A dc voltage sensor fault ride-through modulation strategy for split capacitor converters

Abstract

The application discloses a direct-current voltage sensor fault ride-through modulation strategy of a split capacitor converter, and comprises the following steps: acquiring a voltage modulation wave v r * and a current reference value i g *; dividing intervals of v r * and i g *; and dividing switch states of a split capacitor power unit converter according to the division results; the split capacitor power unit converter comprises three power generation / energy storage modules; when a voltage sensor of a direct-current voltage on an electrolytic capacitor in one of the power generation / energy storage modules fails, direct-current voltage sensor fault ride-through modulation is completed according to the voltage modulation wave v r * and a difference value of the direct-current voltage on the electrolytic capacitor in the other two power generation / energy storage modules. The application can enable the split capacitor power unit converter system to operate in a fault ride-through mode when a direct-current side voltage sensor fails.

Description

Technical Field

[0001] This invention belongs to the field of multilevel power electronic converters and their control, specifically relating to a DC voltage sensor fault ride-through modulation strategy for a split capacitor converter. Background Technology

[0002] A cascaded H-bridge is a typical cascaded multilevel converter. The high power output quality of a cascaded H-bridge not only avoids the need for bulky output filters in grid-connected applications but also reduces torque ripple and insulation stress in motor drive systems. Compared to traditional two-level or three-level converters, the modular structure facilitates the expansion of the output level of the cascaded H-bridge converter, thus eliminating the need for bulky power frequency transformers for connection to medium- and high-voltage power grids. This makes it one of the ideal structures for high-power converters in medium- and high-voltage applications such as high-power battery energy storage systems, large-capacity motor drives, and large-scale photovoltaic power generation systems.

[0003] However, as the number of cascaded H-bridge modules increases, the number of DC voltage sensors required also increases exponentially. Voltage sensor failure is one of the main failures in these multi-module converters, but existing control or modulation techniques do not address how to achieve stable operation of the cascaded H-bridge in the event of DC-side voltage sensor failure. Therefore, implementing fault-crossing operation of the DC-side voltage sensor is an area for improvement in cascaded H-bridges. Summary of the Invention

[0004] Purpose of the invention: The purpose of this invention is to provide a DC voltage sensor fault ride-through modulation strategy for a split capacitor converter, which enables the split capacitor power unit converter system to operate through the fault when the DC side voltage sensor fails.

[0005] Technical solution: The fault ride-through modulation strategy for the DC voltage sensor of the split capacitor converter of the present invention includes the following steps:

[0006] (1) Obtain the voltage modulation wave v r *and current reference value i g *;

[0007] (2) For v r * with i g * Divide the circuit into intervals and, based on the division results, divide the switching states of the split capacitor power unit converter.

[0008] (3) The split capacitor power unit converter includes three power generation / storage modules. When the voltage sensor of the DC voltage on the electrolytic capacitor in one of the power generation / storage modules fails, the voltage modulation wave v will trigger a voltage sensor. r * and the difference in DC voltage across the electrolytic capacitors in the other two power generation / storage modules to complete the fault ride-through modulation of the DC voltage sensor.

[0009] In step (1), the acquisition of the voltage modulation wave v r *and current reference value i g *Specifically, it includes the following:

[0010] (1.1) The DC-side voltages of the power generation / storage module I, power generation / storage module II, and power generation / storage module III of the split capacitor power unit converter are respectively v dc1 v dc2 and v dc3 The grid phase signal θ is obtained by phase-locking the grid voltage;

[0011] (1.2) Use the grid phase signal θ for v g and i g Perform an αβ / dq coordinate transformation to obtain v g and i g The active and reactive components v d v q and i d i q ;

[0012] (1.3) Average DC voltage control loop setting of the outer loop voltage v dcavg Converging to the reference value v dcref v dcref With v dcavg After subtraction, the reference value i of the active component of the grid current is obtained through a PI controller. dref i dref The current reference signal i is obtained by sinusoidalizing the phase with the power grid. g * ;

[0013] (1.4)i dref with i d After the difference is calculated, the current active power error i is obtained through a PI controller. derr , change i derr v d with i q The modulated wave d-axis component v is obtained by adding ωL. dref ω is the angular frequency of the power grid, and L is the value of the grid-connected filter inductance;

[0014] (1.5)i qref with i q The difference is passed through a PI controller to obtain the current active power error i. qerr , change i qerr v q with i d The sum of ωL yields the q-axis component v of the modulated wave. qref ;

[0015] (1.6) The v dref and v qref are transformed by dq / αβ transformation to obtain the voltage modulation wave v r *.

