Control, by an electric motor, of a mechanical machine with a high variation in torque over a revolution.

Abstract

Power supply system for an electric motor driving a rotating mechanical machine with a large torque variation over one revolution. The system includes a power supply device providing an alternating current whose intensity (Iv) varies proportionally to the torque exerted by the motor. The system includes a power regulation device supplying an alternating voltage (Uv) controlled by the current (Iv) and in opposite phase to the current (Iv). Figure for the abbreviation: Fig. 3

Description

Title of the invention: Control, by an electric motor, of a mechanical machine with high torque variation over one revolution. Technical field

[0001] The present invention relates to the control, by an electric motor, of a rotating mechanical machine with a large torque variation over one revolution. The invention relates more particularly to the field of refrigeration machines, especially those for infrared detectors. State of the prior art

[0002] Rotating mechanical machines with high torque variation on a revolution are used in various fields, for functions requiring intermittent forces.

[0003] In the field of refrigeration, rotary machines are sometimes used to alternately compress a gaseous fluid and allow its expansion. This is notably the case for the implementation of the Stirling thermodynamic cycle, a cycle which results in an alternation of compressions and expansions of a gas in a closed circuit.

[0004] A machine that applies the Stirling cycle includes, in particular, a piston for compressing gas in a compression chamber. Together with a connecting rod, the piston forms an assembly driven by a crankshaft. The crankshaft is driven in a circular motion by an electric motor and imparts a rectilinear reciprocating motion to the piston via the connecting rod.

[0005] Since the Stirling cycle comprises four stages, the piston is driven by the engine so that the machine successively performs the four stages. Thus, the machine causes a compression of the gas in the compression chamber, a transfer of the compressed gas to an expansion chamber, an expansion of the gas in said chamber, and then a transfer of the expanded gas back to the compression chamber. The gas heats up during compression and cools down during expansion.

[0006] Machines using the Stirling cycle make it possible to achieve very low cooling levels and to vary the cooling rate very rapidly. This is achieved simply by adjusting the cycle frequency by adjusting the rotational speed of the electric motor. In fact, these machines are often used for applications requiring very intense cooling levels, or precision and responsiveness in cooling control. One application is the temperature regulation of certain infrared detectors.

[0007] According to the Stirling cycle, the gas is highly compressed in the compression chamber. As a result, the connecting rod experiences alternating stresses with extreme values. These factors are very important, and the variations in thermodynamic torque on the crankshaft are correspondingly very significant. These variations are transmitted to the engine, which must therefore provide a drive torque whose variations are also very significant. In cases where the engine is powered at a constant voltage, for example by a battery, the electrical power supplied varies considerably because the current intensity varies considerably. The network supplying the machine when it is cold must cope with these variations in electrical power consumption. Sometimes this can cause problems.

[0008] This is the case, for example, of a Stirling cycle cooling machine used for an infrared detector on board an aircraft. The electrical network supplies various components that contribute to the proper functioning of the aircraft. In this case, it is desirable to stabilize the electrical power consumption, that is to say, to make it regular, with small or very small variations, for several reasons.

[0009] For example, regular electricity consumption reduces, or even completely avoids, electrical disturbances on the grid. As a result, grid components, including a motor power supply device, are preserved. Their lifespan and reliability are improved.

[0010] Regular electricity consumption also limits the maximum power values ​​that need to be supplied. This allows the use of smaller, lighter components. This is the case, for example, for the motor.

[0011] In practice, to limit the maximum intensity of the electrical torque to be supplied, and therefore to limit the variations in power consumed over a revolution, solutions have been proposed.

[0012] One of these methods involves attaching a flywheel to the crankshaft. The flywheel accumulates energy before the gas is compressed, and releases it by inertia during compression. The mechanical energy supplied by the flywheel is added to the instantaneous electrical energy supplied by the grid to the engine, until the gas reaches its maximum pressure. As a result, the maximum current is lower than it would be without a flywheel. The variation in power consumption per revolution is reduced.

[0013] This phenomenon is visualized by figures 1 and 2, which are part of a set presented later.

[0014] Figure 1 shows the energy evolution within the machine, represented by a coordinate system where the x-axis (Ox) represents time and the y-axis (Oy) represents current. The curve Iv represents the current variation, and the curve Cv represents the mechanical torque variation, which is itself linked to the gas pressure variations. The electric current Iv varies proportionally to the mechanical torque Cv, with both the current and torque being simultaneously high or low.

