Control device of neutralpointclamped power converter apparatus, and control method of neutralpointclamped power converter apparatus

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First Claim
1. A control device of a neutralpointclamped power converter apparatus, comprising:
 a 3phase/2phase converter configured to convert threephase currents flowing to threephase loads, which are driven by the neutralpointclamped power converter apparatus that is connected to a DC power supply having three potentials and is capable of outputting voltages of three levels, to a daxis current and a qaxis current of a rotating coordinate system;
a 2phase/3phase current converter configured to convert a daxis filter current and a qaxis filter current, which were obtained by passing the daxis current and the qaxis current through a filter having a time constant which is greater than an inverse number of a fundamental wave frequency of the threephase currents, to threephase currents;
a neutralpoint potential controller configured to calculate, based on the threephase currents converted by the 2phase/3phase current converter, a zerophase voltage instruction value for controlling voltages into which a DC input voltage is divided at a neutral point of the power converter apparatus, as an instruction value which is superimposed on threephase voltage instruction values for the power converter apparatus; and
a 2phase/3phase voltage converter configured to convert a daxis filter voltage instruction value and a qaxis filter voltage instruction value, which were obtained by passing a daxis voltage instruction value and a qaxis voltage instruction value of the rotating coordinate system through a filter having a time constant which is greater than an inverse number of a fundamental wave frequency of the threephase voltage instruction values, to threephase voltage instruction values,wherein the neutralpoint potential controller is configured to calculate the zerophase voltage instruction value by calculating a zerophase voltage feedforward instruction value for controlling the voltages into which the DC input voltage is divided at the neutral point, based on the threephase currents converted by the 2phase/3phase current converter and the threephase voltage instruction values converted by the 2phase/3phase voltage converter.
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Abstract
According to one embodiment, there is provided a control device of a neutralpointclamped power converter apparatus including a converter configured to convert current which were obtained by passing a daxis current and a qaxis current of a rotating coordinate system through a filter having a time constant which is greater than an inverse number of a fundamental wave frequency of a threephase currents, to threephase currents, and a controller configured to calculate, based on the threephase currents converted, a zerophase voltage instruction value for controlling voltages into which a DC input voltage is divided at a neutral point, as an instruction value which is superimposed on threephase voltage instruction values.
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5 Claims
 1. A control device of a neutralpointclamped power converter apparatus, comprising:
a 3phase/2phase converter configured to convert threephase currents flowing to threephase loads, which are driven by the neutralpointclamped power converter apparatus that is connected to a DC power supply having three potentials and is capable of outputting voltages of three levels, to a daxis current and a qaxis current of a rotating coordinate system; a 2phase/3phase current converter configured to convert a daxis filter current and a qaxis filter current, which were obtained by passing the daxis current and the qaxis current through a filter having a time constant which is greater than an inverse number of a fundamental wave frequency of the threephase currents, to threephase currents; a neutralpoint potential controller configured to calculate, based on the threephase currents converted by the 2phase/3phase current converter, a zerophase voltage instruction value for controlling voltages into which a DC input voltage is divided at a neutral point of the power converter apparatus, as an instruction value which is superimposed on threephase voltage instruction values for the power converter apparatus; and a 2phase/3phase voltage converter configured to convert a daxis filter voltage instruction value and a qaxis filter voltage instruction value, which were obtained by passing a daxis voltage instruction value and a qaxis voltage instruction value of the rotating coordinate system through a filter having a time constant which is greater than an inverse number of a fundamental wave frequency of the threephase voltage instruction values, to threephase voltage instruction values, wherein the neutralpoint potential controller is configured to calculate the zerophase voltage instruction value by calculating a zerophase voltage feedforward instruction value for controlling the voltages into which the DC input voltage is divided at the neutral point, based on the threephase currents converted by the 2phase/3phase current converter and the threephase voltage instruction values converted by the 2phase/3phase voltage converter.  View Dependent Claims (2)
 3. A control device of a neutralpointclamped power converter apparatus, comprising:
a 3phase/2phase converter configured to convert threephase currents flowing to threephase loads, which are driven by the neutralpointclamped power converter apparatus that is connected to a DC power supply having three potentials and is capable of outputting voltages of three levels, to a daxis current and a qaxis current of a rotating coordinate system; a 2phase/3phase current converter configured to convert a daxis filter current and a qaxis filter current, which were obtained by passing the daxis current and the qaxis current through a filter having a time constant which is greater than an inverse number of a fundamental wave frequency of the threephase currents, to threephase currents; a neutralpoint potential controller configured to calculate, based on the threephase currents converted by the 2phase/3phase current converter, a zerophase voltage instruction value for controlling voltages into which a DC input voltage is divided at a neutral point of the power converter apparatus, as an instruction value which is superimposed on threephase voltage instruction values for the power converter apparatus; and a 2phase/3phase voltage converter configured to convert a daxis filter voltage instruction value and a qaxis filter voltage instruction value, which were obtained by passing a daxis voltage instruction value and a qaxis voltage instruction value of the rotating coordinate system through a filter having a time constant which is greater than an inverse number of a fundamental wave frequency of the threephase voltage instruction values, to threephase voltage instruction values, wherein the neutralpoint potential controller is configured to calculate the zerophase voltage instruction value, based on (a) signs of the threephase currents converted by the 2phase/3phase current converter, (b) signs of the threephase voltage instruction values converted by the 2phase/3phase voltage converter, and (c) a difference between a highpotentialside voltage and a lowpotentialside voltage which are divided at the neutral point.
