A Single-Stage Three-Phase Energy Storage Converter Charging Current Ripple Suppression Method Applicable to Distorted Grid Voltage

Abstract

The present invention discloses a method for suppressing the charging current ripple of a single-stage three-phase energy storage converter applicable to distorted grid voltages. Based on the basic control link of the traditional converter, the present invention adds a three-phase harmonic current control calculation module to obtain the phase and amplitude of the corresponding harmonic waves of the required order, and uses a harmonic current controller for control, which can suppress the charging current ripple of the energy storage battery. The present invention solves the problem that in the case of distorted grid voltages, the fifth harmonic voltage causes a six-times power frequency ripple in the DC-side current of the single-stage three-phase energy storage converter. This method does not require additional circuits, which is beneficial to reducing the loss of the ripple current in the battery unit and extending the service life of the energy storage battery.

Description

Technical Field

[0001] The present invention relates to the field of power electronic converter control, and in particular to a method for suppressing the charging current ripple of a single-stage three-phase energy storage converter. Background Art

[0002] Traditional energy storage converters are connected to energy storage batteries and the power grid through a two-stage scheme of a DC-DC converter and a DC-AC converter. The charging current ripple caused by the power grid can be controlled by the DC-DC converter and does not flow into the battery. A single-stage DC-AC energy storage converter can reduce the volume of the energy storage system, reduce costs, and improve energy transfer efficiency. However, when the grid voltage is distorted, there are higher harmonic components such as the fifth and seventh harmonics. These harmonic components will cause ripple in the charging current of the energy storage battery, resulting in additional battery loss and reduced battery life. Summary of the Invention

[0003] The object of the present invention is to provide a method for suppressing the charging current ripple of a single-stage three-phase energy storage converter applicable to distorted grid voltages, so that when the grid voltage is distorted, the charging current ripple of the energy storage converter for the energy storage battery is small, and the cycle life of the energy storage battery is extended.

[0004] The present invention provides a method for suppressing the charging current ripple of a single-stage three-phase energy storage converter applicable to distorted grid voltages. Its main circuit includes an energy storage battery, a single-stage three-phase energy storage converter, and a distorted power grid; the energy storage battery is connected to the DC side of the energy storage converter, and the AC side of the energy storage converter is connected to the distorted power grid; its control part includes a PLL phase-locked loop module, a fundamental voltage extraction module, a fifth harmonic voltage extraction module, a fundamental current extraction module, a fifth harmonic current extraction module, a fifth harmonic current control calculation module, a current regulator A, a current regulator B, a dq inverse transformation module A, and a dq inverse transformation module B; the sampled grid voltages v a 、v b 、v c are connected to the input ends of the PLL phase-locked loop module, the fundamental voltage extraction module, and the fifth harmonic voltage extraction module; the sampled inductor currents i a 、i b 、i c are connected to the input ends of the fundamental current extraction module and the fifth harmonic current extraction module; the output end of the PLL phase-locked loop module outputs a phase angle θ and is connected to the input ends of the fundamental voltage extraction module, the fundamental current extraction module, the fifth harmonic voltage extraction module, the fifth harmonic current control calculation module, and the dq inverse transformation module A; the fundamental voltage extraction module outputs the d-axis fundamental voltage v d (1) and the q-axis fundamental voltage v q (1) ,where v d (1)Connected to the input terminals of the fifth - harmonic voltage extraction module and the fifth - harmonic current control calculation module, v q (1) Connected to the input terminal of the fifth - harmonic voltage extraction module; the fifth - harmonic voltage extraction module outputs the d - axis fifth - harmonic voltage v d (5) Connected to the input terminal of the fifth - harmonic current control calculation module; the fundamental - wave current extraction module outputs the d - axis fundamental - wave current i d (1) and the q - axis fundamental - wave current i q (1) , where i d (1) Connected to the input terminals of the fifth - harmonic current control calculation module, the fifth - harmonic current extraction module, and current regulator A, i q (1) Connected to the input terminals of the fifth - harmonic current extraction module and current regulator A; the fifth - harmonic current extraction module outputs the d - axis fifth - harmonic current i d (5) and the q - axis fifth - harmonic current i q (5) Both are connected to the input terminal of current regulator B; the fifth - harmonic current control calculation module outputs the d - axis fifth - harmonic current reference value I dref (5) and the fifth - harmonic current dq - axis phase - locked angle where I dref (5) Connected to the input terminal of current regulator B, Connected to the input terminals of the fifth - harmonic current extraction module and dq inverse transformation module B; the other input terminal of current regulator B is the q - axis fifth - harmonic current reference value I qref (5) , and outputs the d - axis fifth - harmonic modulation wave u md (5) and the q - axis fifth - harmonic modulation wave u mq (5) , both are connected to the input terminal of dq inverse transformation module B; the other two input terminals of current regulator A are the d - axis and q - axis fundamental - wave current reference values I dref (1) and I qref (1) , and outputs the d - axis fundamental - wave modulation wave u md (1) and the q - axis fundamental - wave modulation wave u mq (1) , both are connected to the input terminal of dq inverse transformation module A; the three - phase fifth - harmonic modulation waves u ma (5) 、u mb (5) 、umc (5) and the three-phase fundamental modulation wave u output by the dq inverse transformation module A ma (1) 、u mb (1) 、u mc (1) After addition, the final three-phase modulation wave u ma 、u mb 、u mc is obtained.

