A control method, system and related components for balanced midpoint voltage

Abstract

The present application discloses a control method, system and related components for balancing the midpoint voltage, which relates to the field of carrier pulse width modulation and is applied to the thirteen-segment carrier pulse width modulation process. The method includes: sorting the three instantaneous voltage values ​​of the current three-phase sine wave; judging the sign of the intermediate voltage value to determine the midpoint current; determining the modulation wave compensation amount according to the midpoint current and the midpoint voltage imbalance value; adding the modulation wave compensation amount to each corresponding upper modulation wave or lower modulation wave respectively to generate the corresponding phase drive signal. The present application effectively eliminates narrow pulses in the low-profile system area while balancing the midpoint voltage. The control does not change the positive and negative polarity of the output voltage. The midpoint voltage is balanced by injecting compensation into a specific modulation wave. It is easy to implement in engineering and has high reliability and practicality.

Description

Technical Field

[0001] The present invention relates to the field of carrier pulse width modulation, and particularly relates to a control method, system and related components for balancing the neutral point voltage. Background Art

[0002] The three-level neutral point clamped (NPC) converter, abbreviated as the three-level converter, has a main circuit topology as Figure 1 , compared with the traditional two-level converter, the phase voltage of the three-level NPC converter can output three voltage states, so the voltage stress of each device is lower and the current harmonic performance is better; compared with the cascaded H-bridge converter, the three-level NPC converter does not require a phase-shifting transformer, and its structure is simpler and the control is more convenient. Based on the above advantages, the three-level NPC converter has been widely used in the fields of new energy power generation, metallurgy and mining, and electric locomotive traction.

[0003] When the output motor of the three-level NPC converter operates in the starting or low-speed light-load state, the three-level NPC converter works in the low modulation ratio region. At this time, in order to ensure the normal drive of the power device and accurately output the target voltage, the pulse width modulation method needs to pay attention to eliminating narrow pulses. The traditional carrier pulse width modulation and space vector pulse width modulation cannot effectively eliminate narrow pulses in the low modulation ratio region, resulting in output voltage distortion and an increase in the current harmonic content, reducing the output performance of the three-level NPC converter.

[0004] In addition to eliminating narrow pulses, the neutral point voltage balance control is also a key issue for the three-level NPC converter. Unbalanced neutral point voltage will exacerbate the output voltage distortion, increase the turn-off voltage of the device, reduce the reliability of the converter system, and increase the low-frequency harmonics of the converter output. Therefore, it is necessary to balance the neutral point voltage of the three-level NPC converter.

[0005] Therefore, how to provide a solution that can both eliminate narrow pulses and balance the neutral point voltage is a problem that those skilled in the art need to solve currently. Summary of the Invention

[0006] In view of this, the purpose of the present invention is to provide a control method, system and related components for balancing the neutral point voltage. The specific solutions are as follows:

[0007] A control method for balancing the neutral point voltage, which is applied to the thirteen-segment carrier pulse width modulation process, includes:

[0008] Obtain three instantaneous voltage values of the current three-phase sine wave and sort them to obtain the maximum voltage value, the intermediate voltage value, and the minimum voltage value;

[0009] Determine whether the intermediate voltage value is positive. If it is, determine that the midpoint current is the opposite of the instantaneous current value of the phase corresponding to the minimum voltage value. If not, determine that the midpoint current is the instantaneous current value of the phase corresponding to the maximum voltage value;

[0010] Determine the modulation wave compensation amount according to the midpoint current and the midpoint voltage imbalance value;

[0011] Add the modulation wave compensation amount to the upper modulation wave or the lower modulation wave corresponding to each phase of the current three-phase sine wave respectively to generate the drive signal for the corresponding phase;

[0012] Both the upper modulation wave and the lower modulation wave are obtained through the thirteen-segment carrier pulse width modulation process.

[0013] Preferably, before adding the modulation wave compensation amount to the upper modulation wave or the lower modulation wave corresponding to each phase of the current three-phase sine wave respectively to generate the drive signal for the corresponding phase, it further includes:

[0014] Determine whether the absolute value of the modulation wave compensation amount is greater than the maximum compensation amount;

[0015] If so, reset the absolute value of the modulation wave compensation amount to the maximum compensation amount, and keep the sign of the modulation wave compensation amount unchanged.

[0016] Preferably, when the intermediate voltage value is negative, the maximum compensation amount is specifically the quotient obtained by dividing the difference between the maximum voltage value and the intermediate voltage value by 2;

[0017] When the intermediate voltage value is positive, the maximum compensation amount is specifically the quotient obtained by dividing the difference between the intermediate voltage value and the minimum voltage value by 2.

[0018] Preferably, the process of adding the modulation wave compensation amount to the upper modulation wave or the lower modulation wave corresponding to each phase of the current three-phase sine wave respectively to generate the drive signal for the corresponding phase includes:

[0019] When the intermediate voltage value is negative, add the modulation wave compensation amount to the upper modulation wave of the phase corresponding to the maximum voltage value, the lower modulation wave of the phase corresponding to the intermediate voltage value, and the lower modulation wave of the phase corresponding to the minimum voltage value;

[0020] When the intermediate voltage value is positive, add the modulation wave compensation amount to the upper modulation wave of the phase corresponding to the maximum voltage value, the upper modulation wave of the phase corresponding to the intermediate voltage value, and the lower modulation wave of the phase corresponding to the minimum voltage value.

[0021] Preferably, the process of determining the modulation wave compensation amount according to the midpoint current and the midpoint voltage imbalance value includes:

[0022] Judge whether the positive and negative signs of the midpoint current and midpoint voltage imbalance values are the same. If so, determine that the modulation wave compensation direction flag bit is 1. If not, determine that the modulation wave compensation direction flag bit is -1;

[0023] Input the modulation wave compensation direction flag bit into a hysteresis controller to obtain the modulation wave compensation amount.

