5511results about "Harmonic reduction arrangement" patented technology

The Electric Power Converter has the qualifications for an uninterruptable power supply, battery management, energy conversion, micro-grid formation, Power Factor Correction including Total Harmonic Distortion correction in real time. Uninterruptable power supply's use is for always-on, real-time, all-time, reduced distortion with functions of load reduction and management during peak load events. The Electric Power Converter as well has the ability to provide maintenance for most types of batteries including charging and discharge regiments to increase the overall lifetime of a battery, the maintenance, incorporating restorative functions that can refurbish dead batteries or can further increase the overall efficiency and useful function of weaker / aged / defective batteries. Energy conversion capabilities allow for the conversion of AC or DC to AC or DC with high efficiency and ability to actively vary the frequency in accordance to the required parameters. The Electric Power Converter is able to establish and sustain a micro-grid with multiple and varying sources of power generation and load conditions. The Electric Power Converter is achieving dynamic, real-time, interactive Power Factor Correction (PFC) function with advanced voltage harmonic distortion correction with a high efficiency ratio. The Electric Power converter is designed to function with the emerging Smart Grid technologies and provide an overall higher level of operating efficiency and higher quality of electrical power.

A system and method for providing grid connected utility pole distributed solar power generation is disclosed. The system includes a utility pole, an inverter and one or more solar panels. Each of the one or more solar panels is mounted on the utility pole. The method includes receiving solar energy at the one or more solar panels. The one or more solar panels convert the solar energy to direct current (DC) electrical energy. Further, the method includes transmitting the DC electrical energy to the inverter, which is mounted on the utility pole. The inverter can be integrated with one or more solar panels to form an alternating current photovoltaic (AC PV) module. Furthermore, the method includes converting the DC electrical energy to alternating current (AC) electrical energy by the inverter and transmitting the AC electrical energy to a grid for power distribution.

The invention provides a method and system for operating a solar farm inverter as a Flexible AC Transmission System (FACTS) device—a STATCOM—for voltage control. The solar farm inverter can provide voltage regulation, damping enhancement, stability improvement and other benefits provided by FACTS devices. In one embodiment, the solar farm operating as a STATCOM at night is employed to increase the connectivity of neighbouring wind farms that produce peak power at night due to high winds, but are unable to connect due to voltage regulation issues. The present invention can also operate during the day because there remains inverter capacity after real power export by the solar farm. Additional auxiliary controllers are incorporated in the solar farm inverter to enhance damping and stability, and provide other benefits provided by FACTS devices.

The invention in the simplest form is an improved variable speed engine / generator set with an integrated power conditioning system and control method, used to generate high quality AC power with optimum fuel efficiency and reduced emissions. The variable speed generator control scheme allows for load adaptive speed control of engine and generator field. The transformerless power inverter topology and control method provides the necessary output frequency, voltage and / or current waveform regulation, harmonic distortion rejection, and provides for single phase, or unbalanced loading.

The invention relates to a super capacitor energy storage type power quality compensator. A system structure comprises a compensation transformer, a series compensator, a parallel compensator, a super capacitor group, a current foldback circuit, a bidirectional DC / DC chopper circuit, a signal sampling circuit, a control circuit, a drive circuit, a human-computer interface and corresponding auxiliary circuits, which form a three-phase three-wire system topological structure. By utilizing the excellent characteristics of great power density, high charging and discharging speed and long cycle life of a super capacitor, the super capacitor energy storage type power quality compensator is matched with the DC / DC chopper circuit to form an energy storage control system which plays the roles of adjusting power and stabilizing the voltage of a direct current bus in work. The invention also has the functions of dynamic voltage recovery, active filter and reactive compensation and can ensure that a load can obtain rated sine voltage and the current of a grid is sine current with the same direction (unit power factor) with that of a voltage fundamental wave positive sequence active component, thereby comprehensively improving the quality of power. The invention has positive generalization and application value for both the public grid and users.

A protective circuit for a multi-level converter including a DC link capacitor bank includes: an energy absorbing element; switches, wherein at least two of the switches each couple the energy absorbing element to the capacitor bank; and a controller configured to provide control signals to the switches to selectively actuate the switches to enable control of energy dissipation and to enable control of voltage balance on the capacitor bank of the multi-level converter.

