CN110417333B - Switching frequency half fundamental wave period segmentation random space vector pulse width modulation method - Google Patents
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02P—CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
- H02P27/00—Arrangements or methods for the control of AC motors characterised by the kind of supply voltage
- H02P27/04—Arrangements or methods for the control of AC motors characterised by the kind of supply voltage using variable-frequency supply voltage, e.g. inverter or converter supply voltage
- H02P27/06—Arrangements or methods for the control of AC motors characterised by the kind of supply voltage using variable-frequency supply voltage, e.g. inverter or converter supply voltage using dc to ac converters or inverters
- H02P27/08—Arrangements or methods for the control of AC motors characterised by the kind of supply voltage using variable-frequency supply voltage, e.g. inverter or converter supply voltage using dc to ac converters or inverters with pulse width modulation
- H02P27/085—Arrangements or methods for the control of AC motors characterised by the kind of supply voltage using variable-frequency supply voltage, e.g. inverter or converter supply voltage using dc to ac converters or inverters with pulse width modulation wherein the PWM mode is adapted on the running conditions of the motor, e.g. the switching frequency
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Abstract
The invention discloses a switching frequency half fundamental wave period segmentation random space vector pulse width modulation method. This novel random modulation technique is with two half fundamental wave periods around whole fundamental wave period split is, through introducing frequency of squinting and random frequency's mode, and rationally distributes both sizes, carries out the segmentation random to the switching frequency in single fundamental wave period to optimize switching frequency and distribute, further cut down higher harmonic amplitude. The method disclosed by the invention can further weaken the switching frequency and the harmonic waves near integral multiples thereof in a narrower switching frequency variation range, realize better dispersion of higher harmonic waves, further effectively reduce the electromagnetic interference of the inverter and contribute to the application and popularization of a random modulation technology.
Description
Technical Field
The invention discloses a switching frequency half fundamental wave period segmentation random space vector pulse width modulation method, and belongs to the technical field of power generation, power transformation or power distribution.
Background
In recent years, with the rapid development of the fields of new energy automobiles, aerospace, ship propulsion and the like, a great amount of various advanced electrical devices are used, the defects brought by the traditional Space Vector Pulse Width Modulation (SVPWM) technology are more and more concerned, and especially the electromagnetic compatibility becomes an important investigation index in the field of electric traffic. When the traditional SVPWM is adopted, a large amount of higher harmonics are generated at the switching frequency and integral multiples of the switching frequency by the output voltage, so that a large amount of electromagnetic noise and interference are brought, and the electromagnetic compatibility of a system is influenced.
The random SVPWM technology directly generates a driving signal by randomly changing parameters such as a switching signal period, a pulse position and the like, controls an electromagnetic interference source from a source, and can realize good dispersion of higher harmonics in a wider frequency range under the conditions of not changing a system topological structure and not increasing hardware cost, thereby effectively reducing electromagnetic interference and improving the electromagnetic compatibility of a system. Because of this, it has received extensive attention and intensive research in recent years.
According to the difference of randomized objects in random modulation technology, the method can be divided into random pulse position modulation technology and random switching frequency modulation technology. The random pulse position modulation technology has to be improved in the capability of dispersing higher harmonics, and the random switching frequency modulation technology is widely researched due to the good harmonic dispersion effect.
Generally, the maximum value and the minimum value of the random switching frequency are symmetrically distributed on two sides of the average switching frequency, and the upper limit of the random switching frequency is limited by a switching device; if the switching frequency variation range is wide, the lower limit of the switching frequency variation range is also small, so that the current ripple is increased, and the steady-state performance of the system is affected. Meanwhile, the wider switching frequency range can bring about the phenomenon of frequency spectrum aliasing, so that higher harmonics between the switching frequency and twice the switching frequency are superposed, and the electromagnetic interference is increased. In addition, when random modulation is implemented using digital control techniques, the sampling frequency is usually kept the same as the switching frequency. In the random switching frequency modulation mode, the sampling frequency also changes synchronously, if the change range is large, the system transfer function and the frequency domain characteristic also change greatly, and accordingly the design of the regulator parameters also considers the influence of the change of the sampling frequency. These factors can significantly reduce the practical effect of random switching frequency modulation and increase the difficulty of engineering applications.
