Controlling, by means of an electric motor, a mechanical machine with high torque variation over a revolution

Abstract

The invention relates to a system for supplying power to an electric motor for driving a rotary mechanical machine with high torque variation over a revolution, wherein the system comprises a power supply device supplying an alternating current, the intensity (Iv) of which varies in proportion to the torque exerted by the motor. The system comprises a device for regulating the power supplied to the motor, wherein the regulating device supplies an alternating voltage (Uv) controlled by the current (Iv) and in phase opposition to the current (Iv).

Description

[0001] DESCRIPTION

[0002] TITLE: Control, by an electric motor, of a mechanical machine with high torque variation on a lathe.

[0003] Technical field

[0004] The present invention relates to the control, by an electric motor, of a rotating mechanical machine with high torque variation on a lathe. The invention relates more particularly to the field of cold machines, in particular those for infrared detectors.

[0005] State of the prior art

[0006] Rotating mechanical machines with high torque variation on a lathe are used in various fields, for functions requiring intermittent forces.

[0007] In the field of refrigeration, rotary machines are sometimes used to alternately compress a gaseous fluid and allow its expansion. This is particularly the case for the implementation of the Stirling thermodynamic cycle, a cycle which results in alternating compressions and expansions of a gas in a closed circuit.

[0008] A machine that applies the Stirling cycle includes a piston designed to compress the gas in a compression chamber. With a connecting rod, the piston forms a unit driven by a crankshaft. This is driven in a circular motion by an electric motor and imposes a rectilinear alternating motion on the piston via the connecting rod.

[0009] Since the Stirling cycle consists of four stages, the piston is driven by the engine so that the machine performs the four stages successively. Thus, the machine causes a compression of the gas in the compression chamber, a transfer to an expansion chamber of the compressed gas, an expansion of the gas in said chamber, then a transfer of the expanded gas to the compression chamber. The gas heats up during compression, and cools down during expansion.

[0010] Machines using the Stirling cycle allow very low cold values ​​to be achieved and the cooling speed to be varied very quickly. This is achieved by adjusting the frequency of the cycles by adjusting the rotation speed of the electric motor. In fact, these machines are often used for applications that require very intense cold levels, or precision and responsiveness in cold management. One application is the temperature regulation of certain infrared detectors.

[0011] According to the Stirling cycle, the gas is highly compressed in the compression chamber. As a result, the connecting rod experiences alternating forces with very high extremes, and the variations in thermodynamic torque on the crankshaft are correspondingly very high. These variations are passed on to the engine, which must consequently provide a driving torque whose variations are also very high. In cases where the engine is powered at constant voltage, for example by means of a battery, the electrical power supplied varies greatly because the current intensity varies greatly. The network that supplies the cold machine must cope with the variations in electrical power consumed. Sometimes this can be a problem.

[0012] 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 low or very low variations, for several reasons.

[0013] For example, regular electricity consumption reduces, or even completely avoids, electrical disturbances on the network. As a result, network components, including a motor power supply device, are preserved. Their lifespan and reliability are improved. Regular electricity consumption also limits the maximum power values ​​to be supplied. This allows the use of smaller, lighter components. This is the case, for example, for the motor.

[0014] In practice, to limit the maximum intensity of the electric torque to be supplied, and therefore to limit the variations in power consumed over a revolution, solutions have been proposed.

[0015] One of these involves attaching a flywheel to the crankshaft. The flywheel stores 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 network to the engine, until the gas reaches its maximum pressure. As a result, the maximum current is less intense than it would be in the absence of a flywheel. The variation in power consumed over a revolution is reduced.

[0016] This phenomenon is visualized in Figures 1 and 2, which are part of a game presented later.

[0017] Figure 1 shows energy changes in the machine, using a reference frame whose abscissa axis Ox corresponds to time and whose ordinate axis Oy corresponds to intensities. The curve Iv represents the variation in current and the curve Cv represents the variation in mechanical torque, itself linked to variations in gas pressure. The electric current Iv varies proportionally to the mechanical torque Cv, the current and the torque being strong or weak simultaneously.

