Battery-boosted variable-frequency motor drive system for high-torque operation of ac induction motors and permanent magnet synchronous motors (PMSM)

Abstract

A battery-boosted variable-frequency motor drive system 100 for use during power outages, but not limited thereto, for use with an electric motor 102 for operating a mechanical load, such as, but not limited thereto, an industrial door, during a power outage. The battery-boosted variable-frequency motor drive system has: i. a power supply 101 connected to an electric motor 102 such that power is adapted to be supplied to the electric motor during normal operation where the power is uninterrupted so as to allow the normal operation of electric motor drive the mechanical load; and ii. a backup connected to the electric motor such that when the power supply is interrupted, due to a power outage, stored DC power is supplied through a DC / DC voltage boost converter 114 to a DC to 3 phase AC inverter switching means (112) to supply power to the electric motor to allow the electric motor to drive the mechanical load during a backup mode when there is a power outage.

Description

[0001] Battery-Boosted Variable-Frequency Motor Drive System for High- Torque Operation of AC Induction Motors and Permanent Magnet Synchronous Motors (PMSM)

[0002] FIELD OF THE INVENTION

[0003] The invention relates to electric motor drives, particularly three-phase inverters powered from low voltage batteries using a DC-DC step-up stage and a non-sinusoidal waveform strategy to increase torque in AC induction motors and to drive PMSMs. The invention allows for low voltage motor control that is suitable, but not limited thereto, to drive a mechanical load during power outages, but not limited thereto, e.g. for use with an electric motor for an industrial door during a power outage.

[0004] BACKGROUND OF INVENTION

[0005] The actuation of industrial electric motors during a mains power outage is a necessary requirement, especially for health and safety reasons. For example, immediate access maybe required if persons are trapped inside a building where egress is controlled by an industrial automatic door operated by a mains driven industrial motor.

[0006] In many installations the motor is controlled in normal operation by a mains-powered variablefrequency drive (VFD) that supplies the motor, with any backup AC source (if present) feeding the VFD input.

[0007] Where backup operation is required, a common approach is to install a double-conversion uninterruptible power supply (UPS) upstream of the existing motor controller — typically a VFD — so that, on loss of mains, the UPS delivers AC to the VFD input. A UPS of this class detects failure of the AC power supply and quickly delivers a closely matching AC voltage generated by an inverter powered from a battery bank. To support motor drives, the UPS, charging hardware, and inverter are often sized to the predicted startup load of the motor, which is generally significantly higher than the steady state load, which tends to increase battery capacity, volume, and cost. Using a UPS system as a backup for a motor drive has several drawbacks. The UPS systems are generally physically large, and correspondingly bulky and expensive, and sensitive to industrial environments of high humidity, extremes of temperature and mechanically fragile. A protected enclosure is generally necessary to provide the required controlled working environment to match the specification of the UPS.

[0008] Further, the high power often required to operate industrial motor control means the specification may require very large units, which are then costly to maintain or replace. In particular, AC induction motors and many other types of commonly used motors (e.g. PMSMs) have very large initial startup power demands, meaning that the inverter and battery used may have to be substantially larger to cope with the initial power surge required, often twice as high as the maximum steady state load.

[0009] Conventional three-phase UPS architectures. Industrial backup power for three-phase loads is commonly provided by double-conversion uninterruptible power supplies (UPS). In a double-conversion UPS, the incoming AC is rectified to a DC bus and then inverted back to AC for the load, with batteries connected to the DC bus to ride through outages. Two architectural families are prevalent:

[0010] • Transformerless UPS: A rectifier / PFC stage establishes a high-voltage DC bus (hundreds of volts). Long series battery strings (or an internal DC-DC stage) maintain that high bus, and a multi-level inverter synthesises the three-phase output directly without a line-frequency transformer. This yields high efficiency and lower size / weight and is common in modern IT / data-centre UPSs.

[0011] • Transformer-based UPS: The inverter feeds a line-frequency isolation / step-up transformer to produce the three-phase output and manage neutral / voltage adaptation. This architecture is still used in many industrial installations for robustness and isolation, but the transformer adds volume, mass, and loss. Functionally, this resembles a battery —> inverter —> three-phase transformer chain.

[0012] When used with motor drives, such a UPS is typically connected on the AC line side of a VFD so the VFD continues to control the motor; less commonly, a UPS is tied to a VFD’s DC bus via a dedicated interface. Both arrangements inherit the UPS size and cost penalties described above. Limitations of conventional UPSs for induction motor loads.

[0013] Most UPS products are optimised for electronic loads (servers, drives with active rectifiers) that present modest inrush current. When asked to start or accelerate motors either across-the- line or via a VFD they encounter heavy transient demands.

[0014] Across-the-line AC induction motors draw high locked-rotor current (often multiple times fullload current) and significant reactive power during start-up. As a result:

[0015] • The UPS must be oversized to tolerate motor starting surges, which drives cost and footprint.

[0016] • Protection and control loops intended for IT loads can trip or current-limit during motor starts, preventing reliable acceleration to speed.

[0017] • Lower-end or stepped-wave inverters (in some UPS classes) exhibit poorer motor performance and additional heating compared with high-quality sinusoidal sources.

[0018] • In transformer-based UPSs, the line-frequency transformer adds further impedance and loss, increasing voltage sag during inrush.

[0019] Consequences for portable / backup industrial drives. Where the objective is to run industrial three-phase induction motors from battery power during a mains outage, conventional UPS solutions become large and expensive if sized for reliable starts. The requirement to maintain a high-voltage AC output using a transformer or long battery strings also imposes packaging and cost penalties, especially when the battery system is nominally low voltage (e.g., 48 V).

[0020] Currently there are few readily available systems for backup AC power supply for industrial motor control use that ameliorate the disadvantages of a UPS backup system as a backup for a driving an industrial electric motor.

[0021] There is a need for a backup system that does not require a large battery bank, does not require a large initial power demand and is not costly to maintain and replace.

[0022] There is also a need for a solution that, during backup operation, isolates the motor and any electromagnetic brake from the mains and drives them independently so as to avoid back feed and simplify integration with existing VFD-controlled installations. There is a further need for a compact battery-powered three-phase drive that: i. avoids the bulk of a line frequency transformer, ii. reduces inverter switching currents by operating from a boosted DC bus, and iii. employs a non-sinusoidal, bounded-class waveform tailored to increase average electromagnetic torque in AC induction motors enabling reliable starting and operation without oversizing the power stage. This approach also permits operation of permanent-magnet synchronous motors (PMSMs) from the same hardware during loss of mains.

[0023] DEFINITIONS

[0024] It is acknowledged that the term ‘comprise’ may, under varying jurisdictions, be attributed with either an exclusive or an inclusive meaning. For the purpose of this specification, and unless otherwise noted, the term ‘comprise’ shall have an inclusive meaning - i.e. that it will be taken to mean an inclusion of not only the listed components it directly references, but also other non-specified components or elements. This rationale will also be used when the term ‘comprised’ or 'comprising' is used in relation to one or more steps in a method or process.

[0025] For clarity in this specification:

[0026] “CM: Contactor - Mains side

[0027] “CI”: is the inverter-side contactor that connects the motor to the VFD’s three-phase output only during backup. It’s interlocked with CM so the motor is never tied to mains and inverter at the same time.

[0028] “High-voltage (HV) DC bus” or simply “DC bus (VDC)”: the regulated DC link supplied by the step-up stage. In boost embodiments, VDC is controlled at or above the instantaneous battery / input voltage, subject to device limits. The nominal value is application-selectable (examples include -120 V, 180 V, and higher).

[0029] “Galvanic isolation” or “air-gapped isolation”: a state in which all conductive paths between the motor windings and / or brake coil and the AC mains are open, preventing any backfeed or cross-connection. “Contactor / relay”: includes electromechanical contactors, relays, and solid-state relays or switches that provide equivalent isolation.

[0030] “All-pole isolation”: switching of each phase conductor and, where present, the neutral conductor.

[0031] “Electromagnetic brake”: a spring-applied, power-to-release brake coil mounted to the motor or drivetrain.

[0032] “Site supply”, “installation supply”, or “line-side source”: the supply present in normal operation upstream of the motor connection point, which may be an AC line supply, a mains- derived auxiliary DC supply (e.g., 24 VDC), or an intermediate-voltage supply, and which is used for outage / restoration detection and, in some embodiments, to charge the backup energy source.

[0033] “Galvanically isolated input”: an input interface that provides electrical isolation (no conductive path) between external signaling circuits and the system electronics, realisable by optocouplers, digital isolators, isolation transformers / amplifiers, capacitive or magnetic isolators, or relay contacts.

[0034] “EMI”: Electromagnetic interference.

[0035] “Power Supply”: includes, but not limited to, mains power supply, VDF power supply, a three phase mains power supply or any other suitable known power source..

[0036] “TVS”: Transient-voltage suppressor (clamping device for spikes).

[0037] “RC snubber / damper”: Series resistor-capacitor network to damp ringing and absorb transient energy.

