METHOD OF CONTROLLING A THREE-PHASE INVERTER IMPLEMENTING A VECTOR MODULATION

Abstract

The disclosed embodiment relates to a method of controlling a system including at least one inverter with six switches, which is linked to a battery, and supervised by a processor. The method implements a vector modulation, so that it is able to prevent the current linking the battery from passing through zero amperes by means of appropriate control logic. The disclosed embodiment also relates to device for controlling an electronic component.

Claims

1. A method of controlling a system comprising at least one six-switch inverter, linked to a battery, and piloted by a processor, said method comprising the following steps: allocation of a zero time to two predetermined near active-vectors; and determination of a new reference vector on the basis of the two near active-vectors, so as to prevent the current linking the battery from passing through zero Amperes.

2. The method as claimed in claim 1, further comprising a step of modifying a circular vector into another form which, as a function of the radius of a reference vector, can be transferred to the surface of a hexagon.

3. The method as claimed in claim 1, further comprising a step of calculating the resulting zero time, and a step of allocating this time to the near vectors, by allocating k percent to the first vector in each sector and (1−k) percent to the second vector, k lying between 0 and 1.

4. A device for controlling a system comprising at least one six-switch inverter, linked to a battery, and piloted by a processor, the device comprising: means for allocating a zero time to two predetermined near active-vectors; and means for determining a new reference vector on the basis the two near active-vectors, so as to prevent the current linking the battery from passing through zero Amperes by means of appropriate control logic.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The disclosed embodiment will be better understood with the aid of the description, given hereinafter purely by way of explanation, of an aspect of the disclosed embodiment, with reference to the Figures in which:

[0025] FIG. 1 illustrates a three-phase inverter structure with fictitious or non-fictitious capacitive midpoint O;

[0026] FIGS. 2A and 2B represent a simulation result for a reference vector, within the framework of the presently disclosed embodiment (FIG. 2A with a radius of 0.5 P.u and FIG. 2B with a radius of 0.8 P.u.);

[0027] FIG. 3 illustrates the switching logic within the framework of the method according to the presently disclosed embodiment;

[0028] FIG. 4 represents the amplitude of the fundamental of the output voltage divided by the mean voltage of the DC bus as a function of the radius of the reference circle;

[0029] FIG. 5 illustrates the DC mode current within the framework of the method according to the presently disclosed embodiment, by injecting an active power of 1 pu;

[0030] FIGS. 6A and 6B represent the AC mode current for a traditional SVM method of control (FIG. 6A) and for a method according to the presently disclosed embodiment (FIG. 6B) by injecting an active power only;

[0031] FIGS. 7A and 7B illustrate the operating zone with k=0.33 (FIG. 7A) and k=0.66 (FIG. 7B); and

[0032] FIG. 8 illustrates results obtained relating to the temperature of the inverter.

DETAILED DESCRIPTION

[0033] The previous SVM methods are characterized by the following relation. To construct the reference vector, the third term (t.sub.zV.sub.0) must be zero.

T.sub.sV.sub.ref=t.sub.iV.sub.i+t.sub.i+1V.sub.i+1+t.sub.zV.sub.0

T.sub.s=t.sub.i+t.sub.i+1+t.sub.z

[0034] In the method according to the presently disclosed embodiment, the zero time is avoided by allocating in an equal manner a calculated zero time to two near active-vectors as follows.

[00001]$t_{i\left(\mathrm{new}\right)}=\left(t_i+t_z/2\right)$$t_{i+1.Math.\left(\mathrm{new}\right)}=\left(t_{i+1}+t_z/2\right)$$T_s.Math.V_{\mathrm{ref}\left(\mathrm{new}\right)}=\left(t_i+t_z/2\right).Math.V_i+\left(t_{i+1}+t_z/2\right).Math.V_{i+1}$$V_{\mathrm{ref}\left(\mathrm{new}\right)}=\left({\alpha }_i+{\alpha }_z/2\right).Math.V_i+\left({\alpha }_{i+1}+{\alpha }_z/2\right).Math.V_{i+1}.Math..Math.\mathrm{with}.Math..Math.{\alpha }_i=\frac{t_i}{T_S}=\frac{.Math.V_{\mathrm{ref}}.Math.}{.Math.V_i.Math.}.Math.\frac{\sin \left(\frac{\pi }{3}-\theta \right)}{\sin \left(\frac{\pi }{3}\right)},.Math.{\alpha }_{i+1}=\frac{t_{i+1}}{T_S}=\frac{.Math.V_{\mathrm{ref}}.Math.}{.Math.V_{i+1}.Math.}.Math.\frac{\sin \left(\theta \right)}{\sin \left(\frac{\pi }{3}\right)}.Math..Math.\mathrm{and}.Math..Math.{\alpha }_z=1-{\alpha }_i-{\alpha }_{i+1}$$T_s.Math..Math.\mathrm{is}.Math..Math.\mathrm{the}.Math..Math.\mathrm{sampling}.Math..Math.\mathrm{period}.$

[0035] The last equation can be reformulated as the following two equations. Thus, a new reference vector is created. This new reference is calculated as the sum of two near vectors by subtracting V.sub.i+1 from V.sub.i which is multiplied by (α.sub.i−α.sub.i+1).

