The present disclosure relates to an apparatus and method for performing space vector modulation for PWM control for creating AC waveforms using pseudo zero vectors or enhanced space vector modulation, or both, for example, in motor control applications.
Space vector modulation (SVM) is an algorithm for the control of pulse width modulation (PWM). It is used for the creation of alternating current (AC) waveforms; most commonly to drive three-phase AC powered motors at varying speeds from DC. There are numerous variations of SVM that result in different quality and computational requirements.
A three phase inverter 100 as shown in
To implement space vector modulation a reference signal Vref is sampled with a frequency fs (Ts=1/fs). The reference signal may be generated from three separate phase references using the αβγ transform, for example. The reference vector is then synthesized using a combination of the two adjacent active switching vectors and one or both of the zero vectors. Various strategies of selecting the order of the vectors and which zero vector(s) to use exist. Strategic selection of the vectors will affect the harmonic content and the switching losses.
The present disclosure is directed to a method of performing space vector modulation for PWM control for creating AC waveforms. The method includes generating and sampling a reference signal to generate reference samples and performing a reference vector approximation to synthesize a reference vector associated with at least one of the reference samples. The reference vector approximation employs active vectors, one or more zero vectors, and one or more pseudo zero vectors in the formation thereof.
In one embodiment of the method, the pseudo vector comprises a combination of two active vectors that have an angle difference therebetween of 180°. In another embodiment, the two active vectors that in combination form the pseudo vector have a scalar amplitude that is the same.
In another embodiment of the method, the pseudo vector comprises a combination of three active vectors that have an angle difference therebetween of 120°. In still another embodiment, the three active vectors that in combination form the pseudo vector have a scalar amplitude that is the same.
In one embodiment of the method, the active vectors in the reference vector approximation comprise adjacent active vectors. In another embodiment, a portion of the reference vector is approximated by two adjacent active vectors, and a remaining portion of the reference vector is approximated by two non-adjacent active vectors. In accordance with one embodiment, the portion of the reference vector driven by active vectors is represented by a variable m, wherein 0≦m≦1, and the remaining portion of the reference vector driven by active vectors is represented by 1−m. When m=1, the entire reference vector driven by active vectors is approximated by two adjacent vectors, and when m=0 the entire reference vector driven by active vectors is approximated by two non-adjacent active vectors. In one embodiment, the non-adjacent active vectors are separated from one another by 120°.
In accordance with another embodiment of the disclosure, a control system comprises a space vector modulator configured to receive a plurality of reference signal samples and perform a reference vector approximation to synthesize a reference vector associated with at least one of the reference signal samples. The reference vector approximation employs active vectors, one or more zero vectors, and one or more pseudo zero vectors in the formation thereof, wherein the space vector modulator outputs timing signals based on the reference vector approximation. The control system further comprises a pulse width modulation unit configured to receive the timing signals from the space vector modulator, and output pulse width modulation control signals based thereon, and a three phase inverter configured to receive the pulse width modulation control signals and generate alternating current waveforms based thereon.
In one embodiment of the control system a pseudo vector comprises a combination of two active vectors that have an angle difference therebetween of 180°. In another embodiment, the two active vectors that in combination form the pseudo vector have a scalar amplitude that is the same.
In another embodiment of the control system a pseudo vector comprises a combination of three active vectors that have an angle difference therebetween of 120°. In still another embodiment, the three active vectors that in combination form the pseudo vector have a scalar amplitude that is the same.
In one embodiment of the control system the active vectors in the reference vector approximation comprise adjacent active vectors. In another embodiment, a portion of the reference vector is approximated by two adjacent active vectors, and a remaining portion of the reference vector is approximated by two non-adjacent active vectors. In one embodiment, the portion of the reference vector is represented by a variable m, wherein 0≦m≦1, wherein the remaining portion of the reference vector is represented by 1−m. When m=1 the entire reference vector driven by active vectors is approximated by two adjacent active vectors, and when m=0 the entire reference vector driven by active vectors is approximated by two non-adjacent active vectors. In one embodiment, the non-adjacent vectors are separated from one another by 120°.
