An edge-aligned PWM modulation method

Abstract

An edge-aligned PWM modulation method includes the following steps: Step 1) Determine the sector according to the synthesized voltage vector and determine the conduction sequence of PWM according to different sectors; Step 2) Calculate the action duration of the effective vector according to the synthesized voltage vector; Step 3) Insert the U7 vector based on the known action time of the effective vector; Step 4) Perform phase-shifting operations according to different sectors. The present invention solves the problems existing in the phase current sampling and reconstruction process in the existing single-bus current system, such as inaccurate reconstruction, increased extra conduction times, dependence on motor model parameters, high cost, large volume, etc. Compared with the conventional method, the method provided by the present invention is easy to implement, has a small amount of calculation, does not increase the switching times of power devices, and improves the three-phase current reconstruction accuracy.

Description

Technical Field

[0001] The present invention belongs to the field of pulse-width modulation (PWM), and relates to a PWM modulation method applicable to a single-bus current sensor inverter. Background Art

[0002] Three-phase inverters usually have two or three current sensors to obtain the phase currents of a three-phase system. However, for medium and small-sized frequency converters, cost requirements are relatively high. The proportion of the current sampling circuit in the overall machine cost cannot be ignored, and conventional multi-current sensors have problems such as current harmonics caused by inconsistent amplification factors. Therefore, using a single busbar current sensor to detect the busbar current and reconstruct the phase currents can avoid errors caused by inconsistent sensor performance, reduce system costs, and decrease the volume of the motor control board. This has high application value in scenarios with high requirements for control board size and cost. However, when reconstructing three-phase currents with a single busbar current sensor, there will be a problem that due to the too short effective vector action time, the effective phase current information cannot be collected. Usually, there are the following solutions to this problem: (1) PWM phase-shifting method. The solution proposed in the literature "Single-resistance Sampling Reconstruction of Permanent Magnet Synchronous Motors Considering Non-observable Region Compensation" (Wei Haifeng, etc., Jiangsu University of Science and Technology, 2018) is the PWM phase-shifting method. When the length of the sampling effective vector is insufficient, while keeping the high-level duration of the PWM unchanged, the PWM is shifted to make the PWM present an asymmetric form to meet the requirement of the minimum sampling time. This method is simple, but the relative positions of the current sampling moments within each PWM cycle are changing, and there will be a large error between the collected current and the actual value. (2) Inserting additional measurement voltage method. The solution based on applying additional measurement pulses proposed in the literature "Current control for AC motor drives using a single DC-link current sensor and measurement voltage vectors" (Hongrae Kim, etc., IEEE Trans. Ind. Appl. 2006) is to inject three additional measurement pulses U4, U2, and U1 when the effective vector length cannot meet the minimum sampling time requirement. This method has the following problems: due to the addition of the additional measurement pulses, the modulation ratio decreases; the number of switching times increases; and the current harmonics increase. (3) Current observer method. The literature "Improved saliency-based position sensorless control of interior permanent-magnet synchronous machines with single DC-link current sensor using current prediction method" (Jun-Hyuk Im, etc., Trans. Ind. Electron. 2018) proposed a current observer method that can achieve consistent reconstruction of dq-axis currents and zero vector sampling results, but the method depends on motor parameters. (4) Current sampling method with improved topology.The literature "ANovel Open-Circuit Fault Diagnosis Method for VoltageSource Inverters WithaSingleCurrentSensor" (Hao Yan, etc., IEEE Trans. Power Electron.) simultaneously collects the sum of the currents of phases A and C through a Hall sensor, and then reconstructs the phase currents using a current decoupling algorithm. However, this method requires current sampling using a Hall sensor and changing the hardware structure, which makes this method unsuitable for low-cost small drives.

[0003] The above methods can all achieve current reconstruction of a single bus current sensor in an unobservable state, but there are some problems as follows:

[0004] (1) The PWM phase-shifting method cannot ensure a fixed current sampling moment, which will cause a large error between the reconstructed current and the actual value;

[0005] (2) The method of inserting an additional measured voltage has problems such as an increase in the number of switching times and an increase in the number of sampling times;

[0006] (3) The method of reconstructing three-phase currents through a current observer has a problem of large computational complexity and is not very suitable for application scenarios of low-performance processors limited by cost;

[0007] (4) The method of realizing three-phase current reconstruction using a single current sensor by modifying the hardware current sampling topology generally uses current sensors based on electromagnetic principles, such as current transformers, current Hall sensors, or Rogowski coils. These current sensors have high costs, large volumes, and low bandwidths, which limit their use in conventional low-cost solutions. Summary of the Invention

[0008] In order to solve the problems existing in the existing single-bus current system, such as inaccurate phase current sampling and reconstruction, increased additional conduction times, dependence on motor model parameters, high cost, and large volume, the present invention provides an edge-aligned PWM modulation method. Compared with the conventional method, this method is easy to implement modulation, is suitable for low-performance processors, and at the same time, this method does not increase the switching times of power devices and improves the accuracy of three-phase current reconstruction.

