Novel voltage source inverter control for unbalanced and nonlinear loads

Abstract

An interface circuit to dock an energy source to a power bus of a microgrid includes a switching inverter circuit, an output filter circuit coupled between an output of the three-phase inverter circuit and the power bus, and a control circuit loop to control switches of the switching inverter circuit. The control circuit loop is coupled to the output filter circuit and switching inverter and includes a proportional-integral oscillator-based repetitive (PIOR) controller.

Description

Technical Field

[0001] This document relates to energy microgrids for use in the workplace, and more specifically to an interface circuit for connecting energy sources to the microgrid. Background Technology

[0002] Powering large mobile work machines (e.g., wheel loaders, mining trucks, etc.) with zero-emission sources requires large mobile electrical energy sources (e.g., energy storage batteries or battery systems) or tethered electrical connections capable of providing current (e.g., tens to hundreds of amperes). Construction sites where several large electric work machines operate are often remote locations where machines using energy storage batteries need recharging, and tethered or pole-mounted work machines may require off-grid energy storage systems to stabilize voltage and frequency and minimize electricity costs during peak electricity price and / or peak demand periods. Furthermore, at remote construction sites, the public grid electrical infrastructure for charging the work machine's batteries or off-grid energy storage systems is either very limited or nonexistent. Microgrids can be built at the construction site to provide or enhance the infrastructure needed to power the work machines. Microgrids can supply power to construction sites using energy generated from various types of energy assets, such as generator sets (or gensets), energy storage systems (ESS), photovoltaic (PV) sources (e.g., solar panels), wind turbines, fuel cells, hydrogen production and storage, etc. Controllers are typically used to connect the output of energy sources to the power bus of the microgrid. However, connecting unconventional energy sources (such as PV sources) to a microgrid can be challenging. Conventional controllers used to connect such energy sources may malfunction during grid imbalance conditions. Summary of the Invention

[0003] Electric large mobile work machines use high-capacity battery systems that require charging or tethered electrical connections. The goal is to use microgrid systems that utilize multiple energy assets to power work machines at remote construction sites.

[0004] An example interface circuit for connecting an energy source to a power bus of a microgrid includes a switching inverter circuit, an output filter circuit coupled between the output of the three-phase inverter circuit and the power bus, and a control circuit loop for controlling the switches of the switching inverter circuit. The control circuit loop is coupled to the output filter circuit and the switching inverter, and includes a proportional-integral oscillator-based repetitive (PIOR) controller.

[0005] An example method for connecting an energy source to a microgrid includes: receiving DC power from a DC source of the microgrid; converting the DC power into AC power using a switching inverter circuit; filtering the AC power using an output filter circuit; generating control signals for the switching inverter circuit using a PIOR controller included in a first control circuit loop connected to the output filter circuit; and applying the filtered AC power to a power bus of the microgrid. Attached Figure Description

[0006] Figure 1 This is a diagram of an example microgrid system based on the present disclosure.

[0007] Figure 2 It is a circuit diagram of an interface circuit for connecting an energy source to a microgrid, according to this disclosure.

[0008] Figure 3 This is a circuit diagram of various parts of an example interface circuit for connecting an energy source to a microgrid, according to the present disclosure.

[0009] Figure 4 This is a circuit diagram of various parts of an interface circuit for connecting an energy source to a microgrid, according to another example of the present disclosure.

[0010] Figure 5 This is a circuit diagram of another example of an interface circuit for connecting an energy source to a microgrid, according to the present disclosure.

[0011] Figure 6 and 7 This is a circuit diagram of an additional example of an interface circuit for connecting an energy source to a microgrid, according to the present disclosure.

[0012] Figure 8 It is a control diagram based on the control scheme of the control section of the interface circuit for connecting an energy source to a microgrid, according to the present disclosure.

[0013] Figure 9 This is a block diagram of an example of a proportional-integral oscillator-based repetitive (PIOR) control scheme for the control section of an interface circuit used to connect an energy source to a microgrid, according to the present disclosure.

[0014] Figure 10 This is a block diagram illustrating the operation of the PIOR controller according to this disclosure in the continuous time domain or (s) domain.

[0015] Figure 11 This is a block diagram illustrating the operation of the PIOR controller according to this disclosure in the discrete time domain or (z) domain.

[0016] Figure 12It is a graph of the frequency response of the PIOR controller according to this disclosure.

[0017] Figure 13 It is a graph of the frequency response of the repetitive controller according to this disclosure.

[0018] Figure 14 It is a graph of the z-domain pole migration of the PIOR controller according to this disclosure.

