阅读说明：本技术 基于整流电压控制变速驱动器的功率单元 (Power unit for controlling variable speed drive based on rectified voltage ) 是由 T.德沃斯 F.马尔雷特 于 2019-12-13 设计创作，主要内容包括：本发明涉及一种用于控制变速驱动器的方法,该变速驱动器针对多相中的每一相包括串联连接的Ni个低电压功率单元,i是相索引。该方法包括重复P次迭代,包括：-激活(201)一个或多个相的至少一个单元,并且停用变速驱动器的其他功率单元,其中基于取决于迭代索引的预定义激活控制来选择至少一个激活的单元；-在电气设备的端子上针对至少一个相接收(205)在变速驱动器的至少一个输出电压；此外,该方法包括,在P次迭代结束时,根据所测量的变速驱动器的输出电压,确定(206)变速驱动器的功率单元的各个整流级的输出端的整流电压值,并且存储所获得的整流电压,这些整流电压分别与变速驱动器的功率单元相关联。(The present invention relates to a method for controlling a variable speed drive comprising Ni low voltage power cells connected in series for each of a plurality of phases, i being a phase index. The method includes repeating P iterations, including: -activating (201) at least one cell of one or more phases and deactivating other power cells of the variable speed drive, wherein the at least one activated cell is selected based on a predefined activation control depending on the iteration index; -receiving (205) at least one output voltage at the variable speed drive for at least one phase at a terminal of the electrical device; furthermore, the method comprises, at the end of the P iterations, determining (206) rectified voltage values at the output of the respective rectification stages of the power cell of the variable speed drive from the measured output voltage of the variable speed drive, and storing the obtained rectified voltages, which are respectively associated with the power cells of the variable speed drive.)

1. A method for determining a rectified voltage of a power unit of a variable speed drive (102) responsible for supplying power to an electrical apparatus (100), the variable speed drive comprising, for each of a plurality of phases, Ni low voltage power units (101) connected in series, N being greater than or equal to 2, i being a phase index, characterized in that the method comprises the following operations:

a) repeating the following P iterations, P being a predefined integer greater than or equal to 2:

-activating (201) at least one cell of one or more phases and deactivating other power cells of the variable speed drive, wherein at least one activated cell is selected based on a predefined activation control depending on an iteration index;

-receiving (205) at least one output voltage of the variable speed drive (102) for at least one phase on terminals of the electrical device (100);

wherein the method further comprises, at the end of the P iterations:

b) determining (206) a rectified voltage value at the output of each rectification stage of a power cell of the variable speed drive from the measured output voltage of the variable speed drive;

c) storing the determined rectified voltage values, each associated with a power cell of the variable speed drive.

2. The method of claim 1, wherein the integer P and the activation control are predefined in a matrix form, the matrix comprising P rows or P columns per phase, representing the activation control, and being equal to the number of power cells of the variable speed drive in rank.

3. The method of claim 2, wherein the variable speed drive includes N power cells for each of three phases, and for each iteration of index t, t is between 1 and P:

M_t＝KALL_t x VBALL；

where KA LL _ t denotes a matrix with 3 rows and 3N columns comprising [ K1-K2K 0; K0K 2-K3; K1K 0K 3], where K1, K2 and K3 are the respective activation controls of the three phases and are vectors of size N in binary values, the first value corresponding to activation and the second value corresponding to deactivation, where K0 is a zero vector of size N,

the VBA LL is a column vector with the length of 3N and composed of VB1, VB2 and VB3, wherein VB1, VB2 and VB3 are vectors with the magnitude of N of rectified voltages of the power units of the three corresponding phases;

where M _ t is a vector of three voltages measured on the terminals of the electrical device in a given iteration, the measured motor voltages corresponding to the three output voltages of the variable speed drive (the measured motor voltages being determinable from the three output voltages of the variable speed drive).

4. A method according to one of the preceding claims, wherein P is equal to the number of power cells of the variable speed drive, and wherein a single power cell is activated in each iteration, the activated power cells being separate for two different iterations.

5. The method of one of the preceding claims, further comprising, during a current phase of supplying power to the electrical device (100), for each power unit, adjusting a command for controlling the power unit based on the rectified voltage associated therewith.

