JP7219665B2 - POWER CONVERSION DEVICE AND ABNORMALITY DETECTION METHOD - Google Patents

Description

The present invention relates to a power converter and an abnormality detection method using a single-phase three-level converter.

A single-phase three-level converter internally includes an assembly composed of semiconductor switching elements for two phases, and controls an AC voltage output to an AC output terminal by PWM control of the semiconductor switching elements in the assembly. As a result, desired AC power is transferred to and from the load or the AC system (power system).

A three-level converter (eg an inverter) has potentials in its DC part from two DC voltage circuits. As the two DC voltage circuits, two power storage circuits represented by capacitors are provided, and the voltage balance of the two DC voltage circuits is corrected by the command value of the output AC voltage.

Voltage balance control can be realized by, for example, a DC bias superimposition method. If the DC voltage sensor indicates an abnormal value and the detected value is different from the actual output voltage of the DC voltage circuit, the 3-level inverter will not be able to output the desired AC voltage. As a result, if the deviation between the detected value and the actual output voltage becomes excessively large, the overvoltage protection of the semiconductor switching element cannot be performed normally, and there is a possibility that the element will fail. Therefore, it is necessary to quickly detect an abnormality in the DC voltage sensor.

In Patent Document 1, a DC voltage sensor is redundantly installed on the output side of a diode rectifier circuit, and when the DC voltage sensor used for output voltage control of the converter indicates an abnormal value, the value of another sensor is used. A method of controlling using is shown.

JP 2014-54089 A

In the technique described in Patent Document 1, more DC voltage sensors than necessary are installed, so the size of the equipment increases and the cost increases.
The present invention, including solving the above problems, detects an abnormality in a DC voltage sensor provided in a single-phase three-level converter based on information on the AC output constantly monitored in the single-phase three-level converter. be.

In order to solve the above problems, a power converter according to the present invention detects DC voltages of a single-phase three-level converter and positive-side and negative-side DC voltage circuits that constitute the single-phase three-level converter. and a DC voltage sensor, assuming that the detected value of the DC voltage sensor is equal to the true value, control is performed to keep the DC voltages of the positive side and negative side DC voltage circuits equal, and the output from the single-phase three-level converter is controlled. AC voltage sensor for detecting AC voltage, AC current sensor for detecting AC current output from the single-phase three-level converter, command value and detection value of active power of output power from the single-phase three-level converter an output voltage command calculation unit for calculating an output voltage command value for a single-phase three-level converter based on the difference, the difference between the command value and the detected value of the reactive power of the output power, and the output AC current; and a voltage comparator for determining an abnormality of the DC voltage sensor by comparing it with the output voltage command value.

According to the present invention, it is possible to detect an abnormality of a DC voltage sensor used in a single-phase three-level converter without providing additional equipment therefor.

It is a figure which shows an example of a structure of the power converter device which applies this invention. FIG. 4 is a diagram showing an AC voltage output pattern by ON/OFF switching of a semiconductor switching element; It is a figure which shows the waveform of the alternating current line voltage output from a single phase 3 level converter. FIG. 4 is a diagram showing a comparison between a detected value and a true voltage value of a DC voltage sensor in normal and abnormal conditions; FIG. 5 is a diagram showing a difference in output AC voltage depending on whether or not there is an abnormality in the DC voltage sensor; BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows an example of a structure of the power converter device which concerns on Example 1 of this invention. FIG. 4 is a diagram showing a control block that constitutes an output voltage command calculator; 8 is a diagram showing an example of a configuration of a power control block shown in FIG. 7; FIG. FIG. 3 shows the vector relationships for calculating the converter output voltage;

First, the principle of detecting an abnormality in the DC voltage sensor by comparing the output voltage command value for the single-phase three-level converter with the actual output AC voltage will be described below. After that, an embodiment of the power converter according to the present invention will be described. Here, the abnormality of the DC voltage sensor means a state in which the detection error increases due to aged deterioration of the sensor, etc., and an abnormal value is presented. does not mean

FIG. 1 is a diagram showing an example of the configuration of a power converter to which the present invention is applied.
A power conversion device 1000 is a device that outputs active power and reactive power to an AC system 1001 . The power conversion device 1000 includes an AC voltage detector 1002, an interconnection transformer 1003, a current detector 1004, a DC voltage sensor 1005, a control device 1006, a semiconductor switching element 1007, a positive electrode capacitor 1008, a negative electrode capacitor 1009, and a U-phase converter. It is composed of a single-phase three-level converter 1010 (solid line frame) composed of a section 1011 (two-dot chain line frame) and a V-phase conversion section 1012 (one-dot chain line frame). U-phase conversion section 1011 and V-phase conversion section 1012 each output an AC voltage.

