Control method and control device for neutral-point potential balance

Abstract

The invention discloses a control method and a control device for neutral-point potential balance. The method comprises the following steps: acquiring a three-phase modulation signal and a bridge arm current corresponding to the three-phase modulation signal; the sizes of the three-phase modulation signals are compared, and the maximum value umax, the minimum value umin and the intermediate value umid of the modulation signals are determined; the bridge arm current corresponding to the three-phase modulation signal is compared, and the maximum value imax, the minimum value imin and the intermediate value imd of the bridge arm current are determined; according to the minimum value u < min >, the intermediate value u < mid > and the maximum value u < max > of the modulation signal, the boundary value of the zero-sequence voltage u < z > is calculated; determining a direction factor kz of the zero-sequence voltage uz according to the intermediate value umid of the modulation signal and the intermediate value imid, the minimum value imin and the maximum value imax of the bridge arm current; and according to the boundary value of the zero-sequence voltage uz and the direction factor kz, adjusting the average current inpv of the injected midpoint so as to control the potential balance of the midpoint. According to the technical scheme, the program storage space of the control method for neutral-point potential balance is reduced, and the program running speed of the control method for neutral-point potential balance is increased.

Description

Technical Field

[0001] The embodiments of the present invention relate to the field of power electronics technology, and in particular to a control method and a control device for midpoint potential balance. Background Art

[0002] The inherent problem of midpoint potential balance in three-level inverters is a technical bottleneck that limits the widespread application of three-level inverters. The unbalanced midpoint potential of three-level inverters will increase the turn-off voltage of some switching devices, causing device overvoltage and increasing the AC harmonic content of the inverter output.

[0003] The traditional vector modulation-based method requires complex trigonometric calculations, sector division and selection of a certain current direction to determine the direction of the midpoint balance control quantity, and the logic of program judgment is relatively complex.

[0004] The existing three-level inverter midpoint potential balance control method has the problem of complex program judgment logic, large program storage space and time overhead, which has become a technical problem that needs to be solved urgently in the industry. Summary of the invention

[0005] The embodiments of the present invention provide a control method and a control device for midpoint potential balance, so as to solve the problems in the existing midpoint potential balance control method of a three-level inverter that the program judgment logic is complex, the program storage space is occupied and the time overhead is large.

[0006] In order to achieve the above technical problems, the present invention adopts the following technical solutions:

[0007] An embodiment of the present invention provides a method for controlling midpoint potential balance, comprising:

[0008] Acquire a three-phase modulation signal and a bridge arm current corresponding to the three-phase modulation signal;

[0009] Compare the magnitudes of the three-phase modulation signals and determine the maximum value u of the modulation signal max , minimum value u min and the intermediate value u mid ; Compare the size of the bridge arm current corresponding to the three-phase modulation signal to determine the maximum value of the bridge arm current i max , minimum value i min and the intermediate value i mid ;

[0010] According to the minimum value u of the modulation signal min , the middle value u mid and the maximum value u max , calculate the zero sequence voltage u z The boundary value of

[0011] According to the intermediate value u of the modulation signalmid , the middle value of the bridge arm current i mid , minimum value i min and the maximum value i max , determine the zero-sequence voltage u z The direction factor k z ;

[0012] According to the zero-sequence voltage u z The boundary value and the direction factor k z , adjust the average current injected into the midpoint i npv , to control the midpoint potential balance.

[0013] Optionally, the minimum value u of the modulation signal min , the middle value u mid and the maximum value u max , calculate the zero sequence voltage u z The boundary values ​​include:

[0014] When the modulated signal has an intermediate value u mid When it is greater than zero, according to the minimum value u of the modulation signal min , the intermediate value u mid and the maximum value u max , the zero-sequence voltage u is calculated based on the first objective function z The first boundary value of

[0015] When the intermediate value of the modulation signal is less than or equal to zero, according to the minimum value u of the modulation signal min , the intermediate value u mid and the maximum value u max , the zero-sequence voltage u is calculated based on the second objective function z The second boundary value of the zero-sequence voltage u z The boundary values ​​include the first boundary value and the second boundary value.

[0016] Optionally, the zero-sequence voltage u z The first boundary value and the second boundary value are calculated using the following formula:

[0017]

[0018] Optionally, the intermediate value u of the modulation signal mid , the middle value of the bridge arm current i mid , minimum value i min and the maximum value i max , determine the zero-sequence voltage u z The direction factor k z ,include:

[0019] k z =-(i max +sgn(u mid )i mid -i min )or,

[0020] Optionally, the zero-sequence voltage u z The boundary value and the direction factor k z , adjust the average current injected into the midpoint i npv , to control the midpoint potential balance, including:

[0021] According to the zero-sequence voltage u z The boundary value of the zero-sequence voltage u z ;

[0022] According to the maximum value u of the three-phase modulation signal max , the middle value u mid and the minimum value u min , and the maximum value of the bridge arm current i max , minimum value i min and the intermediate value i mid , determine the first midpoint current component i formed by the duty cycle instruction of the three-phase modulation signal in the O state ointr ;

[0023] According to the zero-sequence voltage u z and the direction factor k z , determine the injected zero-sequence voltage u z The second midpoint current component i generated ouz ;

[0024] According to the first midpoint current component i ointr and the second midpoint current component i ouz , determine the average current i injected into the midpoint npv ;

[0025] By changing the second midpoint current component i ouz , adjust the average current injected into the midpoint i npv , to control the midpoint potential balance.

[0026] Optionally, the zero-sequence voltage u z and the direction factor k z , determine the injected zero-sequence voltage u z The second midpoint current component i generated ouz ,include:

[0027] According to the zero-sequence voltage u z and the direction factor k zThe product of the injected zero-sequence voltage is used as the second midpoint current component i ouz .

[0028] Optionally, the first midpoint current component i ointr and the second midpoint current component i ouz , determine the average current i injected into the midpoint npv ,include:

[0029] According to the first midpoint current component i ointr and the second midpoint current component i ouz The sum of the values ​​generates the average current i injected into the midpoint npv .

