Method for controlling power system of electric vehicle

Abstract

A control method of a power system of an electric vehicle is provided. A method of controlling an electric power system (18) of an electric vehicle (1), said electric power system (18) being provided with at least two electric machines (4) and two respective electronic DC-AC power converters (9). The steps provided are: controlling the first electronic power converter (9) with a main switching period (Tmaster); to control the second electronic power converter (9) from the switching period (Tslave); establishing a desired time difference ([delta] t *) between a switching action of the first electronic power converter (9) and a switching action of the second electronic power converter (9); determining an actual time difference ([delta] t) between a switching action of the first electronic power converter (9) and a switching action of the second electronic power converter (9); and uniquely changing the slave switching period (Tslave) if necessary on the basis of a comparison between the desired time difference ([Delta] t *) and the actual time difference ([Delta] t *).

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This patent application claims the priority of Italian patent application No. 102023000023958 filed on November 13, 2023, the entire disclosure of which is incorporated herein by reference. Technical Field

[0003] The invention relates to a method for controlling an electric power system of an electric vehicle. Background Art

[0004] An electric vehicle includes at least one electric motor electrically connected to a battery and mechanically connected to drive wheels. In particular, the electric vehicle's power system includes at least one electronic bidirectional DC-AC power converter (i.e., inverter) connected to the battery on the DC side and to the motor on the AC side and having the function of controlling the motor.

[0005] During operation of the electronic power converter, a significant voltage ripple is present on the DC side at the switching frequency of the electronic power converter (directly depending on the rotational speed of the motor); this ripple in the voltage on the DC side subjects the electrochemical cells of the battery to significant stress and must therefore be filtered by installing a filter capacitor with a suitable (i.e. high enough) capacity on the DC side.

[0006] If the vehicle comprises more electric machines (for example two electric machines connected to the two front and rear axles, or four electric machines connected to the four wheels), it is obvious to provide just as many electronic bidirectional DC-AC power converters (inverters), all of which are connected to the same battery; in this case, the ripples of the voltage on the DC side determined by all the electronic power converters can also be summed (at least for several moments) and it is therefore necessary to size the filter capacitor so as to be able to compensate for the sum of all the ripples of the voltage caused by all the electronic power converters.

[0007] Patent application US2012235617A1 describes a system for controlling a rotating electrical machine to reduce current ripple on a DC bus.

[0008] Patent application US2004160201A1 describes a multi-inverter system with low power bus ripple.

[0009] Patent US7425806B2 describes a system for controlling a variable speed drive. Summary of the invention

[0010] The object of the present invention is to provide a method for controlling an electrical system of an electric vehicle, which control method allows reducing the weight, volume and cost of the filter capacitors and which at the same time is easy and cost-effective to implement.

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

[0012] The claims describe preferred embodiments of the invention which form an integral part of the present description. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The present invention will now be described with reference to the accompanying drawings, which illustrate non-limiting example embodiments of the present invention, in which:

[0014] Figure 1 is a schematic plan view of an electric road vehicle;

[0015] Figure 2 yes Figure 1 Schematic diagram of the electrical system of a road vehicle;

[0016] Figure 3 Is Figure 2 A schematic diagram of a control mode executed by a control unit of an electric power system; and

[0017] Figure 4 It is shown in Figure 2 Block diagram of the control logic implemented in a control unit of an electric power system. DETAILED DESCRIPTION

[0018] exist Figure 1 1 , reference numeral 1 generally denotes an electric vehicle provided with two drive wheels 2 (two front drive wheels 2 and two rear drive wheels 2 ).

[0019] The vehicle 1 includes an electric propulsion system 3 arranged at a front position (i.e., connected to two front drive wheels 2) and an electric propulsion system 3 arranged at a rear position (i.e., connected to two rear drive wheels 2), which is structurally identical to the electric propulsion system 3 arranged at the front position and mechanically completely independent and separated from the electric propulsion system 3 arranged at the front position.

