ITTV20120065A1 - ELECTRONIC CONTROL SYSTEM FOR AN ELECTRIC MOTOR OF A COMPRESSOR OF A REFRIGERATED MACHINE AND ITS OPERATING METHOD - Google Patents

Description

â € œ ELECTRONIC CONTROL SYSTEM OF AN ELECTRIC MOTOR OF A COMPRESSOR OF A REFRIGERATOR AND RELATIVE OPERATING METHODâ €

The present invention relates to an electronic control system of an electric motor of a compressor of a refrigeration machine, and relative method of operation.

In particular, the present invention relates to an electronic control system of an electric motor of the compressor of a cooling circuit present in a refrigeration machine, such as for example a refrigeration unit, a refrigerator, a freezer, a blast chiller, a chiller, one or more cold rooms, abatement cells or tunnels, or any refrigeration unit suitable for refrigerating / freezing food; to which the following discussion will explicitly refer without losing generality.

Refrigerating machines are known of the type comprising an external boxed frame, a refrigeration cell or chamber arranged inside the frame to house and cool / refrigerate / freeze food, and a structured cooling circuit to cool the refrigeration chamber thus to bring and keep the latter at a certain temperature.

The cooling circuit is typically provided with a heat pump apparatus of the type comprising: a first heat exchanger configured to absorb heat from the refrigeration chamber through a refrigerant fluid so as to cool the food present in the chamber itself; a second heat exchanger configured to release the heat of the refrigerant fluid to the outside; a lamination valve and a compressor, which is interposed between the first and the second heat exchanger and is structured in such a way as to compress the refrigerant fluid directed towards the second heat exchanger.

The compressor typically comprises a piston pump connected to the first and second heat exchanger through relative ducts crossed by the refrigerant fluid, and an electric motor, which is connected to the power supply network through a switch device to receive a power supply voltage. . In this case, the electric motor is mechanically connected to the piston pump and is able to operate the latter in such a way as to cause compression of the refrigerant fluid in the cooling circuit.

In order to ensure correct operation of the electric motor and prevent damage, some of the latest generation refrigeration machines have been equipped with an electronic control system, which includes a measuring device configured to measure the power supply voltage of the electric motor. , and an electronic motor-control unit, which is configured in such a way as to command the opening of the switch so as to automatically switch off the electric motor when the measured motor-power supply voltage is outside a preset voltage range delimited by a minimum nominal voltage threshold and a maximum nominal voltage threshold.

If on the one hand, the use of the aforementioned control in refrigeration machines is particularly advantageous as it protects the electric motor from possible damage and / or stress conditions caused by variations in the supply voltage outside the aforementioned voltage range, on the other hand, it can be critical as regards the correct storage of food in the refrigeration machine. In fact, when the measured voltage reaches a value that is less than or greater than the minimum nominal voltage threshold or respectively the maximum nominal voltage threshold, the system automatically switches off the motor so as to prevent damage, but causes the interruption of the refrigeration / freezing of the refrigeration chamber causing, in case of prolonged interruption, the deterioration of the food present in the chamber itself.

The Applicant has carried out an in-depth study with the aim of identifying a solution that would specifically achieve the goal of guaranteeing both the protection of the electric motor from possible damage caused by significant voltage variations, and the correct storage of the food present in the cell.

The object of the present invention is therefore that of providing a solution that allows to achieve the above indicated objective.

This object is achieved by the present invention as it relates to an electronic control system of an electric motor of a compressor present in a refrigeration machine, as defined in the attached claims.

Preferably, the present invention also relates to a method of controlling a compressor present in a refrigeration machine, as defined in the attached claims.

Preferably, the present invention also relates to a refrigeration machine, as defined in the attached claims.

Preferably, the present invention finally relates to a computer program, as defined in the attached claims.

