Power conversion system

Abstract

Power conversion system, comprehensive: - a large number of interconnected power modules (1, 2); - a multitude of control circuits (7, 8) which each control the multitude of power modules (1, 2) based on input signals; - a multitude of correction sections (9, 10) which each correct the input signals fed into the multitude of control circuits (7, 8) based on a multitude of correction values; - a temperature detection section (3) that detects the operating temperatures of the plurality of power modules (1, 2); and - a calculation section (12), - estimates the current switching characteristics of the plurality of power modules (1, 2) based on the measured operating temperatures and a temperature dependence of the switching characteristics of the plurality of power modules (1, 2) and - the multitude of correction values ​​calculated based on the estimated current switching characteristics to reduce fluctuations in currents flowing through the multitude of power modules (1, 2), wherein the switching characteristic is at least a rise time, a fall time, a time period required to switch on, a time period required to switch off, a switch-on delay time, a switch-off delay time, a total value of a switch-on delay time and a rise time, and a total value of a switch-off delay time and a fall time.

Description

Background of the invention: Area

[0001] The present invention relates to a power conversion system capable of reducing fluctuations in currents flowing through a plurality of parallel interconnected power modules. background

[0002] A power conversion system, such as an inverter device, is composed of a multitude of power modules equipped with switching devices, such as IGBTs or MOSFETs, connected in parallel and configured to achieve a required output capacity by causing these power modules to perform switching operations. It is known that an unbalanced current distribution, caused by fluctuations in the characteristics of the multitude of power modules, not only leads to system malfunctions or adverse effects on the characteristics, but also to temperature increases due to current concentration, system failure, or a reduction in the system's lifetime. A method is proposed which determines ON / OFF times, or...- Time controls of a large number of parallel interconnected switching devices based on information about the electrical characteristics of the switching devices, which was generated on the basis of test results (e.g. see patent literature 1: JP 2009- 225 531 A).

[0003] Publication JP 2017-158 319 A discloses a control circuit for power semiconductors that can compensate not only for current imbalances during a switching operation but also for current imbalances during normal operation. This known control circuit for power semiconductors comprises several driver components, each corresponding to several power semiconductors connected in parallel. A host control circuit section is provided to control the driver components. This section converts the gate voltage dependence of the turn-on voltages of the power semiconductors at a target current into linearly approximated functions and calculates the gate voltage of the power semiconductors based on these linearly approximated functions for a target turn-on voltage. The driver components then control the power semiconductors based on the gate voltage calculated by the host control circuit section. Summary

[0004] However, the switching characteristics of the parallel-connected power modules are not solely determined by the characteristics of the respective switching devices. For example, temperature fluctuations can occur due to the influence of the arrangement of power modules on a cooling system, which in actual operation generates fluctuations in the currents flowing through the multitude of power modules, resulting in a deviation in the switching characteristics.

[0005] The present invention was implemented to solve the problems described above, and it is an object of the present invention to provide a power conversion system capable of reducing fluctuations in currents flowing through a plurality of power modules connected in parallel.

[0006] The problem underlying the invention is solved according to the invention in a power conversion system by the features of claim 1. Advantageous further developments are the subject of the respective dependent claims.

[0007] A power conversion system according to the present invention comprises: a plurality of power modules connected in parallel; a plurality of drive circuits, each of which drives the plurality of power modules based on input signals; a plurality of correction sections, each of which corrects the input signals fed into the plurality of drive circuits based on a plurality of correction values; a temperature detection section, which detects operating temperatures of the plurality of power modules;and a calculation section that estimates the current switching characteristics of the multitude of power modules based on the measured operating temperatures and a temperature dependence of the switching characteristics of the multitude of power modules, and calculates the multitude of correction values ​​based on the estimated current switching characteristics to reduce fluctuations in currents flowing through the multitude of power modules. The switching characteristic is at least one consisting of a rise time, a fall time, a time required to turn on, a time required to turn off, a turn-on delay time, a turn-off delay time, a total value of a turn-on delay time and a rise time, and a total value of a turn-off delay time and a fall time.