6. The method of claim 5, wherein adjusting the command to control the power unit (101) comprises determining a duty cycle of the power unit (101) based on the rectified voltage associated with the power unit.

7. Method according to one of the preceding claims, further comprising analyzing (209) the obtained rectified voltage for the purpose of detecting deviations from nominal operation.

8. The method of any of claims 1-7, wherein the method is repeated at a plurality of separate time instants, and wherein analyzing (209) the rectified voltage comprises determining a trend of variation of the rectified voltage of the power cell, and comparing the trend with nominal operation.

9. Method according to one of the preceding claims, which is started after a stop of the electrical device (100).

10. The method according to claim 9, wherein the method is automatically started upon detection of a stop of the electrical device (100).

11. The method according to claim 9, wherein the method is started manually after a stop of the electrical device (100).

12. A computer program executable by a processor (300) comprising instructions to carry out the steps of the method according to one of claims 1 to 11 when the instructions are executed by the processor.

13. An apparatus for controlling a variable speed drive (102) responsible for supplying power to an electrical apparatus (100), the variable speed drive comprising, for each of a plurality of phases, Ni piezoelectric voltage power cells (101) connected in series, N being greater than or equal to 2, i being a phase index, characterized in that the control apparatus comprises:

a processor (300) capable of controlling, via an output interface, repetition of P iterations, P being a predefined integer greater than or equal to 2:

activating (201) at least one cell of one or more phases and deactivating other power cells of the variable speed drive, wherein at least one activated cell is selected based on a predefined activation control depending on an iteration index;

receiving at least two output voltages of the variable speed drive (102) for two phases on terminals of the electrical device (100) via an input interface (302);

the processor (300) is further capable of determining a rectified voltage value at the output of each rectification stage of the power cell of the variable speed drive at the end of P iterations from the measured output voltage of the variable speed drive,

a memory (301) storing the determined rectified voltage values, each associated with a power cell of the variable speed drive.

14. A variable speed drive responsible for providing three phase power to an electrical device, the variable speed drive comprising Ni low voltage power cells connected in series for each of a plurality of phases, wherein N is greater than or equal to 2, i is a phase index, and the variable speed drive comprising the control device of claim 13.

Technical Field

The present invention relates to the management of variable speed drives responsible for supplying power to electrical devices, such as electric motors.

Background

According to one power topology, a variable speed drive provides a high voltage by connecting in series a number of low voltage converters (these converters are referred to as power cells). The control of these power cells allows to provide a multi-level voltage or a multi-level voltage, one voltage per power cell increase, allowing to reach a continuous voltage level.

According to european standards, low voltage is understood to mean a voltage with AC between 0 and 1000 volts and DC between 0 and 1500 volts. High voltage is understood to mean a voltage with AC higher than 1000 volts and DC higher than 1500 volts.

For example, the variable speed drive may include N power cells, N being greater than or equal to 2. When the variable speed drive provides three phase power, it may include 3 x N power cells dedicated to each of the three phases.

In a multi-stage variable speed drive topology, only motor voltage measurements can be used to reduce product cost, rather than a single rectified voltage or DC bus voltage DC. These rectified voltages correspond to the voltage at the output of a rectifier bridge (mainly a diode bridge or a thyristor bridge) at the input of each power cell of the variable speed drive.

In the above-described multi-stage architecture, the output voltage of each power cell is generated by applying a duty cycle to the rectified voltage of the power cell. Therefore, a rectified voltage or DC bus voltage of each power cell is necessary in order to calculate the duty cycle to be applied in order to reach the target output voltage on the motor.

According to prior art solutions, a fixed rectified voltage common to all power units is considered, which is based on the theoretical value of the DC bus in an ideal case.

However, this solution causes errors in the output voltage applied to the motor, since in practice the rectified voltages of the power cells differ from each other. This is because there are various disturbances and affect the level of the rectified voltage of each power cell (the voltage at the input of the variable speed drive, transformer, etc.).

This error can be compensated by motor voltage measurement, but this requires an accurate motor voltage sensor so that the corrector can constrain the voltage generated at the output of the variable speed drive. Thus, the voltage reference may consist of two terms: direct terms and corrections derived from the corrector.

