Method for controlling a dual inverter

Abstract

A method for controlling a first and second inverter (300, 400) with output terminals connected together with an electric motor (200), the method comprising: Comparing all voltage commands for operating the electric motor (200) with the magnitude of a common DC voltage applied to the first and second inverters (300, 400); and Generating a first voltage command with reference to an output of the first inverter (300) and a second voltage command with reference to an output of the second inverter (400) by selectively applying a high-gain overvoltage modulation (HOVM) depending on a result of the comparison, where, if the magnitudes of all voltage commands are lower than the magnitude of the DC voltage in the comparison step, a HOVM is applied to generate the first voltage command and the second voltage command. including generating the first voltage command and the second voltage command: Performing a first conversion to phase-shift all voltage commands by a predetermined angle, to convert the phase-shifted voltage commands into three-phase phase voltage commands, and to convert the three-phase phase voltage commands into three-phase terminal voltage commands using a space vector pulse width modulation; Perform a second conversion to convert the three-phase terminal voltage commands into d / q axis voltage commands; Calculating a gain to apply a HOVM based on the magnitudes of the d / q-axis voltage commands and the magnitude of the DC voltage; Performing a third conversion to convert the d / q axis voltage commands into three-phase phase voltage commands and to convert the three-phase phase voltage commands into three-phase terminal voltage commands by means of a space vector pulse width modulation; Multiplying the three-phase terminal voltage commands converted by the third conversion by the gain to generate the first voltage command; Performing a fourth conversion to convert the first voltage command into a d / q axis voltage command; Phase shifting of the d / q-axis voltage command, converted by the second transformation, in a direction opposite to the direction of the predetermined angle; and Converting a value generated by subtracting the d / q-axis voltage command transformed by the fourth conversion from the shifted d / q-axis voltage command into a three-phase phase voltage command and converting the three-phase phase voltage command into a three-phase terminal voltage command by a space vector pulse width modulation to generate the second voltage command.

Description

Technical field

[0001] The present invention relates to a double inverter control method. background

[0002] As global warming and pollution have emerged as serious problems, research and development of environmentally friendly vehicles suitable for minimizing pollution has been actively pursued, and markets for these vehicles have gradually expanded. Electric vehicles, hybrid vehicles, and plug-in hybrid vehicles are now available worldwide as environmentally friendly vehicles. These vehicles use electric motors to generate power from electrical energy, instead of engines that generate power by burning fossil fuels.

[0003] Most environmentally friendly vehicle technologies that use electrical energy generate vehicle propulsion power by supplying electrical energy to an electric motor, which is stored in a vehicle's high-voltage battery.

[0004] Such a motor drive control system, used in environmentally friendly vehicles, requires an inverter to convert direct current (DC) power supplied by a battery into the multiphase alternating current (AC) power necessary for driving the motor. Although a method for supplying multiphase AC power to a motor using a single inverter has been used, research has begun on a dual-inverter method for supplying power to an electric motor using two inverters.

[0005] An inverter converts a direct current (DC) voltage supplied by a battery into an alternating current (AC) voltage using pulse-width modulation (PWM). This AC voltage is then supplied to an electric motor to drive the motor. By supplying the AC voltage to the electric motor in six stages, the current consumed by the motor can be reduced under the same power conditions. A six-stage voltage supply to the electric motor can improve the system and fuel efficiency of environmentally friendly vehicles such as electric vehicles, hybrid vehicles, and fuel cell vehicles equipped with an electric motor, as well as increase the power and efficiency of both the inverter and the electric motor.

[0006] In accordance with the relevant technical field, a dual inverter control method is required which is suitable for improving the power efficiency of an inverter and an electric motor by controlling a dual inverter via a 6-step control to apply a voltage to the electric motor in a motor operating system using the dual inverter.

[0007] The publication by VT Somasekhar, MR Baiju, and K. Gopakumar, entitled "Dual two-level inverter scheme for an open-end winding induction motor drive with a single DC power supply and improved DC bus utilization," was published in April 2004 in IEE Proceedings - Electric Power Applications, pages 230-238; DOI: 10.1049 / ipepa:20040023. It describes a two-level dual inverter with an open-end winding induction motor drive and a single DC power supply. The proposed scheme generates voltage space vector positions identical to those of a conventional three-level inverter.

