JP6131360B1 - Power converter - Google Patents

Abstract

A power converter capable of suppressing fluctuations in neutral point potential is provided. A DC power source includes a positive electrode side capacitor and a negative electrode side capacitor that are connected in series between a positive electrode side and a negative electrode side of a DC power source and have a connection point as a neutral point. Level inverter 10 that converts AC power into AC power and supplies it to the motor, a current detector 16 that detects the current flowing through the motor as an output current, and a rotational speed detector 17 that detects the rotational speed of the motor as the motor rotational speed, A voltage command calculation unit that calculates an output voltage command value for the three-level inverter using the output current and the motor rotation speed, and voltage detection that detects the voltages of the positive side capacitor and the negative side capacitor as the positive side voltage and the negative side voltage Based on the potential difference between the positive electrode side voltage and the negative side voltage, the polarity of the output current, and the polarity of the output voltage command value, the potential difference is reduced. And a neutral point potential control unit for compensating an output voltage command value. [Selection] Figure 1

Description

  The present invention relates to a power conversion device using a three-level inverter.

  Conventionally, two carrier waves, which are a triangular wave that changes between zero and the positive side and a triangular wave that changes between zero and the negative side, are compared with the modulated wave that is the output voltage command value. A power conversion device that generates a gate signal for turning on or off a switching element based on the relationship and controls a three-level inverter according to the gate signal is known (see, for example, Patent Document 1).

JP-A-1-47277

However, the prior art has the following problems.
That is, when a neutral point potential is output by a three-phase three-level inverter, there are a period during which the positive-side capacitor is charged and a period during which the negative-side capacitor is charged depending on the switching state of the switching element. It is known that the potential changes at a frequency three times the output frequency.

  When the neutral point potential fluctuates, the voltage burden on each switching element and the capacitor becomes unbalanced, which may cause overvoltage breakdown of the capacitor. Further, in the case of a motor load, an error occurs in the amplitude of the output voltage due to fluctuations in the neutral point potential, so that the output current may be distorted and torque pulsation may increase.

  Here, in order to prevent overvoltage breakdown, it is necessary to increase the breakdown voltage of the capacitor. Moreover, in order to suppress the fluctuation of the neutral point potential, it is necessary to increase the capacitance of the capacitor. These have the problem that the volume of the capacitor increases, the size of the device increases, and the cost of the device increases.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to obtain a power conversion device that can suppress fluctuations in neutral point potential.

The power conversion device according to the present invention includes a positive-side capacitor and a negative-side capacitor that are connected in series between a positive electrode side and a negative electrode side of a DC power source and that have a connection point as a neutral point. A three-level inverter that converts DC power into AC power and supplies it to the motor, a current detector that detects the current flowing through the motor as an output current, a rotational speed detector that detects the rotational speed of the motor as a motor rotational speed, A voltage command calculation unit that calculates an output voltage command value for the three-level inverter using the output current and the motor rotation speed, and a voltage detection unit that detects the voltages of the positive side capacitor and the negative side capacitor as the positive side voltage and the negative side voltage Output voltage so as to reduce the potential difference based on the potential difference between the positive side voltage and the negative side voltage, the polarity of the output current, and the polarity of the output voltage command value. And the neutral point potential control unit for compensating the command value, based on the output voltage command value after compensation, a PWM generating unit for generating a gate signal of the 3-level inverter, comprising a neutral point potential control unit, 3 The output voltage command value is compensated for each phase of the level inverter .

According to the power conversion device of the present invention, the neutral point potential control unit is configured such that the potential difference between the positive side voltage and the negative side voltage in the positive side capacitor and the negative side capacitor connected in series with each other as the neutral point. Based on the polarity of the output current of the three-level inverter and the polarity of the output voltage command value for the three-level inverter, the output voltage command value is compensated so that the potential difference between the positive side voltage and the negative side voltage becomes small.
Therefore, fluctuations in the neutral point potential can be suppressed.