[0024] Preferably, the thirteen-segment carrier pulse width modulation process includes:

[0025] Determine the double modulation wave parameters of the corresponding phase according to the maximum voltage value, the intermediate voltage value, and the minimum voltage value;

[0026] Determine the upper modulation wave and the lower modulation wave of the corresponding phase according to the double modulation wave parameters of each phase.

[0027] Preferably, the process of determining the double modulation wave parameters of the corresponding phase according to the maximum voltage value, the intermediate voltage value, and the minimum voltage value includes:

[0028] Determine the double modulation wave parameters of the corresponding phase of the maximum voltage value according to the first formula;

[0029] Determine the double modulation wave parameters of the corresponding phase of the intermediate voltage value according to the second formula;

[0030] Determine the double modulation wave parameters of the corresponding phase of the minimum voltage value according to the third formula;

[0031] The double modulation wave parameters include a first parameter and a second parameter, and the first formula is:

[0032]

[0033] The second formula is:

[0034]

[0035] The third formula is:

[0036]

[0037] Wherein, V max , V mid and V min are the maximum voltage value, the intermediate voltage value, and the minimum voltage value respectively, P max and N max are the first parameter and the second parameter of the corresponding phase of the maximum voltage value, P mid and N mid are the first parameter and the second parameter of the corresponding phase of the intermediate voltage value, P min and Nmin The first parameter and the second parameter of the corresponding phase of the minimum voltage value.

[0038] Correspondingly, the present application also discloses a control system for balancing the neutral point voltage, which is applied to the thirteen-segment carrier pulse width modulation process and includes:

[0039] A sorting module, configured to obtain three instantaneous voltage values of the current three-phase sine wave and sort them to obtain a maximum voltage value, a middle voltage value, and a minimum voltage value;

[0040] A judgment module, configured to judge whether the middle voltage value is positive. If so, determine that the neutral point current is the opposite of the instantaneous current value of the corresponding phase of the minimum voltage value. If not, determine that the neutral point current is the instantaneous current value of the corresponding phase of the maximum voltage value;

[0041] A calculation module, configured to determine a modulation wave compensation amount according to the neutral point current and the neutral point voltage imbalance value;

[0042] A compensation module, configured to add the modulation wave compensation amount to the upper modulation wave or the lower modulation wave corresponding to each phase of the current three-phase sine wave respectively to generate a drive signal for the corresponding phase;

[0043] Both the upper modulation wave and the lower modulation wave are obtained through the thirteen-segment carrier pulse width modulation process.

[0044] Correspondingly, the present application also discloses a control device for balancing the neutral point voltage, including:

[0045] A memory, configured to store a computer program;

[0046] A processor, configured to implement the steps of the control method for balancing the neutral point voltage as described in any one of the above when executing the computer program.

[0047] Correspondingly, the present application also discloses a readable storage medium, on which a computer program is stored, and when the computer program is executed by a processor, the steps of the control method for balancing the neutral point voltage as described in any one of the above are implemented.

[0048] The present application discloses a control method for balancing the midpoint voltage, which is applied to the thirteen-segment carrier pulse width modulation process and includes: obtaining three instantaneous voltage values of the current three-phase sine wave and sorting them to obtain the maximum voltage value, the intermediate voltage value, and the minimum voltage value; determining whether the intermediate voltage value is positive. If it is, determining that the midpoint current is the opposite of the instantaneous current value of the phase corresponding to the minimum voltage value; if not, determining that the midpoint current is the instantaneous current value of the phase corresponding to the maximum voltage value; determining the modulation wave compensation amount according to the midpoint current and the midpoint voltage imbalance value; adding the modulation wave compensation amount to the upper modulation wave or the lower modulation wave corresponding to each phase of the current three-phase sine wave respectively to generate the drive signal corresponding to each phase. The thirteen-segment carrier pulse width modulation process can effectively eliminate narrow pulses in the low modulation ratio region, and the control method of the present application can further balance the midpoint voltage in this modulation process. This control does not change the positive and negative polarities of the output voltage, and balances the midpoint voltage by injecting a compensation amount into a specific modulation wave, which has the advantage of being easy to implement in engineering and improves the reliability and practicability of the carrier pulse width modulation. Description of the Drawings

[0049] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only the embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained according to the provided drawings without creative efforts.

[0050] Figure 1 It is a main circuit topology diagram of a three-level converter;

[0051] Figure 2 It is a step flowchart of a control method for balancing the midpoint voltage;

[0052] Figure 3 It is a voltage vector sequence diagram of the thirteen-segment carrier pulse width modulation;

[0053] Figure 4 It is a simulation effect diagram when the control method for balancing the midpoint voltage of this embodiment is not applied to the thirteen-segment carrier pulse width modulation;

[0054] Figure 5 and Figure 6 They are respectively the simulation effect diagram and the simulation result diagram when the control method for balancing the midpoint voltage of this embodiment is applied to the thirteen-segment carrier pulse width modulation;

[0055] Figure 7 and Figure 8 They are respectively the simulation effect diagram and the simulation result diagram when the control method for balancing the midpoint voltage of this embodiment is applied to the thirteen-segment carrier pulse width modulation;

[0056] Figure 9 The simulation effect diagram when the control method of the balanced midpoint voltage of the thirteen-segment carrier pulse width modulation is not applied in this embodiment;

[0057] Figure 10 The simulation effect diagram when the control method of the balanced midpoint voltage of the thirteen-segment carrier pulse width modulation is applied in this embodiment;

[0058] Figure 11 The structural distribution diagram of a control system for balancing the midpoint voltage in the embodiment of the present invention. Specific implementation manners

[0059] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0060] Traditional carrier pulse width modulation and space vector pulse width modulation cannot effectively eliminate narrow pulses in the low modulation degree region, resulting in output voltage distortion and an increase in current harmonic content, reducing the output performance of the three-level NPC converter. In addition to eliminating narrow pulses, midpoint voltage balance control is also a key issue for the three-level NPC converter. Unbalanced midpoint voltage will exacerbate output voltage distortion, cause an increase in the turn-off voltage of devices, reduce the reliability of the converter system, and increase the low-frequency harmonics of the converter output. How to provide a solution that can both eliminate narrow pulses and balance the midpoint voltage is a problem that those skilled in the art need to solve currently.

