KR20090126993A - Multilevel converter consisting of building-block module having power regeneration capability - Google Patents

Abstract

PURPOSE: A module for a multilevel converter regenerating the power and the multilevel converter using the same are provided to reduce the weight and the volume of the system to 40 to 60% by implementing the multilevel converter with mutual independent DC source without a transformer. CONSTITUTION: A reactor(11) controls the current of an input AC power side and prevents the short between unit cells. A PWM rectifier(12) converts the AC power from the reactor into the DC power and outputs the DC power. A capacitor(13) controls the AC flowing in the reactor by absorbing the current ripple element in the PWM rectifier and maintaining the constant voltage. A PWM inverter(14) converts the DC power to the AC power and outputs the AC power to the load. The PWM rectifier comprises H-bridge circuit using a power semiconductor switching device. The power semiconductor switching device is turned on or off.

Description

Multilevel converter module capable of power regeneration and multilevel converter using the same {Multilevel converter consisting of building-block module having power regeneration capability}

The present invention relates to a multi-level converter module capable of power regeneration and a multi-level converter using the same, and more particularly, based on an LHCH basic cell composed of a reactor, an H-bridge converter, a capacitor, and an H-bridge inverter. Multi-level output voltage can be implemented and modularized by a plurality of independent DC power supplies configured using a connected reactor. As a result, the number of output voltage levels and the capacity of the system can be greatly increased. The present invention relates to a multilevel converter module capable of easily regenerating power and a multilevel converter using the same.

In particular, the present invention relates to a multilevel converter module capable of regenerating power and allowing a continuous operation of the system by bypassing a failed module even when some modules fail during operation of the system, and a multilevel converter using the same. .

In a power converter, a multilevel converter refers to a multilevel inverter and a multilevel rectifier, respectively or collectively. In the case of a multilevel inverter, a high voltage DC power source or a plurality of separate DC power sources are used. A multilevel rectifier is a device for generating a high voltage DC voltage or a plurality of separate DC voltages from an AC input voltage of a sine wave.

In general, multi-level rectifiers and multi-level converters are used in combination with back-to-back connections in applications that convert alternating current to other types of alternating current.

According to the trend of the large-capacity electric devices in the general industry, multi-level converters are continuously being developed to be applied to high-voltage large-capacity power conversion systems. Such multi-level converters have the following characteristics.

First, as the output voltage level increases, the dV / dt generated during switching and the magnitude of the surge voltage decrease, and when applied to AC motor driving, failures due to insulation breakdown of the motor stator winding and damage to the bearing of the motor can be significantly reduced. . It also provides the suppression of the common mode current.

Second, the same output harmonic characteristics can be obtained at a lower switching frequency than the two-level converter, so that switching losses can be reduced to increase efficiency.

Third, since the voltage applied to the switch is limited to the DC link voltage, it is possible to appropriately set the rated voltage level of the power semiconductor switch by adjusting the number of levels.

The types of multilevel converters developed so far are roughly classified into three types, such as diode clamping, flying capacitor, and H-bridge.

The diode clamping multilevel converter is capable of back-to-back connection by sequentially switching to multiple taps obtained from multiple capacitors connected in series with a single high voltage DC link. It is put to practical use and applied.

However, a control method is needed to solve the DC link voltage imbalance problem. As the number of levels increases, it is difficult to realize a system, an imbalance voltage is applied to the clamping diode, and the current of the main switch elements becomes unbalanced. there is a problem.

Flying-capacitor multilevel converters do not cause diode voltage imbalance problems, but as the level increases, an additional voltage is required to secure the initial voltage of the internal capacitor in a system that requires a large number of capacitor banks and a single input rectifier. In addition to the need for a conventional circuit, the switching control for maintaining the voltage of the capacitor is complicated, and the switching loss is also increased due to the increased switching frequency, which makes it difficult to put to practical use.

The H-bridge multilevel converter is a method of obtaining a multilevel output voltage by connecting a plurality of converter outputs of a conventional H-bridge configuration in series with each other. Although it has the advantage of being simple and easy to control, it requires a large number of independent DC power supplies to obtain multi-level outputs. It is true.