[0015] Figure 2 shows the impact of the variation in current intensity Iv on the electrical power Pv, using two coordinate systems in each of which the x-axis Ox represents time. In the left-hand coordinate system, the y-axis Oy represents the motor's supply voltage Uc. This voltage Uc is constant. In the right-hand coordinate system, the y-axis Oy represents the electrical power Pv consumed by the motor. This power Pv is variable because the voltage Uc is constant and the current intensity Iv is variable.

[0016] It appears that the power Pv varies despite the presence of the flywheel. Moreover, the flywheel increases the mass, size, and cost of the machine.

[0017] Another proposed solution for limiting variations in power consumption during a revolution involves using an electrical circuit comprising one or more capacitors. However, this solution has the disadvantage of being bulky; it requires large capacitors because the charging and discharging frequencies are low, linked to the rotational speeds of the cold machine.

[0018] There is therefore a need to improve the management of the electrical power consumed on a lathe by a cold machine. Statement of the invention

[0019] The invention seeks to overcome the aforementioned disadvantages and has the general aim of reducing, or even completely eliminating, the variations in power consumed over a revolution.

[0020] The invention also seeks to prevent any harmful electrical influence, such as current surges, interference, or the like.

[0021] The invention also aims to reduce the mass of a cold machine, to decrease its size, and to lower its manufacturing and maintenance costs.

[0022] Another objective of the invention is to mitigate, or even eliminate, the disruptive effects of mechanical phenomena such as vibrations, shocks, or others.

[0023] To this end, the invention proposes a power supply system for an electric motor for driving a rotating mechanical machine with high torque variation over a revolution, the system comprising a power supply device providing an alternating current whose intensity varies proportionally to the torque exerted by the motor.

[0024] The system includes a device for regulating the power supplied to the motor, the regulating device providing an alternating voltage controlled by the current and in opposite phase to the current.

[0025] The voltage decreases when the current increases and vice versa. The voltage is at its minimum level when the current is at its maximum level, and the voltage is at its maximum level when the current is at its minimum level. The voltage values ​​are set so that the electrical power obtained allows the operation of the Refrigeration machine. The electrical power consumed by the refrigeration machine is much more stable. One resulting advantage is a significant reduction in electrical disturbances on the grid. Subsequent benefits include the preservation of grid components, as well as an improvement in their lifespan and reliability. Another advantage is a limitation on the maximum electrical power required, because it allows the use of smaller and lighter components.

[0026] A low-frequency portion of the control device regulates average power based on average current, and a high-frequency portion of the control device regulates average power based on instantaneous current. This allows for a virtually instantaneous adjustment of the appropriate voltage value. As a result, the phase opposition between current and voltage is effective regardless of the machine's load level.

[0027] The low-frequency section delivers a low-frequency voltage, and the high-frequency section delivers a high-frequency voltage. The voltage setpoint provided by the control device is the sum of the low-frequency and high-frequency voltages. Adding the two voltage values ​​is a simple operation that improves the reliability of the motor control. Based on the final voltage, a voltage setpoint is generated for a voltage generation unit of the refrigeration unit.

[0028] The low-frequency section first calculates a saturated low-frequency voltage from a saturated power and a saturated average current, and then obtains the effective low-frequency voltage by limiting the slope and filtering the saturated low-frequency voltage. This method allows for gradual, smooth voltage variations, whether rapid or slow.

[0029] The high-frequency part determines a saturated high-frequency weighting ramp and, in parallel, calculates a reference high-frequency voltage by subtracting the effective low-frequency voltage from a theoretical high-frequency voltage, which is obtained from a saturated power and a saturated current, itself obtained by quadratic extrapolation of a measured current, the saturated high-frequency weighting ramp and the reference high-frequency voltage then being combined to obtain the saturated high-frequency voltage, which is subjected to slope limitation and filtering, to deliver the effective high-frequency voltage.

[0030] This method allows for an almost instantaneous balancing of the current intensity by the voltage, for an optimization of the stabilization of the power consumed.

[0031] The power regulation for the low-frequency part is carried out according to a value between 40 and 100 Hz, and the power regulation for the high-frequency part is carried out according to a value equal to or greater than 4000 Hz. Values ​​from 5000 to 10000 Hz have given good results.

[0032] The invention also relates to a cold machine which includes a power supply system for an electric motor for driving a rotating mechanical machine with high torque variation on a revolution, as presented above.

