A synchronous motor control algorithm

Abstract

A synchronous motor control algorithm is proposed to solve the inherent DC side capacitor midpoint voltage offset of NPC structure three-level inverter and the traditional SVPWM algorithm with multiple sector divisions and complex calculations. A target flux linkage simplified tracking algorithm with hidden midpoint vector is proposed in this paper. The input voltage space vector is divided into large and small sectors to improve the SVPWM algorithm: based on the principle of hiding the midpoint vector and using zero vector, small vector and large vector for modulation, the area where the voltage space vector passes is divided into 18 asymmetric sectors to form an SVPWM control model. Finally, a Simulink simulation platform is built to verify the correctness of the improved algorithm under different modulation degrees. The correctness of the line voltage output waveform and the feasibility of balanced control of the midpoint potential of the DC side capacitor of the three-level inverter. This design can not only realize the balanced control of the midpoint potential, but also reduce the amount of calculation by half and the waveform distortion rate is small.

Description

Technical Field

[0001] The present invention relates to a synchronous motor control target flux simplification algorithm based on an NPC structure three-level inverter with hidden mid-point vector, which is specifically suitable for optimizing sector division and realizing balanced control of mid-point potential. Background Art

[0002] At present, two-level inverters are limited by the switching stress and rated power level of semiconductor devices and cannot be adapted to high-power load applications such as mine hoisting and locomotive traction. Compared with two-level inverters, diode-clamped NPC three-level inverters subdivide the DC bus voltage into three levels through a group of capacitors in series, thereby avoiding the problem of excessive voltage drop of a single semiconductor device. With the series distribution of three-phase symmetrical semiconductor devices and SVPWM algorithm, the quality of the output voltage waveform is better and the switching loss of a single device is lower, making it widely used in the above-mentioned high-voltage and high-power equipment.

[0003] When the DC side is powered by a single rectifier, the capacitor voltage balancing problem is a difficult problem for NPC inverter control. The existing technology also considers many methods to solve this problem:

[0004] Method 1: It is proposed to introduce positive and negative vector time adjustment factors and use PI controller to adjust the capacitor voltage. However, there are a lot of assumptions and repeated verifications in the PI parameter setting process.

[0005] Method 2: It is proposed to use an active bridge voltage chopper to control the capacitor voltage, but this method has limited ability to adjust the voltage range.

[0006] Method 3: It is proposed to power each capacitor with a separate isolated BUCK / BOOST DC power supply. This method is likely to increase hardware and maintenance costs.

[0007] Method 4: A "prediction-verification-correction" zero-sequence voltage injection method is proposed. The three-phase positive-sequence voltage sign is used to estimate the required injected zero-sequence voltage, and then the judgment rule is used for verification and correction to obtain a zero-sequence voltage that meets the requirements.

[0008] Method 5: A modulation method based on the nearest virtual vector is proposed. This method eliminates the influence of the center vector on the capacitor voltage fluctuation, but the calculation process involves the cross-sector synthesis of the voltage vector, and the output voltage waveform has a large amount of odd harmonic components. Summary of the invention

[0009] The purpose of the present invention is to overcome the problem in the prior art that the unbalanced midpoint potential of an NPC structure three-level inverter leads to unbalanced charging and discharging of capacitors, and to provide a simplified algorithm for synchronous motor control target flux linkage based on an NPC structure three-level inverter with hidden mid vector to achieve balanced control of the midpoint potential.

[0010] To achieve the above objectives, the technical solution of the present invention is:

[0011] A synchronous motor control algorithm, the synchronous motor control algorithm is used to control the NPC structure three-level inverter circuit of the permanent magnet synchronous motor,

[0012] Step 1: Analyze the unbalanced mechanism of the midpoint potential on the DC side of the NPC structure three-level inverter, and draw the conclusion that the influence of the neutral vector on the voltage value of capacitors C1 and C2 is uncontrollable;

[0013] Step 2: Divide the input voltage space vector into large and small sectors, and improve the SVPWM algorithm: Based on the principle of hiding the middle vector and using zero vector, small vector, and large vector for modulation, the area where the voltage space vector passes is divided into 18 asymmetric sectors;

[0014] Step 3: Arrange the switching sequence of each small sector inverter to form a switching sequence chart. To reduce the stress of the switching device, a switching cycle T sw The inverter outputs 7 symmetrical voltage vectors in succession within the range, according to the target space voltage vector V ref The sector number it falls into is used to formulate the action sequence table of the basic voltage vector;

[0015] Step 4: Determine the action time of each switching vector, form the SVPWM control model, and select the vector V on the left side of the large sector. s1 , the vector V on the right s2 and zero vector V s0 Synthesized target voltage vector V ref , V s1 、V s2 、V s0 The vector action times correspond to T1, T2, and T0 respectively. According to the vector synthesis rules of different small sectors, the vector action time in each small sector is calculated respectively; then, the combined switch control pulse situation corresponding to each sector is obtained according to the basic vector action time. Finally, according to the switching state and trigger time of each sector, the trigger time table of the switch devices in each sector is sorted out to form the SVPWM control model.

[0016] The DC bus voltage in the NPC structure three-level inverter circuit is V dc , two capacitors C1 and C2 of the same capacitance are connected in series on the DC bus, the connection point of capacitors C1 and C2 is the DC side midpoint o, the DC side positive pole is point P, and the DC side negative pole is point N; the NPC structure three-level inverter circuit inverts DC power into three-phase power, and a three-phase bridge arm is set in the circuit, and each phase bridge arm has four parallel freewheeling diodes D xn The IGBT tube S connected in series xn , and set two clamping diodes Dx5 , D x6 The midpoint of the two series-connected IGBT tubes is connected to the midpoint o of the DC side capacitor through a clamping diode, so that the output voltage is clamped at the potential of the DC side midpoint o, that is, the voltage on each IGBT tube is limited to a capacitor voltage. The clamping diode D x5 , D x6 Another function of is to provide a current channel to prevent the capacitor from short-circuiting when the IGBT tube is turned on; the midpoint of each phase bridge arm is connected to the load and then connected to the load midpoint o'; in the above subscripts: x represents any phase among the three phases A, B, and C, and n represents the serial number of the switch tube of each phase, with a value range of 1 to 4;

