CN114900031A - Robust system design method for balancing PFC output capacitor voltage - Google Patents
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- H—ELECTRICITY
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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
- H02M7/02—Conversion of ac power input into dc power output without possibility of reversal
- H02M7/04—Conversion of ac power input into dc power output without possibility of reversal by static converters
- H02M7/12—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
- H02M7/21—Conversion of ac power input into dc 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
- H02M7/217—Conversion of ac power input into dc 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
- H02M7/2173—Conversion of ac power input into dc 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 in a biphase or polyphase circuit arrangement
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- Y02B70/00—Technologies for an efficient end-user side electric power management and consumption
- Y02B70/10—Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes
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Abstract
The invention provides a robust system design method for balancing PFC output capacitor voltage, and a system designed by the method enables a PFC module to have stronger anti-interference and self-adaptive capacity, smaller static error and no overshoot. The invention comprises the following steps: a, sampling parameters of all ADC channels of a PFC module respectively according to Robin ring circulation before the PFC module works normally until the Robin ring circulation of a set number of times is finished; step b, calculating a reference value of the parameter by a second-order filtering method according to the sampling value of the ADC channel; step c, automatically adjusting control parameters of the PFC module according to the obtained reference value, and step d, calibrating sampling data of the ADC channel in real time according to the reference value after the PFC module normally works; and e, detecting whether the PFC module normally operates, if the system is normal, continuing to execute the step d, otherwise, stopping the PFC module. The invention can be applied to the technical field of power electronics.
Description
Technical Field
The invention relates to the technical field of power electronics, in particular to a robust system design method for balancing PFC output capacitance voltage, wherein PFC is a PFC module applied to a three-phase Vienna topological structure.
Background
With the rapid development of power electronic technology, three-phase and three-level converters appear in certain high-power occasions, so that higher requirements are put forward on the three-level converter technology, and the three-level converter technology draws wide attention of numerous scholars at home and abroad. With the development of fully-controlled power electronic devices, PWM rectification is gradually replacing traditional uncontrolled rectification and phase-controlled rectification due to its advantages of being capable of operating with unit power factor, faster response speed, bidirectional energy transmission, etc. At present, the applied rectifiers are various in types and the classification method is also quite various. The most basic method is to divide the PWM rectifier into two categories, i.e., a voltage type and a current type, according to whether an energy storage element in the rectifier is an inductor or a capacitor. There are other classification methods, such as number of phases per grid, number of modulation levels, etc.
Many improved circuit topologies have been proposed based on the basic topology of a multilevel converter. Vienna rectifiers are an improvement and development over diode-clamped three-level rectifiers, the circuit topology of which is shown in fig. 1.
Vienna rectifiers are pulse width modulated rectifiers that receive three-phase ac power, and are also power factor correction circuits, invented by Johann w.kolar in 1990. PFC is a technique for improving the Power Factor of a consumer, and is generally called "Power Factor Correction" in english, meaning "Power Factor Correction". There are many topologies to which PFC can be applied, one of which is a three-phase vienna rectifier.
During the operation of the PFC module applying the three-phase Vienna topology, each bridge arm has 3 output voltages according to the current direction and the switching state, namely that
These three output voltages are defined as states 1,0, -1. Thus, such a circuit will have three level states (-1,0,1) during operation, which is a three level converter. As with conventional three-level converters, the mid-point potential balancing problem is one of the key issues that must be addressed. Influencing three-level vienna rectificationThe factors of the point balance in the device comprise the dispersion of hardware parameters, load mutation, selection of a control strategy and the like. For the problem of balancing the midpoint potential of the three-level vienna rectifier, the following solutions are generally available in the conventional technology:
1. open loop passive control method
The method controls the midpoint potential by selecting vectors and determining the action sequence of the vectors, namely, in a voltage vector synthesis algorithm, the action time of positive and negative small vectors is evenly distributed. However, when the load is disturbed, the method is difficult to control the neutral point potential balance, and the disturbance rejection performance is poor, so that the performance of the PFC module is affected.
2. Hardware midpoint balance control method
There are many hardware-based balance control methods, two common methods are available, the first method is to make the midpoint current flow into the newly added converter between the dc power supply and the capacitor, and not flow from the midpoint, so as to achieve midpoint balance, but the method is more complex, and has high cost, which is not beneficial to implementation; the second is to use the Buck and Boost circuits to perform charge and discharge control on two capacitors on the direct current side, and to detect the voltage difference between the two capacitors to realize voltage-sharing control.
