JP2011188655A - Dc-ac power conversion controller - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem that, in a step-up chopper circuit part of a DC-AC conversion circuit, operation efficiency is reduced due to high voltage conversion ratio in a single bidirectional step-up chopper circuit, and a high breakdown voltage exceeding a DC circuit voltage is required for a switching element, to solve a problem that, when an inverter is operated from a step-up controlled DC voltage source, a high breakdown voltage exceeding the DC circuit voltage is required for the switching element due to a high DC voltage during high speed operation, and moreover, to solve a problem that, when on/off switching is directly controlled under a high DC voltage, peripheral equipment is affected by switching loss or switching noise. <P>SOLUTION: From a battery voltage, two sets of high DC voltages are obtained which have a neutral point voltage by serially connecting two sets of DC voltage outputs, stepped up by operation of two sets of step-up chopper switch circuits via one step-up reactor, in two stages, and the two sets of stepped up and controlled DC voltage sources having the neutral point voltage are connected to an NPC inverter to control the waveform and voltage continuously by operation of level 2 at low speed, and operation of level 3 at high speed. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an NPC inverter technology including a step-up chopper circuit used in the field of power supply for electric vehicles. In particular, it is a technology that contributes to energy saving and quality improvement of a storage battery (battery) by continuously controlling the charge / discharge circuit from 2 to 3 levels to improve operation efficiency and reduce noise.

In recent years, a drive power supply system for an electric vehicle often controls a battery by directly connecting a battery to an inverter, or boosting a battery voltage by a boost chopper circuit and then connecting the battery to the inverter to control the inverter.

When driving an electric vehicle at a low speed, the booster chopper circuit does not increase the DC voltage of the inverter, but when driving at a high speed, the inverter is often controlled after increasing to a high DC voltage, and the boost ratio is high. There is a problem that it is difficult to obtain high conversion efficiency.

As an inverter circuit configuration for driving an electric vehicle, a two-level inverter having a three-phase bridge configuration is generally used. However, it is used in an electric railway or the like for the purpose of reducing the switching element withstand voltage and improving the output voltage waveform of the inverter. In addition, there is no example of using an NPC inverter (see Patent Documents 1 to 4 and Non-Patent Document 1) for an electric vehicle.

In order to make this NPC invar work, a neutral point potential is required for the DC power source. Usually, two capacitors are connected in series to obtain two power sources with a neutral point and connected to the NPC inverter. However, the neutral point voltage may fluctuate depending on the load state and control state connected to the NPC inverter, and normal operation may not be performed. Although various measures have been studied, there are problems such as the presence of an inverter control mode that cannot essentially control the neutral voltage.

In electric vehicles, etc., a battery is used as a DC power supply, so it can be used as a DC power supply for an NPC inverter by connecting two sets of storage batteries in series. However, the configuration becomes more complicated when the DC voltage is increased. In addition, the load balance between the two sets of storage batteries may be disrupted, which is considered impractical.

  According to the prior art, when the battery voltage is directly connected to the inverter and the AC motor is controlled by the inverter, the switching loss of the inverter is large if the inverter is operated at a low speed under a high DC voltage suitable for high speed operation. Operating efficiency is lowered. Further, when high-speed operation is performed at a low voltage, the motor current becomes very large, accompanied by a large resistance loss, and the operation efficiency is lowered.

Therefore, as a control method of the inverter in a recent hybrid vehicle, the battery voltage is not directly connected to the inverter, but the DC voltage is controlled to an appropriate voltage value and connected to the inverter via the boost chopper circuit according to the operation state. The method is adopted.

With this control circuit configuration, during high-speed operation, the battery voltage is boosted by the boost chopper circuit and then the inverter output is obtained, thereby suppressing a current value that leads to a large resistance loss. Further, since the inverter is operated with a low DC voltage by suppressing the step-up ratio by the step-up chopper circuit during low-speed operation, switching loss during low-speed operation can also be suppressed.

However, when aiming at further improvement in operating efficiency, there is a need to further increase the DC operating voltage during high-speed rotation, but in inverter operation at a high DC voltage, a higher switching element withstand voltage is required and higher. Since switching noise and the like accompanying PWM switching control from the voltage also increase, the DC operating voltage is in a state where it can be suppressed to about several 500 V to 600 V.

Furthermore, when trying to obtain a higher DC voltage from the battery voltage, the voltage conversion ratio of the step-up chopper increases, leading to a decrease in conversion efficiency. From this point of view, it is difficult to operate the inverter with a high DC voltage.