 4. A control method of a neutralpointclamped power converter apparatus which is connected to a DC power supply having three potentials and is capable of outputting voltages of three levels, the method comprising:
converting threephase currents flowing to threephase loads, which are driven by the power converter apparatus, to a daxis current and a qaxis current of a rotating coordinate system; converting a daxis filter current and a qaxis filter current, which were obtained by passing the daxis current and the qaxis current through a filter having a time constant which is greater than an inverse number of a fundamental wave frequency of the threephase currents, to threephase currents; calculating, based on the converted threephase currents, a zerophase voltage instruction value for controlling voltages into which a DC input voltage is divided at a neutral point of the power converter apparatus, as an instruction value which is superimposed on threephase voltage instruction values for the power converter apparatus; converting a daxis filter voltage instruction value and a qaxis filter voltage instruction value, which were obtained by passing a daxis voltage instruction value and a qaxis voltage instruction value of the rotating coordinate system through a filter having a time constant which is greater than an inverse number of a fundamental wave frequency of the threephase voltage instruction values, to threephase voltage instruction values; and calculating, based on the converted threephase currents and the converted threephase voltage instruction values, the zerophase voltage instruction value by calculating a zerophase voltage feedforward instruction value for controlling the voltages into which the DC input voltage is divided at the neutral point.
 5. A control method of a neutralpointclamped power converter apparatus which is connected to a DC power supply having three potentials and is capable of outputting voltages of three levels, the method comprising:
converting threephase currents flowing to threephase loads, which are driven by the power converter apparatus, to a daxis current and a qaxis current of a rotating coordinate system; converting a daxis filter current and a qaxis filter current, which were obtained by passing the daxis current and the qaxis current through a filter having a time constant which is greater than an inverse number of a fundamental wave frequency of the threephase currents, to threephase currents; calculating, based on the converted threephase currents, a zerophase voltage instruction value for controlling voltages into which a DC input voltage is divided at a neutral point of the power converter apparatus, as an instruction value which is superimposed on threephase voltage instruction values for the power converter apparatus; converting a daxis filter voltage instruction value and a qaxis filter voltage instruction value, which were obtained by passing a daxis voltage instruction value and a qaxis voltage instruction value of the rotating coordinate system through a filter having a time constant which is greater than an inverse number of a fundamental wave frequency of the threephase voltage instruction values, to threephase voltage instruction values; and calculating the zerophase voltage instruction value, based on (a) signs of the converted threephase currents, (b) signs of the converted threephase voltage instruction values, and (c) a difference between a highpotentialside voltage and a lowpotentialside voltage which are divided at the neutral point.
1 Specification
This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2014214004, filed Oct. 20, 2014, the entire contents of which are incorporated herein by reference.
Embodiments of the invention relate generally to a control device of a neutralpointclamped power converter apparatus, and a control method of the neutralpointclamped power converter apparatus.
A neutralpointclamped (NPC) power converter apparatus is configured such that at least four switching elements are connected in series, and can output a high voltage of several kV˜severalten kV. In addition, since the neutralpointclamped power converter apparatus outputs phase voltages of three levels, a higher harmonic wave that occurs is small. Thus, the ripple of the waveform is small, and a current with a smooth waveform is supplied to loads. In addition, of the abovedescribed four switching elements, two elements are switched at the same timing, and the other two are not switched. Thus, the switching loss of the apparatus as a whole is small. Therefore, the neutralpointclamped power converter apparatuses are widely used in railway cars, driving apparatuses for industrial uses, and power system voltage stabilizing apparatuses.