[0030] Optionally, the first midpoint current component i ointr and the second midpoint current component i ouz The calculation is done using the following formula:

[0031]

[0032] Optionally, by changing the second midpoint current component i ouz , adjust the average current injected into the midpoint i npv , to control the midpoint potential balance, including:

[0033] In the zero sequence voltage u z Within the boundary value range, adjust the zero sequence voltage u z size;

[0034] By adjusting the zero-sequence voltage u z The size of the second midpoint current component i ouz ;

[0035] By adjusting the second midpoint current component i ouz , adjust the average current injected into the midpoint i npv ;

[0036] By adjusting the average current injected at the midpoint i npv The polarity and size of the resistor control the midpoint potential balance.

[0037] According to another aspect of the present invention, the midpoint potential balance control device provided in this embodiment includes:

[0038] An acquisition module, used for acquiring a three-phase modulation signal and a bridge arm current corresponding to the three-phase modulation signal;

[0039] A comparison module is used to compare the magnitudes of the three-phase modulation signals and determine the maximum value u of the modulation signal. max , minimum value u minand the intermediate value u mid ; Compare the size of the bridge arm current corresponding to the three-phase modulation signal to determine the maximum value of the bridge arm current i max , minimum value i min and the intermediate value i mid ;

[0040] A boundary value determination module is used to determine the minimum value u of the modulation signal according to the min , the middle value u mid and the maximum value u max , calculate the zero sequence voltage u z The boundary value of

[0041] A direction factor determination module is used to determine the intermediate value u of the modulation signal according to the mid , the middle value of the bridge arm current i mid , minimum value i min and the maximum value i max , determine the zero-sequence voltage u z The direction factor k z ;

[0042] The midpoint current determination module is used to determine the zero-sequence voltage u z The boundary value and the direction factor k z , adjust the average current injected into the midpoint i npv , to control the midpoint potential balance.

[0043] The control method for midpoint potential balance provided by the embodiment of the present invention obtains a three-phase modulation signal and a bridge arm current corresponding to the three-phase modulation signal. Then, the magnitude of the three-phase modulation signal is compared to determine the maximum value u of the modulation signal. max , minimum value u min and the intermediate value u mid ; Compare the size of the bridge arm current corresponding to the three-phase modulation signal to determine the maximum value of the bridge arm current i max , minimum value i min and the intermediate value i mid Then according to the minimum value u of the modulation signal min , the middle value u mid and the maximum value u max , calculate the zero sequence voltage u z The boundary value of the modulation signal. And according to the middle value u mid , the middle value of the bridge arm current i mid , minimum value i min and the maximum value i max , determine the zero sequence voltage u z The direction factor k z Then according to the zero sequence voltage u z The boundary value and direction factor kz , adjust the average current injected into the midpoint i npv , in order to control the midpoint potential balance. Compared with the existing technology of calculating the current flowing into or out of the midpoint after dividing the sectors, the technical solution provided by this embodiment determines the added zero-sequence voltage u on the basis of ensuring that the logical relationship of the three-phase modulation signal remains unchanged and does not exceed the stacked carrier boundary. z According to the middle value u of the modulation signal mid The sign of the zero-sequence voltage u that controls the midpoint voltage balance can be obtained. z The direction factor k z , thereby changing the average current injected into the midpoint i npv The polarity and size of the midpoint are used to control the midpoint potential balance. Compared with the existing method of calculating the current flowing into or out of the midpoint after sector selection, the calculation is simplified, the storage space and time overhead occupied by the program are reduced, and the efficiency of the midpoint potential balance control of the three-level inverter is improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments of the present invention. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the contents of the embodiments of the present invention and these drawings without paying any creative work.

[0045] Figure 1 is a flow chart of a midpoint potential balance control method provided by an embodiment of the present invention;

[0046] Figure 2 1 is a topological diagram of a diode-clamped three-level inverter circuit provided by an embodiment of the present invention;

[0047] Figure 3 is a schematic diagram of an equivalent circuit of a diode-clamped three-level inverter circuit provided by an embodiment of the present invention;

[0048] Figure 4 is a schematic diagram of an equivalent circuit of another diode-clamped three-level inverter circuit provided by an embodiment of the present invention;

[0049] Figure 5 is a flow chart of another midpoint potential balance control method provided by an embodiment of the present invention;

[0050] Figure 6 The embodiment of the present invention provides a method for modulating a carrier wave in a same direction when driving the carrier wave in a stacked manner. mid >0,u z >0, the zero sequence voltage u is injected zThen the up and down movement occurs to generate the carrier PWM schematic diagram;

[0051] Figure 7 The embodiment of the present invention provides a method for modulating a carrier wave in a same direction when driving the carrier wave in a stacked manner. mid >0,u z When the zero-sequence voltage u is injected z Then the up and down movement occurs to generate the carrier PWM schematic diagram;

[0052] Figure 8 The embodiment of the present invention provides a method for modulating a carrier wave in a same direction when driving the carrier wave in a stacked manner. mid <0,u z >0, the zero sequence voltage u is injected z Then the up and down movement occurs to generate the carrier PWM schematic diagram;

[0053] Fig. 9 The embodiment of the present invention provides a method for modulating a carrier wave in a same direction when driving the carrier wave in a stacked manner. mid <0,u z When the zero-sequence voltage u is injected z Then the up and down movement occurs to generate the carrier PWM schematic diagram;

[0054] Fig.10 The embodiment of the present invention provides a reverse carrier stacking drive when the modulation signal is u mid >0,u z >0, the zero sequence voltage u is injected z Then the up and down movement occurs to generate the carrier PWM schematic diagram;

[0055] Fig.11 The embodiment of the present invention provides a reverse carrier stacking drive when the modulation signal is u mid >0,u z When the zero-sequence voltage u is injected z Then the up and down movement occurs to generate the carrier PWM schematic diagram;

[0056] Fig.12 The embodiment of the present invention provides a reverse carrier stacking drive when the modulation signal is u mid <0,u z >0, the zero sequence voltage u is injected z Then the up and down movement occurs to generate the carrier PWM schematic diagram;

[0057] Fig.13 The embodiment of the present invention provides a reverse carrier stacking drive when the modulation signal is u mid <0,u z When the zero-sequence voltage u is injected z Then the up and down movement occurs to generate the carrier PWM schematic diagram;

