Circulating current control method for hybrid device inverter

Abstract

The invention discloses a circulation control method for a hybrid device inverter, and the method comprises the steps: firstly, dynamically adjusting the proportion of different working modes of a hybrid device in a single power frequency period, and actively distributing the influence of circulation on two units in the hybrid device in a dynamic commutation process; secondly, the loss of the hybrid device is reduced by optimizing the turn-on delay of the hybrid device; and finally, the junction temperature of the device is stabilized in a normal range by dynamically adjusting the switching frequency of the hybrid device, the thermal characteristics of the hybrid device are improved through the three control links, and fine control of the energy conversion process is realized on the premise of not sacrificing the system performance, so that the reliability of the hybrid device is improved, and the service life of the hybrid device is prolonged.

Description

Technical Field

[0001] The invention relates to the technical field of power electronics, and in particular to a circulating current control method for a hybrid device inverter. Background Art

[0002] The hybrid device is composed of two units, Si IGBT (Silicon Insulated Gate Bipolar Transistor) and SiC MOSFET (Silicon Carbide Metal Oxide Semiconductor Field Effect Transistor), connected in parallel. By controlling the switching mode of the hybrid device, the switching loss of the hybrid device can be reduced, the switching frequency can be increased, and the overall performance of the inverter can be improved at a very low cost. At present, the control method for hybrid devices generally adopts the method of changing the switching mode of the hybrid device so that the SiC MOSFET is turned on ahead of the Si IGBT and the SiC MOSFET is turned off behind the Si IGBT to achieve control. In this switching mode, the Si IGBT with large switching loss can be turned on and off at zero voltage, reducing the switching loss of the hybrid device. At the same time, the Si IGBT with small transmission loss bears most of the forward current of the hybrid device to reduce the transmission loss of the hybrid device. However, in this switching mode, due to the unbalanced parasitic inductance between the SiC MOSFET and Si IGBT units inside the hybrid device, a loop current will be formed between the two units when the Si IGBT is turned on. This loop current will cause the current flowing through the SiC MOSFET to change slowly, causing the SiC MOSFET to continue to bear most of the conduction current, resulting in increased losses and increased junction temperature.

[0003] The differences in thermal performance and heat dissipation requirements between SiC MOSFET and SiIGBT, as well as the differences in switching characteristics and driving requirements, require users to have complex control systems with effective thermal management and effective driving to ensure that the advantages of the two devices are fully utilized while avoiding performance conflicts. However, under the currently commonly used control strategies of hybrid devices, there is a problem of excessive differences in the junction temperatures of the internal units, which has an important impact on the performance, efficiency, reliability and life of power devices. In extreme cases, excessive differences in junction temperature will cause individual units in the hybrid device to exceed their limited junction temperature, and even cause thermal breakdown or accelerated device aging, thereby failing to take advantage of the hybrid device and limiting the performance of the converter. Summary of the invention

[0004] In view of the deficiencies in the prior art, the present invention aims to provide a method for actively allocating the circulating current impact of a hybrid device inverter, by dynamically adjusting the switching mode and turn-on delay of the hybrid device, and dynamically allocating the thermal stress caused by the circulating current on SiC MOSFET and Si IGBT during the turn-on process of the hybrid device, so as to achieve fine control of the energy conversion process without sacrificing system performance, so as to improve the reliability and life of the hybrid device.

[0005] To achieve the above object, the present invention adopts the following technical solution:

[0006] A circulating current control method for a hybrid device inverter, wherein the inverter comprises a hybrid device, wherein the hybrid device comprises at least two switch elements, wherein the two switch elements are SiC MOSFET and Si IGBT respectively, and the on state or off state of the hybrid device is controlled by the two switch elements so that the inverter can convert direct current into alternating current. The circulating current control method is characterized by comprising the following steps:

[0007] S01. Obtaining the maximum junction temperature of the SiC MOSFET in the current power frequency cycle, wherein the power frequency cycle refers to the cycle of the output voltage or current of the inverter;

[0008] S02, comparing the maximum junction temperature of the SiC MOSFET in the current power frequency cycle with a preset temperature value,

[0009] If the highest junction temperature of the SiC MOSFET in the current power frequency cycle is greater than or equal to the preset temperature value, then adjusting the duration of the working mode of the hybrid device in the next power frequency cycle, wherein the working modes of the hybrid device include at least: mode 1, mode 2 and mode 3;

[0010] S03, repeating steps S01 and S02 until the maximum junction temperature of the SiC MOSFET is stabilized within a safe range, and the safe range is less than the preset temperature value.

[0011] Further, when the operation mode of the hybrid device is mode 1: the SiC MOSFET and the Si IGBT are simultaneously transformed into an on state, and the Si IGBT is first transformed into an off state, and then the SiC MOSFET is transformed into an off state;

[0012] When the operation mode of the hybrid device is mode 2: the Si IGBT is first in an on state, and the SiC MOSFET is then in an on state, and the Si IGBT is first changed to an off state, and the SiC MOSFET is then changed to an off state;

[0013] When the operation mode of the hybrid device is mode three: the SiC MOSFET is alone in an on state.

