US-12620914-B2 - Systems and methods for control of nonisolated bidirectional power converters

US12620914B2US 12620914 B2US12620914 B2US 12620914B2US-12620914-B2

Abstract

Disclosed are implementations that include a power converter system and method including an N-phase power converter stage having to an alternating current (AC) side and a direct current (DC) side, with N≥1. The system and method further include an N-phase LC filter comprising one or more capacitors, wherein respective one or more neutral points of the one or more capacitors are electrically connected to a DC negative terminal of a DC source. A control system drives power switching elements of the N-phase power converter stage to convert received power and to output converted power. The control system drives the power switching elements using variable frequency soft switching at a frequency of at least 20 kHz. The power converter may have bidirectional operation to operate in a traction mode to drive a motor or a charging mode to charge a DC source.

Inventors

Matthias Preindl
Liwei Zhou
William-Michael Eull
Matthew Jahnes

Assignees

THE TRUSTEES OF COLUMBIA UNIVERSITY IN THE CITY OF NEW YORK

Dates

Publication Date: 20260505
Application Date: 20220727

Claims (20)

1 . A non-isolated power converter system, the system comprising: an N-phase power converter stage having to an alternating current (AC) side and a direct current (DC) side, with N≥1; an N-phase LC filter comprising one or more capacitors, wherein respective one or more neutral points of the one or more capacitors are electrically connected to a DC negative terminal of a DC source; and a control system configured to drive power switching elements of the N-phase power converter stage to convert received power and to output converted power, the control system configured to drive the power switching elements using variable frequency soft switching at a frequency of at least 20 kHz, where the control system is a cascaded control system comprising: a central controller including a processing unit, the central controller configured to: determine rotational reference frame targets, and generate N control reference targets; and at least one local controller, each of the at least one local controller including a local processing unit, each of the at least one local controller configured to: receive a control reference target of the N control reference targets, and drive a portion of the power switching elements, associated with the local controller, in accordance with the control reference target.
2 . The power converter system of claim 1 , wherein, to drive the portion of the power switching elements in accordance with the control reference target, each of the at least one local controller is configured to: implement model predictive control (MPC) to generate control signaling for the portion of the power switching elements.
3 . The power converter system of claim 1 , wherein the central controller is further configured to: receive at least one electrical operational characteristic from each of the at least one local controller, the electrical operational characteristics in a stationary reference frame; convert the at least one electrical operational characteristic to the rotating reference frame; and determine a direct axis (D-axis) component and a quadrature axis (Q-axis) component of the rotational reference frame targets based on the at least one electrical operational characteristic in the rotating reference frame.
4 . The power converter system of claim 3 , wherein the central controller is further configured to: determine a zero-sequence component target of the rotational reference frame targets based on a DC offset of half a DC voltage across a positive terminal of the DC source and the negative terminal of the DC source.
5 . The power converter system of claim 3 , wherein the central controller is further configured to: determine a zero-sequence component target of the rotational reference frame targets based on a DC offset and multiple of N-th phase harmonic injection.
6 . The power converter system of claim 5 , wherein, to generate the N control reference targets in the stationary reference frame based on the rotational reference frame targets, the central controller is further configured to: convert the D-axis voltage component, Q-axis voltage component, and the zero-sequence component target to the stationary reference frame.
7 . The power converter system of claim 1 , wherein the power switching elements include, for each phase of the N phases of the power converter stage, a high-side element and a low-side element connected at a midpoint node, and wherein the midpoint node of each phase of the N phases of the power converter stage is coupled to a respective LC filter of the N-phase LC filter that includes (i) an inductor coupled between the midpoint node and a filter node of the respective LC filter, and (ii) a capacitor, of the one or more capacitors of the N-phase LC filter, coupled between the filter node of the respective LC filter and the negative DC terminal.
8 . The power converter system of claim 7 , wherein each respective LC filter further includes a second capacitor coupled between the filter node of the respective LC filter and a positive DC terminal of the DC source.
9 . The power converter system of claim 7 , further comprising: an N-phase common mode inductor coupled between the filter nodes and N interface terminals.
