KR200390534Y1 - High efficiency charge and discharge system of DVR using EDLC - Google Patents

Abstract

  The present invention relates to an EDLC (Electric Double Layer Capacitor) high efficiency charge and discharge system of an instantaneous voltage drop dynamic voltage restorer (DVR) that compensates for an instantaneous voltage drop or instantaneous power failure in a power system.

  The present invention provides a constant current control during charging of EDLC, which is an electrical energy storage device of an instantaneous voltage drop dynamic voltage compensator (hereinafter referred to as "DVR"), and a charge / discharge complementary type DC / controlled to control a constant voltage when discharging the EDLC. The DC converter 50 and the control circuit 80 are configured to have high efficiency of operation.

  Unlike the uninterruptible power supply (UPS), which adopts full voltage and on-line compensation, the DVR compensates for the instantaneous voltage drop of the system but only the voltage fluctuation during instantaneous power failure. Among the many factors related to power quality, the problem caused by the instantaneous voltage drop of the system accounts for more than 80% of the total, so the DVR application is more efficient and cost-effective than the UPS.

  The DVR compensates for voltage fluctuations by using lead acid batteries or electrolytic capacitors as electrical energy storage devices. DVR systems with lead acid batteries have problems in terms of charge / discharge speed, lifespan, and environment, and DVR systems using electrolytic capacitors. Has the disadvantage of very low energy density, but the emergence of an electric double layer capacitor (EDLC) has made it possible to overcome the problem.

  In the present invention, a high efficiency EDLC charge and discharge system of the DVR system to which EDLC is applied, which is more advantageous than the existing UPS, lead acid battery or DVR system to which an electrolytic capacitor is applied, in terms of charge and discharge speed, life and environment, and energy density. In order to realize this, the charge / discharge complementary DC / DC converter 50 and the control circuit 80 are devised to control the constant current when the EDLC is charged and to control the constant voltage when the EDLC is discharged.

  The present invention is expected to be widely applied to the high-efficiency operation of the power quality compensator for supplying stable and high-quality power to power consumers in Korea, which is promoting the transition to high value-added industries requiring high power quality.

Description

High efficiency charge and discharge system of instantaneous voltage drop dynamic voltage compensator with electric double layer capacitor

  Recently, due to the development of automation process and information communication field based on computer network construction, the use of disturbance-sensitive load facilities such as microprocessors and power electronic devices has exploded and interest in power quality has increased. Consumer demand is also growing.

  The power quality problem is a phenomenon caused by the variation of voltage, current and frequency in the power system, which means the reliability of power supply and the characteristics of power equipment. Factors related to power quality include momentary interruptions, voltage sags or voltage rises, and harmonics. Most of them are used in the same sense as voltage quality, and the most representative problem that can directly affect the economic deterioration of production activities is the instantaneous voltage drop or instantaneous power interruption because it can cause downtime and malfunction of the customer equipment. Can be. In addition, among the factors related to power quality, the problem caused by the instantaneous voltage drop of the system occupies more than 80 [%] of the total, and is pointed as the most important item.

  In the past, a constant voltage transformer (CVT) was mainly used as a method of compensating instantaneous voltage drop, but it is not effective for variable load because the output voltage is fixed. Recently, researches on voltage drop compensation using a power conversion device that can compensate for these drawbacks have been actively conducted, and a method of installing an uninterruptible power supply (UPS) has been very commonly used, but since it uses a battery, There is a disadvantage in that it can be used only in a limited load range because maintenance is required periodically and capacity is limited. In addition, due to the weakness in efficiency and cost by adopting the full voltage and on-line compensation methods, recently, a more economical dynamic voltage compensator (DVR) is applied to the power system.

  The DVR system compensates for voltage fluctuations using energy storage devices such as lead acid batteries or electrolytic capacitors. Such systems have disadvantages in terms of charge / discharge rate, lifespan and environment, and have very low energy density. With the advent of double layer capacitors (EDLC), the problem is overcome.

  Therefore, in the present invention, an EDLC composed of a high efficiency and multifunctional control circuit and a protection circuit is applied to a DVR, and a compensation system having excellent performance is devised. The charging and discharging control circuit (complementary DC / DC converter) was configured to be controlled with constant current when charging the EDLC and to be controlled with constant voltage when discharging so that it can be operated with high efficiency.