[0016] In step (2), the v r * and i g * are divided into intervals, and the switching states of the split-capacitor power cell converter are divided according to the division results as follows:

[0017] When v r *>0 and i g *>0, v r * and i g * are in the operating interval I;

[0018] When v r *<0 and i g *>0, v r * and i g * are in the operating interval II;

[0019] When v r *<0 and i g *<0, v r * and i g * are in the operating interval III;

[0020] When v r *>0 and i g *<0, v r * and i g * are in the operating interval IV;

[0021] The switching states in the operating interval I are I1 to I6, the switching states in the operating interval II are II1 to II6, the switching states in the operating interval III are III1 to III6, and the switching states in the operating interval IV are IV1 to IV6.

[0022] In step (3), when the voltage sensor of v dc1 fails, the DC voltage sensor fault ride-through modulation is completed according to the voltage modulation wave v r * and the difference between v dc2 and v dc3 . Specifically, take Δv dc = v dc2 - v dc3 , and take 0<k<0.1; in the operating interval I, when 0<v r *<1, when Δv dc >0, then select the switching states I1 and I3 to switch, when Δv dc< 0, then switch the selection switch states I2 and I3; when 1 < v r * < 2, when |Δv dc | > k, then switch the selection switch states I4 and I3; when |Δv dc | < k, then switch the selection switch states I5 and I3; when 2 < v r * < 3, when |Δv dc | > k, then switch the selection switch states I4 and I6; when |Δv dc | < k, then switch the selection switch states I5 and I6; in operating range II, when -1 < v r * < 0, when Δv dc > 0, then switch the selection switch states II1 and II3; when Δv dc < 0, then switch the selection switch states II2 and II3; when -2 < v r * < -1, when |Δv dc | > k, then switch the selection switch states II4 and II3; when |Δv dc | < k, then switch the selection switch states II5 and II3; when -3 < v r * < -2, when |Δv dc | > k, then switch the selection switch states II4 and II6; when |Δv dc | < k, then switch the selection switch states II5 and II6; in operating range III, when -1 < v r * < 0, when Δv dc > 0, then switch the selection switch states III1 and III3; when Δv dc < 0, then switch the selection switch states III2 and III3; when -2 < v r * < -1, when |Δv dc | > k, then switch the selection switch states III4 and III3; when |Δv dc | < k, then switch the selection switch states III5 and III3; when -3 < v r * < -2, when |Δv dc | > k, then switch the selection switch states III4 and III6; when |Δv dc | < k, then switch the selection switch states III5 and III6; in operating range IV, when 0 < v r * < 1, when Δv dc > 0, then switch the selection switch states IV1 and IV3; when Δv dc < 0, then switch the selection switch states IV2 and IV3; when 1 < v r * < 2, when |Δv dc | > k, then switch the selection switch states IV4 and IV3; when |Δvdc If |Δv| < k, then select the switching of switch states IV5 and IV3; when 2 < v r * < 3, when |Δv dc | > k, then select the switching of switch states IV4 and IV6; when |Δv dc | < k, then select the switching of switch states IV5 and IV6.

[0023] In step (3), when the voltage sensor of v dc2 fails, according to the voltage modulation wave v r * and v dc1 and the difference between v dc3 to complete the DC voltage sensor fault ride-through modulation. Specifically, take Δv dc = v dc1 - v dc3 ; in the operating range I, when 0 < v r * < 1, if Δv dc > 0, then select the switching of switch states I1 and I3; if Δv dc < 0, then select the switching of switch states I2 and I3; when 1 < v r * < 2, if Δv dc > 0, then select the switching of switch states I4 and I3; if Δv dc < 0, then select the switching of switch states I5 and I3; when 2 < v r * < 3, if Δv dc > 0, then select the switching of switch states I4 and I6; if Δv dc < 0, then select the switching of switch states I5 and I6; in the operating range II, when -1 < v r * < 0, if Δv dc > 0, then select the switching of switch states II1 and II3; if Δv dc < 0, then select the switching of switch states II2 and II3; when -2 < v r * < -1, if Δv dc > 0, then select the switching of switch states II​​​​​​​​​​​​​​r When Δv < -1 dc > 0, switch states III4 and III3 are selected for switching. When Δv dc < 0, switch states III5 and III3 are selected for switching; when -3 < v r When Δv < -2 dc > 0, switch states III4 and III6 are selected for switching. When Δv dc < 0, switch states III5 and III6 are selected for switching; in operating range IV, when 0 < v r When Δv < 1 dc > 0, switch states IV1 and IV3 are selected for switching. When Δv dc < 0, switch states IV2 and IV3 are selected for switching; when 1 < v r When Δv < 2[[ID=twenty]] dc > 0, switch states IV4 and IV3 are selected for switching. When Δv dc < 0, switch states IV5 and IV3 are selected for switching; when 2 < v r When Δv < 3 dc > 0, switch states IV4 and IV6 are selected for switching. When Δv dc < 0, switch states IV5 and IV6 are selected for switching.

