Method for controlling and testing three-phase current type rectifier

Abstract

The invention relates to a method for controlling and testing a three-phase current type rectifier. The method comprises the following steps: acquiring a zero crossing point of three-phase input alternating current voltage by using a software phase locking method; outer-loop control calculation is started at the zero crossing point, so that the output voltage is stabilized at a target value, and an output value of outer-loop control serves as a fine adjustment amount of a reference in inner-loop PI closed-loop control; inner ring PI closed-loop control is started, and a direct current control method is adopted to realize a unit power factor; an output value of inner ring PI closed-loop control is subjected to coordinate transformation to obtain a space vector control variable of an alpha-beta axis, then a seven-segment PWM pulse is obtained through sector division and switching time calculation, and the pulse drives a main circuit MOS tube; and the upper computer carries out detection to obtain a change track of the key parameters, so that data visualization is realized. The output voltage of the current type rectifier is controllable, a main circuit is simplified, and the correctness of a space vector control algorithm and the running reliability of the rectifier are improved through anti-saturation processing of alpha-beta axis parameters of a static two-phase coordinate system.

Description

Technical Field

[0001] The invention relates to the technical field of high-power switching power supplies, and in particular to a control and testing method for a three-phase current-type rectifier. Background Art

[0002] Compared with three-phase voltage-type PWM rectifiers, three-phase current-type rectifiers do not have output short-circuit fault protection issues, and input current control is simple, but due to the addition of DC-side inductance, the weight and volume are relatively large. For step-down current-type rectifiers, the use of step-up voltage-type rectifiers requires the addition of a DC / DC step-down link. Obviously, current-type rectifiers are more suitable and more efficient in low-voltage power supply situations. In addition, current-type rectifiers also have the advantages of controllable DC current, higher safety performance during short circuits, and easy parallel connection to increase capacity.

[0003] Compared with the three-phase voltage-type PWM rectifier, the three-phase current-type rectifier adds two-value / three-value logic conversion and zero-state discrimination, and the space vector modulation is also more complicated to implement. In addition, the outer loop control and inner loop control are also difficult to design. For digital power supply, the visualization of the data processing process of key control parameters in any period of time greatly improves the product design efficiency, which is also the design difficulty of digital power supply.

[0004] At present, the function of the outer loop control of the three-phase current source rectifier is to stabilize the output current, and the output voltage is in an uncontrollable state. Therefore, it is necessary to add a DC / DC converter at the output end of the rectifier to stabilize the output voltage. In addition, since the three-phase current source rectifier uses I d * c That is, the output current target value is calculated as the instruction vector modulus, and there is no control function for the target output voltage, which increases the design difficulty in most applications that require voltage regulation output. At present, the host computer system used for digital power supply testing can display data and historical curves, but due to the delay of serial communication, CAN communication or other communication methods, the data displayed by the host computer is not real-time data, and it is impossible to intercept multiple real-time key data of any period for comparative analysis, which increases the difficulty of digital power supply development to a certain extent. Summary of the invention

[0005] In order to solve the deficiencies in the prior art, an object of the present invention is to provide a control and testing method for a three-phase current source rectifier.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] A control and testing method for a three-phase current source rectifier, the method comprising the following steps:

[0008] S1, software phase lock

[0009] Obtain the input side voltage and use the software phase-locking method to obtain the zero-crossing point of the three-phase input AC voltage;

[0010] S2, outer loop control

[0011] Obtain the output side voltage, and start the outer loop control calculation at the zero-crossing point obtained by software phase locking to stabilize the output voltage at the target value, and use the output value of the outer loop control as the fine-tuning amount of the benchmark in the inner loop PI closed-loop control;

[0012] S3, inner PI closed loop control

[0013] Obtain the input side current, start the inner loop PI closed-loop control, and use the direct current control method to achieve unity power factor;

[0014] S4, seven-segment space vector modulation

[0015] The output value of the inner PI closed-loop control is transformed into a space vector control variable of the αβ axis of the stationary two-phase coordinate system. After sector division and switching time calculation, the space vector control variable is converted into a seven-segment PWM pulse, which is used to drive the main circuit MOS tube;

[0016] S5. Host computer detection and visualization processing

[0017] The host computer is used to detect the software phase-locked control, outer loop control, inner loop PI closed-loop control and space vector control processes, obtain the change trajectory of key parameters in the control process, and perform data visualization.