[0009] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0010] An edge-aligned PWM modulation method includes the following steps:

[0011] Step 1) Determine the sector according to the synthesized voltage vector, and determine the conduction sequence of PWM according to different sectors;

[0012] Step 2) Calculate the action duration of the effective vector according to the synthesized voltage vector;

[0013] Step 3) Insert the U7 vector based on the known action time of the effective vector;

[0014] Step 4) Perform phase shift operations according to different sectors.

[0015] Furthermore, in the said Step 1), the synthesized voltage vector U ref can be represented by the α-axis voltage vector U α and the β-axis voltage vector U β and determine the sector where the synthesized vector is located according to the following conditions:

[0016] When U α > 0, U β > 0 and at this time, U ref is in the first sector;

[0017] When U β > 0 and at this time, U ref is in the second sector;

[0018] When U α < 0, U β > 0 and at this time, U ref is in the third sector;

[0019] When U α < 0, U β < 0 and at this time, U ref is in the fourth sector;

[0020] When U β < 0 and at this time, U ref is in the fifth sector;

[0021] When U α < 0, U β < 0 and at this time, U ref is in the sixth sector;

[0022] After determining the sector where U ref is located, continue to determine the conduction sequence of PWM:

[0023] The PWM conduction sequence in the first sector is A, B, C;

[0024] The PWM conduction sequence in the second sector is B, A, C;

[0025] The PWM conduction sequence of the third sector is B, C, A;

[0026] The PWM conduction sequence of the fourth sector is C, B, A;

[0027] The PWM conduction sequence of the fifth sector is C, A, B;

[0028] The PWM conduction sequence of the sixth sector is A, C, B.

[0029] Furthermore, in step 2), according to the synthesized voltage vector U ref calculate the action duration of the effective vector:

[0030] When U ref is in the first sector,

[0031]

[0032] where T S is the period of PWM, U DC is the DC bus voltage, θ is the angle between U ref and the α-axis, and after arranging equation (1), we get:

[0033]

[0034] Similarly, when U ref is in the second sector,

[0035]

[0036] When U ref is in the third sector,

[0037]

[0038] When U ref is in the fourth sector,

[0039]

[0040] When U ref is in the fifth sector,

[0041]

[0042] When U ref is in the sixth sector,

[0043]

[0044] Furthermore, in step 3), on the basis of the known action time of the effective vector, insert the U7 vector, and the duration of U7 is 2T min, T min Limited by the ADC sampling time T ADC , the current formation time T delay and the inverter dead time T dead :

[0045] T min ≥ T ADC + T delay + T dead (8)

[0046] After inserting the U7 vector, U can be obtained ref When in the first sector, the conduction durations of the ABC-phase PWM are as follows:

[0047]

[0048] When U ref is in the second sector, the conduction durations of the ABC-phase PWM are as follows:

[0049]

[0050] When U ref is in the third sector, the conduction durations of the ABC-phase PWM are as follows:

[0051]

[0052] When U ref is in the fourth sector, the conduction durations of the ABC-phase PWM are as follows:

[0053]

[0054] When U ref is in the fifth sector, the conduction durations of the ABC-phase PWM are as follows:

[0055]

[0056] When U ref is in the sixth sector, the conduction durations of the ABC-phase PWM are as follows:

[0057]

[0058] In step 4), the phase-shifting operation is performed according to different sectors, and the process is as follows:

[0059] Perform the phase-shifting operation according to the determined PWM conduction sequence:

[0060] When U ref is in the first sector, the rising and falling times of the ABC three-phase PWM are respectively:

[0061]

[0062] When U ref is in the second sector, the rising and falling times of the ABC three-phase PWM are respectively:

[0063]

[0064] When U ref is in the third sector, the rising and falling times of the ABC three-phase PWM are respectively:

[0065]

[0066] When U ref is in the fourth sector, the rising and falling times of the ABC three-phase PWM are respectively:

[0067]

[0068] When U ref is in the fifth sector, the rising and falling times of the ABC three-phase PWM are respectively:

[0069]

[0070] When U ref is in the sixth sector, the rising and falling times of the ABC three-phase PWM are respectively:

[0071]

[0072] The beneficial effects of the present invention are mainly manifested in:

[0073] (1) The method is simple to implement, does not increase the computing burden of the controller, and is applicable to low-cost controllers; (2) The method does not increase the number of switching times and sampling times;

[0074] (3) The method can ensure that there is enough time for ADC sampling in each PWM cycle and the sampling moment is relatively fixed, reducing the error between the reconstructed current and the actual value. Brief Description of the Drawings

[0075] Figure 1 is the flowchart of the edge-aligned PWM modulation method described in the present invention.