The present invention will now be described with reference to the attached drawings, which illustrate a non-limiting example of embodiment, in which:

Figure 1 schematically shows a refrigerating machine provided with an electronic control system made according to the dictates of the present invention;

Figure 2 shows a block diagram of the electronic control system shown in Figure 1;

- Figures 3 and 4 show as many portions of a flow diagram relating to the operation of the electronic control system shown in Figure 2; while

- Figure 5 shows an example of a time chart indicating the operations implemented by the electronic control system as the power supply voltage of the electric motor varies.

The present invention will now be described in detail with reference to the attached Figures to allow a skilled person to make and use it. Various modifications to the embodiments described will be immediately evident to those skilled in the art and the generic principles described can be applied to other embodiments and applications without thereby departing from the protective scope of the present invention, as defined in the attached claims. Therefore, the present invention should not be considered limited to the embodiments described and illustrated, but should be accorded the widest protective scope in accordance with the principles and characteristics described and claimed herein.

In particular, the present invention is essentially based on the principle of measuring the electrical supply voltage fed to the electric motor; determining whether the measured supply voltage and a predetermined electrical voltage range satisfy a first condition with each other; switch off the electric motor of the compressor when the first condition is not satisfied; keep the electric motor of the compressor off during a protection / shutdown time interval including at least one pre-established initial protection / shutdown interval; carry out one or more measurements of the supply voltage during said protection time interval; determine if the measured voltage satisfies the first relationship; vary the duration of said protection / shutdown time interval, extending said initial pre-established protection interval by one or more additional pre-established protection time intervals when said supply voltage measured during said initial protection time interval and / or during each said time interval predetermined additional protection does not satisfy said first relationship; generate a machine event for each time extension performed; determining a forced ignition condition when the number of machine events generated reaches a predetermined threshold; and finally to force the ignition of said electric motor of the compressor when the forced ignition condition is detected.

According to a preferred embodiment shown schematically in Figure 1, the number 1 generally indicates a refrigeration unit corresponding for example to a refrigeration unit, a refrigerator, a freezer, a blast chiller, a chiller, one or more refrigeration cells , abatement cells or tunnels, or any refrigeration unit suitable for refrigerating / freezing food.

Preferably, the refrigeration machine 1 comprises a boxed frame 2, a refrigeration cell or chamber 3 arranged inside the frame 2 to house and cool / refrigerate / freeze food (not shown), and a cooling circuit 4 structured to cool the refrigeration chamber 3 on the basis of a certain temperature established / set by a user TT, for example through a control panel 9.

The cooling circuit 4 is of a known type and will not be described further except to specify that, in the example illustrated, it is provided with a heat pump equipment 5 comprising: a first heat exchanger 6 configured to absorb heat from the refrigeration chamber 3 through a refrigerant fluid so as to cool the food present in the refrigeration chamber 3 itself; a second heat exchanger 7 configured to release the heat of the refrigerant fluid outside the refrigeration chamber 3; a lamination valve 10 and a compressor 8, which is interposed between the first 6 and the second heat exchanger 7 and is structured in such a way as to compress the refrigerant fluid directed towards the second heat exchanger 7.

According to a preferred embodiment, the compressor 8 comprises a piston pump 8a connected to the first 6 and to the second heat exchanger 7 through corresponding ducts crossed by the refrigerant fluid, and an electric motor 8b, which is mechanically connected, so known, to the piston pump 8a, and is adapted to actuate the latter in such a way as to cause compression of the refrigerant fluid circulating in the cooling circuit 4.

According to a preferred embodiment, the refrigeration unit 1 is provided with an electrical control system 16 comprising a regulator device 14, which is configured in such a way as to: receive the set temperature TT and a measured temperature TM, for example through sensors of temperature 15 present in the refrigeration chamber 3, compare the set temperature TT with the measured temperature TM and generate a command signal S1 to command the ignition (ON) / shutdown (OFF) of the motor 8b / compressor 8 based on the result of this comparison.