In the case of using the neutralpointclamped power converter apparatus having the abovedescribed features, neutralpoint potential control is required. The neutralpoint potential control is a control to equally divide a DC input voltage by a highpotentialside capacitor and a lowpotentialside capacitor, and to equally hold a highpotentialside DC voltage and a lowpotentialside DC voltage. In the case where the neutralpointclamped power converter apparatus is applied to a twophase output or a threephase output, there is known a method of executing the neutralpoint potential control by applying to the respective phases an identical voltage (zerophase voltage) which is calculated from voltage instruction values and load currents of the respective phases.
However, when the load current is small, for example, when the load current has a value close to zero, a higher harmonic wave current is relatively greater than a fundamental wave current. Thus, there is a case in which the sign of the fundamental wave current, which contributes to a neutralpoint potential variation, and the sign of a detected load current are different. As a result, in some cases, the sign of the calculated zerophase voltage is reverse to the sign of the voltage that is to be normally applied to the apparatus, and the highpotentialside DC voltage and lowpotentialside DC voltage are not balanced.
In general, according to one embodiment, there is provided a control device of a neutralpointclamped power converter apparatus, including a 3phase/2phase converter configured to convert threephase currents flowing to threephase loads, which are driven by the neutralpointclamped power converter apparatus that is connected to a DC power supply having three potentials and is capable of outputting voltages of three levels, to a daxis current and a qaxis current of a rotating coordinate system. The control device includes a 2phase/3phase current converter configured to convert a daxis filter current and a qaxis filter current, which were obtained by passing the daxis current and the qaxis current through a filter having a time constant which is greater than an inverse number of a fundamental wave frequency of the threephase currents, to threephase currents. The control device includes a neutralpoint potential controller configured to calculate, based on the threephase currents converted by the 2phase/3phase current converter, a zerophase voltage instruction value for controlling voltages into which a DC input voltage is divided at a neutral point of the power converter apparatus, as an instruction value which is superimposed on threephase voltage instruction values for the power converter apparatus.
Embodiments will be explained below with reference to the accompanying drawings. Note that portions common to these drawings will be denoted by the same reference numerals or the same reference numerals given suffixes, and a repetitive explanation will be omitted as needed.
To begin with, a first embodiment is described.
As illustrated in
Hereinafter, taking the U phase as an example, the configuration of the NPC leg is described.
In the NPC leg of the U phase, four selfturnoff switching elements sw_u1, sw_u2, sw_u3 and sw_u4 are connected in series from the high potential side to the low potential side. In addition, freewheel diodes d_u1, d_u2, d_u3 and d_u4 are connected in parallel with, and in an opposite direction to, the switching elements sw_u1, sw_u2, sw_u3 and sw_u4 in a onetoone correspondence.
Furthermore, a clamp diode d_u5 is connected between the emitter of the switching element sw_u1 and the neutral point, and a clamp diode d_u6 is connected between the neutral point and the emitter of the switching element sw_u3. The anode of the clamp diode d_u5 is connected to the neutral point, and the cathode of the clamp diode d_u5 is connected to the emitter of the switching element sw_u1. The anode of the clamp diode d_u6 is connected to the emitter of the switching element sw_u3, and the cathode of the clamp diode d_u6 is connected to the neutral point.
The emitter of the switching element sw_u2 and the collector of the switching element sw_u3 are connected to a load l_u. In this manner, the NPC leg of the U phase is composed of the selfturnoff switching elements sw_u1, sw_u2, sw_u3 and sw_u4, freewheel diodes d_u1, d_u2, d_u3 and d_u4, and clamp diodes d_u5 and d_u6. The NPC legs of the V phase and W phase have the same configuration as described above. Threephase currents i_u, i_v and i_w are supplied to threephase loads l_u, l_v and l_w from the NPC legs of the respective phases.
Next, a control device of the neutralpointclamped power converter apparatus is described.