With knowledge of the rectified voltage, the larger the magnitude of the error in the direct term, the more measures the corrector needs to take to suppress the error. Therefore, the generation of the voltage will depend on the dynamics of the corrector and affect the overall control performance.

Furthermore, additional sensors may be provided to provide diagnostics for the power cell. For example, the temperature probe may be provided on a transformer upstream of the variable speed drive, for example. However, no diagnostics are provided for the input stage of the variable speed drive.

Therefore, it is necessary to improve control of the output voltage transmitted to the motor by the variable speed drive by suppressing various disturbances (variable gain of the transformer, and downtime of the switching operation of the switches of the power unit) of the power conversion system.

The present invention overcomes the above-mentioned disadvantages.

Disclosure of Invention

A first aspect of the invention relates to a method for determining a rectified voltage of a power cell (power cell) of a variable speed drive responsible for supplying power to an electrical device, the variable speed drive comprising, for each of a plurality of phases, Ni low voltage power cells connected in series, N being greater than or equal to 2, i being a phase index. The method comprises the following operations:

repeating the following P iterations, P being a predefined integer greater than or equal to 2:

-activating at least one cell of one or more phases and deactivating other power cells of the variable speed drive, wherein the at least one activated cell is selected based on a predefined activation control depending on the iteration index;

-receiving at least one output voltage of the variable speed drive for at least one phase at a terminal of the electrical device;

wherein the method further comprises, at the end of the P iterations:

determining a rectified voltage value at the output of each rectification stage of the power unit of the variable speed drive based on the measured output voltage of the variable speed drive;

the determined rectified voltage values are stored, each associated with a power cell of the variable speed drive.

The term "motor voltage" is used hereinafter to refer to the voltage at the terminals of the electrical device being powered by the variable speed drive.

According to one embodiment, the integer P and the activation control may be predefined in the form of a matrix comprising P rows or P columns per phase, representing the activation control, and equal to the number of power cells of the variable speed drive in rank.

Therefore, all the rectified voltage values can be obtained (access) by minimizing the number of measurements.

Further, the variable speed drive includes N power cells for each of the three phases, and for each iteration of the index t, t is between 1 and P:

m_t＝KALL_t×VBALL；

where KA LL _ t denotes an included matrix with 3 rows and 3 x N columns, comprising [ K1-K2K 0; K0K 2-K3; K1K 0K 3], where K1, K2 and K3 are the respective activation controls of the three phases and are vectors of size N in binary values, the first value corresponding to activation and the second value corresponding to deactivation, where K0 is a zero vector of size N,

the VBA LL is a column vector with the length of 3 × N, which is composed of VB1, VB2 and VB3, wherein VB1, VB2 and VB3 are vectors with the magnitude of the rectified voltage of the power units of three corresponding phases being N;

where M _ t is a vector of three voltages measured at the terminals of the electrical device in a given iteration, the three measured voltages corresponding to three output voltages of the variable speed drive (the three measured voltages may be determined from the three output voltages of the variable speed drive).

According to one embodiment, P is equal to the number of power cells of the variable speed drive, and a single power cell may be activated in each iteration, the activated power cells being separate for two different iterations.

Such an embodiment allows easy acquisition of each of the rectified voltages of the power cells.

The method according to the invention thus allows to obtain the rectified voltage of the power unit without the need to add additional sensors.

According to one embodiment, the method may further comprise adjusting, for each power cell, a command for controlling the power cell based on a rectified voltage associated with the power cell during a current phase of supplying power to the electrical device.

This embodiment thus allows to generate a target motor voltage that requires little or even no correction. Thus, better dynamics are allowed in the generation of the target motor voltage.

Further, adjusting the command to control the power unit includes determining a duty cycle of the power unit based on a rectified voltage associated with the power unit.

According to one embodiment, the method may further comprise analyzing the obtained rectified voltage for the purpose of detecting deviations from nominal operation.

Thus, failure of the power stage can be anticipated and preventative maintenance performed.

According to one embodiment, the method may be repeated at a plurality of separate times, and the analysis of the rectified voltage may include determining a trend of change of the rectified voltage of the power cell and comparing the trend to nominal operation.

Thus, failure of the power stage can be anticipated and preventative maintenance performed.

According to one embodiment, the method may be started after a stop (stop) of the electrical device.

