138 results about "Space vector pwm" patented technology

A space vector pulse-width modulator (SVPWM) and a method implemented by the modulator. A precalculation module accepts Ua and Ub modulation indexes and in response thereto, outputs modified Ua and Ub information; a sector finder has a U module which receives the modified Ua information and outputs a U sector; and a Z module which receives the U sector and the modified Ub information and outputs a Z sector. The U sector and the Z sector are 2-phase control signals for implementing 2-phase modulation. For 3-phase modulation, the SVPWM and method further possess an active vectors calculation module and an assign vectors module which receive the modified Ua and Ub information and the U sector, and which calculate active vectors for 3-phase modulation; a zero vector selector which receives the Z sector and calculates zero vectors for 3-phase modulation; and a PWM counter block which receives the active vectors and zero vectors and outputs 3-phase control signals for implementing 3-phase modulation. The SVPWM and method may have a symmetrical PWM mode, an asymmetrical PWM mode, or both. Advantageously there may also be a rescale and overmodulation module which receives duration information corresponding to the vectors and in response thereto, detects the occurrence of overmodulation. Overmodulation may be detected in response to a negative zero vector time. The module may respond to overmodulation by clamping the zero vector time to zero and rescaling the active vector times to fit within the PWM cycle. The rescaling may restrict a voltage vector to stay within hexagonal boundaries on the space vector plane, while preserving voltage phase.

The invention provides a method capable of reconstructing a three-phase current of an electromotor in full range at any time when the electromotor is driven by a space vector pulse-width modulation mode, which has simple algorithm, high university and relatively good control effects. In the method, an asymmetrical pulse-width modulation (PWM) mode is used for modulation, modulation vectors in a non-observation area are decomposed and one of the decomposed vectors has at least two different non-zero basic space vectors of which the continuous action time is longer than or equal to the action time of a minimal vector in a PWM period; and thus, the non-observation areas are avoided in a space vector PWM process , and the full-time and full-range three-phase current reconstruction and detection of the electromotor are realized, in particular vector distortion is avoided when the electromotor is controlled to be at a low speed. Moreover, the method has the advantages of greatly improving reliability, obviously reducing cost, along with simple algorithm, small code occupation and little increase of current harmonics.

A voltage source inverter generating a poly phase AC signal is provided that includes an SVPWM controller. The controller is adapted to modify the switching pattern at low sine-wave frequencies creating a more even distribution of the conduction losses. The switching pattern periodically changes the sequence (or rotational sense) of the space vector components from clock-wise to counter-clock-wise direction, and vice-versa.

The invention discloses a system and method for controlling the current of a permanent magnet synchronous motor for an electric vehicle. The system comprises a rotating speed / position detection module used for detecting the rotating speed value omega and the position angle theta of the permanent magnet synchronous motor, a current sensor, a first coordinate transformation module, a second coordinate transformation module, a PI speed ring controller used for conducting PI operation on the motor rotating speed value omega obtained through the rotating speed / position detection module and a given motor rotating speed value omega r to obtain a q-axis current reference value, a current ring prediction control module, a sliding formwork disturbance observation module, a third coordinate transformation module and a space vector pulse width duration modulation module, wherein the space vector pulse width duration modulation module is used for calculating u alpha and u beta to obtain six-path PWM signal output, PWM signals are used for controlling an inverter, and thus three-phase output voltage is obtained to drive the motor to operate. An advanced continuous time generalized prediction control method is adopted for the tracking and controlling of the current of the permanent magnet synchronous motor for the electric vehicle, and the system and method have the advantages of being small in calculated amount, good in control effect and the like.