[0017] The analysis process of step 1 is as follows:

[0018] 36-sector NPC three-level voltage inverter, can output three voltages, namely: V dc / 2, 0, and -V dc / 2;

[0019] IGBT switch variable S xn There are only two possible values: 1 and 0. The corresponding working states of the x-phase circuit are shown in Table 1:

[0020] Table 1 Switching signal and x-phase circuit working state table

[0021]

[0022] The inverter output voltage is expressed in matrix form:

[0023]

[0024] In the above formula: In the above formula: U a is the A-phase voltage output by the inverter, U b is the B-phase voltage output by the inverter, U c is the C-phase voltage output by the inverter, U A is the output voltage of the A-phase bridge arm, U B is the output voltage of the B-phase bridge arm, U C is the output voltage of the C phase bridge arm;

[0025] Define the three-phase voltage space vector U s , then:

[0026]

[0027] In the above formula: S A is the switch variable of the A-phase bridge arm, S B is the switch variable of the B-phase bridge arm, S C is the switch variable of the C-phase bridge arm, j represents the imaginary axis;

[0028] From formula (2), we can see that the three switching signals can output 27 voltage space vectors, including zero vector, amplitude A small vector with a magnitude of The mean vector and magnitude of A large vector of

[0029] Define the DC side midpoint voltage as V0, midpoint current as i0, and the current flowing through capacitors C1 and C2 as i c1 、i c2 , the real-time voltage value of the capacitor is V c1 、V c2 , the initial voltage value is V c10 、V c20 ,but:

[0030]

[0031] The voltage and current across the DC side capacitors C1 and C2 can be expressed as:

[0032]

[0033] From formula (4), it can be seen that the main reason for the unbalanced potential at the DC side midpoint is that the midpoint current i0 causes unbalanced charging / discharging of the DC link capacitor; in the large vector switching state, the current loop does not pass through the DC side midpoint o, at this time i0 = 0, so the large vector has no effect on the midpoint voltage V0; in the medium vector switching state, the current flows from point p through the upper bridge arm of phase A to the load midpoint o ′ , the other two phases of the three-phase load flow in / out from the DC side midpoint o and point N through the B-phase and C-phase lower bridge arms respectively. Taking i0 as the current flowing into / out of the DC side midpoint o, it can be obtained that when the B-phase current flows into the bus, the capacitor C1 is charged and C2 is discharged; when the B-phase current flows out of the bus, the capacitor C1 is discharged and C2 is charged; because the direction of i0 cannot be determined, the influence of the neutral vector on the voltage value of the capacitors C1 and C2 is uncontrollable; and the redundant small vector switch state currents have equal magnitudes and opposite directions on the DC side midpoint o. By adjusting the action time of the small vector and the redundant small vector, the balanced control of the midpoint potential can be achieved.

[0034] The specific division method of step 2 is as follows:

[0035] 2.1 In the mutually perpendicular α and β vector coordinate systems, the α and β vector coordinate systems are equally divided into 6 large sectors. The angle θ with the α axis is 0 to 60 degrees, which is the No. 3 large sector; the angle θ with the α axis is 60 to 120 degrees, which is the No. 1 large sector; the angle θ with the α axis is 120 to 180 degrees, which is the No. 5 large sector; the angle θ with the α axis is 180 to 240 degrees, which is the No. 4 large sector; the angle θ with the α axis is 240 to 300 degrees, which is the No. 6 large sector; the angle θ with the α axis is 300 to 360 degrees, which is the No. 2 large sector;

[0036] 2.2 Hide the middle vector and use the zero vector, small vector and large vector for modulation. According to the above modulation method, each sector only needs to be divided into 3 small sectors. The division rules are as follows:

[0037] The zero vector corresponds to the coordinate origin. The area completely modulated by the small vector in each large sector belongs to small sector No. 1, the area completely modulated by the large vector belongs to small sector No. 2, and the area modulated by a large vector and a small vector belongs to small sector No. 3.

[0038] The target voltage vector is V ref , target voltage vector V ref The angle between the α axis and the voltage vector is determined to be V according to the angle θ. ref The number of the large sector where the target voltage vector V ref The angle θ is converted to the No. 3 large sector to obtain the converted angle θ':

[0039]

[0040] The target voltage vector V ref By combining the large sector number with the small sector number, the target voltage vector V ref The full sector number of

[0041] When dividing the area where a large vector and a small vector are modulated in coordination, that is, small sector No. 3, the division rule is: the target voltage vector V is synthesized by using the large vector on the left side of the large sector and the small vector on the right side to modulate the coordination. ref ;

[0042] It can be concluded that according to V α and V β The value of determines the rule for determining the small sector number, and the determination rules are as follows:

[0043] Satisfy at the same time Belongs to small sector No. 1;

[0044] Satisfy at the same time Belongs to small sector No. 2;

[0045] Satisfy at the same time Belongs to small sector No. 3.

[0046] When dividing the area where a large vector and a small vector are modulated in coordination, that is, small sector No. 3, the division rule is: the large vector on the right side of the large sector and the small vector on the left side are used to synthesize the target voltage vector V for coordinated modulation. ref ;

[0047] It can be concluded that according to V α and V βThe value of determines the rule for determining the small sector number, and the determination rules are as follows:

[0048] Satisfy at the same time Belongs to small sector No. 1;

[0049] Satisfy at the same time Belongs to small sector No. 2;

[0050] Satisfy at the same time Belongs to small sector No. 3.