In this way, the method does not interrupt the operation of the electrical apparatus.

Furthermore, the method may be automatically started when a stop of the electrical device is detected.

No operator intervention is required. Furthermore, the method can be started automatically at a given frequency when the electrical device is stopped.

Alternatively, the method may be manually initiated after the stopping of the electrical device.

Thus, the operator may conduct an inspection of the operation of the power cell.

A second aspect of the invention relates to a computer program executable by a processor, comprising instructions such that when the instructions are executed by the processor, the steps of the method according to the first aspect of the invention are carried out.

A third aspect of the invention relates to a device for controlling a variable speed drive responsible for providing three phase power to an electrical device, the variable speed drive comprising Ni low voltage power cells connected in series for each of a plurality of phases, N being greater than or equal to 2, i being a phase index. The control apparatus includes:

a processor capable of controlling, via the output interface, repetition of P iterations of P being a predefined integer greater than or equal to 2:

activating at least one cell of one or more phases and deactivating other power cells of the variable speed drive, wherein the at least one activated cell is selected based on a predefined activation control that depends on the iteration index;

receiving at least two output voltages of the variable speed drive for two phases at terminals of the electrical device via the input interface;

furthermore, the processor is capable of determining, at the end of the P iterations, a rectified voltage value at the output of each rectification stage of the power cell of the variable speed drive from the measured output voltage of the variable speed drive,

a memory storing the determined rectified voltage values, each associated with a power cell of the variable speed drive.

A fourth aspect of the invention relates to a variable speed drive responsible for providing three phase power to an electrical device, the variable speed drive comprising N low voltage power cells in series for each of the three phases, N being greater than or equal to 2, and the variable speed drive comprising a control device according to the third aspect of the invention.

Drawings

Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

FIG. 1 illustrates a system for controlling power to an electrical device according to one embodiment of the present invention;

FIG. 2 is a diagram illustrating method steps according to one embodiment of the invention;

fig. 3 shows a structure of a control apparatus according to an embodiment of the present invention.

Detailed Description

Fig. 1 illustrates a system for supplying power to an electrical device, such as a motor 100 (e.g., an induction motor), powered by a variable three-phase power source. Such a motor is given by way of illustration, but the invention should not be limited to this single example, and can be applied to any electrical apparatus powered by a variable speed drive comprising a plurality of power cells.

The variable speed drive includes a transformer 111 that receives variable three phase power from a power source (mains) 110. The transformer 111 may be a multi-winding transformer capable of delivering three-phase voltages to a plurality of power cells, as described below.

The variable speed drive 102 according to the present invention may include a power stage that includes one or more low voltage power cells 101. In the example shown in fig. 1, the motor receives three-phase power, and the variable speed drive 102 includes 3 x N power cells, where N power cells are dedicated to each phase, and N is greater than or equal to 2.

Referring to fig. 1, a system with 3 × N power cells is shown. However, the present invention is equally applicable to systems having 3 x (N +1) power cells, one power cell remaining per phase in case of failure of one of the active power cells. Such examples are given for illustrative purposes only. Consider the example of a three-phase power supply, but the invention is also applicable to systems having N or N +1 power cells. The invention is also applicable to systems with N +2 (or more than N +2) power cells (or 3 x (N +2) power cells for a three-phase power supply) with two replacement power cells per phase. Further, the present invention can be applied to a case where the number of phases is other than three. Further, the number of power cells may be different per phase, in which case each phase includes the number of power cells Ni, and i is a phase index. For illustration only, the following description considers the case of a three-phase power supply, where each phase has the same number of N power cells.

Each power unit 101 receives at its input the secondary three-phase power from the transformer 111 and may include at its input a rectifier (not shown in fig. 1) capable of rectifying the received three-phase power to provide a DC voltage. The DC rectified voltage obtained for each power cell 101 is also referred to as a DC bus voltage, DC or bus voltage. The rectifier may comprise a diode bridge, a thyristor bridge, or any other known system for rectifying a voltage.