The invention aims to solve the technical problems of obvious stator current distortion and zero-sequence ring current of the direct current bus-shared open-end winding asynchronous motor caused by pure suppression of the zero sequence ring current in a modulation strategy link and neglecting of non-linearity and counter electromotive force zero sequence component in the prior art; on the basis, the invention provides a space vector PWM modulation scheme with controllable zero sequence voltage; by performing active control on the zero sequence voltage of the direct current bus-shared open-end winding asynchronous motor system, suppression of the zero sequence ring current is realized; and meanwhile, use of a zero vector is avoided, so that the common-mode voltage of the open-end winding asynchronous motor system is lowered.

The disclosed modulation technology for three-level high-voltage frequency converter comprises: to three-level NPC frequency converter, using asynchronous SVPWM when frequency less than 45Hz, and obtaining switch frequency as 600Hz; using special eliminating-harmonic PWM when frequency over 45Hz, and obtaining the switch number is seven. This invention avoids defects of space-vector PWM and special eliminating-harmonic PWM, improves waveform quality, reduces heat loss and request on filter, and ensures system security and reliability.

A simplified self noise-immunity controller formation method of PMSM (permanent magnet synchronous motor) is applicable to the high performance control of PMSM. It constructs the expanding voltage-controlled inverter (2) by the voltage control voltage source inverter (1) and space vector pulse width modulation; it constructs a composite controlled object (10) by the expanding voltage-controlled inverter and current controller (3), the coordinate transformation (4), the permanent magnet synchronous motor (7), the workload (8) and the photoelectric encoder (9); it constructs the second-order state observer (52) by compositing the input and output signals of the controlled object; It constructs the composite speed feedback (54) by the weighted sum of the two speed measurement value; it constructs the composite controller (53) by the superposition of the generalized rate error square controller (51) and the compensation value of the system perturbation (-z2 / b); it series connects the composite controller before the composite controlled object, and finally, it constructs the simplified self noise-immunity controller (5) by the composite controller and the expanding second-order state observer.

A space vector pulse-width modulator (SVPWM) and a method implemented by the modulator. A precalculation module accepts Ua and Ub modulation indexes and in response thereto, outputs modified Ua and Ub information; a sector finder has a U module which receives the modified Ua information and outputs a U sector; and a Z module which receives the U sector and the modified Ub information and outputs a Z sector. The U sector and the Z sector are 2-phase control signals for implementing 2-phase modulation. For 3-phase modulation, the SVPWM and method further possess an active vectors calculation module and an assign vectors module which receive the modified Ua and Ub information and the U sector, and which calculate active vectors for 3-phase modulation; a zero vector selector which receives the Z sector and calculates zero vectors for 3-phase modulation; and a PWM counter block which receives the active vectors and zero vectors and outputs 3-phase control signals for implementing 3-phase modulation. The SVPWM and method may have a symmetrical PWM mode, an asymmetrical PWM mode, or both. Advantageously there may also be a rescale and overmodulation module which receives duration information corresponding to the vectors and in response thereto, detects the occurrence of overmodulation. Overmodulation may be detected in response to a negative zero vector time. The module may respond to overmodulation by clamping the zero vector time to zero and rescaling the active vector times to fit within the PWM cycle. The rescaling may restrict a voltage vector to stay within hexagonal boundaries on the space vector plane, while preserving voltage phase.

The invention discloses an input and output power resonance control method of a PWM (pulse width modulation) rectifier under a voltage unsymmetrical fault. The input and output power resonance control method of the PWM rectifier under the voltage unsymmetrical fault comprises the following steps of: calculating the difference between given pulse values of second harmonic frequencies of output active power and input reactive power of a system and practical values of active power and reactive power of the system; obtaining second harmonic frequency offset items of the output active power and the input reactive power respectively through a proportion resonance controller and by second harmonic frequency offset voltage calculation, adding a voltage reference value obtained by conventional vector control to the second harmonic frequency offset items respectively; performing reverse Park transformation by taking a power grid voltage position angle as a transformation angle to obtain a voltage in two-phase static coordinates; and after voltage signals are subjected to space vector pulse width modulation, generating on-and-off signals for controlling power instruments. By using the input and output power resonance control method of the PWM rectifier under the voltage unsymmetrical fault, pulses of the input reactive power and the output active power of the PWM rectifier can be directly compensated, and unit power factor operation and direct current busbar voltage of the system are stably controlled.