In addition, the midpoint potential balancing technique of the general three-phase vienna PFC cannot realize the adaptation of the control parameters. In other words, each PFC module is required to specifically adjust parameters of the control loop when the PFC module leaves the factory. Moreover, when the working environment changes, the parameters of the control loop are not well adapted to the new environmental conditions.
In addition, the distribution algorithm of the action time of the positive and negative small vectors of the common three-phase vienna PFC midpoint potential balance technology is unreasonable, and the problems of large static error, overshoot fluctuation and the like are caused.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provides a robust system design method for balancing PFC output capacitance voltage.
The technical scheme adopted by the invention is as follows: the method is applied to a PFC module with a three-phase Vienna rectifier topology structure, and comprises the following steps:
step a, before a PFC module is started and normally works, sampling three parameters of input voltage, input current and output voltage of all ADC channels of the PFC module respectively according to Robin ring circulation until the Robin ring circulation of set times is completed, wherein the structure of the Robin ring is set according to a specific system;
step b, calculating the reference values of the input voltage, the input current and the output voltage of each ADC channel by a second-order filtering method according to the sampling value of the ADC channel;
step c, automatically adjusting control parameters of the PFC module according to the reference values obtained by calculation in the step b, wherein vector classification is obtained according to the vector relation synthesized in different output states of the PFC module and the magnitude of a vector module, three vectors in the region where the target vector is located are synthesized to obtain a target vector, action time of the vector is calculated, time of a switching variable of the three-phase Vienna rectifier in a unit switching period is controlled according to the action time of the vector, and then three-phase alternating-current side current and direct-current side voltage are distributed to obtain controllable direct-current voltage;
d, after the PFC module is started and normally works, calibrating the sampling data of the ADC channel in real time according to the reference value;
and e, detecting whether the PFC module normally operates, if the system is normal, continuing to execute the step d, otherwise, stopping the PFC module.
Further, in the step a, a series of SOC events adopted by the ADC channels are set according to the number of the ADC channels, the trigger mode, and the action time, and the corresponding ADC channels are operated according to the schedule of the robin loop.
Still further, in the step b, the process of calculating the reference value by the second-order filtering method includes: weighting the sampling value of the ADC channel at this time and the last filtering output value to obtain an effective filtering value, enabling the output to have a feedback effect on the input, then establishing a corresponding transfer function, and obtaining a reference value from the sampling value of the ADC channel according to the transfer function.
Further, in the step d, the specific process of calibrating the sampling data of the ADC channel in real time according to the reference value is as follows: after each ADC sampling, subtracting the reference value on the basis of the corresponding ADC sampling value, and calculating the formula of V-V ADC -V Benchmark In the formula, V ADC Is the ADC sample value, V Benchmark Is the reference value and V is the parameter that finally participates in the control loop.
More specifically, in step c, the specific steps of synthesizing three-state space vectors of the PFC module and calculating the action time of each vector (especially, the positive and negative small vectors) are as follows:
step c1, dividing the period of a single input voltage into six equal parts according to the topological structure of the three-phase vienna converter, and analyzing the current flowing state of three switching circuits in the topology under each switching state, wherein the division principle of the equal parts is as follows: the polarity of each phase voltage in each interval is kept unchanged, and zero crossing does not exist; the six equal parts are respectively defined as sectors 1-6, and each sector is equally divided into 6 areas;
step c2, depending on the current direction and the switching state, each leg in the topology has 3 output voltages, i.e.
0、
Defining the three output voltages as states 1,0 and-1, obtaining 25 states of the output state of the rectifier due to the absence of the states 1, 1 and the states-1, 1 and-1, and synthesizing vectors in each state to obtain vectors synthesized by the rectifier in different states and a mode of the vectors;
step c3, dividing the vector into a zero vector, a large vector, a positive small vector and a negative small vector according to the magnitude of the modulus of the vector;
and c4, calculating the action time of each vector in each sector to obtain the action time of the composite vector in each area in each sector.
Still more specifically, in step c2, the vectors synthesized by the rectifier under different conditions and the modulus of the vectors are:
wherein, V 0 Is a zero vector, V 1 ～V 6 Is a large vector, V 11 ～V 66 Is a medium vector, V 1p ～V 6p Is a positive small vector, V 1n ～V 6n Is a negative small vector, U AN ～U CN Space vector, U, of Vienna rectifier dc Is the output voltage.
