KR100689325B1 - H-bridge multi-level inverter - Google Patents

Abstract

An H-bridge multi-level inverter is provided to improve reliability of a system by generating the same starting torque by outputting a constant setting voltage. In an H-bridge multi-level inverter, a plurality of power cell controllers(72A) forms each phase by connecting power cell(72) in serial as multi stages of N number. The power cell(72) is an independent unit inverter. The power cell controllers(72A) supply a multi-phase electric motor with power by combining each phase by a transformer. The transformer charges a DC link voltage. The power cell controllers(72A) control each power cell(72) by transmitting and receiving various data by communicating with a main controller. The power cell controllers(72A) has an AVR(Automatic Voltage Regulation) part. The AVR part operates standard voltage in advance by detecting an input voltage inputted to corresponding power cell(72). The AVR part operates a correcting value in real time for input voltage changes by comparing a detected input voltage and the standard voltage. The AVR part supplies the electric motor with a regular output voltage.

Description

H-bridge multi-level inverter {H-BRIDGE MULTI-LEVEL INVERTER}

1 is a block diagram of a multi-level inverter according to the prior art.

2 is an explanatory diagram showing an optical communication connection relationship between a main controller and a power cell;

3 is a detailed configuration diagram of a power cell.

4 is another explanatory diagram showing an optical communication connection relationship between a main controller and a power cell;

5 is a conceptual diagram of the AVR operation according to the prior art.

6 is a schematic diagram of an AVR computing system according to the prior art.

7 is an overall block diagram of an H-bridge multi-level inverter driven induction motor to which the present invention is applied.

8 is a block diagram of an automatic voltage regulator of an H-bridge multi-level inverter according to the present invention.

9 is a conceptual diagram of the AVR operation according to the present invention;

10 is a schematic diagram of an AVR computing system according to the present invention;

* Description of the symbols for the main parts of the drawings *

71: three-phase input transformer 72: power cell

72A: power cell controller 73: main controller

80: automatic voltage control unit 81: V / F control unit

82: reference voltage generator 83: reference voltage calculator

84: input voltage fluctuation compensator 85: selector

The present invention relates to an H-Bridge multi-level inverter, and in particular, each power cell controller provided in a plurality of power cells having an independent single-phase inverter structure in an H-Bridge multi-level inverter. Has an automatic voltage regulation unit that can perform automatic voltage regulation (AVR) function that calculates and sets the reference voltage by itself, so that even if there is a variation in the input voltage applied from the transformer, The present invention relates to an H-bridge multi-level inverter capable of generating the same starting torque by outputting an output voltage automatically adjusted to a set voltage on the power cell side.

In recent years, multi-level inverters have gained increasing interest as a topology for high voltage high capacity inverter systems because of the efficient and flexible operation of power systems such as flexible transmission systems (FACTS) in the power industry. It is necessary to develop high voltage power equipment for the purpose, and the development of electric motor drive system or industrial equipment requiring variable rotational force control has introduced high voltage large capacity inverter which is a power conversion device for variable frequency and DC-AC conversion. .

Multi-level inverters have the advantage of being suitable for high voltage and large capacity. In the case of multi-level inverters with N-levels, power conversion devices increase the voltage by (N-1) times compared to the conventional two-level inverters. It has the advantage of large capacity, and by having more voltage level than 2-level inverter, more sinusoidal output voltage waveform can be obtained, and this sinusoidal output voltage can not only reduce harmonics, but also output filter design. The filter size can be reduced and the electromagnetic interference (EMI) can be reduced by reducing the dv / dt and surge voltage generated during the switch transient state.

Such multi-level inverters include a diode clamp inverter, an H-bridge inverter, and a flying capacitor inverter. Among them, an H-bridge inverter is a unit having independent DC-Links by connecting low voltage H-bridges in series. It is composed of power cells to generate output voltage according to the number of power cells.

However, the biggest disadvantage of the H-bridge inverter is that the independent DC-Link power must be supplied because the short circuit can be formed through the DC-Link voltage and the switch according to the switching state output from the inverter. .