It is a circuit diagram which shows the 3 level inverter of the power converter device which concerns on Embodiment 1 of this invention with a DC power supply and a motor. It is a block block diagram which shows the control part of the power converter device which concerns on Embodiment 1 of this invention. It is a timing chart for demonstrating operation | movement of the PWM production | generation part of the power converter device which concerns on Embodiment 1 of this invention. (A), (b) is a timing chart for demonstrating operation | movement of the neutral point electric potential control part of the power converter device which concerns on Embodiment 1 of this invention. (A)-(d) is another timing chart for demonstrating operation | movement of the neutral point electric potential control part of the power converter device which concerns on Embodiment 1 of this invention. It is explanatory drawing which shows the simulation result in case the fluctuation | variation of a neutral point electric potential is not suppressed. It is explanatory drawing which shows the simulation result of the power converter device which concerns on Embodiment 1 of this invention. It is an enlarged view which shows the simulation result of the power converter device which concerns on Embodiment 1 of this invention.

  Hereinafter, preferred embodiments of a power conversion device according to the present invention will be described with reference to the drawings. In the drawings, the same or corresponding parts will be described with the same reference numerals.

  First, prior to description of the embodiments, an outline of a power conversion device according to the present invention will be described. From the polarity of the output voltage command value output to the three-level inverter and the polarity of the output current (neutral point current) of the three-level inverter, the power conversion device of the present invention suppresses fluctuations in the neutral point potential. It compensates the output voltage command value of each phase.

  In other words, the neutral point current is controlled so as to suppress the fluctuation of the neutral point potential. Neutral point current control is based on the policy of detecting the voltages of the positive and negative capacitors of the 3-level inverter and increasing or decreasing the neutral point current according to the potential difference. It is executed to suppress.

  Specifically, the on-time of the neutral point element and the positive electrode side and negative electrode side elements is adjusted based on a policy of increasing or decreasing the neutral point current. At this time, the output voltage command value is compensated in order to adjust the on-time of the neutral point element and the positive electrode side and negative electrode side elements. This is performed individually for each of the three phases.

  As a result, fluctuations in the neutral point potential are suppressed and voltage imbalance is improved, so there is no need to unnecessarily increase the withstand voltage and capacitance of the capacitor, reducing costs and downsizing the device. can do. Further, the output voltage distortion of the three-level inverter is also improved, and the torque ripple of the motor can be suppressed, which leads to improvement of the inverter control performance. Since the output voltage command value is compensated, it can be applied regardless of the control type, such as V / F control and vector control.

Embodiment 1 FIG.
1 is a circuit diagram showing a three-level inverter of a power conversion device according to Embodiment 1 of the present invention, together with a DC power supply and a motor. In FIG. 1, a three-level inverter 10 is connected to a DC power source 1 and a motor 2 whose neutral points are grounded.

The three-level inverter 10 is connected in series between the positive electrode side and the negative electrode side of the DC power source 1, and includes a positive electrode capacitor 11 and a negative electrode capacitor 12 having a connection point as a neutral point, and four capacitors per phase. A three-phase arm 13 composed of switching elements Q _{1 to} Q ₄ , and converts DC power from the DC power source 1 into AC power and supplies it to the motor 2.

Here, the four switching elements constituting the arm 13 for one phase include two neutral point elements Q ₃ and Q ₄ connected as a bidirectional switch to the neutral point, and the positive side of the DC power supply 1. and and a positive electrode side element Q ₁ and the negative electrode side element Q ₂ to which are connected in series between the negative electrode side, this is achieved by three levels.

The three-level inverter 10 is provided with voltage sensors 14 and 15 that detect the voltages of the positive side capacitor 11 and the negative side capacitor 12 as the positive side voltage V _c1 and the negative side voltage V _c2 , respectively. Further, the three-level inverter 10 is provided with a current sensor 16 that detects a current flowing through the motor 2 as an output current, and a rotation speed sensor 17 that detects a rotation speed of the motor 2 as a motor rotation speed.

  FIG. 2 is a block configuration diagram showing a control unit of the power conversion apparatus according to Embodiment 1 of the present invention. In FIG. 2, the control unit includes a vector control unit 20, a neutral point potential control unit 30, and a PWM (Pulse Width Modulation) generation unit 40.

  The vector control unit 20 uses the output current detected by the current sensor 16, the motor rotational speed detected by the rotational speed sensor 17, and the motor rotational speed command value and the d-axis current command value input from the host control system. An output voltage command value for the three-level inverter 10 is calculated. The vector control unit 20 includes a speed controller 21, a power supply frequency calculation unit 22, a three-phase / dq axis coordinate conversion unit 23, current controllers 24 and 25, and a dq axis / three-phase coordinate conversion unit 26. .