[0014] Furthermore, the step S02 further includes:

[0015] If the highest junction temperature of the SiC MOSFET in the current power frequency cycle is greater than or equal to the preset temperature value, the mode 2 is used as the working mode of the hybrid device in the maximum forward conduction current stage in the next power frequency cycle.

[0016] Furthermore, the step S02 of adjusting the duration of the working mode of the hybrid device in the next power frequency cycle includes:

[0017] A power frequency cycle of the inverter is divided into three stages, namely stage 1, stage 2 and stage 3.

[0018] The first stage is when the forward current I hy <The inflection point current I of the Si IGBT knee When the switching operation of the hybrid device is performed by adopting the mode 3;

[0019] The second stage is when the forward current I hy <Forward current mark value I of the hybrid device HY_max When the switching operation of the hybrid device is performed by adopting the mode 1;

[0020] The third stage is when the forward current I hy >The forward current mark value I of the hybrid device HY_max When the switching operation of the hybrid device is performed, the mode 2 is adopted.

[0021] Furthermore, the forward current mark value I of the hybrid device in the next power frequency cycle HY_max The method of obtaining the value of is:

[0022] In the current power frequency cycle, if the maximum junction temperature of the SiC MOSFET is greater than or equal to the preset temperature value, the forward current mark value I of the hybrid device is HY_max The value of is the forward current peak value of the hybrid device in the current power frequency cycle.

[0023] Furthermore, after executing step S03, the method further includes:

[0024] S04, adjusting the opening delay of the hybrid device, the specific adjustment method is as follows:

[0025] The maximum junction temperature of the SiC MOSFET is stabilized within a safe range, and the loss P of the SiC MOSFET in the current switching cycle is used. loss_MOS (k,j-1) and the loss P of the SiC MOSFET in the previous switching cycle loss_MOS The difference ΔP of (k,j-2) loss_MOS (k,j-1), adjust the turn-on delay t of the hybrid device in the next switching cycle on_delay (k,j),

[0026] Wherein, one power frequency cycle includes a plurality of switching cycles, and the switching cycle is a time interval for the hybrid device to switch from an on state to an on state again;

[0027] The turn-on delay is the turn-on time difference between the SiC MOSFET and the Si IGBT in the hybrid device. If the SiC MOSFET is converted to the turn-on state before the Si IGBT, the turn-on delay is a negative number; if the Si IGBT is converted to the turn-on state before the SiC MOSFET, the turn-on delay is a positive number.

[0028] Further, adjusting the turn-on delay of the hybrid device in the next switching cycle includes:

[0029] In the j-1th switching cycle of the kth power frequency cycle, k and j are integers greater than zero.

[0030] If the difference ΔP loss_MOS When (k, j-1)>0, the relationship between the turn-on delay of the hybrid device in the next switching cycle and the turn-on delay of the hybrid device in the current switching cycle is:

[0031] t on_delay (k,j)=t on_delay (k,j-1)+Δt on_delay

[0032] If the difference ΔP loss_MOS When (k, j-1)<0, the relationship between the turn-on delay of the hybrid device in the next switching cycle and the turn-on delay of the hybrid device in the current switching cycle is:

[0033] t on_delay (k,j)=t on_delay (k,j-1)

[0034] Among them, t on_delay (k, j) is the turn-on delay of the hybrid device in the next switching cycle,

[0035] t on_delay(k,j-1) is the turn-on delay of the hybrid device in the current switching cycle,

[0036] Δt on_delay =0.002us.

[0037] Furthermore, the maximum junction temperature of the SiC MOSFET and / or the Si IGBT is obtained by the loss of the hybrid device, and the loss of the hybrid device includes turn-on loss, conduction loss and turn-off loss, wherein the calculation formula of the conduction loss of the hybrid device is:

[0038] If δ i >t trans (i)

[0039]

[0040] If δ i <t trans (i)

[0041]

[0042] Wherein, δi is the pulse width of the i-th pulse in unipolar modulation, that is, the conduction time of the hybrid device in the i-th switching cycle; t trans (i,T j_MOS ) is the circulating current decay time in the i-th switching cycle; E cond_MOS (i,T j_MOS ) is the conduction loss of SiC MOSFET in the i-th switching cycle;

[0043] E cond_IGBT (i,T j_IGBT ) is the conduction loss of Si IGBT in the i-th switching cycle; I MOS (i) is the steady current flowing through the SiC MOSFET after the hybrid device is asynchronously turned on; I IGBT (i) is the steady current flowing through the Si IGBT when the hybrid device is asynchronously turned on; R MOS (T j_MOS ) is the on-resistance of SiC MOSFET;

[0044] R IGBT (T j_IGBT ) is the equivalent on-resistance of Si IGBT;

[0045] The calculation formula of δi is:

[0046]

[0047] θ i is the center point of the ith pulse; i is an integer; T sis the power frequency cycle; n is the number of pulses in half a power frequency cycle; U r is the modulation wave; U dc Input DC voltage;