[0020] According to different embodiments not shown, the vehicle 1 includes a single electric propulsion system 3 (arranged in a front position or in a rear position) and therefore has only two drive wheels 2; in this embodiment, the vehicle 1 can also alternatively include a thermal propulsion system connected to the drive wheels 2 that do not receive movement from the single electric propulsion system 3.

[0021] exist Figure 1In the illustrated embodiment, each electric propulsion system 3 includes a pair of reversible (i.e., operable both as electric motors that absorb electrical energy and generate mechanical torque and as generators that absorb mechanical energy and generate electrical energy) motors 4 provided with corresponding shafts and a pair of transmission devices 5 connecting the motors 4 (i.e., the shafts of the motors 4) to the corresponding drive wheels 2 without intervening any friction.

[0022] The vehicle 1 includes a battery 6 provided with a container 7 and a plurality of electrochemical cells arranged inside the container 7 and used to convert accumulated chemical energy into electrical energy and vice versa.

[0023] according to Figure 2 As shown, the road vehicle 1 is provided with an electric power system 11, which comprises a battery 6 and four electronic DC-AC power converters (inverters) 9, each of which controls a corresponding motor 4; i.e., each electronic power converter 9 has a DC side connected to the battery 6 and comprises a three-phase AC side connected to the corresponding motor 4.

[0024] A filter capacitor 10 is interposed between the electronic power converter 9 and the battery 6 , and the filter capacitor 10 has a function of filtering high-frequency voltage ripple determined by the operation of the electronic power converter 9 .

[0025] A control unit 11 is provided for controlling the operation of each electronic power converter 9 so as to follow the speed target of the corresponding electric machine 8 (positive for forward movement and negative for reverse movement) and the torque target delivered or absorbed by the electric machine 8 (positive in the case of operation as a motor and negative in the case of operation as a generator).

[0026] In use, each electronic power converter 9 applies a three-phase alternating voltage to the terminals of the motor 8 (and therefore delivers / absorbs a three-phase alternating current flowing through the terminals of the motor 8). In particular, the control unit 11 converts a "mechanical" target (rotation speed of the motor 8 and torque delivered / absorbed) into an "electrical" target (the electrical power that must be supplied to / absorbed by the motor 8).

[0027] The control unit 11 identifies only one of the electronic power converters (inverters) 9 as a master (i.e., identified as a leader), and identifies all other electronic power converters (inverters) 9 as slaves (i.e., identified as followers of the master electronic power converter 9). Figure 3 The control logic implemented in the control unit 11 is illustrated (for simplicity, the behavior of only one slave electronic power converter 9 is shown), which shows the activation sequence of the three phases within each switching cycle based on time t. Figure 3 As shown, the control unit 11 uses the main switching cycle Tmaster Control the master electronic power converter 9 and the corresponding slave switching period T slave Each slave electronic power converter 9 is controlled (may be different for each slave electronic power converter 9 ).

[0028] The control unit 11 uniquely determines the main switching period T based on the speed of the corresponding motor 4. master That is, the main switching period T is established only based on the control requirements of the corresponding motor 4 master In order to perform the best possible control of the corresponding electric machine 4 .

[0029] In use and according to Figure 4 As shown, the control unit 11 establishes an expected time difference Δt* between the switching action of the master electronic power converter 9 and the switching action of each slave electronic power converter 9; in particular, for each slave electronic power converter 9, the expected time difference Δt* may be different, that is, the three expected time differences Δt* are not (always) the same as each other. In particular, the expected time difference Δt* is based on the master switching period T master to determine (i.e., the expected time difference Δt* with the main switching period T master ).

[0030] In the 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 expected time difference Δt* is approximately the main switching period T master In an embodiment where 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, equal to the main switching period T master One quarter, one half and three quarters of a person’s life.

