Static frequency converter current loop feedforward control method and system

Abstract

The invention discloses a static frequency converter current loop feedforward control method and system, and the method comprises the steps: firstly obtaining a real-time phase angle and an actual line voltage effective value of an actual AC line voltage, and building an AC side line voltage through the phase angle and the line voltage effective value; calculating each commutation time of the bridge; and determining a machine bridge direct current voltage instantaneous value according to the working interval by combining the commutation time, and directly superposing the machine bridge direct current voltage instantaneous value to the output end of a current loop regulator by taking the machine bridge direct current voltage instantaneous value as a current control loop feed-forward quantity. According to the technical scheme, the machine bridge direct-current voltage instantaneous value is reconstructed only through the alternating-current voltage, the alternating-current current signal and the system internal control quantity, and the machine bridge direct-current voltage instantaneous value is directly fed forward and superposed to the output end of the current controller; the constructed machine bridge direct-current voltage instantaneous value is not influenced by network bridge direct-current voltage and commutation peak voltage, filtering processing is not needed before the machine bridge direct-current voltage instantaneous value participates in feed-forward control, observation and feed-forward compensation of loop current loop disturbance quantity are achieved, and loop current fluctuation can be well restrained.

Description

Technical Field

[0001] The present invention belongs to the field of electrical engineering technology, and in particular relates to a loop current feedforward control method and system of a static frequency converter (Static Frequency Converter, hereinafter referred to as SFC). Background Art

[0002] SFC is a current source inverter with an AC-DC-AC structure composed of phase-controlled thyristors. The energy storage element of its DC circuit is a smoothing reactor. SFC is also called load-commutated inverter, thyristor-free inverter motor, etc. Figure 1 As shown. SFC has the advantages of simple structure, high power density, high reliability, etc., and is easy to build a high-voltage and large-capacity frequency conversion system. At present, SFC is still the most reasonable solution for application scenarios such as pumped storage unit starting and gas unit starting.

[0003] Bridge ③ rectifies the grid-side AC voltage into a DC voltage U dr (like Figure 1 As shown in ⑧), the machine bridge ④ inverts the AC voltage into a pulsating DC voltage U di (like Figure 1 (as shown in ⑨). dr and U di Acting together on the smoothing reactor ⑥, a pulsating DC current I dc From the control perspective, SFC adjusts the bridge trigger angle α in real time. N (i.e. control U dr ) to realize the loop current I dc Precise control and suppression of U di The disturbance introduced. That is, α N is the direct control quantity, and U di It is the direct disturbance of the loop current.

[0004] To improve the anti-interference ability of the current loop, the most direct approach is to measure U with a DC voltage sensor. di , and use it to realize the feedforward control of the loop current loop. However, this method has some problems, including: the need to introduce unnecessary DC voltage sensors; for applications with higher voltage levels, it will increase the system volume and cost; the direct measurement of U di There is a coupling U dr Interference signals such as high-frequency harmonics and commutation spike voltages need to be filtered before they can be used as feedforward quantities, but filtering will introduce phase lag and affect the feedforward effect. Summary of the invention

[0005] The purpose of the present invention is to provide a static frequency converter current loop feedforward control method and system, which can complete the reconstruction of the instantaneous value of the SFC machine bridge DC voltage without using a DC voltage sensor and realize the feedforward control of the system current loop.

[0006] In order to achieve the above object, the solution of the present invention is:

[0007] A static inverter current loop feedforward control method comprises the following steps:

[0008] Step 1: Use the digital phase-locked loop algorithm to obtain the real-time phase angle θ of the actual AC line voltage, and use the single-point vector algorithm to obtain the actual line voltage effective value U m , and using θ and U m Establish the AC side line voltage U ′ ac , U ′ ba , U ′ cb ;

[0009] Step 2, the switching time t of the computer bridge μ ;

[0010] Step 3, combined with the commutation time t μ , according to the working range, determine the instantaneous value of the bridge DC voltage U di_art , and use it as the current control loop feedforward directly added to the output of the current loop regulator.

