Three-phase current reconstruction method of motor driving system
阅读说明：本技术 一种电机驱动系统的三相电流重构方法 (Three-phase current reconstruction method of motor driving system ) 是由 骆光照 赵文学 马鹏 黄晓东 刘春强 于 2020-06-01 设计创作，主要内容包括：本发明涉及一种电机驱动系统的三相电流重构方法。目的是为了克服现有单电流传感器采样三相电流重构技术中开关状态相移法导致的PWM波形不对称、PWM周期外附加测量矢量法导致有效工作区域的缩减和PWM信号中间插入测量矢量法改变了原有的PWM波形的问题,同时能够实现低调制区域和扇区切换区域的相电流重构。方法包括如下步骤：对由SVPWM算法产生的PWM信号,进行测量矢量插入调制,再输送给逆变器；依据测量矢量插入调制后的PWM信号,计算出与之相对应的电流采样时刻,对直流母线电流进行采样；根据以上特定时刻的直流母线电流采样结果,以及逆变器不同开关状态下母线电流和相电流的关系重构出三相电流。(The invention relates to a three-phase current reconstruction method of a motor driving system. The method aims to solve the problems that in the existing single current sensor sampling three-phase current reconstruction technology, a PWM waveform is asymmetric due to a switching state phase shift method, an effective working area is reduced due to the fact that a measurement vector method is added outside a PWM period, and the original PWM waveform is changed by inserting the measurement vector method in the middle of a PWM signal, and meanwhile, phase current reconstruction of a low modulation area and a sector switching area can be achieved. The method comprises the following steps: performing measurement vector insertion modulation on a PWM signal generated by an SVPWM algorithm, and then transmitting the PWM signal to an inverter; inserting the modulated PWM signal according to the measurement vector, calculating the corresponding current sampling time, and sampling the direct current bus current; and reconstructing three-phase current according to the direct current bus current sampling result at the specific moment and the relation between the bus current and the phase current of the inverter in different switching states.)
1. A three-phase current reconstruction method of a motor driving system is characterized by comprising the following steps:
step 1: collecting three-phase PWM signals output by an SVPWM algorithm, a sector where a motor rotor is located currently and two effective voltage vector action times T4, T6 and a zero vector action time T0 of a first half PWM period in the sector;
the sampling time tmin is td + ton + tset + tAD;
wherein: td: dead time, ton: switching device on-time, tset: bus current settling time, tAD: a sample and hold time;
step 2, performing measurement vector insertion modulation on the PWM signal according to the relation of T4, T6, T0 and tmin: if T4< tmin, T6 > tmin, T0 > 2tmin, or T4 > tmin, T6< tmin, T0 > 2tmin, the inverter output voltage vector is in a sector switching blind area, selecting an effective voltage vector which can sample the third phase current information from six effective voltage vectors of the SVPWM algorithm as a measurement vector to be respectively inserted into a head end zero vector and a tail end zero vector of a PWM signal according to two-phase current information which can be sampled by the effective voltage vector corresponding to T4 and T6, and the action time of the inserted measurement vector is tmin;
if T4< tmin and T6< tmin, the inverter output voltage vector is in a low modulation blind area, inserting effective voltage vectors corresponding to T4 and T6 and effective voltage vectors opposite to the effective voltage vectors as measurement vectors into a head end zero vector and a tail end zero vector of a PWM signal in turn in two adjacent PWM periods, and the action time of the inserted measurement vectors is tmin; if T4 is greater than or equal to tmin and T6 is greater than or equal to tmin, the output voltage vector of the inverter is in a non-blind area, and the PWM signal is not processed; if T0 is less than 2min, the output voltage vector of the inverter is in a high modulation blind area, and the PWM signal is not processed;
and 3, inserting the measurement vector into the modulated PWM signal and transmitting the PWM signal to an inverter, and calculating three sampling times t1, t2 and t3 of the direct current bus current in the first half PWM period:
if T4< tmin, T6 ≧ tmin and T0 ≧ 2tmin, then T1 ═ tmin/2, T2 ═ 0, T3 ═ T0/2+ T4+ T6/2; if T4 is more than or equal to tmin, T6< tmin and T0 is more than or equal to 2tmin, T1 is tmin/2, T2 is T0/2+ T4/2, and T3 is 0; if T4< tmin, T6< tmin, T1 is tmin/4, T2 is 0, and T3 is 0;
if T4 is more than or equal to tmin, T6 is more than or equal to tmin, or T0 is less than 2min, T1 is 0, T2 is T0/2+ T4/2, T3 is T0/2+ T4+ T6/2, and the sampling time is 0, which means that the sampling is not triggered at this time;
