Hereinafter, the present invention will be further described in detail with reference to the drawings and specific embodiments:
figure 1 It is a typical H-bridge PWM rectifier circuit in the prior art. When the voltage and current on the AC side of a single-phase converter fluctuate sinusoidally at the same frequency, a secondary pulsating power of the same magnitude as the system power will be generated, which appears as a secondary voltage ripple on the DC side. The expression of the sine variation of the AC side voltage and current is as follows:
When the converter is running at the ideal unit power factor, the switching tube frequency is much higher than the grid frequency, ignoring the loss and switching tube on and off time, assuming the voltage and waveform expressions are as follows:
Where Urms , Irms Is us, IsThe effective value of us, IsIs the instantaneous value of AC voltage and current
The energy stored on the AC inductor is expressed as:
The power on the inductor obtained by derivation is:
PL=-LIrms 2sin(2ωt) (Equation 3)
Since the total instantaneous power is balanced, the instantaneous power on the DC side can be expressed as:
It can be seen from the above formula that when the single-phase converter operates at unity power factor, its DC power is composed of a DC component and a double frequency component. The double frequency component will reduce the life of the device and also cause low-order harmonics in the alternating current. Therefore, it is necessary to construct a suitable algorithm and topological structure to solve this problem.
The existing methods for the secondary ripple of the DC bus of single-phase converters can be roughly divided into passive filtering methods and active filtering (APF) methods. The energy storage components used to compensate for the secondary pulsating power can be capacitors or capacitors. Can be inductance.
figure 2 It is an active filter topology in the prior art-secondary ripple suppression circuit, which is equipped with two fully-controlled switches S5And S6, And two diodes D1And D2, This circuit uses the inductor as the energy storage element to absorb and compensate the secondary pulsating power input by the converter. In this circuit, the current in the inductor can only flow in one direction, and the core loss is large, because in this circuit, the inductor current will rise sharply at its minimum value, in order to ensure that the inductor current has a large enough rate of change to track The command current and the value of the energy storage inductor cannot be too large, but the value of the inductance cannot be too small, because too small an inductance will increase the amplitude of the inductor current and its ripple will increase, and the current stress of the switch tube It will also be larger.
In order to solve the above problems, the present invention provides a single-phase converter DC bus voltage secondary ripple suppression circuit and method. A secondary harmonic auxiliary absorption circuit is built on the existing converter. The absorption circuit includes a first power switch. Device S5And the second power switching device S6,, a control unit, a filter inductor L2, A filter capacitor C2;
Among them, the first power switching device S5And the second power switching device S6In series, the first power switching device S5The other end of the DC bus capacitor C1One end of the connection, DC bus capacitor C1And the second power switching device S6,The other end of the series is connected, filter inductance L2And filter capacitor C2Connected in series with the second power switching device S6in parallel.
The present invention applies a proportional integral (PI) controller. Because the PI regulator cannot achieve zero error tracking of the AC signal, it also uses a proportional resonance (PR) controller, which is also based on the ratio P, Resonance R controls the system. Since the PR regulator has an infinite gain at the corresponding resonance point, the DC side voltage can have no steady-state error relative to the given voltage at the corresponding frequency.
Furthermore, the present invention proposes a method for suppressing the secondary ripple of the DC bus voltage of a single-phase converter. By building a sampling circuit for controlling the secondary harmonic absorption circuit, the filter inductor voltage UL2And filter inductor current IL2After sampling and conditioning, send to the controller;
Collect AC voltage UsAnd calculate its phase angle w;
Set the appropriate Uc-dc Command value
Calculate the RMS AC input voltage and current of the converter;
According to the AC voltage phase angle w, the preset C2Voltage DC component Uc-dc Command value and Irms , Urms , Solve for C2Double frequency component U in terminal pressurec-2nd :
C in auxiliary circuit2The end pressure expression is as follows:
U calculated in the above formulacThe theoretical calculation value is used as the Uc2Voltage command value Uc2_ref , Will Uc2The difference between the command value and the actual sampled value is used as the input of the first PI controller and the first PR controller, and the sum of the output of the first PI controller and the first PR controller is used as the capacitance current command Ic2_ref , Where the first PI controller controls the DC component in the command, and the first PR controller controls the AC component in the command, constructing such a composite controller to realize the auxiliary loop voltage outer loop control function;
Set the capacitance current command Ic2_ref And actual capacitance current Ic2The difference is used as the input of the second PI controller and the second PR controller, and the sum of the output of the second PI controller and the second PR controller is used as the modulation wave generated by the PWM pulse to finally generate the PWM pulse and control the second The first power switching device and the second power switching device in the sub-harmonic auxiliary absorption circuit realize Uccontrol.
The invention also relates to a single-phase converter DC bus voltage secondary ripple suppression circuit, including a secondary harmonic auxiliary absorption circuit, specifically including a first power switching device and a second power switching device, a control unit, and a filter Inductance, a filter capacitor.
Further, the control unit includes a first PI controller, a second PI controller, a first PR controller, a second PR controller, and a PWM generation module, wherein the first PI controller and the first PR controller Connected in parallel to form the first parallel circuit, the second PI controller and the second PR controller are connected in parallel to form a second parallel circuit. The first parallel circuit and the second parallel circuit are connected in series, and the second parallel circuit is connected to the PWM generation module. The generating module is used to generate PWM pulses for controlling the first power tube and the second power tube.
In order to make the DC bus capacitance c1The upper voltage is stable and there is no double frequency fluctuation, that is, no double frequency power, the auxiliary L is hereby constructed2C2The loop absorbs the double frequency power input from the AC side. When C2The voltage at both ends is Uc-dc +Uc-2nd , That is, when the DC component and the double frequency component are included, and the current contains only the double frequency component, the inductor L2There is quadruple frequency power, filter capacitor C2The quadruple frequency power and the double frequency power flow up. By setting the appropriate filter capacitor C2The voltage value of both ends can ensure the filter capacitor C2And filter inductor L2The quadruple frequency component is very small, which meets the harmonic requirements of the system.
The single-phase converter DC bus voltage secondary ripple suppression circuit and method proposed in this patent are also applicable to single-phase converters of other topologies, such as the figureFigure 5As shown, the DC bus voltage secondary ripple suppression circuit and method proposed in this patent are applied to the circuit diagram of a totem pole converter. Its DC bus voltage secondary ripple suppression controller is designed asFigure 4 Shown.
Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. After reading this application, those skilled in the art can make various modifications or changes to the present invention with reference to the above embodiments. The pending claims of the present invention are within the scope of protection.