[0008] US 7,701,156 B2 concerns a control system for an electric motor and control procedures for it. Here, a voltage command value of a converter is determined by, among other things, the step of determining a candidate voltage of a system voltage VH as the converter output voltage within a voltage range between the minimum required voltage, which corresponds to the induction voltage of a motor generator, and a maximum output voltage of the converter.

[0009] KR 10 1 601 444 B1 relates to a device and a method for controlling a 6-stage inverter of a motor drive system, in particular for controlling a 6-stage inverter of a motor drive system, with which the output power of an inverter and a motor can be improved by applying a voltage to a motor by using a 6-stage control technique with which the input voltage of the inverter can be used to the maximum extent.

[0010] JP 2016 - 48 997 A relates to a method and a device for controlling a power converter, in particular for controlling the current of open windings connected between several inverters.

[0011] The subject matter described in this section serves only to improve an understanding of the general background of the invention and should not be taken as an acknowledgment or any kind of suggestion that the subject matter constitutes prior art already known to the person skilled in the art. Summary

[0012] The present invention relates to a dual-inverter control method and, in certain embodiments, a dual-inverter control method suitable for improving the power efficiency of an inverter and an electric motor by controlling a dual inverter via a 6-step controller to apply a voltage to the electric motor in a motor drive system by means of the dual inverter. The present invention is defined by the subject matter of claim 1, which can partially or completely solve the problems described above.

[0013] According to one embodiment of the present invention, a dual-inverter control method can be used to control a first and a second inverter with output terminals connected to an electric motor. The method comprises comparing all voltage commands for operating the electric motor with the magnitude of a DC voltage applied to both the first and second inverters, and generating a first voltage command with respect to an output of the first inverter and a second voltage command with respect to an output of the second inverter by selectively applying high-gain overvoltage modulation (HOVM) depending on a comparison result.

[0014] In one embodiment of the present invention, if the magnitudes of all voltage commands are less than the magnitude of the DC voltage in the comparison step, a HOVM can be used to generate either the first voltage command or the second voltage command.

[0015] In one embodiment of the present invention, generating the first voltage command and the second voltage command may comprise: a first conversion of a phase shift of all voltage commands by a predetermined angle, a conversion of the phase-shifted voltage commands into three-phase phase voltage commands, and a conversion of the three-phase phase voltage commands into three-phase terminal voltage commands via space vector pulse width modulation; a second conversion to convert the three-phase terminal voltage commands into d / q axis voltage commands; a calculation of a gain for an application of a HOVM based on the magnitudes of the d / q axis voltage commands and the magnitude of the DC voltage; a third conversion to convert the d / q axis voltage commands into three-phase phase voltage commands and a conversion of the three-phase phase voltage commands into three-phase terminal voltage commands via space vector pulse width modulation;Multiplying the three-phase voltage connection commands converted by the third conversion by the gain to generate the first voltage command; a fourth conversion to convert the first voltage command into a d / q axis voltage command; a phase shift of the d / q axis voltage command converted by the second conversion in a direction opposite to the direction of the predetermined angle; a conversion of a value obtained by subtracting the d / q axis voltage command converted by the fourth conversion from the shifted d / q axis voltage command into a three-phase phase voltage command and converting the three-phase phase voltage command into a three-phase connection voltage command by a space vector pulse width modulation to generate the second voltage command.

[0016] In one embodiment of the present invention, the generation of the first voltage command and the second voltage command can further include close magnitude overmodulation to change the three-phase terminal voltage commands converted by the first conversion into linearly output voltages by means of close magnitude overmodulation, if the three-phase terminal voltage commands converted by the first conversion are not linear output voltages (linearly output voltages).

[0017] In one embodiment of the present invention, a termination variable overmodulation can cause a voltage range within which a common-mode voltage of the first inverter and the second inverter is obtained to lie within a range of the value shifted by the predetermined angle.