[0024] In step (3), when the voltage sensor at v dc3 fails, the DC voltage sensor fault ride-through modulation is completed according to the voltage modulation wave v r * and the difference between v dc1 and v dc2 . Specifically, take Δv dc = v dc1 - v dc2 , and take 0 < k < 0.1; in operating range I, when 0 < v r When Δv < 1 dc > 0, switch states I1 and I3 are selected for switching. When Δv dc < 0, switch states I2 and I3 are selected for switching; when 1 < v r When |Δv dc |> k, switch states I5 and I3 are selected for switching. When |Δv dc |< k, switch states I4 and I3 are selected for switching; when 2 < v r When |Δv dc |> k, switch states I5 and I6 are selected for switching. When |Δv dc |< k, switch states I4 and I6 are selected for switching; in operating range II, when -1 < v r When Δv < 0dc > 0, then select the switching of switch states II1 and II3. When Δv dc < 0, then select the switching of switch states II2 and II3; when -2 < v r * < -1, when |Δv dc | > k, then select the switching of switch states II5 and II3. When |Δv dc | < k, then select the switching of switch states II4 and II3. When -3 < v r * < -2, when |Δv dc | > k, then select the switching of switch states II5 and II6; when |Δv dc | < k, then select the switching of switch states II4 and II6; in operating range III, when -1 < vr* < 0, when Δv dc > 0, then select the switching of switch states III1 and III3. When Δv dc < 0, then select the switching of switch states III2 and III3; when -2 < v r * < -1, when |Δv dc | > k, then select the switching of switch states III5 and III3. When |Δv dc | < k, then select the switching of switch states III4 and III3; when -3 < v r * < -2, when |Δv dc | > k, then select the switching of switch states III5 and III6. When |Δv dc | < k, then select the switching of switch states III4 and III6; in operating range IV, when 0 < vr* < 1, when Δv dc > 0, then select the switching of switch states IV1 and IV3. When Δv dc < 0, then select the switching of switch states IV2 and IV3; when 1 < v r * < 2, when |Δv dc | > k, then select the switching of switch states IV5 and IV3. When |Δv dc | < k, then select the switching of switch states IV4 and IV3; when 2 < v r * < 3, when |Δv dc | > k, then select the switching of switch states IV5 and IV6. When |Δv dc | < k, then select the switching of switch states IV4 and IV6.

[0025] Advantageous effects: Compared with the prior art, the technical solution of the present invention has the following advantageous effects: When the DC-side voltage sensor fails, the DC voltages of each module of the split-capacitor power unit converter system can still be balanced with each other, and the quality of the grid-connected current is not affected by the failure, thereby achieving fault ride-through operation. Description of the Drawings

[0026] Figure 1 This is a schematic diagram of the process of the present invention;

[0027] Figure 2 To generate v in the split capacitor power unit converter of this invention r * with i g *Control block diagram;

[0028] Figure 3 v in this invention r * with i g *Switch state diagram in operating range I;

[0029] Figure 4 v in this invention r * with i g *Switch state diagram in operating range II;

[0030] Figure 5 v in this invention r * with i g *Switch state diagram in operating range III;

[0031] Figure 6 v in this invention r * with i g * Switching state diagram in operating range IV;

[0032] Figure 7 For the split capacitor power unit converter in this invention, under operating condition 1, v dc3 Experimental waveform diagram of voltage sensor fault ride-through operation;

[0033] Figure 8 For the split capacitor power unit converter in this invention, under operating condition 2, v dc3 Experimental waveform diagram of voltage sensor fault ride-through operation;

[0034] Figure 9 For the split capacitor power unit converter in this invention, under operating condition 3, v dc3 Experimental waveform diagram of voltage sensor fault ride-through operation;

[0035] Figure 10 For the split capacitor power unit converter in this invention, under operating condition 4, v dc3 Experimental waveform diagram of voltage sensor fault ride-through operation. Detailed Implementation

[0036] The technical solution of the present invention will now be described in detail with reference to specific embodiments and accompanying drawings.

[0037] like Figure 1As shown, the DC voltage sensor fault ride-through modulation strategy of the split capacitor converter of the present invention includes the following steps:

[0038] (1) As Figure 2 As shown, the voltage modulation wave v is obtained. r *and current reference value i g * Specifically, it includes the following:

[0039] (1.1) The DC-side voltages of the power generation / storage module I, power generation / storage module II, and power generation / storage module III of the split capacitor power unit converter are respectively v dc1 v dc2 and v dc3 The grid phase signal θ is obtained by phase-locking the grid voltage;

[0040] (1.2) Use the grid phase signal θ for v g and i g Perform an αβ / dq coordinate transformation to obtain v g and i g The active and reactive components v d v q and i d i q ;

[0041] (1.3) Average DC voltage control loop setting of the outer loop voltage v dcavg Converging to the reference value v dcref v dcref With v dcavg After subtraction, the reference value i of the active component of the grid current is obtained through a PI controller. dref i dref The current reference signal i is obtained by sinusoidalizing the phase with the power grid. g * ;