[0038] “VFD”: Variable frequency drive

[0039] OBJECT OF THE INVENTION

[0040] It is an object of the invention to provide a battery -boosted variable-frequency motor drive system for high-torque operation of AC induction motors and permanent magnet synchronous motors (PMSMs) that ameliorates some of the disadvantages and limitations of the known art or at least provide the public with a useful choice.

[0041] It is a further object of the invention is to provide a battery -boosted variable-frequency motor drive system to allow for low voltage motor control that is suitable, but not limited thereto, to drive a mechanical load during power outages, but not limited thereto, e.g. for use with an electric motor for an industrial door during a power outage that ameliorates some of the disadvantages and limitations of the known art or at least provide the public with a useful choice.

[0042] SUMMARY OF INVENTION

[0043] In a first aspect the invention resides in a battery-boosted variable-frequency motor drive system for use during power outages, but not limited thereto, for use with an electric motor for operating a mechanical load, such as, but not limited thereto, an industrial door, during a power outage, wherein the battery-boosted variable-frequency motor drive system having: i. a power supply connected to an electric motor such that power is adapted to be supplied to the electric motor during normal operation where the power is uninterrupted so as to allow the normal operation of electric motor drive the mechanical load; and ii. a backup means connected to the electric motor such that when the power supply is interrupted, due to a power outage, stored DC power is supplied through a DC / DC voltage boost converter to a DC to 3 phase AC inverter switching means so as to supply power to the electric motor so as to allow the electric motor to drive the mechanical load during a backup mode when there is a power outage.

[0044] In a second aspect the invention resides in a battery-boosted variable-frequency motor drive system configured to operate an electric motor during an AC mains outage, the system comprising: a. a site-supply interface configured to receive power and / or presence information from at least one of: i. an AC line supply, ii. a mains-derived auxiliary DC supply, or iii. an intermediate-voltage supply; the site-supply interface providing at least an auxiliary supply for monitoring and / or battery charging; b. a line-side contactor arrangement configured to connect the motor to the AC mains during normal operation and to provide galvanic isolation by opening all poles in response to an interruption; c. a low-voltage DC energy source; d. a DC-DC step-up converter configured to generate a regulated high-voltage DC bus from the low-voltage source; e. a three-phase inverter supplied from the high-voltage DC bus; f. an inverter-side contactor arrangement configured to connect the inverter to the motor; and g. a transfer arrangement configured, upon detecting loss of a site supply (including loss of an associated auxiliary supply such as 24 VDC), to open the line-side contactor arrangement to provide galvanic isolation, effect a break- before-make interval, and then close the inverter-side contactor arrangement so that the motor is driven from the low-voltage DC energy source while preventing back feed to the site supply, and to perform an inverse sequence upon restoration of the site supply; the transfer arrangement comprising any one or more of controller logic, a time-delay relay, an undervoltage-release device, or mechanical / electrical interlocks.

[0045] Preferably, the site-supply interface comprises an isolated charger powered from a mains- derived auxiliary DC supply, the charger maintaining the low-voltage DC energy source while the motor circuit remains isolated from the site supply.

[0046] Preferably, the site-supply interface alternatively comprises a rectifier or power module configured to accept an AC line supply or an intermediate-voltage DC supply and to provide both outage / restoration detection and charging power.

[0047] Preferably, the backup means has motor driving circuitry, DC / DC voltage boost convertor circuitry, brake control circuitry, low voltage DC power storage battery, main logic control means, battery management and charging means, an inverter, an inverter-side contactor arrangement configured to connect the inverter to the motor AC mains, voltage detection means and human control input means, wherein the main logic control means having motor drive waveform generation means, motor brake control means data logging means.

[0048] Preferably, the electric motor is an AC induction motor or permanent magnet synchronous motor.

[0049] Preferably, the motor drive waveform generation means generates at least a non-sinusoidal waveform for increasing the average electromagnetic torque in the AC induction motor or permanent magnet motor so as to enable reliable starting and operation of said motors without oversizing the power outage stage.

[0050] Preferably, the motor drive waveform generation means generates and selects among a family of three-phase waveforms, including i. a substantially sinusoidal waveform member, and ii. non-sinusoidal waveform members such that under high-torque or start-up conditions or power outages, the selected non-sinusoidal members increases the average electromagnetic torque at equal Root Mean Square (RMS) current and Voltage Direct Current (Vdc).

[0051] Preferably, the output frequency of the non-sinusoidal waveform members adapted to match to match the frequency of the motors RPM.

[0052] Preferably, the system includes a dedicated, isolated high-voltage DC supply for a brake coil, routed through a double-pole double-throw (DPDT) relay that switches both brake terminals, ensuring the brake circuit is isolated from mains during backup mode and automatically reconnected to mains when mains power is restored.

[0053] Preferably, the system is able to be activated by manual input and / or by an external control signal with priority logic co-ordinating transfer, waveform selection, and brake release.

[0054] In a third aspect the invention resides in a battery-boosted variable-frequency motor drive system comprising: a. a low-voltage DC energy source; b. a DC-DC step-up stage configured to generate a regulated high-voltage DC bus; c. a three-phase inverter; d. a mains-side switching device configured to connect a motor to an AC mains supply in a first state and disconnect in a second state; e. an inverter-side switching device configured to connect the motor to the inverter in said second state; and f. a controller configured to, upon detecting loss of the AC mains, open the mains-side switching device and close the inverter-side switching device to operate the motor from the high-voltage DC bus, and upon mains restoration perform the inverse sequence, thereby maintaining air-gapped isolation between the motor circuit and the AC mains during backup operation.

[0055] Preferably, the system includes an inverter-side contactor arrangement configured to connect the inverter to the motor.

[0056] Preferably, the mains-side switching device and the inverter-side switching device are interlocked to prevent simultaneous closure and are sized to the motor load.

[0057] Preferably, the system further comprising a charging interface powered from the AC mains by a low-voltage auxiliary line configured to charge the low-voltage DC energy source while the motor circuit remains isolated from the AC mains.

[0058] Preferably, the controller is configured to generate a family of three-phase output waveforms using space-vector PWM or an equivalent carrier based modulation with zero-sequence injection, and to select among a substantially sinusoidal member and one or more non- sinusoidal members responsive to torque demand, EMC limits, battery current, or device temperature.

[0059] Preferably, the sinusoidal member is a special case of the waveform family obtained by choosing references or dwell fractions that inject no non-fundam ental content. Preferably, the controller commands an output frequency (f_out) within a range (f min, f max) mapped to motor speed and co-ordinates DC-bus setpoint and modulation index to satisfy current and voltage limits.

[0060] Preferably, the system further comprising an isolated high-voltage DC supply of 80-120 Vdc configured to energise a motor brake coil during backup operation, and a double-pole doublethrow relay arranged to switch both brake terminals between a mains-side brake circuit and said isolated supply, thereby isolating the brake circuit from the AC mains during backup operation.

[0061] Preferably, the controller applies brake voltage for [t release] ms after commanding the inverter torque and removes the brake voltage prior to transfer back to AC mains

[0062] Preferably, the controller selects a non-sinusoidal member of the waveform family under starting or high-torque conditions to increase average electromagnetic torque relative to a sinusoidal member at equal RMS phase current and DC-bus voltage, and selects the sinusoidal member when required to satisfy an EMC or acoustic constraint.

[0063] Preferably, the controller is adapted to perform a soft-start by ramping a modulation factor from zero to a target value while holding the commanded output frequency substantially constant.

[0064] Preferably, the controller adapted to ramp both the modulation factor and the output frequency towards respective targets with independent rates.

[0065] Preferably, the system includes over-current protection that is provided by gate-driver desaturation or over-stress detection independent of the controller.

[0066] Preferably, the system includes two-shunt reconstruction or three-shunt / in-line sensors with sampling synchronised to the PWM in order to provide per-phase current measurements.

[0067] Preferably, the controller stores in memory a lookup table of modulation values indexed by electrical angle and scales said values by a modulation factor derived from a power or torque request, and the output frequency is generated by a digital phase accumulator that indexes the table and the table is stored in non-volatile memory and updateable by firmware. Preferably, the DC-DC step-up stage comprises a single-phase synchronous boost converter controlled in peak current-mode.

[0068] Preferably, the DC-DC step-up stage comprises M interleaved channels (M > 2) with PWM carriers mutually phase-shifted by approximately 360° / M to reduce input and output ripple.

[0069] Preferably, the system further comprising human and external activation interfaces, including a momentary pushbutton and a galvanically isolated input 12 / 24 V input from a safety or fire alarm system, either interface being configured to command entry into backup operation.

[0070] Preferably, in backup operation, the inverter-side contactor arrangement connects the inverter output directly to the motor terminals downstream of any mains-powered controller or VFD, while the mains-powered controller and the AC mains are isolated from the motor.