In one embodiment of the control system the three phase inverter comprises a first series-connected switch pair connected together at a node that forms a first phase output, a second series-connected switch pair connected together at a node that forms a second phase output, and a third series-connected switch pair connected together at a node that forms a third phase output. The inverter further comprises a shunt resistor connected with a first terminal to a bottom node of each of the first, second and third series-connected switch pairs, and a second terminal coupled to a reference potential, and an amplifier having first and second inputs coupled to the first and second terminals of the shunt resistor, respectively, wherein an output of the amplifier reflects a current level conducting through the shunt resistor.
Example embodiments according to the disclosure will be explained in more detail in the following text with reference to the attached figures, in which:
In some cases, the same reference symbols are used in the following text for objects and functional units that have the same or similar functional characteristics. Furthermore, optional features of the various example embodiments can be combined with one another or replaced by one another.
For industry and automotive motor control applications, SVM is ubiquitously used in the sinusoidal commutation control (such as V/f, FOC (field oriented control), and DTC (direct torque control)) of PMSM (permanent magnet synchronous motor) and ACIM (alternating current induction motor) to generate sine waveforms from three-phase inverters. Sinusoidal commutation motor control with a single-shunt current sensing resistor inserted in the inverter DC link is a desirable solution when compared to dual-shunt and triple-shunt current sensing techniques, owing to its important advantages such as low cost, simplicity and etc. However, two current samples within one pulse width modulation (PWM) cycle are needed for correct motor phase current reconstruction with single-shunt current sensing. However, with conventional SVM techniques, the accurate current construction is difficult in the following situations: (1) The reference voltage space vector is crossing a sector border as only one current sample can be measured (this occurs in many instances) and (2) When the modulation index is low and the sampling intervals are too short, none of the current samples can be taken (this normally happens in ultra-low speed motor control).
The present disclosure proposes a new concept of a pseudo zero vector (alternatively this may be called a quasi zero vector, or a synthetic zero vector) to SVM to address the above-mentioned problems. With the new SVM using pseudo zero vectors, one is able to provide low-cost, high-quality, more reliable, and unique motor control solutions (e.g., sensorless FOC with single-shunt current sensing) to customers. The new SVM with pseudo zero vectors may also be used in three-phase power inverter control for uninterruptible power supplies, renewable energy, and etc.
The space vector diagram (a regular hexagon) 120 and reference vector approximation 130 of the existing conventional SVM are shown in
Using volt-second balancing:
Solving the Equations (1) and (2), one obtains:
T
1
=K sin(60°−θrel)·TS (3)
T
2
=K sin(θrel)·TS (4)
Adding the Equations (3) and (4), one obtains:
T
1
+T
2
=K sin(60°+θrel)·TS (5)
So the zero vector time is:
T
0
=T
S−(T1+T2)=[1−K sin(60°+θrel)]·TS(6)
where:
T0—Time of the zero vector(s) is/are applied. The zero vector(s) can be {right arrow over (V)}0 [000], or {right arrow over (V)}7 [111], or both
T1—Time of the 1st active vector (e.g., {right arrow over (V)}1 in sector A) is applied within one sampling period,
T2—Time of the 2nd active vector (e.g., {right arrow over (V)}2 in sector A) is applied within one sampling period,
K—
|{right arrow over (V)}ref| is the amplitude of {right arrow over (V)}ref, and VDC is the inverter DC link voltage,
TS—Sampling period, e.g., TS=50 μs
As T0≧0 (or T1+T2≦TS) all the time, so K≦1. We have inverter DC link voltage utilization without over-modulation:
Plots of normalized time T1 140 and T2 150 of Equations (3) and (4) are shown in
For example, motor phase current construction from DC link current via a single-shunt resistor is done by limiting T1 and T2 with a time Tmin (which is PWM dead time+driver delay+ADC sampling time) for ADC to sample the correct current values. However, limiting T1 and T2 will generate a distorted voltage vector, and therefore result in high torque ripple, high vibration & acoustic noise, and even unstable motor control with high dynamic loads. A very fast ADC is required to optimize the system performance in such instances.
