Method to control electric power system of electric vehicle

Abstract

To provide a method for controlling an electric power system of an electric vehicle provided with at least two electric machines and two respective electronic DC-AC power converters.SOLUTION: A method for controlling an electric power system of an electric vehicle comprises the steps of: controlling a first electronic power converter by using a master switching period (Tmaster); controlling a second electronic power converter by using a slave switching period (Tslave); establishing a desired time difference (Δt*) between a switching of the first electronic power converter and a switching of the second electronic power converter; determining an actual time difference (Δt) between the switching of the first electronic power converter and the switching of the second electronic power converter; and changing, a sole slave switching period (Tslave) based on a comparison between the desired time difference (Δt*) with the actual time difference (Δt).SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This patent application claims priority to Italian Patent Application No. 102023000023958, filed on November 13, 2023, the entire disclosure of which is incorporated herein by reference.

[0002] The present invention relates to a method for controlling a power system of an electric vehicle. [Background technology]

[0003] An electric vehicle includes at least one electric machine electrically connected to a battery and mechanically connected to a drive wheel. In particular, the power system of the electric vehicle includes at least one electronic bidirectional DC-AC power converter (i.e., inverter) having a DC side connected to the battery and an AC side connected to the electric machine and capable of controlling the electric machine.

[0004] During operation of the electronic power converter, on the DC side, a pronounced ripple in the voltage appears at the switching frequency of the electronic power converter (which is directly determined by the rotational speed of the electric machine); this ripple in the voltage on the DC side exerts significant stress on the electrochemical cells of the battery and must therefore be eliminated by installing a filter capacitor with a suitable (i.e. sufficiently high) capacitance on the DC side.

[0005] If the electric vehicle comprises more electric machines (for example two electric machines connected to two front and rear axles, or four electric machines connected to four wheels), then of course the same number of electronic bidirectional DC-AC voltage converters (inverters) are provided, all connected to the same battery. In this situation, the ripples of the voltage on the DC side determined by all electronic power converters may be summed up (at least for a few moments), and therefore the filter capacitors must be dimensioned to be able to compensate for the sum of all ripples of the voltage caused by all electronic power converters.

[0006] US Pat. No. 5,399,633 describes a system for controlling a rotating electrical machine to reduce current ripple on a DC bus.

[0007] US Pat. No. 5,399,633 describes a multi-inverter system with low power bus ripple.

[0008] Patent document 3 describes a system for controlling a variable speed drive. It explains. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] U.S. Patent Application No. 2012235617(A1) [Patent Document 2] U.S. Patent Application No. 2004160201(A1) [Patent Document 3] US Patent No. 7425806(B2) Summary of the Invention [Problem to be solved by the invention]

[0010] It is an object of the present invention to provide a method for controlling the power system of an electric vehicle that reduces the weight, volume and cost of filter capacitors while at the same time being easily and cost-effectively implemented. [Means for solving the problem]

[0011] According to the present invention, a method for controlling a power system of an electric vehicle is provided in accordance with what is claimed in the accompanying claims.

[0012] The claims set forth preferred embodiments of the invention and form an integral part of this specification.

[0013] The present invention will now be described with reference to the accompanying drawings, which show non-limiting exemplary embodiments of the invention. [Brief description of the drawings]

[0014] [Figure 1] FIG. 1 is a schematic plan view of an electric road vehicle. [Diagram 2] FIG. 2 is a schematic diagram of an electrical power system for the road vehicle of FIG. 1. [Diagram 3] 3 is a schematic diagram of a control mode implemented by a control unit of the power system of FIG. 2. [Figure 4] FIG. 3 is a block diagram showing control logic implemented in a control unit of the power system of FIG. 2. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] In FIG. 1, reference number 1 indicates as a whole an electric vehicle with two drive wheels 2 (two front drive wheels 2 and two rear drive wheels 2).

[0016] The vehicle 1 is equipped with an electric propulsion system 3 arranged in a front position (i.e. connected to the two front drive wheels 2) and an electric propulsion system 3 arranged in a rear position (i.e. connected to the two rear drive wheels 2), which is structurally identical to the electric propulsion system 3 arranged in the front position and is completely mechanically independent and separated from the electric propulsion system 3 arranged in the front position.

