the resistance values areR on Resistance value of at turn-offR off The on-off states of the four switches are determined by the switch state matrix,i cj （t) Represents the direct current of the power module,i r （t) Represents the alternating current of said converter chain,V dcj （t-ΔT）= V dcj （t k-1），V dcj （t k-1) Is an equivalent historical voltage source.
Further, the direct current voltage of the power modulev dcj （t) The conditional expression is satisfied:
Figure 570380DEST_PATH_IMAGE003
wherein the content of the first and second substances,V dcj （t k-1) The equivalent historical voltage source satisfies the conditional expression:
Figure 966727DEST_PATH_IMAGE004
。
wherein the content of the first and second substances,krepresenting the number of samples taken by the current transformer.
Further, after the step of calculating the dc voltage of the power module according to the dc current of the power module, the method further includes:
calculating the calculation error of the direct-current voltage of the power module by adopting a corresponding error formula according to the current stage of the power module;
and adjusting the calculation parameters of the direct current voltage of the power module according to the calculation error.
Further, when the power module is in a steady-state operation stage, the error formula is:
Figure 151589DEST_PATH_IMAGE005
in the formula (I), the compound is shown in the specification,ΔTin order to calculate the step size,Cis the capacity of the dc capacitor in the power module,Δv dcj is the calculation error of the dc voltage of the power module,i cj （t-ΔT) Representst-ΔTThe time corresponds to the direct current of the power module.
Further, when the power module is in a transient operation phase or a control phase, the error formula is:
Figure 266176DEST_PATH_IMAGE006
in the formula (I), the compound is shown in the specification,Δv dcj （t k ) Is as followskThe calculation error of the dc voltage of the power module corresponding to the sub-sampling time,ε 2is the relative error of sampling of the current transformer,i cj （t k ) Represents the firstkThe power module direct current corresponding to the sub-sampling time,
Figure 250312DEST_PATH_IMAGE002
，ΔTin order to calculate the step size,Cthe capacity of the direct current capacitor in the power module.
According to the embodiment of the invention, the device for detecting the direct-current voltage of the cascaded H-bridge power module comprises:
the information acquisition module is used for acquiring alternating current of a current conversion chain acquired by a current transformer arranged on the current conversion chain of the cascade H bridge and acquiring the current stage of a power module on the current conversion chain;
the current calculation module is used for calculating the direct current of the power module according to the alternating current of the commutation chain when the power module is in an uncontrolled stage; when the power module is in a control stage, acquiring a switch state matrix of each switch of the power module, and calculating direct current of the power module according to the switch state matrix and alternating current of the converter chain;
and the voltage calculation module is used for calculating the direct current voltage of the power module according to the direct current of the power module.
The invention further provides a computer-readable storage medium, on which a computer program is stored, which, when executed by a processor, implements the method for detecting a dc voltage of a cascaded H-bridge power module as described above.
The invention further provides a device for detecting the direct-current voltage of the cascaded H-bridge power module, which comprises a memory, a processor and a computer program stored on the memory and capable of running on the processor, wherein when the processor executes the program, the method for detecting the direct-current voltage of the cascaded H-bridge power module is realized.
Compared with the prior art: the direct-current voltage of the cascaded H-bridge power module is indirectly detected based on the alternating current of the converter chain, the calculation accuracy of the method is irrelevant to the number of the power modules, the method is not influenced by the number of the power modules, the calculation accuracy and the calculation response time are not influenced by the increase of the number of the power modules, and the method can be applied to a high-voltage system and has wider applicability.
Drawings
Fig. 1 is a typical topology diagram of a chain STATCOM provided by an embodiment of the present invention;
fig. 2 is a monitoring point position diagram of the chain STATCOM according to the embodiment of the present invention;
fig. 3 is a flowchart of a method for detecting dc voltage of a cascaded H-bridge power module according to a first embodiment of the present invention;
FIG. 4 is an equivalent circuit diagram of a power module in an uncontrolled phase according to an embodiment of the present invention;
fig. 5 is an equivalent circuit diagram of a power module in a control phase according to an embodiment of the present invention;
fig. 6 is a flowchart of a method for detecting dc voltage of a cascaded H-bridge power module according to a second embodiment of the present invention;
FIG. 7 is a schematic diagram of an embodiment of the present inventionΔT=500usComparing the direct current voltage results in an uncontrolled charging stage;
FIG. 8 is a schematic diagram of an embodiment of the present inventionΔT=50usComparing the direct current voltage results in an uncontrolled charging stage;
FIG. 9 is a schematic diagram of an embodiment of the present inventionΔT=500usComparing direct current voltage results in a +20A steady-state operation stage;
FIG. 10 is a schematic diagram of an embodiment of the present inventionΔT=50usComparing direct current voltage results in a +20A steady-state operation stage;
FIG. 11 is a schematic diagram of an embodiment of the present inventionΔT=500usComparing the direct current voltage results in a transient state stage from-20A to + 20A;
FIG. 12 is a schematic diagram of an embodiment of the present inventionΔT=50usComparing the direct current voltage results in a transient state stage from-20A to + 20A;
FIG. 13 is a diagram illustrating the measured DC voltage at the transient stage from-20A to +20A according to an embodiment of the present invention;
FIG. 14 is a comparison graph of DC voltage results during a transient phase from-20A to +20A in accordance with an embodiment of the present invention;
fig. 15 is a schematic structural diagram of a dc voltage detection apparatus for a cascaded H-bridge power module according to a third embodiment of the present invention;
fig. 16 is a schematic structural diagram of a device for detecting a dc voltage of a cascaded H-bridge power module according to a fourth embodiment of the present invention.