[0033] The machine implements the Stirling thermodynamic cycle.

[0034] This cycle allows for very low levels of cold, or adjustments to very rapid cooling value.

[0035] During the operation of the machine, a required temperature generates a motor rotation speed setpoint, said speed setpoint itself generating an average electrical power setpoint.

[0036] There is a close correlation between temperature and engine operation.

[0037] The invention further relates to an infrared detector comprising a machine as described above. The performance of a refrigeration machine implementing the Stirling cycle is particularly well suited to temperature stabilization of a refrigeration machine sensor. Brief description of the drawings

[0038] Other objects, features and advantages of the invention will become apparent from the following description, given by way of a single, non-limiting example, and made with reference to the accompanying drawings in which:

[0039] [Fig-1] represents a variation of a mechanical torque and a variation of a current electric, for a refrigeration machine according to the prior art,

[0040] [Fig.2] represents an electrical voltage and power for the machine according to [Fig.1],

[0041] [Fig.3] represents an electrical voltage and power for a refrigeration machine according to the embodiment example of the invention,

[0042] [Fig.4] is a diagram which shows overall a power regulation for the machine according to [Fig.3],

[0043] [Fig.5] is a diagram that details a low-frequency part of the regulation of [Fig.4],

[0044] [Fig.6] is a diagram that details a high-frequency part of the regulation of [Fig.4],

[0045] Detailed description of an example of Fin vention implementation

[0046] A refrigeration machine equipped with a feeding system according to the invention is presented summarily without figure.

[0047] The machine implements the Stirling thermodynamic cycle, through successive compressions and expansions of a gas in a closed circuit. To this end, the machine includes, in particular, a piston designed to compress the gas in a compression chamber. Together with a connecting rod, the piston forms an assembly driven by a crankshaft. This mechanism is driven by an electric motor, which imparts a reciprocating linear motion to the piston via the connecting rod. Each crankshaft revolution corresponds to a mechanical torque, the intensity of which varies considerably between a maximum and a minimum. When the gas is compressed to its highest pressure, the torque is at its maximum. Conversely, when the gas is expanded, the torque is at its minimum.

[0048] An electric motor of the machine drives the crankshaft in rotation and, consequently, provides an electrical torque that balances the mechanical torque. For powering the motor, a system of the machine includes a power supply device that provides an alternating current Iv whose intensity varies proportionally to the torque exerted by the motor. The current Iv was previously shown with reference to [Fig. 1]. The system includes a power regulation device Ps supplied to the motor, the regulation device providing an alternating voltage Uv that is controlled by the current Iv and in opposite phase to the current Iv.

[0049] Figure 3 shows the impact of the voltage variation Uv on the electrical power Ps, using two coordinate systems in each of which the x-axis (Ox) represents time. In the left-hand system, the y-axis (Oy) represents the motor's supply voltage Uv. This voltage Uv is variable. In the right-hand system, the y-axis (Oy) represents the electrical power Ps consumed by the motor. This power Ps is stable, almost constant, because the voltage Uv is variable and the current Iv is variable such that the voltage Uv and the current Iv are out of phase.

[0050] This advantageously results in the electrical network supplying the refrigeration machine being subjected to a regular load. This protects its components and also allows them to be sized to a minimum. A smaller component is lighter and less bulky.

[0051] As shown in [Fig. 4], to control the electric motor of the refrigeration machine, a low-frequency (LF) portion of the control device regulates an average power Pc as a function of an average current Imoy, and a high-frequency (HF) portion of the control device regulates the average power Pc as a function of an instantaneous current I, which is measured. The average power value Pc is given by a power setpoint. A gain G_HF between 0 and 1 is applied to a high-frequency voltage U_HF delivered by the HF portion. This allows for an almost instantaneous adjustment of the adapted voltage value. A low-frequency voltage U_BF delivered by the LF portion and the high-frequency voltage U_HF are summed to form a voltage setpoint Uc, which is sent to a voltage generation unit Uv that supplies the refrigeration machine motor.It follows that the phase opposition between the current Iv and the voltage Uv is effective regardless of the... regardless of the machine's load level. This method allows for precise control of the current intensity, optimizing the stabilization of power consumption.