[0018] In one embodiment of the present invention, the generation of the first voltage command and the second voltage command may include a termination variable overmodulation to change the three-phase terminal voltage commands converted by the third conversion into linear output voltages if the three-phase terminal voltage commands are not linear output voltages.

[0019] In one embodiment of the present invention, the output voltage overmodulation can be performed within a maximum voltage range of the first inverter.

[0020] In one embodiment of the present invention, generating the first voltage command may include changing values ​​obtained by multiplying the three-phase terminal voltage commands converted by the third conversion with the gain into linear output voltages, if the values ​​are not linear output voltages.

[0021] In one embodiment of the present invention, generating the first voltage command can include changing the multiplied values ​​into linear output voltages by means of a termination variable overmodulation within the maximum voltage range of the first inverter.

[0022] In one embodiment of the present invention, generating the first voltage command and the second voltage command may include applying a HOVM to generate the first voltage command and the second voltage command if the magnitudes of all voltage commands exceed the magnitude of the DC voltage.

[0023] In one embodiment of the present invention, generating the first voltage command and the second voltage command may comprise: a first shift to phase-shift all voltage commands by a predetermined angle; a first conversion to convert all phase-shifted voltage commands by the first shift into three-phase phase voltage commands and to convert the three-phase phase voltage commands into three-phase terminal voltage commands by space vector pulse-width modulation; calculating a first gain to apply a HOVM based on the magnitudes of all phase-shifted voltage commands by the first shift and the magnitude of the DC voltage; generating the first voltage command by multiplying the three-phase terminal voltage commands converted by the first conversion by the first gain;a second shift to phase-shift all voltage commands in a direction opposite to the direction of the predetermined angle; a second conversion to convert all phase-shifted voltage commands into three-phase phase voltage commands and to convert the three-phase phase voltage commands into three-phase terminal voltage commands by a space vector pulse-width modulation; calculating a second gain to apply a HOVM based on the magnitudes of all phase-shifted voltage commands and the magnitude of the DC voltage; and generating the second voltage command by multiplying the three-phase terminal voltage commands converted by the second conversion by the second gain.

[0024] In one embodiment of the present invention, generating the first voltage command and the second voltage command can further include changing the three-phase terminal commands converted by the first conversion into linear output voltages by means of a termination variable overmodulation if the three-phase terminal voltage commands are not linear output voltages.

[0025] In one embodiment of the present invention, the overmodulation can be carried out within the maximum voltage range of the first inverter.

[0026] In one embodiment of the present invention, generating the first voltage command may include changing values, which are obtained by multiplying the three-phase terminal voltage commands converted by the first conversion with the first gain, into linear output voltages if the values ​​are not linear output voltages.

[0027] In one embodiment of the present invention, generating the first voltage command can include changing the multiplied values ​​into linear output voltages by means of a termination variable overmodulation within the maximum voltage range of the first inverter.

[0028] In one embodiment of the present invention, generating the first voltage command and the second voltage command may include changing the three-phase terminal commands converted by the second conversion into linear output voltages by means of a termination variable overmodulation if the three-phase terminal voltage commands are not linear output voltages.

[0029] In one embodiment of the present invention, the overmodulation can be carried out within a maximum voltage range of the second inverter.

[0030] In one embodiment of the present invention, generating the second voltage command may include changing values, which, if the values ​​are not linear output voltages, are obtained by multiplying the three-phase terminal voltage commands converted by the second conversion with the second gain.

[0031] In one embodiment of the present invention, generating the second voltage command can include changing the multiplied values ​​into linear output voltages by means of a termination variable overmodulation within the maximum voltage range of the second inverter.

[0032] According to the dual inverter control method described above, inverter voltage utilization can be improved to increase power and efficiency, thereby significantly improving the fuel efficiency of environmentally friendly vehicles using this control method.

[0033] Additionally, the double inverter control method can be implemented by modifying just one algorithm in a hardware design, which does not result in any additional cost increase due to the addition of hardware.

[0034] Furthermore, the double inverter control method does not lead to a problem with regard to the current controllability of a motor of an environmentally friendly vehicle that uses the control method, since voltage utilization during current control is improved.