Japanese Patent No. 4212212 JP 10-52049 A JP-A-9-56172 JP 2001-136750 A

"Power Electronics Circuits" edited by the Institute of Electrical Engineers of Japan, Semiconductor Power Conversion System Research Special Committee (Ohm Co., Ltd., published on November 30, 2000) pages 45 to 92, pages 137 to 210

  In a step-up chopper circuit part in a DC-AC converter circuit intended for applications in electric vehicles, etc., when a high DC voltage is obtained from a single DC voltage source such as a battery during high-speed operation, voltage conversion is performed with a single bidirectional step-up chopper circuit. The ratio becomes high and the operation efficiency is lowered, and there is a problem that a switching element that is required requires a high withstand voltage that exceeds the DC circuit voltage.

  In addition, when the inverter is operated from a DC voltage source that has been boosted and controlled, the inverter circuit section requires a high withstand voltage that exceeds the DC circuit voltage because the DC voltage increases during high-speed operation. When direct on / off switching control is performed under a high DC voltage, there are problems such as concern that switching loss and switching noise may affect peripheral devices.

  In addition, when a DC voltage source is divided by a capacitor to obtain a neutral point voltage and connected to an NPC inverter, it is known that the neutral point voltage cannot be controlled depending on the output waveform control of the inverter and the state of the load. Therefore, there is a problem in controlling the neutral point voltage of the NPC inverter.

The main point of the present invention is that two sets of boosted DC voltage outputs are serially connected from the battery voltage through the operation of two boost chopper circuits (two-stage cascade boost chopper circuit) through one boosting reactor. By connecting in two stages, two sets of high DC voltages having neutral point voltage are obtained, and two sets of boosted DC voltages having neutral point voltage are connected to an NPC inverter as a power source, and low speed Then, the above-mentioned problems are solved by performing waveform / voltage control continuously in two-level operation and in high-speed three-level operation.

That is, the first invention for solving the problem is that the output of the DC / DC voltage control unit capable of transmitting / receiving bidirectional power to obtain two sets of DC outputs having a DC neutral point capable of DC voltage control from a DC voltage source. Is connected to a DC / AC converter circuit section with a neutral point clamp diode inverter (NPC inverter) circuit configuration, so that the DC voltage applied to the inverter can be controlled and the waveform of the output voltage of the NPC inverter can be reduced from two levels. A DC / AC power conversion control device that enables control between three levels and continuously controls the amplitude of the output voltage of the NPC inverter and the PWM control waveform.

According to a second aspect of the present invention, in the DC / AC power conversion control device, two sets of switching circuits each having a connection point in which two switch circuits each having a diode connected in reverse parallel to the switching element are connected in series are connected. Two sets that share a boosting reactor by connecting a capacitor from both ends of two switching circuits connected in series, while connecting from a DC voltage source via a boosting reactor to two connection points The DC / AC power conversion control device is characterized in that two sets of voltage control outputs connected in series are obtained by switching control of the booster circuit operation and connected to an NPC inverter circuit.

Furthermore, the third invention provides two sets of voltages connected in series by switching control of two sets of boosting circuits sharing a boosting reactor in the DC / DC voltage control unit in the DC / AC power conversion control device. A DC / AC power conversion control device including a DC / DC voltage control unit, wherein the control output value is controlled to the same value.

Furthermore, the fourth invention is the DC / AC power conversion control device according to the first invention, wherein a three-phase AC motor is connected to the AC output of the three-phase NPC inverter. It is.

Furthermore, in the DC / AC power conversion control device according to the first to fourth inventions, the control of the DC / DC voltage control unit by the switch switching control of the two boosting circuits sharing the boosting reactor and the DC / AC voltage constituted by the NPC inverter. A DC / AC power conversion control device that performs speed torque control of a three-phase AC motor by combining and controlling an AC voltage control unit.

Furthermore, in the DC / AC power conversion control device of the first to fifth inventions, when the three-phase AC motor is operated at low speed, the output voltage in the DC / DC voltage control unit is lowered and the three-phase NPC in the DC / AC conversion circuit unit. A DC / AC power conversion control device characterized in that the inverter has a PWM control waveform in a two-level operation and the three-phase NPC inverter has a PWM control waveform in a three-level operation during high-speed operation.

  The step-up chopper circuit switching control method of the present invention can suppress the step-up ratio of the step-up chopper when boosting the DC voltage to ½, so that the efficiency of the step-up chopper circuit can be increased and the switching element can be The breakdown voltage can be reduced to 1/2 of the maximum boosted voltage.

In addition, the multi-level PWM control output waveform can be obtained independently of the neutral point voltage control by using the NPC inverter power supply for the boosted output voltage connected in series of the DC / DC voltage control circuit unit of the present invention. To improve the efficiency by lowering the DC voltage during low speed operation and operating at 2 levels, and increasing the DC voltage at high speed operation and operating at 3 levels to improve the PWM controlled output voltage waveform In addition, the switching control width can be suppressed to ½, switching noise and the like can be suppressed low, and the switching element withstand voltage can be suppressed to ½ of the maximum DC voltage.