[0018] As a further improvement of the above technical solution, in step S2, the output side voltage is obtained, and at the zero-crossing point obtained by software phase locking, the outer loop control calculation is started to stabilize the output voltage at the target value, and the output value of the outer loop control is used as the fine-tuning amount of the benchmark in the inner loop PI closed-loop control, including:

[0019] S21, obtaining the output side voltage, and starting the outer loop control calculation at the zero-crossing point obtained by software phase locking;

[0020] S22. Use the output value of the outer loop control as the fine-tuning amount of the reference in the inner loop PI adjustment and set an upper limit; when unloaded, if the actual output voltage is too high, the output value of the outer loop control will exceed the upper limit, then the PWM drive pulse is turned off to prevent overmodulation; when normally loaded, the actual output voltage is compared with the reference voltage in the outer loop control. If the actual output voltage is too high, that is, the actual output voltage is greater than the reference voltage, then the inner loop control reference value is reduced. Conversely, if the actual output voltage is too low, that is, the actual output voltage is less than the reference voltage, then the inner loop control reference value is increased; if the actual output voltage is equal to the reference voltage, the inner loop control reference value remains unchanged.

[0021] As a further improvement of the above technical solution, in step S3, the input side current is obtained, the inner loop PI closed-loop control is started, and the unity power factor is achieved by using a direct current control method, including:

[0022] S31. Determine the relationship between the inner loop control reference value and the output current target value using formula (1):

[0023]

[0024] In formula (1), I drefQ is the inner loop control reference value, η is the efficiency, is the output current target value, U out is the output voltage, U m is the input voltage amplitude;

[0025] Depend on It can be seen that the condition for formula (1) to be valid is the inner loop control reference value I drefQ Equal to the input current amplitude I m .

[0026] S32. After the coordinate transformation of the three-phase input AC current, the control inner loop is designed based on the dq axis rotation coordinate system; the input side current is obtained, the d axis is selected as the active parameter reference axis, and the q axis is selected as the reactive parameter reference axis. The three-phase input AC current is transformed into the dq axis using equations (2) and (3):

[0027]

[0028]

[0029] In formula (2), I m is the AC current amplitude, that is, the input current amplitude; ω0 is the AC current fundamental angular frequency; From formula (2), we can see that the d-axis control variable I dQ Equal to the input current amplitude.

[0030] S33, the inner loop control reference I drefQ with IdQ As the error amplifier input, after PI regulation, it drives the MOS tube through space vector modulation to control the input current amplitude I m Equal to I drefQ ; Similarly, through PI adjustment, the q-axis variable I qQ is zero, when I qQ When it is zero, it means that the input voltage and input current are in phase, thus achieving unity power factor.

[0031] As a further improvement of the above technical solution, in step S4, the output value of the inner loop PI closed-loop control is subjected to coordinate transformation to obtain a space vector control variable of the αβ axis of the stationary two-phase coordinate system, and the space vector control variable is subjected to sector division and switching time calculation to obtain a seven-segment PWM pulse, and the seven-segment PWM pulse is used to drive the main circuit MOS tube, including:

[0032] S41, using equation (4) to transform the output value of the inner PI closed-loop control to obtain the space vector control variable of the αβ axis of the stationary two-phase coordinate system;

[0033]

[0034] Among them, I α and I β is the control variable of αβ axis, I dr and I qr is the control variable of dq axis, ω0 is the fundamental angular frequency of AC current;

[0035] S42, after the space vector control variable is sectorized and the switching time is calculated, a seven-segment PWM pulse is obtained, and the seven-segment PWM pulse is used to drive the main circuit MOS tube;

[0036] S43. Use equation (5) to process the saturation phenomenon in space vector control:

[0037]

[0038] Among them, I α and I β is the control variable of αβ axis, is the output current target value.

[0039] As a further improvement of the above technical solution, in step S5, the upper computer is used to detect the software phase lock, outer loop control, inner loop PI closed loop control and space vector control process, obtain the change trajectory of key parameters in the control process, and perform data visualization, including:

[0040] S51. The upper computer programming software is VB6. It communicates with DSP by serial communication. The communication format is: baud rate 19200bps, 1stop bit, odd parity, 8char bits, async mode. The data is sent or received in the following byte arrangement order in the data frame: [frame header][address][function code][number of bytes][data 1 high byte][data 1 low byte][data 2 high byte][data 2 low byte]...[data N high byte][data N low byte][Xor check][frame tail];

[0041] S52, intercepting data of up to 3 key parameters in any period of time in the software algorithm and transmitting them to the external EEPROM storage area through IIC communication;

[0042] S53, transmitting the data of the key parameters to the host computer through the serial port, and the host computer processes and displays the data of the key parameters in a graphical manner.

[0043] Compared with the prior art, the advantages of the present invention are:

[0044] (1) The present invention proposes a control method for directly stabilizing the output voltage, which does not require adding a DC / DC converter step-down circuit at the output end of the rectifier. The method changes the output current control of the current-source rectifier into output voltage control. The present invention not only realizes the controllable output voltage of the current-source rectifier, reduces a DC / DC step-down circuit, simplifies the main circuit, but also improves the correctness of the space vector control algorithm and the reliability of the rectifier operation through the anti-saturation processing of the αβ axis parameters of the stationary two-phase coordinate system.