[0031] In use and according to Figure 4 As shown, the control unit 11 determines the actual time difference Δt between the switching action of the master electronic power converter 9 and the switching action of each slave electronic power converter 9 (obviously, the actual time difference Δt may be different for each slave electronic power converter 9), and therefore compares each expected time difference Δt* with the corresponding actual time difference Δt. In addition, the control unit 11 uniquely determines the slave switching period T based on the comparison between the corresponding expected time difference Δt* and the corresponding actual time difference Δt, if necessary. slave ; That is, the main switching period T master is always constant and uniquely established based on the rotational speed of the respective motor 4 , and the (possible) difference between the expected time difference Δt* and the respective actual time difference Δt only determines (if necessary) the corresponding slave switching period T slave changes.

[0032] If the expected time difference Δt* is the same as the corresponding actual time difference Δt, then the corresponding slave switching period T slave is set to the main switching period T master The same (ie no further switching action needs to be inserted between the master electronic power converter 9 and the corresponding slave electronic power converter 9).

[0033] If the desired time difference Δt* differs (substantially) from the corresponding actual time difference Δt, the corresponding slave switching period T slave is set to be different from the main switching period T master (ie, another switching action needs to be inserted between the master electronic power converter 9 and the corresponding slave electronic power converter 9 in order to eliminate the difference between the desired time difference Δt* and the corresponding actual time difference Δt).

[0034] According to a preferred embodiment, if the expected time difference Δt* is (substantially) greater than the corresponding actual time difference Δt, the corresponding slave switching period T slave is set to be greater than the main switching period T master , and if the expected time difference Δt* is (substantially) smaller than the corresponding actual time difference Δt, then the corresponding slave switching period T slave is set to be smaller than the main switching period T master .

[0035] According to a preferred embodiment, the difference ε between the expected time difference Δt* and the corresponding actual time difference Δt is calculated (ε=Δt*-Δt): if the difference ε between the expected time difference Δt* and the corresponding actual time difference Δt is less than the lower threshold Δt UP (has a negative value, i.e. less than zero), then the corresponding slave switching period T slave is set to be smaller than the main switching period T master and preferably equal to the minimum value TS MIN (significantly smaller than the main switching period T master ), if the difference ε between the expected time difference Δt* and the corresponding actual time difference Δt is greater than the upper threshold Δt LOW (has a positive value), then the corresponding slave switching period T 从 is set to be greater than the main switching period T master and preferably equal to the maximum value TS MAX (significantly longer than the main switching period T master ), and if the difference ε between the expected time difference Δt* and the corresponding actual time difference Δt is included in the lower limit threshold Δt UP (with negative value) and upper threshold Δt LOW (with positive value), the corresponding switching period T slave is set to the main switching period Tmaster same.

[0036] According to a preferred embodiment, the control unit 11 is based on the main switching period T master Determine the lower threshold Δt UP (with negative value) and upper threshold Δt LOW (has a positive value); that is, in the main switching period T master When the lower threshold Δt changes UP and upper threshold Δt LOW Similarly, according to a preferred embodiment, the control unit 11 is based on the main switching period T master Determine the minimum TS MIN and the maximum value TS MAX That is, in the main switching period T master When changing, the minimum TS MIN and the maximum value TS MAX Also changed.

[0037] Preferably, the control unit 11 assumes that the switching frequency difference ΔF is applied (by addition or subtraction) to the main switching period T master , to determine the minimum value TS MIN and the maximum value TS MAX The switching frequency difference ΔF must be high enough to allow very fast correction of the corresponding difference ε between the desired time difference Δt* and the corresponding actual time difference Δt, but it must not be too large to avoid the main switching period T master With the switching cycle T slave (ie, in order to avoid compromising the quality of the control of the corresponding slave electronic power converter 9). MIN and the maximum value TS MAX The switching frequency difference ΔF is added to the main switching period T master Or from the main switching period T master minus, which may be constant and predetermined, or may be variable (e.g., based on the main switching period T master , that is, the switching frequency difference ΔF in the main switching period T master decreases when it increases).