Another conventional solution is modifying the SVM switching pattern to a minimum measurement time window in order to allow two current samples to be taken. This pattern modification could generate some current ripple; moreover, more CPU resources are needed to implement the algorithm due to modification of patterns and correction of the same modifications.
Another conventional solution employs use of asymmetrical PWM pulses (with two PWM pulses shifted to obtain enough time for current sampling while duty cycles for all the PWM pulses preserved) only partly solves the problem. It can be found that both T1 and T2 are close or equal to zero if K is very small or K=0, which causes the problem (2) mentioned above. Using the asymmetrical PWM pulses just mentioned can only partly solve this problem.
The present disclosure proposes a new concept of a pseudo zero vector to SVM, with which the approximation of the reference vector with more than two active vectors becomes relatively easy and straightforward. (In contrast, existing SVM uses only two adjacent active vectors to approximate the reference vector). The pseudo zero vectors shown in
A basic pseudo zero vector is either a combination of two active vectors 160, 170, or 180 as shown in
The advantages of the new concept of a pseudo zero vector according to the present disclosure are that there are many more choices of “zero vectors” in the SVM approximation. The approximation of the reference vector with more than two active vectors becomes very easy and convenient. Additionally, the corresponding calculations are similar to those of the existing SVM, and thus are relatively simple and fast.
Two SVM examples according to the present disclosure are provided below with selective utilization of the pseudo zero vectors. Both new SVM examples have non-zero time intervals for two single-shunt current samplings within any PWM cycle, and hence can easily solve the above-mentioned problem (1). Further, and advantageously, new SVM Example #2 can completely solve problem (2) mentioned above.
In the new SVM examples, engineers can tune the pseudo zero vector time Tz to obtain different current sampling intervals based on different system requirements and hardware designs, so as to achieve the best performance of motor control with single-shunt current sensing. Particularly, as the long ADC sampling intervals can be obtained easily by selecting longer pseudo zero vector time Tz, it is also possible to use a low-speed, common and low-cost operational amplifier (if any) for DC link current signal amplification to further lower the system cost.
Table 1 summarizes the basic voltage space vectors for the SVM with the new concept of a pseudo zero vector.
An element of the disclosure is the introduction of the new concept of a pseudo zero vector to SVM. With the new pseudo zero vectors, there are many more choices of zero vectors compared to the only two in existing or conventional SVM, which gives more flexibility for the approximation of the reference vector as well as the design of the SVM switching sequences. The approximation of a reference vector with more than two active vectors becomes relatively easy and convenient. In addition, the corresponding calculations are similar to that of existing SVM, and hence relatively simple and fast.
This section shows two examples of selective utilization of pseudo zero vectors in SVM to straightforwardly solve the single-shunt motor control problems that the existing SVM has difficulties in dealing with effectively.
Using sector A as an example as shown in
in
Using sector A as an example as shown in
is actually approximated by four active vectors. The new SVM Example #2 is elaborated in greater detail below as well.
Table 2 compares and summarizes the existing SVM and the new SVM examples with pseudo zero vectors.
