EP-4738674-A1 - METHOD FOR CONTROLLING AC/DC CONVERTER FOR ELECTRIC VEHICLE CHARGING STATION

Abstract

The object of the invention is a method for controlling an AC/DC converter for an electric vehicle charging station, stabilising voltage in a DC circuit under voltage dip conditions during reduced capacitance in a DC link. A method for controlling an AC/DC converter for electric vehicle charging stations, stabilising voltage in a DC circuit under voltage dip conditions during reduced capacitance in a DC link constituting the first conversion stage of a converter power module CPM, with reduced capacitance C DC in the direct current link DC_link, for applications in electric vehicle charging stations DC_EVCS, involving the determination of reference currents I ref,αβ using the method of symmetrical components, characterised in that the reference currents I ref,αβ are determined in the control system, and the negative sequence component of the measured power grid voltage U conv is modified by introducing factors k, m and r allowing for arbitrary shaping of the converter current I conv .

Inventors

• CHUDZIK, Przemyslaw
• KRYNSKI, Arkadiusz
• KANIEWSKI, JACEK
• JARNUT, MARCIN
• STANDO, Dariusz
• Stynski, Sebastian
• Swiechowicz, Tomasz

Assignees

• Ekoenergetyka - Polska Spolka Akcyjna

Dates

Publication Date

20260506

Application Date

20251030

Claims (5)

1. A method for controlling an AC/DC converter for electric vehicle charging stations, stabilising voltage in a DC circuit under voltage dip conditions during reduced capacitance in a DC link constituting the first conversion stage of a converter power module CPM, with reduced capacitance C DC in the direct current link DC_link, for applications in electric vehicle charging stations DC_EVCS, involving the determination of reference currents I ref,αβ using the method of symmetrical components, characterised in that the reference currents I ref,αβ are determined in the control system, and the negative sequence component of the measured power grid voltage U conv is modified by introducing factors k, m and r allowing for arbitrary shaping of the converter current I conv , the determination of the reference currents I ref,αβ comprising the following steps: d) factor m is selected with regard to the limitations of the rated currents of the converter, and the values of the reference currents I ref,αβ are determined for two characteristic values of factor k: k = 0.5 and k = 1, wherein the effective values of the three-phase currents I a , I b , I c are determined after conversion from the α-β system to the a-b-c system (αβ/abc), whereas for the determined currents, with factor k = 0.5 and k = 1, the maximum values I max(k=0.5) and I max(k=1) are selected and, in order to limit the maximum value of current I max(k=1) from factor k = 1, the characteristics of changes in the effective value of current are approximated as a function of factor k, and subsequently, the determined values of the maximum currents from factor k equal to 0.5 I max(k=0.5) and k equal to 1 I max(k=1) are taken into account, and factor m resulting from the limit currents of the converter is calculated according to the following equation, its range being limited from a value of 0.5 to a value of 1: m = 0 , 5 + 0 , 5 I lim − I max k = 0 , 5 I max k = 1 − I max k = 0 , 5 ; e) factor r is determined as the ratio of the negative sequence component of the measured voltage U n to the positive sequence component U p , and the value of the ratio of the negative sequence component of the voltage U n to the positive sequence component U p (U n /U p ) and the linear dependence of factor r on the ratio of the negative and positive sequence components (U n /U p ) are determined using the following formula: r = 4 − 5 ⋅ U n U p where: U n U p = 0.5 U αd 2 + U αq 2 + U βd 2 + U βd 2 + U βq U αd − U βd U αq 0.5 U αd 2 + U αq 2 + U βd 2 + U βd 2 − U βq U αd − U βd U αq wherein the value of factor r is determined depending on the calculated symmetrical components of the supply voltage, and if the value of the ratio of the negative sequence component to the positive sequence component of the voltage (U n /U p ) takes on values below 0.6 (U n /U p < 0.6), factor r permanently takes on a value of 1 (r = 1), whereas, if the value of the ratio of the negative sequence component to the positive sequence component of the voltage (U n /U p ) is higher than 0.8 (U n /U p > 0.8), factor r permanently takes on a value of 0 (r = 0), and the value of factor r depends on the ratio of the negative to positive sequence symmetrical components of the voltage (U n /U p ); f) for factor m determined in step a) and the value of factor r from step b), the lower value is chosen, the reference currents I ref,αβ are subsequently calculated according to the following equation: I ref , α I ref , β = F 1 − k jk − jk 1 − k U α U β , where: F = U dc , avg I dc , ref 3 4 U αd 2 + U αq 2 + U βd 2 + U βq 2 1 − k − 2 k U βq U αd − U βd U αq .
2. The method for controlling a three-wire AC/DC converter according to claim 1, characterised in that factor k takes on a value between 0 and 1, so that a value of k = 0.5 is assumed under nominal conditions of power supply and no voltage dip; a value of factor k from a range of 0 < k ≤ 1 is assumed during a voltage dip.
3. The method for controlling a three-wire AC/DC converter according to claims 1 - 2, characterised in that the value of factor k equalling zero k = 0 results in generation of currents with shapes corresponding to voltages in the power grid PG, factor k with a value of 0.5 k = 0.5 results in elimination of the negative sequence component of the measured voltage U conv and generation of currents of the positive sequence component, and factor k with a value of 1 k = 1 results in setting the negative sequence component of the measured voltage U conv with an opposite sign.
4. The method for controlling a three-wire AC/DC converter according to claims 1 - 3, characterised in that in the event when the maximum value of the current I max(k=1) exceeds the converter current limit I lim , factor k is selected by approximating the characteristics of changes in the effective value of the converter current as a function of factor k, from a range of 0.5 to 1.
5. The method for controlling a three-wire AC/DC converter according to claims 1 - 4, characterised in that, for a normative voltage dip - that is, a 0% dip with a phase shift, the ripple in the direct current link DC_link is eliminated when the generation of sinusoidal currents I conv is insufficient, their distortion is introduced, further minimising the ripples by means of parameter P ratio ; which is determined from the ratio of the power setpoint from an RE regulator to an instantaneous value resulting from the reference current I ref,αβ and the power grid voltage U conv,αβ returned from a filter F2, according to the following equation: P ratio = I dc , ref ⋅ U dc , avg 3 2 I ref , α U αd + I ref , β U βd whereas the offset I αβ,u between the determined reference current I ref,αβ and the measured current I conv,αβ after passing through a current regulator RI is passed on to a space vector modulator SVM system in the AC/DC converter.