  The present invention has been devised for the purpose of implementing a high efficiency EDLC charge and discharge system of a DVR system to which EDLC is advantageous in terms of charge and discharge speed, life and environment, and energy density, than an existing UPS or DVR system. In order to realize this, the charge / discharge complementary DC / DC converter 50 and the control circuit 80 are devised to control the constant current when the EDLC is charged and to control the constant voltage when the EDLC is discharged.

  The main circuit and the control circuit 80 of the charge / discharge DC / DC converter 50 of the EDLC 60 are shown in FIG. 2. Complementary DC / DC converter 50 for the current control to use the reactor 55 to smooth the current. At this time, in the complementary DC / DC converter 50, while the main switch 51 is turned on for charging and discharging the EDLC 60, the sub-switch 52 is turned off while keeping the current value constant. In addition, the magnetic energy is accumulated by the reactor 55 inserted while the sub-switch 52 is turned on while the main switch 51 is turned off, and the magnetic energy accumulated in the reactor 55 while the main switch 51 is turned on again. The energy is regenerated to make efficient use of energy and to smooth the current.

  The control of the DC / DC converter 50 for constant current control shown in FIG. 2 calculates the PI controller 82 result and the feedback value of the actual reactor current IL with respect to the error voltage of the EDLC charging command voltage V_ref_DC and the detected feedback voltage VDC. The resulting value was compared with the sawtooth wave 84 to adjust the DC / DC converter duty ratio. As a result, the duty ratio signal is connected to the main switch 51 of the complementary DC / DC converter 50 for the constant current control of FIG. 2, and the complementary signal is connected to the sub switch 52 while the charging voltage of the EDLC 60 is maintained. And a controller method capable of controlling current.

  Description of Figure 1

  The PWM Inverter 70 is a power circuit for converting DC into energy. It receives DC voltage as input and generates AC output to make AC voltage to compensate. For this purpose, a semiconductor switch is used and a gate turn off thyristor (GTO) is used as a switch, but an IGBT with a fast switching speed is used.

  The filter 96 serves to suppress harmonics generated at the output terminal of the PWM inverter 70. Since the inverter output voltage becomes a pulse of square wave due to switching, an L-C lowpass filter is usually installed at the output stage to extract the fundamental wave from this waveform.

  In the case of the DVR of the present invention, the reactive power can be compensated for, but its main purpose is to supply the active power to the load, so a separate energy storage system (ESS) is required. The energy storage device converts power using an AC / DC rectifier 40 or a PWM converter, and the converted power is converted into an electrolytic capacitor bank or battery (Battery ESS: BESS), a flywheel energy storage (FES) system, and a SMES. Although it can be stored using a superconducting magnetic energy storage system, it must be carefully determined in consideration of various conditions such as price and performance. However, in the present invention, instead of the electrolytic capacitor bank or battery, which is frequently used in the past, the circuit is constructed by applying an EDLC which is an environmentally friendly material and can serve as a bridge between these two devices.

  The matching transformer 20 is normally operated with an inductance connected in series with the system, and this value can be neglected since it is much smaller than the line inductance of most systems. Therefore, the most important function of the matching transformer is to connect the inverter and the system during compensation. The primary side of the transformer can be △ connection or Y connection, but most of them use △ connection so that no image is generated. In this case, although the capacity of the power circuit does not change according to the turns ratio of the transformer, it may be advantageous to set the primary side higher than the secondary side because the linear operation region of the inverter is related to the magnitude of the voltage.

  Static switch (91 ~ 93) should use this switch for isolation from the grid when the DVR is installed off-line, and most of the two thyristors with high withstand voltage capability as shown in FIG. Use in reverse parallel connection. Since the electric energy is charged to the EDLC Storage System 60 through the rectifier 40, a switching switch 94 is also required in the charging system. As a result, the two pairs of switching switches should be configured to charge the EDLC Storage System 60 when the system is normal through complementary operation, and to inject voltage into the system through the series transformer in case of an accident.

