CN106655182A - Composite-control active filter based on high-compensated precision current loop and control method thereof - Google Patents

Abstract

The present invention relates to the technical field of active filter current loop composite control, in particular to a composite control active filter and a control method based on a high compensation precision current loop. Control circuit, the general control circuit of the active filter includes a harmonic separation module; the output end of the harmonic separation module is connected to the load side power grid through the current loop compound controller and the filter module in turn; the filter module The output terminal of is connected to the input terminal of the current loop composite controller. The invention can effectively eliminate all periodic errors included in the stable closed loop and improve the steady-state precision.

Description

Compound Control Active Filter Based on High Compensation Precision Current Loop and Its Control Method

technical field

The invention relates to the technical field of active filter current loop composite control, in particular to a composite control active filter and a control method based on a high compensation precision current loop.

Background technique

Since the birth of the thyristor, because of its derivative power electronic products constantly changing people's daily life, the superiority of the power electronic products based on the thyristor has attracted more and more attention and references. At the same time, a large number of power electronic devices based on nonlinear loads such as thyristors have been introduced into the power grid, resulting in serious harmonic pollution of the power grid. This is mainly due to the non-linear, impact and unbalanced power consumption characteristics of these loads. Therefore, the active filter technology used for harmonic suppression has gradually become one of the research hotspots in the fields of power electronics and electrical engineering and electricity utilization at home and abroad in recent years. Active power filter (APF) is a new type of power electronic device used to dynamically suppress harmonics and compensate reactive power. It is based on modern control technology and advanced digital high-speed processors to process relevant data at high speed, making it It can quickly track and compensate harmonics with different amplitudes and frequencies, and respond quickly in microseconds, so that the total vector sum of harmonics in the power grid system is zero. Compared with the passive filter, which can only perform zero-crossing switching response speed in the power frequency cycle and can only passively absorb harmonics of fixed frequency and size, the active filter can sample the load current and carry out various Separation of sub-harmonic and reactive power, through the control of active filter and actively send out the magnitude, frequency and phase of the current, and respond quickly to offset the corresponding harmonics in the load

The current realizes dynamic tracking compensation, which can not only compensate harmonics and reactive power but also deal with imbalance problems.

The active filter starts from the collection of load current or system current, and quickly processes the collected data in real time, and quickly eliminates the harmonics, reactive power and unbalance problems of the system according to the collected data, thereby improving the power supply quality of the power grid. Compared with the traditional passive filter, the active filter has a more flexible compensation method and a more comprehensive compensation function. It can compensate all harmonics and can also compensate according to the specified order of harmonics. In addition to compensating harmonics At the same time, it can also compensate some reactive power and three-phase unbalanced current.

At present, the parallel APF achieves the function of harmonic single separation and reactive power separation, and the separation of unbalanced current through related control algorithms. The separated related current is used as the reference command current IRa and the device output current ICa as the error value. Through the current tracking control algorithm, the device can send out the vector value opposite to the harmonic component in the system in time and quickly. However, the traditional current tracking control strategies are mostly hysteresis control, traditional PI tracking, modified PI control algorithm, etc. Among them, the hysteresis control will generate a wide harmonic spectrum, and there is no fixed switching frequency, so it is impossible to control the input grid. The sub-harmonic current of the switching frequency causes the parameters of the output filter of the APF to be uncertain; for the traditional PI controller, it has been used for the tracking control of the DC flow without static error. For the harmonic current of the APF, the tracking It is an AC quantity, and PI cannot realize tracking control without static error. For the error value of the reference command current IRa and the current sent by the device, the action speed and accuracy are low, and complete tracking control cannot be realized, resulting in a low compensation rate of the device, which cannot reach Completely offset the harmonic current in the system.