[0035] Furthermore, the dual inverter control method can easily control a dual inverter while keeping a common-mode voltage at zero, thereby improving controllability. Brief description of the characters Fig. Figure 1 is a simplified circuit diagram of a dual inverter system in which a dual inverter control method according to an embodiment of the present invention is used. Fig. Figure 2 is a block diagram of the entire control system in which the double inverter control method according to an embodiment of the present invention is applied. Fig. Figure 3 is a flowchart which represents a first inverter voltage command generation technique in the double inverter control method according to an embodiment of the present invention. Fig. Figure 4 is a flowchart which illustrates a second inverter voltage command generation technique in the double inverter control method according to an embodiment of the present invention. Fig. Figure 5 is a flowchart which represents a high-gain generation technique which is used in the dual inverter control method according to an embodiment of the present invention. Fig. 6 and Fig. 7 represent voltage limiting regions of a termination variable overmodulation, which is based on the in Fig. The 5 shown double inverter control methods are applied. Fig. 8 is a flowchart which provides an example, where the Fig. 3 and Fig. The 4 inverter voltage command generation techniques shown can be applied. Detailed description of descriptive embodiments

[0036] A description of dual inverter control methods according to various embodiments of the present invention is given with reference to the accompanying figures.

[0037] Fig. Figure 1 is a simplified circuit diagram of a dual inverter system in which a dual inverter control method according to an embodiment of the present invention is used.

[0038] With reference to Fig. 1 The inverter system, in which the double inverter control method according to an embodiment of the present invention is applied, can comprise a DC power supply unit 100 such as a battery, an electric motor 200 and two inverters 300 and 400 for converting the DC power of the DC power supply unit 100 into AC power and for providing the AC power to the electric motor 200.

[0039] The two in Fig. The inverters 300 and 300 shown are each connected to the DC power supply unit 100 via a common DC connection and are supplied with DC power. They can comprise six switching elements such that two switching elements are assigned per phase to provide three-phase voltage and current to the electric motor. Accordingly, the Fig. 1 The double inverter system shown operates or regenerates the electric motor by controlling the six switching elements included in the first inverter 300 and the six switching elements included in the second inverter 400.

[0040] Fig. Figure 2 is a block diagram of the entire control system in which the double inverter control method according to an embodiment of the present invention is applied.

[0041] In Fig. The electric motor 200, the first inverter 300 and the second inverter 400 indicate that in Fig. 1 configurations shown.

[0042] A current command card 500 outputs a current command IdqREF based on a torque command and an inverse magnetic flux value, input from an external higher-level control unit. The current command output from the current command card 500 can be a d-axis current command and a q-axis current command in a steady-state frame.

[0043] The current command card 500 can be generated by prior mapping of torque commands and inverse magnetic flux values, entered into it, with corresponding current commands via an experimental or a theoretical procedure. Although Fig. Figure 2 shows that the current command card 500 outputs a current command pre-mapped to a torque command and an inverse magnetic flux value. This is merely an example, and a current command can be output in a different form based on an input value. Furthermore, the current command card 500 is an exemplary method for generating a current command, and a current command can be output by a mathematical calculation instead of using the card.

[0044] A current control unit 600 receives a d-axis current and a q-axis current, obtained by a coordinate transformation of all or part of three-phase currents actually measured by a current sensor (not shown) provided at the output of the first inverter, and compares the d-axis and q-axis currents with the current command issued by the current command card 500. The current control unit 600 compares the d-axis and q-axis current commands received from the current command card 500 with an actual measured d-axis and q-axis current and generates voltage commands using the differences between them. The current control unit 600 is configured as a proportional-integral (PI) control unit and generates a d-axis voltage command and a q-axis voltage command in a steady-state frame.

[0045] An inverter voltage command generator 10 generates voltage commands for the first inverter 300 and the second inverter 400 based on the d-axis voltage command and the q-axis voltage command, which are generated in the current control unit 600, and generates PWM signals for switching elements included in the inverters, which belong to the voltage commands of the inverters, and outputs these to control the first inverter 300 and the second inverter 400.

