CN106655736A - Inverter power supply current limiting control method of variable controller parameters - Google Patents

Abstract

The invention discloses an inverter power supply current limiting control method of variable controller parameters. The treatment of the following steps is carried out circularly: (1) judging whether a load current effective value of an inverter power supply is greater than 3 times of rated load current, and if so, executing step (2); otherwise, executing step (3); (2) judging whether an output voltage effective value of the inverter power supply is smaller than a rated output voltage, and if so, executing step (4); otherwise, executing step (3); (3) setting an attenuation factor kc of the controller parameters as 1, and executing step (5); (4) correcting the attenuation factor kc of the controller parameters, and executing step (5); (5) filtering the attenuation factor kc by using a low pass filter; and according to the method disclosed by the invention, on the basis of the existing double-loop control method, the problems of poor quality of output waveforms under the working conditions of short circuit faults and switch in or switch out short circuit working conditions of the inverter power supply in the prior art can solved just by changing the controller parameters.

Description

A Current Limiting Control Method of Inverter Power Supply with Variable Controller Parameters

technical field

The invention belongs to the technical field of inverter power supply, and more specifically relates to a current-limiting control method of inverter power supply with variable controller parameters.

Background technique

For the inverter power supply, it is particularly important to ensure reliable and safe operation and good output waveform quality under complex working conditions (such as short-circuit faults). It is of great significance to take into account the reliability and power quality of the inverter power supply.

The existing technology often adopts a double-loop control strategy for the inverter power supply. When the system is working under a short-circuit fault, in order to limit the increase of the inductor current, the command value of the inductor current is restricted by a limiting method. However, after the current is limited by this method, since the output voltage is lower than the given value, and the outer loop controller has a larger gain at the fundamental wave, the waveform output by the outer loop controller is a waveform whose amplitude is much larger than the limiting value. The current command, after limiting, is a sine wave with a clipped top, which contains a large number of harmonics, resulting in poor output waveform quality. In addition to possibly causing adverse effects on the load, a large number of harmonics will also make it emit harsh noise when passing through the transformer. , heating intensifies, and even damages the transformer in serious cases.

In the existing technology, there is another way to switch between the voltage loop and the current loop, that is, when a short-circuit fault occurs, it will switch to the current loop to work to ensure that the system can work safely, but the command mutation caused by the switching process will cause the system output waveform to oscillate, especially The reason is that the dynamic performance is not good when suddenly adding or unloading to a short-circuit fault. In the existing technology, there is another way of combining software and hardware. First, hardware is used to quickly weaken the sudden increase of the inductor current, and then the double-loop control method is used to ensure the normal operation of the system. Although this method is safe and reliable, it requires additional hardware costs.

To sum up, in the prior art, when there is a short-circuit fault in the inverter power supply, after the inner loop command passes the limiter, the output waveform quality is poor, and a large number of harmonics pass through the transformer, causing it to emit ear-piercing noise and heat, and in severe cases even damage to transformers etc.

Contents of the invention

Aiming at the above defects or improvement needs of the prior art, the present invention provides a current-limiting control method of inverter power supply with variable controller parameters, the purpose of which is to solve the short-circuit failure, cut-in or cut-out short circuit of the inverter power supply in the prior art The output waveform quality is poor under working conditions.

In order to achieve the above object, according to one aspect of the present invention, a current limiting control method of inverter power supply with variable controller parameters is provided, and the following steps are performed according to the sampling period or control period time:

(1) Judging whether the effective value of the load current of the inverter power supply is greater than 3 times the rated load current, if so, proceed to step (2); if not, proceed to step (3);

(2) judging whether the effective value of the output voltage of the inverter power supply is less than the rated output voltage, if so, then enter step (4), if not, then enter step (3);

(3) Set the attenuation factor k _c of the controller parameter to 1, and enter step (5);

(4) Modify the attenuation factor k _c of the controller parameter, and enter step (5);

(5) The attenuation factor k _c is filtered by a low-pass filter.

Preferably, in the above inverter power supply current limiting control method, the rated load current is the effective value of the output current of the inverter power supply under normal working conditions, which is determined by the system capacity and the rated output voltage.

Preferably, in the current limiting control method of the inverter power supply, the rated output voltage is the effective value of the output voltage of the inverter power supply under normal working conditions.

Preferably, in the above-mentioned inverter power supply current limiting control method, the attenuation factor k _c of the controller parameter in step (4) =3I _LRMS /[A·(u _ref -U _ORMS )];

Among them, A is the gain value of the controller of the inverter power supply at the fundamental frequency, u _ref is the reference command voltage of the output voltage of the inverter power supply, U _ORMS is the effective value of the output voltage of the inverter power supply, and I _LRMS is the rated inductance of the inverter power supply current.

Preferably, the expression of the low-pass filter used in the above inverter current limiting control method is 1/(τs+1), where τ is a filter time constant, and s is a Laplace operator.