[0071] In a fourth aspect the invention resides in a method of operating a battery-boosted variablefrequency motor drive system comprising: a) charging a low-voltage DC energy source from an AC mains supply; b) upon detecting mains loss i. opening a mains-side switching device, ii. closing an inverter-side switching device, iii. driving the motor from a DC-DC step-up-derived high voltage DC bus via a three-phase inverter, iv. generating, at a commanded frequency f out within f min-f max, a three-phase output waveform selected from a family comprising a substantially sinusoidal member and one or more non-sinusoidal members, responsive to torque demand, EMC limits, or device constraints, v. energising a motor brake via an isolated high-voltage DC supply; and c) upon mains restoration, removing inverter torque, deenergising the brake, opening the inverter-side switching device, and closing the mains-side switching device. Preferably, waveform selection is responsive to at least one of required torque margin, EMC or acoustic constraints, battery current limit, or device temperature; and wherein start-up is effected by ramping a modulation factor from zero to a target value.

[0072] Preferably, when upon detecting mains loss an inverter-side contactor arrangement connects the inverter output directly to the motor terminals downstream of any mains-powered controller or VFD, while the mains-powered controller and the AC mains are isolated from the motor.

[0073] In a fifth aspect the invention resides in a method of operating a battery-boosted variablefrequency motor drive system comprising: a) providing a site-supply interface configured to receive power and / or presence information from at least one of: i. an AC line supply, ii. a mains-derived auxiliary DC supply, or iii. an intermediate-voltage supply; the site-supply interface providing at least an auxiliary supply for monitoring and / or battery charging; b) configuring a line-side contactor arrangement to connect the motor to the AC mains during normal operation and to provide galvanic isolation by opening all poles in response to an interruption; c) providing a low-voltage DC energy source; d) configuring a DC-DC step-up converter to generate a regulated high-voltage DC bus from the low-voltage source; e) supplying a three-phase inverter supplied from the high-voltage DC bus; f) configuring an inverter-side contactor arrangement to connect the inverter to the motor; and g) configuring a transfer arrangement upon detecting loss of a site supply (including loss of an associated auxiliary supply such as 24 VDC), to open the line-side contactor arrangement to provide galvanic isolation, effect a break-before-make interval, and then close the inverter-side contactor arrangement so that the motor is driven from the low-voltage DC energy source while preventing back feed to the site supply, and to perform an inverse sequence upon restoration of the site supply; the transfer arrangement comprising any one or more of controller logic, a time-delay relay, an undervoltage-release device, or mechanical / electrical interlocks.

[0074] Preferably, during backup operation, isolating the motor and any electromagnetic brake from the mains and driving them independently so as to avoid back feed and simplify integration with existing VFD-controlled installations.

[0075] Preferably, dedicating, isolating the high-voltage DC supply for an electromagnetic brake coil, routing through a double-pole double-throw (DPDT) relay to switch both brake terminals between a mains-side brake circuit in normal operation and the isolated supply in backup operation, thereby galvanically isolating the brake circuit from the AC mains during backup.

[0076] Preferably, operating system independently of a mains power source, so that the system is able to be used as a secondary backup to an existing UPS system and is able to stand independently along side an integrated UPS.

[0077] Preferably, power supply is a mains or VDF power supply, preferably a three phase mains power supply or any suitable known power source.

[0078] In a sixth aspect the invention resides in a battery-boosted variable-frequency motor drive system for operating an electric motor (AC induction or PMSM) during a power outage, suitable for mechanical loads such as industrial doors, the system comprising: i. a three-phase mains input for normal operation; ii. a mains-side contactor arrangement configured to connect the motor to the AC mains during normal operation and, in response to an interruption, to open all poles to provide galvanic isolation between the motor (and any brake coil) and the AC mains; iii. a low-voltage DC energy source and a DC / DC step-up converter configured to generate a regulated high-voltage DC bus; iv. a three-phase inverter supplied from the high-voltage DC bus; v. an inverter-side contactor arrangement configured to connect the inverter to the motor only when the mains-side contactor arrangement is open; and vi. a controller configured to detect mains loss, to enforce break-before-make transfer by opening the mains-side contactor arrangement, verifying the open state, waiting a defined dead-time, and then closing the inverter-side contactor arrangement so that the motor is driven independently from the backup source while preventing back feed to the AC mains, and to perform the inverse sequence upon mains restoration.

[0079] Preferably, the system further comprises a dedicated, isolated high-voltage DC supply for an electromagnetic brake coil, routed through a double-pole double-throw (DPDT) relay that switches both brake terminals between a mains-side brake circuit in normal operation and the isolated supply in backup operation, thereby galvanically isolating the brake circuit from the AC mains during backup.

[0080] Any other aspects herein described.

[0081] BRIEF DESCRIPTION

[0082] The invention will now be described, by way of example only, by reference to the accompanying drawings:

[0083] Figure l is a flow diagram of a battery -boosted variable-frequency motor drive system for use during power outages in accordance with a first preferred embodiment of the invention.

[0084] Figure 2 is a flow diagram showing the operational steps of the battery-boosted variablefrequency motor drive system as shown in figure 1.

[0085] Figure 3 is a detailed flow diagram of the battery-boosted variable-frequency motor drive system for use during power outages in accordance with a second preferred embodiment of the invention.

[0086] Figure 4 is a flow diagram showing the operational steps of the battery-boosted variablefrequency motor drive system as shown in figure 3.

[0087] DESCRIPTION OF THE PREFERRED EMBODIMENT(S) The following description will describe the invention in relation to preferred embodiments of the invention, namely a battery-boosted variable-frequency motor drive system for operating an electric motor for an industrial door during a power outage, it is envisioned that other applications of the invention to other electric motor driven machinery, equipment, apparatus, etc that require actuation during a power outage would be readily apparent without departing from the scope of the invention.

[0088] The invention is in no way limited to these preferred embodiments as they are purely to exemplify the invention only and that possible variations and modifications would be readily apparent without departing from the scope of the invention.

[0089] It is sometimes necessary to drive 3 phase induction motors from a secondary low voltage power source, such as in industrial applications when human safety or stock may be compromised by a machinery dead stop due to a power outage. Often it is not necessary to drive a motor at full speed to rectify this situation, and the present invention is designed to achieve this using a particularly efficient and unique way, that is able to be applied to electric motor driven automatic doors or any machinery driven by electric motors. In this preferred embodiment of the invention the load applied to the motor is that from an automatic industrial door, but with minor adaptation the low voltage electric motor control system could be used for variety of motor control applications for industrial use.

[0090] Normally, three phase AC power is used to drive AC induction motors from either AC mains power directly, or variable frequency drives (VFD). This consists of 3 sinusoidal voltage waves spaced 120 degrees apart. Any given 3 phase induction motor has a torque output that is relative to a rotating current in the field windings and the induced current in the rotor.

[0091] A common method used to increase torque at a given motor RPM is to employ a VFD to change the frequency of the 3 phase AC to one closer to optimal for that speed. The field windings and interaction with the rotor of the AC induction motor restrict the current to allow for the safe operation of the motor in normal circumstances. If the voltage is reduced, the current in the field windings will be proportionally reduced. Motor torque can be maintained up to a limit, by varying the AC frequency. The present invention is to a battery-boosted variable-frequency motor drive system that comprises a combination of several systems to enable the efficient driving of a 3 phase induction motor during a power outage.

[0092] The battery-boosted variable-frequency motor drive system of the preferred invention produces a substantially higher motor torque at any given voltage in the 3 phase induction motors used. A motor controlled by the battery -boosted variable-frequency motor drive system exhibits a high efficiency while being driven by a specific and non-sinusoidal, bounded-class waveform selected to increase average electromagnetic torque at equal RMS current and DC- bus voltage. With the drive frequency optimised, the battery -boosted variable-frequency motor drive system is able to be powered from a relatively small battery bank, by using a DC / DC voltage boosting device to raise the voltage.

[0093] Figures 1 to 4 show flow diagrams of an embodiment of a battery-boosted variable-frequency motor drive system as applied to a door egress (e.g. industrial door) in accordance within the scope of the invention.

[0094] An embodiment of the invention is to a battery -boosted variable-frequency motor drive system for actuating power doors, e.g. industrial doors, during a power outage, utilising a combination of technologies for an innovative and unique application of motor driving 3 phase AC waveform to efficiently drive 3 phase induction motors designed for much higher voltages, at or above their full rated torque at much lower voltages.

[0095] Turning to Figure 1, a battery-boosted variable-frequency motor drive system (100) is shown. A three-phase mains supply (101) connects to the motor (102) via a mains-side contactor arrangement CM (all poles switched). An inverter-side contactor arrangement CI connects the motor (102) to a DC-to-three-phase inverter power stage (112) during backup. CM and CI are mechanically and / or electrically interlocked so they are never simultaneously closed. In normal mode (mains present), CM is closed and CI is open, and the industrial automatic door (103) operates normally. Upon mains interruption, the controller opens CM, verifies open via auxiliary contacts, enforces a break-before-make dead-time, and then closes CI so that the inverter (112), powered from a DC / DC boost converter (114) fed by the storage battery (115), drives the motor (102). The battery (115) is charged from the mains (104) via an isolated charger during readiness. Turning to figure 2 which shows a flow diagram (200) of the operational steps for the battery- boosted variable-frequency motor drive system shown in figure 1. When main power is off (200) the motor is automatically connected to the backup drive system (202). The backup system lights up a button (205) with “wait for button press” (203). Upon the pressing of the button, releasing the brake and then the door is driven open by the backup system (204). Then upon the pressing the button press 207 the door is driven closed by the backup system (205).