[0019] Figure 15 This is a flowchart illustrating an example of a method for connecting an energy source to a microgrid according to this disclosure. Detailed Implementation

[0020] Examples of this disclosure relate to systems and methods for improving the interface between energy sources or energy assets and microgrid systems.

[0021] Figure 1 This is a diagram illustrating various parts of an example of a microgrid system 100. The microgrid system 100 includes multiple energy assets of various energy asset types, which are connected to a high-voltage bus 118 (HV bus) or a power bus via a microgrid switch 116. Figure 1 The example illustrates multiple sets of energy assets, including fuel assets such as generator set (or genset) 102, and renewable energy assets such as photovoltaic 104 and wind turbine 106. Generator set 102 can be a diesel-powered generator set, a gas reciprocating generator set, a gas turbine generator set, a hydrogen reciprocating generator set, a hydrogen turbine generator set, a hybrid fuel generator set, etc. Microgrid system 100 may include a connection to public power grid 108.

[0022] The microgrid system 100 also includes one or more energy storage systems 110 (ESS). ESS 110 may include battery systems, hydrogen storage systems with electrolyzers, pumped hydro storage systems, etc. The microgrid's ESS 110 can be used to store excess energy generated by energy assets, or to store energy from the utility grid 108 during periods of low grid energy costs. Multiple loads 112 may be present on the microgrid system 100. For example, if the microgrid system 100 is powering a mining site, load 112 may include chargers for battery-powered work machines, or load 112 may include tethered / pole-mounted work machines. The microgrid system 100 includes a microgrid controller 120 that performs supervisory functions of the microgrid system 100, such as scheduling energy assets based on power demand on the microgrid system 100. As explained earlier herein, connecting energy assets to the microgrid system 100 can be challenging.

[0023] Figure 2It is used to connect energy sources to microgrids (e.g., Figure 1 A block diagram of an example of the interface circuit 230 of the power bus in a microgrid system 100. Energy source 232 is shown as a direct current (DC) voltage source V. DC Energy source 232 can be a renewable energy source, such as a photovoltaic source, a wind turbine, or a fuel cell. In another example, energy source 232 can be an ESS (Emergency Power Supply) that provides backup energy to a microgrid. Energy source 232 can also be a non-renewable energy source, such as a generator set. Switching inverter circuit 234 converts the DC input from a DC source into an alternating current (AC) output. The AC power is filtered using filter circuit 235, and the output of filter circuit 235 is provided to power bus 118. Interface circuit 230 also includes control circuitry 238 to provide control signals to switching inverter 234.

[0024] Figure 3 This is a circuit diagram of various portions of an example interface circuit 330 used to connect energy source 232 to a three-phase power grid (3Φ grid). Interface circuit 330 includes a switching three-phase inverter circuit 334 using insulated-gate bipolar transistors (IGBTs) as switches. Interface circuit 330 also includes an inductor-capacitor-inductor (LCL) filter circuit 336. The switching three-phase inverter circuit 334 can supply power to the grid (e.g., 50 kW or more) with regulated voltage or regulated current.

[0025] Figure 4 This is a circuit diagram of portions of an interface circuit 430 used to connect energy source 232 to a single-phase power grid (1Φ grid), the power of which is (e.g., 15 kW or less) less than... Figure 3 Example. Interface circuit 430 includes a switched half-bridge inverter circuit 434 and a filter circuit as an LCL circuit 436.

[0026] Figure 5 This is a circuit diagram of parts of an interface circuit 530 used to connect energy source 232 to a single-phase power grid. The interface circuit 530 includes a switched full-bridge inverter 534 and an LCL filter circuit 436. Figure 6 and 7 This is an additional example circuit diagram of an interface circuit used to connect energy source 232 to a single-phase power grid. Figure 6 The interface circuit 630 includes a switched full-bridge inverter 534, and an inductor 638 connects the output of the switched full-bridge inverter 534 to a single-phase power grid. Figure 7 The interface circuit 730 includes a switched full-bridge inverter 534 and an inductor 638 at the output of the switched full-bridge inverter 534. A transformer T1 connects the inductor 638 to a single-phase power grid.

[0027] return Figure 2 The control circuit 238 can provide for Figure 3 Three-phase inverter circuit 334 or Figure 4-7 The control signal for the switching of a single-phase inverter circuit. Traditionally, proportional-integral (PI) controllers are used to control switching inverter circuits, but PI controllers may not be sufficient during periods of weak grid conditions or grid imbalance.