Generally speaking, compared with the prior art, the above technical solutions conceived by the present invention can achieve the following beneficial effects:

(1) The current-limiting control method of the inverter power supply with variable controller parameters provided by the present invention, on the basis of the existing double-loop control method, only needs to change the parameters of the outer loop controller in the inherent control structure, without adding additional hardware. It can ensure the safe operation of the system, reduce the cost and realize simple;

(2) In the current-limiting control method of inverter power supply with variable controller parameters provided by the present invention, the parameters of the outer loop controller can be adjusted in real time, and after the parameters are adjusted, a low-pass filter is used to alleviate the modulation caused by the sudden change of the controller parameters through filtering The wave value increases sharply to ensure the dynamic performance of the inverter during fault cut-in or cut-out;

(3) The current limiting control method of the inverter power supply with variable controller parameters provided by the present invention, when the inverter works under normal conditions, the parameters of the outer loop controller remain unchanged, thus ensuring the Steady state and dynamic performance.

Description of drawings

Fig. 1 is the schematic flow chart of the current-limiting control side of the inverter power supply with variable controller parameters provided by the embodiment;

Fig. 2 is the dual-loop control schematic diagram of inverter power supply in the embodiment;

Fig. 3 is the schematic diagram of the waveform of the load current and the output voltage when the inverter power supply short-circuit fault cuts in in the embodiment;

Fig. 4 is a schematic diagram of the waveforms of the load current and the output voltage when the inverter power supply is switched out due to a short-circuit fault in the embodiment.

detailed description

In order to make the object, technical solution and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described here are only used to explain the present invention, not to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not constitute a conflict with each other.

Aiming at the shortcomings of the existing dual-loop control technology for inverter power, the present invention proposes a current-limiting control method for inverter power with variable controller parameters, which can reduce the harmonic content of the command value of the inductance current when a short-circuit fault occurs when cut-in or cut-out. Therefore, the sine degree of the output voltage is higher when the inverter power supply is cut in or cut out.

In order to further illustrate the present invention, a current-limiting method of an inverter power supply with variable controller parameters provided below in conjunction with the embodiments and the accompanying drawings are specifically described as follows. The current-limiting method of an inverter power supply provided by the embodiment is shown in Figure 1. shown, including the following steps:

(1): Detect the load current of the inverter power supply, and judge whether the effective value of the load current is greater than 3 times the rated load current, if so, go to step (2); if not, go to step (3); the rated load current Determined according to system capacity and rated output voltage;

(2) judging whether the effective value of the output voltage of the inverter power supply is less than the rated output voltage, if so, then enter step (4), if not, then enter step (3);

(3) Set the attenuation factor k _c of the controller parameter to 1, and enter step (5);

(4) Modify the attenuation factor k _c of the controller parameter to make k _c =3I _LRMS /[A·(u _ref -U _ORMS )], and enter step (5);

Among them, A is the gain value of the controller 1 of the inverter power supply at the fundamental frequency, u _ref is the output voltage reference command voltage, U _ORMS is the effective value of the output voltage, and I _LRMS is the rated inductor current;

(5) The low-pass filter that adopts expression to be 1/(τs+1) carries out filter processing to attenuation factor _kc ; Wherein τ is filter time constant, and s is Laplacian operator; In the embodiment, τ Select the reciprocal of the cutoff frequency of the LC filter that is less than or equal to the inverter power supply.

As shown in Fig. 2, it is a schematic diagram of the double-loop control of the inverter power supply in the embodiment, and the double-loop control structure includes a subtractor 1, a subtractor 2, a controller 1, a controller 2, an amplifier 1 and an amplifier 2; 1 input terminal is the output voltage command value, the second input terminal of subtractor 1 is the output voltage of LC filter; the input terminal of controller 1 is connected to the output terminal of subtractor 1, and the output terminal of controller 1 is the output terminal of amplifier 1 Input terminal; the output terminal of amplifier 1 is the first input terminal of subtractor 2, and the second input terminal of subtractor 2 is the inductor current of LC filter; The input terminal of controller 2 is connected to the output terminal of subtractor 2, controls The output end of the device 2 is connected to the input end of the amplifier 2, and the output end of the amplifier 2 is connected to the input end of the LC filter;

The implementation of the double-loop control method with variable controller parameters provided by the embodiment in the above-mentioned double-loop structure is as follows: Controller 1 is a proportional fundamental resonance + harmonic resonance controller, which is used to suppress low-order harmonic voltage under normal working conditions ; Controller 2 is a proportional fundamental resonance controller, which is used to track the inverter side inductor current control and limit the output value of controller 1; in this control structure, the key lies in the proportional fundamental resonance of controller 1 The outer loop controller obtained by multiplying the control parameter by the attenuation factor of the amplifier 2 is variable, and the attenuation factor is selected according to the method provided in the embodiment and judged according to the flow chart in FIG. 1 .