The connection pattern between the two DC voltage circuits and the AC system that constitute the single-phase 3-level converter 1010 is switched by the ON/OFF combination of the semiconductor switching element 1007, and the U-phase and the V-phase are each connected to the AC system 1001 in three types. outputs voltages with different output levels.

FIG. 2 is a diagram showing an AC voltage output pattern by ON/OFF switching of the semiconductor switching element 1007. As shown in FIG.
FIG. 2(a) is a diagram extracting U-phase 1010 or V-phase 1011 and capacitors 1008 and 1009 shown in FIG. P, C and N shown on the circuit represent potentials, and when potential C is set to 0 potential, potential P is equal to the voltage of capacitor 1008 and potential N is equal to the voltage of capacitor 1009 . In FIGS. 2(a) to 2(c), paths indicated by dotted lines are energization paths.

As shown in FIG. 2, the potential P is connected to the semiconductor switching element 1007 in (a), the potential C is connected in (b), and the potential N is connected in (c). It can be seen that the voltage output from the U-phase or the V-phase differs depending on the potential connected to the semiconductor switching element 1007, and all three types of output voltages are obtained.

By controlling the duty ratios of these three types of output voltages in the U phase or the V phase, an AC line voltage as shown in FIG. 3 is output between the UV phases. FIG. 3 is a diagram showing the waveform of the AC line voltage output from the single-phase three-level converter, where the horizontal axis is time and the vertical axis is interphase voltage. As shown in the figure, the phase-to-phase voltage is a rectangular wave voltage with five potential levels determined by the difference between the phase voltages having three DC circuit potentials depending on the conducting state of the semiconductor switching element 1007 .

Next, the behavior of the DC voltage when the DC voltage sensor 1005 indicates an abnormality will be described by comparing the presence or absence of an abnormality in the DC voltage sensor 1005. FIG. Note that the numbering is omitted below.

First, the relationship between the true value of the DC voltage and the value detected by the DC voltage sensor is shown. After that, the voltage operation of the two DC voltage circuits that constitute the single-phase three-level converter will be described based on the control of the single-phase three-level converter when the DC voltage sensor is normal and abnormal.

In a circuit in which a DC voltage sensor is installed in a DC voltage circuit, the detection value of the DC voltage sensor is the product of the actual value of the DC voltage (hereinafter referred to as the “true value”) multiplied by the voltage sensor detection gain, which is a constant. becomes.

Here, the relationship between the true value and the detected value of the DC voltage sensor is shown in Equation (1). In equation (1), E _TCP is the true value of the P-side DC voltage, E _FBCP is the detection value of the P-side DC voltage sensor, and G _CP is the detection gain value of the P-side DC voltage sensor. When the DC voltage sensor is normal, _GCP is 1 because the true voltage value and the detected voltage value are equal. On the other hand, _{G_CP} takes a value other than 1 when abnormal. That is, it corresponds to the occurrence of an error between the detected value and the true value. P is added to the end of the suffix to indicate the P side, and N is added to the end of the suffix to indicate the N side.
_EFBCP = _ETCP x _GCP (1)

In the single-phase three-level converter, control is performed to keep two DC voltages equal by DC voltage balance control. However, a difference may occur between the voltages of the two DC voltage circuits due to loss variations in the semiconductor switching elements and imbalance in the capacitance of the DC circuit capacitors. Therefore, the single-phase three-level converter requires control to keep the voltages of the two DC voltage circuits equal, assuming that the detected value of the DC voltage sensor is equal to the true value.

Due to the DC voltage balance control, when the DC voltage sensor is normal, the voltages of the two DC voltage circuits are equal, but when the DC voltage sensor is abnormal, the voltage detection values of the two DC voltage circuits are equal. there will be a difference.

