CN116865548A - Z-source inverter control method and device for optimizing switching loss under variable power factor - Google Patents

Abstract

The invention discloses a Z-source inverter control method and device for optimizing switching loss under variable power factor. The method is based on a space vector control method. The method includes: through the voltage reference vector and the coordinate axis α in the α - β coordinate system The angle θ of the axis and the modulation degree M corresponding to the voltage reference vector are combined with the sector to calculate the action time of the voltage vector and the through-vector insertion zero vector action time; according to the set switch state and basic voltage vector, vector action time and The switching sequence is determined by inserting the zero vector action time of the cut-through vector and the sector where the voltage reference vector is located; controlling the insertion method of the cut-through vector according to the change of the load power factor, and determining the loss-optimized switching sequence in combination with the switching sequence to achieve variable power factor Z source inverter control. The present invention realizes that the through current passing through the switching device is offset by the AC side output current as much as possible to achieve lower switching loss and conduction loss effects.

Description

A Z-source inverter control method with switching loss optimization under variable power factor and device

Technical field

The present invention relates to the field of power electronics technology, and in particular to a Z-source inverter control method and device for optimizing switching loss under variable power factor.

Background technique

In the field of fuel cells or photovoltaic power generation, due to the unstable voltage, a two-stage inverter is generally required, that is, the DC voltage is first boosted and converted, and then a traditional inverter is used to convert the DC into AC. The discovery of the Z-source inverter (ZSI) can replace the two-stage structure and achieve DC link voltage boost by adding a Z-source network and a special pass-through modulation method. Not only that, the special structure of the Z-source inverter allows it to achieve direct connection between the upper and lower bridge arms. Therefore, the Z-source inverter does not need to consider the dead zone, which increases the reliability of the system.

The development of Z-source inverter modulation also follows the development of topology. The early modulation method of Z-source inverter generally adopts the carrier-based modulation method. On this basis, control methods such as simple boost modulation, maximum boost modulation, and maximum constant boost modulation have been developed. Early modulation methods mainly focused on exploring the topological boost capability and device voltage and current stress. Since then, space vector modulation has been developed, including a series of modulation methods such as ZSVM6, ZSVM4, ZSVM2 and ZSVM1 among the ZSVMs (Z-source inverter space vector modulations) modulation methods. In recent years, Z-source inverter modulation methods have made a lot of progress in reducing switching losses and optimizing inductor ripple. However, the new modulation method lacks a modulation method that combines power factor changes, and cannot achieve better loss effects when the power factor changes. Therefore, it makes sense to discuss issues such as switching losses under varying power factors.

Contents of the invention

In order to solve the above problems, the present invention proposes a Z-source inverter control method and device that optimizes switching loss under variable power factor.

The present invention is implemented according to the following technical solutions:

In a first aspect, the present invention provides a Z-source inverter control method with switching loss optimization under variable power factor. The method is based on a space vector control method and includes:

Set the switching state and basic voltage vector of the three-phase two-level Z source inverter bridge arm;

Set the voltage reference vector that needs to be modulated by the three-phase two-level Z source inverter, and determine the sector where the voltage reference vector is located;

Through the angle θ between the voltage reference vector and the coordinate axis α in the α-β coordinate system, and the modulation degree M corresponding to the voltage reference vector, the action time of the voltage vector and the action time of the through vector insertion zero vector are calculated based on the sector in which it is located;

The switching sequence is determined according to the set switching state and basic voltage vector, vector action time and through vector insertion zero vector action time, as well as the sector where the voltage reference vector is located;

Calculate the load power factor by collecting the AC side current and voltage of the load;

The insertion method of the pass-through vector is controlled according to the change of the load power factor, and the loss-optimized switching sequence is determined in combination with the switching sequence to realize Z-source inverter control under variable power factor.

In one implementation, the setting of the three-phase bridge arm switching state of the three-phase two-level Z source inverter includes:

When the switch state is 1, the upper arm switching device is turned on and the lower arm switching device is closed;

When the switch state is 0, the upper arm switching device is turned off and the lower arm switching device is turned on;

When the switch state is sh, the upper arm switching device and the lower arm switching device are turned on at the same time.