As illustrated in
The 3phase/DQ converter 21 detects threephase currents i_u, i_v and i_w flowing to the threephase loads l_u, l_v and l_w. The 3phase/DQ converter 21 executes 3phase/DQ conversion (3phase/2phase conversion: conversion from a coordinate system at rest to a rotating coordinate system) of the threephase currents i_u, i_v and i_w. By executing this conversion, the 3phase/DQ converter 21 outputs a daxis current i_d of the rotating coordinate system to the automatic current regulator 22, and outputs a qaxis current i_q, which is perpendicular to the daxis in the rotating coordinate system, to the automatic current regulator 23.
The automatic current regulator 22 executes a PI (proportionalintegral) arithmetic operation on the daxis current i_d so that the daxis current i_d follows a daxis current instruction value i_d*. By this arithmetic operation, the automatic current regulator 22 outputs a daxis voltage instruction value v_d* to the DQ/3phase converter 24 and neutralpoint potential controller 30. In addition, the automatic current regulator 23 executes a PI arithmetic operation on the qaxis current i_q so that the qaxis current i_q follows a qaxis current instruction value i_q*. By this arithmetic operation, the automatic current regulator 23 outputs a qaxis voltage instruction value v_q* to the DQ/3phase converter 24 and neutralpoint potential controller 30.
The DQ/3phase converter 24 executes DQ/3phase conversion (2phase/3phase conversion: conversion from the rotating coordinate system to the coordinate system at rest) of the daxis voltage instruction value v_d* and qaxis voltage instruction value v_q*. By executing this conversion, the DQ/3phase converter 24 outputs, as threephase voltage instruction values, a Uphase voltage instruction value v_u*0, a Vphase voltage instruction value v_v*0 and a Wphase voltage instruction value v_w*0 to the PWM controller 25.
The neutralpoint potential controller 30 calculates a zerophase voltage instruction value v_z*. This zerophase voltage instruction value v_z* is a voltage for controlling the voltages into which the DC input voltage v_dc is divided at the neutral point. The zerophase voltage instruction value v_z* is superimposed (added) on the voltage instruction values v_u*0, v_v*0 and v_w*0 of the respective phases by adders 26, 27 and 28 which correspond to the respective phases. The resultant superimposed values become a Uphase voltage instruction value v_u*, a Vphase voltage instruction value v_v* and a Wphase voltage instruction value v_w* as ultimate threephase voltage instruction values to the PWM controller 25.
Based on these voltage instruction values, the PWM controller 25 generates, by PWM control, a gate signal of a switching element corresponding to the leg of each phase, and turns on/off each switching element by using this gate signal.
Next, the generation of the abovedescribed zerophase voltage instruction value v_z* is described.
As illustrated in
The zerophase voltage instruction value v_z* is the sum of a feedforward value v_z*_ff and a feedback value v_z*_fb. To begin with, a description is given of the calculation of the feedforward value v_z*_ff by the neutralpoint potential controller 30.
To start with, an arithmetic operation relating to current values for calculating the feedforward value v_z*_ff is described. The 3phase/DQ converter 31 detects threephase currents i_u, i_v and i_w and executes 3phase/DQ conversion of these currents. By this conversion, the 3phase/DQ converter 31 outputs a daxis current i_d of the rotating coordinate system to the lowpass filter 32. In addition, the 3phase/DQ converter 31 outputs, by 3phase/DQ conversion, a qaxis current i_q, which is perpendicular to the daxis in the rotating coordinate system, to the lowpass filter 33.
The daxis current i_d passes through the lowpass filter 32, and is output to the DQ/3phase converter 34 as a daxis filter current i_d_f. In addition, the qaxis current i_q passes through the lowpass filter 33, and is output to the DQ/3phase converter 34 as a qaxis filter current i_q_f.
The time constant of the lowpass filter 32, 33 is greater than an inverse number of the fundamental frequency of the threephase currents. Besides, when the lowpass filter 32, 33 is a movingaverage filter, the movingaverage cycle is greater than the inverse number of the fundamental frequency of the threephase currents.
The DQ/3phase converter 34 executes DQ/3phase conversion of the daxis filter current i_d_f from the lowpass filter 32 and the qaxis filter current i_q_f from the lowpass filter 33. The DQ/3phase converter 34 outputs a Uphase filter current i_u_f, a Vphase filter current i_v_f and a Wphase filter current i_w_f, which are obtained by this conversion, to the arithmetic unit 38.