1 shows an example of a circuit configuration of an H-bridge type multilevel inverter composed of three H-bridge converters and three independent DC power supplies. In FIG. 1, since the DC input voltage of each H-bridge converter is V _dc , each of the H-bridge output voltages is possible in three cases of {V _dc , 0, -V _dc }, and thus, the multilevel inverter output voltage Vo The number of cases is {3V _dc , 2V _dc , V _dc , 0, -V _dc , -2V _dc , -3V _dc } to be 7 levels. Intuitively, it can be seen that the circuit of FIG. 1 has a modular structure and is easily obtained through the expansion of the converter module of the level.

In order to obtain the independent DC voltage shown in FIG. 1, a separate diode rectifier or a PWM rectifier is used. In this case, a plurality of independent single phase transformers or phase shift transformers insulated from each other by a secondary side are necessary for each isolation. However, such an isolation transformer occupies about 40% to 60% of the weight and volume of the entire system. In particular, the manufacturing cost is high, which is a major increase in the price of the entire system, and also reduces the operation efficiency of the system.

On the other hand, the multi-level inverter shown in Figure 1 is a back-to-back configuration is not possible to consume the regenerative energy as a resistor during the power regeneration operation of the AC-side load or a separate DC-DC converter for recovering the regenerated energy or There is a problem that requires a DC-AC converter.

In order to solve the above problems, the present invention enables the back-to-back configuration of the H-bridge multi-level inverter using a distributed linkage reactor without using a phase shift isolation transformer, thereby enabling power regeneration. An object of the present invention is to provide a multilevel converter module and a multilevel converter using the same.

More specifically, the present invention is based on a basic cell (hereinafter referred to as LHCH basic cell) consisting of a reactor, an H-bridge PWM rectifier, a capacitor, and an H-bridge PWM inverter, and cascaded these basic cells by By implementing the multi-level, it is very easy to expand the number of levels and the capacity of the system, and to provide a multi-level converter module capable of power regeneration and a multi-level converter using the same.

In addition, the present invention is a multi-level converter module capable of power regeneration to enable continuous operation of the system by bypassing the failed module even if some modules fail during operation of the system and a multi-level converter using the same The purpose is to provide.

In order to achieve the above object, the multi-level converter module capable of power regeneration according to the present invention includes a reactor that facilitates current control on the input AC power supply side and prevents a short circuit between unit cells, and through the reactor. It converts the input AC power into DC power and outputs it, converts the regenerated DC power into AC and supplies it to the AC input power side through the reactor, and absorbs the current ripple component generated by the PWM rectifier The capacitor and the converted DC power for smoothly controlling the AC current flowing through the reactor by maintaining the voltage is converted into AC power and output to the load side, and converts the regenerative power of AC input from the load side to DC to the PWM rectifier And a PWM inverter for supplying the capacitor.

Preferably, the PWM rectifier and the PWM inverter is characterized in that the H-bridge circuit composed of a power semiconductor switching element.

Particularly, the power semiconductor switching element is at least one of a self-protection type power semiconductor switching element capable of turning on and off.

In order to achieve the above object, the present invention provides a single-phase multi-level converter in which at least two of the above modules are connected in cascade.

Preferably, at least two cascades of the modules are connected, and the switching elements of the PWM rectifiers configured in each module are controlled to selectively operate the power supply mode and the power regeneration mode.

In order to achieve the above object, the present invention is a three-phase multi-level converter, characterized in that connected to at least two cascade (Cascade) in each phase of the three-phase power source.

In addition, the present invention can be configured not only three-phase, but also any n-phase multi-level converter, the object of the present invention is to provide an n-phase multi-level converter in which at least two cascades of the above modules in each phase. have.

By the above solution, the present invention can implement a multi-level converter having a mutually independent DC power source without using a transformer, it is possible to reduce the weight and volume of the entire system by 40% to 60%, Since expensive transformers are eliminated, manufacturing costs are also significantly reduced.