In one implementation, according to the switching status of the three-phase bridge arm of the three-phase two-level Z source inverter, 8 basic voltage vectors are obtained, which are recorded as voltage vectors V ₀ , V ₁ , V ₂ , V ₃ , respectively. V ₄ , V ₅ , V ₆ and V ₇ ; the switching state combinations corresponding to the 8 basic voltage vectors are the A-phase switching state, B-phase switching state and C-phase switching state. The specific states are as follows:

The switch state corresponding to the voltage vector V0 is (000);

The switching state corresponding to the voltage vector V1 is (100);

The switching state corresponding to the voltage vector V2 is (110);

The switch state corresponding to voltage vector V3 is (010);

The switch state corresponding to the voltage vector V4 is (011);

The switch state corresponding to voltage vector V5 is (001);

The switch state corresponding to the voltage vector V6 is (101);

The switch state corresponding to voltage vector V7 is (111);

Among them, V ₀ and V ₇ are zero vectors, and the other six voltage vectors are non-zero vectors; any bridge arm of the Z-source inverter can form a pass-through vector Vsh by adopting a pass-through state. The switch state combinations corresponding to the pass-through vector Vsh include: (shXX), (XshX) and (XXsh); among them,

In one implementation, the determination of the sector where the voltage reference vector is located includes:

On the α-β axis static coordinate system, starting from the direction of the α axis, the counterclockwise direction is divided into six 60° sectors, and each sector is named sector 1 to sector according to the number along the counterclockwise direction. 6;

Project the voltage reference vector onto the coordinate axes α and β axes, and their components are respectively recorded as the voltage reference vector α axis component V _α and the voltage reference vector β axis component V _β ;

The sector where the voltage reference vector is located is determined based on the α-axis component V _α of the voltage reference vector and the β-axis component V _β of the voltage reference vector.

In one implementation, the angle θ between the voltage reference vector and the coordinate axis α in the α-β coordinate system is:

Among them, V _α and V _β are the components that project the voltage reference vector onto the coordinate axes α and β respectively; the modulation degree M corresponding to the voltage reference vector is:

Among them, V _dc is the DC link voltage of the Z-source inverter, and |V _ref | is the voltage reference vector amplitude.

In one implementation, the action time of the voltage vector is:

Among them, T _s is the switching period, Modulation degree, i is the sector number; the first sector T ₁ is the action time of the basic voltage vector V ₁ , T ₂ is the action time of the voltage vector V ₂ ; the second sector T ₁ is the action time of the voltage vector V ₂ , and T ₂ is The voltage vector V ₃ acts on time; the third sector T ₁ is the voltage vector V ₃ acts on time, T ₂ is the voltage vector V ₄ acts on time; the fourth sector T ₁ is the voltage vector V ₄ acts on time, T ₂ is the voltage vector V ₅ action time; the fifth sector T ₁ is the voltage vector V ₅ action time, T ₂ is the voltage vector V ₆ action time; the sixth sector vector T ₁ is the voltage vector V ₆ action time, T ₂ is the voltage vector V ₁ action time; T ₀ is the action time of voltage vectors V ₀ and V ₇ ;

When the pass-through vector all occupies the zero vector action time, its pass-through duty cycle can be expressed as:

Since the zero vector action time T ₀ does not necessarily use all through vectors, D ₀ is defined below,

Among them, D ₀ represents the ratio of through time to T ₀ time. When D ₀ <1, the zero vector action time is not all the through vector action time.

In one implementation, the method of controlling the insertion of the pass-through vector according to changes in load power factor specifically includes:

When using a resistive-inductive load, when its power factor angle is φ, the original sector switching sequence will not be changed, and the sequence of generated pass-through vectors will be delayed backward by φ angle; when its power factor angle is between 0 and φ, The sixth sector in the original ZSVM2 modulation method uses the pass-through bridge arm as the bridge arm inserted by the pass-through vector; when its power factor angle is between φ-π/3, the first sector of the original ZSVM2 is used as the pass-through insertion bridge arm.

In one implementation, if a resistive-capacitive load is used and the current leads the voltage, the through vector generation position will move forward accordingly.

In a second aspect, the present invention provides a Z-source inverter control device with optimized switching loss under variable power factor, which device includes:

Setting module one is used to set the switching state and basic voltage vector of the three-phase bridge arm of the three-phase two-level Z source inverter;

Setting module two is used to set the voltage reference vector that needs to be modulated by the three-phase two-level Z source inverter, and determine the sector where the voltage reference vector is located;

The vector action time calculation module is used to obtain the angle θ between the voltage reference vector and the coordinate axis α in the α-β coordinate system and the modulation degree M corresponding to the voltage reference vector according to the setting of the setting module 2, and combine it with the fan The area calculates the action time of the voltage vector and the action time of the through vector insertion zero vector;

The switch sequence generation module is used to determine the switch sequence based on the settings of the setting module one, the action time of the voltage vector calculated by the vector action time calculation module, the zero vector action time of the through vector insertion, and the sector where the voltage reference vector is located;

The load power factor module is used to calculate the load power factor by collecting the AC side current and voltage of the load;

The pass-through vector optimization module is used to control the insertion method of the pass-through vector according to the change of load power factor, and determine the loss-optimized switching sequence in combination with the switching sequence to realize Z-source inverter control under variable power factor.