[0038] That is, the minimum value TS is calculated using the following equation MIN and the maximum value TS MAX :

[0039] TS MIN =1 / (1 / T master +ΔF)

[0040] TS MAX =1 / (1 / T master -ΔF)

[0041] As an example, the minimum value TS is usually MIN and the maximum value TS MAX With the main switching period T master The difference is 0.1 to 10%.

[0042] Minimum TS MIN Significantly lower than the maximum TS MAX , and therefore when the switching cycle T slave is set equal to the minimum value TS MIN , the corresponding slave electronic power converter 9 accelerates relative to the master electronic power converter 9 (faster than the master electronic power converter 9), and when the slave switching period T slave is set equal to the maximum value TS MAX , the corresponding slave electronic power converter 9 slows down relative to the master electronic power converter 9 (slower than the master electronic power converter 9).

[0043] In short, if the difference ε between the expected time difference Δt* and the corresponding actual time difference Δt is less than the lower limit threshold Δt UP (has a negative value), it means that the actual time difference Δt is higher than the expected time difference Δt* (ε=Δt*-Δt), and therefore the corresponding slave electronic power converter 9 needs to be accelerated to reduce the corresponding slave switching period T slave Set to be less than the main switching period T master and is equal to the minimum value TS MIN However, if the difference ε between the expected time difference Δt* and the corresponding actual time difference Δt is greater than the upper threshold Δt LOW (with a positive value), it means that the actual time difference Δt is lower than the expected time difference Δt* (ε=Δt*-Δt), and therefore the corresponding slave electronic power converter 9 needs to be slowed down, thereby reducing the corresponding slave switching period T slave Set to be greater than the main switching period T master and is equal to the maximum value TS MAX Finally, if the difference ε between the expected time difference Δt* and the corresponding actual time difference Δt is within the lower limit threshold Δt UP (with negative value) and upper threshold Δt LOW (having a positive value), it means that the actual time difference Δt is very (sufficiently) similar to the expected time difference Δt* (ε=Δt*-Δt), and therefore the corresponding slave electronic power converter 9 can have the same speed as the corresponding master electronic power converter 9, thereby reducing the corresponding slave switching period T slave Set to the main switching period T master same.

[0044] According to a preferred embodiment, the control unit 11 generates a synchronization signal SYNCH (at Figure 3 that is, the synchronization signal SYNCH indicates the operation of the master electronic power converter 9. Therefore, the control unit 11 uses the synchronization signal SYNCH as a reference to determine the actual time difference Δt of each slave electronic power converter 9.

[0045] According to a preferred embodiment, the control unit 11 performs a comparison between each expected time difference Δt* and the corresponding actual time difference Δt, and the corresponding slave switching period T slave With each switching cycle of the electronic power converter 9, the following changes (if necessary) may be made. That is, with each switching cycle of the electronic power converter 9, each switching cycle T slave It may be adapted to eliminate possible differences between the respective expected time difference Δt* and the respective actual time difference Δt.

[0046] According to a preferred embodiment, when the absolute value of the difference between the rotation speeds of the motor 4 exceeds the synchronization threshold, the control unit 11 temporarily interrupts the switching cycle T based on a comparison between the expected time difference Δt* and the corresponding actual time difference Δt. slave In other words, in order to perform good control of the motor 4, the switching period must be adapted to the rotational speed of the motor 4: when all motors 4 have approximately the same speed (i.e., when the vehicle 1 is traveling along a straight road), each motor 4 can be changed from the switching period T slave Set to the main switching period T master same as, or in any case with, the main switching period T master The difference is not great, and alternatively, when the motors 4 have different speeds (i.e. when the vehicle 1 is travelling along a curve and therefore the wheels 2 outside the curve must rotate faster than the wheels 2 inside the curve), it may be more convenient not to change the switching period T from slave Linked to the main switching period T master , so as to freely select a slave switching period T that is more suitable for the actual speed of the corresponding motor 4 slave It is important to observe that during travel around bends, the fact that the electric machine 4 is hardly ever known to produce or absorb high torque and mechanical power (ie close to the maximum), and the voltage ripple on the DC side is therefore compensated in a less effective way, is less detrimental to (stressing) the battery 6 .

