A five-level active neutral point clamped inverter space vector modulation method

Abstract

The application discloses a five-level active neutral point clamped inverter space vector modulation method, which is based on a five-level active neutral point clamped inverter combined in series by a base frequency structure unit and a high frequency structure unit, wherein the base frequency structure unit adopts a space vector modulation strategy, and the high frequency structure unit adopts a carrier phase-shift modulation strategy. The method has the advantages of low algorithm complexity, convenient implementation, easy digital implementation and the like.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of converter control, and particularly relates to a five-level active neutral point clamped inverter space vector modulation method. BACKGROUND

[0002] Multi-level converters have the advantages of high power factor, low switching loss, low harmonic content, low dv / dt, etc., and have been widely applied in new energy power generation, high-voltage variable frequency speed regulation, power system flexible AC / DC transmission and distribution, etc. Among them, the five-level active neutral point clamped inverter has a significant reduction in the number of clamping diodes and floating capacitors compared with the traditional diode clamped inverter and flying capacitor inverter, and is easy to realize the balance control of capacitor voltage, and is receiving more and more attention.

[0003] The SVPWM modulation strategy has the advantages of high voltage utilization rate and small harmonic, however, with the increase of the number of levels and switching tubes of the multi-level inverter, the number of space voltage vectors increases exponentially, among them, the five-level active neutral point clamped inverter has 125 basic space voltage vectors, and the existence of a large number of redundant voltage vectors directly leads to the difficulty of digital implementation of the SVPWM modulation algorithm of the five-level active neutral point clamped inverter. SUMMARY

[0004] In view of the above problems, the purpose of the present application is to provide a five-level active neutral point clamped inverter space vector modulation method, which has the advantages of small algorithm calculation amount and easy digital implementation.

[0005] The application adopts the following technical scheme: a five-level active neutral point clamped inverter space vector modulation method, based on a five-level active neutral point clamped inverter composed of series combination of a fundamental frequency structure unit and a high-frequency structure unit, adopting a space vector modulation strategy for the fundamental frequency structure unit and a carrier phase shift modulation strategy for the high-frequency structure unit, specifically comprising the following steps:

[0006] Step 1, giving a reference voltage U α , U β , calculating the modulation wave U refa , U refb , U refc of the fundamental frequency structure unit according to the three-level inverter space vector modulation method;

[0007] Step 2, calculating the three-phase modulation wave U refa_half , U refb_half , U refc_half of the high-frequency structure unit according to the carrier phase shift PSPWM modulation method;

[0008] Step 3, two-level half-bridge structure carrier wave phase-shift modulation: in order to keep the balance control of suspension capacitor voltage and bus midpoint potential, fine-tune the three-phase modulation wave, and the fine-tuning amount is respectively ΔU refa_com , ΔU refb_com , ΔU refc_com , ΔU ref_dc ;

[0009] Step 4, after comparing the fine-tuned three-phase modulation wave with the corresponding triangular carrier wave, output the final PWM pulse to drive the five-level active neutral point clamped inverter.

[0010] Further, the specific process of the step 1 is:

[0011] Step 1.1, according to the reference voltage U α , U β , the large sector is divided, and the division principle is:

[0012] The first large sector U β > 0 and

[0013] The second large sector U β > 0, and

[0014] The third large sector: U β > 0 and

[0015] The fourth large sector: U β < 0 and

[0016] The fifth large sector: U β < 0 and and

[0017] The sixth large sector: U β < 0 and

[0018] Step 1.2, according to the reference voltage U α , U β , the small sector is divided, and the division principle of the first large sector is:

[0019] The first small sector I_a and

[0020] The first small sector I_b 1-U β -U α > 0 and

[0021] The first small sector I_c and And 0.5-U β >0 and

[0022] sector I_d and And 0.5-U β >0 and

[0023] Sector I_e, 0.5-U β <0;

[0024] sector I_f

[0025] Step 1.3, based on the reference voltage U α U β The sector in question is referenced by a composite voltage vector formed from the three nearest basic voltage vectors. The composition principle and the order of action of the basic vectors are as follows:

[0026] The I_ath small sector: OON-OOO-POO-PPO-POO-OOO-OON;

[0027] I_b small sector: ONN-OON-OOO-POO-OOO-OON-ONN;

[0028] Sector I_c: OON-PON-POO-PPO-POO-PON-OON;

[0029] Sector I_d: ONN-OON-PON-POO-PON-OON-ONN;

[0030] Sector I_e: OON-PON-PPN-PPO-PPN-PON-OON;

[0031] Sector I_f: ONN-PNN-PON-POO-PON-PNN-ONN;

[0032] Step 1.4, based on the reference voltage U α U β The magnitude of the value and the sector where the reference voltage vector is located are used to calculate the duration of the basic voltage vector using the space vector equivalence method. Following the sequence of action of the three basic voltage vectors described in step 1.3, the durations are denoted as T1, T2, and T3 respectively.