and 4, step 4: sampling the direct current bus current at the three sampling moments, and converting the direct current bus current sampling result into corresponding phase current information according to the corresponding relation between the direct current bus current and the phase current of the inverter in different switching states;
when the output voltage vector of the inverter is in a non-blind area and a sector switching blind area, two-phase current information is obtained by sampling, but in a low modulation blind area, only one-phase current information can be obtained by sampling each time, and the other-phase current information is the sampling result of the previous PWM period;
after obtaining the two-phase current information, a third phase current is calculated according to a formula iu + iv + iw ═ 0, wherein iu, iv, iw respectively represent the phase currents of u, v, w phases.
2. The three-phase current reconstruction method of the motor drive system according to claim 1, characterized in that: in the step 3, sampling is carried out in the middle of the effective voltage vector or the measurement vector action time of the second half PWM period, and the average value of the corresponding vector measurement sampling results is taken as the final sampling result.
Technical Field
The invention belongs to the technical field of motor control, and relates to a three-phase current reconstruction method of a motor driving system, in particular to a three-phase current reconstruction method of single current sensor sampling.
Background
In a motor driving system, in order to reduce the volume and reduce the cost, a three-phase current reconstruction technology of single current sensor sampling is widely adopted. As shown in fig. 1, the principle of the single current sensor sampling technology is to obtain bus current information by sampling through a current sensor installed on a dc bus, and extract motor three-phase current information from the bus current information through a suitable algorithm. The technology omits a two-phase current sensor, so that the cost can be saved, the volume can be reduced, and the sampling error caused by different gains of the sensors can be avoided. In order to further save cost, the direct current bus current is usually acquired by a voltage acquisition mode of connecting a bus in series with a low-resistance low-temperature drift resistor. Therefore, the technology is also called a three-phase current reconstruction technology of single resistance sampling.
The three-phase current reconstruction technology of single-resistor sampling can realize the reconstruction of phase current in most regions. Since in practical circuitry there are many non-ideal factors such as dead time, on-off delay of the switching devices, minimum sample-and-hold time of the AD converter, etc. When the effective voltage vector action time is less than the minimum sampling time (tmin), the MCU cannot accurately sample the current, thereby generating a phase current reconstruction blind area. Much research has been carried out on the problem, wherein the most widely applied solution is a switching state phase shift method, and the effective voltage vector action time meets the minimum sampling time in a mode of translating the PWM signal, so that the MCU can accurately sample the current. However, the adoption of the method can cause the output PWM waveform to be asymmetric, and increase the harmonic component of the current. Another more applied method is to insert measurement vectors, which can be sampled not only during the active voltage vector time but also during the active time of the measurement vector. In the conventional vector insertion method, generally, a measurement vector is added outside a PWM period and inserted in the middle of a PWM signal. The method of adding the measurement vector outside the PWM period results in a reduction in the effective operating area due to the change of the actual PWM period. The method of inserting the measurement vector in the middle has no cycle problem, but changes the original PWM waveform.
Disclosure of Invention
Technical problem to be solved
In order to avoid the defects of the prior art, the invention provides a three-phase current reconstruction method of a motor driving system, which can reduce the asymmetry of a PWM output waveform, does not influence an effective working area, has small influence on an original PWM signal and can realize low modulation blind area and sector switching blind area three-phase current reconstruction.
