JP4942569B2 - Power converter - Google Patents

Description

  The present invention relates to a power conversion device including a shunt resistor as a current detection resistor element.

  As a current detector for a three-phase inverter, a shunt current detection system that detects the current value of each phase based on the voltage drop of a shunt resistor provided between the lower arm element of each phase of the three-phase inverter and the DC power supply negative electrode side However, it is known as a low-cost system with a simple configuration (see, for example, Patent Document 1).

JP 2003-164259 A (paragraph number 0016 and FIG. 1)

  In the conventional pulse width modulation type three-phase inverter, there is a problem that a power loss that cannot be ignored occurs in a shunt resistor as a current detecting resistance element provided between the lower arm element of each phase and the DC power source negative electrode side. there were. Further, when the switching frequency of the switching element is high, the switching loss is inevitably increased. The present invention solves the above-described problems, and an object of the present invention is to obtain a power conversion device that can reduce power loss due to a current detecting resistance element and a switching element.

  In the power converter according to the present invention, the switching element of the upper arm and the switching element of the lower arm are connected in series, the switching element of the upper arm is connected to the positive electrode side of the DC power supply, and the switching element of the lower arm Is connected in series to the switching element of the lower arm for at least two phases of the arm circuit for three phases connected to the negative electrode side of the DC power source and the arm circuit for the three phases, respectively. A current detection resistor element for detecting a current flowing through the element, and a switching element for the upper arm and the lower arm by pulse width modulation by comparing a three-phase voltage command wave signal generated based on the current and a carrier wave. Provided with a control device for on / off control and shifting the three-phase voltage command wave signal equally in the positive direction It is intended.

  Further, the switching element of the upper arm and the switching element of the lower arm are connected in series, the switching element of the upper arm is connected to the positive side of the DC power supply, and the switching element of the lower arm is connected to the negative side of the DC power supply. A current for detecting a current flowing through the lower arm switching element inserted in series in the lower arm switching element for at least two phases of the three phase arm circuit to be connected A resistance element for detection, and a three-phase voltage command wave signal generated based on the current and a carrier wave are compared, and the switching elements of the upper arm and the lower arm are controlled on and off by pulse width modulation. The maximum of the three-phase voltage command wave signals at the moment is equal to the peak of the carrier wave When the three-phase voltage command wave signal is shifted equally in the positive direction, the sum of the switching loss of each switching element and the power loss of the current detection resistor element, and the three-phase voltage command wave signal Switching loss of each switching element and power of the current detecting resistor element when the three-phase voltage command wave signal is shifted in the negative direction so that the minimum of the carrier wave is equal to the size of the valley of the carrier wave A shift direction selection control device is provided that compares the total sum with loss and selects the one with the smaller total sum to shift the three-phase voltage command wave signals equally.

  In the power converter according to the present invention, the switching element of the upper arm and the switching element of the lower arm are connected in series, the switching element of the upper arm is connected to the positive electrode side of the DC power supply, and the switching element of the lower arm Is connected in series to the switching element of the lower arm for at least two phases of the arm circuit for three phases connected to the negative electrode side of the DC power source and the arm circuit for the three phases, respectively. A current detection resistor element for detecting a current flowing through the element, and a switching element for the upper arm and the lower arm by pulse width modulation by comparing a three-phase voltage command wave signal generated based on the current and a carrier wave. Provided with a control device for on / off control and shifting the three-phase voltage command wave signal equally in the positive direction Therefore, by shifting the three-phase voltage command wave signal equally in the positive direction, while maintaining the three-phase line voltage, the conduction period of the lower arm switching element, that is, the current detection resistor element Since the current passing period can be shortened, the power loss of the current detection resistor element can be reduced.

  Further, the switching element of the upper arm and the switching element of the lower arm are connected in series, the switching element of the upper arm is connected to the positive side of the DC power supply, and the switching element of the lower arm is connected to the negative side of the DC power supply. A current for detecting a current flowing through the lower arm switching element inserted in series in the lower arm switching element for at least two phases of the three phase arm circuit to be connected A resistance element for detection, and a three-phase voltage command wave signal generated based on the current and a carrier wave are compared, and the switching elements of the upper arm and the lower arm are controlled on and off by pulse width modulation. The maximum of the three-phase voltage command wave signals at the moment is equal to the peak of the carrier wave When the three-phase voltage command wave signal is shifted equally in the positive direction, the sum of the switching loss of each switching element and the power loss of the current detection resistor element, and the three-phase voltage command wave signal Switching loss of each switching element and power of the current detecting resistor element when the three-phase voltage command wave signal is shifted in the negative direction so that the minimum of the carrier wave is equal to the size of the valley of the carrier wave Compared with the total loss, the shift direction selection control device that selects the smaller total sum and shifts the three-phase voltage command wave signal equally is used. By selecting the smaller one, the power loss of the power converter can be further reduced.