[0045] (2) The present invention also proposes a visualization method for graphically processing key real-time control parameter data in any period of time. The method uses an external EEPROM chip to store data and performs visualization processing on the host computer, which speeds up the digital power debugging process. In addition, this method can read and write data at any time, and will not affect the normal operation of the rectifier due to the need to transmit a large amount of data in serial communication. The present invention realizes the visualization processing of key parameter data in any period of time, verifies the correctness of the software algorithm, speeds up the debugging process, and the external EEPROM can read and write key parameter data packets at any time without affecting the normal operation of the program. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 It is a method flow chart of the control and testing method of the three-phase current source rectifier in the present invention;

[0047] Figure 2 It is a principle block diagram of the control and testing method of the three-phase current source rectifier in the present invention;

[0048] Figure 3 It is a structural diagram of a three-phase current source rectifier in the present invention;

[0049] Figure 4 Schematic diagram of the spatial vector distribution in the present invention;

[0050] Figure 5 Schematic diagram of six switch states of sector 1 in the present invention;

[0051] Figure 6 It is a connection diagram between DSP and external EEPROM in the present invention;

[0052] Figure 7 It is a schematic diagram of the EEPROM storage area of ​​the present invention;

[0053] Figure 8 is a control block diagram of the outer loop and the inner loop in the present invention, Figure 8 In, T d is the sampling and control system delay, R L is the load, L0 is the output DC inductor, and C0 is the output side capacitor;

[0054] Fig. 9 It is a visualized waveform diagram of three key parameter data in the present invention;

[0055] Figure 10 to Figure 13 It is the matlab simulation result diagram of the present invention, wherein, Fig.10 It is the simulation waveform of the αβ axis control variable of the stationary two-phase coordinate system; Fig.11 The yellow line in the middle is the input voltage waveform, and the red line is the input current waveform; Fig.12 The yellow line in the middle is the three-phase input current waveform; Fig.13 The yellow line in the middle is the output voltage waveform. DETAILED DESCRIPTION

[0056] The present invention will be further described below in conjunction with the accompanying drawings:

[0057] The control part of the three-phase current source rectifier is composed of software function modules, namely space vector control, software phase lock, inner loop and outer loop control; the detection part is composed of the host computer and EEPROM circuit. Figure 2 As shown, the output side voltage is conditioned by the sampling circuit and used as the input variable of the outer loop control; the software phase-locked circuit determines the zero-crossing point of the three-phase input AC voltage, thereby providing the current grid phase angle ω0t for the coordinate transformation; the input side current is conditioned by the sampling circuit and used as the feedback of the inner loop control, thereby realizing direct current control; the host computer and EEPROM circuit realize the graphical processing of key real-time control parameter data in any period of time, thereby debugging the process.

[0058] like Figure 3As shown, the main circuit of the three-phase current-type rectifier includes a six-switch structure rectifier bridge. Each bridge arm of the rectifier bridge adopts a switch tube and a diode in series to block the reverse current on the bridge arm and reduce the reverse voltage of the switch tube. The DC side adopts inductive energy storage, and its main function is to filter out the pulsating ripple of the DC current.

[0059] like Figure 1 A control and test method for a three-phase current source rectifier is shown, the method comprising the following steps:

[0060] S1, software phase lock

[0061] The input side voltage is obtained, and the zero-crossing point of the three-phase input AC voltage is obtained using the software phase-locked method.

[0062] After the software is initialized, the zero-crossing point of the three-phase input AC voltage is obtained through the software phase-locked technology. The zero-crossing point is used as the start-up time of the outer loop control. The outer loop control calculation starts at the zero-crossing point to stabilize the output voltage at the target value. This operation provides an accurate start-up time for subsequent control steps. During unity power factor control, since the input voltage and current are in phase, starting the outer loop control at the zero-crossing point can greatly reduce the current spike on the input side and make the control process more stable.

[0063] S2, outer loop control

[0064] The output voltage is obtained, and at the zero-crossing point obtained by software phase locking, the outer loop control calculation is started to stabilize the output voltage at the target value, and the output value of the outer loop control is used as the fine-tuning amount of the reference in the inner loop PI closed-loop control. The outer loop control calculation is simple, and the outer loop control output is only used as the fine-tuning amount of the reference in the inner loop PI regulation.

[0065] S3, inner PI closed loop control

[0066] The input side current is obtained, the inner PI closed-loop control is started, and the direct current control method is used to achieve unity power factor.

[0067] S4, seven-segment space vector modulation

[0068] The output value of the inner PI closed-loop control is transformed into the space vector control variable of the αβ axis of the stationary two-phase coordinate system. After sector division and switching time calculation, the space vector control variable is converted into a seven-segment PWM pulse, which is used to drive the main circuit MOS tube.