[0047] In the embodiment shown in the accompanying drawings, there are four electronic power converters (inverters) 9, and therefore there is one master electronic power converter 9 and three slave electronic power converters 9; according to other embodiments not shown, a different number of electronic power converters (inverters) 9 is provided, for example two or three electronic power converters (inverters) 9, and therefore one master electronic power converter 9 and one or two slave electronic power converters 9.

[0048] The embodiments described herein may be combined with each other without departing from the scope of protection of the present invention.

[0049] The control method described above has many advantages.

[0050] Firstly, the above control method allows minimizing the voltage ripple on the DC side, since the voltage ripples generated by the various electronic power converters (inverters) 9 tend to compensate (reduce) each other rather than add. In other words, the above control method allows obtaining destructive interference rather than constructive interference between the voltage ripples generated by the various electronic power converters (inverters) 9, and therefore allows reducing the voltage ripple on the DC side in a substantial manner.

[0051] Therefore, due to the above control method, the capacitance of the filter capacitor 10 can be reduced: some simulations have shown that due to the above control method, the capacitance of the filter capacitor 10 can be reduced by 40-50%. In this way, the filter capacitor 10 is smaller (smaller in volume), lighter and cheaper.

[0052] Furthermore, the control method described above is easy and cost-effective to implement since it does not require high computing power, does not require an associated memory footprint and in particular does not require the installation of any additional physical components (hardware) relative to what is normally provided (and the control method described above can therefore also be installed in existing road vehicles 1 using a simple software update).

[0053] LIST OF REFERENCE NUMBERS IN THE DRAWINGS

[0054] 1 Vehicle

[0055] 2 wheels

[0056] 3 Propulsion system

[0057] 4 Motor

[0058] 5 Transmission

[0059] 6 Batteries

[0060] 7 Container

[0061] 8 Power System

[0062] 9 Electronic power converter

[0063] 10 Filter capacitor

[0064] 11 Control Unit

[0065] t time

[0066] T master Main switching cycle

[0067] T slave From the switching cycle

[0068] Δt* Expected time difference

[0069] Δt Actual time difference

[0070] Δt UP Lower threshold

[0071] Δt LOW Upper threshold

[0072] ε difference

[0073] TS MIN Minimum

[0074] TS MAX Maximum

[0075] SYNCH Synchronization signal

Claims

1. A control method for an electric vehicle (1) power system (18), the power system (18) being provided with at least two electric machines (4); the power system (18) comprising two electronic DC-AC power converters (9), each electronic DC-AC power converter (9) having a DC side connected to a battery (6) and an AC side connected to the respective electric machine (4); the control method comprising the following steps: The main switching period (T master ) controlling a first electronic power converter (9); From the switching period (T slave ) controlling a second electronic power converter (9); and establishing a desired time difference (Δt*) between a switching action of the first electronic power converter (9) and a switching action of the second electronic power converter (9); The control method is characterized in that it comprises the following steps: determining an actual time difference (Δt) between a switching action of the first electronic power converter (9) and a switching action of the second electronic power converter (9); comparing the expected time difference (Δt*) with the actual time difference (Δt); and Based on the comparison between the expected time difference (Δt*) and the actual time difference (Δt), the switching period (T slave ).

2. The control method according to claim 1, wherein: If the expected time difference (Δt*) is the same as the actual time difference (Δt), then the slave switching period (T slave ) is set to match the main switching period (T master )same.

3. The control method according to claim 1, wherein: If the expected time difference (Δt*) is different from the actual time difference (Δt), the slave switching period (T slave ) is set to be different from the main switching period (T master ).