[0061] The thirteen-segment carrier pulse width modulation process can ensure the effective elimination of narrow pulses in the low modulation degree region, and the control method of the present application can further balance the midpoint voltage during this modulation process. This control does not change the positive and negative polarities of the output voltage, and balances the midpoint voltage by injecting a compensation amount into a specific modulation wave, which has the advantage of being easy to implement in engineering and improves the reliability and practicability of the carrier pulse width modulation.

[0062] The embodiment of the present invention discloses a control method for balancing the midpoint voltage, which is applied to the thirteen-segment carrier pulse width modulation process. Refer to Figure 2 As shown, this control method includes:

[0063] S1: Obtain three instantaneous voltage values of the current three-phase sine wave and sort them to obtain the maximum voltage value, the intermediate voltage value, and the minimum voltage value;

[0064] S2: Determine whether the intermediate voltage value is positive. If it is, determine that the neutral point current is the opposite of the instantaneous current value of the phase corresponding to the minimum voltage value; if not, determine that the neutral point current is the instantaneous current value of the phase corresponding to the maximum voltage value.

[0065] It can be understood that there are only two cases regarding the positive and negative of the three instantaneous voltage values, namely one positive and two negative or one negative and two positive. The maximum voltage value among the three instantaneous voltage values must be positive, and the minimum voltage value must be negative. The positive or negative of the intermediate voltage value here determines whether these three instantaneous voltage values are one positive and two negative or one negative and two positive.

[0066] At the same time, the signs of the three instantaneous voltage values actually correspond to the phase regions of the current triangular sine wave. Define the three instantaneous voltage values of the three-phase sine wave as V A 、V B and V C . The case of one positive and two negative includes:

[0067] When V A > 0, V B < 0 and V C < 0, the phase angle region is 60 degrees to 120 degrees at this time;

[0068] When V B > 0, V A < 0 and V C < 0, the phase angle region is 180 degrees to 240 degrees at this time;

[0069] When V C > 0, V A < 0 and V B < 0, the phase angle region is 300 degrees to 360 degrees at this time;

[0070] Similarly, the case of one negative and two positive includes:

[0071] When V B < 0, V A > 0 and V C > 0, the phase angle region is 0 degrees to 60 degrees at this time;

[0072] When V C < 0, V A > 0 and V B > 0, the phase angle region is 120 degrees to 180 degrees at this time;

[0073] When V A < 0, V B > 0 and V C > 0, the phase angle region is 240 degrees to 300 degrees at this time.

[0074] For the case of one positive and two negative, the intermediate current is the instantaneous current value of the phase corresponding to the maximum voltage value. For example, VA >0>V B >V C When it is, let the intermediate current Neucur = I A ; For the case of one negative and two positives, its intermediate current is the opposite of the instantaneous current value of the corresponding phase of the minimum voltage value. For example, when V A >V B >0>V C When it is, let the intermediate current Neucur = -I C ; And so on for other cases. It should be noted that the corresponding phase here is any one of the ABC three phases located and determined based on the magnitude sorting of the voltage values. The positive or negative of the instantaneous voltage value of a certain phase does not represent the positive or negative of the instantaneous current value of that phase, and its instantaneous current value is the load current under that instantaneous voltage value.

[0075] S3: Determine the modulation wave compensation amount according to the neutral point current and the neutral point voltage unbalance value;

[0076] Specifically, step S3 can be implemented through the following steps:

[0077] Judge whether the positive and negative signs of the neutral point current and the neutral point voltage unbalance value are the same. If so, determine that the modulation wave compensation direction flag bit is 1. If not, determine that the modulation wave compensation direction flag bit is -1;

[0078] Input the modulation wave compensation direction flag bit into the hysteresis controller to obtain the modulation wave compensation amount.

[0079] It can be understood that the neutral point voltage unbalance value is usually the difference between the upper bridge arm voltage and the lower bridge arm voltage on the DC side of the three-level inverter. In addition to comparing the sign with the neutral point current in step S3, the neutral point voltage unbalance value is also used to judge whether to enable the control method in this embodiment. That is, before step S1, it may also include: judging whether the neutral point voltage unbalance value exceeds the unbalance threshold. If so, execute steps S1 - S5.

[0080] It can be understood that in this embodiment, the value (1 or -1) of the modulation wave compensation direction flag bit is used as the input of the hysteresis controller, and the entire control method is carried out in per-unit values. When actual parameters are needed, the per-unit value of the parameter can be converted through the reference value.

[0081] Further, considering that the modulation wave compensation amount may exceed the modulation capability range, a compensation amount interval can be set. When the modulation wave compensation amount output by the hysteresis controller exceeds the interval, the upper limit or the lower limit of the interval is taken as the modulation wave compensation amount and applied to the next step. Specifically, the compensation amount interval can be set as [-maxcom, maxcom], where maxcom is the maximum compensation amount. Before step S4 adds the modulation wave compensation amount to the corresponding upper modulation wave or lower modulation wave of each phase of the current three-phase sine wave to generate the drive signal for the corresponding phase, it further includes:

[0082] Judge whether the absolute value of the modulation wave compensation amount is greater than the maximum compensation amount;

[0083] If so, reset the absolute value of the modulation wave compensation amount to the maximum compensation amount, and keep the sign of the modulation wave compensation amount unchanged.