According to a preferred embodiment, the electrical control system 16 of the refrigeration unit 1 further comprises an electronic control device 17 configured in such a way as to: receive the command signal S1 indicative of the on / off request of the compressor 8, and control the motor electrical 8b on the basis of the command signal S1 by implementing the control method described in detail below.

In the example shown in Figure 2, the electric motor 8b is connected to an electrical supply network 18 placed at a specific supply voltage V (for example V = 220-230V), through a switch device 19 such as a switch with electric or electronic actuation or similar, while the electronic control device 17 comprises a measuring device 20 configured so as to measure the voltage V of the power supply network 18 intended to power the electric motor 8b, and an electronic control device 21 configured to receive the command signal S1 and the measured supply voltage V and implements the operations of the control method (described in detail below) to command the switch device 19 so as to cause the ignition / shutdown of the electric motor 8b on the basis of the measured supply voltage V and the control signal S1.

According to a possible embodiment, the measuring device 20 comprises a high impedance stage 22 connected to the electrical supply network 18 to detect the supply voltage V, and an analog / digital converter stage 23 configured to receive the supply voltage Analog V supplied at the output by the high impedance stage 22, and convert it into a suitably filtered digital voltage value.

According to a preferred embodiment, the electronic control device 21 can comprise a microprocessor, configured so as to receive the digital value of the supply voltage V measured by the input stage 20, to receive the command signal S1, and to implement the control method thus ¬ to properly control the switching on / off of the electric motor 8a of the compressor 8.

With reference to Figures 3 and 4, the operations envisaged by the control method implemented by the electronic control device 21 will be described below.

Before continuing with this description, for reasons of clarity, it is necessary to define some control quantities and variables that will be used by the method:

Î ”tp is a first time variable containing the time measured by a first timer;

Î ”ta is a second time variable containing the time measured by a second timer;

Î ”to a third time variable containing the time measured by a third timer;

tp1 corresponds to a predetermined initial protection time interval of the electric motor 8b; in particular, the pre-established initial protection time interval is included in an overall protection / shutdown interval during which the engine is kept off;

tp2 corresponds to a predetermined additional protection time interval of the electric motor 8b;

tout corresponds to a pre-established shutdown time threshold;

tacc corresponds to a predetermined switch-on time threshold;

Î ”V corresponds to a predetermined nominal voltage range including the range of supply voltages within which the electric motor 8b operates under nominal operating conditions; in particular, the nominal voltage range Î ”V is included between a predetermined minimum voltage threshold Vmin and a predetermined maximum voltage threshold Vmax;

Vacc is a predetermined nominal ignition voltage of the electric motor 8b; according to a preferred embodiment Vacc corresponds to an intermediate voltage included in the predetermined nominal voltage range; according to a possible embodiment Vacc is equal to the minimum voltage threshold Vmin;

Ev is a machine event counter;

NE is a predetermined machine-event threshold.

With reference to Figure 3 in the initial phase (Block 100), the electronic control device 21 reads the digital value of the supply voltage V and checks, on the basis of the command signal S1, whether the regulator electrical system 14 has requested the € ™ ignition of compressor 8 (Block 110). In other words, in this phase the electronic control device 21 measures / samples the supply voltage V.

In the negative case (NO output from Block 110) or if the regulator electrical system 14 has not requested the compressor 8 to be switched on, the electronic control device 21 checks whether the command signal S1 has just been switched from ON (corresponding to a request to switch on), to OFF corresponding to a request to switch off compressor 8 (Block 120). Preferably, the term `` just switched '' means that the switching of the command signal S1 from ON to OFF took place during the execution by the electronic control device 21 of the control cycle immediately preceding the execution of the control cycle in progress.

In the positive case (YES output from Block 120), or if the command signal S1 of the electrical regulator system 14 has just been switched from ON to OFF, the electronic control device 21 establishes or restores the nominal voltage range Î " V, depending on whether or not the dynamic modification function of the nominal voltage thresholds has been activated (described in detail below) (Block 130).