<Normal DVR Operation>

  Normal DVR operation is as follows. In the block diagram as shown in FIG. 1, the thyristors 91 to 93, which are switching switches of each phase between the power supply 10 and the load 30, are turned on, and the inverter 70 of each phase including the filter 96 is turned on. Off the system voltage is supplied to the load side 30 through the thyristor (91 ~ 93). At this time, the EDLC 60 accumulates charges through the three-phase rectifier 40 and the DC / DC converter 50 of the constant current control, and initializes or equalizes the voltage by the high-performance controller 70 of the EDLC, and the charge / discharge switching circuit. Various protection device circuits are operated.

<DVR operation during instantaneous voltage drop and momentary power failure>

  If the instantaneous voltage drop or instantaneous power failure occurs in the power system, the thyristors 91 to 93 are turned off, and the inverter 70 of each phase is turned on so that the undervoltage or the blackout voltage of the system is different from the voltage generated by the inverter 70. In addition, the voltage is supplied to the load side 30. At this time, since the inverter of each phase compensates for the voltage drop or the electrostatic voltage by using the charge accumulated in the EDLC 60, the voltage of the load side 30 may be normally supplied.

  In this case, since the charge / discharge control circuit 50 for maintaining the DC link voltage at an appropriate level operates even in the EDLC 60, the compensation operation may be continuously performed in the PWM inverter 70. .

  Description of Figure 2

  The main circuit and the control circuit 80 of the charge / discharge DC / DC converter 50 of the EDLC 60 are shown in FIG. 2. At this time, when the EDLC main charging voltage is charged directly through the rectifier 40 at a high power supply voltage, the pulsed peak current may be introduced during the initial charging of the EDLC 60, thereby destroying the capacitor. Therefore, it is possible to make it easy to prevent accidents and gain tuning of the controller of the DC / DC converter 50.

  Complementary DC / DC converter 50 for the current control to use the reactor 55 to smooth the current. At this time, in the complementary DC / DC converter 50, while the main switch 51 is turned on for charging and discharging the EDLC 60, the sub-switch 52 is turned off while keeping the current value constant. In addition, the magnetic energy is accumulated by the reactor 55 inserted while the sub-switch 52 is turned on while the main switch 51 is turned off, and the magnetic energy accumulated in the reactor 55 while the main switch 51 is turned on again. The energy is regenerated to make efficient use of energy and to smooth the current.

  The control of the DC / DC converter 50 for constant current control shown in FIG. 2 calculates the PI controller 82 result and the feedback value of the actual reactor current IL with respect to the error voltage of the EDLC charging command voltage V_ref_DC and the detected feedback voltage VDC. The resulting value was compared with the sawtooth wave 84 to adjust the DC / DC converter duty ratio. As a result, the duty ratio signal is connected to the main switch 51 of the complementary DC / DC converter 50 for the constant current control of FIG. 2, and the complementary signal is connected to the sub switch 52 while the charging voltage of the EDLC 60 is maintained. And a controller method capable of controlling current.

  Description of FIGS. 3 and 4

<Efficiency improvement by current source control circuit during charging>

  When the fully discharged capacitor is charged by the generator as shown in FIG. 3 (a), that is, when the electromotive force V of the generator is applied to the large-capacity EDLC 103 whose voltage is 0 and the internal resistance is R 104, the charging current I is V. It can flow as much as / R, but from the generator's perspective, the load is almost short-circuited and the generator will soon burn out without a protection circuit. In addition, the capacitor terminal voltage V rises at a rate of V = Q / C due to the charge Q flowed by the charge, but when the capacitance C is small, a large current similar to that of the short-circuit state of the load flows, thereby charging in a very short time. Will be over. In this case, charging of the voltage source is not suitable and charging by the current source control circuit is required. Since the lead acid battery, which is a secondary battery, is itself a voltage source, charging from a voltage source does not cause any problem, but the EDLC 103 is not suitable for charging by a voltage source.