The following detailed description will further illustrate the invention in conjunction with the above-described figures.
Detailed Description
To facilitate an understanding of the invention, the invention will now be described more fully with reference to the accompanying drawings. Several embodiments of the invention are presented in the drawings. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete.
It will be understood that when an element is referred to as being "secured to" another element, it can be directly on the other element or intervening elements may also be present. When an element is referred to as being "connected" to another element, it can be directly connected to the other element or intervening elements may also be present. The terms "vertical," "horizontal," "left," "right," and the like as used herein are for illustrative purposes only.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used in the description of the invention herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items.
The following embodiments can be applied to the chain-type STATCOM system shown in fig. 1, where fig. 1 shows a typical topology (cascaded H-bridge) of the chain-type STATCOM, which includes three converter chains, where each converter chain is connected in series with a smoothing reactor, and all inductance values are all inductance valuesL. Inverting voltage of current converting chain isu ca 、u cb 、u cc And the three current-converting chains have currents ofi ab 、i bc 、i ca . In fig. 1, FB corresponds to H-bridge sub-modules, that is, referred to as power modules, each power module includes 4 switches and a dc capacitor C, and the switches are specifically Insulated Gate Bipolar Transistors (IGBTs). Wherein, the 4 IGBTs are numbered in sequence asT 1、T 2、T 3AndT 4the diodes connected with the same are sequentially numbered asD 1、D 2、D 3AndD 4. Take AB commutation chain as an example, forjThe voltage of the DC capacitor of each power module is defined asv dcjThe current of the DC capacitor is defined asi dcjThe inverter voltage of the power module is defined asu Hj ，j=1,2,3,…NThe dc voltage of the power module is the voltage of the dc capacitor of the power module, that is, the voltage of the dc capacitor of the cascaded H-bridge power module is actually detected.
At present, the direct-current voltage of the cascaded H-bridge power module is generally indirectly detected based on a voltage transformer (PT) on a converter chain, and the arrangement position of the voltage transformer (PT) is as shown in fig. 2, and the specific principle is as follows:
first, according to the chain STATCOM module parameters shown in table 1 below, we can obtain:
Figure 766744DEST_PATH_IMAGE007
（1）
table 1:
Figure 873241DEST_PATH_IMAGE008
taking phase a as an example, the inversion voltage of the commutation chain and the capacitor voltage of the power module satisfy:
Figure 678386DEST_PATH_IMAGE009
（2）
the capacitor voltage can not be suddenly changed within a short time, namely:
Figure 13683DEST_PATH_IMAGE010
（3）
by looking for N linearly independent switch states in a short time, it is possible to obtain
Figure 650201DEST_PATH_IMAGE011
（4）
Wherein the content of the first and second substances,u ca 、u cb 、u cc for inverting the voltage of the current-converting chain, S kj Is in the on-off state.
Order to
Figure 865281DEST_PATH_IMAGE012
（5）
Equation (4) may then be changed to:
U=SV（6）
if switch state matrixSIs satisfied withrank（S）=NThen inevitably proceed to the lineFormula (xvii) according to Crammer rule:
V=S -1 U （7）
the dc voltages of all power modules over a short period of time can be solved.
PT sampling errors can have a large impact on indirect detection accuracy. Assume PT samples with relative error ofε 1。
According to equation (2), a modulation ratio is introduced
Figure 954460DEST_PATH_IMAGE013
And then:
Figure 342716DEST_PATH_IMAGE014
（8）
the condition that the voltages of the respective power modules in normal operation are approximately equal is utilized here.
Then the absolute value of the PT measurement is
Figure 771424DEST_PATH_IMAGE015
（9）
In the limit situation, all the calculation errors are reflected on the calculation result of a certain power module, and the relative error of the direct current voltage of the power module at the moment is
Figure 203411DEST_PATH_IMAGE016
（10）
In steady operation, 0<m<1, according to the standardε 1Less than or equal to 2%, generallyε 1=1%。
When in useN=At the time of 3, the water-soluble polymer,η<3% and the error of the DC voltage is generally 10%, so the test method has good effect.