Note
1
Note
1:
Note
2:
Note
3:
As shown in
Calculations when 0°≦θrel<ΘTr
Using the reference vector 210 in sector A as shown in
Choose Tz more than or equal to Tmin (which is PWM dead time+driver delay+ADC sampling time). For simplicity, select
T
3
=T
z
=λT
S
≧T
min (10)
where:
λ—A constant and
e.g., if TS=50 μs and Tmin=2 μs, we can select
T
1
=K sin(60°−θrel)·TS (11)
T
2
=T
2
′+T
z
=[K sin(θrel)+λ]·TS (12)
T
1
+T
2
+T
3
=[K sin(60°+θrel)+2λ]·TS (13)
So the zero vector time is
T
0
=T
S−(T1+T2+T3)=[(1−2λ)−K sin(60°+θrel)]TS (14)
where:
T0—Time of existing zero vector(s) is applied. The zero vector(s) can be {right arrow over (V)}0 [000], or {right arrow over (V)}7 [111], or both
Tz—Time of pseudo zero vector is applied
T1—Time of the 1st active vector is applied within one sampling period
T2—Time of the 2nd active vector is applied within one sampling period
T3—Time of the 3rd active vector is applied within one sampling period, which is part of the pseudo zero vector being used
K—
|Vref| is the amplitude of {right arrow over (V)}ref, and VDC is the inverter DC link voltage
TS—Sampling period
As T0≧0 all the time, from Equation (14) we find K≦1-2λ, so the inverter DC link voltage utilization without over-modulation is
Calculations when ΘTr≦θrel<60°
Using the reference vector 220 in sector A as shown in
Similarly, select Tz=λTS, i.e.,
T
3
=λT
S
≧T
min (18)
T
1
=T
1
′+T
z
=[K sin(60°−θrel)+λ]·TS (19)
T
2
=K sin(θrel)·TS (20)
T
1
+T
2
+T
3
=[K sin(60°+θrel)+2λ]·TS (21)
So the zero vector time is
T
0
=T
S−(T1+T2+T3)=[(1−2λ)−K sin(60°+θrel)]·TS (22)
Likewise, it can be found that the inverter DC link voltage utilization without over-modulation is the same as Equation (15). So the new SVM Example #1 has one maximum inverter DC link voltage utilization without over-modulation, which is
A plot of Equation (23) is shown in
Plots of normalized time T1 250, T2 260, and T3 270 for the new SVM Example #1 are shown in
Using the reference vector 230 in sector A as shown in
Similarly, select Tz=λTS, i.e.,
T
3
=T
4
=λT
S
≧T
min (26)
T
1
=T
1
′+T
z
=[K sin(60°−θrel)+λ]·TS (27)
T
2
=T
2
′+T
z
=[K sin(θrel)+λ]·TS (28)
T
1
+T
2
+T
3
+T
4
=[K sin(60°+θrel)+4λ]·TS (29)
So the zero vector time is
T
0
=T
S−(T1+T2+T3+T4)=[(1−4λ)−K sin(60°+θrel)]·TS (30)
where:
T0—Time of existing zero vector(s) is applied. The zero vector(s) can be {right arrow over (V)}0 [000], or {right arrow over (V)}7 [111], or bot.
Tz—Time of pseudo zero vectors are applied
T1—Time of the 1st active vector is applied within one sampling period
T2—Time of the 2nd active vector is applied within one sampling period
T3, T4—Time of the 3rd and 4th active vectors are applied within one sampling period, which are part of the pseudo zero vectors being used
K—
|Vref| is the amplitude of {right arrow over (V)}ref, and VDC is the inverter DC link voltage
TS—Sampling period
As T0≧0 all the time, from Equation (30) we find K≦1-4λ, so the inverter DC link voltage utilization without over-modulation is
So the maximum inverter DC link voltage utilization without over-modulation is
Plot of Equation (32) is shown in
Plots of normalized time T1 290, T2 300, T3 and T4 310 for new SVM Example #2 are shown in
Usage of new SVM in motor control: The connections of SVM in a motor control are shown in
V
α
=|V
ref|cos(θ) (33)
V
β
=|V
ref|sin(θ) (34)
With Equations (33) and (34), all the formulas listed in Table 2 can be transferred to format with inputs of Vα and Vβ. For example, the time calculations of New SVM Example #1 in sector A1 become
Inverter with single-shunt current sensing: The connection of a three-phase two-level voltage source inverter and a motor are shown in
The motor windings can be wired in a star (as shown) or a delta configuration. SVM is used to control the PWM to create three-phase sinusoidal waveforms to the motor windings. The shunt resistor Rshunt 460 is inserted into the inverter DC link to sense the DC link current. If needed, the amplifier 480 is used to amplify the resistor voltage drop which is proportional to the DC link current. Note that a Hall sensor, a current transformer, or other current sensors can replace the shunt resistor to sense the DC link current.