Technical scheme
A three-phase current reconstruction method of a motor driving system is characterized by comprising the following steps:
step 1: collecting three-phase PWM signals output by an SVPWM algorithm, a sector where a motor rotor is located currently and two effective voltage vector action times T4, T6 and a zero vector action time T0 of a first half PWM period in the sector;
the method includes sampling direct current bus current within effective voltage vector acting time, wherein minimum sampling time tmin is effective voltage vector minimum acting time capable of accurately sampling direct current bus current;
the sampling time tmin is td + ton + tset + tAD;
wherein: td: dead time, ton: switching device on-time, tset: bus current settling time, tAD: a sample and hold time;
step 2, performing measurement vector insertion modulation on the PWM signal according to the relation of T4, T6, T0 and tmin: if T4< tmin, T6 > tmin, T0 > 2tmin, or T4 > tmin, T6< tmin, T0 > 2tmin, the inverter output voltage vector is in a sector switching blind area, selecting an effective voltage vector which can sample the third phase current information from six effective voltage vectors of the SVPWM algorithm as a measurement vector to be respectively inserted into a head end zero vector and a tail end zero vector of a PWM signal according to two-phase current information which can be sampled by the effective voltage vector corresponding to T4 and T6, and the action time of the inserted measurement vector is tmin;
if T4< tmin and T6< tmin, the inverter output voltage vector is in a low modulation blind area, inserting effective voltage vectors corresponding to T4 and T6 and effective voltage vectors opposite to the effective voltage vectors as measurement vectors into a head end zero vector and a tail end zero vector of a PWM signal in turn in two adjacent PWM periods, and the action time of the inserted measurement vectors is tmin; if T4 is greater than or equal to tmin and T6 is greater than or equal to tmin, the output voltage vector of the inverter is in a non-blind area, and the PWM signal is not processed; if T0 is less than 2min, the output voltage vector of the inverter is in a high modulation blind area, and the PWM signal is not processed;
and 3, inserting the measurement vector into the modulated PWM signal and transmitting the PWM signal to an inverter, and calculating three sampling times t1, t2 and t3 of the direct current bus current in the first half PWM period:
if T4< tmin, T6 ≧ tmin and T0 ≧ 2tmin, then T1 ═ tmin/2, T2 ═ 0, T3 ═ T0/2+ T4+ T6/2; if T4 is more than or equal to tmin, T6< tmin and T0 is more than or equal to 2tmin, T1 is tmin/2, T2 is T0/2+ T4/2, and T3 is 0; if T4< tmin, T6< tmin, T1 is tmin/4, T2 is 0, and T3 is 0;
if T4 is more than or equal to tmin, T6 is more than or equal to tmin, or T0 is less than 2min, T1 is 0, T2 is T0/2+ T4/2, T3 is T0/2+ T4+ T6/2, and the sampling time is 0, which means that the sampling is not triggered at this time;
and 4, step 4: sampling the direct current bus current at the three sampling moments, and converting the direct current bus current sampling result into corresponding phase current information according to the corresponding relation between the direct current bus current and the phase current of the inverter in different switching states;
when the output voltage vector of the inverter is in a non-blind area and a sector switching blind area, two-phase current information is obtained by sampling, but in a low modulation blind area, only one-phase current information can be obtained by sampling each time, and the other-phase current information is the sampling result of the previous PWM period;
after obtaining the two-phase current information, a third phase current is calculated according to a formula iu + iv + iw ═ 0, wherein iu, iv, iw respectively represent the phase currents of u, v, w phases.
In the step 3, sampling is carried out in the middle of the effective voltage vector or the measurement vector action time of the second half PWM period, and the average value of the corresponding vector measurement sampling results is taken as the final sampling result.