[0008] In the present invention, the current switching characteristics of the plurality of power modules are estimated based on the measured operating temperature and the temperature dependence of the switching characteristics. A plurality of correction values ​​are calculated based on the estimated current switching characteristics to reduce fluctuations in the currents flowing through the plurality of power modules. A plurality of input signals, which are to be fed into the plurality of control circuits, are each corrected based on the plurality of correction values. This makes it possible to reduce fluctuations in the currents flowing through the plurality of power modules connected in parallel.

[0009] Other and further tasks, features and advantages of the invention will become more fully apparent from the following description. Brief description of the drawings Fig. Figure 1 is a circuit diagram illustrating a power conversion system according to a first embodiment. Fig. Figure 2 is a diagram illustrating a collector current Ic and a collector-emitter voltage Vce of the switching device controlled based on an input signal VIN. Fig. Figure 3 is a diagram illustrating a method for estimating the switching characteristic. Fig. Figure 4 is a diagram illustrating a flowing current when the ON timers of the two power modules do not match. Fig. Figure 5 is a diagram illustrating a flowing current when the ON timers of the two power modules are synchronized. Fig. Figure 6 is a diagram illustrating a power conversion system according to a second embodiment. Fig. Figure 7 is a diagram illustrating a power conversion system according to a third embodiment. Description of embodiments

[0010] A power conversion system according to the embodiments of the present invention is described with reference to the drawings. The same components are designated by the same symbols, and their repeated description can be omitted. First embodiment

[0011] Fig. Figure 1 is a diagram illustrating a power conversion system according to a first embodiment. A plurality of power modules 1 and 2, connected in parallel, operate in phase with each other. Each of the power modules 1 and 2 is a half-bridge circuit containing two switching devices SW1 and SW2, such as IGBTs or MOSFETs. Freewheeling diodes D1 and D2 are connected in reverse parallel to the switching devices SW1 and SW2, respectively.

[0012] Power modules 1 and 2 are each equipped with a temperature detection section 3, and the temperature detection section 3 outputs an operating temperature of the corresponding power module. The temperature detection section 3 is, for example, a temperature-sensing diode arranged on the switching device SW1 or SW2, such as a thermistor located on a current path or near the switching device SW1 or SW2.

[0013] A control section 4 controls the switching devices SW1 of power modules 1 and 2, and a control section 5 controls the switching devices SW2 of power modules 1 and 2. A configuration of control section 4 is described below, and a similar configuration also applies to control section 5. In control section 4, an input signal generation section 6, such as a CPU, generates an input signal. A plurality of control circuits 7 and 8 control the switching devices SW1 of the plurality of power modules 1 and 2 based on their respective input signals.

[0014] Fig. Figure 2 is a diagram showing a collector current Ic and a collector-emitter voltage Vce based on an input signal V INThe controlled switching device is illustrated. Reference symbol "tr" denotes a rise time, also known as an increase time, which represents the time required for a current to increase from 10% to 90%, assuming, for example, that the current in the ON state is 100%. Reference symbol "tf" denotes a fall time, also known as a decrease time, which represents the time required for a current to decrease from 90% to 10%.

[0015] Reference symbol "tc(on)" denotes a time interval required to turn on, representing the time required after the current rises to 10% until an applied voltage decreases to 10%, where, for example, the current in the ON state is assumed to be 100% and the voltage in the OFF state is assumed to be 100%. Reference symbol "tc(off))" denotes a time interval required to turn off, representing, for example, the time required after the applied voltage rises to 10% until the current decreases to 10%. Reference symbol "td(on)" denotes a turn-on delay time, representing, for example, the time required after an input signal turns ON until the current reaches 10%.The reference symbol "td(off))" denotes a switch-off delay time, which, for example, represents the time required after the input signal switches OFF until the current decreases to 90%. The reference symbol "ton" denotes a combined value of td(on) and tr. The reference symbol "taus" denotes a combined value of td(off) and tf.

[0016] A multitude of correction sections 9 and 10 each correct input signals fed into the multitude of control circuits 7 and 8 based on a multitude of correction values. Correction sections 9 and 10 are delay circuits or similar devices that advance or delay an input signal according to the correction values.