  The speed controller 21 performs q-axis current by PI control or the like so that the deviation between the motor rotational speed command value Wr * input from the host control system and the motor rotational speed Wr detected by the rotational speed sensor 17 becomes zero. Command value Iq * is generated.

  The power supply frequency calculation unit 22 generates a dq axis based on the d-axis current command value Id *, the q-axis current command value Iq *, the motor rotation speed Wr, and the secondary time constant τr (motor constant) input from the host control system. / A phase angle θ required for three-phase coordinate conversion is calculated.

The three-phase / dq-axis coordinate conversion unit 23 uses the phase angle θ calculated by the power supply frequency calculation unit 22 to perform coordinate conversion of the output currents I _u , I _v , I _w detected by the current sensor 16, and d The axis current detection value Id and the q axis current detection value Iq are output.

  The current controller 24 generates the d-axis voltage command value Vd * by PI control or the like so that the deviation between the d-axis current command value Id * and the d-axis current detection value Id becomes zero. Further, the current controller 25 generates the q-axis voltage command value Vq * by PI control or the like so that the deviation between the q-axis current command value Iq * and the q-axis current detection value Iq becomes zero.

The dq-axis / 3-phase coordinate conversion unit 26 uses the phase angle θ calculated by the power supply frequency calculation unit 22 and the d-axis voltage command value Vd * from the current controller 24 and the q-axis voltage from the current controller 25. The command value Vq * is coordinate-converted, and three-phase output voltage command values V _u *, V _v *, and V _w * are output.

The neutral point potential control unit 30 includes a polarity determination unit 31, a polarity determination unit 32, and a voltage command compensation calculation unit 33. The polarity determining unit 31 determines whether the value is positive or negative for each phase of the output currents I _u , I _v , and I _w . The polarity discriminating unit 32 discriminates whether the value is positive or negative for each phase of the output voltage command values V _u *, V _v *, and V _w *.

The voltage command compensation calculation unit 33 includes a potential difference ΔV between the positive side voltage V _c1 and the negative side voltage V _c2 , the voltage Ed / 2 of the DC power supply 1, the polarities of the output currents I _u , I _v , I _w , and the output voltage command Based on the polarities of the values V _u *, V _v *, V _w *, the output voltage command values V _u *, V _v *, V _w * are compensated so that the potential difference ΔV becomes smaller, and the output voltage after compensation Command values V _uu *, V _vv *, and V _www * are output. The detailed control of the voltage command compensation calculation unit 33 will be described later.

The PWM generator 40 generates a gate signal of the three-level inverter 10 based on the compensated output voltage command values V _uu *, V _vv *, and V _ww *. Here, the PWM generation unit 40 converts the output voltage command value to the rated DC voltage Ed / 2, two carriers that are a triangular wave that changes between zero and the plus side, and a triangular wave that changes between the zero and the minus side. Is compared with the modulation factor a standardized in step (b), and a gate signal for turning on or off the switching elements Q _{1 to} Q ₄ is generated based on the comparison result.

FIG. 3 is a timing chart for explaining the operation of the PWM generator of the power conversion apparatus according to Embodiment 1 of the present invention. In FIG. 3, the relationship between the carrier and the modulation factor a, the operation of the switching elements Q _{1 to} Q ₄ and the output voltage (phase voltage) from the three-level inverter 10 at this time are shown for the u phase.

In Figure 3, when the modulation factor a is positive, when the modulation factor a is larger than the carrier, the switching element Q ₁ is turned on, the switching element Q ₃ is turned off. At this time, the switching element Q ₄ are a normally on.

In contrast, when the modulation factor a is negative, when the modulation factor a is less than the carrier, the switching element Q ₂ is turned on, the switching element Q ₄ is turned off. At this time, the switching element Q ₃ are always in the ON state.

  Next, detailed control of the voltage command compensation calculation unit 33 will be described with reference to FIGS. FIGS. 4A and 4B are timing charts for explaining the operation of the neutral point potential control unit of the power conversion device according to Embodiment 1 of the present invention. FIGS. 5A to 5D are other timing charts for explaining the operation of the neutral point potential control unit of the power conversion device according to the first embodiment of the present invention.