[0017] According to a different embodiment not shown, the vehicle 1 is equipped with one single electric propulsion system 3 (located in the front position or in the rear position) and therefore has only two drive wheels 2. In this embodiment, the vehicle 1 can alternatively also be equipped with a thermal propulsion system connected to drive wheels 2 that do not receive motion from the single electric propulsion system 3.

[0018] In the embodiment shown in FIG. 1 , each electric propulsion system 3 comprises a pair of reversible (i.e. capable of operating both as an electric motor absorbing electrical energy and generating mechanical torque, and as a generator absorbing mechanical energy and generating electrical energy) electric machines 4 provided with respective shafts and a pair of transmissions 5 connecting the electric machines 4 (i.e. the shafts of the electric machines 4) to the corresponding drive wheels 2 without friction.

[0019] The vehicle 1 comprises a battery 6 comprising a container 7 and a number of electrochemical cells arranged inside the container 7 and adapted to convert stored chemical energy into electrical energy and conversely convert electrical energy into chemical energy.

[0020] According to what is shown in FIG. 2 , the road vehicle 1 is provided with a power system 8 comprising a battery 6 and four electronic DC-AC power converters (inverters) 9, each controlling a respective electric machine 4, i.e. each electronic power converter 9 has a DC side connected to the battery 6 and a three-phase AC side connected to a respective electric machine 4.

[0021] Between the electronic power converter 9 and the battery 6 there is interposed a filter capacitor 10 which has the function of filtering out high frequency voltage ripples determined by the operation of the electronic power converter 9 .

[0022] A control unit 11 is provided which controls the operation of each electronic power converter 9 to comply with a rotational speed target of the respective electric machine 8 (positive for forward motion, negative for reverse motion) and a torque target delivered or absorbed by the electric machine 8 (positive when operating as a motor, negative when operating as a generator).

[0023] In use, each electronic power converter 9 applies a three-phase AC voltage to the terminals of the electric machine 8 (and thus delivers / absorbs a three-phase AC current flowing through the terminals of the electric machine 8). In particular, the control unit 11 converts "mechanical" targets (rotational speed and delivered / absorbed torque of the electric machine 8) into "electrical" targets (power that needs to be provided to / absorbed by the electric machine 8).

[0024] The control unit 11 identifies only one of the electronic power converters (inverters) 9 as the master (i.e., guide) and all other electronic power converters (inverters) 9 as slaves (i.e., followers of the master electronic power converter 9). Figure 3 shows the control logic implemented in the control unit 11 (for simplicity, the behavior of only one slave electronic power converter 9 is shown). This control logic shows the actuation sequence of the three phases for each switching cycle based on time t. According to what is shown in Figure 3, the control unit 11 determines the master switching period T master , and controls the master electronic power converter 9 with each slave switching period T slave (possibly different for each slave electronic power converter 9 ) to control each slave electronic power converter 9 .

[0025] The control unit 11 determines the master switching period T based solely on the rotation speed of the corresponding electric machine 4. master That is, the master switching period T master is established solely based on the control needs of the corresponding electric machine 4 so as to achieve the best control of the corresponding electric machine 4 .

[0026] In use, the control unit 11 establishes a desired time difference Δt* between the switching of the master electronic power converter 9 and the switching of each slave electronic power converter 9, according to what is shown in Fig. 4. In particular, the desired time difference Δt* may possibly differ for each slave electronic power converter 9, i.e. the three desired time differences Δt* are not (necessarily) the same as each other. In particular, the desired time difference Δt* may be determined by a time period T master (i.e., the desired time difference Δt* is determined based on the master switching period T master (This varies depending on the fluctuation of

[0027] In an embodiment where there are only two electronic power converters 9 (one master electronic power converter 9 and one slave electronic power converter 9), the only desired time difference Δt* is the master switching period T master In an embodiment in which there are four electronic power converters 9 (one master electronic power converter 9 and three slave electronic power converters 9), the three desired time differences Δt* are different from each other and may be, for example, one-fourth of the master switching period T master may be equal to one-quarter, one-half, and three-quarters of a square.