Embodiment 1 FIG.
1 to 6 show a first embodiment of the present invention. FIG. 1 is a configuration diagram of a power converter, FIG. 2 is a configuration diagram of a PWM control unit, and FIG. 3 is an operation of a voltage correction unit. FIG. 4 is a waveform diagram showing the operation waveform of each part of the power converter, FIG. 5 is a waveform diagram showing the operation waveform of each part of the conventional power converter, and FIG. 6 shows the voltage waveform of the U-phase shunt resistor. It is a comparison waveform diagram which compares and shows the power converter device of the form of this, and the conventional power converter device.

  In FIG. 1, a motor 3 is connected to a DC power source 1 via a power converter 11. The power converter 11 includes a smoothing capacitor 2, shunt resistors 4, 5, and 6, which are current detection resistance elements, a PWM control unit 7, a current detection unit 8, a motor control unit 9, a voltage command correction unit 10, and switching of the upper arm. Elements Qu, Qv, Qw, and lower arm switching elements Qx, Qy, Qz are included. The upper arm switching element Qu and the lower arm switching element Qx are connected in series, the upper arm switching element Qv and the lower arm switching element Qyz are connected in series, and the upper arm switching element Qw and the lower arm switching element Qx are connected in series. The switching element Qz is connected in series to constitute an arm circuit for three phases in the present invention. For example, field effect transistors are used as the switching elements Qu, Qv, Qw, Qx, Qy, and Qz. The PWM control unit 7, the motor control unit 9, and the voltage command correction unit 10 are the control devices in the present invention. The smoothing capacitor 2 is connected to the DC power source 1, and the DC power is converted into AC power by switching the switching elements Qu, Qv, Qw, Qx, Qy, Qz in the power converter 11 and supplied to the motor 3.

  The current detection unit 8 includes voltages vRu, vRv, and vRw generated in the shunt resistors 4, 5, and 6, a resistance value of the shunt resistor, and gate signals Gu, Gv, Gw, Gx, Gy, and Gz output from the PWM control unit 7. The U-phase to W-phase motor currents iu, iv, iw are detected based on the above. Based on the detected motor currents iu, iv, iw and a speed command f * given from the outside, the motor control unit 9 performs a U-phase AC voltage command wave signal eu, a V-phase AC voltage command wave signal ev, and a W-phase. AC voltage command wave signal ew is output. The voltage command correction unit 10 performs predetermined correction on the U-phase to W-phase AC voltage command wave signals eu, ev, and ew that are the outputs of the motor control unit 9, and the corrected voltage command wave signals ehu, ehv, Output ehw.

  The PWM control unit 7 includes a carrier wave generation unit 101, a U-phase comparison unit 102, a V-phase comparison unit 103, a W-phase comparison unit 104, and inversion units 105, 106, and 107 as shown in FIG. The carrier wave generation unit 101 outputs a carrier wave C that is a triangular wave having a frequency fc based on the carrier wave frequency command. The U-phase comparator 102 that outputs the gate signal Gu compares the corrected voltage command wave signal ehu with the carrier C, and outputs an H level when the corrected voltage command wave signal ehu is large, and an L level when the corrected voltage command wave signal ehu is small. Is output. The inverting unit 105 that outputs the gate signal Gx outputs an H level when the gate signal Gu is at an L level, and outputs an L level when the gate signal Gu is at an H level.

Similarly, the V-phase comparison unit 103 that outputs the gate signal Gv compares the corrected voltage command wave signal ehv with the carrier wave C, and outputs an H level when the corrected voltage command wave signal ehv is large, and when it is small. Outputs L level. The inversion unit 106 that outputs the gate signal Gy outputs an H level when the gate signal Gv is at an L level, and outputs an L level when the gate signal Gv is at an H level. Further, the W-phase comparison unit 104 that outputs the gate signal Gw compares the corrected voltage command wave signal ehw with the carrier wave C, and outputs an H level when the corrected voltage command wave signal ehw is large, and when it is small. Output L level. The inversion unit 107 that outputs the gate signal Gz outputs an H level when the gate signal Gw is at an L level, and outputs an L level when the gate signal Gw is at an H level.
The PWM control unit 7 outputs the gate signals Gu, Gv, Gw, Gx, Gy, and Gz as described above, and controls the switching of the switching elements Qu, Qv, Qw, Qx, Qy, and Qz.

  Here, the operation of the voltage command correction unit 10 will be described with reference to the flowchart of FIG. First, the offset Eoffset is set to a predetermined positive voltage E0 (step S11). Next, a positive offset Eoffset (= E0) having a constant value is added to the U-phase to W-phase AC voltage command wave signals eu, ev, ew, and the corrected voltage command wave signals ehu, ehv, ehw are output. (Step S12).