[0046] The double inverter control method according to an embodiment of the present invention is implemented by the inverter voltage command generator 10.

[0047] The inverter voltage command generator 10 can be used in the Fig. 3 and Fig. Selectively use the 4 illustrated inverter voltage command generation techniques.

[0048] Fig. Figure 3 is a flowchart which illustrates a first inverter voltage command generation technique in the double inverter control method according to an embodiment of the present invention, and Fig. Figure 4 is a flowchart which illustrates a second inverter voltage command generation technique in the double inverter control method according to an embodiment of the present invention.

[0049] With reference to Fig. 3 The first inverter voltage command generation technique, which is used in the double inverter control method according to an embodiment of the present invention, shifts d-axis and q-axis voltage commands VdqRef, which are input by the current control unit 600, for a terminal variable overmodulation by -30 degrees (or +30 degrees (S11), converts the voltage commands into three-phase phase voltage commands VabcRef (S12) and then converts the three-phase phase voltage commands into three-phase terminal voltage commands VabcdnRef by a space vector pulse width modulation (S13).

[0050] If the three-phase terminal voltage commands VabcnRef include a voltage that cannot be output linearly, the voltage is changed to one that can be output linearly by terminal voltage overmodulation (S14). Terminal voltage overmodulation is a method for setting a new voltage command vector such that a magnitude difference of a three-phase terminal voltage command vector is reduced. A detailed description of terminal voltage overmodulation is omitted, as this is known from the prior art. When terminal voltage overmodulation (S14) is applied, the voltage range must be within a range shifted by -30 degrees (or +30 degrees) from the voltage range within which the common-mode voltage of the first inverter is 300° and that of the second inverter is 400°.

[0051] The three-phase connection voltage commands, which are subject to a termination variable overmodulation in step S14, are converted into d / q axis voltage commands (S15).

[0052] Consequently, the d / q-axis voltage commands generated in step S15 are converted into three-phase voltage commands (S16), a space vector pulse width modulation is performed on the three-phase voltage commands (S17), and then a termination overmodulation is performed on them. A gain calculation is performed by a high-gain calculation unit for high-gain overvoltage modulation (HOVM) using the d / q-axis voltage commands generated in step S15 (S19).

[0053] This is a voltage range of a final variable overmodulation within a range of a maximum voltage that can be output by the first inverter 300.

[0054] If a voltage that cannot be output linearly is generated when the three-phase terminal voltage commands generated by a termination overmodulation performed in step S18 are multiplied by the output of the high-gain calculation unit (S20), the voltage is changed to a voltage that can be output linearly using a termination overmodulation (S21) and the modified three-phase terminal voltage commands are output as final three-phase terminal voltage commands to control the switching elements of the first inverter 300 (S22).

[0055] The three-phase connection voltage commands generated in step S21 are transformed into d / q axis voltage commands Vdqinv2Res and subtracted from a value generated by shifting the values ​​generated in step S15 by +30 degrees (or -30 degrees) (shifting in a direction opposite to the shift direction of step S11) (S23) in step S25.

[0056] Since the voltage commands generated by subtraction in step S25 belong to d / q axis voltage commands of the second inverter 400, the voltage commands are converted into three-phase phase voltage commands (S26), transformed into three-phase terminal voltage commands by a space vector pulse width modulation (S27) and provided as a pulse width modulation output of the second inverter 400 (S28).

[0057] At the in Fig. The inverter voltage command generation process shown in step 3 can be a high-gain calculation in step S19 as shown in Fig. 5 will be shown.

[0058] Fig. Figure 5 is a flowchart illustrating a high gain generation technique used in the double inverter control method according to an embodiment of the present invention.