[0028] In use, in accordance with what is shown in Figure 4, the control unit 11 determines the actual time difference Δt between the switching of the master electronic power converter 9 and the switching of each slave electronic power converter 9 (of course the actual time difference Δt may possibly differ for each slave electronic power converter 9) and therefore compares each desired time difference Δt* with the respective actual time difference Δt. Furthermore, the control unit 11 determines, if necessary, the sole slave switching period T slave That is, the master switching period T master is always constant and is established solely on the basis of the rotation speed of the respective electric machine 4, and the (possible) difference between the desired time difference Δt* and the respective actual time difference Δt is determined (if necessary) by the corresponding slave switching period T slaveDetermine only the variation of

[0029] If the desired time difference Δt* is the same as the respective actual time difference Δt, then the corresponding slave switching period T slave is the master switching period T master (i.e. no additional switching needs to be inserted between the master electronic power converter 9 and the corresponding slave electronic power converter 9).

[0030] If the desired time difference Δt* differs (substantially) from the respective actual time difference Δt, the corresponding slave switching period T slave is the master switching period T master (i.e., additional switching needs to be inserted between the master electronic power converter 9 and the corresponding slave electronic power converter 9 to eliminate the difference between the desired time difference Δt* and the respective actual time difference Δt).

[0031] According to a preferred embodiment, if the desired time difference Δt* is (substantially) greater than the respective actual time difference Δt, then the corresponding slave switching period T slave is the master switching period T master and the desired time difference Δt* is (substantially) smaller than the respective actual time difference Δt, the corresponding slave switching period T slave is the master switching period T master is set to a smaller value.

[0032] According to a preferred embodiment, a difference ε between the desired time difference Δt* and the respective actual time difference Δt is calculated (ε=Δt*−Δt), and the difference ε between the desired time difference Δt* and the respective actual time difference Δt is set to a lower limit Δt UP (having a negative value, i.e., less than zero), the respective slave switching period T slave is the master switching period T master It is preferably set to a minimum value TS MIN(Of course, the master switching period T master (smaller than Δt), the difference ε between the desired time difference Δt* and the respective actual time difference Δt is limited to an upper limit Δt LOW (has a positive value), the respective slave switching period T slave is the master switching period T master It is preferably set to a value greater than the maximum value TS MAX (Of course, the master switching period T master (greater than Δt), the difference ε between the desired time difference Δt* and the respective actual time difference Δt is within the lower bound Δt UP (has a negative value) and upper limit Δt LOW (having a positive value), the respective slave switching period T slave is the master switching period T master is set to the same as

[0033] According to a preferred embodiment, the control unit 11 determines the master switching period T master Based on the lower limit Δt UP (has a negative value) and upper limit Δt LOW (having a positive value), i.e., the master switching period T master When fluctuates, the lower limit Δt UP and upper limit Δt LOW Similarly, according to a preferred embodiment, the control unit 11 varies the master switching period T master Based on the minimum value TS MIN and the maximum value TS MAX Determine the master switching period T master When fluctuates, the minimum value TS MIN and the maximum value TS MAX also fluctuates.

[0034] Preferably, the control unit 11 determines whether the switching frequency difference ΔF is equal to or smaller than the master switching period T master Assume that the minimum value TS applies to MIN and the maximum value TS MAXThe switching frequency difference ΔF must be large enough to allow fairly rapid correction of the corresponding difference ε between the desired time difference Δt* and the respective actual time difference Δt, but large enough to allow for a relatively rapid correction of the master switching period T master and the slave switching period T slave , should not be too large to avoid excessive differences between the respective electronic power converters 9 (i.e., to avoid compromising the quality of the control of the respective electronic power converter 9). MIN and the maximum value TS MAX To determine the master switching period T master Added to the master switching period T master The switching frequency difference ΔF that is subtracted from the master switching period T may be constant, may be predetermined, or may be variable (e.g., master That is, the master switching period T master (When the switching frequency is shortened, the switching frequency difference ΔF increases.)