[0069] S5. Host computer detection and visualization processing

[0070] The host computer is used to detect the software phase lock, outer loop control, inner loop PI closed loop control and space vector control process, obtain the change trajectory of key parameters in the control process, and perform data visualization. The host computer is used to depict the change trajectory of key parameters in the DSP software control process and realize visualization.

[0071] As a further improvement of the above technical solution, in step S2, the output side voltage is obtained, and at the zero-crossing point obtained by software phase locking, the outer loop control calculation is started to stabilize the output voltage at the target value, and the output value of the outer loop control is used as the fine-tuning amount of the benchmark in the inner loop PI closed-loop control, including:

[0072] S21, obtaining the output side voltage, and starting the outer loop control calculation at the zero-crossing point obtained by software phase locking.

[0073] S22. Use the output value of the outer loop control as the fine-tuning amount of the reference in the inner loop PI adjustment and set an upper limit; when unloaded, if the actual output voltage is too high, the output value of the outer loop control will exceed the upper limit, then the PWM drive pulse is turned off to prevent overmodulation; when normally loaded, the actual output voltage is compared with the reference voltage in the outer loop control. If the actual output voltage is too high, that is, the actual output voltage is greater than the reference voltage, then the inner loop control reference value is reduced. Conversely, if the actual output voltage is too low, that is, the actual output voltage is less than the reference voltage, then the inner loop control reference value is increased; if the actual output voltage is equal to the reference voltage, the inner loop control reference value remains unchanged.

[0074] The main task of the outer loop control is to stabilize the output voltage at the target value. The above process simplifies the calculation amount of DSP and improves the control efficiency. In order to further simplify the output voltage control of the current source rectifier, the outer loop control does not adopt the traditional PI adjustment method. Instead, the actual output voltage is compared with the reference voltage in the outer loop control. If the actual voltage is too high, the inner loop control reference value is reduced. Otherwise, the inner loop control reference value is increased to stabilize the output voltage, which simplifies the calculation amount of DSP.

[0075] As a further improvement of the above technical solution, in step S3, the input side current is obtained, the inner loop PI closed-loop control is started, and the unity power factor is achieved by using a direct current control method, including:

[0076] S31. Determine the relationship between the inner loop control reference value and the output current target value using formula (1):

[0077]

[0078] In formula (1), I drefQ is the inner loop control reference value, η is the efficiency, is the output current target value, U out is the output voltage, Um is the input voltage amplitude; It can be seen that the condition for formula (1) to be valid is the inner loop control reference value I drefQ Equal to the input current amplitude I m .

[0079] S32. After the coordinate transformation of the three-phase input AC current, the control inner loop is designed based on the dq axis rotation coordinate system; the input side current is obtained, the d axis is selected as the active parameter reference axis, and the q axis is selected as the reactive parameter reference axis. The three-phase input AC current is transformed into the dq axis using equations (2) and (3):

[0080]

[0081] In formula (2), I m is the AC current amplitude, that is, the input current amplitude; ω0 is the AC current fundamental angular frequency i A 、i B 、i C is the instantaneous value of the grid current, i dQ 、i qQ is the grid current converted to dq axis variables; from formula (2), we can see that the d axis control variable I dQ Equal to the input current amplitude.

[0082] S33, the inner loop control reference I drefQ with I dQ As the error amplifier input, after PI regulation, it drives the MOS tube through space vector modulation to control the input current amplitude I m Equal to I drefQ ; Similarly, through PI adjustment, the q-axis variable I qQ is zero, when I qQ When it is zero, it means that the input voltage and input current are in phase, thus achieving unity power factor.

[0083] As a further improvement of the above technical solution, in step S4, the output value of the inner loop PI closed-loop control is subjected to coordinate transformation to obtain a space vector control variable of the αβ axis of the stationary two-phase coordinate system, and the space vector control variable is subjected to sector division and switching time calculation to obtain a seven-segment PWM pulse, and the seven-segment PWM pulse is used to drive the main circuit MOS tube, including:

[0084] S41, using equation (4) to transform the output value of the inner PI closed-loop control to obtain the space vector control variable of the αβ axis of the stationary two-phase coordinate system;

[0085]

[0086] Among them, I α and Iβ is the control variable of αβ axis, I dr and I qr is the controlled variable of dq axis, ω0 is the fundamental angular frequency of AC current.

[0087] S42: In order to further reduce the harmonic content of input current and reduce switching loss, a seven-segment space vector modulation method is provided. After the space vector control variable is sectored and the switching time is calculated, a seven-segment PWM pulse is obtained, and the seven-segment PWM pulse is used to drive the main circuit MOS tube.