[0017] A recording section 11 records acceptance and inspection results of the switching characteristics of the multitude of power modules 1 and 2 that underwent shipping inspections, and inspection temperatures, which are operating temperatures during the inspections, as shipping inspection results. Recording section 11 also records matrix data showing a correlation between the switching characteristics and the operating temperatures as a calculation table. Note that the calculation table can be generated using typical switching characteristic information plotted with operating temperatures and flowing currents, which is provided by a power module manufacturer.Without being limited to this, the calculation table can also be generated based on results of a confirmation of a temperature dependence of switching characteristics in the actual use of the power modules mounted on the actual power conversion system within ranges of expected operating temperatures, applied voltages and flowing currents.

[0018] Examples of common shipping inspections include a DC flow test (static characteristic evaluation), an insulation test, and a switching test under single-pulse or multi-pulse current flowing across a half-bridge circuit with an L-load. The switching characteristics tested are at least one of tr, tf, tc(on), tc(off)), td(on), td(off)), tein, and taus. Each power module is assigned an identification number, such as a batch number or serial number, and is thus shipped with a one-to-one correspondence to multiple values ​​of the shipping inspection results.

[0019] A calculation section 12 estimates the temperature dependence of the switching characteristics of the multitude of power modules 1 and 2 based on the shipping control results and estimates the actual switching characteristics of the multitude of power modules 1 and 2 based on the measured operating temperature and the estimated temperature dependence of the switching characteristics. Note that, since the temperature dependence of the switching characteristics of each of the power modules 1 and 2 is specific and unchanging for each power module, these can be saved in the recording section 11 to reduce the calculation time.

[0020] Fig. Figure 3 is a diagram illustrating a method for estimating the switching characteristic. If the switching characteristic of power module 1 exhibits a first temperature dependence and the operating temperature of power module 1 is T1, the current switching characteristic of power module 1 is estimated to be a rise time tr1. Similarly, if the switching characteristic of power module 2 exhibits a second temperature dependence and the operating temperature of power module 2 is T2, the current switching characteristic of power module 2 is estimated to be a rise time tr2.

[0021] Fig. Figure 4 is a diagram illustrating a current flow when the ON timings of the two power modules do not match. A common input signal V INCurrent is fed into the two power modules; however, since their rise times tr1 and tr2 are different, the ON timings do not align. In this case, a current flows temporarily, or transiently, and intensely through the power module that starts earlier. Subsequently, when the other power module starts, the current is distributed between the two power modules according to the degree of gate opening, an inductance component of external or internal wiring, capacitance components of the modules, or similar factors. In this case, di / dt and dv / dt fluctuate. A transient current concentration can cause larger switching losses than expected, and a recurrence of such a loss can raise concerns about temperature rise and a drastic reduction in the lifetime of the power modules.

[0022] Therefore, calculation section 12 aligns the ON / OFF switching times of the multitude of power modules 1 and 2 based on the estimated current switching characteristics and calculates a multitude of correction values ​​to reduce fluctuations in the currents flowing through the multitude of power modules 1 and 2. A difference Δt between the estimated rise times of power modules 1 and 2 is used here as one correction value.

[0023] Fig. Figure 5 is a diagram illustrating the flow of current when the ON timings of the two power modules are synchronized. The ON timings are synchronized by adjusting the delay values ​​of the input signals V. IN1 and V IN2The currents to be fed into the two power modules are set. Once both power modules are in a steady ON state, the current flow is distributed so that the voltage drop during excitation of both modules is constant. This prevents the current from concentrating on one power module and can thus prevent an increase in circuit losses, a concomitant temperature rise of the switching devices, and an extreme reduction in service life. Since excessive current concentration can be suppressed, the fluctuation of the device temperature also decreases, and consequently, so do the fluctuations of di / dt and dv / dt.

[0024] If calculation section 12 is of a timer type, it reads temperature information every constant period and recalculates a correction value. If calculation section 12 is of an event type, it recalculates a correction value at a time when an operating temperature increases or decreases by a specific amount, for example, 5°C, from the previous calculation. Since the recalculated correction value must be applied in an OFF state or in a situation where the current is 0 A or similar, a process is performed that clears any stored old correction value for the application of the next or any input signal, thus replacing it with a new correction value.Furthermore, if the switching characteristics of each power module are estimated at a specific operating temperature and a correction value is calculated, the correction value can be held for a specific period of time, and input signals such as PWM (pulse width modulation) signals can be continuously corrected in a simplified manner. This allows switching characteristics to be fed back during actual operation without increasing the computational load.