[0028] Figure 8 It is aimed at Figure 3 The control scheme of the control section of the interface circuit 330 is shown in control diagram 800. Control diagram 800 includes multiple control circuit loops connected to the LCL filter circuit 336. The control circuit loops convert three-phase voltage and current into two-phase voltage and current. The two-phase voltage is input to a repetitive (PIOR) controller based on a proportional-integral oscillator with a transfer function (PIOR(s)), and the two-phase current is input to a proportional (P) controller with a transfer function (K). The PIOR controller and the P controller provide pulse width modulation (PWM) 840 control signals to control the switching of the three-phase inverter circuit 334.

[0029] Figure 9 It is aimed at Figure 2 A block diagram of an example PIOR control scheme 900 for the control section of the interface circuit 230. This control scheme, for example, involves generating a control... Figure 2 The switching inverter circuit 234 is controlled by a PWM control signal. The control scheme includes an internal control circuit loop 942 and an external control circuit loop. The internal control circuit loop includes a P controller 944 (K block), and the external control circuit loop includes a PIOR controller 946. PWM The block represents the modulation index.

[0030] Figure 10 This is a block diagram illustrating the operation of the PIOR controller 1046 in the continuous time domain or (s) domain. The PIOR controller 1046 is a stationary reference coordinate system controller. (For example, using the Clarke transform) A stationary two-phase coordinate system is derived from a three-phase AC signal. The PIOR controller 1046 integrates PI controller elements with an oscillator containing repetitive elements. The result is a PIOR controller 1046 resembling an infinite series of parallel-connected (oscillator + PI) units. The continuous-time transfer function "PIOR(s)" calculated or operated by the PIOR controller is... , in .

[0031] The infinite series in the previous equation for G(s) can also be expressed in terms of the hyperbolic cotangent (Coth) function. .

[0032] Figure 10 The hyperbolic cotangent (Coth) term of the inner frame is .

[0033] Figure 11 This is a block diagram illustrating the operation of the PIOR controller 646 in the discrete time domain or (z) domain. For , Coth term in continuous time domain Converted to the discrete time domain . The continuous-time transfer function “PIOR(z)” calculated or operated by the PIOR controller is:

[0034] return Figure 9 The internal control circuit loop is connected to Figure 2 The inductor in the filter circuit 236, and the input of the P controller 944 in the internal circuit loop 942 is the inductor current i. Lf (For example, the current of the inverter-side inductor in an LCL filter). The external control circuit loop is connected to the capacitor of the filter circuit, and the input of the PIOR controller 946 is the capacitor voltage V. C This control scheme allows interface circuit 230 to regulate one or both of the voltage and current applied to power bus 118. In some examples of the control scheme, a PI controller is used instead of P controller 944. In a simpler, lower-power version of interface circuit 230, the control scheme includes only a PIOR controller 946, and the input to the PIOR controller is the inductor current, and the control scheme generates a regulated current at the output of interface circuit 230.

[0035] Figure 12 This is a graph of the frequency response of the PIOR controller 946. The frequency response includes a pole at 1250 at the fundamental frequency of the microgrid (e.g., 60 Hz), and exhibits very high gain at that frequency. The frequency response also includes poles at higher harmonics of the fundamental frequency. Below the fundamental frequency, the frequency response flattens out to DC with little or no gain. Figure 13This is a graph showing the frequency response of the repetitive control (RC) circuit. The graph illustrates the gain of the RC controller at frequencies below the fundamental frequency. It should be noted that the RC controller has a slow dynamic response, typically resulting in a delay equivalent to one fundamental cycle, and its performance can be affected by fluctuations in the mains frequency. Therefore, compared to the RC, the PIOR controller 946 improves the tracking of both the negative-sequence and positive-sequence components at the fundamental frequency and its harmonics, and reduces distortion from non-harmonic frequencies. Figure 14 This is a graph showing the z-domain pole shift of the PIOR controller. The graph demonstrates that the PIOR controller provides a stable response up to 30 gain.

[0036] A control scheme utilizing a PIOR controller connects unconventional energy assets (such as renewable energy assets) to a microgrid. Interface circuits with PIOR control and renewable energy assets can form energy assets within a microgrid system.

[0037] Industrial applicability

[0038] Figure 15 This is a flowchart illustrating an example of method 1500 for connecting an energy source to a microgrid. Method 1500 can use... Figure 2 The interface circuit 230 is used to perform this. At block 1505, DC power is received from an energy source. The energy source can be a renewable energy asset of the microgrid system, such as a photovoltaic source (e.g., solar panels), a wind turbine, a fuel cell, etc. In some examples, the energy source is a battery energy storage system (ESS) of the microgrid system.