<Stable voltage supply by voltage source control circuit during discharge>

  In a voltage source circuit as shown in FIG. 3A, a current i flowing after t seconds through a resistor R connected between the EDLC 103, which is the capacitance C, and the constant voltage source V, may be represented by Equation (1).

     i = (V / R) × exp (-t / CR) (1)

  In addition, the power consumed by the resistor R can be obtained as shown in Equation (2), which is equivalent to the energy that can be accumulated in the capacitor. Therefore, when charging and discharging in a constant voltage source, the energy efficiency is 50 [%]. It can be seen that.

(2)

  However, as shown in FIG. 3B, the charge and discharge efficiency by the current source is as follows. In other words, when charging or discharging at constant current I for t time, the charge is Q, as shown in equation (3).

     Q = I × t (3)

  Therefore, the amount of power A stored in the EDLC capacitor is expressed as Equation (4), and the amount of power B consumed in the resistor R can be written as Equation (5).

(4)

(5)

  Using the two equations (4) and (5), the ratio k of the loss and the power storage capacity is obtained as shown in equation (6).

     k = B / A = 2RC / t (6)

  In Equation (6), the longer the charge / discharge time t is, the lower the ratio k of the loss to the amount of power storage can be reduced. As a result, the charge / discharge efficiency can be controlled by the current source control circuit.

  Moreover, based on Formula (6), the efficiency EC at the time of charge by a constant current source, and the efficiency ED at the time of discharge can be written like Formula (7) and Formula (8).

     EC = A / (A + B) = t / (t + 2RC) (7)

     ED = (A-B) / A = 1-(2RC / t) (8)

Therefore, the charge / discharge control circuit of the EDLC requires a configuration of a controller capable of switching charge and discharge as shown in FIG. 4. At this time, the current source circuit can be configured with a typical PI controller, and the voltage source circuit can be obtained by the duty ratio control 111 of the DC / DC converter.

    As such, when the EDLC is charged, it operates as a current source control circuit to improve efficiency, and when the EDLC is discharged, it operates as a voltage source control circuit to increase the stability of the voltage supply, thereby effectively controlling the charging efficiency and stable discharge function of the EDLC.

  In the present invention, a high efficiency EDLC charge / discharge system of a DVR system to which EDLC is applied, which is advantageous in terms of charge / discharge rate, lifespan, environment, and energy density, is better than a conventional UPS or DVR system. As a power quality compensation device, the DVR is expected to be widely used in place of the UPS in the future, and the application of EDLC, which is advantageous in terms of charging and discharging speed, life and environment, and energy density, is expected to be more widely expanded as an energy storage device of the DVR. The present invention is to improve the charging and discharging efficiency of the EDLC, which can be widely used to improve the charging and discharging efficiency when the EDLC which is rapidly being used is applied to various systems. In particular, it is expected to be effectively used for improving the charging and discharging efficiency of EDLC by applying to the DVR system requiring rapid charging and discharging.

  The present invention is expected to be widely applied to the high-efficiency operation of the power quality compensator for supplying stable and high-quality power to power consumers in Korea, which is promoting the transition to high value-added industries requiring high power quality.

  1: Overall Configuration of DVR System with EDLC

  2: Constant current charging circuit and control diagram of DVR system using EDLC

  3: Conceptual diagram of charging and discharging of a voltage source and a current source of EDLC

  4: Charge / discharge switching circuit of EDLC

<Explanation of Signs for Main Parts>

10: Power Source

  Power supply source for supplying power to the load side 30 using power

20: Matching Transformer

  Normally, the secondary winding is operated with an inductance connected in series on a grid line connected from the power source 10 to the load side 30, and this value can be neglected since it is much smaller than the line inductance of the grid in most cases. In case of instantaneous voltage drop and instantaneous power failure due to system accident or disturbance, the voltage is applied to the load side 30 by transferring the compensation voltage to the system for the voltage drop or the blackout voltage generated by the operation of the inverter of each phase (70). To play a role.

30: Sensitive Load

  Electrical applications and devices that can cause large losses due to instantaneous voltage drops and momentary power outages.