At present, most researches on random switching frequency modulation are carried out in a wider switching frequency range, but in practical application, software and hardware limitations of a motor driving system can limit the switching frequency variation range to a certain extent, so that the dispersion effect of higher harmonics generated by random modulation is poor, and the application occasions are correspondingly limited.
Aiming at the problem, the invention provides a switching frequency half fundamental wave period segmented random space vector pulse width modulation method, which can further reduce the amplitude of higher harmonics concentrated near the switching frequency and integral multiples thereof under the condition of narrower switching frequency variation range so as to better inhibit electromagnetic noise and interference.
Disclosure of Invention
The invention aims to provide a switching frequency half fundamental wave period segmented random space vector pulse width modulation method aiming at the defects of the background technology, improves the traditional full fundamental wave period random switching frequency modulation method, independently randomizes the switching frequencies of two half fundamental wave periods respectively, and solves the technical problem that the amplitude of higher harmonic wave is larger under the condition that the switching frequency variation range is narrower in the traditional modulation method.
The invention adopts the following technical scheme for realizing the aim of the invention:
a switching frequency half fundamental wave period segmentation random space vector pulse width modulation method comprises the following steps:
1. firstly, dividing a fundamental wave period according to a beta axis voltage vector under a static coordinate system;
2. then, determining a sign bit of the offset frequency according to the divided two half fundamental wave periods;
3. then, calculating according to the random number and the absolute value of the offset frequency to obtain the random frequency of the next switching period;
4. then, combining the offset frequency, the offset frequency sign bit, the random frequency and the average switching frequency of the whole fundamental wave period to obtain the switching frequency of the next switching period;
5. and finally, calculating the action time of the corresponding voltage vector according to an SVPWM algorithm and determining each switching signal.
Further, in a method for modulating the switching frequency half fundamental wave period segmented random space vector pulse width, the specific method in step 1 is as follows: beta axis voltage vector U obtained according to coordinate transformationβThe voltage fundamental wave period is divided into two parts, and the invention divides the voltage fundamental wave period into UβNot more than 0 and Uβ>0 two half the fundamental period.
Still further, in a method for modulating the switching frequency half fundamental wave period segmented random space vector pulse width, the specific method in step 2 is as follows: defining an offset frequency Δ foffsIs the average switching frequency f in a half fundamental periodahWith the average switching frequency f over the entire fundamental periodafThe absolute value of the difference, i.e. Δ foffs＝|fah-fafL. Determining the offset frequency delta f according to the divided two half fundamental wave periodsoffsSign bit signb. The invention adopts UβWhen the frequency is less than or equal to 0, the sign bit sign of the offset frequency is-1, Uβ>At 0, the offset frequency sign bit signb is 1.
Still further, in a switching frequency half fundamental wave period segmented random space vector pulse width modulation method, step 3The specific method comprises the following steps: defining a random frequency range Deltaf within a half fundamental periodrangeIs half of the whole fundamental wave period switching frequency variation range delta f and the offset frequency delta foffsThe difference, i.e. Δ frange＝Δf/2-Δfoffs. Calculating to obtain a 16-bit signed random number R of the next switching period by adopting a linear congruence method, and calculating to obtain the random frequency delta f of the next switching periodrandThe calculation formula is Deltafrand＝[Δfrange·R/215]Wherein [ x ]]Rounding off for x.
Still further, in a method for modulating the switching frequency half fundamental wave period segmented random space vector pulse width, the specific method in step 4 is as follows: will shift by frequency Δ foffsOffset frequency sign bit signb, random frequency Δ frandAnd the average switching frequency f of the whole fundamental periodafCombined to obtain the switching frequency f of the next switching periodnextThe calculation formula is fnext＝faf+Δfoffs·signb+Δfrand。
Still further, in a method for modulating the switching frequency half fundamental wave period segmented random space vector pulse width, the specific method in step 5 is as follows: switching frequency f according to the next switching cyclenextAnd calculating the action time of the corresponding voltage vector according to the SVPWM principle and determining each switch action signal.
