110 results about "Vienna rectifier" patented technology

The invention discloses an intelligent charging pile core module based on a VIENNA structure, an electric energy quality management method, system and equipment and a storage medium, and belongs to the field of electric power system energy storage equipment.The intelligent charging pile core module based on the VIENNA structure comprises the steps that an integrated power conversion unit is constructed, the power conversion unit adopts a VIENNA rectifier topology, three-phase alternating current is converted into direct current, and the direct current is converted into direct current; a harmonic suppression structure linked with the control interface is arranged; state information in the operation process is collected and serves as input of the control strategy module; based on the state information, a modulation control instruction is generated in the control strategy module to drive the switching action of the power conversion unit; on the basis of the modulation control instruction, the switch control is executed, meanwhile, the direct-current side midpoint potential of the power conversion unit is synchronously adjusted, and the distribution of direct-current bus capacitor voltage is controlled; and identifying the current operation condition according to the state information, switching to a control template corresponding to the operation condition in the control strategy module, and generating a modulation control instruction.

The present application relates to a rectification control system, a charger and a control method for a charger. The rectification control system includes: a Vienna rectifier, which includes input terminals and output terminals, an output capacitor circuit, and a rectifying circuit which includes a u-phase bridge arm branch, a v-phase bridge arm branch and a w-phase bridge arm branch, each bridge arm branch comprising a switch device and a bidirectional switch unit which are connected in series; a voltage acquisition unit, which is connected to the three input terminals and is configured to acquire voltages Uuv, Uvw and Uwu; a fault detection unit, which is connected to the bidirectional switch units and is configured to detect whether any of the bidirectional switch units fails; and a control unit, which is connected to the voltage acquisition unit and the fault detection unit and is configured to control closing or opening of three switch devices according to voltage input format, voltage connection mode and detection result of the fault detection unit, so as to switch circuit and working mode, making a charger suitable for applications in multiple scenarios and multiple formats.

The invention discloses an electric vehicle high-power direct current charging station and a control optimization method thereof, and the method comprises the following steps: inputting an external three-phase alternating current into a Vienna rectifier serving as a pre-stage charging circuit, and inputting an output voltage value of the Vienna rectifier into a pre-stage control circuit; after the pre-stage control circuit obtains an output voltage value of the Vienna rectifier, the direction of the voltage is determined, synthesis is carried out by adopting a nearest three-vector method and utilizing three basic voltage vectors closest to a target voltage vector, a three-level SVPWM algorithm based on a two-level theory is adopted in the synthesis process, and finally the action time of the target voltage vector is obtained. And therefore, the Vienna rectifier can be controlled. The operation burden of the control system is reduced, the power grid loss is reduced, and the stability and efficiency of power grid operation are improved.

The invention provides a method for reducing input current harmonic distortion of a Vienna rectifier of an electric vehicle charging module. Belongs to the technical field of power electronic switching, and comprises the following steps: comparing an actual DC voltage with a reference DC voltage, calculating an error signal, and processing the calculated error signal through a voltage regulator to generate a reference voltage; and generating a three-phase current reference signal according to the phase and the amplitude of the power grid voltage. Through the technical scheme of the invention, the low-order current harmonic of the source side current can be selectively eliminated without depending on current / voltage conversion, a phase-locked loop or a space vector modulation module, so that the calculation requirement is remarkably reduced; due to the fact that the calculation requirement is obviously reduced, the transient response speed of the method is higher.

The invention discloses a charging module impedance modeling method and system for an electric vehicle charging pile, and the method comprises the steps: enabling an AC system to be equivalent to a DC system through abc / dq coordinate transformation, obtaining a DC working point, introducing disturbance on the DC working point, and building a small signal model of a front-stage VIENNA rectifier; the method comprises the following steps: dividing a circuit into independent sub-modules based on an equivalent circuit method, performing small signal analysis on each sub-module, and then establishing a small signal model of a post-stage full-bridge LLC resonant converter; according to the small-signal model of the front-stage VIENNA rectifier and the small-signal model of the rear-stage full-bridge LLC resonant converter, an overall small-signal model is established in combination with the front-stage and rear-stage control strategies; the output impedance transfer function and the voltage and current transfer function of the front and back stages are calculated through the overall small signal model, and then the impedance model of the charging module is obtained, so that a foundation is laid for subsequent analysis of the stability of the parallel charging module; and establishing a system simulation model in the platform to verify the impedance model of the charging module.