[0042] (1.4)i dref with i d After the difference is calculated, the current active power error i is obtained through a PI controller. derr , change i derr v d with i q The modulated wave d-axis component v is obtained by adding ωL. dref ω is the angular frequency of the power grid, and L is the value of the grid-connected filter inductance;

[0043] (1.5)i qref with i q The difference is passed through a PI controller to obtain the current active power error i. qerr , change i qerr v qwith i d The sum of ωL yields the q-axis component v of the modulated wave. qref ;

[0044] (1.6) v dref With v qref The voltage modulation wave v is obtained after dq / αβ transformation. r *

[0045] (2) For v r * with i g * Divide the circuit into intervals and, based on the division results, divide the switching states of the split capacitor power unit converter.

[0046] In v r *>0 and i g When *>0, v r * with i g *In operating range I; in v r *<0 and i g When *>0, v r * with i g *In operating range II; in v r *<0 and i g When *<0, v r *and i g *In operating range III; in v r *>0 and i g When *<0, v r * with i g *In the operating range IV.

[0047] like Figure 3 As shown, the switch states in operating range I are I1 to I6. Figure 4 As shown, the switch states in operating range II are II1 to II6. (As...) Figure 5 As shown, the switch states in operating range III are III1 to III6. (As...) Figure 6 As shown, the switching states in the operating range IV are IV1 to IV6.

[0048] (3) The split capacitor power unit converter includes three power generation / storage modules. When the voltage sensor of the DC voltage on the electrolytic capacitor in one of the power generation / storage modules fails, the voltage modulation wave v will trigger a voltage sensor. r * and the difference in DC voltage across the electrolytic capacitors in the other two power generation / storage modules to complete the fault ride-through modulation of the DC voltage sensor;

[0049] The following is in v dc1 When the voltage sensor fails, according to v dc2 With v dc3Complete the DC voltage sensor fault ride-through modulation according to the magnitude of Δv, and take Δv dc = v dc2 - v dc3 , and take 0 < k < 0.1;

[0050] In the operating range I, when 0 < v r * < 1, if Δv dc > 0, then select the switching of switch states I1 and I3; if Δv dc < 0, then select the switching of switch states I2 and I3; when 1 < v r * < 2, if |Δv dc | > k, then select the switching of switch states I4 and I3; if |Δv dc | < k, then select the switching of switch states I5 and I3; when 2 < v r * < 3, if |Δv dc | > k, then select the switching of switch states I4 and I6; if |Δv dc | < k, then select the switching of switch states I5 and I6;

[0051] In the operating range II, when -1 < v r * < 0, if Δv dc > 0, then select the switching of switch states II1 and II3; if Δv dc < 0, then select the switching of switch states II2 and II3; when -2 < v r * < -1, if |Δv dc | > k, then select the switching of switch states II4 and II3; if |Δv dc | < k, then select the switching of switch states II5 and II3; when -3 < v r * < -2, if |Δv dc | > k, then select the switching of switch states II4 and II6; if |Δv dc | < k, then select the switching of switch states II5 and II6;

[0052] In the operating range III, when -1 < v r * < 0, if Δv dc > 0, then select the switching of switch states III1 and III3; if Δv dc < 0, then select the switching of switch states III2 and III3; when -2 < v r * < -1, if |Δv dc | > k, then select the switching of switch states III4 and III3; if |Δv dc | < k, then select the switching of switch states III5 and III3; when -3 < v r * < -2, if |Δv dc|> k, then select the switching of switch states III4 and III6. When |Δv dc |< k, then select the switching of switch states III5 and III6;

[0053] In the operating range IV, when 0 < v r * < 1, when Δv dc > 0, then select the switching of switch states IV1 and IV3. When Δv dc < 0, then select the switching of switch states IV2 and IV3; When 1 < v r * < 2, when |Δv dc |> k, then select the switching of switch states IV4 and IV3. When |Δv dc |< k, then select the switching of switch states IV5 and IV3; When 2 < v r * < 3, when |Δv dc |> k, then select the switching of switch states IV4 and IV6. When |Δv dc |< k, then select the switching of switch states IV5 and IV6.

[0054] The following is when the voltage sensor fails at v dc2 , and complete the DC voltage sensor fault ride-through modulation according to the magnitudes of v dc1 and v dc3 . Take Δv dc = v dc1 - v dc3 ;

[0055] In the operating range I, when 0 < v r * < 1, when Δv dc > 0, then select the switching of switch states I1 and I3. When Δv dc < 0, then select the switching of switch states I2 and I3; When 1 < v r * < 2, when Δv dc > 0, then select the switching of switch states I4 and I3. When Δv dc < 0, then select the switching of switch states I5 and I3; When 2 < v r * < 3, when Δv dc > 0, then select the switching of switch states I4 and I6. When Δv<00​​​​​​​​​​​​dc If Δv > 0, then switch states II4 and II3 are selected for switching. dc If the value is less than 0, then switch states II5 and II3 are selected for switching; if the value is less than -3, then switch state II5 and II3 are selected for switching. <v r When *<-2, when Δv dc If Δv > 0, then switch states II4 and II6 are selected; when Δv dc If the value is less than 0, then switch states II5 and II6 can be selected.