Advantageous effects
The invention provides a three-phase current reconstruction method of a motor driving system, which comprises the steps of carrying out measurement vector insertion modulation on a PWM signal generated by an SVPWM algorithm, calculating three sampling moments according to a modulation result, then sampling a direct current bus current at the three sampling moments, and finally reconstructing according to a sampling result to obtain a three-phase current. According to the invention, the measurement vectors are inserted in the zero vector action time of the head end and the tail end of the PWM, so that the system can also sample and obtain phase current information in the action time of the original zero vector, the problem that the phase current of the motor cannot be measured in a low modulation blind area and a sector switching blind area can be effectively avoided, and the reconstruction of the three-phase current sampled by a single resistor is realized. Effective vectors are inserted in the action time of the first and the tail end zero vectors, the influence on the original PWM waveform is small, the reduction of an effective working area cannot be caused, and the asymmetry of the output waveform is obviously reduced compared with a switching state phase shift method.
Drawings
Fig. 1 is a schematic diagram of a circuit structure for reconstructing a three-phase current by single-resistance sampling in the prior art.
Fig. 2 is a three-phase PWM signal for a low modulation dead zone and a sector switching dead zone.
Fig. 3 is a schematic diagram of a three-phase current reconstruction method based on single-resistor sampling.
Fig. 4 is a schematic diagram of the PWM signal and the sampling timing after the measurement vector insertion modulation is performed in
Detailed Description
The invention will now be further described with reference to the following examples and drawings:
the embodiment provides a three-phase current reconstruction method based on single-resistor sampling, which is used for overcoming the defects of the prior art and solving the problem that the bus current cannot be accurately sampled in a low modulation blind area and a sector switching blind area in fig. 2. Fig. 3 is a schematic diagram of a single-resistor sampling three-phase current reconstruction method provided by the present invention, and the method is implemented as follows.
S1, collecting three-phase PWM signals output by an SVPWM algorithm, and action time T4, T6 and zero vector action time T0 of a sector where a motor rotor is located currently and a first half PWM period in the sector; the method samples the direct current bus current in the effective voltage vector action time, the minimum sampling time tmin is the effective voltage vector minimum action time which can accurately sample the direct current bus current, and the sampling time tmin is calculated by a formula td + ton + tset + tAD, wherein td: dead time, ton: switching device on-time, tset: bus current settling time, tAD: the sample and hold time.
S2, performing measurement vector insertion modulation on the PWM signal according to the relation between T4, T6, T0 and tmin: if T4< tmin, T6 > tmin, T0 > 2tmin, or T4 > tmin, T6< tmin, T0 > 2tmin, the inverter output voltage vector is in a sector switching blind area, selecting an effective voltage vector which can sample the third phase current information from six effective voltage vectors of the SVPWM algorithm as a measurement vector to be respectively inserted into a head end zero vector and a tail end zero vector of a PWM signal according to two-phase current information which can be sampled by the effective voltage vector corresponding to T4 and T6, and the action time of the inserted measurement vector is tmin; if T4< tmin and T6< tmin, the inverter output voltage vector is in a low modulation blind area, inserting effective voltage vectors corresponding to T4 and T6 and effective voltage vectors opposite to the effective voltage vectors as measurement vectors into a head end zero vector and a tail end zero vector of a PWM signal in turn in two adjacent PWM periods, and the action time of the inserted measurement vectors is tmin; if T4 is greater than or equal to tmin and T6 is greater than or equal to tmin, the output voltage vector of the inverter is in a non-blind area, and the PWM signal is not processed; if T0<2min, the inverter output voltage vector is in a high modulation blind area, and the PWM signal is not processed.
The measurement vector insertion modulation results are shown in table 1. The table uses the inserted zero vector to indicate that no vector insertion operation is performed.
TABLE 1
Wherein: vi, i ∈ {0, 1, 2, …, 7} represents eight basic voltage space vectors of the two-level three-phase voltage source inverter output, V0 and V7 are zero vectors, and the rest are effective voltage vectors. (Vx, Vy) represents an inserted measuring vector pair, Vx is inserted in a zero vector at the head end of the PWM signal, Vy is inserted in a zero vector at the tail end of the PWM signal, and Vx and Vy are equal in size and opposite in direction. (,) or (,) indicates that two sets of measurement vector pairs are inserted in turn. Here, the minimum sampling time is set to 4us, and the action time of the inserted measurement vector is set to the minimum sampling time.