  Next, the operation of the PWM control unit 7 will be described. FIG. 4 shows the waveform of each part of the power conversion apparatus with time on the horizontal axis. Each waveform will be described in order from the top of FIG. FIG. 4A shows the U-phase to W-phase AC voltage command wave signals eu, ev, ew, the carrier wave C for pulse width modulation of the AC voltage command wave signal, and the corrected voltage command wave signals ehu to ehw and other waveforms. It is. FIG. 4B shows the waveform of the gate signal Gu. When the corrected voltage command wave signal ehu is large by comparing the U-phase corrected voltage command wave signal ehu and the carrier C, the waveform is L. It is obtained by making it into a level. FIG. 4C shows the waveform of the gate signal Gx, which is L level when the gate signal Gu is H level, and is H level when the gate signal Gu is L level. When the gate signal Gu is at the H level, the switching element Qu is turned on and the switching element Qx is turned off. On the other hand, when the gate signal Gu is at L level, the switching element Qu is turned off and the switching element Qx is turned on.

  FIG. 4D shows the waveform of the gate signal Gv, which is obtained in the same manner as the gate signal Gu from a comparison between the V-phase corrected voltage command wave signal ehv and the carrier wave C. FIG. 4E shows the waveform of the gate signal Gy. The operations of the gate signal Gy and the switching elements Qv and Qy with respect to the gate signal Gv are the same as the operations of the gate signal Gx and the switching elements Qu and Qx with respect to the gate signal Gu. FIG. 4F shows the waveform of the gate signal Gw, which is obtained in the same manner as the gate signal Gu from the comparison between the W-phase corrected voltage command wave signal ehw and the carrier wave C. FIG. 4G shows the waveform of the gate signal Gz. The operations of the gate signal Gz and the switching elements Qw and Qz with respect to the gate signal Gw are the same as the operations of the gate signal Gx and the switching elements Qu and Qx with respect to the gate signal Gu. FIG. 4H is a waveform of the motor current flowing from the power converter 11 to the motor 3, and the U-phase to W-phase motor currents iu, iv, and iw are the U-phase and switching element Qv to which the switching element Qu is connected. Corresponds to the V phase to which is connected and the W phase to which the switching element Qw is connected.

  FIG. 4I shows a waveform of the voltage vRu of the U-phase shunt resistor 4. When the gate signal Gx is H, the switching element Qx is turned on, the U-phase motor current iu flows through the U-phase shunt resistor 4, and the product of the resistance value of the U-phase shunt resistor 4 and the magnitude of the U-phase motor current iu. A voltage vRu corresponding to FIG. 4J shows the waveform of the voltage vRv of the V-phase shunt resistor 5. When the gate signal Gy is H, the switching element Qy is turned on and the V-phase motor current iv flows through the V-phase shunt resistor 5, and the product of the resistance value of the V-phase shunt resistor 5 and the magnitude of the V-phase motor current iv. A voltage vRv corresponding to is generated. FIG. 4K is a waveform of the voltage vRw of the W-phase shunt resistor 6. When the gate signal Gz is H, the switching element Qz is turned on, and the W-phase motor current iw flows through the W-phase shunt resistor 6, and the product of the resistance value of the W-phase shunt resistor 6 and the magnitude of the W-phase motor current iw. A voltage vRw corresponding to is generated.

  The current detector 8 detects a current in synchronization with the gate signal. For example, the shunt resistor 4 is energized when the gate signal Gx becomes H level and the switching element Qx is on. At this time, the voltage of the shunt resistor 4 is sampled, divided by the resistance value, and the sign is inverted to thereby invert the U phase. The current Iu is detected. When the gate signal Gy becomes H level and the switching element Qy is turned on and the shunt resistor 5 is energized, the V-phase current Iv becomes low when the gate signal Gz becomes H level and the switching element Qz is turned on. Detected when the resistor 6 is energized. Even if the AC voltage command wave signals eu, ev, and ew are equally shifted in the positive direction, the motor 3 is not DC-excited because the three-phase voltage is a difference in output voltage.

  In this embodiment, the corrected voltage command wave signals ehu, ehv, ehw are positive offsets Eoffset equal to the U-phase to W-phase AC voltage command wave signals eu, ev, ew, which are the outputs of the motor control unit 9. Has been added. Thereby, the period during which the gate signals Gu, Gv, and Gw are at the H level, that is, the time during which the switching elements Qu, Qv, and Qw that are the upper arm elements are turned on is long, and the period during which the gate signals Gx, Gy, and Gz are at the H level. The time for which the switching elements Qu, Qv and Qw which are the lower arm elements are turned on is shortened. As a result, in FIG. 4, the time during which the voltage is applied to the shunt resistors 4, 5 and 6, that is, the passing time of the shunt resistors 4, 5 and 6, is shortened, and the power loss of the shunt resistors is reduced.