[0059] As in Fig. As shown in Figure 5, the high-gain generation step S19 can take the size |VdqREF_LPF| of a d-axis / q-axis voltage command, which belongs to the output value of the current control unit 600, calculate a difference VmagErr between the size |VpqREF_LPF| of the d-axis / q-axis voltage command and a value obtained by dividing an inverter input voltage Vdc_LPF by the square root of 3 (S51), and then obtain a high gain from the error value VmagErr, which is calculated in step S51, by an integrator. The high gain calculated in this way is multiplied by the three-phase connection voltage command values, which were subjected to a final quantity overmodulation in step S18, by step S42 and the multiplication result is subjected to a final quantity overmodulation (S21) and provided as a pulse width modulation output of the first inverter 300.

[0060] The Fig. 6 and Fig. 7 represent voltage limiting ranges of a termination variable overmodulation, applied in the case of the in Fig. The 5 double inverter taxation methods shown. In particular, it shows Fig. 6 a voltage limiting range of one in step S14 from Fig. 5 applied termination variable overmodulation. In this case, a voltage range is limited to the range specified by "A", taking into account the voltage vectors of the two inverters 300 and 400. Fig. Figure 7 shows a voltage limiting range of a termination variable overmodulation applied in steps S18 and S21. In this case, the voltage range is limited to the range indicated by "B", taking into account the voltage vectors of the first inverter 300.

[0061] With reference to Fig. 4 controls another inverter voltage command generation technique, which is used in the dual inverter control method according to an embodiment of the present invention, the first inverter 300 and the second inverter 400 by HOVM.

[0062] For pulse-width modulation output of the first inverter 300, d-axis and q-axis voltage commands VbqRef, input by the current control unit 600, are shifted by -30 degrees (or +30 degrees) (S31), converted into three-phase phase voltage commands VabcsRef (S32), and then into three-phase terminal voltage commands VabcnRef by space vector pulse-width modulation (S33). If the three-phase terminal voltage commands VabcnRef include a voltage that cannot be output linearly in step S33, the voltage is changed to one that can be output linearly using terminal variable overmodulation (S34).

[0063] A gain calculation is performed by a high-gain calculation unit for a HOVM using the d / q-axis voltage commands generated in step S31 (S35). A gain calculation by the high-gain calculation unit can be performed in essentially the same way as with respect to Fig. As described in section 5, the following steps are performed to calculate a gain for a high-gain module (HOVM) based on the magnitudes of the phase-shifted voltage commands and the magnitude of the DC voltage. If a voltage that cannot be output linearly is generated when the three-phase terminal voltage commands generated by a terminal overmodulation performed in step S18 are multiplied by the output of the high-gain calculation unit (S36), the voltage is changed to a voltage that can be output linearly using a terminal overmodulation (S37) and are output as final three-phase terminal voltage commands to control the switching elements of the first inverter 300 for pulse-width modulation with reference to the first inverter (S38).

[0064] Here, a final variable overmodulation must be performed in steps S34 and S37 within the maximum voltage range of the first inverter 300.

[0065] For a pulse-width modulation output of the second inverter 400, similar to the procedure for generating a pulse-width modulation output of the first inverter 300, d-axis and q-axis voltage commands VdqRef input by the current control unit 600 are shifted by -30 degrees (or +30 degrees) (S39), converted into three-phase phase voltage commands VabcsRef (S40), and then converted into three-phase terminal voltage commands VabcnRes by space vector pulse-width modulation (S41). If the three-phase terminal voltage commands VabcnRef include a voltage that cannot be output linearly in step S41, the voltage is changed to a voltage that can be output linearly using terminal variable overmodulation (S42).

[0066] A gain calculation is performed by a high-gain calculation unit for a HOVM using the d / q-axis voltage commands generated in step S39 (S43). A gain calculation by the high-gain calculation unit is essentially the same as the one performed with reference to Fig. 5. Gain calculation described. If a voltage that cannot be output linearly is generated when the three-phase terminal voltage commands generated by a termination overmodulation performed in step S42 are multiplied by the output of the high-gain calculation unit (S43), the voltage is changed to a voltage that can be output linearly using a termination overmodulation (S45) and output as final three-phase terminal voltage commands to control the switching elements of the second inverter 400 for pulse width modulation with reference to the second inverter (S46).

[0067] Here, a final voltage overmodulation must be performed in steps S42 and S45 within the maximum voltage range of the second inverter 400.