The invention discloses a rotary speed control system and method of a permanent magnet synchronous motor. A current sensor module is connected with the permanent magnet synchronous motor; the currentsensor module, a Clark coordinate conversion module and a Park coordinate conversion module are connected in sequence; the Park coordinate conversion module is connected with a nonlinear disturbance observator and a back-stepping controller separately; the nonlinear disturbance observator is connected with the back-stepping controller; the back-stepping controller, a Park coordinate inverse conversion module, a voltage space vector PWM module and an inverter are connected in sequence; the inverter is connected with the permanent magnet synchronous motor; and a rotary speed / position detection module is connected with the nonlinear disturbance observator, the back-stepping controller, the Park coordinate conversion module and the Park coordinate inverse conversion module separately. By adopting back-stepping control and the nonlinear disturbance observator method to replace the conventional PI controller, and by adopting a rotary speed-current single loop control mode to replace the conventional rotary speed loop and current loop cascading control structure, quick tracking control of rotary speed and current is realized.

The invention discloses a simplified multilevel space vector pulse width modulation method and a space vector pulse width modulation soft core applicable to a three-phase cascaded H-bridge converter. The method includes: firstly, at the starting moment of each switching period Ts, sampling a reference space voltage vector to obtain a corresponding reference space voltage vector of each unit; then, completing sector judgment on the reference space voltage vectors , and respectively by the aid of shared computing resources, rotating the corresponding reference space voltage vectors to a first sector to obtain , and , computing an actual sector N in which switching time is mapped to the reference space voltage vectors; finally, distributing the corresponding switching time of each unit by means of multichannel signal selection and completing corresponding PWM (pulse width modulation) signal generation of each unit. The method can be used for achieving modulation of the three-phase cascaded H-bridge converter, is easy to achieve balanced energy distribution of each power unit, good in harmonic characteristic, high in extendibility, low in computation complexity, easy in digitization implementation and good in dynamic and steady-state performance, and is applicable to simplified multilevel space vector pulse width modulation of a high-voltage high-power speed regulating system, a high-voltage direct-current power transmission system and an electric railway traction power supply system.

The invention discloses a simplified multi-level space vector pulse width modulation method for an any-level single-phase cascaded H-bridge type converter and a modulation soft core thereof. At starting time of each switching period Ts, sampling of reference space voltage vectors Ur<(N)> is carried out to obtain reference space voltage vectors of all units one by one; section determination is carried out on the reference space voltage vectors Ur(1) <(N)>, Ur(2) <(N)>, ... Ur(n) <(N)> by using shared computing resources and calculation is carried out to obtain switching time; and shunting is carried out on switching time corresponding to all units based on multi-path signal selection and generation of PWM signals corresponding to all units is completed. With the method, modulation of the single-phase cascaded H-bridge type converter can be realized. On the basis of the technology, balanced energy distribution of all power units can be realized easily; the harmonic characteristics are good; the expandability is high; the computation complexity is low; digital realization becomes easy; and the dynamic and steady performances are excellent. The method can be applied to fields like a high-voltage high-power speed regulation system, a high-voltage direct-current power transmission system, and an electrical railway traction power supply system and the like.

The invention relates to the three-phase independent H-bridge drive circuit voltage space vector PWM (pulse width modulation) control technology of a three-phase alternating-current permanent magnet synchronous torque servo motor, and aims to provide a voltage space vector PWM control method based on a three-phase independent H-bridge drive circuit. Fourteen fundamental voltage space vectors including six long vectors, six short vectors and two zero vectors in voltage space vectors are designed, an orthohexagonal internally tangent voltage vector circular track is formed through the vectors, and a voltage vector circle is divided into twelve sectors by the aid of the twelve short and long vectors. A vector time calculation method and a sector determination method are provided, radius and sector number of the voltage vector circle formed by voltage space vector PWM control of the three-phase independent H-bridge drive circuit are two times of radius and sector number of a voltage vector circle formed by a traditional three-leg drive circuit voltage space vector PWM control mode, and generated maximum torque value and torque adjustment accuracy are also two times of those of the tradition mode.