  First, derivation of the voltage command compensation formula will be described. Hereinafter, the u phase, the v phase, and the w phase of the three-level inverter 10 are collectively referred to as u, v, and w.

First, when the potential difference ΔV ≠ 0 between the positive electrode side voltage V _c1 and the negative electrode side voltage V _c2 , the output voltage from the three-level inverter 10 is as follows according to the states of the switching elements Q _{1 to} Q _4. It is divided into.

State 1: E _{u, v, w} = Ed / 2 (1)
State 2: E _{u, v, w} = −Ed / 2 (2)
State 3: E _{u, v, w} = ΔV (3)

Here, State 1, State 2, and State 3 in the U phase will be described. State 1 shows a state in which only the switching element to Q ₁ positive side is turned on, state 2 shows a state in which only the switching element Q ₂ on the negative electrode side is turned on, the state 3, the neutral point Only the switching elements Q ₃ and Q ₄ are turned on. Regarding the V phase and the W phase, the states in which the switching elements corresponding to Q ₁ , Q ₂ , Q ₃ , and Q ₄ of each phase are turned on are shown as state 1, state 2, and state 3.

Further, from FIG. 1, since Ed / 2−V _c1 −ΔV = 0 and ΔV−V _c2 + Ed / 2 = 0, the potential difference ΔV between the positive side voltage V _c1 and the negative side voltage V _c2 is It is represented by Formula (4).

From equation (4), when ΔV ≠ 0, in order to output the output voltage command values V _{u, v, w} * output voltages E _{u, v, w} , how is the modulation factor a controlled? Think about it. In other words, consider how to control the duty ratio and on-time of the switching element.

First, consider the case of modulation rate a> 0 (V _{u, v, w} ** 0) shown in FIG. As described above, the modulation factor a, the output voltage instruction value V _{u, v,} since it is obtained by normalizing the _{w *,} the output voltage command value V _{u, v,} be considered to _{w *} synonymous it can. In FIG. 4A, since the carrier period T is very short with respect to the period of the modulation factor a, the modulation factor a can be treated as a straight line.

Fig. 4 (a), the output voltage _{E u} of 1 carrier period _{T, v,} the average value _{Eave u} of _{w, v, w} are, _{E u} of state _{1, v,} w = Ed / 2 and state 3 _{E u , V, w} = ΔV and is expressed by the following equation. In this equation, T ₁ / T can be replaced with a because the modulation factor a is treated as a straight line.

Subsequently, in this formula, in order to set Eave _{u, v, w} = V _{u, v, w} *, the average value Eave _{u, v, w} is replaced with the output voltage command value V _{u, v, w} *, and the modulation is performed. Solving for rate a yields:

さらに、この式を展開すると、次式（５）が得られる。

Furthermore, when this equation is expanded, the following equation (5) is obtained.

  In equation (5), when ΔV> 0, the second term is always a positive value, and therefore the modulation factor a is corrected in a decreasing direction. On the other hand, when it is desired to increase the modulation factor a, the output voltage command value is compensated by the control amount of the second term of the equation (5), and the following equation (5) 'is obtained.

Next, consider the case of modulation rate a <0 (V _{u, v, w} ** 0) shown in FIG. As described above, the modulation factor a, the output voltage instruction value V _{u, v,} since it is obtained by normalizing the _{w *,} the output voltage command value V _{u, v,} be considered to _{w *} synonymous it can. In FIG. 4B, since the carrier period T is very short with respect to the period of the modulation factor a, the modulation factor a can be treated as a straight line.

From FIG. 4B _, the average values Eave _{u, v, w} of the output voltages E _{u, v, w} in one carrier period T are E _{u, v, w} = −Ed / 2 in state 2 and E in state 3 _As a value combining _{u, v, w} = ΔV, it is expressed by the following equation. In this equation, -T ₂ / T can be replaced with a because the modulation factor a is treated as a straight line.

Subsequently, in this formula, in order to set Eave _{u, v, w} = V _{u, v, w} *, the average value Eave _{u, v, w} is replaced with the output voltage command value V _{u, v, w} *, and the modulation is performed. Solving for rate a yields:

  Furthermore, when this equation is expanded, the following equation (6) is obtained.

