Power conversion device

Abstract

To provide a power conversion device capable of suppressing voltage and current ripple more effectively.SOLUTION: A three-phase inverter 3 is configured by connecting an upper arm switch SW1 and a lower arm switch SW2 in series for each phase, and connecting n chopper cells 1 in series in parallel with the lower arm switch SW2, each chopper cell having an LC series resonant circuit. A motor control unit 11 outputs control information based on input command values Idx, Iqx, and the output parameters generated by MG4. A pulse generation unit 12 outputs pulse signals that control the switching of each chopper cell 1 constituting the three-phase inverter 3 according to the control information.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a power conversion device. [Background technology]

[0002] Patent Document 1 discloses a power conversion device that includes a power conversion circuit with multiple chopper cells connected in series and a control device that controls the DC voltage of the multiple chopper cells according to the output voltage of the power conversion circuit, and can suppress an increase in harmonics even when the output voltage is low.With this configuration, by controlling the voltage gradation depending on the number of multiple chopper cells to be driven, it is possible to generate a voltage waveform that is more accurate than normal PWM control. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-175863 Summary of the Invention [Problem to be solved by the invention]

[0004] However, with the above configuration, the number of gradations in the output voltage waveform depends on the number of chopper cell stages, resulting in a stepped voltage and error. Furthermore, to generate a lower output voltage, the number of stages must be reduced, further reducing the accuracy of the voltage waveform reproduction. These resulting voltage errors result in harmonics being generated as ripples in the output current.

[0005] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a power conversion device that can further suppress voltage and current ripples. [Means for solving the problem]

[0006] According to the power conversion device of claim 1, the power conversion unit (3) is configured by connecting upper and lower switching elements (SW1, SW2) in series and connecting n chopper cells (1) in series, each having an LC series resonant circuit (15) in parallel with the lower switching element. The control unit (11) outputs control information according to an input command value and an output parameter generated by a motor (4) driven by the power conversion unit. The pulse generation unit (12, 38) outputs a pulse signal for controlling the switching of each chopper cell constituting the power conversion unit in accordance with the control information.

[0007] By connecting n chopper cells, each with an LC series resonant circuit, in series and controlling the output voltage of each chopper cell, the number of gradations in the output voltage of the power conversion unit can be increased.In addition, by controlling the switching of each chopper cell using a control unit and a pulse generation unit to control each output voltage, it is also possible to suppress ripples in the output voltage and output current of the power conversion unit.

[0008] According to the power conversion device of claim 2, an element drive unit (21) of the pulse generation unit drives a switching element constituting a chopper cell. A zero current detection unit (22) detects that the current output from the chopper cell has become zero and outputs a detection signal. A pulse signal output unit (23, 35) calculates the switching period and on-time of the switching element and a phase difference in the switching timing so as to operate the power conversion unit in the current boundary mode, and outputs a pulse signal to the element drive unit. By operating the power conversion unit in the current boundary mode in this way, ripples in the output voltage and output current can be suppressed.

[0009] According to the power conversion device of claim 3, the pulse signal output unit (35) measures a fixed time from when the detection signal is input from the zero current detection unit using the timer (36), and delays the timing of turning on the next chopper cell by the fixed time. This makes it possible to control a minute current without increasing the switching frequency. [Brief explanation of the drawings]

[0010] [Figure 1] Electrical configuration diagram for one phase in the first embodiment [Figure 2] Overall electrical diagram [Figure 3] Chopper cell control configuration diagram [Figure 4] A diagram showing the waveform of the inductor current IL in one chopper cell [Figure 5] A diagram showing the waveform of the output current Iout of one phase, which is a combination of the waveforms of the inductor currents IL1 to IL4 of the four chopper cells. [Figure 6] A diagram showing the waveform of the single-phase output voltage Vout obtained by combining the waveforms of the output voltages Vo1 to Vo4 of the four chopper cells. [Figure 7] 4. Diagram showing the waveform of the current output by each multiplexed chopper cell and the combined current waveform. [Figure 8] Timing chart showing the on / off control of switches SW1 and SW2 [Figure 9] FIG. 2 is a control configuration diagram of a chopper cell according to a second embodiment. [Figure 10] Timing chart showing the on / off control of switches SW1 and SW2 [Figure 11] FIG. 10 is a timing chart illustrating the on / off control of the switches SW1 and SW2 according to the third embodiment. [Figure 12] This is a fourth embodiment, and is an overall electrical configuration diagram. [Figure 13] FIG. 10 is a diagram illustrating a configuration of a parallel chopper cell according to a fifth embodiment. [Figure 14] FIG. 10 is a diagram illustrating a configuration of a parallel chopper cell according to a sixth embodiment. [Figure 15] FIG. 10 is a diagram illustrating a schematic diagram of switching control of each chopper cell when, for example, two parallel chopper cells of the fifth embodiment are connected in series. DETAILED DESCRIPTION OF THE INVENTION