The power unit includes H bridge inverter circuit, capacitance in DC section connected to DC bus in inverter circuit, and control circuit for controlling operation of the power unit. The power unit also includes a clipping energy consumption circuit. Combining a small quantity of active power absorbed by active electric power filter, the method realizes controlling DC bus voltage of power unit. The active electric power filter includes following parts: inverter with each phase including at least one power unit; voltage detection circuit, central control system, filtering circuit, precharge circuit, income line switch, interface and communication circuit, and cooling unit etc.

The invention discloses a mixed type power quality controlling device comprising an active part and a passive part, wherein the active part comprises active power filters (APFs) and static var generators (SVGs), the SVGs are used for supplying transient reactive power, and the APFs are used for filtering harmonic waves; the number of the APFs and the SVGs is at least two groups, and the APFs and the SVGs are connected with a three-phase power grid in parallel through a transformer isolation mode; the passive part comprises a static var compensator (SVC) which is used for supplying steady-state var power, wherein the SVC comprises a thirstier switching capacitor (TSC), a thirstier control reactor (TCR), and a fixed capacitance compensator (FC); the TSC, the TCR and the FC are directly connected with the three-phase power grid, the TSC is used for supplying high-capacity capacitive var power, the FC is used for supplying low-capacity var power and is also used as a main subharmonic filtering branch circuit to carry out harmonious comprehensive compensation and harmonic control on a power system.

This invention relates to a method for controlling capacity and voltage at the DC side uniformly of bridge-H cascade active power filter, which first of all takes the harmonic current, passive current needed to be compensated by the power net and load system as the compensation current required by the filter, takes the sum of the expected compensation current and fundamental wave positive sequence active current absorbed from the net as the APF reference current to get the APF inverter desired output voltage via a current following controller to drive the APF output current to follow the reference current, computes the micro-tune volume of the output voltage of the cascade unit, carries out micro-micro adjustment to the expected output voltage by the balance controller based on the cascade unit capacitance and voltage deviation and the APF output current to adjust the charge and discharge time of the unit floating capacitance to further realize the balance control of the floated capacitance and voltage takes the adjusted expected output voltage as the reference one of said unit to be modulated in pulse width to get trigger signals of the cascaded bridge-H power device to drive the primary circuit power device.

The invention relates to a modularized multi-level converter with an auxiliary diode. The modularized multi-level converter comprises a three-phase valve body, and three active energy feedback circuits respectively connected to the three-phase valve body, wherein each phase of valve body comprises 2M half-bridge inversion units and 2M-1 auxiliary diodes; direct current capacitors of the 1-(2M-1)th serially connected half-bridge inversion units are respectively connected with one auxiliary diode, and the final (2M)th half-bridge inversion unit is serially connected to form the valve body; the 1-Mth half-bridge inversion units form the upper-half part of the valve body to output a negative polarity voltage; and the (M+1)th to 2Mth half-bridge inversion units form the lower-half part of the valve body to output a positive polarity voltage. The auxiliary diodes and the active energy feedback circuits form a capacitor voltage sharing loop, the modularized multi-level converter realizes capacitance self voltage sharing effect, and realizes that the unit capacitance voltage is measured by using less direct current voltage sensors, thus the detection and the control of multi-level topology are greatly simplified. The modularized multi-level converter can be used in occasions such as reaction compensation and harmonic treatment of a medium-voltage or high-voltage power grid.

The invention discloses a control circuit for a voltage dropping type power factor corrector, which is used for controlling a voltage dropping converter to realize the power factor correction function. Inductance current critical intermittent control of changed on-time is performed on a Buck circuit through the control circuit to ensure that the on-time of a switching tube rises in the power frequency period along with increase of input voltage; and the critical intermittent working mode of inductance current in the Buck circuit is controlled, and when the inductance current is greater than zero, the junction capacitance of the switching tube and inductance are resonated, and the switching tube is connected when the voltage resonance of the junction capacitance reaches the volley bottom. The control circuit for the voltage dropping type power factor corrector has the characteristics of ensuring high power factors in the whole input voltage range, and meeting the harmonic requirements of IEC 61000-3-2 Class C, Class D, along with high efficiency.