[0025] As described above, in the present embodiment, the current switching characteristics of the plurality of power modules 1 and 2 are estimated based on the measured operating temperature and a temperature dependence of the switching characteristics. A plurality of correction values ​​are then calculated based on these estimated current switching characteristics to reduce fluctuations in the currents flowing through the plurality of power modules 1 and 2. A plurality of input signals to be fed into the plurality of control circuits 7 and 8 are each corrected based on these correction values. This makes it possible to reduce fluctuations in the currents flowing through the plurality of power modules 1 and 2 connected in parallel.

[0026] The switching characteristics fluctuate according to operating temperature, applied voltage, current, circuit conditions, or similar factors. Compared to fluctuations due to applied voltage and current, however, larger fluctuations can generally be attributed to circuit conditions such as the routing of main electrodes or signal wiring, and temperatures. Therefore, in the case of a power conversion system such as an inverter with fixed applied voltage and current ranges, it is possible to estimate the current switching characteristics of the power modules based on the measured operating temperature and the temperature dependence of the switching characteristics.

[0027] When switching characteristics, whose fluctuations are large relative to those of the flowing current or applied voltage, are used as dispatch control results, there is concern that the correction accuracy may deteriorate if the flowing current or applied voltage fluctuates considerably during startup, ramp-up, high-load operation, or similar situations. Therefore, the switching characteristics are preferably at least one of tr, tf, tc(on), tc(off)), td(on), td(off)), tein, and taus. Since fluctuations of these switching times caused by a current or voltage are small, it is possible to correct a switching timing control more accurately through simple calculations and to improve current imbalances.Note that switching times generally exhibit low current dependence, but this dependence varies depending on the structure of a switching device, such as an IGBT or MOSFET, and the material, such as Si or SiC. Therefore, it is necessary to select a shipping control result according to these characteristics. For example, in the case of a power module equipped with a Si IGBT, td(on), td(off)), tein, taus, or similar values ​​generally have low current dependence and are suitable for shipping control results. On the other hand, in the case of a power module equipped with a driver circuit, since td(on), td(off)), tein, or taus includes a delay time of the driver circuit, such a power module has the advantage that corrections can be made to account for characteristic variations.

[0028] The computation section 12 is implemented by a processing circuit such as a CPU or a system LSI, which executes a program stored in memory. Furthermore, multiple processing circuits can work together to perform the functions described above. An input signal can be corrected by software utilizing computation section 12; however, correcting an input signal by hardware using correction sections 9 and 10 can further reduce the load and the number of output pins of computation section 12.

[0029] Fluctuations in the current flow are generated by the arrangement of the switching devices SW1 and SW2 in the power modules 1 and 2, by the parallel connection of power modules 1 and 2, by the position of the power supply or an electrolytic capacitor, or similar components, relative to a DC voltage source, or by the length or routing of main or external wiring such as signal wiring. Furthermore, fluctuations in switching characteristics are also generated by temperature variations due to the placement of power modules on a cooling system. In such cases, it is preferable to improve the arrangement of the switching devices or power modules, the routing of signal wiring, or similar components. However, there may be instances where a uniform arrangement is not possible due to installation limitations.Consequently, it is preferable to confirm the effects on the switching characteristics of the arrangement of switching devices or power modules, the routing of wiring, or the like, by evaluating initial products of the power conversion system or similar methods, and to reflect these effects in the calculation table. By superimposing these effects on the characteristics of each power module, which are estimated based on the operating temperature and shipping control results, it is possible to calculate a more accurate correction value for each power module.

[0030] For example, when a three-phase inverter circuit is constructed by connecting two power modules with six switching devices in parallel, correction values ​​for the switching devices are derived for each phase using a common calculation table. Corrections are then applied according to the position relative to the main electrode and circuit conditions such as the routing of signal wiring. Therefore, even if the shipping control result and operating temperature are the same, correction values ​​can vary from one phase to another.