In one embodiment, the second setting module includes a reference voltage given module and a sector judgment module; the reference voltage given module is used to give the voltage reference vector to be modulated; the sector judgment module , used to determine the sector where the voltage reference vector is located; the vector action time calculation module includes a vector time calculation module and a through time calculation module; the vector action time calculation module is used to pass the voltage reference vector and α-β The angle θ of the coordinate axis α in the coordinate system and the modulation degree M corresponding to the voltage reference vector are combined with the sector to calculate the action time of the voltage vector; the through time calculation module is used to calculate based on the zero vector action time. Through vector action time.

In a third aspect, the present invention provides a Z-source inverter control system, which system includes a three-phase two-level Z-source inverter module and any one of the above-mentioned Z-sources with optimized switching loss under variable power factor. Inverter control unit.

Beneficial effects of the present invention:

The invention is suitable for Z source/quasi-Z source inverters that do not use all bridge arms for pass-through modulation strategy in one switching cycle; the invention realizes the pass-through of the switching sequence in a sector according to the change of load power factor. By changing the insertion method, the through current passing through the switching device is offset by the AC side output current as much as possible, thereby achieving lower switching losses and conduction losses.

Description of the drawings

In order to more clearly explain the embodiments of the present invention or the technical solutions in the prior art, the drawings needed to describe the embodiments or the prior art will be briefly introduced below.

Figure 1 is a topological structure diagram of a three-phase two-level voltage inverter involved in the present invention;

Figure 2 is a flow chart of a Z-source inverter control method for optimizing switching loss under variable power factor provided by an embodiment of the present invention;

Figure 3 is a schematic diagram comparing the position of the AC side current and the through current of the switching device under the ZSVM2 modulation method and the adjusted ZSVM2 modulation method of the present invention;

Figure 4 is a vector sequence diagram of the adjusted ZSVM2 modulation method provided by an embodiment of the present invention (the first sector is taken as an example);

Figure 5 is a schematic diagram of a bridge arm generated by the adjusted ZSVM2 modulation method according to an embodiment of the present invention;

Figure 6 is a schematic structural diagram of a Z-source inverter control system with optimized switching loss under variable power factor provided by an embodiment of the present invention;

Figure 7 is a comparison diagram of the efficiency of the ZSVM2 strategy and the recommended modulation strategy under different output powers when using the Z-source inverter control method for optimizing switching loss under variable power factor provided by the present invention;

Figure 8 is an infrared thermal imaging diagram of an IGBT device when using the Z-source inverter control method for optimizing switching loss under variable power factor provided by the present invention.

Detailed ways

In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions 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. The following examples are used to illustrate the present invention. , but are not used to limit the scope of the present invention.

Figure 1 is a three-phase two-level voltage-type inverter topology involved in the present invention. As can be seen from Figure 1, the Z-source inverter topology involved in this strategy includes a DC source E and a capacitor that constitutes the Z-source network topology. C1, C2, inductor L1, L2 and diode VD ₁ , the three-phase two-level inverter structure includes a total of 6 switching tubes with anti-parallel diodes. The 6 switching tubes are respectively recorded as switching tube S1, switching tube S2, switch tube Tube S3, switch tube S4, switch tube S5, switch tube S6.

Define the status when the upper and lower bridge arm devices are turned on at the same time as sh; when the upper bridge arm device is turned on and the lower bridge arm device is turned off, the status is 1; when the lower bridge arm device is turned on and the upper bridge arm is turned off, the status is 0. For Z-source inverters, when the pass-through vector is considered, the current flow situation of the A-phase bridge arm becomes complicated. The through current will be affected by the previous state I _ac . When the state changes from (100→sh00), under a resistive-inductive load, the current passing through the upper arm is I _sh and the current passing through the lower arm is I _sh -I _ac . The through current passing through the upper arm is:

It can be seen from the above formula that regardless of the upper arm or lower arm switching device, the current passing through it at the switching moment will be affected by the AC side output current. Define the current flowing through the switching device at the switching moment as the switching current. Under steady-state operation, the through current I _sh is basically unchanged. A larger AC-side output current allows the upper-side or lower-side device to pass lower through-current. Lower shoot-through current not only reduces switching losses when switching states, but also reduces conduction losses when maintaining states. When the load power factor changes, the AC side output current waveform will move relative to the output AC voltage waveform as the power factor changes. In the traditional Z-source inverter modulation method, the through vector generation position corresponds to the AC side output voltage, and the phase movement will affect the phase relationship between the AC side output current and the through current. Based on the above findings, the present invention proposes a Z-source inverter control method under variable power factor. The modulation method of the present invention is mainly based on the space vector modulation method. As shown in Figure 2, the specific implementation steps of this method are as follows:

Step S100: Set the switching state and basic voltage vector of the three-phase two-level Z-source inverter bridge arm;

In the embodiment of this application, setting the switching state of the three-phase bridge arm of the three-phase two-level Z source inverter includes:

When the switch state is 1, the upper arm switching device is turned on and the lower arm switching device is closed;

When the switch state is 0, the upper arm switching device is turned off and the lower arm switching device is turned on;

When the switch state is sh, the upper arm switching device and the lower arm switching device are turned on at the same time.