[0096] Turning to Figure 3, AC mains power (301) feeds a normal running control system (302). A mains-side contactor CM (306) connects the motor (303) to the AC mains in normal operation; an inverter-side contactor CI connects the motor (303) to the backup inverter during outage. CM and CI are mechanically and / or electrically interlocked and provide all-pole isolation (each phase and neutral, where present). The motor (303) includes an electromagnetic brake (305) whose two terminals are switched by a DPDT brake relay RB to either a mains-side brake circuit in normal operation or to an isolated brake supply in backup. The backup subsystem comprises motor driving circuitry (307), a DC / DC boost converter (308), brake control circuitry (311), a low-voltage storage battery (309), a main logic controller implementing waveform generation, brake control and data logging (312), battery management and charging with AC mains detection (310), and human / external control input (313).

[0097] Turning to figure 4 which shows a flow diagram (400) of the operational steps for the battery- boosted variable-frequency motor drive system shown in figure 3. When mains power is on the door is driven by mains power (401). When mains is power off the backup system automatically operates (402) dis-connecting the motor and brake from the mains powered system and then connecting it to the backup system (403). The backup system displays lights up “wait for button press” (404). An operator then presses button (405) which then activates, releasing the brake and then the door is driven open by the backup system (406). The operator is then able to press the button (407) in order for the door to be driven closed by back the up system (408).

[0098] Some points of the architecture that are unique to the present invention are:

[0099] The use of a boost converter to raise the voltage available from the battery to then drive the motor control circuitry. The use of a specific waveform.

[0100] During normal operation:

[0101] With the mains power on, the door is powered by normal door control systems by mains electricity. During this time the backup door system maintains the battery in an optimal charge state that balances the maintenance interval of the backup battery with having sufficient charge to operate the door during a power outage.

[0102] In the event of a power outage:

[0103] The backup system control processor senses the loss of mains power and after a short delay to ensure the de-energisation of the mains controlled system, The door motor is disconnected from the mains circuit and is connected to the backup drive system.

[0104] After a timed delay, the backup system goes into active mode, lighting the control box to indicate the system is operable. Low power LED lighting is also optionally enabled to guide any person to the door area.

[0105] To operate the door the open button on either the inside or outside of the door is pressed, triggering the control system to start the motor driving part of the software.

[0106] A DC / DC converter now boosts the battery voltage and the motor is driven for a short time to build torque, at this point the electric brake is driven off from by a sufficient voltage from a DC / DC boost converter, and the door begins to open.

[0107] When the door is sufficiently open, either automatically by a timed or sensed height achieved, or by direct control via the button, the brake is now turned back on and the control system stops driving the motor.

[0108] The door can be now closed again via a separate button press, reversing the above process.

[0109] If, at any time mains power is restored, the system reverts to mains power operation.

[0110] In operation of the battery -boosted variable-frequency motor drive system • a low-voltage DC source (48 V nominal; operable 12-200 V) feeds a DC-DC step-up stage that generates a regulated high-voltage (HV) DC bus of 48-200V for a three- phase inverter, avoiding any line-frequency step-up transformer.

[0111] • a three-phase inverter driven from the boosted bus delivers the output with significantly lower switching currents than low-voltage-plus-transformer approaches, enabling smaller, lighter, and more efficient power stages.

[0112] • a controller generates and selects among a family of three-phase waveforms, including i. a substantially sinusoidal member, and ii. non-sinusoidal members; output frequency is commanded across [f min- f rnax] Hz to match motor RPM.

[0113] Under high-torque or start-up conditions, the controller selects a non-sinusoidal member to increase average electromagnetic torque at equal Root Mean Square (RMS) current and Voltage Direct Current (Vdc); under compatibility constraints it selects a sinusoidal member.

[0114] Speed command with or without feedback: From standstill the controller ramps output frequency from zero while modulating amplitude (modulation index / duty ratio) to deliver above-rated starting torque, thereby assuming movement of the load in the absence of mechanical failure. Where positional feedback is available from the mechanism, the controller computes motor speed from position (and known gearing) and sets output frequency accordingly, transitioning between open loop (assumed-motion) and closed-loop (measured) modes.

[0115] Upon detecting mains loss, the system operates independently of outside power: it opens a mains-side switching device and closes an inverter-side switching device (relay / contactor sized to the motor), providing true air-gapped isolation between the motor / brake and the mains during backup operation and the inverse on restoration.

[0116] Backfeed prevention. In backup mode the motor windings and brake coil are air-gapped from all mains conductors; the battery, step-up converter, inverter and brake supply have no conductive path to the AC mains bus, preventing backfeed into the installation. The system provides a dedicated, isolated high-voltage DC supply (~ [80-120] Vdc, adjustable) for the motor brake coil, routed through a double-pole double-throw (DPDT) relay that switches both brake terminals, ensuring the brake circuit is isolated from mains during backup and automatically reconnected to mains when restored.

[0117] The system can be activated by human input (e.g., pushbutton) and / or by an external control signal (e.g., 12 / 24 V from a fire alarm or plant interlock), with priority logic co-ordinating transfer, waveform selection, and brake release.

[0118] Co-ordinated DC-bus regulation Vdc (co, load) and waveform selection limit battery current, bus ripple, and device stress during start-up and transients.

[0119] The same hardware and boosted DC bus also operate PMSM motors, with an appropriate commutation / FOC mode selectable by the controller.

[0120] In a representative retrofit, a 300 x 400 x 800 mm, 142 kg UPS can be replaced with a 570 x 165 x 130 mm, 9 kg device (volume 96.0 12.23 L, ~87% reduction; mass 142 9 kg,

[0121] ~94% reduction), while maintaining reliable motor starting and operation at full rated torque.

[0122] Battery-boosted variable-frequency motor drive System overview

[0123] 1. A low-voltage DC source (48 V nominal; operable 12-200 V) supplies a DC-DC step- up stage that generates a regulated DC bus of 200-450 V for a three-phase inverter. A controller regulates the step-up stage and commands the inverter to produce a family of three-phase voltage waveforms (including sinusoidal and non-sinusoidal members) according to constraints below. a. AC mains interface, outage detection, and charging

[0124] Charging interface: The only connection to the AC mains during normal readiness is a low-voltage auxiliary feed (e.g., 24 VDC) to charge and monitor the system battery via an isolated charger.

[0125] Outage detection: The controller monitors mains presence (e.g., phase / neutral voltage, frequency window, ride-through timer [t deadband] ms) and declares outage when outside thresholds for [T detect] ms. Restore detection: Mains restoration is latched after continuous in-window operation for [T restore] ms to avoid chatter. b. Transfer switching and air-gapped isolation

[0126] Switching devices: A mains-side switching device (relay / contactor CM) connects the motor circuit to the mains during normal operation; an inverterside switching device (relay / contactor CI) connects the motor to the inverter during backup. Devices are sized to the motor and may include mechanical and / or electrical interlocks.

[0127] Sequencing (break-before-make): On outage: open CM, verify open (auxiliary contact feedback), then close CI; on restoration: open CI, verify open, then close CM. CM and CI are never simultaneously closed.

[0128] Air-gapped isolation: During backup, both the motor power conductors and brake conductors are physically disconnected from mains, providing galvanic isolation. c. Brake coil supply and isolation

[0129] Brake driver: An isolated HV DC supply ~ [100 VDC] (range [80-120 Vdc], programmable) energises the brake coil during backup operation.

[0130] DPDT isolation: A two-pole double-throw relay switches both brake terminals between the mains side brake circuit and the internal brake supply, with suppression components [RC / snubber / TVS] across the coil to control surge and EMI.

[0131] During backup operation both brake terminals are disconnected from all mains- side conductors and connected only to the isolated brake supply, such that no conductive path exists from the brake coil to the AC mains.

[0132] 2. DC-DC step-up stage (functional envelope + scalability + alternatives + best method)

[0133] Functional envelope (broad):

[0134] Input: 12-200 V battery (48 V nominal). Output: regulated Vdc = 48-200 V.

[0135] Power rating (scalable): The unit can be driven from zero power, linearly up to the maximum rating of the components of the system can safely tolerate, within thermal limits. Typically at least 200 W continuous, scalable to higher ratings by increasing device ratings and / or the number of interleaved phases; demonstrated embodiments 200 W-1.2 kW (typical 750 W).

[0136] Scalability: Power-stage components (inductors, switches, diodes, capacitors, thermal path) are dimensioned to the required rating. Higher ratings may use interleaved phases (M > 1) and / or paralleled modules, while maintaining the same regulation and modulation strategy. Bus conditioning (non-limiting): Inductance and capacitance are selected to provide suitable ripple attenuation and dynamic behaviour for the inverter across the commanded waveform family; exact values are implementation-dependent.