[0035] That is, the minimum value TS MIN and the maximum value TS MAX is calculated using the following formula: TS MIN = 1 / (1 / T master + ΔF) TS MAX = 1 / (1 / T master - ΔF)

[0036] As an example, in general, the minimum value TS MIN and the maximum value TS MAX is the master switching period T master and differs by 0.1 to 10%.

[0037] Minimum TS MIN is the maximum value TS MAX is obviously smaller than the slave switching period T slave is the minimum value TS MINWhen the slave switching period T slave is the maximum value TS MAX , each slave electronic power converter 9 is throttled back relative to the master electronic power converter 9 (runs slower than the master electronic power converter 9).

[0038] In summary, the difference ε between the desired time difference Δt* and each actual time difference Δt is a lower bound Δt UP (has a negative value), the actual time difference Δt is greater than the desired time difference Δt* (ε=Δt* - Δt), and therefore the respective slave electronic power converter 9 must be accelerated to reduce the respective slave switching period T slave The master switching period T master Set it smaller than the minimum value TS MIN , while the difference ε between the desired time difference Δt* and the respective actual time difference Δt must be set equal to the upper limit Δt LOW (having a positive value), the actual time difference Δt is less than the desired time difference Δt* (ε=Δt* - Δt), and therefore the respective slave electronic power converter 9 is slowed down to reduce the respective slave switching period T slave The master switching period T master Set it to be larger than the maximum value TS MAX Finally, the difference ε between the desired time difference Δt* and the respective actual time difference Δt must be set equal to the lower limit Δt UP (has a negative value) and upper limit Δt LOW (having a positive value), the actual time difference Δt is close enough to the desired time difference Δt* (ε=Δt* - Δt), and therefore each slave electronic power converter 9 has the same speed as each master electronic power converter 9, and each slave switching period T slave The master switching period T master This means that it can be set to be equal to

[0039] According to a preferred embodiment, the control unit 11 generates a synchronization signal SYNCH (shown in FIG. 3) that is strictly synchronized to the switching of the master electronic power converter 9, i.e. the synchronization signal SYNCH indicates the operation of the master electronic power converter 9. The control unit 11 therefore determines the actual time difference Δt of each slave electronic power converter 9 using the synchronization signal SYNCH as a reference.

[0040] According to a preferred embodiment, the control unit 11 performs a comparison of each desired time difference Δt* with the respective actual time difference Δt and, if necessary, calculates a respective slave switching period T slave That is, in some cases, each slave switching period T is adjusted to eliminate possible differences between the respective desired time differences Δt* and the respective actual time differences Δt for each switching cycle of the electronic power converter 9. slave can be adapted.

[0041] According to a preferred embodiment, the control unit 11 determines the slave switching period T based on a comparison of the desired time difference Δt* and the respective actual time difference Δt when the absolute value of the difference between the rotational speeds of the electric machines 4 exceeds the synchronization threshold. slave In other words, in order to achieve good control of the electric machines 4, the switching periods must be suitable for the rotation speed of the electric machines 4, and when all the electric machines 4 have approximately the same speed (i.e. when the vehicle 1 is traveling along a straight road), each slave switching period T slave The master switching period T master or set equal to the master switching period T masterIt is possible to set it to a value that is not very different. Instead, when the electromechanics 4 have different speeds (i.e., when the vehicle 1 is traveling along a curve, and thus the outer wheels 2 of the curve need to rotate faster than the inner wheels 2 of the curve), the slave switching period T slave is freely selected so that the slave switching period T slave is not linked to the master switching period T master may be more convenient. During curve driving, the electromechanics 4 are rarely called upon to generate or absorb high torque and mechanical force (i.e., close to the maximum value), and thus it is important to note that even if the compensation for the DC-side voltage ripple is not very effective, it is not disadvantageous (not a heavy burden) for the battery 6.