The electronic control device 21 assigns a null value to the machine-event counter Ev = 0 (Block 140), commands the reset of the first timer, activates the timing of the first time variable Î "tp (Î" tp = 0), commands the resetting of the second timer Î "ta, activates the timing of the first time variable Î" ta (Î "ta = 0), commands the resetting of the third timer, activates the timing of the third time variable Î" to ( Î ”to = 0) (Block 150) and executes the reading operation again (Block 100) and the subsequent operations.

If not, (Output No from Block 120), that is, if the command signal S1 of the electric regulator system 14 has not just switched from ON to OFF, or if during the execution of the control cycle immediately preceding the Execution of the control cycle in progress, the command signal S1 was OFF, the electronic control device 21 verifies, moment by moment, whether the first time variable Î "tp has reached the threshold associated with the protection time interval initial tp1, Î "tp = tp1 (Block 160)

If the first time variable Î "tp has not exceeded the initial protection interval tp1 Î" tp <tp1 (NO output from block 160), the electronic control device 21 carries out a new reading of the value of the supply voltage V ( Block 100), and implements the operations of the Blocks described above.

If, on the other hand, the first time variable Î "tp has reached the initial protection time interval tp1 Î" tp = tp1 (Si output from Block 160), the electronic control device 21 stops / blocks the count of the first timer and therefore maintains the first time variable Î ”tp to the value corresponding to the initial protection interval tp1, Δ tp = tp1.

From what has been described above, it is appropriate to specify that the assignment of the initial protection interval tp1 to the first time variable Î "tp conveniently allows motor protection to be guaranteed for a time Î" tp even when the motor 8b is switched off following receipt of the S1 = OFF shutdown command generated by the regulator system 14.

With reference to Figure 3, if the command signal S1 generated by the regulator electrical system 14 contains a request to switch on the electric motor / compressor 8, i.e. S1 = ON, (YES output from Block 110), the electronic control device 21 checks if compressor 8 has already passed into the ignition state on the basis of a forced ignition condition (which will be described in detail below) (Block 180) and in the positive case (YES output from block 180), the electronic device control unit 21 again reads / measures the digital value of the supply voltage V (Block 100).

In the negative case (NO output from Block 180), i.e. if the compressor 8 has not passed into the ignition state on the basis of a forced ignition condition, the electronic control device 21 checks whether the supply voltage V read / measured and the nominal voltage range Î ”V satisfy a first condition / predetermined relationship (Block 190). According to a preferred embodiment, the first condition is satisfied when the read / measured supply voltage V is included in the nominal voltage range Î ”V.

In the event that the read / measured / sampled supply voltage V and the nominal voltage range Î "V do not meet the first pre-established condition, that is, if the supply voltage V is lower than the minimum voltage Vmin or the supply voltage V is greater than the maximum voltage Vmax (NO output from Block 190), the electronic control device 21 resets the second time variable Î ”ta, and activates its timing by means of the second timer (Block 200). In this phase, the third timer measures the time interval during which the supply voltage V and the nominal voltage interval Î "V do not satisfy the first condition and assigns the time interval measured to the third time variable Î "To.

In detail, the electronic control device 21 measures through the third timer the time interval during which the supply voltage V remains, continuously, below the minimum voltage threshold Vmin (as shown in the example of Figure 5), or it is maintained continuously above the maximum voltage threshold Vmax and assigns the measured time interval a to the third time variable Î ”to.

The electronic control device 21 checks whether the third time variable Î "to is greater than or equal to the first safety time threshold tout (Block 210, Figure 5) and if not, or if Î" to <tout, (NO output from Block 210), the electronic control device 21 again reads / measures the supply voltage V (Block 100) and sequentially executes the operations envisaged in the subsequent Blocks.