[0048] I MOS (i) and (I) IGBT The calculation formulas for (i) are:

[0049]

[0050] I hy (i) is the forward current of the hybrid device in the i-th switching cycle; I peak is the peak forward current of the hybrid device; i is an integer; T j_MOS is the junction temperature of SiC MOSFET during operation; T j_IGBT is the junction temperature of Si IGBT during operation; V knee is the knee voltage of Si IGBT;

[0051] E trans_MOS is the commutation loss of SiC MOSFET, E trans_IGBT is the commutation loss of Si IGBT, t trans is the circulation decay time, and the calculation formula is:

[0052]

[0053]

[0054] Among them, [p 00 , p 10 , p 01 , p 20 , p 11 , p 02 , p 21 , p 12 , p 03 ] T is the fitting parameter of SiC MOSFET commutation loss under double pulse experiment; [q 00 ,q 10 ,q 01 ,q 20 ,q 11 ,q 02 ,q 21 ,q 12 ,q 03 ] T is the Si IGBT commutation loss fitting parameter; [r 00 , r 10 , r 01 , r 20 , r 11 , r 02, r 21 , r 12 , r 03 ] T is the circulation decay time fitting parameter, E on_MOS is the turn-on loss of SiC MOSFET.

[0055] Further, after the maximum junction temperature of the SiC MOSFET is stabilized within a safe range less than the preset temperature value and the loss of the SiC MOSFET is reduced and reaches a stable state, the method further includes:

[0056] S05. In the current power frequency cycle, if the highest junction temperature of the Si IGBT is greater than the preset temperature value, the switching frequency of the next power frequency cycle is adjusted.

[0057] Furthermore, the specific method for adjusting the switching frequency is:

[0058] f(k)=f(k-1)-Δf, Δf=0.1·f(k-1)

[0059] Wherein, f(k-1) is the switching frequency of the current power frequency cycle;

[0060] f(k) is the switching frequency of the next power frequency cycle.

[0061] The beneficial effects of the present invention are:

[0062] The present invention discloses a hybrid device inverter circulating current control method, by adjusting the proportion of mode one and mode two of the hybrid device in a single power frequency cycle, if the highest junction temperature of SiC MOSFET exceeds the set limit, then in the next power frequency cycle, the maximum forward conduction current stage is gradually introduced as the hybrid device working mode, thereby improving the thermal stress caused by the circulating current to the SiC MOSFET in the hybrid device; by optimizing the switching delay of the hybrid in each stage, the loss of the hybrid device is reduced; by reducing the switching frequency of the hybrid device, the loss of Si IGBT is reduced, so that the junction temperature of Si IGBT is stabilized in a normal range. Through the above three control links, the thermal characteristics of the hybrid device are improved, and the reliability of the hybrid device is maximized while maintaining the normal working range of the inverter. BRIEF DESCRIPTION OF THE DRAWINGS

[0063] The drawings constituting a part of this application are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0064] Figure 1 Flow chart of the circulating current control method of the hybrid device inverter of the present invention;

[0065] Figure 2 The hybrid device inverter topology structure and circulating current control block diagram of the present invention;

[0066] Figure 3 The hybrid inverter of the present invention controls the switching mode within one power frequency cycle;

[0067] Figure 4 The hybrid device inverter circulation control flow chart of the present invention;

[0068] Figure 5 The hybrid device turn-on loss and the transfer loss caused by the circulating current vary with the turn-on delay;

[0069] Figure 6 Unipolar PWM modulation principle. DETAILED DESCRIPTION

[0070] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0071] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0072] It should be noted that the terms "first", "second", etc. in the specification and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchanged where appropriate, so as to describe the embodiments of the present invention described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0073] Figure 2 This is a topology and control block diagram of a hybrid device inverter. In the figure, A represents the hybrid device inverter topology, B represents the voltage and current dual-loop control, C represents the circulating current influence controller, and D represents the thermocouple hybrid model.

[0074] The method of the present invention is based on Figure 2The hybrid device inverter topology shown in the figure is designed, the DC side of the inverter is connected to a DC power supply, and the AC side is connected to a filter circuit and a resistive load. The overall design concept of the present invention is to improve the thermal characteristics of the hybrid device, reduce the cost of the hybrid device, and improve the life and reliability of the hybrid device without affecting the output voltage and current distortion rate.

[0075] Figure 2 A in U dc is the power supply; C dc is the DC side capacitance; S n (n=1,2,3,4) is a hybrid device; L n (n=1,2) is the filter inductor; C is the filter capacitor; R is the load, I0 is the output current, and U0 is the output voltage.

[0076] Figure 2 In B, PWM is a pulse modulation controller, PID is a proportional, differential, integral controller, PI is a proportional, integral controller, Uref is a reference voltage, t on_delay represents the turn-on delay, and f represents the switching frequency, that is, the carrier frequency of the PWM pulse modulation controller.