[0137] Scalability details — interleaving and parallelisation (how higher power is achieved): Interleaved phases (DC-DC stage): For M > 1 (where M = 1 denotes the single-phase) the step-up stage may be realised as M channels; for M > 2, implement M interleaved channels (each with its own inductor and switches) using evenly phase-shifted Pulse Width Modulation (PWM) carriers with mutual phase shift ~ 360° / M (time offset t_phase ~ T_s / M; allowable skew ±[Acp]°). Interleaving lifts the effective ripple frequency to M f sw and provides input / output ripple cancellation, enabling smaller magnetics / capacitors and lower current ripple / EMI for a given total power.

[0138] Current sharing: Use average-current-mode control (per-phase current loops with a balancing loop) or equivalent, so each phase carries ~ 1 / M of the average input current. Phase management: At light load the controller may shed phases down to M = 1 for efficiency, and re-enable phases as load increases, without altering the regulation or modulation strategy.

[0139] Paralleled modules (optional): Additional power can be realised by paralleling converter modules and / or paralleling inverter devices per phase, with current sharing maintained by the same control; the waveform family and control objectives remain invariant across ratings. Implementation alternatives (support for broad claims):

[0140] The step-up stage may be implemented as one or more of: interleaved synchronous boost; current-fed push-pull; full-bridge step-up with high-frequency transformer; resonant (e.g., LLC) step-up; or other topologies providing equivalent step-up performance. Isolation may be present or absent.

[0141] Best method (one workable example):

[0142] Topology: Single-phase synchronous boost (non-isolated), peak current-mode control.

[0143] Setpoint: Vdc set = [value] V (within 80-180 V); soft-start to limit inrush.

[0144] Magnetics & switching: L = 30pH ; f_sw = 120 kHz; diode(s) synchronous-rectified; bus capacitance selected so that the HV DC bus ripple is compatible with the inverter’s modulation strategy.

[0145] Limits & thermal: Input current 30 A; thermal path sized to the selected rating.

[0146] EMI / conditioning (non-limiting): Layout to minimise loop area; optional RC / TVS snubbers to suppress switching transients on the HV bus.

[0147] EMI means Electromagnetic interference.

[0148] TVS means Transient Voltage Suppression.

[0149] RC means a Resistor Capacitor based filter / energy damping network, commonly used damp voltage ringing and to dissipate the energy of transient voltage spikes.

[0150] Non-limiting variants (scaling options):

[0151] Two-phase interleaved boost (M = 2): Two channels with 180° mutual phase shift (t_phase = T_s / 2) to reduce ripple and share current; control loops and inverter modulation unchanged. Four-phase interleaved boost (M = 4): Four channels with ~90° mutual phase shift; current sharing via average-current-mode control.

[0152] Inverter stage

[0153] Functional envelope (broad):

[0154] Type: Three-phase voltage- source inverter (VSI) supplied by the HV DC bus described in 2 above.

[0155] Topology: Conventional six-switch (2 -level) bridge. Alternatives: 3 -level NPC or 3- level T-type may be used when lower device voltage stress and reduced dv / dt are desired (e.g., higher bus voltages or very long motor leads).

[0156] Semiconductor devices: MOSFET / SiC MOSFET / IGBT suitable for the bus voltage and target rating; isolated gate drives.

[0157] Modulation: Space-vector or carrier-based PWM implementing the waveform family (sinusoidal and non-sinusoidal members), including zero-sequence injection and bounded dwell control where applicable.

[0158] Voltage measurement: HV DC-bus sense for protection / feed-forward; optional phasevoltage sense for observers / diagnostics.

[0159] Switching frequency & dead-time: [f_sw] kHz, dead-time [t_dt] ns with dead-time compensation if required.

[0160] DC-link energy storage: Capacitors selected for the commanded waveforms and transients; low inductance layout (e.g., laminated bus or equivalent). dv / dt & common-mode control: Per-1 eg snubbers and / or an output dv / dt filter; optional common mode choke and Y capacitors to chassis. Motor-lead length / insulation are considered for reflected- wave effects.

[0161] Thermal: Heatsink / airflow (or cold-plate) sized to the selected rating; temperature sensing for protection / derating.

[0162] Sensing and protection: Present embodiment (protection-only): Gate-driver desaturation / over-stress monitors provide fast hardware over-current / short-circuit protection independent of the controller. HV bus voltage is sensed. No continuous per-phase current sensing is required for start-up and assumed-motion modes; the controller may estimate phase currents from switching state, bus voltage, and a motor model for limiting and diagnostics.

[0163] Variant (measured-current): Per-phase current measurement is provided for enhanced control modes, using two-shunt reconstruction (low-side shunts in two phases) or three-shunt / in-line Hall / CT sensors. Sampling is synchronised to the PWM; bandwidth / resolution support the waveform family.

[0164] Best method (one workable example — present hardware):

[0165] Topology: Conventional six-switch, three-phase VSI (2 -level).

[0166] Devices & gate drive: [e.g., 650 V MOSFET] with isolated gate drivers including desaturation / overcurrent, soft shutdown, and Miller clamp (as applicable).

[0167] Sensing & protection: Gate-driver desat / over-stress trip with blanking; HV bus sense; optional DC-link shunt for logging (non-control).

[0168] Modulation & waveform: Space-vector PWM (SVPWM) implementing (i) sinusoidal mode and (ii) non-sinusoidal mode (An equivalent carrier-based PWM with optimal zero sequence injection may be used in alternative embodiments). dv / dt management: RC / RCD snubbers per leg; optional dv / dt output filter for long motor leads.

[0169] Protections (implementation notes): DC-bus OVP / UVP, per-phase over-current trip (via desat), shoot-through detection, temperature limits; stop behaviour co-ordinated with brake control.

[0170] Implementation option (measured-current variant): Sensing: Two-shunt (A & C) with current reconstruction across all sectors or three- shunt / in-line Hall / CT; ADC sampling aligned to PWM centre; offset / temperature compensation as required.

[0171] Control impact: Enables tighter current limiting, closed-loop torque control, and improved observer convergence; waveform family and selection logic are unchanged.

[0172] Notes on scalability:

[0173] Same control, larger hardware: Higher ratings may use paralleled devices per leg and increased DC-link capacitance; control algorithms and waveform family remain unchanged.

[0174] 3-level migration (optional): At higher bus voltage or where lower dv / dt is required, a 3-level NPC or T-type inverter may be used with the same torque and waveform objectives; only the space vector mapping / dwell computation changes. Control

[0175] Mode and source management

[0176] The controller implements Source = {Mains, Battery} and Waveform = {Sinusoidal, Non-sinusoidal} states. Transitions are governed by outage / restore detection, external / human activation inputs, and device limits. a. Boost control

[0177] Vdc regulation profile Vdc(co, load) and co-ordination with inverter torque mode. b. Waveform family, frequency command, and selection

[0178] Modulation realisation: Implemented as space-vector PWM (SVPWM) using a lookup table indexed by electrical angle, or an equivalent carrier-based PWM with optimal zero sequence injection.

[0179] Sinusoidal mode: realisable via SVPWM or carrier-based PWM with zerosequence injection when a substantially sinusoidal output is desired. Non-sinusoidal mode: the controller selects SVPWM dwell fractions (from the lookup table or an equivalent parameter set) within the inverter’s linear region to produce a non-sinusoidal three phase waveform chosen to meet a torque objective, subject to current, voltage, and device-stress limits. The sinusoidal waveform is a special case obtained by choosing dwell fractions that yield zero harmonic injection.

[0180] Frequency command: f out is commanded within f min-f max (Hz) and mapped to synchronous motor speed n s ~ 120 f out / P (P = total pole count; equivalently, n s ~ 60 f out / p with p = pole pairs). The amplitude and DC- bus setpoint Vdc, as a function of speed and load, are co-ordinated to meet torque and current limits.

[0181] Selection logic: On high starting-torque or transient demand, select Non- sinusoidal to achieve T > T ref x (1 + 5) at equal RMS current and Vdc; otherwise select Sinusoidal to satisfy EMC / THD or acoustic constraints. c. External and human activation

[0182] The system can be commanded to enter backup operation by (i) human input (momentary pushbutton) and / or (ii) external signals including 12 V or 24 V logic from a fire alarm or plant controller. Inputs are opto-isolated and debounced; priority / arbitration resolves conflicts and logs source of activation. d. Inverter modulation and “bounded waveform family” (concise)

[0183] Overview. The controller generates a bounded family of three-phase waveforms chosen to meet a torque objective while respecting safe operating limits. The waveform may be realised by SVPWM (lookup table or computed dwell times), by an equivalent carrier-based modulation with zero sequence injection, or by pre-computed duty / dwell sequences specific to a motor. A substantially sinusoidal output is a special case within this family.

[0184] Minimal bounds (principles-based). A waveform is admissible if all of the following hold: • Electrical safety: Voltages and currents remain within device and installation ratings.

[0185] • Switching behaviour: The switching frequency and number of commutations per period remain within controller-defined limits for thermal / EMI reasons.

[0186] • Operating region: Modulation avoids DC-bus clipping in normal operation; an over-modulation mode may be entered deliberately when required.