  Here, the situation where the flow time of the shunt resistors 4, 5 and 6 is shorter than that of the conventional power converter will be described in detail. FIG. 5 shows the waveform of each part when each switching element is controlled based on the conventional U-phase to W-phase AC voltage command wave signals eu, ev, and ew, and FIGS. FIG. 5A is a waveform diagram corresponding to FIGS. 4A to 4K, FIG. 5A is a carrier wave C and corrected voltage command wave signals ehu to ehw, and FIG. 5B is a gate signal Gu. 5 (c) is a gate signal Gx, FIG. 5 (d) is a gate signal Gv, FIG. 5 (e) is a gate signal Gy, FIG. 5 (f) is a gate signal Gw, FIG. 5 (g) is a gate signal Gz, 5 (h) is a U-phase motor current iu, V-phase motor current iv, and W-phase motor current iw flowing from the power converter to the motor. FIGS. 5 (i) to 5 (k) are U-phase to W-phase shunt resistors. 4 is a waveform of 4 to 6 voltages vRu, vRv, and vRw. 6 shows a waveform A of the voltage vRu of the U-phase shunt resistor 4 in FIG. 4 (i) (shown by hatching the energization width) and the conventional U-phase shunt resistor 4 in FIG. 5 (i). A waveform B of the voltage vRu of FIG. As apparent from FIG. 6, the energization time of the waveform A is shorter than the waveform B.

Embodiment 2. FIG.
7 and 8 show the second embodiment, FIG. 7 is a flowchart showing the operation of the voltage command correction unit, and FIG. 8 is a waveform diagram showing the operation waveforms of each unit of the power converter. In this embodiment, what is different from the first embodiment is processing performed by the voltage command correction unit (see FIG. 1). Hereinafter, processing performed by the voltage command correction unit will be described. As shown in FIG. 7, the voltage command correction unit sets the maximum value of the U-phase to W-phase AC voltage command wave signals eu, ev, ew at each moment as Emax (step S21). Next, an offset Eoffset, which is a value to be added to the maximum value Emax, is calculated so that the maximum value Emax becomes equal to a predetermined positive voltage E1 (Eoffset varies with time) (step S22), and the U phase to the W phase In addition to the AC voltage command wave signals eu, ev, and ew, the corrected voltage command wave signals ehu, ehv, and ehw are output (step S23).

  Here, the operation waveform of each part will be described with reference to FIG. 8A, FIG. 8A shows the carrier C and the corrected voltage command wave signals ehu to ehw, etc. FIG. 8B shows the gate signal Gu, FIG. 8C shows the gate signal Gx, and FIG. The gate signal Gv, FIG. 8 (e) is the gate signal Gy, FIG. 8 (f) is the gate signal Gw, FIG. 8 (g) is the gate signal Gz, and FIG. 8 (h) is the U-phase motor that flows from the power converter to the motor. The current iu, the V-phase motor current iv, and the W-phase motor current iw, FIGS. 8 (i) to 8 (k) are waveforms of the voltages vRu, vRv, and vRw of the U-phase to W-phase shunt resistors 4-6.

  As shown in FIG. 8A, the corrected voltage command wave signals ehu, ehv, and ehw are the maximum of the U-phase to W-phase AC voltage command wave signals eu, ev, and ew that are output from the motor control unit 9. The value Emax is equally shifted so as to be equal to E1. For example, in the sections t1, t2, and t3 in FIG. 8A, the AC voltage command wave signals eu, ev, and ew have the maximum values (the largest values) among the AC voltage command wave signals eu, ev, and ew, respectively. ) Since Emax, ehu, ehv, and ehw are shifted to E1 in the respective sections t1, t2, and t3. Accordingly, a period during which the gate signals Gu, Gv, and Gw in FIGS. 8B, 8D, and 8F are at the H level, that is, a time during which the switching elements Qu, Qv, and Qw are turned on is long, and FIG. , (E) and (g), the period when the gate signals Gx, Gy and Gz are at the H level, that is, the time during which the switching elements Qu, Qv and Qw are turned on is shortened. As a result, as shown in FIGS. 8 (i) to 8 (k), the time during which voltage is applied to the shunt resistors 4, 5 and 6, that is, the flow time of the shunt resistors 4, 5 and 6 is shortened, and the power loss of the shunt resistors is reduced. Is done.

Embodiment 3 FIG.
FIG. 9 is a waveform diagram showing operation waveforms of respective parts of the power conversion device according to the third embodiment. This embodiment is an example in which the predetermined voltage E1 in the second embodiment is set to the maximum value Ec of the carrier C, and three-phase U-phase to W-phase AC voltage command wave signals eu, ev, ew are This is an example in which the line voltage can be maintained and the maximum shift in the positive direction is possible, that is, the power loss of the shunt resistor can be reduced most. Further, when the U-phase AC voltage command wave signal eu is equal to the maximum value Ec of the carrier wave C, the gate signal Gu is not switched from the H level to the L level or from the L level to the H level, that is, the switching elements Qu and Qx are switched. Therefore, the switching loss of the switching elements Qu and Qx is eliminated.

  Similarly, when the V-phase AC voltage command wave signal ev is equal to the maximum value Ec of the carrier wave C, there is no switching loss between the switching elements Qv and Qy, and the W-phase AC voltage command wave signal ew is the maximum value Ec of the carrier wave C. , The switching loss of the switching elements Qw and Qz is eliminated.