[0077] Figure 2 C and Figure 2 D, G HYS represents the driving signal of the hybrid device, G MOS Represents the driving signal of SiC MOSFET, G IGBT Represents the driving signal of Si IGBT, I hy I hy is the forward current of the hybrid device; the turn-on and turn-off delays of the hybrid device include the turn-on delay t on_delay and turn-off delay t off_delay , t on_delay If it is negative, it means that the hybrid device SiC MOSFET is turned on earlier, t on_delay The positive expression indicates the delayed turn-on time of the hybrid device SiC MOSFET; t off_delay represents the turn-off time of the hybrid device, i.e., the turn-off time of the SiC MOSFET lags behind that of the Si IGBT;

[0078] T j_MOS is the junction temperature of SiC MOSFET during operation; T j_IGBT is the junction temperature of Si IGBT during operation; P loss_MOS is the loss of SiCMOSFET; P loss_IGBT is the loss of SiIGBT; P loss_all is the loss of the hybrid device; T C_MOS is the case temperature of SiCMOSFET during operation; T C_IGBT is the case temperature of the Si IGBT during operation.

[0079] The power frequency cycle refers to the cycle of the output voltage or current of the inverter. The output voltage cycle refers to the time length for the voltage to complete one positive and one negative change in a complete cycle; the output current cycle refers to the time length for the current to complete one positive and one negative change in a complete cycle. A power frequency cycle includes multiple switching cycles, and the switching cycle is the time interval for the hybrid device to switch from the on state to the on state again.

[0080] A hybrid device inverter circulating current control method in this embodiment includes three control links:

[0081] The first step: adjusting the working mode of the hybrid device: In this embodiment, the switching mode of the hybrid device is adjusted according to the value of the maximum junction temperature of the SiC MOSFET to ensure that the SiC MOSFET operates at a normal junction temperature. If the maximum junction temperature of the SiC MOSFET is greater than or equal to the preset temperature value in the current power frequency cycle, and the preset temperature value is 150°C, then in the next power frequency cycle, the maximum forward conduction current stage is gradually introduced as the working mode of the hybrid device. That is, by adjusting the duration of different working modes of the hybrid device in the next power frequency cycle, the influence of the circulating current on the two units inside the hybrid device under different forward currents is optimized, the thermal characteristics of the hybrid device are improved, and the reliability of the hybrid device is maximized while maintaining the normal working range of the inverter.

[0082] The standard maximum operating junction temperature of commercial SiC MOSFET is 175°C, and the standard maximum operating junction temperature of commercial Si IGBT is 150°C. In the present invention, after the switch mode is changed, part or all of the turn-on process loss of the hybrid device is borne by the Si IGBT during the switching cycle with a large forward current, but the SiC MOSFET still bears all the turn-off losses of the hybrid device. Therefore, the selected SiC MOSFET maximum junction temperature critical value needs to leave a junction temperature rise margin, and the temperature value is 150°C.

[0083] like Figure 2 As shown, the hybrid device in this embodiment has the following three working modes:

[0084] Mode 1: Si IGBT and SiC MOSFET are turned on at the same time, and SiC MOSFET is turned off later than Si IGBT.

[0085] Mode 2: Si IGBT is turned on before SiC MOSFET, and SiC MOSFET is turned off later than Si IGBT.

[0086] Mode 3: SiC MOSFET is turned on independently.

[0087] This embodiment adjusts the working mode of the hybrid device in the next power frequency cycle according to the working condition of the inverter in the current power frequency cycle.

[0088] like Figure 2 As shown, within one power frequency cycle of the inverter, according to symmetry, a quarter of the power frequency cycle can be optimized. In this embodiment, one power frequency cycle of the inverter is divided into three stages:

[0089] When the hybrid device forward current I hy <Hybrid Devices The inflection point current I of Si IGBT in hybrid devices knee It is stage 1, at this time, the hybrid device transmission current is small, and the turn-on condition of the Si IGBT in the hybrid device is not met. All the forward current flows through the SiC MOSFET in the hybrid device, and mode 3 is used to perform the switching operation of the hybrid device;

[0090] When I hy Hybrid device forward current < Hybrid device forward current marked value I HY_max It is stage two, and switching mode one is adopted. In this stage, the loss caused by the circulating current is small, and mode one is adopted to perform the switching operation of the hybrid device. In this mode, the SiC MOSFET bears the impact caused by the circulating current.

[0091] When the hybrid device forward current I hy > Hybrid device forward current mark value I HY_max It is stage three. In this stage, the loss caused by the circulating current is large. Mode two is used to perform the switching operation of the hybrid device, so that the influence of the circulating current is transferred to the Si IGBT. The Si IGBT bears the influence of the circulating current, alleviates the influence of the circulating current on the SiC MOSFET, and ensures that the SiC MOSFET works at a normal junction temperature.