[0011] The specific content of the above step 1 is:

[0012] Step 11: According to the three-phase voltage U at the AC side of the bridge obtained by real-time measurement and sampling ac , U ba , U cb , using the digital phase-locked loop PLL algorithm to lock the AC voltage phase angle θ, θ∈[0 ° ,360 ° ];

[0013] Step 12: According to the real-time measurement and sampling of the three-phase voltage U at the AC side of the bridge ac , U ba , U cb , use the single-point vector algorithm to obtain the effective value of the line voltage U m ;

[0014] Step 13, using θ and U m , establish the AC side line voltage U according to the following formula ′ ac , U ′ ba , U ′cb :

[0015]

[0016] Among them, U m is the effective value of the line voltage, and θ is the phase angle of the AC voltage.

[0017] In the above step 12, the three-phase voltage U at the AC side of the bridge is measured and sampled in real time. ac , U ba , U cb , first calculate the vector sum Then use a digital low-pass filter to filter it and get the effective value of the line voltage U m .

[0018] The specific content of the above step 2 is,

[0019] Step 21, based on the real-time measurement and sampling of the bridge AC three-phase current i a 、i b 、i c , use the following formula to calculate the instantaneous value of the circuit DC current i dc_fb :

[0020] i dc_fb =max(|i a |,|i b |,|i c |)

[0021] Step 22, calculate the commutation time t of the thyristor fully controlled bridge according to the following formula: μ :

[0022]

[0023] Among them, β M =π-α M is the lead angle of the bridge converter, α M is the trigger angle of the bridge converter; L c is the commutation inductance value of the thyristor fully controlled bridge; ω m is the angular frequency of the current bridge AC voltage; U m is the effective value of line voltage.

[0024] In the above step 3, the commutation time t after the rising edge of each trigger pulse of the machine bridge is μ The average voltage of the two phases involved in the commutation is taken as the instantaneous value of the bridge DC voltage U di_art In the remaining working range, the line voltage connected to the conduction valve group is used as the instantaneous value of the bridge DC voltage U di_art .

[0025] A static inverter current loop feedforward control system, comprising:

[0026] The AC side line voltage reconstruction module is used to obtain the real-time phase angle θ of the actual AC line voltage using the digital phase-locked loop algorithm, and to obtain the actual line voltage effective value U using the single-point vector algorithm. m , and using θ and U m Establish the AC side line voltage U ′ ac , U ′ ba , U ′ cb ;

[0027] The machine bridge commutation time calculation module is used to calculate the commutation time t of the computer bridge μ ;as well as,

[0028] The current control loop feedforward determination module is used to combine the commutation time t μ , according to the working range, determine the instantaneous value of the bridge DC voltage U di_art , and use it as the current control loop feedforward directly added to the output of the current loop regulator.

[0029] The above-mentioned AC side line voltage reconstruction module includes:

[0030] The AC voltage phase angle locking module is used to lock the three-phase voltage U on the AC side of the bridge according to the real-time measurement and sampling. ac , U ba , U cb , using the digital phase-locked loop PLL algorithm to lock the AC voltage phase angle θ, θ∈[0 ° ,360 ° ];

[0031] The line voltage effective value acquisition module is used to obtain the three-phase voltage U on the AC side of the bridge according to the real-time measurement and sampling. ac , U ba , U cb , use the single-point vector algorithm to obtain the effective value of the line voltage U m ;as well as,

[0032] AC side line voltage establishment module, used to use θ and U m , establish the AC side line voltage U according to the following formula ′ ac , U ′ ba , U ′ cb :

[0033]

[0034] Among them, Um is the effective value of the line voltage, and θ is the phase angle of the AC voltage.

[0035] The above-mentioned line voltage effective value acquisition module further includes:

[0036] The line voltage vector and calculation module is used to calculate the three-phase voltage U on the AC side of the bridge according to the real-time measurement and sampling. ac , U ba , U cb ,use Compute the vector sum; and,

[0037] A digital low-pass filter is used to filter the above-mentioned line voltage vector sum to obtain the effective value of the line voltage U m .

[0038] The above-mentioned machine bridge commutation time calculation module further includes:

[0039] The loop DC current instantaneous value calculation module is used to calculate the AC three-phase current i of the machine bridge based on the real-time measurement and sampling. a 、i b 、i c , use the following formula to calculate the instantaneous value of the circuit DC current i dc_fb :

[0040] i dc_fb =max(|i a |,|i b |,|i c |)

[0041] ;as well as,

[0042] The commutation time calculation module is used to calculate the commutation time t of the thyristor full-controlled bridge according to the following formula μ :

[0043]

[0044] Among them, β M =π-α M is the lead angle of the bridge converter, α M is the trigger angle of the bridge converter; L c is the commutation inductance value of the thyristor fully controlled bridge; ω m is the angular frequency of the current bridge AC voltage; U m is the effective value of line voltage.