Specifically, when the switching state of the A-phase arm of the three-phase two-level inverter is set to 1, the upper arm switching device S1 is turned on, and the lower arm switching device S2 is closed. When its switching state is 0, the upper arm switching device S1 is turned on. The switching device S1 is turned off, and the lower arm switching device S2 is turned on. In the same way, we can know the definition of the status of the B-phase and C-phase switch bridge arms and the device opening status. Z source/quasi Z source inverter has a pass-through state. It is set that when the A-phase bridge arm switch state is sh, the upper bridge arm switching device S1 and the lower bridge arm switching device S2 are turned on at the same time. In the same way, the turn-on status of the devices in the pass-through state of the B-phase and C-phase bridge arms can be set.

Furthermore, according to the switching status of the three-phase bridge arm of the three-phase two-level inverter, 8 basic voltage vectors are obtained, which are recorded as voltage vectors V0, V1, V2, V3, V4, V5, V6 and V7 respectively. 8 basic voltage vectors The specific states of the switch state combinations (A-phase switch state, B-phase switch state, C-phase switch state) corresponding to the voltage vector are as follows:

The switch state corresponding to the voltage vector V0 is (000);

The switching state corresponding to the voltage vector V1 is (100);

The switching state corresponding to the voltage vector V2 is (110);

The switch state corresponding to voltage vector V3 is (010);

The switch state corresponding to the voltage vector V4 is (011);

The switch state corresponding to voltage vector V5 is (001);

The switch state corresponding to the voltage vector V6 is (101);

The switch state corresponding to voltage vector V7 is (111);

Among them, V0 and V7 are zero vectors, and the other six voltage vectors are non-zero vectors. Any bridge arm of the Z-source inverter can form a pass-through vector Vsh in the pass-through state. In the present invention, a single-phase straight-through form is adopted, that is, only one phase bridge arm is in a straight-through state. The switch state combinations corresponding to the pass-through vector Vsh include: (shXX), (XshX) and (XXsh). Among them, X represents any 1 or 0 state. sh represents the straight-through state in which the upper and lower switch tubes are turned on at the same time.

Step S200, set the voltage reference vector that needs to be modulated by the three-phase two-level Z source inverter, and determine the sector where the voltage reference vector is located;

In the embodiment of this application, the voltage reference vector that needs to be modulated by the three-phase two-level Z source inverter is set, and the sector where the voltage reference vector is located is determined; specifically including:

On the α-β axis static coordinate system, starting from the direction of the α axis, the counterclockwise direction is divided into six 60° sectors, and each sector is named sector 1 to sector according to the number along the counterclockwise direction. 6;

Project the voltage reference vector onto the coordinate axes α and β axes, and their components are respectively recorded as the voltage reference vector α axis component V _α and the voltage reference vector β axis component V _β ;

The sector where the voltage reference vector is located is determined based on the α-axis component V _α of the voltage reference vector and the β-axis component V _β of the voltage reference vector.

Specifically, on the α-β axis static coordinate system, starting from the α-axis direction, the counterclockwise direction is divided into six 60° sectors, and each sector is named sector 1 according to the number along the counterclockwise direction. ~Sector 6; Assume that the voltage reference vector that needs to be modulated by the three-phase two-level inverter is V _ref . Project the voltage reference vector V _ref onto the coordinate axes α and β axes, and its components are respectively recorded as the voltage reference vector α axis. The sector where the voltage reference vector V _ref is located is determined _based on the voltage reference vector α axis component V _α and _the voltage reference vector β axis component V _β . The voltage reference vector V _ref is actually the target voltage output by the AC side of the inverter, and can usually be considered a known quantity.

Step S300: Based on the angle θ between the voltage reference vector and the coordinate axis α in the α-β coordinate system and the modulation degree M corresponding to the voltage reference vector, the action time of the voltage vector and the through-vector insertion zero vector action are calculated based on the sector where it is located. time;

Furthermore, the angle θ between the voltage reference vector V _ref and the coordinate axis α in the α-β coordinate system and the modulation degree M corresponding to the voltage reference vector V _ref are calculated as follows:

Among them, V _α and V _β are the components that project the voltage reference vector onto the coordinate axes α and β axes respectively;

Among them, V _dc is the DC link voltage of the Z-source inverter, and |V _ref | is the voltage reference vector amplitude.