When in useN=At the time of 3, the water-soluble polymer,η<12%, the maximum error exceeds the allowable range of the direct-current voltage.
Therefore, for the existing indirect detection scheme, the PT sampling error causes a large indirect detection error when the number of power modules is large.
The calculation delay generally adopts Gauss elimination method to solve the rank of the matrix, and the calculation complexity is
Figure 45465DEST_PATH_IMAGE017
(ii) a The inverse operation is generally performed by LU decomposition, Cholesky decomposition or QR decomposition, and the calculation complexity of these algorithms is also
Figure 175095DEST_PATH_IMAGE018
. Thus, the computational complexity of the indirect detection algorithm is satisfied
Figure 520626DEST_PATH_IMAGE019
（11）
Assume a basic calculation time ofT 1 One time calculation of N power modulesT N Can be approximated as
Figure 343088DEST_PATH_IMAGE020
（12）
The computation time of 12 power modules is about 64 times the computation time of 3 power modules. If the number of power modules is increased, the calculation time will increase rapidly, resulting in a large delay.
Searching N linearly independent switch states, calculating at least N times, and delayingT d Satisfy the requirement of
Figure 141280DEST_PATH_IMAGE021
（13）
Typical valueT 1 ≈1us。
N=3，T d >81us；N=12，T d ≥20.1ms. At this time, the delay exceeds 1 power frequency period, so that the formula (3) cannot be ensured) If it is true, the equation will not be solved accurately.
Therefore, in the existing method for indirectly detecting the direct-current voltage of the cascaded H-bridge power module based on the PT, the calculation accuracy is greatly influenced by the number of the power modules and the sampling accuracy, so that the method is difficult to be applied to a high-voltage system. Therefore, the direct-current voltage of the cascaded H-bridge power module is indirectly detected based on the alternating current of the converter chain, the calculation accuracy of the method is irrelevant to the number of the power modules, the method is not influenced by the number of the power modules, and the method can be applied to a high-voltage system. The details of the novel process are set forth in the examples which follow.
Example one
Referring to fig. 3, a method for detecting a dc voltage of a cascaded H-bridge power module in a first embodiment of the invention is shown, and the method specifically includes steps S01-S04.
Step S01, obtaining an alternating current of a converter chain collected by a current transformer on the converter chain of the cascaded H bridge, and obtaining a current stage of a power module on the converter chain.
As shown in fig. 2, a diagram of an arrangement position of a Current Transformer (CT) on a converter chain is shown, which is different from an arrangement position of a conventional PT. The currently located stage of the power module includes an uncontrolled stage and a controlled stage. In specific implementation, the current transformer samples the alternating current of the converter chain every preset time, the preset time is the calculation step length delta T, and the direct current of the power module is calculated correspondingly every time the alternating current of the converter chain is acquired.
And step S02, when the power module is in the uncontrolled stage, calculating the direct current of the power module according to the alternating current of the converter chain.
Specifically, the uncontrolled phase is a charging phase, i.e., a phase of charging through a diode. In the uncontrolled stagei cj The direction is not reversible, neglecting IGBT, the diode is equivalent to a small resistanceR Dj The equivalent circuit of the power module during the uncontrolled charging phase is shown in fig. 4. Wherein, the commutator indicates that negative voltage/negative current is converted into positive voltage/negative current. Due to the fact thatHere, at this time, the direct current of the power module satisfies the conditional expression:
i cj （t）=| i r （t）| （16）
wherein the content of the first and second substances,i cj （t) Represents the direct current of the power module,i r （t) Representing the alternating current of said converter chain.
Step S03, when the power module is in the control phase, acquiring a switching state matrix of each switch of the power module, and calculating a dc current of the power module according to the switching state matrix and an ac current of the converter chain.
In the control phase, the IGBT and the diode can be equivalent to an adjustable resistor, and a circuit of the equivalent power module can be obtained as shown in fig. 5. At this time, the direct current of the power module is solved according to a node voltage method, that is, the direct current of the power module satisfies the conditional expression:
Figure 887650DEST_PATH_IMAGE022
wherein the content of the first and second substances,
Figure 25370DEST_PATH_IMAGE002
，ΔTin order to calculate the step size,Cis the capacity of the dc capacitor in the power module,R 1-R 4the resistance values of the four switches of the power module are respectively, and when the switches are switched on, the resistance values areR on Resistance value of at turn-offR off The on-off states of the four switches are determined by the switch state matrix,i cj （t) Represents the direct current of the power module,i r （t) An alternating current representative of said converter chain; in the following, four switch state matrices for the normal operation of the power mode in the control phase in table 1 above will be describedS kj Respectively solving the formula, whichThe four switch states are respectively differentS kj The values (1, 0, -1, 0 correspond to two states) to distinguish the identification, in particular:
when in useS kj =When the pressure of the mixture is 1, the pressure is lower,R 1=R 4=R on ，R 2=R 3=R off then, then
Figure 815472DEST_PATH_IMAGE023
（17）
When in useS kj =At 0 time, then
Figure 366539DEST_PATH_IMAGE024
（18）
In the practical case where the temperature of the molten metal is high,R off is very large, so that at this time
Figure 837971DEST_PATH_IMAGE025
When in useS kj =When-1, then
Figure 892515DEST_PATH_IMAGE026
（19）
Step S04, calculating a dc voltage of the power module according to the dc current of the power module.