The invention relates to a power distribution network fault arc extinction method by connecting a neutral point to the ground through multi-level converter. The power distribution network fault arc extinction method is characterized in that the cascade H-bridge multi-level converter is adopted and directly connected at the position of the neutral point of a power distribution network through a reactor; at the initial moment when the power distribution network has a single-phase earth fault, synthetic operation is conducted to generate offset currents needed to be injected (img file='69356dest_path_image001. TIF'wi'19' he'=25' / ), then the offset currents are quickly put into the multi-level converter, the multi-level converter is controlled by aid of the current tracking control algorithm and the PWM (Pulse-Width Modulation) modulation strategy to generate offset currents (img file='652784dest_path_image001. TIF'wi'19' he'=25' / ), and the offset currents are put into the neutral point of the power distribution network so as to compensate grounding total currents of the fault point. In addition, the fault phase voltage is forced to be 0 constantly so the instantaneous grounding fault can be cleared automatically, and further the technical problem of the existing fault arc extinction technology of poor arc extinction effect can be solved.

The invention provides a method for injecting a harmonic voltage to restrain a harmonic current of a PMSM (permanent magnet synchronous motor), which is characterized in that a ring to restrain the harmonic current is added to realize the closed-loop control for the harmonic current on the basis of extracting harmonic current components in the PMSM in real time, thus calculating to obtain harmonic voltage components which are required to be injected to restrain 5-order and 7-order harmonic currents of the PMSM; and then the obtained harmonic voltage components are injected into a three-phase control voltage in a speed control system of the PMSM so as to offset the 5-order and 7-order harmonic components in a motor current when the PMSM runs, thereby reaching the purpose of restraining the 5-order and 7-order harmonic currents. The method is used to solve the technical difficulty that current ZCP (zero crossing point) is required to detect accurately in a traditional mode to restrain the harmonic current, remarkably improves the current waveform of the motor, effectively restrains the 5-order and 7-order harmonic currents caused by the nonlinear characteristics of an inverter and the air-gap field distortion of the motor, effectively reduces the additional loss caused by the 5-order and 7-order harmonic current components, reduces the electromagnetic torque and the revolving speed pulse of the PMSM and improves the running efficiency and the running reliability of the PMSM.

The invention relates to a battery energy storage system based power conversion system and a control method thereof. The power conversion system comprises a battery energy storage system, a bidirectional DC / DC (direct-current) converter, a grid-side current transformer, a filter circuit and an isolated voltage transformer. The battery energy storage system is in parallel connection with a direct-current bus of the grid-side current transformer through the bidirectional DC / DC converter; the grid-side current transformer, the filter circuit and the isolated voltage transformer are connected in sequence; and the isolated voltage transformer accesses to a power grid. The control method includes sequentially monitoring the battery energy storage system, the bidirectional DC / DC converter, the grid-side current transformer, the filter circuit and the isolated voltage transformer by a control circuit. Since the battery energy storage system utilizes battery cells connected in series and is in parallel connection with the common direct-current bus through the bidirectional DC / DC converter, circulation among battery packs is avoided, and capacity expansion of the system is facilitated. Further, by the aid of the monitoring control strategy for SOC (super capacitor state of charge) of the battery energy storage system and battery end voltage, excessive charge or discharge state of the battery energy storage system is avoided, service lives of the battery packs are prolonged, and comprehensive service cost is lowered.

A method and system to detect and evaluate harmonic distortion in an electrical power system is disclosed. A plurality of monitoring devices is installed in the electrical power system. The hierarchy of the electrical power system is received. Data indicative of harmonic distortion on the electrical power system is received from at least two of the monitoring devices. The data indicative of harmonic distortion is automatically aligned in a temporal or pseudo-temporal context. An electrical characteristic of the harmonic distortion from the data indicative of harmonic distortion is determined.

An active filter (300) generates multi-phase compensating current in an AC power supply system (10) that supplies a load (200). The filter (300) includes a compensating current output device (34) outputting multi-phase compensating current to an AC power line (50); and a controller (310) for controlling the compensating current output (340) such that the multi-phase compensating current compensates for current harmonics and power factor on said AC power line (50). The controller (310) estimates current harmonics and power factor compensating values as a function of multi-phase power measurements.

A method and system to detect and evaluate harmonic distortion in an electrical power system is disclosed. A plurality of monitoring devices is installed in the electrical power system. The hierarchy of the electrical power system is received. Data indicative of harmonic distortion on the electrical power system is received from at least two of said plurality of monitoring devices. The data indicative of harmonic distortion is automatically aligned in a temporal or pseudo-temporal context. An electrical characteristic of the harmonic distortion from the data indicative of harmonic distortion is determined.