The invention discloses a unique velocity sensorless vector control method for single bus current detection of a three-phase alternating-current motor. The velocity sensorless vector control method comprises the steps of detecting the bus current by a shunt resistor mounted on the bus low voltage side of a frequency changer, determining the trigger time adopted by the bus current according to the pulse width modulation PWM duty ratio of a control switch, and correspondingly reconstructing three-phase current of the motor. According to the motor current reconstruction method, a motor current direct detection hardware circuit is detected, so that the hardware cost is saved, and the same performance as the vector control of the motor three-phase current direct detection can be achieved. The velocity sensorless vector control method is suitable for a space vector PWM mode and is favorable for solving the problems of sector boundary and low modulation region in a vector method based on space switching. Analysis of experimental results shows that the motor current reconstruction method is also suitable for other any switch modulation mode and is higher in commonality and practicality. Particularly in small current and low modulation regions, the three-phase current of the motor also can be precisely reconstructed.

The embodiment of the invention provides a magnetic encoder, a calibration method and calibration device thereof, a motor and an unmanned aerial vehicle, and belongs to the field of electronic control. The calibration method comprises the following steps of acquiring a detection angle detected by the magnetic encoder; adjusting an electric angle of a rotor of a three-phase symmetric motor based onthe space vector pulse width according to the difference between the detection angle and a to-be-calibrated given mechanical angle, thereby enabling the difference to be located in the preset threshold range; under the condition that the difference is located in the preset threshold range, taking the current electric angle as a first electric angle calibration value corresponding to the given mechanical angle to store in a storage unit corresponding to the given mechanical angle, thereby accomplishing the calibration on the given mechanical angle. Therefore, the calibration between the detection angle of a side type magnetic encoder and the electric angle of the three-phase symmetric motor can be accomplished, so that the side magnetic encoder can be applied to the angle detection of thethree-phase symmetric motor, thereby realizing a miniaturization design aim of the cloud cradle and like equipment.

The invention discloses a voltage-type PWM (pulse-width modulation) rectifier output power control method under a power grid unsymmetrical fault. The technical scheme provided by the invention is characterized in that through the voltage-type PWM rectifier output power control method under the power grid unsymmetrical fault, the output active power and output reactive power which are obtained through calculation are subjected to negation through a band pass filer and a controller; a double frequency offset voltage is obtained through offset voltage calculation, and is offset to the output voltage in traditional vector control; and finally a reference voltage under a two-phase static coordinate system is obtained, a voltage signal generates a switch signal for controlling the power device after being subjected to space vector pulse width modulation, and the output active power and the output reactive power are controlled stably. According to the invention, under the condition of power grid unsymmetrical fault, positive sequence component and negative sequence component in a system are not required to be calculated and resolved; the power pulse of the voltage-type PWM rectifier can be offset directly; the direct-current bus voltage is controlled stably; and the calculation method is simple and can be easily realized.

A method generates space vector modulation signals for a multi-level power inverter using space vector pulse width modulation (SVPWM). A reference voltage and a triangle region for the reference voltage are determined. Vertices for a space vector that is closest to the reference voltage is outputted. Then, the vertices are adjusted so that the space vector is in a valid region of the triangle region. Lastly, the space vector modulation signals a, b, and c corresponding to the space vector in the valid region are outputed.