Next, a description is given of an arithmetic operation relating to voltage instruction values for calculating the feedforward value v_z*_ff. The daxis voltage instruction value v_d* from the automatic current regulator 22 passes through the lowpass filter 35, and is output to the DQ/3phase converter 37 as a daxis filter voltage instruction value v_d*_f. In addition, the qaxis voltage instruction value v_q* from the automatic current regulator 23 passes through the lowpass filter 36, and is output to the DQ/3phase converter 37 as a qaxis filter voltage instruction value v_q*_f.
The time constant of the lowpass filter 35, 36 is greater than an inverse number of the fundamental frequency of the threephase voltage instruction values. Besides, when the lowpass filter 35, 36 is a movingaverage filter, the movingaverage cycle is greater than the inverse number of the fundamental frequency of the threephase voltage instruction values.
The DQ/3phase converter 37 executes DQ/3phase conversion of the daxis filter voltage instruction value v_d*_f from the lowpass filter 35 and the qaxis filter voltage instruction value v_q*_f from the lowpass filter 36. The DQ/3phase converter 37 outputs a Uphase filter voltage instruction value v_u*_f, a Vphase filter voltage instruction value v_v*_f and a Wphase filter voltage instruction value v_w*_f, which are obtained by this conversion, to the arithmetic unit 38.
Using the values of the filter currents of the U phase, V phase and W phase from the DQ/3phase converter 34 and the filter voltage instruction values of the U phase, V phase and W phase from the DQ/3phase converter 37, the arithmetic unit 38 calculates the feedforward value v_z*_ff according to the following equation (1).
v_z*_ff={(1−v_u*_f)*i_u_f+(1−v_v*_f)*i_v_f+(1−v_w*_f)*i_w_f}/{sign(v_u*_f)*i_u_f+sign(v_v*_f)*i_v_f+sign(v_w*_f)*i_w_f} equation (1)
In equation (1), sign(v_u*_f), sign(v_v*_f), sign(v_w*_f) are signs of filter voltage instruction values of the respective phases. The feedforward value v_z*_ff is not a value which is calculated by taking into account a variation of the neutralpoint potential, due to variances in leak currents of the capacitor c_p, c_n, and switching elements. Thus, feedback control is necessary. Therefore, the neutralpoint potential controller 30 calculates a feedback value v_z*_fb, as described below.
A subtracter 39 subtracts the value of the DC voltage v_dc_n from the value of the DC voltage v_dc_p. A PI arithmetic unit 40 executes a PI arithmetic operation on the value from the subtracter 39.
In addition, a sign unit 41 calculates a sign of the feedforward value v_z*_ff which was calculated by the arithmetic unit 38. To calculate the sign of a certain value is to output “1” if the sign of an input value is positive, and to output “−1” if the sign of the input value is negative. A multiplier 42 multiplies together the calculated sign and the calculated value by the PI arithmetic unit 40. Thereby, a feedback value v_z*_fb is calculated. The arithmetic expression of the feedback value v_z*_fb is given by the following equation (2).
v_z*_fb=(v_dc_p−v_dc_n)*(kp+ki/s)*sign(v_z*_ff) equation (2)
An adder 43 adds the feedback value v_z*_fb from the multiplier 42 to the feedforward value v_z*_ff from the arithmetic unit 38. Thereby, a zerophase voltage instruction value v_z* is generated. As described above, this zerophase voltage instruction value v_z* is superimposed on the Uphase voltage instruction value v_u*0, Vphase voltage instruction value v_v*0 and Wphase voltage instruction value v_w*0, which are threephase voltage instruction values from the DQ/3phase converter 24. Thereby, the Uphase voltage instruction value v_u*, Vphase voltage instruction value v_v* and Wphase voltage instruction value v_w*, which are the ultimate threephase voltage instruction values to the PWM controller 25, are generated.
Only a fundamental wave component affects a neutralpoint potential variation. Thus, in some cases, when the fundamental wave current component was particularly small relative to the higher harmonic wave current component, the sign of the feedforward value v_z*_ff or feedback value v_z*_fb was reversed to the normal sign due to the effect of the higher harmonic wave component. As a result, there was concern that the neutralpoint potential deviates, and the application voltage to the switching element or capacitor exceeds the breakdown voltage, leading to breakdown.