[0057] In operating range III, at -1 <v r When *<0, when Δv dc If Δv > 0, then switch states III1 and III3 are selected for switching. dc If the value is less than 0, then switch states III2 and III3 are selected; if the value is less than -2, then switch state III2 and III3 are selected. <v r When *<-1, when Δv dc If Δv > 0, then switch states III4 and III3 are selected for switching. dc If the value is less than 0, then switch between states III5 and III3; if the value is less than -3, then switch between states III5 and III3. <v r When *<-2, when Δv dc If Δv > 0, then switch states III4 and III6 are selected for switching. dc If the value is less than 0, then select switch state III5 and III6 to switch.

[0058] In the operating interval IV, at 0 <v r When *<1, if Δvdc>0, then switch states IV1 and IV3 are selected for switching; if Δv dc If <0, then switch state IV2 and IV3 are selected; if 1 <v r When *<2, when Δv dc If Δv > 0, then switch states IV4 and IV3 are selected for switching. dc If <0, then switch state IV5 and IV3 are selected; in 2 <v r When *<3, when Δv dc If Δv > 0, then switch states IV4 and IV6 are selected for switching. dc If the value is less than 0, then switch between IV5 and IV6.

[0059] The following is in v dc3 When the voltage sensor fails, according to v dc1 With v dc2 The magnitude of Δv is used to complete the fault ride-through modulation of the DC voltage sensor. dc =v dc1 -v dc2 Take 0 <k<0.1;

[0060] In the operating range I, when 0 < v r * < 1, if Δv dc > 0, then select the switching of switch states I1 and I3; if Δv dc < 0, then select the switching of switch states I2 and I3; when 1 < v r * < 2, if |Δv dc | > k, then select the switching of switch states I5 and I3; if |Δv dc | < k, then select the switching of switch states I4 and I3; when 2 < v r * < 3, if |Δv dc | > k, then select the switching of switch states I5 and I6; if |Δv dc | < k, then select the switching of switch states I4 and I6;

[0061] In the operating range II, when -1 < v r * < 0, if Δv dc > 0, then select the switching of switch states II1 and II3; if Δv dc < 0, then select the switching of switch states II2 and II3; when -2 < v r * < -1, if |Δv dc | > k, then select the switching of switch states II5 and II3; if |Δv dc | < k, then select the switching of switch states II4 and II3; when -3 < v r * < -2, if |Δv dc | > k, then select the switching of switch states II5 and II6; if |Δv dc | < k, then select the switching of switch states II4 and II6;

[0062] In the operating range III, when -1 < vr * < 0, if Δv dc > 0, then select the switching of switch states III1 and III3; if Δv<​​​​​​​​​​​​​​​​​When *< 1 and Δv dc > 0, switch the states of switches IV1 and IV3. When Δv dc < 0, switch the states of switches IV2 and IV3; when 1 < v r When *< 2 and |Δv dc | > k, switch the states of switches IV5 and IV3. When |Δv dc | < k, switch the states of switches IV4 and IV3; when 2 < v r When *< 3 and |Δv dc | > k, switch the states of switches IV5 and IV6. When |Δv dc | < k, switch the states of switches IV4 and IV6.

[0064] Example 1

[0065] Take the case of a voltage sensor failure of v dc3 . Complete the DC voltage sensor fault ride-through modulation according to the magnitudes of v dc1 and v dc2 . Let Δv dc = v dc1 - v dc2 . Take 0 < k < 0.1. In operating range I, when 0 < v r When *< 1 and Δv dc > 0, switch the states of switches I1 and I3. When Δv dc dc < 0, switch the states of switches I2 and I3; when 1 < v r When *< 2 and |Δv dc | > k, switch the states of switches I5 and I3. When |Δv dc | < k, switch the states of switches I4 and I3; when 2 < v r When *< 3 and |Δv dc | > k, switch the states of switches I5 and I6. When |Δv dc | < k, switch the states of switches I4 and I6; in operating range II, when -1 < v r When *< 0 and Δv dc > 0, switch the states of switches II1 and II3. When Δv dc < 0, switch the states of switches II2 and II3; when -2 < v r When *<-1 and |Δv dc | > k, switch the states of switches II5 and II3. When |Δv dc | < k, switch the states of switches II4 and II3. When -3 < v r When *<-2 and |Δv dcIf |>k, then switch the states of switches II5 and II6; when |Δv dc |<k, then switch the states of switches II4 and II6; in operating range III, when -1 < vr* < 0, if Δv dc >0, then switch the states of switches III1 and III3, if Δv dc <0, then switch the states of switches III2 and III3; when -2 < v r * < -1, if |Δv dc |>k, then switch the states of switches III5 and III3, if |Δv dc |<k, then switch the states of switches III4 and III3; when -3 < v r * < -2, if |Δv dc |>k, then switch the states of switches III5 and III6, if |Δv dc |<k, then switch the states of switches III4 and III6; in operating range IV, when 0 < v r * < 1, if Δv dc >0, then switch the states of switches IV1 and IV3, if Δv dc <0, then switch the states of switches IV2 and IV3; when 1 < v r * < 2, if |Δv dc |>k, then switch the states of switches IV5 and IV3, if |Δv dc |<k, then switch the states of switches IV4 and IV3; when 2 < v r * < 3, if |Δv dc |>k, then switch the states of switches IV5 and IV6, if |Δv dc |<k, then switch the states of switches IV4 and IV6.