  In Expression (6), when ΔV> 0, the second term is always a positive value, and thus the modulation factor a is corrected in a decreasing direction. On the other hand, when it is desired to increase the modulation factor a, the output voltage command value is compensated by the control amount of the second term of the equation (6), and the following equation (6) 'is obtained.

That is, if the modulation factor a is corrected as shown in Equation (5), Equation (5) ′, Equation (6), or Equation (6) ′, the output voltage E according to the output voltage command value V _{u, v, w} *. _{u, v, w} are obtained.

Next, a control policy for neutral point potential control will be described.
First, from FIG. 1, the current flowing through the positive capacitor 11 i, and the current _{i-i n} flowing through the negative electrode side capacitor 12, the following equation (7) and the following equation (8) holds.

  Moreover, following Formula (9) is obtained from Formula (4), Formula (7), and Formula (8).

From this equation (9), it can be seen that ΔV decreases when the neutral point current i _n > 0 flowing through the neutral point, and ΔV increases when i _n <0.

  As for the output current from the three-level inverter 10, the following equations (10) to (13) are established from FIG.

i _su = i _su ′ + i _nu + i _su ″ (10)
i _sv = i _sv ′ + i _nv + i _sv ″ (11)
i _sw = i _sw '+ i _nw + i _sw ″ (12)
i _n = i _nu + i _nv + i _nw (13)

Here, in FIGS. 5A to 5D, the output current waveforms when the output current i _su > 0 or i _su <0 in each of the modulation rates a> 0 and a <0 are shown as u. The phase is shown. 5 (a) to 5 (d), since the carrier period T is very short, an almost constant current is applied to any switching element during this period due to the action of the inductance of the motor 2. It is thought to flow.

Subsequently, in FIGS. 5A to 5D, focusing on the period during which the neutral point current i _nu flows, when the equation (13) is integrated during the carrier period T, the neutral point current i _{For n} , the following equation (14) is obtained.

In the equation (14), the on-times of the neutral point elements Q ₃ and Q ₄ are expressed by the following equations (15) and (16).

When a> 0, T _u = T−T _1u , T _v = T−T _1v , T _w = T−T _1w (15)
When a <0, T _u = T−T _2u , T _v = T−T _2v , T _w = T−T _2w (16)

However, in the formulas (15) and (16), T ₁ and T ₂ of each phase in FIGS. 5A to 5D are respectively _expressed as T _1u , T _1v , T _1w and T _2u , T _2v , T _2w. It is represented by

Here, it can be seen from the equation (14) that the neutral point current i _nu of each phase is equal to the output current during the period when the neutral point elements Q ₃ and Q ₄ are on. Therefore, based on the above relational expression, the control policy for neutral point potential control of the capacitor is determined as follows.

Policy 1: When the potential difference ΔV = (V _c2 −V _c1 ) / 2> 0, the positive side voltage V _c1 is increased and the negative side voltage V _c2 is decreased.
At this time, the neutral point current i _n > 0 basically suffices from the equation (9), but when the neutral point current i _n > 0, the neutral point current i _n is further increased. Further, when the neutral point current i _n <0, the neutral point current i _n is increased so as to gradually become positive.

Policy 2: When the potential difference ΔV = (V _c2 −V _c1 ) / 2 <0, the negative side voltage V _c2 is increased and the positive side voltage V _c1 is decreased.
At this time, from the equation (9), it is basically sufficient that the neutral point current i _n <0, but when the neutral point current i _n <0, the neutral point current i _n is further reduced. Further, when the neutral point current i _n > 0, the neutral point current i _n is decreased and gradually becomes negative.

  Policy 3: When the modulation factor a is corrected based on the policies 1 and 2, Formula (5), Formula (5) ′, Formula (6), or Formula (6) obtained to generate the commanded voltage Apply '' solution. That is, the compensation of Expression (5), Expression (5) ′, Expression (6), or Expression (6) ′ is performed so that the potential at the neutral point becomes zero.