The existing Chinese invention patent application document with the announcement number CN201510018591 discloses a "A Fast Current Tracking Control Method Based on PI Control Active Filter", including "Step 1: Set the maximum error current response value △imax; Step 2: Obtain the error current value △i; Step 3: Divide the error current value △i by the maximum error current response value △imax to obtain its integer multiple value n and error remainder current △i'; Step 4: Error remainder current △ i' directly enters the PI regulator to calculate the first output voltage V1, and calculates the integer multiple value n through the volt-second characteristic to obtain the second output voltage V2; Step 5: Add the first output voltage V1 and the second output voltage V2 to obtain Modulation voltage V. By adding input error limit before PI regulation, and then supplementing after PI output, the output voltage responds to the current without delay.” However, this invention patent needs to set the maximum error current response value, which is not a closed-loop automatic Adaptive control cannot adjust itself with the dynamic change of load current. The entire control method adopts open-loop control. When the set value and the actual required value of the system load are too large, it is easy to cause over-compensation or under-compensation. It is difficult to define the maximum error current response value in the entire control system, and it is difficult to determine a reasonable value for the maximum error current response value in places where the actual load changes frequently. In addition, in this control algorithm system, the error between the harmonic target current and the output current always tends to change continuously, and the obtained error value is then calculated with the set maximum error current response value for integer multiples and remainder multiples, which is just a disguised Making the difference of PI tracking smaller can not really achieve the purpose of tracking without static error.

Contents of the invention

The technical problem to be solved by the present invention is to provide a compound circuit based on a high-compensation precision current loop with high steady-state precision, fast response speed, and the ability to eliminate static errors by tracking the AC volume. Control type active filter and control method.

For solving the above problem, a kind of technical scheme of the present invention is:

The composite control active filter based on the high compensation precision current loop of the present invention includes a general control circuit of the active filter connected to the power grid on the sampling side, and the general control circuit of the active filter includes a harmonic separation module; The output end of the harmonic separation module described above is connected to the load-side grid through the current loop compound controller and the filter module in turn; the output end of the filter module is connected to the input end of the current loop compound controller.

Further, the current loop composite controller includes a current outer loop control system and a current inner loop control system.

Further, the current outer loop control system includes a forward channel modulation unit and a backward channel feedback unit.

Further, the current inner loop control system includes a current inner loop PI control unit.

A control method of a compound control active filter based on a high compensation precision current loop, comprising the following steps:

S1. The general control circuit of the active filter collects and processes the grid voltage, load current and device output current ICa, the harmonic separation module outputs the reference command current IRa, and outputs the reference command current IRa and the device The current ICa is input to the current loop composite controller for operation;

S2. The difference between the reference command current IRa and the device output current ICa is calculated to obtain the error value error, and the error value error is passed through the current outer loop control system of the current loop composite controller based on the internal model principle. Process to the channel modulation unit and the backward channel feedback unit to obtain the periodic error value △error1;

S3. The periodic error value Δerror1 is processed by the current inner loop PI control unit of the current inner loop control system, and PI control is used to adjust the mutation error.

Further, in the step S1,

S1.1. Collect grid voltage, load current, and device output current ICa. Based on the grid system voltage at the sampling side, through relevant phase-locked loop algorithm processing, the phase angle Ф of phase A of the grid system is obtained, and the phase angle Ф Find the sine and cosine values;

S1.2, the collected load current and the sine and cosine values of the phase angle of the positive sequence of the A phase obtained in step S1.1, through the harmonic separation algorithm, the collected load current is harmonically separated, and each time The amplitude, phase and vector direction of the harmonic current are separated, and then each harmonic is added to obtain the reference command current IRa;

S1.3. The output current ICa of the device reaches the AD input range through the external acquisition circuit and related conditioning circuit, and is input to the current loop compound controller together with the reference command current IRa in the previous step after being digitized by AD.

Further, the harmonic separation algorithm is FFT or DQ0 or PR.

Further, in the step S2,

S2.1. The error value error is obtained after the difference operation between the reference command current IRa and the device output current ICa, and the error value is summed with the correction value of the backward channel composite function Q(Z)*S(Z) based on the internal model principle The operation gets sum;

S2.2. The sum value is input to the first cycle delay integrator function S(n), and the delay integral function below the number of cycle points is corrected, and the corrected value is △error;

S2.3. Send the △error obtained in the previous step into the second-order low-pass filter function C(Z), and obtain △error1 through the filter.