An example of the basic circuit block diagram concerning the direct-current / alternating-current power conversion control device of the present invention. An example of the connection diagram of the switching circuit concerning the direct-current / alternating-current power conversion control device of the present invention. An example of the DC / DC voltage control circuit diagram of the present invention. Explanatory drawing of a short circuit current path | route (1) when energy is accumulate | stored in the pressure | voltage rise reactor in pressure | voltage rise operation | movement with the direct current | DC / DC voltage control circuit of this invention. Explanatory drawing of a short circuit current path | route (2) when making the capacitor | condenser Cd1 carry out voltage | pressure | voltage rise operation | movement with the boosting reactor accumulation | storage energy in pressure | voltage rise operation in the direct current | DC / DC voltage control circuit of this invention. Explanatory drawing of a short circuit current path (3) when making the capacitor | condenser Cd2 perform a boosting operation with the energy stored in the boosting reactor in the boosting operation in the DC / DC voltage control circuit of the present invention. 1 is a configuration example of a main circuit configuration and a control system including a load state for confirming a power running operation and a regenerative operation in the DC / DC voltage control circuit according to the first embodiment of the present invention. FIG. 3 is a diagram illustrating simulation waveform data of the DC / DC voltage control circuit according to the first embodiment. The example of a structure of the main circuit and control system containing the three-phase RL load connected in order to confirm the control action of the direct current | flow / AC power conversion control apparatus of Example 2 of this invention. The figure which shows the simulation waveform data of the DC / AC power conversion control apparatus which concerns on Example 2. FIG.

  The present invention provides a neutral point by connecting two boosted DC voltage outputs in series in two stages from a battery voltage through two boost chopper circuit operations through one boosting reactor. A DC voltage twice as high as the voltage is obtained, and the two boosted DC voltages having a neutral point voltage are connected to the NPC inverter as a power source to drive the AC motor from a DC voltage source such as a battery. A DC / AC power conversion control device to be controlled.

FIG. 1 shows a DC / AC power conversion control device 200 in which two sets of voltage sources E _d1 and E _d2 boosted from a DC voltage source 100 are connected in series and an AC motor 300 is operated as a power source for an NPC inverter 220. It is a basic circuit structural example.

  FIG. 2 shows a power conversion circuit constituting the DC / AC power conversion control device. Two sets of switch circuits 211, 212, 213 in which two switching arms in which switching elements (IGBT, etc.) and diodes are connected in antiparallel are connected in series from the DC voltage source 100 through one step-up reactor 217, and The booster circuit 210 is configured by connecting 214 in series, the boost reactor 217 is short-circuited, and then the neutral circuit is operated by alternately operating the booster output capacitors 215 and 216. By obtaining two sets of boosted voltage outputs at the center and connecting them to the DC / AC power converter circuit unit (NPC inverter) 220, the NPC inverter can respond to the control signal without causing the problem of neutral potential fluctuation. Two-level operation and three-level operation can be arbitrarily controlled.

  FIG. 3 is a circuit configuration example of the DC / DC voltage control unit 210 including switch circuits 211, 212, 213, and 214 using diodes connected in antiparallel with switching elements (IGBT or the like).

4, of the illustration of the step-up chopper operation principle of a DC-DC voltage control unit 210, to form a short circuit from the switch S ₀₂ -S ₀₃ route through the boost reactor (L) from a DC power source 100, energy The short circuit current path diagram (1) which accumulates is shown.

FIG. 5 is an explanatory diagram of the operation principle of the step-up chopper in the direct current / direct current voltage control unit 210, in which the energy accumulated in the step-up reactor (L) from the direct-current power source is formed through the switch S ₀₁ -S ₀₃ route. FIG. 9 shows a short-circuit current path diagram (2) for causing the boost output capacitor C _d1 to perform a boost operation.

6, of the illustration of the step-up chopper operation principle of a DC-DC voltage control unit 210, the energy stored in the boost reactor (L) from a DC power source to form a more step-up path switch S ₀₂ -S ₀₄ pathway FIG. 9 shows a short-circuit current path diagram (3) for causing the boost output capacitor C _d2 to perform a boost operation.

As an embodiment of the present invention, a DC load circuit 230 shown in FIG. 7 is connected in the DC / DC voltage control unit 210, the boost reactor L = 10 mH, the capacitor C _d1 = C _d2 = 5000 μF, and the DC voltage E _B = 100V. Originally, the boosting voltage is set to E _d1 = E _d2 = 150V, the resistance R of the load circuit 230 is set to 10Ω, the voltage Vs of the load circuit 230 is set to 145V, and the power running operation is performed to extract energy to the load side. Simulation analysis was performed for two cases where the voltage Vs of the load circuit 230 was set to 155 V and energy was regenerated from the load side to the DC voltage source E _B 100 of the DC / DC voltage conversion circuit 210.