[0011] (First embodiment) The first embodiment will be described below. As shown in Fig. 2, chopper cells 1U1-1Un, 1V1-1Vn, 1W1-1Wn are connected to batteries VINU1-VINUn, VINV1-VINVn, VINW1-VINWn, respectively. Each of batteries VINU1-VINWn is a unit cell that constitutes a battery pack of, for example, an electric vehicle, and is a storage battery such as a nickel-metal hydride storage battery or a lithium storage battery.

[0012] Chopper cells 1U1-1Un, 1V1-1Vn, 1W1-1Wn are connected in series to form multilevel converters 2u, 2v, and 2w. Multilevel converters 2u, 2v, and 2w form a three-phase inverter 3 as a power conversion unit. A motor / generator (hereinafter referred to as MG) 4 is connected to the three-phase inverter 3. MG 4 is a power generation device that drives the wheels of, for example, a hybrid vehicle or an electric vehicle, and is, for example, a permanent magnet synchronous motor (PMSM).

[0013] As shown in Figure 3, each chopper cell 1 is configured as a step-down non-inverting buck converter equipped with an upper arm switch SW1, a lower arm switch SW2, an inductor L, and a capacitor C, and converts the voltage of the battery VIN to a desired level. The upper arm switch SW1 and the lower arm switch SW2 are configured as power switches such as N-channel power MOSFETs, and freewheeling diodes D1 and D2 are connected between the drain and source, respectively, to commutate the load current. An LC series resonant circuit 15 consisting of an inductor L and a capacitor C is connected in parallel to the lower arm switch SW2. The upper and lower arm switches SW1 and SW2 correspond to the upper and lower switching elements, respectively.

[0014] Fig. 4 shows the waveform of the inductor current IL in one chopper cell 1, and the curve represents the effective value of the current. Fig. 5 shows the waveform of the output current Iout for one phase, which is a combination of the waveforms of the inductor currents IL1 to IL4 of the four chopper cells 1. Fig. 6 shows the waveform of the output voltage VOUT for one phase, which is a combination of the waveforms of the output voltages Vo1 to Vo4 of the four chopper cells 1.

[0015] In the control system according to this embodiment, a control device 10 is connected to a three-phase inverter 3, and control is mainly performed by the control device 10. The control device 10 is configured by a computer equipped with multiple CPU cores and the like, and functionally comprises a motor control unit 11 and a pulse generation unit 12.

[0016] Current sensors 14u, 14v, and 14w are provided in the current path of inductor L constituting chopper cells 1u1, 1v1, and 1w1. An inductor current IL detected by current sensors 14u-14w is input to zero current detection unit 22. D-axis current and q-axis current command values ​​Idx and Iqx calculated by command unit 5 according to the required torque are input to motor control unit 11, which outputs control information Iu_cmd, Iv_cmd, and Iw_cmd corresponding to the current command values ​​Idx and Iqx to pulse generation unit 12. The current command value IoutC shown in FIG. 3 corresponds to the control information Iu_cmd, Iv_cmd, and Iw_cmd. The update cycle of current command values ​​Idx and Iqx is set to be sufficiently short compared to the cycle of the AC frequency, allowing for precise setting of current command values ​​Idx and Iqx, which change with the AC frequency.

[0017] The motor control unit 11 receives an input of the rotor angle θ from a rotational position sensor 4a, such as a resolver, installed on the motor 4. Current sensors 33u, 33v, and 33w are connected to the output terminals of the pulse generation units 12u, 12v, and 12w of each phase. The phase currents Iu, Iv, and Iw detected by these current sensors 33u, 33v, and 33w are also input to the motor control unit 11. Based on these inputs, the motor control unit 11 performs vector control calculations using a three-phase to two-phase converter 34 to generate a d-axis current Id and a q-axis current Iq.

