阅读说明：本技术 五电平有源中点钳位h桥变频器单相空间矢量调制方法 (Five-level active neutral point clamped H-bridge frequency converter single-phase space vector modulation method ) 是由 肖飞 胡亮灯 蒋林飞 辛子越 吴文捷 楼徐杰 任强 于 2020-12-16 设计创作，主要内容包括：本发明公开了一种五电平有源中点钳位H桥变频器单相空间矢量调制方法,根据变频器共模电压最小原则和开关状态切换约束对变频器的开关状态进行筛选-确定期望输出电压矢量所在矢量区间采用的基本电压矢量-根据伏秒平衡原理计算基本电压矢量的作用时间-根据基本电压矢量的作用时间、反馈回来的中点电位偏差和悬浮电容器电压偏差计算各开关状态的作用时间-根据开关动作次数最小的原则确定一个控制周期内开关状态序列-根据一个控制周期内开关状态序列及各开关状态的作用时间生成脉冲发送给变频器。通过综合考虑输出电压、中点电位平衡、悬浮电容器电压平衡来产生脉冲,实现中点电位和悬浮电容器电压的解耦控制。(The invention discloses a single-phase space vector modulation method of a five-level active neutral point clamping H-bridge frequency converter, which comprises the steps of screening the switching state of the frequency converter according to the minimum principle of common-mode voltage of the frequency converter and the switching state switching constraint, determining a basic voltage vector adopted in a vector interval where an expected output voltage vector is located, calculating the action time of the basic voltage vector according to the volt-second balance principle, calculating the action time of each switching state according to the action time of the basic voltage vector, the fed back neutral point potential deviation and the voltage deviation of a suspension capacitor, determining a switching state sequence in a control period according to the principle that the number of switching actions is minimum, and generating pulses according to the switching state sequence in the control period and the action time of each switching state and sending the pulses to the frequency converter. The decoupling control of the midpoint potential and the voltage of the suspension capacitor is realized by generating pulses by comprehensively considering the output voltage, the midpoint potential balance and the voltage balance of the suspension capacitor.)

1. A single-phase space vector modulation method for a five-level active neutral point clamped H-bridge frequency converter is characterized by comprising the following steps: the modulation method comprises the following steps:

1) screening the switching state of the frequency converter according to a frequency converter common-mode voltage minimum principle and switching state switching constraint;

2) determining a vector interval where an expected output voltage vector is located and a basic voltage vector adopted;

3) calculating the action time of a basic voltage vector according to a volt-second balance principle;

4) calculating the action time of each switch state according to the action time of the basic voltage vector, the fed back midpoint potential deviation and the voltage deviation of the suspension capacitor;

5) determining a switching state sequence in a control period according to the principle that the switching action times are minimum;

6) and generating pulses according to the switching state sequence in one control period and the action time of each switching state, and sending the pulses to the frequency converter.

2. The single-phase space vector modulation method of the five-level active midpoint clamping H-bridge frequency converter according to claim 1, characterized in that: in the step 1), the principle of screening the on-off state of the frequency converter specifically includes: 1) the common-mode voltage is minimum, the common-mode voltage of the frequency converter is defined as half of the sum of the output voltages of the two bridge arms, and the switching vector with the common-mode voltage larger than E/2 is eliminated; 2) the switching vectors are convenient to switch, unexpected output voltage jump does not occur in the switching process and before and after switching, and the switching action times are reduced.

3. The single-phase space vector modulation method of the five-level active midpoint clamping H-bridge frequency converter according to claim 1, characterized in that: in the step 2), the adopted basic voltage vector is determined according to the vector interval where the expected output voltage vector is located, and the expected output voltage vector expression is as follows:

V^*＝V_mcos(ωt)＝4mEcos(ωt) (15)

wherein, omega is the angular frequency of the modulation wave, m is the modulation ratio, E is the voltage value corresponding to the difference between the adjacent levels;

the vector interval and the modulation ratio correspond to each other as follows:

4. the single-phase space vector modulation method of the five-level active midpoint clamping H-bridge frequency converter according to claim 1, characterized in that: in said step 3), usingRepresenting a voltage vector of smaller modulus, T₁To representThe acting time is as long as the composition is applied,representing a voltage vector of greater modulus, T₂To representTime of action, T_sRepresents a control cycle, and the calculation formula is as follows:

5. the single-phase space vector modulation method of the five-level active midpoint clamping H-bridge frequency converter according to claim 1, characterized in that: in the step 4), the action time of each switch state meets the following conditions:

wherein t is₁～t₈The action time for 8 switch states. x is the number of₁～x₈、y₁～y₈、z₁～z₈Are close in absolute value; the parameters A, B, C, D, E are defined as:

wherein: c_dFor the capacitance of the DC support capacitor, C_fIs the capacitance value of the floating capacitor, i_oIs the load current u_d1、u_d2For supporting the capacitor C for DC_d1、C_d2Voltage of u_fa、u_fbIs a floating capacitor C_fa、C_fbVoltage of u_dcIs the value of the DC power supply voltage.