[0045] The above current control loop feedforward determination module determines the instantaneous value of the bridge DC voltage U di_art The specific method is to use the commutation time t after the rising edge of each trigger pulse of the machine bridge. μThe average voltage of the two phases involved in the commutation is taken as the instantaneous value of the bridge DC voltage U di_art In the remaining working range, the line voltage connected to the conduction valve group is used as the instantaneous value of the bridge DC voltage U di_art .

[0046] After adopting the above scheme, the present invention reconstructs the instantaneous value of the DC voltage of the machine bridge only through the AC voltage, AC current signal and the internal control quantity of the system, and directly feeds forward and superimposes the instantaneous value of the DC voltage of the machine bridge to the output end of the current controller; the constructed instantaneous value of the DC voltage of the machine bridge is not affected by the DC voltage of the network bridge and the commutation peak voltage, and no filtering processing is required before participating in the feedforward control, thereby realizing the observation and feedforward compensation of the loop current loop disturbance quantity, and can better suppress the loop current fluctuation. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 It is a schematic single-line diagram of the SFC system;

[0048] Among them, the components are:

[0049] ①It is the input medium voltage power circuit breaker of the SFC system;

[0050] ②Isolation transformer on the input side of the SFC system;

[0051] ③ is the SFC bridge-side converter, referred to as bridge;

[0052] ④ is the SFC bridge-side converter, referred to as the bridge;

[0053] ⑤Isolation transformer on the output side of the SFC system;

[0054] ⑥ is the SFC DC circuit smoothing reactor, which is the main energy storage component of the system and is used to smooth the circuit current fluctuation;

[0055] ⑦ is the secondary control block diagram of the SFC loop current.

[0056] PT1 is the bridge AC voltage sensor;

[0057] CT1 is the bridge AC current sensor;

[0058] PT2 is the bridge AC current sensor;

[0059] CT2 is the bridge AC current sensor.

[0060] VT1~VT6 are the six bridge arms of the SFC machine bridge, among which VT1, VT3, and VT5 are a common cathode connection group, and VT2, VT4, and VT6 are a common anode connection group.

[0061] Among them, the control quantities are:

[0062] U dr is the rectified voltage on the DC side of the bridge, and its waveform is shown in the dotted box⑧;

[0063] U di is the rectified voltage on the DC side of the machine bridge, and its waveform is shown in the dotted box ⑨;

[0064] I dc is the DC loop current of the SFC system, and its waveform is shown in the dotted box ⑩;

[0065] I AC It is the measured value of AC current of SFC system bridge;

[0066] I dc_fb is the SFC system loop current I dc The calculated value is used as the closed-loop control feedback of the loop current;

[0067] I dc_ref It is the reference quantity for the closed-loop control of the loop current of the SFC system;

[0068] ACR (Auto Current Regulator) is a closed-loop controller for the loop current of the SFC system, usually using a PI controller;

[0069] α N It is the output of ACR, which is the trigger angle of the bridge and is used to adjust the bridge DC voltage U in real time. dr , in order to suppress the loop disturbance and maintain the loop current I dc Tracking I dc_ref ;

[0070] α M It is the trigger angle of the SFC system machine bridge. This angle is adjusted according to the working conditions to maintain the safe and reliable operation of the machine bridge at the largest possible power factor.

[0071] Figure 2 This is a schematic diagram of the SFC bridge waveform;

[0072] Among them, the variables are:

[0073] U ac , U ba , U cb is the AC line voltage waveform of the machine bridge;

[0074] θ is the phase angle of the AC line voltage of the machine bridge locked by the digital phase-locked loop algorithm;

[0075] CP1~CP6 are the trigger pulses of the six valve arms of the SFC bridge;

[0076] Figure 3 It is a schematic diagram of the present invention. DETAILED DESCRIPTION

[0077] like Figure 3 As shown, the present invention provides a static inverter current loop feedforward control method, which only uses the real-time measured machine bridge AC voltage, AC current and internal control quantity to construct the machine bridge DC voltage instantaneous value U di_art , and U di_art It is superimposed on the current control loop of the SFC system as a feedforward quantity to realize the instantaneous value feedforward control of the DC voltage of the SFC current loop bridge.