In the first embodiment, the threephase currents and threephase voltage instruction values, which relate to the neutralpoint control, are converted to the values of two axes (d axis, q axis) of the rotating coordinate system, respectively, and are passed through the lowpass filters. Further, in the first embodiment, based on the threephase filter currents and threephase filter voltage instruction values, which were reversely converted to the threephase values of the coordinate system at rest, the feedforward value v_z*_ff and feedback value v_z*_fb are calculated and these values are used for the neutralpoint potential control. Thereby, after the higher harmonic wave current component is eliminated from the threephase currents, the fundamental wave current component can be extracted without a phase delay, and the exact neutralpoint potential control can be executed even if the value of the load current is close to zero. Therefore, the neutralpoint potential can be stabilized in the region in which the load current ranges from zero to the maximum.
Next, a second embodiment is described. Incidentally, in the configuration of each of the embodiments to be described below, a detailed description of the same parts as described in the first embodiment is omitted.
As illustrated in
Like the first embodiment, a highpotentialside capacitor c_p and a lowpotentialside capacitor c_n are connected in series between a highpotentialside terminal and a lowpotentialside terminal of a DC power supply 11. These capacitors are common to each phase, and a connection point between these capacitors forms a neutral point.
Inputside terminals of a Uphase converter cnv_u, a Vphase converter cnv_v and a Wphase converter cnv_w are connected to a highpotentialside terminal, the neutral point and a lowpotentialside terminal of the capacitor c_p and capacitor c_n which are common to each phase. In addition, outputside terminals of the Uphase converter cnv_u are connected to DC windingside terminals of a Uphase transformer tr_u. Outputside terminals of the Vphase converter cnv_v are connected to DC windingside terminals of a Vphase transformer tr_v. Outputside terminals of the Wphase converter cnv_w are connected to DC windingside terminals of a Wphase transformer tr_w. Electric currents are supplied from AC windingside terminals of these transformers to the threephase loads l_u, l_v and l_w.
As illustrated in
Hereinafter, taking the U phase as an example, the configuration of the NPC legs is described.
In a first NPC leg of the U phase, four selfturnoff switching elements sw_a1, sw_a2, sw_a3 and sw_a4 are connected in series from the high potential side to the low potential side, and freewheel diodes d_a1, d_a2, d_a3 and d_a4 are connected in parallel with, and in an opposite direction to, these switching elements in a onetoone correspondence.
Furthermore, a clamp diode d_a5 is connected between the emitter of the switching element sw_a1 and the neutral point, and a clamp diode d_a6 is connected between the neutral point and the emitter of the switching element sw_a3.
Similarly, in a second NPC leg of the U phase, four selfturnoff switching elements sw_b1, sw_b2, sw_b3 and sw_b4 are connected in series from the high potential side to the low potential side, and freewheel diodes d_b1, d_b2, d_b3 and d_b4 are connected in parallel with, and in an opposite direction to, these switching elements in a onetoone correspondence.
Furthermore, a clamp diode d_b5 is connected between the emitter of the switching element sw_b1 and the neutral point, and a clamp diode d_b6 is connected between the neutral point and the emitter of the switching element sw_b3.
An output voltage v_out to the Uphase transformer tr_u is output from between the emitter of the switching element sw_a2 and the collector of the switching element sw_a3, and from between the emitter of the switching element sw_b2 and the collector of the switching element sw_b3. The NPC legs of the V phase and W phase have the same configuration as this.
The neutralpointclamped power converter apparatus in the second embodiment can execute onepulse control which switches the switching element of the converter of each phase once in one cycle of the output AC voltage.
As illustrated in
The functions of the 3phase/DQ converter 21 and automatic current regulators (ACR) 22 and 23 are the same as in the first embodiment.
The DQ/3phase converter 24 executes DQ/3phase conversion of the daxis voltage instruction value v_d* and qaxis voltage instruction value v_q*. By this conversion, the DQ/3phase converter 24 obtains a Uphase voltage instruction value v_u*0, a Vphase voltage instruction value v_v*0 and a Wphase voltage instruction value v_w*0, and outputs these values to the onepulse controller 51 as threephase voltage instruction values.
Based on these instruction values and a sign calculation result from the neutralpoint potential controller 30b, the onepulse controller 51 generates a gate signal of the switching element corresponding to the leg of each phase, and drives each switching element by using this gate signal. In the generation of this gate signal, the onepulse controller 51 determines the phase at which the voltage of the gate signal is raised, in accordance with the magnitude (modulation factor) of the voltage instruction value of each phase. The sign calculation by the neutralpoint potential controller 30b will be described later.
Here, taking the U phase as an example, the neutralpoint potential control is described.