The invention relates to a virtual synchronous generator control method based on self-adapting moment inertia. The output of a grid-connected inverter in distributed generation is connected with an AC bus of a filter capacitor Cf which is in parallel connection with the grid-connected inverter through a filter inductor Lf; sampling is performed to obtain the output power, the voltage and the current of an output interface of an inverter; the output power, the voltage and the current are transmitted to a VSG (virtual synchronous generator) algorithm; the calculated terminal voltage of a VSG stator is sent to be controlled by a voltage external loop; the voltage external loop adopts a PI controller to stably load the voltage; the current of the filter capacitor is sent to be controlled by a voltage internal loop; the voltage internal loop adopts a PI controller to increase the response speed; a control signal is outputted by a voltage-current dual-closed loop to the grid-connected inverter; the moment inertia in the virtual synchronous generator in the control method can be changed in a self-adapted manner according to the change capacity of the system frequency. Through the adoption of the virtual synchronous generator control method disclosed by the invention, the transient state process of the system is reduced; a great deal of harmonic waves in the system is offset; the stability of frequency and the stability of voltage can be improved; the adaptability and the power supply quality of a micro-electrical network are improved; the problem that in a conventional method, the output frequency is reduced, is solved.

The invention discloses a control method for a quality control system of micro source internetworking electric energy. A primary side of the coupling voltage transformer on a serial active power filter side of a UPQC (unified power quality controller) is connected with a larger current-limiting inductor in parallel, and a direct-current large-capacitance side of the UPQC is connected with a photovoltaic generating power supply in parallel. Due to effects of cooperative control, the photovoltaic power supply is internetworked for power generation during normal operation, active power is provided for a power grid by the parallel active power filter of the UPQC, and the harmonic current from a load side and the voltage fluctuation and harmonic voltage from the power grid side are governed and compensated by the UPQC. In the case of short-circuiting failure on the load side, the main circuit of the UPQC stops operating, a secondary side of the coupling voltage transformer is subjected to high impedance, and the current can be limited by the parallel current-limiting large inductor. By adopting the method, the functions of failure current limitation, harmonic treatment, voltage support, photovoltaic power generation and the like can be realized during micro grid internetworking operation, and the optimized protection and operation of the quality of electric energy in micro grid internetworking can also be realized.

The invention relates to a vehicle-to-grid (V2G)-technology-based vehicle-mounted charging and discharging device and a control method thereof. The device comprises a power supply input part, a battery, a power grid side controller, a power grid side converter, a battery side controller and a battery side converter, wherein the power supply input part, the power grid side converter and the battery side converter are connected with the battery in turn; the battery side controller adopts a hysteresis loop comparison control mode and compares voltage and current amount which is detected in real time with the set value, and a duty ratio of the battery side converter is subjected to hysteresis loop output control, so that Boost chopped wave conversion during constant current, constant voltage charging and grid connection is realized; and the power grid side controller adopts a double closed loop control mode of a voltage outer ring and a current inner ring to realize charging adaptation and grid-connected inversion of the power grid side converter. The device overcomes the defects that the traditional bidirectional converter circuit is complex in structure, high in cost and low in efficiency in the V2G technology, and the requirement of operating the same circuit in two working modes is met.

The invention relates to a single-phase universal electric energy quality controller for power supply for electrified railways, and belongs to the technical field of flexible AC power transmission and distribution; the invention comprises a single-phase multi-coil transformer composed of a primary coil and n secondary coils, so that the secondary coils of the transformer can be connected in parallel with n voltage sources of current transformers; n capacitors are connected with n voltage source current transformers, so as to form a single-phase chain-type H-bridge current transformer with n chains; the AC terminal of the H-bridge current transformer is directly connected with the traction grid through a reactor. The invention has the functions of active power control, reactive power compensation and harmonic compensation, so as to resolve three-phase voltage unbalance, voltage fluctuation, low power factor and harmonic pollution and so on that exist in ER traction transformer stations, effectively lower the capacity of traction transformers, increase ER transport capacity and transportation capability. Moreover, the invention is characterized in small occupied area, little loss and low cost, in order to gain perfect harmonic suppression characteristics and dynamic response features, and provide convenience in industrial production and improve device reliability.