[0078] The instantaneous value of the bridge DC voltage U di_art It is constructed based on the virtual bridge line voltage according to the set rules. Specifically, the real-time phase angle θ of the actual AC line voltage can be obtained by using the digital phase-locked loop algorithm. At the same time, the effective value U of the actual line voltage can be obtained by using the single-point vector algorithm. m ; and using θ and U m A perfectly symmetrical sinusoidal line voltage is established; in addition, the commutation time t of the bridge is calculated in real time. μ , after the rising edge of each trigger pulse of the bridge μ In the working interval (calculating the commutation time), the average value of the two phase voltages involved in the commutation is taken as the instantaneous value of the DC voltage of the machine bridge; in the remaining working interval, the line voltage connected to the conducting valve group is taken as the instantaneous value of the DC voltage of the machine bridge U di_art The instantaneous value of the bridge DC voltage U di_ary It does not go through any filtering process and is directly fed forward and superimposed to the output end of the current loop regulator.

[0079] The implementation scheme of the present invention will be described below through a specific embodiment.

[0080] The static inverter loop current feedforward control method proposed by the present invention comprises the following steps:

[0081] (1) Use PT2 to measure and sample the three-phase voltage U on the AC side of the bridge in real time ac , U ba , U cb , and the system controller uses the digital phase-locked loop PLL algorithm to lock its AC voltage phase angle θ, θ∈[0 ° ,360 ° ],like Figure 2 In this embodiment, when the phase-locked loop is phase-locked, U ac At the positive peak, corresponding to θ=360 ° . Using a digital low-pass filter with a time constant of T = 20ms, the vector and Filter and obtain the filtered line voltage effective value U m . And using θ and U m Reconstruct the AC side line voltage, the formula is as follows:

[0082]

[0083] (2) Use CT2 to measure and sample the three-phase AC current i of the bridge in real time a 、i b 、i c The three-phase current envelope can be calculated using the following formula, that is, the instantaneous value of the DC current in the loop i dc_fb :

[0084] i dc_fb =max(|i a |,|i b |,|i c |) Formula ②

[0085] According to formula ③, calculate the commutation time t of the thyristor fully controlled bridge μ ,like Figure 2 shown.

[0086]

[0087] In formula ③:

[0088] For the machine bridge converter, β is the lead angle β of the machine bridge converter. M , β M =π-α M , calculated in real time by the SFC control system, where α M is the trigger angle of the bridge converter;

[0089] L c is the commutation inductance value of the thyristor fully controlled bridge, which is a known system parameter;

[0090] ω m is the angular frequency of the current machine bridge AC voltage, which is calculated in real time by the SFC control system.

[0091] (3) Using the control pulses CP1 to CP6 generated inside the control system, the U constructed in step 1 ′ ac , U ′ ba , U ′ cb , t calculated in step 2 μ , construct a virtual bridge DC voltage U di_art .like Figure 3 As shown, the t μ During the time, U is constructed by taking the average value of the phase voltages involved in the commutation di_art Between two adjacent CPs (i.e. during the commutation period on both sides), the line voltage of the conducting valve group is used to construct U di_art The phase voltage U in the table ′a , U ′ b , U ′ c According to the relationship between phase voltage and line voltage, U ′ ac , U ′ ba , U ′ cb calculate.

[0092] Table 1

[0093]

[0094]

[0095] (4) Eliminate the DC voltage sensor to construct a U di_art Replace U di Feed forward to the loop current control loop of the SFC system, such as Figure 3 As shown. Since the present invention uses the phase angle θ locked by PLL to reconstruct U ac , U ba , U cb , which no longer contains high-frequency harmonic voltages, does not require digital filtering again, and will not introduce phase lag.