At the output of the rectifier, each power unit 101 may comprise a capacitor capable of storing electrical energy and a module for generating a pulse width modulation (pwm) signal. Such a generating module may comprise an H-bridge comprising four switches controlled two by two. An electronic power system using this chopping voltage principle applies a voltage proportional to one or more rectified voltages to electric motor 100 per phase. On average, the applied ratio corresponds to the ratio between the target voltage at the output of the power cell and the rectified reference voltage (defined below). The operation of H-bridges is well known and will not be described further in this application.

The switches of the H-bridge may be IGBT (Insulated Gate Bipolar Transistor) type transistors, which have the advantage of being able to switch quickly.

The switching of the power unit 101 is controlled by the control unit 103 of the power unit 101.

The system further comprises a control device 120, which control device 120 is capable of controlling the operation of the power unit 101 of the variable speed drive 102 in order to control the supply of electric power to the electric motor 100. For this purpose, the control device 120 may control the control unit 103 of the power unit 101. Further, the control device 120 may control the switch 104, allowing a subset of the N power cells for each phase to be connected in series. As a variant, these switches are controlled by the control device 120 through the control unit 103.

Power unit 101 may receive a control signal from control device 120, based on which power unit 101 may control the switching action of the switches of the H-bridge.

Thus, the motor 100 is supplied with powerThe electrical three-phase voltage or the motor voltage is the PWM output voltage (denoted V in fig. 1) of the power unit 101 (referred to below as "active unit") by which the switch 104 is opened_cell) And summing the results. The switch 104 allows the power cell 101 to be "bypassed" without controlling the switches of the H-bridge of the power cell. However, such a switch 104 is optional, as the power unit 101 may be deactivated by controlling the H-bridge of the power unit 101 such that the power unit 101 has a zero duty cycle and thus a zero output voltage from the power unit.

The system according to the invention further comprises measuring means 130 for measuring the three-phase voltage for supplying the electric motor. The measuring means 130 are able to transmit the measured motor voltage(s) to the control device 120.

The control device 120 according to the invention is configured to control the various power units 101 and the bypass switches directly or indirectly (directly or via the control unit 103). In particular, according to the invention, the control device 120 is able to control the power cells 101 or the bypass switch 104 such that some cells do not provide a voltage, so that for example the motor voltage is provided by only one power cell. Thus, in embodiments where a single power cell is activated at a time, the measured motor voltage allows the output voltage of the selected power cell to be obtained, as explained in detail later, and thus allows the DC bus voltage to be obtained based on the duty cycle applied to the power cell.

FIG. 2 is a diagram illustrating method steps according to one embodiment of the invention.

In step 200, the method according to the invention is carried out. Such an implementation may be caused by a stoppage of the motor 100. For example, after the motor 100 has stopped, the method is triggered automatically or manually via the human-machine interface of the control device 120.

In step 201, the control device 120 controls the switches 104 or H-bridges of the various units in order to activate a subset of the power units of the variable speed drive 102, for example only the first unit 101 of the first phase_1,1. Operation of an embodiment for simultaneously activating multiple power cells will be described later, and FIG. 2 is a diagram of successive activation based on power cells (activating a single power cell at each iteration)Element) are described within the framework of embodiments of the invention.

Meanwhile, in step 202, the control device 120 determines the value of the voltage to be applied to the variable speed drive 102. The voltage to be applied may be direct or calculated by a current regulator, for example, allowing the output current of a variable speed drive through the motor 100 to be controlled.

In step 203, the control device 120 determines to be applied to the activated power cell 101_1,1So as to generate a target output voltage V to be applied to the motor 100₀. For other inactive cells, the bypass switch 104 is closed or the duty cycle is zero.

In step 204, the variable speed drive 102 is powered and the power unit 101 is controlled according to steps 202 and 203.

Then in step 205, the motor voltage is measured, for example by a sensor, and then received by the control device 120, the motor voltage being received by the first power unit 101_1,1Provided is a method.

In step 206, the control device 120 determines whether all the power cells 101 have been continuously activated. If this is the case, the method moves to step 207. More generally, the number of iterations P is predefined, P being greater than or equal to 2. Thus, in step 207, the iteration index may be compared to P. If the iteration index is equal to P, the method moves to step 207.

Otherwise, by activating the next power cell (e.g., power cell 101)_1,1The following power unit 101_1,2) Or in the general case that will be described later, a subsequent plurality of power units is activated and the method returns to step 201 by deactivating all other power units 101. In an alternative embodiment, the method returns to step 201, but also to step 202. In this alternative embodiment, steps 202 and 203 are implemented differently for each iteration of the method.