In addition, an additional capacitor bank of the clamping diode of the diode clamping multilevel converter and the flying capacitor multilevel converter is unnecessary.

In addition, since the DC link stage voltage control is easy, the level can be easily expanded, and the regenerative braking is possible, it is energy-saving and there is no loss by the transformer, thereby improving the efficiency of the system.

In particular, since each module can be manufactured modularly and it is very easy to expand the number of levels of multi-levels based on this module, it is very flexible to cope with capacity expansion, and some modules fail during operation of the system. Even if the failed module is bypassed, continuous operation is possible, thereby improving the reliability of the system.

Examples of a multilevel converter module capable of regenerating power and a multilevel converter using the same according to the present invention may be variously applied. Hereinafter, the proposed scheme will be described with an example with reference to the accompanying drawings.

First, prior to the detailed description of the present invention, in the present invention, a PWM rectifier converting AC to DC and a PWM inverter converting DC to AC are collectively referred to as converters.

2 is a circuit diagram showing an embodiment of a multi-level converter module according to the present invention, the module 10 of the present invention serves to facilitate the input AC power supply side (V _s ) current control and to prevent a short circuit between unit cells. And a reactor 11 for converting AC, a PWM rectifier 12 for converting alternating current into direct current, a capacitor 13 having a constant capacitance, and a PWM inverter 14 for converting direct current into alternating current.

Here, in the power regenerative mode operation, the flow of power is reversed, so the PWM rectifier 12 converts direct current to alternating current, and the PWM inverter 14 converts alternating current to direct current, according to the power conversion method. Although the name is preferably changed, for convenience of description of the present invention, the side connected to the reactor 11 is called a PWM rectifier 12 and the side connected to the load 20 is a PWM inverter ( 14).

In the following description, the module 10 is mixed with the unit cell 10.

The reactor 11 facilitates the current control of the input AC power supply V _s so that the current waveform is similar to the voltage waveform, and even if a plurality of cascades are connected to the module 10 of the present invention. This function prevents short circuit between unit cells.

The PWM rectifier 12 converts the AC power input through the reactor 11 into DC power in the power supply mode operation and outputs the DC power. In the power regenerative mode operation, the regenerative power supplied from the PWM inverter 14 is output. Is converted into alternating current and supplied to the reactor (11).

Preferably, the PWM rectifier 12 is configured in the form of an H-bridge circuit using a power semiconductor switching element, and the power supply mode and the power regenerative mode by the switching operation of the power semiconductor switching element. Configure it to work as one.

Here, since the power semiconductor switching device should be able to turn on and turn off at any time, self-protection such as Insulated Gate Bipolar Transistors (IGBTs), Integrated Gate Commutated Thyristors (IGCT), and Gate Turn-Off thyristors (GTO) It is preferable to implement with a type power semiconductor switching element.

The capacitor 13 forms a direct current link stage to absorb the ripple component of the direct current side current and maintains a constant voltage to smoothly control the alternating current flowing through the reactor 11, its type and capacitance. Various modifications are possible depending on the purpose of use of the module 10 and the needs of those skilled in the art.

The PWM inverter 14 converts the DC power converted by the PWM rectifier 12 into AC power in the power supply mode operation and outputs the AC power to the load 20 side, and supplies the power from the load 20 side in the power regeneration mode operation. The regenerative power of the alternating current is converted into direct current and supplied to the PWM rectifier 12 and the capacitor 13.

Therefore, the switching operation of the PWM rectifier 12 and the PWM inverter 14 of the module 10 of the present invention as described above, as well as supplying power to the load 20 side, the input AC power supply from the load 20 side You can also regenerate power to the side.

In addition, when the reactor 11 cascades the module 10 of the present invention to configure a multilevel converter, the reactor 11 enables stable supply and regeneration of power without a short circuit between modules.

Hereinafter, an embodiment of a single-phase multilevel converter will be described with reference to FIGS. 3 and 4.