[0084] Specifically, if the modulation wave compensation amount modcom < -maxcom, then let modcom = -maxcom; if the modulation wave compensation amount modcom > maxcom, then let modcom = maxcom. If the modulation wave compensation amount does not exceed the compensation amount interval, no change is required.

[0085] Among them, the calculation of the maximum compensation amount includes: when the intermediate voltage value is negative, the maximum compensation amount is specifically the quotient obtained by dividing the difference between the maximum voltage value and the intermediate voltage value by 2; when the intermediate voltage value is positive, the maximum compensation amount is specifically the quotient obtained by dividing the difference between the intermediate voltage value and the minimum voltage value by 2.

[0086] Specifically, the maximum voltage value, the intermediate voltage value, and the minimum voltage value are respectively V max 、V mid and V min , when V mid is negative, Maxcom = (V max -V mid ) / 2; when V mid is positive, Maxcom = (V mid -V min ) / 2.

[0087] S4: Add the modulation wave compensation amount to the corresponding upper modulation wave or lower modulation wave of each phase of the current three-phase sine wave respectively to generate the drive signal for the corresponding phase;

[0088] Among them, both the upper modulation wave and the lower modulation wave are obtained through a thirteen-segment carrier pulse width modulation process.

[0089] Further, considering that the control method is applied to the working bridge arm, it is only necessary to add the modulation wave compensation amount to the current working upper modulation wave or lower modulation wave. Therefore, the process of adding the compensation amounts in step S4 to the corresponding upper modulation wave or lower modulation wave of each phase of the current three-phase sine wave to generate the drive signal of the corresponding phase may include:

[0090] When the intermediate voltage value is negative, add the modulation wave compensation amounts to the upper modulation wave of the corresponding phase of the maximum voltage value, the lower modulation wave of the corresponding phase of the intermediate voltage value, and the lower modulation wave of the corresponding phase of the minimum voltage value respectively;

[0091] When the intermediate voltage value is positive, add the modulation wave compensation amounts to the upper modulation wave of the corresponding phase of the maximum voltage value, the upper modulation wave of the corresponding phase of the intermediate voltage value, and the lower modulation wave of the corresponding phase of the minimum voltage value respectively.

[0092] Specifically, at this time, the upper modulation waves of the three-phase modulation waves are respectively P A 、P B and P C , and the lower modulation waves of the three-phase sine waves are respectively N A 、N B and N C . In step S5, inject the modulation wave compensation amount Modcom into the upper modulation wave of the positive-direction sine wave and the lower modulation wave of the negative-direction sine wave. The specific situations are as follows:

[0093] If V A >0, V B <0 and V C <0, let P A =P A +Modcom, N B =N B +Modcom, N C =N C +Modcom;

[0094] If V B >0, V A <0 and V C <0, let P B =P B +Modcom, N A =N A +Modcom, N C =N C +Modcom;

[0095] If V C >0, V A <0 and V B <0, let P C =P C +Modcom, NA = N A + Modcom, N B = N B + Modcom;

[0096] If V B < 0, V A > 0 and V C > 0, let P A = P A + Modcom, P C = P C + Modcom, N B = N B + Modcom;

[0097] If V C < 0, V A > 0 and V B > 0, let P A = P A + Modcom, P B = P B + Modcom, N C = N C + Modcom;

[0098] If V A < 0, V B > 0 and V C > 0, let P B = P B + Modcom, P C = P C + Modcom, N A = N A + Modcom.

[0099] The present application discloses a control method for balancing the midpoint voltage, which is applied to the thirteen-segment carrier pulse width modulation process and includes: obtaining three instantaneous voltage values of the current three-phase sine wave and sorting them to obtain the maximum voltage value, the intermediate voltage value, and the minimum voltage value; determining whether the intermediate voltage value is positive, and if so, determining that the midpoint current is the opposite of the instantaneous current value of the phase corresponding to the minimum voltage value, and if not, determining that the midpoint current is the instantaneous current value of the phase corresponding to the maximum voltage value; determining the modulation wave compensation amount according to the midpoint current and the midpoint voltage imbalance value; adding the modulation wave compensation amount to the upper modulation wave or the lower modulation wave corresponding to each phase of the current three-phase sine wave respectively to generate the drive signal corresponding to each phase. The thirteen-segment carrier pulse width modulation process can effectively eliminate narrow pulses in the low modulation ratio region, and the control method of the present application can further balance the midpoint voltage in this modulation process. This control does not change the positive and negative polarities of the output voltage, and balances the midpoint voltage by injecting a compensation amount into a specific modulation wave, which has the advantage of being easy to implement in engineering and improves the reliability and practicability of the carrier pulse width modulation.

[0100] An embodiment of the present invention discloses a specific control method for balancing the midpoint voltage. Compared with the previous embodiment, this embodiment further explains and optimizes the technical solution. Specifically, the thirteen-segment carrier pulse width modulation process is often applied to the low modulation ratio working condition and includes:

[0101] Determining the double modulation wave parameters of the corresponding phase according to the maximum voltage value, the intermediate voltage value, and the minimum voltage value;

[0102] Determining the upper modulation wave and the lower modulation wave of the corresponding phase according to the double modulation wave parameters of each phase.

[0103] It can be understood that the upper modulation wave and the lower modulation wave determined here will be applied to be added to the modulation wave compensation amount in step S4 to generate a new modulation wave, which is compared with the triangular carrier wave to generate the drive signal corresponding to each phase.