Finally, in step c4, the calculation process of the action time of the resultant vector in each region in each sector is as follows:
step c41, decomposing each variable on the three-phase stationary coordinate of the three-phase Vienna rectifier into two-phase rotating coordinates; transformation relation of transforming three-phase stationary coordinates into two-phase rotating coordinates:
the coordinate transformation relation related to the switching functions of the three switching circuits in the rectifier is as follows:
s is a switching function defined as:
wherein S is ap 、S bp 、S cp 、S an 、S bn 、S cn 、S ao 、S bo And S co Representing the switching function, S, in a three-phase stationary coordinate system dp 、S qp 、S dn 、S qn 、S do 、S qo Representing the switching function in a two-phase rotating coordinate system,
the mathematical model obtained by converting the three-phase stationary coordinates into the two-phase rotating coordinates is:
an equivalent circuit model of the vienna rectifier in a two-phase rotating coordinate system can be obtained, wherein the alternating current side of the vienna rectifier is equivalent to two controlled voltage sources, the direct current side is equivalent to two controlled current sources,
wherein i d And i q Is the current in a two-phase rotating coordinate system, U d And U q Is the voltage under a two-phase rotating coordinate system, R is the equivalent load resistance, omega is the angular frequency, L is the inductance, S dp S dn S qp S qn Respectively, the switching functions, i, corresponding to the positive and negative current sources in the two-phase rotating coordinate system RL For load current, U c1 And U c2 Positive and negative capacitances for the load;
step c42, setting the switching period of the three-phase Vienna rectifier as T S The synthesis time of the three vectors is T 1 、T 2 、T 3 Target vector voltage is V ref And an included angle θ with the α axis, for region 1 of sector 1: target vector is composed of vector V 1n 、V 1p 、 V 2n 、V 2p 、V 0 Synthesis due to V 1n And V 1p Same effect, V 2n And V 2p The effect is the same, and V is set 1n And V 1p The action time is T 1 ，V 2n And V 2p The action time is T 2 ，V 0 The action time is T 3 Then, there are:
T 1 +T 2 +T 3 ＝0
will | V ref |cosθ＝V α ，|V ref |sinθ＝V β ，
Substituting the three formulas to calculate:
wherein, V ref Is a target vector voltage, T S For a switching period, T 1 Is a V 1n And V 1p Time of action of (T) 2 Is a V 2n And V 2p Time of action of (T) 3 Is a V 0 Action time of V α And V β For the decomposition of the target synthetic vector on the two-phase stationary coordinate system, | V ref |cosθ＝V α ，|V ref |sinθ＝V β ；
And c43, according to the vector action time calculated in the step c42, in a unit switching period, the alternating current side current and the direct current side voltage are distributed and adjusted according to the obtained vector action time, and the controllable direct current voltage is obtained.
The invention has the beneficial effects that: according to the method, the Robin ring cyclic sampling is carried out on all ADC channels before the PFC module is started and works normally, the reference value can be automatically measured, the relevant control parameters of the PFC module are automatically adjusted according to the reference value, and the trouble that each machine needs to be debugged one by one when leaving a factory is avoided; the Robin ring cyclic sampling can ensure that the sampling data is more reliable so as to improve the robustness of the system; in addition, the three-state space vectors of the PFC module are synthesized, and the action time of each vector (particularly positive and negative small vectors) is calculated, so that the problem of midpoint potential balance is solved, the voltage sharing of positive and negative capacitors is output, and controllable direct-current voltage is output.
Drawings
FIG. 1 is a circuit topology diagram of a Vienna rectifier;
FIG. 2A is a schematic diagram of the beginning of a Robin ring;
FIG. 2B is a schematic diagram of a robinbo loop first step cycle;
FIG. 2C is a schematic diagram of a second step loop of the robinbo loop;
FIG. 2D is a schematic diagram of a third step cycle of the Robin ring;
FIG. 2E is a schematic diagram of a fourth step cycle of the Robin loop;
FIG. 3 is a schematic diagram of the operation of the switching tube of the three-phase Vienna rectifier;
fig. 4 is a space vector plan view of the PFC module;
FIG. 5 is a control block diagram of a one-phase circuit in a Vienna circuit topology;
fig. 6 is an equivalent circuit model equivalent diagram of the vienna rectifier in a two-phase rotating coordinate system.
Detailed Description
The embodiments of the present invention are specifically as follows.
As shown in fig. 1 to 6, the present invention is based on a three-term vienna rectifier, and is mainly used to control and maintain the voltage balance between two capacitors at the output terminal thereof, so as to improve the stability and performance thereof.