[0058] Fig.14 It is a zero-sequence voltage u during reverse carrier stacking driving provided by an embodiment of the present invention. z Schematic diagram of carrier PWM when the value is less than the critical value;

[0059] Fig.15 It is a zero-sequence voltage u during reverse carrier stacking driving provided by an embodiment of the present invention. z Schematic diagram of carrier PWM when the value is greater than the critical value;

[0060] Fig.16 is a flow chart of another midpoint potential balance control method provided by an embodiment of the present invention;

[0061] Fig.17 It is a midpoint potential balance control block diagram provided by an embodiment of the present invention;

[0062] Fig.18 is a schematic diagram of a simulation waveform of a midpoint potential offset Δu provided by an embodiment of the present invention;

[0063] Fig.19 It is a schematic diagram of a midpoint potential balance control device provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0064] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0065] It should be noted that the terms "first", "second", etc. in the specification and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchanged where appropriate, so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units that are clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0066] Based on the above technical problems, this embodiment proposes the following solutions:

[0067] The midpoint potential balance control method provided by the embodiment of the present invention is applied to a diode clamped three-level inverter circuit.

[0068] Figure 1 is a flow chart of a method for controlling midpoint potential balance provided by an embodiment of the present invention. Figure 1 , the midpoint potential balance control method provided by the embodiment of the present invention includes:

[0069] S101, obtaining a three-phase modulation signal and a bridge arm current corresponding to the three-phase modulation signal.

[0070] Specifically, the A-phase bridge arm current i corresponding to the three-phase modulation signal is obtained respectively A , the B-phase bridge arm current i corresponding to the three-phase modulation signal B , the C-phase bridge arm current i corresponding to the three-phase modulation signal C The modulation signal includes the A phase modulation signal u A , B phase modulation signal u B and C phase modulation signal u C . And obtain the A phase modulation signal u respectively A , B phase modulation signal u B , C phase modulation signal u C .

[0071] S102, comparing the magnitudes of the three-phase modulation signals and determining the maximum value u of the modulation signal max , minimum value u min and the intermediate value u mid ; Compare the size of the bridge arm current corresponding to the three-phase modulation signal to determine the maximum value of the bridge arm current i max , minimum value i min and the intermediate value i mid .

[0072] Specifically, the A phase modulation signal u A , B phase modulation signal u B , C phase modulation signal u C Compare them and take the largest value among the three as the maximum value u of the modulation signal. max , the middle value among the three is taken as the middle value u of the modulation signal mid , the smallest value among the three is taken as the minimum value u of the modulation signal min .

[0073] The A-phase bridge arm current i corresponding to the three-phase modulation signal A , the B-phase bridge arm current i corresponding to the three-phase modulation signal B The C-phase bridge arm current i corresponding to the three-phase modulation signal CCompare them and take the largest value among the three as the maximum value i of the bridge arm current corresponding to the three-phase modulation signal. max , the middle value among the three is taken as the middle value i of the bridge arm current corresponding to the three-phase modulation signal mid The smallest value among the three is taken as the minimum value i of the bridge arm current corresponding to the three-phase modulation signal. min .

[0074] S103, according to the minimum value u of the modulation signal min , the middle value u mid and the maximum value u max , calculate the zero sequence voltage u z The boundary value of .

[0075] Specifically, on the basis of ensuring that the logical relationship of the three-phase modulation signal remains unchanged and does not exceed the stacked carrier boundary, the added zero-sequence voltage u is determined. z The boundary of zero sequence voltage u z The boundary includes the maximum boundary of zero sequence voltage u zmax and the minimum boundary u of zero sequence voltage zmin .

[0076] S104, according to the intermediate value u of the modulation signal mid , the middle value of the bridge arm current i mid , minimum value i min and the maximum value i max , determine the zero-sequence voltage u z The direction factor k z .

[0077] Specifically, the middle value u of the modulation signal mid The symbol is used to determine the injected zero-sequence voltage u z direction is the key. When the middle value u of the modulation signal mid >0, the injected zero-sequence voltage u z The direction remains unchanged; when the middle value u of the modulation signal mid ≤0, the injected zero-sequence voltage u z The direction is reversed. This eliminates the need to calculate the midpoint current after dividing the sectors and then determine the direction of the midpoint current, thus simplifying the calculation.

[0078] According to the middle value u of the modulation signal mid The sign of the modulated signal is u mid The middle value of the bridge arm current i mid The product of the bridge arm current and the minimum value i min The difference between the bridge arm current and the maximum value i max The sum of the values ​​determines the direction factor k of the zero-sequence voltage. z .

[0079] Exemplary, an optional implementation, the direction factor k of the zero-sequence voltage z It can be calculated using the following formula: z =-(i max +sgn(u mid )i mid -i min ).

[0080] Exemplarily, in another optional implementation, the direction factor k of the zero-sequence voltage is z It can also be calculated using the following formula: No limitation is made here.

[0081] S105, according to the zero sequence voltage u z The boundary value and the direction factor k z , adjust the average current injected into the midpoint i npv , to control the midpoint potential balance.

[0082] Specifically, according to the maximum boundary u of zero-sequence voltage zmax and the minimum boundary u of zero sequence voltage zmin , the average current i flowing into the midpoint when using two different forms of carrier npv After simplification, the average current i flowing into the midpoint npv The first midpoint current component i is formed by the duty cycle instruction ointr and injected zero sequence voltage u z The second midpoint current component i generated ouz Two parts. The second midpoint current component i ouz By injecting zero sequence voltage u z and the direction factor k z The first midpoint current component i formed by the duty cycle instruction ointr It is determined by the modulation signal and the bridge arm current value, but the modulation signal and the bridge arm current value are uncontrollable. z The size of the second midpoint current component i ouz The size of the injected midpoint average current i npv size, thereby controlling the midpoint potential balance.

