POWER CONVERTER PROTECTION DEVICE AND POWER CONVERTER DEVICE

Description

[0001] The invention lies in the field of power electronics and, more particularly, in the field of protecting a power converter configured to deliver an alternating current, for example, from a power inverter, in the event of a short circuit causing an increase in the current flowing in the power switches of the power converter.

[0002] The invention applies in particular to the protection of power converters used in aeronautics to deliver an alternating voltage intended to supply an on-board network of an aircraft.

[0003] The current delivered by a power inverter is conventionally regulated by a control loop in which the effective current flowing at the output of an inverter output filter is measured and compared to a predetermined threshold value. When the effective current flowing at the output of the inverter output filter exceeds the threshold value, the output current is regulated by acting on the duty cycle of the power switches so that it returns to a value less than or equal to the threshold value.

[0004] However, the reaction time of such a solution is relatively long, which does not prevent the effective output current from increasing until it reaches a relatively high tripping threshold which causes a circuit breaker to trip, making the inverter unavailable. This solution also does not prevent large current variations. This solution therefore has the disadvantage of requiring the power switches and the power components of the switch output filter to be sized so that they can withstand a high maximum current and large current variations, making these components relatively bulky and heavy.

[0005] Document D1 (US 6,351,359 B1) describes a circuit for blocking a semiconductor switching device in the event of an overcurrent, which comprises a monitoring device, a current sensor and a control device. The circuit reduces the overvoltage in the switching device when the switching device is blocked due to an overcurrent. Document D2 (US 2016 / 020684 A1) describes a protection device which comprises a first inverter and a second inverter; the output current is limited to a limiter value when the output current reaches the limiter value.

[0006] The aim of the invention is to limit at least one of the aforementioned drawbacks.

[0007] The invention is set forth in the attached set of claims.

[0008] Other characteristics, details and advantages of the invention will emerge from reading the description given with reference to the attached drawing given by way of example and which represents: [ Fig.1 ] there figure 1 schematically represents a power conversion device D comprising a power converter and a protection device DP according to the invention.

[0009] The power conversion device D comprises a power converter CONV capable of delivering a single-phase or polyphase alternating voltage, for example three-phase. This converter CONV is, for example, an inverter (DC / AC converter) or an alternating / alternating converter (AC / AC converter).

[0010] Typically, the CONV converter includes power switches.

[0011] Power switches are typically electronic switches formed by power transistors, for example insulated gate bipolar transistors or IGBTs ("Insulated Gate Bipolar Transistor"). Other types of power switches can of course be used, for example, MOSFET, COOLMOS, JFET type transistors or thyristors, for example based on gallium nitride (GaN) or silicon carbide (SiC)

[0012] In the non-limiting example of the figure 1 , the CONV converter is a three-phase inverter delivering three phases ϕ1, ϕ2, ϕ3 intended to supply a user network, for example an on-board network of an aircraft, through a filtering assembly comprising an output filter F1, F2, F3 per phase ϕ1, ϕ2, ϕ3. Each output filter is intended to filter the signal circulating on one of the phases ϕ1, ϕ2, ϕ3.

[0013] Each output filter F1, F2, F3 is a low-pass filter. It has a high cut-off frequency compared to the switching frequency of the CONV power converter so that the output filter cuts the high-frequency component of the output signal of the CONV converter while retaining its variable component without influencing its average value so that the user network is supplied by a three-phase alternating voltage of zero average value or by a three-phase alternating current of zero average value depending on whether the inverter is controlled to be a current or voltage inverter.

[0014] In other words, each output filter F1, F2 or F3 is configured so that each phase is sinusoidal at the output of the output filter F1, F2 or F3.

[0015] Each output filter F1, F2 or F3 is, for example, an RLC filter.

[0016] The power conversion device D comprises a regulator R configured to determine a duty cycle Rc, at a predetermined switching frequency Fd, from a target current Ic and measurements of the effective current leff1, leff2, leff3 and / or the effective voltage Ueff1, Ueff2, Ueff3 at the output of the output filters F1, F2, F3 delivered by a current measuring device MES and / or voltage measurements.

