WO2013093235A2

WO2013093235A2 - Dc power electrical system stabilized by active filtering

Info

Publication number: WO2013093235A2
Application number: PCT/FR2012/000527
Authority: WO
Inventors: El Hadj MILIANI; Alexandre BATTISTON; Serge PIERFEDERICI
Original assignee: IFP Energies Nouvelles; Universite De Lorraine
Priority date: 2011-12-20
Filing date: 2012-12-18
Publication date: 2013-06-27
Also published as: FR2984619A1; FR2984619B1; WO2013093235A3

Abstract

The invention relates to an electrical system including: at least one DC power source (S); at least one electrical device (DE) connected to said source (S) and supplied with a current i_e provided by said source (S) and a voltage v_DC at the terminals of said source (S); and a capacitor (C) connected to said electrical device (DE) in parallel, characterized in that the electric system further comprises a controlled active filtering means (7, 7') between said source (S) and said electrical device (DE), for feeding or absorbing waves of the current i_e provided by said source, and for reducing fluctuations in the voltage v_DC at the terminals of said source.

Description

ELECTRICAL SYSTEM WITH CONTINUOUS POWER STABILIZED BY FILTERING

ACTIVE

The present invention relates to the optimization of electrical networks with continuous power, in particular on board vehicles.

Nowadays, the development of distributed continuous power electrical network architectures concerns many fields of activity such as automobile, railway construction, shipbuilding or aeronautics. This is why the search for reliable, compact and low-cost solutions for the optimization of these systems is necessary. Although these systems offer the possibility of connecting several electrical devices (DE), also called charges, of different natures to a common DC bus (1) (FIG. 1), the interactions between these electrical devices (DE) can lead to behavior. unstable system.

Indeed, certain electrical devices (DE) such as those consisting of an inverter assembly (3) and electrical machines (4) modify the harmonic content of the continuous quantities, that is to say the current and voltage. It may thus be necessary to reduce or even eliminate this harmonic pollution caused by the cutting of the inverter according to PWM (Pulse Width Modulation) techniques commonly used to synthesize alternative signals using all-or-nothing operation). Two fundamental constraints weigh on this type of system; the stability and quality of embedded energy. The mastering of these two constraints thus makes it possible to reduce the size (volume and weight) of these systems and to better control the quantities guaranteeing an increased service life of the power source elements such as, for example, the battery in the automotive case.

In response to the problem raised, a widely used solution is the use of "capacitor assemblies" (2) of high capacity (combination of capacitors in series and in parallel) whose role is to provide a passive filtering allowing the absorption of polluting harmonics. These capacitors are generally placed directly upstream of the inverters (3) and dimensioned to obtain a very good quality of the energy and in particular of the DC bus voltage (FIG. 2). The following documents describe such solutions:

Nicolas PATIN, The Dung NGUYEN, and Guy FRIEDRICH. Impact of control strategies and inverter topologies on DC bus stabilization in embedded systems. EF Conference, September 2009. The Dung NGUYEN, Nicolas PATIN, and Guy FRIEDRICH. Analysis of the stresses on the inverter DC bus filter capacitors for embedded applications. Workshop, 2010.

However, to guarantee these performances, these capacitor sets (2) with high capacities are bulky and represent about a third of the volume and the cost of the power inverters. This is why it is necessary to seek to reduce these passive elements while controlling the two main constraints of stability and quality of the continuous network.

In a simple way, the stability can be defined as the fact that the state quantities of a system remain "close" to an operating point defined for example by their equilibrium state even though the system is subject to to external disturbances. The influence of the capacitance value for a system consisting of a battery (5) (input voltage source), a filter capacitor C _dc (2) and an inverter assembly (3) and Electrical machine (4) is studied to illustrate the connection between the capacitor value and the stability problem. The leakage inductance L _f due to the wiring is modeled by an inductance (6) between the source and the capacitor of the equivalent bus (FIG. 3).