[0018] The subtractor 30 subtracts the d-axis current Id and the q-axis current Iq from the d-axis current command value Idx and the q-axis current command value Iqx, respectively, and outputs the results to the current controller 31. The current controller 31 outputs d-axis and q-axis current command values ​​Id_cmd and Iq_cmd to the two-phase to three-phase converter 32, for example, by proportional-integral control. The two-phase to three-phase converter 32 converts the d-axis and q-axis current command values ​​Idx and Iqx input from the current controller 31 into current command values ​​Iu_cmd, Iv_cmd, and Iw_cmd for each of the three phases of the motor 4, and outputs them to the pulse generator 12.

[0019] The pulse generating unit 12 generates multiple pulses, i.e., multilevel pulses, to perform multiple operations on the 3×n chopper cells 1 of the three-phase inverter 3 based on control information input from the motor control unit 11. As shown in Fig. 1 and Fig. 3, the pulse generating unit 12 has functional configurations as a gate driving unit 21, a zero current detecting unit 22, and a pulse calculating unit 23 corresponding to the pulse signal output unit.

[0020] The pulse calculation unit 23 calculates the parameters of the on-time Ton and off-time Toff of the upper arm switch SW1 or the lower arm switch SW2, the period T, and the phase difference Td between the multiple pulses input to the multiple chopper cells 1 of the same phase when each chopper cell 1 of the multilevel converters 2u, 2v, and 2w of each phase is operated in the current boundary mode. These parameters are shown in Fig. 7. The current boundary mode is a mode in which the upper arm switch SW1 and the lower arm switch SW2 are switched on and off when it is detected that the inductor current IL has become zero.

[0021] A gate driver 21 corresponding to the element driver drives the three-phase inverter 3 based on the calculation results of the pulse calculator 23. The gate driver 21 drives the upper arm switch SW1 or the lower arm switch SW2 to turn on or off based on the on time Ton, off time Toff, period T, and phase difference Td calculated by the pulse calculator 23. For example, if the current command value IoutC for the U phase exceeds zero, the pulse calculator 23 causes the gate driver 21 to turn on the upper arm switch SW1. If the current command value IoutC is less than zero, the pulse calculator 23 causes the gate driver 21 to turn on the lower arm switch SW2.

[0022] Next, the operation of this embodiment will be described. First, the calculation of each parameter will be described. If the output current of the chopper cell 1 according to the current command value IoutC is Iout and the number of multiplexed chopper cells 1 is n, then the average current I of the converter 5 is Iout / n, and the peak current ILp of the inductor current IL is twice the average current I, or 2I.

[0023] When the current command value IoutC>0, the pulse calculation unit 23 calculates the on-time Ton and off-time Toff of the upper arm switch SW1, as well as the period T and phase difference Td, based on the following equations (1) and (2), respectively. VINxn: Input voltage of chopper cell 1xn (x=U, V, W) VOUTxn: Output voltage of chopper cell 1xn Ton1: ON time of upper arm switch SW1 Toff1: Off time of upper arm switch SW1 T1: On-off cycle Td1: Phase difference between each on timing L: Inductance of the inductor ILp: Peak current flowing through the inductor Let's say.

[0024] If the command value IoutC is a positive value, the pulse generating unit 12 turns on the upper arm switch SW1. Ton1=ILp×L / (VINxn-VOUTxn) Toff1=ILp×L / VOUTxn T1=Ton1+Toff1 Td1=T1 / n …(1) A multi-pulse signal is generated to drive the

[0025] Also, Ton2: On time of lower arm switch SW2 Toff2: Off time of lower arm switch SW2 T2: On-off cycle Td2: Phase difference between each on timing Let's say.

[0026] If the current command value IoutC is a negative value, the pulse generating unit 12 turns on the lower arm switch SW2. Ton2=ILp×L / VOUTxn Toff2=ILp×L / (VINxn-VOUTxn) T2=Ton2+Toff2 Td2=T2 / n …(2) A multi-pulse signal is generated to drive the

[0027] 8 shows the turn-on timing of the upper-arm switch SW1 when the current command value exceeds zero and n=4. When the current detection unit 22 detects the zero-crossing point ZCS where the polarity of the current changes from negative to positive, it outputs a detection pulse. At this timing, the upper-arm switch SW1 is turned on. In this timing chart, the lower-arm switch SW2 is also controlled to perform synchronous rectification, but the switch SW2 may be turned off to allow the current to reflux via the freewheel diode D2.