In order to illustrate the embodiment more clearly, a specific example is used here for illustration; in the example, the rated power of the three-phase inverter power supply is 10kVA, the rated output voltage is 115V, the single-phase power is 3.3kVA, the rated output current is 29A, and the effective value of the inductor current is is 22.7A; the design index is to limit the current to 3 times the load current, and the effective value is 87A, so this effective value can be used as the threshold current for judging the short circuit in step (1); under the short circuit fault, the actual output voltage will decrease, while the national standard requires It is that the voltage under the fault is not lower than 110V, so in this instance, the threshold voltage threshold value of step (2) is set as 110V; Step (4) revises the attenuation factor of controller parameter, makes k _c =3I _LRMS /[A·(u _ref -U _ORMS )]; in this example, I _LRMS =22.7A, u _ref =115V, U _ORMS is the effective value of the sampling output voltage, and A is the fundamental wave gain value, which can be based on the open-loop Bode diagram under actual normal working conditions The decibel value at 50Hz is generally designed to be 40dB to ensure that there is no steady-state error. In this example, the value is 34dB; according to 20lg(A)=34dB, the gain value A=50 is solved;

Therefore, in step (4), the attenuation factor of the controller parameter is corrected to k _c =1.3/(115-U _ORMS ); considering that the division calculation in the actual DSP digital implementation will temporarily use a large amount of calculation time, the step (4) can be The linearization of the attenuation factor k _c can be implemented by referring to the relevant curve fitting method.

In the filtering step of step (5), the filter delay time is determined according to the resonant frequency of the LC filter. In the embodiment, the filter inductance L=280uH, the filter capacitor C=50uF, then the filter frequency is set as f=1345Hz;

In this embodiment, considering that the filter does not affect the actual system bandwidth, the value is slightly greater than or equal to the cut-off frequency of the LC filter, which can be approximated to τ≈7×10 ^-4 , and the filter expression is thus obtained as 1/(7×10 ⁻⁴ ·s+1).

Fig. 3 and Fig. 4 respectively have given the inverter power supply current-limiting control method with variable controller parameters provided by this embodiment, the output waveforms when the inverter power supply is short-circuited and cut in, wherein, Fig. 3 (a) is Schematic diagram of the waveform of the output voltage when the short-circuit cut-in fault of the inverter power supply occurs. Figure 3(b) is a schematic diagram of the waveform of the load current when the short-circuit cut-in fault of the inverter power supply occurs; among them, Figure 4(a) is a schematic diagram of the waveform of the load current when the short-circuit cut-in fault of the inverter power supply occurs. Figure 4(b) is a schematic diagram of the waveform of the load current when the inverter short-circuit cut-out fault occurs; it can be seen that the output voltage and the load current have no obvious overshoot in the whole process, indicating that the system is stable and safe Reliable operation; on the other hand, according to the cut-in or cut-out adjustment time, the whole process is about 15ms, which is less than the 30ms required by the national standard, indicating that the dynamic performance is guaranteed; from these two figures, we can also see the entire output voltage and load current The waveform has a good sine degree, indicating that the method of the embodiment ensures good output waveform quality.

It is easy for those skilled in the art to understand that the above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present invention, All should be included within the protection scope of the present invention.

Claims (5)

1. it is a kind of become controller parameter inverter Current limited Control method, it is characterised in that comprise the steps：

(1) whether the load current virtual value for judging inverter is more than 3 times of nominal load current, if so, then enters step (2)；If it is not, then entering step (3)；

(2) judge that the output voltage virtual value of inverter, whether less than rated output voltage, if so, then enters step (4), if It is no, then into step (3)；

(3) by decay factor k of controller parameter_c1 is set to, into step (5)；

(4) decay factor k of modifier controller parameter_c, into step (5)；

(5) using low pass filter to decay factor k_cIt is filtered process.

2. inverter Current limited Control method as claimed in claim 1, it is characterised in that the nominal load current is inversion Output current virtual value under power supply nominal situation.

3. inverter Current limited Control method as claimed in claim 1 or 2, it is characterised in that the rated output voltage is Output voltage virtual value under inverter nominal situation.

4. inverter Current limited Control method as claimed in claim 1 or 2, it is characterised in that the controller of the step (4) Decay factor k of parameter_c=3I_LRMS/[A·(u_ref-U_ORMS)]；

Wherein, A for inverter yield value of the controller at fundamental frequency, u_refRefer to for the reference of inverter output voltage Make voltage, U_ORMSFor inverter output voltage virtual value, I_LRMSFor inverter inductance ratings electric current.

5. inverter Current limited Control method as claimed in claim 1 or 2, it is characterised in that the low pass that step (5) is adopted The expression formula of wave filter is 1/ (τ s+1), and wherein τ is filter temporal constant, and s is Laplace operator.