In particular, voltage formula according to capacitance
Figure 368365DEST_PATH_IMAGE027
The pull type transformation expression is
Figure 875569DEST_PATH_IMAGE028
According to the bilinear transformation method, assume a calculation step size of
Figure 150693DEST_PATH_IMAGE029
The expression of the dc voltage of the power module is:
Figure 590902DEST_PATH_IMAGE030
（14）
in the formula (14), an equivalent calculated resistance is defined
Figure 457226DEST_PATH_IMAGE031
Then equivalent history voltage source
Figure 920569DEST_PATH_IMAGE032
Comprises the following steps:
Figure 281274DEST_PATH_IMAGE033
（15）
wherein the content of the first and second substances,krepresents the number of samples taken by the current transformer,t k represents the time of the k-th sampling,i cj （t k ) Represents the firstkAnd the power module direct current corresponding to the sub-sampling time.
In the case of an indirect detection, the detection,ΔTand (4) controllable. Capacitor with a capacitor elementCIt is known that the capacity value is influenced negligibly by the environment. If the initial DC voltage of the power module is known, i.e. the DC voltage of the power module at the beginning of the detection is known, and the DC current of the power modulei cj （t) Known, i.e. can be solved by iterationv dcj （t). That is, by combining the equations (14), (15) and (16), the DC voltage of each power module at the uncontrolled stage can be obtainedv dcj （t). By combining the formulas (14), (15) and (17) - (19), the DC voltage of each power module in the control stage can be obtainedv dcj （t）。
In summary, in the method for detecting the dc voltage of the cascaded H-bridge power module in the above embodiments of the present invention, the dc voltage of the cascaded H-bridge power module is indirectly detected based on the alternating current of the commutation chain, the calculation accuracy of the method is independent of the number of the power modules and related to the controllable calculation step, and is not affected by the number of the power modules, and the calculation accuracy and the calculation response time are not affected by the increase of the number of the power modules, so that the method can be applied to a high-voltage system, and has a wider applicability.
Example two
Referring to fig. 6, a method for detecting a dc voltage of a cascaded H-bridge power module in a second embodiment of the present invention is shown, and the method specifically includes steps S11-S16.
Step S11, obtaining an alternating current of a converter chain collected by a current transformer on the converter chain of the cascaded H bridge, and obtaining a current stage of a power module on the converter chain.
And step S12, when the power module is in the uncontrolled stage, calculating the direct current of the power module according to the alternating current of the converter chain.
Step S13, when the power module is in the control phase, acquiring a switching state matrix of each switch of the power module, and calculating a dc current of the power module according to the switching state matrix and an ac current of the converter chain.
Step S14, calculating a dc voltage of the power module according to the dc current of the power module.
And step S15, calculating the calculation error of the direct current voltage of the power module by adopting a corresponding error formula according to the current stage of the power module.
And step S16, adjusting the calculation parameters of the direct current voltage of the power module according to the calculation error.
The calculation error of the detection method for the direct-current voltage of the cascaded H-bridge power module is only related to the calculation step length delta T, so that the calculation step length delta T only needs to be adjusted, and the final error is within an allowable range.
When the power module is in steady-state operation,i cj no abrupt change occurs, and the error is caused byΔTIs poor in output result due to the delay ofAnd (3) distinguishing. The error can be evaluated in increments of the current term, i.e.
Figure 575989DEST_PATH_IMAGE034
（20）
In the formula (I), the compound is shown in the specification,ΔTin order to calculate the step size,Cis the capacity of the dc capacitor in the power module,Δv dcj is the calculation error of the dc voltage of the power module,i cj （t-ΔT) Representst-ΔTThe time corresponds to the direct current of the power module. This means that the step size is calculatedΔTThe larger the error.