The invention relates to a method for controlling a three-phase Vienna rectifier (20) comprising three switching arms (1, 2, 3), each switching arm being associated with an electrical phase (a, b, c), each switching arm (1, 2, 3) comprising a high controlled power switch (M1H, M2H, M3H) connected in series and oppositely to a low controlled power switch (M1L, M2L, M3L); when the switching arm comprises a faulty switch (M2H, M2L), the method comprising: - the step of calculating the duty cycle of the high controlled switch and the low controlled switch to be applied to the two active arms according to the received voltage value (V13) between the two active arms and according to the measured DC voltage value (VDC) so that no current flows through the faulty switching arm (2).

The application discloses a single-phase rectifier control method, device and system based on PR control, and belongs to the technical field of rectifier control. The method is as follows: collecting operation data of a single-phase rectifier, wherein the operation data comprises an input voltage, an upper capacitor voltage, a lower capacitor voltage and an inductor current; inputting the operation data into a current loop PR controller and a voltage loop PI controller, calculating a voltage loop error and a current loop error, and outputting a current control instruction; calculating a feedforward duty ratio of the single-phase rectifier through a feedforward controller according to the input voltage and a preset voltage reference value; performing pulse width modulation based on the current control instruction and the feedforward duty ratio, outputting a driving signal, and driving a switching tube of the single-phase rectifier to be on or off through the driving signal. Therefore, by implementing the application, the single-phase Vienna rectifier is regulated and controlled through PR control, and beneficial effects such as reduction of harmonics, stabilization of bus voltage and improvement of input power factor are achieved.

The present invention relates to a high power factor soft switch Vienna rectifier circuit, comprising a first rectifier diode D1, a second rectifier diode D2, a first DC link capacitor C01, a second DC link capacitor C01, a first main switch S1 and a second main switch S2, the rectifier circuit also comprises two active buffer circuits respectively arranged in the loop where the first rectifier diode D1 and the second rectifier diode D2 are located, each active buffer circuit is composed of a blocking diode, a buffer inductor, an auxiliary switch, a transformer and a resistor-capacitor diode clamping circuit. Compared with the prior art, the present invention has the advantages of reducing reverse recovery loss, avoiding ringing problems, realizing zero voltage switching of Vienna switches and zero current switching of auxiliary circuit switches, etc.

The invention relates to the technical field of power electronic converters, in particular to a single-phase Vienna rectifier circuit and a control method thereof. The single-phase Vienna rectifier circuit comprises a single-phase alternating current power supply, a switch module, a first capacitor and a second capacitor, the switch module is connected with the output end of the single-phase alternating current power supply, the switch module comprises a first switch piece and a second switch piece, and the first switch piece and the second switch piece are connected in series; the first capacitor and the second capacitor are connected in series with the output end of the single-phase AC power supply, and the switch module is connected between the first capacitor and the second capacitor; wherein the single-phase Vienna rectifier circuit is configured to select a current mode according to the output voltage of the single-phase AC power supply, and the switch module controls the first switch member and the second switch member according to the current mode. The circuit switches on and off of the switch module according to the output voltage and the current, so that hysteresis control of a high power factor is achieved.

The invention relates to a soft start control method for a Vienna rectifier, and the method comprises the steps: calculating a soft start modulation signal for controlling the Vienna rectifier based on a preset modulation signal, an output voltage, a working frequency, and a switching period count of the Vienna rectifier in a process of switching the Vienna rectifier to Vienna control, a switching tube unit of the Vienna rectifier is controlled based on the soft start modulation signal; the switching tube period count is the number of switching periods passed in the process of switching the Vienna rectifier to Vienna control. By implementing the soft start control method of the Vienna rectifier, the Vienna rectifier can be controlled to be slowly turned on according to the switching time, so that the input current when the Vienna control is switched in is effectively reduced, the voltage resistance and current resistance requirements of the switching tube in the switching tube unit of the Vienna rectifier are further reduced, and the switching efficiency of the Vienna rectifier is improved. The service life of the switch tube is prolonged.