[0104] Further, the process of determining the double modulation wave parameters of the corresponding phase according to the maximum voltage value, the intermediate voltage value, and the minimum voltage value includes:

[0105] Determining the double modulation wave parameters of the phase corresponding to the maximum voltage value according to the first formula;

[0106] Determining the double modulation wave parameters of the phase corresponding to the intermediate voltage value according to the second formula;

[0107] Determining the double modulation wave parameters of the phase corresponding to the minimum voltage value according to the third formula;

[0108] The double modulation wave parameters include a first parameter and a second parameter, and the first formula is:

[0109]

[0110] The second formula is:

[0111]

[0112] The third formula is:

[0113]

[0114] Among them, V max , V mid and V min are the maximum voltage value, the intermediate voltage value and the minimum voltage value respectively, P max and N max are the first parameter and the second parameter of the corresponding phase of the maximum voltage value, P mid and N mid are the first parameter and the second parameter of the corresponding phase of the intermediate voltage value, P min and N min are the first parameter and the second parameter of the corresponding phase of the minimum voltage value.

[0115] Specifically, the process of determining the upper modulation wave and the lower modulation wave of any phase according to the dual modulation wave parameters of this phase includes:

[0116] According to the dual modulation wave parameters of any phase, determine that the amplitude of the upper modulation wave of this phase is the first parameter, and determine that the amplitude of the lower modulation wave of this phase is the sum of the second parameter and a voltage reference value.

[0117] Taking the case where the reference voltage is in the phase angle region of 90° to 120° as an example, the voltage vector sequence of the thirteen-segment carrier pulse width modulation is as Figure 3 shown, where a group of three redundant zero vectors and two groups of four redundant small vectors are used simultaneously within one sampling period. Since the number and type of the voltage vectors used are different, the thirteen-segment carrier pulse width modulation cannot directly use the traditional method of redistributing the action time of the two redundant small vectors to control the neutral point voltage balance, while the control method of this application does not require the two redundant small vectors in the traditional neutral point voltage balance, and can successfully achieve the effect of neutral point voltage balance in the thirteen-segment carrier pulse width modulation.

[0118] It can be understood that the thirteen-segment carrier pulse width modulation can ensure that the phase voltage pulse width of the high-power three-level inverter in the low modulation ratio region is greater than the minimum switching time of the device, so as to effectively eliminate the narrow pulse, and the method of this application further balances the neutral point voltage, thus achieving the effect of both eliminating the narrow pulse and balancing the control of the neutral point voltage.

[0119] The embodiment of the present invention discloses a specific control method for balancing the neutral point voltage. Compared with the previous embodiment, this embodiment further explains and optimizes the technical solution.

[0120] Specifically, in the embodiments of the present application, a three-level converter model is built with the aid of PSIM software, and the effectiveness of the midpoint voltage balance control method of the thirteen-segment carrier pulse width modulation of the present application is verified by simulation. The simulation conditions of the embodiment are as follows: the simulation step size is set to 2 μs, the DC side voltage is set to 540 V, the triangular carrier frequency is 2000 Hz, and the sampling frequency is 4000 Hz.

[0121] See Figure 4 As shown, the simulation conditions are as follows: the upper capacitor voltage of the DC side of the three-level converter is 400 V, the lower capacitor voltage is 140 V, the modulation degree is 0.2, the fundamental frequency is 10 Hz, and the midpoint voltage deviation value, phase voltage, and double modulation waves of the thirteen-segment carrier pulse width modulation without adding the control method for balancing the midpoint voltage of this embodiment are as shown in Figure 4 As shown. It can be seen from Figure 4 that when the three-level converter uses thirteen-segment carrier pulse width modulation and the midpoint voltage is unbalanced, if no further balance adjustment is made to the midpoint voltage, the midpoint voltage imbalance value on the DC side will always exist. The unbalanced midpoint voltage will exacerbate the distortion of the output voltage, cause an increase in the turn-off voltage of the device, reduce the reliability of the converter system, and increase the low-frequency harmonics of the converter output. Therefore, in order to improve the reliability and output performance of the three-level NPC converter when using thirteen-segment carrier pulse width modulation, an effective midpoint voltage balance control method must be added to the thirteen-segment carrier pulse width modulation.

[0122] See Figure 5 and Figure 6 As shown, the simulation conditions are as follows: the upper capacitor voltage of the DC side of the three-level converter is 400 V, the lower capacitor voltage is 140 V, the modulation degree is 0.2, the fundamental frequency is 10 Hz, and the midpoint voltage deviation value, phase voltage, double modulation wave before compensation, and double modulation wave after compensation when using the midpoint voltage balance control method of the present application are as shown in Figure 5 and Figure 6 As shown. Figure 5 is the full-process simulation result of the midpoint voltage balance control, Figure 6 is the simulation result during the midpoint voltage balance control process. Comparing Figure 5 and Figure 4 , when the midpoint voltage deviation value is positive, after using the midpoint voltage balance control method of the present application, the midpoint voltage deviation value quickly decreases to within 2% of the DC side voltage value. Therefore, the method of the present application can effectively balance the midpoint voltage when the midpoint voltage deviation value is positive. In addition, Figure 6 shows that when the midpoint voltage deviation value is positive, the method of the present application will not change the positive and negative polarities of the output voltage and will not cause a two-level jump of the phase voltage during the process of balancing the midpoint voltage. Therefore, the method of the present application has good safety.