Based on the motor voltage measured in the successive step 205, the control device 120 according to the invention derives a rectified voltage of the power unit in step 206.

In order to determine the rectified voltage of the power unit, the control device 120 takes into account the measured motor voltage and the duty cycle that has been applied.

It is noted that in embodiments where the method is iterated 3 x N times by activating a single power cell at a time (when the variable speed drive includes N power cells for each of the three phases), the rectified voltage of the activated power cell during a given iteration may be determined at the end of the given iteration (rather than at the end of all iterations).

At the end of the determination of the rectified voltage of the power unit 101 of the variable speed drive 102, the method moves to step 208.

In step 208, the rectified voltage of the power unit of the variable speed drive is stored in the memory of the control device 120. The rectified voltage may be stored by replacing a previous value of the rectified voltage. As a variant, the rectified voltage is stored in association with the date of implementation of the iteration of the method according to the invention, allowing to implement a tracking of the variations of the rectified voltage of each power cell 101 of the variable speed drive 102.

In optional step 209, an analysis of the rectified voltage is performed. Such analysis may include a comparison with the nominal rectified voltages and triggering an alarm in case of a deviation from one of the nominal rectified voltages. If the rectified voltage is stored in association with a corresponding date, a trend of change of the rectified voltage may be determined for each power unit 101, and a warning may be generated based on the trend.

The generation of the warning allows to prevent the implementation of the maintenance.

Independently of steps 208 and 209, the variable speed drive changes to an "active" or "ready" mode in step 210, allowing the motor 100 to start in step 211.

After steps 209 and 210, the control apparatus 120, upon receiving the motor control, determines a target motor voltage and controls the variable speed drive 102 based on the target motor voltage and based on the previously determined rectified voltage in step 211. To this end, the control device 120 determines a respective duty cycle for the power unit 101. The generation of the target motor voltage is then more accurate because the rectified voltage of the power unit is known and can be updated periodically (e.g., each time the motor 100 stops).

According to some embodiments, such a variable speed drive further comprises a corrector that corrects the control of the input to the control device 120 based on the voltage measured on the electric motor 100. In this case, according to the present invention, the effect of such a corrector is reduced, allowing the dynamics of the generation of the output voltage applied to the motor 100 to be improved.

The method may then be repeated at a later time, for example after the motor 100 is stopped again in step 200.

Alternatively, the method may be repeated at a given frequency, for example weekly, after the motor has stopped. In this case, a minimum interval of one week separates the implementation of two iterations of the method.

With reference to fig. 2, a specific embodiment involving activating a single power cell in each iteration has been described. Such an embodiment is easy to implement and the rectified voltage of each power cell is easily obtained once the motor voltage is measured. More generally, the present invention may, in each iteration, activate a subset of at least one power cell at step 201, provide one or more output voltages produced by the subset at step 204, and measure one or both motor voltages at step 205. This is because there is no need to measure more than two motor voltages, since the third motor voltage can be derived from the first and second motor voltages (see voltages U12, U23 and U31 described below).

The power cells to be activated in each iteration and the motor voltage to be measured in each iteration may be determined from a predefined matrix. Such a matrix is predefined in order to ensure that at the end of all iterations a sufficient number of equations have been obtained to determine the value of each unknown of the system of equations (e.g., 3N rectified voltages of a power cell when the variable speed drive includes 3N power cells). For this purpose, the rank of the predefined matrix is equal to the number of unknowns (or 3 × N).

If i is the phase index (varying from 1 to 3) and k is the power cell index within the phase (varying from 1 to N in a power stage with 3 x N power cells), then the power cell with phase i and index k:

activation with a duty cycle r (between-1 and 1);

having a rectified voltage VB (i, k) which constitutes an unknown quantity of the system of equations;

providing a potential difference r x VB (i, k)

A column vector VBi may be defined having N components, each component having an index k in the value of the rectified voltage VB (i, k).

The combination of the control of the units for activating the branches of the power stage dedicated to phase i can be represented by a linear quantity Ki having N values (0: inactive power unit, 1: active power unit).