  In addition, the operation waveform of each part is shown in FIG. 9, FIG. 9 (a) shows the carrier wave C and corrected voltage command wave signals ehu to ehw, etc. FIG. 9 (b) shows the gate signal Gu, FIG. 9 (c) shows the gate signal Gx, and FIG. The gate signal Gv, FIG. 9 (e) is the gate signal Gy, FIG. 9 (f) is the gate signal Gw, FIG. 9 (g) is the gate signal Gz, and FIG. 9 (h) is the U-phase motor that flows from the power converter to the motor. The current iu, the V-phase motor current iv, and the W-phase motor current iw, FIGS. 9I to 9K are waveforms of the voltages vRu, vRv, and vRw of the U-phase to W-phase shunt resistors 4 to 6.

  As shown in FIG. 9A, the corrected voltage command wave signals ehu, ehv, and ehw are the outputs of the U-phase to W-phase AC voltage command wave signals eu, ev, and ew that are outputs of the motor control unit 9 at each moment. Of these, the maximum value Emax is equally shifted so as to be equal to the maximum value Ec of the carrier wave C. Accordingly, a period during which the gate signals Gu, Gv, and Gw in FIGS. 9B, 9D, and 9F are at the H level, that is, a time during which the switching elements Qu, Qv, and Qw are turned on is long, and FIG. , (E) and (g), the period when the gate signals Gx, Gy and Gz are at the H level, that is, the time during which the switching elements Qu, Qv and Qw are turned on is shortened. As a result, as shown in FIGS. 9 (i) to 9 (k), the time during which voltage is applied to the shunt resistors 4, 5 and 6, that is, the flow time of the shunt resistors 4, 5 and 6 is shortened, and the power loss of the shunt resistors is reduced. Is done. Furthermore, since the phase in which the voltage command is equally shifted so as to be equal to the maximum value Ec of the carrier wave C is not switched for this period (see FIGS. 9B to 9G), there is no switching loss.

Embodiment 4 FIG.
10 and 11 show the fourth embodiment. FIG. 10 is an explanatory diagram for explaining whether or not current detection by a shunt resistor is possible. FIG. 11 is a waveform diagram showing operation waveforms of each part of the power converter. . For example, in FIG. 4 described above, when the corrected voltage command wave signal ehu shown in FIG. 4A is lower in voltage than the carrier C, the gate signal Gx shown in FIG. During this period, the switching element Qx is turned on. FIG. 10 shows this relationship. As the corrected voltage command wave signal ehu is shifted in the positive direction, the period T of the carrier wave C> = corrected voltage command wave signal ehu gradually decreases, and after correction. When the voltage command wave signal ehu reaches a certain voltage Elim, a predetermined time width Tmin is obtained. If the ON time of the switching element Qx, that is, the conduction period of the shunt resistor is less than Tmin, the U phase may not be able to detect the shunt current. The same applies to the other V and W phases.

  This phenomenon occurs when the duty ratio of the switching element Qx is small, depending on the voltage detection sampling timing by the shunt resistor 4, sampling may not be possible when current is flowing, and current detection may not be possible. The same applies to the shunt resistors 5 and 6. The voltage Elim at the minimum energization time Tmin in which current detection by the shunt resistor can be performed is defined as a limit voltage. The limit voltage is a predetermined limit value in the present invention, and the minimum energization time Tmin is a lower limit value in the present invention.

  Therefore, if the corrected voltage command wave signals ehu to ehw do not exceed the limit voltage Elim, that is, if E1 is Elim in the second embodiment, all three-phase currents are converted into shunt resistors in each cycle of the carrier wave. Can be detected. The operation waveform of each part at this time is shown in FIG. 11, FIG. 11A shows the carrier wave C and the corrected voltage command wave signals ehu to ehw, etc. FIG. 11B shows the gate signal Gu, FIG. 11C shows the gate signal Gx, and FIG. 11 (e) is the gate signal Gy, FIG. 11 (f) is the gate signal Gw, FIG. 11 (g) is the gate signal Gz, and FIG. 11 (h) is the U-phase motor that flows from the power converter to the motor. The current iu, the V-phase motor current iv, and the W-phase motor current iw, FIGS. 11 (i) to 11 (k) are waveforms of the voltages vRu, vRv, and vRw of the U-phase to W-phase shunt resistors 4-6.

  As shown in FIG. 11A, the corrected voltage command wave signals ehu, ehv, and ehw are among the U-phase to W-phase AC voltage command wave signals eu, ev, and ew that are output from the motor control unit 9. The maximum voltage command is shifted equally so as not to exceed the limit voltage Elim. Accordingly, the period during which the gate signals Gu, Gv, and Gw in FIGS. 11B, 11D, and 11F are at the H level, that is, the time during which the switching elements Qu, Qv, and Qw are turned on is long, and FIG. , (E) and (g), the period when the gate signals Gx, Gy and Gz are at the H level, that is, the time during which the switching elements Qu, Qv and Qw are turned on is shortened. As a result, as shown in FIGS. 11 (i) to 11 (k), the time that voltage is applied to the shunt resistors 4, 5, and 6, that is, the flow time of the shunt resistors 4, 5, and 6 is shortened, and the power loss of the shunt resistors is reduced. Is done.