[0123] See Figure 7 andFigure 8 As shown, the simulation conditions are as follows: the upper capacitor voltage on the DC side of the three-level converter is 140V, the lower capacitor voltage is 400V, the modulation index is 0.2, the fundamental frequency is 10Hz. The midpoint voltage deviation value, phase voltage, double modulation waves before compensation, and double modulation waves after compensation when using the midpoint voltage balance control method of this application are as Figure 7 and Figure 8 shown. Among them, Figure 7 is the full-process simulation result of midpoint voltage balance control, Figure 8 is the simulation result during the midpoint voltage balance control process. Analyzing Figure 7 , when the midpoint voltage deviation value is negative, after using the midpoint voltage balance control method of this application, the midpoint voltage deviation value quickly decreases to within 2% of the DC side voltage value. Therefore, the method of this application can effectively balance the midpoint voltage when the midpoint voltage deviation value is negative. In addition, Figure 8 shows that when the midpoint voltage deviation value is negative, the method of this application will not change the positive and negative polarities of the output voltage and will not cause two-level jumps in the phase voltage during the process of balancing the midpoint voltage. Therefore, the method of this application has good safety.

[0124] See Figure 9 shown. The simulation conditions are as follows: the upper capacitor voltage on the DC side of the three-level converter is 450V, the lower capacitor voltage is 90V, the modulation index varies from 0 to 0.3, the fundamental frequency varies from 0Hz to 15Hz. The midpoint voltage deviation value, phase voltage, current, and double modulation waves when the thirteen-segment carrier pulse width modulation does not add the midpoint voltage balance control method are as Figure 9 shown. It can be seen from Figure 9 that when the midpoint voltage is unbalanced and the fundamental frequency and modulation index are constantly changing, if a suitable midpoint voltage balance control method is not added, the midpoint voltage imbalance value on the DC side will always exist, seriously affecting the output performance of the three-level NPC converter when using the thirteen-segment carrier pulse width modulation method.

[0125] See Figure 10 shown. The simulation conditions are as follows: the upper capacitor voltage on the DC side of the three-level converter is 450V, the lower capacitor voltage is 90V, the modulation index varies from 0 to 0.3, the fundamental frequency varies from 0Hz to 15Hz. The midpoint voltage deviation value, phase voltage, current, double modulation waves before compensation, and double modulation waves after compensation when using the midpoint voltage balance control method of this application are as Figure 9 shown. Comparing Figure 9 and Figure 10 , when the three-level converter uses the thirteen-segment carrier pulse width modulation and the midpoint voltage is unbalanced, even if the modulation index and fundamental frequency are constantly changing, after adding the midpoint voltage balance control method of this application, the midpoint voltage deviation value can still quickly decrease to within 2% of the DC side voltage value. Therefore, the method of this application has good robustness.

[0126] Further analysis Figures 5 to 10 That is, by injecting a compensation amount into a specific dual modulation wave, the method of the present application can control the neutral point voltage balance when the modulation strategy is the thirteen-segment carrier pulse width modulation, which has the advantage of being easy to implement in engineering.

[0127] As Figures 4 to 10 shown, the simulation results verify the effectiveness of the neutral point voltage balance control method of the thirteen-segment carrier pulse width modulation of the present application. When the three-level converter uses the thirteen-segment carrier pulse width modulation and the neutral point voltage is unbalanced, regardless of whether the neutral point voltage deviation value is positive or negative, and regardless of whether the modulation degree and the fundamental frequency are fixed or variable, the method of the present application can control the neutral point voltage to resume balance again, and during the process of balancing the neutral point voltage, the positive and negative polarities of the output voltage will not be changed, and there will be no two-level jump of the phase voltage. Therefore, the method of the present application significantly improves the safety and reliability of the three-level NPC converter under the action of the thirteen-segment carrier pulse width modulation. In addition, by injecting a compensation amount into a specific dual modulation wave, the method of the present application can control the neutral point voltage balance, which also has the advantage of being easy to implement in engineering.

[0128] Correspondingly, the present application also discloses a control system for balancing the neutral point voltage, which is applied to the thirteen-segment carrier pulse width modulation process. Refer to Figure 11 shown, including:

[0129] Sorting module 1, configured to obtain three instantaneous voltage values of the current three-phase sine wave and sort them to obtain the maximum voltage value, the intermediate voltage value, and the minimum voltage value;

[0130] Judgment module 2, configured to judge whether the intermediate voltage value is positive. If so, determine that the neutral point current is the opposite of the instantaneous current value of the phase corresponding to the minimum voltage value. If not, determine that the neutral point current is the instantaneous current value of the phase corresponding to the maximum voltage value;

[0131] Calculation module 3, configured to determine the modulation wave compensation amount according to the neutral point current and the neutral point voltage unbalance value;

[0132] Compensation module 4, adding the modulation wave compensation amount to the upper modulation wave or the lower modulation wave corresponding to each phase of the current three-phase sine wave respectively to generate the drive signal corresponding to each phase;

[0133] Both the upper modulation wave and the lower modulation wave are obtained through the thirteen-segment carrier pulse width modulation process.

[0134] The thirteen - segment carrier pulse - width modulation process can effectively eliminate narrow pulses in the low modulation index region, and the present application can further balance the mid - point voltage in this modulation process. This control does not change the positive and negative polarities of the output voltage. By injecting a compensation amount into a specific modulation wave to balance the mid - point voltage, it has the advantage of being easy to implement in engineering, improving the reliability and practicality of carrier pulse - width modulation.

[0135] In some specific embodiments, before the compensation module 4 adds the modulation wave compensation amounts to the corresponding upper or lower modulation waves of each of the current three - phase sine waves to generate the drive signals for the corresponding phases, it further includes:

[0136] Judging whether the absolute value of the modulation wave compensation amount is greater than the maximum compensation amount;

[0137] If so, reset the absolute value of the modulation wave compensation amount to the maximum compensation amount, and keep the sign of the modulation wave compensation amount unchanged.

[0138] In some specific embodiments, when the intermediate voltage value is negative, the maximum compensation amount is specifically the quotient obtained by dividing the difference between the maximum voltage value and the intermediate voltage value by 2;

[0139] When the intermediate voltage value is positive, the maximum compensation amount is specifically the quotient obtained by dividing the difference between the intermediate voltage value and the minimum voltage value by 2.