[0066] The working conditions are shown in Table 1. The powers of the power generation / storage modules 1 to 3 are p pv1 、p pv2 and p pv3 , respectively, and are divided into 3 working conditions. In working condition 1, p pv1 >p pv2 >p pv3 ; in working condition 2, p pv2 >p pv1 >p pv3 ; in working condition 3, p pv3 >p pv2 >p pv1 ; in working condition 4, p pv3 =p pv2 =p pv1 . Table 2 shows the experimental system parameters of the split-capacitor power cell converter.

[0067] Table 1 Operating conditions of the split capacitor power unit converter

[0068] Power generation / energy storage module Operating Condition 1 Operating Condition 2 Operating Condition 3 Operating Condition 4 Power generation / energy storage module 1 1.0 PU (200W) 0.6pu 0.3pu 1p.u. Power generation / energy storage module 2 0.6pu 1.0pu 0.6pu 1p.u. Power generation / energy storage module 3 0.3pu 0.3pu 1.0pu 1.0pu

[0069] Table 2 Experimental System Parameters for Split Capacitor Power Unit Converter

[0070] System parameters symbol value Active rated power <![CDATA[P rated ]]> 0.2kW Reactive power rating <![CDATA[Q rated ]]> 0.2kVar Photovoltaic power benchmark <![CDATA[P pvb ]]> 0.1kW Grid voltage amplitude / frequency <![CDATA[v g / f g ]]> 50V / 50Hz Number of power generation / energy storage modules N 3 DC side voltage reference value <![CDATA[v dcj ]]> 40V DC side capacitor <![CDATA[C dcj ]]> 940μF Filter inductor L 5mH Switching frequency <![CDATA[f sw ]]> 10kHz

[0071] Experimental results are as follows Figures 7 to 10 As shown, Figures 7 to 10 The waveforms are for operating conditions 1 through 4, respectively. The left side of each graph shows the waveforms for operating conditions 1 through 4. dc3 The steady-state experimental waveform before the sensor malfunctions; the middle waveform is the simulated waveform for the entire experimental period; and the right waveform is v. dc3 The experimental waveforms at steady state after the sensor malfunction. From top to bottom, the waveforms represent the grid voltage v. g Grid current i g DC link voltage v dc1 ~v dc3 The current i flowing through bidirectional bridge arm #2 b2 and port voltage v ab .

[0072] like Figures 7 to 10 As shown, in v dc3 When the voltage sensor is not faulty, the DC link voltage v dc1 ~v dc3 Converging to the instruction value 40V, v g with i g In-phase operation achieves unity power factor, and bidirectional arm #2 performs power exchange under all three operating conditions. At v dc3 When the voltage sensor fails, the voltages of the three DC links rise simultaneously under the action of the self-balancing mechanism. When the DC voltage increment Δv reaches a certain value, the system switches to dual-sensor operation, and the system returns to stability. After the DC voltage sensor fault ride-through operation, the waveforms of each component's electrical quantity in steady state are almost identical to those before the voltage sensor failure, verifying the effectiveness of the control and DC-side voltage sensor fault ride-through modulation strategy.