  However, it is not always necessary to limit the corrected voltage command wave signals ehu, ehv, and ehw so that the three phases do not exceed the limit voltage Elim. A shunt resistor is provided in all of the three-phase switching elements Qu, Qv, and Qw, and only a corrected voltage command wave signal of a certain one phase has a limit voltage Elim that is determined by a conduction period Tmin of the shunt resistor that is necessary for shunt current detection. If the conduction period is less than Tmin and detection by the shunt current may not be possible, it is possible to calculate from the other two-phase currents using the fact that the sum of the three-phase currents is zero. it can. For example, when the U-phase motor current iu cannot be detected, the calculation can be performed as iu = −iv−iw. That is, three-phase motor currents iu to iw can be detected as long as at least the two-phase corrected voltage command wave signal does not exceed the limit voltage Elim. As a result, the U-phase to W-phase AC voltage command wave signals eu, ev, and ew are positive in the range in which the three-phase motor current can be detected in each cycle of the carrier wave C, as compared with the fourth embodiment. The power loss of the shunt resistor can be reduced accordingly.

Embodiment 5 FIG.
12 and 13 show the fifth embodiment, FIG. 12 is a flowchart showing the operation of the voltage command correction unit, and FIG. 13 is a waveform diagram showing the operation waveforms of the respective units of the power conversion device. In this embodiment, what is different from the first embodiment is processing performed by the voltage command correction unit (see FIG. 1). Hereinafter, processing performed by the voltage command correction unit will be described. As shown in the flowchart of FIG. 12, the voltage command correction unit extracts the maximum value Emax and the second largest voltage value Esec among the three-phase AC voltage command wave signals eu, ev, and ew at each moment (step) S51). Next, an offset Eoffset that is a value to be added so that the largest voltage value Emax is equal to the maximum value Ec of the carrier wave C is calculated, that is, Eoffset = Ec−Emax is obtained (step S52).

  Then, it is determined whether or not the value (Esec + Eoffset) obtained by adding the offset Eoffset to the second largest voltage value Esec exceeds the limit voltage Elim (step S53). If there is a possibility that it will be impossible, the offset Eoffset (= Elim−Esec) is calculated so that the second largest voltage command Esec becomes equal to the limit voltage Elim (step S54). The offset Eoffset is added to the U-phase to W-phase AC voltage command wave signals eu, ev, and ew, respectively, to obtain corrected voltage command wave signals ehu, ehv, and ehw (step S55).

  The operation waveform of each part of the power converter in this case is shown in FIG. As shown in FIG. 13 (a), the corrected voltage command wave signals ehu, ehv, and ehw are basically shifted so that the maximum value Emax is equal to the maximum value Ec of the carrier wave C. Exceeds the limit voltage Elim, the current detection by the shunt may be impossible, and the three-phase voltage command is shifted equally so that Esec is equal to the limit voltage Elim. As a result, in the range in which the three-phase U-phase to W-phase motor currents can be detected in each cycle of the carrier wave C, the period during which the gate signals Gu, Gv, and Gw are at the H level compared to the case of the fourth embodiment, that is, the switching element The time during which Qu, Qv, and Qw are turned on is much longer, and the time during which the gate signals Gx, Gy, and Gz are at the H level, that is, the time during which the switching elements Qu, Qv, and Qw are turned on becomes much shorter. As a result, as shown in FIGS. 13 (i) to 13 (k), the time during which voltage is applied to the shunt resistors 4, 5 and 6, that is, the flow time of the shunt resistors 4, 5 and 6 is shortened, and the power loss of the shunt resistors is reduced. Is done.

  In this embodiment, when the amplitude of the U-phase to W-phase AC pressure command wave signals eu, ev, and ew increases, the line voltage of each phase AC voltage command wave signal is maintained in the positive direction. The amount that can be shifted is reduced. At this time, the minimum of the AC voltage command wave signals eu, ev, ew is less than reducing the shunt resistance loss by shifting the three-phase AC voltage command wave signals eu, ev, ew equally in the positive direction. Is shifted to be equal to the minimum value (−Ec) of the carrier wave C, and the switching loss of the phase in which the AC voltage command wave signal is made equal to the minimum value (−Ec) of the carrier wave C is eliminated. In some cases, loss can be reduced.