[0140] In some specific embodiments, the process in which the compensation module 4 adds the modulation wave compensation amounts to the corresponding upper or lower modulation waves of each of the current three - phase sine waves to generate the drive signals for the corresponding phases includes:

[0141] When the intermediate voltage value is negative, add the modulation wave compensation amounts to the upper modulation wave of the corresponding phase of the maximum voltage value, the lower modulation wave of the corresponding phase of the intermediate voltage value, and the lower modulation wave of the corresponding phase of the minimum voltage value;

[0142] When the intermediate voltage value is positive, add the modulation wave compensation amounts to the upper modulation wave of the corresponding phase of the maximum voltage value, the upper modulation wave of the corresponding phase of the intermediate voltage value, and the lower modulation wave of the corresponding phase of the minimum voltage value.

[0143] In some specific embodiments, the calculation module 3 is specifically used for:

[0144] Judging whether the positive and negative signs of the mid - point current and the mid - point voltage imbalance value are the same. If so, determine that the modulation wave compensation direction flag bit is 1. If not, determine that the modulation wave compensation direction flag bit is - 1;

[0145] Input the modulation wave compensation direction flag bit into the hysteresis controller to obtain the modulation wave compensation amount.

[0146] In some specific embodiments, the thirteen-segment carrier pulse width modulation process includes:

[0147] Determine the double modulation wave parameters of the corresponding phase according to the maximum voltage value, the intermediate voltage value, and the minimum voltage value;

[0148] Determine the upper modulation wave and the lower modulation wave of the corresponding phase according to the double modulation wave parameters of each phase.

[0149] Preferably, the process of determining the double modulation wave parameters of the corresponding phase according to the maximum voltage value, the intermediate voltage value, and the minimum voltage value includes:

[0150] Determine the double modulation wave parameters of the corresponding phase of the maximum voltage value according to the first formula;

[0151] Determine the double modulation wave parameters of the corresponding phase of the intermediate voltage value according to the second formula;

[0152] Determine the double modulation wave parameters of the corresponding phase of the minimum voltage value according to the third formula;

[0153] The double modulation wave parameters include a first parameter and a second parameter, and the first formula is:

[0154]

[0155] The second formula is:

[0156]

[0157] The third formula is:

[0158]

[0159] Wherein, V max , V mid and V min are the maximum voltage value, the intermediate voltage value, and the minimum voltage value respectively, P max and N max are the first parameter and the second parameter of the corresponding phase of the maximum voltage value, P mid and N mid are the first parameter and the second parameter of the corresponding phase of the intermediate voltage value, P min and N min are the first parameter and the second parameter of the corresponding phase of the minimum voltage value.

[0160] In some specific embodiments, the process of determining the upper modulation wave and the lower modulation wave of a certain phase according to the double modulation wave parameters of any phase includes:

[0161] According to the dual modulation wave parameters of any phase, determine that the amplitude of the upper modulation wave of this phase is the first parameter, and determine that the amplitude of the lower modulation wave of this phase is the sum of the second parameter and a voltage reference value.

[0162] Correspondingly, an embodiment of the present application also discloses a control device for balancing the neutral point voltage, including:

[0163] A memory for storing a computer program;

[0164] A processor for implementing the steps of the control method for balancing the neutral point voltage as described in any one of the above when executing the computer program.

[0165] Correspondingly, an embodiment of the present application also discloses a readable storage medium, on which a computer program is stored, and when the computer program is executed by a processor, the steps of the control method for balancing the neutral point voltage as described in any one of the above are implemented.

[0166] Among them, for the specific details of the control method for balancing the neutral point voltage, reference can be made to the relevant descriptions in the above embodiments, and details will not be elaborated here.

[0167] Among them, the control device for balancing the neutral point voltage and the readable storage medium in this embodiment have the same technical effects as the control method for balancing the neutral point voltage in the above embodiments, and details will not be elaborated here.

[0168] Finally, it should also be noted that in this article, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variant thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements not only includes those elements, but also includes other elements not expressly listed, or elements inherent to such process, method, article or device. Without further limitation, an element defined by the phrase "including a..." does not exclude the existence of additional identical elements in the process, method, article or device including the element.

[0169] The above has introduced in detail a control method, system and related components for balancing the neutral point voltage provided by the present invention. Specific examples are used in this article to elaborate on the principle and implementation manner of the present invention. The description of the above embodiments is only used to help understand the method and its core idea of the present invention; at the same time, for those of ordinary skill in the art, according to the idea of the present invention, there will be changes in the specific implementation manner and application scope. In summary, the content of this specification should not be construed as a limitation to the present invention.

Claims

1. A method for controlling a balanced midpoint voltage, characterized in that: Applied in the thirteen-segment carrier pulse width modulation process, including: Obtain three instantaneous voltage values ​​of the current three-phase sine wave and sort them to obtain the maximum voltage value, the middle voltage value and the minimum voltage value; Determine whether the intermediate voltage value is positive, if so, determine the midpoint current to be the opposite of the instantaneous current value of the phase corresponding to the minimum voltage value, if not, determine the midpoint current to be the instantaneous current value of the phase corresponding to the maximum voltage value; Determining a modulation wave compensation amount according to the unbalanced values ​​of the midpoint current and the midpoint voltage; The modulation wave compensation amount is added to each corresponding up-modulation wave or down-modulation wave of the current three-phase sine wave to generate a driving signal of the corresponding phase; The upper modulation wave and the lower modulation wave are both obtained through the thirteen-segment carrier pulse width modulation process; Wherein, the control method of the balanced midpoint voltage is applied to a three-level midpoint clamped converter; The process of adding the modulation wave compensation amount to each corresponding upper modulation wave or lower modulation wave of the current three-phase sine wave to generate the driving signal of the corresponding phase includes: when the intermediate voltage value is negative, adding the modulation wave compensation amount to the upper modulation wave of the phase corresponding to the maximum voltage value, the lower modulation wave of the phase corresponding to the intermediate voltage value, and the lower modulation wave of the phase corresponding to the minimum voltage value; when the intermediate voltage value is positive, adding the modulation wave compensation amount to the upper modulation wave of the phase corresponding to the maximum voltage value, the upper modulation wave of the phase corresponding to the intermediate voltage value, and the lower modulation wave of the phase corresponding to the minimum voltage value; The process of determining the modulation wave compensation amount according to the midpoint current and midpoint voltage unbalance values ​​includes: judging whether the positive and negative signs of the midpoint current and midpoint voltage unbalance values ​​are the same; if so, determining that the modulation wave compensation direction flag is 1; if not, determining that the modulation wave compensation direction flag is -1; and inputting the modulation wave compensation direction flag into the hysteresis controller to obtain the modulation wave compensation amount.