[0051] Step 3: Arrange the switching sequence of each small sector inverter to form a switching sequence chart. In order to reduce the stress of the switching device, a switching cycle T sw The inverter outputs 7 symmetrical voltage vectors in succession within the range, according to the target space voltage vector V ref According to the sector number, a basic voltage vector action sequence table is formulated; as shown in Table 2:

[0052] Table 2 Space voltage vector action sequence table

[0053] Sector Number <![CDATA[T0 / 4]]> <![CDATA[T1 / 2]]> <![CDATA[T2 / 2]]> <![CDATA[T0 / 2]]> <![CDATA[T2 / 2]]> <![CDATA[T1 / 2]]> <![CDATA[T0 / 4]]> 31 0-1 -1 0 0-1 0 0 0 1 0 0 0 0 0 0 0-1 0-1-1 32 0-1 -1 1-1 -1 1 1-1 1 0 0 1 1 -1 1-1-1 0-1-1 33 0 0 -1 0-1 -1 1 1-1 1 1 0 1 1 -1 0-1-1 0 0-1 11 0 0-1 0 1 0 0 0 0 1 1 0 0 0 0 0 1 0 0 0-1 12 0 0-1 1 1 -1 -1 1-1 1 1 0 -1 1-1 1 1-1 0 0-1 13 -1 0-1 0 0 -1 -1 1-1 0 1 0 -1 1 -1 0 0-1 -1 0-1 51 -1 0-1 -1 0 0 0 0 0 0 1 0 0 0 0 -1 0 0 -1 0-1 52 -1 0-1 -1 1-1 -1 1 1 0 1 0 -1 1 1 -1 1-1 -1 0-1 53 -1 0 0 -1 0-1 -1 1 1 0 1 1 -1 1 1 -1 0-1 -1 0 0 41 -1 0 0 0 0 0 0 0 1 0 1 1 0 0 1 0 0 0 -1 0 0 42 -1 0 0 -1 1 1 -1-1 1 0 1 1 -1-1 1 -1 1 1 -1 0 0 43 -1-1 0 -1 0 0 -1-1 1 0 0 1 -1 -1 1 -1 0 0 -1-1 0 61 -1-1 0 0-1 0 0 0 0 0 0 1 0 0 0 0-1 0 -1-1 0 62 -1-1 0 -1 -1 1 1-1 1 0 0 1 1-1 1 -1-1 1 -1-1 0 63 0-1 0 -1 -1 0 1-1 1 1 0 1 1 -1 1 -1-1 0 0-1 0 21 0-1 0 0 0 0 1 0 0 1 0 1 1 0 0 0 0 0 0-1 0 22 0-1 0 1 -1 1 1-1 -1 1 0 1 1 -1 -1 1-1 1 0-1 0 23 0-1 -1 0 -1 0 1-1 -1 1 0 0 1 -1 -1 0-1 0 0-1-1

[0054] Table 2 specifies the order of action of the basic voltage vectors.

[0055] In step 4, select the vector V on the left side of the large sector. s1 , the vector V on the right s2 and zero vector V s0 Synthesized target voltage vector V ref , V s1 、V s2 、V s0 The vector action time is recorded as T1, T2, T0, then:

[0056]

[0057] According to the vector synthesis law of different small sectors, the action time of each vector in each small sector is calculated respectively, and the intermediate variable is defined The values ​​of T1, T2, and T0 can be calculated as:

[0058]

[0059] Table 3 Determination of voltage space vector action time

[0060]

[0061] Combine table (2) and formula (7) to solve the basic vector action time of each sector, and then obtain the combined switch control pulse situation corresponding to each sector according to the basic vector action time;

[0062] Due to the asymmetric sector modulation, the algorithm output contains 9 different types of pulses. Using 5-pulse output, the switch trigger variables X, Y, Z, U, V, and W are defined, and the following are taken:

[0063]

[0064] Define the controller scan cycle as T sw , and each trigger variable is connected to a period of T sw , amplitude is 0.5T sw The isosceles triangle carrier is compared with the trigger variable. If the instantaneous value of the triangle carrier is greater than the trigger variable, a 1 pulse is output; otherwise, a 0 pulse is output. According to the switching state and trigger time of each sector, the trigger time table of the switch devices in each sector is sorted out to form the control model of SVPWM.

[0065] The synchronous motor control algorithm also includes: Step 5: simulation verification, using Simulink to establish a simulation platform for the algorithm, performing simulation operations on the obtained SVPWM control model, and comparing its waveform quality and harmonic level.

[0066] Compared with the prior art, the present invention has the following beneficial effects:

[0067] 1. In step 2 of a synchronous motor control algorithm of the present invention, the middle vector is hidden and modulation is performed using zero vector, small vector and large vector, thereby eliminating the uncontrollability affected by the voltage value of the middle vector capacitors C1 and C2. Only zero vector, small vector and large vector are used for modulation, so balanced control of the midpoint potential can be achieved.

[0068] 2. In the step 2 of the synchronous motor control algorithm of the present invention, the synthesis of the space voltage vector of each sector only involves small vectors and large vectors. Compared with the traditional 36-sector three-level SVPWM algorithm, the amount of calculation is reduced by half.

[0069] 3. The inverter switching cycle range in step 3 of the synchronous motor control algorithm of the present invention outputs 7 symmetrical voltage vectors in succession, which effectively reduces the distortion rate of the inverter output line voltage and improves the output waveform quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0070] Figure 1 It is a schematic diagram of the NPC structure three-level inverter of the present invention.

[0071] Figure 2 This is a comparison diagram of the switch vectors in step 1 of the present invention.

[0072] Figure 3 It is a flow chart of the implementation of the algorithm of the present invention.

[0073] Figure 4 This is the sector division method of embodiment 1 of the present invention.

[0074] Figure 5 This is the sector division method of embodiment 2 of the present invention.

[0075] Figure 6 This is the switch combination diagram of sectors 31 to 33 and 11 to 13 in Example 1.

[0076] Figure 7 It is the three-phase symmetrical load line voltage waveform when the modulation index m is 0.3 / 0.9 in Example 1.