[0005] In the above control scheme, the calculation method of the d-axis fifth harmonic current reference value I dref (5) output by the fifth harmonic current calculation and control module is as follows:

[0006]

[0007] where ω is the angular frequency of the grid voltage, and L is the inductance value of the inductor between the three-phase grid and the three-phase energy storage converter.

[0008] The calculation method of the fifth harmonic current dq-axis phase-locked angle output by the fifth harmonic current calculation and control module is as follows:

[0009]

[0010] where V1 is the amplitude of the grid fundamental voltage.

[0011] The other input terminal I qref (5) of the current regulator B should satisfy

[0012] I qref (5) = 0

[0013] Compared with the prior art, the present invention has the following beneficial effects:

[0014] By adopting the control method of the present invention, the charging current ripple can be suppressed when the single-stage three-phase energy storage converter charges the energy storage battery under the distorted grid voltage. Therefore, the single-stage three-phase energy storage converter can operate under a wider range of grid conditions without causing additional losses to the battery or affecting the battery life. At the same time, the control of the present scheme when the grid voltage is not distorted will not affect the normal operation of the traditional scheme, nor does it require additional hardware devices, thereby ensuring the power density of the energy storage system. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 is a connection diagram of the single-stage three-phase energy storage converter with the energy storage battery and the grid;

[0016] Figure 2 The distorted three-phase grid voltage waveform of the specific embodiment;

[0017] Figure 3 The battery charging current waveform of the traditional scheme under the specific embodiment;

[0018] Figure 4 The proposed single-stage three-phase energy storage converter charging current ripple suppression scheme under the distorted grid;

[0019] Figure 5 The battery charging current waveform after adopting the method of the present invention under the specific embodiment; Detailed implementation manners

[0020] The present invention will be described in detail below in conjunction with specific embodiments and the accompanying drawings. The following embodiments will help those skilled in the art to further understand the invention, but do not limit the invention in any form. It should be noted that any deformation or improvement made without departing from the inventive concept is within the protection scope of the present invention.

[0021] Referring to Figure 1 , the main circuit includes an energy storage battery 201, a single-stage three-phase energy storage converter 202, and a distorted grid 203; the energy storage battery is connected to the DC side of the energy storage converter, and the AC side of the energy storage converter is connected to the distorted grid; where v a , v b , v c are the three-phase grid voltages, i a , i b , i c are the three-phase inductor currents, all sampled to the control part for control, and the inductance values of the filter inductors L a , L b , L c are all L = 380 μH.

[0022] Select a system as the implementation object of this control method. Considering that the fundamental grid voltage amplitude is v d (1) = 220 V (rms), and the grid voltage is distorted. Assuming that the fifth harmonic voltage amplitude is 11 V (rms), at this time, the distorted three-phase grid line voltages v ab (t), v bc (t), v ca (t) within a power frequency period T s are as shown in Figure 2 , the energy storage battery voltage is V battery = 800 V. At this time, the energy storage converter works in the state of charging the energy storage battery with a power P = 100 kW, then the expression of the energy storage battery charging current i dc (t) can be written as

[0023]

[0024] Wherein

[0025]

[0026] V1 is the amplitude of the fundamental grid voltage, I1 is the amplitude of the fundamental inductor current, V5 is the amplitude of the fifth harmonic grid voltage, I5 is the amplitude of the fifth harmonic inductor current, and ω is the working angular frequency of the grid voltage;

[0027] According to the above expressions, the charging current i dc (t) within a power frequency period T s has a waveform as shown in Figure 3 where there is a current ripple of six times the power frequency and a relatively large amplitude. This current will be injected into the energy storage battery along with the charging current, causing additional losses to the battery and shortening its lifespan.