Therefore, independently separated power supplies are typically supplied through phase-shift transformers, and the DC-Link of each power cell must maintain a constant value as an independent power supply. The output voltage drops due to the impedance error of the transformer.

1 is a block diagram of a H-bridge multi-level inverter according to the prior art, in which the H-bridge multi-level inverter is a phase-shift for charging the input DC-Link voltage of the H-bridge multi-level inverter. Transformer 11; A plurality of power cells 12; It can be seen that the main controller 13 is configured to send and receive information of the plurality of power cells 12.

Here, the phase-shift transformer 11 is composed of an extended delta connection to charge a DC-Link voltage having a predetermined phase difference (± 20 °) to the secondary winding. A1 / A2 / A3 of each power cell 12 determine one leg and are connected in series paths, respectively.

In addition, the power cell controller 12A, which is provided in each of the power cells 12 having the independent single-phase inverter structure and controls the power cells, transmits data in optical communication with the master controller 13 as shown in FIG. It is configured to send and receive.

The main controller 13 is instantaneous power restart, speed search, emergency stop, auto energy save, auto-diagnosis, S / L, auto tuning, frequency limit, stall prevention, 110% / 1 minute In charge of the function. Then, the output voltage command, synchronization signal, motor overheat, transformer overheat, fan error, command loss, external failure, communication error, power cell setting error, output from the main controller 13 to the power cell controller 12A. It transmits information such as phase loss through optical communication, and on the contrary, overvoltage, undervoltage, overcurrent, arm short, ground fault, fuse open, heat sink overheat, from power cell controller 12A to main controller 13, Information such as hardware (H / W) abnormality, power cell output imaging and input imaging is transmitted.

3 shows a configuration of power cells constituting each DC-Link, and shows an inverter configuration in which three power cells are connected in series.

The main controller 13 receives the cell voltage from each power cell 12 and transmits reference voltage information to them again, and each power cell 12 receiving the reference voltage information receives the DC-Link voltage. And outputs a corresponding voltage to the motor 14 as a load, wherein the applied frequency is varied to obtain starting torque of the motor 14 shown in FIG. 1 and to control the speed of the motor 14 at the same time. Used as

Meanwhile, a communication function between the main controller 13 and the power cell controller 12A according to the related art will be described with reference to FIG. 4.

Here, the main controller 13 has a built-in controller for the variable speed control of the electric motor 14, and calculates the voltage / current value required for this. It also performs monitoring and diagnostics at the system level, monitoring, protection, MMI, communications, and other auxiliary functions.

In addition, each of the power cell controllers 12A, 12B, and 12C is located in each power cell, and performs monitoring and protection functions in units of power cells according to the command value of the main controller 13, and the main controller 13 ) Is connected to each of the power cell controllers 12A, 12B, and 12C by a high-speed link made of an optical cable to transmit and receive data in a serial communication method. In addition, a measurement controller communication network (CAN) is used for communication between the main controller 13 and the power cell controllers 12A, 12B, and 12C.

The main controller 13 receives the information on the rotational speed of the motor 14 and the inverter output current to control the rotational speed and the current of the motor 14. To this end, the main controller 13 synchronizes the reference voltage values of the three phases, which are the outputs of the current controller, to each of the phases and transmits them to the power cell controllers 12A, 12B, and 12C using CAN communication using an optical cable. do. Accordingly, each of the power cell controllers 12A, 12B, and 12C generates a PWM signal using the DC-Link voltage of each power cell 12 and the reference voltage value of the main controller 13.

However, in the case of the H-bridge multi-level inverter having the above structure and operation, each DC-Link secures an independent power supply, but in the case of the H-bridge multi-level inverter in comparison to the V / F driving system of the conventional general-purpose inverter, The transformer winding method is complicated and the output voltage may not be the original target value due to the% impedance. When charging a power supply with a slight voltage variation tolerance, the voltage of each power cell is combined because of the characteristics of the multi-level inverter. As the error range of the output voltage going out becomes larger, it was difficult to generate the exact output voltage desired by the user.

In the AVR operation unit of the conventional general-purpose inverter used for accurate output voltage, the main controller senses the DC-Link voltage of the power cell controller and receives the average voltage reference value as the input voltage to the power cell, and then outputs the output frequency in V / F ratio. The output voltage is determined by determining.