[0083] The control method for midpoint potential balance provided in this embodiment obtains a three-phase modulation signal and a bridge arm current corresponding to the three-phase modulation signal. Then, the magnitude of the three-phase modulation signal is compared to determine the maximum value u of the modulation signal. max , minimum value u min and the intermediate value u mid ; Compare the size of the bridge arm current corresponding to the three-phase modulation signal to determine the maximum value of the bridge arm current imax , minimum value i min and the intermediate value i mid Then according to the minimum value u of the modulation signal min , the middle value u mid and the maximum value u max , calculate the zero sequence voltage u z The boundary value of the modulation signal. And according to the middle value u mid , the middle value of the bridge arm current i mid , minimum value i min and the maximum value i max , determine the zero sequence voltage u z The direction factor k z Then according to the zero sequence voltage u z The boundary value and direction factor k z , adjust the average current injected into the midpoint i npv , to control the midpoint potential balance.

[0084] Compared with the existing technology of calculating the current flowing into or out of the midpoint after dividing the sectors, the technical solution provided in this embodiment determines the added zero-sequence voltage u on the basis of ensuring that the logical relationship of the three-phase modulation signal remains unchanged and does not exceed the stacked carrier boundary. z According to the middle value u of the modulation signal mid The sign of the zero-sequence voltage u that controls the midpoint voltage balance can be obtained. z The direction factor k z , thereby changing the average current injected into the midpoint i npv The polarity and size of the midpoint are used to control the midpoint potential balance. Compared with the existing method of calculating the current flowing into or out of the midpoint after sector selection, the calculation is simplified, the storage space and time overhead occupied by the program are reduced, and the efficiency of the midpoint potential balance control of the three-level inverter is improved.

[0085] For example, Figure 2 The present invention provides a topology diagram of a diode-clamped three-level inverter circuit. Figure 3 It is a schematic diagram of an equivalent circuit of a diode-clamped three-level inverter circuit provided by an embodiment of the present invention. Figure 4 is a schematic diagram of an equivalent circuit of another diode clamped three-level inverter circuit provided by an embodiment of the present invention. Figures 2 to 4 In order to illustrate the difference between the midpoint potential balance control method of the present invention and the conventional midpoint potential balance control method, Figure 1 Taking the diode clamped inverter circuit topology shown in the figure as an example, the zero-sequence voltage u z The average current i injected into the midpoint npv .

[0086] It should be noted that Figure 2 In the example, P is shown as the positive pole, N is the negative pole, and O is the midpoint. SA1-SA4 are the drive signals of the A-phase power semiconductor device, SB1-SB4 are the drive signals of the B-phase power semiconductor device, and SC1-SC4 are the drive signals of the C-phase power semiconductor device. C1 is the first capacitor between P and O, and C2 is the second capacitor between N and O. The voltage across the first capacitor is Udc1, and the voltage across the second capacitor is Udc2. L is the load inductance, and R is the load resistance.

[0087] The working principle of the diode clamped three-level inverter is based on the neutral point clamped (NPC) topology. It achieves three-level output by adding a pair of clamping diodes on the basis of two power semiconductor devices in series. The main components of the three-level inverter include power semiconductor devices and fast recovery diodes.

[0088] It should be noted that Figure 3 and Figure 4 for Figure 2 Equivalent circuit diagram of .

[0089] Depend on Figure 3 It can be seen that the average current injected into the midpoint O in the POO state is i A .Depend on Figure 4 It can be seen that the average current injected into the midpoint O in the ONN state is -i A Since POO and ONN are a pair of complementary small vectors, the magnitude of the average current injected into the midpoint under the action of the complementary small vectors is the same, but the direction is opposite. Similarly, the average current injected into the midpoint under the action of the remaining 5 pairs of complementary small vectors can be obtained as np The average current injected into the midpoint under the action of each different small vector is shown in Table 1.

[0090] Table 1 shows the midpoint current under the action of small vector

[0091]

[0092]

[0093] It can be seen from Table 1 that when the switch state of each phase is O, it will cause the midpoint current to change. Introducing the switching function

[0094] When the switch state of each phase is P, S i =1; when each phase switch state is O state, S i =0; when the switch state of each phase is N state, S i = -1. According to the summary in Table 1, the switch function S A , S B and S C The average injection midpoint current i is directly derivednp for:

[0095] i np =(1-|S A |)i A +(1-|S B |)i B +(1-|S C |)i C (1).

[0096] Since the midpoint current changes only when the switch state of each phase is in the O state, it is necessary to calculate the time when the switch state of each phase is in the O state. Define the time when the switch state of phases A, B, and C is in the O state in a switching cycle as T o , T0=(1-|u x |)T s , x=A,B,C,u x represents the three-phase modulation signal of A, B, and C, then the duty cycle in the O state is 1-|u x |, formula (1) can be further simplified as:

[0097] i np =(1-|u A |)i A +(1-|u B |)i B +(1-|u C |)i C (2).

[0098] Define the maximum, middle and minimum values ​​of the three-phase modulation signals A, B and C as u respectively. max 、u mid and u min ,i max 、i mid and i min is the maximum, middle and minimum value of the bridge arm current corresponding to the three-phase modulation signal. Assuming that the zero-sequence voltage is u z , give A, B, C three-phase modulation signal u x Add zero sequence voltage u z After that, the new modulation signal becomes u′ x , where u′ x =u x +u0, at this time the duty cycle in the O state becomes 1-|u′ x |, substituting into formula (2), we can get the injected zero-sequence voltage u z The average current i flowing into the midpoint during the next switching cycle npv for:

[0099] i npv =(1-|u max+u z |)i max +(1-|u mid +u z |)i mid +(1-|u min +u z |)i min (3).

[0100] Optional, Figure 5 FIG. 1 is a flow chart of another midpoint potential balance control method provided by an embodiment of the present invention. Figure 5 , the midpoint potential balance control method provided by the embodiment of the present invention includes:

[0101] S101, obtaining a three-phase modulation signal and a bridge arm current corresponding to the three-phase modulation signal.

[0102] S102, comparing the magnitudes of the three-phase modulation signals and determining the maximum value u of the modulation signal max , minimum value u min and the intermediate value u mid ; Compare the size of the bridge arm current corresponding to the three-phase modulation signal to determine the maximum value of the bridge arm current i max , minimum value i min and the intermediate value i mid .