[0017] The regulator R is configured to determine the duty cycle Rc such that each of the effective currents leff 1, leff2, leff3 is equal or substantially equal to the target current Ic at the switching frequency Fd.

[0018] The power conversion device D comprises a control device CC intended to control the switching of the power switches of the converter CONV via a driver device DA to modulate the current, for example the direct current, injected at the input of the converter CONV in order to produce the three alternating phases of a three-phase voltage or a three-phase current, at the output of the output filters F1, F2, F3, each having an effective current equal or substantially equal to the target current Ic or an effective voltage Ueff equal or substantially equal to the target voltage Uc.

[0019] Typically, pulse width modulation (PWM) is used.

[0020] The CC control device delivers commands intended to switch the switches of the CONV converter at the switching frequency Fd with the duty cycle Rc.

[0021] These commands are, for example, switching pulses I1, I2, I3 delivered at the switching frequency Fd with a duty cycle Rc defined by the regulator R.

[0022] The switching pulses I1, I2, I3 are, for example, applied to the power switches of the power converter CONV via a driver device DA to control successive switching of each of the switches between the conductive state and the blocking state at the switching frequency Fd with the duty cycle Rc.

[0023] According to the invention, the power conversion device D comprises a particular protection device DP surrounded by dotted lines on the figure 1 .

[0024] The DP protection device according to the invention comprises: a set of at least one sensor comprising, here, sensors C1, C2, respectively C3, each making it possible to deliver a measurement m1, m2, respectively m3 representative of the instantaneous current flowing at the output of the power converter CONV on one of the phases ϕ1, ϕ2, respectively ϕ3, between power switches of the converter CONV and the output filter F1, F2, respectively F3, filtering the phase considered ϕ1, ϕ2, respectively ϕ3, a protective device CP intended to receive the measurement representative of the instantaneous current m1, m2, respectively m3, delivered by each sensor C1, C2, C3, and to be connected to the control device CC and to the power converter CONV so that the switching pulses I1, I2, I3, or more generally the commands, delivered by the control device CC are transmitted to the power converter CONV via the protective device CP,the protective device CP being configured to inhibit the switching pulses I1, I2, I3, or, more generally, the commands, when the absolute value of at least one of the measurements taken among m1, m2 and m3 exceeds a first predetermined positive threshold S1 so that the switches of the power converter CONV are kept in the blocking state.

[0025] The driver device DA is configured to maintain the power switches of the power converter CONV in the blocking state when it does not receive switching or control pulses from the control device CC, i.e. when the absolute value of at least one of the measurements taken among the measurements m1, m2 and m3 exceeds the first threshold S1, and to apply the switching or control pulses to the power switches of the converter CONV, when the driver device DA receives the switching pulses from the control device CC, i.e. when none of the absolute values ​​of the measurements m1, m2 and m3 exceeds the first threshold S1, so as to switch each of the power switches of the converter CONV between its conductive state and its blocking state at the switching frequency Fd with the duty cycle Rc.

[0026] This solution has a limited reaction time, makes it possible to avoid an excessive increase in the current flowing in the power switches following an increase in the effective current and makes it possible to avoid excessively large current differences, which makes it possible to limit the sizing of the power switches and the output filter. This solution also makes it possible to protect the converter in the event of a transient or ephemeral short circuit. It makes it possible, for example, to react before a control loop based on the regulator determining, when the measurement of at least one of the effective output currents leff1, leff2, leff3 exceeds a predetermined short-circuit current value, a particular duty cycle defined to decrease the absolute value of the effective current when the control device controls the switches from this particular duty cycle.

[0027] This solution also keeps the short-circuit current at an acceptable level while the network circuit breaker trips, which protects the converter during a permanent short circuit.

[0028] Each of the sensors C1, C2, C3 advantageously comprises a Hall effect sensor. The measurement at the sensor output is an instantaneous voltage image of the instantaneous current or a measurement of the instantaneous current. The first threshold S1 and each threshold mentioned in the remainder of the patent application is then a positive voltage or current threshold.