The invention discloses an electrified railway traction power supply and energy storage device and a method of the electrified railway traction power supply and energy storage device. The energy storage device is connected between a feeding arm alpha or feeding arm beta at the output end of a traction transformer and a steel rail, or two energy storage devices are connected between the feeding arm alpha and the steel rail and between the feeding arm beta and the steel rail respectively, wherein the energy storage device is arranged in a traction substation. The energy storage device comprises a control unit, an isolation transformer, a PWM current transformer, an energy transformation circuit and an energy storage element, wherein the PWM current transformer, the energy transformation circuit and the energy storage element are connected in sequence, and the control unit is used for carrying out calculation according to the voltage, current and direction of the feeding arm alpha and / or feeding arm beta to complete control over the PWM current transformer and the energy transformation circuit and achieve energy exchange between the energy storage device and the feeding section connected with the energy storage device. The electrified railway traction power supply and energy storage device can fully recycle locomotive braking feedback electric energy, improve the energy utilization ratio of a traction power supply system, reduce the installation billing capacity of the traction transformer, reduce cost and absorb and store energy even in electricity valleys, has the effect of peak load shifting and further has the functions of dynamic reactive-power compensation and low-order harmonic suppression.

The invention in one embodiment is an improved variable speed engine / generator set with an integrated power conditioning system and control method including load shedding to generate high quality AC power with improved fuel efficiency and reduced emissions. The variable speed generator control scheme allows for load adaptive speed control of engine and generator field. The transformerless power inverter topology and control method provides the necessary output frequency, voltage and / or current waveform regulation, harmonic distortion rejection, and provides for single phase, or unbalanced loading.

The invention belongs to the field of electrical engineering, distributed power generation and power quality control, and aims to provide a multi-functional grid-connected inverter and a grid-connected inverter control method. The grid-connected inverter comprises a direct-current bus bar with a capacitor and three sets of single-phase full-bridge inverter circuits sharing the direct-current bus bar, the direct-current output ends of a distributed power supply or a grid-connected energy-storing generating set are connected to both ends of the capacitor of the direct-current bus bar, the output of each set of single-phase full-bridge inverter circuit is connected to a filter, and the output ends of each filter are connected with a distribution network of the 380V voltage class through a single-phase step-up isolation transformer. According to the invention, the grid-connected inverter equipment is effectively utilized to carry out effective control on the power quality of points of interconnection, so that the grid-connected inverter is multi-purpose and multi-functional, the cost performance of the grid-connected inverter is enhanced, the investment, operation and maintenance cost of a system can be reduced, and the reliability of the system can be enhanced. The principle of the provided control scheme is clear, and the control scheme is highly operable and reliable in operation.

The invention discloses a control method of an alternating voltage sensorless high voltage direct current transmission converter, belonging to the technical field of electrical equipment and comprising the following steps: establishing a stator resistor and an inductor for a virtual motor; building relative position relationships among a current vector, a voltage vector and a flux linkage vector, and analyzing a vectorgram; establishing a converter and flux linkage mathematic model, and calculating a virtual flux linkage vector of a system to obtain a power feedback quantity of the system; acquiring an active control signal and a reactive control signal of the system through a direct power control algorithm, and generating a PWM trigger converter for respectively and independently controlling the active power and reactive power of the system; and utilizing MATLAB simulation software to set up a system model for verifying, and obtaining a systematic selection device when the verification is successful. By utilizing Matlab / Simulink to set up a corresponding simulation model, the designed method is verified to have rapid response speed, the voltage and power after startup can still reach stable values after about 2 power frequency periods and have high steady state precision.

A hybrid conditioner for filtering harmonics in a power system that includes a non-linear load. The hybrid conditioner includes an active filter structured and controlled to filter one or more high-order harmonic currents of the fundamental frequency, and a passive filter structured to filter one or more low-order harmonic currents of the fundamental frequency. The active filter and the passive filter are electrically connected in parallel with one another. The hybrid conditioner may also be for providing reactive power compensation for the power system, wherein the active filter is further controlled to provide a compensatory reactive power for compensating for the reactive power that is consumed by the load. The hybrid conditioner may also provide oscillation dampening for the power system, wherein the active filter is further controlled to damp oscillating currents that exist between the passive filter and the AC source.