When the power module is in a transient operation stage, CT sampling is easily interfered by factors such as harmonic waves and the like to cause sampling errors. Assume CT samples have a relative error of ε2Also according to the standard2= 1%. The initial time ist 0At the next momentt 1= t 0+Δ T. From the formula (16), it can be found
Figure 816478DEST_PATH_IMAGE035
（21）
t 1At a moment of time, have
Figure 829433DEST_PATH_IMAGE036
（22）
t 2The time of day is obtained from equations (14) and (15)
Figure 243097DEST_PATH_IMAGE037
（23）
t 3At the moment, then
Figure 330002DEST_PATH_IMAGE038
Can be easily proved by induction method
Figure 318555DEST_PATH_IMAGE039
（25）
When the H-bridge power module operates normally, the charging current is approximately equal to the discharging current, so that the charging current is approximately equal to the discharging current
Figure 490910DEST_PATH_IMAGE040
Therefore, it is not only easy to use
Figure 442686DEST_PATH_IMAGE041
（26）
In the formula (I), the compound is shown in the specification,Δv dcj （t k ) Is as followskThe calculation error of the dc voltage of the power module corresponding to the sub-sampling time,ε 2is the relative error of sampling of the current transformer,i cj （t k ) Represents the firstkThe power module direct current corresponding to the sub-sampling time,
Figure 711993DEST_PATH_IMAGE002
，ΔTin order to calculate the step size,Cthe capacity of a direct current capacitor in the power module;
when the power module is in the control phase, there is still a power module according to equations (17) - (19) since the iteration is still according to equations (14) and (15)
Figure 91022DEST_PATH_IMAGE042
（27）
The formula differs from the formula (21) only by constant coefficients, so the calculation method is the same as the formulas (22) to (26), and the conclusion is similar, i.e. the formula (21) has only constant coefficients
Figure 750673DEST_PATH_IMAGE043
（28）
In general
Figure 522451DEST_PATH_IMAGE044
Then the formula (28) becomes
Figure 583948DEST_PATH_IMAGE045
（29）
I.e., consistent with the conclusion of equation (26). Therefore, compared with the existing indirect detection algorithm, the error of the proposed algorithm caused by PT sampling is independent of the number of modules, and the maximum error is
Figure 399458DEST_PATH_IMAGE046
. If it is notΔT=500usAccording to
Figure 608722DEST_PATH_IMAGE002
The calculation error is aboutΔT=50usTen times higher.
Therefore, the novel rapid indirect detection method for the direct-current voltage of the cascade H-bridge power module can be suitable for uncontrolled and controlled stages, and errors are small.
Experiments and simulation analysis are carried out to verify the novel rapid indirect detection method for the direct-current voltage of the cascaded H-bridge power module, which is provided by the invention, as follows:
firstly, a simulation and experiment platform is built according to the parameters of the cascaded H-bridge system of N power modules as shown in the following table 2.
Table 2:
Figure 902300DEST_PATH_IMAGE047
simulation results are shown in fig. 7-12, and the simulation settings are as follows: (1) the uncontrolled charging stage is set to be charged by a soft starting resistor before 0.4s, and the soft starting resistor is charged by a bypass circuit after 0.4 s; (2) in a +20A steady-state operation stage, the initial direct-current voltage is set to be 36V, and 0.25s is input into the chain type STATCOM to operate at + 20A; (3) transient phase from-20A to +20AThe initial direct current voltage is set to be 36V, 0.25s is input into the chain type STATCOM to operate at-20A, and the transient operation stage of the chain type STATCOM is changed from 1.0s to + 20A. FIGS. 7 and 8 are respectivelyΔT=500usAndΔT=50uscomparing the direct current voltage results in the uncontrolled charging stage, and comparing the two schemes of 500us and 50us of the calculation step length of the algorithm, so as to obtain the direct current voltage comparison methodΔT=500usWhen the error is large, the absolute error is 0.2V, and the relative error is 0.5%; at 50us, the absolute error is about 0.02V, and the relative error is 0.05%; FIG. 9 and FIG. 10 are respectivelyΔT=500usAndΔT=50uscomparing the direct current voltage results in the +20A steady-state operation stage, the absolute error reaches 55V and the relative error is 152.8 percent under the influence of sampling error, time delay and other factors in the existing algorithmΔT=500usWhen the error is large, the absolute error is 0.2V, and the relative error is 0.5%; at 50us, the absolute error is about 0.02V, and the relative error is 0.05%; FIG. 11 and FIG. 12 are respectivelyΔT=500usAndΔT=50usthe comparison of the DC voltage results in the transient stage from-20A to +20A can be found inΔT=500usWhen the error is large, the absolute error is 0.2V, and the relative error is 0.5%; in thatΔT=50usThe absolute error is about 0.02V, and the relative error is 0.05%.
In addition, experiment comparison is carried out, 12H bridge power modules on each layer are installed on 6 board cards in the experiment platform of the experiment, the number of the three layers is 36, the worst working condition is a transient state stage from-20A to +20A, and only data of the stage is recorded in the experiment. The experimental design is as follows: firstly, the algorithm is programmed into a DSP board, and the DSP board obtains information such as PWM states, alternating currents and the like of all 12 paths, so that the direct current voltage value of the first module of the A phase can be calculated by using the algorithm, and the calculation step length is set to be 50us by interruption; then setting the initial value of the running state of the DSP to be-20A, setting the running state of the DSP to be +20A at a certain moment, sampling and recording the actual direct current voltage through an oscilloscope, and sampling and recording the result calculated in the whole process at the moment by utilizing a CAN bus; and finally, importing two results by adopting MATLAB and comparing. The experimental results are shown in fig. 13-14, fig. 13 and 14 are the measured results and the comparison results of the dc voltage at the transient stage from-20A to +20A, respectively, the curve in fig. 13 is a 36V dc voltage curve, the absolute error of the proposed algorithm is about 0.3V and the relative error is 0.83% at 50us step length, although the sampling causes additional error, the relative error still meets the national standard regulation within 2%.