The invention discloses an air conditioner control method, an air conditioner power supply system and an air conditioner, the air conditioner control method is applied to the air conditioner power supply system, the air conditioner power supply system comprises a Vienna rectifier module, and the Vienna rectifier module is used for converting alternating current input by an alternating current power supply into direct current so as to output bus voltage and bus midpoint voltage. The air conditioner control method comprises the steps that after a fan in an air conditioner is controlled to be started for preset time according to a starting signal, bus voltage and bus midpoint voltage are obtained; and controlling a Vienna rectifier module to start according to the bus voltage and the bus midpoint voltage to increase the bus midpoint voltage, so that the fan obtains the target voltage. According to the application, the problem of loss caused by immediately starting the Vienna rectifier module after the air conditioner is started can be relieved, and the fan can be ensured to obtain the target voltage and can be normally started to work, so that the power supply stability of the fan is improved, and the fan control stability is improved.

The invention provides a PWM wave optimization method and system based on VIENNA rectifier single-period control. The PWM wave optimization method comprises the steps that three-phase input current is sampled; determining the position of the corresponding PWM wave high level in the switching period according to the current direction of each phase; the method specifically comprises the following steps: for each PWM output channel, according to a phase current symbol associated with the PWM output channel, selecting to place a high level at two ends or in the middle of a switching period; and based on the determined PWM high level position and the calculated duty ratio, generating and outputting a PWM driving signal used for controlling a VIENNA rectifier switch tube. According to the method, PWM generation logic is redesigned, a non-optimal voltage vector combination used in traditional synthesis is abandoned, and three vectors (namely vectors corresponding to three vertexes of a small triangle where a target vector is located) closest to the target voltage vector are adopted for synthesis; according to the optimization, on the premise that the switching frequency is not increased and extra hardware cost is not increased, output current harmonics are remarkably reduced.

The invention discloses a control system of a three-phase Vienna rectifier and a Boost-PFC circuit, the control system of the three-phase Vienna rectifier comprises a current control inner ring and a voltage control outer ring, the voltage control outer ring samples a bus voltage Vout output by the rectifier, outputs a voltage Vc after loop control, and outputs the voltage Vc after loop control; vc is multiplied by an input AC voltage sample Vg to serve as a reference current of the current control inner ring, the current control inner ring samples an input AC current ig of the rectifier, and a difference value obtained by subtracting the input AC current ig from the reference current is calculated through a current inner ring compensator; the current control loop further comprises a current feed-forward loop connected between an input AC voltage sampling end and an output end of the current inner loop compensator. By adopting the technical scheme of the invention, the PF and THD indexes of the three-phase Vienna rectifier can be optimized.

The invention relates to a direct current charging pile three-phase six-switch tube Vienna rectifier open-circuit fault diagnosis method, and belongs to the field of direct current charging pile fault diagnosis. The method comprises the following steps: acquiring alternating-current side three-phase current and direct-current side voltage data of the Vienna rectifier in real time; frequency domain information of alternating-current side three-phase current and direct-current side voltage is extracted from the collected data through fast Fourier transform, and then normalized open-circuit fault characteristic quantity is obtained; and inputting the normalized open-circuit fault characteristic quantity into the trained open-circuit fault diagnosis model of the Vienna rectifier of the direct-current charging pile to obtain an open-circuit fault diagnosis result of the Vienna rectifier. The Vienna rectifier single-tube and double-tube open-circuit fault diagnosis method can realize Vienna rectifier single-tube and double-tube open-circuit fault diagnosis only by acquiring alternating current side current and direct current side voltage data, and has an important value for reducing the fault maintenance time and the operation and maintenance cost of a direct current charging pile.

This invention discloses a general fast modulation method for a VIENNA rectifier, comprising: 1) establishing a mathematical model of nine switches based on the mathematical model of the VIENNA rectifier, obtaining the equality constraints between the duty cycle of the nine switches and the modulation wave; 2) establishing two equations satisfying the control voltage constraint through newly defined variables, and providing a general solution satisfying the equality constraint conditions; 3) obtaining six states based on the different directions of the three-phase current; obtaining inequality constraints under different states based on these six states; and obtaining the upper and lower limits of the free variables based on the inequality constraints under the six states; 4) solving for the compensation amount for neutral point potential balance control starting from the control equation for the capacitor neutral point potential control of the VIENNA rectifier. The modulation model and solution process of the VIENNA rectifier disclosed in this invention have a small computational workload, significantly reducing the computation time compared to the SVPWM modulation technology of three-level converters.