Next, a specific control method of the voltage command compensation calculation unit 33 is shown below. Here, in FIG. 1, the neutral point current i _n, the discharge direction from the negative electrode side capacitor 12 and positive. Thus, the higher the negative electrode side voltage _{V c2} of the negative electrode side capacitor 12, ([Delta] V> 0 if) to increase the neutral point current _{i n} (policy 1). Also, the higher the positive electrode side voltage _{V c1} of the positive capacitor 11, to reduce the ([Delta] V <0 if) neutral current _{i n} (policy II).

Here, the potential difference ΔV between the positive side voltage V _c1 and the negative side voltage V _c2 , the voltage Ed / 2 of the DC power supply 1, the polarities of the output currents I _u , I _v , I _w , and the output voltage command value V _u *, Depending on the polarity of V _v * and V _w *, the operation pattern of the voltage command compensation calculation unit 33 can be divided into the following eight cases. The voltage command compensation calculation unit 33 suppresses fluctuations in the neutral point potential by applying an appropriate voltage compensation formula to each operation pattern as described below.

Operation Pattern 1: Voltage command _{value> 0, ΔV> 0 (V} c2> V c1), in order to increase the neutral point current _{i n} the case of the output current> 0, on the neutral point element _Q 3, _{Q 4} Increase time. Thereby, the modulation factor a is lowered. At this time, Formula (5) is applied as a voltage command compensation formula.

Operation Pattern 2: Voltage command _{value> 0, ΔV> 0 (V} c2> V c1), in order to increase the neutral point current _{i n} the case of the output current <0, on the neutral point element _Q 3, _{Q 4} Reduce time. Thereby, the modulation factor a is increased. At this time, Equation (5) ′ is applied as a voltage command compensation equation.

Operation Pattern 3: voltage command _{value> 0, ΔV <0 (V} c2 <V c1), the output current> in order to reduce the neutral point current _{i n} the case of 0, on the neutral point element _Q 3, _{Q 4} Reduce time. Thereby, the modulation factor a is increased. At this time, Formula (5) is applied as a voltage command compensation formula.

Operation pattern 4: Voltage command _{value> 0, ΔV <0 (V} c2 <V c1), if the output current <0 in order to reduce the neutral point current _{i n,} the neutral point element _Q 3, on the _{Q 4} Increase time. Thereby, the modulation factor a is lowered. At this time, Equation (5) ′ is applied as a voltage command compensation equation.

Operation Pattern 5: Voltage command value _{<0, ΔV> 0 (V} c2> V c1), in order to increase the neutral point current _{i n} the case of the output current <0, on the neutral point element _Q 3, _{Q 4} Reduce time. Thereby, the modulation factor a is lowered. At this time, Equation (6) is applied as a voltage command compensation equation.

Operation Pattern 6: Voltage command value _{<0, ΔV> 0 (V} c2> V c1), in order to increase the neutral point current _{i n} the case of the output current> 0, on the neutral point element _Q 3, _{Q 4} Increase time. Thereby, the modulation factor a is increased. At this time, Equation (6) ′ is applied as a voltage command compensation equation.

Operation Pattern 7: voltage command value _{<0, ΔV <0 (V} c2 <V c1), if the output current <0 in order to reduce the neutral point current _{i n,} the neutral point element _Q 3, on the _{Q 4} Increase time. Thereby, the modulation factor a is increased. At this time, Equation (6) is applied as a voltage command compensation equation.

Operation Pattern 8: voltage command value _{<0, ΔV <0 (V} c2 <V c1), in order to reduce the neutral point current _{i n} the case of the output current> 0, on the neutral point element _Q 3, _{Q 4} Reduce time. Thereby, the modulation factor a is lowered. At this time, Equation (6) ′ is applied as a voltage command compensation equation.

  Next, the simulation result of the power conversion device according to Embodiment 1 of the present invention will be described in comparison with the simulation result in the case where the fluctuation of the neutral point potential is not suppressed. FIG. 6 is an explanatory diagram showing a simulation result when the fluctuation of the neutral point potential is not suppressed. FIG. 7 is an explanatory diagram showing a simulation result of the power conversion device according to Embodiment 1 of the present invention.

6 and 7, when the fluctuation of the neutral point potential is not suppressed, the potential difference ΔV between the positive side voltage V _c1 and the negative side voltage V _c2 gradually increases when the motor rotation speed command value Wr * changes. On the other hand, it can be seen that the potential difference ΔV converges to zero by using the power conversion device according to the first embodiment of the present invention.