[0068] Fig. 8 is a flowchart which provides an example, where the Fig. 3 and Fig. The 4 inverter voltage command generation techniques shown can be applied.

[0069] As in Fig. As shown in Figure 8, in one embodiment of the present invention an inverter voltage command generator can be used to generate the signal in Fig. 3 use the inverter voltage command generation technique shown, which compares the size of an input voltage command vector with the size Vdc of a DC bus voltage supplied to inverters 300 and 400 from the DC power supply unit (battery) 100 (S61), applies a HOVM to a process to generate a pulse width modulation signal of the first inverter 300 when the size of the voltage command vector is less than the size Vdc of the DC voltage (S62), and derives a pulse width modulation signal of the second inverter 400 by subtracting a voltage command used to control the first inverter from all voltage commands (S63).

[0070] If the size of the voltage command vector exceeds the size Vdc of the DC voltage in step S61, the inverter voltage command generation technique can be used. Fig.4 are used, which generates the pulse width modulation signals of the first inverter 300 and the second inverter 400 using an HOVM.

[0071] The dual inverter control methods according to various embodiments of the present invention, which are described above, can improve performance and efficiency by increasing inverter voltage utilization, thereby increasing fuel efficiency.

[0072] Furthermore, the dual inverter control methods according to various embodiments of the present invention can be implemented by modifying only one algorithm in a hardware design, which means that no additional cost increase is caused by adding hardware.

[0073] In addition, the double inverter control methods according to various embodiments of the present invention can increase voltage utilization while current control is performed, and thus do not cause a problem with current controllability of drive electric motors in environmentally friendly vehicles in which the control methods are applied.

[0074] Furthermore, the dual inverter control methods according to various embodiments of the present invention can control inverters while a common-mode voltage is held at zero, which improves controllability.

[0075] Although certain embodiments of the present invention have been described for illustrative purposes, the person skilled in the art understands that various modifications, additions and substitutions are possible without deviating from the scope of protection as disclosed in the accompanying claims.