[0028] Adopting the control method shown in reference Figure 4 , the control part includes a PLL phase-locked loop module 101, a fundamental voltage extraction module 102, a fifth harmonic voltage extraction module 103, a fundamental current extraction module 104, a fifth harmonic current extraction module 105, a fifth harmonic current control calculation module 106, a current regulator A 107, a current regulator B 108, a dq inverse transformation module A 109, and a dq inverse transformation module B 110; Sampling the grid voltages v a , v b , v c and connecting them to the input ends of the PLL phase-locked loop module 101, the fundamental voltage extraction module 102, and the fifth harmonic voltage extraction module 103; Sampling the inductor currents i a , i b , i c and connecting them to the input ends of the fundamental current extraction module 104 and the fifth harmonic current extraction module 105; The output end of the PLL phase-locked loop module 101 outputs a phase angle θ and connects it to the input ends of the fundamental voltage extraction module 102, the fundamental current extraction module 104, the fifth harmonic voltage extraction module 103, the fifth harmonic current control calculation module 106, and the dq inverse transformation module A 109; The fundamental voltage extraction module 102 outputs the d-axis fundamental voltage v d (1) and the q-axis fundamental voltage v q (1) , where v d (1) is connected to the input ends of the fifth harmonic voltage extraction module 103 and the fifth harmonic current control calculation module 106, and v q (1)is connected to the input terminal of the fifth harmonic voltage extraction module 103; the fifth harmonic voltage extraction module 103 outputs the d-axis fifth harmonic voltage v d (5) is connected to the input terminal of the fifth harmonic current control calculation module 106; the fundamental wave current extraction module 104 outputs the d-axis fundamental wave current i d (1) and the q-axis fundamental wave current i q (1) , where i d (1) is connected to the input terminals of the fifth harmonic current control calculation module 106, the fifth harmonic current extraction module 105, and the current regulator A107, and i q (1) is connected to the input terminals of the fifth harmonic current extraction module 105 and the current regulator A107; the fifth harmonic current extraction module 105 outputs the d-axis fifth harmonic current i d (5) and the q-axis fifth harmonic current i q (5) are both connected to the input terminal of the current regulator B108; the fifth harmonic current control calculation module 106 outputs the d-axis fifth harmonic current reference value I dref (5) and the fifth harmonic current dq-axis phase-locked angle where I dref (5) is connected to the input terminal of the current regulator B108, is connected to the input terminals of the fifth harmonic current extraction module 105 and the dq inverse transformation module B110; the other input terminal of the current regulator B108 is the q-axis fifth harmonic current reference value I qref (5) , and outputs the d-axis fifth harmonic modulation wave u md (5) and the q-axis fifth harmonic modulation wave u mq (5) , which are both connected to the input terminal of the dq inverse transformation module B110; the other two input terminals of the current regulator A107 are the d-axis and q-axis fundamental wave current reference values I dref (1) and I qref (1) , where the reference values I dref (1) and I qref (1) are determined by the active current and reactive current required during the actual operation of the three-phase energy storage converter, and outputs the fundamental wave modulation wave d-axis fundamental wave modulation wave u md (1) and the q-axis fundamental wave modulation wave u mq (1), are all connected to the input end of the dq inverse transformation module A109; the three-phase fifth harmonic modulation wave u output by the dq inverse transformation module B110 ma (5) , u mb (5) , u mc (5) and the three-phase fundamental wave modulation wave u output by the dq inverse transformation module A109 ma (1) , u mb (1) , u mc (1) are added together to obtain the final three-phase modulation wave u ma , u mb , u mc .

[0029] A specific implementation manner of each module in the control part can be referred to as follows:

[0030] The phase-locked loop module can obtain the phase angle θ of the grid voltage through the software phase-locked algorithm.

[0031] The fundamental wave voltage extraction module can obtain the d-axis fundamental wave voltage v d (1) and the q-axis fundamental wave voltage v q (1) .

[0032] The fundamental wave current extraction module can obtain the d-axis fundamental wave current i d (1) and the q-axis fundamental wave current i q (1) .

[0033] Both the current regulator A and the current regulator B are composed of PI controllers, and the difference between the current reference value and the feedback value is controlled to zero through the PI controller to achieve current regulation.

[0034] The fifth harmonic voltage extraction module first performs dq inverse transformation on the d-axis fifth harmonic voltage v d (5) and the q-axis fifth harmonic voltage v q (5) to obtain the values of the fifth harmonic voltage on the abc axis v a (5) , v b (5) , v c (5) , and subtracts the sampled values to obtain the values of the total harmonic voltage on the abc axis v ah , v bh , vch Perform a dq inverse transformation on v ah with a phase angle of -5θ to obtain the d-axis fifth harmonic voltage v bh and the q-axis fifth harmonic voltage v ch d (5) q (5) d (5) .