[0031] Power modules 1 and 2 can be used as power modules with one or six devices, or as power modules for a single-phase inverter, a three-phase inverter circuit, or the like. Protection circuits for overheating, short-circuit, supply voltage reduction, or the like can be provided. Although the input signal generation section 6 is separate from the computation section 12, an input signal can be generated by software using the computation section 12 and the recording section 11. Although a control circuit is connected for each switching device, the plurality of switching devices in a power module or the plurality of power modules 1 and 2 can be switched by a common control circuit such as an LVIC.An input signal can be level-shifted using a drive circuit such as an HVIC, and the P-side (high side) and the N-side (low side) of the same phase, or a multitude of phases such as all phases of the P-side, can be switched using a common drive circuit. Second embodiment

[0032] Fig. Figure 6 is a diagram illustrating a power conversion system according to a second embodiment. In the present embodiment, power modules 1 and 2 are each provided with a recording section 13. The recording section 13 records a shipping control result of the corresponding power module. This ensures, in a simple manner, that the power modules are in one-to-one correspondence with their shipping control results. The control section 4 reads the shipping control results from power modules 1 and 2 upon initial startup or at each start-up and records the shipping control results in the recording section 11. A product assembly step can be simplified because the shipping control results of the respective power modules 1 and 2 do not need to be entered into the recording section 11 of the control section 4 when assembling the power conversion section.Furthermore, the power modules can be replaced or exchanged on-site as maintenance after the power conversion system has been shipped. In this case, the system can be reset and read again after maintenance. Note that if the shipping control results in recording section 11 of control section 4 are retained for the initial startup, the system can be reset and read again after on-site maintenance. Third embodiment

[0033] Fig.Figure 7 is a diagram illustrating a power conversion system according to a third embodiment. In the present embodiment, the power module 1 is provided with not only the recording section 13, but also a control circuit 7, such as an HVIC or LVIC, and a correction section 9. Similarly, the power module 2 is provided with a control circuit 8 and a correction section 10. The recording section 13 records not only shipping control results, but also calculated correction values.

[0034] At the time of a power-off switch-off, the control circuit 7 reads a correction value from the recording section 13 either every time or once every several times. The control circuit 7 selects a delay circuit of the correction section 9 according to the correction value, and the correction section 9 corrects input signals with a specific phase or all phases. Note that the control circuit 7 can also read a correction value at a time when the correction value is being rewritten, or at a time when all three phases of the input signals are switched off, according to an instruction from the calculation section 12 of the control section 4.

[0035] Since input signals are corrected in power modules 1 and 2, the input signals applied to power modules 1 and 2 are generated jointly. Because this simplifies the routing of wiring in control section 4, the design of control section 4 is simplified, and it is possible to use a cost-effective printed circuit board and signal wiring for control section 4.

[0036] Note that a control circuit that selects a delay circuit for correction section 9 may be provided in the power device. If the correction value is changed due to a change in temperature conditions or the like, a new correction value can be overwritten at the same address of recording section 13. It is possible to read data from and write data to recording section 13 from the computation section, such as the microcomputer, CPU, or DSP of control section 4, located outside of power modules 1 and 2. At least one of correction section 9 and recording section 13 may be implemented in the drive circuit 7, which makes it possible to improve accuracy and reduce transmission delay time.

[0037] The correction section 9 is not limited to a delay circuit that corrects an input signal using hardware, but can also be a microcomputer that corrects an input signal using software. When an input signal is corrected using software, the number of outputs of the microcomputer increases according to the number of power modules connected in parallel, since the input signal corrected for each of the power modules 1 and 2 is calculated and output in the first and second embodiments. On the other hand, in the third embodiment, since the common input signal is applied to power modules 1 and 2, there is no need to increase the number of outputs of the microcomputer or the like.For example, in the case of a three-phase PWM control system where two power modules, each containing 6 devices, are connected in parallel and controlled, the number of required microcomputer outputs is 6 devices × 2 = 12 pins in the first and second embodiments, whereas it is 6 pins in the third embodiment. Consequently, the substrate wiring design becomes simpler, and a more cost-effective PCB substrate can be used.

[0038] Without being limited to the configuration in which the recording section 13 and the drive circuit 7 are connected to each of the switching devices SW1 and SW2, a configuration can be adopted in which a common recording section and a common drive circuit are connected to a plurality of switching devices or a plurality of phases. A configuration can also be adopted in which an input signal is level-shifted by a drive circuit such as an HVIC, and the P-side (high side) and the N-side (low side) of the same phase or of a plurality of phases, such as all phases of the P-side, are switched using a common memory and a common drive circuit.