[00002]$V_{\mathrm{ref}\left(\mathrm{new}\right)}=\frac{1}{2}.Math.\left(1+{\alpha }_i-{\alpha }_{i+1}\right).Math.V_i+\frac{1}{2}.Math.\left(1-{\alpha }_i+{\alpha }_{i+1}\right).Math.V_{i+1}$$V_{\mathrm{ref}\left(\mathrm{new}\right)}=\frac{V_i+V_{i+1}}{2}+\left({\alpha }_i-{\alpha }_{i+1}\right).Math.\frac{V_i-V_{i+1}}{2}$$C={\alpha }_i-{\alpha }_{i+1}.Math..Math.\mathrm{designates}.Math..Math.\mathrm{the}.Math..Math.\mathrm{coefficient}.Math..Math.\mathrm{indicated}.Math..Math.\mathrm{in}.Math..Math.\mathrm{FIG}..Math.2.Math.A.Math..$

[0036] Thus, the method according to the presently disclosed embodiment has changed the circular vector into another form which, as a function of the radius of the reference vector, can be transferred to the surface of the hexagon, as illustrated in FIGS. 2A and 2B. V.sub.ref new is obtained by projecting V.sub.ref onto the hexagon in a manner parallel to the first bisector of the sector considered.

[0037] On the basis of the method according to the presently disclosed embodiment, only two near vectors have been used. Consequently, the zero vectors have been eliminated. Table 2 shows the resulting changes of switching in each sector. As illustrated for each individual sector, two switches have been kept fixed at 1 or 0.

TABLE-US-00002 TABLE 2 Switching strategy within the framework of the presently disclosed embodiment Breaker Sector 1 Sector 2 Sector 3 Sector 4 Sector 5 Sector 6 s1 1 x 0 0 x 1 s3 x 1 1 x 0 0 s5 0 0 X 1 1 x

[0038] Within the framework of the traditional SVM methods, the vectors can be implemented through varied modulation schemes.

[0039] As mentioned in Table 2 hereinabove, within the framework of the presently disclosed embodiment, only two changes of switching are performed.

[0040] Thus, within the framework of the method according to the presently disclosed embodiment, the switching losses can be reduced by 66% in comparison with the traditional SVM methods.

[0041] FIG. 3 illustrates the switching strategy within the framework of the method according to the presently disclosed embodiment.

[0042] FIG. 3 shows the behavior of the switches in the method according to the presently disclosed embodiment, implemented by a right-aligned sequence.

[0043] In the method according to the presently disclosed embodiment, a new reference which operates according to a hexagon is imposed instead of implementing a circular reference.

[0044] FIG. 4 represents the amplitude in voltage per DC voltage as a function of radius.

[0045] FIG. 4 shows that in the method according to the presently disclosed embodiment, performance is not linear as in the traditional SVM methods and can vary between 0.73 P.u and 0.65 P.u.

[0046] The main results obtained by virtue of the method according to the presently disclosed embodiment are as follows: decrease the current undulation, attenuate the common-mode voltage (CMV), reduce the electromagnetic interactions, avoid the current at zero Amperes, prolong the lifetime of the battery and finally decrease the cost and size of the battery.

[0047] FIG. 5 illustrates the DC mode current within the framework of the method according to the presently disclosed embodiment, by injecting an active power of 1 pu.

[0048] As may be seen in FIG. 5, the DC mode current is approximately constant by injecting an active power. Without passing through zero, it can satisfy the above-mentioned objectives.

[0049] FIGS. 6A and 6B represent the AC mode current for a traditional SVM method (FIG. 6A) and for a method according to the presently disclosed embodiment (FIG. 6B) by injecting solely an active power. Consequently, the phase voltage in AC mode would have the same form as that represented in FIGS. 6A and 6B.

[0050] Hereinafter, we will describe a particular aspect of the disclosed embodiment.

[0051] After having calculated the resulting zero time from the traditional SVM methods, this time can be allocated in an equal or non-equal manner to the near vectors. By allocating k percent to the first vector in each sector and (1−k) percent to the second vector, the performance of the method can be modified. By applying the previous concepts to one of the previous equations, it is possible to extract the following equation, in which k is a value chosen arbitrarily between 0 and 1.