[0039] At block 1510, DC power is converted to AC power. This DC-to-AC power conversion can be performed using any switching inverter circuit described herein. At block 1515, the AC power is filtered using an output filter. The circuitry that connects power from the energy source to the microgrid includes a control circuit loop that regulates the AC power supplied to the microgrid. To regulate the AC power, the control circuit loop feeds back one or more output signals to a PIOR controller (e.g., ...). Figure 9 (PIOR controller 946 in the middle).

[0040] At box 1520, the PIOR controller generates a control signal to regulate the AC power. In some examples, the PIOR controller and control circuit loop generate a PWM control signal to regulate the output of the switching inverter circuitry used to convert DC power to AC power. At box 1525, the filtered and regulated AC power is applied to the microgrid.

[0041] Unless explicitly excluded, the use of the singular to describe a component, structure, or operation does not preclude the use of a plurality of such components, structures, or operations or their equivalents. In the context of describing the invention (particularly in the context of the following claims), the terms “a” and “an” and “the” and “at least one” or the terms “one or more” and similar references should be interpreted to encompass both the singular and plural, unless otherwise stated herein or explicitly contradicted by the context. The use of the term “at least one” followed by a list of one or more items (e.g., “at least one of A and B” or one or more of A and B) should be interpreted to indicate a selection of one item (A or B) from the listed items or any combination of two or more of the listed items (A and B; A, A and B; A, B and B), unless otherwise stated herein or explicitly contradicted by the context. Similarly, as used herein, the word “or” refers to any possible permutation of a set of items. For example, the phrase “A, B or C” means at least one of A, B, C or any combination thereof, such as any of the following: A; B; C; A and B; A and C; B and C; A, B and C; or multiple items such as A and A; B, B and C; A, A, B, C and C, etc.

[0042] The detailed description above is intended to be illustrative, not restrictive. Therefore, the scope of this disclosure should be determined by reference to the appended claims and the full scope of their equivalents.

Claims

1. An interface circuit (230) for connecting an energy source to a power bus (118) of a microgrid (100), the interface circuit comprising: Switching inverter circuit (234); Output filter circuit (236), said output filter circuit being coupled between the output of the switching inverter circuit and the power bus; and A first control circuit loop is used to control the switching of the switching inverter circuit, wherein the first control circuit loop is coupled to the output filter circuit and the switching inverter circuit, and includes a proportional-integral oscillator-based repetitive (PIOR) controller (946).

2. The interface circuit according to claim 1, comprising: The second control circuit loop is an inner control circuit loop (942), and the first control circuit loop is an outer control circuit loop. The internal control circuit loop is coupled to the output filter circuit and includes a proportional (P) controller (944); and The output filter includes an inductor and a capacitor, with an internal control loop coupled to the inductor and an output control loop coupled to the capacitor.

3. The interface circuit according to claim 1, comprising: The second control circuit loop is an internal control circuit loop, and the first control circuit loop is an external control circuit loop; and The internal control circuit loop is coupled to the output filter circuit and includes a proportional-integral (PI) controller; and The output filter includes an inductor and a capacitor, with an internal control loop coupled to the inductor and an output control loop coupled to the capacitor.

4. The interface circuit of claim 1, wherein the filter circuit includes at least one inductor, and the PIOR controller is configured to control the switching of the switching inverter circuit to regulate the current of the inductor.

5. The interface circuit according to claim 1, The switching inverter circuit mentioned above is a three-phase switching inverter circuit (334); and The filter circuit mentioned above is an LCL filter circuit (336).

6. The interface circuit according to claim 1, wherein the frequency response of the PIOR controller has a pole (1250) at the base frequency and the harmonics of the base frequency of the microgrid, and a flat response at frequencies less than the base frequency.

7. The interface circuit according to claim 2, wherein the PIOR controller is a stationary reference coordinate system controller.

8. The interface circuit of claim 1, wherein the PIOR controller is configured to compute a discrete-time transfer function PIOR(z) to control the switching of the switching inverter circuit, wherein... 。 9. The interface circuit according to claim 1, The inverter circuit described herein is a three-phase inverter circuit including insulated-gate bipolar transistors (IGBTs), and pulse width modulation (PWM) (840) is used to control the switching of the IGBTs to convert the DC input of the three-phase inverter circuit into the AC output of the three-phase inverter circuit; and The first control circuit loop provides PWM control to the three-phase inverter circuit.

10. A method for connecting an energy source to a microgrid (100), the method comprising: Receive direct current (DC) power from the energy source of the microgrid; The DC power is converted into AC power using a switching inverter circuit (234); The AC power is filtered using an output filter circuit (236); A proportional-integral oscillator-based repetitive (PIOR) controller (946), included in a first control circuit loop connected to the output filter circuit, generates control signals for the switching inverter circuit. as well as Filtered AC power is applied to the power bus (118) of the microgrid.

Images