The simulation results are shown in FIG. 4. When the capacitance is low (100 F) and the large leakage inductance, the interaction between the filter L _r C _dc and the inverter-machine assembly causes a loss of stability that the divergence of observed magnitudes illustrates (Figure 4a). On the other hand, a capacity ten times higher makes it possible to ensure the stability of the system (FIG. 4b). It is recalled that the capacity of the capacitor depends on the size of the latter, so a high capacity requires a large volume.

If on the other hand the leakage inductance due to wiring (uncontrollable) is relatively low, stability is ensured but the amplitude of the ripples related to the modulation caused by the cutting of the inverter is increased.

These few results show that the capacitor of the continuous bus has a dual utility. It firstly makes it possible to eliminate the risks of loss of stability by reducing the range of interaction between the filter (L _r C _dc ) and the load. It also makes it possible to strongly attenuate the variations of amplitude of undulations guaranteeing practically smooth continuous quantities. Therefore, any reduction in the size of these passive elements must be accompanied by a corrective action aimed at stabilizing and reducing the ripple of the electrical quantities of the DC bus.

The electrical system according to the invention is based on the use of an active filter, ensuring a stabilization of electrical quantities, this active filter being connected in parallel with a capacitor of reduced capacity compared to conventional solutions. This reduces the volume and weight of the system, while maintaining quality and stability onboard electrical energy. The invention also makes it possible to reduce the cost of such a system.

The electrical system according to the invention

The invention relates to an electrical system comprising at least one DC power source, at least one electrical device connected to said source and powered by a current i _e supplied by said source and a voltage _DC across said source. , and a capacitor connected in parallel with said electrical device. The electrical system further comprises active filtering means controlled between said source and said electrical device to inject or absorb the undulations of the current supplied by said _ith source and to reduce fluctuations in the voltage at the terminals of said source.

According to the invention, the system further comprises means for dynamically stabilizing the current supplied by said source and the voltage at the terminals of said source.

According to the invention, said active filtering means are connected directly in parallel with said capacitor.

According to the invention, the active control of said filter means is dependent on two variables which are the sign of the ripple of the input current of the inverter ¾ _c and the corrugations of the bus voltage V _DC.

According to one embodiment of the invention, said active filtering means consist of four controlled switches forming an H-bridge and an inductor.

In a variant, said active filtering means consist of eight controlled switches forming two H-bridges and two inductors.

Preferably, the switches are controlled by two control loops, respectively comprising a high-pass filter and a regulator, each control loop controlling two switches.

Advantageously, said regulator is a hysteresis comparator.

The control of the switches can be performed analogically.

Advantageously, said dynamic stabilization means correspond to a control loop in the control of the electrical device which has the same effect as a resistor R which would be directly placed in parallel with the capacitor and the active filtering system.

Preferably, the regulation loop of said dynamic stabilization means consists of a gain- and a low-pass filter. The invention also relates to a vehicle, in particular hybrid or electric, which comprises an electrical system according to the invention, at least one of said electrical device of said system being an electric machine. Brief presentation of the figures

Other features and advantages of the method according to the invention will appear on reading the following description of nonlimiting examples of embodiments, with reference to the appended figures and described below.

Figure 1, already described, illustrates a distributed electric power system.

Figures 2 and 3, already described, show an electrical system according to the prior art.

Figures 4a) and 4b), already described, are curves representing simulation results for the solution of the prior art.

Figure 5 illustrates the invention.

Figure 6 shows a first variant of the invention.

Figures 7 and 8 show an embodiment of the control of the first variant of the invention.

Figure 9 shows another embodiment of the control of the first variant of the invention.

Figure 10 illustrates a time response of the system according to the invention.

FIG. 11 illustrates a frequency response of the system according to the invention.

Figures 12a) and 12b) illustrate another time response of the system according to the invention, for which the wiring inductance is no longer negligible.

Figure 13 shows a second embodiment of the invention.

Figure 14 shows a third embodiment of the invention.

FIG. 15 represents a control of the third variant embodiment.

Figures 16a), 16b) illustrate temporal responses for the first embodiment of the invention.

Figure 17 illustrates temporal responses for the third embodiment of the invention.