6. The single-phase space vector modulation method of the five-level active midpoint clamping H-bridge frequency converter according to claim 1, characterized in that: in the step 4), if the calculated action time of the switch state is negative, the variable C, D, E is changed to be half of the original value to be recalculated, and if the action time is negative, the above process is repeated until the solution meets the condition.

Technical Field

The invention relates to the technical field of five-level active neutral point clamped multiphase H-bridge frequency converters, in particular to a single-phase space vector modulation method of a five-level active neutral point clamped H-bridge frequency converter.

Background

In order to adapt to the increase of load of ships and warships, the direct-current voltage of a future integrated power system can be increased to a higher level, the device voltage-withstanding level is combined, the device adaptability is considered, the topology suitable for the field of variable-frequency speed regulation is mainly a five-level active neutral point clamped topology, and the topology is one of the topologies with application prospects at present. The medium-high voltage multi-phase open winding motor system can meet the requirements of a high-power electric propulsion system on large capacity, good reliability, high torque density and the like, and becomes a preferred scheme of a ship high-capacity propulsion frequency converter. The frequency converter of the matched multiphase open winding motor system can adopt a five-level active neutral point clamped H-bridge topological scheme. As shown in fig. 1, a multiphase H-bridge frequency converter topology is shown, a single five-level active midpoint clamping H-bridge frequency converter can output nine levels, the increase of the number of levels also increases the space vector selection range, the modulation technology becomes more complex, and if the multiphase H-bridge frequency converter adopts uniform space vector control, the realization is very complex, and the improvement of the control independence of the multiphase H-bridge frequency converter and the redundancy of device fault operation are not facilitated. In addition, considering that each five-level active midpoint clamping H-bridge unit main circuit and control are relatively independent, a separate space vector control strategy can be adopted for each H-bridge topology frequency converter for the multiphase H-bridge topology.

For a five-level active neutral point clamped H-bridge frequency converter, the problem of balancing control of the voltage of a direct current capacitor and the voltage of a suspension capacitor exists, and the balance of the voltage of the direct current capacitor and the voltage of the suspension capacitor is needed to be realized while multi-level pulse output is needed in control. In addition, coupling exists between the direct current capacitor voltage of the five-level active neutral point clamped H-bridge frequency converter and the control of the voltage of the suspension capacitor, and the conventional carrier phase shift modulation is inconvenient to realize decoupling control. The switching state of the switching tube can be flexibly appointed by adopting a space vector modulation technology, and the control target is easy to realize.

The conventional control method is to control the midpoint potential and the voltage of the floating capacitor respectively, control the midpoint potential by injecting common mode voltage, and control the voltage of the floating capacitor by selecting a redundant vector. The midpoint potential is controlled before, the floating capacitor voltage is controlled after, and different redundant states also have influence on the midpoint average current, thereby possibly causing the midpoint potential to be deteriorated. Take two redundant states with an output level of-E as an example. As shown in fig. 2 and 3, the output levels of both states are-E, which has opposite effects on the floating capacitor, while the current in fig. 2 discharges the floating capacitor without affecting the midpoint potential; the current charging the floating capacitor in fig. 3 affects the midpoint potential, and the voltages of the floating capacitors can be balanced by switching the two redundant states. However, the problem arises that changing the redundant state causes additional midpoint current, which causes the midpoint potential to fluctuate.

Disclosure of Invention

The invention aims to provide a single-phase space vector modulation method of a five-level active neutral point clamped H-bridge frequency converter, aiming at the defects of the technology, which can realize the complete decoupling of neutral point potential and suspension capacitor voltage control and can accurately compensate according to the deviation of the neutral point potential and the suspension capacitor voltage.

In order to achieve the purpose, the single-phase space vector modulation method of the five-level active neutral point clamped H-bridge frequency converter is as follows:

1) screening the switching state of the frequency converter according to a frequency converter common-mode voltage minimum principle and switching state switching constraint;

2) determining a vector interval where an expected output voltage vector is located and a basic voltage vector adopted;

3) calculating the action time of a basic voltage vector according to a volt-second balance principle;

4) calculating the action time of each switch state according to the action time of the basic voltage vector, the fed back midpoint potential deviation and the voltage deviation of the suspension capacitor;

5) determining a switching state sequence in a control period according to the principle that the switching action times are minimum;

6) and generating pulses according to the switching state sequence in one control period and the action time of each switching state, and sending the pulses to the frequency converter.