FIG. 4 is a diagram showing a comparison between the detected value and the true voltage value of the DC voltage sensor in the normal state and in the abnormal state.
When the DC voltage sensor is normal, the detected value of the DC voltage sensor=the true value of the DC voltage (capacitor voltage), so if the detected values are controlled to be equal, the true values will also be equal. On the other hand, when one of the two DC voltage sensors becomes abnormal and the detection gain (G _CP ) becomes a value other than 1, a capacitor charging current flows to equalize the detected DC voltage values by DC voltage balance control. , resulting in a difference between the true values of the two capacitor voltages.

Next, regarding the output voltage to the AC system when the voltages of the two DC voltage circuits are not equal, by comparing the output AC voltage to the AC system and the output voltage command value for the single-phase 3-level converter, The reason why the abnormality of the voltage sensor can be determined will be explained.

FIG. 5 is a diagram showing a difference in output AC voltage depending on whether or not the DC voltage sensor is abnormal. The display form of FIG. 5 is the same as that of FIG. 2, and the potentials are P=E _TCP , C=0, and N=-E _TCN . If the DC voltage sensor is abnormal, the two DC voltages are not equal, so that the absolute values of the positive and negative output AC voltages differ. Therefore, when the DC voltage sensor indicates an abnormality, the output AC voltage of the AC system does not reach the desired value. Therefore, when the AC voltage value output by the single-phase three-level converter is different from the output voltage command value for the single-phase three-level converter, it can be determined that the DC voltage sensor is abnormal.

An example of an embodiment for diagnosing an abnormality in a DC voltage sensor according to the present invention will be described below as Example 1 of the present invention.
FIG. 6 is a diagram showing an example of a configuration of a power converter according to Example 1 of the present invention. FIG. 6 shows the minimum functional blocks necessary for the function of diagnosing an abnormality in the DC voltage sensor.

The first embodiment has a configuration in which a power control processor 6001 including a CPU for executing control calculations is added to the single-phase three-level converter 1010, the DC voltage sensor 1005, and the AC voltage sensor 6002 shown in FIG. Become.

A function of diagnosing an abnormality of the DC voltage sensor 1005 is implemented in the power control processor 6001 . The functional blocks implemented by the power control processor 6001 are composed of an output voltage command calculator 6003 , an AC voltage detector 6005 and a voltage comparator 6004 .

Output voltage command calculation unit 6003 calculates the active power and reactive power of the output power from single-phase three-level converter 1010 and A voltage command value for the single-phase three-level converter 1000 is calculated based on the output alternating current .

FIG. 7 is a diagram showing control blocks forming the output voltage command calculation unit 6003. As shown in FIG.
The deviation between the active power command value P _ref of the output power from the single-phase three-level converter 1010 and the current active power detection value P _fb is input to the active power control block APR, and the output current active component command value i _{dref is input} . is calculated. In addition, the deviation between the reactive power command value Q _ref of the output power from the single-phase three-level converter 1010 and the current reactive power detection value Q _fb is input to the reactive power control block AQR, and the command value of the output current reactive component i _qref is computed.

The power control block ACR calculates a voltage command value _V1 required to output the command values _idref and _iqref calculated by the active power control block APR and the reactive power control block AQR, respectively.

FIG. 8 shows an example of the configuration of power control block ACR shown in FIG. 7. Referring to FIG.
Multiplying the command value i _dref of the active component of the output current by the cosine component (cos θ) of the system voltage phase θ, and multiplying the command value i _qref of the reactive component of the output current by the sine component (sin θ) of the system voltage phase θ, The current output current command value I _ref is calculated from the sum of both. Here, the system voltage phase θ is detected by, for example, a PLL (Phase Locked Loop).

The power control block ACR performs feedback control so that the difference between the output current command value _Iref and the current output AC current detection value _Ifb becomes zero. In short, in the control system by the active power control block APR and the reactive power control block AQR, the difference between the command value Pref and the detected value Pfb for the active power and the difference between the command value Qref and the detected value Qfb for the reactive power are 0. will be controlled so that

AC voltage detection unit 6005 detects the AC output voltage of single-phase three-level converter 1010 using AC voltage sensor 6002 . In Embodiment 1, the AC voltage sensor 6002 that detects the output voltage on the AC side is used to calculate the actual AC output voltage, but the method is not limited to this method.