2. The control method according to claim 1, characterized in that: Before adding the modulation wave compensation amount to each corresponding up-modulation wave or down-modulation wave of the current three-phase sine wave to generate a driving signal of the corresponding phase, the method further includes: Determining whether the absolute value of the modulation wave compensation amount is greater than the maximum compensation amount; If so, the absolute value of the modulation wave compensation amount is reset to the maximum compensation amount, and the sign of the modulation wave compensation amount remains unchanged.

3. The control method according to claim 2, characterized in that: When the intermediate voltage value is negative, the maximum compensation amount is specifically the quotient of the maximum voltage value and the intermediate voltage value divided by 2; When the intermediate voltage value is positive, the maximum compensation amount is specifically a quotient of the intermediate voltage value subtracted from the minimum voltage value and divided by 2.

4. The control method according to any one of claims 1 to 3, characterized in that: The thirteen-segment carrier pulse width modulation process comprises: Determining the dual modulation wave parameters of the corresponding phase according to the maximum voltage value, the intermediate voltage value and the minimum voltage value; According to the dual modulation wave parameters of each phase, the upper modulation wave and the lower modulation wave of the corresponding phase are determined.

5. The control method according to claim 4, characterized in that: The process of determining the dual modulation wave parameters of the corresponding phase according to the maximum voltage value, the intermediate voltage value and the minimum voltage value includes: According to the first formula, determining the dual modulation wave parameter of the phase corresponding to the maximum voltage value; Determine the dual modulation wave parameter of the corresponding phase of the intermediate voltage value according to the second formula; According to the third formula, determining the dual modulation wave parameter of the phase corresponding to the minimum voltage value; The dual modulation wave parameters include a first parameter and a second parameter, and the first formula is: The second formula is: The third formula is: Among them, V max 、V mid and V min are the maximum voltage value, the intermediate voltage value and the minimum voltage value respectively, P max and N max are the first parameter and the second parameter of the phase corresponding to the maximum voltage value, P mid and N mid are the first parameter and the second parameter of the phase corresponding to the intermediate voltage value, P min and N min The first parameter and the second parameter of the phase corresponding to the minimum voltage value.

6. A control system for balancing midpoint voltage, characterized in that: Applied in the thirteen-segment carrier pulse width modulation process, including: A sorting module is used to obtain three instantaneous voltage values ​​of the current three-phase sine wave and sort them to obtain a maximum voltage value, an intermediate voltage value and a minimum voltage value; A judging module, configured to judge whether the intermediate voltage value is positive, and if so, to determine whether the midpoint current is the opposite of the instantaneous current value of the phase corresponding to the minimum voltage value; and if not, to determine whether the midpoint current is the instantaneous current value of the phase corresponding to the maximum voltage value; A calculation module, used to determine the modulation wave compensation amount according to the unbalanced value of the midpoint current and the midpoint voltage; A compensation module, which adds the modulation wave compensation amount to each corresponding up-modulation wave or down-modulation wave of the current three-phase sine wave to generate a driving signal of the corresponding phase; The upper modulation wave and the lower modulation wave are both obtained through the thirteen-segment carrier pulse width modulation process; Wherein, the control method of the balanced midpoint voltage is applied to a three-level midpoint clamped converter; The process of adding the modulation wave compensation amount to each corresponding upper modulation wave or lower modulation wave of the current three-phase sine wave to generate the driving signal of the corresponding phase includes: when the intermediate voltage value is negative, adding the modulation wave compensation amount to the upper modulation wave of the phase corresponding to the maximum voltage value, the lower modulation wave of the phase corresponding to the intermediate voltage value, and the lower modulation wave of the phase corresponding to the minimum voltage value; when the intermediate voltage value is positive, adding the modulation wave compensation amount to the upper modulation wave of the phase corresponding to the maximum voltage value, the upper modulation wave of the phase corresponding to the intermediate voltage value, and the lower modulation wave of the phase corresponding to the minimum voltage value; The process of determining the modulation wave compensation amount according to the midpoint current and midpoint voltage unbalance values ​​includes: judging whether the positive and negative signs of the midpoint current and midpoint voltage unbalance values ​​are the same; if so, determining that the modulation wave compensation direction flag is 1; if not, determining that the modulation wave compensation direction flag is -1; and inputting the modulation wave compensation direction flag into the hysteresis controller to obtain the modulation wave compensation amount.

7. A control device for balancing midpoint voltage, characterized in that: include: Memory for storing computer programs; A processor, configured to implement the steps of the method for controlling the balanced midpoint voltage as claimed in any one of claims 1 to 5 when executing the computer program.

8. A readable storage medium, characterized in that: The readable storage medium stores a computer program, and when the computer program is executed by a processor, the steps of the method for controlling a balanced midpoint voltage as claimed in any one of claims 1 to 5 are implemented.

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