[0088] In step S4, space vector modulation is performed. The operation steps of the space vector modulation are:

[0089] The αβ-axis control quantity of the stationary coordinate system is processed to prevent saturation, and the sector where the instruction vector is located is determined; the three nearest vectors are found in the sector to determine the switch state; the duration of each switch state is calculated from the αβ-axis control quantity of the stationary coordinate system and the switch cycle; the calculated switch state is assigned to the corresponding switch tube.

[0090] S43. In order to further improve the reliability of the space vector algorithm, an anti-saturation processing method for the αβ axis control parameters of the stationary two-phase coordinate system is given.

[0091] The stationary coordinate system αβ axis control quantity is processed to prevent saturation, and the sector where the command vector is located is determined. According to the anti-saturation relationship of the stationary two-phase coordinate system αβ axis parameters in the space vector algorithm, anti-saturation processing is performed, that is, the saturation phenomenon in the space vector control is processed using formula (5):

[0092]

[0093] Among them, I α and I β is the control variable of αβ axis, I d * c is the output current target value.

[0094] It is necessary to ensure that formula (5) holds true at all times, otherwise saturation may occur in space vector control.

[0095] The difficulty of SVPWM current control based on fixed switching frequency lies in determining the sector in which the space vector falls, and then obtaining the three switching state components of the synthetic command vector. Figure 4As shown, the present invention divides a power grid power frequency cycle into 6 sectors, and distributes the space vector according to the sector action order based on the principle of less switching times of the switch tube, thereby ensuring that the seven-segment space vector modulation method can obtain smaller input current harmonics while reducing switching losses. The sector action order of the seven-segment space vector modulation method and the space vector allocation corresponding to each sector reduce switching losses to the greatest extent. The sector action order and the space vector selection corresponding to each sector are shown in Table 1:

[0096] Table 1 Sector action sequence and space vector selection table

[0097] Sector <![CDATA[I n ]]> <![CDATA[I n ]]> <![CDATA[I0]]> 1 <![CDATA[I6]]> <![CDATA[I1]]> <![CDATA[I7]]> 2 <![CDATA[I1]]> <![CDATA[I2]]> <![CDATA[I9]]> 3 <![CDATA[I2]]> <![CDATA[I3]]> <![CDATA[I8]]> 4 <![CDATA[I3]]> <![CDATA[I4]]> <![CDATA[I7]]> 5 <![CDATA[I4]]> <![CDATA[I5]]> <![CDATA[I9]]> 6 <![CDATA[I5]]> <![CDATA[I6]]> <![CDATA[I8]]>

[0098] In Table 1, sector 1 is composed of I6, I1 and I7 to synthesize the target vector. When these three switch states are switched, Figure 3 to Figure 5 As shown, the upper bridge arm switches Q1-Q3 remain normally open or normally closed, and only the lower bridge arm switches Q4-Q6 are turned on or off, with a small number of switching times. Similar to sector 1, sectors 2-6 have a group of upper bridge arm or lower bridge arm switch tubes that remain normally open or normally closed in a switching cycle, thereby reducing switching losses.

[0099] The space vector modulus length of the three-phase current-type PFC is Generally speaking, the inner circle of the space vector is the upper limit of the command vector modulus. If it exceeds the upper limit, it will be overmodulated. The command vector modulus of the inner circle of the space vector is the outer circle radius. Then the instruction vector modulus is In this way, the command vector module length of the αβ axis control quantity synthesis of the static two-phase coordinate system does not exceed the output current target value The target output voltage variable is included in the synthetic instruction vector modulus calculation.

[0100] From the above theoretical analysis, we know that it is necessary to prevent the saturation phenomenon that may occur in space vector operations. If the operation is saturated, it will lead to errors in the calculation of the switch tube drive pulse width. In serious cases, the main circuit switch tube will burn out.

[0101] As a further improvement of the above technical solution, in step S5, the upper computer is used to detect the software phase lock, outer loop control, inner loop PI closed loop control and space vector control process, obtain the change trajectory of key parameters in the control process, and perform data visualization, including:

[0102] S51. The upper computer programming software is VB6, which uses serial communication to communicate with DSP. The communication format is: baud rate 19200bps, 1stop bit, odd parity, 8char bits, async mode, and sends or receives data in the following byte arrangement order in the data frame: [frame header][address][function code][number of bytes][data 1 high byte][data 1 low byte][data 2 high byte][data 2 low byte]...[data N high byte][data N low byte][Xor check][frame tail].

[0103] S52, intercepting the data of up to 3 key parameters in any period of time in the software algorithm and transmitting them to the external EEPROM storage area through IIC communication. According to the test needs, 3 key parameters are selected, and the data of each key parameter is composed of 210 data points, which are stored in the external EEPROM in real time through IIC communication. In order to further simplify the debugging process of the control algorithm, the test method adopts the IIC communication mode of EEPROM, and can read and write key parameter data packets at any time, and perform visual graphics processing on the host computer.