FIG. 8 shows operation waveforms when simulation analysis is performed under the two operating conditions of Example 1. In FIG. 8A, in the power running operation, a positive steady current flows through a transient state, and (b ) In regenerative operation, a negative steady-state current flows through a transient state, and it can be confirmed that bidirectional power can be exchanged and the boost operation can be performed without any problem.

As another embodiment of the present invention, in the DC / AC power conversion control circuit according to the present invention including the DC / DC voltage control unit 210 and the DC / AC power conversion unit 220 shown in FIG. 9, the step-up reactor L = 10 mH, the capacitor C _{Under the condition of d1} = C _d2 = 5000μF and DC voltage E _B = 100V, the boost voltage was set to E _d1 = E _d2 = 150V, and the simulation analysis was performed with R = 10Ω and L ₁ = 10mH as a three-phase load. .

FIG. 10 is an operation waveform when the frequency is increased by the constant V / f control in the DC / AC power conversion control circuit of the second embodiment. From the DC power supply voltage E _B = 100 V by the step-up chopper operation, E _d1 = E _d2 = 150V is obtained, and it can be confirmed that the frequency increases and the voltage waveform can be controlled to a multilevel-controlled PWM waveform from the two-level operation to the three-level operation.

In the DC / AC power conversion control device according to the present invention, the DC / DC voltage control unit can improve the operating efficiency especially during boosting, and the DC / AC power conversion circuit unit can operate at low speed, and the required switching element breakdown voltage. Can be suppressed to 1/2 of the maximum DC voltage value after boosting, and the device withstand voltage can be afforded, so that it can be operated at a higher DC operating voltage that is advantageous for improving the efficiency. It can be effectively used as a control power source.

DESCRIPTION OF SYMBOLS 100 ... DC power supply 200 ... DC / AC power converter unit 210 ... DC / DC voltage control circuit unit
211 to 214... Switching circuits 215 and 216 with a diode connected in antiparallel with the switching element 215. Boosting output capacitor 217... Boosting reactor 220 .. DC / AC power conversion circuit (NPC inverter)
230 ... DC load circuit 300 for confirming power running operation and regenerative operation ... AC load (AC motor, three-phase RL load)
400: control signal generation circuit unit 410: control circuit example of DC / DC voltage control circuit unit 420 ... control circuit example of DC / AC power conversion circuit unit (PWM control unit)

Claims (6)

DC / DC voltage control unit capable of bi-directional power transfer to obtain two sets of DC outputs with DC neutral points capable of DC voltage control from DC voltage source Neutral point clamp diode inverter (NPC inverter) circuit configuration By connecting to the DC / AC conversion circuit unit by the DC, it is possible to control the DC voltage applied to the inverter, and the waveform of the output voltage of the NPC inverter can be controlled from 2 levels to 3 levels, A DC / AC power conversion control device characterized in that the output voltage amplitude and PWM control waveform of an NPC inverter can be continuously controlled. 2. The DC / AC power conversion control device according to claim 1, wherein two sets of switching circuits each having a connection point in which two switching circuits each having a diode connected in reverse parallel to the switching element are connected in series, Two sets of boosting circuits that share the boosting reactor by connecting the capacitor between the two connection points via the boosting reactor from the power source and connecting capacitors to both ends of the two switching circuits connected in series. A DC / AC power conversion control device characterized in that two sets of voltage control outputs connected in series are obtained by switch switching control and connected to an NPC inverter circuit. 3. The DC / DC voltage control unit in the DC / AC power conversion control device according to claim 1, wherein two sets of voltage control outputs connected in series by switch switching control of two sets of boosting circuits sharing a boosting reactor. A DC / AC power conversion control device including a DC / DC voltage control unit, wherein the value of the DC is controlled to the same value. 2. The DC / AC power conversion control device according to claim 1, wherein a three-phase AC motor is connected to the AC output of the three-phase NPC inverter. 5. The DC / AC power conversion control device according to claim 1, wherein the DC / DC voltage control unit is configured by control of DC / DC voltage control by switching control of two sets of boosting circuits sharing a boosting reactor and an NPC inverter. A DC / AC power conversion control device that performs speed torque control of a three-phase AC motor by combining and controlling a control unit. 6. The DC / AC power conversion control device according to claim 1, wherein when the three-phase AC motor is operated at a low speed, the output voltage in the DC / DC voltage control unit is lowered and the three-phase NPC inverter in the DC / AC conversion circuit unit is set. A DC / AC power conversion control device characterized in that the PWM control waveform is a two-level operation, and the three-phase NPC inverter is a PWM control waveform in a three-level operation during high-speed operation.

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