T.sub.sV.sub.ref(new)=(t.sub.i+(1−k)*t.sub.z)V.sub.i+(t.sub.i+1+k*t.sub.z)V.sub.i+1

α.sub.i(new)=(α.sub.i+(1−k)*α.sub.z)

α.sub.i+1(new)=(α.sub.i+1+k*α.sub.z)

[0052] Through a non-equal allocation (k≠0.5), the operating zone has a tendency toward the first vector or toward the second vector. Hereinafter, by allocating more time to the first vector (FIG. 7A), the operating zone moves toward the right side of the hexagon. Conversely, by imposing more time toward the left vector (FIG. 7B), it tends to operate on the left side.

[0053] FIGS. 7A and 7B illustrate the operating zone with k=0.33 (FIG. 7A) and k=0.66 (FIG. 7B).

[0054] The main factors to be analyzed in order to evaluate the performance are:

[0055] the common-mode voltage, this creating common-mode current and leading to the failure of the motor in it windings insulation (consequently, the life of the motor may be shortened);

[0056] the electromagnetic interference noise, which depends greatly on the evolution of the common-mode voltage level;

[0057] the DC mode zero current, which may shorten the life expectancy of the battery.

[0058] The number of switchings depends on the number of “ON” (closed) and “OFF” (open) durations in a constant switching time, as shown in the following Table 3. The number of switchings has a direct relation to switching losses.

TABLE-US-00003 TABLE 3 Number of switchings Method according to the disclosed Method Traditional SVM embodiment Reduction in loss Number of 6 2 66% switchings Novelty No Yes Yes

[0059] Thus, we see that the number of switchings has been divided by three.

[0060] In the traditional SVM methods, the common-mode voltage may attain the values of

[00003]$\pm \frac{V_{\mathrm{dc}}}{2}$

because of the zero vectors and

[00004]$\pm \frac{V_{\mathrm{dc}}}{6}$

because of the active vectors. The electromagnetic interference relates to changes of level of the common-mode voltage which attains

[00005]$\frac{V_{\mathrm{dc}}}{3}$

in the best of situations and

[00006]$\frac{2.Math.V_{\mathrm{dc}}}{3}$

in the worst or situations. Within the framework of the method according to the presently disclosed embodiment, given that Ts is allocated solely to the active vectors, the common-mode voltage may be limited to

[00007]$\pm \frac{V_{\mathrm{dc}}}{6}$

and the electromagnetic interference is the result of a change of just

[00008]$\frac{V_{\mathrm{dc}}}{3}$

of the common-mode voltage. The following Table 4 provides a summary of the common-mode voltage for each method.

TABLE-US-00004 TABLE 4 Common-mode voltage Method according to the Reduction in the Method Traditional SVM disclosed embodiment common-mode voltage Maximum common- mode voltage [00009]$\pm \frac{V_{\mathrm{dc}}}{2}$ [00010]$\pm \frac{V_{\mathrm{dc}}}{6}$ 66%

[0061] The inventors of the presently disclosed embodiment have carried out tests and have noted that the method according to the presently disclosed embodiment allows a clear reduction in electromagnetic interference.

[0062] The following Table 5 illustrates the electromagnetic interference reduction, which is obtained by virtue of the method according to the presently disclosed embodiment.

TABLE-US-00005 TABLE 5 Common-mode voltage and electromagnetic interference Maximum electromagnetic Measured maximum interference due to the Method common-mode voltage common-mode voltage Method according to the presently disclosed embodiment  66.6 V [00011]$\frac{2*66.6}{T_s}$ Traditional SVM   190 V [00012]$\frac{2*190}{T_s}$ Improvement Reduction of 65% Reduction

[0063] The method according to the presently disclosed embodiment also makes it possible to reduce the temperature of the inverter.

[0064] FIG. 8 and Table 6 hereinbelow illustrate results obtained relating to the temperature of the inverter.

TABLE-US-00006 TABLE 6 Temperature of the inverter Temperature Temperature with method Operating time with traditional SVMs according to the (minutes) (centigrade) invention (centigrade) 0 31 31.1 1 33.6 32.5 2 36.7 33.8 3 37.8 35 4 39.3 35.7 5 41.1 36.6 6 42.5 37.2 7 44 38.2 8 44.9 38.7 9 45.9 39.1 10 47.4 39.8 11 48.2 40.3 12 49 44.9 13 49.4 41.3

[0065] The performance of the inverter is in particular defined the efficiency as the ratio between the AC mode output power of the inverter (in effective value) and the DC mode input power which is imposed as input source.

[0066] The performance obtained by virtue of the presently disclosed embodiment is represented in Table 7 hereinbelow:

TABLE-US-00007 DC mode DC mode Input Output Method voltage current power power Efficiency Traditional SVMs 401 Volts 6.78 2718 2500 91.4% Amperes Watts Watts Method according 402 Volts 7.29 2930 2820 96.7% to the disclosed Amperes Watts Watts embodiment

[0067] Thus, the efficiency of the system has been improved by more than 5%.

[0068] The disclosed embodiment is described in the foregoing by way of example. It is understood that the person skilled in the art is able to carry out different variants of the disclosed embodiment without, however, departing from the scope of the disclosed embodiment.