[0028] As described above, according to this embodiment, the three-phase inverter 3 is configured by connecting an upper arm switch SW1 and a lower arm switch SW2 in series for each phase, and connecting n chopper cells 1, each having an LC series resonant circuit, in parallel with the lower arm switch SW2. The motor control unit 11 outputs control information according to the input command values ​​Idx, Iqx and the output parameters generated by the MG4. The pulse generation unit 12 outputs pulse signals that control the switching of each chopper cell 1 constituting the three-phase inverter 3 in accordance with the control information.

[0029] By connecting n chopper cells 1, each having an LC series resonant circuit 15, in series and controlling the switching of each chopper cell 1 using the motor control unit 11 and the pulse calculation unit 23 to control the output voltages Vo1 to Von of each chopper cell 1, it is possible to increase the number of gradations of the output voltage VOUT of the three-phase inverter 3. It is also possible to suppress ripples in the output voltage VOUT and the output current IOUT.

[0030] A gate driver 21 of the pulse generator 12 drives the upper and lower arm switches SW1 and SW2 that constitute the chopper cell 1. A zero current detector 22 detects when the current IL output from the chopper cell 1 becomes zero and outputs a detection signal. A pulse calculator 23 calculates the switching period T and on-time Ton of the upper and lower arm switches SW1 or SW2, as well as the phase difference Td of the switching timing, so as to operate the three-phase inverter 3 in the current boundary mode, and outputs a pulse signal to the gate driver 21. By operating the three-phase inverter 3 in the current boundary mode in this way, ripples in the output voltage and output current can be suppressed.

[0031] Furthermore, if the current command value is a positive value, the pulse generating unit 12 generates a multi-pulse signal to drive the upper arm switch SW1 that constitutes the chopper cell 1 according to equation (1), and if the command value is a negative value, the pulse generating unit 12 generates a multi-pulse signal to drive the lower arm switch SW2 that constitutes the chopper cell 1 according to equation (2). In this way, the multi-pulse signal can be generated specifically according to equations (1) and (2).

[0032] (Second embodiment) Hereinafter, the same parts as those in the first embodiment will be assigned the same reference numerals and their explanation will be omitted, and only the different parts will be explained. As shown in Fig. 9, in the second embodiment, a timer 36 is provided in a pulse calculation unit 35 that replaces the pulse calculation unit 23. The timer 36 starts timing when a detection signal is input from the zero current detection unit 22, and times a fixed time Tdcm.

[0033] As shown in Figure 10, the pulse calculation unit 35 delays the timing of turning on the upper arm switch SW1 by the fixed time Tdcm. This allows the current to be controlled in discontinuous mode. In discontinuous mode, it is possible to control a smaller current without increasing the switching frequency of the upper arm switch SW1 or SW2.

[0034] (Third embodiment) 11, in the third embodiment, similarly to FIG. 8 of the first embodiment, when n=4, the signal waveforms are shown when the inductance values ​​of the inductors L of the second and fourth multiplexed chopper cells 1 are changed relative to the same inductance values ​​of the first and third multiplexed chopper cells 1. In this way, the amount of output current may be changed for each chopper cell 1.

[0035] (Fourth embodiment) As shown in FIG. 12, in the fourth embodiment, a control device 37 that replaces the control device 10 includes a pulse generating unit 38 that replaces the pulse generating unit 12. In the pulse generating unit 38, a gate driving unit 21, a zero current detecting unit 22, and a pulse calculating unit 40 are individually provided for each of the n-multiplexed chopper cells 1. The function of the pulse calculating unit 23 in the first embodiment is shared between a pulse command unit 39 and pulse calculating units 40(1) to 40(n). With this configuration, the command values ​​output to each of the chopper cells 1(1) to 1(n) may be individually changed.

[0036] (Fifth and Sixth Embodiments) 13 and 14 show configuration examples in which chopper cells connected in parallel are connected in series as in the first embodiment. In the fifth embodiment shown in Fig. 13, two chopper cells 1a and 1b are connected in parallel to a common DC power supply VIN to form a parallel chopper cell 41. In the sixty-seventh embodiment shown in Fig. 14, two chopper cells 1a' and 1b' are connected in parallel to individual DC power supplies VIN1 and VIN2, but so that the capacitor C is shared by both, to form a parallel chopper cell 42.