The invention relates to an active damping method of an LCL grid-connected inverter system. The active damping method is realized through the following steps of: setting conjugated zero points or independent zero points to set off conjugated resonance limit points generated by an LCL filter in the grid-connected inverter system or to draw the conjugated resonance limit points to a stable area, and adopting grid-side inductive current to feed back and introduce a state variable in the LCL filter to conduct feedback compensation. By conducting feedback compensation on grid-side inductive voltage, the resonance damping of the LCL filter is controlled, the waveform and the amplitude of grid current of the grid-connected inverter system are controlled and the influence of grid voltage harmonic wave on the grid current can be effectively suppressed. The active damping method is a simple and effective realization method. A realization circuit comprises parallel and series active damping circuits.

The invention relates to a renewable energy source integrated complementary power generation technology for a distributed power supply and provides a multi-energy integrated complementary power generation method and multi-energy integrated complementary power generation device consisting of water energy, wind energy, solar energy and other renewable energy sources. According to the method, the water energy serves as a main body, the peculiar mountain valley wind of a hydropower station is fully utilized, the solar energy, the biomass energy and other renewable energy sources which can be relatively concentrated are locally utilized and are gathered around the hydropower station, a low-voltage alternating current bus [W1] of the hydropower station serves as a grid-connected access point, and a water, wind, solar and biomass multi-energy integrated complementary power generation system which takes water and electricity as the center and takes the water and wind complementation as the basis. According to the device, a hydropower station [G1] serves as a main body, the electric energy generated by power generation subsystems [G2], [G3], [G4] and [G5] is subjected to full power conversion and is connected to the [W1] in a grid-connected mode, the original switching device and grid line of the hydropower station are utilized, and a multi-type renewable energy source integrated complementary distributed power supply which can supply power in a grid-connected mode and independently operate is formed.

A method of controlling the grid-side current of a single-phase grid-connected converter having an LCL filter connected between the output of the converter and the grid. The method includes measuring a grid voltage (vS) and at least one signal in a group of signals consisting of a grid-side current (i0), a converter-side current (i1) and a capacitor voltage (vC0). The method includes estimating the fundamental component (vS,1) of the grid voltage (vS), forming a grid-side current reference (i0*), a converter-side current reference (i1*) and a capacitor voltage reference (vC0*) for the grid-side current of the LCL filter using the fundamental component of the grid voltage (vS,1), forming estimates for the non-measured signals in said group of signals, forming a grid-side current difference term (ĩ0), a converter-side current difference term (ĩ1) and a capacitor voltage difference term ({tilde over (v)}C0) from the differences between the references and measured / estimated values of said signals, forming an injection term for damping the resonance of the LCL filter by using an active damping injection mechanism (ADI), in which the grid-side current difference term (ĩ0), the converter-side current difference term (ĩ1) and the capacitor voltage difference term ({tilde over (v)}C0) are used, forming an estimate of harmonic distortion term ({circumflex over (φ)}) using the grid-side current difference term (ĩ0), and controlling the output voltage (e) of the converter on the basis of the grid voltage, formed injection term and formed estimate of the harmonic distortion term ({circumflex over (φ)}) to produce a grid side (i0) current corresponding to the current reference.

The invention discloses a high-efficiency stable multifunctional single-stage photovoltaic single-phase grid-connected control method, and belongs to the technical field of photovoltaic power generation control. The method is characterized in that: the method adopts a high-speed digital signal processor and applies a C language dynamic fixed-point algorithm to form a high-performance control algorithm of a whole grid-connected control system; the method adopts a single-stage grid-connected control structure and a quick smooth maximum power point tracking method to directly transmit the maximum energy sent by a photovoltaic array to a local urban power grid through first-stage DC / AC transformation; the harmonic and idle work produced by a local load can be compensated by adopting an FBD method, so the method is favorable for improving the electrical energy quality of the local power grid; and a proportional resonant converter is used to implement precise closed-loop control for the grid-connected current so that the photovoltaic grid-connected current and the commercial single-phase voltage are totally synchronous while implementing maximum power point tracking of the photovoltaic array. The power factor is high, the system efficiency is high, the operation of the whole system is safe and reliable, and the aberration rate of the grid-connected current harmonic is lower than 3 percent.