If, on the other hand, the third time variable Î "to measured is greater than or equal to the first time threshold tout, Î" to> = tout (YES output from Block 210), the electronic control device 21 checks whether the motor 8b / compressor 8 is It is lit (Block 220). In the positive case, (YES output from Block 220), the electronic control device 21 commands the shutdown of motor 8b / compressor 8 (Block 230), restores the minimum voltage values Vmin maximum Vmax and ignition Vacc (Block 240), commands the resetting of the first Î "tp (Î" tp = 0), second Î "ta (Î" ta = 0) and third time variable Î "to (Î" to = 0), and a new timing of the through the first, second and third timers Î ”to (Δ to = 0) (Block 250).

At this point, the electronic control device 21 starts a timing of the first time variable Î "tp through the first timer, and keeps compressor 8 off for a time interval Î" tp = tp1 equal to the initial protection time interval tp1 .

The electronic control device 21 again reads / measures the supply voltage V (Block 100) and implements the operations envisaged in the Blocks subsequent to block 100.

If, on the other hand, the electronic control device 21 detects that the motor 8b / compressor 8 is off (NO output from block 220 in Fig. 4), then it checks whether the first time variable Î "tp satisfies the relationship Î" tp = tp1 + ( N * tp2) (where N is a natural number and tp2 is the additional protection time interval) (Block 260, Fig. 4) (Fig. 5).

If the relation Î "tp = tp1 + (N * tp2) is not satisfied at (NO output from block 260), then the electronic control device 21 reads again the supply voltage V and carries out the operations envisaged in the following Blocks to Block 100.

It should be noted that in blocks 100, 190, 260 the electronic control device 21 substantially changes the overall protection time interval by extending the initial protection interval tp1 with one or more additional protection time intervals tp2 and that during each additional protection time interval tp2, the measurement of the supply voltage V is carried out and its comparison with the nominal voltage interval Î ”V is carried out.

If the relation Î "tp = tp1 + (N * tp2) is satisfied (YES output from block 260), the electronic control device 21 preferably, but not necessarily, detects whether a function for dynamic modification of the thresholds has been enabled. nominal voltage (Block 270 in Fig. 4). For this purpose, the electronic control device 21 can receive at its input, for example, a command signal S2 indicative of the request for enabling the variation of the thresholds.

If so, (YES output from block 270 in Fig. 4), the electronic control device 21 varies the voltage thresholds Vmin, Vmax, Vacc on the basis of respective predetermined values (Block 280), generates a machine-event and increases the machine-event counter Ev (Ev = Ev + 1) (Block 290).

In particular, the electronic control device 21 can be configured so as to subtract from the voltage threshold Vmin a predetermined voltage value Î ”Vmin (Vmin = Vmin-Δ Vmin); and / or subtract from Vacc a predetermined voltage value Î ”Vacc (Vacc = Vacc-Δ Vacc); and / or add to Vmax a predetermined voltage value Î ”Vmax (Vmax = Vmax Δ Vmax). Conveniently, the electronic control device 21 can be configured so as to vary, ie repeatedly increase / decrease the aforesaid voltage thresholds on the basis of the number of machine-events generated, until respective predetermined limit thresholds are reached.

In the negative case (NO output from block 270), the electronic control device 21 generates a machine event, increments the machine event counter Ev, (Ev = Ev + 1) (Block 290) and determines whether the machine event counter Ev has reached or minus a pre-established machine-event threshold NE (Block 300, Fig. 4).

If the machine-event counter Ev has not reached the predetermined machine-event threshold NE (NO output from block 300), the electronic control device 21 reads again the supply voltage V (Block 100) and implements the operations envisaged in the Blocks following Block 100.

If, on the other hand, the machine-event counter Ev has reached the preset machine-event threshold NE (YES output from block 300), the electronic control device 21 detects an ignition forcing condition, commands the ignition of the electric motor 8b / compressor 8 (Block 310), reads the supply voltage V again (Block 100) and implements the operations envisaged in the subsequent Blocks.