By adopting the technical scheme, the invention has the following beneficial effects:
(1) the random frequency of the next switching period is randomly generated in a random frequency range determined according to the half-cycle frequency offset, and the offset frequency and the random frequency of the next switching period are counted in the generation of the switching frequency of the next switching period, so that the amplitude of the higher harmonic concentrated around the switching frequency and the integral multiple thereof can be reduced in the case that the variation range of the switching frequency is narrow.
(2) The invention adopts the linear congruence method to generate random numbers, does not need to add extra hardware and is convenient to realize.
(3) The technology disclosed by the invention is a general technology and is suitable for three-phase and multi-phase motor driving systems.
Drawings
Fig. 1 is a schematic diagram of implementation of a switching frequency half fundamental wave period segmented random space vector pulse width modulation technique.
Fig. 2 is a three-phase inverter fundamental voltage vector distribution diagram.
Fig. 3 is a switching frequency half fundamental period segmented random space vector pulse width modulation switching signal.
Fig. 4 shows the distribution characteristics of higher harmonics according to the disclosed technology.
Detailed Description
The technical scheme of the invention is explained in detail in the following with reference to the attached drawings.
The implementation schematic diagram of the switching frequency half fundamental wave period segmented random space vector pulse width modulation technology is shown in fig. 1, and firstly, the fundamental wave period is divided according to a voltage vector obtained by coordinate transformation; then, determining a sign bit sign b of the offset frequency according to the divided two half fundamental wave periods; a linear congruence method is then used to generate the pseudo-random number R. The recursion formula of the linear congruence method is:
Rj+1≡(A×Rj+ B) (congruence M) (j ═ 0,1, 2.) (1),
wherein R isjIs the value at time j, Rj+1The value of the time j +1 is A, B, M, which is a parameter selected by the designer, and the initial values adopted by the invention are a-97, B-59 and M-32768.
Then, the magnitude of the absolute value of the offset frequency is Δ f according to the random number RoffsCalculating to obtain the random frequency delta f of the current switching periodrandThe calculation formula is Deltafrand＝[Δfrange·R/215](ii) a Then shift the frequency Δ foffsOffset frequency sign bit signb, random frequency Δ foffsAnd the average switching frequency f of the whole fundamental periodafCombined to obtain the switching frequency f of the next switching periodnextThe calculation formula is fnext＝faf+Δfoffs·signb+Δfrand(ii) a And finally calculating the action time of the corresponding voltage vector according to an SVPWM algorithm and determining each switching signal.
The three bridge arms of the three-phase inverter have 6 switching tubes,all possible combinations thereof are eight kinds, including 6 non-zero vectors U1(001)、U2(010)、U3(011)、U4(100)、U5(101)、U6(110) And two zero vectors U0(000)、U7(111) They are distributed in the α β coordinate system as shown in fig. 2. If a reference space voltage vector U is required to be output currentlyrefIn sector I, it can be represented by two voltage space vectors adjacent to it:
in the formula, theta is the included angle between the reference space voltage vector and the alpha axis, TzFor a switching period, i.e. Tz＝1/fnext。T6，T4Are respectively a voltage vector U6And U4The action time of (1).
The time allocated for the zero vector is:
T0＝T7＝(Tz-T4-T6)/2 (3)，
the two types of zero vectors are equally distributed in time through the above formula, so as to generate symmetrical PWM signals, and finally obtain the switching signals of the random modulation technique disclosed by the present invention, as shown in fig. 3.
