Inverter for electrical machine

Abstract

The invention relates to an inverter configured to operate in association with a rotating electrical machine, particularly a three-phase type. The inverter comprises H-bridges (20), for example, three for a three-phase rotating electrical machine. Each H-bridge has two bridge arms, each with two transistors (T1, T2, T3, T4) and a midpoint between them. Each H-bridge is configured to allow each phase (AB) of the rotating electrical machine to be connected to the midpoints of the associated H-bridge. (See Fig. 3 for abbreviations.)

Description

Title of the invention: Inverter for electrical machine

[0001] The invention relates to the field of inverters for high-speed electrical machines, for example capable of rotating at a maximum speed greater than 20,000 rpm, or greater than 25,000 rpm to 30,000 rpm.

[0002] Conventional three-phase high-voltage machines are known, associated with inverters equipped with standard IGBT bridges (for example, a standard inverter equipped with 2-level IGBT or SiC MOSFET bridges), comprising a "high-side" power module and a "low-side" power module. The inverter operates between 0 and the battery DC bus voltage, for example, 400V or 800V nominal battery voltage. The machine phases are connected to the midpoint of the bridge.

[0003] By "high side" (high voltage level) is meant transistors whose source electrode for MOSFETs or emitter electrode for IGBTs is placed at a floating potential which can be high, and which can vary rapidly with respect to the reference potential of the control circuit.

[0004] By "low side" (low voltage level), we describe transistors whose source electrode for MOSFETs or emitter electrode for IGBTs is placed at the same potential as the reference potential of the control circuit.

[0005] It is known to consider connecting the phases of a rotating electrical machine by placing windings in series at low speeds to increase torque through a higher number of turns. However, as the speed increases, this number of turns will halve the power because the electromotive force will increase (this is proportional to the number of turns and the speed). It will then be necessary to deflux the machine much more, to the detriment of power and efficiency.

[0006] The present invention aims in particular to provide an electric machine that allows both strong starting torque and high power at high speeds.

[0007] The invention thus relates to an inverter configured to operate in association with a rotating electrical machine, in particular of the three-phase type, the inverter comprising H-bridges, for example 3 for a three-phase rotating electrical machine, each H-bridge comprising two bridge arms with, on each bridge arm, two transistors and a midpoint between these two transistors, each H-bridge being configured to allow each phase of the rotating electrical machine to be connected to the midpoints of the associated H-bridge.

[0008] For example, for a three-phase rotating electrical machine, we have 6 phase outputs for the complete machine.

[0009] In particular, each H-bridge comprises four transistors, including two "high side" transistors and two "low side" transistors.

[0010] The present invention makes it possible to have a rotating electrical machine which has a higher number of turns, for example a number which can be doubled compared to a conventional high voltage three-phase machine.

[0011] For example, in such a conventional high-voltage three-phase machine, the number of turns is typically between 16 and 32. For the purposes of this invention, the number of turns can, for example, be doubled. For instance, a number of turns between 32 and 64 is proposed within the same slot dimensions. This allows for double the torque at low speeds, or the same torque as a conventional machine with half the phase current. As soon as the speed increases, the machine's electromotive force and power will be reduced for the same voltage (because the number of turns has increased).Thanks to the H-bridges in the invention, for a battery voltage of 800V, for example, there is a voltage of +800V or -800V across the switches / power transistors, therefore a maximum possible voltage of 1600V across the phase, compared to a voltage of 800V obtained for conventional bridges (such a conventional bridge is connected to ground on one side and to the battery voltage on the other, with the phase connected to the midpoint of the bridge). By doubling the voltage, the initial voltage value of a conventional machine is recovered.

[0012] Furthermore, the H-bridge architecture allows for greater flexibility in operational reliability because there are more modes or degrees of freedom. Degraded mode operation is particularly improved. Indeed, with the H-bridge, the architecture is equivalent to a dual inverter (A) and (B), and the machine windings are connected between the two inverters. Therefore, in the event of a failure of (A) or (B), the MOSFETs or IGBTs can be reconfigured, that is, the machine windings can be shared, and inverter (B) can be driven in half-bridge inverter mode.

[0013] According to one aspect of the invention, the transistors defining the H-bridge comprise IGBT transistors (for insulated gate bipolar transistors) or MOSFET transistors (for insulated gate field-effect transistors) of the SiC type.

