阅读说明：本技术 一种改善准z源逆变器开关器件电流应力的调制方法 (Modulation method for improving current stress of switching device of quasi-Z-source inverter ) 是由 谭天诚 刘平 张桂斌 谭天利 吴刚 吴文昊 于 2020-12-08 设计创作，主要内容包括：本发明提供了一种改善准Z源逆变器开关器件电流应力的调制方法,该调制方法的调制波有3个,分别为相位互差120°的传统电压空间矢量调制SVPWM的马鞍波减去自身的最大值,三相马鞍波按此变换后波形的最大值为一条直线,将此直线再向上平移M/2,M为将调制波和三角载波在0到1之间标幺化后调制波最大值与最小值之间的距离。该调制方法门级信号的生成过程较简单,开关损耗低,在输入直流侧没有低频的交流成分,且大大减小了开关器件的电流应力,延长了开关器件寿命。(The invention provides a modulation method for improving current stress of a switching device of a quasi-Z-source inverter, wherein 3 modulation waves of the modulation method are respectively saddle waves minus the maximum value of the modulation waves, the saddle waves are the saddle waves of traditional voltage space vector modulation SVPWM with the phase difference of 120 degrees, the maximum value of the converted waveform of a three-phase saddle wave is a straight line, the straight line is translated upwards by M/2, and M is the distance between the maximum value and the minimum value of the modulation waves after the modulation waves and a triangular carrier are subjected to per unit between 0 and 1. The modulation method has the advantages of simple generation process of gate-level signals, low switching loss, no low-frequency alternating current component on the input direct current side, greatly reduced current stress of the switching device and prolonged service life of the switching device.)

1. A modulation method for improving current stress of a switching device of a quasi-Z-source inverter is characterized by specifically comprising the following steps:

obtaining a reference vector V_refFrom a reference vector V_refDetermines the base vector V of the sector in which the reference vector is located_jAnd V_j+1And the time T of the base vector action_jAnd T_j+1And further determining the switching time T of the vector_a，T_bAnd T_cIn conventional SVPWM modulation, there is the following expression:

where i e {1, 2.,. 6} represents the i-th sector, T₁，T₂For base vector action time, T_sFor PWM switching period, T₀When acting as a conventional zero vectorIn the middle of the furnace, the gas-liquid separation chamber,is the modulation ratio, V_dcIs the dc side voltage.

The conventional SVPWM modulated a, b, c three phase adjacent voltage vector and conventional zero vector switching times are as follows:

the improved modulation wave is obtained by changing the saddle wave modulated by the traditional SVPWM, namely the saddle wave modulated by the traditional SVPWM subtracts the upper envelope line and then shifts up by M/2, and the vector switching time after changing is as follows:

the quasi-Z source inverter is controlled by a three-phase full bridge, 3 three-phase modulation waves respectively subtract the maximum value of the saddle wave of the traditional voltage space vector modulation SVPWM with the phase difference of 120 degrees, the maximum value of the waveform of the three-phase saddle wave after the three-phase saddle wave is converted is a straight line, the straight line is translated upwards by M/2, and M is the distance between the maximum value and the minimum value of the modulation wave after the modulation wave and the triangular carrier are subjected to per unit conversion between 0 and 1.

2. The modulation method for improving the current stress of the switching devices of the quasi-Z source inverter as claimed in claim 1, wherein when the upper envelope lines of the 3 three-phase modulation waves are smaller than the triangular carrier, the switching devices of the three-phase bridge arm are all turned on at the same time, so that the three-phase bridge arm is directly connected.

3. A modulation system for improving current stress in a switching device of a quasi-Z source inverter, comprising:

at least one processor and at least one memory communicatively coupled to the processor, wherein: the memory stores program instructions executable by the processor, the processor invoking the program instructions to enable performance of the modulation method of improving quasi-Z source inverter switching device current stress of any of claims 1-2.

4. A non-transitory computer-readable storage medium storing computer instructions for causing a computer to perform the modulation method for improving quasi-Z source inverter switching device current stress of any one of claims 1-2.

Technical Field

The invention belongs to the field of inverter control, and particularly relates to a modulation method for improving current stress of a switching device of a quasi-Z-source inverter.

Background

With the increasingly prominent environmental problems, new energy industries are vigorously developed in various countries. The mainstream inverter topology in the new energy field is a Voltage Source Inverter (VSI), which is evolved from a Buck converter and can only operate in a Buck mode. In order to satisfy a wide range of voltage input of the subsequent inverter, the new energy power generation system generally adopts a structure of a direct current-direct current (DC-DC) conversion circuit + the inverter. The multilevel converter has large energy loss, and has limitations in conversion efficiency, reliability, cost and the like. On the other hand, the upper and lower switching tubes of the same bridge arm of the VSI cannot be simultaneously conducted, otherwise, a through short circuit occurs to damage the inverter, and if the dead time is inserted, the output voltage is distorted, the harmonic content is increased, and the quality of the output electric energy is deteriorated.