Further, in the step 1), the principle of screening the switching state of the frequency converter specifically includes: 1) the common-mode voltage is minimum, the common-mode voltage of the frequency converter is defined as half of the sum of the output voltages of the two bridge arms, and the switching vector with the common-mode voltage larger than E/2 is eliminated; 2) the switching vectors are convenient to switch, unexpected output voltage jump does not occur in the switching process and before and after switching, and the switching action times are reduced.

Further, in step 2), the adopted basic voltage vector is determined according to the vector interval where the expected output voltage vector is located, and the expected output voltage vector expression is as follows:

V^*＝V_mcos(ωt)＝4mEcos(ωt) (1)

wherein, omega is the angular frequency of the modulation wave, m is the modulation ratio, E is the voltage value corresponding to the difference between the adjacent levels;

the vector interval and the modulation ratio correspond to each other as follows:

further, in the step 3), theRepresenting a voltage vector of smaller modulus, T₁To representThe acting time is as long as the composition is applied,representing a voltage vector of greater modulus, T₂To representTime of action, T_sRepresents a control cycle, and the calculation formula is as follows:

further, in the step 4), the action time of each switch state satisfies:

wherein t is₁ t₈The action time for 8 switch states. x is the number of₁～x₈、y₁～y₈、z₁～z₈Are close in absolute value; the parameter A, B, C, D, E is defined as:

wherein: c_dFor the capacitance of the DC support capacitor, C_fIs the capacitance value of the floating capacitor, i_oIs the load current u_d1、u_d2For supporting the capacitor C for DC_d1、C_d2Voltage of u_fa、u_fbIs a floating capacitor C_fa、C_fbVoltage of u_dcIs the value of the DC power supply voltage.

Further, in the step 4), if the calculated action time of the switch state is negative, the variable C, D, E is changed to the original half to be recalculated, and if the action time is negative, the above process is repeated until the solution meets the condition.

Compared with the prior art, the invention has the following advantages: the invention discloses a five-level active neutral point clamped H-bridge frequency converter single-phase space vector modulation method which generates pulses by comprehensively considering output voltage, neutral point potential balance and suspension capacitor voltage balance to realize decoupling control of neutral point potential and suspension capacitor voltage. The control of the midpoint potential and the voltage of the suspension capacitor is converted into the change of the action time of each switch state, and the accurate compensation of the midpoint potential and the voltage deviation of the suspension capacitor can be realized.

Drawings

FIG. 1 is a schematic diagram of a five-level active midpoint clamped multiphase H-bridge frequency converter in the prior art;

FIG. 2 is a schematic diagram of the current discharge to the floating capacitor of FIG. 1;

FIG. 3 is a schematic diagram of the current flow of FIG. 1 charging the floating capacitor;

FIG. 4 is a schematic diagram of a five-level active midpoint clamped H-bridge frequency converter according to the present invention;

FIG. 5 is a modulation flow diagram of FIG. 4;

FIG. 6 is a voltage space vector diagram of FIG. 4;

FIG. 7 is a schematic diagram of the voltage vector synthesis of FIG. 4;

FIG. 8 is a schematic diagram of the switch state sequence of FIG. 4;

fig. 9 is a waveform diagram of the modulation method of fig. 4.

Detailed Description

The invention is described in further detail below with reference to the figures and the specific examples.

Fig. 4 shows a structure of a five-level active midpoint clamped H-bridge frequency converter, which includes two bridge arms having completely identical structures, and each bridge arm is a five-level active midpoint clamped topology structure. The five-level active neutral point clamped H-bridge frequency converter comprises a direct-current power supply, 24 switching tubes, anti-parallel diodes of the switching tubes, 1 current sensor, 4 voltage sensors, a controller, an AD sampling chip and a start-end motor winding. DC power supply anode and DC support capacitor C_d1Positive electrode of (2), direct currentSource cathode and DC support capacitor C_d2The output ends of two bridge arms of the H bridge are respectively connected with two ends of a phase winding of the end motor, two ends of each capacitor in the five-level active neutral point clamping H bridge frequency converter are provided with a voltage sensor, the output ends are provided with current sensors, secondary side signals are connected with an AD sampling chip, the AD sampling chip is connected to a controller, and the controller outputs pulses to a switching tube.