[0077] Figure 8 It is a fast Fourier analysis diagram of the DC side midpoint voltage / current waveform (m=0.9) and the load line voltage in Example 1. DETAILED DESCRIPTION

[0078] The present invention is further described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0079] See also Figures 1 to 3 , a synchronous motor control algorithm, characterized in that:

[0080] The synchronous motor control algorithm is used to control the NPC structure three-level inverter circuit of the permanent magnet synchronous motor. The DC bus voltage in the NPC structure three-level inverter circuit is V dc , two capacitors C1 and C2 of the same capacitance are connected in series on the DC bus, the connection point of capacitors C1 and C2 is the DC side midpoint o, the DC side positive pole is point P, and the DC side negative pole is point N; the NPC structure three-level inverter circuit inverts DC power into three-phase power, and a three-phase bridge arm is set in the circuit, and each phase bridge arm has four parallel freewheeling diodes D xn The IGBT tube S connected in series xn , and set two clamping diodes D x5 , D x6 The midpoint of the two series-connected IGBT tubes is connected to the midpoint o of the DC side capacitor through a clamping diode, so that the output voltage is clamped at the potential of the DC side midpoint o, that is, the voltage on each IGBT tube is limited to a capacitor voltage. The clamping diode D x5 , D x6 Another function of is to provide a current channel to prevent the capacitor from short-circuiting when the IGBT tube is turned on; the midpoint of each phase bridge arm is connected to the load and then connected to the load midpoint o'; in the above subscripts: x represents any phase among the three phases A, B, and C, and n represents the serial number of the switch tube of each phase, with a value range of 1 to 4;

[0081] Step 1: Analyze the unbalanced mechanism of the DC side midpoint potential of the NPC structure three-level inverter. The 36-sector NPC three-level voltage inverter can output three voltages, namely: V dc / 2, 0, and -Vdc / 2;

[0082] IGBT switch variable S xn There are only two possible values: 1 and 0. The corresponding working states of the x-phase circuit are shown in Table 1:

[0083] Table 1 Switching signal and x-phase circuit working state table

[0084]

[0085] The inverter output voltage is expressed in matrix form:

[0086]

[0087] In the above formula: In the above formula: U a is the A-phase voltage output by the inverter, U b is the B-phase voltage output by the inverter, U c is the C-phase voltage output by the inverter, U A is the output voltage of the A-phase bridge arm, U B is the output voltage of the B-phase bridge arm, U C is the output voltage of the C phase bridge arm;

[0088] Define the three-phase voltage space vector U s , then:

[0089]

[0090] In the above formula: S A is the switch variable of the A-phase bridge arm, S B is the switch variable of the B-phase bridge arm, S C is the switch variable of the C-phase bridge arm, j represents the imaginary axis;

[0091] From formula (2), we can see that the three switching signals can output 27 voltage space vectors, including zero vector, amplitude A small vector with a magnitude of The mean vector and magnitude of A large vector of

[0092] Define the DC side midpoint voltage as V0, midpoint current as i0, and the current flowing through capacitors C1 and C2 as i c1 、i c2 , the real-time voltage value of the capacitor is V c1 、V c2 , the initial voltage value is V c10 、V c20 ,but:

[0093]

[0094] The voltage and current across the DC side capacitors C1 and C2 can be expressed as:

[0095]

[0096] From formula (4), it can be seen that the main reason for the unbalanced potential at the DC side midpoint is that the midpoint current i0 causes unbalanced charging / discharging of the DC link capacitor; in the large vector switching state, the current loop does not pass through the DC side midpoint o, at this time i0 = 0, so the large vector has no effect on the midpoint voltage V0; in the medium vector switching state, the current flows from point p through the upper bridge arm of phase A to the load midpoint o ′ , the other two phases of the three-phase load flow in / out from the DC side midpoint o and point N through the lower bridge arms of phase B and phase C respectively. Taking i0 as the current flowing in / out of the DC side midpoint o, it can be obtained that when the B-phase current flows into the bus, the capacitor C1 is charged and C2 is discharged; when the B-phase current flows out of the bus, the capacitor C1 is discharged and C2 is charged; because the direction of i0 cannot be determined, the influence of the neutral vector on the voltage value of the capacitors C1 and C2 is uncontrollable; and the redundant small vector switch state current has equal magnitude and opposite direction on the DC side midpoint o. By adjusting the action time of the small vector and the redundant small vector, the balanced control of the midpoint potential can be achieved;

[0097] Step 2: Divide the input voltage space vector into large and small sectors. The area through which the voltage space vector passes is divided into 18 asymmetric sectors. The specific division method is as follows:

[0098] 2.1 In the mutually perpendicular α and β vector coordinate systems, the α and β vector coordinate systems are equally divided into 6 large sectors. The angle θ with the α axis is 0 to 60 degrees, which is the No. 3 large sector; the angle θ with the α axis is 60 to 120 degrees, which is the No. 1 large sector; the angle θ with the α axis is 120 to 180 degrees, which is the No. 5 large sector; the angle θ with the α axis is 180 to 240 degrees, which is the No. 4 large sector; the angle θ with the α axis is 240 to 300 degrees, which is the No. 6 large sector; the angle θ with the α axis is 300 to 360 degrees, which is the No. 2 large sector;

[0099] 2.2 Hide the middle vector and use the zero vector, small vector and large vector for modulation. According to the above modulation method, each sector only needs to be divided into 3 small sectors. The division rules are as follows:

[0100] The zero vector corresponds to the coordinate origin. The area completely modulated by the small vector in each large sector belongs to small sector No. 1, the area completely modulated by the large vector belongs to small sector No. 2, and the area modulated by a large vector and a small vector belongs to small sector No. 3.

[0101] The target voltage vector is V ref , target voltage vector V ref The angle between the α axis and the voltage vector is determined to be V according to the angle θ. refThe number of the large sector where the target voltage vector V ref The angle θ is converted to the No. 3 large sector to obtain the converted angle θ':

[0102]

[0103] Then according to V α and V β The value of determines the minor sector number, and the determination rules are as follows:

[0104] Satisfy at the same time Belongs to small sector No. 1;

[0105] Satisfy at the same time Belongs to small sector No. 2;

[0106] Satisfy at the same time Belongs to small sector No. 3;

[0107] The target voltage vector V ref By combining the large sector number with the small sector number, the target voltage vector V ref The full sector number of

[0108] Step 3: Arrange the switching sequence of each small sector inverter to form a switching sequence chart. To reduce the stress of the switching device, a switching cycle T sw The inverter outputs 7 symmetrical voltage vectors in succession within the range, according to the target space voltage vector V ref According to the sector number, the action sequence table of the basic voltage vector is formulated, as shown in Table 2:

[0109] Table 2 Space voltage vector action sequence table

[0110]

[0111]

[0112] Step 4: Determine the action time of each switching vector, form the SVPWM control model, and select the vector V on the left side of the large sector. s1 , the vector V on the right s2 and zero vector V s0 Synthesized target voltage vector V ref , V s1 、V s2 、V s0 The vector action time is recorded as T1, T2, T0, then:

[0113]

[0114] According to the vector synthesis law of different small sectors, the action time of each vector in each small sector is calculated respectively, and the intermediate variable is defined The values ​​of T1, T2, and T0 can be calculated as:

[0115]

[0116] Table 3 Determination of voltage space vector action time

[0117]

[0118] Combine table (2) and formula (7) to solve the basic vector action time of each sector, and then obtain the combined switch control pulse situation corresponding to each sector according to the basic vector action time;

[0119] Due to the asymmetric sector modulation, the algorithm output contains 9 different types of pulses. Using 5-pulse output, the switch trigger variables X, Y, Z, U, V, and W are defined, and the following are taken:

[0120]

[0121] Define the controller scan cycle as T sw , and each trigger variable is connected to a period of T sw , amplitude is 0.5T sw The isosceles triangle carrier is compared with the trigger variable. If the instantaneous value of the triangle carrier is greater than the trigger variable, a 1 pulse is output; otherwise, a 0 pulse is output. According to the switch state and trigger time of each sector, the trigger time table of the switch device of each sector is sorted out to form the control model of SVPWM.

[0122] Step 5: Simulation verification: Use Simulink to establish the algorithm simulation platform, simulate the SVPWM control model obtained, and compare its waveform quality and harmonic level.

[0123] The principle of the present invention is described as follows:

[0124] The NPC structure three-level inverter is an NPC structure three-level inverter circuit, and the DC bus voltage in the NPC structure three-level inverter circuit is V dc , two capacitors C1 and C2 of the same capacitance are connected in series on the DC bus, the connection point of capacitors C1 and C2 is the DC side midpoint o, the DC side positive pole is point P, and the DC side negative pole is point N; the NPC structure three-level inverter circuit inverts DC power into three-phase power, and a three-phase bridge arm is set in the circuit, and each phase bridge arm has four parallel freewheeling diodes D xn The IGBT tube S connected in series xn , and set two clamping diodes D x5 , D x6The midpoint of the two series-connected IGBT tubes is connected to the midpoint o of the DC side capacitor through a clamping diode, so that the output voltage is clamped at the potential of the DC side midpoint o, that is, the voltage on each IGBT tube is limited to a capacitor voltage. The clamping diode D x5 , D x6 Another function is to provide a current channel to prevent the capacitor from short-circuiting when the IGBT tube is turned on; the midpoint of each phase bridge arm is connected to the load and then to the midpoint o' of the load; in the above subscripts: x represents any phase among the three phases A, B, and C, and n represents the serial number of the switch tube of each phase, with a value range of 1 to 4.

[0125] Embodiment 1:

[0126] Step 1: Analyze the unbalanced mechanism of the DC side midpoint potential of the NPC structure three-level inverter. The 36-sector NPC three-level voltage inverter can output three voltages, namely: V dc / 2, 0, and -V dc / 2;

[0127] IGBT switch variable S xn There are only two possible values: 1 and 0. The corresponding working states of the x-phase circuit are shown in Table 1:

[0128] Table 1 Switching signal and x-phase circuit working state table

[0129]

[0130] The inverter output voltage is expressed in matrix form:

[0131]

[0132] In the above formula: In the above formula: U a is the A-phase voltage output by the inverter, U b is the B-phase voltage output by the inverter, U c is the C-phase voltage output by the inverter, U A is the output voltage of the A-phase bridge arm, U β is the output voltage of the B-phase bridge arm, U C is the output voltage of the C-phase bridge arm; S a1

[0133] Define the three-phase voltage space vector U s , then:

[0134]

[0135] In the above formula: S A is the switch variable of the A-phase bridge arm, S B is the switch variable of the B-phase bridge arm, S C is the switch variable of the C-phase bridge arm, j represents the imaginary axis;

[0136] From formula (2), we can know that the midpoint voltage of the DC side is defined as V0, the midpoint current is i0, and the current flowing through capacitors C1 and C2 is i c1 、i c2 , the real-time voltage value of the capacitor is V c1 、V c2 , the initial voltage value is V c10 、V c20 ,but:

[0137]

[0138] The voltage and current across the DC side capacitors C1 and C2 can be expressed as:

[0139]

[0140] From formula (4), it can be seen that the main reason for the unbalanced potential at the DC side midpoint is that the midpoint current i0 causes unbalanced charging / discharging of the DC link capacitor; in the large vector switching state, the current loop does not pass through the DC side midpoint o, at this time i0 = 0, so the large vector has no effect on the midpoint voltage V0; in the medium vector switching state, the current flows from point p through the upper bridge arm of phase A to the load midpoint o ′ , the other two phases of the three-phase load flow in / out from the DC side midpoint o and point N through the B-phase and C-phase lower bridge arms respectively. Taking i0 as the current flowing into / out of the DC side midpoint o, it can be obtained that when the B-phase current flows into the bus, the capacitor C1 is charged and C2 is discharged; when the B-phase current flows out of the bus, the capacitor C1 is discharged and C2 is charged; because the direction of i0 cannot be determined, the influence of the neutral vector on the voltage value of the capacitors C1 and C2 is uncontrollable; and the redundant small vector switch state currents have equal magnitudes and opposite directions on the DC side midpoint o. By adjusting the action time of the small vector and the redundant small vector, the balanced control of the midpoint potential can be achieved.

[0141] Step 2: Divide the input voltage space vector into large and small sectors, and improve the SVPWM algorithm: Based on the principle of hiding the middle vector and using zero vector, small vector, and large vector for modulation, the area where the voltage space vector passes is divided into 18 asymmetric sectors;

[0142] like Figure 4 As shown in (a), the algorithm divides the area through which the voltage space vector passes into 18 asymmetric sectors (sector numbers are: 11, 12, 13, 21, 22, 23, 31, 32, 33, 41, 42, 43, 51, 52, 53, 61, 62, 63), and the synthesis of the space voltage vector of each sector only involves small vectors and large vectors. Compared with the traditional 36-sector three-level SVPWM algorithm, the amount of calculation is reduced by half.