[0018] Figure 2 shows the impact of the variation in current intensity Iv on the electrical power Pv, by two reference frames for each of which the abscissa axis Ox corresponds to time. In the left-hand frame, the ordinate axis Oy corresponds to the voltage Uc supplying the motor. This voltage Uc is constant. In the right-hand frame, the ordinate axis Oy designates the electrical power Pv consumed by the motor. This power Pv is variable, because the voltage Uc is constant and the intensity Iv is variable. It appears that the power Pv varies despite the presence of the flywheel. In addition, the flywheel increases the mass, size and cost of the machine.

[0019] Another proposed solution to limit variations in power consumption on a lathe is to use 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 rotation speeds of the machine when cold.

[0020] There is therefore a need to improve the management of the electrical power consumed on a lathe by a cold machine.

[0021] Statement of the invention

[0022] The invention seeks to overcome the aforementioned drawbacks and has the general aim of reducing, or even completely eliminating, variations in power consumed on a lathe.

[0023] The invention also seeks to prevent any harmful electrical influence, such as current draws, interference, or the like.

[0024] The invention also aims to reduce the mass of a cold machine, to reduce its size, and to lower its manufacturing and maintenance costs.

[0025] Another aim of the invention is to reduce, or even eliminate, the disruptive effects of mechanical phenomena such as vibrations, shocks, or others.

[0026] To do this, the invention proposes a system for supplying an electric motor for driving a rotating mechanical machine with high torque variation on a revolution, the system comprising a supply device providing an alternating current whose intensity varies proportionally to the torque exerted by the motor.

[0027] 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 phase opposition to the current. 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 machine to operate in cold conditions. The electrical power consumed by the machine in cold conditions is much more stable. A resulting advantage is the significant reduction of electrical disturbances on the network. Subsequent advantages are the preservation of network components, and also an improvement in their lifespan and reliability.Another advantage is a limitation of the maximum electrical power to be supplied, because it allows the use of smaller and lighter components.

[0028] A low-frequency part of the control device regulates average power based on average current, and a high-frequency part of the control device regulates average power based on instantaneous current. This allows for almost 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.

[0029] The low-frequency part delivers a low-frequency voltage, the high-frequency part delivers a high-frequency voltage, a voltage setpoint provided by the regulation device being the sum of the low-frequency voltage and the high-frequency voltage. The addition of two voltage values ​​is a simple operation which brings reliability to the motor control. On the basis of the final voltage, a voltage setpoint is formed intended for a block for developing the cold machine voltage.

[0030] The low-frequency part first calculates a saturated low-frequency voltage, from a saturated power and a saturated average current, to then obtain the effective low-frequency voltage from a slope limitation and then a filtering of the saturated low-frequency voltage. This method allows for gradual voltage variations, without jolts, whether fast or slow.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 subject to slope limitation and filtering, to deliver the effective high-frequency voltage.

[0031] This method allows almost instantaneous balancing of current intensity by voltage, for optimization of the stabilization of the power consumed.

[0032] Power regulation for the low-frequency part is done according to a value between 40 and 100 Hz, and power regulation for the high-frequency part is done according to a value equal to or greater than 4000 Hz. Values ​​of 5000 to 10000 Hz have given good results.

[0033] The invention also relates to a cold machine which comprises a system for supplying an electric motor for driving a rotating mechanical machine with high torque variation on a lathe, as presented above.

[0034] The machine implements the Stirling thermodynamic cycle.

[0035] This cycle allows for very low cold levels, or very rapid cold value adjustments.

[0036] During machine operation, a required temperature generates a motor rotation speed setpoint, said speed setpoint itself generating an average electrical power setpoint.

[0037] There is a close correlation between temperature and engine operation.

[0038] The invention also relates to an infrared detector comprising a machine as presented above. The performance of a cold machine implementing the Stirling cycle is particularly suitable for stabilizing the temperature of a cold machine sensor.