[0187] • Control objective: For a given RMS phase current and DC-bus voltage, the waveform is selected to meet a torque or start-up margin target; a sinusoidal waveform may be selected to satisfy EMC / acoustic constraints.

[0188] • Inclusion of sine: The sinusoidal waveform is obtained by choosing references / dwell fractions that inject no non-fundamental content.

[0189] Best method (present embodiment). Implement the family using an SVPWM lookup table indexed by electrical angle. A modulation scale m derived from power / torque request (with optional Vdc compensation) scales the table entries; m and f out are rate-limited. Alternative motor-specific duty / dwell sequences may be stored and selected per motor profile.

[0190] Notes. Motor-specific profiles (tables or parameter sets) may be stored in nonvolatile memory and updated by firmware. These profiles are design data and do not limit the waveform family. e. Soft-start and frequency setting

[0191] Present embodiment (simple soft-start)

[0192] • The controller sets a target output frequency f out target and ramps the modulation factor m from 0 —> m target over [t ramp], while holding f out = f out target. The ramp of m is rate-limited to respect current and voltage limits; over- current / over-voltage events trigger a safe stop (co-ordinated with the brake logic).

[0193] • This open-loop soft-start has been validated without phase-current sensors; protection is provided by gate-driver desaturation / over-stress.

[0194] Variant A (dual-ramp, future option)

[0195] • For loads that benefit from a gentler start, the controller ramps both f out: 0 —> f out target and m: 0 — > m target with independent rates [t ramp f], [t ramp m].

[0196] Variant B (with phase-current feedback)

[0197] • When per-phase current sensing is fitted, the controller shapes m(t) (and optionally f_out(t)) to maintain I_phase < I limit, using measured current for limiting.

[0198] • Without phase sensors, the controller may estimate current from switching state and Vdc and still enforce conservative limits; desat remains the hard trip.

[0199] Notes

[0200] • Back-EMF naturally reduces current as speed rises; the above soft-start relies on this effect and has proven adequate on current builds.

[0201] • Parameters [t ramp], [t ramp f], m target are design settings and may be updated in firmware. f. Lookup-table implementation (best method)

[0202] Electrical angle & frequency: A digital phase accumulator advances by A0 each PWM period, with A0 = 27t f_out / f_pwm. The accumulator index selects the current entry in the SVPWM lookup table. Table content: Each entry stores duty (or dwell) fractions sufficient to realise SVPWM forthat angle / sector (e.g., Ta, Tb, Tc or Tl, T2, TO over the switching period). The table includes a sinusoidal member as a special case; non- sinusoidal members are alternative tables (or parameter sets) selectable by the controller.

[0203] Amplitude / power scaling: A modulation scale m is computed from the power / torque request with optional DC-bus compensation, e.g. m = clamp (k_power • V_ref / V_dc_meas, 0, m_max). The selected table’s duty / dwell values are then multiplied by m before being applied to the gates.

[0204] Selection: The controller selects the table (sinusoidal or non-sinusoidal) according to the selection logic.

[0205] Interpolation (optional): Linear interpolation between adjacent entries reduces quantisation artefacts.

[0206] Limits & rate-limiting: Output m and A0 are rate-limited to respect current and voltage limits; overcurrent / over-voltage events revert to a safe state (coordinated with brake control).

[0207] Updatability: Tables / parameters may be stored in non-volatile memory and updated by firmware; values are design data and are not fixed by this description. Operating modes

[0208] Overview. The controller supports operation with AC induction motors (IM) and PMSMs. For either motor, the system may run in backup (battery) or mains-through conditions as described in 1 above; brake release and transfer sequencing. Waveform selection and soft-start. a. Induction motor mode (IM)

[0209] Start / low speed (present embodiment): Apply the soft-start by modulation ramp with f out = f out target. Use the non-sinusoidal member when higher starting torque is required; otherwise use the sinusoidal member for EMC / acoustic reasons. Release the brake before torque is applied.

[0210] Transition to nominal running: After the mechanism is moving and current settles, the controller may retain the selected waveform or switch to the sinusoidal member to reduce distortion, according to site constraints. Optional frequency ramp (6.4.5 Variant A) may be used for sensitive loads.

[0211] Speed / torque behaviour: Above base speed the controller may reduce modulation (and optionally apply field-weakening in future variants) to respect current and voltage limits. In the present embodiment, open-loop V / f behaviour with modulation scaling is sufficient.

[0212] Stall / fault handling: If movement is not inferred within [t stall] or a limit trip occurs (desaturation, over-voltage), execute a safe stop: remove torque, deenergise brake, and follow the transfer rules. b. PMSM mode

[0213] Start (alignment and ramp): If a position sensor is available, start with the sinusoidal member and closed-loop commutation. If sensor less, perform a brief alignment pulse then an open-loop ramp until back-EMF is observable, after which closed-loop commutation is used. Brake release follows.

[0214] Running: Default operation is sinusoidal (FOC-equivalent) excitation with modulation scaling; a non-sinusoidal member may be selected where torque or acoustic behaviour warrants it. Future variants may implement explicit FOC (i_d / i_q) or trapezoidal commutation; the waveform family remains applicable.

[0215] Fault handling: As for IM: on limit trips or loss of synchronism, remove torque, manage the brake, and perform a safe stop / transfer. c. Regeneration and deceleration (present embodiment; low power)

[0216] For commanded deceleration or overhauling loads, the controller holds a steady output frequency and duty / modulation that yields near-zero torque; the motor’s resistive (copper) and core losses and the mechanism’s natural drag dissipate the regenerative energy at the demonstrated ratings.

[0217] No braking chopper or energy return path is required in this embodiment. The DC-bus is monitored; if bus voltage approaches an over-voltage threshold, the controller reduces modulation toward zero (coast) and executes a safe stop if needed (co-ordinated with brake control).

[0218] For PMSMs, a zero-torque sinusoidal command (or equivalent) is applied during deceleration; if back-EMF drives the bus upward, modulation is reduced to zero and the drive coasts.

[0219] Variants (non-limiting, for higher power if adopted later): Add a braking resistor / chopper or an active dump path, or use frequency shaping during decel to manage DC-bus rise while maintaining control of the mechanism. d. Source / transfer interaction

[0220] Mode changes honour the break-before-make sequencing. On mains restoration, the controller removes inverter torque, de-energises the brake, opens CI, and closes CM in that order.

[0221] On outage, the inverse sequence applies before soft-start.

[0222] 5. Protections and safety

[0223] Over-current, over-voltage, short-circuit, thermal derating; isolation monitoring (if present).

[0224] Unique waveform application:

[0225] While adjusting the frequency to the optimum as standard practice, by applying a unique waveform to drive the motor, the torque can be maintained at significantly lower voltages than otherwise be the case with standard sinusoidal drive used in variable frequency drives (VFD).

[0226] The unique waveform results in higher efficiency and lower cost cf, to the standard practice of adjusting the frequency to the optimum. As the system of the invention is designed to run from a backup battery, a DC / DC voltage boost circuit is employed to raise the voltage adequately to drive the motor.

[0227] Due to the lower voltages required due to the waveforms employed, the voltage required is lower, allowing for a smaller converter unit, that is more efficient due to the lower degree of voltage level shifting required.

[0228] In a further embodiment the battery-boosted variable-frequency motor drive system for operating an electric motor (AC induction or PMSM) during a power outage, suitable for mechanical loads such as industrial doors can comprise: a) a three-phase mains input for normal operation; b) a mains-side contactor arrangement configured to connect the motor to the AC mains during normal operation and, in response to an interruption, to open all poles to provide galvanic isolation between the motor (and any brake coil) and the AC mains; c) a low-voltage DC energy source and a DC / DC step-up converter configured to generate a regulated high-voltage DC bus; d) a three-phase inverter supplied from the high-voltage DC bus; e) an inverter-side contactor arrangement configured to connect the inverter to the motor only when the mains-side contactor arrangement is open; and f) a controller configured to detect mains loss, to enforce break-before-make transfer by opening the mains-side contactor arrangement, verifying the open state, waiting a defined dead-time, and then closing the inverter-side contactor arrangement so that the motor is driven independently from the backup source while preventing back feed to the AC mains, and to perform the inverse sequence upon mains restoration.

[0229] During backup operation, the invented system is able to isolate the motor and any electromagnetic brake from the mains and drives them independently so as to avoid back feed and simplify integration with existing VFD-controlled installations.

[0230] The inventive system can include a dedicated, isolated high-voltage DC supply for an electromagnetic brake coil, routed through a double-pole double-throw (DPDT) relay that switches both brake terminals between a mains-side brake circuit in normal operation and the isolated supply in backup operation, thereby galvanically isolating the brake circuit from the AC mains during backup.

[0231] The inventive system is able to operate independently of a mains power source, so that the system is also able to be used as a secondary backup to an existing UPS system. As well the invented system is able to stand independently along side an integrated UPS.

[0232] The invented system in the event that the UPS battery was not in a condition to work, or the UPS was okay but the PLC or operating device, usually run on 24v, had lost power, would kick in and drive the motor independently of a UPS or PLC.