The Quasi-Z-Source inverter (qZSI) has the voltage lifting regulation and inversion output capacity as a single-stage topology, allows bridge arms to be directly connected, does not need dead time, is high in reliability and electromagnetic compatibility, breaks through the limitation of the existing inversion scheme in the aspects of voltage regulation range, conversion efficiency, size, cost and the like, and becomes a powerful competitive scheme of the inverter in the field of new energy.

The quasi-Z source inverter can adopt sine pulse width modulation (SPWM modulation) and space voltage vector modulation (SVPWM modulation), and compared with the SPWM, the impedance source inverter under the SVPWM modulation has the advantages of lower power device loss, higher direct-current voltage utilization rate and wider modulation range. The ability to regulate the output voltage can be achieved by adding a through zero vector to the 8 vectors (6 and active vectors and 2 zero vectors) of the conventional SVPWM modulation to participate in the modulation. The effect of the direct zero vector is consistent with that of the traditional zero vector, and the direct zero vector and the traditional zero vector both present a short-circuit state to the load.

The three-phase quasi-Z source inverter can adopt any one of modulation strategies suitable for the three-phase impedance source inverter, and the modulation strategies can be classified into the following types: (1) the three-phase bridge arm direct connection continuous modulation strategy (2) and the single-phase bridge arm direct connection continuous modulation strategy (3) are respectively a discontinuous modulation strategy.

(1) A continuous modulation strategy of three-phase bridge arm direct connection: according to the difference of the modulation waves, the modulation waves can be subdivided into simple boost modulation (SBS), maximum boost Modulation (MBS), constant boost modulation (CBS) and single boost vector modulation (SBSV). These modulation strategies use three standard modulation signals v in addition to_a ^*,v_b ^*,v_c ^*In addition, two additional signals e are required₁ ^*,e₂ ^*To produce a through zero vector inserted into a conventional zero vector, increases the complexity of gate level switching signal generation.

(2) A continuous modulation strategy of single-phase bridge arm direct connection: through-out zero vector action time T by vertically translating traditional SVPWM (space vector pulse width modulation) modulated three-phase saddle wave_STFor example: t is_ST6 (1/6 of through time) or T_STAnd/4 (1/4 for through time) and then compared to the triangular carrier to generate the switching signal. This strategy will pass through the zero vector action time T_STA few aliquots, for example: six equal divisions (or four equal divisions) are inserted into the conversion time of the effective vector and the traditional zero vector, so that the switching time of the upper and lower tubes of the same bridge arm is advanced or delayed by T_ST6 (or T)_STAnd/4) generating a through state at the time when the switching signals overlap. The switching devices of the quasi-Z source inverter under the strategy are commutated with high current stress in the whole fundamental wave period.

(3) Discontinuous modulation strategy: the maximum value (upper envelope line) of the three-phase saddle wave modulated by the traditional SVPWM is replaced by a straight line, the position of the straight line is coincided with the positive peak value of the triangular carrier wave, and the rest three-phase saddle wave is vertically translated by T_ST6 (1/6 of through time) or T_ST/4 (1/4 for through time) and compared to the triangular carrier to generate a switching signal, producing a through state at the moment the switching signal overlaps. The strategy is similar to the continuous modulation strategy for the single-phase bridge arm direct connection, and a direct connection zero vector is inserted into a switching signal of the single-phase bridge arm instead of a three-phase bridge arm, so that a switching device has higher current stress.