The single bridge arm five-level active neutral point clamped topological structure comprises a direct current support capacitor C_d1And C_d2First to twelfth switching tubes S_x1-S_x12And a floating capacitor C_fx. Wherein, the first to the twelfth switching tubes S_x1-S_x12All having anti-parallel diodes. Fifth switch tube S_x5Emitter and sixth switching tube S_x6Collector electrode connection of, sixth switching tube S_x6Emitter and first switch tube S_x1Collector electrode connection of, first switching tube S_x1Emitter and second switch tube S_x2Collector electrode connection of, a second switching tube S_x2Emitter and third switch tube S_x3Collector electrode connection, third switching tube S_x3Emitter and fourth switching tube S_x4Collector electrode connection, fourth switching tube S_x4Emitter of (2) and eleventh switch tube S_x11Collector electrode of (1), eleventh switching tube S_x11Emitter and twelfth switch tube S_x12Collector electrode connection of, sixth switching tube S_x6Emitter and seventh switching tube S_x7Collector electrode connection of, seventh switching tube S_x7Emitter and eighth switching tube S_x8Collector electrode of (1), an eighth switching tube S_x8Emitter and ninth switching tube S_x9Collector electrode of (1), ninth switching tube S_x9Emitter and tenth switching tube S_x10Collector electrode connection, fifth switching tube S_x5Collector electrode of (1) and (C)_d1Positive electrode of the switching tube S_x12Emitter and C of_d2Negative electrode connection and suspension capacitor C_fxPositive electrode of (2) and seventh switching tube S_x7Emitter-connected, floating capacitor C of_fxNegative pole of (2) and ninth switching tube S_x9Is connected to the eighth switching tube S_x8Is connected to the load, and DC supports the capacitor C_d1Negative electrode of (2) and DC support capacitor C_d2Is connected to the positive electrode.

As shown in fig. 5, the single-phase space vector modulation method of the five-level active midpoint clamping H-bridge frequency converter is as follows:

1) screening the switch state of the frequency converter according to the common-mode voltage minimum principle and the switch state switching constraint of the frequency converter

The principle of screening the on-off state of the frequency converter is as follows: 1) the common-mode voltage is minimum, the common-mode voltage of the frequency converter is defined as half of the sum of the output voltages of the two bridge arms, and the switching vector with the common-mode voltage larger than E/2 is eliminated; 2) the switching vectors are convenient to switch, unexpected output voltage jump does not occur in the switching process and before and after switching, and the switching action times are reduced. After screening, 28 available switch states are obtained.

2) Determining the vector interval in which the desired output voltage vector is located and the basic voltage vector used

Determining the adopted basic voltage vector according to the vector interval where the expected output voltage vector is located, wherein the expected output voltage vector expression is as follows:

V^*＝V_mcos(ωt)＝4mEcos(ωt) (6)

where ω is the angular frequency of the modulated wave, m is the modulation ratio, and E is the voltage value corresponding to the difference between adjacent levels.

The vector interval and the modulation ratio correspond to each other as follows:

where m is the modulation ratio.

3) Calculating the action time of the basic voltage vector according to the volt-second balance principle

By usingRepresenting a voltage vector of smaller modulus, T₁To representThe acting time is as long as the composition is applied,representing a voltage vector of greater modulus, T₂To representTime of action, T_sRepresents a control cycle, and the calculation formula is as follows:

4) calculating the action time of each switch state according to the action time of the basic voltage vector, the fed back midpoint potential deviation and the voltage deviation of the suspension capacitor

The action time of each switch state is determined to be capable of controlling the midpoint potential and the floating capacitors of the two bridge arms, and the form of the expression is unified as much as possible and satisfies the following conditions:

wherein t is₁～t₈The action time for 8 switch states. x is the number of₁～x₈、y₁～y₈、z₁～z₈As close as possible to the absolute value of (c). The parameter A, B, C, D, E is defined as:

wherein: c_dFor the capacitance of the DC support capacitor, C_fIs the capacitance value of the floating capacitor, i_oIs the load current u_d1、u_d2For supporting the capacitor C for DC_d1、C_d2Voltage of，u_fa、u_fbIs a floating capacitor C_fa、C_fbVoltage of u_dcIs the value of the DC power supply voltage.

If the calculated on-time of the switch state is negative, then the variable associated with the midpoint potential and floating capacitor control (i.e., variable C, D, E) is recalculated to half it, and if it is negative, the process is repeated until the solution satisfies the condition.