FIG. 8 is an enlarged view showing a simulation result of the power conversion device according to Embodiment 1 of the present invention. In FIG. 8, the time axis of the simulation result shown in FIG. 7 is enlarged to show one cycle of the output current _Iu .

8, the period a _{is, V u *> 0, I} u <0, a [Delta] V> 0, with respect to _{V u *,} is intended to increase correct _{V uu} *, corresponding to the operation pattern 2 above . Period b, e _{is, V u *> 0, I} u <0, a [Delta] V <0, to _{V u *,} is intended to correct small _{V uu} *, corresponding to the operation pattern 4 described above.

The period c is V _u *> 0, I _u > 0, and ΔV <0, and greatly corrects V _uu * with respect to V _u *, and corresponds to the operation pattern 3 described above. Period d _{is, V u *> 0, I} u> 0, a [Delta] V> 0, with respect to _{V u *,} is intended to correct small _{V uu} *, corresponding to the operation pattern 1 described above.

A period f _{is, V u * <0, I} u> 0, a [Delta] V <0, to _{V u *,} is intended to correct small _{V uu} *, corresponding to the operation pattern 8 described above. The period g is V _u * <0, I _u > 0, ΔV> 0, and corresponds to the above-described operation pattern 6 that greatly corrects V _uu * with respect to V _u *.

A period h, j _{is, V u * <0, I} u <0, a [Delta] V> 0, with respect to _{V u *,} is intended to correct small _{V uu} *, corresponding to the operation pattern 5 described above . Period i _{is, V u * <0, I} u <0, a [Delta] V <0, to _{V u *,} is intended to increase correct _{V uu} *, corresponding to the operation pattern 7 described above.

As described above, according to the first embodiment, the neutral point potential control unit includes the positive-side voltage and the negative-side voltage in the positive-side capacitor and the negative-side capacitor that are connected in series with each other as the neutral point. The output voltage command value is compensated so as to reduce the potential difference between the positive side voltage and the negative side voltage based on the potential difference between the three level inverters and the polarity of the output voltage command value for the three level inverter. . Further, the compensation of the voltage command value is performed individually for each of the U phase, the V phase, and the W phase.
Therefore, fluctuations in the neutral point potential can be suppressed.
Compared with the two-level inverter, the three-level inverter halves the output voltage dv / dt. Therefore, the microsurge voltage generated at the motor terminal can be suppressed by using the three-level inverter.

  1 DC power supply, 2 motor, 10 3-level inverter, 11 positive side capacitor, 12 negative side capacitor, 13 arm, 14 voltage sensor (voltage detection unit), 16 current sensor (current detection unit), 17 rotation speed sensor (rotation speed) Detection unit), 20 vector control unit (voltage command calculation unit), 21 speed controller, 22 power supply frequency calculation unit, 23 3-phase / dq axis coordinate conversion unit, 24 current controller, 25 current controller, 26 dq axis / 3-phase coordinate conversion unit, 30 neutral point potential control unit, 31 polarity determination unit, 32 polarity determination unit, 33 voltage command compensation calculation unit, 40 generation unit.

Claims (1)

Connected in series between the positive electrode side and negative electrode side of the DC power source, and has a positive electrode side capacitor and a negative electrode side capacitor with the connection point as a neutral point, and converts DC power from the DC power source into AC power A three-level inverter that supplies the motor with
A current detector that detects the current flowing through the motor as an output current;
A rotational speed detector for detecting the rotational speed of the motor as a motor rotational speed;
A voltage command calculation unit that calculates an output voltage command value for the three-level inverter using the output current and the motor rotation speed;
A voltage detection unit for detecting voltages of the positive side capacitor and the negative side capacitor as a positive side voltage and a negative side voltage;
Based on the potential difference between the positive side voltage and the negative side voltage, the polarity of the output current, and the polarity of the output voltage command value, a neutral point potential that compensates the output voltage command value so that the potential difference becomes small A control unit;
A PWM generator that generates a gate signal of the three-level inverter based on the output voltage command value after compensation;
Equipped with a,
The neutral point potential control unit compensates the output voltage command value for each phase of the three-level inverter .

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