One currently existingThe modulation strategy is an improved simple boosting SVPWM (SBMSV), a gate-level switching signal of a switching device of the modulation strategy is generated as shown in a figure 2, and a quasi-Z source inverter circuit is shown in a figure 1. Under the strategy, the generation principle of the switching signal is as follows: when v is_a ^*Is v is_a ^*，v_b ^*，v_c ^*Maximum value of (1) or v_a ^*When the voltage is more than or equal to the triangular carrier, the upper tube of the a-phase bridge arm is continuously conducted, and when the voltage is v_a ^*When the number of the lower tubes is less than or equal to the triangular carrier, the lower tube of the a-phase bridge arm is conducted; when v is_b ^*Is v is_a ^*，v_b ^*，v_c ^*Maximum value of (1) or v_b ^*When the voltage is more than or equal to the triangular carrier wave, the upper tube of the b-phase bridge arm is continuously conducted, and when v is greater than or equal to the triangular carrier wave_b ^*When the lower tube is smaller than or equal to the triangular carrier, the lower tube of the b-phase bridge arm is conducted; when v is_c ^*Is v is_a ^*，v_b ^*，v_c ^*Maximum value of (1) or v_c ^*When the voltage is more than or equal to the triangular carrier wave, the upper tube of the c-phase bridge arm is continuously conducted, and when v is larger than or equal to the triangular carrier wave, the upper tube of the c-phase bridge arm is continuously conducted_c ^*And when the lower tube is smaller than or equal to the triangular carrier, the lower tube of the c-phase bridge arm is conducted. As seen from fig. 2, any straight-through moment is a straight-through moment of a single-phase bridge arm, and a dotted line frame is any straight-through moment of an a-phase bridge arm. However, the SBMSV strategy may result in large current stress of the switching device due to continuous commutation, thereby affecting the lifetime of the switching device.

In summary, it can be seen that the modulation strategy applied to the quasi-Z source inverter at present has the following drawbacks:

(1) the switching loss of the device is increased due to the fact that the switching device has more commutation times;

(2) the traditional SVPWM (space vector pulse width modulation) strategy needs to use 5 reference signals, so that the generation process of a gate-level signal for controlling the on or off of a device is complex;

(3) the continuous commutation of the switching devices during the fundamental frequency period can result in large current stresses on the switching devices of some quasi-Z source inverters that employ conventional modulation strategies.

Therefore, it is urgently needed to design a quasi-Z source inverter modulation method to solve the above problems.

Disclosure of Invention

Technical problem to be solved

Based on the method, the generation process of the gate-level signal is simple, the switching loss is low, low-frequency alternating current components do not exist on the input direct current side, the current stress of the switching device is greatly reduced, and the service life of the switching device is prolonged.

(II) technical scheme

According to an aspect of the present invention, there is provided a modulation method for improving current stress of a switching device of a quasi-Z-source inverter, the modulation method specifically includes:

obtaining a reference vector V_refFrom a reference vector V_refDetermines the base vector V of the sector in which the reference vector is located_jAnd V_j+1And the time T of the base vector action_jAnd T_j+1And further determining the switching time T of the vector_a，T_bAnd T_cIn conventional SVPWM modulation, there is the following expression:

where i e {1, 2.,. 6} represents the i-th sector, T₁，T₂For base vector action time, T_sFor PWM switching period, T₀In order to realize the action time of the traditional zero vector,is the modulation ratio, V_dcIs the dc side voltage.

The conventional SVPWM modulated a, b, c three phase adjacent voltage vector and conventional zero vector switching times are as follows:

the improved modulation wave is obtained by changing the saddle wave modulated by the traditional SVPWM, namely the saddle wave modulated by the traditional SVPWM subtracts the upper envelope line and then shifts up by M/2, and the vector switching time after changing is as follows:

the quasi-Z source inverter is controlled by a three-phase full bridge, 3 three-phase modulation waves respectively subtract the maximum value of the saddle wave of the traditional voltage space vector modulation SVPWM with the phase difference of 120 degrees, the maximum value of the waveform of the three-phase saddle wave after the three-phase saddle wave is converted is a straight line, the straight line is translated upwards by M/2, and M is the distance between the maximum value and the minimum value of the modulation wave after the modulation wave and the triangular carrier are subjected to per unit conversion between 0 and 1.

Furthermore, the switching tubes of the three-phase full bridge of the quasi-Z source inverter are all IGBTs.

Further, when the upper envelope lines of the 3 three-phase modulation waves are smaller than the triangular carrier wave, the switching devices of the three-phase bridge arms are all switched on simultaneously, and the three-phase bridge arm is directly connected.

Furthermore, in one period, the number of times that the switching devices of the three-phase bridge arm are simultaneously turned on is more than 6.

In addition, the invention also discloses a modulation system for improving the current stress of the switching device of the quasi-Z source inverter, which comprises the following components:

at least one processor and at least one memory communicatively coupled to the processor, wherein: the memory stores program instructions executable by the processor, the processor invoking the program instructions to perform a modulation method for improving quasi-Z source inverter switching device current stress as any one of the above.

In addition, the invention also discloses a non-transitory computer readable storage medium, which stores computer instructions for causing the computer to execute the modulation method for improving the current stress of the quasi-Z source inverter switching device.

(III) advantageous effects

The modulation method for improving the current stress of the switching device of the quasi-Z source inverter has the following advantages:

(1) the modulation strategy only needs 3 modulation waves as given signals, so the generation process of the gate-level signals of the switching devices is simple.