Compared to dual-shunt and triple-shunt current sensing, single-shunt current sensing has the following important advantages:
1) Cost reduction as a result of only one current sensor, one amplifier (if any), and one ADC channel are used. In contrast, dual-shunt current sensing and triple-shunt current sensing need multiple current sensors, amplifiers (if any) and ADC channels.
2) No need to calibrate amplifier gains and offsets (which may due to component tolerance, fluctuating temperature, aging, and etc) since the same current sensing circuit and ADC channel are used for all the current measurements of motor phases.
3) Simpler and easier electronic schematics and PCB design.
Switching sequence design: There are a lot of switching sequence combinations for the new SVMs, depending on different sequencings of active/zero vectors, splitting of the duty cycles of the vectors, and choice of existing zero vectors (i.e., to choose zero vector {right arrow over (V)}0 [000], or {right arrow over (V)}7 [111], or both). It is difficult to list all the switching sequences here. This section only gives some examples of the switching sequences, which can be easily implemented using Infineon microcontrollers or other type microcontrollers.
Current reconstruction: Two/three motor phase currents can be reconstructed by using single-shunt current sensing. In each PWM cycle, the inverter DC link current is measured at least twice during two different active vector segments to get two motor phase currents. The ADC samplings are normally triggered near the center of the active vector segments to avoid current transitions. Table 3 shows the inverter DC link current of different PWM segments. As an example,
Note 1
Using a reference vector {right arrow over (V)}ref in sector A as an example,
As highlighted above, SVM is regularly employed for industry and automotive motor control applications, and used in the sinusoidal commutation control (such as V/f, FOC, and DTC) of PMSM and ACIM to generate sine waveforms from three-phase inverters. Sinusoidal commutation motor control with a single-shunt current sensing resistor inserted in the inverter DC link is a desired solution when compared to dual-shunt and triple-shunt current sensing techniques, owing to its important advantages such as low cost, simplicity and etc. However, two current samples within one PWM cycle are needed for correct motor phase current reconstruction with single-shunt current sensing. But with existing SVM, the accurate current construction is difficult when the reference voltage space vector is crossing a sector border, as in that situation only one current sample can be measured. It is a problem for most of the normal speed motor control with SVM and single-shunt current sensing.
The enhanced SVM proposed in accordance with one embodiment of the disclosure can solve the above-mentioned problem. With the new SVM technology, one can offer low-cost, high-quality, more reliable, and unique motor control solutions (e.g., sensorless FOC with single-shunt current sensing) to customers. The enhanced SVM may also be used in three-phase power inverter control for uninterruptible power supplies, renewable energy, and etc.
To solve the problems highlighted above associated with conventional SVM, the present disclosure according to the present embodiment introduces innovative approximations of the reference vector with different active vectors, instead of two adjacent active vectors in existing SVM. New approximations of the enhanced SVM are shown in
Table 4 compares and summarizes the existing SVM and proposed new SVMs.
Note
1:
Note
2:
Note
3:
As highlighted previously, enhanced SVM has advantages over conventional SVM techniques. For example, enhanced SVM is well suited for three-phase motor control with single-shunt current sensing, so it can fully use the advantages of a single-shunt current sensing technique as elaborated in greater detail below. Another advantage of the enhanced SVM is that customers can tune the factor m to obtain different current sampling intervals based on different system requirements and hardware designs, so as to achieve the best performance of motor control with single-shunt current sensing. As three adjacent active vectors are used for the approximation in the enhanced SVM, if necessary, it is possible to take three ADC samplings of the inverter DC link current within one PWM cycle to get three motor phase currents directly (which will be discussed in greater detail below). It will be useful for the application cases that the sum of three motor winding currents is not zero but still use single-shunt current sensing. It is also possible to take only two ADC samplings of the interested motor phase current (e.g., IU and IV only) directly within any PWM cycle.