Detailed description of the invention

The electrical system according to the invention comprises at least one DC power source (S), at least one electrical device (DE) connected to said source and consuming a current i _e supplied by said source (S) and a voltage v _oc across said source (S), and a capacitor (2) connected in parallel with said device power (DE) and the active filter means controlled (7, 7 ') between said source (S) and said electrical device (DE), to inject or absorb the undulations of the current supplied i _e by said source and to reduce fluctuations in the voltage v _DC at the terminals of said source (FIG. 5).

The invention is suitable for being embedded in a vehicle, including automobile, rail or naval, hybrid or electric, however it may also be suitable for any system operating batteries.

Active filtering means (7, 7 ') are means that perform current filtering, for injecting or absorbing current ripples and fluctuations in the bus voltage. These means can be controlled, unlike the passive filtering means. The passive filtering means consist solely of capacitors, resistors and inductors, which can not be controlled. These active filtering means (7, 7 ') associated with a capacitor (2') of reduced capacitance with respect to the conventional solution play the role of the capacitor set (2) used in the prior art; that is, to stabilize the bus current and voltage, while allowing a decrease in the size of the capacitor bank. The capacitor (2 ') makes it possible to reduce the fluctuations of the bus voltage v _DC .

An electrical device (DE), a device requiring a current and a voltage to function, can be an electrical machine (4) for pulling the vehicle, or any type of electrical device that can be installed on board. vehicles or powered by an electric battery, such as steering members, tools, compressors ... However, in the following description and in Figures 2 to 17, we will focus primarily on electrical devices consisting of an electric machine (4) and an inverter (3). Indeed, this type of electrical device (DE) is the one that most modifies the harmonic content of the continuous quantities provided by the source. Such an electric machine (4) can be a three-phase synchronous electric machine. The inverter (3) makes it possible to convert a continuous electrical signal into an alternating electrical signal adapted in particular for powering an electric machine.

A source of electrical energy (S) is any means for supplying a current and an electrical voltage, it is essentially in our case electric batteries (5) capable of supplying continuous current and voltage to at least one electrical device ( OF).

In a preferred embodiment, said electrical device (DE) is connected to said source by a common DC bus (1), on which are also connected said active filtering means (7, 7 ').

The objective of the active filtering (7, 7 ') proposed is to allow the injection and the absorption of the undulations and therefore the harmonics of the input current i _DC of the electric device (DE), especially in the case where it comprises an inverter (3) and reduce the fluctuations of the DC bus voltage v _ÛC (equal to the voltage across the source (S)). The inverter input current i _DC is that flowing in the electrical device (DE). By applying the mesh law to the electrical diagram of FIG. 8, the input current of the inverter / ^' _oc can be calculated as a function of the current supplied by the source i _e , of the current flowing in the capacitor i _c and of the current flowing in the active filter means (7) i _fill :

In one embodiment, this filter may consist of four switches (T1 to T4) controlled forming an H-bridge and an inductor (L), placed in parallel with said bridge (FIG. 6), it then has a topology of single phase inverter. It is bidirectional in voltage and current and is connected directly in parallel with the reduced capacitor (2 '). It allows the injection of a current i _ind via a current source composed of an inductance inductor L. Advantageously, the control of the switches T1 to T4 is performed by two control loops respectively comprising a high-pass filter (8). ) and a regulator (9) (Figures 7a, 7b, 8), each control loop controlling two switches. The regulators (9) used in these switch control loops may be hysteresis comparators. The high-pass filters (8) used are characterized by their cutoff frequency w ,. and w _c which are determined to retain only the high frequency ripples of the voltage v _DC and the current i _DC , i.e. only the ripple of the current Ï ^' _dc and the voltage v _DC . Note that the variable of the Laplace transform is denoted s. In addition, C 1 and C ₂ denote the control signals (all or nothing) originating from the control loops of the control of the active filtering means (7), these signals are applied directly, or after inversion to the switches T1 to T4. The switches T2 and T4 depend only on the state of the control C, and therefore on the hysteresis terminals reached by the bus voltage v _ÛC . The frequency of change of the state of the control C, thus depends on the speed of growth or decrease of the voltage v _ÛC and the width of the hysteresis band, and is thus influenced by the value of the capacitance of the capacitor. capacitor (2 '). In fact, the larger the capacitance, the lower the slope of the voltage, which induces a lower frequency of reaching the hysteresis terminals (9). But if the capacity is low (for example less than 100μΡ), the switching frequency of the switches T2 and T4 is increased and may become impossible to achieve and the frequency also increases the switching losses. The value of the capacity of the capacitor (2 ') therefore has a direct influence on the control topology of the active filter, which limits the value of the capacitor (2'). For example, a capacitor (2 ') with a capacitance greater than 100 iF seems acceptable, indeed from this capacitance value, the necessary switching frequency is of the order of 100 kHz. We recall that we saw in Figure 4a) that a capacity of 100 F caused instability of the electrical system of the prior art.