[0033] Sector I_a: T1 = 2U β ,

[0034] Sector I_b: T2=2U β ,

[0035] Sector I_c: T3 = 1 - 2U β ;

[0036] Sector I_d: T1 = 1 - 2U β ,

[0037] Sector I_e: T3 = 2U β -1;

[0038] Sector I_f: T3 = 2U β ;

[0039] Step 1.5: Following the methods described in steps 1.1 to 1.4, after coordinate transformation, calculate the voltage vector duration when the reference voltage vector is located in other large sectors. The three-phase modulation wave of the fundamental frequency structural unit is denoted as U. refa U refb U refc .

[0040] Furthermore, the modulation waves of the high-frequency structural units of phase A, phase B, and phase C are respectively U refa_half =U refa U refb_half =U refb U refc_half =U refc .

[0041] Furthermore, the five-level active neutral-point clamping inverter achieves bus neutral-point potential and floating capacitor voltage balance control by fine-tuning the modulation waves of the base frequency structure unit and the high frequency structure unit. The fine-tuning amount for floating capacitor voltage balance control is denoted as ΔU. refa_com , ΔU refb_com , ΔU refc_com The fine-tuning amount for the bus midpoint potential balance control is denoted as ΔU. ref_dc The three-phase modulation wave of the fine-tuned fundamental frequency structure unit is as follows:

[0042]

[0043] The three-phase modulation wave of the fine-tuned high-frequency structural unit is as follows:

[0044]

[0045] Furthermore, the triangular carrier used in the baseband structure unit is denoted as C1, and the triangular carrier used in the high-frequency structure unit is denoted as C2. The phase difference between triangular carrier C1 and triangular carrier C2 is 180°.

[0046] The present invention has the following technical effects: the method of the present invention has the advantages of low algorithm complexity, convenient implementation and easy digital implementation. Attached Figure Description

[0047] Figure 1 This is a flowchart of the space vector modulation method of the present invention;

[0048] Figure 2 This is a topology diagram of the five-level active neutral-point clamping inverter of the present invention;

[0049] Figure 3 This is a schematic diagram of the spatial voltage vector distribution of the fundamental frequency structure unit of the present invention;

[0050] Figure 4 The voltage vector synthesis sequence and action time of the fundamental frequency structure unit of this invention;

[0051] Figure 5 This is a schematic diagram of the carrier phase-shift modulation strategy of the baseband structure unit and the high-frequency structure unit of the present invention.

[0052] The figures are labeled as follows: 1—fundamental frequency structural unit, 2—high frequency structural unit. Detailed Implementation

[0053] To further illustrate the purpose and technical solution of this invention, a detailed description is provided below in conjunction with the accompanying drawings and specific embodiments.

[0054] Reference Figure 1 , Figure 2 As shown, the present invention discloses a space vector modulation method for a five-level active midpoint clamp inverter, which is based on a five-level active midpoint clamp inverter composed of a base frequency structure unit 1 and a high frequency structure unit 2 connected in series. The base frequency structure unit 1 adopts a space vector modulation strategy, and the high frequency structure unit 2 adopts a carrier phase shift modulation strategy. Figure 3 The diagram shows the spatial voltage vector distribution of the fundamental frequency structure unit 1. The spatial voltage vector coordinate system is divided into six large sectors, and each large sector is further divided into six small sectors. Taking the I large sector as an example, it can be divided into six small sectors: a, b, c, d, e, and f.

[0055] The space vector modulation method for a five-level active midpoint clamped inverter of the present invention includes the following steps:

[0056] Step 1, give a reference voltage U α U β The modulation wave U of the fundamental frequency structural unit 1 is calculated based on the space vector modulation principle of the three-level inverter. refa U refb U refc The specific process of step 1 is as follows:

[0057] Step 1.1, based on the reference voltage U α U β The principle for dividing sectors into large sectors is as follows:

[0058] Largest sector U β >0 and

[0059] Second largest sector U β >0, and

[0060] Third major sector: U β >0 and

[0061] Fourth major sector: U β <0 and

[0062] Vth largest sector: U β <0 and and

[0063] VI Major Sector: U β <0 and

[0064] Step 1.2, based on the reference voltage U α U β The process involves dividing the data into smaller sectors, taking the I-th largest sector as an example. The principle for this division is as follows:

[0065] Sector I_a and

[0066] Sector I_b, 1-U β -U α >0 and

[0067] Sector I_c and And 0.5-U β >0 and

[0068] sector I_d and And 0.5-U β >0 and

[0069] Sector I_e, 0.5-U β <0;