According to the volt-second balance principle, the action time of the vector is the time that the switching state of the corresponding three-phase bridge arm is maintained.

Further, the voltage vector time can be calculated by the following formula:

Among them, T _s is the switching period, Modulation degree, i is the sector number; the first sector T ₁ is the action time of the basic voltage vector V ₁ , T ₂ is the action time of the voltage vector V ₂ ; the second sector T ₁ is the action time of the voltage vector V ₂ , and T ₂ is The voltage vector V ₃ acts on time; the third sector T ₁ is the voltage vector V ₃ acts on time, T ₂ is the voltage vector V ₄ acts on time; the fourth sector T ₁ is the voltage vector V ₄ acts on time, T ₂ is the voltage vector V ₅ action time; the fifth sector T ₁ is the voltage vector V ₅ action time, T ₂ is the voltage vector V ₆ action time; the sixth sector vector T ₁ is the voltage vector V ₆ action time, T ₂ is the voltage vector V ₁ action time; T ₀ is the action time of voltage vectors V ₀ and V ₇ .

When the pass-through vector all occupies the zero vector action time, its pass-through duty cycle can be expressed as:

Since the zero vector action time T ₀ does not necessarily use all through vectors, D ₀ is defined below,

Among them, D ₀ represents the ratio of through time to T ₀ time. When D ₀ <1, the zero vector action time is not all the through vector action time.

Step S400: Determine the switching sequence according to the set switching state and basic voltage vector, vector action time and through vector insertion zero vector action time, and the sector where the voltage reference vector is located;

Step S500: Calculate the load power factor by collecting the AC side current and voltage of the load;

Step S600: Control the insertion method of the pass-through vector according to the change of the load power factor, and determine the loss-optimized switching sequence in combination with the switching sequence to realize Z-source inverter control under variable power factor.

In the embodiment of this application, the insertion method of the pass-through vector is controlled according to the change of the load power factor, which specifically includes:

When a resistive-inductive load is used, when the power factor angle is φ, the original sector switching sequence is not changed, and the sequence of generating the pass-through vector is delayed backward by the φ angle;

If the power factor angle is between 0 and φ, the sixth sector in the original ZSVM2 modulation method uses the pass-through bridge arm as the bridge arm inserted by the pass-through vector;

If the power factor angle is between φ-π/3, use the first sector of the original ZSVM2 to pass through the bridge arm;

If a resistive-capacitive load is used, when the power factor angle is φ, the original sector switching sequence will not be changed, and the sequence of the pass-through vector will be moved forward by the φ angle.

Specifically, the following uses ZSVM2 as an example to describe in detail the adjusted ZSVM2 modulation method of the present invention. The ZSVM2 modulation method is implemented by inserting a pass-through vector based on the traditional inverter SVPWM modulation strategy. The pass-through vector action time occupies zero vector time. The ZSVM2 modulation method does not change its pass-through insertion position due to external parameters. The through-vector insertion method of the Z-source inverter control method with optimized switching loss proposed by the present invention changes according to the load power factor, which can achieve the purpose of optimizing the switching loss.

The switch conduction time and sequence in the first sector are shown in the following table:

In the ZSVM2 modulation method, the pass vector is only inserted into the zero vector. At this time, there are A-phase bridge arm and C-phase bridge arm in the first sector using pass-through vectors. If you want to change the through vector to follow the power factor angle, you need to use the B-phase bridge arm to insert the through vector. As shown in Figure 3, using this control method, the relative phase relationship between the through current through the switching device and the AC side current can be maintained at a power factor of 1. When the power factor is 1, the AC side current can offset the most through current, so the optimal loss effect can also be achieved. As shown in Figure 4, when the power factor angle is when, then at The sixth sector in the original ZSVM2 modulation uses the pass-through bridge arm as the bridge arm inserted by the pass-through vector, while in The original ZSVM2 first sector pass-through insertion bridge arm is still used.

Based on the ZSVM2 modulation method, the through vector insertion method in adjusting the ZSVM2 modulation method of the present invention will be described below. in the first sector The switching sequence and conduction time within the range are shown in the following table:

When the power factor angle of the resistive-inductive load is When , the original sector switching sequence is not changed, and the sequence of generating pass-through vectors is delayed backwards/> angle. At this time, the AC side current can offset the most through current, which can produce the smallest switching loss. For vector modulation, it is easy to generate separate pass-through vectors and vector switching times. Taking the first sector as an example, when the power factor angle is between 0-π/3,/> The direct vector between them produces a bridge arm that changes from the original A and C phases to the A and B phases in sector six. At this time/> The through vector between the resulting bridge arms remains unchanged. When the power factor further increases to between π/3-2π/3, at this time/> The bridge arms generated by the direct connection are B and C phases, and/> The bridge arms generated by the direct connection are A and B phases, as shown in Figure 5. The same principle can be extended to other power factor angles for correction. The movement of the pass-through vector generation position does not necessarily just lag behind the original modulation strategy. If a resistive-capacitive load is used and the current leads the voltage, the position of the through vector will move forward accordingly.