The invention discloses a control method of a sine wave linear motor for feed driving of a high-precision numerical control machine, comprising the specific steps as follows: a motion trail tracking module transmits the generated displacement error E and the error change rate dE to a position control loop; the position control loop adopts a self-adaption fuzzy control algorithm, and the output speed amount of the fuzzy controller and the measured speed signals are compared and transmitted to a speed control loop; the speed control loop transmits the generated error signal and the d-axle component error signals to a current control loop; the current control loop controls the current output by an inverter by using a space vector PWM (Pulse-Width Modulation) technology with a PI (Proportional-Integral) regulator so as to control the output torque of the motor; a feedback signal detection module outputs the feedback signals to the current control loop and regulates the output torque of the motor. The invention combines self-adaption control, fuzzy control and vector control of an alternative-current motor together, and improves the stability, the accuracy and the dynamic response capacity of a linear servo motor.

The invention provides an off-grid double-fed wind power generation system and a maximum wind energy capture method thereof. The power generation system comprises a double-fed generator, a rotor side converter, a load side converter, a bidirectional DC / DC (direct current) converter, a load side variable-current controller, a rotor side variable-current controller, a DC / DC variable-current controller and the like. The load side variable-current controller adopted by the invention can calculate a stator current reference value required for realizing the maximum wind energy capture according to the wind turbine speed and a maximum power curve, input a deviation between the stator current reference value and a feedback value to a proportional integral controller, produce a control voltage of the load side converter and generate a space vector PWM (pulse width modulation) signal to drive a power switch device of the load side converter. The rotor side converter can control the stator voltage of the double-fed generator to maintain at a rated value, and the load side converter can control the stator output power of the double-fed generator, thus the problem that output voltage stabilization and maximum wind energy capture cannot be simultaneously realized in the existing off-grid double-fed wind power generation system can be solved, and the wind energy utilization rate and economic benefit of the generating system can be improved.

The invention provides a method for determining duty ratio of universal pulse width for control of a three-phase AD motor PWM (pulse width modulation). The method comprises the following steps: determining normalization three-phase current set values Ia, Ib and Ic of the three-phase AD motor; calculating each two-phase current difference Iab, Ibc and Iac according to the normalization three-phase current set values Ia, Ib and Ic; calculating the maximum value max{|Iab|, |Ibc| and |Iac|} of absolute values of each two-phase current difference; determining the duty ratios ka, kb and kc according to three conditions of the max{|Iab|, |Ibc| and |Iac|} through four arithmetic operations. Compared with the conventional six sector vector decomposition method for determining the duty ratio of three-phase pulse, the method has the same result; but because of simple process and prevention of complicated vector determination and trigonometric function operation, the method has less realized code amount, small occupied hardware resources and high operation efficiency, can realize multiple PWM control modes including control modes of SPWM (sine pulse width modulation) and SVPWM (space vector pulse width modulation), and is particularly applicable to high-precision SVPWM control of the three-phase AD motor.

The invention discloses a motor control method using space vector pulse width modulation and a controller thereof. The method comprises the steps that an output signal of a current detecting module connected in series with a lower bridge arm electronic switch of an inverse bridge is collected when the inverse bridge is in a V0 state; beginning time sampled by a triggering current is controlled tocause the sampling process to be in the V0 period and cause the sampled current signals Ia and Ib to be in positive proportion to a motor phase current when V0 voltage vector time t0out for outputtinga space vector PWM signal is more than the minimum value t0min of the V0 voltage vector time; the V7 time t7out is controlled to be less than V0 time t0out when the V0 time is less than t0min duringthe partial modulation to compensate the V0 time so that the V7 time t7out is more than t0min, and the effective voltage vector time t1out and the effective voltage vector time t2out are relatively prolonged so as to improve the motor acceleration and the highest speed. The motor controller using the method has lower current detection hardware cost, can stabilize the phase current of the detectingmotor and simultaneously reduce or eliminate the influence on the motor acceleration and the highest speed due to current sampling as much as possible.