[0029] Each sensor may include a filter and / or an amplifier to filter and / or amplify the measurement from the Hall effect sensor.

[0030] In the non-limiting embodiment of the figures, the protective device CP comprises: a comparator device COMP configured to compare the absolute value of the measurement m1, m2, m3, representative of the instantaneous output current i1, i2, i3, delivered by each of the sensors C1, C2, C3 to the first threshold S1, an inhibitor IN connected to the converter CONV and to the control device CC so that the switching pulses or commands delivered by the control device CC are transmitted to the power converter CONV via the inhibitor IN, the inhibitor IN being configured to inhibit, i.e. mask, the switching pulses, or commands, coming from the control device CC, when the absolute value of at least one of the measurements taken among m1, m2 and m3 is greater than the first threshold S1, so as to maintain the power switches of the power converter CONV in the blocking state.

[0031] The comparator device COMP comprises, for example, three comparators CO1, CO2, CO3. Each comparator CO1, CO2 and CO3, respectively, is configured to compare the absolute value of the measurement m1, m2, and m3, respectively, representative of one of the instantaneous output currents, to the first threshold S1. Each comparator CO1, CO2, and CO3, respectively, is configured to deliver an output signal equal to 0 when the absolute value of the measurement considered m1, m2, and m3, respectively, is greater than the first threshold S1 and equal to 1 when the measurement considered m1, m2, and m3, respectively, is less than or equal to the first threshold S1.

[0032] The inhibitor IN comprises, for example, a first logic circuit ET1 with three AND inputs receiving the outputs of the three comparators CO1, CO2, CO3 and configured to deliver an output equal to 1 when the three outputs of the comparators are equal to 1 and an output equal to 0 when the output of at least one of the comparators is equal to 0.

[0033] Thus the commands or pulses I1, I2, I3 delivered by the control device CC are transmitted to the drive device DA only when the absolute values ​​of each of the measurements m1, m2 and m3 are less than or equal to the first threshold S1.

[0034] In the non-limiting example of the figures, the control device CC delivers three sets of switching pulses I1, I2, I3. Each set of switching pulses I1, I2, I3 is intended to control a subset of power switches intended to generate one of the output phases ϕ1, ϕ2, ϕ3 of the converter CONV. For this purpose, the control device CC comprises three outputs s1, s2, s3. The control device CC delivers to each of these outputs s1, s2, s3 one of the three sets of switching pulses I1, I2, I3. The inhibitor IN then comprises three second logic circuits in AND: ET21, ET22, ET23. The first input of each of the second logic circuits ET21, ET22, ET23 receives the output of the first logic circuit ET1. The second input of each of the second logic circuits ET21, ET22, ET23 is connected to one of the outputs s1, s2, s3 of the control device CC so as to receive one of the sets of switching pulses I1, I2, I3.

[0035] The output of each of the second logic circuits ET21, ET22, and respectively ET23 is thus equal to 0 when the absolute value of at least one of the measurements taken among m1, m2 and m3 is greater than the first threshold S1. The output of each of the second logic circuits ET21, ET22, and respectively ET23 is thus equal to the switching pulses I1, I2, and respectively I3, or more generally to the commands generated by the control device CC and transmitted via said output s1, s2, respectively s3, connected to the second logic circuit considered, when the absolute values ​​of the three measurements m1, m2 and m3 are less than or equal to the first threshold S1.

[0036] The driver device DA comprises, for example, three individual driver devices Da1, Da2, Da3. Each individual driver device Da1, Da2, and respectively Da3, is connected to the output of one of the second logic circuits ET21, ET22, and respectively ET23, so as to transmit the set of switching pulses I1, I2, and respectively I3, received at the input of the individual driver device Da1, Da2, and respectively Da3, to the power switches of the converter CONV which make it possible to adjust the corresponding phase ϕ1, ϕ2, and respectively ϕ3.

[0037] Advantageously, the protection device DP is configured to maintain the power switches of the converter CONV in the blocking state as long as the absolute value of at least one of the measurements taken among m1, m2 and m3 is greater than a second threshold S2 lower than the first threshold S1.