The enhanced SVM at m=0 is also well suited for motor control with single-shunt current sensing. It has long current sampling time intervals within every PWM cycle, so it is possible to use a low-speed, common and low-cost operational amplifier for current signal amplification to further lower the system cost. The enhanced SVM at m=0 has a lower DC link bus voltage utilization. It is not a problem for applications with high DC link voltage, e.g., low-cost PMSM ceiling fan drive with very high DC link voltage (up to 400V DC due to the use of power factor correction).
Enhanced SVM: Using the reference vector in sector A as an example as shown in
Calculations when ΘTr≦θrel<60°: Using reference vector in sector A as shown in
Add both sides of Equations (39) and (40),
T
1
′=mK sin(60°−θrel)·TS (43)
T
1″=(1−m)K sin(120°−θrel)·TS (44)
T
2
=mK sin(θrel)·TS (45)
T
3=(1−m)K sin(θrel)·TS (46)
where:
T0—Time of zero vector(s) is applied. The zero vector(s) can be {right arrow over (V)}0 [000], or {right arrow over (V)}7 [111], or both
T1—Time of the 1st active vector is applied within one sampling period
T2—Time of the 2nd active vector is applied within one sampling period
T3—Time of the 3rd active vector is applied within one sampling period
K—
|Vref| is me amplitude of {right arrow over (V)}ref, and VDc is the inverter DC link voltage
TS—Sampling period
Add both sides of Equations (43) and (44), it can be found that
T
1
=T
1
′+T
1″=√{square root over (1−m(1−m))}·K sin(Θ1−θrel)·TS (47)
where Θ1 is an angle depending on the factor m only, and
where k is an integer and k=0, ±1, ±2, ±3, or . . . . Select k so that 60°≦Θ1≦120° for 0≦m≦1, e.g.: Θ1=120° when m=0.
Add both sides of Equations (45), (46) and (47) to get
T
1
+T
2
+T
3=√{square root over (3−m(3−m))}·K sin(Θ2+θrel)·TS (49)
where:
Θ2—An angle depending on m only, and
e.g.: Θ2=30° when m=0. The zero vector time is
As T0≧0 (or T1+T2+T3≦TS) all the time, so √{square root over (3−m(3−m))}·K≦1, so the inverter DC link voltage utilization without over-modulation is
Calculations when 60°≦θrel<60°+ΘTr: Using reference vector in sector A as an example as shown in
Solve Equations (52) and (53), we have
T
1=(1−m)K sin(120°−θrel)·TS (54)
T
2
=mK sin(120°−θrel)·TS (55)
T
3
=T
3
′+T
3″=√{square root over (1−m(1−m))}·K sin(θrel−Θ3)·TS (56)
where:
θ3—An angle depending on the factor m only, and
is an integer and k=0, ±1, ±2, ±3, or . . . . Select k so that 0°≦Θ3≦60° for 0≦m≦1, e.g.: Θ3=0° when m=0. The zero vector time is
T
0
=T
S
−T
1
−T
2
−T
3=[1−√{square root over (3−m(3−m))}·K sin(θ4+θrel)]·TS (57)
where:
Θ4—An angle depending on m only, and
e.g.: Θ4=30° when m=0. Likewise, it can be found that the inverter DC link voltage utilization without over-modulation is the same as Equation (51). So the enhanced SVM has one maximum inverter DC link voltage utilization without over-modulation, which is
Plot of Equation (58) is shown in
which has been stated in earlier Equation (7); when m=0, it becomes the special case of the enhanced SVM at m=0 and
(to be discussed in greater detail below).
Plots of normalized time T1 650, T2 660, and T3 670 for the enhanced SVM are shown in
A user can choose the value of m based on the required maximum DC link voltage utilization, and the minimum time needed for the current sampling (i.e., make sure Tminimum≧Tmin, where Tmin is PWM dead time+driver delay+ADC sampling time).