Claims

[1] A method for controlling a first and second inverter (300, 400) with output terminals connected to an electric motor (200), the method comprising: Comparing all voltage commands for operating the electric motor (200) with the magnitude of a common DC voltage applied to the first and second inverters (300, 400); and Generating a first voltage command with reference to an output of the first inverter (300) and a second voltage command with reference to an output of the second inverter (400) by selectively applying a high-gain overvoltage modulation (HOVM) depending on a result of the comparison, where, if the magnitudes of all voltage commands are lower than the magnitude of the DC voltage in the comparison step, a HOVM is applied to generate the first voltage command and the second voltage command. including generating the first voltage command and the second voltage command: Performing a first conversion to phase-shift all voltage commands by a predetermined angle, to convert the phase-shifted voltage commands into three-phase phase voltage commands, and to convert the three-phase phase voltage commands into three-phase terminal voltage commands using a space vector pulse width modulation; Perform a second conversion to convert the three-phase terminal voltage commands into d / q axis voltage commands; Calculating a gain to apply a HOVM based on the magnitudes of the d / q-axis voltage commands and the magnitude of the DC voltage; Performing a third conversion to convert the d / q axis voltage commands into three-phase phase voltage commands and to convert the three-phase phase voltage commands into three-phase terminal voltage commands by means of a space vector pulse width modulation; Multiplying the three-phase terminal voltage commands converted by the third conversion by the gain to generate the first voltage command; Performing a fourth conversion to convert the first voltage command into a d / q axis voltage command; Phase shifting of the d / q-axis voltage command, converted by the second transformation, in a direction opposite to the direction of the predetermined angle; and Converting a value generated by subtracting the d / q-axis voltage command transformed by the fourth conversion from the shifted d / q-axis voltage command into a three-phase phase voltage command and converting the three-phase phase voltage command into a three-phase terminal voltage command by a space vector pulse width modulation to generate the second voltage command. [2] Method according to claim 1, wherein the generation of the first voltage command and the second voltage command further comprises performing a termination variable overmodulation to change the three-phase terminal voltage commands converted by the first conversion into linearly output voltages using termination variable overmodulation if the three-phase terminal voltage commands converted by the first conversion are non-linearly output voltages. [3] Method according to claim 2, wherein the final variable overmodulation causes a voltage range within which a common-mode voltage of the first value and the second inverter (400) becomes substantially equal to 0 lies within a range of the value shifted by the predetermined angle. [4] Method according to claim 1, wherein generating the first voltage command and the second voltage command comprises performing a termination variable overmodulation to change the three-phase terminal voltage commands converted by the third conversion into linearly output voltages if the three-phase terminal voltage commands are not linearly output voltages. [5] Method according to claim 4, wherein the final variable overmodulation is performed within a maximum voltage range of the first inverter (300). [6] Method according to claim 1, wherein generating the first voltage command comprises changing values ​​obtained by multiplying the three-phase terminal voltage commands converted by the third conversion by the gain into linearly output voltages, if the values ​​are not linearly output voltages. [7] Method according to claim 6, wherein generating the first voltage command comprises changing the multiplied values ​​into linearly output voltages using a termination variable overmodulation within a maximum voltage range of the first inverter (300). [8] Method according to claim 1, wherein generating the first voltage command and the second voltage command comprises applying a HOVM to generate the first voltage command and the second voltage command when the magnitudes of all voltage commands exceed the magnitude of the DC voltage. [9] Method according to claim 8, wherein generating the first voltage command and the second voltage command comprises: Performing a first shift to phase-shift all voltage commands by a predetermined angle; Performing a first conversion to convert all phase-shifted voltage commands by the first shift into three-phase phase voltage commands and to convert the three-phase phase voltage commands into three-phase terminal voltage commands by a space vector pulse width modulation; Calculating a first gain to apply a HOVM based on the magnitudes of all voltage commands phase-shifted by the first shift and the magnitude of the DC voltage; Generating the first voltage command by multiplying the three-phase terminal voltage commands converted by the first conversion with the first gain; Performing a second shift to phase-shift all voltage commands in a direction opposite to the direction of the predetermined angle; Performing a second conversion to convert all phase-shifted voltage commands due to the second shift into three-phase phase voltage commands and to convert the three-phase phase voltage commands into three-phase terminal voltage commands using a space vector pulse width modulation; Calculating a second gain for applying a HOVM based on the magnitudes of all voltage commands phase-shifted by the second shift and the magnitude of the DC voltage; and Generating the second voltage command by multiplying the three-phase terminal voltage commands converted by the second conversion with the second gain. [10] Method according to claim 9, wherein generating the first voltage command and the second voltage command further comprises changing the three-phase terminal voltage commands converted by the first conversion into linearly output voltages using a terminal variable overmodulation if the three-phase terminal voltage commands are not linearly output voltages. [11] Method according to claim 10, wherein the overmodulation is carried out within a maximum voltage range of the first inverter (300). [12] Method according to claim 9, wherein generating the first voltage command comprises changing values ​​obtained by multiplying the three-phase terminal voltage commands converted by the first conversion with the first gain into linearly output voltages, if the values ​​are not linearly output voltages. [13] Method according to claim 12, wherein generating the first voltage command comprises changing the multiplied values ​​into linearly output voltages using a termination variable overmodulation within a maximum voltage range of the first inverter (300). [14] Method according to claim 9, wherein generating the first voltage command and the second voltage command comprises changing the three-phase terminal voltage commands converted by the second conversion into linearly output voltages using a terminal variable overmodulation if the three-phase terminal voltage commands are not linearly output voltages. [15] Method according to claim 14, wherein the overmodulation is carried out within a maximum voltage range of the second inverter (400). [16] Method according to claim 9, wherein generating the second voltage command comprises changing values ​​obtained by multiplying the three-phase terminal voltage commands converted by the second conversion with the second gain into linearly output voltages, if the values ​​are not linearly output voltages. [17] Method according to claim 16, wherein generating the second voltage command comprises changing the multiplied values ​​into linearly output voltages using a termination variable overmodulation within a maximum voltage range of the second inverter (400).

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