[0038] For this purpose, each of the comparators CO1, CO2, respectively CO3, is, for example, a comparator with two thresholds, including the first threshold S1 and the second threshold S2, and is configured so that its output is equal to 0, when the absolute value of the measurement m1, m2, respectively m3, is greater than the first threshold S1, and remains equal to 0 as long as the absolute value of the measurement m1, m2, respectively m3 that it receives, is greater than the second threshold S2. Each of the comparators CO1, CO2, respectively CO3 is also configured so that its output is equal to 1, once the measurement m1, m2, respectively m3, injected at the input of the comparator becomes lower than or equal to the second threshold S2 and remains equal to 1 as long as the measurement m1, m2, respectively m3, is lower than or equal to the first threshold S1.

[0039] The different thresholds thus ensure stability of control and power during a short circuit, the switches remaining in the blocking state as long as the current is between the first threshold S1 and the second threshold S2.

[0040] Advantageously, the regulator R is configured: to set the switching frequency Fd to a predetermined reference switching frequency Fref when the absolute value of each measurement m1, m2 and m3 is less than or equal to a third threshold S3 lower than the first threshold S1 and the second threshold S2 and to set the switching frequency Fd to a protection switching frequency Fpro when the absolute value of at least one of the measurements taken among m1, m2 and m3 is greater than the third threshold S3, and / or to determine the duty cycle Rc from a value of the target current Ic equal to a predetermined reference current Iref when the absolute value of each of the measurements m1, m2 and m3 is less than or equal to a third threshold S3 lower than the first threshold S1 and the second threshold S2, and to determine the duty cycle RC from a value of the target current Ic equal to a protection current Ipro lower than the reference current Iref,when the absolute value of at least one of the measurements taken among m1, m2 and m3 is greater than the third threshold S3.,

[0041] Advantageously, the duty cycle is determined from the fixed switching frequency Fd and from the fixed duty cycle.

[0042] The DC control device uses the duty cycle Rc and the value of the switching frequency Fd to generate the switching commands or pulses.

[0043] Changing the switching frequency protects the power switches from wear by limiting the losses dissipated by the power switches, and therefore the heating of these power switches, due to the reduction in the switching frequency of the converters when the third threshold S3, from which a short circuit is considered to begin, is exceeded.

[0044] Modifying the target current Ic makes it possible to bring the instantaneous current, which tends to distort in the event of a short circuit, closer to a sinusoid, which makes it possible to eliminate harmonics and therefore to size the power switches less, which is beneficial for the mass and volume of these switches.

[0045] Additionally, the controller may be configured, but is not required to be configured, to compare the RMS current measurements to a threshold RMS current and to determine, when the measurement of at least one of the RMS currents exceeds a predetermined short-circuit current, a particular duty cycle, such that the RMS current decreases when the control device operates the switches from this particular duty cycle.

[0046] In the advantageous embodiment of the figure, each sensor is intended to deliver a measurement m1, m2, respectively m3, representative of the instantaneous current flowing at the output of the power converter CONV on one of the phases ϕ1, ϕ2, respectively ϕ3, between power switches of the converter CONV and the output filter F1, F2, respectively F3, filtering the phase considered ϕ1, ϕ2, respectively ϕ3. In other words, each sensor measures a quantity representative of the instantaneous current at the input of the associated output filter.

[0047] Alternatively, each sensor measures a quantity representative of the instantaneous current at the output of the associated output filter or, for example, between an inductance and a capacitor of the output filter when the latter is an LC or RLC filter.

[0048] In the example of the figure, the protection device DP is offset relative to the driving device DA and is intended to be interposed between the driving device DA and the control device CC. Alternatively, the protection device DP is integrated into the driving device DA.

[0049] The invention has been described in the case of an inverter delivering a three-phase alternating voltage but it applies to any power converter delivering a single-phase or polyphase alternating voltage.

[0050] Those skilled in the art will be able to adapt the invention in these other cases by modifying in particular the number of comparators and the number of attack devices, each of these numbers having to be equal to the number of phases delivered by the power converter.