[0042] In the embodiment shown in the accompanying figures, there are four electronic power converters (inverters) 9, and thus there is one master electronic power converter 9 and three slave electronic power converters 9. In other embodiments not shown, different numbers of electronic power converters (inverters) 9, for example, two or three electronic power converters (inverters) 9 are provided, and thus one master electronic power converter 9 and one or two slave electronic power converters 9 are provided.

[0043] The embodiments described herein can be combined with each other without departing from the scope of protection of the present invention.

[0044] The control method described above has a number of advantages.

[0045] Firstly, the control method described above makes it possible to minimize the ripple of the voltage on the DC side, since the voltage ripples generated by the various electronic power converters (inverters) 9 tend to compensate (reduce) rather than add to each other. In other words, the control method described above makes it possible to obtain destructive interference rather than constructive interference between the voltage ripples generated by the various electronic power converters (inverters) 9, thus making it possible to substantially reduce the ripple of the voltage on the DC side.

[0046] Thus, the control method described above can reduce the capacitance of filter capacitor 10, and some simulations have demonstrated that the control method described above can reduce the capacitance of filter capacitor 10 by 40-50%. Thus, filter capacitor 10 is smaller (less bulky), lighter, and less expensive.

[0047] Furthermore, the control method described above is easy and cost-effective to implement, as it does not require high computational power, does not require any associated memory occupation and does not particularly require the installation of additional physical components (hardware) to those that are typically provided (hence the control method described above can also be installed in existing road vehicles 1 by means of a simple software update). [Explanation of symbols]

[0048] 1 vehicle 2 wheels 3. Propulsion System 4. Electrical Machinery 5. Transmission 6 Battery 7 Container 8. Power System 9 Electronic Power Converter 10 Filter Capacitor 11 Control unit t time T masterMaster Switching Period T slave Slave Switching Period Δt* desired time difference Δt Actual time difference Δt UP lower limit Δt LOW upper limit ε Difference TS MIN Minimum TS MAX Maximum SYNCH Synchronization signal

Claims

1. 1. A method for controlling a power system (8) of an electric vehicle (1) provided with at least two electric machines (4), the power system (8) comprising two electronic DC-AC power converters (9), each having a DC side connected to a battery (6) and an AC side connected to a respective electric machine (4), comprising: Master switching period (T ｍａｓｔｅｒ ) controlling a first electronic power converter (9); Slave switching period (T ｓｌａｖｅ ) controlling a second electronic power converter (9); establishing a desired time difference (Δt*) between the switching of the first electronic power converter (9) and the switching of the second electronic power converter (9); In a method comprising: determining an actual time difference (Δt) between the switching of the first electronic power converter (9) and the switching of the second electronic power converter (9); comparing the desired time difference (Δt*) with the actual time difference (Δt); Based on the comparison of the desired time difference (Δt*) and the actual time difference (Δt), a unique slave switching period (T ｓｌａｖｅ ) and the step to change A control method comprising:

2. If the desired time difference (Δt*) is the same as the actual time difference (Δt), the slave switching period (T ｓｌａｖｅ ) is the master switching period (T ｍａｓｔｅｒ 2. The control method according to claim 1 , wherein the setting is the same as the setting of the first and second inputs.

3. If the desired time difference (Δt*) differs from the actual time difference (Δt), the slave switching period (T ｓｌａｖｅ ) is the master switching period (T ｍａｓｔｅｒ 2. The control method according to claim 1, wherein the setting is different from the setting of the first threshold value.

4. If the desired time difference (Δt*) is greater than the actual time difference (Δt), the slave switching period (T ｓｌａｖｅ ) is the master switching period (T ｍａｓｔｅｒ ), and the desired time difference (Δt*) is smaller than the actual time difference (Δt), the slave switching period (T ｓｌａｖｅ ) is the master switching period (T ｍａｓｔｅｒ 4. The control method according to claim 3, wherein the control is set to be smaller than the predetermined value.