As another method, that is, a modification of the first embodiment, the converter output voltage of the single-phase three-level converter is calculated from the output current of the single-phase three-level converter, and the calculated converter output voltage and the single-phase three-level conversion Abnormality of the DC voltage sensor may be detected by comparing the difference with the output voltage command value for the device.

FIG. 9 is a diagram showing the vector relationships for calculating the converter output voltage. Converter output current Ia detected by current detector 1004 (FIG. 1), AC system voltage Vac detected by AC voltage detector 1002 (FIG. 1), both calculated by PLL from converter output current Ia and AC system voltage Vac using the phase difference (system voltage phase) θ and the impedance Zt of the interconnection transformer 1003, the converter output voltage Vc is calculated from their vector relationship. The units shown in FIG. 9 are all units of pu.

The voltage difference corresponding to the vector from the AC system voltage Vac vector to the converter output voltage Vc vector is the voltage drop due to the impedance Zt of the link transformer 1003 and the converter output current Ia. Here, since the interconnection transformer 1003 can be regarded as having only a reactor component, the difference between the converter output voltage Vc and the AC system voltage Vac advances the converter output current Ia by 90 degrees. That is, the value of the voltage drop is the amplitude of converter output current Ia×impedance Zt of interconnection transformer 1003 . Therefore, the converter output voltage Vc can be obtained from the AC system voltage Vac, the converter output current Ia, the phase difference between the AC voltage and the current (system voltage phase) θ, and the impedance Zt of the interconnection transformer 1003 using the cosine theorem as follows: can be calculated by the formula (2).
Vc={Vac ² +(Ia×Zt) ² −2*Vac*(Ia×Zt)*cos(90−θ)} ^1/2 (2)

The voltage comparator 6004 compares the amplitude of the output voltage command value from the output voltage command calculator 6003 and the amplitude of the AC output voltage from the AC voltage detector 6005, and the difference between the two is equal to or greater than a preset threshold. At times, it is determined that the DC voltage sensor 1005 has failed.

A DC voltage sensor failure alarm 6006 outputs a failure of the DC voltage sensor 1005 determined by the voltage comparison unit 6004 as an alarm to the user.

As described above, in the first embodiment, an abnormality of the DC voltage sensor can be detected without redundantly installing the DC voltage sensor.

As Example 2 of the present invention, an example of an embodiment for detecting an abnormality in an AC voltage sensor will be shown. In addition, from the first embodiment and the second embodiment, it is possible to distinguish between an abnormality in the DC voltage sensor and an abnormality in the AC voltage sensor.

The case where the output voltage of the AC system differs from the output voltage command value for the single-phase 3-level converter is not limited to the case where there is a difference between the DC voltages of the two DC voltage circuits. It is assumed that there is an abnormality. These two cases can be distinguished by comparing the reactive power flowing into or out of the single-phase three-level converter with the command value for the reactive power.

When the AC voltage sensor is abnormal, the detected value of the AC voltage sensor used for the reactive power control block AQR is different from the true value of the output AC voltage. On the other hand, since the reactive power depends on the amplitude of the AC voltage, if there is a difference between the true value of the AC voltage and the value detected by the AC voltage sensor, the reactive power will be output according to the command value for the reactive power. should not. Therefore, by calculating the reactive power output based on the output AC voltage detected by the AC voltage sensor and comparing it with the command value corresponding to the reactive power, the abnormality of the AC voltage sensor can be detected.
Further, by combining the second embodiment with the first embodiment, it is possible to determine whether the AC voltage sensor is abnormal or the DC voltage sensor is abnormal.