[0103] S201, when the middle value u of the modulation signal mid When it is greater than zero, according to the minimum value u of the modulation signal min , the intermediate value u mid and the maximum value u max , the zero-sequence voltage u is calculated based on the first objective function z The first boundary value of .

[0104] Specifically, the average current i injected into the midpoint npv Based on the diode clamped three-level inverter topology, the influence of 6 pairs of complementary small vectors on the injected midpoint current is analyzed, and then the average current i injected into the midpoint is derived. npv The zero vector and the large vector will not affect the offset of the midpoint potential, and the effect of the medium vector on the offset of the midpoint potential is uncertain, so only the effect of the small vector is considered.

[0105] Zero sequence voltage u z The first boundary value is: max(-1-u min ,-u mid )≤u z ≤ min (1-u max ,-u min).

[0106] S202: When the middle value of the modulation signal is less than or equal to zero, according to the minimum value u of the modulation signal min , the intermediate value u mid and the maximum value u max , the zero-sequence voltage u is calculated based on the second objective function z The second boundary value of the zero-sequence voltage u z The boundary values ​​include the first boundary value and the second boundary value.

[0107] Specifically, the zero-sequence voltage u z The second boundary value of is: max (-1-u max ,-u max )≤u z ≤ min (1-u max ,-u mid ).

[0108] Optionally, based on the above embodiment, the first boundary value and the second boundary value may be calculated using the following formula:

[0109]

[0110] Among them, u max is the maximum value of the modulation signal, u mid is the middle value of the modulation signal and u min is the minimum value of the modulation signal.

[0111] For example, the added zero-sequence voltage u is calculated in the case of co-directional carrier stacking and reverse carrier stacking. z the border.

[0112] From formula (3), it can be seen that by injecting zero-sequence voltage u z The average current i flowing into the midpoint can be changed npv , control the balance of the midpoint voltage, consider increasing u z The basic principle is to ensure the maximum value u of the three-phase modulation signal max , the middle value u mid , minimum value u min The logical relationship of the three-phase modulation signal remains unchanged and does not exceed the boundary of the stacked carrier, so the zero-sequence voltage u is obtained z The border size.

[0113] First, calculate the zero-sequence voltage u when the same-direction carrier is stacked z The boundary value of . Figure 6 The embodiment of the present invention provides a method for modulating a carrier wave in a same direction when driving the carrier wave in a stacked manner. mid>0,u z >0, the zero sequence voltage u is injected z Then up and down movement occurs to generate the carrier PWM schematic diagram. Figure 7 The embodiment of the present invention provides a method for modulating a carrier wave in a same direction when driving the carrier wave in a stacked manner. mid >0,u z When the zero-sequence voltage u is injected z Then up and down movement occurs to generate the carrier PWM schematic diagram. Figure 8 The embodiment of the present invention provides a method for modulating a carrier wave in a same direction when driving the carrier wave in a stacked manner. mid <0,u z >0, the zero sequence voltage u is injected z Then up and down movement occurs to generate the carrier PWM schematic diagram. Fig. 9 The embodiment of the present invention provides a method for modulating a carrier wave in a same direction when driving the carrier wave in a stacked manner. mid <0,u z When the zero-sequence voltage u is injected z Then up and down movement occurs to generate the carrier PWM schematic diagram.

[0114] Depend on Figures 6 to 9 The following relationship can be obtained:

[0115]

[0116]

[0117] To sum up:

[0118]

[0119] It should be noted that Figures 6 to 9 In the figure, the changes of the modulation signal and PWM signal when the same-direction carrier is stacked and driven. The dotted line is the original modulation signal, the solid line is the modulation signal after the zero-sequence voltage is injected, and the yellow rectangle indicates the change area of ​​the PWM signal width after the zero-sequence voltage is injected.

[0120] Second, calculate the zero-sequence voltage u in the case of reverse carrier stacking z The boundary value of . Fig.10 The embodiment of the present invention provides a reverse carrier stacking drive when the modulation signal is u mid >0,u z >0, the zero sequence voltage u is injected z Then up and down movement occurs to generate the carrier PWM schematic diagram. Fig.11 The embodiment of the present invention provides a reverse carrier stacking drive when the modulation signal is u mid >0,u z When the zero-sequence voltage u is injected zThen up and down movement occurs to generate the carrier PWM schematic diagram. Fig.12 The embodiment of the present invention provides a reverse carrier stacking drive when the modulation signal is u mid <0,u z >0, the zero sequence voltage u is injected z Then up and down movement occurs to generate the carrier PWM schematic diagram. Fig.13 The embodiment of the present invention provides a reverse carrier stacking drive when the modulation signal is u mid <0,u z When the zero-sequence voltage u is injected z Then up and down movement occurs to generate the carrier PWM schematic diagram.

[0121] It should be noted that Figures 10 to 13 In the figure, the changes of the modulation signal and PWM signal during reverse carrier stacking drive. The dotted line is the original modulation signal, the solid line is the modulation signal after the zero-sequence voltage is injected, and the yellow rectangle indicates the change area of ​​the PWM signal width after the zero-sequence voltage is injected.

[0122] Fig.14 It is a zero-sequence voltage u during reverse carrier stacking driving provided by an embodiment of the present invention. z Schematic diagram of carrier PWM when the voltage is less than the critical value. Fig.15 It is a zero-sequence voltage u during reverse carrier stacking driving provided by an embodiment of the present invention. z Schematic diagram of carrier PWM when the value is greater than the critical value. Figures 10 to 15 , if the zero-sequence voltage u z Less than the critical value, (10-1) vector action time t mid for:

[0123] t mid =-(2u z +u mid +u min )T s (5).

[0124] Injected zero sequence voltage u z After that, the time t of the vector action (100) uz for:

[0125] t uz =2u z T s (6).

[0126] In this case, the current i flowing into the midpoint of the switching cycle npv for:

[0127] i npv =i mid t mid +(-imax )t uz

[0128] =[-(u mid +u min )i mid -2u z (i max +i mid )]T s

[0129] =[-(u mid +u min )i mid +2u z i min ]T s (7).