In the embodiment shown in FIGS. 6 to 8, the generation of the current at the filter output is controlled by the two variables, which are the undulations of the voltage of the DC bus V _DC and those of the input current of the inverter. _c . The variations of these quantities around their continuous components are called voltages of the voltage and the current, we note the undulations 7 and v.

The regulation of the inductor current to be injected i _{jnd is} effected via the regulation of the DC bus voltage. The DC bus voltage across the reduced capacitor (2 ') can serve as a voltage source which allows the regulation of the current i _ind . Thus, in order to regulate the current to its constant value determined theoretically, we add to the undulations of voltage v _oc the error obtained by: i * _d ^f - i _ind . By this approach, the hysteresis regulator makes it possible to correct the error of the inductor current at the same time as the confinement of the voltage v _DC in the hysteresis band. The control scheme is given in FIG. 8. In this figure, the reference sign 10 designates an inverted door, allowing the implementation of an embodiment of the control of the system according to the invention:

• When the current ripple ï _DC is positive, that is to say, flowing through the electric device (DE), the active filter (7) injects the inductive current i _ind on the DC bus (1). For this purpose, the switches controlled by the control signals T1 and T4 are closed (T2 and T3 being open).

• When the ripple of i _DC is negative, thus injected on the bus (1), the active filter absorbs the current and consequently the switches controlled by T2 and T3 are closed (T1 and T4 being open).

• Two freewheeling states are allowed (T1 and T2 closed or T3 and T4 closed) and allow to increase or decrease the bus voltage v _DC across the capacitor (2 ') depending on whether it exceeds the limits of amplitude of specified corrugations, for example of the hysteresis comparator. Although the filter also acts on the stabilization of the system, it may be necessary to correct the low damping to improve the speed of convergence of the quantities. Indeed, although they are confined as shown in Figure 12b, the magnitudes converge by oscillations very little damped. In a preferred embodiment of the invention, illustrated in FIG. 14, the improvement of the speed of convergence of the quantities is achieved by dynamic stabilization means (11), which can correspond to a regulation loop (11 '). in the control of the active filtering means, which can be achieved by adding a "virtual" damping. The goal is to introduce virtually the behavior of a resistor R (11) which would be directly placed in parallel with the DC bus capacitor and the active filter as shown in the diagram of FIG. 13. The use of a resistor virtual is described in particular in the document:

- Ahmed-Bilal AWAN and Babak NAHID-MOBARAKEH. "Nonlinear stabilization of a dcbus- supplying a constant power load". IEEE, 2009

The idea is to generate a power proportional to the square of the undulations of the

2

DC bus voltage P ⁼ ~ ^ ~ · This power p is then added to the nominal power P ₀ of the electrical device that adapts its power demand according to the more or less strong fluctuations in voltage. The power thus determined p is used in the control (12) of the electrical device (DE), for example of the electric machine

(4), to adapt the behavior of the electrical device (DE) to avoid the occurrence of oscillations in the DC bus. Thus, the fluctuations of the current and the voltage of the DC bus are avoided thanks to the control of the electric device (DE). The combination of the virtual resistor (11) with the active filter (7) provides an effective means to provide stability and improve the quality of electrical energy. In one embodiment, illustrated in FIG. 15, the dynamic stabilization means consist of a gain-, R

R

being the value of the virtual resistor (11), and a low-pass filter. In this diagram, the common bus has a resistor r and an inductor L for modeling the internal resistance and inductance (wiring inductance) of the connections and the battery.