[0104] S53, transmitting the data of the key parameters to the host computer through the serial port, and the host computer processes and displays the data of the key parameters in a graphical manner.

[0105] These data can be transmitted to the host computer through the serial port at any time to draw graphics, which will not affect the normal program operation of the rectifier main control DSP; each key parameter data is composed of 210 data points, that is, 210 data points constitute the key parameter data packet. The data point interval is the cycle of the DSP interrupt control program. For example, if the interrupt frequency is 100kHz, 3 key parameter data with any time period length of 210 / 100kHz=2.1ms can be sampled and graphed at the same time. The communication method between EEPROM and DSP is as follows Figure 6 As shown, the data interval of EEPROM is allocated as follows Figure 7 shown.

[0106] The relationship between the output current target value and the output voltage in this embodiment is shown in formula (6):

[0107]

[0108] In formula (6), I m is the input current amplitude, η is the efficiency, I d * c is the output current target value, U o * ut is the target output voltage, Um is the input voltage amplitude.

[0109] Table 2 is a distribution table of the action time of adjacent space vectors in the seven-segment modulation method, which is used to calculate the switch action time in sectors 1 to 6. Figure 5 As shown, taking the seven-segment space vector control of sector 1 as an example, in Table 2, T1 represents the switching action time of stage I6 as Y, T2 represents the switching action time of stage I1 as X, and T S -T1-T2 is the switching time of stage I7, T s is the switching cycle.

[0110] Table 2 Switch state action X, Y, Z time distribution table

[0111] Sector 1 2 3 4 5 6 <![CDATA[T1]]> Y -Y X -X -Z Z <![CDATA[T2]]> X Z -Z -Y Y -X

[0112] The calculation expressions of X, Y, and Z in Table 2 are as follows:

[0113]

[0114] In formula (7), Indicates the DC output current, T s is the switching cycle, I' allfa and I' beta is the control variable of the stationary coordinate system αβ. The modulus of the synthesized instruction vector is Substituting formula (6) into formula (7), the output voltage target value can be obtained: The switch state action time is calculated. The synthesized command vector calculation includes the target output voltage variable. In order to further simplify the output voltage control of the current source rectifier, the synthesized command vector module length calculation in the space vector algorithm includes the target output voltage variable.

[0115] like Figure 8 As shown in the figure, after determining the output voltage target value, the outer loop fine-tunes the inner loop control reference value, and then the inner loop PI adjustment can stabilize the output voltage. The rectifier is simulated using matlab, and the simulation results are shown in Figure 10 to Figure 13 shown.

[0116] like Figure 5 As shown, taking the seven-segment space vector control of sector 1 as an example, according to the sector action sequence and space vector selection method in Table 1, the switch tube switches less times, the upper bridge arm switch tube remains normally on or normally off in a switching cycle, and the lower bridge arm switch tube generates a PWM drive pulse according to the calculated switch state and switching time. The DSP software programming is also simple, the upper bridge arm switch tube does not need to calculate the pulse width and can directly give a high / low level, and only the lower bridge arm switch tube needs to calculate the drive pulse width.

[0117] Taking the drive pulse programming of the upper / lower bridge arm switch of phase A as an example, the DSP programming statement for the upper bridge arm switch is as follows:

[0118] Epwm1.AQCTLA.ZRO=2;

[0119] Epwm1.AQCTLB.ZRO=2;

[0120] The DSP programming statement for the lower bridge arm switch is as follows:

[0121] Epwm1.AQCTLB.bit.CAU=2;

[0122] Epwm1.AQCTLB.bit.CAD=1;

[0123] EPwm1Regs.CMPA.half.CMPA=cmp1;

[0124] Epwm1.AQCTLB.bit.CBU=1; Epwm1.AQCTLB.bit.CBD=2;

[0125] EPwm1Regs.CMPb=cmp3.

[0126] As shown in formula (5), the synthesized instruction vector modulus does not exceed I d * c , which can prevent the saturation phenomenon that may occur in space vector operations. The calculation steps for preventing saturation are as follows:

[0127] If formula (5) holds true, then the control variable I of the αβ axis of the stationary two-phase coordinate system is α and I β Output directly without correction; if formula (5) does not hold, then the control variable I α and I β The calculation formula of is shown in formula (8):

[0128]

[0129] According to formula (8), the control variable I α and I β After correction, saturation can be effectively prevented, and the correctness of space vector modulation and the reliability of rectifier operation are increased.

[0130] like Figure 6As shown in the figure, the IIC interface of DSP is directly connected to the corresponding pins of EEPROM, and the pins A0~A2 of EEPROM are shorted to ground, indicating that the physical address of EEPROM on the IIC bus is 0x50 and it is a slave device. The clock signal SCL generated by the master device DSP is sent to the bus. According to the IIC communication protocol, DSP and EEPROM convert the data into serial signals and send them to the SDA line to realize bidirectional data transmission.