[0233] In different applications of the invented system, it is clear and would be readily understood by a skilled addressee that the High voltage Bus voltage range could be significantly higher due to the design of the motor being driven, or to achieve higher rotational speeds in certain cases. It would not be unrealistic to expect a HV DC bus voltage of -450V. Likewise, for example in applications requiring particularly high power or higher voltage, or where a boost converter is difficult to implement because of stringent EMI requirements or thermal limits, the low voltage battery voltage may be required to be significantly higher than the nominal voltage previously stated.

[0234] ADVANTAGES

[0235] Advantages of the invention:

[0236] • Torque improvement [X-Y %] at [speed / slip] .

[0237] • Real-world retrofit with the invention: A 300 x 400 x 800 mm, 142 kg three-phase UPS replaced with a 570 x 165 x 130 mm, 9 kg device. Enclosure volume reduced from 96.0 L to 12.23 L (~87.3% reduction) and mass reduced by ~93.7%. The floor footprint reduced from 0.120 m2to 0.094 m2(—21.6%), and the longest dimension from 800 mm to 570 mm (—28.8%).

[0238] • Modulation advantage vs plain sinusoidal PWM: Using SVPWM (or an equivalent scheme with optimal zero-sequence injection) provides higher DC-bus utilisation and lower current distortion than plain sinusoidal PWM, improving starting margin and torque delivery at the same bus voltage and RMS current.

[0239] • Operational benefits: Alongside the size and mass reductions, the boosted-bus architecture lowers inverter switching currents, enabling smaller silicon and reduced thermal management for comparable motor duties. The invention uses a range of technologies to effectively deliver backup control for induction motor control where none meaningfully exist.

[0240] • The invention is compact and yet is able to deliver full motor drive torque, enabling the movement of machinery in loss of power or emergency, from a very reliable and compact device, that is a fully self-contained system that manages its own charging and requires a minimum of maintenance.

[0241] • The invention allows for a customisable run time- but even in a minimum form runs for a relatively long period due to very high efficiency and motor control specifically designed to run from a relatively small battery pack. This makes the system significantly cheaper.

[0242] • The invention uses automatic detection of mains power outage, the system is preprogrammed to switch to backup battery operation without operator input, and also reverts back to allow the default system operation when mains power is restored and maintains and charges the battery bank to be ready for the next operation event. It is as such a fully self-regulating system.

[0243] • The Invention uses a unique system involving DC voltage boosting where required to control the motor brake, this means a motor can drive a roller door open almost immediately, as opposed to manual systems for brake release which are both slow and require special equipment that can be lost in the case of an emergency.

[0244] • Where used to open a roller door, the invention allows for the system to be activated to open the door from both inside and outside of the enclosed area- allowing to check to see if all personnel have evacuated in an emergency.

[0245] The invention incorporates modern battery chemistry coupled with modem battery charging techniques, that greatly prolongs the battery service life. The battery management system maintains each cell in the system at a lower cell voltage than fully charged, increasing the service live of the battery bank substantially, while maintaining sufficient stored power to operate the system during a mains supply power outage.

[0246] • The invention incorporates data logging and data retention for operator and manufacturer system operational optimisation and control via data feedback.

[0247] • The invention is designed to be highly resistant to debris and moisture ingress and is mechanically robust and compact, and is easily installed onto new or existing workplaces with a minimum of room.

[0248] • Simplified components for driving of the motor are utilised and thus reduces the cost of production as the ratings of all components are reduced.

[0249] EQUIVALENTS CLAUSE

[0250] The Invention may also broadly be said to consist in the parts, elements and features referred or indicated in the specification, individually or collectively, and any or all combinations of any of two or more parts, elements, members or features and where specific integers are mentioned herein which have known equivalents such equivalents are deemed to be incorporated herein as if individually set forth.

[0251] The examples and the particular proportions set forth are intended to be illustrative only and are thus non-limiting.

[0252] VARIATIONS

[0253] The invention has been described with particular reference to certain embodiments thereof. It will be understood that various modifications can be made to the above-mentioned embodiment without departing from the ambit of the invention. The skilled reader will also understand the concept of what is meant by purposive construction.

[0254] KIT OF PARTS

[0255] It will also be understood that where a product, method or process as herein described or claimed and that is sold incomplete, as individual components or steps, or as a “Kit of Parts”, that such exploitation will fall within the ambit of this invention even though there may not be any claim to a kit of parts included in the following claims.