[0130] If u z Greater than the critical value, the time t of the (110) vector action mid for:

[0131] t mid =(2u z +u mid +u min )T s (8).

[0132] Injected zero sequence voltage u z After that, the time t of the vector action (100) uz for:

[0133] t uz =(2u z -t mid )T s (9).

[0134] In this case, the current i flowing into the midpoint of the switching cycle npv for:

[0135] i npv =i min t mid -i max t uz

[0136] =[(2u z +u mid +u min )i min +(u mid +u min )i max ]T s

[0137] =[-(u mid +u min)i mid +2u z i min ]T s (10).

[0138] From the above derivation, we can know that the zero-sequence voltage u z The average current injected at the midpoint greater than the critical value and the average current injected at the midpoint less than the critical value are the same in one switching cycle, which are both the system midpoint current before the superposition vector plus the minimum current of the modulation wave amplitude at the zero-sequence voltage. Therefore, the zero-sequence voltage u under the reverse carrier superposition z The boundary value of is the same as that of the same-direction carrier stacking. Similarly, in other cases, the zero-sequence voltage u z The boundary of can also be verified using the above method, which will not be repeated here.

[0139] S104, according to the intermediate value u of the modulation signal mid , the middle value of the bridge arm current i mid , minimum value i min and the maximum value i max , determine the zero-sequence voltage u z The direction factor k z .

[0140] In an optional implementation manner, according to the intermediate value u of the modulation signal mid , the middle value of the bridge arm current i mid , minimum value i min and the maximum value i max , determine the zero-sequence voltage u z The direction factor k z ,include:

[0141] k z =-(i max +sgn(u mid )i mid -i min ),or,

[0142] S105, according to the zero sequence voltage u z The boundary value and the direction factor k z , adjust the average current injected into the midpoint i npv , to control the midpoint potential balance.

[0143] Specifically, according to the determined zero-sequence voltage u z The maximum boundary u zmax and zero sequence voltage u z The minimum boundary u zmin , the simplified injection midpoint average current i npv, the average current i injected into the midpoint npv The first midpoint current component i is formed by the duty cycle instruction ointr and injected zero sequence voltage u z The second midpoint current component i generated ouz Two parts.

[0144] In an optional implementation manner, according to the zero-sequence voltage u z The boundary value and the direction factor k z , adjust the average current injected into the midpoint i npv , to control the midpoint potential balance, including:

[0145] According to the zero-sequence voltage u z The boundary value of the zero-sequence voltage u z .

[0146] According to the maximum value u of the three-phase modulation signal max , the middle value u mid and the minimum value u min , and the maximum value of the bridge arm current i max , minimum value i min and the intermediate value i mid , determine the first midpoint current component i formed by the duty cycle instruction of the three-phase modulation signal in the O state ointr .

[0147] According to the zero-sequence voltage u z and the direction factor k z , determine the injected zero-sequence voltage u z The second midpoint current component i generated ouz .

[0148] According to the first midpoint current component i ointr and the second midpoint current component i ouz , determine the average current i injected into the midpoint npv .

[0149] By changing the second midpoint current component i ouz , adjust the average current injected into the midpoint i npv , to control the midpoint potential balance.

[0150] Specifically, by setting the zero-sequence voltage u z The boundary value and direction factor k z , determine the second midpoint current component i injected into the midpoint ouz , according to the maximum value u of the three-phase modulation signal max , the middle value u mid and the minimum value u min And the maximum value of the corresponding bridge arm current imax , minimum value i min and the intermediate value i mid , determine the first midpoint current component i formed by the duty cycle instruction of the modulation signal in the O state ointr , and then determine the average current i injected into the midpoint npv .

[0151] Optionally, based on the above embodiment, according to the zero-sequence voltage u z and the direction factor k z , determine the injected zero-sequence voltage u z The second midpoint current component i generated ouz ,include:

[0152] According to the zero sequence voltage u z and the direction factor k z The product of the injected zero-sequence voltage is used as the second midpoint current component i ouz .

[0153] Optionally, based on the above embodiments, according to the first midpoint current component i ointr and the second midpoint current component i ouz , determine the average current i injected into the midpoint npv ,include:

[0154] According to the first midpoint current component i ointr and the second midpoint current component i ouz The sum of the values ​​generates the average current i injected into the midpoint npv .

[0155] Optionally, the first midpoint current component i ointr and the second midpoint current component i ouz The calculation is done using the following formula:

[0156]

[0157] Among them, i ointr is the first midpoint current component, i ouz is the second midpoint current component.

[0158] Specifically, in the zero-sequence voltage u z Under the constraint of boundary conditions, equation (3) is simplified and the simplified result is as follows:

[0159]

[0160] When the zero-sequence voltage u is injected z After that, i npv Divide into two parts and define i ointr is the first midpoint current component formed by the duty cycle command, iouz is the second midpoint current component generated by injecting zero-sequence voltage, where i ointr and i ouz The expression is as follows:

[0161]

[0162] Definition of the injected zero-sequence voltage u z The second midpoint current component i ouz The direction factor is k z , let k z =-(i max +sgn(u mid )i mid -i min ), formula (12) can be simplified as: npv =i ointr +u z k z .

[0163] According to i ouz =k z u z It can be seen that when the middle value u of the three-phase modulation signal mid >0, the direction factor k z Greater than 0, the zero-sequence voltage u injected into the midpoint z The direction remains unchanged, and the zero-sequence voltage u is injected z The second midpoint current component i generated ouz Also remains unchanged; when the middle value u of the three-phase modulation signal mid <0, the direction factor k z Less than 0, the zero-sequence voltage u injected into the midpoint z In the opposite direction to the original direction, the zero-sequence voltage u is injected z The generated midpoint current i ouz It is also opposite to the original direction.

[0164] Optional, Fig.16 FIG. 1 is a flow chart of another method for controlling midpoint potential balance provided by an embodiment of the present invention. Fig.16 , the midpoint potential balance control method provided by the embodiment of the present invention includes:

[0165] S101, obtaining a three-phase modulation signal and a bridge arm current corresponding to the three-phase modulation signal.