[0070] sector I_f

[0071] Step 1.3, based on the reference voltage U α U β The sector in question is referenced by a composite voltage vector formed from the three nearest basic voltage vectors. The composition principle and the order of action of the basic vectors are as follows:

[0072] The I_ath small sector: OON-OOO-POO-PPO-POO-OOO-OON;

[0073] I_b small sector: ONN-OON-OOO-POO-OOO-OON-ONN;

[0074] Sector I_c: OON-PON-POO-PPO-POO-PON-OON;

[0075] Sector I_d: ONN-OON-PON-POO-PON-OON-ONN;

[0076] Sector I_e: OON-PON-PPN-PPO-PPN-PON-OON;

[0077] Sector I_f: ONN-PNN-PON-POO-PON-PNN-ONN;

[0078] Step 1.4, based on the reference voltage U α U β The magnitude of the value and the sector where the reference voltage vector is located are used to calculate the duration of the basic voltage vector using the principle of space vector equivalence. Following the sequence of action of the three basic voltage vectors described in step 1.3, the durations are denoted as T1, T2, and T3 respectively.

[0079] Sector I_a: T1 = 2U β ,

[0080] Sector I_b: T2=2U β ,

[0081] Sector I_c: T3 = 1 - 2U β ;

[0082] Sector I_d: T1 = 1 - 2U β ,

[0083] Sector I_e: T3 = 2U β -1;

[0084] Sector I_f: T3 = 2U β ;

[0085] Step 1.5: Following the methods described in steps 1.1 to 1.4, after coordinate transformation, calculate the voltage vector duration when the reference voltage vector is located in other large sectors. The three-phase modulation wave of the fundamental frequency structure unit 1 is denoted as U. refa U refb U refc .

[0086] Step 2: Calculate the three-phase modulation wave U of high-frequency structural unit 2 based on the carrier phase-shifted PSPWM modulation principle. refa_half U refb_half U refc_half .

[0087] Step 3, Two-level half-bridge structure carrier phase-shift modulation: To maintain the balance control of the floating capacitor voltage and the bus midpoint potential, the three-phase modulation wave is fine-tuned, and the fine-tuning amount is denoted as ΔU. refa_com , ΔU refb_com , ΔU refc_com , ΔU ref_dc .

[0088] Step 4: After comparing the finely tuned three-phase modulation wave with the corresponding triangular carrier wave, the final PWM pulse is output to drive the five-level active midpoint clamp inverter.

[0089] The modulation waves of the high-frequency structural units 2 of phase A, phase B, and phase C are respectively U refa_half =U refa U refb_half =U refb U refc_half =U refc .

[0090] The five-level active neutral-point clamping inverter achieves bus neutral-point potential and floating capacitor voltage balance control by fine-tuning the modulation waves of the base frequency structural unit 1 and the high frequency structural unit 2. The fine-tuning amount for floating capacitor voltage balance control is denoted as ΔU. refa_com , ΔU refb_com , ΔU refc_com The fine-tuning amount for the bus midpoint potential balance control is denoted as ΔU. ref_dc The three-phase modulation wave of the fine-tuned fundamental frequency structure unit 1 is as follows:

[0091]

[0092] The three-phase modulation wave of the fine-tuned high-frequency structural unit 2 is as follows:

[0093]

[0094] The triangular carrier used in the fundamental frequency structure unit 1 is denoted as C1, and the triangular carrier used in the high frequency structure unit 2 is denoted as C2. The phase difference between triangular carrier C1 and triangular carrier C2 is 180°.

[0095] Figure 4 The diagram shows the principle and sequence of voltage vector synthesis for fundamental frequency structural unit 1 in sector I. When the voltage vector is located in other sectors, coordinate transformation can be used to represent it in sector I, thereby determining the sequence of basic voltage vector action and calculating the voltage vector action time.

[0096] Figure 5 The diagram shows the carrier phase-shift modulation strategy of the baseband structural unit 1 and the high-frequency structural unit 2. After the calculated three-phase modulation waves of the baseband structural unit 1 and the high-frequency structural unit 2 are compared with the triangular carrier with a phase difference of 180°, the PWM signal is obtained to drive the five-level active midpoint clamp inverter, realizing an equivalent five-level active midpoint clamp inverter space vector modulation strategy.

[0097] The above embodiments are merely illustrative of the principles and effects of the present invention. For those skilled in the art, various modifications and improvements can be made without departing from the inventive concept of the present invention, and these modifications and improvements all fall within the protection scope of the present invention.