The neutralpoint potential varies when the NPC leg on one side of each phase is connected to the neutral point. Thus, the neutralpoint potential becomes controllable when the output voltage v_out of the NPC leg of each phase is +v_dc/2 or −v_dc/2.
As illustrated in
The switching pattern of the switching elements by the onepulse controller 51, as illustrated in
As illustrated in
The functions of the 3phase/DQ converter 31 and lowpass filters 32 and 33 are the same as in the first embodiment.
The DQ/3phase converter 34 executes DQ/3phase conversion of the daxis filter current i_d_f from the lowpass filter 32 and the qaxis filter current i_q_f from the lowpass filter 33. By this conversion, the DQ/3phase converter 34 obtains a Uphase filter current i_u_f, a Vphase filter current i_v_f and a Wphase filter current i_w_f. The DQ/3phase converter 34 outputs the Uphase filter current i_u_f to the sign unit 61, the Vphase filter current i_v_f to the sign unit 62, and the Wphase filter current i_w_f to the sign unit 63.
The sign unit 61 calculates the sign of the Uphase filter current i_u_f. The sign unit 62 calculates the sign of the Vphase filter current i_v_f. The sign unit 63 calculates the sign of the Wphase filter current i_w_f.
A subtracter 64 subtracts the value of the DC voltage v_dc_n from the value of the DC voltage v_dc_p. The sign unit 65 calculates the sign of a value from the subtracter 64.
A multiplier 66 calculates a sign Sign_u for the U phase, by multiplying the sign calculated by the sign unit 61 with respect to the Uphase filter current i_u_f, and the sign calculated by the sign unit 65.
In addition, a multiplier 67 calculates a sign Sign_v for the V phase, by multiplying the sign calculated by the sign unit 62 with respect to the Vphase filter current i_v_f, and the sign calculated by the sign unit 65.
Besides, a multiplier 68 calculates a sign Sign_w for the W phase, by multiplying the sign calculated by the sign unit 63 with respect to the Wphase filter current i_w_f, and the sign calculated by the sign unit 65. The signs for the respective phases are output to the onepulse controller 51.
In this manner, in each phase, the sign of the filter current and the sign of the neutralpoint potential are used for the neutralpoint potential control. Thereby, the neutralpoint potential control can be executed by excluding the effect of the higher harmonic wave current.
A modification of the second embodiment is described. In this modification, the PWM control described in the first embodiment is used in place of the abovedescribed onepulse control.
As illustrated in
The functions of the 3phase/DQ converter 21 and automatic current regulators (ACR) 22 and 23 are the same as in the first embodiment.
The DQ/3phase converter 24 executes DQ/3phase conversion of the daxis voltage instruction value v_d* and qaxis voltage instruction value v_q*. By this conversion, the DQ/3phase converter 24 obtains a Uphase voltage instruction value v_u*0, a Vphase voltage instruction value v_v*0 and a Wphase voltage instruction value v_w*0 as threephase voltage instruction values.
An adder 74 adds a zerophase voltage instruction value v_u_z* of the U phase, which was calculated by the neutralpoint potential controller 30c, to the Uphase voltage instruction value v_u*0 generated by the DQ/3phase converter 24. A value from the adder 74 is output to the PWM controller 25c as a Uphase voltage instruction value v_u*_a.
A multiplier 71 multiplies the Uphase voltage instruction value v_u*0 by “−1”. An adder 75 adds the zerophase voltage instruction value v_u_z* of the U phase to a value from the multiplier 71. A value from the adder 75 is output to the PWM controller 25c as a Uphase voltage instruction value v_u*_b.
The same applies to the V phase and W phase. Specifically, an adder 76 adds a zerophase voltage instruction value v_v_z* of the V phase, which was calculated by the neutralpoint potential controller 30c, to the Vphase voltage instruction value v_v*0 generated by the DQ/3phase converter 24. A value from the adder 76 is output to the PWM controller 25c as a Vphase voltage instruction value v_v*_a.
A multiplier 72 multiplies the Vphase voltage instruction value v_v*0 by “−1”. An adder 77 adds the zerophase voltage instruction value v_v_z* of the V phase to a value from the multiplier 72. A value from the adder 77 is output to the PWM controller 25c as a Vphase voltage instruction value v_v*_b.
In addition, an adder 78 adds a zerophase voltage instruction value v_w_z* of the W phase, which was calculated by the neutralpoint potential controller 30c, to the Wphase voltage instruction value v_w*0 generated by the DQ/3phase converter 24. A value from the adder 78 is output to the PWM controller 25c as a Wphase voltage instruction value v_w*_a.