[0166] S102, comparing the magnitudes of the three-phase modulation signals and determining the maximum value u of the modulation signal max , minimum value u min and the intermediate value u mid; Compare the size of the bridge arm current corresponding to the three-phase modulation signal to determine the maximum value of the bridge arm current i max , minimum value i min and the intermediate value i mid .

[0167] S103, according to the minimum value u of the modulation signal min , the middle value u mid and the maximum value u max , calculate the zero sequence voltage u z The boundary value of .

[0168] S104, according to the intermediate value u of the modulation signal mid , the middle value of the bridge arm current i mid , minimum value i min and the maximum value i max , determine the zero-sequence voltage u z The direction factor k z .

[0169] S301, in the zero sequence voltage u z Within the boundary value range, adjust the zero sequence voltage u z size.

[0170] S302, by adjusting the zero sequence voltage u z The magnitude and direction factor k z , adjust the second midpoint current component i ouz .

[0171] S303, by adjusting the second midpoint current component i ouz , adjust the average current injected into the midpoint i npv .

[0172] S304, by adjusting the average current i injected at the midpoint npv The polarity and size of the resistor control the midpoint potential balance.

[0173] Specifically, add the zero-sequence voltage u z After the midpoint current i is injected npv It consists of two parts, namely the first midpoint current component i ointr and the second midpoint current component i ouz According to the maximum value u of the three-phase modulation signal max , the middle value u mid and the minimum value u min And the maximum value of the bridge arm current i max , minimum value i min and the intermediate value i mid , determine the first midpoint current component i formed by the duty cycle instruction of the modulation signal in the O stateointr According to the zero sequence voltage u z The boundary value and direction factor k z , determine the second midpoint current component i injected into the midpoint ouz Then according to the first midpoint current component i ointr and the second midpoint current component i ouz , determine the average current i injected into the midpoint npv .

[0174] Among them, the first midpoint current component i ointr is uncontrollable because the first midpoint current component i ointr is the three-phase modulation signal and the corresponding bridge arm current. The second midpoint current component i ouz is controllable, the second midpoint current component i ouz By adjusting the zero sequence voltage u z The size of the second midpoint current component i ouz Therefore, by changing the second midpoint current component i ouz The size of the injected midpoint average current i npv , achieving midpoint potential balance.

[0175] Specifically, Fig.17 This is a midpoint potential balance control block diagram provided by an embodiment of the present invention. Fig.17 , according to the average current i injected at the midpoint npv The mathematical model of the first midpoint current component i formed by the duty cycle instruction ointr As a disturbance, a standard model is established to control the midpoint balance. The key to achieving midpoint potential balance is to control the average current i injected into the midpoint. npv is 0, at which point the charging and discharging of the capacitor of the BUS busbar reaches a balance, thus preventing the midpoint potential from shifting.

[0176] Continue to see Fig.17 , as long as you know the voltage intermediate value u mid The sign of the zero-sequence voltage u that controls the midpoint voltage balance can be obtained. z The direction factor k z , and then the injected zero-sequence voltage u is obtained z The average current injected into the midpoint is i npv This setting saves the need to calculate the current flowing into or out of the midpoint after dividing the sector, thus simplifying the calculation.

[0177] Determine the injected zero-sequence voltage u z Direction factor k z It can be further simplified to:

[0178]

[0179] According to the simplified k z The above average injection midpoint current i can be further simplified npv mathematical model to simplify the calculation.

[0180] Fig.18 is a schematic diagram of a simulation waveform of a midpoint potential offset Δu provided by an embodiment of the present invention. Fig.18 According to the above method provided by the embodiment of the present invention, simulation is performed in Simulink, and the voltage offset Δu across the BUS capacitor is less than 1V, which effectively realizes the balanced control of the midpoint potential.

[0181] This embodiment provides a control device for midpoint potential balance. Fig.19 Schematic diagram of a midpoint potential balance control device provided by an embodiment of the present invention. Fig.19 The midpoint potential balance control device provided in this embodiment includes:

[0182] An acquisition module 41 is used to acquire a three-phase modulation signal and a bridge arm current corresponding to the three-phase modulation signal;

[0183] The comparison module 42 is used to compare the magnitudes of the three-phase modulation signals and determine the maximum value u of the modulation signal. max , minimum value u min and the intermediate value u mid ; Compare the size of the bridge arm current corresponding to the three-phase modulation signal to determine the maximum value of the bridge arm current i max , minimum value i min and the intermediate value i mid ;

[0184] The boundary value determination module 43 is used to determine the minimum value u of the modulation signal according to the minimum value u of the modulation signal. min , the middle value u mid and the maximum value u max , calculate the zero sequence voltage u z The boundary value of

[0185] Direction factor determination module 44, used for determining the direction factor according to the intermediate value u of the modulation signal mid , the middle value of the bridge arm current i mid , minimum value i min and the maximum value i max , determine the zero-sequence voltage u z The direction factor k z ;

[0186] The midpoint current determination module 45 is used to determine the current according to the zero-sequence voltage u z The boundary value and the direction factor k z, adjust the average current injected into the midpoint i npv , to control the midpoint potential balance.

[0187] Optionally, the midpoint current determination module 45 is specifically configured to determine the maximum value u of the three-phase modulation signal according to the value u of the three-phase modulation signal. max , the middle value u mid and the minimum value u min And the maximum value of the bridge arm current i max , minimum value i min and the intermediate value i mid , determine the first midpoint current component i formed by the duty cycle instruction of the modulation signal in the O state ointr According to the zero sequence voltage u z The boundary value and direction factor k z , determine the second midpoint current component i injected into the midpoint ouz , and then determine the average current i injected into the midpoint npv .

[0188] The control device for midpoint potential balance provided in this embodiment analyzes the influence of the small vector on the midpoint current and then derives the injected zero-sequence voltage u z The average current i injected into the midpoint of the three-level inverter npv The mathematical model of the injected zero-sequence voltage u is then determined under the conditions of in-phase carrier stacking and reverse carrier stacking. z Finally, at the zero-sequence voltage u z Under the boundary of npv Control modeling was performed, and the effectiveness of the midpoint potential balance control device provided by the embodiment of the present invention was verified through experiments. Compared with the traditional midpoint potential balance control device, the midpoint potential balance control device provided by the embodiment of the present invention can reduce the complexity of program judgment logic, reduce program storage space and time overhead, and improve the utilization rate of the control chip to achieve midpoint potential balance control of the three-level inverter.