The application discloses a SVPWM modulation method suitable for a staggered parallel Vienna rectifier and belongs to the technical field of power electronics. The method comprises the following steps: judging a sector where a reference voltage vector is located; selecting a corresponding small vector according to the sector, mapping a three-level space to a two-level space to obtain an equivalent reference voltage vector; adopting a traditional two-level SVPWM algorithm to calculate the action time of the equivalent reference voltage vector; introducing a vector distribution factor k to adjust the action time distribution of two switch states of a specific small vector in each sector; and generating a PWM signal. The application simplifies the calculation complexity of the SVPWM through equivalent two-level mapping, simultaneously realizes unified regulation of midpoint voltage balance and input current zero-crossing distortion by using the vector distribution factor k, effectively improves the input current quality, and reduces total harmonic distortion.

The invention discloses a Vienna rectification type EC fan control method and system under a power grid imbalance condition, and the method comprises the steps: firstly collecting three-phase power grid voltage, AC side current, DC side filter capacitor voltage and load current, extracting a power grid phase angle through a phase-locked loop, and completing the coordinate transformation from abc to dq; the voltage outer loop sliding mode controller generates an active current instruction according to a direct current side voltage error, an ADRC current loop dynamically tracks active and reactive current components, and control output is sent to SVPWM through inverse transformation to generate a switching signal. Meanwhile, neutral-point voltage balance control is introduced, and the problem of asymmetric direct-current side capacitor voltage is solved. The system effectively solves the problem of voltage and current control under the unbalanced power grid, improves the bus stability and the electric energy quality, is suitable for the operation of the Vienna rectifier under complex working conditions, and has high robustness and control precision.

This invention discloses a VIENNA rectifier control method based on simplified SVPWM, relating to the field of VIENNA rectifier technology. The method includes: based on a modulation signal and three-phase input current, performing the following operations: determining one of six major sectors where the reference voltage vector is located according to the polarity of the three-phase input current; performing coordinate correction on the modulation signal according to the major sector to obtain the corresponding center correction vector; using the center correction vector to determine the position of the reference voltage vector in a small sector within the corresponding major sector; calculating the corresponding two-phase basic vector action time using only the first small sector within the first major sector as a reference; for small sectors within any other major sector, using a coordinate rotation recursive method to process the corresponding center correction vector to obtain the two-phase basic vector action time of the corresponding sector; and generating a PWM drive signal based on the obtained two-phase basic vector action time to control the switching transistors in the VIENNA rectifier main circuit. This improves the real-time performance and execution efficiency of the algorithm.

The invention relates to the technical field of direct current charging piles, and discloses a high-efficiency direct current charging pile based on a SiC device, which comprises a rectifier module, a DC-DC conversion module, an output filtering and battery interface module, a control and communication module, an auxiliary power supply and heat dissipation module and a safety and protection module. According to the invention, the Vienna rectifier is utilized to carry out efficient rectification on three-phase alternating current input, a power factor correction (PFC) mechanism is introduced to realize power factor correction, and the SiC MOSFET device is introduced to support high-frequency and high-efficiency switching operation, so that the conduction and switching loss is obviously reduced, and the power factor correction is realized. And the phase-shift full-bridge converter is matched to realize efficient and isolated conversion from the DC bus voltage to the output voltage of the charging end, so that electric vehicle batteries with different voltage levels are adapted, and the problems of low efficiency and low power factor in the traditional scheme are effectively solved.

The application discloses a variable clamping interval carrier discontinuous modulation method of a three-phase Vienna rectifier. ma , u mb , u mc ; a balanced continuous component u bc , a zero-crossing clamping component u oc and a peak clamping component u pc are calculated; a variable interval clamping coefficient k VAC is set according to different modulation ratios, and a variable interval clamping component u VAC is calculated according to a formula u VAC =k VAC (1-m); a zero sequence voltage u z is calculated, and the zero sequence voltage u z is injected into three-phase normalized sinusoidal waves to obtain three-phase Vienna rectifier variable clamping interval modulation waves u ref_a , u ref_b and u ref_c of A phase, B phase and C phase. The variable clamping interval carrier discontinuous modulation method can reduce terminal voltage error, reduce midpoint potential fluctuation, improve input current quality, and has the advantages of simple calculation and convenient implementation.