[0035] The fifth harmonic current extraction module first performs a dq inverse transformation on the d-axis fifth harmonic current i d (5) and the q-axis fifth harmonic current i q (5) to obtain the values of the fifth harmonic current on the abc axes as i a (5) , i b (5) , i c (5) , and subtract the sampled values to obtain the values of the total harmonic current on the abc axes as i ah , i bh , i ch . Perform a dq inverse transformation on i ah , i bh , i ch with a phase angle of to obtain the d-axis fifth harmonic current i d (5) and the q-axis fifth harmonic current i q (5) .

[0036] The d-axis fifth harmonic current reference value I dref (5) output by the fifth harmonic current calculation and control module (106) can be calculated as

[0037]

[0038] The dq-axis phase-locked angle of the fifth harmonic current output by the fifth harmonic current calculation and control module (106) can be calculated as

[0039]

[0040] After adopting the control method of the present invention, the charging current i dc (t) becomes

[0041]

[0042] i dc (t) within one power frequency cycle is as shown in Figure 5 shown, compared withFigure 3 , the charging current ripple caused by the fifth harmonic voltage of the power grid can be effectively suppressed.

Claims

1. A method for suppressing the charging current ripple of a single-stage three-phase energy storage converter applicable to distorted grid voltage, characterized in that, The control part includes: a PLL phase-locked loop module, a fundamental voltage extraction module, a fifth harmonic voltage extraction module, a fundamental current extraction module, a fifth harmonic current extraction module, a fifth harmonic current control calculation module, a current regulator A, a current regulator B, a dq inverse transformation module A, and a dq inverse transformation module B; the sampled grid voltages v a 、v b 、v c are connected to the input ends of the PLL phase-locked loop module, the fundamental voltage extraction module, and the fifth harmonic voltage extraction module; the sampled inductor currents i a 、i b 、i c are connected to the input ends of the fundamental current extraction module and the fifth harmonic current extraction module; the output end of the PLL phase-locked loop module outputs a phase angle θ, which is connected to the input ends of the fundamental voltage extraction module, the fundamental current extraction module, the fifth harmonic voltage extraction module, the fifth harmonic current control calculation module, and the dq inverse transformation module A; the fundamental voltage extraction module outputs the d-axis fundamental voltage v d (1) and the q-axis fundamental voltage v q (1) ,v d (1) are connected to the input ends of the fifth harmonic voltage extraction module and the fifth harmonic current control calculation module, and v q (1) is connected to the input end of the fifth harmonic voltage extraction module; the fifth harmonic voltage extraction module outputs the d-axis fifth harmonic voltage v d (5) which is connected to the input end of the fifth harmonic current control calculation module; the fundamental current extraction module outputs the d-axis fundamental current i d (1) and the q-axis fundamental current i q (1) ,i d (1) are connected to the input ends of the fifth harmonic current control calculation module, the fifth harmonic current extraction module, and the current regulator A, and i q (1) is connected to the input ends of the fifth harmonic current extraction module and the current regulator A; the fifth harmonic current extraction module outputs the d-axis fifth harmonic current i d (5) and the q-axis fifth harmonic current i q (5) are both connected to the input end of the current regulator B; the fifth harmonic current control calculation module outputs the d-axis fifth harmonic current reference value I dref (5) and the fifth harmonic current dq-axis phase-locked angle I dref (5) Connected to the input terminal of current regulator B, Connected to the input terminals of the fifth - harmonic current extraction module and dq inverse transformation module B; Another input terminal of current regulator B is the q - axis fifth - harmonic current reference value I qref (5) , and outputs the d - axis fifth - harmonic modulation wave u md (5) and the q - axis fifth - harmonic modulation wave u mq (5) , both of which are connected to the input terminals of dq inverse transformation module B; The other two input terminals of current regulator A are the d - axis and q - axis fundamental current reference values I dref (1) and I qref (1) , and outputs the d - axis fundamental modulation wave u md (1) and the q - axis fundamental modulation wave u mq (1) , both of which are connected to the input terminals of dq inverse transformation module A; The three - phase fifth - harmonic modulation waves u ma (5) 、u mb (5) 、u mc (5) output by dq inverse transformation module B and the three - phase fundamental modulation waves u ma (1) 、u mb (1) 、u mc (1) output by dq inverse transformation module A are added to obtain the final three - phase modulation waves u ma 、u mb 、u mc ; The said I dref (5) and The calculation method is as follows: Where, ω is the angular frequency of the grid voltage, L is the inductance value of the inductor between the three-phase grid and the three-phase energy storage converter; V1 is the amplitude of the fundamental grid voltage.

2. A method for suppressing the charging current ripple of a single-stage three-phase energy storage converter applicable to distorted grid voltage according to claim 1, characterized in that, Another input terminal I of the current regulator B qref (5) shall satisfy: I qref (5) ＝0。

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