[0092] The working mode of the hybrid device in the next power frequency cycle is adjusted according to the working condition of the inverter in the current power frequency cycle. Specifically, the junction temperature T of the SiC MOSFET in the current power frequency cycle of the inverter is adjusted. j_MOS , set the duration of different working modes of the hybrid device in the next power frequency cycle, and complete the adjustment of the working mode of the hybrid device. The specific situation is as follows:

[0093] In the early stage of hybrid inverter operation, switch mode 1 and switch mode 3 are used in segments within a power frequency cycle. The critical switching point is when the forward current of the hybrid device reaches the knee current, that is, Iknee. If the load power of the hybrid inverter is continuously increased, the current power frequency cycle is defined as the kth power frequency cycle. If the junction temperature T j_MOS_max(k) When the device reaches the set safe operation junction temperature critical value, the peak value of the hybrid device forward current at this time is recorded as I HY_max (k), then in the k+1th power frequency cycle, when the forward current I hy (k+1,j)>I HY_max (k), then switch mode 2 is used from now on. Repeat the above method to adjust the proportion of switch mode 1 and switch mode 2 in each power frequency cycle after the load power of the hybrid device increases until the junction temperature of the SiC MOSFET is stabilized within the normal range, completing the first stage of regulation.

[0094] In the first stage, the turn-on delay and turn-off delay of the hybrid device are fixed values, which facilitates the rapid optimization of this stage and ensures that the hybrid device operates at a safe junction temperature.

[0095] The second link: adjust the switching delay of the hybrid device. As the load power of the hybrid device inverter increases, under the regulation of the first link, the proportion of the switching operation of the hybrid device in one power frequency cycle using mode 2 increases, so that the impact of the circulating current gradually transfers to the IGBT. It is necessary to further optimize the opening delay t of the hybrid device at each stage. on_delay , and reduce the loss of hybrid devices. Ensuring that the hybrid devices work at a safe junction temperature, while reducing device losses and improving converter efficiency, is of great significance for improving the thermal characteristics of hybrid devices and increasing the life and reliability of hybrid devices.

[0096] The maximum junction temperature of SiC MOSFET is stable within the normal range. That is, after the first stage, the proportion of switching mode has been determined and the optimization of t on_delay To reduce the loss of the hybrid device, the turn-on delay of the SiC MOSFET in the next switching cycle is adjusted by comparing the loss of the SiC MOSFET in the current switching cycle with that in the previous switching cycle. Figure 5 It can be seen that the turn-on loss of the hybrid device and the commutation loss caused by commutation both reach a minimum value near the turn-on delay of 0us. In order to make the hybrid device work at a safe junction temperature and achieve the minimum loss at the same time, the fixed turn-on delay of the switch mode 1 used in the present invention is 0us. Therefore, it is only necessary to optimize the turn-on delay of the switch mode 2, which specifically includes:

[0097] In the j-1th switching cycle of the kth power frequency cycle, if ΔP loss_MOS (k,j-1)=P loss_MOS (k,j-1)-P loss_MOS When (k,j-2)>0, it means that the loss of the MOSFET unit is increasing. Then, in the next switching cycle, t on_delay (k,j)=t on_delay (k,j-1)+Δton_delay , if ΔP loss_MOS When (k,j-1)<0, it means that the loss of the MOSFET unit is decreasing. Then, in the next switching cycle, t on_delay (k,j)=t on_delay (k,j-1), and so on to complete the switching delay optimization of all switching cycles included in the third stage within the kth power frequency cycle, so that the loss of SiC MOSFET is reduced and reaches a stable state.

[0098] Complete one power frequency cycle [0,1 / 4T S After the optimization in the period, according to the symmetry, the switching delay in the remaining period is [0,1 / 4T S ]The switch delay distribution during the period is the same.

[0099] After the switch delay within one quarter of the power frequency cycle is optimized in this embodiment, the switch delays of the remaining parts are made equal according to symmetry, thereby reducing the calculation amount of the controller.

[0100] This embodiment calculates the loss and junction temperature by establishing a hybrid device loss model and a junction temperature estimation model.

[0101] In each switching cycle of the hybrid device, the loss of each unit in the hybrid device is calculated and compared with the loss of each unit in the hybrid device in the previous switching cycle, and then the turn-on delay in the next switching cycle is changed. The loss of each unit in the hybrid device is related to the turn-on delay and the size of the forward current. Its loss needs to be modeled to achieve active distribution of the impact of circulating current during the operation of the hybrid device. According to the switching process, the operating loss of the power device is divided into turn-on loss, conduction loss and turn-off loss. Due to its unique turn-on mode, there is a dynamic current flow between internal units of the hybrid device, and the working energy consumption includes commutation loss caused by circulating current. Therefore, the conduction loss of the hybrid device is divided into commutation loss and transmission loss. According to the current change during the switching operation of the hybrid device, the conduction loss of the hybrid device is divided and modeled in detail. Among them, the calculation formula of the conduction loss of the hybrid device is:

[0102] If δ i >t trans (i)

[0103]

[0104] If δ i <t trans (i)

[0105]

[0106] Among them, δ iis the pulse width of the ith pulse in unipolar modulation, i.e., the on-time of the hybrid device in the ith switching cycle, t trans (i,T j_MOS ) is the circulating current decay time in the i-th switching cycle, E cond_MOS (i,T j_MOS ) is the conduction loss of SiC MOSFET in the i-th switching cycle,

[0107] E cond_IGBT (i,T j_IGBT ) is the conduction loss of Si IGBT in the i-th switching cycle, t on_delay (i) is the turn-on delay of the hybrid device in the i-th switching cycle, f s is the power frequency, t is the time; R MOS (T j_MOS ) is the on-resistance of SiC MOSFET, R IGBT (T j_IGBT ) is the equivalent on-resistance of Si IGBT, I MOS (i) and I IGBT (i) The steady current flowing through the SiC MOSFET and Si IGBT after the hybrid device is asynchronously turned on.