Further, the feedback of the backward channel is sequentially processed by the auxiliary compensator Q(Z) and the cycle point delay correction function S(Z) to obtain a compound function Q(Z)*S(Z).

Further, in the step S3,

3.1. Sum1 is obtained by summing △error1 and the reference command current IRa, and △error2 is obtained by sum1 and the difference operation of the device output current ICa;

3.2. The Δerror2 responds to the error immediately through the current inner loop PI controller, and performs a fast dynamic response.

Compared with the prior art, the present invention aims at the defects of the prior art,

Aiming at the problem that the traditional current tracking control algorithm cannot achieve no static error tracking for the AC quantity, the invention proposes a compound controller based on the internal model principle and PI control. The composite controller will repeat the distortion of the waveform in the previous cycle at the same time of the next fundamental wave cycle, and then the controller determines the required correction signal according to the error between the command signal and the feedback signal, and in the next cycle At the same time, this correction signal is superimposed on the original control signal, thereby eliminating the repetitive distortion that will appear in each cycle in the future, effectively eliminating all periodic errors included in the stable closed loop, and improving the steady-state accuracy. In order to increase the dynamic response time while improving the steady-state accuracy, the forward channel and backward channel control algorithms based on the internal model principle are embedded in the inner loop of the PI controller, and the PI is used to speed up the dynamic response speed of the system, thereby improving the overall current loop. The steady-state accuracy and dynamic performance of the control ensure the best effect of current tracking compensation accuracy.

The present invention proposes a compound control algorithm for current tracking without static error, which solves the problem that PI tracking of AC volume cannot achieve no static error tracking, and also solves the problem that the quasi-proportional resonant controller (PR) needs multiple channels and the parameter matching is cumbersome The problem. Through compound innovation, the present invention adopts multiple control algorithms for the current loop, repairs and corrects the harmonic reference command current IRa within a fixed period of time in the current outer loop, continuously makes it approach the harmonic current value in the system, and improves the system performance. Steady-state accuracy, the current inner loop uses tracking control to quickly make a dynamic response to improve the dynamic accuracy, and to improve the filtering performance of the active filter.

The error correction controller based on the internal model principle of the present invention corrects the error between the target current value and the output current value of the device point by point after work, so that the command current of the next cycle is close to the current value of the previous cycle, In this way, there will be no sudden change in the PI controller, which is suitable for the PI controller. With closed-loop control, there is no need to set error parameters. The control system performs closed-loop error correction based on the difference between the actual target current and the output current of the device, without considering the optimal dynamic response value. Since the integral parameter in the PI control system is within the cycle, the integral value is finally zero, and the integral correction effect does not exist. The corrector based on the internal model principle can make up for the integral effect and compensate the integral of PI.

Description of drawings

Fig. 1 is the overall structure schematic diagram of the active filter involved in the present invention

Fig. 2 is a structural schematic diagram of a current loop composite controller based on high compensation precision involved in the present invention.

Fig. 3 is a flow chart of the control algorithm transfer function of the current loop composite controller involved in the present invention.

detailed description

The present invention will be further described in detail below in conjunction with the accompanying drawings and examples, but the protection scope of the present invention is not limited thereto.

Referring to Fig. 1, the present invention is based on the composite control type active filter of high compensation precision current loop, comprises the active filter common control circuit connected on the sampling side power grid, and described active filter general control circuit includes harmonic Separation module; the output end of the harmonic separation module is connected to the load-side power grid through the current loop compound controller and the filter module in turn; the output end of the filter module is connected to the input end of the current loop compound controller.

The current loop composite controller includes a current outer loop control system and a current inner loop control system.

The current outer loop control system includes a forward channel modulation unit and a backward channel feedback unit.

The current inner loop control system includes a current inner loop PI control unit.