[0143] according to Figure 3The algorithm implementation process shown in the figure first determines the sector number where the target magnetic link falls. Taking sectors 31 to 33 as an example, Figure 2 (b) Define θ as the target voltage vector V ref The angle between V ref Decomposed into mutually perpendicular α and β coordinate systems, we have:

[0144]

[0145] The basic rules for the voltage space vector to fall in each sector are shown in Table 2 (taking sectors 31 to 33 as an example). When determining the corresponding sector number for the remaining sectors, the angle θ needs to be converted to the third sector.

[0146] Table 2 Sector number judgment rules (taking sectors 31 to 33 as an example)

[0147]

[0148] To reduce the stress of switching devices, a switching cycle T sw The inverter outputs 7 symmetrical voltage vectors in succession according to the target space voltage vector V ref According to the sector number, a table of the action sequence of the basic voltage vector is formulated, as shown in Table 3.

[0149] Table 3 Space voltage vector action sequence table

[0150] Sector Number <![CDATA[T0 / 4]]> <![CDATA[T1 / 2]]> <![CDATA[T2 / 2]]> <![CDATA[T0 / 2]]> <![CDATA[T2 / 2]]> <![CDATA[T1 / 2]]> <![CDATA[T0 / 4]]> 31 0-1 -1 0 0-1 0 0 0 1 0 0 0 0 0 0 0-1 0-1-1 32 0-1 -1 1-1 -1 1 1-1 1 0 0 1 1 -1 1-1-1 0-1-1 33 0 0 -1 0-1 -1 1 1-1 1 1 0 1 1 -1 0-1-1 0 0-1 11 0 0-1 0 1 0 0 0 0 1 1 0 0 0 0 0 1 0 0 0-1 12 0 0-1 1 1 -1 -1 1-1 1 1 0 -1 1-1 1 1-1 0 0-1 13 -1 0-1 0 0 -1 -1 1-1 0 1 0 -1 1 -1 0 0-1 -1 0-1 51 -1 0-1 -1 0 0 0 0 0 0 1 0 0 0 0 -1 0 0 -1 0-1 52 -1 0-1 -1 1-1 -1 1 1 0 1 0 -1 1 1 -1 1-1 -1 0-1 53 -1 0 0 -1 0-1 -1 1 1 0 1 1 -1 1 1 -1 0-1 -1 0 0 41 -1 0 0 0 0 0 0 0 1 0 1 1 0 0 1 0 0 0 -1 0 0 42 -1 0 0 -1 1 1 -1-1 1 0 1 1 -1-1 1 -1 1 1 -1 0 0 43 -1-1 0 -1 0 0 -1-1 1 0 0 1 -1 -1 1 -1 0 0 -1-1 0 61 -1-1 0 0-1 0 0 0 0 0 0 1 0 0 0 0-1 0 -1-1 0 62 -1-1 0 -1 -1 1 1-1 1 0 0 1 1-1 1 -1-1 1 -1-1 0 63 0-1 0 -1 -1 0 1-1 1 1 0 1 1 -1 1 -1-1 0 0-1 0 21 0-1 0 0 0 0 1 0 0 1 0 1 1 0 0 0 0 0 0-1 0 22 0-1 0 1 -1 1 1-1 -1 1 0 1 1 -1 -1 1-1 1 0-1 0 23 0-1 -1 0 -1 0 1-1 -1 1 0 0 1 -1 -1 0-1 0 0-1-1

[0151] by Figure 4 Taking sector 31 in (b) as an example, select a small vector V s1 (0 0-1), small vector V s2 (0 -1-1 / 1 0 0) and zero vector V s0 Synthesized target voltage vector V ref , V s1 、V s2 、V s0 The vector action time is recorded as T1, T2, T0, then:

[0152]

[0153] Defining intermediate variables The values ​​of T1, T2, and T0 can be calculated as:

[0154]

[0155] Table 4 Determination of voltage space vector action time (taking sectors 31 to 33 as an example)

[0156]

[0157] Combining Table (3) and Formula (7), the basic vector action time of each sector is solved as shown in Table 5 (taking sectors 31 to 33 as an example). Based on this, the switch combination diagram of each sector can be drawn as shown in Figure 6 , taking sectors 31 to 33 and 11 to 13 as examples, S a1 , S a2 , S b1 , S b2 , S c1 , S c2 They correspond to the switching states of the upper bridge arms of the three phases A, B, and C respectively, where 1 pulse corresponds to a high level during the switching cycle, and 0 pulse corresponds to a low level.

[0158] Due to the asymmetric sector modulation, compared with the 36-sector three-level SVPWM algorithm (5 pulse outputs), the output of this algorithm contains 9 different types of pulses, namely Figure 4 Middle pulses ①~⑨. Define switch trigger variables X, Y, Z, U, V, W, and take:

[0159]

[0160] Define the controller scan cycle as T sw , and each trigger variable is connected to a period of T sw , amplitude is 0.5T sw The isosceles triangle carrier is compared with the trigger variable. If the instantaneous value of the triangle carrier is greater than the trigger variable, a 1 pulse is output; otherwise, a 0 pulse is output. According to the above rules, the triggering schedule of the switch devices in each sector can be sorted out as shown in Table 5 (taking sectors 11-13, 31-33, and 51-53 as examples).

[0161] Table 5 Triggering schedule of switch devices in each sector

[0162]

[0163] The algorithm simulation platform was established using Simulink, and the parameter settings are shown in Table 6. Figure 7 The figure shows the three-phase symmetrical load line voltage waveform when the modulation index m is 0.3 / 0.9. By comparison, the number of load line voltage levels, amplitude, and period are basically consistent with the 36-sector three-level SVPWM algorithm, but the harmonic component is significantly reduced and the waveform output quality is better.

[0164] Table 6 Simulation model parameters

[0165]

[0166] Figure 8(a) shows the DC side midpoint voltage / current waveform of the algorithm (m = 0.9). Over time, the steady-state voltage difference between capacitors C1 and C2 is about 10V. Compared with the 36-sector three-level SVPWM algorithm, this algorithm has a better effect on midpoint voltage balance control.