[0108] δ i The calculation formula is:

[0109]

[0110] θ i is the center point of the ith pulse, i is an integer, T s is the switching cycle, n is the number of pulses in half a power frequency cycle, U r Rated voltage, U dc is the input DC voltage,

[0111] I MOS (i) and I IGBT The calculation formula for (i) is:

[0112]

[0113] I hy (i) is the forward current of the hybrid device in the i-th switching cycle, I peak is the peak forward current of the hybrid device, i is an integer, T s is the power frequency cycle, n is the number of pulses in half a power frequency cycle, f s is the power frequency, T j_MOS is the junction temperature of the SiC MOSFET during operation, T j_IGBT is the junction temperature of Si IGBT during operation, R MOSis the on-resistance of SiC MOSFET, R IGBT is the equivalent on-resistance of Si IGBT, V knee is the Si IGBT knee voltage.

[0114] Where E trans_MOS , E trans_IGBT are the commutation losses of SiC MOSFET and Si IGBT, respectively. trans is the circulation decay time, and the calculation formula is:

[0115]

[0116] Among them, [p 00 , p 10 , p 01 , p 20 , p 11 , p 02 , p 21 , p 12 , p 03 ] T is the fitting parameter of SiC MOSFET commutation loss under double pulse experiment; [q 00 ,q 10 ,q 01 ,q 20 ,q 11 ,q 02 ,q 21 ,q 12 ,q 03 ] T is the Si IGBT commutation loss fitting parameter; [r 00 , r 10 , r 01 , r 20 , r 11 , r 02 , r 21 , r 12 , r 03 ] T is the circulation decay time fitting parameter, E on_MOS is the turn-on loss of SiC MOSFET

[0117] The third step: adjust the switching frequency.

[0118] As the load power increases, the hybrid device forward current I hyThe third stage proportion increases accordingly, that is, in one power frequency cycle, the Si IGBT is turned on more often. Since the Si IGBT turn-on loss is large, the Si IGBT junction temperature increases. In this example, the switching frequency of the hybrid device is reduced to reduce the loss, so that the Si IGBT junction temperature is stabilized within the normal range. The specific method is as follows:

[0119] In the k-1th power frequency cycle, if the maximum junction temperature of the Si IGBT exceeds the set device safe operation junction temperature critical value, which is 150°C, then in the k+1th power frequency cycle, f(k)=f(k-1)-Δf, Δf=0.1·f(k-1).

[0120] like Figure 4 As shown, the circulating current control process of the hybrid device inverter of the present invention is as follows:

[0121] S1. Estimation of T j_MOS_max (k-1), T j_IGBT_max (k-1);

[0122] T j_MOS_max (k-1) is the maximum junction temperature of SiC MOSFET in the current power frequency cycle, T j_IGBT_max (k-1) is the maximum junction temperature of Si IGBT in the current power frequency cycle;

[0123] S2. Judge T j_MOS_max (k-1) is greater than or equal to 150℃; if not, let t on_delay (k) = t on_delay (k-1)=0; if yes, proceed to step S3;

[0124] t on_delay (k) is the turn-on delay of the hybrid device in the next power frequency cycle, t on_delay (k-1) is the turn-on delay of the hybrid device in the current power frequency cycle;

[0125] S3. Judge T j_IGBT_max (k-1) is greater than or equal to 150°C; if so, let f(k)=f(k-1)-Δf and go to step S4; if not, let f(k)=f(k-1) and go to step S4;

[0126] f(k) is the frequency of the next power frequency cycle, f(k-1) is the frequency of the current power frequency cycle, Δf=0.1·f(k-1);

[0127] S4. Let I HY_max =I peak (k-1), and judge I peak (k,j-1)>I HY_maxIs it true? If so, calculate △P loss_mos =P loss_mos (k,j-1)-P loss_mos (k, j-2), and go to step S5; if not, let t on_delay (k,j)=t on_delay (k,j-1)=0;

[0128] I HY_max is the forward current mark value of the hybrid device, I peak (k-1) is the peak forward current of the hybrid device in the current power frequency cycle, I(k,j-1) is the forward current value of the hybrid device in the current switching cycle, P loss_MOS (k,j-1) is the loss of the SiC MOSFET in the current switching cycle, P loss_MOS (k,j-2) is the loss of the SiC MOSFET in the previous switching cycle, ΔP loss_MOS (k,j-1) is P loss_MOS (k,j-1) and P loss_MOS The difference between (k,j-2). on_delay (k,j) is the turn-on delay of the hybrid device in the next switching cycle, t on_delay (k,j-1) is the turn-on delay of the current switching cycle.