5. The difference (ε) between the desired time difference (Δt*) and the actual time difference (Δt) is a lower limit (Δt ＵＰ ), the slave switching period (T ｓｌａｖｅ ) is the master switching period (T ｍａｓｔｅｒ ) is set to be smaller than The difference (ε) between the desired time difference (Δt*) and the actual time difference (Δt) is an upper limit (Δt ＬＯＷ ), the slave switching period (T ｓｌａｖｅ ) is the master switching period (T ｍａｓｔｅｒ ) is set to be greater than The difference (ε) between the desired time difference (Δt*) and the actual time difference (Δt) is within the lower limit (Δt ＵＰ ) and the upper limit (Δt ＬＯＷ ) and the slave switching period (T ｓｌａｖｅ ) is the master switching period (T ｍａｓｔｅｒ The control method according to claim 1 , wherein the setting is the same as the setting of the first and second inputs.

6. The lower limit (Δt ＵＰ ) is negative, and the upper limit (Δt ＬＯＷ 6. The method of claim 5, wherein: ##EQU1## is positive.

7. The master switching period (T ｍａｓｔｅｒ ) based on the lower limit (Δt ＵＰ ) and the upper limit (Δt ＬＯＷ 6. The method of claim 5, further comprising the step of determining

8. The difference (ε) between the desired time difference (Δt*) and the actual time difference (Δt) is within the lower limit (Δt ＵＰ ), the slave switching period (T ｓｌａｖｅ ) is the master switching period (T ｍａｓｔｅｒ ) is smaller than the minimum value (TS ＭＩＮ ) and The difference (ε) between the desired time difference (Δt*) and the actual time difference (Δt) is ＬＯＷ ), the slave switching period (T ｓｌａｖｅ ) is the master switching period (T ｍａｓｔｅｒ ) ＭＡＸ 6. The method of claim 5, wherein the control is set equal to

9. The master switching period (T ｍａｓｔｅｒ ) based on the minimum value (TS ＭＩＮ ) and the maximum value (TS ＭＡＸ 9. The method of claim 8, further comprising the step of determining

10. The minimum value (TS ＭＩＮ ) and the maximum value (TS ＭＡＸ ) is the master switching period (T ｍａｓｔｅｒ 10. The method of claim 9, wherein the switching frequency difference (ΔF) is applied to the first and second inputs.

11. The minimum value (TS ＭＩＮ ) and the maximum value (TS ＭＡＸ ) is expressed as follows: TS ＭＩＮ = 1 / (1 / T ｍａｓｔｅｒ + ΔF) TS ＭＡＸ = 1 / (1 / T ｍａｓｔｅｒ - ΔF) It is calculated using, where: T.S. ＭＩＮ is the minimum value, T.S. ＭＡＸ is the maximum value, T ｍａｓｔｅｒ is the master switching period, 11. The method of claim 10, wherein ΔF is a switching frequency difference.

12. - generating a synchronization signal (SYNCH) that corresponds exactly to the switching period of the first electronic power converter (9); A control method according to claim 1 , further comprising the step of: determining the actual time difference (Δt) with reference to the synchronization signal (SYNCH).

13. The master switching period (T ｍａｓｔｅｒ 5. The method of claim 1, further comprising the step of determining the desired time difference (Δt*) based on

14. The desired time difference (Δt*) is ｍａｓｔｅｒ 14. The method of claim 13, wherein the temperature is about one-fourth of the temperature of the first electrode.

15. The master switching period (T ｍａｓｔｅｒ 5. The method according to claim 1, wherein the rotational speed of the corresponding electric machine (4) is determined solely on the basis of the rotational speed of the corresponding electric machine (4).

16. The comparison of the desired time difference (Δt*) and the actual time difference (Δt) is performed and, if necessary, the slave switching period (T ｓｌａｖｅ 5. The method of claim 1 , wherein a resulting change in the

17. When the absolute value of the difference between the rotational speeds of the two electric machines (4) exceeds a synchronization threshold, the slave switching period (T) is determined based on a comparison between the desired time difference (Δt*) and the actual time difference (Δt). ｓｌａｖｅ 5. The method of claim 1, further comprising the further step of temporarily suspending said modification of said first parameter.

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