(5).

This embodiment of the invention is an interesting embodiment with a view to reducing the passive elements, improving the quality of the energy of the continuous bus as well as reducing the stresses on the source of power. embedded energy (battery). The reduction of the stresses on the on-board energy source (S) makes it possible to increase the service life of the latter. This variant ensures a good quality of electrical energy and prevents the system from entering an unstable state by control and containment electrical quantities of the continuous bus. The combination of the active filtering means and the dynamic stabilization is effective for reducing the constraints related to the weight and volume (bulk) of the capacitors. For example, in the automotive field, the capacities currently used are of the order of 3000 pF. The invention allows a reduction of this value six times; with the invention, a capacitor of 500 pF can be sufficient. The detailed roles of the active filter and the dummy resistor are shown in Figure 17. Without a stabilizing system, the excessive reduction of the capacitors causes unstable system behavior. At t = 0.02s, the activation of the fictitious resistor alone implies a convergence of the bus voltage but the fluctuations caused by the modulation of the inverter remain unchanged. These are suppressed when activating the active filter at t = 0.04s. The bus voltage is then controlled even if the capacitor of the bus is reduced.

The proposed solution is thus perfectly adaptable to any type of embedded systems and therefore to the fields of activity mentioned above (automobile, rail, aeronautical and naval).

Example of realization

Simulations of the electrical system comprising the active filtering means (7) illustrated in FIG. 7, that is to say a system composed of a battery (5), an active filter (7) and an inverter assembly (3) and an electric machine (4). A capacitor of low capacitance (100 pF) is used. It is recalled that with such capacity, the solution of the prior art causes instability. In addition, it is assumed that the leakage inductance due to the wiring is low (a few μΗ) which ensures the stability of the system. The results are given in Figure 10.

Starting from t = 0.035 s, the active filtering means is activated, the activation of the active filter enables the confinement of the DC bus voltage and the source current inside a hysteretic band whose width has been specified. The filter makes it possible to eliminate the variations of ripples due to the modulation of the inverter.

The results of FIGS. 11a and 11b show how the filter acts on the frequency spectra of the quantities of FIG. 10 (source current i _e and DC bus voltage v _DC ). The switching frequency of the inverter {f _d ) is 10 kHz to obtain signals on the alternating side (f) of 50 Hz. The modulation caused by MLI provides spectral lines at frequencies: 9.85 kHz; 10.15 kHz; 20 kHz; 29.85 kHz; 30.15 kHz; 40kHz ... which correspond to (2M + 1) f _d ± 3 / and (2n) f _d ± 6 /, n being the rank of harmonic.

Activation of the active filter causes spread spectrum and very conservatively retains the DC component. The maximum amplitudes of the harmonics for the source current i _e and the bus voltage v _DC remain lower respectively at

0.5% and 0.05% of the "fundamental" whereas they represented 17% and 1, 25% before activation of the active filter. These results are comparable in their objectives to those obtained on the alternative side when using the particular PWM techniques (SVM: "Random Space Vector Modulation" or hysteresis).

A second simulation is undertaken where the wiring inductance is no longer negligible (installation of aircraft or rail edge for example), and which causes unstable behavior of the system. The effect of the active filter (7) on the stability of the system is illustrated in Figures 12a and 12b. At t = 0.05s, the active filtering means are activated, and they are deactivated at t = 0.1s. Without an active filter, the system evolves into an unstable state that results in the divergence of the DC bus voltage v _oc and the source current i _e from their operating point. The activation of the active filter (7) causes a stabilization of the system whose convergence of the quantities testifies to the efficiency. As soon as the active filter is deactivated, the unstable state reappears.