With reference to Figure 3, if the measured supply voltage V is included in the rated voltage range Î "V, that is, it is not greater than the minimum rated voltage threshold Vmin (Figure 5) or less than the maximum rated voltage threshold Vmax (YES output from Block 190), the electronic control device 21 resets the third time variable Î "to (Block 320) commands the timing of the third timer, and determines whether the supply voltage V is greater than or equal to the preset ignition voltage Vacc (Block 330).

From what has been described above, it is appropriate to specify that the third time variable Î ”to is repeatedly maintained at a null value until the first predetermined condition / relationship is satisfied (Block 190). Consequently, when the first condition / predetermined relationship is not satisfied (NO output from block 190) the third timer is free to continue counting without interruptions so as to measure the third time variable Î "to and compare it with the shutdown time threshold (Block 210 described above). Similarly, the second time variable Î ”ta is repeatedly maintained at a null value until the first predetermined condition / relationship remains unsatisfied (Block 190). Consequently, when the first predetermined condition / relationship is satisfied (YES output from block 190) the second timer is able to continue its count without interruptions so as to measure the second time variable Î ”ta.

If the electronic control device 21 determines that the supply voltage V is lower than the preset ignition voltage threshold Vacc (NO output from Block 330), then it resets the second time variable Î "ta (Block 340), it commands the ™ activation of the second timer and detects whether motor 8a of compressor 8 is off (Block 350). If the electronic control device 21 determines that motor 8b of compressor 8 is on (NO output from Block 350), then it carries out again the reading of the supply voltage V (Block 100) and implements the operations foreseen in the following Blocks.

If, on the other hand, the electronic control device 21 determines that the compressor 8 is off, then it carries out the operations envisaged in the blocks 260-310 described above.

With reference to Figure 3, if the electronic control device 21 detects that the supply voltage V is greater than or equal to the preset ignition voltage threshold Vacc (YES output from Block 330), then it determines the second time variable Î "ta indicative of the time interval during which the supply voltage V remained greater than or equal to the pre-established ignition voltage threshold Vacc. The electronic control device 21 determines whether or not the second time variable has reached the second safety time threshold tacc (Block 360).

If the second time variable Î "ta measured has not reached the second safety time threshold tacc (NO output from Block 360), then the electronic control device 21 continues to read the supply voltage V (Block 100) and repeats the operations envisaged in the subsequent Blocks.

If, on the other hand, the second time variable Î "ta measured has reached the time threshold tacc (YES output from Block 360) (Figure 3), then the electronic control device 21 checks whether the first time variable Î" tp has reached the ™ initial tp1 preset protection interval (Block 370).

If the first time variable Î "tp measured has not reached the initial predetermined protection interval tp1 (NO output from Block 370), then the electronic control device 21 continues to read the supply voltage V (Block 100) and repeats the operations envisaged in the blocks following Block 100.

If, on the other hand, the first time variable Î "tp measured has reached the initial preset protection interval tp1 (YES output from Block 370) (Figure 4), then the electronic control device 21 resets and reactivates the second timer associated with the second variable time Î "ta (Block 380) and detects whether motor 8b / compressor 8 is off (Block 390). In the negative case (motor 8b / compressor 8 on) (NO output from block 390) the voltage reading is carried out again power supply V (Block 100) and the operations envisaged in the subsequent Blocks are repeated.

If the electronic control device 21 detects that the motor 8b / compressor 8 is off (YES output from block 390), then it commands the ignition of the motor 8b / compressor 8 (Block 400), increases the machine-events counter Ev = Ev + 1 (Block 290) and carries out the operations described in Blocks 300-310.

The electronic control device 21 carries out the aforementioned adjustment on the basis of the command signal S1 by cyclically carrying out the reading operation provided for in Block 100 and the subsequent operations.