Embodiment 6 FIG.
14 and 15 show the sixth embodiment, FIG. 14 is a flowchart showing the operation of the voltage command correction unit, and FIG. 15 is a waveform diagram showing the operation waveforms of each unit of the power converter. In this embodiment, what is different from the first embodiment is processing performed by the voltage command correction unit (see FIG. 1). Although not shown, the PWM control unit 7, the motor control unit 9, and the voltage command correction unit in this embodiment are the shift direction selection control device in the present invention. Hereinafter, processing performed by the voltage command correction unit will be described. In FIG. 14, steps S51 to S55 are the same processing as the processing of the voltage command correction unit in the fifth embodiment. After step S55, the loss PE1 of the power conversion device 11 of the fifth embodiment is calculated (step S61). Next, the minimum value Emin is detected from the U-phase to W-phase AC voltage command wave signals eu, ev, ew (step S62), and this Emin is shifted to be equal to the minimum value (−Ec) of the carrier wave C. The offset Eoffset is obtained (step S63), and the corrected voltage command wave signals ehu2, ehv2, ehw2 added to the AC voltage command wave signals eu, ev, ew are output (step S64).

  Next, the loss PE2 of the power converter 11 when the smallest one of the AC voltage command wave signals eu, ev, ew is shifted to be equal to the minimum value (−Ec) of the carrier C is calculated (step) S65). The minimum PE1 of power converter 11 in the case of Embodiment 5 and the AC voltage command wave signals eu, ev, ew in this embodiment are made equal to the minimum value (−Ec) of carrier C. The loss PE2 of the power converter 11 when shifted equally is compared (step S66). If the former PE1 is smaller, the corrected voltage command wave signals ehu, ehv, and ehw are corrected in the case of the fifth embodiment. Voltage command wave signals ehu, ehv, ehw are employed (step S67). In step S65, if the latter PE2 is smaller, the smallest one of the AC voltage command wave signals eu, ev, ew as the corrected voltage command wave signals ehu, ehv, ehw is the minimum value (−Ec) of the carrier wave C. The corrected voltage command wave signals ehu2, ehv2, and ehw2 that are shifted equally to be equal to are adopted (step S68).

  Therefore, basically, as in the fifth embodiment, the AC voltage command wave signal eu is set so that the maximum value Emax of the corrected voltage command wave signals ehu, ehv, ehw at each moment is equal to the maximum value Ec of the carrier C. , Ev, ew are shifted equally, and the two phases of the corrected voltage command wave signals ehu, ehv, ehw exceed the limit voltage Elim determined by the conduction period Tmin of the shunt resistor necessary for detecting the shunt current. When detection is impossible, the U-phase to W-phase AC voltage command wave is set so that the second largest voltage value Esec is equal to the limit voltage Elim determined by the conduction period Tmin of the shunt resistor necessary for detecting the shunt current. The signals eu, ev, ew are shifted equally. However, the loss of the power converter 11 is reduced when the smallest one of the U-phase to W-phase AC voltage command wave signals eu, ev, and ew is shifted equally so as to be equal to the minimum value (−Ec) of the carrier C. If it can be further reduced, the minimum one of the U-phase to W-phase AC voltage command wave signals eu, ev, and ew is shifted equally so as to be equal to the minimum value (−Ec) of the carrier wave C.

  The operation waveform of each part of the power converter in this case is shown in FIG. 15, FIG. 15 (a) shows the carrier wave C and corrected voltage command wave signals ehu to ehw, etc. FIG. 15 (b) shows the gate signal Gu, FIG. 15 (c) shows the gate signal Gx, and FIG. FIG. 15E shows the gate signal Gy, FIG. 15F shows the gate signal Gw, FIG. 15G shows the gate signal Gz, and FIG. 15H shows the U-phase motor flowing from the power converter to the motor. The current iu, the V-phase motor current iv, and the W-phase motor current iw, FIGS. 15 (i) to 15 (k) are waveforms of the voltages vRu, vRv, and vRw of the U-phase to W-phase shunt resistors 4-6.

  As shown in FIG. 15 (a), the corrected voltage command wave signals ehu, ehv, and ehw have the second largest voltage value Esec among the corrected voltage command wave signals ehu, ehv, and ehw at each moment. It is shifted equally so as not to exceed Elim (ie, to be equal). Accordingly, a period during which the gate signals Gu, Gv, and Gw in FIGS. 15B, 15D, and 15F are at the H level, that is, a time during which the switching elements Qu, Qv, and Qw are turned on is long, and FIG. , (E) and (g), the period when the gate signals Gx, Gy and Gz are at the H level, that is, the time during which the switching elements Qu, Qv and Qw are turned on is shortened. As a result, as shown in FIGS. 15 (i) to 15 (k), the time during which voltage is applied to the shunt resistors 4, 5 and 6, that is, the flow time of the shunt resistors 4, 5, and 6 is shortened, and the power loss of the shunt resistors is reduced. Is done.

  Thereby, compared with Embodiment 5, the loss of the power converter device 11 including the loss of the shunt resistors 4, 5 and 6 and the switching elements Qu, Qv, Qw, Qx, Qy and Qz can be further reduced.