A control method of a compound control active filter based on a high compensation precision current loop, comprising the following steps:

S1. The general control circuit of the active filter collects and processes the grid voltage, load current and device output current ICa, the harmonic separation module outputs the reference command current IRa, and outputs the reference command current IRa and the device The current ICa is input to the current loop composite controller for operation;

S2. The difference between the reference command current IRa and the device output current ICa is calculated to obtain the error value error, and the error value error is passed through the current outer loop control system of the current loop composite controller based on the internal model principle. Process to the channel modulation unit and the backward channel feedback unit to obtain the periodic error value △error1;

S3. The periodic error value Δerror1 is processed by the current inner loop PI control unit of the current inner loop control system, and PI control is used to adjust the mutation error.

In the step S1,

S1.1. Collect grid voltage, load current, and device output current ICa. Based on the grid system voltage at the sampling side, through relevant phase-locked loop algorithm processing, the phase angle Ф of phase A of the grid system is obtained, and the phase angle Ф Find the sine and cosine values;

S1.2, the collected load current and the sine and cosine values of the phase angle of the positive sequence of the A phase obtained in step S1.1, through the harmonic separation algorithm, the collected load current is harmonically separated, and each time The amplitude, phase and vector direction of the harmonic current are separated, and then each harmonic is added to obtain the reference command current IRa;

S1.3. The output current ICa of the device reaches the AD input range through the external acquisition circuit and related conditioning circuit, and is input to the current loop compound controller together with the reference command current IRa in the previous step after being digitized by AD.

The harmonic separation algorithm is FFT or DQ0 or PR.

In the step S2,

S2.1. The error value error is obtained after the difference operation between the reference command current IRa and the device output current ICa, and the error value is summed with the correction value of the backward channel composite function Q(Z)*S(Z) based on the internal model principle The operation gets sum;

S2.2. The sum value is input to the first cycle delay integrator function S(n), and the delay integral function below the number of cycle points is corrected, and the corrected value is △error;

S2.3. Send the △error obtained in the previous step into the second-order low-pass filter function C(Z), and obtain △error1 through the filter.

The feedback of the backward channel is sequentially processed by the auxiliary compensator Q(Z) and the cycle point delay correction function S(Z) to obtain the composite function Q(Z)*S(Z).

In the step S3,

3.1. Sum1 is obtained by summing △error1 and the reference command current IRa, and △error2 is obtained by sum1 and the difference operation of the device output current ICa;

3.2. The Δerror2 responds to the error immediately through the current inner loop PI controller, and performs a fast dynamic response.

A composite control active filter of a high compensation precision current loop according to the present invention includes the general control circuit of the active filter, a composite current loop controller, and a filtering module, and the general control circuit of the active filter includes an analog signal A conditioning circuit, a digital processor (FPGA+DSP), and the filtering module includes an IGBT driver, an inverter module, and an LCL filtering networking module. A brief introduction to its working process is as follows: the analog signal conditioning circuit will obtain the sampling side power grid voltage and current flow analog signal conditioning, and convert the conditioned analog signal to a digital processor (FPGA+DSP) for digital conversion and send it to the processor for further processing. Phase-locked operation and harmonic separation calculation, after the separated current is used as the reference command current IRa, the difference between the reference command current IRa and the actual device output current ICa is calculated by the current loop composite controller, and the drive signal is output to The IGBT driver drives the IGBT to turn on to output the filter current used to filter the harmonic current of the system.

It should be noted that the FPGA (Field Programmable Gate Array) mentioned in the present invention, that is, Field Programmable Gate Array, appears as a semi-custom circuit in the field of application specific integrated circuits, and its purpose is to improve the flexibility of circuit design. Parallel processing can greatly improve the running speed of the control algorithm and solve the problem of sequential execution of traditional processors. The rich logic gate array can solve the logic control of the load, and make each logic control execute in parallel, fully meet the consistent requirements in the execution action, and improve the precision of the control system.

The DSP (Digital signal processor) mentioned in the present invention is a microprocessor that is biased towards digital signal processing. It is a device that processes a large amount of information with digital signals, and mainly processes data that is discrete in time and amplitude. It mainly analyzes, transforms, filters, detects, modulates, etc. the signal. It has strong programmability and computing speed. Its real-time running speed can reach tens of millions of complex instruction programs per second, and its performance far exceeds that of general-purpose controllers. .