[0096] The embodiment of the present invention further provides a static inverter current loop feedforward control system, comprising:

[0097] The AC side line voltage reconstruction module is used to obtain the real-time phase angle θ of the actual AC line voltage using the digital phase-locked loop algorithm, and to obtain the actual line voltage effective value U using the single-point vector algorithm. m , and using θ and U m Establish the AC side line voltage U ′ ac , U ′ ba , U ′ cb ;

[0098] The machine bridge commutation time calculation module is used to calculate the commutation time t of the computer bridge μ ;as well as,

[0099] The current control loop feedforward determination module is used to combine the commutation time t μ , according to the working range, determine the instantaneous value of the bridge DC voltage U di_art , and use it as the current control loop feedforward directly added to the output of the current loop regulator.

[0100] Wherein, the AC side line voltage reconstruction module includes:

[0101] The AC voltage phase angle locking module is used to lock the three-phase voltage U on the AC side of the bridge according to the real-time measurement and sampling. ac , U ba , U cb , using the digital phase-locked loop PLL algorithm to lock the AC voltage phase angle θ, θ∈[0 ° ,360 ° ];as well as,

[0102] The line voltage effective value acquisition module is used to obtain the line voltage effective value U using a single-point vector algorithm m .

[0103] Wherein, the line voltage effective value acquisition module further includes:

[0104] The line voltage vector and calculation module is used to calculate the three-phase voltage U on the AC side of the bridge according to the real-time measurement and sampling. ac , U ba , U cb ,use Compute the vector sum; and,

[0105] A digital low-pass filter is used to filter the above-mentioned line voltage vector sum to obtain the effective value of the line voltage U m .

[0106] The AC side line voltage reconstruction module uses θ and U m According to formula ①, the AC side line voltage U ′ ac , U ′ ba , U ′ cb .

[0107] The machine bridge commutation time calculation module further includes:

[0108] The loop DC current instantaneous value calculation module is used to calculate the AC three-phase current i of the machine bridge based on the real-time measurement and sampling. a 、i b 、i c , use formula ② to calculate the instantaneous value of the circuit DC current i dc_fb ;as well as,

[0109] The commutation time calculation module is used to calculate the commutation time t of the thyristor full-controlled bridge according to formula ③ μ .

[0110] The current control loop feedforward determination module determines the instantaneous value of the bridge DC voltage U di_art The specific method is to use the t μIn (calculation of commutation time), the average value of the two phase voltages involved in commutation is taken as the instantaneous value of the bridge DC voltage U di_art In the remaining working range, the line voltage connected to the conduction valve group is used as the instantaneous value of the bridge DC voltage U di_art .

[0111] The above embodiments are only for illustrating the technical idea of ​​the present invention, and cannot be used to limit the protection scope of the present invention. Any changes made on the basis of the technical solution in accordance with the technical idea proposed by the present invention shall fall within the protection scope of the present invention.

Claims

1. A static inverter current loop feedforward control method, characterized in that The steps include: Step 1: Use the digital phase-locked loop algorithm to obtain the real-time phase angle θ of the actual AC line voltage, and use the single-point vector algorithm to obtain the actual line voltage effective value U m , and using θ and U m Establish the AC side line voltage U' ac , U′ ba , U′ cb ; Step 2, the switching time t of the computer bridge μ ; Step 3, combined with the commutation time t μ , according to the working range, determine the instantaneous value of the bridge DC voltage U di_art , and use it as the current control loop feedforward directly added to the output of the current loop regulator.

2. The static inverter current loop feedforward control method according to claim 1, characterized in that: The specific content of step 1 is: Step 11: According to the real-time measurement and sampling of the three-phase voltage U at the AC side of the bridge ac , U ba , U cb , using the digital phase-locked loop PLL algorithm, lock its AC voltage phase angle θ, θ∈[0°, 360°]; Step 12: According to the real-time measurement and sampling of the three-phase voltage U at the AC side of the bridge ac , U ba , U cb , use the single-point vector algorithm to obtain the effective value of the line voltage U m ; Step 13, using θ and U m , establish the AC side line voltage U′ according to the following formula ac , U′ ba , U′ cb : Among them, U m is the effective value of the line voltage, and θ is the phase angle of the AC voltage.

3. The static inverter current loop feedforward control method according to claim 2, characterized in that: In step 12, the three-phase voltage U at the AC side of the bridge is measured and sampled in real time. ac , U ba , U cb , first calculate the vector sum Then use a digital low-pass filter to filter it and get the effective value of the line voltage U m .