[0039] Brief description of the drawings

[0040] Other aims, characteristics and advantages of the invention will appear on reading the following description, given with a single non-limiting example, and made with reference to the appended drawings in which:

[0041] [Fig. l] represents a variation of a mechanical torque and a variation of an electric current, for a cold machine according to the prior art,

[0042] [Fig.2] represents an electrical voltage and power for the machine according to [Fig. l ],

[0043] [Fig.3] represents an electrical voltage and power for a cold machine according to the example of implementation of the invention,

[0044] [Fig.4] is a diagram which generally presents a power regulation for the machine according to [Fig.3],

[0045] [Fig.5] is a diagram detailing a low frequency part of the regulation of [Fig.4],

[0046] [Fig.6] is a diagram detailing a high frequency part of the regulation of [Fig.4],

[0047] Detailed description of an exemplary embodiment of the invention

[0048] A cold machine equipped with a supply system according to the invention is presented briefly without a figure.

[0049] The machine implements the Stirling thermodynamic cycle, by successive compressions and expansions of a gas in a closed circuit. To this end, the machine includes a piston intended to compress the gas in a compression chamber. With a connecting rod, the piston forms a unit driven by a crankshaft. This is driven in a circular motion by an electric motor and imposes a rectilinear alternating motion on the piston via the connecting rod. Each revolution of the crankshaft corresponds to a mechanical torque whose intensity varies greatly between a maximum and a minimum. When the gas is compressed to the highest pressure, the torque is maximum. Conversely, when the gas is expanded, the torque is minimal.

[0050] An electric motor of the machine drives the crankshaft in rotation and, thus, provides an electric torque that balances the mechanical torque. To power 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 presented before using Figure 1. The system includes a device for regulating the power Ps 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.

[0051] Figure 3 shows the impact of the variation in voltage Uv on the electrical power Ps, using two reference frames for each of which the abscissa axis Ox corresponds to time. In the left-hand frame, the ordinate axis Oy corresponds to the voltage Uv supplying the motor. This voltage Uv is variable. In the right-hand frame, the ordinate axis Oy designates 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 so that the voltage Uv and the current Iv are in phase opposition.

[0052] This advantageously results in the electrical network that powers the refrigeration machine being used regularly. This preserves its components, and also allows them to be dimensioned to a minimum. A smaller component is lighter and less bulky.

[0053] As shown in Figure 4, to control the electric motor of the cold machine, a low-frequency part BF 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, 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 high-frequency part HF. This allows an almost instantaneous adjustment of the adapted voltage value. A low-frequency voltage U_BF delivered by the low-frequency part BF and the high-frequency voltage U HF are summed to form a voltage setpoint Uc, which is sent to a block for developing the voltage Uv which supplies the motor of the cold machine.As a result, the phase opposition between the current Iv and the voltage Uv is effective regardless of the level of stress on the machine. This method allows the current intensity to be measured, for optimized stabilization of the power consumed.

[0054] As shown in Figure 5, 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 and then a filtering of the saturated low frequency voltage U_BF_O. The slope limitation adjusts the saturated low frequency voltage U_BF_O to a value U_BF_1, which is filtered to provide the effective low frequency voltage U_BF. This method allows gradual voltage variations, without jolts, whether fast or slow.

[0055] As shown in Figure 6, 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 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 being then combined to obtain the saturated high-frequency voltage U_HF_0, which is subjected to slope limitation and filtering, to deliver the effective high-frequency voltage U HF. The slope limitation adjusts the saturated high-frequency voltage U_HF_O to a value U_HF_1 , which is filtered to provide the effective high-frequency voltage U HF.This method allows for gradual, smooth voltage variations, whether rapid or slow.

[0056] The motor drive presented above is implemented for an infrared detector which includes a sensor, an optical device, and a diaphragm. To capture images accurately and consistently, the detector must be kept 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 cold 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.

[0057] 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 which 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) as a function of an average current (Imoy), and a high frequency part (HF) of the regulation device regulates the average power (Pc) as a function of 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. System according to any one of claims 2 to 5, in which the power regulation for the low frequency (LF) part is done according to a value between 40 and 100 Hz, and the power regulation for the high frequency (HF) part is done 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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