That is, in the conventional AVR computing device of the general-purpose inverter is calculated as "output voltage = input voltage * output voltage%" as shown in Figure 5, where "output voltage%" is determined by the output frequency and the boost voltage. It can be seen that.

In this conventional general-purpose inverter, when the output frequency is determined, the corresponding input voltage% is determined and the final output voltage is output. For example, when the frequency is changed from 60 Hz to 30 hz, the output voltage is output at 50% of the input voltage. In this input voltage fluctuation (permissible value: -15% to + 10%), the inverter must operate the motor without tripping.

On the other hand, the operation process used in the conventional H-bridge multi-level inverter for the AVR operation will be described below with reference to FIG.

First, the main controller 13 generates a power cell phase voltage reference value, generates a reference voltage VasRef / VbsRef / VcsRef, receives the DC-Link value of each power cell, calculates an AVR (①), and then each power cell. Collects Vdclink information of AVR to generate AVR compensation voltage, generates new phase voltage reference value per power cell considering power compensation voltage of each power cell (②, ③), and finally, main controller 13 and each power cell controller 12A Exchange new phase voltage threshold and Vdclink information per power cell (④).

As mentioned above, the AVR algorithm used for accurate output voltage in the H-bridge multi-level inverter has the error of the output voltage due to the combination of the tolerance of the output voltage due to the% impedance and the voltage of each power cell. As the range becomes larger, the conventional method of receiving a voltage from each power cell controller, calculating the average value of the main controller, and applying a common command to each power cell controller again, starts torque if the input voltage is smaller than the set time. The motor may not start due to lack of power. On the contrary, if the input voltage is large, overcurrent trip may occur. Therefore, the DC-Link voltage change due to the input voltage fluctuation causes unbalance of the phase voltage, resulting in a load. Cause the user to not be able to produce the desired output voltage, There was the inconvenience of haejueoya reset voltage value.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems, and an object of the present invention is to ensure that a phase voltage is always output at a predetermined voltage even when an input voltage fluctuates in an H-bridge multi-level inverter. The automatic voltage regulator (AVR) is provided to the power cell controller separately.

Another object of the present invention is to calculate and calculate the voltage reference value required for output voltage by the individual power cells independently receiving different DC-LINK voltages in the H-bridge multi-level inverter, so that the user can When the boost voltage used for the V / F control is set, the set voltage is always outputted without generating a separate setting even if the input voltage is changed, thereby providing the same starting torque.

The present invention devised to achieve the object as described above,

Each phase is composed by connecting a series of independent unit power cells to N multiple stages, and each phase is combined with a transformer that charges a DC link voltage to supply power to a multi-phase load. An H-bridge multi-level inverter having a plurality of power cell controllers for transmitting and receiving various data to control the respective power cells,

The power cell controller calculates a reference voltage in advance by sensing an independent power source according to a magnetic input, compares the detected inverter input voltage with the calculated reference voltage, and calculates a correction value for an input voltage change in real time, thereby outputting a constant output. And an automatic voltage regulation (AVR) unit for supplying a voltage to the load.

Preferably, the automatic voltage control (AVR) unit includes a reference voltage generator configured to receive a load-side rated voltage and generate and output a reference voltage, and receives a reference voltage from the reference voltage generator, and receives an input voltage input to the inverter. A reference voltage calculator configured to receive an input and calculate an output correction value for an input voltage change; and receive an output frequency and a set boost value to calculate a ratio of an output voltage value to the input voltage by V / F control. VF control unit; And an input voltage variation compensator configured to determine an output voltage by multiplying an output correction value of the reference voltage calculator by a ratio calculated by a V / F controller, and further output from the V / F controller as it is. And a selector for selecting a reference voltage or selecting an output voltage compensated by the input voltage variation compensator and outputting the output voltage to a corresponding power cell.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

7 and 8 show a block configuration according to the present invention, and FIG. 7 shows the entire block configuration of the H-bridge multi-level inverter to which the present invention is applied. The block configuration of the automatic voltage regulator 80 in the power cell controller 72A provided in the power cell 72 is shown.