[0167] Figure 8 (b) is the fast Fourier analysis diagram of the load line voltage. When m = 0.9, the voltage signal distortion rate is 10.09%. This algorithm increases the total number of output pulses of the three-phase bridge arm of the inverter, which is easy to increase the switching stress of semiconductor devices and increase the voltage pulsation harmonic distortion rate, but it is better than the 36-sector three-level SVPWM algorithm overall.

[0168] Table 7 Model calculation efficiency and simulation results analysis

[0169]

[0170] Embodiment 2:

[0171] Embodiment 2 is substantially the same as Embodiment 1, except that:

[0172] See also Figure 4 , when dividing small sectors, the zero vector corresponds to the coordinate origin. In each large sector, the area completely modulated by the small vector belongs to small sector No. 1, the area completely modulated by the large vector belongs to small sector No. 2, and the area modulated by a large vector and a small vector belongs to small sector No. 3;

[0173] When dividing the area where a large vector and a small vector are modulated in coordination, that is, small sector No. 3, the division rule is: the target voltage vector V is synthesized by using the large vector on the left side of the large sector and the small vector on the right side to modulate the coordination. ref ;

[0174] It can be concluded that according to V α and V β The value of determines the rule for determining the small sector number, and the determination rules are as follows:

[0175] Satisfy at the same time Belongs to small sector No. 1;

[0176] Satisfy at the same time Belongs to small sector No. 2;

[0177] Satisfy at the same time Belongs to small sector No. 3.

[0178] Embodiment 3:

[0179] Embodiment 3 is substantially the same as Embodiment 2, except that:

[0180] See also Figure 5, when dividing small sectors, the zero vector corresponds to the coordinate origin. In each large sector, the area completely modulated by the small vector belongs to small sector No. 1, the area completely modulated by the large vector belongs to small sector No. 2, and the area modulated by a large vector and a small vector belongs to small sector No. 3;

[0181] When dividing the area where a large vector and a small vector are modulated in coordination, that is, small sector No. 3, the division rule is: the large vector on the right side of the large sector and the small vector on the left side are used to synthesize the target voltage vector V for coordinated modulation. ref ;

[0182] It can be concluded that according to V α and V β The value of determines the rule for determining the small sector number, and the determination rules are as follows:

[0183] Satisfy at the same time Belongs to small sector No. 1;

[0184] Satisfy at the same time Belongs to small sector No. 2;

[0185] Satisfy at the same time Belongs to small sector No. 3.

Claims

1. A synchronous motor control algorithm, characterized in that: The synchronous motor control algorithm is used to control the NPC structure three-level inverter circuit of the permanent magnet synchronous motor. Step 1: Analyze the unbalanced potential mechanism of the DC side midpoint of the NPC structure three-level inverter, and draw the conclusion that the influence of the neutral vector on the voltage value of capacitors C1 and C2 is uncontrollable. In the NPC structure three-level inverter circuit, two capacitors C1 and C2 with the same capacitance are connected in series on the DC bus, and the connection point of capacitors C1 and C2 is the DC side midpoint o; Step 2: Divide the input voltage space vector into large and small sectors, and improve the SVPWM algorithm: Based on the principle of hiding the middle vector and using zero vector, small vector, and large vector for modulation, the area where the voltage space vector passes is divided into 18 asymmetric sectors; 2.1 In the mutually perpendicular α and β vector coordinate systems, the α and β vector coordinate systems are equally divided into 6 large sectors. The angle θ with the α axis is 0 to 60 degrees, which is the No. 3 large sector; the angle θ with the α axis is 60 to 120 degrees, which is the No. 1 large sector; the angle θ with the α axis is 120 to 180 degrees, which is the No. 5 large sector; the angle θ with the α axis is 180 to 240 degrees, which is the No. 4 large sector; the angle θ with the α axis is 240 to 300 degrees, which is the No. 6 large sector; the angle θ with the α axis is 300 to 360 degrees, which is the No. 2 large sector; 2.2 Hide the middle vector and use the zero vector, small vector and large vector for modulation. According to the above modulation method, each sector only needs to be divided into 3 small sectors. The division rules are as follows: The zero vector corresponds to the coordinate origin. The area completely modulated by the small vector in each large sector belongs to small sector No. 1, the area completely modulated by the large vector belongs to small sector No. 2, and the area modulated by a large vector and a small vector belongs to small sector No.

3. The target voltage vector is V ref , target voltage vector V ref The angle between the α axis and the voltage vector is determined to be V according to the angle θ. ref The number of the large sector where the target voltage vector V ref The angle θ is converted to the No. 3 large sector to obtain the converted angle θ': The target voltage vector V ref By combining the large sector number with the small sector number, the target voltage vector V ref The full sector number of Step 3: Arrange the switching sequence of each small sector inverter to form a switching sequence chart. To reduce the stress of the switching device, a switching cycle T sw The inverter outputs 7 symmetrical voltage vectors in succession within the range, according to the target space voltage vector V ref The sector number it falls into is used to formulate the action sequence table of the basic voltage vector; Step 4: Determine the action time of each switching vector, form the SVPWM control model, and select the vector V on the left side of the large sector. s1 , the vector V on the right s2 and zero vector V s0 Synthesized target voltage vector V ref , V s1 、V s2 、V s0 The vector action times correspond to T1, T2, and T0 respectively. According to the vector synthesis rules of different small sectors, the vector action time in each small sector is calculated respectively; then, the combined switch control pulse situation corresponding to each sector is obtained according to the basic vector action time. Finally, according to the switching state and trigger time of each sector, the trigger time table of the switch devices in each sector is sorted out to form the SVPWM control model.