The invention discloses an electric vehicle charging pile control method based on generalized second-order differential, and belongs to the technical field of electrics. The charging pile topology comprises a three-phase alternating current power grid, a filter inductor L, a three-phase VIENNA rectifier, a full-bridge three-level DC / DC converter, an LC filter circuit and a load resistor R. The control method comprises the steps of sampling, rectifier control and converter control. Wherein the three-phase VIENNA rectifier adopts common PI control based on voltage and current double closed loops, and the full-bridge three-level DC / DC converter adopts double-loop control based on a generalized second-order differential PID (Proportion Integration Differentiation) controller. The generalized second-order differential function not only retains the phase lead compensation differential effect on a specific frequency range, but also eliminates the inherent high-frequency noise amplification effect of the traditional differential function. According to the control method, the dynamic performance of the system can be effectively improved, the output signal ripple is small, and the control speed is high.

The invention discloses an unbalanced power and bipolar voltage cooperative control method for a Vienna rectifier without an electrolytic capacitor, and belongs to the technical field of Vienna rectifier control. The invention aims to solve the problem of system control instability caused by violent bipolar voltage oscillation when a Vienna rectifier is connected with a load with a relatively large power level difference at a direct current side. Comprising the following steps: comparing an unbalanced power boundary with a real-time power unbalance degree, and if the unbalanced power boundary is smaller than the real-time power unbalance degree, selecting a bipolar voltage difference control mode; otherwise, selecting a bipolar voltage balance control mode; in the balance control mode, selecting the optimal clamping mode of intermittent pulse width modulation according to the comparison result of the midpoint voltage at the adjacent next moment and the voltage hysteresis boundary; and under a bipolar voltage difference control mode, calculating an optimal voltage unbalance degree, performing vector synthesis on two adjacent vectors in a voltage vector non-synthesis region, and obtaining a modulation wave after track optimization by calculating a duty ratio. According to the invention, grid-side current harmonics can be reduced.

The invention discloses a control method for a three-phase six-switch VIENNA rectifier, and the method comprises the steps: building a double-closed-loop PI control model of the three-phase six-switch VIENNA rectifier, and enabling the double-closed-loop PI control model to comprise current inner-loop control and voltage outer-loop control; current inner loop control in the double-closed-loop PI control model is improved by adopting a fractional order PI algorithm; and adopting a linear active disturbance rejection controller (LADRC) to improve voltage outer loop control in the double closed loop PI control model. Based on the method, the invention further provides a control system of the three-phase six-switch VIENNA rectifier, and the control system comprises a fractional order PI current inner loop control module, an LADRC voltage outer loop control module, an SVPWM modulation module and a neutral-point potential balance module. According to the invention, the output accuracy of the rectifier in a steady state is improved, the purposes of high steady-state current accuracy and low harmonic distortion rate are achieved, the overshoot of the system is reduced, and the dynamic response speed is high and the robustness is strong.

The invention provides a single-cycle control three-phase VIENNA rectifier power factor correction method and device, and belongs to the technical field of rectifiers, and the method comprises the steps: obtaining three-phase input current sampling signals ia, ib and ic; acquiring a bus voltage sampling signal Upfc and a bus voltage loop output sampling signal Vm; acquiring a voltage difference UNO between the three-phase input N line or the virtual N line and the midpoint O of the BUS capacitor; and according to the three-phase input current sampling signal, the bus voltage sampling signal, the bus voltage loop output sampling signal and the voltage difference, calculating the duty ratio of each phase of full-control switch tube. By indirectly or directly detecting the voltage difference between a three-phase input N line or a virtual N line and a BUS capacitor midpoint and introducing the voltage difference into a single-cycle control loop, decoupling control in a three-phase VIENNA single-cycle control technology is realized, so that total harmonic distortion (THD) in a full-load range is remarkably reduced, and a power factor (PF) index is improved.

The application discloses an interleaved Vienna rectifier device and a control method thereof. Positive and negative sequence separation is performed on a positive-negative voltage sequence component and a positive-negative current sequence component, to separate a positive voltage sequence component from a negative voltage sequence component, and a positive current sequence component from a negative current sequence component. The positive voltage sequence component, the negative voltage sequence component, the positive current sequence component and the negative current sequence component are controlled separately. A Proportional-Integral (PI) controller and a Harmonic Elimination (PR) controller are used within a current inner loop to control the positive voltage sequence component, the negative voltage sequence component, the positive current sequence component and the negative current sequence component for generating a plurality of control signals to control the switches of the interleaved Vienna rectifier circuit.