The method is applied to a PFC module with a three-phase Vienna rectifier topology structure, and comprises the following steps:
step a, before a PFC module is started and normally works, sampling three parameters of input voltage, input current and output voltage of all ADC channels of the PFC module respectively according to Robin ring circulation until the Robin ring circulation of set times is completed, wherein the structure of the Robin ring is set according to a specific system;
step b, calculating the reference values of the input voltage, the input current and the output voltage of each ADC channel by a second-order filtering method according to the sampling value of the ADC channel;
step c, automatically adjusting control parameters of the PFC module according to the reference values obtained by calculation in the step b, wherein vector classification is obtained according to the vector relation synthesized in different output states of the PFC module and the magnitude of a vector module, three vectors in the region where the target vector is located are synthesized to obtain a target vector, action time of the vector is calculated, time of a switching variable of the three-phase Vienna rectifier in a unit switching period is controlled according to the action time of the vector, and then three-phase alternating-current side current and direct-current side voltage are distributed to obtain controllable direct-current voltage;
step d, after the PFC module is started and normally works, calibrating the sampling data of the ADC channel in real time according to the reference value;
and e, detecting whether the PFC module normally operates, if the system is normal, continuing to execute the step d, otherwise, stopping the PFC module.
Specifically, in the step a, a series of SOC events adopted by the ADC channels are set according to the number of the ADC channels, the trigger mode, and the action time, and the corresponding ADC channels are operated according to the schedule of the robin loop. For development, since time and trigger timing required for sampling different parameters may be required, a series of SOC events (abbreviated as Start of conversion, SOC is a "configuration set defining a single conversion of a single channel", for example, SOC1 may be defined as sampling current of 200ns of PWM signal in a trigger manner for ADC channel 1, a specific sampling manner and setting hardware conditions of specific ADC peripherals, which is to be referred to simply as that the configuration set of SOC will include parameters such as its trigger manner, number of channels and action time) are required to be set, and the corresponding ADC channel is operated according to the schedule of the robin loop. Specific examples of the robine ring are shown in fig. 2A-2E.
One SOC event will interrupt the cycle rotation after any current conversion is completed. After any current conversion is completed, insert itself as the next conversion. After its conversion is complete, the loop round will continue where it was interrupted. If two high priority SOCs are triggered at the same time, the lower numbered SOCs that should be triggered in sequence will be prioritized.
As FIG. 2A is after reset, SOC0 is the most preferred SOC. SOC7 receives the flip-flops. The channel configured by SOC7 is immediately switched.
RRPOINTER changes to point to SOC7 as shown in FIG. 2B. SOC8 is now the most preferred SOC. Where RRPOINTER is a shorthand for register points, typically some register that holds the pointer value.
The flip-flops of SOC2 and SOC12 return simultaneously as in FIG. 2C. SOC12 is the first in the cycle wheel. The channels of the SOC12 configuration are switched while SOC2 remains suspended.
RRPOINTER changes to point to SOC12 as shown in FIG. 2D. The channel of the SOC2 configuration is being converted.
RRPOINTER changes to point to SOC2 as shown in FIG. 2E. SOC3 is now the most preferred SOC.
In the step b, the process of calculating the reference value by the second-order filtering method is as follows: weighting the sampling value of the ADC channel at this time and the last filtering output value to obtain an effective filtering value, enabling the output to have a feedback effect on the input, then establishing a corresponding transfer function, and obtaining a reference value from the sampling value of the ADC channel according to the transfer function. Specifically, the ADC sampling parameter is calculated, which is mathematically similar to a second-order filter, and the specific implementation method is to obtain an effective filter value by weighting the current sampling value and the last filtering output value, so that the output has a feedback effect on the input. The bandwidth requirement is determined by the concrete engineering condition and hardware parameter, and then the corresponding transfer function is established. A reference value is derived from the sampled values of the ADC channels according to the transfer function.
An example of a simple low-pass second-order filtering procedure is as follows:
clc；
clear；
close all；
％％Import data
Data＝xlsread('data.xlsx')；
fs＝100；％sample frequency is 100Hz
N＝length(Data)；
t＝[0:1/fs:(N-1)/fs]'；
subplot(221)；
plot(t,Data)；
title('Filtering data')subplot(223)；
plot((-N/2:N/2-1)*fs/N,abs(fftshift(fft(Data,N)))*2/N)％plot spectrum，
X axis is frequency title('Filtering spectrum')axis([00.50.2])；
Filter OutputData(1)＝Data(1)；
CutoffFreq＝0.1；
for i＝2:length(Data)
OutputData(i)＝FilterFactor*Data(i)+(1-FilterFactor)*OutputData(i-1)；
plot(t,OutputData')title('Filtered data(cutoff frequency 0.1Hz)')axis([0160 0.41.8])；
subplot(224)；
plot((-N/2:N/2-1)*fs/N,abs(fftshift(fft(OutputData,N)))*2/N)％％plot spectrum，X axis is frequency axis([00.50.2])；
title('Filtered frequency')
the calculation of the reference value can be realized by the above-described procedure.