The IGBT (Insulated Gate Bipolar Transistor) mentioned in the present invention refers to an insulated gate bipolar transistor, a high-speed electronic switching device. The reference current refers to the current that is expected to be output by the device from the perspective of eliminating grid harmonics, and the reference current may vary with changes in the load current.

The present invention adjusts the cycle-by-cycle error based on the internal model principle of the forward channel and backward feedback of the current loop composite controller, so that the error of the reference command current IRa of each cycle is zero, thereby improving the system steady-state accuracy and tracking accuracy .

In addition, in step S2, since the frequency range of the active filter compensation is 0 to 2.5KHz, when designing the controller, it is only necessary to ensure the control effect of the middle and low frequency bands. Considering the overall performance requirements, only a second-order low pass filter to increase the suppression of high frequencies, and △error is sent to the second-order low-pass filter.

FIG. 2 is a structural schematic diagram of a tracking current loop control method of a compound control active filter based on a high-precision compensation current loop according to the present invention. As shown in Figure 2, the present invention is based on a high-precision compensating current loop compound controller, through the dual-loop current control based on the internal model principle and PI control, combined with related algorithms, and correcting the error of each cycle through software, Improve steady-state error accuracy. Using the control of the PI current inner loop, on the premise that there is no error in the steady-state accuracy, the rapid response of the PI controller to the error is used to comprehensively improve the dynamic response speed of the current. The combination of the two makes the current loop tracking control achieve no static purpose of error control.

The algorithm adopted in the present invention includes the harmonic current separation algorithm of the general control circuit of the active filter, and also includes the current tracking compound control algorithm of the current loop compound controller described in the present invention without static error, and the DC side voltage control algorithm, SPWM Generation algorithm, IGBT inverter module, networked LCL filter module. The compound control algorithm module includes the reference command current IRa of the harmonic separation module, the device output current ICa, the current outer loop control system (multi-cycle action controller) and the current inner loop control system (PI controller). First, simply point out the working principle of the whole machine as follows: the general control circuit of the parallel active filter obtains the voltage signal and current signal of the power grid on the sampling side, performs analog signal conditioning, and sends the conditioned analog quantities to the digital processing chip for digital conversion. Send the converted result to the processor to calculate the phase and frequency, use the calculated phase and frequency to separate the harmonic current, reactive power and unbalanced current, and output the separated reference command current IRa and the device The current ICa is input into the current loop composite controller of the present invention, and through the current loop composite controller, the processed target value is given to the SPWM generator to generate a PWM signal to drive the IGBT to perform the inverter output of the reference command current IRa, Through the smoothing reactor and grid-connected reactance, the output current is sent to the system to generate a vector with the opposite direction and the same magnitude as the harmonic current in the system to eliminate the harmonic current in the system, thereby improving the power supply quality of the power grid system.

In view of the AC characteristics of the harmonic current and the shortcomings of the traditional tracking controller, the present invention specifically aims at the tracking error problem existing in the current loop, and proposes a control algorithm for quickly correcting the error, so that the entire harmonic current approaches the harmonic current existing in the system , through the compound control of the current loop, the fast output without static error and the current value of the system harmonic current are equal in magnitude and opposite in direction, so as to completely eliminate the harmonic current in the system. It solves the disadvantage that the traditional current loop controller has static error in tracking and cannot completely eliminate system harmonics, thereby improving the compensation performance of the equipment and optimizing the overall performance of the active filter.

The above are only descriptions of the preferred embodiments of the present invention, but should not be construed as limiting the claims. The present invention is not limited to the above embodiments, and all changes made within the protection scope of the independent claims of the present invention are within the protection scope of the present invention.

Claims (10)

1. a kind of composite control type active filter based on high compensation precision electric current loop, samples on the electrical network of side including being connected to Active filter universal control circuit, described active filter universal control circuit includes harmonic wave separation module；Its feature exists In the output end of described harmonic wave separation module passes sequentially through electric current loop composite controller, filtration module and is connected into load-side electrical network； The output end of described filtration module connects the input of electric current loop composite controller.