It is a block diagram which shows the structure of the power converter device which is Embodiment 1 of this invention. It is a block diagram of a PWM control part. It is a flowchart which shows operation | movement of a voltage correction part. It is a wave form diagram which shows the operation | movement waveform of each part of the power converter device which is Embodiment 1 of this invention. It is a wave form diagram which shows the operation | movement waveform of each part of the conventional power converter device. FIG. 6 is a comparative waveform diagram showing a voltage waveform of a U-phase shunt resistor by comparing the power converter of this embodiment with a conventional power converter. It is a flowchart which shows operation | movement of the voltage command correction | amendment part which is Embodiment 2 of this invention. It is a wave form diagram which shows the operation | movement waveform of each part of the power converter device which is Embodiment 2 of this invention. It is a wave form diagram which shows the operation | movement waveform of each part of the power converter device which is Embodiment 3 of this invention. It is explanatory drawing explaining the possibility of the electric current detection by shunt resistance which is Embodiment 4 of this invention. It is a wave form diagram which shows the operation | movement waveform of each part of the power converter device which is Embodiment 4 of this invention. It is a flowchart which shows operation | movement of the voltage command correction | amendment part which is Embodiment 5 of this invention. It is a wave form diagram which shows the operation | movement waveform of each part of the power converter device which is Embodiment 5 of this invention. It is a flowchart which shows operation | movement of the voltage command correction | amendment part which is Embodiment 6 of this invention. It is a wave form diagram which shows the operation | movement waveform of each part of the power converter device which is Embodiment 6 of this invention.

Explanation of symbols

1 DC power supply, 3 motor, 4-6 shunt resistor, 7 PWM controller,
8 current detection unit, 9 motor control unit, 10 voltage command correction unit,
Qu to Qw Upper arm switching element, Qx to Qz Lower arm switching element, 11 Power converter, 101 Carrier wave generation unit, 102 U phase comparison unit,
103 V phase comparison unit, 104 W phase comparison unit, 105-107 inversion unit.

Claims (7)

The switching element of the upper arm and the switching element of the lower arm are connected in series, the switching element of the upper arm is connected to the positive side of the DC power supply, and the switching element of the lower arm is connected to the negative side of the DC power supply A three-phase arm circuit, a current detection resistor for detecting a current flowing through the lower arm switching element inserted in series in the lower arm switching element of at least two phases of the three phase arm circuit The device and the three-phase voltage command wave signal generated based on the current and the carrier wave are compared, and the switching elements of the upper arm and the lower arm are controlled on and off by pulse width modulation. The power converter device provided with the control apparatus which shifts a voltage command wave signal equally to a positive direction. The control device sets the three-phase voltage command wave signal in a positive direction so that the maximum of the shifted three-phase voltage command wave signals is equal to the peak of the carrier wave at each moment. The power conversion device according to claim 1, wherein the power conversion device shifts equally. The control device shifts the three-phase voltage command wave signal equally in the positive direction so that the maximum of the shifted three-phase voltage command wave signals does not exceed a predetermined limit value at each moment. 2. The electric power according to claim 1, wherein the predetermined limit value is determined from a lower limit value of an energization time during which the current can be detected by the current detection resistor element. Conversion device. The control device moves the three-phase voltage command wave signal in a positive direction so that the second largest one of the shifted three-phase voltage command wave signals does not exceed a predetermined limit value at each moment. 2. The predetermined limit value is determined from a lower limit value of an energization time in which the current can be detected by the current detection resistance element, and the predetermined limit value is shifted equally. Power converter. The switching element of the upper arm and the switching element of the lower arm are connected in series, the switching element of the upper arm is connected to the positive side of the DC power supply, and the switching element of the lower arm is connected to the negative side of the DC power supply A three-phase arm circuit, a current detection resistor for detecting a current flowing through the lower arm switching element inserted in series in the lower arm switching element of at least two phases of the three phase arm circuit The on-off control of the switching elements of the upper arm and the lower arm is performed by pulse width modulation by comparing the element and the three-phase voltage command wave signal generated based on the current and the carrier wave, and at each moment The maximum of the three-phase voltage command wave signals is equal to the size of the carrier peak. The sum of the switching loss of each switching element and the power loss of the current detection resistor element when the pressure command wave signal is shifted equally in the positive direction, and the minimum of the three-phase voltage command wave signals Is the sum of the switching loss of each of the switching elements and the power loss of the current detecting resistor element when the three-phase voltage command wave signal is shifted in the negative direction equally so that is equal to the size of the valley of the carrier wave. And a shift direction selection control device that shifts the three-phase voltage command wave signal equally by selecting the one with the smaller total sum. The shift direction selection controller controls the three-phase voltage command wave signal in a positive direction so that the maximum of the shifted three-phase voltage command wave signals does not exceed a predetermined limit value at each moment. 6. The predetermined limit value is determined from a lower limit value of an energization time during which the current can be detected by the current detection resistance element. The power converter described. The shift direction selection control device corrects the three-phase voltage command wave signal so that the second largest one of the shifted three-phase voltage command wave signals does not exceed a predetermined limit value at each moment. The predetermined limit value is determined from a lower limit value of an energization time during which the current can be detected by the current detection resistor element. 5. The power conversion device according to 5.

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