Claims

1. A fault ride-through modulation strategy for a DC voltage sensor in a split-capacitor converter, characterized in that, Includes the following steps: (1) Obtain the voltage modulation wave v r *and current reference value i g *; (2) For v r * with i g * Divide the circuit into intervals and, based on the division results, divide the switching states of the split capacitor power unit converter. (3) The split capacitor power unit converter includes three power generation / storage modules. When the voltage sensor of the DC voltage on the electrolytic capacitor in one of the power generation / storage modules fails, the voltage modulation wave v will trigger a voltage sensor. r * and the difference in DC voltage across the electrolytic capacitors in the other two power generation / storage modules to complete the fault ride-through modulation of the DC voltage sensor; In step (2), the action on v r * with i g *The interval is divided, and the switching state of the split capacitor power unit converter is divided according to the division result as follows: In v r *>0 and i g When *>0, v r * with i g *In operating range I; In v r *<0 and i g When *>0, v r * with i g *In operating zone II; In v r *<0 and i g When *<0, v r *and i g *Currently in operating range III; In v r *>0 and i g When *<0, v r * with i g *In operating range IV; The switch states in operating range I are I1 to I6, the switch states in operating range II are II1 to II6, the switch states in operating range III are III1 to III6, and the switch states in operating range IV are IV1 to IV6. In step (3), in v dc1 When the voltage sensor fails, according to the voltage modulation wave v r *and v dc2 With v dc3 The difference is used to complete the fault ride-through modulation of the DC voltage sensor, specifically, Δv is taken. dc =v dc2 -v dc3 Take 0 <k<0.1; Among them, v dc1 v dc2 and v dc3 These are the DC-side voltages of power generation / storage module I, power generation / storage module II, and power generation / storage module III, respectively. In the operating range I, when 0 < v r *<1 and Δv dc > 0, the switching of switch states I1 and I3 is selected; when Δv dc < 0, the switching of switch states I2 and I3 is selected; when 1 < v r *<2 and |Δv dc | > k, the switching of switch states I4 and I3 is selected; when |Δv dc | < k, the switching of switch states I5 and I3 is selected; when 2 < v r *<3 and |Δv dc | > k, the switching of switch states I4 and I6 is selected; when |Δv dc | < k, the switching of switch states I5 and I6 is selected; In the operating range II, when -1 < v r * < 0, if Δv dc > 0, then select the switching of switch states II1 and II3; if Δv dc < 0, then select the switching of switch states II2 and II3; when -2 < v r * < -1, if |Δv dc | > k, then select the switching of switch states II4 and II3; if |Δv dc | < k, then select the switching of switch states II5 and II3; when -3 < v r * < -2, if |Δv dc | > k, then select the switching of switch states II4 and II6; if |Δv dc | < k, then select the switching of switch states II5 and II6; In the operating range III, when -1 < v r * < 0, if Δv dc > 0, then select the switching of switch states III1 and III3; if Δv dc < 0, then select the switching of switch states III2 and III3; when -2 < v r * < -1, if |Δv dc | > k, then select the switching of switch states III4 and III3; if |Δv dc | < k, then select the switching of switch states III5 and III3; when -3 < v r * < -2, if |Δv dc | > k, then select the switching of switch states III4 and III6; if |Δv dc | < k, then select the switching of switch states III5 and III6; In the operating range IV, when 0 < v r * < 1, if Δv dc > 0, then select the switching of switch states IV1 and IV3; if Δv dc < 0, then select the switching of switch states IV2 and IV3; when 1 < v r * < 2, if |Δv dc | > k, then select the switching of switch states IV4 and IV3; if |Δv dc | < k, then select the switching of switch states IV5 and IV3; when 2 < v r * < 3, if |Δv dc | > k, then select the switching of switch states IV4 and IV6; if |Δv dc | < k, then select the switching of switch states IV5 and IV6.