[0076] Figure 2 is the schematic diagram of the sector where the synthesized voltage vector is located.

[0077] Figure 3 is the schematic diagram of the PWM conduction sequence in different sectors.

[0078] Figure 4Schematic diagram of the effective vector action duration with the synthetic vector in the third sector as an example.

[0079] Figure 5 Schematic diagram of adding the U7 vector to the effective vector with the synthetic vector in the third sector as an example.

[0080] Figure 6 Schematic diagram of PWM after the final phase shift is completed with the synthetic vector in the third sector as an example. Specific implementation mode

[0081] The present invention will be further described below with reference to the accompanying drawings.

[0082] Refer to Figures 1 to 6 , an edge-aligned PWM modulation method, comprising the following steps:

[0083] Step 1) Determine the sector where the synthetic voltage vector is located, and determine the conduction sequence of PWM according to different sectors;

[0084] Step 2) Calculate the action duration of the effective vector according to the synthetic voltage vector;

[0085] Step 3) Insert the U7 vector on the basis of the known action time of the effective vector;

[0086] Step 4) Perform phase shift operations according to different sectors.

[0087] Refer to Figure 2 , in the said step 1), the synthetic voltage vector U ref can be represented by the α-axis voltage vector U α and the β-axis voltage vector U β , and determine the sector where the synthetic vector is located according to the following conditions:

[0088] When U α > 0,, U β > 0 and when, U ref is in the first sector;

[0089] When U β > 0 and when, U ref is in the second sector;

[0090] When U α < 0, U β > 0 and when, U ref is in the third sector;

[0091] When U α < 0, U β < 0 and when, Uref In the fourth sector;

[0092] When U β < 0 and then, U ref is in the fifth sector;

[0093] When U α < 0, U β < 0 and then, U ref is in the sixth sector;

[0094] Refer to Figure 3 to determine the sector where U ref is located, and then continue to determine the conduction sequence of PWM:

[0095] The conduction sequence of PWM in the first sector is A, B, C;

[0096] The conduction sequence of PWM in the second sector is B, A, C;

[0097] The conduction sequence of PWM in the third sector is B, C, A;

[0098] The conduction sequence of PWM in the fourth sector is C, B, A;

[0099] The conduction sequence of PWM in the fifth sector is C, A, B;

[0100] The conduction sequence of PWM in the sixth sector is A, C, B;

[0101] In step 2), calculate the action duration of the effective vector according to the synthesized voltage vector U ref :

[0102] When U ref is in the first sector,

[0103]

[0104] In the formula, T S is the period of PWM, U DC is the DC bus voltage, θ is the angle between U ref and the α-axis. After arrangement, (1) is obtained as:

[0105]

[0106] Similarly, when U ref is in the second sector,

[0107]

[0108] When U ref is in the third sector,

[0109]

[0110] When U ref is in the IV sector,

[0111]

[0112] When U ref is in the V sector,

[0113]

[0114] When U ref is in the VI sector,

[0115]

[0116] Figure 4 Taking U ref in the III sector as an example, at this time, the action duration of the effective vector U2 the action duration of U3

[0117] Referring to Figure 5 , in step 3), based on the known action time of the effective vector, the U7 vector is inserted, and the duration of U7 is 2T min , T min is limited by the ADC sampling time T ADC , the current formation time T delay and the inverter dead time T dead :

[0118] T min ≥T ADC +T delay +T dead (8)

[0119] After inserting the U7 vector, when U ref is in the I sector, the conduction durations of the ABC-phase PWM are:

[0120]

[0121] When U ref is in the II sector, the conduction durations of the ABC-phase PWM are:

[0122]

[0123] When U ref is in the III sector, the conduction durations of the ABC-phase PWM are:

[0124]

[0125] When U ref is in the IVth sector, the conduction durations of the ABC-phase PWM are as follows:

[0126]

[0127] When U ref is in the Vth sector, the conduction durations of the ABC-phase PWM are as follows:

[0128]

[0129] When U ref is in the VIth sector, the conduction durations of the ABC-phase PWM are as follows:

[0130]

[0131] Figure 5 Taking U ref being in the IIIrd sector as an example, Figure 5 the shaded part in it is the inserted U7 vector. After inserting the U7 vector, the action times of the ABC three-phase PWM are:

[0132]

[0133] Referring to Figure 6 , in step 4), phase-shifting operations are performed according to different sectors. The specific operations are: phase-shifting operations are performed according to the determined PWM conduction sequence,