4. The control method according to claim 3, wherein: If the expected time difference (Δt*) is greater than the actual time difference (Δt), the slave switching period (T slave ) is set to be greater than the main switching period (T master ), and if the expected time difference (Δt*) is less than the actual time difference (Δt), then the slave switching period (T slave ) is set to be smaller than the main switching period (T master ).

5. The control method according to any one of claims 1 to 4, wherein: If the difference (ε) between the expected time difference (Δt*) and the actual time difference (Δt) is less than the lower limit threshold (Δt UP ), then the slave switching period (T slave ) is set to be smaller than the main switching period (T master ); If the difference (ε) between the expected time difference (Δt*) and the actual time difference (Δt) is greater than the upper threshold (Δt LOW ), then the slave switching period (T slave ) is set to be greater than the main switching period (T master );as well as If the difference (ε) between the expected time difference (Δt*) and the actual time difference (Δt) is included in the lower limit threshold (Δt UP ) and the upper threshold value (Δt LOW ), then the slave switching period (T slave ) is set to match the main switching period (T master )same.

6. The control method according to claim 5, wherein: The lower threshold (Δt UP ) is negative, and the upper threshold (Δt LOW ) is positive.

7. The control method according to claim 5 further comprises: master ) to determine the lower threshold (Δt UP ) and the upper threshold value (Δt LOW ) steps.

8. The control method according to claim 5, wherein: If the difference (ε) between the expected time difference (Δt*) and the actual time difference (Δt) is less than the lower limit threshold (Δt UP ), then the slave switching period (T slave ) is set equal to the ratio of the main switching period (T master ) Small minimum value (TS MIN );as well as If the difference (ε) between the expected time difference (Δt*) and the actual time difference (Δt) is greater than the upper threshold (Δt LOW ), then the slave switching period (T slave ) is set equal to the ratio of the main switching period (T master )The maximum value (TS MAX ).

9. The control method according to claim 8, further comprising: master ) determines the minimum value (TS MIN ) and the maximum value (TS MAX ) steps.

10. The control method according to claim 9, wherein: Assume that the switching frequency difference (ΔF) is applied to the main switching period (T master ), to determine the minimum value (TS MIN ) and the maximum value (TS MAX ).

11. The control method according to claim 10, wherein: The minimum value (TS) is calculated using the following equation MIN ) and the maximum value (TS MAX ): TS MIN =1 / (1 / T master +ΔF) TS MAX =1 / (1 / T master -ΔF) TS MIN is the minimum value; TS MAX is the maximum value; T master For the main switching cycle; ΔF is the switching frequency difference.

12. The control method according to any one of claims 1 to 4, comprising the following steps: generating a synchronization signal (SYNCH) that corresponds precisely to a switching period of the first electronic power converter (9); as well as The actual time difference (Δt) is determined using the synchronization signal (SYNCH) as a reference.

13. The control method according to any one of claims 1 to 4, further comprising: master ) step of determining the expected time difference (Δt*).

14. The control method according to claim 13, wherein: The desired time difference (Δt*) is approximately the main switching period (T master ) is one quarter of the total.

15. The control method according to any one of claims 1 to 4, wherein: The main switching period (T master ) is uniquely determined based on the rotational speed of the corresponding motor (4).

16. The control method according to any one of claims 1 to 4, wherein: With each switching cycle of the electronic power converter (9), a comparison between the desired time difference (Δt*) and the actual time difference (Δt) and, if necessary, a comparison from the switching period (T slave ) of the subsequent changes.

17. The control method according to any one of claims 1 to 4, further comprising the following steps: When the absolute value of the difference between the rotational speeds of the two motors (4) exceeds a synchronization threshold, the slave switching period (T) is temporarily interrupted based on the comparison between the expected time difference (Δt*) and the actual time difference (Δt). slave ) changes.

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