2. The DC voltage sensor fault ride-through modulation strategy for the split capacitor converter according to claim 1, characterized in that, In step (1), the acquisition of the voltage modulation wave v r *and current reference value i g *Specifically, it includes the following: (1.1) The DC-side voltages of the power generation / storage module I, power generation / storage module II, and power generation / storage module III of the split capacitor power unit converter are respectively v dc1 v dc2 and v dc3 The grid phase signal θ is obtained by phase-locking the grid voltage; (1.2) Use the grid phase signal θ for v g and i g Perform an αβ / dq coordinate transformation to obtain v g and i g The active and reactive components v d v q and i d i q ; ( 1.3) Average DC voltage control loop setting of the outer loop voltage v dcavg Converging to the reference value v dcref v dcref With v dcavg After subtraction, the reference value i of the active component of the grid current is obtained through a PI controller. dref i dref The current reference signal i is obtained by sinusoidalizing the phase with the power grid. g * ; ( 1.4)i dref with i d After the difference is calculated, the current active power error i is obtained through a PI controller. derr , change i derr v d with i q The modulated wave d-axis component v is obtained by adding ωL. dref ω is the angular frequency of the power grid, and L is the value of the grid-connected filter inductance; (1.5)i qref with i q The difference is passed through a PI controller to obtain the current active power error i. qerr , change i qerr v q with i d The sum of ωL yields the q-axis component v of the modulated wave. qref ; ( 1.6) v dref With v qref The voltage modulation wave v is obtained after dq / αβ transformation. r * 3. The DC voltage sensor fault ride-through modulation strategy for the split capacitor converter according to claim 1, characterized in that, In step (3), in v dc2 When the voltage sensor fails, according to the voltage modulation wave v r *and v dc1 With v dc3 The difference is used to complete the fault ride-through modulation of the DC voltage sensor, specifically, Δv is taken. dc =v dc1 -v dc3 ; In the operating interval I, at 0 <v r When *<1, when Δv dc If Δv > 0, then switch states I1 and I3 are selected for switching. dc If <0, then switch states I2 and I3 are selected; if 1 <v r When *<2, when Δv dc If Δv > 0, then switch states I4 and I3 are selected for switching. dc If <0, then switch states I5 and I3 are selected; in 2 <v r When *<3, when Δv dc If Δv > 0, then switch states I4 and I6 are selected for switching. dc If the value is less than 0, then switch states I5 and I6 can be toggled. In operating range II, at -1 <v r When *<0, when Δv dc If Δv > 0, then switch states II1 and II3 are selected for switching. dc If the value is less than 0, then switch states II2 and II3 are selected; if the value is less than -2, then switch states II2 and II3 are selected. <v r When *<-1, when Δv dc If Δv > 0, then switch states II4 and II3 are selected for switching. dc If the value is less than 0, then switch states II5 and II3 are selected for switching; if the value is less than -3, then switch state II5 and II3 are selected for switching. <v r When *<-2, when Δv dc If Δv > 0, then switch states II4 and II6 are selected; when Δv dc If the value is less than 0, then switch states II5 and II6 can be selected. In operating range III, at -1 <v r When *<0, when Δv dc If Δv > 0, then switch states III1 and III3 are selected for switching. dc If the value is less than 0, then switch states III2 and III3 are selected; if the value is less than -2, then switch state III2 and III3 are selected. <v r When *<-1, when Δv dc If Δv > 0, then switch states III4 and III3 are selected for switching. dc If the value is less than 0, then switch between states III5 and III3; if the value is less than -3, then switch between states III5 and III3. <v r When *<-2, when Δv dc If Δv > 0, then switch states III4 and III6 are selected for switching. dc If the value is less than 0, then select switch state III5 and III6 to switch. In the operating interval IV, at 0 <v r When *<1, when Δv dc If Δv > 0, then switch states IV1 and IV3 are selected for switching. dc If <0, then switch state IV2 and IV3 are selected; if 1 <v r When *<2, when Δv dc If Δv > 0, then switch states IV4 and IV3 are selected for switching. dc If <0, then switch state IV5 and IV3 are selected; in 2 <v r When *<3, when Δv dc If Δv > 0, then switch states IV4 and IV6 are selected for switching. dc If the value is less than 0, then switch between IV5 and IV6.

4. The DC voltage sensor fault ride-through modulation strategy for the split capacitor converter according to claim 1, characterized in that, In step (3), in v dc3 When the voltage sensor fails, according to the voltage modulation wave v r *and v dc1 With v dc2 The difference is used to complete the fault ride-through modulation of the DC voltage sensor, specifically, Δv is taken. dc =v dc1 -v dc2 Take 0 <k<0.1; In the operating range I, when 0 < v r * < 1, if Δv dc > 0, then select the switching of switch states I1 and I3; if Δv dc < 0, then select the switching of switch states I2 and I3; when 1 < v r * < 2, if |Δv dc | > k, then select the switching of switch states I5 and I3; if |Δv dc | < k, then select the switching of switch states I4 and I3; when 2 < v r * < 3, if |Δv dc | > k, then select the switching of switch states I5 and I6; if |Δv dc | < k, then select the switching of switch states I4 and I6; In operating range II, when -1 < v r * < 0, if Δv dc > 0, then select the switching of switch states II1 and II3; if Δv dc < 0, then select the switching of switch states II2 and II3; when -2 < v r * < -1, if |Δv dc | > k, then select the switching of switch states II5 and II3; if |Δv dc | < k, then select the switching of switch states II4 and II3; when -3 < v r * < -2, if |Δv dc | > k, then select the switching of switch states II5 and II6; if |Δv dc | < k, then select the switching of switch states II4 and II6; In operating range III, when -1 < vr* < 0, if Δv dc > 0, then select the switching of switch states III1 and III3. If Δv dc < 0, then select the switching of switch states III2 and III3. When -2 < v r * < -1, if |Δv dc | > k, then select the switching of switch states III5 and III3. If |Δv dc | < k, then select the switching of switch states III4 and III3. When -3 < v r * < -2, if |Δv dc | > k, then select the switching of switch states III5 and III6. If |Δv dc | < k, then select the switching of switch states III4 and III6; In the operating range IV, when 0 < vr* < 1, if Δv dc > 0, then select the switching of switch states IV1 and IV3. If Δv dc < 0, then select the switching of switch states IV2 and IV3. When 1 < v r * < 2, if |Δv dc | > k, then select the switching of switch states IV5 and IV3. If |Δv dc | < k, then select the switching of switch states IV4 and IV3; When 2 < v r * < 3, when |Δv dc | > k, then select the switching of switch states IV5 and IV6. When |Δv dc | < k, then select the switching of switch states IV4 and IV6.

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