Each of the unit cells 10 shown in FIG. 3 is as shown in FIG. 2, and the number of unit cells 10 may be variously modified to provide an extended single-phase multilevel converter.

Hereinafter, a case in which three basic cells 10 as shown in FIG. 4 are connected by cascade will be described in more detail with reference to an embodiment.

The operation of the PWM rectifier 12 in the power supply mode operation is to increase the current I _s of the power supply in a period in which the voltage V _s of the supplied power supply is positive (+). ) and the number 2 and the switch _{(Q 11, Q 12, 1} Q 21, Q 22, Q 31, turns on (Turn-on) to Q _32).

In this case, the current of the AC power supply is expressed by Equation 1 below.

Here, 'I _s0' is 'I _s' value just before (t ₀₎ being the switch of the six pairs of turn-on.

When the current (I _s ) shown in Equation 1 reaches the preset maximum value, the current must be decreased again, in which case the switches 1 and 4 of each PWM rectifier 12 (Q ₁₁ , Q ₁₄ , Q ₂₁ , Q ₂₄ , Q ₃₁ and Q ₃₄ ) are turned on.

In this case, the current of the AC power supply is expressed by Equation 2 below.

Here, 'I _s1 ' is a 'I _s ' value immediately before the six pairs of switches are turned on (t ₁ ), and 'V _d ' is 'V _d1 + V _d2 + V _d3 '.

In Equation 2, since 'V _d ' is larger than 'V _s ', the sign of the integral term becomes negative (-) and the current decreases.

By controlling the PWM rectifier 12 so that the above Equations 1 and 2 alternately, the AC input current 'I _s ' may be generated to be an in-phase sine wave as shown in FIG. 6.

FIG. 7 shows that when the current is controlled in this manner, the DC link voltages V _d1 , V _d2 and V _d3 of each basic cell are equally made.

On the other hand, the operation of the PWM rectifier 12 in the power regenerative mode operation that regenerates power from the load 20, the third and second switches Q ₁₃ , Q ₁₂ , Q ₂₃ , Q _{22 of} each PWM rectifier 12 , Q ₃₃ , Q ₃₂ ) is turned on to increase the current I _s in a section in which the voltage V _s of the power supply is negative (−).

In this case, the current becomes as shown in Equation 3 below.

Here, 'I _s2 ' is a value of 'I _s ' just before the pair of six switches are turned on (t ₂ ).

When the current (I _s ) shown in Equation 3 reaches a preset maximum value, the current must be decreased again, and at this time, switches 3 and 4 of each unit cell 10 (Q ₁₃ , Q ₁₄ , Q ₂₃ , Q ₂₄ , Q ₃₃ , Q ₃₄ ) is turned on.

In this case, the current of the AC power supply is expressed by Equation 4 below.

Here, I _s3 is 'I _s ' just before the six pairs of switches are turned on (t ₃ ).

By controlling the PWM rectifier 12 to alternately generate the above Equations 3 and 4, the AC input current 'I _s ' may be generated to be a sinusoidal wave inverse to the AC power supply voltage as shown in FIG. 8.

Meanwhile, the PWM inverter 14 converts the DC power of the DC link terminal (both ends of 'C') to supply AC power to the load 20 side or to regenerate power from the load 20 side. This will be described below in more detail with reference to FIG. 9.

9 shows the switching state of the PWM inverter 14 and the waveform of the inverter output voltage. Basically, the output voltage 'V _o ' denotes the output voltages' V _o1 ',' V _o2 ', and' V of each unit cell 10. _o3 '.

First, looking at the positive section of the first cycle, only 'V _o3 ' is output in the 't _S0 -t _S1 ' section, and the voltages of 'V _o2 ' and 'V _o1 ' do not appear at the output terminal.

Next, in the 't _S1 -t _S2 ' section, 'V _o3 ' and 'V _o2 ' are output and 'V _o1 ' does not appear at the output terminal.

Next, all three DC link voltages are output in the section 't _S2- t _S3 '.