Claims

CLAIMS:Claim 1 : A battery -boosted variable-frequency motor drive system for use during power outages, but not limited thereto, for use with an electric motor for operating a mechanical load, such as, but not limited thereto, an industrial door, during a power outage, wherein the battery- boosted variable-frequency motor drive system having: i. a power supply connected to an electric motor such that power is adapted to be supplied to the electric motor during normal operation where the power is uninterrupted so as to allow the normal operation of electric motor drive the mechanical load; and iii. a backup means connected to the electric motor such that when the power supply is interrupted, due to a power outage, stored DC power is supplied through a DC / DC voltage boost converter to a DC to 3 phase AC inverter switching means so as to supply power to the electric motor so as to allow the electric motor to drive the mechanical load during a backup mode when there is a power outage.Claim 2: A battery -boosted variable-frequency motor drive system configured to operate an electric motor during an AC mains outage, the system comprising: a. a site-supply interface configured to receive power and / or presence information from at least one of: i. an AC line supply, ii. a mains-derived auxiliary DC supply, or iii. an intermediate-voltage supply; the site-supply interface providing at least an auxiliary supply for monitoring and / or battery charging; b. a line-side contactor arrangement configured to connect the motor to the AC mains during normal operation and to provide galvanic isolation by opening all poles in response to an interruption; c. a low-voltage DC energy source;d. a DC-DC step-up converter configured to generate a regulated high-voltage DC bus from the low-voltage source; e. a three-phase inverter supplied from the high-voltage DC bus; f. an inverter-side contactor arrangement configured to connect the inverter to the motor; and g. a transfer arrangement configured, upon detecting loss of a site supply (including loss of an associated auxiliary supply such as 24 VDC), to open the line-side contactor arrangement to provide galvanic isolation, effect a break-before-make interval, and then close the inverter-side contactor arrangement so that the motor is driven from the low-voltage DC energy source while preventing back feed to the site supply, and to perform an inverse sequence upon restoration of the site supply; the transfer arrangement comprising any one or more of controller logic, a timedelay relay, an undervoltage-release device, or mechanical / electrical interlocks.Claim 3: The system as claimed in Claim 2, wherein the site-supply interface comprises an isolated charger powered from a mains-derived auxiliary DC supply, the charger maintaining the low-voltage DC energy source while the motor circuit remains isolated from the site supply.Claim 4: The system as claimed in Claim 2, wherein the site-supply interface alternatively comprises a rectifier or power module configured to accept an AC line supply or an intermediate-voltage DC supply and to provide both outage / restoration detection and charging power.Claim 5: The system as claimed in claim 1, wherein the backup means has motor driving circuitry, DC / DC voltage boost convertor circuitry, brake control circuitry, low voltage DC power storage battery, main logic control means, battery management and charging means, an inverter, an inverter-side contactor arrangement configured to connect the inverter to the motor AC mains, voltage detection means and human control input means, wherein the main logic control means having motor drive waveform generation means, motor brake control means data logging means.Claim 6: The system as claimed in claim 5, wherein the electric motor is an AC induction motor or permanent magnet synchronous motor.Claim 7 : The system as claimed in claim 6, wherein the motor drive waveform generation means generates at least a non-sinusoidal waveform for increasing the average electromagnetic torque in the AC induction motor or permanent magnet motor so as to enable reliable starting and operation of said motors without oversizing the power outage stage.Claim 8 : The system as claimed in claim 7, wherein the motor drive waveform generation means generates and selects among a family of three-phase waveforms, including i. a substantially sinusoidal waveform member, and ii. non-sinusoidal waveform members such that under high-torque or start-up conditions or power outages, the selected non-sinusoidal members increases the average electromagnetic torque at equal Root Mean Square (RMS) current and Voltage Direct Current (Vdc).Claim 9: The system as claimed in claim 8, wherein the output frequency of the non- sinusoidal waveform members adapted to match to match the frequency of the motors RPM.Claim 10: The system as claimed in claim 9, wherein the system includes a dedicated, isolated high-voltage DC supply for a brake coil, routed through a double-pole double-throw (DPDT) relay that switches both brake terminals, ensuring the brake circuit is isolated from mains during backup mode and automatically reconnected to mains when mains power is restored.Claim 11 : The system as claimed in claim 10, wherein the system is able to be activated by manual input and / or by an external control signal with priority logic co-ordinating transfer, waveform selection, and brake release.Claim 12: A battery-boosted variable-frequency motor drive system comprising: a. a low-voltage DC energy source; b. a DC-DC step-up stage configured to generate a regulated high-voltage DC bus; c. a three-phase inverter;d. a mains-side switching device configured to connect a motor to an AC mains supply in a first state and disconnect in a second state; e. an inverter-side switching device configured to connect the motor to the inverter in said second state; and f. a controller configured to, upon detecting loss of the AC mains, open the mains-side switching device and close the inverter-side switching device to operate the motor from the high-voltage DC bus, and upon mains restoration perform the inverse sequence, thereby maintaining air-gapped isolation between the motor circuit and the AC mains during backup operation.Claim 13 : The system as claimed in claim 12, wherein the system includes an inverter-side contactor arrangement configured to connect the inverter to the motor.Claim 14: The system as claimed in claim 13, wherein the mains-side switching device and the inverter-side switching device are interlocked to prevent simultaneous closure and are sized to the motor load.Claim 15: The system as claimed in any one of claims 1 and 5, wherein the system further comprising a charging interface powered from the AC mains by a low-voltage auxiliary line configured to charge the low-voltage DC energy source while the motor circuit remains isolated from the AC mains.Claim 16: The system of any one of claims 12 to 14, wherein the controller is configured to generate a family of three-phase output waveforms using space-vector PWM or an equivalent carrier based modulation with zero-sequence injection, and to select among a substantially sinusoidal member and one or more non-sinusoidal members responsive to torque demand, EMC limits, battery current, or device temperature.Claim 17: The system of claim 16, wherein the sinusoidal member is a special case of the waveform family obtained by choosing references or dwell fractions that inject no nonfundamental content.Claim 18: The system of any one of claims 12 to 14, wherein the controller commands an output frequency (f_out) within a range (f min, f max) mapped to motor speed and coordinates DC-bus setpoint and modulation index to satisfy current and voltage limits.Claim 19: The system of any one of claims 12 to 14 and 16 to 18, wherein the system further comprising an isolated high-voltage DC supply of 80-120 Vdc configured to energise a motor brake coil during backup operation, and a double-pole double-throw relay arranged to switch both brake terminals between a mains-side brake circuit and said isolated supply, thereby isolating the brake circuit from the AC mains during backup operation.Claim 20: The system of claim 19, wherein the controller applies brake voltage for [t release] ms after commanding the inverter torque and removes the brake voltage prior to transfer back to AC main.Claim 21 : The system of any one of claims 12 to 14 and 16 to 20, wherein the controller selects a non-sinusoidal member of the waveform family under starting or high-torque conditions to increase average electromagnetic torque relative to a sinusoidal member at equal RMS phase current and DC-bus voltage, and selects the sinusoidal member when required to satisfy an EMC or acoustic constraint.Claim 22: The system of any one of claims 12 to 14 and 16 to 21, wherein the controller is adapted to perform a soft-start by ramping a modulation factor from zero to a target value while holding the commanded output frequency substantially constant.Claim 23: The system of any one of claims 12 to 14 and 16 to 22, wherein the controller adapted to ramp both the modulation factor and the output frequency towards respective targets with independent rates.Claim 24: The system of any one of claims 12 to 14 and 16 to 24, wherein the system includes over-current protection that is provided by gate-driver desaturation or over-stress detection independent of the controller.Claim 25: The system of any one of claims 12 to 14 and 16 to 25 wherein the system includes two-shunt reconstruction or three-shunt / in-line sensors with sampling synchronised to the PWM in order to provide per-phase current measurements.Claim 26: The system of any one of claims 12 to 14 and 16 to 25, wherein the controller stores in memory a lookup table of modulation values indexed by electrical angle and scales said values by a modulation factor derived from a power or torque request, and the outputfrequency is generated by a digital phase accumulator that indexes the table and the table is stored in non-volatile memory and updateable by firmware.Claim 27: The system of any one of claims 12 to 14 and 16 to 26, wherein the DC-DC step-up stage comprises a single-phase synchronous boost converter controlled in peak currentmode.Claim 28: The system of any one of claims 12 to 14 and 16 to 27, wherein the DC-DC step-up stage comprises M interleaved channels (M > 2) with PWM carriers mutually phase- shifted by approximately 360° / M to reduce input and output ripple.Claim 29: The system of any one of claims 12 to 14 and 16 to 28, wherein the system further comprising human and external activation interfaces, including a momentary pushbutton and a galvanically isolated input 12 / 24 V input from a safety or fire alarm system, either interface being configured to command entry into backup operation.Claim: 30: The system as claimed in any one of the preceding claims wherein, in backup operation, the inverter-side contactor arrangement connects the inverter output directly to the motor terminals downstream of any mains-powered controller or VFD, while the mains- powered controller and the AC mains are isolated from the motor.Claim 31 : A method of operating a battery -boosted variable-frequency motor drive system comprising: a) charging a low-voltage DC energy source from an AC mains supply; b) upon detecting mains loss i. opening a mains-side switching device, ii. closing an inverter-side switching device, iii. driving the motor from a DC-DC step-up-derived high voltage DC bus via a three-phase inverter, iv. generating, at a commanded frequency f out within f min-f max, a three-phase output waveform selected from a family comprising a substantially sinusoidal member and one or more non-sinusoidalmembers, responsive to torque demand, EMC limits, or device constraints, v. energising a motor brake via an isolated high-voltage DC supply; and c) upon mains restoration, removing inverter torque, deenergising the brake, opening the inverter-side switching device, and closing the mains-side switching device.Claim 32: The method of claim 31, wherein waveform selection is responsive to at least one of required torque margin, EMC or acoustic constraints, battery current limit, or device temperature; and wherein start-up is effected by ramping a modulation factor from zero to a target value.Claim 33: The method as claimed in anyone of claims 31 and 32, wherein when upon detecting mains loss an inverter-side contactor arrangement connects the inverter output directly to the motor terminals downstream of any mains-powered controller or VFD, while the mains-powered controller and the AC mains are isolated from the motor.Claim 34: A method of operating a battery-boosted variable-frequency motor drive system comprising: a) providing a site-supply interface configured to receive power and / or presence information from at least one of: i. an AC line supply, ii. a mains-derived auxiliary DC supply, or iii. an intermediate-voltage supply; the site-supply interface providing at least an auxiliary supply for monitoring and / or battery charging; b) configuring a line-side contactor arrangement to connect the motor to the AC mains during normal operation and to provide galvanic isolation by opening all poles in response to an interruption; c) providing a low-voltage DC energy source; d) configuring a DC-DC step-up converter to generate a regulated high-voltage DC bus from the low-voltage source;e) supplying a three-phase inverter supplied from the high-voltage DC bus; f) configuring an inverter-side contactor arrangement to connect the inverter to the motor; and g) configuring a transfer arrangement upon detecting loss of a site supply (including loss of an associated auxiliary supply such as 24 VDC), to open the line-side contactor arrangement to provide galvanic isolation, effect a break-before-make interval, and then close the inverter-side contactor arrangement so that the motor is driven from the low- voltage DC energy source while preventing back feed to the site supply, and to perform an inverse sequence upon restoration of the site supply; the transfer arrangement comprising any one or more of controller logic, a time-delay relay, an undervoltagerelease device, or mechanical / electrical interlocks.Claim 35: The method of any one of claims 31 to 34, wherein the method includes during backup operation, isolating the motor and any electromagnetic brake from the mains and driving them independently so as to avoid back feed and simplify integration with existing VFD-controlled installations.Claim 36: The method of any one of claims 31 to 34, wherein the method includes dedicating, isolating the high-voltage DC supply for an electromagnetic brake coil, routing through a double-pole double-throw (DPDT) relay to switch both brake terminals between a mains-side brake circuit in normal operation and the isolated supply in backup operation, thereby galvanically isolating the brake circuit from the AC mains during backup.Claim 37: The method of any one of claims 31 to 36, wherein the method includes operating system independently of a mains power source, so that the system is able to be used as a secondary backup to an existing UPS system and is able to stand independently along side an integrated UPS.Claim 38: A battery -boosted variable-frequency motor drive system for operating an electric motor (AC induction or PMSM) during a power outage, suitable for mechanical loads such as industrial doors, the system comprising: a) a three-phase mains input for normal operation;b) a mains-side contactor arrangement configured to connect the motor to the AC mains during normal operation and, in response to an interruption, to open all poles to provide galvanic isolation between the motor (and any brake coil) and the AC mains; c) a low-voltage DC energy source and a DC / DC step-up converter configured to generate a regulated high-voltage DC bus; d) a three-phase inverter supplied from the high-voltage DC bus; e) an inverter-side contactor arrangement configured to connect the inverter to the motor only when the mains-side contactor arrangement is open; and f) a controller configured to detect mains loss, to enforce break-before-make transfer by opening the mains-side contactor arrangement, verifying the open state, waiting a defined dead-time, and then closing the inverter-side contactor arrangement so that the motor is driven independently from the backup source while preventing back feed to the AC mains, and to perform the inverse sequence upon mains restoration.Claim 39: The system as claimed in claim 398, wherein the system includes a dedicated, isolated high-voltage DC supply for an electromagnetic brake coil, routed through a doublepole double-throw (DPDT) relay that switches both brake terminals between a mains-side brake circuit in normal operation and the isolated supply in backup operation, thereby galvanically isolating the brake circuit from the AC mains during backup.

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