The potential difference Vi generated by a branch of index i is equal to the sum of the potential differences of all the cells of the branch, or: Vi-Kix VBi

The measuring device 130 can provide three-phase voltages between U12-V1-V2, U23-V2-V3, and U31-V3-V1. As a variant, the measuring device 130 is designed to measure the voltages V1, V2 and V3 directly.

Corresponding to an iteration of the method (t can be the date or iteration index of the method), in particular an iteration of step 205, the three measurements at time t may be associated in a column vector M _ t equal to [ U12; U23; U31], or: M _ t ═ KA LL _ t × VBA LL

Wherein K0 is a zero vector of the same dimension as K1, K2 or K3,

and KA LL _ t represents a matrix with 3 rows and 3N columns consisting of [ K1-K2K 0; K0K 2-K3; K1K 0K 3 ];

VBA LL represents a column vector of length 3N, consisting of [ VB 1; VB 2; VB3 ].

The combinations K1-K3 are selected according to the invention by "stacking" or aggregating matrices KA LL _ t for times (iterations) t1, t 2-tP_u(u varies between 1 and P) such that the matrix KA LL _ t_ALLConstructed as 3 rows and 3 columns, KA LL _ t_ALLIs a matrix with a rank of 3 x N, so that 3 x N unknowns (rectified voltage of the power cell) of the system of equations can be determined.

The embodiment described with reference to fig. 2 is a special case of such a general embodiment.

This particular embodiment provides for each time t_uA single cell is activated, u being an index between 1 and 3 × N.

When the cell is activated with the index "u-INT [ (u-1)/N ] × N" of the branch "1 + INT [ (u-1)/N ]", where INT denotes the function of the integer part, the following results are obtained in the case where N ═ 3 (given as an example, without limiting the scope of the invention):

at time t1, K1 ═ 100, [ K2 ═ 000, [ K3 ═ 000 ]. matrix KA LL _ t1 is [ 100000000; 000000000; -100000000 ];

at time t2, K1 ═ 010; K2 ═ 000; K3 ═ 000;. matrix KA LL _ t2 is [ 010000000; 000000000; 0-10000000 ].

By constructing each matrix KA LL _ tu, the first row consists of 0's except for the u (u is 1) — it should be understood that, according to the above rule, after 3 × 3 times, the first 9 rows together form an identity matrix, which guarantees a rank of 9 (or the number of unknowns of the system).

Fig. 3 shows the structure of the control device 120 according to one embodiment of the present invention.

The control device 120 comprises a processor 300, the processor 300 being configured to communicate unidirectionally or bidirectionally with a memory 301 via one or more buses, the memory 301 being for example a memory of the "random access memory" RAM type, or of the "read only memory" ROM type, or of any other type (flash memory, EEPROM (erasable programmable read only memory), etc.).

The memory 301 is capable of permanently or temporarily storing at least some of the data using and/or derived from embodiments of the method according to the present invention. In particular, the memory 301 is able to store the rectified voltage values of the power units, optionally associated with respective dates.

The processor 300 is capable of executing instructions for carrying out the steps of the method according to the invention, as shown in fig. 2.

The control device 120 may also comprise an input interface 302 and an output interface 303 for communicating with other entities of the system according to the invention.

In particular, the input interface 302 can receive a speed command, and the processor 300 can determine a target motor voltage (one target motor voltage per phase) from the speed command.

The output interface 303 is able to provide control commands to the power units 101 such that they generate duty cycles, in particular via their H-bridges. To this end, the control commands may comprise commands for switching IGBT-type switches, for example partially (commands for switching only two IGBT switches from the top for each power cell) or fully (four IGBT switches) switching the H-bridge. These switching commands may be calculated by the control device 120 by comparing the reference voltage with the triangular wave signal corresponding to each power cell. Such techniques are well known and will not be described in detail.

Although the present invention has been described above with reference to specific embodiments, it is in no way limited to the forms described. The present invention is limited only by the contents defined in the claims, and embodiments other than the above-described embodiments may be included within the scope of the claims.

Moreover, although embodiments have been described above as a combination of components and/or functions, it should be appreciated that alternative embodiments may be obtained by other combinations of components and/or functions without departing from the scope of the present invention.