In FIG. 7, the H-Bridge multi-level inverter connects the power cells 72, which are independent unit inverters, in three plural stages to configure each phase of the U, V, and W phases. It is configured to supply power to the motor 74, which is a three-phase load, combined with a transformer 71 that charges the DC link voltage. Each of the power cells 72 is integrally or separately provided by the power cell controller 72A. Each power cell controller 72A is configured to transmit and receive various data by data communication with the main controller 73 so that each power cell 72 obtains data to be controlled.

In particular, the power cell controller 72A is provided with an automatic voltage regulation (AVR) unit 80, which is the most essential part of the present invention, and the function of the automatic voltage regulator 80 will be described in brief. The reference voltage may be calculated in advance by sensing an independent power supply, and a correction value for input voltage variation may be calculated in real time by comparing the detected inverter input voltage with the calculated reference voltage to supply a constant output voltage to the load. In the present invention, the rated voltage of the motor 74 which is the three-phase load mentioned above may be input and used as an independent power source that calculates a reference voltage in advance.

Preferably, the automatic voltage control (AVR) unit 80 includes a reference voltage generator 82, a reference voltage calculator 83, a V / F controller 81, and an input voltage variation compensation unit 84. The output selector 85 is further connected to the / F control unit 81 and the input voltage fluctuation compensator 84 so as to receive both outputs.

More specifically, the reference voltage generator 82 is configured to generate and output a reference voltage by receiving a rated voltage (MOTOR VOLTAGE) on the side of the motor 74 as a load. The input voltage is converted into the reference voltage by the data stored in the program table stored in the power cell controller 72A, and the reference voltage calculated offline by the user is input. It could be.

Meanwhile, the reference voltage calculator 83 is configured to receive a reference voltage from the reference voltage generator 82 and to receive an input voltage input to a power cell 72 having a single-phase inverter. However, the reference voltage calculator 83 is configured to calculate an output correction value of how much DC-LINK correction should be performed on a value in which the input voltage fluctuates in real time, and the calculated output correction value is an input voltage fluctuation compensator ( 84).

The V / F controller 81 is configured to receive an input voltage to the power cell 72 together with the reference voltage calculator 83 as shown in FIG. 8, and is input to the V / F controller 81 together with the input voltage. The output frequency is determined and input by the deceleration slope and the operation command. The output frequency is inputted with the output frequency and the set boost value, and the ratio of the output voltage value to the input voltage to the power cell 72 is controlled by V / F control. Configured to calculate.

The input voltage fluctuation compensator 84 is configured to multiply the output correction value of the reference voltage calculator 83 by the ratio calculated by the V / F controller 81 to determine the output voltage. By compensating the input voltage fluctuation in real time by multiplying the output correction value by the ratio calculated by the V / F controller 81, it is configured to compensate for the constant output voltage irrelevant to the fluctuation of the DC-LINK.

For reference, the V / F control is a method of controlling the average torque by proportionally controlling the stator voltage effective value and the frequency of the induction motor. In the case of the V / F control, the induction motor maintains the magnetic flux even if the speed and torque change. The magnitude is kept constant and close to the rated torque value of the induction motor, which means constant flux operation.

The output selector 85 is configured to select and apply the reference voltage output from the V / F controller 81 as it is and the output voltage compensated by the input voltage fluctuation compensator 84. ) Is configured to output the final output value of the V / F control as it is, or to output the set reference value.

The operation of the present invention having the above configuration is as follows.

In the automatic voltage control (AVR) unit 80 of any power cell controller 72A, the reference voltage generator 82 receives the motor rated voltage from the inverter to generate a reference voltage in advance, and the reference voltage calculator 83 The output voltage of the reference voltage generator 82 and the input voltage of the inverter input from the inverter input voltage detector are input in real time to calculate an output correction value for the input voltage variation.

The input voltage fluctuation compensator 84 compensates for the input voltage fluctuation in real time by multiplying the correction value calculated through the above process and the output voltage ratio calculated by the V / F controller 81. The output voltage is constantly output regardless of the input voltage fluctuations.