A multiplier 73 multiplies the Wphase voltage instruction value v_w*0 by “−1”. An adder 79 adds the zerophase voltage instruction value v_w_z* of the W phase to a value from the multiplier 73. A value from the adder 79 is output to the PWM controller 25c as a Wphase voltage instruction value v_w*_b.
Based on these voltage instruction values, the PWM controller 25c generates, by PWM control, a gate signal of a switching element corresponding to the leg of each phase, and drives each switching element by using this gate signal.
As illustrated in
The functions of the 3phase/DQ converter 31 and lowpass filters 32, 33, 35 and 36 are the same as in the first embodiment.
The DQ/3phase converter 34 executes DQ/3phase conversion of the daxis filter current i_d_f from the lowpass filter 32 and the qaxis filter current i_q_f from the lowpass filter 33. Thereby, the DQ/3phase converter 34 obtains a Uphase filter current i_u_f, a Vphase filter current i_v_f and a Wphase filter current i_w_f. The DQ/3phase converter 34 outputs the Uphase filter current i_u_f to a sign unit 81, the Vphase filter current i_v_f to a sign unit 82, and the Wphase filter current i_w_f to a sign unit 83.
The sign unit 81 calculates the sign of the Uphase filter current i_u_f. The sign unit 82 calculates the sign of the Vphase filter current i_v_f. The sign unit 83 calculates the sign of the Wphase filter current i_w_f.
The DQ/3phase converter 37 executes DQ/3phase conversion of the daxis filter voltage instruction value v_d*_f from the lowpass filter 35 and the qaxis filter voltage instruction value v_q*_f from the lowpass filter 36. Thereby, the DQ/3phase converter 37 obtains a Uphase filter voltage instruction value v_u*_f, a Vphase filter voltage instruction value v_v*_f and a Wphase filter voltage instruction value v_w*_f. The DQ/3phase converter 37 outputs the Uphase filter voltage instruction value v_u*_f to a sign unit 84, the Vphase filter voltage instruction value v_v*_f to a sign unit 85, and the Wphase filter voltage instruction value v_w*_f to a sign unit 86.
The sign unit 84 calculates the sign of the Uphase filter voltage instruction value v_u*_f. The sign unit 85 calculates the sign of the Vphase filter voltage instruction value v_v*_f. The sign unit 86 calculates the sign of the Wphase filter voltage instruction value v_w*_f.
A subtracter 87 subtracts the value of the DC voltage v_dc_n from the value of the DC voltage v_dc_p. A multiplier 88 multiplies a value from the subtracter 87 by “−1”. A PI arithmetic unit 89 executes a PI arithmetic operation on the value from the multiplier 88.
In addition, a multiplier 90 multiplies the sign of the Uphase filter current i_u_f as the sign calculated by the sign unit 81, and the sign of the Uphase filter voltage instruction value v_u*_f as the sign calculated by the sign unit 84. A multiplier 93 multiplies a sign, which is a calculation result of the multiplier 90, and a calculation value by the PI arithmetic unit 89, thereby outputting a zerophase voltage instruction value v_u_z* of the U phase.
A multiplier 91 multiplies the sign of the Vphase filter current i_v_f as the sign calculated by the sign unit 82, and the sign of the Vphase filter voltage instruction value v_v*_f as the sign calculated by the sign unit 85. A multiplier 94 multiplies a sign, which is a calculation result of the multiplier 91, and the calculation value by the PI arithmetic unit 89, thereby outputting a zerophase voltage instruction value v_v_z* of the V phase.
A multiplier 92 multiplies the sign of the Wphase filter current i_w_f as the sign calculated by the sign unit 83, and the sign of the Wphase filter voltage instruction value v_w*_f as the sign calculated by the sign unit 86. A multiplier 95 multiplies a sign, which is a calculation result of the multiplier 92, and the calculation value by the PI arithmetic unit 89, thereby outputting a zerophase voltage instruction value v_w_z* of the W phase.
Unlike the first embodiment, in the case of using the singlephase NPC as in the modification of the second embodiment, the neutralpoint potential does not vary in principle. Thus, the abovedescribed feedforward control is needless, and it should suffice if feedback control using the subtracter 87, multiplier 88 and PI arithmetic unit 89 is executed.
While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel embodiments described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.