In addition, the present invention determines the generation area of the through vector based on the phase of the AC output current. The insertion position of the pass-through vector in the traditional Z-source inverter modulation strategy is generally determined by the AC side output voltage. This method optimizes the phase relationship between the through current passing through the switching device and the AC side output current, and makes full use of the offset effect of the AC side output current on the through current, so that the total average current value passing through the device in the through state is reduced. This in turn reduces the switching losses of the device. At the same time, since the current passing through the device in the straight-through state is reduced, the conduction loss is also reduced slightly.

The present invention has a wide range of applications and can be used in modulation methods such as ZSVM2 and ZSVM1 that do not use all bridge arms to generate pass-through vectors in one switching cycle. When all bridge arms generate pass-through vectors within a switching cycle, the phase transformation between the pass-through current generation area and the AC side output current cannot be achieved. Therefore, optimization of losses cannot be achieved. It can effectively reduce switching losses and conduction losses caused by switching devices under load conditions where the power factor is not 1.

In a specific embodiment, the simulation platform uses matlab/Simulink combined with PLECS. The simulated load power factor PF = 0.866, D ₀ = 0.85, the modulation degrees M are 1, 0.9, 0.8, 0.7, 0.65, 0.6 respectively, and the corresponding output powers are 141.32W, 165.81W, 205.57W, 283.5W, 352.83W respectively. 470.34W. When PF=0.966, R=12.5Ω, L=10.67mH, the corresponding output powers are 153.72W, 180.96W, 225.37W, 380.78W, 383.02W, 500W respectively. As shown in Figure 7, a comparison of the efficiency of the ZSVM2 strategy and the recommended modulation strategy under different output powers is given. It can be seen from Figure 7 that the modulation strategy of the present invention can improve the efficiency of the inverter, and the smaller the power factor, the more obvious the efficiency optimization. In addition, this embodiment also uses a thermal imager to verify the effectiveness of the modulation method used in the present invention. As can be seen from Figure 8, when the recommended modulation is used, the temperature of the IGBT device decreases by 1 to 3 degrees Celsius. It can be seen that the recommended modulation can reduce device loss.

In one embodiment, a Z-source inverter control device with optimized switching loss under variable power factor is proposed. Referring to Figure 6, the device includes:

Setting module one is used to set the switching state and basic voltage vector of the three-phase bridge arm of the three-phase two-level Z source inverter;

Setting module two is used to set the voltage reference vector that needs to be modulated by the three-phase two-level Z source inverter, and determine the sector where the voltage reference vector is located;

The vector action time calculation module is used to obtain the angle θ between the voltage reference vector and the coordinate axis α in the α-β coordinate system and the modulation degree M corresponding to the voltage reference vector according to the setting of the setting module 2, and combine it with the fan The area calculates the action time of the voltage vector and the action time of the through vector insertion zero vector;

The switch sequence generation module is used to determine the switch sequence based on the settings of the setting module one, the action time of the voltage vector calculated by the vector action time calculation module, the zero vector action time of the through vector insertion, and the sector where the voltage reference vector is located;

The load power factor module is used to calculate the load power factor by collecting the AC side current and voltage of the load;

The pass-through vector optimization module is used to control the insertion method of the pass-through vector according to the change of load power factor, and determine the loss-optimized switching sequence in combination with the switching sequence to realize Z-source inverter control under variable power factor.

Furthermore, the second setting module includes a reference voltage given module and a sector judgment module; a reference voltage given module, used to give the voltage reference vector to be modulated; and a sector judgment module, used to determine the sector where the voltage reference vector is located. Make a judgment; the vector action time calculation module includes a vector time calculation module and a through time calculation module; the vector action time calculation module is used to pass the angle θ between the voltage reference vector and the coordinate axis α in the α-β coordinate system, the voltage reference vector The corresponding modulation degree M is used to calculate the action time of the voltage vector in combination with the sector; the through time calculation module is used to calculate the action time of the through vector based on the zero vector action time.

It should be noted that the Z-source inverter control device with optimized switching loss under variable power factor provided by the above embodiments and the Z-source inverter control method embodiment with optimized switching loss under variable power factor belong to the same concept. For details on the implementation process, see a Z-source inverter control method for optimizing switching loss under variable power factor, which will not be described again here.

In one embodiment, the present invention proposes a Z-source inverter control system, as shown in Figure 6. The system includes a three-phase two-level Z-source inverter module and any one of the power conversion power converters described above. Z-source inverter control device with optimized switching loss under factor. Among them, the Z-source inverter control device with optimized switching loss under variable power factor refers to the above description and will not be described again here.