In this embodiment, the 1 st sector is taken as an example, and measurement vector insertion modulation is performed. In
Similarly, the insertion of the 2 nd to 6 th sector measurement vectors may be performed.
Five PWM signals are generated after the measurement vector insertion modulation is performed, as shown in fig. 4. Fig. 4(a) shows a PWM signal without measurement vector insertion. In fig. 4(b) and 4(c), the minimum sampling time interval between the head and the tail of the PWM signal is changed from zero vector 000 to
S3, inserting the measurement vector into the modulated PWM signal and transmitting the PWM signal to an inverter, and calculating three sampling times t1, t2 and t3 of the direct current bus current in the first half PWM period: if T4< tmin, T6 ≧ tmin and T0 ≧ 2tmin, then T1 ═ tmin/2, T2 ═ 0, T3 ═ T0/2+ T4+ T6/2; if T4 is more than or equal to tmin, T6< tmin and T0 is more than or equal to 2tmin, T1 is tmin/2, T2 is T0/2+ T4/2, and T3 is 0; if T4< tmin, T6< tmin, T1 is tmin/4, T2 is 0, and T3 is 0; if T4 is greater than or equal to tmin, T6 is greater than or equal to tmin, or T0 is less than 2min, T1 is 0, T2 is T0/2+ T4/2, T3 is T0/2+ T4+ T6/2, and the sampling time is 0, which means that the sampling is not triggered at this time.
In the embodiment, sampling is performed three times in the first half PWM period, and the sampling time is set as the middle point of the effective voltage vector or the acting time of the measurement vector. The setting of the sampling timing is shown in table 2 and fig. 4. In order to improve the sampling precision, the sampling can be carried out only in the middle of the effective voltage vector or the measuring vector action time of the first half PWM period, and the sampling can be carried out in the middle of the effective voltage vector or the measuring vector action time of the second half PWM period, and the average value of the corresponding vector measuring sampling results is taken as the final sampling result. .
TABLE 2
In this embodiment, the
S4, sampling the direct current bus current at the three sampling moments, and converting the direct current bus current sampling result into corresponding phase current information according to the corresponding relation between the direct current bus current and the phase current of the inverter in different switching states; when the output voltage vector of the inverter is in a non-blind area and a sector switching blind area, two-phase current information can be obtained by sampling, but in a low modulation blind area, only one-phase current information can be obtained by sampling each time, and the other-phase current information is the sampling result of the previous PWM period; after obtaining the two-phase current information, a third phase current is calculated according to a formula iu + iv + iw ═ 0, wherein iu, iv, iw respectively represent the phase currents of u, v, w phases.
In this embodiment, taking
the bus current values sampled at sampling times t1, t2, and t3 are i1 (including i11 and i12), i2, and i3, respectively, as shown in fig. 4. The i1 phase current value is equal to the v phase current value, the i2 phase current value is equal to the u phase current value, and the i3 phase current value is equal to the i12 phase current value. And adding the positive sign and the negative sign to the bus current sampling value according to the direction of the actual phase current to obtain the actual phase current. i1, i11 and i12 are all current values sampled at time t1, wherein i1 represents sampled values in the application time of the measurement vector in the sector switching dead zone, and i11 and i12 represent sampled values in the application time of the measurement vector inserted by the current in two adjacent PWM periods in the low modulation dead zone. After sampling to obtain two-phase currents, the third-phase current can be obtained by the formula iu + iv + iw being 0. And similarly, the three-phase current reconstruction conditions of other sectors can be obtained.
The calculation formula listed in table 3 can be derived from the sector in which the rotor of the motor is currently located. In the table, (i ═ indicates that this sampling result is the sampling value of the previous PWM period. The plus sign indicating the direction is omitted from the table.
TABLE 3
The single-resistor sampling three-phase current reconstruction method can perform three-phase current reconstruction in both a low modulation blind area and a sector switching blind area, is high in current reconstruction accuracy, has small influence on an original PWM signal, and is low in waveform asymmetry.