By switching 'S ₁₁ -S ₃₄ ' in this manner, an output voltage waveform as shown in FIG. 9 can be obtained.

Looking at the positive interval of the second cycle, we can see that each switch conduction time is different from the first cycle.

The conduction time of 'S ₂₁ ' and 'S ₂₄ ' in the second cycle is the same as the 'S ₃₁ ' and 'S ₃₄ ' of the first cycle, and the conduction time of 'S ₃₁ ' and 'S ₃₄ ' is 'S ₁₁ '. ', Like' S ₁₄ '.

The reason why the conduction time is sequentially changed is to maintain the voltage balance of the capacitor 13 of the DC link terminal.

In addition to the above method, there are various methods for obtaining the output voltage of the PWM inverter, but FIG. 9 illustrates the simplest method as an example.

In the above, a multilevel converter module capable of regenerating power according to the present invention and a multilevel converter using the same have been described. Such a technical configuration of the present invention will be understood by those skilled in the art that the present invention can be implemented in other specific forms without changing the technical spirit or essential features of the present invention.

Therefore, the above-described embodiments are to be understood in all respects as illustrative and not restrictive, and the scope of the present invention is indicated by the appended claims rather than the foregoing description, and the meanings of the claims and All changes or modifications derived from the scope and the equivalent concept should be construed as being included in the scope of the present invention.

1 is a circuit diagram showing an example of an H-bridge type multi-level inverter having a conventional seven-level output voltage.

2 is a circuit diagram illustrating an embodiment of a multi-level converter module according to the present invention.

3 is a block diagram illustrating an embodiment of a single-phase multilevel converter configured by cascading two or more modules shown in FIG. 2.

FIG. 4 is a circuit diagram illustrating in detail the cascade connection of three modules of FIG. 2.

FIG. 5 is a block diagram illustrating an embodiment of a three-phase multilevel converter configured by cascading two or more modules shown in FIG. 2.

6 is a graph showing an AC input voltage and a current when a multilevel converter having a modular structure capable of power regeneration according to the present invention operates in a power supply mode.

FIG. 7 is a graph illustrating input voltages and DC link voltages of respective modules when three cascaded modules are connected to each other.

8 is a graph illustrating an AC input voltage and a current when the multilevel converter having a modular structure capable of power regeneration according to the present invention operates in a power regeneration mode.

9 is a graph illustrating a load side voltage and a switching state of a multilevel converter according to the present invention.

<Explanation of symbols for the main parts of the drawings>

10: unit cell 11: reactor

12: PWM Rectifier 13: Capacitor

14: PWM inverter 20: LOAD

Claims (7)

A reactor that facilitates current control on the input AC power supply side and prevents a short circuit between unit cells; A PWM rectifier for converting and outputting AC power input through the reactor into DC power, and converting the regenerated DC power into AC and supplying it to the AC input power side through the reactor; A capacitor for smoothly controlling the AC current flowing through the reactor by absorbing the current ripple component generated by the PWM rectifier and maintaining a constant voltage; Converts the converted DC power into AC power and outputs it to the load side, and converts the regenerative power of the AC input from the load side into DC and includes a PWM inverter for supplying power to the PWM rectifier and the capacitor. module. The method of claim 1, The PWM rectifier is a power semiconductor switching device for power regeneration capable multi-level converter module, characterized in that the H-bridge circuit is configured. The method of claim 2, The power semiconductor switching element is a power regeneration capable multi-level converter module, characterized in that at least one of the self-protection type power semiconductor switching element capable of turning on and off. The method of claim 1, The PWM inverter is a power semiconductor switching device for power regeneration capable multi-level converter module, characterized in that the H-bridge circuit is configured. The method of claim 4, wherein The power semiconductor switching device is a power regeneration capable multi-level converter module, characterized in that at least one of the self-power-type power semiconductor switching device capable of turning on and off. The single-phase multilevel converter of any one of claims 1 to 5, wherein at least two modules are cascaded. The three-phase multilevel converter of any one of claims 1 to 5, wherein at least two cascades are connected to each phase of the three-phase power source.

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