Therefore, the experimental result is consistent with the simulation result, which proves that the novel indirect detection algorithm based on the current conversion chain alternating current CT sampling is superior to the indirect detection algorithm based on the current conversion chain alternating current PT sampling.
EXAMPLE III
Another aspect of the present invention further provides a device for detecting a dc voltage of a cascaded H-bridge power module, please refer to fig. 15, which shows a device for detecting a dc voltage of a cascaded H-bridge power module according to a third embodiment of the present invention, where the device includes:
the information acquisition module 11 is configured to acquire alternating current of a current conversion chain acquired by a current transformer arranged on the current conversion chain of the cascaded H-bridge, and acquire a current stage of a power module on the current conversion chain;
the current calculating module 12 is configured to calculate a direct current of the power module according to an alternating current of the commutation chain when the power module is in an uncontrolled stage; when the power module is in a control stage, acquiring a switch state matrix of each switch of the power module, and calculating direct current of the power module according to the switch state matrix and alternating current of the converter chain;
and the voltage calculation module 13 is configured to calculate a dc voltage of the power module according to the dc current of the power module.
Further, in some optional embodiments of the present invention, when the power module is in the non-control stage, the direct current of the power module satisfies a conditional expression:
i cj （t）=| i r （t）|
wherein the content of the first and second substances,i cj （t) Represents the direct current of the power module,i r （t) Representing the alternating current of said converter chain.
Further, in some optional embodiments of the present invention, when the power module is in the control phase, the direct current of the power module satisfies a conditional expression:
Figure 818304DEST_PATH_IMAGE022
wherein the content of the first and second substances,
Figure 319561DEST_PATH_IMAGE048
，ΔTin order to calculate the step size,Cis the capacity of the dc capacitor in the power module,R 1-R 4the resistance values of the four switches of the power module are respectively, and when the switches are switched on, the resistance values areR on Resistance value of at turn-offR off The on-off states of the four switches are determined by the switch state matrix,i cj （t) Represents the direct current of the power module,i r （t) Representing the alternating current of said converter chain.
Further, in some alternative embodiments of the invention, the dc voltage of the power modulev dcj （t) The conditional expression is satisfied:
Figure 750542DEST_PATH_IMAGE049
wherein the content of the first and second substances,V dcj （t k-1) The equivalent historical voltage source satisfies the conditional expression:
Figure 51074DEST_PATH_IMAGE004
wherein the content of the first and second substances,krepresenting the number of samples taken by the current transformer.
Further, in some optional embodiments of the invention, the apparatus further comprises:
the error calculation module is used for calculating the calculation error of the direct-current voltage of the power module by adopting a corresponding error formula according to the current stage of the power module;
and the parameter adjusting module is used for adjusting the calculation parameters of the direct-current voltage of the power module according to the calculation errors.
Further, in some alternative embodiments of the present invention, when the power module is in a steady-state operation stage, the error formula is:
Figure 883900DEST_PATH_IMAGE005
in the formula (I), the compound is shown in the specification,ΔTin order to calculate the step size,Cis the capacity of the dc capacitor in the power module,Δv dcj is the calculation error of the dc voltage of the power module,i cj （t-ΔT) Representst-ΔTThe time corresponds to the direct current of the power module.
Further, in some optional embodiments of the present invention, when the power module is in a transient operation stage or a control stage, the error formula is:
Figure 41212DEST_PATH_IMAGE006
in the formula (I), the compound is shown in the specification,Δv dcj （t k ) Is as followskThe calculation error of the dc voltage of the power module corresponding to the sub-sampling time,ε 2is the relative error of sampling of the current transformer,i cj （t k ) Represents the firstkThe power module direct current corresponding to the sub-sampling time,
Figure 162752DEST_PATH_IMAGE002
，ΔTin order to calculate the step size,Cthe capacity of the direct current capacitor in the power module.
The functions or operation steps of the modules and units when executed are substantially the same as those of the method embodiments, and are not described herein again.
Example four
Referring to fig. 16, the device for detecting a dc voltage of a cascaded H-bridge power module according to a fourth embodiment of the present invention includes a memory 20, a processor 10, and a computer program 30 stored in the memory and running on the processor, where the processor 10 implements the method for detecting a dc voltage of a cascaded H-bridge power module when executing the computer program 30.
The processor 10 may be a Central Processing Unit (CPU), a controller, a microcontroller, a microprocessor or other data Processing chip in some embodiments, and is used to execute program codes stored in the memory 20 or process data, such as executing an access restriction program.