[0052] As shown in [Fig. 5], the low-frequency (LF) section first calculates a saturated low-frequency voltage U_BF_0 from a saturated power PC_sat and a saturated average current Imoy_sat. It then obtains the effective low-frequency voltage U_BF by limiting the slope and then filtering the saturated low-frequency voltage U_BF_0. The slope limitation adjusts the saturated low-frequency voltage U_BF_0 to a value U_BF_1, which is then filtered to provide the effective low-frequency voltage U_BF. This method allows for gradual, smooth voltage variations, whether rapid or slow.

[0053] As shown in [Fig. 6], the high-frequency (HF) section determines a saturated high-frequency weighting ramp Pond and, in parallel, calculates a reference high-frequency voltage U_HF_r by subtracting the effective low-frequency voltage U_BF from a theoretical high-frequency voltage U_HF_t. This theoretical high-frequency voltage is obtained from a saturated power PC_sat and a saturated current I_sat, itself obtained by quadratic extrapolation of a measured current I. The saturated high-frequency weighting ramp Pond and the reference high-frequency voltage U_HF_r are then combined to obtain the saturated high-frequency voltage U_HF_0, which is subjected to slope limiting and filtering to deliver the effective high-frequency voltage U_HF. The slope limiting adjusts the saturated high-frequency voltage U_HF_0 to a value U_HF_1, which is then filtered to provide the effective high-frequency voltage U_HF.This method allows for gradual, smooth voltage variations, whether rapid or slow.

[0054] The motor control described above is implemented for an infrared detector comprising, in particular, a sensor, an optical device, and a diaphragm. To capture images accurately and consistently, the detector must be maintained at a constant temperature, particularly at the sensor. For this purpose, a cold screen is attached to the sensor and cooled by the action of the refrigeration machine. For example, a finger connects the expansion chamber to the screen. The finger and the screen are good thermal conductors, comprising metals, metal alloys, or equivalent materials.

[0055] Obviously, the invention is not limited to the example of embodiment and implementation described above, and includes all technical equivalents which fall within the scope of the claims that follow.

Claims

Claims

1. Power supply system for an electric motor for driving a rotating mechanical machine with high torque variation on a revolution, the system comprising a power supply device providing an alternating current (Iv) whose intensity varies proportionally to the torque exerted by the motor, characterized in that it comprises a device for regulating the power supplied to the motor, the regulating device providing an alternating voltage (Uv) controlled by the current (Iv) and in phase opposition with the current (Iv).

2. System according to claim 1, in which a low frequency part (LF) of the regulation device regulates an average power (Pc) according to an average current (Imoy), and a high frequency part (HF) of the regulation device regulates the average power (Pc) according to an instantaneous current (I).

3. System according to claim 2, in which the low frequency part (BF) delivers a low frequency voltage (U_BF), the high frequency part (HF) delivers a high frequency voltage (U_HF), a voltage setpoint (Uc) provided by the regulation device being the sum of the low frequency voltage (U_BF) and the high frequency voltage (U_HF).

4. System according to claim 3, in which the low frequency part (BF) first calculates a saturated low frequency voltage (U_BF_0), from a saturated power (PC_sat) and a saturated average current (Imoy_sat), to then obtain the effective low frequency voltage (U_BF) from a slope limitation then a filtering of the saturated low frequency voltage (U_BF_0).

5. System according to claim 3 or 4, in which the high frequency part (HF) determines a saturated high frequency weighting ramp (Pond) and, in parallel, calculates a reference high frequency voltage (U_HF_r) by subtracting the effective low frequency voltage (U_BF) from a theoretical high frequency voltage (U_HF_t), which is obtained from a saturated power (PC_sat) and a saturated current (Imoy_sat), itself obtained by quadratic extrapolation of a measured current (I), the saturated high frequency weighting ramp (Pond) and the reference high frequency voltage (U_HF_r) then being combined to obtain the saturated high frequency voltage (U_HF_0), which is subject to slope limitation and filtering, to deliver the effective high frequency voltage (U_HF).

6. A system according to any one of claims 2 to 5, wherein the power regulation for the low frequency (LF) part is made according to a value between 40 and 100 Hz, and the power regulation for the high frequency (HF) part is made according to a value equal to or greater than 4000 Hz.

7. Cold machine, characterized in that it comprises a system according to one of claims 1 to 6.

8. Machine according to claim 7, which implements the Stirling thermodynamic cycle.

9. Machine according to claim 7 or 8, for which a required temperature generates a motor rotation speed setpoint, said speed setpoint itself generating an average electrical power setpoint (Pc).

10. Infrared detector comprising a machine according to one of claims 7 to 9.

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