[0129] S5. Calculate △P loss_mos =P loss_mos (k,j-1)-P loss_mos (k,j-2), and judge △P loss_mos >0 is true, if so, then t on_delay (k,

[0130] j)=t on_delay (k,j-1)+△t on_delay , if not, then t on_delay (k,j)=t on_delay (k,j-1).

[0131] In summary, the present invention discloses a method for controlling circulating current of a hybrid device inverter. By adjusting the proportion of mode 1 and mode 2 of the hybrid device in a single power frequency cycle, if the maximum junction temperature of the SiC MOSFET exceeds the set limit, mode 2 is gradually introduced as the working mode of the hybrid device in the maximum forward conduction current stage in the next power frequency cycle, thereby adjusting the degree of influence of the circulating current on the two units inside the hybrid device during the dynamic commutation process; by optimizing the switching delay of the mixer in each stage, the loss of the hybrid device is reduced; by reducing the switching frequency of the hybrid device to reduce the SiIGBT loss, the junction temperature of the Si IGBT is stabilized within the normal range, and through the above three control links, the thermal characteristics of the hybrid device are improved, and the reliability of the hybrid device is maximized while maintaining the normal working range of the inverter.

[0132] For those skilled in the art, various other corresponding changes and deformations can be made according to the technical solutions and concepts described above, and all of these changes and deformations should fall within the protection scope of the claims of the present invention.

Claims

1. A circulating current control method for a hybrid device inverter, wherein the inverter comprises a hybrid device, wherein the hybrid device comprises at least two switch elements, wherein the two switch elements are SiC MOSFET and Si IGBT, respectively, and the on state or off state of the hybrid device is controlled by the two switch elements so that the inverter can convert direct current into alternating current. The circulating current control method is characterized in that: The steps include: S01. Obtaining the maximum junction temperature of the SiC MOSFET in the current power frequency cycle, wherein the power frequency cycle refers to the cycle of the output voltage or current of the inverter; S02, comparing the maximum junction temperature of the SiC MOSFET in the current power frequency cycle with a preset temperature value, If the highest junction temperature of the SiC MOSFET in the current power frequency cycle is greater than or equal to the preset temperature value, then adjusting the duration of the working mode of the hybrid device in the next power frequency cycle, wherein the working modes of the hybrid device include at least: mode 1, mode 2 and mode 3; S03, repeating steps S01 and S02 until the maximum junction temperature of the SiC MOSFET is stabilized within a safe range, and the safe range is less than the preset temperature value.

2. The hybrid device inverter circulating current control method according to claim 1, characterized in that: When the operation mode of the hybrid device is mode 1: the SiC MOSFET and the Si IGBT are simultaneously transformed into an on state, and the Si IGBT is first transformed into an off state, and then the SiC MOSFET is transformed into an off state; When the operation mode of the hybrid device is mode 2: the Si IGBT is first in an on state, and then the SiC MOSFET is in an on state, and the Si IGBT is first changed to an off state, and then the SiC MOSFET is changed to an off state; When the operation mode of the hybrid device is mode three: the SiC MOSFET is alone in an on state.

3. A hybrid device inverter circulating current control method according to claim 2, characterized in that: The step S02 further includes: If the highest junction temperature of the SiC MOSFET in the current power frequency cycle is greater than or equal to the preset temperature value, the mode 2 is used as the working mode of the hybrid device in the maximum forward conduction current stage in the next power frequency cycle.

4. A hybrid device inverter circulating current control method according to claim 3, characterized in that: The step S02 of adjusting the duration of the working mode of the hybrid device in the next power frequency cycle includes: A power frequency cycle of the inverter is divided into three stages, namely stage 1, stage 2 and stage 3. The first stage is when the forward current I hy <The inflection point current I of the Si IGBT knee When the switching operation of the hybrid device is performed by adopting the mode 3; The second stage is when the forward current I hy <Forward current mark value I of the hybrid device HY_max When the switching operation of the hybrid device is performed by adopting the mode 1; The third stage is when the forward current I hy >The forward current mark value I of the hybrid device HY_max When the switching operation of the hybrid device is performed, the mode 2 is adopted.

5. A hybrid device inverter circulating current control method according to claim 4, characterized in that: The forward current mark value I of the hybrid device in the next power frequency cycle HY_max The method of obtaining the value of is: In the current power frequency cycle, if the maximum junction temperature of the SiC MOSFET is greater than or equal to the preset temperature value, the forward current mark value I of the hybrid device is HY_max The value of is the forward current peak value of the hybrid device in the current power frequency cycle.