Description

TECHNICAL FIELD The object of the invention is a method for controlling an AC/DC converter for an electric vehicle charging station, stabilising voltage in a DC circuit under voltage dip conditions during reduced capacitance in a DC link. PRIOR ART Energy storages, i.e. batteries in electric vehicles, are characterised by various electrical parameters. Apart from capacitance, they are characterised by their rated voltage and maximum allowable charging current, i.e. the maximum charging power. Depending on the kind, class and type of vehicle, these parameters take on different values. Small and medium-sized passenger vehicles are typically equipped with batteries with voltages ranging from 200 to 500 VDC and capacitances not exceeding 90 kWh. Premium class vehicles are equipped with batteries with capacitances in excess of 90 kWh and voltages up to 900 VDC. Heavy-duty electric vehicles have energy storages with capacitances in hundreds of kWh and voltages even up to 1,500 VDC. The various voltage parameters of electric vehicle batteries require charging stations to provide a wide DC voltage output range of 200-1500 VDC. Apart from the voltage required by a vehicle, a charging station must also provide the required charging current, and thus meet the power demand of the vehicle. In order to carry out the charging process, charging stations are equipped with dedicated AC/DC electronic energy converters, converting alternating current energy into direct current energy with electrical parameters required by the vehicle. The AC/DC electronic energy converters intended for implementation in electric vehicle charging stations are often referred to as power conversion modules, or simply power modules. Due to a wide range of the required output voltage and the need to implement galvanic isolation between an AC input and a DC output, converter modules usually consist of two conversion stages. The first stage is implemented by an AC/DC converter, converting AC voltage from an AC power grid into DC voltage. The second stage is implemented by an isolated DC/DC converter, whose function includes adapting the output voltage level of the charging station to the requirements of the vehicle, and implementing galvanic isolation. In the classical approach, the ability to maintain charging power with voltage dips on the power grid side is achieved by using an energy buffer in a direct current link, between the output of an AC/DC converter, i.e. the output of the first conversion stage, and the input of a DC/DC converter, i.e. the input of the second conversion stage. This buffer is made in the form of high-capacitance electrolytic capacitors, capable of compensating for the energy deficiency during a voltage dip event. Even though it fulfils its function, this solution entails a number of drawbacks. One of them is the high failure rate of the energy buffer, which is made in the form of electrolytic capacitors. Due to the relatively high temperatures existing inside the converter modules, electrolytic capacitors undergo accelerated ageing processes, drastically shortening their service life and consequently leading to their damage and converter dysfunction. Electrolytic capacitors can be replaced with an energy buffer made using a different technology, e.g. by means of solid dielectric capacitors. Unfortunately, they have lower power density compared to electrolytic capacitors, requiring an increase in the size of the energy buffer, thus increasing the dimensions of the converter module. A large-sized energy buffer also impedes the flow of air cooling the converter, which contributes to worsening the cooling conditions of the converter. Furthermore, with constantly increasing power density of charging stations, solutions that increase the dimensions of the converter modules, and consequently the sizes of the stations, cease to be acceptable not only economically, but also commercially. Solutions known from the literature and industrial implementations for stabilising voltage in a DC circuit under voltage dip conditions are based primarily on the use of an energy buffer with adequately large capacitance in a DC link. There are also known solutions in which this buffer is reduced. However, reduction in capacitance at the output of an AC/DC converter causes problems with the stabilisation of DC voltage in the link, which is crucial for the operation of the second conversion stage - the DC/DC converter. Moreover, during a voltage dip on the power grid side, a reduced energy buffer at the output of the AC/DC converter implementing the first conversion stage results in the occurrence of unacceptable voltage ripples in the DC link. These ripples greatly exceed the values found under nominal operating conditions. Along with the voltage ripples, the lack of voltage stabilisation in the DC link constituting a power source for the DC/DC converter lead to a deficiency in the energy necessary for the second conversion stage - the DC/DC conver