Claims

1. A space vector modulation method for a five-level active neutral-point clamped inverter, characterized in that: A five-level active neutral-point clamp inverter, based on a series combination of a baseband structural unit (1) employing a space vector modulation strategy and a high-frequency structural unit (2) employing a carrier phase-shift modulation strategy, includes the following steps: Step 1, give a reference voltage U α U β The modulation wave U of the fundamental frequency structural unit (1) is calculated according to the space vector modulation method of the three-level inverter. refa U refb U refc ; Step 2: Calculate the three-phase modulation wave U of the high-frequency structural unit (2) according to the carrier phase-shifted PSPWM modulation method. refa_half U refb_half U refc_half ; The bus midpoint potential and floating capacitor voltage balance control are achieved by fine-tuning the modulation waves of the fundamental frequency structure unit (1) and the high frequency structure unit (2). The fine-tuning amount of the floating capacitor voltage balance control is denoted as ΔU. refa_com , ΔU refb_com , ΔU refc_com The fine-tuning amount for the bus midpoint potential balance control is denoted as ΔU. ref_dc The three-phase modulation wave of the fine-tuned fundamental frequency structure unit (1) is as follows: The three-phase modulation wave of the fine-tuned high-frequency structural unit (2) is as follows: ; Step 3: Maintain the balance between the floating capacitor voltage and the bus midpoint potential, and fine-tune the three-phase modulation wave by adjusting ΔU. refa_com , ΔU refb_com , ΔU refc_com , ΔU ref_dc ; Step 4: Compare the finely tuned three-phase modulation wave with the corresponding triangular carrier wave, and output the final PWM pulse to drive the five-level active midpoint clamp inverter.

2. The space vector modulation method for a five-level active neutral-point clamped inverter according to claim 1, characterized in that, The specific process of step 1 is as follows: Step 1.1, based on the reference voltage U α U β Perform large sector partitioning: Largest sector U β >0 and U β - U α <0; II Ogi Ward U β > 0, U β - U α >0 and U β + U α >0; Third major sector: U β >0 and U β + U α <0; Fourth major sector: U β <0 and U β - U α >0; V Oogi Ward: U β <0AU β - U α <0AU β + U α <0; VI Major Sector: U β <0 and U β + U α >0; Step 1.2, based on the reference voltage U α U β We will divide the data into smaller sectors, taking the I-th largest sector as an example: No. I_a Koogi Ward 1-U β - U α >0 and U β -U α >0; No. I_b Koogi Ward 1-U β -U α >0 and U β -U α <0; No. I_c Koogi-ku 1-U β - U α >0 and U β - U α +1 > 0 and 0.5 - U β >0 and U β -U α >0; No. I_d Koogi-ku 1-U β - U α <0AU β - U α +1 > 0 and 0.5 - U β >0 and U β -U α <0; Sector I_e, 0.5-U β <0; Sector U of type I_f β - U α +1 < 0; Step 1.3, based on the reference voltage U α U β The sector in question is defined by a reference voltage vector synthesized from the three nearest fundamental voltage vectors: The I_ath small sector: OON-OOO-POO-PPO-POO-OOO-OON; I_b small sector: ONN-OON-OOO-POO-OOO-OON-ONN; Sector I_c: OON-PON-POO-PPO-POO-PON-OON; Sector I_d: ONN-OON-PON-POO-PON-OON-ONN; Sector I_e: OON-PON-PPN-PPO-PPN-PON-OON; Sector I_f: ONN-PNN-PON-POO-PON-PNN-ONN; Step 1.4, based on the reference voltage U α U β The magnitude of the value and the sector where the reference voltage vector is located are used to calculate the duration of the basic voltage vector using the space vector equivalence method. Following the sequence of action of the three basic voltage vectors described in step 1.3, the durations are denoted as T1, T2, and T3 respectively. No. I_a small fan ward: T1=2U β , T2=1- U α -U β , T3= U α -U β ; No. I_b small fan ward: T1= U α -U β T2 = 2U β T3=1- Uα-U β ; Sector I_c: T1=1- U α +U β T2= Uα+U β T3=1-2U β ; Sector I_d: T1 = 1 - 2U β T2=1- Uα+U β T3= Uα+U β ; Sector I_e: T1=2- Uα-U β T2= Uα-U β T3=2U β -1; Sector I_f: T1=2- Uα-U β T2= Uα-U β -1、T3=2U β ; Step 1.5: Following the methods described in steps 1.1 to 1.4, after coordinate transformation, calculate the voltage vector action time when the reference voltage vector is located in other large sectors. The three-phase modulation wave of the fundamental frequency structure unit (1) is denoted as U. refa U refb U refc .

3. The space vector modulation method for a five-level active neutral-point clamped inverter according to claim 2, characterized in that, The triangular carrier used in the baseband structure unit (1) is denoted as C1, and the triangular carrier used in the high-frequency structure unit (2) is denoted as C2. The phase difference between the triangular carrier C1 and the triangular carrier C2 is 180°.

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