[0014] According to one aspect of the invention, the inverter is configured to, during a positive half-period P+, alternate the state of transistors T1 and T2 in the arm (with midpoint A), between conduction (closed or ON) and non-conduction (open or OFF) to create voltage modulation, while transistor T4 is held at zero to have the potential at point B equal to 0.

[0015] Having an H-bridge with the two arms (arm T1-T2 on one side and arm T3-T4 on the other) allows the midpoint B to be brought to 0 and therefore to have an amplitude of +Vdc.

[0016] This operation (also called switching) is carried out using pulse width modulation (PWM) to control the power delivered to the AB winding of the electric machine. The voltage modulation then takes place between 0 V and the battery supply voltage +Vdc over this positive half-period P+, as can be seen on the curve Cl in [Fig.2].

[0017] According to one aspect of the invention, the inverter is configured so that, during a positive half-period P-, the state of transistors T3 and T4 in the arm (with midpoint B) is alternated between conduction (closed or ON) and non-conduction (open or OFF) to create voltage modulation, while transistor T2 is held at zero to have the potential at point A equal to 0.

[0018] Having an H-bridge with the two arms (arm T1-T2 on one side and arm T3-T4 on the other) allows the midpoint A to be brought to 0 and therefore to have an amplitude of +Vdc.

[0019] The invention further relates to an electrical system, in particular for a motor vehicle, comprising a rotating electrical machine, for example an electric motor for the propulsion of the vehicle, and an inverter as described above.

[0020] According to one aspect of the invention, the inverter comprises 6 phase outputs for the three-phase type machine.

[0021] According to one aspect of the invention, the electrical system includes a control system comprising a voltage correction loop configured to attenuate or suppress harmonic currents in the machine.

[0022] According to one aspect of the invention, the voltage correction loop is configured to calculate and deliver at output a correction voltage (Vhk) which is to be added to setpoint voltages calculated in parallel.

[0023] According to one aspect of the invention, the voltage correction loop is configured to add the correction voltage (Vhk) to the setpoint voltages calculated in parallel, with phase alignment between these voltages.

[0024] The invention also relates to a method for controlling the system as previously mentioned, comprising the following steps: - during a positive half-period P+, alternate the state of transistors T1 and T2 in the arm (with midpoint A), between conduction (closed or ON) and non-conduction (open or OFF) to create a modulation of the voltage, while transistor T4 is held at zero to have the potential at point B equal to 0. - during a positive half-period P-, alternate the state of transistors T3 and T4 in the arm (with the midpoint B), between conduction (closed or ON) and non-conduction (open or OFF) to create a voltage modulation, while transistor T2 is held at zero to have the potential at point A equal to 0.

[0025] Other features, details and advantages of the invention will become clearer upon reading the following description on the one hand, and several illustrative and non-limiting examples of embodiments given with reference to the accompanying schematic drawings on the other hand, in which:

[0026] [Fig-1] Fig. 1 is a schematic representation of an electrical system according to the invention;

[0027] [Fig.2] Fig.2 represents curves C1 and C2 which are chronograms associated with one of the windings of the machine in [Fig.1];

[0028] [Fig. 3] Fig. 3 is an isolated view of an H-bridge of the system inverter electric of the [Fig.l];

[0029] [Fig.4] Fig.4 represents the principle of machine control and piloting of bridge H;

[0030] [Fig.5A] The [Fig.5A] represents the principle of adding the additional voltage Vhk, for the point Al;

[0031] [Fig.5B] The [Fig.5B] represents the principle of adding the additional voltage Vhk, for point B1;

[0032] [Fig. 6A] Fig. 6A represents the voltage and current waves in one phase of the machine, with standard H-bridge (without voltage correction loop);

[0033] [Fig. 6B] Fig. 6B represents the voltage and current waves in one phase of the machine, with harmonic current reduction according to the invention.

[0034] The features, variants, and different embodiments of the invention can be combined in various ways, provided they are not incompatible or mutually exclusive. In particular, variants of the invention may be conceived comprising only a selection of features, described hereafter in isolation from the other described features, if this selection of features is sufficient to confer a technical advantage and / or to differentiate the invention from the prior art.

[0035] Figures 1 show an electrical system 100 for a motor vehicle, comprising a rotating electrical machine 50, here an electric motor for the propulsion of the vehicle, and an inverter 1.