It should be clear that the described embodiments are only some, but not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present invention.

In the instructions provided here, a number of specific details are described. However, it is understood that embodiments of the invention may be practiced without these specific details. In some instances, well-known methods, structures, and techniques have not been shown in detail so as not to obscure the understanding of this description.

The above are only preferred embodiments of the present invention, and do not limit the present invention in any form. Although the present invention has been disclosed above in preferred embodiments, it is not intended to limit the present invention. Anyone familiar with the technology of this patent Without departing from the scope of the technical solution of the present invention, personnel can make some changes or modify the above-mentioned technical contents into equivalent embodiments with equivalent changes. Technical Essence Any simple modifications, equivalent changes and modifications made to the above embodiments still fall within the scope of the present invention.

Claims (10)

1. The Z source inverter control method for optimizing the switching loss under the variable power factor is characterized by comprising the following steps of:

setting a switching state and a basic voltage vector of a bridge arm of the three-phase two-level Z-source inverter;

setting a voltage reference vector to be modulated by a three-phase two-level Z source inverter, and judging a sector where the voltage reference vector is located;

calculating the acting time of the voltage vector and the acting time of inserting the direct vector into the zero vector by combining the included angle theta of the voltage reference vector and the coordinate axis alpha in the alpha-beta coordinate system and the modulation M corresponding to the voltage reference vector and the sector where the voltage reference vector is positioned;

determining a switching sequence according to the set switching state, a basic voltage vector, a vector acting time and a direct vector inserting zero vector acting time and a sector where a voltage reference vector is located;

calculating a load power factor by collecting current and voltage of a load alternating-current side;

and controlling the insertion mode of the through vector according to the change of the load power factor, and determining a switching sequence after loss optimization by combining the switching sequence to realize the control of the Z source inverter under the variable power factor.

2. The method for controlling a Z-source inverter with optimized switching loss under a variable power factor according to claim 1, wherein the setting the switching state of the three-phase two-level Z-source inverter leg comprises:

when the switching state is 1, the upper bridge arm switching device is turned on, and the lower bridge arm switching device is turned off;

when the switching state is 0, the upper bridge arm switching device is closed, and the lower bridge arm switching device is opened;

when the switching state is sh, the upper bridge arm switching device and the lower bridge arm switching device are simultaneously turned on.

3. The control method for the Z-source inverter with optimized switching loss under the variable power factor according to claim 2, wherein 8 basic voltage vectors are obtained according to the switching states of the three-phase two-level Z-source inverter bridge arms and are respectively recorded as voltage vectors V ₀ 、V ₁ 、V ₂ 、V ₃ 、V ₄ 、V ₅ 、V ₆ And V ₇ The method comprises the steps of carrying out a first treatment on the surface of the The specific states of the switch state combination A phase switch state, the B phase switch state and the C phase switch state corresponding to the 8 basic voltage vectors are as follows:

the switching state corresponding to the voltage vector V0 is (000);

the corresponding switch state of the voltage vector V1 is (100);

the switch state corresponding to the voltage vector V2 is (110);

the switching state corresponding to the voltage vector V3 is (010);

the switch state corresponding to the voltage vector V4 is (011);

the switch state corresponding to the voltage vector V5 is (001);

the corresponding switch state of the voltage vector V6 is (101);

the switch state corresponding to the voltage vector V7 is (111);

wherein V is ₀ And V ₇ The other six voltage vectors are non-zero vectors;

any bridge arm of the Z-source inverter can form a through vector Vsh by adopting a through state, and a switch state combination corresponding to the through vector Vsh comprises: (shXX), (XshX) and (xxxh); wherein X represents any 1 or 0 state, and sh represents a straight-through state that the upper bridge arm switch tube and the lower bridge arm switch tube are simultaneously conducted.

4. The method for controlling a Z-source inverter with optimized switching loss under a variable power factor according to claim 1, wherein the determining the sector in which the voltage reference vector is located includes:

on an alpha-beta axis static coordinate system, starting from the alpha axis direction, dividing the alpha axis direction into 6 sectors of 60 degrees in the anticlockwise direction, and sequentially naming each sector as a sector 1-a sector 6 according to the serial number in the anticlockwise direction;

projecting the voltage reference vector on the coordinate axis alpha and beta, and respectively marking the components as the voltage reference vector alpha axis component V _α And a voltage reference vector beta axis component V _β ；

According to the alpha-axis component V of the voltage reference vector _α And a voltage reference vector beta axis component V _β And judging the sector where the voltage reference vector is located.