[0131] like Figure 7 As shown in the figure, EEPROM uses bytes as storage units and can store up to 3 key parameters. The data of each key parameter contains 210 data points, and the data type is byte. In order to obtain the visualization effect as quickly as possible, the 210 data points of each key parameter are evenly divided into 3 arrays. After the 70 data of each array are transmitted via the serial port communication, the graphics are drawn on the host computer. Therefore, the 3 key parameter data packets need to be drawn 9 times in total on the host computer, and the results of each drawing are displayed on the same interface of the host computer.

[0132] When the key parameter change trajectory of a certain period in the rectifier software control algorithm is needed, the DSP intercepts the relevant data of this period in the program and stores it in the DSP memory. After the rectifier is shut down, the DSP starts to transfer a total of 3*210 data in the memory to the EEPROM, so the data transmission on the IIC bus will not affect the normal operation of the rectifier. When it is necessary to observe these data at any time, the DSP reads the data from the EEPROM and stores it in the memory again, and then transmits the data packet to the host computer through serial communication for visualization processing.

[0133] In this embodiment, the host computer programming software is VB6, which divides the 3*210 data into 9 data packets for serial communication transmission. After each data packet is transmitted, the trajectory curve of the data change is drawn on the host computer until the trajectory curves of the three key parameters are all drawn. The three completed trajectory curves are displayed on one interface, and the change trajectories of the three key parameters in a certain period of time in the software algorithm can be compared and analyzed, thereby accurately judging the correctness of the software algorithm and whether the control parameter value settings of the software algorithm are reasonable. The visual graphics of the host computer depict the results as shown in the figure. Fig. 9 As shown in the figure, the simulation results of the same key parameters are as follows Fig.10 shown.

[0134] Fig. 9The change trajectory of the αβ axis control variables of the stationary two-phase coordinate system in the DSP software is given in the figure, where the green line is the A-phase input voltage waveform, the red line is the α-axis control variable waveform, and the blue line is the β-axis control variable waveform. The αβ axis variables of the stationary two-phase coordinate system are vector control variables, and the phase difference between these two variables is 90°. Moreover, when the input voltage and input current are in phase, that is, unity power factor is achieved, the phase difference between the α-axis control variable and the A-phase input voltage waveform is 0. Fig. 9 Use a visual waveform to indicate whether unity power factor is currently achieved.

[0135] Fig.10 The simulation method verifies that the phase difference of the αβ axis variables in the stationary two-phase coordinate system is 90°; Fig.11 The simulation verifies that unity power factor is achieved when the input voltage and input current are in phase; Fig.12 The simulation verifies that the phase difference of the three-phase AC current is 120° and the three-phase AC current changes sinusoidally, achieving the design goal of minimizing the total harmonic distortion rate of the AC input current in power factor correction. Fig.13 The simulation verifies that the output voltage of the three-phase rectifier is stable, achieving the design goal of stable output voltage in power factor correction.

[0136] In summary, the present invention provides a control and test method for a three-phase current-type rectifier, wherein the core control is composed of an outer loop and an inner loop, the outer loop does not use PI regulation, and simplifies the DSP calculation process; a seven-segment space vector modulation is used to obtain smaller input current harmonics while reducing switching losses; anti-saturation processing improves the correctness of the space vector control algorithm and the reliability of the rectifier operation; the visualization processing of key parameters speeds up the design and debugging process to a certain extent, and reduces the design difficulty. The control method in the present invention effectively realizes the unity power factor, and the detection method graphically depicts the trajectory changes of key parameters in the software algorithm, which speeds up the design and debugging process to a certain extent and reduces the design difficulty.

[0137] The above-described embodiments are merely descriptions of preferred implementations of the present invention and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the scope of protection determined by the claims of the present invention.

Claims

1. A control and test method for a three-phase current source rectifier, characterized in that: The method comprises the following steps: S1, software phase lock Obtain the input side voltage and use the software phase-locking method to obtain the zero-crossing point of the three-phase input AC voltage; S2, outer loop control Obtain the output side voltage, and start the outer loop control calculation at the zero-crossing point obtained by software phase locking to stabilize the output voltage at the target value, and use the output value of the outer loop control as the fine-tuning amount of the benchmark in the inner loop PI closed-loop control; S3, inner PI closed loop control Obtain the input side current, start the inner loop PI closed-loop control, and use the direct current control method to achieve unity power factor; S4, seven-segment space vector modulation The output value of the inner PI closed-loop control is transformed into a space vector control variable of the αβ axis of the stationary two-phase coordinate system. After sector division and switching time calculation, the space vector control variable is converted into a seven-segment PWM pulse, which is used to drive the main circuit MOS tube; S5. Host computer detection and visualization processing The host computer is used to detect the software phase-locked control, outer loop control, inner loop PI closed-loop control and space vector control processes, obtain the change trajectory of key parameters in the control process, and perform data visualization.