[0189] Note that the above are only preferred embodiments of the present invention and the technical principles used. Those skilled in the art will understand that the present invention is not limited to the specific embodiments described herein, and that various obvious changes, readjustments and substitutions can be made by those skilled in the art without departing from the scope of protection of the present invention. Therefore, although the present invention has been described in more detail through the above embodiments, the present invention is not limited to the above embodiments, and may include more other equivalent embodiments without departing from the concept of the present invention, and the scope of the present invention is determined by the scope of the appended claims.

Claims

1. A method for controlling midpoint potential balance, characterized in that: include: Acquire a three-phase modulation signal and a bridge arm current corresponding to the three-phase modulation signal; Compare the magnitudes of the three-phase modulation signals and determine the maximum value u of the modulation signal max , minimum value u min and the intermediate value u mid ; Compare the size of the bridge arm current corresponding to the three-phase modulation signal to determine the maximum value of the bridge arm current i max , minimum value i min and the intermediate value i mid ; According to the minimum value u of the modulation signal min , the middle value u mid and the maximum value u max , calculate the zero sequence voltage u z The boundary value of According to the intermediate value u of the modulation signal mid , the middle value of the bridge arm current i mid , minimum value i min and the maximum value i max , determine the zero-sequence voltage u z The direction factor k z ; According to the zero-sequence voltage u z The boundary value and the direction factor k z , adjust the average current injected into the midpoint i npv , to control the midpoint potential balance.

2. The method according to claim 1, characterized in that: The minimum value u of the modulation signal min , the middle value u mid and the maximum value u max , calculate the zero sequence voltage u z The boundary values ​​include: When the middle value u of the modulation signal mid When it is greater than zero, according to the minimum value u of the modulation signal min , the intermediate value u mid and the maximum value u max , the zero-sequence voltage u is calculated based on the first objective function z The first boundary value of When the intermediate value of the modulation signal is less than or equal to zero, according to the minimum value u of the modulation signal min , the intermediate value u mid and the maximum value u max , the zero-sequence voltage u is calculated based on the second objective function z The second boundary value of the zero-sequence voltage u z The boundary values ​​include the first boundary value and the second boundary value.

3. The method according to claim 2, characterized in that The zero sequence voltage u z The first boundary value and the second boundary value are calculated using the following formula:

4. The method according to claim 2, characterized in that: The intermediate value u of the modulation signal mid , the middle value of the bridge arm current i mid , minimum value i min and the maximum value i max , determine the zero-sequence voltage u z The direction factor k z , include: k z =-(i max +sgn(u mid )i mid -i min )someone, 5. The method according to claim 1, characterized in that: According to the zero sequence voltage u z The boundary value and the direction factor k z , adjust the average current injected into the midpoint i npv , to control the midpoint potential balance, including: According to the zero-sequence voltage u z The boundary value of the zero-sequence voltage u z ; According to the maximum value u of the three-phase modulation signal max , the middle value u mid and the minimum value u min , and the maximum value of the bridge arm current i max , minimum value i min and the intermediate value i mid , determine the first midpoint current component i formed by the duty cycle instruction of the three-phase modulation signal in the O state ointr ; According to the zero-sequence voltage u z and the direction factor k z , determine the injected zero-sequence voltage u z The second midpoint current component i generated ouz ; According to the first midpoint current component i ointr and the second midpoint current component i ouz , determine the average current i injected into the midpoint npv ; By changing the second midpoint current component i ouz , adjust the average current injected into the midpoint i npv , to control the midpoint potential balance.

6. The method according to claim 5, characterized in that According to the zero sequence voltage u z and the direction factor k z , determine the injected zero-sequence voltage u z The second midpoint current component i generated ouz ,include: According to the zero-sequence voltage u z and the direction factor k z The product of the injected zero-sequence voltage is used as the second midpoint current component i ouz .

7. The method according to claim 5, characterized in that According to the first midpoint current component i ointr and the second midpoint current component i ouz , determine the average current i injected into the midpoint npv ,include: According to the first midpoint current component i ointr and the second midpoint current component i ouz The sum of the values ​​generates the average current i injected into the midpoint npv .

8. The method according to claim 5, characterized in that The first midpoint current component i ointr and the second midpoint current component i ouz The calculation is done using the following formula:

9. The method according to claim 5, characterized in that By changing the second midpoint current component i ouz , adjust the average current injected into the midpoint i npv , to control the midpoint potential balance, including: In the zero sequence voltage u z Within the boundary value range, adjust the zero sequence voltage u z size; By adjusting the zero-sequence voltage u z The size of the second midpoint current component i ouz ; By adjusting the second midpoint current component i ouz , adjust the average current injected into the midpoint i npv ; By adjusting the average current injected at the midpoint i npv The polarity and size of the resistor control the midpoint potential balance.

10. A midpoint potential balance control device, characterized in that: include: An acquisition module, used for acquiring a three-phase modulation signal and a bridge arm current corresponding to the three-phase modulation signal; A comparison module is used to compare the magnitudes of the three-phase modulation signals and determine the maximum value u of the modulation signal. max , minimum value u min and the intermediate value u mid ; Compare the size of the bridge arm current corresponding to the three-phase modulation signal to determine the maximum value of the bridge arm current i max , minimum value i min and the intermediate value i mid ; A boundary value determination module is used to determine the minimum value u of the modulation signal according to the min , the middle value u mid and the maximum value u max , calculate the zero sequence voltage u z The boundary value of A direction factor determination module is used to determine the intermediate value u of the modulation signal according to the mid , the middle value of the bridge arm current i mid , minimum value i min and the maximum value i max , determine the zero-sequence voltage u z The direction factor k z ; The midpoint current determination module is used to determine the zero-sequence voltage u z The boundary value and the direction factor k z , adjust the average current injected into the midpoint i npv , to control the midpoint potential balance.

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