5) And determining a switching state sequence in a control period according to the principle that the switching action times are minimum.

6) And generating pulses according to the switching state sequence in one control period and the action time of each switching state, and sending the pulses to the frequency converter.

And generating pulses according to the calculated switching state sequence and the action time thereof and sending the pulses to the switching tube.

The following is described in further detail with reference to examples.

(1) Table 1 shows the switching state of one arm of the five-level active midpoint clamped H-bridge frequency converter. The switching state of a five-level active midpoint clamping H-bridge frequency converter is represented by mn, where the switching state of the a-bridge arm is Vm, the switching state of the b-bridge arm is Vn, and (m, n is 0,1 … 7).

TABLE 1

The switching states of the frequency converter are screened according to the following principles: 1) the common mode voltage is minimal. The common-mode voltage of the frequency converter is defined as half of the sum of the output voltages of the two bridge arms. And eliminating 26 switching vectors with common mode voltage larger than E/2. 2) The switching between the switching vectors should be facilitated, and unexpected output voltage jump should not occur during and before the switching, and increase of the switching operation frequency should be avoided. Dividing the switch state of one bridge arm of the frequency converter into two groups: g1{ V0, V1, V2, V3} and G2{ V4, V5, V6, V7 }. Defining the switching process of two bridge arms, wherein the first switching process is that the switching state of the bridge arm is switched between G1 and G2, and at the moment, all serial switching tubes and part of non-serial switching tubes are required to act; the second is that the switching state of the bridge arm is switched inside G1 or G2, only partial non-series switching tube action is needed at the moment, and the loss is obviously smaller than that of the first switching process. Through the analysis of the switching state switching, it can be known that when the switching states of the two legs of the H-bridge come from G1 at the same time or from G2 at the same time, the probability of the first switching process occurring increases, and therefore 8 switching vectors in the form of G1G1 and G2G2 are rejected. The remaining switching vectors are combined in the form of G2G1 or G1G 2.

(2) And (3) judging the interval where the expected output voltage vector is located: as shown in FIG. 6, there are nine discrete basic voltage vectors { -4E, -3E, -2E, -E,0, E,2E,3E,4E }, and the basic voltage vector to be used is determined according to the interval in which the desired output voltage vector is located. The desired output voltage vector expression is:

V^*＝V_mcos(ωt)＝4mEcos(ωt) (11)

where ω is the angular frequency of the modulated wave, m is the modulation ratio, and E is the voltage value corresponding to the difference between adjacent levels. The corresponding relation between the modulation ratio and the vector interval is as follows:

(3) the action time of the basic voltage vector is calculated according to the volt-second balance principle, as shown in fig. 7. If it is usedRepresenting a voltage vector of smaller modulus, T₁To representThe acting time is as long as the composition is applied,representing a voltage vector of greater modulus, T₂To representTime of action, T_sRepresenting a control cycle, the calculation of whichThe formula is as follows:

(4) determining the action time of each switch state: the switch states corresponding to the vector sections are numbered 1 to 8 as shown in table 2. The action time t of each switch state can be calculated according to the influence of different switch states on the midpoint potential and the voltage of the floating capacitor₁～t₈As shown in Table 3, the parameter A, B, C, D, E in Table 3 is defined as:

wherein: c_dFor the capacitance of the DC support capacitor, C_fIs the capacitance value of the floating capacitor, i_oIs the load current u_d1、u_d2For supporting the capacitor C_d1、C_d2Voltage of u_fa、u_fbFor supporting the capacitor C_fa、C_fbVoltage of u_dcIs a dc supply voltage.

TABLE 2

TABLE 3

(5) The output sequence of the switch state in one control cycle is determined according to the principle of minimum switching times, as shown in fig. 8:

(6) to facilitate control of the transition between cycles, willAnd generating a pulse according to the calculated switching state sequence and the action time thereof and sending the pulse to the frequency converter.

A simulation result of the five-level active neutral point clamped H-bridge topological frequency converter based on a space vector modulation strategy is provided. The initial voltage values of the DC support capacitors are set to be 6000V and 4000V respectively, (reference value 5000V), and the balance is adjusted for about 120 ms; the initial value of the voltage of the floating capacitor is set to 2000V (reference value 2500V), the balance is adjusted in about 40ms, and the validity of the space vector control strategy is verified. Fig. 9 shows simulation results of a five-level active midpoint clamping H-bridge topology frequency converter based on space vector modulation (simulation waveforms are, from top to bottom, direct-current capacitor voltage, floating capacitor voltage, H-bridge output voltage, and alternating-current output current).