6. The hybrid device inverter circulating current control method according to claim 1, characterized in that: After executing step S03, the method further includes: S04, adjusting the opening delay of the hybrid device, the specific adjustment method is as follows: The maximum junction temperature of the SiC MOSFET is stabilized within a safe range, and the loss P of the SiC MOSFET in the current switching cycle is used. loss_MOS (k,j-1) and the loss P of the SiC MOSFET in the previous switching cycle loss_MOS The difference ΔP of (k,j-2) loss_MOS (k,j-1), adjust the turn-on delay t of the hybrid device in the next switching cycle on_delay (k,j), Wherein, one power frequency cycle includes a plurality of switching cycles, and the switching cycle is a time interval for the hybrid device to switch from an on state to an on state again; The turn-on delay is the turn-on time difference between the SiC MOSFET and the Si IGBT in the hybrid device. If the SiC MOSFET is converted to the turn-on state before the Si IGBT, the turn-on delay is a negative number; if the Si IGBT is converted to the turn-on state before the SiC MOSFET, the turn-on delay is a positive number.

7. A hybrid device inverter circulating current control method according to claim 6, characterized in that: The adjusting the turn-on delay of the hybrid device in the next switching cycle includes: In the j-1th switching cycle of the kth power frequency cycle, k and j are integers greater than zero. If the difference ΔP loss_MOS When (k, j-1)>0, the relationship between the turn-on delay of the hybrid device in the next switching cycle and the turn-on delay of the hybrid device in the current switching cycle is: t on_delay (k,j)=t on_delay (k,j-1)+Δt on_delay If the difference ΔP loss_MOS When (k, j-1)<0, the relationship between the turn-on delay of the hybrid device in the next switching cycle and the turn-on delay of the hybrid device in the current switching cycle is: t on_delay (k,j)=t on_delay (k,j-1) Among them, t on_delay (k, j) is the turn-on delay of the hybrid device in the next switching cycle, t on_delay (k,j-1) is the turn-on delay of the hybrid device in the current switching cycle, Δt on_delay =0.002us。 8. A hybrid device inverter circulating current control method according to claim 1 or 6, characterized in that: The maximum junction temperature of the SiCMOSFET and / or the Si IGBT is obtained by the loss of the hybrid device, and the loss of the hybrid device includes turn-on loss, conduction loss and turn-off loss. The calculation formula of the conduction loss of the hybrid device is: If δ i > t trans (i), if i <t trans (i), Wherein, δi is the pulse width of the i-th pulse in unipolar modulation, that is, the conduction time of the hybrid device in the i-th switching cycle; t trans (i,T j_MOS ) is the circulating current decay time in the i-th switching cycle; E cond_MOS (i,T j_MOS ) is the conduction loss of SiC MOSFET in the i-th switching cycle; E cond_IGBT (i,T j_IGBT ) is the conduction loss of Si IGBT in the i-th switching cycle; I MOS (i) is the steady current flowing through the SiC MOSFET after the hybrid device is asynchronously turned on; I IGBT (i) is the steady current flowing through the Si IGBT when the hybrid device is asynchronously turned on; R MOS (T j_MOS ) is the on-resistance of SiC MOSFET; R IGBT (T j_IGBT ) is the equivalent on-resistance of Si IGBT; The calculation formula of δi is: θ i is the center point of the ith pulse; i is an integer; T s is the power frequency cycle; n is the number of pulses in half a power frequency cycle; U r is the modulation wave; U dc Input DC voltage; I MOS (i) and (I) IGBT The calculation formulas for (i) are: I hy (i) is the forward current of the hybrid device in the i-th switching cycle; I peak is the peak forward current of the hybrid device; i is an integer; T j_MOS is the junction temperature of SiC MOSFET during operation; T j_IGBT is the junction temperature of Si IGBT during operation; V knee is the knee voltage of Si IGBT; E trans_MOS is the commutation loss of SiC MOSFET, E trans_IGBT is the commutation loss of Si IGBT, t trans is the circulation decay time, and the calculation formula is: Among them, [p 00 , p 10 , p 01 , p 20 , p 11 , p 02 , p 21 , p 12 , p 03 ] T is the fitting parameter of SiC MOSFET commutation loss under double pulse experiment; [q 00 ,q 10 ,q 01 ,q 20 ,q 11 ,q 02 ,q 21 ,q 12 ,q 03 ] T is the Si IGBT commutation loss fitting parameter; [r 00 , r 10 , r 01 , r 20 , r 11 , r 02 , r 21 , r 12 , r 03 ] T is the circulation decay time fitting parameter, E on_MOS is the turn-on loss of SiC MOSFET.

9. The hybrid device inverter circulating current control method according to claim 7, characterized in that: After the maximum junction temperature of the SiC MOSFET is stabilized within a safe range less than the preset temperature value and the loss of the SiC MOSFET is reduced and reaches a stable state, the method further includes: S05. In the current power frequency cycle, if the highest junction temperature of the Si IGBT is greater than the preset temperature value, the switching frequency of the next power frequency cycle is adjusted.

10. A hybrid device inverter circulating current control method according to claim 9, characterized in that: The specific method of adjusting the switching frequency is: f(k)=f(k-1)-Δf, Δf=0.1·f(k-1); Where, f(k-1) is the switching frequency of the current power frequency cycle; f(k) is the switching frequency of the next power frequency cycle.

Images