40: Rectifier

  Rectifier converts alternating voltage into direct voltage to charge electric energy in EDLC Storage System (60)

50: DC / DC Converter

  Power conversion device that controls the DC voltage supplied from the rectifier 40 to supply a constant current to the EDLC Storage System 60

60: EDLC Storage System

  PWM Inverter (70) to save electric energy by constant current charging by DC / DC Converter (50), and to operate DVR during instantaneous voltage drop and momentary power failure to supply insufficient voltage to the system. Electrical energy storage system

70: PWM Inverter

  It receives a DC voltage from the EDLC Storage System 60 as an input and generates an AC output to make an AC voltage to compensate. For this purpose, a semiconductor switch is used and a GTO (Gate Turn off Thyristor) is used, but IGBT with a fast switching speed is used.

80: Gate Driver & Controller

  DC / DC Converter (50), EDLC Storage System (60), PWM Inverter (70) drive and DVR operation control

91 to 93: static switch

  Static switch should be used to isolate the system when the DVR is installed off-line, and as shown in Fig. 1, most of the two thyristors with high withstand voltage capability are connected in reverse use. Since the electric energy is charged to the EDLC Storage System 60 through the rectifier 40, a switching switch 94 is also required in the charging system. As a result, the two pairs of switching switches should be configured to charge the EDLC Storage System 60 when the system is normal through complementary operation, and to inject voltage into the system through the series transformer in case of an accident.

94: static switch

  Switch that functions to connect and insulate the power system and DVR when storing electrical energy in the EDLC Storage System (60) through the rectifier (40). Through the complementary operation of the switch 91 ~ 93, the EDLC Storage System (60) is charged in the case of normal system.

95: step down transformer

  When the EDLC 60 is initially charged, the EDLC main charge voltage is charged directly through the rectifier 40 at a high power supply voltage to decrease the voltage to prevent the pulsed peak current from entering the EDLC 60 and destroying the capacitor. Giving transformer

96: Filter

  PWM Inverter 70 serves to suppress harmonics generated in the voltage waveform of the output terminal. Since the inverter output voltage becomes a pulse of square wave due to switching, an L-C lowpass filter is usually installed at the output stage to extract the fundamental wave from this waveform.

51: DC / DC Converter Main Switch

  A semiconductor switching device performing a function of charging electrical energy to the EDLC Storage System (60). The sub-switch 52 is off while the main switch is on while keeping the value of current constant.

52: DC / DC Converter Part Switch

  A semiconductor switching element that operates while the main switch (51) is off to accumulate magnetic energy in the reactor (52). While the main switch 51 is off, magnetic energy is accumulated by the reactor 55 inserted while the sub-switch is turned on. Then, the magnetic energy accumulated in the reactor 55 is regenerated while the main switch 51 is turned on. Energy can be used efficiently and the current smoothing function is provided.

53: DC-Link stage voltage detection circuit

  This circuit senses the voltage of the actual DC-Link stage. The error voltage of the sensing voltage VDC detected by the EDLC charging command voltage V_ref_DC and the DC-Link stage voltage detection circuit is input to the PI controller 82.

54: reactor current detection circuit

  A circuit for sensing the current supplied to the EDLC Storage System (60) through the reactor (55). The result of calculating the PI controller 82 result of the EDLC charge command voltage V_ref_DC and the detected feedback voltage VDC and the feedback value of the actual reactor current IL is compared with the sawtooth wave 84 to determine the DC / DC converter duty ratio. It is used to generate a gate signal for operating the switches 51 and 52 of the DC / DC converter 50 by adjusting.

55: reactor

  While the DC / DC Converter main switch 51 is off, the magnetic energy is accumulated by the reactor 55 inserted while the sub-switch is turned on. Then, the magnetic energy accumulated while the DC / DC converter main switch 51 is on. Regenerative to make efficient use of energy and to smooth the current.

81: charge command voltage generator

  Voltage Reference for generating EDLC charge command voltage (V_ref_DC).

82: PI Controller

  Proportional integral controller that uses error voltage of sensing voltage VDC detected by EDLC charge command voltage V_ref_DC and DC-Link stage voltage detection circuit as input value

83: Controller Limit

  Gain profile of the PI controller 82 results for the EDLC charge command voltage V_ref_DC and the detected feedback voltage VDC and the feedback value of the actual reactor current IL.

84: Carrier Wave

  Triangular wave signal for comparing the PI controller 82 result for the EDLC charge command voltage V_ref_DC and the detected feedback voltage VDC with the feedback value of the actual reactor current IL.