The active filter stabilization (7) with and without virtual resistor (11) is illustrated in Figures 16a and 16b. FIG. 16a represents the behavior of an electrical system according to the first embodiment with active filtering means (7) alone, FIG. 16b represents the behavior of an electrical system according to the third variant with filtering means active element (7) associated with dynamic stabilization means (11). The addition of additional damping via the virtual resistor makes it possible to converge the quantities without oscillations. It is therefore interesting to associate the active filtering with a dynamic stabilization method when it is applied to an unstable system, that is to say following a strong reduction of the continuous bus capacitors compared to the solutions of the prior art.

Variations of realization

The embodiments described below can be carried out alone, in combination with the first embodiment or in combination with the other embodiments.

In the embodiment illustrated in FIG. 8, another type of switch is used in the inverter (3) and in the active filter (7), they are composed of a diode and a transistor. For example, it may be a combination of an IGBT transistor (Insulated Gate Bipolar Transistor) associated in series with a diode. This type of switch can be controlled and has the advantage of being fast and is therefore suitable for use in a method of converting a continuous electrical energy into an alternative electrical energy. As a variant, the control of the active filter is carried out analogically in order to simplify the implementation of the command, an embodiment of this command is shown in FIG. 9. In this embodiment, operational amplifiers are used ( TLxxx), resistors (R1 to R11), capacitors (C) and potentiometers (P).

To reduce the size of the active filtering means, it may be envisaged to reduce the size of the inductor (L) in the first embodiment. However, the reduction in the size of the inductor (L) is limited by the value of the current flowing through it. This is why it has been proposed in Figure 13 a second embodiment of the active filter means (7 ') for reducing the inductor current. The reduction of the inductive current is possible by a modification of the initially proposed topology, this modification corresponds to an input segmentation of the active filtering means (7 '): the active filtering means (7') consist of eight switches (T1 to T4 and ΤΓ to T4 ') forming two H-bridges and two inductors (L), respectively placed in parallel with one of said bridges. The control of the switches is identical to that of the first embodiment described above. The current flowing through each inductor is thus equal to half of the value that must theoretically be injected (or absorbed) on the DC bus. The control of the switches is thus duplicated.

Claims

claims

1) Electrical system comprising at least one DC power source (S), at least one electrical device (DE) connected to said source (S) and powered by a current i _e provided by said source (S) and a voltage _DC at the terminals of said source (S), and a capacitor (C) connected in parallel with said electrical device (DE), characterized in that the electrical system further comprises active filtering means (7, 7 ' ) between said source (S) and said electrical device (dE), to inject or absorb the undulations of the current supplied i _e by said source and to reduce fluctuations in the voltage v _oc across said source, and in that the system comprises dynamic stabilization means (11) of the current supplied by said source and of the voltage at the terminals of said source.

2) Electrical system according to claim 1, wherein said active filtering means (7, 7 ') are connected directly in parallel with said capacitor.

3) electrical system according to one of claims 1 to 2, wherein the control of said active filter means (7, 7 ') is dependent on two variables which are the sign of the ripple of the input current of the inverter T _DC and undulations of the bus voltage v _DC

4) Electrical system according to any one of the preceding claims, wherein said active filter means (7) consist of four switches (T1 to T4) controlled forming an H bridge and an inductor (L). 5) electrical system according to one of claims 1 to 3, wherein said active filtering means (7 ') consist of eight switches (T1 to T4 and T1' to T4 ') controlled forming two bridges in H and two inductors (L).

6) Electrical system according to claim 4, wherein the switches (T1 to T4) are controlled by two control loops, respectively comprising a high pass filter (8) and a controller (9), each control loop controlling two switches.

The electrical system of claim 6, wherein said regulator (9) is a hysteresis comparator. 8) Electrical system according to one of claims 4 to 7, wherein the control of the switches is performed analogically.

9) Electrical system according to one of the preceding claims, wherein said dynamic stabilization means correspond to a control loop (11 ') in the control of the electric device (DE) which has the same effect as a resistor R which _r would be placed directly in parallel with the capacitor and the active filtering system.

The electrical system according to claim 9, wherein the control loop of said dynamic stabilization means (1 V) consists of a gain and a pass filter.

R

low. 11) Vehicle, in particular hybrid or electric, characterized in that it comprises an electrical system according to one of the preceding claims, at least one of said electrical device (DE) of said system being an electric machine (4).