[0036] The rotating electrical machine 50 is of the three-phase type, with three phases, and comprises, for example, a number of turns between 32 and 64.

[0037] The electrical system 100 is connected to a power supply battery 80, for example with a supply voltage Vdc of 400 V (or alternatively 800 V).

[0038] Fig. 3 illustrates one of the three cells Cel, Ce2, Ce3 of the inverter 1, each associated with one of the three phases of the machine 50.

[0039] The cell Cel (the same applies to the other cells) includes an H-bridge (designated by reference 20) comprising two bridge arms with, on each bridge arm, two transistors T1 and T2, respectively T3 and T4, and a midpoint A between the two transistors T1 and T2 and a midpoint B between the two transistors T3 and T4.

[0040] Each H-bridge is configured to allow each phase of the rotating electrical machine to be connected to the midpoints A and B of the associated H-bridge.

[0041] The voltage between points A and B is denoted Vs, which is the voltage across one of the windings.

[0042] Respective currents ia, ib, ic circulate in these H-bridges.

[0043] For example, for a three-phase rotating electrical machine, we have 6 phase outputs for the complete machine.

[0044] Each H-bridge comprises four transistors, including two "high side" transistors and two "low side" transistors, of the IGBT type.

[0045] The electrical system 100 further includes a circuit for delivering PWM signals to the transistors.

[0046] The curves Cl and C2, on [Fig.2], are chronograms associated with one of the windings, here the winding AB (or phase AB) on [Fig.3].

[0047] Curve Cl represents the PWM signals of the voltage applied to a winding of the machine and curve C2 represents the variations of the current in winding AB.

[0048] During this positive half-period P+, the state of transistors T1 and T2 in this arm (with the midpoint A) is alternated between conduction (closed or ON) and non-conduction (open or OFF) to create a modulation of the voltage, while transistor T4 is held at zero to have the potential at point B equal to 0. Indeed, the midpoint B of the bridge arm of transistors T3 and T4 is connected to ground by means of this transistor T4.

[0049] Having an H-bridge with the two arms (arm T1-T2 on one side and arm T3-T4 on the other) allows the midpoint B to be brought to 0 and therefore to have an amplitude of +Vdc.

[0050] This operation (also called switching) is carried out using pulse width modulation (PWM) to control the power delivered to the winding AB of the electric machine. The voltage modulation then takes place between 0 V and the battery supply voltage +Vdc over this positive half-period P+, as can be seen on the curve Cl in [Fig.2].

[0051] During this positive half-period P-, the state of transistors T3 and T4 in this arm (with the midpoint B) is alternated between conduction (closed or ON) and non- conduction (open or OFF) to create voltage modulation, while transistor T2 is held at zero to have the potential at point A equal to 0. Indeed, the midpoint A of the bridge arm of transistors T1 and T2 is connected to ground by means of this transistor T2.

[0052] Having an H-bridge with the two arms (arm T1-T2 on one side and arm T3-T4 on the other) allows the midpoint A to be brought to 0 and therefore to have an amplitude of +Vdc.

[0053] This operation is carried out using pulse width modulation (PWM) to control the power delivered to the AB winding of the electric machine. The voltage modulation then takes place between 0 V and the battery supply voltage -Vdc over this positive half-period P-, as can be seen on the curve Cl in [Fig.2].

[0054] Thus over a complete period P (namely including the positive half-period P+ and the negative half-period P-), the voltage Vs across the terminals of the winding AB (see curve C2) theoretically varies from -Vdc to + Vdc.

[0055] The same applies to the other two windings of the machine, in the case of a three-phase machine.

[0056] Thus, the H-bridge theoretically allows the peak-to-peak amplitude of voltage for winding AB to be doubled.

[0057] Thanks to the invention, with the H-bridge, as the speed increases, the supply voltage experiences a peak-to-peak amplitude increase. Consequently, the supply voltage Vdc is no longer limited by the battery's supply voltage, but a higher voltage is available than the battery's supply voltage Vdc, for example, higher by a factor of 2 or, at the very least, by a factor of 1.5 to 1.7, for example.

[0058] It is noted that, in a known conventional inverter (without an H-bridge), point B is a point which is equal to half the supply voltage, and not equal to a voltage of 0. Thus in a known conventional inverter, the maximum available voltage is the supply voltage itself, and no more.