85: comparator

  The output of the PI controller 82 and the actual reactor current IL for the error voltage of the EDLC charging command voltage V_ref_DC and the detected feedback voltage VDC to generate a gate signal for the operation of the switches 51 and 52 of the DC / DC converter 50. Ability to compare Carrier Wave (84) with the result of calculating feedback value

101: constant voltage source

  Constant Voltage Source for EDLC Charging

102: constant current source

  Constant Current Source for EDLC Charging

103: EDLC

  Charging device used as electric energy storage device of DVR

104: EDLC internal resistance

  Intrinsic Resistance Inside EDLC

105: EDLC capacitance

  Correlation coefficient between the voltage of the EDLC and the amount of charge charge (C = Q / V)

111: Duty Cycle Controller

  Fertilization rate controller for operating as voltage source during EDLC discharge

112: charge and discharge switch

  Switching circuit for operating as a current source during EDLC charging and as a voltage source during EDLC discharge

Claims (4)

The secondary winding is normally connected between the power source 10 that supplies power to the load side 30 using power and the sensitive load 30 that can cause a large loss due to instantaneous voltage drop and momentary power failure. It is operated by inductance connected in series on the grid line connected from the power source 10 to the load side 30. In case of instantaneous voltage drop and instantaneous power failure due to a system accident or disturbance, the voltage generated by the inverter of each phase is operated 70. Matching transformer 20 and EDLC storage system 60 to charge electric energy to the load side 30 so that the voltage is supplied to the load side 30 by providing a compensation voltage to the system. Rectifier 40 converts AC voltage to DC voltage and DC / DC converter 50 is used for constant current charging to store electrical energy. Controls the DC voltage supplied from the EDLC Storage System (60) and Rectifier (40), an electrical energy storage device that supplies power to the PWM Inverter (70) so that the DVR operates to supply insufficient voltage to the system during power failure. The DC / DC Converter (50) and the EDLC Storage System (60), a power converter that functions to supply a constant current to the EDLC Storage System (60) during charging and a constant voltage to the EDLC Storage System (60) during discharge. ) PWM Inverter (70) function to generate AC voltage to receive AC voltage by inputting DC voltage, and Gate Driver & Controller (80) that controls power conversion switching device and DVR operation. ), A static switch (91 to 94) for connecting the power system and the DVR, and the voltage down to prevent destruction of the EDLC (60) by the pulsed peak current during the initial charging of the EDLC (60). Step-down transformers (9 5) and an EDLC-enabled DVR system, comprising a filter 96 that suppresses harmonics generated from the voltage waveform of the PWM inverter output stage.   The secondary switch 52 of claim 1, wherein the DC / DC converter 50 is turned off while the main switch 51 is turned on to maintain the value of the current while the main switch 51 is turned on for charging and discharging the EDLC 60. In addition, the magnetic energy is accumulated by the reactor 55 inserted while the sub-switch 52 is turned on while the main switch 51 is turned off, and the magnetic energy accumulated in the reactor 55 while the main switch 51 is turned on again. EDLC-enabled DVR system that regenerates energy to make efficient use of energy and to smooth current The method according to claim 1, wherein the Gate Driver & Controller (80) enables switching 112 of the control function at the time of EDLC charging and discharging. When the EDLC is discharged, it operates as a voltage source control circuit by the duty ratio control 111 of the DC / DC converter to increase the stability of the voltage supply, thereby effectively controlling the charging efficiency of the EDLC and the stability during discharge. EDLC-enabled DVR system, characterized in that The method according to claim 1, wherein the Gate Driver & Controller 80 and the PI controller 82 results for the error voltage of the EDLC charging command voltage V_ref_DC and the detected feedback voltage VDC for controlling the DC / DC converter 50 for constant current control. The feedback value of the actual reactor current IL is compared with the sawtooth wave 84 to adjust the DC / DC converter duty ratio, and as a result, the duty ratio signal is the complementary DC / DC converter 50 for current control. 51) and the complementary signal is connected to the secondary switch 52, the EDLC is applied to the DVR system characterized in that to perform a control method capable of controlling the current during charging of the EDLC (60)