In the step d, the specific process of calibrating the sampling data of the ADC channel in real time according to the reference value is as follows: after each ADC sampling, subtracting the reference value on the basis of the corresponding ADC sampling value, and calculating the formula of V-V ADC -V Benchmark In the formula, V ADC Is the ADC sample value, V Benchmark Is a reference value, and V is the parameter that finally participates in the control loop (three parameter values of input voltage, input current and output voltage).
As shown in fig. 1, the vienna circuit topology mainly comprises 6 freewheeling diodes (D1+, D1-, D2+, D2-, D3+, D3-), three bidirectional switch circuits S1 (composed of S1, D1, D2, D3, and D4), S2 (composed of S2, D5, D6, D7, and D8), S3 (composed of S3, D9, D10, D11, and D12), series filter capacitors (C1 and C2), and a boost inductor LS; the bidirectional switch circuit has two states, namely on and off; compared with a three-phase full-bridge rectification inverter circuit, the possibility of direct connection of an upper bridge and a lower bridge does not exist, so that dead time does not need to be set for control of a switching tube.
In step c, the synthesis of the three-state space vector of the PFC module and the calculation of the action time of each vector (especially, the positive and negative small vectors) specifically include the following steps:
step c1, dividing the period of a single input voltage into six equal parts according to the topological structure of the three-phase vienna converter, and analyzing the current flowing state of three switching circuits in the topology under each switching state, wherein the division principle of the equal parts is as follows: the polarity of each phase voltage in each interval is kept unchanged, and zero crossing does not exist; the six equal parts are respectively defined as sectors 1-6, and each sector is equally divided into 6 areas; in particular, a switching tube S is provided therein j (j ═ 1,2,3) the on state is 1 and the off state is 0; the combination of three switches has 2 3 As shown in table 1, 8 states:
TABLE 1
In order to facilitate the analysis of the current flow conditions in each switching state, the cycle of a single input voltage is divided into 6 equal parts, and the division principle of the equal parts is as follows: the polarity of each phase voltage in each interval is kept unchanged, and zero crossing does not exist; the division result is as shown in fig. 3. In fig. 3, the settings are:
0-60 DEG is sector 1(Usa >0, Usb <0, Usc > 0); 60-120 DEG is sector 2(Usa >0, Usb <0, Usc < 0);
120-180 DEG is sector 3(Usa >0, Usb >0, Usc < 0); 180 DEG to 240 DEG is sector 4(Usa <0, Usb >0, Usc < 0);
240-300 DEG is sector 5(Usa <0, Usb >0, Usc > 0); 300 DEG to 360 DEG is sector 6(Usa <0, Usb <0, Usc > 0).
Step c2, depending on the current direction and the switching state, each leg in the topology has 3 output voltages, i.e.
0、
The three output voltages are defined as states 1,0, -1, so the output of the rectifier has a total of 3 3 Since the states 1, 1 and the states-1, -1 and-1 do not exist, the output states of the rectifier are only 25 states, and vectors in each state are synthesized to obtain vectors synthesized by the rectifier in different states and the modulus of the vectors. The vector relationships synthesized in the different states are as follows:
wherein, U AN ～U CN Space vector, U, of Vienna rectifier dc Is the output voltage.
Step c3, dividing the vector into zero vectors V according to the magnitude of the modulus of the vector 0 Large vector V 1 ～V 6 Middle vector V 11 ～ V 66 Positive small vector V 1p ～V 6p And a negative small vector V 1n ～V 6n . The distribution of these 25 vectors over the plane is shown in figure 4.
As can be seen from the plan view, these 25 switching states can generate 19 different space voltage vectors; the positive small vector and the negative small vector of the small vector have the same action effect, and only the positive small vector outputs positive voltage, and the negative small vector outputs negative voltage. It can be seen that the positive and negative small vectors have a large influence on the balance of the output voltage neutral point.