2. The control and testing method of a three-phase current source rectifier according to claim 1, characterized in that: In the step S2, the output side voltage is obtained, and at the zero-crossing point obtained by software phase locking, the outer loop control calculation is started to stabilize the output voltage at the target value, and the output value of the outer loop control is used as the fine-tuning amount of the reference in the inner loop PI closed-loop control, including: S21, obtaining the output side voltage, and starting the outer loop control calculation at the zero-crossing point obtained by software phase locking; S22. Use the output value of the outer loop control as the fine-tuning amount of the reference in the inner loop PI adjustment and set an upper limit; when unloaded, if the actual output voltage is too high, the output value of the outer loop control will exceed the upper limit, then the PWM drive pulse is turned off to prevent overmodulation; when normally loaded, the actual output voltage is compared with the reference voltage in the outer loop control. If the actual output voltage is too high, that is, the actual output voltage is greater than the reference voltage, then the inner loop control reference value is reduced. Conversely, if the actual output voltage is too low, that is, the actual output voltage is less than the reference voltage, then the inner loop control reference value is increased; if the actual output voltage is equal to the reference voltage, the inner loop control reference value remains unchanged.

3. The control and testing method of a three-phase current source rectifier according to claim 2, characterized in that: In the step S3, the input side current is obtained, the inner loop PI closed loop control is started, and the unity power factor is achieved by using the direct current control method, including: S31. Determine the relationship between the inner loop control reference value and the output current target value using formula (1): In formula (1), I drefQ is the inner loop control reference value, η is the efficiency, is the output current target value, U out is the output voltage, U m is the input voltage amplitude; S32, obtain the input side current, select the d-axis as the active parameter reference axis, and the q-axis as the reactive parameter reference axis, and use equations (2) and (3) to transform the three-phase input AC current into the dq axis: In formula (2), I m is the AC current amplitude, that is, the input current amplitude; ω0 is the AC current fundamental angular frequency, i A 、i B 、i C is the instantaneous value of the grid current, i dQ 、i qQ is the grid current converted to dq axis variables; from formula (2), we can see that the d axis control variable I dQ Equal to the input current amplitude; S33, the inner loop control reference I drefQ with I dQ As the error amplifier input, after PI regulation, it drives the MOS tube through space vector modulation to control the input current amplitude I m Equal to I drefQ ; Similarly, through PI adjustment, the q-axis variable I qQ is zero, when I qQ When it is zero, it means that the input voltage and input current are in phase, thus achieving unity power factor.

4. The control and testing method of a three-phase current source rectifier according to claim 3, characterized in that: In the step S4, the output value of the inner PI closed-loop control is transformed into a space vector control variable of the αβ axis of the stationary two-phase coordinate system. The space vector control variable is divided into sectors and the switching time is calculated to obtain a seven-segment PWM pulse. The seven-segment PWM pulse is used to drive the main circuit MOS tube, including: S41, using equation (4) to transform the output value of the inner PI closed-loop control to obtain the space vector control variable of the αβ axis of the stationary two-phase coordinate system; Among them, I α and I β is the control variable of αβ axis, I dr and I qr is the control variable of dq axis, ω0 is the fundamental angular frequency of AC current; S42, after the space vector control variable is sectorized and the switching time is calculated, a seven-segment PWM pulse is obtained, and the seven-segment PWM pulse is used to drive the main circuit MOS tube; S43. Use equation (5) to process the saturation phenomenon in space vector control: Among them, I α and I β is the control variable of αβ axis, is the output current target value.

5. The control and testing method of a three-phase current source rectifier according to claim 4, characterized in that: In step S5, the host computer is used to detect the software phase lock, outer loop control, inner loop PI closed loop control and space vector control process, obtain the change trajectory of key parameters in the control process, and perform data visualization, including: S51. The upper computer programming software is VB6. It communicates with DSP by serial communication. The communication format is: baud rate 19200bps, 1stop bit, odd parity, 8char bits, async mode. The data is sent or received in the following byte arrangement order in the data frame: [frame header][address][function code][number of bytes][data 1 high byte][data 1 low byte][data 2 high byte][data 2 low byte]...[data N high byte][data N low byte][Xor check][frame tail]; S52, intercepting data of up to three key parameters in any period of time in the software algorithm, and transmitting them to the external EEPROM storage area through IIC communication; S53, transmitting the data of the key parameters to the host computer through the serial port, and the host computer processes and displays the data of the key parameters in a graphical manner.

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