Enhanced SVM at m=0: Similarly, the calculations of the enhanced SVM at m=0 are shown below:
T
1
=K sin(120°−θrel)·TS (61)
T
3
=K sin(θrel)·TS (62)
T
1
+T
3=√{square root over (3)}·K sin(30°+θrel)·TS (63)
T
0
=T
S−(T1+T3)=[1−√{square root over (3)}·K sin(30°+θrel)]TS (64)
Note that Equations (61) to (64) work for both
Plot of normalized time T1 680 and T3 690 with transition angle ΘTr=30° for all the sectors is shown in
One advantageous element of the disclosure according to this embodiment is that instead of two adjacent active vectors being employed to synthesize a reference vector as in existing SVM, the enhanced SVM uses three adjacent active vectors or two non-adjacent active vectors for the approximation of reference vector {right arrow over (V)}ref. In the new enhanced SVMs, non-zero intervals can be achieved for multiple current samplings within one PWM cycle, and the reconstruction of phase currents with single-shunt current sensing can be easily done without introducing distortion to the resulted motor phase current.
Usage of new SVM in motor control: The connections of SVM in a motor control system 700 are shown in
The input to the new enhanced SVM can be the polar coordinates (i.e., radial coordinate |Vref| and angular coordinate θ) of the reference vector {right arrow over (V)}ref as shown in
The coordinate systems in the SVM space vector hexagon are shown in
V
α
=|V
ref|cos(θ) (67)
V
β
=|V
ref|sin(θ) (68)
With Equations (67) and (68), all the formulas listed in Table 4 can be transferred to format with inputs of Vα and Vβ. For example, the time calculations of the enhanced SVM at m=0 in sector AB become
Inverter with single-shunt current sensing: The connection 780 of a three-phase two-level voltage source inverter 790 and a motor 800 are shown in
The six switching devices of the inverter, which could be MOSFET, IGBT or similar parts, are controlled by microcontroller PWM signals. The motor windings can be wired in star (as shown) or delta. The enhanced SVM discussed above using either three adjacent active vectors or two non-adjacent active vectors to synthesize the reference vector is used to control the PWM to create three-phase sinusoidal waveforms to the motor windings. The shunt resistor Rshunt 860 is inserted into the inverter DC link to sense the DC link current. If needed, the amplifier 880 is used to amplify the resistor voltage drop which is proportional to the DC link current. Note that a Hall sensor, a current transformer, or other current sensors can replace the shunt resistor to sense the DC link current.
There are a lot of switching sequence combinations for the new enhanced SVMs, depending on different sequencings of active/zero vectors, splitting of the duty cycles of the vectors, and choice of existing zero vectors (i.e., to choose zero vector {right arrow over (V)}0 [000], or {right arrow over (V)}7 [111], or both). It is difficult to list all the switching sequences here. This section only gives some examples of the switching sequences, which can be easily implemented using Infineon microcontrollers, or other microcontrollers.
Switching sequence design for enhanced SVM:
Current reconstruction: two/three motor phase currents can be reconstructed by using single-shunt current sensing. In each PWM cycle, inverter DC link current is measured at least twice during two different active vector segments to get two motor phase currents. The ADC samplings are normally triggered near the center of the active vector segments to avoid current transitions.
Table 5 shows inverter DC link current of different PWM segments. As an example,
It can be found from
Note 1
To solve the problem as mentioned above, it is possible to approximate the reference vector {right arrow over (V)}ref in alternative ways as shown in
The exemplary embodiments described above represent only an illustration of the principles of the present invention. It is self-evident that modifications and variations of the arrangements and details described herein may be of interest to other specialists. The aim is therefore that the invention should be restricted only by the scope of protection of the following patent claims and not by the specific details, which have been presented herein on the basis of the description and the explanation of the exemplary embodiments.
Number | Date | Country | |
---|---|---|---|
61766858 | Feb 2013 | US |