The invention discloses a space vector PWM (pulse width modulation) harmonic analysis method. The method comprises the following steps: first storing an acting sequence of a basic voltage vector into a basic voltage vector sequence matrix, secondly calculating an acting time of the basic voltage vector, then storing the acting time of the basic voltage vector in a time matrix, and finally analyzing harmonic characteristics. When the method is used for the harmonic analysis on a three-phase inverter, the basic voltage vector sequence matrix contains three rows which are used for respectively storing a level state corresponding to a switch state of the three phases. The ripple current and the voltage pulse sequences of all space vector PWM strategies are integrated into a same processing formula and process, the output voltage is digitally sampled, the analysis on the harmonic performance is carried out by utilizing a computer derivation and fast Fourier transform method, so that the harmonic characteristic comparison, performance evaluation and development of novel strategies can be rapidly carried out for various space vector PWM strategies.

The invention discloses a control system of an alternating current permanent magnet synchronous motor. The control system comprises a speed regulator, a current command generator, a vector rotation transformation module, a vector rotation inverse transformation module, a space vector pulse width modulation module, a Clarke transformation module, a voltage inverter, a three-phase motor, a position sensor, a speed calculator and a proportional-integral controller; wherein the current command generator comprises a pre-processing module, an optimized control strategy module, a current limit value calculation module and the proportional-integral controller. By virtue of the control system disclosed by the invention, the disturbances on change in parameters including the direct current voltage, the motor stator resistance, inductance and the like can be effectively inhibited, the stator current of motor can be under control and the operational reliability and stability of the system are improved.

The invention discloses a transforming method of random space vector PWM strategies. When a randomized PWM strategy ST1 is transformed into a randomized PWM strategy ST2, a random number matrix of the ST1 is generated, calculation is carried out to obtain a digital signal SIG1 of an output voltage of an inverter, and a spectral characteristic value of the SIG1 is calculated; all elements of a random number matrix RS2 of the ST2 are set as unknown variables, an expression of a digital signal SIG2 of the output voltage of the inverter is calculated, and then a mathematic expression of a spectral characteristic of the SIG2 is calculated; and then a target function of transformation from the ST1 to ST2 is constructed and optimization is carried out, thereby obtaining a numerical value of the RS2. According to the technical scheme, mutual transforming between different random SVPWM strategies can be realized and the complex strategy can be transformed into the simple one; application of the random SVPWM technology and development of the new strategy can be realized conveniently; and thus the method has the great practical value.

To improve a surgical machine with a sensorless electric motor comprising a rotor and at least two motor windings, and with a motor controller for controlling and / or regulating the electric motor, so that the electric motor is operable with optimum efficiency at low rotational speeds and a starting of the motor in accordance with the purpose, also under load, is enabled, it is proposed that a space vector pulse width modulation (SVPWM) method for controlling and / or regulating the electric motor, in which all motor windings are able to be simultaneously supplied with electric current, be performable with the motor controller. A method for controlling and / or regulating a surgical machine is also proposed.

The invention discloses a variable-frequency signal injection embedded permanent magnet synchronous motor maximum torque current ratio control method which comprises the following steps: in a space vector pulse width modulation algorithm, increasing or decreasing the action time of each medium vector in ten sectors to enable a reference voltage vector to generate phase lead or lag during synthesis; the disturbance signal is directly injected into the motor, the disturbance signal enables the flux linkage vector amplitude and the current vector amplitude to generate disturbance with the same frequency, and the d-axis current and the q-axis current of the motor are determined through the maximum torque current ratio point and the rotating speed closed loop; the d-axis voltage and q-axis voltage of the motor are obtained through the rotating speed closed loop, alpha-axis voltage and beta-axis voltage are obtained through Park inverse transformation, and voltage vector synthesis is carriedout in an SVPWM algorithm. The method can improve the frequency of the injection signal in a multiple form along with the increase of the motor speed and the fundamental frequency, so that the injection signal frequency and the motor fundamental frequency do not interfere with each other.