[0039] Note that the switching devices SW1 and SW2 are not limited to silicon-based materials but can also be made of a wide-bandgap semiconductor with a larger bandgap than silicon. Examples of wide-bandgap semiconductors include silicon carbide, gallium nitride, and diamond. A device made of such a wide-bandgap semiconductor exhibits high withstand voltage or high allowable current density and can therefore be miniaturized. Using this miniaturized device also makes it possible to miniaturize and highly integrate the power conversion system containing it. Furthermore, because the device has high thermal resistance, it is possible to reduce the size of a heat sink's cooling fins, replace a water cooling section with an air cooling system, and thereby further miniaturize the power conversion system.Since the device exhibits low power loss and high efficiency, it is also possible to increase the efficiency of the power conversion system.

[0040] When the power module is activated, conduction and switching losses occur, and the temperature rises. As the temperature increases, electrical resistance also increases, reducing the current flow and thus tending to improve current imbalances among a large number of power modules connected in parallel. On the other hand, a power module equipped with a silicon carbide switching device exhibits significantly lower conduction and switching losses than one with a silicon switching device.For example, in an inverter operation utilizing power modules of the same rated current, an inverter using a silicon carbide switching device exhibits a switching loss of approximately 30% of that of an inverter using a silicon switching device and exhibits a lower temperature rise. Therefore, when using a silicon carbide switching device, no improvement in temperature-induced current imbalances can be expected, and thus, as in the present embodiment, it is necessary to reduce fluctuations in currents flowing through a plurality of power modules.

[0041] Moreover, there may also be a case in which, as the temperature rises, the electrical resistance of the switching devices decreases, thus facilitating current flow. In this case, current concentration is more likely to occur, and therefore no improvement can be expected due to the temperature increase. Consequently, it is necessary to reduce fluctuations in the currents flowing through the multitude of power modules, as in the case of the present embodiment.

[0042] The accumulated technology and know-how, such as the quality stability of materials like wafers, manufacturing constraints, and chip structure, of a silicon carbide switching device utilizing a new material and structure is insufficient compared to a silicon switching device. For this reason, concerns exist regarding fluctuations in steady-state or switching characteristics. Correcting these fluctuations in switching characteristics according to the present embodiment allows for a relaxation of the product standard for power modules, leading to improved manufacturing yield and stable production, and enabling the supply and use of more cost-effective silicon carbide power modules.

Claims

[1] Power conversion system, comprehensive: - a large number of interconnected power modules (1, 2); - a multitude of control circuits (7, 8) which each control the multitude of power modules (1, 2) based on input signals; - a multitude of correction sections (9, 10) which each correct the input signals fed into the multitude of control circuits (7, 8) based on a multitude of correction values; - a temperature detection section (3) that detects the operating temperatures of the plurality of power modules (1, 2); and - a calculation section (12), - estimates the current switching characteristics of the plurality of power modules (1, 2) based on the measured operating temperatures and a temperature dependence of the switching characteristics of the plurality of power modules (1, 2) and - the multitude of correction values ​​calculated based on the estimated current switching characteristics to reduce fluctuations in currents flowing through the multitude of power modules (1, 2), wherein the switching characteristic is at least a rise time, a fall time, a time period required to switch on, a time period required to switch off, a switch-on delay time, a switch-off delay time, a total value of a switch-on delay time and a rise time, and a total value of a switch-off delay time and a fall time. [2] Power conversion system according to claim 1, furthermore, comprising a recording section (1, 13) that records control results of switching characteristics of the multitude of power modules (1, 2) and control temperatures as shipping control results, wherein the calculation section (12) estimates a temperature dependence of the switching characteristics of the plurality of power modules (1, 2) based on the shipping control results. [3] Power conversion system according to claim 2, wherein the recording section (1, 13) comprises a plurality of recording sections (1, 13) which are each provided in the plurality of power modules (1, 2) and each record the dispatch control results of the plurality of power modules (1, 2). [4] Power conversion system according to claim 3, wherein: - the multitude of control circuits (7, 8) and the multitude of correction sections (9, 10) are each provided in the multitude of power modules (1, 2), and - the multitude of recording sections (1, 13) each records the multitude of calculated correction values. [5] Power conversion system according to one of the preceding claims, wherein the plurality of power modules (1, 2) includes a plurality of switching devices (SW1, SW2), each consisting of a wide bandgap semiconductor.

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