2. A synchronous motor control algorithm according to claim 1, characterized in that: The DC bus voltage in the NPC structure three-level inverter circuit is V dc , the positive pole on the DC side is point P, and the negative pole on the DC side is point N; the NPC structure three-level inverter circuit inverts DC power into three-phase power, and a three-phase bridge arm is set in the circuit, and each phase bridge arm has four parallel freewheeling diodes D xn The IGBT tube S connected in series xn , and set two clamping diodes D x5 , D x6 The midpoint of the two series-connected IGBT tubes is connected to the midpoint o of the DC side capacitor through a clamping diode, so that the output voltage is clamped at the potential of the DC side midpoint o, that is, the voltage on each IGBT tube is limited to a capacitor voltage. The clamping diode D x5 , D x6 Another function of is to provide a current channel to prevent the capacitor from short-circuiting when the IGBT tube is turned on; the midpoint of each phase bridge arm is connected to the load and then connected to the load midpoint o'; in the above subscripts: x represents any phase among the three phases A, B, and C, and n represents the serial number of the switch tube of each phase, with a value range of 1 to 4; The analysis process of step 1 is as follows: NPC three-level voltage inverter can output three voltages, namely: V dc / 2, 0, and -V dc / 2; IGBT switch variable S xn There are only two possible values: 1 and 0. The corresponding working states of the x-phase circuit are shown in Table 1: Table 1 Switching signal and x-phase circuit working state table The inverter output voltage is expressed in matrix form: In the above formula: U a is the A-phase voltage output by the inverter, U b is the B-phase voltage output by the inverter, U c is the C-phase voltage output by the inverter, U A is the output voltage of the A-phase bridge arm, U B is the output voltage of the B-phase bridge arm, U C is the output voltage of the C-phase bridge arm; Define the three-phase voltage space vector U s , then: In the above formula: S A is the switch variable of the A-phase bridge arm, S B is the switch variable of the B-phase bridge arm, S C is the switch variable of the C-phase bridge arm, j represents the imaginary axis; From formula (2), we can see that the three switching signals can output 27 voltage space vectors, including zero vector, amplitude A small vector with a magnitude of The mean vector and magnitude of A large vector of Define the DC side midpoint voltage as V0, midpoint current as i0, and the current flowing through capacitors C1 and C2 as i c1 、i c2 , the real-time voltage value of the capacitor is V c1 、V c2 , the initial voltage value is V c10 、V c20 ,but: The voltage and current across the DC side capacitors C1 and C2 can be expressed as: From formula (4), it can be seen that the main reason for the unbalanced potential at the DC side midpoint is that the midpoint current i0 causes unbalanced charging / discharging of the DC link capacitor; in the large vector switching state, the current loop does not pass through the DC side midpoint o, at this time i0 = 0, so the large vector has no effect on the midpoint voltage V0; in the medium vector switching state, the current flows from point p through the upper bridge arm of phase A to the load midpoint o ′ , the other two phases of the three-phase load flow in / out from the DC side midpoint o and point N through the B-phase and C-phase lower bridge arms respectively. Taking i0 as the current flowing into / out of the DC side midpoint o, it can be obtained that when the B-phase current flows into the bus, the capacitor C1 is charged and C2 is discharged; when the B-phase current flows out of the bus, the capacitor C1 is discharged and C2 is charged; because the direction of i0 cannot be determined, the influence of the neutral vector on the voltage value of the capacitors C1 and C2 is uncontrollable; and the redundant small vector switch state currents have equal magnitudes and opposite directions on the DC side midpoint o. By adjusting the action time of the small vector and the redundant small vector, the balanced control of the midpoint potential can be achieved.

3. A synchronous motor control algorithm according to claim 1, characterized in that: The synchronous motor control algorithm also includes: Step 5: simulation verification, using Simulink to establish a simulation platform for the algorithm, performing simulation operations on the obtained SVPWM control model, and comparing its waveform quality and harmonic level.

4. A synchronous motor control algorithm according to claim 1, 2 or 3, characterized in that: When dividing the area where a large vector and a small vector are modulated in coordination, that is, small sector No. 3, the division rule is: the target voltage vector V is synthesized by using the large vector on the left side of the large sector and the small vector on the right side to modulate the coordination. ref ; It can be concluded that according to V α and V β The value of determines the rule for determining the small sector number, and the determination rules are as follows: Satisfy at the same time Belongs to small sector No. 1; Satisfy at the same time Belongs to small sector No. 2; Satisfy at the same time Belongs to small sector No.

3.

5. A synchronous motor control algorithm according to claim 1, 2 or 3, characterized in that: When dividing the area where a large vector and a small vector are modulated in coordination, that is, small sector No. 3, the division rule is: the large vector on the right side of the large sector and the small vector on the left side are used to synthesize the target voltage vector V for coordinated modulation. ref ; It can be concluded that according to V α and V β The value of determines the rule for determining the small sector number, and the determination rules are as follows: Satisfy at the same time Belongs to small sector No. 1; Satisfy at the same time Belongs to small sector No. 2; Satisfy at the same time Belongs to small sector No.

3.

6. A synchronous motor control algorithm according to claim 4, characterized in that: Step 3: Arrange the switching sequence of each small sector inverter to form a switching sequence chart. In order to reduce the stress of the switching device, a switching cycle T sw The inverter outputs 7 symmetrical voltage vectors in succession within the range, according to the target space voltage vector V ref According to the sector number, a basic voltage vector action sequence table is formulated; as shown in Table 2: Table 2 Space voltage vector action sequence table Table 2 specifies the order of action of the basic voltage vectors.

7. A synchronous motor control algorithm according to claim 6, characterized in that: In step 4, select the vector V on the left side of the large sector. s1 , the vector V on the right s2 and zero vector V s0 Synthesized target voltage vector V ref , V s1 、V s2 、V s0 The vector action time is recorded as T1, T2, T0, then: According to the vector synthesis law of different small sectors, the action time of each vector in each small sector is calculated respectively, and the intermediate variable is defined The values ​​of T1, T2, and T0 can be calculated as: Table 3 Determination of voltage space vector action time Combine table (2) and formula (7) to solve the basic vector action time of each sector, and then obtain the combined switch control pulse situation corresponding to each sector according to the basic vector action time; Due to the asymmetric sector modulation, the algorithm output contains 9 different types of pulses. Using 5-pulse output, the switch trigger variables X, Y, Z, U, V, and W are defined, and the following are taken: Define the controller scan cycle as T sw , and each trigger variable is connected to a period of T sw , amplitude is 0.5T sw The isosceles triangle carrier is compared with the trigger variable. If the instantaneous value of the triangle carrier is greater than the trigger variable, a 1 pulse is output; otherwise, a 0 pulse is output. According to the switching state and trigger time of each sector, the trigger time table of the switch devices in each sector is sorted out to form the control model of SVPWM.

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