And c4, calculating the action time of each vector in each sector to obtain the action time of the composite vector in each area in each sector. The specific implementation of the step is as follows:
step c41, because the variables of the three phases are coupled with each other under the three-phase static coordinate system, the control difficulty is increased, for the convenience of analysis, each variable on the three-phase static coordinate of the three-phase vienna rectifier is decomposed to the two-phase rotating coordinate, and the three-phase static coordinate is transformed to the transformation relation of the two-phase rotating coordinate:
the coordinate transformation relation related to the switching functions of the three switching circuits in the rectifier is as follows:
wherein S is ap 、S bp 、S cp 、S an 、S bn 、S cn 、S ao 、S bo And S co Representing the switching function, S, in a three-phase stationary coordinate system dp 、S qp 、S dn 、S qn 、S do 、S qo Representing the switching function in a two-phase rotating coordinate system,
the mathematical model obtained by converting the three-phase stationary coordinates into the two-phase rotating coordinates is:
an equivalent circuit model of the vienna rectifier in a two-phase rotating coordinate system can be obtained, wherein the alternating current side of the vienna rectifier is equivalent to two controlled voltage sources and the direct current side is equivalent to two controlled current sources, as shown in fig. 6, wherein i d And i q Is the current in a two-phase rotating coordinate system, U d And U q Is the voltage under a two-phase rotating coordinate system, R is the equivalent load resistance, omega is the angular frequency, L is the inductance, S dp S dn S qp S qn Respectively, the switching functions, i, corresponding to the positive and negative current sources in the two-phase rotating coordinate system RL For load current, U c1 And U c2 Positive and negative capacitances of the load.
From the above analysis, it can be seen that only S needs to be controlled in order to obtain a controllable DC voltage dp 、S qp 、S dn 、S qn The switch variables are all variable, and the inductor current can be assumed to be continuous in one switch period due to the non-abrupt change characteristic of the inductor current, so that the inductor current can be controlled by controlling S dp 、S qp 、S dn 、S qn The time (i.e., duty cycle) allotted within a unit switching period regulates the ac side current and the dc side voltage.
Step c42, as can be seen from the vector plan, the target vector can be a composite of three vectors of the region where the target vector is located, and the switching period of the three-phase vienna rectifier is set to be T S The synthesis time of the three vectors is T 1 、T 2 、T 3 Target vector voltage is V ref And an included angle θ with the α axis, for region 1 of sector 1: target vector is composed of vector V 1n 、V 1p 、V 2n 、V 2p 、V 0 Synthesis due to V 1n And V 1p Same effect, V 2n And V 2p The effect is the same, and V is set 1n And V 1p The action time is T 1 ，V 2n And V 2p The action time is T 2 ，V 0 The action time is T 3 Then, there are:
T 1 +T 2 +T 3 ＝0
will | V ref |cosθ＝V α ，|V ref |sinθ＝V β ，
Substituting the three formulas to calculate:
wherein, V ref Is a target vector voltage, T S For a switching period, T 1 Is a V 1n And V 1p Time of action of (T) 2 Is a V 2n And V 2p Time of action of (T) 3 Is a V 0 Action time of V α And V β For the decomposition of the target synthetic vector on the two-phase stationary coordinate system, | V ref |cosθ＝V α ，|V ref |sinθ＝V β ；
Using the same calculation, for each region of each sector: the action time of the resultant vector is as follows:
wherein V0 is a zero vector, V 1 ～V 6 Is a large vector, V 11 ～V 66 Is a medium vector, V 1p ～V 6p Is a positive small vector, V 1n ～V 6n Is a negative small vector, UAN-UCN is the space vector of the Vienna rectifier, Udc is the output voltage, V α And V β For the decomposition of the target synthetic vector on the two-phase stationary coordinate system, | V ref |cosθ＝V α ，|V ref |sinθ＝V β ，V ref Is a target vector voltage, T S Is a switching cycle.
And c43, according to the vector action time calculated in the step c42, in a unit switching period, the alternating current side current and the direct current side voltage are distributed and adjusted according to the obtained vector action time, and the controllable direct current voltage is obtained.
Since three-phase vienna can be regarded as a topological structure formed by connecting three boosts in a Y shape, a control block diagram of the three-phase vienna can be analyzed and represented by using the Boost PFC of one phase, and the other two Boost PFC can also completely copy the control block diagram. In some engineering applications, due to the problems of insufficient ADC channels or large operation overhead, only the currents of two phases of the ADC channels are sampled. In addition, the input voltage must be sampled for all three phases. While the sampling of the positive and negative capacitances at the output and the sampling of the output voltage are unique.