[0059] We will now describe in more detail, with reference to the block diagram of [Fig.4], the control principle of machine 50 and the piloting of bridge H.

[0060] On this block diagram, block 101 (on the left) represents the input of a control system 150 belonging to the electrical system 100, input which receives a torque command Tq delivered by a motor control unit, also called "ECU" in English, and a speed information Spd of the machine measured by a sensor, in particular a position sensor or a speed sensor.

[0061] Block 101 includes a control law that allows the motor / inverter system 100 to be controlled, in particular to obtain optimized efficiency or high output torque. This control law ensures, based on the input data the aforementioned and also a continuous bus voltage Udc (battery) and temperature information of the stator and rotor, to determine the set of parameters to achieve the target torque.

[0062] The parameter set here includes current signal setpoints Cons(Id*, Iq*) which are current setpoints representative of an optimum operating point calculated by the control laws of block 101.

[0063] The control system 150 aims to achieve the current signal setpoints Cons(Id*, Iq*), and a comparison with measured values ​​Meas(Id, Iq)(ia,ib,ic) of the currents Id and Iq is carried out (block 102).

[0064] By comparing the setpoint inputs with what is measured at the terminals of the electric machine, the system makes it possible to achieve the target torque.

[0065] After the comparison, a corrector (block 103) is provided followed by a calculation (block 104) of the output voltage setpoints Va, Vb, Vc representative of the input setpoint values ​​Cons(Id*, Iq*).

[0066] Blocks 101 to 104 here define a main harmonic control loop (hl) 200.

[0067] Block 120 (the one furthest to the right) represents the output of the control system 150 which delivers control signals SP1, SP2, SP3 to control the three H-bridges (20) from the output voltage setpoints.

[0068] Thus, for the control of an electric machine in torque, control laws are generally used with the sets of setpoints (Id*,Iq*) allowing to optimize an optimal operating criterion, in particular maximizing efficiency, maximizing torque, and this according to the parameters and constraints of the system, the operating range in speeds, supply voltage Udc, and the temperature of the rotor and stator, etc.

[0069] However, the standard control of the arms of the H bridge (arm 1, arm 2 and arm 3) introduces current harmonics into the windings of the machine 50, which degrade the performance of the machine and generate noise as well as vibration (see curves C6A1 and C6A2 of [Fig.6A], which shows significant distortions making the current curves different from sinusoidal shapes).

[0070] To overcome this problem, the control system 150 includes a voltage correction loop 140 configured to attenuate, or even eliminate, harmonic currents in the machine 50.

[0071] The voltage correction loop 140 is configured to work in parallel with the blocks 102, 103, 104 described above, and takes as input the input setpoint values ​​Cons(Id*, Iq*) described above, as well as the rotational speed of the motor Spd.

[0072] The voltage correction loop 140 is configured to act on the output commands of the H-bridge (namely the SP1, SP2, SP3 control signals) to attenuate / suppress harmonics in real time, in particular by allowing a selection of setpoints that attenuate / suppress harmonics.

[0073] The voltage correction loop 140 calculates and delivers at output a correction voltage Vhk which is to be added to the setpoint voltages calculated in block 104, to attenuate / suppress current harmonics.

[0074] The correction voltage Vhk (setpoint value) is given by the formula:

[0075] Vhk = hk.exp(j(k. ©k)

[0076] Here the voltage amplitude hk and the phase angle ©k are a function of (Id*, Iq*, Spd). k is the harmonic rank that we wish to suppress or reduce.

[0077] These parameters (hk, ©k) depend on the design of the machine 50, and can be identified by an experimental test or by a numerical simulation (for example by a finite element model).

[0078] The invention is based in particular on (hk, ©k) varying as a function of (Id*, Iq*, Spd) and thus being able to be implemented with the same principle and calculator as the main harmonic regulation loop.

[0079] The additional voltage setpoint Vhk is used to control the inverter by attenuating harmonic currents. The voltage setpoints Vhk are injected to act on the h3 harmonics, and higher-order harmonics h5, h7, in particular. These setpoints can be determined using the same principle as torque control under multi-criteria and with the parameters and constraints of the electrical system 100.

[0080] The additional voltage setpoint Vhk is somehow added to the voltage setpoint Va in the following manner.