The memory 20 includes at least one type of readable storage medium, which includes a flash memory, a hard disk, a multimedia card, a card type memory (e.g., SD or DX memory, etc.), a magnetic memory, a magnetic disk, an optical disk, and the like. The memory 20 may in some embodiments be an internal storage unit of the detection device of the dc voltage of the cascaded H-bridge power module, for example a hard disk of the detection device of the dc voltage of the cascaded H-bridge power module. The memory 20 may also be an external storage device of the detecting device for the dc voltage of the cascaded H-bridge power module in other embodiments, such as a plug-in hard disk, a Smart Media Card (SMC), a Secure Digital (SD) Card, a Flash memory Card (Flash Card), and the like, which are equipped on the detecting device for the dc voltage of the cascaded H-bridge power module. Further, the memory 20 may also include both an internal storage unit and an external storage device of the detection apparatus of the dc voltage of the cascaded H-bridge power module. The memory 20 may be used not only to store application software installed in the detection device of the dc voltage of the cascaded H-bridge power module and various kinds of data, but also to temporarily store data that has been output or will be output.
It is noted that the configuration shown in fig. 16 does not constitute a limitation of the detection device of the dc voltage of the cascaded H-bridge power module, and in other embodiments, the detection device of the dc voltage of the cascaded H-bridge power module may comprise fewer or more components than those shown, or some components may be combined, or a different arrangement of components.
The embodiment of the present invention further provides a computer-readable storage medium, on which a computer program is stored, where the computer program, when executed by a processor, implements the method for detecting a dc voltage of a cascaded H-bridge power module as described above.
Those of skill in the art will understand that the logic and/or steps represented in the flowcharts or otherwise described herein, e.g., an ordered listing of executable instructions that can be viewed as implementing logical functions, can be embodied in any computer-readable medium for use by or in connection with an instruction execution system, apparatus, or device, such as a computer-based system, processor-containing system, or other system that can fetch the instructions from the instruction execution system, apparatus, or device and execute the instructions. For the purposes of this description, a "computer-readable medium" can be any means that can contain, store, communicate, propagate, or transport the program for use by or in connection with the instruction execution system, apparatus, or device.
More specific examples (a non-exhaustive list) of the computer-readable medium would include the following: an electrical connection (electronic device) having one or more wires, a portable computer diskette (magnetic device), a Random Access Memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), an optical fiber device, and a portable compact disc read-only memory (CDROM). Additionally, the computer-readable medium could even be paper or another suitable medium upon which the program is printed, as the program can be electronically captured, via for instance optical scanning of the paper or other medium, then compiled, interpreted or otherwise processed in a suitable manner if necessary, and then stored in a computer memory.
It should be understood that portions of the present invention may be implemented in hardware, software, firmware, or a combination thereof. In the above embodiments, the various steps or methods may be implemented in software or firmware stored in memory and executed by a suitable instruction execution system. For example, if implemented in hardware, as in another embodiment, any one or combination of the following techniques, which are known in the art, may be used: a discrete logic circuit having a logic gate circuit for implementing a logic function on a data signal, an application specific integrated circuit having an appropriate combinational logic gate circuit, a Programmable Gate Array (PGA), a Field Programmable Gate Array (FPGA), or the like.
In the description herein, references to the description of the term "one embodiment," "some embodiments," "an example," "a specific example," or "some examples," etc., mean that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, the schematic representations of the terms used above do not necessarily refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.
The above-mentioned embodiments only express several embodiments of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the scope of the present invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention. Therefore, the protection scope of the present patent shall be subject to the appended claims.

Claims (7)

1. A method for detecting a DC voltage of a cascaded H-bridge power module is characterized by comprising the following steps:
acquiring alternating current of a current conversion chain acquired by a current transformer on the current conversion chain of the cascaded H bridge, and acquiring the current stage of a power module on the current conversion chain;
when the power module is in an uncontrolled stage, calculating the direct current of the power module according to the alternating current of the current conversion chain;
when the power module is in a control stage, acquiring a switch state matrix of each switch of the power module, and calculating direct current of the power module according to the switch state matrix and alternating current of the converter chain;
calculating the direct current voltage of the power module according to the direct current of the power module;
when the power module is in an uncontrolled stage, the direct current of the power module satisfies a conditional expression:
i cj （t）=| i r （t）|
wherein the content of the first and second substances,i cj （t) Represents the direct current of the power module,i r （t) An alternating current representative of said converter chain;
when the power module is in a control stage, the direct current of the power module meets the conditional expression:
Figure 648705DEST_PATH_IMAGE001
wherein the content of the first and second substances,
Figure 668613DEST_PATH_IMAGE002
，ΔTin order to calculate the step size,Cis the capacity of the dc capacitor in the power module,R 1-R 4the resistance values of the four switches of the power module are respectively, and when the switches are switched on, the resistance values areR on Resistance value of at turn-offR off The on-off states of the four switches are determined by the switch state matrix,i cj （t) Represents the direct current of the power module,i r （t) Represents the alternating current of said converter chain,V dcj （t-ΔT）=V dcj （t k-1），V dcj （t k-1) Is an equivalent historical voltage source,krepresenting the sampling times of the current transformer;
DC voltage of the power modulev dcj （t) The conditional expression is satisfied:
Figure 608887DEST_PATH_IMAGE003
wherein the content of the first and second substances,V dcj （t k-1) The equivalent historical voltage source satisfies the conditional expression:
Figure 397852DEST_PATH_IMAGE004
wherein the content of the first and second substances,krepresenting the number of samples taken by the current transformer.