The distribution characteristics of the higher harmonics in the disclosed technique are shown in fig. 4. Wherein the whole fundamental wave period switching frequency variation range is 2 delta f, and the offset frequency delta foffsIs the difference between the average switching frequency in a half fundamental wave period and the average switching frequency in the whole fundamental wave period, and the random frequency delta frandIs half of the range of switching frequency variation within a half fundamental period. In conventional full fundamental period random switching frequency modulation, the offset frequency is 0 and the random frequency is 2 Δ f. In order to keep the switching loss and the switching frequency variation range unchanged, the absolute values of the offset frequencies of the two half fundamental wave periods are delta foffs. After the technology disclosed by the invention is adopted, the original randomization process for one fundamental period switching frequency is divided into two parts. In the first half of the fundamental period, eachThe envelope of the higher harmonics generated by the switching period is the left-hand dash-dotted line, and the average switching frequency is fs-ΔfoffsThe variation range is [ fs-Δfoffs-Δfrand,fs-Δfoffs+Δfrand](ii) a In the second half of the fundamental period, the envelope of the higher harmonic wave generated in each switching period is a thin solid line on the right side, and the average switching frequency is fs+ΔfoffsThe variation range is [ fs+Δfoffs-Δfrand,fs+Δfoffs+Δfrand]It can be seen that the method disclosed by the application can reduce the amplitude of higher harmonics concentrated around the switching frequency and integer multiples thereof under the condition of narrow variation range of the switching frequency.
Claims (6)
1. A switching frequency half fundamental wave period segmentation random space vector pulse width modulation method is characterized in that, dividing a voltage fundamental wave period into two half-wave periods according to the zero-crossing condition of a voltage vector component under a static coordinate system, determining a sign bit of offset frequency in the half-wave period according to the divided two half-fundamental wave periods, generating a random frequency of a next switching period in a random frequency range within a half fundamental wave period determined by a difference between the offset frequency and a switching frequency variation range of the entire fundamental wave period within the half-fundamental wave period, on the basis of the average switching frequency of the whole fundamental wave period, considering the offset frequency in the half-wave period and the random frequency of the next switching period to obtain the switching frequency of the next switching period, calculating the action time of the corresponding voltage vector according to an SVPWM algorithm, and determining the signal of each switch in the next switching period, wherein the switching frequency of the next switching period is according to an expression: f. ofnext＝faf+Δfoffs·signb+ΔfrandDetermination of fnextThe switching frequency, f, of the next switching cycleafFor average switching frequency, Δ f, over the entire fundamental periodoffsIs the offset frequency in the half fundamental wave period, sign b is the sign bit of the offset frequency in the half fundamental wave period, Δ frandIs the random frequency of the next switching cycle.
2. Root of herbaceous plantThe method of claim 1, wherein the method of dividing the fundamental voltage period into two half-wave periods according to the zero-crossing condition of the voltage vector component in the stationary coordinate system comprises: dividing the fundamental period of voltage into UβNot more than 0 and Uβ>0 two and a half fundamental period, UβIs the beta axis voltage vector.
3. The method as claimed in claim 1, wherein the offset frequency within the half-wave period is an average switching frequency f within the half-wave periodahWith the average switching frequency f over the entire fundamental periodafAbsolute value of the difference, Δ foffs＝|fah-faf|，ΔfoffsIs the offset frequency within a half-wave period.
4. The method of claim 1, wherein the method for determining the sign bit of the offset frequency in the half-wave period according to the divided two half-fundamental wave periods comprises: u shapeβWhen the frequency is less than or equal to 0, the sign bit signb of the offset frequency in the half-wave period is-1; u shapeβ>At 0, sign bit signb of the offset frequency in the half-wave period is 1.
5. The method according to claim 1, wherein the random frequency range in the half fundamental wave period is expressed by the following expression: Δ frange＝Δf/2-ΔfoffsDetermination of Δ frangeIs a random frequency range in a half fundamental wave period, delta f is a change range of the switching frequency of the whole fundamental wave period, and delta foffsIs the offset frequency within a half-wave period.
6. The method of claim 1, wherein the random frequency of the next switching period is generated in a random frequency range within the half fundamental wave period determined by the difference between the shift frequency within the half fundamental wave period and the switching frequency variation range of the entire fundamental wave period by using a linear congruence method.
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