The invention discloses an optimal space vector pulse width modulation (SVPWM) control method for a three-phase inverter based on an immune algorithm. The SVPWM optimizing problem of the three-phase voltage inverter is analyzed and studied; and the optimizing object is to optimize the output voltage waveform quality of the three-phase voltage inverter. Based on a conventional SVPWM control method of the three-phase voltage inverter and the application of the method, an optimizing scheme for optimizing a vector sequence and zero vector action time based on the immune algorithm is put forward according to the optimization freedom in the space voltage vector control of the three-phase voltage inverter; and in consideration of the optimizing effect and efficiency of the optimizing scheme, an optimal SVPWM control scheme is put forward. In addition, the invention takes a voltage weight total harmonic distortion (WTHD) as the standard for measuring the waveform quality by considering that a low order harmonic causes large influence and a high order harmonic causes small influence in an actual power system, so as to meet the actual condition better.

The invention discloses an overmodulation control method for a motor, and relates to a motor modulation technology. The overmodulation control method comprises the following steps of: collecting errorsignals and current feedback signals of a motor feedback rotation speed and a given rotation speed, performing conversion from coordinates of a two-phase rotating coordinate system to coordinates ofa two-phase static coordinate system to obtain command voltage signals U[alpha]* and U[beta]* of the motor, performing SVPWM (Space Vector Pulse Width Modulation) to obtain a binary function F([theta]h, [theta]r) of an angle pair ([theta]h, [theta]r) to obtain a modulation ratio MI and calculate the modulation ratio MI, wherein the modulation ratio MI is in one-to-one correspondence with the anglepair ([theta]h, [theta]r); according to the value of the modulation ratio MI, obtaining a value of the angle pair ([theta]h, [theta]r); and according to the value of the angle pair ([theta]h, [theta]r), calculating a voltage vector required by the motor and a corresponding duty cycle to obtain six-path drive signals of an inverter. The overmodulation control method for a motor only needs to obtain value information of the angle pair ([theta]h, [theta]r) to determine the size of a fundamental wave to be output so as to achieve overmodulation, and therefore, the principle is simple, and the operation is convenient.

The invention discloses a voltage-type PWM (pulse width modulation) rectifier power compensation control method under asymmetrical power grid faults. The technical scheme mainly includes that the voltage-type PWM rectifier power compensation control method under the asymmetrical power grid faults includes: enabling input reactive power and input active power which are obtained by computation to pass through band-pass filters and controllers so that second harmonic compensation voltages are obtained, compensating the second harmonic compensation voltages into output voltage subjected to traditional vector control, and finally, obtaining reference voltages under a two-phase static coordinate system. After voltage signals are subjected to space vector pulse width modulation, switching signals for controlling power devices are generated, and stable control of reactive power and active power is achieved. Under the condition of the asymmetrical power grid faults, computation and decomposition of a positive sequence component and a negative sequence component in a system are not needed, power pulses of the voltage-type PWM rectifier can be compensated directly, stable control of reactive power and active power is achieved, operating capability of the voltage-type PWM rectifier under the condition of the asymmetrical power grid faults can be improved effectively, and the method is simple in algorithm and easy to implement.

The invention discloses a zero fundamental voltage vector randomization method for space vector pulse-width modulation (PWM). According to the method, a modulated wave implied in phase voltage is decomposed into a definitive part and a random part; statistic characteristic parameters such as a mean value and standard deviation of the random part are kept constant at the modulation ratio; the randomization range of a zero fundamental voltage vector is the action time of the minimal zero fundamental voltage vector within a complete modulated wave cycle; and when the randomization method is applied to a seven-segment symmetrical modulation mode, the randomization range is the result that the minimal holding time required for current measurement is added to the minimal value, so that the measurement accuracy is improved. According to the technical scheme of the invention, sufficient randomization can be realized; the statistic characteristic parameters of the random part of the implied modulated wave cannot change along with time; effective application of a plurality of research methods and analysis tools based on the stationary random process is facilitated.