10 . The power converter system of claim 9 , further comprising: an N-phase motor coupled to the N interface terminals.
11 . The power converter system of claim 9 , wherein the N interface terminals include N motor connection points for coupling to an N-phase motor and N grid connection points for coupling to an N-phase power grid.
12 . The power converter system of claim 11 , further comprising a traction mode and a charging mode, wherein: when in the traction mode, the power converter is configured to convert DC power from the DC source to AC power on the N motor connection points to drive the N-phase motor; and when in the charging mode, the power converter is configured to convert AC power from the N grid connection points to DC power to charge the DC source.
13 . The power converter system of claim 1 , wherein a sensor configured to sense a first electrical characteristic of a first component of the N-phase LC filter selected from a group of a switch-side inductor and a capacitor, and to generate sensor data indicative of the first electrical characteristic; and wherein the control system is further configured to: receive the sensor data from the sensor, perform state estimation, based on the sensor data, to estimate a second electrical characteristic of a second component of the N-phase LC filter that is different from the first component, and to drive the power switching elements based on the second electrical characteristic.
14 . The power converter system of claim 1 , wherein to drive the power switching elements using variable frequency soft switching, the control system is configured to determine a switching frequency for driving the power switching elements of the converter based on an electrical characteristic of the N-phase LC filter.
15 . The power converter system of claim 1 , further comprising: N power converter modules, where N>1, each power converter module including: a positive direct current (DC) terminal and a negative DC terminal of the DC side of the N-phase power converter stage, a power switching element pair including a high side power switching element coupled to the positive DC terminal and a low side power switching element coupled to the negative DC terminal, wherein the high side power switching element and the low side power switching element are coupled together at a midpoint node, an LC filter of the N-phase LC filter including a capacitor of the one or more capacitors and an inductor, the inductor coupled between the midpoint node and the capacitor, the capacitor coupled between the inductor and the negative DC terminal, a local controller of the at least one local controllers configured to drive the power switching element pair, wherein the power switching element pair is the portion of power switching elements associated with the local controller, and a circuit board having located thereon the positive and negative DC terminals, the power switching element pair, the LC filter, and the local controller; wherein the positive DC terminal of each of the N power converter modules are coupled together and the negative DC terminal of each of the one or more power converter modules are coupled together.
16 . A method of converting power, the method comprising: receiving input power, by an N-phase power converter stage, from an alternating current (AC) side or a direct current (DC) side, with N≥1; filtering, by an N-phase LC filter comprising one or more capacitors, at the AC side of the N-phase power converter stage, wherein respective one or more neutral points of the one or more capacitors are electrically connected to a DC negative terminal of a DC source; driving, by a control system that is a cascaded control system, power switching elements of the N-phase power converter stage to convert the input power and to output converted power, the control system configured to drive the power switching elements using variable frequency soft switching at a frequency of at least 20 kHz, determining, by a central controller of the cascaded control system, rotational reference frame targets; generating, by the central controller, N control reference targets; receiving, by each of at least one local controller of the cascaded control system, a control reference target of the N control reference targets; and driving a portion of the power switching elements, associated with the local controller, in accordance with the control reference target.
17 . The method of claim 16 , wherein driving, by each of the at least one local controller, the portion of the power switching elements in accordance with the control reference target, comprises: implementing, by each of the at least one local controller, model predictive control (MPC) to generate control signaling for the portion of the power switching elements.
18 . The method of claim 16 , further comprising: receiving, by the central controller, at least one electrical operational characteristic from each of the at least one local controller, the electrical operational characteristics in a stationary reference frame; converting, by the central controller, the at least one electrical operational characteristic to the rotating reference frame; and determining, by the central controller, a direct axis (D-axis) component and a quadrature axis (Q-axis) component of the rotational reference frame targets based on the at least one electrical operational characteristic in the rotating reference frame.