5. The method for controlling a Z-source inverter according to claim 4, wherein an included angle θ between the voltage reference vector and an α -axis of a coordinate axis in the α - β coordinate system is:

wherein V is _α 、V _β The components of the voltage reference vector projected on the coordinate axis alpha and beta are respectively;

the modulation degree M corresponding to the voltage reference vector is as follows:

wherein V is _dc Is the direct current link voltage of the Z source inverter, |V _ref And I is the voltage reference vector amplitude.

6. The method for controlling a Z-source inverter with switching loss optimization at a variable power factor according to claim 5, wherein the duration of the voltage vector is:

wherein T is _s For the switching period of the switch-on and switch-off period,modulation degree, i is sector number; first sector T ₁ As a base voltage vector V ₁ Time of action, T ₂ Is the voltage vector V ₂ The action time; second sector T ₁ Is the voltage vector V ₂ Time of action, T ₂ Is the voltage vector V ₃ The action time; third sector T ₁ Is the voltage vector V ₃ Time of action, T ₂ Is the voltage vector V ₄ The action time; fourth sector T ₁ Is the voltage vector V ₄ Time of action, T ₂ Is the voltage vector V ₅ The action time;fifth sector T ₁ Is the voltage vector V ₅ Time of action, T ₂ Is the voltage vector V ₆ The action time; sixth sector vector T ₁ Is the voltage vector V ₆ Time of action, T ₂ Is the voltage vector V ₁ The action time; t (T) ₀ Is the voltage vector V ₀ And V ₇ The action time;

when the through vectors all occupy zero vector action time, the through duty ratio can be expressed as:

due to zero vector time of action T ₀ The pass vector need not be used in its entirety, D is defined below ₀ ，

Wherein D is ₀ Representing the pass-through time and T ₀ Time ratio. When D is ₀ When less than 1, the zero vector acting time is not the straight-through vector acting time.

7. The method for controlling a Z-source inverter with optimized switching loss under a variable power factor according to claim 1, wherein the inserting mode of the through vector is controlled according to the change of the load power factor, specifically comprising:

when using resistive load, the power factor angle isWhen the original sector switch sequence is not changed, the sequence for generating the through vector is delayed backward by +.>An angle;

if the power factor angle is between 0 and phi, adopting a straight-through bridge arm as a bridge arm inserted by a straight-through vector for a sixth sector in the original ZSVM2 modulation method;

if at its power factor angleDuring the process, the bridge arm is directly inserted by using the first sector of the original ZSVM 2;

if a resistive-capacitive load is used, the power factor angle isWhen the original sector switch sequence is not changed, the sequence for generating the through vector is moved forward +.>Angle.

8. A Z source inverter control device for switching loss optimization under a variable power factor, the device comprising:

the setting module I is used for setting the switching state and the basic voltage vector of a three-phase bridge arm of the three-phase two-level Z-source inverter;

the second setting module is used for setting a voltage reference vector to be modulated by the three-phase two-level Z source inverter and judging a sector where the voltage reference vector is located;

the vector acting time calculation module is used for acquiring an included angle theta of a voltage reference vector and a coordinate axis alpha in an alpha-beta coordinate system and a modulation degree M corresponding to the voltage reference vector according to the setting of the setting module II, and calculating acting time of the voltage vector and acting time of inserting the direct vector into a zero vector by combining the sector where the voltage reference vector is located;

the switching sequence generating module is used for determining a switching sequence according to the setting of the setting module I, the action time of the voltage vector calculated by the vector action time calculating module, the action time of the direct vector inserted zero vector and the sector where the voltage reference vector is located;

the load power factor module is used for calculating a load power factor by collecting current and voltage of a load alternating-current side;

and the direct vector optimization module is used for controlling the insertion mode of the direct vector according to the change of the load power factor, and determining a switching sequence after loss optimization by combining the switching sequence to realize the control of the Z source inverter under the variable power factor.

9. The variable power factor switching loss optimized Z-source inverter control device of claim 8, wherein: the second setting module comprises a reference voltage giving module and a sector judging module; the reference voltage giving module is used for giving a voltage reference vector to be modulated; the sector judgment module is used for judging the sector where the voltage reference vector is located; the vector acting time calculation module comprises a vector time calculation module and a straight-through time calculation module; the vector acting time calculation module is used for calculating the acting time of the voltage vector by combining the included angle theta of the voltage reference vector and the coordinate axis alpha in the alpha-beta coordinate system and the modulation degree M corresponding to the voltage reference vector and the sector where the voltage reference vector is located; and the straight-through time calculation module is used for calculating the straight-through vector acting time according to the zero vector acting time.

10. A Z source inverter control system, characterized by: the system comprises a three-phase two-level Z-source inverter module and the Z-source inverter control device for optimizing the switching loss under the variable power factor according to any one of claims 8-9.