[0051] The control device is, for example, a microcontroller. Each device, taken from among the regulator, the control device, the driver device and the inhibitor may comprise one or more dedicated electronic circuits or a general-purpose circuit. Each electronic circuit may comprise a reprogrammable computing machine (a processor or a microcontroller for example) and / or a computer executing a program comprising a sequence of instructions and / or a dedicated computing machine (for example a set of logic gates such as an FPGA, a DSP or an ASIC, or any other hardware module).

Claims

1. A power conversion device (D) comprising a power converter (CONV) comprising power switches and intended to deliver a set of at least one AC phase, a control device (CC) intended to generate commands intended to switch the power switches between an off-state and an on-state, and a protective device comprising: - a set of at least one sensor (C1, C2, C3), each sensor in the set of at least one sensor making it possible to deliver a measurement (m1, m2, m3) representative of the instantaneous current delivered at the output of the power converter (CONV) on a phase of the set of at least one phase, - a protective device (CP) connected to the control device (CC) and to the power converter (CONV) such that the commands generated by the control device (CC) are transmitted to the power converter (DC) via the protective device (CP), the protective device receiving the measurement representative of the instantaneous current delivered by the set of at least one sensor, the protective device (CP) being configured to inhibit the commands delivered by the control device (CC) when the absolute value of the measurement representative of the instantaneous current and delivered by at least one sensor of the set of at least one sensor exceeds a predetermined first threshold (S1) such that the power switches of the power converter (CONV) are kept in the off-state, characterised in that the power conversion device comprising a regulator configured to determine a duty cycle for a predetermined chopping frequency and a predetermined target current, the control device being configured to generate the commands intended to switch the power switches at the chopping frequency with the duty cycle, the regulator receiving the measurement delivered by each sensor of the set of at least one sensor and being further configured to: - determine the duty cycle from a value of the target current at a predetermined reference current, when the absolute value of the measurement representative of the instantaneous output current and delivered by each sensor of the set of at least one sensor is less than or equal to a third threshold which is less than the first threshold and the second threshold, and to determine the duty cycle from a value of the target current which is equal to a protective current which is less than the reference current, when the absolute value of the measurement representative of the instantaneous output current and delivered by at least one sensor of the set of at least one sensor is greater than the third threshold, - and / or set the value of the chopping frequency at a predetermined reference chopping frequency, when the absolute value of the measurement representative of the instantaneous output current and delivered by each sensor of the set of at least one sensor is less than or equal to a third threshold which is less than the first threshold and the second threshold, and set the chopping frequency at a protective chopping frequency, when the absolute value of the measurement representative of the instantaneous output current and delivered by at least one sensor of the set of at least one sensor is greater than the third threshold.

2. The power conversion device according to the preceding claim, wherein the protective device (CP) comprises: - a set of at least one comparator (CO1, CO2, CO3), each comparator being configured to compare the absolute value of the measurement representative of the instantaneous current and delivered by each sensor (C1, C2, C3) of the set of at least one sensor to a first threshold (S1), - an inhibitor (IN) connected to the output of each comparator (CO1, CO2, CO3) of the set of at least one comparator and being intended to be connected to the control device (CC) and to the power converter (CONV) such that the commands delivered by the control device (CC) are transmitted to the power converter (CONV) via the inhibitor (IN), the inhibitor (IN) being configured to inhibit the commands delivered by the control device when the absolute value of the measurement representative of the instantaneous current and delivered by at least one sensor of the set of at least one sensor is greater than the first threshold (S1).

3. The power conversion device according to any one of the preceding claims, wherein the protective device (CP) is configured to inhibit the commands generated by the control device as long as the absolute value of the measurement representative of one of the instantaneous currents is greater than a second threshold (S2) which is less than the first threshold (S1).

4. The power conversion device according to any one of the preceding claims, wherein the set of at least one sensor comprises a Hall effect sensor.

5. The power conversion device according to any one of the preceding claims, wherein the power conversion device comprises a filtering assembly comprising an output filter associated with each phase of the set of at least one AC phase, each sensor of the set of at least one sensor being intended to measure a quantity representative of the instantaneous current between power switches of the power converter and an output filter of the filtering assembly.