[0134] When U ref is in the Ist sector, the rise and fall times of the ABC three-phase PWM are respectively:

[0135]

[0136] When U ref is in the IInd sector, the rise and fall times of the ABC three-phase PWM are respectively:

[0137]

[0138] When U ref is in the IIIrd sector, the rise and fall times of the ABC three-phase PWM are respectively:

[0139]

[0140] When U ref is in the IVth sector, the rise and fall times of the ABC three-phase PWM are respectively:

[0141]

[0142] When U ref is in the Vth sector, the rise and fall times of the ABC three-phase PWM are respectively:

[0143]

[0144] When U ref is in the VIth sector, the rise and fall times of the ABC three-phase PWM are respectively:

[0145]

[0146] Figure 6 Taking U ref being in the IIIrd sector as an example, Figure 6 for the three-phase PWM form completed after phase shift, the rise and fall times of the three-phase PWM are:

[0147]

[0148] The content described in the embodiments of this specification is only a list of the implementation forms of the inventive concept and is only for illustrative purposes. The protection scope of the present invention should not be regarded as limited to the specific forms stated in this embodiment. The protection scope of the present invention also extends to equivalent technical means that can be conceived by those of ordinary skill in the art based on the inventive concept of the present invention.

Claims

1. An edge-aligned PWM modulation method, characterized in that, The method includes the following steps: Step 1) Determine the sector based on the synthesized voltage vector, and determine the conduction sequence of PWM according to different sectors; Step 2) Calculate the action duration of the effective vector according to the synthesized voltage vector; Step 3) Insert the U7 vector based on the known action time of the effective vector; Step 4) Perform a phase shift operation according to different sectors; In the said step 1), the synthesized voltage vector U ref can be represented by the α-axis voltage vector U α and the β-axis voltage vector U β to determine the sector where the synthesized vector is located according to the following conditions: When U α > 0, U β > 0 and when, U ref is in Sector I; When U β > 0 and , U ref is in the second sector; When U α < 0, U β > 0 and when, U ref is in the third sector; When U α < 0, U β < 0 and when, U ref is in the fourth sector; When U β <0 and , U ref is in the Vth sector; When U α <0, U β <0 and when, U ref is in the VIth sector; Determine U ref After determining the sector where it is located, continue to determine the conduction sequence of PWM: The PWM conduction sequence in the first sector is A, B, C; The PWM conduction sequence in the second sector is B, A, C; The PWM conduction sequence in the third sector is B, C, A; The PWM conduction sequence in the fourth sector is C, B, A; The PWM conduction sequence in the fifth sector is C, A, B; The PWM conduction sequence in the sixth sector is A, C, B.

2. The edge-aligned PWM modulation method according to claim 1, characterized in that, In step 2), according to the synthetic voltage vector U ref Calculate the action duration of the effective vector: When U ref is in the I-th sector, where T S is the period of PWM, U DC is the DC bus voltage, θ is the angle between U ref and the α-axis. After rearrangement, equation (1) gives: Similarly, when U ref is in the second sector, When U ref is in the third sector, When U ref is in the fourth sector, When U ref is in the V sector, When U ref is in the VIth sector, 3. The edge-aligned PWM modulation method according to claim 2, wherein In step 3), the U7 vector is inserted based on the known effective vector action time, and the duration of U7 is 2T min , T min subject to the ADC sampling time T ADC , the current formation time T delay and the inverter dead time T dead Limit: T min ≥ T ADC + T delay + T dead (8) After inserting the U7 vector, U can be obtained ref When in the I-th sector, the conduction duration of the ABC-phase PWM is: When U ref is in the second sector, the conduction duration of the ABC-phase PWM is as follows: When U ref is in the third sector, the conduction durations of the ABC-phase PWM are as follows: When U ref is in the IVth sector, the conduction durations of the ABC-phase PWM are as follows: When U ref is in the Vth sector, the conduction duration of the ABC-phase PWM is as follows: When U ref is in the VIth sector, the conduction duration of the ABC-phase PWM is as follows:

4. The edge alignment type PWM modulation method according to claim 3, wherein In the said step 4), the phase shift operation is performed according to different sectors, and the process is as follows: Perform a phase shift operation according to the determined PWM conduction sequence: When U ref is in the I-th sector, the rise and fall times of the three-phase ABC PWM are respectively: When U ref is in the second sector, the rise and fall times of the three-phase ABC PWM are respectively: When U ref is in the third sector, the rise and fall times of the three-phase ABC PWM are respectively: When U ref is in the IVth sector, the rise and fall times of the ABC three-phase PWM are respectively: When U ref is in the Vth sector, the rise and fall times of the ABC three-phase PWM are respectively: When U ref is in the VIth sector, the rise and fall times of the three-phase ABC PWM are respectively:

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