[0037] When using the parallel chopper cells 41 or 42 as in the fourth and fifth embodiments, for example, the parallel chopper cells 41(1) and 41(2) are connected in series as shown in Fig. 15. Then, by changing the phase of the switching control for each chopper cell 1a, 1b, it is possible to cancel out the current ripple.

[0038] (Other embodiments) Although a step-down type chopper cell 1 is used as the power converter, the present invention is not limited to this and, for example, a step-up type or step-up / step-down type chopper cell 1 can be used. The chopper cell 1 may be either a non-insulated type or an insulated type.

[0039] Although the number of multiple operations n is set to 4 in this embodiment, the number of multiple operations n may be set to 3 or 4 or more. Although the power switches SW1 and SW2 are exemplified as N-channel power MOSFETs, they may be configured with other types of power switching elements. Each DC power source is not limited to a unit cell that constitutes a battery pack of an electric vehicle or the like.

[0040] To commutate the load current to the power MOSFETs that make up the power switches SW1 and SW2, freewheeling diodes D1 and D2 are provided in parallel, respectively, but this is not limiting. Body diodes added to the power MOSFETs may be used instead of the freewheeling diodes D1 and D2. Also, power switches with reverse conductivity, such as RC-IGBTs, may be used.

[0041] Although the present invention has been described based on the above-described embodiment, it is understood that the present invention is not limited to the embodiment or structure. The present invention also encompasses various modifications and modifications within the scope of equivalents. In addition, various combinations and forms, as well as other combinations and forms including one, more, or less than one element, are also within the scope and spirit of the present invention. [Explanation of symbols]

[0042] In the drawing, 1 indicates a chopper cell, 2 indicates a multilevel converter, 3 indicates a three-phase inverter, 10 indicates a control device, 11 indicates a motor control unit, 12 indicates a pulse generation unit, 15 indicates an LC series resonant circuit, 22 indicates a zero current detection unit, SW1 indicates an upper arm switch, and SW2 indicates a lower arm switch.

Claims

1. a power conversion unit (3) including n (n≧2) series-connected chopper cells (1, 1a, 1b, 1a′, 1b′) each having an LC series resonant circuit (15) connected in parallel to an upper-side and lower-side switching element (SW1, SW2); a control unit (11) that outputs control information according to an input command value and an output parameter generated by a motor (4) driven by a power conversion unit; a pulse generating unit (12, 38) that outputs a pulse signal for controlling switching of each chopper cell that constitutes the power converting unit in accordance with the control information.

2. The pulse generating unit includes an element driving unit (21) that drives a switching element that constitutes the chopper cell; a zero current detection unit (22) that detects when the current output from the chopper cell becomes zero and outputs a detection signal; a pulse signal output unit (23, 35) that operates the power conversion unit in a current boundary mode, calculates a switching period and an on time of the switching element, and a phase difference of a switching timing of the switching element, and outputs the pulse signal to the element drive unit.

3. The pulse signal output unit (35) includes a timer (36) that measures a certain time period after the detection signal is input, 3. The power conversion device according to claim 2, wherein the timing of turning on the next chopper cell is delayed by the predetermined time.

4. When the switching period is T, the on-time is Ton, the off-time of the switching element is Toff, the phase difference is Td, the input voltage is VINxn, the phase voltage is VOUTxn, the inductance is L, and the average value of the current output from the plurality of chopper cells is Iout, the pulse signal output unit has the following formula: When Iout>0, the upper arm switching element of the chopper cell is Ton=ILp×L / (VINxn-VOUTxn) Toff=ILp×L / VOUTxn T=Ton+Toff Td = T / n A pulse signal is outputted as follows: When Iout<0, the lower arm switching element of the chopper cell is Ton=ILp×L / VOUTxn Toff=ILp×L / (VINxn-VOUTxn) T=Ton+Toff Td = T / n 3. The power conversion device according to claim 2, wherein the power conversion device outputs a pulse signal such that:

5. 5. The power conversion device according to claim 1, wherein two sets of the chopper cells (1a, 1b, 1a', 1b') are connected in parallel.

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