1000: Power converter 1001: AC system 1002: AC voltage detector 1003: Interconnection transformer 1004: Current detector 1005: DC voltage sensor 1006: Control device 1007: Semiconductor switching elements 1008, 1009: Capacitor 1010: Single phase 3 Level converter 1011: U phase 1012: V phase 6001: Power control processor 6002: AC voltage sensor 6003: Output voltage command calculator 6004: Voltage comparator 6005: AC voltage detector 6006: DC voltage sensor failure alarm

Claims (6)

a single-phase three-level converter; and a DC voltage sensor for detecting the DC voltage of each of the positive-side and negative-side DC voltage circuits constituting the single-phase three-level converter, wherein the detected value of the DC voltage sensor is A power conversion device that performs control to keep the DC voltages of the positive side and the negative side DC voltage circuits equal assuming that they are equal to the true value,
an alternating voltage sensor that detects an output alternating voltage from the single-phase three-level converter;
an alternating current sensor that detects an output alternating current from the single-phase three-level converter;
Output voltage command based on the difference between the command value and the detected value of the active power of the output power from the single-phase three-level converter, the difference between the command value and the detected value of the reactive power of the output power, and the output AC current an output voltage command calculation unit that calculates a value ;
A power converter, comprising : a voltage comparison unit that compares the output AC voltage and the output voltage command value to determine an abnormality of the DC voltage sensor. The power converter according to claim 1,
Comparing the reactive power output by the single-phase three-level converter calculated based on the output AC voltage detected by the AC voltage sensor and the reactive power command value for the single-phase three-level converter, the AC voltage A power converter, further comprising a comparison determination unit that determines abnormality of a sensor. an interconnection transformer connected between a single-phase three-level converter and an AC system that receives output power from the single-phase three-level converter; a positive side and a negative side constituting the single-phase three-level converter and a DC voltage sensor for detecting the DC voltage of each of the DC voltage circuits on the positive side and the DC voltage of the negative side, assuming that the detected value of the DC voltage sensor is equal to the true value. A power conversion device that controls to keep equal ,
an alternating current sensor that detects an output alternating current from the single-phase three-level converter;
Based on the difference between the command value and the detected value of the active power of the output power from the single-phase three-level converter, the difference between the command value and the detected value of the reactive power of the output power, and the output AC current, the single-phase an output voltage command calculator that calculates an output voltage command value for the 3-level converter;
Calculate the actual output AC voltage output by the single-phase three-level converter based on the current and voltage of the AC system and the impedance of the interconnection transformer, and compare the output AC voltage with the output voltage command value. and a voltage comparator for determining an abnormality of the DC voltage sensor. Assuming that the detection value of the DC voltage sensor for detecting the DC voltage of each of the positive and negative DC voltage circuits constituting the single-phase three-level converter is equal to the true value, the positive and negative DC voltage circuits respectively An abnormality detection method in power conversion control that keeps the DC voltages of
a first step of detecting an output AC voltage from the single-phase three-level converter using an AC voltage sensor;
a second step of detecting output alternating current from said single-phase three-level converter using an alternating current sensor;
Based on the difference between the command value and the detected value of the active power of the output power from the single-phase three-level converter, the difference between the command value and the detected value of the reactive power of the output power, and the output AC current, the single-phase a third step of calculating an output voltage command value for the 3-level converter ;
and a fourth step of determining an abnormality of the DC voltage sensor by comparing the output AC voltage and the output voltage command value. The abnormality detection method according to claim 4,
Calculate the reactive power output by the single-phase three-level converter based on the output AC voltage detected by the AC voltage sensor, and compare the calculated reactive power and the reactive power command value for the single-phase three-level converter The abnormality detection method further comprising a fifth step of comparing to determine abnormality of the AC voltage sensor. Assuming that the detection value of the DC voltage sensor for detecting the DC voltage of each of the positive and negative DC voltage circuits constituting the single-phase three-level converter is equal to the true value, the positive and negative DC voltage circuits respectively An abnormality detection method in power conversion control that keeps the DC voltages of
a first step of detecting an output alternating current from the single-phase three-level converter using an alternating current sensor;
Based on the difference between the command value and the detected value of the active power of the output power from the single-phase three-level converter, the difference between the command value and the detected value of the reactive power of the output power, and the output AC current, the single-phase a second step of calculating an output voltage command value for the three-level converter;
Based on the impedance of the interconnection transformer connected between the single-phase 3-level converter and the AC system that receives the output power from the single-phase 3-level converter, and the current and voltage of the AC system, the single-phase a third step of calculating the actual output AC voltage output by the 3-level converter;
and a fourth step of determining an abnormality of the DC voltage sensor by comparing the output AC voltage and the output voltage command value.

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