From what has been described above, it is appropriate to specify that the operations implemented cyclically by the sequence of blocks 180, 190, 200, 210, 220, 260, 270, 290, 300, 310, essentially involve carrying out sequentially: one or more measurements of the supply voltage V during the protection time interval, which includes both the initial pre-established protection interval tp1 and the additional protection intervals tp2 subsequent to tp1; determine if the measured voltage V and the nominal voltage Î ”V satisfy the relationship indicated above (Block 190); vary the duration of an overall protection time interval, during which the motor 8b remains off, extending the initial pre-established protection interval tp1 by at least one additional pre-established protection time interval tp2 when the measured voltage V during the interval initial protection time and / or each predetermined additional protection time interval tp2 does not satisfy said first relationship; determining a forced ignition condition when the number of generated machine events Ev reaches the predetermined threshold NE; force the ignition of the electric motor 8b / 8 when the forced ignition condition is detected.

From what has been described above, it is also appropriate to specify that the operations described above and shown in Figures 3 and 4, can be encoded in a software program stored in the electronic control device 21, and configured in such a way that when loaded into the electronic control device 21 the latter carries out the same operations.

According to a different embodiment, the electronic control device 21 does not perform the operations envisaged in blocks 270,280, that is, it does not envisage modifying the voltage thresholds upon the occurrence of a machine event.

The system described above is advantageous because thanks to the forced ignition of the electric motor based on the number of machine events generated, in addition to the correct functioning of the motor, the preservation of the food present in the refrigeration chamber is also guaranteed.

Finally, it is clear that modifications and variations can be made to the system and method described and illustrated above without thereby departing from the scope of the present invention defined by the attached claims.

Claims (10)