In addition, the selector 85 selects a reference voltage output as it is from the V / F controller 81 or a reference voltage compensated by the input voltage fluctuation compensator 84 according to a user's request. It outputs to the cell 72, and accordingly, the power cell 72 appropriately controls the voltage supplied to the electric motor 74 based on the reference voltage input from the corresponding power cell controller 72A. In this way, the operation is performed by all power cell controllers 72A individually, so that the reference voltage value is calculated and set by itself.

On the other hand, the automatic voltage regulation (AVR) principle according to the present invention will be described with reference to FIG.

The PWM output is generated with the duty ratio of the triangular wave carrier (peak 200V) and the reference voltage carrier, which is half duty. In this case, the user sets the motor voltage to 100V as an example. The voltage input from the inverter, that is, the DC-Link value, may be 90V or 110V instead of a constant value input to 100V set by the user.

As such, when the DC-Link value actually input is smaller than the value set as 90V, the PWM duty is increased to output a constant value of 100. Similarly, when the DC-Link value is 110v and more than 100v is input, the PWM duty is increased. In short, 100v is outputted, so the PWM duty is changed according to the change of DC-Link value so that constant output voltage can be maintained at all times.

Meanwhile, the AVR operation processing process according to the present invention will be described with reference to FIG. 10.

First, the main controller 73 generates the power cell reference voltages VdseRef and VqseRef, and each power cell 72 generates its own phase voltage to perform the acceleration / deceleration function for the electric motor 74. ①②

In addition, since each power cell 72 performs its own AVR function, the load of the main controller 73 is reduced, and the power cell reference voltage VdseRef and the angle between the main controller 73 and each power cell 72 are reduced. The angle (angle) is exchanged, and thus, the communication load between the main controller 73 and the power cell controller 72A is reduced and the reliability is improved.

As described above, the preferred embodiments of the present invention have been described in detail, but those skilled in the art may change or change the present invention as many as possible without departing from the spirit and scope of the present invention. It will be appreciated that the true technical protection scope of the present invention should be defined by the claims.

As described in detail above, since the present invention receives an input voltage variation over time or an isolated independent voltage as a transformer, the user sets one time at the time of configuring the system regardless of the voltage variation due to the transformer winding method and the% impedance voltage drop. The performance can be output equally, and accordingly, the set voltage is always output to generate the same starting torque, thereby improving the reliability of the system.

In addition, according to the present invention, since each power cell controller calculates and sets a voltage reference value by itself, a separate setting change is not required according to the voltage change, thereby reducing the maintenance cost of the system.

Claims (4)

Each phase is formed by connecting a series of independent unit power cells to N multiple stages, and each phase is combined with a transformer that charges a DC link voltage to supply power to the multiphase motor, and to communicate data with the main controller. An H-bridge multi-level inverter having a plurality of power cell controllers for transmitting and receiving various data to control the respective power cells, The power cell controller, Detects an input voltage input to a corresponding power cell to calculate a reference voltage in advance, and compares the detected input voltage with the calculated reference voltage to calculate a correction value for an input voltage change in real time. An H-bridge multi-level inverter characterized in that it has an automatic voltage regulation (AVR) unit for supplying to the electric motor. The method of claim 1, The automatic voltage control (AVR) unit, A reference voltage generator for generating and outputting a reference voltage by receiving the rated voltage of the motor; A reference voltage calculator configured to receive a reference voltage from the reference voltage generator and to receive an input voltage input to the power cell to calculate an output correction value for an input voltage change; A VF controller configured to receive an output frequency and a set boost value and calculate a ratio of an output voltage value to the input voltage by V / F control; And And an input voltage variation compensation unit configured to determine an output voltage by multiplying an output correction value of the reference voltage calculator by a ratio calculated by a V / F controller. The method of claim 2, A selector for selecting a reference voltage output directly from the V / F control unit or selecting an output voltage compensated by the input voltage variation compensator and outputting the output voltage to a corresponding power cell; Level inverter. The method of claim 1, The calculated reference voltage is H-bridge multi-level inverter, characterized in that the rated voltage of the motor is input and used.

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