Fig. 5 is a control block diagram of one phase, and the control loops of the other two phases are identical. For each phase in a three-phase vienna topology, the sampling parameters are three parameters, input voltage, input current and output voltage. The outer ring compares the output voltage with the target voltage to obtain a voltage error, and then performs PI operation. The inner loop is used for carrying out voltage feedforward and multiplication phase discrimination on input voltage and then comparing the input voltage with input current. And then, entering an average current control process, judging the vector area where the current is located, and controlling the current through the vector action time calculated in the previous step.
The invention has the following advantages:
1) the reference point can be automatically measured, the related control parameters of the PFC module can be automatically adjusted according to the reference point, and the trouble that each machine needs to be debugged one by one when leaving a factory is avoided.
2) The robing loop cyclic sampling can make the sampling data more reliable so as to improve the robustness of the system.
The synthesis of three-state space vectors of the PFC module and the calculation method of the action time of each vector (particularly positive and negative small vectors) are favorable for solving the problem of midpoint potential balance and outputting voltage sharing of positive and negative capacitors.
Finally, it should be emphasized that the above-described preferred embodiments of the present invention are merely examples of implementations, rather than limitations, and that many variations and modifications of the invention are possible to those skilled in the art, without departing from the spirit and scope of the invention.
Claims (7)
1. A robust system design method for balancing PFC output capacitor voltage, the method being applied to a PFC module having a three-phase vienna rectifier topology, the method comprising the steps of:
step a, before a PFC module is started and normally works, sampling three parameters of input voltage, input current and output voltage of all ADC channels of the PFC module respectively according to Robin ring circulation until the Robin ring circulation of set times is completed, wherein the structure of the Robin ring is set according to a specific system;
step b, calculating the reference values of the input voltage, the input current and the output voltage of each ADC channel by a second-order filtering method according to the sampling value of the ADC channel;
step c, automatically adjusting control parameters of the PFC module according to the reference values obtained by calculation in the step b, wherein vector classification is obtained according to the vector relation synthesized in different output states of the PFC module and the magnitude of a vector module, three vectors in the region where the target vector is located are synthesized to obtain a target vector, action time of the vector is calculated, time of a switching variable of the three-phase Vienna rectifier in a unit switching period is controlled according to the action time of the vector, and then three-phase alternating-current side current and direct-current side voltage are distributed to obtain controllable direct-current voltage;
d, after the PFC module is started and normally works, calibrating the sampling data of the ADC channel in real time according to the reference value;
and e, detecting whether the PFC module normally operates, if the system is normal, continuing to execute the step d, otherwise, stopping the PFC module.
2. The robust system design method for balancing PFC output capacitor voltage of claim 1, wherein: in the step a, a series of SOC events adopted by the ADC channel are set according to the number of the ADC channel, the triggering mode and the acting time, and the corresponding ADC channel is operated according to the dispatching of the Robin ring.
3. The robust system design method for balancing PFC output capacitor voltage of claim 1, wherein: in the step b, the process of calculating the reference value by the second-order filtering method is as follows: weighting the sampling value of the ADC channel at this time and the last filtering output value to obtain an effective filtering value, enabling the output to have a feedback effect on the input, then establishing a corresponding transfer function, and obtaining a reference value from the sampling value of the ADC channel according to the transfer function.
4. The robust system design method for balancing PFC output capacitor voltage of claim 1, wherein: in the step d, the specific process of calibrating the sampling data of the ADC channel in real time according to the reference value is as follows: after each ADC sampling, the reference value is subtracted on the basis of the corresponding ADC sampling value, and the calculation formula is that V is equal to V ADC -V Benchmark In the formula, V ADC Is the ADC sample value, V Benchmark Is the reference value and V is the parameter that will eventually participate in the control loop.
5. The robust system design method for balancing the PFC output capacitor voltage according to claim 1, wherein in step c, the combination of the three-state space vectors of the PFC module and the calculation of the action time of each vector (especially the positive and negative small vectors) comprises the following specific steps:
step c1, dividing the period of a single input voltage into six equal parts according to the topological structure of the three-phase vienna converter, and analyzing the current flowing state of three switching circuits in the topology under each switching state, wherein the division principle of the equal parts is as follows: the polarity of each phase voltage in each interval is kept unchanged, and zero crossing does not exist; the six equal parts are respectively defined as sectors 1-6, and each sector is equally divided into 6 areas;
step c2, depending on the current direction and the switching state, each leg in the topology has 3 output voltages, i.e.