4. The static inverter current loop feedforward control method according to claim 1, characterized in that: The specific content of step 2 is: Step 21, based on the real-time measurement and sampling of the bridge AC three-phase current i a 、i b 、i c , use the following formula to calculate the instantaneous value of the circuit DC current i dc_fb : i dc_fb =max(|i a |,|i b |,|i c |) Step 22, calculate the commutation time t of the thyristor fully controlled bridge according to the following formula: μ : Among them, β M =π-α M is the lead angle of the bridge converter, α M is the trigger angle of the bridge converter; L c is the commutation inductance value of the thyristor fully controlled bridge; ω m is the angular frequency of the current bridge AC voltage; U m is the effective value of line voltage.

5. The static inverter current loop feedforward control method according to claim 1, characterized in that: In step 3, the commutation time t after the rising edge of each trigger pulse of the machine bridge μ The average voltage of the two phases involved in the commutation is taken as the instantaneous value of the bridge DC voltage U di_art In the remaining working range, the line voltage connected to the conduction valve group is used as the instantaneous value of the bridge DC voltage U di_art .

6. A static inverter current loop feedforward control system, characterized in that include: The AC side line voltage reconstruction module is used to obtain the real-time phase angle θ of the actual AC line voltage using the digital phase-locked loop algorithm, and to obtain the actual line voltage effective value U using the single-point vector algorithm. m , and using θ and U m Establish the AC side line voltage U' ac , U′ ba , U′ cb ; The machine bridge commutation time calculation module is used to calculate the commutation time t of the computer bridge μ ;as well as, The current control loop feedforward determination module is used to combine the commutation time t μ , according to the working range, determine the instantaneous value of the bridge DC voltage U di_art , and use it as the current control loop feedforward directly added to the output of the current loop regulator.

7. The static inverter current loop feedforward control system according to claim 6, characterized in that: The AC side line voltage reconstruction module includes: The AC voltage phase angle locking module is used to lock the three-phase voltage U on the AC side of the bridge according to the real-time measurement and sampling. ac , U ba , U cb , using the digital phase-locked loop PLL algorithm, lock its AC voltage phase angle θ, θ∈[0°, 360°]; The line voltage effective value acquisition module is used to obtain the three-phase voltage U on the AC side of the bridge according to the real-time measurement and sampling. ac , U ba , U cb , use the single-point vector algorithm to obtain the effective value of the line voltage U m ;as well as, AC side line voltage establishment module, used to use θ and U m , establish the AC side line voltage U′ according to the following formula ac , U′ ba , U′ cb : Among them, U m is the effective value of the line voltage, and θ is the phase angle of the AC voltage.

8. The static inverter current loop feedforward control system according to claim 7, characterized in that: The line voltage effective value acquisition module further comprises: The line voltage vector and calculation module is used to calculate the three-phase voltage U on the AC side of the bridge according to the real-time measurement and sampling. ac , U ba , U cb ,use Compute the vector sum; and, A digital low-pass filter is used to filter the above-mentioned line voltage vector sum to obtain the effective value of the line voltage U m .

9. The static inverter current loop feedforward control system according to claim 6, characterized in that: The machine bridge commutation time calculation module further includes: The loop DC current instantaneous value calculation module is used to calculate the AC three-phase current i of the machine bridge based on the real-time measurement and sampling. a 、i b 、i c , use the following formula to calculate the instantaneous value of the circuit DC current i dc_fb : i dc_fb = max(|i a |, |i b |, |i c |);Hereafter, The commutation time calculation module is used to calculate the commutation time t of the thyristor full-controlled bridge according to the following formula μ : Among them, β M =π-α M is the lead angle of the bridge converter, α M is the trigger angle of the bridge converter; L c is the commutation inductance value of the thyristor fully controlled bridge; ω m is the angular frequency of the current bridge AC voltage; U m is the effective value of line voltage.

10. The static inverter current loop feedforward control system according to claim 6, characterized in that: The current control loop feedforward determination module determines the instantaneous value U of the bridge DC voltage di_art The specific method is to use the commutation time t after the rising edge of each trigger pulse of the machine bridge. μ The average voltage of the two phases involved in the commutation is taken as the instantaneous value of the bridge DC voltage U di_art In the remaining working range, the line voltage connected to the conduction valve group is used as the instantaneous value of the bridge DC voltage U di_art .

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