The present application relates to a kind of Vienna rectifier control and its current zero-crossing distortion inhibition method, comprising the following steps: positive and negative sequence separation is carried out to the instantaneous value of collected grid voltage, and positive and negative sequence phase angle is calculated;Based on the control target of Vienna rectifier under the unbalance of grid voltage, control method is selected, and reference current is calculated;The instantaneous value of reference voltage is sorted, and max phase, mid phase and min phase of reference voltage are obtained, and the max phase, mid phase and min phase of current follow the voltage sorting result;According to the relationship between u max 、u mid 、u min And i mid , the region where reference voltage is located is analyzed, and the modulation voltage is calculated using the synthesis method with the minimum synthesis error.The present application can make Vienna rectifier run stably under the unbalance of grid voltage, effectively reduce current zero-crossing distortion in essence, and optimize the control of Vienna rectifier.

The invention provides a Vienna rectifier control method based on a frequency domain feedback projection sliding mode, and the method comprises the steps: constructing a voltage outer loop controller of a frequency domain feedback projection sliding mode structure according to the mathematical modeling of a Vienna rectifier, and obtaining a system control quantity corresponding to the voltage outer loop controller; designing an inversion sliding mode control law of a current inner loop based on a system equation of the Vienna rectifier; and taking the control quantity output by the voltage loop controller as a reference input value of the current loop to realize a voltage regulation target, thereby generating a PWM control signal for driving a switching device of the Vienna rectifier, and realizing stable tracking of a set value by the direct current side output voltage. Compared with the prior art, a projection function is added into a sliding mode surface to form a projection sliding mode, an amplitude limiting threshold value is set, a frequency domain feedback item is introduced into the projection sliding mode, the frequency selective response capability of the controller is enhanced, and switching buffeting is greatly weakened.

The invention relates to the technical field of three-level converters, in particular to an interleaving parallel type three-level three-switch rectifier topology circuit which comprises a first rectifier module, a second rectifier module, a third rectifier module, a first capacitor and a second capacitor. The first diode assembly comprises first to fourth diodes; the second rectification module comprises a second diode assembly and a second switch assembly. The second diode assembly comprises fifth to eighth diodes. The third rectification module comprises a third diode assembly and a third switch assembly. The third diode assembly comprises a ninth diode to a twelfth diode. Therefore, the problem that each phase circuit of the interleaving parallel Vienna rectifier topology is composed of four power switch tubes, and the economic burden is increased is solved. The number of switching tube devices is reduced, and economic cost is reduced.

The present application relates to a kind of Vienna rectifier wide load range operation control method mode, proposes a load power estimation algorithm, by collecting three-phase voltage, three-phase current, DC side upper and lower voltage and combining forgetting iterative filtering algorithm and sliding window filtering algorithm, accurately estimate load power and filter out the noise caused by sampling error.Based on the proposed load power algorithm, a new outer ring structure is proposed, which uses capacitor energy storage feedback and load power feedforward control to separate the control of DC side energy storage capacitor and DC load control.When load mutation occurs, the demand of load can be estimated in advance, and the calculation is introduced to the current loop, which improves the response speed of the system and better stabilizes the DC side voltage.The present application solves the problem of parameter design difficulty of the outer ring of traditional control mode of Vienna rectifier, improves the response speed when load mutation occurs, and solves the overvoltage problem during light load start.

The invention discloses a VIENNA rectifier model-free predictive current control method and system, which belongs to the field of power electronic control. A super-local current model is first constructed to replace the VIENNA rectifier precise model, thereby reducing the dependence on model parameters; a cascade parallel extended state observer is then designed to estimate the lumped disturbance of the super-local model, thereby improving the system's anti-disturbance capability and measurement noise suppression capability; finally, a tolerance serial cost function is established, and a current term and a midpoint potential difference term are progressively evaluated. When the local optimal set of current terms flows to the midpoint potential difference term, a tolerance judgment is performed to obtain an optimal switching state, thereby realizing model-free predictive current control while eliminating weight factors.