2. The method for detecting the direct-current voltage of the cascaded H-bridge power module according to claim 1, wherein the step of calculating the direct-current voltage of the power module according to the direct current of the power module is followed by the step of:
calculating the calculation error of the direct-current voltage of the power module by adopting a corresponding error formula according to the current stage of the power module;
and adjusting the calculation parameters of the direct current voltage of the power module according to the calculation error.
3. The method for detecting the direct-current voltage of the cascaded H-bridge power module according to claim 2, wherein when the power module is in a steady-state operation stage, the error formula is as follows:
Figure 30959DEST_PATH_IMAGE005
in the formula (I), the compound is shown in the specification,ΔTin order to calculate the step size,Cis the capacity of the dc capacitor in the power module,Δv dcj is the calculation error of the dc voltage of the power module,i cj （t-ΔT) Representst-ΔTThe time corresponds to the direct current of the power module.
4. The method for detecting the direct-current voltage of the cascaded H-bridge power module according to claim 2, wherein when the power module is in a transient operation stage or a control stage, the error formula is as follows:
Figure 538163DEST_PATH_IMAGE006
in the formula (I), the compound is shown in the specification,Δv dcj （t k ) Is as followskThe calculation error of the dc voltage of the power module corresponding to the sub-sampling time,ε 2is the relative error of sampling of the current transformer,i cj （t k ) Represents the firstkThe power module direct current corresponding to the sub-sampling time,
Figure 16549DEST_PATH_IMAGE002
，ΔTin order to calculate the step size,Cthe capacity of the direct current capacitor in the power module.
5. A detection device for detecting DC voltage of a cascaded H-bridge power module is characterized by comprising:
the information acquisition module is used for acquiring alternating current of a current conversion chain acquired by a current transformer arranged on the current conversion chain of the cascade H bridge and acquiring the current stage of a power module on the current conversion chain;
the current calculation module is used for calculating the direct current of the power module according to the alternating current of the commutation chain when the power module is in an uncontrolled stage; when the power module is in a control stage, acquiring a switch state matrix of each switch of the power module, and calculating direct current of the power module according to the switch state matrix and alternating current of the converter chain;
the voltage calculation module is used for calculating the direct current voltage of the power module according to the direct current of the power module;
when the power module is in an uncontrolled stage, the direct current of the power module satisfies a conditional expression:
i cj （t）=| i r （t）|
wherein the content of the first and second substances,i cj （t) Represents the direct current of the power module,i r （t) An alternating current representative of said converter chain;
when the power module is in a control stage, the direct current of the power module meets the conditional expression:
Figure 925599DEST_PATH_IMAGE001
wherein the content of the first and second substances,
Figure 464028DEST_PATH_IMAGE002
，ΔTin order to calculate the step size,Cis the capacity of the dc capacitor in the power module,R 1-R 4the resistance values of the four switches of the power module are respectively, and when the switches are switched on, the resistance values areR on Resistance value of at turn-offR off The on-off states of the four switches are determined by the switch state matrix,i cj （t) Represents the direct current of the power module,i r （t) Represents the alternating current of said converter chain,V dcj （t-ΔT）=V dcj （t k-1），V dcj （t k-1) Is an equivalent historical voltage source,krepresenting the sampling times of the current transformer;
DC voltage of the power modulev dcj （t) The conditional expression is satisfied:
Figure 458529DEST_PATH_IMAGE007
wherein the content of the first and second substances,V dcj （t k-1) The equivalent historical voltage source satisfies the conditional expression:
Figure 737676DEST_PATH_IMAGE004
wherein the content of the first and second substances,krepresenting the number of samples taken by the current transformer.
6. A computer-readable storage medium, on which a computer program is stored, which, when being executed by a processor, carries out a method for detecting a dc voltage of a cascaded H-bridge power module according to any one of claims 1 to 4.
7. A device for detecting dc voltage of a cascaded H-bridge power module, comprising a memory, a processor and a computer program stored in the memory and executable on the processor, wherein the processor executes the computer program to implement the method for detecting dc voltage of a cascaded H-bridge power module according to any one of claims 1 to 4.
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