2. a kind of composite control type active filter based on high compensation precision electric current loop according to claim 1, it is special Levy and be, described electric current loop composite controller includes electric current outer shroud control system and current inner loop control system.

3. a kind of composite control type active filter based on high compensation precision electric current loop according to claim 2, it is special Levy and be, described electric current outer shroud control system includes forward path modulating unit and backward channel feedback unit.

4. a kind of composite control type active filter based on high compensation precision electric current loop according to Claims 2 or 3, its It is characterised by, described current inner loop control system includes current inner loop PI control unit.

5. it is a kind of as claimed in claim 4 based on high compensation precision electric current loop composite control type active filter controlling party Method, it is characterised in that comprise the following steps：

S1, described active filter universal control circuit collection line voltage, load current and device output current are simultaneously processed, Described harmonic wave separation module output reference instruction electric current, by described reference instruction electric current and device output current institute is input to The electric current loop composite controller computing stated；

S2, described reference instruction electric current and device output current carry out difference operation, obtain error amount error, error amount Error passes through respectively forward path in the electric current outer shroud control system of described electric current loop composite controller based on internal model principle Modulating unit and backward channel feedback unit are processed, and obtain the error amount △ error1 in cycle；

The current inner loop PI control unit of the current inner loop control system described in S3, the error amount △ error1 Jing in cycle is processed, Mutation Error is adjusted using PI controls.

6. the control of a kind of composite control type active filter based on high compensation precision electric current loop according to claim 5 Method, it is characterised in that：In described step S1,

S1.1, collection line voltage, load current and device output current, pass through on the basis of sampling side network system voltage Related phase-lock-loop algorithm is processed, and draws the phase angle Ф of the A phases of network system, and asks sine value and cosine to phase angle Ф Value；

The sine value and cosine value at the phase angle of the positive sequence of the A phases that S1.2, the load current of collection and step S1.1 are obtained, Jing Harmonic wave separation algorithm is crossed, the load current to gathering carries out harmonic wave separation, the amplitude phase, vector harmonic current each time Direction is separated, and then harmonic wave each time is added and obtains reference instruction electric current；

S1.3, device output current reach the scope of AD inputs, through AD through outside Acquisition Circuit and the modulate circuit of correlation Reference instruction electric current after digitlization and in previous step is input to together described electric current loop composite controller.

7. the control of a kind of composite control type active filter based on high compensation precision electric current loop according to claim 5 Method, it is characterised in that：Described harmonic wave separation algorithm is FFT or DQ0 or PR.

8. the control of a kind of composite control type active filter based on high compensation precision electric current loop according to claim 5 Method, it is characterised in that：In described step S2,

S2.1. reference instruction electric current and device output current carry out obtaining error amount error after difference operation, by error and base Carry out obtaining sum with computing in the correction value of backward channel compound function Q (Z) * S (Z) of internal model principle；

S2.2. described sum values are inputed to into the first cycle time delay integration device function S (n), gives cycle points following time delay Integral function amendment, through revised numerical value be △ error；

S2.3. △ error obtained in the previous step are sent into into second-order low-pass filter function C (Z), through the wave filter △ is obtained error1。

9. the control of a kind of composite control type active filter based on high compensation precision electric current loop according to claim 8 Method, it is characterised in that：The feedback of described backward channel, sequentially passes through auxiliary compensation device Q (Z) and cycle points time delay amendment Function S (Z) process, obtains compound function Q (Z) * S (Z).

10. the control of a kind of composite control type active filter based on high compensation precision electric current loop according to claim 5 Method processed, it is characterised in that：In described step S3,

3.1. △ error1 are done with described reference instruction electric current and obtains sum1 with computing, sum1 passes through defeated with described device Go out electric current and do difference operation to obtain △ error2；

3.2. by △ error2 by described current inner loop PI controller to error summary responses, carry out quickly dynamic and ring Should.