R I V E N D I C A Z I O N I 1. Electronic control system (16) configured to control an electric motor (8b) for driving a compressor (8) adapted to compress a refrigerant fluid circulating in a cooling circuit (4) of a refrigeration unit (1) ; said electric motor (8b) being structured so as to receive a supply voltage (V) from an electric network (18); the electronic control system (16) being also configured in such a way as to: - measure the electrical power supply voltage (V) fed to the electric motor (8b); - determine if the measured supply voltage (V) and a predetermined electrical voltage range (Î ”V) satisfy a first relationship between them; - switch off the electric motor (8b) of the compressor (8) when the first relation is not satisfied; - keeping the electric motor (8b) of the compressor (8) off during a protection / shutdown time interval (tp1, tp2) including at least a pre-established initial protection / shutdown interval (tp1); said electronic control system (16) being characterized in that it is also configured in such a way as to: - carry out one or more measurements of the supply voltage (V) during said protection time interval (tp1, tp2); - determine if the measured voltage (V) satisfies the first relation; - varying the duration of said protection / shutdown time interval, extending said initial pre-established protection interval (tp1) by one or more pre-established additional protection time intervals (tp2) when said supply voltage (V) measured during said initial time interval protection (tp1) and / or during each said additional predetermined protection time interval (tp2) does not satisfy said first relationship; - generate a machine event for each time extension carried out; - determining a forced ignition condition when the number of machine events (Ev) generated reaches a predetermined threshold (NE); - forcing the ignition of said electric motor (8) of said compressor (8) when said forced ignition condition is detected. System according to claim 1, further configured so as to: - measuring said supply voltage (V) during said at least one said predetermined additional protection time interval (tp2) corresponding to a temporal extension; - command the ignition of said motor (8b) and / or generate a machine event (Ev) when the measured supply voltage (V) is maintained continuously above an engine ignition voltage threshold (Vacc ) for a pre-established switch-on time threshold (tacc). System according to any one of the preceding claims, configured in such a way as to: -operating to receive / generate an engine command (S1) indicative of a request for turning on / off said engine (8b); - switch off or keep off the electric motor (8b) of the compressor (8) for the said protection / shutdown interval (tp1, tp2) when it occurs that: said first relation is not satisfied and said motor control (S1) includes a engine start request (ON). 4. System according to any one of the preceding claims, configured in such a way as to: -operate to receive / generate an engine command (S1) indicative of an engine on / off request; - force the ignition of the electric motor (8b) of the compressor (8) when it occurs that: said engine control (S1) includes a request for engine ignition (ON) and said forced ignition condition is satisfied. 5. Electronic control system according to any one of the preceding claims, wherein said predetermined voltage range (Î ”V) is delimited by a predetermined minimum voltage threshold (Vmin) and a predetermined maximum voltage threshold (Vmax); said motor ignition voltage threshold (Vacc) is included in said predetermined voltage range (Î "V): said system being also configured in such a way as to vary the minimum predetermined voltage (Vmin) and / or the maximum predetermined voltage ( Vmax) and / or said motor ignition voltage (Vacc) of respective predetermined voltage values (Î ”Vmin, Δ Vmax, Î ”Vacc) on the basis of the number of machine-events generated (Ev). 6. Electronic control system (16) according to any one of the preceding claims comprising: - an electric regulator system (14) configured so as to generate said motor control (S1) on the basis of the temperature measured in a refrigeration chamber (3) of said refrigeration machine (1); - an electronic control device (21) configured for: - receiving said motor command (S1); And if the engine control (S1) includes a request for engine ignition (ON): - varying the duration of said protection / shutdown time interval by extending said initial pre-established protection interval (tp1) by one or more additional pre-established protection time intervals (tp2) when said voltage measured (V) during said initial protection time interval ( tp1) and / or in each said predetermined additional protection time interval (tp2) does not satisfy said first relationship; - forcing the ignition of said electric motor (8b) of said compressor (8) when said forced ignition condition is detected. 7. Electronic control system (16) according to claim 6, also configured in such a way as to control the ignition of said engine (8b) in the event that said conditions occur: said engine control (S1) indicates the request engine ignition, said first relation is satisfied; and said initial predetermined protection time interval (tp1) has elapsed following the last shutdown of said motor (8b). 8. Method of controlling an electric motor (8b) for driving a compressor (8), which is configured in such a way as to compress a refrigerant fluid circulating in a cooling circuit (4) of a refrigerating machine (1); said electric motor (8b) being structured to be connected to an electric network (18) so as to receive a supply voltage (V); the method including the steps of: - measuring the supply voltage (V) of said electric motor (8b); - determine if the measured supply voltage (V) and a predetermined voltage range (Î ”V) satisfy a first relationship between them; - switch off the electric motor (8b) of the compressor (8) when said first relation is not satisfied; - keeping the electric motor (8b) of the compressor (8) off during a protection / shutdown time interval including at least a pre-established initial protection time interval (tp1); said method being characterized by the fact that it includes the steps of: - carry out one or more measurements of the supply voltage (V) during said protection time interval (tp1, tp2); - determine if the measured voltage (V) satisfies the first relation; - vary the duration of said protection / shutdown time interval, extending said initial pre-established protection interval (tp1) by one or more pre-established additional protection time intervals (tp2) when said supply voltage (V) measured during said initial time interval protection (tp1) and / or during each said additional predetermined protection time interval (tp2) does not satisfy said first relationship; - generate a machine event for each time extension carried out; - determining a forced ignition condition when the number of machine events (Ev) generated reaches a predetermined threshold (NE); - forcing the ignition of said electric motor (8) of said compressor (8) when said forced ignition condition is detected. Method according to claim 8 comprising the steps of: -measuring said supply voltage (V) during said at least one said predetermined additional protection time interval (tp2) corresponding to a temporal extension; - command the ignition of said motor (8b) and / or generate a machine event (Ev) when the measured supply voltage (V) is maintained continuously above a motor ignition voltage threshold (Vacc ) for a pre-established switch-on time threshold (tacc). 10. Computer program that can be loaded into the memory of an electronic control device (21) of a refrigeration machine (1) and designed to implement, when executed by the electronic control device (21), the method according to claims 8 and 9.