19 . The method of claim 18 , further comprising: determining, by the central controller, a zero-sequence component target of the rotational reference frame targets based on a DC offset of half a DC voltage across a positive terminal of the DC source and the negative terminal of the DC source.
20 . The method of claim 18 , further comprising: determining, by the central controller, a zero-sequence component target of the rotational reference frame targets based on a DC offset and multiple of N-th phase harmonic injection.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS This application represents the U.S. national stage entry of International Application No. PCT/US2022/038561 filed Jul. 27, 2022, which claims priority to U.S. Provisional Application No. 63/226,136, filed on Jul. 27, 2021, U.S. Provisional Application No. 63/242,840, filed on Sep. 10, 2021, U.S. Provisional Application No. 63/345,896, filed May 25, 2022, U.S. Provisional Application No. 63/351,768, filed on Jun. 13, 2022, U.S. Provisional Application No. 63/226,059, filed Jul. 27, 2021, U.S. Provisional Application No. 63/270,311, filed Oct. 21, 2021, and U.S. Provisional Application No. 63/319,122, filed Mar. 11, 2022, each of which is hereby incorporated by reference in its entirety. STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH This invention was made with government support under 1653574 awarded by the National Science Foundation. The government has certain rights in the invention. BACKGROUND Power converters of various types have been produced and used in many industries and contexts. Example power converters include alternating current (AC) to direct current (DC) rectifiers, DC to AC inverters, and DC to DC converters. AC to DC rectifiers, also referred to as AC/DC rectifiers, converter AC power to DC power. DC to AC inverters, also referred to as DC/AC inverters, convert DC power to AC power. Power converters can be used for various purposes, such as rectifying AC power from an AC grid power source to DC power for charging a battery, or inverting DC power from a battery to AC power to drive a motor or supply AC power to an AC grid. Further, power converters can be used in various contexts, such as in or connected to an electric vehicle, an engine generator, solar panels, and the like. SUMMARY Power converters may be described in terms of power conversion efficiency, power density, and cost, among other characteristics. Generally, it is desirable to have power converters with higher power efficiency, higher power density, and lower cost. A highly efficient power converter is able to convert power (e.g., AC to DC, DC to AC, and/or DC to DC) without significant losses in energy. A low efficiency power converter experiences higher losses in energy during the power conversion. Such energy losses may manifest as heat generated by the power converter while converting power, for example. Power efficiency for a power converter, inductor, or other electronic component may be expressed as a percentage between 0 and 100% and determined based on the power input to the component and the power output from the component using the equation: Power⁢ Efficiency=Power⁢ OutPower⁢ In. A power converter with high power density has a high ratio of power output by the power converter compared to the physical space occupied by the power converter. The power density can be calculated using the equation: Power⁢ Density=Power⁢ OutVolume⁢ of⁢ Power⁢ Converter. Energy costs, including monetary costs and environmental costs, continue to be an important factor across many industries that incorporate power converters. Accordingly, even slight increases (e.g., of tenths of a percent) in power efficiency for a power converter can be significant and highly desirable. Similarly, reductions in materials and size of power converters can be significant and highly desirable, allowing reductions in costs and physical space to accommodate power converters in systems that incorporate power converters. In grid-connected power converter applications, such as electric vehicle (EV) chargers and photovoltaic (PV) power supplies, leakage current and DC bus utilization are factors that influence the performance. For the leakage current issue, a bulky line frequency transformer is typically installed to block the leakage path at the point of common coupling (PCC) which increases the cost, volume, and weight of the system. For the DC bus utilization, the DC bus voltage needs to be stepped up to be at least twice of the grid voltage amplitude to avoid saturation issue which brings extra switching losses and challenges to the switch voltage tolerance capability. Bidirectional power converters may be used to both charge a DC source using AC power and drive AC motors using DC power from the DC source. Such power converters, when included in an electric vehicle, may also be referred to as an integrated charger. An integrated charger may both be used as a primary charging interface for a battery of the electric vehicle, and also as the traction inverter to drive a motor of the electric vehicle. By using a dual-purpose power converter, rather than separate charger converter and traction inverter, material costs and size may be reduced. However, relative to dedicated power converters, dual-purpose power converters add complexities in designing an efficient and effective converter for both charging and traction modes. Further, the design factors extend beyond efficiency concerns because, without proper d