[0081] In figures 5A and 5B (on which references 61 and 62 designate drivers), A1 and B1 designate signals for controlling the transistor pairs (T1, T2) and (T3, T4) of the H-bridge. The commands are noted Cmd T1, Cmd T2 Cmd T3, Cmd T4.

[0082] We have:

[0083] Us 1 (a,b) = IN 1 if IN 1 > 0 and Us 1 (a, b) = IN3 if IN 1 < 0

[0084] with IN1=Va and IN3=Vhk for Usla

[0085] with IN1=-Va and IN3= -Vhk For Uslb

[0086] Phase alignment is obtained, with the voltages Va and Vhk in phase.

[0087] Thus, the additional voltage setpoints Vhk are used to control the inverter by attenuating the harmonic vibration currents (see curves C6B1 and C6B2 in [Fig. 6B]). It should be noted that, for curves C6B1 (voltage waveform) and C6B2 (current waveform), the harmonics are much less prominent than for curves C6A1 (voltage waveform) and C6A2 (current waveform) in [Fig. 6A] with a standard H-bridge (without voltage correction loop 140), for one phase in one of the bridges. The currents exhibit a much closer sinusoidal shape for the case with voltage correction (C6B curves).

[0088] The invention allows, in summary, a reduction or elimination of harmonic currents.

Claims

Demands

1. Inverter (1) configured to operate in association with a rotating electrical machine (50), in particular of the three-phase type, the inverter (1) comprising H-bridges (20), for example 3 for a three-phase rotating electrical machine, each H-bridge comprising two bridge arms with, on each bridge arm, two transistors (T1, T2, T3, T4) and a midpoint between these two transistors, each H-bridge being configured to allow each phase (AB) of the rotating electrical machine to be connected to the midpoints of the associated H-bridge.

2. Inverter (1) according to the preceding claim, in which each H-bridge comprises four transistors (T1, T2, T3, T4), of which two are "high side" transistors and two are "low side" transistors.

3. Inverter (1) according to any one of the preceding claims, wherein the transistors (T1, T2, T3, T4) defining the H-bridge comprise IGBT transistors or MOSFET transistors.

4. Inverter (1) according to any one of the preceding claims, wherein the inverter (1) is configured to, during a positive half-period (P+), alternate the state of the transistors (T1, T2) in the arm, between conduction (closed or ON) and non-conduction (open or OFF) to create voltage modulation, while the transistor (T4) is held at zero to have the potential at point (B) equal to 0.

5. Inverter (1) according to any one of the preceding claims, wherein the inverter (1) is configured so that, during a positive half-period (P-), the state of the transistors (T3, T4) in the arm is alternated between conduction (closed or ON) and non-conduction (open or OFF) to create voltage modulation, while the transistor (T2) is held at zero to have the potential at point (A) equal to 0.

6. Electrical system, in particular for motor vehicle, comprising a rotating electrical machine (50), for example an electric motor for the propulsion of the vehicle, and an inverter (1) according to any one of the preceding claims.

7. Electrical system according to the preceding claim, wherein the inverter (1) comprises 6 phase outputs for the three-phase type machine.

8. Electrical system according to claim 6 or 7, comprising a control system (150) including a correction loop

9.

10.

11. voltage (140) configured to attenuate, or suppress, harmonic currents in the machine (50). Electrical system according to the preceding claim, wherein the voltage correction loop (140) is configured to calculate and deliver at output a correction voltage (Vhk) which is to be added to setpoint voltages calculated in parallel. Electrical system according to the preceding claim, wherein the voltage correction loop (140) is configured to add the correction voltage (Vhk) to the setpoint voltages calculated in parallel, with phase alignment between these voltages. A method for controlling the system according to any one of claims 6 to 10, comprising the following steps: - during a positive half-period (P+), alternate the state of the transistors (T1, T2) in the arm, between conduction (closed or ON) and non-conduction (open or OFF) to create a modulation of the voltage, while the transistor (T4) is held at zero to have the potential at point (B) equal to 0. - during a positive half-period (P-), alternate the state of the transistors (T3, T4) in the arm, between conduction (closed or ON) and non-conduction (open or OFF) to create a modulation of the voltage, while the transistor (T2) is held at zero to have the potential at point (A) equal to 0.

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