(2) The commutation frequency of the device is effectively reduced, the switching loss is reduced, and the overall efficiency of the system is improved.

(3) The proposed modulation strategy has a fixed through duty cycle, so that there is no low frequency ac component on the input dc side.

(4) The modulation strategy realizes the direct connection of the three-phase bridge arm by changing the vector switching time and translating the modulation wave, greatly reduces the current stress of a switching device and prolongs the service life of the switching period.

Drawings

Fig. 1 is a circuit configuration diagram of a three-phase quasi-Z source inverter according to the present invention.

Fig. 2 is a diagram of the on and off waveforms of the switching device of the SBMSV strategy in the prior art.

Fig. 3 is a diagram of the on and off waveforms of the switching device of the modulation method for improving the current stress of the switching device of the quasi-Z source inverter according to the present invention.

Fig. 4 is a current waveform diagram of a switching device of the SBMSV strategy in the prior art.

Fig. 5 is a current diagram of switching devices of the proposed modulation method for improving current stress of the switching devices of a quasi-Z source inverter.

Detailed Description

The present invention will be described more fully hereinafter with reference to the accompanying drawings and examples, in which the technical problems and advantages of the present invention are solved, wherein the described examples are only intended to facilitate the understanding of the present invention, and are not to be construed as limiting in any way.

The modulation method for improving the current stress of the switching device of the quasi-Z source inverter is used for changing the single-phase bridge arm direct connection into the three-phase bridge arm direct connection on the basis of an improved simple boost space vector modulation (SBMSV) modulation strategy, so that the function of reducing the current stress of the switching device is realized. The specific modulation method of the method is as follows:

the modulation method of the present invention has 3 modulation waves, i.e., v_a ^*，v_b ^*，v_c ^*The maximum value of the saddle wave of the traditional voltage space vector modulation (SVPWM) with the phase difference of 120 degrees is subtracted, the maximum value (namely the upper envelope line) of the waveform of the three-phase saddle wave after the conversion is a straight line, the straight line is translated upwards by M/2, and M is the distance between the maximum value and the minimum value of the modulation wave after the modulation wave and the triangular carrier are subjected to per unit conversion between 0 and 1.

Under the improved strategy, the generation principle of the switching signal is as follows: when v is_a ^*Is v is_a ^*，v_b ^*，v_c ^*Maximum value of (1) or v_a ^*When the voltage is more than or equal to the triangular carrier, the upper tube of the a-phase bridge arm is continuously conducted, and when the voltage is v_a ^*When the number of the lower tubes is less than or equal to the triangular carrier, the lower tube of the a-phase bridge arm is conducted; when v is_b ^*Is v is_a ^*，v_b ^*，v_c ^*Maximum value of (1) or v_b ^*When the voltage is more than or equal to the triangular carrier wave, the upper tube of the b-phase bridge arm is continuously conducted, and when v is greater than or equal to the triangular carrier wave_b ^*When the lower tube is smaller than or equal to the triangular carrier, the lower tube of the b-phase bridge arm is conducted; when v is_c ^*Is v is_a ^*，v_b ^*，v_c ^*Maximum value of (1) or v_c ^*When the voltage is more than or equal to the triangular carrier wave, the upper tube of the c-phase bridge arm is continuously conducted, and when v is larger than or equal to the triangular carrier wave, the upper tube of the c-phase bridge arm is continuously conducted_c ^*And when the lower tube is smaller than or equal to the triangular carrier, the lower tube of the c-phase bridge arm is conducted. Meanwhile, when the upper envelope line of the three-phase modulation wave is smaller than the triangular carrier wave, the switching devices of the three-phase bridge arm are simultaneously switched on, and the three-phase bridge arm is directly connected.

The gate level switching signal of the switching device is generated as shown in fig. 3, and the straight-through time of any three-phase bridge arm is shown in a dotted line frame, wherein S_ap、S_bp、S_cpThe waveform is three upper bridge arm switching tube signal waveforms of a three-phase bridge arm, wherein S_an、S_bn、S_cnThe wave form is a three-phase bridgeThe signal waveforms of the switching tubes of the three lower bridge arms of the arm are black-white images which cannot display color difference because of the images 2-3, so as to ensure v_a ^*，v_b ^*，v_c ^*Intuition and intelligibility of three continuously modulated waves, the invention being directed to the waveform v shown in fig. 3 with an incomplete representation_a ^*Is marked three times (v)_a ^*Half less saddle wave at the left and right ends respectively) to display complete waveform v_b ^*，v_c ^*Labeled twice, of course, as does the modulation waveform in FIG. 2.