0、
Defining the three output voltages as states 1,0 and-1, obtaining 25 states of the output state of the rectifier due to the absence of the states 1, 1 and the states-1, 1 and-1, and synthesizing vectors in each state to obtain vectors synthesized by the rectifier in different states and a mode of the vectors;
step c3, dividing the vector into a zero vector, a large vector, a positive small vector and a negative small vector according to the magnitude of the modulus of the vector;
and c4, calculating the action time of each vector in each sector to obtain the action time of the composite vector in each area in each sector.
6. The method as claimed in claim 5, wherein in step c2, the vectors synthesized by the rectifier under different conditions and the modulus of the vectors are:
wherein, V 0 Is a zero vector, V 1 ～V 6 Is a large vector, V 11 ～V 66 Is a medium vector, V 1p ～V 6p Is a positive small vector, V 1n ～V 6n Is a negative small vector, U AN ～U CN Space vector, U, of Vienna rectifier dc Is the output voltage.
7. The method of claim 5, wherein in step c4, the action time of the resultant vector in each region in each sector is calculated as follows:
step c41, decomposing each variable on the three-phase stationary coordinate of the three-phase Vienna rectifier into two-phase rotating coordinates; transformation relation of transforming three-phase stationary coordinates into two-phase rotating coordinates:
the coordinate transformation relation related to the switching functions of the three switching circuits in the rectifier is as follows:
where S is a switching function defined as:
wherein S is ap 、S bp 、S cp 、S an 、S bn 、S cn 、S ao 、S bo And S co Representing the switching function, S, in a three-phase stationary coordinate system dp 、S qp 、S dn 、S qn 、S do 、S qo Representing the switching function in a two-phase rotating coordinate system,
the mathematical model obtained by converting the three-phase stationary coordinates into the two-phase rotating coordinates is:
an equivalent circuit model of the vienna rectifier in a two-phase rotating coordinate system can be obtained, wherein the alternating current side of the vienna rectifier is equivalent to two controlled voltage sources, the direct current side is equivalent to two controlled current sources,
wherein i d And i q Is the current in a two-phase rotating coordinate system, U d And U q Is the voltage under a two-phase rotating coordinate system, R is the equivalent load resistance, omega is the angular frequency, L is the inductance, S dp S dn S qp S qn Respectively, the switching functions, i, corresponding to the positive and negative current sources in the two-phase rotating coordinate system RL For load current, U c1 And U c2 Positive and negative capacitances for the load;
step c42, setting the switching period of the three-phase Vienna rectifier as T S The synthesis time of the three vectors is T 1 、T 2 、T 3 Target vector voltage is V ref And an included angle θ with the α axis, for region 1 of sector 1: target vector is composed of vector V 1n 、V 1p 、V 2n 、V 2p 、V 0 Synthesis due to V 1n And V 1p Same effect, V 2n And V 2p The effect is the same, and V is set 1n And V 1p The action time is T 1 ，V 2n And V 2p The action time is T 2 ，V 0 The action time is T 3 Then, there are:
T 1 +T 2 +T 3 ＝0
will | V ref |cosθ＝V α ，|V ref |sinθ＝V β ，
Substituting the three formulas to calculate:
wherein, V ref Is a target vector voltage, T S For a switching period, T 1 Is a V 1n And V 1p Time of action of (T) 2 Is a V 2n And V 2p Time of action of (T) 3 Is a V 0 Action time of V α And V β For the decomposition of the target synthetic vector on the two-phase stationary coordinate system, | V ref |cosθ＝V α ，|V ref |sinθ＝V β ；
And c43, according to the vector action time calculated in the step c42, in a unit switching period, the alternating current side current and the direct current side voltage are distributed and adjusted according to the obtained vector action time, and the controllable direct current voltage is obtained.
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| CN104753334A (en) * | 2015-03-02 | 2015-07-01 | 西安理工大学 | Robust variable structure control method for three-phase voltage type power factor correction converter |
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| WO2018229378A1 (en) * | 2017-06-15 | 2018-12-20 | Renault S.A.S | Method for controlling a three-phase vienna rectifier |
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| CN102916600A (en) * | 2012-10-26 | 2013-02-06 | 河南师范大学 | Self-correcting prediction control method of model of three-phase voltage type PWM (Pulse-Width Modulation) rectifier |
| CN104753334A (en) * | 2015-03-02 | 2015-07-01 | 西安理工大学 | Robust variable structure control method for three-phase voltage type power factor correction converter |
| WO2018229378A1 (en) * | 2017-06-15 | 2018-12-20 | Renault S.A.S | Method for controlling a three-phase vienna rectifier |
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