The modulation method specifically comprises the following steps: obtaining a reference vector V_refFrom a reference vector V_refDetermines the base vector V of the sector in which the reference vector is located_jAnd V_j+1And the time T of the base vector action_jAnd T_j+1And further determining the switching time T of the vector_a，T_bAnd T_cIn conventional SVPWM modulation, there is the following expression:

where i e {1, 2.,. 6} represents the i-th sector, T₁，T₂For base vector action time, T_sFor PWM switching period, T₀In order to realize the action time of the traditional zero vector,is the modulation ratio, V_dcIs the dc side voltage.

The conventional SVPWM modulated a, b, c three phase adjacent voltage vector and conventional zero vector switching times are as follows:

the modulation wave of the proposed modulation strategy is obtained by changing the saddle wave modulated by the traditional SVPWM, namely, the saddle wave modulated by the traditional SVPWM subtracts the upper envelope curve and then shifts up by M/2, and the vector switching time after changing is as follows:

the current stress of the switching device is analyzed in connection with the proposed modulation strategy. The current stress of the strategy (SBMSV) of directly connecting only one bridge arm switch tube is as follows, taking a-phase bridge arm as an example, and the current stress of the switch tube on the a-phase bridge arm asThe current stress of the switch tube under the a-phase bridge arm is In order to be the power factor angle,andthe peak current of the quasi-Z source inductor and the peak value of the output phase current are respectively. When the upper envelope line of the three-phase modulation wave is smaller than the triangular carrier wave in the strategy, the switching tubes of the three bridge arms are all conducted, and the current flowing in the switching tubes isThe single-phase bridge arm direct connection is changed into the three-phase bridge arm direct connection, so that the current flowing through the switching device can be effectively dispersed, and the current stress is reduced.

It is worth mentioning that the improved method has a simple modulation mode, does not need to add extra hardware, is particularly suitable for controlling three-phase saddle waves of traditional voltage space vector modulation (SVPWM) with the phase difference of 120 degrees, and can realize three-phase bridge arm through connection in a plurality of times and in a short time in one period by uniformly adjusting three modulation waves, so that the current stress is greatly reduced.

In order to make the objects, technical solutions and advantages of the present invention more clearly apparent, simulation examples are as follows:

a Matlab/Simulink simulation model of a three-phase quasi-Z source inverter is built, the direct-current voltage on the input side is 220V, the modulation ratio M is 0.88, the inductance-capacitance in a Z source network is L1-L2-4 mH, C1-C2-200 muF, and the load of each phase is 30 omega. The waveform of the current flowing through the switching device of the quasi-Z source inverter adopting the SBMSV strategy is shown in fig. 4, after the inverter works stably, the maximum value of the current flowing through the switching device above the A-phase bridge arm is stabilized at about 10A, and the maximum value of the current flowing through the switching device below the A-phase bridge arm is stabilized at about 7.5A. The waveform of the current flowing through the switching device of the quasi-Z source inverter adopting the proposed modulation strategy is as shown in fig. 5, after the inverter works stably, the maximum value of the current flowing through the switching device above the a-phase bridge arm is stabilized at about 5.5A, and the maximum value of the current flowing through the switching device below the a-phase bridge arm is stabilized at about 5.8A. It is evident that the proposed improved SBMSV strategy results in a substantial reduction of the current stress of the switching device.

It should be noted that the finding that "the SBMSV strategy causes large current stress of the switching device due to continuous commutation, thereby affecting the lifetime of the switching device" is difficult, and it has no universality found, because the large current stress is only additionally obvious in the control strategy of the SBMSV; in addition, the inventors have considered that means for specifically solving the technical problem also do not belong to the conventional means in the art.

The modulation method of the present invention described above can be executed as a software program or computer instructions in a non-transitory computer-readable storage medium or in a control system with a memory and a processor, and the calculation program thereof is simple and fast. Each functional unit in the embodiments of the present invention may be integrated into one processing unit, or each unit may exist alone physically, or two or more units are integrated into one unit. The integrated unit can be realized in a form of hardware, or in a form of hardware plus a software functional unit. The integrated unit implemented in the form of a software functional unit may be stored in a computer readable storage medium. The software functional unit is stored in a storage medium and includes several instructions to enable a computer device (which may be a personal computer, a server, or a network device) or a processor (processor) to execute some steps of the methods according to the embodiments of the present invention. And the aforementioned storage medium includes: various media capable of storing program codes, such as a usb disk, a removable hard disk, a Read-Only Memory (ROM), a Random Access Memory (RAM), a magnetic disk, or an optical disk.

The above examples are only intended to illustrate the technical solution of the present invention, but not to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions of the embodiments of the present invention.